Low-carbon aluminum killed steel and manufacturing process thereof

Abstract

The invention relates to the technical field of steel smelting, in particular to low-carbon aluminum killed steel and a manufacturing process thereof. The method comprises the following steps: carrying out desulfurization and dephosphorization pretreatment on molten iron to obtain molten iron of which the content of S is less than or equal to 0.005 wt% and the content of P is less than or equal to 0.005 wt%; and the molten iron is purified through LF and RH refining treatment, the molten iron with the oxygen determination value smaller than 50 ppm is obtained, and finally the low-carbon aluminum killed steel is obtained through casting. And meanwhile, in order to reduce the coarse grain defect in the low-carbon aluminum killed steel, the low-carbon aluminum killed steel is further subjected to heat treatment, and the low-carbon aluminum killed steel with high cleanliness and excellent surface quality is comprehensively obtained.

Description

Technical Field

[0001] The invention relates to the technical field of steel smelting, in particular to a low-carbon aluminum killed steel and a manufacturing process thereof. Background Art

[0002] Low-carbon aluminum-killed steel is widely used in automobile manufacturing, construction, home appliances and other fields due to its excellent mechanical properties and processing properties. At present, mainstream steel mills at home and abroad generally adopt four process routes to produce low-carbon aluminum-killed steel: (1) "hot metal pretreatment → top and bottom blowing converter → CAS-OB → continuous casting"; (2) "hot metal pretreatment → top and bottom blowing converter → argon blowing station → continuous casting"; (3) "hot metal pretreatment → top and bottom blowing converter → RH → continuous casting"; (4) "hot metal pretreatment → top and bottom blowing converter → LF → continuous casting".

[0003] However, with the needs of practical applications, higher requirements are placed on the performance of low-carbon aluminum-killed steel, such as its excellent cleanliness and surface quality. In order to optimize and improve it, the present invention has made corresponding adjustments from steel smelting to heat treatment, and comprehensively obtained a low-carbon aluminum-killed steel with high cleanliness and excellent surface quality, which can be better applied. Summary of the invention

[0004] The object of the present invention is to provide a low-carbon aluminum killed steel and a manufacturing process thereof to solve the problems raised in the prior art.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A low-carbon aluminum killed steel comprises the following chemical components by mass fraction: C≤0.03wt%, Mn 0.15-0.30wt%, Si≤0.03wt%, Als 0.02-0.04wt%, and the rest being Fe and unavoidable impurities.

[0007] Furthermore, the manufacturing process of the low carbon aluminum killed steel comprises the following steps:

[0008] S1: Pretreatment of molten iron for desulfurization and dephosphorization:

[0009] S11: Desulfurization of molten iron with a S content of ≤0.03wt% and a P content of ≤0.12wt% is carried out by KR stirring method, the desulfurization temperature is 1530-1550°C, and slag removal is required before and after adding the desulfurizer to complete the desulfurization;

[0010] S12: After desulfurization, scrap steel and molten iron are added into the converter in a mass ratio of 1:4-5, oxygen is blown from the top and bottom of the converter, and then a dephosphorizing agent is added for dephosphorization treatment. The dephosphorization temperature is 1550-1580°C, and the slag is removed to complete the dephosphorization;

[0011] S2: LF and RH refining treatment of molten iron:

[0012] S21: The pretreated molten iron enters the LF furnace, and its oxygen content and temperature are detected. Argon is blown from the bottom of the LF furnace to adjust the oxygen content and temperature according to the detection results, and then basic refining slag and deoxidizer I are added for refining treatment. The oxygen is measured before leaving the furnace to complete LF refining;

[0013] S22: (1) After LF refining, the molten iron enters the RH furnace for vacuum degassing treatment, and then the molten iron sample I and the slag sample I are taken; (2) The molten iron sample I is analyzed, and manganese alloy and aluminum iron are added according to the Mn and Als content to adjust Mn and Als to "the mass fraction value of the target component + 0.005"; basic refining slag is added according to the color of the slag sample I until the manganese alloy and aluminum iron are added and stirred for 3 to 10 minutes, and the slag color becomes yellow-white or green-white; (3) The fixed oxygen value of the molten iron is measured, and deoxidizer II is added according to the fixed oxygen value, argon is blown for 5 to 10 minutes, the fixed oxygen slag is removed, and the steel is cast to obtain low-carbon aluminum-killed steel.

[0014] Furthermore, the parameters of the KR stirring are: a stirring speed of 100 to 120 r / min, and a stirring time of 30 to 60 min.

[0015] Furthermore, the desulfurizer is composed of CaO, CaCO3, CaF2, and Mg mixed in a mass ratio of 60:25:12:3, and the added amount is 1 to 2% of the weight of the molten iron.

[0016] Furthermore, the parameters of the converter top and bottom blowing are: gas flow rate is 3000-6000Nm 3 / h, and the re-blowing time is 10 to 30 minutes.

[0017] Furthermore, the dephosphorization agent is composed of CaO, CaF2, MgO, and FeO mixed in a mass ratio of 40:12:28:20, and the added amount is 2-4% of the total weight of molten iron and scrap steel.

[0018] Furthermore, after pretreatment, the S content in the molten iron is ≤0.005wt%, and the P content is ≤0.005wt%.

