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The heat content of 19 kinds of iron-carbon alloys ranging from 0.07 to 5.07% carbon were measured at each of different high temperatures up to beyond the melting point by the method of mixture, and their mean and true specific heats were deduced therefrom. From the relation of the heat of peritectic reaction and carbon concentration, a value of 14.7 calories was given as the heat of reaction per gram of the specimen in 0.13% carbon, and the heat of solution of gamma-crystal below 0.13% carbon into delta-crystal decreases with the rise of temperature. The heat content and specific heat of cementite at high temperatures were found by extrapolation of the present results, and the heat of Ao transformation of cementite was estimated to be 9.35 calories. The heat of fusion of delta-crystal to melt into the liquid of the conesponding carbon concentration is 64.90 calories per gram of gamma-crystal in 0.07% carbon. and 65.31 calories for that in 0.03% carbon. The heat of fusion of gamma-crystal on the solidus to melt into the liquid of the corresponding carbon concentration is 57.80 calories per gram of gamma-crystal in 1.70% carbon, and 67.19 calories for that in 0.13% carbon. As the latent heat of fusion of eutectic alloy was found to be 60.91 calories per gram. The heat of transformation of alpha- into gamma-iron at the As transformation point was calculated to be 5.59 calories· per gram for pure iron and 16.60 calories at 7200 for eutectoid steel, respectively. The heat of solution of cementite into gamma-crystal of 0.90% carbon is 11.15 calories per gram at 720°, and decreases with the rise of temperature and carbon concentration of gamma-crystal. The latent heat of fusion was obtained as the limiting value of the heat of fusion, and the former is always somewhat less than the latter. The latent heat of fusion of cementite was found to be 65.0 calories per gram, the melting temperature being estimated to be 1600°. The heat of mixture of any two liquids or solids in the iron-carbon system is proportional to the product of their quantities a and b, and inversely proportional to the sum of these quantities, being always endothermic reaction. So the heat of mixture H1 in these cases will be given as follows H1 = K (ab/(a+b)) where K = f(t) [(C1-C2)exp2] The proportional constant K is a function of temperature and the square of the difference of carbon concentrations C1 and C2 of two liquids or solids.
The results of the pre:lent investigation may be summarized as follows: (1) The heat content of carbon steels at high temperatures was determined by the mixture method, while the oxidation of the specimen was prevented by passing a purified hydrogen gas through the furnace. The specimens were twelve kinds of steels with different carbon contents from 0.09 % to 2.84 % and the range of temperature was 23~250°C. (2) According to A. Meuthen, the specific heat is constant below the A1 point, but the present writer showed that the specific heat is only constant above the A3 point, and that below this point, it increases with the rise of temperature. (3) The quantity of heat for the dissolution of pearlite in iron was determined by measuring the heat content above and below the A1 point. This heat increases proportionally with the content of carbon, reaches a maximum at 0.9 percent and ends at 6.7 percent. For the dissolution of I gr. of carbon in iron, a heat of 1760 calories is required, while, 16.1 calories are necessary for the dissolution of 1 gr. of pearlite in iron. (4) From the heat content-concentration curve, it was found that, the mean specific heat of cementite increases with the rise of temperature; it is 0.149 at 150°C and 02.20 at 850°C. (5) It was observed that the specific heat of the carbon poles with 98 %C increases almost linearly up to 700°C, and afterwards its rate of increase gradually diminishes. (6) It is confirmed by experiments that the A1 transformation is a function of temperature and time, but that the A2 transformation is a definite function of temperature only. (7) From the heat content-concentration curves, the heat of transformation from martensite to pearlite was obtained and found to be proportional to the carbon content. (8) The heat of transformation from austenite to martensite, or that from martensite to pearlite, increases proportionally with the content of eutectoid carbon. The heat of transformation from austenite to martensite for a eutectoid steel amOlmts to 5.9 calories.