Low-temperature steel plate with excellent CTOD performance and manufacturing method

Abstract

According to the low-temperature steel plate with the excellent CTOD performance and the manufacturing method, a low-carbon chemical component system is adopted, and the grain size and precipitated phase composition of steel are controlled by adding alloy elements such as V-N, Ni, W and Zr; three-stage controlled rolling is adopted in the rolling process, the accelerated cooling and stacking slow cooling process is adopted in the rolled steel plate, the internal stress and precipitated phase distribution of the final steel plate are controlled, the yield strength of the steel plate produced through the method is larger than or equal to 550 MPa, and the CTOD value of the steel plate at the temperature of-60 DEG C is larger than 1.2 mm; meanwhile, under the 60 KJ / cm high heat input welding process, the impact absorption energy of a coarse grain area CGHZ of a welding joint at-80 DEG C is larger than or equal to 264 J, and the CTOD value at-60 DEG C is larger than 1.0 mm.

Description

Technical Field

[0001] The invention belongs to the field of metal materials, and in particular relates to a low-temperature steel plate with excellent CTOD performance and a manufacturing method thereof. Background Art

[0002] As conventional exploitable oil and gas resources are gradually depleted, the rich energy reserves in the Arctic region have attracted more and more attention, which has promoted the demand and development of large polar ships such as polar oil tankers, polar LNG ships, and polar container ships with icebreaking capabilities. Polar ships have long been facing the harsh service environment of ultra-low temperatures, which puts forward higher requirements for low-temperature steel for polar ships that meet polar service conditions. Low-temperature steel for polar ships with excellent low-temperature toughness, fracture toughness and easy welding is the development trend.

[0003] CTOD, or crack tip opening displacement, refers to the relative distance between the two surfaces at the original crack tip after the crack body is subjected to an opening load. It is an important indicator for evaluating the fracture toughness of shipbuilding steel. Therefore, the CTOD performance is increasingly used to evaluate the low-temperature performance of steel plates.

[0004] The invention name is “Thick steel plate with excellent low-temperature impact toughness and CTOD characteristics and its manufacturing method”, and the patent document with application number 201780078777.1 discloses a thick steel plate with excellent low-temperature impact toughness and CTOD characteristics, whose chemical composition is: C 0.02%-0.06%, Si 0.005%-0.08%, Mn1.0%-2.0%, P≤0.01%, S≤0.003%, Al 0.001%-0.01%, Ni 0.5%-2.0%, Ti0.001%-0.02%, Nb 0.005%-0.03%, Cu 0.05%-0.4%, N 0.002-0.006%, and the balance is Fe and unavoidable impurities. The steel plate has excellent low-temperature impact toughness and CTOD performance, but its process includes slab heating, recrystallization zone rolling, non-recrystallization zone rolling, cooling, tempering and other processes. The process is complicated and will inevitably increase the production cost of the steel plate.

[0005] The patent document with the invention name "Marine engineering steel with excellent CTOD performance of welded joints and its manufacturing method" and application number 202110788234.7 discloses marine engineering steel with excellent CTOD performance of welded joints and its manufacturing method, and its chemical composition is: C 0.07%-0.12%, Si 005%-0.15%, Mn 1.35%-1.65%, P≤0.012%, S≤0.003%, Cu≤0.25%, Ni 0.15%-0.35%, Cr 0.1%-0.25%, Mo0.05%-0.15%, Ti0.010%-0.030%, N 0.004%-0.008%, Als 0.01%-0.025%, Ce0.010%-0.030%, and the balance is Fe and unavoidable impurities. The -10℃ CTOD of the welded joint of this steel plate is ≥0.38mm, which cannot meet the fracture toughness requirements of large polar ships.

