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Acciai specialie al carbonio
Domenico Surpi
Special and carbon steelsSonder- undKohlenstoffstähleOn CD-ROM
INDEX
INTRODUCTION.....................................................................................................................................................5
BASIC PRINCIPLES.................................................................................................................................................6
STEEL HOT WORKING...........................................................................................................................................8
STEEL COLD WORKING.........................................................................................................................................9
STEEL COLD ROLLING……………………………............................................................................................10
RECRYSTALLIZATION ANNEALING……..............................................................................................................11
DRAWING.............................................................................................................................................................13
PEELING ...............................................................................................................................................................19
GRINDING............................................................................................................................................................21
GALVANIC TREATMENTS.....................................................................................................................................25
CHROMIUM PLATING.........................................................................................................................................26
ZINC PLATING......................................................................................................................................................27
MATERIAL CHARACTERISTIC CHECKING...........................................................................................................31
TERMINOLOGY.....................................................................................................................................................37
DIMENSIONS AND TOLERANCES FOR COLD FINISHED STEEL PRODUCTS.....................................................48
HOT ROLLED PRODUCT QUALITY SURFACE ....................................................................................................49
COLD ROLLED PRODUCT QUALITY SURFACE ..................................................................................................50
DIMENSIONAL TOLERANCES FOR COLD FINISHED BARS................................................................................51
STRAIGHTNESS TOLERANCES FOR COLD FINISHED BARS..............................................................................52
CUSTOM MADE COLD DRAWN PROFILES..........................................................................................................52
COLD DRAWN PRODUCTS FOR KEYS - DIN 6880 TOLERANCE.......................................................................53
5
INTRODUCTION
The years between the XVIII and XIX centuries were characterised by an unprecedented boost of industria-
lization, particularly in the North of Italy.
The small industry dominated the region of Lombardy and its innovations revolutionised working methods,
and developed the drawing process in the metallurgical sector.
Now a days, the Lucefin Group advanced technologies adopted in the Trafilix plants helped the company to
become a world leader in cold drawn plates.
Drawing is not a simple matter. Skill, experience and the will to improve are essential as in all professions.
Thanks to its technology, specific expertise and the active cooperation with suppliers and customers, Trafilix
is able to guarantee both a technical and commercial support, which is constantly updated and innovative
in an always evolving sector, such as that of cold working.
The data sheets of this catalogue describe some of our marketed stainless steels.
Any other product and technical specifications (heat treatments, welding parameters, tempering charts,
tempering values, etc.) can be consulted from the Technical Manual of Lucefin Group.
6
BASIC PRINCIPLES
To be able to appreciate the benefits of a cold worked product, the first step is to describe the origin of the
metal alloy it is composed of. The making of stainless steel involves two manufacturing processes.
Blast furnace production A particular type of furnace covered by refractory bricks and reinforced by a metal structure, in which iron reduc-
tion is needed to form cast iron, then transformed by appropriate treatments in steel.
electric arc furnace productionA furnace with a refractory bottom in which to place the materials to be melted. Three electrodes start the heat
energy transmission, which is the beginning of the fusion process of the scrap.
The material obtained from this two manufacturing techniques, can be casted in an ingot or by continuous casting
for the production of blooms, slabs, and billets, ready for following hot working (such as forging or hot rolling).
The product obtained from hot rolling is called rolled (+AR blank).
Raw finishing, guaranteed dimensional tolerance, absence of edges, not suitable straightness, etc. do not make
from rolled shapes end products, but a semi-finished steel in need of further treatments – with or without score
removal – to meet the industrial engineer’s requests or the user’s expectations.
The finishing obtained through treatments involving score removal (such as degreasing, milling, turning), lead
to an average weight reduction of about 20% compared to the rolled material. However what affects the price
(job economy) are the extra hours of mechanical work needed to shape the final product.
The cold drawn product (+C) is the right answer wherever possible to the points above.
This manufactured product, obtained from the blank, assumes shapes and intrinsic qualities that only cold
working can achieve by the particular drawing technique.
The cold drawn material has an excellent surface finish: smooth and without surface oxide, crucial element in
Blast furnaceElectric arc furnace EAF
7
mechanical working where iron oxide degrades lubricants and causes mechanical breakdown.
The cross-section dimensions are constant over length for many thousands of meters (impossible to achieve
using other technologies), with very tight gaps at centesimal level. The edges can be sharp or calibrated to
specific requests. Straightness can reach 1 mm/m.
coMparison BetWeen Hot rolled and cold draWnFLAT mm ROLLED TOLERANCE DRAWN TOLERANCEwidth 50 ± 1 mm (delta = 2 mm) +0/ – 0,19 (delta = 0,190 mm)
thickness 5 ± 0,5 mm (delta = 1 mm) +0/ – 0.075 (delta = 0,075 mm)
TOLERANCES ROLLED DRAWNStraightness from 2‰ to 4‰ from 1‰ to 1,5‰Roughness Ra 25 μm Ra from 1,6 to 3,2 μm
The cold deformation process (drawing) increases yield strength and rupture points to a Rp 0-2 / R ratio of about
0.90 (rolled near to 0.60 and forged around about 0.67). This last characteristic is well-known and valued by in-
dustrial engineers, who put it to good use to achieve maximum lightness of sturdy sections to support structures.
The advantages of cold drawn product are evident because due to its higher yield strength than other products, a
smaller section (hence less weight) can be used to obtain the needed solidity.
To understand the importance of this steel product, let’s consider finishing, precision of any hexagonal, square,
flat or rounded geometric section. All the more so, the making of more complex structures required by the market
of today, such as guide-ways/drives for scanners, splined-shafts, transmissions for textile machinery and many
other special sections where centesimal precision must be absolutely kept under control. These sections inevitably
led to the use of the cold drawn product, being able to satisfy all these requirements and quicker than any other
technology. Lastly, let’s apply the same reasoning to products obtained through peeling and grinding processes.
In most cases, the cold drawn product is suitable at the supply state, even if lately and very often galvanic treat-
ments have been used such as chromium, zinc, nickel, gloss and painted copper plating, without having to obtain
surfaces oxide-less and apt for anchorage covering. Even if the norms of the product do not guarantee a successful
result from using these techniques and suggest the use of ground or honed pieces, it is well-known how much the
great expansion of the use of cold drawn products has allowed to “bypass” various working phases leading to
economical saving (in terms of time - labour - operating time - electric energy, etc.).
The advantages of the cold drawn product allow to widely retrieve its higher purchasing cost with reduced working
phases if compared to rolled products, together with much less scrap.
To conclude, cold working allowed a considerable cost and time reduction, which greatly contributes to progress
and development of this modern industrial field.
The choice lies within the hands of those who look for innovations within their field of operation at limited costs,
and the cold drawn is a winning product in this sense.
8
STEEL HOT WORKING
The end product of hot working steel is obtained from semi-finished products (blooms, billets, slabs).
Plastic hot deformation processes are those operations through which the semi-finished products undergo
a temperature increase of 0.6 • Tm (melting temperature), then a compressive stress to obtain the finished
dimensions of products such as sheets, rods, bars, billets, profiles, etc. The deformation stress is lower in
plastic hot deformation than cold working steel. Another advantage is that crystalline grains deformed in
hot working by mechanical action, can be re-crystallised during the actual working process into new finer
and more uniform grains, by eliminating the dendritic structure present in ingots or semi-finished products,
due to the hardening process.
The end products from hot working (i.e. rolling), have a non optimal finished surface, showing oxidised
surface and crude geometrical tolerances.
They can be sold at the natural state (i.e. +AR natural rolling state), or after having received heat treatments
(i.e. annealing, normalizing, quenching and tempering), which further improve the structure and mechanical
characteristics, however causing increased costs.
Hot rolled bar
Micro-structural variation during hot rolling The grain dimension has been excessively enlarged to highlight the structural mechanism
original graindeformed and stretched grain
new grains in enlargement phase
new grain in formation
phase
new grain internal
structure
top
cylinder
bottom
cylinder
9
STEEL COLD WORKING
The main task of cold working is to offer users the possibility to obtain: the simplifying of mechanical working
cycles, the reduction of the initial weight, less scrap and higher production with better economic results.
Cold working is obtained by operating end products or those coming from hot working at room temperature,
resulting in bars or rolled/cold drawn coils.
Cold stretching has important repercussions inside the steel mould: the grains forming the basic product
structure are stretched out proportionally to the degree of distortion in the plastic flow direction, causing
the shift of the crystalline structure on well-determined directional layers, to obtain permanent distortions
of the crystalline structure of steel.
The permanent distortion brings about an increase of the mechanical resistance, with a rise of yielding, rupture
and hardness values, but at the same time it causes a decrease of other mechanical characteristics, such as
stretching, tensing and resilience.
