Additions of manganese and nitrogen have been investigated with respect to their effects on the development of recrystallization texture in very low carbon steels. Hot-rolled and decarburized steels with five different manganese contents (0.00 to 0.32 mass%) were individually adjusted to three levels of nitrogen (less than 2, 8 and 120 mass ppm) by atmosphere reactions and then cold-rolled 80% in reduction. These fifteen sheets were annealed up to 973 K with a very slow heating rate under appropriate atmospheres. Texture studies were carried out by X-ray diffraction. Microstructures during recovery and recrystallization were also examined using a scanning electron microscope (back-scattered electron mode) on edge sections parallel to the rolling direction. Optimum textures for deep drawability were obtained with very low contents of manganese in solid solution (less than 0.04%) and intermediate levels of nitrogen (about 8 ppm). Steel chemistry apparently controls the final texture in both the cold rolling and annealing stages of processing. The cold rolling texture varies with manganese and nitrogen content. During recrystallization, nitrogen enhances the development of texture components with (111) parallel to the sheets.
In order to investigate whether the stagnation of strain hardening upon stress reversal which had been observed in aluminium is a general phenomenon in single phase, fcc and bcc pure metals, the strain-hardening behaviour during reversed straining of prestrained aluminium, copper and iron polycrystals was analyzed using the strain-hardening rate vs true stress relation. In all the materials examined, the strain-hardening rate, θ, near (and/or above) the prestress was found to be lower than that obtained during prestraining. This fact implies that the strain-hardening behaviour upon stress reversal is not so simple as has been reported by Orowan. It was also found that the lowering degree of θ increased with increasing amount of prestrain (i.e., with increasing tendency toward cell structure formation). Further, thermal recovery and cyclic stressing after prestraining, which coverted the cell wall consisting of dislocation tangles into a sharp sub-boundary consisting of neat dislocation-networks, gave rise to disappearance of the stagnation. From these results the stagnation of strain hardening upon stress reversal was concluded to be ascribed to the disintegration of cell walls during reversed straining; the lowering of θ may be due to an increase both in the density of mobile dislocations and in their mean free path.
L’interaction à 723 K (450°C) du couple ζs-Si (i.e. ζsynthétique-Si), est étudiée. Le silicium présente une très faible solubilité dans le composé ‘ζ’s. Cependant, la diffusivité de cet élément dans la phase ‘ζ’s est élevée. Lors de la diffusion, le silicium se ségrège dans les joints de grains de ‘ζ’s. Après une durée d’incubation, nécessaire pour atteindre le seuil critique de concentration en silicium dans les joints de grains, une série de composés riches en silicium se forme dans ces endroits. La formation de ces composés est accompagnée par l’apparition d’un appauvrissement relatif en fer dans les joints de grains de la phase synthétique. Il en résulte l’apparition des zones de zinc liquide dans ces endroits qui, lors de son refroidissement, donne naissance aux composés lamellaires très riches en zinc dans les joints de grains.
L’influence du germanium dans un bain aluminisé de galvanisation, sur les caracteristiques des revêstements obtenus au trempé à 723 K (450°C), est étudiée. Dans le cas des aciers effervescents, le germanium associé à l’aluminium augmente significativement l’épaisseur de la couche totale. En revanche, l’épaisseur de la couche diffusionnelle ‘δ1’ se trouve diminuée. Ces effets apparemment contradictoires de Ge+Al sont expliqués. En ce qui concerne les aciers semi-calmés, le germanium renforce l’effet inhibiteur connu de l’aluminium dans la galvanisation de ce type d’acier. Le mécanisme de cet effet intéressant est étudié. Par ailleurs, il s’avère que le comportement particulier des aciers semi-calmés à l’égard du zinc liquide, n’est pas lié à la configuration électronique de silicium.
The present study is concerned with the kinetics of carbon reduction of MnO and the identification of Mn carbide formed in this reduction process by the effluent gas analysis method. Mn carbide (Mn7C3) was formed at an earlier stage of reduction, and the activation energy of 217 kJ/mol nearly equal to that for the Boudouard’s reaction was obtained. When carbon was consumed entirely, the reaction between MnO and Mn7C3 occurred to yield metallic manganese, and the activation energy of 259 kJ/mol corresponding to the reaction of CO2 with Mn7C3 was obtained. Mn carbide formed in the reduction process of MnO was identified to be Mn7C3 phase, by the effluent gas analysis method using the He-O2 mixture. In addition, EPMA and X-ray diffraction examinations showed the presence of Mn7C3 phase in this reduction product.
