Residual Stress Formation Relating to Peak Temperature- and Austenite Grain Size-based Phase Transformation of S355 Steel

Abstract

Nowadays thermal forming processes of steel are state of the art in industrial applications. Nevertheless, the influences of thermal induced phase-transformation on residual stresses and strength have not been fully observed. Times needed for transformation are affected by the initial austenite grain size, while the prevailing peak temperature influences austenite grain growth. Higher temperatures lead to larger austenite grains, leading to increased times for transformation. In order to get an embraced understanding of such effects numerical simulations of phase-transformations are mandatory. In this paper simulations of thermal forming processes, using S355 steel, are presented. Different continuous-cooling-transformation-diagrams (cct–diagrams) of specific austenite grain sizes for temperatures between transformation point AC3 and melting temperature are implemented in the model. It is shown that resulting magnitudes of residual stresses vary between 248 N/mm 2 and 550 N/mm 2 . Finally an approach for the impact on relevant peak temperatures in the heat affected zone is outlined.