2. Incubation Temp.( 0 C) Time at which Transformation Starts/Begins Ends 700S1E1 650S2E2 600S3E3 550S4E4 500S5E5 450S6E6 400S7E7 350S8E8 -----SE SnEn -----SrEr

3. STABLE AUSTENITE Bianite in feather shaped patches Degree of under cooling high Sluggish transformation Au. to Coarse Pearlite Greater time for diffusion Slow rate of diffusion of C atoms retards increased tendency of Au. transformation, 550 550-220 Near A 1

4. Temperature Time (on logarithmic Scale) 400 0 C -600 0 C range 1 sec 1000 sec

5. Stable Austenite Unstable Austenite Transformation starts/begins Transformation ends Coarse Pearlite Fine Pearlite Unstable Austenite Feathery Bainite Acicular Bainite MsMs MfMf Austenite + Martensite Martensite Time-Temperature Transformation Curves

10. STABLE AUSTENITE Bianite in feather shaped patches Degree of under cooling high Sluggish transformation Austenite to Coarse Pearlite Greater time for diffusion Slow rate of diffusion of Carbon atoms retards increased tendency of Austenite transformation, 550 550-220 Near A 1

11. Transformation V/s logarithm of Time plot Isothermal Transformation diagram plot

12. Stable Austenite Unstable Austenite Transformation starts/begins Transformation ends Coarse Pearlite Fine Pearlite Unstable Austenite Feathery Bainite Acicular Bainite M s ≈ 250 0 C M f ≈ -50 0 C Austenite + Martensite Martensite Time-Temperature Transformation Curves 400 0 C -600 0 C range M 90% at 110 0 C

13. Ferrite nucleates first, over which layer of Cementite (Iron Carbide)- Growth is quick.

14. Complete Isothermal Transformation diagram for EUTECTOID composition A- Austenite B- Bainte M- Martensite P- Pearlite

15. Isothermal Transformation Diagram for alloy steel (with 0.40%C, Ni, Cr & Mo small %) A- Austenite B- Bainite P- Peralite M- Martensite F- proeutectoid ferrite

16. Complete Isothermal Transformation diagram for EUTECTOID composition With Continuous Cooling Transformation diagram- CCT superimposed

17. A- fine Pearlite B- M + little Au C D Transformation starts/begins Transformation ends A - 5 0 C/sec(normalising) B - Rapid 400 0 C/sec (water quench) C - 140 0 C/sec- Martensitic D - 50 0 C/sec- P + M + Au EFFECT OF DIFFERENT COOLING RATES Continuous Cooling Transformation diagram Continuous cooling Transformation

18. Moderately rapid [1] and slow cooling [2] curves superimposed on continuous cooling transformation diagram for EUTECTOID [1] Normalising [2] Full Annealing

19. CCT Dependence of final microstructure on transformations occurring during cooling Martensite for quenching rates greater than the critical

20. 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

21. LARGE STEEL PART WHEN COOLED CORE SURFACE MARTENSITE COOLING CURVES BAINITE CORE WITH FINE PEARLITE, SURFACE MARTENSITIC- CALLED MASS EFFECT OF HEAT TREATMENT

22. QUENCH CRACKS MAY FORM, EVEN IF COOLING RATE INCREASED

23. MARTEMPERING Transformation Complete Air Cool E Quenched in bath of temperature E, kept for long, removed and cooled – martensite forms Also called MARQUENCHING

24. AUSTEMPERING Transformation Complete at G Air Cool G FINE BAINITE FORMS, AIR COOLED STRUCTURE AS OF TEMPERED MARTENSITE GOOD FOR INTRICATE SHAPES. BY REPLACING QUENCHING AND TEMPERING, CRACKS AVOIDED

27. Classification scheme for various ferrous alloys