Examination of the oxidation resistance of Cr-Mo-V tool steel by thermal analysis

In the present study, the oxidation behavior of Cr-Mo-V tool steel was examined at different temperatures in air. The examination was conducted by means of thermogravimetric analysis, scanning electron microscopy, and X-ray diffraction (XRD). After non-isothermal oxidation from ambient temperature to 1000 degrees C, it was revealed that the specimen begins to oxidize over 700 degrees C, while over 800 degrees C the oxidation rate increases significantly. Finally over 900 degrees C, this rate has a considerable value, and the specimen's oxidation resistance is inadequate. From these results, four different oxidation temperatures (805, 835, 865, and 895 degrees C) were selected for the isothermal test, as referred above, which correspond to different oxidation rates, to determine the oxidation activation energy of the Cr-Mo-V specimens. Energy dispersive X-ray spectroscopy (EDX) and XRD phase identification of the as-formed scales showed that in every case, it contains two distinguishable regions. The inner layer is a mixture of chrome and iron oxides and the outer layer contains iron oxides and is also characterized by high porosity. This phenomenon was explained by the different diffusion coefficients of every element in the steel matrix.