Metal powders with fine microstructure of high heat-resistant steel for additive manufacturing produced by C-D nozzle

There are numerous manufacturing processes used for metal powders production. Metal powders have been widely utilized in various industry applications, such as additive manufacturing, powders metallurgy, metal injection molding and shot penning etc. Although additive manufacturing has been recognized as having the highest value in metallurgical industry and thus become the key development projects in the world. However, there are rigorous requirements for the metal powders used in additive manufacture, such as the particle size, sphericity, oxygen content etc. In this research, powders of heat-resistant steel was produced by high pressure gas atomization because of the advantages as high sphericity and high fluidity, low oxygen content and fine particle size with narrow distribution. Since the metal powders were produced through the high temperature melting and then fast-curing process, it is expected that the metal powder can achieve the fine microstructure and even possibly amorphous state. In this study, experimental equipment includes four parts, which are melting, atomization, cooling and classification in sequence. In addition, we use Convergent-divergent nozzle with external mixing mechanism in the nozzle design. Result shows that the average particle size of heat-resistant steel is 43pm. It is also found that the powders exhibit spherical shape. The dendritic microstructure of the metal powders are associated with the cooling rate during the processes. The particle size of heat-resistant steel powders which are under 30pm have part of inconspicuous dendrites. The above results are observed in the surface morphology and crystallization patterns. The hardness of heat-rssistant steel powders are enhanced compared with raw materials. We speculate it happened because of the fine microstructure achieved by the gas atomization process. Sum up this study that fine metal powders produced by C-D nozzle can be used to produce the fine metal powders for additive manufacturing applications.