In this study, boride layers on C70W2 steel, obtained by boronizing at temperatures ranging from 870 to 970 °C and durations from 4 to 8 h, were investigated. The characterization of the layers was carried out using a new approach based on the change in the volume fraction of the boride phase. Analysis of the change in volume fraction showed that an increase in temperature and duration resulted in thicker layers, with temperature having a greater influence. Based on the volume fraction of the boride phase, the layer is divided into compact and toothed parts. With increasing temperature, the thicknesses of both parts of the layer increased. The thickness of the toothed part was the highest after 6 h of boronizing and further prolongation of boronizing led to a decrease in the thickness. Regression equations were estimated for the prediction of the volume fraction of the boride phase, the thickness of the compact part, and that of the toothed part of the boride layer as a function of the boronizing parameters. This study has shown that characterization based on the volume fraction of the boride phase offers advantages over the conventional method based on the average thickness of the layer.

Diffusion forming of a hard carbide layer has been used for many years, mostly in Japan (Toyota Diffusion Process, TDR) and in the USA (Thermoreactive Deposition, TRD) but not so much in Europe. Carbide layers on constructive parts and tools formed by a diffusion process, especially a vanadium carbide layer, have excellent tribological properties and some technical and economical advantages in comparison with carbide layers formed by chemical vapour deposition (CVD) and physical vapour deposition (PVD) processes. Diffusion formed layers are thicker with very strong bond to steel substrate and are produced using significantly cheaper equipment than for deposition coating. The process has one disadvantage: partial decarburization of the steel surface beneath the carbide layer reducing hardness and loading capacity of the surface. This disadvantage is eliminated by a developed and patented duplex process introducing previous carburizing to prevent decarburization and to form a hardened case under layer beneath the carbide layer. The new developed process should contribute to widely application of diffusion carbide coating for automotive industry. Mathematical model and program for optimization of process is presented as well as some examples of application: extruders for medium with very abrasive particles, aluminium die casting moulds, etc.