A method for producing high-purity, ultra-low manganese industrial pure iron using a refining duplex process.

Abstract

A method for producing high-purity ultra-low manganese industrial pure iron by a refining double process belongs to the technical field of steel smelting. The method includes molten iron pretreatment, converter dephosphorization, converter decarbonization, LF refining, RH refining, and slab continuous casting process; molten iron pretreatment desulfurization to S≤0.0010wt%; converter decarbonization process controls the tapping temperature to ≤1600℃, lime is added to wash the ladle slag during the tapping process, and strong stirring is used to further dephosphorize and demanganize after the tapping is completed. The LF refining process is heated with oxygen and the slag is modified, and the slag top slag T.Fe is controlled at 16-20wt% for ladle demanganization; the time from RH breaking to continuous casting is controlled to ≥20min. The present invention can control the Mn content in the molten steel to below 0.015wt%, and the purity of the cast billet is stably controlled at 99.90-99.95wt%, which solves the problem of excessive Mn content in the molten steel, and the temperature, composition and total oxygen of the molten steel meet the requirements.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and relates to a method for producing high-purity ultra-low manganese industrial pure iron by a refining double process. Background Art

[0002] Industrial pure iron is an iron alloy with a very low carbon content, excellent thermal conductivity and electromagnetic properties, and excellent toughness. Industrial pure iron is mainly used to smelt various special alloys. Depending on the purity, its application fields vary greatly. In recent years, with the continuous advancement of industrial pure iron smelting technology, its market demand has also increased. At present, the most commonly used smelting method for industrial pure iron is electric furnace smelting, but it is difficult to mass produce due to the content control problems of C, N, P, Mn, etc. in electric furnace smelting. Foreign countries mainly use the method of iron solution electrolysis to produce high-purity pure iron, and few domestic companies have the ability to mass-produce high-purity industrial pure iron. The use of traditional steel smelting technology to smelt industrial pure iron has high requirements for process control. Not only must the composition of the smelting process be controlled, but also TO and impurity elements in molten steel have high requirements, especially the Mn content in the ingot is difficult to meet the composition requirements of high-purity industrial pure iron. It is necessary to control the smelting cost and meet the purity requirements of industrial pure iron. At present, there is no reasonable way to achieve the purpose of taking both into account.

[0003] The Chinese patent application with publication number CN106350631A discloses a method for producing industrial pure iron for amorphous soft magnetic materials, which uses a converter double slag smelting and high temperature steel tapping after the furnace, LF heating and RH forced decarburization to produce industrial pure iron for producing magnetic materials. This method is not only complex in process, but also the P content and Mn content of pure iron are difficult to meet the requirements. The Chinese patent applications with publication numbers CN102382925A, CN104451385A, CN105603312A, CN106367553A, and CN107502696A use a production process combining an electric furnace and a VOD furnace to produce industrial pure iron, but the steel tapping temperature of the electric furnace is high (greater than 1650°C), P is difficult to control, and some do not require the Mn element in the smelting process, and the product purity and molten steel composition are difficult to stably control. The Chinese patent application with publication number CN101353753A discloses a method for manufacturing ultra-low carbon high-purity industrial pure iron, which undergoes desulfurization and phosphorus removal in an electric furnace, then decarbonization by oxygen blowing in AOD, and finally casting to produce high-purity industrial pure iron with a purity of 99.5-99.7%, but the process does not have a Mn content control measure and cannot meet the requirement of low Mn content. The Chinese patent application with publication number CN101948979A discloses a method for producing industrial pure iron, which produces industrial pure iron with a carbon content of less than 0.03% by converter steelmaking, ladle deoxidation and vacuum degassing, but does not use P and Mn removal methods to control its element content, and the converter uses high temperature (1670-1700°C) steelmaking to easily return P and Mn. The Chinese patent application with publication number CN112795720A discloses a method for smelting industrial pure iron by a double converter method, and obtains industrial pure iron with Mn≤0.08% after desulfurization and double converter smelting, but the high temperature (1675-1690°C) steel tapping after the furnace easily causes the increase of P and Mn elements, the element control is unstable and the purity of industrial pure iron is low. The production method of industrial pure iron disclosed in the Chinese patent applications with publication numbers CN113512619A and CN113774277A is simple in process, but without desulfurization and dephosphorization furnaces, the S content, P content and Mn content in the molten steel are difficult to control to meet the target requirements, and the purity is low. At present, the industrial pure iron produced by the electrolytic method adopted by Japan can increase the purity to 99.9%, but its price is relatively expensive.

