Nitrogen-controlled smelting method of steel for automobile panel

Abstract

The invention relates to a nitrogen-controlled smelting method of steel for an automobile panel, which comprises the following steps: 1) electric furnace smelting: adopting a 100% scrap steel smelting process, controlling electric furnace smelting process parameters, putting smelted molten steel into a torpedo ladle filled with molten iron, and mixing to form semi-steel molten steel; 2) converter smelting: adding 5-10% by weight of waste steel and 90-95% by weight of semi-steel molten steel during converter smelting, adopting top-bottom combined blowing, adopting argon in the whole process from the beginning of smelting to tapping bottom blowing, and controlling converter smelting process parameters; the C content at the converter smelting end point is less than or equal to 0.05%, and the oxygen content is 400-600ppm; according to the method, the nitrogen content in the semi-steel molten iron is effectively controlled, the efficient dephosphorization rate is kept while the denitrification efficiency is improved, it is guaranteed that the temperature and component requirements of the molten steel are met during steel smelting and tapping, and meanwhile the aim of smelting carbon reduction is achieved.

Description

Technical Field

[0001] This invention relates to the field of automotive steel smelting technology, and in particular to a nitrogen-controlled smelting method for automotive panel steel. Background Technology

[0002] The steel industry is a major global source of carbon emissions, so energy conservation and emission reduction in the steel industry are receiving increasing attention. Green and low-carbon development has become a new requirement and trend for the steel industry. Among these, carbon reduction technology in smelting is one of the important technical means and also an important way to develop high-quality, low-cost, green and low-carbon steel grades.

[0003] Automotive exterior panels (referred to as automotive panels) often use interstitial ferritic steel (IF steel), a type of steel developed based on IF steel. While IF steel has low C and N content, interstitial IF steel incorporates certain amounts of strong carbonitriding compound-forming elements such as titanium (Ti) and niobium (Nb), completely fixing the interstitial atoms of carbon and nitrogen in the ultra-low carbon steel into carbonitriding compounds, thus obtaining a clean ferritic steel without interstitial atoms. Interstitial IF steel is an ultra-low carbon steel with excellent deep-drawing properties. When used in automobiles, it can meet the requirements of lightweighting and improving fuel economy, while ensuring the safety and reliability of automotive components.

[0004] Interstitial atom-free IF steel is an ultra-low carbon, low-nitrogen steel with strict control over the content of residual elements such as Cr, Ni, and Cu (typically requiring the total amount of residual elements to be less than 0.07%), while also imposing high requirements on the cleanliness of the molten steel. When producing automotive panels using a mixture of electric arc furnace steel and blast furnace iron, automotive sheet briquettes and refined scrap steel are used to effectively control residual elements. However, the ionization of air by the electric arc during electric arc furnace smelting inevitably leads to nitrogen increase in the molten steel, and the nitrogen content in the semi-steel after mixing is still around 80 ppm. Furthermore, the semi-steel has a lower carbon content compared to blast furnace iron, which inevitably affects denitrification efficiency. If continuous casting is carried out directly at this point, nitride precipitation will inevitably occur in the steel, leading to aging and blue brittleness, ultimately causing a decrease in the yield strength, tensile strength, toughness, plasticity, deep drawing performance, hot working performance, and weldability of the finished steel, and also easily causing billet cracking and intergranular corrosion. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a nitrogen-controlled smelting method for automotive panel steel, which effectively controls the nitrogen content in semi-finished steel, and maintains a high dephosphorization rate while enhancing denitrification efficiency, ensuring that the steel meets the temperature and composition requirements when it is tapped, and simultaneously achieving the goal of reducing carbon in smelting.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A nitrogen-controlled smelting method for steel used in automotive panels includes the following steps:

[0008] 1) Electric furnace smelting:

[0009] The process employs 100% scrap steel smelting, with tapping temperature controlled at 1640–1660℃, a smelting cycle of 55–65 minutes, and furnace oxygen consumption of 40–43 Nm³. 3 / t steel, furnace power consumption is 3400~3500kwh / t steel, tapping time is 2~5min, and the temperature at the station is 1635~1650℃; the molten steel is poured into a torpedo ladle containing an equal amount of molten iron, and after mixing, a semi-molten steel is formed.

