Low-temperature steel sheet having excellent ctod performance and method of manufacturing the same

Abstract

The application provides a low-temperature steel plate with excellent CTOD performance and a manufacturing method, adopts a low-carbon chemical composition system, controls the grain size and precipitated phase composition of the steel by adding alloy elements such as V-N, Ni, W and Zr, adopts three-stage controlled rolling in a rolling process, and adopts accelerated cooling + stacking slow cooling process after rolling of the steel plate to control the internal stress and precipitated phase distribution of the final steel plate, the steel plate produced by the application has a yield strength of greater than or equal to 550 MPa, and the CTOD value of the steel plate at -60 DEG C is greater than 1.2 mm; meanwhile, under a large heat input welding process of 60 KJ / cm, the impact absorbed energy of the CGHZ of the welded joint in the coarse grain zone at -80 DEG C is greater than or equal to 264 J, and the CTOD value at -60 DEG C is greater than 1.0 mm.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal materials, and particularly relates to a low-temperature steel plate with excellent CTOD performance and a manufacturing method. BACKGROUND

[0002] With the gradual depletion of conventional recoverable oil and gas energy, the rich energy reserves in the Arctic region have attracted more and more attention, thereby promoting the demand and development of large polar ships such as polar oil tankers, polar LNG ships, polar container ships and the like with icebreaking capacity. The polar ships are long-term exposed to the harsh service environment of ultra-low temperature, and higher requirements are put forward for the low-temperature steel for polar ships that meet the polar service conditions. The low-temperature steel for polar ships with excellent low-temperature toughness, fracture toughness and easy weldability is the development trend.

[0003] CTOD, i.e. crack tip opening displacement, refers to the relative distance of the opening of the two surfaces at the original crack tip after the crack body is subjected to opening load, and is an important index for evaluating the fracture toughness of the steel for ships. Therefore, the CTOD performance is more and more used to evaluate the low-temperature performance of the steel plate.

[0004] The patent document with the title of "Thick steel plate with excellent low-temperature impact toughness and CTOD characteristics and manufacturing method thereof" and the application number of 201780078777.1 discloses a thick steel plate with excellent low-temperature impact toughness and CTOD characteristics, and the chemical composition thereof is: C 0.02%-0.06%, Si 0.005%-0.08%, Mn 1.0%-2.0%, P≤0.01%, S≤0.003%, Al 0.001%-0.01%, Ni 0.5%-2.0%, Ti 0.001%-0.02%, Nb 0.005%-0.03%, Cu 0.05%-0.4%, N 0.002-0.006%, and the balance is Fe and inevitable impurities. The low-temperature impact toughness and CTOD performance of the steel plate are excellent, but the process thereof includes slab heating, recrystallization zone rolling, non-recrystallization zone rolling, cooling, tempering and the like, the process is complex, and the production cost of the steel plate will inevitably be increased.

[0005] The patent with the title of "Offshore steel with excellent CTOD performance of welded joint and manufacturing method thereof" and the application number of 202110788234.7 discloses an offshore steel with excellent CTOD performance of welded joint and a manufacturing method thereof. The chemical composition of the steel is: C 0.07%-0.12%, Si 0.05%-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%, Mo 0.05%-0.15%, Ti 0.010%-0.030%, N 0.004%-0.008%, Als 0.01%-0.025%, Ce 0.010%-0.030%, and the balance of Fe and inevitable impurities. The CTOD of the welded joint of the steel plate at-10℃ is≥0.38mm, which cannot meet the requirements of large polar ships for fracture toughness.

[0006] The patent with the title of "Ultra-high strength offshore engineering steel with excellent CTOD performance of welded joint and manufacturing method thereof" and the application number of 201810393249.1 discloses an ultra-high strength offshore engineering steel with excellent CTOD performance of welded joint. The chemical composition of the steel is: C 0.08-0.16%, Si 0.1-0.35%, 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%, Al 0.02-0.08%, Nb 0.005-0.05%, V 0.01-0.10%, Ti 0.005-0.5%, B 0.001-0.002%, N≤0.004%, and the balance of Fe and inevitable impurities. The patent process includes smelting pouring, rolling, heat treatment and other process, and the heat treatment process is complex. The CTOD of the base material at-10℃ is≥0.8mm, and the CTOD of the welded joint at-10℃ is≥0.4mm. It also cannot meet the requirements of large polar ships for fracture toughness.

