A high-Cr weathering steel strip and a production method of a hot-rolled pickled high-Cr weathering steel strip with excellent surface quality and stable mechanical properties

Abstract

The application discloses a high-Cr weather-resistant steel strip and a production method of a hot-rolled pickling high-Cr weather-resistant steel strip with excellent surface quality and stable mechanical properties, the high-Cr weather-resistant steel strip comprises the following chemical components in percentage by weight: Mn: 0.15%-0.45%, P: 0.015%-0.035%, Cr: 3.50%-5.50%, Cu: 0.20%-0.40%, Sb: 0.020%-0.040%, Als: 0.015%-0.035%, V: 0.020%-0.040%, N: 0.010%-0.015%, C: <=0.010%, Si: <=0.10%, S: <=0.0050%, and the rest is Fe and inevitable impurity elements; the steel strip coil is single ferrite structure, the mechanical properties are stable, the yield strength is 370-450 MPa, the tensile strength is 500-590 MPa, the elongation is 28%-35%, the plasticity is excellent, the atmospheric corrosion resistance is excellent, and the surface quality is excellent.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of weathering steel, and particularly relates to a high-Cr weathering steel strip and a production method of hot-rolled and pickled high-Cr weathering steel strip with excellent surface quality and stable mechanical properties. BACKGROUND

[0002] Atmospheric corrosion is the most common form of corrosion of steel materials. When steel materials are exposed to air for use, they inevitably encounter atmospheric corrosion. Weathering steel has excellent atmospheric corrosion resistance and is widely used in the manufacture of equipment and components such as containers, railway vehicles, bridges, buildings, and photovoltaic supports, thereby improving service life.

[0003] Cr is one of the most common alloying elements in weathering steel, which can effectively improve the atmospheric corrosion resistance of steel. With the increase of Cr content, the atmospheric corrosion resistance of weathering steel is also improved accordingly. However, high Cr content also significantly improves the hardenability of weathering steel products. Due to the fast cooling rate and low temperature of the head and tail of the hot-rolled coil compared to the middle part of the hot-rolled coil, hard phase structures such as bainite and martensite are easily formed at the head and tail of the high-Cr weathering steel coil, resulting in high strength and low elongation at the head and tail of the hot-rolled coil, causing large fluctuations in the strength of the hot-rolled coil, and affecting the use of downstream users. When the Cr content is high, Cr is easily reacted with the steel matrix to form strong adherent oxides at high temperatures, which are difficult to remove by hot rolling and pickling. After pickling, there are still local oxidation bands on the surface of the steel strip, which seriously affect the surface quality of the hot-rolled and pickled high-Cr weathering steel strip and restrict the upgrading of high-end products.

[0004] Currently, the production methods for high-Cr weathering steel strips in the prior art can be divided into two categories: hot continuous rolling process and cold rolling and annealing process, and there is no hot-rolled and pickled high-Cr weathering steel. The current production methods mainly focus on controlling mechanical properties and corrosion resistance, and do not pay attention to the control of surface quality and mechanical property stability of high-Cr weathering steel strips.

[0005] For example, Chinese patents CN101376953A, CN102127717A, CN105274446A, and CN111349850A disclose weathering steels produced by hot continuous rolling process. These patents do not pay attention to the control of surface quality and mechanical property stability of high-Cr weathering steel strips.

[0006] For example, Chinese patents CN112301276A and CN113846269A disclose weathering steels produced by cold rolling and annealing process. These patents do not pay attention to the control of surface quality and mechanical property stability of high-Cr weathering steel strips. SUMMARY

[0007] To solve the above technical problems, the application provides a high Cr weathering steel strip and a production method of the hot-rolled and pickled high Cr weathering steel strip with excellent surface quality and stable mechanical properties.

