Steel for hydrogen transmission pipeline and production method thereof

Abstract

The invention discloses steel for a hydrogen transmission pipeline and a production method of the steel. The continuous casting billet comprises the following chemical components: 0.01 to 0.04 percent of C, 0.12 to 0.18 percent of Si, 0.45 to 0.6 percent of Mn, 0.12 to 0.22 percent of Cr, 0.08 to 0.18 percent of Ni, 0.11 to 0.21 percent of Cu, 0.025 to 0.035 percent of Nb, 0.016 to 0.028 percent of Ti, 0.021 to 0.049 percent of Alt, 5 to 12 ppm of Mg and 12 to 42 ppm of Ca. In the production method, the heating temperature of a casting blank is TMnS-10 DEG C to TMnS + 20 DEG C, and during controlled rolling, the finish rolling temperature is Ar3-30 DEG C to Ar3; during controlled cooling, the water inlet temperature is larger than or equal to Ar3-80 DEG C, the cooling speed is 10-20 DEG C / s, and the final cooling temperature is Bs-140-Bs-70 DEG C.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material preparation, and relates to steel for hydrogen transmission pipeline and a production method thereof. Background Art

[0002] As one of the cleanest energy sources, hydrogen energy is becoming the first choice to replace non-renewable energy with its high energy conversion efficiency and environmental protection characteristics. The storage and transportation of hydrogen energy through pipelines is one of the important links in the development of the hydrogen energy industry, and the material used for pipelines is mainly steel.

[0003] The application of hydrogen pipelines poses severe challenges to steel. Specifically, steel used for hydrogen pipelines needs to have excellent mechanical properties, low-temperature toughness, and excellent hydrogen resistance. This is because during the use of hydrogen pipelines, hydrogen can enter the steel through adsorption, dissociation, penetration, etc., and will accumulate locally in the steel, resulting in a decrease in the performance of the steel, such as hydrogen-induced plasticity loss, hydrogen-induced cracking, and hydrogen-induced delayed fracture.

[0004] In the prior art, either mechanical properties, low-temperature toughness and hydrogen resistance cannot be taken into account at the same time, such as poor hydrogen resistance, or, as in CN113862549A, although quenching + tempering can be used to ensure hydrogen resistance, the additional heat treatment process leads to a long production cycle and high cost.

[0005] Therefore, how to improve the mechanical properties, low-temperature toughness and hydrogen resistance of steel used for hydrogen pipelines and avoid problems such as high production costs and low efficiency will have huge safety and economic benefits in the development of steel used for hydrogen pipelines. Summary of the invention

[0006] The object of the present invention is to provide a steel for hydrogen transmission pipeline and a production method thereof.

[0007] To achieve the above-mentioned purpose, an embodiment of the present invention provides a method for producing steel for hydrogen pipelines. The production method comprises: The continuous casting billet is prepared by smelting and continuous casting; the chemical composition of the continuous casting billet includes, by mass percentage, C 0.010-0.040%, Si 0.12-0.18%, Mn 0.45-0.60%, P≤0.008%, S≤0.0012%, Cr 0.12-0.22%, Ni 0.08-0.18%, Cu 0.11-0.21%, Nb 0.025-0.035%, Ti 0.016-0.028%, Alt 0.021-0.049%, Mg 0.0005-0.0012%, Ca 0.0012-0.0042%, and the rest is iron and unavoidable impurities; Continuous casting billet heating: heating temperature is T MnS-10°C to T MnS +20°C, T MnS = 11625 / (5.02 - lg([Mn]×[S])) - 272.15; Controlled rolling: After the continuous casting billet exits the heating furnace, two-stage rolling is carried out; the starting rolling temperature T in the first stage MnS -130°C to T MnS -30°C, the starting rolling temperature A in the second stage r3 +20°C to A r3 +60°C, the finishing rolling temperature A r3 -30°C to A r3 , the thickness of the steel plate after rolling in the first stage is more than 4 times that of the steel plate after rolling in the second stage; Controlled cooling: Cool the steel plate obtained by controlled rolling, the water entry temperature ≥ A r3 -80°C, the cooling rate is 10 - 20°C / s, and the final cooling temperature is Bs - 140°C to Bs - 70°C.

[0008] Preferably, for the heating of the continuous casting billet: according to the thickness of the continuous casting billet, the heating duration is 1.1 - 1.5 min / mm.

[0009] Preferably, A r3 = 910 - 310[C] - 80[Mn] - 20[Cu] - 15[Cr] - 55[Ni]; Bs = 630 - 45[Mn] - 35[Si] - 30[Cr] - 20[Ni]; In the formula, [C], [Mn], [Cu], [Cr], [Ni], [Si] are respectively the mass percentages of C, Mn, Cu, Cr, Ni, Si in the continuous casting billet.

[0010] Preferably, the smelting includes: in sequence, hot metal pre-desulfurization, converter smelting, LF refining, RH refining; among them, the RH refining includes: the temperature of the molten steel entering the station is 1620 - 1660°C, first blow argon from the bottom at a flow rate of 4 - 5 Nm 3 / h for 1 - 2 min, then vacuum standstill, and then break the vacuum and feed in calcium wire to control the Ca / S mass ratio in the molten steel to be 2 - 4 and the Ca / Alt mass ratio to be above 0.06; then stir statically for 2 - 3 min, add magnesium alloy to control the Mg mass ratio in the molten steel to be 0.0005 - 0.0012%, and finally blow argon from the bottom.

[0011] Preferably, the "then vacuum standstill" includes: standing still for 25 - 30 min under a vacuum degree of ≤ 30 Pa.

[0012] Preferably, the "finally blow argon from the bottom" includes: at a flow rate of 1 Nm 3Blow argon at a flow rate below / h.

[0013] Preferably, the hot metal pre-desulfurization includes: mixing magnesium powder and lime powder and then injecting them into the hot metal to control the mass ratio of S in the hot metal within 0.0012%; the injection amount of magnesium powder is 0.35 - 0.45 Kg per ton of hot metal.

[0014] Preferably, the converter smelting includes: making a slag with an alkalinity of 3.0 - 3.6 and controlling the mass ratio of P within 0.005%.

[0015] Preferably, the LF refining includes: after alloying is completed, feeding in aluminum wire to control the mass ratio of O within 0.0040%, and then tapping the steel.

[0016] Preferably, the continuous casting includes: when casting, the superheat of the molten steel is 8 - 20 °C, and the casting speed is 0.1×L / F - 0.05 - 0.1×L / F + 0.05 m / s, where L and F are the perimeter and area of the cross-section of the continuous casting billet respectively.

[0017] To achieve the above invention object, an embodiment of the present invention provides a pipeline steel. The chemical composition of the steel in mass percentage includes: C 0.010 - 0.040%, Si 0.12 - 0.18%, Mn 0.45 - 0.60%, P≤0.008%, S≤0.0012%, Cr 0.12 - 0.22%, Ni 0.08 - 0.18%, Cu 0.11 - 0.21%, Nb 0.025 - 0.035%, Ti 0.016 - 0.028%, Alt 0.021 - 0.049%, Mg 0.0005 - 0.0012%, Ca 0.0012 - 0.0042%, and the rest is iron and inevitable impurities.

[0018] Preferably, the steel is a steel plate with a thickness ≤ 25 mm, the hydrogen diffusion coefficient D ≤ 1.5×10 -6 cm 2 / s, the yield strength is 380 - 450 MPa, the tensile strength is 480 - 550 MPa, the elongation is ≥ 40%, the yield ratio is ≤ 0.88, the impact energy at -40 °C is ≥ 300 J, and the drop weight tear test shear area ratio at -15 °C is ≥ 95%.

