Steel plate for pure hydrogen transmission pipeline and production method thereof

Abstract

The present invention discloses a steel plate for pure hydrogen transmission pipelines and its production method. The steel plate contains: C 0.021-0.076%, Si 0.07-0.21%, Mn 0.66-0.93%, Cr 0.12-0.3%, 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%, and the remainder is iron. Production method: The start / finish rolling temperature T of the rough rolling is 0.021-0.076%, Si 0.07-0.21%, Mn 0.66-0.93%, Cr 0.12-0.3%, 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%, and the remainder is iron. nr ~Min(T NbC ,T NbN ,T TiC ), the start / end rolling temperature of finishing rolling is Ar3-20℃~Ar3+10℃, the final rolling temperature is Ar3-(40~20)℃; water cooling, Ar3-(80~30)℃ water entry, Min(T VC ,T VN )-300℃~Min(T VC ,T VN )+5℃ water outlet.

Description

Technical Field

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

[0002] The major bottleneck restricting the development of pure hydrogen transmission pipelines is the potential for pipeline steel to degrade or even fail in high-pressure pure hydrogen environments. For example, pipeline steel is susceptible to hydrogen-induced cracking and hydrogen blistering in high-pressure pure hydrogen environments, significantly deteriorating its ductility, fatigue properties, and fracture toughness. Consequently, higher requirements are placed on steel plates used in high-pressure pure hydrogen transmission pipelines: first, they must be resistant to hydrogen-induced cracking, and second, they must exhibit excellent fracture toughness in pure hydrogen environments.

[0003] 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.

[0004] Other existing technologies, such as CN113862549A, CN116694902A, and CN114645215A, have studied pipeline steel production processes. However, these technologies generally require additional heat treatment steps (such as normalizing, quenching, and tempering), resulting in complex, lengthy production processes, high costs, and low efficiency. Furthermore, the technology in CN114645215A is only targeted at hydrogen-doped pipeline steel and cannot meet the application requirements of pure hydrogen pipeline steel. Specifically, it is difficult to address the severe deterioration of steel in a pure hydrogen environment. Summary of the Invention

[0005] The object of the present invention is to provide a steel plate for a pure hydrogen transportation pipeline and a production method thereof.

[0006] To achieve the aforementioned objectives, one embodiment of the present invention provides a steel plate for a pure hydrogen transmission pipeline. The steel plate has a thickness (t) of 8 mm or greater and a chemical composition comprising, 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 0-0.24%, Cu 0-0.24%, Nb 0.014-0.052%, V 0.014-0.050%, Ti 0.009-0.019%, Al 0.015-0.045%, P ≤ 0.01%, S ≤ 0.002%, O ≤ 0.003%, N ≤ 0.005%, H ≤ 0.0002%, with the remainder being iron and unavoidable impurities.

[0007] Preferably, the steel plate satisfies any one, any two, any three or all of the following:

[0008] In the NACE TM0284 standard A solution environment, CLR≤10%, CTR≤3%, CSR≤1%;

[0009] Stress corrosion testing was performed according to NACE TM0177 standard with a loading stress of 0.8σ. s , there is no crack on the surface of the tensile specimen;

[0010] 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;

[0011] In a 6.3 MPa pure hydrogen environment, K 1C ≥100MPa·m 1 / 2 .

[0012] Preferably, 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.

[0013] Preferably, the steel plate has an impact energy of KV2 ≥ 400 J at -20°C and a hardness ≤ 205 HV 10 , -10℃ DWTT drop weight shear area fraction is 100%, -15℃ DWTT drop weight shear area fraction is 100%.

[0014] Preferably, the unevenness of the steel plate is ≤2 mm / m, and the surface stress is ≤35 MPa.

[0015] Preferably, the density of inclusions with a diameter of ≥10 μm on the cross section of the steel plate is ≤10 / cm 2 .

[0016] Preferably, the steel plate has a complex phase structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

[0017] Preferably, the average grain size of the quasi-polygonal ferrite and the acicular ferrite is 2 to 16 μm; and the volume proportion of the quasi-polygonal ferrite structure and the acicular ferrite structure is greater than 95%.

[0018] Preferably, the volume proportion of the quasi-polygonal ferrite structure is 5-90%, the volume proportion of the acicular ferrite structure is 5-94%, the volume proportion of the pearlite structure is 1-5%, and the banded structure is ≤0.5 level.

[0019] To achieve the above-mentioned purpose, one embodiment of the present invention provides a method for producing a steel plate for a pure hydrogen transmission pipeline. The steel plate has a thickness of t≥8 mm and a chemical composition, by mass percentage, comprising: C 0.021-0.076%, Si 0.07-0.21%, Mn 0.66-0.93%, Cr 0.12-0.30%, Ni 0-0.24%, Cu 0-0.24%, Nb 0.014-0.052%, V 0.014-0.050%, Ti 0.009-0.019%, Al 0.015-0.045%, P ≤ 0.01%, S ≤ 0.002%, O ≤ 0.003%, N ≤ 0.005%, H ≤ 0.0002%, and the remainder being iron and unavoidable impurities.

