Welding AISI 304 stainless steel is challenging, especially as fusion-based welding processes (such as arc welding) severely undermine the material's corrosion resistance due to sensitization. Solid-state friction stir welding is one of the most suitable alternatives. Friction stir welding of high-strength high-softening materials such as AISI 304 is difficult mainly because of the non-availability of affordable tools and tool life. In this study, AISI 304 stainless steel was successfully butt-welded by friction stir welding. The experiments were performed using Taguchi's L27 orthogonal array. Shoulder diameter, tool r/min, and traverse speed were selected as the most influential welding parameters. A Tungsten Carbide (WC) tool was employed with a tapered pin profile. Defect-free joints were fabricated successfully for all the welding conditions. Microstructural examinations using optical microscopy and scanning electron microscopy revealed significant grain refinement in the stir zone and the presence of distinct structural features such as stepped, dual, and ditch in various characteristics zones. The presence of precipitates was also observed in samples and was confirmed via energy-dispersive X-ray spectroscopy analysis. The in-process traverse force was measured by a special arrangement of force measuring units attached to the work fixture. The traverse force data were analyzed and optimized. The results of an analysis of variance reveal that the traverse speed was the most important parameter, followed by tool r/min, interaction between the tool shoulder diameter and traverse speed, interaction between the tool shoulder diameter and tool r/min, and, finally, the tool r/min.

中文翻译：

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奥氏体不锈钢搅拌摩擦焊过程中的显微组织表征和过程中的横向力

焊接 AISI 304 不锈钢具有挑战性，特别是因为基于熔合的焊接工艺（例如电弧焊）由于敏化而严重破坏了材料的耐腐蚀性。固态搅拌摩擦焊是最合适的替代方法之一。高强度高软化材料（如 AISI 304）的搅拌摩擦焊接很困难，主要是因为没有负担得起的工具和工具寿命。在本研究中，AISI 304 不锈钢通过搅拌摩擦焊成功对接焊。使用 Taguchi 的 L27 正交阵列进行实验。台肩直径、刀具转数/分钟和横移速度被选为最有影响的焊接参数。采用具有锥形销轮廓的碳化钨 (WC) 工具。在所有焊接条件下都成功制造了无缺陷接头。使用光学显微镜和扫描电子显微镜进行的微观结构检查显示，搅拌区的晶粒显着细化，并且在各种特征区中存在明显的结构特征，如阶梯、双和沟。在样品中也观察到沉淀物的存在，并通过能量色散 X 射线光谱分析证实。过程中的横向力是通过连接到工作夹具上的特殊测力单元来测量的。对横向力数据进行了分析和优化。方差分析结果表明，移动速度是最重要的参数，其次是刀具转数/分钟、刀肩直径和移动速度之间的相互作用，