Enhanced Alloy Recovery In Molten Steel Baths Utilizing Cored Wires Doped With Dispersants

Abstract

The present invention provides increased recovery in additive-enhanced or alloy-enhanced molten steel. This is accomplished by dispersing agents blended with the additive alloys. The dispersant powder reacts with the carbon in the steel forming carbon monoxide gas which provides kinetic energy to the additive alloy particle causing dispersion within the molten bath, resulting in greater dissolution of the particles in the molten bath. The alloy or additive region is enriched, thereby improving the recovery in the molten steel.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. provisional application No. 60/938,670, filed on May 17, 2007, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to adding alloys to molten steel. More particularly, this invention relates to adding alloys and dispersants to molten steel in order to increase recovery in the steel.

BACKGROUND OF THE INVENTION

It is well known to add alloys and other additives to molten steel in order to improve the material properties, including strength and toughness, of the finished steel.

In the prior art, adding alloys and additives to molten steel is often accomplished by encasing powdered alloys and additives in a metal sheath to form a “cored wire” which is subsequently “injected” into the molten steel. U.S. Pat. No. 4,128,414 describes such an injection process. To ensure good mixing of the steel, many steel making companies employ inert-gas-stirring of the molten steel. Generally, argon gas is bubbled through a porous plug in the bottom of the ladle or via an argon lance which is submerged into the molten steel from above. Often, the stirring generated by such devices is not sufficient to achieve good mixing and, as such, a portion of the additive alloys injected into the molten bath will rise to the steel surface. Thus, some of the material injected into the steel does not stay in the steel. In order to efficiently produce additive-enhanced or alloy-enhanced molten steel, it is desirable to increase the “recovery” in molten steel.

“Recovery” is a measure of the amount of alloy and/or additive contained in the molten steel after injection relative to the amount added. Recovery is expressed as the percent of alloy and/or additive injected in the steel that is contained in the steel after injection. The greater the percentage contained in the steel after injection, the greater the recovery will be. Greater recoveries mean lower cost to the steel maker because less cored wire is injected.

It is well known that adding a dispersant powder to the cored wire during its manufacture causes the additive alloy to disperse more fully within the molten metal, thereby enhancing the alloy and additive powder distribution in the molten steel. This is especially true in steel making operations with insufficient stirring capabilities.

One known dispersant is limestone powder, which has been added to cored wire and has been shown to enhance the recovery of lead (Pb) by creating an emulsion of the liquid lead and liquid steel. U.S. Pat. No. 4,892,580 describes one such process. In U.S. Pat. No. 4,892,580, limestone was used to facilitate reducing the size of liquid lead drops and the emulsification of the immiscible liquid lead droplets in the steel.

In another known method described in U.S. Pat. No. 4,049,433, the use of an aqueous mixture of oil and water is added to the surface of bulk additive alloys (e.g., larger, gravel-like chunks of additive alloys added to a molten metal bath in bags, boxes, drums or with a shovel or chute) for the purpose of improving alloy recovery. U.S. Pat. No. 4,049,433 was an attempt to disperse large pieces of additive alloys added in bulk form to molten steel. This method, however, increases the oxygen and hydrogen content of the steel (oxygen is generally undesired in steel and hydrogen is always undesired in steel). Further, due to the larger size of these additive alloy particles (generally on the order of 5 mm to 100 mm in diameter) and the method of adding bulk alloys to molten baths (e.g., hand additions of cans, bags, boxes or adding loose additions by shovel or by chute to the surface of the bath) the effectiveness of this dispersing method is reduced.

Despite the improvements in the prior art, there remains a need to improve upon the recovery in the molten metals, and steel in particular.

SUMMARY OF THE INVENTION

The present invention may be embodied as an alloy delivery device. The delivery device may include a blended substance having at least one solid additive dissolvable alloy and at least one dispersing agent. The blended substance may be encapsulated in a metal jacket, which may take the form of a substantially hollow wire in which the blended substance resides. The metal jacket is described herein as being made from steel, but other materials, including aluminum, copper or zinc, may be used.

The at least one additive dissolvable alloy may be FeNb, FeV, or FeTi. The at least one dispersing agent may be limestone. The dispersing agent may be a powder comprised of particles having a diameter of less than one millimeter. The additive alloy may be ground powder particles having a diameter of less than 1 mm. The dispersing agent may be present in an amount of 5 to 50% of the mixture by weight or volume.

