What is the reason for the type defect of Q345NH weathering steel plate?

The defects in the rolling process of weathering steel plate can be roughly divided into raw material defects, surface spot defects, plate defects and edge defects. The so-called raw material defect refers to some defects caused by the raw material, which are persisted or retained during the cold rolling process. Raw material defects usually include air bubbles, inclusions, sheet pressing, raw material scratches, and roll marks.

Spot defects are mainly due to strip surface rolling oil and iron powder produced in the rolling process of purging unclean caused by rolling residue on the surface of the strip. Black spots are formed by carbonization after annealing, which affects the surface quality of strip steel.

The shape defect of weathering steel plate mainly refers to various waveforms and warpage of continuous rolling products. The main reasons are that the load distribution of the frame is not uniform, the tension between the frame is not set well and the shape of the work roll is not reasonable.

This defect is easy to cause the phenomenon of bonding in the furnace, which has a great impact on the quality of products. Edge defects are mainly caused by poor quality of pickling and trimming or poor ductility of strip.