[0007] The patent document with the invention name of "500MPa grade marine engineering steel plate and its preparation method" and the application number of 202410156277.7 discloses a 500MPa grade marine engineering steel plate, the chemical components of which are as follows: 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 of Fe and inevitable impurities. The yield strength of the steel plate is ≥500MPa, the tensile strength is 560-715MPa, and the CTOD of the steel plate in the coarse grain zone and the critical zone after welding is ≥0.8mm at-10℃. The same cannot meet the requirements of large polar ships on fracture toughness.

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

[0009] 1) The process is complex, resulting in increased production costs of the steel plate.

[0010] 2) The fracture toughness of the steel plate is insufficient, and it is difficult to meet the fracture toughness requirements of large polar ships on low-temperature steel plates. SUMMARY

[0011] The purpose of the present application is to overcome the above problems and deficiencies and provide a low-temperature steel plate with excellent CTOD performance and a manufacturing method, which has a yield strength of ≥550MPa, a CTOD value of >1.2mm at-60℃, and a welded joint with a coarse grain zone having an impact energy of ≥264J at-80℃ and a CTOD value of >1.0mm at-60℃ under a large heat input welding process of 60KJ / cm.

[0012] The purpose of the present application is achieved as follows:

[0013] The low-temperature steel plate with excellent CTOD performance and the manufacturing method, the composition of which is as follows in terms of percentage by weight: 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%, Als: 0.010%-0.025%, W: 0.050%-0.100%, Zr: 0.100%-0.170%, and the balance of Fe and inevitable impurities.

[0014] The low-temperature steel plate has Al / Zr=0.07-0.19.

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

[0016] The low-temperature steel plate has a yield strength ≥550 MPa, a tensile strength of 690-770 MPa, an elongation after fracture ≥24.0%, and a CTOD value of the steel plate at -60 ℃ >1.2 mm.

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

[0018] The component design reasons of the present application are as follows:

[0019] C: a basic strengthening element in the steel, which is the main element for ensuring the strength and hardness in the technical scheme of the present application; when the content of C is low, the amount of carbide generated is reduced, which affects the effect of refining the grains during rolling. When the content of C is high, the content and size of cementite in the steel increase, and the distribution of the cementite is more intensive, the phenomenon of the aggregation of the cementite at the grain boundaries occurs, the aggregation of the large-size cementite at the grain boundaries causes stress concentration, which has an adverse effect on the low-temperature toughness and fracture toughness of the steel plate, and reduces the welding performance of the steel plate. Therefore, considering the cost and performance and other factors, the content of C is controlled in the range of 0.040%-0.100% in the present application.

[0020] Si: a necessary element for deoxidizing the steel, which has a strong solid solution capacity in the steel, can increase the elastic limit and yield strength of the steel, reduce the strength difference between the soft ferrite and the hard phase, and improve the resistance of the crack to initiation and propagation in the steel, but when the content of Si is too high, it has an adverse effect on the low-temperature toughness and surface quality of the steel. The content of Si is controlled in the range of 0.05%-0.30% in the present application.

[0021] Mn: forms a substitutional solid solution in the steel, can be largely solid-solved in the Fe matrix, can delay the ferrite and pearlite transformation in the steel, greatly increase the hardenability of the steel, reduce the brittle transformation temperature of the steel, and improve the impact toughness, but when the content of Mn is too high, segregation is easily formed in the steel, which has an adverse effect on the plasticity and toughness of the steel. Considering comprehensively, the content of Mn is controlled in the range of 0.80%-1.40% in the present application.

[0022] V: strong carbide forming element, less influence on austenite recrystallization, a large amount of carbide of V is precipitated at low temperature, has obvious precipitation strengthening and refining organization effect, thereby improving the plasticity and toughness of the steel, and has very strong solid solution strengthening effect in the steel, promotes the uniformity of the strength of the steel and the uniformity when subjected to external force deformation, in addition, the high hardness precipitated phase particles are dispersed in the steel, which is beneficial to hinder the rapid expansion of cracks in the steel, thereby improving the fracture toughness of the steel. However, when the content is too high, the ductile-brittle transition temperature of the steel plate is reduced. Considering the performance, cost and other factors of the steel, the range of V in the application is 0.050% to 0.180%.

