Offshore seawater systems are commonly manufactured using a monolithic copper–nickel alloy (90%Cu10%Ni). However, because of the high cost of this material, they have been replaced in some Brazilian oil and gas platforms by C–Mn steel pipes clad with a Ni–Cu alloy (70%Ni30%Cu, Monel 400®). Therefore, considering the complex transition zone (TZ) in dissimilar weldments and its influence on the performance of the clad component, the present work aims to characterize the TZ of an API 5L X65 steel pipe clad with a 70%Ni30%Cu alloy by hot-wire gas tungsten arc welding (HW-GTAW). The TZ was evaluated using optical microscopy, scanning electron microscopy, electron backscatter diffraction, Vickers microhardness measurements, and bending tests. It exhibited beach, peninsula, and island macrosegregation morphologies with martensite (high hardness) and type II grain boundaries as well as an abrupt chemical composition gradient and Zone M. Moreover, the cladding solidified epitaxially, even though the cladding and the substrate had different crystal lattices. A solidification grain boundary crack, observed in the pipe end, nucleated in the substrate and propagated through the beach macrosegregation and posteriorly along the cladding grain boundaries. Despite this crack, the API 5L X65 steel pipe clad with 70%Ni30%Cu was approved according to ISO 15614 Part 7 and is a potential candidate for seawater systems.

海上海水系统通常使用整体式镍铜合金（90％Cu10％Ni）制造。但是，由于这种材料的高成本，在一些巴西的石油和天然气平台中，它们已被包覆有Ni-Cu合金（70％Ni30％Cu，Monel400®）的C-Mn钢管所取代。因此，考虑到异种焊件中的复杂过渡区（TZ）及其对复合材料性能的影响，本工作旨在通过热分析表征70％Ni30％Cu合金的API 5L X65钢管复合材料的TZ丝钨极气体保护焊（HW-GTAW）。使用光学显微镜，扫描电子显微镜，电子背散射衍射，维氏显微硬度测量和弯曲测试评估TZ。它展示了沙滩，半岛，以及马氏体（高硬度）和II型晶界以及突然的化学成分梯度和M区的岛宏观偏析形态。此外，即使包层和基体具有不同的晶格，包层也外延凝固。在管端观察到凝固晶界裂纹，在基体中成核，并通过海滩宏观偏析并沿覆层晶界向后传播。尽管存在裂纹，API 70LNi30％Cu包层的API 5L X65钢管仍通过了ISO 15614第7部分的批准，是海水系统的潜在候选者。在管端观察到凝固晶界裂纹，在基体中成核，并通过海滩宏观偏析并沿覆层晶界向后传播。尽管存在裂纹，API 70LNi30％Cu包层的API 5L X65钢管仍通过了ISO 15614第7部分的批准，是海水系统的潜在候选者。在管端观察到凝固晶界裂纹，在基体中成核，并通过海滩宏观偏析并沿覆层晶界向后传播。尽管存在裂纹，API 70LNi30％Cu包层的API 5L X65钢管仍通过了ISO 15614第7部分的批准，是海水系统的潜在候选者。