Cast iron inoculant and method for production of cast iron inoculant
11708618 · 2023-07-25
Assignee
Inventors
Cpc classification
C22C38/002
CHEMISTRY; METALLURGY
C22C38/60
CHEMISTRY; METALLURGY
C22C38/005
CHEMISTRY; METALLURGY
B22D1/007
PERFORMING OPERATIONS; TRANSPORTING
International classification
Abstract
An inoculant for the manufacture of cast iron with spheroidal graphite is disclosed, the inoculant has a particulate ferrosilicon alloy having between 40 and 80% by weight of Si, 0.02-8% by weight of Ca; 0-5% by weight of Sr; 0-12% by weight of Ba; 0-10% by weight of rare earth metal; 0-5% by weight of Mg; 0.05-5% by weight of Al; 0-10% by weight of Mn; 0-10% by weight of Ti; 0-10% by weight of Zr; the balance being Fe and incidental impurities in the ordinary amount, wherein the inoculant additionally contains, by weight, based on the total weight of inoculant: 0.1 to 15% by weight of particulate rare earth metal oxide(s) and at least one of from 0.1 to 15% of particulate Bi.sub.2O.sub.3, and/or from 0.1 to 15% of particulate Bi.sub.2S.sub.3, and/or from 0.1 to 15% of particulate Sb.sub.2O.sub.3, and/or from 0.1 to 15% of particulate Sb.sub.2S.sub.3, and/or from 0.1 to 5% of one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or from 0.1 to 5% of one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, a method for producing such inoculant and use of such inoculant.
Claims
1. An inoculant for the manufacture of cast iron with spheroidal graphite, said inoculant comprises a particulate ferrosilicon alloy consisting of between 40 and 80% by weight of Si, 0.02-8% by weight of Ca; 0-5% by weight of Sr; 0-12% by weight of Ba; 0-10% by weight of rare earth metal; 0-5% by weight of Mg; 0.05-5% by weight of Al; 0-10% by weight of Mn; 0-10% by weight of Ti; 0-10% by weight of Zr; balance being Fe and incidental impurities in the ordinary amount, wherein said inoculant additionally contains, by weight, based on the total weight of inoculant: 0.1 to 15% by weight of particulate rare earth metal oxide(s), and at least one of from 0.1 to 15% of particulate Bi.sub.2O.sub.3, and/or from 0.1 to 15% of particulate Bi.sub.2S.sub.3, and/or from 0.1 to 15% of particulate Sb.sub.2O.sub.3, and/or from 0.1 to 15% of particulate Sb.sub.2S.sub.3, and optionally from 0.1 to 5% of one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or from 0.1 to 5% of one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof.
2. The inoculant according to claim 1, wherein the ferrosilicon alloy comprises between 45 and 60% by weight of Si.
3. The inoculant according to claim 1, wherein the ferrosilicon alloy comprises between 60 and 80% by weight of Si.
4. The inoculant according to claim 1, wherein the rare earth metals include Ce, La, Y and/or mischmetal.
5. The inoculant according to claim 1, wherein the inoculant comprises 0.2 to 12% by weight of particulate rare earth metal oxide(s).
6. The inoculant according to claim 1, wherein the rare earth metal oxide(s) is (are) CeO.sub.2 and/or La.sub.2O.sub.3 and/or Y.sub.2O.sub.3.
7. The inoculant according to claim 1, wherein the inoculant comprises from 0.3 to 10% of particulate Bi.sub.2O.sub.3.
8. The inoculant according to claim 1, wherein the inoculant comprises from 0.3 to 10% of particulate Bi.sub.2S.sub.3.
9. An inoculant for the manufacture of cast iron with spheroidal graphite, said inoculant comprises a particulate ferrosilicon alloy consisting of between 40 and 80% by weight of Si, 0.02-8% by weight of Ca; 0-5% by weight of Sr; 0-12% by weight of Ba; 0-10% by weight of rare earth metal; 0-5% by weight of Mg; 0.05-5% by weight of Al; 0-10% by weight of Mn; 0-10% by weight of Ti; 0-10% by weight of Zr; balance being Fe and incidental impurities in the ordinary amount, wherein said inoculant additionally contains, by weight, based on the total weight of inoculant: 0.1 to 15% by weight of particulate rare earth metal oxide(s), and at least one of from 0.1 to 15% of particulate Bi.sub.2O.sub.3, and/or from 0.1 to 15% of particulate Bi.sub.2S.sub.3, and/or from 0.1 to 15% of particulate Sb.sub.2S.sub.3, and optionally from 0.1 to 5% of one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or from 0.1 to 5% of one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, wherein the inoculant further comprises from 0.3 to 10% of particulate Sb.sub.2O.sub.3.
10. An inoculant for the manufacture of cast iron with spheroidal graphite, said inoculant comprises a particulate ferrosilicon alloy consisting of between 40 and 80% by weight of Si, 0.02-8% by weight of Ca; 0-5% by weight of Sr; 0-12% by weight of Ba; 0-10% by weight of rare earth metal; 0-5% by weight of Ma; 0.05-5% by weight of Al; 0-10% by weight of Mn; 0-10% by weight of Ti; 0-10% by weight of Zr; balance being Fe and incidental impurities in the ordinary amount, wherein said inoculant additionally contains, by weight, based on the total weight of inoculant: 0.1 to 15% by weight of particulate rare earth metal oxide(s), and at least one of from 0.1 to 15% of particulate Bi.sub.2O.sub.3, and/or from 0.1 to 15% of particulate Bi.sub.2S.sub.3, and/or from 0.1 to 15% of particulate Sb.sub.2O.sub.3, and optionally from 0.1 to 5% of one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or from 0.1 to 5% of one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, wherein the inoculant further comprises from 0.3 to 10% of particulate Sb.sub.2S.sub.3.