This plastic cold deformation effect on mechanical characteristics is called work hardening. The deriving structu-
re is thermodynamically instable and often associated with limited toughness. Cold hardened materials which
are exposed to long waits at even very high temperatures can have the tendency to age. To remedy this incon-
venience, some anti-aging such as aluminium (Al), vanadium (V), titanium (Ti) and all other elements combina-
ble with nitrogen (N), which is responsible for friability, are added during casting.
During cold working, hardness increases up to a point that it would not be possible to have a new reduction of
the section, without heat treating the hardened material with annealing.
Heat treatment is also repeatedly applied to eliminate hardness effects in order to enable plastic deformation
of the material. This way allows to have more transformations until the desired dimensional and mechanical
characteristics have been reached, without incurring in dangerous ruptures.
Micro-structural variation during cold rolling
original grain top
cylinder
bottom
cylinder
deformed grain
10
Cold rolled coils annealed under controlledconditions and ready for further drawingThe Lucefin Group rolling mill engineered by Nisva
STEEL COLD ROLLING (+CR Cold Rolled)
The starting products are hot rolled round coils from which coils of flat and square product and profiles
are obtained, that can be drawn, after cold rolling and re-crystallization at 600 - 700 °C in controlled envi-
ronment bell-type furnaces.
Cold rolling occurs in rolling mills quite similar to those for hot rolling, but machines must have more power
and stability.
Lubrication is carried out with cooling-lubricant emulsions to allow friction reduction.
This manufacturing technique has been adopted in Trafilix to solve four main factors linked to flat bars
mainly for drawing, but also for marketing:
1) The hot rolled coil of flat product has rather low weight and therefore inefficient.
2) The hot rolled coil of flat product has elevated costs.
3) From only one size of hot rolled round product, more sizes of cold rolled flat products can be obtained,
hence storage reduction.
4) The difficulty in finding hot rolled thickness below 5 mm.
Cold rolling gives a better thickness uniformity to material, which after adequate annealing heat-treatments,
is further calibrated by drawing, and guarantees very tight tolerances (i.e. h 9 ISO 286-2).
11
RECRYSTILLAZATION ANNEALING
The material hardens though cold plastic deformation, rising the Rm values, Rp 0.2 and hardness, with resulting
decrease of ductility.
If further cold deformations are needed, it is necessary, between one deformation and the other, to give back
plasticity to the material through a specific heat treatment (re-crystallization annealing) which brings it back
to the state before deformation, with lower hardness values, Rm and Rp 0.2 and less tensing residues due to
cold deformation.
This heat treatment is applied below critical temperatures (about 600-700 °C for building steels), aiming to
generate new grains in a previous hardened material, without phase changing.
During the phase of permanence in furnace, the new stress points are unstable and become the nucleation
points of new grains (bond recovery phase). Subsequently grain growth is obtained, until the new grain edges
come into contact. Re-crystallization is thereby achieved (remaining further in the furnace is not recommended
because it causes grain swelling and decrease of material mechanical resistance).
Final cooling must be slow (under bell) up to 300 °C, then the material can be set free in air to reach room
temperature. The degree of material reduction influences the re-crystallization temperature, permanence in
furnace and final structure.
Many degrees of material reduction lead to lower re-crystallization temperatures and timings and a fine grain
structure.
Residual tensions
Hardness, Rm, Rp 0.2
Ductility
Time
Hardened Material Bond recovery Fine recrystallization Swelling
Schema del trattamento termico di ricristallizzazione
12
Tre Valli Acciai annealing furnace for annealing under controlled conditions
Trafitec furnace for annealing under controlled conditions
13
DRAWING (+C Cold dRAWN)
Drawing is a cold plastic deformation, in which hot rolled material, in bars or coils, first undergoes chemical pic-
kling to eliminate the layer of surface oxide, then is forced through a calibrated tool called die, using pulling force.
The lower section of the die is smaller than that of the starting material, therefore the pulling force must be greater
that the yield force, without reaching the rupture point, so that, after die exit, it is permanently deformed following
the shape and dimension set by the die itself. Drawing, as a rule, is carried out at room temperature, but in case of
hard steels (i.e. high speed steels) hot drawing is carried out at a temperature of 300 °C. Sometimes hot drawing
is carried out to give specific properties to the material.
A significant loss of weight to obtain the desired dimensions (milling, turning, etc.) is caused by manufacturing
with score removal, whilst during drawing the weight loss is minimal and limited to: around bar extremities,
the scrap for tip threading and the surface oxide layer eliminated by sand-blasting from the starting material
only. Therefore, section reduction from rolled to drawn product causes a lengthening in direction of drawing.
The following chart shows how much the material lengthens in relation to a set section reduction.
ROuND/HExAgONAL FLAT/SquARERolled dimensions in mm Drawn Rolled dimensions in mm Drawn
Diameter Length Diameter/Girdle Height Thickness Length Height Thickness52 11500 50 47 47 5600 45 45
DRAWN LENgTH DRAWN LENgTH12438 6109
REDuCTiON RATiO REDuCTiON RATiO7,5% 8,3%
Drawing allows to achieve an end product with very tight dimensional tolerances (h11, h9), smooth surfaces, ab-
sence of oxides, limited ovalization, calibrated thickness, good surface finish (Ra 1.6 - 3.2 μ) and optimal straight-
ness 1.5 -1‰. All these features remain stable and constant during the entire production.
Cylindrical casing die
Lubrication system coneRadius of junction
Output coneOutput feeder
Calibration areaExit feeder
Load radius
Exit
Entry bevel
Unloading area
Casing
Core
Bevels
14
The cold drawn product is usually marketed without chemical treatments, but it can be annealed, normalized,
stretched and also quenched and tempered before or after drawing. It is implicit that heat treatments carried out on
the material after drawing must be done in controlled conditions furnaces, to avoid oxide formation and decarburi-
zation. To avoid that the drawn surface is attacked by atmospheric agents or oxidations, it must be protected with
specific mineral oils. In particular cases or sea shipments, specific packaging must be foreseen.
reduction ratio influences on draWn MaterialCold reduction, besides giving interesting dimensional and aesthetic aspects in the mechanics sector, affects
the mechanical characteristics and dimensional defects.
As it can be noted from the diagram, the mechanical properties have a resistance and yielding increase
together with a shrinkage and stretching deterioration.
The reduction ratio resulting from rolled to drawn products must be regulated to avoid excessive stress on
the tools, internal and external cracks in the materials to mainly produce the required mechanical values.
Usually it varies between 7.6 and 12%, but in some cases 30-35% for building steels and 40-60% for
stainless steels can be reached if an increase of rupture and yielding values are desired.
Bevelled plates die Special profile die Die for hexagonal shapes
Reduction ratio
Stretching
Stress
Yielding
Rupture
15
cracKs durinG draWinG process and draWn product defectsThe starting hot rolled quality and operating parameters (the right choice of reduction ratio, pulling force, lubri-
cation, etc.) are fundamental within a correct drawing process.
In hot rolled products there can be defects resulting from manufacturing and steel rolling which can cause
drawing cracks or defects.
Rolling defects noted are:• Non-metallic inclusions
• Metallic inclusions
• Porosity due to the presence of oxygen and hydrogen
• Chevron cracking in the heart of the steel
• Non-homogeneous structures (i.e. caused by absence of heat treatment)
• Non-homogeneous resistance between core and external part which causes unequal creep stresses.
Other drawing defects noted are:• Welding notches, caused by an imperfect jointing among wire rods of several bundles, which can cause
arc cracks
• Wire tangles in rolled bars which under reversed tension can bring about a force overwhelming the mate-
rial mechanical resistance and break the product.
Besides the rolled intrinsic defects, other imperfections may be found in the drawn product due to the drawing process: • Distortions (which can happen later in time or when surface finishing occurs) due to residual inside stresses
formed during non-homogeneous plastic deformation.
• Chevron cracking due to the die reduction angle, excessive pace reduction, excessive friction or enhanced by the
presence of non-metallic inclusions
• Geometric errors due to the wrong positioning of the die or wear and tear
• Surface defects such as folds, often due to improper parameters selection of the process, pressing speed or
inadequate lubrication
• Longitudinal and continue scratches caused by the presence of impurities or very resistant materials attached at
die entry (scratches due to the occasional contact are called mechanical damages).
These inconveniences are avoidable with a proper checking of the manufacturing parameters, pre-straighte-
ners rollers, guide rollers, dies, pulls units, etc.
16
Historical eVolution of pullinG MacHines The continuous pulling system has been operating for over fifty years, through alternative action on two
trolleys with tightening jaws by the use of cams.
This system has evolved to satisfy the ever growing needs of productivity.
In the sixties and seventies, the pulling unit with “progressive” system, consisting of single track cams and
a piston, assured the return of pulling jaws. Jaws closing was pneumatic and the maximum speed around
60-80 rpm.
From the eighties and nineties a new track system was developed with two tracks cams allowing simul-
taneous pulling and return control. Jaws closing becomes hydraulic resulting in a stronger tightening and
maximum speed reaches 120 rpm.
