A smelting method for ultra-low carbon and ultra-low nitrogen steel and ultra-low carbon and ultra-low nitrogen steel

Abstract

The present invention provides a smelting method of ultra-low carbon and ultra-low nitrogen steel and ultra-low carbon and ultra-low nitrogen steel, belonging to the field of steel preparation. The method comprises: smelting the first scrap steel to obtain molten steel; deoxidizing and carbonizing the molten steel to obtain semi-steel molten steel; carbonizing, desulfurizing and heating the semi-steel molten steel through LF refining to obtain desulfurized molten steel; smelting the desulfurized molten steel and the second scrap steel in a converter to obtain converter molten steel; RH refining and full protection pouring of the converter molten steel to obtain ultra-low carbon and ultra-low nitrogen steel. By melting the recycled scrap steel that can be regarded as having near-zero carbon emissions in an electric furnace, carbon dioxide emissions are reduced to the maximum extent, and at the same time, the series process with the converter is matched to remove a large amount of nitrogen through the violent carbon-oxygen reaction of the converter. The technical problem that it is difficult to improve the quality of automobile steel on the basis of meeting low carbon emissions in the prior art is solved.

Description

Technical Field

[0001] The present application relates to the technical field of steel preparation, and in particular to a smelting method of ultra-low carbon and ultra-low nitrogen steel and ultra-low carbon and ultra-low nitrogen steel. Background Art

[0002] At present, all automotive steels with excellent deep drawing and coating properties are produced using the blast furnace-converter long process, using high-carbon raw materials such as coal and coke as the main reducing agents and heat sources. Calculated from the perspective of the entire life cycle, the CO2 emissions per ton of crude steel exceed 2 tons. Adding hot rolling, cold rolling, coating and other processes, the CO2 emissions per ton of steel for automotive steel products will exceed 3 tons, which does not meet the requirements of automobile companies to reduce carbon emissions for automotive steel.

[0003] Different from blast furnace-converter smelting, scrap steel can be smelted in electric furnaces to reduce carbon emissions. However, electric furnace smelting and subsequent refining are difficult to meet the strict requirements of automotive steel for N and C content. Therefore, improving the quality of automotive steel on the basis of meeting low carbon emissions is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application provides a smelting method of ultra-low carbon and ultra-low nitrogen steel and ultra-low carbon and ultra-low nitrogen steel to solve the technical problem in the prior art that it is difficult to improve the quality of automobile steel on the basis of meeting low carbon emissions.

[0005] In a first aspect, the present application provides a method for smelting ultra-low carbon and ultra-low nitrogen steel, the method comprising:

[0006] Melting the first scrap steel to obtain molten steel;

[0007] Deoxidizing and carbonizing the molten steel to obtain semi-steel molten steel;

[0008] Carburizing, desulfurizing and heating the semi-steel molten steel by LF refining to obtain desulfurized molten steel;

[0009] The desulfurized molten steel and the second scrap steel are subjected to converter smelting to obtain converter molten steel;

[0010] The converter molten steel is subjected to RH refining and full protection casting to obtain ultra-low carbon and ultra-low nitrogen steel.

[0011] Optionally, in the molten steel, the mass fraction of carbon is 0.04% to 0.08%, the mass fraction of oxygen is 0.045% to 0.085%, the mass fraction of nitrogen is 0.005% to 0.008%, and the mass fraction of sulfur is 0.015% to 0.025%.

[0012] Optionally, the temperature of the molten steel is 1590°C to 1620°C.

[0013] Optionally, the step of deoxidizing and carbonizing the molten steel to obtain semi-steel molten steel comprises:

[0014] Deoxidizer and carburizer are added into the molten steel, and bottom blowing and stirring are performed to obtain semi-steel liquid; the amount of the deoxidizer added is 0.5Kg / t·steel to 1Kg / t·steel, the amount of the carburizer added is 14Kg / t·steel to 24Kg / t·steel, and the carrier gas flow rate of the bottom blowing and stirring is 1000NL / min to 1500NL / min.

[0015] Optionally, in the desulfurized steel liquid, the mass fraction of aluminum is ≥0.030%, the mass fraction of carbon is 2% to 2.5%, and the mass fraction of sulfur is ≤0.0050%.

[0016] Optionally, the temperature of the desulfurized molten steel is 1640°C to 1660°C.

