Steel for resisting carbon dioxide corrosion at 555mpa and method for manufacturing the same

Abstract

The present application relates to a kind of 555MPa grade carbon dioxide corrosion resistant steel and its manufacturing method, steel chemical composition includes C, Si, Mn, Cr, Cu, Mo, V, Ti, Al, Zr, Zn etc., the rest is Fe and inevitable impurity element.For the existing 555MPa grade pipeline steel coil plate does not have carbon dioxide corrosion resistance, cannot adapt to supercritical carbon dioxide delivery service environment, and plasticity is low, forming property and safety problem such as poor, using low carbon tempering martensite organization design, uniform lath martensite organization, low residual austenite content and change to non-brittle network carbide, good plasticity and toughness are guaranteed, and comprehensive mechanical property is more optimal;Multiple element synergistic strengthening, significantly improve the carbon dioxide corrosion resistance of steel.

Description

Technical Field

[0001] This invention relates to the field of pipeline steel production technology, and in particular to a 555MPa grade carbon dioxide corrosion resistant steel and its manufacturing method. Background Technology

[0002] Carbon capture, utilization and storage (CCUS) technology is a key technology for addressing global climate change, and carbon dioxide transportation is a crucial link in the CCUS industry chain that connects carbon dioxide capture and storage. The efficiency and cost of carbon dioxide transportation will 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, characterized by 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 free water and impurity gases present in supercritical carbon dioxide pipelines are highly corrosive. Existing API carbon steel pipeline systems used for transporting natural gas experience occasional corrosion, potentially leading to leaks and failures.

[0004] Pipes are fundamental to ensuring the safe transportation of goods through pipelines. They constitute a significant portion of the total investment in pipeline construction. Due to factors such as corrosion and damage from third parties, pipe walls may thin or fail, potentially leading to various safety accidents. Key technical requirements for supercritical pipes include: low-temperature brittleness when carbon dioxide leaks and the temperature drops rapidly to -50°C, and the corrosion rate in a supercritical carbon dioxide environment.

[0005] Currently, no 555MPa-class carbon dioxide transmission pipelines for large-capacity, long-distance transportation have been developed, either domestically or internationally. A search revealed the following relatively close patent documents: 1) Chinese patent application CN112941422A discloses "a CO2 corrosion-resistant steel plate and its preparation method." The steel 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%. It is produced using a medium-thick plate rolling mill, and the rolled steel plate requires quenching and tempering heat treatment. The high Cr content of this steel plate classifies it as stainless steel, making it unsuitable for conventional smelting and continuous casting production lines. Furthermore, the excessively high Cr content prevents straight seam welding, and the steel plate's impact toughness is insufficient to meet the crack-stopping requirement of -50℃ during carbon dioxide leakage.

[0006] 2) Chinese patent application CN106498279A discloses "a low-Cr economical X65 pipeline steel resistant to CO2 corrosion and its production method." The steel 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%. The low Mn content in the steel plate leads to poor hardenability during subsequent straight seam welding, making it impossible to guarantee the low-temperature toughness of the weld and heat-affected zone at -50℃. Furthermore, the base material's low-temperature toughness at -20℃ is generally poor, failing to meet the crack-stopping requirement at -50℃ during carbon dioxide leakage. Summary of the Invention

[0007] This invention provides a 555MPa grade steel resistant to carbon dioxide corrosion and its manufacturing method. Addressing the problems of existing 555MPa grade pipeline steel coils lacking resistance to carbon dioxide corrosion, being unsuitable for supercritical carbon dioxide transport environments, and exhibiting poor safety, this invention employs a low-carbon tempered martensitic microstructure design. The uniform lath martensitic structure, low retained austenite content, and absence of brittle network carbides ensure good plasticity and toughness, resulting in superior overall mechanical properties. Multi-element synergistic strengthening significantly enhances the steel's resistance to carbon dioxide corrosion.

[0008] To achieve the above objectives, the present invention employs the following technical solution: The 555MPa grade steel is resistant to carbon dioxide corrosion. The chemical composition of the steel, by weight percentage, is: C: 0.10%–0.15%, Si: 0.60%–0.90%, Mn: 0.60%–0.90%, P≤0.020%, S≤0.002%, Cr: 0.35%–0.50%, Cu: 0.35%–0.50%, Mo: 0.40%–0.60%, V: 0.03%–0.06%, Ti: 0.04%–0.06%, Al: 0.40%–0.70%, Zr: 0.03%–0.07%, Zn: 0.11%–0.15%, N≤0.020%; among which, Mo / C = 1.4–6, Zn / C = 0.2–0.5, Si / Cu = 1.2–2; the remainder is Fe and unavoidable impurity elements.

