A high-strength pressure vessel steel resistant to liquid carbon dioxide corrosion and its manufacturing method

Abstract

This invention discloses a high-strength pressure vessel steel resistant to liquid carbon dioxide corrosion, which contains Fe and unavoidable impurity elements, and also contains the following chemical elements in the following mass percentages: C: 0.085-0.12%, Si: 0.05-0.30%, Mn: 1.05-1.48%, Alt: 0.015-0.038%, Cu: 0.10-0.30%, Cr: 1.05-1.75%, Mo: 0.18-0.50%, 0 < Sn ≤ 0.0013%, 0 < Sb ≤ 0.0012%, 0 < Ni ≤ 0.30%, and at least one of V, B, and Nb in the following amounts: Nb: 0.018-0.045%, 0 < V ≤ 0.050%, B: 0.0006-0.0018%. Accordingly, the present invention also discloses a method for manufacturing the above-mentioned steel, which includes the following steps: (1) smelting and casting; (2) hot charging and hot delivery of continuous casting billet + heating furnace: the charging temperature of the high-temperature continuous casting billet is directly charged into the heating furnace at 780-880℃, and the heating temperature in the heating furnace is controlled at 1105-1250℃, and the heating rate is 8-13 min / cm; (3) rolling; (4) rapid cooling after rolling: the cooling rate is controlled at 13-42℃ / s, and the final cooling temperature is 300-390℃; (5) heat treatment.

Description

Technical Field

[0001] This invention relates to a steel plate and its manufacturing method, and more particularly to a steel plate for pressure vessels and its manufacturing method. Background Technology

[0002] In recent years, with the rapid development of industrial production, pressure vessels have been increasingly used in various industries. Currently, traditional pressure vessels such as large fixed spherical storage tanks and mobile pressure vessels often need to be made of high-strength pressure vessel steel. However, these pressure vessels are often used to hold some special corrosive substances and are easily corroded, especially when subjected to stress and corrosion, which can lead to cracks in the pressure vessel steel.

[0003] As is well known, although pure carbon dioxide does not have corrosive properties, it exhibits extremely strong corrosiveness when dissolved in water. At the same pH value, the total acidity of carbon dioxide is higher than that of hydrochloric acid. Therefore, in practical applications, it is more corrosive to steel than hydrochloric acid.

[0004] In actual use, when pressure vessels contain liquid carbon dioxide, the corrosion caused by liquid carbon dioxide can lead to a service life of the pressure vessel that is much shorter than its design life. Its corrosion rate on low carbon steel can be as high as 7 mm / a, and sometimes even higher. This corrosion rate is considered extremely severe corrosion.

[0005] Research results demonstrate that the higher the strength of steel, the more susceptible it is to cracking under the corrosive effects of carbon dioxide. Therefore, there is an urgent need to obtain a pressure vessel steel with both high strength and good resistance to liquid carbon dioxide corrosion.

[0006] Based on this, the inventors aim to overcome the problems of excessively high strength and excessive hardness of existing pressure vessel steel plates and welded joints, and to solve the problem of carbon dioxide corrosion of the steel plates and welded joints, thereby improving the service life of such steel containers holding liquid carbon dioxide. Therefore, this invention aims to provide a new high-strength pressure vessel steel with resistance to liquid carbon dioxide corrosion and a method for manufacturing the same.

[0007] Although steel plates with resistance to carbon dioxide corrosion already exist in the existing technology, they still cannot meet the performance requirements of specific strength and manufacturing process parameters, and there are still shortcomings in performance.

[0008] For example, Chinese patent document CN103320705A, published on September 25, 2013, entitled "CO2 Corrosion Resistant Pipeline Steel for Ground Gathering and Transportation and its Preparation Method," discloses a CO2 corrosion resistant pipeline steel for ground gathering and transportation and its preparation method. This method employs a low-C and Cr-Mo-Cu-Ni alloy design, with the steel plate being hot-rolled and then directly cooled. However, the strength and performance parameters of the steel plate produced by this method differ significantly from those of the present invention, and it cannot meet the service environment and performance requirements of the present invention.

[0009] For example, Chinese patent document CN102199729A, published on September 28, 2011, entitled "Economic 55Ksi Steel Grade Anti-CO2 Corrosion Oil Well Pipe and its Manufacturing Method," discloses an economic 55Ksi steel grade anti-CO2 corrosion oil well pipe and its manufacturing method. This technical solution uses a Cr-Al alloy system, and its supply state is rolled. However, the strength and performance parameters of this steel plate are still far from those of the present invention, and it cannot meet the service environment and service performance requirements of the present invention.

[0010] For example, Chinese patent document CN106498279A, published on March 15, 2017, entitled "A Low-Cr Economical X65 Pipeline Steel Resistant to CO2 Corrosion and its Production Method," discloses a low-Cr economical X65 pipeline steel resistant to CO2 corrosion and its production method. This technical solution adopts a Cr-Mo-V-Ti alloy system, and its supply state is TMCP. However, the strength and performance parameters of this steel plate are still far from those of the present invention, and it cannot effectively meet the service environment and service performance requirements of the present invention. Summary of the Invention

[0011] One objective of this invention is to provide a high-strength pressure vessel steel resistant to liquid carbon dioxide corrosion. This high-strength pressure vessel steel plate is a steel plate using a low-C-Mn-Cr-Mo-Cu-Ni alloy system. By precisely controlling the chemical composition of the steel during the steel plate production process, excellent comprehensive mechanical properties can be obtained. This pressure vessel steel plate not only possesses good strength and toughness, and resistance to welding cold and hot cracking, but also exhibits good weldability, weldability, and resistance to liquid carbon dioxide corrosion. It can be used to manufacture pressure vessels and has promising application prospects.

[0012] To achieve the above objectives, the present invention provides a high-strength pressure vessel steel resistant to liquid carbon dioxide corrosion, which contains Fe and unavoidable impurity elements, and further contains the following chemical elements in the following mass percentages:

[0013] C: 0.085–0.12%, Si: 0.05–0.30%, Mn: 1.05–1.48%, Alt: 0.015–0.038%, Cu: 0.10–0.30%, Cr: 1.05–1.75%, Mo: 0.18–0.50%, 0 < Sn ≤ 0.0013%, 0 < Sb ≤ 0.0012%, 0 < Ni ≤ 0.30%, and at least one of V, B, and Nb in the following amounts: Nb: 0.018–0.045%, 0 < V ≤ 0.050%, B: 0.0006–0.0018%.

