Steel plate for pure hydrogen conveying pipeline and production method thereof

Abstract

The invention discloses a steel plate for a pure hydrogen conveying pipeline and a production method of the steel plate. The steel plate comprises the following components in percentage by weight: 0.021 to 0.076 percent of C, 0.07 to 0.21 percent of Si, 0.66 to 0.93 percent of Mn, 0.12 to 0.3 percent of Cr, less than or equal to 0.24 percent of Ni, less than or equal to 0.24 percent of Cu, 0.014 to 0.052 percent of Nb, 0.014 to 0.050 percent of V, 0.009 to 0.019 percent of Ti, 0.015 to 0.045 percent of Al and the balance of iron. The production method comprises the following steps: the starting / finishing rolling temperature of rough rolling is Tnr-Min (TNbC, TNbN and TTiC), the starting / finishing rolling temperature of finish rolling is Ar3-20 DEG C-Ar3 + 10 DEG C, and the finishing rolling temperature is Ar3-(40-20) DEG C; and carrying out water cooling, putting Ar3-(80-30) DEG C into water, and discharging water from Min (TVC, TVN)-300 DEG C to Min (TVC, TVN) + 5 DEG C.

Description

Technical Field

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

[0002] The main bottleneck restricting the development of pure hydrogen transmission pipelines is that pipeline steel may experience performance deterioration or even failure in a high-pressure pure hydrogen environment. For example, in a high-pressure pure hydrogen environment, pipeline steel is prone to hydrogen-induced cracking and hydrogen blistering, and its ductility, fatigue performance, and fracture toughness deteriorate significantly. Therefore, higher requirements are put forward for the steel plate used in high-pressure pure hydrogen transmission pipelines. One is that the steel plate for the transmission pipeline has hydrogen-induced cracking resistance, and the other is that the steel plate for the pipeline needs to have excellent fracture toughness in a pure hydrogen environment.

[0003] In some existing technologies, such as CN115094314A, CN115433884A, CN116103568A, etc., research has been carried out on pipeline steel from the aspect of chemical composition. However, the technologies such as those of CN115094314A and CN115433884A have defects such as high alloy element content, complex steelmaking process, and high alloy cost; the technology of CN116103568A has a relatively high carbon content and has problems with poor welding performance, which affects the application of the steel plate in pipeline steel.

[0004] In some other existing technologies, such as CN113862549A, CN116694902A, CN114645215A, etc., research has been carried out on pipeline steel from the aspect of production process. However, these technologies generally require additional heat treatment processes (such as normalizing, quenching, tempering, etc.), resulting in complex production processes, long flow paths, high costs, and low efficiency; moreover, the technology of CN114645215A only targets hydrogen-doped pipeline steel and is difficult to meet the application requirements of pure hydrogen pipeline steel. Specifically, it is difficult to cope with the strong deterioration effect of the pure hydrogen environment on steel. Summary of the Invention

[0005] The purpose of the present invention is to provide a steel plate for pure hydrogen transmission pipelines and a production method thereof.

[0006] To achieve the above-mentioned invention objective, an embodiment of the present invention provides a steel plate for pure hydrogen transmission pipelines. The thickness t of the steel plate is t≥8mm, and the chemical composition 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 inevitable impurities.

[0007] Preferably, the steel plate satisfies any one, any two, any three or all of the following: In the NACE TM0284 standard A solution environment, CLR≤10%, CTR≤3%, CSR≤1%; In the stress corrosion test according to the NACE TM0177 standard, the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen; In a 6.3MPa pure hydrogen environment, the tensile strength, elongation and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 80% and 75% of those in a nitrogen environment; In a 6.3MPa pure hydrogen environment, for the stepped compact tension specimen, K 1C ≥100MPa·m 1 / 2 .

[0008] Preferably, the yield strength R t0.5 ≥330MPa, the tensile strength R m ≥430MPa, the elongation A 50 ≥40%, and the yield ratio is ≤0.87.

[0009] Preferably, the -20°C impact energy KV2 of the steel plate ≥400J, the hardness ≤205HV 10 , the -10°C DWTT drop hammer shear area fraction is 100%, and the -15°C DWTT drop hammer shear area fraction is 100%.

[0010] Preferably, the flatness of the steel plate ≤2mm / m, and the surface stress ≤35MPa.

[0011] Preferably, on the cross-section of the steel plate, the inclusion density with a diameter ≥10μm ≤10 pieces / cm 2 .

[0012] Preferably, the steel plate has a complex phase structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

[0013] Preferably, the average grain size of the quasi-polygonal ferrite and acicular ferrite is 2 - 16 μm; the volume ratio of the quasi-polygonal ferrite structure and acicular ferrite structure is more than 95%.

[0014] Preferably, the volume ratio of the quasi-polygonal ferrite structure is 5 - 90%, the volume ratio of the acicular ferrite structure is 5 - 94%, the volume ratio of the pearlite structure is 1 - 5%, and the banded structure is ≤ 0.5 grade.

[0015] To achieve the above invention object, an embodiment of the present invention provides a production method of a steel plate for pure hydrogen transmission pipeline. The thickness t of the steel plate is ≥ 8 mm, 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%, 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 inevitable impurities; The production method includes: Heating a continuous casting billet with a thickness t0 of 150 - 320 mm; wherein, the heating temperature is not lower than the starting precipitation temperature of NbC, NbN, TiC, VC, VN; Making the continuous casting billet into a steel plate through rough hot rolling, finish hot rolling, and final hot rolling; wherein, the starting rolling temperature and final rolling temperature of the rough hot rolling are both T nr ~Min(T NbC , T NbN , T TiC ), the starting rolling temperature and final rolling temperature of the finish hot rolling are both Ar3 - 20°C ~ Ar3 + 10°C, the final hot rolling is a single-pass hot rolling, and the temperature is Ar3 - (40 - 20)°C; the thicknesses of the steel plate after rough hot rolling, finish hot rolling, and final hot rolling are (3.2 - 4)t, t + (2 - 5) mm, and t respectively; After the steel plate leaves the rolling mill of the final hot rolling, controlled cooling is carried out; wherein, the water inlet temperature is Ar3 - (80 - 30)°C, and the water outlet temperature T is Min(T VC , T VN ) - 300°C ~ Min(T VC , T VN ) + 5°C.

[0016] Preferably, the heating temperature is Max(T NbC ,T NbN ,T TiC ,T VC ,T VN ) + 40°C to Min(Max(T NbC ,T NbN ,T TiC ,T VC ,T VN ) + 120°C, T TiN - 150°C).

[0017] Preferably, the temperature throughout the rough hot rolling is between T nr and Min(T NbC ,T NbN ,T TiC ); The temperature throughout the finish hot rolling is between Ar3 - 20°C and Ar3 + 10°C.

[0018] Preferably, the starting rolling temperature of the rough hot rolling is higher than the finishing rolling temperature, the starting rolling temperature of the finish hot rolling is higher than the finishing rolling temperature, and the temperature of the final hot rolling is lower than the finishing rolling temperature of the finish hot rolling.

[0019] Preferably, the intermediate billet obtained from the rough hot rolling is water-cooled before the finish hot rolling, and the water outlet temperature is between Ar3 - 20°C and Ar3 + 10°C.

[0020] Preferably, during the rough hot rolling, the reduction of the first rolling pass in the non-spreading passes is ≥ 42 mm, and the reduction of each pass is ≥ 31 mm.

[0021] Preferably, during the finish hot rolling, the reduction of each pass is ≥ 22 mm.

[0022] Preferably, the controlled temperature water cooling is carried out on an ultra-fast cooling system, the water pressure is 0.15 - 0.20 MPa, the ratio of upper and lower water is 0.92 - 0.98, the cooling rate is 6 - 16°C / s, and the speed of the cooling roller table of the ultra-fast cooling system is 1.5 - 2.2 m / s.

