TThe correlation among several methods of indicating oxidation and reduction degree of iron ore and their difference were explained and the most reasonable lnethod by which indicatioll of net reduction degree was possible was established. Several tests were conducted on the size and porosity of ore, flow quantity of CO gas per unit time, rate of mixing coke, reduction temperature and reduction time which were regarded as the factors having an influence upon the reducibility of iron ore. In reduction tests with CO gas and coke, better reducibility was obtained with finer ore. Within this test conditions, this trend was observed in the case of the ore especially under about 1.0 mm in diameter, while it was not so remarkable in the larger size ore. In the case of reduction with coke the highest reduction-degree was obtained with a mixing of 30% coke. Reducibility with CO gas showed a gradual increase with an increase of flow quantity of CO(cc/min.) As an influence of porosity on reducibility, increase of 10%in porosity brought about an increase of about 10-13% in the reduction-degree. As to hematite, based chiefly on the result of reduction test, the relative correlation amollg flow quantity of CO gas, ore diameter and reducibility CO gas was considered. And it was presumed that flow quantity of CO gas had more influence on reducibility with CO than the ore diameter in case of large size, and that the effect as the product of a mass of flow quantity of CO per unit time and reduction time was observed.
Oxygen has been commonly used in steel making, but in the production of cast iron scarcely used to improve the quality of molten iron except the some attempts of its use in cupola, because it has been believed excessively that oxygen is harmful element to cast iron. But by blowing the adequate amount of oxygen into molten iron, some interesting results was obtained as follows. (1) Carbon and silicon contents of cast iron could be controlled and its mechanical properties were improved. (2) Oxygen content of cast iron treated by oxygen was not increased and the amount of impurities in cast iron-Ti, Cr, V and etc.-were decreased. (3) Even the unsuitable pig irons for ductile cast iron were perfectly nodularized and elevated in the mechanical properties by magnesium treatment after the blow of oxygen into molten iron.
For studying the relation of the specific rate constant and the concentrations of carbon and oxygen in reactants, the rate of the carbon removal in molten Fe-C alloys containing about 4-0•2% carbon was measured by oxygen gas stream which had previously been prepared to have constant partial pressures of 20, 150, 300mm Hg respectively by mixing pure oxygen (or nitrogen) into air. Then the specific rate constant K0 was estimated at a given concentration of carbon accor- ding to the process used in the preceeding reports. If the reactants combined together to form the activated complex according to the following equation, the specific rate constant K0 might be given by the expression. where differcnt γ terms represented the activity coefficients of the reactants and the activated complex respectively. If the activity coefficient was defined with respect to the infinitely dilute solution as the standard state, k01 was the specific rate constant at the infinite dilute soluton of the reactants. From the ratio of k0 to k01, which was obtained by extrapolating at the zero concentration of carbon, γoγc/γco=f term in the above equation was estimated. Although the rate of the carbon removal increased with the carbon concentration at a given oxygen pressure, k0 increased with the diminution of carbon, in consequence of which it was found that f term was independent of the oxygen pressure at a given carbon concentration and increased with the diminution of the carbon concentration at the partial pressure between 20-300mm Hg. These results might be considered to indicate that the activity coefficient of the reactants at the interface varied with the carbon concentrations on the existence of oxygen. Nitrogen gas which existed together with oxygen gas had no influence on these terms.
Variations of hydrogen in liquid steel on steelmaking process of hundreds of heat molten by basic electric arc furnace or acid high-frequency furnace during 1952 fiscal year were statistically studied. The amount of hydrogen as well as oxygen in steel were determined by a rapid method, by means of vacuum fusion of the specimen and subsequent measurment of the extracted gas by thermoconductivity method. The following conclusions were obtained. 1. Hydrogen in molten steel seemed to have a tendency of reaching some steady values with a given damp pressure in atmosphere. Those values varied with working conditions, especially the state of slag, such as, acid, basic, oxidizing or teducing, and they became highest when steel was molten under basic reducing slag. [H] and √PH2O had linear relations when they were statistically observed, where [H] was hydrogen content in molten steel, and PH2O was damp pressure in the atmosphere. 2. [H] was partially removed by boiling the steel bath in oxidizing condition of b sic electric arc furnace. Δ[H] had linear relation to Δ[C]×[H]2, where Δ[H] was amount of hydrogen removed, Δ[C] was amount of carbon removed and [H] was mean value of hydrogen in steel at the beginning and at the end of oxidation. 3. Rapid increase of hydrogen in steel during earlier stage of reduction in basic electric hearth, in residual oxidizing slag as well as in added meterials, such as, lime, deoxidizer and carburizing meterials, was considered to easily enter into steel. Oxigen and hydrogen in molten steel on the stage, were found to vary with intimate corelations. Ratios of [H]2×[O] at the end of oxidation and that at the earlier stage of reduction of the same heat had almost constant values, although the values [H]2×[O] had wide range according to the melting conditions. 4. Researches were also made on the relations of [H] at tapping of basic electric arc furnace to PH2O on various specificatons of the steel. The lower carbon the steel had, the higher effect of PH2O on [H] at tapping were in the average recognized.
