Ultrahigh-strength low-temperature maritime work wide and thin steel plate with good cold working performance and manufacturing method

Abstract

The invention relates to an ultrahigh-strength low-temperature maritime work wide thin steel plate with good cold working performance and a manufacturing method of the ultrahigh-strength low-temperature maritime work wide thin steel plate. The steel plate comprises the following chemical components in percentage by weight: 0.04% to 0.08% of C, 0.1% to 0.4% of Si, 1.0% to 1.6% of Mn, 5.0% to 8.0% of Ni, 0.4% to 0.7% of Cr, 0.8% to 1.2% of Mo, 1.0% to 1.5% of Cu, 0.2% to 0.3% of V, 0.025% to 0.045% of Ti, 0.025% to 0.040% of Zr, 0.03% to 0.06% of Als, 0.002% to 0.005% of B, less than or equal to 0.005% of P, less than or equal to 0.001% of S and the balance of Fe and inevitable impurities. A low-carbon component design is adopted, elements such as V and Ti are added, and elements such as Ni, Cr, Mo, B and Zr are compositely added; a high-cleanliness smelting control technology, an electroslag remelting technology and a composite ply rolling technology are adopted, a two-stage rolling process, a transverse-longitudinal rolling process and a heat treatment process of quenching, two-phase region quenching and critical temperature tempering are matched, and the finally obtained wide and thin steel plate has excellent comprehensive mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore steel production, and particularly relates to an ultra-high strength low-temperature offshore wide and thin steel plate with good cold working performance and a manufacturing method thereof. Background Art

[0002] With the continuous rise of the global temperature, the development of the Arctic shipping lanes and the exploitation of polar deep-sea oil and gas resources have gradually been carried out in various countries around the world. China has also actively joined the ranks of polar development, and the demand for polar offshore equipment is increasing continuously. The development of materials for polar deep-sea equipment is extremely urgent. The service environment of polar offshore equipment is relatively harsh, and the lowest working temperature can reach -50°C to -60°C. Steel is prone to brittle fracture at low temperatures, and at the same time, it has to face the continuous impact, scouring and abrasion of high-salinity sea ice. Therefore, strict requirements are put forward for the service performance of the steel plate, and it must have ultra-high strength, good ductility and low-temperature toughness. At the same time, thin-gauge steel plates should also have good cold working adaptability to meet the production requirements of the outer plates of some complex-curved offshore equipment.

[0003] Chinese Patent Application with Publication No. CN109913763A discloses a "low-cost cold-rolled dual-phase steel with good cold working performance at 1000MPa level and a manufacturing method thereof". By mass percentage, it includes the following chemical components: C: 0.13 - 0.22, Mn: 1.20 - 1.70, Si: 0.20 - 0.50, Als: 0.30 - 0.80, P≤0.015, S≤0.0010, N≤0.004, Cr: 0.20 - 0.50, Nb: 0.010 - 0.05, Ca: 0.0005 - 0.0025, T[O]≤0.002, and the rest is Fe and inevitable impurities; and, 0.50≤Si + Als≤1.00. It undergoes steelmaking, LF refining, RH refining, continuous casting, hot rolling, cooling, coiling, pickling, cold rolling, annealing and tempering processes; on the basis of selecting a lower alloy element content design and combining rolling and cooling processes, the prepared product has good strength and cold bending properties, and has low requirements for the production process line. However, the steel plate involved belongs to the category of cold-rolled plates, the product thickness is only 0.5 - 1.5mm, and the width of the produced cold-rolled steel plate is relatively narrow, which is not suitable for the manufacture of large deep-sea offshore equipment.

[0004] The Chinese patent application with the publication number CN117778882A discloses "a super high-strength steel and its preparation method". In terms of mass percentage, it consists of the following chemical components: C: 0.38% - 0.43%, Mn: 0.60% - 0.90%, Si: 1.50% - 1.80%, Ni: 1.65% - 2.00%, Al: 0.03% - 0.08%, Cr: 0.70% - 0.90%, V: 0.05% - 0.10%, S ≤ 0.010%, P ≤ 0.010%, H ≤ 0.0001%, O ≤ 0.0015%, N ≤ 0.010%, and the balance is Fe and unavoidable impurities. Through the synergistic effect of each chemical component, the mechanical properties of the super high-strength steel are improved, and the prepared super high-strength steel has both excellent strength and plasticity. At the same time, by strictly controlling harmful elements and residual elements, the purity of the super high-strength steel is improved. However, the elongation of the produced steel plate is relatively low, and only the impact toughness at room temperature is evaluated, which is not suitable for the polar ultra-low temperature environment of -60°C to -80°C.

