Preparation method of HPB300 continuous casting billet

Abstract

The invention discloses a preparation method of an HPB300 continuous casting billet. The production process of the preparation method of the HPB300 continuous casting billet comprises the steps of converter smelting, argon station treatment and square billet continuous casting, the end point carbon content is controlled in the converter smelting process, the argon blowing time, the sulfur content and the manganese content of molten steel are controlled in the argon station treatment process, and continuous casting of the square billet is achieved. And the crystallizer working condition, the pouring superheat degree, the secondary cooling water distribution amount and the pulling speed are controlled in the square billet continuous casting process, so that the quality of the HPB300 continuous casting billet is improved. By optimizing the process in the converter smelting, argon station treatment and continuous casting processes, the problem of casting blank separation is effectively solved, and the defect of internal cracks of the casting blank is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, in particular to a method for preparing a HPB300 continuous casting billet. Background Art

[0002] HPB300 belongs to the category of ordinary carbon steel. Its main components are carbon, silicon, manganese and other elements, among which the carbon content is between 0.14% and 0.22%. This steel has good strength and toughness and is suitable for various mechanical processing and welding processes. HPB300 round steel is usually used as a material in the manufacturing process of mechanical parts, bearings, bicycles, etc., and is also widely used in construction, bridges, etc.

[0003] The existing production of large square billets with medium carbon high aluminum steel billets mainly has the following problems:

[0004] (1) The billet is seriously out of square, and the proportion of the billet diagonal length difference greater than 10 mm is high, which makes it difficult for the billet to bite during the rolling process.

[0005] (2) The ingot has severe internal cracks, which leads to frequent head explosion, steel rot and steel punching accidents during the rolling process. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method for preparing HPB300 continuous casting billet.

[0007] The invention provides a preparation method of an HPB300 continuous casting billet. The production process comprises: converter smelting→argon station treatment→square billet continuous casting, wherein the final carbon content is controlled in the converter smelting process, the argon blowing time and the sulfur content and the manganese content of the molten steel are controlled in the argon station treatment process, and the crystallizer working condition, pouring superheat, secondary cooling water distribution amount and drawing speed are controlled in the square billet continuous casting process, so as to improve the quality of the HPB300 continuous casting billet.

[0008] The present invention has the following beneficial effects:

[0009] The invention provides a method for preparing an HPB300 continuous casting billet. By optimizing the processes in converter smelting, argon station treatment and continuous casting, the quality of the HPB300 casting billet produced is significantly improved, the proportion of the casting billet diagonal length difference greater than 10 mm is reduced to within 0.5%, and the accidents of head explosion, rotten steel and steel punching in the rolling process caused by internal cracks of the casting billet are significantly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0011] Figure 1 The end condition of the casting billet prepared by the method provided in Comparative Example 1;

[0012] Figure 2 The end condition of the casting billet prepared by the method provided in Example 1;

[0013] Figure 3 This is a low-magnification case of the ingot prepared by the method provided in Comparative Example 1;

[0014] Figure 4 This is a low-magnification view of the ingot prepared by the method provided in Example 1. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0016] The following is a detailed description of a method for preparing a HPB300 continuous casting billet provided in an embodiment of the present invention.

[0017] An embodiment of the present invention provides a method for preparing an HPB300 continuous casting billet, wherein the production process comprises: converter smelting→argon station treatment→square billet continuous casting, wherein the final carbon content is controlled in the converter smelting process, the argon blowing time and the sulfur content and manganese content of the molten steel are controlled in the argon station treatment process, and the crystallizer working condition, pouring superheat, secondary cooling water distribution amount and casting speed are controlled in the square billet continuous casting process to improve the quality of the HPB300 continuous casting billet.

[0018] In some optional embodiments, the chemical composition of the HPB300 continuous casting billet, calculated by mass percentage, includes: C: 0.16-0.24%, P: ≤0.045%, S: ≤0.045%, Si: 0.15-0.40%, Mn: 0.55-0.85%, and the remainder is iron and unavoidable impurities or trace elements.

