A hot-rolled L320 grade pipeline steel coil for ground gathering and transportation and its production method

Abstract

The invention relates to an L320 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: 0.0027%-0.003%, Als: 0.030%-0.045%, Ti: 0.026%-0.031%, Cu: 0.23%-0.33%, N≤0.004%, and the remainder is iron and impurities. The yield strength of the hot-rolled coil product is 336-348 MPa, the tensile strength is 487-508 MPa, the elongation after fracture is ≥38%; the Charpy impact energy Akv at -40℃ is ≥336 J; the corrosion rate is 0.0251-0.0286 mm / a, the corrosion potential is ≥-0.464 V, and the corrosion current density is ≤1.13×10 ‑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 L320 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 CN201010243247.8 discloses a "method for preparing X46 pipeline steel." The steel's composition (by weight) is as follows: C 0.07%-0.10%, Si 0.10%-0.30%, Mn 1.10%-1.30%, P ≤ 0.022%, S ≤ 0.008%, Nb 0.015%-0.030%, Ti 0.008%-0.025%, and Al 0.010%-0.040%. The application uses a traditional pipeline steel alloy design, with high Mn, P, and S contents, which negatively impacts corrosion resistance. Furthermore, the corrosion resistance of the pipeline steel is not described.

[0006] Chinese patent application number CN201610684310.9 discloses "a medium-carbon, low-cost L245-L320 grade pipeline steel and its manufacturing method". The steel contains (by weight percentage) C 0.14% to 0.18%, Si 0.10% to 0.30%, Mn 0.50% to 0.70%, S ≤ 0.005%, P ≤ 0.015%, Nb 0.01% to 0.02%, and Ti 0.01% to 0.02%. It also adopts the alloy design of traditional pipeline steel.

[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 properties 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 steels for ground gathering and transportation pipelines involved in the above-mentioned public materials are mostly medium and thick plates and seamless products, and the precious metals Mo and Ni are basically added in the alloy design. Except for the patent applications "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 L320 grade pipeline steel hot-rolled coil for ground gathering and transportation described in the present invention 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

[0011] The present invention provides a hot-rolled coil of L320-grade pipeline steel for ground gathering and transportation and a production method thereof. The coil adopts relatively low contents of C, Mn and Si, and reasonably adds Ti to form nearly spherical and non-deformable Ti4C2S2, so that the product has excellent toughness indicators. In addition, a certain amount of TiC is formed to further improve the strength. The high-temperature rapid firing technology avoids Cu brittleness while maximizing its strengthening and resistance effects, reducing the corrosion rate and increasing the corrosion potential. The small-thickness intermediate billet rolling technology is adopted to break the restriction that the thickness of the intermediate billet of pipeline steel is more than 3.6 times the thickness of the finished product. This technology can reduce the reduction in the finishing rolling stage, thereby reducing the dislocation density and further improving the corrosion resistance.

[0012] In order to achieve the above object, the present invention adopts the following technical solutions:

[0013] The invention discloses an L320 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: 0.0027%-0.003%, Als: 0.030%-0.045%, Ti: 0.026%-0.031%, Cu: 0.23%-0.33%, N≤0.004%, and the remainder is iron and unavoidable impurities.

[0014] A method for producing L320 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:

[0015] 1) Converter smelting; using top blowing or top and bottom combined blowing;

[0016] 2) Refining outside the furnace: light desulfurization and calcium treatment in LF furnace;

[0017] 3) Continuous casting; using dynamic soft reduction method;

[0018] 4) Slab heating: The continuous casting slab is heated in a walking beam furnace under a reducing atmosphere, from 800-850°C to 1185-1200°C within 48-50 minutes;

[0019] 5) rolling; the rough rolling and finishing temperature is 1060-1080°C, the rough rolling is performed for at least 5 passes, the first pass reduction rate is 19.3%-20.7%, and the reduction rate of each subsequent pass gradually increases, and the reduction rate of the last pass is 21.2%-23.1%; after rough rolling, the steel directly enters the finishing rolling without swinging and waiting for temperature, the finishing rolling start temperature is ≤1050°C, the finishing rolling finish temperature is 860-873°C, the finishing rolling is performed for at least 7 passes, the first pass reduction rate is 22.5%-24%, the second pass reduction rate is 23.6%-25.6%, and the reduction rate of each subsequent pass gradually decreases, and the reduction rate of each pass is less than 10%, and the reduction rate of the last pass is 5%-6.2%;

[0020] 6) Laminar cooling and coiling: Cool to 583-600℃ at a rate of 15.6-17.1℃ / s for coiling, and finally air cool to room temperature.

