Iron and Steel Industry
Steel - over 700 000 million tons produced annually - is the world's most important material. Without steel, the world as we know it would not exist: from oil tankers to thumb tacks, from trucks to tin cans, from transmission towers to toasters.
Steel - over 700 000 million tons produced annually - is the world's most important material. Without steel, the world as we know it would not exist: from oil tankers to thumb tacks, from trucks to tin cans, from transmission towers to toasters. Given the huge quantities of steel produced, it is fortunate that the material is easy to recycle. Much of today's steel is produced from scrap. In fact, many of Canada's steel plants make steel totally from scrap.
Iron production requires these raw materials: iron ore, coal and stone (limestone, dolomite). Steel production requires iron, steel scrap and flux ("lime" - calcined limestone). The iron ore is smelted to produce an impure metal called "hot metal" when liquid, or "pig iron" when solid. The hot metal is refined to remove impurities and to develop the desired composition. The liquid steel is continuously cast into blooms, slabs or billets, and these semi-finished products are processed into the desired shapes by rolling or forging.
The iron and steel industry segments into four groups: iron and steel integrated producers, steel integrated companies, steel processors, and foundries and fabricators. Iron and steel integrated producers (ore-based) are typically large firms that produce more than a million tons of steel annually, operate ore and coal mines (frequently as joint ventures), and iron and steelmaking plants. Producers include such companies as Algoma Steel of Sault Ste Marie, Ont, Dofasco and Stelco of Hamilton, Ont, and Sidbec-Dosco of Contrecoeur, Qué.
Integrated steel producers (scrap-based) depend on scrap as their source of iron. They can make the same range of semi-finished (slabs, blooms and billets) and finished steel products as the larger iron and steel integrated producers (hot- and cold-roll strip, plate, rod, bars, shapes). Producers include such companies as Co-Steel Lasco of Whitby, Ont, Sydney Steel of Sydney, NS, and Stelco-McMaster of Contrecoeur, Qué.
Steel processors purchase semi-finished and hot- and cold-rolled steel products from the integrated companies and custom process them for resale to fabricators wanting steel quantities too small for the integrated companies to handle economically. Scrap recycling companies are included in this segment. Processors include such companies as DNN Galvanizing Corporation of Windsor, Ont, for hot dip galvanizing, and Union Drawn Steel of Hamilton, Ont, for bar drawing.
Foundries, often small, produce various grades of cast iron and/or steel. The molten metal is ladled or poured into sand or metal moulds. The cast parts produced can be complex in shape, and often designed to meet one-of-a-kind end uses. Fabricators take the various primary steel mill products and turn them - cut-to-size, shape, machine, thread, punch, join, protective coat, etc. - into a host of commercial and industrial products. Foundries and fabricators include such companies as Baycoat Ltd of Stoney Creek, Ont, for organic coating, and Bombardier Inc of Valcourt, Qué, for stamping and welding.
Integrated steel plants are located wherever it is economically feasible to bring together large quantities of the raw materials required. The biggest steel plants in Canada have been built at locations along the Great Lakes St Lawrence Seaway system, locations to which iron ores from northern Ontario, Québec, Labrador, Minnesota, Wisconsin and Michigan, and coal from Pennsylvania, West Virginia and Kentucky can be transported most economically. Also, they are the locations where the demand for steel is the greatest due to the heavy concentration of manufacturers. Many integrated steel plants, however, have been built throughout Canada wherever abundant scrap and a ready market for finished steel exists.
After oxygen, silicon and aluminium, iron is the fourth most plentiful element in Earth's crust. It occurs as iron minerals, the most important being magnetite, hematite, goethite, pyrrhotite, siderite, ilmenite and pyrite. Pyrite and pyrrhotite, although plentiful, are rarely used as iron ores because of the objectionable amounts of sulphur they contain. Canadian iron ores consist mostly of hematite or magnetite, and some siderite and ilmenite. Besides oxides of iron, the iron ores contained gangue, ie, those minerals not wanted in iron making (eg, quartz). The term "iron ore" is used when rock is sufficiently rich in iron minerals to be mined economically.