[0019] In some optional embodiments, controlling the final carbon content in the converter smelting process includes: controlling the S content of the molten iron entering the furnace to ≤0.035%, the final C content of the converter to 0.08-0.14%, and during the converter tapping process, using a slide plate to block the slag to prevent slag from falling during the tapping process, and for the final C content of the converter <0.08%, 20-50 kg of aluminum iron are manually thrown in during the tapping process to enhance deoxidation.

[0020] In some optional embodiments, the argon blowing time of the molten steel is controlled in the argon station treatment process, including: the total argon blowing time of the argon station is required to be ≥6 minutes, and the argon blowing time is increased by 2 minutes for the first furnace of the continuous casting ladle, the D-type ladle and the E-type ladle, and the bottom ladle. The station sample is taken 3 to 5 minutes after the bottom argon blowing and strong stirring are completed after the steel is tapped. After the alloy and carbon powder or cooling material are added, the bottom argon blowing and strong stirring must be ensured for 3 to 5 minutes, wherein: during the bottom argon blowing and strong stirring, the diameter of the bright circle of the liquid surface at the argon blowing port is controlled at 400-500mm; during the argon station molten steel treatment, it is strictly forbidden to turn off the bottom argon blowing of the ladle or the bottom argon blowing flow is too small to cause slag surface deadening.

[0021] In some optional embodiments, controlling the sulfur content and manganese content of the molten steel in the argon station processing procedure includes: in order to make the Mn / S ratio in the molten steel leaving the argon station ≥25, controlling the content of Mn element in the molten steel leaving the argon station to be 0.66%-0.82%, wherein: when the sulfur content of the molten steel leaving the argon station is ≤0.030%, the manganese leaving the argon station is controlled at a target of 0.70%, and when the sulfur leaving the argon station is greater than 0.030%, the manganese leaving the argon station is controlled at 0.75-0.80%.

[0022] The above control of the carbon content at the converter tapping end point in the converter smelting process and the argon blowing time, sulfur content and manganese content in the argon station treatment process can improve the purity of molten steel, reduce the formation of subsequent inclusions, and reduce the probability of internal cracks. The higher the S content in molten steel, the lower the plastic deformation, resulting in a smaller limit deformation rate of steel, which will cause internal cracks. By optimizing the composition and increasing the Mn / S ratio, the probability of internal cracks can be effectively reduced.

[0023] In some optional embodiments, the crystallizer working conditions are controlled in the billet continuous casting process, including: when producing HPB300, the copper tube life is controlled within 100-700 times, the copper tube wear is ≤350mm, the water gap is controlled within the range of 3.5-5.0mm when the copper tube is installed, the four surface water gap extreme values ​​are <0.5mm, and when the tundish water inlet is centered, an immersion water inlet online centering device is used to achieve precise centering, so that the centering deviation between the immersion water inlet and the crystallizer flange is ≤5mm. By controlling the service life and wear condition of the continuous casting crystallizer and controlling the water inlet centering, the uniformity of the cooling of the billet shell in the crystallizer can be effectively guaranteed, and the problem of billet de-squareness can be effectively improved.

[0024] In some optional embodiments, controlling the pouring superheat in the billet continuous casting process includes: controlling the superheat of the continuous casting molten steel to be 20-35°C.

[0025] In some optional embodiments, controlling the secondary cooling water distribution amount in the billet continuous casting process includes: controlling the secondary cooling water specific water volume to be 0.80-0.85 L / kg, the billet is cooled in the secondary cooling chamber as secondary cooling, and the cooling water volume Q of each zone of the secondary cooling is calculated according to the formula: Q=A×V2+B×V+C, where V is the casting speed, and the water distribution amount of the secondary cooling zone is shown in the following table:

[0026] Second cold district A B C <![CDATA[Foot roller Q, m 3 / h]]> -0.16～-0.20 4.10～4.15 -0.15～-0.18 <![CDATA[Zone Q, m 3 / h]]> 0.79～0.82 0.22～1.9 2.90～3.02 <![CDATA[Zone 2 Q, m 3 / h]]> 0.70～0.75 -0.75～-0.80 1.92～1.95 <![CDATA[Three - zone Q, m 3 / h]]> 0.35～0.40 -0.12～-0.14 0.28～0.31

[0027] By optimizing the continuous casting cooling water volume and the secondary cooling water volume, the temperature gradient of the billet cooling process can be further reduced, the formation of coarse columnar crystals in the billet can be avoided, and internal cracks in the billet can be avoided.

