抄録
The object of this investigation is to analyze the behaviour of hydrogen which is considered to be one of the causes of ice flower like structure formation. Steel exhibits a variable permiability for hydrogen, the solubility of which is much greater in molten steel at high temperature than in the solid steel at room-temperature. During the cooling process the steel releases hydrogen which is absorbed by the molten steel. The relation between the molten steel, hydrogen and oxygen was calculated theoretically and the amount of the dissolved, hydrogen in the metal deposited from various coated electrodes, was measured in accordance with the A. W. S.-A.S.T.M. hydrogen test.
Figure 3 shows the relation between FeO and H; with the increase of oxygen amount, less hydrogen is dissolved in the molten steel.
Among the same type of electrodes, those which result in ice flower like structure evolve more hydrogen than those which do not. For example, the ice flower like structure was not formed by A type electrodes which indicated the evolved gas less than 0.1cc/g. The dissolved hydrogen in steel in the equilibrium state is shown in Fig.8. Under I atmospheric pressure of hydrogen, steel absorbs more than 0.25 cc/g of hydrogen in the molten state, but precipitates the hydrogen when the molten steel solidifies, and leapes about 0.12 cc/g of hydrogen at B point. According to the above results, it is considered that the amount of the dissolved hydrogen in the deposited metal is above B point when ice flower like structure is formed. This large amount of the dissolved hydrogen is rejected through the boundary of the fine columnar crystals, and accordingly the micro-blow holes are formed, when the molten steel is solidified. And its appearance is just like the ice flower. Therefore, the micro-blow holes are formed by the dissolved hydrogen in the deposited metal, and it is considered that the amount of the dissolved hydrogen required to form ice flower like structure is larger than the amount of the dissolved hydrogen in the solid steel at the melting point under 1 atm.
