**1. Introduction**

338 Corrosion Resistance

Thaiwatthana, S., Li, X. Y., Dong, H. and Bell, T.: *Corrosion wear behaviour of low temperature plasma alloyed 316 austenitic stainless steel*, Surface Engineering (2003) 19, *3,* 211-216 X.Y. Li, J. Buhagiar, H. Dong, Characterisation of dual S phase layer on plasma carbonitrided biomedical austenitic stainless steels, *Surf. Eng*. 26 (2010) 67-73. Y. Sun and E. Haruman, Influence of processing conditions on structural characteristics of

Y. Sun and T. Bell.: *Dry sliding wear resistance of low temperature plasma carburised austenitic* 

Y. Sun and T. Bell.: *Effect of layer thickness on the rolling-sliding wear behavior of low- temperature plasma-carburized austenitic stainless steel*, Tribology Letters (2002) 13, *1,* 29-34 Y. Sun, Kinetics of low temperature plasma carburizing of austenitic stainless steels, *J. Mater.* 

Y. Sun, X.Y. Li and T. Bell, Low temperature plasma carburizing of austenitic stainless steels for improved wear and corrosion resistance, *Surf. Eng*. 15 (1999) 49-54. Y. Sun, X.Y. Li and T. Bell, X-ray diffraction characterisation of low temperature plasma

nitrided austenitic stainless steels, *J. Mater. Sci.* 34 (1999) 4793-4802

*stainless steel*, Wear (2002) 253, *5-6,* 689-693

*Proc. Tech.* 168 (2005) 189-194.

4069-4075.

hybrid plasma surface alloyed austenitic stainless steel, *Surf. Coat. Tech.* 202 (2008)

In general, the solid solution austenitic phase (γ) with high chromium content (12 % - 20 %) is responsible about the excellent corrosion performance of austenitic alloys. This advantage allows these alloys to use in biomedical, food and chemical, pulp and paper chemical, petrochemical, heat exchange and nuclear power plant industries [1-4]. However, most of these applications are suffering from their relatively low hardness and poor tribological properties.

Various surface modification technologies such as nitriding, carburizing and nitrocarburizing are used to improve the mechanical and tribological properties of austenitic stainless steels [5-12]. In most cases an increase in surface hardness is accompanied by a decrease in corrosion resistance [13]. The decrease in the corrosion resistance is caused by heavy precipitations of chromium carbide and chromium nitride on the grain boundaries, which are surrounded by chromium-depleted zones [14]. More investigations are succeeded to maintain and sometimes to improve the corrosion resistance of stainless steels after nitriding [15-16]. It is well known that the formation of nitrogen supersaturated solid solution phase without CrN precipitations should maintain the good corrosion resistance of stainless steel [5, 17].

In this paper we present the effect of N2 to C2H2 gas pressure ratio on the corrosion performance and tribological properties of AISI 304 austenitic stainless steel after rf plasma carbonitriding at a relatively low pressure.
