Pressure vessel steel plate for movable tank car and manufacturing method

Abstract

The invention belongs to the technical field of smelting, and particularly relates to a pressure vessel steel plate for a movable tank car, which comprises the following chemical components in percentage by mass: 0.15 to 0.19 percent of C, 0.32 to 0.54 percent of Si, 1.31 to 1.68 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S, 0.46 to 0.59 percent of Ni, 0.05 to 0.12 percent of Nb, 0.014 to 0.026 percent of Ti and the balance of Fe and inevitable impurities. At normal temperature, the tensile strength of the steel plate is not less than 690 MPa and not more than 810 MPa; the yield strength is larger than or equal to 480 MPa and smaller than or equal to 620 MPa; at-60 DEG C, the transverse impact energy is greater than or equal to 100J. According to the method, a refined and pure microscopic structure, second-phase particles which are uniformly and finely distributed in a dispersed manner, and a high-homogeneity structure with the grain size of 8-9 grades and the total inclusion grade of 1.0 or below are obtained, the high plasticity of the steel plate is guaranteed, and meanwhile the steel plate has good hydrogen-induced crack resistance and machining performance.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting, and in particular relates to a pressure vessel steel plate for a mobile tank truck and a manufacturing method thereof. Background Art

[0002] The present invention relates to the field of metal materials, and in particular to a pressure vessel steel plate for a mobile tank truck with uniform structure and excellent performance, and a method for manufacturing the same. The service environment of the steel plate for pressure vessels is relatively complex, such as high temperature, high pressure, hydrogen, and acid-base environment. Therefore, when selecting the main material steel, the smelting, chemical composition, mechanical properties, metallographic structure and welding process of the steel must be strictly controlled. As is known to all, the performance of metal materials is closely related to the structure, and the uniformity of the structure is a strong guarantee for the high performance of the material. Refined and uniform structure can improve the strength and toughness of the steel plate, thereby improving the comprehensive service performance of the steel plate.

[0003] With the upgrading of domestic pressure-bearing manufacturing equipment, domestic petrochemical projects are developing in the direction of large-scale and high-performance. The performance of some traditional pressure-bearing equipment steels and the corresponding manufacturing methods can no longer meet the requirements of this development trend. In addition, although some grades can meet the project design requirements at this stage, there is still a need for upgrading in the long run. In addition, with the introduction of the "dual carbon" requirements, the manufacturing of high-performance pressure-bearing equipment steel has also attracted further attention. Therefore, it is urgent to develop a high-strength key material for pressure-bearing equipment that meets the room temperature strength, forming performance, and adapts to complex service environments (such as high temperature, high pressure, etc.) to support the development needs of my country's large-scale new energy equipment or equipment.

[0004] The disclosed invention patent "A hydrogen corrosion resistant normalizing type mobile tank car low alloy steel and its preparation method (CN106756536A)" describes a steel plate composed of the following weight percentage components: C0.13-0.20%, Si0.20-0.50%, Mn1.20-1.70%, P≤0.030%, S≤0.010%, Ni0.10-0.45%, Nb0.010-0.050%, V0.010-0.20%, 30ppm≤N≤50ppm, H≤2ppm, 8≤w(V) / w(N)≤15, the remainder is Fe and unavoidable impurities; under the above composition, the normalizing heat treatment method is adopted to produce steel plates with thickness specifications of 6-25mm. No research has been conducted on steel plates with thickness greater than 25mm, and no content related to the control of organizational uniformity and the low temperature impact condition below -46℃ is involved, so the scope of application is narrow. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a pressure vessel steel plate for a mobile tank truck and a manufacturing method thereof, wherein the produced steel plate has uniform and pure structure, good strength-toughness matching, and excellent resistance to hydrogen-induced cracking.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A pressure vessel steel plate for a mobile tank truck, the chemical composition mass percentage is: C: 0.15%-0.19%, Si: 0.32%-0.54%, Mn: 1.31%-1.68%, P≤0.02%, S≤0.01%, Ni: 0.46%-0.59%, Nb: 0.05%-0.12%, Ti: 0.014%-0.026%, the balance is Fe and unavoidable inclusions.

[0008] A pressure vessel steel plate for a mobile tank truck, performance indicators: steel plate room temperature: 690MPa≤ tensile strength≤810MPa, 480MPa≤ yield strength≤620MPa, -60℃ lateral impact energy≥100J.

