Modelling of the high-temperature ductility properties during solidification of austenitic stainless steel

Knowledge of the high-temperature ductility properties of steel grades is essential for the processing of steel products due to the existence of critical temperature regions. Embrittlement in the liquid/solid two-phase region and in the precipitation region can be distinguished. In these regions, material failure can occur due to cracking as soon as the appearing strains and stresses exceed the formability of the material at a given temperature. Therefore, the temperature ranges where reduced ductility occurs have to be identified to ensure appropriate processing of the materials in continuous casting or welding. These temperature regions are usually investigated by means of hot tensile testing after melting of the specimen in situ. As these experiments are time-consuming and expensive, a mathematical estimation of the results would be a great advance. The presented research work outlines the possibility of a mathematical description of the most important characteristics in the relationship reduction of area versus testing temperature. Especially the zero ductility temperature and zero strength temperature, the critical solidification interval, the maximum ductility range and the region of the secondary ductility drop, including the beginning of the ductility drop and the minimum ductility, are investigated. Furthermore, the reduction of area values for given testing temperatures can be estimated on the base of the chemical composition and the parameters of the hot tensile tests. For this purpose, a model formulated by means of multiple regression analysis on the basis of published experimental data is proposed for the description of the high-temperature ductility properties of austenitic stainless steel grades of the Cr-Ni- and the Cr-Ni-Mo-type.