[0021] Furthermore, the yield strength of the hot-rolled coil product is 336-348 MPa, the tensile strength is 487-508 MPa, the elongation after fracture is ≥38%; the Charpy impact energy Akv at -40°C is ≥336 J; the corrosion rate is 0.0251-0.0286 mm / a, the corrosion potential is ≥-0.464 V, and the corrosion current density is ≤1.13×10 -5 A.cm -2 .

[0022] 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.

[0023] 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.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 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;

[0026] 2) Using a higher content of Ti, on the one hand, all the long strips of MnS are modified into nearly spherical Ti4C2S2, thereby improving the toughness and corrosion resistance of the product; on the other hand, the excess Ti forms TiC to improve the strength;

[0027] 3) No precious metals Ni and Mo are added, and Cu is added alone to ensure corrosion resistance and strength, giving the product a greater economic advantage;

[0028] 4) The heating furnace requires a reducing atmosphere and adopts high-temperature fast burning technology (heating from 800-850℃ to 1185-1200℃ within 48-50min) to avoid the copper brittleness problem caused by Cu addition;

[0029] 5) Accurately distribute the reduction rate of each pass to enable continuous recrystallization in the first two passes of rough rolling. Combined with the small-thickness intermediate billet rolling technology, this breaks the restriction that the thickness of the intermediate billet of 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

[0030] The present invention discloses an L320 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: 0.0027% to 0.003%, Als: 0.030% to 0.045%, Ti: 0.026% to 0.031%, Cu: 0.23% to 0.33%, N≤0.004%, and the remainder is iron and unavoidable impurities.

[0031] The present invention provides a method for producing a hot-rolled coil of L320 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:

[0032] 1) Converter smelting; using top blowing or top and bottom combined blowing;

[0033] 2) Refining outside the furnace: light desulfurization and calcium treatment in LF furnace;

[0034] 3) Continuous casting; using dynamic soft reduction method;

[0035] 4) Slab heating: The continuous casting slab is heated in a walking beam furnace under a reducing atmosphere, from 800-850°C to 1185-1200°C within 48-50 minutes;

[0036] 5) rolling; the rough rolling and finishing temperature is 1060-1080°C, the rough rolling is performed for at least 5 passes, the first pass reduction rate is 19.3%-20.7%, and the reduction rate of each subsequent pass gradually increases, and the reduction rate of the last pass is 21.2%-23.1%; after rough rolling, the steel directly enters the finishing rolling without swinging and waiting for temperature, the finishing rolling start temperature is ≤1050°C, the finishing rolling finish temperature is 860-873°C, the finishing rolling is performed for at least 7 passes, the first pass reduction rate is 22.5%-24%, the second pass reduction rate is 23.6%-25.6%, and the reduction rate of each subsequent pass gradually decreases, and the reduction rate of each pass is less than 10%, and the reduction rate of the last pass is 5%-6.2%;

[0037] 6) Laminar cooling and coiling: Cool to 583-600℃ at a rate of 15.6-17.1℃ / s for coiling, and finally air cool to room temperature.

[0038] Furthermore, the yield strength of the hot-rolled coil product is 336-348 MPa, the tensile strength is 487-508 MPa, the elongation after fracture is ≥38%; the Charpy impact energy Akv at -40°C is ≥336 J; the corrosion rate is 0.0251-0.0286 mm / a, the corrosion potential is ≥-0.464 V, and the corrosion current density is ≤1.13×10 -5 A.cm -2 .

[0039] 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.

[0040] 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.

