Effect of Niobium as Alloying Element on Austenitic Stainless Steels Oxidation

International audienceThis work shows the influence of sodium carbonate coatings on the austenitic AISI 330 (Fe-35Ni-19Cr-1.3Si) oxidation during 48 h, at 900 °C. The N2-5vol.% H2 gaseous environment was used to simulate industrial heat treatment conditions. Silica scale formation is promoted by low oxygen containing gaseous environments and the high alloy silicon content. On this alloy an amorphous silica scale is formed after the blank material oxidation. It indicates that silicon is free to diffuse in the alloy and forms a silica scale at the internal interface. On Na2CO3 coated specimens, no silica scale is formed. Then, sodium combines with silicon to form amorphous glass particles. A comparison has been performed with results obtained on a AISI 330Cb niobium containing alloy in the same oxidizing conditions. It is then concluded that sodium carbonate coatings could only favours silica formation on niobium containing alloy due to a reaction between sodium and niobium