Pipeline steel for hydrogen energy transportation, casting method of steel billet and production method of steel plate

Abstract

The invention discloses pipeline steel for hydrogen energy transportation, a casting method of a steel billet and a production method of a steel plate. The alloy comprises the following chemical components: 0.021% to 0.076% of C, 0.07% to 0.21% of Si, 0.66% to 0.93% of Mn, 0.12% to 0.30% of Cr, less than or equal to 0.24% of Ni, less than or equal to 0.24% of Cu, 0.014% to 0.052% of Nb, 0.014% to 0.050% of V, 0.009% to 0.019% of Ti, 0.015% to 0.045% of Al, 0.0005% to 0.0012% of Mg, 0.0012% to 0.0042% of Ca and the balance of iron and impurities. According to the invention, trace magnesium and calcium are added to modify inclusions, so that a large amount of fine irreversible hydrogen traps are obtained in the steel, and excessive increase of hydrogen pressure is not caused, thereby improving the hydrogen resistance and HIC resistance of the steel.

Description

Technical Field

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

[0002] The main bottleneck restricting the development of hydrogen energy transmission pipelines is that pipeline steel may experience performance degradation or even failure in a high-pressure hydrogen environment. For example, in a high-pressure hydrogen environment, pipeline steel is prone to hydrogen-induced cracking and hydrogen blistering, and its ductility, fatigue performance, and fracture toughness deteriorate significantly.

[0003] For high-pressure hydrogen pipeline steel, whether it is hydrogen-doped pipeline steel or pipeline steel for hydrogen energy transmission, higher requirements are put forward. One is that the steel plate for the transmission pipeline has hydrogen-induced cracking resistance (abbreviation: HIC) performance, and the other is that the steel plate for the pipeline needs to have excellent fracture toughness in a hydrogen environment.

[0004] In some existing technologies, such as CN115094314A, CN115433884A, CN116103568A, etc., research has been carried out on pipeline steel from the aspect of chemical composition. However, the technologies such as CN115094314A and CN115433884A have defects such as high alloy element content, complex steelmaking process, and high alloy cost; for the technology such as CN116103568A, the carbon content is relatively high, and there is a problem of poor welding performance, which affects the application of the steel plate in pipeline steel.

[0005] Furthermore, the pipeline steel in the existing technologies all has the disadvantages of poor HIC resistance and hydrogen resistance when dealing with a high-pressure hydrogen environment, and it is even more difficult to meet the application requirements of pipeline steel for hydrogen energy transmission. Summary of the Invention

[0006] The purpose of the present invention is to provide a pipeline steel for hydrogen energy transmission, a casting method of steel billets, and a production method of steel plates.

[0007] To achieve the above-mentioned invention purpose, an embodiment of the present invention provides a pipeline steel for hydrogen energy transmission. The chemical composition of the steel includes, by mass percentage: C 0.021~0.076%, Si 0.07~0.21%, Mn 0.66~0.93%, Cr 0.12~0.30%, Ni≤0.24%, Cu≤0.24%, Nb 0.014~0.052%, V 0.014~0.050%, Ti 0.009~0.019%, Al 0.015~0.045%, Mg 0.0005~0.0012%, Ca 0.0012~0.0042%, P≤0.01%, S≤0.002%, O≤0.003%, N≤0.005%, H≤0.0002%, and the balance is iron and unavoidable impurities.

[0008] Preferably, the chemical composition of the steel further satisfies, by mass percentage: 0.02 ≤ Mg / Al ≤ 0.04, and / or 0.01% ≤ Mg×Al / S ≤ 0.06%.

[0009] Preferably, in the steel, some or all of the non-metallic inclusions 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.

[0010] Preferably, in the steel, more than 95% of the non-metallic inclusions have the core-shell structure.

[0011] Preferably, the steel satisfies: in the environment of NACE TM0284 standard solution A, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%; and / or, in the stress corrosion test according to NACE TM0177 standard, the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen.

[0012] Preferably, the steel satisfies: in the 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 80%, and 75% of those in the nitrogen environment; and / or, in the 6.3 MPa pure hydrogen environment, the K 1C ≥ 100 MPa·m 1 / 2 .

[0013] Preferably, the steel satisfies: the hydrogen diffusion coefficient D ≤ 1.5×10 -6 cm 2 / s, and the diffusible hydrogen concentration C0 on the cathode side ≤ 3.0×10 -6 mol / cm 3 .

[0014] Preferably, the steel is a steel plate with a thickness of 8 - 30 mm or a steel billet with a thickness of 210 - 230 mm; on the cross-section of the steel, the density of inclusions with a diameter ≥ 10 μm ≤ 10 pieces / cm 2 .

[0015] Preferably, the yield strength R t0.5 ≥ 330 MPa, the tensile strength R m ≥ 430 MPa, the elongation A 50 ≥ 40%, the yield ratio ≤ 0.87, the impact energy KV2 at -20 °C ≥ 400 J, and the hardness ≤ 205 HV 10, the DWTT drop-weight shear area fraction is 100% at -10°C and 100% at -15°C.

[0016] Preferably, the flatness of the steel is ≤2 mm / m and the surface stress is ≤35 MPa.

[0017] Preferably, the steel has a duplex microstructure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite; Among them, the average grain size of the quasi-polygonal ferrite and acicular ferrite is 2~16 μm, and the volume ratio of the quasi-polygonal ferrite structure and acicular ferrite structure is more than 95%.

[0018] Preferably, the chemical composition of the steel plate also satisfies: CEV (%) is 0.168~0.325, and / or Pcm (%) is 0.069~0.159.

[0019] To achieve the above invention object, an embodiment of the present invention provides a casting method for a pipeline steel billet for hydrogen energy transportation. The chemical composition of the steel billet includes, by mass percentage: C 0.021~0.076%, Si 0.07~0.21%, Mn 0.66~0.93%, Cr 0.12~0.30%, Ni ≤0.24%, Cu ≤0.24%, Nb 0.014~0.052%, V 0.014~0.050%, Ti 0.009~0.019%, Al 0.015~0.045%, Mg 0.0005~0.0012%, Ca 0.0012~0.0042%, P ≤0.01%, S ≤0.002%, O ≤0.003%, N ≤0.005%, H ≤0.0002%, and the rest is iron and inevitable impurities; The casting method prepares the steel billet through sequential hot metal pre-desulfurization, converter smelting, LF refining, RH refining, and continuous casting; Among them, in RH refining: the temperature of the molten steel entering the station is 1620~1660°C. First, blow argon at the bottom with 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 / Al 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 at the bottom.

[0020] Preferably, the "then vacuum standstill" includes: standing still for 25~30 min under a vacuum degree of ≤30 Pa; The "finally blow argon at the bottom" includes: blowing argon at the bottom with a flow rate of 1 Nm 3 / h or less.

[0021] Preferably, in continuous casting: during casting, the superheat of molten steel is 8 - 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 continuously cast steel billet, respectively.

[0022] Preferably, in hot metal pre-desulfurization: after mixing magnesium powder and lime powder, they are blown into the hot metal to control the mass ratio of S in the hot metal within 0.0012%; the blowing amount of magnesium powder is 0.35 - 0.45 Kg per ton of hot metal; In converter steelmaking: slag with an alkalinity of 3.0 - 3.6 is made, and the mass ratio of P is controlled within 0.005%; In LF refining: after alloying is completed, aluminum wire is fed in to control the mass ratio of O within 0.0040%, and then tapping is carried out.

[0023] To achieve the above-mentioned invention purpose, an embodiment of the present invention provides a production method of pipeline steel plate for hydrogen energy transportation. The chemical composition of the steel plate includes, by mass percentage: C 0.021 - 0.076%, Si 0.07 - 0.21%, Mn 0.66 - 0.93%, Cr 0.12 - 0.30%, Ni ≤ 0.24%, Cu ≤ 0.24%, Nb 0.014 - 0.052%, V 0.014 - 0.050%, Ti 0.009 - 0.019%, Al 0.015 - 0.045%, Mg 0.0005 - 0.0012%, Ca 0.0012 - 0.0042%, P ≤ 0.01%, S ≤ 0.002%, O ≤ 0.003%, N ≤ 0.005%, H ≤ 0.0002%, and the rest is iron and unavoidable impurities; The production method prepares a steel plate with a thickness t ≥ 8 mm from a steel billet with a thickness t0 of 150 - 320 mm through the processes of heating, rough hot rolling, finish hot rolling, final hot rolling, and controlled temperature water cooling; Heating process: the heating temperature is not lower than the starting precipitation temperatures T NbC 、T NbN 、T TiC 、T VC 、T VN ; Rough hot rolling process: the starting rolling temperature and the final rolling temperature are both T nr ~Min(T NbC , T NbN , T TiC ), and the plate thickness after rolling is (3.2 - 4)t; Finish hot rolling process: the starting rolling temperature and the final rolling temperature are both Ar3 - 20°C to Ar3 + 10°C, and the plate thickness after rolling is t + (2 - 5) mm; Final hot rolling process: It is single-pass hot rolling, with the temperature being Ar3 - (40~20)°C, and the plate thickness after rolling being t; Controlled-temperature water cooling process: The water inlet temperature is Ar3 - (80~30)°C, and the water outlet temperature T is Min(T VC , T VN ) - 300°C ~ Min(T VC , T VN ) + 5°C.

[0024] Preferably, in the heating process: The heating temperature is Max(T NbC , T NbN , T TiC , T VC , T VN ) + 40°C ~ Min(Max(T NbC , T NbN , T TiC , T VC , T VN ) + 120°C, T TiN - 150°C).

[0025] Preferably, between the rough hot rolling process and the finish hot rolling process, there is also a water cooling process, and the water outlet temperature is Ar3 - 20°C ~ Ar3 + 10°C.

[0026] Preferably, in the controlled-temperature water cooling process: The water inlet temperature is Ar3 - (80~60)°C, and the water outlet temperature T is Min(T VC , T VN ) - 15°C ~ Min(T VC , T VN ) + 5°C; Or, the water inlet temperature is Ar3 - (70~50)°C, and the water outlet temperature T is Min(T VC , T VN ) - (50~30)°C; Or, the water inlet temperature is Ar3 - (60~40)°C, and the water outlet temperature T is Min(T VC , T VN ) - (150~130)°C; Or, the water inlet temperature is Ar3 - (50~30)°C, and the water outlet temperature T is Min(T VC , T VN ) - (300~270)°C.

[0027] Preferably, in the rough hot rolling process: The reduction of the first rolling pass in the non-spreading pass is ≥ 42 mm, and the reduction of each pass is ≥ 31 mm; In the finish hot rolling process: The reduction of each pass is ≥ 22 mm.

