Steel, preparation method thereof and pipeline steel

Abstract

The invention provides steel, a preparation method thereof and pipeline steel, relates to the technical field of pipeline steel, and aims at solving the problem that existing pipeline steel for hydrogen conveying is poor in hydrogen resistance. The steel material comprises at least one of Nb, V and Ti, C, Si, S and Fe, and does not comprise at least one of Cu and Ni. Based on the total mass of the steel, the steel comprises, by mass percent, 0.025%-0.045% of C, 0.08%-0.20% of Si, smaller than or equal to 0.001% of S, and the total content of Nb, V and Ti is larger than or equal to 0.05%.

Description

Technical Field

[0001] This disclosure relates to the field of pipeline steel technology, and in particular to a type of steel and its preparation method, pipeline steel, especially pipeline steel for hydrogen transportation. Background Technology

[0002] Existing hydrogen pipeline steels have poor hydrogen resistance, with a hydrogen embrittlement sensitivity index exceeding 25% in high-pressure hydrogen environments, making them unsuitable for practical applications. Patented hydrogen pipeline steel technologies with better hydrogen resistance have high alloy and heat treatment costs, hindering market adoption. Summary of the Invention

[0003] The purpose of this disclosure is to provide a type of steel and its preparation method, as well as pipeline steel, which aims to solve the problem of poor hydrogen resistance of existing pipeline steel for hydrogen transportation.

[0004] To achieve the above objectives, the present disclosure adopts the following technical solution:

[0005] In a first aspect, this disclosure provides a steel material whose composition includes at least one of Nb, V, and Ti, as well as C, Si, S, and Fe, and excludes at least one of Cu and Ni; wherein, by mass percentage, the steel material composition includes: 0.025% to 0.045% C, 0.08% to 0.20% Si, S ≤ 0.001%, and the total content of Nb, V, and Ti ≥ 0.05%.

[0006] The inventors discovered that dispersed microparticles are formed in the steel disclosed herein. The precipitation of these microparticles in the steel forms a nanoscale phase, which can act as a hydrogen trap to capture hydrogen atoms, reduce hydrogen migration in the steel, hinder hydrogen diffusion, reduce hydrogen-induced embrittlement and crack propagation. Moreover, the nanoscale precipitated phase has a high interfacial area, providing abundant hydrogen trapping sites, enhancing hydrogen barrier properties, and improving the steel's resistance to hydrogen embrittlement.

[0007] In addition, the steel disclosed herein can reduce element segregation, reduce the brittleness of the steel, and improve the hardness, strength and / or wear resistance of the steel.

[0008] Therefore, the steel disclosed herein not only improves the strength of the steel but also forms microalloying elements. The nanophase hydrogen traps precipitated by these microalloying elements can significantly improve the hydrogen resistance of the steel. This reduces segregation, further enhancing the steel's hydrogen resistance, and the elements used are relatively inexpensive, resulting in a superior cost-performance ratio.

[0009] In some embodiments, the total content of Nb, V, and Ti is ≤0.11%.

[0010] In some embodiments, the mass percentage of Nb, when present, is 0.025% to 0.045% based on the total mass of the steel.

[0011] In some embodiments, the mass percentage of V, when present, is 0.015% to 0.040% based on the total mass of the steel.

[0012] In some embodiments, the mass percentage of Ti, when present, is 0.010% to 0.025% based on the total mass of the steel.

[0013] In some embodiments, the steel composition includes Nb, V and Ti.

[0014] In some embodiments, the steel composition does not contain Cu and Ni.

[0015] In some embodiments, the steel composition does not contain Mo.

[0016] In some embodiments, the metallographic structure of the steel does not include pearlite.

[0017] In some embodiments, the metallographic structure of the steel includes a diffusely distributed Mao island structure.

[0018] In some embodiments, the metallographic structure of the steel simultaneously comprises fine-grained quasi-polygonal ferrite, granular bainite, and dispersed Mao islands.

[0019] In some embodiments, the grain size of the steel is determined to be greater than grade 11.

[0020] In some embodiments, the steel composition further comprises one or more of Mn, Cr, Al, P, N, H, and O, wherein preferably, based on the total mass of the steel, the mass percentage of Mn is 1.10% to 1.40% when present; preferably, based on the total mass of the steel, the mass percentage of Cr is 0.20% to 0.30% when present; preferably, based on the total mass of the steel, the mass percentage of Al is ≤0.035% when present; preferably, based on the total mass of the steel, the mass percentage of P is ≤0.012% when present; preferably, based on the total mass of the steel, the mass percentage of N is ≤0.005% when present; preferably, based on the total mass of the steel, the mass percentage of H is ≤0.0002% when present; and preferably, based on the total mass of the steel, the mass percentage of O is ≤0.0030% when present.

[0021] In some embodiments, based on the total mass of the steel, the steel composition by mass percentage includes: 0.025%–0.045% C, 0.08%–0.20% Si, 1.10%–1.40% Mn, 0.20%–0.30% Cr, 0.025%–0.045% Nb, 0.015%–0.040% V, 0.010%–0.025% Ti, Al ≤ 0.035%, S ≤ 0.001%, P ≤ 0.012%, N ≤ 0.005%, H ≤ 0.0002%, O ≤ 0.0030%, with the balance being Fe and unavoidable impurities.

