| 摘要 |
The present invention relates to a silicon nitride based cutting tool insert for chipforming machining of cast iron material having improved mechanical, chemical and wear properties. This is obtained by addition of one or more transition metal oxides which act as sintering aid together with alumina and yttria and also promote the growth of elongated grains of beta silicon nitride during the sintering. Preferably, the inserts are provided with a wear resistant coating as known in the art. The ceramic cutting tool material according to the present invention comprises a beta silicon nitride matrix with total amount of 0.5-10 wt%, preferably 0.5-6 wt%, of an intergranular phase and 0.05-3 wt% of at least one secondary crystalline phase of a transition metal carbide, nitride, carbonitride and/or silicide present as spherical particles with a size of 0.1-2 mu m, preferably submicron (<1 mu m). The transition metal is preferably niobium and/or tantalum. The material has less than 1, preferably less than 0.3, vol% porosity. The beta silicon nitride grains are to at least 10 %, preferably more than 20 %, elongated with an aspect ratio greater than 3, preferably greater than 5. The grain diameter of the beta silicon nitride grains is in the range of 0.2-10 mu m, preferably 0.2-5 mu m, and most preferably 0.2-3 mu m. <IMAGE> |