[0023] Preferably, the production method further includes: After the controlled temperature water cooling, the steel plate is first hot straightened, and the temperature during hot straightening is T - 60°C to T; after leaving the hot straightening machine, the steel plate is placed on the cooling bed for natural air cooling, and the temperature when leaving the cooling bed is 100 - 200°C; then, the steel plate is sequentially subjected to warm straightening and cold straightening.

[0024] Preferably, during the controlled temperature water cooling: The water inlet temperature is Ar3 - (80 - 60)°C, and the water outlet temperature T is Min(T VC ,T VN ) - 15°C to Min(T VC ,TVN ) + 5 °C; Or, the water inlet temperature is Ar3 - (70~50) °C, and the water outlet temperature T is Min(T VC , T VN ) - (50~30) °C; Or, the water inlet temperature is Ar3 - (60~40) °C, and the water outlet temperature T is Min(T VC , T VN ) - (150~130) °C; Or, the water inlet temperature is Ar3 - (50~30) °C, and the water outlet temperature T is Min(T VC , T VN ) - (300~270) °C.

[0025] Preferably, the chemical composition of the steel plate further satisfies: CEV(%) is 0.168~0.325, and / or, Pcm(%) is 0.069~0.159.

[0026] Compared with the prior art, the beneficial effects of the present invention are: (1) In terms of chemical composition, it does not contain expensive alloys such as Mo, and adopts a low-alloy composition system design with compound addition of low-carbon, low-manganese, low-phosphorus and sulfur and Nb+V+Ti precipitation elements, which is easy for steelmaking production and has a low production cost; moreover, reducing the C content in the steel results in excellent welding performance, which is beneficial to the welding effect when preparing pipeline steel; furthermore, appropriate addition of Nb, V, Ti forms carbides and nitrides, which can serve as hydrogen traps to capture hydrogen, thereby reducing the diffusible hydrogen in the steel plate and further enhancing the HIC resistance and hydrogen resistance of the steel; (2) During the hot rolling process, deformation-induced ferrite phase transformation occurs in the steel plate, generating a large number of fine deformation-induced ferrite (such as quasi-polygonal ferrite); on this basis, through controlled-temperature water cooling, the steel plate is cooled to the ferrite phase transformation zone, and ferrite phase transformation continues to obtain a large amount of ferrite phase (for example, forming acicular ferrite), avoiding the generation 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; (3) Furthermore, the control of the water outlet temperature is conducive to the precipitation of carbon and nitride of V, forming more hydrogen traps to capture hydrogen, thereby reducing the diffusible hydrogen in the steel plate and further enhancing the HIC resistance and hydrogen resistance of the steel; (4) Generally speaking, through process control such as chemical composition, hot rolling, and controlled-temperature water cooling, the optimization and control of the steel plate in terms of HIC resistance, hydrogen resistance, etc. are realized, and no additional heat treatment is required after rolling, with excellent welding performance and fast production rhythm, meeting the application requirements of pure hydrogen pipelines. Brief Description of the Drawings

[0027] Figure 1 It is the metallographic structure diagram of the finished steel plate of Embodiment 1 of the present invention; Figure 2 It is the metallographic structure diagram of the finished steel plate of Embodiment 3 of the present invention; Figure 3 It is the metallographic structure diagram of the finished steel plate of Embodiment 5 of the present invention; Figure 4 It is the metallographic structure diagram of the finished steel plate of Embodiment 7 of the present invention. Detailed implementation manners

[0028] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the specific implementation manners of the present invention. Obviously, the described implementation manners are only part of the implementation manners of the present invention, rather than all of them. Based on the implementation manners in the present invention, all other implementation manners obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0029] The present invention provides a steel plate, which can be used for preparing a pure hydrogen transmission pipeline.

[0030] The thickness t of the steel plate ≥ 8 mm. Such a larger thickness can ensure smaller residual stress and can meet the requirements of the pure hydrogen transmission pipeline.

[0031] Preferably, the thickness t of the steel plate is 8 - 30 mm.

[0032] 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 balance is iron and unavoidable impurities.

[0033] The functions of each chemical element in the present embodiment will be introduced in detail below.

[0034] Carbon: Carbon is the most economical strengthening element in steel, which has a solid-solution strengthening effect. At the same time, it forms carbides with niobium, vanadium, titanium, chromium, etc., playing a precipitation strengthening role, and can also act as a hydrogen trap to improve the hydrogen resistance of the steel plate. The increase in carbon content has an obvious effect on improving the strength and hardness of pipeline steel. However, too high carbon will lead to poor low-temperature toughness and weldability, and reduce the low-temperature drop-weight performance of pipeline steel. Reducing the carbon content is beneficial to the homogenization of composition and structure, improving the banded structure, reducing the pearlite content, and is conducive to obtaining more ferrite tissues. Therefore, considering comprehensively, the carbon content is selected to be 0.021 - 0.076%.

[0035] Silicon: Silicon has a solid-solution strengthening effect in steel. However, when the silicon content is relatively high, it will increase the grain boundary segregation of elements such as phosphorus and sulfur, reducing the low-temperature toughness and weldability. At the same time, too much silicon is likely to generate Fe2SiO4 on the surface of continuous casting billets, 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%.

[0036] Manganese: Manganese plays a solid-solution strengthening role in steel, improving strength and hardness. A reasonable manganese content can ensure the strength of pipeline steel at low cost. As the manganese content increases, the strength of pipeline steel increases significantly, while the ductile-brittle transition temperature hardly changes. Too much manganese will lead to center segregation of the casting billet, which is not beneficial to toughness. At the same time, it will increase the level of the banded structure. The higher the level of the banded structure, the more uneven the tissue distribution, and the worse the hydrogen-induced cracking (abbreviation: HIC) resistance and hydrogen resistance. Therefore, considering comprehensively, the manganese content is selected to be 0.66 - 0.93%.

[0037] Chromium: Chromium plays a solid-solution strengthening role in steel. As a ferrite-forming element, more acicular ferrite tissues can be obtained in high-niobium steel. However, when the chromium content is too high, it will increase the microhardness of pipeline steel and reduce the low-temperature toughness. Therefore, considering comprehensively, the chromium content is selected to be 0.12 - 0.30%.

[0038] Nickel: Nickel plays a solid-solution strengthening role in steel, increasing the strength of the steel without significantly increasing its hardness. At the same time, it can improve the low-temperature toughness and weldability of the steel plate. However, when the nickel content is too high, it will increase the alloy cost. Therefore, considering comprehensively, nickel can be considered for addition, and the addition amount does not exceed 0.24%. Of course, nickel is not necessarily added in this application, and it can also be not added in some embodiments.

[0039] Copper: Copper can promote the precipitation of niobium and can make up for the strength loss caused by the decrease in carbon content. Adding a certain amount of nickel while adding copper can effectively inhibit surface cracks. However, when the copper content is relatively high, it is not conducive to weldability. Therefore, considering comprehensively, copper can be considered for addition, and the addition amount does not exceed 0.24%. Of course, copper is not necessarily added in this application, and it can also be not added in some embodiments.

[0040] Niobium: Niobium is an important grain-refining element in steel. During the hot rolling process, niobium strongly inhibits austenite recrystallization and its precipitation in austenite, pins austenite grain boundaries, and refines recrystallized grains. During the cooling process, the dissolved niobium can continue to precipitate in the form of niobium carbonitrides, significantly refining the structure obtained after the material undergoes a phase change 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, when the niobium content is relatively high, it will lead to an increase in alloy cost. Therefore, considering all factors, the niobium content is selected to be 0.014 - 0.052%.

[0041] Vanadium: Vanadium can significantly improve the hardenability of steel, increase its strength, and also play a role in refining grains. Vanadium belongs to strong carbide-forming elements, reacts with carbon and nitrogen in steel to form carbides and nitrides, which can act as hydrogen traps and improve the hydrogen resistance of the steel plate. However, when the vanadium content is too high, the alloy cost will increase significantly. Therefore, considering all factors, the vanadium content is selected to be 0.014 - 0.050%.

