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EFFECT OF CASTING PARAMETERS ON MACROSTRUCTURE OF STEEL PROJECT AT:- VIZAG STEEL PLANT, VIZAG GUIDED BY:- P.V. BHUJANG RAO (AGM, QA & TD, SMS) PRESENTED BY: CHINTALA ABINASH-9420 BOTU SURYA TEJA-9422 MAJETY SREE VENKATA NITHIN-9399 ANKAM JAYARAM-9421 SARVASUDDI AKHILA-9423

EFFECT OF CASTING PARAMETERS ON MACROSTRUCTURE OF STEEL

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Page 1: EFFECT OF CASTING PARAMETERS ON MACROSTRUCTURE OF STEEL

EFFECT OF CASTING

PARAMETERS ON MACROSTRUCTURE OF STEEL

PROJECT AT:-

VIZAG STEEL PLANT, VIZAG

GUIDED BY:-

P.V. BHUJANG RAO (AGM, QA & TD, SMS)

PRESENTED BY:

CHINTALA ABINASH-9420

BOTU SURYA TEJA-9422

MAJETY SREE VENKATA NITHIN-9399

ANKAM JAYARAM-9421

SARVASUDDI AKHILA-9423

Page 2: EFFECT OF CASTING PARAMETERS ON MACROSTRUCTURE OF STEEL

CERTIFICATE

This is to certify that the summer project report entitled “Effect of casting parameters on macrostructure of steel” is a bonafide record of work done by-

CHINTALA ABINASH BOTU SURYA TEJA MAJETY SREE VENKATA NITHIN ANKAM JAYARAM SARVASUDDI AKHILA

of National Institute of Technology pursuing B.TECH (2013-17), Metallurgy & Materials Engineering Course under the supervision of Mr. P.V. Bhujanga Rao (AGM, QA & TD, SMS) Visakhapatnam steel plant (VSP) in partial fulfillment of the academic requirements for the award of the degree of Bachelor of Technology in the Department of Metallurgical and Materials Engineering during the period of 14-12-15 to 26-12-15.

Mr. P.V. Bhujanga Rao AGM (QA&TD,SMS) VISAKHAPATNAM STEEL PLANT PLACE: VISAKHAPATNAM SIGNATURE OF THE PROJECT GUIDE DATE:

Page 3: EFFECT OF CASTING PARAMETERS ON MACROSTRUCTURE OF STEEL

ACKNOWLEDGEMENT

We have the honor submitting this mini project with utmost reverence to the almighty for his ever-loving benediction towards us. Our humble salutations to Visakhapatnam Steel Plant.

The satisfactions of the successful completion of any task would not be complete without the expression of gratitude to the people who made it possible. We would like to acknowledge gratefully the guidance and the encouragement of the people towards the successful completion of this project work.

We wish to sincerely thank our guide and LOKESH RAO, SARTHAK for their constructive suggestions and moral support throughout the project. We are in debt of gratitude to various members of faculty of their help.

Page 4: EFFECT OF CASTING PARAMETERS ON MACROSTRUCTURE OF STEEL

ABSTRACT

A thorough experimental investigation of the effects of melt temperature and casting speed on the structure and defect formation during the continuous casting of steel In addition, the temperature and melt-flow distributions in the sump of billets cast at different melt temperatures are numerically simulated and used in the discussion on the experimental results. Apart from already known phenomena such as segregation of carbon, porosity with casting temperature, a few new observations are made.

The inner structure of the continuously cast semis has a great importance from the point of view of further processing and application. The main reason for this is the very direct effect of the inner structure’s features (i.e. porosity, macro segregations, geometry of primary dendrites) on the technological characteristic features of the semis during further processing (i.e. crack sensitivity, formability, etc.)

The paper deals with the possible ways of macrostructure determination on the basis of the results of super heat and strand speed and other factors of continuous casting process. We pay a special attention to the columnar-equi axed transition as a function of heat parameters of the casting process and to the macro segregation formation caused by the motion of solute enriched inter dendritic liquid in the mushy zone.

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BREIF INTRODUCTION

Visakhapatnam Steel Plant (VSP), the first coast based Steel Plant of India is located, 16 KM South West of city of Destiny i.e. Visakhapatnam. Bestowed with modern technologies, VSP has an installed capacity of 3 million Tons per annum of Liquid Steel and 2.656 million Tons of saleable steel.

The construction of the Plant started on 1st February 1982. Government of India on 18th February 1982 formed a new Company called Rashtriya Ispat Nigam Ltd. (RINL) and transferred the responsibility of constructing, commissioning & operating the Plant at Visakhapatnam from Steel Authority of India Ltd. to RINL.

At VSP there is emphasis on total automation, seamless integration and efficient up gradation, which result in wide range of long and structural products to meet stringent demands of discerning customers within India and abroad. VSP products meet exacting International Quality Standards such as JIS, DIN, BIS, BS etc.

VSP has become the first integrated Steel Plant in the country to be certified to all the threeInternational standards for quality (ISO-9001), for Environment Management (ISO-14001) & forOccupational Health & Safety (OHSAS-18001). The certificate covers quality systems of allOperational, Maintenance and Service units besides Purchase systems, Training and Marketingfunctions spreading over 4 Regional Marketing Offices, 24 branch offices and stock yards located all over the country.

VSP by successfully installing & operating efficiently Rs. 460 crores worth of Pollution Control and Environment Control Equipments and converting the barren landscape by planting more than 3 million plants has made the Steel Plant, Steel Township and surrounding areas into a heaven of lush greenery. This has made Steel Township a greener, cleaner and cooler place, which can boast of 3 to 4° C lesser temperature even in the peak summer compared to Visakhapatnam City.

VSP exports Quality Pig Iron & Steel products' to Sri Lanka, Myanmar, Nepal, Middle East, USA,

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China and South-East Asia. RINL-VSP was awarded "Star Trading House" status during 1997-2000. Having established a fairly dependable export market, VSP plans to make a continuous presence in the export market.

Having a total manpower of about 16,600 VSP has envisaged a labor productivity of 265 Tons per man year of Liquid Steel.

MAJOR SOURCES OF RAW MATERIALSRAW MATERIALS SOURCE

Iron ore lumps and fines Bailadila, Chattisgarh

BF Limestone Jaggayyapeta, AP

SMS limestone Dubai

BF dolomite Madharam, AP

SMS dolomite Madharam, AP

Manganese ore Chipurupalli, AP

Boiler coal Talcher, Orissa

Imported Boiler coal Indonesia

Imported Coking coal Australia/US

Medium Coking coal Kathara/Swang/Rajarappa/kedla

Imported LAM coal China

Quartzite lumps and fines Local

Sand Sarepalli, AP

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MAJOR UNITSDEPARTMENTS ANNUAL

CAPACITY(‘000 T)UNITS (3.0 MT Stage)

Coke Ovens 2,701 4 Batteries of 67 Ovens & 7 mtrs. Height

Sinter Plant 5,256 2 Sinter Machines of 312 Sq. Mtr. grate area each

Blast Furnace 3,400 2 Furnaces of 3200 Cu. Mtr. volume each

Steel Melt Shop 3,000 3 LD Converters each of 133 Cu. Mtr. Volume and Six 4

strand bloom casters

LMMM 710 2 Strand finishing Mill

WRM 850 4 Strand high speed continuous mill with no

twist finishing blocks

MMSM 850 6 strand finishing mill

MAIN PRODUCTS OF VSP

STEEL PRODUCTS BY PRODUCTS

Blooms Nut Coke Granulated Slag

Billets Coke Dust Lime Fines

Channels , Angles Coal Tar Ammonium Sulphate

Beams Anthracene Oil

Squares HP Naphthalene

Flats Benzene

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Re Bars Zylene

Rounds Toulene

Wire Rods Wash Oil

VARIOUS DEPARTMENTS OF VSP:

RAW MATERIAL HANDLING PLANT (RMHP)

VSP Annually require quality raw materials viz. Iron ore, fluxes (Lime stone, Dolomite), coking and non-coking coals etc., to the tune of 12-13 million tons for producing 3 million tones of Liquid Steel. To handle such a large volume of incoming raw materials received from different sources and to ensure timely supply of consistent quality of feed materials to different VSP consumers, Raw Materials Handling Plant serves a vital function. This unit is provided with elaborate unloading, blending, stacking and reclaiming facilities viz. Wagon Tipplers, Ground and Trace Hoppers, Stock Yard Crushing Plant, Vibrating Screen, Single/twin Bloom Sticker, Wheel On Boom and blender Reclaimers.

In VSP peripheral unloading has been adopted for the first time in the country.

COKE OVEN AND COAL CHEMICAL PLANT (CO & CCP)Blast furnace, the mother unit of any steel plant requires huge qualities of strong, hard, and porous solid fuel in the form of hard metallurgical coke for supplying necessary heat for carrying out the reduction and refining reactions besides acting as a reducing agent.

Coke is manufactured by heating of crushed coking coal below 3mm in absence of air at a temperature of 1000 C and above for about 16 -18 hr.

A coke oven comprises of two hallow chambers namely, coal chamber and heating chamber. In the heating chamber a gas is fueled such as blast furnace gas, coke oven gas, etc., is burnt. The heat so generated is conducted through the common will to heat and carbonize the coking coal placed in adjacent coal chamber.

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SINTER PLANT (SP)Sinter is a hard and porous ferrous material obtained by agglomeration of iron ore fines, coke breeze, lime stone fines, metallurgical wastes viz. flow dust, mill scale, L.D slag etc.Sinter is a better feed material to Blast Furnace in comparison to iron ore lumps and it’s uses in blast furnace helps in increasing productivity and decreasing the coke rate and improving the quality of hot metal produced.Sintering is done in two number of 312sq.metre. Sinter machines of DWIGHT-LLOYD type of heating the prepared feed on a continuous metallic belt made of pallets at 1200-1300 C.Hot sinter discharged from sintering machine is crushed to +5mm-50mm size and cooled before dispatching to blast furnaces.

Parameters of sintering machines are:Effective area : 312sq.metreSintering area : 276sq.metreSinter Bed height : 300mmCapacity : 450TPH eachNumber of wind boxes : 24

The dust laden air from the machines are cleans in scrubbers and electrostatic precipitators to reduce the dust content to hundred milligram per cubicmeter level before allowing to escape into the atmosphere and thus helping in maintaining a clean and dust free environment.

