Method for producing interstitial-free steel by adopting full scrap steel and electric arc furnace process

Abstract

The invention discloses a method for producing interstitial-free steel by adopting a full scrap steel and electric arc furnace process, which comprises the steps of scrap steel proportioning, electric arc furnace steelmaking, LF (ladle furnace) refining, RH (relative humidity) refining and slab continuous casting, industrial batch production of high-grade and low-carbon-emission interstitial-free steel with C less than or equal to 0.0025%, N less than or equal to 0.005% and O less than or equal to 0.004% is realized by adopting a short-flow process, and a finished product has better strength and formability and is suitable for large-scale production. The technical problem that an electric arc furnace produces ultra-low carbon steel and ultra-low nitrogen steel is solved, the technical blank in the field is filled, compared with a conventional blast furnace and converter long-process smelting method, the method greatly reduces carbon emission in the interstitial-free steel production process, and obvious environmental benefits are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a method for producing interstitial-free atomic steel by adopting a full scrap steel + electric arc furnace process. Background Art

[0002] Interstitial-free (IF) steel is a type of steel developed by controlling the interstitial atoms C, N and impurity elements in the steel that seriously endanger the deep drawing performance to the lowest possible level, and eliminating the interstitial atoms in the ferrite through alloying with Nb or Ti elements, thereby obtaining ultra-deep drawing performance. It is a new generation of deep drawing steel following the first generation of rimmed steel and the second generation of aluminum-killed steel. It has very excellent deep drawing performance and is widely used as raw materials for stamping parts such as automotive panels and home appliance panels.

[0003] At present, domestic and foreign countries mainly adopt the conventional long process of blast furnace + converter to produce IF steel. The main processes include iron ore sintering, pelletizing, blast furnace ironmaking, oxygen converter steelmaking, etc. From iron ore to qualified continuous casting billets of IF steel, the production process is very long, involving many processes, large carbon emissions, and is not environmentally friendly.

[0004] With the continuous advancement of the "carbon peak and carbon neutrality" work, the steel industry is facing tremendous pressure for low-carbon transformation. Effectively reducing carbon emissions in the steel production process has become a major problem that the steel industry and even the country need to solve urgently. Compared with the long process of blast furnace + converter, the short process of steelmaking with all scrap steel + electric arc furnace can reduce energy consumption per ton of steel by about 50% and carbon emissions by about 70%. Therefore, the development of short-process steelmaking with all scrap steel + electric arc furnace is one of the major trends in the future development of my country's steel industry.

[0005] However, compared with oxygen converter steelmaking, electric arc furnace steelmaking will inevitably ionize nitrogen in the air due to the use of electric arc to heat scrap steel, resulting in an increase in nitrogen in the molten steel, making it difficult to produce ultra-low nitrogen steel, especially IF steel. At present, there is no relevant technology for producing IF steel using all scrap steel + electric arc furnace at home and abroad. Therefore, research on the all scrap steel + electric arc furnace steelmaking process has been conducted, and a method for producing IF steel using the all scrap steel + electric arc furnace process has been developed to reduce dependence on the blast furnace + converter process and reduce carbon emissions, which has become a technical problem that needs to be urgently solved in this field. Summary of the invention

[0006] In order to solve the technical problems existing in the above-mentioned prior art, the present invention provides a method for producing interstitial-free steel by using a full scrap steel + electric arc furnace process, comprising the following steps:

[0007] (1) Scrap steel ratio

[0008] The amount of scrap steel added is controlled to ensure that the mass percentage of the chemical composition in the molten steel after the electric arc furnace is melted and cleared meets the following requirements: P≤0.015%, S≤0.015%, Al≤0.08%, Cr≤0.05%, Ni≤0.05%, Mo≤0.03%, Cu≤0.05%, N≤0.010%, B≤0.0005%, Sn≤0.01%, Nb≤0.01%, V≤0.01%, Ti≤0.01%;

[0009] (2) Electric Arc Furnace Steelmaking

[0010] The scrap steel with good proportion is loaded into the electric arc furnace, and the power is turned on to increase the temperature. The slag blocking operation is carried out during the steel tapping process to control the slag thickness to ≤40mm. The composition of the steel tapped from the electric arc furnace is controlled as follows:

[0011] C To Mn P S Al Cr ≤0.04 ≤0.04 ≤0.10 ≤0.013 ≤0.015 ≤0.07 ≤0.05 In Know Cu N B Sn ≤0.05 ≤0.03 ≤0.05 ≤0.010 ≤0.0005 ≤0.010

[0012] (3) LF refining

[0013] The ladle enters the LF station, and is powered on for heating. During the heating process, slag-forming agent is added to form slag. Aluminum wire or aluminum particles are added to the molten steel for pre-deoxidation. The amount of aluminum wire or aluminum particles added must ensure that the O content in the molten steel is 600-700ppm. Bottom-blown argon is used to stir the molten steel throughout the LF refining process. Before the LF leaves the station, aluminum-containing pre-melted steel slag modifier is evenly added to the slag surface on the top of the ladle. After adding, argon is blown from the bottom for weak stirring for 1-2 minutes before leaving the station.

[0014] (4) RH refining

[0015] The ladle enters the RH station, evacuates, and performs molten steel circulation and decarburization operations. After decarburization, Al alloy, electrolytic manganese, ferrotitanium, and ferroniobium alloy are added to the molten steel for alloying. After alloying, the circulation continues for ≥20 minutes. After the circulation is completed, the air breaking operation is performed. After the RH air breaking, the molten steel is blown with argon gas and weakly stirred before exiting the station. The RH steel composition control is:

[0016] C To Mn P S Al Of Cr ≤0.0015 ≤0.03 0.10～0.20 ≤0.013 ≤0.015 0.04～0.06 0.04～0.08 ≤0.05 In Know Cu N B Sn Nb V ≤0.05 ≤0.05 ≤0.05 ≤0.005 ≤0.0005 ≤0.01 ≤0.01 ≤0.01

[0017] (5) Slab continuous casting

[0018] The continuous casting tundish uses an ultra-low carbon covering agent with a total carbon content of ≤1.5%, and the crystallizer protective slag uses an ultra-low carbon protective slag with a total carbon content of ≤2.0%. Protective casting is implemented during the continuous casting ladle pouring process. The superheat of the continuous casting tundish is controlled at 20-30°C, and the continuous casting drawing speed is controlled at 1.10-1.15m / min.

[0019] Preferably, in the slab continuous casting process, the first tundish furnace uses other ultra-low carbon steel with C≤0.0050% for casting, and the second tundish furnace and subsequent furnaces use molten steel produced by the scrap steel proportioning, electric arc furnace steelmaking, LF refining, and RH refining processes for casting.

[0020] As a specific implementation method, in the above-mentioned method for producing interstitial-free atomic steel using all scrap steel + electric arc furnace process, in the scrap steel proportioning process, scrap steel accounts for ≥95% of all smelting raw materials, wherein the scrap steel includes cold plate briquette scrap steel with a weight percentage of ≥45%, and / or special grade crushed material with a weight percentage of ≥30%, and / or pure iron scrap steel with a weight percentage of ≥10%. The proportion of scrap steel should meet the characteristic elements in the molten steel after electric arc furnace smelting: P≤0.015%, S≤0.015%, Al≤0.08%, Cr≤0.05%, Ni≤0.05%, Mo≤0.03%, Cu≤0.05%, N≤0.010%, B≤0.0005%, Sn≤0.01%, Nb≤0.01%, V≤0.01%, Ti≤0.01%.

[0021] Furthermore, in the above-mentioned method of producing gapless atomic steel using all-scrap steel + electric arc furnace process, in the electric arc furnace steelmaking process, lime, fluorite and red mud balls are added during the smelting process to form slag, coke, ferrosilicon and silicon carbide are added during the smelting process to form slag, and after power is supplied to increase the temperature and melt, power is supplied at a low gear and oxygen is blown into the molten pool to stir, lime and fluorite are added again to increase the slag basicity, oxygen is blown to dephosphorize, and the steel is tapped after the slag is released.

