CN105603156B - Production method of ultra-low sulfur IF steel - Google Patents

Abstract

The present invention relates to the production method of super-low sulfur IF steel, belong to technical field of ferrous metallurgy.Present invention solves the technical problem that it is to provide the production method of super-low sulfur IF steel.The technique that the inventive method is combined by using molten iron pretreatment desulfurizing, converter desulfurization with LF refining, RH refining desulfurations, molten iron pretreatment beginning is terminated desulfurization degree to LF and reach more than 93%, and by technology measures such as converter terminal carbon, temperature, oxygen activity control and the controls of LF, RH procedure parameter, realize the production of Ultra-low carbon, super-low sulfur IF steel.By the integrated application of the inventive method, the super-low sulfur IF steel production of finished product [C]≤0.002%, [S]≤0.004% is realized.This method is simple, easy to operate, and production cost is low, is suitable for producing greatly.

Description

Production method of ultra-low sulfur IF steel

technical field

The invention relates to a production method of ultra-low sulfur IF steel, belonging to the technical field of iron and steel metallurgy.

Background technique

IF steel, that is, ultra-low carbon steel, refers to steel with [C]≤0.005%, and its products are widely used in automobile manufacturing, can manufacturing and other industries. In order to obtain good deep drawing performance, high-quality ultra-low carbon steel has extremely high requirements on the control of C, S, N and other elements in the steel, and the production is very difficult. At present, only a few domestic manufacturers such as Baosteel and Anshan Iron and Steel can produce it. It is difficult to meet the needs of the domestic market, and large quantities of imports are required every year. Therefore, the development of low-sulfur and ultra-low-carbon IF steel plays an important role in improving the viability and competitiveness of enterprises under the current situation.

The invention patent with the application number 201310136410.4 discloses a low-carbon, ultra-low-sulfur steel smelting method, by adding small particles of lime and fluorite when tapping the steel; change. Finally, low-carbon steel with a carbon content of 0.030% to 0.040% and a sulfur content of ≤0.0015% is obtained. The steel obtained by this method is a low-carbon steel, which is tapped in a converter and deoxidized by an alloy. Because the oxygen content in the molten steel in the subsequent process is very low, The oxidation of ladle slag is also very low, which is conducive to deep desulfurization of molten steel. Therefore, in fact, the desulfurization difficulty of low carbon steel is not high. For ultra-low carbon steel with a carbon content of ≤0.002%, the oxygen activity of molten steel is relatively high, and the oxidizing property of ladle slag is also high, so it is very difficult to stably control molten steel sulfur in the process. Therefore, this method is not suitable for the production of ultra-low sulfur IF steel.

The invention patent with application number 201010567336.8 discloses a method for desulfurization and refining of low-carbon steel with high desulfurization rate and stable desulfurization effect. Alloy and desulfurization refining slag are added to the molten steel in the ladle to alloy the molten steel and desulfurize slag. Among them, after the completion of tapping, a slagging agent is added to the ladle slag formed in the ladle. The method can effectively remove the oxygen in the molten steel, reduce the oxidation of the ladle slag, improve the performance and composition of the ladle slag, and greatly increase the desulfurization rate of the molten steel. However, this method is dedicated to the deep desulfurization process in the refining process of deoxidized steel and low-carbon steel with a carbon content of 0.03-0.08%. Due to the high carbon content, the desulfurization process is simpler than that of ultra-low carbon steel.

The invention patent with application number 200610047101.X discloses a deep desulfurizer for ultra-low carbon steel refining and its manufacturing method. The desulfurizer components include: CaO: 60-69%, Al: 11-20%, MgO: 5-10%, SiO ₂ : 5-10%, Al ₂ O ₃ : 1-5%, Fe ₂ O ₃ : 0.5-1.2%, CaF ₂ : 1-3%, B ₂ O ₃ : 1-3% , BaO: 1 to 3%, and the rest are impurities. This desulfurizer is mainly used for deep desulfurization of ultra-low carbon steel, and the desulfurization effect is good. From the examples, it can remove S in the steel to less than 0.001%, but its composition is complicated, and from the examples, this technology can be applied to ultra-low Although the carbon steel has desulfurized to a lower level, the carbon content of molten steel increased from 0.0017% to 0.0024% before and after adding the desulfurizer, which is a large increase, which is not conducive to the production of ultra-low carbon steel.