[0014] Furthermore, in the high-strength pressure vessel steel plate described in this invention, the mass percentage content of each chemical element is as follows:

[0015] C: 0.085–0.12%, Si: 0.05–0.30%, Mn: 1.05–1.48%, Alt: 0.015–0.038%, Cu: 0.10–0.30%, Cr: 1.05–1.75%, Mo: 0.18–0.50%, 0 < Sn ≤ 0.0013%, 0 < Sb ≤ 0.0012%, 0 < Ni ≤ 0.30%, and at least one of V, B, and Nb in the following amounts: Nb: 0.018–0.045%, 0 < V ≤ 0.050%, B: 0.0006–0.0018%; the balance being Fe and unavoidable impurity elements.

[0016] In the above-described technical solution of this invention, a new steel grade was designed using a low-C-Mn-Cr-Mo-Cu-Ni alloy system through a rational chemical composition design. This steel plate requires the addition of at least one of V, B, and Nb. On one hand, the toughness and strength of the NbC precipitate phase are utilized, improving the grain refinement and precipitation strengthening effects of the Nb microalloy. On the other hand, this invention can also add an appropriate amount of V. V can combine with C to form a VC precipitate phase, which further refines the grains, improves the low-temperature fracture toughness of the steel, and lowers the ductile-brittle transition temperature.

[0017] Meanwhile, in the design of the chemical composition, this invention also strictly limits the content of elements such as Alt and Sn in the steel, as well as the content of the impurity element O, to avoid the single or combined effects of these elements impairing the toughness of the steel. It also prevents these elements from segregating and agglomerating during the continuous casting cooling process, especially during the cooling of steel from high temperature to low temperature (980℃ to 700℃), thus preventing further segregation of the continuously cast billet from solidification to low temperature cooling and from rolling into finished steel plates. This prevents the steel plates from experiencing high-probability stress corrosion cracking when used in environments with liquid carbon dioxide stress corrosion.

[0018] The design principles of each chemical element in the high-strength pressure vessel steel plate resistant to liquid carbon dioxide corrosion described in this invention are as follows:

[0019] C: In the high-strength pressure vessel steel plate described in this invention, C is one of the essential elements for improving the strength of the steel. With the increase of C content in the steel, the Fe3C content increases, hardenability also increases, and the yield strength and tensile strength of the steel improve, while elongation and notched impact toughness decrease. Specifically, for every 0.1% increase in C content, the tensile strength increases by approximately 90 MPa, and the yield strength increases by approximately 40-50 MPa. However, it should be noted that the C content in the steel should not be too high. With the increase of C content, the elongation and impact toughness of the steel decrease, especially the low-temperature toughness. Moreover, when welding steel with a high C content, hardening will occur in the heat-affected zone, which will exacerbate the tendency for cold cracking during welding and, when serving in a carbon dioxide corrosive environment, cause the steel plate and welded joints to become weak points for stress corrosion cracking. Therefore, considering the influence of carbon element on the properties of pressure vessel steel, the mass percentage of carbon element in the high-strength pressure vessel steel plate of the present invention is controlled between 0.085% and 0.12%. This ensures that the strength stability of the steel is within a suitable range and is suitable for production operations, thereby improving its applicability and feasibility in industrial production.

[0020] Si: In the high-strength pressure vessel steel plate described in this invention, Si can improve the strength of the steel through solid solution strengthening. When the Si content increases from 0.10% to 0.25%, the strength of the steel remains basically unchanged or increases slightly, while the toughness of the steel can be significantly improved. Appropriately increasing the Si content will increase the substitution solid solution strengthening effect in the steel and refine the grains, thereby improving the toughness of the steel. However, it should be noted that the Si content in the steel should not be too high. If the Si content is too high, SiO2 inclusions are easily formed during the steelmaking process. Therefore, in the high-strength pressure vessel steel plate described in this invention, the mass percentage of Si is controlled between 0.05% and 0.30%.

[0021] Mn: In the high-strength pressure vessel steel plate described in this invention, the element Mn plays a significant role in improving the strength of low-carbon steel. Adding 1% Mn to the steel can increase the tensile strength of the steel by approximately 100 MPa. Generally speaking, controlling the mass percentage of Mn in the steel to below 1.70% is beneficial for improving the toughness of the weld metal. In low-carbon high-strength steel, the Mn content can reach up to 1.80%, but in the steel of this invention, excessive Mn will adversely affect the performance of the steel. In addition, Mn will also increase the solubility of elements such as Nb and V in steel. Based on this, considering the influence of Mn content on the performance of steel, the Mn content must be strictly controlled. In this invention, the mass percentage of Mn is controlled between 1.05% and 1.48%. This ensures that the steel obtains suitable tensile strength without compromising the low-temperature impact toughness and elongation of the steel.

[0022] Alt: In the high-strength pressure vessel steel plate described in this invention, Alt is added as a deoxidation balancing element during the steelmaking process. Specifically, in the early stages of refining, the mass percentage of Alt in the molten steel can be controlled below 0.045%. In the later stages of refining, the oxygen content in the steel is already controlled to a low level; if Alt is added again, large-sized chain-like alumina inclusions will form in the molten steel, severely impairing the low-temperature toughness of the finished steel plate. Furthermore, adding Alt in the later stages of refining will form a large amount of AlN in the steel. AlN easily precipitates in the continuously cast billet cooling range of 800–950°C, reducing the hot plasticity of the continuously cast billet and also forming corner cracks or intergranular cracks on the surface or corners of the billet. Therefore, considering the impact of Alt on the performance of the pressure vessel steel plate in this technical solution, the mass percentage of Alt in the high-strength pressure vessel steel plate described in this invention is controlled between 0.015% and 0.038%.

[0023] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Alt can be preferably controlled between 0.016% and 0.034%.

[0024] Cu: In the high-strength pressure vessel steel plate described in this invention, Cu mainly plays a role in precipitation strengthening. Adding an appropriate amount of Cu to the steel is beneficial for obtaining good low-temperature toughness and increasing the corrosion resistance of the steel plate. However, it should be noted that the Cu content in the steel should not be too high. When the Cu content in the steel is too high, it will not only reduce the toughness of the weld heat-affected zone of the steel plate, but also reduce the solid solubility of Cu in the steel during continuous casting due to the presence of residual elements such as Sn, and form a low-melting-point copper-rich phase in the iron oxide scale on the surface of the billet. Under the bending and straightening stress of continuous casting, this will cause surface cracks in the billet; and network cracks will occur during the rolling process of the steel plate. Based on this, in the high-strength pressure vessel steel plate described in this invention, the mass percentage of Cu is controlled between 0.10% and 0.30%.

