The Study On The Microstructure And Properties Of Iron-based Power Metallurgy Vavle Guides

In this dissertation, Fe-Cu-C vavle guides and Fe-Cu-C-MoS2 vavle guides were produced by powder metallurgy with sintering temperature of 1120℃ and 1150℃. The carbon content of sintering vavle guides were tested by the automation carbon sulfur analyses. By virtue of OM, SEM, XRD, EDS, and properties tested, the influences of basic process parameters such as carbon content, copper content, size parameters, sintering temperature, heat treatment process on the microstructure and properties, as well as the densification and size changes of vavle guides were investigated respectively. Finally, corrosion of sulfide and electrochemical corrosion were analyzed. The results showed that decarburization of vavle guides were controlled to the permissible range, but decarburization at 1120℃ sintering is lower than 1150℃, the microstructure and properties are better than 1150℃, so 1120℃ is the suitable sintering temperature. The density of sintered vavle guide is lower than the density of green, and the size changes is well.Carbon content decided to microstructure, copper improved density by liquid diffusion, molybdenum disulfide improved density. The main microstructure of Fe-Cu-C vavle guides with sintering are lamellar pearlite and ferrite, the molybdenum disulfide is decomposed during the process of sintering under the protect of ammonia decomposition, the main microstructure of Fe-Cu-C-MoS2 vavle guides with sintering are large irregular pearlite, less lamellar and ferrite. After 840 ℃ oil quenched and 180℃ tempering, the main microstructure of all vavle guides are tempered martensite and residual austenite. The hardness and crushing strength of vavle guides are decreased with the decreased of density in the height direction, and after heat treatment, the hardness and crushing strength are improved greatly, but the influences on machining and performance need to be verified. The porous and massive sulphide film are generated in the surface of vavle guide after corrosion of sulfide, and with some crack defects, the main phase of sulphide film are Fe1-xS and Fe7S8. The corrosion resistance of upper surface and lower surface are better than the middle cross-section of vavle guide.