Method for controlling the proportion of columnar grains in a continuously cast strand

Abstract

The application discloses a method for controlling the proportion of columnar crystals in a continuous casting billet, which comprises the following steps: determining an initial value of electromagnetic stirring intensity at a solidification end point in a continuous casting process; monitoring the proportion of columnar crystals in a billet formed at the solidification end point in the continuous casting process in real time, and adjusting the electromagnetic stirring intensity at the solidification end point according to the monitored proportion of columnar crystals, so as to adjust the proportion of columnar crystals in the billet formed at the solidification end point to a target value.

Description

Technical Field

[0001] This application belongs to the field of steel material preparation technology, specifically relating to a method for controlling the proportion of columnar crystals in continuously cast billets. Background Technology

[0002] During the steel production process, the ratio of columnar crystals to equiaxed crystals in the continuously cast billet has a significant impact on subsequent hot rolling and cold rolling production, and can also affect the microstructure of the final steel product, thereby affecting product performance.

[0003] However, the current control of the proportion of columnar crystals and equiaxed crystals in continuous casting billets in the steel industry is based on experience. The adjustment results are difficult to control, and the proportion of equiaxed crystals in continuous casting billets often differs greatly from the expected proportion. This leads to undesirable microstructure and performance deviations in subsequent production and final products, reducing product qualification rate and increasing costs. Summary of the Invention

[0004] The purpose of this application is to provide a method for controlling the proportion of columnar crystals in continuously cast billets.

[0005] To achieve one of the above-mentioned objectives, one embodiment of this application provides a method for controlling the proportion of columnar crystals in a continuously cast billet, the method comprising:

[0006] Determine the initial value of electromagnetic stirring intensity at the solidification end of the continuous casting process; The proportion of columnar crystals in the billet formed at the solidification endpoint during the continuous casting process is monitored in real time, and the electromagnetic stirring intensity at the solidification endpoint is adjusted according to the monitored columnar crystal proportion to adjust the proportion of columnar crystals in the billet formed at the solidification endpoint to the target value.

[0007] As a further improvement to one embodiment of this application, determining the initial value of the electromagnetic stirring intensity at the solidification end of the continuous casting process includes: Determine the initial value I0 of the electromagnetic stirring current at the end of solidification in the continuous casting process; The adjustment of the electromagnetic stirring intensity at the solidification end based on the monitored columnar crystal ratio includes: The electromagnetic stirring current I at the end of solidification is adjusted according to the monitored columnar crystal ratio.

[0008] As a further improvement to one embodiment of this application, the step of adjusting the electromagnetic stirring current I at the end of solidification according to the monitored columnar crystal ratio includes: Based on the monitored columnar crystal ratio and the target value of the columnar crystal ratio, the adjustment amount ΔI of the electromagnetic stirring current at the end of solidification is calculated by the PID algorithm. The electromagnetic stirring current I at the end of solidification is adjusted according to the calculated adjustment amount ΔI.

[0009] As a further improvement to one embodiment of this application, determining the initial value I0 of the electromagnetic stirring current at the end of the solidification process in the continuous casting process includes: The preset value I of the electromagnetic stirring current at the solidification end is calculated based on the alloy element content of the molten steel. y ; Determine the preset value I of the electromagnetic stirring current at the end of solidification. y I0 is the initial value of the electromagnetic stirring current at the end of solidification.

[0010] As a further improvement to one embodiment of this application, the preset value I of the electromagnetic stirring current at the end of solidification is calculated based on the alloy element content in the molten steel. y include: The preset value of the electromagnetic stirring current I at the end of solidification is calculated based on the Si, Al, and Mn element content in the molten steel. y .

[0011] As a further improvement to one embodiment of this application, I y =300+30×Si+20×Al+10×Mn, where the element symbols in the formula represent the mass percentage of the corresponding element.

[0012] As a further improvement to one embodiment of this application, the determination of the initial value I0 of the electromagnetic stirring current at the end of the solidification process in the continuous casting process further includes: The initial value adjustment amount ΔI0 of the electromagnetic stirring current at the end of solidification is determined based on the fluctuation amount Δv of the continuous casting speed, the fluctuation amount ΔT of the superheat of the molten steel, and the fluctuation amount ΔC of the alloy element content in the molten steel. Determine the preset value I of the electromagnetic stirring current at the end of solidification. y The sum of the initial value adjustment ΔI0 of the electromagnetic stirring current at the end of solidification and the initial value adjustment ΔI0 of the electromagnetic stirring current at the end of solidification is the initial value I0 of the electromagnetic stirring current at the end of solidification.

