STEEL DECARBURIZATION USING CARBON DIOXIDE

Abstract

Process to decarburize steel are described. A process can include contacting carbon dioxide with molten steel in an electric arc furnace, a ladle furnace, or a vacuum degassing unit, or a combination thereof.

Claims

1. A process to decarburize steel, the process comprising contacting molten iron-containing material with a sufficient amount of carbon dioxide (CO.sub.2) containing gas to decarburize at least a portion of the molten iron containing material.

2. The process of claim 1, wherein the contacting comprises a temperature of temperature of 500 to 1000° C.

3. The process of claim 1, wherein the CO.sub.2 containing gas is provided during a primary steel processing step of melting direct reduced iron, pig iron, iron ore, scrap iron, or any combination thereof.

4. The process of claim 2, further comprising providing the CO.sub.2 containing gas at a rate sufficient to agitate the iron-containing material.

5. The process of claim 2, further comprising contacting the iron-containing material with an oxygen (O.sub.2) containing gas.

6. The process of claim 5, further comprising providing the CO.sub.2 containing gas in a direction opposite of the flow the oxygen (O.sub.2) containing gas.

7. The process of claim 1, wherein the contact of the iron-containing material and CO.sub.2 containing gas is a secondary steel processing step.

8. The process of claim 7, wherein the iron-containing material comprises molten slag on a top portion of a molten iron oxide material and the method further comprises providing the CO.sub.2 containing gas to a bottom portion of the molten iron oxide material.

9. The process of claim 7, further comprising providing the CO.sub.2 containing gas at a rate of sufficient to agitate the molten iron-containing material.

10. The process of claim 1, wherein the iron-containing material is molten iron oxide and the process further comprises contacting the molten iron oxide material and CO.sub.2 containing gas under a reduced pressure.

11. The process of claim 10, wherein the reduced pressure is a third steel processing step.

12. The process of claim 10, further comprising providing the CO.sub.2 containing gas at a rate of sufficient to agitate the molten iron oxide material.

13. The process of claim 1, wherein the CO.sub.2 containing gas comprises nitrogen (N.sub.2), argon (Ar), or both.

14. The process of claim 1, further comprising producing a steel material from the decarburized iron-containing material, wherein the steel material has a carbon content of less than 0.5 wt. based on the total weight of the steel.

15. A process to decarbonize iron-containing material, the process comprising: (a) contacting an iron-containing material with a sufficient amount of carbon dioxide (CO.sub.2) containing gas to at least partially decarbonize the iron-containing material; (b) providing the at least partially decarbonized iron-containing material to a secondary steel process and contacting the iron-containing material with a sufficient amount of CO.sub.2 containing gas to produce a decarbonized iron containing material having a carbon content lower than the decarbonized iron-containing material of step (a); and (c) contacting the decarbonized iron containing material of step (b) with a CO.sub.2 containing gas under a reduced pressure to produce a decarbonized steel material having a carbon content lower than the decarbonized iron containing material of step (b).

16. The process of claim 15, wherein step (a) is performed in an arc furnace, step (b) is performed in a ladle furnace, and step (c) is performed in a ladle vacuum degassing unit.

17. The process of claim 15, wherein the decarbonized iron-containing material of step (b) and/or step (c) is a steel material having a carbon content of less than 0.5 wt.

18. The process of claim 15, further comprising contacting the iron-containing material of step (a) with an oxygen containing gas.

19. The process of claim 18, further comprising simultaneous or substantially simultaneous contacting the iron-containing material with the CO.sub.2 containing gas and the O.sub.2 containing gas.

20. The process of claim 16, further comprising providing the CO.sub.2 containing gas to a bottom portion of the EAF, a bottom portion of the ladle furnace, a bottom portion of the ladle vacuum degassing unit, or any combination thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings.

[0030] FIG. 1 shows an illustration of a process of the present invention for addition of CO.sub.2 to an EAF.

[0031] FIG. 2 shows an illustration of a process of the present invention for addition of CO.sub.2 to a ladle furnace.

[0032] FIG. 3 shows an illustration of a process of the present invention for addition of CO.sub.2 to vacuum degassing unit.

[0033] FIG. 4 shows an illustration of a process of the present invention for addition of CO.sub.2 to an EAF, a ladle furnace, and a degassing unit.

[0034] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. The drawings may not be to scale.

DETAILED DESCRIPTION OF THE INVENTION

[0035] A discovery has been made that provides a solution to at least some of the problems associated with the reduction of the carbon content in steel (i.e., decarburization of the steel). The addition of CO.sub.2 can provide a more energy efficient process as it reduces the need for oxygen in one or more processing steps to produce steel.

[0036] These and other non-limiting aspects of the present invention are discussed in further detail in the following sections with reference to FIGS. 1-4.

