Change in Iron Powder Properties with Treatment in Rolls

Abstract

621.762Conditioned iron powders are prepared by carbothermal reduction of "Blue Dust" (India) ore concentrate followed by compaction treatment in rolling mill and a decarburizing anneal. The properties of powder prepared by grinding in a vibration and rolling mill are determined. The method makes it possible to control the bulk density of the powder from 1.75 to 2.75 g/cm 3 . Determination of the production properties of the powders obtained and powder NC.100.24 by the same procedure established satisfactory conformity of the results. The technological desirability of preparing conditioned iron powder by treatment in a rolling mill is demonstrated.Powder raw material, prepared by carbothermal reduction of the Indian superconcentrate "Blue Dust," is an agglomerate of fine elongated particles and it exhibits high ductility properties (Fig. 1a). This powder before are after refining in a hydrogen-containing atmosphere (in future, annealing) has a low bulk density (1.0-1.4 g/cm 3 ) that makes it difficult to compact structural articles from it. In order to increase bulk density a special production operation is necessary, i.e. deformation of agglomerate powder particles by prior compaction. It has been demonstrated by the authors of [1] that there is an upper limit of prior compaction for the raw powder above which its compaction does not make sense since after annealing there is a sharp reduction in bulk density, and this does not justify the energy expenditure for compaction before annealing. Relatively simple realization of this operation, i.e. rolling raw powder in a mill with metal balls, does not give a satisfactory result due to the fact that this method requires prolonged treatment (up to 8-16 h) and it leads to chemical contamination by grinding ball material and also to a marked increase in oxygen content. For example, according to our data treatment of a batch of raw powder (original oxygen content 2.5 mass%, bulk density 1.23 g/cm 3 ) in a drum with metal balls for 12 h leads to an increase in bulk density up to 2.42 g/cm 3 and an oxygen content up to 6.3 mass%. An increase is also noted in the proportion of the fraction less than 44 µm, from 18.42 to 47.81%. These factors have a negative effect on further conversion (in particular, it is necessary to increase annealing temperature and duration). A large amount of fine particles leads to agglomeration during annealing, as a result of which the bulk density of the finished powder decreases again to 1.65-1.85 g/cm 3 .An alternative operation aimed at increasing bulk density is processing powder particles in rolling mill followed by comminution [2][3][4]. An advantage includes the fact that rolling occurs in a very short time (reduction in contamination), and the stressed state promotes a reduction in energy expenditure. Use of this method makes it possible to avoid an increase in oxygen content and development of fine fractions (less than 44 µm).