[0025] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage of Cu can be preferably controlled between 0.15% and 0.28%.

[0026] Cr: In the high-strength pressure vessel steel plate described in this invention, Cr is both an element that shrinks the austenite region and a medium-strength carbide-forming element. It can form carbides in steel and can be dissolved in ferrite. Simultaneously, Cr can improve the corrosion resistance of the pressure vessel steel plate. Cr has a high atomic binding energy between metal and oxygen, and it readily forms dense Cr-containing corrosion products such as Cr(OH)3 and Cr2O3 on the steel surface, preventing corrosive ions in the corrosive medium from entering the iron matrix, thereby improving the corrosion resistance of the steel. Cr is also an effective element for improving the hardenability of steel, but the Cr content in the steel should not be too high, as excessive Cr will increase the steel's sensitivity to cold cracking during welding. Therefore, to ensure the performance of the steel, the mass percentage of Cr is controlled between 1.05% and 1.75% in this invention. This ensures that the steel obtains suitable tensile strength and excellent resistance to carbon dioxide corrosion, while not compromising the steel's low-temperature impact toughness and elongation.

[0027] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Cr element can be controlled between 1.15% and 1.65%.

[0028] Mo: In the high-strength pressure vessel steel plate described in this invention, Mo can improve the strength of the steel, especially its high-temperature strength. Its ability to improve the high-temperature strength of steel is higher than that of Mn and Cr. Simultaneously, Mo is also one of the main elements contributing to the steel's resistance to carbon dioxide corrosion. It should be noted that adding 0.50% Mo to steel can increase its resistance to carbon dioxide corrosion by 50%. A small amount of Mo can also improve the toughness of the weld metal. However, adding Mo also increases the hardenability of the steel, thereby increasing its susceptibility to cold cracking during welding. On the other hand, sufficient Mo content can also ensure the stability of the steel plate after tempering, ensuring that the steel plate still has sufficient strength and toughness after tempering. Based on this, considering the influence of Mo on the properties of steel, the mass percentage of Mo in the high-strength pressure vessel steel plate described in this invention is controlled between 0.18% and 0.50%.

[0029] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Mo element can be controlled between 0.20% and 0.48%.

[0030] Sn and Sb: In the high-strength pressure vessel steel plate described in this invention, the addition of Sn and Sb elements increases the strength and hardness of the steel, but reduces its toughness. When Sn or Sb is present in the steel, the solubility of Cu in austenite decreases sharply, promoting the formation of a low-melting-point Cu-rich phase in the iron oxide scale on the steel surface. This leads to surface cracking during hot working and cold forming of the steel plate, severely affecting the metallurgical and surface quality of the steel. Controlling the Sn or Sb content in the steel within a certain range prevents the adverse coupling effects of Cu and Sn or Cu and Sb. Therefore, to ensure the intrinsic metallurgical and surface quality of the steel of this invention, the Sn and Sb elements in the high-strength pressure vessel steel plate described in this invention are controlled within the ranges of 0 < Sn ≤ 0.0013% and 0 < Sb ≤ 0.0012%, respectively.

[0031] Ni: In the high-strength pressure vessel steel plate described in this invention, Ni has a certain strengthening effect. Adding 1.00% Ni to the steel can increase the steel strength by approximately 20 MPa. Simultaneously, Ni can significantly improve the toughness of the steel, especially the low-temperature toughness of low-carbon bainitic and low-carbon martensitic steels. Adding Ni to the steel can significantly improve the low-temperature toughness of both the base material and the weld heat-affected zone. However, it should be noted that the Ni content in the steel should not be too high. When the Ni content is too high, Ni will promote the carbon dioxide corrosion rate of the steel, reducing its resistance to carbon dioxide corrosion. Therefore, in the high-strength pressure vessel steel plate described in this invention, the mass percentage of Ni is controlled to 0 < Ni ≤ 0.30%.

[0032] Nb: In the high-strength pressure vessel steel plate described in this invention, Nb can promote grain refinement of the steel rolling microstructure, improving the strength and toughness of the steel. During controlled rolling, Nb can effectively refine the microstructure by inhibiting austenite recrystallization and can reduce the steel's overheat sensitivity and temper brittleness. During welding, the segregation and precipitation of Nb can hinder the coarsening of austenite grains during heating, ensuring a relatively fine heat-affected zone microstructure after welding, thereby improving weldability. Therefore, considering the beneficial effects of Nb, the mass percentage of Nb in the high-strength pressure vessel steel plate described in this invention is controlled between 0.018% and 0.045%.

[0033] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Nb element can be controlled between 0.019% and 0.043%.

[0034] V: In the high-strength pressure vessel steel plate described in this invention, vanadium (V) is a strong carbonitride forming element. It can refine grains by forming carbides to prevent austenite grain growth. Vanadium carbonitrides in steel can form hydrogen ion traps for hydrogen ions generated from the decomposition of carbonic acid after liquid carbon dioxide dissolves in water, preventing cracking caused by carbon dioxide corrosion. It should be noted that while adding V to steel can significantly improve its strength, the V content should not be too high. Excessive V content increases the number and size of precipitates, leading to a decrease in steel toughness. Therefore, considering the various strengthening and toughening effects of V in steel, the mass percentage of V in the high-strength pressure vessel steel plate of this invention is controlled to 0 < V ≤ 0.050%.

[0035] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of element V can be controlled between 0.015% and 0.043%.

[0036] B: In the high-strength pressure vessel steel plate described in this invention, the addition of element B can compensate for the insufficient hardenability and strength caused by insufficient carbon content in the steel. However, excessive amounts of element B are not necessarily added to the steel. As the element B content in the steel increases, B will undergo severe segregation at the grain boundaries, and there is a tendency to reduce the strength and toughness of the steel. Based on this, in the high-strength pressure vessel steel described in this invention, the mass percentage content of element B is controlled between 0.0006% and 0.0018%.

[0037] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of element B can be controlled between 0.0008 and 0.0016%.

[0038] Furthermore, in the high-strength pressure vessel steel plate of the present invention, among the unavoidable impurity elements, the content of each impurity element satisfies at least one of the following: P≤0.011%, S≤0.0025%, O≤0.0015%.

