구상흑연주철의 기계적 성질 향상을 위한 미세조직 제어에 관한 연구

Abstract

Effects of cooling condition after solidification on the microstructure and the mechanical properties of 0.36 Mn containing ductile cast iron have been studied based on the minimized addition of Cu and Sn for vehicle component applications with better quality and cost competitiveness. Cu and Sn were selected for additional elements judging from the well-known fact of strong tendency of pearlite promotion followed by the tensile property improvement. After pouring of the Mg treated cast iron melt with various chemical compositions into the block specimens, two ways of post solidification cooling conditions were applied for comparison; both cooling in the mold, and cooling in the air after shake-out at 800°C. The pearlite fraction of the mold-cooled specimens was analyzed as 27~44wt.%, with the tensile strength and elongation of 513~568N/㎟ and 10.4~14.3wt.%, respectively. Whilst, the air-cooled specimens showed the pearlite fraction of 77~85%, with the tensile strength and elongation of 728~758N/㎟ and 3.2~6.0%, respectively. It is worthwhile to note that the remarkable improvement of both tensile strength and elongation of the ductile iron was achieved by the present air cooling condition with the minimized combined addition of Cu and Sn to the 0.36 Mn containing ductile iron.