View source for Ductile iron

{{Short description|Type of cast iron}}
{{Steels}}

'''Ductile iron''', also known as '''ductile cast iron''', '''nodular cast iron''', '''spheroidal graphite iron''', '''spheroidal graphite cast iron'''<ref>{{harvnb|Smith|Hashemi|2006|p=432}}.</ref> and '''SG iron''', is a type of [[graphite]]-rich [[cast iron]] discovered in 1943 by [[Keith Millis]].<ref>{{Cite web |url=http://www.moderncasting.com/archive/feature_023_01.html |title=Modern Casting, Inc.<!-- Bot generated title --> |access-date=2005-01-01 |archive-url=https://web.archive.org/web/20041214102034/http://moderncasting.com/archive/feature_023_01.html |archive-date=2004-12-14 |url-status=dead }}</ref> While most varieties of cast iron are weak in tension and [[brittle]], ductile iron has much more impact and fatigue resistance, due to its ''nodular graphite'' inclusions.

Augustus F. Meehan was awarded {{US patent|1790552}} in January 1931 for inoculating iron with [[calcium disilicide|calcium silicide]] to produce ductile iron subsequently licensed as [[Meehanite]], still produced {{as of|2024| lc=y}}. In October 1949 Keith Dwight Millis, [[Albert Paul Gagnebin]] and Norman Boden Pilling, all working for [[INCO]], received {{US patent|2,485,760}} on a cast ferrous alloy using magnesium for ductile iron production.<ref name=us2485760>{{US patent reference|number=2485760|y=1949|m=10|d=25|inventor= Keith Millis|title=Cast Ferrous Alloy}}</ref> 

== Metallurgy ==
{{see also|Cast iron#Ductile cast iron}}
[[Image:Ductile Iron.png|thumb|Etched and polished ductile iron [[microstructure]] at 100× magnification, showing carbon islanding effect<ref name="airuni">{{Cite web|url=https://www.scribd.com/doc/41574523/Lecture-1-Part-II-Engineering-Materials|title=ME-140 Workshop Technology - Slide 25|access-date=2011-10-30|publisher=Air University|year=2009|author=Yaqub, Ejaz|author2=Arshad, Rizwan |format=images}}</ref> around nodules.]]
[[File:Gusseisen mit Kugelgraphit.jpg|thumb|Another micrograph showing the carbon islanding effect, with nodules surrounded by areas depleted of carbon]]

Ductile iron is not a single material but part of a group of materials which can be produced with a wide range of properties through control of their [[microstructure]]. The common defining characteristic of this group of materials is the shape of the graphite. In ductile irons, graphite is in the form of ''nodules'' rather than flakes as in [[grey iron]]. Whereas sharp graphite flakes create stress concentration points within the metal matrix, rounded nodules inhibit the creation of cracks, thus providing the enhanced ductility that gives the alloy its name.<ref>{{cite web |url=http://www.ductile.org/didata/Section2/2intro.htm |title=Ductile Iron Data - Section 2 |website=www.ductile.org |url-status=dead |archive-url=https://web.archive.org/web/20010129000000/http://www.ductile.org/didata/Section2/2intro.htm |archive-date=2001-01-29}}</ref> Nodule formation is achieved by adding ''nodulizing elements'', most commonly [[magnesium]] (magnesium boils at 1100&nbsp;°C and iron melts at 1500&nbsp;°C) and, less often now, [[cerium]] (usually in the form of [[mischmetal]]).<ref name="gillespie">{{Citation | last = Gillespie | first = LaRoux K. | title = Troubleshooting manufacturing processes | page = 4-4<!-- NOT A RANGE! --> | publisher = SME | year = 1988 | edition = 4th | url = https://books.google.com/books?id=SX_SO_CkiUIC&pg=PT195 | isbn = 978-0-87263-326-1 | postscript =.}}</ref> [[Tellurium]] has also been used. [[Yttrium]], often a component of mischmetal, has also been studied as a ''possible nodulizer''.

