AU2007276412A1 - High dimensional cored wires containing oxygen removers and a process for making the same - Google Patents

Description

WO 2008/009414 PCT/EP2007/006323 Patent Application High dimensional cored wires containing oxygen removers and a process for making the same The present invention refers to a high dimensional cored wire containing de-oxidant material (or oxygen remover). Furthermore the invention refers to a process for manufacturing a high di mensional cored wire. De-oxidation plays an important role in the process of steel making, for which a number of de oxidants have been conventionally used. The term de-oxidant means a chemical compound, alloy or element which will remove the active oxygen present in the liquid metal (e.g. steel) and form an oxide as its final product, usually as a distinct phase and easily separable from the liq uid metal. Oxygen, if present in steel in the active/elemental form will result in pinholes and blowholes in the cast product as well as obstruct the process of continuously casting the steel in the modern continuous casting machines. Steel makers are in regular search of a better and more economical method for removing the oxygen in the steel, which will ultimately reduce the consumption of deoxidants. Conventionally de-oxidation of steel was carried out by the addition of ferro-alloys or aluminium ingots, bars or solid aluminium wire. For bars and ingots the recovery (i.e. ratio of actual quan tity and theoretical amount of aluminium) was poor, resulting in greater aluminium consumption. In case of the aluminium wire, the recovery was better, but feeding time was more and often the wire could not reach the depth of the molten steel bath.

WO 2008/009414 PCT/EP2007/006323 2 For doing the primary de-oxidation or the bulk removal of oxygen, (primary killing) in the steel from a higher level of, say, 800- 2000 ppm and above, to a lower level of to around 100-200 ppm, aiioys such as "Feiro-Silicon", "Ferro-Mang-Maeses, and "Coke" are used, though in bulk, and these materials have served the purpose fairly well. These ferro-alloys or compounds have a limitation on the extent to which they can be used in steel making and are limited to the extent of the specification that is allowed in the steel. In almost all grades of steel, silicon and manganese elements are used in various forms for the primary deoxidation along with aluminium in various forms such as bars, ingots, cubes or solid wires, etc. For secondary treatment of steel for the purpose of removing the remnant of oxygen, a number of de-oxidants selected from the group of aluminium, titanium and calcium silicide have been used. However, aluminium has been found to be the most suitable de-oxidant for two reasons, e.g. (i) affinity of aluminium for active oxygen and (ii) the requirement of presence of aluminium in predetermined amounts in some grades of steel in the cast product. Aluminium is capable of removing oxygen present in molten steel at very low levels of around 4p.p.m. or even less. It is also the most economical de-oxidiser element, alloy or compound known at present. Previously, primary deoxidation apart from the use of ferro alloys was carried out by the addition of aluminium ingots or bars and solid wires of dimension of 13 mm, and secondary or final de oxidation by adding ingots, notch bars and sometimes even solid aluminium wire. Addition through solid aluminium wire results in a higher percentage of recovery of aluminium compared to bars and ingots. In this specification, unless otherwise specified, the term 'recovery' defines the ratio of the actual quantity of aluminium to be added to remove the active oxygen to the theoretical amount of aluminium required. For bars and ingots, the recovery was very poor and accordingly consumption of aluminium increased. In case of solid aluminium wire, though the recovery was better than bars and ingots, but feeding time was more. The normal size of the aluminium wire that can be injected into the molten steel is around 3,6,9,13 or 16 mm. The other problem encountered with solid aluminium wire is that due to the high temperatures encountered in steel making, aluminium becomes very soft due to the high temperatures and is not able to penetrate deeply into the molten steel bath which consequently results in lower re covery. To solve a similar problem, it is proposed in CN1498975 to feed aluminium cored wire directly in molten steel for deoxidizing.

