engineering materials-Istanbul .technical University

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Dr.C.ErgunMak 214E

MAK214ESummer 2006-2007

Lecture Notes 2

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Dr.C.ErgunMak 214E Principals of Heat Treatments

• Heat treatment is a process to apply to a certain alloy compositions to obtain specific properties.

You may want to havefollowings:

–High strength,–High hardness,–Ductility,–Machinability,–Small grain size,–Remove the internal stresses,–Homogenous structure.

You may use heat treatments.Process variables to control the resultant

properties:– Processing time,– Processing temperature,– Cooling rate,– The composition of the starting

material-alloying elements– The process history of the starting

material (any process previously performed).

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Dr.C.ErgunMak 214E A Basic Heat Treatment Cycle

0

200

400

600

800

0 1 2 3Time (day, hr, min, sec, etc.)

Tem

pera

ture

(C, F

, K, e

tc.)

Heating rate

Holding time

TreatmentTemperature

Cooling rate

Important Process Parameters

•Heating rate•Holding temperature•Holding time•Cooling rate

Depending on the Cooling rate:• Slow Cooling rate Diffusional phase transformations.• Fast Cooling rate Diffusionless phase transformations.

(Quenching)

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Dr.C.ErgunMak 214E

Types of the phases in steels

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Dr.C.ErgunMak 214E Steels: Fe-Fe3C Phase Diagram

Dividing point between cast

irons and steels

Ferrous alloys we will involve– Plain Carbon steels– Alloy and tool steels– Stainless steels– Cast irons

Phases and Solid solutions– δ Delta iron– γ Austenite– α Ferrite– Fe3C cementite– Martensite– Bainite.

The phase reactiaons:• Peritectic: L 0,53C% + δ 0,009C% γ 0,17C%

• Eutectic: L 0,53C% γ 0,009C% + Fe3C 6,67C%

• Eutectoid: γ 0,77C% α 0,0218C% + Fe3C 6,67C%

Peritectic reac. Eutectic reac.

Eutectoid reac.

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Dr.C.ErgunMak 214E Properties of Phases in Steel

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Dr.C.ErgunMak 214E

γ

γ+Fe3Cα+γ

α+Fe3C

A1

A3Acm

A1, A2, A3 ve Acm temperatures

A2: Manyetikliğin kaybolduğu Curie sıcaklıdır: 769oC.

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Dr.C.ErgunMak 214E

γ

α+γ

αα+Fe3CPe

rlite

I II III

1234

5

1

2

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5

1

2

3

I II IIIγ

Perlite⇑Eutectoid

Composition

α

γ

Perlite

Cementite

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Dr.C.ErgunMak 214E

TTT (Time temperature transformation)

Diagrams

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The second noiseshows that the finishes.

The first noiseshows that the transformation starts.

TTT diagrams

t (logaritmik skala)

T

Tm

Kaba perlit

İnce Perlit

Üst Beynit

Alt BeynitDen

gesi

z os

teni

t

Ostenit

Reaksiyon Başlamamış Sürüyor Tamamlanmış

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Dr.C.ErgunMak 214E TTT diagrams

Fs: Ferrite start temp.Ps: Pearlite start temp.Pf: Pearlite finish temp.Bs: Bainite start temp.Bf: Bainite finish temp.Ms: Martensite start temp.Mf: Martensite finish temp.

Coarse PearliteFine PearliteUpper BainiteLower BainitePh

ase

area

s

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Dr.C.ErgunMak 214E

Cooling curves on TTTDiagrams

(a) Continues cooling(b) Isothermal cooling

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Dr.C.ErgunMak 214E Isothermal Heat Treatment:

