Iron & Steelmaking

See also Iron and Steel Alloys.

Introduction

Iron is the cheapest, most abundant and most useful of all metals.   It is used extensively to construct tools, fasteners, machinery, vehicles, bridges, buildings, and appliances.   Iron is ductile, malleable, machinable, and takes a high polish.   It can be melted and cast into forms and it can welded when hot.   Iron is used as a catalyst in the Haber Process for making ammonia.   Steel is an alloy of iron, carbon, and small amounts of other elements to make it stronger than iron.   Like iron, steel also is of ancient, unknown origin and was used to make simple drilling, digging and cutting tools in ancient Asian and North African cities.   The famous Toledo and Damascus sword blades of the Middle Ages were made of steel by hand, which made them very expensive.   Iron contains (usually) undesirable elements such as silicon, phosphorus, sulfur, and manganese.   In steel these impurities removed and replaced by more desirable elements, called steel alloys to impart special properties for special uses.

The iron produced by extraction from iron ores in a blast furnace is called pig iron.   It is an alloy containing about 3% carbon and varying amounts of sulfur, silicon, manganese, and phosphorus embedded in the ore along with the iron.   It is hard and brittle, so it is usually reworked to make other types of iron and steel with more desirable properties.   Cast iron is molten pig iron poured into a sand or clay mold of desired shape and allowed to harden to produce such items as pots, skillets, weights, and cannons.   Wrought iron contains only a few tenths of one percent of carbon and slag, which gives its fibrous structure.   It is tough, malleable, less fusible than pig iron, and has a fibrous structure that is easily worked by hand tools.   Wrought iron is annealed to free it from stress and toughen it.   Blacksmiths hand-worked pig iron into wrought iron, which they then reworked into useful articles.   Before steel became cheaper and came into common use, wrought iron was used for bridges, aqueducts, buildings and other high-load structures.   When the slag is removed in the steel-making process, wrought iron becomes low carbon steel.

Iron is found combined chemically with other elements and a mixture of other materials in an aggregate called iron ore.   In the earlier years of the U. S., enough iron ore could be found in most parts of the country to operate blast furnaces.   However, as the need for steel grew, larger iron ore deposits were needed.   The Marquette iron range on Michigan's Upper Peninsula, one of the largest concentrations of iron ore in the U.S., was discovered in 1844.   It furnished a plentiful supply of iron ore to the iron mills around the Great Lakes and the upper Ohio, Monongohela, and Allegheny Rivers.   Later, Minnesota became famous for its vast quantities of iron ore, e.g., the Mesabi and Vermillion Ranges.   Large deposits in Quebec & Labrador was also used by American and European steelmakers.   Iron is the fourth most abundant element making up the earth's crust.   Common ores are hematite, Fe₂O₃, and magnetite, Fe₃O₄, which is highly magnetic.   Other ores are ilmenite, FeTiO₃, limonite, HFeO₂ and FeO(OH), and siderite, FeCO₃.   Iron also occurs as sulfides, like pyrite, FeS₂ and FeS, which are more useful as sources of sulfur (S) and other metals associated with iron sulfides.   Iron ores are mined at the earth's surface and underground.   Iron ore can percolate to the top of marsh bogs, which were cheap iron ore sources in early America, when digging tools were simple and easily dulled with use.   Because iron readily combines chemically with other elements to form compounds, it is rarely found in pure form.   Iron oxides ("rust") damage iron when exposed to moist air.   Pure iron is attracted by magnets, but does not retain much of its magnetism after the magnet is removed.

Improvements to iron and steel production have reduced its costs and increased its strength, thus providing stronger and a cheaper construction material for buildings, bridges, machinery, and appliances, all of which use steel extensively, thus making steel products available to more people to improve general living standards.

The extracting of iron from iron ore is called smelting (= melting).   Iron melts at 1,536°C, which is too high for melting in a furnace, but the carbon content in the iron lowers the melting point to 1,150°C, which is low enough for the pig iron to melt and flow from the furnace when it is tapped.   Iron ore is combined with a fuel, such as charcoal or coke, a flux to carry off the waste products, such as limestone, and generous amounts of air, which provides oxygen.   Because iron has a relatively high melting point, charcoal and coke are used rather than wood and coal because they burn at temperatures sufficient to melt the ore.   The melted (smelted) iron falls to the bottom of the meld because it is heavier than the other constituents, which are oxides of calcium, magnesium and aluminum.   These form a mixture known as slag that floats on top of the melted iron and can be drawn off, reprocessed to extract the magnesium and aluminum, and then ground into gravel to fill holes in roads and pits.