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BLAST FURNACE

Hot metal is produced in Blast Furnaces, which are tall, vertical furnaces. The furnace is named as Blast Furnace as it is run with blast at high pressure and temperature. Raw materials such as sinter/iron ore lumps, fluxes (limestone/dolomite) and coke are charged from the top and hot blast at 1100-1300C and 5.745KSCH pressure is blown almost from the bottom. The furnaces are designed for 80% sinter in the burden.

VSP has three 3200cubicmetre Blast Furnaces (largest in INDIA) equipped with Paulworth BELL-LESS TOP EQUIPMENT with conveyer.Provision exist for granulation of 100% liquid slag at Blast Furnace cost house and utilization of Blast Furnace gas top pressure (1.5-2.0 atm) to generate 12MW of power in each furnace by employing gas expansion turbines.

The three furnaces with their novel circular cast house and 4 tap-holes each are capable of producing 1.38 tons of hot metal daily.After, tapping of hot metal at the bottom, then the tap-hole is closed with the help of mud gun, which shoots the water mass.

STEEL MELTING SHOP (SMS)Steel is an alloy of iron and carbon up to 1.8%. Hot metal produced in Blast Furnace contains impurities such as carbon (3.5-4.25%), silicon (0.4-0.5%), manganese (0.3-0.4%), sulphur (0.04% max.) and phosphorous (0.14%max.) is not suitable as a common engineering material.To improve the quality the impurities are to be eliminated or decreased by oxidation process.

VSP produces steel employing three numbers of top blown oxygen convertors called LD convertors or Basic Oxygen furnaces/convertors. Each convertor is having 133 cubic meters volume capable of producing three million tons of

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liquid steel annually. Besides hot metal, steel scrap, fluxes such as calcined lime or dolomite from part of the charge to the convertors.99.5% pure oxygen at 15-16 KSCG pressure is blown in the convertor through oxygen lance having convergent divergent copper nozzles at the blowing end. Oxygen oxidizes the impurities present in hot metals, which are fixed as slag with basic fluxes such as lime. During the process heat is generated by exothermic reactions of oxidation of metalloids viz., silicon, phosphorous, carbon and manganese and temperature rises to 1700 C enabling refining and slag formation.

Different grades of steel of superior quality can be made by this process by controlling the oxygen blow on addition of various ferroalloys or special additives such as Fe-Si, Fe-Mn, Si-Mn, coke breeze,Al etc. in required quantities while liquid steel is being tapped from the convertor into a steel ladleL.D gas produced as byproduct is used as a secondary fuel.

CHARACTERISTICS OF VSP CONVERTORS:

CAPACITY : 150 tons per heat/blowVOLUME : 133 cubic metersCONVERTOR SP. VOLUME : 0.886 meter cube per tonTAP TO TAP TIME : 45-60 minuteHEIGHT TO DIAMETER RATIO : 1.36LINING 1) WORKING : tar dolomite bricks

2) PERMANENT : Chrome Magnesite bricksAVG. LINING LIFE : 2445 heat

Liquid steel produced in LD convertors is solidified in the form of blooms in continuous bloom casters. However, to homogenize the steel and to raise its temperature when needed, Steel is first routed through, Argon rinsing station, IRUT (Injection refining and up temperature)/Ladle furnaces.

CONTINUOUS CASTING DEPARTMENT

Page 12: EFFECT OF CASTING PARAMETERS ON MACROSTRUCTURE OF STEEL

Continuous casting is defined as casting of liquid steel in a mould with a false bottom through which partially solidified ingot/ bar (similar to shape and cross section of mould) is continuously withdrawn at a same rate at which liquid steel is teamed in the mould.

Facility at the continuous casting machine include a lift and turn table called ladles, copper mould, oscillating system tundish, primary and secondary cooling arrangements to cool the steel bloom. Gas cutting machines for cutting the blooms in required length (avg. 6m long) are employed.

At VSP we have six-4 strand continuous casting machine capable of producing 2.82 million tons/year blooms of size 250X250 mm and 250X320 mm . Entire quantity of molten steel produced in SMS-CCD do not find much applications as such and are required to be shape into products such as billets, rounds, squares, angles (equal and unequal), channels, I-PE beams, HE beams, wire rods and reinforcements bars by rolling them in three sophisticated high capacity high speed rollers.

ROLLNG MILLSBlooms produced in SMS-CCD do not find much applications as such and are required to be shape into products such as billets, rounds, squares, angles (equal and unequal), channels, I-PE beams, HE beams, wire rods and reinforcement bars by rolling them in three sophisticated high capacity high speed, fully automated rolling mills, namely LMMM, MMSM and WRM.

LIGHT AND MEDIUM MERCHANT MILL (LMMM)

LMMM comprises of two units. In the billet/breakdown mill 250X320 mm size bloom are rolled into billets of 125X125 mm size after heating them into two no. of walking beam furnaces of 200 tons/hr capacity each. This unit comprises of 7 stands(2 horizontal 850X1200 mm) and 5 alternating vertical and horizontal stands(730x1000 mm & 630x1000 mm) billets are supplied from this to bar mill of LMMM and wire rod mill. The billets for rolling in bar mill of

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LMMM are first heated in two strands roller hearth furnace of 200 tons/hr capacity to temperature of 1150 C – 1200 C.The bar mill comprises of 26 strands – 8 strands double stand roughing train, two No.s of 5 strand, double stand intermedial range and two no.s 4 stand single strand finishing trains.

The mill is facilitated with temperature core heat treatment technology, evaporative cooling system in walking beam furnaces, automated piling and bundling facilities, high degree of automation and computerization.

The LIGHT AND MEDIUM MERCHANT MILLS in VSP is envisaged to produce 7,10,000 tones/annum of LMMM products 2,46,000 tones/annum of billets for sale 8,85,000 tones/annum of billets for WRM at 3.0MT stage

The operation floor on a second story elevation, namely +5.0metres. This arrangement has many advantages. It provides better drainages for lubricants, water and mill scale. The oil cellars can be placed at slightly below the ground Keeping in view the latest developments the LIGHT AND MEDIUM MERCHANT MILL is designed with level without deep excavations but assuring adequate drainage. The oil and water pipes and cable trenches are readily accessible. The material is lifted up the elevated floor onto the working bay means of elevators.

SALIENT FEATURES: High capacity and high speed Automatic minimum tension control in stands Double-side cooling beds of walking beam type High capacity and high productive sawing lines Automatic bundling machines Computerization at the sequential process control and material

tracking Adoption of closed circuit at furnaces Evaporative cooling system and waste heat recovery

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These features help to optimize the production and assure quality products from the mill.

The SMS supplies continuous cast BLOOMS in killed and semi-killed quality of ordinary grade, high carbon and low alloy steels. The bloom storage is at right angles and common to all mills.Bloom inspection and storage, if necessary, is carried out in the common storage.

Mill is designed to produce 7,10,000 tons/annum of various finished products such as rounds, rebars, squares, flats, angles, channels beside billets for sale.

WIRE ROD MILL (WRM)

WRM is a 4 strands, 25 stands fully automated and sophisticated mill. The mill has a four zone combination type reheating furnace (walking beam cum walking hearth) of 200 TPH capacity for heating the billets received from billet mill of LMMM to rolling temperature of 1200 C.

Heated billet are rolled in 4 strands. No twist continuous mill having a capacity of 8,50,000 tons of wire rod coil and having the following configuration :

7 stands two high 4 strand horizontal roughing train 6 stands two high 4 strands horizontal intermediate mills 2 stand 4 strands pre finishing mill 1 stand 4 strands no twist finishing mill

The mill produces rounds in 5.5 – 12 mm range and re-bars in 8-12 mm range.

Mill is equipped with standard and retarded steelmore lines for producing high quality wire rods in low, medium and high carbon grade meeting the stringent national and international standards namely BIS , DIN , JIS ,BS etc and having high ductility , uniform grain size and excellent surface finish.

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MEDIUM MERCHANT AND STRUCTURAL MILL (MMSM)

This mill is a HIGH CAPACITY continuous mill consisting of 20 stands arranged in 3 trains.

Roughing train having a 8 stands (4 two high horizontal stands , two vertical stands and two combination stands).

Intermediate train has 6 mill stands (two high horizontal stands, two combination stands , two horizontal stands/two universal stands).

Finishing train consists of 6 stands(two combination stands, four horizontal stands/4 universal stands).

The feed material to the mill is 250x250 mm size blooms , which is heated to rolling temperature of 1200 C in two walking furnaces each of rounds , squares , flats , angles (equal and unequal) T-bars , channels I- PE beams/ HE-beams (universal beams) having high strength close tolerances.

TECHNOLOGICAL ASPECTS OF SMS 2

HOT METAL AREA:

This zone of SMS is meant for receiving and keeping hot metal coming from Blast furnaces and supplying to convertor when required.

SMS 2 receives hot metal through TLC only and not through open tops. This facilitates better homogeneity(maximum supply of hot metal through blast furnace 3,hence uniformity in chemical composition), less drop in temperature of hot metal(better insulation is provided by TLC), and less contamination from surrounding atmosphere. Another advantage of hot metal supply through TLC is no need of MIXTURE in order to homogenize and raise the temperature of hot metal if required. Hence this saves the cost, time and complexity of the process.

HMDP UNIT:

Page 16: EFFECT OF CASTING PARAMETERS ON MACROSTRUCTURE OF STEEL

Removal of sulphur from hot metal is called Desulphurization of hot metal. Sulphur is a desirable element in steel when good machinability is desired from steel product. Whoever it is an unwanted element in most of application of steel due to following reasons:

Sulphur affects both internal and surface quality of steel Sulphur contributes to the steel brittleness and when it exists in sulphide

phase it acts as a stress raiser in steel products It forms undesirable sulphides which promotes granular weakness and

cracks in steel during solidification It has adverse effect on the mechanical properties It lowers the melting point and inter-granular strength and cohesion of

steel

Unlike other impurities which are removed from the hot metal by oxidation in the oxygen converter, the most economic method of removing sulphur from the hot metal is by reduction either in the transfer ladle or in the charging ladle, before it is charged in the converter. A no. of technologies has been developed for the external desulphurization of hot metal but all of them have the basic requirement of a reagent and a method of mixing. The difference between the technologies used is the properties of the reagents, the effectiveness of the reagent to remove sulphur and the effectiveness of the mixing method to get the reagent into solution.Also the effectiveness of hot metal desulphurization is inversely proportional to the desulphurization reagent injection rate. The most popular desulphurizing process today is deep injection of desulphurizing agent in hot metal.

