Effect of re-melting strategies on pitting corrosion resistance in laser powder bed fusion Ni over-alloyed duplex stainless steel

Abstract

Re-melting during laser powder bed fusion (LPBF) produced 22Cr duplex stainless steel (DSS) enhances austenite distribution homogeneity and elemental dispersion without altering the austenite content (∼35 %). Compared to LPBF 22Cr DSS without re-melt process (critical pitting potential, E_pit = 0.44 V_SCE at 70°C; critical pitting temperature, CPT = 56.9°C), processing with three re-melting cycles increases E_pit by 0.15 V_SCE and CPT by 3.8°C. This improvement in pitting corrosion resistance arises from expanded austenite coverage at grain boundaries—the primary pit nucleation sites. However, localised corrosion volume loss increases from 1.3 × 10⁸ μm³ (without re-melt) to 1.8 × 10⁸ μm³ (3 cycles re-melts), indicating accelerated corrosion propagation. Thus, re-melting exerts opposing effects on pitting nucleation resistance and pit growth kinetics. At lower potentials, austenite promotes pit growth in ferrite via galvanic coupling, evidenced by a 15 mV Volta potential difference (austenite > ferrite) measured by scanning Kelvin probe force microscopy (SKPFM). Conversely, at higher potentials, pits propagate preferentially within melt-pools where both phases corrode. Potentials exceeding E_pit further induce intergranular corrosion.