Since the ultra-low carbon steel such as IF needs to use the [O] in the steel to decarburize during the vacuum treatment process, this type of steel will basically not deoxidize during the converter tapping process, resulting in the molten steel [O] And the ladle slag has high oxidizing property, the ladle slag has no desulfurization ability, and there will be a certain amount of resulfurization in the molten steel refining process. Therefore, metallurgists at home and abroad use the method of spraying desulfurization powder into the vacuum chamber after vacuum decarburization to produce ultra-low sulfur ultra-low carbon steel. For example, the invention patent with the application number 201110211400.3 discloses a high-phosphorus, low-sulfur non-oriented electrical steel and its smelting method. The method is to add a desulfurizer to the vacuum chamber in batches after the RH alloying is completed. Sulfur low carbon steel production. This method will prolong the vacuum treatment time by more than 5 minutes, seriously affecting the production rhythm; meanwhile, the addition of desulfurizer will greatly increase the production cost of steelmaking, resulting in an increase in product cost.

Contents of the invention

The technical problem solved by the invention is to provide a production method of ultra-low sulfur IF steel.

The production method of the ultra-low sulfur IF steel of the present invention sequentially includes molten iron pretreatment, converter smelting, LF refining and RH refining, wherein, in the converter smelting, scrap steel is added, and the scrap steel does not use slag steel, and the sulfur content is ≤ 0.015. % low-sulfur clean steel scrap; when the sulfur content of the previous heat of ultra-low-sulfur IF steel is more than 0.020%, no slag is splashed, and all the slag is poured out;

When the LF is refined, the molten steel reaches the processing position, and 3-5kg/t of active lime is added to the steel, and argon is blown at the bottom, the flow rate of the argon gas is 500-1000NL/min, the temperature is raised and stirred for 10-20min, so that the FeO content in the slag is 7 ~12%, at the end of LF refining, add aluminum-containing slagging agent 1~3kg/t steel, and then blow argon softly for at least 3 minutes;

During the RH refining, before producing IF steel, the vacuum chamber is cleaned with molten steel with a sulfur content of <0.010% and a carbon content of <0.05%; at the beginning of the RH refining, the immersion depth of the insertion tube is 530-800mm; after the RH refining is completed, Add 1-2kg/t aluminum-containing slag adjusting agent to make the oxidizing property of ladle slag after adjusting slag less than 6%.

Further, in LF refining and RH refining, the aluminum-containing slagging agent is composed of the following components in parts by weight: Al ₂ O ₃ : 20-40%, CaO: 20-40%, Al: 10-18%, MgO: 5-10%, FeO<3%, P<0.10%, S<0.15%, and the rest are impurities.

Wherein, in the converter smelting, the semi-steel entering the furnace meets the following conditions: temperature > 1280°C, carbon content ≥ 3.5%, and sulfur content ≤ 0.003%; when the converter starts, scrap steel is added, and the temperature is raised without using a carburant;

The method of slag adjustment at the end of the converter is as follows: add 3-5kg/t steel high-magnesium lime into the furnace at the end of the converter for 2 minutes, and then tap the steel to ensure that the ladle clearance is 400-600mm; Brick flow 100Nm ³ /h;

Control the carbon content at the end point of the converter to 0.04%~0.06%, the sulfur content ≤0.004%, the end point oxygen activity to 0.05~0.08%, and the final slag TFe content to 16~20%; add active lime 2~4kg/t during tapping For steel, control the amount of slag in the converter after tapping to make the ladle slag thickness ≤ 100mm.

Further, the initial oxygen and carbon in RH decarburization satisfy the following formula: [O]≥[C]×4/3+150, where [O] is the initial oxygen content, [C] is the initial carbon content, [O] and The unit of [C] is ppm; at the end of RH decarburization, the oxygen activity is 0.02-0.03%, and the carbon content is ≤0.002%.

Further, the temperature of the molten iron before the pretreatment of the molten iron is >1300° C., the carbon content is ≥4.5%, and the sulfur content is ≤0.06%.

