Effects of different tempering temperatures on the microstructure and mechanical properties of a low-carbon high-strength steel

The mechanical properties of low carbon high strength steel materials used in drilling equipment can be improved effectively by adjusting tempering temperatures of different heat treatments to obtain different material composition. The heat treatment and tempering temperatures were set at 610℃, 630℃ and 650 ℃ respectively, and the microstructure of this low-carbon high-strength steel was compared and analyzed by metallographic microscope and Scanning Electron Microscope(SEM). After tempering, the microhardness, tensile properties and impact energy of the structure were measured respectively by the microhardness tester, universal material testing machine and impact testing machine. The research results show that the performance of the material after quenching and tempering is improved compared with that of the raw material. When the tempering temperature is 610℃, the microstructure is tempered martensite and tempered sorbite, with the maximum yield strength of 1 020 MPa and the microhardness of 332 HV. It also has good plasticity. As the tempering temperature increases, the microstructure recovers and transforms into tempered sorbite. At this time, the yield strength and tensile strength decrease, and the impact energy increases with the highest at 650°C. With the change of tempering temperature, the impact and tensile fractures show multiple failure modes of ductile fracture, quasi-cleavage fracture and mixed fracture. The tempering process can effectively improve the mechanical properties of the low-carbon high-strength steel, which can have a wide application easily in production.