WO2022270226A1 - 溶鋼の精錬方法 - Google Patents
溶鋼の精錬方法 Download PDFInfo
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- WO2022270226A1 WO2022270226A1 PCT/JP2022/021634 JP2022021634W WO2022270226A1 WO 2022270226 A1 WO2022270226 A1 WO 2022270226A1 JP 2022021634 W JP2022021634 W JP 2022021634W WO 2022270226 A1 WO2022270226 A1 WO 2022270226A1
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- Prior art keywords
- molten steel
- gas
- ladle
- plasma
- stirring
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 246
- 239000010959 steel Substances 0.000 title claims abstract description 246
- 238000007670 refining Methods 0.000 title claims abstract description 54
- 238000000034 method Methods 0.000 title claims abstract description 44
- 239000007789 gas Substances 0.000 claims abstract description 119
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 86
- 238000003756 stirring Methods 0.000 claims abstract description 65
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 57
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 39
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 38
- 239000001301 oxygen Substances 0.000 claims abstract description 38
- 238000007664 blowing Methods 0.000 claims abstract description 30
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims abstract description 29
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 29
- 239000011593 sulfur Substances 0.000 claims abstract description 29
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 27
- 239000011261 inert gas Substances 0.000 claims abstract description 14
- 230000008569 process Effects 0.000 claims abstract description 12
- 238000009832 plasma treatment Methods 0.000 claims description 43
- 239000002893 slag Substances 0.000 claims description 26
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N iron oxide Inorganic materials [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 12
- AMWRITDGCCNYAT-UHFFFAOYSA-L manganese oxide Inorganic materials [Mn].O[Mn]=O.O[Mn]=O AMWRITDGCCNYAT-UHFFFAOYSA-L 0.000 claims description 12
- 238000011282 treatment Methods 0.000 claims description 11
- 235000013980 iron oxide Nutrition 0.000 claims description 10
- 238000002347 injection Methods 0.000 claims description 9
- 239000007924 injection Substances 0.000 claims description 9
- VBMVTYDPPZVILR-UHFFFAOYSA-N iron(2+);oxygen(2-) Chemical class [O-2].[Fe+2] VBMVTYDPPZVILR-UHFFFAOYSA-N 0.000 claims description 8
- PPNAOCWZXJOHFK-UHFFFAOYSA-N manganese(2+);oxygen(2-) Chemical class [O-2].[Mn+2] PPNAOCWZXJOHFK-UHFFFAOYSA-N 0.000 claims description 8
- 238000003723 Smelting Methods 0.000 claims description 6
- 238000007667 floating Methods 0.000 claims description 4
- 239000012530 fluid Substances 0.000 claims description 3
- 239000001257 hydrogen Substances 0.000 abstract description 49
- 229910052739 hydrogen Inorganic materials 0.000 abstract description 49
- 239000012535 impurity Substances 0.000 abstract description 20
- 238000006243 chemical reaction Methods 0.000 abstract description 10
- 238000012545 processing Methods 0.000 abstract description 6
- 238000006477 desulfuration reaction Methods 0.000 abstract description 4
- 230000023556 desulfurization Effects 0.000 abstract description 4
- 238000004519 manufacturing process Methods 0.000 abstract description 2
- 238000006392 deoxygenation reaction Methods 0.000 abstract 1
- 230000000694 effects Effects 0.000 description 19
- 238000009849 vacuum degassing Methods 0.000 description 14
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 12
- 230000004907 flux Effects 0.000 description 11
- 229910052751 metal Inorganic materials 0.000 description 11
- 239000002184 metal Substances 0.000 description 11
- 229910052782 aluminium Inorganic materials 0.000 description 10
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 10
- 238000007654 immersion Methods 0.000 description 8
- 230000001678 irradiating effect Effects 0.000 description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 6
- 229910052786 argon Inorganic materials 0.000 description 6
- 239000003795 chemical substances by application Substances 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 6
- 238000012546 transfer Methods 0.000 description 6
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 5
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 5
- 229910002804 graphite Inorganic materials 0.000 description 5
- 239000010439 graphite Substances 0.000 description 5
- 150000002739 metals Chemical class 0.000 description 5
- 229910052710 silicon Inorganic materials 0.000 description 5
- 239000010703 silicon Substances 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 4
- 238000002844 melting Methods 0.000 description 4
- 230000008018 melting Effects 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- 239000000779 smoke Substances 0.000 description 4
- 238000009628 steelmaking Methods 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 125000004429 atom Chemical group 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 238000007872 degassing Methods 0.000 description 3
- 238000006356 dehydrogenation reaction Methods 0.000 description 3
- 230000003009 desulfurizing effect Effects 0.000 description 3
- 229910001873 dinitrogen Inorganic materials 0.000 description 3
- 238000010891 electric arc Methods 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 239000012159 carrier gas Substances 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 238000010494 dissociation reaction Methods 0.000 description 2
- 230000005593 dissociations Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000000700 radioactive tracer Substances 0.000 description 2
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- 229910001021 Ferroalloy Inorganic materials 0.000 description 1
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000012190 activator Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000013019 agitation Methods 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 230000002596 correlated effect Effects 0.000 description 1
- 230000000875 corresponding effect Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005261 decarburization Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 229910001882 dioxygen Inorganic materials 0.000 description 1
- 238000005485 electric heating Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000003631 expected effect Effects 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000001307 helium Substances 0.000 description 1
- 229910052734 helium Inorganic materials 0.000 description 1
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
- 125000004435 hydrogen atom Chemical group [H]* 0.000 description 1
- -1 hydrogen ions Chemical class 0.000 description 1
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 239000001294 propane Substances 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 239000011819 refractory material Substances 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/072—Treatment with gases
Definitions
- the present invention relates to a refining method for producing molten steel with a low content of impurity elements oxygen, nitrogen, and sulfur.
