High-strength steel for pressure vessels resistant to liquid carbon dioxide corrosion and method for manufacturing the same

Abstract

The invention discloses a high-strength steel for pressure vessels resistant to liquid carbon dioxide corrosion, which contains Fe and inevitable impurity elements, and further contains the following chemical elements in the following mass percentages: C: 0.067-0.085%, Si: 0.15-0.45%, Mn: 0.95-1.38%, Alt: 0.015-0.045%, Cu: 0.18-0.30%, Cr: 0.80-1.45%, Mo: 0.15-0.39%, 0<Sn≤0.0016%, 0<Ni<0.25%, and at least one of V, B and Nb in the following contents: Nb: 0.018-0.045%, 0<V≤0.035%, B: 0.0006-0.0015%. Correspondingly, the present invention also discloses a method for manufacturing the above-mentioned steel, which comprises the following steps: (1) smelting and casting; (2) hot charging and hot conveying of continuous casting billets + heating furnace: the charging temperature of the high-temperature continuous casting billets directly charged into the heating furnace is 780-880°C, the heating temperature in the heating furnace is controlled to be 1105-1250°C, and the heating rate is 7.5-14 min / cm; (3) rolling; (4) rapid cooling after rolling: the cooling rate is controlled to be 20-45°C / s, and the final cooling temperature is 290-380°C; (5) heat treatment.

Description

Technical Field

[0001] The present invention relates to a steel plate and a manufacturing method thereof, and in particular to a steel plate for a pressure vessel and a manufacturing method thereof. Background Art

[0002] In recent years, with the rapid development of industrial production, pressure vessels are increasingly used in various industries. At present, 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. These pressure vessels are often used to contain some special corrosive substances and are easily corroded, especially when subjected to force and then corroded, which will cause cracks in the pressure vessel steel.

[0003] As we all know, although pure carbon dioxide does not have corrosive properties, it will become extremely corrosive when dissolved in water. At the same pH value, the total acidity of carbon dioxide is higher than that of hydrochloric acid. Therefore, in actual application, its corrosion to steel is more serious than hydrochloric acid.

[0004] In actual use, when the pressure vessel contains liquid carbon dioxide, the corrosion of liquid carbon dioxide will cause the service life of the pressure vessel to be much lower than the design life. The corrosion rate of liquid carbon dioxide for low carbon steel is as high as 7mm / a, sometimes even higher. This corrosion rate is extremely serious.

[0005] Research results show that the higher the strength of steel, the easier it is to crack under the corrosion of carbon dioxide. Therefore, there is an urgent need to obtain a pressure vessel steel with high strength and good resistance to liquid carbon dioxide corrosion.

[0006] Based on this, the inventor hopes to overcome the problems of high strength and high hardness of steel plates and welded joints in existing pressure vessel steel plates, and to solve the carbon dioxide corrosion problem of steel plates and welded joints, so as to improve the service life of such steel containers containing liquid carbon dioxide. To this end, the present invention aims to provide a new high-strength pressure vessel steel with resistance to liquid carbon dioxide corrosion and a manufacturing method thereof.

[0007] In the prior art, although there are steel plates with carbon dioxide corrosion resistance, they still cannot meet the performance requirements of specific strength and manufacturing process parameters and are still lacking in performance.

[0008] For example: Publication number is CN103320705A, publication date is September 25, 2013, and title is “A CO2-resistant gas generator for ground gathering and transmission 2 The Chinese patent document "Corrosion pipeline steel and its preparation method" discloses a CO2-resistant 2Corrosion pipeline steel and its preparation method, which adopts low C and Cr-Mo-Cu-Ni alloy design, and the steel plate is directly cooled after hot rolling. However, the strength and performance parameters of the steel plate produced by this scheme are far different from those of the present invention, and it cannot meet the service environment and service performance requirements of the present invention.

[0009] Another example: the Chinese patent document with publication number CN102199729A, publication date September 28, 2011, and titled "Economical 55Ksi steel grade CO2 corrosion resistant oil well pipe and its manufacturing method", discloses an economical 55Ksi steel grade CO2 corrosion resistant oil well pipe and its manufacturing method. The technical solution adopts 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] Another example: the Chinese patent document with publication number CN106498279A, publication date March 15, 2017, and titled "A low-Cr economical X65 pipeline steel resistant to CO2 corrosion and production method", discloses a low-Cr economical X65 pipeline steel resistant to CO2 corrosion and production method. The technical solution adopts a Cr-Mo-V-Ti alloy system, and its supply state is TMCP state. 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 of the purposes of the present invention is to provide a high-strength steel for pressure vessels that is resistant to liquid carbon dioxide corrosion. The high-strength steel plate for pressure vessels is a steel plate using a low C-Mn-Cr-Mo-Cu alloy system, which can obtain good comprehensive mechanical properties by accurately controlling the chemical components in the steel during the production process of the steel plate. The high-strength steel plate for pressure vessels not only has good toughness and resistance to cold and hot cracks in welding, but also has good welding processability, welding performance and excellent resistance to liquid carbon dioxide corrosion. It can be used to prepare pressure vessels and has good application prospects.

[0012] In order to achieve the above object, the present invention provides a high-strength steel for pressure vessels resistant to liquid carbon dioxide corrosion, which contains Fe and inevitable impurity elements, and further contains the following chemical elements in the following mass percentages:

[0013] C: 0.067~0.085%, Si: 0.15~0.45%, Mn: 0.95~1.38%, Alt: 0.015~0.045%, Cu: 0.18~0.30%, Cr: 0.80~1.45%, Mo: 0.15~0.39%, 0<Sn≤0.0016%, 0<Ni<0.25%, and at least one of V, B and Nb in the following contents: Nb: 0.018~0.045%, 0<V≤0.035%, B: 0.0006~0.0015%.

[0014] Furthermore, in the high-strength steel plate for pressure vessels of the present invention, the mass percentage of each chemical element is:

[0015] C: 0.067~0.085%, Si: 0.15~0.45%, Mn: 0.95~1.38%, Alt: 0.015~0.045%, Cu: 0.18~0.30%, Cr: 0.80~1.45%, Mo: 0.15~0.39%, 0<Sn≤0.0016%, 0<Ni<0.25%, and at least one of V, B and Nb in the following contents: Nb: 0.018~0.045%, 0<V≤0.035%, B: 0.0006~0.0015%; the balance is Fe and unavoidable impurity elements.

