Ultrahigh-strength ship plate maritime work steel plate and preparation method thereof

Abstract

The invention belongs to the technical field of steelmaking, and relates to an ultrahigh-strength ship plate maritime work steel plate and a preparation method thereof, the heating temperature before rolling is controlled: the steel billet tapping temperature is controlled at 1100-1140 DEG C, and the casting blank in-furnace time is 6.0-9.0 min / cm; rough rolling and finish rolling are both divided into two stages, and the finish rolling temperature is 780-800 DEG C; after finish rolling is finished, rapid water cooling is conducted, the initial cooling temperature is 740-780 DEG C, the final cooling temperature is 300-550 DEG C, and the cooling speed is 5-20 DEG C / s; and the steel plates are rapidly discharged and stacked, good surrounding baffles are ensured, ventilation is avoided, waste heat of the steel plates is utilized for self-tempering, and the ultrahigh-strength ship plate maritime work steel plates are obtained. The production cost of the steel is low, and the steel plate has excellent strength and plasticity, low-temperature impact toughness, lamellar tearing resistance, crack arrest performance, welding performance and anti-seismic performance, is excellent in longitudinal, transverse and full-section comprehensive mechanical properties, and can be widely applied to the fields of polar region ocean engineering, ships, bridges, buildings and the like.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking technology, specifically relating to an ultra-high strength marine engineering steel plate and its preparation method. Background Technology

[0002] In recent years, with the advancement of TMCP technology, which is based on the new generation of ultra-fast cooling, the cooling path control and microstructure regulation of products have been realized. The TMCP process takes into account the low carbon equivalent to ensure good low-temperature toughness and weldability. At the same time, it ensures strength and toughness through fine microstructure control, which has irreplaceable advantages. It has laid a good foundation for the development of high-performance marine platform steel and is conducive to the development of steel for platforms with high wall thickness, high strength, high toughness and high welding heat input.

[0003] In the invention patent CN109439857A, which describes an FO460 marine engineering thick plate and its manufacturing method, the precious metal Mo is added to the steel composition design. In addition, quenching and tempering heat treatments are added to improve the toughness of the steel plate. The production process is long and the technology is complex, which greatly increases the production cycle and production cost.

[0004] In the invention patent CN109112429A concerning FH550 grade thick plates with excellent low-temperature toughness and their manufacturing method, the precious metal Mo is added to the steel composition, resulting in high production costs. Although a TMCP short-process production is adopted, the rolling process requires three stages, which is complex, has a narrow process window, and the third-stage rolling temperature range of 730-780℃ is low, resulting in extremely high mill load, making it difficult to promote and apply the related technology.

[0005] Analysis of existing technologies revealed that the steel grades mentioned in the published literature suffer from high alloy costs, high production difficulty, weak technology applicability, and difficulty in meeting market demand. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide an ultra-high strength marine engineering steel plate and its preparation method. Through low-carbon equivalent composition design, reasonable microalloying content combined with a certain amount of hardenability elements and austenite stabilizing elements, and special thermomechanical control process, the microstructure of the extra-thick plate is made uniform and refined, with a reasonable match between acicular ferrite and granular bainite. The steel plate obtains excellent strength and plasticity, low-temperature impact toughness, resistance to lamellar tearing, crack arrest performance, weldability, and seismic performance. It has superior comprehensive mechanical properties in the longitudinal and transverse directions and across the entire cross section, and can be widely used in polar marine engineering, shipbuilding, bridges, construction and other fields.

[0007] The technical solution adopted by this invention to solve its technical problem is: an ultra-high strength marine engineering steel plate, the chemical composition of which, by weight percentage, includes: C: 0.04%~0.18%, Si: 0.15%~0.35%, Mn: 0.90%~1.50%, P≤0.015%, S≤0.005%, Nb: 0.010%~0.040%, Cu: 0~0.30%, Cr: 0~0.80%, Ni: 0~0.80%, V: 0.008%~0.030%, Ti: 0.005%~0.020%, Als: 0.015%~0.050%, [Ca]: 10ppm~30ppm, N≤30ppm, O≤30ppm, H≤2ppm, with the remainder being iron and unavoidable impurities, wherein Als represents acid-soluble aluminum;

[0008] Marine engineering steel plates have a maximum thickness of 100mm, yield strength ≥460MPa, tensile strength ≥570MPa, yield-to-tensile ratio ≤0.9, elongation after fracture ≥21%, transverse impact strength at -80℃ ≥300J at 1 / 2 thickness, Z-direction reduction of area ≥70%, transverse NDT ≤-75℃, longitudinal NDT ≤-80℃, transverse CTOD ≥0.3mm at -60℃, longitudinal CTOD ≥0.5mm at -60℃, and Kca ≥8000N / mm at -10℃. 3 / 2 .

