低成本800MPa级镀锌超高强度双相钢的微观组织与性能

Microstructure and properties of a low-cost 800MPa galvanized ultra-high strength dual-phase steel

利用光学显微镜、透射电镜(TEM)对800 MPa级双相钢热轧、冷轧及热镀锌后的显微组织进行了观察,分析比较了热镀锌后整卷通板宽不同位置的力学性能。结果表明:试验钢经795℃保温150 s后热涂镀,微观组织以铁素体+马氏体为主,铁素体晶粒尺寸在2.3~6.0μm之间,马氏体体积分数为21%左右。热镀锌后抗拉强度为825 MPa,屈服强度为505 MPa,断后伸长率为19%,沿板宽方向力学性能稳定性较好,抗拉强度波动在20 MPa以内,屈服强度波动在4 MPa以内,断后伸长率波动1%。对热镀锌后整卷钢头中尾部进行了折弯性能评价,以3倍厚度弯心直径进行横向180°折弯试验,结果都没有开裂,能够满足用户对高折弯性能的要求。

Microstructure of hot-rolled,cold-rolled and hot-dip galvanized 800 MPa grade dual-phase steel was observed by means of optical microscope and transmission electron microscope( TEM). The mechanical properties at different positions of the whole rolled plate after hotdip galvanizing were analyzed and compared. The results show that when the tested steel is annealed at 795 ℃ for 150 s and hot-dip galvanized,the microstructure is mainly composed of ferrite and martensite,the grain size of ferrite is between 2. 3-6. 0 μm,and the volume fraction of martensite is about 21%. After galvanizing,the tensile strength and yield strength are 825 MPa and 505 MPa respectively,the elongation after fracture is 19%,and along the width of the plate,the fluctuation of tensile strength is within 20 MPa,that of the yield strength is within 4 MPa,and that of the elongation is within 1%. When the transverse 180° bending test with bending diameter of 3 times of the plate thickness was conducted,the results show that no cracking happens from the head to the tail of the hot-dip galvanized whole coil steel,indicating that the requirements of user for high bending performance are met.