450mpa grade high plasticity carbon dioxide corrosion resistant steel and manufacturing method and application thereof

Abstract

The application discloses 450MPa-grade high-plasticity anti-carbon dioxide corrosion steel and a manufacturing method and application thereof, and belongs to the technical field of metal materials and metallurgical engineering. The application adopts low-carbon and low-manganese design, has low carbon content, small hardening tendency of a heat-affected zone during welding, and is not prone to welding cracks; Co and Ni cooperatively form a stable cobalt-nickel solid solution, and improve plasticity, toughness and carbon dioxide corrosion resistance of the steel; Zn and Mg are added in combination to form a zinc-magnesium solid solution, which can promote densification of a corrosion product layer and greatly improve the carbon dioxide corrosion resistance of the steel. Slow cooling is adopted after rolling to obtain fine ferrite organization, guarantee high strength and high plasticity, and the uniformity of the single ferrite organization is good, the micro-electric couple effect is weak, and the carbon dioxide corrosion resistance is better.

Description

Technical Field

[0001] This invention belongs to the field of metal materials and metallurgical engineering technology, specifically relating to 450MPa grade high plasticity steel resistant to carbon dioxide corrosion and its manufacturing method and application. Background Technology

[0002] CCUS (Carbon Capture, Utilization, and Storage) technology is a key technology for addressing global climate change and an important pathway for China to achieve carbon peaking and carbon neutrality. Carbon dioxide transportation is a crucial link in the CCUS industry chain, connecting carbon dioxide capture and storage. The efficiency and cost of carbon dioxide transportation directly affect the overall scale and economic benefits of CCUS.

[0003] The critical pressure of pure carbon dioxide is 7.38 MPa, and its critical temperature is 31.1℃. Supercritical transport refers to transport at pressures higher than the critical pressure. It possesses high density and low viscosity. When the entire pipeline transport process is in a supercritical state, transportation is most efficient, and wear is minimal. However, the presence of free water and impurity gases in supercritical carbon dioxide pipelines results in extremely strong corrosiveness. Existing API carbon steel pipelines used for natural gas transport are susceptible to occasional corrosion, potentially leading to leaks and failures. Pipe materials are fundamental to ensuring safe pipeline transport. Pipe material costs are a significant portion of the total pipeline construction investment. Factors such as corrosion and third-party damage can cause pipe walls to thin or fail, potentially leading to various safety accidents. Key technical requirements for supercritical pipe materials include: low-temperature brittleness when carbon dioxide leaks and the temperature drops rapidly to -50℃; and the corrosion rate in a supercritical carbon dioxide environment.

[0004] Chinese Patent CN112941422A discloses a CO2 corrosion-resistant steel plate and its preparation method. The composition includes C: 0.03%-0.07%, Cr: 4.0%-6.0%, Ni: 0.15%-2.50%, Nb: 0.01%-0.06%, P≤0.005%, and S≤0.0050%. This invention, disclosed by Beijing University of Science and Technology, is a method for producing carbon dioxide corrosion-resistant steel plates. The product is manufactured using a medium-thick plate rolling mill, and the rolled steel plate requires a quenching and tempering heat treatment process. However, this invention has a high Cr content, classifying it as stainless steel, making it unsuitable for conventional smelting and continuous casting. Furthermore, the excessively high Cr content prevents straight-seam welding, and the steel plate's impact toughness is low, failing to meet the crack-stopping requirement of -50°C during carbon dioxide leakage.

