A hot-rolled L290 grade pipeline steel coil for ground gathering and transportation and its production method

Abstract

The invention relates to an L290 grade pipeline steel hot-rolled plate coil for ground gathering and transportation and a production method thereof. The chemical composition of the steel is C: 0.050%-0.060%, Si: 0.15%-0.25%, Mn: 0.20%-0.28%, P≤0.012%, S≤0.003%, Als: 0.030%-0.045%, Nb: 0.010%-0.017%, Cr: 0.11%-0.17%, N≤0.004%, and the remainder is iron and impurities. The yield strength of the hot-rolled coil product is 302-315 MPa, the tensile strength is 456-478 MPa, and the elongation after fracture is ≥38.5%. The Charpy impact energy Akv at -40℃ is ≥350 J, the corrosion rate is 0.0257-0.0292 mm / a, the corrosion potential is ≥-0.467 V, and the corrosion current density is ≤1.14×10 ‑5 A.cm ‑2 .

Description

Technical Field

[0001] The present invention relates to the technical field of low alloy hot rolled coil production, and in particular to an L290 grade pipeline steel hot rolled coil for ground gathering and transportation and a production method thereof. Background Art

[0002] Surface gathering and transportation pipelines are primarily used to transport crude oil, sewage, and natural gas. Because the transport medium contains a certain amount of chloride ions, pipeline corrosion failures such as perforations, leaks, and bursts are frequent. Currently, surface gathering and transportation pipelines used by major oil and gas fields mostly use 20# steel, 16Mn, stainless steel, or corrosion-resistant alloys. Stainless steel and corrosion-resistant alloys are prohibitively expensive to use on a large scale. Surface gathering and transportation pipelines made of 20# and 16Mn steel require the addition of large amounts of Mo, Cr, Ni, and Cu to ensure corrosion resistance due to their high carbon design, resulting in relatively high alloy costs. Therefore, there is an urgent need to develop a steel for surface gathering and transportation pipelines that is low-cost, highly corrosion-resistant, and possesses excellent comprehensive mechanical properties.

[0003] Chinese patent application number CN201310368061.9 discloses "Chloride-ion corrosion-resistant steel for pipelines and its preparation method." The steel's composition (by weight percentage) is: C 0.008% to 0.02%, Si 0.05% to 0.015%, Mn 0.50% to 0.85%, S ≤ 0.010%, P ≤ 0.01%, Mo 0.8% to 2.0%, Al 0.001% to 0.020%, Ni 0.50 to 1.2%, W 0.02 to 0.08% by weight, with Cr satisfying the following inequality: 2.4 - 0.49 [Mo] + 11.8 [C] + 12.2 [W] ≤ Cr ≤ 3.2 - 0.57 [Mo] + 9.8 [C] + 7.2 [W]. However, the addition of Mo, Ni, and W to the pipeline steel results in a high alloy cost.

[0004] The Chinese patent application with application number CN201910420753.0 discloses "a steel resistant to corrosion by multiple media with a yield strength of 500 MPa and a preparation method thereof". The composition of the steel is (by weight percentage): C 0.06%~0.10%, Si 0.15%~0.40%, Mn 0.70%~1.20%, P≤0.025%, S≤0.01%, Cu 0.20%~0.40%, Ni 0.20~0.50%, Cr 0.50~1.0%, Sb 0.02~0.12%, Sn 0.005~0.030%, Nb 0.02~0.05%, Ti 0.015%~0.025%, Ca 0.001%0~0.003%, N≤0.006%. The addition of Sb, Sn and Ni to the steel results in a higher alloy cost. The yield strength of the steel is ≥500MPa, but the impact energy at -40°C is only 80J. The strength and toughness of the product are poorly matched, making it not a preferred material for ground gathering and transportation pipelines.

[0005] Chinese patent application number CN201610802316.1 discloses a "thick gauge X42 pipeline steel and its production method." The steel's composition (by weight) is as follows: C 0.03% to 0.07%, Si 0.10% to 0.30%, Mn 0.70% to 1.0%, P ≤ 0.020%, S ≤ 0.010%, Nb 0.015% to 0.030%, Ti 0.008% to 0.019%, and Cr 0.15% to 0.30%. This steel utilizes a conventional pipeline steel alloy design, significantly different from the present invention.

