Method for reducing banded structure of q420ne steel plate for wind power

Abstract

The application discloses a method for reducing banded structure of Q420NE steel plate for wind power, and mainly comprises the following steps: continuous casting, heating, rolling, cooling and normalizing; high superheat (25-35 DEG C), high pulling speed (1.0-1.1 m / min), high cooling speed (the cooling water quantity of the crystallizer is greater than 4300 L / min, the water quantity of the first cooling area is greater than 4400 L / min, and the water quantity of the second cooling area is greater than 4100 L / min), no electromagnetic stirring, and large reduction at the solidification end point, wherein the casting blank is subjected to reduction at the solidification end point area in one or two roller sections, the roller opening degree for the reduction is of the shrinkage type, the large reduction is performed when the solid phase rate of the core of the casting blank is 0.8-1.0, and the reduction amount is 5-20 mm. The application reduces the proportion of the equiaxed crystal zone, promotes the growth of the columnar crystal, increases the proportion of the columnar crystal zone, thereby avoiding the generation of a large amount of point segregation in the center of the casting blank, and controlling the generation of the banded structure from the source.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel metallurgy, and particularly relates to a method for reducing band structure of Q420NE steel plate for wind power. BACKGROUND

[0002] At present, continuous casting billets are widely used in the production of medium and heavy plates, and continuous casting billets with a thickness of 200-450 mm can be produced. During the continuous casting process, macroscopic center segregation and center porosity inevitably exist in the continuous casting billets due to dendritic segregation. During the rolling process, ferrite and pearlite bands, and even bainite or martensite bands are formed, which are collectively referred to as band structure. The band structure is mainly caused by the segregation of C, Mn, Si and other alloying elements during the continuous casting process, and the chemical composition has a great influence on it. During the subsequent rolling, only the thickness direction compression deformation is performed, it is difficult to break the dendrites and homogenize the composition, and finally the band structure exists in the steel plate structure.

[0003] Practice shows that the band structure has little effect on the strength of the steel plate, but has a greater effect on the plasticity, especially deteriorating the impact toughness, causing the impact energy to be unqualified. The anisotropy of the steel plate is aggravated, and the hydrogen resistance and acid resistance of the steel plate are deteriorated. The Q420NE wind power steel plate is delivered after normalizing, the carbon content is about 0.16%, and the band structure is serious, which needs to be solved urgently.

[0004] Patent CN109295289A discloses a method for reducing band structure of thin steel plate for resisting hydrogen sulfide corrosion, which comprises the steps of continuous casting, heating, rolling, cooling and heat treatment. The problem of a significant decrease in hydrogen-induced cracking resistance caused by the band structure is solved. However, the method has the following shortcomings: no detailed continuous casting parameters are given, and it is only suitable for 8-20 mm steel plates, and the effect is not good after practice.

[0005] Patent CN109022732B discloses a production method for reducing band structure of medium and high carbon structural steel plate, which comprises the steps of continuous casting after smelting, sectional heating of the continuous casting billet, sectional rolling, laminar cooling and coiling, so that the band structure of the medium and high carbon structural steel plate is controlled below level 1, and the plasticity and toughness of the material are improved, and the fatigue life of the product is improved. However, the method has the following shortcomings: it is only suitable for thin steel strips, and is not suitable for thick steel plates, and the effect is not good after practice.

[0006] Patent CN115198165A discloses a method for reducing band structure of 980MPa grade cold-rolled high-strength steel. The terminal temperature of hot rolling is increased, the coiling temperature is reduced, the heating terminal temperature of the annealing process is reduced, and the holding time after heating is prolonged, so as to reduce the content of the band structure of the cold-rolled high-strength steel. However, the method has the following shortcomings: it is only suitable for cold-rolled steel strips, and is not suitable for thick steel plates, and the effect is not good after practice.

[0007] Patent CN 115921807 A discloses a "method for reducing the band structure level of hot-rolled strip steel", which can reduce the band structure level of hot-rolled strip steel by controlling the continuous casting electromagnetic stirring parameters, controlling the pouring speed and dynamic soft reduction, slab in the furnace time, finish rolling temperature, coiling temperature, improving the hot plate structure under the existing steel composition, hot rolling process and equipment conditions, thereby reducing the band structure level of hot coil. The disadvantage is that it is only suitable for thin steel strip, not for thick steel plate, and the practical effect is not good.

