Method for producing green line steel LX72A through short-process electric furnace

Abstract

The invention belongs to the technical field of metallurgical manufacturing, and particularly relates to a method for producing green line steel LX72A through a short-process electric furnace. The production process comprises electric furnace smelting, LF refining, RH refining and continuous casting. In the LF refining process, refining alkaline slag is desulfurized and then drossing, and acid slag is changed to control the components of molten steel. The production mode of electric furnace production, LF refining process, slagging-off and slag changing process and RH process is utilized, the molten iron pretreatment process is omitted, electric furnace steelmaking is directly adopted, and the production path is shortened; scrap steel is packaged into automobile sheet blocks, LF refining alkaline slag is desulfurized and then drossing is conducted, acid slag is changed to control the sulfur content in molten steel, and therefore strict control over residual elements, inclusions, composition segregation and the like in the steel is achieved. By adopting an electric furnace short-process production process, the mechanical property of the LX72A steel is ensured, and the drawing property of the LX72A steel is also ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical manufacturing, and particularly relates to a method for producing green wire steel LX72A by a short-process electric furnace. Background Art

[0002] Wire steel LX72A is mainly used for producing the skeleton for increasing the radial tires. The original production process is: iron ore, coke → the production process of a combination of blast furnace and converter → rolling → hot-rolled wire rod for steel cord. Its smelting process has a long production flow, high production cost, and serious environmental pollution during the production process. In order to conform to the concept of green design, reduce the impact on the environment, greatly improve the ecological friendliness, and reduce costs and production path links, a short-process electric furnace production path is proposed: electric furnace production → rolling → hot-rolled wire rod for steel cord path.

[0003] The production of wire steel LX72A should not only ensure its strength but also its drawing performance. Therefore, there are strict requirements for residual elements, inclusions, and composition segregation in the steel. All production processes need to strictly control the composition and inclusions, and aluminum deoxidation is strictly prohibited to avoid generating large particles of inclusions. When originally using a converter for production, due to the use of hot metal pretreatment, desulfurization treatment can be carried out in advance. However, for the new short-process electric furnace production path, since there is no hot metal pretreatment process in electric furnace production, it is very difficult to control residual elements, inclusions, composition segregation, etc. in the steel. Summary of the Invention

[0004] The purpose of the invention is to provide a method for producing green wire steel LX72A by a short-process electric furnace, which uses a production mode of "electric furnace production + LF refining process + slag skimming and slag modification process + RH process", cancels the hot metal pretreatment process, directly uses electric furnace steelmaking to shorten the production path; scrap steel is in the form of automotive sheet packing blocks, and after desulfurization with alkaline slag in LF refining, the slag is skimmed and modified to acidic slag to control the sulfur content in the molten steel, so as to achieve strict control of residual elements, inclusions, composition segregation, etc. in the steel. The invention adopts the short-process electric furnace production process to ensure both the mechanical properties and the drawing performance of the steel used for LX72A.

[0005] To achieve the above purpose, the invention is realized by the following technical solutions: A method for producing green wire steel LX72A by a short-process electric furnace, the production process includes electric furnace smelting, LF refining, RH refining, and continuous casting; the technical key point of the invention is that in the LF refining process, after desulfurization with alkaline slag in refining, the slag is skimmed and modified to acidic slag to control the molten steel composition. Specifically: The electric furnace smelting described above includes: scrap steel accounting for 60wt% - 100wt%, hot metal accounting for 0 - 40wt%, and the proportion of automobile sheet packing blocks in the scrap steel being 20wt% - 30wt%; the tapping temperature of the electric furnace is 1610 - 1630°C, the tapping end point C is 0.10% - 0.20%, the electric furnace is smelted with a single slag, the target furnace P ≤ 0.008%, and slagging down is strictly prohibited.

[0006] The addition amount of auxiliary materials per ton of steel in the electric furnace smelting described above is: 52 - 56 kg of active lime and 29 - 33 kg of dolomite.

[0007] For ladle alloying during tapping in the electric furnace smelting: 1.8 - 1.9 kg / t of special ferrosilicon and 3 - 4 kg / t of low-titanium carburizer are used as tapping deoxidizers. The special ferrosilicon, low-titanium carburizer, and alloy are added when 13% - 18% of the steel is tapped, and all materials are added before 60% of the steel is tapped. The slagging materials for tapping are: 7 - 9 kg / t of ladle lime, which is started to be added when 1 / 4 - 1 / 3 of the steel is tapped; Before tapping, bottom blowing argon in the ladle is carried out to ensure the effect of bottom blowing argon during the tapping process. The argon flow rate is adjusted to 500 - 750 L / min during tapping, and the argon flow rate is adjusted to below 150 L / min after tapping. The argon is turned off before the ladle is lifted. Avoid excessive argon gas volume causing the steel liquid surface to be exposed and resulting in secondary oxidation of the steel liquid.