- the present invention relates to a method of refining molten steel by irradiation and removal of impurities by plasma gas.
- Non-metallic inclusions in steel materials are generally known to adversely affect material properties and quality.
- oxide-based non-metallic inclusions clog submerged nozzles in continuous casting, reducing productivity due to a decrease in casting speed and, in the worst case, interrupting casting.
- Examples of non-metallic inclusions include oxide-based deoxidation products generated during deoxidation of molten steel, sulfides and nitrides of alloying elements in steel, and the like.
- inclusions In order to reduce the amount of these non-metallic inclusions (hereinafter also simply referred to as "inclusions"), it is important to reduce oxygen, nitrogen and sulfur in molten steel as much as possible, and various efforts have been made in the past. It's here.
- oxygen in the molten steel by adding a deoxidizer such as aluminum (Al) or silicon (Si), dissolved oxygen in the molten steel is fixed as Al 2 O 3 or SiO 2 .
- the generated oxide-based inclusions are floated and removed by gas stirring treatment of molten steel, circulation treatment in an RH vacuum degassing device, etc., utilizing the difference in specific gravity from molten steel.
- Nitrogen in molten steel is reduced by vacuum processing in vacuum degassing equipment.
- nitrogen in molten steel is affected by surface-active elements such as oxygen and sulfur, and it is difficult to avoid absorption of nitrogen by atmospheric entrainment from outside the vacuum system. The current situation is that there is none.
- Sulfur in molten steel is reduced by adding CaO-based flux or CaO—Al 2 O 3 -based flux (addition of desulfurizing agent).
- CaO-based flux or CaO—Al 2 O 3 -based flux addition of desulfurizing agent.
- argon gas is blown into the molten steel from the bottom of the ladle and stirred to promote the reaction between the molten steel in the ladle and the CaO—Al 2 O 3 system flux, and the flux Sulfur is moved to the side (slag side) to reduce sulfur in the molten steel.
- arc heating is performed by graphite electrodes, carbon is dissolved in the molten steel, and it is difficult to apply the treatment to steel grades such as ultra-low carbon steel.
- the RH vacuum degassing apparatus there is a method of desulfurizing by adding a CaO-based flux or a CaO--Al 2 O 3 -based flux to the molten steel circulating in the vacuum chamber. Furthermore, desulfurization is performed by projecting (spraying) CaO-based flux or CaO-Al 2 O 3 -based flux from a top-blowing lance onto the molten steel circulating in the vacuum chamber using an inert gas such as argon gas as a carrier gas. There is a way. However, with these methods, the reaction time between molten steel and flux is not sufficient, and it is difficult to efficiently obtain molten steel with a low sulfur concentration.
- the use of hydrogen plasma is known as a refining technology that reduces impurities in metals. Since the temperature in the plasma reaches several thousand degrees or more, the hydrogen gas in the plasma gas becomes atoms or ions and becomes very active. By irradiating the surface of molten steel with this, an excellent refining effect that cannot be achieved by normal hydrogen gas irradiation alone can be expected. That is, oxygen, nitrogen, and sulfur in molten steel can be rapidly removed by the reactions of formulas (6) to (8) shown below.