[0020] The production method comprises:

[0021] Heating a continuous casting billet having a thickness t0 of 150 to 320 mm; wherein the heating temperature is not lower than the precipitation start temperature of NbC, NbN, TiC, VC, and VN;

[0022] The continuous casting billet is subjected to rough hot rolling, finish hot rolling and final hot rolling to produce steel plates; wherein the starting rolling temperature and the final rolling temperature of the rough hot rolling are both T nr ~Min(T NbC ,T NbN ,T TiC ), the starting and finishing temperatures of the finishing hot rolling are both Ar3-20℃~Ar3+10℃, the finishing hot rolling is a single pass hot rolling at a temperature of Ar3-(40~20)℃; the thicknesses of the steel plates after rough hot rolling, finishing hot rolling, and final hot rolling are (3.2~4)t, t+(2~5)mm, and t, respectively;

[0023] After the steel plate leaves the final hot rolling mill, it is cooled by controlled water; the water inlet temperature is Ar3-(80~30)℃, and the water outlet temperature T is Min(T VC ,T VN)-300℃~Min(T VC ,T VN )+5℃.

[0024] 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℃).

[0025] Preferably, the temperature during the rough hot rolling is T nr ~Min(T NbC ,T NbN ,T TiC );

[0026] The temperature during the entire finishing hot rolling process is Ar3-20℃~Ar3+10℃.

[0027] Preferably, the starting rolling temperature of the rough hot rolling is higher than the final rolling temperature, the starting rolling temperature of the finish hot rolling is higher than the final rolling temperature, and the temperature of the final hot rolling is lower than the final rolling temperature of the finish hot rolling.

[0028] Preferably, the intermediate billet obtained by the rough hot rolling is water-cooled before the finish hot rolling, and the outlet water temperature is Ar3-20°C to Ar3+10°C.

[0029] Preferably, during the rough hot rolling, the reduction in the initial rolling pass of the non-widening pass is ≥42 mm, and the reduction in each pass is ≥31 mm.

[0030] Preferably, during the finish hot rolling, the reduction in each pass is ≥22 mm.

[0031] Preferably, the temperature-controlled water cooling is carried out on an ultra-fast cooling system with a water pressure of 0.15-0.20 MPa, an upper and lower water ratio of 0.92-0.98, a cooling rate of 6-16°C / s, and a cooling roller speed of 1.5-2.2 m / s in the ultra-fast cooling system.

[0032] Preferably, the production method further comprises:

[0033] After temperature-controlled water cooling, the steel plate is first subjected to hot straightening, and the temperature during hot straightening is T-60℃~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℃; after that, the steel plate is subjected to warm straightening and cold straightening in sequence.

[0034] Preferably, during the temperature-controlled water cooling:

[0035] 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℃;

[0036] Alternatively, the water inlet temperature is Ar3-(70~50)℃, and the water outlet temperature T is Min(T VC ,T VN )-(50~30)℃;

[0037] Alternatively, the water inlet temperature is Ar3-(60~40)℃, and the water outlet temperature T is Min(T VC ,T VN )-(150~130)℃;

[0038] Alternatively, the water inlet temperature is Ar3-(50~30)℃, and the water outlet temperature T is Min(T VC ,T VN )-(300~270)℃.

[0039] Preferably, the chemical composition of the steel plate further satisfies: CEV (%) is 0.168-0.325, and / or Pcm (%) is 0.069-0.159.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) In terms of chemical composition, it does not contain expensive alloys such as Mo, and adopts a low-alloy component system design with low carbon, low manganese, low phosphorus and sulfur and Nb+V+Ti precipitation elements added in combination, which is easy to produce steel and has low production costs. In addition, it reduces the C content in the steel, has excellent welding performance, and is beneficial to the welding effect of the steel plate when preparing pipeline steel. Furthermore, the appropriate amount of Nb, V, and Ti is added to form carbides and nitrides, which can act as hydrogen traps to capture hydrogen, thereby reducing the diffusible hydrogen in the steel plate and improving the HIC resistance and hydrogen resistance of the steel.

[0042] (2) During the hot rolling process, deformation-induced ferrite phase transformation occurs in the steel plate, producing a large number of fine deformation-induced ferrite (such as quasi-polygonal ferrite); on this basis, the steel plate is cooled to the ferrite phase transformation zone through temperature-controlled water cooling, and the ferrite phase transformation continues to obtain a large number of ferrite phases (for example, forming acicular ferrite), avoiding the formation of hard phases such as pearlite, bainite, and MA, thereby ensuring the HIC resistance and hydrogen resistance of the steel plate for pure hydrogen transmission pipelines;

[0043] (3) 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 improving the HIC resistance and hydrogen resistance of the steel;

[0044] (4) In general, through the control of chemical composition, hot rolling, temperature-controlled water cooling and other process controls, the steel plate can be optimized and controlled in terms of HIC resistance and hydrogen resistance. No additional heat treatment is required after rolling. The welding performance is excellent and the production pace is fast, which meets the application requirements of pure hydrogen pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a metallographic structure diagram of the finished steel plate of Example 1 of the present invention;

[0046] Figure 2 is a metallographic structure diagram of the finished steel plate of Example 3 of the present invention;

[0047] Figure 3 is a metallographic structure diagram of the finished steel plate of Example 5 of the present invention;

[0048] Figure 4 This is a metallographic structure diagram of the finished steel plate of Example 7 of the present invention. DETAILED DESCRIPTION

[0049] 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.

[0050] The present invention provides a steel plate, which can be used for preparing pure hydrogen transmission pipelines.

[0051] The thickness of the steel plate is t≥8mm. Such a large thickness can ensure a small residual stress and meet the requirements of the pure hydrogen transmission pipeline.

