Study on fusion boundary microstructure and mechanical properties of austenitic stainless steel-nickel based dissimilar alloy materials welded joints

The metallographic test, microhardness test, and shear punch test of overlayer joint were carried out. The microstructure distribution and micro-zone mechanical properties of overlayer-girth weld fusion boundary (O-G), overlayer-austenitic (O-A) fusion boundary, and austenitic-grith weld fusion boundary (A-G) were studied respectively. At the same time, the type II boundary, DDC, and liquefaction crack were discovered. The results show that the microstructures on both sides of the O-G fusion boundary are gamma phase and austenite-ferrite, respectively. There are three types of fusion limitations: type II boundary, direct fusion boundary, and transition fusion boundary. There are DDCs in the transition fusion boundary of the O-G zone, and liquefaction cracks caused by composition segregation in the inner of overlayer. The microstructures on both sides of the O-A fusion boundary are gamma phase and uniaxial austenite, respectively, and there is no evident transition zone. Microstructures on both sides of the A-G fusion boundary are equiaxed austenite and austenite-ferrite (lath-skeleton-short rod). The average microhardness and shear strength of the O-A-G fusion border overlayer is the highest, 241 HV and 782 MPa respectively, and the microhardness decreases to 215 HV at DDCs defect. The microhardness and shear strength of base metal are 212 HV, 661 MPa, respectively. The microhardness and shear strength of the girth weld are 192 HV, 600 MPa, respectively. The maximum shear work of O zone is 1.62 J, and the minimum O-G fusion boundary is 1.12 J.