500MPa-grade supercritical CO2 corrosion-resistant pipeline coiled plate and manufacturing method thereof

Abstract

The invention discloses a 500MPa-grade supercritical CO2 corrosion-resistant pipeline coil plate and a manufacturing method thereof, and the 500MPa-grade supercritical CO2 corrosion-resistant pipeline coil plate comprises the following chemical components: 0.05 to 0.10 percent of C, 0.6 to 0.9 percent of Si, 1.50 to 1.70 percent of Mn, less than or equal to 0.010 percent of P, less than or equal to 0.002 percent of S, 0.10 to 0.30 percent of Cr, 0.35 to 0.45 percent of Mo, 0.03 to 0.05 percent of Nb, 0.01 to 0.03 percent of Ti, 0.02 to 0.05 percent of Al, 0.20 to 0.30 percent of Co, less than or equal to 0.008 percent of N, 1.2 to 4.3 percent of Mo / Cr, 0.75 to 0.92 percent of Mo + Cr + Co, 2.8 to 3.9 percent of Si / Co 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 540 MPa, Rm is larger than or equal to 640 MPa, Rt0.5 / Rm is smaller than or equal to 0.87, A50 mm is larger than or equal to 36%,-40 DEG C impact energy KV8 is larger than or equal to 220 J, and-20 DEG C drop weight DWTT is larger than or equal to 95%; in the longitudinal direction, Rt0.5 is larger than or equal to 520 MPa, Rm is larger than or equal to 630 MPa, Rt0.5 / Rm is smaller than or equal to 0.86, and A50mm is larger than or equal to 38%; the average corrosion rate in a 14.5 MPa supercritical CO2 environment is 1t; and 0.05 mm / a. The low-carbon medium-manganese molybdenum-chromium-cobalt-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 hot-rolled coil plates of pipeline steel for longitudinally welded pipes, and particularly to a 500 MPa grade supercritical CO2 corrosion-resistant pipeline coil plate and a manufacturing method thereof. Background Art

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

[0003] The critical pressure of pure CO2 is 7.38 MPa, and the critical temperature is 31.1 °C. Supercritical state transportation refers to the transportation form with a transportation pressure higher than the critical pressure, which has the characteristics of high density and low viscosity. When the entire pipeline transportation process is in the supercritical state, the transportation is the most efficient and has less wear; however, when there is free water and impurity gases in the supercritical CO2 pipeline, its corrosivity is extremely strong, and the existing API carbon steel system pipelines for transporting natural gas may leak and fail in the case of occasional corrosion. Pipe materials are the basis for ensuring the safe transportation of pipelines. In the total investment of pipeline construction, the cost of pipe materials accounts for a relatively high proportion. The pipe wall may become thinner or even fail due to factors such as corrosion and third-party damage, and serious accidents may occur in severe cases. The key technical requirements for supercritical pipe materials include: low-temperature brittleness when the temperature drops sharply to -40 °C during CO2 leakage and the corrosion rate in the supercritical CO2 environment.

[0004] At present, there is no large-capacity, long-distance X65M grade CO2 transportation pipeline in China. The following briefly introduces the patents relatively close to the present invention:

[0005] (1) Chinese Patent CN112941422A "A Steel Plate for CO2 Corrosion Resistance 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 production method of a steel plate for CO2 corrosion resistance disclosed by the University of Science and Technology Beijing. The product is produced by a medium plate rolling mill, and the rolled steel plate needs to be subjected to a quenching and tempering heat treatment process. The Cr content of this invention is relatively high and belongs to stainless steel, which cannot be implemented in ordinary smelting and continuous casting. Moreover, too high a Cr content will cause the subsequent inability to longitudinally weld the steel plate, and at the same time result in low impact toughness of the steel plate, unable to meet the crack arrest requirement at -40 °C during CO2 leakage.