Beyond the nineties, the trolley and jaws pulling system has been surpassed. The complicated constant
moving mechanisms require continuous repairing, causing machine stops with loss of productivity and
unacceptable high costs. At the same time steelworks begin the production of higher weight rolled bars of
3000 Kg, and dies, lubricants and more advanced cutting systems can be found on the free market, which
allow the building of draw benches of much higher working speeds.
Thus the hydraulic chain track pulling technique is born. This system allows a more constant and higher
speed pulling power, reaching 300 rpm. The limit of 170 rpm of the 15 ton. CDTMF Trafilix is imposed by the
tools (cutting, lubricants, dies) which cannot stand the new pulling units.
Chain track drawing Cam based drawing
COmPARiSON BETWEEN THE TWO PuLLiNg mETHODS
CAm BASED PuLLiNg CHAiN TRACk PuLLiNg
Lower plant cost Higher plant costAt equal power, machine is bigger and heavier More compact machines
Variable pulling Constant pulling Lower productivity Higher speeds thereby higher productivity
Higher consumption owing to high rate of friction and slideof the moving parts Less energy consumption
Loud noise owing to alternate moving parts Low noiseLong time maintenance and high cost Short time maintenance
17
draWinG floWcHart trafiliX - trafil cZecH
Hot rolled coils flats
Cold drawingFlats coils
Cold-drawingPackage and Shipment
Quality Control
Steelworks
Cold rolling mill
Heat treatment
Hot rolled bars
Anti-friction treatment
18
19
PEELING (+SH Peeled-Rolled)
By peeling (synonym of turning) it is meant the removal of the surface layer of the round bars through pee-
ling head machines. These heads have more sharpeners (usually four tools) rotating in a circular motion and
basically “peeling” the rolled bars.
Bars are pushed through and their linear direction is maintained by rollers or other appropriate devices.
The peelers not only have head peelers but also a roller unit which provides for the rolling and smoothing/
straightening of the bar. In theory this processing can produce a surface free of defects and guarantees an
absence of decarburization. Thus the product is able to bear hardening heat treatments or galvanic treat-
ments.
Rolled products selected for peeling must not have a straightness over 2% and the obtained product has the
same starting straightness, brought to 1% by subsequent rolling.
The bars roughness obtained through peeling is Ra 3.2 μm, after rolling is Ra 0.8 μm.
The product is mainly directed towards marketing or grinding.
The weight loss during this phase is always important and the variability of the initial diameter must not be
forgotten in order to quantify the costs.
ExAmPLES OF WEigHT LOSS iN PERCENTAgERemoving mm 1 2 3 4 5
weight loss % % % % %to obtain Ø 28 7 13 19 24 28
“ Ø 30 7 13 18 23 27“ Ø 32 6 12 17 21 26“ Ø 35 6 11 16 20 24
… … … … … … …“ Ø 90 3 5 7 9 11“ Ø 95 3 5 7 8 10“ Ø 100 2 4 6 8 10
Tre Valli Acciai peeling machine for diameters range of 90 - 200 mm
20
Peeled bars are used when:
1) No more mechanical processing for some areas of the bar is foreseen, and a tight tolerance is required
2) Absence of decarburization and relevant surface defects is required
3) Rigorous surface controls are required (i.e. magnetic detection)
4) A well determined diameter is the starting point for subsequent mechanical processing.
oVerHeatinGTooling overheating during peeling phase: the darkened part shows that the material has reached the tempera-
ture of about 300 °C. The rough-hewing and feed speeds were programmed to work quenched and tempered
material according to EN 10083 with hardness HRC 28 – 36, but the material hardness has resulted to be of 48
HRC (technically speaking, through-hardening) which has caused this unforeseen event.
Subsequent hardening brought back the material to the mechanical strength set for the dimension and the steel
type considered.
Another similar case may happen when induction hardened bars are not settled on the end areas (30-40 mm).
These parts will show excessively higher hardness than the other parts of the material owing to the drastic coo-
ling of the ends which expose more surfaces to heat changes.
Peeling Head
50CrMo4 quenched and tempered steel: raw round bar 85 mm diameter, 80 mm peeled
The round bar has been pulled back o show the surface between raw & peeled
Pre-straightening after peeling Rolling
21
GRINDING (+Sl GRoUNd MATeRIAl)
During the grinding phase, the round bar surface is not removed by cutting tools but by grinding wheels. Some-
times this processing replaces small bar peeling, such as for steels for springs with 8 -15 mm diameter, which
are rough-hewed ground.
Grinding does not alter steel mechanical characteristics if it is correctly done without overheating.
The difference between peeled/ground bars and cold drawn/ground bars is that these last ones will have me-
chanical characteristics typical of the drawn product and the first ones of the rolled one.
Grinding allows to obtain a better surface than the one done by drawing and peeling, by using grinding wheels
of various grain.
For processing requiring the removal of large quantities of material or which must be done on hard steels, the
use of soft grinding wheels is advisable. Besides, if grinding is required with very tight tolerance of shape
and size, it is better to use hard grinding wheels, which keep shape and size for a long time (however giving
up a quick removal of excess metal).
According to ISO 286-2, dimensional tolerances are very tight (h8–h7–h6), the roughness longitudinally mea-
sured by means of surface roughness testers, is very low and equal to Ra standard 0.8 μm e Ra tight 0.6 μm.
The maximum depth of decarburization must be set at starting point because it reflects on production cycle.
Especially, for medium small sizes obtained from cold drawn/ground products where small traces of decar-
burization may still be present, whilst for peeled/ground this risk does not exist (decarburization removal is
done during the peeling phase).
To manufacture a good ground product it is fundamental that machine operators very carefully observe
instructions given for: measurements, speed, roughness, sight inspection, refrigeration, etc.
Other points to be carefully taken into account are the material volume shrinking and increase, due to steel
temperature changes: for example, when the ground material cools at low temperatures, the diameter redu-
ces and when heating the diameter increases.
The ground product must be carefully protected and due attention must be given to transport and storage.
Ground surface Roughness measurement
22
MarKetinG reMarKsIt must be reminded that ground products have different pricing as much as extra-dimensional products are
required, according to h10 - h8 - h7 - h6 tolerances. These differences have an important economic influen-
ce, owing to different production costs, thus it follows that the cost and the risks in producing materials with
h6 tolerance differ a lot from producing with h10 tolerance.
A ground bar is used when:
1) The areas for subsequent processing are little.
2) Tight dimension tolerances are required (ISO h6 - j6 - g6 - f7, etc.).
3) Absence of damaging surface defects is required.
cHeVron cracKs caused By GrindinGThese arise from a combined action of stresses from hardening heat treatment and grinding. During grin-
ding, the heat from the grinding wheel can cause material expansion: if expansion exceeds steel stretching,
without fail breaks will occur. Higher is the material mechanical strength and less is its stretching and higher
are the stresses involved.
The external material expands and goes into tension while the cold layers below have an opposite action.
When the tension force exceeds the maximum material breaking point, chevron cracks appear under the
surface which can cause up-rising scaling.
Tre Valli Acciai grinding centre Dimensional stability is kept bylaser readers
600 mm grinding wheels
Grinding scoring on a 39NiCrMo3 steel shaft of 140 mm diameter; 2.3 mm scales thickness
23
This problem can be also enhanced by the cooling liquid. When the surface is excessively heated by the
grinding wheel, emulsion water may cause a very drastic quench causing other stresses and enhance micro
chevron cracks previously started from grinding. The detachment of material produces heat in proportion to
the material strength times the cutting area, plus the deformation area and volume for plastic upset due to
the grinding wheels.
Other factors causing defects are: grinding wheels which are too hard, passes too deep and grinding wheels
not sharpened.
Grinding can cause a surface tempering, this lows the steel mechanical strength freeing stresses which can
break the material.
tre Valli acciai peeled-rolled and Ground product floW cHart
Steel-work
Raw for rolling
Inductionhardening
Peelingmachine
Straigteningmachine
Reelingmachine
Precision grinding
reeled bars
bright bars
black bars
EC MT UT CC CA
NDTEC = composition - hardness - structureMT = Eddy currentUT = ultrasonic testCC - CA = demagnetization
NDT
24
25
GALVANIC TREATMENTS
The aims of the galvanic coating of a cold worked product are mainly to increase corrosion resistance and the
polished feature.
Galvanic treatments are coating techniques which by using electrolysis, a chemical decomposition based on elec-
trical current flow from an anode (current entry) to a cathode (negative electrode) through an electrolytic solution.
The electrolytic solution (copper, nickel silver, nickel, silver, gold, palladium, ruthenium etc.) is kept in tubs made of
inert polymeric material or a metallic structure internally coated with the same polymeric inert material, carrying
the anodes at the longer sides. The anodes can be active and oxidize during electrolysis, producing ions of the
same type as those depositing on the cathode, or can be inert (titanium, titanium-platinum, etc.) and act only as
a support for the surface electronic exchange, without being involved with the anodic reaction. When anodes are
soluble, special filters are activated to stop the passing and deposit of any particles on the cathode.