[0008] The technical scheme adopted by the application is as follows:

[0009] The application provides a high Cr weathering steel strip, which comprises the following chemical components in percentage by weight: Mn: 0.15%-0.45%, P: 0.015%-0.035%, Cr: 3.50%-5.50%, Cu: 0.20%-0.40%, Sb: 0.020%-0.040%, Als: 0.015%-0.035%, V: 0.020%-0.040%, N: 0.010%-0.015%, C: ≤0.010%, Si: ≤0.10%, S: ≤0.0050%, and the rest is Fe and inevitable impurity elements.

[0010] The high Cr weathering steel strip has a polygonal ferrite microstructure.

[0011] The high Cr weathering steel strip has a yield strength of 370-450 MPa, a tensile strength of 500-590 MPa and an elongation of 28%-35%.

[0012] The application further provides a production method of the hot-rolled and pickled high Cr weathering steel strip with excellent surface quality and stable mechanical properties, which produces the cast blank of the high Cr weathering steel strip with the chemical components through hot continuous rolling and pickling processes.

[0013] When the molten steel is smelted, the LF+RH double-connection process is adopted, and micro-carbon chromium iron is added in the LF and RH processes.

[0014] When the cast blank is produced, the molten steel is cast in a tundish at a temperature of 1530-1560 DEG C, and is protected cast by using a protective slag; the continuous casting blank is drawn at a speed of 1.0-1.4 m / min; the thickness of the continuous casting slab is 230 mm, and the cast blank is directly loaded into a heating furnace after cutting, and the temperature of the cast blank into the heating furnace is greater than or equal to 700 DEG C.

[0015] In the hot continuous rolling process, the billet is heated in a heating furnace with a weak reducing atmosphere with an excess air coefficient of 0.90-0.95, the furnace time is 100-150 min, the soaking time is 25-40 min, and the discharge temperature is 1150-1220℃. The alloying elements are fully solid-solved, and the austenite grain is prevented from being coarsened due to long heating time; the surface oxidation and burning loss of the slab and the enrichment of liquid-phase Cu at the austenite grain boundary are reduced through low-temperature rapid heating and in-furnace reducing atmosphere control.

[0016] In the hot continuous rolling process, the billet is descaled by high-pressure water after being discharged from the furnace, and high-pressure water is used for descaling before each pass of rough rolling; the billet is descaled by high-pressure water again before entering the finishing rolling.

[0017] Further, the descaling water pressure is 20-25 MPa, the descaling water amount is 650-700 m 3 / h, and the distance between the upper and lower nozzles and the slab is 120-140 mm before each pass of rough rolling.

[0018] Further, the descaling water pressure is 30-35 MPa, the descaling water amount is 750-800 m 3 / h, and the nozzle height is 70-100 mm before entering the finishing rolling.

[0019] In the hot continuous rolling process, the rough rolling is performed by two stands in 3+3 passes; the opening rolling temperature is ≤1030℃, and the finishing rolling temperature is 870-910℃. If the finishing rolling temperature is too low, mixed crystals are easily caused in the two-phase region, the plasticity and toughness of the material are reduced, the deformation resistance is increased, and the tail is easily thrown off during rolling of thin specifications; if the finishing rolling temperature is too high, the austenite grains are coarsened before phase transition, the deformation dislocation is recovered, and the strength of the material is reduced.

[0020] The high-temperature strip steel is cooled immediately after the finishing rolling is completed, and the cooling manifold is opened every interval, so that the length of the opened cooling manifold is prolonged. The laminar flow cooling water is immediately gasified after meeting the high-temperature strip steel, and a water vapor film is formed on the surface of the steel, which can reduce the contact between the oxygen in the air and the high-temperature strip steel, and avoid the oxidation of the surface of the strip steel during high-temperature cooling.

