数値解析による狭開先ホットワイヤ・レーザ溶接およびGMA溶接における凝固割れの評価並びに発生予測

広島大学(Hiroshima University)博士(工学)Engineeringdoctora

Comparative study of dissimilar tailor-welded blanks between DP590 and DP980 dual phase steels

This research aims to study the dissimilar tailor-welded blanks between DP590 and DP980 dual phase steels using the autonomous GTAW process. The summarized results are as follows. It was found that utilized welding parameters in DP590 and DP980 steel butt joint were able to achieve complete penetration joint and there were not any defects. Furthermore, the dissimilar weld zone produced the hardness profilevalue between the DP590 and DP980 base metal. In particularly, DP590-HAZ region resulted in harden zone. Meanwhile, DP980-HAZ region induced a soften zone. By the way, the harden DP590-HAZ exhibited fine columnar martensite with a ferrite matrix. On the other hand, the soften DP980-HAZ represented a tempered martensite structures. Comparing the tensile test was carried out in order to investigate dissimilar welded joint strength in the different rolling directions. It was suggested that the specimen welded along to rolling direction was evidently larger tensile strength (1092 MPa) than the welding transverse to rolling direction (638 MPa). Moreover, the weakest fracture occurred apparently on the region of DP590-BM rather than the HAZ region