Pipeline steel plate for hydrogen embrittlement-resistant high-pressure pure hydrogen conveying pipeline and smelting method of pipeline steel plate

Abstract

The invention relates to the technical field of steel smelting, in particular to a pipeline steel plate for a hydrogen embrittlement-resistant high-pressure pure hydrogen conveying pipeline and a smelting method of the pipeline steel plate. The smelting process comprises the steps of converter smelting, CAS refining, LF refining, RH refining and continuous casting. In LF refining, oxygen is determined after molten steel arrives at a station, silicon iron is added for deoxidation, and the oxygen content of the molten steel is stabilized to be 20-80 ppm; 0.10-0.35 kg of ferrozirconium is added for each ton of steel in the LF refining process, and 0.50-0.80 kg of ferrotitanium is added for each ton of steel after heating is conducted for 5-10 min. Under the equipment condition of a conventional smelting mode, through a special deoxidation mode without adding aluminum, ferrozirconium, ferrotitanium and rare earth alloy materials are added according to a specific process, and the whole process of the smelting process is optimized, so that the purity of molten steel is improved, the morphology of inclusions is improved, absorption and diffusion of hydrogen are inhibited, and a structure refining and hydrogen trap system is stably formed; the prepared pipeline steel plate shows higher hydrogen embrittlement resistance in a high-hydrogen environment, and is particularly suitable for long-term service requirements in high-pressure, variable-load and water-containing hydrogen environments.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting technology, specifically to a pipeline steel plate for high-pressure pure hydrogen transportation pipelines resistant to hydrogen embrittlement and its smelting method. Background Technology

[0002] As the global energy structure shifts towards cleaner and lower-carbon energy sources, hydrogen energy, as a crucial component of secondary energy, is seeing its application in energy storage and transportation, industrial manufacturing, and other fields continuously expand. With the increasing pressure levels of hydrogen transmission, especially in applications such as long-distance pipelines and high-pressure storage and transportation systems at hydrogen refueling stations operating under medium- and high-pressure (≥7 MPa) pure hydrogen environments, more stringent requirements are placed on the hydrogen compatibility of pipeline steel. Pipeline steel must simultaneously possess high strength, high toughness, and excellent resistance to hydrogen embrittlement. However, in high-pressure hydrogen environments, especially when hydrogen contains moisture or when there are active defects on the steel surface, hydrogen atoms readily enter the steel's crystal lattice through adsorption, dissociation, and penetration, accumulating at grain boundaries, inclusion interfaces, dislocations, and other microstructures. The diffusion and enrichment of hydrogen in steel leads to decreased ductility, reduced strength, and increased stress corrosion sensitivity, resulting in hydrogen embrittlement. Hydrogen embrittlement not only causes delayed fracture in steel but also leads to microcrack propagation during use, accelerating brittle failure of components and posing a critical risk to the safe operation of high-pressure hydrogen transmission pipelines.

[0003] Chinese patent CN120158576A discloses a method for replacing calcium feeding wire process with rare earth treatment for aluminum deoxidized steel. It adopts aluminum deoxidation technology and improves the morphology of inclusions by replacing calcium with rare earth. However, it is easy to form large-sized inclusions such as Al2O3, CaS, and MnS in the steel. If the medium in contact with the steel contains hydrogen, it is very easy to cause hydrogen accumulation and hydrogen embrittlement, which cannot meet the requirements of high-pressure pure hydrogen transportation pipeline steel.

[0004] Chinese patent CN115679041A discloses a rapid smelting method for low-carbon, aluminum-free deoxidized, and low-sulfur steel, which adopts an aluminum-free deoxidation process and low-sulfur control technology. However, this process only controls the sulfur content to below 0.008%, which cannot meet the requirements for steel used in hydrogen transportation. Furthermore, it does not employ control technology for the composition, morphology, and properties of inclusions, making it impossible to use the steel in a hydrogen environment.