- Patent Document 1 discloses a plasma gas for reducing oxygen, nitrogen, or carbon in metals when melting metals using hydrogen plasma.
- the preferred ranges of the hydrogen concentration and the pressure inside the furnace are disclosed.
- Patent Document 1 there are the following problems in applying the technology of Patent Document 1 to an industrial-scale steelmaking process.
- Patent Document 1 the refining effect is described when several tens of grams to several tens of kilograms of metal is treated in a plasma melting furnace.
- it is necessary to process molten steel exceeding 100 tons, and it is difficult to irradiate the entire molten steel with plasma gas. Therefore, there is a concern that the technology disclosed in Patent Document 1 cannot obtain a rapid impurity removal effect.
- it is important to optimize not only the plasma conditions but also the flow conditions on the molten steel side and perform the hydrogen plasma treatment efficiently.
- Patent Document 1 does not specify the amount of metal to be applied with hydrogen plasma or the relationship between the amount of metal and the plasma gas flow rate. Therefore, even if the plasma gas composition and atmospheric pressure are appropriately controlled, there may be cases where the plasma gas flow rate and the amount of hydrogen are insufficient with respect to the amount of metal, and a sufficient effect of reducing impurities cannot be obtained. Furthermore, Patent Document 1 is not a technique of applying hydrogen plasma to already molten iron, but also has a role of heating and melting a target metal by plasma. Therefore, even if the disclosed plasma gas conditions are applied to steel that has already been melted, as in the steelmaking process, there is concern that the same expected effects may not be obtained.
- the present invention has been made in view of the above circumstances, and the object thereof is to speed up the refining reactions of deoxidation, denitrification, and desulfurization when hydrogen plasma is applied to molten steel in a ladle in the steelmaking process.
- the gist of the present invention for solving the above problems is as follows.
- GP is the plasma gas flow rate (Nm 3 /min)
- H 2 is the hydrogen gas concentration (vol%) in the plasma gas
- Q is the molten steel circulation flow rate (ton/min) of the molten steel in the ladle.
- the gas stirring process is performed by installing one or more gas blowing parts at the bottom of the ladle and blowing gas for stirring into the molten steel in the ladle from the gas blowing part. , and the stirring power ( ⁇ ) calculated by the formula (4) at that time is 25 W/ton or more.
- r is the plasma irradiation range radius (m)
- gB is the injection flow rate of the stirring gas (Nm 3 /min/one gas injection portion).
- the slag floating on the surface of the molten steel contained in the ladle has a total concentration of iron oxides and manganese oxides of 5% by mass or less.
- molten steel contained in a ladle can be appropriately subjected to hydrogen plasma treatment, and as a result, high-purity steel with few impurities can be quickly melted, which is industrially beneficial. effect is brought about.
- the method for refining molten steel according to the present invention is a process in which a stirring gas is blown into the molten steel contained in the ladle to stir the molten steel in the ladle, and the molten steel is in a fluid state due to the gas stirring process.
- the surface of the molten steel in the ladle is irradiated with plasma hydrogen gas or a mixed gas of plasma hydrogen gas and inert gas as plasma gas from a plasma generator installed above the molten steel in the ladle,
- This melting method removes one or more elements selected from among oxygen, nitrogen, and sulfur in molten steel by irradiating the plasma gas to reduce the content thereof.
- irradiating the molten steel surface with hydrogen gas or an inert gas containing hydrogen gas as plasma gas is referred to as "plasma treatment” or "hydrogen plasma treatment”.
- Refining equipment that can implement the present invention is a secondary refining furnace that can stir the molten steel by blowing a stirring gas into the molten steel in the ladle.
- Furnace (Vacuum OxygenDecarburization Furnace), VAD Furnace (Vacuum Arc Decarburization Furnace), REDA (Revolutionary Degassing Activator) vacuum degassing equipment, etc.
- Fig. 1 shows an example of a general ladle smelting furnace in a schematic vertical cross-sectional view.
- reference numeral 1 is a ladle smelting furnace
- 2 is a ladle
- 3 is an upper lid
- 4 is a black smoke electrode
- 5 is a steel shell
- 6 is a lining refractory
- 7 is a permanent refractory
- 8 and 8a are bottom blowing
- a plug 9 is molten steel
- 10 is slag
- 11 and 12 are plasma torches
- 13 is gas bubbles for stirring.
- a ladle 2 for containing molten steel 9 has an outer shell of iron shell 5, and inside the iron shell 5, permanent refractory 7 and lining refractory 6 are applied in this order.
- At least a portion (mainly the slag line) is constructed with MgO-based refractories.