[0019] Preferably, the steel is a steel plate with a thickness ≤ 25 mm, the diffusible free hydrogen concentration C0 on the cathode side ≤ 3.0×10 - 6 mol / cm 3, the yield strength is 380 - 450 MPa, the tensile strength is 480 - 550 MPa, the elongation is ≥40%, the yield ratio is ≤0.88, the impact energy at -40°C is ≥300 J, and the DWTT drop hammer shear area ratio at -15°C is ≥95%.

[0020] Preferably, some or all of the non-metallic inclusions in the steel have a core-shell structure, the core is MgO·Al2O3, and the shell is MnS, CaS, TiN and coats the outer surface of the inner shell.

[0021] Preferably, the density of the non-metallic inclusions in the steel is 40 - 70 per mm 2 , the average diameter is ≤2 μm, the proportion with a diameter ≥15 μm is 0%, the proportion with a diameter of 10 - 15 μm is ≤1%, the proportion with a diameter of 6 - 10 μm is ≤5%, and the proportion with a diameter of 0 - 6 μm is ≥94%.

[0022] Preferably, the chemical composition of the steel also satisfies any one or both of the following two conditions in terms of mass percentage: 0.02 ≤ Mg / Alt ≤ 0.04; 0.01% ≤ Mg × Alt / S ≤ 0.06%.

[0023] Preferably, the central segregation of the continuous casting billet is ≤C1.5 or B1.0, A-class segregation is not allowed, the central porosity is ≤0.5 grade, and the diameter of Al2O3 inclusions is ≤1.0 grade; The carbon segregation ratio of the steel plate is ≤105%, the manganese segregation ratio is ≤105%, the phosphorus segregation ratio is ≤104%, and the sulfur segregation ratio is ≤104%; The inclusions of A, B, and C classes in the steel plate are all ≤0.5 grade, and the inclusions of D and Ds classes are all ≤1 grade.

[0024] Preferably, the microstructure of the steel is quasi-polygonal ferrite + pearlite, the volume fraction of quasi-polygonal ferrite is ≥90%, the volume fraction of pearlite is ≤10%, the average grain size of quasi-polygonal ferrite is 6 - 12 μm, and the banded structure is ≤0.5 grade.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In terms of chemical composition, through low-carbon and low-alloy composition design, adding trace magnesium to modify inclusions, a large number of fine and irreversible hydrogen traps are obtained in the steel to adsorb hydrogen atoms in lattice interstices or dislocations, reducing the diffusible hydrogen in the steel; more importantly, it also avoids the ultra-high aggregation of hydrogen at the interfaces of some non-metallic inclusions, promotes the uniform distribution of hydrogen in the material, reduces the hydrogen aggregation in the irreversible hydrogen traps in the steel (i.e., does not cause excessive increase in hydrogen pressure), and thus improves the hydrogen resistance of the steel, such as reducing the incidence of defects such as hydrogen-induced plastic loss, hydrogen-induced cracking, and hydrogen-induced delayed fracture in hydrogen transmission pipelines; (2) Based on the chemical composition, combined with the specific settings of continuous casting billet heating, controlled rolling, and controlled cooling, not only can the precipitation strengthening effects of Nb, Ti, and Al be fully exerted to make up for the strength loss caused by low carbon, but also the grain size can be refined by a low final rolling temperature. In addition, by a high cooling rate and a low final cooling temperature, the segregation of pearlite and the formation of banded structure can be avoided. In summary, steel with excellent mechanical properties, low-temperature toughness, and hydrogen resistance can be obtained, and the production method of the present application does not require subsequent heat treatment processes such as quenching and tempering, having the advantages of a short process flow, low production cost, and fast delivery. Brief Description of the Drawings

[0026] Figure 1 is the metallographic structure diagram of the steel plate of Example 1 of the present invention; Figure 2 is the metallographic diagram of the inclusions of the steel plate of Example 1 of the present invention. Detailed Description of the Embodiments

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

[0028] In response to the application requirements of hydrogen transmission pipelines, an embodiment of the present invention provides a kind of steel and a production method of the steel.

[0029] In terms of chemical composition, the chemical composition of the steel includes, by mass percentage: C 0.010 - 0.040%, Si 0.12 - 0.18%, Mn 0.45 - 0.60%, P ≤ 0.008%, S ≤ 0.0012%, Cr 0.12 - 0.22%, Ni 0.08 - 0.18%, Cu 0.11 - 0.21%, Nb 0.025 - 0.035%, Ti 0.016 - 0.028%, Alt 0.021 - 0.049%, Mg 0.0005 - 0.0012%, Ca 0.0012 - 0.0042%, and the rest is iron and inevitable impurities.

[0030] The functions of each chemical element in the present embodiment are introduced in detail below.

[0031] C: It is an important element for increasing the strength of steel. However, with the increase of carbon content, the low-temperature impact toughness and welding performance of steel decrease, which is not conducive to the application of steel in hydrogen transmission pipelines. In addition, carbon elements can precipitate soluble carbon at grain boundaries, and this kind of grain boundary carbide is an active channel for hydrogen atoms. The increase of carbon content will reduce the hydrogen resistance of steel when applied to hydrogen transmission pipelines. Considering comprehensively, in one embodiment, the carbon content is controlled at 0.010 - 0.040%, preferably at 0.025 - 0.040%.

[0032] Si: It mainly plays a role in solid solution strengthening. However, adding excessive silicon will cause significant deterioration of plasticity and toughness. In one embodiment, the silicon content is controlled at 0.12 - 0.18%.

[0033] Mn: It can improve the hardenability of steel and play a role in solid solution strengthening at the same time, making up for the strength reduction caused by low carbon. However, with the increase of manganese content, it is easy to cause tissue segregation and form banded structure, resulting in the decrease of hydrogen resistance of steel when applied to hydrogen transmission pipelines. Considering comprehensively, in one embodiment, the manganese content is controlled at 0.45 - 0.60%.

[0034] P: It is a harmful element. It not only deteriorates the mechanical properties of steel, but also causes phosphorus segregation to generate ferrite - pearlite banded structure, forming a hydrogen transmission channel, resulting in the decrease of hydrogen resistance of steel when applied to hydrogen transmission pipelines. In one embodiment, the content of phosphorus is limited to ≤0.008%.

[0035] S: It is a harmful element. Sulfur elements react with manganese elements to form soft MnS inclusions, which will be rolled into long strips during the rolling process. Hydrogen is easy to accumulate around its tip, resulting in too high hydrogen pressure and causing hydrogen-induced cracking. In one embodiment, the sulfur content is controlled at ≤0.0012%.

[0036] Cr: It can be enriched in the corrosion product film. The chromium-containing corrosion product film has anion selectivity and can be quickly repaired after being damaged, thus reducing local hydrogen sensitivity. However, adding a large amount of chromium will reduce toughness and welding performance. Considering comprehensively, in one embodiment, the chromium content is controlled at 0.12 - 0.22%.

[0037] Ni: It can improve strength while maintaining good plasticity and toughness. And nickel elements can significantly increase the corrosion potential of steel and inhibit the dissociation of hydrogen molecules. However, nickel elements are relatively scarce resources and expensive. Considering comprehensively, in one embodiment, the nickel content is limited to 0.08 - 0.18%.

[0038] Cu: It can promote the formation of a passivation film and reduce the intrusion of hydrogen. However, adding too much copper will bring the risk of tissue segregation, reduce the hydrogen resistance of steel when applied to hydrogen transmission pipelines, and cause hot brittleness at the same time. Considering comprehensively, in one embodiment, the copper content is controlled at 0.11 - 0.21%.

[0039] Nb, Ti: Nb element can significantly refine the grains and play a role in solid solution strengthening; Ti element is not only beneficial to deoxidation, but also can form a fine and stable TiN precipitate phase, which is a beneficial irreversible hydrogen trap; if added in excess, the beneficial effect cannot be equivalently improved; considering all factors, in one embodiment, the niobium and titanium contents are controlled at 0.025~0.035% and 0.016~0.028%, respectively.

