WC-10%Co合金の強度におよぼす粒度および炭素量の影響

Abstract

The transverse-rupture strength of the WC-10%Co alloys has been investigated in relation to their mean grain size and binder composition, i.e. carbon contents of the alloys, using the specimens having fairly higher strength than that so far reported by many researchers. The specimens were vacuum-sintered under controlled conditions. The mean grain size of WC ranged from 1.4 to 4.5 μ. The transverse-rupture strength test was mainly conducted according to ASTM B-406-64, and according to JIS B-4104 if necessary.The results obtained were as follows: (1) The alloy exhibited the highest strength at the mean grain size of about 2.0∼2.2 μ, and the arithmetic mean value reached 350∼370 kg/mm2 according to the test of ASTM Standard. (2) It was confirmed that the strength was also affected by the carbon content, in the same way as already pointed out by the present authors in the alloys having usual strength. (3) The strength vs. grain size curves as well as the measured value of the strength appeared to be changeable, depending on both the testing methods and the strength level of specimens. (4) On the fracture surface of each alloy, the region containing the starting point of that fracture was macroscopically observed in the inner region a little apart from the tension-surface. The region was named as “white spot” by the present authors, because the colour of the region looked like silver.