Defects in Heat Treatment of Steels

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.

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