Steel for 360MPa-grade hydrogen-doped conveying pipeline and production method thereof

Abstract

The invention relates to the technical field of production of steel for pipelines, in particular to steel for 360MPa-grade hydrogen-doped conveying pipelines and a production method of the steel. The steel plate comprises the following chemical components in percentage by weight: 0.051%-0.059% of C, 0.10%-0.20% of Si, 0.70%-0.80% of Mn, 0.016%-0.026% of Nb, 0.013%-0.019% of Ti, 0.10%-0.16% of Cr, 0.12%-0.18% of Mo, less than or equal to 0.012% of P, less than or equal to 0.0015% of S, less than or equal to 0.0040% of N and the balance of Fe and impurities. A low-carbon, low-manganese and low-silicon component design is adopted, a pure steel smelting technology is combined, Nb and Ti are comprehensively utilized for microalloying, Mo is added to improve the volume fraction of a precipitated phase, Cr is added to improve the structure uniformity in the thickness direction, and the finished steel plate is good in performance in a hydrogen environment.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline steel production, and in particular to 360MPa-grade hydrogen-doped steel for a transmission pipeline and a production method thereof. Background Art

[0002] As a globally recognized clean energy source, hydrogen represents the direction of global energy restructuring, and its development is bound to accelerate. Pipeline transportation is one of the primary methods of hydrogen transportation and is the most economical and efficient method for long-distance transport. Data shows that over a distance of 500 km, the cost of transporting hydrogen is only 3 to 3.1 yuan per kilogram. Against this backdrop, the research and development of hydrogen pipelines holds great market potential.

[0003] The development and utilization of hydrogen energy in China is relatively late. Currently, the total mileage of hydrogen pipelines in my country is approximately 400 km, primarily distributed around the Bohai Bay and the Yangtze River Delta. The scale of long-distance hydrogen pipelines is relatively small, with only three hydrogen pipelines several dozen kilometers long and two coal-to-gas and hydrogen mixed pipelines over a hundred kilometers long. During the service life of hydrogen pipelines, preventing "hydrogen damage" is a key issue in the development of steel for these pipelines. Existing hydrogen pipeline production technologies primarily focus on medium and heavy plate production, and typically require a "quenching and tempering" conditioning treatment after rolling.

[0004] Chinese patent application number 202310743976.7 discloses a "Method for Producing TMCP Hydrogen-Doped Pipeline Steel." The steel's composition, by weight, is as follows: C = 0.03% to 0.05%, Si = 0.12% to 0.30%, Mn = 0.95% to 1.05%, P ≤ 0.004%, S ≤ 0.0010%, Alt = 0.020% to 0.045%, Nb = 0.040% to 0.050%, Ti = 0.010% to 0.020%, with the balance being Fe and unavoidable impurities. This steel relates to the medium and thick plate industry. While post-rolling heat treatment is not required, the extremely low P content significantly increases steelmaking costs. The steel is therefore only suitable for the production of steel for low-pressure, low-hydrogen-doping ratio hydrogen pipelines.

[0005] Chinese patent application number 202111089004.8 discloses a "Method for Producing L360QS Hydrogen Pipeline Steel." The steel's composition, by weight, includes C = 0.07% to 0.10%, Si = 0.20% to 0.30%, M = 0.80% to 0.90%, P ≤ 0.008%, S ≤ 0.0015%, Alt = 0.025% to 0.035%, Nb = 0.010% to 0.020%, Ti = 0.015% to 0.020%, Cr = 0.10% to 0.15%, B ≤ 0.0005%, and Pcm = 0.16% to 0.19%, with the remainder being Fe and unavoidable impurities. This steel belongs to the medium and thick plate sector and requires heat treatment after rolling, resulting in a complex production process. Furthermore, its high C and Si contents are detrimental to the steel's service performance in hydrogen environments.

