抄録
A study has been perfomed to make clear the factors which govern the microstructure of gray cast iron of different contents of manganese and sulfur. The cast iron used was prepared from pig iron of high purity, metallic manganese and silicon, and pyrite. The experimental results were: 1) In the absence of manganese sulfide, the eutectic temperature of gray iron lowered with increasing the manganese content, while it was not the case when sulfur was present. 2) The increase in manganese conetnt had few influences upon the size of eutectic cells, while it had influence upon the size of graphite flakes. That is, the size of graphite flakes became finer with increasing manganese conetnt, though it became reversely coarser if manganese content was lower than a certain level. 3) The eutectic cells became finer when the sulfur content was increased. The graphite flakes became once coarser and then finer with increasing the sulfur in a way similar to the case when the manganese content was increased. 4) The excessive content of manganese is given by Mn%-1.71S%. The increase in the excessive manganese content resulted in reducing the content of combined carbon and lowering the eutectic temperature. That is, the content of combined carbon gradually decreased as the excessive manganese content was increased up to 0.2%, while it was not the case of low sulfur cast iron. This may be due to the fact that castings in shell mold were less subject to restrain during cooling. 5) To prevent castings fron hot tearing it is necessary to maintain the chemical composition of molten iron, the performances of sand mixture, the conditions of molding and so on, with minimum variation.