Isothermal AnnealingTTT Diagrams

Isothermal annealing for fully pearlitic structure.Ferrite + Perlite for hypoeutectoid steels

orPerlite + Cementite for hypereutectoid steels

Transformation along isothermal curve

Transformation along Continuous cooling curve

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Dr.C.ErgunMak 214E


T

Kaba perlit

Ostenit


T

Kaba perlit

Ostenit

Soru: Yapılar nedir

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Dr.C.ErgunMak 214E


T

Soru: Yapılar nedir

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Dr.C.ErgunMak 214E

Phase transformation

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Dr.C.ErgunMak 214E

Özet

Mechanical Prop vs. Microstructure

– Ferrite– Coarse Pearlite– Fine Pearlite– Upper Bainite– Lower Bainite– Martensite

Hardness

Austenite Peartlite (α+Fe3C)Yavaş

Soğuma

Yayınmalı

Austenite Bainite (α+Fe3C)İzotermalDönüşüm

Yayınmalı

Austenite Martensite (single)Çok hızlıSoğuma

Yayınmasız

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Dr.C.ErgunMak 214E

Kaba perlitİnce perlitPerlit +Martenzit

Martenzit

Zaman (s)

Sıca

klık

(o C)

Kritik soğuma hızı

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Dr.C.ErgunMak 214E Heat Treatments of Steel

• A Simple Heat Treatments– Full Annealing– Normalizing– Spheroidizing– Process Annealing– Stress Releif Annealing– Homogenizing

• Isothermal Heat treatments– Austempering– Isothermal Annealing

• Diffusionless Transformation Treatments– Quenching– Tempering– Martempering– Ausforming

• Surface Hardenning Treatments– Carburizing– Nitriding– Carbonitriding– Induction or Flame Hardening

• Age Hardening Treatments– Precipitation Hardening Treatment

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Dr.C.ErgunMak 214E

Simple Heat treatments

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Aim: Softest structure (Coarse grains): High ducitlity.• Hypoeutectoid steel: Coarse (grained) pearlite and ferrite• Hypereutectoid steel: Coarse pearlite and sementite• First, austenitize the steel,

• A3 + (30 – 50oC) for hypoeutectoid• A1 + (20 – 40oC) for hypereutectoid steels.

• Then, slow (furnace) cooling to room temperature.

Full Annealing

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Dr.C.ErgunMak 214E

Aim: homogeneous and fine distribution of pearlite.•Higher strength and slightly lower ductility by refining grains and reducing segregations.

•First austenitize the steel• A3 + (50-80oC) for hypoeutectoid • Acm + (50-80oC) for hypereutectoid steels

•Air cooling to produce a fine pearlitic structure.•For hypoeutectoid steel; dissolve all the carbides and to response readily to the following treatment (spheroidizing, etc.) or final hardening treatment.

Normalizing

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Dr.C.ErgunMak 214E

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Aim: Improving Machinability:Coarse spheroidal cementite particles in ferrite, by decomposition of lamellar cementite into spheres.Suitable for medium and high C (>0.4%) steels for good machining characteristics.Heat up to just below A1 temperature (above 690oC) for 15-25 hours, cool in air.

Spherodizing Treatment

For Hypereutectoid steels, spheroidizing of large carbides for tougher, softer properties.

Not common for Hypoeutectoid steels for cementites spheroidization but good for spheroidizing of oxides, sulfides.

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Dr.C.ErgunMak 214E

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Eliminating the effect of Cold Work:• Also called recovery but recrystallization and grain growth possible.• Arrangement of dislocations and formation of new grains and consequently

soft structure.• A low-temperature recrystallization heat treatment • Just for hypoetectoid steels. (C < 0.3%). • Heating between 550-650oC for necessary time • Cool in furnace to soften strain hardened- structure high dislocation density.• No further heating to prevent grain growth.

Process Annealing

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Dr.C.ErgunMak 214E

Dayanım

Süneklik

Sertlik.

Tane büyüklüğü

Kalıntı gerilmeler

Elektrik iletkenliği

Recryst

alliza

tion

Recove

ry

Grain Growth

Process Annealing

0.3 0.4 0.6 Th

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Dr.C.ErgunMak 214E Stress relief

Residual stresses are due to thermal and mechanical processes such as casting, inhomogeneous plastic deformation, heat treatment, welding, etc.,

Aim is to reduce internal residual stressesresulted from processes,

Heated up to 500-550oC for necessary time, Cool slowly in furnace,Recovery mechanism (Arrangements of the dislocations)Not major changes on the mechanical properties.

