An ESEM in situ investigation of initial stages of the KCl induced high temperature corrosion of a Fe–2.25Cr–1Mo steel at 400 °C

The initial oxidation of a low-alloyed steel (Fe–2.25Cr–1Mo) in the presence of small amounts of KCl(s) have been investigated through ESEM in situ exposure and analysis at 400 °C. The samples were also characterized by XRD, SEM/EDX and FIB. The present study shows the corrosive nature of KCl towards the low alloyed steel. It is concluded that the initial KCl distribution is important and that a KCl/FeCl2 liquid phase film forms on large parts of the oxide surface in the presence of KCl. It is proposed that Cl increases the oxidation rate (by decorating oxide grain boundaries) and decreases the oxide scale adhesion.

► ESEM in situ investigation of the initial oxidation of a steel in the presence of KCl(s) at 400 °C.
► The present study shows the corrosive nature of KCl towards the low alloyed steel.
► The initial KCl distribution is important.
► A KCl/FeCl2 liquid phase film forms on large parts of the oxide surface.
► Cl increases the oxidation rate (decorating oxide grain boundaries) and decreases scale adhesion.