High-strength ship plate with excellent firework performance and manufacturing method

Abstract

According to the high-strength ship plate with the excellent firework performance and the manufacturing method, a low-carbon chemical component system is adopted, V-N, Ti and other refined grain elements are added, formation of a ferritic structure in steel is promoted, RE elements are added, and the purity of the steel is improved; the manufacturing method comprises the steps of smelting, continuous casting, reheating, rolling, accelerated cooling and stacking slow cooling, the rolling process adopts two-stage controlled rolling, the first-stage rolling adopts a high-temperature fast rolling and high-pressure reduction process, and the second-stage rolling adopts a fast rolling process with high finish rolling temperature; the steel plate produced by using the method has excellent comprehensive mechanical properties and fire performance, the yield strength is greater than 485MPa, and the tensile strength is 560-620MPa; the yield strength of the steel plate after fire work is larger than 475 MPa, the tensile strength is 551-610 MPa, the percentage elongation after fracture is larger than or equal to 25.5%, and the impact absorption energy at the temperature of-80 DEG C is larger than 200 J.

Description

Technical Field

[0001] The invention belongs to the field of metal materials, and in particular relates to a high-strength ship plate with excellent pyrotechnic performance and a manufacturing method thereof. Background Art

[0002] The hull structure is different from other structures. Due to the huge size of the hull, the large number of parts, the complex structure and high rigidity, the various processed longitudinal and transverse components and curved components in the hull intersect and link with each other, which inevitably produces bending deformation, angular deformation, local bulge wave deformation and twisting deformation during the construction process. Therefore, in order to obtain the curved shape of the hull construction design or to avoid the deformation of the steel plate that seriously affects the assembly quality of the hull and the linear smoothness of the hull, pyrotechnics must be used to perform corresponding pyrotechnic forming and water-fire bending plate and other deformation corrections during ship construction.

[0003] Water-fire bending is a process that uses flames to locally heat steel plates and then uses water to cool them to bend them. Current research on the pyrotechnic properties of ship plates shows that despite strict requirements for the pyrotechnic process of ship plates during ship construction, it is still difficult to guarantee the pyrotechnic performance. At present, the production of ship plates also pays more attention to component design, rolling and welding processes, while less attention is paid to water-fire bending and its performance changes during subsequent processing.

[0004] Patent document "A method for producing F36 low-temperature steel thick plate" (application number: 202310903364.X) discloses a F36 low-temperature steel thick plate, whose chemical composition weight percentage is C 0.10%-0.12%, Si 0.05%-0.15%, Mn 1.40%-1.60%, Al 0.02%-0.06%, Ti 0.008%-0.015%, Nb 0.020%-0.050%, Cr 0.20%-0.50%, and the balance is Fe and unavoidable impurity elements; its key process steps include: smelting, heating, controlled rolling and controlled cooling, quenching, normalizing and stress relief tempering. The yield strength of the steel plate is ≥360MPa, the tensile strength is ≥490MPa, and the impact energy at -60℃ is ≥120J. However, the process includes quenching, normalizing and stress relief tempering, which is complicated, increases production costs, and does not pay attention to the pyrotechnic properties of the steel plate.

[0005] The patent document "A low-temperature steel plate for ships with excellent pyrotechnic performance and its manufacturing method" (application number: 201910863007.9) discloses a low-temperature steel for ships with excellent pyrotechnic performance, whose main chemical components are C 0.04%-0.08%, Si 0.15%-0.25%, Mn 0.80%-1.80%, Als0.045%-0.070%, N≤0.0040%, Ti 0.005%-0.020%, and the rest are Fe and unavoidable impurities. Its process includes heating of ingot, two-stage rolling and controlled cooling. The steel plate has excellent comprehensive performance and excellent pyrotechnic performance. However, its tensile strength is only 510MPa, which is difficult to meet the needs of large ship construction.

