使用镍基焊缝金属连接新型高Cr马氏体耐热钢和镍基合金制造了异种金属焊接接头(DMWs)，对该类DMWs进行了高温持久实验以分析其失效机理，其中，应力水平在140~260 MPa，温度为600和620 ℃。结果表明，DMW的断裂位置随应力水平的改变发生转移。高应力水平(≥240 MPa)下，断裂主要发生在马氏体耐热钢母材中，断裂模式以塑性变形为主。中等应力水平(200~240 MPa)下，断裂位置转移至马氏体耐热钢热影响区(HAZ)中的细晶区(FGHAZ)或两相区(ICHAZ)中，该区域的硬度最低且碳化物粗化显著，在粗化的碳化物周围产生了大量的蠕变空洞，此种断裂模式为典型的Ⅳ型断裂。在低应力水平(≤200 MPa)下，DMW的断裂模式为三阶段混合形式：初始阶段，因在焊缝与马氏体耐热钢界面处产生氧化尖缺口沿界面断裂，氧化尖缺口的形成是氧化与应力交互作用的结果；裂纹随后转移至马氏体耐热钢的FGHAZ或ICHAZ中扩展；前2个阶段未发生明显的塑性变形，最后裂纹转移至马氏体耐热钢母材中沿切应力最大的方向扩展直至完全断裂，该阶段发生了明显的塑性变形。此外，研究还发现随应力水平降低，DMW呈现出早期失效的倾向，即低应力水平下的高温持久强度低于由高应力水平数据线性外延得到的数值，早期失效的产生与马氏体耐热钢焊接HAZ微观组织退化和界面氧化有关。

Dissimilar metal welds (DMWs) between high-Cr martensitic heat-resistant steels and nickel-based alloys with nickel-based filler metals are widely used in fossil-fired power plants. Reports of premature failures of DMW joints have attracted considerable attention as such occurrences in the field can lead to significant economic loss and safety issues. Moreover, a comprehensive understanding of the high-temperature performance of new types of DMWs is lacking. In this work, creep tests were conducted over a stress range of 140~260 MPa at of 600 and 620 ℃. A shift in the fracture location with variations in stress was observed, with three typical failure modes. At high stress levels (240~260 MPa), the DMW fractured in the base metal (BM) of martensitic steel, accompanied by a large degree of plastic deformation. At intermediate stress levels (200~240 MPa), the DMW fractured in the fine-grained heat-affected zone (FGHAZ) and the inter-critical heat-affected zone (ICHAZ), with creep cavities around coarsened carbides, indicating a typical type IV crack. At low stress levels (140~200 MPa), the DMW fractured in a mixed mode involving three stages. First, a crack initiated at the interface between the nickel-based weld metal and the martensitic steel, which was attributed to the interaction between the oxidation behavior of the martensitic steels and the thermal stress arising from the mismatch in the coefficients of thermal expansion. Second, the crack deflected into the FGHAZ/ICHAZ and developed into a type IV crack mode. Finally, the crack propagated into the adjacent BM, featuring significant plastic deformation. In addition, in the stress-LMP (Larson-Miller parameter) plot, the creep life at a relatively low stress level was shorter than that predicted by linear extrapolation of the data obtained at a high stress level, indicating a premature failure tendency at low stress. This premature failure tendency can be attributed to microstructure degradation in HAZs and preferential oxidation at the interface at low stress levels.