Influence of coiling temperature on microstructure and mechanical properties of a hot-rolled high-strength steel microalloyed with Ti, Mo and V

Influence of coiling temperature (CT) on the microstructure and mechanical properties of a hot-rolled high-strength steel microalloyed with Ti, Mo and V was elucidated. The precipitation behavior of nano-sized particles was investigated by theoretical calculation and quantitative analysis. And the results revealed that V-enriched (Ti, Mo, V)C precipitated in the ferrite matrix. As the CT decreased, the site fractions of Ti in (Ti, Mo, V)C changed little, the site fractions of Mo increased, and the site fractions of V decreased accordingly. Moreover, the low CT could refine the microstructure and precipitated particles but suppress the precipitation of (Ti, Mo, V)C particles simultaneously, leading to the volume fraction of (Ti, Mo, V)C significantly decreasing, consequently causing an increment of grain refinement strengthening and a reduction in precipitation hardening. When the CT was 600 °C, the steel characterized by fine polygonal ferrite, a small amount of bainite and nano-sized (Ti, Mo, V)C precipitates exhibited the optimum mechanical properties with the ultimate tensile strength of 870 MPa, yield strength of 807 MPa and elongation to fracture of 17%.