A high-toughness, high-crack arrest steel for hydrogen pipeline and preparation method thereof

Abstract

The present invention discloses a high-toughness, high-crack arrest steel for hydrogen pipelines and a preparation method thereof, and belongs to the technical field of pipeline steel preparation. The high-toughness, high-crack arrest steel for hydrogen pipelines includes the following components by mass percentage: C: 0.04-0.07%; Si: 0.30-0.45%; Mn: 0.7-1.0%; Mo: 0.15-0.25%; V: 0.05-0.08%; Nb: 0.02-0.06%; P≤0.012%; S≤0.005%; the balance is Fe. The present invention realizes gradient temperature rolling through controlled rolling and controlled cooling to obtain a gradient flattened ferrite structure, which is beneficial to changing the crack propagation path under the action of low-temperature impact loads, delaying the crack propagation process, and improving the low-temperature toughness and crack arrest performance of hydrogen pipeline steel. In addition, the present invention uses the synergistic effect of cyclic phase transformation and Nb and V micro-alloying to refine the microstructure during the gradient temperature rolling process, further improving its strength and toughness.

Description

Technical Field

[0001] The invention relates to high-toughness, high-crack arrest steel for hydrogen transport pipelines and a preparation method thereof, belonging to the technical field of pipeline steel preparation. Background Art

[0002] Driven by the dual-carbon strategy, hydrogen energy has become one of my country's key development areas due to its advantages such as no pollution and low carbon emissions. The transportation of hydrogen is the key to the effective development and use of hydrogen energy. At present, the transportation of hydrogen mainly includes pipeline transportation, vehicle and ship transportation, etc. Due to the characteristics of large transportation volume, low energy consumption, safety and stability, pipeline transportation has excellent application prospects and has become the preferred option at home and abroad. At present, hydrogen pipelines are mainly made of steel materials, but in a hydrogen environment, hydrogen atoms may penetrate into the steel, causing material deterioration, resulting in reduced toughness and increased crack propagation rate. In addition, high-pressure hydrogen transportation has gradually become a development trend, which also requires steel materials for hydrogen transportation to have higher strength and pressure resistance. Therefore, the development of high-toughness and high crack arrest steel for hydrogen pipelines has become one of the current problems that steel companies urgently need to tackle.

[0003] Chinese patent 202210756438.7 discloses a technical document of "a hot-rolled coil with a yield strength of 245MPa for hydrogen pipelines and its production method", which suppresses component structure segregation by reducing the Mn content in steel, reduces MnS inclusions, and effectively supplements the strength reduction problem caused by the reduction of C and Mn content through Nb alloy elements. However, its strength is still relatively low, and there are still certain limitations for high-pressure hydrogen transportation pipelines.

[0004] Chinese patent 202210304498.5 discloses the technical document of "A L245S hydrogen-doped pipeline steel and its production method", which obtains a low-carbon tempered troostite structure through online quenching + offline tempering. It has good resistance to hydrogen embrittlement and good crack arrest performance, but low strength.

[0005] Chinese patent 202310994333.X discloses a technical document of "a weldable low-alloy high-strength steel and its preparation method and application". By controlling the material composition, specific element ratio and preparation method, high-strength and easy-to-weld alloy steel with tensile strength above 800MPa and low hydrogen embrittlement sensitivity is obtained on the basis of controlling material cost. However, in order to ensure strength, more Mn, Ni, Cr, and Mo elements need to be added, which is prone to segregation and requires additional heat treatment processes, which is costly.

[0006] Chinese patent 202111089004.8 discloses a technical document of "A method for producing L360QS hydrogen pipeline steel", which increases the yield strength to more than 380MPa through controlled rolling and controlled cooling and offline quenching and tempering processes, and the drop weight tear (DWTT) shear area ratio at -30°C reaches more than 85%. However, the additional offline quenching and tempering heat treatment process requires a longer production cycle and is more expensive.

