During the welding process change of chemical and physical properties takes place due to uneven heating and cooling for improving regaining their properties heat treatment processes is one of the best methods. In the similar or dissimilar welded joints, at the welded portion it can be exist in more than one crystalline form and the carbon atom is only 1/30^th size of the iron atom.In this weldment phase changes occurs in solid state due to heating or cooling (allotropic transformation).At welded portion liquid metals cools and solidification temperature approaches initial crystals are formed. These are grown in to large solid grains and each grain acts as different crystallization with the atom. A random grain growth again takes place within the melt boundary, results in a low strength. Within HAZ the grain become coarse only possible to PWHT processes.The weldments are underlying their properties so to achieve the better results that are possible through heat treatment processes.