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Dr.C.ErgunMak 214E

Eliminate the micro-segregationin the cast structure (soaking process of pig casts).Eliminateing macro-segregations dissolving second phases- oxides, carbides, nitrides, sulfides, etc.Heat up to high temperatures (1100-1200oC) held 50 hrs,Then cool in air.Intermediate heat treatment: Get a suitable microstructure for the subsequent heat treatments.

Homogenizing

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Dr.C.ErgunMak 214E Segregation

First solidified solid and the last solidified solids have not the same composition as the last solidified solid.

Called as “micro-segregation”1. To pass slowly the

solidification range or

2. Reduced with homogenizing treatment

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Dr.C.ErgunMak 214E

All simple Heat treatments on the same diagram

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Dr.C.ErgunMak 214E

Yumuşatma Tavı

Normalizasyon

Su Verme

Kaba perlit

İnce perlitPerlit +

MartenzitMartenzit

Ms

Mf

γ

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Dr.C.ErgunMak 214E

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Figure 12.5 The effect of carbon and heat treatment on the properties of plain-carbon steels.

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Dr.C.ErgunMak 214E

Isothermal Heat treatments

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Dr.C.ErgunMak 214E Austempering


Tyüzey

merkez

First austenize.•Quench above Ms•Wait to transform γ to bainite•The final Microstructure:

Full BainiteUpper or Lower Bainitedepending on the transformation temperature

Bainite can only be obtained by isothermal trasnformation!!!

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Dr.C.ErgunMak 214E

Diffusionless Heat treatments

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Dr.C.ErgunMak 214E

•Aim is to obtain fully martensitic structure (very hard but brittle).•Firs , fully austenizing:

•A1 + 30-50oC for hypoeutectoid steels•A3 + 30-50oC for hypereutectoid steels enough time,

•Then cool rapidly (quenching) at high cooling rates higher than critical cooling rate to a temperature below Mf (refer to CCT curve for the steel).

Quenching

γ γ+Fe3Cα+γ

α+Fe3C

A1

A3

Acm

“Critical Cooling rate”.

Quenching –very quick cooling no time for diffusion; a diffusionless transformation forming martensite.

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Dr.C.ErgunMak 214E

The cooling rate just touches the noise is called “Critical Cooling rate”.

For martensitic transformation (diffusionless transformation), the cooling rate should be higher than critical cooling rate so that it does not cut the noise and can not start the diffusional mechanisms.

Otherwise the diffusional mechanism works and γ austenite may transform other phases depending on the steel composition and the location where the noise is crossed (refer to the next slides for the possible phases that austenite may transform.

TTT Curves

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Dr.C.ErgunMak 214EContinuous Cooling curves (CCC) vs. Isothermal Cooling curves

TTT Diagrams

Transformation along isothermal curve

Transformation along Continuous cooling curve

Bainite can only be obtained by isothermal trasnformation!!!

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Dr.C.ErgunMak 214E

A. Slow cooling in furnace (annealing)-Lamellar Coarse pearlite

B. Cooling in still air (normalizing)–fine pearlite

C. Split transformation (oil quenching)-fine pearlite and martensite

D. Rapid cooling (water quenching)-martensite

E. Critical cooling rate-Slowest rate to produce no pearlite

CCT: diagram ITT diagram

CCT and IT curves

Tem

pera

ture

Eutectoid Temperature

Examine the resultant phase in 3 different isothermal cooling conditions

and Martensitic transformation Temperatures.

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Dr.C.ErgunMak 214E

What is the difference in the materials properties between the one produced with continues cooling and the one produced by isothermal cooling?