[0013] As a further improvement to one embodiment of this application, ΔI0=k v ·Δv+k T ·ΔT+k C ·ΔC; Where, Δv=v m -v0, v m v0 is the measured value of the continuous casting speed, and v0 is the preset value of the continuous casting speed. ΔT=T m -T0, T m T0 is the measured value of the superheat of molten steel, and T0 is the preset value of the superheat of molten steel. ΔC=C m -C0,C m C0 is the measured sum of the contents of Si, Al, and Mn elements in molten steel, and C0 is the preset sum of the contents of Si, Al, and Mn elements in molten steel. k v k is the coefficient of variation of continuous casting speed. T k is the coefficient of change in superheat of molten steel. C This is the coefficient of variation of the alloying element content in molten steel.

[0014] As a further improvement to one embodiment of this application, the proportion of columnar crystals in the billet formed at the solidification endpoint during the real-time monitoring of the continuous casting process includes: The proportion of columnar crystals in the billet formed at the solidification endpoint can be detected by X-ray diffraction or by ultrasonic diffraction.

[0015] As a further improvement to one embodiment of this application, the control method includes: When the target value for the proportion of columnar crystals in the billet formed at the solidification endpoint is 50%~80%, electromagnetic stirring is controlled at the solidification endpoint in the continuous casting process, while electromagnetic stirring is not performed in the crystallizer and the secondary cooling zone.

[0016] Compared with the prior art, the beneficial effects of this application include: The method for controlling the proportion of columnar crystals in the continuously cast billet involves real-time monitoring of the proportion R of columnar crystals in the billet formed at the solidification endpoint during the continuous casting process. m And based on the monitored columnar crystal ratio R m Adjusting the intensity of electromagnetic stirring at the end of solidification can effectively regulate the ratio of columnar crystals and equiaxed crystals in the billet, thereby achieving dynamic adjustment of the proportion of columnar crystals in the billet formed at the end of solidification, so that the proportion of columnar crystals in the billet formed at the end of solidification reaches the target value. Detailed Implementation

[0017] The present application will be described in detail below with reference to specific embodiments. However, these embodiments do not limit the present application, and structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are all included within the protection scope of the present application.

[0018] Example 1 One embodiment of this application provides a method for controlling the proportion of columnar crystals in a continuously cast billet.

[0019] The control method includes: Determine the initial value of electromagnetic stirring intensity at the solidification end of the continuous casting process; Real-time monitoring of the proportion R of columnar crystals in the billet formed at the solidification endpoint during the continuous casting process. m And based on the monitored columnar crystal ratio R m Adjust the intensity of electromagnetic stirring at the end of solidification to reduce the proportion R of columnar crystals in the billet formed at the solidification endpoint. mAdjust to the target value.

[0020] When the electromagnetic stirring intensity at the end of solidification is high, it can interrupt the growth of columnar crystals, break up coarse dendrites and disperse them, making them new equiaxed crystal nuclei, thereby increasing the proportion of equiaxed crystals and decreasing the proportion of columnar crystals; conversely, when the electromagnetic stirring intensity at the end of solidification is low, the proportion of equiaxed crystals decreases and the proportion of columnar crystals increases.

[0021] Thus, by real-time monitoring of the proportion R of columnar crystals in the billet formed at the solidification endpoint during the continuous casting process... m And based on the monitored columnar crystal ratio R m Adjusting the intensity of electromagnetic stirring at the end of solidification can effectively regulate the ratio of columnar crystals and equiaxed crystals in the billet, thereby achieving dynamic adjustment of the proportion of columnar crystals in the billet formed at the end of solidification, so that the proportion of columnar crystals in the billet formed at the end of solidification reaches the target value.

[0022] The electromagnetic stirring intensity parameter includes at least one of the electromagnetic stirring current and the electromagnetic stirring frequency. In other words, the electromagnetic stirring intensity can be adjusted by regulating at least one of the electromagnetic stirring current and the electromagnetic stirring frequency.

[0023] One embodiment of this application also provides a continuous casting apparatus, which includes a continuous casting machine and a control system.

[0024] Continuous casting is carried out using continuous casting equipment.

[0025] A continuous casting machine includes a rotary table, tundish, crystallizer, sector section, and straightening machine.

[0026] The rotary table can rotate 180 degrees, moving the ladle to the pouring position to enable continuous pouring of multiple heats of molten steel. The tundish, located below the ladle, serves as a crucial transition vessel, buffering the molten steel, stabilizing the flow rate, and providing time for impurities (such as slag) to rise and purify the steel. The crystallizer initially solidifies the molten steel to form a billet shell. The fan-shaped section supports and further cools the billet exiting the crystallizer. The straightening machine pulls out and straightens the billet.