The Reduction Process ^{How 275}

2C + O₂ ——> 2CO

[carbon from coke + oxygen from air yields cabron monoxide]

Fe₂O₃ + 3CO ——> 2Fe + 3CO₂

[iron oxide + carbon monoxide yields iron + carbon dioxide]

About 25% of the carbon monoxide is excess and can be used as a low-grade fuel.

The earliest method of obtaining wrought iron from iron ore was the bloomery method.   Its use is ancient, but it was practiced in early colonial America before iron furnaces were used.   In this method, iron ore is heated in a charcoal fire so that the ore becomes soft.   A hand bellows is used to force air with oxygen into the fire to increase the charcoal burning rate and fire temperature.   The iron "bloom" is then extracted and beaten with a blacksmith's hammer to drive off the non-iron impurities.   This method permitted production of only small amounts of iron with considerable hand labor by several ironmakers, so iron made in this way was expensive and used only for critical hand tools, like saws, axes, hammers, picks and drills.     The Coventry Iron Works was a notable bloomery in Pennsylvania.

Steel was made since ancient times by processes called cementation and the crucible method.   In cementation, bars of iron from a bloomery were heated with charcoal in a closed furnace so that the surface of the iron acquired a high carbon content from the charcoal, which was then hammered.   The crucible method softens the iron together in a fireclay and graphite crucible and then the iron bars are welded together by repeated hammering.   The famous sword blades of Damascus and of Toledo were made by the crucible and cementation methods.

The iron blast burnace was used in Europe since the 13th century, but not in American until the mid-17th century.   It is a more efficient process for extracting iron from iron ore than the bloomery method.   The furnace is a tall stone structure, shaped like a flattened pyramid.   Stone is able to withstand the high temperatures prevailing in the furnace.   A "flux", usually limestone (calcium carbonate) was used to separate the impurities from the iron.   The iron was extracted from the furnace periodically and cast into consumer, farm, or company products, or else it was cast into pig iron bars that were sold to blacksmiths and refinery forges, called "fineries".   The blast furnace separates iron from the other constituents of iron ore using a continuous blast of air to provide adequate oxygen.   Unheated air provides a "cold blast" and heated air provides a "hot blast".   The latter required an air heater, which added expense, but it did not require that the air be heated in the furnace, which is more efficient.   The fuel used was charcoal or coke.   An iron blast furnace extracts iron from iron ore in larger amounts with considerably less hand labor, so it is more efficient and cheaper than a bloomery.

A steel furnace used a cementation process to convert wrought iron into steel for use in springs, swords, and cutlery, where more resiliency and strength were required than could be provided by wrought iron.

A refinery forge transforms pig iron into wrought iron.   It was then forged by a hammer moved by the power of a water wheel into desired shapes, or sent to rolling or slitting mills to produce plates, bars, or nail rods. ^{NPS 7}

Steel was made by heating and burning off the carbon from the pig iron produced in a furnace to make wrought iron and then adding the required amount carbon in measured amounts.   It was a time-consuming, costly process requiring much hand work.   The Bessemer Process sent a strong blast of cold air through the molten iron to remove excess carbon.   Carbon could be added later in the required amounts.   A drawback to this method was that it required phosphorus-free iron ore, which was not always available.   Nevertheless, the Bessemer Converter made steel much cheaper and therefore more frequently used in the construction of buildings, railroads, locomotives, and ships.   It began the Steel Age. ^{Asimov 372}

The open-hearth uses a type of furnace called a regenerative furnace.   Instead of a firebox at one end and a flue at the other, it has devices at each end for the intake and outflow of both fuel and air. The air is preheated by a system of current reversals that causes very high temperatures.   This process uses iron ore and pig iron and, unlike the Bessemer process, is not affected by the sulfur in the iron ore. ^{Info n.p.}