[0006] Chinese patent application number 202210304498.5 discloses "L245S hydrogen-doped pipeline steel and its production method." The steel's composition, by weight, includes C (0.03% to 0.05%), Si (0.20% to 0.28%), Mn (0.70% to 1.0%), P (≤0.010%), S (≤0.0015%), Alt (0.020% to 0.040%), Nb (0.020% to 0.030%), Ca (≤0.006%), B (≤0.0005%), and Pcm (0.08% to 0.12%). This steel belongs to the medium and thick plate category and requires tempering heat treatment after rolling. This medium-temperature tempering provides excellent resistance to hydrogen embrittlement.

[0007] Chinese patent application number 202310486944.3 discloses "Steel for Hydrogen-Doped Natural Gas Pipelines and Its Preparation Method." The steel's composition, by weight, includes C = 0.02% to 0.05%, Si = 0.20% to 0.30%, Mn = 0.80% to 1.0%, P ≤ 0.008%, S ≤ 0.0020%, Nb = 0.030% to 0.050%, Ti = 0.015% to 0.020%, and Cr = 0.010% to 0.015%. This steel belongs to the medium and thick plate category and requires heat treatment after rolling. Its extremely low P content significantly increases steelmaking costs. Furthermore, it is only suitable for the production of steel for low-pressure, low-hydrogen doping ratio hydrogen transmission pipelines.

[0008] Chinese patent application number 202211036380.5 discloses "An acid-resistant and hydrogen-resistant X70 pipeline steel and its preparation method". The components of the steel include C: 0.02~0.05wt%, Si: 0.15~0.38wt%, Mn: 1.2~1.4wt%, P≤0.005wt%, S≤0.005wt%, Ca: 0.004~0.008wt%, Al: 0.004~0.006wt%, Cr: 0.25~0.50wt%, Ti: 0.008~0.016wt%, Nb: 0.005~0.08wt%, Mg: 0.002~0.004wt%, among which the mass addition ratio of Mg, Ti and Ca elements is 1:(3.8~4.2), (1.8~2.2). It achieves excellent hydrogen embrittlement resistance by adding Mg, Ti and Ca and taking a series of measures in the refining stage to reduce the dissolved oxygen in the molten steel and promote the spheroidization of inclusions. It also belongs to the field of medium and thick plates, and only HIC tests are performed after rolling.

[0009] Chinese patent application number 202211172545.1 discloses an "economical hydrogen pipeline steel and production method." The steel's composition, by weight, includes C: 0.03-0.08%, Si: ≤0.15%, Mn: 0.53-1.19%, P: ≤0.012%, S: ≤0.0015%, Ti: 0.010-0.080%, Al: 0.025-0.048%, N: ≤0.0045%, O: ≤0.002%, Cr ≤0.30%, Mo ≤0.20%, Nb ≤0.04%, or a combination of two or more thereof. This application, filed in the hot-rolled coil (HCR) field, covers a wide range of alloy compositions. The rationale for the addition of Nb, Cr, and Mo is rather vague, and the hydrogen environment test conditions are not described. Further verification of hydrogen resistance is needed.

[0010] As can be seen from the above-mentioned public documents, the currently disclosed production methods for hydrogen pipeline steel, with the exception of the aforementioned "an economical hydrogen pipeline steel and production method," are all in the medium and thick plate field. Hydrogen pipeline steel in the medium and thick plate field generally requires heat treatment after rolling. Furthermore, the hydrogen experimental environment for hydrogen pipeline steel is all low-pressure and low-hydrogen doping ratio, with the delivery pressure below 10 MPa and the hydrogen doping ratio within 10%. Furthermore, the production methods for hydrogen pipeline steel also suffer from complex processes and numerous control parameters. Since hydrogen pipelines at home and abroad generally operate at low pressures and have thin wall thicknesses, production in the medium and thick plate field is far less competitive than in the hot-rolled coil field. Therefore, it is necessary to develop a production method for hot-rolled coils of hydrogen pipeline steel that has a simple process and can safely serve in high-pressure, high-hydrogen doping ratio hydrogen environments. Summary of the Invention

[0011] The present invention provides a 360MPa-grade hydrogen-doped steel for a pipeline and a production method thereof. The steel adopts a low-carbon, low-manganese, and low-silicon composition design, combines pure steel smelting technology, comprehensively utilizes Nb and Ti microalloying, adds Mo to increase the volume fraction of the precipitated phase, and adds Cr to improve the uniformity of the structure in the thickness direction. The finished steel plate exhibits good performance in a hydrogen environment with an operating pressure of 12MPa and a hydrogen doping ratio of ≤30% (hydrogen partial pressure ≤3.6MPa).

