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
  • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
  • C21C5/28—Manufacture of steel in the converter
• • 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
  • C21C1/00—Refining of pig-iron; Cast iron
  • C21C1/04—Removing impurities other than carbon, phosphorus or sulfur
• • 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
  • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
  • C21C5/28—Manufacture of steel in the converter
  • C21C5/30—Regulating or controlling the blowing
  • C21C5/35—Blowing from above and through the bath
• • 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
  • C21C7/068—Decarburising
• • 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
• • 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
  • C21C7/10—Handling in a vacuum

Definitions

• the present invention relates to a method for obtaining low-nitrogen steel by reducing the nitrogen concentration in molten iron after decarburization when decarburizing molten iron having a carbon concentration of 3.0% by mass or less before treatment to obtain molten steel.
• this method is suitable when part or all of the molten iron before treatment is obtained by melting a cold iron source.
• the nitrogen concentration at the time of tapping may be higher than when tapping blast furnace pig iron in a converter.
• nitrogen is removed by adsorbing it into carbon monoxide bubbles generated mainly by decarburization, and the nitrogen concentration at the time of tapping is generally low.
• blast furnace pig iron contains about 4% by mass of carbon, and the amount of carbon monoxide generated by decarburization refining is sufficiently large, so low-nitrogen steel smelting with a nitrogen concentration of about 20 ppm by mass is possible. is.
• the carbon concentration in molten iron after dissolving the cold iron source is low, and the amount of carbon monoxide generated is limited, so it is difficult to remove nitrogen to a low concentration.
• a certain degree of denitrification is possible if the molten iron after melting the cold iron source is subjected to a vacuum degassing process or the like.
• the upper limit of the nitrogen concentration that can be stably melted is about 40 mass ppm.
• reduced iron is generally produced by reduction with natural gas or the like, it contains 0.5 mass % to 2.0 mass % of carbon. For this reason, molten iron obtained by dissolving this reduced iron requires decarburization refining, and denitrification to some extent is possible at this time.
• the molten iron obtained by dissolving reduced iron in an electric furnace or the like is mixed with blast furnace pig iron to increase the carbon concentration in the molten iron, and decarburization is performed in a converter. can be considered.
• blast furnace pig iron will decrease and the consumption of cold iron sources will increase in order to reduce the amount of CO 2 generated.
• the carbon concentration at the time of charging the steel into the converter will decrease, making it difficult to sufficiently reduce the nitrogen concentration of the tapped steel.
• Patent Document 1 molten steel tapped from a converter is carburized, Al deoxidized, and then oxidized during vacuum degassing to decarburize and refining, thereby reducing the N concentration in the molten steel to A method for reducing [N] ⁇ 25 ppm by mass has been proposed.
• Patent Document 2 CaO is added to the bath surface of molten steel without carburizing, and then an Al-containing substance is added, nitrogen in the molten steel is removed as nitrides in slag, and oxygen is transferred.
• a method for denitrification of molten steel has been proposed in which nitrogen gas is removed into the gas phase by performing the above, and the nitrogen concentration is reduced to 20 ppm by mass or less.
• Patent Document 3 in the RH vacuum degassing apparatus, by supplying a hydrocarbon gas as a reflux gas supplied from the immersion tube, the bubbles are made finer and the nitrogen concentration is reduced to 20 mass ppm or less. Vacuum refining A method is proposed.
• the present invention has been made in view of such circumstances, and its object is to prevent a significant decrease in productivity and cost increase under conditions where the amount of cold iron source used is increased, and to remove slag.
• the object of the present invention is to propose a molten iron refining method for stably producing low-nitrogen steel without increasing the amount of CO 2 generated and the amount of CO 2 generated.
• the method for refining molten iron according to the present invention includes pre-treatment molten iron having a carbon concentration [C] i of 0.5% by mass or more and 3.0% by mass or less.
• the molten iron is blown with oxygen under atmospheric pressure, and at the same time, hydrogen gas, hydrocarbon gas, or a mixed gas thereof is blown into the molten iron to decarburize and denitrify the molten iron before treatment.
