A 450MPa grade hydrogen-doped pipeline steel and its production method

Abstract

This invention relates to the field of pipeline steel production technology, and particularly to a 450MPa grade hydrogen-doped pipeline steel and its production method. The chemical composition of the steel 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%, Ni: 0.20%–0.30%, Mo: 0.12%–0.18%, P≤0.012%, S≤0.0015%, N≤0.0040%, with the remainder being Fe and impurities. The steel employs a low-carbon, low-manganese, and low-silicon composition design, combined with pure steel smelting technology. It comprehensively utilizes Nb and Ti microalloying, adds Mo to increase the volume fraction of precipitated phases, and adds Ni to promote dislocation cross-slip. The finished steel plate exhibits excellent performance under hydrogen-containing conditions.

Description

Technical Field

[0001] This invention relates to the field of pipeline steel production technology, and in particular to a 450MPa grade hydrogen-doped pipeline steel and its production method. Background Technology

[0002] Hydrogen, as a globally recognized clean energy source, represents the development direction of global energy structure adjustment, thus the development of hydrogen energy is bound to accelerate. Pipeline transportation is one of the main methods of hydrogen transportation and is the most economical and efficient method for long-distance transportation. Data shows that when the transportation distance is 500km, the cost of transporting hydrogen is only 3-3.1 yuan / kg. Against this backdrop, the research and development of hydrogen transportation pipelines has great market potential.

[0003] China's development and utilization of hydrogen energy started relatively late. Currently, the total length of hydrogen pipelines in my country is approximately 400 km, mainly distributed in the Bohai Bay area and the Yangtze River Delta. The scale of long-distance hydrogen pipelines is relatively small, with only three hydrogen pipelines tens of kilometers long and two coal-to-gas / hydrogen mixed transport pipelines over a hundred kilometers long. How to suppress "hydrogen degradation" during the service of hydrogen pipelines is a key issue to be addressed in the research and development of steel for these pipelines. Existing hydrogen pipeline production technologies are mostly concentrated in the medium and heavy plate sector, and post-rolling processes typically require quenching and tempering.

[0004] Chinese patent application No. 202310743976.7 discloses a "method for producing pipeline steel for TMCP hydrogen-doped hydrogen transportation". The steel composition, by weight percentage, contains: C = 0.03%–0.05%, Si = 0.12%–0.30%, Mn = 0.95%–1.05%, P ≤ 0.004%, S ≤ 0.0010%, Alt = 0.020%–0.045%, Nb = 0.040%–0.050%, Ti = 0.010%–0.020%, with the balance being Fe and unavoidable impurities. This method pertains to medium-thick plates and involves no heat treatment after rolling. However, the extremely low P content significantly increases steelmaking costs. Furthermore, it is only suitable for producing steel for low-pressure, low-hydrogen-doping hydrogen transportation pipelines.

[0005] Chinese patent application No. 202111089004.8 discloses a "production method of L360QS hydrogen pipeline steel". The steel composition, by weight percentage, contains C=0.07%–0.10%, Si=0.20%–0.30%, M=0.80%–0.90%, P≤0.008%, S≤0.0015%, Alt=0.025%–0.035%, Nb=0.010%–0.020%, Ti=0.015%–0.020%, Cr=0.10%–0.15%, B≤0.0005%, Pcm=0.16%–0.19%, with the balance being Fe and unavoidable impurities. This steel belongs to the medium-thick plate category, requiring heat treatment after rolling, making the production process complex. Furthermore, the high C and Si content is detrimental to the steel's performance in hydrogen-rich environments.

[0006] Chinese patent application No. 202210304498.5 discloses "an L245S hydrogen-doped pipeline steel and its production method." The steel composition, by weight percentage, includes C=0.03%–0.05%, Si=0.20%–0.28%, Mn=0.70%–1.0%, P≤0.010%, S≤0.0015%, Alt=0.020%–0.040%, Nb=0.020%–0.030%, Ca≤0.006%, B≤0.0005%, and Pcm=0.08%–0.12%. Belonging to the medium-thick plate category, it requires tempering heat treatment after rolling. The use of medium-temperature tempering gives the steel excellent resistance to hydrogen embrittlement.

[0007] Chinese patent application No. 202310486944.3 discloses "a type of steel for hydrogen-doped natural gas pipelines and its preparation method." The steel composition, by weight percentage, contains C=0.02%–0.05%, Si=0.20%–0.30%, Mn=0.80%–1.0%, P≤0.008%, S≤0.0020%, Nb=0.030%–0.050%, Ti=0.015%–0.020%, and Cr=0.010%–0.015%. This steel belongs to the medium-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 hydrogen pipelines.