[0022] In some embodiments, the steel meets at least one of the following conditions:

[0023] The yield strength of steel at strains of 0.4% to 0.6% ranges from 435 MPa to 510 MPa.

[0024] The tensile strength of steel ranges from 525 MPa to 630 MPa.

[0025] The impact energy of steel at -18℃ to -22℃ is greater than or equal to 320J.

[0026] The Vickers hardness of steel ranges from 170 to 200.

[0027] The reduction of area of ​​the steel in a 6.3 MPa hydrogen atmosphere is greater than or equal to 68%.

[0028] The hydrogen embrittlement sensitivity index of steel is less than or equal to 19%.

[0029] Secondly, this disclosure provides a method for preparing steel. The method for preparing steel includes:

[0030] The raw materials are made into steel billets.

[0031] The steel billet is hot-rolled to obtain the initial steel product.

[0032] The initial steel is cooled to obtain steel containing at least one of Nb, V, and Ti, as well as C, Si, S, and Fe, but excluding at least one of Cu and Ni. Based on the total mass of the steel, the steel comprises, by mass percentage: 0.025%–0.045% C, 0.08%–0.20% Si, S ≤0.001%, and the total content of Nb, V, and Ti ≥0.05%.

[0033] Understandably, this disclosure provides a method for preparing steel, and the beneficial effects that can be achieved are similar to those of the steel described above, and will not be repeated here.

[0034] Making steel billets from raw materials includes making raw materials into cast billets, and then heating the cast billets to obtain steel billets.

[0035] Preferably, the low-magnification rating of the cast billet is less than or equal to C1.0.

[0036] Preferably, the billet is heated to a temperature range of 1190℃ to 1240℃.

[0037] The heating and heat preservation time ranges from 130 min to 160 min.

[0038] In some embodiments, the starting rolling temperature range for hot continuous rolling is 1050°C to 1100°C.

[0039] In some embodiments, the final rolling temperature range of hot continuous rolling is 850°C to 890°C.

[0040] In some embodiments, the reduction rate per pass of hot rolling is greater than 10%.

[0041] In some embodiments, the total reduction rate of hot rolling is greater than 70%.

[0042] In some embodiments, cooling includes reducing the initial steel from a temperature range of 740°C to 770°C to a temperature range of 490°C to 520°C.

[0043] In some embodiments, the cooling rate ranges from 15°C / s to 25°C / s.

[0044] Thirdly, this disclosure provides a type of steel. This steel is obtained by a method for preparing steel.

[0045] Understandably, this disclosure provides a type of steel whose beneficial effects can be referred to the beneficial effects of the steel described above, and will not be repeated here.

[0046] Fourthly, this disclosure provides a pipeline steel, which includes steel or is obtained by a method of preparing steel.

[0047] Understandably, this disclosure provides a pipeline steel for hydrogen transportation, the beneficial effects of which can be referred to the beneficial effects of the steel mentioned above, and will not be repeated here.

[0048] In some embodiments, the pipeline steel is pipeline steel for hydrogen transportation. Attached Figure Description

[0049] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 A flowchart of a method for preparing steel is provided as an embodiment of this disclosure;

[0051] Figure 2 This is a metallographic diagram of the steel used in Embodiment 1 of this disclosure;

[0052] Figure 3 The metallographic structure of the steel in Comparative Example 1 of this disclosure is shown in the diagram.

[0053] Figure 4 The metallographic structure of the steel in Comparative Example 2 of this disclosure is shown in the diagram. Detailed Implementation

[0054] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this disclosure.

[0055] In embodiments of this disclosure, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, article, or apparatus that includes that element.

[0056] In this disclosure, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or illustration. Any embodiment or design described as "exemplary" or "for example" in this disclosure should not be construed as being more preferred or advantageous than other embodiments or designs. Rather, the use of terms such as "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0057] Embodiments of this disclosure provide a pipeline steel for hydrogen transportation. This pipeline steel for hydrogen transportation is made of steel.

[0058] However, the hydrogen resistance of existing pipeline steel technology for hydrogen transportation is poor, with a hydrogen embrittlement sensitivity index greater than 25% in high-pressure hydrogen environments, which is difficult to meet practical needs.

[0059] In existing steel, precious alloying elements such as Cu, Ni, and Mo are usually added to improve hydrogen resistance. However, the addition of Cu (copper) and Ni (nickel) can easily cause segregation, which will reduce the hydrogen resistance of pipeline steel and increase costs.

[0060] Based on this, embodiments of the present disclosure provide a steel. The steel composition includes at least one of Nb (niobium), V (vanadium), and Ti (titanium), as well as C (carbon), Si (silicon), S (sulfur), and Fe (iron), and excludes at least one of Cu and Ni; wherein, based on the total mass of the steel, the steel contains, by mass percentage: 0.025% to 0.045% C, 0.08% to 0.20% Si, S ≤ 0.001%, and the total content of Nb, V, and Ti ≥ 0.05%.

[0061] For example, the mass fraction of C can be 0.025%, 0.028%, 0.030%, 0.033%, 0.035%, 0.040%, 0.044%, or 0.045%, etc., and there is no limitation here.

[0062] For example, the mass fraction of Si can be 0.08%, 0.10%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.19%, or 0.20%, etc., and there is no limitation here.