[0017] Optionally, the raw materials added for carburization include: 5 kg / t·steel to 10 kg / t·steel carburizer, the raw materials added for desulfurization include: activated lime, and the amount of activated lime added L1 and the mass fraction of oxygen [O] in the semi-steel molten steel satisfy the following relationship: 3.5×[O] / 0.01%≤L1≤4.5×[O] / 0.01%, wherein the unit of L1 is Kg / t·steel; and

[0018] Bauxite, the amount of bauxite added L2 and the mass fraction of oxygen [O] in the semi-steel molten steel satisfy the following relationship: 0.44×[O] / 0.01%≤L2≤0.47×[O] / 0.01%, wherein the unit of L2 is Kg / t·steel.

[0019] Optionally, in the converter steel liquid, the mass fraction of carbon is 0.04% to 0.06%, the mass fraction of oxygen is 0.04% to 0.06%, and the mass fraction of nitrogen is 0.002% to 0.004%.

[0020] Optionally, the RH refining adopts a vacuum decarburization process, and the RH refining includes the following process parameters: deep vacuum time ≥ 45 min, and pure cycle time after deoxidation > 15 min.

[0021] In a second aspect, the present application provides an ultra-low carbon, ultra-low nitrogen steel prepared by the method described in any one of the embodiments in the first aspect, in which the mass fraction of nitrogen is ≤0.003%, and the mass fraction of carbon is ≤0.003%.

[0022] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0023] The present application provides a smelting method of ultra-low carbon and ultra-low nitrogen steel, which can be regarded as recycling scrap steel with near-zero carbon emissions by melting it in an electric furnace, thereby reducing carbon dioxide emissions to the maximum extent, and matching the series process with the converter, and removing nitrogen in large quantities through the intense carbon-oxygen reaction of the converter; at the same time, LF refining is adopted, which has a heating function, can reduce the steel tapping temperature of the electric furnace, which is beneficial to the improvement of the life of the electric furnace refractory material; at the same time, at the higher temperature of LF, it is easy to achieve a good slag desulfurization effect, thereby supporting the addition of low-cost high-sulfur scrap steel to the electric furnace, and then under the condition of high temperature and strong stirring of the LF furnace, the absorption rate and stability of the carbon addition are improved. The technical problem that it is difficult to improve the quality of automobile steel on the basis of meeting low carbon emissions in the prior art is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0026] Figure 1 A schematic flow chart of a method for smelting ultra-low carbon and ultra-low nitrogen steel is provided for an embodiment of the present application. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0028] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0029] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (items). For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0030] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0031] Figure 1 A schematic flow chart of a method for smelting ultra-low carbon and ultra-low nitrogen steel is provided for an embodiment of the present application.

[0032] See also Figure 1 The present application provides a method for smelting ultra-low carbon and ultra-low nitrogen steel, the method comprising:

[0033] S1, smelting the first scrap steel to obtain molten steel;

[0034] In some embodiments, in the molten steel, the mass fraction of carbon is 0.04% to 0.08%, the mass fraction of oxygen is 0.045% to 0.085%, the mass fraction of nitrogen is 0.005% to 0.008%, and the mass fraction of sulfur is 0.015% to 0.025%. It should be noted that if the mass fraction of carbon in the molten steel is too low, a large amount of carbon will be added; if the mass fraction of carbon in the molten steel is too high, additional carbon will be required in the electric furnace, affecting the efficiency of the electric furnace. The mass fraction of carbon in the molten steel can be 0.04% to 0.08%, which can reduce the end oxygen content, reduce the consumption of deoxidizer for steel tapping and the amount of carbon powder for steel tapping. The mass fraction of oxygen in the molten steel can be 0.045% to 0.085%, and the oxygen content is made to correspond to the carbon content according to the stirring capacity of the electric furnace. The mass fraction of nitrogen in molten steel is 0.005% to 0.008%, and the mass fraction of sulfur is 0.015% to 0.025%. N is a harmful element that needs to be strictly controlled in this application. In the electric furnace process using all scrap steel as raw materials, it is difficult to control nitrogen, so the N content is reduced as much as possible. The mass fraction of sulfur in molten steel is 0.015% to 0.025%. If the sulfur content is too high, the desulfurization amount of the process will be large, resulting in an extended cycle, thereby affecting the cycle matching between processes; if the sulfur content is too low, it is necessary to reduce the addition of low-priced high-sulfur scrap steel, thereby increasing costs. Exemplarily, the mass fraction of carbon in the molten steel can be 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, etc.; the mass fraction of oxygen in the molten steel can be 0.045%, 0.050%, 0.055%, 0.060%, 0.070%, 0.080%, 0.085%, etc.; the mass fraction of nitrogen in the molten steel can be 0.005%, 0.006%, 0.007%, 0.008%, etc.; the mass fraction of sulfur can be 0.015%, 0.017%, 0.019%, 0.020%, 0.022%, 0.024%, 0.025%, etc.

