Effects of Manganese and Heat Treatment on Mechanical Properties in Spheroidal Graphite Cast Iron

Abstract It is well known that the mechanical properties of spheroidal graphite cast iron deeply depend on the volume of pearlite matrix microstructures. Therefore, the theoretical criterion of pearlite matrix nucleation is considered important in this graphite cast iron that to obtain the higher mechanical properties of graphite cast iron, the pearlite stabilizing element such as Mn or Cu is very important. The present work aims to study the influence of manganese (Mn) content and heat treatment on the mechanical properties of 3% or 4% (Solution Strengthened Ferritic Ductile Iron-SSFDI) of silicon (Si) containing spheroidal graphite cast irons. The six 3.6%C–3%Si melts with different chemical compositions from 0.2 to 1.7 mass% of Mn content were produced using a high-frequency induction furnace. The melt was poured into a Y-block CO 2 sand mold of 25 or 40 mm in thickness. The microstructure analysis and mechanical testing were performed for as-cast and some heat treatment conditions, such as annealing or air cooling. As a result, the tensile strength had a good relationship with the area fraction of pearlite, over 600 MPa in UTS, and high proof stress for some 3 or 4%Si–Mn series samples in the as-cast condition. By the heat treatment from the unique ( α + γ ) region, the 3% Si sample showed over 800 MPa and over 10% in elongation. And 4%Si–1.5%Mn (SSFDI) series sample showed over 600 MPa in UTS and over 15% in elongation which was prepared by annealing heat treatment to reduce to less than 5% of the area fraction of pearlite. This study suggests that it can be understood of the correlation between optimizing the heat treatment condition and mechanical properties of SSFDI cast irons.