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金属学报  2019, Vol. 55 Issue (5): 555-565    DOI: 10.11900/0412.1961.2018.00365
  本期目录 | 过刊浏览 |
退火对热老化308L不锈钢焊材显微结构的影响
林晓冬1,2,彭群家1,3(),韩恩厚1,柯伟1
1. 中国科学院金属研究所核用材料与安全性评价重点实验室 沈阳 110016
2. 中国科学技术大学材料科学与工程学院 沈阳 110016
3. 苏州热工研究院有限公司 苏州 215004
Effect of Annealing on Microstructure of Thermally Aged 308L Stainless Steel Weld Metal
Xiaodong LIN1,2,Qunjia PENG1,3(),En-Hou HAN1,Wei KE1
1. Key Laboratory of Nuclear Materials and Safety Assessment, 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
3. Suzhou Nuclear Power Research Institute, Suzhou 215004, China
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摘要: 

对410 ℃下热老化7000 h的308L不锈钢焊材进行了550 ℃、1 h的退火处理,利用TEM和三维原子探针研究了退火对热老化焊材显微结构的影响,并与未热老化试样进行比较,评价退火回复效果。结果表明,退火后奥氏体无明显变化,而δ铁素体内由热老化导致的调幅分解完全消失,且G相显著减少。此外,热老化导致Ni、Mn、C在δ铁素体/奥氏体相界处发生偏聚,而对相界处Cr、Si、P元素的含量无明显影响。退火后相界处所有元素均无偏聚,但会导致Ni、Mn在靠近相界的奥氏体一侧发生富集。退火后308L不锈钢焊材的显微结构接近于未热老化状态,表明退火回复效果显著。

关键词 不锈钢焊材热老化退火调幅分解G相析出相界偏聚    
Abstract

Austenitic stainless steel weld metal has been widely used as nozzle/safe-end joint and inner surface cladding of reactor pressure vessel, due to its good mechanical property and corrosion resistance. However, long-term thermal ageing at the service temperature (280~330 ℃) could induce hardening and embrittlement of the weld metal. To recover the thermal ageing embrittlement, the annealing treatment has been proposed since the annealing could affect the ageing-induced microstructural changes such as spinodal decomposition and G-phase precipitation in ferrite. However, there is still an incomplete understanding as well as a lack of nanoscale investigation about the annealing effect on the microstructural change of the weld metal. In this work, 308L stainless steel weld metal was thermally aged at 410 ℃ for 7000 h, followed by an annealing treatment at 550 ℃ for 1 h. Since the weld metal has a dual-phase structure of austenite and δ-ferrite, the phase transformation of austenite and δ-ferrite as well as the element segregation at the δ-ferrite/austenite phase boundary were investigated by TEM and atom probe tomography. The results revealed that austenite was unaffected by annealing while the ageing-induced spinodal decomposition of δ-ferrite was completely recovered. In addition, the number density of G phase in δ-ferrite was significantly reduced following annealing. This indicates that austenite has a higher stability compared with δ-ferrite. As for the δ-ferrite/austenite phase boundary, thermal ageing induced the segregation of Ni, Mn and C at the phase boundary, while the contents of Cr, Si and P remained almost unchanged. Following the annealing treatment, the segregation of all elements was eliminated. Further, only a small quantity of Ni and Mn was enriched in austenite near the phase boundary. The results suggested that the microstructure of the annealed specimen was similar to that of the unaged specimen, indicating a good recovery of the microstructure by annealing.

Key wordsstainless steel weld metal    thermal ageing    annealing    spinodal decomposition    G phase precipitation    phase boundary segregation
收稿日期: 2018-08-11     
ZTFLH:  TG139.4  
基金资助:国家自然科学基金项目(51571204)
通讯作者: 彭群家     E-mail: pengqunjia@cgnpc.com.cn
Corresponding author: Qunjia PENG     E-mail: pengqunjia@cgnpc.com.cn
作者简介: 林晓冬,男,1991年生,博士

引用本文:

林晓冬,彭群家,韩恩厚,柯伟. 退火对热老化308L不锈钢焊材显微结构的影响[J]. 金属学报, 2019, 55(5): 555-565.
Xiaodong LIN, Qunjia PENG, En-Hou HAN, Wei KE. Effect of Annealing on Microstructure of Thermally Aged 308L Stainless Steel Weld Metal. Acta Metall Sin, 2019, 55(5): 555-565.

链接本文:

https://www.ams.org.cn/CN/10.11900/0412.1961.2018.00365      或      https://www.ams.org.cn/CN/Y2019/V55/I5/555

图1  308L不锈钢焊材的显微组织和δ铁素体/奥氏体相界区域的HRTEM像
图2  原始态、7000 h热老化和退火试样中奥氏体相的明场像和内部元素分布
图3  原始态、7000 h热老化、退火试样中δ铁素体相的TEM像和Cr元素分布
图4  δ铁素体中调幅分解区域内部Fe、Cr一维成分分布与浓度频率分布
图5  G相的暗场像、电子衍射花样和HRTEM像
图6  原始态、7000 h热老化、退火试样中δ铁素体相内Ni、Si、Mn、P、Cu元素分布
图7  横跨G相的一维成分分布
图8  原始态、7000 h热老化、退火试样中δ铁素体/奥氏体相界区域的元素分布及横跨相界的一维浓度分布
图9  未热老化、7000 h热老化和退火试样调幅分解区域内Fe、Cr的参数V
图10  7000 h热老化和退火试样中靠近相界处的δ铁素体一侧的贫Ni区
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