A method for producing high-strength IF steel with a plate width of ≥1800mm

Abstract

A method for producing high-strength IF steel with a width of 1800mm or greater includes conventional hot rolling and hot rolling to reduce the strip crown; pickling; cold rolling using five stands, with the group spacing refined and the cold rolling reduction controlled according to the finished product thickness; continuous annealing; and smoothing. This method not only produces strip widths 1800mm or greater, but also offers a stable production process, with a qualified rate exceeding 80% from the current 50%, and a tensile strength of 350MPa or greater, meeting user requirements.

Description

Technical Field

[0001] The present invention relates to a method for producing high-strength IF steel, in particular to a method for producing high-strength IF steel with a plate width of ≥1800 mm. Background Art

[0002] With the in-depth development of the automobile market, the market requirements for automobile steel have shown a trend of differentiation and diversification. In order to improve the material utilization rate of steel plates, meet the overall forming requirements of parts, and reduce the welding costs of the original tailor-welded plates, some users require cold-rolled plates with larger plate widths.

[0003] High-strength IF steel boasts excellent stamping properties and high strength, making it suitable for a wide range of automotive body panels. Ultra-wide high-strength IF steel is primarily used in front and rear, side, inner and outer panels, roof panels, and other parts. Compared to conventional width materials, ultra-wide material significantly improves material utilization for large parts, reduces the use of laser-welded blanks, and thus lowers production costs and carbon emissions. The integrated forming of multiple components can also enhance vehicle safety.

[0004] Because the width of ultra-wide high-strength IF steel exceeds 1800mm, it is easy for it to run away and scratch the furnace wall during production in the continuous annealing furnace, which can lead to strip breakage and shutdown. It usually takes more than 20 hours to handle the strip breakage and shutdown accident, which seriously affects the production rhythm and causes huge losses to the company. Therefore, reducing the deviation of ultra-wide high-strength IF steel can effectively improve the production efficiency of the unit, and the most important thing to control the deviation is to control the shape of the steel plate. Secondly, ultra-wide high-strength IF steel is mainly used for automotive covering parts, which has high requirements for the stamping performance and surface quality of the material. Usually, a high-temperature annealing process route is adopted. Therefore, ultra-wide strip steel can easily produce high-temperature thermal buckling in the continuous annealing furnace, which greatly affects the through-plate and surface quality. The high through-plate, high surface quality and high stamping performance requirements of the material have resulted in the inability of existing technologies to efficiently and stably manufacture ultra-wide high-strength IF steel, and the production qualification rate is less than 50%.

[0005] Existing publicly available technologies, such as patent applications CN201210574442.8, CN202010095552.0, and CN201210205030.7, only describe production, processing, or manufacturing methods for a specific steel grade. No effective cold rolling process control technology or technical solution for producing high-strength IF steel with a width of 1800 mm or greater, good stability, and a high pass rate has been reported, either domestically or internationally. Summary of the Invention

[0006] The present invention aims to overcome the shortcomings of the existing technology and provide a method for producing high-strength IF steel with a strip width of ≥1800mm, which not only has a strip width of ≥1800mm, but also has stable production, a qualified rate increased from the current 50% to more than 80%, performance that meets user needs, and a tensile strength of ≥350MPa.

[0007] Technical measures to achieve the above objectives:

[0008] A method for producing high-strength IF steel with a plate width of ≥1800 mm, characterized by the following steps:

[0009] 1) Perform conventional hot rolling and hot-rolled plate surface crown: the plate surface crown value is controlled within 30 to 80 μm, wherein: when the thickness of the hot-rolled plate is ≤4.0 mm, the plate surface crown value is controlled not to exceed 60 μm; when the thickness of the hot-rolled plate is greater than 4.0 to 6.0 mm, the plate surface crown value is controlled not to exceed 80 μm;

[0010] 2) Pickling: control the acid tank temperature at 70-90°C;

[0011] The free acid concentration in the three acid tanks is controlled as follows:

[0012] The acid concentration in No. 1 acid tank shall not be less than 50g / l, that in No. 2 acid tank shall not be less than 70g / l, and that in No. 3 acid tank shall not be less than 130g / l; the pickling speed shall be controlled at no more than 180m / min;

[0013] 3) Use five stands for cold rolling, refine the group spacing and control the cold rolling reduction rate according to the thickness of the finished product:

[0014] When the thickness of the finished product is 0.6mm<≤0.7mm, the thickness of the hot-rolled raw material is selected to be 2.9~≤3.1mm, and the total cold-rolling reduction is controlled at 76~81%;

[0015] When the finished product thickness is 0.7mm<0.8mm, the hot rolling raw material thickness is selected to be 3.3~≤3.5mm, and the total cold rolling reduction is controlled at 76~80%;

[0016] When the finished product thickness is 0.8mm<0.9mm, the thickness of the hot-rolled raw material is selected to be 3.7~≤3.9mm, and the total cold-rolling reduction is controlled at 76~79%;

[0017] When the finished product thickness is 0.9mm<1.0mm, the thickness of the hot-rolled raw material is selected to be 4.1~≤4.3mm, and the total cold-rolling reduction is controlled at 76%~79%;

[0018] When the finished product thickness is 1.0mm<1.2mm, the hot rolling raw material thickness is selected to be 4.5~≤4.7mm, and the total cold rolling reduction is controlled at 73%~79%;

[0019] When the finished product thickness is 1.2mm<1.4mm, the thickness of the hot-rolled raw material is selected to be 4.9~≤5.1mm, and the total cold-rolling reduction is controlled at 71%~76%;

[0020] When the finished product thickness is 1.4mm<1.6mm, the hot rolling raw material thickness is selected to be 5.4~≤5.6mm, and the total cold rolling reduction is controlled at 70~75%;

[0021] When the finished product thickness is 1.6mm<≤2.0mm, the hot rolling raw material thickness is selected to be 5.9~≤6.1mm, and the total cold rolling reduction is controlled at 66~74%;

[0022] And control the emulsion temperature at 45-60℃, and the saponification value is not less than 170KOH / g;

[0023] The crown of the working rolls of each stand is controlled to be 20-40 μm for the working rolls of stands 1 to 4, the crown of the working rolls of stand 5 is no more than 10 μm, and the inclination value of stand 5 is controlled to be no more than 300 μm. The absolute value of the tension difference on both sides of the strip at the mill exit is ≤3 kN.

[0024] 4) Continuous annealing: Before annealing the cold-rolled high-strength IF steel with a plate width of ≥1800mm, first arrange 3-5 coils of DC01 plain carbon steel with a width greater than the width of the high-strength IF steel to be annealed, and the width greater than the width is not less than 5mm; the DC01 steel and the high-strength IF steel are subjected to the same temperature and speed, and then the high-strength IF steel with a plate width of ≥1800mm is continuously annealed;

[0025] Each process operation is carried out as follows:

[0026] The annealing temperature of each section is controlled as follows:

[0027] The annealing temperature in the soaking section is 810-830°C.

[0028] The temperature of the slow cooling section is 630~650℃.

[0029] The temperature of the rapid cooling section is 370-420°C; the rapid cooling rate is not less than 35°C / s;

[0030] The temperature of the over-aging stage is 350~390℃.

[0031] The temperature of the final cooling section is 170-180°C;

[0032] Control annealing speed according to strip thickness:

[0033] When the strip thickness is greater than 0.6 to 1.0 mm, the annealing speed is controlled at 150 to 210 m / min;

[0034] When the strip thickness is greater than 1.0 to 2.0 mm, the annealing speed is controlled at 100 to 180 m / min;

[0035] Control the tension of each segment:

[0036] Heating section:

[0037] The tension of the first and second heating sections is controlled at 7-10KN, and the crown of the furnace roller is controlled at 0.25-0.35mm;

[0038] The tension of the third heating section is controlled at 6~8KN;

[0039] Soaking section:

[0040] The tension of this section is controlled at 5~7KN;

[0041] Slow cooling section and fast cooling section:

[0042] The tension of the two sections is controlled at 12~16KN;

[0043] Over-aging section and final cooling section:

[0044] The tension of the two sections is controlled at 7~12KN;

[0045] 5) For leveling, a constant flow wet leveling mode is adopted, a middle roller string roller is used, and the leveling elongation is controlled at 0.6-1.0%.

