Effects of Normalizing Process Parameters on Microstructure and Mechanical Properties of 20MnV Spring Steel for Rail Transit

20MnV spring steel for rail transit was normalized at different temperatures (780, 830, 880, 930, 980℃) for different times (0.5, 0.75, 1, 1.25 h). The effects of normalizing temperature and normalizing time on microstructure and mechanical properties of the tested steel were studied. The results show that with normalizing temperature increasing, the microstructure of 20MnV spring steel transformed from inhomogeneous ferrite and granular bainite to equiaxed ferrite and massive ferrite. When the normalizing temperature was lower than 830℃, with normalizing temperature increasing, the yield strength and tensile strength of the tested steel decreased, and the elongation after fracture and impact energy at low temperature increased. When the normalizing temperature was higher than 830℃, the yield strength and tensile strength of the tested steel increased with the increase of normalizing temperature. The microstructure of the tested steel were equiaxed ferrite and massive pearlite for different normalizing times. With the extension of normalizing time, the yield strength, tensile strength, elongation after fracture and impact energy at low temperature of tested steel increased first and then decreased. When the normalizing temperature was 930℃ and the normalizing time was 1 h, the mechanical properties of the tested steel were the best.