How to distinguish Hot rolled steel and cold rolled steel

Hot rolled steel and cold rolled steel is steel or steel plate forming process, which has a great influence on the microstructure and mechanical properties of steel, steel rolling are mainly composed of hot rolling, cold rolling is only used in the production of small section steel and sheet.

A hot rolled steel

Advantages: can destroy the ingot casting organization, grain refining of steel, and eliminating the defects of the microstructure, which makes steel group is close-grained, mechanical performance is improved. This improvement is mainly manifested on along the rolling direction, so that the steel to a certain extent, is no longer isotropic body; Pouring formed bubbles, cracks and loose, can also be used in high temperature and pressure are welded together.

Disadvantages: 1. After hot rolling, steel internal non-metallic inclusions (mainly sulfide and oxide and silicate) was pressed into thin slices, appear statified phenomenon (sandwich). Layered make steel along the thickness direction tensile performance is much worse, and may in the weld shrinkage occurs when torn between the layers. Weld shrinkage induced local strain often reach the yield point several times as much, much bigger than the load caused by the strain; 2. The residual stress caused by uneven cooling. Residual stress is without external force within the phase equilibrium under the action of stress and all sorts of cross section of hot rolled steel has this kind of residual stress, the general steel section size, the greater the residual stress. Although the residual stress is the phase equilibrium, but the performance of the steel members under the action of external force still has certain influence. Such as the deformation, stability, fatigue resistance, etc, are likely to produce adverse effect.

2. Cold rolled structural steel pipe

Cold rolled steel is at room temperature, after cold drawn, cold bending, cold drawn cold working steel sheet or strip processing into various types of steel.

Advantages: molding speed, high output, and does not damage the coating, can be made into a variety of cross section form, to meet the needs of the conditions of use; Cold rolling can make the steel produces large plastic deformation, thus improve the yield point of steel.

Disadvantages: 1. Although without hot plastic compression molding process, but remains in the cross section of residual stress, the global and local buckling of steel characteristics will influence; 2. The cold rolled steel style is usually open section, makes the cross section of free torsional rigidity is low. Prone to reverse when bending, easy to appear when compression bending torsional buckling, torsional performance is poorer; 3. The cold rolled steel wall thickness is small, and no upset in the cohesion of the corner panel to locality under concentrated load ability weak.

3. Hot rolled steel and cold rolled steel is the main difference between:

1, cold rolled into sections to allow local buckling section, which can make full use of the bar buckling bearing capacity after; Local buckling and hot rolled steel does not allow cross section.

2, the causes of hot rolled steel and cold rolled steel residual stress is different, so the distribution of cross section also have very big difference. Cold-formed thin-walled steel cross section on the residual stress distribution is curved, and hot rolled steel or welded steel pipe residual stress distribution on cross section is a thin film.

3, hot rolled steel free torsional rigidity is higher than cold rolled steel, so the torsion properties of hot-rolled steel is better than cold rolled steel.
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