[0042] Titanium: Titanium is a nitrogen-fixing element in steel, which can form dispersed titanium nitride particles, serving as hydrogen traps and improving the hydrogen resistance of the steel plate. At the same time, it inhibits the coarsening of austenite grains during the billet heating process and the rolling process. When the addition amount is too high, it is easy to form coarse carbon and nitride precipitates in the center of the continuous casting billet, affecting the low-temperature toughness of the steel plate. Therefore, considering all factors, the titanium content is selected to be 0.009 - 0.019%.

[0043] Aluminum: Aluminum is a deoxidizing element in steel. Excessive aluminum is likely to increase 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%.

[0044] Phosphorus, sulfur, oxygen, nitrogen, hydrogen: These are impurity elements in steel. It is sufficient to control P ≤ 0.01%, S ≤ 0.002%, O ≤ 0.003%, N ≤ 0.005%, and H ≤ 0.0002%. Considering the steelmaking cost, preferably, it can also be controlled to meet any one or more of the following conditions: P 0.0050 - 0.0090%, S 0.0008 - 0.0014%, O 0.0012 - 0.0026%, N 0.0022 - 0.0042%, H 0.00004 - 0.00015%.

[0045] Generally speaking, in terms of chemical composition, this 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 composite addition of Nb+V+Ti precipitation elements, which is easy for steelmaking production and has low production costs. Moreover, reducing the C content in the steel results in excellent welding performance, which is beneficial to the welding effect of the steel plate when preparing pipeline steel. Furthermore, appropriate addition of Nb, V, and Ti forms carbides and nitrides, which can serve as hydrogen traps to capture hydrogen, thereby reducing the diffusible hydrogen in the steel plate and further enhancing the HIC resistance and hydrogen resistance of the steel.

[0046] Thus, this 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 by a short process route without heat treatment.

[0047] Further preferably, the chemical composition of the steel plate may further satisfy: Mn / C is 12 - 26 in mass percentage. In this way, by controlling the manganese-carbon ratio, segregation is reduced, the banded structure is improved, and the tissue distribution is uniform, thereby enhancing the HIC resistance and hydrogen resistance of the steel plate.

[0048] Furthermore, the chemical composition of the steel plate also satisfies: CEV(%) is 0.168 - 0.325.

[0049] The carbon equivalent CEV(%) can be specifically calculated by the following formula: CEV(%) = [C] + [Mn] / 6 + ([Cr] + [V]) / 5 + ([Cu] + [Ni]) / 15. However, this application is not limited to this.

[0050] Preferably, the chemical composition of the steel plate may further satisfy: Pcm(%) is 0.069 - 0.159.

[0051] In one embodiment, Pcm(%) can be specifically calculated by the following formula: Pcm(%) = [C] + [Si] / 30 + ([Mn] + [Cu] + [Cr]) / 20 + [Ni] / 60 + [V] / 10.

[0052] The chemical composition of the steel plate is introduced above. Next, the steel plate will be introduced from the aspect of performance.

[0053] Specifically, the steel plate has excellent mechanical properties.

[0054] For example, the yield strength R of the steel plate t0.5 ≥330 MPa, the tensile strength R m ≥430 MPa, the elongation A 50 ≥40%, and the yield ratio ≤0.87.

[0055] Here, specifically in accordance with GB / T 2975-2018 "Steel and Steel Products - Sampling Locations and Specimen Preparation for Mechanical Property Tests" and GB / T 228.1-2021 "Metallic Materials - Tensile Testing - Part 1: Method of Test at Room Temperature", sampling and mechanical property testing are carried out on the said steel plate.

[0056] Furthermore, the said steel plate has excellent low-temperature toughness.

[0057] For example, the -20°C impact energy KV2 of the said steel plate ≥ 400 J.

[0058] The hardness of the said steel plate ≤ 205 HV 10 .

[0059] The -10°C DWTT drop-weight shear area fraction of the said steel plate is 100%, and the -15°C DWTT drop-weight shear area fraction is 100%.

[0060] Here, specifically in accordance with GB / T 2975-2018 "Steel and Steel Products - Sampling Locations and Specimen Preparation for Mechanical Property Tests" and GB / T 229-2020 "Metallic Materials - Charpy Pendulum Impact Test Method", sampling and low-temperature property testing are carried out on the said steel plate.

[0061] The said steel plate also has excellent hydrogen resistance and HIC resistance.

[0062] For example, the said steel plate also meets any one, any two, any three or all of the following: The first item, in the NACE TM0284 standard A solution environment, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%; The second item, in the NACE TM0177 standard for stress corrosion testing, the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen; The third item, in a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 80%, and 75% of those in a nitrogen environment; The fourth item, in a 6.3 MPa pure hydrogen environment, the K 1C ≥ 100 MPa·m 1 / 2 .

[0063] Here, for the above-mentioned third and fourth items, specifically in accordance with GB / T 34542.2-2018 "Hydrogen Storage and Transportation Systems - Part 2: Test Methods for Compatibility of Metallic Materials with Hydrogen Environments", sampling and testing are carried out on the said steel plate.

[0064] Furthermore, the steel plate has excellent flatness.

[0065] For example, the unevenness of the steel plate is ≤ 2 mm / m. In this way, the internal stress of the steel plate is small, and the hydrogen resistance and HIC resistance can be improved.

[0066] Moreover, the residual stress of the steel plate is small.

[0067] For example, the surface stress of the steel plate is ≤ 35 MPa. In this way, the residual stress of the steel plate is small, and the hydrogen resistance and HIC resistance can be improved.

[0068] The chemical composition and properties of the steel plate have been introduced above. Next, the steel plate will be introduced from the aspect of microstructure.

[0069] The steel plate has a duplex structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

[0070] Among them, the average grain size of the quasi-polygonal ferrite and acicular ferrite is 2 - 16 μm. In this way, the probability of hydrogen-induced cracks generated at the grain boundaries can be reduced, and the HIC resistance can be improved.

[0071] Preferably, the total volume ratio of the quasi-polygonal ferrite and acicular ferrite is more than 95%. This structure can ensure good matching of various mechanical properties of the steel plate, such as strength, low-temperature toughness, yield ratio, hardness, drop-weight performance, etc.

[0072] Specifically, the volume ratio of the quasi-polygonal ferrite structure is 5 - 90%, the volume ratio of the acicular ferrite structure is 5 - 94%, and the volume ratio of the pearlite structure is 1 - 5%.

[0073] Moreover, the banded structure of the steel plate is ≤ grade 0.5. In this way, the hydrogen-induced cracks caused at the banded structure can be reduced, and the hydrogen resistance can be improved.

[0074] Furthermore, the central segregation of the steel plate is ≤ grade 0.5, and the central porosity is ≤ grade 0.5.

[0075] Here, the central segregation can be specifically observed after cold acid etching in accordance with YB / T 4003 - 2016 "Macrostructure Defect Rating Chart for Continuous Cast Steel Slabs".

[0076] The central porosity grade can be specifically determined through macro-etching test in accordance with GB / T 226 - 2015 "Macroexamination of Steel for Macrostructure and Defects by Etching", or can be determined by ultrasonic flaw detection.

[0077] Microscopically speaking, on the cross-section of the steel plate, the inclusion density with a diameter ≥ 10 μm is ≤ 10 pieces / cm 2 . In this way, the hydrogen-induced cracks caused at the inclusions can be avoided.

[0078] Furthermore, the ratings of Class A, B, C, and D inclusions in the steel plate are all ≤ 1 grade, and the sum of the ratings of Class A, B, C, and D inclusions is ≤ 2.5 grades.

[0079] Here, the ratings of Class A, B, C, and D inclusions can specifically be rated by referring to the standard atlas under a microscope in accordance with GB / T 10561-2005 "Determination of Non-Metallic Inclusions in Steel - Microscopic Examination Method Using Standard Rating Charts".

[0080] Furthermore, the present invention also provides a production method for the steel plate.

