Effect of Nb Addition on Tensile and Wear Properties of 18Ni300 Mold Steel Fabricated by LPBF

Abstract:

Laser powder bed fusion (LPBF) is highly suitable for forming 18Ni300 mold steel, thanks to its excellent capability in manufacturing complex shapes and outstanding capacity for regulating microstructures. It is widely used in fields such as injection molding, die casting, and stamping dies. Adding reinforcing particles into steel is an effective means to improve its performance. Nb/18Ni300 composites were fabricated by LPBF using two kinds of Nb powders with different particle sizes, and their microstructures and properties were studied. The results show that the unmelted Nb particles are uniformly distributed in the 18Ni300 matrix and the grains are refined, which is particularly pronounced with fine Nb particles. In addition, element diffusion occurs between the particles and the matrix. The main phases of the base alloy are α-Fe and a small amount of γ-Fe. With the addition of Nb, part of the α-Fe is transformed into γ-Fe, and unmelted Nb phases appear. The addition of Nb also enhances the hardness and wear resistance of the composites but slightly reduces their tensile properties. After aging treatment, the molten pools and grain boundaries become blurred, grains are further refined, and the interfaces around the particles are thinned. The aging treatment also promotes the formation of reverted austenite. The hardness, ultimate tensile strength, and volumetric wear rate of the base alloy reach 51.9 HRC, 1704 MPa, and 17.8×10^-6 mm³/(N·m), respectively. In contrast, the sample added with fine Nb particles has the highest hardness (56.1 HRC), ultimate tensile strength (1892 MPa) and yield strength (1842 MPa), and the volume wear rate of the sample added with coarse Nb particles is reduced by 90% to 1.7×10^-6 mm³/(N·m).