[0027] The fan-shaped section forms the secondary cooling zone in the continuous casting process, meaning that the billet undergoes secondary cooling in the fan-shaped section. The solidification end is part of the secondary cooling zone.

[0028] The sector segment includes the foot roller segment (i.e., sector segment 0) arranged sequentially from the crystallizer to the straightening machine, as well as sector segments 1 to 12.

[0029] The control system is connected to the continuous casting machine and is used to obtain the proportion R of columnar crystals in the billet formed at the monitored solidification endpoint. m And based on the monitored columnar crystal ratio Rm Adjust the intensity of electromagnetic stirring at the end of solidification to reduce the proportion R of columnar crystals in the billet formed at the solidification endpoint. m Adjust to the target value.

[0030] In one embodiment, the electromagnetic stirring intensity parameter includes the electromagnetic stirring current.

[0031] The determination of the initial value of the electromagnetic stirring intensity at the solidification end of the continuous casting process includes: Determine the initial value I0 of the electromagnetic stirring current at the solidification end of the continuous casting process.

[0032] The adjustment of the electromagnetic stirring intensity at the solidification end based on the monitored columnar crystal ratio includes: The electromagnetic stirring current I at the end of solidification is adjusted according to the monitored columnar crystal ratio.

[0033] Thus, by adjusting the electromagnetic stirring current I at the end of solidification, the electromagnetic stirring intensity at the end of solidification can be adjusted, thereby achieving dynamic adjustment of the proportion of columnar crystals in the billet formed at the end of solidification, and the adjustment efficiency is relatively high.

[0034] In one embodiment, adjusting the electromagnetic stirring current I at the solidification end according to the monitored columnar crystal ratio includes: Based on the monitored columnar crystal ratio R m The target value of columnar crystal ratio R is used to calculate the adjustment amount ΔI of the electromagnetic stirring current at the end of solidification using a PID algorithm. The electromagnetic stirring current I at the end of solidification is adjusted according to the calculated adjustment amount ΔI.

[0035] Thus, by monitoring the columnar crystal ratio R m Compared with the target value for the proportion of columnar crystals, if R m If the value is lower than the target value, it indicates that the proportion of columnar crystals is insufficient and the proportion of equiaxed crystals is too high. In this case, the electromagnetic stirring current should be reduced to decrease the electromagnetic stirring intensity and promote the development of columnar crystals; if R m If the value is higher than the target value, it indicates that the proportion of columnar crystals is too high. In this case, the electromagnetic stirring current needs to be increased to increase the electromagnetic stirring intensity and promote equiaxed crystal nucleation; if R m If the target value is met, the current electromagnetic stirring parameters are maintained.

[0036] The PID algorithm, also known as the proportional-integral-derivative control algorithm, calculates a control output based on the error between the target value and the current value, thereby quickly and stably reaching the target value.

[0037] The proportion R of columnar crystals based on monitoring mAnd the columnar crystal ratio target value R, the adjustment amount ΔI of the electromagnetic stirring current at the end of solidification calculated by the PID algorithm includes: Based on the monitored columnar crystal ratio R m The deviation value e(t) from the columnar crystal ratio target value R, and the adjustment amount ΔI of the electromagnetic stirring current at the end of solidification is calculated by the PID algorithm; Among them, ΔI(t)= K p ·e(t)+K i ·∫e(t)dt+K d ·de(t) / dt, e(t)=R - R m .

[0038] In this way, according to the deviation between the currently monitored columnar crystal ratio R m and the columnar crystal ratio target value R, the change of the deviation, and the change rate of the deviation change, the adjustment amount ΔI(t) of the electromagnetic stirring current at the end of solidification is calculated, so that the electromagnetic stirring current can be adjusted smoothly and stably in the direction of making the columnar crystal ratio reach the target value R.

[0039] In one embodiment, K p = 0.5~1.5, K i = 0.05~0.15, K d = 0.02~0.08.

[0040] In one embodiment, the columnar crystal ratio target value R is R1~R2, that is to say, the columnar crystal ratio target value is an interval range.

[0041] In this way, when the monitored columnar crystal ratio R m < R1, the target columnar crystal ratio R is calculated based on R1, e(t)=R1 - R m .

[0042] When the monitored columnar crystal ratio R m > R2, the target columnar crystal ratio R is calculated based on R2, e(t)=R2 - R m .

