PART ONE: MATERIALS 172 making steel in France, by Emil and Pierre Martin in 1863. Siemens set up a small works in Birmingham in 1866 to demonstrate how steel could be made in his furnace, and by 1869 a company at Swansea was producing about 75 tonnes a week. By 1870 the Siemens process (often called the Siemens-Martin process for the obvious reason) was fully established. Wrought iron now had some really serious competition. The Siemens and Bessemer processes were complementary, but both could use phosphoric or non-phosphoric iron. Bessemer was cheaper since it used no fuel, but it needed to be charged with molten iron. This was easy when the Bessemer plant was adjacent to blast furnaces. Molten iron could be used in the Siemens openhearth furnace, and it often was, but an advantage of this process was that it could melt scrap iron. With the spread of industry, scrap had become a useful raw material as machinery of all kinds wore out or was replaced by new and better types and it was cheaper than pig iron. See Figure 2.5. The Siemens process was slower than the Bessemer. A Bessemer charge of iron took about thirty minutes to convert to steel; in the Siemens furnace it took eight to twelve hours. This could be an advantage, for it enabled the furnace operator to make frequent checks on the steel and to adjust its composition as required. Various grades were now demanded, and the new steelmaking processes were able to provide them. In the second half of the nineteenth century steel began, slowly but surely, to push the wrought iron trade out of existence; although it survived in a small way until recently, from about 1870 onwards steel was what really mattered. Cast iron continued to be made, partly for castings but increasingly as the raw material for steel and this is still the position today. Alloy steels Before 1856 there were only two important iron products, cast and wrought iron. A third, carbon steel, was essential for some purposes but its output was small. Bessemer added a fourth, mild steel. In 1868 appeared the first of a fifth group, now called special, or alloy, steel, made by R.F.Mushet in his small works in the Forest of Dean in Gloucestershire. More engineering products meant that more machining had to be done and this needed cutting tools. Before Mushet’s time the only means of cutting iron and steel was a tool made of carbon steel. This can be hardened by making it red hot and cooling it quickly; the obvious way was to plunge it into cold water. Such treatment makes the steel very hard and brittle; it has to be heated again to a lower temperature, and cooled once more to make it both hard and tough. Carbon steel which has been hardened can be softened again by making it red hot and letting it cool naturally. When a carbon steel tool wore or was damaged, it was useful to be able to soften it, file it or machine it back FERROUS METALS 173 Figure 2.5: Like the Bessemer process, open hearth steelmaking is now obsolete. Open hearth furnaces could range in size from 5 or 6 tonnes in the early days to as much as 500 tonnes capacity at the end. British Steel Corporation. PART ONE: MATERIALS 174 to its original shape and reharden it. However, softening was a distinct disadvantage when it occurred accidentally. Heat is always generated during cutting and when iron or steel are cut the temperature can easily reach a point where the tool is softened. Then it is useless until it has been rehardened. Thus there is a limit to the speed or depth of cut which can be made by a carbon- steel tool. Many improved machine tools had appeared in the first half of the nineteenth century. Driven by steam, they were strong and powerful, and capable of heavier work than their cutting tools could achieve. Mushet was asked to make somebody else’s patent tools and, finding them a failure, invented one of his own. He took advantage of the fact that iron and steel will unite with many other elements and experimented with tungsten. Mushet’s tungsten steel could be forged to shape and left to cool naturally in the air, when it became very hard and tough. It only needed grinding to a sharp cutting edge to be ready for use, and when it became blunt from use it was reground. The most useful feature, however, was that the new steel did not soften even at a dull red heat. Engineers and machinists welcomed it, although it was much more expensive than carbon steel. Tungsten steel is still used today, although its detailed composition is often a little different. The best engineers’ drills are usually made of a form of tungsten steel called High Speed Steel introduced in 1900. Others followed Mushet with different alloys for special purposes. R.A. Hadfield, for example, used manganese, in 1887, to make a steel which was particularly tough and wear-resisting. It was used in such things as railway points and crossings, and in rock-crushing machinery. Over the years very many more alloy and special steels have been added to the list, all of them with some special application or group of applications. Stainless steel, in particular, has affected all areas of everyday life. Stainless steel was invented by Harry Brearley, in Sheffield, in 1913. While experimenting with a better steel for rifle barrels he noticed that one of the steels he made was unaffected when he tried to treat it with acid so that he could examine it under the microscope. Attack