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Dr.C.ErgunMak 214E


T

Kaba perlitİnce Perlit

Üst Beynit

Alt BeynitDen

gesi

z os

teni

t

Ostenit

MartenzitMsMf

Ötektoit Çelikγ

α+γ γ+Fe3C

α+Fe3C

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Dr.C.ErgunMak 214ETTT diagrams: Isothermal heat treatment curves.

Hypoeutectoid steels has a wing for ferrite start temperature whereas hypereutectoid steels, a wing for cementite start temperatures.

Hypoeutoctoid Steel γ αWing for ferrite start

temperatures.

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Dr.C.ErgunMak 214E

Hypereutoctoid Steel

γ + Fe3C

γ Fe3CWing for cementite start temperatures.

TTT diagrams: Isothermal heat treatment curves.

Hypereutectoid steels, a wing for cementite start temperatures.

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Dr.C.ErgunMak 214E

Interrupting isothermal heat treatment

To have different phases in the steel.For example, • Austenize the steel• quench to 650oC, and wait 10s to

transform some γ to α and pearlite, • then quench to 350oC and wait for a

while 100s to transform a part of the remained γ to bainite,

• consequently quench below to Mf to convert the last remained γ to martensite.

Final microstructure: Ferrite, pearlite, bainite and martensite.

Inter. HT

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Dr.C.ErgunMak 214E Tempered Martensite

To obtain tougher and more ducitle structure.Martensite transforms to very fine ferritic - perlitic structure.

• Reheating the martensitic steel below eutectoid temperature.

• Temperature level is important for the final hardness.


T yüzeymerkez

Tempering Temperature

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Dr.C.ErgunMak 214E

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Fig 12-11 The effect of tempering temperature on the mechanical properties of a 1050 steel.

Page345

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Dr.C.ErgunMak 214E Martempering (Marquenching)

•Martempering reduces the risk of residual stresses and their results.

•Quench the steel from austenite region to above Ms•Wait to equalize the temperatures of surface and center, then quench to room temperature produce martensite.

During quenching; •Surface cools faster and transforms firstto martensite.•Center transforms later.•If residual stresses are greater than yield strength, quench cracks may occur.

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Dr.C.ErgunMak 214E


Tyüzey

merkez

Austempering

First austenize.• Quench above Ms• Wait to transform γ to

bainite• The final Microstructure:

Full BainiteMs

Mf

Bs BfBainite

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Dr.C.ErgunMak 214E

As C content increases in the steel, •The martensite start temperature, Ms•The finish temperatures, Mf decrease.

So, amount of retained austenite (not demanded), the residual stresses due to the increase in the temperature difference betwen austenite and Ms increase, thus the quench cracking risk increases.

Effect of C on Ms and Mf

Effect of Alloying Elements

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Dr.C.ErgunMak 214E Ausforming

• First, quench the steel austenite region to Bay area,

• Then apply forming processesavoiding to enter pearlite and/or bainite region,

Then; • If quench to below Mf:

martensite forms. • If cooled slowly: bainite forms

The bay area obtained by alloying

A thermomechanical heat treatment in which austenite is plastically deformedbelow the A1 temperature, then permitted to transform to bainite or martensite.

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Dr.C.ErgunMak 214E

1. Increase the hardenability: Alloying elements increase the hardenability of steel. Martensite can form through the large thickness of the parts even very slow cooling rates.

2. Change the shape of Fe-Fe3C phase diagram: (Mn and Ni, austenite stabilizer agent (γ at room T), Cr; ferrite stabilizer)

3. Introduce a bay area in the TTT Diagram; (Ausforming (austenite + forming) becomes possible);

4. Improve the respone toTempering treatment: Alloying elements reduce the rate of tempering compared with that of a plain-carbon steel. Secondary hardening becomes possible.

5. Other: solid solution strengthening, alloy carbides, corrosion resistance, etc. can be obtained.

Effect of Alloying ElementsImportant

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Dr.C.ErgunMak 214E Effect of Alloying Elements

Hardenability

Certain alloying elements, increase the hardenability.In the plain carbon steels, 1050, the surface is hard, but not in deep. The alloyed steel, 4340 hardened deeper. So the hardenability of 4340 is much better. Even slow cooling ratesmay produce the martensite in allcross-section. But hardness is not high since lower C content.

