A numerical and experimental investigation into hot stamping of boron alloyed heat treated steels

Hot stamping of steel sheets using water or nitrogen cooling media was studied on a laboratory scale. Sheets of grade 22MnB5 boron steels in three different thicknesses were investigated and the results of experimental hot stamping tests were considered. Microstructural analysis, linear and surface hardness profiling as well as tensile tests of formed samples were carried out. After hot stamping, mostly fully martensitic microstructures, which yield ultra high strength levels, were produced. It is concluded that die cooling media, i.e., water or nitrogen, have a significant effect on material properties after hot stamping. Using liquid nitrogen as coolant in the punch instead of water increases yield strength by 50 to 65MPa. Moreover, the evolution of the temperature and force during the hot stamping process was simulated by using a coupled thermomechanical FEM program. The results of numerical simulation and experimental results are in good agreement.