[0021] In the hot continuous rolling process, the coiling temperature in the range of 25 m from the head of the hot coil is 720-750℃, the coiling temperature in the range of 50 m from the tail of the hot coil is 700-730℃, and the coiling temperature in other parts of the hot coil is 620-660℃; to further improve the stability of the microstructure and mechanical properties of the hot rolled coil, the hot rolled coil is placed in a holding pit for slow cooling after coiling, the cooling speed is controlled to be ≤2℃ / s, the cooling speed of the head and tail of the hot rolled coil is reduced, and the generation of bainite hard phase microstructure is avoided.

[0022] In the pickling process, the strip is welded after uncoiling, and then the strip is straightened. The straightening machine has an elongation of 1.2-1.8%, which can break the iron oxide scale on the surface of the strip and improve the pickling efficiency.

[0023] In the pickling process, continuous pickling is performed using three ultra-shallow tanks, with an acid spray pressure of 35-50 kPa; the free acid concentration in the first pickling tank is 25-50 g / L, Fe... 2+ Concentration 200-250 g / L; Free acid concentration in the second pickling tank 120-160 g / L, Fe 2+ Concentration 120-160 g / L; Free acid concentration in the third pickling tank 150-200 g / L, Fe 2+ The acid concentration should be 50-100 g / L; the acid temperature should be 70-80℃; and the pickling speed should be 65-80 m / min. A low pickling speed results in excessive immersion time of the base material in the acid, reducing the material yield and output. Furthermore, the hydrogen atoms in the acid diffuse into the steel matrix, affecting product performance. Conversely, an excessively fast pickling speed results in insufficient immersion time of the base material in the acid, leaving some iron oxide scale on the strip surface unremoved and leading to poor surface quality.

[0024] After pickling, the steel strip is rinsed to remove the acid residue on the surface of the steel strip. The rinsing water temperature is 60-80℃.

[0025] In the pickling process, the rinsed strip steel is leveled with a leveling elongation of 0.4%-1.0% and a finished surface roughness of 0.6μm-1.0μm. After leveling, the strip steel is coated with oil at a rate of 0.5g / m. 2 -0.9g / m 2 To avoid oxidation of the steel strip surface.

[0026] The functions and controls of each chemical component in the high-Cr weathering steel strip provided by this invention are as follows:

[0027] C (Carbon): C is the most economical element for increasing the strength of steel and has a significant interstitial solid solution strengthening effect. However, high-Cr weathering steel has strong hardenability and easily forms C-rich hard phase structures such as bainite and martensite, which greatly reduces the plasticity of the material and deteriorates the atmospheric corrosion resistance and weldability of the steel. Therefore, this invention designs the C content to be <0.010%.

[0028] Si (Silicon): Si is one of the important deoxidizing elements in the steelmaking process and can also refine corrosion products and improve atmospheric corrosion resistance. However, if the Si content is too high, it is easy to react with the matrix during heating to form Fe2SiO4, which has strong adhesion to the matrix. It is difficult to completely remove the Si during hot rolling descaling and pickling, thus deteriorating the surface quality of the steel. Therefore, this invention treats Si as a harmful element and controls its content to <0.10%.

[0029] Mn (manganese) : Mn is one of the important solid solution strengthening elements in steel, and is also an important deoxidizing element in the steelmaking process. However, too high Mn content not only increases the manufacturing cost, but also expands the austenite phase region, increases the stability of undercooled austenite, and promotes the formation of bainite and martensite. Therefore, the content is designed to be 0.15-0.45%.

[0030] Als (aluminum) : Al is the main deoxidizing element added in steel, and can also combine with N to precipitate AlN at high temperature, refining the austenite grain size. However, too high Al will increase the oxide inclusions in the steel, reducing the low atmospheric corrosion resistance and H2S corrosion resistance of the steel. Therefore, the content is designed to be 0.015-0.035%.

[0031] Cr (chromium) : Cr is an important alloying element for improving the atmospheric corrosion resistance of steel. High weathering resistance steel improves the atmospheric corrosion resistance by adding a high content of Cr. However, Cr is prone to react with the steel matrix to form strong adhesive oxides, which are difficult to remove by hot rolling and pickling, thus deteriorating the surface quality and welding performance of the steel, and significantly increasing the hardenability of the weathering resistance steel. Therefore, the content of Cr is designed to be 3.5-5.5%.

