Fatigue Crack Growth Behavior of a New Type of 10% Cr Martensitic Steel Welded Joints with Ni-Based Weld Metal

In the present work, the fatigue crack growth (FCG) behavior of a new type of 10% Cr martensitic steel welded joints with Ni-based weld metal was comparatively studied for different regions including base metal (BM), heat-affected zone (HAZ) and weld metal (WM). FCG results indicated that the tempered lath martensite BM has a higher fatigue crack growth resistance than the tempered granular martensite HAZ that without a typical lath structure. In comparison, the austenitic WM has the highest fatigue crack growth threshold. Meanwhile, due to the microstructural and chemical compositional differences between BM and WM, a clear interface existed in the welded joints. At the region of the interface, the microstructures were physically connected and an element transition layer was formed. Although the starter notch was positioned at the region of interface, the fatigue crack gradually deviated from the interface and ultimately propagated along the inter-critically heat-affected zone. The difference in microstructure is considered as the primary factor that resulted in the different fatigue crack growth behaviors of the welded joints. In addition, the continuous microstructure connection and composition transition at the interface contributed to the good fatigue resistance at this region.