Method for preventing sawback steel inter-stand coiler fluctuation

Abstract

The present application belongs to the technical field of metallurgical rolling, and particularly relates to a method for preventing loop fluctuation between finishing stands of sawback steel, comprising the following contents: (1) determining different residence times in the second heating section and soaking section according to the different Mo contents of each steel grade of sawback steel, and as much as possible improving the high-temperature section furnace temperature within the performance allowable range; the higher the Mo content, the longer the residence time; (2) determining the target temperature at the rough rolling outlet and the target temperature at the finishing rolling outlet in order to effectively avoid the M7C3 short rod type alloy carbide precipitation in the finishing rolling area; (3) determining the AGC compensation coefficient of each stand when the thickness precision fully meets the requirements without loop fluctuation according to the thickness of each steel grade. The method distinguishes the Mo content to determine the residence time and target furnace temperature in the high-temperature section of the heating furnace, re-determine the rough rolling outlet temperature and the finishing rolling outlet temperature, and optimizes the AGC compensation coefficient of each stand, which essentially solves the loop fluctuation problem of sawback steel during the finishing rolling in the finishing stand.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical steel rolling technology, and particularly relates to a method for preventing fluctuations in the looper between stands of a saw back steel finishing mill. Background Technology

[0002] Saw back steel is a high-end product in the high-alloy series, mainly used as the backing material for bimetallic composite saw blades. It has a high alloy content and excellent performance, used to match expensive saw blade teeth for sawing valuable hard materials requiring high fatigue life and high machining precision. The main production process of a hot continuous rolling production line involves heating the slab in a furnace at the specified temperature. After reaching the target temperature, it enters the roughing mill for rolling. The vertical rolls control the width, and the horizontal rolls control the thickness. Reversible rolling is performed in the roughing mill, typically in 5-7 passes. After rolling in the roughing mill, the strip achieves the pre-set target thickness, width, and temperature. It then enters the finishing mill for seven-stand continuous rolling, achieving the pre-set target thickness, width, temperature, crown, and straightness. Finally, the strip is coiled into a steel coil by a coiler. The finishing mill has seven stands: F0, F1, F2, F3, F4, F5, and F6. During continuous rolling, equal flow rates between stands are crucial for ensuring stable looper operation. Looper stability is a prerequisite for stable strip rolling and maintaining rolling accuracy throughout the entire strip rolling process. The biggest challenge affecting the stability of saw-back steel rolling is the poor stability and large fluctuations of the loopers between the finishing mill stands. Specifically, after the strip is threaded, irregular rolling pressure fluctuations occur on stands F4, F5, and F6, leading to problems with the #4 looper between F4 and F5, and between F5 and F6. Fluctuations in the 5# looper angle and rolling pressure (with a difference of 1000~3000KN between peaks and troughs) cause significant fluctuations in the looper angle (15°~35°), sometimes exceeding 40°. These looper fluctuations lead to extreme instability in strip rolling. On one hand, they cause significant fluctuations in product precision indicators such as thickness, width, and temperature, resulting in finished product dimensions and performance failing to meet user requirements. On the other hand, severe fluctuations in the looper angle between stands can frequently cause strip breakage and steel accumulation. The specific reasons for looper fluctuations between finishing mill stands are as follows:

[0003] (1) The saw-back steel undergoes a carbide solid solution process in the high-temperature section of the heating furnace, which allows the carbides to fully dissolve into the austenitic matrix, resulting in uniform grain size, hardness, and strength of the strip. However, due to the high Mo content (≥1.0%) in the saw-back steel, the required solid solution time is long. If the strip is not kept in the furnace for a sufficient time in the high-temperature section, the temperature uniformity will be poor, resulting in poor solid solution effect and uneven hardness of the strip. This can easily cause pressure fluctuations during the continuous thinning rolling process. The higher the Mo content, the more obvious this phenomenon becomes.

[0004] (2) At around 900℃ (890~920℃), M7C3 short rod-shaped alloy carbides will precipitate on the back of the saw. The precipitation of these carbides will cause uneven hardness of the strip and cause large fluctuations in the rolling pressure of the mill. At the current rolling process temperature, the precipitation area is located in the F5 and F6 stands. When the temperature is controlled too low, it will extend to the F4 stand.

