A production method of green low-carbon high-strength extra-thick steel plate and the extra-thick steel plate produced

Abstract

The present invention relates to a production method of a green low-carbon high-strength extra-thick steel plate and the extra-thick steel plate produced. First, low Pcm, low CEV, low P, S, H, Cu, Sn, Nb micro-alloying composition design is carried out, and thick casting billets are formed through molten iron pre-desulfurization treatment, converter smelting, ladle refining, RH vacuum refining and continuous casting; then, billet stacking cooling, continuous casting billet heating, three-stage rolling, straightening, water cooling and slow cooling pit stacking are carried out. The service life, core performance and assembly accuracy of the extra-thick steel plate are improved, and the influence on the steel plate structure, performance, plate shape and plate shape accuracy after steel plate cutting and processing is reduced.

Description

Technical Field

[0001] The invention relates to a production method of a green low-carbon high-strength extra-thick steel plate and the extra-thick steel plate produced, belonging to the technical field of new material smelting, in particular to a production method of an extra-thick steel plate. Background Art

[0002] Extra-thick steel plates are key materials used in important engineering fields such as ocean, energy, construction, bridges, and high-end equipment. They are also the basic guarantee for infrastructure construction, expansion of marine rights and interests, and national defense security. The production capacity and physical quality of extra-thick plates reflect the level of national industrial technology. With the rapid development of my country's economy, many major national projects, key projects, and equipment have put forward requirements for steel plates with greater thickness, greater unit weight, and higher quality.

[0003] Among them, the application in marine engineering is mainly concentrated in the construction of equipment and facilities such as offshore drilling platforms, offshore wind towers, cross-sea bridges, and coastal buildings. Due to the extremely complex marine environment, steel plates are often easily corroded by chloride ions in seawater, leading to premature failure, which seriously reduces the service life of equipment and facilities and causes significant economic losses.

[0004] In addition, the use of size-limited continuous casting billets to produce extra-thick steel plates is limited by the insufficient rolling compression ratio, the unevenness of rolling deformation penetration and post-rolling cooling in the thickness direction of the steel plate, and the limitations of the rolling force and torque limit of the thick plate rolling mill, which leads to the problems of extra-thick steel plates being prone to unqualified flaw detection, poor uniformity of the thickness direction, coarse core structure, poor low-temperature toughness, curved plate shape, and difficulty in correction. High-strength extra-thick plates have higher requirements in terms of purity, strength, low-temperature toughness, welding performance, crack arrest performance, and earthquake resistance, so production is extremely difficult.

[0005] In the prior art, patent CN115261746B discloses a super-thick Q420qE bridge steel plate and its production method. In the rolling process, high-temperature one-stage large-reduction rolling is adopted, and the steel plate is subjected to three-stage cooling treatment after rolling, so that a Q420qE steel plate with a maximum thickness of 150 mm can be obtained. The steel plate can meet the Z-direction tensile performance requirements of the Z35 level and the flaw detection requirements of level II or above in the GB / T 2970-2016 standard. However, the chemical composition involved in this patent adds precious metal elements such as Ni, Cr, and Mo, the alloy cost is relatively high, and the carbon equivalent and cold crack sensitivity index are also relatively high. One-stage rolling is adopted, and the steel plate is subjected to three-stage cooling treatment after rolling. The cooling rate and final cooling temperature need to be controlled for each stage of cooling. The cooling process is complicated, the workshop operation is extremely difficult, and the low-temperature toughness of the steel plate is relatively low. Patent CN113584408B discloses a structural steel plate for wind power and its production method. The steel plate is prepared by heating, recrystallization zone rolling, non-recrystallization zone rolling, two-phase zone rolling and cooling bed air cooling in sequence; the steel plate is a complex phase structure composed of polygonal ferrite, deformation induced ferrite and bainite. In this patent, the rolling temperature of the two-phase zone is low and the deformation resistance is large. The production process of this patent cannot be applied to the production of extra-thick plates. Patent CN114480969B discloses a production method of Q460GJ, a super-thick steel with high toughness and high Z-direction performance with a compression ratio of ≤4. The invention adopts continuous casting production, combined with a reasonable controlled rolling and controlled cooling process, and cancels the traditional heat treatment link to obtain 80-100mm thick Q460GJ steel with a compression ratio of ≤4, with a yield strength ratio of ≤0.75, -60℃ impact toughness ≥150J, and Z-direction tensile section shrinkage ≥60%. However, the patented production method can only meet the requirements of 80-100mm thick steel plates, and the steel plates produced are not resistant to seawater corrosion.

[0006] Therefore, it is necessary to design a new production method for extra-thick steel plates to solve the above problems. Summary of the invention

[0007] The present invention provides a method for producing a green, low-carbon, high-strength and extra-thick steel plate and the extra-thick steel plate produced, which improves the service life, core performance and assembly accuracy of the extra-thick steel plate and reduces the influence on the structure, performance, plate shape and plate shape accuracy of the steel plate after cutting and processing.

[0008] The technical solution adopted by the present invention to solve its technical problem is:

[0009] A method for producing a green, low-carbon, high-strength, extra-thick steel plate, wherein the thickness of the extra-thick steel plate ranges from 100 to 160 mm, and the chemical composition of the extra-thick steel plate is set to be as follows by mass percentage: C: 0.07-0.09%, Si: 0.15-0.20%, Mn: 1.45-1.65%, Cu: 0.15-0.25%, Sn: 0.065-0.095%, Nb: 0.035-0.055%, Ti: 0.008-0.018%, Al: 0.03-0.04%, S≤0.002%, P≤0.008%, H≤0.00015%, and the rest is Fe and other unavoidable impurities;

[0010] As a further preferred embodiment of the present invention, in the extra thick steel plate, 0.33≤CEV≤0.38, 0.16≤Pcm≤0.19; wherein CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15, Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B;

[0011] As a further preference of the present invention, the following steps are included:

[0012] Step S1: In the steelmaking process, the molten iron is sequentially subjected to molten iron pretreatment, converter smelting, ladle refining and RH vacuum refining, and then enters the continuous casting stage; during the RH vacuum refining, the vacuum degree is set to be <2mBar, the degassing time is ≥20 minutes, and the soft stirring time is ≥20 minutes;

