Editing Wrought iron (section)

==Properties==
[[File:A231 - Optical micrograph of wrought iron.jpg|thumb|The microstructure of wrought iron, showing dark slag inclusions in [[Allotropes of iron#Alpha iron (α-Fe)|ferrite]] ]]

Wrought iron contains approximately 250,000 slag inclusions, or [[Stringer (slag)|stringers]], per square inch, giving it properties not found in other forms of ferrous metal.<ref name="Daniel1993" /> 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]], but in areas where steel was uncommon or unknown, tools were sometimes cold-worked (hence [[cold iron]]) to harden them.{{citation needed|date=June 2019}} An advantage of its low carbon content is its excellent weldability.<ref name="Daniel1993" /> Furthermore, sheet wrought iron cannot bend as much as steel sheet metal when cold worked.<ref name="Husband1911">{{cite book |last1=Husband |first1=Joseph |last2=Harby |first2=William |year=1911 |title=Structural Engineering |place=New York |publisher=Longmans, Green, and Co. |page=21 |url =https://books.google.com/books?id=pktDAAAAIAAJ |access-date=22 February 2008}}</ref><ref name="Byrne1899">{{cite book |last=Byrne |first=Austin Thomas |year=1899 |title=Inspection of the Materials and Workmanship Employed in Construction |edition=1st |place=New York |publisher=John Wiley & Sons |page=105 |url=https://books.google.com/books?id=2U80AAAAMAAJ |access-date=22 February 2008}}</ref> 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 to melting and casting wrought iron, as compared to using cast iron or steel, both of which are cheaper.<ref name="Scoffern1861">{{cite book |last=Scoffern |first=John |year=1861 |title=The Useful Metals and Their Alloys, Including Mining Ventilation, Mining Jurisprudence, and Metallurgic Chemistry |place=London |publisher=Houlston and Wright |page=328 |url=https://books.google.com/books?id=SSkKAAAAIAAJ |access-date=20 February 2008}}</ref><ref name="Adams1891">{{cite book |last=Adams |first=Henry |year=1891 |title=Handbook for Mechanical Engineers |edition=2nd |place=New York |publisher=E. & F.N. Spon |page=29 |url=https://books.google.com/books?id=0q03AAAAMAAJ |access-date=20 February 2008}}</ref>

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.<ref name="Daniel1993" /><ref>Hudson, J.C., 1931–43, Reports of the Corrosion Committee's Field Tests, Iron and Steel institute.</ref><ref name="chilton">{{cite journal |journal=Material Eyes |publisher=Cambridge University Department of Materials Science and Metallurgy |title=Dr. JP Chilton, 1929–2006 |page=4 |edition=Spring 2007 |url=http://www.msm.cam.ac.uk/department/mat_eyes_issues/Material_Eyes_Issue16_Spring07.pdf#page=4 |access-date=29 November 2008 |archive-url=https://web.archive.org/web/20120901235543/http://www.msm.cam.ac.uk/department/mat_eyes_issues/Material_Eyes_Issue16_Spring07.pdf#page=4 |archive-date=1 September 2012 |url-status=dead}}</ref><ref name="walker">{{cite journal |last=Walker VII |first=Robert |title=The Production, Microstructure, and Properties of Wrought Iron |journal=Journal of Chemical Education |volume=79 |issue=4 |pages=443–447 |date=April 2002 |url=http://www.archaeometry.dk/Jern/Walker%20VII,%20Robert;%20The%20Production,%20Microstructure,%20and%20Properties%20of%20Wrought%20Iron.pdf |archive-url=https://web.archive.org/web/20070924122058/http://www.archaeometry.dk/Jern/Walker%20VII,%20Robert;%20The%20Production,%20Microstructure,%20and%20Properties%20of%20Wrought%20Iron.pdf |archive-date=2007-09-24 |url-status=live |doi=10.1021/ed079p443 |bibcode=2002JChEd..79..443W }}</ref> There are many mechanisms behind its corrosion resistance. Chilton and Evans found that nickel enrichment bands reduce corrosion.<ref>Chilton & Evens, Journal of the Iron and Steel Institute, 1955</ref> 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.<ref name="chilton" /> The slag inclusions have been shown to disperse corrosion to an even film, enabling the iron to resist pitting.<ref name="Daniel1993" /> Another study has shown that slag inclusions are pathways to corrosion.<ref>Harvey, L., The role of Slag Inclusions in the corrosion of wrought iron, dissertation University of Bradford, 1996</ref> Other studies show that sulfur in the wrought iron decreases corrosion resistance,<ref name="walker" /> while phosphorus increases corrosion resistance.<ref name="Balasubramaniam2003">{{cite journal |last=Balasubramaniam |first=R. |title=Delhi iron pillar and its relevance to modern technology |journal=Current Science |volume=84 |issue=2 |pages=162–163 |date=25 January 2003 |url=http://www.iisc.ernet.in/currsci/jan252003/126.pdf |access-date=29 November 2008 |archive-date=4 March 2009 |archive-url=https://web.archive.org/web/20090304071849/http://www.iisc.ernet.in/currsci/jan252003/126.pdf |url-status=dead }}</ref> Chloride ions also decrease wrought iron's corrosion resistance.<ref name="walker" />