[0009] The finished steel plate has a single low-carbon tempered martensitic structure.

[0010] The mechanical properties of the finished steel plate are as follows: transverse / longitudinal yield strength ≥555MPa, tensile strength ≥650MPa, yield ratio ≤0.92, elongation ≥20%, impact energy at -50℃ ≥180J, drop weight DWTT at -20℃ ≥85%, and average corrosion rate in a 14.5MPa supercritical carbon dioxide environment ≤0.25mm / a.

[0011] The manufacturing method of 555MPa grade carbon dioxide corrosion resistant steel includes steelmaking, ladle refining, slab continuous casting, continuous casting billet heating, rolling, cooling, tempering heat treatment, and coiling; the following processes are controlled: 1) Ladle refining: using RH+LF refining process; 2) Slab continuous casting: The continuous casting process adopts electromagnetic stirring or dynamic light reduction; 3) Heating of continuously cast slabs: Heating the continuously cast slabs to 960-1060℃ and holding for 100-200 minutes; 4) Rolling: TMCP rolling process is adopted; the single-pass reduction rate of roughing is 15% to 20%, and the finishing temperature of roughing is 960 to 1000℃; the starting temperature of finishing rolling is 890 to 940℃, the finishing temperature of finishing rolling is 760 to 810℃, and the single-pass reduction rate of finishing rolling is ≤20%; 5) Cooling: The cooling rate is 50-55℃ / s, and the final cooling temperature is <200℃; 6) Tempering heat treatment: Heat the steel plate to 310~410℃, heating rate ≤80℃ / h, hold for 60~120min and then cool with the furnace to below 100℃, then air cool after removal from the furnace.

[0012] Compared with the prior art, the beneficial effects of the present invention are: 1) The low-carbon tempered martensite microstructure design, with its uniform lath martensite microstructure, low residual austenite content, and absence of brittle network carbides, ensures good plasticity and toughness, resulting in superior overall mechanical properties. 2) Low-carbon tempered martensite has a low carbon content, resulting in a small hardening tendency in the heat-affected zone during welding, making it less prone to welding cracks, and the performance of the welded joint is close to that of the base material. 3) After tempering, the microstructure of low-carbon martensite tends to be stable, the passivation film formation ability is improved, and the corrosion resistance is better; 4) The interaction between Si and Cu promotes the enrichment of Cu on the surface, forming a Cu-rich oxide layer and a SiO2 protective oxide film, which synergistically improves the resistance to carbon dioxide corrosion. 5) The addition of Cr and Mo in combination generates Cr2O3, Mo2C and composite carbides, which improves the material's resistance to carbon dioxide corrosion (especially against pitting and crevice corrosion) and synergistically strengthens the matrix. 6) Cr and Al work synergistically. Cr forms a dense Cr2O3 on the metal surface, while Al forms an Al2O3 film. The high stability of Cr2O3 combined with the self-healing properties of Al2O3 significantly improves the material's resistance to carbon dioxide corrosion. Detailed Implementation

[0013] The 555MPa grade carbon dioxide corrosion resistant steel of this invention has the following chemical composition by weight percentage: C: 0.10%–0.15%, Si: 0.60%–0.90%, Mn: 0.60%–0.90%, P≤0.020%, S≤0.002%, Cr: 0.35%–0.50%, Cu: 0.35%–0.50%, Mo: 0.40%–0.60%, V: 0.03%–0.06%, Ti: 0.04%–0.06%, Al: 0.40%–0.70%, Zr: 0.03%–0.07%, Zn: 0.11%–0.15%, N≤0.020%; wherein, Mo / C = 1.4–6, Zn / C = 0.2–0.5, Si / Cu = 1.2–2; the remainder is Fe and unavoidable impurity elements.