[0008] The existing method for controlling band structure mostly considers controlling from heat treatment, hot rolling process and alloy composition. The steel obtained by using the conventional method for controlling band structure needs to be strictly controlled in the cooling process after heat treatment, otherwise the band structure rating may increase again, which brings obstacles to subsequent application. Because the existing method for controlling band structure does not consider adjusting from the continuous casting process where the band structure is generated, it is impossible to fundamentally control the band structure. SUMMARY

[0009] The purpose of the present application is to provide a method for reducing the band structure of Q420NE wind power steel plate, and to solve the problems.

[0010] To solve the above technical problems, the present application adopts the following technical scheme:

[0011] The present application provides a method for reducing the band structure of Q420NE wind power steel plate, which mainly includes continuous casting, heating, rolling, cooling and normalizing; wherein:

[0012] In the continuous casting process, high superheat of 25-35℃, high pulling speed of 1.0-1.1m / min, high cooling speed: crystallizer cooling water quantity greater than 4300L / min, one cooling zone water quantity greater than 4400L / min, and two cooling zone water quantity greater than 4100L / min are adopted; no electromagnetic stirring, solidification end large reduction technology, promote columnar crystal growth, reduce center segregation;

[0013] The solidification end large reduction is to implement reduction on the casting blank in the solidification terminal area 1 or 2 roller sections, the roller opening degree for implementing reduction is shrinkage type, the large reduction is performed when the solid phase rate of the casting blank core is 0.8-1.0, and the reduction amount is 5-20mm;

[0014] The casting blank section is 250mmx1600-2200mm, and the slab is slowly cooled for more than 36 hours;

[0015] The slab is slowly cooled for more than 36 hours;

[0016] The rolling includes an austenite recrystallization section and an unrecrystallization section, wherein the austenite recrystallization section has at least 2 pass reduction ratios controlled at 14% or more, and the austenite unrecrystallization section has a cumulative reduction ratio controlled at 50-66%;

[0017] The steel plate is cooled at a cooling speed of 6-15℃ / s after rolling.

[0018] The steel plate is normalized after being subjected to shot blasting, the normalizing temperature is 860-900℃, and the in-furnace time is 1.7min / mm×thickness+10min.

[0019] Further, the mass percentage chemical composition of the Q420NE is C: 0.16-0.18%, Si: 0.22-0.32%, Mn: 1.52-1.70%, P: ≤0.010%, S: ≤0.003%, Nb: 0.035-0.045%, V: 0.035-0.045%, Ti: 0.010-0.020%, Al: 0.017-0.027%, and the balance is Fe and inevitable impurities.

[0020] Further, the continuous casting process parameters are: superheat 30℃, casting speed 1.0m / min, mold cooling water amount 4400L / min, primary cooling zone water amount 4500L / min, secondary cooling zone water amount 4200L / min, large reduction at the end of solidification 9mm, casting blank section 250mm×2200mm, slab slow cooling 48 hours; the slab is cold charged into a heating furnace, the soaking temperature is 1220℃, and the in-furnace time is 312min; the rolling includes an austenite recrystallization section and an unrecrystallization section, wherein the austenite recrystallization section has at least 2 pass reduction ratios controlled at 14% or more, the rough rolling thickness is 60mm, and the finished product thickness is 20mm; the steel plate is cooled at a cooling speed of 8℃ / s; the steel plate is normalized after being subjected to shot blasting, the normalizing temperature is 860℃, and the in-furnace time is 44min.

[0021] Further, the continuous casting process parameters are: superheat 31℃, casting speed 1.0m / min, mold cooling water amount 4400L / min, primary cooling zone water amount 4500L / min, secondary cooling zone water amount 4200L / min, large reduction at the end of solidification 9mm, casting blank section 250mm×2200mm, slab slow cooling 48 hours; the slab is cold charged into a heating furnace, the soaking temperature is 1225℃, and the in-furnace time is 324min; the rolling includes an austenite recrystallization section and an unrecrystallization section, wherein the austenite recrystallization section has at least 2 pass reduction ratios controlled at 14% or more, the rough rolling thickness is 75mm, and the finished product thickness is 30mm; the steel plate is cooled at a cooling speed of 7℃ / s; the steel plate is normalized after being subjected to shot blasting, the normalizing temperature is 860℃, and the in-furnace time is 61min.

