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Investigation of the Relationship Between Microstructure and Mechanical Properties in Wire and Arc Additive Manufacturing of Low-Carbon Steel

Ghamsaripour Kashani, Zahra | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58363 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pouranvari, Majid
  7. Abstract:
  8. In this thesis, the microstructure and mechanical properties of a wall made of low-carbon steel produced by the wire and arc additive manufacturing (WAAM) method have been investigated. For additive manufacturing, ER70S-6 welding wire was used as the feedstock material, and the CMT process was employed as the heat source. A constant interlayer temperature of 100 °C was used during the wall fabrication. The results showed that the microstructure of the fabricated wall, except for the top layer which consists of columnar grains, is composed of equiaxed ferrite grains along with a small amount of pearlite. The average ferrite grain size and the pearlite fraction in different parts of the wall (except for the top layer) are nearly constant, being approximately 10 micrometers and 8 percent, respectively. The development of fine-grained ferritic microstructure in the wall produced by the wire and arc additive manufacturing method—which is comparable to or even finer than the ferrite size in hot-rolled products—is attributed to the thermal effects of successive layers on the previously deposited layers, repeated austenitization, and the formation of fine ferrite grains during cooling. This relatively homogeneous microstructure resulted in the production of a wall with an average hardness of 150 Vickers and negligible anisotropy in tensile strength (489 MPa) and elongation (34%) in both the build direction and the deposition direction. The Charpy impact energy of samples with notches oriented in the build direction was approximately 24% lower than that of samples with notches oriented in the deposition direction. A heat treatment consisting of re-austenitization followed by water quenching resulted in a reduction of ferrite content and an increase in the bainite phase in the microstructure, leading to an approximately 50% increase in wall hardness, a 23–34% increase in tensile strength depending on the measurement direction, and an approximately 30% decrease in elongation
  9. Keywords:
  10. Wire and Arc Additive Manufacturing ; Microstructure ; Mechanical Properties ; Anisotropy ; Low Carbon Steel

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