The selective chlorination roasting on the fluidized bed for the elimination ofcopper, zinc and sulfur in the pyrite cinder was carried out in the laboratory scale. The results obtained were as follows: (1) Under the preferred roasting conditions of 1.3% Cl2 in air, 900°C and 30mn, the elimination of copper was over 83%. The influence of particle size on the elimination of copper was small. (2) Zinc and sulfur were successfully eliminated and iron loss was small. (3) Accordingly, the present method was entirely satisfactory.
Steels are subject often to an impact load or to a suddenly increasing load in service conditions or in its manufacturing processes. Study on the behaviours of the materials under such impulsive loading or under high rate of strain, which affects remarkably the strength and the deformation characteristics, is not only theoretically interesting but also important for practical purposes. The present authors designed and installed a new impact tensile testing machine, that is equipped with a large rotary disk, by which the testing speed up to 140m/s could be obtained In this paper, the impact tensile properties of a mild steel at a room temperature under various test conditions were reported and the form of the observed load-time curve was discussed theoretically. The load-time curve was measured by a strain-gauge attached on a load cell connected at the back end of the specimen opposite to the impact end. In this measurement, as the impact speed is increased or as the specimen becomes longer, the form of the observed load-time curve deviates from that of the conventional stress-strain curve, which is assumed to be similar to the form of the curve obtained in the static test. The propagation theory of the elastic and plastic strain waves was applied to the interpretation of the difference between the form of the observed load-time curve and that of the conventional stress-strain curve. The load-time curve was divided into two portions, that is, the loading and unloading ones, and the strain wave which corresponds to the latter portion was assumed to propagate at a similar velocity to that of the elastic strain. Thus, it was found that the form of the theoretical load-time curve derived from the conventional stress-strain curve under the above-mentioned assumption was in good agreement with that of the curve recorded experimentally. The impact tensile strength of an annealed mild steel was increased markedly with the impact speed up to 20m/s but the strength was kept unchangedin the test of the larger impact speed than 20m/s. The observed critical impact velocity of the same steel was considerably smaller than the calculated one. This disagreement is due to a disregard of the strain rate effect in the calculation. Finally, the effect of the ferrite grain size of the specimen on the impact tensile properties was reported.
Aluminum nitride precipitates in low-manganese steels, an aluminum-killed low-carbon steer and a medium-carbon steel were directly observed by carbon extraction replica. The steels contained 0.005-0.02% N and 0.03-0.12% Al. 1) AIN precipitates extracted from a forged and normalized steel were hexagonal in structure, and rectangular and of thin sheets in shape. 2) AlN precipitates in the steel heated at the 1200°C or above for 6h after solution-treatment, were of a large rod shape. At 1000-1100°C the precipitates were lengthened, and some of them reached to be distributed into 5μ. or over. At 900°C many AIN precipitates shorter than 1μ were seen to be scattered. The less the content of N and Al in the steel, the smaller the AlN precipitate. They were 0.1μ long or shorter and scattered on large numbers. 3) AlN precipitates were arranged along the grain boundary of austenite. 4) Isothermally treated after solution-treatment AIlN precipitates were present on the subgrain boundaries of ferrite, but not in the austinite. The precipitates at the 700°C heating for 2h were 0.02-0.1mu; long. 5) Si3N4 precipitates were found mixed with the AlN precipitates in the ferrite. The former were granular and of different shape from the latter. By electron-diffraction pattern the former were determined to be Si3N4 precipitates. 6) Fe3C particles seemed to become the nuclei forming AlN and promoted the its precipi tation. 7) AlN precipitates extracted from an aluminum-killed low-carbon steel subject to anneal-ing at 700°C afteri cold rolling; were found in lavers parallel to the rolling direction. 8) Some of the AIN preciepitates extracted from the steel ingot as cast have been previousiy precipitated, at the grain boundaries of austenite, and some of them were later preci-pitatea in tne ferrrue Theitormer were lined at the central part of ferrite net. The shapes of them were variedeivith tide size of ingots and the content of N and Al.
For purpose of making clear the relation between the microstructure and the mechanical properties, firstly the isothermal transformation diagram of the Mn-Cr spring steel were determined, and mechanical properties were also determined with the specimens austenitized a t 850°C and isothermally transformed at each temperature, ranging between 300°C (above Ms point) and 650°C. This diagram presented a doubly curved shape on account of a carbide-forming element such as chromium, and the pearlite transformation was sluggish as compared with the bainite transformation, so it led to be suitable for a hardenability. It was found that the content of the transformed martensite, quenched into an oil bath at 200°C, was less than that into a metal bath on account of the stabilization of austenite. The extraction replica method was the most available for making clear the carbide character, showing that the shapes of carbides in the bainite differed from those in the pearlite, and that the carbide became finer with decrease of transformation temperature in a bainite range. Most of the mechanical properties showed the irregular behavior in the upper bainite range. The mechanical properties were also plotted against Rockwell hardness and it was found that the tensile strength and endurance limit were proportional to the hardness, while the yield strength was out of proportion on account of the lower yield-tensile ratio in the pearlite range. The reduction of area showed a striking drop in the upper bainite range, but was increased gradually with decrease of transformation temperature. It was concluded that the reduction of area was depending mainly on the structure obtained at each temperature. As to the impact value, no remarkable change was observed.
