Application of Vermicular Cast Iron in Automotive Exhaust Manifold

Vermicular graphite iron is an engineering material which was applied in 1970s. It has been applied in many fields and achieved good economic results.For example, BMW V8 diesel engine block, Daimler Chrysler 8-cylinder engine block, DAF 6-cylinder engine block, etc. are all cast with vermicular cast iron; August Kuepper GmbH, Germany, has become a specialized manufacturer of vermicular cast iron.It is mainly used for exhaust pipes and supercharger housing of Audi, Benz, Volkswagen, BMW, Score and other automotive companies; Ford, USA, in cooperation with Sinter, carried out production of V6 vermicular cast iron cylinder in Brazil in 1999; Daros, Sweden, Liftrace Ring Plant, has also successively developed vertible graphite cast iron piston rings.

At the same time, the application raises a climax of further research. Due to the application of computer control technology, the peristalsis rate can reach more than 80%. Its mechanical properties are generally between grey cast iron and nodular cast iron, and it has good casting and heat conduction properties similar to that of grey cast iron.

Exhaust manifold material of EQ140 type automobile in our automobile manufacturer was HT15-33. After 60 hours of use, cracking will occur. After changing to vermicular graphite iron, cracking will be solved.Since 1984, all truck exhaust manifolds and some transmission cases manufactured by FAW have been formally cast with vermicular cast iron.

According to the report of Shandong University of Technology, the volume fraction of ferrite in Vermicular Cast Iron with silicon content of 3%-5% should be above 95% and the working temperature can reach 700-850 C. The short-term tensile strength at high temperature under this working temperature is close to that of medium silicon nodular cast iron, but the elongation is much lower than that of ductile cast iron.The high temperature strength is improved slightly with the increase of the peristalsis rate, but the elongation increases linearly at high temperature.It is also believed that for the exhaust manifold, more spherical graphite can be found in Vermicular Graphite Cast iron, even if the nodularity is as high as 50%, which will not affect the product quality, but will contribute to the enhancement of strength, and a series of related studies are underway.