Effect of TiN-Particles on Fracture of Press-Hardened Steel Sheets and Components

It is known that large TiN particles deteriorate the toughness of high-strength steels. The toughness of press-hardened steel (PHS) sheets with full-martensite microstructure for safety critical components of a car body has, however, seldom been studied. Consequently, the effect of TiN particles on either the toughness of PHS sheets or the performance of hot-stamped components have not been investigated. In this research, the size and distribution of TiN particles are quantitatively analyzed for two 22MnB5 PHS sheets containing nitrogen of 29ppm and 44ppm in mass. Higher populations of coarse TiN particles have a negligible effect on standard tensile properties, but significantly reduce impact toughness by Charpy V-notch impact tests. Hot-formed components with smaller fractions of TiN particles show greater fracture resistance by a three-point bending test.