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Advantages and disadvantages of cold rolling and hot rolling.
Apr 14, 2018

   the concept of cold rolled and hot rolled hot-rolled with continuous casting slab or slab as raw material, by step heating furnace, high pressure water descaling after entering the roughing mill, roughing expected by the cutting head, tail, and then into the finishing mill, and the implementation of computer control rolling and finishing after after laminar cooling (computer controlled cooling rate) and the winder, and became a straight hair volume.

Advantages and disadvantages of hot rolling:

The advantages of hot rolling: it can destroy the casting organization of steel ingots, refine the grain of steel, and eliminate the defects of 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 isotropic in a certain extent; The bubbles, cracks and loose particles formed during pouring can also be welded together under high temperature and pressure.

Disadvantages :1. After hot rolling, the non-metallic inclusions in the steel (mainly sulfide and oxides, and silicates) are pressed into thin slices and layered (sandwich) phenomenon occurs. The lamination causes the steel to deteriorate along the direction of the thickness, and may be torn between layers during the weld shrinkage. The local strain induced by weld contraction is often several times the yield point strain, which is much larger than the strain caused by the load.

2. Residual stresses caused by uneven cooling. Residual stress is the stress of internal self - phase equilibrium without external force, and all kinds of hot rolled steel sections have this kind of residual stress, and the larger the section size is, the greater the residual stress is. Although the residual stresses are self - balanced, the performance of steel components under external forces has some influence. Such as deformation, stability, fatigue and other aspects can have adverse effects.

Advantages and disadvantages of cold rolling:

Advantages: fast forming speed, high yield, and no damage coating, can be made into a variety of cross-section forms to meet the requirements of use conditions; Cold rolling can make the steel produce a large plastic deformation, thus improving the yield point of the steel.

Disadvantages :1. Although there is no hot plastic compression in the forming process, residual stresses still exist in the cross section, which inevitably affect the overall and local buckling characteristics of the steel.

2. The cold rolled steel style is generally open section, which makes the free torsion stiffness of the section lower. It is easy to turn torsion when bending, it is easy to bend and buckle under pressure, and the torsion resistance is poor.

3. The cold rolled steel wall thickness is small, and there is no thickening at the corner of the plate connection, and the capacity of the local concentrated load is weak.

The difference between hot rolling and cold rolling: 1. The section of cold rolled steel is allowed to have local buckling, which can make full use of the bearing capacity after buckling of the bar. The hot rolled section does not allow partial buckling of cross section.

2. There are different reasons for the residual stress of hot rolled steel and cold rolled steel, so the distribution on the cross section is also very different. The residual stress distribution in the section of the cold-formed thin-walled steel section is curved, while the residual stress distribution in the section of hot-zoned steel or welded section is thin film type.

3. The free torsion stiffness of hot rolled steel is higher than that of cold rolled steel, so the torsion performance of hot rolled steel is better than that of cold rolled steel.