by acid, or etching, is a form of corrosion. If the steel would not etch it would not corrode either, at least under many conditions where ordinary steel would. Some possible uses for the new steel suggested themselves at once, including cutlery. Many foods contain weak acids which do not harm people but will stain and corrode ordinary steel. Brearley had some table knives made and found that they stood up to use very well, without losing their bright surface. His original experimental steel contained nearly 13 per cent of chromium and Brearley tried out other proportions, and also added different elements such as nickel. After his experiments had been suspended during the First World War, he and others went on to develop several kinds of stainless steel. One problem was that of hardening the steel: Brearley’s first knives were thick and blunt and FERROUS METALS 175 he once said that he got a name for making knives that would not cut. Over time, several different kinds of stainless steel were developed for particular purposes. One of the commonest for table ware such as dishes and coffee pots contains about 18 per cent chromium and 8 per cent nickel, hence the figures 18/8 which are often found stamped on such goods. Other types, of different composition but all correctly called stainless steel, are used for such things as knives and razor blades, and surgeons’ scalpels. Still further varieties are used in industry to resist the heat of furnaces, or in other severe conditions. Steel manufacturing after 1860 While new types of steel were being invented and improved, developments were also taking place in the manufacture and handling of the product. Rolling mills, in particular, changed drastically. A rolling mill in its simplest form consists of a pair of rolls (never called rollers in the iron and steel industry) mounted one above the other in a strong framework. Their surfaces may be flat, for rolling strip, plates or sheets; or they may have grooves cut in them to shape the iron or steel into, say, a round bar, railway rail or girder. Only a limited amount of shaping can be done in a single passage through the rolls; the metal must be passed through several times. This was done by men with tongs holding the red-hot metal, hard but skilled work. With the Bessemer and Siemens processes steel could be made not only quicker but in bigger individual pieces. Molten steel was cast into rectangular blocks, or ingots, which were rolled to the required shape. As ingots became bigger, men could not handle them and machinery had to take over. Sir John Alleyne, of Butterley in Derbyshire, patented a mechanical device for moving ingots in 1861. He also devised a rolling mill which could rotate the rolls in either direction, enabling the metal to be passed back and forth, some rolling being carried out at each movement, until it was of the required size and shape. These two devices saved time and took over work which was too heavy for men to do. Alleyne’s mill was improved upon by John Ramsbottom, of Crewe railway works, who made the first really successful reversing mill in 1866 by coupling the engine of a railway locomotive to a rolling mill. A railway engine, of course, has to be capable of running in either direction, so it could just as easily rotate the rolls either way; all the man in charge had to do was to pull a lever. These inventions were the basis on which many modern rolling mills operate today. There were several other changes in steel rolling, some of them matters of detail, but all adding up to a general improvement. One development, however, was a completely new idea. This was the continuous rolling mill invented by George Bedson, of Manchester, in 1862. Bedson built a mill, for rolling small iron rods for making into wire, with sets of rolls in a PART ONE: MATERIALS 176 long straight line, so that the metal being rolled came out of one pair of rolls, passed immediately to the next pair and so on down the line until the finished size and shape were achieved. It saved time, needed fewer men and made a better product. The first Bedson mill had sixteen pairs of rolls so the metal was rolled sixteen times before it came to the end of the line. Later mills had even more pairs of rolls and could produce rods at very high speed. The principle was adapted to roll other steel products besides rods, and it is the basis of many modern mills. By the end of the nineteenth century iron- and steelmaking were very much more mechanized, but the source of power was still steam. Electricity had appeared in the iron- and steelworks, but at first only for lighting: some works had electric light in the 1880s. Today it is the source of power in every works and the steam engines survive only in museums. Electricity is also used today in steelworks as a direct source of heat, and its beginnings for this purpose go back a long way. If an electric arc is struck very intense heat is generated; Siemens suggested that it could be used for steelmaking in 1878, but nothing came of it at the time. Nor was there much interest in the arc furnace designed by the Frenchman Paul Héroult in 1886, though he used it himself for making aluminium (see p. 109), and in 1900 actually made steel in it. The electric furnace was ahead of its time, and it was a national emergency which really started it going. In the First World War, munition