Effect Of Alloying Elements And Annealing Process On Microstructure And Properties Of Deep-drawing DP Steel

In order to better adapt to the rapid development trend of lightweight and the competitive pressure of light metal materials,this paper designed two deep-drawing dual-phase steels of Cr-Mo series and Cu-Ni series with different composition systems.Through thermal and dynamic calculations,thermal expansion,salt bath annealing method,the effect of different alloy elements on the structure of the test steel at different cooling rates,and the evolution mechanism of annealing temperature and time on ferrite recrystallization and martensite transformation were studied,and alloy elements were studied The following key conclusions were obtained on the effects of cooling rate and annealing process on the microstructure and mechanical properties of deep-drawn DP steel.(1)Through thermal expansion test research,it was found that 2#test steel Si-Cr-Mo steel and 4#Al-Mn-Cu-Ni steel A_C1were 810°C and 835°C;A_C3were 971°C and 975°C.Among them,the 2#experimental steel is the ferrite transformation zone when the cooling rate is 0.5?10°C/s;the pearlite transformation zone is when the cooling rate is 3?15°C/s;the cooling rate?15°C/s,pearlite disappears and only bainite is in the tissue.The transformation zone of 4#steel bainite is wider,covering the entire test cooling range;when the cooling rate reaches 3°C/s,the pearlite transformation disappears;while the ferrite transformation zone is relatively wide,the cooling rate range covered by it is 0.5?5°C/s.(2)For the 1#Cr-Mo and 2#Si-Cr-Mo deep-drawing DP steels,it is found that the strength increases first and then decreases as the annealing temperature increases;when the annealing temperature further increases,the strength increases slightly and then decrease.The elongation is reduced first and then increased;the optimal annealing temperature of 1#steel is 880°C and 2#steel is 900°C;while the 2#steel under different annealing times,the r value is greater than 1#steel,where The best annealing time for 1#steel is 600 s,and for 2#steel is 900 s.The increase in the Si element mass fraction significantly expands the two-phase region,fully develops the ferrite recrystallization{111}texture,significantly refines the ferrite recrystallization grains when heated in the two-phase region,and improves the structure distribution to make austenite The body has enough time to nucleate,the martensite islands are evenly distributed in the refined ferrite,and the strength and r value are significantly improved.(3)For 3#Cu-Ni and 4#Al-Mn-Cu-Ni deep-drawing DP steels,it was found that 3#steel lacks alloy carbides,resulting in coarsening and deterioration of ferrite grains with increasing annealing temperature Mechanical properties;with the increase of annealing temperature,the strength and elongation of 4#steel are shown to decrease first and then increase;among them,the mechanical properties of 3#steel reach the optimum at 820°C,while the 4#steel reaches the best Excellent and r value up to 1.2.In the study of the annealing time of 4#steel,it is found that with the extension of the annealing time,the strength,elongation,and r value all increase first and then decrease,and the r value is greater than 1,and when the annealing time is 600 s The mechanical properties are optimal.The Al and Mn elements expand the range of the two-phase region of 4#steel,and reduce A_C1,accelerate the martensite transformation while refining the structure grains,ferrite grains are fully developed,and the mechanical properties are greatly improved.