Heat Treatment 2

When an annealed part is removed from the furnace and allowed to cool in air, it is called a "normalizing" heat treatment

Main Objectives

To refine grain structure.
To remove strains
To remove internal stress
To remove dislocations
To improve mechanical properties( strength, hardness and toughness)
To improve machinability of low carbon steels.
        

Martensite formed in the hardening process is converted to TEMPERED MARTENSITE. To improve ductility and toughness

Objective

To improve ductility
To improve toughness
To reduce hardness
To remove internal stress (rapid cooling)
To impart wear resistance.        

Heated to 250? - 650?C and cooled slowly to room temp. This is also done to relieve internal stress
Martensite(BCT) Tempered Martensite
BCT supersaturated carbon
TM stable ferrite and cementite
Hardness decreases with increasing in tempering time..