Low-carbon aluminum-killed steel and manufacturing process thereof

Abstract

The application relates to the technical field of steel smelting, in particular to a low-carbon aluminum-killed steel and a manufacturing process thereof. Through desulfurization and dephosphorization pretreatment of the molten iron, the molten iron with the content of S being less than or equal to 0.005wt% and the content of P being less than or equal to 0.005wt% is obtained; then the molten iron is purified through LF and RH refining treatment, the molten iron with the oxygen value being less than 50ppm is obtained, and finally the low-carbon aluminum-killed steel is obtained through casting. In order to reduce the coarse grain defects in the low-carbon aluminum-killed steel, the low-carbon aluminum-killed steel is further subjected to heat treatment in the application, and the low-carbon aluminum-killed steel with high cleanliness and excellent surface quality is comprehensively obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel smelting, and particularly relates to a low-carbon aluminum killed steel and a manufacturing process thereof. BACKGROUND

[0002] The low-carbon aluminum killed steel is widely applied in the fields of automobile manufacturing, construction, household appliances and the like due to excellent mechanical properties and processing properties. At present, four kinds of process paths are generally adopted by mainstream steel plants at home and abroad to produce the low-carbon aluminum killed steel, i.e., (1) "hot metal pretreatment -> top and bottom combined blowing converter -> CAS-OB -> continuous casting"; (2) "hot metal pretreatment -> top and bottom combined blowing converter -> argon blowing station -> continuous casting"; (3) "hot metal pretreatment -> top and bottom combined blowing converter -> RH -> continuous casting"; and (4) "hot metal pretreatment -> top and bottom combined blowing converter -> LF -> continuous casting".

[0003] However, with the actual application needs, greater requirements are put forward for the performance of the low-carbon aluminum killed steel, such as excellent cleanliness and surface quality. In order to optimize and improve the low-carbon aluminum killed steel, corresponding adjustments are made from steel smelting to heat treatment in the present application, and a low-carbon aluminum killed steel with high cleanliness and excellent surface quality is comprehensively obtained, which can be better applied. SUMMARY

[0004] The present application aims to provide a low-carbon aluminum killed steel and a manufacturing process thereof to solve the problems in the prior art.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0006] The low-carbon aluminum killed steel comprises the following mass fractions of chemical components: C ≤0.03wt%, Mn 0.15~0.30wt%, Si ≤0.03wt%, Als 0.02~0.04wt%, and the rest is Fe and inevitable impurities.

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

[0008] S1: performing desulfurization and dephosphorization pretreatment on the hot metal:

[0009] S11: adopting the KR stirring method to perform desulfurization treatment on the hot metal with the content of S ≤0.03wt% and the content of P ≤0.12wt%, the desulfurization temperature is 1530~1550℃, and slagging is required before and after the desulfurizer is added, and the desulfurization is completed;

[0010] S12: after the desulfurization, the scrap steel and the hot metal are added into the converter at a mass ratio of 1:4~5, oxygen is blown from the top and bottom of the converter, and a dephosphorization agent is added to perform dephosphorization treatment, the dephosphorization temperature is 1550~1580℃, and slagging is performed to complete the dephosphorization;

[0011] S2: The molten iron is subjected to LF and RH refining treatment:

[0012] S21: The pretreated molten iron is introduced into the LF furnace, and the oxygen content and temperature thereof are detected, the oxygen content and temperature are adjusted by blowing argon from the bottom of the LF furnace according to the detection results, and then the molten iron is subjected to refining treatment by adding basic refining slag and deoxidizer I, the oxygen content is measured, and the LF refining is completed.

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

[0014] Further, the parameters of the KR stirring are as follows: the stirring speed is 100-120 r / min, and the stirring time is 30-60 min.

[0015] Further, the desulfurizing agent is composed of CaO, CaCO3, CaF2 and Mg in a mass ratio of 60:25:12:3, and the addition amount is 1-2% of the weight of the molten iron.