[0040] Alt: It is a strong deoxidizing element, which preferentially combines with oxygen in the steel liquid to form Al2O3 with a high melting point. The fine Al2O3 and AlN particles can act as hydrogen traps (irreversible traps), capturing hydrogen atoms and reducing their diffusion capacity, reducing the enrichment of hydrogen at grain boundaries or defects, thereby reducing the sensitivity to hydrogen-induced cracking; adding excessive amounts to form large-sized Al2O3 is extremely detrimental to the hydrogen resistance; taking all factors into consideration, in one implementation, the aluminum content is controlled at 0.021~0.049%.

[0041] Ca: can modify the morphology of sulfides and oxides and improve the toughness of steel. The interface energy of spherical inclusions after Ca treatment is low, which may form weak hydrogen traps and reduce the local enrichment of hydrogen. In addition, calcium treatment can indirectly optimize the distribution of inclusions and reduce the migration rate of hydrogen under stress. If excessive amount is added, the beneficial effect cannot be equivalently improved. Taking all factors into consideration, in one embodiment, the calcium content is controlled at 0.0012~0.0042%.

[0042] Mg: A trace amount of magnesium can modify Al2O3 into fine magnesium-aluminum spinel (MgO·Al2O3); however, when excessive magnesium is added, too many Al-Mg-O-Mn-S inclusions will be produced, and these inclusions are not easy to disperse in the molten steel, and are easily aggregated and merged into larger inclusions, and even chain inclusions will appear, which is not conducive to improving the hydrogen resistance. According to research, in one implementation method, the magnesium content is controlled at 0.0005~0.0012%.

[0043] As mentioned in the background technology, excellent mechanical properties, low-temperature toughness and hydrogen resistance are all necessary properties of steel for hydrogen pipelines. Among them, hydrogen resistance, in particular, is an important factor affecting the safety and service life of hydrogen pipelines.

[0044] Diffusible hydrogen is an important factor affecting hydrogen embrittlement behavior. However, the existing technology for hydrogen pipeline steel does not consider the correlation between chemical composition and diffusible hydrogen.

[0045] In the present application, through the design of chemical composition, an appropriate amount of hydrogen traps are introduced into the steel to capture hydrogen, thereby reducing diffusible hydrogen, thereby greatly improving the hydrogen resistance of the steel while ensuring mechanical properties and low-temperature toughness.

[0046] However, according to the inventors' research, hydrogen traps are divided into two categories: reversible hydrogen traps and irreversible hydrogen traps, among which: Reversible hydrogen traps (such as vacancies, dislocations, small-angle grain boundaries, etc.) have a relatively low binding energy with hydrogen. They can both capture and release hydrogen. Thus, the hydrogen in reversible hydrogen traps is a harmful hydrogen source, which is easy to diffuse and participate in the hydrogen-induced cracking process; Irreversible hydrogen traps (such as large-angle grain boundaries, precipitates, retained austenite, and inclusions, etc.) have a relatively high binding energy with hydrogen. Once hydrogen atoms enter the traps, they are not easy to leave. Thus, the hydrogen in irreversible hydrogen traps is difficult to escape, and the diffusion movement of hydrogen is inhibited, thereby improving the hydrogen resistance of the steel.

[0047] Based on the above research results, in this application, through the design of chemical composition, the hydrogen traps introduced into the steel are mainly irreversible hydrogen traps, such as precipitates and inclusions.

[0048] However, the inventors also found in the research that among the inclusions, the interfaces of non-metallic inclusions (such as MnS and Al2O3) are irreversible hydrogen traps and have a very strong binding ability with hydrogen. Hydrogen is easy to accumulate here and generate hydrogen pressure. When the hydrogen pressure exceeds the material's bearing limit, it will cause material failure, such as hydrogen-induced cracking.

[0049] Based on this, in the chemical composition of this application, through the design of low-carbon and low-alloy compositions, a small amount of magnesium is added to modify the inclusions, so that a large number of fine irreversible hydrogen traps are obtained in the steel to adsorb hydrogen atoms in the lattice interstices or dislocations, reducing the diffusible hydrogen in the steel; more importantly, it also avoids the excessive aggregation of hydrogen at the interfaces of some non-metallic inclusions, promotes the uniform distribution of hydrogen in the material, reduces the hydrogen aggregation in the irreversible hydrogen traps in the steel (that is, does not cause excessive increase in hydrogen pressure), and thus improves the hydrogen resistance of the steel.

[0050] Further, in one embodiment, the chemical composition of the steel in mass percentage also satisfies: 0.02 ≤ Mg / Alt ≤ 0.04. In this way, the complete modification of the inclusion Al2O3 can be achieved.

[0051] Still further, in one embodiment, the chemical composition of the steel in mass percentage also satisfies: 0.01% ≤ Mg×Alt / S ≤ 0.06%. In this way, on the basis of modifying the inclusions with a small amount of magnesium, it further ensures the formation of sufficient nucleation points to promote the formation of soft sulfides, avoiding the generation and agglomeration of long strip-shaped sulfides, thereby increasing and optimizing the non-metallic inclusions with a core-shell structure and improving the hydrogen resistance.

[0052] The steel in one embodiment of the present invention can be in the form of a steel plate, such as a steel plate with a thickness ≤ 25 mm, for example, the specific thickness can be 10 - 25 mm.

[0053] In one embodiment, the steel is excellent in mechanical properties, with a yield strength of 380-450 MPa, a tensile strength of 480-550 MPa, an elongation rate of ≥40%, and a yield ratio of ≤0.88.

[0054] Herein, the measurements of the yield strength, tensile strength, and elongation rate above can be based on GB / T 228.1-2021.

[0055] The steel is also very excellent in low-temperature toughness, with an impact energy at -40°C of ≥300 J.

[0056] Herein, the measurement of the impact energy at -40°C above can be based on GB / T 229-2020.

[0057] From another perspective, in terms of low-temperature toughness, the drop-weight tear test (DWTT) shear area ratio at -15°C of the steel is ≥95%.

[0058] Herein, the measurement of the DWTT shear area ratio at -15°C above can be based on GB / T 8363-2018.

[0059] The steel is excellent in hydrogen resistance, with a hydrogen diffusion coefficient D ≤ 1.5×10 -6 cm 2 / s.

[0060] Herein, the hydrogen diffusion coefficient D above can be measured according to the method disclosed in ISO 17081:2014.

[0061] From another perspective, in terms of hydrogen resistance, the diffusible hydrogen concentration C0 on the cathode side of the steel is ≤ 3.0×10 - 6 mol / cm 3 .

[0062] Herein, the diffusible hydrogen concentration C0 on the cathode side above can be measured according to the method disclosed in GB / T 34542.3-2018 "Test methods for hydrogen embrittlement sensitivity - Part 3: Electrochemical hydrogen charging method".

[0063] In one embodiment, some or all of the non-metallic inclusions in the steel have a core-shell structure, where the core is MgO·Al2O3 and the shell is MnS, CaS, TiN and coats the outer surface of the inner shell.

[0064] As described above, in the present application, trace magnesium is used to modify inclusions. For example, Al2O3 is modified into spherical inclusions MgO·Al2O3, and combined with the design of the contents of Mn, S, Ca, Ti, and N, sulfides and nitrides are induced to precipitate on the surface of the spherical inclusions, so that composite inclusions are formed in the steel in a dispersed distribution, that is, part or all of the non-metallic inclusions have a core-shell structure. Such composite inclusions form irreversible hydrogen traps, and not only the interface between the core and the shell, but also the interfaces between the core or the shell and the steel matrix can effectively capture hydrogen atoms without causing an increase in hydrogen pressure.

[0065] Preferably, among all the non-metallic inclusions in the steel, the proportion of the number of non-metallic inclusions with a core-shell structure is more than 95%, and more preferably more than 98%.