[0004] In summary, there is an urgent need to find a method for producing high-purity industrial pure iron to meet the needs of industrial batch stable production. Summary of the invention

[0005] To solve the above technical problems, the present invention provides a method for producing high-purity ultra-low manganese industrial pure iron by a refining double process, which can control the Mn content in molten steel to below 0.015wt%, and stably control the purity of the ingot to 99.90%-99.95%.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is:

[0007] A method for producing high-purity ultra-low manganese industrial pure iron by a refining double process, comprising molten iron pretreatment, converter dephosphorization, converter decarburization, LF refining, RH refining, and slab continuous casting steps;

[0008] Hot metal pretreatment process: desulfurization until S in the hot metal is less than or equal to 0.0010wt%. Strong stirring during the desulfurization process ensures the desulfurization effect. After desulfurization, slag removal is performed.

[0009] Converter dephosphorization process: The dephosphorization converter controls the scrap steel ratio at 10-13wt%, and the final P content is ≤0.040%;

[0010] Converter decarburization process: tapping temperature ≤ 1600℃, lime is added to wash ladle slag during tapping, strong stirring is used to further remove P and Mn after tapping, and the tapping composition is controlled to be: C 0.020-0.040%, P≤0.005%, S≤0.004%, Mn≤0.020% by weight;

[0011] LF refining process: LF furnace is heated with oxygen and slag is modified, the T.Fe of the slag top is controlled at 16-20wt% for ladle de-Mn, and the Mn of the outgoing molten steel is ≤0.015wt%;

[0012] RH refining process: After RH deoxidation and alloying, the molten steel is subjected to pure circulation degassing treatment;

[0013] The time from RH breaking to continuous casting is controlled within 20 to 25 minutes;

[0014] The purity of the ingot obtained after continuous casting is 99.90-99.95wt%, wherein Mn is less than or equal to 0.015wt%.

[0015] Furthermore, in the molten iron pretreatment step, the temperature of the molten iron entering the furnace is ≥1250°C, and the composition of the molten iron is Si>0.35%, Mn≤0.25%, P≤0.120%, Cr≤0.025%, and S≤0.050% by weight.

[0016] Furthermore, in the converter decarburization process, the slag basicity is controlled at 3.5-4.0, 1.6 kg / t lime and 0.2 kg / t fluorite are added during the steel tapping process, and the strong stirring time is 3-5 minutes.

[0017] Furthermore, in the LF refining process, after the molten steel enters the station, pre-melted refining slag and lime are added to perform slag making and submerged arc heating, and after the LF refining is completed, high-aluminum composite refining slag is added to perform slag modification according to the oxygen level.

[0018] Furthermore, in the RH refining process, the degassing time is 6 to 8 minutes, argon is used as the lifting gas, and the gas flow rate is 60 to 80 NL / min.

[0019] Furthermore, in the slab continuous casting process, a carbon-free tundish is used in the continuous casting process, ultra-low carbon protective slag is used for the protective slag, a carbon-free covering agent is used for the tundish covering agent, protective casting is used in the casting process, the stopper rod, the water inlet and the argon flow between the plates are controlled at 3±0.3L / min, the argon pressure is controlled at ≥0.1bar, the SEN insertion depth in the casting process is controlled between 130 and 150mm, and the crystallizer liquid level fluctuation requirement is ≤4mm.

[0020] Furthermore, the chemical composition and weight percentage of the ingot obtained after continuous casting are: C≤0.0030%, Si≤0.010%, P≤0.005%, S≤0.005%, Als≤0.010%, Ti+Nb+Cr+Ni+Cu≤0.050%, and Mn≤0.015%.

[0021] The beneficial effect of adopting the above technical scheme is that the present invention adopts the "full three removals" refining double process to sequentially carry out pre-desulfurization treatment, dephosphorization treatment and demanganese treatment on the molten iron, and further removes P and Mn by using the decarburization converter low-temperature steel tapping, ladle slag washing, LF oxygen heating and modification technology, RH vacuum refining decarburization, degassing and inclusion removal, and finally slab continuous casting to obtain high-purity ultra-low Mn content industrial pure iron. The present invention solves the problem of excessively high Mn content control in molten steel, controls the Mn content in molten steel to below 0.015%, stably controls the purity to 99.90%-99.95%, and the temperature, composition and total oxygen of the molten steel meet the requirements, and each key control parameter of the smelting process is stable and controllable, and mass production can be achieved. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described below in conjunction with embodiments:

[0023] The composition requirements of industrial pure iron are shown in the following table:

[0024] Table 1. Composition requirements of industrial pure iron (wt%)

[0025] Element C Si Mn P S Als Ti+Cr+Nb+Ni+Cu scope ≤0.003 ≤0.01 ≤0.015 ≤0.005 ≤0.005 ≤0.010 ≤0.050

[0026] Examples 1-5

[0027] The method of the present invention is adopted to smelt industrial pure iron. Taking a converter with a capacity of 250t as an example, the smelting data of 5 furnaces of steel are statistically analyzed. The smelting process control parameters are shown in Tables 2-7 below. The composition and mass percentage of the ingots obtained in each embodiment are shown in Table 8.