[0010] 2) Converter smelting:

[0011] During converter smelting, 5%–10% scrap steel and 90%–95% semi-finished steel are added by weight, and the smelting time is 25–35 minutes. Top and bottom blowing are employed, with argon gas used throughout the bottom blowing process from the start of smelting to tapping, and the blowing time is 9–12 minutes. The oxygen supply from the oxygen lance in the early stages of smelting is 34,000–36,000 Nm³. 3 / h, after process testing, adjust the oxygen lance supply to 37500~38500 Nm³. 3 / h for deep carbon pulling and stirring; during the later stage of blowing, the oxygen lance position is increased to 1.8-2.0m, and the final carbon pulling time is 15-25s; at the end of the converter smelting, the C content is ≤0.05% and the oxygen content is 400-600ppm;

[0012] The composition of the steel tapped from the converter, by mass percentage, is C≤0.05%; Si≤0.03%; Mn≤0.1%; P≤0.01%; S≤0.01%; Cr≤0.03%; Ni+Cu≤0.035%; N≤0.002%; and the tapping temperature is ≥1630℃.

[0013] The scrap steel is briquetteed from automotive steel sheets.

[0014] During electric furnace smelting, alloys and auxiliary materials are added. The alloy is ferrosilicon alloy, and the addition amount is 11-13 kg / t steel. The addition amount of auxiliary materials is as follows: foaming agent 35-40 kg / t steel, carbon blocks 8-8.5 kg / t steel, carbon powder 9-12 kg / t steel, synthetic slag 2-2.2 kg / t steel, active lime with a particle size of 10-70 mm 25-26 kg / t steel, and magnesite with a particle size of 10-60 mm 20-21 kg / t steel.

[0015] The final composition of the molten steel in the electric furnace, by mass percentage, is: C ≥ 0.5%; Si: 0.3%–0.5%; Mn ≤ 0.2%; P ≤ 0.05%; S ≤ 0.05%; Cr ≤ 0.07%; Ni + Cu ≤ 0.08%.

[0016] Before the semi-finished steel enters the converter for smelting, it undergoes pretreatment. The pretreatment temperature at the station is 1390-1420℃, and the temperature at the station is 1370-1390℃. The pretreatment cycle is 35-50 minutes. The pretreatment is then sprayed for 15-30 minutes, using inert gas as a carrier to spray lime and magnesium powder deep into the molten iron. The amount of lime sprayed is 4.5-6.5 kg / t steel, and the amount of magnesium powder sprayed is 0.6-0.8 kg / t steel.

[0017] The composition of the pretreated semi-finished steel, by mass percentage, is: C: 2.6%–3.0%; Si: 0.3%–0.5%; Mn≤0.2%; P≤0.08%; S≤0.04%; Cr≤0.035%; Ni+Cu≤0.035%; N≤0.009%.

[0018] During the converter smelting process, 35-40 kg / t of lime and 15-18 kg / t of dolomite are added to the steel.

[0019] After being smelted in the converter, the molten steel is transported to the argon station and purged with argon for 3-5 minutes; the bottom-blown argon flow rate is 400-800 L / min and the argon pressure is 0.4-0.6 MPa.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. This invention employs an "electric furnace + converter" smelting process. The smelting raw materials are 50% molten iron and 50% molten steel produced by melting and processing all scrap steel in an eco-friendly electric furnace. After the molten iron and molten steel are mixed in a torpedo ladle, a semi-molten steel with a carbon content of 2% to 3% is formed, which is then smelted in the converter. Since the nitrogen content of the mixed semi-molten steel is still relatively high, and the carbon content is lower compared to blast furnace molten iron, the following two optimization measures are adopted to control the nitrogen content of the converter molten steel:

[0022] 1) Increase the oxygen supply flow rate of the oxygen lance from the conventional 40000 Nm 3 / h decreased to approximately 35000 Nm 3 / h, to prolong the carbon-oxygen reaction time;

[0023] 2) Change the bottom blowing mode of the converter smelting process, changing the conventional blowing mode of switching between argon and nitrogen to blowing only argon, while increasing the bottom blowing flow rate and intensity, enhancing the stirring effect of molten steel, and making the carbon-oxygen reaction more complete.