[0032] Cu (copper) : Cu can significantly improve the atmospheric corrosion resistance of the material, and the effect is better when combined with Cr. However, the melting point of Cu is relatively low, only 1083℃, and too high content of Cu can easily lead to continuous casting leakage, surface defects such as edge cracks and buckling during hot rolling, etc. Therefore, the content of Cu is designed to be 0.20-0.40%.

[0033] Sb (antimony) : In industrial atmosphere, the content of SO2, SO3, CO2, nitrogen oxides, etc. is high, which reacts with water vapor in the air to generate acidic media such as sulfurous acid, carbonic acid, nitric acid, etc., which adheres to the surface of the steel and accelerates its corrosion. Sb can significantly improve the acid medium corrosion resistance of the steel, so adding an appropriate amount of Sb can further improve the industrial atmospheric corrosion resistance of the steel, and also reduce the corrosion of hydrochloric acid on the base material during pickling, improving the pickling yield. However, Sb has a relatively low melting point, and too high content of Sb will deteriorate the hot working performance and welding performance of the steel. Therefore, the content of Sb is designed to be 0.015-0.040%.

[0034] V (vanadium) : V is a strong carbonitride forming element with low solid solution temperature. During rolling and cooling, vanadium nitride, vanadium carbonitride, and vanadium carbide two-phase particles are precipitated, which improves the strength and plasticity of the material through fine grain strengthening and precipitation strengthening. In order to improve the surface quality of high Cr content weathering resistance steel, a low temperature heating process is adopted, so vanadium micro-alloying is used, and the content is controlled at 0.020%-0.040%.

[0035] N (nitrogen) : N can be combined with vanadium, and through vanadium-nitrogen micro-alloying, the precipitation of vanadium carbonitride two-phase particles is promoted, the two-phase particle size is refined, and the strengthening effect is improved. In the present application, N is added as a beneficial element, but if the content is too high, the toughness and plasticity of the steel material will be deteriorated. Therefore, the content is controlled at 0.010-0.015%.

[0036] P (phosphorus) : P is one of the most economical elements for improving the atmospheric corrosion resistance of steel, and can also improve the strength of the steel through solid solution strengthening. However, P is prone to segregate at grain boundaries, reducing the low-temperature toughness of the steel and increasing the welding crack sensitivity. Therefore, the P content is controlled at 0.015-0.035%.

[0037] S (sulfur) : S is a harmful residual element in steel, which easily reacts with Mn to form non-metallic inclusions of MnS, destroying the continuity of the steel matrix, acting as a corrosion initiation source to cause pitting corrosion, and deteriorating the atmospheric corrosion resistance of the steel. However, if the S content is too low, the smelting cost will increase. Therefore, the S content in the present application is controlled at ≤0.0050%.

[0038] The high-Cr weathering steel strip provided by the present application has excellent surface quality and corrosion resistance, and stable mechanical properties. The design idea is as follows:

[0039] 1) High Cr content and Cu-Sb-P multi-element alloy complex design are adopted to promote the formation of dense corrosion products, increase the passivation ability of the rust layer, and improve the atmospheric corrosion resistance of the material through the interaction between alloying elements;

[0040] 2) The slab is directly charged into the furnace, rapid heating, low heating temperature and weak reducing atmosphere are controlled to reduce the surface oxidation of the cast slab. The descaling effect is improved by controlling the water pressure, water volume, distance between the descaling nozzle and the slab, etc. to remove the scale on the surface of the strip steel; further, the arrangement of laminar cooling water is used to weaken the oxidation of the strip during the cooling process after finish rolling.

[0041] 3) The scale on the surface of the strip steel is removed and the surface quality is improved by controlling the acid pickling process such as tension leveling, acid concentration and temperature, and pickling speed.

