| Element | Influence | Uses |
| Carbon | Most important alloying element. Is essential to the formation of cementite and other carbides, bainite and iron-carbon martensite. Within limits increasing the carbon content increases the strength and hardness of a steel while reducing its toughness and ductility. | Added to construction steels to increase strength, hardness and hardenability. |
| Nickel | Stabilises gamma phase by raising A4 and
lowering A3. Refines grains in steels and some non-ferrous alloys.
Strengthens ferrite by solid solution. Unfortunatly is a powerful graphitiser.
Can take into solid solution larger proportions of important elements such as chromium, molybdenum and tungsten than can iron. |
Used up to help refine grain size. Used in large
amounts in stainless and heat-resisting steels.
Nickel based alloys can offer corrosion resistance in more aggressive environments and nickel is used as the basis of complex superalloys for high temperature service. |
| Manganese | Deoxidises the melt. Greatly increases the hadenability of steels. Stabilises gamma phase. Forms stable carbides. | High manganese (Hadfield) steel contains 12.5% Mn and is austenitic but hardens on abrasion. |
| Silicon | De-oxidises melt. Helps casting fluidity. Improves oxidation resistance at higher temperatures. | Up to 0.3% in steels for sandcasting, up to 1% in heat resisting steels. |
| Chromium | Stabilises alpha phase by raising A3 and depressing A4. Forms hard stable carbides. Strengthens ferrite by solid solution. In amounts above 13% it imparts stainless properties. Unfortunately increases grain growth. | Small amounts in constructional and tool steels. About 1.5% in ball and roller bearings. Larger amounts in Stainless and heat-resisting steels. |
| Molybdenum | Strong carbide-stabilising influence. Raises high temperature
creep strength of some alloys. Slows tempering response.
When added to stainless steels it greatly improves the pitting and crevice corrosion resistance. There are limits to the proportion that can be taken into an iron based matrix. However up to almost 30% can be incorporated into nickel based alloys which provides excellent corrosion resistance in many aqueous environments. |
Reduces 'temper brittleness' in nickel-chromium steels. Increases red-hardness of tool steels. Now used to replace some tungsten in high-speed steels. |
| Vanadium | Strong carbide forming tendency. Stabilises martensite and increases hardenability. Restrains grain growth. Improves resistance to softening at elevated temperatures after hardening. | Used to retain high temperature hardness, eg in dies for hot-forging and die casting dies. Increasingly used in high speed steels. |
| Tungsten | Stabilises alpha phase and forms stable, very hard carbides, which improves creep resistance and renders transformations very sluggish, hence hardened steels resist tempering influences. | Used in high-speed steels and other tool and die
steels, particularly those for use at high temperatures.
Used in a few stainless steels, in combination with molybdenum. to improve pitting and crevice corrosion resistance. It is also used in some high temperature nickel based alloys and in some high temperature austenitic stainless steels. |
| Cobalt | Has similar corrosion resistance to that of Nickel, but
higher cost means that it is not normally used for such applications.
Provides matrix - strengthening characteristics to stainless and nickel based alloys designed for high temperature applications. Slows the transformation of martensite, hence increases 'red hardness' which is useful in tool steels. |
Used in super high speed steels and maraging steels, permanent magnet steels and alloys. |
| Niobium | In low alloy steels it acts as a carbide former and improves creep resistance.
In stainless steels it combines with carbon, stabilising the steel and reducing the susceptibility to intergranular corrosion |
Used to stabilise stainless steels. |
| Titanium | In stainless steels combines with excess carbon reducing the risk of intergranular corrosion. | Used in stabilised stainless steels.
In nickel based alloys it is used with aluminium to promote age hardening. |
Reference:
'Metals Handbook', ASM, 2nd Desk Edition, 1998, ISBN: 0-87170-654-7.
'The Alloy Tree', by J C M Farrar, CRC Press and Woodhead Publishing, 2004, ISBN: 1 85573 766 3.
Return to module home page.
David J Grieve, revised: 25th May 2007, original: 10th February 2003.