[0006] The invention name is "Ultra-high strength marine engineering steel with excellent weld joint CTOD performance and its manufacturing method", and the patent document with application number 201810393249.1 discloses an ultra-high strength marine engineering steel with excellent weld joint CTOD performance, and its chemical composition is: C 0.08-0.16%, Si0.1-0.35%, Mn 0.5-1.6%, P≤0.015%, S≤0.003%, Cr 0.5-1.5%, Ni 1.5-3.0%, Mo 0.2-0.7%, Cu 0.1-0.6%, Al0.02-0.08%, Nb 0.005-0.05%, V 0.01-0.10%, Ti0.005-0.5%, B 0.001-0.002%, N≤0.004%, and the balance is Fe and unavoidable impurities. The patented process includes smelting, pouring, rolling, heat treatment and other processes, and its heat treatment process is complicated. In addition, the -10℃ CTOD of the base material is ≥0.8mm, and the -10℃ CTOD of the welded joint is ≥0.4mm. It also cannot meet the fracture toughness requirements of large polar ships.

[0007] The patent document with the invention name “500MPa grade steel plate for marine engineering and preparation method thereof” and application number 202410156277.7 discloses a 500MPa grade steel plate for marine engineering, whose chemical composition is: C 0.03-0.09%, Si 0.15-0.25%, Mn 1.15-1.65%, Cr 0.13-0.30%, Ni 0.13-0.35%, Cu 0.13-0.30%, Mo 0.09-0.20%, Nb 0.02-0.04%, Ti 0.01-0.02%, Alt 0.02-0.05%, P≤0.015%, S≤0.003%, N≤0.0045%, O≤0.002%, and the balance is Fe and unavoidable impurities. The yield strength of the steel plate is ≥500MPa, the tensile strength is 560-715MPa, and the CTOD of the coarse grain zone and critical zone of the welded steel plate at -10°C is ≥0.8mm. It also cannot meet the fracture toughness requirements of large polar ships.

[0008] In summary, the current production of low-temperature steel for large polar ships mainly has the following shortcomings.

[0009] 1) The process is complicated, resulting in an increase in the production cost of the steel plate.

[0010] 2) The fracture toughness of the steel plate is insufficient, which makes it difficult to meet the fracture toughness requirements of low-temperature steel plates for large polar ships. Summary of the invention

[0011] The object of the present invention is to overcome the above-mentioned problems and shortcomings and to provide a low-temperature steel plate and a manufacturing method having excellent CTOD performance, wherein the yield strength is ≥550MPa and the CTOD value of the steel plate at -60°C is >1.2mm; at the same time, under a 60KJ / cm high heat input welding process, the impact absorption energy of the coarse-grained zone of the weld joint at -80°C is ≥264J and the CTOD value at -60°C is >1.0mm.

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

[0013] A low-temperature steel plate with excellent CTOD performance and a manufacturing method thereof, wherein the components of the steel plate are as follows by weight percentage: C: 0.040% to 0.100%, Si: 0.05% to 0.30%, Mn: 0.80% to 1.40%, P≤0.007%, S≤0.004%, V: 0.070% to 0.180%, N: 0.0160% to 0.0220%, Cu: 0.55% to 0.90%, Ni: 0.80% to 1.20%, Ti: 0.005% to 0.025%, Als: 0.010% to 0.025%, W: 0.050% to 0.100%, Zr: 0.100% to 0.170%, and the balance is Fe and unavoidable impurities.

[0014] In the low temperature steel plate, Al / Zr=0.07-0.19.

[0015] The microstructure of the low-temperature steel plate is a small amount of ferrite + lath bainite, and by volume percentage: ferrite ≤10%, lath bainite>90%; the average grain size is ≤15μm; the precipitated phases in the low-temperature steel plate are Ti(C,N) and V(C,N), the average size of the precipitated phases is ≤40nm, and they are dispersed.

[0016] The yield strength of the low-temperature steel plate is ≥550MPa, the tensile strength is 690-770MPa, the elongation after fracture is ≥24.0%, and the CTOD value of the steel plate at -60°C is greater than 1.2mm.

[0017] The low-temperature steel plate has a weld joint tensile strength of 690-770 MPa under a 60 KJ / cm high heat input welding process, a weld joint coarse grain zone CGHZ impact absorption energy KV2≥264 J at -80°C, and a CTOD value>1.0 mm at -60°C.