[0016] In the above technical solution of the present invention, the present invention designs a new steel grade by rationally designing chemical composition and adopting a low C-Mn-Cr-Mo-Cu alloy system. At least one of V, B and Nb needs to be added to the steel plate, which, on the one hand, utilizes the toughness effect of the NbC precipitation phase, improves the grain refinement and precipitation strengthening effect of the Nb microalloy, and on the other hand, the present invention can also add an appropriate amount of V, and the V element can cooperate with C to form a VC precipitation phase, which can further refine the grains, improve the low-temperature fracture toughness of the steel and reduce the ductile-brittle transition temperature.

[0017] At the same time, when designing the chemical composition, the present invention also limits the content of elements such as Alt, Cu, Sn, Ni, etc. in the steel within a suitable range, and limits the content of the impurity element O, so as to avoid the single or combined effects of these elements from damaging the toughness of the steel. These elements are prevented from segregating and the low-melting-point element segregation during the continuous casting cooling process, especially during the cooling of the steel from high temperature to low temperature (980°C to 700°C), so that the segregation effect of the continuous casting billet is further enhanced when it is cooled from solidification to low temperature and rolled into a finished steel plate, thereby preventing the steel plate from being subjected to a high probability of stress corrosion cracking when it is in service in a liquid carbon dioxide stress corrosion environment.

[0018] In the high-strength steel plate for pressure vessels resistant to liquid carbon dioxide corrosion according to the present invention, the design principles of the chemical elements are as follows:

[0019] C: In the high-strength pressure vessel steel plate of the present invention, C is one of the indispensable elements in steel to improve the strength of steel. As the C content in steel increases, the Fe 3 As C increases, hardenability will also increase, the yield strength and tensile strength of steel will increase, while the elongation notch impact toughness will decrease. Among them, for every 0.1% increase in the C element content in steel, the tensile strength will increase by about 90MPa, and the yield strength will increase by about 40-50MPa. However, it should be noted that the C element content in steel should not be too high. As the C element content in steel increases, the elongation and impact toughness of the steel will decrease accordingly, especially the low-temperature toughness will decrease to a greater extent. Moreover, when welding steel with a high C content, hardening will also occur in the welding heat affected zone, which will aggravate the tendency of cold cracking during welding, and when serving in a carbon dioxide corrosive environment, the steel plate and the welded joint will become a weak part of stress corrosion cracking. Therefore, considering the influence of C element on the performance of pressure vessel steel, in the high-strength pressure vessel steel plate described in the present invention, the mass percentage of C element is controlled between 0.067 and 0.085%, which not only ensures that the strength stability of the steel is within a suitable range, but also is suitable for production operations, and can improve its applicability and feasibility in industrial production.

[0020] Si: In the high-strength pressure vessel steel plate described in the present invention, the Si element can improve the strength of the steel in the form of solid solution strengthening. When the Si content increases from 0.10% to 0.30%, the strength of the steel remains basically unchanged or slightly increases, while the toughness of the steel can be greatly improved. Properly increasing the Si content will increase the substitutional solid solution strengthening effect in the steel and make the grains finer, which is beneficial to improving the toughness of the steel. However, it should be noted that the Si content in the steel should not be too high. When the Si content is too high, it is easy to form SiO in the steelmaking process. 2 Therefore, in the high-strength steel plate for pressure vessels of the present invention, the mass percentage of Si element is controlled between 0.15 and 0.45%.

[0021] Mn: In the high-strength steel plate for pressure vessels described in the present invention, the Mn element has a very significant effect on improving the strength of low-carbon steel. Adding 1% of Mn element to steel can increase the tensile strength of steel by about 100MPa. Generally speaking, controlling the mass percentage of Mn element in steel below 1.70% is beneficial to improving the toughness of weld metal. In low-carbon high-strength steel, the content of Mn element can reach up to 1.80%, but in the steel of the present invention, too high Mn will have an adverse effect on the performance of steel. In addition, the Mn element will also increase the solubility of elements such as Nb and V in steel. Based on this, considering the influence of the Mn element content on the performance of steel, the Mn element content must be strictly controlled. In the present invention, the mass percentage of Mn element is controlled between 0.95 and 1.38%. In this way, it can ensure that the steel obtains suitable tensile strength, and it can also not damage the low-temperature impact toughness and elongation of the steel.

[0022] Alt: In the high-strength steel plate for pressure vessels described in the present invention, the Alt element is added as a deoxidation balance element in the steelmaking process. In the early stage of refining, the mass percentage of Alt in the molten steel can be controlled within 0.045%; in the later stage of refining, the oxygen in the steel has been controlled to be relatively low. If the Alt element is added again, large-sized chain-like aluminum oxide inclusions will be formed in the molten steel, which will seriously damage the low-temperature toughness of the finished steel plate. In addition, adding the Alt element in the later stage of refining will form a large amount of AlN in the steel. AlN is easy to precipitate in the range of 800 to 950°C during the cooling of the continuous casting billet, reducing the thermoplasticity of the continuous casting billet, and also forming corner cracks or intergranular cracks on the surface or corners of the casting billet. Therefore, considering the influence of the Alt element on the performance of the steel plate for pressure vessels in the technical solution, in the high-strength steel plate for pressure vessels described in the present invention, the mass percentage of Alt is controlled between 0.015 and 0.045%.

[0023] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of Alt can also be preferably controlled between 0.017 and 0.037%.

[0024] Cu: In the high-strength steel plate for pressure vessels described in the present invention, the Cu element mainly plays the role of precipitation strengthening. Adding an appropriate amount of Cu element to the steel is conducive to 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 heat-affected zone of the steel plate welding, but also reduce the solid solubility of Cu steel in the steel due to the presence of residual elements such as Sn during the continuous casting process, and form a low-melting-point copper-rich phase in the iron oxide scale on the surface of the ingot. Under the action of the continuous casting bending and straightening stress, cracks occur on the surface of the ingot; network cracks occur during the rolling process of the steel plate. Based on this, in the high-strength steel plate for pressure vessels described in the present invention, the mass percentage of the Cu element is controlled between 0.18 and 0.30%.

