Effects of heat treatment and build orientation on the evolution of ϵ and α′ martensite and strength during compressive loading of additively manufactured 304L stainless steel
Abstract
The effect of heat-treatment and build orientation on martensitic phase transformation in additively manufactured (AM) 304L stainless steel is studied and compared with conventionally produced wrought material. The relationships between observed martensitic transformations and material microstructures and their effects on mechanical strength are established through experimental observations. In situ high-energy X-ray powder diffraction measurements were performed to monitor the evolution of ϵ and α′ martensite during compressive loading of stainless steel. Electron backscatter diffraction (EBSD) was used to provide insight on initial grain morphology, crystallographic misorientation within grains, and crystallographic texture. Heat treatment alters the microstructure of AM samples creating different initial conditions. This difference in starting microstructure resulted in variability in martensitic transformation during compressive deformation. The rate of martensitic transformation decreased for AM samples treated with temperatures up to 1100∘C, after which the AM microstructures recrystallized, resulting in increased rate of martensitic transformation for those samples treated at higher temperatures. It was also observed that aligning the axis of compression with the AM build direction resulted in a lower rate of strain-induced martensite formation as opposed to aligning the compression axis perpendicular to it. More favorable distribution of crystal orientations in the latter loading orientation promoted martensitic transformation. These and additional experimental observations from EBSD in terms of kernel average misorientation, mean grain orientation spread, and mean crystallite size reveal strong microstructural effects on strength of additively manufactured metallic materials.
Publication Date
8-1-2020
Publisher
Elsevier
Journal Title
Acta Materialia
Digital Object Identifier (DOI)
Document Type
Article
Recommended Citation
Nicholas C. Ferreri, Reeju Pokharel, Veronica Livescu, Donald W. Brown, Marko Knezevic, Jun-Sang Park, Michael A. Torrez, George T. Gray, Effects of heat treatment and build orientation on the evolution of ϵ and α′ martensite and strength during compressive loading of additively manufactured 304L stainless steel, Acta Materialia, Volume 195, 2020, Pages 59-70, ISSN 1359-6454, https://doi.org/10.1016/j.actamat.2020.04.036.
Rights
© 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.