[0023] N: important strengthening and toughening element of the application, the addition of N element is beneficial to promote the formation of V(CN) in the steel, promote the formation of ferrite in the steel, reduce the yield strength ratio of the steel, and refine the grain, improve the plasticity and toughness of the steel. Nitrogen-containing steel not only eliminates the cost increase caused by degassing and denitrification in the steelmaking process, but also fully plays the role of micro-alloying elements by increasing nitrogen in the steel, saves the amount of alloying elements, greatly reduces the production cost, thereby improving the comprehensive mechanical properties. Considering the performance and cost, the range of N in the application is 0.0160% to 0.0220%.

[0024] Cu: can improve the stability of austenite in the steel, increase the hardenability of the steel, improve the strength, plasticity and low temperature toughness of the steel when added in appropriate amount, but when the content is too high, the hot shortness of the steel is deteriorated, and hot cracks are easy to produce. The range of Cu in the application is 0.55% to 0.90%.

[0025] Ni: has no adverse effect on the hardening and toughness of the heat affected zone of the steel, and can improve the plasticity and low temperature toughness of the steel, in addition, the addition of Ni can also reduce the hot cracking tendency when the Cu content is high, considering the cost, performance and other factors, the range of Ni in the application is 0.80% to 1.20%.

[0026] Ti: can produce strong precipitation strengthening effect, improve the strength of the steel, and can also prevent austenite recrystallization; at the same time, can produce grain refinement effect, improve the yield strength of the steel. The carbon and nitride of Ti has high dissolution temperature, which can prevent the growth of austenite grains during heating, 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 strong precipitation strengthening effect, which will deteriorate the toughness of the steel. Considering the above, the range of Ti in the application is 0.005% to 0.025%.

[0027] Al: strong deoxidizing agent in steel, a small amount of addition can generate highly fine, ultra-micro oxide, which is beneficial to improve the purity of the steel, the addition of Al element in the application aims to ensure sufficient deoxidation of the molten steel and create conditions for the subsequent addition of Zr element to prevent the formation of a large amount of ZrO2 after the addition of Zr. The control range of Als in the application is 0.010%-0.025%.

[0028] W: grain refinement, reduces the overheating tendency of the steel, improves the strength, toughness and thermal stability of the steel, and can improve the strength of the steel without reducing the plasticity and toughness. The control range of W in the application is 0.050%-0.100%.

[0029] Zr: strong carbide forming element, a small amount of addition has the effects of degassing, purification and grain refinement, which is beneficial to improve the low temperature performance of the steel, in order to better play its role in grain refinement, Al should be used in conjunction with Zr when adding, and the control of Al / Zr is 0.07-0.19. Considering the cost, performance and other factors, the control range of Zr in the application is 0.100%-0.170%.

[0030] The second technical scheme of the application provides a manufacturing method of a low-temperature steel plate with excellent CTOD performance, which comprises 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 C, Si, Mn, P, S and other elements during converter smelting to be within the range of the application, and adding other alloying elements according to requirements for smelting;

[0033] b) LF refining the molten steel to adjust the contents of other alloying elements to be within the range of the application;

[0034] c) RH treating the refined molten steel, the RH treatment time is 40-60 min, nitrogen is blown throughout the RH treatment, the pressure is 600-660 Pa, the final N content of the steel is ensured to be 0.0160%-0.0220%, the [H] in the steel is controlled to be ≤2.0 ppm, and the [O] is controlled to be ≤10 ppm;

[0035] (2) continuous casting: the molten steel obtained in step (1) is used to produce the required casting blank, the tundish adopts low superheat, the superheat is 10-20℃, the whole process is protected pouring, the casting speed is controlled to be 0.80-1.20 m / min, the specific water quantity of the secondary cooling water is 0.15-0.35 m 3 / t, electromagnetic stirring is used at the end of the continuous casting, the stirring current is 450-550 A, and the light press-down process is used at the end of the continuous casting, the press-down rate is 4.0%-5.0%;

