Microstructure-property relationships of novel ultra-high strength press hardening steels

The industrial significance of microalloyed martensitic steels manufactured via cold rolling, reaustenitization, and quenching has been typically recognized as low. However, it is currently believed that microalloying can improve the in-service properties of ultra-high-strength press hardening steels. In this work, five 34MnB5-based steels were designed to address the role of Ti and V when combined with Cr or Mo. Microstructure-property relationships were analyzed after die quenching and additional bake hardening (BH) heat treatment using advanced methods of microscopy, glow discharge optical emission spectroscopy, quasi-static tensile tests, and three-point bending tests. Results indicate that both Ti and V can provide grain size refinement through the formation of stabile nanosized precipitates. The BH treatment improved postuniform elongation values, indicating a trend of improved ductility. However, the expected improvements in bendability were clearly confirmed only for two V-microalloyed steels with the alloying concepts of 0.3Cr-0.15V-0.03Al-0.02Ti-0.0020B and 0.3Mo-0.15V-0.0060N (without Al-Ti-B additions) (wt pct). Thus, it was discovered that microalloying with V, when combined with either Cr or Mo, provides a promising combination of mechanical properties as far as the austenitization parameters are appropriately controlled.