Iron-bearing rock may be upgraded to iron ore by removing gangue through concentration. This requires fine grinding of the ore to liberate the iron minerals from the gangue, followed by separation of the iron-rich from the gangue particles (eg, magnetic separation). The upgraded iron-rich material ("concentrate") must be agglomerated into larger lumps prior to smelting, either by tumbling it into pellets ("pelletizing") or by heating the concentrate until its particles stick together ("sintering").
Canada is the world's sixth-largest producer and fourth-largest exporter of iron ore. In 1995 the major producers were the Iron Ore Company of Canada, and Wabush Mines in Newfoundland; Compagnie Minière Québec Cartier in Québec, and Algoma Steel Inc-Algoma Ore Division in Ontario. These producers shipped 36.6 million t of iron ore valued at over $1 billion. The Québec-Labrador region accounts for most of Canada's total production; Ontario and BC produce the remainder (see Mineral Resources).
Coke is the partially graphitized solid residue left after the volatile components of bituminous coal are removed by heating in coke ovens. At regular intervals, ore, coke and stone are introduced through the top of the blast furnace. As they slowly descend down the furnace shaft, these materials ("burden") are heated by rising hot gases. The carbon monoxide in these gases reacts with the iron oxides in the ore to form metallic iron and carbon dioxide. The iron formed melts and, as it percolates through the coke column, dissolves carbon. By the time it reaches the hearth, it is saturated with carbon, and it also contains silicon, phosphorus, manganese and sulphur. The stone and ore form a low-melting, free-running liquid slag, which absorbs most of the sulphur entering the furnace (coke is the main sulphur source). Liquid slag, composed of gangue minerals and oxide components of stone, floats on the liquid iron and is separated from the molten metal during furnace tapping. The coke does not melt; it burns on contact with the pressured, preheated air ("blast") entering through the tuyères located just above the hearth.
Several solid-state reduction processes have been developed in which iron ore is converted to metallic iron without melting. Because there is no separation of iron from gangue in the reduction facility, high-grade ores or concentrates (>90% Fe) must be used. Many of these solid-state processes use natural gas as the fuel and as the reducing agent (carbon monoxide and hydrogen). Sidbec-Dosco operates such a process, known as the Midrex Process, at Contrecoeur, Qué.
Solid-state reduced ore and/or pellets, known as DRI (Direct Reduced Iron), are melted in electric arc furnaces and converted to steel in the same way as scrap metal. During the steelmaking process, the gangue in DRI is removed; the gangue minerals contained in DRI combine with the added lime to form a fluid slag. DRI is superior to scrap in purity and uniformity of composition but these benefits come at a higher cost.
Steel is an alloy of pure iron and carbon in which the carbon content varies from about 0.002% (eg, deep-drawing sheet metal) to 1.5% (eg, tool steels). Alloy steels contain additional elements (eg, manganese, nickel, chromium, vanadium, molybdenum) that give them greater strength and specific properties (eg, stainless steel is an alloy of chromium and nickel). In addition to carbon, hot metal and pig iron contain unwanted elements: silicon, phosphorus, and sulphur. During the steelmaking process, these deleterious elements, which make steel brittle, must be removed.
In the steelmaking, the hot metal, along with some scrap, is fed into a refractory-lined vessel ("converter"). Oxygen gas is then injected into the bath of hot metal. Also, lime is added to produce a slag that dissolves sulphur and other unwanted impurities, but does not corrode the converter lining. The injected oxygen gas oxidizes the carbon dissolved in the hot metal to form carbon monoxide and generate heat. When the carbon content of the molten bath drops to the desired level, alloying elements are added, and the liquid steel is tapped into a preheated ladle.
Scrap-based steel producers use electric arc furnaces. The scrap is charged into the furnace and three graphite electrodes descend through the furnace roof. As the electrodes approach the scrap, arcs form (high-voltage power). Due to its higher electrical resistance and to the intense heat radiated by these arcs, the scrap quickly heats to melting temperatures.
The liquid steel destined for demanding applications is further refined in ladle treatment units. The remaining impurities, such as sulphur, hydrogen, nitrogen, and non-metallic inclusions, are removed. The methods used include argon stirring, powder desuphurization, and vacuum degassing.
