Cold rolling and hot rolling are working process for shaped steel or plate, they have a great impact on the microstructure and properties of steel, The rolling of steel is mainly hot rolling while cold rolling only for the production of small steel and thin sheet.
Cold rolling refers to under normal temperature, steel plate or strip process into various types of steel through cold drawing.
Advantages:fast molding, high yield, and no damage to the coating,can be made into a variety of forms, cross section, in order to meet the needs of the conditions of use; cold rolled steel to produce plastic deformation greatly, thus improving the yield point of steel.
Disadvantages:1)although there is no hot plastic compression molding process, there is still residual stress in the section, and effect the bucking characteristics of steel 2)generally open cross section for cold rolling shaped steel,The free torsional rigidity of the cross section is lower.Prone to reverse when bended and flexural torsional buckling when compressed. 3)The steel wall thickness is small, and no thickening in the corner of the slab joining , so the ability to bear the local concentrated load is weak.
Advantages:can destroy the ingot casting, refine steel grain,and eliminate the defects in microstructure, so that make steel dense and improve mechanical properties.Bubbles, cracks and loose formed in pouring, can also be welded under high temperature and pressure.
Disadvantages: 1)After hot rolling, the non metallic inclusions in steel (mainly sulfide and oxide, and silicate) are pressed into thin slices, and there are delamination phenomena.The performance of the steel is greatly deteriorated along the thickness direction, and it is possible to be torn between layers when the seam is contracted. 2)Uneven cooling causes residual stress.which have a certain influence on the steel structure under external force performance. Such as deformation, stability, anti fatigue and other aspects.
Regularly,plate and shaped steel with thicker wall thickness(>4mm) are hot rolled with No.1 or picked ice mill finish while sheet and small shaped steel with thinner wall thickness(<4mm) are cold rolled with 2B mill finish.