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金属学报  2018, Vol. 54 Issue (11): 1705-1714    DOI: 10.11900/0412.1961.2018.00361
  力学性能 本期目录 | 过刊浏览 |
新型25Cr-20Ni奥氏体耐热不锈钢750 ℃持久实验过程中析出相演变
胡国栋1,2, 王培1, 李殿中1(), 李依依1
1 中国科学院金属研究所 沈阳 110016
2 中国科学技术大学材料科学与工程学院 沈阳 110016
Precipitate Evolution in a Modified 25Cr-20Ni Austenitic Heat Resistant Stainless Steel During CreepRupture Test at 750 ℃
Guodong HU1,2, Pei WANG1, Dianzhong LI1(), Yiyi LI1
1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2 School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
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摘要: 

研究了一种新型25Cr-20Ni奥氏体耐热不锈钢在750 ℃不同拉应力持久实验中析出相演变及其对性能的影响。结果表明,当持久应力为180 MPa时,持久寿命为32.6 h,析出相包括M23C6和(Nb, V)(C, N)相。其中M23C6主要分布在晶界位置,(Nb, V)(C, N)相在晶内弥散析出。当持久应力为150和120 MPa时,随着持久时间延长至98.1 h以上,晶界位置的M23C6发生长大和Ostwald熟化,但(Nb, V)(C, N)相具有较好的尺寸稳定性。同时,在持久应力为120 MPa条件下,组织中出现σ相。σ相首先在晶界位置析出,当持久应力为100 MPa时,随持久时间延长至752.3 h,σ相也会在晶内析出。研究还发现,大量σ相依附于(Nb, V)(C, N)相析出,这是由于(Nb, V)(C, N)相的析出导致附近奥氏体基体中局部位置C和N元素含量减少,从而促进了σ相的形核。不同应力条件下试样断裂方式均为沿晶断裂,当持久时间较短时,裂纹在晶界M23C6处产生,引起沿晶开裂。随着持久时间延长,σ相在晶界析出后,裂纹更容易在晶界σ相处产生,导致持久延伸率随持久寿命延长而减小。

关键词 奥氏体耐热不锈钢持久析出相演变σMX    
Abstract

25Cr-20Ni austenitic heat resistant stainless steels are widely used as structural materials in nuclear industries and power plants for their excellent corrosion resistance and creep properties at elevated temperature. It is generally accepted that the precipitation during creep is a key factor influencing the creep properties. However, the evolution of precipitates is complicated due to the interaction of the alloy elements. To investigate the precipitation behaviors, a modified 25Cr-20Ni austenitic heat resistant stainless steel has been crept at 750 ℃ under different stresses varying from 100 MPa to 180 MPa. The microstructure observation indicates that M23C6 and (Nb, V)(C, N) precipitates are formed during 32.6 h creeping deformation under 180 MPa. M23C6 precipitates are mainly generated at grain boundaries and (Nb, V)(C, N) particles are dispersively distributed in austenitic matrix. The grain boundary M23C6 carbides are significantly coarsened and Ostwald ripening process happens during 98.1 h creeping deformation under the stress of 150 MPa and 353.0 h creeping deformation under stress of 120 MPa, while (Nb, V)(C, N) carbonitrides show high dimensional stability. With the creep rupture time further prolonging to 353.0 h and 752.3 h under the creep stress of 120 and 100 MPa, respectively, σ-phases are generated first at grain boundaries and then at inner grains. Meanwhile, large amounts of σ-phases are formed around (Nb, V)(C, N) particles, indicating the σ-phase precipitation is accelerated by (Nb, V)(C, N) carbonitrides. Composition analysis and thermodynamic calculation are subsequently performed to elucidate the precipitation mechanism of σ-phase. Carbon and nitrogen depleted zone is detected at the interface between (Nb, V)(C, N) precipitates and austenitic matrix. A correlation between σ-phase and C/N contents has been calculated by Thermo-Calc, which shows that the mass fraction of σ-phase increases with the decreasing C/N contents. According to the thermodynamic calculations and experimental results, it is reasonably inferred that the formation of σ-phase is induced by the carbon and nitrogen depletion in austenitic matrix. Additionally, the fracture surfaces of creep specimens show intergranular fracture under all creep stresses. When the creep time is comparatively short, cracks are inclined to propagate along grain boundaries owing to the low cohesion between grain boundary M23C6 precipitates and austenitic matrix, resulting in intergranular creep fracture. With the precipitation of σ-phase at grain boundaries after long time creep, the cracks are primarily generated from σ-phase, further deteriorating the creep elongation.

Key wordsaustenitic heat resistant stainless steel    creep rupture    precipitate evolution    σ-phase    MX
收稿日期: 2018-08-01     
ZTFLH:  TG142.1  
基金资助:国家自然科学基金项目No.U1708252
作者简介:

作者简介 胡国栋,男,1991年生,博士生

引用本文:

胡国栋, 王培, 李殿中, 李依依. 新型25Cr-20Ni奥氏体耐热不锈钢750 ℃持久实验过程中析出相演变[J]. 金属学报, 2018, 54(11): 1705-1714.
Guodong HU, Pei WANG, Dianzhong LI, Yiyi LI. Precipitate Evolution in a Modified 25Cr-20Ni Austenitic Heat Resistant Stainless Steel During CreepRupture Test at 750 ℃. Acta Metall Sin, 2018, 54(11): 1705-1714.

链接本文:

https://www.ams.org.cn/CN/10.11900/0412.1961.2018.00361      或      https://www.ams.org.cn/CN/Y2018/V54/I11/1705

图1  新型25Cr-20Ni奥氏体耐热不锈钢固溶态微观组织的SEM像和EDS分析
图2  新型25Cr-20Ni奥氏体耐热不锈钢在750 ℃、180 MPa和150 MPa应力条件下持久实验后微观组织的SEM像和晶界处析出相的TEM像以及SAED花样
图3  新型25Cr-20Ni奥氏体耐热不锈钢在750 ℃、120 MPa和100 MPa应力条件下持久实验后微观组织的SEM像和晶界处析出相的TEM像
图4  新型25Cr-20Ni奥氏体耐热不锈钢持久实验后晶内析出相的TEM像和SAED花样
图5  新型25Cr-20Ni奥氏体耐热不锈钢在750 ℃、100 MPa持久实验后σ相的TEM像和SAED花样
图6  新型25Cr-20Ni奥氏体耐热不锈钢750 ℃、100 MPa持久试样中析出相的TEM像及周围基体元素分布的EDS分析
图7  C、N含量对σ相含量影响以及不同温度下相平衡分数和固溶C、N含量的Thermo-calc热力学计算
图8  750 ℃不同应力条件下新型25Cr-20Ni奥氏体耐热不锈钢的蠕变应变-时间曲线
图9  新型25Cr-20Ni奥氏体耐热不锈钢持久试样断口形貌
图10  新型25Cr-20Ni奥氏体耐热不锈钢持久试样纵剖面裂纹扩展形貌
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