The addition of strontium greatly increases the inoculating power of a standard ferrosilicon in flake graphite grey iron or nodular graphite iron. This is a well established modification that has proven to reduce chill, eliminate carbides and improve nodule shape.
The inoculant alloy is produced by ELKEM ASA at the Bremanger and Chicoutimi plants, using special production methods to achieve high consistency. It is mechanically blended to contain low levels of Calcium and Aluminum, making it easy to handle in liquid iron.
The inoculant is a low calcium ferrosilicon containing strontium and has been found to be highly effective in both flake graphite grey irons and nodular graphite cast irons. The inoculant is also virtually free of aluminium, thus eliminating problems which are caused by small additions of this element automatically made to inoculating grades of ferrosilicon.
In a series of practical experiments it was found that the inoculant was especially effective for nodular graphite cast irons having a high eutectic cell count. Plates from two different taps were treated with the inoculant, one having a normal amount of aluminium and the other a very low amount of calcium. The inoculant was found to be capable of reducing chill considerably with only a very low amount of addition and of producing very good ductility in the cast metal.
The inoculant is particularly useful for gray irons requiring a very low chill level and for nodular graphite cast irons where a very high number of eutectic cells must be produced. It is also very effective for ductile irons and low sulphur cast iron.
In the present invention, there is disclosed a strontium silicon inoculant having high inoculating power and good anti decay capability. It is particularly effective for thin section gray iron castings and also helps in reducing shrinkage. This is accomplished by reducing the eutectic cell size and improving graphite morphology.
This inoculant can be made by using a low calcium ferro-silicon with an addition of 0.5 percent of strontium metal, strontium silicide or strontium ferrite alloy (all having less than 0.15% Ca and less than 0.05%). Tests of this inoculant indicate that it has superior chill removal properties as compared to normal aluminosilicate inoculants containing only 0.5% calcium.
It is possible to produce more machinable cast iron by use of the inoculant thereby helping to satisfy the demand for thinner casting sections and lighter design of castings. The inoculant has excellent inoculating abilities in both nodular and flake graphite cast irons and can be used in conjunction with a deoxidizer/degasser to reduce slag formation in the melting furnace.
According to Elkem, the strontium and zirconium content of the inoculant increases material strength without causing chill which enables the casting of thinner nodular graphite irons. Its low calcium level also allows the addition of large amounts of aluminum and reduces slag formation which extends the service life of ladles and other equipment.
The inoculation of the flake graphite irons with the strontium-containing ferrosilicon is considerably stronger than that achieved with normal additions of calcium and ferrosilicon. This is illustrated by the nodule count of the 0.6 in. diameter bars from melt No. 1 which contains a 1 percent silicon addition compared with the nodule count of the bar from melt No. 2 which has only 0.5 percent of the same addition.
Inoculation was improved even further when the 2% strontium was added in the form of strontium metal together with normal ferrosilicon which contained only 0.8% of calcium (see taps Nos. 4/1 and 4/2). The eutectic cell count and chill removal were considerably higher than with the additions of calcium and ferrosilicon alone.
The inoculant consists of 75% regular ferrosilicon with controlled additions of strontium and aluminum. It performs well in thin section gray iron castings, and it has a very high chill reduction, especially in the thinner sections of the melt. This inoculant also shows a very good tendency to suppress the growth of graphite nodules. In flake graphite irons the strontium addition is stronger than in normal ferrosilicon, and larger additions of strontium silicide show a very positive effect.
In foundry production, the inoculant can be added to the melt in either the furnace, ladle or in-mold. The inoculant can reduce the amount of magnesium required in the melt, which saves metal treatment costs. The inoculant can also improve the mechanical properties of cast products, such as reducing the wall thickness sensitivity of the casting. It can also promote graphite morphology, control the white tendency, increase the matrix hardness and improve the uniformity of graphite in a cast iron.
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