NiAl precipitation in delta ferrite grains of 17-7 precipitation-hardening stainless steel during low-temperature interstitial hardening

Interstitial hardening via low-temperature carburization and nitridation has been studied in 17-7 precipitation-hardening stainless steel. During such interstitial hardening, nanometer-scale NiAl precipitates form in delta ferrite in the bulk, but not in the hardened surface layer. In the carburized ferrite grains, regions of NiAl stoichiometry could be identified, but cannot be identified as regions with a different crystal structure. In the nitrided grains, NiAl particles could neither be detected by corresponding changes in local composition nor by their crystal structure.