[0006] (2) Chinese Patent CN106498279A, "A Low-Cr Economical X65 Pipeline Steel Resistant to CO2 Corrosion and Its Production Method". The composition 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 production method of X65 hot-rolled coil for resisting CO2 corrosion publicly disclosed by Wuhan Iron and Steel Co., Ltd. The low Mn content in this invention results in poor hardenability during the subsequent longitudinal welding process, unable to ensure 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 metal at -20°C is general and cannot meet the crack arrest requirement at -40°C when CO2 leaks. Summary of the Invention

[0007] Aiming at the technical problems that the currently produced pipeline steel coils of 500MPa level do not have the performance of resisting CO2 corrosion, cannot adapt to the service environment of supercritical CO2 transportation, and have poor safety, etc., a hot-rolled coil for longitudinal welded pipes for supercritical CO2 transportation and its manufacturing method are provided, especially relating to a 500MPa-level supercritical CO2 corrosion-resistant pipeline coil and its manufacturing method.

[0008] One of the technical solutions of the present invention is to propose a 500MPa-level supercritical CO2 corrosion-resistant pipeline coil. The chemical composition (by weight, %) is as follows: C: 0.05 - 0.10%, Si: 0.6 - 0.9%, Mn: 1.50 - 1.70%, P: ≤0.010%, S: ≤0.002%, Cr: 0.10 - 0.30%, Mo: 0.35 - 0.45%, Nb: 0.03 - 0.05%, Ti: 0.01 - 0.03%, Al: 0.02 - 0.05%, Co: 0.20 - 0.30%, N: ≤0.008%. Among them, Mo / Cr: 1.2 - 4.3, Mo + Cr + Co: 0.75% - 0.92%, Si / Co: 2.8 - 3.9, and the rest are Fe and inevitable elements.

[0009] The reason for choosing the above alloy element types and their contents in the present invention is as follows:

[0010] C: It is a carbide - forming element, the most effective element for ensuring strength. It can improve hardenability, guarantee the strength and hardness of the material. Its role is second only to P and stronger than elements such as Mn, Cr, and Mo. C significantly increases the strength of steel through solid - solution strengthening and phase - transformation strengthening. Only by ensuring sufficient C can sufficient acicular ferrite be formed. If the C content is too low, the strength and hardness of the material cannot be guaranteed. However, if the C content is too high, it is easy to cause center segregation in the steel plate, which is unfavorable for the corrosion resistance and crack - arrest toughness of the steel plate and will affect the weldability of the product. Its optimal range is 0.05 - 0.10%.

[0011] Si: It can dissolve into ferrite and austenite, playing a certain role in solid - solution strengthening, significantly increasing the hardness and strength of the steel. At the same time, it promotes the coarsening of ferrite grains and reduces the anisotropy of the transverse and longitudinal properties of the steel plate. When the steel containing Si is heated in an oxidizing atmosphere, a SiO2 film will form on the surface, thus protecting the steel from further oxidation. Si combined with elements such as Mo and Cr helps to improve the corrosion resistance and oxidation resistance of the steel. When the Si content is 0.60 - 1.50%, a SiO2 passivation film can be formed, improving the acid - corrosion resistance and high - temperature resistance of the steel, thereby enhancing its comprehensive performance. The form of Si existing in the steel is silicide, which can effectively hinder the entry of oxidants, thus reducing the occurrence of corrosion. However, the increase in Si content will reduce the weldability of the steel, significantly reducing the plasticity and toughness of the steel. Its optimal range is 0.6 - 0.9%.

