Physical and Process Properties of Fine Gas-Atomized R6M5K5 Powders Produced in Different Conditions

Abstract

Fine gas-atomized powders of R6M5K5 tool steel were studied. The spherical powders were produced with two distinct melting procedures, each involving spraying under different modes: at a conventional pressure of 0.6 MPa used to make powders of this steel and a calculated pressure of 2 MPa. To obtain a fine-sized fraction, the powders were sieved through a wire mesh with 50 μm square openings, and the content of this fraction was calculated for each of the two powders. The powders with particle sizes greater than 50 μm were subsequently ground and additionally sieved through a 50 μm mesh. Four types of powders with particle sizes below 50 μm were produced using this method. They varied in particle size distribution and particle shape. Mechanical tests were performed with the powders of this size fraction. The equivalent particle diameter distribution, morphology, and changes in elemental composition of the powders were studied. Distribution characteristics, including d₁₀, d₅₀, and d₉₀, were calculated. The arithmetic mean of flat particle projections was slightly higher for the powder atomized employing the conventional mode (0.6 MPa), measuring 0.914 compared to 0.901 for the powder particles atomized under the calculated mode. The yield of the <50 μm fraction was lower (6 and 55 wt.%, respectively). After grinding, the roundness of both powders decreased, resulting in more complex shapes. The relative bulk density, relative tapped density, and flowability of the powders decreased as the roundness factor reduced. An attempt to classify the tool steel powders using the Hausner ratio and Carr index, commonly applied to pharmaceuticals and some metal powders to evaluate their flowability, indicated that the potential application of this classification required further verification. The flowability of the studied powders correlated well with the magnitude of the repose angle.