Production method for reducing slag runners in spring steel square billet casting process

Abstract

The invention discloses a production method for reducing slag runners in a spring steel square billet casting process, which specifically comprises the following steps: the superheat degree of continuous casting molten steel is 20-40 DEG C, slag is automatically added into a continuous casting square billet, and casting powder is conveyed into a crystallizer by taking compressed air as a carrier, so that a high-concentration compressed air atmosphere at an upper opening of the crystallizer is ensured, and the casting quality is improved. And a combustion-supporting effect is achieved on the casting powder, so that the melting effect of the casting powder is improved. And the insertion depth of the submersed nozzle is 70-80mm, so that the higher temperature of molten steel on the meniscus of the crystallizer is ensured, and the slag surface melting effect is improved. The slag line is not changed in the casting process; the crystallizer uses vibration parameters with high vibration frequency and high amplitude, so that the negative slippage time and the vibration advance amount of the crystallizer are improved, the inflow of liquid casting powder in an air gap between a steel billet and a copper pipe is facilitated, and the slag runner phenomenon in the casting process of the casting blank is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy steel, relates to the production of spring steel billets, and in particular 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 basic material in the manufacturing industry. The surface quality directly affects the spring forming performance and fatigue life, and is an important reason for the failure of the spring during use. When there are slag groove defects on the surface of the ingot, they are often accompanied by longitudinal cracks, and affect the rolling of the next process. How to reduce the slag groove on the surface of the ingot is one of the pursuits in the continuous casting process.

[0003] The cause of slag grooves on the surface of the ingot is mainly related to the melting and inflow state of the protective slag. Considering the specific impact, the protective slag should have a more reasonable consumption. The consumption of protective slag depends not only on the selection of protective slag type, but also on the vibration parameters and pouring speed. Under the influence of vibration, the melted protective slag is brought into the gap between the crystallizer 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 consumption of protective slag. 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 amplitude can easily cause the negative slip time to be too short, thus affecting the consumption of protective slag. Automatic slag addition generally uses nitrogen as the transmission gas for protective slag. Nitrogen flows into the upper mouth of the crystallizer together with the protective slag, resulting in an uneven nitrogen atmosphere at the upper mouth of the crystallizer, 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 poor, and the slag is uneven, which is prone to 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 view of the existing technical status. The method is to increase the negative slip time and the 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 of 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 water 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: A production method for reducing slag grooves during the casting process of spring steel square billets comprises the following steps: Step 1) The qualified ladle after LF or RH treatment is hoisted to the continuous casting ladle turret. After the ladle starts pouring, the temperature is measured manually. After the middle ladle is full of liquid, continuous temperature measurement is used to ensure accurate temperature measurement; Step 2) After the ladle is started to pour, 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 should be aligned, and the insertion depth of the immersion nozzle should be 70-80mm; Step 3) Install the automatic slag adding equipment, add protective slag into the slag adding bucket, and connect the protective slag conveying pipeline on the slag adding bucket to the compressed air as the power transmission source of the protective slag; Step 4) Set the vibration parameters of the crystallizer 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.

[0006] Furthermore, in the 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 continuous casting molten steel is 20-40°C.

[0007] 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.

[0008] Furthermore, in the step 2), when adjusting the centering of the immersion 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 differ by ≤2mm.

[0009] Furthermore, in step 3), the protective slag is high carbon steel protective 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%.

[0010] Furthermore, in the step 3), the protective slag is vertically dropped by its own weight within 2m from the slag adding pipe to the slag adding hopper, and a hole is opened at the 2m 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.

[0011] Furthermore, the compressed air pressure in step 3) is 7 bar.

[0012] Furthermore, in step 4), the amount of cold water is set to 140 m 3 / h, the secondary cooling water volume is set to 0.33L / kg.

[0013] Furthermore, in the step 4), the continuous casting speed is kept constant at 1.2 m / min, with a fluctuation range of ±0.02 m / min.