[0018] The reasons for the composition design of the present invention are as follows:

[0019] C: basic strengthening element in steel, it is the main element to ensure strength and hardness in the technical solution of the present invention; when its content is low, the amount of carbides etc. generated will be reduced, affecting the effect of grain refinement during rolling. When the content is high, the cementite content in the steel will increase, the size will increase, and the distribution will be more dense, and cementite will aggregate at the grain boundary. The large-sized cementite aggregates at the grain boundary will cause stress concentration, which will have an adverse effect on the low-temperature toughness and fracture toughness of the steel plate, and reduce the welding performance of the steel plate. Therefore, considering the cost, performance and other factors, the present invention controls the range of C to be 0.040% to 0.100%.

[0020] Si: An essential element for steelmaking deoxidation. It has a strong solid solubility in steel and can improve the elastic limit and yield strength of steel, reduce the strength difference between the soft phase ferrite and the hard phase, and improve the resistance of crack initiation and expansion in steel. However, when the content is too high, it has an adverse effect on the low temperature toughness and surface quality of steel. The present invention controls the range of Si to be 0.05% to 0.30%.

[0021] Mn: forms substitutional solid solution in steel and can be dissolved in Fe matrix in large quantities. It can delay the transformation of ferrite and pearlite in steel, greatly increase the hardenability of steel, reduce the brittle transition temperature of steel, and improve impact toughness. However, if the Mn content is too high, it is easy to form segregation in steel, which has an adverse effect on the plasticity and toughness of steel. Taking all factors into consideration, the present invention controls the range of Mn to be 0.80% to 1.40%.

[0022] V: A strong carbide-forming element, which has little effect on austenite recrystallization. At low temperatures, a large amount of V carbides precipitate, which has obvious precipitation strengthening and microstructure refinement effects, thereby improving the plasticity and toughness of steel. It also has a strong solid solution strengthening effect in steel, which promotes the uniformity of steel strength and uniformity when deformed by external forces. In addition, its high-hardness precipitation phase particles are dispersed in the steel, which is conducive to hindering the rapid expansion of cracks in the steel, thereby improving the fracture toughness of the steel. However, when the content is too high, the tough-to-brittle transition temperature of the steel plate will be reduced. Taking into account the performance, cost and other factors of the steel, the present invention controls the range of V to be 0.050% to 0.180%.

[0023] N: An important strengthening and 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, promoting the formation of ferrite in the steel, reducing the yield strength ratio of the steel, and making its grains fine, thereby improving the plasticity and toughness of the steel. Nitrogen-containing steel not only eliminates the cost increase caused by degassing and refining and denitrification during the steelmaking process, but also the nitrogen addition in the steel can give full play to the role of micro-alloying elements, save the amount of alloying elements, greatly reduce production costs, and thus improve its comprehensive mechanical properties. Taking into account the performance and cost, the present invention controls the range of N to be 0.0160%-0.0220%.

[0024] 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. However, when the content is too high, the hot brittleness of steel deteriorates and hot cracks are easily generated. The present invention controls the range of Cu to be 0.55% to 0.90%.

[0025] 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. In addition, the addition of Ni can also reduce the tendency of thermal cracking when the Cu content is high. Considering factors such as cost and performance, the present invention controls the range of Ni to be 0.80%-1.20%.

[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 and improving its strength and toughness. However, when the content is too high, it will show a very strong precipitation strengthening effect and deteriorate the toughness of the steel. Taking all factors into consideration, the present invention controls the range of Ti to be 0.005%-0.025%.

[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 create conditions for the subsequent addition of Zr on the basis of ensuring that the molten steel is fully deoxidized, and to prevent the formation of a large amount of ZrO2 after the addition of Zr. The range of Als controlled in the present invention is 0.010%-0.025%.

[0028] W: refines grains, reduces the overheating tendency of steel, improves the strength, toughness and thermal stability of steel, and can improve the strength of steel without reducing plasticity and toughness. The present invention controls W in the range of 0.050%-0.100%.