[0012] Mn: Mn has a solid - solution strengthening effect and can form a solid - solution with Fe, thereby increasing the hardness and strength of ferrite and austenite in the steel. At the same time, Mn is also a carbide - forming element and can enter the cementite to replace part of the iron atoms. Mn can lower the critical transformation temperature in the steel, increase the stability of austenite, and significantly improve the hardenability of the steel, effectively guaranteeing the strength of the steel. In addition, Mn can compensate for the strength decrease caused by the reduction of C content and is the most important and economical strengthening element. Mn can also shift the C - curve to the right, promote the transformation of bainite, be conducive to the formation of acicular ferrite, significantly increase the strength of the steel, and the toughness decreases not significantly. A certain amount of Mn element can ensure the strength of the weld seam and the low - temperature impact toughness at - 40°C during the longitudinal - seam welding process. However, too high Mn content will increase the tendency of center segregation in the continuous - casting billet, increase the banded structure in the steel plate, resulting in an increase in the brittleness of the steel plate and a decrease in plasticity. Its optimal range is 1.50 - 1.70%.

[0013] P, S, N: They are inevitable impurity elements in the steel, and the lower the content, the better. However, the excessive reduction of steel purity will significantly increase production costs. Therefore, on the premise of ensuring the toughness index of this product, P≤0.01%, S≤0.002%, and N≤0.008% in the present invention.

[0014] Cr: Cr can improve strength through solid solution strengthening. Similar to Mn, it dissolves into the solid solution to increase the hardenability of the steel and play a role in enhancing strength. After the Cr element dissolves into austenite, it increases the stability of supercooled austenite, shifts the C curve to the right, promotes the formation of low-carbon bainite in the supercooled structure, and improves the strength and hardness of the steel. Cr has excellent corrosion resistance. As the Cr content increases, the corrosion rate decreases. In the CO2 corrosion system, Cr will form a multi-layer film structure of a mixed phase of FeCO3 and Cr(OH)3. The complete and dense corrosion product film Cr(OH)3 not only hinders the electrode activation reaction but also inhibits the ion diffusion process, effectively reducing the corrosion rate. Cr can also combine with oxygen to form a dense chromium oxide layer (Cr2O3). This passivation layer can prevent oxygen, water, and other corrosion media from further eroding, thus providing protection against CO2 corrosion. The Cr element can also form various stable compounds such as Cr7C3 and Cr2S3. The presence of these compounds can form a hard film on the surface of the steel, thereby improving the CO2 corrosion resistance of the steel. Alloying Cr with Mo can achieve a stronger corrosion resistance effect. However, too high a Cr content will significantly increase the brittle transition temperature of the steel, reduce the elongation rate, easily form coarse carbides, and lead to the deterioration of toughness. The appropriate range is 0.1 - 0.3%.

[0015] Mo: Mo improves the strength of the base material by increasing the hardenability of the steel. Mo is an element that expands the γ-phase region. It can lower the γ→α phase transformation temperature of the steel, and as the Mo content increases, the phase transformation temperature gradually decreases, which can effectively promote bainite transformation and play a role in phase transformation strengthening, resulting in a finer lath bainite structure. Mo can refine the grains of the steel. Mo can significantly increase the hardenability and hot strength of the steel, as well as prevent temper brittleness, and improve the tensile strength and toughness of the steel. When the Mo content is less than 0.3%, the corrosion resistance of the steel remains basically unchanged; when the Mo content is in the range of 0.3 - 1.0%, the corrosion resistance of the steel has a certain improvement; when the Mo content is greater than 1.0%, the corrosion resistance performance of the steel decreases. At the same time, alloying Mo with Cr can achieve a stronger corrosion resistance effect. However, too high a Mo content will increase the alloy cost and reduce its plasticity and toughness. The optimal range is 0.35 - 0.45%, where Mo / Cr: 1.2 - 4.3.

[0016] Nb: Nb is one of the important elements in low-carbon microalloyed steel. Nb can significantly increase the austenite recrystallization temperature of the steel, expand the range of the non-recrystallized zone, and can also inhibit the growth of austenite grains, with significant grain refinement strengthening and precipitation strengthening effects. Part of Nb dissolves into the solid solution, playing a solid solution strengthening role. When it dissolves into austenite, it significantly increases the hardenability of the steel. However, when it exists in the form of carbide and oxide particles, it refines the grains, increases the tempering stability of the steel, and has a secondary hardening effect. Nb can increase the yield strength and impact toughness of the steel, lower the brittle transition temperature. A small amount of Nb can increase the strength of the steel without affecting its plasticity or toughness. Excessive Nb content will increase the alloy cost and have an adverse effect on the toughness of the heat-affected zone of welding. The optimal range is 0.03 - 0.05%.

