Tensile Strength of Ultrafine-Grained Cemented Carbide Containing Ti(C,N)

The bending strength of ultrafine-grained cemented carbides exceeds that of normal-grained cemented carbides. This was thought to be due to the smaller size of defects within the ultrafine-grained cemented carbides. However, this had not been verified because the specimens broke up into numerous smaller pieces during bending tests. In addition, previous studies on the bending strength of normal-grained cemented carbides reported that there is limiting strength which is a region of not increasing bending strength by reducing the defect size. Therefore, in this study, with the aim of clarifying the cause, we conducted tensile test, in which many small pieces are expected to be unlikely to be generated, and additional tests such as bending test. The ratio of bending strength to tensile strength was comparable between the normal- and ultrafine-grained cemented carbides. The number of fragments produced at fracture was also similar between the normal- and ultrafine-grained cemented carbides when they had similar strength. These results indicated that there was no clear difference in the fracture phenomena of these two cemented carbides. It was clear that the tensile strength of both the normal- and ultrafine-grained cemented carbides increased as the size of the defects decreased and the limiting strength did not emerge. This finding encourages further strength enhancement of ultrafine-grained cemented carbides by controlling defects.