[0039] In the above technical solution, P, S, and O are all impurity elements in the high-strength pressure vessel steel plate of the present invention. Where technical conditions permit, to obtain steel with better performance and superior quality, the content of impurity elements in the pressure vessel steel plate should be reduced as much as possible. Only by smelting pure steel can the performance of the steel of the present invention be guaranteed; therefore, the content of P, S, and O elements in the steel must be controlled within a low range. Thus, in the high-strength pressure vessel steel plate of the present invention, the P element content is controlled to P≤0.011%, the S element content is controlled to S≤0.0025%, and the O element content is controlled to O≤0.0015%.

[0040] Furthermore, in the high-strength pressure vessel steel plate described in this invention, each chemical element satisfies at least one of the following formulas:

[0041] 2≤Cr / Mo≤7.5;

[0042] 0.15≤Cu+6(Sn+Sb)≤0.28;

[0043] 15≤Cu / 6(Sn+Sb)≤45;

[0044] 0.6 < Cu / Ni < 1.5;

[0045] Substitute the values ​​of each chemical element in the formula into the values ​​before the percentage sign of the chemical element's mass.

[0046] In the above-described technical solution of this invention, while controlling the mass percentage content of a single chemical element in the steel, this invention can also control the elements in the steel to satisfy the limiting relationship 2≤Cr / Mo≤7.5. Cr and Mo are both hardenable elements; controlling Cr and Mo to satisfy the limiting relationship 2≤Cr / Mo≤7.5 is to limit the hardness of the steel plate within a certain range and ensure that the steel plate has good overall strength and toughness. On the other hand, this limiting relationship allows for precise control of carbides in the steel, forming amorphous Cr oxide on the surface of the steel plate and inhibiting the propagation of carbon dioxide corrosion into the interior of the steel plate.

[0047] Accordingly, while controlling the mass percentage content of a single chemical element in steel, this invention can also control the elements in high-strength pressure vessel steel plates to meet the constraint relationship of 0.15≤Cu+6(Sn+Sb)≤0.28. Controlling 0.15≤Cu+6(Sn+Sb)≤0.28 is to prevent the formation of a low-melting-point enriched Cu liquid phase in the surface shell of the continuously cast billet near 960–1100°C, in the presence of Sn or Sb. This avoids corner cracks and surface cracks in the billet under the straightening stress of continuous casting.

[0048] Furthermore, this invention, while controlling the mass percentage content of a single chemical element, can also control the elements in high-strength pressure vessel steel plates to satisfy the constraint relationship 15≤Cu / 6(Sn+Sb)≤45. Controlling 15≤Cu / 6(Sn+Sb)≤45 is to limit the harmful effects of Sn or Sb segregation at grain boundaries and reduced grain boundary strength, ensuring that Cu in the steel does not exhibit strong coupling with Sn or Sb, thus guaranteeing that Cu plays a beneficial role independently within the steel.

[0049] Furthermore, this invention, while controlling the mass percentage content of a single chemical element, can also control the elements in high-strength pressure vessel steel plates to satisfy the constraint relationship 0.6 < Cu / Ni < 1.5. Controlling the Cu and Ni elements to satisfy this constraint relationship is to reduce the addition of the precious metal Ni while ensuring the low-temperature toughness of the steel plate. On the other hand, adding Ni to steel weakens the carbon dioxide corrosion resistance of added Cu. Therefore, by limiting the Ni content in the steel while still allowing Cu to be added, the carbon dioxide corrosion resistance of the Cu element in the steel can be ensured to remain unchanged or even be enhanced.

[0050] Furthermore, in the high-strength pressure vessel steel plate described in this invention, the mass percentage content of each chemical element also satisfies at least one of the following conditions:

[0051] Alt: 0.016~0.034%;

[0052] V: 0.015~0.043%;

[0053] Nb: 0.019–0.043%;

[0054] Cu: 0.15–0.28%;

[0055] Cr: 1.15–1.65%;

[0056] Mo: 0.20–0.48%;

[0057] B: 0.0008~0.0016%.

[0058] Furthermore, in the high-strength pressure vessel steel plate described in this invention, its microstructure is tempered bainite.

[0059] Furthermore, in the high-strength pressure vessel steel plate described in this invention, its performance meets the following requirements: the yield strength of the steel plate is ≥685MPa, the tensile strength is ≥795MPa, the transverse KV2 at -60℃ is ≥200J, the elongation is ≥17%, the liquid carbon dioxide corrosion rate is 0.012~0.020mm / a, and the hardness HV value of all parts of the steel plate is between 230 and 245; the tensile strength of its welded joint is ≥800MPa, the transverse KV2 at -60℃ is ≥200J, the non-plastic transformation temperature of the weld heat-affected zone is between -85 and -70℃, and the liquid carbon dioxide corrosion rate is 0.008~0.018mm / a.

[0060] Furthermore, in the high-strength pressure vessel steel plate described in this invention, its hardness is: HV=exp[6.21-2.62Pcm-0.00086Vc+(Pcm-0.27)×(97.97(Pcm-0.27)-(Pcm-0.27)×(0.12(Vc-29)+0.0003(Vc-29)]]. 2 )], where Pcm(%)=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B, V c This represents the cooling rate of the steel plate after rolling, with each chemical element in the formula having the value before the mass percentage sign.

[0061] Accordingly, another objective of the present invention is to provide a method for manufacturing the high-strength pressure vessel steel plate described above. The high-strength pressure vessel steel obtained by this manufacturing method has high strength and excellent resistance to liquid carbon dioxide corrosion, as well as good resistance to cold and hot welding cracks, good weldability, and good weldability.

[0062] To achieve the above objectives, the present invention provides a method for manufacturing the aforementioned high-strength steel plate for pressure vessels, comprising the following steps:

[0063] (1) Smelting and casting;

[0064] (2) Hot charging and hot delivery of continuous casting billet + heating furnace: The high temperature of the continuous casting billet is directly charged into the heating furnace at a charging temperature of 780~880℃. The heating temperature in the heating furnace is controlled at 1105~1250℃ and the heating rate is 8~13min / cm.

[0065] (3) Rolling;

[0066] (4) Rapid cooling after rolling: control the cooling rate to be 13-42℃ / s, and the final cooling temperature to be 300-390℃;

[0067] (5) Heat treatment.

[0068] Furthermore, in the manufacturing method described in this invention, in step (1), the dynamic light reduction of the billet in the second cooling water zone of continuous casting is controlled to be 0.65 to 2.5% so as to obtain a ferrite grain size range of 115 to 220 μm for the continuous casting billet.

