Economical high-strength and high-plasticity hot-rolled pickling weathering-resistant steel strip and production method thereof

Abstract

The invention discloses an economical high-strength plasticity hot-rolled pickling weathering-resistant steel strip and a production method thereof. The steel strip comprises the following chemical components in percentage by weight: 0.16%-0.19% of C, 0.10%-0.20% of Si, 0.30%-0.60% of Mn, 0.10%-0.13% of P, less than or equal to 0.008% of S, 0.50%-0.80% of Cr, 0.15%-0.25% of Cu, 0.015%-0.035% of Sb, 0.015%-0.035% of Als, 0.010%-0.020% of Ti and the balance of Fe and inevitable impurity elements, and the metallographic structure of the steel strip is polygonal ferrite and pearlite. Through cooperation of the chemical components, the controlled rolling and controlled cooling process and the acid pickling and leveling process, the steel strip has high strength, high plasticity, good surface quality and excellent corrosion resistance at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of steel materials, and in particular relates to an economical high-strength and plastic hot-rolled pickled weathering steel strip and a production method thereof. Background Art

[0002] Weathering steel boasts superior atmospheric corrosion resistance compared to ordinary carbon steel and is widely used in the manufacture of outdoor equipment and components, including containers, rolling stock, bridges, and photovoltaic mounting systems. As the application of weathering steel continues to expand and its forming becomes increasingly complex, the requirements for steel plate strength, ductility, and cost-effectiveness are becoming increasingly stringent. When used in the hot-rolled, pickled state, weathering steel must exhibit high strength and ductility, good surface quality, and cost-effectiveness to meet these evolving requirements.

[0003] Si and Cr are common alloying elements in weathering steel that improve its atmospheric corrosion resistance. However, Si and Cr easily react with the steel matrix at high temperatures to form highly adherent oxides, which are difficult to completely remove during hot rolling descaling. Strip-like iron oxide defects often remain on the surface of weathering steel strips after pickling. Therefore, surface quality control of weathering steel is extremely difficult.

[0004] Chinese patent CN 116623079 A discloses a method for producing pickled weathering steel sheet for photovoltaic supports with an Rm ≥ 1500 MPa using CSP. The chemical composition and weight percentage of the steel sheet are as follows: C: 0.20-0.25%, Si: 0.10-0.30%, Mn: 1.00-1.40%, P ≤ 0.010%, S ≤ 0.004%, Ti: 0.020-0.040%, Cu: 0.15-0.45%, Cr: 0.10-0.50%, B: 0.0030-0.0040%, with the remainder being Fe and unavoidable impurities. The patent focuses solely on the steel sheet's weathering and mechanical properties, but not its surface quality.

[0005] Chinese patent CN 104611711 A discloses a pickling solution and method for high-alloy corrosion-resistant steel. The pickling solution contains the following substances in their mass ratios: 8-22% hydrochloric acid, 4-10% sulfuric acid, 0.5-1% phosphoric acid, 0.1-1% corrosion inhibitor, 0.05-0.15% surfactant, 0.05-0.15% solution stabilizer, and the balance is water. The annealed hot-rolled wire rod is placed directly into the pickling tank for pickling at a temperature of 45-85°C for 30-40 minutes. After pickling, the steel is rinsed, passivated with nitric acid, and then rinsed with water. This method is suitable for immersion pickling of wire rods but not for pickling strip steel. Summary of the Invention

[0006] The object of the present invention is to provide an economical high-strength and high-ductility hot-rolled pickled weathering steel strip and a production method thereof. The steel strip has high strength, high ductility, good surface quality and excellent corrosion resistance.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] An economical high-strength and plastic hot-rolled pickled weathering steel strip comprises the following chemical components in weight percentage: C: 0.16%-0.19%, Si: 0.10%-0.20%, Mn: 0.30%-0.60%, P: 0.10%-0.13%, S: ≤0.008%, Cr: 0.50%-0.80%, Cu: 0.15%-0.25%, Sb: 0.015%-0.035%, Als: 0.015%-0.035%, Ti: 0.010%-0.020%, and the remainder is Fe and unavoidable impurity elements.

