Metal treatment additive

Abstract

A metal treatment additive for treating molten iron comprising 10 to 90 wt% of an active agent and 90 to 10 wt% of a carrier. The active agent comprises one or more of barium, bismuth, and zirconium as the primary component, and the additive composition comprises less than 0.5 wt% of magnesium. The additive is suitable for inoculating molten iron during casting processes.

Description

[0001] Metal Treatment Additive

[0002] Technical Field

[0003] The present invention relates to methods for treating molten metal. In particular, the present invention relates to the treatment of molten iron and systems and compositions therefor.

[0004] Background

[0005] Metal treatment agents are used to modify the composition, morphology and / or distribution of graphite particles found in molten iron. Metal treatment agents applied to molten iron include nodularising agents and inoculants which are used to alter the morphology of iron structure, and thereby produce Ductile Iron (DI) as well as Compacted Graphite Iron (CGI). Inoculants are additives which introduce nuclei into the molten iron to act as crystallisation points for carbon dissolved within the molten iron - these crystallisation points alter the graphite precipitation and structural formation of the casting. Poor inoculation leads to the undesirable formation of iron carbide within the casting as the iron cools.

[0006] Existing inoculants are mostly alloys based on ferrosilicon as a carrier with additions of “active agents” such as calcium, aluminium, barium, zircon, strontium and rare earth metals. During the inoculation of a molten cast iron, the oxygen and / or sulphur contained therein is fully or partially bound to the active agents within the inoculant composition and thus precipitates out as oxides, sulphides or oxysulphides. These sub- microscopic chemical compounds / precipitates act as crystallization nuclei for the precipitation of the graphite particles of the cast iron during solidification. The inoculant compositions themselves are provided as a powder or granular material, with particles with an average size ranging from 0.2mm up to 15mm.

[0007] During typical inoculation processes, the amount of the inoculant composition necessary is very low e.g. a relatively high addition rate of 0.4 to 0.5 wt% of the inoculant composition relative to the weight of the iron being treated is only 4 to 5 kg per tonne of metal. Furthermore, conventional inoculant compositions have a concentration of around 5% of active agents, corresponding to an addition rate of about amount of material to keep costs low. However, with such low addition rates, significant problems are found with the mixing of the inoculant through the molten iron. For example, the inoculant may be provided within a ladle prior to the molten iron being poured into the ladle. With low weights / volumes of the inoculant composition, should some of the powder be trapped in a corner of the ladle during treatment, then the entire volume of the ladle may be insufficiently inoculated. For in-stream inoculation, low volumes of inoculant are also problematic to control and unless all of the inoculant enters the metal stream, the inoculation will be insufficient.

[0008] Insufficient inoculation (e.g. as a result of poor mixing) leads to poor crystal structure formation and expensive failed castings. To improve mixing, inoculants are usually based on 90% ferrosilicon, wherein ferrosilicon acts as a soluble carrier i.e. the active component of such a ferrosilicon based inoculant may represent only 10% of the total weight or volume of the inoculant composition. The low concentration of the composition means larger amounts of the composition are required but provides a much greater error tolerance and leads to improved mixing through the melt. However, this increases the cost to produce, transport, and use the inoculant composition.

[0009] It is thus desirable to provide an alternative inoculant composition with mitigates or ameliorates one or more of the problems associated with existing inoculant compositions and inoculation processes.

[0010] Summary of Invention

[0011] According to a first aspect of the invention, there is provided an inoculant composition for treating molten iron. The inoculant composition may comprise 10 to 90 wt% of an active agent. The inoculant composition may comprise 90 to 10 wt% of a carrier. The active agent may comprise one or more of barium, bismuth, manganese, and zirconium as the primary component. The inoculant composition may comprise less than 0.5 wt% of magnesium.

[0012] As used herein, the term ‘primary component’ refers to the element or compound within the active agent with the highest addition rate e.g. the highest weight percentage. One or more further components may be included within the active agent. Iron and silicon, either separately or as a ferrosilicon alloy, are not considered active agents.

