Features of anode plasma nitrohardening of steel
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SMIRNOV, A.; AUTOR, Nou; KUSMANOV, S.. Features of anode plasma nitrohardening of steel. In: Materials Science and Condensed Matter Physics. Editia a 7-a, 16-19 septembrie 2014, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2014, p. 280.
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Materials Science and Condensed Matter Physics
Editia a 7-a, 2014
Conferința "Materials Science and Condensed Matter Physics"
Chișinău, Moldova, 16-19 septembrie 2014

Features of anode plasma nitrohardening of steel


Pag. 280-280

Smirnov A., Autor Nou, Kusmanov S.
 
Belarusian State University
 
Disponibil în IBN: 18 martie 2019


Rezumat

The purpose of present research is to study of the effect of electrolyte composition, temperature and duration of treatment on parameters of saturation of steel 45 by nitrogen and obtained surface properties.  The aqueous solution of ammonium chloride (5–15%) and ammonia (2.5–10%) is used as a working electrolyte. The treatment temperature was varied from 650 to 850oC, the duration – from 2 to 5 minutes.  According to X-ray analysis nitrides Fe4N and Fe2-3N, oxides FeO and Fe3O4, martensite, retained austenite and ferrite of the initial structure were observed in the surface layer after nitrohardening. It is shown that the intensity of the line Fe4N is increased when the nitrohardening temperature is increased from 650 to 750oC. The phase of Fe2-3N was detected only at 750oC. Thus, increase in temperature from 650 to 750oC improves diffusion of nitrogen to steel.  According to scanning electron microscopy the surface layer consists of alternating diffusion layers: the surface oxide layer, the nitride zone containing dispersed nitrides Fe4N and Fe2-3N (only after 750°C), the diffusion zone containing only dispersed nitrides Fe4N, solid solution of nitrogen in the steel and the initial ferrite-pearlite structure.   By EDX analysis results, the maximum concentration of nitrogen is observed directly under the oxide layer and then is decreased in depth of the sample. The maximum concentration of nitrogen in the modified layer is reached after the treatment at 750oC. The nitrogen concentration is increased with treatment duration from 5 to 10 minutes. The diffusion of nitrogen leads to decrease in the carbon concentration in the surface layer due to its displacement. Furthermore, the displacement of carbon correlates to the intensity of the nitrogen diffusion under various treatment conditions.  Thickness of the hardened layer is increased when ammonium chloride concentration is rised and ammonia concentration is decreased. It is correlated with the rate of anodic dissolution and thickness of the oxide layer. The maximum thickness of the hardened layer is formed after the treatment at 750°C. Thickness of the diffusion layers are increased trivial with treatment duration.   Microhardness distribution on the surface profile is correlated with the phase composition of the modified layers. The maximum value of microhardness (1200 HV) and the greatest depth of the hardened zone are observed after nitrohardening at 750°C and 10 minutes.  The surface roughness after nitrohardening during 5 minutes in different electrolytes and at different temperature is increased compared to the untreated surface. It is explained by lower anode dissolution rate. The surface roughness decrease is observed after 10 minutes treating only.