[0014] The rationale for the chemical composition design of the 555MPa grade carbon dioxide corrosion resistant steel described in this invention is as follows: Carbon (C) is a carbide-forming element. It significantly improves strength through solid solution strengthening and phase transformation strengthening, making it the most effective element for ensuring strength. Carbon also improves hardenability, ensuring the strength and hardness of materials. Its effect is second only to phosphorus, and stronger than elements such as manganese, nickel, chromium, tungsten, molybdenum, and vanadium. C preferentially forms carbides with Cr, enhancing the strength and resistance to carbon dioxide corrosion of steel. C interacts with V to form stable carbonitrides, refining grains, achieving precipitation strengthening, and improving the strength, toughness, and thermal stability of steel. C interacts with Mo (this invention limits the Mo to C content ratio to 1.4–6) to synergistically form carbides, improving hardenability, high-temperature strength, and creep resistance, while suppressing temper brittleness. In this invention, only sufficient carbon can ensure the formation of low-carbon martensite. If the carbon content is too low, the tensile strength and hardness of the material cannot be guaranteed; however, if the carbon content is too high, it easily causes center segregation in the steel plate, which is detrimental to the corrosion resistance and crack arrest toughness of the steel plate and affects the weldability of the product. Therefore, this invention controls the carbon content to 0.10%–0.15%.

[0015] Si can dissolve into ferrite and austenite, playing a certain role in solid solution strengthening, significantly improving the hardness and tensile strength of steel. Simultaneously, it promotes ferrite grain coarsening, reducing the anisotropy of the steel plate's transverse and longitudinal properties. In silicon-containing steels, the participation of silicon in the corrosion process promotes the formation of a dense oxide film rich in Si (such as an Fe3O4-SiO2 composite film) on the steel surface. This film has a stable structure and low porosity, effectively blocking 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 → Fe). 2＋ +2e － Simultaneously, 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. This invention limits the Si to Cu content ratio to 1.2–2. Si can promote Cu surface enrichment, forming a protective oxide film and synergistically improving carbon dioxide corrosion resistance. However, increasing the silicon content will reduce the low-temperature toughness, plasticity, and weldability of the steel; therefore, this invention controls the silicon content to 0.60%–0.90%.

[0016] Mn: Manganese has a solid solution strengthening effect. Manganese and iron form a solid solution, which can improve the hardness and strength of ferrite and austenite in steel. Simultaneously, manganese is a carbide-forming element, capable of entering cementite and replacing some iron atoms. In steel, manganese lowers the critical transformation temperature, increases austenite stability, strongly enhances hardenability, promotes the formation of low-carbon lath martensite, and effectively ensures the strength and toughness of the steel. In this invention, manganese can compensate for the strength decrease caused by the reduction in carbon content, making it the most important and economical strengthening element. Experiments have shown that when the manganese content is below 1.0%, it can significantly reduce the segregation level of continuously cast billets and improve the product's resistance to carbon dioxide corrosion. However, excessive manganese content will increase the tendency for center segregation in continuously cast billets and increase the banded structure in steel plates, thereby increasing the brittleness and reducing the plasticity of the steel plates; therefore, this invention controls the manganese content to be 0.60%–0.90%.

[0017] P, S, and N are unavoidable impurity elements in steel. The lower their content, the better. However, if the content is too low, it will increase the production cost. Therefore, this invention controls P≤0.020%, S≤0.002%, and N≤0.020%.

[0018] Chromium (Cr): Chromium can improve the strength of steel through solid solution strengthening. Like manganese (Mn), it can also dissolve into solid solutions, improving the hardenability of steel and simultaneously increasing strength. When Cr dissolves into austenite, it increases the stability of supercooled austenite, promoting the formation of low-carbon lath martensite and improving the strength and hardness of steel. Chromium has excellent corrosion resistance; tests show that the corrosion rate decreases with increasing Cr content. In CO2 corrosion systems, chromium forms a multilayer film structure of mixed phases of FeCO3 and Cr(OH)3. This complete and dense corrosion product film of Cr(OH)3 not only hinders electrode activation reactions but also inhibits ion diffusion, effectively reducing the corrosion rate. Chromium can also combine with oxygen to form a dense chromium oxide layer (Cr2O3). This passivation layer prevents further erosion by oxygen, water, and other corrosive media, thus providing protection against carbon dioxide corrosion. Chromium can also form various stabilizing compounds such as Cr7C3 and Cr2S3. The presence of these compounds can form a hard film on the steel surface, thereby improving the steel's resistance to carbon dioxide corrosion. The combined addition of chromium and copper can simultaneously improve yield strength and tensile strength, and its resistance to carbon dioxide corrosion is far greater than that of adding either chromium or copper alone. It also avoids copper embrittlement. However, excessive chromium content significantly increases the brittle transition temperature of steel, reduces elongation, and easily forms coarse carbides, leading to a deterioration in toughness. This invention controls the chromium content to be 0.35%–0.50%.