The present invention may be embodied as a method for providing an additive alloy to molten metal, wherein at least one dispersing agent is blended with at least one solid additive dissolvable alloy to provide a blended substance. Preferably, the additive alloy is dissolvable. The blended substance may be encapsulated in a metal jacket to provide an alloy delivery device. Molten metal may be produced and the alloy delivery device may be injected into the molten steel. The delivery device may be injected into the molten steel by a wire injector and guide tube arrangement. The delivery device may be fed into the molten metal and the metal jacket may be allowed to melt in the molten metal, and once the jacket melts, the additive alloy, in solid particle form is allowed to mix with the molten steel, and the dispersing agent facilitates such mixing. Depending on the alloy, the solid alloy particles may melt, or not, after having been acted on by the dispersing agent.

It is well known that ground additive alloys (typically ground to powders under 1 mm in diameter) encased in a steel jacketed cored wire that is injected deep into molten baths results in a significant improvement in recovery. In this invention, the recovery is enhanced by blending limestone powder in varying amounts (typically, but not limited to, 5% to 50% of the mixture by weight or volume) with the additive alloy that is, at least initially, introduced to the molten steel as a solid particle. The limestone has been shown to react with the carbon in the molten metal resulting in a reaction that generates CO₂ gas. This CO₂ gas expands rapidly in the hot molten metal generating considerable stirring energy which imparts kinetic energy to the fine additive alloy powder upon release from the cored wire deep within the molten bath. The extra kinetic energy causes these fine particles to be further dispersed in the bath, thus, enriching the molten metal with their chemical elements in additive alloy depleted areas of the molten bath that, under normal cored wire injection methods, would not be enriched. As a result of particles being kinetically driven to further reaches of the bath, more of the bath becomes enriched, thereby increasing the recovery of the additive alloy.

Thus, the present invention provides an additive-enhanced or alloy-enhanced molten steel with improved recovery.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention, reference should be made to the accompanying drawings and the subsequent description. Briefly, the drawings are:

FIG. 1 is a flow chart of a method according to the invention.

FIG. 2 depicts an embodiment of the present invention wherein an additive alloy is blended with a dispersant agent, which reacts with the carbon in the molten steel, thereby providing kinetic energy to cause dispersion of the additive alloy particles.

FIG. 3 depicts a cross-sectional end view of a delivery device according to the invention.

FIG. 4 depicts a sectioned side view of the delivery device depicted in FIG. 3.

FURTHER DESCRIPTION OF THE INVENTION

The present invention may be used to provide increased recovery in additive-enhanced or alloy-enhanced molten steel.

FIG. 1 depicts a method according to the invention. In one such method, an additive alloy powder is blended 100 with a dispersant, such as limestone powder, and encapsulated in a steel jacket to form a cored wire. The additive alloy may be FeNb, FeV, or FeTi. The cored wire is injected 103 into a molten metal bath, which may be accomplished by using a wire injector and guide tube arrangement. Then the steel jacket melts 106 into the molten bath releasing the blended powder. Due to the melting temperature of the alloy, the alloy is released from the jacket in solid form. Since the jacket may serve to insulate the alloy, and the limestone may serve as a heat-sink, it is possible to introduce an alloy in solid form to the molten metal even though the melting temperature of the alloy is at or below the temperature of the molten metal bath. The dispersant limestone powder reacts 109 with carbon in the molten bath forming CO₂ gas which expands and moves with great energy. The energy of the expanding and moving CO₂ gas bubbles provides 112 kinetic energy to the additive alloy particle and to the molten metal, thereby causing great dispersion of the alloy particles within the molten bath. The increased dispersion of additive alloy particles results in greater dissolution 115 of the alloy in the molten bath and thus enriching more of the bath volume with the alloy.

FIG. 2 depicts CO₂ bubbles dispersing an additive alloy particle 13. By blending limestone powder with an additive alloy 13, and housing that blend in an annular wire for injection into a molten bath 10, the cored wire will eventually melt, thereby exposing the limestone and alloy powders to the molten steel. By selecting alloys which are solid upon melting of the jacket, it is believed that the alloy is dispersed better than the prior art. It is believed that by selecting materials to provide the alloy as a solid, that more of the mixing energy provided by the dispersant will be used to disperse the alloy. A chemical reaction between the limestone 16 and the carbon contained in the molten bath 10 forms CO₂ bubbles 19, which due to the extreme temperatures of the molten bath, causes the CO₂ gas bubbles 19 to expand rapidly and with great energy. The energetic CO₂ gas bubbles 19 impart kinetic energy to the additive alloy particles 13 and the molten steel 10 which, in turn, drives the alloy particles 13 further from their release point in the bath 10. By driving the additive alloy particles 13 further from their release point, dispersion of the additive alloy particles 13 occurs. Thus, more of the bath volume becomes enriched in the additive alloy 13 than would normally become enriched. Because more of the bath volume becomes enriched, the recovery of the additive alloy 13 is increased.

