Technical Information 16

Elkem ASA, Foundry Products © Copyright Elkem ASAPostal address Office address Telephone Web Revision

+47 22 45 01 00 www.foundry.elkem.com No. 2.1Telefax Org. no. 20.03.2004

P.O.Box 5211 MajorstuenNO-0302 OsloNorway

Hoffsveien 65BOsloNorway +47 22 45 01 52 NO 911 382 008 MVA

Selection of Inoculants for Ductile Cast IronCareful selection of charge materials and nodularisers is often negated by the use of theincorrect inoculant. Due consideration should be given to this essential part of the processand the following points should be taken into account:

• Which kind of nodulariser and treatment process has been used.

• The fade time of the metal, that is the time from adding the inoculant to pouring thelast metal from the ladle.

• The Rare Earth content of the nodulariser (or otherwise added RE).

Pure Mg processes, such as plunging, cored wires or converters, reduce the number density of inherentnuclei in the iron making the iron difficult to inoculate. MgFeSi processes have a net effect of adding nuclei tothe iron. Typically, a higher inoculant addition will be required when pure Mg processes are employed.

Rare Earth's serve to neutralise the effects of some subversive elements found in steel scrap used in thefurnace charge, however, they can have the same effect on certain elements added as integral parts of theinoculant.

Inevitably, inoculation of ductile iron requires greater amounts of treatment agent thangrey iron, principally due to the carbide stabilizing properties of the magnesium usedduring nodularisation. Whereas the graphite flakes govern the properties of grey iron,ductile iron characteristics are dominated by the matrix. Formation of even, roundednodules is therefore essential to obtain the best properties.

Four main groups of inoculants are commonly available, all based on ferrosilicon plusdeliberately added property enhancing elements.

Element ConsiderationsCalciumCa

Foundry Grade ferrosilicons (FG FeSi) containing balanced amounts of calcium and aluminium.Care should be taken in the selection of these materials as many are supplied with very highlevels of aluminium (>3%) which can cause severe pinholing problems in the casting. Good FGFeSi will give satisfactory nodule counts and iron properties in many medium section castings.

BariumBa

Barium containing inoculants are especially useful where the fade time of the iron is long orwhere the solidification of the casting is slow (e.g., heavy sections). Total barium contents in theinoculant above 3% are unnecessary and serve no purpose but may cause slag generation.

StrontiumSr

Strontium containing inoculants may only be used under certain conditions in ductile iron. Stron-tium will give an excellent chill removal and nodule count in iron treated with pure Mg, RE freeprocesses or in many MgFeSi situations where the RE content of the nodulariser is less than1%. High RE contents will neutralise the effects of Strontium.

ZirconiumZr

Zirconium containing inoculants are excellent medium potency and fade resistant materials. Zir-conium has the added advantage of tying up any N2 from the melting process or cores.

Other inoculants are commercially available, containing a variety of elements, rare earth’s,bismuth and manganese for example and details of the properties of these can beobtained from the manufacturers.

All of the types noted above are available in both ladle and stream gradings, details canbe obtained from your local Elkem sales representative.