[0009] The chemical composition of the ultra-high strength marine steel plate of the present invention will be described in detail below.

[0010] Carbon (C): While carbon is the most important solid solution strengthening element, significantly improving the hardenability of steel, it is also the most economical strengthening element in low-carbon steel. However, increasing the carbon content reduces the plasticity and impact toughness of steel, increases its tendency to brittleness and aging, and deteriorates its weldability. Considering that reducing carbon requires increasing the content of other expensive microalloying agents to maintain steel strength, which will significantly increase costs, the appropriate amount of carbon is controlled between 0.04% and 0.18%.

[0011] Si: Si enters ferrite and plays a solid solution strengthening role, reducing the yield strength ratio. However, Si will significantly increase the ductile-brittle transition temperature of steel, and at the same time, it will also deteriorate plasticity and weldability. Therefore, the appropriate amount of Si should be controlled between 0.15% and 0.35%.

[0012] Mn: Mn can lower the critical transformation temperature Ar3, significantly improve the hardenability of steel, and also has a certain solid solution strengthening effect, thus improving the strength and hardness of steel. Due to the strong affinity between manganese and sulfur, MnS exhibits some plasticity at high temperatures, preventing hot brittleness in steel. However, excessive Mn content can affect the weldability of steel and exacerbate center segregation in the cast billet, resulting in severe banded structure in the product, which in turn affects impact toughness. Therefore, the appropriate Mn content should be controlled between 0.90% and 1.50%.

[0013] Phosphorus (P): Phosphorus is a low-temperature brittle element. It significantly expands the two-phase region between the liquid and solid phases. During steel solidification, it segregates between grains, forming a high-phosphorus brittle layer, increasing the grade of banded structure, causing localized structural abnormalities in the steel, resulting in uneven mechanical properties, reduced plasticity, increased brittleness and corrosion resistance, and adversely affecting weldability by increasing weld crack susceptibility. Therefore, the phosphorus content in steel should be minimized. Considering production costs, the P content is controlled below 0.015%.

[0014] S: When sulfur (S) exists in steel in the form of FeS, high S content can easily lead to hot brittleness. When S exists in steel in the form of MnS, it often forms stripes along the rolling direction, creating a severe banded structure that disrupts the continuity of the steel. This significantly affects the properties of the steel in different directions, reducing its plasticity and impact toughness, and increasing the ductile-brittle transition temperature. Therefore, the S content should be controlled below 0.005%.

[0015] Nb: Nb can produce significant grain refinement, precipitation strengthening, and moderate precipitation strengthening effects. Nb dissolved in austenite can improve hardenability. Nb(C,N) precipitates refine grains but reduce hardenability. Furthermore, when the Nb content is too high, Nb easily forms low-melting-point eutectics with elements such as Fe and C, which tends to increase hot cracking in the weld heat-affected zone. Considering all factors, the appropriate Nb content should be controlled between 0.010% and 0.040%.

[0016] Cu: The addition of heavy metal element Cu improves corrosion resistance and effectively reduces the yield strength ratio of ultra-high strength marine steel; however, excessive Cu content will cause copper embrittlement in the steel, which will be detrimental to the hot working of ultra-high strength marine steel. Taking all factors into consideration, the appropriate amount of Cu is controlled between 0 and 0.30%.

[0017] Cr: Cr is effective in improving the strength of steel and is inexpensive. It improves the hardenability and uniformity of cross-sectional structure of water-cooled steel plates, and replaces the precipitation strengthening effect of V, thus reducing production costs. However, excessive Cr content will reduce the plasticity and toughness of steel. The appropriate amount of Cr should be controlled between 0 and 0.80%.

[0018] Ni: Ni strengthens ferrite by forming a simple substitutional solid solution, thus increasing the strength of steel. Simultaneously, Ni is an austenite stabilizing element, significantly improving the low-temperature impact toughness of steel. However, Ni plates are relatively expensive; considering cost factors, the appropriate Ni content is controlled between 0% and 0.80%.