DESULPURIZATION PROCESS

Dip lance process is the most economical, effective and reliable method of desulphurization of hot metal. It consist of pneumatic injection of fine grained desulphurization reagent into the hot metal with high dosing precision via a dispensing a vessel and a refractory lined lance. For each reagent, one separate dispensing vessel is used. All the vessels are identical. Nitrogen gas is normally used as a carrier gas for the desulphurization reagent. The reagent transfer in the injection line is under dense flow conditions. The dense flow conditions maximize reagent delivery as well as reduce abrasion wear of injection lines. The injection of desulphurization reagents through deeply submerged lance causes an intimate mixing of the desulphurization reagent with the hot metal. The process allows the use of several desulphurization reagents, such as lime, calcium carbide and magnesium, which remove the surfer in the hot metal by

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chemical reaction and convert it to the slag. Sulphur rich slag generated during the process is removes immediately after completion of the reagent reaction. The most common method is to tilt the ladleandrakethe slag of with the help of a slag raking machine.

Hot metalsulphur content is reduced in charging ladle or transfer ladle worldwide bythis method. For controlling the operating cost, a combination of dip lance method with mathematical process control and flexible control of the desulphurization plant is adopted. This combination provides a range of possible process technological variations. One of these possibilities is to vary the injection rate (kg/min) to suit the production requirements. Another possibility is to inject different desulphurization reagents during the process of desulphurization. The desulphurization reagents can be injected singly, simultaneously or with a time lag. Accordingly the process variations are known as MONO-INJECTION, CO- INJECTION or MULTI-INJECTION. Dip lance method can reliably reduce the Sulphur content of hot metal to figures as 0.001%.

SALINENT FEATURES: 25-30 heats/day routed through HMDP

• Average treatment time 50 minutes• Desulphurization is done by injecting Calcium Carbide & Mg based compound• Hot metal Sulphur content reduced from 0.04% to0.005%

IMPORTANT ISSUES IN DESULPHURIZATION OF HOT METAL: During the desulphurizing process, the generation of slag is proportional

to the amount of reagent added to the hot metal. Also during the process, some hot metal gets trapped in the slag and gets pulled out of transfer ladle during the slag rimming. This amount is around 1.0%for the co-injection process. Desulphurization slag contains about 50% iron.

The loss of heat during the desulphurizing process is an important factor snce it reduces the sensible heat of the hot metal sent to the convetor. The three primary sources of heat loss are radiation from the surface of hot metal , addition of coal reagents and introduction of cold injection lances into the hot metal. The largest temperature loss occurs during injection rather than skimming. A temperature loss of 30 C is expected during the desulphurization process.

Desulphurizing process does not have any major effect on the refractory lining life of hot metal ladle since the treatment time is small.

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Both reagent injection and slag skimming operation generate fumes which are to be collected and dedusted prior to their release in the environment. The captured fumes are typically cleaned in a pulse jet type bag house designed for metallurgical operation.

RH DEGASSER

Molten steel, taken out of the convertor furnace, is ultimately refined and degassed during the secondary refining process. The RH vacuum degasser is ideal for the swift degassing of large amount of molten steel. The RH vacuum degasser is also suitable for the mass production of high purity steel at integrated steel works, realizing decarburization and heating by injecting pure oxygen gas into the vacuum vessel. Furthermore, it has extended refining functions, such as the acceleration of desulphurization and deoxidation through addition of flux while controlling the form of the impurity.

Pressure dependent reactions are the reason for the treatment of liquid steel in this process. There are many vacuum degassing process but RH degasser are very popular. The RH process has been named after Ruhrstahl and Heraeus, where this process was initially developed in 1950.

The RH circulation degassing process has proved its vast suitability in large number of shops worldwide, for operation with short tap to tap time covering heat sizes upto 400 tons. The vacuum treatment in RH plants produces steel which fulfills the demand of high steel quality. To achieve this, the liquid steel is allowed to circulate in a vacuum chamber where a considerable drop in pressure causes it to disintegrate into the smallest of the parts. The increase in surface area allows the steel to degas to the best possible extent. The process needs reliable vacuum units since it should be able to suck off very large flow rates under very difficult conditions of dusty atmosphere and high temperature.

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Figure - Mechanism of vacuum treatment of liquid steel in RH process

CONVERTOR:

Two 150 tons BOF convertors including Gas cleaning system, bottom purging, slag retaining device and infrared camera has been provided for bath level measurements. The hot metal or liquid pig iron is the primary source of iron units and energy in BOF and the second largest source of iron unit is Scrap.

In SMS 2 Level 2type blowing is done contrary to Level 1 type blowing in SMS 1 which gives consistency in final composition therefore fluctuation of carbon level from determined composition is 0.03-0.05% max. While that of SMS 1 is in the range of 0.05-0.15%. Hence bath carbon finishing problem is there in SMS 1 while on the other hand uniform bath carbon level can be achieved. Slag free tapping can also be achieved through slag retaining device.

Effective combined blowing results in faster slag-metal interface reaction and hence better refining and less blowing time is required or in other words less oxygen consumption per tons of heat is there. This results in less ferrous oxide content in the slag hence less metal loss and less slag volume for same or better metal quality as obtained in SMS-1.

Some of the features of convertors in SMS 2 are summarized below:

• Capacity-150t, H/D Ratio 1.44, • Top Lining, Fixed Bottom• Tilt Drive with Emergency Pneumatic motors• Bottom Stirring With 8 Plugs and BathMeasurement• Tap to Tap Time: 49.5 Min (avg.)• Lance with Rope Drive & Emergency Pneumatic Drive• On-Line Argon Rinsing Stations• Dog House: Reduces dust content in surrounding and facilitate clean working• Secondary Dedusting System• Hydraulic Skirt Drive• Hydraulic Venturi Scrubber• Blowing Time: 16 mins (Max) • Oxygen Flow Rate: 600 cubic meters/min (Max)• Input: 1025kg/TCS

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• Scrap Input: 50-55 Kg/T • Iron Ore Input: 20kg/T• Oxygen Blowing Rate: 3.5 To 4 Nm3 / T/Min • Converter Operation Mode: 2/2 • Number of Heats/Day: 56 Heats (2 Lds)• Number of Heats/Year: 18760• Capacity: 2.80 mtpa• Heat Wt: 150t Avg• Tapping Temp: 1680°C• Slag Free Tapping with Slag Retaining Device

SMS-2 SMS-1

2 LHF and 1 RH degasserOperated

Ladle tilter in LP BayPlatform Car for return ladles

Ladles and Slag pots

1 LHF and 1 IRU2 Hydraulically

No such facility

STC - 4 only for return

Continuous casting at VSP

Continuous Casting Machines (CCM):Continuous casting may be defined as teeming of liquid metal in a mould with a false bottom through which partially solidified ingot (same shape as mould) is continuously withdrawn at the same rate at which liquid metal is poured in the mould.

Steel Bloom Produced by Continuous Casting:

In this process, molten steel flows from a ladle, through a tundish into the mold. The tundish holds enough metal to provide a continuous flow to the mold, even during an exchange of ladles, which are supplied periodically from the steelmaking process. The tundish can also serve as a refining vessel to float out detrimental inclusions into the slag layer.

Once in the mold, the molten steel freezes against the water-cooled walls of a bottomless copper mold to form a solid shell. The mold is oscillated vertically

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in order to discourage sticking of the shell to the mold walls. Drive rolls lower in the machine continuously withdraw the shell from the mold at a rate or “casting speed” that matches the flow of incoming metal, so the process ideally runs in steady state. The liquid flow rate is controlled by restricting the opening in the nozzle according to the signal fed back from a level sensor in the mold. Fig. 2

Fig.3 (Continuous Casting of Bloom)

Test of Steel Bloom:

Non-destructive testing (NDT) is a wide group of analysis techniques used in science and industry to evaluate the properties of a material component or system without causing damage. The terms Nondestructive examination (NDE), Nondestructive inspection (NDI), and Nondestructive evaluation (NDE) are also commonly used to describe this technology. Because NDT does not permanently alter the article being inspected, it is a highly-valuable technique that can save both money and time in product evaluation, troubleshooting, and research. Common NDT methods include Ultrasonic, magnetic particle, liquid penetrate, radiographic, remote visual inspection (RVI), Eddy current testing.

In ultrasonic testing (UT), very short ultrasonic pulse-waves with center frequencies ranging from 0.1-15 MHz and occasionally up to 50 MHz are launched into materials to detect internal flaws or to characterize materials. In ultrasonic testing, an ultrasound transducer connected to a diagnostic machine is passed over the object being inspected. The transducer is typically separated from the test object by a couplant (such as oil) or by water, as in immersion testing.

Advantages:

1.   High penetrating power, which allows the detection of flaws deep in the part.

2.   High sensitivity, permitting the detection of extremely small flaws.3.   Only one surface need be accessible.4.   Greater accuracy than other nondestructive methods in determining the depth of internal flaws and the thickness of parts with parallel surfaces.5.   Some capability of estimating the size, orientation, shape and nature

of defects.

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6.   Nonhazardous to operations or to nearby personnel and has no effect on equipment and materials in the vicinity.7.   Capable of portable or highly automated operation

Bloom Storage Yard (BSY) :

To synchronize the production in continuous casting machine and requirement of rolling mills for blooms, Bloom storage yard (BSY) has been established. Inspection and selective conditions are also carried out in BSY. After cutting the blooms at GCM they are moved to cooling beds and after cooling to 5000C they are transferred to racks. The BSY is served by 11 nos. EOT cranes with rotating cabins and magnet facility. Blooms of particular grade of steel are stored at a particular place. Every bloom is marked by heat no. and machine no.

Blooms Storage And Inspection : The SMS supplies continuous cast blooms in killed and semiskilled quality of ordinary grade, high carbon and low alloy steels. The bloom storage is at right angles and common to all mills. Bloom inspection and storage, if necessary, is carried out in the common storage.

Effect of Various Parameters on Quality of Blooms:-

Casting Temperature:

The liquid steel during continuous casting should be within the specific limits depending upon the grade of steel. A 30 – 40 C above liquidus temperature and high casting speeds are required for good equiaxed cast structure. Increase in casting temperature above the desired level leads to central segregation and formation of longitudinal cracks. Higher the casting temperature longer will be zone of columnar crystal and vice versa. There is a close relation between the degree of control segregation and columnar crystals developed. The later is sensitive to the temperature of molten steel and grows rapidly when the super heat is over 20 C. Further segregation is inversely related to equiaxial zone.

