Influence of Boron on the Matrix of Spheroidal Graphite Cast Iron and Its Counteraction Method

摘要

High-strength steel scrap is usually recycled for producing high-strength spheroidal graphite iron castings, while the alloying element, B, changes the matrix from pearlite to ferrite. In this study, the effect of Mn and Cu on the matrix structure was studied by adding electrolytic manganese or pure copper at the 0.5% and 1.0% levels to the base alloy. The results indicated that both Mn and Cu have a pearlite-promoting effect on the matrix of the spheroidal graphite cast iron. In the study of the ferritization effect of B on the matrix, it was found that the ferrite volume fraction increased with the addition of B and the smoothness of the spheroidal graphite surface was damaged in the Cu-alloyed samples, while there was hardly no change in the Mn-alloyed samples. Therefore, it could be confirmed that the ferritization effect of B exists only in the Cu-alloyed iron. In order to investigate the counteraction method to reduce the damaging effect of B on the matrix, N or Ti was added to the parent alloy to form BN or TiB_2. The results indicated that the addition of N or Ti slightly reduced the ferrite volume fraction and the effect of Ti was more obvious than that of N. Finally, the existence of a thin Cu film on the spheroidal graphite surface was observed in the B-free Cu-alloyed sample; nevertheless, it could not be confirmed in the B-added alloy because of the adverse effect of B on the formation of the Cu film.