Defects formed in steels during heat treatment are listed below.
Decarburization:
Heating of metals for long periods at high temperature in oxidizing atmosphere causes the loss of carbon from the surface. Heating in protective atmosphere can decrease this effect.
Oxidization:
Oxidation will result in a thick layer of scale formed on the surface of the article. This also be avoided by using inert atmosphere.
Quenching cracks:
Quenching cracks occurs when cooling rate is more than critical rate. It is avoided by tempering immediately and avoiding sharp corners.
Warping:
Warping is produced by non-uniform heating.
Overheating:
Heating long period at high temperature produces coarse grain microstructure, resulting in the loss of duality and impact strength. It can be prevented by annealing and normalizing.
Soft spots:
Soft spots appear due to localized decarburization, bubble formation and in-homogeneity of initial structure. It can be avoided by effective quenching.
Excessive or insufficient hardens after tempering:
It is due to insufficient or excessive holding time while tempering produces this defect. A proper tempering temp and holding time or subsequent annealing can prevent this defect.
