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

Abstract

The present invention discloses a method for casting pipeline steel and steel billets for hydrogen energy transportation, as well as a method for producing steel plates. Chemical composition: 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%, and the remainder is iron and impurities. The invention modifies inclusions by adding trace amounts of magnesium and calcium, creating a large number of tiny irreversible hydrogen traps in the steel without causing an excessive increase in hydrogen pressure, thereby improving the steel's hydrogen resistance and HIC resistance.

Description

Technical Field

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

[0002] The major bottleneck restricting the development of hydrogen pipelines is the potential for pipeline steel to degrade or even fail in high-pressure hydrogen environments. For example, in high-pressure hydrogen environments, pipeline steel is susceptible to hydrogen-induced cracking and blistering, significantly deteriorating its ductility, fatigue properties, and fracture toughness.

[0003] For high-pressure hydrogen pipeline steel, whether it is hydrogen-doped pipeline steel or pipeline steel for hydrogen energy transportation, higher requirements are put forward. First, the steel plate for transportation pipelines must have resistance to hydrogen-induced cracking (HIC for short). Second, the steel plate for pipelines must have excellent fracture toughness in a hydrogen environment.

[0004] Some existing technologies, such as CN115094314A, CN115433884A, and CN116103568A, have studied pipeline steel from the perspective of chemical composition. However, technologies such as those in CN115094314A and CN115433884A suffer from high alloying element content, complex steelmaking processes, and high alloy costs. Furthermore, technologies such as those in CN116103568A have high carbon content and poor weldability, hindering the application of steel plates in pipeline steel.

[0005] Furthermore, pipeline steels in existing technologies have disadvantages in terms of poor HIC resistance and hydrogen resistance when dealing with high-pressure hydrogen environments, making it difficult to meet the application requirements of pipeline steels for hydrogen energy transportation. Summary of the Invention

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

[0007] To achieve the above-mentioned object, one embodiment of the present invention provides a pipeline steel for hydrogen transportation. The chemical composition of the steel, in percentage by mass, 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 remainder is iron and unavoidable impurities.

[0008] Preferably, the chemical composition of the steel further satisfies, in percentage by mass: 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 are of a core-shell structure, wherein the core is MgO·Al2O3 and the shell is MnS, CaS, TiN and is coated on the outer surface of the inner shell.

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

[0011] Preferably, the steel meets the following requirements:

[0012] In the NACE TM0284 standard A solution environment, CLR≤10%, CTR≤3%, CSR≤1%;

[0013] And / or, stress corrosion testing according to NACE TM0177 with a loading stress of 0.8σ s , there is no crack on the surface of the tensile specimen.

[0014] Preferably, the steel meets the following requirements:

[0015] In a 6.3MPa pure hydrogen environment, the tensile strength, elongation, and cross-sectional shrinkage of the smooth specimen are greater than or equal to 90%, 80%, and 75% of those in a nitrogen environment, respectively;

[0016] And / or, K of the step-type compact tensile specimen in 6.3 MPa pure hydrogen environment 1C ≥100MPa·m 1 / 2 .

[0017] Preferably, the steel satisfies the following hydrogen diffusion coefficient D≤1.5×10 -6 cm 2 / s, the diffusible hydrogen concentration on the cathode side C0≤3.0×10 -6 mol / cm 3 .

[0018] Preferably, the steel is a steel plate with a thickness of 8 to 30 mm or a steel billet with a thickness of 210 to 230 mm;

[0019] On the cross section of the steel, the density of inclusions with a diameter of ≥10 μm is ≤10 / cm 2 .

[0020] Preferably, the yield strength R of the steel t0.5 ≥330MPa, tensile strength R m ≥430MPa, elongation A 50≥40%, yield strength ratio ≤0.87, -20℃ impact energy KV2 ≥400J, hardness ≤205HV 10 , -10℃ DWTT drop weight shear area fraction is 100%, -15℃ DWTT drop weight shear area fraction is 100%.

[0021] Preferably, the unevenness of the steel is ≤2 mm / m, and the surface stress is ≤35 MPa.

[0022] Preferably, the steel has a complex phase structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite;

[0023] Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite is 2~16μm, and the volume proportion of quasi-polygonal ferrite and acicular ferrite is more than 95%.

[0024] Preferably, the chemical composition of the steel plate further satisfies: CEV (%) is 0.168-0.325, and / or Pcm (%) is 0.069-0.159.

[0025] To achieve the above-mentioned object, one embodiment of the present invention provides a casting method for a pipeline steel billet for hydrogen transportation. The chemical composition of the steel billet, in percentage by mass, 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 remainder is iron and unavoidable impurities.

[0026] The casting method produces the steel billet by sequentially performing molten iron pre-desulfurization, converter smelting, LF refining, RH refining and continuous casting;

[0027] Among them, in RH refining: the temperature of the incoming molten steel is 1620~1660℃, firstly with 4~5Nm 3 / h, blow argon from the bottom for 1-2 minutes, let it stand in vacuum, and then break the vacuum to feed calcium wire to adjust the Ca / S mass ratio of the molten steel to 2-4 and the Ca / Al mass ratio to above 0.06; then stir it for 2-3 minutes, add magnesium alloy to adjust the Mg mass proportion in the molten steel to 0.0005-0.0012%, and finally blow argon from the bottom.

[0028] Preferably, the “re-vacuum standing” comprises: standing for 25 to 30 minutes at a vacuum degree of ≤30 Pa;

[0029] The "final bottom blowing of argon" includes: 3 Bottom blowing of argon at a flow rate of less than / h.

[0030] Preferably, during continuous casting, the superheat of the molten steel during casting is 8-20° C., and the casting speed is 0.1×L / F-0.05-0.1×L / F+0.05 m / s, where L and F are the circumference and area of ​​the cross section of the billet obtained by continuous casting, respectively.

[0031] Preferably, in the pre-desulfurization of molten iron: magnesium powder and lime powder are mixed and sprayed into the molten iron to control the sulfur content in the molten iron to within 0.0012% by mass; the spraying amount of magnesium powder is 0.35-0.45 kg per ton of molten iron;

[0032] In converter smelting: make slag with a basicity of 3.0-3.6 and control the P content within 0.005%;

[0033] During LF refining: After alloying, aluminum wire is fed to control the O mass ratio within 0.0040%, and then the steel is tapped.

[0034] To achieve the above-mentioned object, one embodiment of the present invention provides a method for producing a steel plate for a hydrogen energy transportation pipeline. The chemical composition of the steel plate comprises, by mass percentage, the following: 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 remainder is iron and unavoidable impurities.

[0035] The production method prepares steel plates with a thickness of t0 of 150-320 mm through the processes of heating, rough hot rolling, finish hot rolling, final hot rolling, and temperature-controlled water cooling;

[0036] Heating process: The heating temperature is not lower than the precipitation temperature T of NbC, NbN, TiC, VC, and VN. NbC 、T NbN 、T TiC 、T VC 、T VN ;

[0037] Rough hot rolling process: the starting rolling temperature and the final rolling temperature are both T nr ~Min(T NbC ,T NbN ,T TiC ), plate thickness after rolling (3.2~4)t;

[0038] Finishing hot rolling process: the starting and final rolling temperatures are both Ar3-20℃~Ar3+10℃, and the plate thickness after rolling is t+(2~5)mm;

[0039] Final hot rolling process: one-pass hot rolling, temperature is Ar3-(40~20)℃, and the plate thickness after rolling is t;

[0040] Temperature controlled water cooling process: water inlet temperature is Ar3-(80~30)℃, water outlet temperature T is Min(T VC ,T VN )-300℃~Min(T VC ,T VN )+5℃.

[0041] Preferably, in the heating process: the heating temperature is Max (T NbC ,T NbN ,T TiC ,T VC ,T VN )+40℃~Min(Max(T NbC ,T NbN ,T TiC ,T VC ,T VN )+120℃,T TiN -150℃).

[0042] Preferably, a water cooling process is provided between the rough hot rolling process and the finishing hot rolling process, and the outlet water temperature is Ar3-20°C to Ar3+10°C.

[0043] Preferably, in the temperature-controlled water cooling process:

[0044] The inlet water temperature is Ar3-(80~60)℃, and the outlet water temperature T is Min(T VC ,T VN )-15℃~Min(T VC ,T VN )+5℃;

[0045] Alternatively, the inlet water temperature is Ar3-(70~50)℃, and the outlet water temperature T is Min(T VC ,T VN )-(50~30)℃;

[0046] Alternatively, the water inlet temperature is Ar3-(60~40)℃, and the water outlet temperature T is Min(T VC ,T VN )-(150~130)℃;

[0047] Alternatively, the water inlet temperature is Ar3-(50~30)℃, and the water outlet temperature T is Min(T VC ,T VN )-(300~270)℃.

[0048] Preferably, in the rough hot rolling process, the reduction of the initial rolling pass (non-widening pass) is ≥42 mm, and the reduction of each pass is ≥31 mm;

[0049] Finishing hot rolling process: the reduction of each pass is ≥22mm.

[0050] Preferably, the steel plate obtained in the final hot rolling process is directly fed into the ultra-fast cooling system for temperature-controlled water cooling at a cooling rate of 6-16°C / s;

[0051] After the temperature-controlled water cooling process, hot straightening, natural air cooling on the cooling bed, warm straightening, and cold straightening are carried out in sequence; the temperature during hot straightening is T-60℃~T; the temperature of the lower cooling bed is 100~200℃.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] 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 a composite addition of Nb+V+Ti precipitation elements, which is easy to produce steel and has a low production cost;

[0054] On the other hand, the carbon content in the steel is reduced, the welding performance is excellent, which is beneficial to the welding effect of the steel when preparing pipeline steel;

[0055] On the other hand, appropriate additions of Nb, V, and Ti form carbides and nitrides, which can act as hydrogen traps to capture hydrogen, thereby reducing the diffusible hydrogen in the steel.