[0029] Zr: A strong carbide-forming element. A small amount of Zr has the functions of degassing, purification and grain refinement, which is beneficial to improving the low-temperature performance of steel. In order to better play its role in grain refinement, it needs to be used in combination with Al when added, and Al / Zr is controlled to be 0.07-0.19. Taking into account factors such as cost and performance, the present invention controls the range of Zr to be 0.100%-0.170%.

[0030] The second technical solution of the present invention is to provide a method for manufacturing a low-temperature steel plate with excellent CTOD performance, including smelting, continuous casting, heating, rolling, cooling, and stacking and slow cooling;

[0031] (1) smelting the steel according to the above composition, including converter smelting, LF refining, and RH treatment;

[0032] a) adjusting the contents of elements such as C, Si, Mn, P, S, etc. during converter smelting to be within the scope of the present invention, and adding other alloy components for smelting as required;

[0033] b) subjecting the molten steel to LF refining and adjusting the contents of other alloying elements to within the scope of the present invention;

[0034] c) subjecting the refined molten steel to RH treatment for 40 to 60 minutes, blowing nitrogen throughout the RH treatment at a pressure of 600 to 660 Pa, ensuring that the final nitrogen content of the steel is 0.0160% to 0.0220%, and controlling [H] ≤ 2.0 ppm and [O] ≤ 10 ppm in the steel;

[0035] (2) Continuous casting: The molten steel obtained in step (1) is continuously cast to obtain the desired ingot. The tundish is low superheated, with a superheat of 10-20°C, and the casting is protected throughout the entire process. The casting speed is controlled to be 0.80-1.20 m / min, and the water volume of the secondary cooling water is 0.15-0.35 m 3 / t, electromagnetic stirring is used at the end of continuous casting, the stirring current is 450-550A, and light reduction process is used at the end of continuous casting, the reduction rate is 4.0%-5.0%;

[0036] (3) Ingot cooling: In order to control the grain size of the continuous casting ingot, the high-temperature continuous casting ingot is rapidly cooled after continuous casting, with the cooling temperature of 850-900°C and the cooling rate of 2.0-7.0°C / s. After cooling to 650-700°C, the ingot is stacked and slowly cooled to reduce the internal stress of the continuous casting ingot after rapid cooling, and optimize the distribution of precipitation phases in the continuous casting ingot, so that a large amount of VC precipitation phase is formed in the steel. The stacking time is ≥36h, and the temperature of the continuous casting ingot is guaranteed to be <100°C.

[0037] (4) Heating: heating the ingot obtained in step (3) to 1100° C. to 1220° C., with a holding time of 0.5 to 1.5 h and a total furnace time of ≤5.5 h;

[0038] (5) Rolling: In order to obtain steel plates with fine and uniform grains, the ingot is rolled into hot-rolled steel plates in three stages.

[0039] The first stage adopts a high-speed and large-reduction process based on a large temperature gradient. The ingot is descaled by high-pressure water after it leaves the furnace. After descaling, rolling is carried out directly. The roller speed is controlled at 1.5-2.5 m / s, the first pass reduction is controlled to be greater than 60 mm, the final rolling temperature is above 1060°C, the thickness of the warm ingot is (3.0-3.5) t, and t is the thickness of the final product. In the preferred dephosphorization process, the high-pressure water pressure is 0.9-1.1 MPa to ensure that the temperature difference between the ingot surface temperature and the core temperature is greater than 50°C.

[0040] The second stage also uses a high temperature and large reduction process to further accumulate deformation energy in the steel and prepare conditions for subsequent grain refinement. The starting rolling temperature is 950-1000°C, the final rolling temperature is 850-900°C, the thickness of the warm billet is (1.5-2.0)t, and the reduction rate of each pass is controlled to be ≥7.0%;

[0041] The third stage adopts the rolling in the non-recrystallization zone, with the starting rolling temperature of 780-830℃ and the final rolling temperature of 700-750℃, in order to fully flatten the austenite in the non-recrystallization zone, accumulate dislocation and deformation energy, and refine the subsequent phase transformation grains. The average grain size of the steel plate is finally ≤10μm.