[0005] Chinese patent CN102102138A discloses a method for solving copper segregation in steel. This technology uses aluminum for deoxidation, followed by the addition of ferrosilicon and ferroniobium for further deoxidation and alloying, and finally the addition of ferrizirconium for further deoxidation. This aims to create a large number of dispersed, small-sized inclusions in the steel, hindering copper segregation. However, this patent uses aluminum for deoxidation. Because a large amount of oxygen is present in the steel when aluminum is added, large, sharp-shaped Al₂O₃ and ZrO₂ inclusions are formed. These inclusions easily create gaps between themselves and the steel matrix, leading to hydrogen embrittlement and causing the steel to fail in a hydrogen environment, thus failing to meet the requirements of high-pressure hydrogen applications.

[0006] Chinese patent CN117987615A discloses a method and product for improving the hydrogen compatibility of steel for pure hydrogen transportation pipelines. The resulting steel plate has a certain resistance to hydrogen embrittlement, but its fracture toughness in a 6.3 MPa pure hydrogen environment can only reach 60 MPa·m. 1 / 2 This makes it difficult to meet the safety margin requirements for long-term service under higher pressures. Therefore, a new smelting method is urgently needed to reduce the diffusion, penetration, and accumulation of hydrogen in steel at the source, thereby significantly improving the hydrogen embrittlement resistance of pipeline steel plates used in high-pressure pure hydrogen transportation pipelines and meeting the higher material performance requirements of high-pressure pure hydrogen transportation pipeline projects. Summary of the Invention

[0007] To address the technical problem of hydrogen embrittlement in high-pressure pure hydrogen pipelines, where hydrogen atoms can easily penetrate and permeate the steel material through adsorption and permeation, especially in the presence of moisture, this invention provides a pipeline steel plate resistant to hydrogen embrittlement for high-pressure pure hydrogen transportation pipelines and its smelting method. The specific technical solution is as follows: In a first aspect, the present invention provides a smelting method for pipeline steel plates for high-pressure pure hydrogen transportation pipelines resistant to hydrogen embrittlement. The smelting process is as follows: converter smelting → CAS refining → LF refining → RH refining → continuous casting. In the LF refining process, after the molten steel arrives at the station, the oxygen content is determined, and ferrosilicon is added for deoxidation to stabilize the oxygen content of the molten steel at 20~80ppm. During the LF refining process, 0.10~0.35kg / ton of zirconium iron is added, and after heating for 5~10min, 0.50~0.80kg / ton of ferrotitanium iron is added.

[0008] After the molten steel arrives at the LF treatment station, its oxygen content is determined and then gently deoxidized using ferrosilicon to stabilize the oxygen content in the steel within the range of 20-80 ppm. This ensures the cleanliness of the molten steel and creates a suitable activity environment for the efficient action of microalloying elements such as zirconium and titanium. Subsequently, zirconium-iron is added, allowing zirconium to preferentially combine with residual oxygen to form fine, stable oxides such as ZrO2 and ZrO. These zirconium-based oxides are dispersed and can act as nucleation sites for austenite grains, significantly refining the grain structure. Through interfacial adsorption, they form numerous primary hydrogen traps, hindering the free diffusion of hydrogen. After the molten steel has been sufficiently purified by zirconium and the oxygen activity has been further reduced, titanium-iron is added. This allows titanium to primarily react with nitrogen and carbon in the steel to form stable TiN, TiC, and Ti(C,N) precipitates. These precipitates are fine-grained and uniformly distributed, further refining the high-temperature microstructure of the steel and acting as efficient hydrogen traps, significantly improving the steel's ability to capture diffusing hydrogen, thereby inhibiting rapid hydrogen penetration and localized enrichment. By adding zirconium first and then titanium, this invention avoids the formation of coarse titanium oxide inclusions caused by traditional titanium deoxidation, thus significantly improving the effective utilization rate of titanium.

[0009] Furthermore, the molten iron entering the converter requires a silicon content ranging from 0.30% to 0.60% and a temperature range of 1370 to 1480℃. A suitable silicon content ensures sufficient oxidizing power in the early dephosphorization stage of the converter, making it easier for phosphorus, sulfur, and some oxide inclusions to be absorbed by the initial slag. This avoids insufficient slag reactivity due to excessively low silicon content, and also prevents difficulties in final oxygen control due to excessively high silicon content. A reasonable molten iron temperature reduces temperature loss during the blowing process, allowing both slag-forming processes in the double-slag method to proceed at appropriate temperatures. This significantly improves the effectiveness of dephosphorization, desulfurization, and inclusion removal in the molten steel, further enhancing the initial purity of the molten steel.