[0037] FIG. 1 depicts a schematic for a system to produce molten steel in an electric arc furnace (EAF). System 100 can include EAF 102, Iron-containing material inlet 104, electrodes 106, oxygen containing gas inlet 108, CO.sub.2 containing gas inlet 110, and molten steel outlet 112.

[0038] Iron-containing material 114 can enter EAF 102 through inlet 104. Iron-containing material can be any type of iron-based material (e.g., direct reduced iron (DRI, 80% Fe.sub.2O.sub.3), scrap metal, pig iron, etc.). In a preferred embodiment, the iron-based material is DRI. In EAF 102, iron-containing material 114 is heated to a temperature sufficient to melt the steel precursor material using electrodes 106 to form a molten steel. By way of example, electrodes 106 can be lowered onto the steel precursor material, an arc is struck and the electrodes are then set to bore into the layer of shred at the top of the furnace. Lower voltages can be selected for this first part of the operation to protect the roof and walls from excessive heat and damage from the arcs. Once electrodes 106 have reached the heavy melt at the base of the furnace and the arcs are shielded by the steel precursor material, the voltage can be increased and the electrodes raised slightly, lengthening the arcs and increasing power to the melt. This enables a molten pool to form more rapidly, reducing tap-to-tap times. During the melting process oxygen can enter EAF 102 through oxygen inlet 108 and be blown into the iron-containing material 116, combusting or cutting the material. Oxygen inlet 108 can include supersonic nozzles to enable oxygen jets to penetrate foaming slag and reach the molten iron-containing material. Carbon particles can be introduced to the molten iron-containing material via carbon inlet 118. Addition of carbon to the iron-containing material can provide additional source of carbon and produce an iron-carbon material that can be further processed to produce steel. The addition of carbon to the iron oxide can increase the amount of carbon in the molten iron-oxide/carbon mixture. Increased carbon content in a final steel product can result in the steel being brittle and/or have other undesirable properties. Thus, after the addition of carbon, a portion of the carbon in the iron-carbon alloy is removed.

[0039] During the addition of O.sub.2, and optionally after the addition of carbon, CO.sub.2 containing gas can enter EAF 102 through CO.sub.2 inlet 110 (e.g., a porous plug in the bottom of the EAF). The CO.sub.2 containing gas can include argon and/or nitrogen gases. During the initial addition of O.sub.2 and the melting process, a stream of inert gas absent CO.sub.2 can be enter EAF 102 through inlet 110. CO.sub.2 can then be introduced over time. The CO.sub.2 containing gas can be provided to EAF 102 at a rate sufficient to agitate the iron-containing material. Since the CO.sub.2 is a source of oxygen, the amount of oxygen provided to EAF 102 can be lowered or be used to overcome difficulties in providing an effective amount of oxygen from the top. This provides the advantages of reduced oxygen consumption rate and can enhance the alloys addition yield due to the reduced oxygen opening ppm level in further processing steps (e.g., the ladle furnace). A further advantage to the addition of CO.sub.2 is that it can lead in overall energy consumption optimization due to the potential reduction in Tap-To-Tap time as a result of early refining, bath robust stirring, and optimized foamy slag. Furthermore, addition of CO.sub.2 can initiate decarburization of the molten steel. After heating for a desired period of time, partially decarburized iron containing material can exit EAF 102 through outlet 112 to be further processed through one or more additional steel processing steps or provided to a forming unit.

[0040] FIG. 2 depicts a schematic for a system for refinement of steel from an EAF. System 200 can include a ladle furnace 202. Ladle furnace 202 can include heating source 204 (e.g., electrodes), molten steel inlet 206 (e.g., a hopper), additive inlet 208, treated iron-containing material outlet 210, and CO.sub.2 containing gas inlet 212. Ladle furnace 202 can receive molten iron-containing material via inlet 206. In some embodiments, partially decarburized molten iron-containing material 116 from EAF 102 enters ladle furnace 202. In ladle furnace 202, molten iron-containing material 214 can be further refined (e.g., treated and/or additized) to produce desired grades of steel. Molten iron-containing material 214 can be heated using heat source 204 and additives (e.g., sources of nickel, chromium, manganese, vanadium, silicon, boron, aluminum, cobalt, copper, cerium, niobium, titanium, tungsten, tin, zinc, lead, zirconium or any combination thereof) can be added into the molten iron-containing material through additive inlet 208. Additives can include other metal sources to produce steel alloys. During treatment, CO.sub.2 containing gas can enter ladle furnace 202 via CO.sub.2 inlet 212. In some embodiments, CO.sub.2 inlet 212 is a porous plug. CO.sub.2 containing gas can include CO.sub.2 and argon. Addition of CO.sub.2 can decarburize iron-containing material 216. In some embodiments, the decarburized iron-containing material has a carbon content less than the partially decarburized iron-containing material 112 from EAF 202. Addition of the CO.sub.2 containing gas can also provide agitation of iron-containing material 216. In some embodiments, decarburization of the iron-containing material using CO.sub.2 can lower the carbon level to an extent that vacuum gassing treatment is not necessary. Treated molten iron-containing material can exit ladle furnace 202 via treated iron-containing material outlet 210. In some embodiments treated molten iron-containing material is fully decarburized.

