발간논문

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To recover the iron in the dust which produced in steel-making process, the reduction experiment was performed by means of varing the most effecting factors on the recovery of iron such as the carbon ratio (actual carbon required for reduction of pellets/theoretical carbon required for reduction of pellets), the lime addition ratio and the reduction temperature in a given range. From this experiment, the following conclusions were summarized. 1) By the reduction with char-coal (carbon ratio: 1.5∼3.0, without addition of lime) the luppes were not produced at 1200℃ and 1300℃ but produced at 1400℃. And, at carbon ratio 2.0, the recovery of luppe produced at 1400℃ was optimum (74%). 2) By the addition of lime and the reduction with char-coal (carbon ratio: 2.0) the recovery of luppe was more than 60% at the reduction temperature 1200℃ and 1300℃, the lime addition ratio 30±5%. And in the case that the lime addition ratios were more or less than 30±5%, the luppes were not produced. 3) With the increase of the carbon ratio added with reducing reagent and the increase of the amount of addition of lime used by flux, the volatilization rates were increased and decreased, respectively. 4) In the case of addition of 30% lime the microstructure of graphite of luppes were coaser with increasing the carbon ratio at the reduction temperature 1200℃. At 1300℃ and the carbon ratio 1.5 and 2.0 the graphite was not seen. But at 1300℃ and the carbon ratio 2.5 and 3.0, the graphite was coarser than that at 1200℃ .

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Mechanical properties of zircaloy-4 alloy containing 10ppm to 2500ppm hydrogen have investigated in the range of 25℃ to 700℃ at a strain rate of 6.7×10^(-4)sec^(-1). Up to 500℃, ultimate and yield strength are increased as the hydrogen content increases, but the trend is opposite at 700℃. Total elongation of the alloy are not sensitive to the temperature up to 400℃ but they increase rapidly from 550℃ and uniform elongation have a peak value at 200℃. True stress-true plastic strain curve of the alloy are divided into two stages below 400℃, except the alloy containing 2500ppm hydrogen, and each of which can be represented by the Ludwik equation; σ=σ_0+Kεⁿ. Strain hardening exponent, n₁, of the first stage, in general, decreased as the hydrogen content and temperature increase.

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The blast furnace burdening problem is settled by building the mathmatical model and soving it. In operation, the thermochemical and metallurgical process is expressed as a set of constraints of this model. As the input-output. relationship of model is represented linearly, we use the linear programming. The solution indicates a minimum cost selection of input material and satisfies the constraints. The paper presents a mathmatical formulation of linear programming model in the blast furnace operation

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The susceptibility to temper embrittlement for Ni-Cr steel of various structures has been studied, and following results were obained. 1. The microstructures studied were martensite, bainite and martensite and pearlite which were obtained by means of quenching and isothermal transformations. The transition temperatures of the embrittled steels showed a trend of shift to higher temperature than that of unembrittled steels in all structures, and the shifted temperatures were 82℃ in martensite, 42℃ in bainite and martensite mixture and 28℃ in pearlite steel respectively. 2. The observed transition temperatures for unembrittled steels were -84℃ in martensite, -54℃ in bainite and martensite mixture and -22℃ in pearlite steel. However in the case of embrittled steels the transition temperatures turned out to be near same in all structures. The reason for this is considered that the observed transition temperatures could result from the combined effect of various factors on the impact properties of these embrittled steels. 3. Hardness was not effected on embrittleness of Ni-Cr steel.

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The Lindemann parameters δ, and the root-mean square thermal vibration amplitudes √ of 54 metallic elements both at fusion and at room temperatures are calculated through the combination of the Debye-Waller and the Lindemann equations. The magnitude and ratio of the average Lindermann parameters δ^r_(fi), with i=1, 2 and 3 for the fusion transitions; A₂→liquid, A₁→liquid and A₃→liquid, are respectively δ_(f1)^r=0.226, δ_(f2)^r=0.185 and δ_(f3)^r=0.131 δ_(f1)^r : δ_(f2)^r : δ_(f3)^r=1 : 0.821 : 0.578 The hypotheses of Lindemann, Gilvarry and Shapiro on the fusion phenomena due to lattice vibration of metals are justified. The role of lattice structure of fusion is also demonstrated.

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Roasting of stibnite was studied in a rotary kiln type roaster with air as the oxidizing gas. The roasted ore can be used to prepare pure Sb₂O₃ by leaching process. A couple of fundamental tests was also carried out with thermal gravity analysis and tube furnace type roaster. The results obtained in the present investigation are as follows: 1) The oxidation of -200 mesh stibnite begins at about 250℃. 2) In the tube furnace roasting, the conversion of Sb₂S₃ into Sb₂O₃reaches about 95%. 3) To attain sufficient oxidation for -200 mesh stibnite in the rotary kiln type roaster, 1.8-2.2 times of the calculated amount of air should be blown into the roaster for 60 minutes at the temperature range of 360-400℃.

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The tool steel M-2 was laser surface melted and the microstructures characterized both in the as-melted and subsequently heat-treated condition. The laser melting resulted in the formation of extremely fine microstructures and nearly complete dissolution of carbides. Electron diffraction studies, when compared with previous X-ray analysis, show that the melt region consists of δ-ferrite and austenite formed by nonequilibrium peritectic reaction. The relative amounts of δ and γ vary with position, the top melt region being mostly of δ and the lower melt region predominantly γ. A most important finding is the microstructural change giving rise to a substantial increase in hardness by subsequent conventional heat treatment: ultra-fine carbide particles are formed throughout the melt region which gives a uniform microstructure with a maximum hardness of 1,070 V.H.N. Prelimenary experiments show that electron beam melting may lend itself to the sauce results.

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