Abstract
The pearlite promoting effects of small additions of Sb are evaluated for compacted/vermicular graphite iron castings with 0.6%Ni and 0.9%Cu at two Si levels. Microstructural results for various section sizes of stepped pattern indicate that the level of Sb needed to ensure a nearly fully pearlitic matrix structure is dependent on the Si contents of the iron and the amount of pearlite is relatively insensitive to the section thickness, i.e., 0.057%Sb for lower Si contents iron and 0.1%Sb for high Si contents are required. By the additions of Sb, it is also observed that the graphite begins to modify from compacted graphite which is short and stubby in shape with a rounded edge, to the degenerated graphite which is slightly thinner with needle-like projections. Therefore, the numerical index, i.e., the mean shape factor of graphite K, decreases from 0.57 to 0.40 for 20 mm sections with Sb content. Also, the ultimate tensile strength and elongation of the irons decrease with the same tendency with the change in K value. The neutralizing effects of additions of Ce are investigated for the iron castings with the pearlitic matrix by addition of Sb. Increasing Ce results in the disappearance of degenerated graphite such as those with needle-like projections and thinner ones with sharp edges and in the increase of the K value. By combination of Sb and Ce, the matrix structures become essentialy fully pearlitic and significantly increases hardness and tensile strength.
