발간논문

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The gaseous nitrocarburizing treatment involves the simultaneous nitriding and carburizing at 570℃ in an atmosphere of 50% ammonia and 50% endothermic gas for a period of three hours followed by oil quenching. The treatment produces a compact compound layer 18μ thick on the surface of mild steel. X-ray structural analysis has revealed that this layer consists mainly of the C. P. H. epsilon carbonitride phase together with some Fe₄N and free ferrite chemical analysis has been used to show that C/N ratio in the layer is 0.21 and that it contains a total interstitial content of 29.5 atomic percent, which is close to the lower limit of the ε-carbonitride phase field.

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The transition from plane to cellular interface in dilute solid solution of aluminium containing zinc and copper+zinc has been studied by means of unidirectional solidification. The solid solution. alloys of different initial solute concentration (C_0) have been solidified under the different ratio of temperature gradient (G) to rate of solidification (R), and the cell morphology has been observed. The plane to cell transition has been plotted on a graph of C_0 vs G/R, and the critical transition condition can be described by a straight line in the graph as anticipated by the Tiller`s equation on supercooling. Applying the Tiller`s equation to the experimental result, liquid diffusion coefficient of zinc in aluminium has been estimated to be 1.8×10^(-5) ㎠/sec. The result of aluminium-copper-zinc ternary alloy indicates that there exists an interaction between the copper and zinc atoms, in such a way to decrease the equilibrium distribution coefficient of zinc in aluminium by the addition of copper.

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Effects of the refinement of primary silicon on the hardness and the tensile strength of hypereutectic Al-Si alloy are investigated in this study. Especially the relationship between the refinement and Ni, Cu, Mg elements, which are used usually in the alloy, and effects of heat-treatments, have been studied. The results obtained are as follows : 1) The refinement of primary silicon can not increase the hardness of the alloy, but decreases it. 2) The refinement of primary silicon increases the tensile strength at any case.

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Anthracite has been used as fuel for melting cast iron in the foundry plant because of difficulty of earning good foundry cokes. In this paper, the heat balance of the cupola was calculated with the practical operation data (running time 60.5hrs.) using anthracite in the cupola. The results were compared with the heat balance of the cupola using mixed fuel (anthracite and cokes). And comparisons were made as follow: 1) With approximately same blast temperature, the heat supply by the hot blast to the cupola was 6.35% in case of anthracite while mixed fuel supplied 11.50%. 2) Percent of heat content of the melt had 15.22% in case of anthracite while mixed fuel had 15.86%. 3) Decomposition heat loss by the limestone had 1.68% in case of anthracite while mixed fuel had 2.68%. 4) Heat content in the refractory lining, heat emission, slag formation heat and others had 34.49% in case of anthracite while mixed fuel had 33.53%. 5) Combustion heat value by the CO gas had 39.63% in case of anthracite while mixed fuel had 35.41%. 6) Heat loss percentage by slagging had 3.03% in case of anthracite while mixed fuel had 4.23%.

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In order to examine the effects of fast neutron irradiation on the precipitation process in Al-4%Cu alloy, hardness measurement and transmission electron microscope were employed. Specimens were irradiated to 2.8×10^(19), 3.4×10^(20) and 1.2×10^(21) nvt neutron doses in the Japan Materials Testing Reactor. Their electron micrographs prior to annealing or at the early stage of annealing at 200℃ showed G. P. 2 and even θ` plates, which it can not normally expect to form. The kinetics of growing of θ`plates in Al-4%Cu alloy were measured by means of hot stage transmission electron microscopy, and the lengthening data of θ`plate measured at each temperature and at each neutron dose have been interpreted in terms of the various equations for recent ledge theories of growth. The calculated diffusivity and frequency factor of Arrhenius` equation of specimen irradiated to 2.3×10^(19) nvt neutron are much larger than the un-irradiated one. This may be attributed to excess vacancies or interstitials produced by irradiation. It is concluded that neutron irradiation does not only bring the enhancement of heterogeneous nucleation, but also give rise to enhanced diffusion of solute atom, and the more the neutron dose increases, the greater the growth rate becomes.