[0013] Step S2: continuous casting process, continuously casting the molten steel obtained after refining into a casting billet with a thickness of 310-330 mm;

[0014] Step S3: Cooling the ingots in stacking, with the stack cooling time being ≥ 72 hours;

[0015] Step S4: heating the ingot, using a low temperature furnace to heat the ingot, and setting a time to keep it warm;

[0016] Step S5: performing a three-stage rolling process on the ingot from the low-temperature furnace to form a steel plate, wherein the first and second stages of rolling are both austenite recrystallization zone rolling, and the third stage of rolling is austenite non-recrystallization zone rolling;

[0017] The first stage rolling temperature is 1080-1110℃, and the single pass reduction is set to 35-40mm. The first stage final rolling temperature is 1040-1070℃, and the ingot is sprayed with water for cooling. The surface temperature is cooled to T 再结晶 +15℃-T 再结晶 +25℃, T 再结晶 is the austenite recrystallization temperature;

[0018] T再结晶 +15℃-T 再结晶 +25℃ is used as the second stage rolling temperature, and the single pass reduction is set to 30-36mm, and the second stage final rolling temperature is T 再结晶 +5℃-T 再结晶 +15℃, spray water to cool the ingot again, and cool the surface temperature to A r3 +20℃-A r3 +35℃,A r3 is the starting temperature of the transformation from austenite to ferrite during cooling;

[0019] A r3 +20℃-A r3 +35℃ is used as the third stage rolling temperature, and the single pass reduction is set to 15-25mm. The third stage final rolling temperature is A r3 +10℃-A r3 +25℃;

[0020] Step S6: Straightening process, straightening the steel plate, setting the straightening temperature to A r3 +5℃-A r3 +20℃;

[0021] Step S7: Cooling process, using MULPIC accelerated cooling system to cool the straightened steel plate, setting the lower surface water volume / upper surface water volume of cooling water = 1.2-1.3, and the final cooling temperature is 380-430°C;

[0022] Step S8: stacking the cooled steel plates in a slow cooling pit for a duration of ≥ 24 hours;

[0023] As a further preferred embodiment of the present invention, when heating the ingot, the temperature of the low temperature furnace is set to 1140-1160°C, and the holding time is set to 360-400min;

[0024] As a further preferred embodiment of the present invention, the austenite recrystallization temperature T 再结晶 Obtained by measuring the grain size change or hardness change of the steel plate;

[0025] The starting temperature of the transformation from austenite to ferrite during cooling is A r3 It is measured by the critical point measurement method of steel, specifically by sampling and testing the steel plate and drawing the thermal expansion curve, A r3 That is the point of thermal expansion change shown on the curve;

[0026] As a further preferred embodiment of the present invention, in the cooling process, the water inlet temperature is controlled to be A r3 -A r3+15℃, the MULPIC accelerated cooling system is divided into three cooling zones along the production line from the beginning to the end, namely zone A, zone B and zone C. The total length of the entire MULPIC accelerated cooling system production line is 24m, and the length of each cooling zone is 8m;

[0027] Among areas A, B, and C, the water pressure in area B is the lowest;

[0028] As a further preferred embodiment of the present invention, in zone A, the water pressure is set to 0.5 MPa and the water volume is set to 16000 m 3 / h; in area B, the water pressure is set to 0.25MPa and the water volume is 8000m 3 / h; in area C, the water pressure is set to 0.7MPa and the water volume is 18000m 3 / h;

[0029] The extra thick steel plate obtained according to the production method has a thickness of 100-160 mm;

[0030] Yield strength is ≥420MPa, tensile strength is ≥540MPa, Z-axis tensile section shrinkage is ≥60%, yield strength ratio is ≤0.82, -10℃ crack arrest toughness is ≥8000 N / mm 3 / 2 , the impact energy of the core of extra thick steel plate at -60℃ KV2≥250J;

[0031] The surface quality complies with EN 10163-2 Class B-Sub Class 3 requirements;

[0032] The internal stress of the extra-thick steel plate is uniform at different positions, and the highest internal stress is less than 15MPa;

[0033] Extra thick steel plate unevenness <2mm / m;

[0034] Meet the requirements of Level I flaw detection in GB / T 2970-2016 standard;

[0035] The average annual corrosion rate of the extra-thick steel plate under full immersion in seawater is ≤0.1 mm / a;

[0036] As a further preferred embodiment of the present invention, the structure of the extra thick steel plate is a complex phase structure of acicular ferrite combined with lath bainite, wherein the acicular ferrite accounts for 30-40%, the lath bainite accounts for 60-70%, and the grain size is less than 40 μm.

[0037] Through the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The production method of the green low-carbon high-strength and extra-thick steel plate provided by the present invention reduces alloy consumption by designing low-alloy cost components, reduces gas consumption and CO2 emissions by designing a heat treatment-free production process, improves the seawater corrosion resistance of the steel plate, and ultimately meets the production requirements of the green low-carbon high-strength and extra-thick steel plate;

[0039] 2. The production method of the green low-carbon high-strength and extra-thick steel plate provided by the present invention sets a three-stage rolling process with high pressure in the high-temperature zone during the rolling stage, thereby increasing the deformation penetration of the steel plate and improving the qualified rate of flaw detection of the steel plate. In addition, cooling control is performed during the three-stage rolling process to refine the core structure of the steel plate, improve the core performance of the extra-thick steel plate, and solve the technical problem of producing extra-thick steel plates with a low compression ratio;

[0040] 3. The production method of the green low-carbon high-strength and extra-thick steel plate provided by the present invention adopts high-temperature straightening to reduce the difficulty of straightening the extra-thick plate, reduce the internal stress of the steel plate, reduce the unevenness of the steel plate, improve the assembly accuracy of the steel plate, and reduce the influence of the rolling plate shape problem on the cooling uniformity of the steel plate;

[0041] 4. The production method of the green low-carbon high-strength and extra-thick steel plate provided by the present invention can achieve fine control of the whole production process, improve the purity of the steel plate, and reduce the influence of uneven deformation and uneven cooling on the structure, performance, shape and shape accuracy of the steel plate after subsequent cutting and processing;

[0042] 5. The extra-thick steel plate produced by the production method provided by the present invention not only has high strength and good low-temperature toughness, but also has better seawater corrosion resistance, crack arrest performance, earthquake resistance and plate shape quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0044] Figure 1 It is a flow chart of the production method of the green low-carbon high-strength and extra-thick steel plate provided by the present invention. DETAILED DESCRIPTION

[0045] The present invention will now be described in further detail with reference to the accompanying drawings. In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "left side", "right side", "upper part", "lower part", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and "first", "second", etc. do not indicate the importance of the components, and therefore cannot be understood as a limitation on the present invention. The specific dimensions used in this embodiment are only for illustrating the technical solution by example, and do not limit the scope of protection of the present invention.