[0008] Chinese patent application No. 202211036380.5 discloses "an acid-resistant and hydrogen-resistant X70 pipeline steel and its preparation method". The steel contains, by weight percentage, 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%, and Mg: 0.002-0.004wt%, wherein the mass ratio of Mg, Ti, and Ca is 1:(3.8-4.2):(1.8-2.2). It achieves excellent resistance to hydrogen embrittlement by adding Mg, Ti and Ca, and taking a series of measures during the refining stage to reduce dissolved oxygen in the molten steel and promote the spheroidization of inclusions. It also belongs to the medium and heavy plate field, and only HIC test was performed after rolling.

[0009] Chinese patent application No. 202211172545.1 discloses "An economical hydrogen transmission pipeline steel and its production method." The steel composition, by weight percentage, contains: 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%, or Mo ≤0.20%, or Nb ≤0.04%, or a combination of two or more of these. It belongs to the hot-rolled coil field, with an extremely wide range of alloy compositions. The rationale for adding Nb, Cr, and Mo is described rather vaguely, and the hydrogen environment test conditions are not described. Therefore, its hydrogen resistance performance requires further verification.

[0010] As can be seen from the aforementioned publicly available literature, the production methods for hydrogen pipeline steel, except for the aforementioned "An Economical Hydrogen Transmission Pipeline Steel and Production Method," are all in the medium and heavy plate sector. Hydrogen pipeline steel in the medium and heavy plate sector generally requires heat treatment after rolling. Furthermore, the hydrogen-contaminated experimental environments for hydrogen pipeline steel are all low-pressure, low-hydrogen-doping-ratio, with transmission pressures below 10 MPa and hydrogen doping ratios below 10%. In addition, the aforementioned production methods for hydrogen-doped pipeline steel also suffer from complex processes and numerous control parameters. Since hydrogen-doped pipelines generally operate at relatively low pressures and have relatively thin walls, production in the medium and heavy plate sector is far less competitive than hot-rolled steel. Therefore, there is a need to develop a simple production method for hot-rolled hydrogen-doped pipeline steel that can safely operate in high-pressure, high-hydrogen-doping-ratio hydrogen-contaminated environments. Summary of the Invention

[0011] This invention provides a 450MPa grade hydrogen-doped pipeline steel and its production method. It adopts a low-carbon, low-manganese, and low-silicon composition design, combined with pure steel smelting technology, and comprehensively utilizes Nb and Ti microalloying, adds Mo to increase the volume fraction of precipitated phases, and adds Ni to promote dislocation cross-slip. The finished steel plate exhibits good performance in a hydrogen-exposed environment with an operating pressure of 12MPa and a hydrogen doping ratio of ≤30% (hydrogen partial pressure ≤3.6MPa).

[0012] To achieve the above objectives, the present invention employs the following technical solution:

[0013] A 450MPa grade hydrogen-doped pipeline steel has the following chemical composition 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%, Ni: 0.20%–0.30%, Mo: 0.12%–0.18%, P≤0.012%, S≤0.0015%, N≤0.0040%, with the remainder being Fe and unavoidable impurities.

[0014] The metallographic structure of the finished steel plate is acicular ferrite + M / A structure, and by volume percentage, the acicular ferrite structure accounts for 97.0% to 97.6%, and the M / A structure accounts for 2.4% to 3.0%.

[0015] The mechanical properties of the finished steel plate are as follows: yield strength ≥ 456 MPa, tensile strength ≥ 546 MPa, average drop shear area (SA) at -40℃ ≥ 96%, and average impact energy at -40℃ ≥ 320 J. Acid service performance is as follows: according to NACE TM0284 standard, hydrogen-induced cracking tests were conducted in solution A, and the resistance to HIC (hydrogen sulfide) indicators CLR, CTR, and CSR were all 0. According to NACE TM0177 standard, hydrogen sulfide stress corrosion tests were conducted, and the SSCC (sulfurized steel plate) specimen did not break when the loading force was 0.9 times the actual yield strength. Hydrogen resistance is as follows: in a hydrogen-exposed environment with operating pressure ≤ 12 MPa, hydrogen doping ratio ≤ 30%, and hydrogen partial pressure ≤ 3.6 MPa, the elongation degradation rate is 12.0%–13.7%.