[0009] The metallographic structure of the economical high-strength plastic hot-rolled pickled weathering steel strip is polygonal ferrite and pearlite; wherein the volume fraction of the polygonal ferrite is 88-92%; and the average grain size of the ferrite is 8.5-10 μm.

[0010] The yield strength R of the economical high-strength ductility hot-rolled pickled weathering steel strip eL ≥480MPa, tensile strength R m ≥550MPa, elongation A≥33%.

[0011] The present invention also provides a method for producing the economical high-strength and plastic hot-rolled pickled weathering steel strip, which comprises the following steps: molten steel smelting → continuous casting → heating → controlled rolling and controlled cooling → coiling → cooling to room temperature → uncoiling → pickling → rinsing → leveling;

[0012] In the heating step, a weak reducing atmosphere is used with an excess air coefficient of 0.90 to 0.95, and high-pressure water is used for descaling the slab after it is removed from the furnace;

[0013] In the controlled rolling and controlled cooling step, rough rolling is performed using two four-roll reversible rolling mills for 3+5 passes, with descaling performed in the first and third passes of the first stand and in the first, third and fifth passes of the second stand; secondary high-pressure water descaling is performed before the finishing rolling entrance, and the descaling water is fully opened between the finishing rolling stands;

[0014] In the coiling step, the strip is immediately cooled to 660-720°C at a cooling rate of 10°C / s to 25°C / s after exiting the finishing mill, and the cooling manifolds of the laminar cooling line are fully opened to keep the surface of the strip covered with cooling water from the time the strip exits the finishing mill to the time it enters the coiler. A layer of water vapor film is generated due to the heat exchange between the high-temperature steel strip and the cooling water, thereby preventing the high-temperature strip matrix from being directly in contact with the air and being oxidized. High-temperature coiling is used to obtain a microstructure dominated by polygonal ferrite, and promotes the recovery of deformation dislocations within the ferrite grains, thereby improving the plasticity of the material. However, if the coiling temperature is too high, the oxidation of the steel matrix will be aggravated, the surface quality of the strip will be deteriorated, and the deformation resistance of the steel will be reduced, which can easily cause the hot-rolled coil to flatten; if the coiling temperature is too low, a bainite structure will be generated, resulting in excessive strength of the strip and insufficient plasticity.

[0015] In the pickling step, the strip is straightened before pickling to improve the shape of the hot-rolled strip and break the iron oxide scale on the surface of the strip, thereby improving the pickling efficiency. The elongation of the straightening machine is 0.5-1.8%.

[0016] Furthermore, in the continuous casting step, the continuous casting superheat is 8-20°C, and the casting speed is 0.8-1.3 m / min.

[0017] In the heating step, the temperature of the ingot entering the furnace is ≥600°C, the time in the furnace is 120-160 minutes, and the temperature out of the furnace is 1160°C-1220°C, which promotes the full solid solution of the alloy elements, while avoiding the coarsening of the austenite grains caused by too long heating time, and reduces the oxidation and burning of the iron matrix on the surface of the slab and the enrichment of liquid copper at the austenite grain boundaries during the heating process.

[0018] The descaling water pressure of the first high-pressure water descaling is 18-25MPa, and the distance from the nozzle to the slab is 100-150mm; the descaling water pressure of the rough rolling is 18~25MPa; the descaling water pressure of the second high-pressure water descaling is 25-35MPa, and the nozzle height is 80-130mm.

[0019] The starting rolling temperature in the finishing rolling stage is ≤1030℃, and the cumulative deformation is ≥80%; the final rolling temperature of the finishing rolling is 860-910℃. If the final rolling temperature is too low, rolling in the two-phase region will easily cause mixed crystals, reduce the plasticity of the material, and increase the deformation resistance. Rolling thin specifications will easily cause tail swinging; if the final rolling temperature is too high, the austenite grains before phase transformation will coarsen, deformation dislocations will recover, and the strength of the material will be reduced.

