OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 2 2024 а b Fig. 5. Graphs of the first (a) and second (b) derivatives of the relationship of expansion Δl on temperature T for WC-Co specimens with different cobalt content obtained during cooling An intermediate extremum in the lines of the second derivative for heating may result from the errors caused by the mechanism of the dilatometer and is not observed in cooling. Table 2 summarizes the values of characteristic points T1 and T2 for all WC-Co cemented tungsten carbides obtained during heating (Fig. 4) and cooling (Fig. 5). Fig. 6 shows graphs of the dependence of T1 and T2 on cobalt content, where the black lines show the average values and the red lines show the root-meansquare (RMS) deviations from these values. Ta b l e 2 Temperatures T1 and T2 during heating (↑) and cooling (↓) of WC-Co with different cobalt content Temperature Co, % Mean value 3 6 8 10 15 20 Т1 ↑ 638.8 626.2 630.6 628.6 628.4 633.7 631.1 ↓ 628.1 627.7 631.6 634.6 631.2 634.1 Т2 ↑ 793.5 803.9 791.2 815.1 789.6 809.7 804.1 ↓ 818.5 816.8 801.4 818.5 797.5 793.8 Analysis of the results shows that the values of T1 and T2 during heating and cooling for different cobalt content are very similar. For T1, the maximum deviations from the average value were 1.2 %, and for T2 the maximum deviations from the average value were 1.8 %; the RMS deviations were 0.6 % and 1.4 %, respectively. In absolute terms, the RMS deviations for T1 were ±4 °C, and for T2 the standard deviations were ±11 °C. At the same time, changes in actual temperature values depending on cobalt content is insignificant and random, which is apparently due to experimental errors. Thus, we can conclude that the quantitative composition of WC-Co cemented tungsten carbides has virtually no effect on the temperatures of the onset of oxidation and the transition to active oxidation. Fig. 6. Dependences of characteristic temperatures T1 and T2 on cobalt content, obtained during heating (↑) and cooling (↓)
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