Fatigue Behavior and Fractographic Analysis of Low-Carbon Steel Fabricated by CMT-Based Wire Arc Additive Manufacturing

Wire arc additive manufacturing (WAAM) using the cold metal transfer (CMT) process offers significant advantages for producing large and complex metal components. However, the thermal cycles inherent to layer-by-layer deposition induce variations in microstructure and mechanical properties, which critically affect fatigue behavior and fracture mechanisms. This study evaluates the fatigue resistance and fracture characteristics of ER70S-6 steel deposited by CMT-WAAM. Fatigue tests were performed on seven specimens extracted in the horizontal orientation relative to the deposition direction, under a load ratio of R = 0.1 and a frequency of 20 Hz. The results indicate a fatigue limit of approximately 302 MPa (≈ 0.53 Su), consistent with typical behavior of low-alloy steels. The reuse of a previously tested specimen resulted in a significant reduction in fatigue life, confirming the detrimental effect of prior fatigue damage. Fractographic analysis via SEM revealed crack initiation at defects, followed by propagation characterized by striations and final fracture dominated by ductile dimples. At the highest stress level (0.67 Su), a less distinct fracture pattern and increased ductile features were observed, indicating accelerated crack propagation. The results highlight the dominant role of defects, stress level, and loading history in controlling fatigue performance, providing relevant insights for improving the reliability of WAAM components under cyclic loading.