[0007] In summary, in order to ensure good hydrogen embrittlement resistance, high-pressure hydrogen pipelines have high requirements for the toughness of steel materials. In order to meet the working conditions of high-pressure hydrogen pipelines and improve the safety of hydrogen pipelines, it is necessary to further develop high-toughness and high-crack arrest steel for hydrogen pipelines. Summary of the invention

[0008] In view of the shortcomings of hydrogen pipeline steel, the purpose of the present invention is to provide a method for preparing low-alloy, high-toughness, high-crack-arrest steel for hydrogen pipelines. Based on the composition design, the present invention realizes gradient temperature rolling through controlled rolling and controlled cooling to obtain a gradient flattened ferrite structure, and during the rolling process, the cyclic phase transformation and Nb and V microalloying synergistic effect are used to refine the microstructure, and finally the strength, toughness and crack-arrest performance of hydrogen pipeline steel are further improved through organizational refinement and splitting.

[0009] At the same time, the present invention provides a high-toughness, high-crack-arrest steel for hydrogen pipelines.

[0010] At the same time, the present invention provides a high-toughness, high-crack arrest steel for hydrogen pipelines for use in hydrogen pipelines.

[0011] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0012] A high-toughness, high-crack arrest steel for hydrogen pipelines comprises the following components by mass percentage: C: 0.04-0.07%; Si: 0.30-0.45%; Mn: 0.7-1.0%; Mo: 0.15-0.25%; V: 0.05-0.08%; Nb: 0.02-0.06%; P≤0.012%; S≤0.005%; and the balance is Fe.

[0013] The high-toughness, high-crack arrest steel for hydrogen pipelines of the present invention obtains a gradient flattened ferrite structure, that is, the aspect ratio of ferrite grains in the surface area of ​​the high-toughness, high-crack arrest steel for hydrogen pipelines is 1.88-2.01, and the ferrite grain size is 4.1-4.5μm; the aspect ratio of ferrite grains in the core area of ​​the high-toughness, high-crack arrest steel for hydrogen pipelines is 1.36-1.45, and the ferrite grain size is 4.9-5.2μm; the yield strength of the high-toughness, high-crack arrest steel for hydrogen pipelines is 490-503MPa, the tensile strength is 556-566MPa, the impact energy at -40°C is 376-381J, the DWTT at -30°C is 98-100%, and the hydrogen embrittlement sensitivity is 25-26%.

[0014] A method for preparing high-toughness, high-crack arrest steel for hydrogen pipelines comprises the following steps:

[0015] Step 1: The molten iron from the blast furnace is smelted in a converter and smelted in an LF furnace to complete S, P removal and alloying, and then refined in a VD furnace. After refining, continuous casting is performed to obtain a continuous casting billet with a thickness of 150 to 320 mm;

[0016] Step 2, heating the continuous casting slab of step 1 to 1150-1200°C, keeping the temperature for 180-240min, and then performing three-stage rolling; the first-stage rough rolling temperature is 1080-1150°C; after the first-stage rolling, spray water cooling is directly performed, the surface temperature of the slab is rapidly cooled to 700-800°C, the core temperature of the slab is between 823-900°C, and then the second-stage rolling is immediately performed; after the second-stage rolling, air cooling is performed to 650-680°C for relaxation, and rapid reheating is performed to 750-820°C, and then the third-stage rolling is immediately performed; after the third-stage rolling, water cooling is performed to 650-680°C, and finally air cooling is performed to room temperature;

[0017] The thickness of the slab after the first stage of rolling is 35 to 60 mm, the thickness of the slab after the second stage of rolling is 20 to 30 mm, and the thickness of the slab after the third stage of rolling is 15 to 20 mm.

[0018] Preferably, in step 2, the water cooling rate after the first stage of rolling is 10-50°C / s, the air cooling rate after the second stage of rolling is 0.5-5°C / s, and the water cooling rate after the third stage of rolling is 20-50°C / s.

[0019] Preferably, in step 2, the heating rate during the process of rapidly reheating the intermediate billet from 650-680° C. to 750-820° C. is 5-30° C. / s.

