High‐Temperature Oxidation of 60Si2Mn Spring Steel in Dry Air and Wet Air: Insights from an Experimental and First‐Principles Study

Abstract

During the hot‐rolling process, the 60Si2Mn spring steel is exposed to both dry air and water vapor at high temperatures. However, no precise mechanism or theory is developed to explain the effect of water vapor on the oxide layer from a microscopic atomic perspective. The high‐temperature oxidation of 60Si2Mn spring steel with dry and wet air is investigated herein using a combination of experiments and first‐principles calculations. After high‐temperature oxidation in both dry and wet air, the 60Si2Mn spring steel generates a typical three‐layer structure consisting of Fe2O3, Fe3O4, and FeO + SiO2/Fe2SiO4; however, the oxide layer produced in wet air is significantly thicker. Furthermore, the phase transformation from Fe3O4 to Fe2O3 occurs in the middle Fe3O4 layer, which is associated with H protons derived from H2O molecules penetrating into oxide layers and promoting the development of Fe vacancies in the center of the tetrahedral interstices. The high porosity of the Fe3O4 layer essentially encourages Fe and O diffusion, hence enhancing the growth of the oxide layer and facilitating the transformation from Fe3O4 to Fe2O3. These findings provide a more detailed mechanistic explanation of how water vapor affects the high‐temperature oxidation of 60Si2Mn spring steel at the atomic level.