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

[0013] A 360MPa-grade steel for hydrogen-doped transmission pipelines, wherein the chemical composition of the steel plate is, by weight percentage, C: 0.051%-0.059%, Si: 0.10%-0.20%, Mn: 0.70%-0.80%, Nb: 0.016%-0.026%, Ti: 0.013%-0.019%, Cr: 0.10%-0.16%, Mo: 0.12%-0.18%, P≤0.012%, S≤0.0015%, N≤0.0040%, and the remainder is Fe and unavoidable impurities.

[0014] The metallographic structure of the finished steel plate is ferrite + a small amount of pearlite, and by volume percentage, the proportion of ferrite is 96.8% to 97.4%, and the proportion of pearlite is 2.6% to 3.2%.

[0015] The mechanical properties of the finished steel plate are: yield strength ≥ 252MPa, tensile strength ≥ 364MPa, average value of drop weight shear area SA at -40℃ ≥ 95%, average value of impact energy at -40℃ ≥ 293J; the sour service performance is: in the hydrogen-induced cracking test according to NACE TM0284 standard, in solution A, the HIC resistance performance indicators CLR, CTR, and CSR are all 0; in the hydrogen sulfide stress corrosion test according to NACE TM0177 standard, the SSCC specimen did not break when the loading force was 0.9 times the actual yield strength; the hydrogen resistance performance is: in a hydrogen environment with an operating pressure of ≤ 12MPa, a hydrogen doping ratio of ≤ 30%, and a hydrogen partial pressure of ≤ 3.6MPa, the elongation degradation rate is 8.3% to 9.6%.

[0016] A method for producing 360MPa-grade hydrogen-doped steel for transmission pipelines includes molten iron pretreatment, molten steel smelting, off-furnace refining, LF furnace refining, slab continuous casting, continuous cast slab heating, rolling, cooling, and coiling. The slab continuous casting utilizes electromagnetic stirring or dynamic soft reduction technology to ensure that the slab centerline segregation reaches level 0 or 1 according to ISO 4968. The rolling and cooling processes utilize a two-stage controlled rolling and controlled cooling technology, as follows:

[0017] The continuous casting slab is heated to 1160~1169℃, and the rough rolling and finishing rolling temperature is 1000~1005℃. The rough rolling is carried out for at least 5 passes, of which the first pass reduction rate is 20.4%~21.8%, and the total rough rolling reduction rate is 72.9%~74.1%. The intermediate billet is heated to below 970℃ and then enters the finishing rolling. The finishing rolling temperature is 830~840℃, and the cumulative finishing rolling reduction rate is 68.2%~69.6%. After rolling, it is cooled to 538~547℃ at a rate of 16.1~16.8℃ / s and coiled.

[0018] The thickness of the continuous casting slab is 160-180 mm, the thickness of the intermediate slab is 44-46 mm, and the thickness of the finished steel plate is 13-16 mm.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1) The low C and low Mn design provides a basis for the finished product to obtain excellent comprehensive performance;

[0021] 2) Cr is used to improve hardenability and achieve good uniformity of structure in the thickness direction, thus avoiding excessive stress that causes hydrogen accumulation inside the steel and improving hydrogen resistance.

[0022] 3) The addition of Mo and Nb together forms (NbMo)4C3, which has a higher precipitate phase volume fraction than pure NbC, more hydrogen absorption traps, and effectively improves hydrogen resistance;

[0023] 4) The finished product is a hot-rolled coil, which does not require heat treatment after rolling. The production process is simple and the production efficiency is high. DETAILED DESCRIPTION

[0024] The 360MPa-grade steel for hydrogen-doped transmission pipelines disclosed herein has the following chemical compositions by weight: C: 0.051%-0.059%, Si: 0.10%-0.20%, Mn: 0.70%-0.80%, Nb: 0.016%-0.026%, Ti: 0.013%-0.019%, Cr: 0.10%-0.16%, Mo: 0.12%-0.18%, P≤0.012%, S≤0.0015%, N≤0.0040%, and the remainder being Fe and unavoidable impurities.

