With the improvement of engine efficiency and environmental protection requirements, it is required to improve the heat and corrosion resistance of components of exhaust system, especially the exhaust manifold. Although the use of stainless steel has been increasing in recent years, in order to reduce engine noise, components of exhaust system have the trend of becoming larger and more complex.At the same time, according to different social needs, various displacements of vehicles show different trends.Therefore, from the point of view of saving raw materials, in order to reduce weight and cost, further efforts should be made to develop new materials and new methods of processing them.
The structure and shape of automobile exhaust manifold are complicated. Casting is the best way to produce qualified products. Therefore, various automobile manufacturers prefer cast iron materials.The subject team, together with FAW Foundry Center, refers to the cast iron material of Volkswagen Germany and develops heat-resistant cast iron suitable for automobile exhaust manifold in China. The main products are high silicon molybdenumand high nickel ductile iron.These two materials are used to simulate the specific working environment of automobile exhaust manifold and to explore new materials to meet the requirements of new automobile exhaust manifold.
1) High silicon molybdenum ductile iron and high nickel ductile iron were designed and melted to study the microstructure and mechanical properties of these alloys and the influence of heat treatment on the mechanical properties of the alloys.
2) Determine the ideal operating temperature of the material according to the DTA results of the eyeball ductile iron and high nickel ductile iron.
3) The oxidation resistance of high silicon molybdenum nodular cast iron and high nickel nodular cast iron is analyzed from thermodynamics, kinetics and the characteristics of oxidation film on the surface of cast alloy.
4) Carry out the basic test of corrosion resistance considering the specific working position characteristics of exhaust manifold on the vehicle and the environmental characteristics in northern China.
5) Explore the growth resistance of high silicon molybdenum ductile iron and high nickel ductile iron by thermal expansion test.
It is hoped that the above specific research will provide reliable theoretical basis and experimental reference for the development of new vehicle exhaust manifold material.
1) Domestic target of component innovation pipe material;
2) Process innovation.In the process of material smelting, a newhas been explored for the product characteristics of automobile exhaust manifold. The spheroidizing effect is good, so that the experimental data are not affected by casting defects, have good repeatability, stable product quality and guarantee the possibility of batch application.
3) Method innovation.The research and test contents are carried out according to the current service environment of automobile exhaust manifold, such as thermal fatigue resistance, oxidation resistance, corrosion resistance, growth resistance, etc. The test results have good reference and practicability.By testing and analysis, it is confirmed that the maximum operating temperatures of the developed high silicon molybdenum ductile iron and high nickel ductile iron are 840 ~C and 950 ~C respectively. The high nickel ductile iron has better oxidation resistance, thermal fatigue resistance, electrochemical corrosion resistance and growth resistance than high silicon molybdenum ductile iron.