[0025] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of Cu can also be preferably controlled between 0.19 and 0.29%.

[0026] Cr: In the high-strength steel plate for pressure vessels of the present invention, Cr is an element that reduces the austenite region and is also a medium-strength carbide-forming element. It can form carbides in steel and can be dissolved in ferrite. In addition, Cr can also improve the corrosion resistance of the steel plate for pressure vessels. Cr has a high atomic binding energy between metal and oxygen, and it is easy to preferentially form dense Cr-containing corrosion products such as Cr(OH) on the surface of steel. 3 and Cr 2 O 3 , to prevent the corrosive ions in the corrosive medium from entering the iron matrix, thereby improving the corrosion resistance of the steel. At the same time, Cr is also an effective element to improve the hardenability of steel, but the Cr content in the steel should not be too high. Adding excessive Cr will increase the sensitivity of steel welding cold cracks. Therefore, in order to ensure the performance of the steel, in the present invention, the mass percentage of the Cr element is controlled between 0.80 and 1.45%. In this way, it can ensure that the steel obtains suitable tensile strength and excellent carbon dioxide corrosion resistance, and it can also not damage the low-temperature impact toughness and elongation of the steel.

[0027] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the Cr element may also be controlled between 0.9 and 1.4%.

[0028] Mo: In the high-strength steel plate for pressure vessels described in the present invention, the Mo element can improve the strength of the steel, especially the high-temperature strength of the steel. Its ability to improve the high-temperature strength of the steel is higher than that of Mn and Cr. At the same time, Mo is also one of the main elements that improve the steel's resistance to carbon dioxide corrosion. It should be noted that adding 0.50% of the Mo element to the steel can increase the high-temperature creep strength of the steel by 75%. A small amount of Mo can also improve the toughness of the weld metal, but adding Mo will also increase the hardenability of the steel, thereby increasing the cold crack sensitivity of the steel welding. On the other hand, sufficient Mo content can also ensure the stability of the steel plate after the tempering process, and ensure that the steel plate still has sufficient strength and toughness after tempering. Based on this, considering the influence of the Mo element on the properties of the steel, in the high-strength steel plate for pressure vessels described in the present invention, the mass percentage of the Mo element is controlled between 0.15 and 0.39%.

[0029] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the Mo element can also be controlled between 0.17 and 0.37%.

[0030] Sn: In the high-strength steel plate for pressure vessels described in the present invention, the addition of Sn to the steel will increase the strength and hardness of the steel and reduce the toughness of the steel. When Sn is present in the steel, the solubility of Cu in the austenite in the steel decreases sharply, prompting the formation of a low-melting-point Cu-rich phase in the surface oxide scale of the steel, thereby causing surface cracking during hot working and hot and cold forming of the steel plate, seriously affecting the metallurgical quality and surface quality of the steel. If the Sn in the steel is controlled within a certain range, the adverse coupling effect of Cu and Sn will not occur. Therefore, in order to ensure the intrinsic metallurgical quality and surface quality of the invented steel, in the high-strength steel plate for pressure vessels described in the present invention, the mass percentage of the Sn element is controlled to satisfy 0<Sn≤0.0016%.

[0031] Ni: In the high-strength steel plate for pressure vessels described in the present invention, Ni has a certain strengthening effect. Adding 1.00% Ni element to the steel can increase the strength of the steel by about 20MPa. At the same time, the Ni element can also significantly improve the toughness of the steel, especially the low-temperature toughness of low-carbon bainite and low-carbon martensitic steels. Adding Ni element to the steel can significantly improve the low-temperature toughness of the base material of the steel plate and the heat-affected zone of the weld. However, it should be noted that the Ni element in the steel should not be too high. When the Ni content is too high, Ni will promote the increase of the carbon dioxide corrosion rate of the steel and reduce the steel's resistance to carbon dioxide corrosion. Therefore, in the high-strength steel plate for pressure vessels described in the present invention, the mass percentage of the Ni element is controlled to 0<Ni<0.25%.

[0032] Nb: In the high-strength steel plate for pressure vessels described in the present invention, Nb can promote the grain refinement of the steel rolling microstructure and improve the strength and toughness of the steel. In the controlled rolling process, Nb can effectively refine the microstructure by inhibiting the recrystallization of austenite, and can reduce the overheating sensitivity and temper brittleness of the steel; in the welding process, the segregation and precipitation of Nb can hinder the coarsening of austenite grains during heating, ensuring that a relatively fine heat-affected zone structure is obtained after welding, so as to improve the welding performance. Therefore, considering the beneficial effects of the Nb element, in the high-strength steel plate for pressure vessels described in the present invention, the mass percentage of the Nb element is controlled between 0.018 and 0.045%.

[0033] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the Nb element may also be controlled between 0.019 and 0.040%.

[0034] V: In the high-strength steel plate for pressure vessels described in the present invention, V is a strong carbonitride-forming element, which can form carbides to prevent austenite grain growth and refine grains. Vanadium carbonitrides can form hydrogen ion (carbonic acid formed when carbon dioxide dissolves in water, and carbonic acid decomposes into hydrogen ions and bicarbonate ions) traps in steel to prevent carbon dioxide corrosion and cracking. It should be noted that although the addition of V element to steel can greatly improve the strength of steel, the V element content in the steel should not be too high. When the V element content is too high, the number of precipitates increases and the size increases, which will lead to a decrease in the toughness of the steel. Therefore, considering the various strengthening and toughening effects of V element in steel, in the high-strength steel plate for pressure vessels of the present invention, the mass percentage of V element is controlled to 0<V≤0.035%.

[0035] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the V element may also be controlled between 0.012 and 0.030%.

[0036] B: In the high-strength pressure vessel steel plate described in the present invention, the addition of B element can make up for the problem of insufficient hardenability and strength caused by insufficient carbon content in the steel. However, it is not advisable to add excessive B element to the steel. As the content of B element in the steel increases, B will be seriously segregated at the grain boundary, and the strength and toughness of the steel will tend to decrease. Therefore, in the high-strength pressure vessel steel described in the present invention, the mass percentage of B element is controlled between 0.0006 and 0.0015%.

[0037] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the B element can also be controlled between 0.0007 and 0.0013%.