[0056] On the other hand, adding trace amounts of magnesium and calcium to modify the inclusions can obtain a large number of tiny irreversible hydrogen traps in the steel to adsorb hydrogen atoms in the lattice gaps or dislocations, reduce the diffusible hydrogen in the steel, and avoid the ultra-high aggregation of hydrogen at the interfaces of some non-metallic inclusions, promote the uniform distribution of hydrogen in the material, and reduce the hydrogen aggregation in the irreversible hydrogen traps in the steel (that is, it will not cause excessive increase in hydrogen pressure), thereby improving the steel's hydrogen resistance and HIC resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 is a metallographic structure diagram of the finished steel plate of Test Example 1 of the present invention;

[0058] Figure 2 is a metallographic structure diagram of the finished steel plate of Test Example 2 of the present invention;

[0059] Figure 3 is a metallographic structure diagram of the finished steel plate of Test Example 3 of the present invention;

[0060] Figure 4 is a metallographic structure diagram of the finished steel plate of Test Example 4 of the present invention;

[0061] Figure 5 This is a metallographic image of non-metallic inclusions in the finished steel plate of Test Example 3 of the present invention. DETAILED DESCRIPTION

[0062] To make the objectives, technical solutions, and advantages of the present invention more clear, 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 embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0063] The present invention provides a pipeline steel that is developed from the perspective of chemical composition to improve the steel's hydrogen corrosion resistance in high-pressure hydrogen environments (including pure hydrogen environments and hydrogen-doped environments), including HIC resistance and hydrogen resistance, thereby avoiding performance degradation or even failure.

[0064] 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 remainder is iron and unavoidable impurities.

[0065] The functions of the various chemical elements in this embodiment are described in detail below.

[0066] Carbon: Carbon is the most economical strengthening element in steel, having a solid solution strengthening effect. It also forms carbides with niobium, vanadium, titanium, chromium, etc., which have a precipitation strengthening effect. It can also act as a hydrogen trap to improve the hydrogen resistance of the steel plate. Increasing the carbon content has a significant effect on improving the strength and hardness of pipeline steel. However, too high a carbon content will lead to poor low-temperature toughness and welding performance, and reduce the low-temperature drop hammer performance of pipeline steel. Reducing the carbon content is conducive to homogenizing the composition and structure, improving the banded structure, reducing the pearlite content, and facilitating the acquisition of a larger ferrite structure. Therefore, based on comprehensive considerations, the carbon content is selected to be 0.021~0.076%.

[0067] Silicon: Silicon has a solid solution strengthening effect in steel, but when the silicon content is high, it will increase the grain boundary segregation of elements such as phosphorus and sulfur, reduce low-temperature toughness and weldability. At the same time, excessive silicon will easily produce 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%.

[0068] Manganese: Manganese plays a role in solid solution strengthening in steel, improving strength and hardness. A reasonable manganese content can ensure the strength of pipeline steel at a low cost. As the manganese content increases, the strength of pipeline steel increases significantly, while the ductile-brittle transition temperature hardly changes. Excessive manganese can cause center segregation of the ingot, which is detrimental to toughness. At the same time, it will increase the level of banded structure. The higher the level of banded structure, the more uneven the structure distribution, and the worse the resistance to hydrogen-induced cracking (HIC) and hydrogen resistance. Therefore, based on comprehensive considerations, the manganese content is selected to be 0.66~0.93%.

[0069] Chromium: Chromium plays a role in solid solution strengthening in steel. As a ferrite-forming element, chromium can obtain more acicular ferrite structure in high-niobium steel. However, when the chromium content is too high, it will increase the microhardness of pipeline steel and reduce low-temperature toughness. Therefore, based on comprehensive considerations, the chromium content is selected to be 0.12~0.30%.

[0070] Nickel: Nickel plays a role in solid solution strengthening in steel, improving the strength of steel without significantly increasing the hardness of steel. At the same time, it can improve the low-temperature toughness and welding performance of steel plates. However, when the nickel content is too high, the cost of the alloy increases. Therefore, taking all factors into consideration, it is possible to consider adding nickel, with the addition amount not exceeding 0.24%. Of course, it is not necessary to add nickel in this application, and nickel may not be added in some embodiments.

[0071] Copper: Copper can promote the precipitation of niobium and compensate for the strength loss caused by the decrease in carbon content. Adding a certain amount of nickel at the same time as copper can effectively suppress surface cracks. However, a high copper content is not conducive to welding performance. Therefore, considering all factors, it is possible to consider adding copper, with the addition amount not exceeding 0.24%. Of course, the addition of copper is not required for this application, and copper can also be omitted in some embodiments.

[0072] Niobium: Niobium is an important grain-refining element in steel. During hot rolling, niobium strongly inhibits austenite recrystallization and its precipitation in austenite, pinning the austenite grain boundaries and refining the recrystallized grains. During cooling, the dissolved niobium can continue to precipitate as niobium carbonitrides, significantly refining the resulting microstructure after phase transformation and 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, higher niobium contents can lead to increased alloy costs. Therefore, based on comprehensive considerations, the niobium content is selected to be 0.014-0.052%.

[0073] Vanadium: Vanadium can significantly improve the hardenability and strength of steel, and can also refine the grains. Vanadium is a strong carbide-forming element, reacting with carbon and nitrogen in steel to form carbides and nitrides, which can act as a hydrogen trap and improve the hydrogen resistance of the steel plate. However, when the vanadium content is too high, the alloy cost increases significantly. Therefore, based on comprehensive considerations, the vanadium content is selected to be 0.014~0.050%.

[0074] Titanium: Titanium is a nitrogen-fixing element in steel. It can form dispersed titanium nitride particles, which act as 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 and rolling processes. If the addition amount is too high, coarse carbon and nitride precipitation will easily form in the core of the ingot, affecting the low-temperature toughness of the steel plate. Therefore, based on comprehensive considerations, the titanium content is selected to be 0.009~0.019%.

[0075] Aluminum: A strong deoxidizing element that preferentially combines with oxygen in 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 capacity, reducing hydrogen enrichment at grain boundaries or defects, and thus reducing hydrogen-induced cracking sensitivity. Excessive addition will form large-sized Al2O3, which is extremely detrimental to hydrogen resistance. Taking all factors into consideration, in one embodiment, the aluminum content is selected to be 0.015~0.045%.

[0076] Magnesium: Even trace amounts of magnesium can modify Al2O3 into fine magnesium-aluminum spinel (MgO·Al2O3). However, excessive magnesium addition can produce excessive Al-Mg-O-Mn-S inclusions. These inclusions are difficult to disperse in the molten steel and tend to aggregate and merge into larger inclusions, even forming chain-like inclusions. This is detrimental to improving hydrogen resistance. Research has shown that in one embodiment, the magnesium content is controlled between 0.0005% and 0.0012%.

[0077] Calcium: It can modify the morphology of sulfides and oxides and improve the toughness of steel. The interfacial energy of spherical inclusions after Ca treatment is low, which may form weak hydrogen traps and reduce the local enrichment of hydrogen. In addition, calcium treatment can indirectly optimize the distribution of inclusions and reduce the migration rate of hydrogen under stress. If excessive amount is added, the beneficial effects cannot be equivalently improved. Taking all factors into consideration, in one embodiment, the calcium content is controlled at 0.0012~0.0042%.

[0078] Phosphorus, sulfur, oxygen, nitrogen, and hydrogen: impurity elements in steel can be controlled to P ≤ 0.01%, S ≤ 0.002%, O ≤ 0.003%, N ≤ 0.005%, and H ≤ 0.0002%. Taking into account the cost of steelmaking, it is preferred that any one or more of the following conditions be met: P 0.0050-0.0090%, S 0.0008-0.0014%, O 0.0012-0.0026%, N 0.0022-0.0042%, and H 0.00004-0.00015%.

[0079] The steel of the present invention is designed with the following chemical components:

[0080] 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 a composite addition of Nb+V+Ti precipitation elements, which is easy to produce steel and has a low production cost;

[0081] On the other hand, the carbon content in the steel is reduced, the welding performance is excellent, which is beneficial to the welding effect of the steel when preparing pipeline steel;

[0082] On the other hand, appropriate additions of Nb, V, and Ti form carbides and nitrides, which can act as hydrogen traps to capture hydrogen, thereby reducing the diffusible hydrogen in the steel.

[0083] On the other hand, adding trace amounts of magnesium and calcium to modify the inclusions can obtain a large number of tiny irreversible hydrogen traps in the steel to adsorb hydrogen atoms in the lattice gaps or dislocations, reduce the diffusible hydrogen in the steel, and avoid the ultra-high aggregation of hydrogen at the interfaces of some non-metallic inclusions, promote the uniform distribution of hydrogen in the material, and reduce the hydrogen aggregation in the irreversible hydrogen traps in the steel (that is, it will not cause excessive increase in hydrogen pressure), thereby improving the steel's hydrogen resistance and HIC resistance.

[0084] Next, the technical effects of the modification of inclusions by magnesium and calcium will be introduced in detail from the principle perspective.

[0085] Diffusible hydrogen is an important factor affecting hydrogen embrittlement behavior. An appropriate amount of hydrogen traps are introduced into steel to capture hydrogen, thereby reducing 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, low-angle grain boundaries, etc.) have a low binding energy with hydrogen, and they can both capture and release hydrogen. In this way, the hydrogen in the reversible hydrogen traps is a harmful hydrogen source, which is easy to diffuse and participate in the hydrogen-induced cracking process; irreversible hydrogen traps (such as high-angle grain boundaries, precipitated phases, retained austenite and inclusions, etc.) have a high binding energy with hydrogen. Once hydrogen atoms enter the trap, they will not easily leave. In this way, the hydrogen in the irreversible hydrogen traps is difficult to escape, and the diffusion movement of hydrogen is inhibited, thereby improving the hydrogen resistance of steel.

[0086] However, the inventors discovered in their research that the interface of non-metallic inclusions (such as MnS and Al2O3) in inclusions is an irreversible hydrogen trap and has a very strong binding ability with hydrogen. Although diffusible hydrogen can be captured, hydrogen easily accumulates there and generates hydrogen pressure. When the hydrogen pressure exceeds the material's tolerance limit, it will cause material failure, such as hydrogen-induced cracking.

