1.What is the difference between cold-rolled coils and cold-rolled strips?
Cold-rolled coil: refers to steel that exists in coil form after cold rolling, and is the direct product of the cold rolling process. It is either an intermediate product or a raw material.
Cold-rolled strip: generally refers to a flat product that has been cut to a fixed length or slit. It can be formed from cold-rolled coil through subsequent processing (slitting, cross-cutting).
Key Relationship: In most cases, "cold-rolled strip" is produced from "cold-rolled coil" through processes such as annealing and finishing. Annealing occurs while they are still "coils". Therefore, discussing the differences in their annealing processes essentially means discussing the differences in the "annealing methods experienced by cold-rolled coils in different production processes".
2.What are the characteristics and processes of annealing before forming "strip steel"?
Process Name: Continuous Annealing or Bell-Type Annealing.
Process: Cold-rolled coil → annealed on a continuous annealing line (CAL) or in a bell-type furnace → becomes an "annealed coil" → finishing treatment (leveling, tension straightening) → slitting/cross-cutting → finished cold-rolled strip/plate.
Features:
High Efficiency: The continuous annealing line has extremely high speed (up to hundreds of meters per minute), suitable for large-scale production.
Uniform and Stable Performance: Annealing process parameters (temperature, speed) are precisely controlled, resulting in good consistency in the performance of the entire coil.
Excellent Surface Quality: Typically carried out in a protective atmosphere, resulting in a smooth surface free of oxidation.
3.What are the characteristics and processes of forming "strip steel" first and then annealing it?
Process Name: Single-sheet annealing or single-stack annealing of strip steel (less common).
Process: Cold-rolled coil → Slitting/dividing → Becoming "cold-rolled narrow strip steel" → Single sheet/coil entering an annealing furnace (e.g., box furnace, pit furnace) for annealing → Finished annealed strip steel.
Features:
High flexibility: Suitable for processing small batches, multiple specifications, and special materials.
Minor deformation: Single-sheet annealing allows for more complete stress release, potentially resulting in better sheet shape.
Low efficiency and high cost: Cannot be used for continuous production; high energy consumption; slight surface oxidation may occur.
4.What are the differences between continuous annealing and bell annealing processes?
Continuous annealing: After uncoiling, the strip steel continuously passes through a tunnel furnace with heating, holding, and cooling sections.
Bell-type annealing: The steel coils are stacked, covered with inner and outer covers, and heating, holding, and cooling are completed in a static state.
5.What are the differences in performance control between continuous annealing and bell-type annealing?
Continuous annealing: Precise and rapid, suitable for producing steel grades with high strength and uniform performance requirements (such as automotive steel sheets).
Bell-type annealing: Slow cooling rate, which is beneficial for carbide spheroidization, especially suitable for producing deep-drawing mild steel (such as 08Al), with excellent plasticity.