Bonding integrity of hybrid 18Ni300-17-4 PH steel using the laser powder bed fusion process for the fabrication of plastic injection mould inserts

Abstract

Laser powder bed fusion (LPBF) is a metal additive manufacturing (AM) process for fabricating high-performance functional parts and tools in various metallic alloys, such as titanium, aluminium and tool steels. One specific AM application is fabricating conformal cooling channels (CCC) in plastic injection moulding tool inserts to improve cooling efficiency. This article reports the development of a novel hybrid powder-wrought alloy steel combination intended for injection mould inserts use. In this investigation, cylindrical parts made of 18Ni300 steel powder and wrought 17-4 PH steel were additively fabricated using a hybrid-build LPBF AM technique, followed by various post-build heat treatments. Standard mechanical and microstructural techniques were employed to examine the bonded powder-substrate interface. Microstructure analysis revealed defect-free, fully dense, homogenous powder-substrate fusion across a 280-µm-thick region. Tensile tests confirmed strong powder-substrate bonding due to solid solution strengthening within the region. All tensile fractures were ductile under all heat treatment conditions and occurred about 8 mm from the interface, at the side where the materials were of lower strength. The hybrid-built parts exhibited an ultimate tensile strength of 1009–1329 MPa, with 16.1–17.4% elongation at fracture. Hardness values on the AM-deposited and substrate sides were 31–55 HRC and 32–43 HRC, respectively. A direct post-build 490 °C/1 h age-hardening treatment achieved the best combination of hardness, tensile strength and ductility. The overall result demonstrates that hybrid-built powder 18Ni300-wrought 17-4 PH steel can be a material choice for manufacturing durable and high-performance injection mould inserts for high-volume production.