[0006] Chinese patent application number CN202210190141.9 discloses a "Low-Cost HIC-Resistant L290 Hot-Rolled Steel Plate for Oil and Gas Pipelines and Manufacturing Method." The steel's composition (by weight) is as follows: C 0.03% to 0.042%, Si 0.10% to 0.20%, Mn 0.30% to 0.50%, P ≤ 0.010%, S ≤ 0.005%, Nb 0.035% to 0.055%, and Ti 0.015% to 0.025%. This steel utilizes a conventional pipeline steel alloy design, significantly different from the present invention.

[0007] Chinese patent application number CN20131217916.8 discloses a "CO2 corrosion-resistant pipeline steel for surface gathering and transportation and its preparation method." The steel's composition (by weight percentage) is as follows: C 0.01% to 0.08%, Si 0.10% to 0.50%, Mn 0.50% to 1.50%, P ≤ 0.020%, S ≤ 0.006%, Nb + V + Ti ≤ 0.1%, Cr 1.0 to 3.0%, Mo 0.10% to 0.30%, Cu 0.10% to 0.50%, and Ni 0.10% to 0.50%. However, the patent application relates to the production of medium and thick plates, and incorporates precious metals such as Mo and Ni to achieve excellent corrosion resistance and low-temperature toughness, with a yield strength exceeding 530 MPa.

[0008] Chinese patent application number CN201410247308.6 discloses "5Cr corrosion-resistant steel and its production method." The steel's composition (by weight) is: C 0.05% to 0.07%, Si 0.10% to 0.30%, Mn 0.50% to 0.80%, P ≤ 0.020%, S ≤ 0.01%, Cr 4.5% to 5.5%, and N 0.02% to 0.05%. This application relates to hot-rolled rebar steel, and its mechanical performance requirements differ significantly from those of hot-rolled coil products.

[0009] The paper "Corrosion Resistance Screening and Evaluation Test of Oil Casing and Gathering Pipeline Materials" (authored by Duan Fangwei et al., "Oil and Gas Field Environmental Protection" Issue 6, 2018, pp. 24-28) mentions steel for gathering pipelines. The 20 steel, 16Mn steel, and X65 steel described in the paper are all high-carbon, Nb-free, and compositely added with Cr, Ni, Mo, and Cu alloy designs. The uniform corrosion rate data provided show that the corrosion level of the steel reaches moderate or even severe corrosion. In addition, the paper does not record the production process and mechanical properties of the steel.

[0010] The L290 pipeline steel mentioned in the paper "Chemical Composition Optimization Design of Oil L290M / X42M Pipeline Steel" (authored by Cao Yan et al., published in Welded Pipe, Vol. 39, No. 9, September 2016) has the following composition (by weight): C ≤ 0.080%, Si ≤ 0.20%, Mn 1.00% to 1.50%, Ti 0.01% to 0.02%, and Nb 0.01% to 0.02%. This design uses a conventional acid-resistant pipeline steel alloy, significantly different from the present invention.

[0011] The steels for ground gathering and transportation pipelines involved in the above-mentioned public information are all medium and thick plates and seamless products, and the precious metals Mo and Ni are basically added in the alloy design. Except for the patents "A steel with a yield strength of 500MPa and resistance to corrosion of multiple media and its preparation method" and "Preparation method of CO2 corrosion-resistant pipeline steel for ground gathering and transportation", no Nb is added. The hot-rolled coil of ground gathering and transportation pipeline steel invented by this patent breaks the inherent idea of ​​high-carbon design for ground gathering and transportation steel, and opens up a new way to use low-carbon steel to obtain sufficient strength and good corrosion resistance. Summary of the Invention

[0012] The present invention provides an L290-grade pipeline steel hot-rolled coil for ground gathering and transportation, and a production method thereof. The invention adopts relatively low contents of C, Mn, and Si to ensure that the product has excellent toughness; Nb is added to exert the effect of grain refinement and strengthening; only the most economical Cr is added among the corrosion-resistant elements to obtain excellent corrosion performance, reduce the corrosion rate, and increase the corrosion potential; a low-temperature steelmaking and two-stage rolling process is adopted to ensure that the final product obtains a fine and uniform microstructure; and a small-thickness intermediate billet is used for rolling, breaking the restriction that the thickness of the intermediate billet for pipeline steel must be more than 3.6 times the thickness of the finished product, which can reduce the reduction in the finishing rolling stage, thereby reducing the dislocation density and further improving the corrosion resistance of the product.