[0042] 4) According to the high hardenability characteristics of high-Cr weathering steel, ultra-low C and low Mn design is adopted, combined with the phase transformation characteristics to improve the coiling temperature of the head and tail of the hot-rolled coil, and the steel coil is slowly cooled in the holding pit with a cooling speed ≤2℃ / s, so that the hot-rolled coil is single ferrite structure, thereby improving the stability of the mechanical properties.

[0043] 5) Based on the low heating temperature and the chemical composition characteristics of ultra-low C and low Mn in the present application, vanadium-nitrogen micro-alloying is further adopted to improve the strength of the material.

[0044] Compared with the prior art, the present application has the following beneficial effects:

[0045] 1. The steel strip coil of the present application is single ferrite structure, stable mechanical properties, yield strength 370-450 MPa, tensile strength 500-590 MPa, elongation 28%-35%, excellent plasticity.

[0046] 2. The steel strip of the present application adopts high Cr-Cu-Sb-P multi-alloy composite design, excellent atmospheric corrosion resistance, relative Q345B corrosion rate <25%, especially suitable for equipment and component manufacturing in industrial atmospheric environment, improving service life.

[0047] 3. The present application designs the whole process of chemical composition, hot continuous rolling process and pickling process, and the pickling steel strip has excellent surface quality, solving the problem of high Cr pickling weathering steel strip surface oxidation strip. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The microstructure of the head (a), middle (b) and tail (c) of the high Cr weathering steel coil in Example 1 is polygonal ferrite;

[0049] Figure 2 The microstructure of the head (a), middle (b) and tail (c) of the high Cr weathering steel coil in Comparative Example 1 is as follows: the head is bainite structure, and the tail is bainite + ferrite structure;

[0050] Figure 3 The surface morphology of the high Cr weathering steel hot-rolled strip in Example 2 is shown in Figure 2;

[0051] Figure 4 The surface morphology of the high Cr weathering steel hot-rolled strip in Comparative Example 3 is shown in Figure 4;

[0052] Figure 5 The surface morphology of the high Cr weathering steel strip after pickling in Example 3 is shown in Figure 6;

[0053] Figure 6 The surface morphology of the high Cr weathering steel strip after pickling in Comparative Example 4 is shown in Figure 8. DETAILED DESCRIPTION

[0054] The application provides a high-Cr weather-resistant steel strip, which has the following chemical components and mass percentage contents (wt%): Mn: 0.15%-0.45%, P: 0.015%-0.035%, Cr: 3.50%-5.50%, Cu: 0.20%-0.40%, Sb: 0.020%-0.040%, Als: 0.015%-0.035%, V: 0.020%-0.040%, N: 0.010%-0.015%, C: ≤0.010%, Si: ≤0.10%, S: ≤0.0050%, and the rest is Fe and inevitable impurity elements.

[0055] The chemical components and mass percentages of the examples and the comparative examples are shown in Table 1.

[0056] Table 1 chemical components and mass percentages of the examples and the comparative examples

[0057]

[0058]

[0059] The production process of the high-Cr weather-resistant steel strip is as follows:

[0060] hot metal pretreatment deep desulfurization, converter smelting, secondary refining, continuous casting, heating, rolling, laminar cooling, coiling, cooling to room temperature, uncoiling, welding, straightening, pickling, skin pass, oiling and coiling.

[0061] The main process parameters of the rolling process of the examples and the comparative examples are shown in Table 2.

[0062] Table 2 main process parameters of the rolling and cooling processes

[0063]

[0064]

[0065] The application adopts a continuous pickling process to remove the iron oxide scale on the surface of the strip, and the main process parameters of the pickling process of the examples and the comparative examples are shown in Table 3.

