Modelling of Microstructure and Heat Transfer during Controlled Cooling of Low Carbon Wire Rod

Abstract

The microstructure of TMT (Thermo-Mechanically-Treated) rebars consists of four phases, tempered martensite, bainite, ferrite and pearlite. These four phases are non-homogeneously distributed across the cross section of the wire rod which gives rise to a complex hardness distribution. A coupled heat transfer and phase transformation model has been developed at the R & D Division of Tata Steel that can predict the temperature profile and the fraction of various phases in this type of wire rods efficiently. A fully implicit finite difference scheme has been used for solving the heat transfer equation in cylindrical coordinates; the recalescence due to phase transformation has been taken into consideration that makes the model suitable for use in any industrial application. A model has also been developed based on the volume fraction and strength of the individual phases to predict the hardness at different sections of the wire rod. The predicted hardness distribution has been found to agree well with the micro hardness measurements at various points across the section of the wire rod.