[0069] In this invention, by precisely controlling the chemical composition of the steel during the steel plate production process and controlling the process parameters of the secondary cooling water production stage of the continuous casting billet for pressure vessel steel, the thermoplasticity of the surface and interior of the continuous casting billet is ensured, thus avoiding the production of defective continuous casting billets.

[0070] In the above technical solution of the present invention, in the smelting and casting process of step (1), vanadium microalloying or niobium microalloying can be achieved by converter smelting, nitrogen blowing to raise the temperature at the bottom of the ladle furnace, vacuum removal of gas inclusions, and the dynamic light reduction of the billet in the continuous casting secondary cooling water zone during the casting process can be controlled to be 0.65 to 2.5%, and the ferrite grain size of the billet can be controlled within the range of 115 to 220 μm.

[0071] Furthermore, in the manufacturing method described in this invention, in step (2), the heating temperature in the heating furnace is controlled to be 1110-1250°C.

[0072] In step (2) above, controlling the heating temperature between 1110 and 1250°C can not only save energy and reduce consumption, but also reduce the degree of austenite grain coarsening while ensuring the billet is fully reaustified.

[0073] Furthermore, in the manufacturing method described in this invention, in step (3), the roughing rolling start temperature is controlled to be no less than 1000°C, and the steel plate surface temperature is controlled to be no greater than 960°C during the roughing rolling interval. The cooling rate during the roughing rolling stage is 5-8°C / s, the finishing rolling finish temperature is controlled to be no less than 780°C, and the cumulative reduction rate of the last three passes is controlled to be no less than 30%.

[0074] In step (3) above, non-crystallization controlled rolling technology can be used for rolling, that is, the finishing rolling temperature is controlled to be no less than 780°C, so as to fully reduce the rolling force.

[0075] In this invention, under the condition of reasonable distribution of pass reduction rate, the deformed austenite is ensured to recrystallize above the recrystallization temperature to ensure grain refinement of steel plate. When austenite transforms into ferrite, rapid cooling (cooling rate of 13-42℃ / s) is used to ensure the refinement of martensite or bainite grains after phase transformation. Under the action of rapid cooling, the steel can form a sufficient number of precipitates of appropriate size at the recrystallization temperature, thereby further refining the martensite or bainite grains.

[0076] It should be noted that after the rolling process in step (3), the controlled cooling process of rapid cooling after rolling in step (4) has the effect of adjusting the size of the precipitated phase and improving the toughness of the material.

[0077] Furthermore, in the manufacturing method described in this invention, in step (5), a tempering heat treatment is performed, the tempering temperature is 600-650℃, and the holding time is (15-50) min + t × 1 min / mm, where t represents the plate thickness and its unit parameter is mm.

[0078] In this invention, after the steel is rapidly cooled following rolling, it undergoes a heat treatment process. Appropriate heat treatment can eliminate uneven deformation and internal stress in the formed steel plate generated during hot forming. As shown in the above technical solution, in some preferred embodiments, the heat treatment process can specifically be tempering heat treatment.

[0079] Compared with the prior art, the high-strength pressure vessel steel plate resistant to liquid carbon dioxide corrosion and its manufacturing method described in this invention have the following advantages and beneficial effects:

[0080] In this invention, when high-strength pressure vessel steel is used in service environments resistant to liquid carbon dioxide corrosion cracking, in order to ensure the smooth progress of liquid carbon dioxide corrosion cracking resistance and to ensure that the shape and performance of the welded steel plate meet the usage requirements, fine control can be made on the steel plate composition, steel plate preparation process, parameter design, etc., so that this type of pressure vessel steel can achieve the goal of smooth production in the factory, qualified manufacturing of finished products for downstream users, and ultimately safe use of the product.

[0081] Pressure vessels made using the technical solution of this invention can effectively meet the requirements of pressure vessels for high strength and lightweight, resistance to liquid carbon dioxide corrosion cracking and high parameterization of steel, and ensure that the performance of the steel plate in the liquid carbon dioxide medium environment is comparable to that of the steel plate in the delivery state.

[0082] (1) The high-strength pressure vessel steel of the present invention adopts a low-C-Mn-Cr-Mo-Cu-Ni alloy system. Through chemical composition design, a new type of steel is prepared using the low-C-Mn-Cr-Mo-Cu-Ni alloy system, which can improve the strength, toughness and resistance to carbon dioxide stress corrosion cracking of the steel. In this alloy system, Cr can effectively improve the steel material's resistance to carbon dioxide corrosion on the steel matrix surface and prevent the wet liquid carbon dioxide medium from contacting the iron matrix. Mo promotes the formation of surface passivation in the steel in a reducing wet carbonic acid environment. The combined effect of Cr and Mo can improve the steel's resistance to carbon dioxide pitting corrosion. In order to ensure the strength and toughness of the steel plate of the present invention while taking into account the steel plate's resistance to carbon dioxide corrosion, the Cr and Mo in the steel must be maintained in a certain amount. After rapid cooling after rolling, the Cr and Mo elements give the steel good hardenability, and after a suitable tempering process, the finished steel plate has the strength and toughness required by the present invention. By precisely controlling the Cr / Mo ratio in the steel, the type and quantity of Cr and Mo alloy carbides in the steel can be precisely controlled. Furthermore, when the steel plate is in service with liquid carbon dioxide corrosive media, a protective Cr(OH)3 or Cr2O3 protective film will form on the steel plate surface on the side in contact with the media, preventing carbon dioxide from penetrating the steel plate matrix.

[0083] Accordingly, in the design of the chemical composition, this invention also controls the content of Cu, Sn, and Sb elements in the steel to further improve the strength and toughness of the steel and avoid hot brittleness and cracking of the steel plate during rolling. Simultaneously, the presence of Cu, Sn, and Sb in the steel can lead to the formation of brittle metallic compounds such as CuSn, CuSb, or composite Cu(Sn, Sb) at grain boundaries during the cold and hot forming and welding processes of the finished steel plate. This reduces the toughness of the steel plate during processing and service, resulting in surface cracking or micro-cracks within the steel plate, increasing the safety risks during service. Furthermore, while adding Cu and Ni can improve the strength and toughness of the steel plate, the steel plate of this invention must also ensure good resistance to carbon dioxide corrosion. Cu can improve the carbon dioxide corrosion resistance of the steel plate, but Ni accelerates it. Therefore, the Cu / Ni ratio in the steel must be effectively controlled so that Cu and Ni improve the strength and toughness without compromising its resistance to carbon dioxide corrosion.