- bottom blowing plugs 8, 8a for blowing in a stirring gas such as a rare gas are installed as gas blowing portions.
- the plasma torches 11 and 12 are devices that constitute a part of the plasma generator, and are devices that perform hydrogen plasma treatment by irradiating the surface of the molten steel 9 in the ladle with plasma gas from the tip thereof. 3, and can move up and down in the space surrounded by the ladle 2 and the upper lid 3.
- the number of plasma torches may be one or three or more.
- two bottom blowing plugs are installed, but one bottom blowing plug or three or more bottom blowing plugs may be installed.
- the ladle refining furnace 1 blows a stirring gas such as argon gas into the molten steel 9 in the ladle from the bottom blow plugs 8 and 8a, and adds a refining flux and an alloy material while stirring the molten steel 9.
- Equipment the ladle refining furnace 1 is also equipment for applying electric heating by the graphite electrodes 4 and adjusting the composition and temperature of the molten steel 9 to target values.
- three graphite electrodes 4 are often installed in a facility that conducts heating using an AC power supply, two of the three graphite electrodes 4 are omitted in FIG. It is a diagram showing one.
- the added refining flux is melted to form slag 10 having a desired composition.
- a reaction takes place.
- the reason why the refractory lining 6 of the slag line of the ladle 2 is made of MgO-based refractory is that the MgO-based refractory has high corrosion resistance to the slag 10 .
- the pressure of the atmosphere in the space surrounded by the ladle 2 and the upper lid 3 is equivalent to the atmospheric pressure. That is, in the ladle refining furnace 1, refining under reduced pressure cannot be performed.
- a VOD furnace (not shown) and a VAD furnace (not shown) are equipped with a vacuum chamber connected to an exhaust device, and a ladle 2 containing molten steel 9 is placed inside the vacuum chamber.
- the interior of the vacuum chamber is decompressed, and a rare gas or non-oxidizing gas for stirring is blown in from bottom blow plugs 8 and 8a arranged at the bottom of the ladle 2 .
- a refining agent such as a desulfurizing agent is sprayed onto the molten steel 9 in the ladle from a top-blowing lance installed to penetrate the vacuum chamber, together with oxygen gas or a carrier gas. is.
- the VAD furnace like the ladle refining furnace 1, has black smoke electrodes for heating the molten steel 9.
- VOD and VAD furnaces typically perform refining under reduced pressure.
- the present invention can be carried out by installing a plasma torch in the upper part of the vacuum chamber so as to penetrate the vacuum chamber.
- the REDA vacuum degassing device (not shown) combines bottom-blown stirring of the molten steel in the ladle with a stirring gas and a large-diameter immersion tank whose tip is immersed in the molten steel in the ladle and whose interior is decompressed. It is a degassing furnace, and it refines molten steel by raising it into a large-diameter immersion tank while bottom-blowing and stirring it.
- refining is normally carried out under reduced pressure.
- the present invention can be carried out by placing a plasma torch above the large-diameter immersion tank so as to penetrate the large-diameter immersion tank.
- the surface of the molten steel 9 in the secondary refining furnace such as the ladle refining furnace 1 and the VOD furnace
- a stirring gas such as argon gas
- plasma torches 11 and 12 irradiate hydrogen gas or inert gas containing hydrogen gas as plasma gas. Since the temperature in the plasma reaches several thousand degrees or more, the hydrogen gas in the plasma gas becomes atoms or ions and becomes very active.
- the following reactions (6), (7), and (8) are formed, and oxygen, nitrogen, and sulfur in the molten steel are quickly can be removed.
- the stirring gas is blown from the bottom blow plugs 8 and 8a, but an injection lance (not shown) may be immersed in the molten steel 9 and the stirring gas may be blown into the molten steel 9 from the tip of the injection lance.
- Argon which is an inert gas, or hydrogen gas or propane, which is a reducing gas, can be used as the stirring gas.
- nitrogen gas can be used as the stirring gas when the denitrification reaction is not intended.
- an inert gas or nitrogen gas can be mixed and used, or can be used by appropriately switching during the hydrogen plasma treatment.
- the plasma torches 11 and 12 are one of the devices that generate arc plasma in a form suitable for various applications in a stable and well-controlled manner, mainly using a direct current and by the action of an air current, a water-cooled nozzle, or the like.
- the above-mentioned plasma torch using a DC power supply has a non-transfer type and a transfer type. Since the non-transfer type plasma torch does not require an electrode on the molten steel side, there are few facility restrictions and the installation cost is low. From this point of view, a non-transfer type plasma torch using direct current arc discharge is used. is preferred.
