450~780 MPa系列双相钢扩孔性能实验

目的避免双相钢在成形过程中经常出现的翻边或扩孔开裂的问题,提高生产效率。方法以几种强度级别为450~780 MPa的双相钢为实验对象,测试材料的单向拉伸和扩孔性能,并从微观组织上分析影响双相钢强度和扩孔性能的因素。结果 450~780 MPa强度级别双相钢的屈服强度随铁素体晶粒尺寸的减小而增加,抗拉强度随马氏体体积分数的增加呈近似线性增加。双相钢的扩孔性能随着材料强度的提高呈下降的趋势。DP500与DP450和DP600相比,抗拉强度(579 MPa)居中,伸长率最高,但由于其马氏体形态和分布的差异,其扩孔性能反而最低。结论双相钢的扩孔性能会受到马氏体的含量、尺寸、形态和分布的影响,与材料强度和伸长率没有必然的关系,当马氏体呈颗粒状均匀分布时,具有更好的扩孔性能。

Test on Hole Expansion Property for 450~780 MPa Dual Phase Steel Sheets

The paper aims to avoid flanging or hole-expansion in forming dual-phase steel to improve the productivity. Uniaxial tensile test and hole-expansion test for several dual-phase steels between 450 MPa and 789 MPa were carried out. Effects of microstructure on mechanical properties of dual-phase steels were analyzed. The yield strength for 450~780 MPa dual-phase steels increased with the reduction of ferrite''s grain size. The ultimate tensile strength increased almost linearly with the increase of martensite''s volume fraction. Compared with DP450 and DP600, DP500 had an intermediate ultimate tensile strength (579 MPa) and a maximum elongation; but for the difference of martensite''s shape and distribution, it had a minimum hole-expansion ratio. The hole-expansion ability of dual-phase steel was mainly affected by total volume fraction, size, shape and distribution of martensite particle rather than strength and elongation of material. Uniform distribution of globular martensite particle indicates better hole-expansion ability.