회주철의 진동감쇠능과 기계적 성질에 미치는 오스템퍼링처리의 영향

Effect of Austempering Treatment on Damping Capacity and Mechanical Properties in Gray Cast Iron

Gray cast iron with a high damping capacity has been used for controlling the vibration and noise in various mechanical structures. Nevertheless, its usage has been often restricted due to its poor tensile strength. Therefore, it is necessary to improve tensile strength at the expense of a loss in damping capacity. This study is aimed at finding the best combination of tensile strength and damping capacity by varying austempering time and temperature range from $320^{\circ}C$ to $380^{\circ}C$ after austenization at $900^{\circ}C$ for 1hr. The effect of austempering condition on hardness and the volume fraction of retained austenite is investigated as well. The results obtained are summarized as follows : (1) With an increase in austempering temperature, both tensile strength and hardness decrease while damping capacity improves. (2) Austempering at $350^{\circ}C$, resulting in a mixture of upper and lower bainite with partially retained austenite, exhibits the optimum combination of tensile strength and damping capacity.