[0022] Furthermore, in the above-mentioned method of producing interstitial-free atomic steel using all-scrap steel + electric arc furnace process, in the LF refining process, 800-1000 kg of lime and 200-400 kg of fluorite are added during the heating process to adjust the slag condition, 150-300 m of aluminum wire is added for pre-deoxidation, the total flow rate of bottom blowing argon is 100-500 NL / min, and the LF outlet temperature of the molten steel is controlled to be 1660-1670°C.

[0023] Furthermore, in the above method for producing interstitial-free steel using the all-scrap steel + electric arc furnace process, in the RH refining step:

[0024] The ladle enters the RH station, starts to evacuate and circulate the liquid steel. When the vacuum degree reaches ≤150Pa, start timing, and the vacuum circulation lasts for 6 to 10 minutes for decarburization operation.

[0025] After decarburization is completed, the steel liquid is sampled and analyzed for composition. When the mass percentage of C in the steel liquid is ≤0.0015%, a high-precision oxygen meter is used to determine the oxygen content in the steel liquid. The Al content required for deoxidation and alloying is calculated based on the O content, and the required amount of Al alloy is added to the steel liquid, and then circulated for 3 to 6 minutes.

[0026] According to the interstitial atomic steel target composition, electrolytic manganese, ferrotitanium and ferroniobium alloys are added for alloying, and after circulating for 3 to 4 minutes, the steel liquid composition is sampled and analyzed, and the steel composition is fine-tuned based on the interstitial atomic steel target composition;

[0027] After alloying is completed, when the vacuum degree reaches ≤150Pa, continue to circulate for ≥20 minutes. After the cycle is completed, perform the air-breaking operation. During the air-breaking operation, when the vacuum tank leaves the molten steel surface, quickly add an appropriate amount of aluminum-containing steel slag modifier to the molten steel surface;

[0028] The outlet temperature of molten steel at RH is controlled at 1595~1610℃.

[0029] Furthermore, in the above method for producing interstitial-free steel using the all-scrap steel + electric arc furnace process, in the slab continuous casting process:

[0030] Before continuous casting, the tundish and nozzle are baked online for 2 hours and no longer than 4 hours. The cooling time of the ladle fork arm is controlled to be ≥5 minutes.

[0031] The crystallizer liquid level fluctuation requirement is ±5mm, the stopper argon flow rate is controlled to ≤10NL / min, dynamic light pressure and roller electromagnetic stirrer are used to control center loosening and center segregation. The dynamic light pressure process parameters are: pressure is applied in the range of 50-95% solid phase ratio in the two-phase zone, the total pressure reduction is 3.2mm, and the roller electromagnetic stirring process parameters are: 300A, 6Hz, no reversing.

[0032] In addition, the present invention also provides an interstitial-free steel, the chemical composition of the interstitial-free steel being as follows by mass percentage: C≤0.0025%, Si≤0.03%, Mn≤0.25%, P≤0.015%, S≤0.015%, Al≤0.08%, Ti: 0.03-0.10%, Cr≤0.05%, Ni≤0.05%, Mo≤0.03%, Cu≤0.05%, N≤0.005%, B≤0.0005%, Sn≤0.01%, Nb≤0.01%, V≤0.01%, and the rest being Fe and unavoidable impurities.

[0033] The method of the present invention for producing interstitial-free steel by adopting the whole scrap steel + electric arc furnace process has the following advantages and beneficial effects: the batch production of high-grade, low-carbon IF steel with C≤0.0025%, N≤0.005%, and O≤0.004% is realized by a short process, and the finished product has good strength and forming performance, which solves the technical problem of producing ultra-low carbon steel and ultra-low nitrogen steel by electric arc furnace, and fills the technical gap in this field. Compared with the conventional blast furnace + converter long process smelting method, the method of the present invention greatly reduces the carbon emission in the IF steel production process, and has obvious environmental benefits. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0035] The present invention aims to develop an industrial smelting method for producing high-grade, low-carbon emission interstitial atom-free steel using all-scrap steel + electric arc furnace process, to achieve mass production of high-grade IF steel with C≤0.0025%, N≤0.005%, and O≤0.004%, to solve the technical difficulties of producing ultra-low carbon steel and ultra-low nitrogen steel in electric arc furnaces, and to significantly reduce carbon emissions in the IF steel production process.

