Cast iron inoculant and method for production of cast iron inoculant
11479828 · 2022-10-25
Assignee
Inventors
Cpc classification
C22C28/00
CHEMISTRY; METALLURGY
C21C7/0075
CHEMISTRY; METALLURGY
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; 0-15% 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% of particulate Sb.sub.2S.sub.3, and optionally between 0.1 and 15% of particulate Bi.sub.2O.sub.3, and/or between 0.1 and 15% of particulate Sb.sub.2O.sub.3, and/or between 0.1 and 15% of particulate Bi.sub.2S.sub.3, and/or between 0.1 and 5% of one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or between 0.1 and 5% of one or 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; 0-15% 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 said inoculant additionally contains, by weight, based on the total weight of inoculant: 0.1 to 15% of particulate Sb.sub.2O.sub.3, and at least one of from 0.1 and 15% of particulate Bi.sub.2O.sub.3, between 0.1 and 5% of one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, or between 0.1 and 5% of one or 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 0.5 to 8% by weight of particulate Sb.sub.2O.sub.3.
6. The inoculant according to claim 1, wherein the inoculant comprises from 0.1 to 10% of particulate Bi.sub.2O.sub.3.
7. The inoculant according to claim 1, wherein the inoculant comprises from 0.5 to 3% of one or 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 or more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof.
8. The inoculant according to claim 1, wherein the total amount of the particulate Sb.sub.2O.sub.3 and the at least one of Bi.sub.2O.sub.3, and/or one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one or 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.
9. 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 Sb.sub.2O.sub.3 and the at least one of particulate Bi.sub.2O.sub.3, and/or one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one or more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof.
10. The inoculant according to claim 1, wherein the particulate Sb.sub.2O.sub.3 and the at least one of particulate Bi.sub.2O.sub.3, and/or one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one or 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.
11. 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 Sb.sub.2O.sub.3, and the at least one of particulate Bi.sub.2O.sub.3, and/or one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one or 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 inoculant is in the form of briquettes made from a mixture of the particulate ferrosilicon alloy and the particulate Sb.sub.2O.sub.3, and the at least one of particulate Bi.sub.2O.sub.3, and/or one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one or more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof.
13. The inoculant according to claim 1, wherein the particulate ferrosilicon based alloy and the particulate Sb.sub.2O.sub.3, and the at least one of particulate Bi.sub.2O.sub.3, and/or one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one or 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.
14. A method for producing an inoculant according to claim 1, the method comprises: providing a particulate base alloy consisting of 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; 0-15% 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% of particulate Sb.sub.2O.sub.3, and at least one of from 0.1 and 15% of particulate Bi.sub.2O.sub.3, between 0.1 and 5% of one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, or between 0.1 and 5% of one or more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, to produce said inoculant.
15. The method according to claim 14, wherein the particulate Sb.sub.2O.sub.3, and the at least one of particulate Bi.sub.2O.sub.3, and/or one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one or 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.
16. The method according to claim 14, wherein the particulate Sb.sub.2O.sub.3, and the at least one of particulate Bi.sub.2O.sub.3, and/or one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one or 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.
17. A 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.
18. The method according to claim 17, wherein the particulate ferrosilicon based alloy and the particulate Sb.sub.2O.sub.3, and the at least one of particulate Bi.sub.2O.sub.3, and/or one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one or 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.
19. The method according to claim 17, wherein the particulate ferrosilicon based alloy and the particulate Sb.sub.2O.sub.3, and the at least one of particulate Bi.sub.2O.sub.3, and/or one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one or 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
(1)
(2)
(3)
(4)
DETAILED DESCRIPTION OF THE INVENTION
(5) 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 combined with particulate antimony oxide (Sb.sub.2O.sub.3), and also comprises at least one of other particulate metal oxides and/or particulate metal sulphide chosen from: bismuth oxide (Bi.sub.2O.sub.3), iron oxide (one or more of Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof) and 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 amount of bismuth and antimony 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 Sb and/or Bi.
(6) In the manufacturing process for producing ductile cast iron with 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.
(7) 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.
(8) 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 0-15% 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.
(9) 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 Sb.sub.2O.sub.3 particles, and any additional particulate Bi.sub.2O.sub.3 and/or 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, 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.
