Bake Hardening Behavior of Advanced High Strength Steels under Manufacturing Conditions 2011-01-1053

The demand for the reduction of vehicle weight advanced the development of High Strength Steels. In the 80's, Bake Hardening Steels were developed for parts which are manufactured at high stretch forming capacities, specifically utilizing the increase in strength during the paint process. At the end of the 90's, the demand for even higher strength levels led to the development of Advanced High Strength Steels, e.g. Dual Phase Steels, TRIP-Steels, Martensitic Steels or Complex Phase Steels. Since then, the portion of high strength steels in vehicle bodies has been increasing constantly. In addition to the high strength level, they also possess a remarkable bake hardening potential. Currently, this potential is not taken into consideration sufficiently. The use of Advanced High Strength Steels increases the demands on the production in dealing with these materials. Process windows, such as for welding or painting, are narrowed down further. In this presentation, the bake hardening potential of a well known Bake Hardening Steel CR180BH2 shall be compared with the behavior of CR DP800 and CR DP1000 LCE high strength steels in a defined time-temperature window. The comparison is not limited to the BH-values of the individual steel grades, but includes the mechanical properties, e.g. yield strength, tensile strength and elongation, as well. This comparison aims to illustrate the coherency among the demands for stable material behavior of Advanced High Strength Steels in a defined process window. In addition, the BH potential of Advanced High Strength Steels will be demonstrated and a debate with the goal of improving the specification of bake hardening values in the standardization shall be initiated.