Cast iron inoculant and method for producing cast iron inoculant

Abstract

The invention relates to a cast iron inoculant and a method for producing a cast iron inoculant. The invention relates to a nucleating agent for producing cast iron with spheroidal graphite, comprising a granular ferrosilicon alloy, the invention relates to a granular ferrosilicon alloy consisting of 40% to 80% by weight of Si, 0.02% to 8% by weight of Ca, 0% to 5% by weight of Sr, 0% to 12% by weight of Ba, 0% to 15% by weight of a rare earth metal, 0% to 5% by weight of Mg, 0.05% to 5% by weight of Al, 0% to 10% by weight of Mn, 0% to 10% by weight of Ti, 0% to 10% by weight of Zr, the remainder being Fe and a conventional amount of incidental impurities wherein the inoculant additionally contains only by weight, based on the total weight of the inoculant: from 0.1% to 15% of particulate Bi2S3, and optionally from 0.1% to 15% of particulate Bi2O3; a method for producing such inoculants; and the use of such inoculants.

Description

[0001] This application is a divisional application of the parent application No. 201880083902.2, filed on December 21, 2018; the name of the invention is “Cast Iron Inoculant and Method for Producing Cast Iron Inoculant”. Technical Field

[0002] The present invention relates to a ferrosilicon-based inoculant for producing cast iron with spheroidal graphite and a method for producing the inoculant. Background Art

[0003] Cast iron is typically produced in a cupola or induction furnace and typically contains 2% to 4% carbon. The carbon is intimately mixed with the iron, and the form it takes in the solidified cast iron is crucial to the properties and performance of the casting. If the carbon takes the form of iron carbide, the cast iron is called white cast iron and has hard and brittle physical properties, which are undesirable in most applications. If the carbon takes the form of graphite, the cast iron becomes soft and machinable.

[0004] Graphite can be present in cast iron in lamellar, compacted or spherical form. The spherical shape produces the strongest and most ductile type of cast iron.

[0005] The form in which the graphite takes on and the amount of graphite relative to the iron carbide can be controlled using certain additives that promote the formation of graphite during the solidification process of the cast iron. These additives are called spheroidizers and inoculants, and they are added to the cast iron for spheroidization and inoculation, respectively. In cast iron production, the formation of iron carbide, especially in thin sections, is often challenging. The rapid cooling of the thin sections compared to the slower cooling of the thicker sections of the casting causes the formation of iron carbide. The formation of iron carbide in cast iron products is known in the industry as "chill". The formation of chill is quantified by measuring the "chill depth", and the ability of the inoculant to prevent chill and reduce chill depth is a convenient way to measure and compare the ability of the inoculant, especially in gray iron. In ductile iron, the graphite nodule number density is often used to measure and compare the ability of the inoculant.

[0006] As the industry evolves, stronger materials are needed. This means greater alloying with carbide-promoting elements such as Cr, Mn, V, and Mo, as well as thinner casting sections and lighter casting designs. Consequently, there is a growing need to develop inoculants that reduce the chill depth and improve the machinability of gray cast iron, as well as increase the number density of graphite nodules in ductile cast iron.

[0007] The exact chemistry and mechanism of inoculation and why inoculants work as they do in different cast iron melts is not fully understood, so a great deal of research is devoted to providing the industry with new and improved inoculants.

[0008] Calcium and certain other elements are believed to inhibit the formation of iron carbide and promote the formation of graphite. Most inoculants contain calcium. The addition of these iron carbide inhibitors is often facilitated by the addition of ferrosilicon alloys, with the most widely used ferrosilicon alloys probably being high-silicon alloys containing 70% to 80% silicon and low-silicon alloys containing 45% to 55% silicon. Elements that may be commonly present in inoculants and added to cast iron in the form of ferrosilicon alloys to stimulate graphite nucleation in cast iron include, for example, Ca, Ba, Sr, Al, rare earth metals (RE), Mg, Mn, Bi, Sb, Zr, and Ti.

[0009] Suppressing carbide formation is related to the nucleation performance of the inoculant. Nucleation performance refers to the number of nuclei formed by the inoculant. A high nucleus count leads to an increased graphite nodule density, thereby increasing inoculation efficacy and improving carbide suppression. Furthermore, a high nucleation rate also results in better resistance to inoculation decay during longer molten iron retention times after inoculation. Inoculation decay can be explained by the coalescence and redissolution of the nucleus population, which reduces the total number of potential nucleation sites.

[0010] U.S. Patent No. 4,432,793 discloses an inoculant containing bismuth, lead, and / or antimony. Bismuth, lead, and / or antimony are known to have high inoculating power and provide an increase in the number of nuclei. These elements are also known to be anti-spheroidizing elements, and their increased presence in cast iron is known to degrade the spheroidal graphite structure. The inoculant according to U.S. Patent No. 4,432,793 is a ferrosilicon alloy containing 0.005% to 3% of rare earth elements and 0.005% to 3% of one of the metallic elements bismuth, lead, and / or antimony alloyed in the ferrosilicon.

[0011] According to U.S. Patent No. 5,733,502, the inoculant according to said U.S. Patent No. 4,432,793 always contains some calcium, which increases the yield of bismuth, lead, and / or antimony during alloy production and helps to homogeneously distribute these elements within the alloy, as these elements have poor solubility in the iron-silicon phase. However, during storage, the product tends to disintegrate, and particle size measurements often yield an increased amount of fines. The reduced particle size measurement results are associated with the disintegration of the calcium-bismuth phase, which collects at the inoculant grain boundaries due to atmospheric moisture. In U.S. Patent No. 5,733,502, it was found that the binary bismuth-magnesium phase and the ternary bismuth-magnesium-calcium phase are not attacked by water. This result was only achieved for the high-silicon ferrosilicon alloy inoculant; for the low-silicon FeSi inoculant, the product disintegrated during storage. Thus, the ferrosilicon-based alloy for inoculation according to U.S. Pat. No. 5,733,502 contains (in weight %) 0.005% to 3% rare earth, 0.005% to 3% bismuth, lead and / or antimony, 0.3% to 3% calcium and 0.3% to 3% magnesium, wherein the Si / Fe ratio is greater than 2.

[0012] U.S. Patent Application No. 2015 / 0284830 relates to an inoculant alloy for treating thick cast iron parts, comprising 0.005% to 3% by weight of rare earth elements and 0.2% to 2% by weight of Sb. US Patent Application No. 2015 / 0284830 discloses that antimony, when alloyed with rare earth elements in a ferrosilicon-based alloy, effectively inoculates thick parts and stabilizes spheroids without the drawbacks of adding pure antimony to liquid cast iron. The inoculant according to US Patent Application No. 2015 / 0284830 is described as being typically used in the context of cast iron bath inoculation for preconditioning the cast iron and for spheroidizer treatment. The inoculant according to US Patent Application No. 2015 / 0284830 comprises (by weight %) 65% Si, 1.76% Ca, 1.23% Al, 0.15% Sb, 0.16% RE, 7.9% Ba, with the remainder being iron.