[0038] Furthermore, in the high-strength steel plate for pressure vessels described in the present invention, among the inevitable impurity elements, the content of each impurity element satisfies at least one of the following conditions: P≤0.012%, S≤0.003%, O≤0.0017%.

[0039] In the above technical solution, P, S and O are all impurity elements in the high-strength steel plate for pressure vessels described in the present invention. Under the condition that technical conditions permit, in order to obtain steel with better performance and better quality, the content of impurity elements in the steel plate for pressure vessels should be reduced as much as possible. Only by smelting pure steel can the performance of the steel of the present invention be guaranteed, so the content of P, S and O elements in the steel must be controlled within a relatively low range. Therefore, in the high-strength steel plate for pressure vessels described in the present invention, the content of P element is controlled to be P≤0.012%, the content of S element is controlled to be S≤0.003%, and the content of O element is controlled to be O≤0.0017%.

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

[0041] 3≤Cr / Mo≤7;

[0042] 0.19≤Cu+7Sn≤0.29;

[0043] 33≤Cu / 4Sn≤54;

[0044] Cu / Ni>1.6;

[0045] In the formula, substitute the numerical value before the mass percentage sign of each chemical element.

[0046] In the above technical solution of the present invention, the present invention can control the elements in the steel to satisfy the limiting relationship of 3≤Cr / Mo≤7 while controlling the mass percentage of a single chemical element in the steel. Cr and Mo elements are both hardenability elements. Controlling Cr and Mo to satisfy the limiting relationship of 3≤Cr / Mo≤7 is to limit the hardness of the steel plate to a certain range and ensure that the steel plate has good comprehensive strength and toughness effects; on the other hand, this limiting relationship can make the carbides in the steel be accurately controlled, forming amorphous Cr oxides on the surface of the steel plate, and inhibiting carbon dioxide corrosion from extending into the interior of the steel plate.

[0047] Accordingly, the present invention can control the elements in the high-strength pressure vessel steel plate to satisfy the limiting relationship of 0.19≤Cu+7Sn≤0.29 while controlling the mass percentage of a single chemical element in the steel. The purpose of controlling 0.19≤Cu+7Sn≤0.29 is to prevent the continuous casting billet from being at about 960-1100°C. In the presence of Sn, the Cu in the steel will reduce the melting point of the Cu in the steel, avoid the formation of a low-melting-point enriched Cu liquid phase in the surface shell of the billet, and prevent the billet from being cracked at the corner and surface under the action of the continuous casting straightening stress.

[0048] In addition, the present invention can control the elements in the high-strength pressure vessel steel plate to satisfy the limiting relationship of 33≤Cu / 4Sn≤54 while controlling the mass percentage of a single chemical element. Controlling 33≤Cu / 4Sn≤54 is to limit the harmful effects of Sn element in the steel on grain boundary segregation and reducing grain boundary strength, so that the Cu element in the steel will not have a strong coupling adverse effect with Sn, ensuring that the Cu element plays a beneficial role in the steel alone.

[0049] In addition, the present invention can control the elements in the high-strength pressure vessel steel plate to satisfy the limiting relationship of Cu / Ni>1.6 while controlling the mass percentage of a single chemical element. Controlling the Cu and Ni elements to satisfy the limiting relationship of Cu / Ni>1.6 is to reduce the addition of the precious metal Ni while ensuring the low-temperature toughness of the steel plate; on the other hand, the addition of Ni to the steel will weaken the carbon dioxide corrosion resistance of the Cu added to the steel, so on the basis of adding Cu to the steel, the Ni content in the steel is limited, thereby ensuring that the carbon dioxide corrosion resistance of the Cu element in the steel remains unchanged or is enhanced.

[0050] Furthermore, in the high-strength steel plate for pressure vessels of the present invention, the mass percentage of each chemical element also satisfies at least one of the following items:

[0051] Alt: 0.017~0.037%;

[0052] V: 0.012~0.030%;

[0053] Nb: 0.019~0.040%;

[0054] Cu: 0.19~0.29%;

[0055] Cr: 0.9~1.4%;

[0056] Mo: 0.17~0.37%;

[0057] B: 0.0007~0.0013%.

[0058] Furthermore, in the high-strength steel plate for pressure vessels of the present invention, its microstructure is bainite or tempered bainite.

[0059] Furthermore, in the high-strength steel plate for pressure vessels of the present invention, its performance meets the following requirements: the yield strength of the steel plate is ≥560MPa, the tensile strength is ≥685MPa, and the transverse KV of the steel plate at -60°C is 2 ≥210J, elongation ≥18%, liquid carbon dioxide corrosion rate is 0.015~0.019mm / a, hardness value HV of all positions of steel plate is between 200~232; tensile strength of its welded joint is ≥700MPa, transverse -60℃KV 2 ≥130J, non-plastic transition temperature of welding heat affected zone ≤-75℃, liquid carbon dioxide corrosion rate is 0.015~0.020mm / a.

[0060] Furthermore, in the high-strength steel plate for pressure vessels of the present invention, the hardness thereof is: HV = exp[5.01 + 0.70Pcm + 0.0055V c ], where Pcm(%)=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B, V c is the cooling rate of the steel plate after rapid cooling after rolling, and each chemical element in the formula is substituted into the value before the mass percentage sign.

[0061] Correspondingly, another object of the present invention is to provide a method for manufacturing the high-strength pressure vessel steel plate of the present invention. The high-strength pressure vessel steel obtained by the manufacturing method has high strength and excellent resistance to liquid carbon dioxide corrosion, as well as good resistance to cold and hot cracks in welding, and also has good welding processability and welding performance.

[0062] In order to achieve the above object, the present invention provides a method for manufacturing the above high-strength steel plate for pressure vessels, which comprises the following steps:

[0063] (1) Smelting and casting;

[0064] (2) Hot charging and hot delivery of continuous casting billets + heating furnace: The high-temperature continuous casting billets are directly charged into the heating furnace at a charging temperature of 780-880°C, and the heating temperature in the heating furnace is controlled at 1105-1250°C, and the heating rate is 7.5-14 min / cm;

[0065] (3) rolling;

[0066] (4) Rapid cooling after rolling: Control the cooling rate to 20-45°C / s and the final cooling temperature to 290-380°C;

[0067] (5) Heat treatment.

