Method for improving qualified rate of silicon component of low-silicon aluminum killed steel

Abstract

The invention discloses a method for improving the qualification rate of silicon components of low-silicon aluminum killed steel, and belongs to the field of steel smelting. By controlling the [S] content in the molten iron after molten iron pretreatment, the comprehensive oxygen value at the converter smelting end point and slag stopping tapping, aluminum with proper weight is added according to the molten steel entering oxygen value and the top slag state in the earlier stage of LF refining, and the oxygen content in steel and slag and the aluminum content in the molten steel are controlled to be at the low level; the desulfurization effect is guaranteed in the early stage of molten steel treatment, meanwhile, the reaction amount of steel slag SiO2 is reduced, under the condition that the reducibility of steel and slag in the later stage of LF refining is high, a certain amount of quick lime is added in the aluminum alloying or desulfurization process, the situation that SiO2 in top slag is reduced by Al and enters the molten steel is relieved, the silicon return amount of the molten steel in the later stage is reduced, and the percent of pass of components of the low-silicon-aluminum killed steel is increased. According to the method, the steel grade component percent of pass of a steel plant is increased, the cost loss caused by unqualified components is reduced, and the stability of product performance is improved.

Description

Technical Field

[0001] The present invention belongs to the field of iron and steel smelting, and particularly relates to a method for improving the qualification rate of silicon composition in low-silicon aluminum-killed steel. Background Art

[0002] The composition and temperature of molten steel are the two most important process parameters throughout the steelmaking production process. Among them, the composition of molten steel is the most critical parameter for evaluating the quality of continuous casting billets. It not only determines whether the quality of the steel grade is qualified but also affects the performance of the product after rolling in the next process. How to control the molten steel composition within a narrow window is an important issue for steel mills. The control accuracy of molten steel composition directly affects the smooth progress of production and the stability of quality. Every year, due to unqualified compositions in each process link in steel mills, many hot and cold recycling events occur, seriously affecting the production, quality, and cost of steel mills. Improving the qualification rate of steel grade compositions in steel mills can reduce the cost losses caused by unqualified compositions in steel mills and at the same time improve the stability of product performance.

[0003] Statistics on the unqualified situations of steel grades with unqualified steelmaking compositions. After classifying the unqualified ladle batches according to the influencing elements, the proportion of each element is counted. The proportion of unqualified Si elements is the highest in the overall data, followed by Mo elements, S elements, C elements, P elements, Ni elements, etc. Taking the steel grade as the classification condition, the qualification rate of Si elements in low-silicon steel grades is relatively low. Chinese invention patent CN115747407A discloses a method for smelting low-silicon aluminum-killed low-carbon steel with controllable inclusions, including three sections: converter steelmaking, argon blowing in the ladle, and continuous casting into billets; among them, the steelmaking converter uses a top-bottom combined blowing converter, the smelting cycle is 23 min, and the argon blowing time in the ladle is 6 min. The top-blowing oxygen decarburization time in the converter is 11 min. From the 1st min to the 3rd min of decarburization, the top-blowing oxygen lance adopts a lance position of 1.2 m to 1.5 m, and the oxygen blowing volume is 30000 Nm 3 / h; from the 3rd min to the 9th min of decarburization, the top-blowing oxygen lance adopts a lance position of 0.8 m to 1.2 m, and the oxygen blowing volume is 28000 Nm 3 / h. From the 9th min to the 11th min of decarburization, the top-blowing oxygen lance adopts a lance position of 0.4 m to 0.6 m, and the oxygen blowing volume is 26000 Nm3 / h. The present invention cancels LF refining, further shortens the smelting time and argon blowing time, speeds up the production rhythm, and at the same time adopts controllable oxygen and a ladle slag with high alumina adsorption to control the inclusion content in the molten steel. However, this patent does not involve how to operate to improve the qualification rate of silicon composition in low-silicon aluminum-killed steel. Therefore, researching and developing a method for improving the qualification rate of silicon composition in low-silicon aluminum-killed steel is of great significance for improving production efficiency, reducing production costs, and improving the stability of product performance. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a method for improving the qualification rate of silicon composition in low-silicon aluminum-killed steel. The present invention successfully solves the problem that the reduction of SiO2 in the slag into the molten steel during desulfurization in the LF refining process leads to the non-compliance of the Si element in the composition, improves the qualification rate of steel grades in the steel mill, reduces the cost loss caused by non-compliant components, and improves the stability of product performance.