''[[Austempered]] ductile iron'' (ADI; i.e., [[austenite]] tempered<ref>{{cite web|url=http://www.aditreatments.com/background.php|title=ADI the Material|publisher=ADI Treatments Ltd.|access-date=2010-01-24|url-status=dead|archive-url=https://web.archive.org/web/20101026205100/http://www.aditreatments.com/background.php|archive-date=2010-10-26}}</ref>) was discovered in the 1950s but was commercialized and achieved success only some years later.  In ADI, the metallurgical structure is manipulated through a sophisticated heat treating process.{{citation needed|date=August 2022}}

==Composition==
{| class="wikitable"
|+ Mass fraction (%) for ferritic ductile iron castings<ref>ASTM International. ''A874/A874M-98(2018)e1 Standard Specification for  Ferritic Ductile Iron Castings Suitable for Low-Temperature   Service''. West Conshohocken, PA; ASTM International, 2018. {{doi|10.1520/A0874_A0874M-98R18E01}}</ref>
! [[Iron|Fe]]
! [[Carbon|C]]
! [[Silicon|Si]]
! [[Nickel|Ni]]
! [[Manganese|Mn]]
! [[Magnesium|Mg]]
! [[Chromium|Cr]]
! [[Phosphorus|P]]
! [[Sulfur|S]]
! [[Copper|Cu]]
|-
| {{n/a|Balance}}
| 3.0–3.7
| 1.2–2.3
| 1.0
| 0.25
| 0.07
| 0.07
| 0.03
| 
| 0.1
|-
| {{n/a|Balance}}
| 3.3–3.6
| 2.2–2.8
| 
| 0.1-0.2
| 0.03–0.04
| 
| 0.005–0.04
| 0.005–0.02
| <0.40
|}

Elements such as [[copper]] or [[tin]] may be added to increase tensile and yield strength while simultaneously reducing ductility. Improved corrosion resistance can be achieved by replacing 15–30% of the [[iron]] in the alloy with varying amounts of [[nickel]], copper, or [[chromium]]. Other ductile iron compositions often have a small amount of [[sulfur]] as well.

Silicon as a graphite formation element can be partially replaced by [[Aluminium|aluminum]] to provide better oxidation protection.<ref>{{cite journal | url=https://link.springer.com/article/10.1007/s11665-011-0086-y | doi=10.1007/s11665-011-0086-y | title=The Effect of Isothermal Heat Treatment Time on the Microstructure and Properties of 2.11% al Austempered Ductile Iron | date=2012 | last1=Erfanian-Naziftoosi | first1=H. R. | last2=Haghdadi | first2=N. | last3=Kiani-Rashid | first3=A. R. | journal=Journal of Materials Engineering and Performance | volume=21 | issue=8 | pages=1785–1792 | bibcode=2012JMEP...21.1785E | url-access=subscription }}</ref>
{{-}}

== Applications ==
[[File:Cast fe and cu dwv piping.jpg|thumb|left|Cast-iron "no hub" [[drain-waste-vent system|drain waste and vent]] (DWV) piping]]
[[File:Fluegel-Rahmen.jpg|thumb|upright|Cast iron "harp" of a [[grand piano]]]]

Much of the annual production of ductile iron is in the form of [[ductile iron pipe]], used for water and sewer lines. It competes with [[polymer]]ic materials such as [[polyvinyl chloride]] (PVC), [[high-density polyethylene]] (HDPE), [[low-density polyethylene]](LDPE) and [[polypropylene]], which are all much lighter than steel or ductile iron; being softer and weaker, these require protection from physical damage.

Ductile iron is specifically useful in many automotive components,<!-- Examples? --> where strength must surpass that of aluminum but more expensive steel is not necessarily required. Other major industrial applications include off-highway diesel trucks, class 8 trucks, agricultural tractors, and oil well pumps.<!-- In what applications? --> In the wind power industry ductile iron is used for hubs and structural parts like machine frames. Ductile iron is suitable for large and complex shapes and high (fatigue) loads.

Ductile iron is used in many [[piano]] harps (the iron plates which anchor piano strings).

Ductile iron is used for [[Vise|vises]]. Previously, regular cast iron or steel was commonly used. The properties of ductile iron make it a significant upgrade in strength and durability from cast iron without having to use steel, which is expensive and has poor [[castability]].

==See also==
*[[Malleable iron]]
*[[Wrought iron]]

==References==
{{Reflist}}

===Bibliography===
*{{Citation | last1 = Smith | first1 = William F. | last2 = Hashemi | first2 = Javad | title = Foundations of Materials Science and Engineering | edition = 4th | year = 2006 | publisher = McGraw-Hill | isbn = 0-07-295358-6 | postscript =.}}
*{{Citation | last = Erfanian-Naziftoosi| first = Hamid Reza | title = The Effect of Isothermal Heat Treatment Time on the Microstructure and Properties of 2.11% Al Austempered Ductile Iron | journal = Journal of Materials Engineering and Performance | year = 2012 | volume = 21 | issue = 8 | pages = 1785–1792 | doi = 10.1007/s11665-011-0086-y | bibcode = 2012JMEP...21.1785E | s2cid = 55925760 | postscript =.}}

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[[Category:Cast iron]]
[[Category:Ferrous alloys]]