[0087] Based on this, the present invention uses trace magnesium to modify the inclusions, so that a large number of tiny irreversible hydrogen traps are obtained in the steel to adsorb hydrogen atoms in the lattice gaps or dislocations, thereby reducing the diffusible hydrogen in the steel; more importantly, it also avoids the ultra-high aggregation of hydrogen at the interfaces of some non-metallic inclusions, promotes the uniform distribution of hydrogen in the material, reduces the hydrogen aggregation in the irreversible hydrogen traps in the steel (that is, it will not cause an excessive increase in hydrogen pressure), and thus improves the hydrogen resistance of the steel.

[0088] Furthermore, in the steel, some or all of the non-metallic inclusions are of a core-shell structure, wherein the core is MgO·Al2O3 and the shell is MnS, CaS, TiN and covers the outer surface of the inner shell.

[0089] In this way, Al2O3 is modified into spherical inclusions MgO·Al2O3 by the addition of magnesium and calcium. In combination with the design of the content of Mn, S, Ca, Ti, and N, sulfides and nitrides are induced to precipitate on the surface of the spherical inclusions, so that dispersed composite inclusions are formed in the steel. That is, some or all of the non-metallic inclusions have a core-shell structure. Such composite inclusions constitute irreversible hydrogen traps. 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.

[0090] Preferably, among all the non-metallic inclusions in the steel, the number of non-metallic inclusions with a core-shell structure accounts for more than 95%, and more preferably more than 98%.

[0091] Furthermore, in one embodiment, the chemical composition of the steel material satisfies the following relationship in terms of mass percentage: 0.02≤Mg / Al≤0.04. In this way, the inclusion Al2O3 can be completely modified.

[0092] In another embodiment, the chemical composition of the steel further satisfies, by mass percentage, the following: 0.01% ≤ Mg × Al / S ≤ 0.06%. This, in addition to modifying the inclusions with trace amounts of magnesium, further ensures the formation of sufficient nucleation sites to promote the formation of soft sulfides and prevent the formation and agglomeration of elongated sulfides. This increases and optimizes the number of non-metallic inclusions in the core-shell structure, improving hydrogen resistance.

[0093] Furthermore, the steel may be a steel billet with a thickness of 210 to 230 mm, or may be a steel plate with a thickness of 8 to 30 mm.

[0094] It is understandable that when the steel material is implemented as a steel billet with a thickness of 210-230 mm, it can be cast by smelting and continuous casting.

[0095] When the steel material is implemented as a steel plate with a thickness of 8 to 30 mm, it can be prepared from a steel billet through a process such as hot rolling.

[0096] Furthermore, on the cross section of the steel, the density of inclusions with a diameter of ≥10 μm is ≤10 / cm 2 .

[0097] In this way, through the design of trace magnesium, the inclusions in the steel are refined, softened, and spheroidized, forming dispersed "core-shell" structure inclusions, and forming a large number of tiny irreversible hydrogen traps, which not only reduces diffusible hydrogen but also avoids excessive hydrogen pressure, thereby truly improving the hydrogen resistance and HIC resistance.

[0098] Preferably, the density of non-metallic inclusions in the core-shell structure in the steel is 42 to 68 per mm 2 , average diameter ≤1.8μm.

[0099] Further preferably, the chemical composition of the steel, expressed in mass percentage, may satisfy the following: Mn / C is 12 to 26. Thus, by controlling the manganese-carbon ratio, segregation is reduced, banded structure is improved, and microstructure distribution is uniform, thereby improving the HIC resistance and hydrogen resistance of the steel plate.

[0100] Furthermore, the chemical composition of the steel also satisfies: CEV (%) is 0.168~0.325.

[0101] Carbon equivalent CEV (%) can be calculated using the following formula:

[0102] CEV (%) = [C] + [Mn] / 6 + ( [Cr] + [V]) / 5 + ( [Cu] + [Ni]) / 15. However, the present application is not limited thereto.

[0103] Preferably, the chemical composition of the steel may also satisfy: Pcm(%) is 0.069~0.159.

[0104] In one embodiment, Pcm(%) can be calculated using the following formula:

[0105] Pcm(%)=[C]+[Si] / 30+([Mn]+[Cu]+[Cr]) / 20+[Ni] / 60+[V] / 10.

[0106] Furthermore, when the steel is implemented as a steel plate with a thickness of 8 to 30 mm, the steel plate has excellent mechanical properties.

[0107] For example, the yield strength R of the steel plate t0.5 ≥330MPa, tensile strength R m ≥430MPa, elongation A 50 ≥40%, yield strength ratio ≤0.87.

[0108] Here, the steel plate can be sampled and mechanical properties tested in accordance with GB / T 2975-2018 "Sampling location and specimen preparation for mechanical properties testing of steel and steel products" and GB / T 228.1-2021 "Tensile testing of metallic materials - Part 1: Room temperature test method".

[0109] Furthermore, the steel plate has excellent low-temperature toughness.

[0110] For example, the steel plate has an impact energy KV2 of ≥400J at -20°C.

[0111] The hardness of the steel plate is ≤205HV 10 .

[0112] The steel plate has a -10°C DWTT drop weight shear area fraction of 100%, and a -15°C DWTT drop weight shear area fraction of 100%.

[0113] Here, the steel plate can be sampled and subjected to low-temperature performance testing in accordance with GB / T 2975-2018 "Steel and Steel Products - Sampling Location and Specimen Preparation for Mechanical Properties Tests" and GB / T 229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials".

[0114] The steel plate also has excellent hydrogen resistance and HIC resistance.

[0115] For example, the steel plate also meets the following requirements:

[0116] In the NACE TM0284 standard A solution environment, CLR≤10%, CTR≤3%, CSR≤1%;

[0117] And / or, stress corrosion testing according to NACE TM0177 with a loading stress of 0.8σ s , there is no crack on the surface of the tensile specimen.

[0118] For another example, the steel plate also satisfies:

[0119] In a 6.3MPa pure hydrogen environment, the tensile strength, elongation, and cross-sectional shrinkage of the smooth specimen are greater than or equal to 90%, 80%, and 75% of those in a nitrogen environment, respectively;

[0120] And / or, K of the step-type compact tensile specimen in 6.3 MPa pure hydrogen environment 1C ≥100MPa·m 1 / 2 .

[0121] It can be seen that the steel plate, when used for pure hydrogen transportation pipeline steel, can also have excellent hydrogen corrosion resistance and meet the application of pure hydrogen transportation projects.

[0122] Here, the third and fourth items mentioned above can be specifically sampled and tested on the steel plates in accordance with GB / T 34542.2-2018 "Hydrogen Storage and Transportation Systems Part 2: Test Method for Compatibility of Metallic Materials with Hydrogen Environments".

[0123] Furthermore, the hydrogen diffusion coefficient of the steel is D≤1.5×10 -6 cm 2 The hydrogen diffusion coefficient D can be measured according to the method disclosed in ISO 17081:2014.

[0124] The cathode side diffusible hydrogen concentration of the steel is C0≤3.0×10 -6 mol / cm 3 .

[0125] Here, the cathode side diffusible hydrogen concentration C0 can be measured according to the method disclosed in GB / T 34542.3-2018 "Test method for hydrogen embrittlement sensitivity Part 3: Electrochemical hydrogen charging method".

[0126] Furthermore, the steel plate has an excellent plate shape.

[0127] For example, the unevenness of the steel plate is ≤ 2 mm / m. In this way, the internal stress of the steel plate is small, which can improve the hydrogen resistance and HIC resistance.

[0128] Furthermore, the residual stress of the steel plate is small.

[0129] For example, the surface stress of the steel plate is ≤35 MPa. In this way, the residual stress of the steel plate is small, which can improve the hydrogen resistance and HIC resistance.

[0130] In addition, in terms of structure, the steel plate has a complex phase structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

[0131] The average grain size of quasi-polygonal ferrite and acicular ferrite is 2 to 16 μm, which reduces the probability of hydrogen-induced cracking at grain boundaries and improves HIC resistance.

[0132] Preferably, the total volume proportion of quasi-polygonal ferrite and acicular ferrite is greater than 95%. This structure can ensure a good match of various mechanical properties of the steel plate, such as strength, low-temperature toughness, yield ratio, hardness, and drop weight performance.

[0133] Specifically, the volume proportion of the quasi-polygonal ferrite structure is 5-90%, the volume proportion of the acicular ferrite structure is 5-94%, and the volume proportion of the pearlite structure is 1-5%.

[0134] Furthermore, the banded structure of the steel plate is ≤ grade 0.5, which can reduce hydrogen-induced cracking caused by the banded structure and improve hydrogen resistance.

[0135] Furthermore, the central segregation of the steel plate is ≤0.5 level, and the central porosity is ≤0.5 level.

[0136] Here, the central segregation can be specifically determined in accordance with GB / T 34474-2017 "Methods for evaluating the microstructure of steel", by using the sulfur print method or electron probe to detect the degree of element segregation in the central area of ​​the ingot.

[0137] The central porosity level can be determined by a macro-acid immersion test in accordance with GB / T 226-2015 "Macrostructure and Defect Acid Etching Test of Steel", or by ultrasonic testing.

[0138] Furthermore, the ratings of the A, B, C, and D inclusions of the steel plate are all ≤ level 1, and the sum of the ratings of the A, B, C, and D inclusions is ≤ level 2.5.

[0139] Here, the rating of A, B, C, and D inclusions can be specifically based on GB / T 10561-2005 "Microscopic inspection method for the determination of the content of non-metallic inclusions in steel - standard rating chart", and the rating can be compared with the standard chart under a microscope.

[0140] Furthermore, 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 the steel billet.

[0141] The casting method produces the steel billet through sequential molten iron pre-desulfurization, converter smelting, LF refining, RH refining and continuous casting.

[0142] Among them, RH refining:

[0143] The temperature of the molten steel entering the station is 1620~1660℃, first with 4~5Nm 3 Blow argon gas at a flow rate of / h for 1-2 minutes. This way, the molten steel is stirred significantly by the large flow rate of argon gas at high temperature, which can cause large initial inclusions to float up. In addition, it can also avoid long refining time and thus prevent excessive temperature drop of the molten steel.

