The rates of absorption of nitrogen in liquid iron and liquid iron alloys were measured for inductively melted iron under pure nitrogen at 1600°C. The experimental data show a linear correlation, which gives the apparent mass transfer coefficient, k′, when the variable, log [(Cs-Co)/(Cs-C)] is plotted vs F·t/V. The experimental values of the apparent mass transfer coefficient obtained for lower oxygen melts are as follows: k′=34-35×10-3 cm·sec-1 for 0.005-0.006% O k′=27-29×10-3cm·sec-1 for 0.008-0.013% O At present, it appears that the transfer of nitrogen across the gas/metal interface is controlled by the transport in the metal. Some models of gas absorption in liquid, such as the film theory, the penetration theory and the surface renewal theory, were taken into account to explain the present results. The effects of several alloying elements on the absorption rates were also measured. It is to be noted that carbon, chromium and manganese have practically little influence, silicon, however, has somewhat remarkable influence in the lower concentrations. Namely, mass transfer coefficient increases gradually as silicon increases and reaches the limiting value of 5×10-2 cm·sec-1 at about 2% Si. It seems reasonable to consider that silicon reduces oxygen poison effect which is caused by absorption of dissolved oxygen on the metal surface, even in low oxygen level (0.002% O). Transfer of nitrogen from gas into liquid iron may also be chemically controlled when the liquid iron contains some surface active agents. The role of surface active agents such as oxygen and sulphur will be discussed in the next paper.
Several phenomena which take place in remaining molten steel in large killed steel ingots during solidification process have a great influence on those internal guality. Thus, it is essential in making sound steel ingots, to bring light on this problem. In this report, floatation of segregated molten steel and settling phenomenon of crystals was studied to which especial importance have been attached among those phenomena. The obtained results are as follows: i) During the solidification process of steel ingots, the comparatively fast movement of solutes in remaining molten steel is behaved, and the concentration gradient toward the top is formed in it. Such a phenomenon cannot be explained unless it is supposed that the segregated molten steel moves with some mass. As a mechanism of floatation, various things are thought. According to the result of authors' model experiment; it was shown that the floatation of segregated molten steel is acted even in static steel bath at velocity or the order of 10-2-10-1cm/sec which is able to explain various phenomena taking place in practical steel ingots. ii) It is assumed that the inertia flowing of molten steel taking place in pouring process has a great influence on the movement of solutes in remaining molten steel at the beginning of solidification process. iii) The theory that natural convection (thermal convection and solute convection) will take place in remaining molten steel during solidification process has been strongly supported. But it is still unknown how far it will mainly act. iv) So far the theory (gravity theory and convection one) that crystal particles are formed in remaining molten steel during solidification process, and that they settle down to form the negative segregation zone (settling crystal zone) is strongly supported. However according to the results of authors' experiments, such a conclusion was obtained that this theory has many problems, and it is rather unreasonable to explain various phenomena taking place during solidification process.