[0005] Chinese Patent CN106498279A discloses a low-Cr economical X65 pipeline steel resistant to CO2 corrosion and its production method. The composition includes C: 0.04%-0.05%, Si: 0.18%-0.22%, Mn: 0.50%-0.60%, Cr: 0.1%-0.2%, Mo: 0.10%-0.15%, Nb: 0.035%-0.050%, V: 0.020%-0.030%, Ti: 0.010%-0.020%, P≤0.01%, and S≤0.0030%. This invention is a production method for X65 hot-rolled coils resistant to carbon dioxide corrosion disclosed by Wuhan Iron and Steel Co., Ltd. However, the low Mn content in this invention results in poor hardenability during subsequent straight seam welding, failing to guarantee the -50℃ low-temperature toughness of the weld and heat-affected zone. Furthermore, the base material exhibits only moderate low-temperature toughness at -20℃, which also fails to meet the -50℃ crack arrest requirement during carbon dioxide leakage.

[0006] Currently, 450MPa grade pipeline steel coils lack resistance to carbon dioxide corrosion, cannot adapt to the service environment of supercritical carbon dioxide transportation, have low plasticity, and poor formability and safety. Summary of the Invention

[0007] Therefore, the purpose of this invention is to provide a 450MPa grade high-plasticity steel resistant to carbon dioxide corrosion, its manufacturing method and application, which solves the problems of the current production of 450MPa grade pipeline steel coils lacking carbon dioxide corrosion resistance, being unable to adapt to the supercritical carbon dioxide transportation service environment, and having low plasticity.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] In a first aspect, the present invention provides a 450MPa grade high-ductility steel resistant to carbon dioxide corrosion, composed of the following components by weight percentage: C: 0.05%-0.09%, Si: 0.60%-0.90%, Mn: 1.10%-1.40%, P: ≤0.020%, S: ≤0.002%, Ni: 0.40%-0.60%, Nb: 0.05%-0.07%, V: 0.07%-0.10%, Ti: 0.02%-0.04%, Co: 0.40%-0.60%, W: 0.60%-1.00%, Zn: 0.01%-0.04%, Mg: 0.005%-0.015%, with the remainder being Fe and unavoidable impurities; Based on the above technical solution, the Zn / Mg ratio is further 1.0-5.0, the Co / Ni ratio is 0.6-1.5, and the W / Co ratio is 1.0-2.2.

[0010] C (Carbon) is a carbide-forming element and the most effective element for ensuring strength. It can improve hardenability and guarantee the strength and hardness of the material. Carbon significantly improves strength through solid solution strengthening and phase transformation strengthening. C interacts with Nb to form stable carbonitrides, refining grains, achieving precipitation strengthening, and improving the strength and toughness of steel. If the carbon content is too low, the tensile strength and hardness of the material cannot be guaranteed; however, if the content is too high, it is easy to cause center segregation in the steel plate, which is detrimental to the corrosion resistance and crack arrest toughness of the steel plate and will affect the weldability of the product. The optimal range is 0.05%-0.09%.

[0011] Si (Si): It can dissolve into ferrite and austenite, playing a role in solid solution strengthening. This significantly improves the hardness and tensile strength of steel, while also promoting ferrite grain coarsening and reducing the anisotropy of the steel plate's transverse and longitudinal properties. When silicon participates in the corrosion process, it promotes the formation of a dense, Si-rich oxide film (such as an Fe3O4-SiO2 composite film) on the steel surface. This film has a stable structure and low porosity, effectively blocking hydrogen (H). + (CO2 hydrolyzes to produce H2CO3, which ionizes to release H+) + It penetrates into the steel, inhibiting anodic dissolution (the corrosion of steel is essentially Fe → Fe²⁺). + +2e - Meanwhile, SiO2 particles can enhance the adhesion between the corrosion product film and the steel substrate, preventing "secondary corrosion" caused by film detachment and extending the service life of the steel. However, increasing the silicon content will reduce the low-temperature toughness, plasticity, and weldability of the steel; the optimal range is 0.60%-0.90%.