[0013] WO 95 / 24508 discloses a cast iron inoculant that exhibits an increased nucleation rate. This inoculant is a ferrosilicon-based inoculant containing calcium and / or strontium and / or barium, less than 4% aluminum, and 0.5% to 10% oxygen in the form of one or more metal oxides. However, the reproducibility of the number of nuclei formed using the inoculant according to WO 95 / 24508 was found to be rather low. In some cases, high nuclei were formed in the cast iron, but in other cases, the number of nuclei formed was quite low. For the reasons mentioned above, the inoculant according to WO 95 / 24508 is rarely used in practice.

[0014] It is known from WO 99 / 29911 that the addition of sulphur to the inoculant of WO 95 / 24508 has a positive effect on the inoculation of cast iron and increases the reproducibility of the nuclei.

[0015] In WO 95 / 24508 and WO 99 / 29911, iron oxides FeO, Fe2O3 and Fe3O4 are preferred metal oxides. Other metal oxides mentioned in these patent applications are SiO2, MnO, MgO, CaO, Al2O3, TiO2 and CaSiO3, CeO2, ZrO2. Preferred metal sulfides are selected from the group consisting of FeS, FeS2, MnS, MgS, CaS and CuS.

[0016] US Application No. 2016 / 0047008 discloses a granular inoculant for treating liquid cast iron. The inoculant comprises, on the one hand, carrier particles made of a fusible material in the liquid cast iron, and, on the other hand, surface particles made of a material that promotes graphite germination and growth. The surface particles are arranged and distributed discontinuously on the surface of the carrier particles, exhibiting a particle size distribution such that their diameter (d50) is less than or equal to one-tenth the diameter (d50) of the carrier particles. The inoculant disclosed in US Application No. 2016 / 0047008 is particularly intended for inoculating cast iron components of varying thickness and exhibiting low sensitivity to the basic composition of the cast iron.

[0017] Therefore, it is desirable to provide an inoculant with improved nucleation properties and a high nucleus count, which results in an increased graphite nodule number density, thereby improving inoculation effectiveness. It is also desirable to provide a high-performance inoculant. It is further desirable to provide an inoculant that exhibits improved resistance to inoculation effect degradation during a longer molten iron retention time after inoculation. It is also desirable to provide a bismuth-containing FeSi-based inoculant that has a high bismuth yield in the production of the inoculant compared to prior art bismuth-alloyed inoculants. The present invention, along with other advantages, satisfies at least some of the aforementioned desires, as will become apparent from the following description. Summary of the Invention

[0018] The prior art inoculant according to WO 99 / 29911 is considered to be a high-performance inoculant that produces a high number of nodules in ductile cast iron. It has now been found that when a bismuth sulfide-containing inoculant is added to the cast iron, the addition of bismuth sulfide to the inoculant of WO 99 / 29911 surprisingly leads to a significantly higher nucleus number or nodule number density in the cast iron.

[0019] In a first aspect, the present invention relates to an inoculant for producing cast iron with spheroidal graphite, wherein the inoculant comprises a granular ferrosilicon alloy consisting of 40 to 80 wt% Si, 0.02 to 8 wt% Ca, 0 to 5 wt% Sr, 0 to 12 wt% Ba, 0 to 15 wt% rare earth metals, 0 to 5 wt% Mg, 0.05 to 5 wt% Al, 0 to 10 wt% Mn, 0 to 10 wt% Ti, 0 to 10 wt% Zr. , the remainder being Fe and conventional amounts of incidental impurities, and wherein the inoculant additionally contains, by weight, based on the total weight of the inoculant: 0.1% to 15% particulate Bi2S3, and optionally 0.1% to 15% particulate Bi2O3, and / or 0.1% to 15% particulate Sb2O3, and / or 0.1% to 15% particulate Sb2S3, and / or 0.1% to 5% particulate one or more of Fe3O4, Fe2O3, FeO or mixtures thereof, and / or 0.1% to 5% particulate FeS, FeS2, Fe3S4 or mixtures thereof.

[0020] In one embodiment, the ferrosilicon alloy comprises 45 wt% to 60 wt% Si. In another embodiment of the inoculant, the ferrosilicon alloy comprises 60 wt% to 80 wt% Si.

[0021] In one embodiment, the rare earth metals include Ce, La, Y and / or misch metals. In one embodiment, the ferrosilicon alloy contains up to 10% by weight of rare earth metals. In one embodiment, the ferrosilicon alloy contains 0.5% to 3% by weight of Ca. In one embodiment, the ferrosilicon alloy contains 0% to 3% by weight of Sr. In another embodiment, the ferrosilicon alloy contains 0.2% to 3% by weight of Sr. In one embodiment, the ferrosilicon alloy contains 0% to 5% by weight of Ba. In another embodiment, the ferrosilicon alloy contains 0.1% to 5% by weight of Ba. In one embodiment, the ferrosilicon alloy contains 0.5% to 5% by weight of Al. In one embodiment, the ferrosilicon alloy contains up to 6% by weight of Mn and / or Ti and / or Zr. In one embodiment, the ferrosilicon alloy contains less than 1% by weight of Mg.

[0022] In one embodiment, the inoculant comprises 0.5 wt% to 10 wt% particulate Bi2S3.

[0023] In one embodiment, the inoculant comprises 0.1% to 10% particulate Bi2O3.

[0024] In one embodiment, the inoculant comprises 0.1% to 8% particulate Sb2O3.

[0025] In one embodiment, the inoculant comprises 0.1% to 8% particulate Sb2S3.

[0026] In one embodiment, the inoculant comprises 0.5% to 3% of one or more of particulate Fe3O4, Fe2O3, FeO, or mixtures thereof, and / or 0.5% to 3% of one or more of particulate FeS, FeS2, Fe3S4, or mixtures thereof.

[0027] In one embodiment, the total amount (sum of sulfide / oxide compounds) of granular Bi2S3 and optionally granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or granular Fe3O4, Fe2O3, FeO, or mixtures thereof, and / or granular FeS, FeS2, Fe3S4, or mixtures thereof, is up to 20 wt%, based on the total weight of the inoculant. In another embodiment, the total amount of granular Bi2S3 and optionally granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or granular Fe3O4, Fe2O3, FeO, or mixtures thereof, and / or granular FeS, FeS2, Fe3S4, or mixtures thereof, is up to 15 wt%, based on the total weight of the inoculant.

[0028] In one embodiment, the inoculant is in the form of a blend or mechanical / physical mixture of granular ferrosilicon alloy with granular Bi2S3 and optionally granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or one or more of granular Fe3O4, Fe2O3, FeO or mixtures thereof, and / or one or more of granular FeS, FeS2, Fe3S4 or mixtures thereof.

[0029] In one embodiment, granular Bi2S3 and optionally granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or one or more of granular Fe3O4, Fe2O3, FeO or mixtures thereof, and / or one or more of granular FeS, FeS2, Fe3S4 or mixtures thereof are present as coating compounds on the granular ferrosilicon-based alloy.

