Patent Application
20080314201
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.
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.
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.
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:
The present invention may be used to provide increased recovery in additive-enhanced or alloy-enhanced molten steel.
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
The above embodiment of the present invention is further depicted in
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| 60938670 | May 2007 | US |