WO 2008/009414 PCT/EP2007/006323 A further method of adding aluminium to steel in a ladle for the purpose of deoxidation is known from GB892375. This method comprises progressively feeding a rod or wire of the material to be added at an appreciable depth below the surface of the steel. The material may be in powder or granular form enclosed in a steel tube. A process for manufacturing cored wires containing deoxidizing constituents as pulverized ma terial within a metal tube is known from US 3,915,693. Problem of the invention is to overcome the above drawbacks and provide a high dimensional cored wire as well as a process to manufacture a high dimentional cored wire. The problem is solved by the features of the independent claims. Preferred embodiments of the invention are described in the subclaims. The present invention attempts to overcome the above drawbacks and provides high dimen sional cored wires containing de-oxidant material / oxygen removers preferably formed from cold-rolled steel sheet, said de-oxidant material being in finely divided granular or powdery form at least partially coated with a protective coating material such as herein described, the diame ter of said cored wires varying between 13 and 40 mm, preferably between 19 and 34 mm. Pref erably the coated de-oxidant material filled in the core is held in place in compacted form by the seaming locks provided during formation of the said cored wires after filling. The wire can also be made by totally welding the sheath so that there is no seam. This invention also described a process for producing the above cored wires containing the de oxidant coated with a protective coat in a compacted form ensuring better recovery and rapid feeding of the de-oxidant material in predetermined amounts. In other words, the present invention relates to high dimensional cored wires containing de oxidant material / oxygen removers and process for making the same. More particularly this invention pertains to high dimensional cored wires filled with an oxygen removing material se lected from the group of aluminium, titanium, zirconium and calcium silicide, preferably fine granules of reactive aluminium powder, having a coating of inorganic or/and organic material, the coating can also be a mixture or combination of different materials, or even without a coat ing and simple granules, and a process for preparing such high dimensional cored wires.

WO 2008/009414 PCT/EP2007/006323 4 For the high dimensional wires proposed in the present invention, feeding of higher dimension solid aluminium wire as available now becomes very difficult to feed with the convention! wire feeders. The present invention aims at overcoming the foregoing shortcomings of the prior art and carry out production of steel more effectively maintaining an optimum level of aluminium in steel. This invention has also the advantage to further enhance the recovery of aluminium, simultane ously reducing the quantum of consumption and time of feeding of aluminium to liquid metal. A further advantage of the present invention is to provide a technique to use aluminium scraps as de-oxidant after converting them into granules followed by coating with a protective material like graphite, low density polythene, polyamide, low molecular weight vinyl acetate polymer, talc, steatite, calcium silicide, powdered lime, and the like to prevent fusion or adhesion of the granular particles into a single mass while being pressed and drawn in the wire. It is also possi ble to use the aluminium granules without coating. A still further advantage of this invention is to provide high dimensional cored wires containing aluminium granules coated with graphite which while being drawn through the forming machine, the contents become tightly packed, thereby imparting dimensional rigidity and stiffness to the wire. Another advantage of the present invention is to provide a process for preparing high dimen sional cored wires containing de-oxidants in granular form and coated with a protective coating to prevent sticking and fusing into a single mass while being pressed and drawn into wire. Fur ther, during immersion of the wire into molten steel the wire begins to melt and the (organic) coating vaporizes rapidly thus causing homogeneous and rapid spreading of the de-oxidant material within the molten steel. The subject invention also relates to a process for preparing high dimensional cored wires con taining de-oxidant material / oxygen removers as defined above, comprising especially the steps of (a) slitting cold rolled steel sheet of thickness varying between 0.2 and upto 1 mm. and re quired width of 90-110 mm, providing for the double seaming locks, WO 2008/009414 PCT/EP2007/006323 5 (b) feeding the slit coils into forming rolls which gives the slits the desired near round shape with diameter of 13 to 40 mm, preferably between 19 and 34 mm, (c) filling reactive aluminium powder/granules or other de-oxidants from bunkers or feeders into the blank spaces of the wire, (d) sealing the powder/granule filled wire, either singly or doubly, by the time it comes out of the last forming roll, (e) squeezing the contents of the cored wire by squeezing rolls to reduce the diameter of the cored wire and impart dimensional strength and stability, (f) coiling the thus formed wire over a mandrel with inner diameter varying from 200 mm to 2.5 meters in diameter, generally of around 1 metre in diameter, depending on customer requirement, (g) applying a thin film of oil or anti-rust solution to the exposed surface or outer layer of the coil to prevent rust formation, and (h) strapping and/or wrapping the coils with plastic/stretch film for preventing moisture in gress and then placing over wooden or steel pallets for delivery to the customer. As pointed out earlier, de-oxidants maybe selected from metallic, aluminium, titanium, zirconium and calcium silicide, but aluminium has been found to give best results as the oxide formed may be removed easily due to phase separation and its refractoriness. Aluminium is used in granular or powdery form, coated with graphite. Scrap aluminium obtained from discarded used bever age cans, sheets/foils/strips/old electrical cable and the like are smelted or shredded and con verted into granular form followed by application of a protective coating material like graphite, talc, lime stone dust, calcite, steatite, LDP (low density polyethylene) and the like to prevent fusion or adhesion of granules at the time of being pressed and drawn in the wire. The lacquer coating on the used beverage cans also serve the purpose of protective coating. Size of alumin ium granules should be optimally be around 40 mesh, but finer or coarser sized granules may just as well be used; however, care should be taken to prevent handling loss. While drawing the aluminium granule-filled wire through the forming machine, the contents become tightly packed, thereby imparting dimensional rigidity and stiffness to the wire, ensuring ease of handling the coil. Deoxidation with aluminium by changing the form of aluminium addition, which is carried out by injecting high dimensional cored wire filled with highly reactive aluminium in fine granular form and coated with an organic material like graphite for better recovery and achieving the optimum level of oxygen and aluminium with lesser consumption of aluminium are a unique feature of WO 2008/009414 PCT/EP2007/006323 6 this invention. The coating is not limited to organic materials but can also include inorganic coat ing materials like calcium oxide, talc, chalk powder, and the like. De-oxidation in accordance with the present invention can be carried out both in the primary and the secondary levels, as per requirement of the steel maker. As pointed out earlier, aluminium powder is converted into fine granules and then coated with an inert organic coating material like graphite flakes or any organic or inorganic coating material to prevent the aluminium powder from sticking and fusing into a single mass while being pressed and drawn in the wire. While drawing the aluminium powder filled wire, the contents become tightly packed, thereby imparting dimensional rigidity and stiffness to the wire. This also ensures ease of handling the coil. A notable feature of this invention is to use scrap aluminium of any grade in granular or pow dered form as the de-oxidant, suitably coated with organic or inorganic coating material as de scribed hereinbefore. Use of scrap/waste aluminium bodies effectively adds to the economy of the overall process. As an additional feature of this invention, winding of the powder filled coil is subjected to 'core less coiling' so that the coil can be uncoiled from inner diameter of the stationary coil, generally called a "flipping coil", either vertical or horizontal. The coil can also be made into a spool with a core made of either wooden, synthetic, metal or any such materials. The novel product of this invention, namely, high dimensional cored wire filled with fine granules of aluminium powder coated with graphite and securely held inside, is provided with seaming locks. By 'high dimensional' it is implied that dimensions of the cored wire ranges between 13 and 40 mm, optimally between 19mm and 34mm, and the internal diameter of the wound wire over the mandrel may vary between 200mm to 2.5 meters and the weight of each coil may range between 1 MT to around 20 MT (MT - metric ton, usually abbreviation of which is t), de pending on customer requirement. The present invention will be further illustrated by the experimental data included in the follow ing example, but it is to be understood that the invention is not restricted to the results given therein.

