Post-processing-dependent phase balance and mechanical response of Ni-modified LPBF 2507-type SDSS

This study investigates the effects of stress-relief and solution-annealing treatments on phase redistribution and mechanical response in laser powder bed fusion (LPBF)-fabricated 2507-type super duplex stainless steel modified with 3 wt% elemental Ni. This work extends our earlier investigation of the same alloy, which focused on phase balance and grain-boundary character distribution in the as-built condition. The blended feedstock contained 9.11 wt% Ni and was evaluated as-built, after stress relief at 400–550 °C for 1 h, and after solution annealing at 1100 °C for 15 min followed by water quenching. X-ray diffraction (XRD) with modified Williamson–Hall analysis, scanning electron microscopy, and electron backscatter diffraction (EBSD) characterized phase constitution and microstructure; hardness, tensile, and unnotched pendulum-impact testing quantified mechanical performance. The as-built and stress-relieved states remained ferrite-rich, containing 94%–95% ferrite within the analysed EBSD fields, apparent ferritic crystallite-size estimates of 33–55 nm, and apparent XRD-estimated dislocation-density values of 4– 7 × 1 ⁢ 0 1 4 m −2 . These states exhibited 𝑅 𝑝 ⁢ 0 . 2 = 1 0 9 0 –1210 MPa, 𝑅 𝑚 = 1 2 5 8 –1414 MPa, and total elongation at fracture, 𝐴 𝑡 , of 6.55%–8.53%. SR400 and SR450 delivered the highest measured tensile strengths, whereas SR500 and SR550 provided the most favourable strength–absorbed-energy compromise among the ferrite-rich conditions. Solution annealing produced an austenite-enriched duplex state containing approximately 60% austenite by XRD and 69% within the analysed EBSD field, with 𝑅 𝑝 ⁢ 0 . 2 ≈ 5 6 0 MPa, 𝑅 𝑚 ≈ 8 9 0 MPa, and 𝐴 𝑡 = 2 9 . 6 % , while the unnotched absorbed energy was reported as > 4 5 0 J. We establish a quantitative post-processing–phase-balance–mechanical-response framework that delineates ferrite-rich high-strength states from a solution-annealed, austenite-enriched ductility-dominant regime.