Fig. 4: The 3D morphologies of the corrosion pits with maximum depth of welded joint.

a The 3D morphology of the corrosion pits with maximum depth on BM surface in acidic soil solution without riboflavin; b the 3D morphology of the corrosion pits with maximum depth on HAZ surface in acidic soil solution without riboflavin; c the 3D morphology of the corrosion pits with maximum depth on WZ surface in acidic soil solution without riboflavin; a′ the 3D morphology of the corrosion pits with maximum depth on BM surface in acidic soil solution with 10 ppm riboflavin; b′ the 3D morphology of the corrosion pits with maximum depth on HAZ surface in acidic soil solution with 10 ppm riboflavin; c′ the 3D morphology of the corrosion pits with maximum depth on WZ surface in acidic soil solution with 10 ppm riboflavin.