[0066] In one embodiment, the density of the non-metallic inclusions in the steel is 40-70 per mm 2 , the average diameter is ≤2 μm, the proportion of those with a diameter ≥15 μm is 0%, the proportion of those with a diameter of 10-15 μm is ≤1%, the proportion of those with a diameter of 6-10 μm is ≤5%, and the proportion of those with a diameter of 0-6 μm is ≥94%.

[0067] In this way, through the design of trace magnesium, the inclusions in the steel are refined, softened, and spheroidized, forming "core-shell" structure inclusions in a dispersed distribution, and constituting a large number of small irreversible hydrogen traps, which not only reduce the diffusible hydrogen, but also avoid excessive hydrogen pressure, thus truly improving the hydrogen resistance.

[0068] Preferably, the density of the non-metallic inclusions with a core-shell structure in the steel is 42-68 per mm 2 , and the average diameter is ≤1.8 μm.

[0069] In one embodiment, the central segregation of the continuous casting billet is ≤C1.5 or B1.0, A-class segregation is not allowed to occur, the central porosity is ≤0.5 grade, and the diameter of Al2O3 inclusions is ≤1.0 grade.

[0070] Here, the central segregation, central porosity, and Al2O3 inclusions can be specifically observed by cold acid etching according to YB / T 4003-2016 "Rating Diagram of Macrostructure Defects of Continuous Cast Steel Plates". Among them, A-class segregation is distributed continuously, B-class segregation is distributed intermittently (strip-shaped segregation with a length exceeding 3 mm), and C-class segregation is distributed in dots.

[0071] Furthermore, the carbon segregation ratio of the steel plate is ≤105%, the manganese segregation ratio is ≤105%, the phosphorus segregation ratio is ≤104%, and the sulfur segregation ratio is ≤104%.

[0072] Here, the carbon segregation ratio, manganese segregation ratio, phosphorus segregation ratio, and sulfur segregation ratio can be specifically measured according to GB / T 33165-2016 "Quantitative Analysis Method for Central Segregation of High Carbon Steel Wire Rods".

[0073] For example, the segregation ratio is calculated as M max / M ave × 100%, where M max , M ave are the maximum value and the average value of the element content in the steel, respectively. For example, the carbon segregation ratio is M max-C / M ave-C × 100%, and M max-C , M ave-C are the maximum value and the average value of the C element content in the steel, respectively.

[0074] Furthermore, the inclusions of types A, B, and C in the steel are all ≤ 0.5 grade, and the inclusions of types D and Ds are all ≤ 1 grade.

[0075] Here, for the grading of inclusions of types A, B, C, D, and Ds, specifically, it can be carried out in accordance with GB / T 10561-2023 "Determination of the Content of Non-Metallic Inclusions in Steel - Microscopic Examination Method Using Standard Rating Diagrams", and graded by comparing with the standard diagrams under a microscope.

[0076] In one embodiment, the structure of the steel is quasi-polygonal ferrite + pearlite.

[0077] Among them, the volume fraction of quasi-polygonal ferrite ≥ 90%, and the volume fraction of pearlite ≤ 10%.

[0078] Furthermore, the average grain size of quasi-polygonal ferrite is 6 - 12 μm.

[0079] In addition, the banded structure ≤ 0.5 grade.

[0080] Here, the banded structure of the steel can be graded in accordance with GB / T 34474.1-2017 "Evaluation of Banded Structure in Steel - Part 1: Method Using Standard Rating Diagrams".

[0081] The chemical composition, structure, and properties of the steel in one embodiment of the present application have been introduced above. One embodiment of the present application also provides a production method for the steel.

[0082] Specifically, the production method includes a technological process of smelting, continuous casting, heating of continuous casting billets, controlled rolling, and controlled cooling in sequence, and a steel plate with a thickness ≤ 25 mm is prepared.

[0083] In one embodiment of the present application, continuous casting billets are prepared through smelting and continuous casting.

[0084] It can be understood that the chemical composition of the continuous casting billets is as described above, that is, consistent with the chemical composition of the steel in the present application.

[0085] The continuous casting billet heating process includes: the heating temperature is T MnS -10 °C ~ TMnS +20 °C, T MnS The value is T MnS = 11625 / (5.02 - lg([Mn] × [S])) - 272.15.

[0086] In this way, by low-temperature heating, excessive growth of austenite can be avoided. At the same time, the precipitation of intragranular acicular ferrite induced by inclusions during the controlled rolling process can also be avoided.

[0087] The controlled rolling process includes: after the continuous casting billet exits the heating furnace, two-stage rolling is carried out.

[0088] Among them, the starting rolling temperature T of the first stage MnS -130 °C ~ T MnS -30 °C, and the starting rolling temperature A of the second stage r3 +20 °C ~ A r3 +60 °C, and the finishing rolling temperature A r3 -30 °C ~ A r3 .

[0089] The thickness of the steel plate after rolling in the first stage is more than 4 times the thickness of the steel plate after rolling in the second stage. It can be understood that the thickness of the steel plate after rolling in the second stage is the thickness of the finally obtained steel. As mentioned above, the thickness ≤ 25 mm.

[0090] The controlled cooling process includes: cooling the steel plate obtained by controlled rolling.

[0091] Among them, during cooling, the water inlet temperature ≥ A r3 -80 °C, the cooling rate is 10 - 20 °C / s, and the final cooling temperature is Bs - 140 °C ~ Bs - 70 °C.

[0092] Here, A r3 represents the critical temperature at which austenite (γ-Fe) begins to transform into ferrite (α-Fe) during cooling.

[0093] A r3 The specific value of A has various acquisition methods in this field. In one embodiment, optionally but not limited to this, A r3 = 910 - 310[C] - 80[Mn] - 20[Cu] - 15[Cr] - 55[Ni]. In this formula, [C], [Mn], [Cu], [Cr], and [Ni] are the mass percentages of C, Mn, Cu, Cr, and Ni in the continuous casting billet respectively. For example, if the mass percentage of C in the continuous casting billet is 0.010%, then [C] is the mass percentage 0.010.

[0094] Furthermore, Bs represents the bainite transformation start temperature.

[0095] Specific values of Bs can be obtained in various ways in this field. In one embodiment, optionally but not limited thereto, Bs = 630 - 45[Mn] - 35[Si] - 30[Cr] - 20[Ni]. In the formula, [Mn], [Cr], [Ni], and [Si] are the mass percentages of Mn, Cr, Ni, and Si in the continuous casting billet respectively. For example, if the mass percentage of Mn in the continuous casting billet is 0.45%, then [Mn] is the mass percentage 0.45.

[0096] In the above production method of one embodiment, based on low-temperature heating and through specific settings of controlled rolling and controlled cooling, not only can the precipitation strengthening effects of Nb, Ti, and Al be fully exerted to make up for the strength loss caused by low carbon. For example, the yield strength of the obtained steel plate is 380 - 450 MPa, and the tensile strength is 480 - 550 MPa. At the same time, the final rolling temperature can be used to refine the grain size. For example, the average ferrite grain size is 6 - 12 μm. In addition, through high cooling rates and low final cooling temperatures, the segregation of pearlite and the formation of banded structures can be avoided. For example, the banded structure is ≤ 0.5 grade.

[0097] In summary, steel with excellent mechanical properties, low-temperature toughness, and hydrogen resistance can be obtained, and the production method of this application does not require subsequent heat treatment processes such as quenching and tempering, having the advantages of short process flow, low production cost, and fast delivery.

[0098] Furthermore, the continuous casting billet heating process further includes: according to the thickness of the continuous casting billet, the heating duration is 1.1 - 1.5 min / mm.

[0099] That is, for each mm thickness of the continuous casting billet, the heating duration is 1.1 - 1.5 min. From another perspective, if the thickness of the continuous casting billet is h mm, then the heating duration is (1.1 - 1.5)×h min.

