Post-build thermomechanical processing of wire arc additively manufactured stainless steel for improved mechanical properties and reduction of crystallographic texture

Journal Article · Tue Feb 01 00:00:00 EST 2022 · Additive Manufacturing

DOI:https://doi.org/10.1016/j.addma.2021.102573· OSTI ID:1837606

Elmer, John W.; Fisher, Karl; Gibbs, Gordon; Sengthay, John; Urabe, Dave

Wire-arc additive manufacturing (WAAM) was used to fabricate 304 L stainless steel plates for the purpose of characterizing texture and anisotropic behavior in the as-built parts, followed by post-build rolling and heattreating to modify mechanical properties and reduce texture. The plates were made using a robotic controlled gas metal arc (GMA) welding system designed for high deposition rates and were characterized using uniaxial tensile testing, macro- and micro-hardness, and optical microscopy. In addition, resonant ultrasound spectroscopy (RUS) was used for the first time of WAAM plates to measure the anisotropic elastic modulus, shear modulus and Poisson’s ratio. Post processing consisted of mechanical rolling the walls to 25% and 40% strains followed by heat treating at 650 °C, 850 °C and 1050 °C. Results show that anisotropy of mechanical and physical properties is present in the starting microstructure and persists in the rolled plates prior to heat treating, with elastic modulus in the build direction of 50% of the polycrystalline wrought value, and shear modulus and Poisson’s ratio of 200% of the polycrystalline value. Anisotropy also persists for all samples stress relieved at 650 °C, and in samples annealed at 1050 °C without any prior rolling strain. Heat treating has shown the reduction in texture and anisotropy only in the rolled plates. Complete elimination of texture and anisotropy was observed for WAAM plates rolled and annealed at 1050⁰C, and for plates rolled to 40% and recrystallized at 850 °C. Recrystallization of the rolled plates at temperatures 850 °C or higher increases yield strength, ultimate strength and elongation to failure relative to the as-built parts, with properties that equal or exceed typical wrought or cast alloys of similar composition. These results demonstrate that WAAM can be used to build custom sized semi-finished parts and blanks that can later be mechanically formed, and heat treated into high quality finished components.

• Research Organization: Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-07NA27344
• OSTI ID: 1837606
• Alternate ID(s): OSTI ID: 1879278
• Report Number(s): LLNL-JRNL-831908; S221486042100720X; 102573; PII: S221486042100720X
• Journal Information: Additive Manufacturing, Journal Name: Additive Manufacturing Vol. 50 Journal Issue: C; ISSN 2214-8604
• Publisher: Elsevier
• Country of Publication: Netherlands
• Language: English

Related Subjects

36 MATERIALS SCIENCE
Wire-based additive manufacturing
304 stainless steel
Mechanical rolling and heat treating
Resonant ultrasound spectroscopy
Anisotropic behavior