[0024] By taking the above measures and combining them with converter semi-steel smelting processes such as low-temperature tapping, we ensured that the phosphorus content in the tapped steel was ≤0.01%, the nitrogen content in the converter was <20ppm, and the total Cr+Ni+Cu content in the steel was <0.07%.

[0025] 2. This invention adopts a low-carbon process path of "blast furnace molten iron + electric arc furnace molten steel," achieving a breakthrough in green innovation for iron and steel smelting technology. Molten iron with a carbon content of approximately 4.3% produced in the blast furnace is mixed with molten scrap steel melted in the electric arc furnace at a 1:1 ratio to form semi-molten steel with a carbon content of approximately 2.6%, which is then smelted. Compared to blast furnace molten iron, the carbon content of the semi-molten steel is significantly reduced, thus reducing carbon emissions during the smelting process. Furthermore, the addition of electric arc furnace molten steel not only effectively utilizes scrap steel resources but also reduces carbon emissions caused by the large-scale use of coke compared to the traditional long smelting process of "blast furnace + converter." Detailed Implementation

[0026] The present invention discloses a nitrogen-controlled smelting method for automotive panel steel, comprising the following steps:

[0027] 1) Electric furnace smelting:

[0028] The process employs 100% scrap steel smelting, with tapping temperature controlled at 1640–1660℃, a smelting cycle of 55–65 minutes, and furnace oxygen consumption of 40–43 Nm³. 3 / t steel, furnace power consumption is 3400~3500kwh / t steel, tapping time is 2~5min, and the temperature at the station is 1635~1650℃; the molten steel is poured into a torpedo ladle containing an equal amount of molten iron, and after mixing, a semi-molten steel is formed.

[0029] 2) Converter smelting:

[0030] During converter smelting, 5%–10% scrap steel and 90%–95% semi-steel molten steel are added by weight, and the smelting time is 25–35 minutes. Top and bottom blowing is adopted, and argon gas is used throughout the entire process from the start of smelting to bottom blowing at tapping, with a blowing time of 9–12 minutes.

[0031] The bottom blowing system model is shown in Table 1:

[0032] Table 1

[0033]

[0034] The oxygen supply from the oxygen lance during the early stages of smelting is 34,000–36,000 Nm³. 3 / h, after process testing, adjust the oxygen lance supply to 37500~38500 Nm³. 3 / h for deep carbon pulling and stirring; during the later stage of blowing, the oxygen lance position is increased to 1.8-2.0m, and the final carbon pulling time is 15-25s; at the end of the converter smelting, the C content is ≤0.05% and the oxygen content is 400-600ppm;

[0035] The composition of the steel tapped from the converter, by mass percentage, is C≤0.05%; Si≤0.03%; Mn≤0.1%; P≤0.01%; S≤0.01%; Cr≤0.03%; Ni+Cu≤0.035%; N≤0.002%; and the tapping temperature is ≥1630℃.

[0036] The scrap steel is briquetteed from automotive steel sheets.

[0037] During electric furnace smelting, alloys and auxiliary materials are added. The alloy is ferrosilicon alloy, and the addition amount is 11-13 kg / t steel. The addition amount of auxiliary materials is as follows: foaming agent 35-40 kg / t steel, carbon blocks 8-8.5 kg / t steel, carbon powder 9-12 kg / t steel, synthetic slag 2-2.2 kg / t steel, active lime with a particle size of 10-70 mm 25-26 kg / t steel, and magnesite with a particle size of 10-60 mm 20-21 kg / t steel.

