CN116815042A - Steel sheet for high-strength pressure vessel resistant to hydrogen sulfide corrosion cracking and method for producing same - Google Patents

Abstract

The invention discloses a steel plate for high-strength pressure vessels that is resistant to hydrogen sulfide corrosion and cracking. In addition to Fe and inevitable impurity elements, it also contains the following chemical elements in the following mass percentages: C: 0.07-0.12%, Si: 0.25～0.45%, Mn: 0.90～1.30%, Alt: 0.020～0.045%, Ni: 0.18～0.35%, Cr: 0.18～0.30%, Mo: 0.30～0.45%, Nb: 0.020～0.050%, 0 <V≤0.030%, Cu: 0.10～0.20%, Ti: 0.008～0.020%, B: 0.0008～0.0018%. Correspondingly, the present invention also discloses a method for manufacturing the above-mentioned high-strength pressure vessel steel, which includes the steps: (1) smelting and casting; (2) heating; (3) rolling; (4) rapid cooling: controlling the cooling rate The temperature is 15~45℃/s, and the final cooling temperature is 280~350℃; (5) Heat treatment. The steel for pressure vessels manufactured using the technical solution of the present invention can meet the requirements of high strength, lightweight and high parameterization. The steel plates and welded joints have excellent hydrogen sulfide corrosion performance and no cracks or cracks will occur in the hydrogen sulfide corrosion environment.

Description

High-strength steel plate for pressure vessels resistant to hydrogen sulfide corrosion cracking and method for manufacturing the same

Technical Field

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

In recent years, with the rapid development of industrial production, pressure vessels are increasingly used in various industries. Currently, traditional pressure vessels such as large fixed spherical storage tanks and mobile pressure vessels are usually made of high-strength pressure vessel steel. These pressure vessels are often used to contain some special corrosive substances and are susceptible to corrosion, especially when subjected to force and then corroded, which will cause cracks in the pressure vessel steel. This crack is called stress corrosion cracking (SCC).

At present, in actual use, the most representative medium that can cause cracks in steel is hydrogen sulfide (H ₂ S). The cracks caused by hydrogen sulfide (H ₂ S) are stress corrosion cracks, which are common in equipment for transporting liquefied petroleum gas (LPG).

Research has found that the higher the strength of steel, the easier it is to crack under the action of hydrogen sulfide (H ₂ S). Therefore, currently, there is an urgent need to obtain a pressure vessel steel with high strength and good resistance to hydrogen sulfide corrosion cracking.

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 hydrogen sulfide stress corrosion problem of steel plates and welded joints. To this end, the present invention aims to provide a new high-strength pressure vessel steel plate with excellent resistance to hydrogen sulfide corrosion cracking and a method for manufacturing the same.

In the prior art, although steel plates with hydrogen sulfide stress corrosion resistance already exist, they still cannot meet the performance requirements of specific strength and manufacturing process parameters and are still lacking in performance.

For example, a Chinese patent document with publication number CN106636971A, publication date May 10, 2017, and titled “A 690MPa-grade hydrogen sulfide corrosion resistant steel plate and a production method thereof” discloses a 690MPa-grade hydrogen sulfide corrosion resistant steel plate and a production method thereof, which adopts a design concept of medium-high C and Nb-V-Ti microalloying. However, the chemical composition designed in this scheme will make the strength or hardness of the finished steel plate too high, and it is very easy to crack in a hydrogen sulfide stress corrosion environment, and the safe service performance of the material cannot be guaranteed.

Another example: the Chinese patent document with publication number CN103938092A, publication date July 23, 2014, and titled "A high fatigue strength hot-formed heavy-duty truck bridge shell steel plate and its manufacturing method" discloses a high fatigue strength hot-formed heavy-duty truck bridge shell steel plate, which adopts the design of low C and Nb-Ti alloy, and the steel plate is directly quenched and tempered after hot rolling. However, the strength and performance parameters of the steel plate produced by this scheme are still far from those of the present invention, and it cannot meet the service environment and service performance requirements of the present invention.

Another example: the Chinese patent document with publication number CN106834940A, publication date June 13, 2017, and titled "Hydrogen sulfide corrosion resistant low alloy high strength steel plate for pressure vessels and production method", discloses a hydrogen sulfide corrosion resistant low alloy high strength steel plate for pressure vessels and a production method. The technical solution adopts a Cr-Mo alloy system, and its supply state is quenched + tempered. However, the strength and performance parameters of this steel plate are still far from the present invention, and it cannot meet the service environment and service performance requirements of the present invention.