Hardenability

•Certain alloying elements in the steel moves the noise of the TTT curve to the right direction. •The practical significance; Very low cooling rates, (cooling in air), can produce martensite. •Whole volume of the fabricated massy body can be transformed to martensite even cooling in air.

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Dr.C.ErgunMak 214E Effect of Alloying elements

A bay area may appear.Special processes possible such as “ausforming”.

Alloying elements can also reduce the effect of tempering compared to the plain carbon steels. The alloy steel can be used at high temperatures.

Secondary hardening: Carbide precipitation

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Dr.C.ErgunMak 214E Hardenability Curves and

Jominy Tests• Jominy test - The test used to evaluate

hardenability. An austenitized steel bar is quenched at one end only, thus producing a range of cooling rates along the bar.

• Hardenability curves - Graphs showing the effect of the cooling rate on the hardness of as-quenched steel.

• Jominy distance - The distance from the quenched end of a Jominy bar. The Jominy distance is related to the cooling rate.

Jomminy distance for various steels can be seen in the figure. Plain carbon steels have shallow jomminy distance while alloyed steels may have very deep. However, C provides higher surface hardness compared to the other alloying elements.

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Dr.C.ErgunMak 214EThe cooling rates provided by various quenchants

(quenching media)

The cooling rate provided by the quenchants are represented by a constant value “H”.

the relation between the diameter of the work piece and jomminy distance in the Figure for a given “H” values.

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Dr.C.ErgunMak 214E

A machine part of 1050 steel was quenched in a medium (H=0.2) and hardness at a certain location is 28 HRC. Predict the hardness change at the same point if the oil is agitated during quenching.

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Dr.C.ErgunMak 214E

1610

From Figure 12-23, Page 353


HRCinch 39)(164

⇒

16416

4

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Dr.C.ErgunMak 214E

An AISI 9310 steel bar with a diameter of 40mm have a hardness of 42HRC at the center after quenching. What is the minimum severity of quenching medium in terms of “H coefficient”. Which quenchantwould you recommend to produce the aimed hardness in the steel with the minimum risk of quench cracks?

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Dr.C.ErgunMak 214E


165.6

40 mm = 1.6 inch

165.6


H value should be between 0.5 and 1. But the correct H to providesufficient cooling rate is “1”. The quenchant should be still water (Table12-2, page 348).

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Dr.C.ErgunMak 214E

The fallowing heat treatments were applied to a shaft of 25mm diameter and made of 1050 steel.

a) Heat at 820oC, quench to 25oC in water, temper for one hour at 400oC. Cool to room temperature in air.

b) Heat at 820oC, quench to 400oC in a salt bath, hold for two min. Cool to room temperature in air.

Describe the resultant microstructure and estimate the hardnesses at the end of each treatment. Make comments about the mechanical behaviour of shafts at the end of each treatment.

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Figure 12-8 (a) page 342

a) Tempering of Martensite: Micorstructure:Tempered Martensiteb) Austempering: (Isothermal heat treatment) Microstructure: Lower Bainite

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•Strength / Hardness,(Wear resistance)

• Ductility,• Machinability,• Small grain size,• Residual stresses

stresses,• Homogenous

structure. (Quenching ? Marquenching may be better)

(Retained austenite)

Figure 12-5 page 340

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Dr.C.ErgunMak 214E

Strengthening of materials• Strain hardening: due to the increase in dislocation density and

their interaction with each other, obstacles, grain boundaries, etc.• Martensite strengthening:• Solid Solution hardening: Addition of different atoms provide

additional strength to the material caused by the lattice distortion due to the mismatch of the atoms.

• Dispersion strengthening: The strengthening of a metal or an alloy by incorporating chemically stable submicron size particles of a nonmetallic or intermetallic phases that impede dislocationmovement at elevated temperatures (hard particles in matrix).

