白銑の黒鉛化におよぼすMgの影響

Abstract

Using Cu-Mg (10%) alloy and pure Mg, the graphitization phenomena of white cast irons treated with Mg were investigated. The results were as follows. (1) The graphitization time of white cast irons is shortened with small amounts of residual Mg, because of the strong effect of Mg on the deoxidation and desulphurization of the molten irons and on the contrary, the graphitization time is prolonged with increasing amounts of residual Mg in white cast irons, because of the retarding effect of Mg on the graphitization. Especially, the graphitization of white cast irons with a large content of S is promoted remarkably when treated with Mg. It is believed this phenomenon is caused by the strong desulphurization of the molten irons. The retarding effect of Mg on the graphitization of white cast irons with a large content of Si is not so clear. (2) With increasing amounts of residual Mg in white cast irons, temper carbons become smaller and roundish or spherulitic in form and are remarkably increased in number. (3) With increasing amounts of residual Mg in white cast irons, areas of pearlite in the matrix of specimens, graphitized completely and furnace-cooled, are increased under microscopic examination. Especially, this tendency was remarkable in the case of white cast irons treated with Cu-Mg alloy as Mg.