Microstructures and mechanical properties of ER70S-6 steel fabricated by wire arc additive manufacturing

• Main Author: Guo, Yibo
• Other Authors: Zhou Wei
• Format: Thesis-Master by Research
• Language: English
• Published: Nanyang Technological University 2025
• Subjects: Engineering; Wire arc additive manufacturing
• Online Access: https://hdl.handle.net/10356/182493
• Institution: Nanyang Technological University

Wire Arc Additive Manufacturing (WAAM) possesses advantages of high deposition rate and low cost compared with other metal additive manufacturing processes. Due to these benefits, WAAM has vast potential in building large metallic components in industries. Among the large components, one of the frequently used materials is low carbon steel, as it has a good combination of good strength and ductility at a low cost. Therefore, it is important to conduct a systematically study in finding proper processing conditions for building large low carbon steel components and examining the microstructure and mechanical properties of the components produced by WAAM. In this report, effects of several processing conditions on the microstructures and mechanical properties of WAAM-built ER70S-6 steels have been systematically studied, including effect of arc types, effect of travel speeds, effect of post-processing heat treatment. By conducting the research on the comparison of arc types, the results helped to select plasma WAAM for the following studies, as it has a more homogeneous microstructure with large regions of equiaxed ferrite grains, while GMAW and CMT-based WAAM has coarse and fine grain regions across the whole specimens. Further investigations on the effect of travel speed in plasma WAAM of ER70S-6 show that there is a slight difference in microstructure and mechanical properties when the travel speed varied from 3.4 to 4.2 mm/s. For these samples of different travel speeds, the major parts of them have uniform equiaxed ferrite grains, therefore, performed isotropic during tensile tests. Based on the preliminary process parameters study, a pressure vessel was built by plasma WAAM at the optimized conditions and the part was subjected to standard metallurgical tests then. The pressure vessel was found uniform in microstructure, no matter the thickness of the wall. In the vertical direction of the vessel wall, the ultimate tensile strength can reach 506.4 ± 8.0 MPa, the yield strength is 351.5 ± 9.0 MPa, and the elongation is 38.2 ± 2.8 %. This part of study demonstrates the potential of plasma WAAM in building real industry components.