Abstract In gas tungsten arc welding (GTAW), columnar grains typically grow from the fusion line of a weld to its centerline because of high temperature gradient and small growth rate. This columnar grain often causes premature failure during bending or expansion in the center of the fusion zone. Equiaxed grains, on the other hand, reduce the occurrence of cracks and improve the ductility, strength, and toughness in the fusion zone. Microstructural solidification has a significant effect on the mechanical properties; the columnar-to-equiaxed grain transition (CET) is one factor that significantly improves fusion zone mechanical properties. During GTAW, a thermal gradient occurs on a molten pool owing to the uneven mixing of the elements or the unequal compositions of the base materials, leading to a non-uniform surface tension. This is called the Marangoni effect, which creates a flow inside the molten metal and affects the overall weld shape. The Marangoni effect is associated with a coefficient called the surface tension gradient or the thermal gradient of surface tension that affects the direction of molten metal flow. The content of oxygen and flux affect the surface tension gradient. If the content of oxygen and flux are high, the surface tension gradient becomes positive, with a narrow and deep-penetrating pool. In this study, various experiments and a numerical simulation were performed to analyze the weld pool behavior and CET in GTA welding of ferritic stainless steels with aluminum contents of 100 and 300 ppm. In the experiment, 300 ppm of aluminum was observed to have a wider bead width than that observed for the 100-ppm sample; further, the growth of equiaxed grains in the centerline was promoted. In the numerical simulation, it was confirmed that when the aluminum content was 300 ppm, the outward flow occurring in the arc center formed a wide and shallow penetration. Furthermore, it was revealed that aluminum combines with oxygen to form aluminum oxide, thereby reducing the oxygen content. Therefore, as the aluminum content increased, the surface tension gradient was observed to become negative and affect CET.

中文翻译：

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不同铝含量铁素体不锈钢钨极气体保护焊熔池对流和柱状等轴晶转变行为

摘要 在钨极气体保护焊（GTAW）中，柱状晶粒通常从焊缝的熔合线向其中心线生长，因为温度梯度大，生长速率小。这种柱状晶粒经常在熔合区中心弯曲或膨胀过程中导致过早失效。另一方面，等轴晶可减少裂纹的发生并提高熔合区的延展性、强度和韧性。显微组织凝固对力学性能有显着影响；柱状到等轴晶粒转变 (CET) 是显着改善熔合区机械性能的因素之一。在 GTAW 过程中，由于元素混合不均匀或基材成分不均匀，熔池上会出现热梯度，导致表面张力不均匀。这称为 Marangoni 效应，它在熔融金属内部产生流动并影响整体焊缝形状。Marangoni 效应与称为表面张力梯度或影响熔融金属流动方向的表面张力热梯度的系数相关。氧含量和通量会影响表面张力梯度。如果氧和通量的含量高，表面张力梯度变为正，池子窄而深。在这项研究中，进行了各种实验和数值模拟，以分析铝含量为 100 和 300 ppm 的铁素体不锈钢 GTA 焊接中的熔池行为和 CET。在实验中，观察到 300 ppm 的铝比 100 ppm 的样品具有更宽的焊缝宽度；更多，促进了中心线等轴晶粒的生长。在数值模拟中证实，当铝含量为 300 ppm 时，发生在弧中心的向外流动形成了宽而浅的穿透。此外，发现铝与氧结合形成氧化铝，从而降低氧含量。因此，随着铝含量的增加，观察到表面张力梯度变为负值并影响 CET。