[0068] Furthermore, in the manufacturing method of the present invention, in step (1), the dynamic soft reduction of the cast billet in the second cooling water zone of continuous casting is controlled to be 0.65-2.5% to obtain a ferrite grain size range of 110-210 μm for the continuous casting billet.

[0069] In the present invention, by accurately controlling the chemical components in the steel during the steel plate production process and controlling the secondary cooling water production stage of the continuous casting billet of the pressure vessel steel to meet the above-mentioned process parameters, the thermoplasticity of the surface and internal continuous casting billet can be guaranteed, thereby avoiding the production of defective continuous casting billets.

[0070] In the above technical scheme of the present invention, during the smelting and casting process of step (1), vanadium microalloying can be achieved through converter smelting, nitrogen blowing at the bottom of the ladle furnace to increase the temperature, and gas inclusions can be removed by vacuum, and the dynamic soft reduction of the continuous casting second cooling water zone in the casting process is controlled to be 0.65-2.5%, so as to control the ferrite grain size range of the continuous casting billet within the range of 110-210 μm.

[0071] Furthermore, in the manufacturing method of the present invention, in step (2), the heating rate is controlled to be 8 to 13 min / cm.

[0072] In the above step (2), the heating temperature is controlled between 1105 and 1250° C., which can not only save energy and reduce consumption, but also reduce the degree of austenite grain coarsening while ensuring sufficient re-austenitization of the ingot.

[0073] Furthermore, in the manufacturing method described in the present invention, in step (3), the starting temperature of rough rolling is controlled to be not less than 1000°C, and the surface temperature of the steel plate is controlled to be not more than 960°C during the rough rolling interval, the final rolling temperature is controlled to be not less than 800°C, and the cumulative reduction rate of the last three passes is controlled to be not less than 30%.

[0074] In the present invention, under the condition of reasonable distribution of pass reduction rate, it is ensured that the deformed austenite is recrystallized above the recrystallization temperature to ensure the grain refinement of the steel plate, and when the austenite transforms to ferrite, rapid cooling (the cooling rate of rapid cooling is controlled to be 20-45°C / s) is adopted to ensure the grain refinement of the martensite or bainite after the phase transformation, and under the effect of rapid cooling, the steel can form sufficient precipitates with appropriate sizes at the recrystallization temperature, thereby further refining the martensite or bainite grains.

[0075] It should be noted that after the rolling process in step (3), the rapid cooling controlled cooling process in step (4) has the effect of adjusting the size of the precipitated phase and improving the toughness of the material.

[0076] Furthermore, in the manufacturing method described in the present invention, in step (5), tempering heat treatment is performed, the tempering temperature is 600-650°C, and the holding time is (12-49)min+t×1min / mm, wherein t represents the plate thickness, and its unit parameter is mm.

[0077] In the present invention, the steel is subjected to a heat treatment process after rapid cooling after rolling. Appropriate heat treatment can eliminate the uneven deformation and internal stress of the formed steel plate generated during the hot forming process. As shown in the above technical solution, in some preferred embodiments, the heat treatment process can be specifically selected as a tempering heat treatment.

[0078] Compared with the prior art, the high-strength steel plate for pressure vessels resistant to liquid carbon dioxide corrosion and the manufacturing method thereof of the present invention have the following advantages and beneficial effects:

[0079] In the present invention, when high-strength pressure vessel steel is used in a service environment that resists liquid carbon dioxide corrosion cracking, in order to ensure that the resistance to liquid carbon dioxide corrosion cracking proceeds smoothly and that the shape and performance of the steel plate after welding and forming meet the use requirements at the same time, fine control can be made from the composition of the steel plate, the preparation process of the steel plate, parameter design, etc., so that this type of pressure vessel steel can achieve qualified manufacturing of finished products from factory production to downstream users and ultimately achieve the purpose of safe use of the product.

[0080] The pressure vessel made of the pressure vessel steel manufactured using the technical solution of the present invention can effectively meet the pressure vessel's requirements for high strength and lightweight, resistance to liquid carbon dioxide corrosion and cracking, and high parameterization of the steel, and can maintain the performance of the steel plate in the liquid carbon dioxide medium environment to be equivalent to that of the steel plate in its delivered state.

[0081] (1) The high-strength pressure vessel steel of the present invention adopts a low C-Mn-Cr-Mo-Cu alloy system. Through chemical composition design, a new type of steel is prepared using the low C-Mn-Cr-Mo-Cu alloy system, which can improve the hardenability and resistance to carbon dioxide stress corrosion cracking of the steel. This low C-Mn-Cr-Mo-Cu alloy system increases the electrode potential of the iron matrix through the Cr element and produces a passivation effect. The Cr element can effectively improve the steel material's resistance to carbon dioxide corrosion on the steel matrix surface and prevent wet liquid carbon dioxide media from contacting the iron matrix. The Mo element promotes surface passivation of the steel in a reducing wet carbonic acid environment. Cr and Mo work together to improve the steel's resistance to pitting corrosion.

[0082] In order to ensure the toughness of the steel plate and take into account the carbon dioxide corrosion resistance of the steel plate, the Cr and Mo in the steel must be maintained at a certain amount. After rapid cooling after rolling, the Cr and Mo elements make the steel have good hardenability, and after a suitable tempering process, the finished steel plate has the toughness required by the present invention. The Cu added to the steel further improves the electrode potential of the steel on the basis of the Cr-Mo alloy system and improves the steel's resistance to carbon dioxide pitting corrosion. However, if a certain amount of Sn appears in the steel, the Cu in the steel will form a low-melting copper-rich phase on the surface of the steel matrix, which will have a harmful effect on the metallurgical quality of the steel, such as cracks caused by the Cu low-melting phase on the surface of the steel plate, and Cu cannot effectively play the role of improving the electrode potential of the steel matrix; on the other hand, when Cu is added to the steel, when Ni is added, the steel's resistance to carbon dioxide corrosion will be reduced. Due to the addition of Ni, the electrode potential of the steel matrix will be reduced, accelerating the carbon dioxide corrosion of the steel. Cu and Ni in the steel can also improve the low-temperature toughness of the core of the steel plate on the premise of meeting the requirements of carbon dioxide corrosion.

