Relationship between microstructure, and residual strain and stress in stainless steels in-situ alloyed by double-wire arc additive manufacturing (D-WAAM) process

Abstract

In the field of welding, assembly of thick parts requires the base metal to be chamfered, followed by multipass welding. The process generates thermal, mechanical, and metallurgical phenomena resulting in the formation of residual strains and stresses. Strains must be limited, as they can cause misalignments during welding and leads to geometrical defects. Residual stresses are especially problematic in structural assemblies, as they add to the external stresses applied to the part during service, often reducing its in-service lifetime and increasing the risk of failure.The objective of this study is to use two stainless steel filler metals with different coefficients of thermal expansion (austenitic 304 L and ferritic 430) to reduce residual stresses and strains in the context of deposits produced by the Double-Wire Arc Additive Manufacturing process on 304 L baseplates. To achieve such a goal, the two filler are mixed in various proportions. After deposition and cooling, residual stresses are determined using neutron diffraction and contour method, strains are studied with profilometry. Microstructure is analyzed via EBSD, free dilatometry tests and XRD.We were able to reduce strains and stresses with a three-phase microstructure (austenite, ferrite, and martensite). The part that offers the best compromise (50% 430 - 50% 304 L filler on 304 L baseplate) exhibits a 67% reduction in strain, and stresses are reduced down to 40%, as compared to the 100% 304 L filler on 304 L baseplate part. The results obtained from neutron diffraction and contour method exhibit a close agreement, with a discrepancy standing below 100 MPa.