• the method for refining molten iron according to the present invention includes: (a) the nitrogen concentration [N] f of the molten iron after the decarburization and denitrification treatments is 30 ppm by mass or less; (b) further subjecting the treated molten iron after the decarburization and denitrification treatments to a vacuum degassing treatment; (c) the pre-treatment molten iron includes one obtained by melting a cold iron source; (d) the molten iron before treatment is a mixture of primary molten iron obtained by melting the cold iron source in a melting furnace and molten iron having a carbon concentration of 2.0% by mass or more; (e) the cold iron source comprises reduced iron; (f) the vessel is a converter; etc. is considered to be a more preferable solution.
• the iron source is melted and heated using electrical energy in a steelmaking melting furnace.
• a steelmaking melting furnace for steelmaking, an electric furnace such as an arc furnace or an induction furnace can be used.
• the iron source may be not only a solid iron source such as scrap or reduced iron, but also molten iron melted in another process.
• the thermal energy supplied for melting the solid iron source and heating the iron source may be not only electric energy, but also combustion heat of metal or the like may be used as a complement. These energies are preferably renewable energies from the viewpoint of reducing CO 2 emissions.
• the second step hot water is poured into a container such as a ladle.
• a container such as a ladle.
• the slag removal may be performed with a slag dragger or the like. If the freeboard height of the ladle (the height from the top of the ladle to the surface of the molten iron) is insufficient, the furnace body may be tilted before pouring out the molten iron from the electric furnace to pour out the slag. Alternatively, the furnace body may be tilted before the hot water is discharged from the electric furnace to discharge hot water after the slag, and the slag flowing out together with the molten iron into a container such as a ladle may be further removed.
• the carbon concentration [C] i in the molten iron is adjusted to 0.5% by mass or more and 3.0% by mass or less by mixing with molten iron such as blast furnace iron as necessary, and the mixture is added to the reaction vessel.
• decarburization refining is performed by supplying oxygen gas from a top-blowing lance or the like. If the carbon concentration [C] i of the untreated molten iron is less than 0.5% by mass, the amount of CO gas generated during decarburization is small, so denitrification may be insufficient. On the other hand, when the carbon concentration exceeds 3.0% by mass, the effect of reducing the amount of CO 2 generated becomes small.
• the molten iron used as the lamination is preferably molten iron with a carbon concentration of 2.0% by mass or more. Any one of silicon, dephosphorization and desulfurization or a combination of two or more treatments may be applied.
• a converter is preferable from the viewpoint of the height of the freeboard (the height from the upper end of the reaction vessel to the molten iron surface).
• a ladle or the like may be used as long as it is a container that allows oxygen blowing.
• the oxygen blowing method is not limited to the method of supplying oxygen from the top blowing lance, but the oxygen may be supplied from the bottom blowing tuyere. The supply of oxygen from the top-blowing lance and the supply of oxygen from the bottom-blowing tuyeres may be used in combination.
• a gas containing hydrogen atoms such as hydrogen gas, hydrocarbon gas, or a mixed gas thereof is supplied from a porous plug or the like installed at the bottom of the furnace. It is thought that when a gas containing hydrogen atoms is supplied to molten iron, a dissociation reaction of gas molecules occurs, and then the hydrogen atoms are once dissolved in the molten iron and generated again as fine hydrogen gas bubbles. It is thought that the denitrification reaction progresses between the microbubbles generated here and the molten iron interface.
• the appropriate amount of gas containing hydrogen atoms to be supplied is about 0.1 to 0.3 Nm 3 /min per ton of molten iron.
• Nm 3 means the volume of gas under standard conditions. In this specification, the standard gas state is 0° C. and 1 atm (101325 Pa).
• the supply of oxygen gas is stopped and at the same time, the supply of gas containing hydrogen atoms is stopped.
• an inert gas such as argon gas
• the supply of gas containing hydrogen atoms is not limited to the porous plug, and may be supplied using an injection lance (immersion lance), a single tube, or a double tube.
• the treatment is performed so that the nitrogen concentration [N] f of the molten iron after treatment is 30 mass ppm or less, low nitrogen steel with a product nitrogen concentration N of 30 mass ppm or less at the crude steel stage such as billets can be produced, which is preferable.
• the processing conditions are adjusted so that the amount of hydrogen atoms supplied is increased by increasing the hydrogen gas flow rate or using a hydrocarbon gas with a large hydrogen content per gas volume, and the molten iron after processing is treated.