[0017] Ti: Ti is a strong nitrogen-fixing element. When about 0.015% of Ti is added, fine and high-temperature stable TiN precipitation phases can be formed during slab continuous casting. These fine TiN precipitation phases can effectively prevent the growth of austenite grains during the heating process of continuous casting billets. At the same time, it has an obvious effect on improving the toughness of the heat-affected zone during steel welding. A small amount of precipitated TiC produces a strong precipitation strengthening effect, which can ensure that the grains do not grow significantly during the subsequent normalizing heat treatment of pipe making, thus ensuring the uniformity of the steel pipe properties. However, when the Ti content is too high, the effect is not obvious, and large particle inclusions are easily formed. The optimal range is 0.01 - 0.03%.

[0018] Al: Al is a commonly used deoxidizer. Adding a small amount of Al to the steel can refine the grains, increase the strength and impact toughness of the steel, and can also improve the corrosion resistance of the steel. Especially when used in combination with elements such as Mo, Si, and Cr, the effect is better. The Al content of this invention is 0.02 - 0.05%.

[0019] Co: As a strong solid solution strengthening element, Co can form a solid solution with the iron element in the steel, enhancing the hardness and strength of the steel. It also has the effect of refining grains, increasing the strength and toughness of the steel, thereby improving the overall performance of the steel. Co can reduce the hardenability of the steel, causing the austenite isothermal transformation curve (C curve) of the steel to shift to the left. Adding it alone will reduce the comprehensive mechanical properties. Adding it together with Mo can strengthen the ferrite and improve the hardness and strength. Co can combine with the iron element in the steel to form a stable alloy phase, forming a dense oxide film on the surface of the steel, improving its corrosion resistance to CO2. However, when the Co content is too high, it will significantly reduce the hardenability of the steel, which is not beneficial to the strength of the steel. The appropriate range is 0.2 - 0.3%. Among them, Mo + Cr + Co: 0.75% - 0.92%, Si / Co: 2.8 - 3.9.

[0020] The second technical solution of the present invention is to propose a manufacturing method for a 500 MPa grade supercritical CO2 corrosion-resistant pipeline coil plate, including smelting, slab continuous casting, continuous casting billet heating, rolling, cooling, and coiling. The characteristics are as follows:

[0021] Continuous casting billet heating: The continuous casting slab is heated in a heating furnace to 1100 - 1150 °C and held for 120 - 200 min. This temperature range and holding time can fully dissolve alloys such as Mo, Cr, and Co, and at the same time are conducive to the massive precipitation of Ti, refining the austenite grain size, which is beneficial to improving the yield strength and tensile strength of the steel. During high-temperature heating, a SiO2 film will form on the surface of the casting billet, thereby protecting the steel from further oxidation and improving corrosion resistance.

[0022] Rolling: The finishing rolling end temperature is 980 - 1020 °C, which is conducive to preventing the growth of austenite grains, playing a role in refining grains and increasing strength. The rough rolling start temperature is 920 - 970 °C, and the finishing rolling end temperature is 780 - 830 °C, with a cumulative reduction ratio of 65% - 70%. This appropriate temperature range can fully refine and elongate austenite grains, avoid mixed grain phenomena, and thus ensure low-temperature impact performance and drop-weight performance; adopting a large reduction ratio can generate a large number of dislocations and twins, playing a role in dislocation strengthening, and can significantly improve the yield strength and tensile strength.

[0023] Cooling: After rolling, laminar flow water cooling is adopted, and the cooling rate is 20 - 25 °C / s. This cooling rate is conducive to obtaining a uniform-sized acicular ferrite structure, thereby making it have good low-temperature toughness.