[0144] After blowing argon from the bottom, the steel is left to stand in vacuum. In this way, the oxygen content in the molten steel can be reduced to below 0.003% in a vacuum environment, thus reducing the generation of secondary inclusions.

[0145] Then, the vacuum is broken and the 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. This calcium treatment can completely transform the Al2O3 in the molten steel into liquid or semi-liquid calcium aluminate, thereby promoting the spheroidization of inclusions.

[0146] Then, the steel is stirred for 2 to 3 minutes. This can improve the conversion rate of Al2O3 into liquid or semi-liquid calcium aluminate, for example, the conversion rate can be increased to more than 90%, and the formed liquid or semi-liquid calcium aluminate can be more easily modified into fine and spherical magnesium aluminum spinel (MgO·Al2O3). Then, magnesium alloy is added to adjust the Mg mass proportion in the molten steel to 0.0005 to 0.0012%, and the liquid or semi-liquid calcium aluminate can be fully modified into fine and spherical magnesium aluminum spinel (MgO·Al2O3). Finally, argon is blown from the bottom to promote uniform distribution of inclusions.

[0147] Here, let me explain in principle:

[0148] First, trace amounts of magnesium are used to modify calcium aluminate into magnesium aluminate spinel (MgO·Al2O3). Magnesium aluminate spinel exists in a solid state in molten steel and does not undergo a polymerization growth process. Therefore, the size of inclusions can be reduced and the alumina is modified from an irregular shape to a nearly spherical shape. At the same time, small inclusions have low buoyancy in molten steel and are difficult to float, resulting in an increase in the number of inclusions retained in the steel, forming diffusely distributed irreversible hydrogen traps.

[0149] Second, MnS uses magnesia-alumina spinel as the nucleation core to form Al-Ti-Mg-O-Mn-S-Ca composite inclusions that are soft on the outside and hard on the inside, with a "core-shell" and "core-shell-like" structure. Furthermore, this "core-shell" structured inclusion, on the one hand, can prevent the hard alumina and magnesia-alumina spinel from cutting the steel matrix and reduce the generation of microcracks in the steel. On the other hand, the soft MnS has a hard core, making the inclusions in the steel approximately round, reducing hydrogen-induced cracking caused by excessive hydrogen pressure due to hydrogen enrichment.

[0150] Among them, in the "breaking vacuum and feeding calcium wire", the amount of feeding calcium wire can be controlled to be 200~400m, but is not limited to this.

[0151] Optionally, in RH refining, the "bottom blowing argon followed by vacuum standing" is performed by standing for 25 to 30 minutes at a vacuum degree of ≤30 Pa. Such a high vacuum degree can further reduce the oxygen content in the water.

[0152] In one embodiment, during RH refining, the magnesium alloy is preferably a nickel-magnesium alloy having a magnesium content of 20-40%. This not only allows liquid or semi-liquid calcium aluminate to be fully reformed into fine, spherical magnesium aluminate spinel (MgO·Al2O3), but also helps reduce magnesium vapor pressure and improve magnesium yield.

[0153] In one embodiment, during RH refining, the "finally, bottom blowing argon" is performed at a rate of 1 Nm 3 Blow argon at a flow rate of less than 1 / h, and then stir weakly for 15-20 minutes. In this way, the flow rate of bottom blowing argon is small, which can stabilize the distribution of inclusions.

[0154] Furthermore, during continuous casting: the superheat of the molten steel during casting is 8~20°C, and the billet drawing speed is 0.1×L / F-0.05~0.1×L / F+0.05 m / s, where L and F are the circumference and area of ​​the cross-section of the billet obtained by continuous casting, respectively.

[0155] In this way, through low superheat casting and appropriate drawing speed, the low-multiple mass of the steel billet (i.e., steel billet) obtained by continuous casting can be greatly improved, and the segregation and central porosity in the steel billet can be reduced.

[0156] An optional implementation of continuous casting is introduced above. However, it can be understood that the present invention is not limited to the specific operation of continuous casting, and any feasible continuous casting technology in the art can be used for implementation.

[0157] Furthermore, in one embodiment, the molten iron is pre-desulfurized by mixing magnesium powder and lime powder and spraying them into the molten iron to control the mass proportion of S in the molten iron to within 0.0012%; the spraying amount of magnesium powder is 0.35~0.45Kg per ton of molten iron.

[0158] In one embodiment, in converter smelting, slag with a basicity of 3.0-3.6 is produced, and the P mass ratio is controlled within 0.005%.

[0159] Specifically, during converter smelting, oxygen can be blown from the top and argon from the bottom. By adjusting the blowing pressure, the stirring intensity of the molten pool can be controlled to 0.8~1.2Nm 3 / min·t.

[0160] Furthermore, during converter smelting, lime and dolomite can be used to produce slag with a basicity of 3.0~3.6.

[0161] In one embodiment, LF refining: After the gold treatment is completed, aluminum wire is fed to control the O mass ratio to within 0.0040%, and then the steel is tapped.

[0162] The specific amount of aluminum wire fed is not limited in this application, and is based on ensuring the Alt content in the final molten steel. For example, it can be 100~300m of aluminum wire.

[0163] The above introduces an optional implementation method of molten iron pre-desulfurization, converter smelting, and LF refining. However, it can be understood that the present invention does not limit the specific operations of molten iron pre-desulfurization, converter smelting, and LF refining, and can also be implemented using any feasible technology in the field.

[0164] In another embodiment, when the steel material is further implemented as a steel plate with a thickness of 8 to 30 mm, it can be further prepared from a steel billet with a thickness of 210 to 230 mm. The present invention also provides a method for producing the steel plate.

[0165] The production method prepares a steel plate with a thickness t of 8 to 30 mm through the processes of heating, rough hot rolling, finish hot rolling, final hot rolling, and temperature-controlled water cooling from a steel billet with a thickness t0 of 150 to 300 mm.

[0166] Here, the specific chemical composition of the steel billet used may be as described above.

[0167] Furthermore, the steel billet can be prepared by the casting method described above, but the present application is not limited thereto. For example, any feasible technology in the art can also be used for implementation.

[0168] In the heating process: After the billet leaves the continuous casting machine, it directly enters the heating furnace for heating.

[0169] The heating temperature is not lower than the precipitation start temperature T of NbC, NbN, TiC, VC and VN respectively. NbC 、T NbN 、T TiC 、T VC 、T VN .

[0170] In the rough hot rolling process: the starting rolling temperature and the final rolling temperature are both T nr ~Min(T NbC ,T NbN ,T TiC ), the thickness of the plate after rolling is (3.2~4)t.

[0171] Preferably, the starting rolling temperature of the rough hot rolling may be higher than the finishing rolling temperature.

[0172] Among them, T nr It indicates the lowest temperature of austenite recrystallization, which can be obtained through various methods such as theoretical calculation, experimental measurement and empirical formula.

[0173] For example, in one embodiment, T can be calculated according to the following formula: nr :T nr =887+464[C]+(6445[Nb]-644 )+(732[V]-230 )+890[Ti]+363[Al]–357[Si]. But T nr The value of is not limited to this. nr Other value-taking methods that can be known based on the concept can all be applied to the present invention.

[0174] Furthermore, Min(T NbC ,T NbN ,T TiC ) means: in T NbC , T NbN , T TiC The minimum of these three temperature values.

[0175] Thus, in the rough hot rolling process:

[0176] At the recrystallization temperature T nr The above rolling is carried out to avoid mixed crystals; and the temperature is always controlled at Min (T NbC ,T NbN ,T TiC ) below, to ensure that the carbon and nitride of Nb and the carbide of Ti are effectively precipitated during the rolling process, thereby preventing the growth of recrystallized grains and refining the recrystallized grains;

[0177] Furthermore, rolling in a higher temperature range can reduce the rolling deformation resistance and increase the reduction, which is conducive to the deformation penetration into the core of the billet, improving defects such as core segregation and looseness, and at the same time, reducing banded structure; secondly, adopting large reduction rolling (i.e. rolling from thickness t0 to thickness (3.2~4)t) to fully break up the continuous casting structure and obtain refined recrystallized grains. The greater the total reduction, the more obvious the refinement effect on the austenite grains, and because the temperature is low, the grains will not grow excessively.

[0178] In the finishing hot rolling process: the starting rolling temperature and the final rolling temperature are both Ar3-20℃~Ar3+10℃, and the plate thickness after rolling is t+(2~5)mm.

[0179] Preferably, the starting rolling temperature of the finish hot rolling may be higher than the final rolling temperature.

[0180] Ar3 is the temperature at which austenite (γ-Fe) begins to precipitate ferrite (α-Fe) during cooling, which can be obtained by testing and measuring using a differential scanning calorimeter (DSC) or thermogravimetric analysis (TG), or by an empirical formula.

[0181] 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 of Ar3 is not limited to this. Other values ​​known to those skilled in the art based on the concept of Ar3 can be applied to the present invention.

[0182] In this way, during the finishing hot rolling, the entire process is rolling in the two-phase critical region, and:

[0183] On the one hand, a large reduction deformation is carried out in the non-recrystallization zone (i.e., rolling from a thickness of (3.2~4)t to a thickness of t+(2~5)mm) to obtain a deformed structure, which causes a large number of deformation bands to accumulate in the structure. In the subsequent temperature-controlled cooling process, a fine structure is obtained, thereby improving the low-temperature toughness of the steel plate.

[0184] On the other hand, large reduction deformation can induce the precipitation of the second phase and obtain more fine precipitates;

[0185] On the other hand, rolling deformation within a temperature range of 30°C near the starting point Ar3 of the two-phase transformation can ensure that more deformation-induced ferrite is obtained, for example, a large amount of quasi-polygonal ferrite can be formed, and at the same time, the deformation-induced ferrite grains are relatively fine.

[0186] The final hot rolling process is a single hot rolling process, that is, it only includes one hot rolling process, the temperature is Ar3-(40~20)℃, and the plate thickness after rolling is t.