[0043] When the monitored columnar crystal ratio R m is within the range of R_{1}~R_{2}, the electromagnetic stirring current at the end of solidification remains unchanged.

[0044] That is to say, when the monitored columnar crystal ratio R m is not within the target range, the endpoint value of the target range closest to the monitored columnar crystal ratio R m is used as the target value for calculation and adjustment.

[0045] In one embodiment, the electromagnetic stirring intensity parameter further includes the electromagnetic stirring frequency.

[0046] The determination of the initial value of the electromagnetic stirring intensity at the solidification end of the continuous casting process also includes: The electromagnetic stirring frequency at the end of solidification in the continuous casting process was determined to be 3~7Hz.

[0047] Therefore, there is no need to adjust the electromagnetic stirring frequency at the end of solidification, which simplifies the control method and saves costs.

[0048] In another embodiment, the electromagnetic stirring intensity parameter includes the electromagnetic stirring current.

[0049] The determination of the initial value of the electromagnetic stirring intensity at the solidification end of the continuous casting process includes: Determine the initial value f0 of the electromagnetic stirring frequency at the solidification end of the continuous casting process.

[0050] The proportion R of columnar crystals as monitored m Adjusting the intensity of electromagnetic stirring at the end of solidification includes: Based on the monitored columnar crystal ratio R m Adjust the electromagnetic stirring frequency f at the end of solidification.

[0051] Thus, by adjusting the electromagnetic stirring frequency f at the end of solidification, the intensity of electromagnetic stirring at the end of solidification can be fine-tuned, thereby fine-tuning the proportion of columnar crystals in the billet.

[0052] The initial value f0 of the electromagnetic stirring frequency at the end of solidification is 3~7Hz.

[0053] In one embodiment, determining the initial value I0 of the electromagnetic stirring current at the end of solidification in the continuous casting process includes: The preset value I of the electromagnetic stirring current at the solidification end is calculated based on the alloy element content of the molten steel. y ; Determine the preset value I of the electromagnetic stirring current at the end of solidification. y I0 is the initial value of the electromagnetic stirring current at the end of solidification.

[0054] In this way, the electromagnetic stirring current at the end of solidification can be determined based on the influence of alloying elements in molten steel on columnar and equiaxed crystals during the solidification process of the billet, which is beneficial to control the proportion of columnar crystals in the billet formed at the end of solidification.

[0055] In one embodiment, the preset value I of the electromagnetic stirring current at the solidification end is calculated based on the alloy element content in the molten steel. y include: The preset value of the electromagnetic stirring current I at the end of solidification is calculated based on the Si, Al, and Mn element content in the molten steel. y .

[0056] Since Si and Al significantly reduce the high-temperature thermal conductivity of steel, which is beneficial to the development of columnar crystals during solidification, and Mn can refine the solidification structure and promote the formation of equiaxed crystals, the preset value of the electromagnetic stirring current I at the end of solidification is calculated based on the Si, Al, and Mn element content in the molten steel. y This is to ensure that the proportion of columnar crystals in the billet formed at the solidification endpoint reaches the target value.

[0057] In one embodiment, I y =300+30×Si+20×Al+10×Mn, where the element symbols in the formula represent the mass percentage of the corresponding element.

[0058] In one embodiment, determining the initial value I0 of the electromagnetic stirring current at the solidification end of the continuous casting process further includes: The initial value adjustment amount ΔI0 of the electromagnetic stirring current at the end of solidification is determined based on the fluctuation amount Δv of the continuous casting speed, the fluctuation amount ΔT of the superheat of the molten steel, and the fluctuation amount ΔC of the alloy element content in the molten steel. Determine the preset value I of the electromagnetic stirring current at the end of solidification. y The sum of the initial value adjustment ΔI0 of the electromagnetic stirring current at the end of solidification and the initial value adjustment ΔI0 of the electromagnetic stirring current at the end of solidification is the initial value I0 of the electromagnetic stirring current at the end of solidification.

[0059] Because the temperature and alloy element content of different batches of molten steel will fluctuate during the continuous casting process, and the casting speed will also fluctuate, it is necessary to adjust the initial value of the electromagnetic stirring current at the solidification end according to the different batches of molten steel poured during the continuous casting process and the actual casting speed, so as to make the proportion of columnar crystals in the continuously cast billet reach the target value and have universal applicability.