[0005] (3) Impact of AGC Action: AGC refers to Automatic Thickness Control. The main function of AGC is to dynamically adjust the thickness by adjusting the rolling pressure. The main control parameter of AGC is the AGC compensation coefficient. Under normal control conditions, the larger the AGC compensation coefficient, the faster the rolling pressure correction and the higher the rolling accuracy; conversely, the smaller the AGC compensation coefficient, the slower the rolling pressure correction and the lower the rolling accuracy. When rolling saw-back steel, because the user's requirements for longitudinal thickness difference are higher than those for normal rolled strip steel (saw-back steel requires thickness fluctuation within ±0.03mm), the AGC coefficient is taken at its maximum value. However, in the actual rolling process, due to the large fluctuation of rolling pressure, when the AGC compensation coefficient is too large, it will cause a larger fluctuation of rolling pressure and a larger fluctuation of looper; at the same time, it will also cause a large fluctuation of thickness, and the thickness accuracy will be reduced, which will not meet the user's requirements. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preventing looper fluctuations between stands in a saw-back steel finishing mill, thereby solving the problem of irregular fluctuations in rolling pressure and looper angles between stands in a finishing mill, which leads to extremely unstable strip rolling.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preventing fluctuations in the looper between stands of a saw back steel finishing mill includes the following:

[0009] (1) The furnace dwell time of the second heating section and the soaking section is determined according to the different Mo contents of each steel grade of saw back steel. At the same time, in order to further improve the solid solution effect, the furnace temperature of the high temperature section is increased as much as possible within the performance allowable range; the higher the Mo content, the longer the furnace dwell time.

[0010] (2) In order to effectively avoid the precipitation of M7C3 short rod-shaped alloy carbides in the finishing rolling zone, the target exit temperature of roughing mill and the target exit temperature of finishing mill for each steel grade were determined.

[0011] (3) Based on the influence of the AGC compensation coefficient of each stand on the rolling accuracy and looper fluctuation, the AGC compensation coefficient of each stand is determined according to the thickness of each steel grade when there is no looper fluctuation and the thickness accuracy fully meets the requirements. When the thickness of the saw back steel TSJ31 is ≥4.0mm, the AGC compensation coefficients of stands F0~F6 are 1.2, 1.0, 1.0, 0.85, 0.8, 0.75 and 0.7 respectively; when the thickness of the saw back steel TSJ31 is 3.0mm~4.0mm, the AGC compensation coefficients of stands F0~F6 are 1.17, 0.95, 0.9, 0.75, 0.7, 0.65 and 0.6 respectively; when the thickness of the saw back steel TSJ31 is <3.0mm, the AGC compensation coefficients of stands F0~F6 are 0.97, 0.85, 0.8, 0.7, 0.6, 0.55 and 0.5 respectively; when the thickness of the saw back steel TJB is <3.0mm, the AGC compensation coefficients of stands F0~F6 are 0.97, 0.85, 0.8, 0.7, 0.6, 0.55 and 0.5 respectively. When the thickness of the saw back steel TSJ31 is the same, the AGC compensation coefficients of each frame are the same; when the thickness of the saw back steel TSJ33 is ≥4.0mm, the AGC compensation coefficients of frames F0~F6 are 1.2, 1.1, 1.0, 0.88, 0.83, 0.77 and 0.72 respectively; when the thickness of the saw back steel TSJ33 is 3.0mm~4.0mm, the AGC compensation coefficients of frames F0~F6 are 1 respectively. 19, 1.0, 0.9, 0.77, 0.72, 0.65 and 0.6; When the thickness of the saw back steel TSJ33 is <3.0mm, the AGC compensation coefficients of frames F0~F6 are 0.99, 0.87, 0.83, 0.7, 0.6, 0.55 and 0.5 respectively; When the thickness of saw back steel TSJ35, saw back steel TJB34 and saw back steel TSJ33 is the same, the AGC compensation coefficients of each frame are the same.