[0187] Preferably, the temperature of the final hot rolling is lower than the final rolling temperature of the finish hot rolling.

[0188] In this way, by controlling the reduction (i.e., 2-5 mm) and temperature of the final hot rolling, the shape of the steel plate can be guaranteed and the performance of the final steel plate can be improved.

[0189] In the temperature-controlled water cooling process: the water inlet temperature is Ar3-(80~30)℃, the water outlet temperature T is Min(T VC ,T VN )-300℃~Min(T VC ,T VN )+5℃.

[0190] It can be understood that the water outlet temperature T is lower than the water inlet temperature.

[0191] Among them, Min(T VC ,T VN ) means: in T VC , T VN The minimum of these two temperature values.

[0192] As previously mentioned, deformation-induced ferrite transformation occurs in the steel plate during the finishing and final hot rolling processes, producing a large amount of fine deformation-induced ferrite (such as quasi-polygonal ferrite). Furthermore, a temperature-controlled water cooling process cools the steel plate to the ferrite transformation zone, where the ferrite transformation continues, resulting in a larger amount of ferrite (for example, acicular ferrite). This prevents the formation of hard phases such as pearlite, bainite, and MA, thereby ensuring the HIC and hydrogen resistance of hydrogen pipeline steel.

[0193] Furthermore, the control of the outlet water temperature is conducive to the precipitation of V carbon and nitrides, forming more hydrogen traps for capturing hydrogen, thereby reducing the diffusible hydrogen in the steel plate and further improving the steel's HIC resistance and hydrogen resistance.

[0194] In summary, the production method of the present invention optimizes and controls the steel plate in terms of grain size, banded structure, hard phase structure, inclusion size and quantity, strength, hardness, low-temperature toughness, plate shape, residual stress, HIC resistance, hydrogen resistance, etc. through process control such as chemical composition and hot rolling, temperature-controlled water cooling, etc. No additional heat treatment is required after rolling, and the weldability is excellent, the production pace is fast, and the resulting steel plate has excellent overall performance.

[0195] Preferably, in the heating process: the heating temperature is Max (T NbC ,T NbN ,T TiC ,T VC ,T VN )+40℃~Min(Max(TNbC ,T NbN ,T TiC ,T VC ,T VN )+120℃,T TiN -150℃).

[0196] Among them, Max(T NbC ,T NbN ,T TiC ,T VC ,T VN ) means: in T NbC , T NbN , T TiC , T VC , T VN The maximum value among these five temperature values.

[0197] Min(Max(T NbC ,T NbN ,T TiC ,T VC ,T VN )+120℃,T TiN -150℃) means: at Max(T NbC ,T NbN ,T TiC ,T VC ,T VN )+120℃,T TiN -150℃ is the minimum of the two temperature values, that is, the relatively smaller one of the two.

[0198] In this way, by controlling the heating temperature, the alloy elements are effectively dissolved, ensuring that the carbon and nitrides 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 precipitation during the subsequent recrystallization zone rolling (i.e., rough hot rolling).

[0199] The heating time is preferably controlled to be (1.1~1.3)t0min / mm. That is, according to the thickness t of the steel billet 0， The heating time per millimeter is 1.1~1.3 minutes.

[0200] Furthermore, the whole process temperature of the rough hot rolling process is preferably T nr ~Min(T NbC ,T NbN ,T TiC ).

[0201] The temperature throughout the finishing hot rolling process is preferably in the range of Ar3-20°C to Ar3+10°C.

[0202] In one embodiment, a water cooling process is further provided between the rough hot rolling process and the finish hot rolling process, and the outlet water temperature is Ar3-20°C to Ar3+10°C.

[0203] In this way, after rolling in the recrystallization zone of rough hot rolling, fine recrystallized grains are obtained, and then quickly cooled to below the recrystallization temperature through a water-cooling cooling device. On the one hand, this prevents the recrystallized grains from growing rapidly during the waiting process, thereby causing the final low-temperature toughness of the steel plate to deteriorate; on the other hand, it reduces the waiting time and improves rolling efficiency.

[0204] Furthermore, during the rough hot rolling, the reduction in each pass is ≥31 mm, and the reduction in the initial rolling pass that is not a widening pass is ≥42 mm.

[0205] In this way, when the total reduction of rough hot rolling is large, a large reduction is also used in each pass to fully break up the continuous casting structure and obtain refined recrystallized grains. The larger the total reduction and the larger the reduction in a single pass, the more obvious the refinement effect on the austenite grains.

[0206] During the finishing hot rolling, the reduction in each pass is ≥22mm.

[0207] In this way, a large amount of 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 a fine structure is obtained in the subsequent cooling process, thereby improving the low-temperature toughness of the steel plate.

[0208] Next, the steel plates obtained from the final hot rolling process are directly fed into the ultra-fast cooling system for temperature-controlled water cooling.

[0209] Specifically, on the ultrafast cooling system, the cooling rate is 6~16℃ / s.

[0210] Furthermore, in the temperature-controlled water cooling process, the water pressure of the ultra-fast cooling system is 0.15~0.20MPa, the upper and lower water ratio is 0.92~0.98, and the roller speed is 1.5~2.2m / s.

[0211] Furthermore, the production method also includes performing hot straightening, natural air cooling on a cooling bed, warm straightening, and cold straightening in sequence after the temperature-controlled water cooling process.

[0212] The temperature during hot straightening is T-60℃~T. In this way, the outlet water temperature T of the steel plate in the ultra-fast cooling system is Min(T VC ,T VN )-150℃~Min(T VC ,T VN)-130℃, it is still in the ferrite phase transformation zone, but phase transformation stress and thermal stress already exist in the steel plate. The steel plate enters the hot straightening machine system and undergoes temperature-controlled hot straightening in the high-temperature ferrite phase transformation zone. In this way, the phase 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.

[0213] When the cooling bed is naturally air-cooled, the temperature of the lower cooling bed is 100-200°C. In this way, when the steel plate is naturally air-cooled on the cooling bed, self-tempering will occur, and the ferrite phase transformation can be completed on the cooling bed, thereby further releasing the phase transformation stress and thermal stress.

[0214] It should be noted that in this application, T NbC 、T NbN 、T TiC 、T TiN 、T VC 、T VN They are the precipitation start temperatures of NbC, NbN, TiC, TiN, VC and VN respectively, which can be analyzed by thermodynamic calculation software (such as Thermo-Calc) or laboratory measurement (such as thermal simulation test) combined with the chemical composition of the specific steel billet.

[0215] In one embodiment, T NbC The formula lg([Nb]×[C] 0.875 )=2.97-7500 / (T NbC +273.15) is calculated, but T NbC The value of is not limited to this.

[0216] T NbN This can be done by the formula lg([Nb]×[N])=3.70-10800 / (T NbN +273.15) is calculated, but T NbN The value of is not limited to this.

[0217] T TiC The formula can be obtained by lg([Ti]×[C])=5.33-10475 / (T TiC +273.15) is calculated, but T TiC The value of is not limited to this.

[0218] T TiN It can be calculated by the formula lg([Ti]×[N])=0.32-8000 / (T TiN +273.15) is calculated, but T TiN The value of is not limited to this.

[0219] T VCIt can be calculated by the formula lg([V]×[C])=6.72-9500 / (T VC +273.15) is calculated, but T VC The value of is not limited to this.

[0220] T VN The formula can be used to calculate the value of lg([V]×[N])=3.46-8330 / (T VN +273.15) is calculated, but T VN The value of is not limited to this.

[0221] Those skilled in the art will be able to NbC 、T NbN 、T TiC 、T TiN 、T VC 、T VN Other value-taking methods that can be known based on the respective concepts can all be applied to the present invention.

[0222] In addition, where necessary, in this application, [C], [Si], [Mn], [Cr], [V], [Cu], [Ni], [Nb], [N], [Ti], and [Al] refer to the mass percentages of C, Si, Mn, Cr, V, Cu, Ni, Nb, N, Ti, and Al in the steel, respectively. For example, if the mass percentage of Nb in the steel is 0.044%, then the mass percentage of Nb [Nb] is 0.044.

[0223] The above is a general introduction to the technical purpose of the present invention. The following is a detailed introduction to four different implementation methods based on the technical purpose of the present invention. These four implementation methods correspond to four different grades of pipeline steel.

[0224] [First embodiment]

[0225] This embodiment provides a medium-low strength pipeline steel, such as L245MH grade (i.e., yield strength R t0.5 ≥245MPa) or L290MH grade (also known as yield strength R t0.5 ≥290MPa) pipeline steel, which can be used in pure hydrogen and / or hydrogen-blended transmission pipeline projects.

[0226] The chemical composition of the steel includes, by mass percentage, 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 remainder is iron and unavoidable impurities.

[0227] Furthermore, the chemical composition of the steel material further satisfies: CEV (%) is 0.201-0.289, and / or Pcm (%) is 0.094-0.145.

[0228] The chemical composition of the steel material further satisfies, in terms of mass percentage, the following: 0.02≤Mg / Al≤0.04, and / or, 0.01%≤Mg×Al / S≤0.06%.

[0229] This embodiment provides a method for casting a pipeline steel billet having the above chemical composition.

[0230] The casting method produces the steel billet through sequential molten iron pre-desulfurization, converter smelting, LF refining, RH refining and continuous casting.

[0231] Hot metal pre-desulfurization process: Mix magnesium powder and lime powder and spray them into the hot metal to control the sulfur content in the hot metal to within 0.0012%; the injection rate of magnesium powder is 0.35~0.45Kg per ton of hot metal.

[0232] Converter smelting process: Make slag with a basicity of 3.0~3.6 and control the P mass ratio within 0.005%.

[0233] RH refining process: the temperature of the incoming molten steel is 1620~1660℃, firstly with 4~5Nm 3 / h, blow argon from the bottom for 1-2 minutes, let it stand in vacuum, and then break the vacuum to feed calcium wire to adjust the Ca / S mass ratio of the molten steel to 2-4 and the Ca / Al mass ratio to above 0.06; then stir it for 2-3 minutes, add magnesium alloy to adjust the Mg mass proportion in the molten steel to 0.0005-0.0012%, and finally blow argon from the bottom.

