Manipulating the microstructure and mechanical properties of 18Ni-350 maraging steel through optimizing laser powder bed fusion process and post-heat treatment

• Main Author: Yang, Zhenyong
• Other Authors: Upadrasta Ramamurty
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering
• Online Access: https://hdl.handle.net/10356/177858
• Institution: Nanyang Technological University

Additive manufacturing (AM) has revolutionised conventional manufacturing (CM) processes by enabling the production of complex metal parts directly from digital designs. In recent years, there has been a growing interest in fabricating maraging steels via various AM techniques, as their ultrahigh hardness makes it challenging to produce complex shapes via conventional thermal-mechanical processing. However, given the disparate solidification behaviour and cooling rate between AM and CM, the microstructure of AM maraging steel is in distinct contrast to that of the CM ones. Moreover, the flexible fabrication parameters make it possible to manipulate the microstructures and thus mechanical properties. Therefore, it is of great significance to investigate the process-microstructure-property relationship. In this study, 18Ni-350 maraging steel is taken as an example and aimed to explore the optimised processing parameters of laser powder bed fusion (L-PBF) to produce desired microstructure and mechanical properties in both as-printed and heat-treated conditions. The porosity, morphology, martensite and austenite proportions, microhardness, and tensile properties of the material are investigated using various methods. Results have shown that the melt pool shape, phase fractions, and morphologies of cellular structures can be flexibly adjusted by manipulating the fabrication parameters while ensuring high relative density. Moreover, these samples with distinct microstructures react differently to heat treatment, showing varying peak-aging time, strength, and ductility. These findings contribute to a better understanding of fabricating maraging steel using L-PBF and its future applications.