[0028] In some optional embodiments, controlling the pulling speed in the billet continuous casting process includes: formulating different pulling speeds according to the Mn / S ratio in the molten steel, wherein: the casting machine pulling speed is controlled as follows: when the Mn / S ratio is greater than 28, the pulling speed is 3.0 m / min; when 28 ≥ Mn / S ratio ≥ 25, the pulling speed is 2.8 m / min; when 25 > Mn / S ratio ≥ 23, the pulling speed is 2.6 m / min; when Mn / S ratio is less than 23, the pulling speed is 2.4 m / min. The pulling speed has a significant correlation with the internal cracks of the billet, and formulating different pulling speeds according to the Mn / S ratio can effectively ensure the internal quality of the billet.

[0029] In some optional embodiments, the size of the HPB300 continuous casting billet is 160mm*160mm, and the proportion of the HPB300 billet with a diagonal length difference greater than 10mm is within 0.5%; the internal cracks of the continuous casting billet leading to head explosion, rotten steel, and steel punching accidents during the rolling process are reduced from 5 times / month to 1 time / month.

[0030] The present invention will be further described below in conjunction with the embodiments.

[0031] Example 1

[0032] A method for preparing a HPB300 continuous casting billet, wherein the chemical composition of the HPB300 continuous casting billet, in terms of mass percentage, comprises: C: 0.16-0.24%, P: ≤0.045%, S: ≤0.045%, Si: 0.15-0.40%, Mn: 0.55-0.85%, and the remainder is iron and unavoidable impurities or trace elements. The production process comprises: converter smelting → argon station treatment → billet continuous casting, and the specific steps are as follows:

[0033] Step 1: The S content of molten iron entering the furnace is 0.020%, and the C content at the converter end point is strictly controlled to be 0.09%. A slide plate is used to block the slag to prevent slag from falling during the steelmaking process.

[0034] Step 2: The content of Mn element in molten steel is 0.66%.

[0035] Step 3: Argon station processing control, total argon blowing time is 8 minutes, and the ladle is a Class C ladle. After the steel is tapped, the bottom argon is blown for 3 minutes of strong stirring to take the station sample. After the alloy (including carbon powder) or cooling material is added, the bottom argon must be blown for 3 minutes of strong stirring.

[0036] Step 4: Continuous casting uses a square billet continuous casting machine to produce billet cross-section 160mm*160mm arc radius R10m full arc continuous casting machine.

[0037] 1. In order to improve the casting billet de-squareness, the requirements for the life and working conditions of the crystallizer are: the copper tube life is 120 times, the copper tube wear is ≤350mm, the water gap is controlled within the range of 3.5-5.0mm when the copper tube is installed, and the extreme difference of the water gap on the four surfaces is <0.5mm.

[0038] 2. Requirements for centering of tundish nozzle: Use an online centering device for submerged nozzle to achieve precise centering and control the centering deviation between the submerged nozzle and the crystallizer flange to 5mm.

[0039] 3. Appropriate superheat pouring: Through tracking and comparison, the superheat of continuous casting molten steel is controlled at 25℃.

[0040] 4. Optimize secondary cooling water distribution: The secondary cooling water ratio is 0.80L / kg. The cooling of the billet in the secondary cooling chamber is two-stage cooling. The cooling water volume Q in each zone of the secondary cooling is calculated according to the formula: Q = A × V2 + B × V + C, where V is the casting speed. The water volume control of each zone of the secondary cooling water is as follows:

[0041] Second cold district A B C <![CDATA[Foot roller Q, m 3 / h]]> -0.16 4.10 -0.15 <![CDATA[Zone Q, m 3 / h]]> 0.79 0.22 2.90 <![CDATA[Zone 2 Q, m 3 / h]]> 0.70 -0.75 1.92 <![CDATA[Three - zone Q, m 3 / h]]> 0.35 -0.12 0.28

[0042] 5. According to the S content in the molten steel, different pulling speed control requirements are formulated: the pulling speed of the casting machine is controlled as follows: when Mn / S>28, the pulling speed is 3.0m / min; when 28≥Mn / S≥26, the pulling speed is 2.8m / min; when 25≥Mn / S≥23, the pulling speed is 2.6m / min; when Mn / S<23, the pulling speed is 2.4m / min. In this example, the continuous casting process has S 0.020%, Mn 0.66%, Mn / S=0.66 / 0.020=33, and the pulling speed is controlled at 3.0m / min.

