Calculability of the bake hardening effect of hot rolled multiphase steels

In recent years high strength hot rolled multiphase steels with a thickness of less than 2 mm have become available. These multiphase steels show a good Bake Hardening effect, which makes them important for automotive constructions, because an increase of yield strength may lead to a weight optimised body structure and/or a better crash resistance. In this investigation five different hot rolled multiphase steels were examined. The steels were exposed to different prestrains, temperatures and holding times. Design of Experiments and statistical methods were used to reduce the quantity of experiments. After evaluation of the results it was possible to develop a formula to predict the yield strength for a given prestrain, temperature and time for each steel. Furthermore, a method was found to decide easily if a steel is qualified for further investigation of the Bake Hardening effect, or more exactly, of its response to different annealing temperatures and times.