Plasma paste boronizing treatment of the stainless steel AISI 304

Abstract

Abstract Various surface properties of boride layer formed by plasma paste boronizing were examined. A boride layer of flat structure was formed on the AISI 304 stainless steel substrate by plasma paste boronizing treatment with several different temperatures between 1023 and 1223 K under a gas mixture of Ar/H2:2/1(vol.%). The paste was composed of 30 wt% boron and 70 wt% borax. The properties of boride layer were evaluated by a micro-Vickers hardness tester, scanning electron microscopy, and electron microprobe analysis. The cross-sectional microstructure consisted of a boride layer, a Ni-rich layer, a Cr-rich layer, and a substrate structure in series. The surface boride layer was found to form in a shorter time using plasma paste boronizing, comparing with that using the conventional boronizing method. XRD analysis of boride surface revealed various peaks of FeB, Ni3B, and CrB, showing CrB peaks that were more intense than other peaks. The activation energy for the formation of boride layer in the plasma paste boronizing treatment was calculated to be 123 kJ mol−1, which is lower than that in the conventional boronizing treatment. The microhardness (HV) of these boride layers was measured to be in the range of 180–2000.