A method for controlling the shape of a low carbon equivalent 355mpa grade normalized rolled thin gauge steel plate

Abstract

The application discloses a shape control method for a low-carbon-equivalent 355MPa grade normalized rolled thin-gauge steel plate, wherein the soaking section furnace temperature of a heating furnace for a billet is 1080-1100 DEG C, the time is 45-60 minutes, the total in-furnace time is 250-300 minutes, the single-pass reduction of the last two passes of the billet finishing rolling is controlled to be 1-2mm, the steel plate is controlled to be cooled by using a laminar flow cooling system, the head shielding distance of the controlled cooling system is 500-700mm, the shielding coefficient is 0.8-1.0, the tail shielding distance is 900-1300mm, and the shielding coefficient is 0.5-0.7; and the acceleration of the controlled cooling roller is 0.004-0.006m / s 2 . The steel plate adopts a small straightening force mode, the straightening force is 15-18MK, the straightening speed is 0.3-0.8m / s, and the final straightening temperature is lower than 480 DEG C. The application solves the problems of poor flatness of the normalized rolled 355MPa grade thin-gauge low-alloy steel plate, low steel plate passing rate and influence on rolling efficiency.

Description

TECHNICAL FIELD

[0001] The application relates to a method for optimizing control of a normalizing rolling process of low-carbon-equivalent low-alloy steel, in particular to a shape control method for low-carbon-equivalent 355MPa grade normalizing rolling thin-gauge steel plates, and belongs to the technical field of plate rolling process control. BACKGROUND

[0002] The 355MPa grade low-alloy structural steel in a normalizing state is increasingly demanding on carbon equivalent, and with the decrease of the carbon equivalent, the Ar3 and Ar1 temperatures of the steel plate are correspondingly increased, leading to early phase transition. In this case, if the traditional normalizing rolling is still adopted, the ferrite grains after phase transition are grown, resulting in the decrease of the yield strength of the steel plate and the high rate of waste and inferior products.

[0003] If weak water cooling is applied after the normalizing rolling, the ferrite grains after phase transition can be inhibited from further growth without affecting the phase transition temperature, and good grain refinement effect is achieved. The normalizing rolling is higher in strength and toughness than the traditional normalizing rolling.

[0004] Although the normalizing rolling process requires that the finishing rolling temperature of the steel plate is basically in the range of 870-920 DEG C, which is usually higher than the TMCP process, and is advantageous to the control of the shape, for the 355MPa grade low-alloy steel with low carbon equivalent, the decrease of the carbon equivalent leads to early ferrite phase transition, and the Ar3 temperature is about 813 DEG C. The thin-gauge normalizing rolling steel plate below 20mm usually adopts multiple-size rolling, and the size number reaches 5 at most. The length of the rolled piece in the last three rolling processes is more than 40 meters, leading to large temperature drop of the edge and head-tail of the rolled piece, large temperature difference of the same plate, early phase transition in the local low-temperature area, large difference between the deformation resistance of ferrite and the deformation resistance of low-temperature austenite, large temperature drop of the rolled piece in the last several forming rolling processes, and increased rolling force, so that the shape of the rolled piece is not easy to control, and single-side wave, double-side wave and center wave and other shape defects are easily generated. The batches with the above-mentioned shape defects cannot be completely flattened through hot straightening, leading to the out-of-standard flatness. If the "normalizing rolling+weak water cooling" process is adopted, due to the thinness of the steel plate, the temperature of the steel plate is rapidly dropped after water spraying, the surface temperature of the steel plate is less than 600 DEG C before hot straightening, the deformation resistance is greatly increased, the broken wave of the steel plate is difficult to completely flatten through hot straightening, the steel plate with wave defects cannot pass the online inspection, and the one-time passing rate of the steel plate is seriously affected, so that the rolling efficiency is greatly reduced, and the delivery period of the steel plate is prolonged.

[0005] Therefore, how to solve the shape problem of the 20mm-thick steel plate with carbon equivalent below 0.30% under the normalizing rolling process, and improve the one-time passing rate of the steel plate is the key to the development and application of the 355MPa grade thin-gauge normalizing rolling steel plate with low carbon equivalent.

