Effects of Manganese and Heat Treatment on Microstructure and Mechanical Properties of Heavy Section Ductile Cast Iron

Abstract

  In recent years, the amount of manganese (Mn) contained in cast iron is increasing due to changes in raw materials. It is believed that an increased Mn content adversely affects the mechanical properties of cast iron.

  This study aims to investigate the mechanical properties and structural changes of FCD450-10 with different thicknesses, Mn contents, and effects of heat treatment. The study used spheroidal graphite cast iron specimens with Mn concentrations of 0.3%, 0.6%, 0.9%, and 1.5%. The cooling rates to the eutectic temperature of the specimens with varying thicknesses were 1.90K/s, 0.22K/s, 0.12K/s, and 0.08K/s, respectively.

  It was observed that thick specimens (with cooling rates of 0.12K/s or less) had large graphite and grain diameters as well as micro shrinkage cavities that occurred in the final solidification area. In addition, when the Mn content was 0.9% or more, coarse cementite occurred in the last region to solidify (intercellular structure) with the segregation of Mn to the cell boundary. While tensile strength decreased with decreasing cooling rate, it was largely independent of the effects of Mn. Factors affecting the tensile strength are considered to be increased graphite and grain size. Elongation decreased with increasing Mn content and decreased cooling rate, and is likely to be affected by increased graphite and grain size combined with grain boundary cementite.

  Pearlite area ratios decided by the Mn content and cooling rates have an influence on hardness.