Steels of various kinds were heated in a closed vessel containing CO2 with the cyanide salt of optimum amount, and both the powerful carburizing action of the formed atmosphere and the reaction between the cyanide salt and CO2 were explained. The result of the experiment showed that the carbonitriding power of the atmosphere became maximum, irrespective of the kind of steels, by the addition of about 16 gr K4Fe(CN)6 per litre CO2, which coincided well with the theoretical estimation that the concentration of C2N2O became maximum by the addition of 16•E4 gr K4Fe(CN)6 per litre CO2. As to the case depth and the surface hardness in relation to the heating temperatures, the former generally became the larger but the latter the lower, the higher the heating temperature was raised. In specimens treated at higher temperatures, the maximum hardness was obtained at the inner portion slightly distant from the surface. This was presumably due to the fact (1) that, at the surface of such specimens, the matrix phase was too rich in the carbon and the nitrogen to be hardenable and moreover its amount was small; (2) that, at the inner portion slightly distant from the surface, the amount of the matrix, having optimum concentration of carbon and nitrogen for the good hardenability, became large and that of the proeutectoid constituents small, causing maximum hardness in the carbonitrided layer, and then (3) that, in the further inner portion the hardening effect became small, because the carbon and the nitrogen content decreased.
In the lst report, (Tetsu-to-Hagane Vol. 41, No. 1, 1955 p. 17-22) it was shown that the black, spots acted as defect points for the hot wbrking. In this report, the following studies were carried out. The chemical compositions of the black spots were analysed and their microstructures were examined. About O•15% of sulphur and O.4% manganese were contained and sulphide particles were concentrated remarkably in these spots. The hot-working properties of steel containing the same amount of sulphur as that of the. black spots were investigated by the impact-bending tests and tensile tests at high temperatures. By this investigation, It was shown that the hot-working properties were injured when the sulphur content surpassed O•15%. Therefore, sulphur was found most influential factor for defect points. But increase of manganese content was effective to the improvement in the hot-working Properties of the high-sulphur steel. Beside the numerous MnS inclusions, FeS inclusions were detected in the black spots of some billets. When the billets or ingots containing FeS inclusions were heated at the temperatuee from 800°C to 1200°C for several hours, it was found that the FeS converted into the MnS.
As the first stage of a study on grain size controll in steel-making plant, the authors observed experimentally some problems as stated below, mainly from the view point of grain-growth characteristics of austenite: (i) Change of grain size and grain-growth characteristics during melting and teeming practice, (ii) Relation of grain size and grain-growth characteristics between a ladle sample and a finished product of the same heat, (iii) Dependence of grain-growth characteristics upon the degree of duplication of grains. Results obtained were as follows: (1) In the case of melting of medium-carbon Cr-Mo steel in a basic electric arc furnace, as the reducing proceeds, austenite grains became finer and more uniform, and the coarsening temperature rose. And by the addition of Al, anstenite grains became finer and the coarsening temperature rose higher, but as the time passed on, the coarsening temperature fell. (2) In the case of 0•3% C (Al-killed) steel and Ni-Cr-Mo case-hardening steel, a finished product had nearly the same grain-growth characteristics as a ladle sample, and at 925°C both had the equal grain-size. But in the duplex-grained steel, a finished product had coarser grain and lower coarsening temperature than a ladle sample. (3) In the case of Ni-Cr-Mo case-hardening steel, it was quantitatively derived by means of Dr. T. Akutagawa's method that the degree of duplication becomes maximum in the course of abrupt coarsening of austenite. (4) It was recognized that austenite grain size had a close connection with the acidsoluble Al in steel and that when the percentage of the acid-soluble Al rose beyond 0•020, the grain size in every kinds of steel stated above became finer (No.6-No.7 of McQuaid-Ehn Grain Size Number). (5) Some considerations on the relation of the cause of duplex-grain formation to the primary segregation, and the grain-coarsening curve were given.