Abstract

Chromium, as a strong nitride-forming element, is widely regarded to be an “essential” ingredient for the formation of a nitrogen-expanded lattice in thermochemical nitrogen diffusion treatments of austenitic (stainless) steels. In this article, a proprietary “chrome-free” austenitic iron-nickel alloy, Invar^® 36 (Fe-36Ni, in wt pct), is characterized after triode plasma nitriding (TPN) treatments at 400 °C to 450 °C and compared with a “stainless” austenitic counterpart RA 330^® (Fe-19Cr-35Ni, in wt pct) treated under equivalent nitriding conditions. Cr does indeed appear to play a pivotal role in colossal nitrogen supersaturation (and hence anisotropic lattice expansion and superior surface hardening) of austenitic steel under low-temperature (≤ 450 °C) nitrogen diffusion. Nevertheless, this work reveals that nitrogen-induced lattice expansion occurs below the nitride-containing surface layer in Invar 36 alloy after TPN treatment, implying that Cr is not a necessity for the nitrogen-interstitial induced lattice expansion phenomenon to occur, also suggesting another type of γ_N.

中文翻译：

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三极管等离子体渗氮下非不锈钢奥氏体Invar 36®的氮诱导晶格膨胀

抽象的

铬是一种很强的氮化物形成元素，被广泛认为是奥氏体（不锈钢）钢热化学氮扩散处理中形成氮膨胀晶格的“必不可少”成分。在本文中，一个专有的“无铬”奥氏体铁-镍合金，因瓦^®在400℃下36（FE-36Ni，在重％），其特征在于三极管等离子体氮化（TPN）后处理，以450℃和比较以“不锈”奥氏体对口RA 330 ^®（Fe-19Cr-35Ni，wt wtt）在等效氮化条件下处理。在低温（≤450°C）的氮扩散下，Cr确实确实在奥氏体钢的巨大氮过饱和（因此各向异性晶格膨胀和优异的表面硬化）中起着关键作用。然而，这项工作表明，在TPN处理后，Invar 36合金中的含氮化物表面层下方会发生氮诱导的晶格膨胀，这意味着Cr并不是发生氮间隙诱导晶格膨胀现象的必要条件，这也暗示了另一种类型的γ _ñ。