Mechanical Properties of 18Ni-300 maraging steel manufactured by LPBF

Abstract

The purpose of this document is to investigate the influence of heat treatment on the mechanical properties of parts from MAR 300 (EN 1.2709) produced by LPBF. In order to compare the influence of the heat treatment on the parts properties, some parts were in the state solution annealed and others age hardened tested. For the quality in the LPBF the feedstock powder as starting material is of great importance. Therefore, powder characterization has been performed in order to work out ageing effects after multiple use. As a major ageing effect an increasing oxygen content could be identified which might affect process and parts quality. For industrial acceptance, AM parts need to be produced to the best available tolerances and with well-understood mechanical properties. For this purpose, the mechanical properties of the LPBF samples have been analysed and are compared to those properties for conventional samples. In this investigation, the mechanical tests (hardness test, tensile test and notch impact resistance) have been performed in horizontal and vertical directions of manufacturing by LPBF. The hardness increased from 333~341 HV10 to 640~656 HV10 after heat treatment. Simultaneously, the ultimate tensile strength (Rm) increases from 1056~1096 MPa to 1964~2102 MPa, while the break elongation (εtot) is reduced from 11.3~16.0% to 2.0~4.5%. Aged samples show a significant decrease in toughness in the Notch Impact Test. A specifically designed ball joint test setup has shown that the frame manufactured by LPBF provides comparable results as a conventionally manufactured frame and is robust and suitable for the prototype production and test of car headlamps.