Hardening Layer Characteristics of SUS304 Steel Gas-sulphonitrided in NH_3,N_2,H_2S and C_2H_2 Gaseous Atmosphere

Abstract

Microstructure and mechanical properties in hardened layers of SUS 304 steel gas-sulphonitrided in NH_3,N_2,H_2S and C_2H_2 gaseous atmosphere were investigated and these characteristics were compared with those of SUS304 steel gas-sulphonitrided with CO_2 gas. Addition of C_2H_2 gas in carrier gas increased the depth of hardened layer with the decreased thickness of compound layer, in comparison with CO_2 gas addition. An increase in volume fraction of (Fe, Cr)_<2-3>N was found in superficial sulphide layer and compound layer, resulting from enrichment of chromium and nitrogen. Excellent mechanical properties such as increased hardness and crack initiation resistance were also completed by C_2H_2 gas addition, although Young's modulus was reduced by 20% and dynamic friction coefficient was increased somewhat.