Effect of Phase Transformation on Stress States in Surface Layer of Laser Hardened Carbon Steel

Abstract

A model of simulation of laser hardening was presented in the paper. In the model the coupling of thermal field and phase transformations was considered. The thermal field distribution was determined on the basis of diffusion equation with the convection term, the solution of which was obtained by integration of Green's function over the considered region. The fractions of phases created during the phase transformations were calculated by use of TTT-heating diagram and TTT-cooling diagram. The coupled effects of temperature field and phase transformations were considered by applying the additivity principle and Avrami formulae for diffusion transformations while the Koistinen and Marburger empirical formula was used to calculae the martensite transformation. The stresses were determined on the basis of plastic flow model with linear-isotropic material hardening. In the proposed model the constitutive relationships for plane state of strain were modified in the manner of obtaining the zero value of normal force on the axis direction being perpendicular to section under consideration. The changes in thermomechanical parameters of material as a function of phase contents and thermal field were considered in the stress calculations. The problem was solved by finite element method.