Analysis of Shear Characteristics of Quenchable Boron-Alloyed Steel 22MnB5 During the Hot Mechanical Piercing Process

Hot stamping is a widely adopted technique for manufacturing high-strength vehicle body parts using boron-alloyed steels, such as 22MnB5. This process involves heating the material to 900 celcius or higher in a furnace, followed by in-die quenching to achieve a strength of over 1.5 GPa. The process includes heating, forming, in-die quenching, and trimming. Laser trimming is the conventional method used for this purpose. However, laser trimming has limitations in terms of productivity and energy cost, and alternative methods have been explored, such as mechanical piercing during the hot stamping process at high temperatures. This study aims to optimize the process parameters, including the piercing temperature, time and clearance between the die-punch, to achieve optimal performance and their mechanical stability. The results show that hot piercing is the feasible method for cutting the boron-alloyed steel parts during the hot stamping process. In this study, the optimal performance is achieved under specific process conditions used for hot mechanical piercing, which is corresponding to differential clearance and mechanical piercing time, respectively. The size and distribution of the burr generated by the shearing process were not significantly affected by the hot mechanical piercing time with lower clearance. However, with the larger clearance, the hot mechanical piercing time significantly affected the size and distribution of the burr. In addition, hydrogen embrittlement becomes more severe as the martensitic phase transformation completes, and the hot mechanical piercing time has the greater influence on the process than the clearance conditions. Therefore, when designing the process for optimal performance of hot mechanical piercing, it is crucial to consider the effects of clearance and time as significant variables and verify their effects.