Annealing

Annealing:  

 

Annealing is heating the steel to austenite phase and holding at the temperature for a particular time and then cooling very slowly to room temperature. Cooling is generally in the furnace itself by switching off the power supply. The holding time and temperature depends on various factors like chemical composition of steel, size and shape of the material and the desired final properties.

Purpose of annealing is

1)    To reduce hardness,

2)    To relieve internal stresses,

3)    To improve machinability,

4)    To facilitate further cold working by restoring ductility,

5)    To produce necessary microstructure having the desired mechanical, physical or other properties.

Annealing temperature:

Hypo eutectoid steel                                                : 820-870° C

Eutectoid & hyper eutectoid steel                              : 790-840° C.

                                                      Annealing

 Soaking time: One hour for sections up to 25 mm thickness and 30 minutes for every additional 25 mm thickness.

Cooling rate: For plain carbon steel                    :@50° C/hour

                       For alloy steels                               :@30° C/hour.

Types of annealing:

b)    Full annealing

c)    Isothermal annealing

d)    Re crystallization annealing

e)    Process annealing

f)     Box annealing

g)    Bright annealing