Effect of Austempering Factors and Mn Addition on Mechanical Properties of ADI

오스템퍼링 조건과 Mn의 양이 ADI의 기계적 성질에 미치는 영향

In this study, we investigated effect of austempering factors and Mn addition on mechanical properties of ADI with ferrite-bainite matrix by pearlite-bainite transformation treatment. Ductile cast iron specimens containing various of Mn were austenitized at 875$^{\circ}C$ for 350 sec or 925$^{\circ}C$ for 160 sec and then austempered at 300$^{\circ}C$ or 400$^{\circ}C$ for the various periods(5 to 30 min). Manganese increased pearlite volume fraction in as cast ductile cast iron. The obtained results are as follows ; 1) In austenitizing, hardness of sepecimens austenitized at 875$^{\circ}C$ for 350 sec was higher than that of 925$^{\circ}C$ for 160 sec. 2) In effect of austempering temperature, tensile strength and handness of specimens austempered at 300$^{\circ}C$ was higher than that of 400$^{\circ}C$. However, elongation had reverse tendency. 3) Increasing austempering time decreased hardness due to the increment of bainite and retained austenite fractions. However, toughness are increased.