[0006] At present, the related patents about the shape control method of thin gauge steel plate are as follows:

[0007] The Q345E steel plate shape control method applied by Baotou Steel (application number: 201510012842.3) mainly relates to a low-carbon equivalent 8mm thick Q345E steel plate, the mass percentage composition of which is: C: 0.06-0.08%, Mn: 1.35-1.55%, Si: 0.35-0.48%, Nb: 0.02-0.04%, the balance being Fe and unavoidable impurities, the finish rolling temperature is 880-910℃, and hot straightening is carried out after rolling, and the Q345E steel plate is cooled offline. The Q345E steel plate of the invention adopts low-carbon equivalent design, and the phase change ferrite grains will further grow during the air cooling process after rolling if no water is poured at this finish rolling temperature, which seriously affects the Cpk value of strength and elongation.

[0008] The shape control method of low-cost yield strength 355MPa grade thin steel plate applied by Anshan Steel (application number: 202210897032.0) mainly relates to the shape control of 6-10mm thin gauge steel plate TMCP process rolling, the finish rolling temperature is 750-860℃, and the laminar flow and hot straightening parameters are limited. According to the invention, the surface red temperature of the steel plate below 10mm is difficult to reach above 600℃, and the straightening force is 18000-20000kN. The deformation resistance of the head, tail and edge of the steel plate exceeds the straightening force, and the edge wave cannot be straightened.

[0009] The shape control method of yield strength 235MPa grade thin steel plate applied by Anshan Steel (application number: 202210897286.2) mainly relates to the shape control technology of 5-10mm thick thin gauge plate under straight rolling process, the finish rolling temperature is 800-960℃, and the step cooling bed preheating method is used to solve the problem of uneven heat transfer on the upper and lower surfaces of the steel plate, and a lower finish straightening temperature is set to avoid phase change after hot straightening. This method has certain reference significance for the normalized rolling steel plate which does not need to be water cooled after rolling, but for the normalized rolling steel plate which needs to be water cooled after normalized rolling, the difference in red temperature of the head and tail of the steel plate will affect the distribution of straightening force, and the steel plate will have a large thermal stress after straightening, which is easy to deform again after stress release on the cooling bed. SUMMARY

[0010] The purpose of the present application is to provide a low-carbon equivalent 355MPa grade normalized rolling thin gauge steel plate shape control method, which solves the problems of poor flatness of 355MPa grade thin gauge low alloy steel plate, low steel plate pass rate, and affects the rolling efficiency. At the same time, the shape problem will also lead to an increase in the rate of waste and defective products.

[0011] To solve the above problems, the technical scheme adopted by the present application is as follows:

[0012] A low-carbon equivalent 355MPa grade normalized rolled thin gauge steel plate shape control method, comprising billet heating, billet rolling, steel plate cooling, and steel plate straightening, wherein,

[0013] 1) The billet is heated in the soaking section of the heating furnace, the furnace temperature is 1080-1100 DEG C, the soaking section time is 45-60 minutes, and the total furnace time is 250-300 minutes.

[0014] The soaking section temperature is set to 1080-1100 DEG C, the total furnace time is 250-300 minutes, and the soaking time is greater than 45 minutes, which aims to reduce the temperature difference between the soaking section and the billet as much as possible, so that the overall temperature of the billet approaches the range of 1080-1100 DEG C, and at the same time, the use of low-temperature soaking and low-temperature tapping rolling can reduce the end temperature of rough rolling, and the internal thermal stress of the rolled piece can be reduced by reducing the deformation temperature in the rough rolling stage, which is beneficial to the control of the plate shape in the finishing rolling.

