What Is Hot Rolling?

Hot rolling takes slabs (mainly continuous casting slabs) as raw materials, and after heating, it is made into strip steel by roughing mills and finishing mills. The hot-rolled strip produced by the last finishing mill is cooled to the set temperature by laminar flow and then rolled into the strip by the coiler. After cooling, the strip coils are processed into steel plates, flat coils, and slitting through different finishing lines (leveling, straightening, cross-cutting or slitting, inspection, weighing, packaging, marking) according to different needs of users. Strip products. Simply put, after heating the billet, it is refined and rolled several times, and then the edges are cut and corrected to steel plates, which is called hot rolling. Our company provides a galvanized steel coil.

Hot rolling is to soften the alloy at a temperature higher than the recrystallization temperature and then use the pressing wheel to press the material into a thin section or billet cross-section to deform the material, but the physical properties of the material are unchanged.

Hot-rolled (forged) state: The state where the metal material is no longer subjected to special heat treatment after hot rolling or hot forging and is delivered directly after cooling. The end temperature of hot rolling (forging) is generally 800-960 ℃ and then cooled in air, so the state of hot rolling (forging) is equivalent to normalizing treatment. The surface of the hot-rolled (forged) metal material is covered with an oxide film, which has certain corrosion resistance. Storage, transportation, and storage requirements are not as strict as those delivered by a cold drawing (rolling). For example, large and medium-sized steel and medium-thick steel plates can be stored in the open yard or after covering.

Hot rolling advantages:

It can destroy the casting structure of the ingot, refine the grains of the steel, eliminate structural defects, make the steel structure dense, and improve the mechanical properties. This improvement is mainly reflected in the rolling direction so that the steel is no longer isotropic to a certain extent; bubbles, cracks, and looseness formed during the casting process can also be welded under the action of high temperature and high pressure.

Disadvantages of hot rolling:

1. After hot rolling, non-metallic inclusions (mainly sulfides and oxides, and silicates) in the steel are compressed into thin sheets, resulting in delamination (interlayer). Lamination greatly deteriorates the tensile properties of the steel in the thickness direction, and interlayer tearing may occur when the weld shrinks. The local strain caused by the shrinkage of the weld is often several times the yield point strain, which is much greater than the local strain caused by the load;

2. Residual stress caused by uneven cooling. Residual stress is the internal self-balancing stress without external force, which exists in various hot-rolled steel. Generally, the larger the cross-sectional size, the greater the residual stress. Although the residual stress is self-balanced, it has a certain influence on the performance of the steel member under the action of external forces. Such as deformation, stability, fatigue resistance, and other aspects that may have adverse effects.

The above information is provided by the galvanized steel pipe manufacturer.