冷間鍛造用超硬合金の曲げ疲労特性  [in Japanese] Bending Fatigue Characteristics of Cemented Carbides for Cold Forging Tools  [in Japanese]

It is very important to acquire knowledge on bending fatigue characteristics of cemented carbides tools for cold forging, because the tools are generally applied under strong repeated stress at their use. In this study, the effects of grain size of WC and Co content on the bending fatigue characteristics were mainly investigated for fine and coarse-grained WC-0.5∼1.0mass%Cr<SUB>3</SUB>C<SUB>2</SUB>-10∼22mass%Co alloys and the relation between transverse-rupture strength and fatigue limit was discussed.<BR>The results obtained were as follows: (1) The bending fatigue limit of fine-grained WC alloys was higher than that of coarse-grained WC alloys and that of low Co alloys was higher than that of high Co alloys in each WC grain size. This tendency was similar to the case of transverse-rupture strength. (2) The fracture origin observed in low cycle range was mostly aggregated WC, while that in high cycle range above 10<SUP>5</SUP> cycles showed tendency to change Co pool or its segregation. (3) There was a very strong correlation between transverse-rupture strength and bending fatigue limit, and 45∼55% of the transverse-rupture strength was equivalent to the bending fatigue limit. This relation enables to estimate the fatigue limit of cemented carbides.