A production method for reducing slag grooves during spring steel billet casting

Abstract

The present invention discloses a production method for reducing slag grooves during the casting process of spring steel billets, specifically: the superheat degree of the continuous casting molten steel is between 20 and 40°C, slag is automatically added to the continuous casting billet, and the protective slag is transported to the crystallizer through compressed air as a carrier, thereby ensuring a relatively high concentration of compressed air atmosphere at the upper mouth of the crystallizer, which has a combustion-supporting effect on the protective slag, thereby improving the melting effect of the protective slag. The insertion depth of the submerged nozzle is 70‑80mm, which ensures a relatively high temperature of the molten steel on the meniscus of the crystallizer, thereby improving the melting effect of the slag surface. The slag line remains unchanged during the casting process; the crystallizer uses high-frequency and high-amplitude vibration parameters to increase the negative slip time and the crystallizer vibration advance, which is beneficial to the inflow of liquid protective slag into the air gap between the billet and the copper tube, thereby avoiding the slag groove phenomenon during the billet casting process.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy steel, relates to the production of spring steel billets, and particularly to a production method for reducing slag grooves during the casting process of spring steel billets. Background Art

[0002] Spring steel is a key component and foundational material in the manufacturing industry. Surface quality directly impacts spring forming performance and fatigue life, and is a major cause of spring failure during use. Slag grooves on the ingot surface are often accompanied by longitudinal cracks and affect the subsequent rolling process. Reducing slag grooves on the ingot surface is a key goal during continuous casting.

[0003] The formation of slag grooves on the ingot surface is primarily related to the melting and inflow of mold slag. Considering these specific effects, mold slag consumption should be reasonable. This consumption depends not only on the type of mold slag selected, but also on vibration parameters and pouring speed. Vibration can cause molten mold slag to be drawn into the gap between the mold and the ingot. The consumption of protective slag increases with the increase of negative slip time, so the vibration parameters, pulling speed and protective slag must be matched to have appropriate protective slag consumption. However, in order to control the depth of vibration marks of the ingot, high-carbon steels such as spring steel in the industry usually adopt a high-frequency and small-amplitude design concept. Too small an amplitude can easily cause the negative slip time to be too short, thereby affecting the consumption of protective slag; automatic slag addition generally uses nitrogen as the transmission gas for protective slag, and nitrogen flows into the upper mouth of the crystallizer together with the protective slag, resulting in the upper mouth of the crystallizer being filled with an uneven nitrogen atmosphere, thereby slowing down the melting speed of the protective slag in the crystallizer, resulting in surface slag grooves; in addition, if the submerged nozzle is inserted too deep, the liquid slag surface is inactive and dead, the slag is poorly melted, and the slag is unevenly discharged, which can easily cause defects such as slag grooves on the surface of the ingot. Summary of the Invention

[0004] The purpose of the present invention is to provide a production method for reducing slag grooves during the casting process of spring steel square billets in response to the existing technical status. The method is to increase the negative slip time and vibration advance amount by designing a high-frequency and high-amplitude vibration parameter, thereby increasing the consumption of protective slag and improving the lubrication effect; by changing the transmission gas for automatic slag addition from nitrogen to compressed air to achieve a change in the gas atmosphere at the upper mouth of the crystallizer, thereby promoting the full combustion of the protective slag, increasing the thickness of the liquid slag layer and improving the lubrication effect; by reducing the insertion depth of the submerged nozzle, the activity of the slag surface is increased, thereby further improving the melting and lubrication effect of the protective slag.

[0005] The technical solution adopted by the present invention is:

[0006] A production method for reducing slag grooves during the casting process of spring steel billets comprises the following steps:

[0007] Step 1) After the LF or RH treatment, the qualified ladle is hoisted to the continuous casting ladle turret. After the ladle starts pouring, manual temperature measurement is performed. After the tundish is full, continuous temperature measurement is performed to ensure accurate temperature measurement.

[0008] Step 2) After the ladle is opened for pouring, perform protective casting throughout the entire process to ensure that the molten steel does not come into contact with air. The tundish and nozzle must be aligned, and the immersion nozzle should be inserted to a depth of 70-80mm.

