Anisotropy of the tensile properties in austenitic stainless steel obtained by wire-feed electron beam additive growth

Abstract

Institute of Strength Physics and Materials Science SB RAS, 2 / 4 Akademichesky Av., Tomsk, 634055, Russia Currently, new approaches to the production of metal structures of different sizes are actively developing. These approaches are based on the technologies of additive manufacturing or 3D printing methods, which assume consistent layer-by-layer growth (printing) of parts of structures with a shape and size that are as close as possible to the desired parameters. During these processes, each subsequent layer is formed by fusing the material to preceding layers. Thus, the methods of additive growth are based on heating a part of the material to the melting temperature. Therefore, in the process of printing, the billets experience multiple heating and cooling cycles. As a result, different parts of the billets have different thermal histories and could possess different mechanical properties. In this paper, the anisotropy of the tensile mechanical properties of the billet of austenitic Fe-18Cr-9Ni-0.08C steel produced by wire-feed electron-beam printing was investigated. It was experimentally shown that, after additive growth, the samples of austenitic steel, which were cut from different parts of the steel billet and differently oriented with respect to the growth direction possessed significant anisotropy of mechanical properties under uniaxial tension: yield strength varies in the range from 250 to 310 MPa, and elongation to failure ranges from 48 to 65 %. According to microstructural analysis, this behavior is associated with heterogeneity of the elemental composition, macroscopic heterogeneity of the dendritic structure of ferrite in austenite (layering), heterogeneity of the phase composition and residual stresses in the steel billet obtained by the additive wire-feed growth.

Structure of a 3D frame-bridge NiTi sample deposited on a low carbon steel substrate by wire arc additive manufacturing

“…The production of complex shaped alloy components by additive manufacturing (AM) technologies becomes more intensive [1][2][3]. This allows one to fabricate samples which can not be obtained by traditional methods or makes such production simpler.…”

Temperature-Dependent Deformation Behavior of “γ-austenite/δ-ferrite” Composite Obtained through Electron Beam Additive Manufacturing with Austenitic Stainless-Steel Wire

“…At the expense of the high heat input, depletion of a melting pool with nickel occurs during the EBAM process, and, independently from the processing parameters, EBAM-fabricated parts always contain the residual δ-ferrite. Therefore, the main reason for δ-ferrite formation is the EBAM-assisted variation of a Cr/Ni equivalent of steel and, consequently, the change in solidification mode [7][8][9][10]. Additionally, columnar coarse austenitic grains usually grow during the additive manufacturing and provide the high anisotropy of the mechanical properties in the as-built material [8][9][10].…”

“…Therefore, the main reason for δ-ferrite formation is the EBAM-assisted variation of a Cr/Ni equivalent of steel and, consequently, the change in solidification mode [7][8][9][10]. Additionally, columnar coarse austenitic grains usually grow during the additive manufacturing and provide the high anisotropy of the mechanical properties in the as-built material [8][9][10]. An anisotropic two-phase (γ-austenite + δ-ferrite) microstructure is formed due to the nonequilibrium solidification and crystallization conditions during layer-by-layer deposition of the material and complex thermal history of the resulting bulk product [8][9][10][11][12].…”

“…Additionally, columnar coarse austenitic grains usually grow during the additive manufacturing and provide the high anisotropy of the mechanical properties in the as-built material [8][9][10]. An anisotropic two-phase (γ-austenite + δ-ferrite) microstructure is formed due to the nonequilibrium solidification and crystallization conditions during layer-by-layer deposition of the material and complex thermal history of the resulting bulk product [8][9][10][11][12]. Post-production heat treatment of the additively fabricated stainless steel partially eliminates these effects, i.e, reduces the fraction of δ-ferrite but does not completely dissolve it and retains grain size unaffected [8,9,11].…”

“…An anisotropic two-phase (γ-austenite + δ-ferrite) microstructure is formed due to the nonequilibrium solidification and crystallization conditions during layer-by-layer deposition of the material and complex thermal history of the resulting bulk product [8][9][10][11][12]. Post-production heat treatment of the additively fabricated stainless steel partially eliminates these effects, i.e, reduces the fraction of δ-ferrite but does not completely dissolve it and retains grain size unaffected [8,9,11]. In fact, EBAM-fabricated bulk products made from stainless steels type AISI304 or AISI321 possess dual-phase composite structures because the content of δ-ferrite in them could be as high as 20% [8][9][10].…”