Super duplex stainless steel fabricated by arc-based directed energy deposition: Microstructure evolution and phase field solidification simulation

Abstract

• First phase-field (PF) simulation of super duplex stainless steel (SDSS) solidification during additive manufacturing (AM). • PF simulation reveals microsegregation, dendritic growth, and phase fraction evolution during solidification. • Experiments show ferritic matrix with austenite, good phase balance, minimal sigma phase, and uniform microhardness. Super duplex stainless steels (SDSSs) are often used in corrosive environments owing to their combination of good strength (>450 MPa yield strength and > 600 MPa ultimate tensile strength) and corrosion resistance (PREN > 40). In additive manufacturing (AM), the challenge is achieving phase balance and minimizing microsegregation to reduce sigma phase formation. This work employs multi-phase-field simulations to understand the solidification of a SDSS under AM, and experimental tests to analyze the microstructure and properties of a SDSS (AWS ER2594) deposited wall. Phase field solidification simulations showed epitaxial growth of δ dendrites, followed by solute segregation of ferritizing and austenitizing elements into the δ dendrite cores and interdendritic liquid, promoting γ phase nucleation. The deposited wall showed an almost 50/50 ferrite/austenite phase balance and minimum of 0.3 % of sigma phase, by ANOVA and Tukey analysis no significant difference between phase fraction at different regions, and a variation in microhardness values between the base (273 HV1) and upper (262 HV1) regions of the wall. These results indicate good homogenization and well-chosen AM process parameters for producing a SDSS wall. Nevertheless, this work improves the understanding of solidification, thus microstructural evolution, of SDSS under AM, and provides input for future models of solid-state transformations.

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