Effect of Mn Content on Fatigue Limit of Various Flake Graphite Cast Irons

抄録

In recent years, with the active use of Mn-containing high-tensile strength steels as an automotive body material, it has become increasingly difficult to recycle Mn-containing high tensile strength steel scrap as raw material to produce cast iron, due to the fact that Mn is known as an element promoting the chilling tendency of cast iron melt. Therefore, in this study, the effect of Mn on the fatigue limit of flake graphite cast iron was investigated for the purpose of increasing the strength of cast iron and recycling high tensile strength steel. Flake graphite cast irons with different Mn contents (0.5 mass% and 2.0 mass%, the carbon equivalent corresponding to FC200, FC300 and FC400 of JIS specification (G 5501)) were prepared for plane bending fatigue test.

For melting, pig iron and electrolytic iron were used as iron sources, Fe–Si, Fe–Mn, and Fe–S were used as component adjusting materials, and Ca–Si was used as an inoculant. The melting temperature was 1803 K, the inoculation temperature was 1753 K, and the mold was poured at 1723 K.

Due to the addition of Mn, the Mn/S ratio increases, resulting in the crystallization of A-Type graphite in high-manganese flake graphite cast iron. With the increase of Mn content, the graphite fraction decreases, the lamellar layer becomes denser and homogeneous, the matrix structure is strengthened, and the tensile strength and fatigue limit of high-manganese flake graphite cast iron are improved. Therefore, it was suggested that high-manganese flake graphite cast iron can be used for thin-walled parts as a cast iron with excellent fatigue strength. In addition, in this thin-walled flake graphite cast iron, Mn acts as a matrix structure strengthening element rather than a chilling promoting element.

 

This Paper was Originally Published in Japanese in J. JFS 94 (2022) 601–605.