The influence of small amounts of KCl(s) on the high temperature corrosion of a Fe-2.25Cr-1Mo steel at 400 and 500°C

This paper reports the oxidation behaviour of a low-alloyed steel (Fe-2.25Cr-1Mo) in the presence of small amounts of KCl(s) at 400 and 500 degrees C. Cleaned and polished sample coupons were exposed in a horizontal tube furnace with exposure times ranging from one hour to one week. The flue gas composition was 5% O-2 with 40% H2O in N-2, and 0.1mg KCl/cm(2) was deposited on the samples prior to exposure. X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis were used to characterize the samples. Cross sections were prepared by means of focused ion beam (FIB) and broad ion beam (BIB). At 400 degrees C there was a modest mass gain in the absence of KCl. In the presence of KCl, mass gain is significantly increased and a rapid attack is evident already after short exposure times. At 500 degrees C, the mass gains in the absence of KCl were considerably higher than at 400 degrees C, especially after 168 hours of exposure. KCl had an effect at shorter exposure times, but after one week the samples exposed with and without KCl had mass gains of comparable magnitude.