Interaction of Boron with Copper and Its Influence on Matrix of Spheroidal Graphite Cast Iron

Abstract

High strength steel, which often contains a few tens of ppm B, has been used in the automobile industry due to weight reduction for energy savings. If this steel scrap is recycled for producing high strength spheroidal graphite iron castings, the alloying element, B, changes the matrix from pearlite to ferrite. In this research, the influence of B on the matrix of the high strength spheroidal graphite iron castings and the means of counteracting its bad effects were investigated.
The result of the study on the ferritization effect of B on the matrix showed that the ferrite volume fraction increased with the addition of B. Meanwhile, the smoothness of the spheroidal graphite surface was damaged.
In order to investigate the counteracting measures to the ferritization effect of B, N or Ti was added to the parent alloy to form BN or TiB₂. It was found that the addition of N or Ti reduced the ferrite volume fraction slightly, and the effect of Ti was more obvious.
Some tests were carried out to discuss the interaction of Cu with B. The existence of a thin Cu film on the spheroidal graphite surface was observed in the B-free Cu-added sample; nevertheless, it could not be confirmed in the B-added sample. When Cu was replaced by Mn, there was no difference in the ferrite fraction with the B addition. Therefore, it could be confirmed that the ferritization effect of B exists only in the presence of Cu in spheroidal graphite cast iron.