Following the 19th report (Tetsu-to-Hagané, Vol.40, 1959, No.11, p.44), the rapid softening of hardened high speed steels (SKH2, SKH9) by water-or air-annealing, isothermal transformation- annealing and stepped annealing were studied by means of hardness test and micrography as compared with the full annealing. The results oftained were summariged as follows: (1) With both quench-hardened SKTI2 and SKH9, the minimum hardness was obtained by full annealing in a furnace at 880-90O°C, when the steel was softened fully, but it took long hours in furnace-cooling after annealing. (2) When the quench-hardened steel was annealed in air and water from 800°C, the degree of softening was fairly less than that in the case of full annealing, but the steel developed a machinable hardness such as nearly meeting the purpose of a simple and rapid softening. (3) The method of isothermal transformation annealing showed somewhat less degree of softening as compared with the full annealing method, but softened the steel in such short time that the practical purpose of rapid softening could be attained. (4) When the full annealing in a furnace was suspended and air-or oil-cooling was performed from 600°C (the so-called stepped annealing), the softening equivalent to the full annealing was attained.By the stepped annealing, the slow cooling period at below 600°C was shortened as compared with the method of full annealing and the purpose of rapid annealing was fully attained.It was useful moreover for saving of fuel because the annealing furnace at 600° with residual heat could be utilized for other annealing processes.
In previous reports (Tetsu-to-Hagane Vol.45.(1959), No.1, p.1276; Vol.46, (1960), No.3 and 5, p.375 and 566), the authors reported the effect of Nb, Ti, Mo and W on properties of 18Cr-12 Ni austenitic stainless steels. This report concerned the effect of V, Al and Zr on.aging behaviour, microstructure, precipitates, tensile strength at various temperatures and creep rupture strength of the same steel. The following results were oftained: 1) The steels were hardened during aging by precipitation of VC, Al3Ni and σ phase. The steels containing Zr were scarcely hardened during aging. 2) Grain size became finer in proportion to the content of the elements.It was observed that the precipitates were VS, VN, Cr23C6, γ VC and VC in the steels containing V, and Al3Ni, σ phase, α phase, AlN and Cr23C6 in the steels containing Al, and ZrS2, ZrC and α phase in the steels containing Zr by X-ray diffraction of the electrolytically extracted residues. 3) Tensile strength was much increased linearly with V content and slightly decreased with Zr content.It was invariable with different Al contents, but it was much higher at lower temperature when α phase existed in the steels. 4) Creep rupture strength was almost invariable with different contents of additional elements when C content was low.But when C content was higher, it was much increased with V content and slightly decreased with Al content.Creep rupture strength was maximum at the content of about 0.2% Zr.
The formation of the nitrogen-bearing austenite in 20% Cr-Mn-Fe alloys containing manganese up to 10% by the authors' nitrogen-absorption method and the thermal behavior of the formed austenite were studied. The creep property of the nitrogen-absorbed alloys at elevated temperature was also investigated. The results obtained are as follows: (1) The depth of the single austenite zone formed by the nitrogen-absorption in 20% Cr-Mn-Fe alloys is widened with increase of the manganese content of alloys, and the nitrogen content of the nitrogen-absorbed alloys is also increased as the manganese content is raised. In the alloys containing 8% or more of manganese, the single austenite zone contains about 0.8% nitrogen. (2) When the manganese content of the alloys is 2% or more, the nitrogen-bearing austenite is retained by quenching in water. In the alloys containing 4% or more of manganese, no martensite is formed even by subzero-treatment using the liquid oxygen. (3) In the alloys containing manganese lower than 2%, the austenite decomposes readily by aging at 700°C, while, in the alloys containing 4% or more of manganese, the lamellar phase of nitride is developed from the surface zone to the inner one during aging at 700°C. The hardness of the single austenite zone of the alloys containing about 8% manganese is maintained as high as about Hv 400 even after aging forup to 800 hours. (4) Both the bending creep property and the tensile creep property at elevated temperature of the nitrogen-absorbed 20% Cr-8% Mn-Fe alloy are excellent in the same degree as 316L type alloy shows, and the property is further improved by an intermediate and light rolling prior to solution-quenching of the nitrogen-absorbed alloy. (5) The oxidation resistance of these alloys is lowered to a certain extent by nitrogenabsorption treatment.