Wrought iron is an
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...
with a very low
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
content (less than 0.08%) in contrast to that of
cast iron
Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
(2.1% to 4%). It is a semi-fused mass of iron with fibrous
slag
Slag is a by-product of smelting (pyrometallurgical) ores and used metals. Broadly, it can be classified as ferrous (by-products of processing iron and steel), ferroalloy (by-product of ferroalloy production) or non-ferrous/base metals (by-prod ...
inclusions (up to 2% by weight), which give it a wood-like "grain" that is visible when it is etched, rusted, or bent to
failure
Failure is the state or condition of not meeting a desirable or intended objective (goal), objective, and may be viewed as the opposite of Success (concept), success. The criteria for failure depends on context, and may be relative to a parti ...
. Wrought iron is tough, malleable,
ductile
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
,
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
resistant, and easily
forge welded, but is more difficult to
weld electrically.
Before the development of effective methods of
steelmaking
Steelmaking is the process of producing steel from iron ore and carbon/or scrap. In steelmaking, impurities such as nitrogen, silicon, phosphorus, sulfur and excess carbon (the most important impurity) are removed from the sourced iron, and all ...
and the availability of large quantities of steel, wrought iron was the most common form of malleable iron. It was given the name ''wrought'' because it was hammered, rolled, or otherwise worked while hot enough to expel molten slag. The modern functional equivalent of wrought iron is
mild steel
Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:
* no minimum content is specified or required for chromium, cobalt ...
, also called low-carbon steel. Neither wrought iron nor mild steel contain enough carbon to be hardenable by heating and quenching.
Wrought iron is highly refined, with a small amount of silicate slag forged out into fibres. It comprises around 99.4% iron by mass. The presence of slag can be beneficial for blacksmithing operations, such as forge welding, since the silicate inclusions act as a
flux
Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...
and give the material its unique, fibrous structure. The silicate filaments in the slag also protect the iron from corrosion and diminish the effect of fatigue caused by shock and vibration.
Historically, a modest amount of wrought iron was refined into
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
, which was used mainly to produce
sword
A sword is an edged, bladed weapon intended for manual cutting or thrusting. Its blade, longer than a knife or dagger, is attached to a hilt and can be straight or curved. A thrusting sword tends to have a straighter blade with a pointed ti ...
s,
cutlery
Cutlery (also referred to as silverware, flatware, or tableware), includes any hand implement used in preparing, serving, and especially eating food in Western culture. A person who makes or sells cutlery is called a cutler. The city of Sheffie ...
,
chisel
A chisel is a tool with a characteristically shaped cutting edge (such that wood chisels have lent part of their name to a particular grind) of blade on its end, for carving or cutting a hard material such as wood, stone, or metal by hand, stru ...
s,
axe
An axe ( sometimes ax in American English; see spelling differences) is an implement that has been used for millennia to shape, split and cut wood, to harvest timber, as a weapon, and as a ceremonial or heraldic symbol. The axe has ma ...
s, and other edged tools, as well as springs and files. The demand for wrought iron reached its peak in the 1860s, being in high demand for
ironclad warship
An ironclad is a steam-propelled warship protected by iron or steel armor plates, constructed from 1859 to the early 1890s. The ironclad was developed as a result of the vulnerability of wooden warships to explosive or incendiary shells. Th ...
s and
railway
Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...
use. However, as properties such as brittleness of
mild steel
Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:
* no minimum content is specified or required for chromium, cobalt ...
improved with better
ferrous metallurgy
Ferrous metallurgy is the metallurgy of iron and its alloys. The earliest surviving prehistoric iron artifacts, from the 4th millennium BC in Egypt, were made from meteoritic iron-nickel. It is not known when or where the smelting of iron from ...
and as
steel became less costly to make thanks to the
Bessemer process
The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is steelmaking, removal of impurities from the iron by ox ...
and the
Siemens-Martin process, the use of wrought iron declined.
Many items, before they came to be made of
mild steel
Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:
* no minimum content is specified or required for chromium, cobalt ...
, were produced from wrought iron, including
rivets
A rivet is a permanent mechanical fastener. Before being installed, a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite to the head is called the ''tail''. On installation, the rivet is placed in a punched o ...
,
nails,
wire
Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm
A wire is a flexible strand of metal.
Wire is c ...
,
chains
A chain is a serial assembly of connected pieces, called links, typically made of metal, with an overall character similar to that of a rope in that it is flexible and curved in compression but linear, rigid, and load-bearing in tension. A c ...
,
rails
Rail or rails may refer to:
Rail transport
*Rail transport and related matters
*Rail (rail transport) or railway lines, the running surface of a railway
Arts and media Film
* ''Rails'' (film), a 1929 Italian film by Mario Camerini
* ''Rail'' ( ...
,
railway coupling
A coupling (or a coupler) is a mechanism typically placed at each end of a railway vehicle that connects them together to form a train. A variety of coupler types have been developed over the course of railway history. Key issues in their desig ...
s,
water and steam pipes,
nuts,
bolts,
horseshoe
A horseshoe is a fabricated product designed to protect a horse hoof from wear. Shoes are attached on the palmar surface (ground side) of the hooves, usually nailed through the insensitive hoof wall that is anatomically akin to the human toen ...
s,
handrail
A handrail is a rail that is designed to be grasped by the hand so as to provide safety or support. In Britain, handrails are referred to as banisters. Handrails are usually used to provide support for body or to hold clothings in a bathroom or ...
s, wagon tires, straps for timber
roof truss
A timber roof truss is a structural framework of timbers designed to bridge the space above a room and to provide support for a roof. Trusses usually occur at regular intervals, linked by longitudinal timbers such as purlins. The space between each ...
es, and
ornamental ironwork
Ironwork is any weapon, artwork, utensil, or architectural feature made of iron, especially one used for decoration. There are two main types of ironwork: wrought iron and cast iron. While the use of iron dates as far back as 4000BC, it was th ...
, among many other things.
