Development of a novel powder inspired by the chemistry of S7 tool steel for laser powder bed fusion additive manufacturing

Abstract

Laser powder bed fusion (PBF-LB) requires powders with high and uniform flowability, high packing density and good spreadability. For these reasons, gas or plasma atomization are preferred production processes for PBF-LB feedstocks as they ensure obtaining spherical particles that result in powders having good rheological properties. Nevertheless, the utilization of water atomization to produce ferrous alloys for PBF-LB could be quite interesting given its much higher production rate and significantly lower production costs. This work focuses on the development of metal powders for additive manufacturing with laser powder bed fusion inspired by the chemical composition of S7 tool steel. The results show that optimization of the chemistry combined with the use of a thermo-mechanical spheroidization treatment (TMST) can significantly improve the rheological properties and reduce the final oxygen content of water-atomized powders to a point where they show rheological characteristics that are similar to those measured for gas atomized powders. In addition, mechanical properties measured for specimens produced by PBF-LB (tensile strength, ductility and impact toughness) were equal and even superior to those measured for wrought S7 tool steel. This work provides solid evidence that water-atomized powders can be used in PBF-LB additive manufacturing provided that the chemical composition is optimized to better match the specificities of additive manufacturing processes, particularly in terms of rheological properties.