Microstructure Evolution at Ni/Fe Interface in Dissimilar Metal Weld between Ferritic Steel and Austenitic Stainless Steel

Xiaogang Li; Junfeng Nie; Xin Wang; Kejian Li; Haiquan Zhang

doi:10.3390/ma16186294

Microstructure Evolution at Ni/Fe Interface in Dissimilar Metal Weld between Ferritic Steel and Austenitic Stainless Steel

Materials (Basel). 2023 Sep 20;16(18):6294. doi: 10.3390/ma16186294.

Authors

Xiaogang Li¹, Junfeng Nie¹, Xin Wang¹, Kejian Li², Haiquan Zhang¹

Affiliations

¹ Institute of Nuclear and New Energy Technology, Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education, Tsinghua University, Beijing 100084, China.
² Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China.

Abstract

The formation and evolution of microstructures at the Ni/Fe interface in dissimilar metal weld (DMW) between ferritic steel and austenitic stainless steel were investigated. Layered martensitic structures were noted at the nickel-based weld metal/12Cr2MoWVTiB steel interface after welding and post-weld heat treatment (PWHT). The formation of the interfacial martensite layer during welding was clarified and its evolution during PWHT was discussed by means of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA), focused ion beam (FIB), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), transmission kikuchi diffraction (TKD), phase diagrams, and theoretical analysis. In as-welded DMW, the Ni/Fe interface structures consisted of the BCC quenched martensite layer and the FCC partially mixed zone (PMZ), which was the result of inhomogeneous solid phase transformation due to the chemical composition gradient. During the PWHT process, the BCC interfacial microstructure further evolved to a double-layered structure of tempered martensite and quenched martensite newly formed by local re-austenitization and austenite-martensite transformation. These types of martensitic structures induced inhomogeneous hardness distribution near the Ni/Fe interface, aggravating the mismatch of interfacial mechanical properties, which was a potential factor contributing to the degradation and failure of DMW.

Keywords: Ni/Fe interface; dissimilar metal weld; interfacial performance; martensitic structures; phase transformation.

Grants and funding

This research was funded by Youth Elite Project of CNNC and the Modular HTGR Super-critical Power Generation Technology collaborative project between CNNC and Tsinghua University [grant number ZHJTIZYFGWD20201].