Effects of sulphur, oxygen and silicon on the graphite precipitation in calcium graphite steel were investigated. Sulphur greatly hindered the precipitation from γ solid solution. According as the amount from 0.03 to 0.18% of sulphur, primary cementite appeared not only in the matrix but also in the grain boundary. With increasing oxygen content above 0.008%, graphitization decreased and also primary cementite crystallized out preferentially from the γ solid solution. When the hypereutectoid steel was melted in vacuum, graphitization did not occur without a suitable addition of silicon. Fundamental conditions on graphite precipitation by the calcium treatment were summarized in the following three points : (1) effect of deoxidization and desulphurization, (2) instabilization of cementite to precipitate from the γ solid solution, and (3) formatian of crystal imperfections such as voids in the solidifying process. Effective acceleration of graphite precipitation due to silicon was also discussed