[0016] Further, the parameters of the top and bottom combined blowing of the converter are as follows: the gas flow is 3000-6000 Nm 3 / h, and the combined blowing time is 10-30 min.

[0017] Further, the dephosphorizing agent is composed of CaO, CaF2, MgO and FeO in a mass ratio of 40:12:28:20, and the addition amount is 2-4% of the sum of the weight of the molten iron and scrap steel.

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

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

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

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

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

[0023] Further, 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, 0.3-0.4% of the weight of the molten iron of basic refining slag is added; if the slag sample I is brown, 0.2-0.3% of the weight of the molten iron of basic refining slag is added; if the slag sample I is gray or brown, 0.15-0.2% of the weight of the molten iron of basic refining slag is added; and if it is yellow-white or green-white, nothing is added.

[0025] Further, the deoxidizer II is silicon-calcium wire, aluminum wire, and aluminum particles; in S22, if the oxygen value of the molten iron is >600 ppm, aluminum particles are first added to reduce it to ≤600 ppm; if the oxygen value of the molten iron is 200-600 ppm, 500-700 m of silicon-calcium wire and 100-150 m of aluminum wire are first added; if the oxygen value of the molten iron is 50-200 ppm, 500-700 m of silicon-calcium wire and 10-50 m of aluminum wire are added; if the oxygen value of the molten iron is <50 ppm, 200-300 m of silicon-calcium wire is added; and the maximum oxygen reduction per time is 100 ppm.

[0026] Further, after the RH refining, the oxygen value of the molten iron is <50 ppm.

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

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

[0029] The parameters of the finish rolling are that the rolling start temperature is 1000-1100℃, the rolling end temperature is 900-950℃, the rolling speed is 7-9 mm / s, and the rolling deformation is 80-90%;

[0030] The parameters of the cold rolling are that the rolling temperature is 200-350℃, and the reduction is 70-80%.

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

[0032] The process of the holding section is: holding treatment at 1220-1280 DEG C for 5-20 min;

[0033] The process of the cooling section is: first holding and slow cooling for 20-24 h, then cooling to 200±10 DEG C at a cooling rate of 5-15 DEG C / s, and finally water cooling to room temperature.

[0034] Compared with the prior art, the beneficial effects of the present application are:

[0035] 1. The present application carries out desulphurization and dephosphorization pretreatment on the molten iron, improves the purity of the molten iron, reduces the number of inclusions, and can improve the pouring performance of the molten iron;

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

[0037] 3. The present application carries out heat treatment on the low-carbon aluminum killed steel, and finally achieves the purpose of improving the surface quality of the low-carbon aluminum killed steel;

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

[0039] All other embodiments obtained by those skilled in the art based on the embodiments in the present application without creative labor are within the scope of protection of the present application.

[0040] The process parameters not marked with conditions 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 a manufacturing process thereof:

[0042] S1: Desulphurization and dephosphorization pretreatment is carried out on the molten iron:

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

[0044] S12: After desulfurization, scrap and molten iron are added to the converter in a mass ratio of 1:4.5, top and bottom combined blowing of oxygen gas (gas flow is 5000 Nm 3 / h, combined blowing time is 20 min), and dephosphorization agent (CaO, CaF2, MgO, FeO mixed in a mass ratio of 40:12:28:20, the amount of addition is 3.5% of the weight of molten iron) is added for dephosphorization treatment, dephosphorization temperature is 1560℃, slagging and tapping are completed to finish dephosphorization;

