Experimental investigation of a new low-temperature hot stamping process for boron steels

This paper demonstrates the promise of a new low-temperature hot stamping process with pre-cooling for 22MnB5 boron steels. It is the first time for the new process being successfully implemented for producing an automotive demonstrator component assisted with thorough experimental studies. The studies mainly include hot forming experiments carried out on an industrial prototyping line, post-form examinations, and in-die quenching tests. Automotive B-Pillar components with two designed drawing depths (50 and 64 mm) were hot stamped at a wide range of temperatures and forming speeds, through both the conventional hot stamping processes and the new processes with pre-cooling applied. For the as-formed B-Pillars, 3D shape scanning was conducted to investigate the thickness distribution of the components; uniaxial tensile testing, hardness testing, and scanning electron microscopes (SEM) observation were conducted to assess the final mechanical properties and microstructures. To understand the benefit of the low-temperature hot stamping in reducing cycle time, a separate set of in-die quenching experiments were designed and carried out, with combinations of three different process parameters: workpiece start quenching temperature, initial tool temperature, and die-workpiece contact pressure. The results of this work confirmed that low-temperature hot stamping could be performed successfully in producing complex-shaped components, such as automotive B-Pillars, with much reduced cycle time.