Nitridation Resistance of High-temperature Resistant Cast Alloys - The Effect of Alumina Scales on High-temperature Ammonia Nitridation

Energy vectors, like ammonia as a “hydrogen carrier”, appears to be the ideal solution to reduce greenhouse gas emissions in the energy sector. The carrier vector ammonia has to be cracked into its elements N and H in an endothermic process named Ammonia Cracking, which shares similarities with the steam reforming process. Therefore, the application of centrifugally cast tubes of austenitic high temperature resistant Cr-Ni-Fe alloys is highly probable for ammonia cracking plants due to their high corrosion and excellent creep resistance. This study focuses on the suitability of centrifugally cast austenitic Cr-Ni-Fe-Al alloys forming protective Al2O3 scales under nitridation in ammonia. The influence of alumina scale properties is also addressed. Metallurgical investigations focus on revealing the degradation mechanisms in gas atmospheres of high nitrogen activity.