[0028] Preferably, the steel plate obtained from the finish hot rolling process is directly fed into an ultra-fast cooling system for the controlled temperature water cooling process, and the cooling rate is 6 to 16 °C / s; After the controlled temperature water cooling process, hot straightening, natural air cooling on the cooling bed, warm straightening, and cold straightening are carried out in sequence; among them, the temperature during hot straightening is T - 60 °C to T; the temperature when leaving the cooling bed is 100 to 200 °C.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: On the one hand, it does not contain expensive alloys such as Mo, and adopts a low-alloy composition system design with compound addition of low carbon, low manganese, low phosphorus and sulfur, and Nb + V + Ti precipitation elements, which is easy for steelmaking production and has a low production cost; On the other hand, by reducing the C content in the steel, it has excellent welding performance, which is beneficial to the welding effect of the steel when preparing pipeline steel; On the other hand, by adding appropriate amounts of Nb, V, and Ti to form carbides and nitrides, they can be used as hydrogen traps to capture hydrogen, thereby reducing the diffusible hydrogen in the steel; On the other hand, adding trace amounts of magnesium and calcium to modify inclusions can obtain a large number of fine and irreversible hydrogen traps in the steel, which can adsorb hydrogen atoms in lattice interstices or dislocations, reduce the diffusible hydrogen in the steel, and also avoid the excessive aggregation of hydrogen at the interfaces of some non-metallic inclusions, promote the uniform distribution of hydrogen in the material, reduce the hydrogen aggregation in the irreversible hydrogen traps in the steel (i.e., it will not cause excessive increase in hydrogen pressure), and further improve the hydrogen resistance and HIC resistance of the steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is the metallographic structure diagram of the finished steel plate in Test Example 1 of the present invention; Figure 2 is the metallographic structure diagram of the finished steel plate in Test Example 2 of the present invention; Figure 3 is the metallographic structure diagram of the finished steel plate in Test Example 3 of the present invention; Figure 4 is the metallographic structure diagram of the finished steel plate in Test Example 4 of the present invention; Figure 5 is the metallographic diagram of non-metallic inclusions of the finished steel plate in Test Example 3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] 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 creative efforts shall fall within the protection scope of the present invention.

[0032] The present invention provides a pipeline steel, which is developed from the perspective of chemical composition to improve the hydrogen corrosion resistance of the steel in high-pressure hydrogen environments (including pure hydrogen environments and hydrogen-doped environments), including HIC resistance and hydrogen resistance, and avoid performance deterioration or even failure.

[0033] Specifically, the chemical composition of the steel includes, by mass percentage: C 0.021~0.076%, Si 0.07~0.21%, Mn 0.66~0.93%, Cr 0.12~0.30%, Ni≤0.24%, Cu≤0.24%, Nb 0.014~0.052%, V 0.014~0.050%, Ti 0.009~0.019%, Al 0.015~0.045%, Mg 0.0005~0.0012%, Ca 0.0012~0.0042%, P≤0.01%, S≤0.002%, O≤0.003%, N≤0.005%, H≤0.0002%, and the balance is iron and unavoidable impurities.

[0034] The functions of the various chemical elements in this embodiment are introduced in detail below.

[0035] Carbon: Carbon is the most economical strengthening element in steel, which has a solid solution strengthening effect. At the same time, it forms carbides with niobium, vanadium, titanium, chromium, etc., which has a precipitation strengthening effect and can be used as a hydrogen trap to improve the hydrogen resistance of the steel plate. The increase in carbon content has an obvious effect on improving the strength and hardness of pipeline steel, but too high carbon will lead to poor low-temperature toughness and weldability, and reduce the low-temperature drop-weight performance of pipeline steel. Reducing the carbon content is beneficial to the homogenization of composition and structure, improves the banded structure, reduces the pearlite content, and is beneficial to obtaining more ferrite structures. Therefore, considering comprehensively, the carbon content is selected to be 0.021~0.076%.

[0036] Silicon: Silicon has a solid solution strengthening effect in steel. However, when the silicon content is relatively high, it will increase the grain boundary segregation of elements such as phosphorus and sulfur, reduce the low-temperature toughness and weldability. At the same time, too much silicon is likely to generate Fe2SiO4 on the surface of the steel billet, which is not conducive to the control of the surface quality of the steel plate. Therefore, the silicon content is selected to be 0.07~0.21%.

[0037] Manganese: Manganese has a solid solution strengthening effect in steel, improving strength and hardness. A reasonable manganese content can ensure the strength of pipeline steel at low cost. As the manganese content increases, the strength of pipeline steel increases significantly, while the ductile-brittle transition temperature hardly changes. Too much manganese will lead to central segregation of the continuous casting billet, which is not beneficial to toughness. At the same time, it will increase the level of the banded structure. The higher the level of the banded structure, the more uneven the tissue distribution, and the worse the hydrogen-induced cracking (referred to as HIC) resistance and hydrogen resistance. Therefore, considering comprehensively, the manganese content is selected to be 0.66~0.93%.

[0038] Chromium: Chromium plays a role in solid solution strengthening in steel. As a ferrite-forming element, more acicular ferrite structures can be obtained in high-niobium steel. However, when the chromium content is too high, it will increase the microhardness of the pipeline steel and reduce the low-temperature toughness. Therefore, considering comprehensively, the chromium content is selected to be 0.12 - 0.30%.

[0039] Nickel: Nickel plays a role in solid solution strengthening in steel, increasing the strength of the steel without significantly increasing its hardness. At the same time, it can improve the low-temperature toughness and welding performance of the steel plate. However, when the nickel content is too high, it will increase the alloy cost. Therefore, considering comprehensively, nickel can be considered for addition, and the addition amount does not exceed 0.24%. Of course, it is not necessary to add nickel in this application, and nickel can also not be added in some embodiments.

[0040] Copper: Copper can promote the precipitation of niobium and can compensate for the strength loss caused by the decrease in carbon content. Adding a certain amount of nickel while adding copper can effectively inhibit surface cracks. However, when the copper content is relatively high, it is not conducive to welding performance. Therefore, considering comprehensively, copper can be considered for addition, and the addition amount does not exceed 0.24%. Of course, it is not necessary to add copper in this application, and copper can also not be added in some embodiments.

[0041] Niobium: Niobium is an important grain-refining element in steel. During the hot rolling process, niobium strongly inhibits austenite recrystallization and its precipitation in austenite, pins austenite grain boundaries, and refines recrystallized grains. During the cooling process, the dissolved niobium can continue to precipitate in the form of niobium carbonitrides, making the structure obtained after phase transformation of the material significantly refined, further improving the strength and toughness of the steel. Niobium is a strong carbide-forming element, and its carbides can act as hydrogen traps, improving the hydrogen resistance of the steel plate. However, when the niobium content is relatively high, it will lead to an increase in alloy cost. Therefore, considering comprehensively, the niobium content is selected to be 0.014 - 0.052%.

[0042] Vanadium: Vanadium can significantly improve the hardenability of steel, increase the strength, and also play a role in refining grains. Vanadium belongs to strong carbide-forming elements, reacts with carbon and nitrogen in the steel to form carbides and nitrides, which can act as hydrogen traps and improve the hydrogen resistance of the steel plate. However, when the vanadium content is too high, the alloy cost increases significantly. Therefore, considering comprehensively, the vanadium content is selected to be 0.014 - 0.050%.

[0043] Titanium: Titanium is a nitrogen-fixing element in steel, can form dispersed titanium nitride particles, become hydrogen traps, and improve the hydrogen resistance of the steel plate. At the same time, it inhibits the coarsening of austenite grains during the billet heating process and rolling process. When the addition amount is too high, it is easy to form coarse carbides and nitrides in the center of the continuous casting billet, affecting the low-temperature toughness of the steel plate. Therefore, considering comprehensively, the titanium content is selected to be 0.009 - 0.019%.

[0044] Aluminum: It is a strong deoxidizing element that preferentially combines with oxygen in the molten steel to form high-melting-point Al2O3. Fine Al2O3 and AlN particles can act as hydrogen traps (irreversible traps), capturing hydrogen atoms and reducing their diffusion ability, reducing the enrichment of hydrogen at grain boundaries or defects, thereby reducing the hydrogen-induced cracking sensitivity; adding an excessive amount will form large-sized Al2O3, which is extremely unfavorable for the hydrogen resistance performance; considering comprehensively, in one embodiment, the aluminum content is selected to be 0.015~0.045%.

[0045] Magnesium: A small amount of magnesium can modify Al2O3 into fine magnesium aluminate spinel (MgO·Al2O3); however, when an excessive amount of magnesium is added, too many Al-Mg-O-Mn-S inclusions will be generated, and these inclusions are not easily dispersed in the molten steel and are prone to aggregation and merger into larger-sized inclusions, and even chain-like inclusions may appear, which is not conducive to the improvement of hydrogen resistance performance; through research, in one embodiment, the magnesium content is controlled at 0.0005~0.0012%.

[0046] Calcium: It can modify the morphology of sulfides and oxides, improve the toughness of the steel. The interfacial energy of the spherical inclusions after Ca treatment is relatively low, and weak hydrogen traps may be formed to reduce the local enrichment of hydrogen; in addition, Ca treatment can indirectly optimize the inclusion distribution and reduce the migration rate of hydrogen under stress; adding an excessive amount, the beneficial effects cannot be equivalently improved; considering comprehensively, in one embodiment, the calcium content is controlled at 0.0012~0.0042%.

[0047] Phosphorus, sulfur, oxygen, nitrogen, hydrogen: Impurity elements in the steel. It is sufficient to control P≤0.01%, S≤0.002%, O≤0.003%, N≤0.005%, H≤0.0002%; considering the steelmaking cost, preferably, it can also be controlled to meet any one or more of the following conditions: P 0.0050~0.0090%, S 0.0008~0.0014%, O 0.0012~0.0026%, N 0.0022~0.0042%, H0.00004~0.00015%.

[0048] The steel of the present invention, through the design of chemical composition: On the one hand, it does not contain expensive alloys such as Mo, and adopts a low-alloy composition system design with low carbon, low manganese, low phosphorus and sulfur and the composite addition of Nb+V+Ti precipitation elements, which is easy for steelmaking production and has a low production cost; On the other hand, reducing the C content in the steel has excellent welding performance and is beneficial to the welding effect when the steel is used to prepare pipeline steel; On the other hand, adding appropriate amounts of Nb, V, and Ti to form carbides and nitrides can act as hydrogen traps to capture hydrogen, thereby reducing the diffusible hydrogen in the steel; On the other hand, adding trace amounts of magnesium and calcium to modify the inclusions can result in a large number of fine irreversible hydrogen traps in the steel, which can adsorb hydrogen atoms in the lattice interstices or dislocations, reduce the diffusible hydrogen in the steel, and also avoid the excessive accumulation of hydrogen at the interfaces of some non-metallic inclusions, promoting the uniform distribution of hydrogen in the material and reducing the hydrogen accumulation in the irreversible hydrogen traps in the steel (i.e., not causing an excessive increase in hydrogen pressure), thereby enhancing the hydrogen resistance and HIC resistance of the steel.

