Elkem AS, Foundry Products Division, Hoffsveien 65 b, P.O. Box 5211 Majorstua, N-0303 Oslo, Norway, www.foundry.elkem.com

Common MetallurgicalDefects in Ductile Iron

Elkem produces a complete range of nodularisers and inoculants for the treatment of ductile iron. MgFeSi alloys are available for applications such as sandwich treatments, tundish cover ladles and flow through systems. They are graded so as to be suited for different ladle sizes. Products for in-the-mould processes are also available.

Ultraseed® inoculant is designed for pure Mg produced ductile iron, irons of low oxygen and sulphur levels and dead iron which has been held for extended periods of time. This inoculant will give high nodule counts in ductile iron which is normally difficult to inoculate and will help to prevent micro-shrinkage.

Chunky Graphite

Potential Causes:– Excess rare earth additions, particularly when high purity charges are used. Normally found in thick section castings or at higher carbon equivalents.

Note that once the rare earth addition is reduced, it maytake time to dilute the residual rare earth in return metal,particularly in induction melted iron.

Gas

Gas holes are a totally separate subject and can beinfluenced by melting procedures, metal handling,refractory conditions, mould moisture, sand permeability,core resins, hot spots near cores, slag handling, metal temperature, base metal composition, mould venting, Ti and Al contents amongst other sources.Specialist advice should be sought in cases of gas oncethe above have been investigated.

The photomicrograph given here shows dendrite armsgrowing inside a hydrogen pinhole.

Compacted Graphite

Potential Causes:– Low residual magnesium and/or rare earth from poor nodularisation practice, high temperatures or long holding time.– Excess sulphur in the base iron not balanced by sufficient magnesium.

Potential Causes:– Excess rare earth additions, particularly when high purity charges are used. Normally found in thick section castings or at higher carbon equivalents.

Note that once the rare earth addition is reduced, it maytake time to dilute the residual rare earth in return metal,particularly in induction melted iron.

Spiky Graphite

Potential Causes:– Very small amounts of lead which have not been neutralised by rare earths result in spiky graphite. This has a catastrophic effect on mechanical properties. Bismuth, titanium and antimony can give similar structures but can also be neutralised with rare earths.

Graphite Flotation

Potential causes:– High carbon equivalent.– Excess pouring temperature.– Slow cooling rate in thicker sections.– Insufficient inoculation.

Flake GraphiteSurface Structure

Potential causes:– Excess sulphur build-up in moulding sand. This causes reversion to flake as the magnesium in the iron reacts with the sulphur. The use of higher magnesium / rare earth in the nodulariser or a cerium containing inoculant can overcome this.

Nodule Alignment

Potential causes:– Low carbon equivalent·– Under inoculation causing growth of large dendrites with nodules aligned between arms of the dendrite.– High pouring temperature.

Carbides

Potential causes:– Low carbon equivalent.– Excess magnesium and/or rare earth.– Carbide promoting elements such as Mn, Cr, V, Mo.– Insufficient inoculation.– Rapid cooling rate.

Shrinkage

Potential causes:– Insufficient mould strength causing dilation.– Inadequate feed metal available.– Poor gating design.– Excess magnesium.– Low carbon equivalent.– Under inoculation or over inoculation.

Slag InclusionsIrregular Graphite

Potential causes:– Inadequate slag control from pouring system.– Lack of slag traps or filter.– Low pouring temperature.– Excess additions of slag forming materials.– Turbulent mould filling.

Potential causes:– High holding temperature.– Long holding time which can result in "dead" irons.– Poor inoculation or excessive fading of inoculation.– Graphite shape may be improved by a late addition of a powerful speciality inoculant.

Exploded Graphite

Preseed™ is a powerful preconditioning agent for all cast irons to improve consistency in melting and increase mechanical properties

Please refer to your local Elkem representative for further information on the range of Elkem products for grey, compacted and ductile cast irons.

Ultraseed® is a Registered Trademark of Elkem AS. Preseed™ is a trademark of Elkem AS.