[0006] The patent document "An economical low-temperature toughness E-grade high-strength shipbuilding steel plate and its manufacturing method" (application number: 202110392427.0) discloses an economical low-temperature toughness E-grade high-strength shipbuilding steel plate, whose chemical composition is C 0.11%-0.16%, Si 0.05%-0.14%, Mn 1.45%-1.65%, Als 0.02%-0.04%, N0.003%-0.015%, Nb 0.01%-0.03%, Ti 0.008%-0.014%, and the remainder is Fe and unavoidable impurities; its process includes smelting, continuous casting, rolling and cooling, and the steel plate can meet the technical requirements of shipbuilding steel plates, but its Mn content is relatively high, and it is easy to form segregation in the core, which reduces the toughness and plasticity of the steel plate. The patent only evaluates the -40°C impact toughness of the steel plate, and does not evaluate the pyrotechnic performance of the steel plate.

[0007] To sum up, the current production of shipbuilding steel mainly has the following problems.

[0008] 1) The process is complicated, resulting in an increase in the production cost of the steel plate.

[0009] 2) The strength and toughness of steel plates are relatively low and cannot meet the needs of shipbuilding.

[0010] 3) The pyrotechnic performance of steel plates is relatively low and cannot meet the technological requirements of shipbuilding. Summary of the invention

[0011] The object of the present invention is to overcome the above problems and shortcomings and provide a high-strength steel plate for ships with high toughness and excellent pyrotechnic performance.

[0012] The object of the invention is achieved in this way:

[0013] A high-strength ship plate with excellent pyrotechnic performance. The components of the steel plate are as follows by weight percentage: C: 0.020%-0.120%, Si: 0.60%-1.10%, Mn: 1.50%-2.00%, P≤0.008%, S≤0.005%, V: 0.020%-0.120%, N: 0.012%-0.018%, Cu: 0.20%-0.55%, Ni: 0.35%-0.65%, Mo: 0.20%-0.45%, Ti: 0.005%-0.035%, Als: 0.035%-0.055%, Ce+La: 0.0100%-0.0200%; the balance is Fe and unavoidable impurities.

[0014] In the ship plate, Ni / Mo=1.1-2.0.

[0015] The ship plate metallographic structure is ferrite + bainite structure, wherein the ferrite is 20% to 25% by volume, the average grain size is ≤20 μm, and the average precipitate phase size is ≤50 nm.

[0016] The ship plate has a yield strength of >485MPa, a tensile strength of 560-620MPa, an elongation after fracture of ≥25.5%, and an impact absorption energy of -80°C of >270J; the yield strength of the steel plate after pyrotechnic treatment is >475MPa, a tensile strength of 551-610MPa, an elongation after fracture of ≥25.5%, and an impact absorption energy of -80°C of >200J.

[0017] The reasons for the composition design of the present invention are as follows:

[0018] C: An important strengthening element in steel. In the technical solution of the present invention, it is the main element for controlling the composition of the steel plate, optimizing the precipitation of microalloying elements in the steel, and ensuring the strength and hardness of the steel plate after rolling and pyrotechnic bending. When the content is low, the amount of carbide generated will be reduced, affecting the effect of grain refinement during rolling and pyrotechnic treatment. When the content is high, the cementite content in the steel increases, the size increases, and the distribution becomes more dense. The cementite will aggregate at the grain boundary. The large-sized cementite aggregates at the grain boundary and causes stress concentration, which is unfavorable to the low-temperature toughness and welding performance of the steel plate. Therefore, considering the cost, performance and other factors, the present invention controls C in the range of 0.020% to 0.120%.

[0019] Si: It can improve the strength and hardness of steel and play a role in deoxidation during the steelmaking process. When the content is too high, it will form oxides and silicates with other elements in the matrix, destroying the continuity of the steel matrix, causing the ductile-brittle transition temperature of the steel to rise, and reducing the low-temperature toughness of the steel plate, thereby having an adverse effect on the comprehensive performance of the steel plate after pyrolysis. Taking into account factors such as cost and performance, the present invention controls Si in the range of 0.60% to 1.10%.

[0020] Mn: an element that expands the austenite phase region, forms a substitutional solid solution in steel, can be dissolved in a large amount in the Fe matrix, improves the strength of the steel through solid solution strengthening, and has a positive effect on grain refinement; it can delay the transformation of ferrite and pearlite in steel, greatly increase the hardenability of steel, reduce the toughness-brittle transition temperature of steel, and change the impact toughness. However, if the Mn content is too high, it is easy to form segregation in the steel, which has an adverse effect on the plasticity and toughness of the steel. Taking all factors into consideration, the range of Mn controlled by the present invention is 1.50% to 2.00%.