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

[0046] S21: The pretreated molten iron (S content ≤0.003wt%, P content ≤0.003wt%) enters the LF furnace, the oxygen content and temperature are detected, the oxygen content and temperature are adjusted by blowing argon gas (gas flow is 250 Nm 3 / h) from the bottom of the LF furnace according to the detection results, and basic refining slag (CaO, CaF2 mixed in a mass ratio of 73:27, the amount of addition is 1.5% of the weight of molten iron), deoxidizer I (aluminum particles, coke, SiC mixed in a mass ratio of 40:35:25, the amount of addition is 0.7% of the weight of molten iron) are added for refining treatment, the oxygen content is measured at the outlet, and the LF refining is completed, at this time the oxygen activity of the molten iron is 504 ppm, 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 65 Pa, vacuum deoxidation treatment time is 30 min), then molten iron sample I and slag sample I are taken; (2) analyze the molten iron sample I, add manganese alloy and aluminum iron to adjust Mn and Als to "target component mass fraction value + 0.005" according to the content of Mn and Als; add basic refining slag (CaO, CaF2 mixed in a mass ratio of 73:27, the amount of addition is 0.28% of the weight of molten iron) according to the color of slag sample I (brownish), until the color of slag is yellowish white after the addition of manganese alloy and aluminum iron and stirring for 8 min; (3) the fixed oxygen value of the molten iron is 401 ppm, according to the fixed oxygen value, add 550 meters of silicon calcium wire and 100 meters of aluminum wire in batches, control the single oxygen reduction not more than 100 ppm, blow argon for 10 min, and then perform fixed oxygen slagging, tapping and casting to obtain low-carbon aluminum killed steel;

[0048] S3: heat treatment of the low-carbon aluminum killed steel:

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

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

[0051] Example 2: a low-carbon aluminum killed steel and a manufacturing process thereof:

[0052] S1: desulfurization and dephosphorization pretreatment of the molten iron:

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

[0054] S12: after desulfurization, scrap and molten iron are added to the converter in a mass ratio of 1:4.5, oxygen is blown from the top and bottom of the converter (gas flow is 3000 Nm 3 / h, reblowing time is 10 min), dephosphorizing agent (CaO, CaF2, MgO, FeO mixed in a mass ratio of 40:12:28:20, the amount added is 2% of the weight of the molten iron) is added for dephosphorization treatment, dephosphorization temperature is 1560℃, slagging is performed, and dephosphorization is completed;

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

[0056] S21: the pretreated molten iron (S content ≤0.005wt%, P content ≤0.005wt%) enters the LF furnace, the oxygen content and temperature are detected, argon is blown from the bottom of the LF furnace according to the detection results (gas flow is 200 Nm 3h) Adjusting the oxygen content and temperature, adding basic refining slag (CaO, CaF2 mixed in a mass ratio of 73:27, the amount of which is 1% of the weight of the molten iron), deoxidizer I (aluminum particles, coke, SiC mixed in a mass ratio of 40:35:25, the amount of which is 0.3% of the weight of the molten iron) for refining treatment, and measuring the oxygen content at the outlet to complete the LF refining. At this time, the oxygen activity of the molten iron is 580 ppm, and the temperature is 1640°C.

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

[0058] S3: Hot treatment of the low-carbon aluminum killed steel:

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

[0060] S32: Continuous annealing: heating to 760°C at a heating rate of 50°C / s, then heating to 1250°C at a heating rate of 100°C / h, holding for 5 min, then slow cooling for 20 h, then cooling to 200°C at a cooling rate of 15°C / s, and finally water-cooling to room temperature to obtain finished low-carbon aluminum killed steel.

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

[0062] S1: Desulfurization and dephosphorization pretreatment of the molten iron:

[0063] S11: Desulfurization treatment of molten iron with S content ≤0.03wt%, P content ≤0.12wt% at a rotation speed of 120r / min for 60min by KR stirring method, desulfurization temperature is 1540℃, desulfurizer (CaO, CaCO3, CaF2, Mg mixed in a mass ratio of 60:25:12:3, the amount of addition is 2% of the weight of molten iron) is added, and slagging is needed before and after the addition of desulfurizer to complete desulfurization;