[0005] The Chinese invention patent with the publication number CN110616300B discloses "a steel for low temperature use with excellent CTOD characteristics and its manufacturing method". The weight percentage of its components is: C: 0.050% - 0.090%, Si: ≤ 0.15%, Mn: 1.00% - 1.60%, P: ≤ 0.013%, S: ≤ 0.0020%, Cu: 0.05% - 0.30%, Ni: 0.05% - 0.30%, Nb: 0.010% - 0.030%, Al: ≤ 0.010%, Ti: 0.010% - 0.020%, N: 0.0045% - 0.0085%, Ca: 0.0010% - 0.0040%, B: 0.0010% - 0.0020%, and the rest is Fe and unavoidable inclusions. While obtaining excellent low-temperature toughness of the base metal steel plate, the low-temperature toughness and CTOD of the HAZ during welding with a large heat input are also excellent; it successfully solves the contradictions between low carbon equivalent and high strength, between high strength and low-temperature toughness of the HAZ, especially CTOD, between low-cost manufacturing and excellent low-temperature toughness, and large heat input weldability. However, its strength level is relatively low (only 420 MPa), which cannot meet the requirements of ultra-high strength of materials for deep-sea offshore equipment, and it does not have good cold working performance.

[0006] It can be seen that the current offshore steel with good cold working performance mainly has the following problems:

[0007] 1. The strength level of the steel plate is relatively low, and the elongation and low-temperature toughness are insufficient, which cannot meet the requirements of ultra-high strength of materials for deep-sea offshore equipment.

[0008] 2. The width and thickness specifications of the steel plate cannot meet the usage requirements of offshore steel.

[0009] 3. The cold working performance of the steel plate cannot meet the processing requirements of deep-sea offshore equipment. SUMMARY OF THE INVENTION

[0010] The present invention provides an ultra-high strength low-temperature offshore wide and thin steel plate with good cold working performance and a manufacturing method. A low-carbon composition design is adopted, and elements such as V and Ti are added to refine the grains. Through the combined addition of elements such as Ni, Cr, Mo, B, and Zr, good low-temperature toughness and cold working performance of the ultra-high strength offshore steel are ensured; through high cleanliness smelting control technology and electroslag remelting technology, harmful elements such as P and S and gaseous elements such as N and O are reduced, and the adverse effects of stress concentration generated by non-metallic inclusions on the toughness and cold working performance of the steel plate are reduced; the composite overlay rolling technology is adopted, combined with two-stage rolling and transverse-longitudinal rolling processes, to achieve good control of the plate shape of wide and thin steel plates; the heat treatment adopts the process of "quenching + two-phase region quenching + critical temperature tempering" to regulate the microstructure and properties of the steel plate, greatly improving the strength, low-temperature toughness and cold working performance of the steel plate, and finally obtaining a steel plate with excellent comprehensive mechanical properties.

[0011] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0012] An ultra-high strength low-temperature offshore wide and thin steel plate with good cold working performance, the chemical composition of the steel plate is by weight percentage: C: 0.04% - 0.08%, Si: 0.1% - 0.4%, Mn: 1.0% - 1.6%, Ni: 5.0% - 8.0%, Cr: 0.4% - 0.7%, Mo: 0.8% - 1.2%, Cu: 1.0% - 1.5%, V: 0.2% - 0.3%, Ti: 0.025% - 0.045%, Zr: 0.025% - 0.040%, Als: 0.03% - 0.06%, B: 0.002% - 0.005%, P≤0.005%, S≤0.001%, and the rest is Fe and unavoidable impurities.

[0013] The thickness of the finished steel plate is 6 - 12 mm, and the width ≥ 4100 mm.

[0014] The microstructure of the finished steel plate is tempered sorbite + ferrite + retained austenite. By volume percentage, the proportion of tempered sorbite is 45% - 50%, the proportion of ferrite is 35% - 46%, and the proportion of retained austenite is 9% - 15%.