[0234] LF refining process: After alloying, aluminum wire is fed to control the O mass ratio within 0.0040%, and then the steel is tapped.

[0235] Continuous casting process: During casting, the superheat of molten steel is 8~20℃, and a steel billet with a thickness t0 of 210~230mm is obtained.

[0236] The center segregation of the steel billet is ≤0.5 level, and the center porosity is ≤0.5 level.

[0237] Furthermore, the ratings of the A, B, C, and D inclusions of the steel billet are all ≤ level 1, and the sum of the ratings of the A, B, C, and D inclusions is ≤ level 2.5.

[0238] On the cross section of the billet, the density of inclusions with a diameter of ≥10 μm is ≤10 / cm 2 .

[0239] This embodiment provides a method for producing a pipeline steel plate having the above chemical composition.

[0240] The production method prepares the steel billet into a steel plate with a thickness t of 8 to 30 mm through the processes of heating, rough hot rolling, finish hot rolling, final hot rolling, and temperature-controlled water cooling.

[0241] Heating process: The heating temperature is not lower than the precipitation starting temperature T of NbC, NbN, TiC, VC and VN respectively. NbC 、T NbN 、T TiC 、T VC 、T VN .

[0242] Preferably, the heating temperature is Max(T NbC ,T NbN ,T TiC ,T VC ,T VN )+40℃~Min(Max(T NbC ,T NbN ,T TiC ,T VC ,T VN )+120℃,T TiN -150℃).

[0243] The heating time is preferably controlled to be (1.1~1.3)t0min / mm.

[0244] Rough hot rolling process: the starting rolling temperature and the final rolling temperature are both T nr ~Min(T NbC ,T NbN ,T TiC ), the thickness of the plate after rolling is (3.2~4)t.

[0245] Preferably, the starting rolling temperature of the rough hot rolling can be higher than the finishing rolling temperature, and the whole process temperature is T nr ~Min(T NbC ,TNbN ,T TiC ).

[0246] More preferably, during the rough hot rolling, the reduction in each pass is ≥31 mm, and the reduction in the initial rolling pass which is not a widening pass is ≥42 mm.

[0247] Finishing hot rolling process: the starting rolling temperature and the final rolling temperature are both Ar3-20℃~Ar3+10℃, and the plate thickness after rolling is t+(2~5)mm.

[0248] Preferably, the starting rolling temperature of the finishing hot rolling may be higher than the final rolling temperature, and the temperature throughout the process may be in the range of Ar3-20°C to Ar3+10°C.

[0249] More preferably, during the finish hot rolling, the reduction per pass is ≥ 22 mm.

[0250] Final hot rolling process: It is a single hot rolling process, the temperature is Ar3-(40~20)℃, and the plate thickness after rolling is t.

[0251] Preferably, the temperature of the final hot rolling is lower than the final rolling temperature of the finish hot rolling.

[0252] Temperature-controlled water cooling process: After the steel plate leaves the final hot rolling mill, it is directly subjected to temperature-controlled water cooling.

[0253] Specifically, the water inlet temperature is Ar3-(80~60)℃, and the water outlet temperature T is Min(T VC ,T VN )-15℃~Min(T VC ,T VN )+5℃.

[0254] Preferably, temperature-controlled water cooling is performed on an ultra-fast cooling system with a cooling rate of 6-16°C / s.

[0255] Preferably, the production method of the steel plate further includes: after temperature-controlled water cooling, first performing hot straightening on the steel plate, the temperature during hot straightening being T-60°C~T; after leaving the hot straightening machine, the steel plate is naturally air-cooled on the upper cooling bed, and the temperature of the lower cooling bed is 100~200°C; thereafter, the steel plate is sequentially subjected to warm straightening and cold straightening.

[0256] The steel plate is tested and evaluated in terms of performance, structure, etc. The details are described below.

[0257] The yield strength R of the steel plate t0.5 ≥330MPa, tensile strength R m ≥430MPa, elongation A 50 ≥50%, yield strength ratio ≤0.77.

[0258] The steel plate has an impact energy KV2 of ≥400J at -20°C.

[0259] The hardness of the steel plate is ≤160HV 10 .

[0260] The steel plate has a -10°C DWTT drop weight shear area fraction of 100%, and a -15°C DWTT drop weight shear area fraction of 100%.

[0261] The steel plate meets the following requirements: CLR≤10%, CTR≤3%, and CSR≤1% under the NACE TM0284 standard A solution environment.

[0262] Furthermore, the steel plate meets the following requirements: stress corrosion test in accordance with NACE TM0177 standard, with a loading stress of 0.8σ s , there is no crack on the surface of the tensile specimen.

[0263] Furthermore, the steel plate meets the following requirements: in a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and cross-sectional shrinkage of a smooth specimen are greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment, respectively.

[0264] In addition, the steel plate meets the following requirements: K of the step-type compact tensile specimen under 6.3 MPa pure hydrogen environment 1C ≥110MPa·m 1 / 2 .

[0265] The hydrogen diffusion coefficient of the steel plate is D≤1.5×10 -6 cm 2 / s, the diffusible hydrogen concentration on the cathode side C0≤3.0×10 - 6 mol / cm 3 .

[0266] The unevenness of the steel plate is ≤1 mm / m.

[0267] The surface stress of the steel plate is ≤15 MPa.

[0268] The steel plate has a complex phase structure of quasi-polygonal ferrite+acicular ferrite+a small amount of pearlite.

[0269] Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite is 8~16μm.

[0270] The total volume of quasi-polygonal ferrite and acicular ferrite accounts for more than 95%.

[0271] Specifically, the volume proportion of the quasi-polygonal ferrite structure is 78-90%, the volume proportion of the acicular ferrite structure is 5-20%, and the volume proportion of the pearlite structure is 2-5%.

[0272] Furthermore, the banded structure of the steel plate is ≤ grade 0.5.

[0273] In addition, in the steel plate, some or all of the non-metallic inclusions are in a core-shell structure, wherein the core is MgO·Al2O3 and the shell is MnS, CaS, TiN and covers the outer surface of the inner shell.

[0274] Specifically, in the steel plate, more than 95% (or even more than 98%) of the non-metallic inclusions are of the core-shell structure.

[0275] Among them, the density of non-metallic inclusions in the core-shell structure is 42~68 / mm 2 , average diameter ≤1.8μm.

[0276] In summary, this embodiment has economic advantages such as low alloy content, short process flow (no need for 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, plate shape, hydrogen resistance, and HIC resistance.

[0277] [Second embodiment]

[0278] This embodiment provides a L320MH grade (i.e., yield strength R t0.5 ≥320MPa) pipeline steel, which can be used in pure hydrogen and / or hydrogen-blended transmission pipeline projects.

[0279] The chemical composition of the steel plate includes, by mass percentage, 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 remainder is iron and unavoidable impurities.

[0280] Furthermore, the chemical composition of the steel plate further satisfies: CEV (%) is 0.199-0.287, and / or Pcm (%) is 0.088-0.139.

[0281] The chemical composition of the steel material further satisfies, in terms of mass percentage, the following: 0.02≤Mg / Al≤0.04, and / or, 0.01%≤Mg×Al / S≤0.06%.

[0282] This embodiment also provides a method for casting a pipeline steel billet having the above chemical composition. The casting method of this embodiment is the same as that of the first embodiment, and will not be described in detail.

[0283] This embodiment also provides a method for producing pipeline steel plate having the aforementioned chemical composition. This method differs from the first embodiment only in temperature-controlled water cooling. The following description focuses solely on this difference; the remaining parts remain the same as those of the first embodiment and are omitted.

[0284] In this embodiment, the temperature-controlled water cooling process: the water inlet temperature is Ar3-(70~50)℃, the water outlet temperature T is Min(T VC ,T VN )-(50~30)℃.

[0285] The performance, structure, etc. of the steel billet / steel plate of this embodiment are introduced below.

[0286] The center segregation of the steel billet is ≤0.5 level, and the center porosity is ≤0.5 level.

[0287] Furthermore, the ratings of the A, B, C, and D inclusions of the steel billet are all ≤ level 1, and the sum of the ratings of the A, B, C, and D inclusions is ≤ level 2.5.

[0288] On the cross section of the billet, the density of inclusions with a diameter of ≥10 μm is ≤10 / cm 2 .

[0289] The yield strength R of the steel plate t0.5 ≥392MPa, tensile strength R m ≥454MPa, elongation A 50 ≥43%, yield strength ratio ≤0.86.

[0290] The steel plate has an impact energy KV2 of ≥400J at -20°C.

[0291] The hardness of the steel plate is ≤190HV 10 .

[0292] The steel plate has a -10°C DWTT drop weight shear area fraction of 100%, and a -15°C DWTT drop weight shear area fraction of 100%.

[0293] The steel plate meets the following requirements: CLR≤10%, CTR≤3%, and CSR≤1% under the NACE TM0284 standard A solution environment.

[0294] Furthermore, the steel plate meets the following requirements: stress corrosion test in accordance with NACE TM0177 standard, with a loading stress of 0.8σ s , there is no crack on the surface of the tensile specimen.

[0295] Furthermore, the steel plate meets the following requirements: in a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and cross-sectional shrinkage of a smooth specimen are greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment, respectively.

[0296] In addition, the steel plate meets the following requirements: K of the step-type compact tensile specimen under 6.3 MPa pure hydrogen environment 1C ≥110MPa·m 1 / 2 .

[0297] The hydrogen diffusion coefficient of the steel plate is D≤1.5×10 -6 cm 2 / s, the diffusible hydrogen concentration on the cathode side C0≤3.0×10 - 6 mol / cm 3 .

[0298] The unevenness of the steel plate is ≤2mm / m.

[0299] The surface stress of the steel plate is ≤20 MPa.

[0300] The steel plate has a complex phase structure of quasi-polygonal ferrite+acicular ferrite+a small amount of pearlite.