[0019] Vanadium (V) mainly exists in the matrix and grain boundaries as V(C, N), playing a role in precipitation strengthening and inhibiting grain growth. Due to the strong affinity between vanadium and nitrogen, the addition of V helps to fix free nitrogen in the steel, thus preventing strain aging. On the other hand, while V has a strong precipitation strengthening effect, it also increases the ductile-brittle transition temperature and deteriorates impact toughness. Considering all factors, the appropriate amount of V is controlled between 0.008% and 0.030%.

[0020] Ti: Ti can precipitate TiN particles at high temperatures of 1200–1300℃, which can act as precipitation nuclei for Nb (C, N), thereby reducing the amount of fine niobium precipitates and thus reducing the crack susceptibility of Nb-containing steel. Ti can form fine titanium carbide and nitride particles, which can prevent the coarsening of austenite grains during slab heating, resulting in a finer austenitic microstructure. Ti combines with N to form stable, highly dispersed compounds, which can not only eliminate free nitrogen in steel, but also control grain size in the heat-affected zone during hot working and welding, improving the low-temperature toughness of various parts of the steel structure. Excessive Ti will form micron-sized liquid TiN, which not only fails to refine the grains but also deteriorates the toughness of the steel plate. Therefore, the appropriate amount of Ti should be controlled between 0.005% and 0.020%.

[0021] Al: Al can refine the grain size of steel, improve its strength, and also enhance its impact toughness. Because Al has a strong affinity for N, it can also eliminate the aging sensitivity caused by N. Therefore, the Al content is set at 0.015%–0.050%.

[0022] [Ca]: Ca is a strong deoxidizing element. Appropriately controlling its content can play a spheroidizing role in residual inclusions in steel. However, excessive content can easily cause blockage of the nozzle and affect the pourability of molten steel. Taking all factors into consideration, the Ca content should be controlled between 10ppm and 30ppm.

[0023] Nitrogen (N): Excessive nitrogen content will worsen the impact toughness and aging impact of high-strength steel, and is generally controlled below 30 ppm.

[0024] O: Excessive O content indicates too many inclusions in the steel, which will have an adverse effect on various mechanical properties of the steel. Therefore, the O content should be controlled below 30 ppm as much as possible to improve the cleanliness of molten steel.

[0025] H: H is quite harmful, easily forming white spots and deteriorating low-temperature impact toughness. It also causes non-compliance in flaw detection and needs to be controlled below 2ppm through vacuum treatment and other means.

[0026] Another object of the present invention is to provide a method for preparing the above-mentioned ultra-high strength marine steel plate, comprising the following steps:

[0027] (a) Heating: Control the heating temperature before rolling: the billet exit temperature is controlled at 1100~1140℃, and the billet time in the furnace is 6.0~9.0min / cm;

[0028] (b) Rolling: including roughing and finishing rolling, both of which are divided into two stages, with a final rolling temperature of 780-800℃;

[0029] (c) Cooling: After finishing rolling, rapid water cooling is performed. The initial cooling temperature is 740-780℃, the final cooling temperature is 300-550℃, and the cooling rate is 5-20℃ / s.

[0030] (d) The steel plates are quickly unloaded and stacked to ensure good surroundings and avoid ventilation. The residual heat of the steel plates is used for self-tempering to obtain ultra-high strength marine steel plates.

[0031] Furthermore, the two stages of rough rolling in step (b) specifically include: in the first stage, descaling is carried out in 5 to 7 passes using descaling water on the stand. After the billet temperature drops to 1000 to 1050°C, rolling begins after holding at that temperature for 5 minutes. In the second stage of rough rolling, the reduction amount in at least 2 passes is not less than 40 mm, and the reduction rate in the last 3 passes is not less than 20%. The thickness of the intermediate billet is 1.5 to 5.0 times the thickness of the finished product.

[0032] Furthermore, the two stages of finishing rolling in step (b) specifically include: in the first stage, descaling is carried out in 5 to 7 passes using descaling water on the stand. After the billet temperature drops to 780 to 800°C, the intermediate billet is allowed to warm up to 800 to 820°C before entering the second stage of rolling to avoid empty passes. The final rolling temperature is 780 to 800°C.

[0033] Billet heating: The billet exit temperature is controlled between 1100 and 1140℃. To fully utilize the effects of microalloying elements such as Nb and Ti in delayed austenite recrystallization during controlled rolling and precipitation strengthening during rolling and post-rolling cooling, it is essential to ensure that more microalloying elements dissolve into austenite to fully leverage their solid solution advantages. Therefore, the billet heating temperature should be increased to at least 1100℃. However, considering that excessively high heating temperatures will lead to excessive austenite grain growth, which will be inherited by the rolled steel plate and negatively impact its impact toughness, the billet exit temperature should be controlled below 1140℃ as much as possible. Low-temperature heating also significantly saves energy. Furthermore, to avoid excessive grain growth in the billet due to prolonged heating, the billet time in the furnace is controlled within the range of 6.0–9.0 min / cm.