[0046] As described in the background technology, there are roughly the following difficulties in the current production process of high-strength extra-thick plates: the cooling process is complicated, which makes workshop operation extremely difficult; the design of the rolling stage makes the steel plate deformation resistance large, resulting in the relevant production process cannot be applied to the production of extra-thick plates; or the controlled rolling and controlled cooling process is optimized and the traditional heat treatment process is cancelled, but the strength and toughness can only meet the production requirements of steel plates with a thickness range of 80-100mm.

[0047] In order to solve the above problems, the production method provided in this application has been designed in terms of alloy composition and process procedures. The first is the design of micro-alloying composition of low P, S, H, Cu+Sn+Nb. Among these alloy components, P has corrosion resistance and can also improve the strength of steel plates, but the P element will increase the low-temperature brittleness of steel and easily cause serious segregation. It can also increase welding sensitivity, which is not good for the welding performance of steel. The S element is a harmful element in steel. Sulfur exists in steel in the form of FeS. FeS and Fe form a low melting point (985°C) compound, and the billet heating temperature is generally above 1100°C. Therefore, when the billet is heated, the billet will crack during forging and rolling due to the premature melting of the FeS compound; S is also not good for welding performance and will reduce corrosion resistance. H is the most harmful element in steel. Dissolving H in steel can cause defects such as hydrogen embrittlement and white spots. H, like O and N, has very low solubility in solid steel. It dissolves into molten steel at high temperature and does not have time to escape during cooling, so it accumulates in the organization to form high-pressure fine pores, which sharply reduces the plasticity, toughness and crack arrest toughness of steel. In severe cases, it can cause cracks and brittle fractures. Adding Cu to steel can not only effectively improve the strength and impact toughness of steel, but also enhance the corrosion resistance of steel plates. When copper is added to steel, in a corrosive environment, the copper in the steel will be concentrated and enriched as iron dissolves, and an oxide intermediate film will be formed between the corrosion interface and the copper enrichment layer and adsorbed on the surface of the steel, preventing the corrosive medium from corroding the inside of the steel plate, and finally achieving the effect of corrosion resistance. However, the price of Cu alloy is relatively high, and when the content is high, it is not conducive to hot deformation processing, and copper brittleness will occur during hot deformation processing. The Sn element can promote the transformation of the γ-FeOOH phase to the α-FeOOH phase, increase the content of the α-FeOOH phase in the rust layer, and generate stable acid-insoluble SnO2. The two work together to improve the stability and protection of the rust layer, hinder further corrosion by corrosive ions, and thereby improve the corrosion resistance of low-alloy steel. When Sn and Cu are added at the same time, the corrosion-resistant layer formed will be denser and the corrosion resistance of the steel plate will be better, but too high Sn content is not good for the low-temperature toughness of the steel plate. Therefore, the amount of Sn added needs to be strictly set. Nb solid solution atoms tend to be concentrated at the austenite grain boundaries, which have a dragging effect on the bending and migration of the grain boundaries. Therefore, the growth of austenite grains during the heating process can be inhibited. The Nb carbonitrides precipitated during the rolling stage also have the effect of inhibiting the recrystallization of austenite and the growth of grains after recrystallization. Therefore, trace Nb elements have a good fine grain strengthening effect. Fine grain strengthening can improve the strength of the steel plate without affecting the plasticity and toughness of the steel. At the same time, the precipitation strengthening effect of the Nb element can also increase the tempering stability of the steel and have a secondary hardening effect. However, a trace amount of Nb can play a significant role, and the effect of continuing to add is not obvious. When the content is too high, it is also easy to produce large-sized inclusion brittle phases.

[0048] In addition to the consideration of the above alloying elements, this application also considers C, Si, Mn, Al and Ti elements when designing the chemical composition. These elements are indispensable in the steelmaking process. C is a solid solution strengthening element and is the most effective element for improving the strength of steel plates. However, carbon is not good for the corrosion resistance, welding performance and low temperature toughness of steel plates. In addition, when the C content is greater than 0.09%, it enters the peritectic zone, and the billet is prone to surface cracks during continuous casting. Si is a solid solution strengthening element that can improve the strength of steel plates and enhance the corrosion resistance of steel plates under natural conditions, especially the ability to enhance local corrosion; however, steel plates with high Si content have poor iron oxide scale peeling properties, and iron oxide scale is easy to remain, affecting the surface quality of steel plates; high Si content is also not good for welding performance and is prone to cold brittleness. Mn is also a solid solution strengthening element, which has a significant effect on improving the strength of low carbon steel. Mn can also reduce the critical transformation temperature and phase transformation rate of austenite, increase the hardenability of steel plates and refine the structure after phase transformation; but too high Mn content has an adverse effect on the welding performance of steel plates. Al elements can effectively reduce the oxygen content in steel during steelmaking and play a strong deoxidation role; Al elements can also inhibit surface corrosion and internal oxidation of steel, extending the service life of steel; Al elements can also refine the intrinsic grains of steel and increase the temperature of steel grain coarsening, but when the solid solution metal Al content in steel exceeds a certain value, the austenite grains are prone to grow and coarsen. Ti elements have similar properties to Nb elements, but too high Ti content is also prone to form large-sized inclusions, which is not conducive to low-temperature impact toughness.

[0049] Therefore, the present application provides for the production of extra thick steel plates with a thickness range of 100-160 mm, and the chemical composition of the extra thick steel plates is set as follows by mass percentage: C: 0.07-0.09%, Si: 0.15-0.20%, Mn: 1.45-1.65%, Cu: 0.15-0.25%, Sn: 0.065-0.095%, Nb: 0.035-0.055%, Ti: 0.008-0.018%, Al: 0.03-0.04%, S≤0.002%, P≤0.008%, H≤0.00015%, and the rest are Fe and other unavoidable impurities.

