High-toughness supercritical CO2 delivery pipeline steel coil plate and manufacturing method thereof

Abstract

The invention discloses a high-toughness supercritical CO2 delivery pipeline steel coil plate and a manufacturing method thereof, and the high-toughness supercritical CO2 delivery pipeline steel coil plate comprises the following chemical components: 0.05-0.10% of C, 0.6-0.9% of Si, 1.45-1.70% of Mn, less than or equal to 0.010% of P, less than or equal to 0.002% of S, 0.01-0.03% of Ti, 0.55-0.90% of Ni, 0.03-0.06% of V, 0.02-0.05% of Al, less than or equal to 0.008% of N, 2.1-2.6% of Mn + Ni, 1.2-1.7% of Ni + Si, 10-22% of Ni / V, and the balance of Fe and inevitable elements. The manufacturing method comprises the steps of smelting, slab continuous casting, continuous casting slab heating, rolling, cooling and coiling. In the transverse direction of the rolled plate, Rt0.5 is larger than or equal to 500 MPa, Rm is larger than or equal to 600 MPa, Rt0.5 / Rm is smaller than or equal to 0.87, A50mm is larger than or equal to 38%,-40 DEG C impact energy KV8 is larger than or equal to 300 J, and-20 DEG C drop weight DWTT is larger than or equal to 98%; in the longitudinal direction, Rt0.5 is larger than or equal to 490 MPa, Rm is larger than or equal to 590 MPa, Rt0.5 / Rm is smaller than or equal to 0.84, and A50mm is larger than or equal to 40%; the average corrosion rate in a 14.5 MPa supercritical CO2 environment is 1t; and 0.20 mm / a. The low-carbon medium-manganese nickel-vanadium-containing alloy design is adopted, the low-temperature toughness of a weld joint is guaranteed, the CO2 corrosion resistance and the oxidation resistance are improved, and higher safety is achieved in pipeline engineering.

Description

Technical Field

[0001] The present invention relates to the manufacture of a high-toughness hot-rolled coil of pipeline steel for straight seam welded pipes, and in particular to an X65M-grade high-toughness supercritical CO2 transmission pipeline steel coil and a manufacturing method thereof. Background Art

[0002] CCUS (carbon capture, utilization, and storage) is a key technology for addressing global climate change and a crucial path for China to achieve carbon peak and carbon neutrality. CO2 transportation is a key link in the CCUS industry chain, connecting CO2 capture and storage. The efficiency and cost of CO2 transportation directly impact the overall scale and economic benefits of CCUS.

[0003] The critical pressure of pure CO2 is 7.38 MPa, and its critical temperature is 31.1°C. Supercritical CO2 transportation refers to a form of transportation where the pressure is higher than the critical pressure, characterized by high density and low viscosity. When the entire pipeline transportation process is in a supercritical state, transportation is most efficient and wear is low. However, when free water and impurity gases are present in the supercritical CO2 pipeline, they are extremely corrosive. Existing API carbon steel pipelines used to transport natural gas may leak and fail in the event of occasional corrosion. Pipes are the foundation for ensuring the safe transportation of pipelines. Pipe costs account for a high proportion of the total investment in pipeline construction. Pipe walls may become thinner or even fail due to factors such as corrosion and third-party damage, which in severe cases can lead to various safety accidents. Key technical requirements for supercritical pipes include low-temperature brittleness when the temperature drops sharply to -40°C during CO2 leakage and corrosion rate in a supercritical CO2 environment.

[0004] Currently, China does not have a large-capacity, long-distance X65M-class CO2 transmission pipeline. The following is a brief introduction to patents that are similar to this invention:

[0005] (1) Chinese patent CN112941422A "A CO2 corrosion-resistant steel plate and its preparation method". The composition contains C: 0.03-0.07%, Cr: 4.0-6.0%, Ni: 0.15-2.50%, Nb: 0.01-0.06%, P: ≤0.005%, S ≤0.0050%. This invention is a method for producing CO2 corrosion-resistant steel plates disclosed by the University of Science and Technology Beijing. The products are produced using a medium and thick plate rolling mill, and the rolled steel plates need to undergo a quenching and tempering heat treatment process. The Cr content of this invention is relatively high, belonging to stainless steel, and cannot be implemented in ordinary smelting and continuous casting. Moreover, the excessively high Cr content will make it impossible to subsequently weld the steel plates with straight seams, and at the same time, the impact toughness of the steel plates is not high, which cannot meet the crack arrest requirements at -40°C when CO2 leaks.

