Previous work showed the great possibility of the silicon transfer to liquid iron through SiO gas, the rate of which is significantly dependent upon the carbon concentration in iron. To investigate whether or not this mechanism is really applicable to a practical blast furnace, the rate of the carbon transfer from graphite to liquid iron through CO gas was measured in the present work by use of a system consisting of three phases, graphite disc, iron melt and gaseous space between the former two.
It is interesting to note that the rate of absorption of carbon was found to decrease with rise of temperature between 1550 and 1660°C. The whole process was interpreted by a mix-controlled model of the following three steps, namely the gasification of graphite, the diffusion of CO gas and the chemical reaction on the surface of melt. The numerical values of various kinetic constants as well as the relative chemical resistances of each step were determined experimentally.

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Some characteristics mainly concerning to gas-permeability and stock movement of No 1 B. F.(of 350m³ inner volume) at Nishijima Works, Osaka Seiko Co. were investigated and following results were ob-tained.
(1) Periodic changes from tapping to tapping were observed in blast distribution among tuyeres, top gas composition, radial gas distribution, pressure drop, minute pressure pulsation and stock descending. These changes were quite similar to those obtained in small experimental B. F.(of 0.5m³ inner volume).
(2) Under the normal conditions, vertical pressure distribution was nearly linear from tuyere level to stock line. Pressure drop at combustion zone was estimated to be 26-34.8% of total pressure drop between blow-pipe and furnace top. In the case of unusual state, a part of stock column with large pres-sure drop appeared often at upper level of shaft and then it descended downward.
(3) Even under the normal condition, minute pressure pulsation of 0.6-2.13 Hz frequency, which suggested the occurence of “boiling” of solid particles, was observed. When unusual stock movement appeared at the shaft, increase of energy level of low frequency components, which suggested the occurence of “bubbling” or “near-slugging”, was observed. In the case of irregularities at high-temperature region another type of pulsation with 6-18 Hz frequency, which suggested bubbling in liquid phase, were observed before the appearance of pulsation cited above.
(4) It was presumed that unusual stock movement was mainly caused by the occurence of violent fluidization of solid particles even in high temperature region. It seems to be difficult to attribute the irregularities in the melting zone, where nonuniform distribution of fluid flow is remarkable, to the occurrence of “flooding”.

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A kinetic study is made of dephosphorization of liquid iron-phosphorus alloy with solid CaO and oxidizing gas. Iron-phosphorus alloy is melted in CaO crucible at 1600°C and then phosphorus in molten iron is oxidized by H₂-H₂O gas mixture (PH₂O/PH₂≈0.20-0.65).
The results are summarized as follows.
1) The maximum value and the minimum value of oxygen content of molten Fe-P alloy appear during dephosphorizing.
2) Dephosphorization reaction is divided into three periods; at the first period, chemical reaction is rate limiting step, in the second period, dephosphorization rate depends on the rate of oxygen supply from gas to molten iron, and transport of phosphorus in solid CaO is rate limiting step in the final period.

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A kinetic study is made of dephosphorization reaction of liquid iron-phosphorus alloy with steelmaking slag in laboratory scale. Iron-phosphorus alloys and CaO-FeO-Si0₂ system slags are melted in fused MgO crucible at 1550°C and 1600°C in resistance furnace.
The results presented here are summarized as follows.
1) The dephosphorization reaction is first order reaction with chemical reaction controll.
2) The dephosphorization rate constants are variable with slag composition and it is considered that the optimum slag composition for dephosphorization is the “nose” composition of liquidus line of 2CaOSiO₂in the phase diagram of CaO-FeO-SiO₂ system.

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Precipitation characteristics and strengthening mechanism in 8% Ni-6% Cr-Co-Mo maraging steels were investigated. The precipitates contributing to strengthening of the steel were spherical ones of about 200A in diameter and ribbon-like ones of about 100Å in width and 300-500Å in length. The both types of precipitates were identified with Fe₂Mo Laves phase. In the steel, the addition of Co accelerated precipitation hardening by retarding recovery of dislocation during aging. The precipitation hardening of the steel can be explained in terms of Orowan's theory.

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Carbides in tool steels rapidly quenched from liquid state are extremely fine compared with those in commercial forged tool steels. Therefore, it may be well expected that rapidly quenched tool steels have different heat treatment characteristics from those of forged steels.
In this paper, this was confirmed experimentally using splats, extruded bars made from atomized powders, and beads by electron beam or transfer plasma melting of high speed steel, cold work die steel, and hot work die steel.
The results are summarized as follows.
1) Splats and beads of SKD 1 and SKD 11 cold work die steels showed a hardness value of above H_RC 60 by being quenched from an austenitizing temperature as low as 850°C.
2) Canning extruded SKH9 showed a hardness value higher than H_RC 63, by being quenched from an austenitizing temperature as low as 950°C, while splats did not show such high hardness values.
3) The high hardness values obtained at low austenitizing temperatures may be considered to be highly dependent on the carbides which were so fine as to easily dissolve into austenite.

