PHYSICAL AND PROCESS PROPERTIES OF THIN GAS-ATOMIZED R6M5K5 STEEL POWDERS PRODUCED IN DIFFERENT CONDITIONS

Abstract

Fine gas-atomized powders of the R6M5K5 tool steel were studied. The spherical powders were produced with two melting procedures with spraying in different conditions: at the pressure conventionally used to produced powder of this steel, 0.6 MPa, and calculated pressure, 2 MPa. To obtain a fine size fraction, the powders were sifted through a wire sieve with 50 μm square holes and the content of this fraction was calculated for each of the two powders. The powders with a particle size greater than 50 μm were ground and sifted again through a 50 μm sieve. Four types of <50 μm powders were produced in this way. They differed in particle size distribution and particle shape. Subsequent mechanical tests used the powders of this size fraction. The equivalent particle diameter distribution and the morphology and change in elemental composition of the powders were studied; d10, d50, and d90 and other distribution characteristics were calculated. The calculated arithmetic mean of flat particle projections was slightly higher in the powder atomized according to the conventional mode (0.6 MPa) and was 0.914 compared to 0.901 for the powder particles atomized according to the calculated mode, but yield of the <50 μm fraction was lower (6 and 55 wt.%, respectively). After grinding, the roundness of both powders decreased (the shape became more complicated). The relative bulk density and relative shaking density of the powders and their fluidity decreased with reducing roundness factor. An attempt to classify the tool steel powders using the Hausner ratio and the Carr index applied to pharmaceuticals to evaluate their flowability, as well as to some metal powders, showed that the potential application of this classification required further verification. The fluidity of the studied powders correlated well with the magnitude of the collapse angle.