“Colossal” interstitial supersaturation in delta ferrite in stainless steels: (II) low-temperature nitridation of the 17-7 PH alloy

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• 作者：D. Wang ; H. Kahn ; F. Ernst ; A.H. Heuer
• 关键词：Stainless steel ; Nitridation ; Ferrite ; Transmission electron microscopy
• 刊名：Acta Materialia
• 出版年：2017
• 出版时间：1 February 2017
• 年：2017
• 卷：124
• 期：Complete
• 页码：237-246
• 全文大小：3239 K
• 卷排序：124

文摘

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 M2N1-x are observed at low nitriding temperatures (623 and 653 K), but were absent during nitridation at a higher temperature (713 K).