[0015] The mechanical properties of the finished steel plate are as follows: yield strength ≥ 1050 MPa, tensile strength 1150 - 1250 MPa, elongation after fracture A70 ≥ 14%, V-notch impact energy at -84°C: for 5-mm-thick sample ≥ 70 J, for 10-mm-thick sample ≥ 130 J; V-notch impact energy at -160°C: for 5-mm-thick sample ≥ 55 J, for 10-mm-thick sample ≥ 100 J; d = 8t, α = 105° bending test, no cracks in direct bending, reverse bending and side bending.

[0016] A manufacturing method of an ultra-high strength low-temperature offshore wide thin steel plate with good cold working performance, comprising the following steps:

[0017] (1) Converter smelting: After the hot metal is pretreated by desulfurization, it is charged into the converter. During the converter smelting process, nickel, copper, and molybdenum are first added into the furnace, and the double slag method is used for smelting; then other alloys are added for deoxidation and alloying; during the tapping process, the converter slagging is controlled.

[0018] (2) LF refining: Add deoxidizer to make a reducing slag, finely adjust the chemical composition, remove inclusions in the steel, and achieve deep desulfurization.

[0019] (3) VD refining: After vacuum degassing, weak argon stirring is carried out to further remove inclusions in the steel.

[0020] (4) Continuous casting: During casting, a weak cooling process is adopted, the specific water volume is controlled at 0.65 - 0.80 L / kg, the casting speed is controlled at 0.85 - 1.25 m / min, and a soft reduction process is adopted at the end of continuous casting, with the reduction amount being 5.0 - 7.0 mm.

[0021] (5) Electroslag remelting: The continuous casting billet is used as a consumable electrode to melt and purify in the superheated slag, and is cooled into an ingot in a water-cooled mold. During cooling, a weak cooling method is adopted, and the cooling water volume is controlled at 45 - 65 m 3 / h, and the outlet water temperature ≤ 50°C; the electroslag billet is taken offline for homogenization annealing at 1000 ± 50°C, the slab is taken offline and stacked for slow cooling, and the slow cooling time ≥ 60 h; the slag layer effectively removes non-metallic inclusions such as oxides and sulfides in the metal through chemical adsorption and physical capture, significantly reduces the content of impurities such as S and P, and improves the material purity.

[0022] (6) Billet composite rolling: The billet is sprayed with a release agent in the middle, the billet is welded around and air holes are left, and the weld width ≥ 50 mm; anti-oxidation coatings are sprayed on both the upper surface and the lower surface of the composite billet.

[0023] (7) Two-stage controlled rolling: The composite electroslag ingot is charged into a heating furnace for heating. The heating temperature is 1150 - 1300 °C, and the total time in the furnace is 3 - 5 h. The first-stage rolling adopts a transverse-longitudinal rolling process. The starting rolling temperature is ≥1100 °C, and a multi-pass small reduction rapid rolling method is used. The average single-pass reduction in transverse rolling is 6 - 10 mm, and the average single-pass reduction in longitudinal rolling is 10 - 15 mm. The final rolling temperature in the first stage is 950 - 1050 °C, and the thickness of the billet waiting for temperature in the first stage is 4.0 - 4.5 times the thickness of the finished composite steel plate. The starting rolling temperature in the second stage is 830 - 920 °C, the average single-pass reduction is 8 - 12 mm, and the final rolling temperature is 750 - 850 °C;

[0024] (8) Two-stage quenching + tempering heat treatment: The quenching temperature in the first stage is 850 - 950 °C, and the holding time is 1.2 - 2.5 mm / min. The quenching temperature in the second stage is 650 - 740 °C, and the holding time is 2.2 - 3.0 mm / min. The tempering temperature is 610 - 660 °C, and the holding time is 1.5 - 3.0 mm / min. After being taken out of the furnace, it is air-cooled;

[0025] (9) Steel plate finishing: Finish the slitting of the upper and lower layers of the steel plate and separate the upper and lower layer steel plates.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1) The present invention adopts a low-carbon composition design, adds elements such as V and Ti to refine grains, and through the composite addition of elements such as Ni, Cr, Mo, B, and Zr, ensures the good low-temperature toughness and cold working performance of the ultra-high-strength offshore steel. Through high cleanliness smelting control technology and electroslag remelting technology, harmful elements such as P and S and gaseous elements such as N and O are reduced, and the adverse effects of stress concentration caused by non-metallic inclusions on the toughness and cold working performance of the steel plate are reduced. The composite overlay rolling technology is adopted, combined with the two-stage rolling and transverse-longitudinal rolling processes, to achieve the control of the good plate shape of wide and thin steel plates. The heat treatment adopts the process of "quenching + two-phase zone quenching + critical temperature tempering" to regulate the microstructure and properties of the steel plate, greatly improving the strength, low-temperature toughness and cold working performance of the steel plate. Finally, the obtained steel plate has excellent comprehensive mechanical properties.

