Research On Warm Compaction Of Ferrous Powders With New Binders

P/M iron based structural parts are used widely in machinery, automobile, appliances, electric tools, as well as other military and industry field because of its outstanding technology and economical advantages. Warm compaction technology is a novel method with low cost to fabricate ferrous powders metallurgical materials with high density and good properties. Research on the basic theory and application of warm compaction has great academic and practical significance to explore its potential and promote the development of the technology. So, the forming behaviors of ferrous powders with different binder was systematically studied and properties of sintered were measured in dissertation.The choosing of the binders is one of the key technologies of warm compaction. In dissertation, polyethylene glycol (PEG), polystyrene (PS) and a small content of additives were employed as the binders, and zinc stearate was used as lubricant. Then 0.2 ~ 0.8wt% of the binders, 0.2wt% of the lubricant, 0.6wt% of graphite powders and ferrous powders were mixed together by a wet mixing method which were then use for warm compaction.In the research on forming behaviors of ferrous powders, the flow rate and apparent density of ferrous powders for warm compaction were measured, effect of binder content, warm compacting temperature and compacting pressure on green density, and effect of compacting pressure on green strength, residual elasticity and ejection force were also studied. The results show that the best values of the flow rate and apparent density of ferrous powders were obtained with 0.4wt% binder content. The flow rate and apparent density of pure iron powders were respective 26.9s·50g-1 and 3.18g/cm3 when PEG content was 0.4wt%. The process parameters are different because that PEG and PS have the different glass transition temperature. Under a compacting pressure of 600MPa, the best properties are obtained when ferrous powders are compacted at 75℃with 0.4wt%PEG and compacted at 135℃with 0.4wt% PS. The green density, strength, residual elasticity and ejection force of pure iron powders under optimized process parameters of PEG are respective 7.29g/cm3,28.1MPa,1.9KN and 0.27%. Under the same condition, the green density of warm compacts were about 0.2g/cm3 higher than that of cold ones, and the green strengths of warm compacts were about 3.7MPa higher than that of cold ones. In addition, the results show that the residual elasticity and ejection force of warm compacts were less than that of cold ones. Relationship between compacting pressure and green density are studied, and find it can be described byБаЛЬЩИНand Huang Peiyun equation.In order to further study the effect of warm compaction on ferrous powders, the effects of sintering temperature and compacting pressure on the physical, mechanical property and dimension change of sintered in the protection of hydrogen atmosphere were studied especially, and microstructure of the sintered samples was also observation. With the increasing of the sintering temperature, compressive strength, hardness, density and shrinkage of sintered iron based material all increase. The sintering density, hardness, compressive strength and shrinkage of molybdenum alloy sample, 7.28g/cm3, 67HRB , 455MPa, 0.52% respectively sintering 1200℃for 1.5h with PEG as the binder. The sintering density, hardness, compressive strength and shrinkage of warm compacts sintered were higher than that of cold ones, but they had the same law of changes. Finally, warm compaction technology can enhanced the sintered properties.