Wrought iron may be welded in the same manner as mild steel, but the presence of oxide or [[Inclusion (casting)|inclusions]] will give defective results.<ref>{{cite book |last=Pendred |first=Lough |title=Kempe's Engineer's Year-Book |edition=52nd |year=1945 |publisher=Morgan Brothers |location=London |page=1278 |asin=B0033RUEVW}}</ref>
The material has a rough surface, so it can hold platings and coatings better than smooth steel. For instance, a galvanic zinc finish applied to wrought iron is approximately 25–40% thicker than the same finish on steel.<ref name="Daniel1993" /> In Table 1, the chemical composition of wrought iron is compared to that of pig iron and [[carbon steel]]. 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 in the wrought iron are incorporated into the slag fibers, making wrought iron purer than plain carbon steel.<ref name="msts" />

{| class="wikitable" width=600px
|+Table 1: Chemical composition comparison of pig iron, plain carbon steel, and wrought iron
|-
! Material !! Iron !! Carbon !! Manganese !! Sulfur !! Phosphorus !! Silicon
|-
| Pig iron || 91–94 || 3.5–4.5 || 0.5–2.5 || 0.018–0.1 || 0.03–0.1 || 0.25–3.5
|-
| Carbon steel || 98.1–99.5 || 0.07–1.3 || 0.3–1.0 || 0.02–0.06 || 0.002–0.1 || 0.005–0.5
|-
| Wrought iron || 99–99.8 || 0.05–0.25 || 0.01–0.1 || 0.02–0.1 || 0.05–0.2 || 0.02–0.2
|-
| colspan="7" style="text-align:center;" | All units are percent weight. <br/>'''Source:'''<ref name="msts" />
|}

{| class="wikitable" width=600px
|+ Table 2: Properties of wrought iron
|-
! Property !! Value
|-
| Ultimate tensile strength [psi (MPa)]<ref name="mach-handbook">{{cite book |last1=Oberg |first1=Erik |last2=Jones |first2=Franklin D.|last3=Ryffel |first3=Henry H.|editor-last=McCauley |editor-first=Christopher J. |title=Machinery's Handbook |edition=26th |year=2000 |publisher=Industrial Press, Inc. |location=New York |page=476 |isbn=0-8311-2666-3 }}</ref>
|align="center" |34,000–54,000 (234–372)
|-
| Ultimate compression strength [psi (MPa)]<ref name="mach-handbook" />
|align="center" |34,000–54,000 (234–372)
|-
| Ultimate shear strength [psi (MPa)]<ref name="mach-handbook" />
|align="center" |28,000–45,000 (193–310)
|-
| Yield point [psi (MPa)]<ref name="mach-handbook" />
|align="center" |23,000–32,000 (159–221)
|-
| Modulus of elasticity (in tension) [psi (MPa)]<ref name="mach-handbook" />
|align="center" |28,000,000 (193,100)
|-
| Melting point [°F (°C)]<ref name="etw">{{cite book |last=Smith |first=Carroll |author-link=Carroll Smith |title=Engineer to Win |publisher=MotorBooks / MBI Publishing Company |year=1984 |pages=53–54 |isbn=0-87938-186-8 }}</ref>
|align="center" |2,800 (1,540)
|-
|rowspan=2 |Specific gravity
|align="center" |7.6–7.9<ref>{{cite web |title=Solids and Metals – Specific Gravity |url =http://www.engineeringtoolbox.com/specific-gravity-solids-metals-d_293.html |website=Engineering Toolbox |access-date=20 February 2008}}</ref>
|-
|align="center" |7.5–7.8<ref name="Pole1872">{{cite book |last=Pole |first=William |year=1872 |title=Iron as a Material of Construction: Being the Substance of a Course of Lectures Delivered at the Royal School of Naval Architecture, South Kensington |edition=Revised and Enlarged |place=London |publisher=E. & F.N. Spon |pages=136–137 |url =https://books.google.com/books?id=lwAKAAAAIAAJ |access-date=20 February 2008}}</ref>
|}