[0049] Next, the technical effects produced by the modification of the inclusions by the above-mentioned magnesium and calcium will be introduced in detail again from the principle aspect.

[0050] Diffusible hydrogen is an important factor affecting hydrogen embrittlement behavior. Introducing appropriate hydrogen traps in the steel to capture hydrogen can reduce diffusible hydrogen. However, hydrogen traps are divided into two categories: reversible hydrogen traps and irreversible hydrogen traps. Among them, reversible hydrogen traps (such as vacancies, dislocations, small-angle grain boundaries, etc.) have a low binding energy with hydrogen, and they can both capture and release hydrogen. Thus, the hydrogen in reversible hydrogen traps is a harmful hydrogen source and is prone to diffusion and participation in the hydrogen-induced cracking process. Irreversible hydrogen traps (such as large-angle grain boundaries, precipitates, retained austenite, and inclusions, etc.) have a high binding energy with hydrogen, and once hydrogen atoms enter the traps, they are not easily released. Thus, the hydrogen in irreversible hydrogen traps is difficult to escape, and the diffusion movement of hydrogen is inhibited, thereby enhancing the hydrogen resistance of the steel.

[0051] However, the inventors found in their 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. Although they can capture diffusible hydrogen, hydrogen is prone to accumulate here and generate hydrogen pressure, which can cause material failure when the hydrogen pressure exceeds the material's tolerance limit, such as hydrogen-induced cracking.

[0052] Based on this, the present invention modifies the inclusions with trace amounts of magnesium to obtain a large number of fine irreversible hydrogen traps in the steel, which can adsorb hydrogen atoms in the lattice interstices or dislocations, reduce the diffusible hydrogen in the steel. More importantly, it also avoids the excessive accumulation of hydrogen at the interfaces of some non-metallic inclusions, promotes the uniform distribution of hydrogen in the material, reduces the hydrogen accumulation in the irreversible hydrogen traps in the steel (i.e., not causing an excessive increase in hydrogen pressure), thereby enhancing the hydrogen resistance of the steel.

[0053] Furthermore, in the steel, some or all of the non-metallic inclusions 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.

[0054] Thus, by adding magnesium and calcium, Al2O3 is modified into spherical inclusions MgO·Al2O3. And by designing 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 with a dispersed distribution are formed in the steel, that is, part or all of the non-metallic inclusions have a core-shell structure. Such composite inclusions constitute irreversible hydrogen traps, and not only the interface between the core and the shell, but also the interface between the core or the shell and the steel matrix can effectively capture hydrogen atoms without causing an increase in hydrogen pressure, thereby effectively improving the hydrogen resistance and HIC resistance of the steel.

[0055] 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%.

[0056] Further, in one embodiment, the chemical composition of the steel also satisfies, by mass percentage: 0.02 ≤ Mg / Al ≤ 0.04. In this way, complete modification of the inclusion Al2O3 can be achieved.

[0057] In another embodiment, the chemical composition of the steel also satisfies, by mass percentage: 0.01% ≤ Mg×Al / S ≤ 0.06%. In this way, on the basis of modifying the inclusions with trace magnesium, sufficient nucleation sites are further ensured to promote the formation of soft sulfides, avoid the generation and agglomeration of strip-shaped sulfides, thereby increasing and optimizing the non-metallic inclusions with a core-shell structure and enhancing the hydrogen resistance.

[0058] Further, the steel can be a steel billet with a thickness of 210 - 230 mm, or it can be a steel plate with a thickness of 8 - 30 mm.

[0059] It can be understood that when the steel is implemented as a steel billet with a thickness of 210 - 230 mm, it can be cast by means of smelting and continuous casting.

[0060] When the steel is implemented as a steel plate with a thickness of 8 - 30 mm, it can be prepared from the steel billet through processes such as hot rolling.

[0061] Further, on the cross-section of the steel, the density of inclusions with a diameter ≥ 10 μm ≤ 10 pieces / cm 2 .

[0062] In this way, through the design of trace magnesium, the inclusions in the steel are refined, softened, and spheroidized, forming inclusions with a dispersed "core-shell" structure, and constituting a large number of fine irreversible hydrogen traps, which not only reduce the diffusible hydrogen, but also avoid excessive hydrogen pressure, thus truly improving the hydrogen resistance and HIC resistance.

[0063] Preferably, in the steel, the density of non-metallic inclusions with a core-shell structure is 42 to 68 per mm 2 , and the average diameter is ≤1.8 μm.

[0064] Further preferably, the chemical composition of the steel may further satisfy: Mn / C is 12 to 26 in terms of mass percentage. Thus, by controlling the manganese-carbon ratio, segregation is reduced, the banded structure is improved, and the tissue distribution is uniform, thereby enhancing the HIC resistance and hydrogen resistance of the steel plate.

[0065] Furthermore, the chemical composition of the steel also satisfies: CEV(%) is 0.168 to 0.325.

[0066] The carbon equivalent CEV(%) can be specifically calculated by the following formula: CEV(%) = [C] + [Mn] / 6 + ([Cr] + [V]) / 5 + ([Cu] + [Ni]) / 15. However, this application is not limited thereto.

[0067] Preferably, the chemical composition of the steel may further satisfy: Pcm(%) is 0.069 to 0.159.

[0068] In one embodiment, Pcm(%) can be specifically calculated by the following formula: Pcm(%) = [C] + [Si] / 30 + ([Mn] + [Cu] + [Cr]) / 20 + [Ni] / 60 + [V] / 10.

[0069] Furthermore, when the steel is made into a steel plate with a thickness of 8 to 30 mm, the steel plate has excellent mechanical properties.

[0070] For example, the yield strength R t0.5 ≥330 MPa, the tensile strength R m ≥430 MPa, the elongation A 50 ≥40%, and the yield ratio ≤0.87.

[0071] Here, specifically in accordance with GB / T 2975-2018 "Steel and Steel Products - Sampling Locations and Specimen Preparation for Mechanical Property Tests" and GB / T 228.1-2021 "Metallic Materials - Tensile Testing - Part 1: Method of Test at Room Temperature", the steel plate is sampled and its mechanical properties are tested.

[0072] Furthermore, the steel plate has excellent low-temperature toughness.

[0073] For example, the -20°C impact energy KV2 of the steel plate ≥400 J.

[0074] The hardness of the steel plate ≤205 HV 10 .

[0075] The -10°C DWTT drop-weight shear area fraction of the steel plate is 100%, and the -15°C DWTT drop-weight shear area fraction is 100%.

[0076] Here, specifically in accordance with GB / T 2975-2018 "Steel and Steel Products - Sampling Locations and Specimen Preparation for Mechanical Property Tests" and GB / T 229-2020 "Metallic Materials - Charpy Pendulum Impact Test Method", the steel plate can be sampled and its low-temperature performance tested.

[0077] The steel plate also has excellent hydrogen resistance and HIC resistance.

[0078] For example, the steel plate also meets the following:[[]] In the NACE TM0284 standard A solution environment, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%; And / or, in the stress corrosion test according to the NACE TM0177 standard, the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen.

[0079] Also for example, the steel plate also meets the following:[[]] In a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 80%, and 75% of those in a nitrogen environment; And / or, in a 6.3 MPa pure hydrogen environment, the K 1C ≥ 100 MPa·m 1 / 2 .

[0080] It can be seen that when the steel plate is applied to a pure hydrogen transmission pipeline steel, it can also have excellent hydrogen corrosion resistance and meet the application requirements of the pure hydrogen transmission project.

[0081] Here, for the above third and fourth items, specifically in accordance with GB / T 34542.2-2018 "Hydrogen Storage and Transportation Systems - Part 2: Test Methods for Compatibility of Metallic Materials with Hydrogen Environments", the steel plate can be sampled and tested.

[0082] Furthermore, the hydrogen diffusion coefficient D of the steel ≤ 1.5×10 -6 cm 2 / s. The hydrogen diffusion coefficient D can be measured in the manner disclosed in ISO17081:2014.

[0083] The diffusible hydrogen concentration C0 on the cathode side of the steel ≤ 3.0×10 -6 mol / cm 3 .

[0084] Here, the diffusible hydrogen concentration C0 on the cathode side can be measured in the manner disclosed in GB / T 34542.3-2018 "Test Methods for Hydrogen Embrittlement Sensitivity - Part 3: Electrochemical Hydrogen Charging Method".

[0085] Furthermore, the steel plate has excellent flatness.

[0086] For example, the flatness of the steel plate is ≤ 2 mm / m. In this way, the internal stress of the steel plate is small, and the hydrogen resistance and HIC resistance can be improved.

[0087] Moreover, the residual stress of the steel plate is small.

[0088] For example, the surface stress of the steel plate is ≤ 35 MPa. In this way, the residual stress of the steel plate is small, and the hydrogen resistance and HIC resistance can be improved.

[0089] In addition, in terms of microstructure, the steel plate has a duplex microstructure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

[0090] Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite is 2 - 16 μm. In this way, the probability of generating hydrogen-induced cracks at the grain boundaries can be reduced, and the HIC resistance can be improved.

[0091] Preferably, the total volume fraction of quasi-polygonal ferrite and acicular ferrite is above 95%. This microstructure can ensure good matching of various mechanical properties such as the strength, low-temperature toughness, yield ratio, hardness, and drop-weight performance of the steel plate.

[0092] Specifically, the volume fraction of the quasi-polygonal ferrite microstructure is 5 - 90%, the volume fraction of the acicular ferrite microstructure is 5 - 94%, and the volume fraction of the pearlite microstructure is 1 - 5%.

[0093] Moreover, the banded structure of the steel plate is ≤ 0.5 grade. In this way, the hydrogen-induced cracks caused by the banded structure can be reduced, and the hydrogen resistance can be improved.

[0094] Furthermore, the center segregation of the steel plate is ≤ 0.5 grade, and the center porosity is ≤ 0.5 grade.

[0095] Here, the center segregation can specifically be determined by the sulfur print method or electron probe to detect the degree of element segregation in the central area of the continuous casting billet in accordance with GB / T 34474-2017 "Methods for Microstructure Evaluation of Steel".

[0096] The center porosity grade can specifically be determined by the macroetching test in accordance with GB / T 226-2015 "Macroscopic Structure and Defects of Steel - Etching Test", or can also be determined by ultrasonic flaw detection.

[0097] Furthermore, the ratings of Class A, Class B, Class C, and Class D inclusions in the steel plate are all ≤ Grade 1, and the sum of the ratings of Class A, Class B, Class C, and Class D inclusions is ≤ 2.5 grades.

[0098] Here, for the ratings of Class A, Class B, Class C, and Class D inclusions, specifically, in accordance with GB / T 10561-2005 "Determination of the Content of Non-Metallic Inclusions in Steel - Microscopic Examination Method Using Standard Rating Diagrams", the rating is carried out under a microscope by comparing with the standard diagrams.

