오스템퍼드 구상흑연주철의 기계적 성질 및 감쇠능에 관한 연구

Abstract

This study was investigated effects of copper contents, subzero-treatment and volume fraction of martensite on the mechanical properties and damping capacity in austempered ductile cast irons(ADI) obtained by changing the austenitizing and austempering temperatures. The obtained results are summarized as follows; Carbon concentration in the retained austenite increased with the increase of austenitizing temperature up to 880℃, however the value of concentration showed constant above this temperature. The volume fraction of the retained austenite and the carbon concentration in the retained austenite appeared the maximum value at the austempering temperature of 400℃. After increasing the carbon concentration in retained austenite, the concentration hardly changed with the increase of austempering time. Compared with the two different Cu content irons, the volume fraction of retained austenite and the carbon concentration in austenite appeared lower in the one containing higher Cu content. When the ductile cast iron was austempered, tensile strength and impact value remarkably raised, whereas elongation dropped. With the increase of austempering temperature, tensile strength decreased continuously, however, elongation and impact values dropped abruptly at 450℃ after showing constant value up to 400℃, For the specimen containing 0.57wt% Cu alloyed iron, tensile strength increased, while elongation and impact values decreased compared to those values of 0.15wt%Cu alloyed specimen. Although the austempering treatment extensively decreased damping capacity, it was not affected by temperatures and lasting time of austempering. The higher damping capacity was shown in higher Cu alloyed specimen. Subzero treatment raised tensile strength and hardness, hence elongation and impact value dropped. With lowering temperature of subzero treatment, slight increase in tensile strength and hardness were shown, and elongation decreased slowly, however impact value decreased rapidly. Subzero treatment of the austempered ductile cast iron raised damping capacity exceedingly. Slight increase in damping capacity was shown with lowering temperature of subzero treatment. With the increase of volume fraction of martensite, tensile strength increased, however slow decrease in elongation was shown. The increasing ratio of tensile strength and decreasing ratio of elongation also increased. The hardness and increasing ratio of hardness increased slowly up to 5% of the volume fraction of martensite, however the steep increase in the hardness was shown above 5%. Impact value and decreasing ratio of impact value decreased rapidly up to 5% of the volume fraction of martensite, however, over 5%, the values did not changed. Damping capacity and increasing ratio of damping capacity were rapidly increased with increasing volume fraction of martensite, however, above 5%, those increased slowly.