[0063] For example, the mass fraction of S can be 0.001%, 0.0008%, 0.0007%, 0.0006%, 0.0004%, or 0.0002%, etc., and there is no limitation here.

[0064] For example, the total content of Nb, V and Ti can be 0.05%, 0.06%, 0.07%, 0.08%, 0.09% or 0.1%, etc., and there is no limit here.

[0065] The embodiments of this disclosure provide a steel in which diffusely distributed microparticles are formed. The precipitation of these microparticles in the steel forms a nanoscale phase, which can act as a hydrogen trap to capture hydrogen atoms, reduce hydrogen migration in the steel, hinder hydrogen diffusion, reduce hydrogen-induced embrittlement and crack propagation, and the nanoscale precipitated phase has a high interface area, providing abundant hydrogen trapping sites, enhancing hydrogen barrier properties, and improving the steel's resistance to hydrogen embrittlement.

[0066] In addition, the steel disclosed herein can reduce element segregation, reduce the brittleness of the steel, and improve the hardness, strength and / or wear resistance of the steel.

[0067] Therefore, the steel disclosed herein not only improves the strength of the steel but also forms microalloying elements. The nanophase hydrogen traps precipitated by these microalloying elements can significantly improve the hydrogen resistance of the steel. This reduces segregation, further enhancing the steel's hydrogen resistance, and the elements used are relatively inexpensive, resulting in a superior cost-performance ratio.

[0068] In some embodiments, the total content of Nb, V, and Ti is ≤0.11%.

[0069] For example, the total content of Nb, V and Ti can be 0.055%, 0.065%, 0.075%, 0.085%, 0.095%, 0.105% or 0.11%, etc., and there is no limit here.

[0070] In some embodiments, the mass percentage of Nb, when present, is 0.025% to 0.045% based on the total mass of the steel.

[0071] For example, the mass fraction of Nb can be 0.025%, 0.030%, 0.032%, 0.033%, 0.035%, 0.040%, or 0.045%, etc., and there is no limitation here.

[0072] In some embodiments, the mass percentage of V, when present, is 0.015% to 0.040% based on the total mass of the steel.

[0073] For example, the mass fraction of V can be 0.015%, 0.020%, 0.025%, 0.027%, 0.030%, 0.035%, or 0.040%, etc., and there is no limitation here.

[0074] In some embodiments, the mass percentage of Ti, when present, is 0.010% to 0.025% based on the total mass of the steel.

[0075] For example, the mass fraction of Ti can be 0.010%, 0.012%, 0.014%, 0.015%, 0.016%, 0.017%, 0.018%, 0.020%, 0.022%, or 0.025%, etc., and there is no limitation here.

[0076] Understandably, by further setting the mass percentages of Nb, Ti, and Ni to within the ranges of 0.025%–0.045%, 0.010%–0.025%, and 0.010%–0.025%, it is possible to further improve the strength of the steel while simultaneously forming microalloying elements. The hydrogen traps in the nanophase precipitated by these microalloying elements can significantly improve the hydrogen resistance of the steel. This reduces segregation and further enhances the steel's hydrogen resistance.

[0077] In some embodiments, the steel composition includes Nb, V and Ti.

[0078] Understandably, the simultaneous presence of Nb, V, and Ti in the steel composition not only enhances its strength but also allows for the formation of microalloying elements. The hydrogen traps in the nanophase released by these microalloying elements significantly improve the steel's hydrogen resistance. This reduces segregation and further enhances the steel's hydrogen resistance.

[0079] In some embodiments, the steel composition does not contain Cu and Ni.

[0080] Understandably, omitting Cu and Ni from the steel composition can further reduce elemental segregation, reduce the steel's brittleness, and improve its hardness, strength, and / or wear resistance; it also reduces costs and offers better cost-effectiveness.

[0081] In some embodiments, the steel composition does not contain Mo.

[0082] Understandably, the absence of Mo in the steel composition can further reduce elemental segregation, reduce the brittleness of the steel, and improve the hardness, strength, and / or wear resistance of the steel; it also reduces costs and has a better cost performance.

[0083] In some embodiments, the metallographic structure of the steel does not include pearlite.

[0084] In some embodiments, the metallographic structure of the steel includes a diffusely distributed Mao island structure.

[0085] In some embodiments, the metallographic structure of the steel simultaneously comprises fine-grained quasi-polygonal ferrite, granular bainite, and dispersed Mao islands.

[0086] Understandably, fine-grained quasi-polygonal ferrite gives the grains a near-polygonal shape. The fine grains provide good deformability. Granular bainite, formed by the rapid or controlled cooling of austenite, is a steel microstructure containing fine bainite lamellae dispersed in a granular form, which improves the toughness of the steel. Dispersed martensite islands refer to martensite dispersed as fine particles within other microstructures, forming a uniform reinforcing phase, which increases the strength of the steel and improves its high-strength crack resistance. Furthermore, the absence of pearlite in the microstructure reduces the risk of brittle fracture in steel, making it more ductile and tough under stress.

[0087] In some embodiments, the grain size of the steel is greater than grade 11, as determined according to GB / T 6394-2017 standard.

