An ultra-high strength and toughness wear-resistant marine steel plate based on gradient structure design and a manufacturing method thereof

Abstract

This invention relates to the field of marine engineering steel production technology, and particularly to an ultra-high strength, toughness, and wear-resistant marine engineering steel plate based on gradient microstructure design and its manufacturing method. The chemical composition of the steel plate is as follows (mass fraction): C: 0.03%–0.09%, Si: 0.85%–1.45%, Mn: 1.4%–2.0%, Cr: 0.5%–0.9%, Ni: 5.0%–8.5%, Mo: 0.2%–0.6%, Cu: 0.6%–1.2%, Ti: 0.012%–0.025%, Nb: 0.02%–0.06%, Al: 0.03%–0.07%, Ce: 0.010%–0.018%, B: 0.003%–0.006%, P≤0.005%, S≤0.002%, with the remainder being Fe and unavoidable impurities. This invention achieves an integrated performance upgrade of the steel plate, with wear resistance on one side and high toughness on the other. It greatly improves the wear resistance, elongation and low-temperature toughness of ultra-high strength steel plates.

Description

Technical Field

[0001] This invention belongs to the field of marine engineering steel production technology, and specifically relates to an ultra-high strength, toughness and wear-resistant marine engineering steel plate based on gradient microstructure design and its manufacturing method. Background Technology

[0002] With the opening of the Arctic shipping route and the accelerated development of deep-sea oil and gas resources, marine engineering equipment needs to operate in extreme environments for extended periods. However, the low temperatures (-60℃ to ~80℃), ice load impacts, and high-salt corrosion environments place stringent demands on material properties. Materials must possess ultra-high strength (e.g., yield strength ≥1050MPa), high and low temperature toughness (impact energy ≥120J at ~80℃), and high wear resistance to ensure resistance to brittle fracture under ice impacts. Simultaneously, large marine engineering equipment requires thick steel plates to withstand the high pressure and dynamic loads of the deep sea. Traditional wear-resistant steel plates improve hardness through a single phase, but in the complex marine environment with its coupled corrosion, wear, and impact effects, their elongation and low-temperature toughness are poor, limiting their resistance to low-temperature impacts.

[0003] Chinese patent application CN118147520A discloses a highly ductile, ice-resistant, ultra-high-strength marine engineering steel and its manufacturing method. The composition of the marine engineering steel, by weight percentage, is as follows: C: 0.045–0.065%, Si: 0.25–0.35%, Mn: 1.00–1.30%, Cr: 1.30–1.60%, Ni: 1.10–1.50%, Cu: 0.45–0.65%, Mo: 0.40–0.80%, Sn: 0.05–0.12%, Sb: 0.05–0.12%, Nb: 0.03–0.05%, V: 0.03–0. The composition is as follows: 0.04% Ti: 0.005-0.025%, Ca: 0.006%-0.009%, P: ≤0.01%, S: ≤0.001%, Als: 0.02%-0.05%, with the remainder being Fe and unavoidable impurities. Manufacturing methods include smelting, continuous casting, heating, primary heating, primary rolling, primary cooling, secondary heating, secondary rolling, secondary cooling, and heat treatment. The marine engineering steel plates exhibit tensile elongation after fracture ≥29%, yield strength ≥550MPa, tensile strength 670-830MPa, Charpy impact energy at -60℃ ≥180J, NDTT ≤-70℃, and surface hardness ≥325HBW. However, the strength of the steel plates involved is relatively low and cannot meet the ultra-high strength application requirements for large-scale deep-sea pressure-resistant equipment.

