Method for producing automobile steel by adopting electric furnace and converter

Abstract

The invention discloses a method for producing automobile steel by adopting an electric furnace and a converter, which aims at solving the technical problem of high sulfur content and nitrogen content in production of green automobile steel by an electric furnace path, solves the problem of green'semi-steel 'raw materials by melting waste steel through the electric furnace, and overcomes the technical defect that the electric furnace cannot be desulfurized by adopting a pretreatment process. The converter top-bottom combined blowing process solves the problem that an electric furnace process cannot remove nitrogen. The sulfur content of the automobile steel produced through the method can reach 0.005% or below, the nitrogen content of the automobile steel can reach 0.0030% or below, and the requirements of automobile steel products are completely met; and meanwhile, compared with a traditional automobile steel production process, carbon emission is reduced by 45%-90%, and 0.85-1.35 t of carbon dioxide is reduced per ton of automobile steel.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for producing automobile steel by using an electric furnace and a converter. Background Art

[0002] Carbon emissions from my country's steel industry account for about 15% of the country's total carbon emissions, making it the industry with the largest carbon emissions among the 31 manufacturing sectors. Many steel products are produced using electric furnace processes to achieve the goal of reducing carbon emissions. With the development of the automobile industry, the use of automotive steel has increased dramatically. In 2023, China's demand for automotive steel will be about 55 million tons, so carbon emissions reduction for automotive steel is very important; however, the use of electric furnace processes to produce automotive steel will not solve the problems of high residual nickel and copper elements, high nitrogen content, and high sulfur content. Summary of the invention

[0003] In order to overcome the defects of the above-mentioned prior art, the present invention adopts the process steps of optimizing scrap steel + ecological electric furnace smelting semi-steel + semi-steel desulfurization pretreatment + converter smelting + LF refining / RH vacuum refining + slab continuous casting, which can effectively reduce carbon emissions and solve the problem that the nitrogen content, sulfur content and residual elements cannot be controlled in the production of automotive steel in electric furnaces.

[0004] In order to achieve the above-mentioned invention object, the present invention provides a method for producing automobile steel by using an electric furnace and a converter, wherein the composition of the molten steel of the automobile steel is controlled by mass percentage to be C: 0-0.50%, Si: 0-0.90%, Mn: 0.10%-1.90%, P: 0.005%-1.00%, S≤0.010%, Cr≤0.25%, Als≤0.05%, Ti: 0-0.20%, Nb: 0-0.10%, Cu≤0.25%, Ni≤0.25%, O≤0.0030%, N≤0.0060%, and the balance is iron and unavoidable impurities; the method for producing automobile steel comprises the following steps:

[0005] ① Ecological electric furnace smelting semi-steel

[0006] Scrap steel is used as the charge. The scrap steel used is high-quality scrap steel without impurity elements, with a ratio of 100% and a C content of ≥1.10%. Oxygen is blown to assist melting, and carbon powder is sprayed to make foamed slag. High-power current is used to melt the scrap steel. The steel-making temperature is 1635℃~1650℃. Carbon-increasing agent is added when steel is tapped. The amount of steel per ton is 25~40kg. The carbon content of the ladle is guaranteed to be ≥2.5%. After tapping, the "semi-steel" is lifted by an overhead crane and poured into a torpedo tank, and then transported to the molten iron pretreatment process via the railway line.

[0007] ② Semi-steel desulfurization pretreatment

[0008] The IR method is adopted to spray passivated magnesium powder and calcium oxide powder for desulfurization pretreatment of "semi-steel", wherein the spraying amount of magnesium powder is: 0.01-0.05kg of magnesium powder is added to remove 0.001% of S per ton of "semi-steel", and the weight ratio of calcium oxide powder to magnesium powder is 3:1; to ensure that S in the "semi-steel" after desulfurization is ≤0.002%, and then slag is removed, and the slag is removed cleanly, and the slag amount is ≤0.1t.