[0301] Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite is 4~9μm.

[0302] The total volume of quasi-polygonal ferrite and acicular ferrite accounts for more than 95%.

[0303] Specifically, the volume proportion of the quasi-polygonal ferrite structure is 78-90%, the volume proportion of the acicular ferrite structure is 5-20%, and the volume proportion of the pearlite structure is 2-5%.

[0304] Furthermore, the banded structure of the steel plate is ≤ grade 0.5.

[0305] In addition, in the steel plate, some or all of the non-metallic inclusions are in a core-shell structure, wherein the core is MgO·Al2O3 and the shell is MnS, CaS, TiN and covers the outer surface of the inner shell.

[0306] Specifically, in the steel plate, more than 95% (or even more than 98%) of the non-metallic inclusions are of the core-shell structure.

[0307] Among them, the density of non-metallic inclusions in the core-shell structure is 42~68 / mm 2 , average diameter ≤1.8μm.

[0308] In summary, it can be seen that this embodiment has better mechanical properties than the first embodiment.

[0309] [Third embodiment]

[0310] This embodiment provides a L360MH grade (i.e., yield strength R t0.5 ≥360MPa) pipeline steel, which can be used in pure hydrogen and / or hydrogen-blended transmission pipeline projects.

[0311] The chemical composition of the steel includes, by mass percentage, 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 remainder is iron and unavoidable impurities.

[0312] Furthermore, the chemical composition of the steel material further satisfies: CEV (%) is 0.199-0.287, and / or Pcm (%) is 0.081-0.131.

[0313] The chemical composition of the steel material further satisfies, in terms of mass percentage, the following: 0.02≤Mg / Al≤0.04, and / or, 0.01%≤Mg×Al / S≤0.06%.

[0314] This embodiment also provides a method for casting a pipeline steel billet having the above chemical composition. The casting method of this embodiment is the same as that of the first embodiment, and will not be described in detail.

[0315] This embodiment also provides a method for producing pipeline steel plate having the aforementioned chemical composition. This method differs from the first embodiment only in temperature-controlled water cooling. The following description focuses solely on this difference; the remaining parts remain the same as those of the first embodiment and are omitted.

[0316] In this embodiment, the temperature-controlled water cooling process: the water inlet temperature is Ar3-(60~40)℃, the water outlet temperature T is Min(T VC ,T VN )-(150~130)℃.

[0317] The performance, structure, etc. of the steel billet / steel plate of this embodiment are introduced below.

[0318] The center segregation of the steel billet is ≤0.5 level, and the center porosity is ≤0.5 level.

[0319] Furthermore, the ratings of the A, B, C, and D inclusions of the steel billet are all ≤ level 1, and the sum of the ratings of the A, B, C, and D inclusions is ≤ level 2.5.

[0320] On the cross section of the billet, the density of inclusions with a diameter of ≥10 μm is ≤10 / cm 2 .

[0321] The yield strength R of the steel plate t0.5 ≥410MPa, tensile strength R m ≥472MPa, elongation A 50 ≥48%, yield strength ratio ≤0.87.

[0322] The steel plate has an impact energy KV2 of ≥400J at -20°C.

[0323] The hardness of the steel plate is ≤195HV 10 .

[0324] The steel plate has a -10°C DWTT drop weight shear area fraction of 100%, and a -15°C DWTT drop weight shear area fraction of 100%.

[0325] The steel plate meets the following requirements: CLR≤10%, CTR≤3%, and CSR≤1% under the NACE TM0284 standard A solution environment.

[0326] Furthermore, the steel plate meets the following requirements: stress corrosion test in accordance with NACE TM0177 standard, with a loading stress of 0.8σ s , there is no crack on the surface of the tensile specimen.

[0327] Furthermore, the steel plate meets the following requirements: in a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and cross-sectional shrinkage of a smooth specimen are greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment, respectively.

[0328] In addition, the steel plate meets the following requirements: K of the step-type compact tensile specimen under 6.3 MPa pure hydrogen environment 1C ≥110MPa·m 1 / 2 .

[0329] The hydrogen diffusion coefficient of the steel plate is D≤1.5×10 -6 cm 2 / s, the diffusible hydrogen concentration on the cathode side C0≤3.0×10 - 6 mol / cm 3 .

[0330] The unevenness of the steel plate is ≤2mm / m.

[0331] The surface stress of the steel plate is ≤25 MPa.

[0332] The steel plate has a complex phase structure of quasi-polygonal ferrite+acicular ferrite+a small amount of pearlite.

[0333] Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite is 3~8μm.

[0334] The total volume of quasi-polygonal ferrite and acicular ferrite accounts for more than 95%.

[0335] Specifically, the volume proportion of the quasi-polygonal ferrite structure is 78-90%, the volume proportion of the acicular ferrite structure is 5-20%, and the volume proportion of the pearlite structure is 2-5%.

[0336] Furthermore, the banded structure of the steel plate is ≤ grade 0.5.

[0337] In addition, in the steel plate, some or all of the non-metallic inclusions are in a core-shell structure, wherein the core is MgO·Al2O3 and the shell is MnS, CaS, TiN and covers the outer surface of the inner shell.

[0338] Specifically, in the steel plate, more than 95% (or even more than 98%) of the non-metallic inclusions are of the core-shell structure.

[0339] Among them, the density of non-metallic inclusions in the core-shell structure is 42~68 / mm 2 , average diameter ≤1.8μm.

[0340] [Fourth embodiment]

[0341] This embodiment provides a L415MH grade (i.e., yield strength R t0.5 ≥415MPa) pipeline steel, which can be used in pure hydrogen transmission pipeline projects.

[0342] The chemical composition of the steel includes, by mass percentage, 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 remainder is iron and unavoidable impurities.

[0343] Furthermore, the chemical composition of the steel material further satisfies: CEV (%) is 0.197-0.284, and / or Pcm (%) is 0.075-0.126.

[0344] The chemical composition of the steel material further satisfies, in terms of mass percentage, the following: 0.02≤Mg / Al≤0.04, and / or, 0.01%≤Mg×Al / S≤0.06%.

[0345] This embodiment also provides a method for casting a pipeline steel billet having the above chemical composition. The casting method of this embodiment is the same as that of the first embodiment, and will not be described in detail.

[0346] This embodiment also provides a method for producing pipeline steel plate having the aforementioned chemical composition. This method differs from the first embodiment only in temperature-controlled water cooling. The following description focuses solely on this difference; the remaining parts remain the same as those of the first embodiment and are omitted.

[0347] In this embodiment, the temperature-controlled water cooling process: the water inlet temperature is Ar3-(50~30)℃, the water outlet temperature T is Min(T VC ,T VN )-(300~270)℃.

[0348] The performance, structure, etc. of the steel billet / steel plate of this embodiment are introduced below.

[0349] The center segregation of the steel billet is ≤0.5 level, and the center porosity is ≤0.5 level.

[0350] Furthermore, the ratings of the A, B, C, and D inclusions of the steel billet are all ≤ level 1, and the sum of the ratings of the A, B, C, and D inclusions is ≤ level 2.5.

[0351] On the cross section of the billet, the density of inclusions with a diameter of ≥10 μm is ≤10 / cm 2 .

[0352] The yield strength R of the steel plate t0.5 ≥450MPa, tensile strength R m ≥560MPa, elongation A 50 ≥40%, yield strength ratio ≤0.86.

[0353] The steel plate has an impact energy KV2 of ≥400J at -20°C.

[0354] The hardness of the steel plate is ≤205HV 10 .

[0355] The steel plate has a -10°C DWTT drop weight shear area fraction of 100%, and a -15°C DWTT drop weight shear area fraction of 100%.

[0356] The steel plate meets the following requirements: CLR≤10%, CTR≤3%, and CSR≤1% under the NACE TM0284 standard A solution environment.

[0357] Furthermore, the steel plate meets the following requirements: stress corrosion test in accordance with NACE TM0177 standard, with a loading stress of 0.8σ s , there is no crack on the surface of the tensile specimen.

[0358] Furthermore, the steel plate meets the following requirements: in a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and cross-sectional shrinkage of a smooth specimen are greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment, respectively.

[0359] In addition, the steel plate meets the following requirements: K of the step-type compact tensile specimen under 6.3 MPa pure hydrogen environment 1C ≥110MPa·m 1 / 2 .

[0360] The hydrogen diffusion coefficient of the steel plate is D≤1.5×10 -6 cm 2 / s, the diffusible hydrogen concentration on the cathode side C0≤3.0×10 - 6 mol / cm 3 .

[0361] The unevenness of the steel plate is ≤2mm / m.

[0362] The surface stress of the steel plate is ≤35 MPa.

[0363] The steel plate has a complex phase structure of quasi-polygonal ferrite+acicular ferrite+a small amount of pearlite.

[0364] Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite is 2~8μm.

[0365] The total volume of quasi-polygonal ferrite and acicular ferrite accounts for more than 95%.

[0366] Specifically, the volume proportion of the quasi-polygonal ferrite structure is 5~17%, the volume proportion of the acicular ferrite structure is 80~94%, and the volume proportion of the pearlite structure is 1~3%.

[0367] Furthermore, the banded structure of the steel plate is ≤ grade 0.5.

[0368] In addition, in the steel plate, some or all of the non-metallic inclusions are in a core-shell structure, wherein the core is MgO·Al2O3 and the shell is MnS, CaS, TiN and covers the outer surface of the inner shell.

[0369] Specifically, in the steel plate, more than 95% (or even more than 98%) of the non-metallic inclusions are of the core-shell structure.

[0370] Among them, the density of non-metallic inclusions in the core-shell structure is 42~68 / mm 2 , average diameter ≤1.8μm.

[0371] It can be seen that in addition to the economic advantages of low alloy content, short process flow (no need for coiling and heat treatment), 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 grade, which is extremely difficult in the pipeline steel field and has achieved a breakthrough in the development of pipeline steel.

[0372] The above describes the technical purpose of the present invention and four different implementation methods based on the technical purpose. The present invention is further described below through several specific test examples. Of course, these test examples are only a part of the many variations of the present invention, not all.

