Slab longitudinal crack forecasting method based on broadside heat flow difference and deviation angle attenuation rate

Abstract

The invention relates to the technical field of steelmaking, in particular to a slab longitudinal crack forecasting method based on wide-surface heat flow difference and deviation angle attenuation rate, which comprises the following steps of: calculating an absolute difference value of heat flow densities of an inner arc and an outer arc of a wide surface of a crystallizer in real time, namely calculating a transverse heat flow difference of the wide surface of the crystallizer; four deviation angle areas are selected as detection points, local heat flow data are collected in real time, and the attenuation percentage, namely the deviation angle heat flow attenuation rate, of the heat flow density in unit time is calculated; meanwhile, when the wide-surface heat flow transverse difference of the crystallizer is larger than 150 kW / m < 2 > and the deviation angle heat flow attenuation rate is larger than 4%, longitudinal crack high-risk early warning is triggered; according to the method, the heat flow difference and deviation angle attenuation rate change of the wide surface of the crystallizer are monitored in real time, dynamic adjustment of technological parameters is combined, the sensitivity to uneven transverse cooling of the blank shell is improved, accurate pre-judgment of longitudinal cracks is achieved, the longitudinal crack risk is recognized in advance, the breakout occurrence rate is reduced, and the continuous casting production stability and the slab quality are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steelmaking, and particularly relates to a slab longitudinal crack prediction method based on wide face heat flow difference and deviation angle attenuation rate. BACKGROUND

[0002] In the continuous casting production process, longitudinal cracks are a common surface defect, which is closely related to the uneven growth of the solidification shell. The longitudinal cracks not only affect the slab surface quality, but also can cause a leakage accident, resulting in equipment damage, production interruption and economic losses. In the prior art, the conventional leakage prediction system mainly depends on the temperature change of the thermocouple in the mold for judgment, but the sensitivity and early warning timeliness for longitudinal cracks are insufficient. Longitudinal cracks are one of the main defects in the thin slab continuous casting process, especially under the process conditions of a mold thickness of 70-100 mm and a casting speed of 0.8-1.3 m / min, the shell growth speed is slow and the cooling uniformity requirement is higher. The formation of longitudinal cracks is often closely related to the uneven transverse cooling of the shell in the mold and the stress concentration in the deviation angle area. In the thin slab continuous casting, the heat flow distribution difference between the narrow face and the wide face is small, and the cooling efficiency fluctuation in the deviation angle area is more significant, resulting in insufficient sensitivity and accuracy of the traditional method. In addition, the prior art ignores the dynamic heat flow distribution of the wide face and the local heat flow attenuation characteristics of the deviation angle area, and cannot effectively capture the crack initiation precursor. Therefore, in view of the process characteristics of the thin slab continuous casting, the limitations of the prior art are solved, and a new determination method is provided, which monitors the heat flow difference between the inner and outer arcs of the wide face and the heat flow attenuation rate in the deviation angle area. SUMMARY

[0003] The present application provides a slab longitudinal crack prediction method based on wide face heat flow difference and deviation angle attenuation rate, which monitors the heat flow difference of the wide face of the mold and the change of the deviation angle attenuation rate in real time, combines with the dynamic adjustment of the process parameters, improves the sensitivity to the uneven transverse cooling of the shell, realizes the accurate prediction of the longitudinal cracks, identifies the longitudinal crack risk in advance, reduces the leakage rate, and improves the stability of the continuous casting production and the slab quality.

[0004] In order to achieve the above purpose, the following technical scheme is adopted in the present application:

[0005] A slab longitudinal crack prediction method based on wide face heat flow difference and deviation angle attenuation rate, comprising the following steps:

[0006] S1, calculating the absolute difference value of the heat flow density of the inner arc and the outer arc of the wide face of the mold in real time, that is, calculating the transverse difference of the heat flow of the wide face of the mold;

[0007] S2, selecting four deviation angle areas as detection points to collect local heat flow data in real time, calculating the attenuation percentage of the heat flow density in unit time, that is, the heat flow attenuation rate of the deviation angle;

[0008] S3. Prediction criteria for longitudinal cracks:

[0009] S3.1 Determination of the threshold for transverse heat flow difference across the wide face of the crystallizer: For thin slab crystallizers with a thickness between 70 and 100 mm, when the transverse heat flow difference across the wide face of the crystallizer is >150 kW / m 2 This indicates that the cooling of the inner and outer arcs of the wide face is uneven, and the lateral growth of the billet shell is significantly different.