[0010] Furthermore, the converter smelting process employs a double-slag method. After the initial slag formation and smelting, the slag is discarded, followed by the addition of lime and other materials for a second slag formation. This maintains high basicity and good adsorption capacity in the slag system within the furnace, significantly reducing the content of phosphorus, sulfur, and oxide inclusions in the molten steel. The final oxygen content at the converter endpoint is no higher than 500 ppm, the endpoint temperature is 1580~1660℃, and the final phosphorus content is no higher than 0.003%. Aluminum is not used for deoxidation during the tapping stage, thus preventing the formation of large amounts of high-melting-point, sharp-angled Al2O3 inclusions from the source, providing a foundation for extremely high-purity molten steel in subsequent refining stages. At this point, the number of inclusions in the steel is small, and their morphology is relatively rounded, effectively reducing the tendency for hydrogen to accumulate at the inclusion interface.

[0011] Furthermore, a modifier is added during the CAS refining process to upgrade the steel slag. This modifier contains 90% lime and 10% fluorite, and is aluminum-free, optimizing the slag's fluidity, adsorption capacity, and basicity during refining. This method not only enhances the slag system's adsorption capacity for residual oxides and sulfide inclusions but also effectively reduces Al2O3 inclusion formation caused by secondary aluminum sources by avoiding the use of aluminum-containing modifiers. This maintains the molten steel in a low-aluminum, low-oxygen state, laying a purer foundation for controlling inclusion morphology during subsequent LF refining.

[0012] Furthermore, before leaving the LF refining station, a deep desulfurization technology employing a large slag volume, high temperature, and a high-basicity, high-fluidity slag system is used to control the sulfur content of the molten steel below 0.0010%. White slag formation and silicon-zirconium-titanium composite deoxidation technology are used to control the oxygen content below 0.0030%, without adding aluminum for deoxidation. The extremely low sulfur content avoids the formation of hard, brittle MnS or complex sulfide inclusions that easily become hydrogen aggregation interfaces, reducing hydrogen embrittlement sensitivity from the source. Simultaneously, the oxygen content is controlled within the thermodynamically stable range, which facilitates the precise participation of zirconium, titanium, and other elements in subsequent microalloying, allowing precipitates such as ZrO2, TiN, and TiC to form under more stable conditions. Low oxygen helps reduce large-size oxide inclusions, resulting in a more uniform and finer precipitation system, effectively enhancing the stability of hydrogen traps in the steel.

[0013] Furthermore, in the RH refining process, aluminum granules are added under vacuum, and the Al content is adjusted to 0.015%~0.050%. After maintaining the vacuum for 3 minutes, 0.06~0.10 kg / ton of rare earth alloy is added, without calcium treatment.

[0014] During the RH refining process, the aluminum particles added in this invention precisely control the Al content within the range of 0.015% to 0.050%. The addition of aluminum satisfies the chemical composition requirements of the steel while preventing the oxidation of other elements due to oxygen ingress during subsequent production. It also avoids the formation of large, sharp Al2O3 inclusions, minimizing the formation of strong hydrogen aggregation interfaces. Following the addition of aluminum, a small amount of rare earth alloy is added. Through the directional modification reaction between the rare earth alloy and the residual oxygen in the molten steel, as well as oxides, sulfides, and some zirconium-based inclusions, the original inclusion morphology changes from sharp or irregular peaks to rounded, smaller composite inclusions, such as Re-OS and Re-Al-O. This invention does not employ aluminum deoxidation but instead utilizes a silicon-zirconium-titanium-rare earth composite deoxidation technology. Under the influence of rare earth modification, a Re-S-Ti-Zr-Al-O composite inclusion is formed. The quantity, size, and morphology of the inclusions are significantly improved, enhancing the compatibility between the inclusions and the Fe matrix and preventing the formation of cracks and gaps between the inclusions and the matrix. Simultaneously, the reduced surface energy facilitates the floating of the inclusions into the molten steel and their absorption by the slag, thereby further improving the cleanliness of the molten steel. Compared to traditional calcium treatment, this invention does not add any calcium-containing alloys during the RH refining stage, avoiding problems such as low-melting-point CaO·Al2O3 inclusions and the easy adhesion and nodule formation of CaS. This keeps the inclusion system in the steel stable and prevents the formation of unfavorable morphologies sensitive to hydrogen embrittlement.

