Welding Metallurgy of Super Duplex Stainless Steel UNS S32750: A State-of-the-Art Review of GMAW Process Parameters, Microstructure–Property Relationships and Corrosion Performance

Abstract

Super duplex stainless steel UNS S32750 (SAF 2507) combines a pitting resistance equivalent number above 40 with high strength, but its properties depend on a ferrite–austenite balance that welding readily disturbs. Gas metal arc welding (GMAW) is productive, yet GMAW-specific evidence for this alloy remains limited. A structured narrative review (emphasis 2018–2026) synthesised GMAW-specific findings, drew comparative mechanisms from gas tungsten arc, submerged arc and beam welding, and examined Gaussian process regression (GPR) for parameter optimisation. Data were converted to net heat input and grouped by corrosion test method. Weld-metal ferrite is governed by cooling time through 1200–800°C, nitrogen retention and ER2594 nickel over-alloying, whereas Cr₂N, secondary austenite and σ-phase arise mainly from multipass reheating and interpass temperature. Pulsed GMAW in Ar–He shielding with nitrogen backing met NORSOK M-601 requirements (30–70% ferrite, ≥ 27 J at − 46°C) in 33 mm plate at 1.2–1.6 kJ mm⁻¹ arc energy. Oxidising shielding additions introduce oxide inclusions that degrade pitting resistance. Electrochemical critical pitting temperatures fall from 58–92°C in base metal to 45–71°C in arc welds and rise linearly with austenite fraction. GPR-based Bayesian optimisation located welding optima within 12–25 experiments with quantified uncertainty, but has not yet been applied to super duplex GMAW. Fixed heat-input windows are incomplete because thickness, pass count and gas chemistry shift outcomes; above-guideline parameters are qualified only for heavy sections. Thermal-history-based qualification, nitrogen management, harmonised corrosion testing and constrained GPR optimisation of ferrite, toughness and pitting resistance are priorities.

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