Heat Treatment of Steels
1.Definition
Heating and cooling a solid metal or alloy in such a way as to obtain desired conditions or properties
2.Heat Treatment Methods
-Spheroidization Anneal
-Stress Relief
-Full Annealing
-Normalizing
-Homogenization
-Stabilizing
a.Spheroidization Anneal
-Heating and cooling to produce a spheroidal or globular form of carbide in steel.
-Heating is done below the eutectoid temperature for a prolonged time
b.Stress Relief
-Heating below the eutectoid temperature to relieve stresses due to cold working and/or quenching so as to minimize the possibility of cracking
-Slow cooling is done to minimize the development of new residual stresses.
c.Full Annealing
-Annealing by heating to a temperature 15-40oC above the transformation temp and then cooling slowly in the furnace
-Microstructural product is coarse pearlite (relatively soft and ductile)
d.Normalizing
-Accomplished by heating at 55-85oC above the upper critical temperature and then cooling in air.
-Used to refine the grains and produce a more uniform and desirable size distribution
e.Homogenization
-Heating of the material that involves transformation until only one phase is present in the microstructure (reduce segregation)
-Temperature: as high as possible short of melting or producing excessive grain growth
-Usually for cast metals and alloys
f.Stabilizing
-Any treatment intended to stabilize the structure of an alloy or the dimensions of a part