[0013] In order to achieve the above object, the present invention adopts the following technical solutions:

[0014] The invention discloses an L290 grade pipeline steel hot-rolled coil for ground gathering and transportation. The chemical composition of the steel is, by weight percentage, C: 0.050%-0.060%, Si: 0.15%-0.25%, Mn: 0.20%-0.28%, P≤0.012%, S≤0.003%, Als: 0.030%-0.045%, Nb: 0.010%-0.017%, Cr: 0.11%-0.17%, N≤0.004%, and the remainder is iron and unavoidable impurities.

[0015] A method for producing L290 grade pipeline steel hot-rolled coils for ground gathering and transportation includes the following process steps: molten iron pretreatment, converter smelting, refining outside the furnace, continuous casting, slab heating, rolling, laminar cooling, and coiling; wherein the following processes are controlled:

[0016] 1) Converter smelting; using top blowing or top and bottom combined blowing;

[0017] 2) Refining outside the furnace: light desulfurization and calcium treatment in LF furnace;

[0018] 3) Continuous casting; using dynamic soft reduction method;

[0019] 4) Slab heating: Continuous casting slab is heated to 1082-1105°C;

[0020] 5) Rolling: A two-stage rolling method is adopted; the rough rolling and finishing rolling temperature is 1025-1036°C, the rough rolling is performed for at least 5 passes, the first pass reduction rate is 18.8%-20%, and the reduction rate of each subsequent pass gradually increases, and the reduction rate of the last pass is 22.1%-23%; after rolling, the temperature is allowed to drop below 990°C before entering the finishing rolling, the finishing rolling temperature is 836-848°C, and the finishing rolling is performed for at least 7 passes, the first pass reduction rate is 17.3%-19.2%, and the reduction rate of each subsequent pass gradually decreases, and the last pass reduction rate is 5%-6%;

[0021] 6) Laminar cooling and coiling: Cool to 542-560°C at a rate of 20.3-22.7°C / s for coiling, and finally air cool to room temperature.

[0022] Furthermore, the yield strength of the hot-rolled coil product is 302-315 MPa, the tensile strength is 456-478 MPa, and the elongation after fracture is ≥38.5%; the Charpy impact energy Akv at -40°C is ≥350 J, the corrosion rate is 0.0257-0.0292 mm / a, the corrosion potential is ≥-0.467 V, and the corrosion current density is ≤1.14×10 -5 A.cm -2 .

[0023] Furthermore, in step 5), the ratio of the thickness of the rolling intermediate billet to the thickness of the finished steel plate is ≤3.0.

[0024] Furthermore, the thickness of the continuous casting slab is 168-171 mm, the thickness of the rolling intermediate slab is 50-53 mm, and the thickness of the finished steel plate is 18-20 mm.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1) Breaking the inherent idea of ​​high-carbon design for existing surface gathering and transportation steel, we adopt a low-carbon, low-manganese, low-sulfur and low-phosphorus design to ensure the product has excellent corrosion resistance and weldability;

[0027] 2) Adding an appropriate amount of Nb to play its role in fine grain strengthening and precipitation strengthening to ensure the toughness of the product;

[0028] 3) No precious metals Ni and Mo are added, only low-cost Cr is added to ensure corrosion resistance, giving the product a significant advantage in terms of economy;

[0029] 4) Low-temperature steelmaking technology and two-stage rolling technology are used to obtain products with fine and uniform structure to ensure strength and toughness indicators;

[0030] 5) Accurately allocating the reduction rate for each pass, combined with the small-thickness intermediate billet rolling technology, breaks the limitation that the thickness of the intermediate billet for pipeline steel must be more than 3.6 times the thickness of the finished product, reduces the reduction in the finishing rolling stage, thereby reducing the dislocation density and further improving the corrosion resistance of the steel. DETAILED DESCRIPTION

[0031] The present invention discloses an L290 grade pipeline steel hot-rolled coil for ground gathering and transportation, wherein the chemical composition of the steel is, by weight percentage, C: 0.050% to 0.060%, Si: 0.15% to 0.25%, Mn: 0.20% to 0.28%, P≤0.012%, S≤0.003%, Als: 0.030% to 0.045%, Nb: 0.010% to 0.017%, Cr: 0.11% to 0.17%, N≤0.004%, and the remainder is iron and unavoidable impurities.