[0066] Table 3 main process parameters of the pickling process

[0067]

[0068] The mechanical properties and surface quality of the examples and the comparative examples are shown in Table 4. The yield strength of the head, middle and tail of the pickling coil of the comparative example 1 fluctuates by 290 MPa, the tensile strength fluctuates by 388 MPa, and the elongation fluctuates by 18.5%.

[0069] Table 4 mechanical properties and surface quality of the pickling coil

[0070]

[0071] According to TB / T 2375, a 72h periodic immersion corrosion test is carried out, the test solution is 0.01 mol / L sodium bisulfite, the solution pH value is 4-5, and the sample size is: thickness* width* length = 2-4 mm* 40 mm* 60 mm. Q345B low alloy steel is used as a comparative sample, and the test results are shown in Table 5. The corrosion weight loss rate of each embodiment is ≤25% relative to Q345B ordinary weathering steel, and the weathering steel has excellent atmospheric corrosion resistance.

[0072] Table 5: Atmospheric corrosion resistance of each embodiment and comparative sample

[0073] Average corrosion weight loss rate, (g / (m 2 ·h)) Relative corrosion rate, % Example 1 / / Example 2 1.01 22 Example 3 1.10 24 Example 4 0.97 21 Comparative Example 1 1.16 25 Comparative Example 2 1.52 33 Comparative Example 3 1.11 24 Comparative Example 4 1.15 25 Q345B 4.61 100

[0074] In summary, the hot-rolled pickled high-Cr weathering steel strip prepared according to the chemical composition, smelting, continuous casting, heating, controlled rolling and controlled cooling, and pickling process control technology has a yield strength of 370-450 MPa, a tensile strength of 500-590 MPa, and an elongation of 28%-35%, stable mechanical properties, excellent surface quality, and excellent atmospheric corrosion resistance.

[0075] The above-mentioned reference embodiments for a high-Cr weathering steel strip and a production method of the hot-rolled pickled high-Cr weathering steel strip with excellent surface quality and stable mechanical properties are illustrative rather than limiting, and a number of embodiments can be listed within the limited range, and therefore changes and modifications without departing from the overall concept of the present application shall be within the protection scope of the present application.

Claims

1. A high-Cr weathering steel strip, characterized in that, The high-Cr weathering steel strip comprises the following chemical composition by weight percentage: Mn: 0.15%~0.45%, P: 0.015%~0.035%, Cr: 3.50%~5.50%, Cu: 0.20%~0.40%, Sb: 0.020%~0.040%, Als: 0.015%~0.035%, V: 0.020%~0.040%, N: 0.010%~0.015%, C: ≤0.010%, Si: ≤0.10%, S: ≤0.0050%, with the remainder being Fe and unavoidable impurity elements; The metallographic structure of the high-Cr weathering steel strip is polygonal ferrite; The high-Cr weather-resistant steel strip is produced by hot rolling and pickling processes. In the hot continuous rolling process, the billet is heated in a furnace with a weak reducing atmosphere and an air excess coefficient of 0.90~0.95 for 100~150 min, including a soaking time of 25-40 min, and the exit temperature is 1150℃~1220℃. In the hot continuous rolling process, the billet is descaled once by high-pressure water after exiting the furnace, and high-pressure water is used to descale before each pass of the rough rolling; a second high-pressure water descale is used before entering the finish rolling. After the billet exits the furnace and before each pass of the rough rolling mill, the descaling water pressure is 20-25 MPa, and the descaling water volume is 650-700 m³ / h. 3 / h, the distance from the upper and lower nozzles to the slab is 120-140mm; Before the finishing mill inlet, the descaling water pressure is 30-35 MPa, and the descaling water volume is 750-800 m³ / h. 3 / h, nozzle height 70-100mm; In the hot continuous rolling process, the roughing rolling is carried out in 3+3 passes using two stands; the starting rolling temperature of the finishing rolling stage is ≤1030℃, and the finishing rolling temperature is 870~910℃. In the hot continuous rolling process, the coiling temperature within 25m of the head of the hot coil is 720-750℃, the coiling temperature within 50m of the tail of the hot coil is 700-730℃, and the coiling temperature of other parts of the hot coil is 620-660℃; after coiling, the hot-rolled coil is placed in a heat preservation pit for slow cooling, and the cooling rate is controlled to be ≤2℃ / s. In the pickling process, the strip is welded after uncoiling, and then the strip is tension-straightened with an elongation of 1.2-1.8% using a tension-straightening machine. In the pickling process, continuous pickling is performed using three ultra-shallow tanks, with an acid spray pressure of 35-50 kPa; the free acid concentration in the first pickling tank is 25-50 g / L, Fe... 2+ Concentration 200-250 g / L; Free acid concentration in the second pickling tank 120-160 g / L, Fe 2+ Concentration 120-160 g / L; Free acid concentration in the third pickling tank 150-200 g / L, Fe 2+ Concentration 50-100g / L; acid temperature 70-80℃; pickling speed 65-80m / min.