[0088] Understandably, a grain size greater than 11 indicates that the grains are relatively large or coarse, which can reduce grain boundaries, reduce weak surfaces caused by hydrogen embrittlement, enhance the steel's resistance to hydrogen embrittlement, and reduce the risk of brittle fracture caused by hydrogen.

[0089] In some embodiments, the steel composition further comprises one or more of Mn, Cr, Al, P, N, H, and O, wherein preferably, based on the total mass of the steel, the mass percentage of Mn is 1.10% to 1.40% when present; preferably, based on the total mass of the steel, the mass percentage of Cr is 0.20% to 0.30% when present; preferably, based on the total mass of the steel, the mass percentage of Al is ≤0.035% when present; preferably, based on the total mass of the steel, the mass percentage of P is ≤0.012% when present; preferably, based on the total mass of the steel, the mass percentage of N is ≤0.005% when present; preferably, based on the total mass of the steel, the mass percentage of H is ≤0.0002% when present; and preferably, based on the total mass of the steel, the mass percentage of O is ≤0.0030% when present.

[0090] For example, the mass fraction of Mn can be 1.10%, 1.11%, 1.15%, 1.20%, 1.21%, 1.25%, 1.30%, 1.35%, or 1.40%, etc., and there is no limitation here.

[0091] For example, the mass fraction of Cr can be 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.26%, 0.28%, or 0.30%, etc., and there is no limitation here.

[0092] For example, the mass fraction of Al can be 0.035%, 0.033%, 0.032%, 0.031%, 0.025%, 0.020%, 0.015%, or 0.010%, etc., and there is no limitation here.

[0093] For example, the mass fraction of P can be 0.012%, 0.010%, 0.009%, 0.008%, 0.006%, or 0.004%, etc., and there is no limitation here.

[0094] For example, the mass fraction of N can be 0.005%, 0.004%, 0.0036%, 0.0033%, 0.0032%, 0.003%, 0.002%, or 0.001%, etc., and there is no limitation here.

[0095] For example, the mass fraction of H can be 0.0002%, 0.00018%, 0.00016%, 0.00014%, 0.00012%, 0.00009%, 0.00008%, or 0.00007%, etc., and there is no limitation here.

[0096] For example, the mass fraction of O can be 0.0030%, 0.0028%, 0.0027%, 0.0026%, 0.0025%, 0.0024%, 0.0022%, or 0.0020%, etc., and there is no limitation here.

[0097] Understandably, further adding less than or equal to 0.035% Al, 1.10%–1.40% Mn, and 0.20%–0.30% Cr can refine the grains and act as hardness and strength enhancing elements, reducing brittle fracture tendency, improving the plasticity and toughness of steel, and enhancing its hardness, strength, wear resistance, and fatigue resistance. Simultaneously, adding less than or equal to 0.005% N, less than or equal to 0.0002% H, and less than or equal to 0.0030% O can reduce the impact on steel properties. Furthermore, combining 0.025%–0.045% C, 0.08%–0.20% Si, 0.025%–0.045% Nb, 0.015%–0.040% V, and 0.010%–0.025% Ti can further improve the steel's resistance to hydrogen embrittlement and mechanical properties.

[0098] In some embodiments, based on the total mass of the steel, the steel composition by mass percentage includes: 0.025%–0.045% C, 0.08%–0.20% Si, 1.10%–1.40% Mn, 0.20%–0.30% Cr, 0.025%–0.045% Nb, 0.015%–0.040% V, 0.010%–0.025% Ti, Al ≤0.035%, S ≤0.001%, P ≤0.012%, N ≤0.005%, H ≤0.0002%, O ≤0.0030%, with the balance being Fe and unavoidable impurities.

[0099] Understandably, the above setup allows for the formation of microalloying elements while simultaneously increasing the strength of the steel. The hydrogen traps in the nanophase released by these microalloying elements significantly improve the steel's hydrogen resistance. This reduces segregation, further enhancing the steel's hydrogen resistance, and the use of relatively low-cost elements results in a superior cost-performance ratio.

[0100] In some embodiments, the steel meets at least one of the following conditions:

[0101] The yield strength of steel at strains of 0.4% to 0.6% ranges from 435 MPa to 510 MPa.

[0102] For example, the yield strength of steel at a strain of 0.4% to 0.6% can be 435MPa, 450MPa, 475MPa, 490MPa or 510MPa, etc., and there is no limitation here.

[0103] Understandably, the yield strength of steel at a strain of 0.4% to 0.6% is in the range of 435 MPa to 510 MPa, indicating that the steel has a high yield strength within the strain range of 0.4% to 0.6%, making it suitable for bearing certain loads without permanent deformation.

[0104] The tensile strength of steel ranges from 525 MPa to 630 MPa.

[0105] For example, the tensile strength of the steel can be 525MPa, 550MPa, 575MPa, 600MPa or 630MPa, etc., and there is no limitation here.

[0106] Understandably, steel with a tensile strength in the range of 525MPa to 630MPa indicates that it has a high tensile limit and exhibits good tensile strength, making it suitable for structural applications with heavy loads or requiring high strength.

[0107] The impact energy of steel at -18℃ to -22℃ is greater than or equal to 320J.

[0108] For example, the impact energy of steel at -18℃ to -22℃ can be 320J, 330J, 340J, 350J or 360J, etc., and there is no limit here.