[0028] 2) The microstructure of the steel plate is "tempered sorbite + ferrite + retained austenite", among which, the volume percentage content of tempered sorbite is 45% - 50%, the volume percentage content of ferrite is 35% - 46%, and the volume percentage content of retained austenite is 9% - 15%.

[0029] 3) The product has good mechanical properties: yield strength ≥ 1050 MPa, tensile strength of 1150 - 1250 MPa, elongation after fracture A70 ≥ 14%, V-notch impact energy at -84°C: for 5-mm thick sample ≥ 70 J, for 10-mm thick sample ≥ 130 J; V-notch impact energy at -160°C: for 5-mm thick sample ≥ 55 J, for 10-mm thick sample ≥ 100 J; d = 8t, α = 105° bending test, no cracks in direct bending, reverse bending and side bending; the finished thickness range of the steel plate is 6 - 12 mm, width ≥ 4100 mm. Description of the Drawings

[0030] Figure 1 It is a metallographic structure photo (magnified 500 times) of the ultra-high strength cryogenic offshore wide thin steel plate produced in Example 1 of the present invention. Detailed Embodiments

[0031] For the ultra-high strength cryogenic offshore wide thin steel plate with good cold working performance described in the present invention, the chemical composition of the steel plate by weight percentage is C: 0.04% - 0.08%, Si: 0.1% - 0.4%, Mn: 1.0% - 1.6%, Ni: 5.0% - 8.0%, Cr: 0.4% - 0.7%, Mo: 0.8% - 1.2%, Cu: 1.0% - 1.5%, V: 0.2% - 0.3%, Ti: 0.025% - 0.045%, Zr: 0.025% - 0.040%, Als: 0.03% - 0.06%, B: 0.002% - 0.005%, P ≤ 0.005%, S ≤ 0.001%, and the rest are Fe and inevitable impurities.

[0032] The reasons for the selection of each element and its content in the steel are as follows:

[0033] Element C: Element C is a basic element in steel. A certain amount of C element can improve the strength of the steel through solid solution strengthening, but too high carbon content will reduce the ductile-brittle transition temperature of the steel, seriously affecting its low-temperature toughness. Too high C content will also deteriorate the welding performance of the steel and increase the welding difficulty. The present invention adopts a low-carbon design, controlling the C content range to be 0.04% - 0.08%.

[0034] Element Si: Element Si is a necessary element for deoxidation in steel. At the same time, it can improve the strength, hardness and hardenability of the steel through solid solution strengthening. In addition, a certain amount of silicon can increase the temper brittleness temperature of the steel. In production, combined with low-temperature tempering, it is beneficial to the improvement of the strength and toughness of ultra-high strength steel. The present invention controls the Si content range to be 0.1% - 0.4%.

[0035] Mn element: As a good deoxidizer and desulfurizer, the Mn element can effectively improve the purity of molten steel. At the same time, it is dissolved in austenite, playing a role in expanding the austenite phase region, reducing the martensite transformation temperature, increasing the content of retained austenite after quenching, and being beneficial to improving the strength, toughness and cold working performance of the steel. However, when the Mn content is too high, it will form NiMn phase at the grain boundary with Ni element, inducing cracks along the grain boundary of the steel plate. In the present invention, the Mn content is controlled in the range of 1.0% - 1.6%.

[0036] Ni element: The Ni element expands the austenite region through infinite solid solution with iron, promotes the formation of high-stability reversed austenite during tempering and stabilizes it at the grain boundary, enhances the strength and toughness of the steel, passivates the crack tip, reduces stress concentration, and prevents crack propagation at the cementite film caused by the low hydrogen content in the ferrite phase and martensite phase. In the present invention, the Ni content is controlled in the range of 5.0% - 8.0%.