manufacture produced quite large quantities of small shreds and scraps of metal called swarf, which was very valuable raw material for steelmaking if it could be melted. Neither the Bessemer converter nor the Siemens open-hearth furnace would do this adequately, but the electric furnace would. MODERN STEELMAKING 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 FERROUS METALS 177 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, PART ONE: MATERIALS 178 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. Oxygen steelmaking is another example of the international nature of the industry. It was first put to practical use in Austria in 1953, because it happened to suit local conditions there at that time. From the fact that it was FERROUS METALS 179 used in the Austrian towns of Linz and Donawitz the process was often called by the initials L-D. However, Basic Oxygen Steel (BOS) is now the accepted term in English-speaking countries. The oxygen process has caused a complete revolution in bulk—or to use another common name—tonnage steelmaking. The Bessemer process had been dying out for some time. The last British basic Bessemer converters—at Corby, Northamptonshire—closed down in 1966 and only two converters remained in Britain, at Workington, Cumbria, both of the acid type. They finally closed in 1974. The Bessemer process is now extinct in Britain and practically so throughout the world, and now the BOS process has sealed the fate of the open-hearth furnace, which is being phased out fairly quickly. Speed of production, attractive though it is, brings its problems, one of which is the control of the process. It calls for a very high order of instrumentation. In the days of the open-hearth furnace the more leisurely pace allowed the operator to take samples of steel, have them analysed in the works laboratory, and make adjustments to the furnace charge as required. Now the analysis is done automatically: a small sample of steel is cooled down and polished, then analysed by an automatic spectrograph. Disposing of the steel made in the BOS converter calls for equipment which will work at the same rate. One of the ways of doing so is continuous casting, as revolutionary in its way as the BOS process. Ever since steel was first made in bulk it has been poured molten into moulds to produce rectangular pieces (ingots) or heavy flat ones (slabs). These could then be processed into finished products by rolling. Ingots can now weigh anything from about 45kg (99lb) or so in the case of special steels to as much as 20 tonnes or more in tonnage steels. For many purposes continuous casting, simple in principle but needing very accurate control, has replaced ingots. Liquid steel is poured into an open copper mould of the required size for a billet, bloom or slab. The mould is water-cooled and the outer skin of the metal solidifies rapidly. At the bottom of the mould the metal is solid enough for it to be drawn out at the same rate as the molten metal enters at the top. Water sprays below the mould complete the solidification. As long as molten steel is poured in, a solid product comes out in a continuous length. This is cut up automatically by a flame-cutting head into the lengths required for further processing. Continuous casting is not literally continuous in that it never stops, and produces a billet or slab which would be of infinite length if it were not cut up: in fact steelmaking itself is not continuous, so the casting machine has to deal with batches of molten steel. But it is sometimes possible to get several batches in succession so that the casting machine can have a satisfactorily long run. If steel is cast into ingots there is always a certain amount of unsound metal at the end, which has to be cut off. In continuous casting there is also a small piece at the start and finish of the cast which has to be discarded, but this means that there are only two pieces of scrap for every batch. If a batch of, say, PART ONE: MATERIALS 180 100 tonnes were cast into twenty 5-tonne ingots there would be twenty pieces to discard. The saving is obvious, so it is not surprising that continuous casting has spread all over the industrial world. Compared with steelmaking and casting, rolling mills have evolved in a rather less spectacular way, but development has been impressive nevertheless. Continuous wide strip rolling now produces all the steel sheet used for motor- car bodies, cookers, refrigerators, washing machines and a host of other industrial and domestic purposes. Bedson’s continuous mill is still used in modified form for rolling rod and the idea was adapted for wide strip. It seems logical that this development should have taken place in the USA, for it solved the problem of the time. In the 1920s the growth of the mass-produced car trade, pioneered there, coupled with increased demand for kitchen equipment and canned goods, created a vast market for steel sheets and the old hand-rolling methods of sheet production could not cope with the demand. The answer was mechanization and the Americans provided it in the form of the wide strip mill. A steel slab is heated to rolling temperature and passed through a series of rolls in line until it is reduced to a very long thin plate. This is automatically wound into a coil weighing several tonnes. Then the coils are pickled in acid to clean the surface and passed through