Effects of Thermo-mechanical Process Parameters on Microstructure and Crystallographic Texture of High Ni–Mo Ultrahigh Strength Steel

Abstract

A novel low-carbon micro-alloyed steel has been developed with ultrahigh strength (UTS ~ 1700 MPa), satisfactory ductility (total elongation ~ 13%) and impact toughness (25 J/cm2 at − 40 °C) for light-weight applications in automobile, aerospace and defence sectors. The effect of finish rolling temperatures (850–750 °C) and cooling rate (air cooling versus water quenching) on the evolution of microstructure and crystallographic texture and finally on the mechanical properties of thermo-mechanically controlled processed steel has been studied. A refinement in mixed microstructure comprised of granular/lower bainite and lath/plate martensite and an intensification of Goss and rotated Goss texture components were found with the decrease in finish rolling temperature and increase in cooling rate. Interaction of fine-scale carbide/carbonitride precipitates of Nb and Ti with the dislocation substructure present within bainite and martensite contributed significant precipitation strengthening to the steel.