[0025] Compared to conventional steel for hydrogen-doped pipelines, this steel adopts a low-C, low-Mn, and low-Si composition design. It utilizes the Nb-Ti microalloying mechanism to form fine, dispersed carbonitrides that act as hydrogen traps. The addition of Cr improves structural uniformity through the thickness, and Mo further enhances the effect of Nb. Combined with a suitable rolling process, the resulting structure is a "ferrite + small amount of pearlite" structure, with the volume percentage of pearlite being 2.6% to 3.2%, ensuring the finished product possesses an appropriate balance of strength and toughness and excellent hydrogen resistance. The reasons for the selection of the main elements in the steel are as follows:

[0026] C: Carbon is the most effective element for strengthening steel. As the C content increases, the yield strength and tensile strength of the steel both show an upward trend, but the plasticity, toughness and weldability of the steel will be significantly reduced. In addition, the reduction of the C content will also inhibit the formation of pearlite in the structure, thereby improving the hydrogen resistance. Therefore, the present invention controls the C content to 0.051% to 0.059%.

[0027] Si: Silicon is generally introduced during the steelmaking process as a reducing agent and deoxidizer. In addition, Si can also be dissolved in ferrite and austenite to play a strengthening role, thereby increasing the strength of the steel, but at the same time it also causes a loss of plasticity and toughness. Therefore, the present invention adopts a low Si design and controls the Si content to 0.10% to 0.20%.

[0028] Mn: Manganese is a strengthening element in steel second only to C. It has a solid solution strengthening effect and can improve the hardenability of steel. In addition, on the one hand, Mn easily forms MnS with S, which deforms along the rolling direction. On the other hand, Mn easily forms segregated banded structure with P, both of which split the matrix and seriously reduce the toughness and hydrogen resistance of the material. Therefore, the present invention adopts a low Mn design, controlling the manganese content to 0.70% to 0.80%.

[0029] P, S, and N: All three are inevitable impurity elements in steel. As harmful elements in steel used for hydrogen pipelines, their contents should be as low as possible. However, too low a requirement will increase production costs. In the present invention, the effect of Ti modifying MnS is utilized, and the Ti content is adjusted according to the S and N contents in the steel. On this basis, P is controlled to be ≤ 0.012%, S ≤ 0.0015%, and N ≤ 0.0040%.

[0030] Nb: Niobium is the most important element for controlled rolling in modern microalloyed pipeline steels. Its most important function is grain refinement and strengthening. In the present invention, since the carbon content is not high, only a small amount of Nb is required. Grain refinement improves strength without sacrificing toughness. Smaller grains also result in more grain boundaries, which act as traps, capturing hydrogen as it diffuses into the steel, thereby improving the material's hydrogen resistance. Therefore, the present invention controls the Nb content to 0.016% to 0.026%.

[0031] Ti: Ti plays a two-fold role in this invention. First, because Ti binds S more strongly than Mn, it can "snatch" S from MnS inclusions, forming nearly spherical Ti4C2S2. This sharp-edged Ti4C2S2 acts as a trap for incoming hydrogen and prevents stress concentration, thereby improving hydrogen resistance. Second, research has shown that when Ti = 3.4N + 3S, all MnS can be converted to Ti4C2S2. This means that adding 0.009% to 0.015% Ti can achieve this goal. However, further increasing Ti content, combined with appropriate rolling processes, can form small particles of TiC, which act as precipitation strengthening and hydrogen adsorption, thereby improving the steel's strength and hydrogen resistance. However, excessively high Ti content can form large particles of TiN and Ti(C,N), which in turn compromise toughness and hydrogen resistance. Therefore, this invention precisely controls the Ti content to 0.013% to 0.019%.