[0005] The object of the present invention is achieved in the following way:

[0006] The present invention provides a method for improving the qualification rate of silicon composition in low-silicon aluminum-killed steel. The production process flow of the low-silicon aluminum-killed steel is: hot metal pretreatment → converter smelting → LF refining → continuous casting;

[0007] (1) [S] in the hot metal ≤ 0.005% after hot metal pretreatment;

[0008] (2) The end-point temperature of converter smelting is controlled at 1650 - 1710 °C, the end-point oxygen value of converter smelting ≤ 1000 ppm, slagging-off is carried out during tapping, and the hanging-pot temperature is 1610 - 1680 °C, controlling the slag carry-over amount ≤ 5.0 kg / t;

[0009] (3) After the LF refining furnace is charged, the temperature and oxygen are measured. The temperature is controlled at 1590 - 1620 °C. The first batch of aluminum is added according to the formula based on the oxygen value (ppm) of the molten steel entering the station: the addition amount of the first batch of aluminum (kg) = the weight of the molten steel (t) × [0.001125 × the oxygen value of the molten steel entering the station (ppm) + k], where k = 8.0 - 1.0;

[0010] (4) Argon is blown to stir the molten steel. After the aluminum has melted completely, quicklime is added to the molten steel ladle. The addition amount of quicklime (kg) = the weight of the molten steel (t) × n, where n = 3.0 - 5.0; The molten steel is heated to 1570 - 1610 °C. After the heating is completed, argon is blown to stir the molten steel;

[0011] (5) It is judged whether aluminum needs to be added again according to the FeO content in the slag. When the FeO content in the slag < 2.00%, no aluminum needs to be added; when the FeO content in the slag ≥ 2.00%, aluminum needs to be added. The added weight of aluminum (kg) = (0.4 - 0.6) × the weight of the molten steel (t), and argon is blown to stir the molten steel until the FeO content in the slag < 2.00%;

[0012] (6) The molten steel is sampled. When the [S] content in the sampling result > the target [S] content, desulfurization is required, and quicklime is added. After stirring the molten steel for desulfurization for 6 minutes; when the [S] content in the sampling result ≤ the target [S] content, no desulfurization is required;

[0013] (7) The temperature of the molten steel is measured. The temperature of the molten steel is controlled at 1550 - 1590 °C; 0.20 - 0.40 kg / t of calcium element is fed into the molten steel, and the treatment is completed.

[0014] Based on the above technical solution, further, the chemical elements and weight percentages of the low-silicon aluminum-killed steel are: C: 0.010% to 0.30%, Si ≤ 0.050%, Mn ≤ 2.00%, P ≤ 0.030%, S ≤ 0.030%, Al ≤ 0.10%, and the balance is iron and unavoidable impurities.

[0015] Based on the above technical solution, further, the chemical elements and weight percentages of the low-silicon aluminum-killed steel are: C: 0.040% to 0.10%, Si ≤ 0.030%, Mn: 0.20% to 0.40%, P ≤ 0.010%, S ≤ 0.008%, Al ≤ 0.030%, and the balance is iron and unavoidable impurities.

[0016] Based on the above technical solution, further, [S] in the hot metal after hot metal pretreatment in step (1) ≤ 0.001%.

[0017] Based on the above technical solution, further, the end-point temperature of converter smelting in step (2) is controlled at 1680 - 1700 °C, the end-point oxygen value of converter smelting ≤ 800 ppm, and the ladle hanging temperature is 1630 - 1660 °C.

[0018] Based on the above technical solution, further, the oxygen value after the LF refining furnace enters the station in step (3) is controlled ≤ 500 ppm.

[0019] Based on the above technical solution, further, the argon blowing stirring time during the aluminum melting process in step (4) is controlled at 2 - 10 min, and the argon blowing stirring time of the molten steel after the temperature rise ends is controlled at 10 - 20 min.

