Effect of Coiling Temperature on the Microstructure and Mechanical Properties of Hot-Rolled Ti-Nb Microalloyed Ultra High Strength Steel

A novel low carbon Ti-Nb microalloyed hot rolled steel with minimum yield strength of 700 MPa and good balance of stretch-flangeability and impact toughness has been developed by controlled thermo-mechanical processing following thin slab direct rolling route. In the present work, the effects of two coiling temperatures on the resulting microstructure, micro-texture and mechanical properties on this Ti-Nb microalloyed steel have been studied. It is observed that increase in coiling temperature from 520 to 580 degrees C significantly affects the mechanical properties. Higher dislocation density and increased precipitation along with slightly smaller grain size is observed for 580 degrees C coiling temperature resulting in about 50 MPa increase in yield and tensile strengths as compared to 520 degrees C coiling temperature.