[0043] The result is: See Figure 2 and Figure 4 (The numbers in the figure are production batch numbers). The ends of the ingot prepared in Example 1 are square without de-squareness and slight internal cracks. The ingot rolling in the next process is normal.

[0044] Example 2

[0045] A method for preparing a HPB300 continuous casting billet, wherein the chemical composition of the HPB300 continuous casting billet, in terms of mass percentage, comprises: C: 0.16-0.24%, P: ≤0.045%, S: ≤0.045%, Si: 0.15-0.40%, Mn: 0.55-0.85%, and the remainder is iron and unavoidable impurities or trace elements. The production process comprises: converter smelting → argon station treatment → billet continuous casting, and the specific steps are as follows:

[0046] Step 1: The S content of molten iron entering the furnace is 0.035%, and the C content at the converter end point is strictly controlled to be 0.10%. A slide plate is used to block the slag to prevent slag from falling during the steelmaking process.

[0047] Step 2: The content of Mn element in molten steel is 0.75%.

[0048] Step 3: Argon station processing control, total argon blowing time is 11 minutes, the ladle is a Class D ladle. After the steel is tapped, the bottom argon is blown for 4 minutes for strong stirring to take the station sample, and after the alloy (including carbon powder) or cooling material is added, the bottom argon must be blown for 5 minutes for strong stirring.

[0049] Step 4: Continuous casting uses a square billet continuous casting machine to produce billet cross-section 160mm*160mm arc radius R10m full arc continuous casting machine.

[0050] 1. In order to improve the casting billet de-squareness, the requirements for the life and working conditions of the crystallizer are: the copper tube life is 500 times, the copper tube wear is ≤350mm, the water gap is controlled within the range of 3.5-5.0mm when the copper tube is installed, and the extreme difference of the water gap on the four surfaces is <0.5mm.

[0051] 2. Requirements for the centering of the tundish nozzle: Use an online centering device for the submerged nozzle to achieve precise centering and control the centering deviation between the submerged nozzle and the crystallizer flange to 3mm.

[0052] 3. Appropriate superheat pouring: Through tracking and comparison, the superheat of continuous casting molten steel is controlled at 28℃.

[0053] 4. Optimize secondary cooling water distribution: The secondary cooling water ratio is 0.80L / kg. The cooling of the billet in the secondary cooling chamber is two-stage cooling. The cooling water volume of each zone of the secondary cooling is calculated according to the formula: Q = A × V2 + B × V + C, where V is the casting speed. The water volume of each zone of the secondary cooling water is controlled as follows:

[0054] Second cold district A B C <![CDATA[Foot roller Q, m 3 / h]]> -0.16 4.10 -0.15 <![CDATA[Zone Q, m 3 / h]]> 0.79 0.22 2.90 <![CDATA[Second Zone Q, m 3 / h]]> 0.70 -0.75 1.92 <![CDATA[Three - zone Q, m 3 / h]]> 0.35 -0.12 0.28

[0055] 5. According to the S content in the molten steel, different pulling speed control requirements are formulated: the pulling speed of the casting machine is controlled as follows: when Mn / S>28, the pulling speed is 3.0m / min; when 28≥Mn / S≥26, the pulling speed is 2.8m / min; when 25≥Mn / S≥23, the pulling speed is 2.6m / min; when Mn / S<23, the pulling speed is 2.4m / min. In this example, the continuous casting process S is 0.030%, Mn is 0.70%, Mn / S=0.70 / 0.030=23.3, and the pulling speed is controlled at 2.60m / min.

[0056] The results are as follows: the ends of the ingot are square without any de-squareness, and the ingot rolling in the next process is normal.

