Abstract A 10 mm 316 L stainless steel plate was joined using multi-layer laser-MIG hybrid welding. Results showed that unmixed zone and “real” fusion zone (FZ) existed near the fusion line. Frequently met dendritic ferrite (δ) and newly encountered spherical nanoscale particles trapped in austenite (γ) were only observed in the latter region. Chemically, these particles turned out a SiO2 phase. From base metal to FZ, δ morphology was altered from originally linear to relatively diversely dendritic. Meantime, γ exhibited a converse manner where previously randomly oriented equiaxed was replaced by coarse, columnar and textured. Accordingly, a comparably high Schmidt factor in γ phase was obtained in FZ. Moreover, δ exhibited a relatively higher stress level than γ which presented a decrease in residual stress with grain coarsening in heat affected zone. In FZ, δ fraction displayed a dramatical increase with special BCC-FCC orientation relations established. Finally, tensile test and fracture appearance implied that FZ was exactly the weakest link of the whole welded joint in spite of a qualified strength achieved. In summary, lack in Σ3, largely increased δ fraction, high Schmidt factor in γ and especially being rich in SiO2 particles collectively led to the micro-void coalescence fracture in FZ.

中文翻译：

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316L激光-MIG复合焊接接头宏观变形机制的金相行为和晶体学特征

摘要 10 mm 316 L 不锈钢板采用多层激光-MIG 复合焊连接。结果表明，在融合线附近存在未混合区和“真实”融合区（FZ）。经常遇到的枝晶铁素体 (δ) 和新遇到的困在奥氏体 (γ) 中的球形纳米级颗粒仅在后一区域观察到。从化学上讲，这些颗粒变成了 SiO2 相。从贱金属到 FZ，δ 形貌从最初的线性变为相对多样化的枝晶。同时，γ 表现出相反的方式，以前随机取向的等轴被粗糙的、柱状的和有纹理的取代。因此，在 FZ 中获得了相对较高的 γ 相施密特因子。而且，δ 表现出比 γ 相对更高的应力水平，这表明残余应力随着热影响区晶粒粗化而降低。在 FZ 中，δ 分数显着增加，并建立了特殊的 BCC-FCC 取向关系。最后，拉伸试验和断裂外观表明，尽管达到了合格的强度，FZ 恰恰是整个焊接接头中最薄弱的环节。综上所述，Σ3 的缺乏、δ 分数的大幅增加、γ 的高施密特因子以及特别是富含 SiO2 颗粒共同导致了 FZ 中的微孔合并断裂。拉伸试验和断裂外观表明，尽管达到了合格的强度，FZ 恰恰是整个焊接接头中最薄弱的环节。综上所述，Σ3 的缺乏、δ 分数的大幅增加、γ 的高施密特因子以及特别是富含 SiO2 颗粒共同导致了 FZ 中的微孔合并断裂。拉伸试验和断裂外观表明，尽管达到了合格的强度，FZ 恰恰是整个焊接接头中最薄弱的环节。综上所述，Σ3 的缺乏、δ 分数的大幅增加、γ 的高施密特因子以及特别是富含 SiO2 颗粒共同导致了 FZ 中的微孔合并断裂。