Wrought iron is no longer produced on a commercial scale. Many products described as wrought iron, such as
guard rail
Guard rail, guardrails, or protective guarding, in general, are a boundary feature and may be a means to prevent or deter access to dangerous or off-limits areas while allowing light and visibility in a greater way than a fence. Common shapes ...
s,
garden furniture
Garden furniture, also called patio furniture or outdoor furniture, is a type of furniture specifically designed for outdoor use. It is typically made of weather-resistant materials such as aluminium which is rust-proof.
History
The oldes ...
, and
gate
A gate or gateway is a point of entry to or from a space enclosed by walls. The word derived from old Norse "gat" meaning road or path; But other terms include ''yett and port''. The concept originally referred to the gap or hole in the wall ...
s are made of mild steel.
They retain that description, because they are made to resemble objects which in the past were wrought (worked) by hand by a
blacksmith
A blacksmith is a metalsmith who creates objects primarily from wrought iron or steel, but sometimes from #Other metals, other metals, by forging the metal, using tools to hammer, bend, and cut (cf. tinsmith). Blacksmiths produce objects such ...
(although many decorative iron objects, including fences and gates, were often cast rather than wrought).
Terminology
The word "wrought" is an archaic past participle of the verb "to work," and so "wrought iron" literally means "worked iron". Wrought iron is a general term for the commodity, but is also used more specifically for finished iron goods, as manufactured by a
blacksmith
A blacksmith is a metalsmith who creates objects primarily from wrought iron or steel, but sometimes from #Other metals, other metals, by forging the metal, using tools to hammer, bend, and cut (cf. tinsmith). Blacksmiths produce objects such ...
. It was used in that narrower sense in
British
British may refer to:
Peoples, culture, and language
* British people, nationals or natives of the United Kingdom, British Overseas Territories, and Crown Dependencies.
** Britishness, the British identity and common culture
* British English, ...
Customs
Customs is an authority or agency in a country responsible for collecting tariffs and for controlling the flow of goods, including animals, transports, personal effects, and hazardous items, into and out of a country. Traditionally, customs ...
records, such manufactured iron was subject to a higher rate of duty than what might be called "unwrought" iron.
Cast iron
Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
, unlike wrought iron, is brittle and cannot be worked either hot or cold. Cast iron can break if struck with a hammer.
In the 17th, 18th, and 19th centuries, wrought iron went by a wide variety of terms according to its form, origin, or quality.
While the
bloomery
A bloomery is a type of metallurgical furnace once used widely for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. Bloomeries produce a porous mass of iron and slag called a ''bloom ...
process produced wrought iron directly from ore,
cast iron
Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
or
pig iron
Pig iron, also known as crude iron, is an intermediate product of the iron industry in the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with silic ...
were the starting materials used in the
finery forge
A finery forge is a forge used to produce wrought iron from pig iron by decarburization in a process called "fining" which involved liquifying cast iron in a fining hearth and removing carbon from the molten cast iron through oxidation. Finery ...
and
puddling furnace
Puddling is the process of converting pig iron to bar (wrought) iron in a coal fired reverberatory furnace. It was developed in England during the 1780s. The molten pig iron was stirred in a reverberatory furnace, in an oxidizing environment, ...
. Pig iron and cast iron have higher carbon content than wrought iron, but have a lower melting point than iron or steel. Cast and especially pig iron have excess slag which must be at least partially removed to produce quality wrought iron. At
foundries
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal into a mold, and removing the mold material after the metal has solidified as it cools. The most common metals pr ...
it was common to blend scrap wrought iron with cast iron to improve the physical properties of castings.
For several years after the introduction of Bessemer and open hearth steel, there were different opinions as to what differentiated iron from steel; some believed it was the chemical composition and others that it was whether the iron heated sufficiently to melt and "fuse". Fusion eventually became generally accepted as relatively more important than composition below a given low carbon concentration.
Another difference is that steel can be hardened by
heat treating
Heat treating (or heat treatment) is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also ...
.
Historically, wrought iron was known as "commercially pure iron",
however, it no longer qualifies because current standards for commercially pure iron require a carbon content of less than 0.008
wt%.
Types and shapes
Bar iron is a generic term sometimes used to distinguish it from cast iron. It is the equivalent of an ingot of cast metal, in a convenient form for handling, storage, shipping and further working into a finished product.
The bars were the usual product of the
finery forge
A finery forge is a forge used to produce wrought iron from pig iron by decarburization in a process called "fining" which involved liquifying cast iron in a fining hearth and removing carbon from the molten cast iron through oxidation. Finery ...
, but not necessarily made by that process.
* Rod iron—cut from flat bar iron in a
slitting mill
The slitting mill was a watermill for slitting bars of iron into rods. The rods then were passed to nailers who made the rods into nails, by giving them a point and head.
The slitting mill was probably invented near Liège in what is now Belg ...
provided the raw material for spikes and nails.
* Hoop iron—suitable for the hoops of barrels, made by passing rod iron through rolling dies.
* Plate iron—sheets suitable for use as
boiler
A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central h ...
plate.
*
Blackplate—sheets, perhaps thinner than plate iron, from the black rolling stage of
tinplate
Tinplate consists of sheets of steel coated with a thin layer of tin to impede rusting. Before the advent of cheap milled steel, the backing metal was wrought iron. While once more widely used, the primary use of tinplate now is the manufacture of ...
production.
* Voyage iron—narrow flat bar iron, made or cut into bars of a particular weight, a commodity for sale in
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
for the
Atlantic slave trade
The Atlantic slave trade, transatlantic slave trade, or Euro-American slave trade involved the transportation by slave traders of enslaved African people, mainly to the Americas. The slave trade regularly used the triangular trade route and i ...
. The number of bars per ton gradually increased from 70 per ton in the 1660s to 75–80 per ton in 1685 and "near 92 to the ton" in 1731.