[0064] S12: After desulfurization, scrap and molten iron are added to the converter in a mass ratio of 1:4.5, top and bottom combined blowing of oxygen gas (gas flow is 6000Nm 3 / h, combined blowing time is 30min), and dephosphorization agent (CaO, CaF2, MgO, FeO mixed in a mass ratio of 40:12:28:20, the amount of addition is 4% of the weight of molten iron) is added for dephosphorization treatment, dephosphorization temperature is 1560℃, slagging and tapping are completed to finish dephosphorization;

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

[0066] S21: The pretreated molten iron (S content ≤0.003wt%, P content ≤0.003wt%) enters the LF furnace, the oxygen content and temperature are detected, the oxygen content and temperature are adjusted by blowing argon gas (gas flow is 300Nm 3 / h) from the bottom of the LF furnace according to the detection results, and basic refining slag (CaO, CaF2 mixed in a mass ratio of 73:27, the amount of addition is 2% of the weight of molten iron), deoxidizer I (aluminum particles, coke, SiC mixed in a mass ratio of 40:35:25, the amount of addition is 1% of the weight of molten iron) are added for refining treatment, the oxygen content is measured at the outlet, and the LF refining is completed, at this time the oxygen activity of the molten iron is 472ppm, and the temperature is 1640℃;

[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), then molten iron sample I and slag sample I are taken; (2) analyze the molten iron sample I, add manganese alloy and aluminum iron to adjust Mn and Als to "target component mass fraction value+0.005" according to the content of Mn and Als; add basic refining slag (CaO, CaF2 mixed in a mass ratio of 73:27, the amount of addition is 0.28% of the weight of molten iron) according to the color (brownish) of slag sample I, until the color of the slag is yellowish white after the manganese alloy and aluminum iron are added and stirred for 8min; (3) the fixed oxygen value of the molten iron is measured as 376ppm, 550 meters of silicon calcium wire and 100 meters of aluminum wire are added according to the fixed oxygen value, the single oxygen reduction should not be greater than 100ppm, argon is blown for 10min, the fixed oxygen slagging is performed, and the low-carbon aluminum killed steel is obtained by tapping and casting;

[0068] S3: heat treatment of the low-carbon aluminum killed steel:

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

[0070] S32: continuous annealing: heating to 760℃ at a heating rate of 30℃ / s, then heating to 1250℃ at a heating rate of 100℃ / h, holding for 20 min, then slow cooling for 24 h, then cooling to 200℃ at a cooling rate of 5℃ / s, and finally water-cooling to room temperature to obtain the finished low-carbon aluminum killed steel.

[0071] Based on Example 1, control experiments are performed, and Comparative Examples 1-3 are set, as follows:

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

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

[0074] S1: desulfurization and dephosphorization pretreatment of the molten iron:

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

[0076] S12: after desulfurization, scrap and molten iron are added to the converter in a mass ratio of 1:4.5, oxygen is blown from the top and bottom of the converter (gas flow is 5000 Nm 3 / h, and the reblowing time is 20 min), dephosphorizer (CaO, CaF2, MgO, FeO mixed in a mass ratio of 40:12:28:20, the amount added is 1.5% of the weight of the molten iron) is added for dephosphorization treatment, the dephosphorization temperature is 1560℃, and slagging is performed to complete dephosphorization;

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

[0078] S21: The pretreated molten iron (S content > 0.005wt%, P content > 0.005wt%) enters the LF furnace, and the oxygen content and temperature are detected. According to the detection results, argon is blown from the bottom of the LF furnace (gas flow rate is 250 Nm 3 / h) to adjust the oxygen content and temperature, and then basic refining slag (CaO, CaF2 mixed in a mass ratio of 73:27, and the amount of addition 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, and the amount of addition is 0.7% of the weight of the molten iron) are added for refining treatment. The oxygen content is measured at the outlet, and the LF refining is completed. At this time, the oxygen activity of the molten iron is 814 ppm, and the temperature is 1640°C.

