Modern Steelmaking: New Age Begins

  October 11, 2021   Read time 6 min
Modern Steelmaking: New Age Begins
During much of the first half of the present century two world wars and several years of international trade depression hindered development in the steel industry throughout the world.

But changes were still taking place and many technological improvements were on the way. In the last twenty years or so the industry has altered at an enormous rate, technologically and economically. Iron- and steelmaking are now, technologically, international. Any large modern steelworks, no matter where it is, will use plant and processes from many countries.

The Anchor development of the British Steel Corporation (BSC) at Scunthorpe provides a typical example. Anchor—a code name—was completed at a cost of some £236 million. A multi-product iron and steel complex which will make about 5.2 million tonnes of steel a year, it is not the biggest project in Britain and far from being the biggest in the world. The BSC works at Teesside was designed for an annual output capacity of 12 million tonnes, and the planned capacity at the Fukuyama works in Japan was 16 million tonnes a year. But Anchor is as modern as any and serves as a good example of how international a steelworks is today.

The route to steel at Anchor is the same as at other large integrated works and this pattern is likely to continue for some time. Briefly, iron ore is reduced to cast iron in large blast furnaces, converted to steel by a new method, the Basic Oxygen Steel process (see below), cast into slabs or ingots and rolled into blooms, plates, billets or sections. Some idea of the size of the works can be gained from the fact that the bloom and billet rolling mill building alone is more than 1.6km (1 mile) long.

The blast furnaces are fed with a mixture of British and foreign iron ores, all in the form of sinter, an agglomerated mixture of fine ore and other ironbearing substances which produces a very uniform raw material. Sinter originated in the USA; the use of 100 per cent to form the charge is a British development which took place on an earlier plant at Scunthorpe.

Steel is made by the BOS (Basic Oxygen Steel) process (see p. 178) perfected in Austria, with some background work in Germany and Switzerland. The original idea was Bessemer’s, though he never tried it out. The process needs very large supplies of pure oxygen, which were not available in Bessemer’s time. Much of the steel is made into large slabs by a process called continuous casting. This again was first suggested by Bessemer, but his idea was not successful. As used today the machines are based on the work of S.Junghans in Germany, with important contributions from Britain and the Soviet Union. The first commercial machine was built at Bradford in 1946. The Anchor continuous casting plant was built by a German firm, rolling of the steel is carried out in mills of British and German design, and some of the electrical equipment is Swedish.

Economics, always important in iron- and steelmaking, are even more so today and this is the reason for the changes in blast furnace ore practice and steelmaking. The British, German, French, Belgian and other Western European iron industries developed because there were large local supplies of iron ore and coal, as did those of the USA and the Soviet Union. In most cases there are still large—sometimes very large—reserves of iron ore left, but they are often of low grade, and in Europe and some other parts of the world it is now more economic for ironworks to import high-grade foreign ores. At the Anchor site, for example, the local ores contain about 20 per cent of iron. Vast new deposits have been opened up in Africa, Australia, Canada and South America, and these ores can contain as much as 60 per cent of iron. With supercarriers —ore-carrying versions of the giant oil tanker—these ores can be brought halfway round the world at low cost. Some of the local ores, however, although they are of low grade, are very close to the surface, and can be quarried cheaply by modern earthmoving machines. In some places, therefore, a certain amount of local ores will be used, mixed with larger quantities of imported ores.

Consequently, British bulk iron- and steelmaking are being concentrated at five sites, all near to deep-water ports capable of taking supercarriers of 100,000 tonnes now and expected to become twice as big or even bigger in the near future. These sites are: Scunthorpe, near to the Immingham ore terminal; Port Talbot and Llanwern, both served by the Port Talbot terminal; Lackenby, close to Redcar terminal; and Ravenscraig, Scotland, near Hunterston terminal. Some steelmaking will continue away from the ports and so will a lot of processing, but the bulk tonnages will come from these places. A similar pattern obtains in Europe and Japan, though the latter country, having no local ore reserves of any value, is even more dependent on imports. The Soviet Union alone, among the big steelmaking nations is likely to remain independent of imports.

The blast furnace remains the same in principle, although very much bigger. A blast furnace of the nineteenth century had a hearth—or lower working part — about 1.8–3m (6–10ft) diameter and made 100 tonnes or so of iron a week. Number three new blast furnace at BSC’s Llanwern Steelworks, Gwent, has a hearth diameter of 1 1.2m and will produce at least 5000 tonnes of iron a day, and BSC’s Redcar furnace, Cleveland, can produce 10000 tonnes a day. All modern blast furnaces are of course mechanically charged, the machinery being under push-button control or even automatic, according to a present programme. Mechanical charging originated in the USA towards the end of the nineteenth century and spread in time to all ironmaking countries.

The BOS process is the biggest single development in steelmaking in the present century. It looks rather like the Bessemer process, but it uses pure oxygen instead of air and the oxygen is blown on to the surface of the molten iron at a very high speed, instead of through it as the air was blown in the Bessemer converter. Some modern BOS vessels are very large; there are three of 300 tonnes capacity each both at Port Talbot steelworks, for example, and at Anchor. BOS steelmaking is very fast; a charge of 300 tonnes of iron can be converted into steel in about thirty minutes. Enormous quantities of oxygen are used and the BOS converters have to have their own oxygen plant in a nearby building. The process gives off a vast amount of gas and, under modern anti-pollution regulations, this has to be cleaned and disposed of harmlessly instead of being discharged to the atmosphere, a costly but essential procedure. In fact everything to do with the BOS process is expensive. The BOS plant at Port Talbot, for instance, cost more than £28 million, but the process is so fast, and uses comparatively so little labour, that it is more economic than any other process for bulk steelmaking today.