| The low cost powder metallurgy sintering steels are prepared by the powder metallurgy element mix with water atomized iron powder as the raw material powder in this paper, at the same time by adding trace additives to improve the activity of sintering of powder metallurgy Fe-2Ni-1Cu-0.6C low alloy steel, as well as improve the microstructure and mechanical properties of alloy. The influence of additives to the sintering process, microstructure and mechanical properties are studied separately by optical microscopic analysis, SEM analysis and mechanical property tests. The evolutions of the additives in the powder metallurgy ferroalloy are defined, as well as the affect mechanism to the alloy sintering behavior, microstructure and mechanical properties. What’s more, research of the influence rule of the forming and sintering process to the alloy matrix organization and additive’s effect are conducted by changing the process parameters. The main conclusions are as follows:(1) The addition of Cu3P to the alloy leads to three kind of eutectic liquid phase in the sintering process, which can accelerate the material migration and diffusing of element powders. The addition of Cu3P changed the metallographic structure of sintered alloy, with reduced the blocky ferrite formation in the organization, and made the pearlite lamellar spacing homogenization, the composition of sinterd body structure changed from a mixture of blocky ferrite, large clumps sorbite and small amounts of some piece of lamellar pearlite into structure with homogeneous continuous piece of lamellar pearlite, a small amount of blocky ferrite and sorbite, in addition, the microhardness of ferrite and pearlite are significantly improved. Adding minor Cu3P improved the strength and hardness of the material, while the toughness and plasticity are decreased.(2) Alloys with varying amount of Cu3P are prepared by double press-double sintering process (DP/DS). Bending strength and hardness of the alloys increased firstly and then decreased with the increasing of Cu3P amount, due to the effect of Cu3P addition to the double-pressed densities. By changing the pre-sintering temperature can improve the double-pressed density effectively, as well as improve the strength and hardness of the alloy, in addition, the impact toughness reduction of Cu3P added double pressed-double sintered alloys are well controlled.(3) The sintered density and mechanical properties of the alloys are improved by adding minor Fe2O3, due to its significant performance on promoting the element diffusion between powders and the formation of sintering necks. Bending strength and elongation of the alloys increased firstly and then decreased with the increasing of Fe2O3. The addition of Fe2O3reduced the contents of C and O of sintered alloys. Nanoscale Fe2O3powders are homogeneously distributed among the matrix powders after compacting process, new iron powders with small partical size generated by the reduction of nano Fe2O3have a very high activity, therefore, the activation performance on alloy sintering of nano Fe2O3powders is better than micron-size agglomerated powders.(4)Sintering necks between matrix powders are formed through diffusion bonding at low temperatures with the activation of Fe2O3, therefore rapid sintering of alloys are occurred under900℃by adding0.3wt%nano Fe2O3powders. The improvement performance of Fe2O3to the properties of sintering materials increase with the decreasing of sintering temperature, materials with Fe2O3addition sintered at low temperature have a excellent application and machining performance, due to its high strength, as well as its better plastic than ordinary materials sintered at high temperature. |
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