[0035] In some embodiments, the temperature of the molten steel is 1590°C to 1620°C. It should be noted that, taking into account the subsequent heating cycle of the LF furnace, the tapping temperature of the molten steel is higher than this range, causing unnecessary waste, and the LF heating cycle is increased below this range, resulting in a mismatch in the cycle connection between the processes, thereby affecting the overall production efficiency. Exemplarily, the temperature of the molten steel can be 1590°C, 1595°C, 1600°C, 1605°C, 1610°C, 1615°C, 1620°C, etc.

[0036] S2, deoxidizing and carbonizing the molten steel to obtain semi-steel molten steel;

[0037] In some embodiments, the step of deoxidizing and carbonizing the molten steel to obtain semi-steel molten steel comprises:

[0038] Add deoxidizer and carburizer to the molten steel, and perform bottom blowing and stirring to obtain semi-steel molten steel; the amount of the deoxidizer added is 0.5Kg / t·steel to 1.0Kg / t·steel, the amount of the carburizer added is 14Kg / t·steel to 24Kg / t·steel, and the carrier gas flow rate of the bottom blowing and stirring is 1000NL / min to 1500NL / min. It should be noted that the addition of the deoxidizer is used to deoxidize the molten steel; the addition of the carburizer is used to increase the carbon content of the molten steel, which is beneficial to the subsequent denitrification. Exemplarily, the amount of deoxidizer added can be 0.50Kg / t·steel, 0.60Kg / t·steel, 0.70Kg / t·steel, 0.8Kg / t·steel, 0.9Kg / t·steel, 1.0Kg / t·steel, etc.; the amount of carburizer added can be 14Kg / t·steel, 18Kg / t·steel, 20Kg / t·steel, 22Kg / t·steel, 24Kg / t·steel, etc.

[0039] S3, carburizing, desulfurizing and heating the semi-steel molten steel by LF refining to obtain desulfurized molten steel;

[0040] LF has a heating function, which can reduce the steel-making temperature of the electric furnace, which is beneficial to the improvement of the life of the refractory materials of the electric furnace; at the same time, at the higher temperature of LF, it is easy to achieve a good slag-making and desulfurization effect, thereby supporting the addition of low-cost high-sulfur scrap steel to the electric furnace, and then under the conditions of high temperature and strong stirring in the LF furnace, the absorption rate and stability of the carbon addition are improved.

[0041] In some embodiments, in the desulfurized steel liquid, the mass fraction of aluminum is ≥0.030%, the mass fraction of carbon is 2% to 2.5%, and the mass fraction of sulfur is ≤0.0050%. It should be noted that if the mass fraction of aluminum in the desulfurized steel liquid is low, a good desulfurization effect cannot be guaranteed; if the mass fraction of carbon in the desulfurized steel liquid is low, the carbon-oxygen reaction time in the converter is short, resulting in the failure to achieve the expected denitrification effect, and the mass fraction of carbon in the desulfurized steel liquid is high, which increases the cost. Exemplarily, in the desulfurized steel liquid, the mass fraction of aluminum can be 0.030%, 0.035%, 0.040%, 0.045%, 0.050%, etc., the mass fraction of carbon can be 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, etc., and the mass fraction of sulfur can be 0.0010%, 0.0020%, 0.0030%, 0.0040%, 0.0050%, etc.

[0042] In some embodiments, the temperature of the desulfurized steel liquid is 1640°C to 1660°C. It should be noted that the temperature of the desulfurized steel liquid is 1640°C to 1660°C, which can match the target scrap steel amount and heat balance of the converter, and ultimately ensure that the converter terminal temperature is within a suitable range. Exemplarily, the temperature of the desulfurized steel liquid can be 1640°C, 1645°C, 1650°C, 1655°C, 1658°C, 1660°C, etc.

