Recently many researches on automatic control system of sintering equipments are put in practice in foreign countries as well as in Japan. Especially in U. S. A.& U. S. S. R. its progress is remarkable, the author deals with a new automatic control system which has not been found in even foreign countries as well as in Japan. This equipment is completely different from the ordinary one-man control system which has been misunderstood as the automatic control system to the present. In Yawata Steel Works since 1956 a study of automatic control system of sintering equipments has been made, which was developed from the new idea and comprized a complete loop type system. The outline of an actual example thereof and the recent tendency in foreign countries were explained briefly in comparison with the new automatic control system in Japan.
1) The solubility of graphite in pure cobalt and nickel was determined at various temperatures. Temperature dependence of graphite solubility in nickel and cobalt was as follows: a) Nickel logNc=-875/T 0.521 b) Cobalt logNc=-1050/T-0.265 (2) The solubility of graphite in nickel-cobalt solutions was also determind at 1400°C. From these data, excess partial molar free energy was calculated to be about -300 cal/gram atom, and it showed that the solution of this alloy was not an ideal. (3) Effects of alloying elements such as Si, Mn, Cr, V and Mo on the solubility of graphite in liquid Ni and Co were investigated at 1400°C. The interaction parameter of Wagner εXC=-(∂ln NXC/∂NX) was calculated and found comparable with that of liquid iron. (4) With the systems Ni-Cr-Mn-C and Co-Cr-Mn-C the solubilities of graphite were determind at 1400°C. The experimental results were in good agreement with calculations from the ternary systems in dilute solution.
The molten steel in contact with air has the following chemical reaction: Steel+H2O (in air)⇔2 [H](in steel)+[O](in steel) K=[H] 2·[O]/PH2O Therefore, if the distribution of each gas in the air-slag-steel phase will be constant, the relation between PH2O in air and the gas contents in molten steel of steelmaking practice could explained only by the above equation. But the author presumed in this paper that the [H] 2·[O] value just before tap in steelmaking process with a basic electric arc furnace was not proportional to PH2O in air, because the hydrogen and the oxygen in molten steel in the steelmaking practice were controlled by each of the following phenomena: (1) As the movement of the hydrogen in the air-slag-steel phase was controlled by the velocity of diffusion in slag, which changed with CaO/SiO2 ratio of and temperature of slag, the hydrogen content ([H]) in molten steel in contact with molten slag will be effected by CaO/SiO2 ratio of and the temperature of slag. (2) As the molten steel and the molten slag were not in an ideal state, the ratio between the oxygen content ([O]) in molten steel and the Σ(FeO) content in molten slag would change with the component of steel, the CaO/SiO2 ratio of slag and the bath temperature.
It is one of the problems unsolved for a long time in steel making to make a sound ingot preventing the occurrence of sand marks which are a defect in forged or rolled steels. First of all, the nature of sand marks, namely their type, their distribution and their constituent, should be known in order to solve the problem and then the “origin” of the sand marks would be really grasped in consequence. The authors, therefore, studied the type and the constituent of sand marks in various kinds of forged or rolled steels by optical microscopy, etching test, electron-diffraction reflection method and chemical analysis. It was recognized that there was a close relation between the type of sand marks observed by optical microscopy and its constituents, and moreover between the conditions of austenite-grain refining as well as deoxidation and the type of sand marks.
When the steel surface was finished by mechanical process, for example, turning, grinding and mechanical polishing, its surface is covered by the layer in which the physical and mechanical properties differ from those in mother material. The authors tentatively called this layer in terms of the “machined-surface-layer”. Although it is said that the influence of this layer on mechanical strength of a material is of no negligible amount, but many questions are still left unsolved. Especially in previous studies, only discussions on the influence of residual stress in the surface layer were described, and no attention was paid to the work hardening and other factors. This paper presented the results of an investigation into the influence of the machinedsurface-layer on hardness of the surface of hardened steel.Distribution of the half-value breadth of X-ray diffraction patterns on the ground surface layer was obtained with small specimens heat-treated under various conditions.Then, hardness tests were carried out on the surface layer of Sendzimir rolls finished by some mechanical process.The results of these studies were as follows: (1) Two types of machined-surface-layer were obsereved.One of these had a monotonous distribution of half-value breadth under the surface and the other had the minimum value of half-value breadth directly under the surface.This phenomenon was explained by a “competition” happened between mechanical action and thermal action. (2) The distribution of half-value breadth corresponded with the distribution of hardness. Therefore, the depth of the machined-surface-layer could be determined by the measurements of the distribution of half-value breadth. (3) The strong work-hardening was observed on the machined-surface-layer of a Sendzimir roll finished by turning.It is necessary to remove the surface about 300μ thickness by grinding in order to obtain the reasonable value of Shore hardness.
Fire-cracking characteristics of Cr-Mo steel which was widely used for blooming and stabbing mill rolls were investigated by means of the cyclic thermal stress test developed by the author. The test results were as follows: 1) The maximum crack depth of Cr-Mo steels of various carbon contents and microstructures had the linear relationship on the log-log coordinates with the U-notched Charpy impact value. 2) The relation between hardness and fire-cracking characteristics depended upon the carbon content, and the lower the carbon content the shallower the crack. 3) Among the Cr-Mo steels which had been normalized and annealed at the various temperatures the spheroidized structure had the best characteristics. The structure containing the marked network of the primary cementite was relatively inferior. 4) Longitudinal characteristics were improved by increasing forging reduction, but transverse property showed its best at the rather small forging rate and the excessive forging injured the transverse fire-cracking property. 5) Porosities of cast steel became the starting point of the crack, and with the transverse specimen the crack took its path in the crystalline segregation.
Some Hadfield steels added with 3% Ni and 3% Cu were studied mainly by micrography on isothermal carbide precipitation after solution treatment. By addition of 3% Ni, both carbide precipitation and pearlitic constituent precipitation in Hadfield steels were retarded and these precipitation temperature ranges were limited in a narrow range than those of the standard steel. Growth rate of pearlitic constituents in steels was decreased remarkably by addition of 3% Ni. On the other hand, by addition of 3% Cu, pearlitic constituent precipitation in steels was only slightly retarded, but grain boundary carbide precipitation was accelerated at above about 650°C. Strength of steels after solution treatment was decreased slightly by addition of these elements, but toughness, especially elongation of steels was increased. As the content of carbon in Hadfield steels was lowered, both grain-boundary carbide precipitation and pearlitic-constituent precipitation were gradually decreased. High-Mn steel containing 0.65%C, cooled slowly after solution treatment, had nearly perfect austenitic structure and the strength of these steels was slightly impaired but the toughness was remarkably increased as compared with that of a standard Hadfield steel.