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金属学报  2016, Vol. 52 Issue (1): 17-24    DOI: 10.11900/0412.1961.2015.00180
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σ相在核电一回路主管道不锈钢中的脆化机理*
王永强1(),杨滨2,李娜3,林苏华3,孙立3
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
EMBRITTLEMENT OF σ PHASE IN STAINLESS STEEL FOR PRIMARY COOLANT PIPES OF NUCLEAR POWER PLANT
Yongqiang WANG1(),Bin YANG2,Na LI3,Suhua LIN3,Li SUN3
1 School of Materials Science and Engineering, Anhui University of Technology, Maanshan 243002, China
2 State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China
3 School of Metallurgical Engineering, Anhui University of Technology, Maanshan 243002, China
引用本文:

王永强,杨滨,李娜,林苏华,孙立. σ相在核电一回路主管道不锈钢中的脆化机理*[J]. 金属学报, 2016, 52(1): 17-24.
Yongqiang WANG, Bin YANG, Na LI, Suhua LIN, Li SUN. EMBRITTLEMENT OF σ PHASE IN STAINLESS STEEL FOR PRIMARY COOLANT PIPES OF NUCLEAR POWER PLANT[J]. Acta Metall Sin, 2016, 52(1): 17-24.

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摘要: 

研究了s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s相的脆化机理. 结果表明, s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s相为主的由铁素体共析分解生成的(s+g2)结构的硬度远高于奥氏体基体, 两者变形协调性差, (s+g2)结构阻碍位错滑移, 提高材料强度, 同时降低塑性; (s+g2)结构内部存在大量高能量s/g2a/s/g2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.

关键词 Z3CN20.09M不锈钢s韧性脆化机理    
Abstract

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, undesirable s phase 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 of s phase on mechanical properties of CASS, the mechanism of embrittlement was still lacking. In this work, the effect of s phase on toughness of Z3CN20.09M CASS was investigated, and the embrittlement mechanism of s phase 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 of s phases. The (s+g2) 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 (s+g2) structure and austenite incoordinate in aged specimens. The precipitation of s phase brought more s/g2 and a/s/g2 high energy non-coherent boundaries. These boundaries hindered dislocation movements and brought stress concentrations. So cracks initiated at the s/g2 or a/s/g2 boundaries preferentially and propagated rapidly when the aged specimen bearded impact stress. The much potential cracking sites (s/g2 and a/s/g2 boundaries) in the (s+g2) structure is the main reason of embrittlement of aged Z3CN20.09M CASS with low toughness.

Key wordsZ3CN20.09M stainless steel    s phase    toughness    embrittlement mechanism
收稿日期: 2015-03-31     
基金资助: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 和安徽省自然科学基金项目1508085QE102 资助
图1  原位拉伸试样示意图
图2  固溶态和750 ℃时效不同时间后的Z3CN20.09M不锈钢试样显微组织的SEM像
图3  750 ℃时效200 h后Z3CN20.09M试样显微组织的TEM像及SAED谱
图4  不同温度时效Z3CN20.09M不锈钢的冲击功和s相体积分数
图5  750 ℃时效不同时间Z3CN20.09M不锈钢的冲击功
图6  750 ℃时效不同时间前后Z3CN20.09M不锈钢试样的冲击断口形貌及EDS
图7  Z3CN20.09M不锈钢试样冲击断口附近纵切面观察部位示意图和750 ℃时效不同时间前后试样纵切面SEM像
图8  时效处理前后Z3CN20.09M不锈钢试样中铁素体和奥氏体的显微硬度
图9  时效处理前后Z3CN20.09M不锈钢试样中铁素体和奥氏体显微硬度测量点
图10  原位拉伸实验过程中750 ℃时效200 h 的Z3CN20.09M试样的SEM像
图11  750 ℃时效200 h前后Z3CN20.09M 试样原位拉伸断口附近的表面形貌
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