[0100] Furthermore, the controlled cooling process can be carried out by water cooling on an ultra-fast cooling system.

[0101] Specifically, in terms of water volume control of the ultra-fast cooling system, the headers in zones A, B, C, and D can be opened (i.e., all the headers of the ultra-fast cooling system are opened), the water pressure is 0.23 - 0.27 MPa, the up-down water ratio of each header is 0.75 - 0.95, the flow rate of the header in zone A is 520 - 560 L / s, the total flow rate of the four zones is 1600 - 3600 L / s, and the water temperature ≤ 28°C.

[0102] In addition, the cooling roller table speed of the ultra-fast cooling system is 1.8 - 2.2 m / s, and the roller table acceleration is 0.005 m / s 2 , but this application is not limited thereto.

[0103] Furthermore, the production method further includes a natural cooling process after the controlled cooling process.

[0104] That is, the final cooling temperature is the temperature of the steel plate when it exits the water. After the steel plate exits the water (i.e., leaves the ultra-rapid cooling system), the steel plate is naturally cooled until it is cooled to room temperature.

[0105] Further, the smelting process of the production method specifically includes: in sequence, hot metal pre-desulfurization, converter smelting, LF refining, and RH refining.

[0106] Among them, the RH refining process includes: The temperature of the molten steel entering the station is 1620 - 1660 °C. First, argon gas is blown from the bottom at a flow rate of 4 - 5 Nm 3 / h for 1 - 2 minutes. In this way, through the agitation of a large flow rate of argon gas at high temperature, obvious agitation of the molten steel can be caused, which can promote the floating of large-sized initial inclusions; and it can also avoid long-term refining, thereby avoiding excessive temperature drop of the molten steel; After blowing argon gas from the bottom, vacuum static settling is carried out. In this way, the oxygen content in the molten steel can be reduced to less than 0.003% in a vacuum environment, reducing the generation of secondary inclusions; Then, the calcium wire is fed after breaking the vacuum to control the Ca / S mass ratio in the molten steel to be 2 - 4 and the Ca / Alt mass ratio to be above 0.06; such calcium treatment can make the Al2O3 in the molten steel completely form liquid or semi-liquid calcium aluminate, thereby promoting the spheroidization of inclusions; After that, static stirring is carried out for 2 - 3 minutes. In this way, the conversion rate of Al2O3 to liquid or semi-liquid calcium aluminate can be increased. For example, the conversion rate can be increased to more than 90%, and the formed liquid or semi-liquid calcium aluminate is more likely to be modified into fine, spherical magnesium aluminate spinel (MgO·Al2O3); thus, next, magnesium alloy is added to control the Mg mass ratio in the molten steel to be 0.0005 - 0.0012%. The liquid or semi-liquid calcium aluminate can be fully modified into fine, spherical magnesium aluminate spinel (MgO·Al2O3); finally, argon gas is blown from the bottom to promote the uniform distribution of inclusions.

[0107] Among them, in the "feeding calcium wire after breaking the vacuum", the amount of calcium wire fed can be controlled within 200 - 400 m, but is not limited thereto.

[0108] Optionally, in RH refining, when "after blowing argon gas from the bottom, vacuum static settling is carried out", it is statically settled for 25 - 30 minutes under a vacuum degree of ≤ 30 Pa. Such a high vacuum degree can further reduce the oxygen content in the water.

[0109] In one embodiment, in RH refining, the magnesium alloy is preferably a nickel-magnesium alloy with a magnesium content of 20% to 40%. This not only enables the full modification of liquid and semi-liquid calcium aluminate into fine, spherical magnesium aluminate spinel (MgO·Al2O3), but also helps reduce the magnesium vapor pressure and increase the magnesium recovery rate.

[0110] In one embodiment, during RH refining, when "finally, bottom-blow argon", bottom-blow argon at a flow rate of 1 Nm 3 / h or less, and then weak stirring can be carried out for 15 to 20 minutes. In this way, the flow rate of bottom-blow argon is small, which can stabilize the distribution of inclusions.

[0111] Furthermore, in one embodiment, the hot metal pre-desulfurization includes: mixing magnesium powder and lime powder and then injecting them into the hot metal to control the mass ratio of S in the hot metal within 0.0012%; the injection amount of magnesium powder is 0.35 to 0.45 Kg per ton of hot metal.

[0112] In one embodiment, the converter smelting includes: making a slag with an alkalinity of 3.0 to 3.6 and controlling the mass ratio of P within 0.005%.

[0113] Specifically, during converter smelting, oxygen can also be top-blown and argon can be bottom-blown. By adjusting the blowing pressure, the stirring intensity of the molten bath is controlled at 0.8 to 1.2 Nm 3 / min·t.

[0114] Moreover, during converter smelting, lime and dolomite can be used to make a slag with an alkalinity of 3.0 to 3.6.

[0115] In one embodiment, the LF refining includes: after the goldization is completed, feeding aluminum wire to control the mass ratio of O within 0.0040%, and then tapping the steel.

[0116] The specific amount of aluminum wire fed is not limited in this application and is based on ensuring the Alt content in the final molten steel. For example, it can be 100 to 300 m of aluminum wire.

[0117] The above respectively introduce an optional embodiment of hot metal pre-desulfurization, converter smelting, and LF refining. However, it can be understood that the present invention does not limit the specific operations of hot metal pre-desulfurization, converter smelting, and LF refining, and any feasible technology in the art can also be used for implementation.

[0118] Furthermore, the continuous casting includes: when casting, the superheat of the molten steel is 8 to 20 °C, and the casting speed is 0.1×L / F - 0.05 to 0.1×L / F + 0.05 m / s, where L and F are the perimeter and area of the cross-section of the continuous-cast steel plate, respectively.

[0119] In this way, by means of low superheat casting and appropriate casting speed, the macrostructure quality of the continuously cast steel plate (i.e., the continuous casting billet) can be greatly improved, and the segregation and central porosity in the continuous casting billet can be reduced.

[0120] In addition, the continuous casting further includes: a strong cooling mode can be adopted, and soft reduction is used at the end of continuous casting. This can avoid the segregation of inclusions during the solidification of molten steel, and reduce the segregation ratings of carbon, manganese, phosphorus, sulfur, and inclusions of types A, B, C, D, and Ds.

[0121] Optionally, the thickness of the steel plate obtained in continuous casting can be below 230 mm, for example, the thickness is 210 - 230 mm.

[0122] The above introduces an optional implementation manner of continuous casting. However, it can be understood that the present invention does not limit the specific operation of continuous casting, and any feasible continuous casting technology in the art can also be used for implementation.

[0123] In summary, the beneficial effects of an embodiment of the present invention are as follows: (1) In terms of chemical composition, through low-carbon and low-alloy composition design, adding trace magnesium to modify inclusions, a large number of fine irreversible hydrogen traps are obtained in the steel to adsorb hydrogen atoms in the lattice interstitial or dislocations, reducing the diffusible hydrogen in the steel; more importantly, it also avoids the ultra-high aggregation of hydrogen at the interfaces of some non-metallic inclusions, promotes the uniform distribution of hydrogen in the material, reduces the hydrogen aggregation in the irreversible hydrogen traps in the steel (i.e., does not cause excessive increase in hydrogen pressure), and thus improves the hydrogen resistance of the steel, such as reducing the incidence of defects such as hydrogen-induced plastic loss, hydrogen-induced cracking, and hydrogen-induced delayed fracture in hydrogen transmission pipelines; (2) Based on the chemical composition, combined with the specific settings of continuous casting billet heating, controlled rolling, and controlled cooling, not only can the precipitation strengthening effects of Nb, Ti, and Al be fully exerted to make up for the strength loss caused by low carbon; at the same time, the grain size can be refined by low finishing rolling temperature; in addition, by high cooling rate and low final cooling temperature, the segregation of pearlite and the formation of banded structure can be avoided; in summary, steel with excellent mechanical properties, low-temperature toughness, and hydrogen resistance is obtained, and the production method of the present application does not require subsequent heat treatment processes such as quenching and tempering, and has the advantages of short process flow, low production cost, and fast delivery.

