Spot weldability comparison of high strength steel DP590 with different chemical composition

This paper introduces the cold-rolled DP590 high strength automotive steel sheets produced by Sougang Steel,which involve two different composition systems,one with high Al content and the other with C-Si-Mn.These two materials are pot-welded and the optimized welding current range and the best welding current are obtained.Both the two kinds of materials welding current’s scope is 1 800 A,but the current of C-Si-Mn system DP590 is 1 400 A higher then the high Al content one’ s;when these two kind of materials are welded with the optimal current,the nugget can be get by no defect.There have some difference in these two base materials.High Al DP590 has a bandy metallurgical structure compose with ferrite and martensite,the volume fraction of martensite is 8%,the grain size is 10.5.C-Si-Mn system DP590 compose with ferrite and martensite also while the volume fraction of martensite is 9%,the grain size is 9.5.Weld structure of high Al DP590 are bainite and lath martensite when C-Si-Mn system DP590’s is lath martensite only.The variation of HV is same for these two materials nugget,the length of the are both 10 mm,there have no soft zone in the weld scope.The HV of the both materials are the same of 210 -220.The HV of high Al DP590 weld scope is 280,when C-Si-Mn system DP590 is much more then it with 425.After test these two welded sample get the same failure modes,the maximum shearing resistance and maximum positive tension of high Al DP590 are both less than the C-Si-Mn system DP590.