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

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

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

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

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

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

[0085] S1: Pre-treatment of molten iron for desulfurization and dephosphorization:

[0086] S11: Using the KR stirring method, desulfurize molten iron with S content ≤0.03wt% and P content ≤0.12wt% for 45 minutes at a speed of 110r / min. The desulfurization temperature is 1540℃. Slag removal is required before and after adding the desulfurizing agent (CaO, CaCO3, CaF2, and Mg mixed in a mass ratio of 60:25:12:3, with an addition amount of 1.5% of the molten iron weight) to complete the 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 re-blown from the top and bottom of the converter (gas flow rate of 5000 Nm³). 3 / h, reblowing time is 20min), then add dephosphorizing agent (CaO, CaF2, MgO and FeO are mixed in a mass ratio of 40:12:28:20, and the amount added is 3.5% of the weight of molten iron) for dephosphorization treatment. The dephosphorization temperature is 1560℃. Remove slag and tap the steel to complete the dephosphorization.

[0088] S2: Molten iron undergoes LF and RH refining treatment:

[0089] S21: Pretreated molten iron (with S content ≤0.003wt% and P content ≤0.003wt%) enters the LF furnace, where its oxygen content and temperature are measured. Based on the measurement results, argon gas (gas flow rate of 250 Nm³) is blown from the bottom of the LF furnace. 3 / h) Adjust the oxygen content and temperature, then add alkaline refining slag (CaO and CaF2 mixed in a mass ratio of 73:27, with an addition amount of 0.5% of the weight of molten iron) and deoxidizer I (aluminum granules, coke, and SiC mixed in a mass ratio of 40:35:25, with an addition amount of 0.1% of the weight of molten iron) for refining treatment. Measure the oxygen content at the outlet to complete LF refining. At this time, the oxygen activity of the molten iron is 824 ppm and the temperature is 1640℃.

[0090] S22: (1) After LF refining, the molten iron enters the RH furnace for vacuum degassing treatment (vacuum degree is 65 Pa, vacuum deoxidation treatment time is 30 min), and then molten iron sample I and slag sample I are taken; (2) the molten iron sample I is analyzed, and according to the Mn and Als contents, manganese alloy and aluminum iron are added to adjust the Mn and Als to "the mass fraction value of the target component + 0.005"; according to the color (black) of the slag sample I, basic refining slag (CaO and CaF2 are mixed in a mass ratio of 73:27 to form, 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 slag color is yellowish white after the manganese alloy, aluminum iron is added and stirred for 8 min; (3) the oxygen content of the molten iron is measured to be 657 ppm, and after adjusting the oxygen content of the molten iron to 600 ppm by adding aluminum particles, 550 meters of silicon-calcium wire and 100 meters of aluminum wire are added according to the oxygen content, the oxygen content is controlled to be reduced by no more than 100 ppm each time, argon is blown for 10 min, the oxygen content is adjusted, slag is removed, and the molten steel is cast to obtain low-carbon aluminum killed steel;

[0091] S3: heat treatment of the low-carbon aluminum killed steel:

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

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

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

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

[0096] S1: desulfurization and dephosphorization pretreatment of the molten iron:

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

[0098] S12: After desulfurization, scrap and molten iron are added to the converter in a mass ratio of 1:4.5, top and bottom combined blowing of oxygen gas (gas flow is 5000 Nm 3 / h, combined blowing time is 20 min), and dephosphorization agent (CaO, CaF2, MgO, FeO mixed in a mass ratio of 40:12:28:20, the amount of addition is 3.5% of the weight of molten iron) is added for dephosphorization treatment, dephosphorization temperature is 1560℃, slagging and tapping are completed to finish dephosphorization;

