Mechanism of and method to avoid discoloration of stainless steel surfaces in laser cleaning

Abstract

In laser cleaning of stainless steel surfaces, the discoloration takes place on the surfaces irradiated by excimer lasers in the air as laser fluence and pulse number exceed a discoloration threshold. The color of stainless steel surfaces changes to that of γ-Fe2O3. Based on Auger Electron Spectroscopy analyses and optical microscopic observations, γ-Fe2O3 and Fe3O4 are formed on the stainless steel surface in laser cleaning in the air. Since laser can induce high temperature rise in stainless steel surfaces, the above phenomenon can be explained by a thermochemical reaction between oxygen in the air and the stainless steel. With increasing laser fluences, the temperature rise in the irradiated area of stainless steel surface increases, which enhances oxygen diffusion into the surface and oxidation reaction within the irradiated area. In order to avoid discoloration of stainless steel surfaces, a vacuum system was used to reduce the oxidation reaction between oxygen and stainless steel.