[0084] (2) This invention, through comprehensive control of alloy composition and manufacturing process, yields a high-strength pressure vessel steel plate with excellent comprehensive mechanical properties. Its yield strength is ≥685MPa, tensile strength is ≥795MPa, transverse KV2 at -60℃ is ≥200J, elongation is ≥17%, and the hardness HV at all locations of the steel plate is between 230 and 245. Simultaneously, the welded joints of this high-strength pressure vessel steel plate also possess good mechanical properties, with a tensile strength ≥800MPa, transverse KV2 at -60℃ ≥200J, and a non-plastic transformation temperature in the weld heat-affected zone between -85 and -70℃. Furthermore, both the high-strength pressure vessel steel plate and its corresponding welded joints exhibit good resistance to carbon dioxide corrosion. The carbon dioxide corrosion rate of the high-strength pressure vessel steel plate is 0.012–0.020 mm / a, and the liquid carbon dioxide corrosion rate of its welded joints is 0.008–0.018 mm / a.

[0085] In this invention, by combining controlled rolling and cooling processes with heat treatment processes, the size of martensite or bainite grains in the steel can be refined, resulting in steel plates with good strength and toughness, resistance to cold and hot welding cracks, resistance to stress corrosion cracking by liquid carbon dioxide, and excellent weldability and weldability. This high-strength pressure vessel steel plate with a tensile strength of 790MPa can be used to meet the comprehensive requirements of large-scale, high-strength, thinner, and lighter spherical tanks or mobile containers, and has significant practical implications. Attached Figure Description

[0086] Figure 1 This is a metallographic photograph of the steel plate for a high-strength pressure vessel in Example 3. Detailed Implementation

[0087] The high-strength pressure vessel steel plate and its manufacturing method described in this invention will be further explained and described below with reference to specific embodiments and accompanying drawings. However, this explanation and description do not constitute an undue limitation on the technical solution of this invention.

[0088] Examples 1-8 and Comparative Examples 1-6

[0089] The high-strength pressure vessel steel plates of Examples 1-8 and the comparative steel plates of Comparative Examples 1-6 of this invention were all prepared using the following steps:

[0090] (1) Smelting and casting according to the chemical composition shown in Tables 1-1 and 1-2: vanadium microalloying or niobium microalloying is achieved by converter smelting, nitrogen is blown into the bottom of the ladle to raise the temperature, and gas inclusions are removed by vacuum; during the casting process, the dynamic light reduction of the billet in the second cooling water zone of continuous casting is controlled at 0.65 to 2.5%, and the ferrite grain size of the obtained continuous casting billet is controlled in the range of 115 to 220 μm.

[0091] (2) Hot charging and hot delivery of continuous casting billet + heating furnace: The charging temperature of the high-temperature continuous casting billet directly into the heating furnace is 780~880℃; the heating temperature in the heating furnace is controlled between 1105~1250℃, and preferably controlled between 1110~1250℃; the heating rate in the heating furnace is controlled between 8~13min / cm.

[0092] (3) Rolling: The roughing rolling temperature is controlled to be no less than 1000℃, and the surface temperature of the steel plate is controlled to be no more than 960℃ during the roughing rolling interval. The cooling rate during the roughing rolling stage is 5~8℃ / s. The finishing rolling temperature is controlled to be no less than 780℃. The cumulative reduction rate of the last three passes is controlled to be no less than 30%.

[0093] (4) Rapid cooling after rolling: control the cooling rate to be 13-42℃ / s and the final cooling temperature to be 300-390℃.

[0094] (5) Heat treatment: Perform tempering heat treatment, control the tempering temperature to 600~650℃, and control the holding time to (15~50)min+t×1min / mm, where t represents the plate thickness and its unit parameter is mm.

[0095] It should be noted that the chemical composition design and related processes of the high-strength pressure vessel steel plates in Examples 1-8 all meet the specifications designed in this invention. Although the comparative steel plates in Comparative Examples 1-6 are also prepared using the above steps (1)-(5), there are parameters in the chemical composition design and related processes of the comparative steel plates in Comparative Examples 1-6 that do not meet the design requirements of this invention.

[0096] Tables 1-1 and 1-2 list the mass percentage of each chemical element in the high-strength pressure vessel steel plates of Examples 1-8 and the comparative steel plates of Comparative Examples 1-6.

[0097] Table 1-1. (wt%, balance Fe and other unavoidable impurities besides P, S and O)

[0098]

[0099]

[0100] Table 1-2.

[0101] serial number Cr / Mo Cu / Ni Cu + 6(Sn + Sb) Cu / 6(Sn+Sb) Pcm Example 1 5.00 0.60 0.15 35.71 0.271 Example 2 7.38 1.44 0.27 43.33 0.281 Example 3 4.81 1.20 0.19 23.08 0.273 Example 4 2.38 0.92 0.24 23.96 0.271 Example 5 4.79 1.33 0.25 26.67 0.287 Example 6 4.00 1.13 0.18 21.79 0.260 Example 7 4.70 1.22 0.23 24.44 0.271 Example 8 3.69 0.74 0.21 19.61 0.268 Comparative Example 1 5.76 1.9 0.40 0.90 0.218 Comparative Example 2 3 1.67 0.37 2.10 0.254 Comparative Example 3 5 2 0.36 1.23 0.248 Comparative Example 4 6.58 20 0.33 1.56 0.243 Comparative Example 5 6 2.88 0.39 1.44 0.250 Comparative Example 6 4.12 2.08 0.03 10.98 0.256

[0102] Note: In the table above, for the four relationships Cr / Mo, Cu / Ni, Cu+6(Sn+Sb), and Cu / 6(Sn+Sb), the values ​​of each element in the formula should be substituted with the values ​​before the percentage sign of their mass percentage content, and rounded to two decimal places. Pcm(%)=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B, the values ​​of each chemical element in this formula should be substituted with the values ​​before the percentage sign of their mass percentage content.

[0103] Tables 2-1 and 2-2 list the specific process parameters for the high-strength pressure vessel steel plates of Examples 1-8 and the comparative steel plates of Comparative Examples 1-6.

[0104] Table 2-1.

[0105]

[0106]

[0107] Table 2-2.

[0108]

[0109] Samples of the high-strength pressure vessel steel plates of Examples 1-8 and the comparative steel plates of Comparative Examples 1-6 obtained through the above process steps were taken for observation, analysis and mechanical property testing. The observation results and mechanical property test results are listed in Table 3.