[0037] Cr element: The Cr element can increase the hardenability of the steel plate, improve the oxidation resistance of the steel plate, and promote the secondary hardening effect of the steel plate during tempering; the combined addition of Cr element and Mo element is beneficial to the precipitation of precipitated phases and can prevent grain coarsening. In the present invention, the Cr content is controlled in the range of 0.4% - 0.7%.

[0038] Mo element: The Mo element is a strong hardenability element, which can improve the stability of carbides and the strength of the steel plate. During tempering, it can maintain the tempering stability of the steel plate, increase the tempering resistance, and prevent brittleness during tempering. Mo can also improve the ductility and toughness of the steel, and the steel plate is less likely to break when bent. In the present invention, the Mo content is controlled in the range of: 0.8% - 1.2%.

[0039] Cu element: The Cu element produces copper-rich phases through precipitation strengthening of second-phase particles, promotes the generation of screw dislocations at low temperatures, and improves low-temperature toughness. When the steel plate undergoes cold deformation, even if the strength is increased, the toughness will not decrease. In the present invention, the Cu content is controlled in the range of 1.0% - 1.5%.

[0040] V element: The V element reacts with C and N elements in the steel to form V(C, N) precipitation, promotes the formation of intragranular ferrite, fully refines the grains while eliminating excess N element in the steel, and improves the strength and toughness of the steel plate. At the same time, it can inhibit the work hardening rate, which is beneficial to the cold working performance of the steel plate. In the present invention, the V content is controlled in the range of 0.2% - 0.3%.

[0041] Ti element: The Ti element has a very strong affinity with elements such as N, O, and S in steel, which can reduce the influence of harmful elements on the performance of the steel plate. At the same time, Ti can form carbide particles with Fe and C in the steel, pin the grain boundaries, and thus refine the grains. The TiC particles formed by Ti and C are fine and dispersed in the matrix, which can promote the formation of crystal nuclei, refine the grains, reduce the formation of banded segregation, and improve the low-temperature toughness and bending performance of the steel plate. In the present invention, the Ti content range is controlled to be 0.025% - 0.045%.

[0042] B element: Adding a certain amount of B element to the steel can improve the hardenability of the steel through solid solution strengthening within the crystal. The combined addition of Mo and B elements can make the grain boundary precipitates Fe 23 (C, B)6 disperse on the matrix, which is more beneficial to improving the hardenability. At the same time, B combines with the Ti element in the steel to form TiB2 precipitates, which can improve the low-temperature toughness of the steel. The addition of B element can also improve the cold working performance of the steel plate. In the present invention, the B content range is controlled to be 0.002% - 0.005%.

[0043] Zr element: The Zr element combines with C and N, and precipitates fine ZrC and ZrN particles with high melting points during the tempering process, pinning the grain boundaries and refining the final structure. The combined addition of Zr element and Ti element can form composite carbonitrides (Ti, Zr)(C, N), further refining the grains and enhancing the precipitation strengthening effect. At the same time, it reacts with impurities such as S and O to generate ZrS or ZrO2, reducing the segregation of low-melting sulfides at the grain boundaries, reducing thermal brittleness, and improving toughness and fatigue resistance. However, excessive Zr may lead to coarse carbides or inclusions, damaging the low-temperature toughness. In the present invention, the Zr content range is controlled to be 0.025% - 0.040%.

[0044] Al element: The Al element can refine the essential grains of the steel, reduce the sensitivity of the steel to cracks, lower the ductile-brittle transition temperature and cold brittleness tendency of the steel plate, and improve the low-temperature toughness. At the same time, it can deoxidize and fix nitrogen, purifying the molten steel. In the present invention, the Als content range is controlled to be 0.03% - 0.06%.

[0045] P and S elements: They are not beneficial to the low-temperature toughness and cold working performance of the steel plate. In the present invention, P ≤ 0.005% and S ≤ 0.001% are controlled.

[0046] The manufacturing method of a super-high-strength low-temperature offshore wide and thin steel plate with good cold working performance described in the present invention includes the following steps:

[0047] (1) Converter smelting: After the hot metal is pretreated by desulfurization, it is charged into the converter. During the converter smelting process, alloying elements such as nickel, copper, and molybdenum are first added to the furnace, and the double slag method is used for smelting to reduce the phosphorus content in the steel; then other alloys are added for deoxidation and alloying; during the tapping process, the converter slagging is controlled to reduce the degree of rephosphorization during the later LF refining reduction.