Summary of the invention

One of the purposes of the present invention is to provide a high-strength steel plate for pressure vessels that is resistant to hydrogen sulfide corrosion cracking. The high-strength steel plate for pressure vessels is a steel plate using a low C-Mn-Cr-Mo-V-Nb alloy system. By accurately controlling the chemical components in the steel during the production process of the steel plate, good comprehensive mechanical properties can be obtained. The steel plate for pressure vessels not only has good strength and toughness, resistance to cold and hot cracking in welding, and excellent resistance to hydrogen sulfide stress corrosion cracking, but also has good welding processability and welding performance. It can be used to prepare pressure vessels and can meet the comprehensive requirements of large-scale, high-strength, thin, light, and high-parameterization of spherical tanks or mobile containers.

In order to achieve the above object, the present invention provides a high-strength steel plate for pressure vessels resistant to hydrogen sulfide corrosion cracking, which contains Fe and inevitable impurity elements, and further contains the following chemical elements in the following mass percentages:

C: 0.07～0.12%, Si: 0.25～0.45%, Mn: 0.90～1.30%, Alt: 0.020～0.045%, Ni: 0.18～0.35%, Cr: 0.18～0.30%, Mo: 0.30～0.45%, Nb : 0.020～0.050%, 0<V≤0.030%, Cu: 0.10～0.20%, Ti: 0.008～0.020%, B: 0.0008～0.0018%.

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

C: 0.07～0.12%, Si: 0.25～0.45%, Mn: 0.90～1.30%, Alt: 0.020～0.045%, Ni: 0.18～0.35%, Cr: 0.18～0.30%, Mo: 0.30～0.45%, Nb: 0.020～0.050%, 0＜V≤0.030%, Cu: 0.10～0.20%, Ti: 0.008～0.020%, B: 0.0008～0.0018%; the balance is Fe and unavoidable impurity elements.

In the above technical scheme of the present invention, the present invention adopts a low C-Mn-Cr-Mo-V-Nb alloy system. Through reasonable chemical composition design, a new steel grade is designed by adopting the V-Nb alloy system. On the one hand, the strength and toughness of the VC precipitation phase are utilized to improve the grain refinement and precipitation strengthening effects of the V microalloy. On the other hand, the present invention also adds an appropriate amount of Nb. Nb can be combined with C to form NbC precipitates. The NbC precipitation phase can further refine the grains, improve the low-temperature fracture toughness of the steel and reduce the ductile-brittle transition temperature.

At the same time, when designing the chemical composition, the present invention also strictly controls the content of elements such as Alt, O, Mn, and Ni in the steel to prevent the single or combined effects of these elements from damaging the toughness of the steel. Because these elements will produce segregation in the continuous casting cooling process, especially in the process of cooling the steel from high temperature to low temperature (from 980°C to 700°C), the segregation effect of the continuous casting billet during the cooling from solidification to low temperature and rolling to obtain the finished steel plate is further strengthened, and when serving in a hydrogen sulfide stress corrosion environment, it causes a high probability of stress corrosion cracking of the steel plate.

In the high-strength steel plate for pressure vessels of the present invention, the design principles of the chemical elements are as follows:

C: In the high-strength steel plate for pressure vessels described in the present invention, C is one of the indispensable elements in steel for improving the strength of steel. As the C content in steel increases, Fe ₃ C in the steel increases, the hardenability will also increase, the yield strength and tensile strength of the steel will increase, and the elongation notch impact toughness will decrease. Among them, for every 0.1% increase in the C content in steel, the tensile strength increases by about 90MPa, and the yield strength increases by about 40-50MPa. However, it should be noted that the C content in steel should not be too high. As the C 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 heat affected zone of the weld, which will aggravate the tendency of cold cracking during welding. When serving in a hydrogen sulfide stress corrosion environment, the steel plate and the welded joint will become weak parts of stress corrosion cracking. Therefore, considering the influence of element C on the performance of pressure vessel steel, in the high-strength pressure vessel steel plate described in the present invention, the mass percentage of element C is controlled between 0.07 and 0.12%. This not only ensures that the strength stability of the steel is within an appropriate range, but also is suitable for production operations, thereby improving its applicability and feasibility in industrial production.

Si: In the high-strength steel plate for pressure vessels described in the present invention, the Si element can reduce the graphitization tendency of carbon in the steel and improve the strength of the steel in the form of solid solution strengthening. When the Si content increases from 0.25% to 0.45%, 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, _SiO2 inclusions are easily formed in the steelmaking process. Therefore, in the high-strength steel plate for pressure vessels described in the present invention, the mass percentage of the Si element is controlled between 0.25 and 0.45%.