[0052] Preferably, the thickness t of the steel plate is 8-30 mm.

[0053] 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 0-0.24%, Cu 0-0.24%, Nb 0.014-0.052%, V 0.014-0.050%, Ti 0.009-0.019%, Al 0.015-0.045%, P≤0.01%, S≤0.002%, O≤0.003%, N≤0.005%, H≤0.0002%, and the rest is iron and unavoidable impurities.

[0054] The functions of the various chemical elements in this embodiment are described in detail below.

[0055] 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%.

[0056] 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, too much silicon will easily produce Fe2SiO4 on the surface of the continuous casting 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%.

[0057] 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%.

[0058] 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%.

[0059] 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.

[0060] 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.

[0061] 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%.

[0062] 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%.

[0063] 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%.

[0064] Aluminum: Aluminum is a deoxidizing element in steel. Excessive aluminum can easily increase the Al2O3 inclusions in the steel, affecting the low-temperature toughness of the steel. On the basis of ensuring the deoxidation effect, the aluminum content should be reduced as much as possible; therefore, the aluminum content is selected to be 0.015~0.045%.

[0065] 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%.

[0066] In general, the chemical composition of the present application 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 steel production and has low production costs; in addition, the C content in the steel is reduced, the welding performance is excellent, and it is beneficial to the welding effect of the steel plate when preparing pipeline steel; furthermore, Nb, V, and Ti are added in appropriate amounts to form carbides and nitrides, which can serve as hydrogen traps to capture hydrogen, thereby reducing the diffusible hydrogen in the steel plate, and further improving the HIC resistance and hydrogen resistance of the steel.

[0067] In this way, the present application not only has excellent HIC resistance and hydrogen resistance, meeting the application requirements of pure hydrogen pipeline steel, but also has the advantages of low alloy content, simple steelmaking process, and low alloy cost, and can be prepared through a short process route without heat treatment.

[0068] Further preferably, the chemical composition of the steel plate, in mass percentage, may also satisfy: 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.

[0069] Furthermore, the chemical composition of the steel plate also satisfies: CEV (%) is 0.168~0.325.

[0070] Carbon equivalent CEV (%) can be calculated using the following formula:

[0071] CEV (%) = [C] + [Mn] / 6 + ( [Cr] + [V]) / 5 + ( [Cu] + [Ni]) / 15. However, the present application is not limited thereto.

[0072] Preferably, the chemical composition of the steel plate may also satisfy: Pcm(%) is 0.069~0.159.

[0073] In one embodiment, Pcm(%) can be calculated using the following formula:

[0074] Pcm(%)=[C]+[Si] / 30+([Mn]+[Cu]+[Cr]) / 20+[Ni] / 60+[V] / 10.

[0075] The chemical composition of the steel plate is introduced above, and the steel plate will be introduced from the perspective of performance below.

[0076] Specifically, the steel plate has excellent mechanical properties.

[0077] 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.

[0078] 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".

[0079] Furthermore, the steel plate has excellent low-temperature toughness.

[0080] For example, the steel plate has an impact energy KV2 of ≥400J at -20°C.

[0081] The hardness of the steel plate is ≤205HV 10 .

[0082] 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%.

[0083] 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".

[0084] The steel plate also has excellent hydrogen resistance and HIC resistance.

[0085] For example, the steel plate further satisfies any one, any two, any three or all of the following:

[0086] The first item is: in the NACE TM0284 standard A solution environment, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%;

[0087] The second item is stress corrosion testing according to NACE TM0177 standard, with a loading stress of 0.8σ s, there is no crack on the surface of the tensile specimen;

[0088] The third item is that 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;

[0089] The fourth item is the K of the step-type compact tensile specimen in a 6.3MPa pure hydrogen environment. 1C ≥100MPa·m 1 / 2 .

[0090] 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".

[0091] Furthermore, the steel plate has an excellent plate shape.

[0092] 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.

[0093] Furthermore, the residual stress of the steel plate is small.

[0094] 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.

[0095] The chemical composition and properties of the steel plate are introduced above. The following is an introduction to the steel plate from the perspective of structure.

[0096] The steel plate has a complex phase structure of quasi-polygonal ferrite+acicular ferrite+a small amount of pearlite.

[0097] 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.

[0098] 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.

[0099] 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%.

[0100] 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.

[0101] Furthermore, the central segregation of the steel plate is ≤0.5 level, and the central porosity is ≤0.5 level.

[0102] Here, the central segregation can be specifically observed in accordance with YB / T 4003-2016 "Continuous Cast Steel Slab Macrostructure Defect Rating Chart" through cold acid corrosion.

[0103] 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.

[0104] From a microscopic point of view, the density of inclusions with a diameter of ≥10 μm on the cross section of the steel plate is ≤10 / cm 2 In this way, hydrogen-induced cracking caused by inclusions can be avoided.

[0105] 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.

[0106] Here, the rating of A, B, C, and D inclusions can be specifically based on GB / T 10561-2005 "Microscopic examination 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.

[0107] Furthermore, the present invention also provides a method for producing the steel plate.

[0108] The production method comprises:

[0109] Step 1, heating the continuous casting billet;

[0110] Step 2, subjecting the continuous casting slab to rough hot rolling, finish hot rolling, and final hot rolling to form a steel plate;

[0111] Step 3: After the steel plate leaves the final hot rolling mill, it is temperature-controlled and water-cooled.

