Pressing behavior of atomized iron powders

Conclusions The porous structure of the particles of an atomized iron powder depends on the chemical composition and sieve analysis of the starting powder and also, to a smaller extent, on its own sieve analysis, as determined by the conditions of milling of the sponge produced by annealing. In our study of various powder batches the best combination of degree of particle sponginess and agglomeration and hence pressing characteristics was found to be ensured by the use of a cast iron starting powder containing about 50% of a fine fraction, < 0.063 mm, with a comparatively low oxygen content (6.5%). With the atomized powders, the transition from the first stage of pressing to the second took place more gradually and at a higher pressing pressure (600 MPa) than with the reduced powder (450 MPa). It is shown that the compressibility of an iron powder is the better the greater the contribution from the first stage and hence the smaller the role of the volume plastic deformation of the particles in the attainment of a given density. The best compressibility with a low degree of contanimation with carbon and oxygen can be attained at minimum values of specific surface, degree of sponginess , and degree of agglomeration and also a maximum apparent density resulting from the use of powders of equiaxed particle shape close to spherical. The steady increase in compressibility with increasing apparent and tap densities that is characteristic of reduced iron powders is not always observed with powders pro-duced by atomization and annealing.Translated from Poroshkovaya Metallurgiya, No. 2(218), pp. 23–29, February, 1981.     

Effect of structure of a magnetoabrasive material on its life in the polishing of metals

Conclusions The mechanism by which the particles of a magnetoabrasive powder disintegrate depends on their structure and determines the service performance of the material. The disintegra tion of the particles of the sintered Zh15KT material involves the plucking out of the abrasive component and its removal from the machining space. Under these conditions, the fall in the fraction of the abrasive component in the polishing powder and the resultant decrease of the mechanical wedging forces lower the pressure which the Zh15KT particles exert on the work surface and have an adverse effect on the operating performance of the powder as a whole. The particles of a cast material cease to be effective mainly through attrition. As their nonporous matrices possess high hardness and strength and contact be tween the magnetic matrices and the abrasive over their interfaces is continuous, the service life of a cast powder is much (more than twice) longer than that of the sintered Zh15KT powder agglomerates, in which, because of their high porosity, contact on the interfaces between the iron and titanium carbide particles is discontinuous.Translated from Poroshkovaya Metallurgiya, No. 3(231), pp. 98–101, March, 1982.