Hot rolling uses slabs (mainly continuous casting slabs) as raw materials. After heating, the rough rolling mill and the finishing mill are used to make strip steel. The hot steel strip from the last rolling mill of finishing rolling is cooled to the set temperature by laminar flow, and then coiled into steel coil by the coiler. The cooled steel coil will undergo different finishing operations according to the different needs of users. Lines (flattening, straightening, cross-cutting or slitting, inspection, weighing, packaging and marking, etc.) are processed into steel plates, flat coils and slit steel strip products. To put it simply, a piece of steel billet is heated (that is, the hot steel block that is burning red on the TV) after several passes, then trimmed, and straightened into a steel plate. This is called hot rolling.
Cold rolling: Hot-rolled steel coil is used as raw material, after pickling to remove oxide scale, cold rolling is carried out. The finished product is hard-rolled coil. The cold-work hardening caused by continuous cold deformation increases the strength, hardness and toughness of the hard-rolled coil. The plastic index drops, so the stamping performance will deteriorate, and it can only be used for simple deformed parts. Hard-rolled coils can be used as raw materials for hot-dip galvanizing plants, because hot-dip galvanizing units are equipped with annealing lines. The weight of the rolled hard coil is generally 6 to 13.5 tons, and the steel coil is continuously rolled on the hot-rolled pickled coil at room temperature. The inner diameter is 610mm.
Product features: Because it has not been annealed, its hardness is very high (HRB greater than 90), and its machining performance is extremely poor. It can only be processed with a simple directional bending less than 90 degrees (perpendicular to the coiling direction).
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 sheets at room temperature. Although the rolling process will heat up the steel plate, it is still called cold rolling. Because the hot rolling is cold rolled after continuous cold deformation, the mechanical properties are relatively poor and the hardness is too high. It must be annealed to restore its mechanical properties, and the ones that are not annealed are called rolled hard coils. Rolled hard coils are generally used to make products that do not need to be bent or stretched.
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