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The operation condition far improvement of reduction degradation index (RDI) at 550℃ was investigated by analyzing the daily operation reports of minter plant during the period of 1983 Jan.-Dec. The experimental test on the base of the adopted factors was performed in a pot of 240㎜Φwith bed height 390㎜ under the condition of the same basicity and coke ratio. The applied test based on th findings of the important factors was conducted at the same sinter plant. The results obtained may be summarized as follows: For the improvement of RDI, followings should be carefully controlled 1) Magnetite ratio of raw mix: under 16% 2) Slag volume ratio : about 20.0% 3) TiO₂ ratio : under 0.21% 4) Bed height should be controlled with the change of burnt lime addition ratio.

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The formation and growth behavior of transformed ferrite with intercritical annealing time and cooling rate in a dual-phase steel was investigated. The formation of transformed ferrite in the specimen with the short intercritical annealing time, 140 sec, started when cooled to the low temperature. The temperature at which transformed ferrite initiated to form was lower at the higher cooling rate. The effect of cooling rate on the formation behavior of transformed ferrite was similar regardless of the intercritical annealing times. However, because the partitioning of substitutional alloying elements in case of the short intercritical annealing time, 140 sec, could be neglected, the growth behavior of transformed ferrite was not affected by the substitutional alloying elements.

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The effect of intercritical annealing temperature on the formation behavior of transformed ferrite in a dual-phase steel has been investigated. At high intercritical annealing temperatures, the transformed ferrite grew on the retained ferrite surrounding the austenite particle. At low intercritical annealing temperature, however, the transformed ferrite grew on both the retained ferrite within the austenite particle and the cusp region of the retained ferrite surrounding the austenite particle. This difference in the growth behavior of the transformed ferrite seemed to be affected by the partitioning of substitutional alloying elements, the existence of the retained ferrite remained in the austeniter the morphology of the retained ferrite-austenite interface, and the magnitude of the driving force for the austenite to transformed ferrite reaction during cooling stage.

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The influence of pre-aging treatment on the creep properties in AISI 316 stainless steel has been investigated in the temperature range of 923∼1023 K and stresses in the range of 130∼228 MPa. Specimens were pre-aged at 1073K in air atmosphere up to 300 hours to clarity the effects of pre-aging time on creep rate. The steady state creep rate and the rupture strain increased with pre-aging treatment while the rupture time decreased with pre-aging treatment. Creep rate acceleration with pre-aging time could be described by ◎ =1.6686×10＾(-4) t＾(0.865) where t is the pre-aging time in seconds. Creep rate acceleration for pre-aged specimens was not strongly influenced by temperature and stress changes. Activation energy for creep decreased with pre-aging treatment and stress exponent represented by power relation increased with pre-aging time.

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The hot deformation behavior of copper has been studied in the temperature range from 0.55 Tm to 0.65 Tm and the strain rate range from 1.26×10(-3) S(-1) to 5.71×10(-3) by hot torsion. The hot softening mechanism of copper has been found to result from dynamic recrystallization through the flow curve and change of microstructure. Strain for the onset of dynamic recrystallization is represented by ε_c=0.039 LnZ-0.531 using Zener-Hollomon parameter Z and strain for the completion of dynamic recrystallization is represented by ε_x=0.276 LnZ-4.571. The time required for dynamically recrystallized grains decreased with increasing deformation temperature and strain rates. The dynamically recrystallized grains are smaller than statically recrystallized grains, and hardness is larger than statically recrystallized grains.

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Equilibrium segregation of solute atoms to grain boundaries was studied for the ∑5 [100] and ∑3[110] tilt boundaries of the Ni-Cu binary system. The regular solution theory was applied to define atomic interactions. The results obtained from this study are as follows: 1. Copper segregation to the grain boundaries in the Ni-Cu system follows the Gibbsian equilibrium segregation behavior in which the segregation is localized on a few atomic layers, and its amount decreases with increase in temperature. 2. The amount of segregation on the ∑5 boundary appears to be greater than that on the ∑3 boundary. 3. Equilibrium segregation reduces grain boundary energy and its reduction is significant at lower temperature.

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Phase transformations during slow cooling after intercritical annealing for a short time have been investigated using Fe/l.6Mn/0.7Si/0.1C dual phase steel with initial structures of fine ferrite-pearlite as cold rolled state. It was observed by using scanning and transmission electron microscopes that the growth of austenite, formation of ferrite and pearlite transformation occurred in sequence during slow cooling from intercritical temperature. The scanning electron micrographs showed that austenite particles of submicron size were retained as a isolated type at the ferrite grain boundaries or inside of ferrite grains. Because of concentration gradient in an austenite grain, a part of the austenite was transformed into pearlite and the other region remained as austenite. As a result, the pearlite was located at the ferrite-martensite interface.

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The strip temperature during cold rolling has been estimated by a mathematical model established in the present work. The model was evaluated on a selected steels of which compressive yield strength can be related to the total reduction ratio in terms of σ_c=A+B·γ_t (A and B are material constants) The followings are the results drawn. 1. The strip temperature after finishing cold rolling can be estimated by (수식) 2. The mean value of the difference between the estimated and the measured strip temperature was corresponded to 5.9% of the absolute value measured on the selected steel. 3. It has been found that the best effective way to control the strip temperature is the rolling schedule design.

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