[0083] Accordingly, in the design of chemical composition, the present invention also controls the content of Cr and Mo elements in the steel to further improve the carbon dioxide corrosion resistance and toughness of the steel, and reduce the adverse effect of uneven hardness of the steel plate on the carbon dioxide stress corrosion cracking resistance of the steel plate; at the same time, the present invention also reasonably controls the content of Cu and Sn to effectively reduce the reduction of the hot workability of the steel due to the formation of a low-melting-point Cu-rich phase on the surface of the steel when Cu and Sn exist at the same time, and ensure that the Cu in the steel plays the greatest role in the carbon dioxide corrosion resistance, and when Cu exists in the steel, the harmful effect of the coupling of Cu and Sn generated by the simultaneous appearance of Sn in the steel is reduced to a minimum, thereby improving the hot workability of the steel and improving the carbon dioxide corrosion resistance of the finished steel plate.

[0084] (2) The present invention obtains a high-strength pressure vessel steel plate with excellent comprehensive mechanical properties through comprehensive regulation of alloy composition and manufacturing process, with a yield strength of ≥560MPa, a tensile strength of ≥685MPa, and a transverse KV of -60°C. 2 ≥210J, elongation ≥18%, and hardness value HV of all positions of the steel plate is between 200 and 232. At the same time, the welded joint of the high-strength pressure vessel steel plate also has good mechanical properties, with tensile strength ≥700MPa, transverse -60℃ KV 2 ≥130J, no plastic transition temperature of welding heat affected zone ≤-75℃. In addition, the high-strength steel plate for pressure vessels and its corresponding welded joints have good carbon dioxide corrosion resistance. The carbon dioxide corrosion rate of the high-strength steel plate for pressure vessels is 0.015-0.019mm / a, and the liquid carbon dioxide corrosion rate of its welded joints is 0.015-0.020mm / a.

[0085] (3) In the present invention, by cooperating with the controlled rolling and controlled cooling process and the heat treatment process, the size of the martensite or bainite grains in the steel can be refined, and a steel plate with strong toughness, good resistance to welding cold and hot cracks, good resistance to liquid carbon dioxide stress corrosion cracking, and excellent welding processability and welding performance can be obtained. This high-strength pressure vessel steel plate with a tensile strength of 700MPa can be used to achieve the comprehensive requirements of large-scale, high-strength, thin and light-weight, and high-parameterization of spherical tanks or mobile containers, and has very important practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Figure 1 This is a metallographic structure photograph of the high-strength pressure vessel steel plate of Example 3. DETAILED DESCRIPTION

[0087] The high-strength steel plate for pressure vessels resistant to liquid carbon dioxide corrosion and the method for manufacturing the same described in the present invention will be further explained and illustrated below in conjunction with specific embodiments and the accompanying drawings of the specification. However, such explanation and illustration do not constitute an undue limitation on the technical solution of the present invention.

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

[0089] The high-strength steel plates for pressure vessels of Examples 1-8 of the present invention and the comparative steel plates of Comparative Examples 1-6 are prepared by the following steps:

[0090] (1) Smelting and casting are carried out according to the chemical compositions shown in Table 1-1 and Table 1-2: vanadium microalloying is achieved through converter smelting, nitrogen is blown from the bottom of the ladle to increase the temperature, and gas inclusions are removed by vacuum; during the casting process, the dynamic light reduction of the ingot in the second cooling water zone of continuous casting is controlled to be 0.65-2.5%, and the ferrite grain size of the obtained continuous casting ingot is in the range of 110-210 μm.

[0091] (2) Hot charging and hot delivery of continuous casting billets + heating furnace: The high-temperature continuous casting billets are directly charged into the heating furnace at a charging temperature of 780-880°C; the heating temperature in the heating furnace is controlled to be 1105-1250°C, and the heating rate is controlled to be 7.5-14 min / cm. In some preferred embodiments, the heating rate can be further controlled to be between 8-13 min / cm.

[0092] (3) Rolling: The starting rolling temperature of rough rolling is controlled to be no less than 1000°C, and the surface temperature of the steel plate is controlled to be no more than 960°C during the interval of rough rolling. The final rolling temperature of fine rolling is controlled to be no less than 800°C, and 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 20-45°C / s and the final cooling temperature to 290-380°C.

[0094] (5) Heat treatment: Tempering heat treatment is performed, the tempering temperature is controlled to be 600-650°C, and the holding time is controlled to be (12-49) min + t × 1 min / 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 of Examples 1-8 all meet the specification requirements of the present invention. Although the steps adopted by the comparative steel plates of Comparative Examples 1-6 are also prepared by the above steps (1)-(5), the chemical composition design and related processes of the comparative steel plates of Comparative Examples 1-6 all have parameters that do not meet the design requirements of the present invention.

[0096] Table 1-1 and Table 1-2 list the mass percentages of the chemical elements of 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%, the balance is Fe and other inevitable impurities except P, S and O)

[0098]

[0099]

[0100] Table 1-2.

[0101] serial number Cr / Mo Cu / Ni Cu+7Sn Cu / 4Sn Pc Example 1 5.76 1.9 0.20 33.93 0.211 Example 2 3.00 1.09 0.26 41.67 0.250 Example 3 5.00 2.00 0.21 50 0.249 Example 4 6.58 20 0.21 41.67 0.245 Example 5 6.00 2.88 0.24 52.27 0.252 Example 6 4.12 2.08 0.28 42.19 0.258 Example 7 4.33 2.55 0.29 53.85 0.233 Example 8 4.13 2.63 0.22 35 0.254 Comparative Example 1 5.76 1.9 0.30 3.17 0.208 Comparative Example 2 3 1.67 0.38 3.47 0.245 Comparative Example 3 5 2 0.28 4.17 0.246 Comparative Example 4 6.58 20 0.34 2.5 0.241 Comparative Example 5 6 2.88 0.41 2.3 0.249 Comparative Example 6 4.12 2.08 0.28 42.19 0.253

[0102] Note: In the above table, in the two relationship formulas of Cr / Mo, Cu+7Sn, Cu / 4Sn and Cu / Ni, the elements in the formula are substituted by the numerical values ​​before the percentage sign of the mass percentage content of the element; Pcm(%)=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B, and each chemical element in the calculation formula is substituted by the numerical value before the percentage sign of the mass percentage content.

