Technical Information 12 Effects of Minor and Trace Elements in Cast Iron Small quantities of many elements can occur in cast irons and have a marked influence on the structure and properties of the castings. Some are present as deliberate additions while others arise from trace impurities in the raw materials. Several of these elements have beneficial effects, particularly in grey irons, while others are very damaging and must be avoided as far as possible. The following table lists the common sources of these elements, the levels at which they are likely to occur and their principle effects. The use of some of these elements (e.g. chromium) as major alloying elements is not included in the table. Element Aluminium Al Antimony Sb Arsenic As Barium Ba Bismuth Bi Boron B Calcium Ca Cerium Ce Chromium Cr Cobalt Co Copper Cu Hydrogen H Normal Levels (%) Effects in Cast Irons Promotes hydrogen pinholes in light sections Al-killed steel scrap, above about 0.005 %Al. Neutralizes nitrogen. inoculants, ferro-alloys, light Up to Promotes dross formation. Detrimental to nodular alloy components, additions 0.03 graphite above approx. 0.08%. May be neutralized of aluminium. by cerium. Strong graphite stabilizer. Steel scrap, vitreous Up to Strong pearlite and carbide promoter. enamel scrap, bearing 0.02 Inhibits nodularity in absence of rare earth’s. shells, deliberate additions Up to Strong pearlite and carbide promoter. Pig iron, steel scrap. 0.05 Improves nodular graphite shape. Barium containing Up to Improves graphite nucleation and reduces fading. 0.003 Reduces chilling tendency and promotes graphite inoculants. Promotes chill and undesirable graphite forms. Rarely Deliberate additions, mould Increases nodule number in ductile irons above coatings containing Bi. containing rare earth’s (cerium). Excessive nodule 0.01 counts may cause shrinkage problems. Above 5 ppm promotes ferrite. Above 10 ppm proVitreous enamel scrap, Up to motes carbides particularly in ductile irons. 20 ppm 0.01 deliberate additions as FeB. improves annealing of malleable irons. Improves spheroidization of graphite nodules. Ferro-alloys, nodularizers, Up to Improves graphite nucleation. 0.01 inoculants. Reduces chilling tendency and promotes graphite. Normally not used in grey irons. Most magnesium alloys or Up to Suppresses deleterious elements in ductile irons. added as mishmetall or 0.02 Improves spheroidization of graphite. Carbide other rare earth sources. stabilizing due to segregation. Alloy steel, chromium plate, Promotes chill and pearlite. Increases strength. Up to Form carbide segregates in ductile irons above some pig irons, ferro0.3 0.05%. chromium. Up to Tool steel No significant effects in cast irons. 0.02 Copper wire, copper-based Promotes pearlite. Improves strength. Up to Impairs ferritization in ductile irons. alloys, steel scrap, 0.5 No harmful effects. deliberate additions of Cu. Produces sub-surface pinholes. Has a mild chillDamp refractories, mould promoting action. Promotes "inverse chill" when materials and humid there is insufficient manganese present to additions. neutralize sulphur. Promotes coarse graphite. Common Sources Elkem ASA, Foundry Products Postal address P.O.Box 5211 Majorstuen NO-0302 Oslo Norway Office address Hoffsveien 65B Oslo Norway © Copyright Elkem ASA Telephone +47 22 45 01 00 Telefax +47 22 45 01 52 Web www.foundry.elkem.com Org. no. NO 911 382 008 MVA Revision No. 2.1 20.03.2004 Technical Information 12 Element Common Sources Lead Pb Old paints, some vitreous enamel, free-cutting steel, terne plate, solder, petrol engine deposits. Magnesium Mg Additions of magnesium alloys (nodularizers). Most pig irons, steel scrap, additions of ferro manganese lump or briquettes. Refined pig irons, alloy Molybdenium steels, ferro-molybdenum Mo additions. Nickel Nickel plate, steel scrap, Ni refined irons, NiMg alloy. Coke, carburizers, core Nitrogen binders, steel scrap, N additions of nitrided ferromanganese. Manganese Mn Phosphorous Phosphoric pig iron and P scrap, additions of FeP. Silicon Si Ferro-silicon alloys, steel scrap, pig iron. Sulphur S Coke, carburizers, pig iron, scrap iron, additions of iron sulphide. Strontium Sr Strontium containing inoculants. Tellurium Te Free-cutting copper, mould coatings, cooling curve carbon samples. Tin Sn Titanium Ti Solder, tin plated steel scrap, bronze components, tin additions. Some pig irons, some paints and vitreous enamels, CG-iron returns, additions of titanium or ferro-titanium 2 Normal Levels (%) Effects in Cast Irons Causes spiky and undesirable graphite structures in grey irons and severely reduces strength at levels above 0.004 %. Promotes pearlite and Up to carbides. 0.005 Cause degenerated nodular graphite forms. Effects on graphite in ductile irons are neutralized by rare earth’s (cerium). Promotes nodular graphite in ductile irons. 0.03 - 0.08 Carbide stabilizing effect in ductile irons. Not used in grey irons. Neutralizes sulphur by forming MnS. Promotes pearlite formation. Forms carbide 0.2 - 1.0 segregates in ductile irons. Promotes gas holes at high levels in conjunction with high sulphur levels. Mild pearlite promoter. Up to Increases strength. 0.1 Can promote shrinkage and carbides. Up to Small amounts have little effects. 0.5 Graphitizing effect in larger quantities. Compacts flake graphite. Promotes pearlite. Increases strength. High levels causes fissure Up to defects in heavier sections. Can be neutralized by 0.015 Al, Ti and Zr. Has little effect in ductile irons. Increases CEV. Increases fluidity. Forms Up to phosphide eutectic. Damaging in ductile irons 0.1 above 0.05 %. At levels above 0.04%, can cause metal penetration. Promotes graphitization, reduces chill, stabilizes 0.8-4.0 ferrite, improves castability. Very damaging to structure and properties unless Up to 0.15 balanced by manganese. Improves grey irons (grey response to most inoculants. Increases Mg irons) requirements in ductile irons. Should be below 0.03 % in ductile irons. Up to Improves graphite nucleation in grey and ductile. 0.003 Strongly reduces chilling tendency in grey irons. Strongly promotes carbides. Causes many undesirable forms of graphite. Effects observed as Up to low as 0.0003 %. Effects reduced by combination 0.003 with Mg and Ce in ductile irons. Strongly promotes pearlite. Improves strength. Up to Embrittles ductile irons above 0.08 %. 0.15 No other harmful effects. Up to 0.10 Neutralizes nitrogen in grey irons. Promotes hydrogen pinholing due to aluminium. Promotes undercooled graphite in grey iron. Suppresses nodular graphite in CG-irons. Tungsten W High speed tool steel Up to 0.05 Rarely found in significant amounts. Mild pearlite promoter. Vanadium V Steel scrap, tool steel, some pig irons, ferrovanadium additions. Up to 0.10 Promotes chill formation. Refines flake graphite. Markedly increases strength.