关键词: 连续退火工艺, DH780钢, 力学性能, 显微组织

Abstract: Annealing temperature and slow cooling temperature of DH780 steel were simulated by using a continuous annealing simulation experimental machine. The effect of annealing process on the microstructure and mechanical properties of DH780 steel was quantitatively studied by using OM, SEM, EBSD, XRD and tensile experiments. The results show that as the annealing temperature increases from 770 ℃ to 830 ℃, the ferrite content in the microstructure decreases from 53.6% to 43.6%, and the martensite content increases from 42.6% to 51.8%. The yield strength decreases and then increases with the increase of annealing temperature, while the tensile strength continues to increase. As the slow cooling temperature decreases from 720 ℃ to 680 ℃, the amount of secondary ferrite precipitated from undercooled austenite during the slow cooling process increases, and the ferrite content in the final structure increases from 45.9% to 50.1%, while the decrease in austenite content leads to a decrease in the final volume fraction of martensite. The tensile strength of the tested steel decreases from 829.2 MPa to 785.8 MPa. Under the continuous annealing process at an annealing temperature of 800 ℃ and a slow cooling temperature of 700 ℃, the retained austenite content reaches a maximum of 7.2%, and the comprehensive mechanical properties of the tested steel are also the best, with product of strength and elongation of 22.1 GPa·%.

Key words: continuous annealing process, DH780 steel, mechanical properties, microstructure