[0057] Example 3

[0058] A method for preparing a HPB300 continuous casting billet, wherein the chemical composition of the HPB300 continuous casting billet, in terms of mass percentage, comprises: C: 0.16-0.24%, P: ≤0.045%, S: ≤0.045%, Si: 0.15-0.40%, Mn: 0.55-0.85%, and the remainder is iron and unavoidable impurities or trace elements. The production process comprises: converter smelting → argon station treatment → billet continuous casting, and the specific steps are as follows:

[0059] Step 1: The S content of molten iron entering the furnace is 0.030%, and the C content of the converter end point is strictly controlled to 0.06%. A slide plate is used to block the slag to prevent slag from falling during the steel-making process. During the steel-making process, 40 kg of aluminum iron is manually thrown in to enhance deoxidation.

[0060] Step 2: The content of Mn element in molten steel is 0.72%.

[0061] Step 3: Argon station processing control, total argon blowing time is 11 minutes, the ladle is a Class D ladle. After the steel is tapped, the bottom argon is blown for 4 minutes for strong stirring to take the station sample, and after the alloy (including carbon powder) or cooling material is added, the bottom argon must be blown for 5 minutes for strong stirring.

[0062] Step 4: Continuous casting uses a square billet continuous casting machine to produce billet cross-section 160mm*160mm arc radius R10m full arc continuous casting machine.

[0063] 1. In order to improve the casting billet de-squareness, the requirements for the life and working conditions of the crystallizer are: the copper tube life is 680 times, the copper tube wear is ≤350mm, the water gap is controlled within the range of 3.5-5.0mm when the copper tube is installed, and the extreme difference of the water gap on the four surfaces is <0.5mm.

[0064] 2. Requirements for the centering of the tundish nozzle: Use an online centering device for the submerged nozzle to achieve precise centering and control the centering deviation between the submerged nozzle and the crystallizer flange to 3mm.

[0065] 3. Appropriate superheat pouring: Through tracking and comparison, the superheat of continuous casting molten steel is controlled at 28℃.

[0066] 4. Optimize secondary cooling water distribution: The secondary cooling water ratio is 0.83L / kg. The cooling of the billet in the secondary cooling chamber is two-stage cooling. The cooling water volume of each zone of the secondary cooling is calculated according to the formula: Q = A × V2 + B × V + C, where V is the casting speed. The water volume of each zone of the secondary cooling water is controlled as follows:

[0067] Second cold district A B C <![CDATA[Foot roller Q, m 3 / h]]> -0.16 4.10 -0.15 <![CDATA[Area Q, m 3 / h]]> 0.82 0.22 3.0 <![CDATA[Zone 2 Q, m 3 / h]]> 0.73 -0.75 1.92 <![CDATA[Three - zone Q, m 3 / h]]> 0.36 -0.12 0.29

[0068] 5. According to the S content in the molten steel, different pulling speed control requirements are formulated: the pulling speed of the casting machine is controlled as follows: when Mn / S>28, the pulling speed is 3.0m / min; when 28≥Mn / S≥26, the pulling speed is 2.8m / min; when 25≥Mn / S≥23, the pulling speed is 2.6m / min; when Mn / S<23, the pulling speed is 2.4m / min. In this example, the continuous casting process S is 0.028%, Mn is 0.76%, Mn / S=0.76 / 0.028=27.1, and the pulling speed is controlled at 2.80m / min.

[0069] The results are as follows: the ends of the ingot are square without any de-squareness, and the ingot rolling in the next process is normal.

[0070] Comparative Example 1 (Original Process)

[0071] A method for preparing a HPB300 continuous casting billet, wherein the chemical composition of the HPB300 continuous casting billet, in terms of mass percentage, comprises: C: 0.16-0.24%, P: ≤0.045%, S: ≤0.045%, Si: 0.15-0.40%, Mn: 0.55-0.85%, and the remainder is iron and unavoidable impurities or trace elements. The production process comprises: converter smelting → argon station treatment → billet continuous casting, and the specific steps are as follows:

[0072] Step 1: No requirements are made for the S content of molten iron entering the furnace and the C content at the converter end point. If the S content of molten iron entering the furnace is too high, the original S content in the molten steel will be high. There are no relevant requirements for the end point C content. If the end point C of the molten steel is low and no abnormal treatment is performed, the oxygen and sulfur content in the molten steel will be too high. The high oxygen content molten steel will make it difficult to remove the S in the subsequent treatment, and a large number of inclusions will be produced in the process.