11. The inoculant according to claim 1, wherein the inoculant comprises from 0.5 to 3% of one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or from 0.5 to 3% of one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof.
12. The inoculant according to claim 1, wherein the total amount of the particulate rare earth metal oxide(s) and the at least one of particulate Bi.sub.2O.sub.3, and/or particulate Bi.sub.2S.sub.3, particulate Sb.sub.2O.sub.3, and/or particulate Sb.sub.2S.sub.3, and/or one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof is up to 20% by weight, based on the total weight of the inoculant.
13. The inoculant according to claim 1, wherein the inoculant is in the form of a blend or a physical mixture of the particulate ferrosilicon alloy and the particulate rare earth metal oxide(s), and the at least one particulate Bi.sub.2O.sub.3, particulate Bi.sub.2S.sub.3, particulate Sb.sub.2O.sub.3, particulate Sb.sub.2S.sub.3, one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof and/or one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof.
14. The inoculant according to claim 1, wherein the particulate rare earth metal oxide(s), and the at least one particulate Bi.sub.2O.sub.3, particulate Bi.sub.2S.sub.3, particulate Sb.sub.2O.sub.3, particulate Sb.sub.2S.sub.3, one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof and/or one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof are present as coating compounds on the particulate ferrosilicon based alloy.
15. The inoculant according to claim 1, wherein the inoculant is in the form of agglomerates made from a mixture of the particulate ferrosilicon alloy and the particulate rare earth metal oxide(s), and the at least one particulate Bi.sub.2O.sub.3, particulate Bi.sub.2S.sub.3, particulate Sb.sub.2O.sub.3, particulate Sb.sub.2S.sub.3, one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof and/or one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof.
16. The inoculant according to claim 1, wherein the inoculant is in the form of briquettes made from a mixture of the particulate ferrosilicon alloy and the particulate rare earth metal oxide(s), and the at least one particulate Bi.sub.2O.sub.3, particulate Bi.sub.2S.sub.3, particulate Sb.sub.2O.sub.3, particulate Sb.sub.2S.sub.3, one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof and/or one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof.
17. The inoculant according to claim 1, wherein the particulate ferrosilicon based alloy and the particulate rare earth metal oxide(s), and the at least one particulate Bi.sub.2O.sub.3, particulate Bi.sub.2S.sub.3, particulate Sb.sub.2O.sub.3, particulate Sb.sub.2S.sub.3, one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof and/or one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, are added separately but simultaneously to liquid cast iron.
18. A method for producing an inoculant according to claim 1, comprising: providing a particulate base alloy comprising between 40 to 80% by weight of Si, 0.02-8% by weight of Ca; 0-5% by weight of Sr; 0-12% by weight of Ba; 0-10% by weight of rare earth metal; 0-5% by weight of Mg; 0.05-5% by weight of Al; 0-10% by weight of Mn; 0-10% by weight of Ti; 0-10% by weight of Zr; the balance being Fe and incidental impurities in the ordinary amount, and adding to the said particulate base, by weight, based on the total weight of inoculant, 0.1 to 15% by weight of particulate rare earth metal oxide(s) and at least one of from 0.1 to 15% of particulate Bi.sub.2O.sub.3, and/or from 0.1 to 15% of particulate Bi.sub.2S.sub.3, and/or from 0.1 to 15% of particulate Sb.sub.2O.sub.3, and/or from 0.1 to 15% of particulate Sb.sub.2S.sub.3, and optionally from 0.1 to 5% of one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or from 0.1 to 5% of one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, to produce said inoculant.
19. The method according to claim 18, wherein the particulate rare earth metal oxide(s), and the particulate Bi.sub.2O.sub.3, and/or the particulate Bi.sub.2S.sub.3, and/or the particulate Sb.sub.2O.sub.3, the particulate Sb.sub.2S.sub.3, the one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or the one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, are mixed or blended with the particulate base alloy.
20. The method according to claim 18, wherein the particulate rare earth metal oxide(s), and the particulate Bi.sub.2O.sub.3, and/or the particulate Bi.sub.2S.sub.3, and/or the particulate Sb.sub.2O.sub.3, the particulate Sb.sub.2S.sub.3, the one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or the one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, are mixed before being mixed with the particulate base alloy.
21. Method for manufacturing cast iron with spheroidal graphite, by adding the inoculant according to claim 1 to the cast iron melt prior to casting, simultaneously to casting or as an in-mould inoculant.
22. The method according to claim 21, wherein the particulate ferrosilicon based alloy and the particulate rare earth metal oxide(s), and the particulate Bi.sub.2O.sub.3, and/or the particulate Bi.sub.2S.sub.3, and/or the particulate Sb.sub.2O.sub.3, the particulate Sb.sub.2S.sub.3, the one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or the one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, are added as a mechanical mixture or a blend to the cast iron melt.
23. The method according to claim 21, wherein the particulate ferrosilicon based alloy and the particulate rare earth metal oxide(s), and the particulate Bi.sub.2O.sub.3, and/or the particulate Bi.sub.2S.sub.3, and/or the particulate Sb.sub.2O.sub.3, the particulate Sb.sub.2S.sub.3, the one of more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or the one of more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, are added separately but simultaneously to the cast iron melt.