[0009] Step 3) Install the automatic slag feeding equipment, add mold slag into the slag feeding hopper, and connect the mold slag delivery pipe on the slag feeding hopper to compressed air as the power transmission source for the mold slag;

[0010] Step 4) Set the crystallizer vibration parameters to a frequency of 182 cpm and an amplitude of ±4.5 mm; set the flow rates of the primary and secondary cooling water, and perform continuous casting at a constant casting speed until the tundish casting is completed.

[0011] Furthermore, in step 1), the temperature of the ladle after the qualified LF or RH treatment is raised to the liquidus temperature + 60-80°C, and the superheat degree of the continuous casting molten steel is 20-40°C.

[0012] Furthermore, in the step 1), when the tundish is full, the molten steel tonnage in the tundish is 26-30 tons, and the deviation between the manual temperature measurement and the continuous temperature measurement is within ±2°C.

[0013] Furthermore, in step 2), when adjusting the centering of the tundish submerged nozzle, the front-to-back distance and the left-to-right distance of the nozzle inserted into the crystallizer from the copper tube wall are ≤2 mm.

[0014] Furthermore, in step 3), the mold slag is made of high carbon steel mold slag, the heating temperature is controlled at 70-90° C., the melting point is 950±20° C., the basicity is 8.5-9.0, and the water content by mass is ≤0.5%.

[0015] Furthermore, in the step 3), the protective slag is allowed to fall vertically by its own weight within 2 m from the slag feeding pipe to the slag feeding hopper, and a hole is opened at the 2 m position to connect compressed air gas, and the protective slag is evenly blown into the crystallizer from top to bottom according to the flow control of 40±2NL / min.

[0016] Furthermore, the compressed air pressure in step 3) is 7 bar.

[0017] Furthermore, in step 4), the amount of cold water is set to 140 m 3 / h, and the secondary cooling water volume is set to 0.33L / kg.

[0018] Furthermore, in step 4), the continuous casting speed is kept constant at 1.2 m / min, with a fluctuation range of ±0.02 m / min.

[0019] The beneficial effects of the present invention are:

[0020] First, the present invention provides a production method for reducing slag grooves during the casting process of spring steel square billets. The vibration parameters designed in this method can increase the negative slip time and the vibration advance amount, ensuring that after the protective slag is normally melted, there is enough flow channel to allow the protective slag to be consumed, thereby increasing the consumption of protective slag and improving the lubrication effect.

[0021] Second, the present invention provides a production method for reducing slag grooves during the casting process of spring steel square billets. By changing the transmission gas for automatic slag addition from nitrogen to compressed air, the gas atmosphere at the upper mouth of the crystallizer is changed, thereby promoting the full combustion of the protective slag, ensuring a sufficient liquid slag layer thickness, and improving the lubrication effect.

[0022] Third, the present invention provides a production method for reducing slag grooves during the casting process of spring steel square billets, which increases the activity of the slag surface by reducing the insertion depth of the submerged nozzle, thereby further improving the melting and lubrication effects of the protective slag.

[0023] Fourth, the present invention provides a production method for reducing slag grooves during the casting process of spring steel square billets. By optimizing the continuous casting process technology, the melting effect of the protective slag in the crystallizer is improved, a sufficient liquid slag layer can be formed, and the liquid slag flow channel can be expanded to completely consume the generated liquid slag, thereby achieving a dynamic balance between the generation and consumption of liquid slag in production. The average consumption reaches 0.40 kg / t, thereby ensuring the surface quality of the casting billet and eliminating the slag groove defects on the surface of the spring steel. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0025] A production method for reducing slag grooves during spring steel billet casting comprises the following steps:

[0026] 1) After the LF or RH treatment, the qualified ladle (temperature increased to liquidus temperature + 60~80℃, continuous casting molten steel superheat 20~40℃) is hoisted to the continuous casting ladle turntable. Manual temperature measurement is used after the ladle starts pouring. After the tundish is full, continuous temperature measurement is used to ensure accurate temperature measurement. When the tundish is full, the tonnage of molten steel in the tundish is 26-30 tons, and the deviation between manual temperature measurement and continuous temperature measurement is within ±2℃.

[0027] 2) After the ladle starts pouring, the whole process of protective casting should be carried out to ensure that the molten steel does not come into contact with the air. The tundish and the nozzle need to be aligned, and the insertion depth of the submerged nozzle is 70-80mm; when adjusting the alignment of the submerged nozzle of the tundish, the front-to-back distance and the left-to-right distance of the nozzle inserted into the crystallizer from the copper tube wall should differ by ≤2mm.

