4. Purpose of Heat Treatment
• To obtain desired structure and properties
• To increase strength
• To improve toughness
• To increase hardness
• To improve ductility
• To refine grain size
• To homogenize the structure
• To releaf internal stresses developed dring cold
working or heavy annealing
5. Steels can be heat treated because of the structural
changes that can
take place within solid iron-carbon alloys
Heat
Temperi
ng
Hardenin
g
Increases the hardness of steel by 2-3 times
Normali
zing
Increases Strength of steel suitable for many
engineering applications
Anneali
ng
A softening treatment applied to steel (may or may
not be cold worked) to increase ductility at the
expense of hardness and strength
A specialized treatment applied to hardened steel
to recover strength at the cost of lower hardness
Heat Treatment Fundamentals
6. Heat
Soaking temperature is
usually 50 to 100 C above
upper critical temperature
(A3) for hypo-eutectoid steel
and usually 50 to 100 C
above lower critical
temperature (A3,1) for hyper-
eutectoid steel