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

[0100] S21: The pretreated molten iron (S content ≤0.003wt%, P content ≤0.003wt%) enters the LF furnace, the oxygen content and temperature are detected, the oxygen content and temperature are adjusted according to the detection results by blowing argon gas (gas flow is 250 Nm 3 / h) from the bottom of the LF furnace, and basic refining slag (CaO, CaF2 mixed in a mass ratio of 73:27, the amount of addition is 1.5% of the weight of molten iron), deoxidizer I (aluminum particles, coke, SiC mixed in a mass ratio of 40:35:25, the amount of addition is 0.7% of the weight of molten iron) are added for refining treatment, oxygen is measured at the outlet, and LF refining is completed, at this time the oxygen activity of the molten iron is 504 ppm, 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 65 Pa, vacuum deoxidation treatment time is 30 min), then molten iron sample I and slag sample I are taken; (2) analyze the molten iron sample I, add manganese alloy and aluminum iron to adjust Mn and Als to "target component mass fraction value + 0.005" according to the content of Mn and Als; add basic refining slag (CaO, CaF2 mixed in a mass ratio of 73:27, the amount of addition is 0.28% of the weight of molten iron) according to the color (brownish) of slag sample I until the color of the slag is yellowish white after the addition of manganese alloy and aluminum iron and stirring for 8 min; (3) measure the oxygen value of the molten iron as 401 ppm, add silicon calcium wire 550 meters and aluminum wire 100 meters in batches according to the oxygen value, control the single oxygen reduction not more than 100 ppm, blow argon for 10 min, and perform oxygen setting and slagging, then tap and cast to obtain low-carbon aluminum killed steel;

[0102] S3: heat treatment of the low-carbon aluminum killed steel:

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

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

[0105] Table 1

[0106] Example Oxygen activity (ppm) Oxygen content (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 low-carbon aluminum killed steel is shown in Table 2 below:

[0108] Table 2

[0109] Example 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 is pickled with 15wt% hydrochloric acid for 2min, and then the surface area of the network defects of the two is compared, and the results are shown in Table 3 below:

[0111] Table 3

[0112] Example Proportion (%) Example 1 0 Comparative Example 3 34

[0113] Result analysis: from Tables 1 and 2, it can be seen that the low-carbon aluminum killed steel prepared by the present application has obvious deoxidization degree and excellent purity after desulfurization and dephosphorization pretreatment, LF furnace and RH furnace refining, and the composition is within the appropriate range; in addition, from the data in Table 3, it can be seen that the present application has prepared a low-carbon aluminum killed steel with high purity and excellent surface quality.