[0016] A method for producing 450MPa grade hydrogen-doped steel for pipelines includes hot metal pretreatment, steelmaking, ladle refining, LF furnace refining, slab continuous casting, slab heating, rolling, cooling, and coiling processes. The slab continuous casting employs electromagnetic stirring or dynamic light reduction technology to ensure that the slab center segregation meets ISO 4968 standard level 0 or 1. The rolling and cooling processes utilize a two-stage controlled rolling and cooling technology, as detailed below:

[0017] The continuously cast slab is heated to 1180~1189℃, and the roughing rolling temperature is 1015~1020℃. The roughing rolling process involves at least 5 passes, with the first pass having a reduction rate of 20.4%~21.8% and the total roughing rolling reduction rate of 72.9%~74.1%. The intermediate slab is heated to 950~960℃ before entering the finishing rolling process, with the finishing rolling temperature at 810~818℃ and the cumulative finishing rolling reduction rate of 68.2%~69.6%. After rolling, the slab is cooled to 520~528℃ at a rate of 18.7~19.7℃ / s and then coiled.

[0018] The thickness of the continuously cast 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 foundation for the excellent overall performance of the finished product;

[0021] 2) Adding Ni promotes the cross-slip of dislocations. The use of rough rolling with large reduction technology reduces the dislocation density in the finishing rolling stage, reduces the generation of dislocation pile-up, and avoids the aggregation of hydrogen atoms interacting with dislocations to form hydrogen gas and generate hydrogen-induced cracks, thereby improving the hydrogen resistance of the product.

[0022] 3) The addition of Mo and Nb together form (NbMo)4C3, which has a higher volume fraction of precipitated phase than pure NbC, thereby improving 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 Implementation

[0024] The present invention discloses a 450MPa grade hydrogen-doped pipeline steel, the chemical composition of which, 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%, Ni: 0.20%–0.30%, Mo: 0.12%–0.18%, P≤0.012%, S≤0.0015%, N≤0.0040%, with the remainder being Fe and unavoidable impurities.

[0025] Compared to conventional steels used in hydrogen-doped pipelines, this invention employs a low-C, low-Mn, and low-Si composition design. Utilizing the Nb-Ti microalloying mechanism, it forms finely dispersed carbonitrides as hydrogen traps to secure hydrogen. The addition of Mo further enhances the effect of Nb, forming (NbMo)₄C₃ with a higher mass fraction to increase the number of hydrogen traps. The addition of Ni promotes dislocation cross-slip, interacting with hydrogen entering the steel to prevent hydrogen-induced cracking due to stress concentration. Combined with a suitable rolling process, a acicular ferrite + M / A microstructure is obtained, with the acicular ferrite volume percentage being 97.0%–97.6% and the M / A microstructure volume percentage being 2.4%–3.0%, ensuring the product has a suitable strength-toughness ratio and good hydrogen resistance. The rationale for the selection of the main elements in the steel is 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 steel both tend to increase, but the plasticity, toughness and weldability of steel will be significantly reduced. In addition, the reduction of C content will also inhibit the formation of pearlite in the microstructure, thereby improving the hydrogen resistance. Therefore, the present invention controls the C content at 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 improving the strength of steel, but at the same time, it will also reduce plasticity and toughness. Therefore, this invention adopts a low-Si design, controlling the Si content at 0.10% to 0.20%.

[0028] Mn: Manganese is the second most important strengthening element in steel after C. It has a solid solution strengthening effect and can improve the hardenability of steel. However, 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 structures with P. Both of these structures cut the matrix and severely reduce the toughness and hydrogen resistance of the material. Therefore, this invention adopts a low Mn design, controlling the manganese content at 0.70% to 0.80%.

[0029] P, S, and N: These three are unavoidable impurity elements in steel. As harmful elements in steel used for hydrogen pipelines, their content should be as low as possible, but excessively low content will increase production costs. In this invention, the role of Ti in modifying MnS is utilized, and the Ti content is adjusted according to the S and N content in the steel. Based on this, P ≤ 0.012%, S ≤ 0.0015%, and N ≤ 0.0040% are controlled.

[0030] Niobium (Nb) is the most important element for controlled rolling in modern microalloyed pipeline steel, and its most important role is grain refinement and strengthening. This invention adds Mo to further enhance the effect of Nb; therefore, adding an appropriate amount of Nb is sufficient. By refining the grains, strength can be increased without sacrificing toughness. Furthermore, smaller grains mean more grain boundaries, which act as traps, capturing hydrogen as it diffuses into the steel, thus improving the material's hydrogen resistance. The combined effect of Mo and Nb will be described in detail later in the section on the role of Mo. Therefore, this invention controls the Nb content to be between 0.016% and 0.026%.