[0109] Understandably, steel has high toughness at temperatures between -18℃ and -22℃ and can withstand large impact loads, indicating that steel has good impact resistance and is suitable for impact vibration environments.

[0110] The Vickers hardness of steel ranges from 170 to 200.

[0111] For example, the Vickers hardness of the steel can be 170, 180, 190 or 200, etc., and there is no limitation here.

[0112] Understandably, a Vickers hardness of 170 to 200 indicates that the steel is in a relatively medium hardness range, meaning that the steel has a certain degree of hardness, which can ensure a certain degree of wear resistance without being too brittle.

[0113] The reduction of area of ​​the steel in a 6.3 MPa hydrogen atmosphere is greater than or equal to 68%.

[0114] For example, the reduction of area of ​​steel in a 6.3MPa hydrogen environment can be 68%, 69%, 70%, 71% or 72%, etc., and there is no limitation here.

[0115] Understandably, a steel with a section reduction of area greater than or equal to 68% in a 6.3MPa hydrogen environment indicates that the steel has good hydrogen resistance, can maintain high plasticity and toughness in a hydrogen environment, and is not prone to cracking or fracture.

[0116] The hydrogen embrittlement sensitivity index of steel is less than or equal to 19%.

[0117] For example, the hydrogen embrittlement sensitivity index of steel can be 19%, 18%, 17%, 16% or 15%, etc., and there is no limitation here.

[0118] Understandably, a hydrogen embrittlement sensitivity index of steel of less than or equal to 19% indicates that the steel is less sensitive to hydrogen embrittlement, the performance degradation caused by hydrogen is relatively minor, and it has good toughness and reliability in hydrogen-containing environments.

[0119] Currently, some methods improve the hydrogen resistance of steel by performing complex heat treatments during the steel preparation process, such as tempering after hot rolling. However, the cost of heat treatment is relatively high, which is not conducive to market promotion and application.

[0120] Embodiments of this disclosure provide a method for preparing steel. For example... Figure 1 As shown, the preparation method of this steel includes: S1 to S3.

[0121] S1: The raw materials are made into steel billets.

[0122] S2: The steel billet is hot-rolled to obtain the initial steel product.

[0123] S3: Cool the initial steel, coil it to obtain steel, the steel composition of which includes at least one of Nb, V and Ti, as well as C, Si, S and Fe, and does not include at least one of Cu and Ni; wherein, by mass percentage, the steel composition includes: 0.025% to 0.045% C, 0.08% to 0.20% Si, S≤0.001%, and the total content of Nb, V and Ti ≥0.05%.

[0124] Understandably, S1 forms the raw material into a steel billet, then S2 hot-rolls the billet to improve material consistency, transforming the billet into the required thickness and shape to form the initial steel. S4 cools the initial steel and then winds it into a coil. Moreover, the steel preparation method disclosed herein can obtain steel with good hydrogen resistance without complex heat treatment, resulting in low cost and facilitating market promotion and application.

[0125] S1 involves making the raw materials into steel billets, including making the raw materials into castings and then heating the castings to obtain steel billets.

[0126] For example, the raw materials are melted into molten iron and then subjected to desulfurization, decarburization, deoxidation, and impurity removal treatments before continuous casting to obtain a cast billet. The cast billet is then heated to obtain a steel billet.

[0127] For example, S1 melts the raw materials into molten iron and then performs desulfurization, decarburization, deoxidation and impurity removal treatments before continuous casting to obtain a billet. The billet's low-magnification rating is less than or equal to C1.0.

[0128] Here, low-magnification rating is a classification of the quality or defects inside the billet. According to GB / T9711-23, it mainly reflects the uniformity of the internal structure, grain structure, and distribution of inclusions and defects inside the billet.

[0129] Understandably, a low-magnification rating of C1.0 or less indicates that the billet has good microstructure uniformity, high quality, and few internal defects. This means that the billet has fewer microscopic defects and impurities, which facilitates subsequent heat treatment and grain refinement processes. It can reduce the proportion of ferrite (high ferrite content has an adverse effect on the strength, hardness, and wear resistance of steel), thereby improving the mechanical properties of steel.

[0130] For example, the billet is heated to a temperature range of 1190°C to 1240°C.

[0131] For example, the heating temperature of the billet can be 1190℃, 1200℃, 1210℃, 1220℃, 1230℃ or 1240℃, etc., and there is no limit here.

[0132] Understandably, setting the billet heating temperature within the range of 1190℃ to 1240℃ allows for the full dissolution of Nb, V, and Ti elements, forming microalloys and resulting in fine, uniform carbides and nitrides. This refines the original austenite grain size in the billet, thereby improving the steel's hydrogen resistance.

[0133] For example, the billet is heated, and the holding time ranges from 130 min to 160 min.

[0134] For example, the holding time for heating the billet can be 130 min, 140 min, 150 min or 160 min, etc., and there is no limit here.

[0135] Understandably, setting the holding time for billet heating within the range of 130 min to 160 min allows Nb, V, and Ti elements to fully diffuse and dissolve, forming fine carbide / nitride strengthening phases, effectively refining austenite grains, thereby obtaining a finer grain structure during S4 cooling, and thus improving the hydrogen resistance of the steel.

[0136] In some embodiments, S2 hot-rolls the steel billet, with the initial rolling temperature range being 1050°C to 1100°C and the final rolling temperature range being 850°C to 890°C.

