Preamble

Heat treatment is another finishing operation which is done on the finished or semi-finished product to create desired properties by altering number, size and distribution of phases through heating and cooling. Steels are heated to a single phase region to form austenite and then cooled to form a particular structure. By changing the rate of cooling, different combinations of phases with different morphologies can be generated in all types of steel to obtain the desired property.

Martensite

Martensite is a metastable phase. It consists of a supersaturated interstitial solid solution of carbon in body centered tetragonal iron. Steel is heated to a temperature within the austenitic region and is then quenched. The temperature at which austenite to martensite transformation begins is called martensite start ,and the temperature at which transformation finishes is called martensite finish temperature. Increase in weight percent carbon increases temperature for Fe-C alloys.

The hardness and strength of Fe-C martensite increase with increase in carbon content. However, ductility and toughness decrease with increase in carbon content. Most martensitic plain carbon steels are tempered at , i.e. below the transformation temperature.