Hot rolling method for reducing dot-shaped peeling defects of steel coil

Abstract

The invention relates to a hot rolling method for reducing point-shaped peeling defects of a steel coil. The mass content of the Ti element in the steel coil is 0.01%-0.025%, and / or the mass content of the Mn element in the steel coil is 1.7%-3%; the method comprises the following steps that the charging temperature of a plate blank and the Ar1 temperature of the plate blank are obtained, and the Ar1 temperature is the temperature at which austenite is decomposed into ferrite and pearlite in the plate blank cooling process; judging whether the charging temperature is greater than the Ar1 temperature or not; if yes, cooling is started, the plate blank is cooled to the preset target temperature before entering the furnace, and the preset target temperature is smaller than the Ar1 temperature. The hot rolling method provided by the invention can reduce the occurrence rate of hot charging cracks of the plate blank.

Description

Technical Field

[0001] The present application relates to the field of steel technology, and specifically relates to a hot rolling method for reducing the dot peeling defect of steel coils. Background Art

[0002] Hot rolling is a rolling method in which a steel billet is heated to a temperature above the recrystallization temperature. After heating, the steel billet undergoes multiple rolling passes, and then is trimmed and straightened into a steel plate. Hot rolling can significantly reduce energy consumption and costs. In addition, during hot rolling, the plasticity of the metal is high and the deformation resistance is low, which can greatly reduce the energy consumption of metal deformation. Moreover, hot rolling can improve the processing performance of metals and alloys. It can break coarse grains in the as-cast state, significantly heal cracks, reduce or eliminate casting defects, transform the as-cast structure into a deformed structure, and improve the processing performance of alloys.

[0003] For hot charging crack-sensitive steel grades, the temperature of the steel coil entering the heating furnace during hot rolling is generally between 600°C and 800°C. Entering the furnace at this temperature easily causes dot peeling defects in the elliptical area on the surface of the steel coil, resulting in batch rejection or downgrading of the steel coil / steel plate. In the prior art, in order to prevent quality defects from occurring when hot charging crack-sensitive steel grades are charged into the furnace between 600°C and 800°C, the following methods are generally adopted: one is to extend the stacking and cooling time of the slab to make the slab entering the furnace temperature lower than the Ar1 temperature (the temperature at which austenite decomposes into ferrite and pearlite); the second is to increase a strong cooling device on the continuous casting segment or the conveying roller table to make the surface temperature of the slab lower than 500°C to complete the phase transformation of austenite decomposing into ferrite and pearlite; the third is to increase the slab entering the furnace temperature to make the slab entering the furnace temperature higher than the Ar3 temperature (the temperature at which ferrite begins to precipitate during cooling).

[0004] However, there are still many problems with the above solutions. In the first method, since the temperature drop of the slabs at each position during stacking and cooling of the slabs is inconsistent (the difference is 200°C - 500°C), the temperature of the slab in the middle of the stack is the highest. In order to ensure that the temperature of the slab in the middle of the stack entering the furnace is less than the Ar1 temperature, the temperature of other slabs entering the furnace is too low, resulting in high gas consumption in the heating furnace. In the second method, due to the inconsistent production rhythms of the hot rolling process and the continuous casting process and process requirements, the slabs produced by continuous casting need to be taken offline for buffering. The time interval (the time from slab cutting to slab entering the furnace) and the temperature of the slab entering the furnace are uncertain; the temperature of most slabs entering the furnace is relatively low, resulting in high gas consumption in the heating furnace. In the third method, when the slab entering the furnace temperature is higher than the Ar3 temperature, the slab can only adopt the direct charging process. Due to the inconsistent production rhythms of the hot rolling process and the continuous casting process, the production capacity of the hot rolling process will decrease.

