Glossary of terms used in heat treatment of steel...

          Glossary of terms used in heat treatment of steel Various terms used in the heat treatment of steels are described below: Ageing – It describes a time temperature dependent change in the properties of certain alloy steels. It is a change in properties that may occur gradually at atmospheric temperature (Natural ageing) and more rapidly at higher temperature (Artificial ageing). Quench ageing – It is a change in properties that may occur gradually at atmospheric temperature and more rapidly at higher temperature following rapid cooling (Precipitation hardening). Strain ageing – It is a change in properties that may occur gradually at atmospheric temperature and more rapidly at higher temperature following plastic straining. Annealing – It is a term denoting a treatment, consisting of heating to and holding at a suitable temperature followed by cooling at a suitable rate, used primarily to soften but also to simultaneously produce desired changes in other properties or in microstructure. The purpose of such changes may be, but is not confined to: Inducing softness Improving machinability Improving cold working properties Improving mechanical or electrical properties Increasing stability of dimensions Obtaining a desired structure Removing stresses The time temperature cycle used vary widely both in maximum temperature attained and in cooling rate employed, depending on the composition of the steel, its condition, and the result desired. Various types of annealing processes are as follows: Bright annealing– It is annealing in a protective medium to prevent discoloration of the bright surface. Cycle annealing – It is an annealing process employing a predetermined and closely controlled time temperature cycle to produce specific properties or microstructure. Flame annealing – It is an annealing process in which the heat is applied directly by a flame. Full annealing – It is heating to and...