Influence of Austenitizing Time on Machinability of Ductile Cast Iron with Ferrite-Martensite Dual Phase Matrix

In this research, the effects of partially austenitising time on the machinability of spheroidal graphite (SG) cast iron with ferrite-martensite dual matrix structure (DMS) were investigated to optimize its machinability. Specimens with non-alloy ferrite matrix structure were prepared by the casting process. Then the specimens were austenitized at temperatures of 900 oC at various times (5 to 25 min) and subsequently quenched into the water to produce DMS with martensite volume fractions. The Brinell hardness test method was used to determine the hardness of specimens. The machinability of the workpieces with ferrite and dual structures were investigated by measuring the surface roughness and primary cutting force. According to the results, the Johnson-Avram kinetic model was valid for correlation between the martensite volume fraction and autenitising time. The surface roughness was increased and the cutting force was decreased with increasing austentising time to 12 min, and consequently, with increase the hardness to 168 BHN. The heating at 900 oC for 12 min resulted in 16-20% and 15-23% improvement on the cutting force and specific cutting power, respectively, when compared to as-cast specimen, while the surface quality remained at the same level. The cutting force was correlated with feed rate as a power model with exponents of 0.77 and 0.73 for DMS (with 30% martensite) and ferritic as-cast samples, respectively.