[0041] The composition of the L320 grade pipeline steel for surface gathering and transportation described in the present invention is designed using a C-Mn-Ti-Cu alloy. By adding Ti and combining it with high-temperature rapid firing technology, the Cu brittleness problem of copper-containing steel is suppressed. The strengthening and corrosion-resistant effects of Cu are utilized to ensure that the product has excellent strength, toughness and corrosion resistance. The functions and reasons for the selection of the main elements in the steel are as follows:

[0042] 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%.

[0043] Si: It is an important reducing agent and deoxidizer in the steelmaking process. Many carbon steels contain 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%.

[0044] 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%.

[0045] P: It is very easy to highly segregate during solidification of molten steel, forming a banded FP structure. P also significantly reduces the benefits of reducing carbon in the steel, reducing the steel's toughness and corrosion resistance. Therefore, as a harmful element in steel, P should be minimized. In the present invention, the P content is controlled to below 0.012%.

[0046] S: is an inevitable impurity element in steel, which will reduce the toughness and corrosion resistance of the steel material. Generally, the lower the better. The present invention utilizes the effect of Ti element to modify MnS, so that Ti and a certain amount of S in the molten steel form Ti4C2S2 with greater stability than MnS, which can improve the corrosion resistance and toughness indicators of the product; therefore, the present invention controls the S content to 0.0027% to 0.003%.

[0047] AlS is an inevitable deoxidizing element in steel. Adding an appropriate amount of Al can form fine dispersed AlN particles, which is beneficial for refining grains and improving the strength and toughness of steel. Therefore, the AlS content of the present invention is 0.030% to 0.045%.

[0048] Ti: A strong nitride-forming element, Ti is utilized in the present invention for its three functions: one is nitrogen fixation; the second is to convert the elongated MnS into nearly spherical Ti4C2S2, depending on the S and N content in the product, thereby improving the toughness and corrosion resistance of the product; and the third is that as the Ti content increases, some TiC is formed, which acts as precipitation strengthening to increase strength. However, excessive Ti content can reduce the toughness of the steel. Therefore, the Ti content in the present invention is controlled to 0.026% to 0.031%.

[0049] Cu: When an appropriate amount of copper is added to steel, it will precipitate secondary precipitation on its surface to form a cathode, promoting anodic passivation of the steel in contact with it and forming a rust layer on the surface, increasing its corrosion resistance. Copper can also increase the overall potential of the steel, thereby improving its corrosion resistance. However, once the Cu content exceeds 0.5%, the plasticity of the steel will decrease significantly, and when Cu is greater than 0.2%, the tendency to copper embrittlement increases. The present invention avoids the occurrence of copper embrittlement by adding other chemical components and adjusting process parameters. To ensure that the steel has good corrosion resistance and mechanical properties, the present invention controls the Cu content to 0.23% to 0.33%.

[0050] N: Increasing the nitrogen content significantly increases the strength of steel, but also significantly reduces plasticity, especially toughness, weldability, and 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%.

[0051] The present invention describes a method for producing L320-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:

[0052] 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, and light desulfurization treatment and calcium treatment are used to control the number and morphology of inclusions to improve the plasticity and toughness of the steel; dynamic light reduction method is adopted for continuous casting to reduce central porosity and improve the quality of continuous casting billets.

[0053] 2) Slab heating, rolling and laminar cooling process: The continuous casting slab is heated to 1185-1200℃ in a walking beam furnace (under a reducing atmosphere). The combination of Ti and N can inhibit the growth of austenite grains during slab heating. In addition, the slab is heated from 800-850℃ to 1185-1200℃ within 48-50 minutes, that is, the "high temperature fast burning" technology is adopted to avoid the copper brittleness problem of Cu-containing steel. Subsequently, thermomechanical rolling (TMCP) is adopted, and the rough rolling finishing temperature is 1060-1080℃. The rough rolling is carried out for at least 5 passes, with the first pass reduction rate of 19.3%-20.7%. The reduction rate of each subsequent pass gradually increases, and the reduction rate of the last pass is 21.2%-23.1%. No swing is required after rough rolling. The steel is kept at a constant temperature and then enters the finishing rolling directly after rolling. The starting temperature of the finishing rolling is ≤1050℃, the final rolling temperature of the finishing rolling is 860-873℃, and the finishing rolling is performed for at least 7 passes. The reduction rate of the first pass is 22.5%-24%, the reduction rate of the second pass is 23.6%-25.6%, and the reduction rate of each pass is gradually reduced. The reduction rate of each pass is less than 10% (no recrystallization occurs), and the reduction rate of the last pass is 5%-6.2%. There are fewer dislocations caused by deformation in the finishing rolling stage (defects such as dislocations are microscopic substructures that are weak to corrosion), and the dislocation density is reduced, which can improve the corrosion resistance of the finished product. Subsequently, laminar cooling is adopted at a speed of 15.6-17.1℃ / s to finally cool to 583-600℃ for coiling, and finally air-cooled to room temperature.