[0020] Based on the above technical solution, further, in step (6), according to the quicklime addition amount (kg) ≥ [molten steel weight (t) × 1000 × m] ÷ (5% ÷ [S] aim ), [S] aim is the target desulfurization rate, [S] aim = (sampling result [S] content - target [S] content) ÷ sampling result [S] content × 100%, m = 0.000616, and the minimum quicklime addition amount is calculated.

[0021] Based on the above technical solution, further, the molten steel temperature in step (7) is controlled at 1570 - 1590 °C.

[0022] LF refining is to avoid excessive reduction of Si element into the molten steel. In operation, two principles must be followed. One is to quickly desulfurize in the early stage of refining, and the other is to reduce silicon reversion with a large slag volume in the later stage. When LF refining treats low-silicon aluminum-killed steel, desulfurization and silicon reversion are two mutually contradictory processes. In order to quickly reduce the reducibility of the top slag and enable CaO to react smoothly with S to effectively remove the S content in the molten steel, it is necessary to find the balance point between the two processes to ensure that both S and Si elements ultimately meet the composition requirements.

[0023] In the early stage of LF refining, the oxygen activities in the slag and molten steel are high, and the contents of FeO, MnO, and SiO2 in the slag are all relatively high. At this time, due to the higher reactivity of FeO and MnO than SiO2, adding a large amount of aluminum alloy will first react with FeO and MnO in the slag, and the reaction efficiency of SiO2 in the slag with aluminum is poor, and the amount of Si element transferred from the slag to the molten steel is less. Therefore, in the early stage of LF refining, a sufficient amount of aluminum alloy needs to be added to quickly reduce the oxygen activities in the steel and slag, establish a good desulfurization environment, and quickly desulfurize by slag washing, so as to achieve the purpose of low silicon reversion and high desulfurization.

[0024] In the later stage of LF refining, the contents of FeO and MnO in the slag are very low, and both the molten steel and the top slag are reducing, and there is sufficient Al element in the molten steel. At this time, if normal slag washing is carried out, the reaction conditions between Al and SiO2 are sufficient, and silicon reversion is very likely to occur. At this time, the slag volume of the top slag should be increased, a large amount of CaO should be introduced to reduce the concentration of SiO2 in the slag, so as to achieve the purpose of reducing the reaction rate between Al and SiO2 and avoid a large amount of silicon reversion during the alloying process in the later stage of LF refining.

[0025] The beneficial effects of the present invention compared with the prior art are as follows:

[0026] 1. In the early stage of LF refining, according to the oxygen value of the molten steel entering the station and the state of the top slag, add aluminum with a suitable weight to control the oxygen content in the steel and slag and the aluminum content in the molten steel at a relatively low level, and reduce the reaction amount of SiO2 in the steel slag while ensuring the desulfurization effect in the early stage of molten steel treatment.

[0027] 2. In the later stage of LF refining when the reducibility of the steel and slag is relatively high, add a certain amount of quicklime during aluminizing or desulfurization to reduce the reduction of SiO2 in the top slag by Al element into the molten steel, reduce the silicon reversion amount of the molten steel in the later stage, and improve the component qualification rate of low-silicon aluminum-killed steel. Specific Embodiments

[0028] The present invention will be described in detail below in conjunction with embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only part of the embodiments of the present invention. For those skilled in the art, without creative labor, obtaining other similar embodiments all fall within the protection scope of the present invention.

[0029] Example 1

[0030] Taking a 200t converter as an example, [C]: 0.050%, upper limit of [Si]: 0.030%, [Mn]: 0.30%, [P]: 0.010%, [S]: 0.008%, [Al]: 0.030%, and the balance is iron and inevitable impurities. The production process flow is hot metal pretreatment → converter smelting → LF refining → continuous casting; it includes the following steps:

[0031] (1) Hot metal pretreatment, [S] in the treated hot metal: 0.001%;

[0032] (2) Converter smelting, the end point temperature is 1680°C, the comprehensive oxygen value at the end point is 540 ppm, slag blocking and tapping, the hanging ladle temperature is 1630°C, and the controlled slag carryover < 5.0 kg / t;