[0015] Furthermore, before continuous casting begins, the interior of the tundish is thoroughly cleaned using an industrial vacuum cleaner, and argon is introduced into the tundish to prevent air from entering the molten steel surface and to inhibit secondary oxidation. This measure effectively reduces the risk of inclusion regeneration, secondary metal oxide scale entering the molten steel, and the adsorption of aluminum oxide film into the steel stream, ensuring high purity of the molten steel before entering the crystallizer. Argon protection also creates an inert atmosphere, reducing the contact interface between the steel stream and air, thereby further inhibiting the secondary absorption of hydrogen and nitrogen into the steel.

[0016] Furthermore, the surface fluctuation of the crystallizer during continuous casting is controlled within 3 mm, and the slag layer thickness is 20-30 mm, ensuring stable and good heat flow and lubrication conditions within the crystallizer. With minimal surface fluctuation, excessive crystallizer slag or oxides are not entrained in the molten steel, allowing for more sufficient time for inclusions to rise, thus significantly reducing macroscopic and microscopic inclusion defects. In addition, a moderate slag layer thickness maintains uniform heat insulation and lubrication, improves the uniformity of the solidified shell, and reduces the probability of segregation and defects.

[0017] Furthermore, during the continuous casting stage, the oxygen content of the molten steel is controlled to be ≤20ppm and the nitrogen content to be ≤30ppm. This ensures that no secondary oxidation or nitrogen increase occurs during the solidification process, avoids the formation of large-sized oxides and brittle nitride inclusions, improves the density and purity of the solidified structure, and further enhances the steel plate's resistance to hydrogen permeation.

[0018] Furthermore, the thickness of the slab obtained from continuous casting is 150-300 mm, and the thickness of the rolled steel plate is 6-25 mm. A thicker slab allows for a more uniform and slower solidification process, significantly reducing defects such as central segregation and inclusion aggregation, and improving the uniformity of the microstructure during subsequent rolling. After matching the final rolling temperature and reduction, a fine and uniform ferrite / bainite microstructure is obtained, allowing trace amounts of TiN, TiC, and ZrO2 precipitates to be evenly distributed at grain boundaries and within grains, forming a more continuous and stable hydrogen diffusion barrier system. Through the reasonable matching of slab and steel plate thicknesses, this invention ensures that precipitation strengthening, grain refinement, and hydrogen diffusion inhibition mechanisms are fully manifested in the final product.

[0019] Secondly, the present invention also provides a pipeline steel plate for high-pressure pure hydrogen transportation pipelines that is resistant to hydrogen embrittlement, prepared using the above-mentioned smelting method.

[0020] Furthermore, the pipeline steel plate for high-pressure pure hydrogen transportation pipelines resistant to hydrogen embrittlement comprises the following components by weight percentage: C 0.030~0.055%, Si 0.15~0.30%, Mn 0.90~1.20%, P≤0.0050%, S≤0.0015%, Nb 0.030~0.050%, V 0.020%~0.035%, Ti 0.008~0.020%, Cr 0.15~0.25%, with the balance being Fe and other unavoidable impurities.

[0021] The beneficial effects of this invention are as follows: 1. The present invention provides a pipeline steel plate for high-pressure pure hydrogen transportation pipelines resistant to hydrogen embrittlement and its smelting method. Under conventional smelting equipment conditions, a special deoxidation method without adding aluminum is used, and zirconium iron, titanium iron, and rare earth alloy materials are added according to a specific process. This forms a fine and uniform metallographic structure inside the steel plate, mainly composed of acicular ferrite (AF) and a small amount of polygonal ferrite (PF). This significantly extends the diffusion path of hydrogen in the steel, significantly reduces the diffusion rate, and increases the difficulty of local hydrogen enrichment, thereby effectively inhibiting the initiation and propagation of hydrogen-induced cracks.