[0112] Specifically, in step 1, the thickness t0 of the continuous casting billet is 150-320 mm, preferably 220 mm.

[0113] The chemical composition of the continuous casting slab is the same as that of the steel plate.

[0114] Furthermore, it will be understood by those skilled in the art that the inclusion level, center segregation level, and center porosity level of the continuous casting slab are the same as those of the steel plate.

[0115] For example, the ratings of A, B, C, and D inclusions in the continuous casting billet are all ≤1, and the sum of the ratings of A, B, C, and D inclusions is ≤2.5; on the cross section of the continuous casting billet, the density of inclusions with a diameter of ≥10μm is ≤10 / cm 2 ; The central segregation of the continuous casting billet is ≤0.5 level, and the central porosity is ≤0.5 level.

[0116] The continuous casting billet can be prepared specifically through smelting and continuous casting technology, and the smelting technology can specifically include molten iron pre-desulfurization, converter smelting, LF refining, and RH refining in sequence.

[0117] The present invention does not introduce the specific operations of molten iron pre-desulfurization, converter smelting, LF refining, RH refining, and continuous casting in detail, and any feasible technology in the field can be used for implementation.

[0118] In step 1, after the continuous casting billet leaves the continuous casting machine, it directly enters the heating furnace for heating.

[0119] 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 .

[0120] In step 2, the thicknesses of the steel plate after rough hot rolling, after finish hot rolling, and after final hot rolling are (3.2-4) mm, t+(2-5) mm, and t, respectively.

[0121] That is, the continuous casting billet leaving the heating furnace is first subjected to rough hot rolling to be rolled to a steel plate thickness of (3.2~4)t; then subjected to fine hot rolling to be rolled to a steel plate thickness of t+(2~5)mm; finally subjected to final hot rolling to be rolled to a steel plate thickness of t.

[0122] The final hot rolling is a single hot rolling, that is, from thickness t+(2~5)mm to thickness t, only one hot rolling is performed.

[0123] The starting and finishing temperatures of the rough hot rolling are both T nr ~Min(T NbC ,T NbN ,T TiC ).

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

[0125] Among them, T nr It indicates the lowest temperature of austenite recrystallization, which can be obtained through theoretical calculation, experimental measurement, empirical formula and other methods.

[0126] 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.

[0127] Furthermore, Min(T NbC ,T NbN ,T TiC ) means: in T NbC , T NbN , T TiC The minimum of these three temperature values.

[0128] Thus, during rough hot rolling:

[0129] 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;

[0130] 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.

[0131] The starting and finishing temperatures of hot rolling are both Ar3-20℃~Ar3+10℃.

[0132] Preferably, the starting rolling temperature of the finish hot rolling may be higher than the final rolling temperature.

[0133] Among them, 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.

[0134] 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.

[0135] In this way, during the finishing hot rolling, the entire process is rolling in the two-phase critical region, and:

[0136] 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.

[0137] On the other hand, large reduction deformation can induce the precipitation of the second phase and obtain more fine precipitates;

[0138] 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.

[0139] The final hot rolling temperature is Ar3-(40~20)℃.

[0140] Preferably, the temperature of the final hot rolling is lower than the final rolling temperature of the finish hot rolling.

[0141] 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.

[0142] Next, in step 3, the steel plate is directly temperature-controlled and water-cooled after leaving the hot rolling mill.

[0143] The inlet water temperature is Ar3-(80~30)℃, and the outlet water temperature T is Min(T VC ,T VN )-300℃~Min(T VC ,T VN )+5℃.

[0144] It can be understood that the water outlet temperature T is lower than the water inlet temperature.

[0145] Among them, Min(T VC ,T VN ) means: in T VC , T VN The minimum of these two temperature values.

[0146] As previously mentioned, during the hot rolling process in step 2, deformation-induced ferrite transformation occurs in the steel plate, producing a large amount of fine deformation-induced ferrite (e.g., quasi-polygonal ferrite). Furthermore, through temperature-controlled water cooling in step 3, the steel plate is cooled to the ferrite transformation zone, where the ferrite transformation continues, resulting in a larger amount of ferrite (e.g., acicular ferrite). This avoids the formation of hard phases such as pearlite, bainite, and MA, thereby ensuring the HIC and hydrogen resistance of the steel plate used in pure hydrogen transmission pipelines.

[0147] 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.

[0148] 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.

[0149] Preferably, in step 1, 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℃).

[0150] 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.

[0151] Min(Max(T NbC ,T NbN ,T TiC ,T VC ,T VN )+120℃,TTiN -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.

[0152] 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).

[0153] In step 1, the heating time is preferably controlled to be (1.1-1.3) t0min / mm. That is, according to the thickness t 0， The heating time per millimeter is 1.1~1.3 minutes.

[0154] Furthermore, in step 2, the temperature of the whole process of rough hot rolling is T nr ~Min(T NbC ,T NbN ,T TiC ).

[0155] Furthermore, in step 2, the temperature during the entire finishing hot rolling process is within the range of Ar3-20°C to Ar3+10°C.

[0156] Preferably, in step 2, after the rough hot rolling is completed, the obtained steel plate can be water-cooled and then subjected to finish hot rolling; here, the outlet water temperature of the water cooling is Ar3-20°C~Ar3+10°C.

[0157] 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.

