Cold rolling process of steel
Date:2025-07-15View:16Tags:SSAW steel pipe,LSAW steel pipe,Epoxy pipe
Cold rolling is not an isolated link, but an interlocking finishing system:
Raw material preparation: The starting point is the steel coil (hot rolled coil) that has been hot rolled and coiled. These coils are usually between 1.5mm and 6mm thick and are covered with iron oxide scale (scale) formed at high temperature.
Pickling and descaling: The hot rolled coil enters the pickling line (usually using hydrochloric acid or sulfuric acid), and the surface iron oxide scale is completely removed by chemical dissolution, revealing a clean and active metal surface, providing a basis for subsequent rolling.
Cold rolling forming: The clean steel strip enters the core link - the cold rolling mill. At room temperature, the steel passes through a rack composed of high-strength rollers (single-stand reversible or multi-stand continuous), and is repeatedly rolled under great pressure. This process:
Significant thinning: The thickness can be reduced to 0.1mm or even thinner (such as ultra-thin strips).
Work hardening: The grains are elongated and refined, significantly improving the strength and hardness (yield strength, tensile strength) of the steel.
Improved surface: The precision finish of the roll itself is directly copied to the surface of the strip, achieving a mirror-like effect.
Precise control: Modern rolling mills are equipped with advanced automatic thickness control (AGC) and flatness control (AFC) systems to ensure that the thickness tolerance reaches the micron level and the plate shape is straight.
Annealing softening (key): The high strength brought by rolling is accompanied by a sharp drop in plasticity and toughness (work hardening). In order to restore the formability of the material, the coil needs to be annealed in a protective atmosphere (such as a nitrogen-hydrogen mixture):
Bell furnace annealing: Suitable for small batches or special steel grades, the steel coil stack is slowly heated and cooled in the furnace.
Continuous annealing line (CAL): The mainstream method with higher efficiency and more uniform performance. The strip steel continuously passes through strictly controlled temperature zones such as heating, soaking, slow cooling, and rapid cooling (aging treatment) to accurately adjust the final organization and properties (such as the {111} texture required for deep drawing steel).
Finishing treatment:
Smoothing (pass-through rolling): Slight rolling (small reduction rate) eliminates the slight yield platform produced by annealing, improves surface finish, and obtains more uniform mechanical properties and excellent plate shape.
Tensile straightening: Through the combined action of stretching and bending, the plate shape is further improved (eliminating wave shape, warping, etc.) and the straightness is improved.
Surface treatment/coating (optional): According to the final use, electrogalvanizing (EG), hot-dip galvanizing (GI/GA), aluminum zinc plating (GL), color coating (PPGI/PPGL), etc. can be carried out to give the steel special functions such as anti-corrosion and decoration.
Inspection and coiling: After strict online or offline testing (surface, size, performance), the final product is slit, re-coiled, and packaged according to customer requirements.