[0030] In one embodiment, granular Bi2S3 and optionally granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or one or more of granular Fe3O4, Fe2O3, FeO or mixtures thereof, and / or one or more of granular FeS, FeS2, Fe3S4 or mixtures thereof are mechanically mixed or blended with the granular ferrosilicon alloy in the presence of a binder.

[0031] In one embodiment, the inoculant is in the form of agglomerates made from a mixture of granular ferrosilicon alloy and granular Bi2S3 and optionally granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or granular Fe3O4, Fe2O3, FeO or one or more mixtures thereof, and / or granular FeS, FeS2, Fe3S4 or one or more mixtures thereof, in the presence of a binder.

[0032] In one embodiment, the inoculant is in the form of a compact made from a mixture of granular ferrosilicon alloy and granular Bi2S3 and optionally granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or granular Fe3O4, Fe2O3, FeO or one or more mixtures thereof, and / or granular FeS, FeS2, Fe3S4 or one or more mixtures thereof, in the presence of a binder.

[0033] In one embodiment, the granular ferrosilicon alloy is added to the liquid cast iron separately but simultaneously with the granular Bi2S3 and optionally granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or one or more of granular Fe3O4, Fe2O3, FeO or mixtures thereof, and / or one or more of granular FeS, FeS2, Fe3S4 or mixtures thereof.

[0034] In a second aspect, the present invention relates to a method for producing an inoculant according to the present invention, the method comprising: providing a granular base alloy comprising 40 to 80 wt% Si, 0.02 to 8 wt% Ca, 0 to 5 wt% Sr, 0 to 12 wt% Ba, 0 to 15 wt% rare earth metals, 0 to 5 wt% Mg, 0.05 to 5 wt% Al, 0 to 10 wt% Mn, 0 to 10 wt% Ti, 0 to 10 wt% Zr, and the remainder being F. e and conventional amounts of incidental impurities; and adding to the granular base, by weight, based on the total weight of the inoculant: 0.1% to 15% granular Bi2S3, and optionally 0.1% to 15% granular Bi2O3, and / or 0.1% to 15% granular Sb2O3, and / or 0.1% to 15% granular Sb2S3, and / or 0.1% to 5% granular Fe3O4, Fe2O3, FeO or one or more of their mixtures, and / or 0.1% to 5% granular FeS, FeS2, Fe3S4 or one or more of their mixtures, to produce the inoculant.

[0035] In one embodiment of the method, granular Bi2S3 and optionally granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or granular Fe3O4, Fe2O3, FeO or one or more mixtures thereof, and / or granular FeS, FeS2, Fe3S4 or one or more mixtures thereof, if present, are mechanically mixed or blended with the granular base alloy.

[0036] In one embodiment of the process, granular Bi2S3 and optionally granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or granular Fe3O4, Fe2O3, FeO or one or more mixtures thereof, and / or granular FeS, FeS2, Fe3S4 or one or more mixtures thereof, if present, are mechanically mixed before mixing with the granular base alloy.

[0037] In one embodiment of the process, granular Bi2S3 and optionally granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or granular Fe3O4, Fe2O3, FeO or one or more of their mixtures, and / or granular FeS, FeS2, Fe3S4 or one or more of their mixtures, if present, are mechanically mixed or blended with the granular base alloy in the presence of a binder. In another embodiment of the process, the mechanically mixed or blended granular base alloy, granular Bi2S3 and optionally granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or granular Fe3O4, Fe2O3, FeO or one or more of their mixtures, and / or granular FeS, FeS2, Fe3S4 or one or more of their mixtures, if present, are further formed into agglomerates or briquettes in the presence of a binder.

[0038] In another aspect, the present invention relates to the use of an inoculant as defined above for producing cast iron with spheroidal graphite by adding the inoculant to the cast iron melt before casting, as an in-mould inoculant or while casting.

[0039] In one embodiment of the described use of the inoculant, the granular ferrosilicon-based alloy is added to the cast iron melt as a mechanical / physical mixture or blend with granular Bi2S3 and optionally granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or granular Fe3O4, Fe2O3, FeO or one or more mixtures thereof, and / or granular FeS, FeS2, Fe3S4 or one or more mixtures thereof.

[0040] In one embodiment of the described use of the inoculant, the granular ferrosilicon alloy is added separately but simultaneously to the cast iron melt from the granular Bi2S3 and optionally the granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or one or more of granular Fe3O4, Fe2O3, FeO or mixtures thereof, and / or one or more of granular FeS, FeS2, Fe3S4 or mixtures thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 : Shows the ball number density (ball number / mm) in the cast iron sample of melt E of Example 1 2 , abbreviated as N / mm 2 ) picture.

[0042] Figure 2 : Shows the ball number density (ball number / mm) in the cast iron sample of melt F of Example 1 2 , abbreviated as N / mm 2 ) picture.

[0043] Figure 3 : Shows the ball number density (ball number / mm) in the cast iron sample of the melt H of Example 2 2 , abbreviated as N / mm 2 ) picture.

[0044] Figure 4 : Shows the ball number density (ball number / mm) in the cast iron sample of melt 1 of Example 2 2 , abbreviated as N / mm 2 ) picture.

[0045] Figure 5 : Shows the ball number density (ball number / mm) in the cast iron sample of melt Y of Example 3 2 , abbreviated as N / mm 2 ) picture.

[0046] Figure 6 : Shows the ball number density (ball number / mm) in the cast iron sample of melt X of Example 4 2 , abbreviated as N / mm 2 ) picture.

[0047] Figure 7 : Shows the ball number density (ball number / mm) in the cast iron sample of melt Y of Example 4 2 , abbreviated as N / mm 2 ) picture.

[0048] Figure 8 : Shows the ball number density (ball number / mm) in the cast iron sample of Example 5 2 , abbreviated as N / mm 2 ) picture. DETAILED DESCRIPTION

[0049] According to the present invention, a high-performance inoculant for producing cast iron with spherical graphite is provided. The inoculant comprises an FeSi base alloy combined with particulate bismuth sulfide (Bi2S3), and optionally further comprises other particulate metal oxides and / or particulate metal sulfides selected from the group consisting of bismuth oxide (Bi2O3), antimony sulfide (Sb2S3), antimony oxide (Sb2O3), iron oxides (one or more of Fe3O4, Fe2O3, FeO, or mixtures thereof), and iron sulfides (one or more of FeS, FeS2, Fe3S4, or mixtures thereof). The inoculant according to the present invention is easy to manufacture, and the amounts of bismuth and antimony in the inoculant can be easily controlled and varied. This avoids complex and expensive alloying steps, and thus the inoculant can be manufactured at a lower cost than prior art inoculants containing Bi and / or Sb.