[0081] The production method includes: Step 1, heating the continuous casting billet; Step 2, making the continuous casting billet into a steel plate through rough hot rolling, finish hot rolling, and final hot rolling; Step 3, after the steel plate exits the rolling mill of the final hot rolling, perform controlled temperature water cooling.

[0082] Specifically, in Step 1, the thickness t0 of the continuous casting billet is 150 - 320 mm, and preferably it can be 220 mm.

[0083] The chemical composition of the continuous casting billet is the same as that of the steel plate.

[0084] Furthermore, those skilled in the art can understand that the inclusion grade, center segregation grade, and center porosity grade of the continuous casting billet are the same as those of the steel plate.

[0085] For example, the ratings of Class A, B, C, and D inclusions in the continuous casting billet are all ≤ 1 grade, and the sum of the ratings of Class A, B, C, and D inclusions is ≤ 2.5 grades; on the cross-section of the continuous casting billet, the density of inclusions with a diameter ≥ 10 μm is ≤ 10 pieces / cm 2 ; the center segregation of the continuous casting billet is ≤ 0.5 grade, and the center porosity is ≤ 0.5 grade.

[0086] The continuous casting billet can specifically be prepared by smelting and continuous casting techniques, and the smelting technique can specifically include, in sequence, hot metal pre-desulfurization, converter smelting, LF refining, and RH refining.

[0087] The present invention does not introduce too much about the specific operations of hot metal pre-desulfurization, converter smelting, LF refining, RH refining, and continuous casting, and any feasible technique in the art can be used for implementation.

[0088] In Step 1, after the continuous casting billet exits the continuous caster, it directly enters the heating furnace for heating.

[0089] The heating temperature is not lower than the respective starting precipitation temperatures T of NbC, NbN, TiC, VC, and VN NbC 、TNbN , T TiC , T VC , T VN .

[0090] In Step 2, the thicknesses of the steel plate after rough hot rolling, finish hot rolling, and final hot rolling are (3.2 - 4)t, t + (2 - 5) mm, and t, respectively.

[0091] That is, the continuous casting billet leaving the heating furnace is first subjected to rough hot rolling until the thickness of the steel plate reaches (3.2 - 4)t; then it undergoes finish hot rolling until the thickness of the steel plate reaches t + (2 - 5) mm; and finally, it undergoes final hot rolling until the thickness of the steel plate reaches t.

[0092] The final hot rolling is a single - pass hot rolling, that is, from a thickness of t + (2 - 5) mm to a thickness of t, it only undergoes a single - pass hot rolling.

[0093] 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 ).

[0094] Preferably, the starting rolling temperature of the rough hot rolling can be greater than the finishing rolling temperature.

[0095] Wherein, T nr represents the lowest temperature of austenite recrystallization, and its value can be obtained mainly through various methods such as theoretical calculation, experimental determination, and empirical formulas.

[0096] For example, in one embodiment, T nr can be calculated according to the following formula: T nr = 887 + 464[C] + (6445[Nb] - 644 ) + (732[V] - 230 ) + 890[Ti] + 363[Al] – 357[Si]. However, the value - taking method of T nr is not limited to this. Other value - taking methods known to those skilled in the art based on the concept of T nr can be applied to the present invention.

[0097] Furthermore, Min(T NbC , T NbN , T TiC ) means: the minimum value among the three temperature values of T NbC , T NbN , T TiC .

[0098] Thus, during rough hot rolling: At the recrystallization temperature T nrPerform rolling as above to avoid mixed crystals; and the temperature is always controlled below Min(T NbC ,T NbN ,T TiC ), to ensure the effective precipitation of Nb carbides and nitrides and Ti carbides during rolling, preventing the growth of recrystallized grains and refining the recrystallized grains; Furthermore, rolling in a higher temperature range can reduce the rolling deformation resistance, increase the reduction ratio, facilitate the penetration of deformation to the core of the billet, improve defects such as core segregation and porosity, and at the same time, reduce the banded structure; Secondly, adopt large reduction rolling (i.e., rolling from thickness t0 to thickness (3.2 - 4)t), fully break the as-cast structure, obtain refined recrystallized grains, the greater the total reduction ratio, the more obvious the refinement effect on austenite grains, and because the temperature is low, the grains will not grow excessively.

[0099] The starting rolling temperature and the finishing rolling temperature of finish hot rolling are both Ar3 - 20°C to Ar3 + 10°C.

[0100] Preferably, the starting rolling temperature of finish hot rolling can be greater than the finishing rolling temperature.

[0101] Among them, Ar3 is the temperature at which austenite (γ-Fe) starts to precipitate ferrite (α-Fe) during cooling, and its specific value can be obtained through experiments and measurements using a differential scanning calorimeter (DSC) or thermogravimetric analysis (TG), or can also be obtained through an empirical formula.

[0102] For example, in one embodiment, Ar3 can be calculated according to the following formula: Ar3 = 910 - 203[C] - 15.2[Ni] + 44.7[Si] + 30[Mn] + 70[Cr] + 66.5[V]. However, the value-taking method of Ar3 is not limited to this. Other value-taking methods that can be known to those skilled in the art based on the concept of Ar3 can all be applied to the present invention.

[0103] In this way, during finish hot rolling, the whole process is rolling in the two-phase critical zone, and: On the one hand, perform large reduction deformation in the non-recrystallized zone (i.e., rolling from thickness (3.2 - 4)t to thickness t + (2 - 5)mm), obtain a deformed structure, so that a large number of deformation bands are accumulated in the structure, and fine structure is obtained during the subsequent controlled cooling process, improving the low-temperature toughness of the steel plate; On the other hand, large reduction deformation can induce the precipitation of the second phase, obtaining more fine precipitates; On the other hand, perform rolling deformation within 30°C near the two-phase phase transformation starting point Ar3, which can not only ensure the formation of more deformation-induced ferrite, for example, a large number of quasi-polygonal ferrite can be formed, and at the same time, the deformation-induced ferrite grains are relatively fine.

[0104] The temperature of the final hot rolling is Ar3 - (40~20)°C.

[0105] Preferably, the temperature of the final hot rolling is lower than the finishing temperature of the finish hot rolling. However, the present application is not limited thereto.

[0106] In this way, by controlling the reduction (i.e., 2~5 mm) and temperature during the final hot rolling of the last pass, the shape of the steel plate can be ensured, and the performance of the final steel plate can be improved.

[0107] Next, in step 3, after the steel plate leaves the hot rolling mill, it is directly subjected to controlled temperature water cooling.

[0108] The water inlet temperature is Ar3 - (80~30)°C, and the water outlet temperature T is Min(T VC , T VN ) - 300°C ~ Min(T VC , T VN ) + 5°C.

[0109] It can be understood that the water outlet temperature T is lower than the water inlet temperature.

[0110] Among them, Min(T VC , T VN ) means: the minimum value among the two temperature values of T VC , T VN .

[0111] Based on the foregoing, during the hot rolling process in step 2, deformation-induced ferrite phase transformation has occurred in the steel plate, generating a large number of fine deformation-induced ferrite (such as quasi-polygonal ferrite). On this basis, through the controlled temperature water cooling in step 3, the steel plate is cooled to the ferrite phase transformation region, and ferrite phase transformation continues to obtain a large number of ferrite phases (for example, acicular ferrite is formed), avoiding the generation of hard phases such as pearlite, bainite, and MA, so as to ensure the anti-HIC performance and anti-hydrogen performance of the steel plate for pure hydrogen transmission pipelines.

[0112] Furthermore, the control of the water outlet temperature is conducive to the precipitation of carbon and nitride of V, forming more hydrogen traps to capture hydrogen, thereby reducing the diffusible hydrogen in the steel plate, and further improving the anti-HIC performance and anti-hydrogen performance of the steel.

