The “Rolling Epic” of Carbon Steel Coil: From Billet to Coil, a Game between High Temperature and Precision

The production of carbon steel coils is a model of "large-scale manufacturing" in the steel industry. The birth of each coil of steel has undergone the dual tests of high-temperature rolling and precision control. This article analyzes its core production process:

Steelmaking and continuous casting: The molten iron produced by the blast furnace is decarburized in the converter (the carbon content is controlled at the target value ±0.02%), and then continuously cast into a slab with a thickness of 200-250mm. The surface of the slab must be free of cracks and inclusions (otherwise defects will be formed after rolling);
Hot rolling into coils: The slab is heated to 1200℃ (austenitizing temperature), rolled to a thickness of 20-30mm by the rough rolling mill, and then entered the finishing mill (multi-roll rolling) to press to 1.2-12mm, and finally cooled by laminar flow (cooling speed is controlled at 20℃/s) to fix the grain structure. The coiler rolls the steel plate into a hot-rolled coil with a diameter of 1.2-2m - a steel plant once had a batch of low-carbon hot-rolled coils with low strength due to a slow cooling speed of 5℃/s, which could not be used for structural parts;
Cold rolling finishing: After the hot-rolled coil is pickled to remove the oxide scale, it enters the cold rolling mill (normal temperature rolling) and passes through 5-7 After several passes of rolling (total reduction rate of 60%-80%), a cold-rolled coil of 0.15-3mm is finally formed, and the thickness tolerance can be controlled at ±0.01mm. The surface finish is improved by 3 levels compared with hot-rolled coils;
Annealing and leveling: Cold-rolled coils are prone to brittleness due to work hardening, and need to be heated to 700-800℃ in a bell furnace for annealing (keeping warm for 10-12 hours), and then the plate shape is adjusted by the leveling machine (ensuring that the wave height per meter is ≤1mm) to meet the processing requirements of stamping, bending, etc.
From steel billets to coils, each ton of carbon steel coil consumes 600kWh of electricity, and the rolling speed reaches 1200m/min (equivalent to the high-speed rail speed of 72km per hour), which can be called "the speed and passion of the steel industry".