a further series of rolls, this time cold, to become finished coils of thin, wide strip. Coils of strip can be used in several ways. They can go to cut-up lines, where they are unwound and the continuous length is cut automatically, without stopping the line, into sheets of a required length. Alternatively the coils can go direct to the user, where they become the raw material for automatic production lines. Or the coils can be passed through an automatic tinning line, where they are given a microscopically thin coating of tin to become tinplate, which is used for making cans (or, as they are often, and wrongly, called, tins). Some coils go through a different automatic production line to be coated with zinc (galvanized). The product, like plain wide strip or tinplate, can be sold in coil form or cut automatically into sheets. If galvanized strip is cut into sheets, many of them will be corrugated to form the product still familiarly and incorrectly known as corrugated iron. It has been made of steel for many years now, but the old name has stuck, as it has with ‘L’-shaped or angle sections which are now of steel, although they are popularly called angle iron. Two other means of finishing strip steel—wide and narrow—are of growing importance: plastic coating and prepainting. Sheets and coils can now be coated on either or both sides with a thin layer of plastic film. It is bonded on to the steel and adheres so tightly that it cannot be pulled off without destroying it. Several different colours and surface finishes are available and plastic-coated sheets have many uses. Office furniture and partitioning are common outlets, as are some domestic appliances such as electric fan heaters. Another use is for the FERROUS METALS 181 sheeting on the outside and roofs of buildings. In prepainted sheets and coils there is also a wide range of colours and types of paint available. All the paints are chemically based and adhere very firmly. Typical uses for prepainted sheets are for car instruments and clock faces: all the customer has to do is to cut out the required shape and print on the figures. Both types of sheet can be shaped by metalworking machinery without damaging the finish, and they save the user having to install expensive finishing equipment. The continuous wide strip mill did not attract much attention outside the USA at first, but as other countries stepped up their demands for more sheet it began to spread. The first outside the USA was put down at Ebbw Vale, Gwent, in 1938. It produced about 5000 tonnes a week which, though not particularly impressive by current standards, was a great advance over anything possible in Britain before. Strip today can be either ‘narrow’ (up to and including 600mm wide) or ‘wide’ if it exceeds that figure. Thickness is now usually stated in millimetres and decimals of a millimetre: it is technically sheet if it is up to and including 3mm; above that it is plate. So tinplate, which is much less than 3mm thick, should really be called sheet—it is neither tin nor plate—but the name is very old and it shows no sign of disappearing. Like any other process operating at high speed the wide strip mill demands very accurate control. Strip can issue from the finishing end of the mill at about 95km/h and the mill could make scrap very fast if anything went wrong. One of the problems found in any rolling mill is that the component parts can stretch and distort when the metal is rolled. The stretch may be very small. It may only cause inaccuracies in the finished strip thickness of a fraction of a millimetre, but such inaccuracies are unacceptable to some buyers of strip and sheet, and allowance has to be made for this problem in the design. A British invention, now used all over the world, which deals with this problem is automatic gauge control. With this device variations in strip thickness are measured as they are actually occurring, and corrective action is taken automatically before there is time for a serious fault to develop. Very remarkable strip accuracy is possible: consistency of strip thickness to within 0.005mm is achieved regularly in commercial production. Such control is automation in the correct sense of the word. Automatic operation of many types of machine—not only in the steel industry—is very common and quite old. It is not, however, automation, for automatic operation merely goes through a preset programme with workers to check the products and adjust the machinery. With true automation the machinery checks its own products and makes its own corrections. This is exactly what automatic gauge control does. As production rates increase, automation is becoming more essential, particularly as customers are now demanding higher standards in their steels than ever before. For some purposes the computer is providing the answer; the steel industry shares with the oil refineries the credit for much pioneering work in this field. . 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. fan heaters. Another use is for the FERROUS METALS 181 sheeting on the outside and roofs of buildings. In prepainted sheets and coils there is also a wide range of colours and types of paint available roll other steel products besides rods, and it is the basis of many modern mills. By the end of the nineteenth century iron- and steelmaking were very much more mechanized, but the source of power