[0113] In summary, the production method of the present invention realizes the optimization and control of the steel plate in terms of grain size, banded structure, hard phase structure, inclusion size and quantity, strength, hardness, low-temperature toughness, shape, residual stress, anti-HIC performance, anti-hydrogen performance, etc. through the control of chemical composition, hot rolling, controlled temperature water cooling and other processes. After rolling, no additional heat treatment is required, the welding performance is excellent, the production rhythm is fast, and the comprehensive performance of the obtained steel plate is excellent.

[0114] Preferably, in step 1, the heating temperature is Max(TNbC , T NbN , T TiC , T VC , T VN ) + 40°C to Min(Max(T NbC , T NbN , T TiC , T VC , T VN ) + 120°C, T TiN - 150°C).

[0115] Among them, Max(T NbC , T NbN , T TiC , T VC , T VN ) means: the maximum value among the five temperature values of T NbC , T NbN , T TiC , T VC , T VN these five temperature values.

[0116] Min(Max(T NbC , T NbN , T TiC , T VC , T VN ) + 120°C, T TiN - 150°C) means: the minimum value among the two temperature values of Max(T NbC , T NbN , T TiC , T VC , T VN ) + 120°C and T TiN - 150°C, that is, the relatively smaller one of the two.

[0117] In this way, through the control of the heating temperature, the alloying elements are effectively solid-solved, ensuring that the carbides and nitrides of Nb and V and the carbide of Ti in the steel can be completely dissolved, and the austenite grains do not grow excessively, preparing for the precipitation during the subsequent rolling in the recrystallization zone (i.e., rough hot rolling).

[0118] In step 1, the heating duration is preferably controlled to be (1.1 - 1.3)t0 min / mm. That is, according to the thickness t of the continuous casting slab 0， the heating duration per millimeter is 1.1 - 1.3 min.

[0119] Furthermore, in step 2, the whole process temperature of the rough hot rolling is in the range of T nr ~ Min(T NbC , T NbN , T TiC ).

[0120] Furthermore, in Step 2, the temperature throughout the finish hot rolling is in the range of Ar3 - 20°C to Ar3 + 10°C.

[0121] 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 temperature of the water-cooling is in the range of Ar3 - 20°C to Ar3 + 10°C.

[0122] In this way, after rolling in the recrystallization zone of the rough hot rolling, fine recrystallized grains are obtained, and then rapidly cooled below the recrystallization temperature by the water-cooling device. On the one hand, it avoids the rapid growth of recrystallized grains during the holding process, which may lead to poor low-temperature toughness of the final steel plate; on the other hand, it reduces the holding time and improves the rolling efficiency.

[0123] Furthermore, in Step 2, during the rough hot rolling, the reduction per pass ≥ 31 mm, and for the first pass of the non-spreading passes, the reduction ≥ 42 mm.

[0124] For example, the rough hot rolling includes several non-spreading passes, and for the first pass (i.e., the initial rolling pass) among these non-spreading passes, the reduction ≥ 42 mm.

[0125] In this way, when the total reduction of the rough hot rolling is large, a large reduction is also adopted for each pass, fully breaking the as-cast structure to obtain refined recrystallized grains. The greater the total reduction and the greater the reduction per pass, the more obvious the refinement effect on austenite grains.

[0126] In Step 2, during the finish hot rolling, the reduction per pass ≥ 22 mm.

[0127] In this way, large reduction deformation is carried out in the non-recrystallization zone to obtain a deformed structure, so that a large number of deformation bands are accumulated in the structure, and fine structures are obtained during the subsequent cooling process, improving the low-temperature toughness of the steel plate.

[0128] In addition, in Step 2, the final hot rolling can adopt skin pass rolling, with a biting speed of 1.5 ± 0.2 m / s and a rolling speed of 6 ± 2 m / s. This can reduce the stress of the steel plate.

[0129] Next, in Step 3, the steel plate obtained from the final hot rolling can directly enter the ultra-fast cooling system for controlled water cooling.

[0130] Specifically, on the ultra-fast cooling system, the water pressure is 0.15 - 0.20 MPa, the upper and lower water ratio is 0.92 - 0.98, the cooling rate is 6 - 16°C / s, and the speed of the cooling roller table of the ultra-fast cooling system is 1.5 - 2.2 m / s.

[0131] Furthermore, the production method further includes: After controlled-temperature water cooling, the steel plate is first subjected to hot straightening at a temperature of T - 60°C to T; After leaving the hot straightening machine, the steel plate enters the cooling bed for natural air cooling, and the temperature when leaving the cooling bed is 100 - 200°C; After that, the steel plate is sequentially subjected to warm straightening and cold straightening.

[0132] That is, the steel plate undergoes controlled-temperature water cooling on the ultra-fast cooling system. After discharging water, it directly enters the hot straightening machine for hot straightening. Moreover, the temperature during hot straightening is within 60°C below the water discharge temperature T of the controlled-temperature water cooling.

[0133] In this way, the water discharge temperature T of the steel plate on the ultra-fast cooling system is Min(T VC , T VN ) - 150°C to Min(T VC , T VN ) - 130°C. At this time, it is still in the ferrite phase transformation zone, but there are already phase transformation stresses and thermal stresses in the steel plate. The steel plate enters the hot straightening machine system for controlled-temperature straightening in the high-temperature ferrite phase transformation zone. In this way, the phase transformation stresses and thermal stresses in the steel plate can be released, and thus the initiation of hydrogen-induced cracks at stress concentration points can be avoided, reducing hydrogen-induced brittle fracture.

[0134] In addition, during natural air cooling on the cooling bed, self-tempering of the steel plate will occur, and ferrite phase transformation can be completed on the cooling bed, further releasing phase transformation stresses and thermal stresses.

[0135] It should be noted here that in this application, T NbC , T NbN , T TiC , T TiN , T VC , T VN are the starting precipitation temperatures of NbC, NbN, TiC, TiN, VC, and VN respectively, and can be specifically analyzed through thermodynamic calculation software (such as Thermo-Calc) or laboratory measurement (such as thermal simulation test) in combination with the chemical composition of the specific continuous casting billet.

[0136] In one embodiment, T NbC can be calculated by the formula lg([Nb] × [C] 0.875 ) = 2.97 - 7500 / (T NbC + 273.15), but the value-taking method of T NbC is not limited to this.

[0137] T NbN can be calculated by the formula lg([Nb] × [N]) = 3.70 - 10800 / (T NbN + 273.15), but the value-taking method of T NbN is not limited to this.

[0138] T TiC It can be calculated by the formula lg([Ti]×[C]) = 5.33 - 10475 / (T TiC + 273.15), but the value-taking method of T TiC is not limited to this.

[0139] T TiN It can be calculated by the formula lg([Ti]×[N]) = 0.32 - 8000 / (T TiN + 273.15), but the value-taking method of T TiN is not limited to this.

[0140] T VC It can be calculated by the formula lg([V]×[C]) = 6.72 - 9500 / (T VC + 273.15), but the value-taking method of T VC is not limited to this.

[0141] T VN It can be calculated by the formula lg([V]×[N]) = 3.46 - 8330 / (T VN + 273.15), but the value-taking method of T VN is not limited to this.

[0142] Those skilled in the art can obtain other value-taking methods based on the respective concepts of T NbC 、T NbN 、T TiC 、T TiN 、T VC 、T VN and all can be applied to the present invention.

[0143] In addition, it should be noted that in this application, [C], [Si], [Mn], [Cr], [V], [Cu], [Ni], [Nb], [N], [Ti], [Al] respectively represent the mass percentages of C, Si, Mn, Cr, V, Cu, Ni, Nb, N, Ti, Al in steel. For example, if the mass percentage of Nb in steel is 0.044%, then the mass percentage [Nb] of Nb is 0.044.

[0144] The above gives a general introduction to the technical purpose of the present invention. Next, four different implementation manners under the technical purpose of the present invention will be introduced in detail respectively. These four implementation manners correspond to four different grades of pipeline steel.

[0145]

First Embodiment

[0146] The thickness t of the steel plate is ≥8 mm, preferably 8 - 30 mm.

[0147] 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 balance is iron and unavoidable impurities.

