CORROSION EVALUATION OF SUPER DUPLEX STAINLESS STEEL MADE BY LPBF

This study investigated the electrochemical corrosion performance of printed and heat -treated 2507 Super Duplex Stainless Steel (SDSS). The corrosion was studied by Tafel polarization and electrochemical impedance spectroscopy (EIS) methods in a 3.5% NaCl solution. For this purpose, the as -built and heat -treated printed samples (solution annealed and stress -relieved) were examined by LOM/SEM and X-ray diffraction to evaluate the phase changes of steel at different processing stages. The correlation between corrosion resistance, structure, and heat treatment was assessed. As a result of the very fast cooling rate of the laser powder bed fusion (LPBF) process, SDSS reveals ferrite as the major phase in the printed samples. The ferrite grains are elongated in the build direction, with some austenite precipitation along the grain boundaries or as Widmanstatten laths. Because the ferrite phase's corrosion potential is lower than that of austenite, corrosion preferentially proceeds in the steel matrix. For this reason, balancing the two-phase structure or reducing residual stresses after the printing process has a positive effect on improving the corrosion resistance of duplex stainless steel produced by LPBF. The stress -relieved and as -printed SDSS exhibits reduced corrosion characteristics by around 20% compared to the solution -annealed SDSS, according to anodic polarization curves. Based on EIS results, the solution -annealed SDSS revealed an almost double increase in corrosion resistance (based on charge transfer resistance values) compared to the as -printed and stressrelieved conditions.