[0048] (2) LF refining: Add deoxidizer to make reducing slag, finely adjust the chemical composition, remove inclusions in the steel, and achieve deep desulfurization.

[0049] (3) VD refining: After vacuum degassing, carry out weak argon stirring to further remove inclusions in the steel.

[0050] (4) Continuous casting: Adopt a weak cooling process during pouring, control the specific water volume at 0.65 - 0.80 L / kg, control the casting speed at 0.85 - 1.25 m / min, and adopt a soft reduction process at the end of continuous casting with a reduction amount of 5.0 - 7.0 mm.

[0051] (5) Electroslag remelting: The continuous casting billet is used as a consumable electrode to melt and purify in superheated molten slag, and is cooled into an ingot in a water-cooled mold. During cooling, a weak cooling method is adopted, and the cooling water volume is controlled at 45 - 65 m 3 / h, and the outlet water temperature ≤ 50 °C to prevent surface cracks from occurring; the electroslag billet is taken off the line for homogenization annealing at 1000 ± 50 °C, and the slab is taken off the line and stacked for slow cooling with a slow cooling time ≥ 60 h;

[0052] (6) Billet composite rolling: To ensure good plate shape of the thin - gauge ultra - high - strength steel plate, adopt the billet composite rolling technology; spray release agent in the middle of the billet, weld and leave air holes around the billet, and the weld width ≥ 50 mm; spray anti - oxidation coating on both the upper and lower surfaces of the composite billet.

[0053] (7) Two - stage controlled rolling: The composite electroslag billet is loaded into the heating furnace for heating, the heating temperature is 1150 - 1300 °C, and the total time in the furnace is 3 - 5 h; after heating, carry out two - stage finish rolling. In the first stage of rolling, adopt the transverse - longitudinal rolling process, the starting rolling temperature ≥ 1100 °C, and adopt the multi - pass small reduction amount and fast rolling method to prevent the composite billet from cracking; first carry out transverse rolling for width spreading, with an average single - pass reduction amount of 6 - 10 mm, and then carry out longitudinal rolling, with an average single - pass reduction amount of 10 - 15 mm for longitudinal rolling; the final rolling temperature in the first stage is 950 - 1050 °C, and the thickness of the billet waiting for temperature in the first stage is 4.0 - 4.5 times the thickness of the finished composite steel plate; the starting rolling temperature in the second stage is 830 - 920 °C, the average single - pass reduction amount is 8 - 12 mm, and the final rolling temperature is 750 - 850 °C.

[0054] (8) Two - stage quenching + tempering heat treatment: The quenching temperature in the first stage is 850 - 950 °C, and the holding time is 1.2 - 2.5 mm / min; the quenching temperature in the second stage is 650 - 740 °C, and the holding time is 2.2 - 3.0 mm / min; the tempering temperature is 610 - 660 °C, and the holding time is 1.5 - 3.0 mm / min; air - cool after leaving the furnace.

[0055] (9) Finish machining of steel plate: Determine the cutting line of the steel plate, complete the slitting of the upper and lower layers of the steel plate, and separate the upper and lower layer steel plates by using a suction cup.

[0056] To more intuitively illustrate the present invention, the implementation manners of the present invention will be further described in combination with embodiments. The following embodiments are only preferred specific implementation manners of the present invention, but the protection scope of the present invention is not limited thereto. Any technical solutions that can be obtained obviously by those skilled in the art within the technical scope disclosed by the present invention, including simple changes or equivalent replacements, are all within the protection scope of the present invention.

[0057]

Embodiment

[0058] The chemical compositions of the steel in each embodiment are shown in Table 1, the smelting and billet pretreatment process parameters of the steel in each embodiment are shown in Table 2, the slab heating and rolling process parameters in each embodiment are shown in Table 3, the steel plate heat treatment process parameters in each embodiment are shown in Table 4, and the microstructures and properties of the finished steel plates in each embodiment are shown in Table 5.