[0099] Further, in one embodiment, the steel material is a steel billet with a thickness of 210 - 230 mm, and the present invention also provides a casting method for this steel billet.

[0100] The casting method obtains the steel billet through sequential processes of hot metal pre-desulfurization, converter smelting, LF refining, RH refining, and continuous casting.

[0101] Among them, in RH refining: The temperature of the molten steel entering the station is 1620 - 1660 °C. First, argon gas is bottom-blown at a flow rate of 4 - 5 Nm 3 / h for 1 - 2 minutes. In this way, by agitating the molten steel with a large flow rate of argon gas at high temperature, obvious agitation of the molten steel can be achieved, 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 bottom-blowing argon gas, vacuum static holding 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, 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; by performing such calcium treatment, the Al2O3 in the molten steel can be completely formed into liquid or semi-liquid calcium aluminates, 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 into liquid or semi-liquid calcium aluminates can be increased. For example, the conversion rate can be increased to more than 90%, and the formed liquid or semi-liquid calcium aluminates are more likely to be modified into fine, spherical magnesium aluminate spinel (MgO·Al2O3); thus, next, magnesium alloy is added to control the Mg mass fraction in the molten steel to be 0.0005 - 0.0012%, and the liquid or semi-liquid calcium aluminates can be fully modified into fine, spherical magnesium aluminate spinel (MgO·Al2O3); finally, argon gas is bottom-blown to promote the uniform distribution of inclusions.

[0102] Here, a supplementary explanation is made from the principle: First, by adding trace amounts of magnesium, calcium aluminate is modified into magnesium aluminate spinel (MgO·Al2O3). Magnesium aluminate spinel exists in a solid state in molten steel and does not have a process of aggregation and growth. Therefore, the size of inclusions can be reduced, and alumina is modified from an irregular shape to an approximately spherical shape. At the same time, the buoyancy of small particle inclusions in molten steel is small and it is difficult for them to float upward, resulting in an increase in the number of inclusions retained in the steel, forming a dispersed and irreversible hydrogen trap. Second, 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 similar "core-shell" structure. Furthermore, this kind of inclusion with a "core-shell" structure can, on the one hand, avoid the splitting of the steel matrix by hard alumina and magnesium aluminate spinel, reducing 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 hydrogen-induced cracking caused by excessive hydrogen pressure due to hydrogen enrichment.

[0103] Among them, in the "feeding calcium wire under broken vacuum", the amount of calcium wire fed can be controlled within 200 - 400 m, but not limited to this.

[0104] Optionally, in RH refining, when "after bottom-blowing argon and then vacuum standing", it is stood for 25 - 30 min under a vacuum degree of ≤ 30 Pa. Such a high vacuum degree can further reduce the oxygen content in the water.

[0105] In one embodiment, in RH refining, the magnesium alloy is preferably a nickel-magnesium alloy with a magnesium content of 20 - 40%. This can not only fully modify liquid and semi-liquid calcium aluminate into fine and spherical magnesium aluminate spinel (MgO·Al2O3), but also help reduce the magnesium vapor pressure and improve the magnesium recovery rate.

[0106] In one embodiment, in RH refining, when "finally, bottom-blowing argon", the argon is bottom-blown at a flow rate of 1 Nm 3 / h or less, and then weak stirring can be carried out for 15 - 20 min. In this way, the flow rate of bottom-blowing argon is small, which can stabilize the distribution of inclusions.

[0107] Furthermore, in continuous casting: during casting, the superheat of 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 continuously cast steel billet, respectively.

[0108] In this way, by casting with a low superheat and an appropriate casting speed, the macrostructure quality of the continuously cast steel billet (i.e., the steel billet) can be greatly improved, and segregation and central porosity in the steel billet can be reduced.

[0109] The above describes 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.

[0110] Further, in one implementation manner, hot metal pre-desulfurization: After mixing magnesium powder and lime powder, it is blown into the hot metal to control the mass ratio of S in the hot metal within 0.0012%; the blowing amount of magnesium powder is 0.35 - 0.45 Kg per ton of hot metal.

[0111] In one implementation manner, converter smelting: Make a slag with an alkalinity of 3.0 - 3.6 and control the mass ratio of P within 0.005%.

[0112] 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 - 1.2 Nm 3 / min·t.

[0113] Furthermore, during converter smelting, lime and dolomite can be used to make a slag with an alkalinity of 3.0 - 3.6.

[0114] In one implementation manner, LF refining: After the goldization is completed, aluminum wire is fed in to control the mass ratio of O within 0.0040%, and then tapping is carried out.

[0115] The specific amount of aluminum wire fed in is not limited in this application, and it is based on ensuring the Alt content in the final molten steel. For example, it can be 100 - 300 m of aluminum wire.

[0116] The above separately describes an optional implementation manner 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.

[0117] In another implementation manner, when the steel is further implemented as a steel plate with a thickness of 8 - 30 mm, it can be specifically prepared from a steel billet with a thickness of 210 - 230 mm. The present invention also provides a production method for this steel plate.

[0118] The production method prepares a steel plate with a thickness of t of 8 - 30 mm from a steel billet with a thickness of t0 of 150 - 300 mm through processes of heating, rough hot rolling, finish hot rolling, final hot rolling, and controlled water cooling.

[0119] Here, the specific chemical composition of the used steel billet can be as described in the previous chemical composition.

[0120] Furthermore, the steel billet can be prepared by the casting method described above. Of course, this application is not limited thereto. For example, any feasible technology in the art can also be used for implementation.

[0121] In the heating process: after the billet leaves the continuous caster, it directly enters the heating furnace for heating.

[0122] The heating temperature is not lower than the respective precipitation start temperatures T of NbC, NbN, TiC, VC, and VN NbC , T NbN , T TiC , T VC , T VN .

[0123] In the rough hot rolling process: the starting rolling temperature and the finishing rolling temperature are both T nr ~Min(T NbC , T NbN , T TiC ), and the plate thickness after rolling is (3.2 - 4)t.

[0124] Preferably, the starting rolling temperature of the rough hot rolling can be greater than the finishing rolling temperature.

[0125] Among them, T nr represents the lowest temperature of austenite recrystallization, and its value can be obtained mainly through various methods such as theoretical calculation, experimental measurement, and empirical formula.

[0126] For example, in one embodiment, T nr can be calculated according to the following formula: T nr =887 + 464[C] + (6445[Nb] - 644 ) + (732[V] - 230 ) + 890[Ti] + 363[Al] – 357[Si]. However, the value-taking method of T nr is not limited to this. Other value-taking methods that can be known by those skilled in the art based on the concept of T nr can be applied to the present invention.

[0127] Furthermore, Min(T NbC , T NbN , T TiC ) means: the minimum value among the three temperature values of T NbC , T NbN , T TiC .

[0128] Thus, in the rough hot rolling process: Rolling is carried out above the recrystallization temperature T nr to avoid mixed crystals; and the temperature is always controlled within Min(T NbC , T NbN , T TiC)Next, ensure the effective precipitation of Nb carbides and nitrides and Ti carbides during the rolling process to prevent the growth of recrystallized grains and refine the recrystallized grains. Furthermore, rolling at a relatively high temperature range can reduce the rolling deformation resistance, increase the reduction, facilitate the penetration of deformation to the core of the billet, improve defects such as core segregation and porosity, and at the same time, reduce the banded structure. Secondly, adopt large reduction rolling (i.e., rolling from thickness t0 to thickness (3.2 - 4)t), fully break the as-cast structure, and obtain refined recrystallized grains. The greater the total reduction, the more obvious the refinement effect on austenite grains, and because the temperature is relatively low, the grains will not grow excessively.

[0129] In the finish hot rolling process: The starting rolling temperature and the finishing rolling temperature are both Ar3 - 20°C to Ar3 + 10°C, and the thickness of the rolled plate is t + (2 - 5)mm.

[0130] Preferably, the starting rolling temperature of the finish hot rolling can be greater than the finishing rolling temperature.

[0131] Among them, Ar3 is the temperature at which austenite (γ-Fe) begins to precipitate ferrite (α-Fe) during cooling. It can be specifically obtained through experiments and measurements using a differential scanning calorimeter (DSC) or thermogravimetric analysis (TG), or it can also be obtained through an empirical formula.

[0132] For example, in one embodiment, Ar3 can be calculated according to the following formula: Ar3 = 910 - 203[C] - 15.2[Ni] + 44.7[Si] + 30[Mn] + 70[Cr] + 66.5[V]. However, the value-taking method of Ar3 is not limited to this. Other value-taking methods that those skilled in the art can obtain based on the concept of Ar3 can all be applied to the present invention.

[0133] In this way, during finish hot rolling, the whole process is rolling in the two-phase critical zone, and: On the one hand, perform large reduction deformation in the non-recrystallized zone (i.e., rolling from thickness (3.2 - 4)t to thickness t + (2 - 5)mm) to obtain a deformed structure, so that a large number of deformation bands are accumulated in the structure, and fine structures are obtained during the subsequent controlled cooling process, improving the low-temperature toughness of the steel plate. On the other hand, large reduction deformation can induce the precipitation of the second phase and obtain more fine precipitates. On the other hand, perform rolling deformation within 30°C near the two-phase phase transformation starting point Ar3, which can not only ensure the formation of more deformation-induced ferrite, for example, a large number of quasi-polygonal ferrite can be formed, but also the deformation-induced ferrite grains are relatively fine.

[0134] The final hot rolling process is a single-pass hot rolling, that is, it only includes a single-pass hot rolling. The temperature is Ar3 - (40 - 20)°C, and the thickness of the rolled plate is t.

[0135] Preferably, the temperature of finish hot rolling is lower than that of finish rolling in finish hot rolling. However, the present application is not limited thereto.

[0136] In this way, by controlling the reduction (i.e., 2-5 mm) and temperature control of finish hot rolling in the last pass, the shape of the steel plate can be ensured and the performance of the final steel plate can be improved.

[0137] In the controlled temperature water cooling process: the water inlet temperature is Ar3 - (80 - 30) °C, and the water outlet temperature T is Min(T VC , T VN ) - 300 °C to Min(T VC , T VN ) + 5 °C.

[0138] It can be understood that the water outlet temperature T is lower than the water inlet temperature.

[0139] Among them, Min(T VC , T VN ) means: the minimum value among the two temperature values of T VC , T VN .

[0140] Based on the foregoing, in the finish hot rolling and finish hot rolling processes, deformation-induced ferrite phase transformation has occurred in the steel plate, and a large number of fine deformation-induced ferrite (such as quasi-polygonal ferrite) have been generated. On this basis, through the controlled temperature water cooling process, the steel plate is cooled to the ferrite phase transformation zone, and ferrite phase transformation continues to obtain more ferrite phases (for example, acicular ferrite is formed), avoiding the generation of hard phases such as pearlite, bainite, and MA, so as to ensure the anti-HIC performance and anti-hydrogen performance of the pipeline steel for hydrogen energy transmission.

