通过观察新型奥氏体耐热不锈钢(AFA不锈钢)试样在不同条件下再结晶的金相组织, 研究了AFA不锈钢再结晶过程中的组织演变行为. 结果表明, 冷轧20%的AFA不锈钢试样在1473 K等温2 h以上才能完全再结晶; 完全再结晶的试样在1023 K, 应变速率为6.4×10^-7 s^-1条件下拉伸时, 稳态流变强度保持在130 MPa左右, 并且具有良好的塑性变形能力和明显的加工硬化效果. 但若不能完全再结晶, 在相同实验条件下试样具有较高的强度(150 MPa), 但是塑性变差. AFA不锈钢再结晶晶粒长大过程受到NbC相析出的影响, 其晶粒长大指数由理想晶粒长大的2变为3, 表观激活能为234.7 kJ/mol, 与Nb在奥氏体钢中沿晶界扩散的激活能吻合.

Energy crisis and global warming demand development of high-performance structural materials to improve energy efficiency. For efficient energy conversion, the operating temperature and pressure of a heat engine used in boiler/steam turbine power plants should be as high as possible and materials used for the engine components must be able to withstand the high operating temperature. As such, next-generation structural materials simultaneously possessing higher creep strength and larger oxidation-resistance at elevated temperatures than those currently used are required. The conventional austenitic stainless steels, which rely on the formation of a tenacious Cr₂O₃ scale, would lose its protection capability at temperatures above 923 K, in particular in the presence of sulfur and water vapor. The alumina-forming austenitic (AFA) stainless steels are a relatively new class of dispersion-strengthened austenitic steels which showed superior oxidation-resistance to conventional stainless steels due to formation of the Al₂O₃-based protective scale at high temperatures. Recently, research focuses in this field have been mainly placed on high temperature oxidation-resistance, while little attention was paid to the mechanical property of these steels, particularly at elevated temperatures. In order to fully understand the deformation mechanisms at high temperatures, the recrystallization behavior in a typical AFA stainless steel under different conditions, including different annealing temperatures and durations, were investigated. The high-temperature mechanical properties of the AFA stainless steel samples heat-treated under different conditions were also studied. The sample was fully recrystallized upon heat treatment at 1473 K for at least 2 h and showed tensile strength about 130 MPa when tested at 1023 K with a strain rate 6.4×10^-7 s^-1. The specimen was partially recrystallized upon heat treatment at 1373 K for 0.5 h and exhibited a higher tensile strength of 150 MPa with decreased plasticity when tested under the same condition. Further investigation shows that the grain growth was influenced by the precipitation of NbC. The grain growth exponent, n, was determined to be 3 and the apparent activation energy for grain growth is 234.7 kJ/mol, which is consistent with that of the Nb diffusion along the grain boundary in the austenite.