| In this dissertation, two kinds of typical materials valve seat V513 and V571 were prepared by powder metallurgy method. SEM, EDS and X-ray diffraction were used to investigate the pore distribution, microstructure and phase structure of valve seat. The effect of different process on density, hardness and crushing strength of valve seat were discussed. This dissertation also studied the corrosion resistance of two kinds of valve seat in the way of electrochemical experiments and high temperature sulfidation experiments. The results showed that the best process of V513 valve seat is 1120℃ sintering,1150℃ infiltration sintering for V571, the best heat treatment process is 850℃ quenching and 600℃ tempering. The density of valve seat is closely related to the number, size and shape of pores, increasing the sintering temperature and melting copper can increase the density of the valve seat, a combination of both can significantly reduce the number and size of pores, and spherical pores, significantly reduce the porosity of valve seat, improve density. The microstructure of sintered state mainly pearlite, the good wettability of copper can promote the diffusion of elements after infiltration, the fine particles are uniformly distribute on the matrix, After tempering, the tempered sorbite structure with good comprehensive properties is appeared. The results of corrosion experiments showed that, the corrosion resistance of the same valve seat in different solution follows the order below:HNO3>HaSO4> HC1, the corrosion resistance of the same valve seat in different states follows the order below:infiltration>tempered>sintered. Phase analysis and the distribution of elements from sulfide film shows that, the main phase of film sulfide on sintered materials is iron-sulfide, and with iron and copper sulfides after infiltration or tempering, it has more copper-sulfides after tempering. In general, the mechanical and corrosion resistance properties of V571 are better than those of the V513. |
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