[0036] (3) Slab cooling: In order to control the grain size of the continuous casting slab, the high-temperature continuous casting slab is rapidly cooled after continuous casting, the open cooling temperature is 850-900℃, the cooling speed is 2.0-7.0℃ / s, and the slab is cooled to 650-700℃ and then is offline stacked and slowly cooled to reduce the internal stress of the slab after rapid cooling and to optimize the distribution of precipitated phases in the slab, so that a large number of VC precipitated phases are formed in the steel, the stacking time is ≥36h, and the temperature of the slab is ensured to be <100℃;

[0037] (4) Heating: the slab obtained in step (3) is heated to 1100-1220℃, the holding time is 0.5-1.5h, and the total furnace time is ≤5.5h;

[0038] (5) Rolling: in order to obtain a steel plate with fine and uniform grains, the slab is rolled into a hot-rolled steel plate through three-stage rolling,

[0039] The first stage adopts a high-speed large reduction process based on a large temperature gradient, the slab is descaled by high-pressure water after being discharged from the furnace, and then is directly rolled, the roll speed is controlled to be 1.5-2.5m / s, the first pass reduction is controlled to be >60mm, the finish rolling temperature is >1060℃, the warm slab thickness is (3.0-3.5)t, t is the thickness of the final product, and the high-pressure water pressure is 0.9-1.1MPa in the dephosphorization process, so that the temperature difference between the surface and the center of the slab is >50℃,

[0040] The second stage also adopts a high-temperature large reduction process, and further accumulates deformation energy in the steel to prepare conditions for subsequent grain refinement, the open rolling temperature is 950-1000℃, the finish rolling temperature is 850-900℃, the warm slab thickness is (1.5-2.0)t, and the reduction rate of each pass is controlled to be ≥7.0%;

[0041] The third stage adopts non-recrystallization zone rolling, the open rolling temperature is 780-830℃, and the finish rolling temperature is 700-750℃, so as to fully flatten the austenite in the non-recrystallization zone, accumulate dislocations and deformation energy, and refine the subsequent phase change grains. Finally, the average grain size of the steel plate is ≤10μm.

[0042] (6) Cooling: in order to maintain the fine grains after rolling and prevent the grains from growing, the steel plate is accelerated cooled after rolling, the open cooling temperature is 650-690℃, the cooling speed is 10.0-20.0℃ / s, and the re-red temperature is 430-480℃;

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

[0044] The beneficial effects of the present application are as follows:

[0045] (1) the low carbon chemical composition system is adopted to improve the low temperature toughness of the steel, the grain size of the steel and the composition of precipitated phase are controlled by adding alloy elements such as V-N, Ni, W and Zr, the low superheat is adopted in the smelting process to reduce the center segregation of the casting blank, and the electromagnetic stirring and light pressing are put into the end of continuous casting to further reduce the segregation of the casting blank; the three-stage controlled rolling is adopted in the rolling process, the high-speed large reduction process based on the large cross-section temperature gradient is adopted in the first stage rolling, the high-pressure water rapid descaling process is used to form a large temperature gradient between the surface and the center of the casting blank, and the deformation is transmitted to the center; the high temperature large reduction process is also adopted in the second stage to further accumulate the deformation energy in the steel to prepare the conditions for subsequent grain refinement; the non-recrystallization zone rolling is adopted in the third stage to refine the grain size of the steel; and the accelerated cooling + stacking slow cooling process is adopted after rolling to control the internal stress and precipitated phase 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 ≤15 μm, the precipitated phase is composed of Ti(C, N) and V(C, N), the average size is ≤40 nm, and the distribution is dispersed. The small grain size and the dispersed distribution of the precipitated phase can increase the resistance of crack propagation in the steel, thereby improving the CTOD value of the steel plate, the CTOD value of the final steel plate is >1.2 mm at-60 ℃, the CTOD value of the welded joint coarse grain zone (CGHZ) is >1.0 mm under the large heat input welding process of 60 KJ / cm. The preparation process of the three-stage TMCP is adopted in the application, and subsequent heat treatment is not needed, thereby reducing the production cost of the steel plate. DETAILED DESCRIPTION

[0047] The application will be further described by examples.

