The production process of hot-rolled steel coil is a key link in steel manufacturing. It mainly forms the steel billet into the required plate shape through high-temperature rolling. The following are its core steps:
Raw Material Preparation
Use continuous casting billet or initial rolling billet as raw material, and the billet thickness is usually 150-300mm.
The billet is surface cleaned (such as flame cleaning or mechanical grinding) to remove oxide scale and defects to ensure rolling quality.
Heating
The billet is sent to a step-beam heating furnace and heated to 1100-1300℃ to make the billet reach the austenitizing temperature and enhance plasticity.
Control the heating time and temperature uniformity to avoid overburning or insufficient temperature.
Rough Rolling
The billet thickness is reduced to 30-50mm through a reversible rough rolling mill (such as a two-roll or four-roll mill) to form an intermediate billet.
High-pressure water descaling may be performed after each rolling pass to remove the surface oxide layer.
Finishing Rolling
The intermediate billet enters the finishing mill (usually 6-7 four-roll or six-roll mills), and is gradually thinned to the target thickness (such as 1.2-25mm) through continuous rolling.
AGC (automatic thickness control) and plate shape control system are used to ensure dimensional accuracy and plate shape straightness.
The rollers need to be cooled and lubricated during rolling to prevent thermal deformation and wear.
Cooling
A laminar cooling system is used to quickly cool the steel strip from the final rolling temperature (about 800℃) to room temperature by controlling the water volume and cooling rate (such as 30-50℃/s).
The cooling process directly affects the microstructure (such as ferrite and pearlite ratio) and mechanical properties of the steel coil.
Coiling
The steel strip is rolled into a steel coil through the pinch roller and coiler, and the tension is controlled at 100-500N/mm² to ensure that the coil shape is tight and there is no loose coil.
The coiling temperature is usually controlled at 550-700℃ to optimize performance.
Subsequent Treatment
Surface treatment: pickling to remove oxide scale, or galvanizing, aluminum plating and other coating treatments.
Annealing: improve material ductility (such as recrystallization annealing before cold rolling).
Smoothing: eliminating the yield platform and improving surface finish through small reduction rate rolling.
Quality inspection and packaging: check the size, mechanical properties and surface quality, and roll, bundle and mark according to customer requirements.