2. The high-Cr weathering steel strip according to claim 1, characterized in that, The high-Cr weathering steel strip has a yield strength of 370~450MPa, a tensile strength of 500~590MPa, and an elongation of 28%~35%.

3. A method for producing hot-rolled pickled high-Cr weathering steel strip with excellent surface quality and stable mechanical properties, characterized in that, The high-Cr weathering steel strip with the chemical composition as described in claim 1 is produced by hot rolling and pickling processes. In the hot continuous rolling process, the billet is heated in a furnace with a weak reducing atmosphere and an air excess coefficient of 0.90~0.95 for 100~150 min, including a soaking time of 25-40 min, and the exit temperature is 1150℃~1220℃. In the hot continuous rolling process, the billet is descaled once by high-pressure water after exiting the furnace, and high-pressure water is used to descale before each pass of the rough rolling; a second high-pressure water descale is used before entering the finish rolling. After the billet exits the furnace and before each pass of the rough rolling mill, the descaling water pressure is 20-25 MPa, and the descaling water volume is 650-700 m³ / h. 3 / h, the distance from the upper and lower nozzles to the slab is 120-140mm; Before the finishing mill inlet, the descaling water pressure is 30-35 MPa, and the descaling water volume is 750-800 m³ / h. 3 / h, nozzle height 70-100mm; In the hot continuous rolling process, the roughing rolling is carried out in 3+3 passes using two stands; the starting rolling temperature of the finishing rolling stage is ≤1030℃, and the finishing rolling temperature is 870~910℃. In the hot continuous rolling process, the coiling temperature within 25m of the head of the hot coil is 720-750℃, the coiling temperature within 50m of the tail of the hot coil is 700-730℃, and the coiling temperature of other parts of the hot coil is 620-660℃; after coiling, the hot-rolled coil is placed in a heat preservation pit for slow cooling, and the cooling rate is controlled to be ≤2℃ / s. In the pickling process, the strip is welded after uncoiling, and then the strip is tension-straightened with an elongation of 1.2-1.8% using a tension-straightening machine. In the pickling process, continuous pickling is performed using three ultra-shallow tanks, with an acid spray pressure of 35-50 kPa; the free acid concentration in the first pickling tank is 25-50 g / L, Fe... 2+ Concentration 200-250 g / L; Free acid concentration in the second pickling tank 120-160 g / L, Fe 2+ Concentration 120-160 g / L; Free acid concentration in the third pickling tank 150-200 g / L, Fe 2+ Concentration 50-100g / L; acid temperature 70-80℃; pickling speed 65-80m / min.

4. The production method according to claim 3, characterized in that, In the hot continuous rolling process, laminar cooling is performed immediately after finishing rolling, and the cooling manifolds are turned on every other row.

5. The production method according to claim 3, characterized in that, In the pickling process, the rinsed strip steel is leveled with a leveling elongation of 0.4%-1.0%, and then oiled.

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