[0038] The final composition of the molten steel in the electric furnace, by mass percentage, is: C ≥ 0.5%; Si: 0.3%–0.5%; Mn ≤ 0.2%; P ≤ 0.05%; S ≤ 0.05%; Cr ≤ 0.07%; Ni + Cu ≤ 0.08%.

[0039] Before the semi-finished steel enters the converter for smelting, it undergoes pretreatment. The pretreatment temperature at the station is 1390-1420℃, and the temperature at the station is 1370-1390℃. The pretreatment cycle is 35-50 minutes. The pretreatment is then sprayed for 15-30 minutes, using inert gas as a carrier to spray lime and magnesium powder deep into the molten iron. The amount of lime sprayed is 4.5-6.5 kg / t steel, and the amount of magnesium powder sprayed is 0.6-0.8 kg / t steel.

[0040] The composition of the pretreated semi-finished steel, by mass percentage, is: C: 2.6%–3.0%; Si: 0.3%–0.5%; Mn≤0.2%; P≤0.08%; S≤0.04%; Cr≤0.035%; Ni+Cu≤0.035%; N≤0.009%.

[0041] During the converter smelting process, 35-40 kg / t of lime and 15-18 kg / t of dolomite are added to the steel.

[0042] After being smelted in the converter, the molten steel is transported to the argon station and purged with argon for 3-5 minutes; the bottom-blown argon flow rate is 400-800 L / min and the argon pressure is 0.4-0.6 MPa.

[0043] The carbon-oxygen reaction is the core reaction in the converter (reaction formulas: C + O₂ = CO₂↑, 2C + O₂ = 2CO↑). During the reaction, a large amount of CO and CO₂ gases are generated. These gases form bubbles in the molten pool and rise to the surface, carrying away a significant amount of nitrogen from the molten steel, thus achieving denitrification. Simultaneously, the carbon-oxygen reaction causes violent fluctuations in the molten pool, which has a stirring effect, increasing the contact between the molten steel and the gas phase, facilitating nitrogen diffusion into the gas phase. According to the principle of gas diffusion, as nitrogen diffuses into the gas phase, the partial pressure of nitrogen in the molten steel decreases, further driving more nitrogen to escape from the molten steel into the gas phase, making nitrogen removal easier. Therefore, the intensity of the carbon-oxygen reaction determines the denitrification efficiency.

[0044] The principle of denitrification using the carbon-oxygen reaction can be analyzed from both thermodynamic and kinetic perspectives. Thermodynamic principles determine the feasibility and limits of the carbon-oxygen reaction, while kinetic principles ensure efficient reaction through optimized mass transfer and stirring. The combined effect of thermodynamic feasibility and kinetic enhancement mechanisms determines the final outcome of the carbon-oxygen reaction.

[0045] From a thermodynamic perspective, carbon's affinity for oxygen is significantly higher than that of iron, silicon, and manganese at converter steelmaking temperatures. The Gibbs free energy change of the relevant reactions is a large negative value, ensuring the reaction can proceed spontaneously in the forward direction. Simultaneously, the carbon-oxygen reaction is endothermic, and around 1700℃, the equilibrium constant increases, strengthening the forward reaction tendency and lowering the activation energy, thus enhancing the reactivity of carbon with oxygen. Furthermore, the CO and CO2 produced are gaseous products that rise from the molten iron system due to their density difference, continuously disrupting the reaction equilibrium and driving the continuous removal of carbon according to Le Chatelier's principle. All these processes together constitute the thermodynamic basis of the carbon-oxygen reaction, determining its feasibility and limits.

[0046] From a kinetic perspective, the enhancement of the carbon-oxygen reaction depends on the optimization of mass transfer conditions, stirring intensity, concentration gradient, and reaction interface. The supersonic oxygen flow generated by the high-pressure oxygen lance increases the gas-liquid interface area, enhancing the oxygen mass transfer rate. Simultaneously, it triggers vigorous stirring of the molten pool, promoting carbon diffusion to the interface. Molten pool stirring reduces the diffusion boundary layer thickness, increases the carbon diffusion coefficient, and causes carbon to continuously migrate into the reaction zone, leading to rapid product detachment. The significant gradient between the high oxygen partial pressure at the oxygen lance outlet and the carbon concentration in the molten iron constitutes the mass transfer driving force, increasing the collision frequency of carbon and oxygen at the interface. The emulsion zone formed by the oxygen jet impact greatly expands the reaction interface, allowing the reaction to proceed simultaneously over a larger area. These kinetic mechanisms ensure the efficient conduct of the carbon-oxygen reaction.

