Post on 15-Nov-2014
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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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Dr.C.ErgunMak 214E
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 (logaritmik skala)
T
Kaba perlit
Ostenit
t (logaritmik skala)
T
Kaba perlit
Ostenit
Soru: Yapılar nedir
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Dr.C.ErgunMak 214E
t (logaritmik skala)
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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Dr.C.ErgunMak 214E
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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Dr.C.ErgunMak 214E
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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Dr.C.ErgunMak 214E
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
t (logaritmik skala)
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 (logaritmik skala)
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 (logaritmik skala)
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
t (logaritmik skala)
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
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
From Figure 12-23, Page 353
165.6
40 mm = 1.6 inch
165.6
From Figure 12-24, Page 355
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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Dr.C.ErgunMak 214E
Figure 12-8 (a) page 342
a) Tempering of Martensite: Micorstructure:Tempered Martensiteb) Austempering: (Isothermal heat treatment) Microstructure: Lower Bainite
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Dr.C.ErgunMak 214E
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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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Dr.C.ErgunMak 214E
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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Quizz:
What is the streghthening mechanism of age hardening? Explain briefly the steps for a typical age hardening treatment.
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( ) 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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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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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