Assessment of the universality of duplex stainless steel powder in laser additive repair based on Schaeffler diagram

Abstract

The type and quantity of repair materials used in ocean or field environment is unclear. This study investigated the effective methods for evaluating the universality of a specific powder for multiple materials using a self-made universal duplex stainless steel powder (UDSS) as the object and tensile strength (σ) of the additive repair part in the normal direction of the interface as the index. Based on the Schaeffler diagram, the equivalent distances of Cr and Ni were used to characterize the chemical composition difference between the material to be repaired and the UDSS powder, and the angle θ was used to characterize the difference in microstructures. Three models, σ-(Cr eq , Ni eq ) , σ-ρ equivalent distance linear, and σ -( ρ,θ ) polar coordinate models, were proposed for predicting the strength of the additive repaired part. These models were verified using the results of repair tests on five substrates. The mean prediction error, pf, of the σ -( ρ, θ ) polar coordinate model was minimum, that is, approximately 9.68%. Under the conditions of this study, the maximum normal strengths of the repaired specimen interface in the normal direction were 689, 704, and 957 MPa in the austenite, ferritic, and ferrite + austenite regions, respectively, thus proving the universality of the UDSS powder used. This study provides a novel and a reliable method for evaluating the universality of UDSS powder for laser-additive repair. The relationship between the tensile strength and evolution of the microstructure, chemical composition, and microhardness near the interface is discussed.