The process of pickling involves removing oxide scales from the surface of the hot rolled steel by treating it with dilute hydrochloric acid (HCL). Process is generally a combination of chemical reaction and mechanical separation of tertiary scales.
The thickness accuracy of cold rolled / reduced steel is determined by the cold rolling process. Rolling force and strip tension are controlled based on measurements of the strip thickness at the entry and exit sides of the mill for achieving required dimensions in cold rolling.
The formability of product is determined by annealing. Because cold rolling significantly increases material hardness and make forming difficult, annealing is performed to improve ductility by inducing a recrystallized structure in the steel. In batch annealing furnace (BAF), coils are piled and covered by the box and annealed in a batch hence this is called the batch annealing.
Annealed coils are lightly rolled by the skinpass mill to prevent a defect called stretcher strain, improve strip shape, and adjust mechanical properties. Skinpass rolling is also used to produce dull finish and bright finish products.
Coils are processed at finishing lines, where they are cut to produce product final sizes as per customer requirement. CTL is processed in length and width is changed in slitting to specified dimensions.
Product dimensions, shape and surface quality is inspected and mechanical properties are tested using specimens taken at the finishing line.