Hydrogen environment embrittlement (HEE) of additive manufactured (AM) 316L steel

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Additively manufactured (AM) steel with its superior combination of high strength and ductility offers the potential of weight reduction and near net-shaped production of construction parts. In hydrogen-containing environments, 316L steel is among the most widely used structural materials due to its inherent resistance against hydrogen environmental embrittlement (HEE). While the number of publications on basic structural and mechanical properties of AM316L is rapidly increasing, little is known on its interaction with hydrogen to this day. The mechanical properties of AM316L are related to its unique, defect-rich microstructure with scale-bridging features such as melt-pool boundaries, high-angle grain boundaries, pores and high-density dislocations in sub-grain cellular networks as well as deformation-induced structures such as dislocations and twins or new phases like martensite. Hydrogen is considered to modify the defect self energies, for example by lowering the formation energy of microstructural defects such as dislocations, stacking faults and cracks in materials. This can result in parts’ premature and catastrophic failure. First studies have already demonstrated that AM316L is detrimentally affected by the presence of hydrogen and provides reduced resistance against HEE. This project aims to study the HEE susceptibility of AM316L on different length scales, down to the nano-scale. Main hypothesis is here, that HEE bases on the unique microstructure of the AM material, with specific dominant defect types being mainly responsible for HEE. In this project we intend to elucidate these defect types and to understand the main embrittlement mechanisms in AM316L. By successive defect type reduction, we intend to improve the AM316L HHE susceptibility while maintaining as much as possible the superior mechanical properties of the AM material. Hence, with this project proposal we intend to contribute to the fundamental understanding of HEE of AM316L. This knowledge allows for microstructural improvements of the base material and to design AM316L construction parts exposed to hydrogen