[0019] Furthermore, the parameters of the LF furnace bottom blowing are: gas flow rate is 200-300Nm 3 / h.

[0020] Furthermore, the basic refining slag is composed of CaO and CaF2 mixed in a mass ratio of (70-80):(20-30), and the added amount is 1-2% of the weight of the molten iron.

[0021] Furthermore, the deoxidizer I is composed of aluminum particles, coke, and SiC mixed in a mass ratio of 40:35:25, and the added amount is 0.3-1% of the weight of the molten iron.

[0022] Furthermore, the oxygen activity of the molten iron after LF refining is 200-600 ppm, and the temperature is 1600-1650°C.

[0023] Furthermore, the vacuum deoxidation treatment time is ≥20 min, and the vacuum degree is ≤70 Pa.

[0024] Further, in S22, if the slag sample I is black, add 0.3-0.4% of basic refined slag by weight of the molten iron; if the slag sample I is brown, add 0.2-0.3% of basic refined slag by weight of the molten iron; if the slag sample I is gray or brown, add 0.15-0.2% of basic refined slag by weight of the molten iron; if it is yellow-white or green-white, do not add it.

[0025] Furthermore, the deoxidizer II is calcium silicon wire, aluminum wire, and aluminum particles; in S22, if the fixed oxygen value of the molten iron is greater than 600ppm, aluminum particles are added first to reduce it to ≤600ppm; if the fixed oxygen value of the molten iron is 200-600ppm, 500-700 meters of calcium silicon wire are added first, and 100-150 meters of aluminum wire are added; if the fixed oxygen value of the molten iron is 50-200ppm, 500-700 meters of calcium silicon wire and 10-50 meters of aluminum wire are added; if the fixed oxygen value of the molten iron is less than 50ppm, 200-300 meters of calcium silicon wire are added; wherein the maximum single oxygen reduction is 100ppm.

[0026] Furthermore, after RH refining, the fixed oxygen value of the molten iron is less than 50ppm.

[0027] Furthermore, after the low-carbon aluminum-killed steel is cast, it needs to be heat treated; the heat treatment is rolling and continuous annealing in sequence; wherein rolling is divided into rough rolling, finish rolling and cold rolling; and continuous annealing is divided into heating section, insulation section and cooling section.

[0028] The parameters of the rough rolling are: rolling temperature of 1150-1200°C, rolling speed of 3-5m / s, and rolling deformation of 75-80%;

[0029] The parameters of the finishing rolling are: the rolling starting temperature is 1000-1100°C, the rolling ending temperature is 900-950°C, the rolling speed is 7-9 mm / s, and the rolling deformation is 80-90%;

[0030] The cold rolling parameters are: rolling temperature of 200-350° C., and reduction rate of 70-80%.

[0031] The process of the heating section is: heating to 750±10°C at a heating rate of 30-50°C / s, and then heating to 1220-1280°C at a heating rate of 100°C / h;

[0032] The process of the heat preservation section is: heat preservation treatment at 1220-1280°C for 5-20 minutes;

[0033] The process of the cooling section is: first keep warm and slowly cool for 20 to 24 hours, then cool to 200±10°C at a cooling rate of 5 to 15°C / s, and finally water cool to room temperature.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The present invention performs desulfurization and dephosphorization pretreatment on molten iron, thereby improving the purity of molten iron, reducing the number of inclusions, and improving the pouring performance of molten iron;

[0036] 2. The present invention further improves the purity of molten iron through LF and RH refining, and controls the amount of basic refining slag and deoxidizer II added according to the actual situation of molten iron, so as to better improve the purity and deoxidation degree of molten iron;

[0037] 3. The present invention heat treats low-carbon aluminum killed steel, and ultimately achieves the purpose of improving the surface quality of low-carbon aluminum killed steel;

[0038] 4. The present invention comprehensively prepares a low-carbon aluminum-killed steel with excellent deoxidation degree and high purity through "desulfurization and dephosphorization pretreatment → LF, RH refining → heat treatment", and its surface quality is also significantly improved. DETAILED DESCRIPTION

[0039] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0040] The process parameters not specified in the following examples are all conventional conditions; the raw materials can be obtained from public commercial channels.

[0041] Example 1: A low-carbon aluminum-killed steel and its manufacturing process:

[0042] S1: Pretreatment of molten iron for desulfurization and dephosphorization:

[0043] S11: Desulfurization treatment is performed on molten iron with a S content of ≤0.03wt% and a P content of ≤0.12wt% by KR stirring method at a speed of 110r / min for 45min, and the desulfurization temperature is 1540°C. Slag removal is performed before and after adding a desulfurizer (CaO, CaCO3, CaF2, and Mg are mixed in a mass ratio of 60:25:12:3, and the added amount is 1.5% of the weight of the molten iron) to complete desulfurization;

[0044] S12: After desulfurization, scrap steel and molten iron are added to the converter at a mass ratio of 1:4.5, and oxygen is blown from the top and bottom of the converter (gas flow rate is 5000Nm 3 / h, the re-blowing time is 20min), and then add a dephosphorizing agent (CaO, CaF2, MgO, FeO are mixed in a mass ratio of 40:12:28:20, and the added amount is 3.5% of the weight of the molten iron) for dephosphorization treatment, the dephosphorization temperature is 1560℃, and the slag is removed to complete the dephosphorization;