- the plasma generator is not particularly limited as long as it can be installed above the molten steel 9 and can stably supply hydrogen plasma to the surface of the molten steel.
- hydrogen plasma treatment is performed in the ladle refining furnace 1, hydrogen gas or an inert gas containing hydrogen is supplied into the arc generated from the graphite electrode 4, and the hydrogen gas or the inert gas containing hydrogen gas is plasmatized. It is also possible to use a method that allows In addition, for a process that does not have a heating electrode such as a VOD furnace, an electrode for generating an AC arc is provided above the molten steel 9, and hydrogen gas or an inert gas containing hydrogen gas is supplied between the electrodes. Thus, hydrogen plasma treatment can be performed.
- hydrogen gas or a mixed gas of hydrogen gas and inert gas is used.
- the reason for using hydrogen gas is that impurities in molten steel can be directly removed by converting hydrogen gas into plasma, as described above. In order to obtain a rapid impurity removal effect, it is preferable to mix 0.5% by volume or more of hydrogen gas in the plasma gas.
- Argon gas or helium gas can be used as the inert gas.
- the three factors of plasma gas flow rate, hydrogen gas concentration in plasma gas, and molten steel circulation flow rate of molten steel in the ladle are appropriately controlled. should be controlled within a reasonable range.
- the plasma gas flow rate ( GP ), the hydrogen concentration in the plasma gas ( H2), and the molten steel circulation flow rate (Q) of the molten steel in the ladle It is necessary that the three elements satisfy the relationship of the following formula (1). Also, the relationship between the three elements ( GP ⁇ (H 2 )/Q) is preferably 0.1 or more, more preferably 0.5 or more.
- GP is the plasma gas flow rate (Nm 3 /min)
- H 2 is the hydrogen gas concentration (% by volume) in the plasma gas
- Q is the molten steel circulation flow rate of the molten steel in the ladle. (ton/min).
- the "Nm 3 /min" of the flow rate of the plasma gas is a unit indicating the volume flow rate of the plasma gas
- “Nm 3 " means the volume of the plasma gas in the standard state.
- the standard state of plasma gas is 0° C. and 1 atm (101325 Pa).
- the molten steel circulation flow rate (Q) of the molten steel in the ladle is affected by the molten steel mass in the ladle and the stirring power of the bottom-blowing gas. Therefore, for each of these conditions, the molten steel circulation time in the ladle is measured in the actual ladle 2, and the molten steel mass in the ladle is divided by the measured molten steel circulation time. The molten steel circulation flow rate (Q) of the molten steel 9 can be obtained.
- a tracer element for example, copper, nickel, etc.
- the fluctuation of the tracer element concentration of the sample for component analysis taken in time series from the ladle is within ⁇ 5%.
- the uniform mixing time is the time required for uniform mixing
- the molten steel circulation time is about 1/3 of the uniform mixing time. can.
- the molten steel circulation time in the molten steel in the ladle can be obtained by an empirical regression equation shown in the following equation (3), and the stirring power ( ⁇ ) in the following equation (3) is It is well known that it can be obtained by an empirical regression formula shown by the following equation (4). Therefore, it is preferable to obtain the molten steel circulation flow rate (Q) of the molten steel in the ladle using the following formulas (2), (3) and (4).
- Q is the molten steel circulation flow rate (ton/min) of molten steel in the ladle
- Wm is the mass of molten steel in the ladle (ton)
- tc is the molten steel circulation of molten steel in the ladle.
- Time (min) D is the average diameter of the molten steel bath in the ladle (m)
- H is the depth of the molten steel bath in the ladle (m)
- ⁇ is the stirring power (W/ton)
- GB is the molten steel in the ladle total stirring gas blowing flow rate (Nm 3 /min)
- TL is the molten steel temperature (K) of the molten steel in the ladle
- P 0 is the atmospheric pressure (torr) of the plasma irradiation area.
- Nm 3 means the total volume of gas for stirring under standard conditions, and 0° C.
- the side wall of the ladle 2 may have an upwardly sloping shape. It is the average value with the diameter.
- Molten steel 9 stored in a ladle and before being subjected to hydrogen plasma treatment is tapped from a converter or an electric furnace into a ladle 2, for example, vacuum degassing in a vacuum degassing equipment such as an RH vacuum degassing device. After passing through the gas refining process, it may be transported to a gas stirring process in which a stirring gas is blown to stir the molten steel in the ladle.