[0050] In order to further reduce alloy consumption, the extra-thick steel plate is also set to have low CEV and low Pcm, which can ensure that the steel plate has good welding performance; specifically, 0.33≤CEV≤0.38, 0.16≤Pcm≤0.19; among which, CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15,

[0051] Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

[0052] The CEV and Pcm calculation methods also include some elements that are not intentionally added, such as Ni, Cr, Mo, V, and B. Based on actual smelting experience, the residual elements are controlled at Ni≤0.02%, Cr≤0.02%, Mo≤0.02%, V≤0.002%, and B≤0.0002%.

[0053] Next, the present application provides a method for producing the green low-carbon high-strength and extra-thick steel plate. Figure 1 As shown, the entire production method includes molten iron pretreatment → converter smelting → ladle refining → RH vacuum refining → continuous casting → ingot stacking cooling → ingot heating → rolling → straightening → water cooling → slow cooling pit stacking. By optimizing the alloy composition and production process, the purpose of heat treatment exemption is achieved, which can reduce gas consumption and carbon dioxide emissions, and improve the corrosion resistance of the steel plate, that is, a green, low-carbon, high-strength and extra-thick steel plate is obtained.

[0054] The previous molten iron pretreatment → converter smelting → ladle refining → RH vacuum refining are summarized as steelmaking processes in the explanation. The molten iron enters the continuous casting process after being processed in sequence. During steelmaking, the RH vacuum refining sets the vacuum degree <2mBar, ensures the degassing time ≥20 minutes, and the soft stirring time ≥20 minutes, which can improve the purity of the steel plate and the comprehensive mechanical properties of the extra-thick steel plate. In the continuous casting process, the molten steel obtained after refining is continuously cast into a billet with a thickness of 310-330mm. In actual smelting, the extra-thick steel plate targeted by this application needs to be formed into a billet with a thickness of 320mm after the continuous casting process, and then enters the billet stacking cooling, and the stacking cooling time is ≥72 hours, which can make the billet and steel plate fully dehydrogenate and improve the low-temperature toughness and crack arrest performance of the steel plate.

[0055] When heating the ingot, a low-temperature furnace is used to heat the ingot, and the low-temperature furnace temperature is set to 1140-1160℃, which can not only avoid abnormal growth of austenite structure, but also improve the surface quality of the steel plate, so that the surface quality of the steel plate meets the relevant requirements of EN 10163-2 Class B-Sub Class 3. The low-temperature furnace is set to hold the temperature for 360-400min. Long-term holding can make the ingot fully "burn through", which not only improves the temperature uniformity of the ingot but also makes the alloy elements fully dissolved. The uniform temperature of the ingot is an important prerequisite for ensuring uniform deformation of the steel plate. Improving deformation uniformity can improve the shape quality of the steel plate; full solid solution of alloy elements is an important prerequisite for ensuring the strength of the steel plate.

[0056] After the heating of the ingot is completed, the rolling process begins. The rolling process provided in this application is a three-stage rolling process to form a steel plate. The first and second stages of rolling are both rolling in the austenite recrystallization zone, and the austenite structure is refined by deformation and recrystallization. The first stage rolling temperature is 1080-1110°C, and the single-pass reduction is set to 35-40mm. The first stage final rolling temperature is 1040-1070°C. The higher temperature in the first stage can ensure a larger single-pass reduction of the ingot and refine the whole plate structure; water cooling after the first stage rolling, that is, spraying water to cool the ingot, and the surface temperature is cooled to T 再结晶 +15℃-T 再结晶 +25℃(T 再结晶 is the austenite recrystallization temperature), there is a large temperature difference between the surface and the core after water cooling, the surface temperature is relatively low, the deformation resistance is large, the core temperature is high, the deformation resistance is small, this difference can ensure that the deformation of the steel plate is fully penetrated into the core of the steel plate during the second stage of rolling, ensuring a large deformation in the core, and after austenite recrystallization, the core of the steel plate also has a finer austenite structure.

[0057] T 再结晶 +15℃-T 再结晶 +25℃ is used as the second stage rolling temperature, and the single pass reduction is set to 30-36mm, and the second stage final rolling temperature is T 再结晶 +5℃-T 再结晶 +15℃, spray water to cool the ingot again, and cool the surface temperature to A r3 +20℃-A r3 +35℃(A r3 is the starting temperature of the transformation from austenite to ferrite during the cooling process); in the second stage of post-rolling cooling, not only can a large temperature difference be formed in the thickness direction, further increasing the deformation of the core of the steel plate, but also the waiting time can be reduced, avoiding the growth of austenite structure after recrystallization, and improving the rolling efficiency of extra-thick steel plates.

[0058] The third stage of rolling is the rolling in the austenite non-recrystallization zone. r3 +20℃-A r3 +35℃ is used as the third stage rolling temperature, and the single pass reduction is set to 15-25mm, and the final rolling temperature is A r3 +10℃-A r3 +25℃ can make the steel plate structure fully deformed, promote intracrystalline nucleation, and further refine the structure through subsequent phase transformation, but two-phase rolling should also be avoided, as the uniformity of the two-phase rolling structure is poor.

[0059] In the three-stage rolling process, a larger single-pass reduction is set, which can improve deformation penetration, increase the deformation of austenite structure, and refine the steel plate structure; however, considering the bearing capacity of the rolling mill, at the same deformation temperature, the greater the single-pass deformation, the greater the deformation resistance, and at the same single-pass reduction, the lower the deformation temperature, the greater the deformation resistance. Therefore, the single-pass reduction in the first stage is set to 35-40mm, the single-pass reduction in the second stage is set to 30-36mm, and the single-pass reduction in the third stage is set to 15-25mm.

[0060] In the three-stage rolling process, two temperatures are involved, namely the austenite recrystallization temperature T 再结晶 And the starting temperature A of the transformation from austenite to ferrite during cooling r3 , where T 再结晶 A is obtained by measuring the change in grain size or hardness of the steel plate. r3 It is measured by the critical point measurement method (expansion method) of steel, specifically, sampling and testing the steel plate and drawing the thermal expansion curve, A r3 This is the point where the thermal expansion changes as shown on the curve.