[0045] S2: LF and RH refining treatment of molten iron:

[0046] S21: The pretreated molten iron (with a S content of ≤0.003wt%, a P content of ≤0.003wt%) enters the LF furnace, where its oxygen content and temperature are detected. Argon gas (gas flow rate of 250Nm 3 / h) to adjust the oxygen content and temperature, then add basic refining slag (CaO, CaF2 mixed in a mass ratio of 73:27, the addition amount is 1.5% of the weight of the molten iron), deoxidizer I (aluminum particles, coke, SiC mixed in a mass ratio of 40:35:25, the addition amount is 0.7% of the weight of the molten iron) for refining treatment, measure oxygen at the exit, and complete LF refining. At this time, the oxygen activity of the molten iron is 504ppm and the temperature is 1640℃;

[0047] S22: (1) After LF refining, the molten iron enters the RH furnace for vacuum degassing treatment (vacuum degree is 65Pa, vacuum deoxidation treatment time is 30min), and then the molten iron sample I and slag sample I are taken; (2) The molten iron sample I is analyzed, and manganese alloy and aluminum iron are added according to the content of Mn and Als to adjust Mn and Als to "the mass fraction value of the target component + 0.005"; according to the color of the slag sample I (brown), basic refining slag (CaO and CaF2 are mixed in a mass ratio of 73:27, and the addition amount is 0.28% of the weight of the molten iron) is added until the manganese alloy and aluminum iron are added and stirred for 8min, and the color of the slag is yellow-white; (3) The fixed oxygen value of the molten iron is measured to be 401ppm, and 550 meters of silicon calcium wire and 100 meters of aluminum wire are added in batches according to the fixed oxygen value, and the single oxygen reduction is controlled not to be greater than 100ppm, argon is blown for 10min, the fixed oxygen slag is removed, and the steel is cast to obtain low-carbon aluminum-killed steel;

[0048] S3: Heat treatment of low carbon aluminum killed steel:

[0049] S31: rolling: when the low carbon aluminum killed steel is cooled to 1170°C, rolling is performed at a speed of 4m / s, and the rolling deformation is 78%; then when it is naturally cooled to 1050°C, rolling is performed at a speed of 8mm / s, and the rolling deformation is 88%, and the rolling end temperature is 924°C; then it is water-cooled to 300°C, cold-rolled, and the reduction rate is 75%, and the rolling is completed;

[0050] S32: Continuous annealing: After heating to 760℃ at a heating rate of 40℃ / s, then heating to 1250℃ at a heating rate of 100℃ / h, and keeping warm for 15min; then slowly cooling it for 24h, then cooling it to 200℃ at a cooling rate of 10℃ / s, and finally water cooling it to room temperature to obtain the finished low-carbon aluminum killed steel.

[0051] Example 2: A low-carbon aluminum-killed steel and its manufacturing process:

[0052] S1: Pretreatment of molten iron for desulfurization and dephosphorization:

[0053] S11: Desulfurization treatment is performed on molten iron with a S content of ≤0.03wt% and a P content of ≤0.12wt% by KR stirring method at a speed of 100r / min for 30min, the desulfurization temperature is 1540°C, and slag removal is performed before and after adding a desulfurizer (CaO, CaCO3, CaF2, Mg are mixed in a mass ratio of 60:25:12:3, and the added amount is 1% of the weight of the molten iron) to complete desulfurization;

[0054] S12: After desulfurization, scrap steel and molten iron are added to the converter at a mass ratio of 1:4.5, and oxygen is blown from the top and bottom of the converter (gas flow rate is 3000Nm 3 / h, the re-blowing time is 10min), and then add a dephosphorizing agent (CaO, CaF2, MgO, FeO are mixed in a mass ratio of 40:12:28:20, and the added amount is 2% of the weight of the molten iron) for dephosphorization treatment, the dephosphorization temperature is 1560℃, and the slag is removed to complete the dephosphorization;

[0055] S2: LF and RH refining treatment of molten iron:

[0056] S21: The pretreated molten iron (with a S content of ≤0.005wt%, a P content of ≤0.005wt%) enters the LF furnace, where its oxygen content and temperature are detected. Argon gas (gas flow rate of 200Nm 3 / h) to adjust the oxygen content and temperature, then add basic refining slag (CaO and CaF2 mixed in a mass ratio of 73:27, added in an amount of 1% of the weight of the molten iron) and deoxidizer I (aluminum particles, coke, and SiC mixed in a mass ratio of 40:35:25, added in an amount of 0.3% of the weight of the molten iron) for refining treatment, measure oxygen at the exit, and complete LF refining. At this time, the oxygen activity of the molten iron is 580ppm and the temperature is 1640°C;

