弛豫时间对1200 MPa级热轧双相钢组织性能的影响

Effect of relaxation time on microstruture and mechanical properties of 1200 MPa hot rolled dual phase steel

基于合金减量化原则,采用以超快冷技术为核心的新一代TMCP技术制备了1200MPa级热轧双相钢,研究了弛豫时间对试验钢组织和性能的影响。研究表明:随着弛豫时间增加,试验钢铁素体晶粒尺寸和体积分数均增加,屈服强度降低,伸长率均在10.0%以上;组织中马氏体均以块状马氏体为主,并由块状向小岛状转变,其体积分数减少,抗拉强度降低,屈强比减小,n值增加。弛豫时间影响到铁素体和马氏体的体积分数及内部结构。弛豫9 s的试验钢,铁素体体积分数为44.2%,铁素体晶粒尺寸为3.4μm,组织中块状马氏体中板条束条宽细化至0.3μm及较多的小岛状马氏体有利于n值,抗拉强度达到1258 MPa,伸长率为12.0%,屈强比最低为0.55,n值高达0.13,其综合性能最好。

Based on the principle of alloy reduction, a 1200 MPa hot rolled dual phase steel was prepared by a new generation of TMCP technology with ultrafast cooling as the core technology, and the effect of relaxation time on microstructure and mechanical properties of the tested steel was studied. The results show that with the increase of relaxation time, the grain size and volume fraction of ferrite of the tested steel increase, the yield strength decreases, and the elongation is more than 10. 0%;the martensite in the microstructure is dominated by block martensite and changes from block to small island, and the volume fraction of the martensite and the tensile strength decrease;the ratio of yield strength to tensile strength decreases and the n value increases. The volume fraction and internal structure of ferrite and martensite are affected by relaxation time. When the relaxation time is 9 s, the volume fraction and the grain size of the ferrite are 44. 2% and 3. 4 μm, respectively. Because the strip width of the lath martens让e in the microstructure is refined to 0. 3μm and there are more small island martensite, it is favorable to improve the n value, and in this situation the tensile strength, elongation, yield ratio and n value of the tested steel are 1258 MPa, 12. 0%, 0. 55 and 0. 13, respectively, and shows the best comprehensive property.