Microstructural control and mechanical properties of 590 MPa grade hot-rolled V-N high strength steel

The controlled rolling and controlled cooling test was conducted on low-cost V-N microalloyed steel. The transformation mechanisms and precipitation behavior were discussed, and the comprehensive mechanical properties were systematically studied. The results indicated that the microstructure composes of polygonal ferrite, granular bainite and small amount of acicular ferrite. The nano-scaled V(C, N) precipitates distribute dispersedly in the matrix of ferrite or bainite-ferrite. The experimental steel with tensile strength 615 MPa possesses excellent elongation-after-fracture. The cold bending property is qualified. The hold-expansion ratio is 95%, which meet the demand of the automotive wheel disc. The low temperature impact toughness is outstanding. The fine grain strengthening, dislocation strengthening, precipitation hardening and transformation strengthening are the main strengthening mechanisms.