Some years ago, the majority of steel was cast into ingots. Ingots are large, rectangular blocks of steel, most of which are shaped subsequently into semi-finished products- blooms, slabs, billets or special shapes - by primary rolling or forging. Today, continuously casting (CC) is the principal way to solidify and shape liquid steel into semi-finished products. CC eliminates the primary operations. In the CC machine, liquid steel is poured into the top of a water-cooled, oscillating copper mould, and the slab, bloom or billet is discharged continuously from the bottom. In recent years, thin slab casting has gained favour as it eliminates several production steps. Some Canadian steel producers have thin slab casting machines, while others have plans to install them before the new millennium.
Hot and Cold Rolling
For the most part, slabs, blooms and billets are reduced in rolling mills to hot- and cold-rolled products such as plate, strip, rail, structural shapes, bar and wire rod. Some steels (eg, sheet, strip) are finished by cold rolling at room temperature to obtain close dimensional tolerances, high-quality surface finish and an exact degree of hardness.
Heat treatments include annealing, normalizing, quenching, and tempering. These treatments change the properties of steel by altering its microstructure (steel is crystalline in form).
Steel corrodes in many environments to which it is subjected. To slow the oxidation of steel (rusting) steel products are coated. The most common coatings include zinc, tin, aluminum, vitreous-enamel and organic coatings (eg, paint).
In Canada, the Forges Saint-Maurice, near Trois-Rivières, Qué, produced iron from local bog iron ore and charcoal to supply settlers and the military (see Blacksmithing). The first ironworks in Upper Canada, the Marmora Ironworks, near Peterborough, Ont, began production in 1822. It consisted of two charcoal-fired blast furnaces, a forge with two sets of water-powered hammers and special hearths for the production of iron bar. In the late 19th century both the Marmora and the St-Maurice ironworks were closed; they could no longer compete with more modern ironworks in Ontario and Nova Scotia, which employed coke-fired blast furnaces.
Steel products were first manufactured in Canada in the 1880s. By the early 1900s steelmaking centres had been established in Hamilton and Sault Ste Marie, Ont, and in Sydney, NS. Iron and steel production grew slowly until WWII and then rapidly as the post-war economic boom created a tremendous demand for steel.
The Bessemer Process, invented in England in 1856, was the first large-scale steelmaking process. This method was followed by the invention, a few years later, of the open-hearth process, which from about 1900 to the early 1960s accounted for most of the steel production in the world. By 1910 the Bessemer Process was no longer in use in North America.
The Basic Oxygen Process (BOP) - known first as the LD Process - originated in Austria. Dofasco Inc introduced the BOP to North America in 1954 and since then the dominant open-hearth process steadily declined, and none are in use today.
Canadians have made notable contributions to the advancement of the iron and steel industry. In the early 1960s Canadian Liquid Air designed an injector that made it possible to introduce pure oxygen through the bottom of BOP vessels. This method was developed to industrial scale in Germany (Q-BOP) in 1968. The first successful continuous casting machine for steel in North America was developed by Atlas Steels, Welland, Ont, in 1954.
In 1959 Stelco Inc introduced low slag volume blast furnace practice that decreased coke consumption by about 40%, saving the world over 200 million tons of coal a year. Stelco developed the Stelmor rod cooling process, and the Coilbox, a major energy saving device used in hot-strip rolling mills. Also, it developed the short annealing cycle, another energy saving development, universally adopted by the steel industry. And Stelco developed the Ardox spiral nail. Lasco developed a slit-rolling technique to make two bars from a single billet. Ipsco was the first company to install a spiral-weld pipe mill.
Projet Bessemer Inc, a consortium of Canadian steel producers and the National Research Council of Canada, has undertaken research into strip casting at Boucherville, Qué - the ultimate goal in steelmaking: one step from liquid steel to finished strip.
Craig Heron, Working in Steel, The Early Years in Canada, 1883-1935 (1988); A.R. Dunn, The Early History of Iron in Canada (1980); United States Steel, Association of Iron and Steel Engineers, The Making, Shaping and Treating of Steel (1985).