[0046] Furthermore: during continuous annealing, when the unit has an abnormality and needs to be slowed down, the heating furnace adopts a step-by-step speed reduction method, that is, the speed is reduced step by step, and the single speed reduction does not exceed 20m / min. At the same time, the minimum operating speed is controlled at not less than 80m / min.

[0047] Function and mechanism of the main process in the present invention

[0048] The present invention controls the convexity of the hot-rolled raw material. Good strip shape primarily stems from a good hot-rolled raw material profile and proportional extension across the strip width during cold rolling. The hot-rolled raw material profile has the most direct impact on strip shape. The cold-rolled strip exit convexity depends on both the hot-rolled raw material convexity and the mill roll gap convexity; the difference between the two determines the strip's wave shape. Regarding the shape control of ultra-wide, high-strength IF steel, conventional shape control methods, such as bending and stringing, cannot achieve optimal shape control because the width of the strip reaches the maximum length of the mill rolls. Therefore, appropriate hot-rolled raw material convexity can reduce the degree of intermediate strip extension during rolling and improve the strip shape. Extensive production experience has shown that for ultra-wide, high-strength IF steel with a hot-rolled raw material thickness ≤4.0mm, the strip convexity is 30-60μm; for ultra-wide, high-strength IF steel with a hot-rolled raw material thickness >4.0 to 6mm, the strip convexity is 30-80μm, resulting in even better cold-rolled strip shape control.

[0049] The present invention controls the acid tank temperature at 70-90° C., the free acid concentrations in the three acid tanks, acid tank No. 1 not less than 50 g / l, acid tank No. 2 not less than 70 g / l, and acid tank No. 3 not less than 130 g / l, and the pickling speed is controlled below 180 m / min, in order to avoid over-pickling and under-pickling of the steel coil and improve the surface quality of the product.

[0050] The reason why the present invention controls the emulsion temperature at 45-60° C. and the saponification value at not less than 170KOH / g is to control the plate shape of ultra-wide high-strength IF steel and reduce residual oil and iron on the surface of the steel coil, thereby improving the surface quality of the product.

[0051] The present invention refines the group spacing during cold rolling, specifically for ultra-wide, high-strength IF steel with a finished thickness of less than 1.0 mm, by grouping the finished steel with a group spacing of 0.1 mm to control the total reduction rate. When the width exceeds 1800 mm, the increased deformation causes a sharp increase in the rolling force of the rolling mill, significantly affecting the effectiveness of bending and shifting rolls in regulating the plate shape. It also poses extreme challenges to the mill's cooling system, causing the mill motor to overheat, further hindering stable plate shape control. As the rolling rate increases, the plate shape deteriorates further. Therefore, the deformation, or the total reduction rate, is controlled, especially for ultra-wide, high-strength IF steel with a thickness of less than 1.0 mm, to below 80%.

[0052] The present invention controls the crown of the work rolls of stands 1-5 to 20-40 μm, and the crown of the work rolls of stand 5 to no more than 10 μm. The inclination of stand 5 is also controlled to below 300 μm, ensuring that the absolute tension difference between the two sides of the strip at the mill exit is ≤3 kN. Reducing the tension difference between the two sides of the strip improves strip shape quality, especially in the width direction, and significantly reduces the risk of deviation in the continuous annealing unit.

[0053] The present invention uses 3-5 rolls of DC01 plain carbon steel because the width of the DC01 steel needs to be greater than the width of the ultra-wide, high-strength IF steel used in this invention. The lead stock needs to be pre-adjusted to the production process for ultra-wide, high-strength IF steel. To ensure smooth passage of the ultra-wide, high-strength IF steel into the annealing furnace, minimize temperature differences between the strip and the furnace rollers along the length, and reduce thermal stress differences across the strip width, a certain amount of lead stock is pre-heated before production to minimize strip buckling and deviation.