[0012] Mn (manganese): Manganese has a solid solution strengthening effect. The solid solution formed by manganese and iron increases the hardness and strength of ferrite and austenite in steel. It is also a carbide-forming element, entering cementite to replace some iron atoms. In steel, manganese lowers the critical transformation temperature, increases austenite stability, and strongly enhances hardenability, effectively ensuring the strength and toughness of the steel. Manganese expands the austenite phase region and refines the ferrite grains after rolling. The finer the grains, the more dislocation slip paths there are, resulting in better plasticity. As a substitutional solid solution element, it has low stress concentration sensitivity after solution treatment, reducing plastic loss. It can also reduce the resistance to dislocation movement in ferrite, making it easier for the steel to undergo uniform plastic deformation under stress. Excessive manganese content can increase the tendency for center segregation in continuously cast billets, leading to an increase in banded structures in the steel plate, increasing brittleness and decreasing plasticity. The optimal range is 1.10%-1.40%.

[0013] P and S are unavoidable impurity elements in steel, and it is desirable to keep them as low as possible. However, excessively low requirements will increase production costs. In this invention, P ≤ 0.020% and S ≤ 0.002%.

[0014] Ni (Ni): Nickel enhances the strength of steel while maintaining good plasticity and toughness. It exhibits high resistance to acid and alkali corrosion. Ni is insoluble in carbides and enters entirely into austenite, thus maximizing its hardenability-enhancing effect. Adding Ni inhibits pearlite formation. Simultaneous addition of Ni and Co ensures a Co / Ni ratio of 0.6-1.5, making them a core pairing for high-strength, high-toughness steel, balancing low-temperature toughness, plasticity, and resistance to carbon dioxide corrosion. The addition of Ni compensates for the reduced strength caused by lower C content, ensuring the steel pipe retains good mechanical properties and weld strength. Ni increases the self-corrosion potential of steel, improving its resistance to localized corrosion and effectively preventing pipeline corrosion perforation. Ni does not combine with C or N in the steel to form embrittled phases; it functions entirely in a solid solution state, enhancing plasticity and synergistically improving CO2 corrosion resistance. Excessive Ni content leads to high alloy costs. A suitable range is 0.40%-0.60%.

[0015] Niobium (Nb) enhances strength primarily through two mechanisms: first, by forming NbC / Nb(CN) dispersed precipitates, achieving efficient precipitation strengthening; and second, by strongly inhibiting austenite grain growth, refining the grain size, and achieving fine-grain strengthening. Niobium is a synergistic element for strengthening and toughening; by refining the grain size, it reduces grain boundary brittleness sources, while simultaneously inhibiting pearlite transformation and refining precipitates, significantly improving the low-temperature impact toughness and fracture toughness of steel. Nb grain refinement makes the steel matrix more uniform, reducing micro-cell corrosion sites; the refined precipitates can hinder corrosion crack propagation and reduce the risk of carbon dioxide corrosion cracking. Its optimal range is 0.05%-0.07%.

[0016] Vanadium (V): Vanadium forms stable compounds with carbon, nitrogen, and oxygen, mainly existing in steel as carbides. It refines the microstructure and grain size, reduces overheating sensitivity, and improves strength and toughness. Vanadium carbonitrides precipitate uniformly in ferrite in a fine, dispersed form, significantly improving material strength. Vanadium refines grain size and improves weldability. Refining dispersed VC, VN, or V2O3 can significantly refine the steel grain size, making the Fe3O4 / FeCO3 corrosion product film formed during corrosion more uniform and dense, reducing film porosity and defects, thereby lowering the CO2 corrosion rate. Weak passivation and isolation effects: V2O3 has a certain degree of chemical stability and can form an extremely thin passivation film or physical isolation layer on the steel surface, slightly hindering CO2 molecules and H2O. + It penetrates into the matrix, slowing down anodic dissolution. Fixing carbon and nitrogen reduces harmful effects, thereby decreasing the formation of corrosion microcells and indirectly improving CO2 corrosion resistance. However, excessively high content does not significantly improve strength and increases alloy cost; the appropriate range is 0.07%-0.10%.