[0020] Preferably, in step one, converter smelting and LF furnace smelting to complete S, P removal and alloying include the following steps: blast furnace molten iron is smelted in a converter, the furnace entry temperature is 1550-1600°C, the terminal temperature is 1700-1750°C, the oxygen pressure during the smelting process is controlled at 0.7-1.1MPa, and the slag basicity is controlled at 2.8-3.5 by adding lime and fluorite; then LF furnace refining is adopted, the refining temperature is 1640-1680°C, the refining time is 35-50min, the argon pressure during the refining process is controlled at 0.6-1.0MPa, and the CaO-SiO2-Al2O3 slag system is selected to control the basicity at 3.3-3.7, and S, P removal and alloying are completed.

[0021] Preferably, in step one, VD furnace refining and continuous casting include the following steps: degassing in a VD furnace, the vacuum degree of the degassing process is controlled at 30-65 Pa, the vacuum holding time is controlled at 14-18 min, and the argon blowing intensity is 220-330 L / min; followed by continuous casting, the pouring temperature of the continuous casting tundish is 1520-1540°C, the pulling speed is controlled at 0.7-1.0 m / min, the reduction is controlled at 4-7 mm, and a continuous casting billet with a thickness of 150-320 mm is obtained.

[0022] Application of high-toughness, high-crack-arrest steel for hydrogen pipelines in hydrogen pipelines.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] The present invention combines the size of the billet, and realizes gradient temperature rolling through rapid water cooling and rolling temperature design during the rolling process, thereby obtaining a gradient flattened ferrite structure. The aspect ratio of the ferrite grains in the surface area of ​​the gradient flattened structure is 1.88-2.01; the aspect ratio of the ferrite grains in the core area is 1.36-1.45. Compared with conventional blocky equiaxed ferrite structure, the gradient flattened structure helps to change the crack propagation path under external load, promotes the generation of delamination, improves low-temperature toughness, and enhances crack arrest performance.

[0025] The present invention refines the ferrite structure through the synergistic effect of cyclic phase transformation and low final rolling temperature. In addition, the relaxation effect of the air cooling and reheating process between the second stage rolling and the third stage rolling process promotes the dispersion precipitation of the (Nb, V)C nano second phase, further refining the ferrite structure. Ultimately, the ferrite grain size in the surface area of ​​the gradient flattened structure is about 4μm, and the ferrite grain size in the core area is about 5μm. However, the ferrite grain size is about 7.5μm under conventional production processes. The refinement of the grains helps to improve the final strength and toughness.

[0026] The alloy composition of the method of the present invention is relatively simple, and no alloy elements such as Ni and Ti need to be added, and no additional quenching and tempering treatment is required. The production cycle is short, and the cost is saved to a certain extent.

[0027] The present invention realizes gradient rolling by controlled rolling and controlled cooling to obtain a gradient flattened ferrite structure. Such gradient flattened ferrite grains are conducive to changing the crack propagation path under low-temperature impact loads, delaying the crack propagation process, and thus improving the low-temperature toughness and crack arrest performance of hydrogen pipeline steel. In addition, the present invention uses the synergistic effect of cyclic phase transformation and Nb and V microalloying to refine the microstructure during the gradient rolling process, further improving its strength and toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the controlled rolling and controlled cooling process in the method of the present invention;

[0029] Figure 2 The method of Example 1 of the present invention comprises a flattened ferrite + a small amount of pearlite structure near the surface;

[0030] Figure 3 The method of Example 1 of the present invention comprises a flattened ferrite + a small amount of pearlite structure near the core;

[0031] Figure 4 It is the conventional equiaxed ferrite structure in the method described in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. The following embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0033] Example 1

[0034] like Figure 1 As shown, a method for preparing high-toughness, high-crack arrest steel for hydrogen pipelines comprises the following steps:

[0035] Step 1: The blast furnace iron is smelted in a converter, the furnace temperature is 1550℃, the terminal temperature is 1750℃, the oxygen pressure during the smelting process is controlled at 1.1MPa, and the slag basicity is controlled at 2.8; then the LF furnace is used for refining, the refining temperature is 1640℃, the refining time is 35min, the argon pressure during the refining process is controlled at 1.0MPa, the slag basicity is controlled at 3.3, and the S, P and alloying are completed; then the VD furnace is used for degassing, the vacuum degree of the degassing process is controlled at 65Pa, the vacuum holding time is controlled at 14min, and the argon blowing intensity is 220L / min. Then continuous casting is carried out, the pouring temperature of the continuous casting tundish is 1520℃, the pulling speed is controlled at 0.7m / min, and the reduction is controlled at 4mm to obtain a continuous casting billet with a thickness of 150mm. The composition of the continuous casting slab is calculated by mass percentage: C: 0.07%; Si: 0.30%; Mn: 1.0%; Mo: 0.15%; V: 0.05%; Nb: 0.02%; P: 0.012%; S: 0.0015%; and the balance is Fe.

[0036] Step 2, then heat the continuous casting billet from room temperature to 1200℃, and keep it warm for 240min; the continuous casting billet of step 2 is rolled in three stages. The first stage rough rolling temperature is 1150℃, and the thickness after rolling is 60mm; after the first stage rolling, spray water cooling is directly performed, the cooling rate of water cooling on the surface of the slab is 10℃ / s, the surface temperature of the slab is quickly cooled to 700℃, and the core temperature of the slab is 846℃, and then the second stage rolling is immediately performed, and the thickness after rolling is 30mm; after the second stage rolling, cool to 680℃ at 0.5℃ / s to achieve relaxation, and then reheat to 810℃ at 5℃ / s, and then immediately perform the third stage rolling, and the thickness after rolling is 20mm; after the third stage rolling, water cool to 680℃ at 20℃ / s, and finally air cool to room temperature.

[0037] Application of high-toughness, high-crack-arrest steel for hydrogen pipelines in hydrogen pipelines.

[0038] like Figure 2 As shown, this is the flattened ferrite + a small amount of pearlite structure near the surface of the high-toughness, high-crack arrest hydrogen pipeline steel obtained in this embodiment, Figure 3 The flattened ferrite + a small amount of pearlite structure near the core of this embodiment. It can be seen that in this embodiment, the aspect ratio of the ferrite grains in the surface area is 1.88, and the ferrite grain size is 4.1μm; the aspect ratio of the ferrite grains in the core area is 1.36, and the ferrite grain size is 4.9μm. This embodiment obtains a gradient flattened ferrite structure.

[0039] Example 2

[0040] A method for preparing high-toughness, high-crack arrest steel for hydrogen pipelines comprises the following steps:

[0041] Step 1: The blast furnace iron is smelted in a converter, the furnace temperature is 1550℃, the terminal temperature is 1750℃, the oxygen pressure during the smelting process is controlled at 1.1MPa, and the slag basicity is controlled at 2.8; then the LF furnace is used for refining, the refining temperature is 1640℃, the refining time is 35min, the argon pressure during the refining process is controlled at 1.0MPa, the slag basicity is controlled at 3.3, and the S, P and alloying are completed; then the VD furnace is used for degassing, the vacuum degree of the degassing process is controlled at 65Pa, the vacuum holding time is controlled at 14min, and the argon blowing intensity is 220L / min. Then continuous casting is carried out, the pouring temperature of the continuous casting tundish is 1520℃, the pulling speed is controlled at 0.7m / min, and the reduction is controlled at 4mm to obtain a continuous casting billet with a thickness of 150mm. The composition of the continuous casting slab is calculated by mass percentage: C: 0.07%; Si: 0.30%; Mn: 1.0%; Mo: 0.15%; V: 0.05%; Nb: 0.02%; P: 0.012%; S: 0.0015%; and the balance is Fe.

