Environmental Behavior of Low Carbon Steel Produced by a Wire Arc Additive Manufacturing Process

Abstract

: Current additive manufacturing (AM) processes are mainly focused on powder bed technologies, such as electron beam melting (EBM) and selective laser melting (SLM). However, the main disadvantages of such techniques are related to the high cost of metal powder, the degree of energy consumption, and the sizes of the components, that are limited by the size of the printing cell. The aim of the present study was to evaluate the environmental behavior of low carbon steel (ER70S-6) produced by a relatively inexpensive AM process using wire feed arc welding. The mechanical properties were examined by tension testing and hardness measurements, while microstructure was assessed by scanning electron microscopy and X-ray diffraction analysis. General corrosion performance was evaluated by salt spray testing, immersion testing, potentiodynamic polarization analysis, and electrochemical impedance spectroscopy. Stress corrosion performance was characterized in terms of slow strain rate testing (SSRT). All corrosion tests were carried out in 3.5% NaCl solution at room temperature. The results indicated that the general corrosion resistance of wire arc additive manufacturing (WAAM) samples were quite similar to those of the counterpart ST-37 steel and the stress corrosion resistance of both alloys was adequate. Altogether, it was clearly evident that the WAAM process did not encounter any deterioration in corrosion performance compared to its conventional wrought alloy counterpart.

The Effect of Microstructural Imperfections on Corrosion Fatigue of Additively Manufactured ER70S-6 Alloy Produced by Wire Arc Deposition

“…This shows that the electrochemical tendencies of the two alloys were quite similar, although the stabilization (passivation phase) of the additively manufactured ER70S-6 alloy was obtained at a slightly higher potential. This result complies with the results of the immersion test and salt spray testing in the same corrosive environment as obtained by a previous study of the authors [23]. The mechanical properties of an additively manufactured ER70S-6 alloy and its counterpart ST-37 alloy were measured in terms of tensile strength (475.7 ± 2.3 and 611.2 ± 12.9 MPa, respectively), elongation (34.6% ± 3.6% and 12.6% ± 0.2%, respectively) and hardness (192.4 ± 6 and 259.1 ± 15 HV, respectively) [23].…”

“…This shows that the electrochemical tendencies of the two alloys were quite similar, although the stabilization (passivation phase) of the additively manufactured ER70S-6 alloy was obtained at a slightly higher potential. This result complies with the results of the immersion test and salt spray testing in the same corrosive environment as obtained by a previous study of the authors [23]. The cyclic potentiodynamic polarization analysis results for additively manufactured ER70S-6 alloy and its counterpart ST-37 alloy are shown in Figure 4.…”

“…The microstructure of the ER70S-6 alloy in the XZ plane, as produced by the WAAM process, is shown in Figure 1. This reveals a typical microstructure of low carbon steel with a ferrite matrix and a relatively reduced amount of a secondary pearlite phase, as expected from the limited amount of carbon (0.072% C) and the rapid solidification conditions of the WAAM process [23]. In addition, clear inherent microstructural imperfections were present, as can be discerned in terms of porosity (0.15% by image analysis), impurities (0.08% by image analysis) and lack of fusion (0.04% by image analysis).…”

“…The microstructure of the counterpart ST-37 alloy is shown in Figure 2, indicating that this alloy has a very similar microstructure with a relatively increased amount of secondary pearlite phase due to the higher content of carbon (0.15% C) present in this alloy. The mechanical properties of an additively manufactured ER70S-6 alloy and its counterpart ST-37 alloy were measured in terms of tensile strength (475.7 ± 2.3 and 611.2 ± 12.9 MPa, respectively), elongation (34.6% ± 3.6% and 12.6% ± 0.2%, respectively) and hardness (192.4 ± 6 and 259.1 ± 15 HV, respectively) [23]. The relatively lower mechanical strength and increased ductility of the additively manufactured ER70S-6 alloy are mainly related to the increased content of carbon and subsequently increased amount of pearlite phase in the counterpart ST-37 alloy.…”

“…It should be pointed out that the ER70S-6 alloy is usually used for conventional welding of ST-37 steels [22] that have very similar chemical compositions and mechanical properties. Hence, the present study considers ST-37 steel as a counterpart alloy for reference [23].…”