Development of high strength cast iron cylinder block assuring high machinability

摘要

To improve the product competitiveness (functional improvement) of cast iron cylinder blocks, it is necessary to increase the material strength. Increasing the strength of the casting before machining is essential for this purpose, but will, withthe existing technology, worsen the machinability and lower the productivity. In order to establish a new technology which satisfies both the material strength and machinability, we have analyzed both the materials and machining. The results, indicatethat the material strength can be increased by graphite grain refinement and that the machinability can be improved by the mechanism consisting of (1) graphite chipping action by graphite grain refinement and (2) lubrication and protection by compositeoxides at the tool surface. We have also succeeded in developing a manufacturing technology for controlling graphite refinement and composite oxides by molten metal treatment in the casting process.