[0022] 2. This invention, through meticulous optimization of the entire process, including molten iron composition and temperature, CAS slag modification method, LF refining desulfurization and deoxidation depth, continuous casting process cleanliness control, and matching of billet and steel plate thickness, can further improve the purity of molten steel, improve the morphology of inclusions, inhibit hydrogen absorption and diffusion, and stably form a synergistic structure of microstructure refinement and multi-scale hydrogen traps. This enables the high-pressure pure hydrogen transmission pipeline steel plate to exhibit higher resistance to hydrogen embrittlement in a high-hydrogen-activity environment, making it particularly suitable for the long-term service requirements of high-pressure pure hydrogen transmission pipelines under high pressure, variable load, and water-containing hydrogen environments.

[0023] 3. The pipeline steel plate for high-pressure pure hydrogen transportation pipelines resistant to hydrogen embrittlement provided by this invention was subjected to slow tensile tests in pure hydrogen and pure nitrogen environments, respectively. The hydrogen and nitrogen pressures were 7.2 MPa, the volume of the pure hydrogen and pure nitrogen test chambers was ≥250,000 mL, and the slow tensile rate was ≤2.5 × 10⁻⁶. -5 / s, the test results show that the reduction of area loss in the hydrogen environment is ≤22%, the elongation loss is ≤12%, and the strength loss is ≤0.5% compared to the nitrogen environment; the fracture toughness K1C in the hydrogen environment is ≥80MPa·m 1 / 2 In the fatigue crack propagation test under pure hydrogen environment, the pure hydrogen pressure was 7.2 MPa, the pre-crack length of the standard CT specimen was 1 mm, and the predicted fatigue life was ≥10,000 cycles. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a metallographic diagram of the pipeline steel plate for high-pressure pure hydrogen transportation pipeline prepared in Example 1 of this application.

[0026] Figure 2 This is a metallographic diagram of the pipeline steel plate for high-pressure pure hydrogen transportation pipeline prepared in Example 2 of this application.

[0027] Figure 3 This is a metallographic diagram of the pipeline steel plate for high-pressure pure hydrogen transportation pipeline prepared in Example 3 of this application. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0029] Example 1 A pipeline steel plate for high-pressure pure hydrogen transportation pipelines with a thickness of 14.3 mm comprises, by weight percentage: C 0.037%, Si 0.18%, Mn 0.9%, P 0.0043%, S 0.0009%, Nb 0.045%, V 0.03%, Ti 0.012%, Cr 0.22%, with the balance being Fe and other unavoidable impurities.

[0030] The production method of this steel plate includes smelting and rolling processes. The smelting process is as follows: converter smelting → CAS refining → LF refining → RH refining → continuous casting. The following methods are used in each process: (1) Converter smelting: The silicon content of the molten iron entering the converter is 0.39%, and the temperature is 1408℃. The converter smelting process adopts the double slag method. After the first slag smelting, the slag is poured off, and then lime and other materials are added for the second slag smelting. The oxygen content at the converter endpoint is 427ppm, the endpoint temperature is 1597℃, and the endpoint phosphorus content is 0.0020%. During the tapping process, 2.2kg / ton of ferrosilicon is added for deoxidation. After deoxidation, the oxygen content is 38ppm. No aluminum is added for deoxidation.

[0031] (2) CAS refining: steel slag is modified by adding a modifier. The modifier contains 90% lime and 10% fluorite, but does not contain aluminum.

[0032] (3) LF refining: After the molten steel arrives at the station, the oxygen content is determined to be 37 ppm. 0.22 kg / ton of ferrozirconium is added, and after heating for 7 minutes, 0.66 kg / ton of Ti30 ferrotitanium is added. Then, according to the target composition of the steel grade, the corresponding alloys are added to adjust the composition. Before leaving the station, the sulfur content of the molten steel is 0.0007%, and the oxygen content is 0.0019%.