Mn: In the high-strength steel plate for pressure vessels described in the present invention, the Mn element has a significant effect on improving the strength of low-carbon and medium-carbon pearlite steels. Adding 1% of Mn element to steel can increase the tensile strength of the 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 the 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 the steel, the Mn element content must be strictly controlled. In the present invention, the mass percentage of the Mn element is controlled between 0.90 and 1.30%. In this way, it can ensure that the steel obtains a suitable tensile strength, and the low-temperature impact toughness and elongation of the steel can be preserved.

Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the Mn element can also be preferably controlled between 0.92% and 1.27%.

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 needs to be controlled within 0.045%; in the later stage of refining, the oxygen in the steel has been controlled to a low level. 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 800-950°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 0.020 and 0.045%.

Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of Alt can also be preferably controlled between 0.020 and 0.032%.

Ni: In the high-strength steel plate for pressure vessels described in the present invention, Ni has a certain strengthening effect. Adding 1.00% of 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, it will cause segregation of the Ni element in the steel plate. Therefore, in the high-strength steel plate for pressure vessels described in the present invention, the mass percentage of the Ni element is controlled between 0.18 and 0.35%.

Cr: In the high-strength steel plate for pressure vessels described in the present invention, Cr is not only an element that reduces the austenite zone, but also a medium-strength carbide-forming element. It can form carbides in steel and can be dissolved in ferrite. At the same time, Cr is also an effective element for improving the hardenability of steel. In the case of Cu-Cr-Ni composite addition, the addition of Cr will also increase the cold crack sensitivity of steel welding. Therefore, in the present invention, the mass percentage of Cr is controlled between 0.18 and 0.30%. In this way, it can ensure that the steel obtains appropriate tensile strength without damaging the low-temperature impact toughness and elongation of the steel.

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 0.2% and 0.29%.

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 creep strength of the steel. Its ability to improve the high-temperature creep 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 enhance the hydrogen corrosion resistance of steel. 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 0.30 and 0.45%.

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 0.32% and 0.43%.

Nb: In the high-strength steel plate for pressure vessels described in the present invention, the Nb element 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, and ensure that a relatively fine heat-affected zone structure is obtained after welding 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 0.020 and 0.050%.

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 0.035% and 0.045%.

V: In the high-strength steel plate for pressure vessels described in the present invention, V is a strong carbonitride-forming element, which can refine the grains by forming carbides to prevent the growth of austenite grains, thereby improving the room temperature and high temperature strength of the steel. It should be noted that although the addition of V element to steel can greatly improve the strength of the steel, the V content in the steel should not be too high. When the V 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. In addition, the addition of V element to steel will cause the cementite Fe ₃ C regular lamellae and pearlite clusters in the steel to be blocked by the carbonitride precipitates of V. Therefore, taking into account 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≤0.030%.

Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the V element can also be controlled between 0.005 and 0.02%.

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 cause network cracks 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 0.10 and 0.20%.

Ti: In the high-strength steel plate for pressure vessels described in the present invention, Ti is a strong carbide and nitride forming element, which can significantly improve the room temperature strength and high temperature strength of steel. Since Ti can also refine the grains, it can also improve the toughness of steel. Adding an appropriate amount of Ti to the steel can effectively improve the toughness of the weld metal, but excessive Ti (Ti>0.020%) will form inclusions in the steel. Therefore, in the low-alloy high-strength steel of the present invention, it is more appropriate to add 0.008-0.020% Ti from the perspective of improving the toughness of the weld metal. The second phase particles TiN, Ti (CN) and the like formed by Ti are used to prevent the grain growth of the coarse grain zone in the welding heat affected zone, ensuring that the weld joint has good low-temperature toughness. Therefore, in the present invention, the mass percentage of the Ti element is controlled between 0.008 and 0.020% to ensure that the steel has a suitable tensile strength without damaging the low-temperature impact toughness of the steel.

Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the Ti element can also be controlled between 0.008% and 0.017%.

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 necessary 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. Based on this, in the high-strength pressure vessel steel described in the present invention, the mass percentage of B element is controlled between 0.0008 and 0.0018%.

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 0.0008% and 0.0015%.

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≤0.015%, S≤0.005%, O≤0.0018%.

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≤0.015%, the content of S element is controlled to be S≤0.005%, and the content of O element is controlled to be O≤0.0018%.