[0013] All weight percentages used herein unless otherwise specified refer to the overall inoculant composition.

[0014] The active agent may comprise 3-40 wt% zirconium (relative to the overall weight of the inoculant composition).

[0015] The active agent may comprise at least 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 18, 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, of 38 wt% of zirconium. The active agent may comprise less than 38, 36, 35, 34, 32, 30, 28, 26, 25, 24, 22, 20, 18, 16, 15, 14, 12, 10,

[0016] 9, 8, 7, 6, 5, or 4 wt% of zirconium.

[0017] In some embodiments, the active agent comprises 3 to 25 wt% of zirconium. For example, in some embodiments the active agent comprises 4 to 6 wt%, 8 to 15 wt %, 10 to 12 wt %, or 18 to 22 wt% of zirconium. In a further series of embodiments, the active agent comprises 25 to 40 wt%, and optionally, 30 to 35 wt%, of zirconium.

[0018] The active agent may comprise 3-25 wt% bismuth (relative to the overall weight of the inoculant composition). The active agent may comprise at least 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 18, 20, 22, or 24 wt% of bismuth. The active agent may comprise less than 24, 22, 20, 18, 16, 15, 14, 12, 10, 9, 8, 7, 6, 5, or 4 wt% of bismuth. In some embodiments, the active agent comprises 4 to 6 wt %, or 5 to 15 wt% of bismuth.

[0019] The active agent may comprise 5-40 wt% barium (relative to the overall weight of the inoculant composition). The active agent may comprise at least 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, of 38 wt% of barium. The active agent may comprise at least 6, 7, 8, 9,

[0020] 10, 12, 14, 15, 16, 18, 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, of 38 wt% of barium. The active agent may comprise less than 38, 36, 35, 34, 32, 30, 28, 26, 25, 24, 22, 20, 18, 16, 15, 14, 12, 10, 9, 8, 7, or 6 wt% of barium. In some embodiments, the active agent comprises 5 to 15 wt% barium, or 10 to 12 wt% barium. In some further embodiments, the active agent comprises 30 to 40 wt% barium e.g. 34 to 36 wt% or 35wt% barium. The inoculant composition may comprise a secondary active agent and / or a secondary component. In some embodiments, the inoculant composition comprises a plurality of active agents. As noted above, the primary component would be the active agent with the greatest addition rate to the inoculant composition. Secondary active agents thus provide an additional inoculant effect.

[0021] Secondary components may comprise compound or materials which do not have an inoculant effect and / or which are selected due to other useful properties or effects on the inoculant composition.

[0022] The active agent may further comprise 0-10 wt% calcium (relative to the overall weight of the inoculant composition). The active agent may comprise at least 0.2, 0.3, 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, or 9 wt% of calcium. The active agent may comprise less than 9, 8, 7, 6, 5, 4, 3, 2, 1.5, 1 , 0.5, 0.3, or 0.2 wt% of calcium. In some embodiments, the active agent comprises 0-5 wt%, optionally 0.5 to 2 wt% of calcium. In some embodiments, the active agent comprises 1 to 7 wt %, optionally 1-2 wt% of calcium. The calcium may be present as a secondary active agent or secondary component.

[0023] The active agent may further comprise 0 to 5 wt% of aluminium. The active agent may comprise at least 0.5, 1 , 1.5, 2, 3, or 4 wt% of aluminium. The active agent may comprise less than 4, 3, 2, 1.5, 1, or 0.5 wt% aluminium. In some embodiments, the active agent comprises 1 to 2 wt% of aluminium. In some embodiments, the active agent may comprise no more than 1.5 wt% of aluminium. The aluminium may be present as a secondary active agent or secondary component.