Further, in the ultra-low sulfur IF steel, the sulfur content is ≤0.004%, and the carbon content is ≤0.002%.

The method of the present invention is different from the traditional ultra-low-sulfur ultra-low-carbon steel production method. After the molten iron and the converter are desulfurized, the refining process adopts related technologies to strictly control the sulfur return of the ladle slag and the sulfur increase of the molten steel. The method reduces the RH desulfurization process, reduces the production cost and saves time.

The present invention proposes a combination of hot metal pretreatment-converter-LF-RH refining and desulfurization from the perspective of smooth flow, lower production cost of ultra-low carbon and low-sulfur steel, less harm to the environment and equipment, and easy operation and large-scale production. A production technology of ultra-low sulfur and ultra-low carbon IF steel, which can realize the stable production of finished products [S]≤0.004%, [C]≤0.002%, and the oxidation of ladle slag at the end of RH is well controlled, which is beneficial to Prevent secondary oxidation of molten steel during continuous casting and improve the cleanliness of molten steel. In this method, the pretreatment of molten iron and the desulfurization and sulfur control capabilities of the converter are fully utilized. From the beginning of converter tapping to the end of RH refining, the ladle slag is gradually modified to prevent sulfur return in the process, but it will not greatly reduce the molten steel. Oxygen activity, while ensuring sulfur control, provides the necessary conditions for RH deep decarburization. The technology is simple to operate, does not increase the process time, and is low in cost.

The method of the present invention adopts the process of combining molten iron pretreatment desulfurization, converter desulfurization, LF refining, and RH refining desulfurization, so that the desulfurization rate from the beginning of molten iron pretreatment to the end of LF reaches more than 93%, and the carbon, temperature, and oxygen activity at the end of the converter are passed. Process technology measures such as control and LF, RH process parameter control, without adding desulfurizer separately, have realized the production of ultra-low sulfur and ultra-low sulfur IF steel. Through the comprehensive application of the method of the invention, the production of ultra-low sulfur IF steel with finished product [C]≤0.002% and [S]≤0.004% is realized. The method is simple, easy to operate, low in production cost and suitable for mass production.

detailed description

The production method of the ultra-low sulfur IF steel of the present invention sequentially includes molten iron pretreatment, converter smelting, LF refining and RH refining, wherein, in the converter smelting, scrap steel is added, and the scrap steel does not use slag steel, and the sulfur content is ≤ 0.015. % low-sulfur clean steel scrap; when the sulfur content of the previous heat of IF steel is more than 0.020%, no slag is splashed, and the whole furnace slag is completely poured out.

When the LF is refined, the molten steel reaches the treatment position, 3-5 kg/t of active lime is added to the steel, argon is blown at the bottom of the ladle, the flow rate of the argon gas is 500-1000 NL/min, the temperature is raised and stirred for 10-20 min, and the FeO in the slag is controlled at 7-12%, at the end of LF refining, add 1-3kg/t of aluminum-containing slag control agent to the slag surface of the ladle, and then softly blow argon for at least 3 minutes, which can be controlled for 5-7 minutes, so as to ensure that the aluminum-containing slag control agent is melted evenly , spread on the ladle surface.

During the RH refining, in order to reduce the sulfur and carbon content in the finished product and obtain low-sulfur IF steel, the vacuum chamber is washed with molten steel of [S]<0.010%, [C]<0.05% before producing IF steel Furnace; when RH refining begins, the insertion depth of the pipe is 530-800mm. After RH refining, 200-400kg of aluminum-containing slag-adjusting agent is added to the surface of the ladle, which is the same aluminum-containing slag-adjusting agent as LF, so that the Slag oxidation < 6%.

At present, there are generally two kinds of slag control agents commonly used in this field, one is a common slag control agent with a metal aluminum content of less than 10%; the other is a high aluminum slag control agent with a content of more than 30%. Ordinary slag control agent has poor slag control effect due to low aluminum content, and the dosage is large; while high aluminum slag control agent has high slag control effect, but due to the high aluminum content, the aluminum in the slag control agent will mix with the steel when the molten steel is stirred. The [O] reaction causes the oxygen in the steel to be removed, resulting in insufficient oxygen for vacuum decarburization. In order to overcome the above defects, in the production method of ultra-low sulfur IF steel of the present invention, in LF refining and RH refining, the slagging agent used is composed of the following components by weight: Al ₂ O ₃ : 20-40%, CaO: 20-40%, Al: 10-18%, MgO: 5-10%, FeO<3%, P<0.10%, S<0.15%, and the rest are impurities.