[0009] The reasons for limiting the amount of each chemical element in steel plates are detailed as follows:

[0010] C is the most important element in steel to ensure the strength of steel. If the content is too low, the performance of the steel plate after heat treatment cannot be guaranteed. However, too high a carbon content will affect the machining performance of the steel, and the supersaturated carbide produced will become the source of fracture cracks, affecting the low-temperature performance of the steel plate and the welding performance during subsequent use. Therefore, the present invention sets the C content range to: 0.15% to 0.19%.

[0011] Si is used as a reducing agent and deoxidizer in the steelmaking process. When the silicon content is too high, it is easy to form hard phase compounds, which increases the brittleness of the steel plate and easily causes cracks during later processing. Therefore, the present invention sets the Si content range to 0.32% to 0.54%.

[0012] Mn can be infinitely dissolved with Fe, and is an element that strongly stabilizes austenite and can strengthen pearlite structure. The effect of Mn and C, while improving the strength of steel, has relatively little effect on plasticity, and can reduce the lower critical point of steel, increase the supercooling degree when austenite is cooled, thereby refining the structure and improving the mechanical properties of the steel plate. In addition, the price is relatively cheap. However, too high a Mn content will increase the tendency of hard phase MnS inclusions in steel, so the present invention sets the Mn content range to 1.31% to 1.68%.

[0013] S and P are harmful elements in steel and must be strictly controlled to ensure the purity and plasticity of the steel. It is known that MnS produced in steel will affect the strength and toughness of the steel plate, and the presence of P will increase the brittleness of the steel plate and have a negative impact on welding performance. In order to strictly control the generation of harmful inclusions in the steel plate, the present invention is limited to P≤0.02% and S≤0.01%.

[0014] Ni can be compared with γ Fe It forms an infinite solid solution, thus improving the hardenability of the steel plate. Adding a certain amount of Ni element can strengthen the cast ferrite while increasing the number of pearlite and reducing its size. Steel plates containing Ni are generally not easy to overheat, so they can prevent the growth of grains at high temperatures and maintain the grain size when heated at high temperatures. Ni can improve the strength of steel while maintaining good plasticity and toughness, especially low-temperature toughness. However, since nickel is a scarce resource, considering the control of comprehensive costs, the Ni content is controlled at 0.46% to 0.61%.

[0015] Nb can form interstitial intermediate phases such as NbC or NbN in steel. During the recrystallization process, the pinning of dislocations and the inhibition of grain growth by NbC and NbN greatly increase the recrystallization time. Above the critical temperature, the effect of niobium on recrystallization is manifested as a solute drag mechanism, while below the critical temperature, it is manifested as a precipitation pinning mechanism. In addition, Nb is the most effective alloying element for grain refinement, and has a significant strengthening effect. During heat treatment processes such as controlled rolling and normalizing, it has an extremely strong effect on delaying austenite recrystallization and refining grains, and a relatively low niobium content can play a significant role. However, when the content is too high, it will cause the deterioration of the toughness and plasticity of the steel plate, so the Nb content is controlled at 0.05% to 0.12%.

[0016] Ti is a strong carbide-forming element, which forms stable Ti(C,N) compound particles in steel. When it exists in the form of solid solution, it can significantly improve the hardenability of the steel plate, prevent grain growth, and improve the strength of the steel. After normalizing, the small-sized carbides formed by precipitation can significantly improve the plasticity and impact toughness of the steel. Ti also has a high affinity with O, which can strongly increase the A1 and A3 temperatures of the steel in steel. However, when the Ti content in the steel is too high, large-sized second-phase particles will be generated, increasing the brittleness of the steel plate. Therefore, the present invention controls the Ti content to 0.014% to 0.026%.

[0017] A method for manufacturing a pressure vessel steel plate for a mobile tank truck, the process flow is molten iron inoculation treatment - converter smelting - refining outside the furnace - vacuum degassing - continuous casting - slab heating - controlled rolling and controlled cooling - heat treatment - flaw detection - inspection, including the following specific steps:

[0018] 1) Hot metal inoculation treatment: Hot metal and scrap steel are added into the converter, the weight percentage of hot metal is controlled at 76-81%, and inoculant is added into the hot metal for inoculation treatment, and the height-to-diameter ratio of the hot metal column should be between 1.3 and 1.4;

[0019] 2) Smelting process: dephosphorization oxygen blowing is controlled within 7 to 10 minutes, decarburization oxygen blowing is controlled within 6 to 11 minutes, and the P mass fraction is reduced to less than 0.015%; deep desulfurization treatment is carried out in the LF refining furnace to control the sulfur content below 0.005%; degassing is completed in the VD furnace, the net cycle time is 9 to 12 minutes, and the calming time before pouring is 4 to 9 minutes;