[0048] According to the component proportion of the technical scheme, the application is smelted, continuously cast, rolled, cooled, and stacked and slowly cooled. Specifically,

[0049] (1) the casting blank is cooled: the high-temperature casting blank is rapidly cooled after continuous casting, the cooling temperature is 850-900 ℃, the cooling speed is 2.0-7.0 ℃ / s, and the casting blank is cooled to 650-700 ℃ and then is stacked and slowly cooled, and the stacking time is ≥36 h;

[0050] (2) heating: then the casting blank is heated to 1100 ℃-1220 ℃, the holding time is 0.5-1.5 h, and the total furnace time is ≤5.5 h;

[0051] (3) rolling: the casting blank is rolled into a hot-rolled steel plate by three-stage rolling,

[0052] The first stage is carried out by using high-speed and high-pressing process based on large temperature gradient, the high-pressure water descaling is used for the casting blank, the rolling is directly carried out after descaling, the roller speed is controlled to be 1.5-2.5 m / s, the first pass pressing amount is controlled to be greater than 60 mm, the final rolling temperature is greater than 1060 DEG C, and the warm blank thickness is (3.0-3.5) t, t is the final product thickness;

[0053] The second stage is carried out at the rolling start temperature of 950-1000 DEG C, the rolling end temperature of 850-900 DEG C, and the warm blank thickness of (1.5-2.0) t, and the pressing rate of each pass is controlled to be greater than 7.0%,

[0054] The third stage is carried out by using non-recrystallization zone rolling at the rolling start temperature of 780-830 DEG C and the rolling end temperature of 700-750 DEG C.

[0055] (4) cooling: the steel plate is subjected to accelerated cooling after rolling, the cooling start temperature is 650-690 DEG C, the cooling speed is 10.0-20.0 DEG C / s, and the re-red temperature is 430-480 DEG C;

[0056] (5) stacking and slow cooling: then the steel plate is subjected to stacking and slow cooling, the stacking temperature is greater than or equal to 350 DEG C, and the stacking time is greater than or equal to 20 h.

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

[0058] The molten steel after LF refining is subjected to RH treatment, the RH treatment time is 40-60 min, nitrogen is blown in the whole process during RH treatment, the pressure is 600-660 Pa, the final N content of the steel is ensured to be N: 0.0160%-0.0220%, the [H] in the steel is controlled to be less than or equal to 2.0 ppm, and the [O] is controlled to be less than or equal to 10 ppm.

[0059] Further, the tundish superheat is 10-20 DEG C, the whole process is protected from pouring, the blank pulling speed is 0.80-1.20 m / min, the specific water quantity 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 450-550 A, and the light pressing process is used at the end of continuous casting, and the pressing rate is 4.0%-5.0%.

[0060] Further, the high-pressure water pressure during descaling is 0.9-1.1 MPa, and the difference between the surface temperature and the core temperature of the casting blank is greater than 50 DEG C.

[0061] Further, after the non-recrystallization zone rolling in the third stage, the average grain size of the steel plate is less than or equal to 10 mu m.

[0062] The composition of the steel in the embodiment of the application is shown in Table 1. The main process parameters of the steel in the embodiment of the application are shown in Tables 2-6. The structure and the base material performance of the steel in the embodiment of the application are shown in Tables 7-8.

[0063] Table 1 Composition of the steel of the embodiment of the application (wt%)

[0064] No. 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 smelting the steel of the embodiment of the application

[0066]

[0067] Table 3 Main process parameters for cooling the continuous casting billet of the steel of the embodiment of the application

[0068] No. Start cooling temperature / °C Cooling rate / °C / s Final cooling temperature / °C Stacking time / h Stacking completion temperature / °C 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 the steel of the embodiment of the application

[0070] No. Thickness / mm Heating temperature / °C Soaking time / h Total in-furnace time / h Temperature difference after descaling / °C 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 for rolling the steel of the embodiment of the application

[0072]

[0073] Table 6 Main process parameters for cooling the steel of the embodiment of the application

[0074] No. Start cooling temperature / °C Cooling rate / °C / s Red temperature / °C Stacking temperature / °C 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 Microstructure characteristics of the steel of the embodiment of the application

[0076]

[0077] Table 8 Mechanical properties of the base metal of the steel of the embodiment of the application

[0078]

[0079] Table 9 Welding properties of the steel of the embodiment of the application

[0080]

[0081] Note: The welding properties of the steel plate were evaluated, the welding method was submerged arc welding, the welding line energy was 60 KJ / cm, and the steel plate welded joint properties are shown in Table 9.