[0060] In one embodiment, the initial value adjustment amount of the electromagnetic stirring current at the end of solidification is ΔI0=k. v ·Δv+k T ·ΔT+k C ·ΔC; Where, Δv=v m -v0, v m v0 is the measured value of the continuous casting speed, and v0 is the preset value of the continuous casting speed. m Both v0 and v0 are in m / min. ΔT=T m -T0, T m T0 is the measured value of the superheat of molten steel, and T0 is the preset value of the superheat of molten steel. m The units for T0 are both °C; ΔC=C m -C0,C mC0 is the measured sum of the Si, Al, and Mn element contents in the molten steel, and C0 is the preset sum of the Si, Al, and Mn element contents in the molten steel. m Both C0 and C0 are in units of %.

[0061] In other words, in the above formula, v m v0, T m T0, C m Both C0 and C0 are calculated by substituting the values ​​into the units listed above.

[0062] Where, k v k is the coefficient of variation of continuous casting speed. T k is the coefficient of change in superheat of molten steel. C This is the coefficient of variation of the alloying element content in molten steel.

[0063] k v For 100~200, k T For 8~15, k C It is 20~30.

[0064] In one implementation, k v k T k C The value was determined by linear regression with the electromagnetic stirring current value at the end of solidification.

[0065] In other embodiments, k v k T k C Alternatively, it can be determined by calculating the partial derivative of the initial value I0 of the electromagnetic stirring current at the end of solidification.

[0066] In one embodiment, the proportion of columnar crystals in the billet formed at the solidification endpoint during the real-time monitoring of the continuous casting process includes: The proportion of columnar crystals in the billet formed at the solidification endpoint is determined by X-ray detection.

[0067] The solidification structure of the billet formed at the solidification endpoint, i.e., the continuously cast billet, includes a fine-grained surface region, a columnar grain region, and a central equiaxed grain region. Their distribution and morphology determine the internal uniformity and density of the continuously cast billet, directly affecting the material's mechanical properties. Due to their regular crystal structure and consistent grain orientation, the columnar grain region exhibits measurable differences in X-ray scattering and absorption characteristics compared to the equiaxed grain region.

[0068] X-ray inspection technology utilizes the attenuation characteristics of X-rays as they penetrate matter to obtain internal information about the object being inspected. After X-rays penetrate a continuously cast billet, columnar crystal regions, due to their large grain size, low grain boundary density, and strong crystallographic orientation consistency, exhibit relatively high X-ray transmittance and appear as brighter areas on the detector. Conversely, equiaxed crystal regions, with their fine grains, high grain boundary density, and random orientation, experience stronger X-ray scattering and absorption, resulting in relatively lower transmittance and appearing as darker areas. This difference in brightness forms the material basis for distinguishing between columnar and equiaxed crystals.

[0069] In one embodiment, the continuous casting equipment further includes an online X-ray inspection system. The control system is connected to the online X-ray inspection system and is used to obtain the proportion R of columnar crystals in the billet formed at the solidification endpoint detected by the online X-ray inspection system. m .

[0070] X-ray inspection is performed using an online X-ray inspection system.

[0071] The X-ray online inspection system includes: An X-ray source that emits X-rays at an energy of 150-450 kV; A detector array is located on the side of the billet away from the X-ray source to receive transmitted signals; A collimator, placed between the X-ray source and the detector array, collimates the X-rays emitted by the X-ray source to form a narrow beam of scanning rays, thereby reducing scattering interference. The image processing and control system acquires signals received by the detector array in real time, performs image reconstruction and columnar crystal ratio recognition calculation, and transmits the calculation results to the control system to adjust the electromagnetic stirring intensity at the solidification end.

[0072] The energy emitted by the X-ray source can be automatically adjusted according to the thickness of the billet.

[0073] The detector array can employ high-sensitivity linear or area array detectors. For example, amorphous silicon planar detectors, CdTe semiconductor detectors, or CdZnTe semiconductor detectors.

[0074] Specifically, when X-rays pass through a continuously cast billet, their intensity follows the Lambert-Beer attenuation law: .

[0075] Where I is the intensity of the transmitted X-rays, I0 is the intensity of the incident X-rays, and μ is the linear attenuation coefficient, with units of cm. -1 μ reflects the absorption capacity of the medium (such as columnar crystals or equiaxed crystals) for X-rays; x is the path length of X-rays propagating in the medium, in cm.

