Aluminium, copper, silver and nickel-base dispersion-strengthened materials were studied by many researchers. There are, however, few reports on dispersion strengthened iron. In the present work, the hardness and the thermal expansion of dispersion-strengthened iron and copper were studied. Pure powders of iron or copper were used as base metal and fine powders of alumina, magnesia and silica as dispersed particles. These powders were mixed and pressed at room temperature, and sintered at 1300°C and 10000°C for iron and copper, respectively. The results obtained were as follows. (1) In both iron and copper, alumina proved to be the most effective and silica to be the least as dispersion-strengthening particles. (2) The less the expansion coefficient, the stronger the effect of dispersion-strengthening. (3) Cold-worked iron or copper containing silica softens at recrystallization temperature, while that containing alumina softens little, even in austenite temperature range.
The quenching stresses of 18mmφ commercial steel cylinders were measured by the Sachs’ method utilizing electric spark machining. The influences of carbon content of steel and of the bulk of unhardened core upon these stresses were investigated. The results area summarized as follows: (1) The stress distribution of water-quenched, through-hardened steels were of thermal stress-transformational stress superposition type. The center compression declined continuously with decrease of the carbon content and the surface compression exhibited its maximum at medium carbon content. The tension peak in the intermediate zone, was located near the surface in high-carbon steel and shifted deep inward with decrease of the carbon content, which constitutes one of the reasons why a low-carbon steel is less susceptible to quenching crack than a high-carbon steel. (2) The stress distribution of oil-quenched, through-hardened high-carbon steel was of transformational stress type. But, when the steel has a small unhardened core, the longitudinal stress in this area was converted into an exceedingly great tension and that in the hardened area into a small compression; as the core increased in the bulk, the tension in the core again dropped abruptly, while the compression in the hardened area increased. Owing to these stress distribution, a through-hardened steel is more liable to suffer a quenching crack (longitudinal) than a core-hardened, but an inner-crack (transverse) would occur even in the latter, if the core is small. Meanwhile, between these two dangerous cases, there exists a remarkable hardened state, in which the quenching stresses are small as a whole and no cracking is caused.
Contamination of radioactive nuclides on metallic copper surface was studied using oxygen free sulfaric acid solution containing fission products. Experiments for the influences of varions factors such as acidity of the solutions, co-existence of heavy metal ions and cation surface-active agents, and various treatments of copper surface were carried out. The radioactive contamination of metallic copper surface in non-corrosive solution was generally less than that in corrosive solution, and copper surface was contaminated selectively by some radioactive nuclides. The radioactive contamination of copper surface was extreamly decreased by additition of heavy metal ions (Fe3+, Cr3+) or cation surface-active agent into the solutions, and was also influenced by the condition of copper metal surface.
By analysing experimental data obtained from saggers with 250 mm inside diameter, the reduction mechanism of Höganäs sponge iron process was clarified. The reduction velocity of magnetite pellet by carbon monoxide, which was obtained from thermobalance measurement, was compared with the data of sagger experiments. As the result, it was concluded that magnetite layer in a sagger is reduced by carbon monoxide gas, and that the rate determining stage is diffusional removal of the reducing gas through sponge iron layer.
The data obtained by experiments of small scale are readily explained by the reduction mechanism which was previously reported(1)(2). The diffusion constant of CO gas through sponge iron layer at 1000°C(Dvs) is 0.62 cm2/sec. Carburization, sulfur elimination and tin removal are also discussed. The conditions used for plant layout are calculated by the method which was obtained in the previous reports(1)(2).
The composition and the structure of the alloy layer formed on steel, which was hot-dipped in molten aluminum and Al-3.3%Si alloy, were determined by some metallurgical methods including metallography, micro-hardness test, etching pits, X-ray diffraction and electron probe X-ray micro-analysis. The change in the thickness of alloy layer against immersion time at 700°∼850°C was also measured. The results obtained were as follows: (1) In the pure aluminum coating the alloy layer was composed of FeAl3 and Fe2Al5 but in the Al-3.3%Si alloy coating it was sheer FeAl3. (2) The FeAl3 layer was constituted of fine grains and the Fe2Al5 layer of relatively large columnar ones almost perpendicular to the steel surface. (3) The thin layer in the Al-Si coating is due to the accelerated diffusion of iron into the molten Al-Si alloy. (4) The mechanism of the formation of the alloy layer was also discussed.
Using the static method, a thermodynamic study has been carried out on the reaction between alumina crucible and carbon dissolved in iron in the temperature range of 1430°∼1700°C. The results were as follows: (1) The reaction being studied can be formulated as, Al2O3 (solid) + 3C (in molten Fe) = 3CO (gas) + 2Al (in molten Fe). (2) The standard free energy change of the reaction (where the standard state of activity of aluminium is defined as aAl⁄NAl=1, when NAl→0) has been obtaied as, ΔG°1703−1973°K=308,710−144.78T (3) Deoxidation constants of aluminium obtained from this study were in agreement within experimental error with the results by dynamic method of previous investigator and with calculated values based upon the hypothesis of regular solution for dilute solution of Al in Fe-Al binary system.
The influence of the spacing between particles on the mechanical properties, especially on the fatigue strength, was summarily investigated by using dispersion-strengthened nickel-aluminium bronzes which had a constant quantity of precipitates. The cast specimens made from high purity materials were quenched in water from the temperature of 1000°C and then aged at 650°C from 15 to 1000 hours to obtain 6 specimen of alloys which had different mean spacings under the condition of a constant quantity of precipitates. The following results were obtained: (1) The fatigue strength of an alloy which had smaller spacing between precipitates was not necessarily higher than that of an alloy which had larger spacing, and there was the maximum strength in an alloy which had a certain mean spacing. (2) The relationship between fatigue strength and the mean spacing did not correspond to that between yield strength and the spacing but to that between the true rupture strength and the latter.