[0057] S22: (1) After LF refining, the molten iron enters the RH furnace for vacuum degassing treatment (vacuum degree is 65Pa, vacuum deoxidation treatment time is 20min), and then the molten iron sample I and slag sample I are taken; (2) the molten iron sample I is analyzed, and manganese alloy and aluminum iron are added according to the content of Mn and Als to adjust Mn and Als to "the mass fraction value of the target component + 0.005"; according to the color of the slag sample I (black), basic refining slag (CaO and CaF2 are mixed in a mass ratio of 73:27, and the addition amount is 0.35% of the weight of the molten iron) is added until the manganese alloy and aluminum iron are added and stirred for 10min, and the color of the slag is yellow-white; (3) the fixed oxygen value of the molten iron is measured to be 478ppm, and 550 meters of silicon calcium wire and 100 meters of aluminum wire are added in batches according to the fixed oxygen value, and the single oxygen reduction is controlled not to be greater than 100ppm, argon is blown for 10min, the fixed oxygen slag is removed, and the steel is cast to obtain low-carbon aluminum-killed steel;

[0058] S3: Heat treatment of low carbon aluminum killed steel:

[0059] S31: rolling: when the low carbon aluminum killed steel is cooled to 1170°C, rolling is performed at a speed of 5m / s, and the rolling deformation is 78%; then when it is naturally cooled to 1050°C, rolling is performed at a speed of 9mm / s, and the rolling deformation is 88%, and the rolling end temperature is 924°C; then it is water-cooled to 300°C, cold-rolled, and the reduction rate is 75%, and the rolling is completed;

[0060] S32: Continuous annealing: After heating to 760℃ at a heating rate of 50℃ / s, then heating to 1250℃ at a heating rate of 100℃ / h, and keeping warm for 5 minutes; then slowly cooling it for 20h, then cooling it to 200℃ at a cooling rate of 15℃ / s, and finally water-cooling it to room temperature to obtain the finished low-carbon aluminum killed steel.

[0061] Example 3: A low-carbon aluminum-killed steel and its manufacturing process:

[0062] S1: Pretreatment of molten iron for desulfurization and dephosphorization:

[0063] S11: Using KR stirring method, desulfurization treatment is performed on molten iron with S content ≤ 0.03wt% and P content ≤ 0.12wt% at a speed of 120r / min for 60min, the desulfurization temperature is 1540°C, and slag removal is performed before and after adding desulfurizer (CaO, CaCO3, CaF2, Mg are mixed in a mass ratio of 60:25:12:3, and the added amount is 2% of the weight of the molten iron) to complete desulfurization;

[0064] S12: After desulfurization, scrap steel and molten iron are added to the converter at a mass ratio of 1:4.5, and oxygen is blown from the top and bottom of the converter (gas flow rate is 6000Nm 3 / h, the re-blowing time is 30min), and then add a dephosphorizing agent (CaO, CaF2, MgO, FeO are mixed in a mass ratio of 40:12:28:20, and the added amount is 4% of the weight of the molten iron) for dephosphorization treatment, the dephosphorization temperature is 1560℃, and the slag is removed to complete the dephosphorization;

[0065] S2: LF and RH refining treatment of molten iron:

[0066] S21: The pretreated molten iron (with a S content of ≤0.003wt%, a P content of ≤0.003wt%) enters the LF furnace, where its oxygen content and temperature are detected. Argon gas (gas flow rate of 300Nm 3 / h) to adjust the oxygen content and temperature, then add basic refining slag (CaO and CaF2 mixed in a mass ratio of 73:27, added in an amount of 2% of the weight of the molten iron) and deoxidizer I (aluminum particles, coke, and SiC mixed in a mass ratio of 40:35:25, added in an amount of 1% of the weight of the molten iron) for refining treatment, measure oxygen at the exit, and complete LF refining. At this time, the oxygen activity of the molten iron is 472ppm and the temperature is 1640°C;

[0067] S22: (1) After LF refining, the molten iron enters the RH furnace for vacuum degassing treatment (vacuum degree is 65Pa, vacuum deoxidation treatment time is 30min), and then the molten iron sample I and slag sample I are taken; (2) the molten iron sample I is analyzed, and manganese alloy and aluminum iron are added according to the content of Mn and Als to adjust Mn and Als to "the mass fraction value of the target component + 0.005"; according to the color of the slag sample I (brown), basic refining slag (CaO and CaF2 are mixed in a mass ratio of 73:27, and the addition amount is 0.28% of the weight of the molten iron) is added until the manganese alloy and aluminum iron are added and stirred for 8min, and the color of the slag is yellow-white; (3) the fixed oxygen value of the molten iron is measured to be 376ppm, and 550 meters of silicon calcium wire and 100 meters of aluminum wire are added in batches according to the fixed oxygen value, and the single oxygen reduction is controlled not to be greater than 100ppm, argon is blown for 10min, the fixed oxygen slag is removed, and the steel is cast to obtain low-carbon aluminum-killed steel;

[0068] S3: Heat treatment of low carbon aluminum killed steel:

[0069] S31: rolling: when the low carbon aluminum killed steel is cooled to 1170°C, rolling is performed at a speed of 3m / s, and the rolling deformation is 78%; then when it is naturally cooled to 1050°C, rolling is performed at a speed of 7mm / s, and the rolling deformation is 88%, and the rolling end temperature is 924°C; then it is water-cooled to 300°C, cold-rolled, and the reduction rate is 75%, and the rolling is completed;

[0070] S32: Continuous annealing: After heating to 760°C at a heating rate of 30°C / s, then heating to 1250°C at a heating rate of 100°C / h, and keeping warm for 20 minutes; then slowly cool it for 24 hours, then cool it to 200°C at a cooling rate of 5°C / s, and finally water-cool it to room temperature to obtain the finished low-carbon aluminum killed steel.