[0047] In this invention, the carbon content of semi-finished steel is approximately 2.6%, while that of molten iron is approximately 4.3%. The significant difference in carbon content between the two inevitably weakens the carbon-oxygen reaction in the semi-finished steel, thus reducing denitrification efficiency. This invention differs from conventional smelting denitrification methods in that: firstly, the oxygen lance flow rate is increased from the conventional 40,000 Nm³. 3 / h decreased to approximately 35000 Nm 3 The flow rate is increased to approximately [value missing] / h to prolong the carbon-oxygen reaction time. This extended reaction time effectively prolongs the denitrification time, facilitating the removal of nitrogen from the molten steel. Secondly, the bottom-blowing mode of the converter smelting process is changed from the conventional alternating argon and nitrogen blowing mode to an argon-only blowing mode. Using argon reduces nitrogen contact with the molten steel, minimizing nitrogen incorporation. Simultaneously, the bottom-blowing flow rate and intensity are increased, enhancing the steel agitation and inducing vigorous stirring of the molten pool, promoting carbon diffusion to the interface. Molten pool stirring reduces the diffusion boundary layer thickness, increases the carbon diffusion coefficient, and causes carbon to continuously migrate towards the reaction zone, aiding in rapid product detachment. By enhancing kinetic conditions, the carbon-oxygen reaction becomes more complete, promoting nitrogen diffusion into the gas phase.

[0048] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0049]

Example 1

[0050] The nitrogen-controlled smelting process for automotive panel steel in this embodiment is as follows:

[0051] 1. Process route design;

[0052] The process route is: 50% electric furnace molten steel + 50% blast furnace molten iron → molten iron pretreatment → converter steelmaking.

[0053] 2. Electric furnace smelting;

[0054] The process employs 100% scrap steel smelting, using automotive sheet briquettes; the tapping temperature is 1657℃, the smelting cycle is 59 minutes, and the furnace oxygen consumption is 41.89 Nm³. 3 / t steel, furnace power consumption 3450kwh / t steel. Tap time 3min, outlet temperature 1640℃. Ferrosilicon alloy 12.1kg / t steel is added during smelting. Auxiliary materials include: foaming agent 36.4kg / t steel, carbon blocks 8.2kg / t steel, synthetic slag 2kg / t steel, and active lime (particle size...). 25kg / t steel, magnesite (particle size) 20.2 kg / t steel. The molten steel is poured into a torpedo ladle containing 170 tons of molten iron, and after mixing, a semi-molten steel is formed.

[0055] The final composition of the electric furnace smelting was: C: 0.43%; Si: 0.379%; Mn: 0.128%; P: 0.0043%; S: 0.033%; Cr: 0.068%; Ni: 0.032%; Cu: 0.035%.

[0056] 3. Hot metal pretreatment;

[0057] The temperature at the station is 1401℃, and the temperature at the station is 1373℃. The pretreatment is sprayed for 26 minutes. Lime and magnesium powder are sprayed into the depth of the molten iron using nitrogen as a carrier. The amount of lime sprayed is 4.60 kg / t steel, and the amount of magnesium powder sprayed is 0.67 kg / t steel.

[0058] The composition of the pretreated semi-finished steel was: C: 2.62%; Si: 0.427%; Mn: 0.085%; P: 0.075%; S: 0.001%; ​​Cr: 0.025%; Ni+Cu: 0.02%; N: 0.0087%.

