The equilibrium in the reaction between sulphur in molten iron and hydrogen gas has been studied by many investigators in various methods. In this investigation, using a carbontube resistance furnace and a gas-bubbling technique, the authors reestablished above equilibrium relation for the temperature range of 1550°C-1750°C and sulphur concentration up to 5% It is, generally, considered that in such a reaction between gas mixture and a constituent in molten iron, the bubbling of gas into melt is effective for the prevention of it from thermal diffusion and may shorten the time required for equilibrium.
From the results of this experiment, the following equilibrium relation was obtained:
The values of equilibrium constant Ks were in good agreement with those of J. Chipman et al. below 1600°C, while considerable differences between both values were recognized above 1600°C.
It was proved that the activity coefficient of sulphur in molten iron, that is f_s, decreased with the increase of its concentration, and an experimental equation indicating the relationship among the f_s, sulphur concentration and temperature was given as follows:

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As the further study of the previous work, (Tetu-to-Hagané, Vol. 43, 1957, p. 790) the effect of alloying element on the equilibrium of carbon and oxygen in molten iron saturated with carbon was investigated for liquid alloys containing up to 5.2% Si, 20% Cr and 40% Mn at 1400°C 1500°C and 1600°C, respectively.
It was disclosed that the addition of silicon decreased the concentration of carbon and oxygen in molten iron, and the addition of Cr or Mn increased them.
From these data, the following results were obtained.
1) The effect of an alloying element on the solubility of graphite.
These functions were independent of temperature
where
N^C_C=mole fraction of carbon in carbon-saturated iron
N^X_C=mole fraction of carbon in Fe-C-X liquid alloy saturated with carbon
NX=mole fraction of alloying element dissolved in liquid alloy
2) For the interaction parameter of oxygen and carbon in molten iron e^(C)_O, the following value was obtained approximately.

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The authors investigated the relations between variations of chemical elements and gases in molten steel near the solid during solidification process and contents of chemical elements and gases in the same position after the solidification of the ingot (12 ton ingot), and the occurrence of various defects.
The results obtained were as follows:
i) Even in case of such molten steel as most unlikely to incur defects at the time of immediately before casting, the process concentration into the liquid phase along with the progress of solidification enhanced remarkably the possiblity of blowholes and deoxidation products to appear.
ii) Such being the circumstances, the molten steel near the solidus-liquidus border line was in such a condition that the percentage of probability for various defects to appear was rather high, and even a slight difference in the conditions of solidification was most likely to result in the occurrence of such defects in ingots.
iii) The concentration of each chemical element into the liquid phase was mostly at equal ratio to a theoretical quantity if positions in the tested ingot were fixed, and in the case of a 12 tons ingot it was regarded as 10-30% at a lower half of the ingot.
iv) It was possible to account for the negative segregation which arose in the lower part of the ingot by means of the difference in concentration which took place in case the solid phase and liquid co-existed.

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Generally, the origin of sand marks is considered as the ingot defects, such as non-metallic inclusions, blow holes, pin holes, cavities and segregations.
In the present investigation, the authers are convinced that the origin of sand mark is (mostly) non-metallic inclusions in the ingot.
The statistics of the number of sand marks on the high-carbon low-chromium bearing steel rod shown in this first report.
The results are summarized as follows:
(1) The number of the smaller sand marks, 0.1mm to 0.4mm long, shows no change by the position of the ingot.
(2) As for the larger sand marks, about 0.5mm long, the number of them at the top of ingot is higher than the bottom of ingots, and there is the same tendency among the number of sand marks to the ingot position when ingot is rolled as the same rolling ratio at the top of ingots and the bottom of ingots.
(3) The number of the larger sand marks is proportional to the rolling ratio of steel rods.
(4) With increase of the rolling ratio, there is a tendency that the number of the smaller sand marks is decreased and the number of the larger sand marks is increased and finally, sand marks disappeared when the rolling ratio is much larger (such as 250 rolling ratio).

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In order to study hot-ductility of austenitic stainless steels, hot twist tests of these steels were carried out. The experiments were made with 304 and 316 type stainless steels and the twist values were compared with pierceability of the materials by a Mannesmann piercer.
Further, relations between hot-ductility and gas or structure of the materials were studied by the same test.
As a result, it was found that twist curves which showed the relation between twist values and temperature had the close connection with pierceability of materials. Therefore, the twist test gave good measure of the pierceability of the materials by the Mannesmann piercer.
The hot-ductility of the austenitic stainless steel was affected by at least two factors, that is oxygen content and composition balance. The hot-ductility decreased with increase of the oxygen content. Also those steels which had γ+α phase at high temperature showed low hot-ductility at these temperatures and were proved to have poor pierceability.

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The relations between the cooling ability and the process of oxidation and polymerization of oil by Indiana method are examined. The cooling ability increases slightly in the induction period of oxidation and polymerization process of oil and becomes progressively rapid in the peroxide formation period up to the maximum at the end of this period. Then it decreases gradually in the peroxide decomposition period and rapidly in the polymerization period.
The variations of other properties are also associated closely with these oxidation process. When the cooling ability becomes the maximum, the peroxide value becomes the maximum and the viscosity and the amount of sludge begin to increase. These variations of cooling ability can be nearly represented by a quadratic equation. The blowing time (τH_max) at which the cooling ability becomes the maximum can be a criterion experessing the life of quenching oils and the radius of curvature (γH_max) of the curve at the maximum cooling a bility can be used as an index representing the degree of the variation of cooling ability resulted from the deterioration of oils.

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Recently, in order to improve hot workability of high grade stainless steel, adding rare earth metals in a bath have been widely taken in stainless-steel melting practice. As regards determination of Ce in steels, W. Westwood and A. Mayer²⁾ reported in their paper that Ce in cast iron was separated from iron by using citric acid ammonia buffer solution, then extracted with chloroform and at last determined by oxine colorimetry.
To determinate Ce in stainless steel which was treated with misch-metal, the author made some experiments concerning the following matters:
(i) Separability of all rare earth metals from the steel using HF solution.
(ii) Applicability of Knorre's method to Ce in separated rare earth metals.
As a result of experiments, the author ascertained applicability of Knorre's method to determine the Ce in steel.

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