鋼中に於ける水素の擧動に就て(II)

Abstract

We have some proofs, even if indirect, that there are many minute cavities in steel. Modified the hydrogen theory of white spot studied by German investigators, Prof. K. Honda advanced the cavity theory (Containing also the thermal and transformation stress theory). The author tried to consider more extensively about the effect of cavity on the behaviours of hydrogen in steel.The discussion covers the hydrogen pressure in cavity and the effect of cavity on the diffusion of hydrogen in steel. In the ideal case when the hydrogen equilibrium between metal and cavities is always realized without any hydrogen loss from metal body, the hydrogen pressure attains to its maximum at nearly about 150°C, and the maximum value increases with hydrogen content and with reciprocal of cavity's volume.The hydrogen pressure becomes very high at the segregated zone even in the case of normal hydrogen content, soon after the most segregated part transforms prom γ to α phase, and this may be one of reason why flakes are apt to appear in the segregated zone, while it does never flake in austenitic condition according to the higher solubility of hydrogen in austenite. Actually, it takes time to attain to the hydrogen equilibrium in the case of variation of physical condition, and the lower the temperature is, the longer the time. On the other hand, the greater part of hydrogen in steel precipitates into cavities at lower temperature, and yet, if the total volume of cavities is considerably large, the quantity of hydrogen in cavities can not be neglected up to higher temperature, espceially in the case of a phase. In this case, the diffusion of hydrogen in steel and the escape of hydrogen from steel body are retarded to a great extent.