[0110] The relevant performance testing methods are as follows:

[0111] (1) Tensile property test: The tensile test was conducted in accordance with GB / T 228.1 "Metallic materials - Tensile test - Part 1: Test method at room temperature" to test the yield strength, tensile strength and elongation of the steel plates in each embodiment and comparative example.

[0112] (2) Impact performance test: The transverse impact performance KV2 values ​​of the steel plates of each embodiment and comparative example were tested according to GB / T 229 "Metallic materials Charpy pendulum impact test method". The test results are shown in Table 3.

[0113] Accordingly, in the various embodiments and comparative examples of this invention, the reference standard for evaluating the metallographic structure of steel is GB / T 13298 "Metallic Materials - Test Methods for Microstructure"; the reference standard for evaluating the Vickers hardness (HV) of steel is GB / T 4340.1 "Metallic Materials - Vickers Hardness Test - Part 1 Test Methods".

[0114] HV=exp[6.21-2.62Pcm-0.00086Vc+(Pcm-0.27)×(97.97(Pcm-0.27)-(Pcm-0.27)×(0.12(Vc-29)+0.0003(Vc-29) 2 )).

[0115] Wherein, Pcm(%)=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B, V c This represents the cooling rate of the steel plate after rolling, with each chemical element in the formula having the value before the mass percentage sign.

[0116] It should be noted that the chemical composition of the steel and the cooling rate after rolling are the most critical factors affecting HV. By controlling these two factors, the hardness of the finished steel plate can be effectively controlled within the range required by this invention. The above HV formula mainly illustrates how HV can be limited to a certain range through composition control and adjustment of post-rolling cooling rate parameters.

[0117] Table 3 lists the observation results and mechanical property test results of the high-strength pressure vessel steel plates of Examples 1-8 and the comparative steel plates of Comparative Examples 1-6.

[0118] Table 3.

[0119]

[0120]

[0121] Note: HV=exp[6.21-2.62Pcm-0.00086Vc+(Pcm-0.27)×(97.97(Pcm-0.27)-(Pcm-0.27)×(0.12(Vc-29)+0.0003(Vc-29) 2 ), where Pcm(%)=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B, where Vc is the cooling rate of the steel plate after rolling and rapid cooling. The values ​​of each chemical element in the formula are substituted into the values ​​before the mass percentage sign.

[0122] Microscopic observation of the high-strength pressure vessel steel plates of Examples 1-8 shows that the matrix of the microstructure of the high-strength pressure vessel steel plates of Examples 1-8 is tempered bainite.

[0123] As shown in Table 3, compared with the comparative steel plates of Comparative Examples 1-6, the high-strength pressure vessel steel plates of Examples 1-8 of this case have better comprehensive mechanical properties. In particular, the transverse impact energy KV2 of the high-strength pressure vessel steel plates of Examples 1-8 at -60℃ is much greater than that of the comparative steels of Comparative Examples 1-6, and it has excellent low-temperature toughness.

[0124] In this invention, the high-strength pressure vessel steel plates of the above embodiments 1-8 have a yield strength between 768-805 MPa, a tensile strength between 795-840 MPa, a transverse -60°C impact energy KV2 between 273-323 J, an elongation between 18-20%, and a hardness value HV of 232-245 at all locations of the steel plate.

[0125] Accordingly, in order to demonstrate that the high-strength pressure vessel steel plates of Examples 1-8 of the present invention have good weldability and welding performance, the inventors also conducted welding process tests on the high-strength pressure vessel steel plates of Examples 1-8 and the comparative steel plates of Comparative Examples 1-5, and tested the performance of the welded joints after welding. The relevant test results are listed in Table 4 below.

[0126] Welding process test conditions: The welding heat input was controlled at 18–45 kJ / cm, and the time t for the weld pool temperature to drop from 800 degrees to 500 degrees was controlled. 8 / 5 Cooling time should be controlled within the range of 15 to 48 seconds.

[0127] In this invention, the tensile strength of the welded steel plate joints in Examples 1-8 and Comparative Examples 1-6 was measured using GB / T228.1 "Metallic materials, tensile testing - Part 1: Room temperature test method", the impact energy KV2 of the welded joint at -60℃ was measured using GB / T 229 "Metallic materials, Charpy pendulum impact test method", and the non-plastic transformation temperature (NDTT) of the weld heat-affected zone was tested using GB / T6803 "Ferritic steel, non-plastic transformation temperature drop hammer test method".

[0128] Table 4 lists the mechanical properties of the welded joints of the high-strength pressure vessel steel plates of Examples 1-8 and the comparative steel plates of Comparative Examples 1-6.

[0129] Table 4.

[0130]

[0131] Therefore, as can be seen from Tables 3 and 4 above, the high-strength pressure vessel steel plates of Examples 1-8 and their corresponding welded joints exhibit significantly superior overall performance compared to the comparative steel plates of Examples 1-6. The high-strength pressure vessel steel plates of Examples 1-8 of this invention not only possess excellent comprehensive mechanical properties and resistance to cold and hot welding cracks, but also exhibit good weldability and weldability.

[0132] As shown in Table 4, in this invention, the welded joints corresponding to the high-strength pressure vessel steel plates of Examples 1-8 all have excellent mechanical properties. The tensile strength of their respective welded joints is between 802-843 MPa, and the transverse impact energy KV2 of the welded joint at -60℃ is between 203-255 J. The non-plastic transformation temperature of the weld heat-affected zone is between -80℃ and -75℃.

[0133] In addition, to further illustrate that the high-strength pressure vessel steel plates of Examples 1-8 of the present invention have good resistance to liquid carbon dioxide corrosion, it is necessary to conduct carbon dioxide corrosion tests on the steel plates of Examples 1-8 and Comparative Examples 1-6 of the present invention and their corresponding welded joints, and the results of the corrosion tests are listed in Table 6 below.

[0134] In this invention, the test standards for the resistance of steel plates and welded joints to liquid carbon dioxide corrosion are: ISO 11945 "Corrosion of metals and alloys - General principles of corrosion testing" and ISO 9224 "Corrosion of metals and alloys - Corrosion of climate - Guiding numerical values ​​for classification of corrosion" and NACERP-0775-91 standard regarding the degree of CO2 corrosion.

[0135] Table 5 lists the test parameters for the steel plates and their corresponding welded joints in Examples 1-8 and Comparative Examples 1-6 during the carbon dioxide corrosion test.

[0136] Table 5.