[0071] Based on Example 1, a control experiment is carried out, and comparative examples 1 to 3 are set as follows:

[0072] Comparative Example 1: Comparative Example 1 is based on Example 1, and the dosage of the desulfurizer and the dephosphorization agent is adjusted, and other processes remain unchanged, specifically:

[0073] A low-carbon aluminum-killed steel and its manufacturing process:

[0074] S1: Pretreatment of molten iron for desulfurization and dephosphorization:

[0075] S11: Desulfurization treatment is performed on molten iron with a S content of ≤0.03wt% and a P content of ≤0.12wt% by KR stirring method at a speed of 110r / min for 45min, the desulfurization temperature is 1540°C, and slag removal is performed before and after adding a desulfurizer (CaO, CaCO3, CaF2, Mg are mixed in a mass ratio of 60:25:12:3, and the added amount is 0.5% of the weight of the molten iron) to complete desulfurization;

[0076] S12: After desulfurization, scrap steel and molten iron are added to the converter at a mass ratio of 1:4.5, and oxygen is blown from the top and bottom of the converter (gas flow rate is 5000Nm 3 / h, the re-blowing time is 20min), and then add a dephosphorizing agent (CaO, CaF2, MgO, FeO are mixed in a mass ratio of 40:12:28:20, and the added amount is 1.5% of the weight of the molten iron) for dephosphorization treatment, the dephosphorization temperature is 1560℃, and the slag is removed to complete the dephosphorization;

[0077] S2: LF and RH refining treatment of molten iron:

[0078] S21: The pretreated molten iron (S content> 0.005wt%, P content> 0.005wt%) enters the LF furnace, and its oxygen content and temperature are detected. According to the test results, argon gas (gas flow rate is 250Nm 3 / h) to adjust the oxygen content and temperature, then add basic refining slag (CaO and CaF2 mixed in a mass ratio of 73:27, the addition amount is 1.5% of the weight of the molten iron) and deoxidizer I (aluminum particles, coke, SiC mixed in a mass ratio of 40:35:25, the addition amount is 0.7% of the weight of the molten iron) for refining treatment, measure oxygen at the exit, and complete LF refining. At this time, the oxygen activity of the molten iron is 814ppm and the temperature is 1640℃;

[0079] S22: (1) After LF refining, the molten iron enters the RH furnace for vacuum degassing treatment (vacuum degree is 65Pa, vacuum deoxidation treatment time is 30min), and then the molten iron sample I and slag sample I are taken; (2) The molten iron sample I is analyzed, and manganese alloy and aluminum iron are added according to the content of Mn and Als to adjust Mn and Als to "the mass fraction value of the target component + 0.005"; according to the color of the slag sample I (brown), basic refining slag (CaO and CaF2 are mixed in a mass ratio of 73:27, and the addition amount is 0.28% of the weight of the molten iron) is added until the manganese alloy and aluminum iron are added and stirred for 8min, and the color of the slag is yellow-white; (3) The fixed oxygen value of the molten iron is measured to be 612ppm, and 550 meters of silicon calcium wire and 100 meters of aluminum wire are added in batches according to the fixed oxygen value, and the single oxygen reduction is controlled not to be greater than 100ppm, argon is blown for 10min, the fixed oxygen slag is removed, and the steel is cast to obtain low-carbon aluminum-killed steel;

[0080] S3: Heat treatment of low carbon aluminum killed steel:

[0081] S31: rolling: when the low carbon aluminum killed steel is cooled to 1170°C, rolling is performed at a speed of 4m / s, and the rolling deformation is 78%; then when it is naturally cooled to 1050°C, rolling is performed at a speed of 8mm / s, and the rolling deformation is 88%, and the rolling end temperature is 924°C; then it is water-cooled to 300°C, cold-rolled, and the reduction rate is 75%, and the rolling is completed;

[0082] S32: Continuous annealing: After heating to 760℃ at a heating rate of 40℃ / s, then heating to 1250℃ at a heating rate of 100℃ / h, and keeping warm for 15min; then slowly cooling it for 24h, then cooling it to 200℃ at a cooling rate of 10℃ / s, and finally water cooling it to room temperature to obtain the finished low-carbon aluminum killed steel.