[0033] (3) After the LF refining furnace is in the station, measure the temperature and determine the oxygen content. The temperature is 1590°C and the oxygen value is 240 ppm; according to the oxygen value (ppm) of the molten steel entering the station, according to the formula: the first batch of aluminum addition amount (kg) = molten steel weight (t) × [0.001125 × oxygen value of molten steel entering the station (ppm) + 0.9], the first batch of aluminum addition amount is 234 kg;

[0034] (4) Argon blow and stir the molten steel for 3 min. After the aluminum is completely melted, add quicklime to the molten steel ladle. The quicklime addition amount (kg) = molten steel weight (t) × 4.0, the quicklime addition amount is 800 kg, heat up the molten steel for 7 min, heat up to 1590°C, and after the heating is completed, blow argon and stir the molten steel for 13 min;

[0035] (5) Detect the FeO content of the slag sample, the FeO content is 1.26%, and no aluminum needs to be added;

[0036] (6) Take a sample of the molten steel. The sampling result shows that the [S] content is 0.012%, the target [S] content is 0.008%, and desulfurization is still required. The target desulfurization rate [S]%: 33.33%. According to the quicklime addition amount (kg) ≥ [molten steel weight (t) × 0.616] ÷ (5% ÷ [S] aim ), calculate the minimum quicklime addition amount to be 821 kg, and add 850 kg of quicklime.

[0037] (7) After stirring the molten steel for desulfurization for 6 min, measure the temperature and take a sample of the molten steel. The molten steel temperature is 1585°C, feed 60 kg of calcium wire into the molten steel, and the treatment is completed.

[0038] Example 2

[0039] Taking a 200t converter as an example, [C]: 0.050%, upper limit of [Si]: 0.030%, [Mn]: 0.30%, [P]: 0.010%, [S]: 0.008%, [Al]: 0.030%, and the balance is iron and inevitable impurities. The production process flow is hot metal pretreatment → converter smelting → LF refining → continuous casting; it includes the following steps:

[0040] (1) Hot metal pretreatment, [S] in the treated hot metal: 0.001%;

[0041] (2) Converter smelting, the end point temperature is 1690°C, the end point comprehensive oxygen value is 450 ppm, slag blocking for tapping, the hanging ladle temperature is 1640°C, and the slag carrying amount is controlled < 5.0 kg / t;

[0042] (3) After the LF refining furnace is in service, measure the temperature and determine the oxygen content. The temperature is 1600°C and the oxygen value is 150 ppm; according to the oxygen value (ppm) of the molten steel entering the station, according to the formula: the first batch of aluminum addition amount (kg) = molten steel weight (t) × [0.001125 × oxygen value of molten steel entering the station (ppm) + 0.9], the first batch of aluminum addition amount is 214 kg;

[0043] (4) Argon blow and stir the molten steel for 4 min. After the aluminum is completely melted, add quicklime to the molten steel ladle. The quicklime addition amount (kg) = molten steel weight (t) × 4.0, the quicklime addition amount is 800 kg; heat up the molten steel for 4 min, heat up to 1580°C, and after the heating is completed, blow argon and stir the molten steel for 12 min;

[0044] (5) Detect the FeO content of the slag sample. The FeO content is 3.55%. Aluminum needs to be added continuously. The aluminum addition weight (kg) = 0.5 × molten steel weight (t) = 100 kg;

[0045] (6) After blowing argon and stirring for 3 min again, detect the FeO content of the slag sample. The FeO content is 0.79%, and no aluminum needs to be added;

[0046] (7) Take a sample of the molten steel. The sampling result shows that the [S] content is 0.015%, and the target [S] content is 0.008%. Desulfurization is still required. The target desulfurization rate [S]%: 46.67%. According to the quicklime addition amount (kg) ≥ [molten steel weight (t) × 0.616] ÷ (5% ÷ [S] aim ), calculate the minimum quicklime addition amount of 1150 kg, and add 1200 kg of quicklime.