[0158] Furthermore, in step 2, during the rough hot rolling, the reduction of each pass is ≥31 mm, and the reduction of the initial rolling pass of the non-widening pass is ≥42 mm.

[0159] For example, the rough hot rolling includes several non-widening passes, and the reduction of the first pass (ie, the initial rolling pass) among these non-widening passes is ≥42 mm.

[0160] 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.

[0161] In step 2, during the finish hot rolling, the reduction in each pass is ≥ 22 mm.

[0162] 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.

[0163] In addition, in step 2, the final hot rolling can be performed by temper rolling with a bite speed of 1.5±0.2 m / s and a rolling speed of 6±2 m / s, which can reduce the stress of the steel plate.

[0164] Next, in step 3, the steel plate obtained by the final hot rolling can be directly put into the ultra-fast cooling system for temperature-controlled water cooling.

[0165] Specifically, in the ultra-fast cooling system, the water pressure is 0.15~0.20MPa, the upper and lower water ratio is 0.92~0.98, the cooling rate is 6~16℃ / s, and the cooling roller speed of the ultra-fast cooling system is 1.5~2.2m / s.

[0166] Furthermore, the production method further comprises:

[0167] After temperature-controlled water cooling, the steel plate is first hot straightened at a temperature of T-60℃~T;

[0168] After leaving the hot straightening machine, the steel plate is naturally cooled on the cooling bed, and the temperature of the lower cooling bed is 100~200℃;

[0169] Afterwards, the steel plate undergoes warm straightening and cold straightening in sequence.

[0170] That is, the steel plate is cooled by controlled water in the ultra-fast cooling system and then directly fed into the hot straightening machine for hot straightening. The temperature during hot straightening is kept within 60°C of the outlet water temperature T of the controlled water cooling system.

[0171] 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.

[0172] In addition, when natural air cooling is carried out on the cooling bed, the steel plate will undergo self-tempering and the ferrite phase transformation can be completed on the cooling bed, thereby further releasing the phase transformation stress and thermal stress.

[0173] It should be noted that in this application, T NbC 、T NbN 、T TiC 、T TiN 、T VC 、T VN They are the starting precipitation 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 continuous casting billet.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] T VC It 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.

[0179] T VN The formula can be used to calculate the value of lg([V]×[N])=3.46-8330 / (TVN +273.15) is calculated, but T VN The value of is not limited to this.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] [First embodiment]

[0184] This embodiment provides a medium-low strength pipeline steel plate, 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 plates can be used in pure hydrogen transportation pipeline projects.

[0185] The thickness of the steel plate is t≥8 mm, preferably 8-30 mm.

[0186] The chemical composition of the steel plate 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%, O≤0.003%, N≤0.005%, H≤0.0002%, P≤0.01%, S≤0.002%, O≤0.003%, N≤0.005%, H≤0.0002%, and the rest is iron and unavoidable impurities.

[0187] Furthermore, the chemical composition of the steel plate further satisfies: CEV (%) is 0.201-0.289, and / or Pcm (%) is 0.094-0.145.

[0188] 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.

[0189] The steel plate has an impact energy KV2 of ≥400J at -20°C.

[0190] The hardness of the steel plate is ≤160HV 10 .

[0191] 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%.

[0192] The steel plate further satisfies any one, any two, any three or all of the following:

[0193] The first item is: in the NACE TM0284 standard A solution environment, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%;

[0194] The second item is stress corrosion testing according to NACE TM0177 standard, with a loading stress of 0.8σ s , there is no crack on the surface of the tensile specimen;

[0195] Third, in a 6.3MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of ​​the smooth specimen are greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment, respectively;

[0196] The fourth item is the K of the step-type compact tensile specimen in a 6.3MPa pure hydrogen environment. 1C ≥110MPa·m 1 / 2 .

[0197] The unevenness of the steel plate is ≤1 mm / m.

[0198] The surface stress of the steel plate is ≤15 MPa.

[0199] The steel plate has a complex phase structure of quasi-polygonal ferrite+acicular ferrite+a small amount of pearlite.

[0200] Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite is 8~16μm.

[0201] The total volume of quasi-polygonal ferrite and acicular ferrite accounts for more than 95%.

[0202] 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%.

[0203] Furthermore, the banded structure of the steel plate is ≤ grade 0.5.

[0204] The central segregation of the steel plate is ≤ level 0.5, and the central porosity is ≤ level 0.5.

[0205] On the cross section of the steel plate, the density of inclusions with a diameter of ≥10 μm is ≤10 / cm 2 .

[0206] 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.

[0207] Furthermore, the production method of the steel plate includes the following steps.

[0208] Step 1: heating the continuous casting billet.

[0209] The thickness t0 of the continuous casting billet is 150-320 mm, preferably 220 mm.

[0210] 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 .

[0211] 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℃).

[0212] The heating time is preferably controlled to be (1.1~1.3)t0min / mm.

[0213] Step 2: subjecting the continuous casting slab to rough hot rolling, water cooling of the intermediate slab, finishing hot rolling, and final hot rolling to produce a steel plate.

[0214] Specifically, the thicknesses of the steel plate after rough hot rolling, after finish hot rolling, and after final hot rolling are (3.2-4) mm, t+(2-5) mm, and t, respectively.

[0215] Among them, the starting rolling temperature and the finishing rolling temperature of the rough hot rolling are both T nr ~Min(T NbC ,T NbN ,T TiC ).

