A Study of Selective Laser Melting Technology on the Ultra-High Strength Tool Steel Use—Quality, Mechanical Properties and Fatigue

Abstract

During the last few years, laser based powder bed fusion (PBF) processes have received an increasing attention as a section of additive manufacturing technologies with a rapidly growing number of established and potential industrial applications. This paper investigates the effect that key parameters in PBF processes have on critical material properties in high-alloyed steel samples, manufactured under controlled process conditions such as scanning strategy, energy density and orientation of samples in the build chamber. A Concept Laser M2 Cusing Machine, (Concept Laser, Lichtenfels, Germany) was used for the fabrication of samples made from MARLOK® C1650, an independent maraging (precipitation hardening) tool steel. This steel is specially designed to be used in highly demanding applications, including tools for aluminum die casting in long series with high requirements for surface quality in the product and high fatigue resistance in the tooling. Two series of samples were made with different hatch spacing of the laser beam and with different orientation and angles in the build chamber. The samples were prepared according to relevant standards including CNC machining, with exception for a few samples that were kept in as-built condition for comparison. Evaluation of the 3D surface quality of the machined samples and the morphology of the fracture were done with the contact-less Alicona Infinite G4 machine and a Tescan Mira 3GM scanning electron microscope. Fatigue testing was performed with an Instron 8874 Servohydraulic Dynamic Testing machine. The investigations include the influence of process parameters on mechanical properties in the final material, as well as the effect on the parameters measured in cyclic material fatigue tests. A special test for assessment of machinability of the sintered materials with turning in terms of specific cutting force has also been performed. The results confirmed a statistically significant influence of technological variables on the mechanical and fatigue properties. Some porosity found in the material apparently has been the origin of several mechanisms of crack initiation and propagation. However despite this, the results are encouraging since optimized process conditions apparently can produce a material of good quality and high fatigue resistance.