[0012] Preferably, in (1), the Mo content of the saw back steel TJB32 is 1.29%-1.34%, the secondary furnace temperature is 1270±20℃, the secondary furnace dwell time is not less than 70 minutes, and the soaking furnace temperature is 1260±20℃. The soaking furnace dwell time is not less than 65 minutes; the Mo content of the saw back steel TJB34 is 1.05%-1.20%, the secondary furnace temperature is 1290±20℃, the secondary furnace dwell time is not less than 60 minutes, and the soaking furnace temperature is 1280±20℃. The soaking furnace dwell time is not less than 50 minutes; the Mo content of the saw back steel TSJ31 is 1.28%-1.33%, the secondary furnace temperature is 1290±20℃, the secondary furnace dwell time is not less than 68 minutes, and the soaking furnace temperature is 1280±20℃. The soaking time in the furnace should be no less than 65 minutes; for TSJ33 sawn back steel with a Mo content of 1.25%-1.30%, the secondary furnace temperature should be 1290±20℃, the secondary furnace time should be no less than 65 minutes, and the soaking furnace temperature should be 1280±20℃. The soaking time in the furnace should be no less than 60 minutes; for TSJ35 sawn back steel with a Mo content of 1.05%-1.25%, the secondary furnace temperature should be 1280±20℃, the secondary furnace time should be no less than 60 minutes, and the soaking furnace temperature should be 1270±20℃. The soaking time in the furnace should be no less than 55 minutes.

[0013] Preferably, in (2), the roughing exit temperature of the saw back steel TJB32 is 1110±20℃ and the finishing exit temperature is 920±20℃, the roughing exit temperature of the saw back steel TJB34 is 1130±20℃ and the finishing exit temperature is 930±20℃, the roughing exit temperature of the saw back steel TSJ31 is 1130±20℃ and the finishing exit temperature is 930±20℃, the roughing exit temperature of the saw back steel TSJ33 is 1130±20℃ and the finishing exit temperature is 930±20℃, and the roughing exit temperature of the saw back steel TSJ35 is 1120±20℃ and the finishing exit temperature is 930±20℃.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0015] (1) The method of the present invention determines the furnace dwell time and target furnace temperature in the high-temperature section of the heating furnace based on the difference in Mo content. The strip steel has sufficient dwell time in the high-temperature section, good temperature uniformity, and improved solid solution effect. The strip steel has uniform hardness and avoids large fluctuations in pressure and looper angle during rolling.

[0016] (2) The method of the present invention re-determines the roughing mill exit temperature and the finishing mill exit temperature to prevent the precipitation of M7C3 short rod type alloy carbides, ensure uniform strip hardness, and avoid large fluctuations in mill rolling pressure and looper angle.

[0017] (3) Based on the thickness of each steel grade, the AGC compensation coefficient of each stand is determined, the rolling pressure adjustment rate is corrected, the rolling pressure is prevented from fluctuating more significantly, and the looper angle is prevented from fluctuating more significantly, thus improving the rolling accuracy. This fundamentally solves the problem of large fluctuations in the looper angle when saw back steel is rolled on the finishing mill stand. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments, but the present invention is not limited to the scope of the embodiments described herein.

[0019] Experimental methods in the following examples that do not specify specific conditions were performed according to conventional methods and conditions. Example 1

[0020] This embodiment uses TJB32 steel for rolling saw back steel, coil number: 941053201, billet thickness: 220mm, billet width: 1030mm. The main chemical composition (%) is: C: 0.307; Si: 0.238; Mn: 0.998; Cr: 3.982; Ni: 0.751; Mo: 1.315. The target thickness of the finished product is 3.4mm, and the target width of the finished product is 1005mm.

[0021] A method for preventing fluctuations in the looper between stands of a saw back steel finishing mill includes the following:

[0022] (1) The furnace temperature and furnace dwell time in the high-temperature section are controlled as shown in the table below:

[0023]

[0024] (2) Target temperature for rough rolling: 1110℃; actual temperature after rough rolling: 1113℃; target temperature for finish rolling: 920℃;

[0025] (3) The AGC compensation coefficients for each stand (F0~F6) in the finishing mill are as follows: 1.17, 0.95, 0.9, 0.75, 0.7, 0.65, and 0.6, respectively. After the finishing mill calculation is completed, the relevant calculation parameters for each stand are shown in the table below:

[0026]

[0027] Note: All rack outlet thicknesses are calorific values.