Origin
* Charcoal iron—until the end of the 18th century, wrought iron was smelted from ore using charcoal, by the
bloomery
A bloomery is a type of metallurgical furnace once used widely for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. Bloomeries produce a porous mass of iron and slag called a ''bloom ...
process. Wrought iron was also produced from
pig iron
Pig iron, also known as crude iron, is an intermediate product of the iron industry in the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with silic ...
using a
finery forge
A finery forge is a forge used to produce wrought iron from pig iron by decarburization in a process called "fining" which involved liquifying cast iron in a fining hearth and removing carbon from the molten cast iron through oxidation. Finery ...
or in a
Lancashire hearth
The Lancashire hearth was used to fine pig iron, removing carbon to produce wrought iron.
Origins
Until the early 19th century, the usual method of producing wrought iron involved a charcoal-fired finery in a finery forge. In the beginning of ...
. The resulting metal was highly variable, both in chemistry and slag content.
*
Puddled iron—the
puddling process was the first large-scale process to produce wrought iron. In the puddling process, pig iron is refined in a
reverberatory furnace
A reverberatory furnace is a metallurgical or process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases. The term ''reverberation'' is used here in a generic sense of ''re ...
to prevent contamination of the iron from the sulfur in the coal or coke. The molten pig iron is manually stirred, exposing the iron to atmospheric oxygen, which decarburizes the iron. As the iron is stirred, globs of wrought iron are collected into balls by the stirring rod (rabble arm or rod) and those are periodically removed by the puddler. Puddling was patented in 1784 and became widely used after 1800. By 1876, annual production of puddled iron in the UK alone was over 4 million tons. Around that time, the
open hearth furnace
An open-hearth furnace or open hearth furnace is any of several kinds of industrial Industrial furnace, furnace in which excess carbon and other impurities are burnt out of pig iron to Steelmaking, produce steel. Because steel is difficult to ma ...
was able to produce steel of suitable quality for structural purposes, and wrought iron production went into decline.
*
Oregrounds iron
Oregrounds iron was a grade of iron that was regarded as the best grade available in 18th century England. The term was derived from the small Swedish city of Öregrund, the port from which the bar iron was shipped. It was produced using the Wal ...
—a particularly pure grade of bar iron made ultimately from
iron ore
Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the fo ...
from the
Dannemora mine in
Sweden
Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
. Its most important use was as the raw material for the
cementation process
The cementation process is an obsolete technology for making steel by carburization of iron. Unlike modern steelmaking, it increased the amount of carbon in the iron. It was apparently developed before the 17th century. Derwentcote Steel F ...
of steelmaking.
* Danks iron—originally iron imported to Great Britain from
Gdańsk
Gdańsk ( , also ; ; csb, Gduńsk;Stefan Ramułt, ''Słownik języka pomorskiego, czyli kaszubskiego'', Kraków 1893, Gdańsk 2003, ISBN 83-87408-64-6. , Johann Georg Theodor Grässe, ''Orbis latinus oder Verzeichniss der lateinischen Benen ...
, but in the 18th century more probably the kind of iron (from eastern Sweden) that once came from Gdańsk.
* Forest iron—iron from the English
Forest of Dean
The Forest of Dean is a geographical, historical and cultural region in the western part of the county of Gloucestershire, England. It forms a roughly triangular plateau bounded by the River Wye to the west and northwest, Herefordshire to the n ...
, where
haematite ore enabled tough iron to be produced.
* Lukes iron—iron imported from
Liège
Liège ( , , ; wa, Lîdje ; nl, Luik ; german: Lüttich ) is a major city and municipality of Wallonia and the capital of the Belgian province of Liège.
The city is situated in the valley of the Meuse, in the east of Belgium, not far from b ...
, whose Dutch name is "Luik."
* Ames iron or amys iron—another variety of iron imported to England from northern Europe. Its origin has been suggested to be
Amiens
Amiens (English: or ; ; pcd, Anmien, or ) is a city and commune in northern France, located north of Paris and south-west of Lille. It is the capital of the Somme department in the region of Hauts-de-France. In 2021, the population of ...
, but it seems to have been imported from
Flanders
Flanders (, ; Dutch: ''Vlaanderen'' ) is the Flemish-speaking northern portion of Belgium and one of the communities, regions and language areas of Belgium. However, there are several overlapping definitions, including ones related to culture, ...
in the 15th century and
Holland
Holland is a geographical regionG. Geerts & H. Heestermans, 1981, ''Groot Woordenboek der Nederlandse Taal. Deel I'', Van Dale Lexicografie, Utrecht, p 1105 and former province on the western coast of the Netherlands. From the 10th to the 16th c ...
later, suggesting an origin in the
Rhine
), Surselva, Graubünden, Switzerland
, source1_coordinates=
, source1_elevation =
, source2 = Rein Posteriur/Hinterrhein
, source2_location = Paradies Glacier, Graubünden, Switzerland
, source2_coordinates=
, so ...
valley. Its origins remain controversial.
* Botolf iron or Boutall iron—from
Bytów
Bytów (; csb, Bëtowò; formerly german: Bütow ) is a town in the Gdańsk Pomerania region of northern Poland with 16,730 inhabitants as of December 2021. It is the capital of Bytów County in the Pomeranian Voivodeship.
The origins of Byt ...
(Polish
Pomerania
Pomerania ( pl, Pomorze; german: Pommern; Kashubian: ''Pòmòrskô''; sv, Pommern) is a historical region on the southern shore of the Baltic Sea in Central Europe, split between Poland and Germany. The western part of Pomerania belongs to ...
) or
Bytom
Bytom (Polish pronunciation: ; Silesian: ''Bytōm, Bytōń'', german: Beuthen O.S.) is a city in Upper Silesia, in southern Poland. Located in the Silesian Voivodeship of Poland, the city is 7 km northwest of Katowice, the regional capital ...
(Polish
Silesia
Silesia (, also , ) is a historical region of Central Europe that lies mostly within Poland, with small parts in the Czech Republic and Germany. Its area is approximately , and the population is estimated at around 8,000,000. Silesia is split ...
).
* Sable iron (or Old Sable)—iron bearing the mark (a
sable
The sable (''Martes zibellina'') is a species of marten, a small omnivorous mammal primarily inhabiting the forest environments of Russia, from the Ural Mountains throughout Siberia, and northern Mongolia. Its habitat also borders eastern Kaza ...
