Process Properties of Gas-Atomized and Ground Fine High-Speed Steel Powder Mixtures

The influence of ground R6M5K5 tool steel powder in mixture with gas-atomized powder on the process properties of the powder mixtures was studied. Both powders were sifted through a 50 mu m sieve. The ground powder was present in amounts of 0, 10, 20, 30, 40, 50, and 100%. The bulk density, tapped density, flowability, and repose angle of the powder mixtures were determined. Additionally, the Carr index, Hausner ratio, and flow rate were calculated. The bulk density exhibited minimal changes because of a high content of near-spherical particles in the ground powder. The flowability of the mixtures decreased with increasing content of the ground powder (flow time for the standard weighed sample increased). Grinding the powder resulted in reduction of its flowability by nearly 35%. The flowability of the gas-atomized powder was 22.49 sec/50 g. When the mixtures contained 50% ground powder, the flowability became 25.72 sec/50 g, representing a decrease of 14%. The linear fitting of the dependencies relating the bulk density (BD), flowability (tau), and flow rate (V) to the ground powder content (weight percent) in mixture with the gas-atomized powder (X) provided the following results with a high coefficient of determination (R2): BD = 4.52 - 0.0043X (R2 = 0.98), tau = 23.48 + 0.07X (R2 = 0.95), and V = 36.32 - 0.012X (R2 = = 0.97). The linear dependence of the relative bulk density (expressed in percentage) on the ground powder content demonstrated that the effect from the amount of ground powder could be assessed using the slope angle of the dependence on the abscissa axis. The slope angle of the dependence is less than 1 deg, indicating a very weak effect of the ground powder content on the relative bulk density of the powder mixtures.