[0050] In the manufacturing process for producing ductile cast iron with spheroidal graphite, the cast iron melt is typically treated with a spheroidizing agent (e.g., using a MgFeSi alloy) prior to inoculation. The purpose of the spheroidizing treatment is to change the form of graphite from flakes to spheres as it precipitates and subsequently grows. This is achieved by altering the interfacial energy of the graphite / melt interface. Mg and Ce are known elements that alter interfacial energy, with Mg being more effective than Ce. When Mg is added to the base iron melt, it initially reacts with oxygen and sulfur, and only "free magnesium" has a spheroidizing effect. The spheroidizing reaction is violent and causes the melt to agitate, producing a slag that floats to the surface. This violent reaction causes most of the graphite nucleation sites already in the melt (introduced by the raw materials), as well as other inclusions, to become part of the top slag and be removed. However, some MgO and MgS inclusions produced during the spheroidizing treatment remain in the melt. These inclusions themselves are not good nucleation sites.

[0051] The main function of inoculation is to prevent carbide formation by introducing graphite nucleation sites. In addition to introducing nucleation sites, inoculation also transforms MgO and MgS inclusions formed during spheroidization into nucleation sites by adding a layer (containing Ca, Ba or Sr) on these inclusions.

[0052] According to the present invention, the granular FeSi base alloy should contain 40 wt % to 80 wt % Si. Pure FeSi alloy is a weak inoculant, but it is a common alloy carrier for active elements, thereby allowing good dispersibility in the melt. Therefore, there are a variety of known inoculant FeSi alloy compositions. Conventional alloying elements in FeSi alloy inoculants include Ca, Ba, Sr, Al, Mg, Zr, Mn, Ti and RE (especially Ce and La). The amount of alloying elements can vary. Typically, inoculants are designed to meet different requirements in the production of gray iron, compacted iron and ductile iron. The inoculant according to the present invention may comprise a FeSi base alloy having a silicon content of about 40 wt % to 80 wt %. The alloying elements may include about 0.02 wt% to 8 wt% Ca, about 0 wt% to 5 wt% Sr, about 0 wt% to 12 wt% Ba, about 0 wt% to 15 wt% rare earth metals, about 0 wt% to 5 wt% Mg, about 0.05 wt% to 5 wt% Al, about 0 wt% to 10 wt% Mn, about 0 wt% to 10 wt% Ti, about 0 wt% to 10 wt% Zr, with the remainder being Fe and conventional amounts of incidental impurities.

[0053] The FeSi base alloy can be a high silicon alloy containing 60% to 80% silicon or a low silicon alloy containing 45% to 60% silicon. Silicon is commonly present in cast iron alloys and is a graphite stabilizing element in cast iron, forcing carbon to precipitate from the solution and promoting the formation of graphite. The particle size of the FeSi base alloy should be within the conventional range of the inoculant, for example, between 0.2 mm and 6 mm. It should be noted that FeSi alloys with smaller particle sizes, such as fine particles, can also be used to make the inoculant in the present invention. When using a very small particle FeSi base alloy, the inoculant can be in the form of an agglomerate (e.g., granules) or a compact. To prepare agglomerates and / or briquettes of the inoculant of the present invention, BiS particles and any additional granular BiO, and / or SbO, and / or one or more of FeO, FeO, FeO, or mixtures thereof, and / or one or more of FeS, FeS, FeS, or mixtures thereof, are mixed with granular ferrosilicon alloy by mechanical mixing or blending in the presence of a binder, and the powder mixture is then agglomerated according to known methods. The binder may be, for example, a sodium silicate solution. The agglomerates may be granules of a suitable product size, or may be crushed and sieved to the desired final product size.

[0054] A variety of different inclusions (sulfides, oxides, nitrides, and silicates) can form in the liquid state. Sulfides and oxides of Group IIA elements (Mg, Ca, Sr, and Ba) have very similar crystalline phases and high melting points. Group IIA elements are known to form stable oxides in molten iron, and therefore, inoculants and spheroidizers based on these elements are known to be effective deoxidizers. Calcium is the most common trace element in ferrosilicon inoculants. According to the present invention, the granular FeSi-based alloy contains from about 0.02% to about 8% calcium by weight. In some applications, it is desirable to have a low content of Ca in the FeSi-based alloy, for example, 0.02% to 0.5% by weight. Compared to conventional inoculant ferrosilicon alloys containing alloyed bismuth (in which calcium is considered an essential element to increase bismuth (and antimony) yield), in the inoculant according to the present invention, calcium is not required for solubility purposes. In other applications, the Ca content can be higher, for example, from 0.5% to 8% by weight. High levels of Ca can increase slag formation, which is generally undesirable. Various inoculants contain about 0.5 wt. % to 3 wt. % Ca in the FeSi alloy.

[0055] The FeSi base alloy should contain a maximum of about 5 wt. % Sr. Amounts of 0.2 wt. % to 3 wt. % Sr are generally suitable.

[0056] Barium may be present in the FeSi inoculant alloy in an amount up to about 12% by weight. Ba is known to provide better resistance to inoculation fading over longer molten iron holding times after inoculation and higher efficiency over a wider temperature range. Many FeSi alloy inoculants contain about 0.1% to 5% by weight of Ba. If barium is used in combination with calcium, the two work together to reduce white cast to a greater extent than an equal amount of calcium.

[0057] Magnesium may be present in the FeSi inoculant alloy in an amount up to about 5 wt%. However, since Mg is typically added during spheroidization for the production of ductile iron, the amount of Mg in the inoculant may be lower, for example, up to about 0.1 wt%. In contrast to conventional inoculant ferrosilicon alloys containing alloyed bismuth, in which magnesium is considered an essential element for stabilizing the bismuth-containing phase, magnesium is not required in the inoculant according to the present invention for stabilization purposes.

[0058] The FeSi base alloy may contain up to 15 wt% rare earth metals (RE). RE includes at least Ce, La, Y and / or misch metals. Mich metals are alloys of rare earth elements, typically containing about 50% Ce and 25% La, as well as small amounts of Nd and Pr. Adding RE is often used to restore the number of graphite nodules and the spheroidization rate in ductile iron containing trace elements such as Sb, Pb, Bi, Ti, etc. In some inoculants, the amount of RE is up to 10 wt%. In some cases, excessive RE can lead to the formation of coarse graphite. Therefore, in some applications, the amount of RE should be lower, for example between 0.1 wt% and 3 wt%. Preferably, RE is Ce and / or La.

[0059] Aluminum is reported to be very effective as a white cast iron reducer. Al is often combined with Ca in FeSi alloy inoculants to produce ductile iron. In the present invention, the Al content should be up to about 5% by weight, for example, 0.1% to 5% by weight.

[0060] Zirconium, manganese, and / or titanium are also typically present in the inoculant. Similar to the above-mentioned elements, Zr, Mn, and Ti play an important role in the nucleation of graphite, which is believed to be formed due to heterogeneous nucleation events during solidification. The amount of Zr in the FeSi base alloy can be up to about 10% by weight, such as up to about 6% by weight. The amount of Mn in the FeSi base alloy can be up to about 10% by weight, such as up to about 6% by weight. The amount of Ti in the FeSi base alloy can be up to about 10% by weight, such as up to about 6% by weight.

