Effects of Tin Addition on Microstructure and Mechanical Properties of Spheroidal Graphite Cast Iron Containing Small Amount of Boron

Abstract

  A small amount of boron in spheroidal graphite cast iron has been reported to decrease the hardness as well as the pearlite matrixes in pearlitic ductile cast iron. The pearlite content in spheroidal graphite cast iron can be increased by the addition of pearlite promoting alloying elements such as tin. This research was conducted to determine the effects of the tin addition on the mechanical properties and microstructure of spheroidal graphite cast iron containing 50ppm boron. All pearlite matrixes can be achieved by the addition of 0.4% tin. 0.05-0.2% tin addition exhibited greater tensile strength and hardness compared to ductile cast iron not containing boron and tin. In this research, we investigated the tin rich cementite layer on the surface of the graphite nodule, assumed to serve as the barrier to carbon diffusion to the graphite, which is thought to promote pearlite formation during eutectoid transformation.