Cause Analysis on Unqualified Performance of S355ML+Z35 Steel Plate in Thickness Direction

Thickness direction (z-direction) performance of S355ML+Z35 plate with PL20 mm×3 000 mm×12 000 mm was not qualified before using. The reasons for the disqualification of z-direction performance of S355ML+Z35 steel plate were analyzed by macro fracture analysis, chemical composition analysis, mechanical properties test, metallographic test and so on. The results show that the disqualification of z-direction performance was due to incorrect welding operation for the specimens. It is suggest that the CO₂ gas shielded arc welding operation should be standardized to reduce the diffusion hydrogen in the weld.