[0032] Cr: Cr can improve hardenability and increase the uniformity of the steel's structure through the thickness, thereby enhancing the material's hydrogen resistance. Furthermore, Cr contributes more to tensile strength than yield strength, which is beneficial for controlling low yield ratios, thereby improving pipeline service safety. However, Cr is an element that easily segregates. Excessive Cr content can cause structural segregation and, in turn, split the matrix. It is also prone to interacting with hydrogen to form hydrogen-induced cracking. Therefore, the present invention controls the Cr content to 0.10% to 0.16%.

[0033] Mo: Mo is a strong carbide-forming element that improves the strength of carbon steel by forming carbides. In the present invention, Mo is added together with Cr to promote the formation of M / A, thereby improving the strength. However, at the same time, it will reduce the Bauschinger effect after pipe making. When the Mo content exceeds 0.12%, it can work together with Nb to form (NbMo)4C3, which can increase the volume fraction of the precipitated phase and has a stronger hydrogen absorption capacity than simple NbC. However, if too much Mo is added, the size of the formed M / A is large, which is not conducive to toughness and hydrogen resistance. In addition, Mo is a precious metal, and excessive addition will significantly affect economic efficiency. Therefore, the Mo content is controlled within 0.12% to 0.18% in the present invention.

[0034] The production method for 360MPa-grade hydrogen-doped steel for transmission pipelines described in this invention includes molten iron pretreatment, molten steel smelting, off-furnace refining, LF furnace refining (light desulfurization and calcium treatment to control inclusion morphology and improve the steel's ductility, toughness, and cold bending properties), slab continuous casting (using electromagnetic stirring or dynamic soft reduction technology to ensure the slab's centerline segregation reaches ISO 4968 Grade 0 or Grade 1), and continuous slab heating, rolling, cooling, and coiling. A two-stage controlled rolling and cooling technology is employed, specifically as follows:

[0035] The 160-180 mm thick continuous casting slab is heated to 1160-1169°C, followed by two-stage controlled rolling and controlled cooling; the final rough rolling temperature is 1000-1005°C, with the first pass reduction rate being 20.4%-21.8% and the total rough rolling reduction rate being 72.9%-74.1%. Recrystallization occurs in each rough rolling pass, continuously refining the structure, increasing the number of grain boundaries, and thereby improving the hydrogen absorption capacity.

[0036] After rough rolling, the 44-46mm thick intermediate bar is heated to below 970°C before finishing rolling. The final finishing temperature is 830-840°C, and the cumulative reduction during finishing is 68.2%-69.6%. The lower reduction during the finishing stage is intended to reduce dislocation generation and accumulation, thus preventing hydrogen atoms interacting with dislocations from aggregating and forming hydrogen gas, which can lead to hydrogen-induced cracking. This improves the product's hydrogen damage resistance.

[0037] The rolled steel plate is cooled to 538-547°C at a rate of 16.1-16.8°C / s and then coiled. The finished product thickness is 13-16 mm.

[0038] Through the above production process, the hot-rolled coil can be guaranteed to have good strength, toughness and hydrogen resistance.

[0039] The final structure of the hot-rolled coil is "ferrite + a small amount of pearlite", with the volume percentage of ferrite being 96.8% to 97.4% and the volume percentage of pearlite being 2.6% to 3.2%.

[0040] The final mechanical properties of the hot-rolled coil are: yield strength ≥ 252MPa, tensile strength ≥ 364MPa, -40℃ drop hammer shear area SA (average) ≥ 95%, -40℃ impact energy (average) ≥ 293J.

[0041] The sour service performance of the hot-rolled coil is as follows: in the hydrogen-induced cracking test according to the NACE TM0284 standard, in solution A, the anti-HIC performance indicators CLR, CTR, and CSR are all 0; in the hydrogen sulfide stress corrosion test according to the NACE TM0177 standard, when the loading force is 0.9 times the actual yield strength, the SSCC specimen does not break.

[0042] The hydrogen resistance of hot-rolled coil is: in a hydrogen environment with an operating pressure of ≤12MPa and a hydrogen partial pressure of ≤3.6MPa (hydrogen doping ratio ≤30%), the elongation degradation rate is 8.3% to 9.6%.