[0033] (4) RH refining: Add aluminum granules at the target value of Als 0.015%~0.050% under RH vacuum, and after maintaining vacuum for 3 minutes, add 0.068 kg / ton of rare earth alloy containing 85% cerium; after the RH degassing treatment is completed, no calcium treatment is performed.

[0034] (5) Continuous casting: Before casting, the interior of the tundish is cleaned with an industrial vacuum cleaner and argon is filled into the tundish; during the continuous casting process, the fluctuation of the crystallizer page is controlled within 3mm, the thickness of the slag layer in the crystallizer is controlled at 20~30mm, the oxygen content of the molten steel is 17ppm, and the nitrogen content is 25ppm.

[0035] The slab thickness obtained from continuous casting is 150mm. After rolling (final rolling temperature 861℃, initial cooling 785℃, final cooling 520℃, cooling rate 8℃ / s), a pipeline steel plate with a thickness of 14.3mm for high-pressure pure hydrogen transportation pipelines is obtained.

[0036] Example 2 A pipeline steel plate for high-pressure pure hydrogen transportation pipelines with a thickness of 17.5 mm comprises, by weight percentage: C 0.042%, Si 0.18%, Mn 1.02%, P 0.0041%, S 0.0010%, Nb 0.037%, V 0.025%, Ti 0.013%, Cr 0.18%, with the balance being Fe and other unavoidable impurities.

[0037] The production method of this steel plate includes smelting and rolling processes. The smelting process is as follows: converter smelting → CAS refining → LF refining → RH refining → continuous casting. The following methods are used in each process: (1) Converter smelting: The silicon content of the molten iron entering the converter is 0.55%, and the temperature is 1441℃. The converter smelting process adopts the double slag method. After the first slag smelting, the slag is poured off, and then lime and other materials are added for the second slag smelting. The oxygen content at the converter endpoint is 409ppm, the endpoint temperature is 1620℃, and the endpoint phosphorus content is 0.0027%. During the tapping process, 2.4kg / ton of ferrosilicon is added for deoxidation. After deoxidation, the oxygen content is 32ppm. No aluminum is added for deoxidation.

[0038] (2) CAS refining: steel slag is modified by adding a modifier. The modifier contains 90% lime and 10% fluorite, but does not contain aluminum.

[0039] (3) LF refining: After the molten steel arrives at the station, the oxygen content is determined to be 51 ppm. 0.20 kg / ton of ferrozirconium is added, and after heating for 10 min, 0.70 kg / ton of Ti30 ferrotitanium is added. Then, according to the target composition requirements of the steel grade, the corresponding alloys are added to adjust the composition. Before leaving the station, the sulfur content of the molten steel is 0.0008%, and the oxygen content is 0.0024%.

[0040] (4) RH refining: Add aluminum granules at the target value of Als 0.015%~0.050% under RH vacuum, and after maintaining vacuum for 3 minutes, add 0.070 kg / ton of rare earth alloy containing 85% cerium; after the RH degassing treatment is completed, no calcium treatment is performed.

[0041] (5) Continuous casting: Before casting, the interior of the tundish is cleaned with an industrial vacuum cleaner and argon is filled into the tundish; during the continuous casting process, the fluctuation of the crystallizer page is controlled within 3mm, the thickness of the slag layer in the crystallizer is controlled at 20~30mm, the oxygen content of the molten steel is 19ppm, and the nitrogen content is 28ppm.

[0042] The billet obtained by continuous casting has a thickness of 150mm. After rolling (final rolling temperature 845℃, initial cooling 775℃, final cooling 490℃, cooling rate 9℃ / s), a pipeline steel plate with a thickness of 17.5mm for high-pressure pure hydrogen transportation pipelines is obtained.

[0043] Example 3 A pipeline steel plate for high-pressure pure hydrogen transportation pipelines with a thickness of 19.0 mm comprises, by weight percentage: C 0.040%, Si 0.18%, Mn 1.00%, P 0.0049%, S 0.0010%, Nb 0.035%, V 0.025%, Ti 0.012%, Cr 0.18%, with the balance being Fe and other unavoidable impurities.