[0031] Ti plays a two-fold role in this invention. Firstly, because Ti has a stronger affinity for S than Mn, it can "remove" S from MnS inclusions, forming nearly spherical Ti4C2S2. The absence of sharp corners in Ti4C2S2 acts as a trap for diffused hydrogen phases and prevents stress concentration, thus improving hydrogen resistance. Secondly, research shows that when Ti = 3.4N + 3S, all MnS can be modified into Ti4C2S2, meaning that adding 0.009% to 0.015% Ti achieves this goal. However, with further increases in Ti content and appropriate rolling processes, small TiC particles can be formed, which act as precipitation strengthening and hydrogen adsorption, thereby improving the steel's strength and hydrogen resistance. But excessively high Ti content leads to the formation of large TiN and Ti(C, N) particles, which negatively impacts toughness and hydrogen resistance. Therefore, this invention precisely controls the Ti content to 0.013% to 0.019%.

[0032] Ni is the third most important austenite stabilizing element after C, N, and Mn. It can effectively prevent the growth of austenite grains at high temperatures and maintain a fine-grained structure, ensuring that the product structure contains fine original austenite. Ni can also play a role in solid solution strengthening, thereby improving strength. In addition, Ni can promote the cross-slip of dislocations, effectively improving the toughness of the product. When the Ni content in steel exceeds 0.2%, its resistance to HIC is excellent in highly acidic A solution. However, Ni alloys are expensive, and excessive addition will affect the economics of the product. Therefore, this invention controls the Ni content at 0.20% to 0.30%.

[0033] Mo: As a strong carbide-forming element, Mo increases the strength of carbon steel by forming carbides. In this invention, Mo is added together with Cr to promote the formation of the microstructure (M / A), thereby increasing strength, but it also reduces the Bauschinger effect after tube manufacturing. When the Mo content exceeds 0.12%, it can react with Nb to form (NbMo)4C3, which can increase the volume fraction of the precipitated phase and has a stronger hydrogen absorption capacity than NbC alone. However, if too much Mo is added, the resulting M / A structure will be large, which is detrimental to toughness and hydrogen resistance. In addition, Mo is a precious metal, and adding too much significantly affects economic efficiency. Therefore, this invention controls the Mo content to be between 0.12% and 0.18%.

[0034] This invention discloses a method for producing 450MPa grade hydrogen-doped pipeline steel, comprising: hot metal pretreatment, steelmaking, ladle refining, LF furnace refining (including light desulfurization and calcium treatment to control inclusion morphology and improve steel ductility, toughness, and cold bending performance), slab continuous casting (using electromagnetic stirring or dynamic light reduction technology to ensure that slab center segregation reaches ISO 4968 level 0 or 1), and continuous casting billet heating, rolling, cooling, and coiling processes. A two-stage controlled rolling and cooling technology is employed, as detailed below:

[0035] A 160–180 mm thick continuously cast slab is heated to 1180–1189 °C, and then subjected to rough rolling in more than 5 passes using a two-stage controlled rolling and cooling technology. The final rough rolling temperature is 1015–1020 °C, the first pass reduction is 20.4%–21.8%, and the total rough rolling reduction is 72.9%–74.1%. This process causes recrystallization in each pass of the rough rolling, continuously refining the microstructure, increasing the number of grain boundaries, and improving hydrogen absorption capacity.

[0036] After rough rolling, an intermediate billet with a thickness of 44–46 mm is obtained. This billet is then heated to 950–960℃ before entering the finish rolling stage. The final finishing rolling temperature is 810–818℃, and the cumulative reduction rate is 68.2%–69.6%. The relatively low reduction rate in the finish rolling stage aims to reduce dislocation generation, decrease dislocation pile-up, prevent hydrogen atoms interacting with dislocations from accumulating and forming hydrogen gas, thus avoiding hydrogen-induced cracking and improving the product's resistance to hydrogen damage.

[0037] The rolled steel sheet is cooled to 520-528℃ at a rate of 18.7-19.7℃ / s and then coiled, with a finished thickness of 13-16mm.

[0038] The above production process ensures that the hot-rolled coil has good strength, toughness, and hydrogen resistance.

