Hot bearing and cold rolling are both processes to form steel plates or profiles, and they have a great impact on the structure and performance of steel.
Steel bearing is mainly hot bearing and cold rolling is generally used only to produce small steels and thin plates with precision sizes.
Hot and cold rolling situations of steel:
Wire: diameter5.5-40 mm, rolled up, all hot rolled. After being pulled by cold, it is a material pulled by cold.
Round steel: in addition to the brilliant materials of size precisely, it is generally truncated hot and there are also forged materials (the surface has traces of forging).
Strip: The hot bearing and the cold bearing are both available and cold rolling materials are generally thin.
Steel plate: cold plates are generally thinner, such as car plates; The medium hot plates are thicker, and there are those with thicknesses similar to significantly different appearances.
Aclet angle: all are hot rolled.
Steel hose: Hot bearing and cold drawing are used for welding.
Canal steel andH -shaped steel: hot roll.
Rearn: Warm rolled material.
Hot rolled
By definition, ingots or billets are difficult to deform at room temperature and are difficult to treat.The bearing is made at 1100 ~ 1250 ℃.
The termination temperature of the hot bearing is generally800-900 ° C, then it is generally cooled in the air, so the hot rolling condition is equivalent to normalizing the treatment.
Most of the steel is rolled by hot bearing. The steel delivered in a hot rolled state has an iron oxide layer on the surface due to the high temperature, it therefore has a certain resistance to corrosion and can be stored outdoors.
However, this layer of iron oxide also makes the surface of the hot steel rough and the size fluctuates considerably, so that the steel with a smooth surface, precise dimensions and good mechanical properties must be produced at the ‘Help of semi-finished hot-rolled products or finished products as a man raw materials and then cold truncated.
advantage:
Rapid training speed, high yield and does not damage the coating.; Cold rolling can cause a large plastic deformation of steel, thus improving the steel point of view.
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1. Although plastic thermal compression is not carried out during the molding process, the residual constraint still exists in the transverse cut, which will inevitably affect the characteristics of global and local buckling of steel;
2. The cold raised steel style is generally an open cross section, so that the free torsion rigidity of the transverse section is lower. The torsion is subject to occur during flexion, flexion and flexion during pressure, and poor torsion resistance;
3. The thickness of the wall of the cold raised steel is small, and it is not thickened in the corners of the plates connection, so it has a low capacity to resist the local concentrated loads.
Cold ride
The cold ride refers to the rolling method which uses the roll pressure to change the shape of the steel at room temperature. Although the processing process also heats the steel plate, it is always called cold bearing. To be more specific, the hot steel coil for cold rolling is used as a raw material, and the scale is eliminated by acid washing and the pressure treatment is carried out, and the finished product is a turtle rolled coil .
Generally, cold steel such as galvanized and colorful steel plates must be received, so that plasticity and elongation are also good and are widely used in industries such as cars, household appliances and equipment . The surface of the cold rolled baking sheet has a certain finish and is relatively smooth to the touch of the hand, which is mainly due to the stripping effect. The surface finish of the hot rolled baking sheet generally does not meet the requirements, so the hot line steel strips require a cold bearing, and the thickness of the hot steel strips is generally the thinnest.1.0 mm, cold bearing can reach 0.1 mm. The hot bearing rolls above the crystallization temperature point and the cold ride rolls below the crystallization temperature point.
The change in the shape of steel by cold rolling is a continuous cold deformation.
For terminal use, the cold rolling is deteriorating the stamping performance and the product is suitable for simple deformation parts.
advantage::
It can destroy the flow structure of the steel ingot, refine the steel grains and eliminate the defects of the microstructure, thus making the structure in dense steel and the mechanical properties have improved. This improvement is mainly reflected in the direction of rolling, so that steel is no longer isotropic to a certain extent; Bubbles, cracks and relaxation formed during the casting can also be welded under a high temperature and pressure.
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1. After the hot bearing, the non -metallic inclusions (mainly sulphides and oxides, as well as silicates) inside the steel are pressed in fine leaves, resulting in superimposition. The superposition deteriorates considerably, the performance of the steel being tense in the direction of the thickness and can cause an intercouche tear when the welding shrinks. The local deformation induced by the narrowing of the welding often reaches several times the deformation of the point of yield, which is much greater than the deformation caused by the load;
2. Residual stress caused by unequal cooling. Residual stress is the stress of the balance of the internal phase without external force. Although the residual constraint is balanced by self-shame, it always has a certain impact on the performance of steel components under the external forces. For example, it can have harmful effects on deformation, stability, fatigue resistance, etc.
To summarize:
The temperature of the cold rolling and hot bearing is mainly the rolling process.“Fresh” is at room temperature and the “heat” is at high temperature.
From a metallographic point of view, the border between cold rolling and hot bearing must be distinguished by the recrystallization temperature. In other words, the bearing below the recrystallization temperature is cold ride, and the bearing above the recrystallization temperature is hot bearing. The recrystallization temperature of steel is450 ～ 600 ℃。
The main differences between the hot bearing and the cold rolling are:
1. Surface appearance and quality:
Since the cold plate is obtained by the heating plate after the cold rolling process and that the cold bearing will also make a certain surface finish, the quality of the cold plate is in the cold plate.(like surface roughness) is better than hot plates, so if there are high requirements for the quality of the product’s post-sequence coating, cold plates are generally selected and hot plates are divided into plates marinated and in marinated plates not. From the plate, the marinated plate becomes a normal metallic color due to sailors, but it is not cold rolled, so the surface is still not as high as the cold plate. or layer of blackened iron tetroxide. In secular terms, it’s like a fire, and if the storage environment is not good, it usually has a little rust.
2. Performance: In general, the mechanical properties of hot plates and cold plates are considered indistinguishable in engineering. required. However, no matter how high the cold plate has higher resistance than the heating plate.
3. Training performance since the performance of cold and hot plates are fundamentally different, the factors affecting training performance depend on the difference in surface quality. Since the quality of the surface is better from the cold plate, the steel plates of the same material are generally referred to steel plates.
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