[0017] Ti: Prefers to form TiC and TiN particles, serving as heterogeneous nucleation sites for austenitic phase transformation and refining grain size; it fixes free C and N in steel, eliminating the adverse effects of age-induced embrittlement and the brittle cementite phase; TiC particles can enhance the adhesion between corrosion product films and the matrix, improving corrosion resistance. Titanium prevents free C from combining with Cr to form Cr. 23 The C6 grain boundary embrittlement phase prevents free nitrogen from forming the Fe4N embrittlement phase, eliminating intergranular embrittlement at its source. The resulting ultrafine carbonitrides can also act as grain refinement nuclei, improving plasticity. Its optimal range is 0.02%-0.04%.

[0018] Cobalt (Co) exhibits significant solid solution strengthening effects, enhancing the strength and hardness of steel. At high temperatures, it suppresses dislocation movement, significantly improving the endurance strength of steel. Cobalt solution also improves toughness and hardenability. Since cobalt does not form carbides with carbon, it promotes carbon diffusion in steel, indirectly increasing the carbide precipitation efficiency of other carbide-forming elements (V), thus synergistically strengthening the steel. When added in combination with niobium (Nb), it accelerates the precipitation of Nb carbonitrides, refines grains, and achieves a triple effect of "grain refinement strengthening + solid solution strengthening + precipitation strengthening." Cobalt exists primarily in solid solution in steel, forming small amounts of compounds such as Co3O4 and Co(OH)2 (dense films / dispersed particles). These compounds enhance corrosion product films and increase cathodic polarization resistance, improving CO2 corrosion resistance. The optimal range is 0.40%-0.60%.

[0019] Tungsten can form carbides in steel, and some dissolves into iron to form a solid solution, resulting in strong solid solution strengthening. Combined testing of tungsten and Ni can significantly improve hardenability, thereby increasing strength. During tempering, WC or M6C type carbides are formed, exhibiting significant precipitation strengthening effect and enhancing the strength of the steel. During the corrosion process of steel, tungsten accumulates in the corrosion product film (mainly FeCO3) in the form of tungstates (such as FeWO4). Tungstates have a stable and dense crystal structure, which can fill the pores and defects of the FeCO3 film, reducing film permeability and hindering H2O. + HCO3 - This slows down the diffusion of corrosive media into the steel substrate, thereby mitigating the cathodic hydrogen evolution reaction and the anodic iron dissolution reaction, optimizing the corrosion product film structure, and enhancing CO2 corrosion resistance. Simultaneous addition of W and Co ensures a W / Co ratio of 1.0-2.2, resulting in synergistic solid solution strengthening. Co increases the solubility of W in the matrix, promoting the formation of MC and M. 23 C 66 Uniform precipitation of carbides enhances high-temperature strength and resistance to carbon dioxide corrosion (especially acid corrosion). However, a higher tungsten content can significantly reduce the toughness of the steel; the appropriate range is 0.60%-1.00%.

[0020] Zinc (Zn): Zinc solid solution strengthening improves processing performance. Zn dissolves in ferrite / austenite to form a solid solution, hindering dislocation movement and increasing yield strength and tensile strength by 20-60 MPa and 30-80 MPa, respectively. Zn reduces the deformation resistance of steel, improves plastic flowability, and significantly enhances plasticity. ZnO forms a dense passivation film on the steel surface, physically isolating CO2 molecules from the steel matrix while inhibiting anodic dissolution and slowing corrosion rates. Zinc has a lower electrode potential than iron and preferentially dissolves in corrosive environments, providing weak "sacrificial anodic protection" to the steel matrix, mitigating localized corrosion and improving resistance to carbon dioxide corrosion. Simultaneous addition of Zn and Mg, ensuring a Zn / Mg ratio of 1.0-5.0, forms intermetallic compounds and a zinc-magnesium solid solution, promoting densification of the corrosion product layer (forming basic zinc-magnesium carbonate) and significantly improving resistance to carbon dioxide corrosion. The optimal range is 0.01%-0.04%.