[0103] Table 2-1 and Table 2-2 list the specific process parameters of the high-strength steel plates for pressure vessels 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] The high-strength pressure vessel steel plates of the finished products of Examples 1-8 and the comparative steel plates of Comparative Examples 1-6 obtained through the above process steps were sampled respectively, observed and analyzed, and mechanical properties were tested, and the obtained observation results and mechanical properties 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 “Tensile test of metallic materials - Part 1: Room temperature test method” to obtain the yield strength, tensile strength and elongation of the steel plates of each embodiment and comparative example.

[0112] (2) Impact performance test: The lateral impact performance KV of the steel plates of each embodiment and comparative example was tested according to GB / T 229 "Charpy pendulum impact test method for metallic materials" 2 The test results are shown in Table 3.

[0113] Accordingly, in each embodiment and comparative example of the present invention, the reference standard for judging the metallographic structure in steel is GBT13298 “Methods for Examination of Metal Microstructure”.

[0114] The reference standard for judging the Vickers hardness HV in steel is GB T 4340.1 "Metallic materials. Vickers hardness test. Part 1 test method", HV = exp[5.01 + 0.70Pcm + 0.0055V c ], where Pcm(%)=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B, V c is the cooling rate of rapid cooling after rolling, and each chemical element in the formula is substituted into the value before the mass percentage sign.

[0115] 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 the above two factors, the hardness of the finished steel plate can be effectively controlled within the range required by the present invention. The above HV formula mainly shows that HV is limited to a certain range by adjusting the parameters of the composition control and the cooling rate after rolling.

[0116] Table 3 lists the observation results and mechanical property test results of the high-strength steel plates for pressure vessels of Examples 1-8 and the comparative steel plates of Comparative Examples 1-6.

[0117] Table 3.

[0118]

[0119]

[0120] Through the observation of the microstructure of the high-strength steel plates for pressure vessels of the finished products of Examples 1-8, it can be known that the matrix of the microstructure of the high-strength steel plates for pressure vessels of Examples 1-8 can be specifically bainite or tempered bainite.

[0121] As shown in Table 3, compared with the comparative steel plates of Comparative Examples 1-6, the comprehensive mechanical properties of the high-strength steel plates for pressure vessels of Examples 1-8 of the present case are more excellent, especially the transverse -60°C impact energy KV of the high-strength steel plates for pressure vessels of Examples 1-8 of the present case. 2 It is much larger than the comparative steels of comparative examples 1-6 and has very excellent low temperature toughness.

[0122] In the present invention, the yield strength of the high-strength steel plates for pressure vessels of the above-mentioned embodiments 1-8 is between 568-680 MPa, the tensile strength is between 706-794 MPa, and the transverse -60°C impact energy KV 2 Between 253-313J, the elongation is between 18-21%, and the hardness value HV of all positions of the steel plate is between 201-231.

[0123] Accordingly, in order to illustrate that the high-strength steel plates for pressure vessels 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 steel plates for pressure vessels of Examples 1-8 and the comparative steel plates of Comparative Examples 1-6, and tested the performance of the welded joints after welding. The relevant test results are listed in Table 4 below.

[0124] The relevant welding process test conditions are as follows: the welding line energy is controlled to be 18-45 kJ / cm, and the time t for the temperature of the welding pool to drop from 800 degrees to 500 degrees is 8 / 5 The cooling time is controlled within the range of 15 to 48 seconds.

[0125] In the present invention, the tensile strength performance test of the welded joints of the steel plates of Examples 1-8 and Comparative Examples 1-6 was conducted using GB / T228.1 "Metallic Material Tensile Test Part 1: Room Temperature Test Method", and the impact energy KV of the welded joints at -60°C was 2 The indicators are measured using GB / T 229 "Charpy pendulum impact test method for metallic materials", and the non-plastic transition temperature (NDTT) test of the welding heat affected zone is tested using GB / T6803 "Drop hammer test method for non-plastic transition temperature of ferritic steel".

[0126] Table 4 lists the mechanical properties of the welded joints of the high-strength steel plates for pressure vessels of Examples 1-8 and the comparative steel plates of Comparative Examples 1-6.

[0127] Table 4.

[0128]

[0129] Therefore, it can be seen from the above Table 3 and Table 4 that the comprehensive performance of the high-strength steel plates for pressure vessels of Examples 1-8 and their corresponding welded joints is significantly better than that of the comparative steel plates of Comparative Examples 1-6. The high-strength steel plates for pressure vessels of Examples 1-8 of the present invention not only have excellent comprehensive mechanical properties and resistance to cold and hot cracks in welding, but also have good welding processability and good welding performance.

[0130] As shown in Table 4, in the present invention, the welded joints corresponding to the high-strength pressure vessel steel plates of Examples 1-8 all have excellent mechanical properties, and the tensile strength of the corresponding welded joints is between 715-765 MPa, and the transverse impact energy KV of the welded joints at -60°C is 2 Between 135-183J, the non-plastic transition temperature of the welding heat affected zone is between -80 and -75℃.

[0131] In addition, in order to further illustrate that the high-strength steel plates for pressure vessels of Examples 1-8 of the present invention have good resistance to liquid carbon dioxide corrosion, it is necessary to conduct liquid carbon dioxide corrosion resistance tests on the steel plates of Examples 1-8 of the present invention and Comparative Examples 1-6 and their corresponding welded joints, respectively, and the results of the corrosion tests are listed in the following Table 6.

[0132] In the present invention, the liquid carbon dioxide corrosion resistance test standards of the steel plates and welded joints of Examples 1-8 and Comparative Examples 1-6 are: ISO 11945 "Corrosion of metals and alloys - General principles for corrosion testing" and ISO 9224 "Corrosion of metals and alloys - Corrosivity of climates - Guidance values ​​for corrosivity classification" and NACERP-0775-91 standard on CO 2 Provisions for the degree of corrosion.

[0133] Table 5 lists various test parameters of the steel plates of Examples 1-8 and Comparative Examples 1-6 and their corresponding welded joints in the liquid carbon dioxide corrosion resistance test.

[0134] Table 5.

[0135] Inspection Standards ISO 11945 Experimental temperature 35℃ Total gas pressure 3.8MPa CO2 partial pressure 1.5MPa Flow rate Dynamic 1.5m / s Test cycle 438 hours (about 2.6 weeks) Test solution 98% (wt,%) liquid carbon dioxide + 2% water (wt,%) pH 3.0

[0136] Table 6 lists the liquid carbon dioxide corrosion resistance test results of the steel plates of Examples 1-8 and Comparative Examples 1-6 and their corresponding welded joints.

