Effect of WC concentration on structure and properties of the gradient tool materials

Purpose: The goal of this work is to obtain the contemporary gradient materials based on the tungsten carbide reinforced high-speed steel using the conventional powder metallurgy method and increasing the high-steel hardness (80 HRA = 800 HV) by introducing the tungsten carbide as the reinforcing phase, with hardness exceeding 2200 HV. Design/methodology/approach: The materials were fabricated with the conventional powder metallurgy method consisting in compacting the powder in the closed die and finally sintering it. Forming methods were developed for powders of the HS6-5-2 high speed steel and WC, making it possible to obtain material with seven layers in the structure. Findings: It was found out basing on the microhardness tests that hardness of test pieces grows along with the sintering temperature and with WC content in the interface layers and in the high-speed steel ones. It was also observed that porosity decreases along with the WC concentration increase in these layers. It was found out, basing on the comparison of structures and properties of the compacted and sintered test pieces, that in structures of all examined test pieces in the sintered state fine carbides occurred distributed homogeneously in the high-speed steel layer. Research limitations/implications: It was noticed, that increase of the sintering temperature results in the uncontrolled growth and coagulation of the primary carbides and melting up to forming of eutectics in layers consisting of the high-speed steel. Practical implications: Material presented in this paper has layers consisting on one side from the mix of the high-speed steel and WC, and on the other side the high-speed steel, characteristic of the high ductility. Such material is tested for milling cutters. Originality/value: The layers were poured in such way that the surface layer consists of the mix of the high-speed steel and WC, and the middle one from the high-speed steel. The layers inside the material are mixes of the high-speed steel and WC in the relevant proportions.