[0047] (8) After stirring the molten steel for desulfurization for 6 min, measure the temperature and take a sample of the molten steel. The molten steel temperature is 1585°C, and feed 65 kg of calcium wire into the molten steel, and the treatment is completed.

[0048] Example 3

[0049] Taking a 200t converter as an example, [C]: 0.050%, upper limit of [Si]: 0.030%, [Mn]: 0.30%, [P]: 0.010%, [S]: 0.008%, [Al]: 0.030%, and the balance is iron and inevitable impurities. The production process flow is hot metal pretreatment → converter smelting → LF refining → continuous casting; it includes the following steps:

[0050] (1) Hot metal pretreatment, [S] in the treated hot metal: 0.001%;

[0051] (2) Converter smelting, the end point temperature is 1700°C, the comprehensive oxygen value at the end point is 670 ppm, slag blocking and tapping, the ladle hanging temperature is 1660°C, and the slag carrying amount is controlled < 5.0 kg / t;

[0052] (3) After the LF refining furnace is in station, measure the temperature and determine the oxygen content. The temperature is 1620°C and the oxygen value is 450 ppm; according to the oxygen value (ppm) of the molten steel entering the station, according to the formula: the first batch of aluminum addition amount (kg) = molten steel weight (t) × [0.001125 × oxygen value of molten steel entering the station (ppm) + 0.9], the first batch of aluminum addition amount is 281 kg;

[0053] (4) Argon blow and stir the molten steel for 4 min. After the aluminum is completely melted, add quicklime to the molten steel ladle. The quicklime addition amount (kg) = molten steel weight (t) × 4.0, the quicklime addition amount is 800 kg; do not heat up the molten steel, and argon blow and stir the molten steel for 12 min;

[0054] (5) Detect the FeO content of the slag sample. The FeO content is 2.65%. Aluminum needs to be added continuously. The aluminum addition weight (kg) = 0.5 × molten steel weight (t) = 100 kg;

[0055] (6) After argon blowing and stirring for 3 min again, detect the FeO content of the slag sample. The FeO content is 1.12%, and no aluminum needs to be added;

[0056] (7) Take a sample of the molten steel. The sampling result shows that the [S] content is 0.006%, and the target [S] content is 0.008%, so desulfurization is not required.

[0057] (8) Measure the temperature of the molten steel. The molten steel temperature is 1570°C; heat up the molten steel for 4 min, heat up to 1585°C, and feed 55 kg of calcium wire into the molten steel to end the treatment.

[0058] Comparative Example 1

[0059] Taking a 200t converter as an example, [C]: 0.050%, upper limit of [Si]: 0.030%, [Mn]: 0.30%, [P]: 0.010%, [S]: 0.008%, [Al]: 0.030%, and the balance is iron and inevitable impurities. The production process flow is hot metal pretreatment → converter smelting → LF refining → continuous casting; it includes the following steps:

[0060] (1) Hot metal pretreatment, [S] in the treated hot metal: 0.001%;

[0061] (2) Converter smelting, the end point temperature is 1670°C, the end point comprehensive oxygen value is 1250 ppm, the tapping temperature is 1610°C, and the slag carrying amount is 6.0 kg / t;

[0062] (3) After the LF refining furnace is charged, measure the temperature and determine the oxygen content. The temperature is 1570°C and the oxygen value is 850 ppm; the first batch of aluminum addition amount is 500 kg;

[0063] (4) Argon blow stirring of the molten steel for 4 min. After the aluminum is completely melted, add quicklime to the ladle, and the quicklime addition amount is 800 kg; heat up the molten steel for 10 min to 1565°C. After the heating is completed, argon blow stir the molten steel for 12 min;

[0064] (5) Detect the FeO content of the slag sample, the FeO content is 3.75%, and continue to add 200 kg of aluminum;

[0065] (6) After argon blow stirring for 3 min again, check the FeO content of the slag sample. The FeO content is 1.21%, and no aluminum needs to be added;

[0066] (7) Take a sample of the molten steel. The sampling result shows that the [S] content is 0.006%, the target [S] content is 0.008%, and no desulfurization is required; the [Si] content is 0.036%, exceeding the upper limit requirement of the composition.