[0019] Mo (Mo): Molybdenum improves the hardenability of steel, thereby increasing the strength of the base metal. Mo expands the γ-phase region, lowering the γ→α phase transformation temperature of steel; the transformation temperature gradually decreases with increasing Mo content. Mo refines the grain size of steel (more effectively than tungsten), significantly improving hardenability and hot strength, preventing temper brittleness, and enhancing tensile strength and toughness. Experiments have shown that Mo forms MoO3 (a dense surface film) and MoS2 (a lubricating and protective phase) in corrosive environments, with some existing in the matrix as solid solution. In steel, it is often uniformly dispersed or forms composite corrosion product films with Fe, Cr, etc. These compounds can combine with FeCO3 to form a dense Fe-Mo-C composite film, blocking film pores and hindering H2O. ＋ HCO 3－ The diffusion of corrosion ions significantly improves resistance to CO2 corrosion. Furthermore, alloying molybdenum with chromium enhances corrosion resistance. However, excessively high Mo content increases alloying costs and impairs the steel's plasticity and toughness. Therefore, this invention controls the molybdenum content to 0.4%–0.6%.

[0020] Cu (Copper): Copper improves hardenability and enhances the strength of steel during hot rolling and tempering heat treatment. Copper also strengthens steel through precipitation hardening and improves corrosion resistance; in particular, copper forms a passivation film on the steel surface. When combined with Cr and Mo, Cu promotes the formation of a more stable oxide film (containing Cr₂O₃, MoO₃, and CuO) on the steel surface, enhancing film adhesion and corrosion resistance, preventing localized corrosion caused by film detachment, and improving resistance to carbon dioxide corrosion. The addition of appropriate amounts of copper can enhance the yield strength and yield ratio of steel without affecting weldability. High copper content easily leads to copper embrittlement. To avoid this, this invention adds chromium in equal proportions. However, excessively high copper content can cause difficulties in smelting and continuous casting, and increase alloy costs; therefore, this invention controls the copper content to 0.35%–0.50%.

[0021] Vanadium (V) forms stable compounds with carbon, nitrogen, and oxygen, primarily existing in steel as carbides. It refines the microstructure and grain size, reduces overheating sensitivity, and enhances strength and toughness. Vanadium carbonitrides precipitate uniformly in ferrite in a fine, dispersed form, significantly improving material strength. When dissolved in solid solution at high temperatures, V increases hardenability and enhances tempering stability and secondary hardening effect during the self-tempering process after sheet coiling. Vanadium refines grain size and improves weldability. Refining dispersed VC, VN, or V2O3 significantly refines steel grain size, resulting in a more uniform and dense Fe3O4 / FeCO3 corrosion product film formed during corrosion, reducing porosity and defects, thereby lowering the CO2 corrosion rate. However, excessively high vanadium content not only fails to significantly improve strength but also increases alloy costs; therefore, this invention controls the vanadium content to 0.03%–0.06%.

[0022] Al: Aluminum is a commonly used deoxidizer. Adding a small amount of aluminum to steel can refine the grain, improve strength and impact toughness, and also enhance the steel's corrosion resistance. Al mainly forms Al₂O₃ and AlN in steel. The Al-rich oxide film on the surface can firmly adhere to the substrate, isolating H₂ generated from CO₂. ＋ CO 2－ Corrosion ions prevent the substrate from being eroded; the internally dispersed Al compounds refine the grains and reduce corrosion channels; at the same time, the synergistic effect of Al and Cr elements further improves the density of the corrosion product film and reduces the corrosion rate, especially when used in combination with Mo, Si, and Cr elements. This invention controls the Al content to be 0.40%–0.70%.