[0373] The chemical compositions of the steel plates of these test examples are shown in Table 1. In Table 1, “-” means that the corresponding element was not intentionally added during the preparation of the steel and was not detected in the steel or the detected amount was very small and not recorded.

[0374] [Table 1]

[0375]

[0376] 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.

[0377] Among them, some important parameters in the production process are shown in Table 2.

[0378] [Table 2]

[0379]

[0380] [Table 2 continued]

[0381]

[0382] The steel plates of each test case were tested for structure and performance, and the test results are as follows:

[0383] (1) The steel plate is a composite structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite; the metallographic structures of test examples 1, 2, 3, and 4 are respectively Figure 1 、 2 , 3, 4; Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite, the volume proportion of each structure in the complex phase structure, and the banded structure grade are shown in Table 3;

[0384] [Table 3]

[0385]

[0386] (2) On the cross section of the steel plate, the density of inclusions with a diameter of ≥10 μm is ≤10 / cm 2 ;

[0387] (3) For the steel plates of each test case, the -15℃ DWTT drop weight shear area fraction is 100%, and the strength, elongation, -20℃ impact energy KV2, hardness, roughness, surface stress, etc. are shown in Table 4;

[0388] [Table 4]

[0389]

[0390] (4) Under the NACE TM0284 standard A solution environment, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%; stress corrosion test is carried out according to the NACE TM0177 standard, and the loading stress is 0.8σ s , there is no crack on the surface of the tensile specimen;

[0391] (5) For the steel plates of Test Examples 1 to 3, the tensile strength, elongation, and reduction of area of ​​the smooth specimens in a 6.3 MPa pure hydrogen environment are greater than or equal to 90%, 85%, and 80%, respectively, of those in a nitrogen environment; for the steel plates of Test Example 4, the tensile strength, elongation, and reduction of area of ​​the smooth specimens in a 6.3 MPa pure hydrogen environment are greater than or equal to 90%, 80%, and 75%, respectively, of those in a nitrogen environment;

[0392] (6) For the steel plates of test examples 1 to 3, the K of the step-type compact tensile specimens in a 6.3 MPa pure hydrogen environment is 1C ≥110MPa·m 1 / 2 ; The steel plate of Test Example 4, in a 6.3MPa pure hydrogen environment, the K of the step-type compact tensile specimen 1C ≥100MPa·m 1 / 2 ;

[0393] (7) In the steel plates of Test Examples 1 to 4, most of the non-metallic inclusions have a core-shell structure, where the core is MgO·Al2O3 and the shell is MnS, CaS, and TiN coated on the surface of the inner shell; for example, Figure 5 The metallographic image of the inclusions of Test Example 3 is shown; and Table 4 shows the hydrogen diffusion coefficient D, cathode-side diffusible hydrogen concentration C0, and the proportion of the core-shell structure in the non-metallic inclusions of each test example.

Claims

1. A pipeline steel for hydrogen transportation, characterized in that: The chemical composition of the steel comprises, 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 remainder is iron and unavoidable impurities; The steel meets the following requirements: K of the step-type compact tensile specimen under 6.3MPa pure hydrogen environment 1C ≥100MPa·m 1 / 2 ; Hydrogen diffusion coefficient D≤1.5×10 -6 cm 2 / s.

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

3. The pipeline steel for hydrogen transportation according to claim 1, characterized in that: In the steel, part or all of the non-metallic inclusions form a core-shell structure, wherein the core is MgO·Al2O3 and the shell is MnS, CaS, TiN covering the outer surface of the inner shell.

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

5. The pipeline steel for hydrogen transportation according to claim 1, characterized in that: The steel meets the following requirements: In the NACE TM0284 standard A solution environment, CLR≤10%, CTR≤3%, CSR≤1%; And / or, stress corrosion testing according to NACE TM0177 with a loading stress of 0.8σ s , there is no crack on the surface of the tensile specimen.

6. The pipeline steel for hydrogen transportation according to claim 1, characterized in that: The steel meets the following requirements: In a 6.3MPa pure hydrogen environment, the tensile strength, elongation and cross-sectional shrinkage of the smooth specimen are greater than or equal to 90%, 80% and 75% of those in a nitrogen environment, respectively.

7. The pipeline steel for hydrogen transportation according to claim 1, characterized in that: The steel satisfies the following requirements: cathode side diffusible hydrogen concentration C0≤3.0×10 -6 mol / cm 3 .

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

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

10. The pipeline steel for hydrogen transportation according to claim 1, characterized in that: The unevenness of the steel is ≤2mm / m, and the surface stress is ≤35MPa.

11. The pipeline steel for hydrogen transportation according to claim 1, characterized in that: The steel has a complex phase structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite; Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite is 2~16μm, and the volume proportion of quasi-polygonal ferrite and acicular ferrite is more than 95%.

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

159.

13. A method for casting a steel billet for a pipeline steel for hydrogen transportation according to claim 1, characterized in that: The chemical composition of the steel billet comprises, 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 remainder is iron and unavoidable impurities; The casting method produces the steel billet by sequentially performing molten iron pre-desulfurization, converter smelting, LF refining, RH refining and continuous casting; Among them, in RH refining: the temperature of the incoming molten steel is 1620~1660℃, firstly with 4~5Nm 3 / h, blow argon from the bottom for 1-2 minutes, let it stand in vacuum, and then break the vacuum to feed calcium wire to adjust the Ca / S mass ratio of the molten steel to 2-4 and the Ca / Al mass ratio to above 0.06; then stir it for 2-3 minutes, add magnesium alloy to adjust the Mg mass proportion in the molten steel to 0.0005-0.0012%, and finally blow argon from the bottom.

14. The method for casting a steel billet for a hydrogen transport pipeline according to claim 13, wherein: The re-vacuum standing comprises: standing for 25 to 30 minutes at a vacuum degree of ≤30Pa; The final bottom blowing of argon includes: 3 Bottom blowing of argon at a flow rate of less than / h.

15. The method for casting a steel billet for a pipeline steel for hydrogen transportation according to claim 13, wherein: During continuous casting: the superheat of the molten steel during casting is 8~20℃, and the billet drawing speed is 0.1×L / F-0.05~0.1×L / F+0.05 m / s, where L and F are the circumference and area of ​​the cross-section of the billet obtained by continuous casting, respectively.

16. The method for casting a steel billet for a pipeline steel for hydrogen transportation according to claim 13, wherein: In the pre-desulfurization of molten iron: After mixing magnesium powder and lime powder, spray it into the molten iron to control the sulfur content in the molten iron to within 0.0012% by mass; the injection rate of magnesium powder is 0.35~0.45kg per ton of molten iron; In converter smelting: make slag with a basicity of 3.0-3.6 and control the P content within 0.005%; During LF refining: After alloying, aluminum wire is fed to control the O mass ratio within 0.0040%, and then the steel is tapped.

17. A method for producing a pipeline steel plate for hydrogen 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 remainder is iron and unavoidable impurities; The steel plate meets the following requirements: K of the step-type compact tensile specimen under 6.3MPa pure hydrogen environment 1C ≥100MPa·m 1 / 2 ; Hydrogen diffusion coefficient D≤1.5×10 -6 cm 2 / s; The production method prepares steel plates with a thickness of t0 of 150-320 mm through the processes of heating, rough hot rolling, finish hot rolling, final hot rolling, and temperature-controlled water cooling; Heating process: The heating temperature is not lower than the precipitation temperature 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 ), plate thickness after rolling (3.2~4)t; Finishing hot rolling process: the starting and final rolling temperatures are both Ar3-20℃~Ar3+10℃, and the plate thickness after rolling is t+(2~5)mm; Final hot rolling process: one-pass hot rolling, temperature is Ar3-(40~20)℃, and the plate thickness after rolling is t; Temperature controlled water cooling process: water inlet temperature is Ar3-(80~30)℃, water outlet temperature T is Min(T VC ,T VN )-300℃~Min(T VC ,T VN )+5℃.

18. The method for producing a pipeline steel plate for hydrogen transportation according to claim 17, characterized in that: During the heating process: the heating temperature is Max(T NbC ,T NbN ,T TiC ,T VC ,T VN )+40℃~Min(Max(T NbC ,T NbN ,T TiC ,T VC ,T VN )+120℃,T TiN -150℃).

19. The method for producing a pipeline steel plate for hydrogen transportation according to claim 17, wherein: There is also a water cooling process between the rough hot rolling process and the finishing hot rolling process, and the water outlet temperature is Ar3-20℃~Ar3+10℃.

20. The method for producing a pipeline steel plate for hydrogen transportation according to claim 17, wherein: In the temperature-controlled water cooling process: The inlet water temperature is Ar3-(80~60)℃, and the outlet water temperature T is Min(T VC ,T VN )-15℃~Min(T VC ,T VN )+5℃; Alternatively, the water inlet temperature is Ar3-(70~50)℃, and the water outlet temperature T is Min(T VC ,T VN )-(50~30)℃; Alternatively, the water inlet temperature is Ar3-(60~40)℃, and the water outlet temperature T is Min(T VC ,T VN )-(150~130)℃; Alternatively, the water inlet temperature is Ar3-(50~30)℃, and the water outlet temperature T is Min(T VC ,T VN )-(300~270)℃.

21. The method for producing a pipeline steel plate for hydrogen transportation according to claim 17, wherein: Rough hot rolling process: the reduction of the initial rolling pass without widening pass is ≥42mm, and the reduction of each pass is ≥31mm; Finishing hot rolling process: the reduction of each pass is ≥22mm.

22. The method for producing a pipeline steel plate for hydrogen transportation according to claim 17, wherein: The steel plates obtained from the final hot rolling process are directly fed into the ultra-fast cooling system for temperature-controlled water cooling at a cooling rate of 6-16°C / s. After the temperature-controlled water cooling process, hot straightening, natural air cooling on the cooling bed, warm straightening, and cold straightening are carried out in sequence; the temperature during hot straightening is T-60℃~T; the temperature of the lower cooling bed is 100~200℃.

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