[0137] Inspection standards ISO 11945 Experimental temperature 35℃ Total gas pressure 4MPa <![CDATA[Partial pressure of CO2]]> 1.8MPa Flow rate Dynamic 1.5m / s test cycle 438 hours (approximately 2.6 weeks) test solution 98% (wt,%) liquid carbon dioxide + 2% (wt,%) water pH value 3.0

[0138] Table 6 lists the carbon dioxide corrosion test results of the steel plates and their corresponding welded joints in Examples 1-8 and Comparative Examples 1-6.

[0139] Table 6.

[0140]

[0141] As can be seen from Table 6 above, compared with Comparative Examples 1-6, the steel plates and their corresponding welded joints of Examples 1-8 exhibit lower corrosion rates and superior resistance to liquid carbon dioxide corrosion. In this invention, the liquid carbon dioxide corrosion rate of the high-strength pressure vessel steel plates of Examples 1-8 is between 0.012 and 0.017 mm / a, and the liquid carbon dioxide corrosion rate of the welded joints corresponding to the steel plates of Examples 1-8 is between 0.008 and 0.017 mm / a.

[0142] In summary, it can be seen that the high-strength pressure vessel steel with a tensile strength of 790MPa manufactured using the technical solution of the present invention can meet the requirements of high strength and toughness and resistance to carbon dioxide corrosion. This steel has high production efficiency, low production energy consumption, and low-carbon environmentally friendly characteristics with corrosion resistance.

[0143] Figure 1 This is a metallographic photograph of the steel plate for a high-strength pressure vessel in Example 3.

[0144] like Figure 1 As shown, in this embodiment, the metallographic structure of the high-strength pressure vessel steel plate of Example 3 is tempered bainite, and its original austenite grain size is grade 8.

[0145] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0146] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A high-strength pressure vessel steel resistant to liquid carbon dioxide corrosion, characterized in that, Its mass percentage content of each chemical element is as follows: C: 0.085–0.12%, Si: 0.05–0.30%, Mn: 1.05–1.48%, Alt: 0.015–0.038%, Cu: 0.10–0.30%, Cr: 1.05–1.75%, Mo: 0.18–0.50%, 0 < Sn ≤ 0.0013%, 0 < Sb ≤ 0.0012%, 0 < Ni ≤ 0.30%, and at least one of the following contents of V, B, and Nb: Nb: 0.018–0.045%, 0 < V ≤ 0.050%, B: 0.0006–0.0018%; the balance being Fe and unavoidable impurity elements; wherein each chemical element satisfies at least one of the following formulas: 2≤Cr / Mo≤7.5; 0.15≤Cu+6(Sn+Sb)≤0.28; 15≤Cu / 6(Sn+Sb)≤45; 0.6 < Cu / Ni < 1.5; Substitute the values ​​of each chemical element into the values ​​before the mass percentage sign for each chemical element in the formula. The liquid carbon dioxide corrosion rate of the steel plate is 0.012 to 0.020 mm / a, and the hardness value HV of all parts of the steel plate is between 230 and 245; the liquid carbon dioxide corrosion rate of the welded joint is 0.008 to 0.018 mm / a.

2. The high-strength pressure vessel steel as described in claim 1, characterized in that, Among the unavoidable impurity elements, the content of each impurity element must satisfy at least one of the following conditions: P≤0.011%, S≤0.0025%, O≤0.0015%.

3. The high-strength pressure vessel steel as described in claim 1, characterized in that, The mass percentage content of each chemical element also satisfies at least one of the following conditions: Alt: 0.016~0.034%; V：0.015～0.043％； Nb: 0.019–0.043%; Cu: 0.15–0.28%; Cr：1.15～1.65％； Mo: 0.20–0.48%; B：0.0008～0.0016％。 4. The high-strength pressure vessel steel as described in claim 1, characterized in that, Its microstructure is tempered bainite.

5. The high-strength pressure vessel steel as described in claim 1, characterized in that, Its performance meets the following requirements: the yield strength of its steel plate is ≥685MPa, the tensile strength is ≥795MPa, the transverse KV2 at -60℃ is ≥200J, the elongation is ≥17%, the liquid carbon dioxide corrosion rate is 0.012~0.020mm / a, and the hardness HV value of all parts of the steel plate is between 230 and 245; the tensile strength of its welded joint is ≥800MPa, the transverse KV2 at -60℃ is ≥200J, the non-plastic transformation temperature of the weld heat-affected zone is between -85 and -70℃, and the liquid carbon dioxide corrosion rate is 0.008~0.018mm / a.

6. The high-strength pressure vessel steel as described in claim 1, characterized in that, Its hardness is: HV=exp[6.21-2.62Pcm-0.00086Vc+(Pcm-0.27)×(97.97(Pcm-0.27)-(Pcm- 0.27)×(0.12(Vc-29)+0.0003(Vc-29) 2 )],in Pcm(%)=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B, V c For steel The cooling rate of the plate after rolling is given by substituting the values ​​of each chemical element in the formula before the mass percentage sign.

7. The method for manufacturing high-strength pressure vessel steel according to any one of claims 1-6, characterized in that, It includes the following steps: (1) Smelting and casting; (2) Hot charging and hot delivery of continuous casting billet + heating furnace: The high temperature of the continuous casting billet is directly charged into the heating furnace at a charging temperature of 780~880℃. The heating temperature in the heating furnace is controlled at 1105~1250℃ and the heating rate is 8~13min / cm. (3) Rolling; (4) Rapid cooling after rolling: control the cooling rate to be 13-42℃ / s, and the final cooling temperature to be 300-390℃; (5) Heat treatment.

8. The manufacturing method as described in claim 7, characterized in that, In step (1), the dynamic light reduction of the billet in the second cooling water zone of continuous casting is controlled to be 0.65 to 2.5% so as to obtain a ferrite grain size range of 115 to 220 μm for the continuous casting billet.

9. The manufacturing method as described in claim 7, characterized in that, In step (2), the heating temperature is controlled at 1110 to 1250°C in the heating furnace.

10. The manufacturing method as described in claim 7, characterized in that, In step (3), the roughing rolling start temperature is controlled to be no less than 1000℃, and the steel plate surface temperature is controlled to be no more than 960℃ during the roughing rolling interval. The cooling rate during the roughing rolling stage is 5-8℃ / s. The finishing rolling temperature is controlled to be no less than 780℃. The cumulative reduction rate of the last three passes is controlled to be no less than 30%.

11. The manufacturing method as described in claim 7, characterized in that, In step (5), tempering heat treatment is performed at a temperature of 600-650℃ and a holding time of (15-50) min + t × 1 min / mm, where t represents the plate thickness and its unit parameter is mm.

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