[0028] Table 2. Hot metal pretreatment process parameters

[0029]

[0030] Table 3. Parameters of converter dephosphorization process

[0031] Furnace No. Scrap steel ratio / % End point P content / % 1 10 0.040 2 11 0.030 3 10 0.040 4 12 0.040 5 13 0.035

[0032] Table 4. Converter decarburization process parameters

[0033]

[0034] Table 5. LF refining process parameters

[0035]

[0036]

[0037] Table 6. RH refining process parameters

[0038]

[0039] Table 7. Slab continuous casting process parameters

[0040] Furnace No. Argon gas flow rate / L / min Argon pressure / bar SEN insertion depth / mm Crystallizer liquid level fluctuation / mm 1 2.8 0.2 140 3 2 2.9 0.2 140 3 3 2.7 0.1 130 2 4 3.3 0.2 150 4 5 3.2 0.1 145 2

[0041] Table 8. Composition and mass percentage of the ingots obtained in each embodiment (%)

[0042] Furnace No. 1 2 3 4 5 C 0.0015 0.0020 0.0030 0.0010 0.0025 Si 0.002 0.005 0.010 0.002 0.008 Mn 0.015 0.013 0.015 0.010 0.012 P 0.003 0.002 0.005 0.002 0.004 S 0.004 0.003 0.005 0.002 0.004 Als 0.008 0.009 0.010 0.008 0.008 Ti+Nb+Cr+Ni+Cu 0.035 0.040 0.050 0.030 0.045 purity / % 99.93 99.93 99.90 99.95 99.92

Claims

1. A method for producing high-purity ultra-low manganese industrial pure iron by refining double process, characterized in that: Including hot metal pretreatment, converter dephosphorization, converter decarburization, LF refining, RH refining, and slab continuous casting processes; Hot metal pretreatment process: desulfurization until S in the hot metal is less than or equal to 0.0010wt%. Strong stirring during the desulfurization process ensures the desulfurization effect. After desulfurization, slag removal is performed. Converter dephosphorization process: The dephosphorization converter controls the scrap steel ratio at 10-13wt%, and the final P content is ≤0.040%; Converter decarburization process: tapping temperature ≤ 1600℃, lime is added to wash the ladle slag during tapping, strong stirring is used to further remove P and Mn at the end of tapping, and the tapping composition is controlled to be: C 0.020~0.040%, P≤0.005%, S≤0.004%, Mn≤0.020% by weight; LF refining process: LF furnace is heated with oxygen and slag is modified, the T.Fe of the top slag is controlled at 16-20wt% for ladle de-Mn, and the Mn of the outgoing molten steel is ≤0.015wt%; RH refining process: After RH deoxidation and alloying, the molten steel is subjected to pure cycle degassing treatment, the degassing time is 6 to 8 minutes, argon is used as the lifting gas, and the gas flow rate is 60 to 80 NL / min; The time from RH breaking to continuous casting start is controlled at ≥20min; The purity of the ingot obtained after continuous casting is 99.90-99.95wt%, and the chemical composition and weight percentage are: C≤0.0030%, Si≤0.010%, P≤0.005%, S≤0.005%, Als≤0.010%, Ti+Nb+Cr+Ni+Cu≤0.050%, and Mn≤0.015%.

2. The method for producing high-purity ultra-low manganese industrial pure iron by refining double process according to claim 1, characterized in that: In the molten iron pretreatment process, the temperature of the molten iron entering the furnace is ≥1250°C, and the composition of the molten iron is Si>0.35%, Mn≤0.25%, P≤0.120%, Cr≤0.025%, and S≤0.050% by weight.

3. The method for producing high-purity ultra-low manganese industrial pure iron by refining double process according to claim 2, characterized in that: In the converter decarburization process, the slag basicity is controlled at 3.5-4.0, 1.6 kg / t lime and 0.2 kg / t fluorite are added during the steel tapping process, and the strong stirring time is 3-5 minutes.

4. The method for producing high-purity ultra-low manganese industrial pure iron by refining double process according to claim 3, characterized in that: In the LF refining process, after the molten steel enters the station, pre-melted refining slag and lime are added to perform slag making and submerged arc heating. After the LF refining is completed, high-aluminum composite refining slag is added to perform slag modification.

5. The method for producing high-purity ultra-low manganese industrial pure iron by refining double process according to claim 4, characterized in that: The time from RH breaking through the air to the start of continuous casting is controlled within 20 to 25 minutes.

6. The method for producing high-purity ultra-low manganese industrial pure iron by refining double process according to claim 5, characterized in that: In the slab continuous casting process, a carbon-free tundish is used in the continuous casting process, ultra-low carbon protective slag is used for the protective slag, a carbon-free covering agent is used for the tundish covering agent, protective casting is used in the casting process, the flow rate of argon gas between the stopper rod, the water inlet and the plates is controlled at 3±0.3L / min, the argon pressure is controlled at ≥0.1bar, the SEN insertion depth in the casting process is controlled between 130 and 150mm, and the crystallizer liquid level fluctuation requirement is ≤4mm.

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