Supermartensitic stainless steels (SMSSs) are commonly employed as pipes and mandrels in off-shore oil and gas production. These materials are known to exhibit higher corrosion resistance than conventional martensitic stainless steels and also present a lower installation cost than duplex/superduplex steels and Ni alloys. After the occurrence of a certain number of failures of mandrels, manufacturers purchased samples of pipes and forged fittings in order to promote several stress corrosion tests. In this work, the specimens obtained from a grade UNS S41426 pipe steel failed at the four point test under milder conditions than the limit of NACE 0175/ISO 15156 standard. The metallurgical analysis revealed that the pipe purchased by a specific producer has been carburized at high temperature, probably as an attempt to improve superficial hardness and wear resistance. However, it resulted in an inadequate microstructure with sensitized austenitic grains, without significant increase of superficial hardness. Consequently, the material suffered severe corrosion attack during the four point tests, indicating high chances of failure at service conditions.

超马氏体不锈钢（SMSS）通常用作海上石油和天然气生产中的管道和心轴。已知这些材料显示出比常规马氏体不锈钢更高的耐腐蚀性，并且还比双相/超双相钢和Ni合金具有更低的安装成本。在发生一定数量的心轴故障后，制造商购买了管道和锻造配件的样品，以促进多次应力腐蚀测试。在这项工作中，从UNS S41426级钢管获得的样品在比NACE 0175 / ISO 15156标准的极限更温和的条件下在四点测试中失败。冶金分析表明，特定生产商购买的管道已在高温下进行了渗碳处理，可能是为了改善表面硬度和耐磨性。然而，这导致了具有敏化奥氏体晶粒的微观结构不足，而表面硬度没有显着提高。因此，该材料在四点测试中遭受了严重的腐蚀侵蚀，表明在使用条件下极有可能发生故障。