Newly Designed Cr-Mn Alloyed Ultra-high Strength Steel without Boron Addition for Hot-stamping Processing

A newly designed hot-stamping steel alloyed by chromium (Cr) and manganese (Mn) without boron (B) addition was developed for automobile mass reduction. The experimental results showed the Cr-Mn alloyed steel could be quenched to full martensite microstructure when the cooling rate was higher than 14 °C /s. Yield strength, tensile strength and elongation of the experimental hot stamping part reached 1180 MPa, 1 645 MPa and 8.4%, respectively. The experimental hot stamping part possessed higher tensile strength and elongation, compared with conventional hot-stamping steel of 22MnB5. Furthermore, excellent processing flexibility would be obtained in this novel hot-stamping steel because of its lower critical cooling rate and phase transformation temperature. The design of the composition and investigations of microstructure, mechanical properties and hot-stamping processing were also studied.