[0010] S3.2 Determination of the threshold of heat flow attenuation rate at deviation angle: At a drawing speed of 0.8 to 1.3 m / min, if the heat flow attenuation rate at any deviation angle region is >4%, that is, the heat flow decreases by more than 4% within 3 minutes, it is determined to be a local rapid thinning of the billet shell.

[0011] Simultaneously satisfying the lateral heat flux difference of the wide face of the crystallizer >150kW / m 2 Furthermore, when the rate of heat flux decay at the deviation angle is greater than 4%, a high-risk warning for longitudinal cracks is triggered.

[0012] Furthermore, the thickness of the thin slab crystallizer is 70-100 mm, and the working speed is 0.8-1.3 m / min.

[0013] Furthermore, step S1 specifically includes:

[0014] Calculate the lateral difference in heat flux across the wide face of the crystallizer:

[0015] ΔQ 宽 =|Q 宽内弧 -Q 宽外弧 |

[0016] Among them, Q 宽内弧 Q is the heat flux density of the inner arc of the wide face of the crystallizer. 宽外弧 The heat flux density is the outer arc of the wide face of the crystallizer.

[0017] Furthermore, a high-precision temperature sensor is installed at the center line of the inner arc of the wide surface of the crystallizer, 8-12 mm away from the surface of the copper plate of the crystallizer, and the sensor spacing is 40-60 mm.

[0018] Furthermore, the rate of heat flux decay at the deviation angle is calculated as follows:

[0019]

[0020] Among them, Q t0 This represents the heat flux density at the boundary between the wide and narrow faces of the deviation angle region at the initial time point t0, expressed in kW / m³. 2 ; This represents the heat flux density at the same deviation angle at time point t1=t0+3, reflecting the change in the cooling state of the region after 3 minutes.

[0021] Further, the real-time acquisition of local heat flow data is collected by using a micro-thermocouple, the micro-thermocouple is arranged at four deviated angle regions of the crystallizer, i.e. wide inner arc-narrow left, wide inner arc-narrow right, wide outer arc-narrow left and wide outer arc-narrow right, and is embedded in the copper plate of the crystallizer by 4-6 mm.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] 1) By real-time monitoring of the heat flow difference of the wide surface of the crystallizer and the attenuation rate change of the deviated angle, combined with dynamic adjustment of the process parameters, the sensitivity to the transverse cooling unevenness of the billet shell is improved, and the present application can more accurately capture the cooling unevenness phenomenon of the slab in the continuous casting process. The combination of real-time monitoring and dynamic adjustment not only improves the sensitivity to the transverse growth difference of the billet shell, but also makes the prediction of longitudinal cracks more accurate, realizes accurate prediction of longitudinal cracks, identifies the risk of longitudinal cracks in advance, reduces the occurrence rate of breakout, and improves the stability of continuous casting production and the quality of slabs;

[0024] 2) When the transverse difference of the heat flow of the wide surface of the crystallizer exceeds the preset threshold, it indicates that there is significant unevenness in the cooling state of the inner arc and the outer arc of the wide surface, which leads to inconsistent growth speed of the billet shell in the transverse direction, increasing the risk of longitudinal cracks; at the same time, by monitoring the heat flow attenuation rate of the deviated angle, the present application can timely find the rapid thinning phenomenon of the local billet shell, which is also an important precursor of longitudinal crack formation;

