Study On High Compressibility Reduced Iron Powder For Automobile Shock Absorber

Iron based powder metallurgy automobile shock absorber parts are subjected to alternating loads during use,and require very high comprehensive performance,including fatigue strength.The high compressibility iron based powder is the key to ensure the good performance of this kind of parts.The compression properties of reduced iron powder prepared by the existing process in Anhui Ma-steel Powder Metallurgy Co.Ltd.are generally lower than 6.80g/cm3,It is difficult to complete densification sintering of powder metallurgy products,and it is difficult to obtain the structure of powder metallurgy automobile shock absorber with excellent comprehensive property.This article aims at this problem,starting from the first reduction process,the second reduction temperature and atmosphere,and the batch process,the influence of these factors on the compressibility of reduced iron powder and the control key was systematically studied.The research results are applied to the piston of powder metallurgy automobile shock absorber.The main conclusions are as follows:1)A tunnel kiln reduction temperature up to 1160℃,compared to 1120℃and1180℃,sponge iron particles of high compaction,smaller porosity,uniform distribution,chemical purity,and will not be burned.It is beneficial to the two reduction and compression performance improvement.2)Using pure hydrogen instead of ammonia pyrolysis gas as reducing atmosphere,fully decarbonization,fully deoxidation,and can prevent iron nitriding,improve the purity of iron powder,can be obtained reduced iron powder with iron content higher than 99%,thereby improving the compression of iron powder.3)The two reduction temperature of the fine reduction furnace is up to930℃,which improves the annealing and softening effect of iron powder,improves the plasticity of iron powder and improves the compression performance of the products.4)The proportion of ingredients for particles of more than 105μm of about28~32%and less than or equal to 75μm about 50~54%,blending time is 28~30min,can beacquired more than 6.86g/cm3(500MPa pressure)of high quality iron powder.5)The powder metallurgy automobile shock absorber piston with high compressibility reduced iron powder as base powder,adding 0.8% graphite and 1.6%300 mesh copper powder has good comprehensive performance,mainly manifested as:the pressure distribution is stable during forming,the compact density is up to6.57g/cm3,hardness of outside diameter of sinter blank HRB67-73,hardness of outer normal HRB45-50,crushing force 9.77-10.40 kN.Therefore,the scientific and effective control of the production process of reduced iron powder has been verified.