[0004] Chinese patent application CN119614998A discloses a field of steel smelting technology, specifically relating to a high-strength, high-toughness, fine-grained, multiphase-structured wear-resistant steel and its preparation method, comprising the following components by weight percentage: C 0.12%–0.20%, Si 0.1%–0.4%, Mn 1.6%–2.0%, Ti 0.045%–0.08%, Cr 0.15%–0.3%, Mo 0.05%–0.16%, Al 0.02%–0.05%, P ≤ 0.01%, S ≤ 0.003%, N ≤ 0.002%, H ≤ 0.0002%, B 0.002%–0.004%, (30C + 0.5Mn) × 100 ≥ 4.4, B / S ≥ 3, 0.3 ≤ Ti / Mo ≤ 0.6, with the remainder being Fe and unavoidable impurities. The wear-resistant steel involved has high strength, high hardness and good low-temperature toughness, but its low-temperature toughness is relatively low. It was only evaluated that the impact absorption energy at -40℃ is ≥48J, and it is not suitable for use in temperatures from -60℃ to -80℃.

[0005] Chinese patent application CN117845132A discloses a 1000MPa grade ultra-high strength steel and its preparation method, relating to the field of steel smelting-grade rolling technology. The chemical composition of the ultra-high strength steel, by mass fraction, includes: C: 0.15%–0.20%, Si: 0.30%–0.45%, Mn: 1.5%–2.0%, P≤0.008%, S: 0.006%–0.012%, Alt: 0.025%–0.040%, Ni: 0.08%–0.15%, Mo: 0.20%–0.50%, Cu: 0.20%–0.35%, Sb: 0.05%–0.10%, Nb: 0.03%–0.06%, with the balance being Fe and unavoidable impurities. The method includes: obtaining molten steel after smelting; continuously casting the molten steel to obtain a slab; heating and holding the slab, followed by hot rolling, coiling, pickling, continuous annealing, and leveling to obtain 1000MPa grade ultra-high strength steel resistant to hydrochloric acid corrosion; the ultra-high strength steel prepared by the above method has a yield strength ≥980MPa, tensile strength ≥1000MPa, elongation A50 ≥9%, and a microstructure of tempered martensite and a small amount of ferrite, meeting the requirement of no cracking when formed at 180 degrees with d=2a, and its hydrochloric acid corrosion resistance is improved by more than 85% compared with conventional 980MS, and its hydrogen embrittlement sensitivity index is improved by more than 40%. Pipes made from it meet the requirement of no cracking after pickling with 10%~20% hydrochloric acid for 10min~20min. However, the wear resistance of the steel plate involved has not been evaluated, and the steel plate is relatively thin, making it difficult to adapt to ultra-deep-sea large-scale marine pressure-resistant equipment.

[0006] It is evident that existing marine engineering steel plates mainly suffer from the following problems:

[0007] 1. The steel plate has a low strength level and low-temperature toughness, and is not adaptable to extreme marine environments, which cannot meet the requirements of deep-sea marine engineering equipment for ultra-high toughness materials.

[0008] 2. The steel plate surface has insufficient wear resistance and is difficult to resist the impact wear caused by sea ice on local marine engineering structures, as well as the cutting wear caused by underwater silt and sand.

[0009] 3. The steel plate thickness is insufficient, making it difficult to adapt to ultra-deep-sea large-scale marine engineering pressure-resistant equipment. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide an ultra-high strength and toughness wear-resistant marine steel plate based on gradient microstructure design and its manufacturing method, so that the surface of the steel plate is distributed with high hardness and high wear resistance microstructure, and the inner side is distributed with high toughness and plasticity microstructure, thereby realizing the integrated performance upgrade of the steel plate with wear resistance on the surface and toughness on the inner side.

[0011] To achieve the above objectives, the present invention employs the following technical solution:

[0012] An ultra-high strength, toughness and wear-resistant marine engineering steel plate based on gradient microstructure design has the following chemical composition by mass fraction: C: 0.03%–0.09%, Si: 0.85%–1.45%, Mn: 1.4%–2.0%, Cr: 0.5%–0.9%, Ni: 5.0%–8.5%, Mo: 0.2%–0.6%, Cu: 0.6%–1.2%, Ti: 0.012%–0.025%, Nb: 0.02%–0.06%, Al: 0.03%–0.07%, Ce: 0.010%–0.018%, B: 0.003%–0.006%, P≤0.005%, S≤0.002%, with the remainder being Fe and unavoidable impurities.