The cathode bar on which the parts to be treated are fixed is put over the tub, central to the anodes, and can
have longitudinal movements. Normally it consists of brass frames with harmonic steel hooks. Generally the anode
surface is at least twice the size of the cathode one.
A Straightener
B Chemical solution
C Material to be chrome plated
D Anode
During hot processing, the tubs are equipped with steam heating systems by means of titanium spires to avoid cor-
rosion (electric current with ceramic or Teflon protected resistors is used in small plants). The temperature is con-
trolled and regulated by special thermostats. The solution is stirred by means of pumps with hourly capacity 10-20
times higher than the tubs content, with a filtering system removing any particles from parts to be treated or from
the anodes. Other tubs components are level sensors and relative dispensers, including those for bright finish. The
voltage is of 6-8 V and alternating current is transformed into direct current, to obtain the most linear wave. The
manufactured items to be coated must be as smooth as possible and without material and machining imperfections.
So that no corrosion occurs, slag must not be porous (to avoid electrolytic contamination between two separate
layers). Porosity and sometimes chevron cracks usually found in all coatings, can be avoided by taking advantage
of the deposit thickness.
26
CHROMIUM PLATING
During the manufacturing of heavy duty mechanical parts, manufactured products surface is usually pro-
tected by a galvanic chromium plating. Cylinder shanks, scroll-bars, pneumatic / oil hydraulic controls, press
columns, etc. can be cheaply obtained working on already chromium plated bars, instead of chromium pla-
ting the single elements after machining. The chromium plating process is electrolytic and normally covers
a metal surface by means of immersion in a tub containing a chromic acid solution. Chromium thickness is
usually between 0.015 and 0.040 mm up to hypothetical 0.7 – 0.8 mm. A higher deposit than that is not
recommended owing to the tub low performance and higher brittleness. Before chromium plating, metal
surface finish must be optimised with roughness of max 0.4 μm RA. Stress-relieving of the chromium layer
and surface polishing / lapping, if required, can follow chromium plating.
traditional cHroMiuM platinG By iMMersion The bars are fixed onto a frame and immerged in the tub. The frame is connected to the negative pole, while
electrodes (“anodes”) are placed in the tub and connected to the positive pole. Thus electric current is tran-
sformed into chemical energy (electric current causes a chemical reaction which otherwise would not happen
spontaneously). However this traditional technology is polluting, both for disposal and steams due to tub
temperature. Bar retrieval causes chromic acid droppings and big tubs involve the uneasy management of
thousands litres of contaminating solutions.
tHe continuous cHroMiuM platinG process The bars enter into the tub horizontally one after the other. The current loss is a lot less than using the abo-
ve described method. The bar forward movement and rotation leads to a uniform thickness of chromium
plating all over the surface material. The shorter distance between anode and bar allows to increase the
electrical performance. The tub is rather small, contains less chemical solutions, produces less steams, easily
directed towards extractor hoods. The nearly fully-automated process allows higher productivity, recurrence
and product quality.
Chromium plated surfacesContinuous automatic plant
27
ZINC PLATING
Coating process of a steel manufactured product with a zinc layer to improve corrosion resistance.
The zinc as a protective factor for steel is owed to its very good properties such as: very good substrate
adherence, water resistance, resistance to abrasion and chemical attack. If damage of the plating occurs,
corrosion is limited to the zinc and not to the steel.
There are various methods to lay down a layer of zinc, the most commons of which are:
1) Hot zinc plating - process of laying down a layer of zinc on the metal base by heat immersion.
2) Electrolytic zinc plating - process of laying down a layer of zinc on the metal base by electro-galvanization.
Generally hot zinc plating is the immersion in molten zinc at average temperatures of 455 °C. During this phase,
zinc not only coats the steel, but also bonds with the surface layer, conferring mechanical strength and the right
anchorage to the treated material.
The process can be divided in the following separate phases:
• Pickling and degreasing using HCL and surfactants at room temperature;
• Fluxing by immersion in ammonium chloride and zinc chloride;
• Zinc plating, immersion, prior pre-heating at 100 °C in a molten zinc tub at 455 °C for a varying time from 1.5
to 5 min (for complex shapes immersion may need over 10 min).
Hot zinc plating is carried out on carbon steels, steels weekly or medium bonded with grey cast iron and
malleable cast iron. Generally this coating treatment is not ideal for steels with controlled sulphur, re-
sulphurized steels, lead steels.
Zinc honeycomb panelsBasket
28
factors tHet Mostrly influence Hot Zinc platinG Steel is mainly formed by iron and carbon with the more or less desired presence of other elements, classified
as impurities or bonding elements.
Different chemical compounds can cause various reactions during zinc diffusion into the surface layer of
products. Thus non-homogeneous coating layers can be noted for colouring, thickness and adherence. Ele-
ments such as silicon, carbon and phosphorus tend to increase the Fe/Zn alloy layer thickness, producing
near bright shiny steels. The greater zinc thickness is not always a sign of good coating and in some instances
the layers can be composed of Fe/Zn alloys alone, without the necessary outside layer of pure zinc. Generally
thin layers of (~ 0.08 mm) are more adhesive and plastic, therefore more apt to bending. Those more consistent
(~ 0.20 mm) have a greater hardness and brittleness, therefore less apt to resist knocks and vibrations.
However some physics and chemistry experiments showed the effects that silicon has during this process.
From the above graph, it can be noted that the silicon percentage from 0.03 to 0.12% and over 0.3% can
induce a consistent Fe/Zn reaction leading to increased deposits thickness but also less silicon adherence.
The silicon-phosphorus combined effect can influence the process and to better control it, these aspects may
be taken into account.
1) Formula: Si + 2.5 P max 0.09% for rolled products and Si + 2.5 P max 0.04% for products after cold
deformation.
2) Keep silicon percentage below 0.25%.
Limited quantities of carbon (0.10 - 0.18%) in steel do not have any bearings on the zinc layer, but in
percentages over 0.35% they can speed up the Fe/Zn reaction, thus increase thickness.
Quantities of sulphur over 0.20% can speed up the zinc plating process and can onset corrosion of the
steel ready for plating.
Zinc
pla
ting
thic
knes
s in
mm
Silicon content in %
Zinc
imm
ersio
n te
mpe
ratu
re
452 °C
440°C431 °C
0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45
0.25
0.24
0.22
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0
29
Chromium, manganese, nickel, niobium, titanium and vanadium, present in steel as residual elements have
a similar effect to that of sulphur.
Field experiments have shown that aluminium “killed” material allows a greater adherence and a more
precise thickness control.
Another very important factor for a correct zinc plating is to contain the tendency to brittle from steel
aging.
Steel aging predisposition and consequent brittleness risk are mainly caused by nitrogen content in steel,
which in turn largely depends on the production process and strain hardening degree during cold plastic
deformation.
Aging brittleness is a metallurgic phenomenon which regards all steel types.
Depending on the degree of cold deformation, the steel strength Rm increases, while ductility (stretching %
and toughness (resilience Kv) decrease. It must be considered that each 1% cold deformation will cause a 3
°C transition temperature drop (a 12% reduction will cause a 36 °C transition temperature drop).
To better explain: if a steel has its transition point at -20 °C (rapid loss of toughness normally measured in
J and resilience Kv), a 12% drop will cause the phenomenon at +16 °C.
To reduce the brittleness factor a non-aging steel must be deployed, thus a steel with added V (vanadium),
Nb (niobium) and Ti (titanium), which by nitrogen fixing can oppose aging hardness, or aluminium “killed”
steels (common praxis in modern steelworks).
The reduction ratio for cold deformation must be kept as low as possible. A stress-relieving heat treatment
before proceeding to the following pickling and hot zinc plating must be applied if this condition cannot be
satisfied.
Surface finish can also considerably influence the deposit thickness.
If the product to be coated is very rough (i.e. sand-blast pieces with Ra 3.2 μm roughness), the surface will
allow a greater molten zinc even up to 20% more than a material with Ra 1.6 μm, with resulting increase
of the zinc layer and of the processing cost.
Piece surface must be very clean and without defects such as micro-cavities, scoring, etc., because zinc pla-
ting does not have a covering effect, will not hide, on the contrary will highlight the majority of defects.
Some defects such as peeling cannot be seen during pickling but will certainly be seen during zinc plating.
Oil, varnish and grease stains have a negative impact on the final appearance of zinc plating.
For cleaning, even the burning of particles attached to the surface may be necessary, because during zinc
plating they develop gasses, thus inhibiting adherence. Remove welding clinkers by chipping or sand-blast,
because they are acid resistant. Protect male threads with canvas isolating tape (not plastic) which can be
simply removed by a metal brush once zinc plating has ended. Protect female threads with standard window
filler or wood pins.
