| With the development of morden industry and mechanical manufacturing, the requirement on the performance of PM part increases. Due to their usage as constructral materials, many PM parts are requested to have good wearing and corrosion resistance as well as higher surface hardness, making surface mordification of PM parts a very important field in material science. For the most widely used Fe-based PM parts, how to improve wearing resistance and corrosion resistance of the surface has been a challenging task and attracted a strong interest of many researchers. Due to the shortage oerformances of Fe-based PM compacts such as low density, poor wear and corrosion, and easy to make defects, surface chemical heat treatment such as boroning is one of the ways to solve above problems. Boronization can increase the surface hardness and further improve the parts'wearing resistance. However, the shallow boronizing layer and the existence of brittle FeB phase resulted in a low bearing capacity and caused the shedding easily. In this thesis, Charcoal was added to boronizing agents, and with the new process, we completed borocarburizing in one heating process, finally the surface hardened of Fe-pased PM was achieved.We studied the effects of sintering temperature and carburizing agent content on the microstructures of boronizing layer. A formation mechanism of the microstructures of boronizing layer was proposed. The performance of Fe-2Cu-0.2C powder compacts after be borocar burized were tested. The following are the conclusions we derived:1).After the iron and Fe-2Cu-0.2C powder compacts sintered in the process of borocarburizing, the sample surface was determined to be composed mainly by Fe, Fe2B and Fe3C phase. With the increase of carbon content in the agent, Fe2B phase decreased while Fe3C phase increased. 2).Under the experimental conditions, the carbon could played a role in urging diffuision, and then the eutectic microstructure was appearance in the layer when the carbon content in the agent was less than 30wt.%; when the carbon content in the agent was 40wt.%, the diffusion layer did not formed eutectics.3).After borocarburizing of iron powder compacts, the thickness of borocarburizing layer decreased with the increase of carbon content in the agent. With the increase of the sintered temperature, eutectic microstructure appeared and the role of carburizing in the layer became more obvious. When the temperature of sintering-borocarburizing was 1120oC, the microsturctures of boronizing layer were changed by the carburizing, and the eutectic phase Fe2B was achieved. With the carbon content in the agent increased, the mount of eutectic phase Fe2B in the layer comparatively reduced and in the number of pearlite the forefront of layer increased.4).In the process of borocarburizing of the Fe-2Cu-0.2C powder compacts at 1120oC, the Fe2B eutectic microstructure can be deirved when the carbon content in the agent was less than 30wt.%. After the borocarburized samples were quenched, the eutectic phase did not change, while the pearlite transformed into the martensite in the matrix and the diffusion layer. Moreover Fe2B off net and crack have not appeared after quenching.5).Research on the performance of Fe-2Cu-0.2C powder compacts after being borocarburized, we obtained: The micro-hardness of boronizing layer can reach 480-680HV0.3. Compared with samples without borocarburizing, the wear resistance improved and corrosion rate decreased 19 times. The erosion corrosion test results also showed that the borocarburized surface of the sample was better than un-borocarburized surface. Reaearch on the properties of three-point bending, we found: the flexural strength of direct borocarburizing sintered sample increased compared to the sintered sample (31.5-48.8%) when the carbon content in the agents decreasesed. The bending strength of the quenched samples has been significantly improved, the sample displayed a highest flexural strength of 1265MPa, when the carbon content of 30wt.%.
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