Li Xiaogang, Nie Junfeng, Wang Xin, Li Kejian, Zhang Haiquan
Institute of Nuclear and New Energy Technology, Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education, Tsinghua University, Beijing 100084, China.
Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China.
Materials (Basel). 2023 Sep 20;16(18):6294. doi: 10.3390/ma16186294.
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.
研究了铁素体钢与奥氏体不锈钢异种金属焊缝（DMW）中Ni/Fe界面微观结构的形成与演变。焊接及焊后热处理（PWHT）后，在镍基焊缝金属/12Cr2MoWVTiB钢界面处发现了层状马氏体组织。通过扫描电子显微镜（SEM）、电子背散射衍射（EBSD）、电子探针微分析（EPMA）、聚焦离子束（FIB）、透射电子显微镜（TEM）、能量色散X射线（EDX）、透射菊池衍射（TKD）、相图和理论分析，阐明了焊接过程中界面马氏体层的形成，并讨论了其在PWHT过程中的演变。在焊态DMW中，Ni/Fe界面结构由体心立方（BCC）淬火马氏体层和面心立方（FCC）部分混合区（PMZ）组成，这是由于化学成分梯度导致的不均匀固相转变的结果。在PWHT过程中，BCC界面微观结构进一步演变为回火马氏体和通过局部再奥氏体化及奥氏体-马氏体转变新形成的淬火马氏体的双层结构。这些类型的马氏体组织在Ni/Fe界面附近引起不均匀的硬度分布，加剧了界面力学性能的不匹配，这是导致DMW退化和失效的一个潜在因素。
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