[0022] Further, the continuous casting process parameters are as follows: superheat 29 DEG C, casting speed 1.0 m / min, mold cooling water amount 4400 L / min, one cooling zone water amount 4500 L / min, two cooling zone water amount 4200 L / min, solidification end large reduction 9 mm, casting blank section 250 mm x 2200 mm, slab slow cooling 48 hours; the slab is cold charged into a heating furnace, soaking temperature 1231 DEG C, in-furnace time 327 min; rolling includes austenite recrystallization section rolling and non-recrystallization section rolling, wherein the austenite recrystallization section has at least 2 passes with reduction control at 14% or above, rough rolling thickness 80 mm, finished product thickness 40 mm; the steel plate cooling speed is 9 DEG C / s; the steel plate is normalized after shot blasting, normalizing temperature 860 DEG C, in-furnace time 78 min.

[0023] Further, the continuous casting process parameters are as follows: superheat 29 DEG C, casting speed 1.0 m / min, mold cooling water amount 4400 L / min, one cooling zone water amount 4500 L / min, two cooling zone water amount 4200 L / min, solidification end large reduction 9 mm, casting blank section 250 mm x 2200 mm, slab slow cooling 48 hours; the slab is cold charged into a heating furnace, soaking temperature 1231 DEG C, in-furnace time 327 min; rolling includes austenite recrystallization section rolling and non-recrystallization section rolling, wherein the austenite recrystallization section has at least 2 passes with reduction control at 14% or above, rough rolling thickness 80 mm, finished product thickness 40 mm; the steel plate cooling speed is 9 DEG C / s; the steel plate is normalized after shot blasting, normalizing temperature 860 DEG C, in-furnace time 78 min.

[0024] Compared with the prior art, the present application has the beneficial technical effects that:

[0025] The process of increasing the superheat of the molten steel, increasing the cooling speed and not adding electromagnetic stirring. Because under the electromagnetic stirring condition described in the present application, the flow of the molten steel in front of the columnar crystal is greatly slowed down, the growth of the columnar crystal is not affected, the superheat is increased to 25-35 DEG C and close to the upper limit of production, which can provide favorable growth conditions for the columnar crystal, reduce the proportion of equiaxed crystal zone, promote the growth of columnar crystal and increase the proportion of columnar crystal zone, thereby avoiding the generation of a large amount of point segregation in the center of the casting blank and controlling the generation of banded structure from the source.

[0026] The mechanism of the large reduction at the solidification end is that when the large reduction is implemented on the casting blank at the solidification end, the impurity-rich molten steel at the solidification front is expelled, the center segregation of the casting blank is reduced or eliminated, the generation of banded structure is controlled from the source, and the product quality is improved.

[0027] The use of relatively high heating temperature and long heating time can make the composition of the casting blank more uniform, reduce segregation and thus reduce the banded structure of the steel plate.

[0028] The large deformation in the non-recrystallization zone can increase the intracrystalline dislocation, subgrain boundary and other defects, to provide nucleation sites for the phase transition of ferrite and pearlite in the austenite crystal, instead of nucleating along the segregation band to form banded structure; the rapid cooling is to inhibit the carbon diffusion to the segregation band rich in alloying elements to form pearlite strips due to the formation of proeutectoid ferrite in the medium-high carbon structural steel.

[0029] The normalizing can further homogenize the components and reduce the banded structure of the steel plate.

[0030] The method principle of the application is clear, has obvious improvement effect, strong operability, small control difficulty, low production cost and other advantages, and has good effect on reducing the banded structure of the Q420NE wind power steel plate. BRIEF DESCRIPTION OF DRAWINGS

[0031] The application will be further described below in combination with the description of the drawings.

[0032] Figure 1 The low-magnification macrostructure diagram of the conventional process casting blank in Example 1;

[0033] Figure 2 The low-magnification macrostructure diagram of the casting blank in Example 1. DETAILED DESCRIPTION

[0034] A method for reducing the banded structure of the Q420NE wind power steel plate, the process mainly includes continuous casting, heating, rolling, cooling and normalizing.

[0035] In the continuous casting process, high superheat (25-35℃), high pulling speed (1.0-1.1m / min), high cooling speed (the cooling water quantity of the crystallizer is greater than 4300L / min, the water quantity of the first cooling zone is greater than 4400L / min, and the water quantity of the second cooling zone is greater than 4100L / min), no electromagnetic stirring, solidification end large reduction technology are adopted to promote the growth of columnar crystals and reduce the center segregation.

[0036] The solidification end large reduction is to implement the reduction of the casting blank at one or two roller sections in the solidification terminal region, the roller opening degree of the reduction is shrinkage type, the large reduction is performed when the solid phase rate of the core of the casting blank is 0.8-1.0, and the reduction amount is 5-20mm.