[0076] A detector array acquires X-ray grayscale images of the cross-section of the continuously cast billet. After filtering, noise reduction, and contrast enhancement, a clear image of the solidification structure is obtained. Edge detection operators such as the Canny and Sobel operators are used to extract grayscale abrupt boundary changes and automatically delineate the inner contour lines of columnar crystal regions, thereby identifying the columnar crystal regions. Then, the pixel area of ​​the columnar crystal region is calculated, and the ratio of the pixel area of ​​the columnar crystal region to the total pixel area of ​​the cross-section is the columnar crystal area ratio R. Based on the low-magnification imaging principle of the solidification structure of the continuously cast billet, the area ratio of the columnar crystal region can be directly equivalent to the volume ratio of the columnar crystals, and is fed back to the control system as a feedback quantity for the image processing and control system.

[0077] In one embodiment, X-ray detection performs cross-sectional scanning and proportion calculation every 5 to 30 seconds to achieve continuous online monitoring of the proportion of columnar crystals in the billet formed at the solidification endpoint.

[0078] Specifically, the X-ray online detection system can use fan-shaped beamline scanning or multi-source array static scanning to perform scanning, with a detection frequency of 5 to 30 seconds per scan.

[0079] In another embodiment, the real-time monitoring of the proportion of columnar crystals in the billet formed at the solidification endpoint during the continuous casting process includes: The proportion of columnar crystals in the billet formed at the solidification endpoint is detected by ultrasonic testing.

[0080] The significant difference in grain size between columnar and equiaxed crystals affects the scattering and attenuation of ultrasound waves. Columnar crystals have large, uniformly oriented grains, resulting in lower ultrasound attenuation, higher echo amplitude, and narrower frequency distribution. In contrast, equiaxed crystals have small, randomly oriented grains, resulting in greater ultrasound attenuation, lower echo amplitude, and wider frequency distribution.

[0081] By propagating ultrasound in the billet, reflection and scattering occur when it encounters the boundary between columnar and equiaxed crystal regions. Based on the echo time-domain signal, the proportion of columnar crystals in the billet formed at the solidification endpoint can be detected.

[0082] In one embodiment, the continuous casting equipment further includes an online ultrasonic detection system. The control system is connected to the online ultrasonic detection system and is used to acquire the proportion R of columnar crystals in the billet formed at the solidification endpoint detected by the online ultrasonic detection system. m .

[0083] Ultrasonic testing is performed using an online ultrasonic testing system.

[0084] The ultrasonic online testing system includes: An electromagnetic ultrasonic transducer (EMAT) includes a high-frequency coil and a bias magnetic field system. The high-frequency coil includes a transmitting coil and a receiving coil.

[0085] An ultrasonic pulse transmitting and receiving system is used to generate high-voltage pulses to excite the EMAT to transmit ultrasonic waves and to receive the echo signals.

[0086] The signal processing unit is used to amplify, filter, perform analog-to-digital conversion, analyze the spectrum, extract features, and classify patterns in the echo signal.

[0087] The control system interface will use the calculated columnar crystal ratio R m Feedback is sent to the control system to adjust the intensity of electromagnetic stirring at the end of solidification.

[0088] Among them, the electromagnetic ultrasonic transducer (EMAT) performs non-contact detection by using non-contact electromagnetic induction to excite and receive ultrasonic transverse waves, which can operate without coupling agent and can operate in high-temperature environments.

[0089] The working principle of EMAT is based on electromagnetic acoustic transduction. When a high-frequency current passes through the high-frequency coil, the resulting alternating magnetic field induces eddy currents on the surface of the billet. The eddy currents interact with the bias static magnetic field to generate Lorentz force, thereby exciting high-frequency elastic waves (transverse or longitudinal waves) inside the billet. The high-frequency elastic waves propagate in the billet and are reflected and scattered when they encounter the microstructure boundaries of columnar and equiaxed crystal regions. The echo signal is received by EMAT.

[0090] An electromagnetic ultrasonic transducer (EMAT) can be installed at the exit of the fan-shaped section of the secondary cooling zone of a continuous casting machine. By installing at least one EMAT probe in the width direction of the billet, the echo signal can be detected.

[0091] In one embodiment, ultrasonic detection performs scanning and proportion calculation every 10 to 20 seconds to achieve continuous online monitoring of the proportion of columnar crystals in the billet formed at the solidification endpoint.

[0092] In one embodiment, the control method further includes: The X-ray or ultrasonic testing is calibrated using a low-magnification acid immersion method.

[0093] Specifically, when changing steel grades or at the beginning of each casting, a sample of the billet at the end of solidification is taken. After low-magnification acid etching, the solidification structure (including fine-grained region, columnar region, and equiaxed region) is observed. By comparing the boundary of the columnar region measured by X-ray detection or ultrasonic detection with the boundary of the columnar region in the low-magnification acid etching photograph, a calibration curve is established to calibrate the X-ray detection or ultrasonic detection.

