Effect of vermicularization rate on internal porosity of castings

Diesel engine is widely used, working environment is poor, working time is long. Because the cylinder head of diesel engine bears the effect of high pressure and high temperature gas for a long time, it is required that the cylinder head can not be deformed and cracked. At the same time, considering the cost, the weight of the cylinder head needs to be controlled, so the material requirements of the cylinder head are higher and higher, especially for the cylinder head of high-power diesel engine with high speed, the gray cast iron material can not meet the use requirements. In this case, our company began to trial produce vermicular graphite cast iron cylinder head, the first selected variety is zc170 cylinder head.

Z C170 cylinder head is widely used in marine high-power engine, generator set, etc. it is not allowed to crack under long-term operation conditions. It is difficult to improve the mechanical properties of gray cast iron after reaching HT300 grade, and gray cast iron has no toughness and is easy to crack, while vermicular cast iron has good ductility, thermal conductivity and fatigue resistance. After several times of trial production, our company was not ideal at first, but after adjustment, we were finally able to mass produce vermicular graphite cast iron cylinder heads to meet the requirements of customers.

1) In the production process, the raw materials must be kept clean, the operation process of each link must be strictly carried out, and the raw liquid iron WS < 0.02%, wre residue = 0.02% ~ 0.04%, WMG residue = 0.005% ~ 0.015% must be controlled. The creep rate needs to reach more than 80% in order to reduce the porosity tendency of castings.

2) Strengthen the inspection, make a test block for each ladle of molten iron, and mark the castings, so that once the batch with poor vermicularization is found, it can be detected smoothly, and the products with poor vermicularization can not leave the factory.

3) If there is no instrument to accurately detect vermicular iron and sulfur in front of the furnace, the raw materials that affect the purity of molten iron such as carburizer and recycled material should be used or not used as much as possible to prevent the final vermicular effect from affecting the casting quality.

After a series of improvement and adjustment, zc170 cylinder head made of vermicular graphite cast iron can be mass produced, which meets the requirements of customers and reduces the production cost.