) of the
Demidov
The House of Demidov (russian: Деми́довы) also Demidoff, was a prominent Russian Empire, Russian noble family during the 18th and 19th centuries. Originating in the city of Tula, Russia, Tula in the 17th century, the Demidovs found suc ...
family of
Russia
Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
n
ironmaster
An ironmaster is the manager, and usually owner, of a forge or blast furnace for the processing of iron. It is a term mainly associated with the period of the Industrial Revolution, especially in Great Britain.
The ironmaster was usually a large ...
s, one of the better brands of
Russian iron.
Quality
;Tough iron: Also spelled "tuf", is not brittle and is strong enough to be used for tools.
;Blend iron: Made using a mixture of different types of
pig iron
Pig iron, also known as crude iron, is an intermediate product of the iron industry in the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with silic ...
.
;Best iron: Iron put through several stages of piling and rolling to reach the stage regarded (in the 19th century) as the best quality.
;Marked bar iron: Made by members of the
Marked Bar Association
In linguistics and social sciences, markedness is the state of standing out as nontypical or divergent as opposed to regular or common. In a marked–unmarked relation, one term of an opposition is the broader, dominant one. The dominant defau ...
and marked with the maker's brand mark as a sign of its quality.
Defects
Wrought iron is a form of commercial iron containing less than 0.10% of carbon, less than 0.25% of impurities total of sulfur, phosphorus, silicon and manganese, and less than 2% slag by weight.
Wrought iron is ''
redshort Red-short, hot-short refers to brittleness of steels at red-hot temperatures. It is often caused by high sulfur levels, in which case it is also known as sulfur embrittlement.
Description
Iron or steel, when heated to above 900 °F (460 ...
'' or ''hot short'' if it contains sulfur in excess quantity. It has sufficient tenacity when cold, but cracks when bent or finished at a red heat.
Hot short iron was considered unmarketable.
''Cold short'' iron, also known as ''coldshear'', ''colshire'', contains excessive phosphorus. It is very brittle when cold and cracks if bent.
It may, however, be worked at high temperature. Historically, coldshort iron was considered sufficient for
nails.
Phosphorus is not necessarily detrimental to iron. Ancient Near Eastern smiths did not add lime to their furnaces. The absence of
calcium oxide
Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, Caustic (substance), caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime (material), lime''" co ...
in the slag, and the deliberate use of wood with high phosphorus content during the smelting, induces a higher phosphorus content (typically <.3%) than in modern iron (<.02-.03%).
Analysis of the
Iron Pillar of Delhi
The iron pillar of Delhi is a structure high with a diameter that was constructed by Chandragupta II (reigned c. 375–415 AD), and now stands in the Qutb complex at Mehrauli in Delhi, India.Finbarr Barry Flood, 2003"Pillar, palimpsets, and pr ...
gives 0.11% in the iron.
The included slag in wrought iron also imparts corrosion resistance.
The presence of phosphorus (without carbon) produces a ductile iron suitable for
wire drawing
Wire drawing is a metalworking process used to reduce the cross-section of a wire by pulling the wire through a single, or series of, drawing die(s). There are many applications for wire drawing, including electrical wiring, cables, tension-lo ...
for
piano
The piano is a stringed keyboard instrument in which the strings are struck by wooden hammers that are coated with a softer material (modern hammers are covered with dense wool felt; some early pianos used leather). It is played using a keyboa ...
wire.
History
Western world
![Chinese fining](https://upload.wikimedia.org/wikipedia/commons/c/c4/Chinese_fining.png)
Wrought iron has been used for many centuries, and is the "iron" that is referred to throughout Western history. The other form of iron,
cast iron
Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
, was in use in China since ancient times but was not introduced into Western Europe until the 15th century; even then, due to its brittleness, it could be used for only a limited number of purposes. Throughout much of the Middle Ages, iron was produced by the direct reduction of ore in manually operated
bloomeries, although
water power
Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water to produce electricity or to power machines. This is achieved by converting the gravitational potential or kinetic energy of a wa ...
had begun to be employed by 1104.
The raw material produced by all indirect processes is pig iron. It has a high carbon content and as a consequence, it is brittle and cannot be used to make hardware. The
osmond process
Osmond iron (also spelt osmund and also called osborn) was wrought iron made by a particular process. This is associated with the first European production of cast iron in furnaces such as Lapphyttan in Sweden.
Osmonds appear in some of the ear ...
was the first of the indirect processes, developed by 1203, but bloomery production continued in many places. The process depended on the development of the blast furnace, of which medieval examples have been discovered at
Lapphyttan
Lapphyttan or Lapphyttejarn in Norberg Municipality, Sweden, may be regarded as the type site for the Medieval Blast Furnace. Its date is probably between 1150 and 1350. It produced cast iron, which was then fined to make ferritic wrought iron c ...
, Sweden and in
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
.
The bloomery and osmond processes were gradually replaced from the 15th century by
finery processes, of which there were two versions, the German and Walloon. They were in turn replaced from the late 18th century by
puddling, with certain variants such as the Swedish
Lancashire process. Those, too, are now obsolete, and wrought iron is no longer manufactured commercially.
China
During the Han dynasty (202 BC – 220 AD), new iron smelting processes led to the manufacture of new wrought iron implements for use in agriculture, such as the
multi-tube seed drill and
iron plough. In addition to accidental lumps of low-carbon wrought iron produced by excessive injected air in ancient Chinese
cupola furnace
A cupola or cupola furnace is a melting device used in foundries that can be used to melt cast iron, Ni-resist iron and some bronzes. The cupola can be made almost any practical size. The size of a cupola is expressed in diameters and can range f ...
s. The ancient Chinese created wrought iron by using the
finery forge
A finery forge is a forge used to produce wrought iron from pig iron by decarburization in a process called "fining" which involved liquifying cast iron in a fining hearth and removing carbon from the molten cast iron through oxidation. Finery ...
at least by the 2nd century BC, the earliest specimens of
cast
Cast may refer to:
Music
* Cast (band), an English alternative rock band
* Cast (Mexican band), a progressive Mexican rock band
* The Cast, a Scottish musical duo: Mairi Campbell and Dave Francis
* ''Cast'', a 2012 album by Trespassers William
* ...
and
pig iron
Pig iron, also known as crude iron, is an intermediate product of the iron industry in the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with silic ...
fined into wrought iron and
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
found at the early Han Dynasty site at Tieshengguo.
