Effect of coating on oxidation of impure (C,Mn) iron at 700 degrees C: Yttrium-impurity interactions

A study of the interactions between cai bon and manganese impurities and yt trium has been performed during the oxidation of iron base specimens under an oxygen partial pressure of 0.04 Pa and at a temperature of 700 degrees C . It was found that yttrium coated specimens always exhibit better oxidatio n behaviour than uncoated specimens. For a manganese containing alloy (Fe-0 .2Mn), the protective effect of yttrium is attributed to the formation of a YMnO3 subscale at the oxide/metal interface. On Fe and Fe-0.054C substrate s the beneficial effect is attributed to the formation of Fe2YO4 (which is more protective than YMnO3). The best improvement is obtained with coated F e-0.18-Mn-0.041C alloys as a result of the formation of a YMnO3 subscale at the scale/alloy interface, and because the yttrium coating hinders carbon segregation at the oxide/alloy interface, thus producing better scale adhes ion.