A method for controlling surface cracks and inclusions in high-carbon alloy steel continuously cast slabs

Abstract

The application discloses a method for controlling surface cracks and slag inclusions of high-carbon alloy steel continuous casting slabs, and mainly solves the technical problem of surface cracks and slag inclusions of high-carbon alloy steel continuous casting slabs. The technical scheme is as follows: a method for controlling surface cracks and slag inclusions of high-carbon alloy steel continuous casting slacks, comprising the following steps: 1) in the continuous casting process, the thickness of the continuous casting slab is 200-250 mm, the width is 800-1600 mm, and the CaO-SiO2-Al2O3-Na2O-CaF2-B2O3 multi-component slag system is used as the mold powder; 2) in the continuous casting process, the pulling speed of the continuous casting machine is 0.3-1.5 m / min, and the superheat of the molten steel in the tundish is 5-30 DEG C; 3) in the continuous casting process, the vibration parameters of the mold are controlled. The high-carbon alloy steel continuous casting slab produced by the method is directly hot sent to a heating furnace for heating, and the hot-rolled steel plate obtained after hot rolling has no defects caused by the surface cracks and slag inclusions of the slab.

Description

Technical Field

[0001] This invention relates to a method for controlling the surface quality of continuously cast slabs, and particularly to a method for controlling surface cracks and inclusions in high-carbon alloy steel continuously cast slabs, belonging to the field of steelmaking continuous casting technology. Background Technology

[0002] High-carbon alloy steel has a wide range of applications and is currently typically produced using a steelmaking-continuous casting-hot rolling process. The continuous casting process involves producing square billets and slabs. Slab continuous casting offers advantages such as low product cost and stable performance, but slab production is more challenging, particularly in controlling surface quality. Surface quality defects occurring during the continuous casting production of high-carbon alloy steel slabs mainly include: corner transverse cracks and subsurface slag porosity.

[0003] High-carbon alloy steel is produced using a hot-charged, continuously cast billet rolling process to prevent phase transformation stress and cracking during repeated cooling and heating. Therefore, good billet surface quality is required. Billets with no surface defects can be sent directly to the rolling mill for further processing without further surface finishing.

[0004] A method for controlling edge defects in hot-rolled high-carbon steel is disclosed in Chinese patent application number CN202210343695.8. This invention application relates to a control method for the hot rolling process, used to control defects in the steel rolling process.

[0005] Chinese patent application No. 201710871386.7 discloses a method for controlling center segregation and porosity in fine-stamped steel continuous casting slabs. This invention application relates to a method for controlling the internal quality of fine-stamped steel continuous casting slabs. Summary of the Invention

[0006] The purpose of this invention is to provide a method for controlling surface cracks and inclusions in high-carbon alloy steel continuous casting slabs, mainly solving the technical problems of surface cracks and inclusions in existing high-carbon alloy steel continuous casting slabs; the high-carbon alloy steel continuous casting slabs produced by the method of this invention can be directly hot-sent to the hot rolling process and enter the heating furnace, and then the surface of the hot-rolled plate after hot rolling is free of defects caused by surface cracks and inclusions in the slab.

[0007] The basic technical idea of ​​this invention is that, due to the characteristics of high-carbon alloy steel, such as large temperature difference between the solid and liquid phases, low initial solidification shell temperature, low strength, and small shrinkage, it is prone to surface cracks and inclusions. Therefore, for high-carbon alloy steel, an appropriate mold flux is used to ensure sufficient lubrication within the mold, especially in the initial solidification area of ​​the molten steel at the top of the mold, between the surface of the mold copper plate and the initially solidified shell of the billet; at the same time, an appropriate mold vibration curve is used to reduce the periodic deformation of the meniscus.