[0020] 3) Continuous casting process: After breaking the vacuum, the slab continuous casting machine is used for casting through the ladle turret, and the temperature of the molten steel flowing into the crystallizer, i.e., the casting temperature, is controlled to be 1469-1496°C, the superheat is set to be 8-15°C, the billet drawing rate during casting is 1.2-1.4 m / min, the continuous casting billet light reduction process is adopted, the light reduction rate is controlled at 5-7%, the billet is stacked and slowly cooled after it comes off the line, the stacking slow cooling time is not less than 24h, and the cooling rate is controlled at 19-24°C / min;

[0021] 4) Heating process: The continuous casting slab is sent to the heating furnace for heating. The heating temperature range is 1195-1235°C, and the slab soaking time is controlled at 1.5-2.1h;

[0022] 5) Rolling process: rolling adopts two-stage controlled rolling and controlled cooling, the end temperature of the recrystallization zone rolling is 1100-1145℃, 3-5 passes, and the single pass reduction rate is controlled at 15-19%; the start rolling temperature of the non-recrystallization zone is 965-989℃, the final rolling temperature is 870-890℃, 8-10 passes, and the total reduction rate is controlled at 35-46%; controlled cooling, wherein the starting temperature of the first cold section is 742-760℃, the cooling water pressure is controlled between 0.8-1.2Mpa, and the cooling rate is 65-84℃ / s; the starting temperature of the second cold section cooling is 452-478℃, and the cooling rate is controlled at 21-30℃ / s;

[0023] 6) Heat treatment process: normalizing treatment + high temperature homogenization treatment. The first stage of normalizing treatment: control the temperature at 862-915°C and keep it warm for 20-35 minutes. The second stage adopts the homogenization treatment process: control the temperature at 560-600°C and keep it warm for 1.3-2.1 min / mm.

[0024] In step 1), the particle size of the inoculant is 5 to 10 mm.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention, based on the strengthening elements of C, Si and Mn, adds appropriate amounts of Ni, Nb and Ti alloy elements, and strictly controls the content of harmful elements P and S. It adopts a combination of advanced iron inoculation treatment + ingot heating process + two-stage rolling method + efficient heat treatment process (normalizing treatment-high temperature homogenization treatment) system to produce a steel plate for pressure vessels with a thickness of 5 to 35 mm, obtains a refined and pure microstructure, uniform and finely dispersed second phase particles, a grain size of 8 to 9, and a highly homogeneous structure with a total inclusion grade of less than 1.0, which ensures the strong plasticity of the steel plate while having good hydrogen-induced crack resistance and processing performance. Steel plate room temperature: 690MPa≤ tensile strength≤810MPa, 480MPa≤ yield strength≤620MPa, -60℃ transverse impact energy≥100J. According to GB / T 8650-2006 "Evaluation Method for Hydrogen-Induced Cracking of Pipeline Steel and Pressure Vessel Steel", the crack length rate CLR, crack thickness rate CTR, and crack sensitivity rate CSR of the hydrogen sulfide corrosion resistance test in solution A and B are all 0%, meeting the manufacturing and application requirements of mobile tank truck steel for high-performance pressure vessels. DETAILED DESCRIPTION

[0027] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by technicians in the technical field of this application; the terms used in the specification of the application herein are only for the purpose of describing specific embodiments and are not intended to limit the present application. The reference to "embodiment" in this article means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] A pressure vessel steel plate for a mobile tank truck, the chemical composition mass percentage is: C: 0.15%-0.19%, Si: 0.32%-0.54%, Mn: 1.31%-1.68%, P≤0.02%, S≤0.01%, Ni: 0.46%-0.59%, Nb: 0.05%-0.12%, Ti: 0.014%-0.026%, the balance is Fe and unavoidable inclusions.

[0029] A method for manufacturing a pressure vessel steel plate for a mobile tank truck, the process flow is molten iron inoculation treatment - converter smelting - furnace refining (LF) - vacuum degassing (VD) - continuous casting - slab heating - controlled rolling and controlled cooling - heat treatment (normalizing treatment - homogenization treatment) - flaw detection - inspection, including the following specific steps:

[0030] 1) Hot metal inoculation treatment: To improve smelting efficiency, molten steel is smelted in a converter. To reduce production costs, high-quality scrap steel and hot metal are used as raw materials, and the hot metal content is controlled at 76-81%. In order to promote nucleation, inhibit growth, and achieve the purpose of grain refinement of steel plates, the hot metal is pre-inoculated, the inoculant addition time is controlled at 15-20 minutes, and the inoculant particle size is controlled at 5-10 mm. In order to reduce the loss of steel plates and prevent hot metal from splashing during production, the height-to-diameter ratio of the hot metal column should be between 1.3 and 1.4;

[0031] 2) Converter smelting process: In order to ensure the purity of steel, effectively control the content of harmful elements P, and ensure the efficiency of decarburization, dephosphorization and decarburization are carried out separately in the converter. The oxygen blowing for dephosphorization is controlled at 7 to 10 minutes, and the oxygen blowing for decarburization is controlled at 6 to 11 minutes, and finally the P mass fraction is reduced to less than 0.015%; deep desulfurization treatment is carried out in the LF refining furnace, and the sulfur content is strictly controlled below 0.005%; degassing is completed in the VD furnace, the net cycle time is 9 to 12 minutes, and the calming time before pouring is 4 to 9 minutes.

