A high-performance steel plate for pressure-bearing equipment and its preparation method

Abstract

This invention relates to a high-performance steel plate for pressure equipment and its preparation method. The chemical composition and weight percentage content of the steel plate are as follows: C: 0.12%~0.2%, Si: 0.14%~0.34%, Mn: 0.42%~0.84%, P: ≤0.015%, S: ≤0.005%, Mo: 0.25%~0.35%, V: 0.16%~0.34%, Co: 0.14%~0.19%, Alt: 0.020%~0.037%, with the balance being Fe and unavoidable inclusions. The main method employed is a high-efficiency heating process (continuous casting billet heating process + steel plate heat treatment process control) + TMCP controlled rolling + ultra-fast cooling plate forming control process to prepare the steel plate for pressure equipment. The steel plate has a uniform microstructure, good strength and toughness matching, and excellent low-temperature performance, high-temperature service performance, and resistance to hydrogen-induced cracking.

Description

Technical Field

[0001] This invention relates to the field of metallic materials, and in particular to a high-performance steel plate for pressure equipment and its preparation method. Background Technology

[0002] Steel plates for pressure equipment are widely used in industries such as chemical, machinery, metallurgy, petrochemical, shipbuilding, and nuclear power. They come in a wide variety of types and specifications and are used in complex environments.

[0003] When designing steel for hydrogen-bearing pressure vessels in the petrochemical industry, in addition to considering factors such as high temperature, high pressure, and acid / alkali environments, the influence of hydrogen must also be taken into account. The phenomenon where metallic materials absorb hydrogen, leading to reduced plasticity and deteriorated performance, is called hydrogen damage, also known as hydrogen embrittlement. Hydrogen generated during pickling, electrolysis, or corrosion reactions, residual hydrogen inside the metal after solidification, and hydrogen in the surrounding environment can all be absorbed by the material and diffuse into its interior, causing hydrogen embrittlement. Hydrogen damage can lead to various forms of material failure, such as hydrogen blistering, hydrogen-induced embrittlement cracking, and high-temperature hydrogen corrosion. Therefore, the design of steel plates for hydrogen-bearing pressure vessels should also take into account resistance to hydrogen-induced cracking.

[0004] The announcement is for Chinese Patent CN104805380A, which provides a low-temper brittleness Cr-Mo series high-temperature pressure-bearing equipment steel plate and its preparation method. The steel plate is composed of the following components by weight percentage: C: 0.05%~0.17%, Si: ≤0.30%, Mn: 0.40%~0.65%, S≤0.035%, P≤0.015%, Cr: 0.80%~1.15%, Mo: 0.45%~0.60%, Sn≤0.005%, Sb≤0.005%, As≤0.005%, with the remainder being Fe and trace impurities. The steel plate for high-temperature pressure-bearing equipment is produced by normalizing and tempering heat treatment with the above composition. However, the steel plate does not take into account the resistance to hydrogen-induced cracking. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the technical problem solved by this invention is to provide a high-performance steel plate for pressure equipment and its preparation method. This invention mainly adopts a high-efficiency heating process (continuous casting billet heating process + steel plate heat treatment process control) + TMCP controlled rolling + ultra-fast cooling plate forming control process to prepare a steel plate for pressure equipment. In addition to having good strength, low-temperature toughness and high-temperature service performance, this steel plate also has good resistance to hydrogen-induced cracking.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A high-performance pressure-bearing steel plate, wherein the chemical composition and weight percentage content of the steel plate are as follows:

[0008] C: 0.12%–0.2%, Si: 0.14%–0.34%, Mn: 0.42%–0.84%, P: ≤0.015%, S: ≤0.005%, Mo: 0.25%–0.35%, V: 0.16%–0.34%, Co: 0.14%–0.19%, Alt: 0.020%–0.037%, with the balance being Fe and unavoidable inclusions.

[0009] The mechanical properties of the steel plate are as follows: at room temperature, 390MPa≤Rel≤520MPa, 580MPa≤Rm≤710MPa; at -20℃, KV2≥100J.

[0010] The reasons for selecting the chemical elements and composition ranges for the steel plate of this invention are briefly explained below:

[0011] Carbon (C) is the most important element for increasing the strength of steel. Its combination with strong carbide alloying elements in steel plays a role in precipitation strengthening. However, excessively high carbon content can easily cause segregation in the steel plate, affecting its resistance to hydrogen-induced cracking. Supersaturated carbides also reduce the low-temperature toughness and high-temperature service performance of the steel plate. Therefore, this invention sets the C content range to 0.12%–0.2%.