[0037] The section of the casting blank is 250mm*1600-2200mm, and the slab is slowly cooled for more than 36 hours.

[0038] The chemical composition C of the Q420NE mass percentage: 0.16-0.18%, Si: 0.22-0.32%, Mn: 1.52-1.70%, P: ≤0.010%, S: ≤0.003%, Nb: 0.035-0.045%, V: 0.035-0.045%, Ti: 0.010-0.020%, Al: 0.017-0.027%, and the balance of Fe and inevitable impurities.

[0039] The slab is cold charged into a heating furnace, the soaking temperature is 1200-1240 DEG C, the furnace time is above 270 min, and the temperature and composition in the thickness, width and length directions of the slab are as uniform as possible.

[0040] The rolling includes an austenite recrystallization section rolling and an unrecrystallization section rolling, wherein the austenite recrystallization section has at least 2 pass reduction ratios controlled above 14%, and the austenite unrecrystallization section has a cumulative reduction ratio controlled at 50-66%.

[0041] The cooling speed of the steel plate after rolling is controlled at 6-15 DEG C / s.

[0042] The steel plate is subjected to normalizing treatment after shot blasting, the normalizing temperature is 860-900 DEG C, and the furnace time is 1.7 min / mm*thickness+10 min.

[0043] In the embodiment, the Q420NE is sampled according to GB / T13298-2015 "Metal Microstructure Test Method" for banded structure rating, and the rating standard is GB / T13299-1991 "Steel Microstructure Rating Method".

[0044] The application will be described in more detail below with reference to the embodiments and the accompanying drawings.

[0045] Example 1:

[0046] A steel plant wide plate production line Q420NE steel grade, chemical composition C: 0.16%, Si: 0.24%, Mn: 1.52%, P: 0.010%, S: 0.003%, Nb: 0.036%, V: 0.036%, Ti: 0.012%, Als: 0.022%, the balance is Fe and inevitable impurities. Continuous casting process parameters: superheat 30℃, casting speed 1.0m / min, mold cooling water 4400L / min, one cooling zone water 4500L / min, two cooling zone water 4200L / min, solidification end large reduction 9mm, billet section 250mm x 2200mm, slab slow cooling 48 hours. Slab cold charging into heating furnace, soaking temperature 1220℃, in-furnace time 312min. Rolling including austenite recrystallization section rolling and unrecrystallization section rolling. Among them, the austenite recrystallization section has at least 2 passes with reduction rate controlled at 14% or more, rough rolling thickness 60mm, finished product thickness 20mm. Plate cooling speed 8℃ / s. The plate is normalized after shot blasting, normalizing temperature 860℃, in-furnace time 44min.

[0047] Example 2:

[0048] A steel plant wide plate production line Q420NE steel grade, chemical composition C: 0.16%, Si: 0.24%, Mn: 1.52%, P: 0.010%, S: 0.003%, Nb: 0.036%, V: 0.036%, Ti: 0.012%, Als: 0.022%, the balance is Fe and inevitable impurities. Continuous casting process parameters: superheat 30℃, casting speed 1.0m / min, mold cooling water 4400L / min, one cooling zone water 4500L / min, two cooling zone water 4200L / min, solidification end large reduction 9mm, billet section 250mm x 2200mm, slab slow cooling 48 hours. Slab cold charging into heating furnace, soaking temperature 1220℃, in-furnace time 312min. Rolling including austenite recrystallization section rolling and unrecrystallization section rolling. Among them, the austenite recrystallization section has at least 2 passes with reduction rate controlled at 14% or more, rough rolling thickness 60mm, finished product thickness 20mm. Plate cooling speed 8℃ / s. The plate is normalized after shot blasting, normalizing temperature 860℃, in-furnace time 44min.

[0049] Example 3:

[0050] A steel plant wide plate production line Q420NE steel grade, chemical composition C: 0.17%, Si: 0.26%, Mn: 1.54%, P: 0.010%, S: 0.002%, Nb: 0.038%, V: 0.037%, Ti: 0.013%, Als: 0.024%, the balance is Fe and inevitable impurities. Continuous casting process parameters: superheat 29℃, casting speed 1.0m / min, mold cooling water 4400L / min, one cooling zone water 4500L / min, two cooling zone water 4200L / min, solidification end heavy reduction 9mm, casting blank section 250mm x 2200mm, slab slow cooling 48 hours. Slab cold charging into heating furnace, soaking temperature 1231℃, in-furnace time 327min. Rolling includes austenite recrystallization section rolling and unrecrystallization section rolling. Among them, the austenite recrystallization section has at least 2 passes with a reduction rate of more than 14%, the rough rolling thickness is 80mm, and the finished product thickness is 40mm. The steel plate is cooled at a speed of 9℃ / s. The steel plate is subjected to normalizing treatment after shot blasting, normalizing temperature 860℃, in-furnace time 78min.