[0005] Therefore, how to improve the dot defects on the surface of the steel coil without affecting the existing process and without increasing energy consumption costs is one of the urgent problems to be solved in the current hot rolling process. Summary of the Invention

[0006] In view of the problems existing in the prior art, an embodiment of the present application provides a hot rolling method for reducing the punctate peeling defect of steel coils. This method is applicable to hot charging crack-sensitive steel grades with a Ti element mass content of 0.01%-0.025% and / or an Mn element mass content of 1.7%-3% in the steel coil. The hot rolling method includes the following steps:

[0007] Obtain the furnace inlet temperature of the slab and the Ar1 temperature of the slab, where the Ar1 temperature is the temperature at which austenite decomposes into ferrite and pearlite during the cooling process of the slab;

[0008] Judge whether the furnace inlet temperature is greater than the Ar1 temperature;

[0009] If so, start cooling, and cool the slab to a preset target temperature before entering the furnace, and the preset target temperature is less than the Ar1 temperature.

[0010] In this application, in view of the problem that punctate peeling defects are likely to occur during the rolling process of hot charging crack-sensitive steel grades, the surface temperature of the slab is detected before the slab enters the heating furnace. When the surface temperature of the slab is greater than the Ar1 temperature, the slab can be rapidly cooled by a cooling device to lower the temperature of the slab below the Ar1 temperature, so that the surface temperature of the slab can be charged into the furnace near the Ar1 temperature, thereby maintaining the relative stability of the surface temperature of the slab and reducing the gas consumption of the heating furnace; at the same time, this temperature control method will not affect the progress of other processes, can maintain the rhythm consistency between the hot rolling process and the continuous casting process, and reduce the impact on hot rolling production capacity.

[0011] In some embodiments, the preset target temperature is denoted as T1, and the Ar1 temperature is denoted as T Ar1 , 60°C ≤ T Ar1 -T1 ≤ 100°C.

[0012] In some embodiments, the step of cooling the slab to the preset target temperature includes: simultaneously spraying water on the upper surface and the lower surface of the slab for cooling. By simultaneously spraying water on the upper surface and the lower surface of the slab, the cooling rate can be accelerated, and the slab can be cooled more evenly, so that each part of the slab has a substantially constant temperature when entering the furnace.

[0013] In some embodiments, the water flow rate for spraying water on the upper surface of the slab is W1, and the water flow rate for spraying water on the lower surface of the slab is W2, and 1.6 ≤ W2 / W1 ≤ 2.

[0014] In some embodiments, the water flow rate W1 for spraying water on the upper surface of the slab satisfies: W1 = 220 L / min + δ T ×K, where δ T= T0 - T1, where T0 is the temperature upon furnace charging, and 2 L / min / °C ≤ K ≤ 7 L / min / °C.

[0015] In some embodiments, 220 L / min < W1 ≤ 900 L / min.

[0016] In some embodiments, 400 L / min ≤ W2 ≤ 1700 L / min.

[0017] In some embodiments, the water pressure for spray cooling is 6 Mpa - 8 MPa.

[0018] In some embodiments, the hot charging crack incidence rate of the slab is less than or equal to 0.1%. Detailed implementation manners

[0019] The features and exemplary embodiments of each aspect of the present application will be described in detail below. In the following detailed description, many specific details are set forth in order to provide a comprehensive understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without some of these specific details. The following description of the embodiments is only intended to provide a better understanding of the present application by showing examples of the present application. In the following description, at least some of the well-known structures and technologies are not shown in order to avoid unnecessarily obscuring the present application; and, for clarity, the dimensions of some structures may be exaggerated. In addition, the features, structures, or characteristics described below may be combined in any suitable manner in one or more embodiments.

[0020] It should be noted that in this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. In the description of the present application, it should be noted that unless otherwise specified, the meaning of "a plurality" is two or more. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover a non-exclusive inclusion, such that a process, method, article or device including a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0021] An embodiment of the present application provides a hot rolling method for reducing the dot peeling defect of steel coils. This hot rolling method is applicable to hot charging crack-sensitive steel grades, that is, the mass content of Ti element in the steel coil is 0.01% - 0.025%, and / or the mass content of Mn element in the steel coil is 1.7% - 3%. The hot rolling method includes the following steps:

[0022] Obtain the furnace inlet temperature of the slab and the Ar1 temperature of the slab, where the Ar1 temperature is the temperature at which austenite decomposes into ferrite and pearlite during the cooling process of the slab;

[0023] Judge whether the furnace inlet temperature is greater than the Ar1 temperature;

[0024] If so, start cooling and cool the slab to a preset target temperature before entering the furnace. The preset target temperature is less than the Ar1 temperature.

