In the use of hot-rolled H-shaped steel, problems of the steel itself often occur, such as peeling and pitting on the surface. This situation seriously affected the construction project. Therefore, in order to reduce the occurrence of this situation and improve the quality of hot-rolled H-shaped steel, we need to understand the reasons for this situation.
If the surface of hot-rolled H-shaped steel has continuous depressions without obvious cracks, it is because the iron oxide scale on the surface is not cleaned after the slab is heated and before rolling. The presence of pitting on the surface is because there are many bubbles and iron oxide scale on the surface of the cast slab. Therefore, we must be rigorous during the rolling process and carefully implement the phosphorus removal process, so that the occurrence of pitting will be reduced. After looking at the metallographic structure, the structure in the depression is no different from the general structure and there is no decarburization. Next, let’s take a look at the metallographic analysis of those tongue-shaped and scaly skins.
Hot-rolled H-shaped steel is mainly ferrite and pearlite. The peeling on the surface is mainly caused by the turning of the surface of the cast slab and other reasons. Through metallographic observation, it can also be seen that the cracks do not extend from the surface, but exist inside the steel near the surface. The internal impurities are steel slag.
The problems of the cast billet are mainly manifested in defects such as subcutaneous bubbles near the surface, surface pinholes and slight scarring.
From the above, it can be seen that the reasons for the surface problems of H-shaped steel are firstly defects in the casting billet, and secondly, the heating and descaling effect of the casting billet, which causes the surface oxide scale to be pressed in. Therefore, in order to solve the problem, we can start from the two processes of smelting and rolling.
During the smelting process, it is necessary to pay attention to the moisture content, control the degree of roasting of the raw materials, maintain a balance between dryness and moisture, and prevent surface pinholes and subcutaneous bubbles from appearing in the cast slab. In the rolling process, in order to better remove phosphorus, it is necessary to adjust the appropriate water pressure and adjust the temperature range to above the middle limit during operation. After completing these steps, the smelting supply and demand and rolling process will be more stable, and the surface quality and internal quality of the slab will be greatly changed, becoming smoother and better.
