奥氏体不锈钢中添加Nb会造成铸态组织中出现大尺寸初生NbC，不利于后续二次NbC的析出控制，是制约含Nb奥氏体不锈钢发展的重要因素。本工作采用OM、SEM、TEM和单轴拉伸实验等研究了Nb含量和均质化处理对奥氏体不锈钢铸态组织和力学性能的影响。结果表明，Nb含量的变化改变了晶界初生NbC和M₂₃C₆碳化物的析出行为，未添加Nb的合金在晶界处析出了连续分布的M₂₃C₆碳化物；Nb含量为0.30% (质量分数)时，形成了初生NbC +奥氏体的共晶组织，但晶界仍析出M₂₃C₆碳化物；Nb含量进一步提高到0.90%可完全抑制M₂₃C₆析出，但共晶组织数量显著增加。随着Nb含量增加到0.90%，合金的屈服强度提高，这是由于M₂₃C₆析出被抑制而使Cr元素固溶强化、Nb元素固溶强化、晶粒细化带来的细晶强化以及二次NbC的沉淀强化作用提高。然而，初生NbC与奥氏体间较差的变形协调性易诱发微裂纹的萌生，裂纹沿网状分布的NbC快速扩展造成了沟壑状的脆性断裂，显著降低了合金延伸率。1250 ℃均质化处理后，初生NbC由长棒状转变为球状或椭球状，提高了NbC与奥氏体界面处微裂纹形成所需的临界应力，抑制了微裂纹的萌生；同时初生NbC由网状分布转变为断续分布，避免了微裂纹沿初生NbC的扩展，在基本不影响奥氏体不锈钢强度的基础上，大幅度提高了延伸率。

The corrosion and mechanical properties of austenitic stainless steels can be enhanced considerably by adding Nb. Newly developed Nb-stabilized austenitic stainless steels, such as 347HFG, 316Nb, TP310HCb, NF709, and HT-UPS, exemplify this advancement. The required Nb content varies across these steels. Prior research has indicated that in the as-cast microstructure of these steels, coarse and unevenly distributed primary NbC often forms, adversely affecting their mechanical and corrosion properties. Furthermore, this coarse primary NbC depletes the solid solution of Nb, which is counterproductive for fine secondary NbC precipitation. Notably, modifying the morphology and size of primary NbC through hot working and heat treatment is challenging. To enhance the microstructure and mechanical properties of Nb-stabilized austenitic stainless steel, this study investigated the effects of Nb content and homogenization treatment on these steels. The microstructure and tensile properties of cast austenitic stainless steel were analyzed using OM, SEM, TEM, and tensile test. The findings reveal that varying Nb content influences the precipitation of primary NbC and M₂₃C₆ carbides. In Nb-free steel, M₂₃C₆ carbides precipitate continuously at grain boundaries. This precipitation still occurs in steel with 0.30%Nb (mass fraction), alongside the formation of NbC + γ eutectic structures. Increasing Nb content to 0.90% can suppress M₂₃C₆ carbide precipitation, although the eutectic structures become more prevalent. A notable enhancement in yield strength accompanies an increase in Nb content to 0.90%. This improvement is attributed to the solid solution strengthening by Cr (due to suppressed M₂₃C₆ carbides) and Nb, grain boundary strengthening from refined grain sizes, and precipitation strengthening by secondary NbC. However, microcracks are easily nucleated at primary NbC/γ interface under plastic deformation, leading to rapid crack propagation along primary NbC networks and resulting in trench-like brittle fractures. This mechanism significantly reduces elongation. Post-homogenization treatment at 1250 ^oC alters the primary NbC morphology from rod-like to spherical/ellipsoid. This change increases the critical stress required for microcrack nucleation at NbC/γ interfaces, thereby inhibiting microcrack initiation. Additionally, the primary NbC networks transform from continuous to discontinuous distributions, impeding microcrack propagation. Consequently, this treatment significantly enhances elongation without compromising strength.