[0051] Example 4:

[0052] A steel plant wide plate production line Q420NE steel grade, chemical composition C: 0.17%, Si: 0.26%, Mn: 1.54%, P: 0.010%, S: 0.002%, Nb: 0.038%, V: 0.037%, Ti: 0.013%, Als: 0.024%, the balance is Fe and inevitable impurities. Continuous casting process parameters: superheat 29℃, casting speed 1.0m / min, mold cooling water 4400L / min, one cooling zone water 4500L / min, two cooling zone water 4200L / min, solidification end heavy reduction 9mm, casting blank section 250mm x 2200mm, slab slow cooling 48 hours. Slab cold charging into heating furnace, soaking temperature 1231℃, in-furnace time 327min. Rolling includes austenite recrystallization section rolling and unrecrystallization section rolling. Among them, the austenite recrystallization section has at least 2 passes with a reduction rate of more than 14%, the rough rolling thickness is 80mm, and the finished product thickness is 40mm. The steel plate is cooled at a speed of 9℃ / s. The steel plate is subjected to normalizing treatment after shot blasting, normalizing temperature 860℃, in-furnace time 78min.

[0053] Comparative Example 1:

[0054] A steel plant wide plate production line Q420NE steel grade, chemical composition same as Example 1. The difference from Example 1 is mainly in the continuous casting process, wherein the superheat is 21℃, the casting speed is 0.8m / min, the weak cooling mode is adopted, the electromagnetic stirring is adopted, the current is 380A, the frequency is 5HZ, and the stirring position is at 3 and 4 sections. The solidification end adopts light reduction, and the reduction amount is 4mm.

[0055] Comparative Example 2:

[0056] A steel plant wide plate production line Q420NE steel, chemical composition of example 2. And example 2 is different mainly in continuous casting process, wherein the superheat 20 ℃, the pulling speed 0.8 m / min, using weak cold way, using electromagnetic stirring, current 380 A, frequency 5HZ, stirring position in 3 and 4 section. Solidification end adopts light pressing down, the amount of pressing down 4mm.

[0057] The experimental data of the above examples and comparative examples are as follows in Table 1:

[0058] Table 1

[0059]

[0060]

[0061] The above described examples are only to describe the preferred mode of the present application, and not to limit the scope of the present application, without departing from the design spirit of the present application, the person skilled in the art to the technical scheme of the present application makes various deformation and improvement, all should fall into the protection scope determined by the claims of the present application.

Claims

1. A method of mitigating banded structure in a Q420NE steel plate strip for wind power, characterized by: The process mainly comprises continuous casting, heating, rolling, cooling and normalizing; wherein: In the continuous casting process, high superheat of 25-35℃, high pulling speed of 1.0-1.1m / min, high cooling speed: the cooling water quantity of the crystallizer is greater than 4300L / min, the water quantity of the first cooling zone is greater than 4400L / min, and the water quantity of the second cooling zone is greater than 4100L / min; no electromagnetic stirring, large reduction at the solidification end, promoting columnar crystal growth and reducing center segregation; The large reduction at the solidification end is to implement reduction on the casting blank in one or two roller sections at the solidification end, the roller opening degree for implementing the reduction is shrinkage type, the large reduction is implemented when the solid phase rate at the core of the casting blank is 0.8-1.0, and the reduction amount is 5-20mm; The cross section of the casting blank is 250mm×1600-2200mm, and the slab is slowly cooled for more than 36 hours; The slab is cold charged into the heating furnace, the soaking temperature is 1200-1240℃, and the furnace time is more than 270min to ensure the uniformity of the temperature and composition in the thickness, width and length directions of the slab; The rolling comprises austenite recrystallization section rolling and non-recrystallization section rolling, wherein the reduction rate of the austenite recrystallization section is controlled to be more than 14% in at least two passes, and the cumulative reduction rate of the austenite non-recrystallization section is controlled to be 50-66%; The cooling speed of the steel plate after rolling is controlled to be 6-15℃ / s; The steel plate is subjected to normalizing treatment after shot blasting, the normalizing temperature is 860-900℃, and the furnace time is 1.7min / mm×thickness+10min; The mass percentage chemical composition of the Q420NE is C: 0.16-0.18%, Si: 0.22-0.32%, Mn: 1.52-1.70%, P: ≤0.010%, S: ≤0.003%, Nb: 0.035-0.045%, V: 0.035-0.045%, Ti: 0.010-0.020%, Als: 0.017-0.027%, and the balance is Fe and inevitable impurities.