[0021] Mg: Magnesium can combine with nitrogen and oxygen in steel to form fine, dispersed inclusions such as MgO and Mg3N2, which enhance the strength of steel through precipitation strengthening and grain refinement. These inclusions can hinder dislocation movement, inhibit the growth of austenite grains during heating, refine the final grain structure, and indirectly improve strength. The grain-refining effect of appropriate amounts of magnesium can significantly improve the low-temperature toughness of steel and lower the ductile-brittle transition temperature. Magnesium oxide inclusions can reduce the amount of free sulfur and phosphorus in steel, mitigate pitting corrosion to some extent, weaken the cutting effect of sulfides on the matrix, and improve plasticity. Dispersed MgO particles can form a thin and dense oxide film on the steel surface, which can physically block CO2 molecules and H2 produced by hydrolysis. + When in contact with the steel substrate, magnesium slows down the corrosion rate. During the corrosion process, magnesium promotes the formation of a Fe3O4-MgO composite corrosion film on the steel surface. The addition of MgO fills the tiny pores in the film, reducing its permeability, enhancing the stability of the corrosion product film, and reducing film detachment. The optimal range is 0.005%-0.015%.

[0022] Based on the above technical solution, further, the yield strength is ≥450MPa, tensile strength is ≥560MPa, elongation A50mm is ≥45%, impact energy at -50℃ is ≥220J, DWTT at -20℃ is ≥90%, and the average corrosion rate in a 14.5MPa supercritical carbon dioxide environment is ≤0.35mm / a.

[0023] Secondly, the present invention provides a method for manufacturing the above-mentioned 450MPa grade high-plasticity carbon dioxide corrosion-resistant steel, comprising the following steps: S1: Molten steel is smelted, refined outside the furnace, hydrogen and oxygen content is controlled in the RH furnace, light desulfurization and calcium treatment are carried out in the LF furnace, and slabs are continuously cast to obtain continuously cast billets. S2: Heat the continuous casting billet to 1000℃-1100℃ and hold for 150min-250min; S3: Continuously cast billets are rolled; roughing rolling temperature is 930℃-990℃, single-pass reduction rate is 20%-40%, finishing rolling temperature is 850℃-900℃, and finishing rolling temperature is 780℃-840℃. S4: After rolling, the coil is cooled and rolled to obtain a coil plate; the cooling rate is 5℃ / s-10℃ / s, and the final cooling temperature is 620℃-670℃.

[0024] Among them: light desulfurization treatment and calcium treatment in LF furnace to control the morphology of inclusions and improve the ductility, toughness and cold bending performance of steel; Slab continuous casting employs electromagnetic stirring or dynamic light reduction; Heating is carried out in a heating furnace; rolling is carried out using thermomechanical rolling. Heating the continuously cast billet to 1000℃-1100℃ and holding it for 150min-250min allows Nb, V and other alloys to be fully dissolved, which is beneficial to improving yield strength and tensile strength. A roughing and finishing rolling temperature of 930℃-990℃ helps prevent austenite grain growth, homogenizes grains, and improves the uniformity of microstructure and properties. A single-pass reduction rate of 20%-40% ensures effective grain breakage and improves strength and plasticity; The initial rolling temperature for finishing rolling is 850℃-900℃, and the final rolling temperature is 780℃-840℃. This temperature range refines the flattening of austenite grains, thereby refining the ferrite grain size and ensuring high strength and high plasticity. Cooling rate is 5℃ / s-10℃ / s, final cooling temperature is 620℃-670℃; slow cooling is adopted after rolling. The combination of this cooling rate and final cooling temperature results in a fine ferrite structure, ensuring high strength and high plasticity.

[0025] The final microstructure of the coiled plate is ferrite.

[0026] Based on the above technical solution, the smelting conditions in S1 are further as follows: smelting temperature 1500℃-1700℃, basicity 2.6-3.8, top and bottom combined blowing of N2 or Ar2, flow rate 0.06m³ / h. 3 t -1 min -1 -0.08m 3 t -1 min -1 .