[0042] (6) Cooling: In order to maintain fine grains after rolling and prevent grain growth, the steel plate is cooled at an accelerated rate of 650 to 690 °C, a cooling rate of 10.0 to 20.0 °C / s, and a red-return temperature of 430 to 480 °C.

[0043] (7) Stacking and slow cooling: In order to release the internal stress formed during the rolling and cooling process of the steel plate and further form fine VC precipitation phase, the cooled steel plate is stacked and slowly cooled, with the stacking temperature ≥350℃ and the stacking time ≥20h.

[0044] The beneficial effects of the present invention are:

[0045] (1) A low-carbon chemical composition system is adopted to improve the low-temperature toughness of steel. The grain size and precipitate composition of steel are controlled by adding alloying elements such as VN, Ni, W, and Zr. Low superheat is used in the smelting process to reduce the center segregation of the ingot. Electromagnetic stirring and light reduction are used at the end of continuous casting to further reduce the segregation of the ingot. The rolling process adopts a three-stage controlled rolling process. The first stage of rolling adopts a high-speed and large-reduction process based on a large cross-sectional temperature gradient. The high-pressure water rapid descaling process is used to form a large temperature gradient between the surface and the core of the ingot, which promotes the transmission of deformation to the core. The second stage also adopts a high-temperature and large-reduction process to further accumulate deformation energy in the steel and prepare conditions for subsequent grain refinement. The third stage adopts non-recrystallization zone rolling to refine the grain size of the steel. The rolled steel plate adopts an accelerated cooling + stacking slow cooling process to control the internal stress and precipitate distribution of the final steel plate.

[0046] (2) The metallographic structure of the steel plate is a small amount of ferrite + lath bainite structure, the average grain size of the steel plate is ≤15μm, and the precipitate phase is composed of Ti(C,N) and V(C,N), with an average size of ≤40nm and dispersed distribution. The fine grain size and dispersed distribution of the precipitate phase can increase the resistance to crack propagation in the steel, thereby improving the CTOD value of the steel plate. The final CTOD value of the steel plate at -60°C is greater than 1.2mm, and under the 60KJ / cm high heat input welding process, the CTOD value of the coarse grain zone (CGHZ) of the welded joint is greater than 1.0mm. The present invention adopts a three-stage TMCP preparation process, does not require subsequent heat treatment, and reduces the production cost of the steel plate. DETAILED DESCRIPTION

[0047] The present invention will be further described below by way of examples.

[0048] The embodiment of the present invention performs smelting, continuous casting, rolling, cooling, and stacking and slow cooling according to the component ratio of the technical solution. Specifically:

[0049] (1) Ingot cooling: After continuous casting, the high-temperature ingot is rapidly cooled, with a cooling temperature of 850-900°C and a cooling rate of 2.0-7.0°C / s. After cooling to 650-700°C, the ingot is stacked and slowly cooled offline, with a stacking time of ≥36h.

[0050] (2) Heating: The ingot is then heated to 1100°C to 1220°C, with a holding time of 0.5 to 1.5 hours, and a total furnace time of ≤5.5 hours;

[0051] (3) Rolling: The ingot is rolled into hot-rolled steel plate in three stages.

[0052] The first stage is carried out by adopting a high-speed and large-reduction process based on a large temperature gradient. The ingot is descaled by high-pressure water after it leaves the furnace, and rolling is carried out directly after descaling. The roller speed is controlled at 1.5-2.5 m / s, the first pass reduction is controlled to be greater than 60 mm, the final rolling temperature is above 1060°C, and the thickness of the warm ingot is (3.0-3.5) t, where t is the thickness of the final product.

[0053] The second stage rolling temperature is 950~1000℃, the final rolling temperature is 850~900℃, the thickness of the warm billet is (1.5~2.0)t, and the reduction rate of each pass is controlled to be ≥7.0%.

