What are the objectives of heat treatment of metals?

Objectives of heat treatment-

Cause relief of internal stresses developed during cold working, welding, forging, casting etc. Harden and strengthen metals. Change grain size. Improve machinability. Soften metals for further working as in wire drawing or cold rolling. Improve toughness and ductility.

Increase, wear, heat and corrosion resistance of materials. Improve magnetic and electrical properties. Homogenise structure to remove coring or segregation. Spheroidize tiny particles, like those of Fe₂C in steel, by diffusion.

Some of the precautions to be carried out when heating are - Metal/alloy has to be heated to a definite temperature. Holding at that sufficient temperature to allow change to occur. Tempering relieves residual stresses, improves ductility. Improve toughness, and reduces hardness increase % elongation.