This paper confirms at first that the P/M products from 1.4%C cast iron swarf powder shows nodular graphite, though the products from 2.0%C powder reveals flake graphite. Secondly this paper investigates in detail the variation of graphite morphology and its effects on tensile strength using Fe–Si–C mixed powders. Fe–Si–C mixed powders were prepared from reduced iron, atomized ferrosillicon (17%Si), and graphite powders. Blended mixtures contained 2.5%Si and various C contents in the range of 0–2.7%. The preforms were compacted at 600 MPa. Some of them were sintered at 1423 K in dry H₂ atmosphere for various times up to 43 ks, followed by air cool (1 K/s), the others were powder-forged at about 1100 K, 1200 MPa during a sintering.
The product containing about 1%C, sintered for a long-time or powder-forged, showed high tensile strength (900–1200 MPa), because graphite was nodularized in them. It was not, however, the case of the products containing more than 2%C. In the former, sintering proceeds in the state of all C being dissolved in γ phase; consequently, pores between powder particles spheroidize in a long-time sintering or powder-forging process. During cooling, the supersaturating C atoms crystallize as graphite on the surface of spheroidal pores and fill them up. In the latter, graphite which cannot be dissolved in the γ phase remains along powder particle boundaries. During cooling, the supersaturating C atoms precipitate as graphite onto the residual graphite and/or unspheroidal pores.

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A new type micro-Vickers hardness tester with a loading-rate controllable device has been developed for a high temperature microscope. The main advantage of this hot hardness tester is to keep the loading rate constant during each test, in the five steps from 0.00196 to 1.96 N/s (0.2 to 200 gf/s), by means of the magnetic repulsive force between a permanent magnet and an electromagnet. On this tester, an indenter mounted to a plunger is free to move without any friction on the optical axis of the microscope, and the minimum load can be lowered to 0.098 N. Then, this hot micro-hardness tester has a capability to select an appropriate loading rate corresponding with each physical and mechanical property with which the hardness is correlated, and also to select the rate depending on temperature. The maximum available temperature reaches 1870 K.
This hot micro-hardness tester has been successfully used to study the loading rate dependence on hardness of a silicon-iron alloy, an alloy tool steel and a eutectoid carbon steel, together with the temperature dependence on hardness. The loading rate dependence was found to be remarkable in the temperature range at which structural changes and phase transformations of materials take place.

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The effects of applied stress on the equilibrium intergranular segregation of solute atoms have been studied theoretically, with special reference to the solute phosphorus/host iron system under the application of a comparatively small tensile stress. The theoretical applied stress effects deduced from the free energy interaction between the solute misfit strain, solute elastic inhomogeneity or grain boundary elastic inhomogeneity and the applied stress were very small compared with that calculated from the free energy change due to the plastic work contribution of solute migration under stress, in the system considered. The latter was comparable to the applied stress effects observed in some steels.

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In order to obtain the thermodynamic properties of Fe₂B and FeB, the emf measurements of the oxygen concentration cells: Fe, Fe₂B, B₂O₃ (or Fe₂B, FeB, B₂O₃)|solid oxide electrolyte| reference electrode have been carried out using calcia-stabirized zirconia, yttria-stabirized zirconia and yttria-doped thoria as the electrolyte, and selecting air and Cr, Cr₂O₃ and Fe, Fe₂B, B₂O₃ as the reference electrode. The standard free energy of formation of each boride obtained from all the cells belonging to the corresponding test electrode system were in good agreement with each other regardless of the differences in the electrolyte and/or the reference electrode. These results were summarized in the equations: ΔG_Fe2B°=−101340+20.04T±1250 J/mol (1000∼1300 K) and ΔG_FeB°=−93010+24.04T±1250 J/mol (1000∼1350 K).

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Stress corrosion cracking of α brasses and effects of hydrogen on it are investigated. Hydrogen permeation into the alloys increases with increasing zinc content, although it is affected by the cathodic charging condition used. Permeated hydrogen evolves out completely by aging at room temperature after charging. Though tensile properties of alloys are not affected, the stress corrosion cracking life is lowered by hydrogen permeation and recovered by evolution of hydrogen. It is concluded that hydrogen has some effect on stress corrosion cracking of α brasses studied.

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The composition depth-profiles of the surfaces of 304 and 316 stainless steels prepared with a variety of surface treatment have been measured by a simultaneous use of argon ion sputter-etching and Auger electron spectroscopy. Chromium was enriched in the surface oxide films, whereas nickel was enriched at the film/substrate interface. The degree of Cr-enrichment in surface films depended on the surface treatment and increased in the following order; mechanical polishing with emery paper in water<chemical etching in mixed acid of 1%HF+10%HNO₃<electropolishing in mixed acid of CH₃COOH+HClO₄ (20 : 1)<chemical treatment in 10%HNO₃ or chemical passivation in 30%HNO₃. The degree of nickel enrichment at the film/substrate interface increased with increasing degree of chromium enrichment in the film. The surface oxide films on 304 stainless steel were always thicker than those on 316 stainless steel, irrespective of the surface treatments. The aging of specimen for one week in dessicator gave rise to decrease in chromium-enrichment and to increase in film thickness. Discussion was made on the relationship between pitting potential and surface composition of stainless steels.

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Thermodynamic implication of the equilibrium phase diagram for order-disorder phase transitions in Fe₃Al alloy has been investigated by a statistical approach employing the Bragg-Williams approximation, in which the magnetic interactions are taken into account in the first and the second neighbor iron atoms as well as the usual atomic interactions up to the second neighbors. It is shown in the calculated diagram that the α+B2 phase is caused by the competition of both the atomic and magnetic interactions, with a ferromagnetic interaction between the first neighbor iron atoms and an antiferromagnetic interaction between the second neighbor iron atoms. It is also suggested from the configurational free energy curve that spinodal decomposition is expected within the α+B2 phase field in accordance with the result of our previous experimental observation.

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The dissolution of copper into molten tin-lead alloys has been studied at 673 K under static conditions using three kinds of reaction couple method. The dissolution of copper increased with increasing tin concentration of the melt owing to the difference in the saturation concentration of the melt. The differences in the dissolution of copper between the liquid lower and upper conditions and between the upper and lower coppers under the liquid sandwiched condition were obtained in tin-rich alloys. The differences were attributed to the natural convection resulting from the density difference in the melt. The thickness of the alloy layer formed at a solid-liquid interface increased with approaching to the saturation and with increasing concentration of tin in the melt.

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