[0020] In the pickling step, three sections of ultra-shallow tanks are used for continuous pickling, the acid liquid spray pressure is 35-50 kPa; the acid liquid temperature is 75-85° C., and the pickling speed is 50-80 m / min. A low pickling speed causes the base material to be immersed in the acid liquid for too long, reducing the material yield and output, and the hydrogen atoms in the acid liquid diffuse into the interior of the steel matrix, affecting the performance of the product. An excessively fast pickling speed causes the base material to be immersed in the acid liquid for too short a time, and part of the iron oxide scale on the surface of the strip is not removed, resulting in poor surface quality.

[0021] The free acid concentration in the first pickling tank is 25-50g / L, Fe 2+ Concentration 200-250g / L; free acid concentration in the second pickling tank is 120-160g / L, Fe 2+ Concentration 120-160g / L; free acid concentration in the third pickling tank 150-200g / L, Fe 2+ Concentration 50-100g / L;

[0022] The rinsing water temperature is 60-80℃; the tempering rolling force is 350-450 tons. The yield strength of the material is increased by 50-100MPa through the deformation strengthening effect of the tempering process, and the impact on plasticity is small, which effectively avoids the contradiction between increased strength and reduced plasticity of steel, and also avoids increasing strength by adding alloys to increase costs, reducing manufacturing costs, and ensuring the high strength, plasticity and economy of the steel strip while obtaining high surface quality.

[0023] Finished product roughness 0.6μm-1.0μm; after leveling, the strip surface is oiled with an oiling amount of 0.5g / m 2 -0.9g / m 2 , to avoid oxidation of the strip surface.

[0024] In the economical high-strength and plastic hot-rolled pickled weathering steel strip provided by the present invention, the functions and controls of the various components are as follows:

[0025] Carbon (C): Carbon significantly increases material strength through interstitial solid solution strengthening without increasing smelting costs, allowing for reduced addition of manganese and microalloying elements, thereby lowering alloy costs. Properly increasing the carbon content allows for the use of economical alloys such as high-carbon ferromanganese and high-carbon ferrochrome during steelmaking, reducing the alloy cost of weathering steel. However, excessive carbon content can reduce the steel's plasticity and weldability. To avoid the peritectic zone, prevent cracking in the cast ingot, and reduce cast cleaning costs, the present invention sets the carbon content to 0.16-0.19%.

[0026] Si (Silicon): Si is a deoxidizing element used in the steelmaking process and can also refine corrosion products and improve atmospheric corrosion resistance. However, excessive Si content can easily react with the substrate during heating to form Fe2SiO4, which adheres strongly to the substrate and is difficult to remove through descaling and pickling, thus deteriorating the surface quality of the steel. Therefore, the Si content in this invention is designed to be 0.10-0.20%.

[0027] Mn (Manganese): Mn is an important solid solution strengthening element in steel and a crucial deoxidizing element during the steelmaking process. However, excessive Mn content not only increases manufacturing costs and deteriorates the weldability of the steel, but also increases the stability of supercooled austenite and promotes bainite transformation. Therefore, its content is designed to be between 0.30% and 0.60%.

[0028] Al (aluminum): Al is the primary deoxidizing element added to steel. It also combines with nitrogen to precipitate AlN at high temperatures, refining the austenite grain size. However, excessive Al content can increase oxide inclusions in the steel, reducing the steel's atmospheric corrosion resistance and increasing alloy cost. Therefore, its content is designed to be between 0.015% and 0.035%.

[0029] Cr (chromium): Cr is a key alloying element that improves steel's atmospheric corrosion resistance. It accumulates in the rust layer within the steel and promotes the transformation of corrosion products into dense α-FeOOH, enhancing the protective properties of the rust layer. Cr binds more strongly to oxygen than Fe does. Excessive Cr content can easily form a Cr2O3 oxide film on the steel surface, which is tightly bonded to the substrate. This film is difficult to remove during descaling and pickling, resulting in black oxide strips on the steel surface after pickling. Therefore, the Cr content is designed to be between 0.50% and 1.10%.