[0043] In some embodiments, the raw materials added for carburization include: 5Kg / t·steel to 10Kg / t·steel carburizer, the raw materials added for desulfurization include: activated lime, the amount of activated lime added L1 and the mass fraction of oxygen [O] in the semi-steel molten steel satisfy the following relationship: 3.5×[O] / 0.01%≤L1≤4.5×[O] / 0.01%, wherein the unit of L1 is Kg / t·steel; and bauxite, the amount of bauxite added L2 and the mass fraction of oxygen [O] in the semi-steel molten steel satisfy the following relationship: 0.44×[O] / 0.01%≤L2≤0.47×[O] / 0.01%, wherein the unit of L2 is Kg / t·steel. It should be noted that according to the carbon content of LF arriving at the station after the ladle is carbonized, the carbon content is adjusted according to the target carbon content of 2.3%. Lime and slag deoxidizer are added according to the oxygen content and slag oxidizability. 0.01% oxygen is added in the amount of 3.5Kg / t·steel to 4.5Kg / t·steel lime and 0.44Kg / t·steel to 0.47Kg / t·steel slag deoxidizer. Adding too much increases the cost and causes waste, while adding too little fails to achieve the expected desulfurization effect. Exemplarily, the amount of the carburizer added can be 5Kg / t·steel, 6Kg / t·steel, 7Kg / t·steel, 8Kg / t·steel, 9Kg / t·steel, 10Kg / t·steel, etc.

[0044] In some embodiments, the amount of activated lime added is 20Kg / t·steel to 30Kg / t·steel, and the amount of bauxite added is 2Kg / t·steel to 4Kg / t·steel.

[0045] S4, smelting the desulfurized molten steel and the second scrap steel in a converter to obtain a converter molten steel;

[0046] In some embodiments, in the converter steel liquid, the mass fraction of carbon is 0.04% to 0.06%, the mass fraction of oxygen is 0.04% to 0.06%, and the mass fraction of nitrogen is 0.002% to 0.004%.

[0047] It should be noted that the positive effect of controlling the mass fraction of carbon in the converter steel liquid to 0.04% to 0.06% is: meeting the conditions for subsequent RH decarburization; too high a mass fraction of carbon causes low oxygen, insufficient oxygen for RH decarburization, a large amount of oxygen blowing, affecting the cycle and temperature drop; too low a mass fraction of carbon causes a short RH carbon-oxygen reaction time, which is not conducive to RH denitrification. Exemplarily, the mass fraction of carbon in the converter steel liquid can be 0.04%, 0.05%, 0.06%, etc.

[0048] The positive effect of controlling the mass fraction of oxygen in the converter steel liquid to 0.04% to 0.06% is that the conditions for subsequent RH decarburization are met. If the mass fraction is too low, the oxygen for RH decarburization will be insufficient, the oxygen blowing amount will be large, and the cycle and temperature drop will be affected. If the mass fraction is too high, the carbon will be low, resulting in a short carbon-oxygen reaction time for RH, which is not conducive to RH denitrification. For example, the mass fraction of oxygen in the converter steel liquid can be 0.04%, 0.05%, 0.06%, etc.

[0049] Positive effects of controlling the mass fraction of nitrogen in the converter steel liquid to 0.002% to 0.004%: N is a harmful element that needs to be strictly controlled in this application, so the N content is reduced as much as possible. Exemplarily, the mass fraction of nitrogen in the converter steel liquid can be 0.002%, 0.003%, 0.0035%, 0.004%, etc.

[0050] S5. The converter molten steel is subjected to RH refining and full protection casting to obtain ultra-low carbon and ultra-low nitrogen steel.

[0051] In some embodiments, the RH refining adopts a vacuum decarburization process, the deep vacuum time of the RH refining is ≥45min, and the pure circulation time after deoxidation is >15min. It should be noted that the deep vacuum time of the RH refining is ≥45min to ensure a stable denitrification effect; the pure circulation time after deoxidation after alloy element adjustment is >15min, which can ensure that inclusions are fully floated and removed, and ensure that the cleanliness of the molten steel meets the requirements of the steel grade.

[0052] In the RH refining process, a vacuum decarburization process is adopted to increase the amount and duration of CO bubble formation, and further improve the nitrogen control ability of the overall process. For example, the deep vacuum time of RH refining can be 45min, 46min, 47min, 49min, 50min, 52min, 55min, etc., and the pure cycle time can be 15.5min, 16min, 16.5min, 17min, 17.5min, 18min, 18.5min, etc.