[0009] ③Converter smelting

[0010] The smelting process is to use semi-steel and refined scrap steel, and the production process is to use a combined blown converter. The dephosphorization operation is performed by a single slag or double slag method. The single slag method uses a batch of materials, and the materials are added in 3 to 5 batches within 5 to 6 minutes of blowing. The double slag method uses 30% of the total slag-making material, and the materials are added within 3 minutes of blowing. The rest is added in small batches after the slag is poured. The final slag basicity (R) is 2.8 to 3.3, the final slag (MgO) is 8.0% to 11.0%, and the final slag (FeO) is ≤20.0%. Low-carbon and low-phosphorus ferromanganese, silicon-manganese, low-carbon ferrochrome and ferrosilicon are used for alloying; the steel-making time is 5 to 7 minutes; the final oxygen is controlled at 300 to 700ppm, and the top and bottom combined blowing is used, and supplementary blowing is prohibited. The final C is ≤0.04%, P ≤0.015%, and S ≤0.015%. The steel-making process is to use a slide plate to block the slag for steel-making, and it is strictly prohibited to discharge slag, and no deoxidation is performed. The steel-making temperature is above 1650℃.

[0011] ④LF refining

[0012] When producing ultra-low sulfur steel, LF furnace "white slag" refining and desulfurization are used. Active lime 6-10 kg / t is added, and aluminum wire precipitation deoxidation and aluminum particle diffusion deoxidation are used to make white slag, and sulfur is removed to below 0.001%.

[0013] ⑤RH refining

[0014] Non-ultra-low sulfur furnaces are directly treated with RH vacuum decarburization. The temperature of RH is 1630℃~1650℃, and RH adopts forced decarburization mode. After the pump is turned on for 8 minutes, the vacuum degree reaches below 1kPa and oxygen is added. The oxygen addition amount is 50~200Nm 3 , ensure that the oxygen content at the end of decarburization is not less than 300ppm, and the carbon at the RH end is ≤0.0020%. After decarburization, deoxidation is carried out according to the oxygen content in the steel. After deoxidation, low-carbon ferrosilicon, metal manganese and other alloys are used for alloying according to the composition requirements to ensure that the composition meets the requirements of the corresponding steel grade.

[0015] ⑥Continuous casting

[0016] Control the pouring tonnage of the tundish and the remaining amount of the ladle, and do not allow slag; the superheat of the tundish is 20℃~40℃; the soft pressure reduction function is used during the steel pouring process; the pulling speed is maintained at a constant speed of 1~1.2m / min during the steel pouring process; the crystallizer liquid level fluctuation is ≤±3mm; the aluminum burn loss is ≤0.009%; the ingot is hot charged or pile cooled.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention aims at the technical problem that the production of green automobile steel by electric furnace cannot solve the high sulfur and nitrogen content. The problem of green "semi-steel" raw materials is solved by melting scrap steel in electric furnace, and the technical defect that electric furnace cannot desulfurize is overcome by pretreatment process. The problem that electric furnace process cannot denitrify is solved by converter top and bottom double blowing process. The sulfur content of automobile steel produced by this method can reach below 0.005%, and the nitrogen content can reach below 0.0030%, which fully meets the requirements of automobile steel products; at the same time, compared with the traditional automobile steel production process, carbon emissions are reduced by 45% to 90%, and carbon dioxide emissions are reduced by about 0.85 to 1.35 tons per ton of automobile steel. DETAILED DESCRIPTION

[0019] The present invention is further described below in conjunction with specific examples, but the present invention is not limited in any way. To avoid redundant description, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0020] The invention discloses a method for producing automobile steel by using an electric furnace and a converter. The composition of the molten steel of the automobile steel is controlled as follows by mass percentage: C: 0-0.50%, Si: 0-0.90%, Mn: 0.10-1.90%, P: 0.005-1.00%, S≤0.010%, Cr≤0.25%, Als≤0.05%, Ti: 0-0.20%, Nb: 0-0.10%, Cu≤0.25%, Ni≤0.25%, O≤0.0030%, N≤0.0060%, and the remainder is iron and unavoidable impurities.

