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Hot Rolled VS Cold Rolled Stainless Steel

Aug 16, 2021

Definition of hot rolling and cold rolling

 

Hot rolling

Hot rolling uses slabs (mainly continuous casting slabs) as raw materials, which are heated to produce strip steel through roughing mills and finishing mills. The hot steel strip from the last finishing mill is cooled to a set temperature by laminar flow, and then rolled into a steel strip by a coiler. The cooled steel strip coil is processed into steel plate, flat coil and slit steel through different finishing lines (leveling, straightening, cross-cutting or slitting, inspection, weighing, packaging, marking) according to the different needs of users. Bring products. To put it simply, the billet (that is, the red hot steel on the TV) is heated, and then subjected to multiple finish rolling, and then trimmed and corrected into a steel plate. This is the so-called hot rolling.


stainless steel plates


Cold rolling

Cold rolling is made from hot rolled sheets at room temperature. Although the plate will heat up during the rolling process, it is still called cold rolling. Due to continuous cold rolling after hot rolling, the mechanical properties of cold rolling are relatively poor and the hardness is too high. The mechanical properties can only be restored after annealing. Unannealed ones are called hard rolls. Hard rollers are generally used to make products that are not bent and stretched, and the bending thickness is less than 1.0 lucky two-sided or four-sided.


stainless steel plates


Available Grades

Hot rolled stainless steel plates: 201/202/304/316/409/2205/430 stainless steel plates, etc.

Cold rolled stainless steel plates: 201/202/304/310/316/409/430/2205 stainless steel sheet, etc.

 

Advantages and disadvantages of hot rolling and cold rolling

Both hot rolling and cold rolling are forming processes of section steel or steel plate, which have a great influence on the structure and performance of stainless steel. The rolling of steel is mainly hot rolling, and cold rolling is only used to produce small section steel and thin plates.

 

1. Hot rolled

Advantage:

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

 

Disadvantage:

1. After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, causing delamination (interlayer). Delamination will greatly deteriorate the tensile properties of the steel along 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 larger than the local strain caused by the load;

2. Residual stress is an internal self-balanced stress without external force, which exists in various hot-rolled profiles. However, uneven cooling of the steel will cause residual stress. Generally, the larger the section size of the steel section, the larger the residual stress. Although the residual stress is self-balancing, it has a certain influence on the performance of the steel member under the action of external force. Such aspects as deformation, stability, fatigue resistance, etc. may have adverse effects.

 

Cold rolling refers to the processing of steel plates or strips into various types of steel by cold drawing, cold bending, and cold drawing at room temperature.

 

Advantage:

The forming speed is fast, the coating is not damaged, the output is high, and it can be made into a variety of cross-sectional forms to meet the needs of the use conditions; cold rolling can produce greater plastic deformation of the stainless steel, thereby increasing the yield point of the steel.

 

Disadvantage:

1. Although there is no thermoplastic compression during the molding process, there are still residual stresses in the section, which will inevitably affect the overall and local buckling characteristics of the steel;

2. Cold-rolled steel generally has an open section, which makes the free torsional rigidity of this section low. Easy to twist when bending, easy to bend and twist when compressed, poor torsion resistance;

3. The wall thickness of the cold-rolled steel plate is small, the corners of the plate connection are not thickened, and the ability to withstand local concentrated loads is weak.

 

The main difference between hot rolling and cold rolling:

 

1. The cold-rolled part allows local buckling, which can make full use of the post-buckling bearing capacity of the member; the hot-rolled part does not allow local buckling.

2. The causes of residual stress in the hot-rolled section and the cold-rolled section are different, so the distribution on the section is also very different. The residual stress distribution of the cold-formed thin-walled section is curved, and the residual stress of the hot-rolled or welded section is distributed in a thin film.


3. The free torsion rigidity of hot-rolled steel is higher than that of cold-rolled steel, so the torsion resistance of hot-rolled steel is better than that of cold-rolled steel.