(10) 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 and/or antimony, 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.
(11) 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.
(12) The FeSi base alloy may comprise up to 15% 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. Preferably the RE is Ce and/or La.
(13) 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%.
(14) 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.
(15) 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.
(16) Antimony and bismuth 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. According to the present invention, the amount of particulate Sb.sub.2O.sub.3 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 is 0.1-8% by weight. A high nodule count is also observed when the inoculant contains 0.2 to 7% by weight, based on the total weight of inoculant, of particulate Sb.sub.2O.sub.3.
(17) Introducing Sb.sub.2O.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 Sb yield (Sb/Sb.sub.2O.sub.3 remaining in the melt) is expected to be high. The Sb.sub.2O.sub.3 particles should have a small particle size, i.e. micron size (e.g. 10-150 μm) resulting in very quick melting or dissolution of the Sb.sub.2O.sub.3 particles when introduced into the cast iron melt. Advantageously, the Sb.sub.2O.sub.3 particles are physically/mechanically mixed with the particulate FeSi base alloy, and the at least one of the particulate Bi.sub.2O.sub.3 and/or 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, prior to adding the inoculant into the cast iron melt.
(18) Adding Sb in the form of Sb.sub.2O.sub.3 particles instead of alloying Sb with the FeSi alloy, provide several advantages. Although Sb is a powerful inoculant, the oxygen is 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.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.
(19) 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 8% by weight, based on the total weight of inoculant. The particle size of the Bi.sub.2O.sub.3 should be micron size, e.g. 1-10 μm.
(20) Adding Bi in the form of 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 composition of 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.
(21) 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.I 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.
(22) 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.
(23) One of the purposes of adding 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.
(24) It should be understood that the total amount of the Sb.sub.2O.sub.3 particles, and any of the said particulate Bi oxide, and/or Fe oxide/sulphide, 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.
(25) 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 Sb will typically need a lower addition rate.
(26) 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 the particulate Sb.sub.2O.sub.3, and at least one of particulate Bi.sub.2O.sub.3 and/or one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one or more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, to produce the present inoculant. The Sb.sub.2O.sub.3 particles and the at least one of particulate Bi.sub.2O.sub.3 and/or one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one or more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, 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 Sb.sub.2O.sub.3 particles and the at least one of particulate Bi.sub.2O.sub.3 and/or one or more of particulate Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeO, or a mixture thereof, and/or one or more of particulate FeS, FeS.sub.2, Fe.sub.3S.sub.4, or a mixture thereof, may also be blended with the FeSi base alloy particles, providing a homogenously mixed inoculant. Blending the Sb.sub.2O.sub.3 particles, 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 Sb.sub.2O.sub.3 particles, 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 Sb.sub.2O.sub.3 particles, 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, Sb.sub.2O.sub.3 particles, and any of the said particulate Bi oxide and/or Fe oxide/sulphide, if present, may also be formed to agglomerates or briquettes according to generally known methods.
(27) The following Examples show that the addition of Sb.sub.2O.sub.3 particles and the at least one of the Bi.sub.2O.sub.3 and/or 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 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. A higher nodule count allows reducing the amount of inoculant necessary to achieve the desired inoculating effect.
EXAMPLES
(28) 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.
(29) 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.
(30) 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
(31) Three inoculation trials were performed out of one ladle of 275 kg molten cast iron treated with magnesium by addition of 1.05 wt % MgFeSi nodularizing alloy in a tundish cover treatment ladle. 0.9 wt % steel chips were used as a cover. The MgFeSi nodularizing alloy had the following composition, in % by weight: 46.2% Si, 5.85% Mg, 1.02% Ca, 0.92% RE, 0.74% Al, the balance being iron and incidental impurities in the ordinary amount.