[0137] For example, the initial rolling temperature of hot continuous rolling can be 1050℃, 1060℃, 1070℃, 1080℃, 1090℃ or 1100℃, etc., and there is no limit here.

[0138] For example, the final rolling temperature of hot continuous rolling can be 850°C, 860°C, 870°C, 880°C or 890°C, etc., and there is no limit here.

[0139] Understandably, setting the initial rolling temperature of hot continuous rolling within the range of 1050℃ to 1100℃ results in higher plasticity of the billet, reducing deformation resistance and facilitating deformation. This allows for greater deformation of the billet in the austenitic region, preventing cracks and strain concentration during deformation. It also contributes to grain refinement and microstructure homogenization, which is beneficial for subsequent microstructure adjustment. Furthermore, setting the final rolling temperature of hot continuous rolling within the range of 850℃ to 890℃ allows the austenite in the billet to further transform into a finer microstructure. This helps control the grain size of the steel, thereby achieving grain refinement and obtaining a fine-grained quasi-polygonal ferrite microstructure, granular bainite microstructure, and dispersed austenite microstructure, thus improving the mechanical properties of the steel.

[0140] In some embodiments, the reduction rate per pass of hot rolling is greater than 10%, and the total reduction rate of hot rolling is greater than 70%.

[0141] For example, the reduction rate per pass in hot rolling can be 10%, 11%, 12%, 13% or 14%, etc., and there is no limitation here.

[0142] For example, the total reduction rate of hot rolling can be 70%, 71%, 72%, 73% or 74%, etc., and there is no limitation here.

[0143] Understandably, setting the reduction rate per pass in hot continuous rolling to be greater than 10%, meaning that the deformation of the billet in each rolling pass accounts for more than 10% of the original thickness, provides higher deformation efficiency. This avoids requiring more deformation passes, reduces process time, and promotes grain breakage and refinement through larger deformation amounts, improving microstructure uniformity and contributing to the formation of fine, uniform grain structures. It also promotes the breakage and refinement of austenite, contributing to the formation of fine grains and improving the toughness of the steel. Simultaneously, setting the total reduction rate in hot continuous rolling to be greater than 70%, meaning that the entire hot continuous rolling process compresses more than 70% of the original thickness, ensures sufficient overall deformation to achieve the desired microstructure refinement and performance improvement goals. This allows deformation to be fully transferred and distributed throughout the rolling process, promoting microstructure uniformity.

[0144] In some embodiments, S3 cools the initial steel, and the cooling includes: using water to reduce the initial steel from a temperature range of 740°C to 770°C to a temperature range of 490°C to 520°C.

[0145] For example, the initial temperature of the initial steel can be 770°C, 760°C, 750°C or 740°C, etc., and there is no limitation here.

[0146] For example, the initial finishing temperature of the steel can be 490°C, 500°C, 510°C, 520°C, or 530°C, etc., and there is no limitation here.

[0147] Understandably, by utilizing the high thermal conductivity and cooling rate of water, the initial steel can be cooled quickly from a higher temperature range to the target temperature range. With phase transformation control, the austenite structure can be further transformed into a finer structure. Setting the initial steel temperature range from 740℃~770℃ to 490℃~520℃ is conducive to the formation of fine-grained quasi-polygonal ferrite, granular bainite, and dispersed Mao island structure in the steel, thereby improving the performance of the steel.

[0148] In some embodiments, the cooling rate ranges from 15°C / s to 25°C / s.

[0149] For example, the cooling rate can be 15℃ / s, 17℃ / s, 19℃ / s, 21℃ / s, 23℃ / s or 25℃ / s, etc., and there is no limit here.

[0150] Understandably, during steel manufacturing, uneven segregation can easily lead to the formation of banded pearlite, which manifests as fine-grained banded structures distributed along grain boundaries or grain regions. Higher cooling rates can reduce intergranular migration and segregation of austenite, inhibiting the continuous growth of banded structures along grain boundaries, thus achieving grain refinement and structural homogenization. Therefore, setting the cooling rate within the range of 15℃ / s to 25℃ / s can interrupt the intergranular migration paths of segregation and banded structures, forming a uniform and fine structure. This effectively suppresses banded structures, avoids the formation of wide and coarse structures, improves structural uniformity, optimizes the microstructure, and forms fine-grained, uniform pearlite or bainite, resulting in a grain size greater than grade 11. The resulting microstructure consists of fine-grained quasi-polygonal ferrite, granular bainite, and dispersed Mao islands, reducing the pearlite structure that is detrimental to the steel's hydrogen resistance. This allows the steel to not only possess good hydrogen resistance but also high strength and toughness.

[0151] For example, the steel prepared by the steel preparation method in the above embodiments has a ferrite and pearlite structure of 35%, and a polygonal ferrite, granular bainite and pearlite structure of 30%. The steel prepared by the steel preparation method of this disclosure is applicable to X60 grade (yield strength ≥ 415 MPa) pipeline steel, and has low cost and excellent hydrogen resistance.

[0152] Example 1

[0153] Example 1 provides a type of steel. The preparation method of this steel includes steps (1) to (4).