[0059] Table 1 Chemical composition of steel, wt%

[0060] Example C Si Mn Ni Cr Mo Cu V Ti Als B Zr P S 1 0.065 0.23 1.24 5.86 0.52 0.80 1.32 0.25 0.028 0.037 0.0020 0.038 0.0031 0.0010 2 0.073 0.10 1.20 8.00 0.61 1.12 1.00 0.21 0.031 0.041 0.0035 0.035 0.0044 0.0007 3 0.055 0.37 1.00 7.31 0.59 0.85 1.41 0.24 0.037 0.048 0.0041 0.027 0.0034 0.0008 4 0.080 0.24 1.59 6.32 0.64 0.93 1.21 0.20 0.025 0.060 0.0028 0.040 0.0030 0.0009 5 0.064 0.19 1.12 6.92 0.70 0.87 1.35 0.28 0.038 0.039 0.0050 0.033 0.0050 0.0010 6 0.046 0.31 1.04 5.68 0.67 0.99 1.31 0.22 0.026 0.052 0.0034 0.036 0.0042 0.0007 7 0.040 0.27 1.48 5.32 0.49 1.19 1.26 0.24 0.041 0.056 0.0042 0.031 0.0039 0.0009 8 0.077 0.40 1.37 5.00 0.46 1.14 1.18 0.30 0.040 0.030 0.0047 0.037 0.0048 0.0008 9 0.052 0.34 1.11 6.31 0.40 1.06 1.36 0.27 0.042 0.038 0.0037 0.035 0.0037 0.0010 10 0.069 0.18 1.60 7.53 0.51 1.20 1.50 0.28 0.045 0.045 0.0031 0.029 0.0041 0.0009 11 0.059 0,21 1.21 7.32 0.49 0.96 1.42 0.22 0.035 0.053 0.0026 0.030 0.0039 0.0010 12 0.043 0.33 1.31 6.99 0.63 1.03 1.39 0.27 0.032 0.047 0.0044 0.025 0.0047 0.0010

[0061] Table 2 Smelting and billet pretreatment process parameters of steel

[0062]

[0063] Table 3 Slab heating and rolling process parameters

[0064]

[0065] Table 4 Steel plate heat treatment process parameters

[0066] Example First stage First stage quenching Second stage Second stage quenching Tempering Tempering hold 1 Quench at 879 degrees Hold for 1.7 hours Quench at 697 degrees Hold for 2.3 hours 634 degrees 1.65 hours 2 895 1.53 676 2.5 628 1.84 3 923 1.64 651 2.8 618 2.18 4 910 2.31 721 2.7 610 2.56 5 850 2.50 704 2.2 632 1.92 6 916 2.32 685 2.8 640 1.50 7 864 2.27 740 2.9 616 2.16 8 879 1.73 737 2.6 628 2.19 9 920 1.20 693 2.9 656 2.32 10 949 1.29 663 3.0 649 3.00 11 937 2.13 690 2.5 660 2.73 12 907 2.11 712 2.6 652 2.95

[0067] Table 5 Microstructures and properties of finished steel plates

[0068]

[0069] The metallographic structure photograph (magnified 500 times) of the ultra-high strength and low-temperature offshore wide and thin steel plate produced in Example 1 is as Figure 1 shown.

[0070] As can be seen from the above embodiments, the steel plates produced by the present invention have ultra-high strength (yield strength ≥ 1050 MPa, tensile strength 1150 - 1250 MPa), high elongation (elongation after fracture A70 ≥ 14%), excellent ultra-low temperature toughness (V-notch impact energy at -84°C: for 5-mm thick samples ≥ 80 J, for 10-mm thick samples ≥ 130 J; V-notch impact energy at -160°C: for 5-mm thick samples ≥ 55 J, for 10-mm thick samples ≥ 100 J), good cold working performance (d = 8t, α = 105° bending test, no cracks in direct bending, reverse bending and side bending), and characteristics such as large width and thin gauge dimensions (thickness range 6 - 12 mm, width ≥ 4100 mm), and are suitable for manufacturing deep-sea offshore equipment.

[0071] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, should be covered by the protection scope of the present invention.

Claims

1. An ultra-high strength and low temperature marine engineering wide thin steel plate with good cold working performance, characterized in that: The chemical composition of the steel plate is calculated by weight as follows: C: 0.04% ~ 0.08%, Si: 0.1% ~ 0.4%, Mn: 1.0% ~ 1.6%, Ni: 5.0% ~ 8.0%, Cr: 0.4% ~ 0.7%, Mo: 0.8% ~ 1.2%, Cu: 1.0% ~ 1.5%, V: 0.2% ~ 0.3%, Ti: 0.025% ~ 0.045%, Zr: 0.025% ~ 0.040%, Als: 0.03% ~ 0.06%, B: 0.002% ~ 0.005%, P ≤ 0.005%, S ≤ 0.001%, and the rest is Fe and unavoidable impurities.