[0024] Coiling: After cooling, coiling is carried out, and the coiling temperature is 500 - 550 °C. This temperature range combined with a specific cooling rate is conducive to obtaining a uniform-sized acicular ferrite structure and controlling the M-A volume fraction ratio to be less than 1%, making it have good strength, low-temperature toughness, and CO2 corrosion resistance.

[0025] Furthermore, after the molten steel is smelted, secondary refining is carried out. RH furnace is used for secondary refining to control the H and O contents, and LF furnace is used for mild desulfurization treatment and calcium treatment to control the inclusion morphology and improve the ductility, toughness, and cold bending performance of the steel.

[0026] Furthermore, the thickness of the continuous casting slab is 170 - 200 mm, and electromagnetic stirring or dynamic soft reduction is applied during the continuous casting process to reduce the center segregation of the continuous casting billet.

[0027] Preferably, the final structure of the coil plate is a mixed structure of acicular ferrite and a small amount of M-A, and the M-A volume fraction ratio is less than 1%.

[0028] The 500 MPa grade supercritical CO2 corrosion-resistant pipeline coil plate produced by applying the above chemical composition and process has excellent comprehensive performance. The final mechanical properties of the coil plate are: transverse R t0.5≥540 MPa, transverse R m ≥640 MPa, transverse R t0.5 / R m ≤0.87, transverse A 50mm ≥36%, transverse -40°C impact energy KV8≥220 J, transverse -20°C drop weight tear test DWTT≥95%; longitudinal R t0.5 ≥520 MPa, longitudinal R m ≥630 MPa, longitudinal R t0.5 / R m ≤0.86, longitudinal A 50mm ≥38%; average corrosion rate in 14.5 MPa supercritical CO2 environment <0.05 mm / a.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) Adopting a low C medium Mn alloy design containing Mo, Cr, and Co can ensure the low-temperature toughness of the weld and fully refine the grains at the same time;

[0031] (2) Mixing and adding an appropriate amount of Si element and Co element. Both of them have the ability to resist CO2 corrosion and can form complex Si and Co compounds such as SiCo3. This kind of compound also has better corrosion resistance and oxidation resistance. At the same time, Si can also reduce the anisotropy of the transverse and longitudinal properties of the steel plate;

[0032] (3) Alloying with Mo and Cr elements can significantly improve the CO2 corrosion resistance;

[0033] (4) An appropriate amount of Co element can form a stable alloy phase with the Fe element in the steel, forming a dense oxide film on the surface of the steel, thereby improving the CO2 corrosion resistance and making the steel have higher safety in pipeline engineering applications. Detailed implementation manners

[0034] In order to make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. The following description of an exemplary embodiment of the experimental device and method is actually only illustrative and shall in no way be construed as a limitation to the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0035] The following embodiments are only some of the optimal implementation schemes of the present invention and do not impose any restrictions on the scope of the aforementioned invention and technical means. Among them, Table 1 shows the chemical compositions of Examples 1 to 8, Table 2 shows the process parameters of heating, rolling, cooling and coiling for each example, and Table 3 shows the mechanical property test results and tissue ratios of each example.

[0036] Table 1 Chemical Compositions of the Steels in Examples (wt, %)