[0008] The technical solution adopted in this invention is a method for controlling surface cracks and inclusions in high-carbon alloy steel continuously cast slabs, the method comprising:

[0009] 1) During continuous casting, the thickness of the continuously cast slab is controlled to be 200-250 mm, and the width of the continuously cast slab is controlled to be 800-1600 mm. The mold flux adopts a CaO-SiO2-Al2O3-Na2O-CaF2-B2O3 multi-element slag system. The weight percentage of the mold flux components is: Al2O3 8%~12%, the sum of Na2O and CaF2 content ≤5%, B2O3 4.50%~6.50%, the binary basicity of the mold flux is 0.85~0.95, the melting point temperature of the mold flux is 980~1020℃, the viscosity of the mold flux at 1300℃ is ≤0.12 Pa·s, and the surface tension of the mold flux is ≤300×10⁻⁶. -3 N / m;

[0010] 2) During continuous casting, the casting speed of the continuous casting machine is controlled at 0.3 to 1.5 m / min, and the superheat of the molten steel in the tundish is 5 to 30°C;

[0011] 3) During continuous casting, the non-sinusoidal vibration parameters of the crystallizer are controlled, including the crystallizer's vibration stroke, vibration frequency, and non-sinusoidal vibration coefficient α. The non-sinusoidal vibration coefficient α is a constant, with a value of 0.3. The crystallizer's vibration stroke and vibration frequency are calculated using the following formula:

[0012] h = 3 + 2Vc (Formula 1)

[0013] f = 210 - 30Vc (Formula 2);

[0014] In formulas 1 and 2, h is the vibration stroke of the crystallizer in mm; Vc is the casting speed of the continuous casting machine in m / min; and f is the vibration frequency of the crystallizer in 1 / min.

[0015] The binary basicity of the crystallizer protective slag described in this invention is the weight percentage of CaO in the crystallizer protective slag / the weight percentage of SiO2; that is, (%CaO) / (%SiO2) in the crystallizer protective slag.

[0016] The chemical composition of the high-carbon alloy steel described in this invention is as follows (by weight percentage): C: 0.3-0.80%, Si: 0.2-0.45%, Mn: 0.60-1.20%, P≤0.018%, S≤0.010%, Al: 0.01-0.08%, Cr≤5.0%, Ni≤1.0%, Mo≤2.2%, V≤0.5%, with the remainder being iron and unavoidable impurities.

[0017] Furthermore, the non-sinusoidal vibration curve parameters of the crystallizer of the present invention have the following characteristics: negative sliding time is 0.1 seconds within the casting speed range of the continuous casting machine; negative sliding advance amount NSA ≥ 3 mm; when the casting speed Vc of the continuous casting machine is 1.0-1.5 m / min, the negative sliding time ratio NSR < 60%; and the positive sliding speed difference ΔV < 3.14 m / min.

[0018] The negative sliding time of the non-sinusoidal vibration curve parameters of the crystallizer described in this invention within the casting speed range of the continuous casting machine is the time when the vibration speed of the crystallizer is higher than the casting speed of the continuous casting machine.

[0019] The reasons for determining the process control parameters in this invention are as follows:

[0020] The [C] content in the high-carbon alloy steel is above 0.30%. As the carbon content in the steel increases, the solid-liquid phase temperature difference increases, while the thermal conductivity decreases and the solidification shrinkage is small. During continuous casting of high-carbon alloy steel, under the static pressure of molten steel, the billet shell and the mold wall are in close contact. During the billet drawing process, the billet shell experiences high frictional resistance, making it easy for the billet shell to adhere to the mold wall and form slag entrapment.

[0021] 1. Basis for setting the protective slag for the crystallizer

[0022] To facilitate steel production, a specially designed continuous casting mold flux is used. The flux's phase composition contains less than 10% total content of lanceolite (3CaO·2SiO2·CaF2), calcium aluminum feldspar (2CaO·Al2O3·SiO2), and nepheline (Na2O·Al2O3·2SiO2). A CaO-SiO2-Al2O3-Na2O-CaF2-B2O3 multi-element slag system is employed, with Al2O3 content of 8–12%, Na2O+CaF2 content ≤5%, and B2O3 content of 4.50–6.50%. The (%CaO) / (%SiO2) ratio in the flux is 0.85–0.95, and the flux has a melting point of 1000±20℃. The viscosity of the flux at 1300℃ is ≤0.12 Pa·s, and the surface tension is ≤300 × 10⁻⁶. -3 N / m.