[0027] Based on the above technical solution, the conditions for ladle refining in S1 are: arrival temperature ≥1550℃, heating time ≤30min, total processing time 40min-50min, soft blowing time ≥9min, and settling time 5min-7min.

[0028] Based on the above technical solution, further, the conditions for controlling the hydrogen and oxygen content in the RH furnace in S1 are: working vacuum degree <60Pa, holding time 10-25min, final hydrogen content <1.0ppm, and oxygen content <15ppm.

[0029] Based on the above technical solution, further, the conditions for light desulfurization treatment in the LF furnace in S1 are: slag basicity > 4.0, of which CaO > 50%, temperature 1580℃-1650℃, stirring for 20min-30min; The conditions for calcium treatment in the LF furnace in S1 are as follows: using CaSi or pure Ca wire with a Ca content of 20%-30%, the Ca addition amount is 0.60 kg / t-0.80 kg / t, and soft blowing argon for 30 m. 3 / h-50m 3 / h, time ≥6 minutes.

[0030] Thirdly, the present invention provides the application of the above-mentioned 450MPa grade high-plasticity carbon dioxide corrosion resistant steel in the preparation of high-plasticity pipelines.

[0031] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention adopts a low-carbon and low-manganese design. The low carbon content results in a small hardening tendency in the heat-affected zone during welding, making it less prone to welding cracks. Co and Ni synergistically form a stable cobalt-nickel solid solution, improving the plasticity, toughness, and carbon dioxide corrosion resistance of the steel. The composite addition of Zn and Mg forms a zinc-magnesium solid solution, which can promote the densification of the corrosion product layer and significantly improve the steel's resistance to carbon dioxide corrosion. The resulting steel has a yield strength ≥450MPa, tensile strength ≥560MPa, elongation A50mm ≥45%, impact energy at -50℃ ≥220J, DWTT at -20℃ ≥90%, and an average corrosion rate ≤0.35mm / a in a 14.5MPa supercritical carbon dioxide environment.

[0032] 2. The present invention adopts a slow cooling method after rolling to obtain a fine ferrite structure, which ensures high strength and high plasticity. The uniformity of the single ferrite structure is good, the microcouple effect is weak, and the resistance to carbon dioxide corrosion is better. Attached Figure Description

[0033] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0034] Figure 1This is a metallographic micrograph (ferrite) of Example 2 of the present invention. Detailed Implementation

[0035] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0036] Based on the process flow of the present invention, using the weight percentage components in Table 1 as raw materials and the process conditions in Table 2, hot-rolled coils of Examples 1 to 8 were prepared.

[0037] The process flow of this invention is as follows: S1: Molten steel is smelted, refined outside the furnace, hydrogen and oxygen content is controlled in the RH furnace, light desulfurization and calcium treatment are carried out in the LF furnace, and slabs are continuously cast to obtain continuously cast billets. S2: Heat the continuous casting billet to the corresponding temperature and hold for 150-250 minutes; S3: The continuously cast billet is rolled; S4: After rolling, the coil is cooled and wound to obtain a sheet.

[0038] Mechanical properties were tested on the hot-rolled coils from Examples 1 to 8. The test results are shown in Table 3. The test results of Examples 1 to 8 are all suitable for the supercritical carbon dioxide transportation service environment.

[0039] The corrosion rate was determined using a carbon dioxide corrosion resistance test. The medium was a standard NACE A solution, the test temperature was 30℃, the CO2 pressure was 2.0MPa, the stirring speed was 3m / s, and the test time was 72h. The corrosion rate was obtained by the weight loss method.

[0040] Metallographic image acquisition was performed on the hot-rolled coil obtained in Example 2, such as... Figure 1 As shown, the final microstructure of the coil is ferrite.

[0041] Table 1: Chemical composition of the examples / wt%.

