Defects in Ductile Iron
Compacted Graphite Exploded Graphite Chunky Graphite Spiky Graphite
Potential Causes; Cause;· Cause;· Potential causes;
Low residual magnesium and/or rare earth from Excess rare earth additions, particularly when high Excess rare earth additions, particularly when high Very small amounts of lead which have not been
poor nodularisation practice, high temperatures or purity charges are used. Normally found in thick purity charges are used. Normally found in thick neutralised by rare earths result in spiky graphite.
long holding time. section castings or at higher carbon equivalents. section castings or at higher carbon equivalents. This has a catastrophic effect on mechanical
Excess sulphur in the base iron not balanced by properties.
sufficient magnesium. Note that once the rare earth addition is reduced, it may Note that once the rare earth addition is reduced, it may Bismuth, titanium and antimony can give similar
take time to dilute the residual rare earth in return metal, take time to dilute the residual rare earth in return metal, structures but can also be neutralised with rare
particularly in induction melted iron. particularly in induction melted iron. earths.
Graphite Flotation Surface Structure Nodule Alignment Carbides
Potential causes; Cause; Potential causes; Potential causes;
High carbon equivalent. Excess sulphur build-up in moulding sand. This Low carbon equivalent· Low carbon equivalent.
Excess pouring temperature. causes reversion to flake as the magnesium in the Under inoculation causing growth of large Excess magnesium and/or rare earth.
Slow cooling rate in thicker sections. iron reacts with the sulphur. The use of higher dendrites with nodules aligned between arms of Carbide promoting elements such as Mn,Cr,V,Mo.
Insufficient inoculation. magnesium / rare earth in the nodulariser or a cerium the dendrite. Insufficient inoculation.
containing inoculant can overcome this. High pouring temperature. Rapid cooling rate.
Irregular Graphite Slag Inclusions Shrinkage Gas
Potential causes; Potential causes; Potential causes; Gas holes are a totally separate subject and can be
High holding temperature. Inadequate slag control from pouring system. Insufficient mould strength causing dilation. influenced by melting procedures, metal handling,
Long holding time which can result in "dead" irons. Lack of slag traps or filter. Inadequate feed metal available. refractory conditions,mould moisture,sand
Poor inoculation or excessive fading of Low pouring temperature. Poor gating design. permeability,core resins,hot spots near cores,slag
inoculation. Excess additions of slag forming materials. Excess magnesium. handling,metal temperature,base metal
Graphite shape may be improved by a late addition of a Turbulent mould filling. Low carbon equivalent. composition,mould venting, Ti and Al contents amongst
powerful speciality inoculant. Under inoculation or over inoculation. other sources.
Specialist advise should be sought in cases of gas once
the above have been investigated.
The photomicrograph given here shows dendrite arms
growing inside a hydrogen pinhole.
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 Revised September 2004 © Copyright Elkem ASA
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.
This is one example of the new generation of Elkem inoculants.
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. www.foundry.elkem.com
Elkem ASA, Foundry Products Division, Hoffsveien 65B, PO Box 5211 Majorstua, N-0303 Oslo, Norway. Tel: +47 22 45 01 00 Fax: +47 22 45 01 52