[0141] Furthermore, the control of the water outlet temperature is conducive to the precipitation of carbon and nitride of V, forming more hydrogen traps to capture hydrogen, thereby reducing the diffusible hydrogen in the steel plate, and further improving the anti-HIC performance and anti-hydrogen performance of the steel.

[0142] In summary, the production method of the present invention realizes the optimization and control of the steel plate in terms of grain size, banded structure, hard phase structure, inclusion size and quantity, strength, hardness, low-temperature toughness, shape, residual stress, anti-HIC performance, anti-hydrogen performance, etc. through the control of chemical composition, hot rolling, controlled temperature water cooling and other processes. No additional heat treatment is required after rolling, the welding performance is excellent, the production rhythm is fast, and the comprehensive performance of the obtained steel plate is excellent.

[0143] Preferably, in the heating process: the heating temperature is Max(T NbC , T NbN , T TiC , T VC , T VN ) + 40 °C to Min(Max(TNbC , T NbN , T TiC , T VC , T VN ) + 120 °C, T TiN -150 °C).

[0144] Among them, Max(T NbC , T NbN , T TiC , T VC , T VN ) means: the maximum value among the five temperature values of T NbC , T NbN , T TiC , T VC , T VN these five temperature values.

[0145] Min(Max(T NbC , T NbN , T TiC , T VC , T VN ) + 120 °C, T TiN -150 °C) means: the minimum value among the two temperature values of Max(T NbC , T NbN , T TiC , T VC , T VN ) + 120 °C, T TiN -150 °C, that is, the relatively smaller one of the two.

[0146] In this way, through the control of the heating temperature, the alloying elements are effectively solid-solved, ensuring that the carbonitrides of Nb and V and the carbides of Ti in the steel can be completely dissolved, and the austenite grains do not grow excessively, preparing for the precipitation during the subsequent rolling in the recrystallization zone (i.e., rough hot rolling).

[0147] The heating duration is preferably controlled to be (1.1~1.3) t0 min / mm. That is, according to the thickness t of the steel billet 0， the heating duration per millimeter is 1.1~1.3 min.

[0148] Furthermore, the whole-process temperature of the rough hot rolling process is preferably in the range of T nr ~Min(T NbC , T NbN , T TiC ).

[0149] The whole-process temperature of the finish hot rolling process is preferably in the range of Ar3 - 20 °C ~ Ar3 + 10 °C.

[0150] In one embodiment, between the rough hot rolling process and the finish hot rolling process, there is also a water cooling process, and the outlet water temperature is Ar3 - 20°C to Ar3 + 10°C.

[0151] In this way, after rolling in the recrystallization zone of rough hot rolling, fine recrystallized grains are obtained, and then rapidly cooled below the recrystallization temperature through a water cooling device. On the one hand, it avoids the rapid growth of recrystallized grains during the holding temperature process, which may lead to poor low-temperature toughness of the final steel plate; on the other hand, it reduces the holding time and improves the rolling efficiency.

[0152] Furthermore, during rough hot rolling, the reduction per pass ≥ 31 mm, and for the first pass of non-spreading passes, the reduction ≥ 42 mm.

[0153] In this way, in the case of a large total reduction in rough hot rolling, a large reduction is also adopted for each pass to fully break the as-cast structure and obtain refined recrystallized grains. The larger the total reduction and the larger the reduction per pass, the more obvious the refinement effect on austenite grains.

[0154] During finish hot rolling, the reduction per pass ≥ 22 mm.

[0155] In this way, large reduction deformation is carried out in the non-recrystallization zone to obtain a deformed structure, so that a large number of deformation bands are accumulated in the structure, and fine structures are obtained during subsequent cooling, improving the low-temperature toughness of the steel plate.

[0156] Next, the steel plate obtained from the finish hot rolling process is directly fed into an ultra-fast cooling system for temperature-controlled water cooling.

[0157] Specifically, on the ultra-fast cooling system, the cooling rate is 6 - 16°C / s.

[0158] Furthermore, in the temperature-controlled water cooling process, the water pressure of the ultra-fast cooling system is 0.15 - 0.20 MPa, the ratio of upper and lower water is 0.92 - 0.98, and the roller table speed is 1.5 - 2.2 m / s.

[0159] Further, the production method further includes, after the temperature-controlled water cooling process, successively performing hot straightening, natural air cooling on the cooling bed, warm straightening, and cold straightening.

[0160] The temperature during hot straightening is T - 60°C to T. In this way, the outlet water temperature T of the steel plate on the ultra-fast cooling system is Min(T VC , T VN ) - 150°C to Min(T VC , T VN) - 130 °C. At this time, it is still in the ferrite phase transformation region, but transformation stress and thermal stress already exist in the steel plate. The steel plate enters the hot straightening machine system for temperature-controlled straightening in the high-temperature ferrite phase transformation region. In this way, the transformation stress and thermal stress in the steel plate can be released, thereby avoiding the initiation of hydrogen-induced cracks at stress concentration points and reducing hydrogen-induced brittle fracture.

[0161] When air cooling naturally on the cooling bed, the temperature of the lower cooling bed is 100 - 200 °C. In this way, when air cooling naturally on the cooling bed, self-tempering of the steel plate will occur, and ferrite phase transformation can be completed on the cooling bed, further releasing transformation stress and thermal stress.

[0162] It should be noted here that in this application, T NbC 、T NbN 、T TiC 、T TiN 、T VC 、T VN are the starting precipitation temperatures of NbC, NbN, TiC, TiN, VC, and VN respectively. Specifically, they can be analyzed by thermodynamic calculation software (such as Thermo-Calc) or laboratory measurement (such as thermal simulation test) in combination with the chemical composition of the specific steel billet.

[0163] In one embodiment, T NbC can be calculated by the formula lg([Nb] × [C] 0.875 ) = 2.97 - 7500 / (T NbC + 273.15), but the value-taking method of T NbC is not limited to this.

[0164] T NbN can be calculated by the formula lg([Nb] × [N]) = 3.70 - 10800 / (T NbN + 273.15), but the value-taking method of T NbN is not limited to this.

[0165] T TiC can be calculated by the formula lg([Ti] × [C]) = 5.33 - 10475 / (T TiC + 273.15), but the value-taking method of T TiC is not limited to this.

[0166] T TiN can be calculated by the formula lg([Ti] × [N]) = 0.32 - 8000 / (T TiN + 273.15), but the value-taking method of T TiN is not limited to this.

[0167] T VCIt can be calculated by the formula lg([V]×[C]) = 6.72 - 9500 / (T VC + 273.15), but the value-taking method of T VC is not limited to this.

[0168] T VN It can be calculated by the formula lg([V]×[N]) = 3.46 - 8330 / (T VN + 273.15), but the value-taking method of T VN is not limited to this.

[0169] Those skilled in the art can apply other value-taking methods that can be known based on the respective concepts of T NbC 、T NbN 、T TiC 、T TiN 、T VC 、T VN to the present invention.

[0170] In addition, it should be noted that in this application, [C], [Si], [Mn], [Cr], [V], [Cu], [Ni], [Nb], [N], [Ti], [Al] involved are respectively the mass percentages of C, Si, Mn, Cr, V, Cu, Ni, Nb, N, Ti, Al in steel. For example, if the mass percentage of Nb in steel is 0.044%, then the mass percentage [Nb] of Nb is 0.044.

[0171] The above gives a general introduction to the technical purpose of the present invention. Next, four different implementation manners under the technical purpose of the present invention will be introduced in detail respectively. These four implementation manners correspond to four different grades of pipeline steel.

[0172]

First Embodiment

[0173] The chemical composition of the steel in mass percentage includes: C 0.046 - 0.076%, Si 0.15 - 0.21%, Mn 0.85 - 0.93%, Cr 0.12 - 0.20%, Nb 0.014 - 0.022%, V 0.014 - 0.022%, Ti 0.009 - 0.017%, Al 0.015 - 0.045%, Mg 0.0005 - 0.0012%, Ca 0.0012 - 0.0042%, P ≤ 0.01%, S ≤ 0.002%, O ≤ 0.003%, N ≤ 0.005%, H ≤ 0.0002%, and the rest is iron and inevitable impurities.

[0174] Furthermore, the chemical composition of the steel also satisfies: CEV(%) is 0.201 - 0.289, and / or, Pcm(%) is 0.094 - 0.145.

[0175] The chemical composition of the steel in mass percentage also satisfies: 0.02 ≤ Mg / Al ≤ 0.04, and / or, 0.01% ≤ Mg×Al / S ≤ 0.06%.

[0176] This embodiment provides a casting method for a pipeline steel billet having the above chemical composition.

[0177] The casting method obtains the steel billet through sequential processes of hot metal pre - desulfurization, converter smelting, LF refining, RH refining, and continuous casting.

[0178] Hot metal pre - desulfurization process: After mixing magnesium powder and lime powder, it is blown into the hot metal to control the mass ratio of S in the hot metal within 0.0012%; the blowing amount of magnesium powder is 0.35 - 0.45 Kg per ton of hot metal.

[0179] Converter smelting process: Slag with an alkalinity of 3.0 - 3.6 is made, and the mass ratio of P is controlled within 0.005%.

[0180] RH refining process: 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 min, then it is vacuum - static, and then calcium wire is fed after breaking the vacuum to adjust the Ca / S mass ratio in the molten steel to 2 - 4 and the Ca / Al mass ratio above 0.06; then it is statically stirred for 2 - 3 min, magnesium alloy is added to adjust the mass ratio of Mg in the molten steel to 0.0005 - 0.0012%, and finally argon is blown from the bottom.

[0181] LF refining process: After alloying is completed, aluminum wire is fed to control the mass ratio of O within 0.0040%, and then tapping is carried out.

[0182] Continuous casting process: During casting, the superheat of the molten steel is 8 - 20 °C, and a billet with a thickness t0 of 210 - 230 mm is obtained.

[0183] The central segregation of the billet is ≤ 0.5 grade, and the central porosity is ≤ 0.5 grade.

[0184] Furthermore, the ratings of inclusions of types A, B, C, and D in the billet are all ≤ 1 grade, and the sum of the ratings of inclusions of types A, B, C, and D is ≤ 2.5 grades.

[0185] On the cross-section of the billet, the density of inclusions with a diameter ≥ 10 μm is ≤ 10 pieces / cm 2 .

[0186] This embodiment provides a production method of a pipeline steel plate having the above chemical composition.

[0187] The production method prepares a steel plate with a thickness t of 8 - 30 mm by subjecting the billet to processes of heating, rough hot rolling, finish hot rolling, final hot rolling, and controlled temperature water cooling.

[0188] Heating process: The heating temperature is not lower than the respective starting precipitation temperatures T NbC , T NbN , T TiC , T VC , T VN .