- the molten steel 9 before the hydrogen plasma treatment may be in a non-deoxidized state. It may be deoxidized. Preliminary deoxidation with a reducing gas prior to plasma treatment makes it possible to start plasma treatment in a state where the oxygen concentration in the molten steel has decreased to some extent. can be timed.
- the molten steel 9 is deoxidized by adding a deoxidizing agent such as aluminum or silicon before the plasma treatment to reduce the oxygen concentration in the molten steel in advance.
- a deoxidizing agent such as aluminum or silicon
- the deoxidizing effect of plasma treatment is limited.
- Oxygen in molten steel functions as a surface-active element, and by reducing the oxygen concentration in molten steel through deoxidation, nitrogen gas, hydrogen nitride, and hydrogen sulfide are released from the molten steel surface into the gas phase (atmosphere in the ladle).
- the plasma output (E) more preferably satisfies the following formula (9).
- the plasma output should satisfy the relationship of the expression (9).
- the plasma output should be selected according to the desired balance between quality and cost.
- E is the plasma power (kW).
- Impurities can be reduced more efficiently by giving the molten steel 9 in the ladle more than a certain level of flow during plasma treatment. That is, since the plasma irradiation is a relatively localized area of the surface of the molten steel, the concentration of impurities in the entire molten steel in the ladle can be quickly reduced by continuing to send new molten steel 9 to the plasma irradiation part by stirring the molten steel.
- the stirring power ( ⁇ ) is preferably 25 W/ton or more. If the stirring power ( ⁇ ) is less than 25 W/ton, the circulation and mixing between the surface of the molten steel, which is the plasma-irradiated portion, and the bulk molten steel are stagnant, and a rapid impurity reduction effect cannot be obtained. There is no particular upper limit for the stirring power ( ⁇ ), but if the stirring power ( ⁇ ) is too large, the blow-through of gas and the scattering of molten steel increase, so it is desirable to set it to 150 W/ton or less.
- a suitable range for the position to be irradiated with plasma there is a suitable range for the position to be irradiated with plasma. That is, it is preferable to irradiate the hydrogen plasma at or near the position where the stirring gas blown from the bottom blowing plugs 8, 8a forms the stirring gas bubbles 13 and floats on the surface of the molten steel.
- a plasma torch 11 is installed vertically above the bottom blowing plug 8
- a plasma torch 12 is installed vertically above the bottom blowing plug 8a. That is, in the present invention, within the plasma irradiation range radius (r) calculated by the following formula (5), centered on the surface of the molten steel vertically above at least one of the gas injection parts (bottom blow plug) is preferably irradiated with the plasma gas.
- r is the radius of the plasma irradiation range (m)
- gB is the blowing flow rate of the stirring gas (Nm 3 /min/one gas blowing portion).
- Nm 3 means the volume of the stirring gas in the standard state, and the standard state is 0° C. and 1 atm (101325 Pa).
- the area within the plasma irradiation range radius (r) is the area where the flow is the fastest (intense) on the surface of the molten steel in the ladle, and by irradiating the plasma there, the reaction between the hydrogen plasma and the molten steel in the ladle progresses rapidly.
- the region corresponding to the radius (r) of the plasma irradiation range is a region where the molten steel 9 rising together with the stirring gas bubbles 13 pushes the slag 10 away and the surface of the molten steel is exposed, or where the slag thickness is relatively thin. Therefore, plasma treatment can be performed on the molten steel surface without being hindered by the slag 10 .
- the atmosphere is preferably under reduced pressure, specifically at 150 torr or less.
- the plasma gas By irradiating the plasma gas under a reduced pressure of 150 torr or less, it is expected to increase the flow velocity of the plasma jet and further promote the dissociation of hydrogen gas molecules into atoms and ions.
- the effect of reducing impurities is increased. If the atmospheric pressure is higher than 150 torr, the effect of reducing the pressure is not obtained because the above effect is small.
- a specific example for performing hydrogen plasma treatment under reduced pressure is shown below.
- a ladle 2 containing molten steel 9 is placed in a vacuum chamber, and the surface of the molten steel in the ladle is irradiated with hydrogen plasma from a plasma generator installed above the vacuum chamber.
- the large-diameter immersion tank is immersed in the molten steel in the ladle, the inside of the large-diameter immersion tank is evacuated to create a reduced pressure atmosphere, and the plasma provided at the top of the large-diameter immersion tank Plasma is applied to the surface of the molten steel sucked into the large-diameter immersion tank from the generator.
