During the development of the cylinder block in the early stage, it was found that there was shrinkage defect at the oil channel position by dissecting the cylinder block, as shown in the figure. After reviewing the production process, it was found that when the content of molten iron w (C) was below 3.80%, the compacted graphite cast iron cylinder block was prone to shrinkage defects.
Considering the complexity of the cylinder block structure, it is difficult to place cold iron to solve the shrinkage problem. In the later stage, the w (C) amount is adjusted from 3.70%~3.80% to 3.80%~3.85%, and the carbon equivalent is controlled at 4.45%~4.55%. At the same time, each ladle of molten iron is flushed into the imported carburizing agent according to the holding time of the medium frequency furnace, and no shrinkage defects are found after dissection.