Factors affecting the high‐temperature carburisation behaviour of chromium‐nickel alloys in gaseous environments

Abstract

Abstract The paper is concerned with the corrosion behaviour of a range of commercial and simpler “model” high chromium‐nickel alloys exposed to gaseous carburising environments of low oxygen activity, at temperatures within the range 825°C to 1000°C. H 2 ‐CH 4 mixtures have been used and carbon activities of 0.3 and 0.8 studied by varying the proportion of CH 4 in the mixture. The surface condition of the specimens and its effect upon carburisation behaviour has been investigated as a variable by the use of standardised surface preparation techniques. The kinetics of the corrosion process have been studied by the use of conventional gravimetric techniques and cross‐sectional microstructural examinations have aided in establishing the factors of primary importance in the degradation of materials by carburisation. The contributions made by the temperature and carbon activity of the gaseous environment have been highlighted and the important material variables such as metallurgical form, composition and surface condition have been investigated in order to evaluate their significance.