[0025] The mass contents of Ti element and Mn element have an important impact on the mechanical properties and surface quality of the steel coil. By controlling their contents, the dot peeling defect can be effectively reduced. The Ar1 temperature is the critical temperature at which austenite decomposes into ferrite and pearlite. By obtaining the furnace inlet temperature and the Ar1 temperature of the slab, it can be judged whether the cooling program needs to be started. If the furnace inlet temperature is higher than the Ar1 temperature, the slab needs to be cooled to ensure that the slab reaches the preset target temperature before entering the furnace, and this temperature is lower than the Ar1 temperature, thereby avoiding the generation of dot peeling defects. Specifically, the cooling process can be achieved in various ways, such as by using spray cooling, air cooling or combined cooling methods. Spray cooling can be further refined to spray cool the upper surface and the lower surface simultaneously to ensure that the overall temperature of the slab drops evenly. In addition, the cooling water flow rate and water pressure can be adjusted according to actual needs to achieve the best cooling effect. This application judges and cools the furnace inlet temperature and Ar1 temperature of the slab for the quality problems caused by hot charging of hot charging crack-sensitive steel grades with the mass content of Ti element being 0.01% - 0.025% and / or the mass content of Mn element in the steel coil being 1.7% - 3%, effectively reducing the occurrence of dot peeling defects of the steel coil. Compared with the prior art, this method significantly improves the surface quality of the steel coil without increasing the energy consumption cost and solves the actual problems in the hot rolling process.

[0026] In this application, the charging temperature of the slab refers to the temperature of the slab before entering the heating furnace in the hot rolling process. For the problem that the hot charging crack-sensitive steel grades are prone to occur with dot peeling defects during the rolling process, the hot rolling method provided by the embodiments of this application detects the surface temperature of the slab before the slab enters the heating furnace. When the surface temperature of the slab is greater than the Ar1 temperature, the slab can be rapidly cooled by a cooling device to lower the temperature of the slab below the Ar1 temperature, so that the surface temperature of the slab can be charged near the Ar1 temperature, thereby maintaining the relative stability of the surface temperature of the slab and reducing the gas consumption of the heating furnace; at the same time, this temperature control method will not affect the progress of other processes, can maintain the rhythm consistency between the hot rolling process and the continuous casting process, and reduce the impact on the hot rolling production capacity.

[0027] In this application, the charging temperature of the slab can be obtained by common methods and instruments in the art. For example, a temperature measuring device can be installed on the charging roller table to detect the surface temperature of the slab in real time through the temperature measuring device. The temperature measuring device can be a temperature detection device such as a thermometer, and the embodiments of this application do not limit this.

[0028] In some embodiments, the preset target temperature is denoted as T1, and the Ar1 temperature is denoted as T Ar1 , 60°C ≤ T Ar1 - T1 ≤ 100°C.

[0029] The temperature difference range between the preset target temperature T1 and the Ar1 temperature T Ar1 is limited to between 60°C and 100°C. This temperature difference range is set to ensure that the austenite can effectively complete the phase transformation into ferrite and pearlite during the cooling process of the slab, while avoiding quality problems caused by too large or too small temperature differences. For example, when the temperature difference is too small, the phase transformation may not be fully completed, resulting in dot peeling defects in the elliptical area on the surface of the steel coil; while when the temperature difference is too large, it may lead to too fast cooling speed, generating internal stress or cracks, and increasing the energy consumption of the heating furnace due to the low charging temperature.

[0030] As a preferred implementation manner, the temperature difference of T Ar1 - T1 can be set to 80°C to ensure the stability of the cooling process and the sufficiency of the phase transformation. In addition, the specific setting of the temperature difference can also be adjusted according to the material, thickness of the slab and the performance of the cooling equipment to achieve the best cooling effect.