[0189] Preferably, the heating temperature is Max(T NbC , T NbN , T TiC , T VC , T VN ) + 40 °C ~ Min(Max(T NbC , T NbN , T TiC , T VC , T VN ) + 120 °C, T TiN - 150 °C).

[0190] The heating duration is preferably controlled to be (1.1 - 1.3)t0 min / mm.

[0191] Rough hot rolling process: The starting rolling temperature and the final rolling temperature are both T nr ~ Min(T NbC , T NbN , T TiC ), and the plate thickness after rolling is (3.2 - 4)t.

[0192] Preferably, the starting rolling temperature of the rough hot rolling can be greater than the final rolling temperature, and the whole process temperature is within T nr ~ Min(T NbC , TNbN , T TiC ).

[0193] More preferably, during rough hot rolling, the reduction per pass ≥ 31 mm, and the reduction of the first rolling pass in non-spreading passes ≥ 42 mm.

[0194] Finish hot rolling process: The starting rolling temperature and the finishing rolling temperature are both Ar3 - 20°C to Ar3 + 10°C, and the plate thickness after rolling is t + (2 - 5) mm.

[0195] Preferably, the starting rolling temperature of finish hot rolling can be greater than the finishing rolling temperature, and the whole-process temperature is in the range of Ar3 - 20°C to Ar3 + 10°C.

[0196] More preferably, during finish hot rolling, the reduction per pass ≥ 22 mm.

[0197] Final hot rolling process: It is a single-pass hot rolling, the temperature is Ar3 - (40 - 20)°C, and the plate thickness after rolling is t.

[0198] Preferably, the temperature of final hot rolling is lower than the finishing rolling temperature of finish hot rolling.

[0199] Controlled-temperature water cooling process: After the steel plate leaves the rolling mill of final hot rolling, controlled-temperature water cooling is carried out directly.

[0200] Specifically, the water inlet temperature is Ar3 - (80 - 60)°C, and the water outlet temperature T is Min(T VC , T VN ) - 15°C to Min(T VC , T VN ) + 5°C.

[0201] Preferably, controlled-temperature water cooling is carried out on an ultra-fast cooling system, and the cooling rate is 6 - 16°C / s.

[0202] Preferably, the production method of the steel plate further includes: after controlled-temperature water cooling, first perform hot straightening on the steel plate, and the temperature during hot straightening is T - 60°C to T; after leaving the hot straightening machine, the steel plate goes onto the cooling bed for natural air cooling, and the temperature when leaving the cooling bed is 100 - 200°C; then, the steel plate is sequentially subjected to warm straightening and cold straightening.

[0203] Perform inspections and evaluations on the performance, microstructure, etc. of the steel plate. Specific introductions are given below.

[0204] The yield strength R of the steel plate t0.5 ≥ 330 MPa, the tensile strength R m ≥ 430 MPa, the elongation A 50 ≥ 50%, and the yield ratio ≤ 0.77.

[0205] The -20°C impact energy KV2 of the steel plate ≥ 400 J.

[0206] The hardness of the steel plate is ≤160 HV 10 。

[0207] The -10℃ DWTT drop-weight shear area fraction of the steel plate is 100%, and the -15℃ DWTT drop-weight shear area fraction is 100%.

[0208] The steel plate meets the requirements: in the environment of NACE TM0284 standard A solution, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%.

[0209] Moreover, the steel plate meets the requirements: in the stress corrosion test according to NACE TM0177 standard, the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen.

[0210] Furthermore, the steel plate meets the requirements: in a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment.

[0211] In addition, the steel plate meets the requirements: in a 6.3 MPa pure hydrogen environment, the K 1C ≥110 MPa·m 1 / 2 。

[0212] The hydrogen diffusion coefficient D of the steel plate is ≤1.5×10 -6 cm 2 / s, and the diffusible hydrogen concentration C0 on the cathode side is ≤3.0×10 - 6 mol / cm 3 。

[0213] The flatness of the steel plate is ≤1 mm / m.

[0214] The surface stress of the steel plate is ≤15 MPa.

[0215] The steel plate has a duplex structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

[0216] Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite is 8~16 μm.

[0217] The total volume fraction of quasi-polygonal ferrite and acicular ferrite is more than 95%.

[0218] Specifically, the volume fraction of the quasi-polygonal ferrite structure is 78~90%, the volume fraction of the acicular ferrite structure is 5~20%, and the volume fraction of the pearlite structure is 2~5%.

[0219] Furthermore, the banded structure of the steel plate is ≤0.5 grade.

[0220] In addition, in the steel plate, some or all of the non-metallic inclusions 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.

[0221] Specifically, in the steel plate, more than 95% (even more than 98%) of the non-metallic inclusions have the core-shell structure.

[0222] Among them, the density of the non-metallic inclusions with the core-shell structure is 42-68 per mm 2 , and the average diameter is ≤1.8 μm.

[0223] In summary, this embodiment has economic advantages such as low alloy content, short process flow (without coiling and heat treatment), and low production cost. At the same time, the steel plate has excellent properties, including welding performance, mechanical properties, low-temperature toughness, hardness, flatness, hydrogen resistance, and HIC resistance.

[0224]

Second Embodiment

[0225] The chemical composition of the steel plate in mass percentage includes: C 0.036-0.066%, Si 0.11-0.17%, Mn 0.77-0.85%, Cr 0.17-0.25%, Cu 0.10-0.18%, Nb 0.024-0.032%, V 0.024-0.032%, Ti 0.010-0.018%, Al 0.015-0.045%, Mg 0.0005-0.0012%, Ca 0.0012-0.0042%, P≤0.01%, S≤0.002%, O≤0.003%, N≤0.005%, H≤0.0002%, and the rest is iron and inevitable impurities.

[0226] Furthermore, the chemical composition of the steel plate also satisfies: CEV(%) is 0.199-0.287, and / or, Pcm(%) is 0.088-0.139.

[0227] The chemical composition of the steel in mass percentage also satisfies: 0.02≤Mg / Al≤0.04, and / or, 0.01%≤Mg×Al / S≤0.06%.

[0228] This embodiment also provides a casting method for a pipeline steel billet with the above chemical composition. The casting method of this embodiment is the same as the previous first embodiment and will not be repeated.

[0229] This embodiment also provides a production method for pipeline steel plates having the above chemical composition. The difference between this production method and the first embodiment described above is only: controlled-temperature water cooling. Only this difference will be introduced below, and the other parts not mentioned are the same as those in the first embodiment above and will not be elaborated.

[0230] In this embodiment, for the controlled-temperature water cooling process: the water inlet temperature is Ar3 - (70~50)°C, and the water outlet temperature T is Min(T VC , T VN ) - (50~30)°C.

[0231] The properties, microstructure, etc. of the billet / steel plate in this embodiment will be introduced below.

[0232] The central segregation of the billet is ≤ 0.5 grade, and the central porosity is ≤ 0.5 grade.

[0233] Furthermore, the ratings of inclusions of types A, B, C, and D in the billet are all ≤ 1 grade, and the sum of the ratings of inclusions of types A, B, C, and D is ≤ 2.5 grades.

[0234] On the cross-section of the billet, the density of inclusions with a diameter ≥ 10 μm is ≤ 10 pieces / cm 2 .

[0235] The yield strength R t0.5 of the steel plate ≥ 392 MPa, the tensile strength R m ≥ 454 MPa, the elongation A 50 ≥ 43%, and the yield ratio is ≤ 0.86.

[0236] The -20°C impact energy KV2 of the steel plate ≥ 400 J.

[0237] The hardness of the steel plate is ≤ 190 HV 10 .

[0238] The -10°C DWTT drop-weight shear area fraction of the steel plate is 100%, and the -15°C DWTT drop-weight shear area fraction is 100%.

[0239] The steel plate meets the requirements: in the NACE TM0284 standard A solution environment, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%.

[0240] Moreover, the steel plate meets the requirements: in the stress corrosion test carried out according to the NACE TM0177 standard, the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen.

[0241] Furthermore, the steel plate satisfies the following conditions: in a pure hydrogen environment of 6.3 MPa, the tensile strength, elongation, and reduction of area of a smooth specimen are respectively greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment.

[0242] In addition, the steel plate satisfies the following condition: in a pure hydrogen environment of 6.3 MPa, the K of a stepped compact tension specimen 1C ≥110 MPa·m 1 / 2 .

[0243] The hydrogen diffusion coefficient D of the steel plate ≤ 1.5×10 -6 cm 2 / s, and the diffusible hydrogen concentration C0 on the cathode side ≤ 3.0×10 - 6 mol / cm 3 .

[0244] The flatness of the steel plate ≤ 2 mm / m.

[0245] The surface stress of the steel plate ≤ 20 MPa.

[0246] The steel plate has a duplex structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

[0247] Among them, the average grain size of the quasi-polygonal ferrite and acicular ferrite is 4 - 9 μm.

[0248] The total volume fraction of the quasi-polygonal ferrite and acicular ferrite is above 95%.

[0249] Specifically, the volume fraction of the quasi-polygonal ferrite structure is 78 - 90%, the volume fraction of the acicular ferrite structure is 5 - 20%, and the volume fraction of the pearlite structure is 2 - 5%.

[0250] Furthermore, the banded structure of the steel plate ≤ 0.5 grade.

[0251] In addition, in the steel plate, some or all of the non-metallic inclusions 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.

[0252] Specifically, in the steel plate, more than 95% (even more than 98%) of the non-metallic inclusions have the core-shell structure.

[0253] Among them, the density of the non-metallic inclusions with the core-shell structure is 42 - 68 per mm 2 , and the average diameter ≤ 1.8 μm.

[0254] In summary, compared with the first embodiment, this embodiment has more excellent mechanical properties.

[0255]

Third Embodiment

[0256] The chemical composition of the steel, by mass percentage, includes: C 0.026 - 0.056%, Si 0.08 - 0.14%, Mn 0.69 - 0.77%, Cr 0.22 - 0.30%, Ni 0.07 - 0.15%, Cu 0.16 - 0.24%, Nb 0.034 - 0.042%, V 0.034 - 0.042%, Ti 0.011 - 0.019%, Al 0.015 - 0.045%, Mg 0.0005 - 0.0012%, Ca 0.0012 - 0.0042%, P≤0.01%, S≤0.002%, O≤0.003%, N≤0.005%, H≤0.0002%, and the balance is iron and unavoidable impurities.

[0257] Furthermore, the chemical composition of the steel also satisfies: CEV(%) is 0.199 - 0.287, and / or, Pcm(%) is 0.081 - 0.131.

[0258] The chemical composition of the steel, by mass percentage, also satisfies: 0.02 ≤ Mg / Al ≤ 0.04, and / or, 0.01% ≤ Mg×Al / S ≤ 0.06%.

[0259] This embodiment also provides a casting method for a pipeline steel billet having the above chemical composition. The casting method of this embodiment is the same as the previous first embodiment and will not be elaborated here.

