Hot Rolled and Cold Rolled Steel Coils - China Suppliers and Factory for Versatile Steel Solutions
Specifications
| Parameter | Range / Options |
|---|---|
| Thickness |
Hot Rolled 1.2 mm – 25.4 mm Cold Rolled 0.15 mm – 4.0 mm Galvanized 0.2 mm – 3.2 mm |
| Width | 600 mm – 1,880 mm (standard ranges) |
| Coil Weight | 3 – 25 metric tons (typical) |
| Inner Diameter | 508 mm / 610 mm (standard) |
| Surface | Mill finish, pickled & oiled, galvanized, coated |
Types of Steel Coil
| Type | Manufacturing Process | Characteristics | Typical Thickness |
|---|---|---|---|
| Hot Rolled Coil (HRC) | Rolled above recrystallization temperature (1,000°C+) | Rough, bluish-gray surface; scaled finish; lower cost; good formability | 1.2 – 25.4 mm |
| Cold Rolled Coil (CRC) | Hot rolled coil further processed at room temperature | Smooth, shiny surface; tighter tolerances; increased strength; improved appearance | 0.15 – 4.0 mm |
| Galvanized Steel Coil (GI) | Zinc coating applied via hot-dip process | Corrosion-resistant; spangled or spangle-free finish; extended service life | 0.2 – 3.2 mm |
| Galvalume / Aluzinc Coil | Aluminum-zinc alloy coating (55% Al, 43.5% Zn) | Superior corrosion resistance; better heat reflection; cut-edge protection | 0.2 – 2.5 mm |
| Prepainted / Color Coated Coil (PPGI) | Galvanized substrate with paint application | Decorative colors; enhanced durability; coil coating process | 0.2 – 1.5 mm |
| Pickled & Oiled Coil (P&O) | Hot rolled with surface scale removed via acid bath | Clean surface; oiled for temporary rust protection; ready for further processing | 1.5 – 6.0 mm |
Manufacturing Process
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1Raw Material PreparationSteel coil production begins with high-quality raw materials—iron ore, coal, and limestone—which are melted in blast furnaces to produce molten steel. Continuous casting forms the liquid steel into slabs, which are then prepared for rolling.
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2Hot RollingSteel slabs are heated above recrystallization temperature (approximately 1,000°C) and passed through large rollers that reduce thickness and stretch the material into long sheets. This process yields hot rolled coils with characteristic scaled surfaces.
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3PicklingHot rolled coils may undergo pickling in hydrochloric acid tanks to remove surface oxides (scale) formed during hot rolling. This operation ensures surface quality for subsequent cold rolling or direct use. The process includes trimming edges and applying oil for temporary protection.
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4Cold RollingPickled hot rolled coils are further processed at room temperature through tandem rolling mills. The combined action of loads and pulls reduces thickness while improving surface finish, flatness, and mechanical properties.
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5AnnealingCold rolled coils may receive heat treatment to relieve internal stresses and restore ductility lost during cold working.
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6GalvanizingFor corrosion-resistant products, coils pass through continuous hot-dip galvanizing lines using the Sendzimir process. The strip immerses in molten zinc with small aluminum additions to improve adhesion and flexibility.
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7Coating / PaintingCoil coating lines apply paint via rollers, followed by heat treatment to polymerize coatings. The process includes degreasing, chemical pre-treatment, primer application, top coat finishing, and quality control testing.
Frequently Asked Questions
Q
What is the difference between hot rolled and cold rolled steel coil?
Hot rolled coil (HRC) is produced by rolling steel above its recrystallization temperature (~1,000°C), resulting in a rough, scaled surface and thicker gauges (1.2–25.4 mm). Cold rolled coil (CRC) is processed at room temperature from pickled hot rolled material, producing a smoother, shinier surface with tighter dimensional tolerances and thinner gauges (0.15–4.0 mm). CRC generally offers improved mechanical properties and surface quality for precision applications.
Q
What are the standard dimensions and coil weights available?
Standard widths range from 600 mm to 1,880 mm, with thickness options varying by product type—hot rolled (1.2–25.4 mm), cold rolled (0.15–4.0 mm), and galvanized (0.2–3.2 mm). Coil weights typically range from 3 to 25 metric tons. Inner diameters are standardized at 508 mm or 610 mm to suit most decoiling equipment.
Q
What is the difference between galvanized (GI) and Galvalume (Aluzinc) steel coil?
Galvanized steel coil (GI) is coated with pure zinc via a hot-dip process, offering good corrosion resistance and a spangled or spangle-free finish. Galvalume (Aluzinc) coil uses an aluminum-zinc alloy coating (55% Al, 43.5% Zn), which provides superior corrosion resistance, better heat reflectivity, and improved cut-edge protection compared to standard galvanized coil. Galvalume is preferred in roofing and cladding applications requiring longer service life.
Q
What is PPGI and what are its main applications?
PPGI (Prepainted / Color Coated Steel Coil) is produced by applying paint coatings onto a galvanized substrate through a continuous coil coating process. It is available in a wide range of decorative colors and offers enhanced durability against weathering and corrosion. PPGI is widely used in construction (roofing, wall panels, ceilings), home appliances, and general fabrication where aesthetics and surface protection are both important.
Q
What is Pickled & Oiled (P&O) coil and why is it used?
Pickled & Oiled coil is hot rolled steel that has been treated in an acid bath (typically hydrochloric acid) to remove surface scale, then coated with a thin layer of oil to prevent rust during storage and transportation. It provides a clean, scale-free surface suitable for direct forming, welding, or further processing such as cold rolling or coating. P&O coil is commonly used in automotive, pipe manufacturing, and general fabrication industries.
Q
Why is annealing performed on cold rolled steel coils?
During cold rolling, steel undergoes significant work hardening, which increases strength but reduces ductility and formability. Annealing is a heat treatment process applied to cold rolled coils to relieve internal stresses, restore ductility, and improve formability. This makes the material easier to stamp, bend, or deep draw in downstream manufacturing processes. The annealing temperature and atmosphere are carefully controlled to achieve the desired mechanical properties without surface oxidation.