[0083] Comparative Example 2: Comparative Example 2 is based on Example 1, and the dosage of basic refining agent, deoxidizer I, and deoxidizer II is adjusted, and other processes remain unchanged, specifically:

[0084] A low-carbon aluminum-killed steel and its manufacturing process:

[0085] S1: Pretreatment of molten iron for desulfurization and dephosphorization:

[0086] S11: Desulfurization treatment is performed on molten iron with a S content of ≤0.03wt% and a P content of ≤0.12wt% by KR stirring method at a speed of 110r / min for 45min, and the desulfurization temperature is 1540°C. Slag removal is performed before and after adding a desulfurizer (CaO, CaCO3, CaF2, and Mg are mixed in a mass ratio of 60:25:12:3, and the added amount is 1.5% of the weight of the molten iron) to complete desulfurization;

[0087] S12: After desulfurization, scrap steel and molten iron are added to the converter at a mass ratio of 1:4.5, and oxygen is blown from the top and bottom of the converter (gas flow rate is 5000Nm 3 / h, the re-blowing time is 20min), and then add a dephosphorizing agent (CaO, CaF2, MgO, FeO are mixed in a mass ratio of 40:12:28:20, and the added amount is 3.5% of the weight of the molten iron) for dephosphorization treatment, the dephosphorization temperature is 1560℃, and the slag is removed to complete the dephosphorization;

[0088] S2: LF and RH refining treatment of molten iron:

[0089] S21: The pretreated molten iron (with a S content of ≤0.003wt%, a P content of ≤0.003wt%) enters the LF furnace, where its oxygen content and temperature are detected. Argon gas (gas flow rate of 250Nm 3 / h) to adjust the oxygen content and temperature, then add basic refining slag (CaO and CaF2 are mixed in a mass ratio of 73:27, and the added amount is 0.5% of the weight of the molten iron) and deoxidizer I (aluminum particles, coke, and SiC are mixed in a mass ratio of 40:35:25, and the added amount is 0.1% of the weight of the molten iron) for refining treatment, measure oxygen at the exit, and complete LF refining. At this time, the oxygen activity of the molten iron is 824ppm and the temperature is 1640℃;

[0090] S22: (1) After LF refining, the molten iron enters the RH furnace for vacuum degassing (vacuum degree of 65 Pa, vacuum deoxidation treatment time of 30 min), and then the molten iron sample I and the slag sample I are taken; (2) The molten iron sample I is analyzed, and manganese alloy and aluminum iron are added according to the content of Mn and Als to adjust Mn and Als to "the mass fraction value of the target component + 0.005"; according to the color of the slag sample I (black), basic refining slag (CaO, CaF2 mixed in a mass ratio of 73:27) is added , the first addition amount is 0.38% of the weight of the molten iron, and the second addition amount is 0.16% of the weight of the molten iron), until the manganese alloy and aluminum iron are added and stirred for 8 minutes, and the slag color is yellow-white; (3) the fixed oxygen value of the molten iron is measured to be 657ppm, and aluminum particles are added to adjust the fixed oxygen value of the molten iron to 600ppm. Then, 550 meters of calcium silicon wire and 100 meters of aluminum wire are added in batches according to the fixed oxygen value, and the single oxygen reduction is controlled not to be greater than 100ppm. Argon is blown for 10 minutes, the fixed oxygen slag is removed, and the steel is cast to obtain low-carbon aluminum-killed steel;

[0091] S3: Heat treatment of low carbon aluminum killed steel:

[0092] S31: rolling: when the low carbon aluminum killed steel is cooled to 1170°C, rolling is performed at a speed of 4m / s, and the rolling deformation is 78%; then when it is naturally cooled to 1050°C, rolling is performed at a speed of 8mm / s, and the rolling deformation is 88%, and the rolling end temperature is 924°C; then it is water-cooled to 300°C, cold-rolled, and the reduction rate is 75%, and the rolling is completed;

[0093] S32: Continuous annealing: After heating to 760℃ at a heating rate of 40℃ / s, then heating to 1250℃ at a heating rate of 100℃ / h, and keeping warm for 15min; then slowly cooling it for 24h, then cooling it to 200℃ at a cooling rate of 10℃ / s, and finally water cooling it to room temperature to obtain the finished low-carbon aluminum killed steel.

[0094] Comparative Example 3: Comparative Example 3 is based on Example 1, with the following adjustments: low-carbon aluminum killed steel is not subjected to continuous annealing, and other processes remain unchanged, specifically:

[0095] A low-carbon aluminum-killed steel and its manufacturing process:

[0096] S1: Pretreatment of molten iron for desulfurization and dephosphorization:

[0097] S11: Desulfurization treatment is performed on molten iron with a S content of ≤0.03wt% and a P content of ≤0.12wt% by KR stirring method at a speed of 110r / min for 45min, and the desulfurization temperature is 1540°C. Slag removal is performed before and after adding a desulfurizer (CaO, CaCO3, CaF2, and Mg are mixed in a mass ratio of 60:25:12:3, and the added amount is 1.5% of the weight of the molten iron) to complete desulfurization;

[0098] S12: After desulfurization, scrap steel and molten iron are added to the converter at a mass ratio of 1:4.5, and oxygen is blown from the top and bottom of the converter (gas flow rate is 5000Nm 3 / h, the re-blowing time is 20min), and then add a dephosphorizing agent (CaO, CaF2, MgO, FeO are mixed in a mass ratio of 40:12:28:20, and the added amount is 3.5% of the weight of the molten iron) for dephosphorization treatment, the dephosphorization temperature is 1560℃, and the slag is removed to complete the dephosphorization;

[0099] S2: LF and RH refining treatment of molten iron:

[0100] S21: The pretreated molten iron (with a S content of ≤0.003wt%, a P content of ≤0.003wt%) enters the LF furnace, where its oxygen content and temperature are detected. Argon gas (gas flow rate of 250Nm 3 / h) to adjust the oxygen content and temperature, then add basic refining slag (CaO, CaF2 mixed in a mass ratio of 73:27, the addition amount is 1.5% of the weight of the molten iron), deoxidizer I (aluminum particles, coke, SiC mixed in a mass ratio of 40:35:25, the addition amount is 0.7% of the weight of the molten iron) for refining treatment, measure oxygen at the exit, and complete LF refining. At this time, the oxygen activity of the molten iron is 504ppm and the temperature is 1640℃;

[0101] S22: (1) After LF refining, the molten iron enters the RH furnace for vacuum degassing treatment (vacuum degree is 65Pa, vacuum deoxidation treatment time is 30min), and then the molten iron sample I and slag sample I are taken; (2) The molten iron sample I is analyzed, and manganese alloy and aluminum iron are added according to the content of Mn and Als to adjust Mn and Als to "the mass fraction value of the target component + 0.005"; according to the color of the slag sample I (brown), basic refining slag (CaO and CaF2 are mixed in a mass ratio of 73:27, and the addition amount is 0.28% of the weight of the molten iron) is added until the manganese alloy and aluminum iron are added and stirred for 8min, and the color of the slag is yellow-white; (3) The fixed oxygen value of the molten iron is measured to be 401ppm, and 550 meters of silicon calcium wire and 100 meters of aluminum wire are added in batches according to the fixed oxygen value, and the single oxygen reduction is controlled not to be greater than 100ppm, argon is blown for 10min, the fixed oxygen slag is removed, and the steel is cast to obtain low-carbon aluminum-killed steel;

[0102] S3: Heat treatment of low carbon aluminum killed steel:

[0103] S31: Rolling: When the low carbon aluminum killed steel is cooled to 1170°C, it is rolled at a speed of 4m / s, and the rolling deformation is 78%; then when it is naturally cooled to 1050°C, it is rolled at a speed of 8mm / s, and the rolling deformation is 88%, and the rolling termination temperature is 924°C; then it is water-cooled to 300°C and cold-rolled with a reduction rate of 75% to complete the rolling; the finished low carbon aluminum killed steel is obtained.

[0104] The oxygen activity of the molten iron after LF refining and the fixed oxygen value of the molten iron after RH refining are shown in Table 1 below:

[0105] Table 1

[0106] Examples Oxygen activity (ppm) Oxygen value (ppm) Example 1 504 20 Example 2 580 28 Example 3 472 18 Comparative Example 1 814 30 Comparative Example 2 824 34 Comparative Example 3 504 20

[0107] The composition analysis of the above low carbon aluminum killed steel is shown in Table 2 below:

[0108] Table 2

[0109] Examples C (wt%) Mn (wt%) Si (wt%) Als (wt%) Example 1 0.020 0.210 0.014 0.020 Example 2 0.027 0.210 0.013 0.035 Example 3 0.018 0.210 0.013 0.030 Comparative Example 1 0.045 0.210 0.012 0.051 Comparative Example 2 0.035 0.210 0.012 0.047 Comparative Example 3 0.020 0.210 0.014 0.020

[0110] The low carbon aluminum killed steel prepared in Example 1 and Comparative Example 3 was pickled with 15wt% hydrochloric acid for 2 minutes, and then the surface areas of the network defects on the surfaces of the two were compared, as shown in Table 3 below:

[0111] Table 3

[0112] Examples Proportion (%) Example 1 0 Comparative Example 1 34

[0113] Analysis of results: It can be seen from Tables 1 and 2 that the low carbon aluminum killed steel prepared by the present invention has a significant degree of deoxidation and excellent purity after desulfurization and dephosphorization pretreatment, LF furnace and RH furnace refining, and its composition is within an appropriate range; in addition, combined with the data in Table 3, it can be seen that the present invention has prepared a low carbon aluminum killed steel with high purity and excellent surface quality.

[0114] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for manufacturing low carbon aluminum killed steel, characterized in that: The following steps are involved: S1: Pretreatment of molten iron for desulfurization and dephosphorization: S11: Desulfurization of molten iron with a S content of ≤0.03wt% and a P content of ≤0.12wt% is carried out by KR stirring method, the desulfurization temperature is 1530-1550°C, and slag removal is required before and after adding the desulfurizer to complete the desulfurization; S12: After desulfurization, scrap steel and molten iron are added into the converter in a mass ratio of 1:4-5, oxygen is blown from the top and bottom of the converter, and then a dephosphorizing agent is added for dephosphorization treatment. The dephosphorization temperature is 1550-1580°C, and the slag is removed to complete the dephosphorization; S2: LF and RH refining treatment of molten iron: S21: The pretreated molten iron enters the LF furnace, and its oxygen content and temperature are detected. Argon is blown from the bottom of the LF furnace to adjust the oxygen content and temperature according to the detection results, and then basic refining slag and deoxidizer I are added for refining treatment. The oxygen is measured before leaving the furnace to complete LF refining; S22: (1) After LF refining, the molten iron enters the RH furnace for vacuum degassing, and then the molten iron sample I and the slag sample I are taken; (2) The molten iron sample I is analyzed, and manganese alloy and aluminum iron are added according to the content of Mn and Als to adjust Mn and Als to "the mass fraction value of the target component + 0.005"; basic refining slag is added according to the color of the slag sample I until the manganese alloy and aluminum iron are added and stirred for 3 to 10 minutes, and the color of the slag is yellow-white or green-white; (3) The fixed oxygen value of the molten iron is measured, and deoxidizer II is added according to the fixed oxygen value, argon is blown for 5 to 10 minutes, the slag is deoxidized, and the steel is cast to obtain low-carbon aluminum-killed steel.