Pigott speculates that the finery forge existed in the previous
Warring States period
The Warring States period () was an era in History of China#Ancient China, ancient Chinese history characterized by warfare, as well as bureaucratic and military reforms and consolidation. It followed the Spring and Autumn period and concluded ...
(403–221 BC), due to the fact that there are wrought iron items from China dating to that period and there is no documented evidence of the
bloomery
A bloomery is a type of metallurgical furnace once used widely for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. Bloomeries produce a porous mass of iron and slag called a ''bloom ...
ever being used in China.
The fining process involved liquifying cast iron in a fining hearth and
removing carbon from the molten cast iron through
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
.
Wagner writes that in addition to the Han Dynasty hearths believed to be fining hearths, there is also pictorial evidence of the fining hearth from a
Shandong
Shandong ( , ; ; alternately romanized as Shantung) is a coastal province of the People's Republic of China and is part of the East China region.
Shandong has played a major role in Chinese history since the beginning of Chinese civilizati ...
tomb mural dated 1st to 2nd century AD, as well as a hint of written evidence in the 4th century AD Daoist text ''
Taiping Jing
''Taipingjing'' ("Scriptures of the Great Peace") is the name of several different Taoist texts. At least two works were known by this title:
:*, 12 Chapters, contents unknown, author: Gan Zhongke
:*, 170 Chapters, only 57 of which survive v ...
''.
Bloomery process
Wrought iron was originally produced by a variety of smelting processes, all described today as "bloomeries". Different forms of bloomery were used at different places and times. The bloomery was charged with
charcoal
Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, cal ...
and iron ore and then lit. Air was blown in through a
tuyere
A tuyere or tuyère (; ) is a tube, nozzle or pipe through which air is blown into a furnace or hearth.W. K. V. Gale, The iron and Steel industry: a dictionary of terms (David and Charles, Newton Abbot 1972), 216–217.
Air or oxygen is in ...
to heat the bloomery to a temperature somewhat below the melting point of iron. In the course of the smelt, slag would melt and run out, and
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
from the charcoal would reduce the ore to iron, which formed a spongy mass (called a "bloom") containing iron and also molten silicate minerals (slag) from the ore. The iron remained in the solid state. If the bloomery were allowed to become hot enough to melt the iron, carbon would dissolve into it and form pig or cast iron, but that was not the intention. However, the design of a bloomery made it difficult to reach the melting point of iron and also prevented the concentration of carbon monoxide from becoming high.
After smelting was complete, the bloom was removed, and the process could then be started again. It was thus a batch process, rather than a continuous one such as a blast furnace. The bloom had to be forged mechanically to consolidate it and shape it into a bar, expelling slag in the process.
During the
Middle Ages
In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire a ...
, water-power was applied to the process, probably initially for powering bellows, and only later to hammers for forging the blooms. However, while it is certain that water-power was used, the details remain uncertain.
That was the culmination of the direct process of ironmaking. It survived in
Spain
, image_flag = Bandera de España.svg
, image_coat = Escudo de España (mazonado).svg
, national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond")
, national_anthem = (English: "Royal March")
, i ...
and southern
France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
as Catalan Forges to the mid 19th century, in
Austria
Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
as the ''stuckofen'' to 1775,
and near
Garstang
Garstang is an ancient market town and civil parish within the Wyre borough of Lancashire, England. It is north of the city of Preston and the same distance south of Lancaster.
In 2011, the parish had a total resident population of 4,268; ...
in England until about 1770; it was still in use with
hot blast
Hot blast refers to the preheating of air blown into a blast furnace or other metallurgical process. As this considerably reduced the fuel consumed, hot blast was one of the most important technologies developed during the Industrial Revolution. ...
in
New York
New York most commonly refers to:
* New York City, the most populous city in the United States, located in the state of New York
* New York (state), a state in the northeastern United States
New York may also refer to:
Film and television
* '' ...
in the 1880s. In
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
the last of the old ''
tatara'' bloomeries used in production of traditional
tamahagane
''Tamahagane'' (玉鋼) is a type of steel made in the Japanese tradition. The word ''tama'' means "precious". The word ''hagane'' means "steel". Tamahagane is used to make Japanese swords, knives, and other kinds of tools.
The carbon content ...
steel, mainly used in swordmaking, was extinguished only in 1925, though in the late 20th century the production resumed on a low scale to supply the steel to the artisan swordmakers.
Osmond process
Osmond iron
Osmond iron (also spelt osmund and also called osborn) was wrought iron made by a particular process. This is associated with the first European production of cast iron in furnaces such as Lapphyttan in Sweden.
Osmonds appear in some of the ear ...
consisted of balls of wrought iron, produced by melting pig iron and catching the droplets on a staff, which was spun in front of a blast of air so as to expose as much of it as possible to the air and oxidise its carbon content. The resultant ball was often forged into bar iron in a hammer mill.
Finery process
In the 15th century, the
blast furnace
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. ''Blast'' refers to the combustion air being "forced" or supplied above atmospheric ...
spread into what is now
Belgium
Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in Northwestern Europe. The country is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to th ...
where it was improved. From there, it spread via the
Pays de Bray
The Pays de Bray (, literally ''Land of Bray'') is a small (about 750 km²) natural region of France situated to the north-east of Rouen, straddling the French departments of the Seine-Maritime and the Oise (historically divided among the ...
on the boundary of
Normandy
Normandy (; french: link=no, Normandie ; nrf, Normaundie, Nouormandie ; from Old French , plural of ''Normant'', originally from the word for "northman" in several Scandinavian languages) is a geographical and cultural region in Northwestern ...
and then to the
Weald
The Weald () is an area of South East England between the parallel chalk escarpments of the North and the South Downs. It crosses the counties of Hampshire, Surrey, Sussex and Kent. It has three separate parts: the sandstone "High Weald" in the ...
in England. With it, the finery forge spread. Those remelted the pig iron and (in effect) burnt out the carbon, producing a bloom, which was then forged into bar iron. If rod iron was required, a slitting mill was used.
