强碳化物形成元素与碳的配比关系和稳定化处理对310S奥氏体不锈钢析出相行为的影响
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摘要
高Cr/Ni含量的奥氏体不锈钢由于具有优异的综合性能而有望被用作超临界水冷堆的燃料包壳材料,但是该类奥氏体不锈钢存在组织稳定性差的问题,即在873～1 123 K温度下长期时效后晶界上会析出大量的Cr_(23)C_6和σ相,从而导致材料的脆化和晶间腐蚀。为了提高该类不锈钢的高温组织稳定性,本工作系统研究了强碳化物形成元素M(M=Nb、Ti、Ta和Zr)与C的配比关系以及稳定化处理工艺对310S高温下析出相行为的影响。设计合金采用铜模快冷技术吸铸成直径为6 mm的棒材,并对其进行1 473 K/0.5 h固溶处理、1 173 K/0.5 h稳定化处理(部分样品)、1 073 K/24 h时效处理。分别采用OM、SEM-EDS、EPMA和TEM等手段对合金不同热处理状态的析出相进行表征。研究结果表明,M的加入均能促进MC粒子的析出,促进效果为Ta>Nb/Ti>Zr,且M与C的最佳比例关系为1/1(原子比);当M与C的原子比为2/1时会促进脆性相σ析出,而当M与C的原子比为1/1时,1 073 K/24 h时效后晶界上只有Cr_(23)C_6析出。稳定化处理能使MC优先析出,可减少时效过程中粗大Cr_(23)C_6的析出量。本工作为超临界水冷堆燃料包壳材料的开发提供了有效的基础数据支撑,并为下一步的工作指明了方向。
High Cr/Ni 310 S-type austenitic stainless steels(ASSs) exhibit good comprehensive properties of creep-, corrosion-and oxidation-resis-tances, as well as moderate neutron irradiation-resistance, which are potential as fuel-cladding candidate materials applied into the super-critical water reactors(SCWRs). However, one underlying issue for this kind of ASSs is their microstructural stability, i.e., a large amount of coarse Cr_(23)C_6 and σ are precipitated on grain boundaries(GBs) after a long-term aging at 873—1 123 K, as a result of the embrittlement and intergranular corrosion of materials. In order to improve their microstructural stability at high temperatures, the present work investigated systematically the effects of the ratios of strong carbide-forming elements M(M=Nb, Ti, Ta, and Zr) to C(in atomic percent at%), and the stabilization treatment on the precipitation behaviors of 310 S ASS. The designed alloy rods were solid-solutioned at 1 473 K for 0.5 h plus water quenched, stabilized at 1 173 K for 0.5 h, and then aged at 1 073 K for 24 h. The microstructure and precipitated phases at different heat-treatment states were characterized with OM, SEM-EDS, EPMA and TEM, respectively. It was found that the addition of M favors to the precipitation of MC-type carbides effectively. A high ratio of M to C(2/1) can accelerate the formation of brittle σ phase, in contrast, only Cr_(23)C_6 precipitates exist on GBs after 1 073 K/24 h aging in alloys with M/C=1/1. In addition, the Cr_(23)C_6 could be inhibited effectively by stabilization heat-treatment. This work provides effective basic data support for the development of fuel cladding materials for SCWRs, and point the way for the further research.
High Cr/Ni 310 S-type austenitic stainless steels(ASSs) exhibit good comprehensive properties of creep-, corrosion-and oxidation-resis-tances, as well as moderate neutron irradiation-resistance, which are potential as fuel-cladding candidate materials applied into the super-critical water reactors(SCWRs). However, one underlying issue for this kind of ASSs is their microstructural stability, i.e., a large amount of coarse Cr_(23)C_6 and σ are precipitated on grain boundaries(GBs) after a long-term aging at 873—1 123 K, as a result of the embrittlement and intergranular corrosion of materials. In order to improve their microstructural stability at high temperatures, the present work investigated systematically the effects of the ratios of strong carbide-forming elements M(M=Nb, Ti, Ta, and Zr) to C(in atomic percent at%), and the stabilization treatment on the precipitation behaviors of 310 S ASS. The designed alloy rods were solid-solutioned at 1 473 K for 0.5 h plus water quenched, stabilized at 1 173 K for 0.5 h, and then aged at 1 073 K for 24 h. The microstructure and precipitated phases at different heat-treatment states were characterized with OM, SEM-EDS, EPMA and TEM, respectively. It was found that the addition of M favors to the precipitation of MC-type carbides effectively. A high ratio of M to C(2/1) can accelerate the formation of brittle σ phase, in contrast, only Cr_(23)C_6 precipitates exist on GBs after 1 073 K/24 h aging in alloys with M/C=1/1. In addition, the Cr_(23)C_6 could be inhibited effectively by stabilization heat-treatment. This work provides effective basic data support for the development of fuel cladding materials for SCWRs, and point the way for the further research.
引文
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4 Azevedo C R F.Engineering Failure Analysis,2011,18,1943.
5 Zhang L F,Bao Y C,Tang R.Nuclear Engineering Design,2012,249,180.
6 Sun C,Hui R,Qu W,et al.Corrosion Science,2009,51,2508.
7 Was G S,Ampornrat P,Gupta G,et al.Journal of Nuclear Materials,2007,371,176.
8 Luo X,Tang R,Long C,et al.Nuclear Engineering Technology,2008,40,147.
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12 Zinkle S J,Was G.Acta Materialia,2013,61,735.
13 Wang Y Q,Yang B,Li N,et al.Acta Metallurgica Sinica,2016,52(1),17(in Chinese).王永强,杨滨,李娜,等.金属学报,2016,52(1),17.
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21 Pardo A,Merino M C,Coy A E,et al.Acta Materialia,2007,55,2239.
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25 Zhou D Q,Zhao W X,Mao H H,et al.Materials Science and Enginee-ring A,2015,622,91.
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31 H?ttestrand M,Larsson P,Chai G,et al.Materials Science and Engineering A,2009,499,489.
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