[0028] 3) Install the automatic slag feeding equipment and add mold slag to the slag feeding hopper. Use high-carbon steel mold slag, control the heating temperature at 70-90°C, the melting point at 950±20°C, the alkalinity at 8.5-9.0, and the moisture content by mass at ≤0.5%. Connect the mold slag delivery pipe on the slag feeding hopper to compressed air at a pressure of 7 bar as the power transmission source for the mold slag. Allow the mold slag to fall vertically under its own weight within 2m of the slag feeding pipe. At the 2m position, open a hole to connect compressed air. Control the flow rate at 40±2NL / min and blow the mold slag evenly from top to bottom into the crystallizer.

[0029] 4) Set the crystallizer vibration parameters to a frequency of 182 cpm and an amplitude of ±4.5 mm; set the cooling water volume to 140 m3 3 / h, the secondary cooling water ratio is set to 0.33L / kg, and continuous casting is carried out at a constant casting speed. The continuous casting speed is constant at 1.2m / min, with a fluctuation range of ±0.02m / min, until the tundish casting is completed.

[0030] For example, the applicant's steelmaking workshop carries out industrial production of 55Cr3, 60Si2Mn, 9SiCr and other steel grades. The specific implementation plan is as follows:

[0031] Example 1: Using the process of the present invention in the production of 55Cr3 steel

[0032] 1) After the LF treatment, the ladle is measured to have a superheat of 75°C. It is then hoisted onto the continuous casting ladle turntable and rotated to the casting position.

[0033] 2) Install the automatic slag feeder, confirm that high carbon steel protective slag is used, and confirm that the slag hopper is connected to compressed air; set the vibration parameters to ensure that the vibration frequency is 182 cpm and the amplitude is ±4.5 mm at a pulling speed of 1.2 m / min; set the first cooling water volume to 140 m 3 / h; the secondary cooling water volume is set to 0.33L / kg; after the tundish starts pouring, measure and adjust the immersion nozzle insertion depth to 75mm.

[0034] 3) During production, the thickness of the liquid slag layer was measured to be 11 mm, and the slag consumption was 0.42 kg / t. After casting, approximately 40 ingots from one furnace were randomly selected for shot blasting and magnetic particle inspection to check if there were any slag grooves or cracks on the surface. Samples of approximately 50 mm in length were then taken for hot pickling to check if there were any slag grooves or cracks on the surface.

[0035] Example 2: Using the process of the present invention in the production of 60Si2Mn steel

[0036] 1) After the LF treatment, the ladle is measured to have a superheat of 75°C. It is then hoisted onto the continuous casting ladle turntable and rotated to the casting position.

[0037] 2) Install the automatic slag feeder, confirm the use of high-carbon steel protective slag, and confirm that the slag hopper is connected to compressed air; set the vibration parameters to ensure that the vibration frequency is 182 cpm and the amplitude is ±4.5 mm at a pulling speed of 1.2 m / min; set the primary cooling water volume to 140 m3 / h; set the secondary cooling water volume to 0.33 L / kg; after the tundish starts pouring, measure and adjust the immersion nozzle insertion depth to 70 mm.

[0038] 3) During production, the thickness of the liquid slag layer was measured to be 10 mm, and the slag consumption was 0.40 kg / t. After casting, about 40 ingots from one furnace were randomly selected for shot blasting and magnetic particle inspection to check whether there were any slag grooves or cracks on the surface. Samples of about 50 mm in length were then taken for hot pickling to check whether there were any slag grooves or cracks on the surface.

[0039] Example 3: Using the process of the present invention in the production of 9SiCr steel

[0040] 1) After the LF treatment, the ladle is measured to have a superheat of 75°C. It is then hoisted onto the continuous casting ladle turntable and rotated to the casting position.

[0041] 2) Install the automatic slag feeder, confirm the use of high-carbon steel protective slag, and confirm that the slag hopper is connected to compressed air; set the vibration parameters to ensure that the vibration frequency is 182 cpm and the amplitude is ±4.5 mm at a pulling speed of 1.2 m / min; set the primary cooling water volume to 140 m3 / h; set the secondary cooling water specific water volume to 0.33 L / kg; after the tundish starts pouring, measure and adjust the immersion nozzle insertion depth to 80 mm.