Description
BRIEF DESCRIPTION OF DRAWINGS
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DETAILED DESCRIPTION OF THE INVENTION
(9) According to the present invention a high potent inoculant is provided, for the manufacture of cast iron with spheroidal graphite. The inoculant comprises a FeSi base alloy particles combined with particulate rare earth metal oxide(s) and also comprises at least one of particulate bismuth oxide (Bi.sub.2O.sub.3), and/or bismuth sulphide (B.sub.2S.sub.3), and/or antimony oxide (Sb.sub.2O.sub.3), and/or antimony sulphide (Sb.sub.2S.sub.3), and/or iron oxide (one or more of Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof) and/or iron sulphide (one or more of FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof). The inoculant according to the present invention is easy to manufacture and it is easy to control and vary the amounts of RE, Bi and or Sb in the inoculant. Complicated and costly alloying steps are avoided, thus the inoculant can be manufactured at a lower cost compared to prior art inoculants containing rare earth metals, Bi and/or Sb.
(10) In the manufacturing process for producing ductile cast iron with compacted or spheroidal graphite the cast iron melt is normally treated with a nodulariser, e.g. by using an MgFeSi alloy, prior to the inoculation treatment. The nodularisation treatment has the objective to change the form of the graphite from flake to nodule when it is precipitating and subsequently growing. The way this is done is by changing the interface energy of the interface graphite/melt. It is known that Mg and Ce are elements that change the interface energy, Mg being more effective than Ce. When Mg is added to a base iron melt, it will first react with oxygen and sulphur, and it is only the “free magnesium” that will have a nodularising effect. The nodularisation reaction is violent and results in agitation of the melt, and it generates slag floating on the surface. The violence of the reaction will result in most of the nucleation sites for graphite that were already in the melt (introduced by the raw materials) and other inclusions being part of the slag on the top and removed. However some MgO and MgS inclusions produced during the nodularisation treatment will still be in the melt. These inclusions are not good nucleation sites as such.
(11) The primary function of inoculation is to prevent carbide formation by introducing nucleation sites for graphite. In addition to introducing nucleation sites the inoculation also transform the MgO and MgS inclusions formed during the nodularisation treatment into nucleation sites by adding a layer (with Ca, Ba or Sr) on the inclusions.
(12) In accordance with the present invention, the particulate FeSi base alloys should comprise from 40 to 80% by weight Si. A pure FeSi alloy is a week inoculant, but is a common alloy carrier for active elements, allowing good dispersion in the melt. Thus, there exists a variety of known FeSi alloy compositions for inoculants. Conventional alloying elements in a FeSi alloy inoculant include Ca, Ba, Sr, Al, Mg, Zr, Mn, Ti and RE (especially Ce and La). The amount of the alloying elements may vary. Normally, inoculants are designed to serve different requirements in grey, compacted and ductile iron production. The inoculant according to the present invention may comprise a FeSi base alloy with a silicon content of about 40-80% by weight. The alloying elements may comprise about 0.02-8% by weight of Ca; about 0-5% by weight of Sr; about 0-12% by weight of Ba; about 0-10% by weight of rare earth metal; about 0-5% by weight of Mg; about 0.05-5% by weight of Al; about 0-10% by weight of Mn; about 0-10% by weight of Ti; about 0-10% by weight of Zr; and the balance being Fe and incidental impurities in the ordinary amount.
(13) The FeSi base alloy may be a high silicon alloy containing 60 to 80% silicon or a low silicon alloy containing 45 to 60% silicon. Silicon is normally present in cast iron alloys, and is a graphite stabilizing element in the cast iron, which forces carbon out of the solution and promotes the formation of graphite. The FeSi base alloy should have a particle size lying within the conventional range for inoculants, e.g. between 0.2 to 6 mm. It should be noted that smaller particle sizes, such as fines, of the FeSi alloy may also be applied in the present invention, to manufacture the inoculant. When using very small particles of the FeSi base alloy the inoculant may be in the form of agglomerates (e.g. granules) or briquettes. In order to prepare agglomerates and/or briquettes of the present inoculant, the rare earth metal oxide(s) and the at least one of Bi.sub.2O.sub.3, and/or Bi.sub.2S.sub.3, and/or Sb.sub.2O.sub.3, and/or Sb.sub.2S.sub.3, and/or iron oxide (one or more of Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof) and/or iron sulphide (one or more of FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof), are mixed with the particulate ferrosilicon alloy by mechanical mixing or blending, in the presence of a binder, followed by agglomeration of the powder mixture according to the known methods. The binder may e.g. be a sodium silicate solution. The agglomerates may be granules with suitable product sizes, or may be crushed and screened to the required final product sizing.
(14) A variety of different inclusions (sulphides, oxides, nitrides and silicates) can form in the liquid state. The sulphides and oxides of the group IIA-elements (Mg, Ca, Sr and Ba) have very similar crystalline phases and high melting points. The group IIA elements are known to form stable oxides in liquid iron; therefore inoculants, and nodularisers, based on these elements are known to be effective deoxidizers. Calcium is the most common trace element in ferrosilicon inoculants. In accordance with the invention, the particulate FeSi based alloy comprises between about 0.02 to about 8% by weight of calcium. In some applications it is desired to have low content of Ca in the FeSi base alloy, e.g. from 0.02 to 0.5% by weight. Compared to conventional inoculant ferrosilicon alloys containing alloyed bismuth, where calcium is regarded as a necessary element to improve the bismuth (and antimony) yield, there is no need for calcium for solubility purposes in the inoculants according to the present invention. In other applications the Ca content could be higher, e.g. from 0.5 to 8% by weight. A high level of Ca may increase slag formation, which is normally not desired. A plurality of inoculants comprise about 0.5 to 3% by weight of Ca in the FeSi alloy. The FeSi base alloy should comprise up to about 5% by weight of strontium. A Sr amount of 0.2-3% by weight is typically suitable. Barium may be present in an amount up to about 12% by weight in the FeSi inoculant alloy. Ba is known to give better resistance to fading of the inoculating effect during prolonged holding time of the molten iron after inoculation, and gives better efficiencies over a wider temperature range. Many FeSi alloy inoculants comprise about 0.1-5% by weight of Ba. If barium is used in conjunction with calcium the two may act together to give a greater reduction in chill than an equivalent amount of calcium.
