Cast austenitic stainless steels (CASS) are excellent alloys because they combine high corrosion resistance with high strength and toughness. However, they are susceptible to embrittlement upon long-term thermal aging at elevated temperatures. Thus, the microstructural evolution pathways during thermal aging need to be understood to predict and potentially prevent embrittlement. Atom probe tomography was used to identify and quantify the microstructural evolution pathways of the δ-ferrite in different CASS alloys aged for up to 10,000 h at temperatures between 290 °C and 400 °C. The four steels – CF8, CF8M, CF3, and CF3M − which vary by Mo and C concentration, each experienced spinodal decomposition of the δ-ferrite, and precipitation of G-phase clusters and Cu clusters attached to the G-phase. There were large differences in the extent of these features due to their Mo and C concentration. Using radial distribution function analysis, the interactions of constituent elements was found to determine the evolution of these features, with Mo and C specifically influencing the movement of Cr, Ni, Si, Mn, and Cu atoms due to their relative miscibility with these elements. The results will help inform predictive models for the use of duplex stainless steels for extended operation at high temperatures.

铸造奥氏体不锈钢（CASS）是出色的合金，因为它们兼具高耐腐蚀性，高强度和韧性。但是，它们在高温下长期热老化后易脆化。因此，需要了解热老化过程中的微观结构演化途径，以预测并潜在地防止脆化。原子探针层析成像用于鉴定和量化290°C至400°C的温度下长达10,000 h时效的不同CASS合金中δ铁素体的微观组织演化途径。四种钢-CF8，CF8M，CF3和CF3M-随Mo和C浓度的变化而变化，每种钢都经历了δ铁素体的旋节线分解，以及G相团簇和Cu团簇附着在G相上的析出。由于它们的Mo和C浓度，这些特征的程度存在很大差异。使用径向分布函数分析，发现构成元素的相互作用决定了这些特征的演变，而Mo和C由于与这些元素的相对混溶性而特别影响Cr，Ni，Si，Mn和Cu原子的运动。结果将有助于为使用双相不锈钢在高温下长时间运行提供预测模型。