[0036] In the method of the present invention for producing interstitial-free atomic steel by adopting all scrap steel + electric arc furnace process, "all scrap steel" means that scrap steel accounts for ≥95% of all smelting raw materials, and the scrap steel includes but is not limited to cold plate briquette scrap steel, special grade crushed material, pure iron scrap steel, and silicon steel scrap steel.

[0037] Specifically, the method of producing interstitial-free steel using the full scrap steel + electric arc furnace process of the present invention comprises the following steps:

[0038] (1) Scrap steel ratio

[0039] The amount of scrap steel added is controlled to ensure that the mass percentage of the chemical composition in the molten steel after melting in the electric arc furnace meets the following requirements: P≤0.015%, S≤0.015%, Al≤0.08%, Cr≤0.05%, Ni≤0.05%, Mo≤0.03%, Cu≤0.05%, N≤0.010%, B≤0.0005%, Sn≤0.01%, Nb≤0.01%, V≤0.01%, Ti≤0.01%.

[0040] (2) Electric Arc Furnace Steelmaking

[0041] The scrap steel with good proportion is loaded into the electric arc furnace, the electrode is lowered, and the power is turned on to increase the temperature. During the steelmaking process of the electric arc furnace, an appropriate amount of limestone, coke and other auxiliary materials can be added to the electric arc furnace, and an appropriate amount of oxygen is introduced to assist in heating and melting. During the steel-making process, slag blocking operation is performed to avoid slag as much as possible, and the slag thickness is controlled to be ≤40mm. No deoxidation or alloying operations are performed during the steel-making process to avoid rephosphorization of steel-making.

[0042] The composition control of the steel tapping from the electric arc furnace is shown in Table 1 below:

[0043] Table 1 Composition of steel produced from electric arc furnace (mass percentage, the rest is Fe and unavoidable impurities)

[0044] C To Mn P S Al Cr ≤0.04 ≤0.04 ≤0.10 ≤0.013 ≤0.015 ≤0.07 ≤0.05 In Know Cu N B Sn ≤0.05 ≤0.03 ≤0.05 ≤0.010 ≤0.0005 ≤0.010

[0045] (3) LF refining

[0046] The ladle enters the LF station for temperature measurement. According to the temperature of the molten steel, the electrode is used to send electricity to heat up. During the heating process, an appropriate amount of lime, fluorite and other slag-forming agents are added to make slag. An appropriate amount of aluminum wire or aluminum particles can be added to the molten steel for pre-deoxidation, but it is necessary to ensure that the O content in the molten steel is 600-700ppm for RH decarburization. Bottom blowing argon is used to stir the molten steel throughout the LF refining process. Before the LF leaves the station, an appropriate amount of aluminum-containing pre-melted steel slag modifier is evenly added to the slag surface of the top of the ladle. After adding, argon is blown weakly and stirred for 1-2 minutes before leaving the station. The temperature of the molten steel at the LF station is 1660-1670℃. The molten steel only undergoes heating and slag-making operations in the LF process, without desulfurization or alloying.

[0047] (4) RH refining

[0048] The ladle enters the RH station for temperature measurement, vacuuming, and steel liquid circulation and decarburization operations. After decarburization is completed, Al alloy and electrolytic manganese, ferrotitanium, ferroniobium and other alloys are added to the steel liquid for alloying according to the target composition of IF steel. After alloying is completed, the circulation continues for ≥20 minutes. After the circulation is completed, the vacuum operation is performed. The temperature of the steel liquid at the RH station is 1595~1610℃.

[0049] In the RH refining process, the vacuum lifting gas is argon, and the lifting gas flow rate is 90-100% of the limit flow rate. The RH steel composition control is shown in Table 2 below:

[0050] Table 2RH steel composition (mass percentage, the rest is Fe and unavoidable impurities)

[0051] C To Mn P S Al Of Cr ≤0.0015 ≤0.03 0.10～0.20 ≤0.013 ≤0.015 0.04～0.06 0.04～0.08 ≤0.05 In Know Cu N B Sn Nb V ≤0.05 ≤0.03 ≤0.05 ≤0.005 ≤0.0005 ≤0.01 ≤0.01 ≤0.01

[0052] (5) Slab continuous casting

[0053] The continuous casting tundish uses ultra-low carbon covering agent with a total carbon content of ≤1.5%, and the mold protection slag uses ultra-low carbon protection slag with a total carbon content of ≤2.0%. The continuous casting ladle is cast in protective casting during the pouring process, and the increase of N and C is strictly controlled. The superheat of the continuous casting tundish is implemented at 20-30℃. The continuous casting and drawing speed of the double-strand continuous casting machine is controlled at 1.10-1.15m / min.

