Abnormal oxidation behavior of Fe in Ti(C,N)-304ss cermet during early oxidation stage

In this work, the oxidation experiments of Ti(C,N)- 304 stainless steel (304ss) cermet were carried out at 650 °C in the air. Abnormal oxidation behavior of Fe in the Ti(C,N)- 304ss cermet was observed for the first time, and it was investigated by field emission scanning electron microscope (FESEM) and 3D laser scanning confocal microscope (LSCM). A gap was generated in the TiO2/304ss interface due to the volume shrinkage led by the oxidation of Ti(C,N). When the tip of the gap propagated to the Cr-depleted region in 304ss, Fe atoms in this area reacted with O atoms and formed iron-contain oxides. Cations (Fe3+ and Ti4+) in oxidation products interdiffused to each other and formed Fe2TiO5 in the gap at high temperature. The gap is a rapid diffusion path for atoms, and Fe atoms outward diffused along the gap to the oxidation surface and formed Fe2O3 covering the oxidation surface. •Ti(C,N)-304ss cermets were oxidized in air at 650 °C for 4–120 min.•A gap was appeared at the boundary of TiO2/304ss.•Fe in 304 stainless steel was oxidized seriously to form (Fe,M)2O3 after exposed in air for a short time.•The existence of the gap and the formation of Cr-depleted region contributed to the abnormal oxidation phenomenon.