Decrease in casting temperature below desired level is also harmful for the quality of ingot as it leads to thicker and colder skin having poor plasticity. During withdrawal of ingots especially in radial m/c transverse cracks develop. Low temperature metal also leads to slag inclusion. Higher is the casting temperature higher is the columnar structure.

At high casting temperature crystals that form in the mould initially remelt. Columnar zone length is important for:

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1. It is more susceptible to cracking than the equiaxed zone.

2. Long columnar zone will be susceptible to severity of centerline segregation and porosity.

Thus to minimize columnar zone length, the casting temperature should be as low as possible. Too low a temperature however may result in nozzle chocking. Low casting temperatures do not promote the float out of inclusions and may result in an increase in inclusion levels.

Facilities and equipments at CCM platform: Lift and turn stand:To accommodate the steel ladles and place them in casting position as and when required to facilitate sequence casting. It lifts the ladle and places he ladle at the casting position by turning it and swing back the empty ladle after completion of casting.Mould oscillating system:To facilitate easy withdrawal of concast blooms (partially solidified) from the mould.Oscillation frequency: 60-100 cycle/minute.Mould oscillation amplitude: 6-8mm.Copper mould:The foremost important factor in the continuous casting is the copper mould which decides the efficiency of the process. The material selected for mould and the design of mould play a prominent role in obtaining the bloom of greater surface finish, better mechanical properties with minimum casting defects. A mould with good design associated by good cooling system gives quality blooms, provided a great care, is exercised during casting.In VSP, square (250mm x 250mm) and rectangular (320mm x250mm) cross-sectional moulds are used. These moulds are provided taper towards the bottom(327 x 255 top,324 x 252.5 bottom in case of a 320 x 250 bloom) to maintain the contact between partially solidified strands and it is made of copper which is necessary for achieving the necessary cooling rate.

Copper is an ideal material for mould because it is having-1. Good thermal conductivity.2. Mechanical strength must be retained at operating temperatures 250oC.3. Recrystallization temperature above 3000 C.4. Low friction co-efficient and good resistance to wear.5. Chemical immunity with reference to Steel.

Cu-Ag 0.1 P-F 25-possess all the above properties.Length of mould at VSP is 1.0m.Radius of mould 12m

Strand Cooling:

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Strand cooling is carried in two stages: Primary and Secondary cooling.

Primary Cooling:The boiler feed water is used for this purpose with pH 7-9, total hardness-0.2dh. This water is repeatedly pumped through the mould in a closed cycle with re-cooling blot. This water has to be treated and anti-corrosive agent etc. should be added. This water is supplied at a pressure of 4-5 bar. The inlet water comes from the bottom and leaves the mould through the outlet valve which is located at the top of mould. This is indirect type of cooling. Secondary Cooling:The water that is spread over the strand should cool the strand uniformly throughout the length to avoid undercooling of some parts of the strand. The pressure will be 6 bar. The counteracting flow problem due to corrosion, the pipeline will be made of stainless steel. In secondary cooling, strand (bloom) will be completely solidified leaving no liquid steel at all. The secondary cooling zone begins from just below the mould. Water for secondary cooling should have pH: 7-9Total Hardness: 20dh.Carbonate hardness: 0.7dh.Dummy Bar:The function if dummy bar is to seal the mould bottom, for the starting of casting and to withdraw solidified shell until the hot strand has passed to strengthening and withdrawing machines.

Backup Roller Sections N1 & N2:These sections are intended for supporting and directing the dummy bar and strand in course of casting. N1 is a four roll section installed on post underneath the secondary cooling sections while N2 is a six roll section installed after the four high strands.Withdrawal and Strengthening rollers:There are 4 strands which are used withdrawing and strengthening the curved bloom. These 4 strands are designated as TK1, TK2, TK3, TK4.TK1:4 high strands.TK2: 2 high strands.TK3:2 high strands.TK4:2 high strands.Technical details of CC machineAverage casting speed for 320 x 250 bloom size is 0.78 M/min for 250 x250 bloom size is 0.82 M/min.Gas Cutting Machines (GCM):The strand which continuously comes from the copper mould after getting completely solidified should be cut as per our requirement, to facilitate easy handling etc. In order to cut the blooms accurately, a gas cutting machine, using LPG, is used. Since the bloom travels with certain speed, the machine used for cutting for the bloom .For this gripper are used ,which grips the bloom and

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travels along with it , taking the LPG flame with it .Each CC machine has been provided with 4 cutting machines to cut the four blooms at a time.Bloom storage yard (BSY):To synchronize the production in continuous casting machine and requirement of rolling mills for blooms, Bloom storage yard (BSY) has been established. Inspection and selective conditions are also carried out in BSY. After cutting the blooms at GCM they are moved to cooling beds and after cooling to 5000C they are transferred to racks. The BSY is served by 11 nos. EOT cranes with rotating cabins and magnet facility .Blooms of particular grade of steel are stored at a particular place. Every bloom is marketed by heat no. and machine no.

The Continuous Casting MachineThe continuous casting machine can be divided into three regions:1. Water cooled copper mould section (A)2. The secondary cooling section (B)3. The radiant cooling section (C)The description of the various parts is as follows:

Fig.4A. The Mould:The mould is the heart of the continuous casting machine. It is the primary heat extraction device where a shell of adequate thickness is formed. The mould also provides support to the newly formed shell. It influences, profoundly, the quality of the steel. Design which does not suit the operating conductions or excessive distortion in the mould that may develop in the course of prolonged

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operation have been found to increase the number of defects e.g. the longitudinal corner cracks etc.Different types of moulds have been developed like the straight mould and curved mould. The three major types of moulds are:-1. The solid block mould.2. The plate mould which consists of a copper mould backed with cast iron plates.3. The tubular mould.

The heat transfer in the mould occurs in a series of steps:-1. Conduction and radiation across the air gap separating the mould and the strand.2. Conduction through the mould wall.3. Convection at the mould/cooling water interfaces.

The moulds are reciprocated during casting. The principle was first developed by Junghan‟s to reduce the risk of breakout caused by the rupture of the skin. With the introduction of „Negative Strip‟ high speedcasting became possible. Negative Strip means that on the down stroke the mould moves at a higher velocity than that of the withdrawing strand. This process prevents mould strand adhesion and averts rupture of the shell during subsequent upward motion of the mould. Another major advantage is that the mould lubricant, from the top of the mould, is transferred to the lower sections.B. The Secondary Cooling Section:This section follows the mould in the continuous casting machine. The secondary cooling section consists of support rolls and water spray nozzles. The rolls primarily give support to the thin shell that forms in the mould. The water sprays continue the heat extraction process that is initiated in the mould. This section varies from as little as Ø.4 m up to 4.0 m. The water sprays operate on the principle of pressure atomization that is water under high pressure when forced through an orifice breaks up into droplets. The sprays used generally give a full cone pattern. Sometimes a V pattern is used for the lower portion of this section. Generally for bloom casting sets of four nozzles, one for each face, are placed in rows. These nozzles are connected and classified into zones so that the water flow rate and thereby the heat extraction rate may be controlled.As a major part of the shell forms in this section the heat extraction and solidification should be continued at a controlled rate without the generation of tensile stresses of magnitude that may cause shape defects, surface cracks or internal cracks. Water flux has a major effect on heat extraction. But the conduction of heat through the shell becomes the rate limiting process. The primary effect of spray cooling is to alter the temperature distribution through the shell.Improper spray pattern cause a large no. of defects in the blooms. The most common defect is the midway crack. The other defect though not as common, is

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rhomboidity, which arises due to a symmetrical cooling pattern as a result of clogged nozzles etc.C. The Radiant Cooling Section:This section follows the secondary cooling zone. The strand is left open to the atmosphere. There is no control over the solidification or the heat transfer rate in this zone.The Gas Cutting Machine:This is the last part of the machine. It follows the radiant cooling section. The function of this section is to cut the strand into blooms of the desired length. The gas cutting machine is a welded steel construction wherein a gas torch is fixed. This torch is mounted on a car which moves along with the strand. The car is provided with grippers are pneumatically operated. The torch is provided with transverse movement. When the strand moves up to the desired length the gripper is engaged. The strand and the gas cutting torch move with the same speed. The cutting LPG is switched on and the torch is moved in the transverse direction cutting on the strand. When the cutting is completed the bloom is taken away by operating the withdrawal rolls and the gas cutting machine is brought back to its initial position.

MACRO ETCHING

Terminology:

Dendritic structure: Primary crystals of dendritic structure formed during solidification of steel, still remaining after working.

Ingot pattern : A pattern which appears during solidification of ingot which appears as a zone of demarcation between the columnar and heterogeneous region of ingot and persists even after reduction to the stage of inspection.

Segregation: Variation in the density of corrosive effect caused by segregation during solidification. When this phenomenon occurs at the central portion it is known as centre segregation.

Porosity/looseness: A spongy pattern caused by the development of fast corrosive effect on the entire section or the central portion of the steel material.

Pit/pin hole: A spotty pattern of small visible cavities caused by etching out of inclusions or micro constituents from the finished surface of the specimen.

Pipe: A discontinuity associated with segregated impurities caused by the shrinkage during solidification of steel. This may be carried through the various manufacturing processes to the finished product.

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Burst: A distinct pattern of cracks in the central region without any segregated impurities caused by forging or rolling.

Seam,Laps: A surface imperfection on wrought steel due to folding of one portion of surface metal over another at any stage of working without being unwelded.

Thermal cracks or flakes: Short discontinuous internal cracks caused by stresses produced by localized transformation and hydrogen solubility effects during cooling after hot working. And also called shatter cracks and hairline cracks.

Flow lines: Lines which appear on the polished and macroetched surface of a metal and indicate the direction in which plastic flow has taken place during fabrication.