[0024] In some embodiments, the aluminium and / or calcium may be derived from their inclusion with other minerals or components. For example, aluminium and / or calcium are often present in sources of barium and other, particularly natural, minerals. In some embodiments, additional aluminium or calcium maybe added to the inoculant composition beyond the natural occurring content within other components.

[0025] The inoculant composition may comprise 0-22 wt% manganese (relative to the overall weight of the inoculant composition). The inoculant composition may comprise at least 0.2, 0.3, 0.5, 1 , 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 18, or 19 wt% of manganese. The inoculant composition may comprise less than 19, 18, 16, 15, 14, 12, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1.5, 1, 0.5, 0.3, or 0.2 wt% of manganese. In some embodiments, the inoculant composition comprises 0.3 to 20 wt %, 0.3 to 15 wt%, or 10 to 12 wt% of manganese. The manganese may be present as a secondary component. Manganese is effective in lowering the melting point of the inoculant composition alloy, thus improving the treatment process.

[0026] In one series of embodiments (combinable with the above), the active agent comprises 8 to 15 wt% of zirconium and 0.3 to 15 wt% of manganese. In a further series of embodiments, the active agent comprises 25 to 40 wt% of zirconium and 0.3 to 20 wt% of manganese. In some embodiments, the active agent comprises no more than 1.5 wt% of aluminium. Alloys of zirconium e.g. with manganese or other metals, are particularly desirable due to the lower solubility of zirconium within molten iron.

[0027] In one series of embodiments (combinable with the above), the active agent comprises 3 to 25 wt% of zirconium and 3 to 25 wt % of bismuth. For example, the active agent may comprise 4 to 6 wt% of zirconium and 4 to 6 wt% of bismuth. The active agent may optionally comprise 0 to 5 wt % of manganese. The active agent may comprise 0 to 5 wt% of aluminium, and optionally, 1 to 2 wt% of aluminium. In some embodiments, the active agent comprises 18 to 22 wt% of zirconium and 5 to 15 wt % of bismuth. The active agent may comprise 0 to 22 wt% of manganese. The active agent may comprise 0 to 5 wt% of aluminium, and optionally, 1 to 2 wt% of aluminium.

[0028] In one series of embodiments (combinable with the above), the active agent comprises 20 to 40 wt% of barium and 0 to 10 wt% of calcium. In some embodiments, the active agent comprises 30 to 35 wt% of barium and 1 to 6 wt% of calcium. In some embodiments, the active agent comprises no more than 1.5 wt% of aluminium.

[0029] The inoculant composition may comprise less than 0.5wt% carbon, less than 0.1 wt% sulphur, and / or less than 0.5wt% phosphorus.

[0030] The carrier may comprise iron, silicon, and / or ferrosilicon. The carrier may comprise 10 to 70 wt% silicon (relative to the overall weight of the inoculant composition), either as silicon or as ferrosilicon. The carrier may comprise at least 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, or 65 wt% of silicon. The carrier may comprise less than 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, or 15 wt% of silicon. In some embodiments, the carrier comprises 10 to 20 wt% of silicon. In some embodiments, the carrier comprises 45 to 60 wt% of silicon.

[0031] The balance of the inoculant composition may comprise iron, either as iron or as ferrosilicon. In some embodiments, the carrier comprises 18 to 85 wt% of iron. The carrier may comprise at least 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, or 80 wt% of iron. The carrier may comprise less than 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, or 15 wt% of iron. In some embodiments, the carrier comprises 19 to 50 wt% of iron, 30 to 55 wt% of iron, or 24 to 85 wt% of iron.

[0032] In embodiments comprising ferrosilicon, the ferrosilicon comprising 50-70% silicon, and preferably, 60-70% silicon. These alloys are advantageous, since they have the lowest melting point of the ferrosilicon alloys, of around 1100°C. Cast iron requires a small amount of silicon therein, so the silicon content is not usually problematic so long as it is kept below a limit. High silicon additions can lead to remelting problems with the iron.

