A vacuum fusion technique was applied to determine the solubility of water in liquid oxides. Reproducibility of determined hydrogen in liquid oxides was usually ±4 to 5 ppm for samples containing. about 50 ppm hydrogen. Liquid oxides were equilibrated with the gas mixture of argon and water vapour in the range of temperature from 1500°C to 1600°C. In the lime-silica system, a minimum of water solubility was observed near the metasilicate composition. The effects of addition of P₂0₅, B₂0₃, Ge0₂, Al₂0₃ and TiO₂ respectively to the CaO-Si0₂ system (%CaO/%SiO₂=0.59) on the solubility of waterwere studied at 1500°C. The addition of acid oxides such as P₂0₅, B₂0₃ and Ge0₂ increases the solubility of water, but amphoteric oxides as Al₂0₅ and TiO₂ decrease the solubility of water. A minimum of water solubility was observed at approximately 20 moles percent of AlO_1.5 in the CaO-Si0₂-Al₂0₈ system. It was found that the effect of an addition of acid or an amphoteric oxide on the solubility of water might be closely related to the ion-oxygen attraction of cation in oxide.

View full abstract

The solubility of hydrogen in liquid cobalt and in liquid iron alloys have been determined by Sieverts' method at the temperature range from 1550° to 1670°C and under an atmospheric pressure of hydrogen.
The solubility of hydrogen in liquid iron decreases by addition of W, Mo, Cu and Co, and increases by addition of Ti, Nb, V and Cr. The results obtained are summarized as follows.

View full abstract

The changes of hardness, Cahrpy impact value, lattice parameter of ferrite, internal stress in matrix, carbide reaction, elements in carbide, and electron microstructure occuring during isothermal tempering of hot-work tool steels of 3Cr-5W-0.3V(DSS), 3Cr-9W-0.3V/(DSH), 3Cr-5W-0.3V-3Co(CoSS), 3Cr-9W-0.3V -3Co(CoSH), 12Cr-7W-0.5V-5Co(DSE), and 12Cr-7W-0.5V-10Co(DSF) types for up to 1000 hr in the range 400-700°C have been studied.
The results obtained were plotted against the tempering parameter P=T(20+logt) x 10^-8, and discussed in detail. Peak of secondary hardening appeares in P=17-18 for 3Cr-W-(Co) type, and at about P=16 for 12Cr-W-Co type. Charpy impact values show a broad valley near the parameter of peak hardness for 3Cr type, and show it in higher parameter than that of peak hardness for 12Cr type. Lattice parame-meters of matrix in DSS and DSE decrease with increasing parameter, and a maximum internal stressof about 100 kg/mm² is obtained at about P=16 and 15.5 for DSS and DSE, respectively. On the above isothermal tempering, the following sequence of changes in the carbides takes place in each type: Fe₈C→Fe₈C+W₂C→W₂C→W₂C+M₆C→M₆C→ for 3Cr-5W-(Co) type, Fe₈C→resolution→W₂C→W₂C+M₆C→M₈C for 3Cr-9W-(Co)type, Fe₃C→resplution→M₇C₃→M₇C₃+M₂₃C₆→M₂₃C₆+M₇C₃+Fe₂W→Fe²W+M₂₃C₆ for 12Cr-W-Co type. Cobalt decreases the rate of growth of carbide, and the increase of resistance to softening during tempering is attributed to this effect.

View full abstract

Since the dilatometer curves indicate the irreversible increase and unusual changes in dimension, thermal behaviors of cast iron can not be understood merely by thermal expansion and phase transformation. However, the behaviors can clearly be explained by taking the migration of carbon in cast iron as a factor of analysis, in addition to the other factors. Formerly, a new mechanism of growth in cast iron was suggested by the present author by regarding the migration of carbon as the main source of growth. The present investigation is intended to analyse the dilatometer curves based on the same concept of argument.
In cast iron the graphite is distributed separately in the continuous matrix. In this model of structure, the matrix must expand with the increase of carbon and contraction of graphite must simultaneously accompany, so far as the solubility of carbon in the matrix increases. In such process, as contarction of inner graphite would not restrict the expansion of outer matrix, the total volume should at least nominally change and some porosity must exist within the graphite. These relations and changes in volume can easily be explained by performing some calculations.
Under the process of cooling, precipitation of graphite is seen and the dilatometer curves usualy show a nature of irreversibility. This change means a redistribution of graphite. These phenomena can also be explained by some calculations based on migration of graphite carbon. In conclusion, a thermal cycle of growth in cast iron includes two steps: the porosity formation followed by dissolving and the redictribution of graphite caused by precipitation. And after this cycle porosity remains irreversibly. By applying the concept obtained in this manner concerning the growth in austenite region, one can well understand the nature of the sawteeth-like curve and the change of thermal expansion during the cyclic heating. Further, the growth in critical range can also be explained theoretically. Because, carbon migrates from graphite to matrix when the ferritic matrix transforms to austenite, and under the process of cooling carbon also migrates following the reverse process in heating, so far as the austenite changes into ferrite by graphitization in the critical range. Usually ferrous metals contract in the critical range of heating and expand in cooling, but in cast iron the ferritic matrix transforms into austenite without contraction, and austenite dose not expand in the following process of cooling in its transformation into ferrite by direct graphitization. These changes can properly be explained in the same mathematical formulation, because the dilatometer curves of cast iron in critical range also indicate nominal changes.
As a result of the present investigation, it is recognized that the porosity formation by carbon migration is an essential phenomenon in the growth of cast iron. Therefore, a consideration on this problem was performed from a viewpoint of physical metallurgy to conclude that carbon may migrate by a flow of vacancies and porosity may take place at the diffusion zone supersaturated with vacancies within the graphite crystal, but a flow of vacancies scarcely occurs in the process of precipitation. Graphite must precipitate at the surface and porosity must remain within the graphite. Irreversibility in the diffusion mechanism of graphite carbon is an important metallurgical problem in the growth of cast iron.

View full abstract