炭素量の変化を考慮してのWC-10%Co合金の性質と粒度との関係

Abstract

It has been reported that the composition of the binder-phase of two phase alloys changes remarkably from about 2∼3% to 9∼10%W due to a small change of their carbon content, so that the properties and the aging characteristics of cemented carbides are directly influenced by the composition. In this report, some properties of cemented carbides affected by the particle size are investigated in close consideration of the composition of the binder phase. The properties such as hardness, strength, magnetic saturation, coercive force and electrical resistivity of the alloys and the lattice parameter of binder phase, are measured.The results obtained may be summarized as follows. (1) The value of coercive force is not only dependent upon the particle size, but also upon the tungsten content of the binder phase. Therefore, the determination of the mean particle size by a coercive force method is erroneous. (2) The hardness and electrical resistivity decrease with increasing of the particle size and the carbon content. (3) The transverse-rupture strength shows a maximum under the condition that the mean particle size is about 2.0μ and the carbon content of WC is about 6.20% which is almost the maximum carbon content of the two-phase alloy. And as a condition to obtain a maximum strength, it is generally accepted in the two-phase alloy that the carbon content should be almost maximum, if the particle size is nearly equal to or less than about 2.0μ, but in the case of a fairly coarser particle size it should be almost minimum. (4) Both the lattice constant of the binder phase and the magnetic saturation of the alloy are not influenced by the particle size of WC, that was developed after sintering. Therefore, it is clear that the tungsten content in the solid binder phase has no relation to the particle size, provided that the carbon content of the alloy is invariable. (5) But the rate of precipitation of Co3W, when low carbon alloys are annealed at low temperatures, is sensitive to the particle size. A carbide structure of coarse and homogeneous particle size is desirable to stabilize the properties of low carbon alloys at a higher temperature.