|Effects of Alloying Additions to Steels|
|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.||Used up to help refine grain size. Used in large amounts in stainless and heat-resisting steels.|
|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.||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 very hard carbides. renders transformations very sluggish, hence hardened steels resist tempering influences.||Used mainly in high-speed steels and other tool and die steels, particularly those for use at high temperatures.|
|Cobalt||Slows the transformation of martensite, hence increases 'red hardness'.||Used in super high speed steels and maraging steels, permanent magnet steels and alloys.|
'Metals Handbook', ASM, 2nd Desk Edition, 1998, ISBN: 0-87170-654-7.
David J Grieve, 10th February 2003.
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