[0032] The present invention provides a method for producing a hot-rolled coil of L290 grade pipeline steel for ground gathering and transportation, comprising the following process steps: molten iron pretreatment, converter smelting, refining outside the furnace, continuous casting, slab heating, rolling, laminar cooling, and coiling; wherein the following processes are controlled:

[0033] 1) Converter smelting; using top blowing or top and bottom combined blowing;

[0034] 2) Refining outside the furnace: light desulfurization and calcium treatment in LF furnace;

[0035] 3) Continuous casting; using dynamic soft reduction method;

[0036] 4) Slab heating: Continuous casting slab is heated to 1082-1105°C;

[0037] 5) Rolling: A two-stage rolling method is adopted; the rough rolling and finishing rolling temperature is 1025-1036°C, the rough rolling is performed for at least 5 passes, the first pass reduction rate is 18.8%-20%, and the reduction rate of each subsequent pass gradually increases, and the reduction rate of the last pass is 22.1%-23%; after rolling, the temperature is allowed to drop below 990°C before entering the finishing rolling, the finishing rolling temperature is 836-848°C, and the finishing rolling is performed for at least 7 passes, the first pass reduction rate is 17.3%-19.2%, and the reduction rate of each subsequent pass gradually decreases, and the last pass reduction rate is 5%-6%;

[0038] 6) Laminar cooling and coiling: Cool to 542-560°C at a rate of 20.3-22.7°C / s for coiling, and finally air cool to room temperature.

[0039] Furthermore, the yield strength of the hot-rolled coil product is 302-315 MPa, the tensile strength is 456-478 MPa, and the elongation after fracture is ≥38.5%; the Charpy impact energy Akv at -40°C is ≥350 J, the corrosion rate is 0.0257-0.0292 mm / a, the corrosion potential is ≥-0.467 V, and the corrosion current density is ≤1.14×10 -5 A.cm -2 .

[0040] Furthermore, in step 5), the ratio of the thickness of the rolling intermediate billet to the thickness of the finished steel plate is ≤3.0.

[0041] Furthermore, the thickness of the continuous casting slab is 168-171 mm, the thickness of the rolling intermediate slab is 50-53 mm, and the thickness of the finished steel plate is 18-20 mm.

[0042] The L290-grade pipeline steel for surface gathering and transportation described in this invention utilizes a C-Mn-Nb-Cr alloy. Low-temperature sintering technology produces a uniform, fine ferrite-pearlite (FP) structure, ensuring excellent strength and toughness. The addition of Nb and Cr ensures excellent corrosion resistance. The functions and reasons for the selection of the main elements in the steel are as follows:

[0043] Carbon is the most economical element in steel for increasing its strength. However, as the carbon content increases, the steel's toughness and weldability gradually deteriorate. Excessive carbon content also negatively impacts corrosion resistance. Therefore, a low carbon content is essential for ensuring excellent strength, toughness, weldability, and corrosion resistance in surface gathering and transportation pipeline steel. In this invention, the carbon content is controlled within a range of 0.050% to 0.060%.

[0044] Si: It is an important reducing agent and deoxidizer in the steelmaking process. Carbon steel contains less than 0.5% Si. Si can significantly improve the strength of the ferrite-pearlite structure type, but a high Si content will reduce the plasticity and toughness of the material. Therefore, the present invention controls the Si content to a lower level, that is, the Si content is controlled at 0.15% to 0.25%.

[0045] Mn: Manganese has a solid solution strengthening effect and can also reduce the γ-α phase transformation temperature, thereby refining the ferrite grains. However, manganese is prone to segregation. Excessive manganese content will cause severe segregation, resulting in a loss of toughness and corrosion resistance. Therefore, the present invention controls the manganese content to 0.20% to 0.28%.

[0046] P: It is very easy to highly segregate during the solidification of molten steel, forming a banded FP structure. P will also greatly reduce the benefits of reducing C in steel, resulting in a loss of toughness and corrosion resistance of the steel. Therefore, P, as a harmful element in steel, should be minimized. In the present invention, the P content is controlled to below 0.012%.

[0047] S: is an inevitable impurity element in steel that reduces the toughness and corrosion resistance of the steel. Generally, the lower the better, but too low a requirement will increase production costs. Therefore, the present invention controls S to ≤ 0.003%.

[0048] AlS: is an inevitable deoxidizing element in steel. Adding an appropriate amount of Al can form fine and dispersed AlN particles, which is beneficial for grain refinement and improving the strength and toughness of steel. Therefore, the AlS content in the present invention is controlled to 0.030% to 0.045%.