[0216] 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 ,T NbN ,T TiC ).

[0217] 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.

[0218] Furthermore, the starting rolling temperature and the final rolling temperature of the finishing hot rolling are both Ar3-20℃~Ar3+10℃.

[0219] Preferably, the starting rolling temperature of the finishing hot rolling may be higher than the final rolling temperature, and the temperature throughout the entire process is within the range of Ar3-20°C to Ar3+10°C.

[0220] More preferably, during the finish hot rolling, the reduction per pass is ≥ 22 mm.

[0221] In addition, the temperature of the final hot rolling is Ar3-(40~20)℃.

[0222] Preferably, the temperature of the final hot rolling is lower than the final rolling temperature of the finish hot rolling.

[0223] Step 3: After the steel plate leaves the final hot rolling mill, it is directly temperature-controlled and water-cooled.

[0224] 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℃.

[0225] It can be understood that the water outlet temperature T is lower than the water inlet temperature.

[0226] Preferably, temperature-controlled water cooling is performed on an ultra-fast cooling system.

[0227] Among them, the water pressure is 0.15~0.20MPa, the upper and lower water ratio is 0.92~0.98, the cooling rate is 6~16℃ / s, and the cooling roller speed of the ultra-fast cooling system is 1.5~2.2m / s.

[0228] Preferably, the method for producing the steel plate further comprises:

[0229] After temperature-controlled water cooling, the steel plate is first hot straightened at a temperature of T-60℃~T;

[0230] After leaving the hot straightening machine, the steel plate is naturally cooled on the cooling bed, and the temperature of the lower cooling bed is 100~200℃;

[0231] Afterwards, the steel plate undergoes warm straightening and cold straightening in sequence.

[0232] [Second embodiment]

[0233] This embodiment provides a L320MH grade (i.e., yield strength R t0.5 ≥320MPa) pipeline steel plates can be used in pure hydrogen transportation pipeline projects.

[0234] The thickness of the steel plate is t≥8 mm, preferably 8-30 mm.

[0235] 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%, P ≤ 0.01%, S ≤ 0.002%, O ≤ 0.003%, N ≤ 0.005%, H ≤ 0.0002%, and the rest is iron and unavoidable impurities.

[0236] Furthermore, the chemical composition of the steel plate further satisfies: CEV (%) is 0.199-0.287, and / or Pcm (%) is 0.088-0.139.

[0237] 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.

[0238] The steel plate has an impact energy KV2 of ≥400J at -20°C.

[0239] The hardness of the steel plate is ≤190HV 10 .

[0240] 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%.

[0241] The steel plate further satisfies any one, any two, any three or all of the following:

[0242] The first item is: in the NACE TM0284 standard A solution environment, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%;

[0243] The second item is stress corrosion testing according to NACE TM0177 standard, with a loading stress of 0.8σ s , there is no crack on the surface of the tensile specimen;

[0244] Third, in a 6.3MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of ​​the smooth specimen are greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment, respectively;

[0245] The fourth item is the K of the step-type compact tensile specimen in a 6.3MPa pure hydrogen environment. 1C ≥110MPa·m 1 / 2 .

[0246] The unevenness of the steel plate is ≤2mm / m.

[0247] The surface stress of the steel plate is ≤20 MPa.

[0248] The steel plate has a complex phase structure of quasi-polygonal ferrite+acicular ferrite+a small amount of pearlite.

[0249] Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite is 4~9μm.

[0250] The total volume of quasi-polygonal ferrite and acicular ferrite accounts for more than 95%.

[0251] 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%.

[0252] Furthermore, the banded structure of the steel plate is ≤ grade 0.5.

[0253] The central segregation of the steel plate is ≤ level 0.5, and the central porosity is ≤ level 0.5.

[0254] On the cross section of the steel plate, the density of inclusions with a diameter of ≥10 μm is ≤10 / cm 2 .

[0255] 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.

[0256] The steel plate production method of this embodiment differs from the first embodiment only in temperature-controlled water cooling. The following only describes this difference. Other parts not mentioned are the same as the first embodiment and will not be repeated.

[0257] In this embodiment, in step 3, the steel plate is directly temperature-controlled and water-cooled after leaving the finishing hot rolling mill.

[0258] Specifically, the water inlet temperature is Ar3-(70~50)℃, and the water outlet temperature T is Min(T VC ,T VN )-(50~30)℃.

[0259] [Third embodiment]

[0260] This embodiment provides a L360MH grade (i.e., yield strength R t0.5 ≥360MPa) pipeline steel plates can be used in pure hydrogen transportation pipeline projects.

[0261] The thickness of the steel plate is t≥8 mm, preferably 8-30 mm.

[0262] The chemical composition of the steel plate 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%, P≤0.01%, S≤0.002%, O≤0.003%, N≤0.005%, H≤0.0002%, and the rest is iron and unavoidable impurities.

[0263] Furthermore, the chemical composition of the steel plate further satisfies: CEV (%) is 0.199-0.287, and / or Pcm (%) is 0.081-0.131.

[0264] 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.

[0265] The steel plate has an impact energy KV2 of ≥400J at -20°C.

[0266] The hardness of the steel plate is ≤195HV 10 .

[0267] 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%.

