Defects formed in steels during heat treatment are listed below.
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.
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 occurs when cooling rate is more than critical rate. It is avoided by tempering immediately and avoiding sharp corners.
Warping is produced by non-uniform heating.
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 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.