[0023] The protective slag is in a glassy state when it is molten at high temperature. In the actual continuous casting process, the protective slag comes into contact with the molten steel of the steel grade at the steel-slag interface in the crystallizer. No high-melting-point crystalline substances are precipitated from the protective slag, which ensures lubrication and heat transfer between the billet shell and the copper wall surface of the crystallizer. This can effectively prevent the formation of slag holes or slag entrapment at the solidification front of the billet, and thus prevent the formation of subsurface slag holes or slag entrapment in the billet.

[0024] 2. Basis for setting the vibration parameters of the crystallizer

[0025] Generally, the lubrication effect of the crystallizer is evaluated by the consumption of protective slag, and the consumption of protective slag is determined by the performance parameters of the protective slag and the vibration settings of the crystallizer.

[0026] Furthermore, to ensure adequate consumption of the protective slag, thus guaranteeing lubrication between the billet shell and the copper wall of the crystallizer, and to reduce the depth of oscillation marks on the billet surface and prevent corner cracks, appropriate crystallizer vibration parameters are employed. The basic parameters of crystallizer vibration are the vibration frequency f, vibration stroke h, and non-sinusoidal vibration coefficient α. The non-sinusoidal vibration coefficient is a constant, and the vibration frequency and stroke are functions of the continuous casting speed Vc. These basic parameters further determine the corresponding process parameters: negative sliding time tn, negative sliding time ratio NSR, negative sliding lead NSA, and positive sliding speed difference ΔV, etc.

[0027] The high-carbon alloy steel has a large liquidus-solid phase temperature difference, resulting in a large two-phase region with low strength at the solidification front. Another purpose of vibration parameters is to reduce the pressure of the steel-slag interface on the meniscus at the solidification front. A reasonable negative sliding time can optimally reduce the pressure deformation on the meniscus while ensuring demolding.

[0028] Optionally, the present invention sets the negative sliding time of each vibration cycle to 0.1 seconds.

[0029] Optionally, appropriate values ​​can be selected for the negative sliding time ratio (NSR), negative sliding lead (NSA), and positive sliding speed difference (ΔV) to reduce the friction between the billet shell and the copper wall of the crystallizer. Simultaneously, the consumption of protective slag can be increased to enhance the thickness of the liquid slag film, resulting in a significant improvement in lubrication. (The values ​​for NSR, NSA, and ΔV are implied but not explicitly stated.)

[0030] The specific crystallizer vibration parameters used in this invention are as follows:

[0031] Furthermore, the non-sinusoidal vibration coefficient α can be taken in the range of 0 to 0.4. The larger the value, the more beneficial it is to shorten the negative slip time, but the larger the value, the closer it is to the equipment limit and the more unstable the equipment operation becomes. When the non-sinusoidal vibration coefficient α is 0.3, the effect is good.

[0032] Based on the above selections, the relevant parameters are determined by the following formula:

[0033] Vibration stroke h = 3 + 2Vc (Formula 1)

[0034] Vibration frequency f = 210 - 30Vc (Formula 2)

[0035] Negative sliding time

[0036] Negative sliding time ratio

[0037] Negative slip lead

[0038] Positive sliding speed difference

[0039] 3. Within the selected cross-sectional area, the maximum pulling speed can reach 1.5 m / min. When the cross-sectional size is smaller than the range, the maximum pulling speed will be higher than 1.5 m / min; when the cross-sectional size is larger than the range, the maximum pulling speed will be lower than 1.5 m / min.

[0040] Compared with the prior art, the present invention has the following positive effects: 1. The non-sinusoidal vibration curve parameters set in the present invention achieve a shorter negative sliding time (i.e., the time when the vibration speed exceeds the casting speed), while ensuring that the negative sliding advance (NSA) reaches more than 3mm, so as to ensure effective demolding between the billet and the mold; when the casting speed (Vc) is in the normal working range of 1.0-1.5m / min, the negative sliding time (NSR) is less than 60%, and the positive sliding speed difference (ΔV) is less than 3.14m / min, which is beneficial to increase the consumption of protective slag and reduce the friction between the billet and the mold. 2. Using the method of the present invention, the amount of protective slag used in the mold is reduced from 0.3kg / m 2 Increase to 0.4-0.5 kg / m 2 3. The method of this invention completely eliminates the defects of transverse cracks at the corners and subcutaneous slag holes on the surface of high-carbon alloy steel slabs, with an incidence rate of 0. The high-carbon alloy steel continuous casting slabs produced by this invention are directly hot-fed into the heating furnace for heating, and the hot-rolled steel plates obtained after hot rolling are free from defects caused by surface cracks and slag inclusions on the slabs. Detailed Implementation

[0041] The present invention will be further described below with reference to Examples 1 and 2, as shown in Tables 1 to 4.