[0021] The method for producing automobile steel comprises the steps of smelting semi-steel in an ecological electric furnace, pre-treatment of semi-steel desulfurization, converter smelting, LF refining / RH refining, and slab continuous casting;

[0022] ① Ecological electric furnace smelting semi-steel: 100% scrap steel is used as the furnace charge, and the carbon content is ≥1.10%; the tapping temperature is 1635℃~1650℃, and a carbon enhancer is added to the tapping, 25~40kg per ton of steel, and the carbon content of the ladle is guaranteed to be ≥2.5%;

[0023] ② Desulfurization pretreatment of semi-steel: Use IR method to spray passivated magnesium powder and calcium oxide powder to desulfurize the semi-steel;

[0024] ③ Converter smelting: using semi-steel and refined scrap steel for smelting, double-blowing converter production, and single slag method or double slag method for dephosphorization operation;

[0025] ④LF refining: When producing ultra-low sulfur steel, add 6-10kg / t of active lime, and use aluminum wire precipitation deoxidation and aluminum particle diffusion deoxidation to make white slag to remove sulfur to below 0.001%;

[0026] ⑤RH refining: non-ultra-low sulfur furnaces are directly subjected to RH vacuum decarburization treatment;

[0027] ⑥Continuous casting: Control the pouring tonnage of the tundish and the remaining amount of the ladle, and do not allow slag to be discharged.

[0028] The matters not described in the following embodiments are the same as the description of the above specific implementation methods.

[0029] Example 1

[0030] A method for producing automobile steel by using an electric furnace and a converter, using the technical solution of the present invention to manufacture green automobile steel DX56D+Z-LV, the actual production steps are as follows:

[0031] ① Ecological electric furnace smelting semi-steel

[0032] Scrap steel is used as the charge. The scrap steel used is high-quality scrap steel without impurity elements, with a ratio of 100% and a C content of ≥1.15%. Oxygen is blown to assist melting, and carbon powder is sprayed to make foamed slag. High-power current is used to melt the scrap steel. The steel-making temperature is 1645℃, and a carbon-increasing agent is added when the steel is tapped. The steel is weighed 28kg per ton, and the carbon content of the ladle is 2.55%. After tapping, the "semi-steel" is lifted by an overhead crane and poured into a torpedo tank, and then transported to the molten iron pretreatment process via the railway line.

[0033] ②“Semi-steel” desulfurization pretreatment

[0034] The IR method was used to spray passivated magnesium powder and calcium oxide powder for desulfurization pretreatment of the "semi-steel", in which the spraying amount of magnesium powder was 162kg and that of calcium oxide powder was 498kg; after desulfurization, the S content in the "semi-steel" was 0.002%, and after slag removal, the slag amount was 0.02t.

[0035] ③Converter smelting

[0036] The smelting process is semi-steel plus refined scrap steel, with a semi-steel loading of 170t and low-sulfur refined scrap steel of 21t. The double-blowing converter is used for production, and the single slag method is used for dephosphorization operation. The dephosphorization is completed in 5 batches within 5 minutes of blowing. The final slag basicity (R) is 2.95, the final slag (MgO) is 10.0%, and the final slag (FeO) is ≤19.0%. The steel-making time is 5.5min; the final oxygen is 540ppm. The final C is ≤0.035%, P is ≤0.006%, and S is ≤0.005%. The steel-making is tapped with a slide plate to block the slag, and the slag is not discharged. The steel-making temperature is 1645℃.

[0037] ④RH refining

[0038] The RH temperature was 1630℃, and the RH was in forced decarburization mode. After the pump was turned on for 8 minutes, the vacuum degree reached 0.9kPa and oxygen was added. The oxygen addition amount was 100Nm 3 , the oxygen content at the decarburization end point is 310ppm, and the carbon at the RH end point is ≤0.0010%. After decarburization, deoxidation is carried out according to the oxygen content in the steel, and 168kg of aluminum particles are added. After deoxidation, 54kg of metal manganese and 206kg of ferrotitanium are alloyed according to the composition requirements to ensure that the composition meets the requirements of the corresponding steel grade. The chemical composition mass content of the molten steel after RH is shown in Table 1:

[0039] Table 1 Chemical composition of molten steel after RH refining in Example 1

[0040]

[0041] ⑤Continuous casting

[0042] Control the pouring tonnage of the tundish and the remaining amount of the ladle, and do not allow slag; the superheat of the tundish is 25℃~42℃; the soft pressure function is used during the steel pouring process; the casting speed is maintained at a constant speed of 1.1m / min during the steel pouring process; the crystallizer liquid level fluctuation is ≤±2mm; the aluminum burn loss is ≤0.003%; the ingot is pile cooled.