Of course, in some preferred embodiments, in order to obtain better implementation effects, in actual implementation, the mass percentage of P in the above steel can be specifically limited to 0.008-0.013%. Among them, the P content in the steel is controlled to be not less than 0.008%, which is to ensure the operability of the steel of the present invention in the steelmaking process control link, which comprehensively considers the process cost and steel plate performance.

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:

17≤Alt/O≤70;

9≤(Mn+Ni)/C≤22;

0.009≤200Mo/Cr×Nb×B≤0.022; the elements in the formula are substituted into the values before the percentage sign of the mass percentage content of the element.

In the above technical solution of the present invention, while controlling the mass percentage of a single chemical element in steel, the present invention can also control the elements in the steel to satisfy the limiting relationship of 17≤Alt/O≤70, wherein the above elements are all substituted into the numerical values before the percentage sign of the mass percentage of the element. In this limiting relationship, controlling Alt/O to be greater than 17 is to ensure that the Alt added to the steel is the minimum content, and to ensure that the inclusions formed by Alt and O in the steel are reduced to the minimum value; and controlling Alt/O to be less than 70 is to ensure that the Alt added to the steel can effectively reduce the content of O in the steel, avoid the formation of oxide inclusions and clustering between O and other elements in the steel, and the harmful effects on the performance of the steel, and improve the metallurgical quality and low temperature impact resistance of the steel.

Accordingly, the present invention can control the elements in the steel plate for pressure vessels to satisfy the limiting relationship of 9≤(Mn+Ni)/C≤22 while controlling the mass percentage of a single chemical element in the steel, wherein the elements are substituted into the numerical values before the percentage sign of the mass percentage of the element. In this limiting relationship, controlling (Mn+Ni)/C to be greater than 9 not only ensures the minimum addition amount of Mn and Ni in the steel, but also enables C to exert a better solid solution strengthening effect and minimize the segregation degree in the steel; and controlling (Mn+Ni)/C to be less than 22 can ensure that the Mn and Ni added in the steel do not form severe center segregation in the continuous casting billet and the finished steel plate, thereby further improving the metallurgical quality and hydrogen sulfide stress corrosion cracking resistance of the steel.

In addition, while controlling the mass percentage of a single chemical element, the present invention can also control the elements in the steel plate for pressure vessels to satisfy the limiting relationship of 0.009≤200Mo/Cr×Nb×B≤0.022, where the elements are substituted into the numerical values before the percentage sign of the mass percentage of the element. In this limiting relationship, controlling 200Mo/Cr×Nb×B to be greater than 0.009 can ensure that the steel reaches the predetermined hardenability and strength in the rapid cooling or quenching heat treatment process, and minimize the segregation in the steel; and controlling 200Mo/Cr×Nb×B to be less than 0.022 can ensure that the finished steel obtains a higher hardenability, thereby further improving the metallurgical quality and hydrogen sulfide stress corrosion cracking resistance of the steel.

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:

Mn: 0.92～1.27%;

Alt: 0.020～0.032％;

V: 0.005～0.02％;

Nb: 0.035～0.045%;

Cr: 0.2～0.29%;

Mo: 0.32～0.43%;

Ti: 0.008～0.017%;

B: 0.0008～0.0015%.

Furthermore, in the high-strength steel plate for pressure vessels of the present invention, its microstructure is tempered troostite.

Furthermore, in the high-strength steel plate for pressure vessels described in the present invention, the original austenite grain size is greater than grade 9.

Furthermore, in the high-strength steel plate for pressure vessels of the present invention, the properties thereof meet the following requirements: yield strength ≥ 760 MPa, hardness value HV at all positions of the steel plate is 225-245, and KV ₂ ≥ 185 J at -60°C transverse direction of the steel plate.

Further, in the high-strength steel plate for pressure vessels of the present invention, the hardness value range of the welded joint of the steel plate is: CRHV=exp[(-1627.25)+29547.3×Pcm-200254.7×Pcm ² +602441.1×Pcm ³ -678806.1×Pcm ⁴ ], wherein Pcm(%)=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B, and each chemical element in the above calculation formula is substituted into the value before the percentage sign of the mass percentage content.

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 good resistance to cold and hot cracks in welding, as well as good welding processability and good welding performance.

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 steps of:

(1) Smelting and casting;

(2) Heating;

(3) rolling;

(4) Rapid cooling: Control the cooling rate to 15-45°C/s and the final cooling temperature to 280-350°C;

(5) Heat treatment.

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 0.6-2.5% to obtain a ferrite grain size range of 110-225 μm for the cast billet.

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.