[0054] The third stage adopts non-recrystallization zone rolling, with the starting rolling temperature of 780-830℃ and the final rolling temperature of 700-750℃;

[0055] (4) Cooling: After rolling, the steel plate is cooled at an accelerated rate of 650 to 690°C, a cooling rate of 10.0 to 20.0°C / s, and a red-return temperature of 430 to 480°C.

[0056] (5) Stacking and slow cooling: The steel plates are then stacked and slowly cooled, with the stacking temperature ≥350°C and the stacking time ≥20h.

[0057] Further; smelting: including converter smelting, LF refining, RH treatment;

[0058] The molten steel after LF refining is subjected to RH treatment for 40 to 60 minutes. Nitrogen is blown throughout the RH treatment at a pressure of 600 to 660 Pa to ensure that the final N content of the steel is N: 0.0160% to 0.0220%, and [H] in the steel is controlled to be ≤2.0ppm and [O] ≤10ppm.

[0059] Furthermore, the tundish superheat is 10-20°C, the casting is protected throughout the process, the billet drawing speed is 0.80-1.20 m / min, and the secondary cooling water volume is 0.15-0.35 m 3 / t, electromagnetic stirring is adopted at the end of continuous casting, the stirring current is 450-550A, and light reduction process is adopted at the end of continuous casting, the reduction rate is 4.0%-5.0%.

[0060] Furthermore, during the descaling process, the high-pressure water pressure is 0.9-1.1 MPa, and the temperature difference between the surface temperature and the core temperature of the ingot is greater than 50°C.

[0061] Furthermore, after rolling in the third stage non-recrystallization zone, the average grain size of the steel plate is ≤10μm.

[0062] The composition of the steel of the present invention is shown in Table 1. The main process parameters of the steel of the present invention are shown in Table 2 to Table 6. The microstructure and parent material properties of the steel of the present invention are shown in Table 7 to Table 8.

[0063] Table 1 Composition of steel according to the present invention (wt%)

[0064] serial number C Si Mn V N Cu Ni P S Ti Al W Zr Al / Zr 1 0.048 0.16 1.14 0.072 0.0164 0.67 1.07 0.005 0.003 0.007 0.013 0.063 0.167 0.08 2 0.057 0.08 0.89 0.177 0.0172 0.64 1.03 0.002 0.003 0.023 0.019 0.074 0.154 0.12 3 0.097 0.27 1.03 0.168 0.0218 0.89 0.96 0.003 0.002 0.014 0.014 0.076 0.158 0.09 4 0.069 0.29 0.97 0.084 0.0196 0.87 1.12 0.006 0.004 0.017 0.017 0.068 0.133 0.13 5 0.073 0.09 1.26 0.156 0.0166 0.58 1.09 0.002 0.003 0.019 0.012 0.082 0.141 0.09 6 0.051 0.22 1.08 0.093 0.0179 0.62 0.82 0.004 0.001 0.022 0.021 0.097 0.114 0.18 7 0.064 0.26 1.37 0.144 0.0194 0.78 0.89 0.002 0.003 0.024 0.022 0.092 0.126 0.17 8 0.086 0.09 0.83 0.108 0.0188 0.82 1.19 0.005 0.004 0.013 0.024 0.054 0.149 0.16 9 0.094 0.13 0.94 0.136 0.0181 0.73 1.16 0.004 0.002 0.014 0.016 0.058 0.163 0.10 10 0.043 0.07 1.09 0.114 0.0209 0.67 0.93 0.002 0.001 0.021 0.018 0.088 0.106 0.17

[0065] Table 2 Main process parameters for steel smelting in the embodiment of the present invention

[0066]

[0067] Table 3 Main process parameters for cooling the steel continuous casting billet according to the embodiment of the present invention

[0068] serial number Cooling temperature / ℃ Cooling speed / ℃ / s Final cooling temperature / ℃ Stacking time / h Stacking completion temperature / ℃ 1 862 3.2 664 38 88 2 886 4.1 686 43 79 3 892 6.2 693 44 92 4 873 6.6 671 37 83 5 878 3.7 676 41 74 6 869 4.6 667 42 97 7 881 5.1 683 36 64 8 898 5.7 696 39 68 9 854 2.3 652 43 84 10 859 2.7 656 41 89