[0148] Furthermore, the chemical composition of the steel plate also satisfies: CEV(%) is 0.201 - 0.289, and / or, Pcm(%) is 0.094 - 0.145.

[0149] The yield strength R of the steel plate t0.5 ≥330 MPa, the tensile strength R m ≥430 MPa, the elongation A 50 ≥50%, and the yield ratio ≤0.77.

[0150] The -20°C impact energy KV2 of the steel plate ≥400 J.

[0151] The hardness of the steel plate ≤160 HV 10 .

[0152] The -10°C DWTT drop - weight shear area fraction of the steel plate is 100%, and the -15°C DWTT drop - weight shear area fraction is 100%.

[0153] The steel plate also satisfies any one, any two, any three or all of the following: The first item, in the NACE TM0284 standard A solution environment, CLR ≤10%, CTR ≤3%, CSR ≤1%; The second item, in the stress corrosion test according to the NACE TM0177 standard, the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen; Third, in a pure hydrogen environment of 6.3 MPa, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment; Fourth, in a pure hydrogen environment of 6.3 MPa, for the stepped compact tension specimen, K 1C ≥110 MPa·m 1 / 2 .

[0154] The flatness of the steel plate is ≤1 mm / m.

[0155] The surface stress of the steel plate is ≤15 MPa.

[0156] The steel plate has a duplex structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

[0157] Among them, the average grain size of the quasi-polygonal ferrite and acicular ferrite is 8 - 16 μm.

[0158] The total volume ratio of the quasi-polygonal ferrite and acicular ferrite is more than 95%.

[0159] Specifically, the volume ratio of the quasi-polygonal ferrite structure is 78 - 90%, the volume ratio of the acicular ferrite structure is 5 - 20%, and the volume ratio of the pearlite structure is 2 - 5%.

[0160] Furthermore, the banded structure of the steel plate is ≤0.5 grade.

[0161] The central segregation of the steel plate is ≤0.5 grade, and the central porosity is ≤0.5 grade.

[0162] On the cross-section of the steel plate, the density of inclusions with a diameter ≥10 μm is ≤10 pieces / cm 2 .

[0163] The ratings of type A, B, C, and D inclusions of the steel plate are all ≤1 grade, and the sum of the ratings of type A, B, C, and D inclusions is ≤2.5 grades.

[0164] Furthermore, the production method of the steel plate includes the following steps.

[0165] Step 1, heating the continuous casting billet.

[0166] The thickness t0 of the continuous casting billet is 150 - 320 mm, and preferably it can be 220 mm.

[0167] The heating temperature is not lower than the respective starting precipitation temperatures T of NbC, NbN, TiC, VC, and VN NbC , T NbN , T TiC , T VC , T VN .

[0168] Preferably, the heating temperature is Max(T NbC , T NbN , T TiC , T VC , T VN ) + 40°C to Min(Max(T NbC , T NbN , T TiC , T VC , T VN ) + 120°C, T TiN - 150°C).

[0169] The heating duration is preferably controlled to be (1.1 to 1.3)t0 min / mm.

[0170] Step 2: The continuous casting billet is made into a steel plate through rough hot rolling, intermediate billet water cooling, finish hot rolling, and final hot rolling.

[0171] Specifically, the thicknesses of the steel plate after rough hot rolling, finish hot rolling, and final hot rolling are (3.2 to 4)t, t + (2 to 5)mm, and t respectively.

[0172] 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 ).

[0173] Preferably, the starting rolling temperature of the rough hot rolling can be greater than the finishing rolling temperature, and the whole - process temperature is within T nr ~Min(T NbC , T NbN , T TiC ).

[0174] More preferably, during the rough hot rolling, the reduction per pass ≥ 31 mm, and for the initial rolling pass of the non - width - spreading passes, the reduction ≥ 42 mm.

[0175] Furthermore, the starting rolling temperature and the finishing rolling temperature of the finish hot rolling are both Ar3 - 20°C to Ar3 + 10°C.

[0176] Preferably, the starting rolling temperature of the finish hot rolling can be greater than the finishing rolling temperature, and the whole - process temperature is within Ar3 - 20°C to Ar3 + 10°C.

[0177] More preferably, during the finish hot rolling, the reduction per pass ≥ 22 mm.

[0178] In addition, the temperature of the final hot rolling is Ar3 - (40 to 20)°C.

[0179] Preferably, the temperature of the final hot rolling is lower than the finishing rolling temperature of the finish hot rolling.

[0180] Step 3, after the steel plate leaves the finishing hot rolling mill, it is directly subjected to controlled temperature water cooling.

[0181] Specifically, the water inlet temperature is Ar3 - (80 - 60)°C, and the water outlet temperature T is Min(T VC ,T VN ) - 15°C to Min(T VC ,T VN ) + 5°C.

[0182] It can be understood that the water outlet temperature T is less than the water inlet temperature.

[0183] Preferably, the controlled temperature water cooling is carried out on an ultra-fast cooling system.

[0184] Among them, the water pressure is 0.15 - 0.20 MPa, the ratio of upper and lower water is 0.92 - 0.98, the cooling rate is 6 - 16°C / s, and the cooling roller table speed of the ultra-fast cooling system is 1.5 - 2.2 m / s.

[0185] Preferably, the production method of the steel plate further includes: After the controlled temperature water cooling, the steel plate is first subjected to hot straightening, and the temperature during hot straightening is T - 60°C to T; After leaving the hot straightening machine, the steel plate is placed on a cooling bed for natural air cooling, and the temperature of leaving the cooling bed is 100 - 200°C; After that, the steel plate is sequentially subjected to warm straightening and cold straightening.

[0186]

Second Embodiment

[0187] The thickness t of the steel plate is ≥8 mm, preferably 8 - 30 mm.

[0188] The chemical composition of the steel plate in mass percentage includes: C 0.036 - 0.066%, Si 0.11 - 0.17%, Mn 0.77 - 0.85%, Cr 0.17 - 0.25%, Cu 0.10 - 0.18%, Nb 0.024 - 0.032%, V 0.024 - 0.032%, Ti 0.010 - 0.018%, Al 0.015 - 0.045%, P≤0.01%, S≤0.002%, O≤0.003%, N≤0.005%, H≤0.0002%, and the rest is iron and inevitable impurities.

[0189] Furthermore, the chemical composition of the steel plate also satisfies: CEV(%) is 0.199 - 0.287, and / or, Pcm(%) is 0.088 - 0.139.

[0190] The yield strength R of the steel plate t0.5 ≥392 MPa, and the tensile strength R m ≥454 MPa, and the elongation A 50 ≥43%, and the yield ratio ≤ 0.86.

[0191] The -20°C impact energy KV2 of the steel plate ≥ 400 J.

[0192] The hardness of the steel plate ≤ 190 HV 10 .

[0193] The -10°C DWTT drop-weight shear area fraction of the steel plate is 100%, and the -15°C DWTT drop-weight shear area fraction is 100%.

[0194] The steel plate also satisfies any one, any two, any three, or all of the following: The first item, in the NACE TM0284 standard A solution environment, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%; The second item, in the NACE TM0177 standard for stress corrosion testing, the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen; The third item, in a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment; The fourth item, in a 6.3 MPa pure hydrogen environment, the K of the stepped compact tension specimen 1C ≥110 MPa·m 1 / 2 .

[0195] The flatness of the steel plate ≤ 2 mm / m.

[0196] The surface stress of the steel plate ≤ 20 MPa.

[0197] The steel plate is a duplex structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

[0198] Among them, the average grain size of the quasi-polygonal ferrite and acicular ferrite is 4 - 9 μm.

[0199] The total volume ratio of the quasi-polygonal ferrite and acicular ferrite is more than 95%.

[0200] Specifically, the volume ratio of the quasi-polygonal ferrite structure is 78 - 90%, the volume ratio of the acicular ferrite structure is 5 - 20%, and the volume ratio of the pearlite structure is 2 - 5%.