[0028] During the rolling process of this steel block, there was no pressure fluctuation in the rolling pressure of each stand, and the looper angle between each stand remained stable without fluctuation. The actual exit temperature of the finishing mill was 924℃, the actual thickness of the finished product was 3.40mm, and the actual width was 1012mm. The rolling accuracy met the user's requirements. Example 2

[0029] This embodiment uses TJB32 steel for rolling saw back steel, coil number: 943127309, billet thickness: 230mm, billet width: 1030mm. The main chemical composition (%) is: C: 0.314; Si: 0.257; Mn: 0.994; Cr: 3.95; Ni: 0.759; Mo: 1.332. The target thickness of the finished product is 4.0mm, and the target width is 1005mm.

[0030] A method for preventing fluctuations in the looper between stands of a saw-back steel finishing mill includes the following:

[0031] (1) The furnace temperature and furnace dwell time in the high-temperature section are controlled as shown in the table below:

[0032]

[0033] (2) Target temperature for rough rolling: 1110℃; The actual temperature after rough rolling is 1114℃; Target temperature for finish rolling: 920℃.

[0034] (3) The AGC compensation coefficients for each stand (F0~F6) in the finishing mill are as follows: 1.2, 1.0, 1.0, 0.85, 0.8, 0.75, and 0.7. After the finishing mill calculation is completed, the relevant calculation parameters for each stand are shown in the table below:

[0035]

[0036] Note: All rack outlet thicknesses are calorific values.

[0037] During the rolling process of this steel block, there was no pressure fluctuation in the rolling pressure of each stand, and the looper angle between each stand remained stable without fluctuation. The actual exit temperature of the finishing mill was 922℃, the actual thickness of the finished product was 4.03mm, and the actual width was 1013mm. The rolling accuracy met the user's requirements. Example 3

[0038] This embodiment uses TJB34 steel for rolling saw back steel, coil number: 942161702, billet thickness: 222mm, billet width: 1030mm. The main chemical composition (%) is: C: 0.353; Si: 0.27; Mn: 0.955; Cr: 3.975; Ni: 0.755; Mo: 1.13. The target thickness of the finished product is 3.5mm, and the target width is 1005mm.

[0039] A method for preventing fluctuations in the looper between stands of a saw-back steel finishing mill includes the following:

[0040] (1) The furnace temperature and furnace dwell time in the high-temperature section are controlled as shown in the table below:

[0041]

[0042] (2) Target temperature for rough rolling: 1130℃; The actual temperature after rough rolling is 1128℃; Target temperature for finish rolling: 930℃.

[0043] (3) The AGC compensation coefficients for each stand (F0~F6) in the finishing mill are as follows: 1.19, 1.0, 0.9, 0.77, 0.72, 0.65, and 0.6, respectively. After the finishing mill calculation is completed, the relevant calculation parameters for each stand are shown in the table below:

[0044]

[0045] Note: All rack outlet thicknesses are calorific values.

[0046] During the rolling process of this steel block, there was no pressure fluctuation in the rolling pressure of each stand, and the looper angle between each stand remained stable without fluctuation. The actual exit temperature of the finishing mill was 932℃, the actual thickness of the finished product was 3.51mm, and the actual width was 1011mm. The rolling accuracy met the user's requirements. Example 4

[0047] This embodiment uses TSJ31 steel for rolling saw back steel, coil number: 943110901, billet thickness: 230mm, billet width: 1030mm. The main chemical composition (%) is: C: 0.333; Si: 0.253; Mn: 1.005; Cr: 3.928; Ni: 0.752; Mo: 1.322. The target thickness of the finished product is 2.9mm, and the target width is 1000mm.

[0048] A method for preventing fluctuations in the looper between stands of a saw-back steel finishing mill includes the following:

[0049] The furnace temperature and dwell time in the high-temperature section are controlled as shown in the table below:

[0050]

[0051] (2) Target temperature for rough rolling: 1130℃; The actual temperature after rough rolling is 1132℃; Target temperature for finish rolling: 930℃.

[0052] (3) The AGC compensation coefficients for each stand (F0~F6) in the finishing mill are as follows: 0.97, 0.85, 0.8, 0.7, 0.6, 0.55, and 0.5, respectively. After the finishing mill calculation is completed, the relevant calculation parameters for each stand are shown in the table below:

[0053]

[0054] Note: All rack outlet thicknesses are calorific values.