[0030] Cu (copper): Cu can significantly improve the atmospheric corrosion resistance of the material, and the effect of improving atmospheric corrosion resistance is even better when combined with Cr. It can also precipitate two-phase particles to increase material strength. However, Cu has a low melting point of only 1083°C. Excessive content can easily lead to steel leakage during continuous casting and surface defects such as edge cracks and warping during hot rolling. In addition, the cost of Cu is much higher than that of Cr. Therefore, the Cu content is designed to be 0.15-0.25%.

[0031] Sb (antimony): Sulphurous acid (sulfurous acid) in the air reacts with water vapor to form sulfurous acid, which adheres to the surface of steel and exacerbates corrosion. Adding an appropriate amount of Sb can significantly improve the material's corrosion resistance in industrial atmospheres and reduce hydrochloric acid corrosion during pickling. However, Sb has a low melting point, and excessive Sb content can deteriorate the steel's hot workability and weldability. Therefore, the Sb content in this invention is designed to be 0.015-0.035%.

[0032] Ti (Titanium): Ti and N have a strong bond, forming TiN particles with a high melting point. During high-temperature heating, Ti inhibits austenite grain coarsening and refines austenite grains, thereby improving the enrichment of liquid copper at austenite grain boundaries. It also inhibits grain growth in the heat-affected zone during welding, improving weldability. However, excessive Ti content increases costs, tends to form oversized TiN particles, and reduces the material's plasticity. Therefore, the Ti content in this invention is designed to be between 0.010% and 0.020%.

[0033] Phosphorus (P): P is the most economical element for improving steel's atmospheric corrosion resistance. It can also increase strength through solid solution strengthening. However, P tends to segregate at grain boundaries, increasing weld crack susceptibility. Therefore, the P content is controlled within a range of 0.10% to 0.13%.

[0034] Sulfur (S): S is a harmful residual element in steel. It easily reacts with manganese to form MnS non-metallic inclusions, which induce pitting corrosion and deteriorate the steel's atmospheric corrosion resistance. However, too low a S content increases smelting costs. Therefore, the present invention controls the S content to ≤ 0.008%.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1) The present invention uses the coordinated design of chemical composition, controlled rolling and controlled cooling process and pickling and leveling process to ensure that the pickled and leveled strip has high strength and excellent plasticity: yield strength R eL ≥480MPa, tensile strength R m ≥550MPa, elongation A≥33%.

[0037] 2) The present invention appropriately increases the C content. On the one hand, the material strength is improved through the interstitial solid solution strengthening effect of C atoms, which reduces the addition of other strengthening alloy elements and reduces the alloy cost. It can also increase the use of economical alloys such as high-carbon ferromanganese and high-carbon ferrochrome, thereby reducing the alloy cost. It avoids the peritectic zone, reduces cracks in the ingot, and saves the cost of cleaning the corners of the ingot. Through hot charging and rolling, the energy consumption of the heating furnace is further reduced, thereby reducing the manufacturing cost.

[0038] 3) The present invention increases the yield strength of the material by 50-100 MPa through the deformation strengthening effect of the pickling and leveling process, with little effect on plasticity. This avoids the contradiction between increased steel strength and reduced plasticity, and also avoids the need to increase strength by adding alloys, reducing manufacturing costs. While achieving high surface quality, it also ensures high strength, plasticity and cost-effectiveness of the steel strip.

[0039] 4) The present invention achieves good surface quality of the steel strip after pickling through coordinated control of low-temperature rapid heating, high-pressure descaling, laminar continuous cooling and pickling processes, thus solving the problem of controlling iron oxide strips on the surface of weathering steel.

