Samples of reduced ore powder were prepared by reducing Hamersley hematite ore with pressurized hydrogen gas at about 900°C in a pilot plant for fluidized bed reduction. Cold and hot pressed briquets were produced from the reduced ore powder using a die at various temperatures. The influences of compacting load at various temperatures on the crushing strength, density and rate of reoxidation with a mixture of oxygen and nitrogen gases at 250° to 800°C were investigated.
The following results were obtained.
(1) To obtain briquets of high crushing strength and high density, it is desirable to use reduced ore powder above the reduction degree of 90%.
(2) The maximum rate of reoxidation of briquets was observed at about 400°C. This reason was assumed that the surface of particles reoxidized at temperature above 400°C was covered with thin and dense oxide film.
(3) Hot pressing at 500° to 600°C was more favorable for high crushing strength of briquets than cold pressing under higher compacting load.
(4) The reoxidation of briquets obeyed a parabolic law and became slow with increase in the briquet density.
(5) Sintering of briquets at temperatures of 850° to 1100°C for 4hr resulted in little increase in the density.

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The effect of cold working on stress corrosion cracking (SCC) susceptibility of semiaustenitic precipitation-hardening stainless steel has been investigated in the present study. The specimens, prepared from A-treated SUS 631 stainless steel sheets containing delta ferrite, were prestrained at low or high strain rate and successively subjected to TH-treatment. The SCC susceptibility of these specimens was estimated in boiling MgCl₂ solution under the constant applied stress.
The cold working gives a remarkable effect not only for the mechanical properties but for the SCC susceptibility of A- and TH-treated specimens. Namely, the strength of TH-treated specimens decreased with increasing prestrain, and the strength level of these specimens prestrained at high strain rate was larger than those at low strain rate. But, the abovementioned behavior of TH-treated specimens was the very reverse to that of A-treated specimens. While, the SCC susceptibility of A- and TH-treated specimens decreased with increasing prestrain, and its susceptibility of these specimens prestrained at high strain rate was larger than those at low strain rate.
On the basis of the results obtained above, the effects of prestrain and strain rate on the SCC susceptibility of SUS 631 stainless steel were discussed.

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Refining of the solidification structures of Type 430 stainless steel by the mechanical vibration and the liquid surface vibration was tried. The structures of 15kg test ingots were remarkable improved by these vibration methods. Change of structure into the equiaxed one starts after the superheat of liquid steel disappears.
The liquid surface vibration was applied to 6t ingots for practical use and its effect on structure refining was confirmed. By the investigation of size of crystals and negative segregation in the equiaxed zone, it was concluded that the structure refining was caused by the showering of the free crystals.
In the case of continuously cast slabs, the liquid surface vibration was effective only under low superheat.

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The transitional behavior of burden and gas distribution in the blast furnace was studied aerodynamically by a blast furnace model. When ore is charged under a gas flow, a coke column (hereinafter referred to as the central coke column) forms in the central region. On the basis of the experimental observation, the formation process of the column consists of the following three steps.
(1) With the progressive covering of the stack surface by the flow of ore from the periphery to the center, the furnace gas concentrates to the central region.
(2) The coke layer expands upward in the region where the gas velocity exceeds the minimum fluidization velocity of the coke layer.
(3) Some of the coke lump in the expanded layer are pushed into the central part by the flow of charged ore.
The central coke column is formed more easily by pellet charging rather than by sinter charging. The gas velocity in the central part has been related to the thickness and area of ore layer and the permeability ratio of ore to coke, and it has been expressed by the following equations. U_C/U_T=1/{A_C/A_T+(A_W/A_T)/(U_C/U_W)} U_C/U_W=C₀{(H/R)•(k₁/k₂)^0.778(A_C/A_T)^-0.483}ⁿ where, A is the sectional area, U, the gas velocity, H, the ore thickness, R, the throat radius, K₁ and K₂, the permeability indices of coke and ore, respectively, C₀ and n, constants, suffix C and W, the central region without ore and the peripheral region covered with ore, respectively, and suffix T, the throat. The radius of central coke column has been estimated from three relations to be about 0.58m.
The pressure drop in the stack of blast furnace is decreased by the formation of a central coke column, while the distribution of gas through the coke layers in the softening-melting zone hardly changes.