Further, in the converter smelting, the semi-steel entering the furnace meets the following conditions: temperature > 1280°C, [C] ≥ 3.5%, [S] ≤ 0.003%; when the converter starts, scrap steel is added, and the temperature is raised without using a recarburizer .

The slag adjustment method at the end of the converter is as follows: add 3-5kg/t steel high-magnesia lime and 1.5-2.5kg/t steel modifier into the furnace at the end of the converter, and tap the steel after 2 minutes of thick slag treatment to ensure that the ladle clearance is 400-600mm; From the end of smelting to the bottom blowing and stirring for 1-2 minutes, the flow rate of a single brick is 100Nm ³ /h.

Converter end point control: [C] is 0.04%~0.06%, [S]≤0.004%, end point oxygen activity is 0.05~0.08%, final slag TFe is 16~20%; active lime is added 2~4kg/t during tapping For steel, control the amount of slag in the converter after tapping to make the ladle slag thickness ≤ 100mm.

The high-magnesium lime and active lime described in the present invention are common auxiliary materials in the steelmaking process, and the active lime mainly contains CaO, and its content is not less than 88wt%. High magnesium lime mainly contains CaO and MgO, the mass fraction of CaO is 35-45%, and the mass fraction of MgO is 35-55%.

Further, the initial oxygen and carbon in RH decarburization satisfy the following formula: [O]≥[C]×4/3+150, where [O] is the initial oxygen content, [C] is the initial carbon content, [O] and The unit of [C] is ppm; at the end of RH decarburization, the oxygen activity is 0.02-0.03%, and the carbon content is ≤0.002%.

Wherein, during the RH refining, if the initial oxygen and carbon contents of decarburization do not satisfy the formula, forced decarburization is performed to make it satisfy the formula. The forced decarburization method can adopt existing methods in the art, and can also adopt the following methods: the oxygen blowing time is VCD start (6-8) min, the gun position is 440-480 cm, the flow rate is 2400-2800 m ³ /h, [O] after oxygen meets the concentration requirements of [C] and [O] when RH enters the station above, but in order to prevent molten steel from peroxidation, [O] should be considered as the lower limit when blowing oxygen.

In the production method of the ultra-low sulfur IF steel of the present invention, the temperature of the molten iron before the pretreatment of the molten iron is >1300°C, [C]≥4.5%, and [S]≤0.06%;

In the ultra-low sulfur IF steel of the present invention, [S]≤0.004%, [C]≤0.002%.

[S] in the present invention is the sulfur content, [C] is the carbon content, unless otherwise specified, the percentage signs in the present invention are all mass percentages.

In the production process of the present invention, in order to strictly control the carbon content, a carbon-free steel ladle is used throughout.

The method of the present invention is different from the traditional ultra-low-sulfur ultra-low-carbon steel production method. After the molten iron and the converter are desulfurized, the refining process adopts related technologies to strictly control the sulfur return of the ladle slag and the sulfur increase of the molten steel. The method reduces the RH desulfurization process, reduces the production cost and saves time.

The specific implementation of the present invention will be further described below in conjunction with the examples, and the present invention is not limited to the scope of the examples.

Example 1

The following method is used to produce ultra-low sulfur IF steel.

(1) Hot metal pretreatment

The molten iron before pretreatment meets the following conditions: molten iron temperature>1300°C, C≥4.5%, S≤0.06%.

(2) Converter smelting

Conditions for entering the semi-steel into the converter: the carbon of the semi-steel entering the furnace is ≥ 3.5%, the temperature is > 1280°C, and the S is ≤ 0.003%. The loading capacity is 220-230 tons. Scrap steel does not use slag steel, but uses low-sulfur (S≤0.015%) clean scrap steel with an amount of ≤8 tons. No carburant is used to raise the temperature. Bottom blowing argon throughout the blowing process. When the sulfur content of the furnace before smelting IF steel is >0.020%, no slag is splashed, and the whole furnace slag is completely poured out. See Table 1 for details.

