This document discusses various heat treatment processes including hardening, annealing, normalizing, and tempering. It explains that heat treatment involves heating and cooling metals to change their grain structure and improve mechanical properties. Specific processes like hardening form martensite to increase strength and hardness, while annealing involves furnace cooling to increase ductility and machinability at the cost of strength. Tempering is used after hardening to relieve stresses and increase toughness. The document compares the effects of different processes on properties and discusses surface hardening techniques and time-temperature-transformation diagrams.

1. HEAT TREATMENT

2. CONTENTS
What and Why
Process
Hardening
Annealing
Normalizing
Tempering
Comparisons
Surface Hardening
Carborizing, Nitriding & Cyaniding
TTT
100% Martensite and Bainite
What if it’s a Non Ferrous alloy?

3. WHAT AND WHY
• Secondary treatment process - To improve mechanical properties
• Only by heating and cooling, to change grain structure

4. PROCESS

5. HARDENING
• Applied to :- All types of steels
• To increase strength & Hardness
• 50ºC above UCT ( HypoEutectoid)
and 50ºC above LCT(Hyper)
• Rapid Cooling to form Martensite.

6. DISADVANTAGES:-
• Large residual stresses
• Not directly used for application purposes.

7. ANNEALING
1) Full Annealing:-
• Same temperature limits
• Applicable to LCS,MCS, HCS.
• Furnace cooling is done
Advantages :-
High Ductility, Machinability, low residual stresses
Disadvantages:-
Low strength and hardness

8. ANNEALING
2) Process Annealing:-
• Applicable to LCS & MCS
• 50ºC below LCT
• Furnace cooling is done
Advantages :-
Machinability, low residual stresses
Disadvantages:-
Low hardness

9. ANNEALING
3) Spherodize Annealing:-
• Applicable to HCS
• Just below LCT
• Furnace cooling is done
• Spherical form of cementite grains are formed
Advantages :-
Machinability, low residual stresses
Disadvantages:-
Low hardness

10. ANNEALING
4) Diffusion Annealing:-
• Applicable to HCS
• Furnace cooling is done
Advantages :-
To get uniform chemical composition
Disadvantages:-
Low hardness

11. NORMALIZING
• Applicable to all types of steels
• Air cooling is done
• 50ºC above UCT for both Hypo and Hyper
• Pearlite(Thin lamellar Cementite) is formed
Advantages :-
Finer grains than Annealing
Disadvantages:-
Low hardness

12. TEMPERING
• MCS & HCS
• Done after hardening
• To increase toughness and relieve
residual stresses
Low Temp Tempering:-
Heated upto 250ºC [Trusite ]
High Temp Tempering:-
Heated upto 650ºC [Sorbite]

13. COMPARISONS
Grain Size:- H<T<S<N<PA<FA
Strength/Hardness:- H>T>S>N>PA>FA
Residual Stresses:- H>T>S>N>PA>FA
Ductility:- H<T<S<N<PA<FA
• H=Hardening
• T=Trusite
• S=Sorbite
• N=Normalizing
• PA=Process Annealing
• FA=Full Annealing

14. SURFACE HARDENING
•

15. CARBORIZING, NITRIDING, CYANIDING
• •

16. TIME-TEMPERATURE-TRANSFORMATION
• Isothermal Diagram
• Martensite- Rapid cooling of Austenite
Fine grained, with large residual stresses
• Pearlite-Air cooling of Austenite
Coarse grained(high grains), High ductility,
low strength
• Bainite- Fast + Isothermal cooling
High strength, Ductility, low residual
stresses

17. 100% MARTENSITE AND BAINITE
• AUSTEMPERING- 100% of Austenite
Process:-Quenching Austenite in water
upto 300ºC and then air cooling.
• MARTEMPERING-100% of Bainite
Process:- Quenching upto 600ºC, then air
cooling upto 500ºC, then isothermal
cooling.

18. WHAT IF IT IS A NON-FERROUS ALLOY?
•

19. THANKYOU