[0073] Step 2: Composition control, control according to the target composition of the steel grade. Failure to adjust the Mn in the molten steel in time according to the S content in the molten steel leads to large fluctuations in the Mn / S ratio.

[0074] Step 3: Argon station treatment control, the total argon blowing time is required to be ≥ 6 minutes. If the argon blowing time is only specified without adjusting the treatment requirements for some special situations in the process (such as ladle bottoming) and key disposal points (such as adding alloy), it will lead to insufficient stirring of molten steel and difficulty in desulfurization.

[0075] Step 4: Continuous casting uses a square billet continuous casting machine to produce billet cross-section 160mm*160mm arc radius R10m full arc continuous casting machine.

[0076] 1. Crystallizer life and working condition requirements: Controlled according to the normal life of 0 to 1000 times. When the crystallizer is cycled less than 100 times, the friction resistance is large, increasing the crack tendency; when the crystallizer is cycled more than 700 times, the crystallizer wear is serious, resulting in uneven cooling of the ingot, which significantly increases the incidence of corner cracks.

[0077] 2. Tundish nozzle centering requirements: Use an immersion nozzle online centering device to achieve precise centering, and control the centering deviation between the immersion nozzle and the crystallizer flange to ≤10mm. If the centering deviation is too large, the heat flow of the ingot in the crystallizer will be uneven.

[0078] 3. Superheat of molten steel The superheat of molten steel for continuous casting is controlled at ≤40℃. According to tracking and comparison, when the superheat is higher than 35℃, the crack incidence rate increases. When the temperature is lower than 15℃, the castability of molten steel deviates and the low-temperature flow of molten steel is prone to occur.

[0079] 4. Secondary cooling water distribution: The water volume of secondary cooling water is 1.10-1.25L / kg. A large water volume can make the billet cool quickly, but it will increase the stress of the billet and cause the billet to crack.

[0080] 5. Continuous casting drawing speed control requirements: fixed drawing speed of 2.8m / min. Low manganese-sulfur ratio leads to increased generation of low-melting-point FeS at the grain boundary of the ingot, and enhanced crack sensitivity of the ingot. Drawing speed also has a significant relationship with ingot cracks. Usually, the faster the drawing speed, the easier it is to crack, but a low drawing speed will lead to reduced production efficiency. Therefore, the drawing speed should be increased as much as possible while ensuring the quality of the ingot. The corresponding drawing speed control system is formulated according to the manganese-sulfur ratio in the molten steel in order to maximize productivity while ensuring the quality of the ingot.

[0081] The result is: See Figure 1 and Figure 3 (The numbers in the figure are production batch numbers). The ends of some of the ingots prepared in this comparative example 1 were obviously rhombic, the overall de-squareness ratio reached 10%, and there were serious internal cracks. The next process of casting had an ingot head explosion and steel piling accident.

[0082] Comparative Example 2

[0083] The steps are similar to those in Example 1, except that no requirements are made for the S content of the molten iron entering the furnace and the C content at the converter end point. The S content of the molten iron entering the furnace is 0.042%, the C content at the converter end point is 0.07%, and no aluminum iron is added to strengthen deoxidation. In this comparative example, the S in the continuous casting process is 0.036%, Mn is 0.66%, Mn / S=0.66 / 0.036=18.3, and the drawing speed is controlled at 2.40m / min. Although the drawing speed is subsequently reduced, the high initial S of the molten steel will lead to high original S in the molten steel and low C at the end point of the molten steel. Failure to perform abnormal treatment will lead to high oxygen and sulfur content in the molten steel. The high oxygen content of the molten steel will make it difficult to remove S in subsequent treatment.

[0084] The results showed that the ingot had strong crack sensitivity, some ingot ends had obvious rhombus changes, and the overall de-squareness ratio reached 5%.