[0006] (2) Chinese patent CN106498279A, "A low-Cr economical X65 pipeline steel resistant to CO2 corrosion and its production method." The steel contains 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%, S ≤0.0030%. This invention is a method for producing X65 hot-rolled coil for CO2 corrosion resistance disclosed by Wuhan Iron and Steel Co., Ltd. The Mn content of this invention is relatively low, resulting in poor hardenability in the subsequent straight seam welding process, and unable to guarantee the low-temperature toughness of the weld and heat-affected zone at -40°C. At the same time, the low-temperature toughness of the base material at -20°C is average, and cannot meet the crack arrest requirements at -40°C when CO2 leaks. Summary of the Invention

[0007] In view of the technical problems that the current production of X65M pipeline steel coils has no CO2 corrosion resistance, cannot adapt to the supercritical CO2 transportation service environment, and has poor safety, a high-toughness supercritical CO2 transportation pipeline steel coil and a manufacturing method thereof are specially provided.

[0008] One of the technical solutions of the present invention is to propose a high-toughness supercritical CO2 transmission pipeline steel coil, the chemical composition (weight, %) of which is as follows: C: 0.05-0.10%, Si: 0.6-0.9%, Mn: 1.45-1.70%, P: ≤0.010%, S: ≤0.002%, Ti: 0.01-0.03%, Ni: 0.55-0.90%, V: 0.03-0.06%, Al: 0.02-0.05%, N: ≤0.008%, wherein Mn+Ni: 2.1-2.6%, Ni+Si: 1.2-1.7%, Ni / V: 10-22, and the rest are Fe and unavoidable elements.

[0009] The present invention selects the above alloying element types and contents because:

[0010] C: A carbide-forming element, it is the most effective element for ensuring strength. It can improve hardenability and ensure material strength and hardness. Its effect is second only to P and is stronger than elements such as Mn, Ni, and V. C significantly improves the strength of steel through solid solution strengthening and phase transformation strengthening. Only with sufficient C content can sufficient acicular ferrite be formed. Too low a C content cannot guarantee the material's strength and hardness. However, too high a C content can easily cause center segregation in the steel plate, which is detrimental to the steel's corrosion resistance and crack arrest toughness, and affects the product's weldability. The C content should be controlled within the range of 0.05-0.10%.

[0011] Si: It can dissolve in ferrite and austenite, playing a certain role in solid solution strengthening, significantly improving the hardness and strength of steel, while promoting the coarsening of ferrite grains and reducing the transverse and longitudinal anisotropy of the steel plate. When steel containing Si is heated in an oxidizing atmosphere, a layer of SiO2 film will form on the surface, thus protecting the steel from further oxidation. When the Si content is between 0.60 and 1.50%, a SiO2 passivation film can be formed, which improves the acid corrosion resistance and high temperature resistance of the steel, thereby enhancing its overall performance. Si exists in the form of silicide in steel, which can effectively hinder the entry of oxidants, thereby reducing the occurrence of corrosion. However, an increase in Si content will reduce the welding performance of steel and significantly reduce the plasticity and toughness of steel. Its range should be controlled within 0.6 to 0.9%.

