Effect of Finish Rolling Temperature on Microstructure and Mechanical Properties of 500 MPa Grade Gantry Mounting Structural Steel

The microstructures and mechanical properties of 500 MPa grade gantry mounting structural steel at three different finish rolling temperature processes were investigated. It was found that the microstructures were polygonal ferrite, pearlite and nanometer-sized precipitates. With the decrease in finish rolling temperature, the tensile strength and impact energy significantly increased, and the cleavage fracture gradually transformed into ductile fracture mode. The specific strengthening mechanisms were discussed. Maximum tensile strength (690 MPa) and Charpy impact toughness (121.5 J) were observed at the finish rolling temperature of 860 °C. The formation of fine nanometer-sized precipitates with elliptical and rod-shaped was mainly through the mechanism of interphase precipitation and dispersion precipitation. The precipitates with less than ~ 10 nm in diameter and less than ~ 30 nm in row spacing primarily formed during γ /α phase transformation after hot rolling process.