[0034] Rough rolling is divided into two stages: The first stage utilizes descaling water on the stand for 5-7 passes of descaling, during which there is no rolling deformation. This rapidly reduces the surface temperature of the workpiece during the austenite recrystallization stage, widening the temperature difference between the surface and core of the billet. Due to the lower surface temperature, the deformation resistance increases, causing the rolling force to penetrate more towards the center of the thickness, significantly increasing the deformation rate of the core of the workpiece during the austenite recrystallization stage, refining the core microstructure, and improving center segregation. After the billet temperature drops to 1000-1050℃, rolling begins after holding at that temperature for 5 minutes. This helps to raise the temperature of the billet edges and corners, improving the overall temperature uniformity of the billet and greatly reducing the risk of mill trips due to heavy loads during subsequent rolling processes. Simultaneously, the mill's reduction capacity can be significantly increased. The second stage, with a suitable rolling speed, ensures that the reduction in at least two passes is not less than 40 mm, and the reduction rate in the last three passes is not less than 20%. The intermediate billet is rolled longitudinally to a thickness of 1.5 to 5.0 times that of the finished product, which promotes further homogenization of the cross-sectional structure and significantly improves the crack-arresting performance of the steel plate.

[0035] The finishing rolling is divided into two stages: In the first stage, the descaling water in the stand is used to perform 5 to 7 passes of descaling. The temperature of the intermediate billet drops rapidly and enters the non-recrystallized austenite region to avoid rapid grain growth. The intermediate billet is allowed to warm up to 800 to 820°C before entering the second stage of rolling. At the same time, in order to ensure that the rolled steel plate can directly enter the water cooling equipment and avoid empty passes, the final rolling temperature is 780 to 800°C.

[0036] Cooling: After finishing rolling, the roller speed is increased to shorten the travel time of the steel plate between the rolling mill and the water cooling equipment. The initial cooling temperature is 740-780℃, and the maximum cooling capacity is used to reduce the temperature of the steel plate to below Ar1 point. The cooling water pressure is 0.5MPa. This ensures that the high deformation energy formed by the cumulative reduction during the finishing rolling stage, combined with the strong cooling rate, promotes the rapid transformation of the microstructure from austenite to polygonal ferrite, or even acicular ferrite, avoiding the formation of proeutectoid ferrite in the subcritical region. At the same time, it also minimizes the formation of large pearlite particles, greatly refines the microstructure of the steel plate, and achieves the strengthening and toughening of the steel plate. The final cooling temperature is 300-550℃, and the cooling rate is 5-20℃ / s.

[0037] The steel plates are quickly unloaded and stacked, ensuring good perimeter protection and avoiding ventilation. The residual heat of the steel plates is used for self-tempering, which achieves uniform and refined substructure in the microstructure and complete separation of two-phase particles. This results in excellent crack arrest performance while keeping the yield ratio within a low range, significantly improving the safety of the application process of extra-thick plates.

[0038] The present invention has the following beneficial effects:

[0039] (1) The ultra-high strength marine steel plate of the present invention has stable strength and excellent low temperature toughness and anti-lamellar tearing performance, which can ensure better overall safety of various welded steel structures. At the same time, the specifications that can be produced can basically cover the market demand for thin plates, medium plates, thick plates and extra-thick plates.

[0040] (2) By comprehensively analyzing the properties of steel plates of different thicknesses, the coupling effect of Si / Mn / Cr and Nb / V / Ti microalloying on microstructure and properties can be fully utilized, the amount of precious metals added can be reduced, and the heat treatment process can be eliminated, so as to achieve the production of high-performance steel plates at low cost. The production cost and energy consumption index can be significantly reduced.

[0041] (3) The ultra-high strength marine steel plate of this invention can stably reach a high level in terms of transverse NDT, longitudinal NDT, transverse CTOD, longitudinal CTOD, and -10℃ Kca. Its excellent crack arrest performance makes the steel plate applicable to the construction of key parts of ultra-large container ships and polar offshore platforms.