[0033] The inoculant composition may be formed as a single alloy comprising all of the components therein.

[0034] The inoculant composition may be formed into powder, granules, and / or tablets. In some embodiments, the inoculant composition is provided in pre-portioned packages. The pre-portioned packages may comprise the powder, granules, and / or tablets therein. The pre-portioned packages may comprise a paper or card material, a metal foil, and / or a plastics material, filled with the inoculant composition.

[0035] In some embodiments, the inoculant composition is provided within a cored wire. The wire may comprise an iron or steel outer tube filled with the inoculant composition.

[0036] The inoculant composition may comprise particles or grains with the size of 0.2 mm to 12 mm. For example, the inoculant composition may comprise 90% of particles or grains which fall within the range of 0.2mm to 12 mm. In some embodiments, the particles size may be 0.2 to 0.7 mm. Such fine particles are desirable for use with in- stream inoculation systems. In some embodiments, the particles or grains may comprise 0.2 to 2mm, 2 to 6mm and / or 6 to 12mm. In a second aspect of the invention, there is provided a method for inoculating molten iron. The method may comprise providing an inoculant composition as described herein to a vessel. The method may comprise adding molten iron to the vessel. The vessel may be a transfer ladle. The method may comprise adding no more than 0.5 wt% of the inoculant composition relative to the weight of molten iron being treated. In some embodiments, the methods comprises adding less than 0.45, less than 0.4, less than 0.35, 0.3, 0.25, 0.2, 0.15, 0.1 , 0.8, 0.6, 0.5, 0.4, 0.2, 0.1 , 0.08, 0.06, 0.05, 0.04, or 0.02 wt% of the inoculant composition relative to the weight of molten iron.

[0037] The inventors have found that the present invention can inoculate molten iron and provide high quality castings, even at much lower addition rates. By reducing the quantity of inoculant composition necessary to inoculate a melt, significant cost savings can be achieved. Although the inoculant composition itself is more expensive to produce, at the lower addition rates it is more cost effective for the foundry while still maintaining a high quality.

[0038] In some embodiments, the method may comprise stirring the molten iron e.g. using a rotor. In some embodiments, the method may comprise supplying the molten iron with the inoculant composition through a rotor.

[0039] In a third aspect of the invention, there is provided a method for inoculating molten iron comprising spraying an inoculant composition as described herein into a stream of molten iron. The method may comprise spraying the inoculant composition into a stream of molten metal between a transfer ladle and a mould.

[0040] In a fourth aspect of the invention, there is provided a method for producing an inoculant composition as described herein. The method may comprise: reacting silica, iron and carbon in a submerged arc furnace to form ferrosilicon and carbon dioxide, or remelting a ferrosilicon alloy in an induction furnace. The method may comprise adding one or more active agents to the furnace to form an alloyed inoculant composition comprising the carrier and the active agent. The method may comprise cooling and solidifying the inoculant composition. The method may comprise crushing the inoculant composition to produce a granular and / or powdered inoculant composition. The method may comprise crushing the inoculant composition to a particle size and / or grain size of between 0.2mm and 12mm, or within the ranges described previously. The method may comprise removing particles with a size less than 0.2mm.

[0041] The method may further comprise mixing the granular and / or powdered inoculant composition with a further granular and / or powdered active agent. The method may comprise mixing the granular and / or powdered inoculant composition with a further carrier.

[0042] Embodiments of the invention will now be described herein with reference to the following experimental data.

[0043] Experiment - casting trials

[0044] Several powdered inoculant compositions E1 to E5 were prepared as described in

[0045] Table 1 :

[0046] Table 1 - compositions of the inoculant compositions

[0047] In a series of tests, each of E1 to E5 were measured into predetermined weights and wrapped in aluminium foil to form pre-portioned packages. The pre-portioned packages were added to the top of a transfer ladle filled with 360kg molten iron. The addition rates of E1 to E5 were between 0.23wt% and 0.06wt% of the molten iron. As a comparative example, 0.7wt% of C1 was added to a transfer ladle comprising 360kg of molten iron. The inoculated iron was then poured into a mould and allowed to cool. Tests using compositions E1 , E2 and E5 were found to have an excellent recovery of zirconium of between 60% and 70%. ‘Recovery’ of the metal is the amount present in to the final casting and not lost during the casting process, and is thus a measure of efficiency.