Table 1 Conditions for entering the converter

Melting number steel type Loading capacity/t temperature/℃ Add steel scrap/t [C]/% [S]/% 1 IF3 225 1285 0 3.52 0.0030 2 IF3 228 1287 3 3.63 0.0029 3 IF3 230 1290 6 3.55 0.0026 4 IF3 225 1292 2 3.58 0.0029

Requirements for slag adjustment at the end of the converter: add 3-5kg/t steel high-magnesia lime and 1.5-2.5kg/t steel modifier thick slag into the furnace at the end of the converter to treat for 2 minutes and then tap the steel to ensure that the ladle clearance is 400-600mm. From the end of the blowing to the bottom of the steel, blowing and stirring, the flow rate of a single brick is 100Nm3/h, 1~2min. See Table 2 for details.

Table 2 Requirements for slag adjustment at the end of converter

Converter end point control: [C] is 0.04%~0.06%, [S]≤0.004%, end point oxygen activity is 0.05~0.08%, and final slag TFe is controlled at 16~20%. Requirements for slag modification in the tank after tapping: add active lime 2-4kg/t steel during the tapping process, and control the amount of slag dropped by the converter after tapping to make the ladle slag thickness ≤ 100mm. See Table 3 for details.

Table 3 End point control of converter and requirements for slag modification in tank after tapping

(3) LF refining

LF refining starts: molten steel reaches the treatment position, and 3-5kg/t of active lime is added to steel. The flow rate of argon blowing at the bottom of the ladle is controlled at 500-1000 NL/min, the temperature is raised and stirred for 10-20 minutes, and the FeO in the slag is controlled at 7-12%.

End of LF refining: Add molten steel slag adjusting agent 1~3kg/t steel to the slag surface of the ladle, and softly blow argon for ≥3 minutes after adding to ensure that the slag adjusting agent melts evenly and spreads on the surface of the ladle.

The main components of the slagging agent are: Al ₂ O ₃ : 20-40%, CaO: 20-40%, MAl: 10-18%, MgO: 5-10%, FeO<3%, P<0.10%, S <0.15%, the rest are impurities.

The LF refining parameters corresponding to each melting number are shown in Table 4.

Table 4 LF process control

(4) RH refining

Before producing IF steel, the vacuum chamber is cleaned with high-temperature molten steel of [S]<0.010%, [C]<0.05%.

Molten steel conditions at the start of RH refining: the immersion depth of the insertion tube is controlled between 530 and 800mm, vacuum treatment is started, and the vacuum main valve is opened.

RH decarburization treatment: [O] initial (ppm) ≥ [C] initial (ppm) × 4/3 + 150. If the [O] initial (ppm) is insufficient, carry out forced decarburization, control the end of decarburization a[O] at 0.02-0.03%, decarburization target C: ≤20ppm.

The deep decarburization time (15-20) min when the vacuum degree is less than 3mbar.

RH refining slag adjustment: After RH refining, add 200-400kg slagging agent to the surface of the ladle, which is the same slag adjusting agent as that added in LF refining, and the oxidizing property of ladle slag after slagging adjustment is less than 6%.

The LF refining parameters corresponding to each melting number are shown in Table 5. Among them, smelt Nos. 2 and 4 require forced decarburization.

Table 5 RH process control

The control of sulfur content in the whole steelmaking process is shown in Table 6.

Table 6 Sulfur content control % in process steel

Hot metal pretreatment starts Converter into the furnace converter end point LF outbound RH outbound finished product 0.055 0.0024 0.0021 0.0019 0.002 0.0021 0.060 0.0028 0.0023 0.0023 0.0024 0.0024 0.051 0.0030 0.0043 0.0036 0.0038 0.0037 0.053 0.0026 0.0050 0.0046 0.0037 0.0036

It can be seen from Table 6 that through the effective control of converter smelting and LF and RH refining processes, the sulfur content of the finished product has been effectively controlled, and the production of ultra-low sulfur and ultra-low carbon IF steel has been successfully realized.

