Microstructure and Mechanical Properties of 550MPa Yield-Strength-Class Hot Rolled Plate Steel

Two test steels,i.e.,microalloyed CSiMnCuNiMo(A) and CSiMnCuNiCrMo(B) were investigated to develop a 550MPa yield-strength-class high strength hot plate steel with an assured CVN energy of 37J at-60℃.The continuous cooling transformation(CCT) kinetics in the designed thermomechanical processing conditions was investigated for the test steel A employing a Gleeble 3800 thermomechanical simulator.A series of thermomechanical rolling and accelerated cooling operations were exercised employing a two high reversing pilot rolling mill coupled with accelerated cooling system.The thermomechanical rolling specification is that the minimum reduction rate of 65% during finishing rolling is necessary followed by accelerated cooling at 20℃/s interrupted at 500℃ for the steel A and 13℃/s interrupted at 400℃/s for steel B,respectively.Minimum yield strength of 550 MPa and average Charpy V impact energy values of 307J and 164J were attained in the test steels A and B,respectively.