[0054] In particular, since the molten steel will directly contact various carbon-containing raw and auxiliary materials in the tundish and crystallizer during the continuous casting process, such as the tundish covering agent, the tundish coating material, the crystallizer protective slag, etc., the C element in the carbon-containing raw and auxiliary materials will inevitably transfer to the molten steel, resulting in an increase in the C content of the molten steel. Generally speaking, the C content of the first tundish furnace in the continuous casting process is more obvious, usually 7 to 12 ppm, and the C content will be significantly reduced from the second furnace. The 7 to 12 ppm C content of the first tundish furnace is likely to cause the C content of the molten steel in the final smelting analysis to exceed 0.0025%. Therefore, in order to ensure the smelting of high-grade interstitial-free steel, the continuous casting process does not increase C or increases C less. When the slab is continuously cast, the first tundish furnace uses other ultra-low carbon steel with C ≤ 0.0050% for casting, and the second tundish furnace and subsequent furnaces use the molten steel produced by the above-mentioned scrap steel ratio, electric arc furnace steelmaking, LF refining, and RH refining processes for casting.

[0055] In the slab continuous casting process, when the remaining weight of the molten steel in the continuous casting ladle is 40-60% of the total weight of the molten steel in the ladle, the chemical composition of the produced IF steel can be obtained by sampling in the tundish, as shown in Table 3 below:

[0056] Table 3 Chemical composition of IF steel (mass percentage, the rest is Fe and unavoidable impurities)

[0057] C To Mn P S Al Of Cr ≤0.0025 ≤0.03 ≤0.25 ≤0.015 ≤0.015 ≤0.08 0.03～0.10 ≤0.05 In Know Cu N B Sn Nb V ≤0.05 ≤0.03 ≤0.05 ≤0.005 ≤0.0005 ≤0.01 ≤0.01 ≤0.01

[0058] The following is a description of the method for producing interstitial-free steel by using all scrap steel + electric arc furnace process of the present invention in conjunction with Example 1 and Example 2. The method for producing interstitial-free steel by using all scrap steel + electric arc furnace process of Examples 1 and 2 of the present invention is carried out according to the aforementioned scrap steel proportioning, electric arc furnace steelmaking, LF refining, RH refining, slab continuous casting and other processes, and the specific implementation process is as follows:

[0059] In the scrap steel proportioning process, the scrap steel proportioning conditions of Example 1 and Example 2 are shown in Table 4 below:

[0060] Table 4 Scrap steel ratio composition of Examples 1 and 2

[0061]

[0062] In the steelmaking process of the electric arc furnace, a basket is used to load the scrap steel with good proportion into the electric arc furnace, the electrode is lowered, and the power is turned on to increase the temperature. During the smelting process, auxiliary materials such as lime, fluorite, and red mud balls are added to make slag. During the smelting process, coke, ferrosilicon, and silicon carbide are added to make slag. After the power is supplied to heat and melt, the power is supplied at a small gear and an appropriate amount of oxygen is blown into the molten pool to ensure that the temperature in the furnace is uniform and there is no sticky steel. An appropriate amount of lime and fluorite are added again to increase the slag alkalinity, oxygen is blown to dephosphorize, and the steel is tapped after the slag is released. No deoxidation or alloying operations are performed during the steel tapping process to avoid phosphorus return during steel tapping. Slag blocking operations are performed during the steel tapping process to avoid slag as much as possible and control the slag thickness to ≤40mm. If the slag blocking fails during the steel tapping process and the amount of slag is large, the slag removal operation can be performed during the steel tapping process, and the slag thickness after slag removal is required to be ≤40mm.

