切边工艺对高强钢成形性能与断裂模式影响的实验研究

Experimental study on influence of cutting process on formability and fracture mode for high strength steel

选用DP980钢与QP980钢材料,采用铣削、水洗、线切割和冲裁的方式加工试样,并利用基于DIC方法的剪切边拉伸实验比较不同的切边工艺对试样的断裂伸长率和断裂应变的影响,对不同切边工艺下试样的拉伸断裂过程进行追踪,分析不同钢种的颈缩变形与断口形貌,阐述了基于颈缩原理建立的传统成形极限图不再适用于预测高强钢边部开裂的原因,因此,断裂失效模型必须考虑切边工艺对边部影响。实验结果表明,剪切边拉伸实验会产生两种断裂模式:颈缩断裂和剪切边断裂。QP980钢比DP980钢对切边工艺更敏感,局部成形性能更好,对于QP980钢来说,采用边部去除材料的冷加工方法(水洗、铣削)得到的材料性能优于热加工方法(线切割),且优于冲裁边缘。对于两钢种来说,打磨冲裁边缘可以有效提高材料性能。

For DP980 steel and QP980 steel materials,the specimens were machined by milling,water jet cutting,wire electrical dis-charge machining and blanking,and the influences of different cutting processes on fracture elongation and fracture strain were compared by the shear edge tensile experiments based on DIC method.Then,the tensile fracture process of specimens under different cutting processes was tracked,and the necking deformation and fracture morphology of different steels were analyzed.Furthermore,the reason why the traditional forming limit diagram,which was established based on necking principle,could not accurately predict the edge crack-ing of high strength steel was explained.And so the influence of the cutting process on the edge must be considered in the fracture failure model.The experiment results show that necking fracture and shear edge fracture are two typical fracture modes in the shear edge tensile experiment,and QP980 steel is more sensitive to the cutting process and has better local formability than DP980 steel.For QP980 steel,the properties of material obtained by cold working methods(water jet cutting and milling)which removes material from the edges is better than that of hot working methods(wire electrical discharge machining),and it is superior to blanking edge.Thus,for two kinds of steel,grinding the blanked edges can effectively improve the material properties.