[0053] Based on a general inventive concept, the present application provides an ultra-low carbon, ultra-low nitrogen steel, in which the mass fraction of nitrogen is ≤0.003%, and the mass fraction of carbon is ≤0.003%.

[0054] The ultra-low carbon and ultra-low nitrogen steel is realized based on the preparation method of the ultra-low carbon and ultra-low nitrogen steel mentioned above. The specific steps of the preparation method of the ultra-low carbon and ultra-low nitrogen steel can refer to the above embodiment. Since the ultra-low carbon and ultra-low nitrogen steel adopts part or all of the technical solutions of the above embodiment, it at least has all the beneficial effects brought by the technical solutions of the above embodiment, which will not be repeated here one by one.

[0055] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[0056] Example 1

[0057] Example 1 provides a method for smelting ultra-low carbon and ultra-low nitrogen steel, which adopts a process route of electric arc furnace → electric furnace steel tapping and carbon matching → LF → converter → RH → continuous casting, and adopts the following smelting process, specifically:

[0058] S11. Add high-quality scrap steel into an electric arc furnace for melting, introduce argon gas into the bottom of the electric furnace for stirring, spray carbon powder and oxygen to the top of the molten pool through an oxygen-burning gun to form foamed slag, add carbon blocks into the molten pool, and obtain molten steel. The terminal temperature of the molten steel is 1595° C., and the mass fraction of carbon in the molten steel is 0.0462%, the mass fraction of oxygen is 0.0692%, the mass fraction of nitrogen is 0.0066%, and the mass fraction of sulfur is 0.0183%;

[0059] S21, in the steel-making process, according to the measured oxygen content in the steel, the amount of deoxidizer added is 0.855 kg based on the mass of 1 ton of molten steel; based on the mass of 1 ton of molten steel, 20 kg of carburizer is used to prepare carbon, and the carrier gas flow rate of bottom blowing and stirring is 1000 NL / min to obtain semi-steel molten steel, and the mass fraction of carbon in the semi-steel molten steel is 1.52%;

[0060] S31, transferring the semi-steel molten steel ladle to a ladle refining furnace for further carbonization and desulfurization and heating, based on the mass of 1 t of semi-steel molten steel, the amount of lime added is 24.92 kg, the amount of bauxite added is 3.11 kg, and the amount of carburizer added is 9.5 kg, to obtain desulfurized molten steel, wherein the mass fraction of aluminum in the desulfurized molten steel is 0.032%, the mass fraction of sulfur is 0.0048%, the mass fraction of carbon is 2.28%, and the temperature of the molten steel is 1653°C;

[0061] S41. The composition and temperature of the desulfurized molten steel are transmitted to the secondary model of the converter, and the amount of scrap steel added to the converter is calculated according to the endpoint requirements of the steel type and the heat of the molten steel. According to the calculation results of the secondary model, the corresponding weight of molten steel and scrap steel are added to the converter, and smelted according to the oxygen content, gun position, auxiliary raw material addition amount calculated by the secondary model to obtain converter molten steel. The mass fraction of carbon at the converter endpoint is 0.0405%, the mass fraction of oxygen at the converter endpoint is 0.0520%, the mass fraction of nitrogen is 0.0024%, and the mass fraction of sulfur is 0.0078%;

[0062] S51, the converter steel liquid is subjected to vacuum decarburization process under RH extreme vacuum, the deep vacuum time is 46 minutes, and the pure circulation time after the alloy elements are adjusted is controlled to be 16.5 minutes, to obtain refined steel liquid, the mass fraction of nitrogen in the refined steel liquid is 0.0028%, the mass fraction of carbon is 0.0019%, and the mass fraction of sulfur is 0.0085%. The refined steel liquid is fully protected and poured to prevent nitrogen from increasing in the molten steel, to obtain low nitrogen steel, the mass fraction of nitrogen is 0.0028%.

