Differences, Advantages and Disadvantages of Cold-rolled and Hot-Rolled Stainless Steel

1. Cold-rolled steel allows local buckling of the cross section, so that the bearing capacity of the bar after buckling can be fully utilized; while hot-rolled steel does not allow local buckling of the cross section.

2. The causes of residual stress in hot-rolled and cold-rolled steel are different, so the distribution on the section is also very different. The residual stress distribution on the section of cold-bent thin-walled steel is bending type, while the residual stress distribution on the section of hot-rolled steel or welded steel is film type.

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

Cold Rolling: hot-rolled steel coil is used as raw material, and cold rolling is carried out after pickling to remove the oxide scale. The finished product is hard-rolled coil. Due to the cold hardening caused by continuous cold deformation, the strength and hardness of the hard-rolled coil increase, and the toughness and plasticity index decrease, so the stamping performance will deteriorate, and it can only be used for parts with simple deformation. Hard-rolled coil can be used as raw material for hot-dip galvanizing plants, because hot-dip galvanizing units are equipped with annealing lines. The weight of hard-rolled coil is generally 20-40 tons. The steel coil is continuously rolled at room temperature for hot-rolled pickled coil. The inner diameter is 610mm.

（Figure below: cold-rolled stainless steel plate）

Product features: Because it has not been annealed, its hardness is very high (HRB greater than 90), and its mechanical processing performance is extremely poor. Only a simple directional bending process of less than 90 degrees (perpendicular to the coiling direction) can be carried out.

To put it simply, cold rolling is processed and rolled on the basis of hot-rolled coils. Generally speaking, it is a process of hot rolling-pickling-cold rolling.

Cold rolling is processed from hot-rolled plates at room temperature (simply speaking, it means that at room temperature, steel plates or steel strips are processed into various types of steel through cold processing such as cold drawing, cold bending, and cold drawing). Although the steel plate will heat up during the processing process due to rolling, it is still called cold rolling. Because the cold rolling is formed by continuous cold deformation of hot rolling, the mechanical properties are relatively poor and the hardness is too high. It must be annealed to restore its mechanical properties. Those without annealing are called hard-rolled coils.Hard rolled coils are generally used to make products that do not require bending or stretching. Products with a thickness below 1.0 can be bent on two or four sides with good luck.

Additional correction: Cold rolling is generally annealed.

Hot Rolling: advantages: It can destroy the casting structure of the ingot, refine the grains of the steel, and eliminate the defects of the microstructure, so that the steel structure is dense and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer an isotropic body to a certain extent; the bubbles, cracks and looseness formed during pouring can also be welded under high temperature and pressure.

（Figure below: hot-rolled stainless steel plate）

Disadvantages: 1. After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, and stratification (interlayer) occurs. Stratification greatly deteriorates the tensile properties of the steel along the thickness direction, and interlayer tearing may occur when the weld shrinks. The local strain induced by weld shrinkage often reaches several times the yield point strain, which is much larger than the strain caused by the load.

2. Residual stress caused by uneven cooling. Residual stress is the internal self-balanced stress without external force. Hot-rolled steel sections of various cross-sections have this type of residual stress. Generally, the larger the cross-section size of the steel section, the greater the residual stress. Although the residual stress is self-balanced, it still has a certain impact on the performance of steel components under external forces. For example, it may have an adverse effect on deformation, stability, fatigue resistance, etc.

3. Hot-rolled steel products are difficult to control in terms of thickness and side width. We are familiar with thermal expansion and contraction. Since the length and thickness of hot-rolled products meet the standards at the beginning, there will still be a certain negative difference after cooling. The wider the side width and the thicker the thickness. 

Therefore, for large-sized steel, the side width, thickness, length, angle, and side line of the steel cannot be too precise.