[0040] 5) The present invention takes into account both the high surface quality and atmospheric corrosion resistance requirements of the pickled weathering steel strip. Through the design of a small amount of diversified chemical composition of Si-P-Cr-Cu-Sb, it has excellent atmospheric corrosion resistance, with a corrosion rate of ≤43% relative to Q345B. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 1 is the metallographic structure diagram of the steel strip in Example 1;

[0042] Figure 2 The surface of the steel strip after pickling in Example 1;

[0043] Figure 3 The surface of the steel strip after pickling in Example 2;

[0044] Figure 4 The surface of the steel strip after pickling in Comparative Example 1 has oxidized strips on the surface;

[0045] Figure 5 This is the surface of the steel strip after pickling in Comparative Example 3, and there are oxidized strips on the surface. DETAILED DESCRIPTION

[0046] The present invention provides an economical high-strength and plastic hot-rolled pickled weathering steel strip, which comprises the following chemical components in weight percentage: C: 0.16% to 0.19%, Si: 0.10% to 0.20%, Mn: 0.30% to 0.60%, P: 0.10% to 0.13%, S: ≤0.008%, Cr: 0.50% to 0.80%, Cu: 0.15% to 0.25%, Sb: 0.015% to 0.035%, Als: 0.015% to 0.035%, Ti: 0.010% to 0.020%, and the remainder is Fe and unavoidable impurity elements.

[0047] The production method of the economical high-strength and plastic hot-rolled pickled weathering steel strip comprises the following steps: molten steel smelting → continuous casting → heating → controlled rolling and controlled cooling → coiling → cooling to room temperature → uncoiling → pickling → rinsing → leveling;

[0048] In the continuous casting step, the continuous casting superheat is 8 to 20°C, and the casting speed is 0.8 to 1.3 m / min;

[0049] In the heating step, the temperature of the slab entering the furnace is ≥600°C, the time in the furnace is 120-160 minutes, the temperature out of the furnace is 1160-1220°C, a weak reducing atmosphere is used, the air excess coefficient is 0.90-0.95, and the slab is descaled once with high-pressure water after being taken out of the furnace. The descaling water pressure is 18-25 MPa, and the distance from the nozzle to the slab is 100-150 mm.

[0050] In the controlled rolling and controlled cooling step, rolling is carried out in two stages: roughing and finishing. Roughing is performed using two four-roll reversible rolling mills with 3+5 passes. Descaling is performed in the first and third passes of the first stand, and in the first, third, and fifth passes of the second stand. The descaling water pressure for roughing is 18-25 MPa. A secondary high-pressure water descaling process is used before the finishing entrance to remove the surface oxide scale on the intermediate billet. The descaling water pressure is 25-35 MPa, the nozzle height is 80-130 mm, and the descaling water between the finishing stands is fully open. The starting rolling temperature in the finishing stage is ≤1030°C, and the cumulative deformation is ≥80%. The final rolling temperature for finishing is 860-910°C.

[0051] In the coiling step, the strip is immediately cooled to 660-720°C at a cooling rate of 10°C / s to 25°C / s after leaving the finishing mill and is coiled. The cooling manifolds of the laminar cooling line are fully opened to keep the surface of the strip covered with cooling water from the time the strip leaves the finishing mill to the time it enters the coiler, thereby preventing the high-temperature strip substrate from being oxidized by direct contact with the air.

[0052] In the pickling step, laser welding is used after uncoiling, and then the strip is straightened, with an elongation of 0.5-1.8%. A three-stage ultra-shallow tank is used for continuous pickling, with an acid injection pressure of 35-50kPa. The free acid concentration in the first pickling tank is 25-50g / L, and Fe 2+ Concentration 200-250g / L; free acid concentration in the second pickling tank is 120-160g / L, Fe 2+ Concentration 120-160g / L; free acid concentration in the third pickling tank 150-200g / L, Fe 2+ Concentration 50-100g / L. Acid temperature 75-85℃, pickling speed 50-80m / min.

[0053] After pickling, the steel strip is rinsed with the rinsing water temperature at 60-80°C.

[0054] The temper rolling force is 350-450 tons, and the finished product roughness is 0.6μm-1.0μm.