[0025] 3) When the two parameters meet the preset conditions at the same time, the present application can trigger a high-risk warning of longitudinal cracks, reminding the operator to take timely measures for adjustment, thereby effectively reducing the occurrence rate of breakout and improving the stability of continuous casting production and the quality of slabs; in addition, the technical scheme of the present application also has high flexibility and adaptability, and can be adjusted and optimized according to specific production conditions to achieve the best prediction effect;

[0026] 4) Accurate early warning: through the dual-parameter judgment of the wide surface heat flow difference and the deviated angle attenuation rate, the early warning time is 20% earlier than the traditional method;

[0027] 5) Adapt to thin slab process: more suitable for the process characteristics of low pulling speed and thin slab, and the detection rate of longitudinal cracks is improved;

[0028] 6) Strong compatibility: can be directly integrated into the existing thin slab continuous casting control system, and only the sensor and algorithm module need to be upgraded. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a method flowchart of an embodiment of the present application. DETAILED DESCRIPTION

[0030] The specific embodiments of the present application are further described below with reference to the accompanying drawings:

[0031] The present application is a slab longitudinal crack prediction method based on wide face heat flow difference and deviation angle decay rate, the thickness of the crystallizer of the present application is 70-100mm, the working pulling speed is 0.8-1.3m / min, the wide face heat flow difference and the deviation angle decay rate are calculated to dynamically predict the formation of longitudinal cracks, which is suitable for thin slabs, meets the low pulling speed process requirements, and covers high carbon steel, micro alloy steel, and cold rolled products with high surface quality requirements.

[0032] The thickness of the crystallizer of a certain steel plant is 100mm, the working pulling speed is 1.0m / min, the steel variety is high carbon steel, and the type of the protective slag is high lubricity and low melting point slag. Two groups of temperature sensors are arranged on the inner arc and the outer arc of the wide face, with a spacing of 50mm, for real-time detection of heat flux density; four deviation angle regions (wide inner arc-narrow left, wide inner arc-narrow right, wide outer arc-narrow left, and wide outer arc-narrow right) are embedded with micro thermocouples, with a sampling frequency of 10Hz; see Figure 1 The method flowchart of the present application is shown in the figure, and the method specifically includes the following steps:

[0033] S1, real-time calculation of the absolute difference value of the heat flux density of the inner arc and the outer arc of the wide face of the crystallizer, that is, calculation of the wide face heat flow transverse difference ΔQ of the crystallizer 宽 ; high-precision temperature sensors are arranged at the center line position of the inner arc of the wide face for measuring the real-time temperature of the crystallizer, which is 10mm away from the surface of the copper plate of the crystallizer to ensure the stability of data acquisition, and the spacing between the sensors is 50mm to adapt to the narrow space of the thin slab; the calculation process is as follows:

[0034] The heat flux density represents the heat passing through a unit area per unit time, and its calculation formula is:

[0035]

[0036] Wherein, ρ represents the density of cooling water (kg / m 3 ), c represents the specific heat capacity of cooling water (kJ / kg.℃), , T 3 , T 出水 , T 进水 represent the outlet and inlet temperatures of the cooling water of the crystallizer (℃), and A represents the effective cooling area of the copper plate of the crystallizer (m 2 );

[0037] The wide face heat flow transverse difference ΔQ of the crystallizer 宽 The calculation formula is as follows:

[0038] ΔQ 宽 = |Q 宽内弧 -Q 宽外弧 |

[0039] wherein Q 宽内弧 is the heat flux density of the inner arc of the wide face of the crystallizer, Q 宽外弧 is the heat flux density of the outer arc of the wide face of the crystallizer.

[0040] S2, four deviated corner regions are selected as detection points, one micro-thermocouple is arranged in each of the four deviated corner regions (wide inner arc-narrow left, wide inner arc-narrow right, wide outer arc-narrow left, and wide outer arc-narrow right), embedded in the copper plate of the crystallizer by 5 mm, real-time collection of local heat flux data is performed, and the heat flux density decay percentage in a unit time, i.e., the deviated corner heat flux decay rate, is calculated, and the formula is as follows:

[0041]

[0042] wherein Q t0 represents the heat flux density at the initial time point t0 at the junction of the wide face and the narrow face of the deviated corner region, and the unit is kW / m 2 , which represents the cooling efficiency of the region at a certain moment, and the higher the value, the better the contact between the billet shell and the copper plate of the crystallizer, and the heat transfer is sufficient; represents the heat flux density of the same deviated corner at the time point t1=t0+3, which reflects the change in the cooling state of the region after 3 min, and if decreases by 20%, it indicates that the billet shell is locally thinned.