WO 2008/009414 PCT/EP2007/006323 7 Example High Dimensional Cored 'vire (Powder Density) Wire Bulk Density Bulk Density (Max) Sheath Fill Rate Fill Rate Diameter (Min) g/cm 3 g/cm 3 Thickness (Min) g/m (Max) g/m (mm) (mm) 19 1.4 2.5 0.4 364 650 20 1.4 2.5 0.4 405 724 21 1.4 2.5 0.4 449 801 22 1.4 2.5 0.4 494 883 23 1.4 2.5 0.4 542 968 24 1.4 2.5 0.4 592 1057 25 1.4 2.5 0.4 644 1150 26 1.4 2.5 0.4 698 1247 27 1.4 2.5 0.4 755 1348 28 1.4 2.5 0.4 814 1453 29 1.4 2.5 0.4 875 1562 30 1.4 2.5 0.4 938 1674 31 1.4 2.5 0.4 1003 1791 32 1.4 2.5 0.4 1070 1912 33 1.4 2.5 0.4 1140 2036 34 1.4 2.5 0.4 1212 2165 35 1.4 2.5 0.4 1286 2297 36 1.4 2.5 0.4 1363 2433 37 1.4 2.5 0.4 1441 2573 38 1.4 2.5 0.4 1522 2718 39 1.4 2.5 0.4 1605 2866 40 1.4 2.5 0.4 1690 3018 WO 2008/009414 PCT/EP2007/006323 8 Various advantages of the products of the present invention may be briefly outlined as under: 1. An increasing amount of de-oxidant like aluminium can be filled per unit length of w'ire, and as more material is compacted per meter of wire of larger dimension, the cost of the steel sheathing becomes less. 2. There is substantial rise in the feeding rate, thereby saving feeding time and resulting in an enhanced time available for steel making. 3. Due to larger dimension, better rigidity and stiffness, the high dimensional wire allows for deeper penetration into steel, thereby resulting in better recovery and homogenization of aluminium. 4. Graphite coated fine granules of aluminium are used as filler material for making high di mensional cored wire (known as "REACTIVE ALUMINIUM"), which results in an estimated 15-25% higher recovery than the conventional solid aluminium wire. The reactivity is at tained by smaller aluminium grains and hence larger surface area for reaction. The recovery can even be more depending on the steel making practices over the current system in vogue for aluminium addition into molten steel. 5. Since the Aluminium cored wire is of "flipping type", there is a saving on the conversion cost in converting the solid aluminium wire into "flipping type". 6. Lesser consumption of aluminium in-turn will reduce the production cost of steel, particularly in view of the use of required grade of scrap aluminium of any grade and coated with protec tive coated material. 7. Less consumption of packing material brings down production cost. As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described experi mental data are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and ambit as defined in the claims appended hereinafter, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds, are therefore in tended to be embraced by the appended claims.