[0055] The amount of oil applied to the strip surface after leveling is 0.5g / m 2 -0.9g / m 2 .

[0056] The present invention is described in detail below with reference to the embodiments.

[0057] The chemical compositions of the examples and comparative examples are shown in Table 1.

[0058] Table 1 Chemical compositions of various embodiments and comparative examples

[0059]

[0060] The hot rolling process of the present invention is conventionally performed in a continuous hot strip rolling process, and the pickling process is performed using a continuous steel strip pickling line. The manufacturing process includes: molten steel smelting → continuous casting → heating → controlled rolling and controlled cooling → coiling → cooling to room temperature → uncoiling → pickling → rinsing → leveling. The main process parameters for the hot rolling and pickling processes of the embodiment and comparative example are shown in Tables 2 and 3, respectively.

[0061] Table 2 Main process parameters of hot rolling process

[0062]

[0063]

[0064] Table 3 Main process parameters of pickling process

[0065]

[0066] The mechanical properties and surface quality of the pickled steel strips produced using the chemical composition and process described in the examples and comparative examples are shown in Table 4. The tensile properties test was conducted in accordance with GB / T 228.1-2010 "Tension Tests on Metallic Materials - Part 1: Room Temperature Test Methods".

[0067] Table 4 Mechanical properties and surface quality of pickled weathering steel strip

[0068]

[0069] Cyclic immersion corrosion testing was conducted according to TB / T 2375, with a 72-hour test period, 0.01 mol / L NaHSO₃ solution, and a pH of 4.4-4.8. The corrosion specimens were sized 40 mm x 60 mm x 2-4 mm, with five replicates per group. The results are shown in Table 5.

[0070] Table 5 Corrosion resistance of examples and comparative examples

[0071]

[0072]

[0073] In summary, the pickled weathering steel strip obtained according to the chemical composition of the steel grade, heating process, descaling process, controlled rolling and cooling process, and pickling process control technology of the present invention has a yield strength of ≥480MP, a tensile strength of ≥550MPa, an elongation of ≥33%, and a corrosion rate relative to Q345B of ≤43%. It has high strength and plasticity, excellent atmospheric corrosion resistance, good surface quality, and low manufacturing cost, and can be used in the manufacture of railway vehicles, containers, etc.

[0074] In Comparative Example 1, the slab is heated in the heating furnace for too long, resulting in the formation of thick iron oxide scale on the surface of the slab. In the subsequent rolling process, the descaling water pressure is low, the descaling nozzle height is too high, and the straightening elongation before pickling is low. After pickling, iron oxide strips appear on the surface of the steel strip.

[0075] In Comparative Example 2, a 0.25C-1.0Mn composition design is adopted, and a low-temperature coiling process is used for hot rolling. Although the steel plate has high strength, the elongation is low, which restricts the forming application of the steel strip.

[0076] In Comparative Example 3, the 0.5Si-1.70Cr composition design is adopted, and the iron oxide on the surface of the hot-rolled steel strip is difficult to remove, and the free acid concentration of the pickling is low, resulting in the presence of iron oxide strips on the surface of the steel strip after pickling.

[0077] In Comparative Example 4, the Cr and Cu contents were low, and Sb was absent, resulting in insufficient corrosion resistance. The hot-rolled descaling water pressure was low, and the nozzle was too close to the steel plate, making it difficult to remove the iron oxide scale from the hot-rolled steel strip. The pickling speed was high, and the acid solution temperature was low, resulting in poor pickling results, with iron oxide streaks forming on the steel strip surface.

[0078] In Comparative Example 5, the temper rolling force is only 50 tons, which has limited effect on improving the strength of the steel strip and the strength of the material is insufficient.

