The Microstructure And Properties Of High-silicon Molybdenum Ductile Iron And High-nickel Ductile Iron Exhaust Pipe

The exhaust manifold connected with flange and engine, which is the highest temperature of the exhaust system components. So requires exhaust manifold with the good molding, high-temperature oxidation, high-temperature fatigue and corrosion resistance properties. High silicon molybdenum ductile iron (referred to as the high-silicon molybdenum ductile iron) and high-nickel austenitic ductile iron (referred to as the high-nickel ductile iron) are kinds of heat-resistant cast iron which to meet these needs with very good oxidation resistance, thermal fatigue and corrosion resistance.High-silicon- molybdenum ductile iron will not meet the above requirements and cost-appropriate, the productions of high-performance exhaust manifold are widely used. Because of higher volume Si can guarantee hypoeutectic graphite components and to prevent floating, so C required volume is less than C required volume of ferritic Ductile Iron, the higher Si content can ensure that the ductile iron at temperature 649℃with excellent oxidation resistance, while Si can also form a protective membrane in order to reduce the grain boundary oxidation; Mo will not only increase the yield strength of ductile iron, but also enhance its resistance to creep strength.Ductile Ni-resist cast iron is one kind of alloyed austenitic cast irons containing Nickel element that ranged from 13 percent to 38 percent in weight, which fine texture is consisted of matrix austenite with little spheroidal graphite and small amount of carbide within it. Because of the matrix austenite, this kind of material takes on some perfect performance especially in resistance to elevated temperature and corrosion resistance;Meanwhile, this material has been studied and used in thermal parts in foreign industry such as Automobile engine exhaust pipe.However, we have hardly carried out any research about cast iron with high nickel element in weight. Thereby, we set out to research Casting process, microstructure and properties for Ni-resist cast iron, in order that we can exploit and manufacture ductile Ni-resist castings and can save some cost as well.Based on the fine textured Ni-resist cast iron, we should take two relevant problems into account:Firstly, Nickel is one kind of precious metal, which is of important element guaranteeing the matrix austenite. This means when we come to determine the component content, not only should we consider Nickel's influence to metallurgical structure and properties of ductile Ni-resist cast iron, we should also care about the costs from the precious metal.Secondly, what's the other important aspect we should care about is the shape of graphite. This decides we should select suitable nodularizer, inoculant and adding method during liquid iron treating process. The high melted temperature and much more alloy elements in ductile Ni-resist cast iron take great influence to spheroidizing and inoculating process.According to our research and experimental analysis, we have drawn some important conclusions as following:The content of various components in ductile Ni-resist cast iron (project related) has great effect on the shape of especially C, Si and Ni. For example, when Ni content in weight is not less than 13 percent, matrix textile can meet the demand as austenite. As a whole, when we take the two aspects into account, we have got a reasonable content range about the three elements.Reasonable pouring temperature of ductile Ni-resist cast iron should be1450℃or so and a proper supreheat temperature at1600℃or so is necessary typically .Too high or too low will be easy to lead to casting defects.During nodularizing treatment process, Ni-Mg alloyed nodularizer can acquire better effect than traditional Mg alloyed nodularizer, which spheroidal graphite with perfect roundness can be acquired. Moreover, fading of nodularizing will take place at 6 minutes later after tap of liquid iron (under the condition of lab).After nodularizing treatment process, We use highly efficient inoculant and breeding of high-dose inoculant testing. At large doses of breeding, the promotion of graphite, point-like graphite and crystalline graphite sticks completely disappeared, spheroidizing rate at 3-4 grade level can be achieved to meet the requirements of the matrix ball.In this paper, two heat-resistant cast iron of the German brand (GGGNiSiCr35 5 2 and GGGSiMo 5 1)for the organization and performance studies. Study shows that: the microstructure of high-silicon molybdenum ductile iron is ferrite and a small amount of pearlite, above the distribution of a large number of spherical graphite and can be seen a certain number of white organizations exist at the grain boundary, to judge from its initial form for the grain boundary carbides. The microstructure of high nickel ductile iron is a small amount of carbides on the austenite matrix spherical distribution of graphite. In addition, high nickel ductile iron has better thermal fatigue properties and high temperature oxidation.ProCAST using finite element software to predict the existence of macro-casting cavity, intuitive reflect the temperature field, temperature gradient, liquid metal flow behavior, hot section parts, such as shrinkage cavity of filling and solidification. Prediction results are coincide with actual casting results. ProCAST almost as a result of simulation analysis of the production process of any casting problems that may arise in research for the casting foundry process engineers a new way to give them the opportunity to see the type cavity what happened in order to generate a new design. ProCAST software simulation of casting process, in order to predict casting defects, producing high-quality castings to provide a powerful tool in optimizing the design of casting process has wider significance.With the continuous improvement of the performance of internal combustion engines, the heat load and mechanical load of their parts are also increasing, the engine exhaust manifold are the major pieces of heating, hot work load, and high thermal stress, working environment is extremely poor. Because of the quality of a larger complex structure of poor casting process, quality is not easy to grasp, this chapter in order to objects to simulation exhaust manifold, useing of secondary development ProCAST software for simulation and analysis its casting process, which identified best casting process. By numerical simulation, the process improvements to optimize the casting process, which greatly reduces the preparation process cycle, reducing trial costs.