The oxidative leaching reactions of Ni3S2 are interesting connection with a hydrometallurgical treatment of nickel matte as well as complex nickel sulfide ores. However, the stoichiometries of Ni3S2 and nickel matte vary over a wide range ratio, because its nickel and sulfur species have deficient character, and thus there still remains an ambiguity in the leaching mechanism. In this study, the effects of non-stoichiometries on the oxidative leaching of Ni3S2 samples in nitric acid solutions are discussed from a kinetic aspect based on leaching rate, stoichiometry of the leaching reaction, measurement of electric properties and analysis of leaching products. From the kinetic consideration, the following conclusion is obtained. The leaching rate is directly proportional to both the concentration of nitric acid and the surface area of the samples used. The overall reaction of oxidative leaching of Ni3±αS2 in nitric acid solutions is controlled by a chemical surface reaction step, and the rate equation is given by the following equation. −[Ni3±αS2]⁄dt=Z·exp(−Ea⁄RT)·ANi3±αS2·[HNO3].
The present study reports the results of investigation on the effects of impressed d.c. current on the growth of FeO layer on iron. The atmosphere and the temperature range of study chosen were CO–CO2 gas mixtures and from 973 to 1123 K. Except for the initial part, the kinetics of FeO layer growth under normal oxidation, under impressed current of both the polarities and under short-circuited condition followed the parabolic growth law. Under cathodic condition of the sample as well as under short-circuited condition, the rates were found to be more than that under normal oxidation condition. Decrease in oxidation rate was observed during the later part of oxidation, when the iron sample was made anodic. However, at lower temperatures, 973 K and 1023 K, the rates were found to be more than that under normal oxidation condition. The results have been qualitatively interpreted on the basis of expected changes in situations with regard to defect concentrations at the metal/oxide and oxide/gas interfaces as well as on the basis of changed transport coefficient of defects through the FeO layer. A thermogravimetric method was employed for following up the kinetics. A new method of field application was used.
Kinetic studies have been made on the reduction of dense wüstite at 1073 K in CO–CO2 atmosphere under normal reduction, under impressed d. c. current of both the polarities as well as under short-circuited conditions. The initial part of the kinetic curves conforms to a surface controlled reaction till the complete coverage of FeO with precipitated iron. The later part conforms to a parabolic growth law, and kinetics of reduction is controlled by diffusion of dissolved oxygen within the precipitated dense iron layer on FeO. The rates of reduction have been found to be more when the iron sample, on which dense wüstite has been formed, is made cathodic and when it is short-circuited to the outer platinum mesh electrode. The results reverses when the samples is made anodic. The results have been qualitatively interpreted on the basis of changed defect concentrations at the interfaces and within the layer. Wüstite soaked in 60% KOH solution has exhibited a tremendously increased rate of reduction, and linear kinetics is found to be valid upto almost 100% reduction of FeO. The influence of impressed current under this condition is also pronounced when the sample is made anodic. The effect of short-circuiting in presence of K+ ions is also large. A new method of field application has been used, and the thermogravimetric method was employed for following up the kinetics.
The solidification phenomenon was directly observed through an optical microscope on samples of 99.9% Sn, and Sn–Pb alloys containing 0.5, 10.0, 30.0, 38.1, 50.0, and 70.0 mass%Pb under two different temperature gradients, in order to study the influence of composition and temperature gradient on the formation of equiaxed crystals. It was observed that the solid-liquid interface advanced from the cooling end to the hotter part in the pure Sn, the Sn-0.5 mass%Pb and the Sn–Pb eutectic alloy under any temperature gradient. When the content of Pb, in the hypo-eutectic alloy, was increased to more than 5.0 mass%, the separation of equiaxed crystals from the cooling end was clearly observed under lower temperature gradient (900 K/m). Only the growth of dendritic crystals was observed, when the temperature gradient was larger (1800 K/m). The macrostructures of these samples were fine equiaxed crystals and thick columnars. In the hypo-eutectic alloy, the floatation of primary crystals was observed during the initial stage of solidification, and the eutectic solidification finally appeared regardless the existence of primary crystals.