Abstract: An optimized low-temperature chromizing process at 500oC was realized on a plain medium-carbon steel with 0.45 wt pct carbon via a duplex chromizing process which consists of a precursor plasma nitriding, and a followed salt bath thermoreactive dposition and diffusion (TRD) chromizing process. CrN layer with a thin diffusion layer underneath was formed. The duplex chromizing process was studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). It was found that the chromizing speed at 500oC was successfully enhanced by adding more Cr-Fe powders into the salt bath, and the CrN layer formed at the cost of the prior nitride compound layer. A CrN layer with average 8.1μm in thickness and 1382 HV0.01 in microhardness was formed on the substrate by duplex chromizing at 500oC for 24 h. Further more, the CrN layer consisted of nanocrystalline CrN grains.

Key words: Chromizing, Plasma nitriding, Thermoreactive deposition and diffusion (TRD), CrN