[0054] The reason why the present invention controls the annealing temperature of different process sections is that the temperature of the soaking section is 810-830°C, the temperature of the slow cooling section is 630-650°C, the temperature of the rapid cooling section is 370-420°C, the temperature of the over-aging section is 350-390°C, and the temperature of the final cooling section is 170-180°C. This is mainly to improve the deep drawing performance of the material. Therefore, high-temperature annealing is required in the soaking section. Properly lowering the temperature of the slow cooling section and the rapid cooling section is beneficial to reducing the temperature difference between the strip and the furnace rollers, reducing the risk of cold buckling, and at the same time, increasing the cooling rate is beneficial to improving the strength of the material. Turning on the electric heating device of the over-aging section can improve the temperature assurance and stability of the aging section, reduce the change of the roller shape, and reduce the probability of cold buckling.

[0055] The reason why the present invention controls the annealing speed is that for strip thickness > 0.5 to 1.0 mm, the annealing speed is 150 to 220 m / min; for strip thickness > 1.0 to 2.0 mm, the annealing speed is 100 to 180 m / min. For high-strength IF steel, a certain cooling rate is required to make the material reach a certain strength, so it is necessary to control a suitable speed to ensure the cooling rate of the material annealing. At the same time, in order to reduce the influence of the furnace roller shape on the wide strip, the operating speed of the annealing furnace needs to be increased, but the speed increase is likely to cause the strip to deviate, and in severe cases, cause the strip to break, and the low annealing speed is likely to cause intermittent thermal buckling of the strip in the heating section. Set the minimum operating speed, that is, the safe operating speed of the plate. If the unit is lower than this speed, it is likely to cause serious buckling, thereby causing serious production accidents such as unit shutdown and strip breakage. In summary, the control of the annealing speed requires comprehensive consideration.

[0056] The reason why the present invention controls the tension in each process section is mainly to control the deviation and warping of ultra-wide strip steel and reduce the fluctuation of the plate. In the first and second heating sections, since the strip steel enters a higher temperature from a lower temperature, the stress in the strip steel is released, and the strip steel is prone to deviation. The ultra-wide high-strength IF steel plate has a poor shape or the tension difference on both sides of the strip steel is too large, which will aggravate the deviation of the strip steel. Therefore, the crown of the furnace roller in this area should be improved and controlled at 0.25-0.35mm. At the same time, the tension of the first and second heating sections needs to be increased and controlled at 7-10KN. In the third heating section, since the strip steel temperature reaches above 800℃ and the steel is relatively soft, the ultra-wide strip steel is prone to thermal warping, and the tension needs to be relatively small and controlled at 6-8KN. In the equalization section, since the strip steel is kept above 800℃ for a period of time and the steel is even softer, the tension needs to be further reduced and controlled at 5-7KN. In the slow and rapid cooling sections, lowering the temperature in these sections helps reduce the temperature difference between the strip and the furnace rollers, thus reducing the risk of cold buckling. However, the temperature reduction is achieved through the cooling bellows, which have high wind speeds and can easily cause the strip to shake and cause scratches. Ultra-wide strips experience even greater shaking, causing more severe scratches. Therefore, the tension needs to be higher, controlled at 12 to 16 kN. In the over-aging and final cooling sections, excessive tension in these areas can aggravate cold buckling, while too little tension can increase the severity of scratches. Therefore, the tension value in these areas should be set to take into account both scratches and buckling, and controlled at 7 to 12 kN.

[0057] The present invention's leveling process utilizes a constant-flow wet leveling mode and a skewed intermediate roll configuration to ensure consistent rolling force across the width, thus guaranteeing the optimal flatness of the finished ultra-wide, high-strength IF steel product. Prior to producing ultra-wide, high-strength IF steel, new work rolls are replaced, and the leveling elongation is controlled between 0.6% and 1.0%, primarily to ensure high surface quality and mechanical properties of the finished product.

