Adaptation of Fracture Mechanics Methods for Quality Assessment of Tungsten Carbide Cutting Inserts

Tungsten carbide (WC) is well known as one of the hardest materials widely used in machining, cutting and drilling, especially for cutting tools production. Knowing fracture toughness grants the opportunity to prevent catastrophic wear of a tool. Moreover, fracture toughness of WC-based materials may vary because of different material compositions, as well as a different way of production. Hence, each material should be treated individually. In this paper, SM25T (HW) tungsten carbide (HW-uncoated grade, TNMR 401060 SM25T, manufactured by Baildonit company, Katowice, Poland) was taken into consideration. Sintered carbides-designated as S-are designed to be applied for machining steel, cast steel and malleable cast iron. Fracture mechanics methods were adapted to make a quality assessment of WC cutting inserts. Both quasi-statical three-point bending tests, as well as Charpy dynamic impact tests, were performed to calculate static and dynamic fracture toughness (K_IC and K_ID, respectively). In addition, a special emphasis was placed on the microscopic analysis of fracture surfaces after impact tests to discuss material irregularities, such as porosity, cracks and so-called "river patterns". There is a lack of scientific works in this field of study. However, cutting engineers are interested in obtaining the experimental results of that kind. Although there are a few standardized methods that may be used to determine fracture toughness of hard metals, none of them is expected to be the most reliable. Moreover, there is a lack of scientific works in the field of determining static and dynamic fracture toughness of WC by the presented method. The proposed examination solution can be then successfully used to calculate toughness properties of WC-based materials, as the results obtained seem to be with a good agreement with other works.