[0048] Samples of each casting were then taken through a thin wall section and a thick wall section of the casting and prepared for metallographic examination. The images from the examination of the thin wall are shown in Figure 1 and of the thick wall sections are shown in Figure 2. Further data from the examination is shown in Table 2 below.

[0049] Table 2 - results of metallographic examinations As shown in Figures 1 and 2, and in Table 2 above, the results of the tests show that E1 and E3 can be used at half the addition rate in comparison to the standard product. E2 and E4 can be used at a quarter of the addition rate in comparison to the standard product.

[0050] The inventors have also surprisingly found that the inoculant composition E5 (when compared with a commercial inoculant product comprising 4% Zr, 3% Mn, 1.2% Ca, 1% Al, and the balance being ferrosilicon (62-69% Si)) improves the performance of castings (e.g. fewer casting defects) with a low cooling rate at a wall thickness of above 50 mm.

[0051] All of the tested compositions E1 to E5 were comparable to the comparative composition, despite the much lower addition rates of the example compositions E1 to E5.

Claims

CLAIMS:

1. An inoculant composition for treating molten iron, the composition comprising:10 to 90 wt% of an active agent; and90 to 10 wt% of a carrier, wherein the active agent comprises one or more of barium, bismuth, manganese, and zirconium as the primary component, and wherein the inoculant composition comprises less than 0.5 wt% of magnesium.

2. The inoculant composition according to any one of the preceding claims, wherein the active agent comprises 3-40 wt% zirconium.

3. The inoculant composition according to claim 2, wherein the active agent comprises 3-25 wt% bismuth.

4. The inoculant composition according to either claim 2 or 3, wherein the active agent comprises 0.3-22 wt% manganese.

5. The inoculant composition according to claim 1, wherein the active agent comprises 20-40wt% barium.

6. The inoculant composition according to any one of the preceding claims, wherein the active agent comprises 0-10 wt% calcium.

7. The inoculant composition comprises less than 0.5wt% carbon, less than 0.1wt% sulphur, and / or less than 0.5wt% phosphorus.

8. The inoculant composition according to any one of the preceding claims, wherein the carrier comprises ferrosilicon.

9. The inoculant composition according to any one of the preceding claims, wherein the inoculant composition is formed into powder, granules, and / or tablets, and optionally, wherein the inoculant composition is provided in pre-portioned packages.

10. The inoculant composition according to claim 9, wherein the inoculant composition has a particle size or grain size of 0.2 mm to 12 mm.

11. A method for inoculating molten iron comprising: providing an inoculant composition according to any one of the preceding claims to a vessel, adding molten iron to the vessel.

12. A method for inoculating molten iron comprising spraying an inoculant composition according to any one of claims 1 to 10 into a stream of molten iron.

13. The method of claim 11 or claim 12, wherein the method comprises adding less than 0.5 wt% of the inoculant composition relative to the weight of the molten iron.

14. A method for producing an inoculant composition according to any one of claims 1 to 10, comprising: reacting silica, iron and carbon in a submerged arc furnace to form ferrosilicon and carbon dioxide, or remelting a ferrosilicon alloy in an induction furnace; adding one or more active agents to the furnace to form an inoculant composition comprising a ferrosilicon alloyed with the active agent; cooling and solidifying the inoculant composition; and crushing the inoculant composition to produce a granular and / or powdered inoculant composition.

15. The method according to claim 14, further comprising mixing the granular and / or powdered inoculant composition with a further granular and / or powdered active agent.

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