[0031] Therefore, this application ensures the phase transformation quality of the slab during the cooling process by precisely controlling the temperature difference between the preset target temperature and the Ar1 temperature, thereby effectively reducing the occurrence of dot peeling defects in the steel coil. Compared with the prior art, this solution not only improves the control accuracy of the cooling process, but also avoids the increase in energy consumption or the complication of the process caused by improper temperature difference, and has significant technical advantages.

[0032] In this application, the cooling of the slab can adopt the methods and instruments commonly used in the art. For example, a water cooling device can be used to spray water on the slab for cooling.

[0033] In some embodiments, the temperature measuring device can be arranged on the furnace inlet roller table on the side of the water cooling device away from the heating furnace. The distance between the temperature measuring device and the water cooling device can be 12 meters to 15 meters. Thus, after the surface temperature of the slab is detected in real time by the temperature measuring device, cooling can be started immediately according to the surface temperature of the slab to cool the surface of the slab.

[0034] In some embodiments, the step of cooling the slab to a preset target temperature can include: spraying water on the upper surface and the lower surface of the slab simultaneously. By spraying water on the upper surface and the lower surface of the slab simultaneously, the cooling rate can be accelerated, and the slab can be cooled more evenly, so that each part of the slab has a substantially constant temperature when entering the furnace.

[0035] Specifically, the water flow rate of the water spraying cooling can be adjusted according to actual needs. Among them, the water flow rate of the upper surface is W1, the water flow rate of the lower surface is W2, and the ratio range of W2 to W1 is 1.6 to 3. By spraying water on the upper surface and the lower surface simultaneously, it can be ensured that the temperature of the slab drops evenly, avoiding the problem of uneven temperature gradient caused by single-sided cooling, thereby effectively reducing the occurrence of dot peeling defects in the steel coil.

[0036] During the implementation process, the water pressure of the water spraying cooling can be controlled between 0.1 Mpa and 0.9 MPa to ensure the cooling effect while avoiding uneven cooling or low efficiency caused by too high or too low water pressure. In addition, the calculation formula of the water flow rate W1 is W1 = 220 L / min + δ T ×K, where δ T = T0 - T1, T0 is the furnace inlet temperature, and 2 L / min / °C ≤ K ≤ 7 L / min / °C. Through this formula, the water flow rate can be dynamically adjusted according to the actual temperature of the slab, further optimizing the cooling effect.

[0037] The technical solution of this application can effectively solve the problem of dot peeling defects in the steel coil caused by single-sided cooling or uneven cooling in the prior art by spraying water on the upper surface and the lower surface simultaneously and combining precise control of the water flow rate and water pressure. Compared with the prior art, this solution not only improves the cooling efficiency but also ensures the uniformity of the slab temperature, thus significantly improving the surface quality of the steel coil.

[0038] In some embodiments, the water pressure for spraying water on the surface of the slab can be 6 Mpa - 8 MPa. For example, it can be 6.0 Mpa, 6.5 MPa, 7.0 MPa, 7.5 MPa, 8.0 MPa, or the range composed of any of the above values.

[0039] In some embodiments, the water flow rate for spray cooling the upper surface of the slab is W1, and the water flow rate for spray cooling the lower surface of the slab is W2. W1 and W2 can satisfy: 1.6 ≤ W2 / W1 ≤ 3. For example, the value of W2 / W1 can be 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, or a range composed of any of the above numerical values.

[0040] In some embodiments, the water flow rate for spray cooling the slab can be adjusted according to the furnace inlet temperature of the slab. Specifically, the higher the surface temperature of the slab, the greater the water flow rate for spray cooling can be, and the water flow rate for spray cooling can vary positively with the surface temperature of the slab.

[0041] Controlling the ratio of the water flow rates W1 and W2 between 1.6 and 3 can effectively balance the cooling rates of the upper and lower surfaces of the slab, and avoid problems such as slab deformation or internal stress concentration caused by uneven cooling. Specifically, the ratio of W1 and W2 can be achieved by adjusting the valve opening of the spray device or the pump power, so as to precisely control the cooling water flow rate. As a preferred embodiment, the ratio of W1 and W2 can be set to 2 to achieve the best cooling effect.