The finery process existed in two slightly different forms. In Great Britain, France, and parts of Sweden, only the
Walloon process
A Walloon forge (or Walloon process) is a type of finery forge that decarbonizes pig iron into wrought iron.
The process was conceived in the Liège region, and from there extended to France, then England around the end of the 15th century. ...
was used. That employed two different hearths, a finery hearth for finishing the iron and a chafery hearth for reheating it in the course of drawing the bloom out into a bar. The finery always burnt charcoal, but the chafery could be fired with mineral
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when dea ...
, since its impurities would not harm the iron when it was in the solid state. On the other hand, the German process, used in Germany, Russia, and most of Sweden used a single hearth for all stages.
The introduction of
coke for use in the blast furnace by
Abraham Darby Abraham Darby may refer to:
People
*Abraham Darby I (1678–1717) the first of several men of that name in an English Quaker family that played an important role in the Industrial Revolution. He developed a new method of producing pig iron with ...
in 1709 (or perhaps others a little earlier) initially had little effect on wrought iron production. Only in the 1750s was coke pig iron used on any significant scale as the feedstock of finery forges. However, charcoal continued to be the fuel for the finery.
Potting and stamping
From the late 1750s, ironmasters began to develop processes for making bar iron without charcoal. There were a number of patented processes for that, which are referred to today as
potting and stamping Potting and stamping is a modern name for one of the 18th-century processes for refining pig iron without the use of charcoal.
Inventors
The process was devised by Charles Wood of Lowmill, Egremont in Cumberland and his brother John Wood of We ...
. The earliest were developed by John Wood of
Wednesbury
Wednesbury () is a market town in Sandwell in the county of West Midlands, England. It is located near the source of the River Tame. Historically part of Staffordshire in the Hundred of Offlow, at the 2011 Census the town had a population of ...
and his brother Charles Wood of Low Mill at
Egremont, patented in 1763.
Another was developed for the
Coalbrookdale
Coalbrookdale is a village in the Ironbridge Gorge in Shropshire, England, containing a settlement of great significance in the history of iron ore smelting. It lies within the civil parish called the Gorge.
This is where iron ore was first s ...
Company by the
Cranage brothers. Another important one was that of John Wright and Joseph Jesson of
West Bromwich
West Bromwich ( ) is a market town in the borough of Sandwell, West Midlands, England. Historically part of Staffordshire, it is north-west of Birmingham. West Bromwich is part of the area known as the Black Country, in terms of geography, ...
.
Puddling process
![Puddling furnace](https://upload.wikimedia.org/wikipedia/commons/5/51/Puddling_furnace.jpg)
A number of processes for making wrought iron without charcoal were devised as the
Industrial Revolution
The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going f ...
began during the latter half of the 18th century. The most successful of those was puddling, using a puddling furnace (a variety of the
reverberatory furnace
A reverberatory furnace is a metallurgical or process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases. The term ''reverberation'' is used here in a generic sense of ''re ...
), which was invented by
Henry Cort
Henry Cort (c. 1740 – 23 May 1800) was an English ironware producer although formerly a Navy pay agent. During the Industrial Revolution in England, Cort began refining iron from pig iron to wrought iron (or bar iron) using innovative producti ...
in 1784. It was later improved by others including
Joseph Hall, who was the first to add iron oxide to the charge. In that type of furnace, the metal does not come into contact with the fuel, and so is not contaminated by its impurities . The heat of the combustion products pass over the surface of the puddle and the roof of the furnace reverberates (reflects) the heat onto the metal puddle on the fire bridge of the furnace.
Unless the raw material used is white cast iron, the pig iron or other raw product of the puddling first had to be refined into
refined iron
Pig iron, also known as crude iron, is an intermediate product of the iron industry in the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with sil ...
, or finers metal. That would be done in a refinery where raw coal was used to remove
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...
and convert carbon within the raw material, found in the form of graphite, to a combination with iron called cementite.
In the fully developed process (of Hall), this metal was placed into the hearth of the puddling furnace where it was melted. The hearth was lined with oxidizing agents such as
haematite and iron oxide.
The mixture was subjected to a strong current of air and stirred with long bars, called puddling bars or rabbles,
through working doors.
The air, the stirring, and the "boiling" action of the metal helped the oxidizing agents to oxidize the impurities and carbon out of the pig iron. As the impurities oxidize, they formed a molten slag or drifted off as gas, while the remaining iron solidified into spongy wrought iron that floated to the top of the puddle and was fished out of the melt as puddle balls, using puddle bars.
Shingling
There was still some slag left in the puddle balls, so while they were still hot they would be shingled
to remove the remaining slag and cinder.
That was achieved by forging the balls under a hammer, or by squeezing the bloom in a machine. The material obtained at the end of shingling is known as bloom.
The blooms are not useful in that form, so they were rolled into a final product.
Sometimes European
ironwork
Ironwork is any weapon, artwork, utensil, or architectural feature made of iron, especially one used for decoration. There are two main types of ironwork: wrought iron and cast iron. While the use of iron dates as far back as 4000BC, it was th ...
s would skip the shingling process completely and roll the puddle balls. The only drawback to that is that the edges of the rough bars were not as well compressed. When the rough bar was reheated, the edges might separate and be lost into the furnace.
Rolling
The bloom was passed through rollers and to produce bars. The bars of wrought iron were of poor quality, called muck bars
or puddle bars.
To improve their quality, the bars were cut up, piled and tied together by wires, a process known as
faggoting or piling.