[0124] Here, regarding the improvement of hydrogen resistance, an explanation is given from the principle: First, through trace magnesium, calcium aluminate is modified into magnesium aluminate spinel (MgO·Al2O3), and magnesium aluminate spinel exists in a solid state in molten steel and has no process of polymerization and growth. Therefore, the inclusion size can be reduced, and alumina is modified from an irregular shape to an approximate spherical shape; at the same time, the buoyancy of small particle inclusions in molten steel is small and it is difficult to float, resulting in an increase in the number of inclusions retained in the steel, forming a dispersed distribution of irreversible hydrogen traps; Second, and, MnS takes magnesium aluminate spinel as the nucleation core to form an Al-Ti-Mg-O-Mn-S-Ca composite inclusion with a soft outer layer and a hard inner layer, presenting a "core-shell" and a quasi-"core-shell" structure; furthermore, for this kind of inclusion with a "core-shell" structure, on the one hand, it can prevent the hard alumina and magnesium aluminate spinel from splitting the steel matrix and reduce the generation of microcracks in the steel; on the other hand, the soft MnS has a hard core, making the inclusions in the steel approximately circular and reducing the hydrogen-induced cracking caused by excessive hydrogen pressure due to hydrogen enrichment.

[0125] The detailed descriptions listed above are only specific descriptions of the feasible implementation manners of the present invention. The following introduces the specific implementation manners of the present invention through several specific embodiments.

[0126] Example 1 This example provides a steel plate with a thickness of 15 mm.

[0127] The chemical composition of the steel plate in mass percentage includes: C 0.035%, Si 0.15%, Mn 0.60%, P 0.006%, S 0.0008%, Cr 0.21%, Ni 0.12%, Cu 0.15%, Nb 0.028%, Ti 0.020%, Alt 0.025%, Ca 0.0022%, Mg 0.0010%, and the rest is iron and inevitable impurities.

[0128] The production process of the steel plate is as follows: Hot metal pre-desulfurization: After mixing magnesium powder and lime powder, it is blown into the hot metal for desulfurization. The blowing amount of magnesium powder is 0.39 Kg per ton of hot metal; the mass ratio of S in the hot metal when leaving the station is 0.0010%; Converter smelting: Slag with an alkalinity of 3.2 is made, and the mass ratio of P after tapping is 0.0011%; LF refining: After alloying is completed, 260 m of aluminum wire is fed in, the mass ratio of O is 0.0038%, and then tapping is carried out; In RH refining: The temperature of the molten steel entering the station is 1650 °C. First, argon is bottom-blown at a flow rate of 4.6 Nm 3 / h for 1.3 min, then it is statically held for 26 min under a vacuum degree of 25 Pa, and the active oxygen is 0.0023%; then the vacuum is broken and calcium wire is fed in to adjust the Ca / S mass ratio in the molten steel to 2.7 and the Ca / Alt mass ratio to 0.09; then it is statically stirred for 2.2 min, magnesium alloy is added to adjust the mass ratio of Mg in the molten steel, and finally argon is bottom-blown at a flow rate of 1.2 Nm 3 / h, weakly stirred for 16 min, and then tapping is carried out; Continuous casting: During casting, the superheat of the molten steel is 12 °C, and the casting speed is 0.95 m / s, obtaining a continuous casting slab with a thickness of 220 mm; Heating of the continuous casting slab: The heating temperature is 1120 °C, and the heating time is 270 min; Controlled rolling: After the continuous casting slab exits the heating furnace, two-stage rolling is carried out; The starting rolling temperature in the first stage is 1050 °C, and the thickness of the rolled steel plate after rolling is 65 mm; The starting rolling temperature in the second stage is 880 °C, the finishing rolling temperature is 820 °C, and the thickness of the rolled steel plate after rolling is 15 mm; Controlled cooling and natural cooling: The steel plate obtained by controlled rolling is water-cooled on the ultra-rapid cooling system, the water inlet temperature is 780 °C, the cooling rate is 18 °C / s, and the final cooling temperature is 480 °C; After discharging water, natural cooling is carried out until room temperature.

[0129] The steel plate of this example is subjected to microstructure detection, such as Figure 1 , and the detection result is: The microstructure is quasi-polygonal ferrite + pearlite. The volume fraction of quasi-polygonal ferrite is 92%, the volume fraction of pearlite is 8%, and the average grain size of quasi-polygonal ferrite is 10 μm; The center segregation of the continuous casting slab is C1.0, the center porosity is 0.5, and the diameter of Al2O3 inclusions is 0.5 grade; In the finished steel plate, the carbon segregation ratio is 101%, the manganese segregation ratio is 102%, the phosphorus segregation ratio is 102%, and the sulfur segregation ratio is 102%; The inclusions of types A, B, and C are all grade 0, and the inclusions of types D and Ds are all grade 0.5; 98% of the non-metallic inclusions have a core-shell structure. The core is MgO·Al2O3, and the shell is MnS, CaS, and TiN, which coat the outer surface of the inner shell; For example Figure 2 , showing the non-metallic inclusions with a core-shell structure in the metallographic structure of the steel plate of this example; The density of non-metallic inclusions is 66 / mm 2 , the average diameter is 1.3 μm, the proportion of diameters ≥15 μm is 0%, the proportion of 10 - 15 μm is 0.2%, the proportion of 6 - 10 μm is 3.8%, and the proportion of 0 - 6 μm is 96.0%.

[0130] The mechanical properties of the steel plate of this example are measured. The yield strength is 405 MPa, the tensile strength is 515 MPa, the elongation is 42%, the impact energy KV2 at -40 °C is 410 J, and the drop weight tear test (DWTT) shear area fraction at -15 °C is 100%.

[0131] In addition, the hydrogen resistance of the steel plate of this example is detected, and the hydrogen diffusion coefficient D is 0.8×10 -6 cm 2 / s, and the diffusible hydrogen concentration C0 on the cathode side is 1.6×10 -6 mol / cm 3 , indicating excellent hydrogen resistance.

[0132] Example 2 This example provides a steel plate with a thickness of 18 mm.

[0133] The chemical composition of the steel plate in mass percentage includes: C 0.039%, Si 0.14%, Mn 0.55%, P 0.007%, S 0.0010%, Cr 0.20%, Ni 0.10%, Cu 0.13%, Nb 0.032%, Ti 0.022%, Alt 0.038%, Ca 0.0028%, Mg 0.0009%, and the rest is iron and inevitable impurities.

[0134] The production process of the steel plate is as follows: Hot metal pre-desulfurization: After mixing magnesium powder and lime powder, it is blown into the hot metal for desulfurization. The blowing rate of magnesium powder is 0.36 Kg per ton of hot metal; the mass ratio of S in the hot metal when leaving the station is 0.0009%; Converter smelting: Slag with an alkalinity of 3.4 is made, and the mass ratio of P after tapping is 0.0018%; LF refining: After alloying is completed, 280 m of aluminum wire is fed in, the mass ratio of O is 0.0036%, and then tapping is carried out; In RH refining: The temperature of the molten steel entering the station is 1655 °C. First, argon is blown from the bottom at a flow rate of 4.5 Nm 3 / h for 1.5 min, then it is left standing for 27 min under a vacuum degree of 25 Pa, and the active oxygen is 0.0022%; then the vacuum is broken and calcium wire is fed in to control the Ca / S mass ratio in the molten steel to be 2.8 and the Ca / Alt mass ratio to be 0.07; then it is statically stirred for 2.6 min, magnesium alloy is added to control the mass ratio of Mg in the molten steel, and finally argon is blown from the bottom at a flow rate of 1.3 Nm 3 / h, and weakly stirred for 18 min, then tapping is carried out; Continuous casting: When casting, the superheat of the molten steel is 15 °C, and the casting speed is 0.95 m / s to obtain a continuous casting billet with a thickness of 220 mm; Heating of continuous casting billet: The heating temperature is 1125 °C and the heating time is 290 min; Controlled rolling: After the continuous casting billet exits the heating furnace, two-stage rolling is carried out; the starting rolling temperature in the first stage is 1040 °C and the thickness of the rolled steel plate is 80 mm; the starting rolling temperature in the second stage is 870 °C, the finishing rolling temperature is 815 °C, and the thickness of the rolled steel plate is 18 mm; Controlled cooling and natural cooling: The steel plate obtained by controlled rolling is water-cooled on the ultra-rapid cooling system, the water inlet temperature is 775 °C, the cooling rate is 16 °C / s, and the final cooling temperature is 460 °C; after exiting the water, natural cooling is carried out until room temperature.