[0014] The beneficial effects of the present invention are: First, the present invention provides a production method for reducing slag grooves during the casting process of a spring steel square billet. The vibration parameters designed in the method can increase the negative slip time and the vibration advance amount, ensuring that after the protective slag is normally melted, there is a sufficient inflow channel so that the protective slag can be consumed, thereby increasing the consumption of the protective slag and improving the lubrication effect.

[0015] Second, a production method for reducing slag grooves during the casting process of spring steel square billets of the present invention realizes the change of the gas atmosphere at the upper mouth of the crystallizer by changing the transmission gas for automatic slag addition from nitrogen to compressed air, thereby promoting the full combustion of the protective slag, ensuring a sufficient liquid slag layer thickness and improving the lubrication effect.

[0016] Thirdly, a production method for reducing slag grooves during the casting process of a spring steel square billet of the present invention 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.

[0017] Fourth, a production method for reducing slag grooves during the casting process of a spring steel square billet of the present invention improves the melting effect of the protective slag in the crystallizer through the optimization of the continuous casting process technology, can form a sufficient liquid slag layer, and can expand the liquid slag flow channel to completely consume the generated liquid slag, thereby achieving a dynamic balance between the generation and consumption of liquid slag in production, with an average consumption of 0.40Kg / 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

[0018] 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 used to limit the scope of the present invention.

[0019] The production method for reducing slag grooves during spring steel billet casting comprises the following steps: 1) After the qualified ladle of LF or RH treatment (temperature rises to liquidus temperature + 60~80℃, superheat of continuous casting molten steel is 20~40℃), it is hoisted to the continuous casting ladle turntable. Manual temperature measurement is used after the ladle starts pouring. After the middle ladle is full of liquid level, continuous temperature measurement is used to ensure accurate temperature measurement; when the middle ladle is full of liquid level, the tonnage of molten steel in the middle ladle is 26-30 tons, and the deviation between manual temperature measurement and continuous temperature measurement is within ±2℃.

[0020] 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 immersion nozzle is 70-80mm; when adjusting the alignment of the immersion nozzle of the tundish, the nozzle is inserted into the crystallizer. The front and back distance and the left and right distance of the copper tube wall should differ by ≤2mm.

[0021] 3) Install the automatic slag adding equipment, add protective slag into the slag adding hopper. The protective slag should be high carbon steel protective slag, the heating temperature should be controlled at 70-90℃, the melting point should be 950±20℃, the alkalinity should be 8.5-9.0, and the water content should be ≤0.5%. Connect the protective slag conveying pipeline on the slag adding hopper to the compressed air with a pressure of 7bar as the power transmission source for the protective slag. The protective slag should fall vertically within 2m of the slag adding pipeline and the compressed air should be opened at the 2m position. The protective slag should be evenly blown into the crystallizer from top to bottom according to the flow control of 40±2NL / min.

[0022] 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 m 3 / h, the secondary cooling water ratio is set to 0.33L / kg, and continuous casting is carried out with 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.

[0023] 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: Embodiment 1: Adopting the process of the present invention in the production of 55Cr3 steel 1) After the qualified ladle has been treated with LF, the superheat is measured to be 75℃, and it is hoisted to the continuous casting ladle turntable and rotated to the casting position.

[0024] 2) Install the automatic slag feeder, confirm that high carbon steel protective slag is used, and confirm that the slag bucket is connected to compressed air; set the vibration parameters to ensure that the vibration frequency is 182cpm and the amplitude is ±4.5mm at a pulling speed of 1.2m / min; set the first cold water volume to 140m 3 / h; the secondary cooling water volume is set to 0.33L / kg; after the tundish is poured, measure and adjust the insertion depth of the immersion nozzle to 75mm.

[0025] 3) During production, the thickness of the liquid slag layer was measured to be 11mm, and the slag consumption was 0.42Kg / t. After casting, about 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 with a length of about 50mm were taken again for hot pickling to check if there were any slag grooves or cracks on the surface.