They were then reheated to a welding state, forge welded, and rolled again into bars. The process could be repeated several times to produce wrought iron of desired quality. Wrought iron that has been rolled multiple times is called merchant bar or merchant iron.
Lancashire process
The advantage of puddling was that it used coal, not charcoal as fuel. However, that was of little advantage in Sweden, which lacked coal.
Gustaf Ekman
Gustav, Gustaf or Gustave may refer to:
*Gustav (name), a male given name of Old Swedish origin
Art, entertainment, and media
*Primeval (film), ''Primeval'' (film), a 2007 American horror film
*Gustav (film series), ''Gustav'' (film series), a Hu ...
observed charcoal fineries at
Ulverston
Ulverston is a market town and a civil parish in the South Lakeland district of Cumbria, England. In the 2001 census the parish had a population of 11,524, increasing at the 2011 census to 11,678. Historically in Lancashire, it lies a few mi ...
, which were quite different from any in Sweden. After his return to Sweden in the 1830s, he experimented and developed a process similar to puddling but used firewood and charcoal, which was widely adopted in the
Bergslagen
Bergslagen is a historical, cultural, and linguistic region located north of Lake Mälaren in northern Svealand, Sweden, traditionally known as a mining district. In Bergslagen, the mining and metallurgic industries have been important since th ...
in the following decades.
Aston process
In 1925, James Aston of the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
developed a process for manufacturing wrought iron quickly and economically. It involved taking molten steel from a
Bessemer converter
The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is removal of impurities from the iron by oxidation w ...
and pouring it into cooler liquid slag. The temperature of the steel is about 1500 °C and the liquid slag is maintained at approximately 1200 °C. The molten steel contains a large amount of dissolved gases so when the liquid steel hit the cooler surfaces of the liquid slag the gases were liberated. The molten steel then froze to yield a spongy mass having a temperature of about 1370 °C.
The spongy mass would then be finished by being
shingled and
rolled
Rolling is a Motion (physics)#Types of motion, type of motion that combines rotation (commonly, of an Axial symmetry, axially symmetric object) and Translation (geometry), translation of that object with respect to a surface (either one or the ot ...
as described under puddling (above). Three to four tons could be converted per batch with the method.
Decline
Steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
began to replace iron for railroad rails as soon as the
Bessemer process
The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is steelmaking, removal of impurities from the iron by ox ...
for its manufacture was adopted (1865 on). Iron remained dominant for structural applications until the 1880s, because of problems with brittle steel, caused by introduced nitrogen, high carbon, excess phosphorus, or excessive temperature during or too-rapid rolling.
By 1890 steel had largely replaced iron for structural applications.
Sheet iron (Armco 99.97% pure iron) had good properties for use in appliances, being well-suited for enamelling and welding, and being rust-resistant.
In the 1960s, the price of steel production was dropping due to recycling, and even using the Aston process, wrought iron production was labor-intensive. It has been estimated that the production of wrought iron is approximately twice as expensive as that of low-carbon steel.
In the United States, the last plant closed in 1969.
The last in the world was the Atlas Forge of
Thomas Walmsley and Sons
Thomas Walmsley and Sons was a company that manufactured wrought iron. It was founded in 1866 or 1869 by Thomas Walmsley at the Atlas Forge on a site bounded by Bridgeman Street and Fletcher Street in Bolton, then in Lancashire, England. The forge ...
in
Bolton
Bolton (, locally ) is a large town in Greater Manchester in North West England, formerly a part of Lancashire. A former mill town, Bolton has been a production centre for textiles since Flemish people, Flemish weavers settled in the area i ...
, Great Britain, which closed in 1973. Its 1860s-era equipment was moved to the
Blists Hill site of
Ironbridge Gorge Museum for preservation. Some wrought iron is still being produced for heritage restoration purposes, but only by recycling scrap.
Properties
![A231 - Optical micrograph of wrought iron](https://upload.wikimedia.org/wikipedia/commons/8/8d/A231_-_Optical_micrograph_of_wrought_iron.jpg)
The slag inclusions, or
stringers, in wrought iron give it properties not found in other forms of ferrous metal. There are approximately 250,000 inclusions per square inch.
A fresh fracture shows a clear bluish color with a high silky luster and fibrous appearance.
Wrought iron lacks the carbon content necessary for hardening through
heat treatment
Heat treating (or heat treatment) is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also ...
, but in areas where steel was uncommon or unknown, tools were sometimes cold-worked (hence
cold iron
Iron has a long and varied tradition in the mythology and folklore of the world.
While iron is now the name of a chemical element, the traditional meaning of the word "iron" is what is now called wrought iron. In East Asia, cast iron was also ...
) to harden them. An advantage of its low carbon content is its excellent weldability.
Furthermore, sheet wrought iron cannot bend as much as steel sheet metal when cold worked.
Wrought iron can be melted and cast, however the product is no longer wrought iron, since the slag stringers characteristic of wrought iron disappear on melting, so the product resembles impure, cast, Bessemer steel. There is no engineering advantage as compared to cast iron or steel, both of which are cheaper.
Due to the variations in iron ore origin and iron manufacture, wrought iron can be inferior or superior in corrosion resistance, compared to other iron alloys.
There are many mechanisms behind its corrosion resistance. Chilton and Evans found that nickel enrichment bands reduce corrosion. They also found that in puddled, forged, and piled iron, the working-over of the metal spread out copper, nickel, and tin impurities that produce electrochemical conditions that slow down corrosion.
The slag inclusions have been shown to disperse corrosion to an even film, enabling the iron to resist pitting.
Another study has shown that slag inclusions are pathways to corrosion. Other studies show that sulfur in the wrought iron decreases corrosion resistance,
while phosphorus increases corrosion resistance.
Chloride ions also decrease wrought iron's corrosion resistance.
Wrought iron may be welded in the same manner as mild steel, but the presence of oxide or
inclusions will give defective results.
The material has a rough surface, so it can hold platings and coatings better. For instance, a galvanic zinc finish applied to wrought iron is approximately 25–40% thicker than the same finish on steel.