[0013] An ultra-high strength, toughness and wear-resistant marine engineering steel plate based on gradient microstructure design, with the following performance indicators:

[0014] Water-cooled wear-resistant side of steel plate: yield strength ≥1100MPa, tensile strength 1250~1350MPa, elongation ≥14%, V-shaped impact energy at -84℃ ≥110J, V-shaped impact energy at -100℃ ≥90J, Vickers hardness HV ≥390.

[0015] Air-cooled side of steel plate: yield strength ≥950MPa, tensile strength 1100~1200MPa, elongation ≥18%; V-shaped impact energy at -84℃ ≥140J, V-shaped impact energy at -100℃ ≥110J; Vickers hardness HV≥300.

[0016] The reasons for selecting the elements and their contents in steel are as follows:

[0017] Carbon (C): C forms carbides with microalloying elements in steel. During the tempering process, the C diffusion coefficient affects the carbide formation rate, controls the precipitate size distribution, and plays a role in precipitation strengthening, thereby improving the strength and wear resistance of the steel plate. However, excessively high C content will severely affect low-temperature toughness and greatly increase welding difficulty. This invention adopts a low-carbon design, controlling the C content within the range of 0.03% to 0.09%.

[0018] Si (Si): Si plays a role in solid solution strengthening in steel, delaying carbon diffusion in austenite, prolonging the bainite transformation incubation period, and promoting bainite formation. As a low-cost, high-efficiency alloying element, it achieves synergistic improvement in strength, toughness, and wear resistance in ultra-high strength and toughness marine steel through multi-scale effects. However, excessive Si content can promote phosphorus (P) grain boundary segregation, increase carbon equivalent, and promote temper brittleness and welding cold cracking susceptibility. This invention controls the Si content within the range of 0.85% to 1.45%.

[0019] Mn: Mn is a strong austenite stabilizing element, significantly reducing the A3 temperature, expanding the γ phase region, and extending the austenite cooling window. It inhibits the precipitation of proeutectoid ferrite and promotes a bainite or martensite-dominated microstructure. Synergistically with C, it reduces carbon activity, inhibits cementite coarsening, and promotes the uniform precipitation of nano-carbides. Synergistically with Nb and Mo, it promotes the precipitation of (Nb,Mo)C composite carbides, improving precipitation strengthening efficiency. However, excessively high Mn content can form Mn-enriched bands and combine with S to form MnS inclusions, leading to hydrogen-induced crack initiation and deteriorating the strength and toughness of the steel plate. This invention controls the Mn content within the range of 1.4% to 2.0%.

[0020] Cr: Cr combines with C during high-temperature tempering to form fine Cr particles. 23 C6, pinning dislocations, enhances the strength and hardness of steel plates. During low-temperature tempering, it suppresses ε-carbide coarsening and reduces the size of precipitated phases. When added in combination with Mo, it forms (Cr,Mo). 23 C6 composite carbides effectively suppress temper brittleness. However, excessive Cr content promotes the formation of MA components in the coarse-grained region of the HAZ, becoming crack initiation points and reducing the strength and toughness of the steel plate. This invention controls the Cr content within the range of 0.5% to 0.9%.

[0021] Ni: Ni segregates at austenite grain boundaries, lowering grain boundary energy, inhibiting cleavage crack formation, and reducing the ductile-brittle transition temperature of steel, thus improving its low-temperature toughness. Ni can also lower the martensitic transformation initiation temperature, promote the retention of thin-film austenite between lath martensite, and generate the TRIP effect, which absorbs energy during deformation to inhibit crack propagation, thus benefiting the low-temperature toughness and fatigue performance of steel. However, excessive Ni content will significantly increase costs and cause temper brittleness in steel plates. This invention controls the Ni content within the range of 5.0% to 8.5%.

[0022] Mo: Mo can inhibit the dynamic recrystallization of austenite and refine the grain size of the rolled microstructure through the solute dragging effect. It can also reduce the critical cooling rate and promote a high-strength microstructure dominated by bainite or martensite. In conjunction with Nb and V, it can promote the precipitation of (Nb,Mo)C / V(CN) nano-precipitates, improving the strength, toughness, and wear resistance of the steel plate. However, excessively high Mo content increases the susceptibility of the steel plate to cold cracking during welding and increases the risk of high-temperature brittleness. This invention controls the Mo content to be within the range of 0.2% to 0.6%.