[0015] 2) The single pass reduction amount of the billet in the last 2 passes of finishing rolling is controlled to be 1-2 mm; the single pass reduction amount of the billet in the last 2 passes is controlled by installing a high-precision thickness gauge and a speed meter at the outlet of the rolling mill after rolling, and the displacement sensor installed at the neck of the roll is started before the last 3 passes of finishing rolling, and the real-time load roll gap is obtained during the passage of the rolled piece through the rolling mill, the points with the transverse thickness roll gap value exceeding the standard are selected, compared with the target roll gap setting thickness, the multi-point load roll gap adjustment amount of the last 2 passes is obtained, and the AGC hydraulic cylinder adjustment amount is converted; specifically, before the last 2 passes of finishing rolling, the four column hydraulic cylinders of the rolling mill reach the given position according to the set roll gap value, and during the process of throwing the rolled piece, the thickness value of the rolled piece measured by the thickness gauge at the outlet of the rolling mill is sent to the position controller (PID regulator), and the output value of the position controller and the output value of the pressure controller with the pressure limit reference as the set value are sent to the comparator, and the smaller one of the two is output to the servo amplifier as the given value, and then the servo valve is driven, so that the up and down movement of the hydraulic cylinder is controlled to adjust the hydraulic cylinder roll gap setting on line. After the last 2 passes of rolling are completed, the real-time load roll gap value of the last 2 passes is compared with the roll gap setting value of the last 2 passes, and the hydraulic servo valve program is adjusted again to adjust the hydraulic cylinder roll gap of the last 1 pass, and the last 1 pass is rolled, and finally the rolled piece plate shape is adjusted on line by finishing rolling with load reduction in the last 2 passes, and the biting speed in the last 2 passes of finishing rolling is controlled to be 1.5-1.8 m / s -1 , and the rolling speed is controlled to be 2.0-2.2 m / s -1 .

[0016] The single-pass reduction of the last two passes is controlled at 1-2 mm, and the purpose is to ensure that the rolling piece is mainly surface deformation, and the center wave and edge wave are eliminated through the lateral flow of the surface metal of the steel plate, and the pre-straightening of the steel plate is completed through the single-pass variable load roll gap design. The pre-straightening of the steel plate is realized through the small reduction rate of the last two passes, the real-time adjustment of the multi-point roll gap, and the single-pass dynamic variable load roll gap design, which replaces the traditional pre-straightening machine. The advantages are as follows: on the one hand, the characteristics of the uniform non-recrystallized austenite grain structure before the end of the finishing rolling are utilized to ensure the uniform lateral flow of the metal, and the steel plate adopting the traditional pre-straightening process often has a ferrite phase change during pre-straightening, and the uneven distribution of the lateral temperature gradient will cause the non-uniformity of the phase change, and the difference in the structure will cause the difference in the strength of the steel plate, thereby causing the uneven lateral flow of the metal, and the pre-straightening machine is difficult to solve the problem of the rolling edge wave; on the other hand, the pre-straightening machine is replaced by the variable roll gap design of the last two passes of the finishing rolling, and the pre-straightening machine is not needed to be repeatedly invested, thereby reducing the process and equipment costs and improving the rolling efficiency.

[0017] 3) Steel plate cooling, the steel plate adopts a laminar flow cooling system to control cooling, and head and tail shielding is adopted for the investment of the control cooling system: the head shielding distance is 500-700 mm, and the shielding coefficient is 0.8-1.0; the tail shielding distance is 900-1300 mm, and the shielding coefficient is 0.5-0.7; the control cooling roller acceleration is 0.004-0.006 m / s 2 .

[0018] Since the thin-gauge steel plate below 20 mm has a length of more than 40 m, the steel plate runs on the conveying roller of the laminar flow cooling system for a long time, and the interval time of the head and tail water inlet is long, which is 15-25 s. Since the longitudinal air cooling time of the steel plate is inconsistent, the water inlet temperature difference is large, and therefore the acceleration of 0.004-0.006 m / s 2 is set to reduce the interval time of the head and tail water inlet, and the heat dissipation of the head and tail positions is fast, and therefore the head and tail shielding technology needs to be invested, the head and tail regions of the rolling piece are respectively set to the shielding distance and the shielding coefficient according to the above parameter range, the water amount of the head and tail regions is set to be reduced in advance, the whole plate surface temperature difference is reduced, the thermal stress of the rolling piece head and tail is reduced, and therefore the plate shape problem after the thermal straightening is avoided. The finishing rolling is performed in the normalizing heat treatment temperature range, and the weak water cooling is cooperated, the head and tail shielding and the roller acceleration process parameters are designed in the weak water cooling process, the thermal stress of the control cooling steel plate is always within the controllable range, and the stress release after the thermal straightening is avoided to cause the deformation of the steel plate on the cooling bed again.