In the above technical solution of the present invention, during the smelting and casting process of step (1), vanadium-niobium microalloying can be achieved by converter smelting, followed by ladle furnace deep desulfurization, and then gas inclusions are removed by vacuum, and the dynamic light reduction of the cast billet in the continuous casting secondary cooling water zone is controlled to be 0.6-2.5%, so as to control the ferrite grain size range of the continuous casting billet within the range of 110-225 μm. This operation can not only ensure the stable formation of the continuous casting surface shell of the continuous casting billet, but also can further reduce the central segregation and looseness of the continuous casting billet through a certain reduction, improve the homogeneity and density of the continuous casting billet, and thus improve the metallurgical quality of the continuous casting billet.

Furthermore, in the manufacturing method of the present invention, in step (2), the heating temperature is controlled to be 1156-1275° C.; and/or the heating rate is controlled to be 8-13 min/cm.

In the above step (2), the heating temperature is controlled between 1156 and 1275° C., which can not only achieve energy saving and consumption reduction, but also reduce the degree of austenite grain coarsening while ensuring sufficient re-austenitization of the ingot.

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, the starting temperature of finishing rolling is controlled to be not less than 960°C, the final rolling temperature of finishing rolling is controlled to be 800-940°C, and the cumulative reduction rate of the last three passes is controlled to be not less than 30%.

In the above step (3), the recrystallization controlled rolling technology can be used for rolling, that is, the finishing rolling start temperature is controlled to be not less than 960°C to fully reduce the rolling force. The finishing rolling final temperature is controlled within the range of 800-940°C to avoid edge cracks at the edge of the steel plate.

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 15-45°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.

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.

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 (15-50)min+t×1min/mm, wherein t represents the plate thickness, and its unit parameter is mm.

In the present invention, the steel is subjected to a heat treatment process after rapid cooling after rolling, and 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.

The high-strength steel plate for pressure vessels and the manufacturing method thereof of the present invention have the following advantages and beneficial effects compared with the prior art:

In the present invention, when high-strength pressure vessel steel is used in a service environment resistant to hydrogen sulfide stress corrosion cracking, in order to ensure that the resistance to hydrogen sulfide stress 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.

The pressure vessel steel manufactured using the technical solution of the present invention can effectively meet the requirements of spherical tanks or mobile containers for high strength and lightweight, resistance to hydrogen sulfide stress corrosion cracking and high parameterization of steel. It has good uniform hardness performance in the process of manufacturing the container, and can keep the performance of the steel plate during processing and forming equivalent to that of the steel plate in its delivered state.

(1) The high-strength pressure vessel steel of the present invention adopts a low C-Mn-Cr-Mo-V-Nb alloy system. Through chemical composition design, a new type of steel is prepared using the V-Nb alloy system, which can improve the low-temperature fracture toughness of the steel and reduce the ductile-brittle transition temperature. The design of this V-Nb alloy system can not only achieve the effect of precipitation strengthening and refinement of martensite or bainite grains by the carbonitrides of V and Nb precipitated during the cooling process of the steel plate after rolling, but also play a role in inhibiting the growth of austenite grains in a suitable welding process, and continue to play its precipitation strengthening role during the heat treatment of the finished product.

Accordingly, in the design of chemical composition, the present invention also controls the content of Al and O elements in the steel to further improve the toughness of the steel and avoid causing hot brittleness of the steel and cracking of the steel plate during rolling; at the same time, the present invention also reasonably controls the content of Mn, Ni and C to effectively reduce the adverse effects of Mn, Ni segregation and C hardenability on the steel plate's resistance to hydrogen sulfide stress corrosion cracking. In addition, the present invention also reasonably controls the content of Cr, Mo, B and Nb, which can effectively reduce the contradiction between the hardenability and toughness of the steel plate and reduce the adverse effects of uneven hardness of the steel plate on the steel plate's resistance to hydrogen sulfide stress corrosion cracking.

(2) The present invention obtains a high-strength steel plate for pressure vessels with excellent comprehensive mechanical properties through comprehensive regulation of alloy composition and manufacturing process, wherein the yield strength is ≥760MPa, the hardness value HV of all positions of the steel plate is 225-245, and the transverse KV ₂ of the steel plate at -60°C is ≥185J. At the same time, the hardness value range of the welded joint of the high-strength steel plate for pressure vessels is: CRHV=exp[(-1627.25)+29547.3×Pcm-200254.7×Pcm ² +602441.1×Pcm ³ -678806.1×Pcm ⁴ ], wherein Pcm(%)=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B, and each chemical element in the above calculation formula is substituted into the value before the percentage sign of the mass percentage content.