[0023] Ti: Titanium is a strong nitrogen-fixing element. Adding approximately 0.015% Ti can form high-temperature stable and fine TiN precipitates during slab continuous casting. These fine TiN precipitates effectively prevent the growth of austenite grains during heating of the continuously cast slab, and also significantly improve the toughness of the heat-affected zone during steel welding. Ti preferentially forms TiN and TiC nanoscale precipitates with N and C in steel. These precipitates can hinder austenite grain growth (especially during hot working and welding), refine austenite grains, increase the yield strength of steel by 30–80 MPa, increase impact toughness by 20%–50%, and lower the brittle-to-cold transition temperature. When Ti is combined with microalloying elements Nb and V, TiC can promote the dispersed precipitation of NbC and VC, producing a "dispersion strengthening" effect, further improving the strength of the steel without significantly sacrificing toughness. Ti improves film uniformity by refining grain size. Refining dispersed TiO2 and TiN significantly refines the steel grains, making the steel surface more uniform. This promotes the formation of a denser, more continuous Fe3O4 corrosion product film during corrosion, enhancing film adhesion and protective capabilities, and reducing the CO2 corrosion rate. However, excessive titanium content can easily lead to the formation of large particle inclusions. This invention controls the titanium content to be 0.04%–0.06%.

[0024] Zr: Trace amounts of zirconium have deoxidizing, purifying, and grain-refining effects, significantly altering inclusions and improving the low-temperature toughness of steel. ZrO2 and ZrN are mostly nano-sized fine spheres or granules, uniformly dispersed in the steel matrix and tightly bonded to it, thus refining the grains and improving the uniformity of the film. The finely dispersed ZrO2 and ZrN significantly refine the steel grains, making the steel surface more uniform, thereby promoting the formation of a denser and more uniform Fe3O4 corrosion product film during corrosion, enhancing the film's protective ability. ZrO2 itself has extremely high chemical stability and can form a very thin physical isolation layer on the steel surface, slightly blocking CO2 molecules from contacting the matrix and slowing down the corrosion rate. This invention controls the Zr to C content ratio to be 0.2–0.5. Within this range, highly stable ZrC and ZrN carbonitrides can be formed, achieving the effects of grain refinement, improved thermal strength, and high-temperature corrosion resistance. Excessive zirconium content easily leads to the formation of blocky or strip-shaped ZrO2 or ZrN inclusions. Some of these inclusions aggregate along grain boundaries, resulting in a decrease in the toughness and processing performance of the steel. This invention controls the zirconium content to be 0.03%–0.07%.

[0025] Zinc (Zn) has solid solution strengthening properties, improving the processing performance of steel. The solid solution formed by Zn dissolving in ferrite / austenite hinders dislocation movement, 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 reduces the risk of cracking. ZnO forms a dense passivation film on the steel surface, physically isolating CO2 molecules from the steel matrix and inhibiting anodic dissolution, thus slowing down the corrosion rate. Zinc has a lower electrode potential than iron and preferentially dissolves in corrosive environments, providing weak "sacrificial anodic protection" to the steel matrix, slowing localized corrosion, and improving resistance to carbon dioxide corrosion. This invention controls the zinc content to be 0.11%–0.15%.

[0026] The manufacturing method of the 555MPa grade carbon dioxide corrosion resistant steel of the present invention includes the following process flow: steelmaking, ladle refining, slab continuous casting, continuous casting billet heating, rolling, cooling, tempering treatment and coiling; wherein the following processes are controlled: 1) Ladle refining: The RH+LF refining process is adopted; RH refining controls the hydrogen and oxygen content, while LF refining carries out light desulfurization and calcium treatment to control the morphology of inclusions and improve the ductility, toughness and cold bending performance of steel.

[0027] 2) Slab continuous casting: The continuous casting process adopts electromagnetic stirring or dynamic light pressure.

[0028] 3) Heating of continuous casting billet: The continuous casting billet is heated to 960-1060℃ in a heating furnace and held for 100-200min. This temperature range and holding time can fully dissolve alloys such as Mo, Cr, and Cu, and at the same time facilitate the precipitation of Ti in large quantities, refine the austenite grain size, and improve the yield strength and tensile strength of the steel.

[0029] 4) Rolling: TMCP rolling process is adopted; the single-pass reduction in roughing is 15%–20% to ensure grain fragmentation and reduce internal stress after martensite transformation. The final roughing temperature is 960–1000℃; this temperature helps prevent austenite grain growth, homogenizes the grains, and improves the uniformity of microstructure and properties. The initial finishing temperature is 890–940℃, and the final finishing temperature is 760–810℃. This temperature range helps refine the flattening of austenite grains, thereby refining the final martensite grain size and ensuring high strength and low-temperature impact toughness. The single-pass reduction in finishing is ≤20%.

[0030] 5) Cooling: After rolling, ultra-fast cooling is adopted, with a cooling rate of 50-55℃ / s, exceeding the critical cooling rate. The purpose is to suppress the pearlite / bainite transformation and directly obtain a low-carbon martensite structure; the final cooling temperature is <200℃. The above-mentioned final cooling temperature and cooling rate are conducive to obtaining a low-carbon martensite structure with uniform dimensions, giving the product high strength and certain low-temperature toughness.

