| Powder metallurgy (P/M) parts, which have many excellent and unique properties, such as net shape, economization on material and energy, cost-effective, unpolluted and good integrated properties, have been employed in the manufacture of all kinds of machine accessories. Sintering ferrous P/M products are the most widely used P/M materials. Nowadays, property requirement to sintering ferrous parts becomes much higher than ever before. It is very important and emergent to develop high performance ferrous P/M parts.In the experiments, densification, microstructure and properties of carbusintering ferrous materials have been studied using Fe-2Ni,Fe-2Ni-xCu,Fe-2Ni-xCr alloys as examples. Due to the porosity of P/M materials, the performance of P/M steel is lower than that of dense steel. Improving densification is a crucial method to enhance mechanical properties of P/M materials and also the precondition of alloyage and heat treatment toughening. In this thesis, the influences of three main factors i.e. sintering temperature, green density and additive alloy elements on sintered density are studied. Meanwhile, the microstructures are also analyzed and the influences of factors affecting sintered density on microstructure are examined, too. Based on experiments and discussion, the conclusion can be drawn that, the best condition to get a higher sintered density in carbusintering is a temperature of 1120℃and a green density of 6.8g/cm~3. Sequentially, alloy strengthening and heat treatment are employed to improve the performance of P/M materials. The influences of alloy elements amount on hardness and intensity of P/M materials are studied in carbusintering. Then the performance testing is processed after quenching and tempering, the influence of heat treatment conditions on materials performance are also involved.The microstructures and properties of the carbusintering materials are also studied in detail using SEM with EDS, XRD, MTS810 electromechanical testing machine and MM-200 wear testing machine. Conclusions are listed as follow:1. When carbusintering sintering temperature increases from 1050℃, 1120℃to 1150℃, densification parameter of the specimens are 14.5%,18.2% and 18.6%, respectively, which demonstrates that the increase of densification parameter is only 0.4% when the temperature beyond 1120℃. When the green density increases from 6.0g/cm~3 to 7.0g/cm~3, the max densification parameter is 13% when the green density beyond 6.6g/cm~3.2. The Fe-2Ni-xCu alloys'densification parameter goes down and then up with the increase of content of copper. The max densification parameter of general sintering and carbusintering both at 20.0%Cu, they are -6.04% and -0.65%; The Fe-2Ni-xCr alloys'max densification parameter at 0.5%Cr, both general sintering and carbusintering, they are 14% and 18%.3. As the sintering temperature goes up from 1050℃to 1180℃, the microstructure changes from pearlite to pearlite plus cementite network. It shows that a higher temperature is favorable to the diffusion of carbon atoms. As the green density increases form 6.6g/cm~3 to 7.0g/cm~3 the microstructure changes from continuous cementite network to discrete cementite network.4. For Fe-2Ni-xCu alloys, its maximum tensile strength is 471MPa which is reached at the composition of 5.0% Cu and its maximum hardness is 85 HRB which is reached at the composition of 8.0% Cu. For Fe-2Ni-xCr alloys, both the maximum tensile strength, 350MPa, and hardness, 74.8 HRB, appear at the composition of 2.5%Cr.5. The heat treatment study on Fe-2Ni-1.5Cu-1Cr alloy reveals that the hardness displays a graduate distribution from surface to centre. The maximum hardness, 60.5 HRC, is reached at 740℃, while 870℃induce the most uniform hardness distribution which is mainly in the range of 36 to 44 HRC and the hardenability reaches its best at this temperature, too. Specimens tempered at 150℃exhibit highest hardness and smaller hardness deviation in different depth. The comparing experiments on Fe-2Ni-1.5Cu-1Cr alloys between general sintering and carbusintering show that fracture stress is significantly intensified by carbusintering compared with general sintering. Furthermore, the strength can be further improved by post heat treatment.
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