Correspondingly, 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 good strength and toughness, resistance to welding cold and hot cracks, resistance to hydrogen sulfide stress corrosion cracking, and excellent welding processability and welding performance can be obtained. This high-strength steel plate for pressure vessels 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

FIG. 1 is a metallographic photograph of a high-strength pressure vessel steel plate of Example 3.

DETAILED DESCRIPTION

The high-strength steel plate for pressure vessels and the method for manufacturing the same according to 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 improper limitation on the technical solution of the present invention.

Examples 1-8 and Comparative Examples 1-5

The high-strength steel plates for pressure vessels of Examples 1-8 of the present invention and the comparative steel plates of Comparative Examples 1-5 are prepared by the following steps:

(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, gas inclusions are removed by vacuum and the nitrogen content in the steel is controlled to achieve vanadium-nitrogen microalloying. During the casting process, the dynamic light reduction of the continuous casting second cooling water zone ingot is controlled to be 0.6-2.5%, and the ferrite grain size of the obtained continuous casting ingot is in the range of 110-225 μm.

(2) Heating: Control the heating temperature to 1156-1275°C and the heating rate to 8-13 min/cm.

(3) Rolling: The starting temperature of rough rolling is controlled to be not less than 1000°C, the starting temperature of finishing rolling is controlled to be not less than 960°C, the final rolling temperature of finishing rolling is controlled to be 800-940°C, and the cumulative reduction rate of the last three passes is controlled to be not less than 30%.

(4) Cooling: After controlled rolling, cooling is carried out, the cooling rate is controlled to be 15-45°C/s, and the final cooling temperature is controlled to be 280-350°C.

(5) Heat treatment: Tempering heat treatment is performed, the tempering temperature is controlled at 600-650°C, and the holding time is controlled at (15-50)min+t×1min/mm, where t represents the plate thickness, and its unit parameter is mm.

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 design specification requirements of the present invention. Although the comparative steel plates of Comparative Examples 1-5 are also prepared by the above steps (1)-(5), there are parameters in the chemical composition design and related processes that do not meet the design requirements of the present invention.

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 1-5.

Table 1-1. (wt%, the balance is Fe and other inevitable impurities except P, S and O)

Table 1-2.

serial number Alt/O (Mn+Ni)/C 200Mo/Cr×Nb×B Pc Example 1 68.00 15.56 0.0126 0.208 Example 2 35.71 20.43 0.201 0.204 Example 3 26.00 20.63 0.0137 0.215 Example 4 17.50 17.88 0.0119 0.210 Example 5 50.00 14.42 0.0219 0.219 Example 6 24.67 15.1 0.0177 0.230 Example 7 31.25 9.33 0.0092 0.240 Example 8 22.73 20.57 0.0161 0.202 Comparative Example 1 70 8.19 0.0126 0.272 Comparative Example 2 42.86 15.8 0.021 0.234 Comparative Example 3 30 13.75 0.0137 0.191 Comparative Example 4 333.33 5.56 0.0119 0.258 Comparative Example 5 6.43 17.22 0.027 0.193

Note: In the above table, in the two relationship formulas of Alt/O, (Mn+Ni)/C and 200Mo/Cr×Nb×B, 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, each chemical element in the calculation formula is substituted by the numerical value before the percentage sign of the mass percentage content.

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 1-5.

Table 2-1.

Table 2-2.

The high-strength steel plates for pressure vessels of the finished products of Examples 1-8 and the comparative steel plates of Comparative Examples 1-5 obtained through the above process steps were sampled respectively, and observed and tested for mechanical properties. The obtained observation results and mechanical property test results are listed in Table 3.

The relevant performance testing methods are as follows:

(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.

(2) Impact performance test: The lateral impact performance KV ₂ value was tested according to GB/T 229 “Charpy pendulum impact test method for metallic materials”. The analysis results are shown in Table 3.

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 Microstructures"; the reference standard for judging the Vickers hardness in steel is GB T 4340.1 "Metallic Materials. Vickers Hardness Test. Part 1 Test Method".

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 1-5.

Table 3.

Through the microstructure observation of the finished high-strength steel plates for pressure vessels of Examples 1-8, it can be seen that the matrix of the microstructure of the high-strength steel plates for pressure vessels of Examples 1-8 is tempered troostite, and the original austenite grain size is greater than level 9.

As shown in Table 3, compared with the comparative steel plates of Comparative Examples 1-5, 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 ₂ of the steel plates of the present case is much greater than that of the comparative steels of Comparative Examples 1-5.

