Editing Cast iron (section)

===Alloying elements===
[[File:FeC-phase-diagram--multilingual.svg|thumb|400px|right|'''Iron-cementite''' meta-stable diagram]]
Cast iron's properties are changed by adding various alloying elements, or [[alloyant]]s. Next to [[carbon]], [[silicon]] is the most important alloyant because it forces carbon out of solution. A low percentage of silicon allows carbon to remain in solution, forming iron carbide and producing white cast iron. A high percentage of silicon forces carbon out of solution, forming graphite and producing grey cast iron. Other alloying agents, [[manganese]], [[chromium]], [[molybdenum]], [[titanium]], and [[vanadium]] counteract silicon, and promote the retention of carbon and the formation of those carbides. Nickel and copper increase strength and machinability, but do not change the amount of graphite formed. Carbon as [[graphite]] produces a softer iron, reduces shrinkage, lowers strength, and decreases density. [[Sulfur]], largely a contaminant when present, forms [[Iron(II) sulfide|iron sulfide]], which prevents the formation of graphite and increases [[hardness]]. Sulfur makes molten cast iron viscous, which causes defects. To counter the effects of sulfur, [[manganese]] is added, because the two form into [[manganese sulfide]] instead of iron sulfide. The manganese sulfide is lighter than the melt, so it tends to float out of the melt and into the [[slag]]. The amount of manganese required to neutralize sulfur is 1.7 × sulfur content + 0.3%. If more than this amount of manganese is added, then [[manganese carbide]] forms, which increases hardness and [[chill (foundry)|chilling]], except in grey iron, where up to 1% of manganese increases strength and density.<ref name="gillespie">{{Cite book | last = Gillespie | first = LaRoux K. | title = Troubleshooting manufacturing processes | pages = 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 }}</ref>

[[Nickel]] is one of the most common alloying elements, because it refines the [[pearlite]] and graphite structures, improves toughness, and evens out hardness differences between section thicknesses. [[Chromium]] is added in small amounts to reduce free graphite, produce chill, and because it is a powerful [[carbide]] stabilizer; nickel is often added in conjunction. A small amount of [[tin]] can be added as a substitute for 0.5% chromium. [[Copper]] is added in the ladle or in the furnace, on the order of 0.5–2.5%, to decrease chill, refine graphite, and increase fluidity. [[Molybdenum]] is added on the order of 0.3–1% to increase chill and refine the graphite and pearlite structure; it is often added in conjunction with nickel, copper, and chromium to form high strength irons. [[Titanium]] is added as a degasser and deoxidizer, but it also increases fluidity. [[Vanadium]] at 0.15–0.5% is added to cast iron to stabilize cementite, increase hardness, and increase resistance to [[wear]] and heat. [[Zirconium]] at 0.1–0.3% helps to form graphite, deoxidize, and increase fluidity.<ref name="gillespie"/>

In malleable iron melts, [[bismuth]] is added at 0.002–0.01% to increase how much silicon can be added. In white iron, [[boron]] is added to aid in the production of malleable iron; it also reduces the coarsening effect of bismuth.<ref name="gillespie"/>