[0135] The microstructure of the steel plate in this example is detected, and the detection results are as follows: The structure of the steel is composed of quasi-polygonal ferrite and pearlite. The volume fraction of quasi-polygonal ferrite is 93%, and the volume fraction of pearlite is 7%. The average grain size of quasi-polygonal ferrite is 9μm. For the continuous casting billet, the central segregation of C is 1.0, the central porosity is 0.5, and the diameter of Al2O3 inclusions is grade 0.5. In the finished steel plate, the carbon segregation ratio is 102%, the manganese segregation ratio is 102%, the phosphorus segregation ratio is 102%, and the sulfur segregation ratio is 102%. The inclusions of types A, B, C, and D are all grade 0, and the inclusions of type Ds are all grade 0.5. 99% of the non-metallic inclusions have a core-shell structure. The core is MgO·Al2O3, and the shell is MnS, CaS, and TiN, which coats the outer surface of the inner core. The density of non-metallic inclusions is 62 / mm 2 , the average diameter is 1.5μm, the proportion with a diameter ≥15μm is 0%, the proportion with a diameter of 10 - 15μm is 0.1%, the proportion with a diameter of 6 - 10μm is 3.2%, and the proportion with a diameter of 0 - 6μm is 96.7%.

[0136] For the steel plate of this example, the mechanical properties are measured as follows: the yield strength is 400MPa, the tensile strength is 505MPa, the elongation is 45%, the impact energy KV2 at -40°C is 390J, and the shear area fraction of DWTT at -15°C is 100%.

[0137] In addition, the hydrogen resistance of the steel plate of this example is detected, and the hydrogen diffusion coefficient D is 0.6×10 -6 cm 2 / s, and the diffusible hydrogen concentration C0 on the cathode side is 1.8×10 -6 mol / cm 3 , indicating excellent hydrogen resistance.

[0138] Comparative Example This comparative example provides a steel plate with a thickness of 18mm.

[0139] The chemical composition of the steel plate in mass percentage includes: C 0.033%, Si 0.15%, Mn 0.56%, P 0.008%, S 0.0009%, Cr 0.19%, Ni 0.11%, Cu 0.12%, Nb 0.035%, Ti 0.021%, Alt 0.032%, Ca 0.0032%, and the rest is iron and unavoidable impurities.

[0140] The production process of the steel plate is as follows: Hot metal pre-desulfurization: After mixing magnesium powder and lime powder, they are blown into the hot metal for desulfurization. The blowing amount of magnesium powder is 0.42 Kg per ton of hot metal. The mass fraction of S in the hot metal when leaving the station is 0.0009%. Converter smelting: Slag with an alkalinity of 3.3 is produced, and the mass fraction of P after tapping is 0.002%. LF refining: After alloying, 250 m of aluminum wire is fed in. The mass fraction of O is 0.0038%, and then tapping is carried out. During RH refining: The temperature of the molten steel entering the station is 1658 °C. First, argon is bottom-blown at a flow rate of 4.6 Nm 3 / h for 1.4 min, then it is left standing for 22 min under a vacuum of 26 Pa, and the active oxygen is 0.0028%; then the vacuum is broken and calcium wire is fed in to adjust the Ca / S mass ratio in the molten steel to 3.6 and the Ca / Alt mass ratio to 0.1; then argon is bottom-blown at a flow rate of 1.2 Nm 3 / h, with weak stirring for 19 min, and then tapping is carried out. Continuous casting: During casting, the superheat of the molten steel is 12 °C, and the casting speed is 1.00 m / s to obtain a continuous casting slab with a thickness of 220 mm. Heating of the continuous casting slab: The heating temperature is 1180 °C, and the heating time is 295 min. Controlled rolling: After the continuous casting slab exits the heating furnace, two-stage rolling is carried out; the starting rolling temperature in the first stage is 1045 °C, and the thickness of the rolled steel plate after rolling is 80 mm; the starting rolling temperature in the second stage is 870 °C, the finishing rolling temperature is 820 °C, and the thickness of the rolled steel plate after rolling is 18 mm. Controlled cooling and natural cooling: The rolled steel plate obtained by controlled rolling is water-cooled on the ultra-fast cooling system. The water inlet temperature is 776 °C, the cooling rate is 17 °C / s, and the final cooling temperature is 455 °C; after discharging water, natural cooling is carried out until room temperature.

[0141] The steel plate of this example is subjected to microstructure detection, and the detection results are as follows: The microstructure is quasi-polygonal ferrite + pearlite. The volume fraction of quasi-polygonal ferrite is 91%, the volume fraction of pearlite is 9%, and the average grain size of quasi-polygonal ferrite is 12 μm. The center segregation of the continuous casting slab is C1.0, the center porosity is 0.5, and the diameter of Al2O3 inclusions is grade 0.5; in the finished steel plate, the carbon segregation ratio is 105%, the manganese segregation ratio is 104%, the phosphorus segregation ratio is 104%, and the sulfur segregation ratio is 105%; the inclusions of types A, B, C, and D are all grade 0, and the inclusions of type Ds are all grade 0.5. The non-metallic inclusions are single Al2O3, MnS, CaS, and TiN. The density of non-metallic inclusions is 42 pieces / mm 2 , the average diameter is 4.5 μm, the proportion with a diameter ≥ 15 μm is 1.6%, the proportion with a diameter of 10 - 15 μm is 12.3%, the proportion with a diameter of 6 - 10 μm is 16.1%, and the proportion with a diameter of 0 - 6 μm is 70.0%.

[0142] The mechanical properties of the steel plate in this embodiment were measured, with a yield strength of 395 MPa, a tensile strength of 495 MPa, an elongation of 36%, a Charpy impact energy KV2 of 360 J at -40°C, and a DWTT shear area fraction of 98% at -15°C.

[0143] In addition, the hydrogen resistance of the steel plate in this embodiment was detected, and the hydrogen diffusion coefficient D was obtained as 15×10 -6 cm 2 / s, and the diffusible hydrogen concentration C0 on the cathode side was 22×10 -6 mol / cm 3 , indicating poor hydrogen resistance.