[0019] 4) Steel plate straightening, a small straightening force mode is adopted, the straightening force is 15-18 MK, and the straightening speed is 0.3-0.8 m·s -1 The final straightening temperature is less than 480℃.

[0020] The reason for setting the straightening force 15-18MK is that: after normalizing rolling, water cooling is adopted, the steel plate has certain residual stress after cooling, and the large straightening force mode will cause the residual stress to further increase after hot straightening, and for the thin gauge steel plate below 20mm, the stress resistance is weak, and the deformation on the cooling bed is more likely to occur, therefore, the small straightening force mode is adopted in the present application, which can completely flatten the wave area, and at the same time, does not increase the residual stress, by limiting the straightening speed and the final straightening temperature, the residual stress can be fully released during the straightening, and the deformation on the cooling bed does not occur any more, which ensures the good flatness of the steel plate.

[0021] The design 0.3-0.8m·s -1 The straightening speed and the final straightening temperature are less than 480℃, the purpose is to reduce the straightening rhythm, the phase change stress release and the thermal stress release are performed in the relatively long time during the straightening process, and when the final straightening temperature is lower than 480℃, the rolled piece can continue to generate phase change stress on the cooling bed to cause secondary deformation.

[0022] The small straightening force mode is adopted in the hot straightening process, and the corresponding straightening speed and the final straightening temperature are given, which avoids the large increase of the residual stress caused by the hot straightening deformation, and the residual curvature and the plastic deformation rate of the steel plate are optimally matched, and the steel plate will not generate secondary deformation due to the non-uniform cooling of the lower surface of the steel plate on the cooling bed after the hot straightening.

[0023] Further, the chemical composition of the steel billet is that: C: 0.08%-0.12%, Si: 0.20%-0.35%, Mn: 0.90%-1.25%, Nb: 0.02%-0.03%, P: less than 0.030%, S: less than 0.025%, and the rest is Fe and unavoidable inclusions. The carbon equivalent of the steel plate is 0.30% or less, and the yield strength is 355-390MPa.

[0024] Further, the steel billet is a continuous casting billet, the thickness of the casting billet is 130-250mm, and the thickness of the steel plate obtained after rolling is 6-20mm.

[0025] Considering that the multiple lengths of the finished plate are more than 40 meters, the pure rolling time of the rolled piece through the rolling mill in each pass is basically 14-18s, which seriously affects the rolling efficiency, and the surface temperature of the rolled piece in the last few passes of the finishing rolling is seriously reduced, because the heat dissipation conditions of the head and tail positions and the center position of the rolled piece are inconsistent, there is always a temperature difference of 40-60℃ between the head and tail and the center position, and the cumulative deformation caused by the large reduction rate of the single pass of the rough rolling and the finishing rolling will cause the head and tail to be raised, the present application limits the thickness of the continuous casting billet to 130-250mm, which can ensure that the rolling pass number of the single pass of the rough rolling and the finishing rolling is reduced under the premise of meeting the rolling compression ratio, and the head and tail raising phenomenon caused by the temperature difference of the head and tail and the cumulative deformation of the large reduction rate is reduced.

[0026] Further, the heating furnace is a walking beam heating furnace, the billet stays in the preheating section for 25-30 minutes, the billet stays in the heating 1 section furnace at a temperature of 930-950℃ for 75-90 minutes; and stays in the heating 2 section furnace at a temperature of 1100-1120℃ for 110-130 minutes.

[0027] Further, the bite speed of the last 2 passes of the finishing rolling is controlled at 1.5-1.8m / s -1 , and the rolling speed is controlled at 2.0-2.2m / s -1 .

[0028] The bite speed of the last 2 passes of the finishing rolling is selected at 1.5-1.8m / s -1 , so as to reduce the speed fluctuation of the up and down main motors of the rolling mill in the bite stage of the steel plate and reduce the wavy defects in the head region of the rolled piece.

