Introduction:

Heat treatment can be defined as an operation or combination of operations, involving heating and cooling of metal or alloy, in solid state, to obtain desired properties. The reson for heat treatment are to obtain higher strength & hardness, toughness, to homogenise the meterial, remove segregation, refine the grainsize, remove cold work effects, soften the meterial, improve machinability, relieve internal stresses, improve wear & corrosion resistance.

Purpose:

• To avoid haz / weld metal cold cracking (by preventing the formation susceptible micro  structure and allowing the diffusion of hydrogen away from the joint)

• To minimize residual stress

• To provide sufficient ductility in the weld metal and haz

Post Weld Heat Treatment:

Heat treatment of the welded joint, normally to sub-critical       temperatures, after completion of welding operations

Pre Heat Treatment:

Heating of the base metal, at the area to be welded is performed prior to commencement of welding

• To relieve internal / residual stress

• To remove hydrogen

• To improve the metallurgical properties of weld joint by tempering of haz

• To obtain dimensional stability