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A study of the removal of nitrogen from rimmed sheet steel and high carbon piano wire has been performed. The denitrogenizing annealing was carried out at temperatures from 500 to 1000°C in dry or wet hydrogen atmosphere and also in alternating atomspheres of dry hydrogen and vacuum. The following results were obtained.
The rate of nitrogen removal from rimmed sheet steel containing 004 to 005% C is increased appreciably with increase in temperature up to about 700 to 720°C, where the gamma phase appears, while it is decreased with further increase in temperature. The rate of nitrogen removal is also increased with an increase in flow rate of hydrogen up to 350cc/min under the present experimental condition, but any more increase in the rate is hardly observed with further increase in the flow rate of hydrogen.
When the flow rate of hydrogen is higher than 350cc/min under the present experimental condition, the rate of nitrogen removal is controlled by the diffusion of nitrogen in steel, and when the flow rate of hydrogen is lower than 100cc/min the rate of nitrogen removal follows the first order rate law, i.e., the logarithm of the ratio of nitrogen content to that of initial nitrogen is proportional to the time of treatment.
The water vapor up to about 20 vol% in hydrogen of 350ccimin has no effect on the rate of nitrogen removal from sheet steel, and the water vapor up to about 2 to 5 vol% in hydrogen of 100cc/min has a slight effect to increase the rate of nitrogen removal while the rate is decreased with further increase in water vapor.
Decarburization is not observed by dry hydrogen atmosphere while by the small addition of water vapor to hydrogen the rate and extent of decarburization are increased appreciably.
Judging from the present experimental results and the previous investigations, it is concluded that 1) if the process of nitrogen removal is performed in hydrogen of high flow rate, the rate of nitrogen removal is controlled by the diffusion of nitrogen in steel while 2) if it is performed in hydrogen of low flow rate the rate of nitrogen removal is controlled by the rate of outgoing transfer of the gases produced by denitrogenizing reaction from the reaction chamber.
It is suggested that the annealing by alternating treatment by hydrogen and vacuum can save the hydrogen consumption and the rapid and homogeneous nitrogen removal throughout the coil may be possible with a relatively small consumption of hydrogen when this technique is applied to the open coil annealing.

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The paper describes a simple and systematic state analysis of iron in pseudo-rust including various iron compounds-ferrous hydroxide, green rust-I, metallic iron, goethite, and magnetite-by utilizing the difference of solubilities of these compounds.
The outline of procedure is as follows:
Sample is treated with 100 ml of 3N cold hydrohlocric acid in water bath (about 15°C) for 5 to 10 minutes by passing nitrogen gas. In this condition, ferrous hydroxide and green rust-1 are dissolved and metallic iron, goethite and magnetite stay undissolved. The solution is rapidly filtered off by the apparatus of Fig. 1 to avoid the dissolution of metallic iron, goethite and magnetite. Ferrous hydroxide and green rust-1 in filtrate are determined by potassium bichromate titration method.
Residue including metallic iron, goethite and magnetite is treated with conventional brome-ethanol method, and then metallic iron is dissolved and other iron compounds are remained as insoluble residue.
Metallic iron in filtrate is determined by EDTA titration method. Residue is dissolved with hydrochloric acid (1: 1) in water bath at a constant temperature (about 70°C) while passing nitrogen gas and goethite and magnetite are determined by potassium bichromate titration method.

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No 2 LD Plant, Muroran Works, produces various kinds of steel with very high productivity establishing a new world record of 2 762 heats per month in April 1970. By introducing a mini process computer, a unique control system has been brought into the plant.
The system has achieved splendid accomplishment, e. q. improvement of the end point control, reducing the workers required and mechanization of tabulation.
The system embodies three features.
1. Linkage with the central computer: The process computer has been directly linked with the large central computer.
2. Display units: Cathode Ray Tube (CRT) has been introduced instead of typewriters first in steel making process control system.
3. Dynamic temperature control: The bath temperature during blowing is measured by the sub-lance and taken into the process computer.

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The structure and composition of a titanium carbo-nitrogen sulphide in steels have been determined by means of X-ray diffraction, electron diffraction and electron-probe microanalysis.
The carbo-nitrogen sulphide has a structure similar to that of TiP with a dimension of hexagonal unit cell of α=3.210Å, c= 11.20Å, and c/a= 3.49. Its chemical formula is shown by Ti₄ (C_m, N_n) ₂S₂, where m+n= 1. The ratio of m to n depends on the chemical composition, solidification condition and thermal history of steels.
The carbo-nitrogen sulphide is chemically stable as to be extracted from various steels containing titanium by mineral acid-dissolution and electrolytic methods using these acids, but decomposes gradually in hot mineral acids and oxidizing reagents.

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