[0059] 4. Converter smelting;

[0060] During converter smelting, 7.5% scrap steel and 92.5% semi-finished steel were added by weight, with a smelting time of 27 minutes. Lime (39.2 kg / t steel) and dolomite (17.8 kg / t steel) were added during the smelting process. Top and bottom blowing was used, with a blowing time of 10.44 minutes. The oxygen supply from the oxygen lance in the early stages of smelting was 34500 Nm³. 3 / h, adjusted to 38000 Nm after process testing. 3 Deep carbon extraction and stirring were performed at / h. During the later stages of blowing, the oxygen lance position was increased to 1.92m, and the final carbon extraction time was 25s. The final C content in the converter was 0.048%, and the final oxygen content was 495ppm.

[0061] The bottom blowing system model is shown in Table 2.

[0062] Table 2 Bottom Blowing System Model

[0063]

[0064] The steel composition from the converter is: C: 0.023%; Si: 0.0024%; Mn: 0.038%; P: 0.0045%; S: 0.0024%; Cr: 0.021%; Ni+Cu: 0.022%; N: 0.0016%; and the tapping temperature is 1630℃.

[0065] After being smelted in the converter, the molten steel is transported to the argon station and blown with argon for 4 minutes. The bottom blowing argon flow rate is 700 L / min and the argon pressure is 0.5 MPa.

[0066]

Example 2

[0067] The nitrogen-controlled smelting process for automotive panel steel in this embodiment is as follows:

[0068] 1. Process route design;

[0069] The process route is: 50% electric furnace molten steel + 50% blast furnace molten iron → molten iron pretreatment → converter steelmaking.

[0070] 2. Electric furnace smelting;

[0071] The process employs 100% scrap steel smelting, using automotive sheet briquettes; the tapping temperature is 1660℃, the smelting cycle is 60 minutes, and the furnace oxygen consumption is 42.45 Nm³. 3 / t steel, furnace power consumption 3490kwh / t steel. Tap time 4min, outlet temperature 1649℃. Ferrosilicon alloy 11.3kg / t steel is added during smelting. Auxiliary materials include: foaming agent 38kg / t steel, carbon blocks 8.4kg / t steel, synthetic slag 2kg / t steel, and active lime (particle size...). 25kg / t steel, magnesite (particle size) 20.5 kg / t steel. The molten steel is poured into a torpedo ladle containing 170 tons of molten iron, and the mixture forms a semi-molten steel.

[0072] The final composition of the electric furnace smelting was: C: 0.49%; Si: 0.415%; Mn: 0.20%; P: 0.005%; S: 0.037%; Cr: 0.043%; Ni: 0.030%; Cu: 0.029%.

[0073] 3. Hot metal pretreatment;

[0074] The temperature at the station was 1396℃, and the temperature at the station was 1371℃. The pretreatment was sprayed for 16 minutes. Lime and magnesium powder were sprayed into the depth of the molten iron using nitrogen as a carrier. The amount of lime sprayed was 4.10 kg / t steel, and the amount of magnesium powder sprayed was 0.668 kg / t steel.

[0075] The composition of the pretreated semi-finished steel was: C: 2.68%; Si: 0.448%; Mn: 0.088%; P: 0.075%; S: 0.0017%; Cr: 0.025%; Ni+Cu≤0.02%; N≤0.0082%.

[0076] 4. Converter smelting;

[0077] During converter smelting, 5.5% scrap steel and 94.5% semi-finished steel were added by weight, with a smelting time of 28 minutes. Lime (39.2 kg / t steel) and dolomite (16.8 kg / t steel) were added during the smelting process. Top and bottom blowing was used, with a blowing time of 11.12 minutes. The oxygen supply from the oxygen lance in the early stages of smelting was 35200 Nm³. 3 / h, adjusted to 38000 Nm after process testing. 3 Deep carbon extraction and stirring were performed at / h. During the later stages of blowing, the oxygen lance position was increased to 1.83m, and the final carbon extraction time was 20s. The final C content in the converter was 0.034%, and the final oxygen content was 480ppm.

[0078] The bottom blowing system model is shown in Table 3.