[0023] Cu: Cu will precipitate the ε-Cu phase in a supersaturated solid solution form, improving the strength and wear resistance of the steel plate. It can also refine the microstructure and inhibit the coarsening of brittle phases, which is beneficial to the low-temperature toughness of the steel plate. Excessive Cu content will cause oxidation of Cu-rich areas on the steel plate surface during hot rolling, forming liquid Cu-O eutectic and inducing cracks. This invention controls the Cu content within the range of 0.6% to 1.2%.

[0024] Ti: Ti combines with N to form high-temperature stable fine TiN, which inhibits austenite grain growth through pinning force, thus refining the grains. It also reduces the brittle BN / AlN phase at grain boundaries, which is beneficial for low-temperature toughness. When added in combination with Nb, it forms (Nb,Ti)(C,N) composite precipitation, which strengthens the steel plate and improves its strength and wear resistance. When added synergistically with B, B segregates at grain boundaries to inhibit ferrite nucleation, while Ti fixes N to prevent BN embrittlement, synergistically improving hardenability. A higher Ti content can lead to the formation of coarse TiN during solidification, which can become crack initiation sites. This invention controls the Ti content to be within the range of 0.012% to 0.025%.

[0025] Nb: Nb combines with C / N to form nanoscale Nb(C,N), which precipitates in the austenite region, pinning and inhibiting grain growth. Nb increases the recrystallization temperature of austenite, accumulating high-density deformation bands during rolling in the non-recrystallized region, providing nucleation sites for phase transformation, and refining bainite and martensite laths, which is beneficial to the strength and toughness of the steel plate. Excessive content leads to supersaturated precipitation, causing Nb(C,N) coarsening, resulting in decreased steel plate strength and deteriorated toughness. This invention controls the Nb content within the range of 0.02% to 0.06%.

[0026] Al: During steelmaking, Al combines with O to form Al2O3, effectively reducing the oxygen content of molten steel and decreasing porosity and oxide inclusions. Al also combines with N to form AlN, which precipitates in the austenite region, pinning and inhibiting grain growth. Excessive Al content can also lead to the formation of large-sized clusters of Al2O3, becoming crack initiation sites and affecting the strength and toughness of the steel plate. This invention controls the Al content within the range of 0.03% to 0.07%.

[0027] Ce: Ce has a strong affinity for O and S, preferentially forming fine Ce₂O₃ and CeS, reducing the content of free O and S in steel and purifying the molten steel. It also transforms elongated MnS into spherical Ce-OS composite inclusions, reducing stress concentration, hindering crack propagation paths, and improving the low-temperature toughness of the steel plate. Furthermore, it synergistically interacts with Nb and Ti to form Ce-Ti-O / Nb-O composite precipitation, promoting extremely fine grain refinement. In this invention, the Ce content is controlled within the range of 0.010% to 0.018%.

[0028] Boron (B): Boron atoms segregate at austenite grain boundaries, lowering grain boundary energy, hindering the nucleation of proeutectoid ferrite and pearlite, significantly improving hardenability, and combining with dislocations to form Cottrell atmospheres, increasing deformation energy storage, delaying dynamic recrystallization, and promoting ultrafine grain structure. However, excessive B enrichment at grain boundaries forms the brittle Fe2B phase, reducing the toughness of the steel plate. This invention controls the B content to be within the range of 0.003% to 0.006%.

[0029] P and S elements: These are harmful elements that do not benefit the low-temperature toughness and wear resistance of steel plates. This invention controls P ≤ 0.005% and S ≤ 0.002%.