Amongst its other properties, wrought iron becomes soft at [[red heat]] and can be easily [[forged]] and [[forge weld]]ed.<ref name="Richter1885">{{cite book |last1=Richter |first1=Victor von |last2=Smith |first2=Edgar Fahs |year=1885 |title=A Text-book of Inorganic Chemistry |edition=2nd |place=Philadelphia |publisher=P. Blakiston, Son & Co. |page=396 |url=https://books.google.com/books?id=7Q45AAAAMAAJ |access-date=21 February 2008}}</ref> It can be used to form temporary [[magnet]]s, but it cannot be magnetized permanently,<ref name="American1916">{{cite encyclopedia |publisher=American Technical Society |year=1916 |title=Cyclopedia of Applied Electricity |volume=1 |page=14 |url=https://books.google.com/books?id=zaMOAAAAYAAJ |access-date=21 February 2008}}</ref><ref name="Timbie1922">{{cite book |last1=Timbie |first1=William Henry |last2=Bush |first2=Vannevar |year=1922 |title=Principles of Electrical Engineering |place=New York |publisher=John Wiley & Sons, Inc. |pages=318–319 |url =https://books.google.com/books?id=X6dEAAAAIAAJ |access-date=21 February 2008}}</ref> and is [[ductile]], [[malleable]], and [[Toughness|tough]].<ref name="msts" />

===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 in the early 1800s, 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 a design by Lagerhjelm in Sweden. Because of misunderstandings about tensile strength and ductility, their work did little to reduce failures.<ref name="Gordon1996" />

The importance of ductility was recognized by some very early in the development of tube boilers, evidenced by Thurston's comment:

{{Blockquote|1=If made of such good iron as the makers claimed to have put into them "which worked like lead," they would, as also claimed, when ruptured, open by tearing, and discharge their contents without producing the usual disastrous consequences of a boiler explosion.<ref>{{cite web |url=http://www.history.rochester.edu/steam/thurston/1878/ |archive-url=https://web.archive.org/web/19970629015211/http://www.history.rochester.edu/steam/thurston/1878/ |archive-date=29 June 1997 |url-status=dead |last=Thurston |first=Robert |date=1878 |title=A history of the growth of the steam engine |page=165}}</ref>}}

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.<ref name="Hunter">{{cite book |title=A History of Industrial Power in the United States, 1730–1930 |volume=2: Steam Power |last1=Hunter |first1=Louis C. |year=1985 |publisher =University Press of Virginia |location= Charlottesville |url=https://books.google.com/books?id=upQBtQEACAAJ}}<!-- Possibly the most comprehensive work on steam power --></ref> 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, iron in steam engines was being displaced by steel, whilst the old cylindrical boilers with fire tubes were displaced by inherently safer water tube boilers.<ref name="Hunter" />

===Purity===
In 2010, Gerry McDonnell<ref>{{cite periodical |last=McDonnell |first=G |date=9 September 2010 |title=Metallurgical Report on the Iron Smelted for the Master Crafts Series |periodical=Transmitted |edition=Spring 2010}}{{full citation needed|date=August 2011}}</ref> 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.