(32) Three different inoculants were used. The three inoculants consisted of a ferrosilicon alloy, Inoculant A, containing, in % by weight: 74.2% Si, 0.97% Al, 0.78% Ca, 1.55% Ce, the remaining being iron and incidental impurities in the ordinary amount. To one part of Inoculant A it was added 1.2 wt % Sb.sub.2O.sub.3 and 1 wt % FeS in particulate form, and mechanically mixed to provide the inoculant of the present invention. To another part of Inoculant A it was added 1.2 wt % Sb.sub.2O.sub.3, 1 wt % FeS and 2 wt % Fe.sub.3O.sub.4, and mechanically mixed to provide the inoculant of the present invention. To another part of Inoculant A it was added 1 wt % FeS and 2 wt % Fe.sub.3O.sub.4, and mechanically mixed. This is the inoculant according to WO 99/29911.
(33) The MgFeSi treatment temperature was 1550° C. and pouring temperatures were 1387-1355° C. Holding time from filling the pouring ladles to pouring was 1 minute for all trials. The inoculants were added to cast iron melts in an amount of 0.2 wt %.
(34) The final cast iron chemical compositions for all treatments were within 3.5-3.7 wt % C, 2.3-2.5 wt % Si, 0.29-0.33 wt % Mn, 0.009-0.011 wt % S, 0.04-0.05 wt % Mg.
(35) Table 1 shows an overview of the inoculants used. The amounts of antimony oxide, iron oxide and iron sulphide are the percentage of sulphide/oxide compound based on the total weight of the inoculants.
(36) TABLE-US-00001 TABLE 1 Inoculant compositions. Base Addition rates (wt %) inoculant FeS Fe.sub.3O.sub.4 Sb.sub.2O.sub.3 Reference Melt Inoculant A 1% 2% — Prior art W Inoculant A 1% — 1.2% Inoc A + Sb2O3/FeS Inoculant A 1% 2% 1.2% Inoc A + Sb2O3/FeS/Fe3O4
(37) The results are shown in
Example 2
(38) Two inoculation trials were performed out of one ladle of 275 kg molten cast iron treated with magnesium by addition of 1.2-1.25 wt % MgFeSi nodularizing alloy in a tundish cover treatment ladle. 0.9 wt % steel chips were used as a cover. The MgFeSi nodularizing alloy had the following composition, in % by weight: 46% Si, 4.33% Mg, 0.69% Ca, 0.44% RE, 0.44% Al, the balance being iron and incidental impurities in the ordinary amount.
(39) Two different inoculants were used. The two inoculants consisted of a ferrosilicon alloy, Inoculant A, having the same composition as specified in Example 1. To one part of Inoculant A it was added 1.2 wt % Sb.sub.2O.sub.3 and 1.11 wt % Bi.sub.2O.sub.3 in particulate form, and mechanically mixed to provide the inoculant of the present invention. To another part of Inoculant A it was added 1 wt % FeS and 2 wt % Fe.sub.3O.sub.4, and mechanically mixed. This is the inoculant according to WO 99/29911.
(40) The MgFeSi treatment temperature was 1500° C. and pouring temperatures were 1398-1392° C. Holding time from filling the pouring ladles to pouring was 1 minute for all trials. The inoculants were added to cast iron melts in an amount of 0.2 wt %.
(41) The final cast iron chemical compositions for all treatments were within 3.5-3.7 wt % C, 2.3-2.5 wt % Si, 0.29-0.33 wt % Mn, 0.009-0.011 wt % S, 0.04-0.05 wt % Mg.
(42) Table 2 shows an overview of the inoculants used. The amounts of antimony oxide, bismuth oxide, iron oxide and iron sulphide are based on the total weight of the inoculants.
(43) TABLE-US-00002 TABLE 2 Inoculant compositions. Addition rates (wt %) Base inoculant FeS Fe.sub.3O.sub.4 Sb.sub.2O.sub.3 Bi.sub.2O.sub.3 Reference Melt X Inoculant A 1% 2% — Prior art Inoculant A 1.2% 1.11% Sb2O3 + Bi2O3 (Invention)
(44) The results are shown in
Example 3
(45) Two inoculation trials were performed out of one ladle of 275 kg molten cast iron treated with magnesium by addition of 1.25 wt % MgFeSi nodularizing alloy in a tundish cover treatment ladle. The MgFeSi nodularizing alloy had the following composition by weight: 46 wt % Si, 4.33 wt % Mg, 0.69 wt % Ca, 0.44 wt % RE, 0.44 wt % Al, the balance being iron and incidental impurities in the ordinary amount.
