σ相在核电一回路主管道不锈钢中的脆化机理  

EMBRITTLEMENT OF σ PHASE IN STAINLESS STEEL FOR PRIMARY COOLANT PIPES OF NUCLEAR POWER PLANT

作　　者：王永强[1] 杨滨[2] 李娜[3] 林苏华[3] 孙立[3] 

机构地区：[1]安徽工业大学材料科学与工程学院,马鞍山243002 [2]北京科技大学新金属材料国家重点实验室,北京100083 [3]安徽工业大学冶金工程学院,马鞍山243002

出　　处：《金属学报》2016年第1期17-24,共8页Acta Metallurgica Sinica

基　　金：国家自然科学基金项目51501001;国家高技术研究发展计划项目2012AA03A507;安徽省自然科学基金项目1508085QE102资助~~

摘　　要：研究了σ相对核电一回路主管道Z3CN20.09M不锈钢冲击韧性的影响,利用原位拉伸、显微硬度、断口形貌等手段分析了σ相的脆化机理.结果表明,σ相显著降低一回路主管道不锈钢的冲击韧性,时效处理Z3CN20.09M不锈钢中以σ相为主的由铁素体共析分解生成的(σ+γ2)结构的硬度远高于奥氏体基体,两者变形协调性差,(σ +γ2)结构阻碍位错滑移,提高材料强度,同时降低塑性;(σ+γ2)结构内部存在大量高能量σ/γ2和a/σ/γ2非共格界面,变形时应力在此处集中,成为潜在裂纹源,易萌生裂纹.高应变速率下,裂纹迅速在其内部产生、扩展是材料韧性降低、变脆的本质原因.Cast austenite stainless steel（CASS） possesses excellent mechanical properties, good workability and high resistance to localized corrosion in chloride environments due to the dual phase microstructure in which the island a-ferrite phase distributes in the g-austenite matrix. So they are widely used in the primary coolant pipes of nuclear power plants. However, undesirableσphase can precipitate in these steels when they are welded or heat treated and it severely decreases the toughness of stainless steels. Although some works have been done to investigate the effect ofσphase on mechanical properties of CASS, the mechanism of embrittlement was still lacking. In this work, the effect ofσphase on toughness of Z3CN20.09 M CASS was investigated, and the embrittlement mechanism ofσphase in CASS was discussed by using in situ tensile test, microhardness technology and fracture analysis. It was found that the impact energy of specimens aged at 750 ℃ decreased severely due to the presence ofσphases. The（s＋γ2） structure formed by the eutectoid decomposition of a phase is very hard and its hardness is much higher than that of austenite. This makes the deformation between（σ＋γ2） structure and austenite incoordinate in aged specimens. The precipitation ofσphase brought more σ/γ2 and a/σ/γ2 high energy non-coherent boundaries.These boundaries hindered dislocation movements and brought stress concentrations. So cracks initiated at the σ/γ2 or a/s/γ2 boundaries preferentially and propagated rapidly when the aged specimen bearded impact stress. The much potential cracking sites（s/γ2 and a/σ/γ2boundaries） in the（σ ＋ γ2） structure is the main reason of embrittlement of aged Z3CN20.09 M CASS with low toughness.

关 键 词：Z3CN20.09M不锈钢 Σ相 韧性 脆化机理 

分 类 号：TG142.71[一般工业技术—材料科学与工程]