[0063] Example 2

[0064] Example 2 provides a method for smelting ultra-low carbon and ultra-low nitrogen steel, which adopts a process route of electric arc furnace → electric furnace steel tapping and carbon mixing → LF → converter → RH → continuous casting, and adopts the following smelting process, specifically:

[0065] S11. Add high-quality scrap steel into an electric arc furnace for melting, introduce argon gas into the bottom of the electric furnace for stirring, spray carbon powder and oxygen to the top of the molten pool through an oxygen-burning gun to form foamed slag, add carbon blocks into the molten pool, and obtain molten steel. The terminal temperature of the molten steel is 1618° C., and the mass fraction of carbon in the molten steel is 0.0695%, the mass fraction of oxygen is 0.0462%, the mass fraction of nitrogen is 0.0056%, and the mass fraction of sulfur is 0.0206%;

[0066] S21, in the steel-making process, according to the measured oxygen content in the steel, the amount of deoxidizer added is 0.57 kg based on the mass of 1 ton of molten steel; based on the mass of 1 ton of molten steel, 19 kg of carburizer is used to prepare carbon, and the carrier gas flow rate of bottom blowing and stirring is 1200 NL / min, and semi-steel molten steel is obtained, and the mass fraction of carbon in the semi-steel molten steel is 1.52%;

[0067] S31, transferring the semi-steel molten steel ladle to a ladle refining furnace for further carbonization and desulfurization and heating, based on the mass of 1 t of semi-steel molten steel, the amount of lime added is 20.3 kg, the amount of bauxite added is 2.12 kg, and the amount of carburizer added is 9.52 kg, to obtain desulfurized molten steel, wherein the mass fraction of aluminum in the desulfurized molten steel is 0.040%, the mass fraction of sulfur is 0.0042%, the mass fraction of carbon is 2.43%, and the temperature of the molten steel is 1658°C;

[0068] S41. The composition and temperature of the desulfurized molten steel are transmitted to the secondary model of the converter, and the amount of scrap steel added to the converter is calculated according to the endpoint requirements of the steel type and the heat of the molten steel. According to the calculation results of the secondary model, the corresponding weight of molten steel and scrap steel are added to the converter, and smelted according to the oxygen content, gun position, auxiliary raw material addition amount calculated by the secondary model to obtain converter molten steel. The mass fraction of carbon at the converter endpoint is 0.0498%, the mass fraction of oxygen at the converter endpoint is 0.0563%, the mass fraction of nitrogen is 0.0030%, and the mass fraction of sulfur is 0.0086%;

[0069] S51, the converter steel liquid is subjected to vacuum decarburization process under RH extreme vacuum, the deep vacuum time is 54min, and the pure circulation time after the alloy elements are adjusted is controlled to be 17.9min, to obtain refined steel liquid, the mass fraction of nitrogen in the refined steel liquid is 0.0023%, the mass fraction of carbon is 0.0018%, and the mass fraction of sulfur is 0.0088%. The refined steel liquid is fully protected and poured to prevent nitrogen from increasing in the molten steel, to obtain low nitrogen steel, the mass fraction of nitrogen is 0.0024%.

[0070] Example 3

[0071] Example 3 provides a method for smelting ultra-low carbon and ultra-low nitrogen steel, which adopts a process route of electric arc furnace → electric furnace steel tapping and carbon mixing → LF → converter → RH → continuous casting, and adopts the following smelting process, specifically:

[0072] S11. Add high-quality scrap steel into an electric arc furnace for melting, introduce argon gas into the bottom of the electric furnace for stirring, spray carbon powder and oxygen to the top of the molten pool through an oxygen-burning gun to form foamed slag, add carbon blocks into the molten pool, and obtain molten steel. The terminal temperature of the molten steel is 1603° C., and the mass fraction of carbon in the molten steel is 0.0767%, the mass fraction of oxygen is 0.0477%, the mass fraction of nitrogen is 0.0078%, and the mass fraction of sulfur is 0.0214%;

[0073] S21, steel-making process: according to the measured oxygen content in the steel, the amount of deoxidizer added is 0.53kg based on the mass of 1t of molten steel; based on the mass of 1t of molten steel, 21.9kg of carburizer is used to prepare carbon, and the carrier gas flow rate of bottom blowing and stirring is 1500NL / min, to obtain semi-steel molten steel, and the mass fraction of carbon in the semi-steel molten steel is 1.81%;

[0074] S31, transferring the semi-steel molten steel ladle to a ladle refining furnace for further carbonization and desulfurization and heating, based on the mass of 1 t of semi-steel molten steel, the amount of lime added is 20.9 kg, the amount of bauxite added is 2.19 kg, and the amount of carburizer added is 6.19 kg, to obtain desulfurized molten steel, wherein the mass fraction of aluminum in the desulfurized molten steel is 0.047%, the mass fraction of sulfur is 0.0045%, the mass fraction of carbon is 2.36%, and the temperature of the molten steel is 1647°C;