[0043] In order to more intuitively embody the present invention, the embodiments of the present invention are further described in conjunction with examples. The following examples are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solution that can be obviously obtained by a person skilled in the art within the technical scope disclosed in the present invention, including simple changes or equivalent replacements, is within the scope of protection of the present invention.

[0044] [Example]

[0045] The chemical composition of the steels of Examples 1 to 10 is shown in Table 1, the heating, rolling and cooling process parameters are shown in Table 2, and the finished product properties and metallographic structure test results are shown in Table 3.

[0046] Table 1 Chemical composition of steel (wt%)

[0047]

[0048] Table 2 Heating, rolling and cooling process parameters

[0049]

[0050] Table 3 Finished product properties and metallographic structure

[0051]

[0052] As can be seen from Tables 1-3, the 360 MPa grade pipeline steel hot-rolled coil produced by the production method of the present invention has excellent strength, low-temperature toughness and hydrogen resistance, and can be used in natural gas hydrogen-blended transmission pipeline projects.

[0053] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A 360MPa grade steel for hydrogen-doped pipelines, characterized in that: The chemical composition of the steel plate by weight percentage is: C: 0.051%~0.059%, Si: 0.10%~0.20%, Mn: 0.70%~0.80%, Nb: 0.016%~0.026%, Ti: 0.013%~0.019%, Cr: 0.10%~0.16%, Mo: 0.12%~0.18%, P≤0.012%, S≤0.0015%, N≤0.0040%, and the rest is Fe and unavoidable impurities.

2. The 360MPa grade hydrogen-doped pipeline steel according to claim 1, characterized in that: The metallographic structure of the finished steel plate is ferrite + a small amount of pearlite, and by volume percentage, the proportion of ferrite is 96.8% to 97.4%, and the proportion of pearlite is 2.6% to 3.2%.

3. The 360MPa grade steel for hydrogen-doped pipelines according to claim 1, characterized in that: The mechanical properties of the finished steel plate are: yield strength ≥ 252MPa, tensile strength ≥ 364MPa, average value of drop hammer shear area SA at -40℃ ≥ 95%, average value of impact energy at -40℃ ≥ 293J; the sour service performance is: in the hydrogen-induced cracking test according to the NACE-TM0284 standard, in solution A, the HIC resistance performance indicators CLR, CTR, and CSR are all 0; in the hydrogen sulfide stress corrosion test according to the NACE-TM0177 standard, the SSCC specimen did not break when the loading force was 0.9 times the actual yield strength; the hydrogen resistance performance is: in a hydrogen environment with an operating pressure of ≤ 12MPa, a hydrogen doping ratio of ≤ 30%, and a hydrogen partial pressure of ≤ 3.6MPa, the elongation degradation rate is 8.3% to 9.6%.

4. A method for producing 360 MPa grade hydrogen-doped pipeline steel according to claim 1, 2 or 3, characterized in that: The process includes molten iron pretreatment, molten steel smelting, refining outside the furnace, LF furnace refining, slab continuous casting, continuous casting heating, rolling, cooling and coiling. Among them, slab continuous casting adopts electromagnetic stirring or dynamic soft reduction technology to ensure that the center segregation of the slab reaches level 0 or level 1 of the ISO-4968 standard. The rolling and cooling process adopts a two-stage controlled rolling and controlled cooling technology, as follows: The continuous casting slab is heated to 1160~1169℃, and the rough rolling and finishing rolling temperature is 1000~1005℃. The rough rolling is carried out for at least 5 passes, of which the first pass reduction rate is 20.4%~21.8%, and the total rough rolling reduction rate is 72.9%~74.1%. The intermediate billet is heated to below 970℃ and then enters the finishing rolling. The finishing rolling temperature is 830~840℃, and the cumulative finishing rolling reduction rate is 68.2%~69.6%. After rolling, it is cooled to 538~547℃ at a rate of 16.1~16.8℃ / s and coiled.

5. The method for producing 360MPa grade hydrogen-doped pipeline steel according to claim 4, characterized in that: The thickness of the continuous casting slab is 160-180 mm, the thickness of the intermediate slab is 44-46 mm, and the thickness of the finished steel plate is 13-16 mm.

Images