"Colossal" interstitial supersaturation in delta ferrite in stainless steels: (II) low-temperature nitridation of the 17-7 PH alloy. (1st February 2017)

• Record Type: Journal Article
• Authors: Wang, D.; Kahn, H.; Ernst, F.; Heuer, A.H.
• Is Part Of: Acta materialia. Volume 124(2017)
• Page Start: 237
• Page End: 246
• Publication Date: 2017-02-01
• Subjects: Stainless steel -- Nitridation -- Ferrite -- Transmission electron microscopy; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2016.11.004
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Low-temperature gas-phase nitridation has been studied in interstitially-hardened 17-7 precipitation-hardening stainless steel. After nitridation, conventional transmission electron microscopy reveals that delta ferrite grains in such alloys show a uniform weak diffraction contrast. Chemical analysis reveals that the weak-contrast ferrite grains contain an enormous interstitial nitrogen supersaturation (>20 at.%). Surprisingly, there is no significant tetragonality in these weak-contrast ferrite grains. Such weak diffraction contrast is attributed to a nanometer-scale nitridation-induced spinodal decomposition of delta ferrite grains. In addition, nitride nanoparticles are observed in the steel, and were identified as rocksalt-structured MN nitride (M: Fe, Cr, Ni, and Al). Further, platelets of hexagonal M2 N1- x are observed at low nitriding temperatures (623 and 653 K), but were absent during nitridation at a higher temperature (713 K). Graphical abstract: Image 1