[0061] After rolling, the steel plate enters the straightening process to straighten it, which can reduce the residual stress caused by uneven deformation during the rolling process and reduce the unevenness of the steel plate. The unevenness is an intuitive reflection of the quality of the plate shape and is also an important factor affecting the cooling uniformity. The straighter the steel plate, the better the cooling uniformity. Extra thick steel plates are easier to straighten at high temperatures, so the straightening temperature is set to A. r3 +5℃-A r3 +20℃.

[0062] The next step is the cooling process, where only one cooling is performed after rolling, and multiple cooling is not required. The water inlet temperature is controlled to A r3 -A r3 +15℃, the straightened steel plate is cooled by MULPIC accelerated cooling system. The entire MULPIC accelerated cooling system production line is divided into three cooling zones from beginning to end, namely zone A, zone B and zone C. In zone A, the water pressure is set to 0.5MPa and the water volume is 16000m 3 / h; the water pressure in area B decreases, the water pressure is set to 0.25MPa, and the water volume is 8000m 3 / h; in area C, the water pressure is set to 0.7MPa and the water volume is 18000m 3 / h. For the water pressure setting of the three zones, the water film on the surface of the steel plate is first blown off with the maximum water pressure, so that the steel plate cools down quickly and penetrates quickly, while suppressing the ferrite and pearlite phase transformation in the high temperature zone of austenite. The water pressure in the middle zone B is reduced, the temperature of the core of the steel plate returns to the surface of the steel plate, and the surface cooling penetrates into the core. The thermal cycle in the thickness direction of the steel plate has the effect of uniformizing the temperature in the thickness direction of the steel plate. At the same time, the steel plate can obtain 30%-40% acicular ferrite. The acicular ferrite grows inside the austenite grains, and the orientation of the acicular ferrite is randomly distributed during growth, which can effectively prevent the expansion of cracks and effectively refine the steel plate structure. This is very beneficial to improving the crack arrest performance of the steel plate, and this is an important prerequisite for ensuring that the steel plate has a low yield strength ratio. The C zone continues to set a large water pressure and a large amount of water to obtain a 60-70% lath bainite structure to ensure that the steel plate has high strength and good low-temperature toughness.

[0063] In the entire cooling system production line, the cooling water lower surface water volume / upper surface water volume = 1.2-1.3 is also accurately set to ensure the quality of the steel plate shape after cooling. The final cooling temperature after water cooling is 380-430℃, and the steel plate can be guaranteed to have a high straightness without secondary straightening.

[0064] Finally, the cooled steel plates are stacked in a slow cooling pit for a duration of ≥24 hours. This can not only further expel hydrogen, but also allow the steel plates to undergo self-tempering, homogenize the steel plate structure, improve the steel plate's yield strength, low-temperature toughness and fracture resistance, and further eliminate the residual stress caused by lattice distortion inside the microstructure through the precipitation of Nb and Ti carbonitrides.

[0065] The thickness of the extra-thick steel plate produced by the above production method fully meets the expected requirement of 100-160mm; in order to verify the steel plate structure and related properties, the extra-thick steel plate produced was extracted from the obtained steel plate thickness section metallographic sample, and after grinding and polishing, and then corroded by 4% nitric acid alcohol solution, its microstructure was observed under a Zeiss optical microscope.

[0066] The steel plate structure is a duplex structure of acicular ferrite + lath bainite, of which acicular ferrite accounts for 30-40%, lath bainite accounts for 60-70%, and the grain size is less than 40μm. The duplex structure of acicular ferrite + lath bainite makes the steel plate less prone to brittle fracture, less prone to cracks and other defects during welding, and maintains better fatigue resistance.

[0067] Specifically, the steel plate has the following properties: yield strength ≥420MPa, tensile strength ≥540MPa, Z-axis tensile section shrinkage ≥60%, yield strength ratio ≤0.82, and -10℃ crack arrest toughness ≥8000 N / mm 3 / 2, the impact energy of the core of the extra-thick steel plate at -60℃ KV2≥250J; the surface quality meets the requirements of EN 10163-2 Class B-Sub Class 3; the internal stress at different positions of the extra-thick steel plate is uniform, and the highest internal stress is <15MPa; the unevenness of the extra-thick steel plate is <2mm / m; it meets the requirements of Level I flaw detection in GB / T 2970-2016 standard; and the annual average corrosion rate of the extra-thick steel plate under full immersion in seawater is ≤0.1mm / a.

[0068] Next, this application provides examples and comparative examples to demonstrate that the extra-thick steel plates produced using the application components and process design meet the preset requirements. Example

[0069] Weigh each component raw material according to the formula ratio, and then carry out smelting. The smelting steps include molten iron desulfurization, converter smelting, ladle refining, RH vacuum refining (under the condition of vacuum degree less than 2mBar, degassing time is 20 minutes, soft stirring time is 20 minutes), and molten steel is obtained. The chemical composition of the extra thick steel plate is as follows by mass percentage: C: 0.08%, Si: 0.15%, Mn: 1.60%, Cu: 0.20%, Sn: 0.080%, Nb: 0.035%, Ti: 0.015%, Al: 0.03%, S: 0.002%, P: 0.008%, H: 0.00015%, and the rest is Fe and other unavoidable impurities. Set CEV=0.36, Pcm=0.175.

[0070] The molten steel is continuously cast into 320mm thick ingots; the ingots are stacked and cooled for 72 hours; the continuous casting ingots are heated at a low furnace temperature of 1160°C and the insulation time is 400 minutes.

[0071] In the rolling stage, the first stage rolling temperature is 1110℃, and the single-pass reduction is set to 40mm, the first stage final rolling temperature is 1070℃, and the billet thickness is 240mm after the first stage rolling. The billet is sprayed with water for cooling, and the surface temperature is cooled to 985℃; then the billet is put into the rolling mill at the fastest speed for two-stage rolling, 985℃ is used as the second-stage rolling temperature, the steel plate is warmed up during the rolling process, the single-pass reduction is set to 30mm, the second-stage final rolling temperature is 975℃, the billet is sprayed with water for cooling again, and the surface temperature is cooled to 795℃; then the billet is put into the rolling mill at the fastest speed for three-stage rolling, 795℃ is used as the third-stage rolling temperature, the steel plate is warmed up during the rolling process, the single-pass reduction is 25mm, and the three-stage final rolling temperature is 785℃;

[0072] After rolling, the steel is straightened at a temperature of 780°C. Then it is cooled in water at a temperature of 775°C. The MULPIC accelerated cooling system has three zones from front to back. The water pressure in the front zone A is set to 0.5MPa and the water volume is 16000m3 / h, the water pressure in the middle zone B is set to 0.25MPa, and the water volume is 8000m 3 / h, the water pressure in the C zone behind is set to 0.7MPa, 18000m 3 / h, cooling water lower surface water volume / upper surface water volume = 1.3, final cooling temperature 430℃; stacking in slow cooling pit for 24 hours.