[0012] Mn: Mn has a solid solution strengthening effect, forming a solid solution with Fe, thereby increasing the hardness and strength of the ferrite and austenite in the steel. Mn is also a carbide-forming element and can enter cementite to replace some iron atoms. Mn in steel can lower the critical transition temperature, increase the stability of austenite, and significantly improve the hardenability of the steel, effectively ensuring the strength of the steel. Furthermore, Mn can compensate for the strength loss caused by a reduction in C content, making it the most important and economical strengthening element. Mn also shifts the C curve to the right, promoting bainite transformation and favoring the formation of acicular ferrite, significantly increasing the strength of the steel without significantly decreasing toughness. A certain amount of Mn can ensure weld strength and low-temperature impact toughness at -40°C during straight seam welding. However, excessive Mn content increases the tendency for central segregation in the continuous casting ingot, increasing banded structure in the steel plate, increasing brittleness, and reducing ductility. Mn should be controlled within the range of 1.45% to 1.70%.

[0013] P, S, and N are unavoidable impurity elements in steel. The lower their content, the better. However, excessive reduction in steel purity significantly increases production costs. Therefore, while ensuring the toughness of this product, the present invention sets P ≤ 0.01%, S ≤ 0.002%, and N ≤ 0.008%.

[0014] V: V forms stable compounds with carbon, nitrogen, and oxygen, primarily existing in steel as carbides. This helps refine the structure and grain size, reduce overheating sensitivity, and improve strength and toughness. V carbonitrides precipitate uniformly in the ferrite as fine dispersions, significantly increasing the material's strength. When dissolved in solid solution at high temperatures, V increases the steel's hardenability and enhances tempering stability and secondary hardening during the autotempering process after coiling. V also refines grain size and improves weldability. However, excessive V content has little effect on strength and increases alloy cost. The optimal V content should be between 0.03 and 0.06%.

[0015] Ti: Ti is a strong nitrogen-binding element. Adding approximately 0.015% Ti forms high-temperature stable, fine TiN precipitates during slab continuous casting. These fine TiN precipitates effectively prevent austenite grain growth during heating and significantly improve the toughness of the heat-affected zone during steel welding. Small amounts of precipitated TiC produce a strong precipitation strengthening effect, preventing significant grain growth during subsequent normalizing heat treatment, thereby ensuring uniform performance in the steel pipe. However, excessive Ti content is ineffective and can easily form large inclusions. The optimal range is 0.01-0.03%.

[0016] Ni: Ni can greatly improve the strength of steel and keep it always at a very high low-temperature toughness. Ni is insoluble in carbides and completely enters austenite, thereby fully exerting its role in improving hardenability, lowering the critical point and increasing the stability of austenite. When Ni is combined with C, the hardenability is improved more significantly. The addition of Ni can improve the weldability of steel, making the steel easy to form by hot and cold processing, and facilitating the preparation of steel pipes; Ni lowers the low-temperature brittle transition temperature of steel, weakens the toughness weakening effect caused by the addition of Si, and ensures the low-temperature impact toughness of the steel plate at -40°C. When the Ni content is greater than 0.5%, as the Ni content increases, the corrosion resistance of the steel will increase. It is not only acid-resistant, but also alkali-resistant, and has corrosion resistance to the atmosphere and salt, significantly improving the resistance to CO2 corrosion. However, if the Ni content is too high, the steel will become more brittle and the alloy cost will increase. The optimal range should be controlled at 0.55-0.90%, among which Mn+Ni: 2.1-2.6%, Ni+Si: 1.2-1.7%, and Ni / V: 10-22.

[0017] Al: Al is a commonly used deoxidizer. Adding a small amount of Al to steel can refine the grains, improve the strength and impact toughness of the steel, and also improve the corrosion resistance of the steel. The effect is particularly good when used in combination with Si. The Al content of the present invention is 0.02-0.05%.

[0018] The second technical solution of the present invention is to propose a method for manufacturing high-toughness supercritical CO2 transmission pipeline steel coil, including smelting, slab continuous casting, continuous casting billet heating, rolling, cooling, and coiling, which is characterized by:

[0019] Continuous Casting Slab Heating: Continuous casting slabs are heated in a furnace to 1180-1250°C and held for 180-260 minutes. This temperature range and holding time allow for the full solid solution of alloys such as V and Ni, while also facilitating the precipitation of large amounts of Ti, refining the austenite grain size, and improving the yield strength and tensile strength of the steel. During high-temperature heating, a SiO2 film forms on the surface of the slab, protecting the steel from further oxidation and enhancing corrosion resistance.

