High temperature properties and the crack susceptibility of new steel grades for automotive purposes

The use of new high-strength steels with good plasticity in automobiles offers a remarkable potential for improvements in the area of weight reduction with simultaneous improvement in crash-safety. For the steel industry, this trend to highly-alloyed, high-strength steels means a considerable potential for metallurgical research. Continuous casting in particular appears to be a big challenge for such steels. The focus of the investigations documented here are: high temperature properties, crack behavior, non-metallic inclusions and segregation effects in new lightweight steels with induced plasticity (LIP). It is possible to investigate these, especially the high-temperature properties and the crack susceptibility, using the SSCT (submerged split chill tensile) test. Preliminary results for these steels show higher crack sensitivity due to the micro-segregation behavior and non-metallic inclusions, which are crack initiators. In addition, the high-temperature strength of these new steel grades is significantly higher than that of common steel grades. For a better understanding of the experimental results, a numerical model of the SSCT test was used. Due to a lack of documented high-temperature properties of these new steel grades, e.g. elasto-plastic parameters, the comparison of experimental and computational results gives a first approximate indication of these important high-temperature parameters. Knowledge of the high-temperature mechanical properties and crack sensitivity provides an important basis for the development of industrial-scale production processes for these new steel grades using the continuous casting process.