[0260] This embodiment also provides a production method for a pipeline steel plate having the above chemical composition. The difference between this production method and the previous first embodiment is only: controlled-temperature water cooling. Only this difference will be introduced below, and other parts not mentioned are the same as the previous first embodiment and will not be elaborated here.

[0261] In this embodiment, for the controlled-temperature water cooling process: the water inlet temperature is Ar3 - (60 - 40) °C, and the water outlet temperature T is Min(T VC , T VN ) - (150 - 130) °C.

[0262] Next, the performance, microstructure, etc. of the steel billet / steel plate of this embodiment will be introduced.

[0263] The central segregation of the steel billet is ≤ 0.5 grade, and the central porosity is ≤ 0.5 grade.

[0264] Furthermore, the ratings of Class A, B, C, and D inclusions in the steel billet are all ≤ 1 grade, and the sum of the ratings of Class A, B, C, and D inclusions is ≤ 2.5 grades.

[0265] On the cross-section of the steel billet, the density of inclusions with a diameter ≥ 10 μm is ≤ 10 pieces / cm 2 .

[0266] The yield strength R of the steel plate t0.5 ≥ 410 MPa, the tensile strength R m ≥ 472 MPa, the elongation A 50 ≥ 48%, and the yield ratio is ≤ 0.87.

[0267] The impact energy KV2 of the steel plate at -20 °C ≥ 400 J.

[0268] The hardness of the steel plate is ≤ 195 HV 10 .

[0269] The shear area fraction of the -10 °C DWTT drop hammer of the steel plate is 100%, and the shear area fraction of the -15 °C DWTT drop hammer is 100%.

[0270] The steel plate meets the requirements: in the environment of NACE TM0284 standard A solution, CLR ≤ 10%, CTR ≤ 3%, and CSR ≤ 1%.

[0271] Moreover, the steel plate meets the requirements: in the stress corrosion test according to NACE TM0177 standard, the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen.

[0272] Furthermore, the steel plate meets the requirements: in a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment.

[0273] In addition, the steel plate meets the requirements: in a 6.3 MPa pure hydrogen environment, the K of the stepped compact tension specimen 1C ≥ 110 MPa·m 1 / 2 .

[0274] The hydrogen diffusion coefficient D of the steel plate is ≤ 1.5×10 -6 cm 2 / s, and the diffusible hydrogen concentration C0 on the cathode side is ≤ 3.0×10 - 6 mol / cm 3 .

[0275] The flatness of the steel plate is ≤ 2 mm / m.

[0276] The surface stress of the steel plate is ≤ 25 MPa.

[0277] The steel plate has a complex phase structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

[0278] Among them, the average grain size of the quasi-polygonal ferrite and acicular ferrite is 3 - 8 μm.

[0279] The total volume fraction of the quasi-polygonal ferrite and acicular ferrite is more than 95%.

[0280] Specifically, the volume fraction of the quasi-polygonal ferrite structure is 78 - 90%, the volume fraction of the acicular ferrite structure is 5 - 20%, and the volume fraction of the pearlite structure is 2 - 5%.

[0281] Furthermore, the banded structure of the steel plate is ≤ grade 0.5.

[0282] In addition, in the steel plate, some or all of the non-metallic inclusions 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.

[0283] Specifically, in the steel plate, more than 95% (even more than 98%) of the non-metallic inclusions have the core - shell structure.

[0284] Among them, the density of the non-metallic inclusions with the core - shell structure is 42 - 68 per mm 2 , and the average diameter is ≤ 1.8 μm.

[0285]

Fourth Embodiment

[0286] The chemical composition of the steel in mass percentage includes: C 0.021 - 0.051%, Si 0.07 - 0.13%, Mn 0.66 - 0.74%, Cr 0.22 - 0.30%, Ni 0.16 - 0.24%, Cu 0.16 - 0.24%, Nb 0.042 - 0.050%, V 0.042 - 0.050%, Ti 0.011 - 0.019%, Al 0.015 - 0.045%, Mg 0.0005 - 0.0012%, Ca 0.0012 - 0.0042%, P ≤ 0.01%, S ≤ 0.002%, O ≤ 0.003%, N ≤ 0.005%, H ≤ 0.0002%, and the rest is iron and unavoidable impurities.

[0287] Furthermore, the chemical composition of the steel also satisfies: CEV (%) is 0.197 - 0.284, and / or, Pcm (%) is 0.075 - 0.126.

[0288] The chemical composition of the steel also satisfies, by mass percentage: 0.02 ≤ Mg / Al ≤ 0.04, and / or, 0.01% ≤ Mg×Al / S ≤ 0.06%.

[0289] This embodiment also provides a casting method for a pipeline steel billet having the above chemical composition. The casting method of this embodiment is the same as the first embodiment described above and will not be elaborated here.

[0290] This embodiment also provides a production method for a pipeline steel plate having the above chemical composition. The difference between the production method and the first embodiment described above is only: controlled-temperature water cooling. Only this difference will be introduced below, and other parts not mentioned are the same as the first embodiment described above and will not be elaborated here.

[0291] In this embodiment, for the controlled-temperature water cooling process: the water inlet temperature is Ar3 - (50 - 30)°C, and the water outlet temperature T is Min(T VC , T VN ) - (300 - 270)°C.

[0292] The performance, microstructure, etc. of the steel billet / steel plate of this embodiment will be introduced below.

[0293] The central segregation of the steel billet is ≤ 0.5 grade, and the central porosity is ≤ 0.5 grade.

[0294] Furthermore, the ratings of type A, B, C, and D inclusions of the steel billet are all ≤ 1 grade, and the sum of the ratings of type A, B, C, and D inclusions is ≤ 2.5 grades.

[0295] On the cross-section of the steel billet, the density of inclusions with a diameter ≥ 10 μm is ≤ 10 pieces / cm 2 .

[0296] The yield strength R of the steel plate t0.5 ≥ 450 MPa, the tensile strength R m ≥ 560 MPa, the elongation A 50 ≥ 40%, and the yield ratio is ≤ 0.86.

[0297] The -20°C impact energy KV2 of the steel plate ≥ 400 J.

[0298] The hardness of the steel plate is ≤ 205 HV 10 .

[0299] The -10°C DWTT drop hammer shear area fraction of the steel plate is 100%, and the -15°C DWTT drop hammer shear area fraction of the steel plate is 100%.

[0300] The steel plate satisfies the following: in the environment of NACE TM0284 standard A solution, CLR ≤ 10%, CTR ≤ 3%, and CSR ≤ 1%.

[0301] Moreover, the steel plate satisfies the following: in the stress corrosion test carried out according to NACE TM0177 standard, the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen.

[0302] Furthermore, the steel plate satisfies the following: in the 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 85%, and 80% of those in the nitrogen environment.

[0303] In addition, the steel plate satisfies the following: in the 6.3 MPa pure hydrogen environment, for the stepped compact tension specimen, K 1C ≥ 110 MPa·m 1 / 2 .

[0304] The hydrogen diffusion coefficient D of the steel plate ≤ 1.5×10 -6 cm 2 / s, and the diffusible hydrogen concentration C0 on the cathode side ≤ 3.0×10 - 6 mol / cm 3 .

[0305] The flatness of the steel plate ≤ 2 mm / m.

[0306] The surface stress of the steel plate ≤ 35 MPa.

[0307] The steel plate has a duplex structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

[0308] Among them, the average grain size of the quasi-polygonal ferrite and acicular ferrite is 2 - 8 μm.

[0309] The total volume fraction of the quasi-polygonal ferrite and acicular ferrite is more than 95%.

[0310] Specifically, the volume fraction of the quasi-polygonal ferrite structure is 5 - 17%, the volume fraction of the acicular ferrite structure is 80 - 94%, and the volume fraction of the pearlite structure is 1 - 3%.

[0311] Furthermore, the banded structure of the steel plate ≤ 0.5 grade.

[0312] In addition, in the steel plate, some or all of the non-metallic inclusions 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.

[0313] Specifically, in the steel plate, more than 95% (even more than 98%) of the non-metallic inclusions are of the core-shell structure.

[0314] Among them, the density of the non-metallic inclusions with the core-shell structure is 42 - 68 per mm 2 , and the average diameter is ≤1.8 μm.

[0315] It can be seen that in addition to the economic advantages such as low alloy content, short process flow (without coiling and heat treatment), and low production cost, and excellent hydrogen resistance and HIC resistance, the technology of this embodiment also realizes the preparation of high-strength pipeline steel, for example, reaching the L415MH level, which is extremely difficult in the field of pipeline steel and achieves a breakthrough in the development of pipeline steel.

[0316] The above text introduced the technical purpose of the present invention and four different embodiments based on the technical purpose. Next, the present invention will be further introduced through several specific test examples. Of course, these test examples are only a part of the numerous variant embodiments included in the present invention, rather than all of them.

[0317] The chemical compositions of the steel plates of these test examples are shown in Table 1. Among them, "-" in Table 1 indicates that the corresponding element was not specifically added during the preparation of the steel, and thus was not detected or the detected amount was so small that it was not recorded in the steel.

[0318] [Table 1]

[0319] These test examples were all prepared according to the production method introduced in the present invention. Specifically: Test Example 1 was prepared according to the first embodiment described above, Test Example 2 was prepared according to the second embodiment described above, Test Example 3 was prepared according to the third embodiment described above, and Test Example 4 was prepared according to the fourth embodiment described above.

[0320] Among them, some important parameters during the production process are shown in Table 2.

[0321] [Table 2]

[0322] [Continued Table 2]

[0323] The steel plates of each test example were subjected to microstructure and property detection, and the detection results are as follows: (1) The steel plate has a complex phase microstructure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite; The metallographic microstructure diagrams of Test Examples 1, 2, 3, and 4 are respectively referred to Figure 1 , 2, 3, 4; among them, the average grain sizes of the quasi-polygonal ferrite and acicular ferrite, the volume fractions of the respective microstructures in the duplex microstructure, and the banding grade are shown in Table 3 respectively; [Table 3]

[0324] (2)On the cross-section of the steel plate, the inclusion density with a diameter ≥ 10 μm ≤ 10 pieces / cm 2 ; (3)For the steel plates of each test example, the -15 °C DWTT drop-weight shear area fraction is 100%, and the strength, elongation, -20 °C impact energy KV2, hardness, flatness, surface stress, etc. are shown in Table 4; [Table 4]

[0325] (4)In the NACE TM0284 standard A solution environment, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%; in the stress corrosion test according to the NACE TM0177 standard, the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen; (5)For the steel plates of Test Examples 1 to 3, in a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 85%, and 80% of those in the nitrogen environment; for the steel plate of Test Example 4, in a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 80%, and 75% of those in the nitrogen environment; (6)For the steel plates of Test Examples 1 to 3, in a 6.3 MPa pure hydrogen environment, the K 1C ≥ 110 MPa·m 1 / 2 ; for the steel plate of Test Example 4, in a 6.3 MPa pure hydrogen environment, the K 1C ≥ 100 MPa·m 1 / 2 ; (7)In the steel plates of Test Examples 1 to 4, most of the non-metallic inclusions are of the core-shell structure, the core is MgO·Al2O3, and the shell is MnS, CaS, TiN and coats the outer surface of the inner shell; for example, Figure 5 shows the metallographic diagram of the inclusions of Test Example 3; and, the hydrogen diffusion coefficient D, the diffusible hydrogen concentration C0 on the cathode side, and the proportion of the core-shell structure in the non-metallic inclusions are shown in Table 4.