[0201] Furthermore, the banded structure of the steel plate ≤ 0.5 grade.

[0202] The central segregation of the steel plate is ≤ grade 0.5, and the central porosity is ≤ grade 0.5.

[0203] On the cross-section of the steel plate, the density of inclusions with a diameter ≥ 10 μm is ≤ 10 pieces / cm 2 .

[0204] The ratings of type A, B, C, and D inclusions of the steel plate are all ≤ grade 1, and the sum of the ratings of type A, B, C, and D inclusions is ≤ 2.5 grades.

[0205] The production method of the steel plate in this embodiment is only different from that of the first embodiment described above in that: controlled-temperature water cooling. Only this difference point will be introduced below, and the other parts not mentioned are the same as those in the first embodiment described above and will not be elaborated.

[0206] In this embodiment, in step 3, after the steel plate leaves the finishing hot rolling mill, controlled-temperature water cooling is directly carried out.

[0207] Specifically, the water inlet temperature is Ar3 - (70 - 50) °C, and the water outlet temperature T is Min(T VC , T VN ) - (50 - 30) °C.

[0208]

Third Embodiment

[0209] The thickness t of the steel plate ≥ 8 mm, preferably 8 - 30 mm.

[0210] 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 inevitable impurities.

[0211] Furthermore, the chemical composition of the steel plate also satisfies: CEV(%) is 0.199 - 0.287, and / or, Pcm(%) is 0.081 - 0.131.

[0212] The yield strength R of the steel plate t0.5≥410 MPa, Tensile strength R m ≥472 MPa, Elongation A 50 ≥48%, Yield ratio ≤0.87.

[0213] The impact energy KV2 of the steel plate at -20 °C ≥400 J.

[0214] The hardness of the steel plate ≤195 HV 10 。

[0215] The -10 °C DWTT drop-weight shear area fraction of the steel plate is 100%, and the -15 °C DWTT drop-weight shear area fraction is 100%.

[0216] The steel plate also meets any one, any two, any three or all of the following: The first item, in the NACE TM0284 standard A solution environment, CLR ≤10%, CTR ≤3%, CSR ≤1%; The second item, in the NACE TM0177 standard for stress corrosion testing, the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen; The third item, in a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment; The fourth item, in a 6.3 MPa pure hydrogen environment, the K of the stepped compact tension specimen 1C ≥110 MPa·m 1 / 2 。

[0217] The flatness of the steel plate ≤2 mm / m.

[0218] The surface stress of the steel plate ≤25 MPa.

[0219] The steel plate has a duplex structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

[0220] Among them, the average grain size of the quasi-polygonal ferrite and acicular ferrite is 3 - 8 μm.

[0221] The total volume ratio of the quasi-polygonal ferrite and acicular ferrite is more than 95%.

[0222] Specifically, the volume ratio of the quasi-polygonal ferrite structure is 78 - 90%, the volume ratio of the acicular ferrite structure is 5 - 20%, and the volume ratio of the pearlite structure is 2 - 5%.

[0223] Furthermore, the banded structure of the steel plate ≤0.5 grade.

[0224] The central segregation of the steel plate is ≤ grade 0.5, and the central porosity is ≤ grade 0.5.

[0225] On the cross-section of the steel plate, the density of inclusions with a diameter ≥ 10 μm is ≤ 10 pieces / cm 2 .

[0226] The ratings of type A, B, C, and D inclusions in the steel plate are all ≤ grade 1, and the sum of the ratings of type A, B, C, and D inclusions is ≤ 2.5 grades.

[0227] The production method of the steel plate in this embodiment is only different from the first embodiment described above in that: controlled-temperature water cooling. Only this difference will be introduced below, and the other parts not mentioned are the same as those in the first embodiment above and will not be elaborated.

[0228] In this embodiment, in step 3, after the steel plate leaves the finishing hot rolling mill, controlled-temperature water cooling is directly carried out.

[0229] Specifically, the water inlet temperature is Ar3 - (60 - 40) °C, and the water outlet temperature T is Min(T VC , T VN ) - (150 - 130) °C.

[0230]

Fourth Embodiment

[0231] The thickness t of the steel plate is ≥ 8 mm, preferably 8 - 30 mm.

[0232] 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 inevitable impurities.

[0233] Furthermore, the chemical composition of the steel plate also satisfies: CEV(%) is 0.197 - 0.284, and / or, Pcm(%) is 0.075 - 0.126.

[0234] The yield strength R of the steel plate t0.5 ≥ 450 MPa, and the tensile strength R m≥560 MPa, elongation A 50 ≥40%, yield ratio ≤ 0.86.

[0235] The impact energy KV2 of the steel plate at -20 °C ≥ 400 J.

[0236] The hardness of the steel plate ≤ 205 HV 10 。

[0237] The drop-weight tear test (DWTT) shear area fraction of the steel plate at -10 °C is 100%, and the DWTT shear area fraction at -15 °C is 100%.

[0238] The steel plate also meets any one, any two, any three or all of the following: The first item, in the environment of NACE TM0284 standard A solution, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%; The second item, stress corrosion test is carried out according to NACE TM0177 standard, and the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen; The third item, in a pure hydrogen environment of 6.3 MPa, the tensile strength, elongation and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 80% and 75% of those in the nitrogen environment; The fourth item, in a pure hydrogen environment of 6.3 MPa, the K 1C of the stepped compact tension specimen ≥ 100 MPa·m 1 / 2 。

[0239] The flatness of the steel plate ≤ 2 mm / m.

[0240] The surface stress of the steel plate ≤ 35 MPa.

[0241] The steel plate has a duplex structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

[0242] Among them, the average grain size of the quasi-polygonal ferrite and acicular ferrite is 2 - 8 μm.

[0243] The total volume ratio of the quasi-polygonal ferrite and acicular ferrite is more than 95%.

[0244] Specifically, the volume ratio of the quasi-polygonal ferrite structure is 5 - 17%, the volume ratio of the acicular ferrite structure is 80 - 94%, and the volume ratio of the pearlite structure is 1 - 3%.

[0245] Furthermore, the banded structure of the steel plate ≤ 0.5 grade.

[0246] The central segregation of the steel plate ≤ 0.5 grade, and the central porosity ≤ 0.5 grade.

[0247] On the cross-section of the steel plate, the density of inclusions with a diameter ≥ 10 μm is ≤ 10 pieces / cm 2 .

[0248] The ratings of Class A, B, C, and D inclusions in the steel plate are all ≤ Grade 1, and the sum of the ratings of Class A, B, C, and D inclusions is ≤ 2.5 grades.

[0249] The production method of the steel plate in this embodiment is only different from that of the first embodiment described above in that: controlled-temperature water cooling. Only this difference will be introduced below, and other parts not mentioned are the same as those in the first embodiment above and will not be elaborated.

[0250] In this embodiment, in step 3, after the steel plate leaves the finishing hot rolling mill, controlled-temperature water cooling is directly carried out.

[0251] Specifically, the water inlet temperature is Ar3 - (50~30) °C, and the water outlet temperature T is Min(T VC , T VN ) - (300~270) °C.

[0252] The above text has introduced the technical gist of the present invention and four different embodiments based on the technical gist. Below, the present invention will be further introduced through several specific test examples. Of course, these test examples are only a part of the numerous variant embodiments included in the present invention, rather than all of them.

[0253] The chemical compositions of the steel plates in these test examples are shown in Table 1. Among them, "-" in Table 1 indicates that the corresponding element was not specifically added during the preparation of the steel, and thus was not detected or the detected amount was too small to be recorded in the steel.

[0254] [Table 1]

[0255] These test examples are all prepared according to the production method described in the present invention. Specifically: Test Examples 1 and 2 are prepared according to the first embodiment described above, Test Examples 3 and 4 are prepared according to the second embodiment described above, Test Examples 5 and 6 are prepared according to the third embodiment described above, and Test Examples 7 and 8 are prepared according to the fourth embodiment described above.

[0256] Among them, some important parameters during the production process are shown in Table 2.