[0061] Bismuth and antimony are known to have high inoculating power and provide an increase in the number of nuclei. However, the presence of small amounts of elements such as Bi and / or Sb (also known as trace elements) in the melt may reduce the spheroidization rate. This negative effect can be offset by the use of Ce or other RE metals. According to the present invention, the amount of particulate Bi2S3 should be 0.1 wt% to 15 wt% based on the total weight of the inoculant. In some embodiments, the amount of Bi2S3 is 0.2 wt% to 10 wt%. High spheroidization numbers are also observed when the inoculant contains 0.5 wt% to 8 wt% particulate Bi2S3, based on the total weight of the inoculant.

[0062] Introducing Bi2S3 (and optionally Bi2O3) with the FeSi-based alloy inoculant is adding reactants to an already existing system with Mg inclusions and "free" Mg floating around the melt. Adding the inoculant is not a violent reaction, and the Bi yield (Bi / Bi2S3 (and Bi2O3) remaining in the melt) is expected to be high. The Bi2S3 particles should have a small particle size, i.e., micrometer-sized (e.g., 1 μm to 10 μm), so that the particles melt or dissolve very quickly when introduced into the cast iron melt. Advantageously, the Bi2S3 particles are mixed with the particulate FeSi base alloy and (if present) particulate Bi2O3, Sb2O3, Sb2S3, Fe3O4, Fe2O3, FeO, or mixtures thereof, and / or one or more of FeS, FeS2, Fe3S4, or mixtures thereof, before the inoculant is added to the cast iron melt.

[0063] The amount of particulate Bi2O3, if present, should be from 0.1 wt% to 15 wt% based on the total weight of the inoculant. In some embodiments, the amount of Bi2O3 can be from 0.1 wt% to 10 wt%. The amount of Bi2O3 can also be from about 0.5 wt% to about 3.5 wt% based on the total weight of the inoculant. The particle size of Bi2O3 should be similar to that of Bi2S3 particles, i.e., micrometer-sized, for example, 1 μm to 10 μm.

[0064] Adding Bi in the form of Bi2S3 particles and Bi2O3 (if present) rather than alloying Bi with the FeSi alloy has several advantages. Bi has poor solubility in ferrosilicon alloys and, therefore, the yield of Bi metal added to the molten ferrosilicon is low, thereby increasing the cost of the FeSi alloy inoculant containing Bi. In addition, due to the high density of elemental Bi, it may be difficult to obtain a homogeneous alloy during casting and solidification. Another difficulty is that Bi metal is volatile, which is due to its low melting temperature compared to other elements in the FeSi-based inoculant. Compared to traditional alloying processes, adding Bi in the form of sulfides and oxides (if present) together with the FeSi base alloy provides an inoculant that is easy to produce and may have a lower production cost, wherein the amount of Bi is easy to control and is reproducible. In addition, since Bi is added in the form of sulfides and oxides (if present) rather than alloyed in the FeSi alloy, it is easy to change the composition of the inoculant, for example for smaller production series. Furthermore, although Bi is known to have a high inoculating ability, oxygen and sulfur are also important to the performance of the inoculant of the present invention, thus providing another advantage of adding Bi in the form of sulfides and oxides.

[0065] The amount of particulate Sb2O3, if present, should be from 0.1% to 15% by weight, based on the total weight of the inoculant. In some embodiments, the amount of Sb2O3 can be from 0.1% to 8% by weight. The amount of Sb2O3 can also be from about 0.5% to about 3.5% by weight, based on the total weight of the inoculant. The amount of particulate Sb2S3, if present, should be from 0.1% to 15% by weight, based on the total weight of the inoculant. In some embodiments, the amount of Sb2S3 can be from 0.1% to 8% by weight. The amount of Sb2S3 can also be from about 0.5% to about 3.5% by weight, based on the total weight of the inoculant.

[0066] The Sb2O3 particles and Sb2S3 particles should have a small particle size, ie, in the micrometer range (eg, 10 μm to 150 μm), so that the Sb2O3 and / or Sb2S3 particles melt and / or dissolve very quickly when introduced into a cast iron melt.

[0067] Adding Sb in the form of Sb2O3 particles and / or Sb2S3 rather than alloying Sb with FeSi alloys offers several advantages. Although Sb is a powerful inoculant, oxygen and sulfur are also important for the performance of the inoculant. Another advantage is that the inoculant composition has good reproducibility and flexibility, as the amount and homogeneity of particulate Sb2O3 and / or Sb2S3 in the inoculant can be easily controlled. Given the fact that antimony is usually added at ppm levels, the importance of controlling the amount of inoculant and having a homogeneous inoculant composition is obvious. Adding a non-homogeneous inoculant may result in the wrong amount of inoculant element in the cast iron. Another advantage is that the production of the inoculant is more cost-effective than methods involving alloying antimony in FeSi-based alloys.

[0068] The total amount of one or more of particulate Fe3O4, Fe2O3, FeO, or mixtures thereof, if present, should be in the range of 0.1 wt% to 5 wt%, based on the total amount of the inoculant. In some embodiments, the amount of one or more of Fe3O4, Fe2O3, FeO, or mixtures thereof may be in the range of 0.5 wt% to 3 wt%. The amount of one or more of Fe3O4, Fe2O3, FeO, or mixtures thereof may also be in the range of about 0.8 wt% to about 2.5 wt%, based on the total weight of the inoculant. The composition of commercial iron oxide products used in industrial applications such as metallurgy may contain different types of iron oxide compounds and phases. The primary types of iron oxide are Fe3O4, Fe2O3, and / or FeO (including Fe II and Fe III Other mixed oxide phases; iron (II, III) oxides), all of which can be used in the inoculant according to the present invention. Commercial iron oxide products for industrial applications may contain small amounts (very small amounts) of other metal oxides as impurities.

[0069] The total amount of one or more of particulate FeS, FeS2, Fe3S4, or mixtures thereof, if present, should be in the range of 0.1 wt% to 5 wt%, based on the total amount of the inoculant. In some embodiments, the amount of one or more of FeS, FeS2, Fe3S4, or mixtures thereof may be in the range of 0.5 wt% to 3 wt%. The amount of one or more of FeS, FeS2, Fe3S4, or mixtures thereof may also be in the range of about 0.8 wt% to about 2.5 wt%, based on the total weight of the inoculant. The composition of commercial iron sulfide products for industrial applications such as metallurgy may contain different types of iron sulfide compounds and phases. The main types of iron sulfides are FeS, FeS2, and / or Fe3S4 (iron (II, III) sulfides; FeS, Fe2S3), including non-stoichiometric phases of FeS, Fe 1+x S (x > 0 to 0.1) and Fe 1-yS (y>0 to 0.2), all of which can be used in the inoculant according to the present invention. Commercial iron sulfide products for industrial applications may contain small amounts (very small amounts) of other metal sulfides as impurities.

