발간논문

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An investigation has been carried out for the influences of combined addition of Si, Fe, Mn and Ti on ageprecipitation in compulsive solid solution of Al-2.62wt%Cu-0.42 wt% Mg alloy by the observation of the transmission electron microscopy and the detailed measurement of specific heat and electrical resistivity during ageing at temperatura range between 150℃ and 300℃. The results obtained are summarized as follows. (1) The formation rate of pre-precipitation zones, G. P. B., has been accelerated slightly by the combined addition of Si, Fe, Mn and Ti. This result may be attributed mainly to the effects of Mn and Ti upon the nucleations of G.P.B. zones formation. (2) The nucleation and growth of the S` precipitates on and around the dislocations have been retarded pronouncedly by the combined addition. These results produced the more coarser distributions of S` precipitates in addition elements free alloy than those in addition elements combined alloy. (3) The major effects of combined addition of Si, Fe, Mn and Ti have been resulted more pronouncedly on the nucleation and growth of the S` precipitates than on the formation of the G. P. B. zones. These effects were presented more at the higher ageing temperatures. (4) Reversion temperature of G. P. B zones has been dropped down about 8℃ by the combined addition of Si, Fe, Mn and Ti. This result showed that the growth of G. P. B. zones are modified slightly by the combined addition.

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To study the properties of spheroidal graphite cast iron such as tensile strength, hardness and elongaion, the effects of Si on the properties of the alloy under the constant amount of C were investigated and vice verse. The important results obstained are as follows. 1) Under the 2.5% of silicon with the variation of amouuts of carbon, degree of normalization (SDNsi) and hardness (SHNsi) of the alloy are as follows. SDNsi=-1.95Sc+85.1/15.6Sc+30.9×100 SHNsi=-90.0Sc+287)/105 Sc+31 2) Under 3.21% of carbon with the variation of amount of silicon, SPNc and SHNc of the alloy are as follows SDNc=-68.0Sc+132.2/15.6Sc+30.9×100 SHNc=-410Sc+586/105Sc+31 3) Under 2.35% of silicon the elongation due to variation of amount of carbon is 7.5% when Sc is 1 and the elongation is 4.7% when Sc is 0.8. Therefor the large differences in the elongation between Sc equals 1 and 0.8 were not observed. However, under the constant amount of carbon, differences in the elongation due to variation of silicon are very large.

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The copper-clad steel rod was prepared by drawing of a zinc electroplated steel rod clad in a copper tube and it was subsequently heat treated in a salt bath to enhance the bonding force between different metal layers. The thickness of electrodeposited zince layer and the time and temperature of heat treatment were the main variables investigated. Their effects on the bond strength were discussed on the basis of results of tensile test, microstructures, microhardness test, and fracture surfaces.

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For the utilization of the zinc plant residues composed chiefly of ammoniojarosite and carphosiderite, the separation methods of iron oxide from the residues are studied. By thermal decompositions of the residues, gaseous ammonia and SO₃ were separated at the temperatures of 420° and 710℃ respectively and the remaining solids were iron oxide. When the mixtures of the residues and anhydrous Na₂CO₃ were heated, NH₃ was eliminated at much lower temperature (80°) and the remainders became iron oxide and water soluble Na₂SO₄ at 400℃. In the solutions of Na₂CO₃, the jarosite group compounds of the residues were converted to iron (III) hydroxide with SO²₄^- in solution, The conversion rate was increased and the amount of Na₂CO₃ required was decreased by increasing temperature of the solution. Among the methods studied, the conversion of the zinc plant residues to iron hydroxide in the solutions of Na₂CO₃ was considered the most economical for the recovery of iron oxide from the residues because of its low treatment temperature.

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After melted down the scraps of 18Cr-8Ni stainless steel in the high frequency induction furnace, the samples were obtained at various holding time. With the increase of holding time, the average inclusion size and inclusion contents were measured by means of optical microscopy and Br-Methanol method And the behaviours of inclusions were studied by the X-ray technique. From above experiment. the following results were withdrawn. 1) With increasing holding time after melted down, the inclusion contents and average inclusion size were decreased and increased respectively; from 2.0 and 0.47% just after melted down to 4.22 and 0.13% after 2 hours. 2) In the case of the inclusions of Fe-Cr treated sample, the content was not changed but the size was increased compared with the inclusion content of just holding sample after melted down, The type of inclusion of Fe-Si treated sample was very fine and granulous. In this case, the content of inclusion was remarkably increased. In the case of fine inclusions, the inclusion content of granula shape was more than that of spheroidal shape. 3) In spite of the low bailing point of bromine(58.78℃) the dried inclusions at 100℃ which were extracted from Br-Methanol method were still contained bromine. This was the direct result that the bromine formed amorphous compound with iron oxide and chromium oxide. 4) The extracted inclusions which were dried at 1000℃ were crystallized to Fe₃O₄and Cr₂O₃. And the weight decrease was 7% compared with the inclusions dried at 100℃. And by the X-ray fluorescence analysis, the bromine peak was not detected in dried inclusions at 1000℃.

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A detailed analysis has been made of the creep relation, ε˙_s=A(σ-σ_ο)⁴exp(-ΔH/kT), in dispersion strengthened alloys where Wilshire and co-workers have directly measured the friction or internal stress, σ_ο. Values of a normalized friction stress σ_ο and a applied stress σ are shown to fit a simple empirical relation very well. The stress exponents calculated from the relation when compared with actual values reveal new features in the experimental creep data, such as variation in the constant, A, due to microstructural change. Another interesting feature in this analysis is that stress exponents comparable with those in dispersion strengthened nickel (∼60) may be obtained by suitable choice of parameters.

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The elastic strains and strain energies associated with precipitates are reviewed. Since the classical works of Eshelby were published almost two decades ago. there has been a rapid progress in understanding this interesting problem, especially in the anisotropic case. The elastic strain energy of inhomogenous ellipsoidal precipitates in anisotropic crystalline solids is discussed with some representative numerical results. The nature of the elastic strains associated with a non-ellipsoidal precipitate such as a cuboid is also described. The elastic interaction energy of two spherical precipitates in an anisotropic matrix is discussed in connection with some experimental observations of precipitate alignments. Finally, some of the results are applied to the homogeneous nucleation theory and plastic relaxation of the transformation stress is also briefly discussed.

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An investigation toward a nickel-free ferritic cryogenic Fe-12%Mn-(0.2%Ti) alloy steel was made, and the metallurgical processing techniques which improve the cryogenic mechanical properties are summarized. Retained austenite produced by a heat treatment within the two phase (α+γ) region was found to be effective in suppressing cryogenic brittleness. The inherent intergranular weakness of this alloy was also studied by employing Auger electron spectroscopy and other techniques. The cause of the intergranular brittleness is discussed and a method for its prevention is suggested.

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Fundamental aspects of the design of ferrous alloys are described. The illustrative example demonstrate how the new alloys or optimization of existing alloys can be developed from a rational approach based on the coherent relationship between structure and property. Utilization of phase transformation is of paramount importance in controlling microstructures in a desirable configuration. Martensite transformation in strengthening strong, tough structural steels, retained austenite to improve fracture toughness, ferrite/martensite composite as an ideal system to achieve both strength and formability in low carbon steels, and spinodal transformation in developing permanent magnets were taken as examples in relation to alloy design.

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