- the atmospheric pressure during plasma irradiation is more preferably 100 torr or less, and still more preferably 50 torr or less.
- the total concentration of iron oxides and manganese oxides in the slag 10 is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.
- the total concentration of iron oxide concentration and manganese oxide concentration is higher than 5% by mass, the supply of oxygen from the slag 10 to the molten steel 9 proceeds simultaneously during the plasma treatment, and the impurity reduction effect is sufficiently obtained.
- metal aluminum or aluminum dross is added to the slag 10 floating on the molten steel before plasma treatment, and aluminum is added to iron oxides and manganese oxides. It is effective to carry out the reduction of oxides. It is also effective to remove the slag 10 from the ladle 2 and then add a slag-forming agent to the ladle to newly produce slag with less iron oxides and manganese oxides. Further, by irradiating the slag 10 with hydrogen plasma gas, iron oxides and manganese oxides in the slag can be reduced.
- the timing of adding a deoxidizer such as aluminum or silicon is not particularly limited.
- oxygen is supplied to the molten steel 9 from the atmosphere, the slag 10, or the ladle refractory, and the oxygen concentration in the molten steel increases. It is preferable to add a deoxidizer such as , and keep the oxygen concentration in the molten steel, which has been reduced by the hydrogen plasma treatment, at a low level. If it is necessary to adjust the components of the molten steel in addition to deoxidizers such as aluminum and silicon, predetermined ferroalloys and pure metals are added to the molten steel 9 in the ladle after the hydrogen plasma treatment.
- the hydrogen concentration in the molten steel increases to several ppm by mass or more due to the hydrogen plasma treatment, it is preferable to carry out dehydrogenation treatment for 5 minutes or more under a reduced pressure of 10 torr or less after the hydrogen plasma treatment.
- a vacuum degassing equipment such as an RH vacuum degassing equipment is provided as a post-process, and dehydrogenation is performed in the vacuum degassing equipment.
- dehydrogenation processing is continuously performed after plasma processing.
- oxygen, nitrogen and sulfur in molten steel can be rapidly reduced to 30 ppm by mass or less.
- LF ladle refining furnace
- a VOD furnace was used in an actual machine with a molten steel amount of 200 tons or more and 350 tons or less per charge, and the molten steel tapped from the converter was decompressed.
- a non-transfer type plasma torch using direct current arc discharge was installed on the top of the furnace lid.
- a non-transfer type plasma torch by DC arc discharge is installed in the upper part of the vacuum chamber, and from these plasma torches, the plasma gas flow rate and hydrogen gas concentration in the plasma gas are changed, The surface of molten steel was irradiated with hydrogen plasma.
- the operating conditions and molten steel composition (oxygen concentration, nitrogen concentration, sulfur concentration, etc.) in the ladle refining furnace and VOD furnace were changed.
- the hydrogen plasma treatment in the ladle refining furnace was performed while the arc heating by the black smoke electrode was stopped.
- samples for component analysis were taken from the molten steel in the ladle, and the oxygen concentration, nitrogen concentration, and sulfur concentration in the molten steel were analyzed to confirm the effect of the plasma treatment.
- the plasma treatment time was unified to 15 minutes.
- a deoxidizing agent such as aluminum was not added after the steel was discharged from the converter until the plasma treatment.
- the iron oxide concentration and manganese oxide concentration of the slag in the ladle were adjusted by adding aluminum dross to the slag in the ladle before starting treatment in the ladle smelting furnace or VOD furnace.
- Table 1 shows the test conditions for each test, and Table 2 shows the evaluation results.
- the removal rate of each element from before the start of the plasma treatment to after the end was 94% or more for oxygen in the molten steel, 33% or more for nitrogen in the molten steel, and 20% or more for sulfur in the molten steel.
- the reduction of oxygen, nitrogen, and sulfur in the molten steel was insufficient even after the hydrogen plasma treatment.
- the oxygen content in the molten steel was 90% or less
- the nitrogen content in the molten steel was 19% or less
- the sulfur content in the molten steel was 15% or less, all of which were low.
