Sponge-iron powder, a product of a fluidized bed reduction by H₂ or CO gas, was in a very active state; consequently, it was rapidly oxidized to Fe₃0₄ or Fe₂0₃ at room temperature even with only a trace of oxygen.
The lattice constant of the product will be treated as a function of the equilibria of reduction reactions by which the sponge-iron powder was formed.
The variation of the lattice constant of the product with the reduction temperature ranging from 500 to 600°C suggests a large variation of the lattice strain.
The specific area of the product at 500°C was observed to be 0.9m² per gram while at 800°C 0.1m² per gram.
The active state of the product may be attributed to the large value of the specific surfaceenergy.
In order to prevent the oxidation of the product in the active state, the product must be heated above 680°C.

抄録全体を表示

Deoxidation problems of non-metallic inclusions being formed as reaction products were dealt with from the kinetic viewpoint on the example of silicon and/or manganese deoxidation.
The experimental results are as follows: 1) Silica particles, deoxidation products of silicon addition, are very hard to separate from molten iron because of their poor ability to coalesce. 2) Manganese oxide particles in case of much manganese addition consist of two phases which suggest that liquid and solid phases get together without any difficulty. Thus they grow to rather large particles and are separated in a short time. 3) Even in complex deoxidation of silicon and manganese where solid silica particles are expected to be produced according to equilibrium theory, large and globular particles of iron and manganese silicate were observed. 4) The property of liquid silicate particle to coalesce and be separated from molten steel easrily is confirmed. 5) The motion of iron bath by induction stirring increased the growth rate of all kinds of deoxidation products and proved effective for their removal from molten iron. 6) Crucible materials influenced not on the deoxidation but on the reoxidation behavior as a result of reactions at the metal-crucible interface. 7) The experiment under oxidizing atmosphere showed that the rate of reoxidation is very large and in contradiction to the above-mentioned the addition of only silicon gave desirable results because a viscous film formed prevented the penetration of oxygen into iron bath from atmosphere or slag.
The nucleus size and nucleation rate were calculated and the lattertoroved so large that this step could not be a rate-determining one of deoxidation. The following supposed mechanisms of the growth of deoxidation products were applied to the discussions of the experimental results. These are: 1) Coalescence by Brownian movement, 2) growth by diffusion of oxygen or deoxidizer atom to the surface of particle, and 3) coalescence during floating up.
Finally the maximum particle size to be observed under experimental conditions was calculated; it was in good agreement with measured one.
These experimental results were applied to the explanation of those obtained in the industrial open hearth deoxidation.

抄録全体を表示

A series of experiments were carried out on the effects of rolling variables on the occurrence of fire cracks on the roll surfaces of a universal type slabbing mill.
Types and arrangements of the nozzles for the roll cooling water were changed in succession, while observing the roll surfaces after rolling. It was established from both experiments and theoretical consideration that cooling of roll surface should be done at a location as far from the delivery point of the slabbs as possible, in order to prevent thermal shocking, causing severe fire cracks.Yet, cooling should be performed in such a way that the rolls may be cooled sufficiently to minimize the rise in the overall temperature of the roll.
The maximum temperature of the roll surface at contact with slabbs was determined by inspecting the hardness and microscopic structure of the quenched steel pieces plugged in the roll surfaces before rolling.The surface temperature was found to be from 470°C to 600°C, where the temperature of the bottom rolls was higher than that of the top rolls by about 30 degrees. The depth of heat-affected zone was found to be approximately 2mm from the surface, beyond which an instantaneous rise in temperature was less than 200°C.
The mode of machining and the roughness of the finished roll surface had no apparent effect on the occurrence of randomly oriented fire cracks, while they had definite influence on the occurrence of circumferential cracks.Every sharp notch on roll surfaces created by machining did not fail to lead to severe circumferential cracks.Apparently smooth surface provided by a flat-tipped bit also induced circumferential cracks.On the other hand, considerably rough surfaces provided by a sharp-tipped bit did not lead to such cracks.
Wear profiles of the top and bottom rolls were obtained by micrometer.The top rolls were worn 35% more in average than the bottom rolls.
Roll speed was recorded by means of 16mm motion picture.The top roll was found to revolve 2 degrees more than the bottom roll during a pass, which was an indication of the existence of slip between the top roll and the slabs, causing more wear on the top roll than the bottom roll. The greater wear of the top roll than the bottom roll was considered to be the main cause of the fact that less severe fire cracking was observed on the top roll than on the bottom roll.
Thanks to the two years study reported here, the rolling efficiency twice that of the initial state has been attained.