[0008] The LF refining process includes the following steps: After the ladle is in place, start blowing argon at a rate of 300 - 500 NL / min; when the ladle is moved to the smelting station, add the following: 4.4 - 4.6 kg / t of lime and 2.6 - 2.8 kg / t of fluorite. Start power supply for 3 - 5 minutes. After a thin slag is formed, adjust the argon flow rate to 150 - 250 NL / min. It is not allowed to increase the temperature by strong argon stirring. At the same time, add 0.045 - 0.072 kg / t of silicon carbide and 0.018 - 0.027 kg / t of carbon powder in the first batch, and continue power supply for 5 - 8 minutes; add 0.018 - 0.045 kg / t of silicon carbide and 0.018 - 0.027 kg / t of carbon powder in the second batch; after the total power supply time with the furnace door closed is ≥20 minutes, dip the slag to confirm that the slag is white, then measure the temperature and take a sample once. The silicon carbide is added in the following way: After unpacking, it is stirred evenly with the carbon powder and added through the furnace door. It is strictly prohibited to add the whole bag through the wire feeding hole. The temperature for the first full analysis is 1530℃ - 1570℃. Alloying is carried out according to the components of the first full analysis. The calculated total addition amount reaches the control target. Continue power supply for 10 - 15 minutes and then take a second sample. During this period, add alloys according to the composition of the first sample to adjust the chemical composition. The total amount of silicon carbide used is 0.45 - 0.72 kg / t, added in two batches; after the second full analysis components meet the process requirements (S content ≤ 0.005%), before slag skimming, C is controlled at 0.65 wt% - 0.67 wt%, and the temperature before slag skimming is 1616 - 1626℃. Skim 80% - 90% of the slag on the surface to remove the oxidized slag to prevent sulfur reversion. After slag skimming, re - make an acidic slag. It is prohibited to skim all the slag to prevent the molten steel from being exposed and over - oxidized, increasing oxygen and nitrogen content, and increasing the difficulty of subsequent treatment processes. Add 5 - 5.9 kg / t of lime and 5.5 - 6.5 kg / t of quartz sand. Note that carbon increases during this process, with a carbon increase of 0.05% - 0.08%. The alkalinity R is controlled in the range of 0.9 - 1.2. Considering the carbon increase of the electrode during power supply after adding quartz sand, the temperature should reach 1650 - 1670℃ before adding quartz sand, and the target power supply time after adding quartz sand is controlled within 8 minutes to avoid low - gear high - current heating after adding quartz sand. After adding lime and quartz sand to complete slag making, appropriate alloys need to be added according to the target composition requirements for deoxidation and micro - alloying.

[0009] Measures for nitrogen control: During the whole LF process, the ladle is bottom - blown with argon for stirring. After the components of the second full analysis are adjusted, the argon flow rate is adjusted to 100 - 200 NL / min; during the static blowing waiting period, the argon flow rate is adjusted to 30 - 60 NL / min. Micro - positive pressure operation is required. After breaking the slag crust at the station, reduce the argon flow rate or turn off the argon. When it is moved to below the furnace cover, strong argon stirring can be used for feeding materials.

[0010] During the whole refining process, the furnace door is closed except when measuring the temperature and taking samples, ensuring a reducing atmosphere inside the furnace.

[0011] The RH refining process described above includes: maintaining a vacuum of less than 100 Pa for a duration of ≥ 20 min; performing static argon blowing and stirring for a duration of ≥ 15 min and not exceeding 30 min, and adding 3 - 5 bags of carbonized rice husk; performing soft argon blowing at a rate of 10 - 60 NL / min, with the soft blowing being such that the slag surface slightly moves and the molten steel is not exposed (the diameter of the splashing is not greater than 200 mm).

[0012] The continuous casting process described above includes: the electromagnetic stirring current in the mold is 380 - 420 A and the frequency is 1 - 3 Hz; the electromagnetic stirring current at the end is 380 - 420 A and the frequency is 5 - 9 Hz, and the electromagnetic stirring method at the end is: alternating stirring.

[0013] The temperature of the first furnace turntable for continuous casting is 1550 - 1560 °C, the tundish temperature is 1490 - 1500 °C, the superheat is maintained at 20 - 30 °C, and the casting speed is 1.6 - 1.8 m / min. Protective casting is carried out throughout the process. For the addition of the mold powder: for medium square billets, the slag addition amount is controlled to be: 220 - 240 g / min per strand.

