DP980超高强钢激光焊接接头组织及性能研究
Microstructure and Properties of Laser Welding Ultra-High Strength Steel DP980 Joints

利用Nd：YAG固体激光器对DP980超高强钢进行激光对接焊接, 通过硬度测试、拉伸试验研究DP980超高强钢激光焊接接头力学性能的变化, 采用光学显微镜(OM)、扫描电子显微镜(SEM)等观察显微组织的转变．结果表明：DP980超高强钢经过激光焊接, 焊接接头分为焊缝金属区、完全相变区、不完全相变区、回火区和母材区．焊后焊缝金属区和完全相变区为马氏体组织, 硬度较高; 焊接接头软化现象发生在不完全相变区和回火区：不完全相变区马氏体发生相变使得铁素体含量增加; 回火区组织发生回火, 马氏体析出碳化物, 导致软化．在力学性能方面, 焊接接头抗拉强度略有降低, 延伸率下降明显, 软化区的存在导致在拉伸试验时焊接接头的不均匀变形, 造成了其塑性明显下降; 拉伸试样的断裂发生在焊接接头热影响区, 断口观察发现存在有大小不等、深浅不一的韧窝, 属于塑性断裂．
Ultra-high strength steel DP980 was welded employing Nd: YAG laser. The mechanical properties of welded joints were investigated through hardness test and tensile test，and the evolution of microstructures was observed through optical microscope(OM)and scanning electron microscope(SEM). The results showed that laser-welded DP980 joints could be divided into weld metal(WM) zone，complete phase-transformation zone，incomplete phase-transformation zone，tempered zone and base metal(BM) zone. The weld metal zone and complete phase-transformation zone consisted of martensite，exhibiting higher hardness. The softening of welded joints occurred in incomplete phase-transformation zone and tempered zone. In incomplete phase-transformation zone，the ferrite content increased because of transformation of martensite while in tempered zone carbide precipitated in martensite due to tempering. In terms of mechanical properties，the welded joints witnessed a slight decrease in tensile strength and an obvious decrease in elongation rate due to the inhomogeneous deformation originating from softening of welded joints. The tensile tests revealed that fracture took place in heat-affected zone(HAZ)，presenting the characteristics of plastic fracture and different sizes of dimples