(15) Magnesium may be present in an amount up to about 5% by weight in the FeSi inoculant alloy. However, as Mg normally is added in the nodularisation treatment for the production of ductile iron, the amount of Mg in the inoculant may be low, e.g. up to about 0.1% by weight. Compared to conventional inoculant ferrosilicon alloys containing alloyed bismuth, where magnesium is regarded as a necessary element to stabilise the bismuth containing phases, there is no need for magnesium for stabilisation purposes in the inoculants according to the present invention.
(16) The FeSi base alloy may comprise up to 10% by weight of rare earths metals (RE). RE includes at least Ce, La, Y and/or mischmetal. Mischmetal is an alloy of rare-earth elements, typically comprising approx. 50 Ce and 25% La, with small amounts of Nd and Pr. Lately heavier rare earth metals are often removed from the mischmetal, and the alloy composition of mischmetal may be about 65% Ce and about 35% La, and traces of heavier RE metals, such as Nd and Pr. Additions of RE are frequently used to restore the graphite nodule count and nodularity in ductile iron containing subversive elements, such as Sb, Pb, Bi, Ti etc. In some inoculants the amount of RE is up to 10% by weight. Excessive RE may in some instances lead to chunky graphite formations. Thus, in some applications the amount of RE should be lower, e.g. between 0.1-3% by weight. The inoculant according to the present invention contains RE oxide(s) as an additive to the particulate base ferrosilicon alloy, therefore the ferrosilicon alloy does not need any alloyed RE. Preferably the RE is Ce and/or La.
(17) Aluminium has been reported to have a strong effect as a chill reducer. Al is often combined with Ca in a FeSi alloy inoculants for the production of ductile iron. In the present invention, the Al content should be up to about 5% by weight, e.g. from 0.1-5%.
(18) Zirconium, manganese and/or titanium are also often present in inoculants. Similar as for the above mentioned elements, the Zr, Mn and Ti play an important role in the nucleation process of the graphite, which is assumed to be formed as a result of heterogeneous nucleation events during solidification. The amount of Zr in the FeSi base alloy may be up to about 10% by weight, e.g. up to 6% by weight. The amount of Mn in the FeSi base alloy may be up to about 10% by weight, e.g. up to 6% by weight. The amount of Ti in the FeSi base alloy may also be up to about 10% by weight, e.g. up to 6% by weight.
(19) Bismuth and antimony are known to have high inoculating power and to provide an increase in the number of nuclei. However, the presence of small amounts of elements like Sb and/or Bi in the melt (also called subversive elements) might reduce nodularity. This negative effect can be neutralized by using Ce or other RE metal.
(20) Introducing RE-oxide/Sb.sub.2O.sub.3/Sb.sub.2S.sub.3/Bi.sub.2O.sub.3/Bi.sub.2S.sub.3 together with the FeSi based alloy inoculant is adding a reactant to an already existing system with Mg inclusions floating around in the melt and “free” Mg. The addition of inoculant is not a violent reaction and the RE yield, the Sb yield, if Sb oxide and/or sulphide, is (are) added (Sb/Sb.sub.2O.sub.3/Sb.sub.2S.sub.3 remaining in the melt) and Bi yield, if Bi oxide and/or sulphide, is (are) added (Bi/Bi.sub.2O.sub.3/Bi.sub.2S.sub.3) remaining in the melt is expected to be high.
(21) The amount of rare earth metal oxide(s) should be from 0.1 to 15% by weight based on the total amount of the inoculant. In some embodiments, the amount of rare earth metal oxide(s) should be from 0.2 to 12% by weight. In some embodiments, the amount of rare earth metal oxide(s) should be from 0.5 to 10% by weight. The RE-oxide particles should have a small particle size, i.e. micron size (e.g. 1-50 μm, or e.g. 1-10 μm). The rare earth metal oxide(s) is (are) one or more of CeO.sub.2 and/or La.sub.2O.sub.3 and/or Y.sub.2O.sub.3. The rare earth metal oxide may also include oxides of Nd and/or Pr and other rare earth metals. The inoculant may comprise a mixture of the said rare earth metal oxides. Adding RE as one of more RE oxide combined with a FeSi base alloy is advantageous in several ways; in addition to giving a high number of nodules in cast samples, the present inoculants has an advantage that a ferrosilicon base alloy may be adapted for different uses by varying the amount of RE oxide, and other active inoculant elements (Bi, Sb oxide/sulphide) in a simple manner, thereby costly alloying steps are avoided; and it is possible to produce specific inoculant compositions in small volumes. It is also thought that RE oxide(s) will melt and/or dissolve faster than intermetallic phases, which are generally coarser in a ferrosilicon alloy.
(22) The Sb.sub.2S.sub.3 particles, the Sb.sub.2O.sub.3 particles, the Bi.sub.2S.sub.3 particles and the Bi.sub.2O.sub.3 particles should have a small particle size, i.e. micron size, which result in very quick melting or dissolution of said particles when introduced into the cast iron melt. Advantageously, said RE-oxide particles, and the at least one of Bi and/or Sb and/or Fe oxide/sulphide particles are mixed with the particulate FeSi base alloy, prior to adding the inoculant into the cast iron melt.