[0268] The steel plate further satisfies any one, any two, any three or all of the following:

[0269] The first item is: in the NACE TM0284 standard A solution environment, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%;

[0270] The second item is stress corrosion testing according to NACE TM0177 standard, with a loading stress of 0.8σ s , there is no crack on the surface of the tensile specimen;

[0271] Third, in a 6.3MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of ​​the smooth specimen are greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment, respectively;

[0272] The fourth item is the K of the step-type compact tensile specimen in a 6.3MPa pure hydrogen environment. 1C ≥110MPa·m 1 / 2 .

[0273] The unevenness of the steel plate is ≤2mm / m.

[0274] The surface stress of the steel plate is ≤25 MPa.

[0275] The steel plate has a complex phase structure of quasi-polygonal ferrite+acicular ferrite+a small amount of pearlite.

[0276] Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite is 3~8μm.

[0277] The total volume of quasi-polygonal ferrite and acicular ferrite accounts for more than 95%.

[0278] 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%.

[0279] Furthermore, the banded structure of the steel plate is ≤ grade 0.5.

[0280] The central segregation of the steel plate is ≤ level 0.5, and the central porosity is ≤ level 0.5.

[0281] On the cross section of the steel plate, the density of inclusions with a diameter of ≥10 μm is ≤10 / cm 2 .

[0282] 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.

[0283] The steel plate production method of this embodiment differs from the first embodiment only in temperature-controlled water cooling. The following only describes this difference. Other parts not mentioned are the same as the first embodiment and will not be repeated.

[0284] In this embodiment, in step 3, the steel plate is directly temperature-controlled and water-cooled after leaving the finishing hot rolling mill.

[0285] Specifically, the water inlet temperature is Ar3-(60~40)℃, and the water outlet temperature T is Min(T VC ,T VN )-(150~130)℃.

[0286] [Fourth embodiment]

[0287] This embodiment provides a L415MH grade (i.e., yield strength R t0.5 ≥415MPa) pipeline steel plates can be used in pure hydrogen transportation pipeline projects.

[0288] The thickness of the steel plate is t≥8 mm, preferably 8-30 mm.

[0289] The chemical composition of the steel plate 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%, P≤0.01%, S≤0.002%, O≤0.003%, N≤0.005%, H≤0.0002%, and the rest is iron and unavoidable impurities.

[0290] Furthermore, the chemical composition of the steel plate further satisfies: CEV (%) is 0.197-0.284, and / or Pcm (%) is 0.075-0.126.

[0291] 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.

[0292] The steel plate has an impact energy KV2 of ≥400J at -20°C.

[0293] The hardness of the steel plate is ≤205HV 10 .

[0294] 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%.

[0295] The steel plate further satisfies any one, any two, any three or all of the following:

[0296] The first item is: in the NACE TM0284 standard A solution environment, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%;

[0297] The second item is stress corrosion testing according to NACE TM0177 standard, with a loading stress of 0.8σ s , there is no crack on the surface of the tensile specimen;

[0298] The third item is that 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;

[0299] The fourth item is the K of the step-type compact tensile specimen in a 6.3MPa pure hydrogen environment. 1C ≥100MPa·m 1 / 2 .

[0300] The unevenness of the steel plate is ≤2mm / m.

[0301] The surface stress of the steel plate is ≤35 MPa.

[0302] The steel plate has a complex phase structure of quasi-polygonal ferrite+acicular ferrite+a small amount of pearlite.

[0303] Among them, the average grain size of quasi-polygonal ferrite and acicular ferrite is 2~8μm.

[0304] The total volume of quasi-polygonal ferrite and acicular ferrite accounts for more than 95%.

[0305] 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%.

[0306] Furthermore, the banded structure of the steel plate is ≤ grade 0.5.

[0307] The central segregation of the steel plate is ≤ level 0.5, and the central porosity is ≤ level 0.5.

[0308] On the cross section of the steel plate, the density of inclusions with a diameter of ≥10 μm is ≤10 / cm 2 .

[0309] 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.

[0310] The steel plate production method of this embodiment differs from the first embodiment only in temperature-controlled water cooling. The following only describes this difference. Other parts not mentioned are the same as the first embodiment and will not be repeated.

[0311] In this embodiment, in step 3, the steel plate is directly temperature-controlled and water-cooled after leaving the finishing hot rolling mill.

[0312] Specifically, the water inlet temperature is Ar3-(50~30)℃, and the water outlet temperature T is Min(T VC ,T VN )-(300~270)℃.

[0313] 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.

[0314] 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.

[0315] [Table 1]

[0316]

[0317] These test examples were all prepared according to the production method introduced in the present invention. Specifically: Test Examples 1 and 2 were prepared according to the first embodiment described above, Test Examples 3 and 4 were prepared according to the second embodiment described above, Test Examples 5 and 6 were prepared according to the third embodiment described above, and Test Examples 7 and 8 were prepared according to the fourth embodiment described above.

[0318] Among them, some important parameters in the production process are shown in Table 2.

