Mathematical treatment of non-isothermal transformations

Abstract

AbstractAbstractPrediction of transformation kinetics in steel at varying temperature is of great practical importance in different areas of heat treatment and material science. By formal generalization of the conventional isothermal kinetic functions applied for characterizing thermally activated processes, new types of kinetic function were generated which are suitable for the phenomenological description of non-isothermal processes. On the basis of these generalized kinetic functions, various numerical quantities allowing the concise characterization of the processes taking place at varying temperature may be derived. These quantities involve equivalent time and temperature and extended variants of well known complex time–temperature parameters (e.g. Hollomon–Jaffe parameter). With the help of these quantities, non-isothermal processes may be compared using numerical criteria. Application of the method suggested in the field of heat treatment is demonstrated by two examples. One is related to the prediction of hardness decrease due to tempering in a hardened steel, while the other concerns the development of a new type of tempering chart which can be applied generally for determining the required tempering parameters.MST/496