中文摘要：

针对先进高强双相钢的激光焊接问题,通过拉伸试验、显微硬度测试、扫描电镜（SEM）和光学显微镜（OM）等手段分析研究1.5mm厚DP1000钢板对接接头的性能和组织,讨论了接头强度和塑性降低的主要原因。研究发现激光焊接DP1000双相钢的焊接接头热影响区（HAZ）存在严重的软化现象,软化区集中在其回火区和不完全结晶区,该软化区造成焊接接头的抗拉强度下降了10%~15%,塑性下降了60%以上。强度下降的主要原因是回火区域出现了回火马氏体,其强度低于淬火马氏体;塑性下降的主要原因是焊接热影响区的软化使得焊接接头的不同区域在拉伸过程中出现不协调的变形,变形主要集中在热影响区的软化区,而焊缝金属区、母材区及焊接热影响区的硬化区几乎没有变形。

英文摘要：

Studies on the microstructure and properties of butt joints by laser welding 1.5 mm thickness DP1000 dual phase advanced high strength steel used tensile test,microhardness test,scanning electron microscope（SEM）and optical microscope（OM）are presented.The reason of the decrease of joint′s strength and ductility is discussed.The results show that a serious softening has occurred in heat-affected zone（HAZ）of the welding joints,and the most serious locates in the tempered zone and the incomplete crystalline zone of HAZ.The strength of welding joints decrease by 10%~15%,and the ductility of welding joints exceed 60%.The main reason of the joint′s strength descent is the existence of tempered martensite which is obtained in the welding process,and the tempered martensite′s strength is lower than the quenching martensite.The main reason of the joint′s ductility descent is the uncoordinated tensile deformation of different joint subareas,and the deformation mainly takes place on the softened zone of HAZ.The welding fusion zone,the base metal and other zones of HAZ hardly occur deformation.