[0029] The rolling speed is selected at 2.0-2.2m / s -1 and the roll cooling water is turned off, so as to consider that the roll gap changing rolling under the conditions of the faster rolling speed and the roll cooling water cooling will cause the complex change of the rigidity of the rolling mill, and the appropriate reduction of the rolling speed can reduce the influence of the elastic recovery of the rolled piece and the roll flattening on the rigidity of the rolling mill in the straightening process of the load roll gap.

[0030] Further, the billet opening rolling temperature is 1000-1050℃, the finish rolling temperature is 800-850℃, and the roll cooling water is turned off in advance before the bite of the rolled piece in the last 2 passes of the finishing rolling.

[0031] Further, the programming control of the hydraulic servo valve includes that before the bite of the rolled piece in the last 2 passes of the finishing rolling, the four column hydraulic cylinders of the rolling mill reach the given position according to the set roll gap value, and the thickness value of the rolled piece measured by the thickness gauge at the outlet of the rolling mill is sent to the position controller (PID regulator) during the throwing of the rolled piece, the output value of the position controller and the output value of the pressure controller with the pressure limit reference as the set value are both sent to the comparator, the smaller one of the two is output as the given value to the servo amplifier, and then the servo valve is driven, so as to control the up and down movement of the hydraulic cylinder and adjust the roll gap adjustment setting of the hydraulic cylinder on line.

[0032] Further, the fixed procedure water injection mode is adopted for the controlled cooling system, 1-2 groups of headers are opened, the water quantity of each group of headers is 180-240m 3 / h, and the water flow ratio of the upper and lower headers is 1:1.8-2.0.

[0033] Considering that there is a temperature difference of about 40-60 DEG C between the center and the edge of the steel plate during the cooling process from the rolling to the water entry of the steel plate below 20mm, the shrinkage of the center is greater than that of the edge, thus the edge wave phenomenon is generated, at this time, the water ratio of 1:1.8-2.0 is set in the laminar cooling process, the cooling rate of the upper surface is greater than that of the lower surface, the further shrinkage of the center of the steel plate in the weak water cooling process is inhibited, the thermal stress of the center of the steel plate is reduced, thus the further bending trend of the steel plate is reduced, and the heat straightening pressure is reduced.

[0034] Further, the points with the transverse thickness tolerance range of 0.5mm-5mm are screened out.

[0035] Further, the steel plate grain size reaches above 8.5 level, and the flatness is below 5mm / 2m.

[0036] Compared with the prior art, the beneficial effects of the present application are:

[0037] The present application is to meet the demand of the 355MPa grade low alloy steel below 20mm in thickness for the large line energy welding once forming, the component design is to reach the carbon equivalent below 0.30%, good plate shape, no residual stress, grain size above 8.5 level, and the performance reaches the normalized structure requirement, therefore the 'normalizing rolling + weak water cooling' process is adopted, the intermediate billet thermal stress in the rolling process is reduced by reducing the heating temperature, the on-line straightening is realized by changing the roll gap in the last two passes of the finishing rolling, the laminar cooling and the optimization of the heat straightening parameters, the single edge wave, double edge wave and center wave and other plate shape defects of the thin gauge steel plate below 20mm are successfully solved, and finally the 6-20mm low carbon equivalent 355MPa grade low alloy steel normalized rolling high flatness, thin gauge, meeting the user demand of the large line energy welding once forming is realized. DETAILED DESCRIPTION

[0038] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The described embodiments are only a part of the embodiments of the present application, not all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the present application.

[0039] The low-carbon-equivalent normalized rolled steel plate shape control method of the application is suitable for a 6-20mm-thick, 0.30% or less carbon equivalent, 355MPa-grade low-alloy steel medium plate.

[0040] The steel plate thickness of the application is 6-20mm.

[0041] The steel billet of the application is a continuous casting billet with a thickness of 130-250mm.

[0042] The billet is set to a temperature of 930-950℃ in the first heating furnace, 1100-1120℃ in the second heating furnace, and 1080-1100℃ in the soaking furnace.

[0043] The billet is kept in the preheating section for 25-30 minutes, in the first heating section for 75-90 minutes, in the second heating section for 110-130 minutes, and in the soaking section for 45-60 minutes, with a total furnace time of 250-300 minutes.

[0044] The single-pass reduction of the last two passes of the billet is controlled to be 1-2mm.