[0042] 3) During production, the thickness of the liquid slag layer was measured to be 9 mm, and the slag consumption was 0.38 kg / t. After casting, about 40 ingots from one furnace were randomly selected for shot blasting and magnetic particle inspection to check whether there were any slag grooves or cracks on the surface. Samples of about 50 mm in length were then taken for hot pickling to check whether there were any slag grooves or cracks on the surface.

[0043] The patent of the present invention provides a technical method for improving the lubrication effect of high-carbon steel such as spring steel during the casting process, thereby reducing the surface slag grooves. By designing a high-frequency and high-amplitude vibration parameter, the negative slip time and the vibration advance amount are increased, thereby increasing the consumption of protective slag and improving the lubrication effect; by changing the transmission gas of the automatic slag addition from nitrogen to compressed air to achieve a change in the gas atmosphere at the top of the crystallizer, thereby promoting the full combustion of the protective slag, increasing the thickness of the liquid slag layer and improving the lubrication effect; by reducing the insertion depth of the submerged nozzle, the activity of the slag surface is increased, thereby further improving the melting and lubrication effect of the protective slag. Through the implementation of the measures in the present invention, the slag groove phenomenon on the surface of the spring steel billet is eliminated, thereby improving the surface quality of the ingot and reducing a series of longitudinal cracks and steel leakage problems caused by the slag grooves.

[0044] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as such, will not be interpreted in an idealized or overly formal sense.

[0045] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A production method for reducing slag grooves during the casting process of spring steel billets, characterized in that: The following steps are involved: Step 1) After the LF or RH treatment, the qualified ladle is hoisted to the continuous casting ladle turret. After the ladle starts pouring, the temperature is measured manually. After the tundish is full, continuous temperature measurement is used to ensure accurate temperature measurement. Step 2) After the ladle starts pouring, perform protective casting throughout the entire process to ensure that the molten steel does not come into contact with air. The tundish and nozzle must be aligned, and the immersion nozzle insertion depth must be 70-75mm, excluding 75mm. When adjusting the centering of the tundish submerged nozzle, the difference between the front-to-back distance and the left-to-right distance between the nozzle and the copper tube wall when inserted into the crystallizer should be ≤2mm; Step 3) Install the automatic slag feeding equipment, add mold slag into the slag feeding hopper, and connect the mold slag delivery pipe on the slag feeding hopper to compressed air as the power transmission source for the mold slag; The slag feeding pipe is 2m away from the slag feeding hopper, and the protective slag falls vertically by its own weight. The slag feeding pipe is opened 2m away from the slag feeding hopper to connect to the compressed air gas. According to the flow control of 40±2NL / min, the protective slag is evenly blown into the crystallizer from top to bottom; The compressed air pressure is 7 bar; Step 4) Set the crystallizer vibration parameters to a frequency of 182 cpm and an amplitude of ±4.5 mm; set the flow rates of the primary and secondary cooling water, and perform continuous casting at a constant casting speed until the tundish casting is completed.

2. The method for reducing slag grooves during the casting process of spring steel billets according to claim 1, characterized in that: In step 1), the temperature of the ladle after the LF or RH treatment is raised to the liquidus temperature + 60-80°C, and the superheat of the molten steel is 20-40°C.

3. The method for reducing slag grooves during the casting process of spring steel billets according to claim 1, characterized in that: In the step 1), when the tundish is full, the molten steel tonnage in the tundish is 26-30 tons, and the deviation between the manual temperature measurement and the continuous temperature measurement is within ±2°C.

4. The method for reducing slag grooves during the casting process of spring steel billets according to claim 1, characterized in that: In step 3), the mold slag is made of high carbon steel mold slag, the heating temperature is controlled at 70-90° C., the melting point is 950±20° C., the basicity is 8.5-9.0, and the water content by mass is ≤0.5%.

5. The method for reducing slag grooves during the casting process of spring steel billets according to claim 1, characterized in that: In step 4), the first cooling water volume is set to 140 m3 / h, and the second cooling water volume is set to 0.33 L / kg.

6. The method for reducing slag grooves during the casting process of spring steel billets according to claim 1, characterized in that: In step 4), the continuous casting speed is kept constant at 1.2 m / min, with a fluctuation range of ±0.02 m / min.