Abstract Four metal powder flux-cored wires with added nickel (Ni) were designed to systematically investigate how Ni influences the microstructure and toughness in low-carbon bainitic weld metals (WMs). The microstructure was safely predicted by utilizing reasonable welding craft parameters (i.e., appropriate heat input and proper interpass temperature). Microstructural characterization, crystallographic analysis, microhardness mapping, fracture microparameter measurement, and finite element method calculations were all taken into account. This work showed that more martensite transformation occurs with increasing Ni and that the ductile-brittle transition temperature drops with added Ni. The boundaries with low-angle misorientation (i.e., less than 4°) enhance microhardness and the optimal inclusion size is in the range of 0.3–0.45 μm, thus revealing the reasons for the resulting microhardness and toughness variations. In addition, the high-angle grain boundaries in close-packed plane packets effectually prevent cracks. From a practical perspective, 4 wt.% Ni could be the best design for welding wires in the present work. This work confirmed many of the results found in recently published literature. These results provide a reference for the composition design of welding wires and the processing method of WMs.

中文翻译：

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低碳焊接对接接头中添加镍的显微组织演变和力学性能发展

摘要 设计了四种添加镍 (Ni) 的金属粉末药芯焊丝，以系统地研究镍如何影响低碳贝氏体焊缝金属 (WMs) 的组织和韧性。通过使用合理的焊接工艺参数（即适当的热输入和适当的层间温度）可以安全地预测微观结构。微观结构表征、晶体学分析、显微硬度映射、断裂微参数测量和有限元方法计算都被考虑在内。这项工作表明，随着 Ni 的增加，发生更多的马氏体转变，并且随着 Ni 的加入，韧脆转变温度下降。低角度取向差（即小于 4°）的边界提高显微硬度，最佳夹杂物尺寸在 0.3-0.45 μm 范围内，因此揭示了导致显微硬度和韧性变化的原因。此外，紧密堆积的平面包中的大角度晶界有效地防止了裂纹。从实用的角度来看，4 wt.% Ni 可能是目前工作中焊丝的最佳设计。这项工作证实了最近发表的文献中发现的许多结果。这些结果为焊丝的成分设计和WMs的加工方法提供了参考。