2. The ultra-high strength and low temperature marine wide thin steel plate with good cold working performance according to claim 1, characterized in that: The thickness of the finished steel plate is 6-12mm and the width is ≥4100mm.

3. The ultra-high strength and low temperature marine wide thin steel plate with good cold working performance according to claim 1, characterized in that: The microstructure of the finished steel plate is tempered troostite + ferrite + retained austenite. By volume percentage, tempered troostite accounts for 45% to 50%, ferrite accounts for 35% to 46%, and retained austenite accounts for 9% to 15%.

4. The ultra-high strength and low temperature marine wide thin steel plate with good cold working performance according to claim 1, characterized in that: The mechanical properties of the finished steel plate are: yield strength ≥1050MPa, tensile strength 1150~1250MPa, elongation after fracture A70 ≥14%, V-shaped impact energy at -84℃: 5mm thick sample ≥70J, 10mm thick sample ≥130J; V-shaped impact energy at -160℃: 5mm thick sample ≥55J, 10mm thick sample ≥100J; d=8t,α=105° bending test, there are no cracks in forward bending, back bending and side bending.

5. A method for manufacturing an ultra-high strength and low temperature marine wide thin steel plate with good cold working performance as claimed in any one of claims 1 to 4, characterized in that: The steps include: (1) Converter smelting: After desulfurization pretreatment, molten iron is added to the converter. During the converter smelting process, nickel, copper and molybdenum are first added to the furnace and smelted using the double slag method; then other alloys are added for deoxidation and alloying; during the steelmaking process, the slag of the converter is controlled; (2) LF refining: adding deoxidizer to make reducing slag, fine-tuning the chemical composition, removing inclusions in the steel, and achieving deep desulfurization; (3) VD refining: After vacuum degassing, argon blowing and weak stirring are performed to further remove inclusions in the steel; (4) Continuous casting: weak cooling process is adopted during casting, the water content is controlled at 0.65-0.80L / kg, the casting speed is controlled at 0.85-1.25m / min, and the light pressure reduction process is adopted at the end of continuous casting, with a pressure reduction of 5.0-7.0mm; (5) Electroslag remelting: The continuous casting billet is melted and purified in the superheated slag as a consumable electrode, and then cooled into an ingot in a water-cooled crystallizer. Weak cooling is used during cooling, and the cooling water volume is controlled at 45-65m 3 / h, outlet water temperature ≤50℃; electroslag billets are subjected to homogenization annealing at 1000±50℃, and slabs are subjected to stacking slow cooling, with a slow cooling time of ≥60h; (6) Composite rolling of billets: an isolating agent is sprayed in the middle of the billet, and the billet is welded around and has pores, with a weld width of ≥50 mm; the upper and lower surfaces of the composite billet are sprayed with anti-oxidation coating; (7) Two-stage controlled rolling: the composite electroslag billet is loaded into a heating furnace for heating, the heating temperature is 1150-1300°C, and the total time in the furnace is 3-5h; the first-stage rolling adopts a transverse-longitudinal rolling process, the starting rolling temperature is ≥1100°C, and a multi-pass small reduction fast rolling method is adopted. The average single-pass reduction of transverse rolling is 6-10mm, and the average single-pass reduction of longitudinal rolling is 10-15mm; the first-stage final rolling temperature is 950-10500°C, and the thickness of the first-stage warm billet is 4.0-4.5 times the thickness of the finished composite steel plate; the second-stage starting rolling temperature is 830-920°C, the average single-pass reduction is 8-12mm, and the final rolling temperature is 750-850°C; (8) Two-stage quenching + tempering heat treatment: the first stage quenching temperature is 850-950℃, and the holding time is 1.2-2.5mm / min; the second stage quenching temperature is 650-740℃, and the holding time is 2.2-3.0mm / min; the tempering temperature is 610-660℃, and the holding time is 1.5-3.0mm / min; air cooling after leaving the furnace; (9) Steel plate finishing: Complete the cutting of the upper and lower layers of the steel plate and separate the upper and lower layers of the steel plate.

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