The two main classes of finished steel products are flat products and long products, which are themselves produced from semi-finished steels including slab and billet. The markets for these products are analyzed in depth in Steel: Weekly Market Tracker. The market fundamentals within key producing and consuming markets are detailed monthly on a product-by-product basis while the more volatile pricing movements, particularly but not exclusively in China, are analyzed on a weekly basis in order to keep readers fully updated on the major market movements.
The usage of finished steel is widespread and exceeded 1.4bn tonnes last year according to the World Steel Association (WSA), having risen by nearly 4% per year since 2006. Steel is fundamental to energy supply, transportation systems, urban centres, clean water and safe food supply and according to the Steel Recycling Institute (SRI) reached a recycling rate of as much as 92% in the USA in 2011, just a couple of percentage points below the automotive industry. Construction is the most important end-use sector in developed as well as developing markets and is particularly important to long products such as concrete reinforcing bar (rebar). The automotive industry is the second most important end-use sector and especially significant for flat products such as galvanized sheet.
As with other metals, demand is being driven by developments in China, at over 9% per year, and other emerging markets including India and Egypt though such rapid growth is partly being offset by demand in Europe, which remains significantly below peak levels of 2007, particularly in Spain where it is less than half its former size.
Flat products are usually rolled down from a steel slab cast directly from molten steel, but some narrow flat products can be produced from blooms. The slabs are either passed through a single hot rolling unit, a reversing mill, moving back and forth, until they are reduced to the desired thickness. More commonly the slab passes through a series of rollers arranged in line (in tandem) that reduce its thickness progressively. The slabs may then be rolled down further in a cold-rolling process.
The main categories of flat-rolled products are:
- Hot-rolled (HR) coil or sheet produced on a tandem mill, which may be used directly by customers in a plain or a coated (galvanized) form or subjected to cold rolling.
- Cold-rolled (CR) coil. All extra working of metal tends to improve its physical condition and working cold metal generally strengthens it and improves its surface finish.
- Coated coil, which is usually based on CR coil but may also use HR coil as its starting point. It may be only metal coated, or coated with both metal and organic material, whether paint or plastic. The most common metal coating processes are hot-dip galvanizing, which requires the coil to pass through a bath of molten metal, and electrolytic galvanizing, which requires the coil to be held in an electrolytic bath while an electric current deposits metal on its surface. Zinc is the most common coating metal, but there are processes that use zinc mixed with aluminium or nickel and other metals. Tinplate is very thin CR steel coated electrolytically with tin metal.
- Plate. This term applies to thicker gauges of steel that are clearly flat and not long in character but they are sometimes classified separately from other flat products. The heaviest and highest quality plate is produced in a reversing mill. Frequent passes improve the physical structure of the steel. However, tandem hot rolling mills can be designed to produce coil of moderate thickness that can compete with plate in less demanding applications.
All of these flat products can be further shaped in a steelworks downstream fabricating units to produce forms of pipes and tubes for gas, liquid or slurry transmission or structural tubes and hollow sections. The largest and highest quality transmission pipes are usually made from reversing mill plate, but a large proportion of ordinary pipes and tubes use HR coil from tandem HR lines.
Flat steel products are used in steel manufactures of all kinds. Car bodies are among the most visible as well as the biggest users of high quality CR coil that has been galvanized. They need very high quality coil because the complex shapes of car bodies require high formability and the exposure of car bodies to the weather requires high resistance to corrosion. Lower specification galvanized coil is familiar as a common building material, especially in the simple roll-formed shapes, the corrugations that give steel building sheet extra strength. Painted and plastic-coated steel is used as cladding, inside and outside buildings, and for doors and gates.
Ordinary car and truck wheels use HR coil, which is also visible as street furniture and road barriers. Plate is widely used in the construction industry. A special patterned form, sometimes called checker plate marked with a raised pattern, provides safety flooring and stairs seen in factories and on fire escapes. Heavy-duty plate is used for ships and earth-moving equipment and in high performance structures such as bridges.
Long products are rolled from the first outputs of a mill, semi-manufactures, billets and blooms that are cast from the emerging molten steel. Billets usually have a square cross-section (some, used to produce seamless tubes have a round cross-section), while blooms usually have an oblong cross-section. These semi-manufactures pass through a hot rolling line. Some higher performance products are treated further on a cold rolling and finishing line.
The main categories of long products are:
- Bars, of round, square or oblong cross-section; the simplest are the plain or deformed bars used directly to reinforce concrete (rebars); other bars may be machined, stamped or shaped for final use
- Wire rod; the simplest may be used directly or welded in a mesh as another form of concrete reinforcement; other grades may be machined or shaped, or drawn to be made into wire or wire products such as nails
- Sections; this term usually refers to shapes of open profile such as angles and channels and heavier products such as I beams and H beams. Heavy and light sections are usually separated by their height at 80mm.
A high proportion of long products are used by the construction industry, but some long products, usually in higher performance categories, are used for structural and mechanical (moving) parts of machinery and general manufactures.