Transformation-toughening in cemented carbides: Part II. Thermomechanical treatments

WC-(Fe, Ni, C) cemented carbides can be successfully transformation-toughened by careful control of binder composition and taking into consideration the effect of thermal residual stress on the transformation characteristics of the binder. An additional degree of control on the metastability of the binder phase can be achievedvia thermomechanical treatments. These treatments consist of transforming an austenitic binder to martensite by cooling in liquid nitrogen followed by a suitable high temperature heat treatment to reaustenitize it. Thein situ deformation of the binder caused by the large shape and volume changes that accompany its transformation to martensite thus provides the mechanical component of the thermomechanical treatment. Subsequent heat treatments not only reaustenitize the binder but also modify its susceptibility to undergo stress-induced transformation. It is shown that the hardness/fracture toughness behavior of WC-(Fe, Ni, C) cemented carbides can be significantly improved by the application of such treatments. A qualitative explanation for the enhancements in fracture toughness provided by thermomechanical treatments is offered based on a careful examination of the changes in phase constitution of the binder that occur during these treatments. Formerly Manager, Research-Development, Reed Tool Company, Houston, TX.