• Precipitation hardening: hardening in metals caused by the precipitation of a constituent from a supersaturated solid solution.

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Dr.C.ErgunMak 214E Dispersion Hardening

• Soft matrix-hard precipitates/particles• Homogenuous distribution of precipitates/particles• Fine precipitates/particles• Spherical precipitates/particles

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Dr.C.ErgunMak 214EPhase diagrams with respect to solubilitya) Unlimited solubility: One material can completely dissolve in a second

material without creating a second phase.b) Insolubility: One element can not dissolve in another in any amount. c) Limited solubility: One element can dissolve in another only in certain

amount.

a) b) c)

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Dr.C.ErgunMak 214E

Phases and solubility: The three phases of water.• Water and alcohol - unlimited solubility. • Salt and water - limited solubility. • Oil and water - no solubility.

(a) Liquid Cu and Ni: complete solubility. (Solid Cu-Ni alloys: complete solid solubility in random lattice sites).

(a) In Cu-Zn alloys containing more than 30% Zn, a second phase forms -limited solubility of Zn in Cu.

Solubility and Solid Solutions

Precipitation of a new phase: a

Cu- Zn compound

Complete solute solution of Cu and Ni atoms

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Dr.C.ErgunMak 214E

• Hume-Rothery rules - The conditions for unlimited solid solubility. Hume-Rothery’s rules are necessary but are not sufficient for materials to show unlimited solid solubility.

• Hume-Rothery rules: • Size factor • Crystal structure• Valence• Electronegativity

For Unlimited Solid Solubility

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Dr.C.ErgunMak 214E

Effect of atomic radii alloying atoms added to Cu on the strengthening

Solid-Solution Strengthening

Effect of Zn content in Cu on the propertiesof solid solution.

The mechanical properties of Cu-Nialloys. Pay attention to 60% Ni -40% Cu.

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Dr.C.ErgunMak 214E Precipitation (Age) Hardening

• Small second phase precipitates behaves as small obstacles to dislocation motion.

• Starting from a structure having coarse grained precipitates, 1. Solution treatment: heating the material to the single

phase ragion.2. Queching the material to room temperature having a

supersaturated solid solution with a metastable single phase microstructure.

3. Aging the material at (reheating to) an intermediate temperature to activate solid state diffusion to form fine grained precititates.

• Overaging- aging the material too long causes coarser precipitates loosing the effectiveness to behave as an dislocation barier

Important

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Dr.C.ErgunMak 214E

Çökelme sertleşmesi• İç yapıda, dislokasyon hareketlerini engelleyerek

dayanımın artmasına sebep olan çok küçük ikinci fazların çökeltilmesi işlemidir.

Yaşlandırma sertleşmesi:• Önce Çözündürme işlemi (solution treatment) yapılarak çökelen sert

olan 2. faz, tek faz içerisinde tamamen çözülür. • Daha sonra yapı, hızlı soğutma (su vererek-suda soğutmak) ile ikinci

fazın çökelmesi engellenir ve aşırı doymuş katı çözelti elde edilir.• Daha sonra yaşlandırma işleminde; aşırı doymuş katı çözelti,

çözündürme sıcaklığından daha düşük olana yaşlandırma sıcaklığınatekrar ısıtılarak çok küçük bağdaşık (koherent) ikinci faz tanecikleri çökeltilir. (Bu çökeltiler dislokasyonlara engel teşkil ederek malzemenin dayanımını arttırır).

• Aşırı yaşlanma: çökelmelerin çok büyüyerek bağdaşıklığın (koherentliğin ) kaybolmasi

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Dr.C.ErgunMak 214E

β

α+β

%100 β(single phase)

Equilibrium microstructure:Coarse α Grains in β matrix

Slow cooling

Time

T

Composition

If slowly cooled-(not hardening)

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Dr.C.ErgunMak 214E

α-Grains in β matrix

Solution treatment

Quenching

taging

Sam

e m

icro

stru

ctur

eForming the coherent small precipitation

Sıca

klık

β

α+β

CompositionTime

T

Precipitation (Age) hardeningImportant

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Dr.C.ErgunMak 214E• In the first stage, very small coherent precipitates called -GP zones

(Guinier preston zones) forms, • The empty spaces below the dislocation are good location for nucleating

of these GP zones (decreasing the energy of the system), thus prevents the dislocation motions.