[0014] The chemical composition of the wire - connected steel by weight percentage is: C: 0.70% - 0.74%, Si: 0.18% - 0.28%, Mn: 0.48% - 0.55%, P ≤ 0.015%, S ≤ 0.010%, Alt ≤ 0.005%, Ni ≤ 0.05%, Cr ≤ 0.05%, Cu ≤ 0.05%, O ≤ 0.0045%, N ≤ 0.0050%, and the rest is Fe and unavoidable impurities.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Through single - slag smelting in an electric furnace, the LF process adopts slag - skimming operation and slag - modification treatment. Through composition design, it ensures that the composition is close to that of converter LX72A and the performance meets the requirements, replacing the process of hot metal pretreatment + converter route + converter double - slag smelting, thus reducing costs.

[0016] 2. The low - magnification quality rating of the steel billet of the present invention is: central porosity ≤ 0.5, central segregation ≤ 0.5, and shrinkage cavity is 0; the tensile strength of the wire - connected steel of the present invention is 1000 - 1120 Mpa, the cross - sectional elongation rate A ≥ 10%, and the cross - sectional reduction rate Z ≥ 40%.

[0017] 3. It conforms to the concept of green design, reduces the impact on the environment, greatly improves ecological friendliness, and reduces costs and the production path links.

[0018] 4. In all production processes of the present invention, the composition and inclusions are strictly controlled. The hot metal pretreatment is cancelled, and the sulfur content is controlled through slag - modification treatment; and the slag falling from the electric furnace is strictly controlled, and during the slag - skimming and slag - modification processes in the refining process, the increase of oxygen content and nitrogen content is simultaneously controlled and avoided. Description of the Drawings

[0019] Figure 1 This is the image of the macrostructure defect inspection result of the continuous casting billet in Example 1 of the present invention. Detailed implementation manners

[0020] The following further illustrates the detailed implementation manners of the present invention in conjunction with the examples.

[0021] The steel grade components of the examples of the present invention are shown in Table 1, the process parameters of the electric furnace smelting in the examples are shown in Table 2, the process parameters of the LF refining in the examples are shown in Table 3, the process parameters of the RH refining and continuous casting in the examples are shown in Table 4, the inspection during the production process of the examples is shown in Table 5, the macrostructure quality of the continuous casting billets in the examples is shown in Table 6, and the properties of the rolled products with a diameter of ∅5.5mm of the steel in the examples are shown in Table 7. The inspection result of the macrostructure defects of the continuous casting billet in Example 1 is shown in Figure 1 .

[0022] Table 1 Steel grade components of the examples (wt%)

[0023] Table 2 Process parameters of the electric furnace smelting in the examples

[0024] Table 3 Process parameters of the LF refining in the examples

[0025] Table 3 Process parameters of the LF refining in the examples (continued)

[0026] Table 4 Process parameters of the RH refining and continuous casting in the examples

[0027] Table 5 Inspection during the production process of the examples

[0028] Table 6 Macrostructure quality of the continuous casting billets in the examples

[0029] Table 7 Steel in the examples Properties of the rolled products with a diameter of 5.5mm

[0030] The present invention provides a method for producing green cord steel LX72A by a short-process electric furnace. The green cord steel LX72A is produced by adopting the process of "electric furnace production + LF refining process + slag skimming and slag modification process + RH process". It can be seen from the examples of the present invention that the short-process electric furnace production process of the present invention not only ensures the mechanical properties of the steel for LX72A, but also ensures its drawing properties.

Claims

1. A method for producing green wire rod steel LX72A by a short-process electric furnace, the production process including electric furnace smelting, LF refining, RH refining, and continuous casting, characterized in that, During the LF refining process, the slag is removed after desulfurization of the refining basic slag, and the slag is changed to acidic slag to control the composition of the molten steel. Specifically, after the secondary full analysis composition meets the process requirements, the C content before slag removal is controlled at 0.65wt% - 0.67wt%, the temperature before slag removal is 1616 - 1626°C, 80% - 90% of the slag is removed, and after the slag removal is completed, an acidic slag is re - formed. 5 - 5.9 kg / t of lime and 5.5 - 6.5 kg / t of quartz sand are added, and the basicity R is controlled in the range of 0.9 - 1.

2.

