The influence of recycled materials on the microstructure, characteristics and cutting performance of cemented carbides

Sammanfattning

Cemented carbides are composite materials used in cutting tools that consist of tungsten carbide (WC) embedded in a binder phase, making a good combination of high hardness and good toughness. In some cases, cubic carbides are also added to increase the hardness of the material, however, it will make the material more brittle. The demand for recycled cemented carbide in cutting tools has grown for the past decades due to the expense of tungsten raw material. Powder reclamation by zinc process (PRZ) is one of the direct recycling routes for cemented carbides. A proper sorting of the material to be recycled with this process will allow for a better controlled product while preserving the tungsten carbide grain size. In this project, a study of the microstructure and cutting performance of micro grain as well as gradient (coarse) cutting material was conducted. Different fractions of grade 1 PRZ are investigated within micro grain material as well as different grade 2 and 3 PRZ fractions within gradient material. The gamma phase is also investigated within the gradient material through compositional simulations by Thermo-Calc and through image analysis of backscatter electron imaging (BSE) and a combination of energy dispersive X-ray (EDS) and electron backscatter diffraction (EBSD). The grain size analysis done through SEM-electron backscatter diffraction (EBSD) and an MTEX script confirmed that micro grain cutting tools with grade 1 PRZ contained finer grains with a smaller mean equivalent circle diameter compared to the gradient material containing grade 2- or 3 PRZ. However, the coarse grains analysis performed with the help of light optical microscopy (LOM) showed that an increase in grade 1 PRZ fraction caused more coarse grains to be present within the microstructure, unlike the samples that contained grade 2 or 3, where no coarse grains were found. It was also found that grade 3 PRZ, resulted in finer grains within the microstructure of gradient materials as well as a smaller mean equivalent circle diameter of WC grains. Furthermore, the cutting performance showed that the presence of grade 2 and 3 PRZ within the gradient material will cause less plastic deformation (PD).