The present invention may be embodied as an alloy delivery device. The delivery device may include a blended substance having at least one additive alloy, for example FeNb, FeV, or FeTi, and at least one dispersing agent, which may be limestone. The blended substance may be encapsulated in a steel jacket, which is a metal shell in which the blended substance resides, and which is sometimes referred to herein as a cored wire.

The above embodiment of the present invention is depicted in FIG. 3. Additive alloy 13 is blended with dispersant 16 to provide a blended substance 22. The blended substance 22 is encapsulated in a steel jacket 25. The encapsulated blended substance 22 and steel jacket 25 are injected into the molten steel bath 10.

The above embodiment of the present invention is further depicted in FIG. 4. This figure depicts housing 28 for molten steel 10. In this embodiment, a blended substance 22 contains additive alloy 13 and dispersant 16. The blended substance 22 is encapsulated in a steel jacket 25. The encapsulated blended substance 22 and steel jacket 25 are injected into the molten steel bath 10.

In a preferred embodiment, the dispersing agent may be a powder with particles that have a diameter of less than one millimeter, while the additive alloy is a ground powder particle that has a diameter of less than 1 mm. In another preferred embodiment, the dispersing agent may be present in an amount of 5 to 50% of the mixture by weight or volume.

In one embodiment of the present invention, the melting temperature of the additive alloy is higher than the temperature of the molten steel bath. In another embodiment of the present invention, the melting temperature is lower than the temperature of the molten steel bath, but the jacket is sized and/or the dispersant is selected so that the additive alloy is insulated by the jacket and thus, the additive alloy remains as a solid inside the jacket prior to the jacket melting through.

Further, it is preferable that the additive alloy is dissolvable in the molten steel. By “dissolvable,” it is meant that the additive alloy “dissolves” into the molten steel. By “dissolve” it is meant that the particles that form the solid are released and mixed into the solution. The additive alloy remains inside the jacket as a solid and then when the jacket melts, the additive alloy dissolves and disperses in the molten steel. Because the additive alloy remains a solid prior to the melting of the jacket, it is not necessary for the kinetic energy provided by CO₂ to break apart liquid additive alloy and instead the energy that otherwise would be used to break apart liquid droplets of an alloy is instead used to disperse the alloy particles. Thus, more of the kinetic energy created by the CO₂ can be directed to dispersion and distribution of the additive alloy.

Although the present invention has been described with respect to one or more particular embodiments, it will be understood that other embodiments of the present invention may be made without departing from the spirit and scope of the present invention. Hence, the present invention is deemed limited only by the appended claims and the reasonable interpretation thereof.

Claims

1. An alloy delivery device, comprising:

at least one solid additive dissolvable alloy; and

at least one dispersing agent, the dispersing agent being blended with the alloy to provide a blended substance; and

a metal jacket encapsulating the blended substance;

wherein the dissolvable alloy or the metal jacket, or both are selected so that the alloy remains solid prior to melting of the jacket when the delivery device is added to molten steel.

2. The alloy delivery device of claim 1, wherein the metal jacket is steel.

3. The alloy delivery device of claim 1, wherein the at least one additive alloy is selected from the group consisting of: FeNb, FeV, and FeTi.

4. The alloy delivery device of claim 1, wherein the dispersing agent is limestone.

5. The alloy delivery device of claim 1, wherein the at least one dispersing agent is a powder comprised of particles having a diameter of less than one millimeter.

6. The alloy delivery device of claim 1, wherein the at least one additive alloy is comprised of ground powder particles having a diameter of less than 1 mm.

7. The alloy delivery device of claim 1, wherein the at least one dispersing agent is present in an amount of 5 to 50% of the mixture by weight or volume.

8. A method of providing an additive alloy to molten steel comprising:

blending at least one dispersing agent with at least one solid additive dissolvable alloy, to provide a blended substance;

encapsulating the dispersing agent and additive alloy blend in a metal jacket to provide an alloy delivery device;

producing molten steel;

injecting the alloy delivery device into the molten steel;

allowing the jacket to melt in the molten steel;

releasing the dissolvable alloy in solid form from the melted metal jacket.

9. The method of claim 8, wherein the metal jacket is steel.

10. The method of claim 8, wherein a wire injector and guide tube arrangement is used to inject the alloy delivery device into the molten steel.

11. The method of claim 8, wherein the at least one dispersing agent is limestone powder.

12. The method of claim 8, wherein the at least one additive alloy is selected from the group consisting of: FeNb, FeV, and FeTi.

13. The method of claim 8, wherein the method further comprises the step of allowing the metal jacket to melt.

14. The method of claim 8, wherein the method further comprises the step of dispersing the blended substance.