[0070] One of the purposes of adding one or more of Fe3O4, Fe2O3, FeO or mixtures thereof and / or one or more of FeS, FeS2, Fe3S4 or mixtures thereof to the cast iron melt is to intentionally add oxygen and sulfur to the melt, which can help increase the number of pellets.

[0071] It will be appreciated that the total amount of Bi2S3 particles and any of the particulate Bi oxide, Sb oxide / sulfide, and / or Fe oxide / sulfide (if present) should be a maximum of about 20 wt. % based on the total weight of the inoculant. It will also be appreciated that the composition of the FeSi base alloy can vary within defined limits, and one skilled in the art will appreciate that the amounts of alloying elements add up to 100%. There are a variety of conventional FeSi-based inoculant alloys, and one skilled in the art will appreciate how to modify the FeSi base composition based on these. The inoculant according to the present invention is typically added at a rate of about 0.1 wt. % to 0.8 wt. % relative to the cast iron melt. One skilled in the art will adjust the addition rate based on the elemental levels, for example, an inoculant with high Bi and / or Sb content will typically require a lower addition rate.

[0072] The inoculant of the present invention is produced by providing a granular FeSi base alloy having a composition as defined herein and adding granular Bi2S3 and any granular Bi2O3, and / or granular Sb2O3, and / or granular Sb2S3, and / or granular Fe3O4, Fe2O3, FeO, or mixtures thereof, and / or granular FeS, FeS2, Fe3S4, or mixtures thereof (if present) to the granular base to produce the inoculant of the present invention. The Bi2S3 particles and any of the granular Bi oxides, Sb oxides / sulfides, and / or Fe oxides / sulfides (if present) can be mechanically / physically mixed with the FeSi base alloy particles. Any suitable mixer for mixing / blending granular and / or powdered materials can be used. Mixing can be carried out in the presence of a suitable binder, but it should be noted that the presence of a binder is not required. The Bi2S3 particles and any of the granular Bi oxide, Sb oxide / sulfide and / or Fe oxide / sulfide (if present) may also be blended with the FeSi base alloy particles to provide a homogeneously mixed inoculant. Blending the Bi2S3 particles and the additional sulfide / oxide powder with the FeSi base alloy particles may form a stable coating on the FeSi base alloy particles. However, it should be noted that mixing and / or blending the Bi2S3 particles and any of the granular oxide / sulfide with the granular FeSi base alloy is not mandatory for achieving the inoculation effect. The granular FeSi base alloy and the Bi2S3 particles and any of the granular oxide / sulfide may be added separately but simultaneously to the liquid cast iron. The inoculant may also be added as an in-mold inoculant or simultaneously to the casting. The FeSi alloy, Bi2S3 particles and inoculant particles of any of the particulate Bi oxide, Sb oxide / sulfide and / or Fe oxide / sulfide, if present, may also be formed into agglomerates or compacts according to commonly known methods.

[0073] The following examples show that when an inoculant is added to cast iron, the addition of Bi2S3 particles together with FeSi base alloy particles results in an increased nodule number density compared to the inoculant according to the prior art of WO 99 / 29911. A higher nodule number allows a reduction in the amount of inoculant required to achieve the desired inoculation effect.

[0074] Example

[0075] The microstructure of all test samples was analyzed to determine the ball density. The microstructure was examined in the form of a tensile test bar for each test according to ASTM E2567-2016. The particle limit was set to >10 μm. The tensile specimens were cast in a standard mold according to ISO 1083-2004. The samples were cut and prepared according to standard practice for microstructural analysis and then evaluated using automated image analysis software. Ball density (also known as ball number density) is the number of balls (also known as spheroids) / mm 2 , abbreviated as N / mm 2 .

[0076] The iron oxide used in the following examples is commercial magnetite (Fe3O4) with specifications (provided by the manufacturer) of Fe3O4>97.0% and SiO2<1.0%. Commercial magnetite products may include other iron oxide forms, such as Fe2O3 and FeO. The main impurity in commercial magnetite is SiO2, as described above.

[0077] The iron sulfide used in the following examples is a commercial FeS product. Analysis of the commercial product shows that in addition to FeS, other iron sulfide compounds / phases are present, as well as very small amounts of common impurities.

[0078] Example 1

[0079] Two cast iron melts, each weighing 220 kg, were melted and treated in a tundish cover treatment ladle with 1.05% by weight of a MgFeSi spheroidizing alloy, based on the weight of the cast iron. (The composition of the MgFeSi spheroidizing alloy is 46.2% Si, 5.85% Mg, 1.02% Ca, 0.92% RE, 0.74% Al, with the remainder being Fe and conventional amounts of incidental impurities, with RE (rare earth metals) containing approximately 65% ​​Ce and 35% La.) 0.9% by weight of steel chips was used as a lid. All inoculants were added to each ladle at an addition rate of 0.2% by weight. The MgFeSi treatment temperature was 1500°C, and the pouring temperature for melt E was 1396-1330°C, while the pouring temperature for melt F was 1392-1337°C. (These temperatures were measured in the handling ladle before pouring the first ladle and after pouring the last ladle.) For all tests, the holding time from filling the ladle to pouring was 1 minute.

[0080] In some tests, the inoculant had a base FeSi alloy composition of 74.2 wt% Si, 0.97 wt% Al, 0.78 wt% Ca, 1.55 wt% Ce, the remainder being iron and conventional amounts of incidental impurities, referred to herein as Inoculant A. Mg-treated cast iron melts E and F were inoculated with an inoculant according to the present invention, wherein bismuth sulfide (Bi2S3) was added to Inoculant A and mechanically mixed to obtain a homogeneous mixture. Different amounts of granular Bi2S3 and one or more of bismuth oxide (Bi2O3) in granular form, iron sulfide (FeS) in granular form, and / or iron oxide (Fe3O4) in granular form were added to Inoculant A and mechanically mixed to obtain a homogeneous mixture of the different inoculant components according to the present invention.

[0081] Melt F was also treated with a lower RE-containing inoculant having a base FeSi alloy composition of 70.1 wt% Si, 0.96 wt% Al, 1.45 wt% Ca, 0.34 wt% Ce, and 0.22% La, the remainder being iron and conventional amounts of incidental impurities (referred to herein as Inoculant B), to which particulate bismuth sulfide (Bi2S3) was added and mechanically mixed to obtain a homogeneous mixture. Melt F was also treated with an inoculant according to the present invention, prepared by mixing particulate Inoculant B with particulate Bi2S3 and particulate Bi2O3, see Table 1.

[0082] For comparative purposes, identical cast iron melts, namely melts E and F, were inoculated with inoculant A according to the prior art from WO 99 / 29911 to which only iron oxides and iron sulfides were added.

[0083] The chemical compositions for all treatments were within 3.5% to 3.7% C, 2.3% to 2.5% Si, 0.29% to 0.31% Mn, 0.009% to 0.011% S, 0.04% to 0.05% Mg.