[0042] Step 2, then heat the continuous casting billet from room temperature to 1200℃, and keep it warm for 240min; the continuous casting billet of step 2 is rolled in three stages. The first stage rough rolling temperature is 1150℃, and the thickness after rolling is 35mm; after the first stage rolling, spray water cooling is directly performed, the cooling rate of water cooling on the surface of the slab is 50℃ / s, the surface temperature of the slab is quickly cooled to 700℃, and the core temperature of the slab is about 823℃, and then the second stage rolling is immediately performed, and the thickness after rolling is 20mm; after the second stage rolling, cool to 680℃ at 0.5℃ / s to achieve relaxation, and then reheat to 820℃ at 5℃ / s, and then immediately perform the third stage rolling, and the thickness after rolling is 15mm; after the third stage rolling, water cool to 680℃ at 50℃ / s, and finally air cool to room temperature.

[0043] Application of high-toughness, high-crack-arrest steel for hydrogen pipelines in hydrogen pipelines.

[0044] Example 3

[0045] A method for preparing high-toughness, high-crack arrest steel for hydrogen pipelines comprises the following steps:

[0046] Step 1: The blast furnace iron is smelted in a converter, the furnace temperature is 1600℃, the terminal temperature is 1700℃, the oxygen pressure in the smelting process is controlled at 0.7MPa, and the slag basicity is controlled at 3.5; then the LF furnace is used for refining, the refining temperature is 1680℃, the refining time is 50min, the argon pressure in the refining process is controlled at 0.6MPa, the slag basicity is controlled at 3.7, and the S, P and alloying are completed; then the VD furnace is used for degassing, the vacuum degree of the degassing process is controlled at 30Pa, the vacuum holding time is controlled at 18min, and the argon blowing intensity is 330L / min. Then continuous casting is carried out, the pouring temperature of the continuous casting tundish is 1540℃, the pulling speed is controlled at 1.0m / min, the reduction is controlled at 7mm, and a continuous casting billet with a thickness of 320mm is obtained. The composition of the continuous casting slab is calculated by mass percentage: C: 0.04%; Si: 0.45%; Mn: 0.7%; Mo: 0.25%; V: 0.08%; Nb: 0.06%; P: 0.01%; S: 0.005%; and the balance is Fe.

[0047] Step 2, then heat the continuous casting billet from room temperature to 1200℃, and keep it warm for 180min; the continuous casting billet of step 2 is rolled in three stages. The first stage rough rolling temperature is 1080℃, and the thickness after rolling is 60mm; after the first stage rolling, spray water cooling is directly performed, the cooling rate of water cooling on the surface of the slab is 10℃ / s, the surface temperature of the slab is quickly cooled to 800℃, and the core temperature of the slab is about 900℃, and then the second stage rolling is immediately performed, and the thickness after rolling is 30mm; after the second stage rolling, cool to 650℃ at 5℃ / s to achieve relaxation, and then reheat to 750℃ at 30℃ / s, and then immediately perform the third stage rolling, and the thickness after rolling is 20mm; after the third stage rolling, water cool to 650℃ at 20℃ / s, and finally air cool to room temperature.

[0048] Application of high-toughness, high-crack-arrest steel for hydrogen pipelines in hydrogen pipelines.

[0049] Comparative Example 1

[0050] A method for preparing steel for a hydrogen transmission pipeline comprises the following steps:

[0051] (1) The blast furnace iron was smelted in a converter, with a furnace entry temperature of 1550℃ and a terminal temperature of 1750℃. The oxygen pressure during the smelting process was controlled at 1.1MPa, and the slag basicity was controlled at 2.8. Then, the LF furnace was used for refining, with a refining temperature of 1640℃ and a refining time of 35min. The argon pressure during the refining process was controlled at 1.0MPa, and the slag basicity was controlled at 3.3 to complete the removal of S, P and alloying. Then, the VD furnace was used for degassing, with a vacuum degree during the degassing process controlled at 65Pa, a vacuum holding time controlled at 14min, and an argon blowing intensity of 220L / min. Then, continuous casting was carried out, with a continuous casting tundish pouring temperature of 1520℃, a pulling speed controlled at 0.7m / min, and a reduction amount controlled at 4mm to obtain a continuous casting billet with a thickness of 150mm. The composition of the continuous casting slab is calculated by mass percentage: C: 0.07%; Si: 0.30%; Mn: 1.0%; Mo: 0.15%; V: 0.05%; Nb: 0.02%; P: 0.012%; S: 0.0015%; and the balance is Fe.