Claims (9)

1. The production method of ultra-low sulfur IF steel comprises successively molten iron pretreatment, converter smelting, LF refining and RH refining, and is characterized in that: When the converter is smelting, steel scrap is added, and the scrap steel adopts low-sulfur clean steel scrap with a sulfur content of ≤0.015%; when the sulfur content of the steel in the previous furnace of ultra-low-sulfur IF steel is more than 0.020%, no slag is splashed, and the entire furnace slag is poured out Lose; When the LF is refined, the molten steel reaches the processing position, and 3-5kg/t of active lime is added to the steel, and argon is blown at the bottom, the flow rate of the argon gas is 500-1000NL/min, the temperature is raised and stirred for 10-20min, so that the FeO content in the slag is 7 ~12%, at the end of LF refining, add aluminum-containing slagging agent 1~3kg/t steel, and then blow argon softly for at least 3 minutes; During the RH refining, before producing IF steel, the vacuum chamber is cleaned with molten steel with a sulfur content of <0.010% and a carbon content of <0.05%; at the beginning of the RH refining, the immersion depth of the insertion tube is 530-800mm; after the RH refining is completed, Add 1-2kg/t aluminum-containing slag adjusting agent to make the oxidizing property of ladle slag after adjusting slag less than 6%; The initial oxygen and carbon of RH decarburization satisfy the following formula: [O]≥[C]×4/3+150, where [O] is the initial oxygen content, [C] is the initial carbon content, [O] and [C] The unit is ppm; the oxygen activity at the end of RH decarburization is 0.02-0.03%, and the carbon content is ≤0.002%; the decarburization time is 15-18min when the vacuum degree is controlled to be less than 3mbar. 2. The production method of ultra-low sulfur IF steel according to claim 1, characterized in that: in LF refining and RH refining, the aluminum-containing slagging agent consists of the following components by weight: Al ₂ O ₃ : 20-40%, CaO: 20-40%, Al: 10-18%, MgO: 5-10%, FeO<3%, P<0.10%, S<0.15%, and the rest are impurities. 3. The production method of ultra-low-sulfur IF steel according to claim 1 or 2, characterized in that: in the converter smelting, the semi-steel into the furnace meets the following conditions: temperature > 1280°C, carbon content ≥ 3.5%, sulfur Content ≤ 0.003%; when the converter starts, add scrap steel, do not use carburant to raise temperature; The method of slag adjustment at the end of the converter is as follows: add 3-5kg/t steel high-magnesium lime into the furnace at the end of the converter for 2 minutes, and then tap the steel to ensure that the ladle clearance is 400-600mm; Brick flow 100Nm ³ /h; Control the carbon content at the end point of the converter to 0.04%~0.06%, the sulfur content ≤0.004%, the end point oxygen activity to 0.05~0.08%, and the final slag TFe content to 16~20%; add active lime 2~4kg/t during tapping For steel, control the amount of slag in the converter after tapping to make the ladle slag thickness ≤ 100mm. 4. The production method of ultra-low sulfur IF steel according to claim 1 or 2, characterized in that: the temperature of the molten iron before the pretreatment of the molten iron is > 1300°C, the carbon content is ≥ 4.5%, and the sulfur content is ≤ 0.06%. 5. The production method of ultra-low sulfur IF steel according to claim 3, characterized in that: the temperature of the molten iron before the pretreatment of the molten iron is >1300°C, the carbon content is ≥4.5%, and the sulfur content is ≤0.06%. 6. The method for producing ultra-low-sulfur IF steel according to claim 1 or 2, characterized in that: in the ultra-low-sulfur IF steel, the sulfur content is ≤0.004%, and the carbon content is ≤0.002%. 7. The method for producing ultra-low-sulfur IF steel according to claim 3, characterized in that: in the ultra-low-sulfur IF steel, the sulfur content is ≤0.004%, and the carbon content is ≤0.002%. 8. The method for producing ultra-low-sulfur IF steel according to claim 4, characterized in that: in the ultra-low-sulfur IF steel, the sulfur content is ≤0.004%, and the carbon content is ≤0.002%. 9. The method for producing ultra-low-sulfur IF steel according to claim 5, characterized in that: in the ultra-low-sulfur IF steel, the sulfur content is ≤0.004%, and the carbon content is ≤0.002%.