[0055] During the rolling process of this steel block, there was no pressure fluctuation in the rolling pressure of each stand, and the looper angle between each stand remained stable without fluctuation. The actual exit temperature of the finishing mill was 931℃, the actual thickness of the finished product was 2.89mm, and the actual width was 1008mm. The rolling accuracy met the user's requirements. Example 5

[0056] This embodiment uses TSJ33 steel for rolling saw back steel, coil number: 941063902, billet thickness: 230mm, billet width: 1090mm. The main chemical composition (%) is: C: 0.327; Si: 0.27; Mn: 1.019; Cr: 3.981; Ni: 0.754; Mo: 1.276. The target thickness of the finished product is 3.0mm, and the target width of the finished product is 1070mm.

[0057] A method for preventing fluctuations in the looper between stands of a saw-back steel finishing mill includes the following:

[0058] (1) The furnace temperature and furnace dwell time in the high-temperature section are controlled as shown in the table below:

[0059]

[0060] (2) Target temperature for rough rolling: 1130℃; The actual temperature after rough rolling is 1129℃; Target temperature for finish rolling: 930℃.

[0061] (3) The AGC compensation coefficients for each stand (F0~F6) in the finishing mill are as follows: 1.19, 1.0, 0.9, 0.77, 0.72, 0.65, and 0.6, respectively. After the finishing mill calculation is completed, the relevant calculation parameters for each stand are shown in the table below:

[0062]

[0063] Note: All rack outlet thicknesses are calorific values.

[0064] During the rolling process of this steel block, there was no pressure fluctuation in the rolling pressure of each stand, and the looper angle between each stand remained stable without fluctuation. The actual exit temperature of the finishing mill was 930℃, the actual thickness of the finished product was 2.98mm, and the actual width was 1077mm. The rolling accuracy met the user's requirements. Example 6

[0065] This embodiment uses TSJ35 steel for rolling saw back steel, coil number: 949065101, billet thickness: 230mm, billet width: 1050mm. The main chemical composition (%) is: C: 0.34; Si: 0.30; Mn: 1.001; Cr: 4.102; Ni: 0.825; Mo: 1.151. The target thickness of the finished product is 2.8mm, and the target width is 1030mm.

[0066] A method for preventing fluctuations in the looper between stands of a saw-back steel finishing mill includes the following:

[0067] (1) The furnace temperature and furnace dwell time in the high-temperature section are controlled as shown in the table below:

[0068]

[0069] (2) Target temperature for rough rolling: 1120℃; The actual temperature after rough rolling is 1127℃; Target temperature for finish rolling: 930℃.

[0070] (3) The AGC compensation coefficients for each stand (F0~F6) in the finishing mill are: 0.99, 0.87, 0.83, 0.7, 0.6, 0.55, and 0.5, respectively. After the finishing mill calculation is completed, the relevant calculation parameters for each stand are shown in the table below:

[0071]

[0072] Note: All rack outlet thicknesses are calorific values.

[0073] During the rolling process of this steel block, there was no pressure fluctuation in the rolling pressure of each stand, and the looper angle between each stand remained stable without fluctuation. The actual exit temperature of the finishing mill was 934℃, the actual thickness of the finished product was 2.78mm, and the actual width was 1039mm. The rolling accuracy met the user's requirements.

[0074] After the implementation of this technology, the amount of scrap caused by looper fluctuations between stands has been reduced by more than 1,800 tons per month. At the same time, the variety and specifications of saw back steel have been further expanded, with the thickness increased from more than 3.0 mm to 2.8 mm, resulting in significant economic benefits.