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31
MATERIAL CHARACTERISTIC CHECKING
Melt cHeMical analysisGenerally the melt chemical composition is that supplied by steel producers and must always be compliant
with the reference standards.
product cHeMical analysisIt may differ from the melt one, but anyway able to determine with certainty the steel examined type. A sin-
gle chemical element difference in percentage between melt and product is acceptable, and the respective
values are reported in the official norms. Products must be handled over separately for each melt and must
be maintained throughout the working process.
tensile testThis testing reaching rupture point is the mostly used and versatile, since it allows to measure strength and
ductility at the same time. The values derivable from are: Yield strength (Rp0.2 / ReH), Rupture (Rm / R),
Stretching (A%), Stress (C% / Z%). Testing must be determined from the beginning (order placement) and
production operators must take samples based on values reported in the job sheet.
Reference standard: EN 10002-5.
Hardness
Hardness H is the strength that the material surface opposes to its penetration.
The advantages of hardness testing are: easiness and speed of execution, economics, both in terms of ma-
chine costs and its set up.
This type of test can give an indication on mechanical strength, converting the tensile strength obtained,
using the official tables (i.e. ASTm A 370) which are based on comparisons.
Reference standards: uNi EN iSO 6506, uNi EN 6508.
Tensile testing machine Loads diagram from tensile machine
Quenched and tempered steel
Annealed steel C% 0.70
Annealed steel C% 0.40
Annealed steel C% 0.20
Copper
Brass
ReH
ReH
Rupt
ure
N/m
m2
Rp0.2
Stretching
32
resilience testThis test is called destructive since it leads to sample rupture and is conducted at room temperature, but also
at low and high temperatures.
The main duty of this verification is to determine the toughness degree of steel (resistance to shocks). The
energy expressed in J (Joule) is compared to the resistant sample section previously notched. Other data
obtained are the transition curves ductile-fragile (sample breaking at -10 °C, -20°C,-30 °C, -60 °C, -180
°C to find out when the steel brittles) and aging simulation (samples pressed at 10% of the section and
stretched at 300 °C).
Resilience minimum values for drawn products are not provided for by norms and are not guaranteed.
Reference standards: EN 10045-1 and ASTm A 370.
QuencH test The Jominy End Quench Test is used to determine the steel attitude to hardening through quenching. From
this testing a curve hardness-distance is obtained. Practically, it is adopted to have prior information regar-
ding the hardness of pieces, which will be later quenched by means of industrial techniques. Testing is carri-
ed out on a sample, obtained from the product of a particular melt, heated in the appropriate furnace until
austenitizing temperature (temperature to which steel is transformed into austenite, during heat process).
Cooling by controlled water sprays along the axis follows. The quenched part undergoes a series of hardness
procedures (HRC) starting from 1 mm and usually up to 50 mm, to obtain a descending curve (band).
Reference standard: EN iSO 642.
Pendulum for resilience testing
leGenda 1. Foundation
2. Scaffolding
3. Supports
4. Sample
5. Joule scale (energy-work)
6. Rotation axis
7. Scale Index J
8. Pendulum supports
9. Pendulum rod
10. Bob
11. Cutting edge
Sample cooling Hardness determination
0 11 25 35 50 60 80 100mm
“d”
HRC
100 mm 25 mm
12,5 mm H2 O 20 °C
56
8
7
9
10
11
1
4
32
33
Bend test This test is not to determine mechanical values, but to examine material behaviour under stress.
Normally it is carried out at room temperature, with angles to be set during order phase. The bend test is needed
to establish how good is the material subject to plastic deformation. The material is to be bent without inversion
of flexion direction, to reach the desired angle (90°-180°). Bending must be done slowly, not to hinder the plastic
sliding of the material. After bending the bent sides and the external face must be examined. The material will
be adequate if micro-cracks or defects agreed in the order phase do not appear (often this characteristic is asked
for drawn products). We remind that it is advisable to start from an annealed rolled product, before drawing, to
obtain best results.
If the drawn product shows cracks or ruptures during the bending phase, stretching or bright annealing are useful
to avoid damaging the surface layer and will allow a good predisposition toward this test.
Reference standard: uNi 564.
MetalloGrapHic analysisA correctly carried out metallographic analysis using an optical microscope, allows to inspect the microstruc-
ture and the presence of defects inside the examined material (inclusions, intermetallic compounds, chevron
cracks etc.) which are invisible to the naked eye.
Grain siZe The grain size is an important analysis to assess the manufacturing process and the mechanical characteri-
stics of the material.
Finer grains carry better mechanical characteristics, coarse grains can be attributed to an excessive high
temperature exposure.
A technique called aluminium “kill” is adopted on special steels, to counteract grain swelling and avoid
brittleness.
Optical microscope
34
The reference standards uNi 3245 and ASTm E 112 describe assessments methods and give out informa-
tion by means of baseline images to assess the different sizes.
non-Metallic inclusionsAt solid state all steels contain inclusions being in majority of cases, oxides and sulphurs.
Their quantity and sizes depend on the manufacturing procedures. Their presence weakens the product
physical properties. Imagine for example a wood plank with notches: if under stress, the first rupture point
will occur at the notches, which also happens to metals with inclusions.
Non metallic inclusions cannot deform in the same way as mould, during hot or cold deformation; some may
break or may leave micro-cavities generating into micro-cracks but without deformation.
Others may deform or stretch in the direction of the deformation given by the material. The most damaging
ones are those stretched. The new market demands impose high purity steels.
Reference standards: uNi ENV 10247, uNi 3244, DiN 50602, ASTm E45.
surface decarBuriZation Decarburization depends upon the carbon diffusion coefficient in the steel. Carbon combining with the
furnace atmosphere oxygen or air oxygen, tends to escape from the material surface.
Through decarburization, all the carbon is removed from the surface, but remains in the underlying struc-
ture, visible through the optical microscope as a lighter band on the surface. The decarburization can also
be analytically determined. On the surface, a lower carbon percentage will be found than internally. This is
Grano 1 grosso Grano 6 fine Grano 8 molto fineMicrografie a 100 ingrandimenti
Stretched sulphurs Globular oxidesStretched oxides
35
why it is good practice to remove at least 1-2 mm of material before testing, when product analysis must be
carried out. Another effect caused by decarburization is surface hardness lowering. Also in this case 1-2 mm
must be removed to obtain a true value.
Reference standard: uNi 4839.
BandinG tecHniQueMicro-structural characteristics of materials can greatly influence the machines manufacture outcome and
in worst cases impair it.
The structure that more often causes problems is that of Ferrite-Pearlite “bands”, because of their very diffe-
rent hardness thus the machines are affected by this. Some heat treatments carried out at high temperatures
(normalization, globular annealing, etc.) can ease off the problem.
ASTM A 105 with marked banding technique 11SMnPb30 with marked banding technique
Steel micrograph after heat treatment in a traditional furnace: the decarburized light band is clearly visible
Steel micrograph after heat treatment under controlled conditions in a furnace: absence of decarburization is a guarantee for a homogeneous structure
36
37
TERMINOLOGY
stretcHinG a% It measures the stretching of the material when taken to rupture point using tensile testing. It’s a data allowing
the engineers to know how much steel can be stretched before reaching rupture point.
non MaGnetic It’s a steel showing ferromagnetic properties and that can be demagnetized with adequate heat treatment,
which consists of exceeding the magnetism critical point (769 °C), remaining at that point for a period of
time, and cooling normally in air or furnace.
anisotropHy The crystal shape is different in all directions as well as the physical properties (refraction index, thermal
conductivity, mechanical and magnetic properties, etc.) which vary depending on the direction taken.
anisotropic The specific physical properties inside a material have different values in different directions.
specific Heat capacity Heat quantity necessary to raise temperature of a mass unit by 1 °C.
The specific heat capacity at 20 °C of ferritic and martensitic steels is slightly less than that of austenitic
steels, but grows quicker with raising temperature.
MaGnetic field Magnetic field forming around a magnet or an electrical circuit. It’s marked by H and measured by Ampere/
meter.
ultiMate strenGtH rm-r The ultimate strength determined by stress proportional samples, measured in N/mm2.
This occurs within a solid subject to stress causing the molecular bonds to break.
This testing is used by engineers for dimensioning supporting structures.
38
yield strenGtH rp0.2 Load corresponding to a non-proportional extension, widely used as yield strength at 0.2%.
The value is obtained from tensile testing, measured in N/mm2 and is useful to engineers to determine sections
and safety margin to adopt for structures of a determined construction.
conductiVity It’s the property of a material’s ability to conduct heat or sound energy or electric current.
Symbol: Siemens • m/mm2.
tHerMal conductiVity Thermal conductivity is the W / (m • K) measurement of a body’s ability to conduct heat. It depends from the
nature of the material and not from its shape.