[0042] Example 1: The composition of high-carbon alloy steel is shown in Table 1. A method for controlling surface cracks and inclusions in continuously cast high-carbon alloy steel slabs includes:

[0043] 1) During continuous casting, the thickness of the continuously cast slab is 230 mm, and the width of the continuously cast slab is 1150 mm; the binary basicity (%CaO) / (%SiO2) of the mold flux is 0.92, the melting point temperature of the mold flux is 1010℃, the viscosity of the mold flux at 1300℃ is 0.11 Pa·s, and the surface tension of the mold flux is 250 × 10⁻⁶. -3 N / m; weight percentage of crystallizer protective slag components is shown in Table 2;

[0044] 2) During continuous casting, the casting speed of the continuous casting machine is controlled at 0.3 to 1.2 m / min, the stable casting speed range is 1.0 to 1.2 m / min, and the superheat of the molten steel in the tundish is 15 to 30℃;

[0045] 3) During continuous casting, the vibration parameters of the crystallizer are controlled, including the vibration stroke, vibration frequency, and non-sinusoidal vibration coefficient α; the non-sinusoidal vibration coefficient α is a constant, with a value of 0.3; the vibration stroke and vibration frequency of the crystallizer are calculated using the following formula:

[0046] h = 3 + 2Vc (Formula 1)

[0047] f = 210 - 30Vc (Formula 2);

[0048] In Formulas 1 and 2, h is the vibration stroke of the crystallizer in mm; Vc is the casting speed of the continuous casting machine in m / min; f is the vibration frequency of the crystallizer in 1 / min; the vibration parameters of the crystallizer are shown in Table 3.

[0049] Example 2, the composition of high-carbon alloy steel is shown in Table 1, a method for controlling surface cracks and inclusions in high-carbon alloy steel continuously cast slabs, comprising:

[0050] 1) During continuous casting, the thickness of the continuously cast slab is 210 mm, and the width of the continuously cast slab is 1250 mm; the binary basicity (%CaO) / (%SiO2) of the mold flux is 0.92, the melting point temperature of the mold flux is 1010℃, the viscosity of the mold flux at 1300℃ is 0.11 Pa·s, and the surface tension of the mold flux is 250 × 10⁻⁶. -3 N / m; weight percentage of crystallizer protective slag components is shown in Table 2;

[0051] 2) During continuous casting, the casting speed of the continuous casting machine is controlled at 0.3 to 1.4 m / min, the stable casting speed range is 1.1 to 1.3 m / min, and the superheat of the molten steel in the tundish is 15 to 30℃;

[0052] 3) During continuous casting, the vibration parameters of the crystallizer are controlled, including the vibration stroke, vibration frequency, and non-sinusoidal vibration coefficient α; the non-sinusoidal vibration coefficient α is a constant, with a value of 0.3; the vibration stroke and vibration frequency of the crystallizer are calculated using the following formula:

[0053] h = 3 + 2Vc (Formula 1)

[0054] f = 210 - 30Vc (Formula 2);

[0055] In Formulas 1 and 2, h is the vibration stroke of the crystallizer in mm; Vc is the casting speed of the continuous casting machine in m / min; f is the vibration frequency of the crystallizer in 1 / min; the vibration parameters of the crystallizer are shown in Table 4.

[0056] Table 1 shows the chemical composition (by weight percentage) of the high-carbon alloy steel in the example, with the balance being Fe and unavoidable impurities.

[0057] Table 1 Chemical composition of high-carbon alloy steel in the embodiments of the present invention, unit: weight percentage.

[0058] Example 1 0.3003 0.2919 1.0006 0.0128 0.0013 0.0512 0.6231 3.9586 0.351 1.2327 Example 2 0.30 0.20 0.47 0.015 0.003 0.025 / 0.87 / 0.18

[0059] Table 2. Weight percentage of crystallizer protective slag components in embodiments of the present invention. Unit: weight percentage.

