Plasma post oxidation of nitrocarburized hot work steel samples
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Pulse plasma oxidation of untreated, salt bath nitrocarburized and plasma nitrided/nitrocarburized samples made of hot work steel grade H11 was investigated. A continuous multi-step plasma processing was performed consisting of a half an hour plasma nitriding at 520 degreesC followed by 3.5 h nitrocarburizing at the same temperature and by a subsequent post-oxidation in a low current density H2O glow discharge during 45 min at 450 degreesC. The salt bath nitrocarburizing was carried out at a temperature of 580 degreesC for 210 min and was followed by the oil quench. In order to compare the oxide layer growth on the base material and on the epsilon-Fe-2(N,C)(1-x) layer, the salt bath treated sample. was half cut and plasma post-oxidized in a 80% H2O-20% H-2 glow discharge for 45 min at the temperature of 480 degreesC. In plasma processing pulse power supply was used with 57 mus pulse duration and 3 mus pulse pause. The surface structures were analyzed by optical microscopy, SEM and XRD,... while Vickers microhardness test was used for measuring the surface microhardness and microhardness distribution over the sample cross sections. On the nitrocarburized surfaces XRD analyses revealed the existence of a superficial magnetite oxide layer and the presence of a e phase and a small amount of gamma phase, while a hematite Fe2O3 layer was formed on untreated sample surface. (C) 2003 Elsevier B.V. All rights reserved.
Keywords:plasma nitrocarburizing / plasma post-oxidation / salt bath nitrocarburizing pulse plasma / magnetite / hematite / hot work steel
Source:Surface and Coatings Technology, 2004, 177, 277-283
- 30th International Conference on Metallurgical Coatings and Thin Films, Apr 28-May 02, 2003, San Diego, CA