[0063] The composition of steel tapped from an electric arc furnace is controlled as shown in Table 5 below:

[0064] Table 5 Composition of steel produced from electric arc furnace (mass percentage, the rest is Fe and unavoidable impurities)

[0065]

[0066] In the LF refining process, the ladle enters the LF station for temperature measurement. According to the temperature of the molten steel, the electrode is used to send electricity to raise the temperature. During the heating process, 800-1000kg of lime and 200-400kg of fluorite are added to adjust the slag condition. 150-300m of aluminum wire is added for pre-deoxidation to ensure that 600-700ppm of oxygen is retained in the molten steel for subsequent RH decarburization. Bottom-blown argon is used to stir the molten steel throughout the LF refining process. The total argon flow rate is 100-500NL / min. Before leaving the LF station, an appropriate amount of aluminum-containing pre-melted steel slag modifier is evenly added to the slag surface on the top of the ladle. After adding, bottom-blown argon is weakly stirred for 1-2 minutes before leaving the station. The molten steel temperature at the LF station is 1660-1670℃.

[0067] In the RH refining process, the ladle enters the RH station for temperature measurement, starts to evacuate and circulate the molten steel. When the vacuum degree reaches ≤150Pa, the timing starts, and the vacuum cycle is 6 to 10 minutes for decarburization. After decarburization is completed, the composition of the molten steel is sampled and analyzed. When the mass percentage of C in the molten steel is ≤0.0015%, a high-precision oxygen meter is used to determine the oxygen content in the molten steel. The Al content required for deoxidation and alloying is calculated based on the O content, and the required amount of Al alloy is added to the molten steel, and then circulated for 3 to 6 minutes. According to the target composition of IF steel, an appropriate amount of electrolytic manganese, ferrotitanium, ferroniobium and other alloys are added for alloying. After circulating for 3 to 4 minutes, the composition of the molten steel is sampled and analyzed, and the steel composition is fine-tuned based on the target composition of IF steel. After alloying, when the vacuum degree reaches ≤150Pa, continue to circulate for ≥20 minutes. After the cycle is completed, the vacuum breaking operation is carried out. During the vacuum breaking operation, when the vacuum tank leaves the molten steel surface, an appropriate amount of aluminum-containing steel slag modifier is quickly added to the molten steel surface to improve the oxidizability of the slag in direct contact with the molten steel and reduce the TFe content in the slag. The molten steel outlet temperature at RH is 1595~1610℃.

[0068] The RH tapping composition is controlled as shown in Table 6 below:

[0069] Table 6RH steel composition (mass percentage, the rest is Fe and unavoidable impurities)

[0070]

[0071] In the slab continuous casting process, the tundish and nozzle are baked online before continuous casting. The baking time is 2 hours and no longer than 4 hours. The ladle fork arm calming time is ≥5 minutes. The continuous casting tundish uses ultra-low carbon covering agent with a total carbon content of ≤1.5%, and the crystallizer protective slag uses ultra-low carbon protective slag with a total carbon content of ≤2.0%. Protective casting is implemented during the continuous casting ladle pouring process, and the increase of N and C is strictly controlled. The superheat of the continuous casting tundish is controlled at 20-30℃, and the continuous casting steel drawing speed of the double-strand continuous casting machine is 20-30℃. The degree of control is 1.10-1.15m / min, the crystallizer liquid level fluctuation requirement is ±5mm, the stopper argon flow rate is ≤10NL / min to reduce the disturbance of argon to the crystallizer liquid level, dynamic light pressure and roller electromagnetic stirrer are put into use to control the center loosening and center segregation, and the dynamic light pressure process parameters are: applying pressure in the solid phase ratio range of 50-95% in the two-phase region, the total pressure reduction is 3.2mm, and the roller electromagnetic stirring process parameters are: 300A, 6Hz, no reversing.

[0072] In addition, during continuous casting of slabs, the first tundish furnace uses other ultra-low carbon steel with C≤0.0050% for casting, and the second tundish furnace and subsequent furnaces use molten steel produced by the above-mentioned scrap steel ratio, electric arc furnace steelmaking, LF refining, and RH refining processes for casting.