[0079] The above-mentioned detailed description of the economical high-strength and plastic hot-rolled pickled weathering steel strip and its production method with reference to the embodiments is illustrative rather than restrictive. Several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. An economical high-strength plastic hot-rolled pickled weathering steel strip, characterized in that: The invention comprises the following chemical components in weight percentage: C: 0.16% to 0.19%, Si: 0.10% to 0.20%, Mn: 0.30% to 0.60%, P: 0.10% to 0.13%, S: ≤ 0.008%, Cr: 0.50% to 0.80%, Cu: 0.15% to 0.25%, Sb: 0.015% to 0.035%, Als: 0.015% to 0.035%, Ti: 0.010% to 0.020%, and the rest are Fe and unavoidable impurity elements.

2. The economical high-strength and plastic hot-rolled pickled weathering steel strip according to claim 1, characterized in that: The metallographic structure of the economical high-strength plastic hot-rolled pickled weathering steel strip is polygonal ferrite and pearlite; wherein the volume fraction of the polygonal ferrite is 88-92%; and the average grain size of the ferrite is 8.5-10 μm.

3. The economical high-strength and plastic hot-rolled pickled weathering steel strip according to claim 1, characterized in that: The yield strength R of the economical high-strength ductility hot-rolled pickled weathering steel strip eL ≥480MPa, tensile strength R m ≥550MPa, elongation A≥33%.

4. A method for producing an economical high-strength and plastic hot-rolled pickled weathering steel strip according to claim 1, characterized in that: The production method comprises the following steps: molten steel smelting → continuous casting → heating → controlled rolling and controlled cooling → coiling → cooling to room temperature → uncoiling → pickling → rinsing → leveling; In the heating step, a weak reducing atmosphere is used with an excess air coefficient of 0.90 to 0.95, and high-pressure water is used for descaling the slab after it is removed from the furnace; In the controlled rolling and controlled cooling step, rough rolling is performed using two four-roll reversible rolling mills for 3+5 passes, with descaling performed in the first and third passes of the first stand and in the first, third and fifth passes of the second stand; secondary high-pressure water descaling is performed before the finishing rolling entrance, and the descaling water is fully opened between the finishing rolling stands; In the coiling step, the strip is immediately cooled to 660-720°C at a cooling rate of 10°C / s to 25°C / s after leaving the finishing mill and is coiled. The cooling manifolds of the laminar cooling line are fully opened to keep the surface of the strip covered with cooling water from the time the strip leaves the finishing mill to the time it enters the coiler. In the pickling step, the strip steel is tension-leveled before pickling.

5. The production method according to claim 4, characterized in that: In the heating step, the temperature of the casting into the furnace is ≥600°C, the time in the furnace is 120-160 minutes, and the temperature out of the furnace is 1160-1220°C.

6. The production method according to claim 4, characterized in that: The descaling water pressure of the first high-pressure water descaling is 18-25MPa, and the distance from the nozzle to the slab is 100-150mm; the descaling water pressure of the rough rolling is 18~25MPa; the descaling water pressure of the second high-pressure water descaling is 25-35MPa, and the nozzle height is 80-130mm.

7. The production method according to claim 4, characterized in that: The starting rolling temperature in the finishing rolling stage is ≤1030℃, and the cumulative deformation is ≥80%; the final rolling temperature of the finishing rolling is 860~910℃.

8. The production method according to claim 4, characterized in that: In the pickling step, three sections of ultra-shallow tanks are used for continuous pickling, the acid liquid spraying pressure is 35-50 kPa; the acid liquid temperature is 75-85° C., and the pickling speed is 50-80 m / min.

9. The production method according to claim 8, characterized in that: The free acid concentration in the first pickling tank is 25-50g / L, Fe 2+ Concentration 200-250g / L; free acid concentration in the second pickling tank is 120-160g / L, Fe 2+ Concentration 120-160g / L; free acid concentration in the third pickling tank 150-200g / L, Fe 2+ Concentration 50-100g / L.

10. The production method according to claim 4, characterized in that: The rinsing water temperature is 60-80°C; the temper rolling force is 350-450 tons, and the yield strength is increased by 50-100 MPa; the finished product roughness is 0.6μm-1.0μm; the strip surface is oiled after tempering.

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