Preparation of Nanocrystalline High Nitrogen Stainless Steel Spherical Powders by High Energy Ball Milling

To meet the requirement of traditionally powder metallurgical compression molding and sintering, the nanocrystalline high-nitrogen stainless steel spherical powders were produced by high energy ball milling technology. The crystallite sizes, lattice strains, microstructures and morphologies of milled powders, as well as nitrogen contents, had been also investigated. The results show that with the prolonged milling time, a transition from α ferrite to γ austenite has gradually occurred within the powder compact. With the increased milling time, the crystallite sizes of powders decrease continuously, the lattice strains of powders increase gradually, the nitrogen contents of powders increase significantly, and the degrees of spheroidizing and alloying of powders improve constantly. After milled for 60h, the nanocrystalline high-nitrogen stainless steel spherical powders with a particle size range of 5~10 μm, fine degree of sphericity and uniform components can be obtained, whose crystallite size is about 5.0 nm and lattice strain is about 1.0%. These nanocrystalline spherical powders are quite beneficial to subsequent powder metallurgical compression molding and sintering or powder injection molding process due to their good flowability, formability and sintering activity.