[0073] When the remaining molten steel in the ladle is 90-120 tons, a smelting analysis sample is taken in the tundish, and the chemical composition of the produced IF steel can be obtained, as shown in Table 7 below:

[0074] Table 7 Chemical composition of IF steel (mass percentage, the rest is Fe and unavoidable impurities)

[0075]

[0076] In summary, the present invention provides an industrial smelting method for producing high-grade, low-carbon emission interstitial-free steel by all-scrap steel + electric arc furnace process, which mainly includes a scrap steel proportioning process, an electric arc furnace steelmaking process, an LF refining process, an RH refining process, and a slab continuous casting process. The short-process technology is used to realize the batch production of high-grade IF steel with C≤0.0025%, N≤0.005%, and O≤0.004%. The finished product has good strength and forming properties, solves the technical difficulties of producing ultra-low carbon steel and ultra-low nitrogen steel in an electric arc furnace, and fills the technical gap in this field. Compared with the conventional blast furnace + converter long-process smelting method, the method of the present invention greatly reduces the carbon emissions in the IF steel production process and has obvious environmental benefits.

[0077] It should be noted that, in this article, the term "comprise" or any other variation thereof is intended to cover non-exclusive inclusion, so that an article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such article or device.

[0078] It should also be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. An interstitial-free steel, characterized in that: The chemical composition of the interstitial-free steel is as follows by mass percentage: C≤0.0025%, Si≤0.03%, Mn≤0.25%, P≤0.015%, S≤0.015%, Al≤0.08%, Ti: 0.03-0.10%, Cr≤0.05%, Ni≤0.05%, Mo≤0.03%, Cu≤0.05%, N≤0.005%, B≤0.0005%, Sn≤0.01%, Nb≤0.01%, V≤0.01%, and the rest is Fe and unavoidable impurities.

2. A method for producing interstitial-free atomic steel using all-scrap steel + electric arc furnace process, characterized in that: The method comprises the following steps: (1) Scrap steel ratio The amount of scrap steel added is controlled to ensure that the mass percentage of the chemical composition in the molten steel after the electric arc furnace is melted and cleared meets the following requirements: P≤0.015%, S≤0.015%, Al≤0.08%, Cr≤0.05%, Ni≤0.05%, Mo≤0.03%, Cu≤0.05%, N≤0.010%, B≤0.0005%, Sn≤0.01%, Nb≤0.01%, V≤0.01%, Ti≤0.01%; (2) Electric Arc Furnace Steelmaking The scrap steel with good proportion is loaded into the electric arc furnace, and the power is turned on to increase the temperature. The slag blocking operation is carried out during the steel tapping process to control the slag thickness to ≤40mm. The composition of the steel tapped from the electric arc furnace is controlled as follows: (3) LF refining The ladle enters the LF station, and is powered on for heating. During the heating process, slag-forming agent is added to form slag. Aluminum wire or aluminum particles are added to the molten steel for pre-deoxidation. The amount of aluminum wire or aluminum particles added must ensure that the O content in the molten steel is 600-700ppm. Bottom-blown argon is used to stir the molten steel throughout the LF refining process. Before the LF leaves the station, aluminum-containing pre-melted steel slag modifier is evenly added to the slag surface on the top of the ladle. After adding, argon is blown from the bottom for weak stirring for 1-2 minutes before leaving the station. (4) RH refining The ladle enters the RH station, evacuates, and performs molten steel circulation and decarburization operations. After decarburization, Al alloy, electrolytic manganese, ferrotitanium, and ferroniobium alloy are added to the molten steel for alloying. After alloying, the deep vacuum condition is maintained for circulation for ≥ 20 minutes. After the circulation is completed, the air breaking operation is performed. After the RH air breaking, the molten steel is blown with argon gas for weak stirring and then discharged from the station. The RH steel composition is controlled as follows: (5) Slab continuous casting The continuous casting tundish uses an ultra-low carbon covering agent with a total carbon content of ≤1.5%, and the crystallizer protective slag uses an ultra-low carbon protective slag with a total carbon content of ≤2.0%. Protective casting is implemented during the continuous casting ladle pouring process. The superheat of the continuous casting tundish is controlled at 20-30°C, and the continuous casting drawing speed is controlled at 1.10-1.15m / min.

