Al元素对20Cr25NiNb耐热钢热老化行为的影响研究  

Effect of Al Element on Thermal Aging Behavior of 20Cr25NiNb Heat-Resistant Steel

作　　者：舒茗 周钦[2] 李刚[1] 刘肖[1] 孙永铎[1] 赵可 肖军[1] Shu Ming;Zhou Qin;Li Gang;Liu Xiao;Sun Yongduo;Zhao Ke;Xiao Jun(Nuclear Power Institute of China,Chengdu,610213,China;Institute of Nuclear and New Energy Technology,Tsinghua University,Beijing,100084,China)

机构地区：[1]中国核动力研究设计院,成都610213 [2]清华大学核能与新能源技术研究院,北京100084

出　　处：《核动力工程》2023年第6期140-147,共8页Nuclear Power Engineering

基　　金：四川省自然科学基金(2022NSFSC1191);中国核动力研究设计院原创基金(YF9722003)。

摘　　要：为深入研究超临界气冷堆包壳材料的高温热老化行为以及Al元素对力学性能退化的影响,本文对添加Al元素和不含Al元素的2种20Cr25NiNb奥氏体耐热钢进行了750℃热老化试验,并开展了相应的微观组织分析和力学性能测试。研究发现,固溶态合金基体为奥氏体相,并含有少量微米级NbC。热老化后合金基体中析出了Laves相和σ相,而含Al钢中还观察到了NiAl相的析出。Al元素对20Cr25NiNb的热老化行为产生了双重影响,一方面,Al元素具有固溶强化效果,同时使得热老化后析出的Laves相尺寸更小、数密度更高,从而提升了高温拉伸强度;另一方面,蠕变裂纹主要沿晶界萌生并扩展,热老化后含Al合金中σ相体积分数更高,粗化更严重,严重降低了蠕变断裂寿命。不含Al合金晶界处析出的细小Laves相能有效阻止σ相生长,提升材料的蠕变性能。因此,本研究为超临界气冷堆包壳材料的成分优化提供了有力的支持。In order to comprehensively investigate the high-temperature thermal aging behavior of supercritical gas-cooled reactor(SCGCR)cladding materials and the impact of Al element on the degradation of material mechanical properties,the thermal aging experiments at 750℃were conducted on two types of 20Cr25NiNb austenitic heat-resistant steels:the alloy doped with Al and the Al-free one.Subsequently,corresponding microstructure analysis and mechanical property tests were carried out.The results revealed that the as-solutionized steels consisted of austenite along with a minor amount of micro-sized NbC carbides.After thermal aging,the matrix exhibited the precipitation of Laves andσphases,while the alloy containing Al additionally showed the emergence of NiAl precipitates.The presence of Al element induced dual effects on the thermal aging behavior of 20Cr25NiNb.On one hand,Al element exhibited a solid solution strengthening effect and led to a reduction in size and an increase in number density of Laves particles after thermal aging,thereby enhancing high-temperature tensile strength.On the other hand,creep cracks predominantly initiated and propagated along grain boundaries.After thermal aging,the volume fraction ofσphase in Al steel was higher and the coarsening was more serious,consequently resulting in a notable reduction in creep fracture life.The fine Laves phase precipitated at grain boundaries in the Al-free alloy effectively suppressed the growth ofσphase,thus enhancing creep resistance.As a conclusion,this study offers robust support for the optimization of cladding material composition for SCGCR applications.

关 键 词：20Cr25NiNb 热老化 高温强度 蠕变 AL元素 

分 类 号：TG14[一般工业技术—材料科学与工程] TL424[金属学及工艺—金属材料]