Austenitic stainless steels such as 25Cr-35Ni-Nb, HP-Nb alloys are commonly used in high-temperature applications above 850 °C. The HP-Nb alloys are used in the as-cast condition and exhibit good creep properties due to chromium and niobium eutectic carbide strengthening. The size, morphology and distribution of these carbides are related to the nominal composition and solidification conditions, which result in differences in mechanical properties. Although previous work has provided qualitative relations between composition and microstructure, there is insufficient quantitative information regarding the influence of composition on the solidification behavior and resultant microstructure. Therefore, the objective of this study is to improve the understanding of the solidification of HP-Nb alloys through the development of a quantitative model. A systematic matrix of 12 alloys was characterized via quantitative image analysis, differential thermal analysis and electron microprobe analysis. A quantitative solute redistribution model was developed using solidification equations and an experimentally derived γ-C-Cr-Nb, pseudo-quaternary liquidus projection. The quantitative model was validated for three experimental alloys and two industrial alloys, with good agreement between the measured and predicted percent total eutectic. Experimental results indicate that the volume fraction of chromium carbides are primarily controlled by carbon additions and niobium carbides are primarily controlled by niobium additions. The results of this work show the novel development and application of a pseudo-quaternary liquidus projection and improves the understanding of the relationship between composition and the solidification of austenitic stainless steels.

奥氏体不锈钢如 25Cr-35Ni-Nb、HP-Nb 合金常用于 850°C 以上的高温应用。HP-Nb 合金在铸态条件下使用，并且由于铬和铌共晶碳化物强化而表现出良好的蠕变性能。这些碳化物的尺寸、形态和分布与标称成分和凝固条件有关，从而导致机械性能的差异。尽管以前的工作已经提供了成分和微观结构之间的定性关系，但关于成分对凝固行为和所得微观结构的影响的定量信息不足。因此，本研究的目的是通过开发定量模型来提高对 HP-Nb 合金凝固的理解。通过定量图像分析、差热分析和电子探针分析。使用凝固方程和实验得出的γ开发了定量溶质再分布模型-C-Cr-Nb，拟四元液相线投影。对三种实验合金和两种工业合金验证了定量模型，测量的和预测的总共晶百分比之间具有良好的一致性。实验结果表明，碳化铬的体积分数主要受碳添加量控制，碳化铌主要受铌添加量控制。这项工作的结果显示了伪四元液相线投影的新发展和应用，并提高了对奥氏体不锈钢成分与凝固之间关系的理解。