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The solubilities of titanium and carbon in Fe-C_sat Ti alloys were determined at temperatures from 1300°C to 1500°C. Some of the already reported values of titanium solubility were determined by measuring the acid-soluble titanium dissolved in rapidly cooled samples which inevitably contain the particles of titanium carbide sedimented during cooling. The sedimentation of titanium carbide results in the difficulty in determining the accurate solubility of titanium. In order to solve this difficulty, methods were newly devised to measure the total titanium content in rapidly cooled samples.
The results obtained are as follows;
(1) The solubility of titanium at temperatures from 1300°C to 1500°C was expressed as, log[%Ti]=(-6760/T)+3.965
(2) By the use of the carbon solubility in iron with different concentrations of titanium, the temperature dependence of the interaction coefficient, e^C_Ti, at temperatures from 1350°C to 1500°C was determined as, e^C_Ti=(-221/T)-0.072
(3) The change of standard Gibbs free energy for the reaction, Ti+C_sat=TiC(s), was obtained as ΔG°=-30500+13.3T (cal/mol).

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A study was conducted to determine the effect of cold rolling prior to aging on the strength and toughness of an ultrahigh strength 13Ni-15Co-10Mo maraging steel. The smooth tensile strength of cold rolled and aged maraging steel increased continuously with increasing amount of cold reduction. The cold rolled maraging steel exhibited anisotropy in properties; the tensile strength in the transverse direction was higher than in the longitudinal direction, whereas the reduction of area and elongation showed lower values in the transverse direction. The notch tensile strength and plane strain fracture toughness K_IC also increased with increasing amount of cold reduction, taking maximum value at the 60-70% reduction. For example, longitudinal K_IC value increased from 34Mpa•m^1/2 for 0% reduction to 63Mpa•m^1/2 for 70% reduction. The large amount of K_IC increase was attributable to the formation of delaminations running parallel to the rolling plane. In the presence of delaminations, it is considered that the K_IC test specimen behaved as the sum of a number of thin plates and each thin plate fractured under the plane stress condition. Based on these results, it was concluded that the good combination of the strength and toughness could be obtained at the 60% cold reduction.

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This paper describes a study on immersion bonding which utilizes boric acid and potassium borate as the main salt composition and magnesium powder as a reducing agent. A favorable boride layer was obtained by using magnesium powder as a reducing agent and boric acid and potassium borate as the sources of boron supply. In this study, the best composition for the bonding salt was composed of 4Owt%H₃BO₃, 20wt%K₂B₄O₇• 5H₂O, 15wt%NaF, 15wt%K₂CO₃, and 10wt%Mg powder. The boride layer was formed on steels at above 750°C and no bonding was observed at 700°C. The preferable temperature for bonding of steels was 900°C. The composition of the boride layer was Fe₂B. The thickness of the boride layer in carbon steels decreased slightly with increasin carbon content in the steels.

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In order to establish the basic concepts on oxidizing steelmaking processes, relationships among the oxidation, the decarburization and the dephosphorization were discussed with both thermochemical calculations and data in actual refining processes.
Decarburization reaction is promoted by reducing CO partial pressure. Thermochemical discussion shows the limit of decarburization by refining at one atmospheric pressure and the effect of refining at low CO partial pressure. The characteristics of actual decarburization reactions are described in such processes as VOD, AOD and other modified processes for stainless steel refining as well as LD, Q-BOP, the duplex blowing LD, VOD, Thomas, and DH Processes for carbon steel refining.
The other thermochemical importance is the balance between dephosphorization and decarburization in carbon steel refining. Discussion remarks the characteristics of dephosphorization reactions at one atmospheric pressure in LD, Q-BOP and the duplex blowing LD processes, the effectiveness of higher pressure for dephosphorization of high carbon steel and the usefulness of low temperature for dephosphorization of hot metal.

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Steelmaking equipments newly developed in the past ten years in Japan are summarized with a historical view point. Three new equipments developed in Japan are introduced with their detailed information, together with the details of the improved auxiliary equipments. The reasons of new developments are discussed with some comments on future steelmaking in Japan.

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