SELECTION OF SAMPLE

Defects which are revealed during macroetching testing may be introduced at the various stages of manufacturing. To avoid wasteful work on the defective material sampling ought to be done in an early stage of manufacturing. However the sample should not be taken so early that the further working may introduce serious defects. A few methods of sampling for wrought steel are indicated For billets, blooms and hot rolled products: Discs may be cut from these products near the end not too close to the end to avoid flase structure because of fish tailing. Discs from large blooms may be cut into smaller pieces for easy handling. For Forging and Extrusions: Discs should be cut transverse to the long dimension to reveal flakes, bursts,etc., Forgings cut parallel to the long dimension will show flow line. In complicated castings, to reveal flow lines, method of cutting has to be carefully selected. For Sheets and Plates: For surface defects, a sufficiently large sample should be taken. For convenience in handling several smaller samples may also be taken. For lamination transverse section is taken. In case the width is too large only a portion from the centre may be taken.

SPECIMEN PREPARATION

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If the mas of wrought steel is to be tested is relatively soft the specimen shall be extracted by sawing or some other machining operation. In case of hard steel the specimen shall be extracted by abrasive wheel cutting. For very large section gas cutting is used but the heat affected areas shall be removed by machining or abrasive cutting wheel.

Required surface finish for specimens for macroetching vary from saw cut machined surface to polished surfaces. The degree of surfaces roughness permitted depends on the severity of the etchant and also on the purpose of etching.

For satisfactory result in macroetching the smooth surface prepared by any method shall be with a minimum amount of coldwork. When severe etchant is used the discs shall be faced on lathe or shaper. The usual procedure is to take the roughing cut and then finished cut. This will prepare a smooth surface without any cold work from prior operations. Grinding shall also be conducted on the same way using free cutting wheel and light cutting wheel.

When fine details are required, a far less severe etchant is used and a smother surface is required. The kerf marks produced by sawing operation are removed from surface by means of filing, machine grinding or machining. The finer surface finish is obtained by grinding the specimen on No. 00, or No. 000 metallographic polishing papers.

Whatever method is used in producing smooth surface it is important that during the operation the specimen is kept sufficiently cool to prevent heating of the surface to an excessively high temperature.

Guideline regarding surface finish required for different etching procedureshave been indicated in table 1.

After surface preparation the sample is cleaned carefully with suitable solvents. Any grease, oil, other residues will produce uneven attack. Once cleaned care should be taken not to touch the sample surface or contaminate it in any way. ETCHING REAGENTSThe commonly used etching reagents for wrought steels are listed in table 1. Any other standard reagents may also be used.PROCEDURE Macroetching should be carried out in containers which shall be fairly

resistant to the attack of the etching reagents. Dishes or trays made of

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porcelain, heat resistant glass or carrion resistant glass or a corrosion resistant alloys may be used as etch tanks.

The prepared specimen should be put directly into the etching solution with the surfaces to be examined either face up or vertical to permit the gas generated to escape freely. The specimens being etched should not be too close to each other or to the tank, if it is metallic to avoid non uniform etching.

When etching is carried out above room temperature the etchant should be first heated to the required temperature and then the specimen is immersed in it. To get best reproducible results specially when the total volume of the specimen is higher to the volume of the solution. The specimen should also be heated in a water bath,to the etching solution temperature before immersed in the hot etchant.

The etchant periods recommended in table 1 are only intend as a guide. The time required to develop the desired results in a particular test may be determined by frequent examination of the specimen as etching proceeds. Since it depends on many factors including the method of manufacture to the steel , heat treatment, alloying content,surface preparation,etc., The actual time to develop[ a structure may be quite different from the one suggested in the table 1.

Ranges of etching temperature for various etchants have been indicated in table 1.

After completion of etching the specimen should be washed immediately under running water using a stiff fiber brush to remove a deposit of smutfrom the surface, rinsed again, dried with alcohol and cleaned air and kept in a dry place.INTERPRETATION OF RESULTS

Indications that may be commonly seen after macroetching are given below and also illustrated in table 1.

Center defects-: Pipe, bursts, segregation and porosity or looseness. Surface and sub surface defects- Seams, laps etc., ingot corner segregation or

cracks and pin holes. Miscellaneous defects- Thermal cracks or flakes, foreign inclusion metal or

dirt and ingot pattern.

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Flow line indicating direction of plastic flow. Grain size.

The illustrations are examples of various indications and are not to be used as standards of acceptance or rejection.

REPORTING OF RESULTS

The reports should include full information on type and composition of steel, cross sectional dimensions of the specimen and conditions of the defects observed. The observed defects may be grouped by type and location.

INSPECTION

Whenever macro etch testing is stipulated agreement should be reached between the manufacturer and the purchaser regarding the following

a. The stage of manufacture at which test shall be conducted.b. The number and location of the specimens to be examined.c. The necessary surface preparation prior to etching o the specimen.d. The etching proceduree. The permissible degree to which each of the defects listed above may be

tolerated for each of the end products.

A: saw cut or machined surface, B: average ground surface, C polished surface.

Sl.No.

Composition

Alloys Temperature

Etching

Time

Surface

Required

Characteristics

revealed

1. HCl 50ml

H2O

50 ml

Plain and alloy steels, high speed tool steels, cutlery steels and stainless steels.

70-80 15-60 A or B Segregation,porosity,hardness penetration,cracks,inclusions,dendrites,flow lines,soft spots,structure and

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weld examination.

2. HCl 38ml

H2SO4 12ml

H2O 50ml

Do Do Do B or C Do

3. HCl 50ml

H2SO47ml

H2O 18 ml

Do Do Do A or B Do

4. Ammonium copper chloride 10-35g

H2o

Steels other than stainless and heat resisting steels.

Room temperature

Immerse still for 5 min. remove copper deposit by cloth. Repeat 3-10 times

B Macrostructure of steel material of comparatively large size.

5. HCl 50ml

HNO3 25ml

H2O 25ml

Stainless and high alloy steels.

Do 10-15 A or B Same as 1.

6. HCl 50ml

STAINLESS AND HIGH TEMPERATURE

70-80 15-30 B OR c SAME AS 1.

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Saturated solution of CuSO4 in H2O 25ML

ALLOYS

7. HNO3 5-10%

Water or ethanol rest

Plain and low alloy steels.

Room temperature

5-30 C Carburization, decarburization,hardnesspenetration,cracks,segregation,weld examination.

8. H2SO4 10ml

H2O 90ml

Plain, low and high alloy steels.

Do 24-60 C Inclusions,porosity,pipe,blow holes on large sections.

9. H2SO4 10ml

H2O 90ml

Do 70-80 15-60 C Do

10. CuCl2,2H2o 25g

MgCl2, 6H2O 20g

Ethanol 500ml

Plain and low alloy steels

Room temperature

Until surface appears coppery

B or C Phosphorous rich areas and banding

11. (NH4)2S2O8

50G

H2O 500ml

Do Do Swab until desired etch is obtained

C Grain size and weld observation.

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12. CuCl2 6g

FeCl2 6g

HCl 10g

Ethanol 100ml

Low carbon steel Do Heat specimen to 200 and immerse

C Show strain lines

CONTINUOUS CASTINGINTRODUCTION:-

Continuous Casting is a term applied to casting processes involving in “continuous, high volume production of solid metal sections with a constant cross section from the liquid metal”. The quality, grade and shape of the cast product influence the product end use for subsequently rolling in the finishing mill. It accounts for 90.56% of the global crude steel output & finds extensive use for improving the yield, quality, productivity and economics of steel production in the world. Depending on the desired annual tonnage, liquid steel availability and the anticipated operating hours, the continuous casting machine is designed for the number of strands & casting speeds to match the liquid steel supply from the melting shop. Temperature and chemical composition homogeneity are the primary requirement of steel continuous casting. The molten steel from the furnace is tapped in the ladle and is subjected to various ladle treatments involving alloying and degassing. After this, the ladle is transferred to the casting shop where argon rinsing is done to get the requisite cast flow temperature and placed on a rotating turret. The slide gate of the ladle is opened and oxygen lancing is done to allow

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liquid steel flow via a refractory shroud into a tundish. That allows a reservoir of the metal to feed the casting machine. The tundish possess various flow control devices such as dam, weir, baffles and impact strike pads. That enhances inclusion separation & assure stable stream pattern to the mould. The liquid steel from the tundish is drained into the mould through orifices controlled by stopper rods and metering nozzles. Submerged entry nozzle present between the tundish and the mould in bloom/slab casters help in avoiding re-oxidation of the liquid steel during its flow in the mould.

To start the continuous casting machine, the mould bottom is sealed by a dummy bar that is placed hydraulically through the spray chamber by the straightener withdrawal unit that prevents liquid steel from flowing out of the mould. The steel that is poured into the mould gets partially solidified with a solid outer shell and liquid core.

The mould is equipped with oscillator to prevent sticking of the cast strand to the mould with mould oscillating cycle varying in frequency, stroke and pattern. The friction between shell and mould is reduced through use of mould lubricants like oils or powdered fluxes. Once steel shell has sufficient thickness, the straighter withdrawal unit gets started and proceeds to withdraw the partially solidified strand out of the mould with the dummy bar with liquid steel continuing to fall into the mould. The withdrawal rate is dependent on the cross-section, grade and the quality of the steel. After exiting the mould, the strand with the solid shell enters rollers channel section and the secondary cooling chamber. The support rolls below the mould are of high rigidity and the roll interval is short to bulging caused by ferro-static pressure thus preventing subsequent cracking and segregation due to bulging. Here, the solidified strand is sprayed with water or water-air mixture for promoting solidification. Thus, is preserving the cast shape integrity and the product quality. After the strand is completely solidified, it passes through the straighter withdrawal unit and the dummy bar is disconnected. After this, the strand is cut to required lengths by LPG cutters.The reliability of the continuous casting machine with regard to its availability and utilization is the key towards improved yield and increased productivity. Any operation irregularity during continuous casting leads to the downtime of the caster affecting its availability.

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Hence, it is necessary to take care of operational irregularities to enhance the caster availability.

Continuous casting at VSPContinuous Casting Machines (CCM):Continuous casting may be defined as teeming of liquid metal in a mould with a false bottom through which partially solidified ingot (same shape as mould) is continuously withdrawn at the same rate at which liquid metal is poured in the mould.

Steel Bloom Produced by Continuous Casting:

In this process, molten steel flows from a ladle, through a tundish into the mold. The tundish holds enough metal to provide a continuous flow to the mold, even during an exchange of ladles, which are supplied periodically from the steelmaking process. The tundish can also serve as a refining vessel to float out detrimental inclusions into the slag layer.

