Abstract
Selective laser melting (SLM) processed stainless steel usually exhibits an inhomogeneous microstructure in the as-built condition. The effect of powder chemical composition on the microstructural evolution of SLM processed 17-4 PH in the as-built condition was studied. A path to achieve a fully martensitic 17-4 PH component in the as-built condition by fine-tuning the alloy composition without any post-built heat treatments was demonstrated. The as-built 17-4 PH phase transformation from δ ferrite to austenite (γ) and subsequently to martensite (α’) was governed by the concentrations of ferrite and austenite stabilizing elements as represented by a chromium to nickel equivalent (Creq/Nieq) value. Electron backscatter diffraction (EBSD) analysis revealed that increase in the WRC-1992 equations based Creq/Nieq value to ≥ 2.65 resulted in coarse δ ferrite grains with a <100> preferential crystal orientation along the build direction. Epitaxial growth of semi-circular and columnar δ ferrite grains accompanied by a marginal volume fraction of retained austenite and transformed martensitic phases was observed. Retained austenite and transformed martensitic phases exhibited a fine grain structure preferentially along the coarse ferrite grain boundaries. Decreasing the Creq/Nieq value to 2.36 induced δ ferrite grain refinement with a significant amount of transformed martensite in the as-built condition. EBSD phase composition analysis along with thermodynamic equilibrium modeling implies that a lower Creq/Nieq value promotes martensite formation resulting in a less retained δ ferrite in the as-built condition.
Accepted Version (
Free)
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call