[0021] V: An important strengthening and toughening element of the present invention, a strong carbon and nitride forming element, a strong carbide and nitride forming element, has a strong affinity with nitrogen and carbon, and can form extremely stable carbonitrides with them. The strength of steel is improved by fine grain strengthening, precipitation strengthening and solid solution strengthening in steel. As the V content increases, the tough-to-brittle transition temperature of the steel decreases. However, when the content is too high, the tough-to-brittle transition temperature increases instead. Vanadium carbonitrides can precipitate at a lower temperature to hinder dislocation movement, play a strengthening and toughening role, and have a significant effect on improving the comprehensive mechanical properties of the steel plate after pyrotechnic treatment. Taking all factors into consideration, the present invention controls the range of V to be 0.020% to 0.120%.

[0022] N: Another important toughening element of the present invention. The addition of N element is conducive to promoting the formation of a large amount of V (CN) in the steel, thereby refining its grains and improving the plasticity and toughness of the steel. Nitrogen-containing steel not only eliminates the cost increase caused by degassing and refining and denitrification in the steelmaking process, but also the nitrogen addition in the steel can give full play to the role of micro-alloying elements, saving the amount of alloying elements, thereby greatly reducing production costs. The addition of N can optimize the precipitation of the precipitated phase during the pyrotechnic treatment of the steel, thereby improving its comprehensive mechanical properties. Taking into account the performance and cost, the present invention controls the range of N to be 0.0120% to 0.0180%.

[0023] Cu: It can improve the stability of austenite in steel, increase the hardenability of steel, and improve the strength, plasticity and low-temperature toughness of steel when added in appropriate amounts. During low-temperature treatment, ε-Cu precipitation can be produced, thereby improving the strength of steel. However, when the content is too high, the hot brittleness of steel deteriorates and hot cracks are easily generated. The range of Cu controlled by the present invention is 0.20% to 0.55%.

[0024] Ni: has no adverse effect on the hardenability and toughness of the welding heat affected zone of steel, and can improve the plasticity and low-temperature toughness of steel. When combined with Mo, it has a more detailed fine grain effect. In addition, the addition of Ni can also reduce the tendency of thermal cracking when the Cu content is high. Considering the cost, performance and other factors, the present invention controls the range of Ni to be 0.35% to 0.65%.

[0025] Mo: improves the hardenability of steel, and the effect is more obvious when used in combination with Ni. It can enable the steel to obtain bainite structure within a wider cooling rate and form fine carbides in the steel, which can effectively improve the strength of the steel. Taking into account factors such as steel cost and performance, the present invention controls Mo in the range of 0.20% to 0.45%.

[0026] Ti: It can produce a strong precipitation strengthening effect, improve the strength of steel, and prevent austenite recrystallization; at the same time, it can produce a grain refinement effect and improve the yield strength of steel. The carbon and nitride of Ti have a high dissolution temperature, which will prevent the growth of austenite grains when heated, thereby refining the grain size of the steel plate, improving its strength and toughness, and promoting the comprehensive mechanical properties of the steel plate after pyrotechnic treatment. Taking all factors into consideration, the present invention controls the range of Ti to be 0.005% to 0.035%.

[0027] Al: A strong deoxidizer in steel. A small amount of Al can generate highly fine and ultra-micro oxides, which has a beneficial effect on improving the purity of steel. The purpose of adding Al in the present invention is to ensure that the molten steel is fully deoxidized to create conditions for the subsequent addition of elements such as Ce and La. The range of Als controlled in the present invention is 0.035% to 0.055%.

[0028] Ce, La: Rare metal elements (RE), have good deoxidation and desulfurization effects, improve the fluidity of steel, reduce non-metallic inclusions, make the steel structure dense and pure, improve the anisotropic properties of steel, have a beneficial effect on improving the impact toughness of steel, especially low-temperature impact toughness, and can effectively prevent the growth of steel plate grains during pyrotechnic treatment, thereby improving its comprehensive mechanical properties. The total amount of Ce, La added in the present invention is controlled to be 0.0100% to 0.0200%.