Once in the mold, the molten steel freezes against the water-cooled walls of a bottomless copper mold to form a solid shell. The mold is oscillated vertically in order to discourage sticking of the shell to the mold walls. Drive rolls lower in the machine continuously withdraw the shell from the mold at a rate or “casting speed” that matches the flow of incoming metal, so the process ideally runs in steady state. The liquid flow rate is controlled by restricting the opening in the nozzle according to the signal fed back from a level sensor in the mold.

Test of Steel Bloom:

Non-destructive testing (NDT) is a wide group of analysis techniques used in science and industry to evaluate the properties of a material

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component or system without causing damage. The terms Nondestructive examination (NDE), Nondestructive inspection (NDI), and Nondestructive evaluation (NDE) are also commonly used to describe this technology. Because NDT does not permanently alter the article being inspected, it is a highly-valuable technique that can save both money and time in product evaluation, troubleshooting, and research. Common NDT methods include Ultrasonic, magnetic particle, liquid penetrate, radiographic, remote visual inspection (RVI), Eddy current testing.

In ultrasonic testing (UT), very short ultrasonic pulse-waves with center frequencies ranging from 0.1-15 MHz and occasionally up to 50 MHz are launched into materials to detect internal flaws or to characterize materials. In ultrasonic testing, an ultrasound transducer connected to a diagnostic machine is passed over the object being inspected. The transducer is typically separated from the test object by a couplant (such as oil) or by water, as in immersion testing.Advantages:

1.   High penetrating power, which allows the detection of flaws deep in the part.

2.   High sensitivity, permitting the detection of extremely small flaws.

3.   Only one surface need be accessible.4.   Greater accuracy than other nondestructive methods in determining the depth of internal flaws and the thickness of parts with parallel surfaces.5.   Some capability of estimating the size, orientation, shape

and nature of defects.6.   Nonhazardous to operations or to nearby personnel and has no effect on equipment and materials in the vicinity.7.   Capable of portable or highly automated operation

Bloom Storage Yard (BSY) :

To synchronize the production in continuous casting machine and requirement of rolling mills for blooms, Bloom storage yard (BSY) has been established. Inspection and selective conditions are also

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carried out in BSY. After cutting the blooms at GCM they are moved to cooling beds and after cooling to 5000C they are transferred to racks. The BSY is served by 11 nos. EOT cranes with rotating cabins and magnet facility. Blooms of particular grade of steel are stored at a particular place. Every bloom is marked by heat no. and machine no.

The sequence of operations in brief at different sections of continuous casting shop is given below:

1. Steel ladle from converter after tapping is transferred to Argon Rinsing station.

2. In rinsing station: Argon purging (bottom or top or both) is carried out for a period not less than 12 minutes. During rinsing, Aluminium is also added.

3. The sample and temperature are taken. The sample is sent to lab and composition is verified. If temperature and composition are satisfied, liquid steel is sent to casting platform. If temperature or composition corrections are required, they are done either at ARS or IRUT or LF.

4. In CCM, first of all, dummy bar is inserted through the mould. Some small scrap is charged into mould to enhance cooling rate of liquid steel, to enable the operator to withdraw the dummy bar.

5. In CCM, the ladle with liquid steel is placed on the lift and turn stand and will be fixed with hydraulic cylinder for operating slide gate mechanism to control teeming of liquid steel to mould from ladle.

6. Meanwhile tundish is preheated to about 1000oC. Stopper are checked before the tundish is placed into casting position. After placing the tundish at casting position, nozzles are positioned exactly in the centre of the mould.

7. Ladle is brought to casting position by turning the lift and turn stand. Stoppers of the tundish are kept closed. Slide gate of ladle is opened by hydraulic mechanism. If liquid steel

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stream is not proper or liquid steel is not coming, oxygen lancing is carried out in ladle nozzle.

8. Liquid steel is continuously fed into the tundish and the level in tundish is carefully observed. When it is 2/3 full, stoppers will be opened to allow the steel to fill the mould.

9. Before feeding liquid steel into mould water circulation in the mould is to be ensured.

10. After the steel meniscus reaches certain level, dummy bars withdrawal will be started. Secondary cooling water spray is also started.

11. After the dummy bar passes over the withdrawal rollers, it will be disengaged.

12. Continuously coming bloom is cut by gas cutting machine. The required length of cut blooms are sent to BSY after marking the heat no. and CC machine no. by hot chalk.

13. These blooms are stacked, inspected and heat no. is written by paint over cross section of bloom. Blooms are sent to rolling mills as per requirement.

Blooms Storage And Inspection : The SMS supplies continuous cast blooms in killed and semiskilled quality of ordinary grade, high carbon and low alloy steels. The bloom storage is at right angles and common to all mills. Bloom inspection and storage, if necessary, is carried out in the common storage.

Effect of Various Parameters on Quality of Blooms:-

Casting Temperature:

The liquid steel during continuous casting should be within the specific limits depending upon the grade of steel. A 30 – 40 C above

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liquidus temperature and high casting speeds are required for good equiaxed cast structure. Increase in casting temperature above the desired level leads to central segregation and formation of longitudinal cracks. Higher the casting temperature longer will be zone of columnar crystal and vice versa. There is a close relation between the degree of control segregation and columnar crystals developed. The later is sensitive to the temperature of molten steel and grows rapidly when the super heat is over 20 C. Further segregation is inversely related to equiaxial zone.

Decrease in casting temperature below desired level is also harmful for the quality of ingot as it leads to thicker and colder skin having poor plasticity. During withdrawal of ingots especially in radial m/c transverse cracks develop. Low temperature metal also leads to slag inclusion. Higher is the casting temperature higher is the columnar structure.

At high casting temperature crystals that form in the mould initially remelt. Columnar zone length is important for:

3. It is more susceptible to cracking than the equiaxed zone.

4. Long columnar zone will be susceptible to severity of centerline segregation and porosity.

Thus to minimize columnar zone length, the casting temperature should be as low as possible. Too low a temperature however may result in nozzle chocking. Low casting temperatures do not promote the float out of inclusions and may result in an increase in inclusion levels.

Facilities and equipments at CCM platform: Lift and turn stand:To accommodate the steel ladles and place them in casting position as and when required to facilitate sequence casting. It lifts the ladle and places he ladle at the casting position by turning it and swing back the empty ladle after completion of casting.Mould oscillating system:

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To facilitate easy withdrawal of concast blooms (partially solidified) from the mould.Oscillation frequency: 60-100 cycle/minute.Mould oscillation amplitude: 6-8mm.Copper mould:The foremost important factor in the continuous casting is the copper mould which decides the efficiency of the process. The material selected for mould and the design of mould play a prominent role in obtaining the bloom of greater surface finish, better mechanical properties with minimum casting defects. A mould with good design associated by good cooling system gives quality blooms, provided a great care, is exercised during casting.In VSP, square (250mm x 250mm) and rectangular (320mm x250mm) cross-sectional moulds are used. These moulds are provided taper towards the bottom(327 x 255 top,324 x 252.5 bottom in case of a 320 x 250 bloom) to maintain the contact between partially solidified strands and it is made of copper which is necessary for achieving the necessary cooling rate.

Copper is an ideal material for mould because it is having-1. Good thermal conductivity.2. Mechanical strength must be retained at operating temperatures 250oC.3. Recrystallization temperature above 3000 C.4. Low friction co-efficient and good resistance to wear.5. Chemical immunity with reference to Steel.

Cu-Ag 0.1 P-F 25-possess all the above properties.Length of mould at VSP is 1.0m.Radius of mould 12m

Strand Cooling:Strand cooling is carried in two stages: Primary and Secondary cooling.

Primary Cooling:The boiler feed water is used for this purpose with pH 7-9, total hardness-0.2dh. This water is repeatedly pumped through the mould in a closed cycle with re-cooling blot. This water has to be treated and

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anti-corrosive agent etc. should be added. This water is supplied at a pressure of 4-5 bar. The inlet water comes from the bottom and leaves the mould through the outlet valve which is located at the top of mould. This is indirect type of cooling. Secondary Cooling:The water that is spread over the strand should cool the strand uniformly throughout the length to avoid undercooling of some parts of the strand. The pressure will be 6 bar. The counteracting flow problem due to corrosion, the pipeline will be made of stainless steel. In secondary cooling, strand (bloom) will be completely solidified leaving no liquid steel at all. The secondary cooling zone begins from just below the mould. Water for secondary cooling should have pH: 7-9Total Hardness: 20dh.Carbonate hardness: 0.7dh.Dummy Bar:The function if dummy bar is to seal the mould bottom, for the starting of casting and to withdraw solidified shell until the hot strand has passed to strengthening and withdrawing machines.

Backup Roller Sections N1 & N2:These sections are intended for supporting and directing the dummy bar and strand in course of casting. N1 is a four roll section installed on post underneath the secondary cooling sections while N2 is a six roll section installed after the four high strands.Withdrawal and Strengthening rollers:There are 4 strands which are used withdrawing and strengthening the curved bloom. These 4 strands are designated as TK1, TK2, TK3, TK4.TK1:4 high strands.TK2: 2 high strands.TK3:2 high strands.TK4:2 high strands.Technical details of CC machineAverage casting speed for 320 x 250 bloom size is 0.78 M/min for 250 x250 bloom size is 0.82 M/min.Gas Cutting Machines (GCM):The strand which continuously comes from the copper mould after getting completely solidified should be cut as per our requirement, to

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facilitate easy handling etc. In order to cut the blooms accurately, a gas cutting machine, using LPG, is used. Since the bloom travels with certain speed, the machine used for cutting for the bloom .For this gripper are used ,which grips the bloom and travels along with it , taking the LPG flame with it .Each CC machine has been provided with 4 cutting machines to cut the four blooms at a time.Bloom storage yard (BSY):To synchronize the production in continuous casting machine and requirement of rolling mills for blooms, Bloom storage yard (BSY) has been established. Inspection and selective conditions are also carried out in BSY. After cutting the blooms at GCM they are moved to cooling beds and after cooling to 5000C they are transferred to racks. The BSY is served by 11 nos. EOT cranes with rotating cabins and magnet facility .Blooms of particular grade of steel are stored at a particular place. Every bloom is marketed by heat no. and machine no.