[0084] The amounts of particulate Bi2S3 and one or more of particulate Bi2O3, particulate FeS and / or particulate Fe3O4 added to the FeSi base alloy (Inoculant A or Inoculant B) together with the inoculant according to the prior art are shown in Table 1. In all tests, the amounts of Bi2S3, Bi2O3, FeS and Fe3O4 are percentages of the compounds based on the total weight of the inoculant.

[0085] Table 1: Inoculant composition .

[0086]

[0087] Figure 1The nodule density in the cast iron obtained from the inoculation test carried out in melt E is shown. The results show a very significant trend towards higher nodule density for the Bi2S3 containing inoculants compared to the prior art inoculants.

[0088] Figure 2 The nodule density in cast iron from inoculation tests conducted in Melt F is shown. The results show a very significant trend towards higher nodule density for the Bi2S3-containing and Bi2S3+Bi2O3-containing inoculants compared to the prior art inoculants. The inoculant properties of both the Inoculant A and Inoculant B base inoculants are high, so the lower RE inoculant, Inoculant B, does not significantly alter the microstructure compared to the higher RE base alloy inoculant, Inoculant A.

[0089] Example 2

[0090] Two cast iron melts, Melt H and Melt I, weighing 275 kg each, were melted and treated in a tundish lid ladle with 1.05 wt% of a MgFeSi nodulizer alloy distributed over 50% of a MgFeSi alloy with a composition of 46.6% Si, 5.82% Mg, 1.09% Ca, 0.53% RE, and 0.6% Al (the remainder being Fe and conventional impurities), and 50% of a MgFeSi alloy with a composition of 46.3% Si, 6.03% Mg, 0.45% Ca, 0.0% RE, and 0.59% Al (the remainder being Fe and conventional impurities). 0.7 wt% of steel scrap was used as the lid. All inoculants were added to each ladle at a rate of 0.2 wt%. The MgFeSi treatment temperature was 1500° C., and the pouring temperature for melt H was 1375-1357° C., while the pouring temperature for melt I was 1366-1323° C. The holding time from filling the ladle to pouring was 1 minute for all experiments.

[0091] In both Melt H and Melt I tests, the base FeSi alloy composition of the inoculant was the same as Inoculant A described in Example 1. The base FeSi alloy particles (Inoculant A) were coated with granular Bi2S3 (Melt H) and with granular Bi2S3 and granular Sb2O3 (Melt I) by mechanical mixing to obtain a homogeneous mixture.

[0092] The chemical compositions for all treatments were within 3.5% to 3.7% C, 2.3% to 2.5% Si, 0.29% to 0.31% Mn, 0.009% to 0.011% S, 0.04% to 0.05% Mg.

[0093] The amounts of particulate Bi2S3 and particulate Sb2O3 added to the FeSi base alloy (Inoculant A) together with the inoculant according to the prior art are shown in Table 2. In all tests, the amounts of Bi2S3, Sb2O3, FeS and Fe3O4 are percentages of the compounds based on the total weight of the inoculant.

[0094] Table 2: Inoculant composition .

[0095]

[0096] Figure 3 The ball density in the cast iron obtained from the inoculation tests carried out in melt H is shown. The results show a very significant trend towards much higher ball density for the Bi2S3 containing inoculants compared to the prior art inoculants. The tests carried out with different amounts of Bi sulfide showed a significantly increased ball density over the entire range of different amounts of particulate Bi2S3 coated on inoculant A.

[0097] Figure 4 The nodule density in cast irons obtained from inoculation tests carried out in melt I is shown. The results show a very significant trend towards higher nodule density for the inoculant containing Bi2S3+Sb2O3 compared to the prior art inoculant.

[0098] Example 3

[0099] A 275 kg melt was produced and treated with 1.0% of a RE-free MgFeSi nodularizer alloy, or a composition (in wt. %) of Si: 47, Mg: 6.12, Ca: 1.86, RE: 0.0, Al: 0.54, the remainder being Fe and incidental impurities. 0.7 wt. % of steel chips was used as a cap.

[0100] The Bi2S3 coated inoculant was based on inoculant C, which had a composition (in wt%) of Si: 77.3, Al: 1.07, Ca: 0.92, La: 2.2, with the remainder being Fe and incidental impurities. The composition of inoculant A was the same as in Example 1.

[0101] The inoculant was prepared by adding particulate Bi2S3, Fe3O4, and FeS to the base alloy in the amounts shown in Table 3 below and mechanically mixing to obtain a homogeneous mixture. The inoculant was added to each ladle at a 0.2% addition rate. The MgFeSi treatment temperature was 1500°C, and the pouring temperature was 1388-1370°C. The hold time from filling the ladle to pouring was 1 minute.

[0102] The chemical composition for the treatment is within 3.5% to 3.7% C, 2.4% to 2.5% Si, 0.29% to 0.30% Mn, 0.007% to 0.011% S, 0.040% to 0.043% Mg.

[0103] The amounts of particulate Bi2S3 added to the FeSi base alloy (Inoculant C) together with the inoculant according to the prior art are shown in Table 3. In all tests, the amounts of Bi2S3, FeS and Fe3O4 are percentages of the compounds based on the total weight of the inoculant.

[0104] Table 3: Inoculant composition

[0105]

[0106] The ball density in the cast iron obtained from the inoculation test in melt Y is Figure 5 The analysis of the microstructure shows that the inoculant according to the invention (inoculant C+Bi2S3) has a significantly higher ball density than the prior art inoculant.

[0107] Example 4

[0108] Two cast iron melts, Melt X and Melt Y, weighing 275 kg each, were melted and treated in a tundish lidding ladle with 1.20 to 1.25 wt% MgFeSi nodularizer. The MgFeSi nodularizer 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, with the remainder being iron and conventional amounts of incidental impurities. 0.7 wt% steel shavings were used as lidding. All inoculants were added to each ladle at an addition rate of 0.2 wt%. The nodularizer treatment temperature was 1500°C, and the pouring temperatures for Melt X were 1398-1379°C, while those for Melt Y were 1389-1386°C. For all tests, the holding time from filling the ladle to pouring was 1 minute.

[0109] In the Melt X test, the base FeSi alloy composition of the inoculant was 68.2 wt% Si, 0.95 wt% Ca, 0.94 wt% Ba, 0.93 wt% Al (referred to herein as Inoculant D). The base FeSi alloy particles (Inoculant D) were coated with granular Bi2S3. In the Melt Y test, the base FeSi alloy composition of the inoculant was the same as Inoculant A described in Example 1. The base FeSi alloy particles (Inoculant A) were coated with granular Bi2S3 and granular Sb2S3 by mechanical mixing to obtain a homogeneous mixture.

[0110] The chemical compositions for all treatments were within the range of 3.55% to 3.61% C, 2.3% to 2.5% Si, 0.29% to 0.31% Mn, 0.009% to 0.012% S, 0.04% to 0.05% Mg.

[0111] The amounts of particulate Bi2S3 and particulate Sb2S3 added to FeSi base alloy inoculant A along with the inoculant according to the prior art, and the amount of particulate Bi2S3 added to FeSi base alloy inoculant D are shown in Table 4. In all tests, the amounts of Bi2S3, Sb2S3, FeS, and Fe3O4 are based on the total weight of the inoculant.