Claims (17)

1. High dimensional cored wire containing de-oxidant material arranged in a core of the wire, said de-oxidant material being in finely divided granular or powdery form coated with a protective coating material, the diameter of the said cored wire varying between 13 and 40 mm.

2. High dimensional cored wire as claimed in claim 1, characterized in that it is formed from steel sheet, preferably from cold-rolled steel sheet.

3. High dimensional cored wire as claimed in claim 2, wherein it comprises one or more seaming locks, arranged preferably longitudinal to the axis of the wire.

4. High dimensional cored wire as claimed in claim 3, wherein the coated de-oxidant mate rial filled in the core is held in place in compacted form by the seaming lock provided during formation of the said cored wires.

5. High dimensional cored wire as claimed in claim 4, wherein the coated de-oxidant mate rial is held in place in compacted form by the seaming lock provided during formation of the said cored wires after filling.

6. High dimensional cored wire as claimed in any one of claims 1 to 6, characterized in that the diameter of the cored wire varies between 19 and 34 mm.

7. High dimensional cored wire as claimed in any one of claims 1 to 6, wherein finely di vided granules of aluminium powder coated with graphite is used as the de-oxidant ma terial.

8. High dimensional cored wire as claimed in any one of claims 1 to 7, wherein there is used scrap aluminium, preferably in the form of sheets, foils, strips, as the de-oxidant material. WO 2008/009414 PCT/EP2007/006323 10

9. High dimensional cored wire as claimed in claim 8, wherein the de-oxidant material is converted by mechanical or melting process to finely devided granules or powder.

10. High dimensional cored wire as claimed in claim 8 or 9, wherein the de-oxidant material is a material shredded and converted into granular/powdery form.

11. High dimensional cored wire as claimed in any of claims 1 to 10, wherein the de-oxidant material is partially or totally coated by a protective coating material, the coating prefera bly comprising one ore more of graphite, talc, steatite, lime stone dust, calcite, LDP.

12. High dimensional cored wire as claimed in any one of claims 8 to 11, wherein while drawing aluminium powder/granule filled wire, the contents become tightly packed, thereby imparting dimensional rigidity and stiffness to the wire, ensuring ease of han dling the coil.

13. A process for preparing a high dimensional cored wire containing de-oxidant material as claimed in any of the preceding claims, comprising the steps of (a) slitting cold rolled steel sheet of thickness varying between 0.2 and 1 mm and re quired width of 90-110 mm providing for double seaming locks, (b) feeding the slit coils into the forming rolls which gives the slits the desired near round shape with desired diameter of 13 to 40 mm, (c) filling reactive aluminium powder/granules or other de-oxidants from bunkers or feeders into the blank spaces of the wire, (d) sealing the powder/granule filled wire, either singly or doubly, by the time it comes out of the last forming roll, (e) squeezing the contents of the cored wire by squeezing rolls to reduce the diame ter of the cored wire and impart dimensional strength and stability, (f) coiling the thus formed wire over a mandrel with inner diameter varying from 200 mm to 2.5 meters in diameter, (g) applying a thin film of oil or anti-rust solution to the exposed surface or outer layer of the coil to prevent rust formation, and (h) strapping and/or wrapping the coils with plastic/stretch film for preventing mois ture ingress and then placing over wooden or steel pallets for delivery to the cus tomer. WO 2008/009414 PCT/EP2007/006323 11

14. A process as claimed in claim 13, wherein the thickness of cold-rolled steel sheet (DD and soft grade) varies between 0.2 and 1 mm, 0.4 mm sheet-thickness being preferred, wherein the weight of each coil varies preferably between 1 MT and 20MT.

15. A process as claimed in claim 13 or 14, wherein the diameter of the formed wire varies between 13 and 40mm, preferably between 19 and 34mm.

16. A process as claimed in any one of claims 13 to 15, wherein the wire is coiled over a mandrel with inner diameter of about 1 m.

17. A process as claimed in any one of claims 13 to 16, wherein winding of the de-oxidant filled coil is subjected to coreless winding thereby allowing the said coil to be unwinded or uncoiled from the inner diameter of the stationary coil.