摘要：本文介绍了用预置中间层的方法防止304不锈钢和铌的激光焊焊缝中产生脆性金属化合物μ(Fe7Nb6)和ε(Fe2Nb)，并对获得的焊接接头进行显微组织和力学性能分析。中间层分为三组，第一组的尺寸为50mm×1mm×2mm的Cu/V，第二组是尺寸为50mm×1.5mm×2mm的Cu，第三组是尺寸为50mm×2mm×2mm的Cu。

通过焊缝成形观察、VHX-900超景深数码显微镜、SEM和EDS能谱分析，发现第一组焊缝成形差，多次实验验证显示，实际焊接中钒和铌一侧的熔合很差导致焊接失败，第二、三组焊缝成形良好。焊接接头焊缝区主要是柱状晶、树枝晶；在靠近铌一侧没有检测到Fe，也就是说，中间层在很大程度上控制了脆性金属化合物μ(Fe7Nb6)和ε(Fe2Nb)的生成。焊缝的组织是，奥氏体钢/铜基固溶体ε相/Nb基固溶体（加2mm铜中间层的焊缝中间有未熔铜层）。

由抗拉强度实验可知：加1.5mm铜和加2mm铜的焊接接头都是塑性断裂。加1.5mm铜的焊接接头的拉伸试样断在了Nb母材上，抗拉强度普遍250MPa以上。而加2mm铜的焊接接头都断在中间层Cu上（焊缝处），抗拉强度基本在200MPa左右，其中有一个达到了260MPa，但还是断在了焊缝上。加1.5mmCu中间层的焊缝强度高，主要是Cu与Fe、Nb在液态时充分的进行互扩散达到冶金上的牢固结合，并且有效阻止了脆性金属间化合物的生成。

关键词：钢；铌；激光焊接；显微组织；中间层；力学性能

Abstract：In this paper, In order to prevent the production of the intermetallic compounds μ (Fe7Nb6) and ε (Fe2Nb)  ，laser welding was used in 304 stainless steel and    niobium’swelding by means of preset interlayer, and the microstructure and mechanical properties of the obtained welded joints were analyzed. The interlayers are pided into three groups.the first group is 50mm × 1mm × 2mm Cu / V interlayer, the size of the second group is 50mm × 1.5mm × 2mm Cu interlayer, the size of the third group is 50mm × 2mm × 2mm Cu interlayer.

The observation of weld appearance and VHX-900 optical microscope, SEM and EDS analysis were used to find that the first group of weld appearance is poor, many experiments show that the actual welding of V and Nb side of the fusion zone is poor leading to welding failure, the second and three sets of welds well formed. The weld joints are mainly columnar crystals and dendrites. Fe is not detected on the side near the niobium, that is, the interlayer controls the formation of the intermetallic compounds μ (Fe7Nb6) and ε (Fe2Nb) to a large extent. The Welded structure: austenitic steel / copper solid solution ε phase / Nb solid solution (plus 2mm copper’s weld joints have pure copper phase in the middle).

The tensile test concluded that welded joints of adding 1.5 mm copper and 2 mm copper interlayer were plastic fractures. Plus 1.5mm copper interlayer’s welding joints of the tensile fracture broken in the Nb base material, the tensile strength of more than 250MPa or more. And 2mm copper interlayer’s welding joints are broken in the interlayer of Cu (weld bead), the tensile strength being about 200MPa or so, which has reached a 260MPa, but still broken on the weld. The solid solution strengthening of Cu、Fe and Nb play very important roles in regulating the formation of brittle intermetallic compounds and improving the strength of welds.

Key words: Steel; Niobium; Laser welding; microstructure; interlayer; mechanical properties

目 录

第一章 绪论 1

1.1课题的背景和意义 1

1.2异种金属焊接性的分析