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Characterization of the interpass microstructure in low alloy steel/Alloy 625 HW-GTAW narrow groove welds
Materials Characterization ( IF 4.7 ) Pub Date : 2020-12-01 , DOI: 10.1016/j.matchar.2020.110638
Ryan Buntain , Boian Alexandrov , Gopal Viswanathan

Abstract A dissimilar weld between a low alloy steel (LAS) butter weld joined to a F65 steel pipe using a narrow groove hot wire gas tungsten arc welding (HW-GTAW) procedure with Alloy 625 filler metal was investigated. The weld interpass microstructure is comprised of large swirls formed by a macrosegregation mechanism involving partial, non-uniform mixing of liquid base metal with the lower melting temperature weld pool, followed by fast solidification. This mechanism produces steep gradients in composition and solidification behavior. The resulting swirls are composed of alternating iron-rich peninsulas and partially mixed zones (PMXZ) that are surrounded by planar and cellular zones exhibiting multiple solidification directions. Large austenitic grains, encompassing planar, cellular, and dendritic morphologies, nucleate off peninsulas in direct contact with the weld pool. The highest hardness was found in nickel and chromium rich PMXZs that exhibited a lath martensite microstructure. In the event of exposure to hydrogen containing environments, the PMXZs could serve as nucleation sites for hydrogen assisted cracking.

中文翻译:

低合金钢/合金 625 HW-GTAW 窄坡口焊缝中层间微观结构的表征

摘要 研究了使用窄槽热丝钨极氩弧焊 (HW-GTAW) 工艺与合金 625 填充金属连接到 F65 钢管的低合金钢 (LAS) 黄油焊之间的异种焊缝。焊缝层间微观结构由宏观偏析机制形成的大漩涡组成,涉及液态母材与较低熔化温度的焊池的部分、非均匀混合,然后快速凝固。这种机制在成分和凝固行为方面产生陡峭的梯度。产生的漩涡由交替的富含铁的半岛和部分混合区 (PMXZ) 组成,这些区被具有多个凝固方向的平面和蜂窝区包围。大奥氏体晶粒,包括平面、细胞和树枝状形态,在与焊池直接接触的半岛上成核。在表现出板条马氏体微观结构的富含镍和铬的 PMXZ 中发现了最高的硬度。在暴露于含氢环境的情况下,PMXZ 可作为氢辅助裂解的成核位点。
更新日期:2020-12-01
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