Abstract
In this research, steel alloys based on the Fe-Cr-Mo, Fe-Cr-Mn and Fe-Cr-Mo-Mn-Ni systems have been designed, produced by different atomisation techniques, and processed by laser powder bed fusion (L-PBF) to investigate their microstructural and mechanical behaviour. Both gas atomisation and water atomisation were considered for powder preparation. The resulting different flowability of powders, hence a different densification behaviour during processing, could be compensated by tuning the L-PBF parameters and by the application of a post treatment to improve flowability of the water atomised powders. In agreement with thermodynamic calculations, small-size oxide-based nonmetallic inclusions of the type SiO2, MnO-SiO2, Cr2O3-SiO2 were found within the steel matrix and on the fracture surfaces of the water atomised L-PBF alloys, featuring higher amounts of oxygen than the gas-atomised steels. Analyses on microstructure and hardness of the hardenable as-built steels suggested that during laser processing, the multilayer L-PBF structure undergoes an in-situ tempering treatment. Furthermore, the mechanical properties of the L-PBF steels could be widely tuned depending on the post-thermal treatment conditions.
Highlights
Laser powder bed fusion (L-PBF) process belongs to the additive manufacturing (AM) family.It is considered as the main technology for the processing of metallic parts having relatively small size and complex shapes
It can be observed that water atomisation (WA) powders feature an irregular morphology compared to the spherical-shaped gas atomisation (GA) powder
This is due to the high solidification rate induced by the water spray, estimated to be 10 to 100 times higher than that induced by gas atomizing jets, which does not allow a full redistribution of the surface tension field to reproduce the equilibrium spherical geometry [29]
Summary
Laser powder bed fusion (L-PBF) process belongs to the additive manufacturing (AM) family. It is considered as the main technology for the processing of metallic parts having relatively small size and complex shapes. The reference materials for L-PBF include a limited number of steel grades, titanium, aluminium, nickel and cobalt-based alloys [1,2]. These materials are generally selected among the most castable and weldable grades to ease the processing stage. Starting from a hydrogen-reduced sponge iron powder containing 0.02% wt. carbon, Song et al [10] studied the effect of L-PBF processing parameters on the densification behaviour of Metals 2020, 10, 1474; doi:10.3390/met10111474 www.mdpi.com/journal/metals
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