[0069] Table 4 Main process parameters for heating steel in the embodiment of the present invention

[0070] serial number Thickness / mm Heating temperature / ℃ Insulation time / h Total furnace time / h Temperature difference of ingot after descaling / ℃ 1 75 1189 0.9 4.7 58 2 78 1178 1.2 4.8 69 3 80 1109 1.3 4.9 54 4 85 1137 0.9 5.3 73 5 75 1206 0.8 5.1 62 6 80 1213 1.1 4.6 77 7 75 1194 1.3 4.7 66 8 80 1129 1.1 4.8 64 9 80 1147 0.6 5.4 57 10 80 1158 0.7 5.2 68

[0071] Table 5 Main process parameters of steel rolling in the embodiment of the present invention

[0072]

[0073] Table 6 Main process parameters for cooling steel in the embodiment of the present invention

[0074] serial number Cooling temperature / ℃ Cooling speed / ℃ / s Red return temperature / ℃ Stacking temperature / ℃ Stacking time / h 1 654 19.1 433 393 24 2 668 16.2 446 414 33 3 672 17.1 438 406 28 4 661 10.4 452 418 24 5 672 13.8 476 407 26 6 682 15.7 442 404 31 7 688 12.6 472 387 32 8 657 11.4 457 489 27 9 663 14.7 468 426 23 10 677 18.4 464 411 29

[0075] Table 7 Steel structure characteristics of the present invention

[0076]

[0077] Table 8 Mechanical properties of steel base material in the embodiment of the present invention

[0078]

[0079] Table 9 Welding performance of steel in the embodiment of the present invention

[0080]

[0081] Note: The welding performance of the steel plate was evaluated by submerged arc welding with a welding line energy of 60 KJ / cm. The performance of the steel plate welded joint is shown in Table 9.

[0082] The microstructure of the low-temperature steel plate produced by the present invention is a small amount of ferrite + lath bainite, and by volume percentage: ferrite ≤10%, lath bainite>90%; the average grain size of the steel plate is ≤15μm; the precipitation phase in the low-temperature steel plate is composed of Ti(C,N) and V(C,N), and the average size of the precipitation phase is ≤40nm.

[0083] The yield strength of the parent material is ≥550MPa, the tensile strength is 690~770MPa, the elongation after fracture is ≥24.0%, and the CTOD value of the steel plate at -60℃ is>1.2mm; under the 60KJ / cm high heat input welding process, the tensile strength of the welded joint is 690~770MPa, the impact absorption energy KV2 of the coarse grain zone CGHZ of the welded joint at -80℃ is ≥264J, and the CTOD value at -60℃ is>1.0mm.

[0084] 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 low temperature steel plate with excellent CTOD performance, characterized in that: The components of the steel plate are as follows by weight percentage: C: 0.040% ~ 0.100%, Si: 0.05% ~ 0.30%, Mn: 0.80% ~ 1.40%, P ≤ 0.007%, S ≤ 0.004%, V: 0.070% ~ 0.180%, N: 0.0160% ~ 0.0220%, Cu: 0.55% ~ 0.90%, Ni: 0.80% ~ 1.20%, Ti: 0.005% ~ 0.025%, Al: 0.010% ~ 0.025%, W: 0.050% ~ 0.100%, Zr: 0.100% ~ 0.170%, and the balance is Fe and unavoidable impurities.

2. The low-temperature steel plate with excellent CTOD performance according to claim 1, characterized in that: In the low temperature steel plate, Al / Zr=0.07-0.

19.

3. The low temperature steel plate with excellent CTOD performance according to claim 1, characterized in that: The microstructure of the low-temperature steel plate is a small amount of ferrite + lath bainite, and by volume percentage: ferrite ≤10%, lath bainite>90%; the average grain size is ≤15μm; the precipitated phases in the low-temperature steel plate are Ti(C,N) and V(C,N), and the average size of the precipitated phases is ≤40nm.