[0030] A method for manufacturing ultra-high strength, toughness and wear-resistant marine engineering steel plates based on gradient microstructure design includes steelmaking, continuous casting, electroslag remelting, rolling and heat treatment, with the specific steps as follows:

[0031] 1) Electroslag remelting: The continuously cast billet is melted and purified in superheated slag as a consumable electrode, and then cooled into ingots in a water-cooled crystallizer with the cooling water flow rate controlled at 70-85 m³ / h. 3 / h, outlet water temperature ≤40℃, electroslag billet undergoes homogenization annealing at 950±50℃ after exiting the line, slab is slow-cooled by stacking after exiting the line, slow-cooling time ≥72h; so that the equiaxed crystal ratio of the surface layer is ≥90%;

[0032] 2) Rolling:

[0033] (1) Heating: Three-stage heating, with a preheating temperature of 850-950℃ and a preheating time of 70-90min, a heating temperature of 930-1250℃ and a heating time of 100-150min, and a heat preservation temperature of 1220-1300℃ and a heat preservation time of 80-100min;

[0034] (2) Two-stage rolling: The roughing rolling start temperature is ≥1200℃, the first pass reduction is not less than 45mm, and the average single pass reduction of the remaining passes is 25~30mm; the roughing rolling finish temperature is 980~1120℃, and the thickness of the roughing rolling billet is 2.5~3.0 times the thickness of the finished steel plate; the finishing rolling start temperature is 880~940℃, the average single pass reduction is 18~23mm, and the finishing rolling finish temperature is 790~850℃;

[0035] (3) Cooling: The rolled steel plate adopts online quenching process, with water spray cooling on the upper side. The initial cooling temperature is 700-780℃, and the final cooling surface temperature is 150-250℃. The average surface cooling rate is (0.45t-0.65t)℃ / s, where t is the thickness of the finished steel plate. The lower surface is air cooled.

[0036] (4) Straightening: The rolled steel plate is warm straightened with a straightening force of 3500-4000 kN;

[0037] 3) Heat treatment: The steel plate is subjected to low-temperature tempering heat treatment at a temperature of 250-350℃ and a holding time of 0.4-0.7 min / mm. After being taken out of the furnace, it is air-cooled.

[0038] Steelmaking steps: Pure steelmaking process is adopted. CaO-based desulfurizing agent is injected using the KR method for desulfurization of molten iron. The treated molten iron is added to the converter for oxygen decarburization and dephosphorization using the double slag method. In the LF furnace refining stage, high-carbon ferromanganese, ferrosilicon, and ferroniobium raw materials are added for alloying and composition fine-tuning. Argon blowing and stirring are carried out. Ca-Si wire is fed to modify the inclusions into spherical shapes. RH vacuum refining process is carried out with dynamic soft argon blowing, boron is added, Ce alloy is added, and argon protection is used to prevent oxidation.

[0039] Continuous casting steps: A weak cooling process is adopted during casting, the specific water content is controlled at 0.55~0.70L / kg, the columnar crystal ratio of the continuous casting billet is ≥99%, the surface temperature gradient of the billet is ≤40℃ / m, the casting speed is controlled at 0.75~1.05m / min, and a light reduction process is adopted at the end of continuous casting, with a reduction of 1.2~1.5mm.

[0040] Compared with existing technologies, the beneficial effects of this invention are:

[0041] 1. A specific composition system is designed, with the addition of elements such as Nb and Ti to refine the grains, and the composite addition of elements such as Ni, Cr, Mo, and B to ensure excellent wear resistance and ultra-low temperature toughness. Through a three-stage heating, two-stage rolling, and single-sided water-spray cooling + low-temperature tempering process, the gradient microstructure of the steel plate is controlled, resolving the traditional contradiction between wear resistance and toughness in steel, and achieving an integrated performance upgrade where the steel plate exhibits both wear resistance on one side and high toughness on the other. This significantly improves the wear resistance, elongation, and low-temperature toughness of the ultra-high strength steel plate, resulting in a steel plate with excellent comprehensive mechanical properties.

[0042] 2. The microstructure on the upper side of the finished steel plate consists of tempered martensite and retained austenite, with tempered martensite accounting for 80%–88% and retained austenite accounting for 12%–20% by volume. The microstructure on the lower side of the steel plate consists of bainite and retained austenite, with bainite accounting for 86%–91% and retained austenite accounting for 9%–14% by volume.

