Cause analysis of red oxide iron on hot rolled Q235B steel plate surface

In hot rolling production, the steel slab needs to be heated by high temperature before hot rolling. Due to Q235B steel plate contact oxidation gas at high temperature, it will generate thicker oxide iron on the surface of Q235B carbon steel plate. The continuous casting billet needs descaling processing after getting out of heating furnace before entering the rolling machine. If the surface oxidation iron can not removed completely, it will cause certain negative influence on Q235B carbon steel plate surface quality. The serious one can even affect the following processing quality of the Q235B mild steel plates.The surface oxidation iron of Q235B steel plate have high hardness and hard pickling removal features.

Causes of red oxide iron on hot rolled Q235B steel plate surface:
(1) The return temperature of different parts of Q235B mild steel plates after rolling, and the contact degree with the O2 is different. The two kinds of factors mutual coupling and lead to the oxide iron thickness on side is larger than that in the middle, and presents the variation trend of first increased then decreased.

(2) The oxide iron of hot rolled Q235B steel plates is mainly composed of FeO, Fe3O4 and Fe2O3. FeO fragmentation and FeO break during finishing rolling are the direct causes of red oxide iron.

Therefore, it is necessary to increase the descaling pressure of high pressure water before finishing rolling, and to improve the final rolling temperature on the basis of ensuring Q235B steel plates properties.