[0044] The production method of this steel plate includes smelting and rolling processes. The smelting process is as follows: converter smelting → CAS refining → LF refining → RH refining → continuous casting. The following methods are used in each process: (1) The silicon content of the molten iron entering the converter is 0.39%, and the temperature is 1465℃. The converter smelting process adopts the double slag method. After the first slag smelting, the slag is poured off, and then lime and other materials are added for the second slag smelting. The oxygen content at the converter endpoint is 480ppm, the endpoint temperature is 1655℃, and the endpoint phosphorus content is 0.0024%. During the tapping process, 2.2kg / ton of ferrosilicon is added for deoxidation. After deoxidation, the oxygen content is 87ppm. No aluminum is added for deoxidation.

[0045] (2) CAS refining: steel slag is modified by adding a modifier containing 90% lime and 10% fluorite. The modifier does not contain aluminum.

[0046] (3) LF refining: After the molten steel arrives at the station, the oxygen content is determined to be 49 ppm. 0.22 kg / ton of ferrozirconium is added, and after heating for 10 min, 0.65 kg / ton of Ti30 ferrotitanium is added. Then, according to the target composition of the steel grade, the corresponding alloys are added to adjust the composition. Before leaving the station, the sulfur content of the molten steel is 0.0009%, and the oxygen content is 0.0022%.

[0047] (4) RH refining: Add aluminum granules at the target value of Als 0.015%~0.050% under RH vacuum, and after maintaining vacuum for 3 minutes, add 0.085 kg / ton of rare earth alloy containing 85% cerium; after the RH degassing treatment is completed, no calcium treatment is performed.

[0048] (5) Before continuous casting begins, the interior of the tundish is cleaned with an industrial vacuum cleaner and argon is filled into the tundish. During continuous casting, the fluctuation of the crystallizer page is controlled within 3 mm, the thickness of the slag layer in the crystallizer is controlled within 20~30 mm, the oxygen content of the molten steel is 47 ppm, and the nitrogen content is 22 ppm.

[0049] The slab thickness obtained from continuous casting is 150mm. After rolling (final rolling temperature 848℃, initial cooling 779℃, final cooling 497℃, cooling rate 8℃ / s), a pipeline steel plate with a thickness of 19.0mm for high-pressure pure hydrogen transportation pipelines is obtained.

[0050] Test case 1. The mechanical properties of the pipeline steel plates for high-pressure pure hydrogen transportation pipelines prepared in Examples 1-3 were tested. The yield strength, tensile strength and elongation were measured using GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Test method at room temperature", and the -20℃ DWTT shear area was measured using GB / T 8363-2018 "Ferritic steel - Drop hammer tear test method". The test results are shown in Table 1.

[0051] Table 1 Mechanical properties of pipeline steel plates

[0052] 2. Hydrogen embrittlement resistance test To evaluate the hydrogen embrittlement resistance of the pipeline steel plate prepared by this invention under high-pressure pure hydrogen conditions, tests were conducted according to relevant guidelines for testing hydrogen embrittlement and hydrogen-induced cracking of metallic materials. The specific test methods are as follows.

[0053] (1) Slow tensile test (SSRT) The prepared tensile specimens were placed in gas pressure test chambers with pure hydrogen and pure nitrogen environments for slow tensile testing. The gas pressure inside the test chambers was adjusted to 7.2 MPa, and the chamber volume was not less than 250,000 mL to ensure a stable testing environment. Slow tensile loading was used, with the tensile rate controlled to ≤2.5 × 10⁻⁶. -5 s -1， The reduction of area, elongation and tensile strength of the samples were measured under the two environments respectively, and the performance loss under the hydrogen environment relative to the nitrogen environment was calculated. The results are shown in Table 2.

[0054] (2) Fracture toughness KIc test Fracture toughness tests were conducted in a pure hydrogen environment according to standard GB / T 34542.2-2018 "Hydrogen Storage and Transportation Systems - Part 2: Test Methods for Compatibility of Metallic Materials with Hydrogen Environment". The test environment pressure was set to 7.2 MPa of pure hydrogen gas. Based on the critical load, pre-crack size, and specimen geometry, the linear elastic fracture toughness KIc value under hydrogen environment was calculated, and the results are shown in Table 2.