This property is a lot higher in carbon steels ~ 50 W / (m • K) and bonded steels ~ 40 W / (m • K), it lowers
to ~ 30 W / (m • K) in stainless steels at chromium 15% and lowers ~ 15 W / (m • K) in nickel and molyb-
denum steels.
Thermal conductivity proportionally increases to the part heating and it is a parameter used in heat treat-
ments to define the heat rate.
Heat transfer coefficient Defines the variation of magnetic properties at temperature variation. Normally expressed in variation %
of the part for each degree of temperature.
coerciMeterAutomatic instrument used to measure coercive force of steel samples of any shape (regular or irregular)
and of specific manufacture products alone or assembled with other materials.
Normative widely used for checks: ASTm 341 or iEC 404-7.
coerciVity Defined as the magnetic field, expressed by Hc, needed to reduce induction B or magnetization M to value
zero. Normally measured in Oersted or Ampere/meter. Needed to measure resistance to demagnetization of
a magnetized material.
conductiVity It’s the property of a material’s ability to conduct heat or sound energy or electric current.
Physical size equal to the inverse of resistivity.
39
Hysteresis curVe Graphic representation of the curve obtained by measuring induction B (air + material) or magnetization
M in presence of a magnetic field H. It describes a complete cycle between defined limits for induction or
magnetization saturation from the first to third quadrant.
B = Magnetic flow density Br = Residual magnetic induction
H = Magnetic field Hc = Coercive force
deMaGnetiZation curVe Graphically it is the curve sector of the hysteresis cycle of the second quadrant, which defines the main ma-
gnetic characteristics of a magnetized material. The demagnetization curve describes the induction change
or emanation of the residual value at zero applying a negative magnetic field.
density (Mass per unit VoluMe) This ratio m/v between the mass (m) of a body and its volume (v) is also called specific weight and is mea-
sured in Kg/dm3.
The iron specific weight is 7.86 Kg/dm3 and its atomic mass is 55.847 while that of the main elements of
stainless steel is: 51.996 for chromium, 58.69 for nickel and 95.94 for molybdenum.
Thereby alloys rich in chromium are lighter than iron, while nickel and molybdenum alloys are heavier. The
following example compares the estimated weight of three bars sized 180 mm square and 1500 mm long.
1.8
1.2
0.6
0
-0.6
-1.2
-1.8
-150 -100 -50 0 50 100 150
Br
Hc
B (T
esla
)
H (A/m)
Cycles with induction from 0.3 to 1.7 Tesla
1.7
1.2
0.5
0.3
40
Density values are reported in the data sheets specifications.
42CrMo4 steel (1,80 • 1,80 • 7,85 • 15,00) = Kg 381,51
1.4006 steel (1,80 • 1,80 • 7,70 • 15,00) = Kg 374,22
1.4567 steel (1,80 • 1,80 • 8,027 • 15,00) = Kg 390,11
floW density Defines the induction field as magnetic lines of force per unit area.
dielectricIs an electrical insulator that can be polarized by an applied electric field with accumulated energy. It has the
function of separating parts with different potentials and forcing the current into one single direction.
Hardness Characteristic depending on molecular cohesive forces. Measured through various sizes (HB, HRC, HV, etc.)
within empirical tables, among which only some correlation exists, all in ratio with traction rupture load.
tHerMal eXpansion The thermal expansion or growth is the physical phenomenon which appears when material has a volume
increase, due to temperature increase during heat treatment, function or welding.
The value can be determined by dilatometer testing or according to data sheet specifications contained in the
volume Designing with steel by Lucefin Group.
This data lies within the formula for the theoretical linear e volumetric growth in mm, that steel will endure
when heated at temperatures between: 20 and 100 °C, 20 and 200 °C, 20 and 300 °C, etc.
Lo = Initial length of the bar or the part in mm
ro = Initial radius in mm
E = Constant value from data sheet specification (i.e. as 10-6 • K-1 equal to 10.4 insert 0.0000104)
Δt = Temperature difference between the part to be heated and the environment
L = Length in mm after heating at °C.
V= 3 mm volume after heat treatment
Linear expansion L = Lo • (1 + (E • Δt))
Volumetric expansion V = 3,14 • r2 • Lo • (1 + (2 • E • Δt)) • (1 + (E • Δt)
floW Number of magnetic lines of force measured in Gauss o Tesla. The lines can seen using dry iron powders or
in humidity.
41
ferriticsConsist of non metallic materials made of iron oxides and a bivalent metal (Mg, Mn, Zn, Cu, etc.) and can
be assimilated to ceramic materials for its harness and brittleness. They have a very low conductivity, thus
are suitable to form ferromagnetic nuclei for high frequency applications (5 – 500 kHz). The most common
ferritics are Mn-Zn, Ni.Zn, Mg-Mn.
MaGnetic field forceIt is the magnetizing or demagnetizing force, generally measured in Oersteds, which determines the ability
of an electric current, or a magnetic body, to induce a magnetic field at a given point.
floWMeter Devised used to measure change of magnetic induction flow.
coerciVe force Demagnetizing force necessary to reduce residual induction to zero, as measured on a saturated magnet.
Calculated in Oersted or A/m and KA/m. Symbol: Hc.
intrinsic coerciVe force Measures the resistance of a magnetic material to demagnetization and shows its stability degree at high
temperatures. Symbol: Hci.
GaussUnit of measure of magnetic induction in the CGS electromagnetic system. It shows flow lines for cm2.
GaussMeter Device used to measure the instantaneous value of magnetic induction and residual magnetism.
MaGnetic induction (B)Is the magnetic field induced by an applied field resulting from the laid down field and from the matter. Also
defined as magnetizing or demagnetizing force measured in Oersted, which determines the current ability
or of a magnetic material to induce a magnetic field in a given point. B = μo • H
In any given material: B = μr • μo • H
42
isotropic A magnet is isotropic when its properties are identical in all directions. In the metal material field, magnetic
orientation of particles does not have a preferred direction thus allowing an all round magnetization.
HysteresisIt is a ferromagnetic substance characteristic, in which magnetization intensity does not uniquely depend
from the magnetic field applied, but also from the previous evolution in the magnetic field. It is defined as
the tendency of a magnetic material to retain its magnetization in a demagnetizing energy presence.
MaGnet Is a ferromagnetic body artificially or naturally magnetised. Only certain types of substance are able to ac-
quire a satisfying permanent magnetization, after adequate treatments.
residual MaGnetisMIt is the remaining magnetism in a steel material after having been in contact with an applied magnetic field
(usually lift magnets, induction processes, etc.). Its intensity depends on several factors, some of the most
important are: chemical structure, magnetic field intensity at source, temperature of material.
MaGnetiZation Magnetism for each volume unit, measured in Ampere/meter.
MaGnetostriction It is a property that can cause changes of shape or dimension during the process of magnetization.
MaXiMuM enerGyIn the hysteresis curve it is represented by the point of maximum out come between magnetizing force H
and induction B. Also defined as the energy that a magnetic material can transfer to an external magnetic
circuit in a given point of the demagnetization curve. Symbol: BH max.
antiferroMaGnetic MaterialsThe magnetic structures a and b inside anti-ferromagnetic materials, are precisely equal but opposite, resul-
ting in null magnetization.
Hematite is the best anti-ferromagnetic material.
43
diaMaGnetic MaterialsAre those materials whose magnetization is inversely inducted to that of the inductive field. They are com-
posed of non magnetic atoms placed in complete orbitals without free electrons. This causes an opposition
when in a magnetic field. In other words, a negative magnetization is created, exactly the opposite of what
happens in ferromagnetic materials. Among these diamagnetic materials are quartz, calcite, water and
organic substances.
ferroMaGnetic MaterialsOne of the main characteristics of these materials is the spontaneous magnetization without a magnetic
field and can be increased until it reaches magnetic saturation. Saturation is at high temperatures and mo-
derate magnetic fields.
In particular, each ferromagnetic material at a given temperature called Curie temperature, which differs
from material to material, loses the electrons configuration and becomes paramagnetic. Furthermore, fer-
romagnetic materials can retain a magnetic memory from previously. The best ferromagnetic elements are:
iron, nickel and cobalt. Ferritic and martensitic stainless and duplex steels are among this category.
paraMaGnetic MaterialsThese are made of atoms and ions with unpaired electrons and incomplete orbitals. They have a net ma-
gnetism and can magnetize when exposed to a magnetic field. However it is a weak magnetization, which
disappears when the magnetic field is taken away. Liquid oxygen, aluminium, biotite, pyrite, siderite are
among the paramagnetic materials. Austenitic stainless steels belong to this category (stable austenitic
structure).
MaXWell The measurement unit of the flux produces by a intensity magnetic field in the CGS system in an area of 1 cm2.
