Experimental Investigation On The Material Of Medium Silicon And Molybdenum Ductile Iron Exhaust Pipe

As a key component of engine, the exhaust pipe is a typical complex casting with thin wall. During the engine operation, the exhaust pipe suffers from circulate shock of high temperature and high gas Pressure. Thereofre, the exhaust pipe must have a high quality, in particular its high temperature properties. At present, the exhaust pipe is made of gray casting iron, vermicular graphite cast iron, ductile iron, high-nickel cast iron materials generally. With the improving of the people's awareness of environmental protection laws and regulations , gray casting iron and vermicular graphite cast iron can not meet the engine's emission performance requirements , and ductile iron is less suitable for the application of the exhaust pipe because of the deformation. Therefore, silicon and molybdenum ductile iron has a high temperature in the comprehensive performance and appropriate price of molybdenum silicon iron is gradually substituted for other materials of exhaust pipe.The paper is to complete the development of the material of the silicon molybdenum ductile iron exhaust pipe. According to the technical requirements of the Jiangling's foundry, the experiement adopted Tundish-cover pour-over nodulizing process, selected a good nodularizer and inoculant from the A,B,C types, and adoped the suitable chemical composition, adjusted the addition of inoculant and the Mo Content and other parameters of the trial. In order to obtain low-carbon, low-pearlite, seeking for the best possible preparation process parameters to produce stable high performance as-cast silicon molybdenum ductile iron.According to the results, the trial-produce was successful with A nodularizer and inoculant. Through small batch production verification test, we have a qualified production in the silicon molybdenum ductile iron exhaust pipe to put into mass production. Through the study of the toptic, we have been as follows:(1) The adaptability of A nodularizer and inoculant in production is great, after its spheroidizing and inoculation treatment, the performance of the ductile iron is the best, and the spheroidization rate also stabilizes above 85%.(2) With the inoculant content increased to 1.8% and the means of inoculation process, the evenly distributed, small spherical graphite organization of the ductile iron can be abtained, and the mass fraction of pealiear and carbide reduce significantly.(3) The cooling ratio of the castings greatly impact on the microstructure of the casting, especially the pealiear content and the carbide content. Rapid cooling can effectively reduce the carbon content.(4) A batch trial-produce of Si-Mo ductile iron exhaust pipe has been successful. We have obtained the optimum comprehensive properies: the spheroidization rate is about 90%, the pearlite content is about 5%, the carbide content is about 5%, the tensile strength is 630MPa, the yield strength is 514 MPa, the elongation is 15%, the hardness is 236HB.