[0020] Rolling: The rough rolling and finishing temperatures are 1070-1100°C, which promotes TiC precipitation and hinders austenite grain growth, resulting in grain refinement and increased strength. Finishing rolling starts at 920-1030°C, and ends at 850-900°C, with a cumulative reduction of 65%-70%. This temperature range appropriately coarsens the grain size and reduces the anisotropy of the transverse and longitudinal properties of the steel plate. High reductions generate a large number of dislocations and twins, which promote dislocation strengthening and significantly increase yield strength and tensile strength.

[0021] Cooling: After rolling, laminar water cooling is used at a cooling rate of 14-22°C / s. This cooling rate is conducive to obtaining a uniformly sized acicular ferrite structure, which gives it good low-temperature toughness.

[0022] Coiling: Coil after cooling, with a coiling temperature of 600-670°C. This temperature range combined with a specific cooling rate is conducive to obtaining acicular ferrite structure with uniform size, thus giving it good strength and low-temperature toughness.

[0023] After smelting, the molten steel undergoes external refining, which uses an RH furnace to control the H and O content, and an LF furnace for light desulfurization and calcium treatment to control the morphology of inclusions and improve the steel's ductility, toughness, and cold bending properties.

[0024] Furthermore, the thickness of the continuously cast slab is 170 to 200 mm, and electromagnetic stirring or dynamic soft reduction is applied during the continuous casting process.

[0025] Preferably, the final structure of the rolled plate is a mixed structure of acicular ferrite and a small amount of MA, and the volume fraction of MA is less than 1%.

[0026] The high toughness supercritical CO2 transmission pipeline steel coil produced by the above chemical composition and process has excellent comprehensive performance. The final mechanical properties of the coil are: t0.5 ≥500MPa, transverse R m ≥600MPa, transverse R t0.5 / R m ≤0.87, horizontal A 50mm ≥38%, transverse -40℃ impact energy KV8 ≥300J, transverse -20℃ drop hammer DWTT ≥98%; longitudinal R t0.5 ≥490MPa, longitudinal R m ≥590MPa, longitudinal R t0.5 / R m ≤0.84, longitudinal A 50mm ≥40%; average corrosion rate in 14.5MPa supercritical CO2 environment <0.20mm / a.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The use of low C, medium Mn, Ni and V alloy design can ensure the low-temperature toughness of the weld and ensure sufficient grain refinement. The V element can improve the strength and low-temperature properties of the hot-rolled coil after normalizing, ensuring that the heat-affected zone still has high strength and low-temperature toughness after the hot-rolled coil is welded into a steel pipe.

[0029] (2) Adding appropriate amounts of Si and Ni elements at the same time can not only improve the yield strength of steel, but also improve the low-temperature fracture toughness, ensure weldability, and reduce the anisotropy of the transverse and longitudinal properties of the steel plate, thereby improving the corrosion resistance and oxidation resistance of the steel.

[0030] (3) Adding appropriate amounts of Ni and V elements at the same time can synergistically improve the yield strength of steel, control the transverse and longitudinal yield strength ratio to a low level not higher than 0.87, improve the safety of steel pipes against sudden fracture in pipelines, improve the low-temperature impact toughness of steel plates at -40°C, improve low-temperature DWTT performance, improve CO2 corrosion resistance, and reduce the fracture of steel pipes caused by corrosion. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of an exemplary embodiment of the experimental device and method is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0032] The following examples are intended only to provide some preferred embodiments of the present invention and are not intended to limit the scope of the invention or its technical approach. Table 1 lists the chemical compositions of Examples 1-8, Table 2 lists the heating, rolling, cooling, and coiling process parameters for each example, and Table 3 lists the mechanical properties and microstructure ratios for each example.