[0060] Example 1 35.76 38.83 8.34 2.24 2.73 5.57 6.28 Example 2 35.76 38.83 8.34 2.24 2.73 5.57 6.28

[0061] Table 3. Casting speed and crystallizer vibration parameters of the continuous casting machine in Embodiment 1 of the present invention.

[0062]

[0063]

[0064] As shown in Table 3, the negative sliding time obtained at all continuous casting machines in Example 1 was 0.1 seconds. The positive sliding speed difference ΔV in the stable casting speed range of 1.0 to 1.2 m / min was less than 2.76 m / min, the negative sliding advance NSA was stabilized at 3.2 mm, and the negative sliding time ratio NSR was less than 0.6. These results will help to obtain stable surface oscillation marks and eliminate surface cracks and inclusions.

[0065] Table 4. Casting speed and crystallizer vibration parameters of the continuous casting machine in Embodiment 2 of the present invention.

[0066]

[0067] As shown in Table 4, in Example 2, the negative slip time obtained at all continuous casting machine casting speeds was 0.1 seconds. Within the stable casting speed range, the positive slip velocity difference ΔV was less than 2.89 m / min, the negative slip advance (NSA) stabilized at 3.2 mm, and the negative slip time ratio (NSR) was less than 0.6. These results will help obtain stable surface oscillation marks and eliminate surface cracks and inclusions.

[0068] According to the process combination described, within the full casting speed range, the continuously cast slabs obtained are directly hot-fed and then processed in the hot rolling process without any surface quality problems caused by surface cracks or slag inclusions.

[0069] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method of controlling surface cracks and slag entrapment of high carbon alloy steel continuous casting slab, characterized by, The method includes: 1) During the continuous casting process, the thickness of the continuous casting slab is controlled to be 200-250 mm and the width of the continuous casting slab is controlled to be 800-1600 mm. The mold flux adopts a CaO-SiO2-Al2O3-Na2O-CaF2-B2O3 multi-element slag system. The weight percentage of the mold flux components is as follows: Al2O3 8%~12%, the sum of Na2O and CaF2 content ≤5%, B2O3 4.50%~6.50%, the binary basicity of the mold flux is 0.85~0.95, the melting point temperature of the mold flux is 980~1020 ℃, the viscosity of the mold flux at 1300 ℃ is ≤0.12 Pa·s, and the surface tension of the mold flux is ≤300×10-3 N / m. 2) During continuous casting, the casting speed of the continuous casting machine is controlled at 0.3 to 1.5 m / min, and the superheat of the molten steel in the tundish is 5 to 30℃; 3) During continuous casting, control the non-sinusoidal vibration parameters of the crystallizer, including the crystallizer's vibration stroke, the crystallizer's vibration... Vibration frequency and non-sinusoidal vibration coefficient; the non-sinusoidal vibration coefficient is a constant, with a value of 0.3; the vibration of the crystallizer. The stroke and vibration frequency are calculated using the following formula: h = 3 + 2Vc (Formula 1) f = 210 - 30 Vc (Formula 2) In formulas 1 and 2, h is the vibration stroke of the crystallizer, in mm; Vc is the casting speed of the continuous casting machine, in m / min; and f is the vibration frequency of the crystallizer, in 1 / min. The chemical composition (by weight percentage) of the high-carbon alloy steel is as follows: C: 0.3-0.80%, Si: 0.2-0.45%, Mn: 0.60-1.20%. P≤0.018%, S≤0.010%, Al: 0.01-0.08%, Cr≤5.0%, Ni≤1.0%, Mo≤2.2%, V≤0.5%, The remainder consists of iron and unavoidable impurities.

2. The method of claim 1, wherein the method is characterized by, The non-sinusoidal vibration curve parameters of the crystallizer are as follows: negative sliding time is 0.1 seconds within the casting speed range of the continuous casting machine; negative sliding advance (NSA) is ≥3 mm; when the casting speed (Vc) of the continuous casting machine is 1.0-1.5 m / min, the negative sliding time ratio (NSR) is <60%; and the positive sliding speed difference (ΔV) is <3.14 m / min.

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