A New Interpretation of the 'Breakaway' Oxidation Behaviour Observed at High Temperature on 304 Stainless Steel

摘要

A study has been performed into the high temperature oxidation of an AISI 304 stainless steel in order to explain the so-called "breakaway" oxidation behaviour observed on chromia-forming alloys. The high temperature in situ X-ray diffraction technique was used to detect the structural changes during the high temperature oxidation process at 900 and 1000℃. Chromia-forming alloys generally develop dense and protective slow growing Cr_2O_3 layers. This low growth rate is effectively observed at 1000℃ and is favoured by the establishment of a continuous silica sub-layer at the internal interface. This acts as a barrier against iron diffusion. "Breakaway" oxidation behaviour is observed at 900℃ after 40 hours of oxidation. This phenomenon is related to the initial nucleation of Fe_7SiO_(10), which traps silicon within the oxide layer and inhibits its segregation at the internal interface. The high rate oxidation is then due to the lack of a continuous silica layer at the internal interface, which leads to the formation of less protective iron-containing oxides.