[0079] Table 3 Bottom Blowing System Model

[0080]

[0081] The steel composition from the converter is: C: 0.027%; Si: 0.01%; Mn: 0.041%; P: 0.0051%; S: 0.0028%; Cr: 0.022%; Ni+Cu: 0.023%; N: 0.0017%; and the tapping temperature is 1637℃.

[0082] After being smelted in the converter, the molten steel is transported to the argon station and blown with argon for 5 minutes. The bottom blowing argon flow rate is 700 L / min and the argon pressure is 0.5 MPa.

[0083]

Example 3

[0084] The nitrogen-controlled smelting process for automotive panel steel in this embodiment is as follows:

[0085] 1. Process route design;

[0086] The process route is: 50% electric furnace molten steel + 50% blast furnace molten iron → molten iron pretreatment → converter steelmaking.

[0087] 2. Electric furnace smelting;

[0088] The process employs 100% scrap steel smelting, using automotive sheet briquettes; the tapping temperature is 1650℃, the smelting cycle is 60 minutes, and the furnace oxygen consumption is 41.3 Nm³. 3 / t steel, furnace power consumption 3440kwh / t steel. Tap time 4min, outlet temperature 1645℃. Ferrosilicon alloy 11.5kg / t steel is added during smelting. Auxiliary materials include: foaming agent 37kg / t steel, carbon blocks 8.3kg / t steel, synthetic slag 2.2kg / t steel, and active lime (particle size...). 25.7 kg / t steel, magnesite (particle size) 20.5 kg / t steel. The molten steel is poured into a torpedo ladle containing 170 tons of molten iron, and the mixture forms a semi-molten steel.

[0089] The final composition of the electric furnace smelting was: C: 0.45%; Si: 0.35%; Mn: 0.16%; P: 0.004%; S: 0.045%; Cr: 0.05%; Ni: 0.02%; Cu: 0.04%.

[0090] 3. Hot metal pretreatment;

[0091] The temperature upon arrival at the station is 1412℃, and the temperature upon departure from the station is 1380℃. The pretreatment process involves blowing for 17 minutes, using nitrogen as a carrier to blow lime and magnesium powder deep into the molten iron. The amount of lime blown is 5.30 kg / t steel, and the amount of magnesium powder blown is 0.67 kg / t steel.

[0092] The composition of the pretreated semi-finished steel was: C: 2.71%; Si: 0.422%; Mn: 0.0918%; P: 0.07%; S: 0.0012%; Cr: 0.025%; Ni+Cu≤0.02%; N≤0.0078%.

[0093] 4. Converter smelting;

[0094] During converter smelting, 6.6% scrap steel and 93.4% semi-finished steel were added by weight, with a smelting time of 26 minutes. Lime (39.8 kg / t steel) and dolomite (16.3 kg / t steel) were added during the smelting process. Top and bottom blowing was used, with a blowing time of 10.15 minutes. The oxygen supply from the oxygen lance in the early stages of smelting was 35500 Nm³. 3 / h, adjusted to 38000Nm after process testing. 3 Deep carbon extraction and stirring were performed at / h. During the later stages of blowing, the oxygen lance position was increased to 1.86m, and the final carbon extraction time was 18s. The final C content in the converter was 0.034%, and the final oxygen content was 510ppm.

[0095] The bottom blowing system model is shown in Table 4.

[0096] Table 4 Bottom Blowing System Model

[0097]

[0098] The steel composition from the converter is: C: 0.029%; Si: 0.01%; Mn: 0.055%; P: 0.0046%; S: 0.0026%; Cr: 0.025%; Ni+Cu: 0.025%; N: 0.0018%; and the tapping temperature is 1636℃.

[0099] After being smelted in the converter, the molten steel is transported to the argon station and blown with argon for 5 minutes. The bottom blowing argon flow rate is 800 L / min and the argon pressure is 0.6 MPa.