[0094] In one embodiment, the control method includes: When the target value for the proportion of columnar crystals in the billet formed at the solidification endpoint is 50%~80%, electromagnetic stirring is controlled at the end of solidification in the continuous casting process, but electromagnetic stirring is not performed in the crystallizer.

[0095] Thus, by controlling the crystallizer to not perform electromagnetic stirring, the expansion of the equiaxed crystal zone can be avoided, which is conducive to increasing the proportion of columnar crystals. Furthermore, the proportion of columnar crystals in the billet formed at the solidification endpoint can be monitored in real time, and the intensity of electromagnetic stirring at the solidification endpoint can be adjusted according to the monitored columnar crystal proportion, thereby further adjusting the proportion of columnar crystals so that the proportion of columnar crystals can reach 50~80%.

[0096] In other embodiments, the control method includes: When the target value of columnar crystal proportion in the billet formed at the solidification endpoint is <50%, electromagnetic stirring is controlled in both the crystallizer and the solidification endpoint during the continuous casting process.

[0097] In this way, the equiaxed crystal region can be expanded, which is conducive to increasing the proportion of equiaxed crystals; furthermore, the proportion of columnar crystals in the billet formed at the solidification endpoint can be monitored in real time, and the electromagnetic stirring intensity at the solidification endpoint can be adjusted according to the monitored columnar crystal proportion, so that the columnar crystal proportion is <50%.

[0098] In summary, the method for controlling the proportion of columnar crystals in a continuously cast billet according to one embodiment of this application monitors the proportion R of columnar crystals in the billet formed at the solidification endpoint during the continuous casting process in real time. m And based on the monitored columnar crystal ratio R m Adjusting the intensity of electromagnetic stirring at the end of solidification can effectively regulate the ratio of columnar crystals and equiaxed crystals in the billet, thereby achieving dynamic adjustment of the proportion of columnar crystals in the billet formed at the end of solidification, so that the proportion of columnar crystals in the billet formed at the end of solidification reaches the target value.

[0099] Example 2 The only difference between this embodiment and Embodiment 1 is that this embodiment provides a method for controlling the proportion of equiaxed crystals in continuously cast billets. Specifically, columnar crystals in Embodiment 1 are replaced with equiaxed crystals, and the proportion of equiaxed crystals is negatively correlated with the proportion of columnar crystals; that is, the larger the proportion of equiaxed crystals, the smaller the proportion of equiaxed crystals. All other aspects are the same as in Embodiment 1, and will not be repeated here.

[0100] The control method includes: Determine the initial value of electromagnetic stirring intensity at the solidification end of the continuous casting process; The proportion of equiaxed crystals in the billet formed at the end of solidification during the continuous casting process is monitored in real time, and the electromagnetic stirring intensity at the end of solidification is adjusted according to the monitored proportion of equiaxed crystals to adjust the proportion of equiaxed crystals in the billet formed at the end of solidification to the target value.

[0101] When the electromagnetic stirring intensity at the end of solidification is high, it can interrupt the growth of columnar crystals, break up coarse dendrites and disperse them, making them new equiaxed crystal nuclei, thereby increasing the proportion of equiaxed crystals and decreasing the proportion of columnar crystals; conversely, when the electromagnetic stirring intensity at the end of solidification is low, the proportion of equiaxed crystals decreases and the proportion of columnar crystals increases.

[0102] Thus, by real-time monitoring of the equiaxed crystal ratio in the billet formed at the solidification endpoint during the continuous casting process, and adjusting the electromagnetic stirring intensity at the solidification endpoint based on the monitored equiaxed crystal ratio, the proportion of columnar crystals and equiaxed crystals in the billet can be effectively adjusted. This allows for dynamic adjustment of the equiaxed crystal ratio in the billet formed at the solidification endpoint, ensuring that the equiaxed crystal ratio in the billet formed at the solidification endpoint reaches the target value.

[0103] The detailed descriptions listed above are merely specific descriptions of feasible implementation methods of this application, and are not intended to limit the scope of protection of this application. All equivalent implementation methods or modifications made without departing from the spirit of the art of this application should be included within the scope of protection of this application.

Claims

1. A method for controlling the proportion of columnar crystals in a continuously cast billet, characterized in that, The control method includes: Determine the initial value of electromagnetic stirring intensity at the solidification end of the continuous casting process; The proportion of columnar crystals in the billet formed at the solidification endpoint during the continuous casting process is monitored in real time, and the electromagnetic stirring intensity at the solidification endpoint is adjusted according to the monitored columnar crystal proportion to adjust the proportion of columnar crystals in the billet formed at the solidification endpoint to the target value.

