HIGH TEMPERATURE OXIDATION BEHAVIOR OF AUSTENITIC STAINLESS STEEL WITH HIGH SILICON CONTENT.

A new 13Ni-18Cr-3. 5Si austenitic stainless steel has proved in service to have excellent resistance to high temperature oxidation. In the present investigation the mechanism of this resistance was studied in cyclic oxidation tests at 1000 C. No internal oxide was detected by optical microscopy or electron probe microanalysis of sections, while the adherence of the surface oxide was retained. The formation of a very thin amorphous SiO//2 film was observed beneath the innermost oxide Cr//2O//3 by scanning electron microscopy and electron probe microanalysis of the back of the oxide chemically stripped from the alloy. It was assumed that this thin SiO//2 film contributed to the improvement of the resistance to oxidation. Protective and mechanical properties of the SiO//2 film were markedly affected by strong deoxidation during steelmaking with RE additions. The good oxide adherence on the steel is attributed to the improvement in the plasticity of the thin SiO//2 film formed at oxide/alloy interface by rare earth element as an impurity. An optimum combination of Si addition and strong deoxidation was concluded to further improve the resistance to oxidation at high temperatures.