All coiled flat-rolled steel is initially hot-rolled by passing a slab through a multi-stand rolling mill to reduce its thickness to less than 5⁄8 inch. Hot-rolled steel destined for the sheet market can be either shipped as black band or cleaned in an acid bath and sold as pickled band. These products are used in non-critical surface applications such as automotive frames and wheels, construction products, pipe, off-highway equipment and guardrails.
Cold-rolled sheet is hot-rolled coil that has been further processed through a pickler and then passed through a rolling mill without reheating until the desired gauge, or thickness, and other physical properties have been achieved. Cold-rolling reduces gauge and hardens the steel. Further processing through an annealing furnace and a temper mill improves ductility and formability. Cold-rolling can also impart various surface finishes and textures. Cold-rolled sheet is used in, among other things, steel applications that demand higher surface quality, such as exposed automobile and appliance panels. Cold-rolled sheet prices are usually higher than hot-rolled steel prices. For certain applications, cold-rolled sheet is coated or painted.
Either hot-rolled or cold-rolled coil may be coated with zinc, aluminum or a combination thereof to render it corrosion resistant. Hot-dip galvanized, galvannealed, Galvalume, electrogalvanized and aluminized products are types of coated steel. These are also among the highest value-added sheet products because they require the greatest degree of processing and usually have the strictest quality requirements. Coated steel products are generally used in applications such as automobiles, household appliances, roofing and siding, heating and air conditioning equipment, air ducts, switch boxes, chimney flues, awnings and grain bins.
Plate is steel that is generally more than 3⁄16 inch thick. It can be made on either a coiled plate mill, up to one-inch thick, or a discrete plate mill. The coiled plate, or discrete plate, is then cut into sections for specific end uses. Commodity steel plate is used in a variety of applications, such as storage tanks, ships and railcars, large diameter pipe and machinery parts. More specialized steel plate, such as high-strength, low-alloy, heat-treated or alloy plate, can have superior strength and performance characteristics for particular applications such as the manufacture of construction, mining and logging equipment; pressure vessels and oil and gas transmission lines; and the fabrication of bridges and buildings. Quenched and tempered plate is harder and stronger and can be used in products, such as military armor and hard rock mining equipment.
Tin mill sheet steel is used to produce food packaging and other containers. It is available as black plate, tin plate and tin-free steel. Black plate is an uncoated thin gauge cold-rolled steel; tin plate is black plate, electrolytically plated with metallic tin; and tin-free steel is black plate that has been electrolytically plated with metallic chromium and chromium oxides. Both tin plate and tin-free steel undergo a plating process whereby the molecules from the positively charged tin or chromium anode attach to the negatively charged sheet steel. The thickness of the coating is readily controlled through regulation of the voltage and speed of the sheet through the plating area.