[0037] Example C Si Mn P S Ti Cr Mo Nb Al Co N Mo / Cr Mo+Cr+Co Si / Co 1 0.08 0.8 1.55 0.008 0.002 0.02 0.25 0.35 0.04 0.04 0.24 0.004 1.4 0.84 3.33 2 0.05 0.9 1.50 0.010 0.001 0.03 0.10 0.42 0.04 0.03 0.30 0.005 4.20 0.82 3.00 3 0.09 0.7 1.65 0.007 0.001 0.01 0.22 0.45 0.03 0.02 0.22 0.004 2.0 0.89 3.18 4 0.07 0.9 1.68 0.006 0.002 0.03 0.18 0.36 0.04 0.04 0.28 0.006 2.0 0.82 3.21 5 0.06 0.8 1.53 0.008 0.001 0.02 0.15 0.41 0.03 0.05 0.21 0.005 2.7 0.77 3.81 6 0.05 0.9 1.61 0.007 0.002 0.01 0.25 0.38 0.04 0.02 0.27 0.004 1.5 0.9 3.33 7 0.07 0.7 1.58 0.005 0.001 0.03 0.29 0.37 0.04 0.03 0.25 0.002 1.28 0.91 2.80 8 0.08 0.8 1.59 0.008 0.001 0.02 0.12 0.40 0.03 0.03 0.26 0.006 3.3 0.78 3.08

[0038] Table 2 Process Parameters of Heating, Rolling, Cooling and Coiling for the Steels in Each Example

[0039]

[0040] Table 3 Main Mechanical Properties of the Steels in Each Example

[0041]

Claims

1. A 500MPa grade supercritical CO2 corrosion-resistant pipeline coil plate, characterized in that, The chemical composition content of the steel plate is as follows: C: 0.05% - 0.10%, Si: 0.6% - 0.9%, Mn: 1.50% - 1.70%, P: ≤0.010%, S: ≤0.002%, Cr: 0.10% - 0.30%, Mo: 0.35% - 0.45%, Nb: 0.03% - 0.05%, Ti: 0.01% - 0.03%, Al: 0.02% - 0.05%, Co: 0.20% - 0.30%, N: ≤0.008%. Among them, Mo / Cr: 1.2 - 4.3, Mo + Cr + Co: 0.75% - 0.92%, Si / Co: 2.8 - 3.9, and the rest are Fe and inevitable elements.

2. The 500 MPa grade supercritical CO2 corrosion-resistant pipeline coil plate according to claim 1, wherein The final structure of the coiled plate is acicular ferrite and a small amount of M - A mixed structure, and the volume fraction ratio of M - A is less than 1%.

3. The 500 MPa grade supercritical CO2 corrosion-resistant pipeline coil plate according to claim 1, characterized in that the coil Transverse R of the plate t0.5 ≥540 MPa, transverse R m ≥640 MPa, transverse R t0.5 / R m ≤0.87, transverse A 50mm ≥36%, transverse impact energy KV8 at -40°C ≥ 220 J, transverse drop weight tear test DWTT at -20°C ≥ 95%; longitudinal R t0.5 ≥520 MPa, longitudinal R m ≥630 MPa, longitudinal R t0.5 / R m ≤0.86, longitudinal A 50mm ≥38%.

4. The 500 MPa grade supercritical CO2 corrosion-resistant pipeline coil plate according to claim 1, characterized in that, The average corrosion rate in the 14.5MPa supercritical CO2 environment is <0.05mm / a.

5. A manufacturing method of a 500MPa - grade supercritical CO2 - corrosion - resistant pipeline coiled plate according to any one of claims 1 to 4, including smelting, slab continuous casting, continuous casting billet heating, rolling, cooling, and coiling, characterized in that Continuous casting billet heating: The continuous casting slab is heated in a heating furnace to 1100 - 1150°C and kept warm for 120 - 200min; Rolling: The finishing rolling temperature of rough rolling is 980 - 1020°C, the starting rolling temperature of finish rolling is 920 - 970°C, the finishing rolling temperature is 780 - 830°C, and the cumulative reduction ratio is 65% - 70%; Cooling: After rolling, laminar flow water cooling is adopted, and the cooling rate is 20 - 25°C / s; Coiling: The coiling temperature is 500 - 550°C.

6. The manufacturing method of the 500MPa-class supercritical CO2 corrosion-resistant pipeline coil plate according to claim 5, characterized in that, The thickness of the continuous casting slab is 170 - 200mm, and electromagnetic stirring or dynamic soft reduction is applied during the continuous casting process.

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