(46) Two different inoculants were used. The first inoculant (according to the present invention) consisted of a ferrosilicon alloy, Inoculant B, containing 68.2 wt % Si, 0.93 wt % Al, 0.95 wt % Ca, 0.94 wt % Ba, the remaining being iron and incidental impurities in the ordinary amount. To a part of Inoculant B it was added 1.2 wt % Sb.sub.2O.sub.3 and 1.11 wt % Bi.sub.2O.sub.3 in particulate form, and mechanically mixed to provide the inoculant of the present invention. The second inoculant consisted of a ferrosilicon alloy, inoculant A, having the same composition as specified in Example 1. To a part of Inoculant A it was added 1 wt % FeS and 2 wt % Fe.sub.3O.sub.4, and mechanically mixed. This is the inoculant according to WO 99/29911.
(47) The MgFeSi treatment temperature was 1500° C. and pouring temperatures were 1390-1362° C. Holding time from filling the pouring ladles to pouring was 1 minute for all trials. The inoculants were added to cast iron melts in an amount of 0.2 wt %.
(48) The final cast iron chemical compositions for all treatments were within 3.5-3.7 wt % C, 2.3-2.5 wt % Si, 0.29-0.33 wt % Mn, 0.009-0.011 wt % S, 0.04-0.05 wt % Mg.
(49) Table 3 shows an overview of the inoculants used. The amounts of antimony oxide, bismuth oxide, iron oxide and iron sulphide are based on the total weight of the inoculants.
(50) TABLE-US-00003 TABLE 3 Inoculant compositions. Addition rates (wt %) Base inoculant FeS Fe.sub.3O.sub.4 Sb.sub.2O.sub.3 Bi.sub.2O.sub.3 Reference Melt AG Inoculant A 1% 2% — Prior art Inoculant B 1.2% 1.11% Inoc B + Sb2O3/Bi2O3
(51) The results are shown in
Example 4
(52) A 275 kg melt was produced and treated by 1.20-1.25 wt-% MgFeSi nodulariser in a tundish cover ladle. The MgFeSi nodularizing alloy had the following composition by weight: 4.33 wt % Mg, 0.69 wt % Ca, 0.44 wt % RE, 0.44 wt % Al, 46 wt % Si, the balance being iron and incidental impurities in the ordinary amount. 0.7% by weight steel chips were used as cover. Addition rate for all inoculants were 0.2% by weight added to each pouring ladle. The nodulariser treatment temperature was 1500° C. and the pouring temperatures were 1373-1353° C. Holding time from filling the pouring ladles to pouring was 1 minute for all trials. The tensile samples were 028 mm cast in standard moulds and were cut and prepared according to standard practice before evaluating by use of automatic image analysis software.
(53) The inoculant had a base FeSi alloy composition 74.2 wt % Si, 0.97 wt % Al, 0.78 wt % Ca, 1.55 wt % Ce, the remaining being iron and incidental impurities in the ordinary amount, herein denoted Inoculant A. A mix of particulate bismuth oxide and antimony oxide of the composition indicated in Table 4 was added to the base FeSi alloy particles (Inoculant A) and by mechanically mixing, a homogeneous mixture was obtained.
(54) The final iron had a chemical composition of 3.74 wt % C, 2.37 wt % Si, 0.20 wt % Mn, 0.011 wt % S, 0.037 wt % Mg. All analyses were within the limits set before the trial.
(55) The added amounts of particulate Bi.sub.2O.sub.3 and particulate Sb.sub.2O.sub.3, to the FeSi base alloy Inoculant A are shown in Table 4, together with the inoculants according to the prior art. The amounts of Bi.sub.2O.sub.3, Sb.sub.2O.sub.3, FeS and Fe.sub.3O.sub.4 are based on the total weight of the inoculants in all tests.
(56) TABLE-US-00004 TABLE 4 Inoculant compositions. Base Additions, wt-% inoculant FeS Fe.sub.3O.sub.4 Sb.sub.2O.sub.3 Bi.sub.2O.sub.3 Reference Inoculant A 1 2 — — Prior art Inoculant A — — 5 5 Inoculant A + Bi2SO3/Sb2O3
(57)
(58) 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.