Effects of Minor & Trace Elements in Cast Iron PDF

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 impur...

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. Normal Element Common Sources Levels (%) Effects in Cast Irons Promotes hydrogen pinholes in light sections Al-killed steel scrap, above about 0.005 %Al. Neutralizes nitrogen. Aluminium inoculants, ferro-alloys, light Up to Promotes dross formation. Detrimental to nodular Al alloy components, additions 0.03 graphite above approx. 0.08%. May be neutralized of aluminium. by cerium. Strong graphite stabilizer. Steel scrap, vitreous Antimony Up to Strong pearlite and carbide promoter. enamel scrap, bearing Sb 0.02 Inhibits nodularity in absence of rare earth’s. shells, deliberate additions Arsenic Up to Strong pearlite and carbide promoter. Pig iron, steel scrap. As 0.05 Improves nodular graphite shape. Barium Barium containing Up to Improves graphite nucleation and reduces fading. Ba inoculants. 0.003 Reduces chilling tendency and promotes graphite Promotes chill and undesirable graphite forms. Rarely Bismuth Deliberate additions, mould Increases nodule number in ductile irons above Bi 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 pro- Boron Vitreous enamel scrap, Up to motes carbides particularly in ductile irons. 20 ppm B deliberate additions as FeB. 0.01 improves annealing of malleable irons. Improves spheroidization of graphite nodules. Calcium Ferro-alloys, nodularizers, Up to Improves graphite nucleation. Ca inoculants. 0.01 Reduces chilling tendency and promotes graphite. Normally not used in grey irons. Most magnesium alloys or Cerium Up to Suppresses deleterious elements in ductile irons. added as mishmetall or Ce 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. Chromium Up to some pig irons, ferro- Form carbide segregates in ductile irons above Cr 0.3 chromium. 0.05%. Cobalt Up to Tool steel No significant effects in cast irons. Co 0.02 Copper wire, copper-based Promotes pearlite. Improves strength. Copper Up to alloys, steel scrap, Impairs ferritization in ductile irons. Cu 0.5 deliberate additions of Cu. No harmful effects. Produces sub-surface pinholes. Has a mild chill- Damp refractories, mould Hydrogen promoting action. Promotes "inverse chill" when materials and humid H there is insufficient manganese present to additions. neutralize sulphur. Promotes coarse graphite. Elkem ASA, Foundry Products © Copyright Elkem ASA Postal address Office address Telephone Web Revision P.O.Box 5211 Majorstuen Hoffsveien 65B +47 22 45 01 00 www.foundry.elkem.com No. 2.1 NO-0302 Oslo Oslo Telefax Org. no. 20.03.2004 Norway Norway +47 22 45 01 52 NO 911 382 008 MVA Technical Information 12 2 Normal Element Common Sources Levels (%) Effects in Cast Irons Causes spiky and undesirable graphite structures in grey irons and severely reduces strength at Old paints, some vitreous levels above 0.004 %. Promotes pearlite and Lead enamel, free-cutting steel, Up to carbides. Pb terne plate, solder, petrol 0.005 Cause degenerated nodular graphite forms. engine deposits. Effects on graphite in ductile irons are neutralized by rare earth’s (cerium). Promotes nodular graphite in ductile irons. Magnesium Additions of magnesium 0.03 - 0.08 Carbide stabilizing effect in ductile irons. Mg alloys (nodularizers). Not used in grey irons. Most pig irons, steel scrap, Neutralizes sulphur by forming MnS. Manganese additions of ferro Promotes pearlite formation. Forms carbide Mn manganese lump or 0.2 - 1.0 segregates in ductile irons. Promotes gas holes at briquettes. high levels in conjunction with high sulphur levels. Refined pig irons, alloy Mild pearlite promoter. Molybdenium Up to steels, ferro-molybdenum Increases strength. Mo 0.1 additions. Can promote shrinkage and carbides. Nickel Nickel plate, steel scrap, Up to Small amounts have little effects. Ni refined irons, NiMg alloy. 0.5 Graphitizing effect in larger quantities. Coke, carburizers, core Compacts flake graphite. Promotes pearlite. Nitrogen binders, steel scrap, Increases strength. High levels causes fissure Up to N additions of nitrided ferro- defects in heavier sections. Can be neutralized by 0.015 manganese. Al, Ti and Zr. Has little effect in ductile irons. Increases CEV. Increases fluidity. Forms Phosphorous Phosphoric pig iron and Up to phosphide eutectic. Damaging in ductile irons P scrap, additions of FeP. 0.1 above 0.05 %. At levels above 0.04%, can cause metal penetration. Silicon Ferro-silicon alloys, steel Promotes graphitization, reduces chill, stabilizes 0.8-4.0 Si scrap, pig iron. ferrite, improves castability. Very damaging to structure and properties unless Coke, carburizers, pig iron, Up to 0.15 balanced by manganese. Improves grey irons Sulphur scrap iron, additions of iron (grey response to most inoculants. Increases Mg S sulphide. irons) requirements in ductile irons. Should be below 0.03 % in ductile irons. Strontium Strontium containing Up to Improves graphite nucleation in grey and ductile. Sr inoculants. 0.003 Strongly reduces chilling tendency in grey irons. Strongly promotes carbides. Causes many Free-cutting copper, mould Tellurium undesirable forms of graphite. Effects observed as coatings, cooling curve Up to Te low as 0.0003 %. Effects reduced by combination carbon samples. 0.003 with Mg and Ce in ductile irons. Solder, tin plated steel Strongly promotes pearlite. Improves strength. Tin Up to scrap, bronze components, Embrittles ductile irons above 0.08 %. Sn 0.15 tin additions. No other harmful effects. Some pig irons, some Neutralizes nitrogen in grey irons. Promotes paints and vitreous Titanium hydrogen pinholing due to aluminium. Promotes enamels, CG-iron returns, Up to Ti undercooled graphite in grey iron. Suppresses additions of titanium or 0.10 nodular graphite in CG-irons. ferro-titanium Tungsten Up to Rarely found in significant amounts. High speed tool steel W 0.05 Mild pearlite promoter. Steel scrap, tool steel, Vanadium Up to Promotes chill formation. Refines flake graphite. some pig irons, ferro- V 0.10 Markedly increases strength. vanadium additions.