Claims

1. A method for preventing looper fluctuations between stands in a saw-back steel finishing mill, characterized in that, Includes the following: (1) The furnace dwell time of the second heating section and the soaking section is determined according to the different Mo contents of each steel grade of saw back steel. At the same time, in order to further improve the solid solution effect, the furnace temperature of the high temperature section is increased as much as possible within the performance allowable range; the higher the Mo content, the longer the furnace dwell time. (2) In order to effectively avoid the precipitation of M7C3 short rod-shaped alloy carbides in the finishing rolling zone, the target exit temperature of roughing mill and the target exit temperature of finishing mill for each steel grade were determined. (3) Based on the influence of the AGC compensation coefficient of each stand on the rolling accuracy and looper fluctuation, the AGC compensation coefficient of each stand is determined according to the thickness of each steel grade when there is no looper fluctuation and the thickness accuracy fully meets the requirements. When the thickness of the saw back steel TSJ31 is ≥4.0mm, the AGC compensation coefficients of stands F0~F6 are 1.2, 1.0, 1.0, 0.85, 0.8, 0.75 and 0.7 respectively; the thickness of the saw back steel TSJ31 is 3.0mm~4.0mm. When the thickness of the saw back steel TSJ31 is <3.0mm, the AGC compensation coefficients for frames F0 to F6 are 1.17, 0.95, 0.9, 0.75, 0.7, 0.65, and 0.6, respectively; when the thickness of the saw back steel TSJ31 is <3.0mm, the AGC compensation coefficients for frames F0 to F6 are 0.97, 0.85, 0.8, 0.7, 0.6, 0.55, and 0.5, respectively; when the thickness of the saw back steel TJB32 and the saw back steel TSJ31 is the same, the AGC compensation coefficients for each frame are the same. When the thickness of the TSJ33 backing steel is ≥4.0mm, the AGC compensation coefficients for frames F0~F6 are 1.2, 1.1, 1.0, 0.88, 0.83, 0.77 and 0.72 respectively; when the thickness of the TSJ33 backing steel is 3.0mm~4.0mm, the AGC compensation coefficients for frames F0~F6 are 1.19, 1.0, 0.9, 0.77, 0.72, 0.65 and 0.6 respectively; when the thickness of the TSJ33 backing steel is <3.0mm, the AGC compensation coefficients for frames F0~F6 are 0.99, 0.87, 0.83, 0.7, 0.6, 0.55 and 0.5 respectively; when the thickness of the TSJ35, TJB34 and TSJ33 backing steels is the same, the AGC compensation coefficients for each frame are the same.

2. The method for preventing slippage between stands in a saw-back steel finishing mill according to claim 1, characterized in that, In (1), the Mo content of the saw back steel TJB32 is 1.29%-1.34%, the secondary furnace temperature is 1270±20℃, the secondary furnace dwell time is not less than 70 minutes, the soaking furnace temperature is 1260±20℃, and the soaking furnace dwell time is not less than 65 minutes; the Mo content of the saw back steel TJB34 is 1.05%-1.20%, the secondary furnace temperature is 1290±20℃, the secondary furnace dwell time is not less than 60 minutes, the soaking furnace temperature is 1280±20℃, and the soaking furnace dwell time is not less than 50 minutes; the Mo content of the saw back steel TSJ31 is 1.28%-1.33%, the secondary furnace temperature is 1290±20℃, and the secondary furnace temperature is 1290±20℃. For TSJ33 saw back steel with a Mo content of 1.25%-1.30%, the furnace temperature for the second heating process is 1290±20℃, with a furnace time of not less than 65 minutes, and the furnace temperature for the second heating process is 1280±20℃, with a furnace time of not less than 60 minutes; for TSJ35 saw back steel with a Mo content of 1.05%-1.25%, the furnace temperature for the second heating process is 1280±20℃, with a furnace time of not less than 60 minutes, and the furnace temperature for the second heating process is 1270±20℃, with a furnace time of not less than 55 minutes.

3. A method for preventing looper fluctuations between stands in a saw-back steel finishing mill according to any one of claims 1 or 2, characterized in that, In (2), the roughing exit temperature of TJB32 saw back steel is 1110±20℃, and the finishing exit temperature is 920±20℃; the roughing exit temperature of TJB34 saw back steel is 1130±20℃, and the finishing exit temperature is 930±20℃; the roughing exit temperature of TSJ31 saw back steel is 1130±20℃, and the finishing exit temperature is 930±20℃; the roughing exit temperature of TSJ33 saw back steel is 1130±20℃, and the finishing exit temperature is 930±20℃; and the roughing exit temperature of TSJ35 saw back steel is 1120±20℃, and the finishing exit temperature is 930±20℃.

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