[0043] Example 1 The quality of the green automotive steel DX56D+Z-LV product produced by the electric furnace plus converter method was tested, and the results are shown in Table 2; the oxygen and nitrogen contents of the ingot meet the standard requirements, the surface quality of the ingot is good, the macrostructure is dense and defect-free; and compared with traditional blast furnace molten iron smelting, carbon dioxide emissions are reduced by about 1.28 tons.

[0044] Table 2 Chemical composition of green automotive steel DX56D+Z-LV product prepared in Example 1

[0045]

[0046] Example 2

[0047] A method for producing automobile steel using an electric furnace and a converter. The actual production steps of manufacturing green automobile steel HC340-LV using the technical solution of the present invention are as follows:

[0048] ① Ecological electric furnace smelting semi-steel

[0049] Scrap steel is used as the charge. The scrap steel used is high-quality scrap steel without impurity elements, with a ratio of 100% and a C content of ≥1.25%. Oxygen is blown to assist melting, and carbon powder is sprayed to make foamed slag. High-power current is used to melt the scrap steel. The steel-making temperature is 1655℃, and a carbon-increasing agent is added when steel is tapped. The steel is 30kg per ton, and the carbon content of the ladle is 2.65%. After tapping, the "semi-steel" is lifted by an overhead crane and poured into a torpedo tank, and transported to the molten iron pretreatment process via the railway line.

[0050] ②“Semi-steel” desulfurization pretreatment

[0051] The IR method was used to spray passivated magnesium powder and calcium oxide powder for desulfurization pretreatment of the "semi-steel", in which the spraying amount of magnesium powder was 188kg and that of calcium oxide powder was 578kg; after desulfurization, the S content in the "semi-steel" was 0.002%, and after slag removal, the slag amount was 0.03t.

[0052] ③Converter smelting

[0053] Semi-steel and refined scrap steel are used for smelting, with a semi-steel loading of 174t and low-sulfur refined scrap steel of 22t. The double-blowing converter is used for production, and the single slag method is used for dephosphorization operation. It is divided into 3 batches within 5 minutes of blowing, and each batch is added in small quantities. The final slag basicity (R) is 3.11, the final slag (MgO) is 10.5%, and the final slag (FeO) is ≤18.0%. The steel-making time is 6.5min; the end oxygen is 370ppm. The end point C is ≤0.031%, P is ≤0.011%, and S is ≤0.022%. The slide plate is used to block the slag for steel-making, and the slag is not discharged. The steel-making temperature is 1625℃. 88m of aluminum wire is added to 1 / 4 of the steel for deoxidation. After deoxidation, 719kg of ferrosilicon, 2026kg of silicon manganese, and 1540kg of low-carbon ferromanganese are added for alloying. The chemical composition and mass content of the molten steel after steel-making are shown in Table 3:

[0054] Table 3 Chemical composition of molten steel after converter smelting in Example 2

[0055]

[0056] ④LF refining

[0057] The LF furnace uses "white slag" refining and desulfurization. After entering the station, 8kg / t of active lime is added, 200m of aluminum wire is fed, and white slag is made by feeding aluminum particles for diffusion deoxidation, and sulfur is removed to 0.002%. 303kg of high manganese, 103kg of medium manganese, and 108kg of aluminum particles are added during the LF process to adjust the composition to the target requirements. The chemical composition mass content of the molten steel after LF refining is shown in Table 4:

[0058] Table 4 Chemical composition of molten steel after LF refining in Example 2

[0059]

[0060] ⑤Continuous casting

[0061] Control the pouring tonnage of the tundish and the remaining amount of the ladle, and do not allow slag; the superheat of the tundish is 23℃~38℃; the soft pressure function is used during the steel pouring process; the casting speed is maintained at a constant speed of 1.2m / min during the steel pouring process; the crystallizer liquid level fluctuation is ≤±2mm; the aluminum burn loss is ≤0.004%; the ingot is pile cooled.

[0062] Example 2 The quality of the green automotive steel HC340-LV product produced by the electric furnace plus converter method was tested, and the results are shown in Table 5; the oxygen and nitrogen contents of the ingot meet the standard requirements, the surface quality of the ingot is good, the macrostructure is dense and defect-free; and compared with traditional blast furnace molten iron smelting, carbon dioxide emissions are reduced by about 1.35t.

