Isothermal and non-isothermal oxidation kinetics of nanooxide dispersed high Cr ferritic steel prepared by mechanical alloying

Abstract

Oxidation kinetics based on Kissinger–Akahira–Sunose analysis of high Cr ferritic steel synthesised by mechanical alloying of elemental powder blend of 84Fe–13·5Cr–2·0Al with 0·5 nano-Y₂O₃ (all in wt-%) dispersion followed by cold compaction with 250 MPa pressure and sintering in vacuum (10⁻⁶ mbar) at 1000°C for 1 h have been investigated under isothermal (600–900°C for up to 50 h) and non-isothermal conditions (50–1200°C with heating rates of 10, 20, 30 or 40°C min⁻¹). Mechanism of oxidation was taken place by counterionic transport of oxygen from surface to interior and cations (Cr³⁺/Fe³⁺) from the interior to the surface through grain boundary at low oxidation temperature (∼600°C) and through grains at high oxidation temperature (700–900°C). Early formation of Cr rich spinel layers on the surface improves the oxidation resistance by acting as the diffusion barrier against counterionic transport of ions during oxidation.

Keywords:

• Nanooxide dispersion
• Ferritic steel
• Isothermal oxidation
• Non-isothermal oxidation
• Activation energy

Acknowledgements

The authors would like to thank Professor R. Mitra for providing the oxidation set-up. Partial financial support from CSIR (project no. OLP 280 at CSIR-CGCRI, Kolkata) and INAE (Visvesvarya Chair Professorship to I. Manna) is gratefully acknowledged.