Design And Study Of Valve Seat Insert Which Used For Automobile Engine Of Lead Free Gasoline

The working circumstance of valve seat in automobile engine is very terrible. It's working temperature is as high as about 300～700℃, and it is corroded by exhaust gas at the same time. In addition, the lead free gasoline is being used in the engine, so vavle seat insert (VSI) must be made by scpecial materials. In this paper, the VSI is produced by Powder Metallurgy. Various alloy elements added, porosity and microstructure of materials is considered to affact the VSI's property; matching between the working and none-working layer of VSI is discussed; and the cost reduction of two-layer VSI is analysed as well. Through proper controlling of process, the two-layer VSI which is good at wearing and matching is produced.The experimental results show that the hardness of VSI is the highest when the ingredient of premixed powder is Fe-2Mo-1Co-2Ni-7Cu-1.5C. The crushing strength is 572.0MPa, and the density is 6.65g/cm3. The results of experiment manifest that the VSI made from premixed powder meet the requirement of ChangAn Company.In the specimen of low carbon, ferrite with low hardness and a little pearlite is found; and the specimen of high carbon is made up of pearlite and various alloyed-carbide. The author analyses how alloy and microstructure affect the property of VSI. Macthing between working layer and none-working layer and the ecomomic advantage of two-layer VSI are also discussed at the same time.In order to improve the property of VSI, the prealloyed powder is adopted instead of the premixed powder. Because of some good-wearing elements added, the hardness of material comes up to 98.7 HRB, and the corresponding density is 6.95g/cm3. Some alloyed-carbides are founded by X-ray. After wearing experiment, the amount of wearing is 0.055mm. It is better than premixed powder. All above demonstrate that Co and Cr are good for improving the wear-reliability of VSI.Finally, experiment is carried out on automobile. Unusual phenomenon does not take place. The reliablility of the expierment fits the bill. Now, it has been produced in large quantity and cost reduction is gained.