One Maxwell is 10-8 Weber and equals one line of magnetic flux. Symbol: mx.
elastic Modulus Defined as the strain stress and deformation ratio, in mono-axial loads and elastic behaviour of material.
Used by engineers for flexural strain verification, under exercised stress, to establish the maximum load
factor of a construction. The longitudinal elastic modulus for each steel and the different temperatures to
which a stainless steel product can be worked at, all are reported in the data sheet specification.
m = 1/Poisson coefficient (the Poisson coefficient is reported within some data sheet specification contained
in the volume Stainless Steels by Lucefin Group © 2011).
E = Longitudinal elastic modulus G = Tangent elastic modulus
The result is measured in GPa (GigaPascal). E = G / (m / 2 • (m + 1)) G = (m / (2 • (m + 1)) • E
44
MaGnetisM It is measured in Am2 (Ampere for each m2).
poisson’s ratioWhen a material is compressed in one direction, it usually tends to expand in the other two directions per-
pendicular to the direction of compression. This phenomenon is called Poisson effect. The Poisson ratio is the
ratio of the percent of expansion divided by the percent of compression. It is often used when calculating
elasticity and structural projects.
oersted Unit of measure for the intensity of the magnetic field and measuring the magnetic force.
1 Oe = 1 Gauss = 0,79 A/cm. Symbol: Oe.
perMeaBility (μo) Is the propagation ability of the magnetic flux in a classical vacuum: μo = 1,26 • 10-6 • H/m
μr < 1 Diamagnetic materials (if the magnetic field is weakened inside the material)
μr > 1 Paramagnetic materials (if the field is strengthened inside the material)
μr >> 1 Ferromagnetic and ferromagnetic materials (if the field is strengthened a lot inside the material)
initial perMeaBility Is the ratio between field B and field H measured when H has a zero tendency. Relative permeability or ratio
from material and free space (air) permeability is more useful. Used to indicate weak ferromagnetic steels
used for transformers.
aBsolute MaGnetic perMeaBility Is the parameter of all materials given by the ratio between magnetic induction B produced inside the ma-
terial by the magnetic field and intensity H of the applied field.
Symbol: m. The 1/m opposite of permeability is called specific reluctance.
relatiVe MaGnetic perMeaBilityIn physics terms it defines the ability of a substance to be magnetized by a magnetic field. Symbol: μr and it
is the ratio between absolute permeability μ of a generic material and the permeability μo of free space (va-
cuum). Ferritic and martensitic stainless steels are defines magnetic (a magnet attracts them) when at room
temperature and they lose this characteristic when heated over 769 °C. Austenitic steels are classified as
non-magnetic and their permeability is around 1.02 μr. They can be slightly magnetized during cold drawing
treatment, but a later re-crystallization return them to the initial non-magnetic state.
45
perMeaMeterA device able to do hysteresis cycles and measure magnetization of mild magnetic steels (i.e. stainless for
electro-valves and nuclei). It performs in automatic and determines the following parameters: Br, Hc, Bsat,
Jsat, μmax. Standards used for checking: ASTm 341 or iEC 404-4 for straight samples or bars.
MaGnetic polariZation A substance exposed to a magnetic field directs its atoms magnetism to magnetize for induction. Generally,
term used to describe an alteration of physical state, where some phenomena from isotropic become vector.
resilience Indicates material tenacity when exposed to violent shocks. Resistance measured in J (work - energy), it is
determined through previously cut samples and usually of Kv types. This value also indicate steel predispo-
sition for certain uses.
electrical resistiVity (also KnoWn as specific electrical resistance) It is the resistance of a conductor of unit length and area section unit, measured in Ω • mm2/m. The resisti-
vity of a conductor depends on its nature, temperature, and in some cases on the intensity of magnetic field
in which it is. Under heat treatment the resistivity of the material is null (absolute zero) and increases by 6%
each 100 °C. The increase of resistivity in a material can be obtained by altering its composition (i.e. 4-4.5%
silicon increase).
residual MaGnetisMIt represents residual magnetism when the magnetic field applied is zero. In the graph it is the intersection
of the curve with the y-axis. Symbol: mr.
saturation Phenomenon occurring when, in a ferromagnetic substance subject to a sufficiently intense magnetic field,
magnetization remains practically constant to every increase of magnetic field.
creep (deforMation) The tendency of a solid material to deform under the influence of constant stresses at high temperatures.
The sample is subject to a determined constant load and temperature for long periods. The obtained results
simulate steel behaviour in time.
deMaGnetiZationThis unwanted magnetic force (found in products for grinding, lapping and polishing, galvanic treatments,
46
etc.) attracts filings or iron powder and causes unacceptable surface finishes. It can be diminished or remo-
ved by bringing steel at temperatures above 769 °C or let it through demagnetizing tunnels. Another rather
efficient method is the stress-relieving heat treatment for long periods.
solenoid It is a coil wound into a tightly packed helix, mounted on a cylindrical support bigger than the helix diameter.
curie teMperature It is the temperature above which ferromagnetic materials become paramagnetic. It normally depends on the
chemical composition of the magnetic material, once the material reaches it, loses all of its permanent magne-
tic properties and can no longer keep magnetism. Symbol: Tc = 769 °C.
MaXiMuM operatinG teMperature The maximum temperature of exposure that a material can resists without mechanical or structural changes.
tesla Density unit of magnetic flux: 1 T = 10000 Gauss.
MaGnetic Viscosity It describes the variation of magnetization delay in a ferromagnetic material when the external magnetic
field abruptly changes intensity.
WeBer It is the unit for magnetic flux which when linked at a uniform rate with a single turn electric circuit during
an interval of 1 second, will induce an electromotive force of 1 volt. 1 Weber = 10-8 Maxwell. Simbol: Wb.
47
48
DIMENSIONS AND TOLERANCES Of BRIGHT STEEL BARSEN 10278
diMension cHecKinG• Round bars : distance > 150 mm from bar extremity
• Tailor made round bars: distance > 10 mm from bar extremity
• Non-round shaped bars : distance > 25 mm from bar extremity
FLATS DimENSiONAL TOLERANCES
CARBON mAx 0,20% AND FREE CuTTiNg STEELS LOW C%
CARBON > 0,20% AND ALL STEELS
width limit deviationmm mm mm mm
< 18 + 0 - 0,11 > 18 < 30 + 0 - 0,13 > 30 < 50 + 0 - 0,16 > 50 < 80 + 0 - 0,19 > 80 < 100 + 0 - 0,22 > 100 < 150 + 0,50 - 0,50 > 150 < 200 + 1,00 - 1,00 > 200 < 300 + 2,00 - 2,00 > 300 < 400 + 2,50 - 2,50
THiCkNESS LimiT DEViATiON LimiT DEViATiONmm mm mm mm mm mm > 3 < 6 + 0 - 0,075 + 0 - 0,15 > 6 < 10 + 0 - 0,090 + 0 - 0,18 > 10 < 18 + 0 - 0,11 + 0 - 0,22 > 18 < 30 + 0 - 0,13 + 0 - 0,26 > 30 < 50 + 0 - 0,16 + 0 - 0,32 > 50 < 60 + 0 - 0,19 + 0 - 0,38 > 60 < 80 + 0 - 0,30 + 0 - 0,60 > 80 < 100 + 0 - 0,35 + 0 - 0,70
FLATS STEELS
width mm C% < 0,25C% < 0,25
quenched and temperedstainless,
bearings, tools
mm/m mm/m mm/m
< 120 1,5 1,5 1,5 w w = width1,5 2,0 2,0 t t = thickness
> 120 w / t < 10
1,5 2,0 2,0 w2,0 2,5 2,5 t w/t = ratio
> 120 w / t > 10
2,0 2,5 2,5 w2,5 3,0 3,0 t
SquARESHExAgONS
DimENSiONAL TOLERANCESSTEELS
h11 - h12C% < 0,25 C% > 0,25 stainless
dimens. mm/m mm/m mm/m< 75 1,0 2,0 1,0> 75 1,5 2,5 1,5
ROuNDS DimENSiONAL TOLERANCES
STEELSC% < 0,25 C% > 0,25 stainless
h9 - h10 - h11 - h12all dimensions mm/m mm/m mm/m
1,0 1,5 1,0
STRAigHTNESS TOLERANCES
STRAigHTNESS TOLERANCES
STRAigHTNESS TOLERANCES
mAx DEViATiON FOR WiDTH w AND THiCkNESS t
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HOT ROLLED PRODUCT QUALITY SURfACE
Currently, only very few suppliers can operate surface checks on rolled wire rods because the hot rolling speed and high
temperatures do not allow a trustworthy verification of defects before the final coiling.
Rolled bars allow checking because the depth of the defect related to the rolls, have a less incidence and more trust-
worthy checks do exist.
