High Temperature Oxidation Resistance of 9Ni Steel

Oxidation rates and scale/steel interface configuration of 9Ni steels were investigated at 1000–1250 °C in air. The results revealed that Cu addition caused high temperature oxidation resistance to deteriorate. High temperature oxidation rates increased and scale/steel interface configuration became complicated due to Cu addition. Scale/steel interface appeared to be network above certain temperature. Temperature required to form network scale/steel interface dropped more than 100 °C for 1.5% Cu-containing steel. (Fe, Ni, Cu)x Oy in inner oxidation layer dissociated to Fe-Ni-Cu phase and released active oxygen which can react with base steel easily. So the inner oxidation layer became the second source of oxidizing agent besides atmosphere. Internal stress at austenite grain boundary caused local oxide to fragment. So the scale/steel interface appeared to be network. Liquid Si-rich phase formed at sufficiently high temperature. Penetration of the liquid Si-rich phase along austenite grain enhanced austenite grain oxidizing.