[0032] 3) Continuous casting process:

[0033] After breaking the vacuum, the slab continuous casting machine is used for casting through the ladle turntable, and the temperature of the molten steel flowing into the crystallizer, that is, the casting temperature, is controlled to be 1469-1496°C, the superheat is set to 8-15°C, and the billet drawing rate during casting is 1.2-1.4m / min. Ensure that the billet drawing speed is appropriate for low-temperature casting to increase the grain size of the original cast structure and ensure the quality of the billet. In order to further adjust and reduce the central segregation and looseness of the continuous casting billet, the continuous casting billet light reduction process is adopted, in which the light reduction rate is controlled at 5-7%, the billet is stacked and slowly cooled after it comes off the line, the stacking slow cooling time is not less than 24h, and the cooling rate is controlled at 19-24°C / min.

[0034] 4) Heating process: The continuous casting slab is sent to the heating furnace for heating. In order to improve the heating efficiency while ensuring the internal quality of the steel plate, the heating temperature range is 1195-1235℃. The slab soaking time is controlled at 1.5-2.1h. When the heating temperature is lower than 1195℃, 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 higher than 1235℃ and the heating time in the high temperature section is too long, it is easy to cause the fine precipitates in the continuous casting slab to dissolve again and cause excessive grain growth.

[0035] 5) Rolling process: The rolling adopts two-stage controlled rolling and controlled cooling. The end temperature of the recrystallization zone rolling is 1100-1145℃, 3-5 passes, and the single pass reduction is controlled at 15-19%; the start rolling temperature of the non-recrystallization zone is 965-989℃, the final rolling temperature is 870-890℃, 8-10 passes, and the total reduction rate is controlled at 35-46%. At this time, the austenite grains are further flattened and elongated, and the grains are fully refined as the grain boundary area increases. ; Controlled cooling, the starting temperature of the first cold section is 742-760℃, the cooling water pressure is controlled between 0.8-1.2Mpa, and the cooling rate is 65-84℃ / s; the starting temperature of the second cold section cooling is 452-478℃, and the cooling rate is controlled at 21-30℃ / s.

[0036] 6) Heat treatment process: Since elements such as C, Si, Mn, P, S, Ni, Nb, and Ti are added to the steel, the steel plate can obtain a ferrite + pearlite structure with excellent strength and toughness after rolling. However, the grain size distribution of the steel plate is uneven, there is concentration of structural stress and thermal stress, and delayed cracks are easily generated during flame cutting. Therefore, heat treatment should be used in time to homogenize the structure, soften and eliminate stress. In order to further control the internal structure of the steel plate and ensure high production efficiency at the same time, the present invention adopts normalizing treatment-high temperature homogenization treatment to ensure that the strength of the steel plate is not lost, while having suitable plastic toughness, resistance to hydrogen-induced cracking, and good processing performance. Therefore, the first stage normalizing treatment: control the temperature at 862-915°C, and keep warm for 20-35min; the second stage adopts a homogenization treatment process: control the temperature at 560-600°C, and keep warm for 1.3-2.1min / mm.

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0038] Table 1 shows the chemical composition of the embodiment of the present invention, Table 2 shows the molten iron pretreatment and smelting process parameters of the embodiment steel, Table 3 shows the continuous casting billet heating and rolling process parameters, Table 4 shows the heat treatment parameters of the embodiment steel, Table 5 shows the final effect of the mechanical properties of the embodiment, Table 6 shows the test results of the hydrogen crack resistance of the embodiment. Table 7 shows the test results of the grain size and inclusion grade evaluation of the embodiment steel plate structure.