[0085] Comparative Example 3

[0086] The steps are similar to those in Example 1, wherein the S content of the molten iron entering the furnace is 0.030%, and the C content at the converter end is 0.11%. The only difference is that: the argon station is controlled, the total argon blowing time is 5 minutes, and the ladle is a Class C ladle. After the steel is tapped, the bottom argon is blown and stirred vigorously for 1 minute to take the station sample, and the alloy (including carbon powder) is added and the bottom argon is blown and stirred vigorously for 2 minutes. Insufficient stirring of the molten steel makes desulfurization difficult. In this comparative example, the S in the continuous casting process is 0.029%, Mn is 0.66%, Mn / S=0.66 / 0.029=22.7, and the pulling speed is controlled at 2.60m / min. Although the subsequent measures such as controlling the pulling speed basically avoid the desquaring and corner cracking of the ingot, the reduction in pulling speed due to improper argon station treatment affects the production efficiency.

[0087] The results are: the quality of the end of the ingot is basically normal, and the overall de-squareness ratio is 1.5%.

[0088] Comparative Example 4

[0089] The steps are similar to those in Example 1, except that the number of times of the copper tube of the crystallizer is 950. A high number of crystallizers causes serious wear of the crystallizer in the later stage of use, resulting in uneven cooling of the casting and significantly increasing the incidence of corner cracks.

[0090] The results showed that the ends of some ingots were obviously rhombic and the overall de-squareness ratio reached 3.5%.

[0091] Comparative Example 5

[0092] The steps are similar to those in Example 1, except that the superheat of the continuous casting molten steel is 39° C. The higher the temperature of the molten steel, the higher the crack incidence rate.

[0093] The results showed that part of the ingot was de-squared and the overall de-squared ratio was 1.5%.

[0094] Comparative Example 6

[0095] The steps are similar to those in Example 1, except that the specific water volume of the secondary cooling water is 1.25 L / kg. A large specific water volume can rapidly cool the ingot, but increases the stress of the ingot and causes cracking of the ingot.

[0096] The results showed that part of the ingot was de-squared and the overall de-squared ratio was 1.2%.

[0097] By analyzing the results of the embodiments of the present invention and the comparative examples, it can be seen that:

[0098] (1) The present invention adopts the production process of converter smelting → argon station treatment → billet continuous casting to prepare HPB300. The carbon content of converter steel and AR (argon station) treatment are controlled to improve the purity of molten steel, reduce the subsequent generation of inclusions, and reduce the probability of internal cracks.

[0099] (2) The higher the S content in the molten steel, the lower the plastic deformation, resulting in a smaller limit deformation rate of the steel, which in turn causes internal cracks. By optimizing the composition and increasing the Mn / S ratio, the probability of internal cracks can be effectively reduced.

[0100] (3) The drawing speed has a significant correlation with the internal cracks of the ingot. Different drawing speeds are formulated according to the Mn / S ratio, which can effectively ensure the internal quality of the ingot.

[0101] (4) Optimize the continuous casting cooling water volume and the secondary cooling water volume to further reduce the temperature gradient of the billet cooling process, avoid the formation of coarse columnar crystals in the billet, and avoid internal cracks in the billet.

[0102] (5) By controlling the service life and wear condition of the continuous casting crystallizer and controlling the centering of the water nozzle, the uniformity of cooling of the billet shell in the crystallizer can be effectively guaranteed, and the problem of billet de-squareness can be effectively improved.

[0103] It can be seen from the above content that the quality of the HPB300 ingot produced by adopting the solution provided by the embodiment of the present invention is significantly improved, and the proportion of ingot diagonal length difference greater than 10 mm is reduced from the original 10% to within 0.5%; the accidents of head explosion, rotten steel and steel punching during rolling caused by internal cracks of the ingot are reduced from 5 times / month to 1 time / month.

[0104] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing HPB300 continuous casting billet, characterized in that: The production process includes: converter smelting → argon station treatment → billet continuous casting, among which, the final carbon content is controlled in the converter smelting process, the argon blowing time and sulfur content and manganese content of the molten steel are controlled in the argon station treatment process, and the crystallizer working condition, pouring superheat, secondary cooling water distribution amount and casting speed are controlled in the billet continuous casting process to improve the quality of HPB300 continuous casting billets.

2. The preparation method according to claim 1, characterized in that: The chemical composition of the HPB300 continuous casting billet includes, by mass percentage, C: 0.16-0.24%, P: ≤0.045%, S: ≤0.045%, Si: 0.15-0.40%, Mn: 0.55-0.85%, and the remainder is iron and unavoidable impurities or trace elements.