[0031] 6) Tempering treatment: Heat the steel plate to 310-410℃ at a heating rate of ≤80℃ / h, hold for 60-120 minutes, then cool it in the furnace to below 100℃, and finally air cool it after removal from the furnace. Tempering heat treatment eliminates internal stress and improves low-temperature impact toughness.

[0032] The finished steel plate has a single low-carbon tempered martensitic structure.

[0033] The mechanical properties of the finished steel plate are as follows: transverse / longitudinal yield strength ≥555MPa, tensile strength ≥650MPa, yield ratio ≤0.92, elongation ≥20%, impact energy at -50℃ ≥180J, drop weight DWTT at -20℃ ≥85%, and average corrosion rate in a 14.5MPa supercritical carbon dioxide environment ≤0.25mm / a.

[0034] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0035]

Example

[0036] Table 1 Chemical composition of steel (wt%) Table 2 Heating, Rolling and Cooling Process Parameters Table 3 Heat Treatment Process Table 4 Mechanical Properties of Finished Products Note: The corrosion rate in the table refers to the average corrosion rate in a supercritical carbon dioxide environment of 14.5 MPa. The corrosion test medium was a standard NACE A solution, the test temperature was 30℃, the CO2 pressure was 2.0 MPa, the stirring speed was 3 m / s, the test time was 72 h, and the corrosion rate was obtained by the weight loss method.

[0037] As can be seen from Tables 1-4, the composition design and manufacturing process of this invention can produce hot-rolled coils resistant to carbon dioxide corrosion for supercritical carbon dioxide transportation at a pressure of 555 MPa.

[0038] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. 555MPa grade carbon dioxide corrosion resistant steel, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C: 0.10%–0.15%, Si: 0.60%–0.90%, Mn: 0.60%–0.90%, P≤0.020%, S≤0.002%, Cr: 0.35%–0.50%, Cu: 0.35%–0.50%, Mo: 0.40%–0.60%, V: 0.03%–0.06%, Ti: 0.04%–0.06%, Al: 0.40%–0.70%, Zr: 0.03%–0.07%, Zn: 0.11%–0.15%, N≤0.020%; among which, Mo / C = 1.4–6, Zn / C = 0.2–0.5, Si / Cu = 1.2–2; the remainder is Fe and unavoidable impurity elements.

2. The 555MPa grade carbon dioxide corrosion resistant steel according to claim 1, characterized in that, The finished steel plate has a single low-carbon tempered martensitic structure.

3. The 555MPa grade carbon dioxide corrosion resistant steel according to claim 1, characterized in that, The mechanical properties of the finished steel plate are as follows: transverse / longitudinal yield strength ≥555MPa, tensile strength ≥650MPa, yield ratio ≤0.92, elongation ≥20%, impact energy at -50℃ ≥180J, drop weight DWTT at -20℃ ≥85%, and average corrosion rate in a 14.5MPa supercritical carbon dioxide environment ≤0.25mm / a.

4. The method for manufacturing 555MPa grade carbon dioxide corrosion resistant steel as described in any one of claims 1 to 3, characterized in that, The process flow includes steelmaking, ladle refining, slab continuous casting, continuous casting billet heating, rolling, cooling, tempering heat treatment, and coiling; the following processes are controlled: 1) Ladle refining: using RH+LF refining process; 2) Slab continuous casting: The continuous casting process adopts electromagnetic stirring or dynamic light reduction; 3) Heating of continuously cast slabs: Heating the continuously cast slabs to 960-1060℃ and holding for 100-200 minutes; 4) Rolling: TMCP rolling process is adopted; the single-pass reduction rate of roughing is 15% to 20%, and the finishing temperature of roughing is 960 to 1000℃; the starting temperature of finishing rolling is 890 to 940℃, the finishing temperature of finishing rolling is 760 to 810℃, and the single-pass reduction rate of finishing rolling is ≤20%; 5) Cooling: The cooling rate is 50-55℃ / s, and the final cooling temperature is <200℃; 6) Tempering heat treatment: Heat the steel plate to 310~410℃, heating rate ≤80℃ / h, hold for 60~120min and then cool with the furnace to below 100℃, then air cool after removal from the furnace.

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