Effects of the soaking temperature and over-aging temperature during continuous annealing on microstructure and mechanical properties of C-Si-Mn-Al steel DH780 were investigated by using the Gleeble-3500 thermal simulator,and the microstructure and mechanical properties under different processes were compared and analyzed.The results show that when the soaking temperature is 750 ℃,the martensite content in the microstructure after cooling is about 32％,and there is still obvious banded structure.As the soaking temperature increases,the carbon content of austenite in the two-phase region gradually decreases,and the morphology and proportion of the ferrite and martensite formed by cooling also change.When the soaking temperature is 820 ℃,the microstructure after cooling is composed of about 40％martensite and a small amount of retained austenite and bainite,and ultimately,the tensile strength shows a downward trend,while the yield strength shows an upward trend.As the over-aging temperature increases,the carbon atoms in the martensite diffuse to the grain boundaries,the degree of over-saturation decreases,the high-density dislocations decrease,the retained austenite and part of the martensite decompose,and when the over-aging temperature is higher than 310 ℃,it leads to a downward trend in the final tensile strength and the change of the yield strength is not significant.When the soaking temperature is 800 ℃ and the over-aging temperature is 320 ℃,the tensile strength is 847 MPa and the yield strength is 328 MPa,which can obtain dispersed martensite and basically eliminate the banded structure.The C-Si-Mn-Al steel DH780 can obtain relatively good comprehensive properties.
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维普