[0154] Step (1): After melting the iron ore raw material into molten iron and treating it with desulfurization, decarburization and deoxidation, other alloy raw materials are added and impurities are removed. Then, continuous casting is carried out to obtain the billet.

[0155] Step (2): Heat the billet to 1215℃ and hold for 145 minutes to obtain the steel billet.

[0156] Step (3): The steel billet is hot rolled continuously at an initial rolling temperature of 1100℃ and a finishing rolling temperature of 850℃. The reduction rate of each pass is greater than 10%, and the total reduction rate is greater than 70%, to obtain the initial steel.

[0157] Step (4): The initial steel is cooled with water from 750°C to 500°C at a rate of 20°C / s, and then coiled to obtain steel. The composition of the steel by mass percentage includes: 0.033% C, 0.15% Si, 1.21% Mn, 0.008% P, 0.0008% S, 0.031% Al, 0.21% Cr, 0.035% Nb, 0.025% V, 0.014% Ti, 25ppm O, 33ppm N, 0.9ppm H, with the balance being Fe and unavoidable impurities.

[0158] Figure 2 The metallographic diagram of the steel of Example 1 of this disclosure shows that the unique microstructure of the steel of Example 1 is fine-grained quasi-polygonal ferrite, granular bainite and dispersed Mao islands. The grain size of the fine-grained quasi-deformed ferrite is mostly below 6 μm, and the pearlite microstructure that is detrimental to the hydrogen resistance of the steel is eliminated.

[0159] Example 2

[0160] Example 2 provides a steel. The preparation method of this steel is the same as that of Example 1, except that the composition of this steel, by mass percentage, includes: 0.028% C, 0.16% Si, 1.35% Mn, 0.009% P, 0.0007% S, 0.033% Al, 0.23% Cr, 0.033% Nb, 0.027% V, 0.015% Ti, 26 ppm O, 36 ppm N, 0.8 ppm H, with the balance being Fe and unavoidable impurities.

[0161] Example 3

[0162] Example 3 provides a steel. The preparation method of this steel is the same as that of Example 1, except that the composition of this steel, by mass percentage, includes: 0.044% C, 0.19% Si, 1.11% Mn, 0.008% P, 0.0006% S, 0.032% Al, 0.22% Cr, 0.032% Nb, 0.030% V, 0.017% Ti, 27 ppm O, 32 ppm N, 0.7 ppm H, with the balance being Fe and unavoidable impurities.

[0163] Comparative Example 1

[0164] Comparative Example 1 provides a steel. The preparation method of this steel is the same as that of Example 1, except that the composition of this steel, by mass percentage, includes: 0.063% C, 0.20% Si, 1.38% Mn, 0.011% P, 0.0015% S, 0.028% Al, 0.032% Nb, 0.017% Ti, 29 ppm O, 41 ppm N, 0.9 ppm H, with the balance being Fe and unavoidable impurities.

[0165] Figure 3 The metallographic diagram of the steel of Comparative Example 1 of this disclosure shows that the microstructure of the steel of Comparative Example 1 is ferrite and pearlite.

[0166] Comparative Example 2

[0167] Comparative Example 2 provides a steel. The preparation method of this steel is the same as that of Example 1, except that the composition of this steel, by mass percentage, includes: 0.042% C, 0.21% Si, 1.35% Mn, 0.009% P, 0.0008% S, 0.030% Al, 0.13% Cu, 0.22% Cr, 0.15% Ni, 0.029% Nb, 0.018% V, 0.012% Ti, 28 ppm O, 26 ppm N, 0.8 ppm H, with the balance being Fe and unavoidable impurities.

[0168] Figure 4 The image shows the metallographic structure of the steel in Comparative Example 2 of this disclosure. The steel in Comparative Example 2 has a microstructure of polygonal ferrite, granular bainite and pearlite.

[0169] In the above embodiments and comparative examples, 1 ppm equals 0.0001%; ​​for example, 41 ppm = 0.0041%.

[0170] Performance testing

[0171] The mechanical properties and hydrogen resistance under slow strain rate tensile stress in a hydrogen environment of the steels used in the examples and comparative examples were tested, and the results are shown in Table 1 below.

[0172] Here, the mechanical testing standard refers to GB / T 9711-2023, and the hydrogen resistance performance testing standard refers to GB34542.2018.

[0173] Table 1. Mechanical properties and hydrogen resistance under slow strain rate tensile stress in a hydrogen environment for the steels of the examples and comparative examples.

[0174]

[0175] It can be seen that the hydrogen embrittlement sensitivity index of the steel in Example 1 is 18%, that of the steel in Example 2 is 19%, and that of the steel in Example 3 is 17%, exhibiting excellent hydrogen resistance while maintaining good mechanical properties. Compared with Example 1, Example 2 further reduced the C content while increasing the Mn content; Example 3 further increased the C content but reduced the Mn content.

[0176] The hydrogen resistance and mechanical properties of the steels in Examples 1-3 and Comparative Examples 1 and 2 show that the steels in Examples 1-3 have reduced the content of easily segregated elements such as S, P, C, Mn, Si, and Al, and improved the strength of the steels. They also exhibit a unique fine-grained quasi-polygonal ferrite, granular bainite, and dispersed Mao island structure, resulting in steels with excellent hydrogen resistance and toughness, suitable for X60 grade hydrogen transportation pipeline steel.

