Microstructures and mechanical properties of 3D-printed steels

Abstract

The recent advances in reliably fabricating metallic parts using additive manufacturing (AM) are yet to meet the rapidly evolving requirements of manufacturing industry, with established alloys to be examined and new compositions to be explored. Therefore, expanding the materials library of AM process is of increasing significance. Maraging steel is one of the most commonly used alloy systems, due to its combination of superior strength and toughness. However, except for one specific 18Ni(300) grade, other various types of maraging steels fabricated by AM process are not sufficiently studied. Herein, this research is aimed to study the optimization of printing parameters, microstructures, and mechanical properties of 13Ni(400) maraging steel, using laser beam powder bed fusion (L-PBF) technique. Effect of heat treatment (HT) on the microstructures, hardness, and tensile behaviour, compared to as-printed (AP) condition, is also studied. The main findings are as follows: 1) A wide processing window of energy density was found to enable crack-free fabrication, where change of pore morphology, i.e., lack of fusion and keyhole mode, is found to be related with varying energy densities. 2) Martensitic matrix is achieved in AP sample, which is induced by the intrinsic rapid cooling of L-PBF process. Meso-structures (melt pool and cellular structure) are found in both AP and HT samples. 3) Significant enhancement of mechanical behaviour is seen after HT, which can be attributed to the formation of nanoscale precipitates. These findings contribute to a thorough understanding and future application of 13Ni(400) maraging steel.