[0114] Finally, it should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, and those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements of some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A process for manufacturing a low carbon aluminium killed steel, characterized in that: The method comprises the following steps: S1: desulfurization and dephosphorization pretreatment of the molten iron: S11: desulfurization treatment of the molten iron with S content ≤0.03wt% and P content ≤0.12wt% by using a KR stirring method, the desulfurization temperature is 1530-1550℃, and slagging is needed before and after adding the desulfurizer, and the desulfurization is completed; S12: after desulfurization, scrap steel and molten iron are added into the converter at a mass ratio of 1:4-5, oxygen is blown from the top and bottom of the converter, and dephosphorization agent is added for dephosphorization treatment, the dephosphorization temperature is 1550-1580℃, slagging is performed, and the dephosphorization is completed; S2: LF and RH refining treatment of the molten iron: S21: the pretreated molten iron enters the LF furnace, the oxygen content and temperature are detected, the oxygen content and temperature are adjusted by blowing argon from the bottom of the LF furnace according to the detection results, basic refining slag and deoxidizer I are added for refining treatment, the oxygen content is measured at the outlet, and the LF refining is completed; S22: (1) after LF refining, the molten iron enters the RH furnace for vacuum degassing treatment, and then molten iron sample I and slag sample I are taken; (2) the molten iron sample I is analyzed, Mn and Als contents are adjusted to "target component mass fraction value+0.005" by adding manganese alloy and aluminum iron according to the Mn and Als contents; basic refining slag is added according to the color of the slag sample I until the slag color is yellowish white or greenish white after the manganese alloy and aluminum iron are added and stirred for 3-10 minutes; (3) the fixed oxygen value of the molten iron is measured, deoxidizer II is added according to the fixed oxygen value, argon is blown for 5-10 minutes, the fixed oxygen slagging is performed, and the molten iron is cast to obtain low-carbon aluminum killed steel; S3: heat treatment of the low-carbon aluminum killed steel: The heat treatment is rolling and continuous annealing in sequence; wherein, the rolling is divided into rough rolling, finish rolling and cold rolling; the continuous annealing is divided into heating section, holding section and cooling section; KR stirring parameters in step S11 are as follows: stirring speed is 100-120 r / min, and stirring time is 30-60 min; the desulfurizer is composed of CaO, CaCO3, CaF2 and Mg in a mass ratio of 60:25:12:3, and the adding amount is 1-2% of the weight of molten iron; in step S12, the parameters of top and bottom combined blowing of the converter are as follows: gas flow is 3000-6000 Nm 3 / h, and combined blowing time is 10-30 min; the dephosphorizing agent is composed of CaO, CaF2, MgO and FeO in a mass ratio of 40:12:28:20, and the adding amount is 2-4% of the weight sum of molten iron and scrap steel. The parameters of the LF bottom blowing in the step S21 are as follows: gas flow 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 is added in an amount of 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 is added in an amount of 0.3-1% of the weight of the molten iron; the oxygen activity of the molten iron after LF refining is 200-600 ppm, and the temperature is 1600-1650 DEG C; in the step S22, if the slag sample I is black, 0.3-0.4% of the weight of the molten iron of the basic refining slag is added; if the slag sample I is brown, 0.2-0.3% of the weight of the molten iron of the basic refining slag is added; if the slag sample I is gray or brown, 0.15-0.2% of the weight of the molten iron of the basic refining slag is added; if it is yellowish white or greenish white, nothing is added; the vacuum deoxidation treatment time is greater than or equal to 20 min, and the vacuum degree is less than or equal to 70 Pa; the deoxidizer II is silicon-calcium wire, aluminum wire and aluminum particles; if the oxygen value of the molten iron is greater than 600 ppm, aluminum particles are first added to reduce it to less than or equal to 600 ppm; if the oxygen value of the molten iron is 200-600 ppm, 500-700 meters of silicon-calcium wire and 100-150 meters of aluminum wire are first added; if the oxygen value of the molten iron is 50-200 ppm, 500-700 meters of silicon-calcium wire and 10-50 meters of aluminum wire are added; if the oxygen value of the molten iron is less than 50 ppm, 200-300 meters of silicon-calcium wire is added; wherein the maximum oxygen reduction per time is 100 ppm.

2. The process for manufacturing low carbon aluminium killed steel as claimed in claim 1 wherein: After pretreatment, the S content in the molten iron is ≤0.005wt%, and the P content is ≤0.005wt%.

3. 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 <50ppm.

4. The low-carbon aluminum-killed steel according to any one of claims 1 to 3, characterized in that: Chemical components with the following mass fractions: C ≤0.03wt%, Mn 0.15-0.30wt%, Si ≤0.03wt%, Als 0.02-0.04wt%, and the rest is Fe and inevitable impurities.

5. A low carbon aluminium killed steel according to claim 4, characterized in that: The parameters of the rough rolling are: rolling temperature 1150-1200 DEG C, rolling speed 3-5 m / s, rolling deformation 75-80%; the parameters of the finish rolling are: rolling starting temperature 1000-1100 DEG C, rolling ending temperature 900-950 DEG C, rolling speed 7-9 mm / s, rolling deformation 80-90%; the parameters of the cold rolling are: rolling temperature 200-350 DEG C, reduction 70-80%; the process of the heating section is: heating to 750 DEG C + / - 10 DEG C at a heating rate of 30-50 DEG C / s, then heating to 1220-1280 DEG C at a heating rate of 100 DEG C / h; the process of the holding section is: holding treatment at 1220-1280 DEG C for 5-20 min; the process of the cooling section is: first holding and slow cooling for 20-24 h, then cooling to 200 DEG C + / - 10 DEG C at a cooling rate of 5-15 DEG C / s, and finally water cooling to room temperature.