Manufacture of Steel

“Steel has been part of some of the greatest achievements in history: It was the "iron horse" and steel rails that helped carve a nation out of the frontier. Steel is the backbone of bridges, the skeleton of skyscrapers, the framework for automobiles. And at the dawn of the 21st century, it's still revolutionizing the way we live. It is the high-strength, lighter-than-plastic frames for eyeglasses; it's the stronger, more durable frame in housing; it's the high-tech alloy used in the Space Shuttle's solid fuel rocket motor cases; and it's the precise surgical instruments used in hospital operating rooms around the world.” (American Iron and Steel Institute 2002) Yes steel today is in just about everything we use today. Steel too has changed over the years.
“Iron has been a vital material in technology for well over three thousand years. But until the Industrial Revolution, its mining, smelting, and working were largely done by individuals and small groups. Known since ancient times, steel is made by alloying iron with carbon to produce a harder, stronger metal that will take a much keener edge. But steel was very expensive to manufacture by the primitive methods then available, and its use was largely confined to high-value specialty products such as swords and precision instruments.” (Garraty 1991) “Steel making (in the 18th century) was a laborious and time-consuming process. Flat bars of iron were laid in a furnace chest, side by side on a bed of charcoal. The bars were the covered with charcoal, another layer of iron bars was placed on top of that and the process was repeated until the chest was full. It was then placed in the furnace, covered with a layer of sand and cooked red-hot for a week. During this time the carbon from the charcoal was absorbed into the outer layers of the iron, the carbonized areas forming blisters on the surface of the bars. When the chest was removed and had cooled down, these blisters were hammered off, and the pieces reheated and hammered together. The resultant “blister” steel was brittle and difficult to work.” (Burke 1996) The Blast furnace technique came some time after this. The blast furnace, which consisted of blowing steam or air through molten iron, had become widely used by the ninetieth century. Along came a man by the name Henry Bessemer who would invent a new way to produce steel using the blast method called the Bessemer process, “the most important technique for making steel in the nineteenth century.” (Misa 1995) He first came across this while melting gun metal down. “Bessemer built a crucible with a blow pipe extended into its center. Into the crucible he poured about 10 pounds of unrefined pig iron and then placed the apparatus into a hot furnace; after 30 minutes of blowing air into the metal, he found the crude iron had become malleable iron. This experiment proved air could decarburize pig iron, turning it into a useful product, yet the furnace surrounding the crucible still consumed copious amounts of fuel. Bessemer's real insight was to get rid of the furnace entirely. For this he built a four-foot tall, open-mouthed cylinder with openings, or tuyères, to blow air into the metal from the bottom.” (Misa 1995) “Acceptance of the process was slow at first, so that by 1870 the annual output of Bessemer steel in the United States was a mere 42,000 tons. Production grew rapidly thereafter, rising to 1.2 million tons in 1880. The principal application of Bessemer steel in the 19th century was for the manufacture of railroad rails, which proved far more durable than iron rails. By the 1890s virtually no more iron rails were being produced.”

Basic Oxygen-Furnace Process
The
basic oxygen furnace, roughly resembling the Bessemer converter, is first tilted to receive the scrap and hot-metal charge, then brought upright for the blow. An oxygen lance is lowered into the vessel to a point about 2.5 m (6 ft) above the charge materials. Oxygen under pressure is blown into the furnace for a predetermined length of time, usually 20 to 22 minutes. Consumption of oxygen averages 50 cu m (1766 cu ft) per ton of steel produced. The time to charge, test, and tap is generally equal to the blowing interval: a full cycle is about 45 minutes.

The Electric-Arc Furnace

A large bucket of scrap is charged into the open top of the furnace when the roof assembly has been swung out of the way. With the assembly back in place, three carbon electrodes are lowered through holes in the roof until they are in near contact with the charge. When the power is switched on, arc temperatures approaching 3,300 degrees C (6,000 degrees F) produce a rapid melting of the charge. A second bucket of scrap is usually needed to meet the desired heat weight. Oxygen is often used to accelerate scrap meltdown. When the specified steel requirements are met, the furnace is tilted to tap the heat into a waiting ladle.

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