Yang Maohong, Zhang Zheng, Li Linping
School of Material Science and Engineering, Beihang University, 37 Xueyuan Road, Beijing 100191, China.
Shenhua Guohua (Beijing) Electric Power Research Institute Co., Ltd., No.75 Jian Guo Road, Chaoyang District, Beijing 100025, China.
Materials (Basel). 2021 Sep 2;14(17):5018. doi: 10.3390/ma14175018.
This paper studies the evolution of the microstructure and microhardness in the G115 side of the G115/Sanicro25 dissimilar steel welded joint during the creep process. The joints were subjected to creep tests at 675 °C, 140 MPa, 120 MPa and 100 MPa. A scanning electron microscope equipped with an electron backscattering diffraction camera was used to observe the microstructure of the cross-section. The fracture position of the joint and the relationship between the cavity and the second phase were analyzed. The microstructure morphology of the fracture, the base metal and the thread end was compared and the composition and size of the Laves phase were statistically analyzed. The results show that the fracture locations are all located in the fine-grain heat-affected zone (FGHAZ) zone, and the microstructure near the fracture is tempered martensite. There are two kinds of cavity in the fracture section. Small cavities sprout adjacent to the Laves phase; while large cavities occupy the entire prior austenite grain, there are more precipitated phases around the cavities. The Laves phase nucleates at the boundary of the MC carbide and gradually grows up by merging the MC carbide. Creep accelerates the coarsening rate of the Laves phase; aging increases the content of W element in the Laves phase.
本文研究了G115/Sanicro25异种钢焊接接头G115侧在蠕变过程中的微观组织和显微硬度演变。对接头在675℃、140MPa、120MPa和100MPa下进行蠕变试验。采用配备电子背散射衍射相机的扫描电子显微镜观察横截面的微观组织。分析了接头的断裂位置以及孔洞与第二相之间的关系。对比了断口、母材和螺纹端的微观组织形态，并对Laves相的成分和尺寸进行了统计分析。结果表明，断裂位置均位于细晶热影响区（FGHAZ），断裂附近的微观组织为回火马氏体。断口截面存在两种孔洞。小尺寸孔洞在Laves相附近萌生；而大尺寸孔洞占据整个原奥氏体晶粒，孔洞周围有较多析出相。Laves相在MC碳化物边界形核，并通过合并MC碳化物逐渐长大。蠕变加速了Laves相的粗化速率；时效增加了Laves相中W元素的含量。