[0100] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A nitrogen-controlled smelting method for steel used in automotive panels, characterized in that, Includes the following steps: 1) Electric furnace smelting: The process employs 100% scrap steel smelting, with tapping temperature controlled at 1640–1660℃, a smelting cycle of 55–65 minutes, and furnace oxygen consumption of 40–43 Nm³. 3 / t steel, furnace power consumption is 3400~3500kwh / t steel, tapping time is 2~5min, and the temperature at the station is 1635~1650℃; the molten steel is poured into a torpedo ladle containing an equal amount of molten iron, and after mixing, a semi-molten steel is formed. 2) Converter smelting: During converter smelting, 5%–10% scrap steel and 90%–95% semi-finished steel are added by weight, and the smelting time is 25–35 minutes. Top and bottom blowing are employed, with argon gas used throughout the bottom blowing process from the start of smelting to tapping, and the blowing time is 9–12 minutes. The oxygen supply from the oxygen lance in the early stages of smelting is 34,000–36,000 Nm³. 3 / h, after process testing, adjust the oxygen lance supply to 37500~38500 Nm³. 3 / h for deep carbon pulling and stirring; during the later stage of blowing, the oxygen lance position is increased to 1.8-2.0m, and the final carbon pulling time is 15-25s; at the end of the converter smelting, the C content is ≤0.05% and the oxygen content is 400-600ppm; The composition of the steel tapped from the converter, by mass percentage, is: C ≤ 0.05%; Si ≤ 0.03%; Mn ≤ 0.1%; P ≤ 0.01%. S≤0.01%; Cr≤0.03%; Ni+Cu≤0.035%; N≤0.002%; tapping temperature≥1630℃.

2. The nitrogen-controlled smelting method for automotive panel steel according to claim 1, characterized in that, The scrap steel is briquetteed from automotive steel sheets.

3. The nitrogen-controlled smelting method for automotive panel steel according to claim 1, characterized in that, During electric furnace smelting, alloys and auxiliary materials are added. The alloy is ferrosilicon alloy, and the addition amount is 11-13 kg / t steel. The addition amount of auxiliary materials is as follows: foaming agent 35-40 kg / t steel, carbon blocks 8-8.5 kg / t steel, carbon powder 9-12 kg / t steel, synthetic slag 2-2.2 kg / t steel, active lime with a particle size of 10-70 mm 25-26 kg / t steel, and magnesite with a particle size of 10-60 mm 20-21 kg / t steel.

4. The nitrogen-controlled smelting method for automotive panel steel according to claim 1, characterized in that, The final steel composition of the electric furnace is C ≥ 0.5% by mass percentage; Si: 0.3%~0.5%; Mn≤0.2%; P≤0.05%; S≤0.05%; Cr≤0.07%; Ni+Cu≤0.08%.

5. The nitrogen-controlled smelting method for automotive panel steel according to claim 1, characterized in that, Before the semi-finished steel enters the converter for smelting, it undergoes pretreatment. The pretreatment temperature at the station is 1390-1420℃, and the temperature at the station is 1370-1390℃. The pretreatment cycle is 35-50 minutes. The pretreatment is then sprayed for 15-30 minutes, using inert gas as a carrier to spray lime and magnesium powder deep into the molten iron. The amount of lime sprayed is 4.5-6.5 kg / t steel, and the amount of magnesium powder sprayed is 0.6-0.8 kg / t steel.

6. The nitrogen-controlled smelting method for automotive panel steel according to claim 5, characterized in that, The pretreated semi-finished steel composition, by mass percentage, is C: 2.6%–3.0%; Si: 0.3%~0.5%; Mn≤0.2%; P≤0.08%; S≤0.04%; Cr≤0.035%; Ni+Cu≤0.035%; N≤0.009%.

7. The nitrogen-controlled smelting method for automotive panel steel according to claim 1, characterized in that, During the converter smelting process, 35-40 kg / t of lime and 15-18 kg / t of dolomite are added to the steel.

8. The nitrogen-controlled smelting method for automotive panel steel according to claim 1, characterized in that, After being smelted in the converter, the molten steel is transported to the argon station and purged with argon for 3-5 minutes; the bottom-blown argon flow rate is 400-800 L / min and the argon pressure is 0.4-0.6 MPa.

Images