Principles of continuous casting process:-Continuous casting may be defined as teeming of liquid metal in a short mould with a false bottom through which partially solidified ingot is continuously withdrawn at the same rate at which metal is poured in the mould. The equipment for continuous casting of steel consists of:1. The ladle to hold steel for teeming.2. The tundish to closely regulate the flow of steel into the mould.3. The mould to allow adequate solidification of the product.4. The withdrawal rolls to pull out the ingot continuously from the mould.5. The bending and/or cutting devices to obtain hand able lengths of the product.6. The cooling spray to solidify the ingot completely.7. The auxiliary electrical and/or mechanical gears to help run the machine smoothly.The mould is open at both ends and is water cooled. The operation is started by fixing a dummy plug-bar to temporarily close the bottom of the mould. Steel is slowly poured into the mould via a tundish and as soon as the mould is filled to a certain level withdrawal of the plug begins. The rate of with drawl must match with that of the pouring for smooth operation of the machine. Uninterrupted pouring and

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simultaneous withdrawal gives rise to the whole cast being poured in the form of one piece which may be cut into smaller pieces as per the requirement.In order to expedite the process ingot does not solidify completely in the mould. As soon as sufficiently thick skin, which will be able to stand the pressure of the liquid core, is formed, the withdrawal from the mould commences. It is then cooled by secondary cooling. A small area of the ingot, where the liquid core is able to press the solid skin against the mould walls, maintains a short of seal to prevent liquid from leaking out from the mould. This act as a moving seal if the bar is withdrawn slowly from the mould and an equivalent amount of liquid steel is poured in.If the bar is withdrawn rapidly this seal may fracture and may produce cracks in the ingot or even breakouts. Both of these eventualities can be eliminated and the casting speed can be increased if a moving mould is adopted rather than a stationary mould.The principle of moving the mould is known as Jungham’s principle so named after the investigator. In this, the mould is moved up and down variously through a stroke of 12 to 40 mm. The ratio of speed of downward to upward stroke is nearly 1:3. The downward speed is being equal to that of the speed of withdrawal. If the downward is even slightly less than that of the rate of withdrawal major transverse cracks are formed. In a later modification therefore, the downward speed has been increased to little more than the rate of withdrawal. This results in negative stripping of the ingot and is beneficial in following ways:1. The initially crystallized skin of the ingot is further compacted.2. Formation of tensile stresses is prevented and even compressive stresses may be developed in the initially solidified skin.3. It particularly eliminates the possibility of transverse cracking of the skin.4. Transverse cracks that may be formed earlier are liable to be welded again.5. It allows maximum rate of withdrawal i.e. maximum from a given machine.The solidified strand is taken out from the mould by withdrawal roller and then the strand is subjected to straightening roll section, where it is made horizontal. In the next operation the cast object is cut

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generally by using LPG gas to the required size and sent to storage yard.The Continuous Casting MachineThe continuous casting machine can be divided into three regions:1. Water cooled copper mould section (A)2. The secondary cooling section (B)3. The radiant cooling section (C)The description of the various parts is as follows:

Fig.4A. The Mould:The mould is the heart of the continuous casting machine. It is the primary heat extraction device where a shell of adequate thickness is formed. The mould also provides support to the newly formed shell. It influences, profoundly, the quality of the steel. Design which does not suit the operating conductions or excessive distortion in the mould that may develop in the course of prolonged operation have been found to increase the number of defects e.g. the longitudinal corner cracks etc.Different types of moulds have been developed like the straight mould and curved mould. The three major types of moulds are:-1. The solid block mould.

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2. The plate mould which consists of a copper mould backed with cast iron plates.3. The tubular mould.

The heat transfer in the mould occurs in a series of steps:-1. Conduction and radiation across the air gap separating the mould and the strand.2. Conduction through the mould wall.3. Convection at the mould/cooling water interfaces.

The moulds are reciprocated during casting. The principle was first developed by Junghan‟s to reduce the risk of breakout caused by the rupture of the skin. With the introduction of „Negative Strip‟ high speedcasting became possible. Negative Strip means that on the down stroke the mould moves at a higher velocity than that of the withdrawing strand. This process prevents mould strand adhesion and averts rupture of the shell during subsequent upward motion of the mould. Another major advantage is that the mould lubricant, from the top of the mould, is transferred to the lower sections.B. The Secondary Cooling Section:This section follows the mould in the continuous casting machine. The secondary cooling section consists of support rolls and water spray nozzles. The rolls primarily give support to the thin shell that forms in the mould. The water sprays continue the heat extraction process that is initiated in the mould. This section varies from as little as Ø.4 m up to 4.0 m. The water sprays operate on the principle of pressure atomization that is water under high pressure when forced through an orifice breaks up into droplets. The sprays used generally give a full cone pattern. Sometimes a V pattern is used for the lower portion of this section. Generally for bloom casting sets of four nozzles, one for each face, are placed in rows. These nozzles are connected and classified into zones so that the water flow rate and thereby the heat extraction rate may be controlled.As a major part of the shell forms in this section the heat extraction and solidification should be continued at a controlled rate without the generation of tensile stresses of magnitude that may cause shape defects, surface cracks or internal cracks. Water flux has a major effect on heat extraction. But the conduction of heat through the shell

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becomes the rate limiting process. The primary effect of spray cooling is to alter the temperature distribution through the shell.Improper spray pattern cause a large no. of defects in the blooms. The most common defect is the midway crack. The other defect though not as common, is rhomboidity, which arises due to a symmetrical cooling pattern as a result of clogged nozzles etc.C. The Radiant Cooling Section:This section follows the secondary cooling zone. The strand is left open to the atmosphere. There is no control over the solidification or the heat transfer rate in this zone.The Gas Cutting Machine:This is the last part of the machine. It follows the radiant cooling section. The function of this section is to cut the strand into blooms of the desired length. The gas cutting machine is a welded steel construction wherein a gas torch is fixed. This torch is mounted on a car which moves along with the strand. The car is provided with grippers are pneumatically operated. The torch is provided with transverse movement. When the strand moves up to the desired length the gripper is engaged. The strand and the gas cutting torch move with the same speed. The cutting LPG is switched on and the torch is moved in the transverse direction cutting on the strand. When the cutting is completed the bloom is taken away by operating the withdrawal rolls and the gas cutting machine is brought back to its initial position.Different Types of Machine:-Vertical type:-It is the first continuous casting system where in the mould and the discharge are both vertical. Liquid steel is brought to the machine in a stopper controlled ladle and is teemed in a stopper controlled tundish which regulates the flow of steel to the mould. Below the mould is secondary cooling zone in which rollers are set to make close contact with the ingot. The water spray nozzle is interspersed in between the rollers. The no. of sprays, pressure of water etc. are adjusted to control the degree of cooling .It is also known as a roller apron. The main withdrawal rolls are situated just below the roller apron. The cut off torch travels at the same speed as that of the withdrawal by clamping the product. After cutting, the torch goes back to its position quickly. The product is then laid horizontal and is hoisted to the normal floor level. This type of plant is very tall and hence needs

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either a tall shop or a large pit to accommodate the equipment. The problem is acute if high casting speeds are employed and in consequence longer cooling zone is required. This type of plant is therefore used for larger medium sections. It is good for slabs where in bending is avoided for its adverse metallurgical effects.In the event of breakdown it is easy to repair and restart the machine. It is most simple in construction and most reliable to operate. All steel qualities can be cast and those too high speeds without fear of damage to strand by bending.The vertical – Mould – Horizontal Discharge Type:-This is a modification over the earlier vertical design to reduce the overall height of the machine. The mould, roller apron design & pitch rolls are similar to those in a vertical machine. After the product emerges from the pitch rolls it is bent to obtain the discharge horizontal. The cutting torch moves horizontally. A horizontal set of straightening rolls becomes necessary. A saving of 30% in height is thus possible by this design. The floor space requirement is however more. In the event of a breakdown it is more difficult to repair and restart then the vertical machine. This is quite popular for small and medium size cross-section.The Curved Mould Type(S-Type):In this the mould itself is curved and it oscillates along the same curved path as the axis of the product. The withdrawal rolls carry out the bending also and hence need to be adequate strength. The height of this shop in this case is still less and hence it is called as low head type machine. The bending of the ingot commences even before it is entirely solid in cross-section and hence large sections can also be cast without much of bending problems. It is quite popular for medium size sections. The radius of the curvature should be as high as possible. In the event of a breakout it is very laborious to remove the curved ingot from the machine and restart the operation.

Horizontal Continuous Casting Machine:Steel is poured from the ladle into the tundish and flows horizontally in the mould by a refractory connection (break ring) on the side of the tundish. Partially solidified shells are withdrawn in a pull and pause or pull and push cycle, through a secondary cooling zone where solidification is completed. The solidified shell is then cut into lengths and sent to cooling beds.

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Advantages: Lower investment costLow height and small space requirementsLess labour requirements.Less ferrostatic pressure which minimizes strand bulging and inside tearsAbsence of metal re-oxidation between tundish and mouldShorter metallurgical lengthNo bending of the strand which permits the casting of crack sensitive products

Rotary Casting Machine:-

It is different from other casting machine; in that it has a revolving mould. A water cooled copper ring serves as the mould. In the casting area this ring is closed by a movable steel belt , so that cavity is formed. The steel belt is removed by a 90o turning of wheel. The strand is straightened in an un bending zone. The circumferential speed of the wheel is 4 – 7 m/min. in order to strand from the wheel the mould has a trapezoidal shape.

Advantages:Casting speed can be increased to high value.Yield is more (99%).Energy saving is more.Operational costs are less than conventional casting.General Features of Continuous Casting Machine at VSP:-In VSP there are 6 (3 in stage I and the other 3 in stage II). Continuous casting machines in continuous casing shop. The machines are of radial type in the straight mould. The machines are slated to operate in sequence for ten Heats.TECHNOLOGICAL CHRACTERISTICS OF VSP MACHINE

Sl. no.

Characteristics Bloom casting machine

1. Machine type Radial

2. Machine radius 12 M

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3. No. of strands 4

4. Ladle capacity 150 T

5. Tundish capacity 25 T

6. Metallurgical length 10 M

7. Max. casting speed 1.2 M/min

8. Dummy bar type Link

9. Avg. length of cast blooms 6 M

10. Sections cast 250x250 mm, 250x320mm

11. Casting time for a heat 100 min

12. Water consumption in mould 110-140 M3/hour

Effect of various parameters on the quality of bloom:-1. Casting temperatureLiquid steel during continuous casting should be within the specific limits depending up on the grade of steel.A 30-40oC above liquidus temperature and high casting speed are required for good equiaxed cast structures increase in casting temperature above the desired level leads to central segregation and formation of longitudinal cracks. Higher the casting temperature longer will be the zone of columnar crystal and vice versa.2. Casting Speed:-It is well known that the depth of liquid pool increases as the withdrawal rate increases and that for a given cast cross-section and steel composition, there is a limiting rate of solidification that must not be exceeded if central soundness is to be maintained. Increasing the cast speed reduces the residence time in the mould, thereby decreasing the solidification rate. This will result in an increase in the time required for the removal of superheat, delaying the nucleation and growth of equiaxed crystal, increasing the columnar zone and increasing the extent of axial segregation.The casting speed is related to the thickness of solidified skin of the ingot at the bottom of the mould according to following relation.