[0073] The thickness of the steel plate produced is 160mm, the Z-axis tensile section shrinkage is 66%, and the -10℃ crack arrest toughness is 9000 N / mm 3 / 2 ; The surface quality meets the relevant requirements of EN 10163-2 Class B-Sub Class 3; the internal stress at different positions of the steel plate is relatively uniform, and the highest internal stress is 10MPa; the unevenness of the steel plate is 1mm / m; it meets the requirements of Level I flaw detection in GB / T 2970-2016 standard; and the average annual corrosion rate under full immersion in seawater is 0.05mm / a; the surface of the steel plate: the yield strength is 496MPa, the tensile strength is 634MPa, the yield strength ratio is 0.78, and the impact energy at -60℃ is 326J; the core of the steel plate: the yield strength is 482MPa, the tensile strength is 623MPa, the yield strength ratio is 0.77, and the impact energy at -60℃ is 305J.

[0074] The steel plate structure is a complex phase structure of acicular ferrite + lath bainite. The surface structure of the steel plate is: acicular ferrite accounts for 31%, lath bainite accounts for 69%, and the average grain size is 25μm; the core structure of the steel plate is: acicular ferrite accounts for 35%, lath bainite accounts for 65%, and the average grain size is 36μm.

[0075] Comparative Example 1:

[0076] Weigh each component raw material according to the formula ratio, and then carry out smelting. The smelting steps include molten iron desulfurization, converter smelting, ladle refining, RH vacuum refining (under the condition of vacuum degree less than 2mBar, degassing time is 20 minutes, soft stirring time is 20 minutes), and molten steel is obtained. The chemical composition of the extra thick steel plate is as follows by mass percentage: C: 0.08%, Si: 0.15%, Mn: 1.60%, Cu: 0.20%, Sn: 0.080%, Nb: 0.035%, Ti: 0.015%, Al: 0.03%, S: 0.002%, P: 0.008%, H: 0.00015%, and the rest is Fe and other inevitable impurities. Set CEV=0.36, Pcm=0.175.

[0077] The molten steel is continuously cast into 320mm thick ingots; the ingots are stacked and cooled for 72 hours; the continuous casting ingots are heated at a low furnace temperature of 1160°C and the insulation time is 400 minutes.

[0078] In the rolling stage, the first stage rolling temperature is 1110℃, and the single-pass reduction is set to 40mm, the first stage final rolling temperature is 1070℃, and the billet thickness is 240mm after the first stage rolling. The billet is air-cooled, and the surface temperature is cooled to 985℃; then it enters the rolling mill at the fastest speed for two-stage rolling, 985℃ is used as the second-stage rolling temperature, the steel plate returns to temperature during the rolling process, the single-pass reduction is set to 30mm, the second-stage final rolling temperature is 975℃, the billet is air-cooled again, and the surface temperature is cooled to 795℃; then it enters the rolling mill at the fastest speed for three-stage rolling, 795℃ is used as the third-stage rolling temperature, the steel plate returns to temperature during the rolling process, the single-pass reduction is 25mm, and the three-stage final rolling temperature is 785℃;

[0079] After rolling, the steel is straightened at a temperature of 780°C. Then it is cooled in water at a temperature of 775°C. The MULPIC accelerated cooling system has three zones from front to back. The water pressure in the front zone A is set to 0.5MPa and the water volume is 16000m 3 / h, the water pressure in the middle zone B is set to 0.25MPa, and the water volume is 8000m 3 / h, the water pressure in the C zone behind is set to 0.7MPa, 18000m 3 / h, cooling water lower surface water volume / upper surface water volume = 1.3, final cooling temperature 430℃; stacking in slow cooling pit for 24 hours.

[0080] The thickness of the steel plate produced is 160mm, the Z-axis tensile section shrinkage is 55%, and the -10℃ crack arrest toughness is 5500 N / mm 3 / 2 ; The surface quality meets the relevant requirements of EN 10163-2 Class B-Sub Class 3; the internal stress at different positions of the steel plate is relatively uniform, and the highest internal stress is 13MPa; the unevenness of the steel plate is 1mm / m; it meets the requirements of Level I flaw detection in GB / T 2970-2016 standard; the average annual corrosion rate under full immersion in seawater is 0.09mm / a; the surface of the steel plate: the yield strength is 524MPa, the tensile strength is 652MPa, the yield strength ratio is 0.80, and the impact energy at -60℃ is 334J; the core of the steel plate: the yield strength is 453MPa, the tensile strength is 598MPa, the yield strength ratio is 0.76, and the impact energy at -60℃ is 11J.

[0081] The steel plate structure is a complex phase structure of acicular ferrite + lath bainite. The surface structure of the steel plate is: acicular ferrite accounts for 30%, lath bainite accounts for 70%, and the average grain size is 11μm; the core structure of the steel plate is: acicular ferrite accounts for 36%, lath bainite accounts for 64%, and the grain size is 98μm.

[0082] Comparative Example 2:

[0083] Weigh each component raw material according to the formula ratio, and then carry out smelting. The smelting steps include molten iron desulfurization, converter smelting, ladle refining, RH vacuum refining (under the condition of vacuum degree less than 2mBar, degassing time is 20 minutes, soft stirring time is 20 minutes), and molten steel is obtained. The chemical composition of the extra thick steel plate is as follows by mass percentage: C: 0.08%, Si: 0.15%, Mn: 1.60%, Cu: 0.20%, Sn: 0.080%, Nb: 0.035%, Ti: 0.015%, Al: 0.03%, S: 0.002%, P: 0.008%, H: 0.00015%, and the rest is Fe and other inevitable impurities. Set CEV=0.36, Pcm=0.175.