[0012] In steelmaking, silicon (Si) acts as a reducing agent and deoxidizer. Si is also an inexpensive alloying element; adding an appropriate amount of Si to steel, which dissolves in austenite, can improve the steel's hardness and strength. However, excessive silicon content can easily form hard phase compounds, reducing the steel plate's plasticity and toughness, and making it prone to cracking during later processing. Therefore, this invention sets the Si content range to 0.14%–0.34%.

[0013] Mn is infinitely soluble in Fe and is a strong austenite stabilizer, playing a role in fixing austenite in steel. It can lower the lower critical point of steel, increase the undercooling during austenite cooling, thereby refining the microstructure and improving the mechanical properties of the steel plate. Furthermore, it is relatively inexpensive. However, excessively high Mn content increases the tendency for grain coarsening in steel, and the formation of MnS reduces the steel plate's resistance to hydrogen-induced cracking. Therefore, this invention sets the Mn content range to 0.42%–0.84%.

[0014] S and P are harmful elements in steel. To ensure the purity and toughness of steel, they must be strictly controlled. Therefore, this invention limits P to ≤ 0.015% and S to ≤ 0.005%.

[0015] Mo is a weak solid solution strengthening element. Its main role in steel is to increase the supercooling capacity of austenite, thereby refining the microstructure and having a positive impact on impact toughness and brittle transition temperature. Furthermore, the addition of molybdenum reduces the tendency of steel plates to pit corrosion caused by chloride ions, increasing the corrosion resistance of the steel plates. However, excessive Mo has an adverse effect on the weldability of the steel plates. Therefore, this invention sets the Mo content range to 0.25%–0.35%.

[0016] V is a strong carbide-forming element, primarily existing in steel as carbides. Its main functions are to refine the steel's microstructure and grain size, improving its low-temperature toughness. At high temperatures, it dissolves into the solid solution, increasing hardenability. Appropriate amounts of V combine with C to form fine, dispersed carbides that remain stable at high temperatures, giving the steel good high-temperature service performance. Additionally, adding a small amount of V has a degassing effect. However, excessively high V content can lead to large-sized second-phase inclusions that negatively impact steel performance. Furthermore, due to procurement cost constraints, the V content is controlled between 0.16% and 0.34%.

[0017] Co can form a continuous solid solution with Fe in steel. Adding an appropriate amount of Co can improve the strength of the steel plate without changing its impact toughness. Due to its high stability, adding Co can increase the thermal stability of the steel plate and improve its high-temperature service performance. During heat treatment or later use, Co can inhibit and delay the precipitation and aggregation of special carbides from other elements, ensuring the steel plate's resistance to hydrogen-induced cracking. However, excessive addition of Co can negatively affect the hardenability of the steel plate. Considering production costs, this invention controls the Co content to 0.14%–0.19%.

[0018] Alt is a commonly used deoxidizer in steel. Adding a small amount of aluminum can refine the grains and improve the strength and impact toughness of the steel. However, excessive amounts can affect the hot working properties, weldability, and machinability of the steel. This invention limits the Alt content to the range of 0.020% to 0.037%.

[0019] This invention also provides a method for preparing high-performance pressure-bearing steel plates. The method mainly employs a continuous casting billet heating process + steel plate heat treatment process + TMCP controlled rolling + ultra-fast cooling plate forming controlled process; the specific method is as follows:

[0020] (1) Slab continuous casting: After steel smelting, slab continuous casting machine is used for casting. The tundish steel casting temperature is 1539~1556℃, the superheat is set to 16~24℃, and the billet pulling speed during casting is 1.1~1.4m / min.

[0021] (2) Stacking and slow cooling: The continuous casting slabs are stacked and slow cooled after they come off the line. The stacking and slow cooling time is 36 to 48 hours.

[0022] (3) Heating of continuous casting slab: The continuous casting slab is sent to the heating furnace for heating. The heating temperature range is 1205~1246℃, and the slab soaking time is controlled at 2.1~3.2h.

[0023] (4) TMCP controlled rolling: The rolling adopts the TMCP two-stage controlled rolling method. The rolling end temperature in the recrystallization zone is 1080-1140℃, and the total deformation rate is controlled above 60%. The final rolling temperature in the non-recrystallization zone is 840-880℃, and the reduction per pass is controlled at 5-7%. Small deformation multi-pass rapid rolling is adopted.