[0075] S41, the composition and temperature of the desulfurized molten steel are transmitted to the secondary model of the converter, and the amount of scrap steel added to the converter is calculated according to the endpoint requirements of the steel type and the heat of the molten steel. According to the calculation results of the secondary model, the corresponding weight of molten steel and scrap steel are added to the converter, and smelting is performed according to the oxygen content, gun position, auxiliary raw material addition amount, etc. calculated by the secondary model to obtain converter molten steel. The mass fraction of carbon at the converter endpoint is 0.0586%, the mass fraction of oxygen at the converter endpoint is 0.0492%, the mass fraction of nitrogen is 0.0026%, and the mass fraction of sulfur is 0.0063%.

[0076] S51, the converter steel liquid is subjected to vacuum decarburization process under RH extreme vacuum, the deep vacuum time is 48 minutes, and the pure circulation time after the alloy elements are adjusted is controlled to be 16.8 minutes, to obtain refined steel liquid, the mass fraction of nitrogen in the refined steel liquid is 0.0025%, the mass fraction of carbon is 0.0015%, and the mass fraction of sulfur is 0.0071%. The refined steel liquid is fully protected and poured to prevent nitrogen from increasing in the molten steel, to obtain low-nitrogen steel, the mass fraction of nitrogen is 0.0026%.

[0077] Comparative Example 1

[0078] Comparative Example 1 provides a high-strength steel smelting method, which adopts an arc furnace → RH → continuous casting process route and adopts the following smelting process, specifically:

[0079] S11. Add high-quality scrap steel into an electric arc furnace and melt it by electricity. During this period, introduce argon gas into the bottom of the electric furnace for stirring. Use an oxygen-burning gun to spray carbon powder and oxygen to the top of the molten pool to form foamed slag to obtain molten steel. The terminal temperature of the molten steel is controlled to be 1664°C, the mass fraction of terminal carbon is 0.059%, the mass fraction of terminal oxygen is 0.0824%, and the mass fraction of terminal nitrogen is 0.0063%.

[0080] S21. The molten steel is subjected to a natural decarburization process under RH extreme vacuum, and the pure circulation time is ensured to be 4 minutes, to obtain refined molten steel, wherein the mass fraction of nitrogen in the refined molten steel is 0.0045%, the mass fraction of carbon is 0.0014%, and the mass fraction of sulfur is 0.0075%. The refined molten steel is subjected to full protection pouring to prevent nitrogen addition in the molten steel, to obtain low-nitrogen steel, wherein the mass fraction of nitrogen in the low-nitrogen steel is 0.0048%.

[0081] Comparative Example 2

[0082] Comparative Example 2 provides a high-strength steel smelting method, which adopts an arc furnace → RH → continuous casting process route and adopts the following smelting process, specifically:

[0083] S11. Add high-quality scrap steel into an electric arc furnace and melt it by electricity. During this period, introduce argon gas into the bottom of the electric furnace for stirring. Use an oxygen-burning gun to spray carbon powder and oxygen to the top of the molten pool to form foamed slag to obtain the first molten steel. The terminal temperature of the molten steel is controlled to be 1675°C, the mass fraction of terminal carbon is 0.076%, the mass fraction of terminal oxygen is 0.0675%, and the mass fraction of terminal nitrogen is 0.0072%.

[0084] S21. A natural decarburization process is adopted under RH extreme vacuum, and the pure circulation time is guaranteed to be 4.5 minutes to obtain refined molten steel, in which the mass fraction of nitrogen is 0.0050%, the mass fraction of carbon is 0.0025%, and the mass fraction of sulfur is 0.0059%. The refined molten steel is fully protected and poured to prevent nitrogen from increasing in the molten steel, and low-nitrogen steel is obtained, in which the mass fraction of nitrogen is 0.0052%.

[0085] Comparative Example 3

[0086] Comparative Example 3 provides a high-strength steel smelting method, which adopts an arc furnace → RH → continuous casting process route and adopts the following smelting process, specifically:

[0087] S11. Add high-quality scrap steel into an electric arc furnace and melt it by electricity. During this period, introduce argon gas into the bottom of the electric furnace for stirring. Use an oxygen-burning gun to spray carbon powder and oxygen to the top of the molten pool to form foamed slag to obtain the first molten steel. The terminal temperature of the molten steel is controlled to be 1658°C, the mass fraction of terminal carbon is 0.065%, the mass fraction of terminal oxygen is 0.0732%, and the mass fraction of terminal nitrogen is 0.0078%.