3. The method for producing interstitial-free steel using the full scrap steel + electric arc furnace process according to claim 2, characterized in that: In the scrap steel proportioning process, scrap steel accounts for ≥95% of all smelting raw materials, among which scrap steel includes cold plate briquette scrap steel with a weight percentage of ≥45%, and / or special grade crushed material with a weight percentage of ≥30%, and / or pure iron scrap steel with a weight percentage of ≥10%. The proportion of scrap steel should meet the characteristic elements in the molten steel after electric arc furnace smelting: P≤0.015%, S≤0.015%, Al≤0.08%, Cr≤0.05%, Ni≤0.05%, Mo≤0.03%, Cu≤0.05%, N≤0.010%, B≤0.0005%, Sn≤0.01%, Nb≤0.01%, V≤0.01%, Ti≤0.01%.

4. The method for producing interstitial-free steel using the full scrap steel + electric arc furnace process according to claim 2, characterized in that: In the electric arc furnace steelmaking process, lime, fluorite and red mud balls are added to form slag during the smelting process. Coke, ferrosilicon and silicon carbide are added to form slag. After power is supplied to increase the temperature and melt the steel, power is supplied at a low gear and oxygen is blown into the molten pool to stir it. Lime and fluorite are added again to increase the basicity of the slag, oxygen is blown to remove phosphorus, and the steel is tapped after the slag is released.

5. The method for producing interstitial-free steel using all-scrap steel + electric arc furnace process according to claim 2, characterized in that: In the LF refining process, 800-1000kg of lime and 200-400kg of fluorite are added during the heating process to adjust the slag condition, 150-300m of aluminum wire is added for pre-deoxidation, the total flow rate of bottom blowing argon is 100-500NL / min, and the temperature of the molten steel at the LF outlet is controlled at 1660-1670℃.

6. The method for producing interstitial-free steel using the full scrap steel + electric arc furnace process according to claim 2, characterized in that: In the RH refining process: The ladle enters the RH station, starts to evacuate and circulate the liquid steel. When the vacuum degree reaches ≤150Pa, start timing, and the vacuum circulation lasts for 6 to 10 minutes for decarburization operation. After decarburization is completed, the steel liquid is sampled and analyzed for composition. When the mass percentage of C in the steel liquid is ≤0.0015%, a high-precision oxygen meter is used to determine the oxygen content in the steel liquid. The Al content required for deoxidation and alloying is calculated based on the O content, and the required amount of Al alloy is added to the steel liquid, and then circulated for 3 to 6 minutes. According to the interstitial atomic steel target composition, electrolytic manganese, ferrotitanium and ferroniobium alloys are added for alloying, and after circulating for 3 to 4 minutes, the steel liquid composition is sampled and analyzed, and the steel composition is fine-tuned based on the interstitial atomic steel target composition; After alloying is completed, when the vacuum degree reaches ≤150Pa, continue to circulate for ≥20 minutes. After the cycle is completed, perform the air-breaking operation. During the air-breaking operation, when the vacuum tank leaves the molten steel surface, quickly add an appropriate amount of aluminum-containing steel slag modifier to the molten steel surface; The outlet temperature of molten steel at RH is controlled at 1595~1610℃.

7. The method for producing interstitial-free steel using all-scrap steel + electric arc furnace process according to claim 2, characterized in that: In the slab continuous casting process, the first tundish furnace uses other ultra-low carbon steel with C≤0.0050% for casting, and the second tundish furnace and subsequent furnaces use molten steel produced by the scrap steel ratio, electric arc furnace steelmaking, LF refining, and RH refining processes for casting.

8. The method for producing interstitial-free steel using all-scrap steel + electric arc furnace process according to claim 2, characterized in that: In the slab continuous casting process: Before continuous casting, the tundish and nozzle are baked online for 2 hours and no longer than 4 hours. The cooling time of the ladle fork arm is controlled to be ≥5 minutes. The crystallizer liquid level fluctuation requirement is ±5mm, the stopper argon flow rate is controlled to ≤10NL / min, dynamic light pressure and roller electromagnetic stirrer are used to control center loosening and center segregation. The dynamic light pressure process parameters are: pressure is applied in the range of 50-95% solid phase ratio in the two-phase zone, the total pressure reduction is 3.2mm, and the roller electromagnetic stirring process parameters are: 300A, 6Hz, no reversing.

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