Abstract: Intermittent marks with varying depths were found on the surface of ER50-6 carbon steel solid welding wires during the surface inspection. Through macroscopic observation, chemical composition analysis, metallographic examination, and scanning electron microscopy and energy spectrum analysis, the defect morphology and microstructure characteristics were analyzed, and the causes of the defects were determined. The results show that the surface defects of the welding wires were pitting corrosion defects caused by improper pickling and rinsing process in the manufacturing process. Finally, some improvement suggestions were proposed in combination with the process conditions.