[0042]

[0043] Table 2: Heating, rolling, and cooling process parameters.

[0044]

[0045] Table 3: Mechanical property test results.

[0046]

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A 450MPa grade high-ductility steel resistant to carbon dioxide corrosion, characterized in that, Composed of the following components by weight percentage composition: C: 0.05%-0.09%, Si: 0.60%-0.90%, Mn: 1.10%-1.40%, P: ≤0.020%, S: ≤0.002%, Ni: 0.40%-0.60%, Nb: 0.05%-0.07%, V: 0.07%-0.10%, Ti: 0.02%-0.04%, Co: 0.40%-0.60%, W: 0.60%-1.00%, Zn: 0.01%-0.04%, Mg: 0.005%-0.015%, with the remainder being Fe and unavoidable impurities.

2. The 450MPa grade high-plasticity carbon dioxide corrosion-resistant steel according to claim 1, characterized in that, The Zn / Mg ratio is 1.0-5.0, the Co / Ni ratio is 0.6-1.5, and the W / Co ratio is 1.0-2.

2.

3. The 450MPa grade high-plasticity carbon dioxide corrosion-resistant steel according to claim 1, characterized in that, Yield strength ≥ 450 MPa, tensile strength ≥ 560 MPa, elongation A50 mm ≥ 45%, impact energy at -50℃ ≥ 220 J, DWTT at -20℃ ≥ 90%, average corrosion rate in a 14.5 MPa supercritical carbon dioxide environment ≤ 0.35 mm / a.

4. The method for manufacturing 450MPa grade high-ductility carbon dioxide corrosion-resistant steel as described in any one of claims 1 to 3, characterized in that, The steps include the following: S1: Molten steel is smelted, refined outside the furnace, hydrogen and oxygen content is controlled in the RH furnace, light desulfurization and calcium treatment are carried out in the LF furnace, and slabs are continuously cast to obtain continuously cast billets. S2: Heat the continuous casting billet to 1000℃-1100℃ and hold for 150min-250min; S3: Continuously cast billets are rolled; roughing rolling temperature is 930℃-990℃, single-pass reduction rate is 20%-40%, finishing rolling temperature is 850℃-900℃, and finishing rolling temperature is 780℃-840℃. S4: After rolling, the coil is cooled and rolled to obtain a coil plate; the cooling rate is 5℃ / s-10℃ / s, and the final cooling temperature is 620℃-670℃.

5. The method according to claim 4, characterized in that, The smelting conditions in S1 are: smelting temperature 1500℃-1700℃, basicity 2.6-3.8, top and bottom combined blowing of N2 or Ar2, and flow rate 0.06m³ / h. 3 t -1 min -1 -0.08m 3 t -1 min -1 .

6. The method according to claim 4, characterized in that, The conditions for ladle refining in S1 are: arrival temperature ≥1550℃, heating time ≤30min, total processing time 40min-50min, soft blowing time ≥9min, and settling time 5min-7min.

7. The method according to claim 4, characterized in that, The conditions for controlling the hydrogen and oxygen content in the RH furnace in S1 are: working vacuum degree <60Pa, holding time 10-25min, final hydrogen content <1.0ppm, and oxygen content <15ppm.

8. The method according to claim 4, characterized in that, The conditions for light desulfurization treatment in the LF furnace in S1 are: slag basicity > 4.0, of which CaO > 50%, temperature 1580℃-1650℃, stirring for 20min-30min; The conditions for calcium treatment in the LF furnace in S1 are as follows: using CaSi or pure Ca wire with a Ca content of 20%-30%, the Ca addition amount is 0.60 kg / t-0.80 kg / t, and soft blowing argon for 30 m. 3 / h-50m 3 / h, time ≥6 minutes.

9. The application of the 450MPa grade high-plasticity carbon dioxide corrosion resistant steel as described in any one of claims 1 to 3 in the manufacture of high-plasticity pipelines.

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