In‐situ investigation on the oxidation behaviour of low alloyed steels annealed under N2‐5%H2 protective atmospheres

Abstract

The oxidation behaviour of low alloyed steels, Fe‐0.6%Mn and Fe‐1.5%Mn, under different annealing conditions was studied. Due to the crucial importance of the surface state of the sample, the experiments were performed in an in‐situ device to avoid any contact with air after the annealings. The annealing experiments were carried out under different conditions: high vacuum (~10−6 mbar), N2/H2 protective atmospheres with traces of water (dew point ‐30 °C) and temperatures ranging from 873 to 1073 K. Under this variety of heat treatments, the reconstruction of the Fe surface and the formation of different oxides was observed and characterised, paying special attention to the selective oxidation of manganese. The surface structure and composition was investigated by means of the combined use of reflection high‐energy electron diffraction (RHEED) and X‐ray photoelectron spectroscopy (XPS). The analyses show that the use of RHEED is a good alternative for determining the crystallographic structure of the outermost layers of the surface. With this technique the structures of iron and manganese oxides can be distinguished despite the similar structures and lattice parameters. It is also possible to identify the crystallographic textures present on the oxidation products and to give qualitative information about the surface reconstruction of the grains.