[0088] S21. A natural decarburization process is adopted under RH extreme vacuum, and the pure circulation time is guaranteed to be 4.2 minutes to obtain refined molten steel, in which the mass fraction of nitrogen is 0.0053%, the mass fraction of carbon is 0.0019%, and the mass fraction of sulfur is 0.0082%. The refined molten steel is fully protected and poured to prevent nitrogen from increasing in the molten steel, and low-nitrogen steel is obtained, in which the mass fraction of nitrogen is 0.0053%.

[0089] In addition, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0090] (1) In the embodiment of the present invention, the electric furnace is coupled with the LF furnace to improve the stability of carbon addition, create stable conditions for converter denitrification, and at the same time, a certain amount of low-priced high-sulfur scrap steel can be added, thereby reducing production costs.

[0091] (2) 100% of the raw materials are recycled scrap steel with near-zero carbon emissions, minimizing carbon dioxide emissions.

[0092] (3) In the embodiment of the present invention, a series process is matched with a converter, and a large amount of nitrogen is removed through the violent carbon-oxygen reaction in the converter, ensuring that the nitrogen content in the low-nitrogen steel is ≤30ppm, meeting the quality requirements of automobile steel.

[0093] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for smelting ultra-low carbon and ultra-low nitrogen steel, characterized in that: The method comprises: The first scrap steel is smelted in an electric arc furnace to obtain molten steel, wherein the mass fraction of carbon is 0.04% to 0.08%, the mass fraction of oxygen is 0.045% to 0.085%, the mass fraction of nitrogen is 0.005% to 0.008%, and the mass fraction of sulfur is 0.015% to 0.025%; Deoxidizing and carbonizing the molten steel to obtain semi-steel molten steel; Carburizing, desulfurizing and heating the semi-steel molten steel by LF refining to obtain a desulfurized molten steel, wherein the mass fraction of aluminum in the desulfurized molten steel is ≥0.030%, the mass fraction of carbon is 2% to 2.5%, the mass fraction of sulfur is ≤0.0050%, and the temperature of the desulfurized molten steel is 1640° C. to 1660° C.; The desulfurized molten steel and the second scrap steel are subjected to converter smelting to obtain converter molten steel, wherein the mass fraction of carbon is 0.04% to 0.06%, the mass fraction of oxygen is 0.04% to 0.06%, and the mass fraction of nitrogen is 0.002% to 0.004%; The converter molten steel is subjected to RH refining and full protection casting to obtain ultra-low carbon and ultra-low nitrogen steel, wherein the mass fraction of nitrogen in the ultra-low carbon and ultra-low nitrogen steel is ≤0.003%, and the mass fraction of carbon is ≤0.003%; The raw materials added for the carburization include: 5Kg / t·steel to 10Kg / t·steel carburizer, and the raw materials added for the desulfurization include: Active lime, wherein the amount of active lime added L1 and the mass fraction of oxygen [O] in the semi-steel liquid satisfy the following relationship: 3.5×[O] / 0.01%≤L1≤4.5×[O] / 0.01%, wherein the unit of L1 is Kg / t·steel; and Bauxite, the amount of bauxite added L2 and the mass fraction of oxygen [O] in the semi-steel molten steel satisfy the following relationship: 0.44×[O] / 0.01%≤L2≤0.47×[O] / 0.01%, wherein the unit of L2 is Kg / t·steel.

2. The method according to claim 1, characterized in that The temperature of the molten steel is 1590°C to 1620°C.

3. The method according to claim 1, characterized in that The step of deoxidizing and carbonizing the molten steel to obtain semi-steel molten steel comprises: Deoxidizer and carburizer are added into the molten steel, and bottom blowing and stirring are performed to obtain semi-steel liquid; the amount of the deoxidizer added is 0.5Kg / t·steel to 1Kg / t·steel, the amount of the carburizer added is 14Kg / t·steel to 24Kg / t·steel, and the carrier gas flow rate of the bottom blowing and stirring is 1000NL / min to 1500NL / min.

4. The method according to claim 1, characterized in that: The RH refining adopts a vacuum decarburization process, and the RH refining includes the following process parameters: deep vacuum time ≥ 45 min, and pure cycle time after deoxidation > 15 min.

5. An ultra-low carbon and ultra-low nitrogen steel prepared by the method according to any one of claims 1 to 4.

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