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Thermal behavior of several types of sealing glasses containing PbO, ZnO and B₂O₃, and a borosilicate glass were characterized by differential thermal analysis. Using an isothermal technique, the activation energy for crystallization of a 2PbO·ZnO ·B₂O₃crystalline phase was determined to be 33.6 kilocalorie/mole, and the crystal morphology was plate-like as predicted in the analysis. Using a borosilicate glass and Fe-Ni-Co alloy as a model, reactions between glass-metal systems were evaluated. Microscopic studies of the glass-metal interface indicate the dissolution process of the oxide as well as the precipitation of a second crystalline phase at and near the interface. Two types of Kovar alloys (one standard and the other containing 0.24wt% Cu) were oxidized in air. The oxidation rate of the Kovar alloy containing Cu was slightly lower than that of the standard Kovar at temperatures lover than 850℃. At higher temperature, the effect was negligible. The oxide structure found fur both alloys was a Ni- and Co-containing spinel.

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It is well know that, in the manufacturing of the low C-special steels as the case-hardening steels and the stainless steels, the ingots are apt to be not killed by the hydrogen boiling, especially in the humid seasons. I saw these problems last year in a plant in this country. We suffered formerly, too, about these troublesome hydrogen problems for a long time before vacuum remelting and vacuum degaussing installations. Here I want to introduce the considerations on our bitter experiences to help your practical operations. 1) P_(H₂O)(㎜Hg)=Mean value of the partial pressures of the moisture in the atmosphere in each month measured every day through a year. [H]_(Tap) (cc/100g Fe)=Mean value of the hydrogen contents at the tapping of the low alloy special steels melted by the basic electric are furnaces (B.E.F.) (10-15 ton) in each month. There can be seen relatively higher degree correlations between [H]_(Tap) and P_(H₂O) (n≒380), when we calculate the regression equation, assuming that both keep the linear relation. Of course, the histograms of [H]_(Tap) differ according to the kinds of steels, the melting furnaces and the terms of sampling. 2) Generally [H]_(MD) (at the melt-down) decreases a little by O₂-blowing, then increases very much suddenly at the reducing period and increases a little again at the tapping (n≒135). These amounts of increase of [H] at the reducing period and at the tapping are larger as when P_(H₂O) is higher. However when we check, for example, about the casehardening steels melted only in Jan. -Mar. (n= 120), there seems almost no correlation between [H]_(Tap) and P_(H₂O) when P_(H₂O) is under than about l0㎜Hg. Therefore, to decrease [H]_(Tap), we must investigate the counter-measures in both cases, that is to say, the manuals to decrease [H] in the ordinary melting processes and the special instructions in the humid seasons. The limits of [H]_(Tap) to avoid the hydrogen boiling are about 9-l0cc/100g in the ordinary case-hardening steels and about 12-14cc/100g in the stainless steels. 3) [H]_(MD) is driven out by the agitation of O₂-blowing and by the floating actions of the produced CO bubbles. Although Δ[H] is much smaller than those theoretically calculated from the decarburized amounts, it is sure that the effective conditions of O₂-blowing for decarburization are also effective for dehydrogenation. The ratio of [H]²× [O] at the end of oxidizing period to [H]²×[O] at the earlier period of reduction is kept about 1:1 for the low C-special steels and about 1:0.5 for the medium and high C steels. So that it suppresses the increase of [H] at the earlier period of reduction to decrease not only [H] but also [O] at the end of oxidizing period. 4) About the influences of the amounts of oxidizing slags which are brought into the reducing period, of the exposed area of the bath open to the atmosphere and the exposing time, or of the charging sequences of reducing slag-forming materials, it was difficult to obtain the distinct conclusion in our many practical operations. Next it is unsufficient to emphasize, only abstractively, the effects of the moisture contained in the charging materials, especially in humid seasons, so that I want to warn their importance, showing the test results of the practical operations. Of course, the most important points of ordinary melting processes, that is to say, how to control the temperatures and the basicities in the reducing period, are also very important for dehydrogenation. 5) If [H] increases over the limited value and the bath can not be killed in the humid seasons, even when the sufficients cautions are taken in the melting stages, the forced dehydrogenation methods are introduced, for example, using the dehydrogenation agent Freon 12 (C-CL₂-F₂) or the argon-blowing. Originally hydrogen is driven out only by the mechanical methods, but, in this case, the dehydrogenation is achieved chemically by formation of the hydrogen-halides. In our tes

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