[0257] [Table 2]

[0258] [Continued Table 2]

[0259] The steel plates of each test example are subjected to microstructure and property detection, and the detection results are as follows: (1) The steel plate has a complex phase structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite; the metallographic structure diagrams of Test Examples 1, 3, 5, and 7 are respectively referred to Figure 1 , 2 , 3, and 4; among them, the average grain size of quasi-polygonal ferrite and acicular ferrite, the volume fraction of each structure in the complex phase structure, and the banded structure grade are shown in Table 3 respectively; [Table 3]

[0260] (2) On the cross-section of the steel plate, the inclusion density with a diameter ≥ 10 μm ≤ 10 pieces / cm 2 ; (3) For the steel plates of each test example, the -15°C DWTT drop-weight shear area fraction is 100%, and the strength, elongation, -20°C impact energy KV2, hardness, flatness, surface stress, etc. are shown in Table 4; [Table 4]

[0261] (4) In the NACE TM0284 standard A solution environment, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%; in the stress corrosion test according to the NACE TM0177 standard, the applied stress is 0.8σ s , and there are no cracks on the surface of the tensile specimen; (5) For the steel plates of Test Examples 1 to 6, in a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 85%, and 80% of those in a nitrogen environment; in a 6.3 MPa pure hydrogen environment, the K 1C of the stepped compact tension specimen ≥ 110 MPa·m 1 / 2 ; (6) For the steel plates of Test Examples 7 to 8, in a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of the smooth specimen are respectively greater than or equal to 90%, 80%, and 75% of those in a nitrogen environment; in a 6.3 MPa pure hydrogen environment, the K 1C of the stepped compact tension specimen ≥ 100 MPa·m 1 / 2 .

Claims

1. A production method of a steel plate for pure hydrogen transportation pipelines, characterized in that, The thickness t of the steel plate is t≥8 mm, 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%, 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 inevitable impurities; The production method includes: Heating a continuous casting billet with a thickness t0 of 150~320 mm; wherein, the heating temperature is not lower than the starting precipitation temperature of NbC, NbN, TiC, VC, and VN; The continuous casting billet is made into a steel plate through rough hot rolling, finish hot rolling and final hot rolling; 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 ), the starting rolling temperature and the finishing rolling temperature of the finish hot rolling are both Ar3 - 20°C to Ar3 + 10°C, the final hot rolling is a single-pass hot rolling, and the temperature is Ar3 - (40 - 20)°C; the thicknesses of the steel plate after rough hot rolling, after finish hot rolling, and after final hot rolling are (3.2 - 4)t, t + (2 - 5) mm, and t respectively; After the steel plate leaves the finishing hot rolling mill, controlled temperature water cooling is carried out; among them, the water inlet temperature is Ar3 - (80~30)°C, and the water outlet temperature T is Min(T VC ,T VN ) - 300°C to Min(T VC ,T VN ) + 5°C.

2. The production method of the steel plate for pure hydrogen transmission pipeline according to claim 1, characterized in that, The heating temperature is Max(T NbC ,T NbN ,T TiC ,T VC ,T VN ) + 40°C to Min(Max(T NbC ,T NbN ,T TiC ,T VC ,T VN ) + 120°C, T TiN - 150°C).

3. The production method of the steel plate for pure hydrogen transmission pipeline according to claim 1, characterized in that, The temperature throughout the rough hot rolling is at T nr ~ Min(T NbC , T NbN , T TiC ); The whole process temperature of finish hot rolling is at Ar3 - 20°C to Ar3 + 10°C.

4. The production method of the steel plate for 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 production method of the steel plate for pure hydrogen transmission pipeline according to claim 1, characterized in that, The intermediate billet obtained by rough hot rolling is water-cooled before finish hot rolling, and the water outlet temperature is Ar3 - 20°C to Ar3 + 10°C.

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

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

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

9. The production method of the steel plate for pure hydrogen transportation pipeline according to claim 1, characterized in that, The production method further includes: After the controlled temperature water cooling, the steel plate is first hot-straightened, and the temperature during hot-straightening is T - 60°C to T; after leaving the hot-straightening machine, the steel plate enters the cooling bed for natural air cooling, and the temperature when leaving the cooling bed is 100~200°C; then, the steel plate is sequentially subjected to warm straightening and cold straightening.

10. The production method of the steel plate for pure hydrogen transmission pipeline according to claim 1, characterized in that, During the controlled temperature water cooling: The inlet water temperature is Ar3 - (80~60)°C, and the outlet water temperature T is Min(T VC , T VN ) - 15°C to Min(T VC , T VN ) + 5°C; Alternatively, the water inlet temperature is Ar3 - (70~50) °C, and the water outlet temperature T is Min(T VC , T VN ) - (50~30) °C; Alternatively, the water inlet temperature is Ar3 - (60~40)°C, and the water outlet temperature T is Min(T VC , T VN ) - (150~130)°C; Alternatively, the inlet water temperature is Ar3 - (50~30)°C, and the outlet water temperature T is Min(T VC , T VN ) - (300~270)°C.

11. The production method of the steel plate for pure hydrogen transportation pipeline according to claim 1, characterized in that, The chemical composition of the steel plate also satisfies: CEV(%) is 0.168~0.325, and / or, Pcm(%) is 0.069~0.

159.

12. A steel plate for a pure hydrogen transportation pipeline, characterized in that, The thickness t of the steel plate is t≥8 mm, 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%, 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 inevitable impurities.

13. The steel plate for pure hydrogen transmission pipeline according to claim 12, characterized in that, The steel plate satisfies any one, any two, any three or all of the following: In the NACE TM0284 standard A solution environment, CLR ≤ 10%, CTR ≤ 3%, CSR ≤ 1%; Stress corrosion test was carried out according to NACE TM0177 standard, and the applied stress was 0.8σ s , and there were no cracks on the surface of the tensile specimen; In a 6.3 MPa pure hydrogen environment, the tensile strength, elongation, and reduction of area of smooth specimens are respectively greater than or equal to 90%, 80%, and 75% of those in a nitrogen environment; Under a pure hydrogen environment of 6.3 MPa, the K of the stepped compact tension specimen 1C ≥100 MPa·m 1 / 2 .

14. The steel plate for pure hydrogen transportation pipeline according to claim 12, wherein The yield strength R of the steel plate t0.5 ≥ 330 MPa, the tensile strength R m ≥ 430 MPa, the elongation A 50 ≥ 40%, and the yield ratio ≤ 0.

87.

15. The steel plate for pure hydrogen transmission pipeline according to claim 12, wherein The -20°C impact energy KV2 of the steel plate is ≥400 J, and the hardness is ≤205 HV 10 , the -10°C DWTT drop-weight shear area fraction is 100%, and the -15°C DWTT drop-weight shear area fraction is 100%.

16. The steel plate for pure hydrogen transmission pipeline according to claim 12, characterized in that, The flatness of the steel plate is ≤ 2 mm / m, and the surface stress is ≤ 35 MPa.

17. The steel plate for pure hydrogen transportation pipeline according to claim 12, wherein, On the cross-section of the steel plate, the inclusion density with a diameter ≥ 10 μm is ≤ 10 pieces / cm 2 .

18. The steel plate for pure hydrogen transmission pipeline according to claim 12, characterized in that, The steel plate has a duplex structure of quasi-polygonal ferrite + acicular ferrite + a small amount of pearlite.

19. The steel plate for pure hydrogen transportation pipeline according to claim 18, characterized in that, The average grain size of quasi-polygonal ferrite and acicular ferrite is 2 - 16 μm; the volume fraction of quasi-polygonal ferrite and acicular ferrite is more than 95%.

20. The steel plate for pure hydrogen transportation pipeline according to claim 18, wherein The volume fraction of quasi-polygonal ferrite is 5 - 90%, the volume fraction of acicular ferrite is 5 - 94%, the volume fraction of pearlite is 1 - 5%, and the banded structure is ≤ 0.5 grade.

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