2. The manufacturing process of low carbon aluminum killed steel according to claim 1, characterized in that: In S11, the parameters of the KR stirring are: stirring speed is 100-120r / min, stirring time is 30-60min; the desulfurizer is composed of CaO, CaCO3, CaF2, and Mg mixed in a mass ratio of 60:25:12:3, and the added amount is 1-2% of the weight of the molten iron.

3. The manufacturing process of low carbon aluminum killed steel according to claim 1, characterized in that: In S12, the parameters of the converter top and bottom blowing are: gas flow rate is 3000~6000Nm 3 / h, the re-blowing time is 10 to 30 minutes; the dephosphorization agent is composed of CaO, CaF2, MgO, and FeO mixed in a mass ratio of 40:12:28:20, and the added amount is 2 to 4% of the total weight of molten iron and scrap steel.

4. The manufacturing process of low carbon aluminum killed steel according to claim 1, characterized in that: After the pretreatment, the S content in the molten iron is ≤0.005wt%, and the P content is ≤0.005wt%.

5. The manufacturing process of low carbon aluminum killed steel according to claim 1, characterized in that: In S21, the parameters of the LF furnace bottom blowing are: gas flow rate is 200-300 Nm 3 / h; the basic refining slag is composed of CaO and CaF2 in a mass ratio of (70-80): (20-30), and the added amount is 1-2% of the weight of the molten iron; the deoxidizer I is composed of aluminum particles, coke, and SiC in a mass ratio of 40:35:25, and the added amount is 0.3-1% of the weight of the molten iron; the oxygen activity of the molten iron after LF refining is 200-600ppm, and the temperature is 1600-1650℃.

6. The manufacturing process of low carbon aluminum killed steel according to claim 1, characterized in that: In S22, if the slag sample I is black, add 0.3-0.4% of the weight of the molten iron basic refining slag; if the slag sample I is brown, add 0.2-0.3% of the weight of the molten iron basic refining slag; if the slag sample I is gray or brown, add 0.15-0.2% of the weight of the molten iron basic refining slag; if it is yellow-white or green-white, no basic refining slag is added; the vacuum deoxidation treatment time is ≥20min, and the vacuum degree is ≤70Pa; the deoxidizer II is calcium silicon wire, aluminum wire, aluminum particles; in S22, if If the fixed oxygen value of molten iron is greater than 600ppm, add aluminum particles first to reduce it to ≤600ppm; if the fixed oxygen value of molten iron is 200-600ppm, first add 500-700 meters of calcium silicon wire and 100-150 meters of aluminum wire; if the fixed oxygen value of molten iron is 50-200ppm, add 500-700 meters of calcium silicon wire and 10-50 meters of aluminum wire; if the fixed oxygen value of molten iron is less than 50ppm, add 200-300 meters of calcium silicon wire; among them, the maximum single oxygen reduction is 100ppm.

7. The manufacturing process of low carbon aluminum killed steel according to claim 1, characterized in that: After RH refining, the fixed oxygen value of the molten iron is less than 50ppm.

8. The low-carbon aluminum killed steel manufactured by the manufacturing process of low-carbon aluminum killed steel according to any one of claims 1 to 7 is characterized in that: The invention comprises the following chemical compositions in mass fractions: C≤0.03wt%, Mn 0.15-0.30wt%, Si≤0.03wt%, Als 0.02-0.04wt%, and the rest are Fe and unavoidable impurities.

9. The low carbon aluminum killed steel according to claim 8, characterized in that: The low carbon aluminum killed steel also needs to be heat treated, and the heat treatment is rolling and continuous annealing in sequence; wherein rolling is divided into rough rolling, finish rolling and cold rolling; and continuous annealing is divided into heating section, heat preservation section and cooling section.

10. The low carbon aluminum killed steel according to claim 9, characterized in that: The parameters of the rough rolling are: rolling temperature of 1150-1200°C, rolling speed of 3-5m / s, rolling deformation of 75-80%; the parameters of the finish rolling are: rolling starting temperature of 1000-1100°C, rolling end temperature of 900-950°C, rolling speed of 7-9mm / s, rolling deformation of 80-90%; the parameters of the cold rolling are: rolling temperature of 200-350°C, reduction rate of 70-80% The process of the heating section is: heating to 750±10℃ at a heating rate of 30~50℃ / s, and then heating to 1220~1280℃ at a heating rate of 100℃ / h; the process of the heat preservation section is: heat preservation at 1220~1280℃ for 5~20min; the process of the cooling section is: first keep warm for 20~24h, then cool to 200±10℃ at a cooling rate of 5~15℃ / s, and finally water cool to room temperature.