[0026] Embodiment 2: Adopting the process of the present invention in the production of 60Si2Mn steel 1) After the qualified ladle has been treated with LF, the superheat is measured to be 75℃, and it is hoisted to the continuous casting ladle turntable and rotated to the casting position.

[0027] 2) Install the automatic slag feeder, confirm that high-carbon steel protective slag is used, and confirm that the slag bucket is connected to compressed air; set the vibration parameters to ensure that the vibration frequency is 182cpm and the amplitude is ±4.5mm at a pulling speed of 1.2m / min; set the primary cooling water volume to 140m3 / h; set the secondary cooling water volume to 0.33L / kg; after the tundish is poured, measure and adjust the immersion nozzle insertion depth to 70mm.

[0028] 3) During production, the thickness of the liquid slag layer was measured to be 10mm, and the slag consumption was 0.40Kg / t. After casting, about 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 with a length of about 50mm were taken again for hot pickling to check if there were any slag grooves or cracks on the surface.

[0029] Embodiment 3: Adopting the process of the present invention in the production of 9SiCr steel 1) After the qualified ladle has been treated with LF, the superheat is measured to be 75℃, and it is hoisted to the continuous casting ladle turntable and rotated to the casting position.

[0030] 2) Install the automatic slag feeder, confirm that high-carbon steel protective slag is used, and confirm that the slag bucket is connected to compressed air; set the vibration parameters to ensure that the vibration frequency is 182cpm and the amplitude is ±4.5mm at a pulling speed of 1.2m / min; set the primary cooling water volume to 140m3 / h; set the secondary cooling water volume to 0.33L / kg; after the tundish is poured, measure and adjust the immersion nozzle insertion depth to 80mm.

[0031] 3) During production, the thickness of the liquid slag layer was measured to be 9mm, and the slag consumption was 0.38Kg / t. After casting, about 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 with a length of about 50mm were taken again for hot pickling to check if there were any slag grooves or cracks on the surface.

[0032] 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 upper mouth of the crystallizer, the full combustion of the protective slag is promoted, the thickness of the liquid slag layer is increased, and the lubrication effect is improved; 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.

[0033] 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 generally 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 the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0034] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope 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) The qualified ladle after LF or RH treatment is hoisted to the continuous casting ladle turret. After the ladle starts pouring, the temperature is measured manually. After the middle ladle is full of liquid, continuous temperature measurement is used to ensure accurate temperature measurement; Step 2) After the ladle is started to pour, 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 should be aligned, and the insertion depth of the immersion nozzle should be 70-80mm; Step 3) Install the automatic slag adding equipment, add protective slag into the slag adding bucket, and connect the protective slag conveying pipeline on the slag adding bucket to the compressed air as the power transmission source of the protective slag; Step 4) Set the vibration parameters of the crystallizer 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 casting of spring steel billets according to claim 1, characterized in that: In the 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 casting 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 casting of spring steel billets according to claim 1, characterized in that: In the step 2), when adjusting the centering of the immersion 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 differ by ≤2 mm.

5. The method for reducing slag grooves during casting of spring steel billets according to claim 1, characterized in that: In the step 3), the protective slag is high carbon steel protective 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 is ≤0.5%.

6. The method for reducing slag grooves during casting of spring steel billets according to claim 1, characterized in that: In the step 3), the slag adding pipeline is outside the range of 2m from the slag adding hopper, and the protective slag falls vertically by its own weight. The slag adding pipeline is opened at a position 2m away from the slag adding hopper 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.

7. The method for reducing slag grooves during casting of spring steel billets according to claim 1, characterized in that: The compressed air pressure in step 3) is 7 bar.

8. The method for reducing slag grooves during casting of spring steel billets according to claim 1, characterized in that: In step 4), the amount of cold water is set to 140 m 3 / h, the secondary cooling water volume is set to 0.33L / kg.

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