3. The preparation method according to claim 1, characterized in that: Controlling the final carbon content in the converter smelting process includes: controlling the S content of the molten iron entering the furnace ≤ 0.035%, the final C content of the converter 0.08-0.14%, and during the converter tapping process, using a slide plate to block the slag to prevent slag from falling during the tapping process. For the final C content of the converter < 0.08%, 20-50 kg of aluminum iron is manually thrown in during the tapping process to enhance deoxidation.

4. The preparation method according to claim 1, characterized in that: The argon blowing time of molten steel is controlled in the argon station treatment process, including: the total argon blowing time of the argon station is required to be ≥6 minutes, and the argon blowing time is increased by 2 minutes for the first furnace of the continuous casting ladle, Class D ladle and Class E ladle, and the bottom ladle. In addition, the station sample is taken 3 to 5 minutes after the bottom argon blowing and strong stirring are completed after the steel is tapped. After the alloy and carbon powder or cooling material are added, the bottom argon blowing and strong stirring must be ensured for 3 to 5 minutes, among which: during the bottom argon blowing and strong stirring, the diameter of the bright circle on the liquid surface at the argon blowing port is controlled at 400-500mm; during the argon station molten steel treatment, it is strictly forbidden to turn off the bottom argon blowing of the ladle or the slag surface is blocked by too small a flow rate of bottom argon blowing.

5. The preparation method according to claim 1, characterized in that: The sulfur content and manganese content of the molten steel are controlled in the argon station processing procedure, including: in order to make the Mn / S ratio of the molten steel out of the argon station ≥25, the content of Mn element in the molten steel out of the argon station needs to be controlled to be 0.66%-0.82%; among which: when the sulfur content of the molten steel out of the argon station is ≤0.030%, the manganese out of the argon station is controlled at a target of 0.70%; when the sulfur content of the molten steel out of the argon station is >0.030%, the manganese out of the argon station is controlled at 0.75-0.80%.

6. The preparation method according to claim 1, characterized in that: The crystallizer working conditions controlled in the billet continuous casting process include: when producing HPB300, the copper tube life is controlled within 100-700 times, the copper tube wear is ≤350mm, the water gap is controlled within the range of 3.5-5.0mm when the copper tube is installed, the extreme difference of the water gap on the four surfaces is <0.5mm, and when centering the tundish water inlet, an immersion water inlet online centering device is used to achieve precise centering, so that the centering deviation between the immersion water inlet and the crystallizer flange is ≤5mm.

7. The preparation method according to claim 1, characterized in that: Controlling the pouring superheat in the billet continuous casting process includes: controlling the superheat of the continuous casting molten steel to 20-35°C.

8. The preparation method according to claim 1, characterized in that: Controlling the secondary cooling water distribution in the billet continuous casting process includes: controlling the secondary cooling water specific water volume to be 0.80-0.85L / kg. The billet is cooled in the secondary cooling chamber as secondary cooling. The cooling water volume Q in each zone of the secondary cooling is calculated according to the formula: Q=A×2V+B×V+C, where V is the casting speed. The water distribution volume in the secondary cooling zone is shown in the following table: 。 9. The preparation method according to claim 1, characterized in that: Controlling the pulling speed in the billet continuous casting process includes: formulating different pulling speeds according to the Mn / S ratio in the molten steel, and the casting machine pulling speed is controlled as follows: when the Mn / S ratio is greater than 28, the pulling speed is 3.0 m / min; when 28 ≥ Mn / S ratio ≥ 25, the pulling speed is 2.8 m / min; when 25 > Mn / S ratio ≥ 23, the pulling speed is 2.6 m / min; when the Mn / S ratio is less than 23, the pulling speed is 2.4 m / min.

10. The preparation method according to claim 1, characterized in that: The size of the HPB300 continuous casting billet is 160mm*160mm, and the proportion of the HPB300 billet produced with a diagonal length difference greater than 10mm is within 0.5%; the accidents of head explosion, rotten steel and steel punching during the rolling process caused by internal cracks of the continuous casting billet are reduced from 5 times / month to 1 time / month.

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