[0039] The final microstructure of the hot-rolled coil is acicular ferrite + M / A microstructure, with the volume percentage of acicular ferrite being 97.0% to 97.6% and the volume percentage of M / A microstructure being 2.4% to 3.0%.

[0040] The final mechanical properties of the hot-rolled coil are: yield strength ≥ 456 MPa, tensile strength ≥ 546 MPa, drop shear area SA (mean) ≥ 96% at -40℃, and impact energy (mean) ≥ 320 J at -40℃.

[0041] The acid service performance of hot-rolled coil is as follows: According to the NACE TM0284 standard, the hydrogen-induced cracking test in solution A showed that the resistance to HIC performance indicators CLR, CTR, and CSR were all 0; According to the NACE TM0177 standard, the hydrogen sulfide stress corrosion test showed that the SSCC sample did not break when the loading force was 0.9 times the actual yield strength.

[0042] The hydrogen resistance of hot-rolled coil is as follows: under hydrogen-exposed environment with operating pressure ≤12MPa and hydrogen partial pressure ≤3.6MPa (hydrogen doping ratio ≤30%), the elongation degradation rate is 12.0%~13.7%.

[0043] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0044] Example:

[0045] The chemical composition of the steels in Examples 1 to 10 is shown in Table 1, the heating, rolling and cooling process parameters are shown in Table 2, and the results of the finished product performance and metallographic structure test 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: Results of Finished Product Performance and Metallographic Structure Testing

[0051]

[0052] As can be seen from Tables 1-3, the 450MPa grade pipeline steel hot-rolled coils produced by the production method described in this invention have excellent strength, low-temperature toughness and hydrogen resistance, and can be applied to natural gas hydrogen-blended 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 method for producing 450MPa grade hydrogen-doped pipeline steel, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: 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%, Ni: 0.21%–0.30%, Mo: 0.12%–0.18%, P≤0.012%, S≤0.0015%, N≤0.0040%, with the remainder being Fe and unavoidable impurities. The production method for the 450MPa grade hydrogen-doped pipeline steel includes hot metal pretreatment, steelmaking, ladle refining, LF furnace refining, slab continuous casting, slab heating, rolling, cooling, and coiling processes. The slab continuous casting employs electromagnetic stirring or dynamic light reduction technology to ensure that the slab center segregation meets ISO 4968 standard level 0 or 1. The rolling and cooling processes utilize a two-stage controlled rolling and cooling technology, as detailed below: The continuously cast slab is heated to 1180–1189℃, and the roughing rolling temperature is 1015–1020℃. The roughing rolling process involves at least 5 passes, with the first pass having a reduction rate of 20.4%–21.8% and the total roughing rolling reduction rate of 72.9%–74.1%. The intermediate slab is heated to 950–960℃ before entering the finishing rolling process, with the finishing rolling temperature at 811–818℃ and the cumulative finishing rolling reduction rate of 68.2%–69.6%. After rolling, the slab is cooled to 520–521℃ at a rate of 18.7–19.7℃ / s and then coiled.

2. The method for producing 450MPa grade hydrogen-doped pipeline steel according to claim 1, characterized in that, The metallographic structure of the finished steel plate is acicular ferrite + M / A structure, and by volume percentage, the acicular ferrite structure accounts for 97.0% to 97.6%, and the M / A structure accounts for 2.4% to 3.0%.

3. The method for producing 450MPa grade hydrogen-doped pipeline steel according to claim 1, characterized in that, The mechanical properties of the finished steel plate are as follows: yield strength ≥ 456 MPa, tensile strength ≥ 546 MPa, average drop shear area (SA) at -40℃ ≥ 96%, and average impact energy at -40℃ ≥ 320 J; acid service performance is as follows: according to NACE-TM0284 standard, hydrogen-induced cracking test, in solution A, the resistance to HIC performance indicators CLR, CTR, and CSR are all 0; according to NACE-TM0177 standard, hydrogen sulfide stress corrosion test, when the loading force is 0.9 times the actual yield strength, the SSCC sample does not break; hydrogen resistance is as follows: in a hydrogen-exposed environment with operating pressure ≤ 12 MPa, hydrogen doping ratio ≤ 30%, and hydrogen partial pressure ≤ 3.6 MPa, the elongation degradation rate is 12.0%~13.7%.

4. The method for producing 450MPa grade hydrogen-doped pipeline steel according to claim 1, characterized in that, The thickness of the continuously cast 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.

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