[0024] (5) Ultra-fast cooling plate shape control: After rolling, the steel plate is directly cooled by ultra-fast cooling process and straightened online. After straightening, the steel plate is stacked and slowly cooled to room temperature.

[0025] (6) Heat treatment: The heat treatment temperature of the steel plate is controlled at 880~920℃, the heating rate is 1.2~1.5min / mm, and the net holding time is 10~20min; finally, it is taken out of the furnace and air-cooled to room temperature.

[0026] In step (1), steelmaking is carried out in a converter, and dephosphorization and decarburization are carried out separately in the converter; deep desulfurization is carried out in the LF refining furnace, and the sulfur content is controlled below 0.002%; degassing is completed in the VD furnace, with a net circulation time of 10-16 min and a pre-casting settling time of 2-5 min; oxygen blowing for dephosphorization is controlled at 10-14 min, and oxygen blowing for decarburization is controlled at 9-12 min.

[0027] In step (5), the initial cooling temperature is controlled at 740-765℃, the cooling rate is controlled at 13-19℃ / s, and the final cooling temperature is controlled at 200-240℃.

[0028] In step (1), in order to control the center segregation and porosity of the continuous casting billet, electromagnetic stirring or light reduction process of continuous casting billet is adopted, wherein the light reduction rate is controlled at 5-8%.

[0029] In step (4), the thickness of the rolled steel plate is 10-63 mm.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1) Based on the strengthening elements C, Si, and Mn, this invention adds appropriate amounts of alloying elements such as Mo, V, and Co, while strictly controlling the content of harmful elements P and S. Combined with the optimization of the production process, a refined microstructure is obtained, which ensures the strength, plasticity, and low-temperature toughness of the steel plate, while also having good high-temperature service performance and resistance to hydrogen-induced cracking.

[0032] 2) The steel plate for pressure equipment prepared by the method of the present invention exhibits the following mechanical properties: 390MPa≤Rm≤520MPa at room temperature, 580MPa≤Rel≤710MPa, and KV2≥100J at -20℃. It also has excellent high-temperature service performance and resistance to hydrogen-induced cracking.

[0033] 3) This invention can obtain high-performance steel plates for pressure equipment with thicknesses ranging from 10 to 63 mm. Detailed Implementation

[0034] The specific embodiments of the present invention will be further described below:

[0035] This invention provides a high-performance steel plate for pressure-bearing equipment, wherein the chemical composition and weight percentage content of the steel plate are as follows:

[0036] C: 0.12%–0.2%, Si: 0.14%–0.34%, Mn: 0.42%–0.84%, P: ≤0.015%, S: ≤0.005%, Mo: 0.25%–0.35%, V: 0.16%–0.34%, Co: 0.14%–0.19%, Alt: 0.020%–0.037%, with the balance being Fe and unavoidable inclusions.

[0037] The mechanical properties of the steel plate are as follows: at room temperature, 390MPa≤Rel≤520MPa, 580MPa≤Rm≤710MPa, and KV2≥100J at -20℃.

[0038] This invention also provides a method for preparing high-performance steel plates for pressure equipment. The method mainly employs a high-efficiency heating process (continuous casting billet heating process + steel plate heat treatment process) + TMCP controlled rolling + ultra-fast cooling plate forming controlled process to prepare steel plates for pressure equipment. The steel plates have a uniform microstructure, good strength-toughness ratio, and excellent low-temperature performance, high-temperature service performance, and resistance to hydrogen-induced cracking. The specific method is as follows:

[0039] (1) Slab continuous casting: After steel smelting, slab continuous casting machine is used for casting. The key is to control the casting temperature. The casting temperature of molten steel in the tundish is 1539~1556℃, the superheat is set to 16~24℃, and the billet pulling speed during casting is 1.1~1.4m / min. Low temperature casting is better to refine the original as-cast structure.

[0040] (2) Stacking and slow cooling: The continuous casting slabs are stacked and slow cooled after they come off the line. The stacking and slow cooling time is 36 to 48 hours to prevent defects such as slab cracks caused by incomplete cooling or excessive cooling rate.

[0041] (3) Heating of continuous casting slab: The continuous casting slab is sent to the heating furnace for heating. The heating temperature range is 1205~1246℃, and the slab soaking time is controlled at 2.1~3.2h. When the heating temperature is below 1205℃, the coarse precipitates in the continuous casting slab cannot be dissolved, the austenitization of the steel plate is incomplete, and the final rolling temperature of the first stage cannot be guaranteed. When the heating temperature is above 1246℃, the fine precipitates in the continuous casting slab are easily re-dissolved and excessive grain growth is caused.

