Effects of Heat Treatment Conditions on Formation of Expanded-Austenite Phase in Austenitic Stainless Steels by Combining Active Screen and DC Plasma Carburizing Processes

Abstract

A low temperature plasma carburizing process can produce an expanded-austenite layer (generally called the S phase), which has high hardness and corrosion resistance at the surface of austenitic stainless steels. We have investigated S phase formation behaviors by using a combined process of active screen and DC plasma carburizing for austenitic stainless steels such as JIS SUS304 and 316 with the aim of developing a highly effective and efficient production technique. The influence of carburizing parameters (processing temperature, time, gas atmosphere, etc.) on the formation of the S phase was studied in terms of thickness, hardness, carbon concentration, lattice constant, and residual stress. The mechanical properties and corrosion resistances of the obtained S phases were also evaluated by using a ball-on-disk test and a salt spray test (SST). The results show that S phases produced efficiently by the combined process under a condition of 733 K and a 10.5 vol% of CH₄ gas ratio have both excellent wear and corrosion resistances.

 

This Paper was Originally Published in Japanese in J. Jpn. Soc. Heat Treatment 56 (2016) 352–360.