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The effect of cooling rate from the intercritical annealing temperature on the mechanical properties of dual-phase steel was investigated using a Fe/1.8Mn/1.4Si/0.07C alloy and the results were explained in terms of the microstructures. It was found that within the range of cooling rates studied, better property-combinations were obtained as the cooling rate was slower. Microstructures of the specimen slow-cooled at 5℃/sec. were characterized as fine dispersion of martensite, considerable amount of the retained austenite up to 8% in volume, most of which transformed to martensite upon tensile strain in the strain range 2-6%, and low dislocation density in the ferrite matrix. Those microstructural characteristics in 5℃/sec. cooled specimen were considered responsible for higher strain hardening rate than that of water-quenched specimen during the post elongation after initial 2%, and hence resulted in larger elongation in 5℃/sec. cooled specimen.

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The purpose of the present study is to develope for producing high strength cold-rolled steel sheets having low yield strength suitable for automobile body panels. In recent years the modification of nonmetallic inclusions by a metallic calcium addition has received increasing attention. Calcium in molten steel reacts with the oxides and sulphides to form new calcium containing compounds and complex oxysulphids. As a result, the composition, shape, number and distribution of a non-metallic inclusions are changed, greatly improving the mechanical and other properties of a finished steel. In this study the addition of Ca wire and CaAl wue containing calcium and aluminum into the molten steel (0.1% C) gives the following advantages. 1) Deoxidation and desulphurization more effectively. 2) Increase of the amount of calcium residuals in the steel. 3) Change of shape and distribution of nonmetallic inclusion. 4) Increase of elongation, reduction of cross sectional area and impact values. 5) Improvement of workability and anisotropy.

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The rate and mechanism of oxidation of pyrrhotite have been studied by means of thermodynamic analysis, TG-DTA, and the reactor experiments. The results obtained in these experiments are as follows. 1. According to thermogravimetric analysis, the oxidation of 150/200 mesh pyrrhotite began at about 400℃ and the rate of oxidation increased above 540℃. 2. During the roasting of pyrrhotite in air, the oxidation reaction occurs through the following steps. FeS →Fe₃O₄→Fe₂O₃ 3. The oxidation rate of pyrrhotite increased with the increasing oxygen concentration and reaction temperature. The overall oxidation rate of pyrrhotite was predominantly controlled by the diffusion of oxygen, and the apparent activation energy of the process was evaluated as 27㎉/mole

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In the fabrications of waved form SUS 304 fiber reinforced aluminum alloy composites by vacuum infiltration process, the emphasis was placed on the mechanical properties and interface interactions between fiber and matrix in Composites, The stainless steel fiber (SUS 304) with 0.21 mm diameter was made into wave form, whose wave angle was 71.3˚. The result obtained in this investigation are as follows; 1. The most suitable reinforcement was obtained with the fiber through Al pack cementation at 900℃ for 30 min. 2. The higher value of hardness was shown in the interaction zone between steel fiber and Al alloy matrix due to the formation of intermetallic compound. 3. As the fiber volume fraction was increased in the matrix, tensile strength was increased while impact strength decreased. 4. In the analysis of interaction zones by EDS and WDS, Al, Fe, Cr, Ni, Cu, Mg were detected as the diffused constituents.

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