[0042] In summary, this invention, through low-carbon equivalent composition design, reasonable microalloying content combined with a certain amount of hardenable elements and austenite stabilizing elements, and special thermomechanical control process, achieves uniform and refined microstructure of extra-thick plates, with a reasonable match between acicular ferrite and granular bainite. This results in low steel production costs and steel plates with excellent strength and plasticity, low-temperature impact toughness, resistance to lamellar tearing, crack arrest, weldability, and seismic performance. The steel exhibits superior comprehensive mechanical properties in the longitudinal and transverse directions and across the entire cross section, is not easily fractured or damaged, and is safe and reliable to use. It can be widely applied in polar marine engineering, shipbuilding, bridge construction, and other fields. Attached Figure Description

[0043] Figure 1 This is a microstructure photograph of the steel plate prepared in Example 4 of the present invention. Detailed Implementation

[0044] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention. However, the scope of protection of the present invention is not limited to these embodiments. All changes or equivalent substitutions that do not depart from the concept of the present invention are included within the scope of protection of the present invention.

[0045] An ultra-high strength marine engineering steel plate, the chemical composition of the steel plate by weight percentage includes: C: 0.04%~0.18%, Si: 0.15%~0.35%, Mn: 0.90%~1.50%, P≤0.015%, S≤0.005%, Nb: 0.010%~0.040%, Cu: 0~0.30%, Cr: 0~0.80%, Ni: 0~0.80%, V: 0.008%~0.030%, Ti: 0.005%~0.020%, Als: 0.015%~0.050%, [Ca]: 10ppm~30ppm, N≤30ppm, O≤30ppm, H≤2ppm, the remainder being iron and unavoidable impurities, wherein Als represents acid-soluble aluminum;

[0046] Marine engineering steel plates have a maximum thickness of 100mm, yield strength ≥460MPa, tensile strength ≥570MPa, yield-to-tensile ratio ≤0.9, elongation after fracture ≥21%, transverse impact strength at -80℃ ≥300J at 1 / 2 thickness, Z-direction reduction of area ≥70%, transverse NDT ≤-75℃, longitudinal NDT ≤-80℃, transverse CTOD ≥0.3mm at -60℃, longitudinal CTOD ≥0.5mm at -60℃, and Kca ≥8000N / mm at -10℃. 3 / 2 .

[0047] The preparation method of ultra-high strength marine engineering steel plate includes the following steps:

[0048] (a) Heating: Control the heating temperature before rolling: the billet exit temperature is controlled at 1100~1140℃, and the billet time in the furnace is 6.0~9.0min / cm;

[0049] (b) Rolling: including roughing and finishing, both of which are divided into two stages.

[0050] The two stages of rough rolling specifically include: the first stage uses descaling water on the stand for 5 to 7 passes for descaling, and after the billet temperature drops to 1000 to 1050℃, it is held for 5 minutes before rolling begins. The second stage of rough rolling ensures that the reduction in at least 2 passes is not less than 40mm, and the reduction rate in the last 3 passes is not less than 20%. The thickness of the intermediate billet is 1.5 to 5.0 times the thickness of the finished product.

[0051] The two stages of finishing rolling specifically include: the first stage uses descaling water on the stand for 5 to 7 passes to descale, and waits for the billet temperature to drop to 780 to 800°C. The intermediate billet is then allowed to warm up to 800 to 820°C before entering the second stage of rolling to avoid skipping passes. The final rolling temperature is 780 to 800°C.

[0052] (c) Cooling: After finishing rolling, rapid water cooling is performed. The initial cooling temperature is 740-780℃, the final cooling temperature is 300-550℃, and the cooling rate is 5-20℃ / s.

[0053] (d) The steel plates are quickly unloaded and stacked to ensure good surrounding enclosure and avoid ventilation. The residual heat of the steel plates is used for self-tempering to achieve uniform and refined substructure in the microstructure and complete separation of two-phase particles. This results in excellent crack arrest performance while keeping the yield ratio within a low range, which greatly improves the safety of the application process of extra-thick plates.

[0054] The chemical composition of the ultra-high strength marine engineering steel plates in Examples 1-4 of this invention is shown in Table 1. The chemical composition is smelted in a converter and cast into continuous casting billets or ingots. After the continuous casting billets or ingots are opened, they are heated in a heating furnace and rolled using a medium-thick plate rolling mill. The main process parameters, such as the billet tapping temperature, final rolling temperature, and final cooling temperature, are shown in Table 2. The corresponding tensile strength, impact energy, crack arrest performance, and thickness specifications of the steel plates are listed in Table 3. It can be seen that the steel of this invention has excellent strength and toughness, and excellent crack arrest performance. Figure 1 A photograph of the microstructure of the steel plate prepared in Example 4 is shown, showing that the microstructure consists of polygonal ferrite, acicular ferrite and granular bainite.