[0041] FIG. 3 is a schematic of a system for vacuum degassing of molten iron-containing material. Vacuum degassing can remove unwanted materials (e.g., H.sub.2 and N.sub.2) from the iron-containing material and/or add metals or alloys to the iron-containing material to produce steel or steel alloys having desired compositions and physical properties. H.sub.2 and N.sub.2 gases can both harm the properties of steel so removal of these gases is desirable. By way of example, solubility of H.sub.2 in steel is low at ambient temperature so excess H.sub.2 can be rejected during solidification; resulting in pinhole formation, which increases the porosity in solidified steel. Few ppm (parts per million) of H.sub.2 gas can cause blistering and loss of tensile ductility. In case of N.sub.2 gas, maximum solubility of N.sub.2 in liquid iron is 450 ppm and less than 10 ppm at room temperature. During solidification excess N.sub.2 can be rejected, which can cause formation of either blow holes or nitrides. Excess N.sub.2 can also causes embrittlement of heat affected zone during welding of steels and also impairs cold formability of steel.

[0042] Vacuum degassing system 300 can include vacuum chamber 302, ladle 304, additive inlet 306, and CO.sub.2 containing gas inlet 308. In system 300, ladle 304 can be filled with iron-containing material 310 and placed in vacuum chamber 302. In some embodiments, ladle 304 is in vacuum chamber 302 and molten iron-containing material 310 is added to the ladle. Molten iron-containing material 310 can be decarburized or partially decarburized iron-containing material 212 from ladle furnace 202. In some embodiments, molten iron-containing material 310 has not been treated with CO.sub.2. Vacuum can be applied to vacuum chamber using vacuum source 312, and H.sub.2 and N.sub.2 can be removed from molten steel 310. During the degassing process, a CO.sub.2 containing gas can be provided to molten iron-containing material 310 via CO.sub.2 containing gas inlet 308 (e.g., a porous plug). Sparging of the molten iron-containing material can assist in removing of harmful gases while decarburizing the iron-containing material. In addition to decarburizing iron-containing material, additives (e.g., sources of nickel, chromium, manganese, vanadium, silicon, boron, aluminum, cobalt, copper, cerium, niobium, titanium, tungsten, tin, zinc, lead, zirconium or any combination thereof) can be added under vacuum via additive inlet 306 to the molten iron-containing material. After the iron-containing material has been treated to produce steel or steel alloys of the desired amount of carbon and other additives, the vacuum can be released and the molten steel can be poured from the ladle into molds or other processing equipment to form steel-based products.

[0043] FIG. 4 shows a schematic of system 400 which includes EAF system 200, ladle furnace system 200, and vacuum degassing system 300. System 400, provides a process to applying CO.sub.2 to all three stages of the steel making process to produce decarburized steel. As shown in system 400, molten iron-containing material 116 is treated with CO.sub.2 in EAR 102 to at least partially decarburize the iron-containing material, transferred to ladle furnace 202 where it is further treated with CO.sub.2 to produce decarburized or substantially decarburized iron-containing material 214, which is then transferred to vacuum degassing system 300 and degassed and fully decarburized with CO.sub.2 to produce steel having desired carbon levels and other properties. In system 400, a portion of treated steel 214 can be used as is and not further treated with CO.sub.2 in vacuum degassing chamber 302.

[0044] The steel produced from the process of the present invention contains 0.0 wt. % to 0.5 wt. % of carbon, or less than any one of, equal to any one of, or between any two of 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, 0.01, 0.009, 0.008, 0.007, 0.006, 0.005, 0.004, 0.003, 0.002, 0.001 and 0 wt. % based on the total weight of the steel material.

[0045] Systems 100-400 can include one or more heating and/or cooling devices (e.g., insulation) or controllers (e.g., computers, flow valves, automated values, etc.) that can be used to control the temperature and pressure of the molten iron-containing material. While only one unit (e.g., furnace or ladle) is shown, it should be understood that multiple units can be housed in one unit or a plurality of units housed in one facility or system. In systems 100 to 400, the iron-containing material in the EAF, ladle furnace, ladle in vacuum degassing unit can be heated to a temperature of 500 to 1000° C., or at least any one of, equal to any one of, or between any two of 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 and 1000° C. Gases provided to the EAF, ladle furnace, and vacuum degassing unit can be at rates suitable to the size of the equipment. Persons knowledgeable in the area of steel making can adjust the gas flow rates for optimal agitation and/or delivery of the desired gas.

[0046] Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein can be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.