(23) The amount of particulate Bi.sub.2O.sub.3, if present, should be from 0.1 to 15% by weight based on the total amount of the inoculant. In some embodiments the amount of Bi.sub.2O.sub.3 can be 0.1-10% by weight. The amount of Bi.sub.2O.sub.3 can also be from about 0.5 to about 3.5% by weight, based on the total weight of inoculant.
(24) The amount of particulate Bi.sub.2S.sub.3, if present, should be from 0.1 to 15% by weight based on the total amount of the inoculant. In some embodiments, the amount of Bi.sub.2S.sub.3 can be 0.1-10% by weight. The amount of Bi.sub.2S.sub.3 can also be about 0.5 to about 3.5% by weight, based on the total weight of inoculant. The particle size of Bi.sub.2O.sub.3 and Bi.sub.2S.sub.3 is typically 1-10 μm.
(25) Adding Bi in the form of Bi.sub.2S.sub.3 and Bi.sub.2O.sub.3 particles, if present, instead of alloying Bi with the FeSi alloy has several advantages. Bi has poor solubility in ferrosilicon alloys, therefore, the yield of added Bi metal to the molten ferrosilicon is low and thereby the cost of a Bi-containing FeSi alloy inoculant increases. Further, due to the high density of elemental Bi it may be difficult to obtain a homogeneous alloy during casting and solidification. Another difficulty is the volatile nature of Bi metal due to the low melting temperature compared to the other elements in the FeSi based inoculant. Adding Bi as an oxide, if present, together with the FeSi base alloy provides an inoculant which is easy to produce with probably lower production costs compared to the traditional alloying process, wherein the amount of Bi is easily controlled and reproducible. Further, as the Bi is added as oxide, if present, instead of alloying in the FeSi alloy, it is easy to vary the bismuth amount in the inoculant, e.g. for smaller production series. Further, although Bi is known to have a high inoculating power, the oxygen is also of importance for the performance of the present inoculant, hence, providing another advantage of adding Bi as an oxide.
(26) The amount of particulate Sb.sub.2O.sub.3, if present, should be from 0.1 to 15% by weight based on the total amount of the inoculant. In some embodiments the amount of Sb.sub.2O.sub.3 can be 0.1-8% by weight. The amount of Sb.sub.2O.sub.3 can also be from about 0.5 to about 3.5% by weight, based on the total weight of inoculant.
(27) The amount of particulate Sb.sub.2S.sub.3, if present, should be from 0.1 to 15% by weight based on the total amount of the inoculant. In some embodiments, the amount of Sb.sub.2S.sub.3 can be 0.1-8% by weight. Good results are also observed when the amount of Sb.sub.2S.sub.3 is from about 0.5 to about 3.5% by weight, based on the total weight of inoculant. The particle size of Sb.sub.2O.sub.3 and Sb.sub.2S.sub.3 is typically 10-150 μm.
(28) Adding Sb in the form Sb.sub.2S.sub.3 particles and/or Sb.sub.2O.sub.3 particles instead of alloying Sb with the FeSi alloy, provides several advantages. Although Sb is a powerful inoculant, the oxygen and sulphur are also of importance for the performance of the inoculant. Another advantage is the good reproducibility, and flexibility, of the inoculant composition since the amount and the homogeneity of particulate Sb.sub.2S.sub.3 and/or Sb.sub.2O.sub.3 in the inoculant are easily controlled. The importance of controlling the amount of inoculants and having a homogenous composition of the inoculant is evident given the fact that antimony is normally added at a ppm level. Adding an inhomogeneous inoculant may result in wrong amounts of inoculating elements in the cast iron. Still another advantage is the more cost effective production of the inoculant compared to methods involving alloying antimony in a FeSi based alloy.
(29) The total amount of one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, if present, should be from 0.1 to 5% by weight based on the total amount of the inoculant. In some embodiments the amount of one or more of Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof can be 0.5-3% by weight. The amount of one or more of Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof can also be from about 0.8 to about 2.5% by weight, based on the total weight of inoculant. Commercial iron oxide products for industrial applications, such as in the metallurgy field, might have a composition comprising different types of iron oxide compounds and phases. The main types of iron oxide being Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, and/or FeO (including other mixed oxide phases of Fe.sup.II and Fe.sup.III; iron(II,III)oxides), all which can be used in the inoculant according to the present invention. Commercial iron oxide products for industrial applications might comprise minor (insignificant) amounts of other metal oxides as impurities.
(30) The total amount of one or more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, if present, should be from 0.1 to 5% by weight based on the total amount of the inoculant. In some embodiments the amount of one or more of FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof can be 0.5-3% by weight. The amount of one or more of FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof can also be from about 0.8 to about 2.5% by weight, based on the total weight of inoculant. Commercial iron sulphide products for industrial applications, such as in the metallurgy field, might have a composition comprising different types of iron sulphide compounds and phases. The main types of iron sulphides being FeS, FeS.sub.2 and/or Fe.sub.3S.sub.4 (iron(II, III)sulphide; FeS, Fe.sub.2S.sub.3), including non-stoichiometric phases of FeS; Fe.sub.1+xS (x>0 to 0.1) and Fe.sub.1−yS (y>0 to 0.2), all which can be used in the inoculant according to the present invention. A commercial iron sulphide product for industrial applications might comprise minor (insignificant) amounts of other metal sulphides as impurities.
(31) One of the purposes of adding of one or more of Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof and/or one or more of FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof into the cast iron melt is to deliberately add oxygen and sulphur into the melt, which may contribute to increase the nodule count.