[0049] Nb: Nb is the most essential element for controlled rolling in modern microalloyed pipeline steels. It can lower the γ-α transformation temperature, increase the austenite recrystallization temperature, promote austenite and ferrite refinement, and contribute to grain refinement, while also improving strength and toughness. Furthermore, the NbC formed after hot rolling can also contribute to precipitation strengthening. However, Nb is a precious element, and its strengthening effect is diminished beyond a certain level. Therefore, the present invention limits the Nb content to 0.010% to 0.017%.

[0050] Cr: It effectively improves hardenability and increases product strength, especially tensile strength. It also effectively enhances steel's oxidation resistance, forming a dense passivation film and thus increasing the steel's corrosion resistance. However, excessive addition can lead to a loss of plasticity and toughness. Therefore, the present invention limits the Cr content to 0.11% to 0.17%.

[0051] N: Increasing the nitrogen content significantly increases the strength of steel, but also significantly reduces plasticity and toughness, worsens weldability, and exacerbates cold brittleness. Therefore, the lower the nitrogen content, the better. However, too low a nitrogen content increases steelmaking costs. Therefore, the present invention controls N to ≤ 0.004%.

[0052] The present invention describes a method for producing L290-grade hot-rolled coils of pipeline steel for ground gathering and transportation. The production process includes: molten iron pretreatment - converter smelting - refining (LF+Ca treatment) - continuous casting - slab heating - rolling - laminar cooling - coiling. Unlike existing technologies, the following processes are controlled:

[0053] 1) Smelting to continuous casting process: After molten iron pretreatment, top blowing or top and bottom combined blowing is adopted for converter smelting; LF furnace refining is adopted for refining outside the furnace. Light desulfurization and calcium treatment are adopted during the refining process to control the number and morphology of inclusions to improve the plasticity and toughness of the steel; dynamic light reduction is adopted for continuous casting to reduce central porosity and improve the quality of continuous casting billets.

[0054] 2) Rolling and Laminar Cooling Process: The continuously cast slab is heated to 1082-1105°C in a walking beam furnace. During the heating process, the original austenite structure grows as the heating temperature increases. Since the present invention contains a small amount of Nb, Nb-containing steel can increase the coarsening temperature of the original austenite grains. Furthermore, the low heating temperature of the slab does not provide the thermodynamic conditions for grain growth. Therefore, low-temperature sintering refines the original austenite grain structure. Subsequently, a two-stage rolling process is used, with the continuous cast slab thickness reaching 168-171 mm and the rolled intermediate bar thickness reaching 50-53 mm. The rough rolling temperature is 1025-1036°C, the first pass reduction is 18.8%-20%, and the reduction rate of each subsequent pass gradually increases, with the final pass reduction rate being 22.1%-23%. After rolling, the temperature is lowered to below 990°C before finishing rolling begins. The finishing temperature is 836-848°C, and finishing rolling is performed for at least 7 passes. The first pass reduction rate is 17.3%-19.2%, and the reduction rate of each subsequent pass gradually decreases, with the final pass reduction rate being 5%-6%. The dislocations generated by deformation during the finishing rolling stage are reduced (dislocations and other defects are microscopic substructures that are weak to corrosion) and the dislocation density is reduced, which can improve the corrosion resistance of the finished steel plate. Subsequently, laminar cooling is used to cool the steel plate to 542-560°C at a rate of 20.3-22.7°C / s for coiling, and finally air cooling is performed to room temperature. The thickness of the finished steel plate is 18-20mm.

[0055] The L290 grade pipeline steel hot-rolled coil for ground gathering and transportation disclosed in the present invention has excellent strength, toughness and corrosion resistance: yield strength of 302-315 MPa, tensile strength of 456-478 MPa, elongation after fracture ≥38.5%; -40°C Charpy impact energy (average of 3 samples) Akv ≥350 J, corrosion rate of 0.0257-0.0292 mm / a, corrosion potential ≥-0.467 V, and corrosion current density ≤1.14×10 -5 A.cm -2 .

[0056] The present invention combines conventional corrosion tests and electrochemical corrosion tests to evaluate the corrosion performance of the product; the corrosion test conditions are as follows:

[0057] 1) Place the sample in a saturated sodium chloride solution for a full immersion test for 6 months. After the test, calculate the corrosion rate in mm / a.