[0052] (2) After refining, continuous casting is performed to obtain a continuous casting billet with a thickness of 150 mm, and then the continuous casting billet is heated from room temperature to 1200°C for a holding time of 240 min;

[0053] (3) The continuous casting slab of step (2) is subjected to three-stage rolling. The first stage rough rolling temperature is 1150°C, and the thickness after rolling is 65 mm; after the first stage rolling, it is directly air-cooled to 958°C, and the core temperature of the slab is about 948°C, and then the second stage rolling is immediately carried out, and the thickness after rolling is 30 mm; after the second stage rolling, it is air-cooled to 830°C, and then the third stage rolling is immediately carried out, and the thickness after rolling is 20 mm; after the third stage rolling, it is water-cooled to 680°C at 20°C / s, and finally air-cooled to room temperature.

[0054] like Figure 4 As shown, it is the conventional equiaxed ferrite organization diagram obtained in this comparative example, that is, the ferrite in this comparative example is not flattened.

[0055] Comparative Example 2

[0056] A steel for a hydrogen transmission pipeline and a preparation method thereof, comprising the following steps:

[0057] (1) The blast furnace iron was smelted in a converter, with a furnace entry temperature of 1550℃ and a terminal temperature of 1750℃. The oxygen pressure during the smelting process was controlled at 1.1MPa, and the slag basicity was controlled at 2.8. Then, the LF furnace was used for refining, with a refining temperature of 1640℃ and a refining time of 35min. The argon pressure during the refining process was controlled at 1.0MPa, and the slag basicity was controlled at 3.3 to complete the removal of S, P and alloying. Then, the VD furnace was used for degassing, with a vacuum degree during the degassing process controlled at 65Pa, a vacuum holding time controlled at 14min, and an argon blowing intensity of 220L / min. Then, continuous casting was carried out, with a continuous casting tundish pouring temperature of 1520℃, a pulling speed controlled at 0.7m / min, and a reduction amount controlled at 4mm to obtain a continuous casting billet with a thickness of 150mm. The composition of the continuous casting slab is calculated by mass percentage: C: 0.07%; Si: 0.30%; Mn: 1.0%; Mo: 0.15%; V: 0.05%; Nb: 0.02%; P: 0.012%; S: 0.0015%; and the balance is Fe.

[0058] (2) After refining, continuous casting is performed to obtain a continuous casting billet with a thickness of 150 mm, and then the continuous casting billet is heated from room temperature to 1200°C for a holding time of 240 min;

[0059] (3) The continuous casting slab of step (2) is subjected to three-stage rolling. The first stage rough rolling temperature is 1150°C, and the thickness after rolling is 65 mm; after the first stage rolling, it is directly air-cooled to 958°C, and the core temperature of the slab is about 948°C, and then the second stage rolling is immediately carried out, and the thickness after rolling is 20 mm; after the second stage rolling, it is air-cooled to 770°C, and then the third stage rolling is immediately carried out, and the thickness after rolling is 15 mm; after the third stage rolling, it is water-cooled to 680°C at 20°C / s, and finally air-cooled to room temperature.

[0060] The microstructure obtained in this comparative example is non-gradient flattened ferrite + a very small amount of pearlite.