[0319] [Table 2]

[0320]

[0321] [Table 2 continued]

[0322]

[0323] The steel plates of each test case were tested for structure and performance, and the test results are as follows:

[0324] (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, 3, 5, and 7 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;

[0325] [Table 3]

[0326]

[0327] (2) On the cross section of the steel plate, the density of inclusions with a diameter of ≥10μm is ≤10 / cm 2 ;

[0328] (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;

[0329] [Table 4]

[0330]

[0331] (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;

[0332] (5) For the steel plates of test examples 1 to 6, the tensile strength, elongation, and cross-sectional shrinkage of the smooth specimens under 6.3 MPa pure hydrogen environment are greater than or equal to 90%, 85%, and 80% of those under nitrogen environment, respectively; the K of the step-type compact tensile specimen under 6.3 MPa pure hydrogen environment is greater than or equal to 90%, 85%, and 80%, respectively. 1C ≥110MPa·m 1 / 2 ;

[0333] (6) For the steel plates of test examples 7 and 8, the tensile strength, elongation, and cross-sectional shrinkage of the smooth specimens under 6.3 MPa pure hydrogen environment are greater than or equal to 90%, 80%, and 75% of those under nitrogen environment, respectively; the K of the step-type compact tensile specimens under 6.3 MPa pure hydrogen environment is greater than or equal to 90%, 80%, and 75% of those under nitrogen environment, respectively. 1C ≥100MPa·m 1 / 2 .

Claims

1. A method for producing a steel plate for a pure hydrogen transportation pipeline, characterized in that: The thickness of the steel plate is t≥8mm, and the chemical composition by mass percentage includes: C 0.021~0.076%, Si 0.07~0.21%, Mn 0.66~0.93%, Cr 0.12~0.30%, Ni 0~0.24%, Cu 0~0.24%, Nb0.014~0.052%, V 0.014~0.050%, Ti 0.009~0.019%, Al0.015~0.045%, P≤0.01%, S≤0.002%, O≤0.003%, N≤0.005%, H≤0.0002%, and the rest are iron and inevitable impurities; the steel plate is a complex phase structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite, the average grain size of the quasi-polygonal ferrite and acicular ferrite is 2~16μm, and the volume proportion of the quasi-polygonal ferrite structure and the acicular ferrite structure is more than 95%; The production method comprises: Heating a continuous casting billet having a thickness t0 of 150 to 320 mm; wherein the heating temperature is not lower than the precipitation start temperature of NbC, NbN, TiC, VC, and VN; The continuous casting billet is subjected to rough hot rolling, finish hot rolling and final hot rolling to produce steel plates; wherein the starting rolling temperature and the final rolling temperature of the rough hot rolling are both T nr ~Min(T NbC ,T NbN ,T TiC ), the starting and finishing temperatures of the finishing hot rolling are both Ar3-20℃~Ar3+10℃, the finishing hot rolling is a single pass hot rolling at a temperature of Ar3-(40~20)℃; the thicknesses of the steel plates after rough hot rolling, finishing hot rolling, and final hot rolling are (3.2~4)t, t+(2~5)mm, and t, respectively; After the steel plate leaves the final hot rolling mill, it is cooled by controlled water; the water inlet temperature is Ar3-(80~30)℃, and the water outlet temperature T is Min(T VC ,T VN )-300℃~Min(T VC ,T VN )+5℃.

2. The method for producing a steel plate for a pure hydrogen transportation pipeline according to claim 1, characterized in that: 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℃).

3. The method for producing a steel plate for a pure hydrogen transportation pipeline according to claim 1, characterized in that: The temperature of the whole process of rough hot rolling is T nr ~Min(T NbC ,T NbN ,T TiC ); The temperature during the entire hot rolling process is Ar3-20℃~Ar3+10℃.

4. The method for producing a steel plate for a pure hydrogen transportation pipeline according to claim 1, characterized in that: The starting rolling temperature of rough hot rolling is higher than the finishing rolling temperature, the starting rolling temperature of finish hot rolling is higher than the finishing rolling temperature, and the temperature of finish hot rolling is lower than the finishing rolling temperature of finish hot rolling.

5. The method for producing a steel plate for a pure hydrogen transportation pipeline according to claim 1, characterized in that: The intermediate billet obtained by rough hot rolling is water-cooled before finishing hot rolling, and the outlet water temperature is Ar3-20℃~Ar3+10℃.

6. The method for producing a steel plate for a pure hydrogen transportation pipeline according to claim 1, characterized in that: During rough hot rolling, the reduction of the initial rolling pass of the non-widening pass is ≥42mm, and the reduction of each pass is ≥31mm.

7. The method for producing a steel plate for a pure hydrogen transportation pipeline according to claim 1, characterized in that: During finish hot rolling, the reduction in each pass is ≥22mm.

8. The method for producing a steel plate for a pure hydrogen transportation pipeline according to claim 1, characterized in that: The temperature-controlled water cooling is carried out on an ultra-fast cooling system with a water pressure of 0.15-0.20 MPa, an upper and lower water ratio of 0.92-0.98, a cooling rate of 6-16°C / s, and a cooling roller speed of 1.5-2.2 m / s.

9. The method for producing a steel plate for a pure hydrogen transportation pipeline according to claim 1, characterized in that: The production method further comprises: After temperature-controlled water cooling, the steel plate is first subjected to hot straightening, and the temperature during hot straightening is T-60℃~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℃; after that, the steel plate is subjected to warm straightening and cold straightening in sequence.

10. The method for producing a steel plate for a pure hydrogen transportation pipeline according to claim 1, characterized in that: When the temperature-controlled water cooling is used: 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)℃.

11. The method for producing a steel plate for a pure hydrogen transportation pipeline according to claim 1, characterized in that: The chemical composition of the steel plate further satisfies: CEV is 0.168-0.325%, and / or Pcm is 0.069-0.159%.

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