利用热力学计算软件JMatPro分析了钍基熔盐堆用Ni-Cr-Mo系高温合金GH3535相析出的热力学及动力学特征,研究了不同热处理制度对冷轧态GH3535合金无缝管的晶粒尺寸及其均匀性、碳化物析出特征、硬度、拉伸性能等的影响规律,观察了不同热处理制度下合金拉伸断口的微观形貌,分析了GH3535合金的拉伸断裂机制. 结果表明:在900~1500℃之间,GH3535合金的平衡析出相为富Mo的M6C型碳化物,M6C相在固液两相区时便已经开始形成,M6C相析出所对应的鼻尖温度为1200℃;固溶温度低于1200℃时,合金晶粒尺寸缓慢长大,当固溶温度提高到1230℃,晶粒出现快速长大,平均晶粒尺寸达到160 μm;1180℃保温10 min,合金晶粒尺寸的均匀性较好. 随着固溶温度升高,合金强度降低、延伸率增加,GH3535合金的拉伸断裂机制为微孔聚集型.
In recent years, the development of next-generation nuclear reactors with enhanced requirements for the safe and reliable production of nuclear energy has been attracting increasing attention. The thorium molten salt reactor (TMSR) has been regarded as the most promising prospective next-generation nuclear reactor because of its high security, desirable online refueling properties, minimization of nuclear waste, nuclear non-proliferation, etc. The structural materials for molten salt reactors should exhibit high temperature resistance and good corrosion and neutron irradiation resistance. The Ni-Cr-Mo-based superalloy GH3535 is the preferred material for TMSR applications because of its superior corrosion resistance and good mechanical properties. The Mo content of GH3535 is 15%~18% (mass fraction), which leads to the precipitation of a large amount of Mo-enriched M6C carbides in the matrix. Numerous studies have shown that the precipitation of these carbides directly affects the grain size and mechanical properties of GH3535 alloy. In this study, the effects of heat treatment on the grain size, carbide distribution, and mechanical properties of GH3535 alloy were investigated by cold-rolled-pipe tests. To provide the experimental and theoretical basis for applying heat treatment to control the properties of GH3535 alloy, the thermodynamic and kinetics characteristics of GH3535 were calculated using the JMatPro simulation software. The influence of heat treatments on the size and homogeneity of grains, the precipitation character of carbides, and the mechanical properties of the alloy were investigated. The results show that the equilibrium precipitate of the GH3535 at temperatures between 900℃ and 1500℃ is a Mo-rich carbide of M6C type and that the initial precipitation temperature of this M6C-type carbide is in the liquid-solid phase range. The grains grow slowly when the solution temperature is less than 1200℃. When the solution temperature is increased to 1230℃, the grains grow quickly to an average size of 160 μm; the grains are homogeneous when the temperature is maintained at 1180℃ for 10 min. Tensile tests show that a higher solution temperature decreases the strength and increases the elongation. The tensile fracture mechanism of GH3535 alloy is microporous aggregation.