[0042] Through the above technical solution, the problem of slab deformation caused by inconsistent cooling rates of the upper and lower surfaces during the cooling process can be effectively solved. Among them, by controlling the ratio of W2 / W1, it can be ensured that the cooling rates of the upper and lower surfaces of the slab tend to be consistent, thereby reducing the generation of internal stress in the slab and improving the flatness and quality of the slab. Compared with the prior art, this solution is not only simple to operate, but also can significantly reduce the deformation rate of the slab and improve the surface quality of the hot-rolled steel coil.

[0043] In some embodiments, the water flow rate W1 for spray cooling the upper surface of the slab satisfies: W1 = 220 L / min + δ T ×K, where δ T = T0 - T1, T0 is the furnace inlet temperature, and 2 L / min / °C ≤ K ≤ 7 L / min / °C.

[0044] According to the embodiments of the present application, δ T represents the specific temperature drop value when the surface temperature of the slab drops from the furnace inlet temperature to the preset target temperature, and the cooling water flow rate of the slab is controlled according to the magnitude of the temperature drop value. It has been found through research that controlling the relationship between the cooling water flow rate and the surface temperature drop value of the slab within the above range can effectively cool and reduce the temperature of the slab, and reduce its surface temperature to the preset target temperature before the slab enters the furnace.

[0045] Specifically, in the calculation formula of W1, 220 L / min is the basic water flow rate, and δ T is the difference between the furnace inlet temperature T0 and the preset target temperature T1, and K is the proportionality coefficient. Through this formula, the water flow rate of the spray cooling on the upper surface can be dynamically adjusted according to the difference between the actual furnace inlet temperature and the target temperature, so as to achieve precise control of the slab cooling process. For example, when δ T is large, that is, when the furnace inlet temperature is high, W1 will increase accordingly to ensure that the slab can be quickly cooled to the target temperature; when δ T is small, W1 will decrease to avoid overcooling.

[0046] As a preferred implementation manner, the value range of K can be adjusted according to specific process requirements, usually recommended to be between 2 and 7, and can be selected to be between 3 and 6. In addition, the water flow rate W1 of the spray cooling can also be adjusted in real time through an automated control system to ensure the stability and consistency of the cooling process.

[0047] Thus, the technical solution of this application solves the problem of unstable cooling effect caused by the fluctuation of the furnace inlet temperature in the prior art by introducing a dynamic water flow rate calculation formula. Compared with the prior art, this solution can automatically adjust the cooling water flow rate according to the actual temperature difference, thereby significantly improving the accuracy and efficiency of the cooling process, and at the same time avoiding quality defects caused by overcooling or undercooling.

[0048] In some embodiments, the water flow rate W1 for spray cooling the upper surface of the slab can satisfy 220 L / min < W1 ≤ 900 L / min. For example, W1 can be 210 L / min, 250 L / min, 300 L / min, 350 L / min, 400 L / min, 450 L / min, 500 L / min, 550 L / min, 600 L / min, 650 L / min, 700 L / min, 750 L / min, 800 L / min, 850 L / min, 900 L / min, or any range composed of the above arbitrary values.

[0049] The range of the water flow rate W1 is obtained through experiments and theoretical calculations to ensure that the slab temperature can be effectively reduced during the cooling process, and at the same time avoid problems such as uneven cooling or low cooling efficiency caused by too large or too small water flow rate. Specifically, the lower limit of 200 L / min of the water flow rate W1 ensures the cooling effect, and the upper limit of 900 L / min avoids problems such as waste of resources and excessive load on the cooling equipment caused by too large water flow rate. As a preferred implementation manner, the water flow rate W1 can be dynamically adjusted according to the furnace inlet temperature, target temperature of the slab, and the performance of the cooling equipment to achieve the optimal cooling effect.

[0050] Thus, by defining the range of the water flow rate W1, the technical solution of the present application solves the problems of uneven cooling or low cooling efficiency caused by improper water flow rate control in the prior art. Compared with the prior art, this solution can ensure the stability and high efficiency of the slab cooling process without increasing the energy consumption cost, thereby effectively improving the problem of dot-like peeling defects on the surface of the steel coil and improving the product quality.

