XRD and EPMA Analysis of Carburized Layer in the Carburized Chromium Alloy Steel
Abstract
In this study, the changes of microstructure and reactants before and after gas carburization of IR-20 and C-15 chromium alloy steel for constant velocity joints were investigated.The specimens were carburized at 930 °C for 3-10 hr, diffusion-treated for 1-3 hr and then cooled in furnaces at 840-850 °C. After that, oil quenching was performed at 130 °C for microstructure and martensitic transformation. Gas carburized specimens were cut vertically with vacuum wire cuts to minimize deformation and microstructural changes. The cut specimens were resin-mounted at a temperature of 185 °C, followed by rough grinding, intermediate grinding and polishing grinding in order to make the surface as smooth as possible. XRD and EPMA were used to confirm the presence of microstructure, crystal structure, carbon and alloying elements of the metal microstructures of the uncarburized specimens and the gas carburized specimens. The microstructure was analyzed by ferrite and pearlite structure before the gas carburizing heat treatment, but after the gas carburizing heat treatment, the carbon was transformed into the martensitic structure on the carburized surface. Cementite was ferrite and pearlite structure remained as the carburized amount decreased. XRD and EPMA analysis showed that carbon was very well carburized on the specimen surface after carburizing. Carburized layer showed that carbides, such as Cr23C6, Cr7C3, Cr3C2, and Cr2O3 were formed by reaction with iron, chromium, carbon, and oxygen while carbon diffused inward from the surface. This carbon carburizing reaction is consideredmodify the mechanical properties of specimens, as transformation into fine martensitic structure and formation of chromium carbide. In the future, the wear resistance analysis and the corrosion resistance analysis will be perform to improve the life of carburized steel.
Keywords: chromium alloy steel, gas carburizing, constant velocity joints, XRD analysis, EPMA analysis