2. The method for mitigating banded structure of a steel sheet for Q420NE wind power according to claim 1, characterized in that: The continuous casting process parameters are superheat of 30℃, pulling speed of 1.0m / min, crystallizer cooling water quantity of 4400L / min, first cooling zone water quantity of 4500L / min, second cooling zone water quantity of 4200L / min, solidification end large reduction of 9mm, casting blank cross section of 250mm×2200mm, and slab slow cooling for 48 hours; the slab is cold charged into the heating furnace, the soaking temperature is 1220℃, and the furnace time is 312min; the rolling comprises austenite recrystallization section rolling and non-recrystallization section rolling, wherein the reduction rate of the austenite recrystallization section is controlled to be more than 14% in at least two passes, the open rolling thickness of the finish rolling is 60mm, and the finished product thickness is 20mm; the cooling speed of the steel plate is 8℃ / s; the steel plate is subjected to normalizing treatment after shot blasting, the normalizing temperature is 860℃, and the furnace time is 44min.

3. The method for mitigating band structure of a steel sheet for Q420NE wind power application according to claim 1, characterized in that: The continuous casting process parameters are as follows: superheating degree 31 ℃, casting speed 1.0 m / min, crystallizer cooling water amount 4400 L / min, one cooling zone water amount 4500 L / min, two cooling zone water amount 4200 L / min, solidification end large reduction 9 mm, casting blank section 250 mm×2200 mm, slab slow cooling 48 hours; the slab is cold charged into a heating furnace, soaking temperature 1225 ℃, in-furnace time 324 min; rolling includes austenite recrystallization section rolling and non-recrystallization section rolling, wherein the austenite recrystallization section has at least 2 passes with reduction rate controlled to be above 14%, rough rolling thickness 75 mm, finished product thickness 30 mm; the steel plate cooling speed is 7 ℃ / s; the steel plate is subjected to normalizing treatment after shot blasting, normalizing temperature 860 ℃, in-furnace time 61 min.

4. The method for mitigating band structure of a steel sheet for Q420NE wind power application according to claim 1, characterized in that: The continuous casting process parameters are as follows: superheating degree 29 ℃, casting speed 1.0 m / min, crystallizer cooling water amount 4400 L / min, one cooling zone water amount 4500 L / min, two cooling zone water amount 4200 L / min, solidification end large reduction 9 mm, casting blank section 250 mm×2200 mm, slab slow cooling 48 hours; the slab is cold charged into a heating furnace, soaking temperature 1231 ℃, in-furnace time 327 min; rolling includes austenite recrystallization section rolling and non-recrystallization section rolling, wherein the austenite recrystallization section has at least 2 passes with reduction rate controlled to be above 14%, rough rolling thickness 80 mm, finished product thickness 40 mm; the steel plate cooling speed is 9 ℃ / s; the steel plate is subjected to normalizing treatment after shot blasting, normalizing temperature 860 ℃, in-furnace time 78 min.

5. The method for mitigating band structure of a steel sheet for Q420NE wind power application according to claim 1, characterized in that: The continuous casting process parameters are as follows: superheating degree 29 ℃, casting speed 1.0 m / min, crystallizer cooling water amount 4400 L / min, one cooling zone water amount 4500 L / min, two cooling zone water amount 4200 L / min, solidification end large reduction 9 mm, casting blank section 250 mm×2200 mm, slab slow cooling 48 hours; the slab is cold charged into a heating furnace, soaking temperature 1231 ℃, in-furnace time 327 min; rolling includes austenite recrystallization section rolling and non-recrystallization section rolling, wherein the austenite recrystallization section has at least 2 passes with reduction rate controlled to be above 14%, rough rolling thickness 90 mm, finished product thickness 45 mm; the steel plate cooling speed is 9 ℃ / s; the steel plate is subjected to normalizing treatment after shot blasting, normalizing temperature 860 ℃, in-furnace time 87 min.

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