Steel knowledge

The following are common cold and hot rolling situations of steel:

Wire: diameter 5.5-40mm, coiled, all hot-rolled. After cold drawing, it belongs to cold drawn material.

Round steel: In addition to fine and dense bright materials, it is generally hot-rolled and there are also forged materials (with forging marks on the surface).

Strip steel: Both hot and cold rolling are available, and the cold rolled material is generally thinner.

Steel plate: Cold rolled steel plate is generally thinner, such as automotive plate; There are many hot-rolled medium and thick plates, with a thickness similar to that of cold rolling, and their appearance is significantly different.

Angle steel: all hot-rolled.

Steel pipes: welded, hot rolled, and cold drawn.

Channel steel and H-beam: hot-rolled.

Steel bar: hot-rolled material.

Hot rolling and cold rolling are both processes for forming steel plates or profiles, which have a significant impact on the microstructure and properties of the steel.

The rolling of steel is mainly based on hot rolling, while cold rolling is usually only used to produce fine and dense sized steel products such as small section steel and thin plates.

The ending temperature of hot rolling is generally 800~900 ℃, and then it is generally cooled in air, so the hot rolling state is equivalent to normalizing treatment.

Most steel is rolled using the hot rolling method. Steel delivered in hot-rolled condition, due to high temperature, generates a layer of oxide scale on the surface, which has a certain degree of corrosion resistance and can be stored outdoors.

But this layer of oxide scale also makes the surface of hot-rolled steel rough, with significant size fluctuations. Therefore, steel with smooth surface, precise size, and good mechanical properties is required to be produced using hot-rolled semi-finished or finished products as raw materials and then cold rolled.

Advantages:

The molding speed is fast, the yield is high, and the coating is not damaged. It can be made into various cross-sectional forms to meet the needs of usage conditions; Cold rolling can cause significant plastic deformation of steel, thereby increasing its yield point.

Disadvantages:

Although there is no hot plastic compression during the forming process, residual stress still exists in the cross-section, which inevitably affects the overall and local buckling characteristics of the steel;

2. The style of cold rolled section steel is generally an open section, which reduces the free torsional stiffness of the section. When subjected to bending, it is prone to torsion, and when subjected to compression, it is prone to bending and torsional buckling, resulting in poor torsional performance;

3. The wall thickness of cold rolled formed steel is relatively small, and there is no thickening at the corners where the plates connect, resulting in weak ability to withstand localized concentrated loads.

cold rolling

Cold rolling refers to the rolling method of using the pressure of a rolling roller to compress steel and change its shape at room temperature. Although the processing process also heats up the steel plate, it is still called cold rolling. Specifically, hot rolled steel coils are used as raw materials for cold rolling, and after acid washing to remove oxide scales, they are subjected to pressure processing. The finished product is rolled hard coils.

Generally, cold-rolled steel, such as galvanized and colored steel plates, must be annealed, so their plasticity and elongation are also good. They are widely used in industries such as automobiles, home appliances, and hardware. The surface of cold rolled sheet has a certain degree of smoothness, and it feels relatively smooth to the touch, mainly due to acid washing. Generally, the surface finish of hot-rolled plates cannot meet the requirements, so hot-rolled steel strips need to be cold rolled. Additionally, the thickness of hot-rolled steel strips is generally 1.0mm, and cold rolling can reach 0.1mm. Hot rolling is rolling above the crystallization temperature point