The document files on the continuous casting of steel provide information on the following subjects: the continuous-casting process, its yield and energy savings, its economic benefits in terms of costs and efficiency, surveys of process developments, world continuous-casting installations, U.S. installations and operating data, continuous vs. pressure casting, heat flow in continuous casting, instrumentation and controls for casters, tundish temperature control, semi-horizontal casters, curved-mold casters, casting of spring steels, cast steel for seamless pipe, billet and bloom casting, casters for market mills, slab casting (economic importance, engineering and metallurgy, caster design and operation), thin-slab casting (status and outlook, leading concepts, caster database), thin-slab processes ( CSP, CONROLL, ECCO-Platzer, ISP/Arvedi, Launer Block, Mannesmann Demag, SMS, Tippins/Samsung, and ROCAST), ISP at POSCO, twin-roll strip casting, CASTRIP for micro-mills, Concast AG profile, Irving Rossi process pioneer, and the continuous-casting operations at Appleby-Frodingham, Armco/Mansfield, AVESTA Sheffield, IPSCO, Laclede, McLouth, Roanoke, Republic/Canton, U.S. Steel/Gary, Weirton, Wisconsin, and Yawata Steel. In addition, the Archive’s book and reference collection includes Continuous Casting by D.L. McBride and T.E. Dancy, and the World Survey of Continuous Casting Machines from the Concast Documentation Center .
Analysis: Continuous casting, as the name implies, continuously turns molten steel into solid shapes for further rolling and processing. Like BOF steelmaking, continuous casting represents a genuine technological breakthrough, the two advances, which emerged in the 1950’s, having since combined to transform the refining and shaping of steel from a much slower, batch-type operation into one that is faster and much more efficient.
In continuous casting, molten steel is transferred from a bottom-pour ladle into the casting machine’s tundish, a reservoir and buffer sized to maintain a steady flow of steel into the machine’s casting mold, while providing adequate time for ladle exchanges with the steelmaking shop. As the molten steel descends through the water-cooled, oscillating copper mold, a solidified shell forms against the mold wall and contains the still-liquid center of the developing strand. Engaged by a series of withdrawal rolls, the strand emerges from the mold at a controlled, steady rate, and cooled with air and water, it totally solidifies prior to being cut into the required lengths of semifinished steel.
Shaping steel continuously eliminates the many production steps required by ingot casting, which in 1975 still was processing 86% of all the world’s steel. With continuous casting there is no longer the need to pour the molten steel into ingot molds, wait for the steel to adequately solidify, strip the molds from the cast ingots, place the partially cooled ingots in soaking pits to develop an even rolling temperature, and finally, roll the reheated ingots on a primary rolling mill to obtain the desired semifinished shapes. Without the fore-and-aft cropping losses incurred in rolling ingots, continuous casting results in significant yield savings (11-13% from molten steel to semifinished shape), and by avoiding ingot cooling and soaking-pit reheating, significant energy savings are also realized (some 600 thousand BTU’s per ton).
Continuous casting required some 100 years to move from concept to reality. Sir Henry Bessemer had conceptualized the technology in 1858, and following a lengthy and difficult development, which started to make significant progress in the 1930’s, the process eventually gained limited commercial status in the late 1950’s. Its first real success came in the 1960’s in commercially casting billets and blooms, which helped spur the minimill approach to steel production.
By contrast, the casting of large slabs, the semifinished shape representing most of the steel produced by integrated mills, initially was beset with many difficulties that awaited additional operating experience and process refinement. In 1971, the Oita Works of Nippon Steel Corporation became the first integrated plant solely based on wide-slab casting without any primary-rolling backup. Thereafter, continuous casting started to gain more general acceptance, and by 2000 was used to process 90% of the world’s total steel output.
Nucor Corporation’s 1989 thin-slab-casting breakthrough increased the cost-saving potential of continuous casting by advancing the state of the art in forming molten steel nearer to net shape, which further reduced rolling requirements. More recently, Nucor, POSCO, and a European consortium have been pursuing programs aimed at the near-net-shape casting of steel strip, an objective with added potential to unlock major continuous-casting benefits.