[0043] S3, longitudinal crack prediction condition

[0044] (1) Wide face heat flux transverse difference threshold determination: the thickness of the thin slab crystallizer is small, i.e., 70-100 mm, and the heat flux distribution is more sensitive, and a small transverse difference can cause stress concentration; when ΔQ 宽 > 150 kW / m 2 , it indicates that the cooling of the inner arc and the outer arc of the wide face is uneven, and the transverse growth difference of the billet shell is significant;

[0045] (2) Deviated corner heat flux decay rate threshold determination: under the casting speed of 0.8-1.3 m / min, the billet shell grows slowly, and the local heat flux decay rate is significant; when R 偏离角 > 4%, i.e., the heat flux decreases by more than 4% within 3 min, it is determined that the local billet shell is rapidly thinned;

[0046] When ΔQ 宽 > 150 kW / m 2 and R 偏离角 > 4% are simultaneously satisfied, the high-risk warning of longitudinal cracks is triggered, the main control system automatically alarms and generates operation instructions;

[0047] The computer system calculates these data in real time and displays them on the screen of the monitoring computer in the control room, so that the operator can see the heat flux value and heat flux curve at any time.

[0048] If Q 宽内弧 > Q 宽外弧 , then reduce the inner arc cooling water amount by 2% to 5%, increase the outer arc water amount by 3% to 8%, and target to make AQ 宽 ≤ 80 kW / m 2 ; for the deviation angle area with R 偏离角 exceeding the standard, locally increase the cooling water amount by 20%, replace the circular nozzle with a fan-shaped nozzle to improve the cooling coverage uniformity of the deviation angle area, and reduce the withdrawal speed from 1.0 m / min to 0.8 m / min, and continuously monitor for 3 min.

[0049] S4, effect verification and feedback, observe AQ 宽 and R 偏离角 every 3 min after adjustment, if the parameters return to the safe range (AQ 宽 ≤ 80 kW / m 2 , R 偏离角 ≤ 3%), maintain the current process settings, otherwise further reduce the withdrawal speed.

[0050] The following examples are implemented on the premise of the technical solutions of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following examples. The methods used in the following examples are all conventional methods unless otherwise specified.

[0051] Example 1:

[0052] The thin slab continuous casting longitudinal crack prediction method is specifically as follows:

[0053] The high-carbon steel is cast, the withdrawal speed is 1.2 m / min, the heat flux on the wide face gradually decreases during casting, and decreases to 1300 kW / m 2 As shown in Table 1 below, after the operator predicts using the method of the present application, closely observes this abnormal situation, timely reduces the wide inner arc water amount by 5%, increases the wide outer arc water amount by 8%, increases the narrow left deviation angle water amount by 20%, and reduces the withdrawal speed to 1.0 m / min, and observes the produced casting blank, the quality of the casting blank after adjustment is good, the occurrence of longitudinal cracks is avoided, and the production is ensured to proceed smoothly.

[0054] Table 1 Heat flux of high-carbon steel after taking measures

[0055]

[0056]

[0057] Example 2:

[0058] The thin slab continuous casting longitudinal crack prediction method is specifically described as follows;

[0059] The pouring microalloy steel is 1.0 m / min, the wide surface heat flow density is 1420 kW / m 2 Gradually reduced to 1250 kW / m 2 , the wide outer arc-narrow right deviation angle is greater than 4%, and the longitudinal crack warning is sent; the operator uses the method to predict the operator according to the adjustment measures, the water quantity of the wide outer arc is reduced by 7%, the water quantity of the wide inner arc is increased by 5%, the water quantity of the narrow right deviation angle is increased by 18%, the drawing speed is reduced to 0.85 m / min, and the observed casting blank is qualified, and the deviation angle is not recessed. The heat flow density parameters are shown in Table 2:

[0060] Table 2 Heat flow density of microalloy steel after taking measures

[0061]

Claims

1. A method for predicting longitudinal cracks in slabs based on the difference in heat flux across a wide surface and the attenuation rate of the deviation angle, characterized in that, Includes the following steps: S1. Calculate the absolute difference in heat flux density between the inner and outer arcs of the crystallizer's wide face in real time, i.e., calculate the lateral difference in heat flux across the crystallizer's wide face. S2. Select four deviation angle regions as detection points to collect local heat flux data in real time, and calculate the percentage decrease of its heat flux density per unit time, i.e., the heat flux attenuation rate of the deviation angle. S3. Prediction criteria for longitudinal cracks: S3.1 Determination of the threshold for transverse heat flow difference across the wide face of the crystallizer: For thin slab crystallizers with a thickness between 70 and 100 mm, when the transverse heat flow difference across the wide face of the crystallizer is >150 kW / m 2 This indicates that the cooling of the inner and outer arcs of the wide face is uneven, and the lateral growth of the billet shell is significantly different. S3.2 Determination of the threshold of heat flow attenuation rate at deviation angle: At a drawing speed of 0.8 to 1.3 m / min, if the heat flow attenuation rate at any deviation angle region is >4%, that is, the heat flow decreases by more than 4% within 3 minutes, it is determined to be a local rapid thinning of the billet shell. Simultaneously satisfying the lateral heat flux difference of the wide face of the crystallizer >150kW / m 2 Furthermore, when the rate of heat flux decay at the deviation angle is greater than 4%, a high-risk warning for longitudinal cracks is triggered.

2. The method for predicting longitudinal cracks in slabs based on the difference in heat flow across a wide surface and the attenuation rate of the deviation angle, as described in claim 1, is characterized in that... The thickness of the thin slab crystallizer is 70-100 mm, and the working speed is 0.8-1.3 m / min.

3. The method for predicting longitudinal cracks in slabs based on the difference in heat flow across a wide surface and the attenuation rate of the deviation angle, as described in claim 1, is characterized in that... Step S1 specifically includes: Calculate the lateral difference in heat flux across the wide face of the crystallizer: ΔQ 宽 =|Q 宽内弧 -Q 宽外弧 | Among them, Q 宽内弧 Q is the heat flux density of the inner arc of the wide face of the crystallizer. 宽外弧 The heat flux density is the outer arc of the wide face of the crystallizer.

4. The method for predicting longitudinal cracks in slabs based on the difference in heat flow across a wide surface and the attenuation rate of the deviation angle, as described in claim 3, is characterized in that... A high-precision temperature sensor is installed at the center line of the inner arc of the wide face of the crystallizer, 8-12 mm away from the surface of the copper plate of the crystallizer, and the sensor spacing is 40-60 mm.

5. The method for predicting longitudinal cracks in slabs based on the difference in heat flow across a wide surface and the attenuation rate of the deviation angle, as described in claim 1, is characterized in that... The deviation angle heat flux attenuation rate is calculated as follows: Among them, Q t0 This represents the heat flux density at the boundary between the wide and narrow faces of the deviation angle region at the initial time point t0, expressed in kW / m³. 2 ; This represents the heat flux density at the same deviation angle at time point t1=t0+3, reflecting the change in the cooling state of the region after 3 minutes.

6. The method for predicting longitudinal cracks in slabs based on the difference in heat flow across a wide surface and the attenuation rate of the deviation angle, as described in claim 5, is characterized in that... The real-time acquisition of local heat flow data is performed using miniature thermocouples. These miniature thermocouples are positioned in four offset angular regions of the crystallizer: wide inner arc-narrow left, wide inner arc-narrow right, wide outer arc-narrow left, and wide outer arc-narrow right, and are embedded 4-6 mm inside the copper plate of the crystallizer.

Images