Journal of Materials Processing Technology 168 (2005) 189–194 Kinetics of low temperature plasma carburizing of austenitic stainless steels Y. Sun ∗ School of Materials Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore Received 6 March 2003; received in revised form 6 March 2003; accepted 11 October 2004 Abstract A low temperature plasma carburizing technique has recently been developed to engineer the surfaces of austenitic stainless steels for combined improvement in wear and corrosion resistance. The resultant carburized layer is characterized by the supersaturation of carbon in austenite lattices, the much-increased hardness and wear resistance, and most importantly its superior corrosion resistance. This paper presents recent experimental results on the kinetics of this novel process, in terms of the growth of the precipitation-free layer and its variation with processing temperature, time and substrate material. This work demonstrates that the low temperature carburizing process is a diffusion- controlled process, and only when the processing temperature is sufficiently low can a precipitation-free layer be produced. In addition, the chemical compositions of the substrate material also affect the formation and kinetics of the precipitation-free layer. By proper process control and material selection, a high-quality carburized layer 10–50 m thick can be produced at temperatures between 400 and 500 ◦ C for wear protection in highly corrosive environments. © 2004 Elsevier B.V. All rights reserved. Keywords: Stainless steel; Plasma carburizing; Kinetics; Diffusion 1. Introduction Austenitic stainless steels are the most widely used corrosion-resistant materials in various sectors of industries, due to their excellent chemical and metallurgical properties. However, they are notorious for their poor friction and wear characteristics. Attempts have been made during the past decades to engineer the surfaces of this type of materials so as to improve their surface hardness and wear resistance [1–5]. Most of these efforts, however, result in a decrease in the corrosion resistance of the stainless surface [2,3]. Recent research and development in surface alloying of austenitic stainless steels have therefore been directed towards com- bined improvement in wear and corrosion resistance [5,6].A major breakthrough has been made in this connection, which involves the incorporation of a large amount of carbon into ∗ Fax: +65 67909081. E-mail address: asysun@ntu.edu.sg. the surfaces of austenitic stainless steels at temperatures suf- ficiently low to avoid carbide precipitation [7,8]. This has led to the development of a low temperature plasma carburiz- ing process [9], which is carried out at temperatures between 300 and 600 ◦ C and produces a hardened layer character- ized by the supersaturation of carbon in austenite lattices, the much-increased hardness and wear resistance, and most importantly its superior corrosion resistance [7]. This paper presents recent experimental results on the kinetics of this novel process, in terms of the growth of the precipitation- free layer and its variation with processing temperature, time and substrate material. 2. Experimental Three austenitic stainless steels were used in the present work, including AISI 316, 304 and 321 steels. Table 1 gives the chemical compositions of the investigated materials. Specimens were machined from hot-rolled bars 25.4 mm in 0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2004.10.005