[0029] The second technical solution of the present invention is to provide a method for manufacturing a high-strength ship plate with excellent pyrotechnic performance, including smelting, continuous casting, reheating, rolling, accelerated cooling, and stacking and slow cooling;

[0030] Smelting: Smelt the steel according to the above ingredients.

[0031] a) During converter smelting, the contents of elements such as C, Si, Mn, P, and S are adjusted to be within the scope of the present invention, and other alloy components are added as required for smelting.

[0032] b) refining the molten steel and adjusting the contents of other alloying elements within the scope of the present invention.

[0033] c) subjecting the refined molten steel to RH treatment for 40 to 60 minutes, blowing nitrogen throughout the RH treatment at a pressure of 560 to 600 Pa, ensuring that the final nitrogen content of the steel is within the scope of the present invention, and controlling [H]≤2.0ppm and [O]≤10ppm in the steel.

[0034] d) Add RE element 10 minutes before the end of RH treatment.

[0035] Continuous casting: The obtained molten steel is continuously cast into the required ingot. The tundish adopts low superheat, superheat ≤15℃, full protection casting, and the billet drawing speed is controlled at 1.0-1.5m / min. The water volume of the secondary cooling water is 0.10-0.30m 3 / t, electromagnetic stirring is used during continuous casting, with a stirring current of 400-500A, and a light reduction process is adopted at the end of continuous casting, with a reduction of 5.0-10.0mm.

[0036] Preferably, before reheating, in order to control the grain size of the continuous casting billet, the continuous casting billet is stacked and slowly cooled, the stacking start temperature is 700-750° C., and the slow cooling time is ≥36 h;

[0037] Reheating: Heat the ingot to 1100℃~1250℃, keep warm for 0.5~1.5h, and the total time in the furnace is 3.0~5.0h;

[0038] Rolling: The ingot is rolled into hot-rolled steel plate in two stages. In the first stage, in order to fully break the columnar crystals of the continuous casting ingot and prepare for the subsequent grain refinement, the high-temperature rapid rolling + large reduction method is adopted. The ingot is rolled directly after descaling after leaving the furnace. The roller speed is controlled at 1.5-2.5m / s, and the average reduction of the first three passes is controlled to be 50-60mm. The final rolling temperature is above 1050℃, and the thickness of the warm billet is H+(40-60)mm, where H is the thickness of the final product in mm; the second stage rolling temperature is 830-880℃, and the final rolling temperature is 780-820℃;

[0039] Accelerated cooling: In order to maintain fine grains after rolling and prevent grain growth, the steel plate is cooled at an accelerated rate of 700-750°C, 15.0-30.0°C / s, and 550-650°C.

[0040] Stacking slow cooling: In order to release the internal stress formed during the rolling and cooling process of the steel plate and further form fine precipitation phases, the cooled steel plate is stacked and slowly cooled, with the stacking temperature ≥530℃ and the stacking time ≥20h.

[0041] The beneficial effects of the present invention are:

[0042] (1) The present invention adopts a low-carbon chemical composition system to improve the low-temperature toughness of steel, and adds VN, Ti and other grain-refining elements, while promoting the formation of ferrite structure in steel, and adding RE elements to improve the purity of steel; the continuous casting process adopts low superheat to reduce the center segregation of the ingot, and electromagnetic stirring and light pressure are used to further control the segregation of the ingot; the rolling process adopts two-stage controlled rolling, the first stage of rolling adopts a high-temperature rapid rolling + high pressure reduction process, and the second stage adopts a high final rolling temperature rapid rolling process to obtain refined grains, in preparation for subsequent post-rolling rapid cooling; the rolled steel plate adopts a high start cooling temperature + high return to red temperature accelerated cooling + stacking slow cooling process to control the internal stress and precipitate phase distribution of the final steel plate.

[0043] (2) The metallographic structure of the steel plate is a small amount of ferrite + bainite structure, wherein the ferrite content is 20.0-25.0%, the average grain size is ≤20μm, and the average size of the precipitated phase is ≤50nm. The final steel plate has excellent comprehensive mechanical properties and pyrotechnic properties, with yield strength>485MPa, tensile strength of 560-620MPa, elongation after fracture ≥25.5%, and impact absorption energy at -80℃>270J. The yield strength of the steel plate after pyrotechnic treatment is>475MPa, tensile strength of 551-610MPa, elongation after fracture ≥25.5%, and impact absorption energy at -80℃>200J. DETAILED DESCRIPTION

[0044] The present invention will be further described below by way of examples.

