Phase Transformations Kinematic Model in Steel Austenization Process

When building induction heating numerical models, time-temperature austenization diagrams are source of information about phase transformations. In this connection, an actual task is a kinematic model application allowing to determine the austenite concentration in the heating process with a non-constant velocity. The paper proposes a new phase transformations kinematic model in steel during austenization based on the diffusion process described by hyperbolastic function of type <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$I$</tex>, which will improve the induction and laser hardening installations modeling and design accuracy. The new phase transformations kinematic model in steels austenization process makes it possible to describe analytically the forming phase concentration dependence on temperature and heating rate, as well as to decouple the concentration curve shape determination to time-temperature diagrams type. The proposed model comparison with Leblond's kinematic model is carried out. Correction functions values for describing the steel 45 austenization process by Leblond model are presented. Unlike Leblond model, the proposed kinematic model can be used in modelling quenching with the condition of achieving a certain concentration of the forming phase in a given region. Time-temperature austenization diagrams approximation function is also proposed. An example of time-temperature austenization diagrams approximation of steel 45 is considered. The proposed phase transformations kinematic model application example for steel 45 austenitization process is given.