Dynamic compression and torsion behavior of C300 Maraging steels produced via powder bed fusion technique
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Date
2022-03
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University of New Brunswick
Abstract
Maraging steel components are subjected to dynamic compression and torsion loadings in their applications. Their response in these loading directions is the focus of this study. In order to have a thorough overview of the dynamic torsion behavior of maraging steels, the quasi-static and dynamic compression behavior of maraging steel was evaluated first. Gas atomized C300 metal powders containing two different Ti contents (0.72 and 1.17 wt.%) were used to additively manufacture maraging steel samples via laser powder bed fusion (LPBF). A comprehensive study was conducted to investigate the effects of chemical composition, heat treatment, and building direction on the quasi-static mechanical and dynamic compression and torsion behavior of 18Ni-300 maraging steel parts produced using LPBF. Initially, the effect of Ti on the quasi-static and dynamic responses of additively manufactured maraging steel parts was investigated. A Split Hopkinson pressure bar apparatus (SHPB) was utilized for high strain rate compression tests. In the as-built condition, the results showed that the Ti-rich samples exhibited higher hardness and tensile strength. After heat-treating at 490 °C for 6 h, the Ti-rich maraging steels showed higher strength and ductility (2057.74 MPa and 4.05%). As-built and heat-treated maraging steel samples were subjected to dynamic compression tests and results showed that as-built samples were fractured in strain rate of 3500 s -1 , while heat-treated samples began to fragment in strain rate of 1930 s -1 . Texture development during high strain rate tests of asbuilt and heat-treated samples was also investigated and the results showed that crystallographic texture changed significantly in as-built samples. Vertically built samples fractured in strain rate of 1300 s -1 , while for horizontally built samples, failure occurred in strain rate of 2200 s -1 . The reason for different behavior is related to different microstructures, where columnar and equiaxed microstructures were developed in the vertical and horizontal samples, respectively. High strain rate compressive results showed that until strain rate of 5000 s-1 , the fracture did not happen for Ti-rich samples due to higher fraction of austenite phase in Ti-rich samples. As Ti-rich maraging steel showed exceptional behavior on quasi-static and dynamic compressive loadings, the dynamic torsion behavior of these samples was also evaluated. Finally, a Split Hopkinson torsion bar (SHTB) apparatus was utilized for studying the dynamic torsion behavior of the Ti-rich maraging steel sample in which at an angle of twist of 12 degrees, the failure happened. The Chang-Asaro constitutive model was developed for describing the dynamic compressive behavior of as-built and heat-treated samples and an acceptable agreement between the experimental results and modeling practice was observed. In addition, Johnson-cook and Voyiadjis, and Abed models were employed to describe the dynamic behavior of horizontal and vertical heat-treated samples. Furthermore, Kobayashi-Odd and Nemat-Nasser models were employed for describing the torsion behavior of LPBFmaraging steel parts. Fair agreement between the model results and the experimental findings were observed.