[0043] 3. The steel plate of this invention has ultra-high strength. The upper side of the steel plate has a yield strength ≥1100MPa and a tensile strength of 1250~1350MPa. The lower side of the steel plate has a yield strength ≥950MPa and a tensile strength of 1100~1200MPa.

[0044] High elongation: upper side of steel plate: elongation ≥14%; lower side of steel plate: elongation ≥18%;

[0045] Excellent low-temperature toughness: upper side of the steel plate: V-shaped impact energy ≥110J at -84℃, V-shaped impact energy ≥90J at -100℃; lower side of the steel plate: V-shaped impact energy ≥140J at -84℃, V-shaped impact energy ≥110J at -100℃.

[0046] Excellent wear resistance; upper side of steel plate: Vickers hardness HV≥390; lower side of steel plate: Vickers hardness HV≥300.

[0047] The thickness of the finished steel plate ranges from 80 to 120 mm. Attached Figure Description

[0048] Figure 1 This is a microstructure diagram of the upper side of the steel plate in Example 1. Detailed Implementation

[0049] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein in the specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. The reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0050] An ultra-high strength, toughness and wear-resistant marine engineering steel plate based on gradient microstructure design has the following chemical composition by mass fraction: C: 0.03%–0.09%, Si: 0.85%–1.45%, Mn: 1.4%–2.0%, Cr: 0.5%–0.9%, Ni: 5.0%–8.5%, Mo: 0.2%–0.6%, Cu: 0.6%–1.2%, Ti: 0.012%–0.025%, Nb: 0.02%–0.06%, Al: 0.03%–0.07%, Ce: 0.010%–0.018%, B: 0.003%–0.006%, P≤0.005%, S≤0.002%, with the remainder being Fe and unavoidable impurities.

[0051] A method for manufacturing ultra-high strength, toughness and wear-resistant marine engineering steel plates based on gradient microstructure design includes steelmaking, continuous casting, electroslag remelting, rolling and heat treatment, with the specific steps as follows:

[0052] (1) Steelmaking and continuous casting: A pure steelmaking process is adopted, and CaO-based desulfurizing agent is injected using the KR method for desulfurization of molten iron. The treated molten iron is then added to the converter for oxygen blowing and decarburization, and dephosphorization is carried out using the double slag method. In the LF furnace refining stage, high-carbon ferromanganese, ferrosilicon, ferroniobium and other raw materials are added for alloying and composition fine-tuning. Argon blowing and stirring are used, and Ca-Si wire is fed to modify the inclusions into spherical shapes. In the RH vacuum refining process, dynamic soft argon blowing is used, B is added, Ce alloy is added, and argon gas is used for protection to prevent oxidation. A weak cooling process is adopted during casting, with the specific water volume controlled at 0.55~0.70L / kg, the columnar crystal ratio of the continuous casting billet ≥99%, the surface temperature gradient of the billet ≤40℃ / m, the casting speed controlled at 0.75~1.05m / min, and a light reduction process is adopted at the end of continuous casting, with a reduction of 1.2~1.5mm.

[0053] (2) Electroslag remelting: The continuously cast billet is melted and purified in the superheated slag as a consumable electrode, and then cooled into ingots in a water-cooled crystallizer. The cooling water volume is controlled at 70-85 m³ / h. 3 / h, the outlet water temperature is ≤40℃ to prevent surface cracks; the electroslag billet is subjected to homogenization annealing at 950±50℃ after leaving the line, and the slab is subjected to slow cooling in a stack for ≥72h after leaving the line; so that the equiaxed crystal ratio of the surface layer is ≥90%.

[0054] (3) Rolling process: The electroslag billet is pushed into the heating furnace for three-stage heating. The preheating section temperature is 850-950℃ and the preheating time is 70-90min. The heating section temperature is 930-1250℃ and the heating time is 100-150min. The heat preservation section temperature is 1220-1300℃ and the heating time is 80-100min.

