热输入对超高强钢DP1000激光焊接接头微观组织和断裂机制的影响

利用光学显微镜（OM）、扫描电子显微镜（SEM）观察超高强双相钢DP1000激光焊接接头微观组织的变化，通过显微硬度的测试、拉伸试验研究其不同热输入下焊接接头的力学性能.结果表明，随着热输入的增加，由回火区和两相区组成的软化区的组织发生了明显的变化，软化区内平均硬度值减小，其宽度尺寸增加，导致拉伸试样的断裂位置发生变化.当热输入不高于52 J/mm，焊接试样的抗拉强度是母材的97.75%，软化区宽度最大约为506 μm，断裂发生在母材上；当热输入达到72 J/mm，软化区宽度约为621 μm，断裂发生在软化区内.

Effect of heat input on microstructure and fracture mechanism of ultra high strength DP1000 steel laser welded joint

The microstructure of ultra high strength DP1000 steel laser welded joint was observed by optical microscope (OM) and scanning electron microscope (SEM). The mechanical properties of different heat input welding joints were studied by microhardness test and tensile test. The results show that the microstructure of the softening zone, which is composed of the tempering zone and the two phase zone, changes obviously with the increase of heat input. Furthermore, the average hardness in the softening zone decreases and the width size increases, resulting in the change of the tensile specimen fracture position. When the heat input is not higher than 52 J/mm, the tensile strength of the welded specimen is 97.75% of the base metal, the maximum width of the softening zone is about 506 μm, and the fracture occurs on the base metal. When the heat input reaches 72 J/mm, the width of the softening zone is about 621 μm, and the fracture occurs in the softening area.