[0058] Compared with the prior art, the present invention not only has a strip width of ≥1800mm, but also has a stable production process, a qualified rate increased from the current 50% to over 80%, a tensile strength of ≥350MPa, and performance that meets user needs. DETAILED DESCRIPTION

[0059] The present invention is described in detail below:

[0060] Table 1 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0061] Table 2 is a table of performance test results of various embodiments of the present invention and comparative examples.

[0062] Each embodiment of the present invention is produced according to the following steps

[0063] 1) Perform conventional hot rolling and hot-rolled plate surface crown: the plate surface crown value is controlled within 30 to 80 μm, wherein: when the thickness of the hot-rolled plate is ≤4.0 mm, the plate surface crown value is controlled not to exceed 60 μm; when the thickness of the hot-rolled plate is greater than 4.0 to 6.0 mm, the plate surface crown value is controlled not to exceed 80 μm;

[0064] 2) Pickling: control the acid tank temperature at 70-90°C;

[0065] The free acid concentration in the three acid tanks is controlled as follows:

[0066] The acid concentration in No. 1 acid tank shall not be less than 50g / l, that in No. 2 acid tank shall not be less than 70g / l, and that in No. 3 acid tank shall not be less than 130g / l; the pickling speed shall be controlled at no more than 180m / min;

[0067] 3) Use five stands for cold rolling, refine the group spacing and control the cold rolling reduction rate according to the thickness of the finished product:

[0068] When the thickness of the finished product is 0.6mm<≤0.7mm, the thickness of the hot-rolled raw material is selected to be 2.9~≤3.1mm, and the total cold-rolling reduction is controlled at 76~81%;

[0069] When the finished product thickness is 0.7mm<0.8mm, the hot rolling raw material thickness is selected to be 3.3~≤3.5mm, and the total cold rolling reduction is controlled at 76~80%;

[0070] When the finished product thickness is 0.8mm<0.9mm, the thickness of the hot-rolled raw material is selected to be 3.7~≤3.9mm, and the total cold-rolling reduction is controlled at 76~79%;

[0071] When the finished product thickness is 0.9mm<1.0mm, the thickness of the hot-rolled raw material is selected to be 4.1~≤4.3mm, and the total cold-rolling reduction is controlled at 76%~79%;

[0072] When the finished product thickness is 1.0mm<1.2mm, the hot rolling raw material thickness is selected to be 4.5~≤4.7mm, and the total cold rolling reduction is controlled at 73%~79%;

[0073] When the finished product thickness is 1.2mm<1.4mm, the thickness of the hot-rolled raw material is selected to be 4.9~≤5.1mm, and the total cold-rolling reduction is controlled at 71%~76%;

[0074] When the finished product thickness is 1.4mm<1.6mm, the hot rolling raw material thickness is selected to be 5.4~≤5.6mm, and the total cold rolling reduction is controlled at 70~75%;

[0075] When the finished product thickness is 1.6mm<≤2.0mm, the hot rolling raw material thickness is selected to be 5.9~≤6.1mm, and the total cold rolling reduction is controlled at 66~74%;

[0076] And control the emulsion temperature at 45-60℃, and the saponification value is not less than 170KOH / g;

[0077] The crown of the working rolls of each stand is controlled to be 20-40 μm for the working rolls of stands 1 to 4, the crown of the working rolls of stand 5 is no more than 10 μm, and the inclination value of stand 5 is controlled to be no more than 300 μm. The absolute value of the tension difference on both sides of the strip at the mill exit is ≤3 kN.

[0078] 4) Continuous annealing: Before annealing the cold-rolled high-strength IF steel with a plate width of ≥1800mm, first arrange 3-5 coils of DC01 plain carbon steel with a width greater than the width of the high-strength IF steel to be annealed, and the width greater than the width is not less than 5mm; the DC01 steel and the high-strength IF steel are subjected to the same temperature and speed, and then the high-strength IF steel with a plate width of ≥1800mm is continuously annealed;

[0079] Each process operation is carried out as follows:

[0080] The annealing temperature of each section is controlled as follows:

[0081] The annealing temperature in the soaking section is 810-830°C.