(32) It should be understood that the total amount of the RE-oxide particles, and the at least one of Sb oxide/sulphide particles, Bi oxide/sulphide particles, and any Fe oxide/sulphide, if present, should be up to about 20% by weight, based on the total weight of the inoculant. It should also be understood that the composition of the FeSi base alloy may vary within the defined ranges, and the skilled person will know that the amounts of the alloying elements add up to 100%. There exists a plurality of conventional FeSi based inoculant alloys, and the skilled person would know how to vary the FeSi base composition based on these.
(33) The addition rate of the inoculant according to the present invention to a cast iron melt is typically from about 0.1 to 0.8% by weight. The skilled person would adjust the addition rate depending on the levels of the elements, e.g. an inoculant with high Bi and/or high Sb will typically need a lower addition rate.
(34) The present inoculant is produced by providing a particulate FeSi base alloy having the composition as defined herein, and adding to the said particulate base rare earth metal oxide(s) and at least one of the particulate Sb.sub.2O.sub.3/Sb.sub.2S.sub.3/Bi.sub.2O.sub.3/Bi.sub.2S.sub.3, and optionally one or more of Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof and/or one or more of FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, to produce the present inoculant. The rare earth metal oxide(s) and the at least one of Sb.sub.2O.sub.3, Sb.sub.2S.sub.3, B.sub.2O.sub.3 and/or Bi.sub.2S.sub.3 particles, as well as the Fe oxide/sulphide particles, if present, may be mechanically/physically mixed with the FeSi base alloy particles. Any suitable mixer for mixing/blending particulate and/or powder materials may be used. The mixing may be performed in the presence of a suitable binder, however it should be noted that the presence of a binder is not required. The rare earth metal oxide(s) and the at least one of Sb.sub.2O.sub.3, Sb.sub.2S.sub.3, B.sub.2O.sub.3 and/or Bi.sub.2S.sub.3 particles, as well as the Fe oxide/sulphide particles, if present, may also be blended with the FeSi base alloy particles, providing a homogenously mixed inoculant Blending the rare earth metal oxide(s), and said additional sulphide/oxide powders, with the FeSi base alloy particles, may form a stable coating on the FeSi base alloy particles. It should however be noted that mixing and/or blending the rare earth metal oxide(s) and any other of the said particulate oxides/sulphides, with the particulate FeSi base alloy is not mandatory for achieving the inoculating effect. The particulate FeSi base alloy and rare earth metal oxide(s), and any of the said particulate oxides/sulphides, may be added separately but simultaneously to the liquid cast iron. The inoculant may also be added as an in-mould inoculant. The inoculant particles of FeSi alloy, rare earth metal oxide(s), and any of the said particulate Bi oxide/sulphide, Sb oxide/sulphide and/or Fe oxide/sulphide, if present, may also be formed to agglomerates or briquettes according to generally known methods.
(35) The following Examples show that the addition of rare earth metal oxide(s) and Sb.sub.2O.sub.3/Sb.sub.2S.sub.3/Bi.sub.2O.sub.3/Bi.sub.2S.sub.3 particles together with FeSi base alloy particles results in an increased nodule number density when the inoculant is added to cast iron, compared to an inoculant according to the prior art in WO 99/29911, as defined below. A higher nodule count allows reducing the amount of inoculant necessary to achieve the desired inoculating effect.
EXAMPLES
(36) All test samples were analysed with respect to the microstructure to determine the nodule density. The microstructure was examined in one tensile bar from each trial according to ASTM E2567-2016. Particle limit was set to >10 μm. The tensile samples were Ø28 mm cast in standard moulds according to ISO1083-2004, and were cut and prepared according to standard practice for microstructure analysis before evaluating by use of automatic image analysis software. The nodule density (also denoted nodule number density) is the number of nodules (also denoted nodule count) per mm.sup.2, abbreviated N/mm.sup.2.
(37) The iron oxide used in the following examples, was a commercial magnetite (Fe.sub.3O.sub.4) with the specification (supplied by the producer); Fe.sub.3O.sub.4>97.0%; SiO.sub.2<1.0%. The commercial magnetite product probably included other iron oxide forms, such as Fe.sub.2O.sub.3 and FeO. The main impurity in the commercial magnetite was SiO.sub.2, as indicated above.
(38) The iron sulphide used in the following examples, was a commercial FeS product. An analysis of the commercial product indicated presence of other iron sulphide compounds/phases in addition to FeS, and normal impurities in insignificant amounts.
Example 1
(39) Two melts, Melt P and Melt Q, were prepared and each melt was treated in a tundish cover ladle by 1.20-1.25% by weight of a standard MgFeSi nodularising alloy having a composition of (% by weight) 46.0% Si; 4.33% Mg; 0.69% Ca; 0.44% RE; 0.44% Al, balance Fe and incidental impurities in the ordinary amount (RE is Rare Earth metals containing approx. 65% Ce and 35% La). 0.7% by weight of steel chips were used as cover. The MgFeSi treatment was done at 1500° C. Inoculation trials were performed out of each magnesium treated melt, as shown in table 1, with an addition rate of 0.2 wt %. The holding time was from filling the pouring ladle containing the inoculant to pouring was 1 minute for all trials. The pouring temperatures were 1392-1365° C. for Melt P and 1384-1370° C. for Melt Q. In this example, the treated melts were cast as a step block. The section analysed for the nodule count had a thickness of 20 mm. The final cast iron chemical compositions for all treatments were within 3.4-3.6 wt % C, 2.3-2.5 wt % Si, 0.29-0.31 wt % Mn, 0.007-0.011 wt % S, 0.040-0.043 wt % Mg.
(40) A base FeSi alloy, for an inoculant according to the present invention, had a composition of (in % by weight) 75% Si; 1.57% Al; 1.19% Ca; balance Fe and incidental impurities in the ordinary amount, herein denoted Inoculant A. The Inoculant A base alloy was coated with CeO.sub.2 and Bi.sub.2S.sub.3 in amounts as shown in table 1.