[0067] (8) Conduct heat recovery treatment on the molten steel.

[0068] Table 1 Statistics of the qualified rate of silicon composition of low-silicon aluminum-killed steel in Examples 1-3 and Comparative Example 1

[0069] Production batch Unqualified rate (%) Qualified rate (%) Example 1 20 0 100 Example 2 20 0 100 Example 3 20 0 100 Comparative example 1 20 10 90

[0070] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the qualification rate of silicon content in low-silicon aluminum-killed steel, characterized in that, The production process flow of the low-silicon aluminum killed steel is: hot metal pretreatment → converter smelting → LF refining → continuous casting; (1) After hot metal pretreatment, [S] in the hot metal ≤ 0.005%; (2) The end-point temperature of converter smelting is controlled at 1650 - 1710 °C, the end-point oxygen value of converter smelting ≤ 1000 ppm, slagging-off tapping is carried out, and the ladle hanging temperature is 1610 - 1680 °C, controlling the slag carry-over amount ≤ 5.0 kg / t; (3) After the LF refining furnace is charged, the temperature and oxygen are measured. The temperature is controlled at 1590 - 1620 °C. According to the oxygen value (ppm) of the molten steel entering the furnace, the first batch of aluminum is added according to the formula: the addition amount of the first batch of aluminum (kg) = the weight of the molten steel (t) × [0.001125 × the oxygen value of the molten steel entering the furnace (ppm) + k], where k = 8.0 - 1.0; (4) Argon is blown to stir the molten steel. After the aluminum is completely melted, quicklime is added to the molten steel ladle. The addition amount of quicklime (kg) = the weight of the molten steel (t) × n, where n = 3.0 - 5.0; The molten steel is heated up to 1570 - 1610 °C. After the heating is completed, argon is blown to stir the molten steel; (5) It is judged whether aluminum needs to be added again according to the FeO content in the slag. When the FeO content in the slag < 2.00%, no aluminum needs to be added; when the FeO content in the slag ≥ 2.00%, aluminum needs to be added. The added weight of aluminum (kg) = (0.4 - 0.6) × the weight of the molten steel (t). Argon is blown to stir the molten steel until the FeO content in the slag < 2.00%; (6) The molten steel is sampled. When the [S] content in the sampling result > the target [S] content, desulfurization is required. Quicklime is added and the molten steel is stirred for desulfurization for 6 minutes; when the [S] content in the sampling result ≤ the target [S] content, no desulfurization is required; (7) The temperature of the molten steel is measured. The temperature of the molten steel is controlled at 1550 - 1590 °C; 0.20 - 0.40 kg / t of calcium element is fed into the molten steel, and the treatment is completed.

2. The method according to claim 1, characterized in that The chemical elements and weight percentages of the low-silicon aluminum killed steel are: C: 0.010% - 0.30%, Si ≤ 0.050%, Mn ≤ 2.00%, P ≤ 0.030%, S ≤ 0.030%, Al ≤ 0.10%, and the balance is iron and inevitable impurities.

3. The method according to claim 1, characterized in that, In step (1), [S] in the hot metal ≤ 0.001% after hot metal pretreatment.

4. The method according to claim 1, characterized in that, In step (2), the end-point temperature of converter smelting is controlled at 1680 - 1700 °C, the end-point oxygen value of converter smelting ≤ 800 ppm, and the ladle hanging temperature is 1630 - 1660 °C.

5. The method according to claim 1, wherein In step (4), the argon blowing stirring time during the aluminum melting process is controlled at 2 - 10 minutes, and the argon blowing stirring time of the molten steel after the heating is completed is controlled at 10 - 20 minutes.

6. The method according to claim 1, characterized in that, In step (6), the amount of quicklime added (kg) ≥ [molten steel weight (t) × 1000 × m] ÷ (5% ÷ [S] aim ), [S] aim is the target desulfurization rate, [S] aim = (sampling result [S] content - target [S] content) ÷ sampling result [S] content × 100%, m = 0.000616, and the minimum amount of quicklime added is calculated.

7. The method according to claim 1, characterized in that, In step (7), the temperature of the molten steel is controlled at 1570 - 1590 °C.