Preparation of White Heart Malleable Cast Iron in Na2O-SiO2 Oxide Molten Salt

The preparation process of white heart malleable cast iron in Na2O-SiO2 oxide molten salts was studied. We investigated the effect of the molten salt composition on the decarburization of white cast iron. A specimen of white cast iron ((phi) 8 mm× 8 mm) containing 3.34 mass% carbon was immersed in a Na2O-SiO2 molten salt at 1323 K for 24-72 h. After the heat treatment of white cast iron in Na2O-SiO2 (64-36 mol%) at 1323 K for 48 h, low-carbon surface layer had a thickness of about 100 (mu)m and contained 0.53 mass% carbon. This surface layer was formed as a result of the reaction of carbon in white cast iron with free oxygen in the oxide molten salt. However, no decarburized layer was observed on the specimen surface after the heat treatment in the Na2O-SiO2 (38-62 mol%) molten salt. As the Na2O composition increased within the limit of 41 < Na2O (mol%) <=qq 65, the thickness of the decarburized layer also increased. It was found that white heart malleable cast iron could be prepared from white cast iron in Na2O-SiO2 oxide molten salts, and the degree of decarburization depended on the composition of the molten salts.