[0039] Table 1: Chemical composition of the examples (wt, %)

[0040]

[0041] Table 2: Process parameters for hot metal pretreatment, smelting and continuous casting in the embodiment

[0042]

[0043]

[0044] Table 3: Process parameters of continuous casting heating and rolling

[0045]

[0046] Table 4: Heat treatment process parameters of example steel

[0047]

[0048] Table 5: Final effect of mechanical properties of the examples

[0049]

[0050]

[0051] Table 6: Experimental results of hydrogen crack resistance test

[0052]

[0053] Table 7: Test results of grain size and inclusion grade evaluation of steel plate in Example

[0054]

[0055]

[0056] According to the above results, it can be concluded that the steel plate for mobile tank trucks with uniform structure and excellent performance in a thickness of 5 to 35 mm provided by the present invention has mechanical properties as follows: 690MPa≤Rm≤820MPa, 480MPa≤Rel≤620MPa, -60℃: KV2≥100J at room temperature of the steel plate, and has fine and uniform structure throughout the thickness, excellent plasticity and toughness, low-temperature performance, resistance to hydrogen-induced cracking and good processing performance.

[0057] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and basic spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A pressure vessel steel plate for a mobile tank truck, characterized in that: The chemical composition by mass percentage is: C: 0.15% ~ 0.19%, Si: 0.32% ~ 0.54%, Mn: 1.31% ~ 1.68%, P ≤ 0.02%, S ≤ 0.01%, Ni: 0.46% ~ 0.59%, Nb: 0.05% ~ 0.12%, Ti: 0.014% ~ 0.026%, and the balance is Fe and unavoidable inclusions.

2. The pressure vessel steel plate for a mobile tank truck according to claim 1, characterized in that: Performance indicators: Steel plate at room temperature: 690MPa≤ tensile strength≤810MPa; 480MPa≤ yield strength≤620MPa; -60℃ transverse impact energy≥100J.

3. The method for manufacturing a pressure vessel steel plate for a mobile tank truck according to claim 1, characterized in that: The process is hot metal inoculation treatment - converter smelting - refining outside the furnace - vacuum degassing - continuous casting - slab heating - controlled rolling and controlled cooling - heat treatment - flaw detection - inspection, including the following specific steps: 1) Hot metal inoculation treatment: Hot metal and scrap steel are added into the converter, the weight percentage of hot metal is controlled at 76-81%, and inoculant is added into the hot metal for inoculation treatment, and the height-to-diameter ratio of the hot metal column should be between 1.3 and 1.4; 2) Smelting process: dephosphorization oxygen blowing is controlled within 7 to 10 minutes, decarburization oxygen blowing is controlled within 6 to 11 minutes, and the P mass fraction is reduced to less than 0.015%; deep desulfurization treatment is carried out in the LF refining furnace to control the sulfur content below 0.005%; degassing is completed in the VD furnace, the net cycle time is 9 to 12 minutes, and the calming time before pouring is 4 to 9 minutes; 3) Continuous casting process: After breaking the vacuum, the slab continuous casting machine is used for casting through the ladle turret, and the temperature of the molten steel flowing into the crystallizer, i.e., the casting temperature, is controlled to be 1469-1496°C, the superheat is set to be 8-15°C, the billet drawing rate during casting is 1.2-1.4 m / min, the continuous casting billet light reduction process is adopted, the light reduction rate is controlled at 5-7%, the billet is stacked and slowly cooled after it comes off the line, the stacking slow cooling time is not less than 24h, and the cooling rate is controlled at 19-24°C / min; 4) Heating process: The continuous casting slab is sent to the heating furnace for heating. The heating temperature range is 1195-1235°C, and the slab soaking time is controlled at 1.5-2.1h; 5) Rolling process: rolling adopts two-stage controlled rolling and controlled cooling, the end temperature of the recrystallization zone rolling is 1100-1145℃, 3-5 passes, and the single pass reduction rate is controlled at 15-19%; the start rolling temperature of the non-recrystallization zone is 965-989℃, the final rolling temperature is 870-890℃, 8-10 passes, and the total reduction rate is controlled at 35-46%; controlled cooling, wherein the starting temperature of the first cold section is 742-760℃, the cooling water pressure is controlled between 0.8-1.2Mpa, and the cooling rate is 65-84℃ / s; the starting temperature of the second cold section cooling is 452-478℃, and the cooling rate is controlled at 21-30℃ / s; 6) Heat treatment process: normalizing treatment + high temperature homogenization treatment. The first stage of normalizing treatment: control the temperature at 862-915°C and keep it warm for 20-35 minutes. The second stage adopts the homogenization treatment process: control the temperature at 560-600°C and keep it warm for 1.3-2.1 min / mm. In step 1), the particle size of the inoculant is 5 to 10 mm.

4. The method for manufacturing a pressure vessel steel plate for a mobile tank truck according to claim 3, characterized in that: In step 1), the particle size of the inoculant is 5 to 10 mm.

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