[0055] After heating, a two-stage finished product rolling process is carried out. The roughing rolling temperature is ≥1200℃, and a large reduction method is adopted. The reduction in the first pass is not less than 45mm, and the average reduction per pass in the remaining passes is 25-30mm. The roughing rolling temperature is 980-1120℃, and the thickness of the roughing billet waiting to be heated is 2.5-3.0 times the thickness of the finished steel plate. The finishing rolling temperature is 880-940℃, the average reduction per pass is 18-23mm, and the finishing rolling temperature is 790-850℃.

[0056] Cooling process: The rolled steel plate adopts an online quenching process, with water spray cooling on the upper side. The initial cooling temperature is 700-780℃, and the final cooling surface temperature is 150-250℃. The average surface cooling rate is (0.45t-0.65t)℃ / s, where t is the thickness of the finished steel plate. The lower surface is air cooled.

[0057] (5) Straightening process: The rolled steel plate is warm straightened with a straightening force of 3500-4000kN.

[0058] (6) Heat treatment process: After straightening, the steel plate is subjected to low-temperature tempering heat treatment. The tempering temperature is 250-350℃ and the holding time is 0.4-0.7min / mm. After exiting the furnace, it is air-cooled.

[0059] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0060] Table 1 Chemical composition of steel, wt%

[0061]

[0062] Table 2. Steel smelting and billet pretreatment process parameters

[0063]

[0064] Table 3 Slab Heating Process Parameters

[0065]

[0066] Table 4 Slab Rolling Process Parameters

[0067]

[0068] Table 5. Process parameters for cooling and heat treatment of steel plates

[0069]

[0070] Table 6. Microstructure and Properties of Finished Steel Plates

[0071]

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-strength, high-toughness, and wear-resistant marine engineering steel plate based on gradient microstructure design, characterized in that, The chemical composition by mass fraction is as follows: C: 0.03%–0.09%, Si: 0.85%–1.45%, Mn: 1.4%–2.0%, Cr: 0.5%–0.9%, Ni: 5.0%–8.5%, Mo: 0.2%–0.6%, Cu: 0.6%–1.2%, Ti: 0.012%–0.025%, Nb: 0.02%–0.06%, Al: 0.03%–0.07%, Ce: 0.010%–0.018%, B: 0.003%–0.006%, P≤0.005%, S≤0.002%, with the remainder being Fe and unavoidable impurities. The manufacturing method includes steelmaking, continuous casting, electroslag remelting, rolling, and heat treatment, with the specific steps as follows: 1) Electroslag remelting: The continuously cast billet is melted and purified in superheated slag as a consumable electrode, and then cooled into ingots in a water-cooled crystallizer with the cooling water flow rate controlled at 70-85 m³ / h. 3 / h, outlet water temperature ≤40℃, electroslag billet undergoes homogenization annealing at 950±50℃ after exiting the line, slab is slow-cooled by stacking after exiting the line, slow-cooling time ≥72h; so that the equiaxed crystal ratio of the surface layer is ≥90%; 2) Rolling: (1) Heating: Three-stage heating, with a preheating temperature of 850-950℃ and a preheating time of 70-90min, a heating temperature of 930-1250℃ and a heating time of 100-150min, and a heat preservation temperature of 1220-1300℃ and a heat preservation time of 80-100min; (2) Two-stage rolling: The roughing rolling start temperature is ≥1200℃, the first pass reduction is not less than 45mm, and the average single pass reduction of the remaining passes is 25~30mm; the roughing rolling finish temperature is 980~1120℃, and the thickness of the roughing rolling billet is 2.5~3.0 times the thickness of the finished steel plate; the finishing rolling start temperature is 880~940℃, the average single pass reduction is 18~23mm, and the finishing rolling finish temperature is 790~850℃; (3) Cooling: The rolled steel plate adopts online quenching process, with water spray cooling on the upper side. The initial cooling temperature is 700-780℃, and the final cooling surface temperature is 150-250℃. The average surface cooling rate is (0.45t-0.65t)℃ / s, where t is the thickness of the finished steel plate. The lower surface is air cooled. (4) Straightening: The rolled steel plate is warm straightened with a straightening force of 3500-4000 kN; 3) Heat treatment: The steel plate is subjected to low-temperature tempering heat treatment at a temperature of 250-350℃ and a holding time of 0.4-0.7 min / mm. After being taken out of the furnace, it is air-cooled.