[0055] (3) Fatigue crack propagation test According to standard GB / T 6398-2017 "Metallic Materials Fatigue Testing - Fatigue Crack Propagation Method", standard CT specimens were selected for fatigue crack propagation testing, with the pre-existing crack length set at 1 mm. The test was conducted in a 7.2 MPa pure hydrogen environment. By setting the cyclic load stress ratio and loading frequency, the specimens underwent crack propagation fatigue testing in a hydrogen environment. The number of cycles required for crack propagation to the specified length or specimen failure was recorded, and the number of cycles was used as the fatigue life evaluation index of the material. The results are shown in Table 2.

[0056] Table 2. Test results of hydrogen resistance of pipeline steel plates

[0057] 3. Microscopic tissue observation like Figure 1-3 As shown, the metallographic structure of the pipeline steel plates prepared in Examples 1-3 was observed by optical microscope. It can be seen that the structure is a uniform structure with fine needle-like ferrite (AF) as the main component and a small amount of polygonal ferrite (PF) as a composite component. There is no visible central segregation or banded structure.

[0058] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for smelting pipeline steel plates for high-pressure pure hydrogen transportation pipelines resistant to hydrogen embrittlement, characterized in that, This includes optimizing the smelting process, with the smelting process flow being converter smelting → CAS refining → LF refining → RH refining → continuous casting; in LF refining, after the molten steel arrives at the station, oxygen is determined, and ferrosilicon is added for deoxidation to stabilize the oxygen content of the molten steel at 20~80ppm; during the LF refining process, 0.10~0.35kg / ton of zirconium ferrophosphate is added, and after heating for 5~10 minutes, 0.50~0.80kg / ton of ferrotitanium ferrophosphate is added.

2. The smelting method as described in claim 1, characterized in that, The molten iron entering the converter smelting process must have a silicon content ranging from 0.30% to 0.60% and a temperature range of 1370 to 1480℃.

3. The smelting method as described in claim 1, characterized in that, The converter smelting process adopts the double slag method. After the first slag formation and smelting, the slag is dumped, and then lime and other materials are added for the second slag formation. The oxygen content at the converter endpoint is not higher than 500 ppm, the endpoint temperature is 1580~1660℃, and the endpoint phosphorus content is not higher than 0.003%. Aluminum is not used for deoxidation.

4. The smelting method as described in claim 1, characterized in that, The CAS refining process adds a modifier to the steel slag to modify it. The modifier contains 90% lime and 10% fluorite, but does not contain aluminum.

5. The smelting method as described in claim 1, characterized in that, Before leaving the LF refining station, the sulfur content of the molten steel is controlled below 0.0010%, and the oxygen content is controlled below 0.0030% by using white slag production and silicon-zirconium-titanium composite deoxidation technology.

6. The smelting method as described in claim 1, characterized in that, In RH refining, aluminum granules are added under vacuum, and the Al content is adjusted to 0.015%~0.050%. After maintaining the vacuum for 3 minutes, 0.06~0.10 kg / ton of rare earth alloy is added, and no calcium treatment is performed.

7. The smelting method as described in claim 1, characterized in that, Before continuous casting begins, an industrial vacuum cleaner is used to clean the inside of the tundish, and argon is then purged into the tundish.

8. The smelting method as described in claim 1, characterized in that, The fluctuation of the crystallizer surface during the continuous casting process is controlled within 3mm, the slag layer thickness in the crystallizer is 20~30mm, and the oxygen content and nitrogen content in the molten steel are controlled to be ≤20ppm and ≤30ppm.

9. The smelting method as described in claim 1, characterized in that, The thickness of the billet obtained by continuous casting is 150~300mm, and the thickness of the rolled steel plate is 6~25mm.

10. A pipeline steel plate for high-pressure pure hydrogen transportation pipelines resistant to hydrogen embrittlement, prepared by the smelting method described in any one of claims 1-9.

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