Effects of welding residual stresses and phosphorus segregation on cleavage delamination fracture in thick S355 J2 G3+N steel plate

• Cleavage fracture in thick steel plate occurred due to tensile stresses in the “Z” axis.
• Rolled banded ferrite–pearlite microstructure and phosphorus segregations are characteristic.
• Steel plate has a very good contraction in the “Z” axis.
• Steel plate has a very low toughness in the central part.
• After normalizing the toughness of the central part of the plate was highly improved.

Due to residual tensile stresses acting through the material’s thickness a cleavage fracture occurred in the central part of a thick steel plate during the cooling of a welded T-joint. Steel in the normalized rolled state, without non-metallic inclusions and with a very good contraction in the “Z” axis, is brittle because of its banded, ferrite–pearlite microstructure, which is dependent on phosphorus segregation. A normalizing heat treatment greatly improved the toughness of the central part of the thick plate and prevented its cracking during the cooling of the welded T-joint.