Abstract
This paper reports a study into the process of re-compaction of powder briquettes in the conditions of static pressing at a pressure of 800 MPa. The technological parameters of the pressing process have been analyzed, which make it possible to improve the compaction of powder briquettes based on iron. Such parameters are the outer greasing, which reduces friction between a green compact and the walls of the press tool matrix, and the firing, which removes the deformation strengthening of the green compacts and increases their plasticity.
 The green compacts’ sealing mechanism involved in the final squeezing process has been established, which is associated with the grinding of pre-compressed particles due to the strain in the contact areas. The increase in the stressed state of green compacts following the final squeezing was confirmed by the results of studying the residual micro-strains.
 The change in the stressed state of iron green compacts has been confirmed by the study into the structurally sensitive characteristics, which include the materials’ magnetic and electrical properties. Determining the magnetic characteristics has shown that final squeezing leads to an increase in coercive force, which can be explained by both the increase in the stressed state and the grinding of grains. Investigating the impact exerted by the annealing environment on the value of magnetic characteristics has demonstrated that annealing in hydrogen is more effective in terms of improving magnetic properties than annealing in a vacuum. This is due to the refining of grain boundaries through the processes of reduction of oxide films.
 The study of the mechanical characteristics of green compact materials based on iron powder has established that final squeezing leads to an increase in the hardness and strength of materials depending on the conditions of deformation. A significant improvement in the green compacts’ strength (820‒824 MPa) is due to both a decrease in porosity by 8‒10 % and an increase in the contact area as a result of plastic deformation after the annealing
Highlights
Among the challenges of our time is the long-projec ted resource and energy crisis, which requires an adequate organizational and technological response to counteract it
The latter may include the final squeezing of the resulting powder briquettes; despite the long-standing popularity and seeming triviality of this manufacturing technique, it is not investigated in detail and little used in the practice of powder metallurgy
The following tasks have been set: – to investigate the stressed state of green compacts depending on the conditions of static final squeezing; – to conduct a metallographic study into the structure of iron green compacts depending on the conditions of static final squeezing; – to investigate the magnetic, electrical, and mechanical properties of iron green compacts depending on the conditions of final squeezing
Summary
Among the challenges of our time is the long-projec ted resource and energy crisis, which requires an adequate organizational and technological response to counteract it. It should include strict restrictions on the wide use of expensive and scarce alloying elements and the production of parts with low functional properties. As regards the powder iron metallurgy, this is an improvement in the functional properties of baked products, which is achieved mainly by improving the technology of their manufacture. The creation of conditions under which the non-baked green compacts would demonstrate low porosity and, small shrinkage when baking, is necessary for the development of energy-saving technologies for the manufacture of articles by a powder metallurgy method, which renders relevance to our work
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