(41) Another base FeSi alloy, for an inoculant according to the present invention, had a composition of (in % by weight) 68.2% Si; 0.93% Al; 0.94% Ba; 0.95% Ca; balance Fe and incidental impurities in the ordinary amount, herein denoted Inoculant B. The Inoculant A and Inoculant B base alloy particles were coated with CeO.sub.2 and Bi.sub.2S.sub.3 in amounts as shown in table 1.
(42) The prior art inoculant was an inoculant according to WO99/29911, having a base alloy composition of (in % by weight) 74.2% Si; 0.97% Al; 0.78% Ca; 1.55% Ce, balance Fe and incidental impurities in the ordinary amount, herein denoted Inoculant X.
(43) The added amounts of particulate CeO.sub.2 and particulate Bi.sub.2S.sub.3, to the FeSi base alloys (Inoculant A and Inoculant B) are shown in Table 1, together with the inoculant according to the prior art. The amounts of CeO.sub.2, Bi.sub.2S.sub.3, FeS and Fe.sub.3O.sub.4 are based on the total weight of the inoculants in all tests. The amounts of CeO.sub.2, Bi.sub.2S.sub.3 FeS and Fe.sub.3O.sub.4 are the percentage of compound.
(44) TABLE-US-00001 TABLE 1 Inoculant compositions. Additions, wt-% Base inoculant FeS Fe.sub.3O.sub.4 CeO.sub.2 Bi.sub.2O.sub.3 Bi.sub.2S.sub.3 Reference Melt P Inoculant X 1.00 2.00 Prior art Inoculant A 0.37 0.67 Inoculant A + CeO2/Bi2O3 Melt Q Inoculant X 1.00 2.00 Prior art Inoculant B 1.47 0.74 Inoculant B + CeO2/Bi2S3
(45) The nodule density in the cast irons from the inoculation trials in Melt P are shown in
(46) Analysis of the microstructure showed that both the inoculants according to the present invention had significantly higher nodule density, compared to the prior art inoculant.
Example 2
(47) Three iron melts, Melt W, Y and Z, were prepared and each melt was treated in a tundish over ladle by 1.20-1.25% by weight of a standard MgFeSi nodularising alloy having a composition of (% by weight) 46.0% Si; 4.33% Mg; 0.69% Ca; 0.44% RE; 0.44% Al, balance Fe and incidental impurities in the ordinary amount (RE is Rare Earth metals containing approx. 65% Ce and 35% La). 0.7% by weight of steel chips were used as cover. The MgFeSi treatment was done at 1500° C. Inoculation trials were performed out of each magnesium treated melt, as shown in table 2, with an addition rate of 0.2 wt %. The holding time was from filling the pouring ladle containing the inoculant to pouring was 1 minute for all trials. The pouring temperatures were 1370-1353° C. for Melt W and 1389-1361° C. for Melt Y, and 1381-1363° C. for Melt Z. The final cast iron chemical compositions for all treatments were within 3.5-3.7 wt % C, 2.3-2.5 wt % Si, 0.29-0.31 wt % Mn, 0.007-0.011 wt % S, 0.040-0.043 wt % Mg.
(48) The compositions of the particulate base FeSi alloys were the same as specified in Example 1. The Inoculant A base alloy particles were coated with particulate CeO.sub.2, and particulate Bi.sub.2S.sub.3, Bi.sub.2O.sub.3, Sb.sub.2S.sub.3 and/or Sb.sub.2O.sub.3 in amounts as shown in table 2. The prior art inoculant was an inoculant according to WO99/29911, having a base alloy composition, Inoculant X, as defined in Example 1.
(49) The added amounts of particulate CeO.sub.2 and particulate Bi.sub.2S.sub.3, Bi.sub.2O.sub.3, Sb.sub.2S.sub.3 and Sb.sub.2O.sub.3, to the FeSi base alloy (Inoculant A) are shown in Table 2, together with the inoculant according to the prior art. The amounts of CeO.sub.2, Bi.sub.2S.sub.3, Bi.sub.2O.sub.3, Sb.sub.2S.sub.3, Sb.sub.2O.sub.3, FeS and Fe.sub.3O.sub.4 are the percentage of compound, based on the total weight of the inoculants in all tests.
(50) TABLE-US-00002 TABLE 2 Inoculant compositions. Base Additions, wt-% inoculant FeS Fe.sub.3O.sub.4 CeO.sub.2 Bi.sub.2S.sub.3 Bi.sub.2O.sub.3 Sb.sub.2S.sub.3 Sb.sub.2O.sub.3 Reference Melt W Inoculant X 1.00 2.00 — Prior art Inoculant A 1.23 1.23 1.11 Inoculant A+ CeO2/Bi2S3/Bi2O3 Inoculant A 1.23 2.79 Inoculant A + CeO2/Sb2S3 Melt Y Inoculant X 1.00 2.00 Prior art Inoculant A 1.23 1.11 1.39 Inoculant A + CeO2/Bi2O3/Sb2S3 Inoculant A 1.23 1.23 1.20 Inoculant A + CeO2/Bi2S3/Sb2O3 Inoculant A 1.23 1.11 1.20 Inoculant A + CeO2/Bi2O3/Sb2O3 Inoculant A 1.23 1.23 1.39 Inoculant A + CeO2/Bi2S3/Sb2S3 Melt Z Inoculant X 1.00 2.00 Prior art Inoculant A 9.83 3.34 Inoculant A + CeO2/Bi2O3
(51) The nodule density in the cast irons from the inoculation trials in Melt W are shown in
(52)
(53)
Example 3
(54) Two cast iron melts, Melt AG and Melt AH, each of 275 kg were prepared and treated by 1.20-1.25 wt-% MgFeSi nodulariser of the composition, in wt % 46.0% Si, 4.33% Mg, 0.69% Ca, 0.44% RE, 0.44% Al, balance Fe and incidental impurities, in a tundish cover ladle. 0.7% by weight steel chips were used as cover. Addition rates for all inoculants were 0.2% by weight added to each pouring ladle. The MgFeSi treatment temperature was 1500° C. and pouring temperatures were 1390-1362° C. for Melt AG and 1387-1361° C. for Melt AH. Holding time from filling the pouring ladles to pouring was 1 minute for all trials. The chemical composition for all treatments was within 3.5-3.7 wt % C, 2.3-2.5 wt % Si, 0.29-0.31 wt % Mn, 0.009-0.011 wt % S, 0.04-0.05 wt % Mg.
