Study on Microstructure and Corrosion Resistance of Laser-welded Dissimilar Joints of 17-4PH and 316L Stainless Steels

The welded joints in a type of medical bone nipper are susceptible to rusting, as they are laser-welded using 17-4PH martensitic stainless steel and 316L austenitic stainless steel. The change of the element distribution and the microstructure of the heterogeneous stainless steel joint were analyzed by the microstructure observation and corrosion resistance test, and its effects on the corrosion resistance properties of the joint was analyzed. It is found that the martensitic phase in the 17-4 PH matrix metal exhibits the highest corrosion potential and the lowest corrosion current density due to its structural homogeneity. In contrast, plastic deformation causes Cr segregation in the 316L base material, inducing the formation of a ferrite phase. Consequently, micro-galvanic corrosion occurs between the austenite and ferrite phases, resulting in the lowest corrosion potential and the highest corrosion current density in that area. Microscopic observations reveal that recrystallization takes place in the deformed 316L base metal within the heat-affected zone, leading to the formation of fine equiaxed grains, while the 17-4PH base material retains its original morphology. In summary, the 316L base material that undergoes plastic deformation exhibits the lowest corrosion resistance in the joint, which can be attributed to chromium segregation and the formation of a chromium-poor zone.