Advantages of 1. Hot rolling: it can destroy the casting structure of steel ingot, refine the grain of steel, eliminate the defects of microstructure, make the structure of steel compact and improve the mechanical properties. This improvement is mainly reflected in the rolling direction, which makes the steel no longer isotropic to some extent; Bubbles, cracks and pores formed during pouring can also be welded under the action of high temperature and high pressure.
Disadvantages: 1 After hot rolling, nonmetallic inclusions (mainly sulfides and oxides, and silicates) in steel are pressed into thin sheets, resulting in delamination (interlayer). Delamination greatly deteriorates the tensile properties of steel along the thickness direction, and interlayer tearing may occur when the weld shrinks. The local strain caused by weld shrinkage often reaches several times the yield point strain, which is much greater than the strain caused by load. 2. Residual stress caused by uneven cooling. Residual stress is an internal self-balancing stress without external force, which exists in all kinds of hot rolled steel. Generally speaking, the larger the section size, the greater the residual stress. Although the residual stress is self-balanced, it still has some influence on the performance of steel members under external force. For example, it may adversely affect deformation, stability and fatigue resistance.
2. Cold rolling refers to cold drawing, cold bending and cold drawing of steel plates or steel strips into various types of steel at room temperature.
Advantages: high molding speed, high yield, no damage to the coating, various cross-sectional forms, and meeting the needs of use conditions; Cold rolling can cause great plastic deformation of steel, thus improving the yield point of steel.
Disadvantages: 1 Although there is no thermoplastic compression in the forming process, there is still residual stress in the cross section, which will inevitably affect the overall and local buckling characteristics of steel. 2. The style of cold-rolled steel is generally open section, which makes the free torsion stiffness of the section lower. Torsion is easy to occur when bending, and bending-torsion buckling is easy to occur when compressing, so the torsional performance is poor; 3. The wall thickness of cold-rolled steel is small, and it is not thickened at the corner where the plates are connected, so the ability to bear local concentrated load is weak.
3. The main differences between hot rolling and cold rolling are:
1, cold-rolled steel allows local buckling of the section, which makes full use of the buckling bearing capacity of the bar; However, local buckling of hot rolled steel is not allowed.
2. The causes of residual stress in hot-rolled steel plate and cold-rolled steel plate are different, so the distribution on the cross section is also very different. The residual stress distribution on the section of cold-formed thin-walled steel is curved, while the residual stress distribution on the section of hot-rolled steel or welded steel is thin film.
3. The free torsional stiffness of hot rolled steel is higher than that of cold rolled steel, so the torsional performance of hot rolled steel is better than that of cold rolled steel.
Extended data
Usually, the lubricant used for hot rolling is delivered to the surface of the roll in the form of oil-water mixture, with water as the carrier, and a small amount of oil is evenly dispersed in the water. The action process of oil-water mixture is the transformation process of oil-in-water phase to water-in-oil phase. After the mixed liquid reaches the roller surface, it spreads quickly on the roller surface in the form of oil in water. When entering the deformation zone and contacting with the high-temperature rolled piece, due to the action of temperature and pressure, the water quickly evaporates and becomes water-in-oil phase, and some oil burns into combustion products mainly containing ash. Part of the oil is evenly covered on the contact cambered surface between the roller and the workpiece in the form of oil film, and both of them can play a lubricating role of about 0.0 1s in the deformation zone.
Cold rolling is to further thin 1 steel plate to the target thickness at room temperature. Compared with hot-rolled steel plate, cold-rolled steel plate has more accurate thickness, smooth and beautiful surface, and various superior mechanical properties, especially processability. Because the cold-rolled original coil is brittle and hard, it is not suitable for processing, so in general, cold-rolled steel plates need to be annealed, pickled and leveled before being handed over to customers. The maximum thickness of cold rolling is below 0. 1-8.0 mm, for example, the thickness of cold rolled steel plates in most factories is below 4.5MM; The minimum thickness and width are determined according to the equipment capacity and market demand of each factory.
Stainless steel cold-rolled steel plate is a stainless steel plate produced by cold rolling process. Thickness is not more than 3mm, thickness is more than 3mm, for thick plate. Pipes, containers, medical instruments, ship equipment, etc. Used for manufacturing corrosion-resistant parts, petroleum and chemical industries, and classified and marked as follows:
1. austenitic steel
In addition to hot rolled parts (29 kinds), there are (1) 2cr13mn9ni4 (2)1Cr17ni7 (3)1Cr17ni8.
2. Austenite-ferrite steel
In addition to hot-rolled parts (2 kinds), there are (1)18ni1si4alti (2)1Cr 21ni5ti.
3. Ferrite section steel
Besides hot rolled parts (9 kinds), there are: 00Cr 17.
4. Martensite steel
In addition to hot rolled parts (8 kinds), there are 1Cr 17Ni2.
5. Precipitation hardening section steel: same as hot rolled section steel.
References:
Baidu encyclopedia-cold rolled stainless steel, Baidu encyclopedia-stainless steel hot rolled steel plate