[0063] Table 5 Chemical composition of green automotive steel HC340-LV product prepared in Example 2

[0064]

[0065] For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for producing automobile steel using an electric furnace and a converter, characterized in that: The molten steel composition of the automobile steel is controlled to be C: 0-0.50%, Si: 0-0.90%, Mn: 0.10%-1.90%, P: 0.005%-1.00%, S≤0.010%, Cr≤0.25%, Als≤0.05%, Ti: 0-0.20%, Nb: 0-0.10%, Cu≤0.25%, Ni≤0.25%, O≤0.0030%, N≤0.0060%, and the balance is iron and unavoidable impurities; The method for producing automobile steel comprises the steps of smelting semi-steel in an ecological electric furnace, pre-treatment of semi-steel desulfurization, converter smelting, LF refining / RH refining, and slab continuous casting; ① Ecological electric furnace smelting semi-steel: 100% scrap steel is used as the furnace charge, and the carbon content is ≥1.10%; the tapping temperature is 1635℃~1650℃, and a carbon enhancer is added to the tapping, 25~40 kg per ton of steel, and the carbon content of the ladle is guaranteed to be ≥2.5%; ② Desulfurization pretreatment of semi-steel: Use IR method to spray passivated magnesium powder and calcium oxide powder to pre-treat the desulfurization of "semi-steel"; ③ Converter smelting: using semi-steel and refined scrap steel for smelting, double-blowing converter production, and single slag method or double slag method for dephosphorization operation; ④LF refining: When producing ultra-low sulfur steel, add 6-10 kg / t of active lime, and use aluminum wire precipitation deoxidation and aluminum particle diffusion deoxidation to make white slag to remove sulfur to below 0.001%; ⑤RH refining: non-ultra-low sulfur furnaces are directly subjected to RH vacuum decarburization treatment; ⑥Continuous casting: Control the pouring tonnage of the tundish and the remaining amount of the ladle, and do not allow slag to be discharged.

2. The method for producing automobile steel according to claim 1, characterized in that: In step ②, the injection amount of the magnesium powder is: 0.01-0.05 kg of magnesium powder is added to remove 0.001% of S per ton of "semi-steel"; the weight ratio of the added amount of calcium oxide powder to the added amount of magnesium powder is 3:1; ensure that the S in the "semi-steel" after desulfurization is ≤0.002%, and then slag is removed, and the slag amount is ≤0.1 t.

3. The method for producing automobile steel according to claim 2, characterized in that: In step ③, the single slag method adopts a batch material mode, and the material is added in 3 to 5 batches within 5 to 6 minutes after the blowing starts; the double slag method adds 30% of the total slag-making material, and the material is added within 3 minutes after the blowing starts; the final slag basicity is 2.8 to 3.3, the final slag MgO is controlled to 8.0% to 11.0%, and the final slag FeO is controlled to ≤20.0%.

4. The method for producing automobile steel according to claim 3, characterized in that: Step ③ The tapping time of converter smelting is 5 to 7 minutes; the endpoint oxygen is controlled at 300 to 700 ppm, top and bottom double blowing is adopted, supplementary blowing is prohibited, the endpoint C≤0.04%, P≤0.015%, S≤0.015%; the tapping temperature is above 1650°C.

5. The method for producing automobile steel according to claim 4, characterized in that: Step ⑤ The inlet RH temperature of RH refining is 1630℃~1650℃, and the forced decarburization mode is adopted. After the vacuum degree reaches below 1kPa after the pump is turned on for 8 minutes, oxygen supplementation operation is performed, and the oxygen supplementation amount is 50~200 Nm 3 , ensure that the oxygen content at the decarburization endpoint is not less than 300ppm, and the RH endpoint carbon ≤0.0020%.

6. The method for producing automobile steel according to claim 5, characterized in that: Step ⑥ The continuous casting tundish is superheated at 20°C to 40°C; the soft reduction function is used during the steel pouring process; the pulling speed is maintained constant during the steel pouring process, and the pulling speed is 1 to 1.2 m / min; the crystallizer liquid level fluctuation is ≤±3 mm; the aluminum burn loss is ≤0.009%; the ingot is hot charged or pile cooled.

Images