[0045] The embodiment of the present invention performs smelting, continuous casting, reheating, rolling, accelerated cooling, and stacking slow cooling according to the component ratio of the technical solution.

[0046] Continuous casting: The obtained molten steel is continuously cast into the required ingot. The tundish adopts low superheat, superheat ≤15℃, full protection pouring, and the billet drawing speed is controlled at 1.0~1.5m / min. The water volume of the secondary cooling water is 0.10~0.30m 3 / t, electromagnetic stirring is used during continuous casting, the stirring current is 400-500A, and a light reduction process is used at the end of continuous casting, with a reduction of 5.0-10.0mm;

[0047] Reheating: Billet heating temperature: 1100℃~1250℃, holding time: 0.5~1.5h, total furnace time 3.0~5.0h;

[0048] Rolling: The ingot is rolled into hot-rolled steel plate in two stages by high-temperature rapid rolling + large reduction. The ingot is rolled directly after descaling. The roller speed is controlled at 1.5-2.5 m / s. The average reduction of the first three passes is 50-60 mm. The final rolling temperature is above 1050°C. The thickness of the warm billet is (H+40-60) mm, where H is the thickness of the final product in mm. The second stage rolling temperature is 830-880°C, and the final rolling temperature is 780-820°C.

[0049] Accelerated cooling: cooling temperature 700-750℃, cooling rate 15.0-30.0℃ / s, red-return temperature 550-650℃;

[0050] Stacking and slow cooling: The cooled steel plates are stacked and slowly cooled, with the stacking temperature ≥550℃ and the stacking time ≥20h.

[0051] Furthermore, after continuous casting and before reheating, the continuously cast billets are stacked and slowly cooled, the stacking starting temperature is 700-750°C, and the slow cooling time is ≥36h.

[0052] The composition of the steel of the embodiment of the present invention is shown in Table 1. The main process parameters for smelting the steel of the embodiment of the present invention are shown in Table 2. The main process parameters for heating and rolling the steel of the embodiment of the present invention are shown in Table 3. The main process parameters for cooling the steel of the embodiment of the present invention are shown in Table 4. The structural characteristics of the steel of the embodiment of the present invention are shown in Table 5, the mechanical properties are shown in Table 6, and the pyrotechnic properties are shown in Table 7.

[0053] Table 1 Composition of steel according to the present invention (wt%)

[0054]

[0055] Table 2 Main process parameters for steel smelting in the embodiment of the present invention

[0056]

[0057] Table 3 Process parameters for heating and rolling of steel in the embodiment of the present invention

[0058]

[0059] Table 4 Main process parameters for accelerated cooling of steel in the embodiment of the present invention

[0060] Example Cooling temperature / ℃ Cooling speed / ℃ / s Red return temperature / ℃ Stacking temperature / ℃ Stacking time / h 1 674 27.4 599 544 25 2 716 19.2 646 563 32 3 681 17.4 611 551 38 4 712 24.6 587 566 22 5 689 23.2 573 559 23 6 692 21.3 569 556 27 7 696 26.1 628 531 26 8 678 16.7 604 539 30 9 703 25.6 554 574 28 10 707 15.8 637 568 31

[0061] Table 5 Microstructure characteristics of the steel according to the present invention

[0062] Example Ferrite content Average grain size / μm Precipitation phase size / nm 1 23.4 16.4 49.1 2 22.6 17.6 47.8 3 24.9 19.4 48.1 4 21.1 18.1 48.4 5 24.2 17.9 47.7 6 23.3 19.3 46.8 7 21.6 18.6 37.2 8 20.8 17.1 45.6 9 23.8 16.7 39.4 10 20.3 18.9 38.6

[0063] Table 6 Mechanical properties of steel in the present invention

[0064]

[0065] Table 7 pyrotechnic properties of the steel of the present invention

[0066]

[0067] The ship plate metallographic structure produced by the present invention is ferrite + bainite structure, wherein by volume percentage, ferrite is 20% to 25%, the average grain size is ≤20μm, and the average size of the precipitated phase is ≤50nm. The ship plate yield strength is greater than 485MPa, the tensile strength is 560 to 620MPa, the elongation after fracture is ≥25.5%, and the impact absorption energy at -80℃ is greater than 270J; the yield strength of the steel plate after pyrotechnics is greater than 475MPa, the tensile strength is 551 to 610MPa, the elongation after fracture is ≥25.5%, and the impact absorption energy at -80℃ is greater than 200J.