[0045] The application tracks the rolled piece by installing a high-precision thickness gauge and a speed meter at the exit of the rolling mill, starts the displacement sensor installed at the roll neck before the third pass of the finishing rolling, obtains the real-time load roll gap during the rolling of the rolled piece, screens the points with a transverse thickness tolerance exceeding 0.5mm, compares them with the target roll gap set thickness, obtains the multi-point load roll gap adjustment amount of the second last pass, converts it into the hydraulic cylinder adjustment amount, adjusts the hydraulic cylinder roll gap adjustment setting through the programming control of the hydraulic servo valve before the rolled piece is bitten in the second last pass of the finishing rolling, and completes the online adjustment of the rolled piece shape in the last two passes of the finishing rolling.

[0046] To meet the online shape adjustment effect of the last two passes of the finishing rolling, the biting speed of the rolled piece in the last two passes needs to be controlled to be 1.5-1.8m·s -1 , the rolling speed is controlled to be 2.0-2.2m·s -1 , and the roll cooling water is closed in advance before the rolled piece is bitten in the last two passes of the finishing rolling.

[0047] The cooling of the steel plate is realized by using a laminar flow cooling system, the controlled cooling mode adopts fixed procedure watering, 1-2 groups of header are opened, the water quantity of each group of header is 180-240 m 3 / h; the upper and lower header water flow ratio is 1:1.8-2.0; the head shielding distance of the controlled cooling system is 500-700 mm, the shielding coefficient is 0.8-1.0; the tail shielding distance is 900-1300 mm, the shielding coefficient is 0.5-0.7; the acceleration of the controlled cooling roller is 0.004-0.006 m / s2.

[0048] The steel plate is heated by using a small straightening force mode, the straightening force is 15-18 MK, the straightening speed is 0.3-0.8 m / s, and the final straightening temperature is less than 480 DEG C.

[0049] The present application provides a kind of single rack four-roll reversible plate mill shape control method for normalizing 6-20 mm thick thin gauge plate, especially provides a kind of 355MPa grade hot rolled low alloy steel thin gauge plate shape control method with carbon equivalent below 0.30%.The steel plate is free of various wave defects after hot straightening, and the flatness is high, the steel plate pass rate is 100%, and there is no need to go to cold straightening, effectively solves the low hot straightening temperature of the thin gauge steel plate of normalizing controlled cooling rolling, which causes the poor flatness of the steel plate, the low steel plate pass rate, the slow rolling rhythm, and the high waste and defective product rate.

[0050] The present application will be further described in detail below in combination with specific embodiments.

[0051] A kind of low carbon equivalent 355MPa grade normalizing thin gauge steel plate shape control method, specific implementation is as follows:

[0052] The chemical composition of the blank and the nominal thickness of the rolled steel plate of each embodiment are shown in Table 1.

[0053] Table 1: Chemical composition of steel billet and nominal thickness of steel plate of each embodiment

[0054]

[0055] The heating condition in the heating furnace of each embodiment is shown in Table 2.

[0056] Table 2: Steel billet heating condition of each embodiment

[0057]

[0058] The real-time dynamic multi-point load roll gap adjustment of the last 3 passes is shown in Table 3.

[0059] Table 3: Real-time dynamic multi-point roll gap adjustment value of the last 3 passes

[0060]

[0061] The last two passes bite-in speed, rolling speed and reduction of each embodiment are shown in Table 4.

[0062] Table 4 Rolling speed control and reduction of each embodiment

[0063]

[0064]

[0065] The controlled cooling condition of each embodiment is shown in Table 5.

[0066] Table 5 ACC controlled cooling process parameters of each embodiment

[0067]

[0068] The hot straightening condition of each embodiment is shown in Table 6.

[0069] Table 6 Straightening process parameters

[0070] Example Straightening force / MK straightening speed / m·s -1 ]]> Final straightening temperature / °C 1 15.5 0.77 380 2 16.1 0.58 414 3 17.3 0.41 449 4 17.8 0.32 475

[0071] The mechanical properties, flatness and grain size condition of each embodiment are shown in Table 7.

