Surface carbides are occasionally found at the surface of austenitic stainless steels subjected to low-temperature carburizing surface treatments which are intended to induce an interstitially supersaturated surface layer. The crystallographic nature and chemical composition of the carbides can have a significant influence on the surface properties, especially on the corrosion resistance of the steel. However, their phase identification and chemical characterization via conventional methods (e.g. X-ray diffraction) is difficult due to their complex structure and metastable nature. In this paper, a combined metallographic and electron microscopic approach is applied to characterize the morphology and chemical composition of surface carbides found on AISI 304L and SS2343 after the same Kolsterising® treatment. Exclusively M5C2, also known as Hagg or χ-carbide was found at the surface of 304L, preferentially oriented along (111) deformation bands. In SS2343, however, χ-carbide coexisted with M7C3 (or ω-carbides) and M23C6. The carbides had preferential orientation relationships with the matrix, suggesting a carbide evolution during carburizing. All the carbides show elemental partitioning, with Cr enrichment and Ni depletion. A microstructure development sequence regarding precipitation and growth of surface carbides is proposed in this paper.

中文翻译：

---

低温渗碳奥氏体不锈钢表面碳化物的研究

表面碳化物偶尔会出现在经过低温渗碳表面处理的奥氏体不锈钢表面，这些表面处理旨在产生间隙过饱和表面层。碳化物的结晶性质和化学成分对表面性能，尤其是钢的耐腐蚀性能有显着影响。然而，由于其复杂的结构和亚稳态，它们很难通过传统方法（例如 X 射线衍射）进行相识别和化学表征。在本文中，应用金相和电子显微镜相结合的方法来表征经过相同 Kolsterising® 处理后在 AISI 304L 和 SS2343 上发现的表面碳化物的形态和化学成分。M5C2专属，也称为 Hagg 或 χ-carbide 发现于 304L 表面，优先沿（111）变形带取向。然而，在 SS2343 中，χ-碳化物与 M7C3（或 ω-碳化物）和 M23C6 共存。碳化物与基体具有优先取向关系，表明在渗碳过程中碳化物演变。所有的碳化物都显示出元素分配，Cr 富集和 Ni 贫乏。本文提出了关于表面碳化物析出和生长的微观结构发展顺序。所有的碳化物都显示出元素分配，Cr 富集和 Ni 贫乏。本文提出了关于表面碳化物析出和生长的微观结构发展顺序。所有的碳化物都显示出元素分配，Cr 富集和 Ni 贫乏。本文提出了关于表面碳化物析出和生长的微观结构发展顺序。