[0042] (4) TMCP controlled rolling: The rolling adopts the TMCP two-stage controlled rolling method. The rolling end temperature in the recrystallization zone is 1080-1140℃, which fully refines the original austenite structure. The total deformation rate is controlled above 60%, and large deformation rapid rolling is used to refine the original structure grains. The final rolling temperature in the non-recrystallization zone is 840-880℃, and the reduction per pass is controlled at 5-7%. Small deformation multi-pass rapid rolling is used. At this time, the austenite grains are further flattened and elongated. With the increase of grain boundary area, the grains are fully refined.

[0043] (5) Ultra-fast cooling plate shape control: In order to obtain high-performance pressure equipment steel plates with uniform structure and good strength and toughness under the premise of ensuring efficient production, the steel plates are directly cooled by ultra-fast cooling process after rolling, and the steel plates are straightened online. After straightening, they are stacked and slowly cooled to room temperature.

[0044] (6) Heat Treatment: Due to the presence of elements such as C, Si, Mn, P, S, Mo, V, and Co in the steel, the steel plate can obtain a microstructure with excellent strength and toughness after rolling. However, the grain size distribution of the steel plate is uneven, resulting in concentration of structural and thermal stress, which easily leads to delayed cracking during flame cutting. Therefore, heat treatment should be used in a timely manner to homogenize the microstructure, soften the structure, and relieve stress. To further control the internal microstructure of the steel plate while ensuring high production efficiency, this invention adopts a short-time normalizing heat treatment process to ensure that the strength of the steel plate is not lost, while giving the steel plate suitable plasticity and toughness, low-temperature performance, high-temperature service performance, and good resistance to hydrogen-induced cracking. The heat treatment temperature of the steel plate is controlled at 880-920℃, the heating rate is 1.2-1.5 min / mm, and the net holding time is 10-20 min; finally, the steel plate is air-cooled to room temperature after being removed from the furnace.

[0045] In step (1), steel smelting is carried out in a converter. To effectively control the content of harmful element P and ensure decarburization efficiency, dephosphorization and decarburization are carried out separately in the converter. To reduce production costs, scrap steel and molten iron can be used as raw materials, with the molten iron content controlled at 68-78%. Deep desulfurization is carried out in the LF refining furnace, controlling the sulfur content to below 0.002%. Degassing is completed in the VD furnace, with a net circulation time of 10-16 minutes and a pre-casting settling time of 2-5 minutes. Dephosphorization oxygen blowing is controlled at 10-14 minutes, and decarburization oxygen blowing is controlled at 9-12 minutes.

[0046] In step (5), the initial cooling temperature is controlled at 740-765℃, the cooling rate is controlled at 13-19℃ / s, and the final cooling temperature is controlled at 200-240℃.

[0047] In step (1), in order to control the center segregation and porosity of the continuous casting billet, electromagnetic stirring or light reduction process of continuous casting billet is adopted, wherein the light reduction rate is controlled at 5-8%.

[0048] In step (4), the thickness of the rolled steel plate is 10-63 mm.

[0049] The specific values ​​of element content for each embodiment and comparative example are listed in Table 1. High-performance pressure-bearing equipment steel plates were prepared according to the above preparation method in each embodiment, and the smelting process parameters for each embodiment and comparative example are shown in Table 2. The steel rolling parameters for each embodiment and comparative example are shown in Table 3. The heat treatment parameters for each embodiment and comparative example are shown in Table 4. The final mechanical properties of each embodiment and comparative example are shown in Table 5. The grain size and non-metallic inclusion test results for each embodiment and comparative example are shown in Table 6. The high-temperature tensile property test results for each embodiment and comparative example are shown in Table 7 (unit: MPa). The hydrogen-induced cracking resistance test results for each embodiment and comparative example are shown in Table 8.

[0050] Table 1 Chemical composition (wt, %)

[0051]

[0052] Table 2 Smelting process parameters

[0053]

[0054]

[0055] Table 3 Steel Rolling Parameters

[0056]

[0057] Table 4 Heat treatment process parameters for steel

[0058]

[0059] Table 5 Final Mechanical Properties

[0060]

[0061] Table 6 Results of Non-metallic Inclusion Tests

[0062]

[0063] Table 7 Results of High Temperature Tensile Properties Test

[0064]

[0065]

[0066] Table 8 Results of Hydrogen-Induced Cracking Resistance of Steel Plates

[0067]

[0068] Based on the above results, it can be concluded that the high-performance pressure-bearing steel plate with a thickness of (10-63) mm prepared by the present invention exhibits excellent mechanical properties, namely, 390MPa≤Rel≤520MPa at room temperature, 580MPa≤Rm≤710MPa, and KV2≥100J at -20℃. It also demonstrates excellent high-temperature service performance and resistance to hydrogen-induced cracking.