[0051] In some embodiments, the water flow rate W2 for spray cooling the lower surface of the slab can be 400 L / min - 1700 L / min, for example, it can be 400 L / min, 500 L / min, 600 L / min, 700 L / min, 800 L / min, 900 L / min, 1000 L / min, 1100 L / min, 1200 L / min, 1300 L / min, 1400 L / min, 1500 L / min, 1600 L / min, 1700 L / min, or the range composed of any of the above values.

[0052] The flow rate range of W2 can be achieved by adjusting the pump power or valve opening of the spray cooling equipment. For example, as a preferred implementation, the flow rate of W2 can be increased by increasing the pump power or opening the valve wider, and vice versa to decrease the flow rate. Thus, the flow rate range of W2 can be flexibly adjusted according to the actual production requirements to ensure that the cooling effect of the lower surface of the slab meets the expectations.

[0053] In this regard, by controlling the flow rate range of spray cooling on the lower surface of the slab, the technical solution of the present application can effectively avoid slab quality defects caused by insufficient cooling or overcooling. Specifically, when the flow rate of W2 is lower than 400 L / min, it may cause insufficient cooling of the lower surface of the slab, unable to effectively reduce the slab temperature, and thus affect the quality of the subsequent hot rolling process; while when the flow rate of W2 is higher than 1700 L / min, it may cause overcooling of the lower surface of the slab, resulting in too low slab temperature and increasing the energy consumption of the heating furnace. Therefore, controlling the flow rate of W2 within the range of 400 L / min to 1700 L / min can ensure the cooling effect of the slab while avoiding unnecessary energy waste and improving production efficiency.

[0054] Furthermore, the present application also proposes that the water pressure for spray cooling is 0.1 Mpa - 0.9 MPa. Specifically, the water pressure range for spray cooling is set to be from 0.1 Mpa to 0.9 MPa. This range setting can effectively control the water pressure during the cooling process, ensuring that the slab will not be affected by too high or too low water pressure during the cooling process and thus affecting the cooling effect. For example, too low water pressure may lead to uneven cooling, while too high water pressure may cause damage to the slab surface. As a preferred embodiment, the water pressure can be further optimized to 0.3 Mpa to 0.7 MPa to reduce the impact on the slab surface while ensuring the cooling effect.

[0055] In this regard, this technical solution can effectively avoid quality problems of the slab during the cooling process due to improper water pressure by controlling the water pressure of spray cooling. Specifically, reasonable control of the water pressure can ensure that the cooling water is evenly distributed on the slab surface, avoiding the occurrence of local overheating or overcooling phenomena. Further, the optimization of the water pressure can also reduce the consumption of cooling water and lower the production cost. Thus, while ensuring the cooling effect, this technical solution can also improve the production efficiency and product quality.

[0056] In the embodiment of the present application, by detecting the temperature of the slab before entering the furnace and spraying water to cool the slab, the surface temperature of the slab can be quickly cooled below the Ar1 temperature, which can significantly reduce the problem of point peeling defects in the elliptical area of the steel coil, enable the hot charging rate of the slab (charging temperature ≥ 450 °C) to reach 80%, and the incidence rate of hot charging cracks of the slab is lower than 0.1%.

[0057] By controlling the hot charging rate of the slab, the technical solution of the present application can effectively improve the point peeling defects on the surface of the steel coil on the basis of the existing process, while avoiding increasing the energy consumption cost. Compared with the prior art, by precisely controlling the hot charging rate, the present application not only reduces the temperature difference of the slab during the hot charging process, but also improves the uniformity of the slab charging temperature, thereby reducing the gas fuel consumption of the heating furnace and enhancing the efficiency and product quality of the hot rolling process.

[0058] Embodiment

[0059] Specific embodiments are listed below to illustrate the present application. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those without specific techniques or conditions noted in the embodiments, the techniques or conditions described in the literature in this field or according to the product specification are followed. For reagents or instruments without the manufacturer noted, they are all conventional products that can be obtained through commercial purchase.

