Effect of Coating Damage on the Micro Area Corrosion Performance of HDR Duplex Stainless Steel

Abstract

In order to determine the effect of damaged insulating enamel on the corrosion of high-chromium (H), duplex (D), and corrosion-resistant (R) duplex stainless steel, the corrosion characteristics of HDR duplex stainless steel in 3.5% NaCl solution were studied by means of local electrochemical impedance spectroscopy (LEIS) and micro-morphology analysis. It was shown that the LEIS impedance was stable at about 7.0 × 103 Ω within 10 days when the HDR duplex stainless steel was not coated. The minimum LEIS impedance of exposed HDR at the damaged area fluctuated around 6.5 × 103 Ω within 15 days when the coating of the self-control insulating enamel damaged area was 1 mm × 10 mm. The coating-damaged area from 1 mm × 10 mm reduced to a circular hole with a diameter of φ1 mm, and the LEIS impedance of the exposed HDR increased at the damaged coating. When extending along the damaged coating to the intact coating area, the impedance rapidly increased, and the further the distance from the damage, the greater the increase in impedance. The impedance of coated HDR increased with the prolongation of immersion time and ultimately stabilized. The thicker the coating, the longer the impedance took to reach a stable state. The stabilized coating had a better effect on improving the corrosion resistance of HDR duplex stainless steel. Within 15 days, the HDR ferrite structure at different areas of coating damage prioritized corrosion. Cl− mainly comes from the solution, and Si and S elements mainly come from elements of the collective itself, with Cl− adsorption, S, and Si element inclusion being the main factors influencing the corrosion of the ferrite structure.