[0072] Table 7 Performance, flatness and grain size evaluation of each embodiment

[0073]

[0074] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of each embodiment of the present application.

Claims

1. A method for controlling the shape of a low carbon equivalent 355 MPa grade normalized rolled thin gauge steel plate, comprising billet heating, billet rolling, steel plate cooling, and steel plate straightening, characterized in that, the chemical composition of the billet is, by weight percent, C: 0.08% to 0.12%, Si: 0.20% to 0.35%, Mn: 0.90% to 1.25%, Nb: 0.02% to 0.03%, P < 0.030%, S < 0.025%, and the balance being Fe and unavoidable inclusions; the carbon equivalent of the steel plate is 0.30% or less; the billet is heated, the billet is held at a soaking section furnace temperature of 1080 to 1100°C in a heating furnace, the soaking section is held for 45 to 60 minutes, and the total furnace time is 250 to 300 minutes; The billet is rolled, the billet opening rolling temperature is 1080-1100 DEG C, the final rolling temperature is 800-850 DEG C, the roll cooling water is closed in advance before the last two passes of the finishing rolling piece bites; the single pass reduction amount of the last two passes of the billet finishing rolling is controlled to be 1-2 mm; the single pass reduction amount of the last two passes of the billet is controlled, the high-precision thickness gauge and the speed meter installed at the rolling mill outlet are tracked to locate the rolling piece, the displacement sensor installed at the roll neck is started before the last third pass of the finishing rolling bites, the real-time load roll gap is obtained in the process of the rolling piece passing through the rolling mill, the points with the transverse thickness roll gap value exceeding the tolerance are screened out, the transverse thickness roll gap value exceeding the tolerance is 0.5-0.8 mm, the target roll gap setting thickness is compared, the multi-point load roll gap adjustment amount of the last second pass is obtained, the multi-point load roll gap adjustment amount is converted into the AGC hydraulic cylinder adjustment amount; after the last second pass rolling is completed, the real-time load roll gap value of the last second pass is compared with the roll gap setting value of the last second pass, the roll gap controlled by the hydraulic cylinder of the last first pass is adjusted again through the hydraulic servo valve program, the last first pass rolling is carried out, and finally the rolling piece flatness on-line adjustment is completed under the load reduction of the last two passes of the finishing rolling; the bite speed of the last two passes of the finishing rolling is controlled to be 1.5-1.8 m / s -1 , the rolling speed is controlled to be 2.0-2.2 m / s -1 ; The steel plate is cooled, the steel plate adopts a laminar cooling system to control cooling, head and tail shielding is used in the investment of the control cooling system: the head shielding distance is 500-700 mm, the shielding coefficient is 0.8-1.0; the tail shielding distance is 900-1300 mm, the shielding coefficient is 0.5-0.7; the control cooling roller way acceleration is 0.004-0.006 m / s 2 ; the control cooling system adopts a fixed rule watering mode, 1-2 groups of headers are opened, the water quantity of each group of headers is 180-240 m 3 / h; the upper and lower header water flow ratio is 1:1.8-2.0; the steel plate is straightened using a small straightening force mode, the straightening force is 15 to 18 MK, the straightening speed is 0.3 to 0.8 m / s, and the final straightening temperature is < 480°C.

2. The method of claim 1, wherein the low carbon equivalent 355 MPa grade normalized rolled thin gauge steel plate shape control method is characterized by, The billet is a continuous casting billet, the casting billet thickness is 130 to 250 mm, and the steel plate thickness after rolling is 6 to 20 mm.

3. The method of claim 1, wherein the low carbon equivalent 355 MPa grade normalized rolled thin gauge steel plate shape control method is characterized by, The heating furnace is a walking beam type heating furnace, the billet is held in the preheating section for 25 to 30 minutes, the billet is held at a heating 1 section furnace temperature of 930 to 950°C for 75 to 90 minutes, and the billet is held at a heating 2 section furnace temperature of 1100 to 1120°C for 110 to 130 minutes.

4. The method of claim 1, wherein the low carbon equivalent 355 MPa grade normalized rolled thin gauge steel plate shape control method is characterized by The steel plate grain size is 8.5 or more, and the flatness of the steel plate in any direction is < 5 mm / 2 m.

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