The iron oxide defects on the surface of Q345B low alloy structural steel plate

The thickness, structure and composition of the oxide scale on the surface of hot rolled Q345B low alloy structural steel plate were measured by optical microscope and scanning electron microscope. The results showed that the main reason for the removal of oxide scale was the formation of iron olivine (2FeO.SiO2 or Fe2SiO4) on the substrate-scale interface. In addition, internal oxides of Mn and Cr were also found near the interface.

The plastic deformation of Q345B low alloy structural steel plate with thickness of 8mm exceeds 90 in cold bending. In order to analyze the cause of the crack, fracture analysis, mechanical properties test, metallographic examination, microhardness test and electron backscatter diffraction analysis were carried out. The results show that the impact toughness of Q345B steel plate is low because of the long strip and chain inclusions beyond the field of view, and there is a certain degree of work hardening at the bending angle and the change of crystal structure formed at the inside of the bending angle, which makes the Q345B steel plate in the state of deterioration of reverse bending toughness and plastic mechanical properties. It causes Q345B low alloy structural steel plate to crack in the inner corner of the bend in brittle cleavage.