抄録全体を表示

The present investigation was carried out for the effects of testing temperatures and the ferrite grain diameters on the low temperature torsional deformation and fracture behaviour of O'08 percent carbon steel, using a newly developed dynamic torsion machine.Dynamic torque-twist curves were obtained photographically at various temperatures.
Variation of lower yield stress ry with grain size 2d in torsional deformation satisfied the Petch formula τy=Ti+kyd^-1/2, which was obtained from tension test.Value of τi increased rapidly with a decreasing of the testing temperature and also ky increased with a lowering of the testing temperature.It is shown experimentally that the flow stress τ_ƒ at constant strain is related to the grain diameter by τ_ƒ=τi_ƒ+k_ƒd-1/2 where τ_ƒ and k are constants. Value of kf at various testing temperatures is lower than those of k_y and k_ƒ has a small sensitivity to temperature.
At the slow rate of straining, a transition from ductile to completely brittle behaviour occurs at -183°C, when the grain diameter is d^-1/2≤5.23. Substituting values of τy, d-^1/2and Ky obtained in this experiment into Cottrell's formula of ductile to brittle fracture, the effective surface energy γ is found to be γ≥7.45×10³ erg/cm². This value of the surface energy for fracture is expected to be greater than the true surface energy, but it is the same value as that of γ obtained by tensile test.
Large plastic deformation to fracture took place in the torsion test, even in the specimen broken by cleavage fracture.

抄録全体を表示

The study of isothermal transformation of plain carbon (0.56% C, 0.82% Mn), Si-Mn (0.57% C, 1.65% Si, 0.87% Mn) and Mn-Cr-B steel (0.57% C, 0.84% Mn, 0.75% Cr and 0.003%B) was carried out to establish the relation between the microstructure and the mechanical properties.The results obtained are summarized as below.
1) The effect of Si is observed in the microstructure where a great amount of ferrite (or probainitic ferrite) precipitates in the structure after isothermal transformation.This effect of Si results mainly from a notable retardation of carbide formation, therefore, a bainite that is formed at low temperature contains super-saturated carbon atoms, so that ductility decreases remarkably.
2) The effect of Cr on retardation of transformation curve is remarkable, as compared with that of plain C steel or of Si-Mn steel.Moreover, the additon of a small quantity of B contributes to greater retardation of bainite transformation.In this steel, the hardness change, as a function of isothermal transformation temperature, is characterized by the transformation mechanism.
These are due mainly to a carbide density of structure.The lower bainite structure of this steel represents a high ductility even at high strength level, so that it may be concluded that a reduction of area of isothermal transformation product is independent of the strength level, and that it depends mainly on the microstructure.The isothermal transformation of this Mn-Cr-B steel has a beneficial effect on its mechanical properties.

抄録全体を表示

Studies were made of the decarburization of a steel in wet hydrogen and the effect of carbon content in steel on ceramic coating.
Steel rods were decarburized in wet hydrogen.The decarburization process was found to be controlled by a diffusion mechanism where D₀=1.8cm² per second and Q=37.8 Kcal per mole, when the values were calibrated from the value of volatile Fe in wet hydrogen.
Steel rods of various carbon contents were then coated with coating material and baked in air.The adhesiveness of baked film was calculated by the measurement of the torque which was needed to peel off the film from the surface of steel rod. The adhesiveness of the baked film was remarkably influenced by the carbon content in steel and the baking temperature.

抄録全体を表示