The Basic Oxygen Process (Linz-Donawitz process) produces steel from a charge consisting mostly of pig iron.   The charge is placed in a furnace similar to the one used in the Bessemer process of steelmaking except that pure oxygen instead of air is blown into the charge to separate the iron from the ore.   This process takes less than an hour to produce iron, and is thus much faster than the open-hearth process.   A second advantage of this process is that a major byproduct is carbon monoxide, which can be used as a fuel or a consituent in producing various chemicals, such as acetic acid.   The basic oxygen process also produces less air pollution than methods using air. ^{Info n.p.}

To 1790

Iron is so important to an economy that before 1790 every U.S. state had iron furnaces:

The first iron furnace was established at Falling Creek, VA, in 1619. ^{Schles 37}

In 1642, Joseph Jencks, an English ironmaker, came to Lynn, MA to establish iron and brass works. ^{Carruth 17}

In 1644, an iron works was started on the Saugus R. near Lynn, MA.   The company was headed by colonial governor, John Winthrop. ^{Carruth 17}

In 1709, in England, Abraham Darby first used coke in place of charcoal as fuel for a blast furnace. ^{How 275}

Iron furnaces for smelting (melting) iron ore into pig iron were established in 1714 along the Rapidan River in Virginia by Governor Alexander Spotswood. ^{Carruth 47}   However, the British Iron Act prohibited further iron processing, reserving that for British ironmongers.   This restriction no longer existed in 1790 when the colonies were states under the U.S. Federal Government.

Pennsylvania was the largest iron-making state during colonial times.   The earliest furnace was established by Thomas Rutter in 1720 at Colebrookdale.   Earlier, in 1716, he established an iron bloomery near what is now Pottstown.   The first steel furnace was Coventry Iron Works at Coventry, built in 1732 by Samuel Nutt.   In 1770, Mark Bird built Hopewell Furnace near what is now Morgantown.   Between 1716 and 1776, at least 21 blast furnaces, 45 forges, 4 bloomeries, 6 steel furnaces, 3 slitting mills, 2 plate mills, and 1 wire mill were built in the Pennsylvania colony.   Some of the furnaces formed the nucleus of an entire community, such as at Hopewell and Ringwood.   They were called "plantations", like their southern counterparts, with worker homes, a boarding house, a company store, a farm, church, a "Big House" for the ironmaster, complete with servants, and sometime a modest elementary school.   They were the first of what we now call "company towns". ^{NPS 8,9}

The Principio furnace was established before 1720 at the Chesapeake Bay in Virginia.

In the mid-18th century, Peter Hasenclever, from Germany imported hundreds of German ironworkers into the mountains of northwestern New Jersey for build and work iron furnaces for British investors. ^{NPS 7}   Its center is located at Ringwood Manor.

In 1768, in England, John Wilkinson, first used steam power to produce an air blast instead of a bellows to force air into a blast furnace, thus making it more efficient. ^{How 275}< /p>

By 1776, Massachusetts had 14 blast furnaces, 41 forges, several plate and rod mills, and one steel furnace. ^{NPS 7}

1790-1799

1800-1809

1810-1819

1820-1829

In 1828, in Glasgow, Scotland, James Neilson for the first time used preheated air in the blast for the furnace. ^{How 275}

1830-1839

In 1831, in Germany, ironmakers used the hot gases produced in the reduction process to heat the air blast. ^{How 275}

1840-1849

1850-1859

In 1856, the British metallurgist, Henry Bessemer, invented the Bessemer Process for making steel.

1860-1869

In the U.S., the Bessemer process was first used in Michigan in 1865. ^{Schles 292}

The open-hearth process was invented around 1866 by the Englishman, Sir William Siemens.

In 1868, Abram S. Hewitt of Trenton, NJ, introduced the open-hearth method of producing steel, which was invented in England.   This process made more steel available by the extraction of sulfur and phosphorus from the ore. ^{Carruth 299}

1870-1879

1880-1889

1890-1899

1900-1909

1910-1919

1920-1929

1930-1939

1940-1949

1950-1959

The Basic Oxygen Process (Linz-Donawitz process) was invented in the 1950s.

1960-1969

1970-1979

1980-1989

1990-1999