[0058] 2) An electrochemical corrosion test was conducted in a 3.5% NaCl solution as the corrosive medium; a three-electrode system was used, with the working electrode being the test sample, the auxiliary electrode being a Pt mesh, and a saturated calomel electrode being the reference electrode. The corrosion potential and corrosion current density were calculated using the Tafel curve.

[0059] The following examples are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following examples.

[0060] [Example]

[0061] The chemical composition of the steel in each example is shown in Table 1, the main production process parameters of the steel in each example are shown in Table 2, the main pass reduction ratio of each example is shown in Table 3, and the main performance parameters of the products in each example are shown in Table 4.

[0062] Table 1 Chemical composition of steel in each example (wt, %)

[0063] Example C Si Mn P S Als Nb Cr N 1 0.060 0.16 0.20 0.009 0.003 0.037 0.016 0.16 0.0036 2 0.059 0.21 0.21 0.012 0.0029 0.039 0.010 0.17 0.0040 3 0.059 0.21 0.27 0.011 0.003 0.041 0.015 0.11 0.0039 4 0.050 0.17 0.28 0.012 0.003 0.031 0.017 0.15 0.0040 5 0.052 0.25 0.28 0.010 0.003 0.045 0.012 0.13 0.0037 6 0.058 0.18 0.26 0.011 0.0028 0.043 0.017 0.11 0.0040 7 0.060 0.15 0.20 0.010 0.0028 0.030 0.016 0.17 0.0039 8 0.054 0.23 0.23 0.011 0.0029 0.033 0.011 0.16 0.0040 9 0.051 0.20 0.27 0.009 0.0027 0.031 0.010 0.12 0.0038 10 0.050 0.22 0.22 0.012 0.0028 0.032 0.013 0.13 0.0038

[0064] Table 2 Main production process parameters of each example steel

[0065]

[0066] Table 3 Main pass reduction rates of various examples

[0067]

[0068] Table 4 Main performance parameters of the products in each embodiment

[0069]

[0070]

[0071] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for producing L290 grade pipeline steel hot-rolled coil for ground gathering and transportation, characterized in that: The chemical composition of the steel is calculated by weight as follows: C: 0.050% ~ 0.060%, Si: 0.21% ~ 0.25%, Mn: 0.20% ~ 0.28%, P ≤ 0.012%, S ≤ 0.003%, Als: 0.037% ~ 0.045%, Nb: 0.010% ~ 0.017%, Cr: 0.11% ~ 0.17%, N ≤ 0.004%, and the rest is iron and unavoidable impurities; The production method of L290 grade pipeline steel hot-rolled coil includes the following process: molten iron pretreatment, converter smelting, refining outside the furnace, continuous casting, slab heating, rolling, laminar cooling and coiling; wherein the following processes are controlled: 1) Converter smelting; using top blowing or top and bottom combined blowing; 2) Refining outside the furnace; using LF furnace light desulfurization treatment and calcium treatment; 3) Continuous casting; using dynamic soft reduction method; 4) Slab heating: Continuous casting slab is heated to 1082-1105℃; 5) Rolling: A two-stage rolling method is adopted; the rough rolling and finishing temperature is 1025-1036℃, the rough rolling is performed for at least 5 passes, the first pass reduction rate is 18.8%-20%, and the reduction rate of each subsequent pass gradually increases, and the reduction rate of the last pass is 22.1%-23%; after rolling, the temperature is lowered to below 990℃ before finishing rolling, and the ratio of the thickness of the rolling intermediate billet to the thickness of the finished steel plate is ≤3.0; the finishing rolling temperature is 836-848℃, and the finishing rolling is performed for at least 7 passes, the first pass reduction rate is 17.3%-19.2%, and the reduction rate of each subsequent pass gradually decreases, and the last pass reduction rate is 5%-6%; 6) Laminar cooling and coiling: Cool to 542-560℃ at a rate of 20.3-22.7℃ / s, then coil, and finally air cool to room temperature; The yield strength of the hot-rolled coil product is 302-315 MPa, the tensile strength is 456-478 MPa, and the elongation after fracture is ≥38.5%; the Charpy impact energy Akv at -40℃ is ≥350 J, the corrosion rate is 0.0257-0.0292 mm / a, the corrosion potential is ≥-0.467 V, and the corrosion current density is ≤1.14×10 -5 A.cm -2 ; The thickness of the continuous casting slab is 168-171 mm, the thickness of the rolled intermediate slab is 51-53 mm, and the thickness of the finished steel plate is 18-20 mm.

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