Laser Powder Bed Fusion printability of cobalt-free steel powders for manufacturing injection molds

Abstract

Laser Powder Bed Fusion (LPBF) printing is used for manufacturing conformal cooling injection molds with internal cooling channels. Currently, the steel used to manufacture such molds by LPBF is the maraging 18Ni300. However, this steel is softer at high temperatures and less resistant to corrosion than the reference steel, the AISI H11. Moreover, 18Ni300 contains cobalt, an element that can be harmful to the health of people handling powders made of this steel. In order to find a cobalt-free alternative to 18Ni300, the printability of three different types of steel is studied: maraging stainless steels (CX, L40), martensitic non-stainless steels (42CD4, H11, H13, PM2012) and martensitic stainless steels (X15TN, PM420). The printability of those eight steels is studied through their mechanical properties (Rockwell hardness, Charpy impact test), their internal defects and surface roughness (X-ray tomography), the presence of cracks (optical microscope), and also through their microstructure (X-ray diffraction) in the as-built state. The results show that the stainless steels (PM420, X15TN, L40 and CX) exhibit interesting as-built properties allowing them to be considered as a possible alternative to the maraging steel 18Ni300 to produce LPBFed injection molds. A conformal cooling injection mold was then printed as a demonstrator.