[0084] The molten steel is continuously cast into 320mm thick ingots; the ingots are stacked and cooled for 72 hours; the continuous casting ingots are heated at a low furnace temperature of 1160°C and the insulation time is 400 minutes.

[0085] During the rolling stage, only one-stage rolling is adopted, the starting rolling temperature is 1110°C, the single-pass reduction is set to 40mm, and the final rolling temperature is 1020°C.

[0086] After rolling, the steel is straightened at a temperature of 1010°C. Then it is cooled in water at a temperature of 1005°C. The MULPIC accelerated cooling system has three zones from front to back. The water pressure in the front zone A is set to 0.7MPa and the water volume is 18000m 3 / h, the water pressure in the middle zone B is set to 0.25MPa, and the water volume is 8000m 3 / h, the water pressure in the C zone behind is set to 0.7MPa, 18000m 3 / h, cooling water lower surface water volume / upper surface water volume = 1.3, final cooling temperature 430℃; stacking in slow cooling pit for 24 hours.

[0087] The thickness of the steel plate produced is 160mm, the Z-axis tensile section shrinkage is 58%, and the -10℃ crack arrest toughness is 6200 N / mm 3 / 2 ; The surface quality meets the relevant requirements of EN 10163-2 Class B-Sub Class 3; the internal stress at different positions of the steel plate is relatively uniform, and the highest internal stress is 10MPa; the unevenness of the steel plate is 1mm / m; it meets the requirements of Level I flaw detection in GB / T 2970-2016 standard; and the average annual corrosion rate under full immersion in seawater is 0.08mm / a; the surface of the steel plate: the yield strength is 478MPa, the tensile strength is 621MPa, the yield strength ratio is 0.77, and the impact energy at -60℃ is 65J; the core of the steel plate: the yield strength is 461MPa, the tensile strength is 606MPa, the yield strength ratio is 0.76, and the impact energy at -60℃ is 22J.

[0088] The steel plate structure is a complex phase structure of acicular ferrite + lath bainite. The surface structure of the steel plate is: acicular ferrite accounts for 32%, lath bainite accounts for 68%, and the grain size is 72μm; the core structure of the steel plate is: acicular ferrite accounts for 38%, lath bainite accounts for 62%, and the grain size is 87μm.

[0089] Comparative Example 3:

[0090] Weigh each component raw material according to the formula ratio, and then carry out smelting. The smelting steps include molten iron desulfurization, converter smelting, ladle refining, RH vacuum refining (under the condition of vacuum degree less than 2mBar, degassing time is 20 minutes, soft stirring time is 20 minutes), and molten steel is obtained. The chemical composition of the extra thick steel plate is as follows by mass percentage: C: 0.08%, Si: 0.15%, Mn: 1.60%, Cu: 0.20%, Sn: 0.080%, Nb: 0.035%, Ti: 0.015%, Al: 0.03%, S: 0.002%, P: 0.008%, H: 0.00015%, and the rest is Fe and other inevitable impurities. Set CEV=0.36, Pcm=0.175.

[0091] The molten steel is continuously cast into 320mm thick ingots; the ingots are stacked and cooled for 72 hours; the continuous casting ingots are heated at a low furnace temperature of 1160°C and the insulation time is 400 minutes.

[0092] In the rolling stage, the first-stage rolling temperature is 1110°C, and the single-pass reduction is set to 40mm, the first-stage final rolling temperature is 1070°C, and the billet thickness is 240mm after the first-stage rolling. The ingot is sprayed with water for cooling, and the surface temperature is cooled to 985°C; then the billet is put into the rolling mill at the fastest speed for two-stage rolling, 985°C is used as the second-stage rolling start temperature, and the steel plate is warmed up during the rolling process. The single-pass reduction is set to 30mm, and the second-stage final rolling temperature is 975°C. The ingot is sprayed with water for cooling again, and the surface temperature is cooled to 795°C; then the billet is put into the rolling mill at the fastest speed for three-stage rolling, 795°C is used as the third-stage rolling start temperature, and the steel plate is warmed up during the rolling process. The single-pass reduction is 25mm, and the three-stage final rolling temperature is 785°C;

[0093] After rolling, the steel is straightened at a temperature of 780°C. Then it is cooled in water at a temperature of 775°C. The MULPIC accelerated cooling system has three zones from front to back. The water pressure in Zone A, Zone B, and Zone C is set to 0.48 MPa, and the water volume is 14,000 m 3 / h, cooling water lower surface water volume / upper surface water volume = 1.3, final cooling temperature 430℃; stacking in slow cooling pit for 24 hours.

[0094] The thickness of the steel plate produced is 160mm, the Z-axis tensile section shrinkage is 61%, and the -10℃ crack arrest toughness is 6500 N / mm 3 / 2 ; The surface quality meets the relevant requirements of EN 10163-2 Class B-Sub Class 3; the internal stress at different positions of the steel plate is relatively uniform, and the highest internal stress is 14MPa; the unevenness of the steel plate is 1mm / m; it meets the requirements of Level I flaw detection in GB / T 2970-2016 standard; the average annual corrosion rate under full immersion in seawater is 0.07mm / a; the surface of the steel plate: the yield strength is 569MPa, the tensile strength is 670MPa, the yield strength ratio is 0.85, and the impact energy at -60℃ is 309J; the core of the steel plate: the yield strength is 416MPa, the tensile strength is 553MPa, the yield strength ratio is 0.75, and the impact energy at -60℃ is 126J.

[0095] The structure of the steel plate is a complex phase structure of acicular ferrite + lath bainite. The surface structure of the steel plate is: acicular ferrite accounts for 10%, lath bainite accounts for 90%, and the average grain size is 20μm; the core structure of the steel plate is: acicular ferrite accounts for 60%, lath bainite accounts for 40%, and the grain size is 62μm.

[0096] The parameters of the steel plates obtained in the above-mentioned Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 are presented in the form of Table 1, Table 2 and Table 3, wherein Table 1 and Table 2 are the properties, and Table 3 is the organization.

