Investors in the steel sector often come across terms such as slab, hot dip galvanized sheet, or coated sheet – but the definitions of these terms and interrelationships between the different steel products in the production chain are by no means always clear. In this article, the authors describe the steel product 'production' chain and the flow of products from semi-finished to finished product.
The Three Semi-Finished Product Groups
The three main finished steel product groups are tube, flat products and long products. These finished products are produced from semi-finished steel products which are usually made by continuous casting of liquid steel. These so-called semis corporation,
- billet: typically a square some 6 or 12 meters in length with cross-sectional area of 100 – 120 mm square to a maximum of 180 – 200 mm square – used for long products and seamless tube
- slab: usually up to 12 meters in length and conventionally from ~ 150 mm up to ~ 400 mm thick – used for flat products (and subsequently, welded tube)
- bloom: usually above 180 or 200mm square to around 300 – 360 mm square (to a maximum of ~ 400 mm square) – used for large section and long products.
The Finished Products
Turning to the different finished product groups,
- billet is typically hot-rolled into light long products. These products generally combine bar – which can be round, square, angled etc. This light long category often includes merchant bar products (rounds, squares, hexagons, rectangles, flats etc used mainly as support structures for building, construction, machinery) as well as reinforcing bar (typically 8 – 18 mm in diameter, and used for concrete reinforcement). Light long products can also include wire rod, which is generally under 13.5 mm in diameter, and is formed in coils rather than in lengths. Steel wire, steel mesh, nails and other fasteners are typically made from wire rod.
- slab is typically hot rolled into plate or into hot rolled coil. Beyond this step, there is cold rolling, which typically takes hot rolled steel coil and further reduces the gauge to produce cold-rolled coil. Cold-rolled steel can be used as such (eg in machine components), but is often coated to produce zinc coated sheet or tin plate. Zinc coated sheet is often processed further still – to make so-called organic coated sheet – where a plastic coating further adds to the anti-corrosive properties of the steel.
- bloom is typically roled in a blooming mill, to produce large sections or very big bar shapes.
- welded tube in turn is usually made by bending of hot rolled coil or sheet (made from slab); although plate or cold-rolled steel can also be used for welded tube making depending on the desired wall thickness.
- seamless tube is usually made by billet piercing.
The steel production process chain in summary therefore, usually consist of the following steps:
- production of liquid steel
- production of semis
- hot rolling of semis to make light long products such bar or hot rolled plate or coil
- cold rolling of the hot rolled bar or coil product, to produce cold-rolled coil or cold drawn products such as steel wire.