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

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

[0084] In order to describe the present application, the above-mentioned embodiments are appropriately and sufficiently described by examples, and the above embodiments are only used to illustrate the present application, but not limit the present application. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art without departing from the spirit and scope of the present application shall be included in the protection scope of the present application, and the patent protection scope of the present application shall be defined by the claims.

Claims

1. A low-temperature steel sheet having excellent CTOD performance, characterized by, The steel sheet has the following components in percentage by weight: 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 of Fe and inevitable impurities; The manufacturing method of the low-temperature steel sheet with excellent CTOD performance comprises smelting, continuous casting, casting blank cooling, heating, rolling, cooling, and stack slow cooling. (1) Casting blank cooling: after continuous casting, the high-temperature continuous casting blank is rapidly cooled, the cooling temperature is 850-900℃, the cooling speed is 2.0-7.0℃ / s, and after cooling to 650-700℃, the blank is discharged and stacked for slow cooling, and the stack time is ≥36h; (2) Heating: then the blank is heated to 1100-1220℃, the holding time is 0.5-1.5h, and the total furnace time is ≤5.5h; (3) Rolling: the blank is rolled into a hot-rolled steel sheet in three stages, the first stage adopts a high-speed large reduction process based on a large temperature gradient, the blank is discharged and descaled by high-pressure water, and then directly rolled, the roller speed is controlled to be 1.5-2.5m / s, the first pass reduction is controlled to be >60mm, the final rolling temperature is >1060℃, and the thickness of the warm blank is (3.0-3.5)t, t being the thickness of the final product; the second stage is rolled at a rolling temperature of 950-1000℃ and a final rolling temperature of 850-900℃, and the thickness of the warm blank 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, and the rolling temperature is 780-830℃ and the final rolling temperature is 700-750℃; (4) Cooling: the steel sheet is accelerated cooled after rolling, the cooling temperature is 650-690℃, the cooling speed is 10.0-20.0℃ / s, and the re-red temperature is 430-480℃; (5) Stack slow cooling: then the steel sheet is stacked and slowly cooled, the stack temperature is ≥350℃, and the stack time is ≥20h.

2. The low-temperature steel sheet having excellent CTOD properties according to claim 1, characterized by, In the low-temperature steel sheet, Al / Zr=0.07-0.

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

4. The low-temperature steel sheet having excellent CTOD properties according to claim 1, characterized by, The steel plate has a yield strength ≥550MPa, tensile strength 690~770MPa, elongation after fracture ≥24.0%, and a CTOD value >1.2mm at -60℃. Under a high heat input welding process of 60KJ / cm, the welded joint has a tensile strength of 690~770MPa, and the coarse-grained region (CGHZ) of the welded joint absorbs impact energy at -80℃. KV 2≥264J, CTOD value at -60℃>1.0mm.

5. The low-temperature steel sheet with excellent CTOD performance according to claim 1, characterized in that: smelting: including converter smelting, LF refining, and RH treatment; The LF-refined molten steel is subjected to RH treatment, the RH treatment time is 40-60 min, nitrogen is blown throughout the RH treatment, the pressure is 600-660 Pa, the final N content of the steel is ensured to be N: 0.0160%-0.0220%, the [H] in the steel is controlled to be ≤2.0 ppm, and the [O] is controlled to be ≤10 ppm.

6. The low-temperature steel plate with excellent CTOD performance according to claim 1, characterized in that: Continuous casting: the superheat of tundish is 10-20 ℃, full-protective pouring, the speed of drawing blank is 0.80-1.20 m / min, the specific water consumption of 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 450-550 A, and light press-down process is used at the end of continuous casting, the press-down rate is 4.0%-5.0%.

7. The low-temperature steel sheet having excellent CTOD properties according to claim 1, characterized by: The high-pressure water pressure in the descaling process is 0.9-1.1 MPa, and the difference between the surface temperature and the core temperature of the casting blank is > 50 DEG C.

8. The low-temperature steel sheet having excellent CTOD properties according to claim 1, characterized by: After the third stage of rolling in the unrecrystallized zone, the average grain size of the steel plate is ≤10 μm.

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