STABLE AUSTENITE

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Incubation Temp.( 0C) Time at which Transformation Starts/Begins Ends Time at which Transformation Starts/Begins Ends
700 S1 E1
650 S2 E2
600 S3 E3
550 S4 E4
500 S5 E5
450 S6 E6
400 S7 E7
350 S8 E8
----- S E
----- Sn En
----- Sr Er
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STABLE AUSTENITE
Near A1
Sluggish transformation Au. to Coarse
Pearlite Greater time for diffusion
550
Bianite in feather shaped patches Degree of
under cooling high
550-220
Slow rate of diffusion of C atoms retards
increased tendency of Au. transformation,
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4000C -6000C range
Temperature
1 sec
1000 sec
Time (on logarithmic Scale)
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Transformation ends
Transformation starts/begins
Stable Austenite
Coarse Pearlite
Unstable Austenite
Fine Pearlite
Feathery Bainite
Unstable Austenite
Acicular Bainite
Ms
Austenite Martensite
Mf
Martensite
Time-Temperature Transformation Curves
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STABLE AUSTENITE
Near A1
Sluggish transformation Austenite to Coarse
Pearlite Greater time for diffusion
550
Bianite in feather shaped patches Degree of under
cooling high
550-220
Slow rate of diffusion of Carbon atoms retards
increased tendency of Austenite transformation,
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Transformation V/s logarithm of Time plot
Isothermal Transformation diagram plot
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Transformation ends
Transformation starts/begins
Stable Austenite
Coarse Pearlite
Unstable Austenite
Fine Pearlite
4000C -6000C range
Feathery Bainite
Unstable Austenite
Acicular Bainite
Ms 2500C
Austenite Martensite
M 90 at 1100C
Mf -500C
Martensite
Time-Temperature Transformation Curves
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Ferrite nucleates first, over which layer of
Cementite (Iron Carbide)- Growth is quick.
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Complete Isothermal Transformation diagram for
EUTECTOID composition A- Austenite B-
Bainte M- Martensite P- Pearlite
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Isothermal Transformation Diagram for alloy
steel (with 0.40C, Ni, Cr Mo small ) A-
Austenite B- Bainite P- Peralite M- Martensite F-
proeutectoid ferrite
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Complete Isothermal Transformation diagram for
EUTECTOID composition With Continuous Cooling
Transformation diagram- CCT superimposed
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Transformation starts/begins
Transformation ends
A- fine Pearlite
Continuous cooling Transformation
EFFECT OF DIFFERENT COOLING RATES
A - 50C/sec(normalising) B - Rapid 4000C/sec
(water quench) C - 1400C/sec- Martensitic D -
500C/sec- P M Au
B- M little Au
D
C
Continuous Cooling Transformation diagram
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Moderately rapid 1 and slow cooling 2 curves
superimposed on continuous cooling transformation
diagram for EUTECTOID
2 Full Annealing
1 Normalising
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CCT Dependence of final microstructure on
transformations occurring during
cooling Martensite for quenching rates greater
than the critical
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Quenching Medium

• Media, arranged In order of quenching speed
• 5 Caustic Soda - highest
• 5-20 Brine
• Cold Water
• Warm Water
• Mineral Oil
• Animal Oil
• Vegetable Oil - least

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LARGE STEEL PART WHENCOOLED
COOLING CURVES
CORE WITH FINE PEARLITE, SURFACE MARTENSITIC-
CALLED MASS EFFECT OF HEAT TREATMENT
BAINITE
SURFACE
CORE
MARTENSITE
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QUENCH CRACKS MAY FORM, EVEN IF COOLING RATE
INCREASED
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Quenched in bath of temperature E, kept for long,
removed and cooled martensite forms Also called
MARQUENCHING
E
Air Cool
Transformation Complete
MARTEMPERING
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Transformation Complete at G
FINE BAINITE FORMS, AIR COOLED STRUCTURE AS OF
TEMPERED MARTENSITE GOOD FOR INTRICATE SHAPES. BY
REPLACING QUENCHING AND TEMPERING, CRACKS AVOIDED
G
Air Cool
AUSTEMPERING
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Classification scheme for various ferrous alloys
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