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S = K/√ (Lm/V)Where S = thickness of solidified skin.K = solidification constant varying from 2.3 – 2.9 cm.min1/2 depending upon the grade of steel.Lm = length of mouldV = casting speed in cm/minFrom this relation it can be seen that higher casting speed results in a thinner and hotter skin, which is weaker.In VSP the casting speed is regulated according to the casting temperature as shown in the table

T0c 1530 1535 1540 1545 1550 1555 1560 1565 1570 1575

‘v’

M/min

0.85 0.80 0.75 0.70 0.65 0.60 0.55 0.50 0.45 0.40

Norm for increasing the casting speed of the continuous casing machine at VSP:

Casting speed Length of bloom cast

0.2 M/min 400 mm

0.3 M/min 600 mm

0.4 M/min 800 mm

0.5 M/min 1000 mm

0.7 M/min 1200 mm

0.8 M/min Upto the end of the casting

Casting Powder:-Casting powder is the type of mould flux. This is synthetic slag forming composition which is required to perform a no of functions.1. Thermal insulation – This will prevent bridging / solidification of steel in the mould. The insulation is provided by un-reacted flux over the meniscus.2. Prevent reoxidation- insulation of the steel from the atmosphere.3. Absorbs inclusions- the flux assimilates this material and forms lower melting point, compounds which flow out of the mould with the

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flux. The chemical composition of the flux determines its ability to absorb inclusions.4. Lubrication- Between solidifying shell and mould wall is determined by viscosity and crystallization temperature.5. Uniform heat transfer- between the solidifying shell and mould wall. Occurrence of localised non-uniform heat transfer will usually results in crack formation. Flux viscosity and crystallisation temperature are determining factors.Application of flux:-

1. To provide optimum insulation a “dark” flux practice a layer of 15– 20 mm of unmelted flux should be maintained.

2. At frequent interval nearly 0.7 – 0.8 Kg/Tonne of steel should be used.

3. Chilled slag rings are required to be removed a trouble free operation.

Typical composition of casting powder at VSP Flux parameters:-1. Chemical composition:-

Cao 28-32

Sio2 31-34

Al2O3 5-8

Na2O+k2O 6-8

F 4-5

C 14-16

Viscosity at 13000C = 4-5

Melting range= (±200C)

Softening point (T1) 1050

Melting point(T2) 1140

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Flow point(T3) 1160

Casting parameters:-

Casting speed 0.2-1.2m/min

Section (mm) 250x250,250x320

Steel grade Low carbon

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heat nostrand no

Equi axedzone

Columnarzone

Chilledzone

Superheat

strand speed

total area

area percent area percent area percent 15D01107 1 6800 16.83 20755 51.37 12845 31.79 32 1.5 4040015D01109 5 8100 20.14 22680 56.41 9420 23.43 30.66666 1.59 4020015D01115 3 4900 11.95 24844 60.5 11260 27.46 34.25 1.44 4100415D01115 4 6400 15.92 11930 29.67 21870 54.4 4020015D01138 6 2000 4.9 33717 83.8 4483 11.15 30.66666 1.53 4020015D01149 5 4200 10.39 29838 73.86 6359 15.74 52.33333 1.15 4039715D01150 4 10000 24.87 19070 47.43 11130 27.6 34.33333 1.36 4020015D01931 5 4225 18.5 15655 68.6 2920 18.6 14 2.32 2280015D01967 6 6480 27.86 13286 59.45 2956 12.6 33.5 2.01 2325615E02280 3025 13.2 16856 73.9 2920 12.36 24.4 2.41 2280115E02281 9000 38.9 11164 48.3 2940 12.72 26 2.49 2310415E02282 4225 18.6 15515 68.4 2910 12.8 19.3333 2.52 2265015E02650 6 4200 18.29 14160 61.6 4592 20.001 47.5 1.98 2295215E02863 6 1600 6.8 20156 86.6 1500 6.4 46.75 2.15 23256

15E02863 4 1600 6.8 20156 86.6 1500 6.4 46.75 2.11 23256

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1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.60

5

10

15

20

25

30

EQUIAXED ZONE% VS STRAND SPEED

STRAND SPEED(M/Min)

EQU

IAXE

D ZO

NE%

SPEED ZONE%1.15 261.44 22.87

1.5 221.59 212.32 20.142.32 18.62.52 10.39

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10 15 20 25 30 35 40 45 50 550

5

10

15

20

25

30

EQUIAXED ZONE% VS SUPER HEAT

SUPER HEAT

EQU

I AXE

D ZO

NE%

S.HEAT ZONE%14 26

19.3333 22.8730.6666

6 2232 21

34.25 20.1434.3333

3 18.652.3333

3 10.39

Heat No: 15E02282 (STRAND NO NOT KNOWN)

GRADE: 10B21

CROSS SECTION: 150 X 151mm

DIAGONAL CROSS SECTION: 209X 211

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CHILLED ZONE: 10mm ON ALL SIDES

EQUIAXED ZONE: 65 X 65 MM

TOTAL CROSS SECTIONAL AREA: 22650

EQUIAXED ZONE AREA: 4225

COLUMNAR ZONE AREA: 15515

CHILLED ZONE AREA: 2910

SUPER HEAT: 20,21,17 Avg value 19.33

STRAND SPEED:2.52

CRACK OF LENGTH 28MM OBSERVED AT RIGHT AND BOTTOM COLUMNAR ZONEAND CHILLED ZONE INTERFACE, 10MM CRACK AT BOTTOM, 27MM CRACK AT TOP AND RIGHT SIDE COLUMNAR AREA. 3MM DIA POROSITY OBSERVED.

HEAT NO C MN P S SI AL CR B15E02282 0.19 1.01 0.021 0.013 0.27 0.03 0.008 0.003

Heat No:15E02280 (STRAND NO NOT KNOWN)

GRADE: C20MMN

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CROSS SECTION: 151 X 151mm

DIAGONAL CROSS SECTION: 213X 215

CHILLED ZONE: 10mm ON ALL SIDES

EQUIAXED ZONE: 55 X 55 MM

TOTAL CROSS SECTIONAL AREA: 22801

EQUIAXED ZONE AREA: 3025

COLUMNAR ZONE AREA: 16856

CHILLED ZONE AREA:2920

SUPER HEAT:23,24,25,28,22 Avg value: 24.5

STRAND SPEED: 2.41

CRACK OF LENGTH 27MM OBSERVED AT CORNER BETWEEN LEFT AND BOTTOM SIDES, 10MM CRACK BETWEEN TOP AND RIGHT SIDES.BOTH THESE CRACKS ARE AT THE INTERFACE OF CHILLED AND COLUMNAR ZONES.

HEAT NO C MN P S SI AL CR15E02280 0.2 0.96 0.02 0.007 0.25 0.03 0.006

Heat No:15E02281 (STRAND NO NOT KNOWN)

GRADE: 10B21

CROSS SECTION: 152 X 152mm

DIAGONAL CROSS SECTION: 210X 211

CHILLED ZONE: 10mm ON ALL SIDES

EQUIAXED ZONE: 30 X 30 MM

TOTAL CROSS SECTIONAL AREA: 23104

EQUIAXED ZONE AREA: 900

COLUMNAR ZONE AREA: 11164

CHILLED ZONE AREA:2940

SUPER HEAT: 29,26,23 Avg value: 26

STRAND SPEED: 2.49

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CRACK OF LENGTH 10MM OBSERVED AT CORNER BETWEEN RIGHT AND BOTTOM SIDES, 22MM CRACK BETWEEN LEFT AND BOTTOM CORNER. 10,15MM CRACKS IN THE COLUMNAR ZONE ,3,4,7MM CRACKS AT TOP AND LEFT COLUMNAR ZONE.

HEAT NO C MN P S SI AL CR B15E02281 0.21 1.01 0.022 0.005 0.26 0.024 0.006 0.003

Heat No:15D01967-6

GRADE: PCCG

CROSS SECTION: 152 X 153mm

DIAGONAL CROSS SECTION: 210X 210

CHILLED ZONE: 5mm ON ALL SIDES

EQUIAXED ZONE:80 X 81 MM

TOTAL CROSS SECTIONAL AREA: 23256

EQUIAXED ZONE AREA: 6480

COLUMNAR ZONE AREA: 13826

CHILLED ZONE AREA:2950

SUPER HEAT: 31,36 Avg value: 33.5

STRAND SPEED: 2.01

CRACKS OBSERVED AT CHILLED AND COLUMNAR ZONE INTERFACE OF LENGTHS 7MM, 2MM, 2MM, 2MM, 5MM, 10MM, 6MM.

CENTRE LOOSENESS.

15D01967 0.8 0.7 0.02 0.012 0.2 0.003 0.11

Heat No: 15E02650-6

GRADE: HC75CR

CROSS SECTION: 152 X 151 mm

DIAGONAL CROSS SECTION: 210X 211

CHILLED ZONE: 7MM, 10MM, 10MM, 7MM

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EQUIAXED ZONE: 70 X 60 MM

TOTAL CROSS SECTIONAL AREA: 22952

EQUIAXED ZONE AREA: 4200

COLUMNAR ZONE AREA: 14160

CHILLED ZONE AREA:4592

SUPER HEAT: 37,51,52,50 Avg value: 47.5

STRAND SPEED: 1.98

7 mm length of crack observed in columnar zone. 7 mm, 5 mm, 5 mm ,5 mm and 4 mm length crack observed at the interface of columnar and equiaxed zone. Dispersed porosity throughout the equiaxed zone observed.

HEAT NO C MN P S SI AL CR15E02650 .71 .63 .025 .024 .19 .008 .15

CONCLUSION:

We observed that with increasing super heat the intensity of edge cracks

decreases.