In Table 1, the chemical composition of wrought iron is compared to that of pig iron and
carbon steel
Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:
* no minimum content is specified or required for chromium, cobalt ...
. Although it appears that wrought iron and plain carbon steel have similar chemical compositions, that is deceptive. Most of the manganese, sulfur, phosphorus, and silicon are incorporated into the slag fibers in the wrought iron, making wrought iron purer than plain carbon steel.
Amongst its other properties, wrought iron becomes soft at
red heat
The practice of using colours to determine the temperature of a piece of (usually) ferrous metal comes from blacksmithing. Long before thermometers were widely available it was necessary to know what state the metal was in for heat treating it an ...
and can be easily
forged
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which it ...
and
forge weld
Forge welding (FOW), also called fire welding, is a solid-state welding process that joins two pieces of metal by heating them to a high temperature and then hammering them together. It may also consist of heating and forcing the metals together ...
ed.
It can be used to form temporary
magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...
s, but it cannot be magnetized permanently,
and is
ductile
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
,
malleable
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
, and
tough.
Ductility
For most purposes, ductility rather than tensile strength is a more important measure of the quality of wrought iron. In tensile testing, the best irons are able to undergo considerable elongation before failure. Higher tensile wrought iron is brittle.
Because of the large number of boiler explosions on steamboats, the U.S. Congress passed legislation in 1830 which approved funds for correcting the problem. The treasury awarded a $1500 contract to the Franklin Institute to conduct a study. As part of the study, Walter R. Johnson and Benjamin Reeves conducted strength tests on boiler iron using a tester they had built in 1832 based on the design of Lagerhjelm in Sweden. Unfortunately, because of the misunderstanding of tensile strength and ductility, their work did little to reduce failures.
The importance of ductility was recognized by some very early in the development of tube boilers, evidenced by Thurston's comment:
Various 19th century investigations of boiler explosions, especially those by insurance companies, found causes to be most commonly the result of operating boilers above the safe pressure range, either to get more power, or due to defective boiler pressure relief valves and difficulties of obtaining reliable indications of pressure and water levels. Poor fabrication was also a common problem.
Also, the thickness of the iron in steam drums was low, by modern standards.
By the late 19th century, when metallurgists were able to better understand what properties and processes made good iron, it was being displaced by steel. Also, the old cylindrical boilers with fire tubes were displaced by water tube boilers, which are inherently safer.
Purity
In 2010, Dr. Gerry McDonnell demonstrated in England by analysis that a wrought iron bloom, from a traditional smelt, could be worked into 99.7% pure iron with no evidence of carbon. It was found that the stringers common to other wrought irons were not present, thus making it very malleable for the smith to work hot and cold. A commercial source of pure iron is available and is used by smiths as an alternative to traditional wrought iron and other new generation ferrous metals.
Applications
Wrought iron furniture has a long history, dating back to
Roman
Roman or Romans most often refers to:
*Rome, the capital city of Italy
*Ancient Rome, Roman civilization from 8th century BC to 5th century AD
*Roman people, the people of ancient Rome
*''Epistle to the Romans'', shortened to ''Romans'', a letter ...
times. There are 13th century wrought iron gates in
Westminster Abbey
Westminster Abbey, formally titled the Collegiate Church of Saint Peter at Westminster, is an historic, mainly Gothic church in the City of Westminster, London, England, just to the west of the Palace of Westminster. It is one of the United ...
in London, and wrought iron furniture seemed to reach its peak popularity in Britain in the 17th century, during the reign of
William III and
Mary II
Mary II (30 April 166228 December 1694) was Queen of England, Scotland, and Ireland, co-reigning with her husband, William III & II, from 1689 until her death in 1694.
Mary was the eldest daughter of James, Duke of York, and his first wife ...
. However, cast iron and cheaper steel caused a gradual decline in wrought iron manufacture; the last wrought ironworks in Britain closed in 1974.
It is also used to make home decor items such as
baker's racks,
wine rack
A wine rack is a set of shelves for the organized stores (wine), storage of wine. Wine racks can be built out of a number of different materials. The size of the rack and the number of bottles it can hold can vary widely. Wine racks can be lo ...
s,
pot rack
A pot rack is a functional piece of kitchen furniture that is used to hang or store cooking pot
Cookware and bakeware is food preparation equipment, such as cooking pots, pans, baking sheets etc. used in kitchens. Cookware is used on a stov ...
s,
etageres, table bases, desks, gates, beds, candle holders, curtain rods, bars, and bar stools.
The vast majority of wrought iron available today is from reclaimed materials. Old bridges and anchor chains dredged from harbors are major sources. The greater corrosion resistance of wrought iron is due to the siliceous impurities (naturally occurring in iron ore), namely ferric
silicate
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...
.
Wrought iron has been used for decades as a generic term across the gate and
fencing
Fencing is a group of three related combat sports. The three disciplines in modern fencing are the foil, the épée, and the sabre (also ''saber''); winning points are made through the weapon's contact with an opponent. A fourth discipline, s ...
industry, even though
mild steel
Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:
* no minimum content is specified or required for chromium, cobalt ...
is used for manufacturing these "wrought iron" gates.
This is mainly because of the limited availability of true wrought iron. Steel can also be
hot-dip galvanised to prevent corrosion, which cannot be done with wrought iron.
See also
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Bronze and brass ornamental work
Art in bronze and brass dates from remote Ancient history, antiquity. These important metals are alloys, bronze composed of copper and tin and brass of copper and zinc.
Proportions of each alloy vary slightly. Bronze may be normally considere ...
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Cast iron
Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
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Semi-steel casting Semi-steel casting is a lower cost method to produce a casting that is not quite as strong as a steel casting but less expensive to manufacture. It was used more commonly as a marketing term.
The carbon and silicon percentages are reduced to the ...
Notes
References
Further reading
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External links
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{{Authority control
Architectural elements
Building materials
Chinese inventions
Ferrous alloys
Han dynasty
Iron
Ironmongery
Metalworking