Claims

1. A production method of steel for hydrogen pipelines, characterized in that, The production method includes: Preparing a continuous casting billet through smelting and continuous casting; the chemical composition of the continuous casting billet by mass percentage includes: C 0.010 - 0.040%, Si 0.12 - 0.18%, Mn 0.45 - 0.60%, P ≤ 0.008%, S ≤ 0.0012%, Cr 0.12 - 0.22%, Ni 0.08 - 0.18%, Cu 0.11 - 0.21%, Nb 0.025 - 0.035%, Ti 0.016 - 0.028%, Alt 0.021 - 0.049%, Mg 0.0005 - 0.0012%, Ca 0.0012 - 0.0042%, and the balance is iron and unavoidable impurities; Continuous casting billet heating: The heating temperature is T MnS -10 °C to T MnS +20 °C, where T MnS = 11625 / (5.02 - lg([Mn]×[S])) - 272.15; Controlled rolling: After the continuous casting billet exits the reheating furnace, two-stage rolling is carried out; the starting rolling temperature in the first stage is T MnS -130 °C to T MnS -30 °C, and the starting rolling temperature in the second stage is A r3 +20 °C to A r3 +60 °C, and the finishing rolling temperature is A r3 -30 °C to A r3 , and the thickness of the rolled steel plate after the first stage is more than 4 times that of the rolled steel plate after the second stage; Controlled cooling: Cool the steel plate obtained by controlled rolling, with the water inlet temperature ≥ A r3 -80 °C, the cooling rate is 10 - 20 °C / s, and the final cooling temperature is Bs - 140 °C to Bs - 70 °C.

2. The production method of the steel for hydrogen transmission pipeline according to claim 1, characterized in that, Heating the continuous casting billet: according to the thickness of the continuous casting billet, the heating duration is 1.1 - 1.5 min / mm.

3. The production method of the steel for hydrogen transmission pipeline according to claim 1, characterized in that, A r3 = 910 - 310[C] - 80[Mn] - 20[Cu] - 15[Cr] - 55[Ni]; Bs = 630 - 45[Mn] - 35[Si] - 30[Cr] - 20[Ni]; In the formula, [C], [Mn], [Cu], [Cr], [Ni], [Si] are respectively the mass percentages of C, Mn, Cu, Cr, Ni, Si in the continuous casting billet.

4. The production method of the steel for hydrogen transmission pipeline according to claim 1, characterized in that, The smelting includes: in sequence, hot metal pre - desulfurization, converter smelting, LF refining, RH refining; among them, The RH refining process includes: the temperature of the molten steel entering the station is 1620 - 1660 °C. First, argon is blown from the bottom at a flow rate of 4 - 5 Nm 3 / h for 1 - 2 minutes, then it is vacuum - static, and then the vacuum is broken and a calcium wire is fed to control the Ca / S mass ratio in the molten steel to be 2 - 4 and the Ca / Alt mass ratio to be above 0.06; afterwards, it is statically stirred for 2 - 3 minutes, and a magnesium alloy is added to control the mass fraction of Mg in the molten steel to be 0.0005 - 0.0012%, and finally argon is blown from the bottom.

5. The production method of the pipeline steel according to claim 4, characterized in that, The "re - vacuum standing" includes: standing for 25 - 30 min under a vacuum degree of ≤ 30 Pa.

6. The production method of the pipeline steel according to claim 4, characterized in that, The described "final bottom argon blowing" includes: bottom argon blowing at a flow rate of 1 Nm 3 / h or less.

7. The production method of the pipeline steel according to claim 4, characterized in that The hot metal pre - desulfurization includes: after mixing magnesium powder and lime powder, injecting it into the hot metal to control the mass ratio of S in the hot metal within 0.0012%; the injection amount of magnesium powder is 0.35 - 0.45 Kg per ton of hot metal.

8. The production method of the pipeline steel according to claim 4, characterized in that The converter smelting includes: making a slag with an alkalinity of 3.0 - 3.6 and controlling the mass ratio of P within 0.005%.

9. The production method of the pipeline steel according to claim 4, characterized in that The LF refining includes: after the alloying is completed, feeding in aluminum wire to control the mass ratio of O within 0.0040%, and then tapping the steel.

10. The production method of the pipeline steel according to claim 1, characterized in that, The continuous casting includes: when casting, the superheat of the molten steel is 8 - 20 °C, and the casting speed is 0.1×L / F - 0.05 - 0.1×L / F + 0.05 m / s, where L and F are respectively the perimeter and area of the cross - section of the continuous casting billet.

11. A pipeline steel, characterized in that, The chemical composition of the steel by mass percentage includes: C 0.010 - 0.040%, Si 0.12 - 0.18%, Mn 0.45 - 0.60%, P ≤ 0.008%, S ≤ 0.0012%, Cr 0.12 - 0.22%, Ni 0.08 - 0.18%, Cu 0.11 - 0.21%, Nb 0.025 - 0.035%, Ti 0.016 - 0.028%, Alt 0.021 - 0.049%, Mg 0.0005 - 0.0012%, Ca 0.0012 - 0.0042%, and the balance is iron and unavoidable impurities; The steel is a steel plate with a thickness ≤ 25 mm, a hydrogen diffusion coefficient D ≤ 1.5×10 -6 cm 2 / s, a yield strength of 380 - 450 MPa, a tensile strength of 480 - 550 MPa, an elongation ≥ 40%, a yield ratio ≤ 0.88, an impact energy at -40°C ≥ 300 J, and a DWTT drop hammer shear area ratio at -15°C ≥ 95%.

12. A pipeline steel, characterized in that, The chemical composition of the steel, by mass percentage, includes: C 0.010 - 0.040%, Si 0.12 - 0.18%, Mn 0.45 - 0.60%, P ≤ 0.008%, S ≤ 0.0012%, Cr 0.12 - 0.22%, Ni 0.08 - 0.18%, Cu 0.11 - 0.21%, Nb 0.025 - 0.035%, Ti 0.016 - 0.028%, Alt 0.021 - 0.049%, Mg 0.0005 - 0.0012%, Ca 0.0012 - 0.0042%, and the balance is iron and unavoidable impurities; The steel is a steel plate with a thickness ≤ 25 mm, the diffusible free hydrogen concentration C0 on the cathode side ≤ 3.0×10 -6 mol / cm 3 , the yield strength is 380 - 450 MPa, the tensile strength is 480 - 550 MPa, the elongation is ≥ 40%, the yield ratio is ≤ 0.88, the impact energy at -40°C is ≥ 300 J, and the drop weight tear test (DWTT) shear area ratio at -15°C is ≥ 95%.

13. The pipeline steel according to claim 11 or 12, characterized in that, Some or all of the non-metallic inclusions in the steel have a core-shell structure, the core is MgO·Al2O3, and the shell is MnS, CaS, TiN and coats the outer surface of the inner shell.

14. The pipeline steel according to claim 11 or 12, characterized in that, The density of non-metallic inclusions in the steel is 40 to 70 per mm 2 , the average diameter is ≤ 2 μm, the proportion with a diameter ≥ 15 μm is 0%, the proportion with a diameter of 10 to 15 μm is ≤ 1%, the proportion with a diameter of 6 to 10 μm is ≤ 5%, and the proportion with a diameter of 0 to 6 μm is ≥ 94%.

15. The pipeline steel according to claim 11 or 12, characterized in that, The chemical composition of the steel, by mass percentage, also satisfies any one or both of the following two conditions: 0.02 ≤ Mg / Alt ≤ 0.04; 0.01% ≤ Mg × Alt / S ≤ 0.06%.

16. The pipeline steel according to claim 11 or 12, characterized in that, The center segregation of the steel ≤ C1.5 or B1.0, A-type segregation is not allowed, the center porosity ≤ 0.5 grade, and the diameter of Al2O3 inclusions ≤ 1.0 grade; The carbon segregation ratio of the steel plate ≤ 105%, the manganese segregation ratio ≤ 105%, the phosphorus segregation ratio ≤ 104%, and the sulfur segregation ratio ≤ 104%; The inclusions of types A, B, and C in the steel plate are all ≤ 0.5 grade, and the inclusions of types D and Ds are all ≤ 1 grade.

17. The pipeline steel according to claim 11 or 12, characterized in that, The microstructure of the steel is quasi-polygonal ferrite + pearlite, the volume fraction of quasi-polygonal ferrite ≥ 90%, the volume fraction of pearlite ≤ 10%, the average grain size of quasi-polygonal ferrite is 6 - 12 μm, and the banded structure ≤ 0.5 grade.

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