[0068] In order to describe the present invention, the present invention is appropriately and fully illustrated by the examples in the above. The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made should be included in the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A high-strength ship plate with excellent pyrotechnic performance, characterized in that: The composition of the ship plate is as follows by weight percentage: C: 0.02% ~ 0.12%, Si: 0.60% ~ 1.10%, Mn: 1.50% ~ 2.00%, P ≤ 0.008%, S ≤ 0.005%, V: 0.02% ~ 0.12%, N: 0.012% ~ 0.018%, Cu: 0.20% ~ 0.55%, Ni: 0.35% ~ 0.65%, Mo: 0.20% ~ 0.45%, Ti: 0.005% ~ 0.035%, Als: 0.035% ~ 0.055%, Ce + La: 0.010% ~ 0.020%; the balance is Fe and unavoidable impurities.

2. The high-strength ship plate with excellent pyrotechnic performance according to claim 1, characterized in that: In the ship plate, Ni / Mo=1.1-2.

0.

3. The high-strength ship plate with excellent pyrotechnic performance according to claim 1, characterized in that: The ship plate metallographic structure is ferrite + bainite structure, wherein the ferrite is 20% to 25% by volume, the average grain size is ≤20 μm, and the average precipitate phase size is ≤50 nm.

4. The high-strength ship plate with excellent pyrotechnic performance according to claim 1, characterized in that: The ship plate has a yield strength of >485MPa, a tensile strength of 560-620MPa, an elongation after fracture of ≥25.5%, and an impact absorption energy of -80°C of >270J. The yield strength of the steel plate after pyrotechnic treatment is >475MPa, a tensile strength of 551-610MPa, an elongation after fracture of ≥25.5%, and an impact absorption energy of -80°C of >200J.

5. A method for manufacturing a high-strength ship plate with excellent pyrotechnic performance as claimed in any one of claims 1 to 4, comprising smelting, continuous casting, reheating, rolling, accelerated cooling, and stacking slow cooling; characterized in that: Continuous casting: The obtained molten steel is continuously cast into the required ingot. The tundish adopts low superheat, superheat ≤15℃, full protection pouring, and the billet drawing speed is controlled at 1.0~1.5m / min. The water volume of the secondary cooling water is 0.10~0.30m 3 / t, electromagnetic stirring is used during continuous casting, the stirring current is 400-500A, and a light reduction process is used at the end of continuous casting, with a reduction of 5.0-10.0mm; Reheating: Billet heating temperature: 1100℃~1250℃, holding time: 0.5~1.5h, total furnace time 3.0~5.0h; Rolling: The ingot is rolled into hot-rolled steel plate in two stages by high-temperature rapid rolling + large reduction. The ingot is rolled directly after descaling. The roller speed is controlled at 1.5-2.5 m / s, and the average reduction of the first three passes is controlled to be 50-60 mm. The final rolling temperature is above 1050°C, and the thickness of the warm billet is H+(40-60) mm, where H is the thickness of the final product. The second stage rolling temperature is 830-880°C, and the final rolling temperature is 780-820°C. Accelerated cooling: cooling temperature 700-750℃, cooling rate 15.0-30.0℃ / s, red-return temperature 550-650℃; Stacking and slow cooling: The cooled steel plates are stacked and slowly cooled, with the stacking temperature ≥550℃ and the stacking time ≥20h.

6. The method for manufacturing a high-strength ship plate with excellent pyrotechnic performance according to claim 5, characterized in that: After continuous casting and before reheating, the continuous casting billets are stacked and slowly cooled. The stacking starting temperature is 700-750°C and the slow cooling time is ≥36h.

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