In the present invention, the yield strength of the high-strength pressure vessel steel plates of the above-mentioned embodiments 1-8 is between 767-805 MPa, the tensile strength is between 785-840 MPa, the transverse -60°C impact energy KV ₂ is between 214-303 J, the elongation is between 18-20%, and the hardness value HV is between 228-245.

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, it is necessary to conduct welding process tests on the high-strength steel plates for pressure vessels of Examples 1-8 of the present invention and the comparative steel plates of Comparative Examples 1-5, respectively, and to detect the performance of the welded joints after welding, and the test results are listed in the following Table 4.

The relevant welding process test conditions are as follows: the welding line energy is controlled to be 18-37 kJ/cm, the time t _8/5 for the temperature of the welding pool to drop from 800 degrees to 500 degrees is controlled within the range of 11-36 seconds.

In the present invention, the CRHV performance test of the weld joint hardness of each embodiment and comparative steel plate adopts GB/T2654 "Test method for weld joint hardness", the impact energy _KV2 index adopts GB/T 229 "Charpy pendulum impact test method for metal materials", and the non-plastic transition temperature (NDTT) of the welding heat affected zone is tested by GB/T 6803 "Drop hammer test method for non-plastic transition temperature of ferritic steel".

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 1-5.

Table 4.

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 to 8 is significantly better than that of the comparative steel plates of Comparative Examples 1 to 5. The high-strength steel plates for pressure vessels of Examples 1 to 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.

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 790-836 MPa, and the transverse -60°C impact energy KV ₂ is between 135-183 J, the hardness value CRHV of the welded joint is between 228-246, and the non-plastic transition temperature of the weld heat affected zone is between -75 and -80°C.

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 hydrogen induced cracking, it is necessary to conduct hydrogen induced cracking (HIC) tests on the steel plates of Examples 1-8 of the present invention and Comparative Examples 1-5 and their corresponding welded joints.

In the present invention, the hydrogen induced cracking (HIC) test standards are: NACE TM0284 "Test method for evaluating the performance of pipeline and pressure vessel steels resistant to hydrogen induced cracking" and GB/T 8650 "Evaluation method for pipeline steel and pressure vessel steel resistance to hydrogen induced cracking".

Table 5-1 lists the hydrogen induced cracking test results of the high strength pressure vessel steel plates of Examples 1-8 and the comparative steel plates of Comparative Examples 1-4.

Table 5-1.

Table 5-2 lists the hydrogen induced cracking test results of the welded joints corresponding to the steel plates of Examples 1-8 and Comparative Examples 1-4.

Table 5-2.

In addition, in order to prove that the high-strength pressure vessel steel plates of Examples 1-8 described in the present invention also have excellent resistance to hydrogen sulfide corrosion cracking, the inventors conducted hydrogen sulfide stress corrosion cracking (SSCC) tests on the steel plates and welded joints of the pressure vessel steels of Examples 1-8 and the comparative steels of Comparative Examples 1-5.

In the present invention, the test standards for hydrogen sulfide stress corrosion cracking (SSCC) test are: ASTM G39-99R "Preparation and test methods for bending beam stress corrosion test specimens", ISO 7539-2 "Corrosion stress corrosion testing of metals and alloys Part 2: Preparation and application of bending specimens" and NACE TM0177 "Laboratory test methods for materials resistant to special forms of environmental cracking in _H2S environments".

Table 6 lists the hydrogen sulfide stress corrosion cracking performance test results of the steel plates and welded joints of the pressure vessel steels of Examples 1-8 and the comparative steels of Comparative Examples 1-5.

Table 6.

It can be seen from Table 5-1, Table 5-2 and Table 6 above that the high-strength pressure vessel steel plates and their corresponding welded joints of Examples 1-8 have no hydrogen sulfide stress corrosion cracking phenomenon, indicating that the steel plates and welded joints of the invention have good resistance to hydrogen sulfide corrosion and stress corrosion cracking.

In summary, the pressure vessel steel provided by the present invention is a pressure vessel steel with good strength and toughness and hydrogen sulfide corrosion resistance. It not only has good strength and toughness, resistance to cold and hot cracks in welding, and resistance to hydrogen sulfide stress corrosion cracking, but also has good welding processability and welding performance. This high-strength pressure vessel steel plate can effectively meet the engineering application requirements of pressure vessel steel after welding process, and has very important practical significance.

FIG. 1 is a metallographic photograph of a high-strength pressure vessel steel plate of Example 3.

