Study of selective oxidation by means of glow discharge optical emission spectroscopy

In the continuous annealing process, steel sheets are annealed at 800 °C in an atmosphere of nitrogen and hydrogen (5 vol.%) containing low water partial pressure (20–50 Pa). Under these conditions, the most oxidizable alloying elements in the steel segregate towards the surface where they form oxide particles. The Mn, Al, Si and B concentration gradients resulting from this selective oxidation were measured as a function of annealing time by the glow discharge optical emission spectroscopy method. The manganese and silicon diffusion coefficients in steel were then estimated using Wagner’s diffusion model.

Research highlights
► The diffusion of alloying elements in steel (Mn, Si, Al, B) is visible from 700 °C.
► The concentration profiles are characteristic of the oxidation described by Wagner.
► The oxidation depth is a few hundred nanometer after annealing at 800 °C for 60 s.
► The diffusion coefficients of Mn and Si in the studied steel were estimated at 800 °C.