[0082] The temperature of the slow cooling section is 630~650℃.

[0083] The temperature of the rapid cooling section is 370-420°C; the rapid cooling rate is not less than 35°C / s;

[0084] The temperature of the over-aging stage is 350~390℃.

[0085] The temperature of the final cooling section is 170-180°C;

[0086] Control annealing speed according to strip thickness:

[0087] When the strip thickness is greater than 0.6 to 1.0 mm, the annealing speed is controlled at 150 to 210 m / min;

[0088] When the strip thickness is greater than 1.0 to 2.0 mm, the annealing speed is controlled at 100 to 180 m / min;

[0089] Control the tension of each segment:

[0090] Heating section:

[0091] The tension of the first and second heating sections is controlled at 7-10KN, and the crown of the furnace roller is controlled at 0.25-0.35mm;

[0092] The tension of the third heating section is controlled at 6~8KN;

[0093] Soaking section:

[0094] The tension of this section is controlled at 5~7KN;

[0095] Slow cooling section and fast cooling section:

[0096] The tension of the two sections is controlled at 12~16KN;

[0097] Over-aging section and final cooling section:

[0098] The tension of the two sections is controlled at 7~12KN;

[0099] 5) For leveling, a constant flow wet leveling mode is adopted, a middle roller string roller is used, and the leveling elongation is controlled at 0.6-1.0%.

[0100] Table 1 List of main process parameters of various embodiments of the present invention and comparative examples

[0101]

[0102]

[0103] Table 1

[0104]

[0105]

[0106] Table 2 Performance test results of various embodiments of the present invention and comparative examples

[0107]

[0108] As can be seen from Table 2, Examples 1-11, the ultra-wide high-strength IF steel within the scope of the claims of the present invention, can not only be smoothly and high-quality plate-passed and produced, but also the surface quality and mechanical properties meet the requirements. The performance indicators of Examples 1-6 meet the technical indicators of HC180Y steel, and the performance indicators of Examples 7-11 meet the technical indicators of HC220Y steel. The overall product qualification rate of Examples 1-11 reached 93%. In Comparative Example 1, due to the large tension difference of the strip at the exit of the rolling mill, the strip seriously deviated in the annealing furnace. The unit took emergency speed reduction measures, resulting in surface quality defects such as severe scratches and warping on the surface of the strip. At the same time, the cooling rate was low, resulting in inconsistent product performance. In Comparative Example 2, due to the excessively high heating temperature, the strip was thermally warped. In order to prevent the thermal warping from worsening and causing the strip to break, the unit took emergency speed reduction measures, which again resulted in surface quality defects such as severe scratches on the surface of the strip. At the same time, the cooling rate was low, resulting in inconsistent product performance.

[0109] This specific implementation is only the best example and is not a restrictive implementation of the technical solution of the present invention.