[0033] Table 1 Chemical composition of the steel of the embodiment (wt, %)

[0034] Actual example C Si Mn P S Ti Ni V Al N Mn+Ni Ni+Si Ni / V 1 0.10 0.7 1.50 0.006 0.001 0.01 0.60 0.03 0.05 0.005 2.2 1.3 20 2 0.06 0.8 1.55 0.010 0.001 0.03 0.81 0.05 0.03 0.006 2.4 1.6 16 3 0.08 0.6 1.62 0.009 0.002 0.02 0.65 0.06 0.03 0.004 2.2 1.3 11 4 0.07 0.9 1.70 0.008 0.001 0.02 0.55 0.04 0.04 0.003 2.6 1.5 14 5 0.05 0.8 1.45 0.009 0.002 0.02 0.90 0.05 0.04 0.005 2.3 1.7 18 6 0.06 0.7 1.65 0.010 0.001 0.03 0.70 0.04 0.03 0.007 2.4 1.4 18 7 0.07 0.6 1.53 0.007 0.001 0.02 0.75 0.05 0.02 0.005 2.1 1.4 15 8 0.09 0.7 1.58 0.006 0.002 0.02 0.85 0.04 0.04 0.006 2.3 1.6 21

[0035] Table 2 Process parameters for heating, rolling, cooling and coiling of steel in various examples

[0036]

[0037] Table 3 Main mechanical properties of steels in various examples

[0038]

[0039]

[0040] As can be seen from Tables 1 to 3, the hot-rolled coil for supercritical CO2 transport straight seam welded pipe produced by adopting the composition design and continuous casting billet heating, rolling, cooling and coiling processes of the present invention meets the high toughness X65M grade requirements.

Claims

1. A high-toughness supercritical CO2 transmission pipeline steel coil, characterized in that: The chemical composition of the steel plate is: C: 0.05%~0.10%, Si: 0.6%~0.9%, Mn: 1.45%~1.70%, P: ≤0.010%, S: ≤0.002%, Ti: 0.01%~0.03%, Ni: 0.55%~0.90%, V: 0.03%~0.06%, Al: 0.02%~0.05%, N: ≤0.008%, of which Mn+Ni: 2.1~2.6%, Ni+Si: 1.2~1.7%, Ni / V: 10~22, and the rest are Fe and unavoidable elements.

2. The high-toughness supercritical CO2 transmission pipeline steel coil according to claim 1 is characterized in that: The final microstructure of the rolled plate is a mixed microstructure of acicular ferrite and a small amount of MA, and the volume fraction of MA is less than 1%.

3. The high toughness supercritical CO2 transmission pipeline steel coil according to claim 1 is characterized in that the coil Plate horizontal R t0.5 ≥500MPa, transverse R m ≥600MPa, transverse R t0.5 / R m ≤0.87, horizontal A 50mm ≥38%, transverse -40℃ impact energy KV8 ≥300J, transverse -20℃ drop hammer DWTT ≥98%; longitudinal R t0.5 ≥490MPa, longitudinal R m ≥590MPa, longitudinal R t0.5 / R m ≤0.84, longitudinal A 50mm ≥40%.

4. The high-toughness supercritical CO2 transmission pipeline steel coil according to claim 1 is characterized in that: The average corrosion rate in 14.5MPa supercritical CO2 environment is <0.20mm / a.

5. A method for manufacturing a high-toughness supercritical CO2 transmission pipeline steel coil according to any one of claims 1 to 4, comprising smelting, slab continuous casting, continuous casting billet heating, rolling, cooling, and coiling, characterized in that: Continuous casting slab heating: The continuous casting slab is heated to 1180-1250℃ in a heating furnace and kept warm for 180-260min; Rolling: rough rolling and finishing temperature is 1070-1100℃, finishing rolling starting temperature is 920-1030℃, finishing temperature is 850-900℃, cumulative reduction rate is 65%-70%; Cooling: After rolling, laminar water cooling is adopted, with a cooling rate of 14-22℃ / s; Coiling: Coiling temperature 600~670℃.

6. The method for manufacturing high-toughness supercritical CO2 transmission pipeline steel coil according to claim 5, characterized in that: The thickness of the continuous casting slab is 170 to 200 mm, and electromagnetic stirring or dynamic soft reduction is used during the continuous casting process.

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