Investigation of tailored softening behavior of aluminized boron steel (22MnB5) in hot stamping process using die surface relief patterns

Abstract

The hot stamping process is widely utilized in the global automotive industry for the fabrication of body components, due to its effectiveness in achieving both lightweight structures and crash safety performance. Typically, aluminized 22MnB5 material is predominantly employed, enabling the attainment of a strength of 1.5 GPa. However, producing finished parts through hot stamping requires laser trimming, which results in increased energy costs and extended production times. Efforts to resolve these issues by adopting mechanical trimming have been made, yet achieving a high-quality sheared surface with mechanical trimming remains difficult. Although techniques involving localized softening have been proposed to address this challenge, they necessitate additional costs and investments in equipment. In this study, relief patterns (RPs) were applied to the surface of the hot stamping die to create air pockets, thereby regulating the quenching rate to achieve localized softening. This method aimed to observe the resultant changes in mechanical properties and to assess the mechanical shear performance and quality improvement of components subjected to the hot stamping process. The experimental results indicated an increase in the burnish ratio of the sheared surface and an improvement in micro-cracks on the fracture surface. By employing RPs, approximately 10 % localized softening of mechanical strength was achieved, V-bending was enhanced by approximately 25 %, and the entrapped hydrogen content was reduced by approximately 32 %. These outcomes are expected to significantly contribute to improving the efficiency and quality of the hot stamping process, as well as reducing carbon emissions.