Claims

1. A method for producing high-strength IF steel with a plate width of ≥1800 mm, characterized in that Here are the steps: 1) Perform conventional hot rolling and hot-rolled plate surface crown: the plate surface crown value is controlled within 30-80 μm, wherein: when the thickness of the hot-rolled plate is ≤4.0 mm, the plate surface crown value is controlled not to exceed 60 μm; when the thickness of the hot-rolled plate is greater than 4.0 to 6.0 mm, the plate surface crown value is controlled not to exceed 80 μm; 2) Pickling: Control the acid tank temperature at 70-90°C; The free acid concentration in the three acid tanks is controlled as follows: The acid concentration in No. 1 acid tank shall not be less than 50g / l, that in No. 2 acid tank shall not be less than 70g / l, and that in No. 3 acid tank shall not be less than 130g / l; the pickling speed shall be controlled at no more than 180m / min; 3) Use five stands for cold rolling, refine the group spacing and control the cold rolling reduction rate according to the thickness of the finished product: When the finished product thickness is 0.6mm<≤0.7mm, the hot-rolled raw material thickness is selected to be 2.9~≤3.1mm, and the total cold-rolling reduction is controlled at 76~81%; When the finished product thickness is 0.7mm<≤0.8mm, the hot-rolled raw material thickness is selected to be 3.3~≤3.5mm, and the total cold-rolling reduction is controlled at 76%~80%; When the thickness of the finished product is 0.8mm<≤0.9mm, the thickness of the hot-rolled raw material should be 3.7~≤3.9mm, and the total cold-rolling reduction should be controlled at 76~79%; When the finished product thickness is 0.9mm<1.0mm, the thickness of the hot-rolled raw material should be 4.1~≤4.3mm, and the total cold-rolling reduction should be controlled at 76~79%; When the finished product thickness is 1.0mm<1.2mm, the hot-rolled raw material thickness is selected to be 4.5~≤4.7mm, and the total cold-rolling reduction is controlled at 73%~79%; When the finished product thickness is 1.2mm<1.4mm, the hot-rolled raw material thickness is selected to be 4.9~≤5.1mm, and the total cold-rolling reduction is controlled at 71~76%; When the finished product thickness is 1.4mm<1.6mm, the thickness of the hot-rolled raw material should be 5.4~≤5.6mm, and the total cold-rolling reduction should be controlled at 70~75%; When the finished product thickness is 1.6mm<≤2.0mm, the hot-rolled raw material thickness is selected to be 5.9~≤6.1mm, and the total cold-rolling reduction is controlled at 66~74%; And control the emulsion temperature at 45-60°C, and the saponification value is not less than 170KOH / g; The crown of the working rolls of each stand is controlled to be 20-40 μm for the working rolls of stands 1 to 4, the crown of the working rolls of stand 5 is no more than 10 μm, and the inclination value of stand 5 is controlled to be no more than 300 μm. The absolute value of the tension difference on both sides of the strip at the mill exit is ≤3 kN. 4) Continuous annealing: Before annealing the cold-rolled high-strength IF steel with a plate width of ≥1800mm, first arrange 3-5 coils of DC01 plain carbon steel with a width greater than the width of the high-strength IF steel to be annealed, and the width greater than the width is not less than 5mm; the DC01 steel and the high-strength IF steel are subjected to the same temperature and speed, and then the high-strength IF steel with a plate width of ≥1800mm is continuously annealed; Each process operation is carried out as follows: The annealing temperature of each section is controlled as follows: The annealing temperature in the soaking section is 810-830°C. The temperature of the slow cooling section is 630~650℃. The temperature of the rapid cooling section is 370-420°C; the rapid cooling rate is not less than 35°C / s; The temperature of the over-aging stage is 350~390℃. The temperature of the final cooling section is 170-180°C; Control annealing speed according to strip thickness: When the strip thickness is greater than 0.6 to 1.0 mm, the annealing speed is controlled at 150 to 210 m / min; When the strip thickness is greater than 1.0 to 2.0 mm, the annealing speed is controlled at 100 to 180 m / min; Control the tension of each segment: Heating section: The tension of the first and second heating sections is controlled at 7-10KN, and the crown of the furnace roller is controlled at 0.25-0.35mm; The tension of the third heating section is controlled at 6~8KN; Soaking section: The tension of this section is controlled at 5~7KN; Slow cooling section and fast cooling section: The tension of the two sections is controlled at 12~16KN; Over-aging section and final cooling section: The tension of the two sections is controlled at 7~12KN; 5) For leveling, adopt the wet leveling mode with constant flow, use the middle roller string roller, and control the leveling elongation at 0.6~1.0%.

2. The method for producing high-strength IF steel with a plate width of ≥1800 mm according to claim 1, characterized in that: During continuous annealing, when the unit has an abnormality and needs to be slowed down, the heating furnace adopts a step-by-step speed reduction method, that is, the speed is reduced step by step, and the single speed reduction does not exceed 20m / min. At the same time, the minimum operating speed is controlled at not less than 80m / min.

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