2. The ultra-high strength, toughness, and wear-resistant marine steel plate based on gradient microstructure design according to claim 1, characterized in that, The microstructure on the upper side of the steel plate consists of tempered martensite and retained austenite, with tempered martensite accounting for 80%–88% and retained austenite accounting for 12%–20% by volume percentage; the microstructure on the lower side of the steel plate consists of bainite and retained austenite, with bainite accounting for 86%–91% and retained austenite accounting for 9%–14% by volume percentage.

3. The ultra-high strength, toughness, and wear-resistant marine steel plate based on gradient microstructure design according to claim 1, characterized in that, Performance metrics: Upper side of steel plate: Yield strength ≥1100MPa, tensile strength 1250~1350MPa, elongation ≥14%, V-shaped impact energy at -84℃ ≥110J, V-shaped impact energy at -100℃ ≥90J, Vickers hardness HV≥390; Underside of steel plate: Yield strength ≥950MPa, tensile strength 1100~1200MPa, elongation ≥18%; V-shaped impact energy at -84℃ ≥140J, V-shaped impact energy at -100℃ ≥110J; Vickers hardness HV ≥300.

4. The manufacturing method of an ultra-high strength, toughness, and wear-resistant marine steel plate based on gradient microstructure design according to claim 1, characterized in that, The process includes steelmaking, continuous casting, electroslag remelting, rolling, and heat treatment, with the specific steps as follows: 1) Electroslag remelting: The continuously cast billet is melted and purified in superheated slag as a consumable electrode, and then cooled into ingots in a water-cooled crystallizer with the cooling water flow rate controlled at 70-85 m³ / h. 3 / h, outlet water temperature ≤40℃, electroslag billet undergoes homogenization annealing at 950±50℃ after exiting the line, slab is slow-cooled by stacking after exiting the line, slow-cooling time ≥72h; so that the equiaxed crystal ratio of the surface layer is ≥90%; 2) Rolling: (1) Heating: Three-stage heating, with a preheating temperature of 850-950℃ and a preheating time of 70-90min, a heating temperature of 930-1250℃ and a heating time of 100-150min, and a heat preservation temperature of 1220-1300℃ and a heat preservation time of 80-100min; (2) Two-stage rolling: The roughing rolling start temperature is ≥1200℃, the first pass reduction is not less than 45mm, and the average single pass reduction of the remaining passes is 25~30mm; the roughing rolling finish temperature is 980~1120℃, and the thickness of the roughing rolling billet is 2.5~3.0 times the thickness of the finished steel plate; the finishing rolling start temperature is 880~940℃, the average single pass reduction is 18~23mm, and the finishing rolling finish temperature is 790~850℃; (3) Cooling: The rolled steel plate adopts online quenching process, with water spray cooling on the upper side. The initial cooling temperature is 700-780℃, and the final cooling surface temperature is 150-250℃. The average surface cooling rate is (0.45t-0.65t)℃ / s, where t is the thickness of the finished steel plate. The lower surface is air cooled. (4) Straightening: The rolled steel plate is warm straightened with a straightening force of 3500-4000 kN; 3) Heat treatment: The steel plate is subjected to low-temperature tempering heat treatment at a temperature of 250-350℃ and a holding time of 0.4-0.7 min / mm. After being taken out of the furnace, it is air-cooled.

5. The method for manufacturing an ultra-high strength, toughness, and wear-resistant marine steel plate based on gradient microstructure design according to claim 4, characterized in that, Continuous casting: A weak cooling process is adopted during casting, the specific water content is controlled at 0.55~0.70L / kg, the columnar crystal ratio of the continuous casting billet is ≥99%, the surface temperature gradient of the billet is ≤40℃ / m, the casting speed is controlled at 0.75~1.05m / min, and a light reduction process is adopted at the end of continuous casting, with a reduction of 1.2~1.5mm.

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