[0061] The structural properties of the steel for hydrogen pipeline prepared in Examples 1-3 and Comparative Examples 1-2 were evaluated, and the specific results are shown in Tables 1 and 2. The ferrite grain size was obtained in accordance with the national standard GB / T 6394-2017 "Method for Determining Average Grain Size of Metals"; in the aspect ratio test, the ratio between the major axis and the minor axis of each ferrite grain in the organizational picture was determined by using Image-pro Plus image analysis software, and the ratio was averaged. The yield strength and tensile strength were measured in accordance with the national standard GB / T228.1-2010 "Metallic Material Tensile Test Standard"; the -40°C impact performance test was measured in accordance with the national standard GB / T 229-2007 "Metallic Material Charpy Pendulum Impact Test Method"; the -30°C drop weight tear test (DWTT) was measured in accordance with the national standard GB / T8363-2018 "Steel Drop Weight Tear Test Method". The hydrogen embrittlement sensitivity measurement in a 6.5MPa high-pressure hydrogen environment is obtained in accordance with GB / T 34542.2-2018 "Hydrogen Storage and Transportation System Part 2: Test Method for Compatibility of Metallic Materials with Compressed Hydrogen Environment".

[0062] Table 1 Performance of steel sections of the embodiments of the present invention and comparative examples

[0063]

[0064]

[0065] Table 2 Performance of steel sections of the embodiments of the present invention and comparative examples

[0066]

[0067] It can be seen from Table 1 and Table 2 that the microstructures in Examples 1 to 3 of the present invention are all gradient flattened ferrite structures + very small amounts of pearlite, the ferrite grain size in the surface area is about 4 μm, the aspect ratio is above 1.8, the ferrite grain size in the core area is about 5 μm, the aspect ratio is about 1.4, the yield strength is above 490 MPa, the impact energy at -40 ° C temperature exceeds 370 J, the DWTT at -30 ° C is above 98%, and the hydrogen embrittlement sensitivity is less than 26%; Comparative Example 1 of the present invention obtains blocky equiaxed ferrite The grain size is about 7.5 μm, the aspect ratio is about 1.1, the yield strength is 432 MPa, the impact energy at -40 ° C is 369 J, the DWTT at -30 ° C is 94%, and the hydrogen embrittlement sensitivity is 35%; the comparative example 2 of the present invention obtains non-gradient flattened ferrite, with a grain size of about 6.5 μm, an aspect ratio of about 2.0, a yield strength of 483 MPa, but the impact energy at -40 ° C is slightly lower, 352 J, the DWTT at -30 ° C is 94%, and the hydrogen embrittlement sensitivity is about 34%. Therefore, the ferrite in the steel structure for hydrogen pipelines prepared by the present invention has good toughness and crack arrest performance due to the characteristics of gradient flattening.

[0068] It should be understood that in order to streamline the present disclosure and aid in understanding one or more of the various inventive aspects, in the above description of exemplary embodiments of the present invention, various features of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, this disclosed method should not be interpreted as reflecting the intention that the claimed invention requires more features than those expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in less than all of the features of the previously disclosed embodiments. Therefore, the claims that follow the detailed description are hereby expressly incorporated into the detailed description, with each claim itself serving as a separate embodiment of the present invention.

[0069] Although the present invention has been described according to a limited number of embodiments, it will be apparent to those skilled in the art, with the benefit of the above description, that other embodiments may be envisioned within the scope of the invention thus described. In addition, it should be noted that the language used in this specification is selected primarily for readability and teaching purposes, rather than for explaining or defining the subject matter of the present invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is illustrative, not restrictive, with respect to the scope of the present invention, which is defined by the appended claims.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A high-toughness, high-crack arrest steel for hydrogen pipelines, characterized in that: In terms of mass percentage, it includes the following components: C: 0.04~0.07%; Si: 0.30~0.45%; Mn: 0.7~1.0%; Mo: 0.15~0.25%; V: 0.05~0.08%; Nb :0.02~0.06%; P≤0.012%; S≤0.005%; the balance is Fe; The high-toughness and high-crack-arrest steel for hydrogen pipelines has obtained a gradient flattened ferrite structure, that is, the aspect ratio of the ferrite grains in the surface area of ​​the high-toughness and high-crack-arrest steel for hydrogen pipelines is 1.88~2.01, and the ferrite grain size is 4.1~4.5μm; the aspect ratio of the ferrite grains in the core area of ​​the high-toughness and high-crack-arrest steel for hydrogen pipelines is 1.36~1.45, and the ferrite grain size is 4.9~5.2μm; the yield strength of the high-toughness and high-crack-arrest steel for hydrogen pipelines is 490~503 MPa, the tensile strength is 556~566 MPa, the impact energy at -40℃ is 376~381J, the DWTT at -30℃ is 98~100%, and the hydrogen embrittlement sensitivity is 25~26%.

