Treatment of ferrous melts for the improvement of the sphericity of water atomized powders

This study investigated the effect of a magnesium treatment of ferrous melts before water atomization on powder properties such as their shapes, flows, and apparent and tap densities. Three different ferrous alloys were studied, a high carbon steel alloyed with silicon, a hypereutectic cast iron, and a 304 stainless steel. All the powders that were treated with Mg were more spherical and contained fewer and smaller internal pores. All the Mg-treated powders had better flow and larger apparent and tap densities. The improved sphericity of the Mg-treated particles is caused by a larger solidification time and a smaller spheroidization time of the droplets. The larger solidification time is the result of the creation of a continuously renewed insulating Mg gas layer during solidification of the droplets. The smaller spheroidization time is a result of a larger surface tension of the melt from the reaction of Mg with dissolved sulfur. The decreased amount and size of internal porosities is also caused by the larger surface tension of the melt. This new technology is highly cost-effective and can benefit to the development of the additive manufacturing market. (C) 2017 Elsevier Ltd. All rights reserved.