Abstract
1. When hard-alloy cutting plates are heated to 600°C and higher the cobalt binder begins to react with atmospheric oxygen. As a result of the reaction an oxide film forms on the surface, the microhardness of which is by a factor of 5–45 lower than that of the starting material. 2. Under the experimental conditions the most intense formation of oxides for all the hard alloys was observed at a heating temperature of 800°C. 3. In the 600–800°C temperature range the ratio of the growth rate of the film thickness for the different brands of hard alloys remains about constant and is:vVK8∶vT14K8∶vT15K6∶vT30K4=4∶3.3∶2.5∶1. 4. We can conclude from the ratio of the growth rates of the oxide films of the investigated alloys that hard alloy T30K4 has the least oxidizability in the 600–1100° temperature range. 5. The Rockwell-A hardness (HRA) of the plates in the interior after heating to 800–1100°C and holding for 80–180 min drops by 1–3%. The greatest drop of hardness is observed for alloy VK8 (3%), the least for alloy T15K6. 6. The microhardness H200 of the hard alloys after heating and holding dropped by 7–9%.
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