Before order placement the raw material must be classified and its conformity verified during the sand-blasting phase
before the drawing phase.
surface Quality classification folloWinG en 10221
CLASSNOmiNAL DiAmETER
dN mm
mAximum ADmiSSiBLE DEPTH OF SuRFACE DiSCONTiNuiTiES
mm
A5 ≤ dN ≤ 25 0.50
25 < dN ≤ 150 0.02 x dN
B
5 ≤ dN ≤ 12 0.20
12 < dN ≤ 18 0.25
18 < dN ≤ 30 0.30
30 < dN ≤ 150 0.01 x dN
CStandard requiredby Lucefin Group
5 ≤ dN ≤ 12 0.17
12 < dN ≤ 30 0.23
30 < dN ≤ 120 0.0075 x dN
D
5 ≤ dN ≤ 12 0.15
12 < dN ≤ 40 0.20
40 < dN ≤ 60 0.005 x dN
60 < dN ≤ 80 0.30
E 5 ≤ dN ≤ 60 4)
If products are ordered to be drawn, irregularities or partial repairs which cannot be removed
by drawing are not admitted.
Class C example
Rolls and bars Max. depth
diameter admitted defect
Ø 5 ≤ dN ≤ 12 mm 0.17
Ø 40 x 0.0075 mm 0.3
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COLD ROLLED PRODUCT QUALITY SURfACE
Taking into consideration that surface defects cannot be removed without removing material, the product
technically without defects will only be the peeled rolled and/or ground.
All drawn products, on the contrary, will present the non-magnetic surface defects of initial product.
These are longer and sometimes present a reduction in depth, but will be noticeable due to a better drawn
surface.
The customer will define the wanted class and the supplier will accept or refuse, based upon own production
standards and checking instruments (i.e. sight inspection or using Defectomat, Circograf, etc.).
Generally the supply class is 1, which is the less demanding one, for a straight forward order.
SuRFACE quALiTY CLASSES ACCORDiNg TO EN 10277-1
STATuSCLASS
1 2 3 4
Defect depth
max 0,3 mm per d 1) ≤15 mm
max 0,02 x d per 15 < d ≤ 100 mm
max 0,3 mmper d ≤15 mmmax 0,02 x d
per 15 < d ≤ 75 mmmax 1,5 mm
per d > 75 mm
max 0,2 mm per d ≤20 mmmax 0,01 x d
per 20 < d ≤ 75 mmmax 0,75 mm per d > 75 mm
Technically without Chevron
cracks during production
Max mass % of products supplied
with defectsabove agreed level
4% 1% 1% 0,2%
PRODuCT SHAPE 2)
Round bars + + + +
Square bars + + (per d ≤ 20 mm) - -
Hexagonal bars + + (per d ≤ 50 mm) - -
Plate bars + 3) - - -
1) d = Bar diameter and width related to squares and hexagonals2) + indicates that the shape of the product is available according to classes - indicates that the shape of the product is not available according to classes 3) Max defects depth refers to relative section (width or thickness)
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Usually tolerances are requested in (-), when ordered in (+-) the sum must be equal to what agreed (i.e. +0.10 or + 0.05mm)
DIMENSIONAL TOLERANCES fOR COLD fINISHED BARS EXTRACT fROM ASTM A 108-07 TABLE. A 1.1
STEEL BARS carbon contents
max 0,28 % or less
carbon contents over 0,28 % up to 0,55%
SizE TOLERANCES TOLERANCES
F
LATS
inches mm inches mm inches mm< 3/4 < 19,05 - 0,003 0,076 - 0,004 0,102
> 3/4 < 1-1/2 > 19,05 < 38,10 - 0,004 0,102 - 0,005 0,127> 1-1/2 < 3 > 38,10 < 76,20 - 0,005 0,127 - 0,006 0,152> 3 < 4 > 76,20 < 101,6 - 0,006 0,152 - 0,008 0,203> 4 < 6 > 101,6 < 152,4 - 0,008 0,203 - 0,010 0,254> 6 > 152,4 - 0,013 0,330 - 0,015 0,381
SquA
RES
inches mm inches mm inches mm< 3/4 < 19,05 - 0,002 0,051 - 0,004 0,102
> 3/4 < 1-1/2 > 19,05 < 38,10 - 0,003 0,076 - 0,005 0,127> 1-1/2 < 2-1/2 > 38,10 < 63,50 - 0,004 0,102 - 0,006 0,152> 2-1/2 < 4 > 63,50 < 101,6 - 0,006 0,152 - 0,008 0,203> 4 < 5 > 101,6 < 127,0 - 0,010 0,254 \ \> 5 < 6 > 127,0 < 152,4 - 0,014 0,356 \ \
HEx
AgO
NS
inches mm inches mm inches mm< 3/4 < 19,05 - 0,002 0,051 - 0,003 0,076
> 3/4 < 1-1/2 > 19,05 < 38,10 - 0,003 0,076 - 0,004 0,102> 1-1/2 < 2-1/2 > 38,10 < 63,50 - 0,004 0,102 - 0,005 0,127> 2-1/2 < 3-1/8 > 63,50 < 79,375 - 0,005 0,127 - 0,006 0,152
> 3-1/8 < 4 > 79,375
< 101,60 - 0,005 0,127 - 0,006 0,152
ROu
ND
S
inches mm inches mm inches mm< 1-1/2 < 38,10 - 0,002 0,051 - 0,003 0,076
> 1-1/2 < 2-1/2 > 38,10 < 63,50 - 0,003 0,076 - 0,004 0,102> 2-1/2 < 4 > 63,50 < 101,6 - 0,004 0,102 - 0,005 0,127> 4 < 6 > 101,6 < 152,4 - 0,005 0,127 - 0,006 0,152> 6 < 8 > 152,4 < 203,2 - 0,006 0,152 - 0,007 0,178> 8 < 9 < 9 > 203,2 < 228,6 - 0,007 0,178 - 0,008 0,203
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CUSTOM MADE COLD DRAWN PROfILES
Two wire drawing threads One wire drawing thread
A solid industrial culture producing high-tech traditionally built products
Three wire drawing threads
All quenched and tempered or normalised grades and hardened at max HB 302 before cold finishing and all stretched or annealed grades after cold finishing.Straightness tolerances are not applicable to bars HB over 302. a) Tolerances are based on the following straightness measurement: a bar is placed on a flat horizontal base
or a ruler is deployed and the arc is measured by thickness gauges. b) It is well known that straightness can deteriorate in case of ill treatment. To maintain it extreme care is due
in every successive stage. Sometimes specific tolerances are requested for carbon steels or bonded steels, in this case, the customer informs the supplier of requested tolerances and checking method to use.
STRAIGHTNESS TOLLERANCES fOR COLD fINISHED STEEL BARS
a) b) extract from astM a 108 - 07 tab. a 1.4. straightness tolerances (mm max deviance) in any part equals to 3048 mm of the bar
CARBON CONTENTSmAx 0,28% OR LESS
CARBON CONTENTS OVER 0,28% AND ALL gRADES
THERmALLY TREATEDSizE LENgHT
mm mm ROuNDSSquARES,
HExAgONSROuNDS
SquARES, HExAgONS
less than 15,88 less than 4572 3,17 4,76 4,76 6,35less than 15,88 4572 and over 3,17 7,94 7,94 9,5315,88 and over less than 4572 1,59 3,17 3,17 4,7615,88 and over 4572 and over 3,17 4,76 4,76 6,35
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SquA
RES
SizE mm B Rb x b h9 min max4 x 4
-0.0300,16 0.25
5 x 5
0.25 0.406 x 67 x 7
-0.0368 x 810 x 10
0.40 0.6012 x 12
-0.04314 x 1416 x 1618 x 1820 x 20
-0.0520.60 0.80
22 x 2225 x 25
a richiesta30 x 30
-0.06240 x 4050 x 50
FLAT
S
SizE mm B H Rb x h h9 h9 h11 min max8 x 7
-0.036.. -0.090 0.25 0.40
10 x 6-0.036 ..
0.40 0.60
10 x 812 x 10
-0.04314 x 6
.. -0.09014 x 916 x 1018 x 11
..
-0.110
20 x 10
-0.0520.06 0.80
20 x 1222 x 1424 x 1825 x 1428 x 6 -0.075
28 x 16
-0.130
30 x 1632 x 18
-0.062
36 x 20
1 1.2
40 x 2245 x 2550 x 1650 x 2550 x 2850 x 32
-0.160
50 x 4056 x 32
-0.0741.6 2
60 x 3060 x 4063 x 3270 x 3680 x 20
2.5 380 x 40
100 x 50-0.087
120 x 50
COLD-DRAWN PRODUCTS fOR KEYS – TOLERANCES DIN 6880
Luglio 2011
Lucefin S.p.A.
I-25040 Esine (Brescia) Italy
www.lucefin.com
Progetto grafico: parlatotriplo - Gianico (BS)
Stampa: la Cittadina - Gianico (BS)
Lucefin S.p.A. I-25040 Esine (Brescia) Italy
www.lucefin.com
