Abstract
Recently, liquid-nitrided ferritic spheroidal graphite cast iron with ductile core structure is being used for machine parts to improve strength, resistance to wear and seizure. Impact values and their transition curve are two of the most important properties when it is used for machine parts. In this study, ferritic cast iron (FCD45) was nitrided by the Tufftride process at 750°C for 3hr. Impact test was carried out for U-notch test pieces by 5kg·m impact testing machine at -60°C∼100°C. Maximum impact value of non-nitrided test piece was 2.80kg·m/cm2 at 20°C, but that of nitrided piece fell to 1.70kg·m/cm2 at 20°C. This impact value of nitrided ferritic iron was greater than that of non-nitrided bull’s eye matrix iron (FCD55). The crack of nitrided iron by impact test at 50°C and -20°C, was propageted through the grain boundary due to the presence of Fe-nitride, but that of non-nitrided iron was propagated through the inside of grains and the dimple pattern fracture was obtained.
