Researches on the Diffusion Phenomena in the Thermo-Chemical Treatment of Oxy-nitrocarburizing of Some Grey Cast Irons

Abstract

The thermo-chemical treatment of oxy-nitrocarburizing consists in the enrichment of materials in C, N and O in order to improve the physico-mechanical properties and the use of the materials. This leads to the increase in exploitation life, the increase of wear resistance, galling, corrosion, and slight erosion. The research presented in this article followed the study of the application of this treatment and the results obtained on pearlitic grey cast iron with different chemical compositions, domain in which there are few experimental results published. The results obtained on a number of 10 samples, presented in the article, highlighted the good compatibility of these materials with the thermo-chemical treatment of oxy-nitrocarburizing, obtaining on the surface some white layers which give good anti-corrosive properties, similar to those obtained on steel. There was no correlation between the depth of the white layer and the chemical composition of the studied cast iron. It was also emphasized that the depth of nitrogen diffusion is influenced by the chemical composition of the studied materials which is directly proportional to carbon equivalent (Ceq) of cast iron.

The Effect of Oxidation Process After Nitrocarburization on Tribological Properties of AISI 4140 Steel

“…Fakat çoğu zaman oluşan tabakanın gözenekli yapısından dolayı NK işlemi tek başına yeterli olmamaktadır. NK sonrası oksidasyon işlemi (NK+O) uygulamak malzemenin aşınma ve korozyon direnci arttıracak iyi bir seçenek olarak görülmektedir [13]. Oksidasyon işlemi oksijence zengin gaz veya gaz karışımı atmosferinde, 350-500°C sıcaklık aralığında gerçekleştirilmektedir.…”

Obtaining the Controlled Sulphonitrocarburized Layer Phase Compositions, by the Variation of the Solid Powdery Medium Components

“…The SNC process applied to steel and cast iron products, at temperatures below the eutectic transformation according to the Fe-N diagram, can be performs in a variety of technological variants, differing in terms of phase composition of media provider by the elements in native state and of aggregation state [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. The most commonly solutions that have been called starting with process implementation, are those in liquid media and in this case, the melts which contain components with high toxicity used in initial melting are predominant [1][2][3][4][5][6][7][8]13].…”

“…The information concerning solid powder mixture used in SNC are quite rare, one of these indicating the environments containing K4Fe(CN)6 [7], a hazardous component, and another more recent, representing a pattern request [10,16], which calls for carbamide as active component, a direct source of nitrogen and carbon and to powder Sulphur. Another component it is the ammonium chloride having double role in process, active component (source of ammonia), but also by the surface cleaner/activator.…”