[0060] Embodiment 1

[0061] Slab composition: C element 0.18%, Si element 0.15%, Mn element 0.91%, P element 0.012%, S element 0.0020%, Ti element 0.013%, N element 0.0061%; Calculated / measured Ar1 is 649 °C, Ar3 is 762 °C, slab furnace inlet temperature is 692 °C, the slab cooling device is turned on, W1 = 478 L / min, W2 = 1100 L / min, spray cooling pressure is 0.6 MPa, cooled to 585 °C. The surface quality of the steel coil is normal.

[0062] Example 2

[0063] Slab composition: C element 0.09%, Si element 0.20%, Mn element 2.1%, P element 0.013%, S element 0.0020%, Ti element 0.0020%, N element 0.0065%; Calculated / measured Ar1 is 668 °C, Ar3 is 760 °C, slab furnace inlet temperature is 684 °C, the slab cooling device is turned on, W1 = 604 L / min, W2 = 1270 L / min, spray cooling pressure is 0.6 MPa, cooled to 605 °C. The surface quality of the steel coil is normal.

[0064] Comparative Example 1

[0065] Slab composition: C element 0.17%, Si element 0.15%, Mn element 0.90%, P element 0.012%, S element 0.0020%, Ti element 0.012%, N element 0.0062%; Calculated / measured Ar1 is 649 °C, Ar3 is 764 °C, slab furnace inlet temperature is 682 °C, no cooling is carried out, and hot charging crack defects occur.

[0066] Comparative Example 2

[0067] C element 0.09%, Si element 0.20%, Mn element 2.1%, P element 0.012%, S element 0.0020%, Ti element 0.0020%, N element 0.0062%; Calculated / measured Ar1 is 668 °C, Ar3 is 760 °C, slab furnace inlet temperature is 702 °C, no cooling is carried out, and hot charging crack defects occur.

[0068] The parameters and test results in each example and Comparative Example 1 are referred to Table 1.

[0069] Table 1

[0070]

[0071] Combined with the data in Table 1, it can be seen that the hot rolling method provided by the embodiments of the present application can effectively reduce the incidence of hot charging cracks of the slab.

[0072] Although the present application has been described with reference to the preferred embodiments, various modifications thereof can be made and components thereof can be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any manner. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A hot rolling method for reducing the dot peeling defects of steel coils, characterized in that, The mass content of Ti element in the steel coil is 0.01%-0.025%, and / or the mass content of Mn element in the steel coil is 1.7%-3%; the method includes the following steps: Obtain the furnace inlet temperature of the slab and the Ar1 temperature of the slab, where the Ar1 temperature is the temperature at which austenite decomposes into ferrite and pearlite during the cooling process of the slab; Judge whether the furnace inlet temperature is greater than the Ar1 temperature; If so, start cooling, and cool the slab to a preset target temperature before charging, and the preset target temperature is less than the Ar1 temperature.

2. The method according to claim 1, wherein The preset target temperature is denoted as T1, and the Ar1 temperature is denoted as T Ar1 , 20°C ≤ T Ar1 - T1 ≤ 100°C.

3. The method according to claim 2, wherein The step of cooling the slab to a preset target temperature before charging includes: spraying water for cooling on the upper surface and the lower surface of the slab simultaneously.

4. The method according to claim 3, characterized in that, The water flow rate for spraying water for cooling on the upper surface of the slab is W1, and the water flow rate for spraying water for cooling on the lower surface of the slab is W2, and 1.6≤W2 / W1≤3.

5. The method according to claim 4, wherein The water flow rate W1 for spraying water to cool the upper surface of the slab satisfies: W1 = 220 L / min + δ T ×K, where δ T = T0 - T1, T0 is the furnace inlet temperature, and 2 L / min / °C ≤ K ≤ 7 L / min / °C.

6. The method according to claim 4 or 5, characterized in that, 220L / min<W1≤900L / min.

7. The method according to claim 4 or 5, characterized in that, 400L / min≤W2≤1700L / min.

8. The method according to claim 3, wherein The water pressure of the water spraying for cooling is 0.1Mpa-0.9MPa.

9. The method according to claim 1, wherein The hot charging crack incidence rate of the slab is less than or equal to 0.1%.

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