[0097] Table 1 Properties of the produced extra thick steel plate

[0098]

[0099] Table 2 Properties of the produced extra thick steel plates

[0100]

[0101] Table 3 Microstructure of the produced extra thick steel plate

[0102]

[0103] As can be seen from Tables 1, 2 and 3, the composition and process design of the technology of the present invention are used to produce green, low-carbon, high-strength and extra-thick steel plates with excellent performance. The steel plates not only have high strength and good low-temperature toughness, but also have good seawater corrosion resistance, crack arrest performance, seismic resistance and plate shape quality; the extra-thick plates obtained by not spraying water for cooling in the three-stage rolling process or only using one-stage rolling or no change in water pressure during post-rolling cooling have poor low-temperature toughness in the core of the steel plate and poor crack arrest performance of the steel plate.

[0104] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0105] The meaning of "and / or" described in this application means that the situations where each exists alone or both exist at the same time are included.

[0106] The term “connection” as used in this application may mean a direct connection between components or an indirect connection between components via other components.

[0107] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for producing a green, low-carbon, high-strength, extra-thick steel plate, the thickness of which ranges from 100 to 160 mm, characterized in that: The chemical composition of the extra thick steel plate is set to be: C: 0.07-0.09%, Si: 0.15-0.20%, Mn: 1.45-1.65%, Cu: 0.15-0.25%, Sn: 0.065-0.095%, Nb: 0.035-0.055%, Ti: 0.008-0.018%, Al: 0.03-0.04%, S≤0.002%, P≤0.008%, H≤0.00015%, and the rest is Fe and other inevitable impurities; For extra thick steel plates, 0.33≤CEV≤0.38, 0.16≤Pcm≤0.19; where CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15, Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B; Yield strength is ≥420MPa, tensile strength is ≥540MPa, Z-axis tensile section shrinkage is ≥60%, yield strength ratio is ≤0.82, -10℃ crack arrest toughness is ≥8000 N / mm 3 / 2 , the impact energy of the core of extra thick steel plate at -60℃ KV2≥250J.

2. The method for producing green low-carbon high-strength and extra-thick steel plate according to claim 1, characterized in that: The following steps are involved: Step S1: In the steelmaking process, the molten iron is sequentially subjected to molten iron pretreatment, converter smelting, ladle refining and RH vacuum refining, and then enters the continuous casting stage; during the RH vacuum refining, the vacuum degree is set to be <2mBar, the degassing time is ≥20 minutes, and the soft stirring time is ≥20 minutes; Step S2: continuous casting process, continuously casting the molten steel obtained after refining into a casting billet with a thickness of 310-330 mm; Step S3: Cooling the ingots in stacking, with the stack cooling time being ≥ 72 hours; Step S4: heating the ingot, using a low temperature furnace to heat the ingot, and setting a time to keep it warm; Step S5: performing a three-stage rolling process on the ingot from the low-temperature furnace to form a steel plate, wherein the first and second stages of rolling are both austenite recrystallization zone rolling, and the third stage of rolling is austenite non-recrystallization zone rolling; The first stage rolling temperature is 1080-1110℃, and the single pass reduction is set to 35-40mm. The first stage final rolling temperature is 1040-1070℃, and the ingot is sprayed with water for cooling. The surface temperature is cooled to T 再结晶 +15℃-T 再结晶 +25℃, T 再结晶 is the austenite recrystallization temperature; T 再结晶 +15℃-T 再结晶 +25℃ is used as the second stage rolling temperature, and the single pass reduction is set to 30-36mm, and the second stage final rolling temperature is T 再结晶 +5℃-T 再结晶 +15℃, spray water to cool the ingot again, and cool the surface temperature to A r3 +20℃-A r3 +35℃,A r3 is the starting temperature of the transformation from austenite to ferrite during cooling; A r3 +20℃-A r3 +35℃ is used as the third stage rolling temperature, and the single pass reduction is set to 15-25mm. The third stage final rolling temperature is A r3 +10℃-A r3 +25℃; Step S6: Straightening process, straightening the steel plate, setting the straightening temperature to A r3 +5℃-A r3 +20℃; Step S7: Cooling process, using MULPIC accelerated cooling system to cool the straightened steel plate, setting the lower surface water volume / upper surface water volume of cooling water = 1.2-1.3, and the final cooling temperature is 380-430°C; The water inlet temperature is controlled to A r3 -A r3 +15℃, the MULPIC accelerated cooling system is divided into three cooling zones along the production line from the beginning to the end, namely zone A, zone B and zone C. The total length of the entire MULPIC accelerated cooling system production line is 24m, and the length of each cooling zone is 8m; Among areas A, B, and C, the water pressure in area B is the lowest; Step S8: stacking the cooled steel plates in a slow cooling pit for a duration of ≥ 24 hours.

3. The method for producing green low-carbon high-strength and extra-thick steel plate according to claim 2 is characterized in that: When heating the ingot, set the temperature of the low-temperature furnace to 1140-1160℃ and the holding time to 360-400min.

4. The method for producing green low-carbon high-strength and extra-thick steel plate according to claim 2 is characterized in that: Austenite recrystallization temperature T 再结晶 Obtained by measuring the grain size change or hardness change of the steel plate; The starting temperature of the transformation from austenite to ferrite during cooling is A r3 It is measured by the critical point measurement method of steel, specifically by sampling and testing the steel plate and drawing the thermal expansion curve, A r3 This is the point where the thermal expansion changes as shown on the curve.

5. The method for producing green low-carbon high-strength and extra-thick steel plate according to claim 2 is characterized in that: In area A, the water pressure is set to 0.5MPa and the water volume is 16000m 3 / h; in area B, the water pressure is set to 0.25MPa and the water volume is 8000m 3 / h; in area C, the water pressure is set to 0.7MPa and the water volume is 18000m 3 / h.

6. The extra thick steel plate obtained by any production method according to claim 1-5, characterized in that: The thickness of the extra thick steel plate is 100-160 mm; Surface quality meets EN 10163-2 Class B-Sub Class 3 requirements; The internal stress of the extra-thick steel plate is uniform at different positions, and the highest internal stress is less than 15MPa; Extra thick steel plate unevenness <2mm / m; Meet the requirements of Level I flaw detection in GB / T 2970-2016 standard; The average annual corrosion rate of the extra-thick steel plate under full immersion in seawater is ≤0.1 mm / a.

7. The extra thick steel plate according to claim 6, characterized in that: The structure of the extra-thick steel plate is a complex phase structure of acicular ferrite and lath bainite, wherein the acicular ferrite accounts for 30-40%, the lath bainite accounts for 60-70%, and the grain size is less than 40 μm.

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