Hot Isostatic Pressing of the Water Atomized Steel Powder: Possibilities and Challenges

Gas atomization provides spherical powder with the high purity and hence these grades are typically used for hot isostatic pressing. Water atomized steel powder is significantly cheaper but has some drawbacks when it comes to the powder purity, irregular powder surface, difficulty to produce high alloyed materials, etc. Recent advancement in the water atomization allows manufacturing of iron and low-alloyed steel powders with the purity, close to gas atomized powder from the surface oxide composition point of view. The presented paper reviews the potential of application of the water atomized steel powders for HIP, advantages and challenges connected to the application of such a material. As the model material, industrial water atomized steel powder, prealloyed with 3 wt.% Cr and 0.5 wt.% Mo, is used in this study. Graphite powder is admixed to the base powder (0.4 wt.%) in order to achieve required steel composition and further HIPed as well. Microstructure and fracture surface of the HIPed material are studied in details. The mechanical properties of the HIPed material are evaluated and results are discussed with regard to the influence of residual surface oxides and microstructure. Results indicate that full density components can be easily obtained in case of water atomized powder with the good mechanical performance. Further efforts to improve powder filling are necessary to get full advantage of the HIPing of water atomized powders.