双相钢的力学性能和对成形极限的影响

Mechanical Property of Dual Phase Steel and Its Effect on the Forming Limit

对两个来自不同生产线的冷轧双相钢DP780试样的主要力学性能进行比较,发现相同牌号的DP钢产品性能有显著差异。建立拉伸过程的有限元模型,将拉伸试验和有限元仿真相结合,利用材料失效点主应变二次导数的变化规律准确预测DP780在拉伸过程中的缩颈和破裂。研究发现相同牌号的DP钢产品成形极限亦有明显不同。最后从延伸长度和极限应变两方面定量分析应变强化指数n值和强度系数K值的变化对拉伸过程成形极限的影响。发现应变强化指数n值的变化对成形极限影响较大,强度系数K值的变化对成形极限影响较小。增大n值可以提高发生缩颈和破裂时的延伸长度和极限应变。

The mechanical properties of the DP780 specimens from two different product lines are compared first. It is shown that the mechanical property differences of the same grade DP steels are evident. Then the finite element model of the uniaxial tensile test is established. The principle strain acceleration evolution of the failure point is used to predict the necking and fracture of the DP780 during uniaxial tensile accurately with the combination of tensile test and FEA. It is found that the forming limit of the same grade DP steels is significantly different. Finally the effects of strain hardening exponent n and strength coefficient K varying on the forming limit are analyzed quantitatively. It is shown that the range of the strain hardening exponent n has an obvious influence on the forming limit while the influence of the strength coefficient K is not distinct. The elongation and limit strain at necking and fracture can be improved by increasing the strain hardening exponent n.