Abstract: Microstructure and mechanical properties of the 45CrNiMoVA high-strength steel were studied using five cooling methods (furnace cooling, air cooling, forced air cooling, fog cooling, and water cooling) after full austenitization, as well as tempering treatment. The microstructure of high-strength steel was observed using optical microscope, and the tensile properties were measured using the MTS E45.105 universal testing machine. At the same time, the Vickers hardness was measured using HXD-1000TM digital Vickers hardness tester. The results indicate that under furnace cooling condition, the microstructure of the specimen is composed of pearlite and equiaxed ferrite. Under air cooling condition, the cooling rate increases, the microstructure of the specimen transforms into a mixed structure consisting mainly of bainite and martensite. As the cooling rate further increases, the content of bainite in the microstructure of the specimen decreases, while the content of martensite increases under forced air cooling and fog cooling conditions. Under water cooling, the microstructure of the specimen is completely martensite. The hardness and tensile strength of the specimen furnace cooled are the lowest, being 446.88 HV0.1 and 1430 MPa, respectively, while the microhardness and tensile strength of the specimen water cooled are the highest, being 815.66 HV0.1 and 2430 MPa, respectively. After tempering, the microhardness and tensile strength of the specimen decrease, but the percentage total extension at fracture increases, demonstrating excellent comprehensive mechanical properties.

Key words: 45CrNiMoVA high-strength steel, cooling rate, microstructure, mechanical properties