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- Treatment Of Steel In Its Molten State (AREA)
Abstract
Description
xH+[N]=NHx ……(7)
yH+[S]=HyS ……(8)
ここで、[O]は溶鋼中の酸素、[N]は溶鋼中の窒素、[S]は溶鋼中の硫黄を表す。
前記ガス攪拌処理によって流動状態にある取鍋内溶鋼の表面に、当該取鍋内溶鋼の上方に設置されたプラズマ発生装置から、水素ガスまたは水素ガスを含む不活性ガスをプラズマガスとして下記の(1)式を満たす条件で照射するプラズマ処理を行ない、当該プラズマ処理によって溶鋼中に含まれる酸素、窒素、硫黄のうちから選ばれる1種または2種以上の元素の含有量を低減する、溶鋼の精錬方法。
ここで、GPはプラズマガスの流量(Nm3/min)、(H2)はプラズマガス中の水素ガス濃度(体積%)、Qは取鍋内溶鋼の溶鋼循環流量(ton/min)である。
ここで、Qは取鍋内溶鋼の溶鋼循環流量(ton/min)、Wmは取鍋内溶鋼の質量(ton)、tcは取鍋内溶鋼の溶鋼循環時間(min)、Dは取鍋内溶鋼浴の平均直径(m)、Hは取鍋内溶鋼浴の深さ(m)、εは攪拌動力(W/ton)、GBは取鍋内溶鋼への合計攪拌用ガス吹き込み流量(Nm3/min)、TLは取鍋内溶鋼の溶鋼温度(K)、P0はプラズマ照射領域の雰囲気圧力(torr)である。
ここで、rはプラズマ照射範囲半径(m)、gBは攪拌用ガスの吹き込み流量(Nm3/min/ガス吹き込み部1箇所)である。
xH+[N]=NHx ……(7)
yH+[S]=HyS ……(8)
(6)式、(7)式、(8)式において、[O]は溶鋼中の酸素、[N]は溶鋼中の窒素、[S]は溶鋼中の硫黄を表す。
(9)式において、Eは、プラズマ出力(kW)である。
本発明例においては、15分間の水素プラズマ処理を行うことにより、溶鋼中の酸素濃度、窒素濃度及び硫黄濃度は、同時に且つ速やかに30質量ppm以下まで低減した。プラズマ処理の開始前から終了後までのそれぞれの元素の除去率は、溶鋼中酸素が94%以上、溶鋼中窒素が33%以上、溶鋼中硫黄が20%以上であった。
2 取鍋
3 上蓋
4 黒煙電極
5 鉄皮
6 内張り耐火物
7 永久耐火物
8 底吹きプラグ
9 溶鋼
10 スラグ
11 プラズマトーチ
12 プラズマトーチ
13 攪拌用ガス気泡
Claims (7)
- 取鍋内に収容された溶鋼に攪拌用ガスを吹き込んで取鍋内の溶鋼を攪拌するガス攪拌処理を行う工程において、
前記ガス攪拌処理によって流動状態にある取鍋内溶鋼の表面に、当該取鍋内溶鋼の上方に設置されたプラズマ発生装置から、水素ガスまたは水素ガスを含む不活性ガスをプラズマガスとして下記の(1)式を満たす条件で照射するプラズマ処理を行ない、当該プラズマ処理によって溶鋼中に含まれる酸素、窒素、硫黄のうちから選ばれる1種または2種以上の元素の含有量を低減する、溶鋼の精錬方法。
ここで、GPはプラズマガスの流量(Nm3/min)、(H2)はプラズマガス中の水素ガス濃度(体積%)、Qは取鍋内溶鋼の溶鋼循環流量(ton/min)である。 - 前記ガス攪拌処理は、前記取鍋の底部に1箇所または2箇所以上のガス吹き込み部を設置し、当該ガス吹き込み部から前記取鍋内溶鋼中に攪拌用ガスを吹き込むことで行われ、そのときの(4)式で算出される攪拌動力(ε)が、25W/ton以上である、請求項1または請求項2に記載の溶鋼の精錬方法。
- 前記取鍋内溶鋼にプラズマガスを照射する際の雰囲気圧力が150torr以下である、請求項1から請求項4のいずれか1項に記載の溶鋼の精錬方法。
- 取鍋内に収容した溶鋼の表面に浮遊するスラグは、鉄酸化物の濃度とマンガン酸化物の濃度との合計が5質量%以下である、請求項1から請求項5のいずれか1項に記載の溶鋼の精錬方法。
- 前記プラズマ処理により、溶鋼に含まれる酸素、窒素、硫黄の3元素の含有量を同時に低減する、請求項1から請求項6のいずれか1項に記載の溶鋼の精錬方法。
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JPS61149415A (ja) * | 1984-12-24 | 1986-07-08 | Sumitomo Metal Ind Ltd | 溶鉄からの脱銅・脱錫法 |
JP4305792B2 (ja) | 1999-03-25 | 2009-07-29 | ソニー株式会社 | 金属の精製方法及び精錬方法 |
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