4. The low-temperature steel plate with excellent CTOD performance according to claim 1, characterized in that: The yield strength of the steel plate is ≥550MPa, the tensile strength is 690~770MPa, the elongation after fracture is ≥24.0%, and the CTOD value of the steel plate at -60℃ is >1.2mm; under the 60KJ / cm high heat input welding process, the tensile strength of the welded joint is 690~770MPa, the impact absorption energy KV2 of the coarse grain zone CGHZ of the welded joint at -80℃ is ≥264J, and the CTOD value at -60℃ is >1.0mm.

5. A method for manufacturing a low-temperature steel plate with excellent CTOD performance according to any one of claims 1 to 4, comprising smelting, continuous casting, cooling of ingots, heating, rolling, cooling, and stacking and slow cooling; characterized in that: (1) Ingot cooling: After continuous casting, the high-temperature ingot is rapidly cooled, with a cooling temperature of 850-900°C and a cooling rate of 2.0-7.0°C / s. After cooling to 650-700°C, the ingot is stacked and slowly cooled offline, with a stacking time of ≥36h. (2) Heating: The ingot is then heated to 1100°C to 1220°C, with a holding time of 0.5 to 1.5 hours, and a total furnace time of ≤5.5 hours; (3) Rolling: The ingot is rolled into hot-rolled steel plate in three stages. The first stage is carried out by a high-speed and large-reduction process based on a large temperature gradient. The ingot is descaled by high-pressure water after it leaves the furnace, and rolling is carried out directly after descaling. The roller speed is controlled at 1.5-2.5 m / s, the first pass reduction is controlled to be greater than 60 mm, the final rolling temperature is above 1060°C, and the thickness of the warm ingot is (3.0-3.5) t, where t is the thickness of the final product. The second stage rolling temperature is 950~1000℃, the final rolling temperature is 850~900℃, the thickness of the warm billet is (1.5~2.0)t, and the reduction rate of each pass is controlled to be ≥7.0%. The third stage adopts non-recrystallization zone rolling, with the starting rolling temperature of 780-830℃ and the final rolling temperature of 700-750℃; (4) Cooling: After rolling, the steel plate is cooled at an accelerated rate of 650 to 690°C, a cooling rate of 10.0 to 20.0°C / s, and a red-return temperature of 430 to 480°C. (5) Stacking and slow cooling: The steel plates are then stacked and slowly cooled, with the stacking temperature ≥350°C and the stacking time ≥20h.

6. The method for manufacturing a low-temperature steel plate with excellent CTOD performance according to claim 5, characterized in that: Smelting: including converter smelting, LF refining, and RH treatment; The molten steel after LF refining is subjected to RH treatment for 40 to 60 minutes. Nitrogen is blown throughout the RH treatment at a pressure of 600 to 660 Pa to ensure that the final N content of the steel is N: 0.0160% to 0.0220%, and [H] in the steel is controlled to be ≤2.0ppm and [O] ≤10ppm.

7. The method for manufacturing a low-temperature steel plate with excellent CTOD performance according to claim 5, characterized in that: Continuous casting: Tundish superheat 10-20℃, full protection pouring, casting speed 0.80-1.20m / min, secondary cooling water volume 0.15-0.35m 3 / t, electromagnetic stirring is adopted at the end of continuous casting, the stirring current is 450-550A, and light reduction process is adopted at the end of continuous casting, the reduction rate is 4.0%-5.0%.

8. The method for manufacturing a low-temperature steel plate with excellent CTOD performance according to claim 5, characterized in that: During the descaling process, the high-pressure water pressure is 0.9-1.1 MPa, and the temperature difference between the surface temperature and the core temperature of the ingot is greater than 50°C.

9. The method for manufacturing a low-temperature steel plate with excellent CTOD performance according to claim 5, characterized in that: After rolling in the third stage non-recrystallization zone, the average grain size of the steel plate is ≤10μm.

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