2. The method for controlling the proportion of columnar crystals in a continuously cast billet according to claim 1, characterized in that, The determination of the initial value of the electromagnetic stirring intensity at the solidification end of the continuous casting process includes: Determine the initial value I0 of the electromagnetic stirring current at the end of solidification in the continuous casting process; The adjustment of the electromagnetic stirring intensity at the solidification end based on the monitored columnar crystal ratio includes: The electromagnetic stirring current I at the end of solidification is adjusted according to the monitored columnar crystal ratio.

3. The method for controlling the proportion of columnar crystals in a continuously cast billet according to claim 2, characterized in that, The adjustment of the electromagnetic stirring current I at the end of solidification based on the monitored columnar crystal ratio includes: Based on the monitored columnar crystal ratio and the target value of the columnar crystal ratio, the adjustment amount ΔI of the electromagnetic stirring current at the end of solidification is calculated by the PID algorithm. The electromagnetic stirring current I at the end of solidification is adjusted according to the calculated adjustment amount ΔI.

4. The method for controlling the proportion of columnar crystals in a continuously cast billet according to claim 2, characterized in that, The determination of the initial value I0 of the electromagnetic stirring current at the end of solidification in the continuous casting process includes: The preset value I of the electromagnetic stirring current at the solidification end is calculated based on the alloy element content of the molten steel. y ; Determine the preset value I of the electromagnetic stirring current at the end of solidification. y I0 is the initial value of the electromagnetic stirring current at the end of solidification.

5. The method for controlling the proportion of columnar crystals in a continuously cast billet according to claim 4, characterized in that, The preset value I of the electromagnetic stirring current at the solidification end is calculated based on the alloy element content of the molten steel. y include: The preset value of the electromagnetic stirring current I at the end of solidification is calculated based on the Si, Al, and Mn element content in the molten steel. y .

6. The method for controlling the proportion of columnar crystals in a continuously cast billet according to claim 5, characterized in that, I y =300+30×Si+20×Al+10×Mn, where the element symbols in the formula represent the mass percentage of the corresponding element.

7. The method for controlling the proportion of columnar crystals in a continuously cast billet according to claim 4, characterized in that, The determination of the initial value I0 of the electromagnetic stirring current at the end of solidification in the continuous casting process also includes: The initial value adjustment amount ΔI0 of the electromagnetic stirring current at the end of solidification is determined based on the fluctuation amount Δv of the continuous casting speed, the fluctuation amount ΔT of the superheat of the molten steel, and the fluctuation amount ΔC of the alloy element content in the molten steel. Determine the preset value I of the electromagnetic stirring current at the end of solidification. y The sum of the initial value adjustment ΔI0 of the electromagnetic stirring current at the end of solidification and the initial value adjustment ΔI0 of the electromagnetic stirring current at the end of solidification is the initial value I0 of the electromagnetic stirring current at the end of solidification.

8. The method for controlling the proportion of columnar crystals in a continuously cast billet according to claim 7, characterized in that, ΔI0=k v ·Δv+k T ·ΔT+k C ·ΔC; Where, Δv=v m -v0, v m v0 is the measured value of the continuous casting speed, and v0 is the preset value of the continuous casting speed. ΔT=T m -T0, T m T0 is the measured value of the superheat of molten steel, and T0 is the preset value of the superheat of molten steel. ΔC=C m -C0,C m C0 is the measured sum of the contents of Si, Al, and Mn elements in molten steel, and C0 is the preset sum of the contents of Si, Al, and Mn elements in molten steel. k v k is the coefficient of variation of continuous casting speed. T k is the coefficient of change in superheat of molten steel. C This is the coefficient of variation of the alloying element content in molten steel.

9. The method for controlling the proportion of columnar crystals in a continuously cast billet according to claim 1, characterized in that, The proportion of columnar crystals in the billet formed at the solidification endpoint during the real-time monitoring of the continuous casting process includes: The proportion of columnar crystals in the billet formed at the solidification endpoint can be detected by X-ray diffraction or by ultrasonic diffraction.

10. The method for controlling the proportion of columnar crystals in a continuously cast billet according to claim 1, characterized in that, The control method includes: When the target value for the proportion of columnar crystals in the billet formed at the solidification endpoint is 50%~80%, electromagnetic stirring is controlled at the solidification endpoint in the continuous casting process, while electromagnetic stirring is not performed in the crystallizer and the secondary cooling zone.