Flow and Thermal Analysis during Hot Extrusion of Two Kinds of Stainless Steel: AISI 316Ti and AISI 329A

Abstract

A mathematical model was developed to describe the mechanical and thermal behaviour of stainless steels during hot extrusion. The reference point for the study was the experimental data of the extrusion process performed on two stainless steels in order to take into account the most significant features of the process: temperature, velocities, extrusion ratio and the shape of the extrusion die. The developed simulation approach is based on the Navier-Stokes equations which were used to compute the speed field in the steel during its passage in the die; this formalism allows to reach the resolution of the structural problem from the data easily measured during the industrial practice, i.e. press velocity and velocity of the extruded material at the exit from the die. The behaviour of the steel can be calculated through its constitutive law at high temperature from the fields of velocity, strain rate, strain and stress. The structural model is coupled with a thermal one based on the Fourier equation which provides the thermal field that plays a fundamental role in the microstructural features of the final product. The validation of the computational approach has been realized by an analysis of the obtained velocity distribution in the material and by a comparison between the calculated temperature field, the metallographic structure and the measured micro-hardness values.