As shown in FIG. 1 , in the present embodiment, the metallographic structure of the high-strength pressure vessel steel plate of Example 3 is tempered troostite, and the prior austenite grain size thereof is level 9.

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.

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 by those skilled in the art from the contents disclosed in the present invention, and all should belong to the protection scope of the present invention.

Claims (13)

1. A steel plate for high-strength pressure vessels that is resistant to hydrogen sulfide corrosion and cracking, which contains Fe and inevitable impurity elements. It is characterized in that it also contains the following chemical elements in the following mass percentages: C: 0.07～0.12%, Si: 0.25～0.45%, Mn: 0.90～1.30%, Alt: 0.020～0.045%, Ni: 0.18～0.35%, Cr: 0.18～0.30%, Mo: 0.30～0.45%, Nb : 0.020～0.050%, 0<V≤0.030%, Cu: 0.10～0.20%, Ti: 0.008～0.020%, B: 0.0008～0.0018%. 2. The steel plate for high-strength pressure vessels as claimed in claim 1, characterized in that the mass percentage of each chemical element is: C: 0.07～0.12%, Si: 0.25～0.45%, Mn: 0.90～1.30%, Alt: 0.020～0.045%, Ni: 0.18～0.35%, Cr: 0.18～0.30%, Mo: 0.30～0.45%, Nb : 0.020～0.050%, 0＜V≤0.030%, Cu: 0.10～0.20%, Ti: 0.008～0.020%, B: 0.0008～0.0018%; the balance is Fe and inevitable impurity elements. 3. The steel plate for high-strength pressure vessels according to claim 1 or 2, characterized in that among the inevitable impurity elements, the content of each impurity element satisfies at least one of the following items: P≤0.015%, S≤0.005%, O≤0.0018%. 4. The steel plate for high-strength pressure vessels according to claim 1 or 2, characterized in that each chemical element satisfies at least one of the following formulas: 17≤Alt/O≤70; 9≤(Mn+Ni)/C≤22; 0.009≤200Mo/Cr×Nb×B≤0.022. 5. The steel plate for high-strength pressure vessels according to claim 1 or 2, characterized in that the mass percentage content of each chemical element also satisfies at least one of the following items: Mn: 0.92～1.27%; Alt: 0.020～0.032%; V: 0.005～0.02%; Nb: 0.035～0.045%; Cr: 0.2～0.29%; Mo: 0.32～0.43%; Ti: 0.008～0.017%; B: 0.0008～0.0015%. 6. The steel plate for high-strength pressure vessels according to claim 1 or 2, characterized in that its microstructure is tempered sorbite. 7. The steel plate for high-strength pressure vessels according to claim 1 or 2, characterized in that its performance satisfies: yield strength ≥760MPa, hardness value HV at all positions of the steel plate is 225~245, transverse direction of the steel plate -60°C KV ₂ ≥185J. 8. The steel plate for high-strength pressure vessels according to claim 7, characterized in that the hardness value range of the welded joint of the steel plate is: CRHV=exp[(-1627.25)+29547.3×Pcm-200254.7×Pcm ² +602441.1×Pcm ³ -678806.1×Pcm ⁴ ], among which Pcm(%)=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B, substitute the mass percentage of each chemical element in the above calculation formula The value before the percent sign. 9. The manufacturing method of high-strength pressure vessel steel according to any one of claims 1 to 8, characterized in that it includes the steps: (1) Smelting and casting; (2) Heating; (3) rolling; (4) Rapid cooling: control the cooling rate to 15~45℃/s, and the final cooling temperature to 280~350℃; (5) Heat treatment. 10. The manufacturing method according to claim 9, characterized in that in step (1), the dynamic light reduction of the slab in the second cold water zone of continuous casting is controlled to be 0.6-2.5% to obtain the continuous casting slab. The ferrite grain size range is 110~225μm. 11. The manufacturing method of claim 9, wherein in step (2), the heating temperature is controlled to be 1156-1275°C; and/or the heating rate is controlled to be 8-13 min/cm. 12. The manufacturing method according to claim 9, characterized in that in step (3), the rough rolling opening temperature is controlled to be no less than 1000°C, the finishing rolling opening temperature is controlled to be no less than 960°C, and the finishing rolling temperature is controlled to be no less than 960°C. The final rolling temperature is 800~940℃, and the cumulative reduction rate of the last three passes is controlled to not be less than 30%. 13. The manufacturing method according to claim 9, characterized in that in step (5), tempering heat treatment is performed, the tempering temperature is 600~650°C, and the holding time is (15~50)min+t×1min /mm, where t represents the plate thickness, and its unit parameter is mm.