Cold-rolled coils are strip steel products manufactured from hot-rolled coils as raw material through continuous rolling at ambient temperatures using cold rolling mills. They derive their name from being stored and transported in coiled form upon completion. As the core foundational category within the cold-rolled steel product system, they share the same fundamental origin as cold-rolled sheets.

I. Core Production Process: The ‘Refined Upgrade’ from Hot-Rolled Coil to Cold-Rolled Coil

The production core of cold-rolled coil lies in ‘non-heated rolling’. Through multiple stages, it eliminates hot-rolling defects and enhances performance. The specific process comprises three phases:

Raw Material Pre-treatment: Hot-rolled coils (3-12mm thick) undergo ‘pickling’ to thoroughly remove surface scale (rust layer) formed during hot rolling, preventing its embedding into the steel during subsequent rolling and compromising surface quality. For premium applications, an additional ‘degreasing’ step removes surface oils.

Cold rolling: The pickled hot-rolled coils enter multi-roll cold rolling mills (e.g., four-roll or six-roll mills). Under ambient temperature, continuous rolling through roll pressure reduces thickness to target specifications (typically 0.15–4 mm). During rolling, plastic deformation induces ‘work hardening’ in the steel (increased hardness and reduced ductility). Subsequent annealing (heating to soften) may be applied as required.

Finishing and Coiling: Post-rolling strip undergoes ‘levelling’ (eliminating surface waviness and adjusting surface finish), ‘trimming’ (correcting width and ensuring edge integrity), and is finally coiled (typically with an inner diameter of 508mm or 610mm, weighing 5-30 tonnes per coil). Some coils may be directly uncoiled into cold-rolled flat sheets.

II. Key Characteristics: Precision and Surface Quality as Core Advantages

Compared to hot-rolled coils, cold-rolled coils derive their core value from ‘precision’, exhibiting four key characteristics:

High dimensional accuracy: Thickness tolerances controllable within ±0.01–0.05mm (significantly superior to hot-rolled coils' ±0.1–0.3mm), minimal width deviation, and flat, distortion-free sheet form. Ideal for applications demanding stringent dimensional precision (e.g., electronic components, precision moulds).

Superior Surface Quality: Acid pickling removes oxide scale, while the absence of high-temperature oxidation during cold rolling yields a highly polished surface (available in matt, semi-matt, or high-gloss finishes). Free from pitting or scaling defects, it requires no additional polishing for visible applications (e.g., appliance casings, automotive panels).

Controllable mechanical properties: By adjusting rolling deformation and annealing processes, hardness, strength, and ductility can be flexibly managed. For instance, hard-rolled cold-rolled coils (unannealed) offer high hardness for structural components, while soft-rolled cold-rolled coils (annealed) provide excellent ductility for deep drawing applications (e.g., automotive doors, beverage cans).

Excellent subsequent workability: With a smooth surface and dimensional stability, it facilitates stamping, bending, welding, and coating processes (painting, galvanising) without complex pre-treatment, thereby reducing downstream production costs.

III. Common Specifications and Grades: Tailored for Diverse Applications

1. Common Specifications

Thickness: Mainstream range 0.15–4 mm (most commonly 0.3–2 mm); special requirements extend to 0.05 mm (ultra-thin cold-rolled coil for electronic components).

Width: 600–2000 mm (customisable; e.g., 1250 mm and 1500 mm for household appliances, 1800 mm for automotive applications).

Weight: Single coil 5–30 tonnes (facilitates handling and transportation while aligning with downstream production line efficiency).