발간논문

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This paper discusses the effects of carbon addition and annealing conditions such as annealing temperature and holding time at a bainitic transformation temperature, 400℃, on the formation of retained austenite and mechanical properties in three Fe/1.6Si/0.9Mn steels with varying amounts of carbon. The main findings of this study are as follows. Increasing carbon content increased the yield and tensile strength but decreased the total elongation. The results were attributed to the remarkable increase in the volume fraction of second phase which mainly consisted of bainite and retained austenite. The combination of tensile strength and total elongation had a good correlation with the amount of retained austenite in the annealing temperature range below 810℃. However, in the temperature range from 810℃ to 870℃, the tensile strength-total elongation combination appeared to be influenced by the carbon content of retained austenite rather than by the amount of retained austenite.

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The purpose of this study is to investigate the effect of heat treatment on the martensitic transformation behavior and thermal fatigue characteristics in Ti-:Vi-B alloys with various boron concentration. Three types of heat treatment are given to the specimens ; i) solution treatment ii) aging iii) cold work and low temperature anneal. This research had been performed by electrical resistance measurement, x-ray diffraction and transmission electron microscopy. In solution treated specimens, the Ms has been decreased with the increasing of boron content. However, It has not been affected by aging, while that of 30% cold rolled and annealed specimens has been remarkably increased in the vicinity of recrystallization temperature. R-phase transition which is related to abnormal increase of electrical resistance prior to martensitic, transformation has been formed at a boron content of 0.2at%. The cold worked and annealed specimens have a good thermal fatigue characteristics independent of boron concentration, because a high density of dislocations rearranged by the low temperature annealing after cold work has suppressed the introduction of dislocations during the thermal fatigue cycling.

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