2. The method for preparing a high-toughness, high-crack arrest steel for hydrogen pipeline according to claim 1, characterized in that: The steps include: Step 1: The molten iron from the blast furnace is smelted in a converter and LF furnace to complete S, P removal and alloying, and then refined in a VD furnace. After refining, continuous casting is performed to obtain a continuous casting billet with a thickness of 150-320 mm; Step 2, heating the continuous casting slab in step 1 to 1150°C~1200°C, keeping the temperature for 180~240min, and then performing three-stage rolling; the first stage rough rolling temperature is 1080~1150°C; after the first stage rolling, spray water cooling is directly performed, the surface temperature of the slab is quickly cooled to 700~800°C, the core temperature of the slab is between 823~900°C, and then the second stage rolling is immediately performed; After the second stage of rolling, the steel is air-cooled to 650-680°C for relaxation, and then quickly reheated to 750-820°C, followed by the third stage of rolling immediately; after the third stage of rolling, the steel is water-cooled to 650-680°C, and finally air-cooled to room temperature; The thickness of the slab after the first stage of rolling is 35~60mm, the thickness of the slab after the second stage of rolling is 20~30mm, and the thickness of the slab after the third stage of rolling is 15~20mm.

3. The preparation method according to claim 2, characterized in that: In step 2, the water cooling rate after the first stage of rolling is 10~50℃ / s, the air cooling rate after the second stage of rolling is 0.5~5℃ / s, and the water cooling rate after the third stage of rolling is 20~50℃ / s.

4. The preparation method according to claim 2, characterized in that: In step 2, the intermediate billet is rapidly reheated from 650-680°C to 750-820°C at a heating rate of 5-30°C / s.

5. The preparation method according to claim 2, characterized in that: In step 1, converter smelting and LF furnace smelting complete S, P removal and alloying, including the following steps: The blast furnace iron is smelted in a converter with an entry temperature of 1550~1600℃ and a terminal temperature of 1700~1750℃. The oxygen pressure during the smelting process is controlled at 0.7~1.1MPa, and the slag basicity is controlled at 2.8~3.5 by adding lime and fluorite; then LF furnace refining is adopted with a refining temperature of 1640~1680℃ and a refining time of 35~50min. The argon pressure during the refining process is controlled at 0.6~1.0MPa, and the CaO-SiO2-Al2O3 slag system is selected to control the basicity at 3.3~3.7 to complete the removal of S, P and alloying.

6. The preparation method according to claim 2, characterized in that: In step 1, VD furnace refining and continuous casting includes the following steps: VD furnace is used for degassing, the vacuum degree of the degassing process is controlled at 30~65Pa, the vacuum holding time is controlled at 14~18min, and the argon blowing intensity is 220~330L / min; then continuous casting is carried out, the pouring temperature of the continuous casting tundish is 1520~1540℃, the pulling speed is controlled at 0.7~1.0m / min, the reduction is controlled at 4~7mm, and the continuous casting billet with a thickness of 150~320mm is obtained.

7. Use of the high-toughness, high-crack arrest steel for hydrogen pipelines according to claim 1 in hydrogen pipelines.

8. Use of a high-toughness, high-crack arrest steel for hydrogen pipelines obtained by the preparation method according to any one of claims 2 to 6 in hydrogen pipelines.

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