Microstructure, Strength and Toughness of Hot-rolled Steel Plate with One-step and Two-step Quenching and Partitioning Process

The effects of one-step and two-step quenching and partitioning processes on the microstructure and mechanical properties of hot-rolled high-strength steel were compared by scanning electron microscope, X-ray diffractometer,impact test and electron microprobe. The results show that the microstructure of the one-step quenching and partitioning samples primarily consist of ferrite, bainite and a small amount of martensite and retained austenite. In contrast, the two-step quenching and partitioning samples mainly consist of ferrite, martensite and austenite islands, tempered martensite and a small amount of bainite. The one-step quenching and partitioning samples exhibit low yield strength and ultra-high elongation at an annealing temperature of 840 ℃. And the two-step quenching samples demonstrate high tensile strength of 945 MPa and low elongation of 31.0%. On the whole, the one-step quenching partitioning samples at 840 ℃ exhibit favorable mechanical properties, with yield strength of 590 MPa, tensile strength of 855 MPa, elongation of 39.7%, and impact work at -20 ℃ and -40 ℃ of 50.0 J and 40.0 J, respectively.