[0054] The L320 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 336-348 MPa, tensile strength of 487-508 MPa, elongation after fracture ≥38%; -40°C Charpy impact energy (average of 3 samples) Akv ≥336 J, corrosion rate of 0.0251-0.0286 mm / a, corrosion potential ≥-0.464 V, and corrosion current density ≤1.13×10 -5 A.cm -2 .

[0055] 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:

[0056] 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.

[0057] 2) Electrochemical tests were conducted in a 3.5% NaCl solution containing a corrosive medium using a three-electrode system. The working electrode was the test sample, the auxiliary electrode was a Pt wire mesh, and the saturated calomel electrode was the reference electrode. The corrosion potential and corrosion current density were calculated using the Tafel curve.

[0058] 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.

[0059] [Example]

[0060] The chemical composition of the steel in each example is shown in Table 1, the rolling 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.

[0061] Table 1 Chemical composition of steel in each example (wt, %)

[0062]

[0063]

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

[0065]

[0066] Table 3 Reduction rate of key passes in various embodiments

[0067]

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

[0069]

[0070] 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 L320 grade pipeline steel hot-rolled coil for ground gathering and transportation, characterized in that: The chemical composition of the steel is as follows by weight: C: 0.050% to 0.060%, Si: 0.21% to 0.25%, Mn: 0.20% to 0.28%, P≤0.012%, S: 0.0027% to 0.003%, Als: 0.036% to 0.045%, Ti: 0.026% to 0.031%, Cu: 0.23% to 0.25%, N≤0.004%, and the rest is iron and unavoidable impurities; The production method of L320 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: light desulfurization and calcium treatment in LF furnace; 3) Continuous casting; using dynamic soft reduction method; 4) Slab heating: The continuous casting slab is heated in a walking beam furnace under a reducing atmosphere, from 800-850°C to 1185-1200°C within 48-50 minutes; 5) rolling; the rough rolling and finishing temperature is 1060-1080°C, the rough rolling is performed for at least 5 passes, the first pass reduction rate is 19.3%-20.7%, the subsequent pass reduction rate gradually increases, and the final pass reduction rate is 21.2%-23.1%; after rough rolling, the steel is directly subjected to finishing rolling without swinging and waiting for temperature, 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 start temperature is ≤1050°C, the finishing rolling finish temperature is 866-873°C, the finishing rolling is performed for at least 7 passes, the first pass reduction rate is 22.5%-24%, the second pass reduction rate is 23.6%-25.6%, and the subsequent passes reduction rate gradually decreases, and the reduction rate of each pass is less than 10%, and the final pass reduction rate is 5%-6.2%; 6) Laminar cooling and coiling: Cool to 583-600℃ at a rate of 15.6-17.1℃ / s for coiling, and finally air cool to room temperature; The thickness of the continuous casting slab is 168-171mm, the thickness of the rolling intermediate slab is 51-53mm, and the thickness of the finished steel plate is 18-20mm; The yield strength of the hot-rolled coil product is 336-348 MPa, the tensile strength is 487-508 MPa, the elongation after fracture is ≥38%; the Charpy impact energy Akv at -40℃ is ≥336 J; the corrosion rate is 0.0251-0.0286 mm / a, the corrosion potential is ≥-0.464 V, and the corrosion current density is ≤1.13×10 -5 A.cm -2 .

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