• the steel is treated so that the nitrogen concentration [N] f of is 20 ppm by mass or less, it becomes ultra-low nitrogen steel, which is more preferable.
• the fourth step after the decarburization refining is completed, it is preferable to carry out vacuum degassing treatment, adjust other predetermined components, and then carry out casting.
• Dehydrogenation can be performed by performing vacuum degassing treatment after decarburization refining.
• the vacuum degassing process it is possible to suppress a decrease in productivity as compared with the technique described in Patent Document 3, in which a gas containing hydrogen atoms is supplied.
• an RH-type vacuum processing apparatus, a DH-type vacuum processing apparatus, a facility in which a ladle is installed in a vacuum chamber, or the like can be used.
• Scrap or reduced iron as a source of cold iron was charged into a 150t scale electric furnace, melted, poured into a ladle, and then slag was removed.
• the reduced iron used in the test was produced by reduction with natural gas, and the carbon concentration was analyzed to be 1.0% by mass.
• the molten iron in the ladle after tapping and the blast furnace pig iron were combined in a converter charging ladle to adjust the amount of molten iron to 300 tons. After component analysis of the molten iron, it was charged into a converter and decarburized.
• the amount of carbon contained in the blast furnace pig iron used for the mixed melt was 4.3% by mass.
• the mixing ratio of the molten iron obtained by melting the cold iron source and the blast furnace pig iron was variously changed, and the carbon concentration [C] i (mass %) at the time of charging into the converter was also variously changed.
• Oxygen gas required for decarburization was supplied from a top-blowing lance, and the amount of oxygen gas supplied was determined based on the carbon and other analytical values (indicated by subscript i) in the molten iron before charging into the converter.
• hydrogen gas, propane gas, or a 50% by volume hydrogen-50% by volume propane mixed gas was supplied from a porous plug installed at the bottom of the converter.
• the supply of hydrogen gas, propane gas, or a mixed gas of hydrogen and propane is stopped, the bottom-blowing gas is switched to argon gas, and the steel is tapped into a ladle. Analysis (denoted by subscript f) was performed. After that, the ladle was subjected to a vacuum treatment in a vacuum degassing device, adjusted to a predetermined composition, and then cast.
• Argon gas was used as the reflux gas at this time.
• casting was performed using a continuous casting machine.
• the carbon concentration [C] i charged to the converter exceeds 3.0% by mass, both the nitrogen concentration [N] f (mass ppm) of the steel discharged from the converter and the nitrogen concentration N (mass ppm) of crude steel are low. It was a different result.
• the charged carbon concentration [C] i of the converter falls below 3.0% by mass, both the nitrogen concentration [N] f of the steel discharged from the converter and the nitrogen concentration N of the crude steel are high.
• Hydrogen gas or propane gas was used as the reflux gas at this time.
• a component analysis was performed during the vacuum degassing process, and the vacuum process was continued until the hydrogen concentration became equal to or less than a predetermined concentration.
• casting was performed using a continuous casting machine.
• the nitrogen concentration [N] f of steel discharged from the converter was high, but the denitrification reaction was promoted during the vacuum degassing treatment, and the nitrogen concentration N of crude steel was low. Furthermore, the crude steel hydrogen concentration H also became low.
• the vacuum degassing time was significantly increased.
• the above test conditions and results are summarized in Tables 1-1 to 1-3.
• the product composition in the table is the value obtained by extracting from the cast slab and analyzing the composition as the crude steel composition.
• the method for refining molten iron according to the present invention under conditions where the amount of cold iron source used has increased, there is no significant decrease in productivity or cost increase, and there is no increase in the amount of slag or CO 2 generated. It is possible to stably produce low nitrogen steel with a content of 30 ppm by mass or less. It is industrially useful because it is possible to achieve both reduction of CO2 emissions and production of high-grade steel while simultaneously using blast furnace pig iron and cold iron sources in existing integrated steelworks.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)

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• 2022
  • 2022-04-19 CN CN202280037168.2A patent/CN117377781A/zh active Pending
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  • 2022-04-19 EP EP22811072.2A patent/EP4328330A1/en active Pending
  • 2022-04-19 WO PCT/JP2022/018168 patent/WO2022249798A1/ja active Application Filing
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