[0055] Table 1 below shows the chemical composition of the steels of Examples 1 to 4 of the present invention.

[0056] Table 1. Chemical composition (wt.%) of Examples 1-4 of the present invention

[0057] Example C Si Mn P S Nb Cu Cr Ni V Ti Als 1 0.04 0.15 1.50 0.015 0.003 0.010 0.15 0.28 0.20 0.014 0.015 0.032 2 0.09 0.20 1.35 0.010 0.004 0.020 0.19 0.40 0.40 0.020 0.014 0.050 3 0.18 0.28 0.90 0.008 0.005 0.027 0.25 0.60 0.60 0.008 0.020 0.035 4 0.14 0.35 1.10 0.007 0.004 0.040 0.30 0.80 0.80 0.030 0.005 0.015

[0058] Table 2 below shows the main process parameters of Examples 1 to 4 of the present invention.

[0059] Table 2 Main production process parameters of Examples 1-4 of the present invention

[0060]

[0061] Note: The second stage of rough rolling begins after holding the temperature for 5 minutes.

[0062] Table 3 shows the main mechanical properties of the steel plates produced in Examples 1 to 4 of the present invention.

[0063] Table 3 Mechanical properties of steel plates in Examples 1-4 of the present invention

[0064]

[0065] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

[0066] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A type of ultra-high strength marine engineering steel plate, characterized in that, The chemical composition of the steel plate, by weight percentage, includes: C: 0.04%–0.18%, Si: 0.15%–0.35%, Mn: 0.90%–1.50%, P≤0.015%, S≤0.005%, Nb: 0.010%–0.040%, Cu: 0–0.30%, Cr: 0–0.80%, Ni: 0–0.80%, V: 0.008%–0.030%, Ti: 0.005%–0.020%, Als: 0.015%–0.050%, [Ca]: 10ppm–30ppm, N≤30ppm, O≤30ppm, H≤2ppm, with the remainder being iron and unavoidable impurities. Als represents acid-soluble aluminum. Marine engineering steel plates have a maximum thickness of 100mm, yield strength ≥460MPa, tensile strength ≥570MPa, yield-to-tensile ratio ≤0.9, elongation after fracture ≥21%, transverse impact strength at -80℃ ≥300J at 1 / 2 thickness, Z-direction reduction of area ≥70%, transverse NDT ≤-75℃, longitudinal NDT ≤-80℃, transverse CTOD ≥0.3mm at -60℃, longitudinal CTOD ≥0.5mm at -60℃, and Kca ≥8000N / mm at -10℃. 3 / 2 .

2. The method for preparing ultra-high strength marine engineering steel plates as described in claim 1, characterized in that, Includes the following steps: (a) Heating: Control the heating temperature before rolling: the billet exit temperature is controlled at 1100~1140℃, and the billet time in the furnace is 6.0~9.0min / cm; (b) Rolling: including roughing and finishing rolling, both of which are divided into two stages, with a final rolling temperature of 780-800℃; (c) Cooling: After finishing rolling, rapid water cooling is performed. The initial cooling temperature is 740-780℃, the final cooling temperature is 300-550℃, and the cooling rate is 5-20℃ / s. (d) The steel plates are quickly unloaded and stacked to ensure good surroundings and avoid ventilation. The residual heat of the steel plates is used for self-tempering to obtain ultra-high strength marine steel plates.

3. The method for preparing ultra-high strength marine engineering steel plates as described in claim 2, characterized in that, The two stages of rough rolling in step (b) specifically include: in the first stage, descaling is carried out in 5 to 7 passes using descaling water on the stand. After the billet temperature drops to 1000 to 1050°C and is held for 5 minutes, rolling begins. In the second stage of rough rolling, at least 2 passes are required to reduce the billet by no less than 40 mm, and the reduction rate of the last 3 passes is no less than 20%. The thickness of the intermediate billet is 1.5 to 5.0 times the thickness of the finished product.

4. The method for preparing ultra-high strength marine engineering steel plates as described in claim 2, characterized in that, The two stages of finishing rolling in step (b) specifically include: in the first stage, descaling is carried out in 5 to 7 passes using descaling water on the stand. After the billet temperature drops to 780 to 800°C, the intermediate billet is allowed to warm up to 800 to 820°C before entering the second stage of rolling to avoid empty passes. The final rolling temperature is 780 to 800°C.

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