• Then, these zones form larger coherent precipitates. These precipitates stretches the lattice and cause to strengthening the material.

αβ

GP Zone

Coherent grainformation

Over Aging

Lossing of Coherency

Har

dnes

s

Temperature

Coarsening the precipitates and loosing their ability to strenghening the material.

Coherent Precipitation

Important

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Dr.C.ErgunMak 214E

Overaging

β α

• Overaging: As the precipitates coarsen, the misfit stresses become too large to sustain.

• Then the coherency would be lost the the precipitates becomes uncoherent.

• Thus the effectiveness of the hardening decreases.

• If the material aged long enough, the starting coarse microstructure will be formed.

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taging

Taging(hour)

Tem

pera

ture

Har

dnes

s

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Dr.C.ErgunMak 214E

©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.

Design an age hardening treatment giving the temperature for each step for the alloy having 2 wt.% Cu.

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Dr.C.ErgunMak 214E

©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.

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Dr.C.ErgunMak 214E

Quizz:

What is the streghthening mechanism of age hardening? Explain briefly the steps for a typical age hardening treatment.

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Dr.C.ErgunMak 214E

( ) Austempering is an isothermal heat treatment which transforms austenite to pearlite( ) Process annealing is used to soften steels after quenching( ) Cooling rate in oil quenching is always higher than in water quenching…….. steels cointain ferrite and martensite in their room temperature microstructure.The first manufacturing step to obtain pearlitic melable cast iron from whit cast iron is ……….Dimond brale indenter and 150kgf major load are used to conduct ......... TestHardness of hard metals can be measure by using ............... Tests.Hardness of ceramics can be measure by using ............... Tests.Aşırı yaşlanmış Al alaşımlarında dayanımın düşmesinin sebepleri; çökelti matris

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Dr.C.ErgunMak 214E

Bolt class 6.8 should satisfy the ultimate tensile strength of ….MPa and yield strength of ……..MPa.

a) 800/600 b) 480/600 c) 600/480 d) none of them

……….can be seen in macroscopic examinations of metals which resulted from …….a) flow lines/plastic deformation b) welded section / low hardenabilityc) dislocations/casting process d) none of them

Spherodizing of high C steels is done at temperatureres between .... And ....(a) 690oC-A3 (b) Acm-800oC(c) 690oC-A1 (d) none of them

..........occurs at the temperature higher than 60% of melting point in .....(a)Grain growth/process annealing (b)Full annealing age hardening(c)Overtempering/stress relief (d)none of them

Upeer bainite is ..........(a)Harder than martensite (b)harder than coarse pearlite(c)Softer than ferrite (d) none of them

Fromation of .................. İs the sequence of age hardening(a) Supersaturated solid solution / GP zones / non-coherent precipitates/ coherent precipitates( b) Supersaturated solid solution / GP zones / coherent precipitates / non-coherent precipitates(c) GP zones / coherent precipitates / non-coherent precipitates/ Supersaturated solid solution(d) None of them

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Dr.C.ErgunMak 214E

Jomminy tests are used to evaluate ..... Of steelsa) Ductile/brittle transition b) microstructurec) hardness d) none of them

The risk of quench cracking can be resuced by using.......treatmenta) Tempering b) annealingc) Martempering d) austempering

Secondary hardening can be seen in ......steels(a) High alloy (b) Acm-800oC(c) carburizing (d) high carbon

Galvanized steels is produced by coating......... On the surfaces of sheets(a)Pb (b)Sn(c)Zn (d)none of them

Deep drawing quality steels must exhibit high......(a)Hardenability (b)strength(c)ductility (d)density

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