Annealing – Purpose, Process and Effects.
Annealing – Improves softness and ductility in steel and other cold worked metals.
Purpose :
1. To induce softness in steel.
2. To remove strain hardening and increase ductility of cold worked metals.
3. To refine crystal structure.
4. To remove gases from casting.
5. To alter electrical and magnetic properties.
Process:
1. Heating the steel slowly 30 to 50 deg. Celsius above Upper Critical Temp. for hypo eutectoid steel and about 50 deg. Cel lower than lower critical temp. for hyper eutectoid.
2. Holding the job at that temp. for about 2.5 min./mm of the section thickness of the larger section being treated.
3. Cooling slowly at room temp. below critical range. The part are ordinarily allowed to cool slowly with the furnace or are removed from the furnace and cooled in a medium that ensures a slow rate of cooling. Ex – Inserting in a heap of ashes.
Effects:
Heating removes internal stresses, restore ductility and removes gases. During slow cooling austenite changes back to softer constituents like ferrite, pearlite etc. The grain structures get refined.
Also Read: Heat Treatment