[0137] Table 6.

[0138]

[0139] It can be seen from Table 6 that, compared with Comparative Examples 1-6, the steel plates of Examples 1-8 and their corresponding welded joints have lower corrosion rates and better resistance to liquid carbon dioxide corrosion. In the present invention, the liquid carbon dioxide corrosion rates of the high-strength pressure vessel steel plates of Examples 1-8 are between 0.015-0.019 mm / a, and the liquid carbon dioxide corrosion rates of the welded joints corresponding to the steel plates of Examples 1-8 are between 0.016-0.018 mm / a.

[0140] From the above, it can be seen that the high-strength pressure vessel steel with a tensile strength of 700 MPa manufactured using the technical solution of the present invention can meet the requirements of high strength and toughness and resistance to carbon dioxide corrosion. The steel has high production efficiency, low production energy consumption, and has low-carbon and environmentally friendly characteristics with corrosion resistance.

[0141] Figure 1 This is a metallographic structure photograph of the high-strength pressure vessel steel plate of Example 3.

[0142] 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 the prior austenite grain size thereof is level 8.

[0143] It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0144] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

Claims

1. A high-strength steel for pressure vessels resistant to liquid carbon dioxide corrosion, comprising Fe and unavoidable impurity elements, It is characterized in that It also contains the following chemical elements in the following mass percentages: C: 0.067-0.085%, Si: 0.15-0.45%, Mn: 0.95-1.38%, Alt: 0.015-0.045%, Cu: 0.18-0.30%, Cr: 0.80-1.45%, Mo: 0.15-0.39%, 0<Sn≤0.0016%, 0<Ni<0.25%, and at least one of V, B and Nb in the following contents: Nb: 0.018-0.045%, 0<V≤0.035%, B: 0.0006-0.0015%; The hardness of the high-strength pressure vessel steel is: HV=exp[5.01+0.70Pcm+0.0055V c ],in Pcm(%)=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B, V c For steel plate The cooling rate of rapid cooling after rolling, where each chemical element in the formula is substituted into the value before the mass percentage sign.

2. The high-strength pressure vessel steel according to claim 1, It is characterized in that The mass percentage of each chemical element is: C: 0.067-0.085%, Si: 0.15-0.45%, Mn: 0.95-1.38%, Alt: 0.015-0.045%, Cu: 0.18-0.30%, Cr: 0.80-1.45%, Mo: 0.15-0.39%, 0<Sn≤0.0016%, 0<Ni<0.25%, and at least one of V, B and Nb in the following contents: Nb: 0.018-0.045%, 0<V≤0.035%, B: 0.0006-0.0015%; The balance is Fe and inevitable impurity elements.

3. The high-strength pressure vessel steel according to claim 1 or 2, It is characterized in that Among the inevitable impurity elements, the content of each impurity element satisfies at least one of the following conditions: P≤0.012%, S≤0.003%, O≤0.0017%.

4. The high-strength pressure vessel steel according to claim 1 or 2, It is characterized in that Each chemical element satisfies at least one of the following formulas: 3≤Cr / Mo≤7; 0.19≤Cu+7Sn≤0.29; 33≤Cu / 4Sn≤54; Cu / Ni>1.6; In the formula, substitute the numerical value before the mass percentage sign of each chemical element.

5. The high-strength pressure vessel steel according to claim 1 or 2, It is characterized in that The mass percentage of each chemical element also satisfies at least one of the following: Alt: 0.017~0.037%; V：0.012～0.030％； Nb: 0.019~0.040%; Cu: 0.19~0.29%; Cr：0.9～1.4％； Mo: 0.17~0.37%; B：0.0007～0.0013％。 6. The high-strength pressure vessel steel according to claim 1 or 2, It is characterized in that Its microstructure is bainite or tempered bainite.

7. The high-strength pressure vessel steel according to claim 1 or 2, It is characterized in that Its performance meets the following requirements: the yield strength of the steel plate is ≥560MPa, the tensile strength is ≥685MPa, and the transverse KV of the steel plate is -60℃ 2 ≥210J, elongation ≥18%, liquid carbon dioxide corrosion rate is 0.015~0.019mm / a, and the hardness value HV of all positions of the steel plate is between 200~232; the tensile strength of its welded joint is ≥700MPa, transverse -60℃KV 2 ≥130J, non-plastic transition temperature of welding heat affected zone ≤-75℃, liquid carbon dioxide corrosion rate is 0.015~0.020mm / a.

8. A method for producing a high-strength pressure vessel steel according to any one of claims 1 to 7, It is characterized in that It includes the steps of: (1) Smelting and casting; (2) Hot charging and hot delivery of continuous casting billets + heating furnace: The high-temperature continuous casting billets are directly charged into the heating furnace at a charging temperature of 780-880°C, and the heating temperature in the heating furnace is controlled at 1105-1250°C, and the heating rate is 7.5-14 min / cm; (3) rolling; (4) Rapid cooling after rolling: Control the cooling rate to 20-45°C / s and the final cooling temperature to 290-380°C; (5) Heat treatment.

9. The manufacturing method according to claim 8, It is characterized in that In step (1), the dynamic soft reduction of the cast slab in the secondary cooling water zone of continuous casting is controlled to be 0.65-2.5% to obtain a ferrite grain size range of 110-210 μm for the cast slab.

10. The manufacturing method according to claim 8, It is characterized in that In step (2), the heating rate is controlled to be 8 to 13 min / cm.

11. The manufacturing method according to claim 8, It is characterized in that In step (3), the starting temperature of rough rolling is controlled not lower than 1000°C, and the surface temperature of the steel plate is controlled not higher than 960°C during the interval of rough rolling, the final rolling temperature is controlled not lower than 800°C, and the cumulative reduction rate of the last three passes is controlled not lower than 30%.

12. The manufacturing method according to claim 8, It is characterized in that In step (5), tempering heat treatment is performed, the tempering temperature is 600-650°C, and the holding time is (12-49) min+t×1 min / mm, where t represents the plate thickness, and its unit parameter is mm.

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