A study on high temperature gas nitriding and tempering heat treatment in 17Cr–1Ni–0.5C

The effect of the high tempering gas nitriding (HTGN) and tempering treatment in 17Cr–1Ni–0.5C (CN) steel was experimentally investigated. The HTGN was carried out at 1050 °C for 1 h in a gaseous atmosphere containing 98.07 kPa of nitrogen. Chromium nitrides and the austenite phase appeared in the nitrogen-permeated surface layer, whereas, the interior region, into which nitrogen did not permeate, exhibited martensite and austenite phases along with the chromium carbides. The nitrogen content was approximately 0.3% at a depth of 5 μm below the surface layer in the CN specimen after the HTGN. The hardness of the outmost surface of the HTGN treated specimen measured 538 Hv. When it was tempered at 550 °C for 1 h, the hardness of the outmost surface was 860 Hv as a result of the precipitation of mostly Cr2N along with a small amount of Cr23C6 and the secondary hardening effect.