Influence of laser heat input on the corrosion mitigation of laser textured AISI 301LN steel in molten carbonate salts

Abstract

Laser Surface Texturing (LST) is a surface modification method to mitigate corrosion of the stainless steels by molten carbonate salts in the concentrated solar power (CSP) plants. In this work, for the first time, the influence of the laser-heat input on the corrosion resistance of AISI 301LN stainless steel is investigated. For this purpose, the effect of the laser power and scanning speed on the surface topography, phase transformation, microhardness, and corrosion behavior, of laser textured surfaces is evaluated in detail. AISI 301LN samples were immersed in molten Li₂CO₃-Na₂CO₃-K₂CO₃ at 600 °C for 500 h. The textured surface properties after LST and the oxide scales formed during corrosion tests were evaluated using microanalysis, microscopy and optical characterization techniques. The results revealed that the effectiveness of LST was improved by increasing the laser-heat input, reducing the scanning speed and increasing the laser power, which is supported by statistical analyses. Compared with an untreated surface, the sample treated with the maximum laser-heat input induced a phase shift from austenite (γ) to martensite (α’), resulting in a remarkable increase in microhardness as well as also significantly decreased the corrosion rate by 37 %. This trend maximized the chemisorption of organic compounds and favoured the homogeneous distribution of Fe-Mn-carbides at the oxide-scale surface formed during the corrosion process. In this way, denser protective oxide scales were formed by retaining Cr and Ni in the oxide layers, and reducing the Li diffusion through scales.