[0177] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0178] The above are merely specific embodiments of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A type of steel, characterized in that, The steel composition includes: It contains at least one of Nb, V and Ti, and C, Si, S and Fe, but does not contain at least one of Cu and Ni; Based on the total mass of the steel, the steel comprises, by mass percentage: 0.025% to 0.045% C, 0.08% to 0.20% Si, S ≤ 0.001%, and the total content of Nb, V and Ti ≥ 0.05%.

2. The steel according to claim 1, characterized in that, in: The total content of Nb, V and Ti is ≤0.11%; and / or, Based on the total mass of the steel, the mass percentage of Nb, when present, is 0.025% to 0.045%; and / or, Based on the total mass of the steel, the mass percentage of V, when present, is 0.015% to 0.040%; and / or, Based on the total mass of the steel, the mass percentage of Ti, when present, is 0.010% to 0.025%; and / or, The steel composition simultaneously includes Nb, V, and Ti; and / or, The steel composition does not contain Cu and Ni; and / or, The steel composition does not contain Mo; and / or, The metallographic structure of the steel does not include pearlite; and / or, The metallographic structure of the steel includes a diffusely distributed Mao island structure; and / or, The metallographic structure of the steel simultaneously includes fine-grained quasi-polygonal ferrite, granular bainite, and dispersed Mao islands; and / or According to GB / T 6394-2017 standard, the grain size of the steel is greater than grade 11; and / or, The steel composition further includes one or more of Mn, Cr, Al, P, N, H, and O, wherein preferably, based on the total mass of the steel, the mass percentage of Mn is 1.10% to 1.40% when present; preferably, based on the total mass of the steel, the mass percentage of Cr is 0.20% to 0.30% when present; preferably, based on the total mass of the steel, the mass percentage of Al is ≤0.035% when present; preferably, based on the total mass of the steel, the mass percentage of P is ≤0.012% when present; preferably, based on the total mass of the steel, the mass percentage of N is ≤0.005% when present; preferably, based on the total mass of the steel, the mass percentage of H is ≤0.0002% when present; and preferably, based on the total mass of the steel, the mass percentage of O is ≤0.0030% when present.

3. The steel according to claim 1 or 2, characterized in that, Based on the total mass of the steel, the steel composition, by mass percentage, comprises: 0.025%–0.045% C, 0.08%–0.20% Si, 1.10%–1.40% Mn, 0.20%–0.30% Cr, 0.025%–0.045% Nb, 0.015%–0.040% V, 0.010%–0.025% Ti, Al ≤ 0.035%, S ≤ 0.001%, P ≤ 0.012%, N ≤ 0.005%, H ≤ 0.0002%, O ≤ 0.0030%, with the balance being Fe and unavoidable impurities.

4. The steel according to claim 1 or 2, characterized in that, The steel material satisfies at least one of the following conditions: The yield strength of the steel at a strain of 0.4% to 0.6% ranges from 435 MPa to 510 MPa. The tensile strength of the steel is in the range of 525MPa to 630MPa; The impact energy of the steel at -18℃ to -22℃ is greater than or equal to 320J; The Vickers hardness of the steel is in the range of 170 to 200. The steel exhibits a reduction of area of ​​68% or greater under a hydrogen atmosphere of 6.3 MPa. The hydrogen embrittlement sensitivity index of the steel is less than 30%, less than or equal to 25%, less than or equal to 19%, or less than or equal to 17%.

5. A method for preparing steel, characterized in that, include: The raw materials are processed into steel billets; The steel billet is hot-rolled to obtain the initial steel product; The initial steel is cooled to obtain the steel, the steel composition of which includes at least one of Nb, V and Ti, as well as C, Si, S and Fe, and does not include at least one of Cu and Ni; Based on the total mass of the steel, the steel comprises, by mass percentage: 0.025% to 0.045% C, 0.08% to 0.20% Si, S ≤ 0.001%, and the total content of Nb, V and Ti ≥ 0.05%.

6. The method for preparing steel according to claim 5, characterized in that, The process of making steel billets from raw materials includes making castings from raw materials and then heating the castings to obtain the steel billets. Preferably, the low-magnification rating of the cast billet is less than or equal to C1.

0. Preferably, the heating of the billet is carried out at a temperature range of 1190℃ to 1240℃; and / or the holding time of the heating is carried out at a temperature range of 130min to 160min.

7. The method for preparing steel according to claim 5, characterized in that, in: The starting rolling temperature range of the hot continuous rolling is 1050℃~1100℃; and / or, The final rolling temperature range of the hot continuous rolling is 850℃~890℃; and / or, The reduction rate per pass of the hot continuous rolling is greater than 10%; And / or, The total reduction rate of the hot continuous rolling is greater than 70%, and / or, The cooling includes: reducing the initial steel temperature from a range of 740°C to 770°C to a range of 490°C to 520°C; and / or, The cooling rate ranges from 15°C / s to 25°C / s.

8. Steel prepared by any one of claims 5 to 7.

9. A pipeline steel, characterized in that, The pipeline steel includes steel as described in any one of claims 1 to 4 or steel prepared by the method described in any one of claims 5 to 7.

10. The pipeline steel according to claim 9, characterized in that, The pipeline steel mentioned above is pipeline steel for hydrogen transportation.

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