Claims

1. A pipeline steel for hydrogen energy transportation, characterized in that, The chemical composition of the steel, by mass percentage, includes: C 0.021 - 0.076%, Si 0.07 - 0.21%, Mn 0.66 - 0.93%, Cr 0.12 - 0.30%, Ni ≤ 0.24%, Cu ≤ 0.24%, Nb 0.014 - 0.052%, V 0.014 - 0.050%, Ti 0.009 - 0.019%, Al 0.015 - 0.045%, Mg 0.0005 - 0.0012%, Ca 0.0012 - 0.0042%, P ≤ 0.01%, S ≤ 0.002%, O ≤ 0.003%, N ≤ 0.005%, H ≤ 0.0002%, and the balance is iron and unavoidable impurities.

2. The pipeline steel for hydrogen energy transportation according to claim 1, characterized in that, The chemical composition of the steel, by mass percentage, also satisfies: 0.02 ≤ Mg / Al ≤ 0.04, and / or, 0.01% ≤ Mg×Al / S ≤ 0.06%.

3. The pipeline steel for hydrogen energy transportation according to claim 1, characterized in that, In the steel, some or all of the non-metallic inclusions 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.

4. The pipeline steel for hydrogen energy transportation according to claim 3, characterized in that, In the steel, more than 95% of the non-metallic inclusions have the core-shell structure.

5. The pipeline steel for hydrogen energy transportation according to claim 1, characterized in that The steel satisfies: In the environment of NACE TM0284 standard A solution, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%; And / or, stress corrosion test is carried out according to NACE TM0177 standard with an applied stress of 0.8σ s , and there are no cracks on the surface of the tensile specimen.

6. The pipeline steel for hydrogen energy transportation according to claim 1, characterized in that, The steel satisfies: In a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 80%, and 75% of those in a nitrogen environment; And / or, in a pure hydrogen environment of 6.3 MPa, the K of the stepped compact tension specimen 1C ≥ 100 MPa·m 1 / 2 .

7. The pipeline steel for hydrogen energy transportation according to claim 1, characterized in that, The steel satisfies: the hydrogen diffusion coefficient D ≤ 1.5×10 -6 cm 2 / s, and the diffusible hydrogen concentration C0 on the cathode side ≤ 3.0×10 -6 mol / cm 3 .

8. The pipeline steel for hydrogen energy transportation according to claim 1, characterized in that, The steel is a steel plate with a thickness of 8 - 30 mm or a steel billet with a thickness of 210 - 230 mm; On the cross-section of the steel, the density of inclusions with a diameter ≥ 10 μm is ≤ 10 pieces / cm 2 .

9. The pipeline steel for hydrogen energy transportation according to claim 1, characterized in that, The yield strength R of the steel t0.5 ≥ 330 MPa, the tensile strength R m ≥ 430 MPa, the elongation A 50 ≥ 40%, the yield ratio ≤ 0.87, the impact energy KV2 at -20°C ≥ 400 J, the hardness ≤ 205 HV 10 , the shear area fraction of DWTT drop hammer at -10°C is 100%, and the shear area fraction of DWTT drop hammer at -15°C is 100%.

10. The pipeline steel for hydrogen energy transportation according to claim 1, wherein, The flatness of the steel ≤ 2 mm / m, and the surface stress ≤ 35 MPa.

11. The pipeline steel for hydrogen energy transportation according to claim 1, wherein, The steel has a duplex structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite; Among them, the average grain size of the quasi-polygonal ferrite and acicular ferrite is 2 - 16 μm, and the volume ratio of the quasi-polygonal ferrite structure and the acicular ferrite structure is more than 95%.

12. The pipeline steel for hydrogen energy transportation according to claim 1, characterized in that, The chemical composition of the steel also satisfies: CEV(%) is 0.168 - 0.325, and / or, Pcm(%) is 0.069 - 0.

159.

13. A casting method for pipeline steel billets used in hydrogen energy transportation, characterized in that, The chemical composition of the steel billet, by mass percentage, includes: C 0.021 - 0.076%, Si 0.07 - 0.21%, Mn 0.66 - 0.93%, Cr 0.12 - 0.30%, Ni ≤ 0.24%, Cu ≤ 0.24%, Nb 0.014 - 0.052%, V 0.014 - 0.050%, Ti 0.009 - 0.019%, Al 0.015 - 0.045%, Mg 0.0005 - 0.0012%, Ca 0.0012 - 0.0042%, P ≤ 0.01%, S ≤ 0.002%, O ≤ 0.003%, N ≤ 0.005%, H ≤ 0.0002%, and the balance is iron and unavoidable impurities; The casting method produces the steel billet through the sequential steps of hot metal pre-desulfurization, converter smelting, LF refining, RH refining, and continuous casting; Among them, in the RH refining process: 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 / Al mass ratio to be above 0.06; after that, it is statically stirred for 2 - 3 minutes, magnesium alloy is added to control the Mg mass fraction in the molten steel to be 0.0005 - 0.0012%, and finally argon is blown from the bottom.

14. The casting method of the pipeline steel billet for hydrogen energy transportation according to claim 13, characterized in that, The "re-vacuum standing" includes: standing for 25 - 30 min under a vacuum degree of ≤30 Pa; The described "final bottom argon blowing" includes: bottom argon blowing at a flow rate of 1 Nm 3 / h or less.

15. The casting method of the pipeline steel billet for hydrogen energy transportation according to claim 13, characterized in that, During continuous casting: the superheat of the molten steel during casting is 8 - 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 respectively the perimeter and area of the cross-section of the steel billet obtained by continuous casting.

16. The casting method of the pipeline steel billet for hydrogen energy transmission according to claim 13, wherein, During hot metal pre-desulfurization: after mixing magnesium powder and lime powder, they are blown into the hot metal to control the mass ratio of S in the hot metal within 0.0012%; the blowing amount of magnesium powder is 0.35 - 0.45 Kg per ton of hot metal; During converter smelting: slag with an alkalinity of 3.0 - 3.6 is produced, and the mass ratio of P is controlled within 0.005%; During LF refining: after alloying is completed, aluminum wire is fed in to control the mass ratio of O within 0.0040%, and then the steel is tapped.

17. A production method of pipeline steel plate for hydrogen energy transportation, characterized in that, The chemical composition of the steel plate includes, by mass percentage: C 0.021 - 0.076%, Si 0.07 - 0.21%, Mn 0.66 - 0.93%, Cr 0.12 - 0.30%, Ni ≤ 0.24%, Cu ≤ 0.24%, Nb 0.014 - 0.052%, V 0.014 - 0.050%, Ti 0.009 - 0.019%, Al 0.015 - 0.045%, Mg 0.0005 - 0.0012%, Ca 0.0012 - 0.0042%, P ≤ 0.01%, S ≤ 0.002%, O ≤ 0.003%, N ≤ 0.005%, H ≤ 0.0002%, and the balance is iron and unavoidable impurities; The production method prepares a steel plate with a thickness t ≥ 8 mm from a steel billet with a thickness t0 of 150 - 320 mm through the processes of heating, rough hot rolling, finish hot rolling, final hot rolling, and controlled-temperature water cooling; Heating process: The heating temperature is not lower than the starting precipitation temperatures T of NbC, NbN, TiC, VC, and VN NbC , T NbN , T TiC , T VC , T VN ; Rough hot rolling process: The starting rolling temperature and the final rolling temperature are both T nr ~Min(T NbC ,T NbN ,T TiC ), and the plate thickness after rolling is (3.2 - 4)t; Finish hot rolling process: the starting rolling temperature and the final rolling temperature are both Ar3 - 20 °C to Ar3 + 10 °C, and the thickness of the rolled plate is t + (2 - 5) mm; Final hot rolling process: it is a single-pass hot rolling, the temperature is Ar3 - (40 - 20) °C, and the thickness of the rolled plate is t; Controlled temperature water cooling process: The inlet water temperature is Ar3 - (80~30)°C, and the outlet water temperature T is Min(T VC , T VN ) - 300°C ~ Min(T VC , T VN ) + 5°C.

18. The production method of the pipeline steel plate for hydrogen energy transportation according to claim 17, wherein, In the heating process: the heating temperature is Max(T NbC ,T NbN ,T TiC ,T VC ,T VN ) + 40°C to Min(Max(T NbC ,T NbN ,T TiC ,T VC ,T VN ) + 120°C, T TiN - 150°C).

19. The production method of the pipeline steel plate for hydrogen energy transportation according to claim 17, characterized in that, Between the rough hot rolling process and the finish hot rolling process, there is also a water cooling process, and the water outlet temperature is Ar3 - 20 °C to Ar3 + 10 °C.

20. The production method of the pipeline steel plate for hydrogen energy transportation according to claim 17, characterized in that, During the controlled-temperature water cooling process: The inlet water temperature is Ar3 - (80~60)°C, and the outlet water temperature T is Min(T VC , T VN ) - 15°C to Min(T VC , T VN ) + 5°C; Alternatively, the inlet water temperature is Ar3 - (70~50)°C, and the outlet water temperature T is Min(T VC , T VN ) - (50~30)°C; Alternatively, the inlet water temperature is Ar3 - (60~40)°C, and the outlet water temperature T is Min(T VC , T VN ) - (150~130)°C; Alternatively, the water inlet temperature is Ar3 - (50~30)°C, and the water outlet temperature T is Min(T VC , T VN ) - (300~270)°C.

21. The production method of the pipeline steel plate for hydrogen energy transportation according to claim 17, characterized in that, Rough hot rolling process: the reduction of the first rolling pass in the non-width-expanding pass is ≥42 mm, and the reduction of each pass is ≥31 mm; Finish hot rolling process: the reduction of each pass is ≥22 mm.

22. The production method of the pipeline steel plate for hydrogen energy transportation according to claim 17, characterized in that, The steel plate obtained from the final hot rolling process directly enters the ultra-fast cooling system for the controlled-temperature water cooling process, and the cooling rate is 6 - 16 °C / s; After the controlled-temperature water cooling process, hot straightening, natural air cooling on the cooling bed, warm straightening, and cold straightening are carried out in sequence; among them, the temperature during hot straightening is T - 60 °C to T; the temperature when leaving the cooling bed is 100 - 200 °C.

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