[0112] Table 4: Inoculant composition .

[0113]

[0114] Figure 6 Shown are the nodule densities in cast irons obtained from inoculation tests carried out in melt X. The results show a very significant trend towards a much higher nodule density for the Bi2S3 containing inoculants compared to the prior art inoculants.

[0115] Figure 7 The nodule density in cast irons obtained from inoculation tests carried out in melt Y is shown. The results show a very significant trend towards higher nodule density for the inoculant containing Bi2S3+Sb2S3 compared to the prior art inoculant.

[0116] Example 5

[0117] 275 kg of melt was prepared and treated with 1.20 to 1.25 wt% MgFeSi nodulariser in a tundish cover ladle. The MgFeSi nodulariser 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 remainder being iron and conventional amounts of incidental impurities. 0.7 wt% steel shavings were used as a cover. All inoculants were added to each ladle at an addition rate of 0.2 wt%. The nodulariser treatment temperature was 1500°C and the pouring temperature was 1373-1368°C. The holding time from filling the ladle to pouring was 1 minute for all tests. The tensile specimens were cast in a standard mould. They were cut and prepared according to standard practice and then evaluated using automated image analysis software.

[0118] The inoculant had a base FeSi alloy composition of 74.2 wt% Si, 0.97 wt% Al, 0.78 wt% Ca, 1.55 wt% Ce, with the remainder being iron and conventional amounts of incidental impurities, and is referred to herein as Inoculant A. A mixture of particulate bismuth oxide, bismuth sulfide, antimony oxide, and antimony sulfide having the compositions shown in Table 5 was added to the base FeSi alloy particles (Inoculant A) and mechanically mixed to obtain a homogeneous mixture.

[0119] The final chemical composition of the iron was 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 test.

[0120] The amounts of particulate Bi2S3, particulate Bi2O3, particulate Sb2O3, and particulate Sb2S3 added to the FeSi base alloy inoculant A together with the inoculant according to the prior art are shown in Table 5. In all tests, the amounts of Bi2S3, Bi2O3, Sb2S3, Sb2O3, FeS, and Fe3O4 are based on the total weight of the inoculant.

[0121] Table 5: Inoculant composition .

[0122]

[0123] Figure 8 The ball density in the cast iron obtained from the inoculation tests in Table 5 is shown. The results show a very significant trend that the inoculant according to the present invention, i.e., the FeSi base alloy containing particulate Bi2S3, Bi2O3, Sb2S3 and Sb2O3, has a much higher ball density than the prior art inoculant. Thermal analysis (not shown here) shows a clear trend that TElow is significantly higher in the samples inoculated with the FeSi base alloy inoculant containing Bi2S3, Bi2O3, Sb2S3, Sb2O3 compared to the prior art inoculant.

[0124] Having described various embodiments of the present invention, it will be apparent to those skilled in the art that other embodiments incorporating these concepts may be used. These and other examples of the present invention shown above and in the accompanying drawings are intended to be exemplary only, and the actual scope of the invention should be determined by the following claims.

Claims

1. An inoculant for producing cast iron having spheroidal graphite, the inoculant comprising granular ferrosilicon alloy, the granular ferrosilicon alloy consisting of: 40 to 80 wt% Si; 0.02 wt% to 8 wt% Ca; 0 to 5 wt% Sr; 0 to 12 wt% of Ba; 0 to 15 wt% rare earth metals; 0 to 5 wt% Mg; 0.05 to 5 wt% Al; 0 to 10 wt% Mn; 0 to 10 wt% Ti; 0 to 10 wt% Zr; The remainder is Fe and conventional amounts of incidental impurities. wherein, based on the total weight of the inoculant, the inoculant additionally contains only by weight: 0.5% to 8% granular Bi2S3, and Optionally 0.1% to 15% particulate Bi2O3. 2 . The inoculant according to claim 1 , wherein the ferrosilicon alloy comprises 45 to 60 wt % Si.

3. The inoculant according to claim 1, wherein the ferrosilicon alloy comprises 60 wt% to 80 wt% Si.

4. The inoculant according to any one of the preceding claims, wherein the rare earth metal comprises Ce, La, Y and / or misch metals.

5. The inoculant according to any one of the preceding claims, wherein the inoculant comprises 0.1% to 10% particulate Bi2O3.

6. An inoculant according to any one of the preceding claims, wherein the inoculant is in the form of a blend or physical mixture of the granular ferrosilicon alloy with the granular Bi2S3 and the optional granular Bi2O3.

7. An inoculant according to any one of the preceding claims, wherein the particulate Bi2S3 and the optional particulate Bi2O3 are present as a coating compound on a particulate ferrosilicon-based alloy.

8. An inoculant according to any one of the preceding claims, wherein the inoculant is in the form of an agglomerate made from a mixture of the granular ferrosilicon alloy and the granular Bi2S3 and the optional granular Bi2O3.

9. An inoculant according to any one of the preceding claims, wherein the inoculant is in the form of a compact made from a mixture of the granular ferrosilicon alloy with the granular Bi2S3 and the optional granular Bi2O3.

10. An inoculant according to any one of the preceding claims, wherein the granular ferrosilicon-based alloy is added to the liquid cast iron separately from but simultaneously with the granular Bi2S3 and the optional granular Bi2O3.

11. A method for producing an inoculant according to any one of claims 1 to 10, the method comprising: A granular base alloy is provided, the granular base alloy comprising 40 wt% to 80 wt% Si, 0.02 wt% to 8 wt% Ca; 0 to 5 wt% Sr; 0 to 12 wt% of Ba; 0 to 15 wt% rare earth metals; 0 to 5 wt% Mg; 0.05 to 5 wt% Al; 0 to 10 wt% Mn; 0 to 10 wt% Ti; 0 to 10 wt% Zr; The remainder is Fe and conventional amounts of incidental impurities; and adding to the granular base by weight: 0.5 to 8% of granular Bi2S3, based on the total weight of the inoculant, and optionally 0.1% to 15% of particulate Bi2O3 to produce the inoculant.

12. The method according to claim 11, wherein the particulate Bi2S3 and, if present, the optional particulate Bi2O3 are mixed or blended with the particulate base alloy.

13. The method of claim 12, wherein the granular Bi2S3 and, if present, the optional granular Bi2O3 are mixed before mixing with the granular base alloy.

14. Use of the inoculant according to any one of claims 1 to 10 in producing cast iron with spheroidal graphite by adding the inoculant to a cast iron melt before casting or as an in-mold inoculant.

15. The use according to claim 14, wherein the granular ferrosilicon-based alloy is added to the cast iron melt as a mechanical mixture or blend with the granular Bi2S3 and the optional granular Bi2O3.

16. The use according to claim 14, wherein the granular ferrosilicon-based alloy is added to the cast iron melt separately from but simultaneously with the granular Bi2S3 and the optional granular Bi2O3.

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