2. A method for producing green wire rod steel LX72A by a short-process electric furnace according to claim 1, characterized in that, The electric furnace smelting described above includes: scrap steel accounts for 60wt% - 100wt%, hot metal accounts for 0 - 40wt%, and the proportion of automotive sheet packing blocks in the scrap steel is 20wt% - 30wt%; the tapping temperature of the electric furnace is 1610 - 1630°C, the tapping end C is 0.10% - 0.20%, and the target furnace P ≤ 0.008%.

3. A method for producing green wire rod steel LX72A by a short-process electric furnace according to claim 2, characterized in that, The amount of auxiliary materials added per ton of steel in the electric furnace smelting is: 52 - 56 kg of active lime and 29 - 33 kg of dolomite.

4. A method for producing green wire rod steel LX72A by a short-process electric furnace according to claim 2 or 3, characterized in that During the tapping of the electric furnace for ladle alloying: 1.8 - 1.9 kg / t of ferrosilicon and 3 - 4 kg / t of low - titanium carburizer are used as tapping deoxidizers. Ferrosilicon, low - titanium carburizer, and alloys are added at 13% - 18% of the tapping process, and all materials are added before 60% of the tapping. The tapping slag materials are: 7 - 9 kg / t of ladle lime, which is started to be added when 1 / 4 - 1 / 3 of the tapping is completed; Argon bottom - blowing is carried out before tapping. The argon flow rate is adjusted to 500 - 750 L / min during tapping, and the argon flow rate is adjusted to below 150 L / min after tapping. The argon is turned off before the ladle is lifted.

5. A method for producing green wire rod steel LX72A by a short-process electric furnace according to claim 1, characterized in that, The LF refining described above includes: after the ladle arrives, argon is turned on at 300 - 500 NL / min; when the ladle is moved to the smelting station, 4.4 - 4.6 kg / t of lime and 2.6 - 2.8 kg / t of fluorite are added as supplements. After starting power supply for 3 - 5 minutes, the argon is adjusted to 150 - 250 NL / min. At the same time, 0.045 - 0.072 kg / t of silicon carbide and 0.018 - 0.027 kg / t of carbon powder are added in the first batch, and power supply continues for 5 - 8 minutes; 0.018 - 0.045 kg / t of silicon carbide and 0.018 - 0.027 kg / t of carbon powder are added in the second batch; the temperature of the first full analysis is 1530°C - 1570°C, and alloying is carried out according to the first full - analysis composition; after continuing power supply for 10 - 15 minutes, a second sample is taken. During this period, alloys are added according to the composition of the first sampling to adjust the chemical composition, and the amount of silicon carbide used is 0.45 - 0.72 kg / t; the ladle is bottom - blown with argon for stirring throughout the LF process. After the secondary full - analysis composition is adjusted, the argon is adjusted to 100 - 200 NL / min; during the static blowing waiting period, the argon flow rate is adjusted to 30 - 60 NL / min.

6. A method for producing green wire rod steel LX72A by a short-process electric furnace according to claim 1, characterized in that, The RH refining described above includes: the holding time at a vacuum of below 100 Pa is ≥ 20 min; the static blowing and argon stirring time is ≥ 15 min and does not exceed 30 min, and the soft blowing argon flow rate is 10 - 60 NL / min.

7. A method for producing green wire rod steel LX72A by a short-process electric furnace according to claim 1, characterized in that The continuous casting described above includes: the current of the mold electromagnetic stirring is 380 - 420 A, and the frequency is 1 - 3 Hz; the current of the final electromagnetic stirring is 380 - 420 A, and the frequency is 5 - 9 Hz. The final electromagnetic stirring method is: alternating stirring.

8. A method for producing green wire rod steel LX72A by a short-process electric furnace according to claim 1 or 7, characterized in that The temperature of the first ladle turntable in continuous casting is 1550 - 1560 °C, the tundish temperature is 1490 - 1500 °C, the superheat is maintained at 20 - 30 °C, and the casting speed is 1.6 - 1.8 m / min.

9. A method for producing green wire rod steel LX72A by a short-process electric furnace according to claim 1, characterized in that, The chemical composition of the wire rod steel by weight percentage is: C: 0.70% - 0.74%, Si: 0.18% - 0.28%, Mn: 0.48% - 0.55%, P ≤ 0.015%, S ≤ 0.010%, Alt ≤ 0.005%, Ni ≤ 0.05%, Cr ≤ 0.05%, Cu ≤ 0.05%, O ≤ 0.0045%, N ≤ 0.0050%, and the rest are Fe and unavoidable impurities.

10. A method for producing green wire rod steel LX72A by a short-process electric furnace according to claim 1, characterized in that, The tensile strength of the wire rod steel is 1000 - 1120 Mpa, the elongation at fracture A ≥ 10%, and the reduction of area Z ≥ 40%.

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