Effect of Amount of Chunky Graphite on Mechanical Properties of Spheroidal-Graphite Cast Iron

摘要

Chunky graphite is generated in heavy-section castings, and it is detrimental to the mechanical properties, especially the ductility and toughness, of cast iron. However, there have been few quantitative reviews that show the mechanical properties as functions of the amount of generated chunky graphite. In this study, a cylindrical casting containing chunky graphite was prepared. Pig iron and steel scraps with Fe-Si and rare-earth-Si compounds were used. We extracted some specimens from the casting and measured their mechanical properties through tensile-strength tests and Brinell hardness tests. The amount of chunky graphite in the specimens was determined by analyzing their electron microscope images to determine the ratio between the area of chunky graphite and the total area of all graphite. The specimen with a chunky-graphite content of 0% exhibited a tensile strength of 506 MPa and elongation of 25%. When the chunky-graphite content increased above 20%, the tensile strength of the specimens gradually decreased and finally reached similar to 50 MPa, which is lower than that of the specimen containing no chunky graphite. The elongation decreased quickly among the specimens containing 20% to 40% of chunky graphite, and it eventually reached about 1/5 of that of the specimen containing no chunky graphite. On the other hand, the yield strength and hardness of the specimens were not affected by the chunky-graphite content.