Influence of Minor Alloying Elements on the High Temperature Oxidation Behaviour of a 20 % Cr-25 % Ni-Nb steel

✍ Scribed by J. E. Antill

• Publisher: John Wiley and Sons
• Year: 1971
• Tongue: German
• Weight: 636 KB
• Volume: 22
• Category: Article
• ISSN: 0947-5117
• DOI: 10.1002/maco.19710220608

✦ Synopsis

Abstract

The influence of minor alloying additions of yttrium, silicon and manganese on the oxidation behaviour of a 20% Cr ‐25% Ni‐Nb steel is considered for an environment of carbon dioxide at 800–1100°C. Emphasis is given to the fact that accurate assessments of the effects, based upon comparisons of the behaviour of different steels, frequently require variables such as metallurgical condition and surface finish to be controlled as closely as composition. In particular large grain size is associated with poor oxidation resistance.

Yttrium at the level of 0.1–1.3% increases the adherence of the oxide scale over the whole temperature range considered, but only enhances oxidation resistance at 1000–1100°C. It also results in intergranular oxidation at the higher temperatures. Manganese at a concentration of 0.5–1.0% might exert an adverse influence during the early stages of oxidation but has no effect over the long term (i.e. 1000–6000 h). Silicon is considered beneficial at temperatures up to at least 850°C, with there being an optimum concentration in the region of 0.6–0.7%.

By a process of deduction it is concluded that the oxidation resistance of the basis steel and its derivatives results primarily from the protection afforded by a thin layer of oxide at the oxide/metal interface. The outer scale affords little or no protection.