(55) The added amounts of particulate La.sub.2O.sub.3, Y.sub.2O.sub.3 and CeO.sub.2 and particulate Bi.sub.2O.sub.3 and Sb.sub.2O.sub.3, to the FeSi base alloys (Inoculant A, Inoculant B and Inoculant X, as defined in Example 1) are shown in Table 3 and 4, together with the inoculant according to the prior art. The amounts of particulate La.sub.2O.sub.3, Y.sub.2O.sub.3 and CeO.sub.2 and particulate Bi.sub.2O.sub.3 Sb.sub.2O.sub.3, FeS and Fe.sub.3O.sub.4 are the percentage of compound, based on the total weight of the inoculants in all tests.
(56) TABLE-US-00003 TABLE 3 Inoculant compositions. Base Additions, wt-% inoculant FeS Fe.sub.3O.sub.4 La.sub.2O.sub.3 Bi.sub.2O.sub.3 Sb.sub.2O.sub.3 Reference Melt AG Inoculant X 1.00 2.00 Prior art Inoculant A 1.17 2.39 InoculantA + La2O3/Sb2O3 Inoculant A 1.17 1.11 1.20 InoculantA + La2O3/Sb2O3/Bi2O3 Inoculant B 1.17 2.23 InoculantB + La2O3/Bi2O3
(57) The nodule density in the cast irons from the inoculation trials in Melt AG are shown in
(58) TABLE-US-00004 TABLE 4 Inoculant compositions. Base Additions, wt-% inoculant FeS Fe.sub.3O.sub.4 Y.sub.2O.sub.3 CeO.sub.2 Bi.sub.2O.sub.3 Sb.sub.2O.sub.3 Reference Melt AH Inoculant X 1.00 2.00 Prior art Inoculant A 1.27 2.23 InoculantA + Y2O3/Bi2O3 Inoculant A 1.27 2.39 InoculantA + Y2O3/Sb2O3 Inoculant B 1.23 1.11 1.20 InoculantB + Ce2O3/Sb2O3/Bi2O3
(59) The nodule density in the cast irons from the inoculation trials in Melt AH are shown in
Example 4
(60) One cast iron melt, Melt AK of 275 kg was prepared and treated by 1.20-1.25 wt-% MgFeSi nodulariser alloy of the composition: 46.0 wt % Si, 4.33 wt % Mg, 0.69 wt % Ca, 0.44% RE, 0.44% Al, balance Fe and incidental impurities, in a tundish cover ladle. 0.7% by weight steel chips were used as cover. From the treatment ladle, the melt was poured over to pouring ladles. Addition rates for all inoculants were 0.2% by weight added to each pouring ladle. The MgFeSi treatment temperature was 1500° C. and pouring temperatures were 1378-1368° C. The holding time from filling the pouring ladles to pouring was 1 minute for all trials.
(61) The test inoculants had ferrosilicon base alloys of composition of the prior art as described in Example 1 (herein denoted Inoculant X, with composition as defined in Example 1) and of composition: 74 wt % Si, 2.42 wt % Ca, 1.73 wt % Zr, 1.23 wt % Al herein denoted Inoculant C. The base ferrosilicon alloy particles (Inoculant C) were coated by particulate CeO.sub.2 and particulate Sb.sub.2O.sub.3 by mechanically mixing to obtain a homogenous mixture.
(62) The chemical composition for all treatments was within 3.5-3.7 wt % C, 2.3-2.5 wt % Si, 0.29-0.31 wt % Mn, 0.009-0.011 wt % S, 0.04-0.05 wt % Mg.
(63) The added amounts of particulate CeO.sub.2 and particulate Sb.sub.2O.sub.3, to the FeSi base alloy (Inoculant C) are shown in Table 5, together with the inoculant according to the prior art. The amounts of CeO.sub.2. Sb.sub.2O.sub.3, FeS and Fe.sub.3O.sub.4 are the percentages of compounds, based on the total weight of the inoculants in all tests.
(64) TABLE-US-00005 TABLE 5 Inoculant compositions. Base Additions, wt-% inoculant FeS Fe.sub.3O.sub.4 CeO.sub.2 Sb.sub.2O.sub.3 Reference Melt Inoculant X 1.00 2.00 Prior art AK Inoculant C 0.61 1.20 Inoculant C + CeO.sub.2/ Sb2O3
(65) The nodule density in the cast irons from the inoculation trials in Melt AK are shown in
(66) Having described different embodiments of the invention it will be apparent to those skilled in the art that other embodiments incorporating the concepts may be used. These and other examples of the invention illustrated above and in the accompanying drawings are intended by way of example only and the actual scope of the invention is to be determined from the following claims.