9Cr18Mo/GH3625异种合金燃油组件激光焊接头的组织分析

Microstructure analysis of laser welded joints of dissimilar 9Cr18Mo/GH3625 for fuel assembly

针对发动机燃油组件的焊接性问题,采用光学显微镜观察了9Cr18Mo/GH3625环焊缝脉冲激光焊接头显微组织,采用硬度计测量了接头显微硬度分布,研究了接头各区域的组织演变。结果表明,激光焊接头表面成形良好,由于经历二次加热,接头定位焊点处易出现气孔、热裂纹缺陷。脉冲激光的间隙加热使焊缝组织呈明显的分层,焊缝底部为柱状晶,焊缝中部和顶部均为等轴晶,等轴晶的尺寸在焊缝中部发生突变;接头9Cr18Mo合金侧热影响区宽度约为0. 5 mm,焊接的高温作用使该区发生晶粒长大和碳化物溶解,且越靠近焊缝,碳化物溶解现象越明显; GH3625合金侧热影响区宽度约为0. 4 mm,该区晶粒发生长大;接头自9Cr18Mo合金侧至GH3625合金侧显微硬度逐渐降低,9Cr18Mo合金侧热影响区靠近熔合线位置生成高碳马氏体使显微硬度显著升高。

To study the weldability of engine fuel assemblies, the microstructures of 9Cr18Mo/GH3625 circumferential weld by pulsed laser welding were observed by optical microscopy, the microhardness distribution of the joints was measured by hardness tester, and the microstructural evolution of the joints was studied. The result showed that the surface of laser welded joint is good, and the defects of gas holes and hot cracks are easily occurred at the welded joint due to secondary heating. The gap heating of pulsed laser makes the weld structure layered obviously, the bottom of the weld is columnar grain, the middle and top of the weld are equiaxed grains, and the size of equiaxed grain changes abruptly in the middle of the weld. The width of the heat affected zone on the side of 9Cr18Mo alloy joint is about 0.5 mm, and the high temperature effect in welding makes the grains growth and carbide dissolution occur in the area, and the closer to the weld, the more obvious the carbide dissolution phenomenon is. It is obvious that the width of HAZ on the side of GH3625 alloy is about 0.4 mm, and the grains growth up in this area. The microhardness of the joint decreased gradually from 9Cr18Mo alloy side to GH3625 alloy side. The formation of high carbon martensite near the fusion line in the HAZ on the side of 9Cr18Mo alloy increased the microhardness significantly.