Phase transformation-based finite element modeling to predict strength and deformation of press-hardened tubular automotive part

In this paper, a new tool design for hot stamping taking advantage of both direct quenching and indirect die quenching is proposed to fabricate the coupled torsion beam axle which is formed from the original tubular-shaped part. This newly proposed hot stamping applies spray of the water before the upper die gets into contact with the tubular part, which significantly enhances the cooling capacity. For other region that cannot be covered by the direct spray, the conventional die quenching method in direct hot stamping process is used. Moreover, for the analysis of the deformation behavior during the proposed hot stamping process, the finite element analysis, which takes the deformation and strengthening induced by the cooling and phase transformation into account, has been carried out. From the analysis, the larger shape change when the cooling time is shorter than 15 s could be explained by the incomplete martensitic phase transformation and phase transformation plastic strain. When the cooling time is short the residual stress after cooling is much higher than those for the longer cooling times.