[0069] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. Furthermore, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. In addition, various different embodiments of the present invention can also be arbitrarily combined, as long as they do not violate the spirit of the present invention, they should also be considered as the content disclosed by the present invention.

Claims

1. A high-performance steel plate for pressure-bearing equipment, characterized in that, The chemical composition and weight percentage content of the steel plate are as follows: C: 0.12%–0.2%, Si: 0.14%–0.34%, Mn: 0.42%–0.84%, P: ≤0.015%, S: ≤0.005%, Mo: 0.25%–0.35%, V: 0.16%–0.34%, Co: 0.14%–0.19%, Alt: 0.020%–0.037%, with the balance being Fe and unavoidable inclusions; the mechanical properties of the steel plate are as follows: at room temperature, 390MPa≤Rel≤520MPa, 580MPa≤Rm≤710MPa; KV2≥100J at -20℃.

2. A method for preparing a high-performance pressure-bearing steel plate as described in claim 1, characterized in that, The preparation method mainly employs a continuous casting billet heating process + TMCP controlled rolling + ultra-fast cooling plate forming controlled process + steel plate heat treatment process; the specific method is as follows. (1) Slab continuous casting: After steel smelting, slab continuous casting machine is used for casting. The tundish steel casting temperature is 1539~1556℃, the superheat is set to 16~24℃, and the billet pulling speed during casting is 1.1~1.4m / min. (2) Stacking and slow cooling: The continuous casting slabs are stacked and slow cooled after they come off the line. The stacking and slow cooling time is 36 to 48 hours. (3) Heating of continuous casting slab: The continuous casting slab is sent to the heating furnace for heating. The heating temperature range is 1205~1246℃, and the slab heating time is controlled at 2.1~3.2h. (4) TMCP controlled rolling: The rolling adopts the TMCP two-stage controlled rolling method. The rolling end temperature in the recrystallization zone is 1080-1140℃, and the total deformation rate is controlled above 60%. The final rolling temperature in the non-recrystallization zone is 840-880℃, and the reduction per pass is controlled at 5-7%. Small deformation multi-pass rapid rolling is adopted. (5) Ultra-fast cooling plate shape control: After rolling, the steel plate is directly cooled by ultra-fast cooling process, and the steel plate is straightened online. After straightening, it is stacked and slowly cooled to room temperature. (6) Heat treatment: The heat treatment temperature of the steel plate is controlled at 880-920℃, the heating rate is 1.2-1.5min / mm, and the net holding time is 10-20min; finally, it is air-cooled to room temperature after being taken out of the furnace.

3. The method for preparing a high-performance pressure-bearing steel plate according to claim 2, characterized in that, In step (1), steel smelting is carried out in a converter, and dephosphorization and decarburization are carried out separately in the converter; deep desulfurization is carried out in the LF refining furnace, and the sulfur content is controlled below 0.002%; degassing is completed in the VD furnace, with a net circulation time of 10 to 16 minutes and a pre-casting settling time of 2 to 5 minutes.

4. The method for preparing a high-performance pressure-bearing equipment steel plate according to claim 2, characterized in that, In step (5), the initial cooling temperature is controlled at 740-765℃, the cooling rate is controlled at 13-19℃ / s, and the final cooling temperature is controlled at 200-240℃.

5. The method for preparing a high-performance pressure-bearing steel plate according to claim 3, characterized in that, The oxygen blowing time for dephosphorization is controlled at 10-14 minutes, and the oxygen blowing time for decarbonization is controlled at 9-12 minutes.

6. The method for preparing a high-performance pressure-bearing equipment steel plate according to claim 2, characterized in that, In step (1), in order to control the center segregation and porosity of the continuous casting billet, electromagnetic stirring or light reduction process of continuous casting billet is adopted, wherein the light reduction rate is controlled at 5-8%.

7. The method for preparing a high-performance pressure-bearing steel plate according to claim 2, characterized in that, In step (4), the thickness of the rolled steel plate is 10-63 mm.

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