High-strength and high-toughness steel for ocean engineering equipment with excellent work hardening capacity and manufacturing method of high-strength and high-toughness steel

Abstract

The invention discloses high-strength and high-toughness steel with excellent work hardening capacity for ocean engineering equipment and a manufacturing method of the steel. The steel comprises the following chemical components in percentage by weight: 0.08%-0.15% of C, 0.10%-0.20% of Si, 0.50%-1.00% of Mn, 0.30%-0.80% of Ni, 0.50%-1.50% of Cr, 0.10%-0.50% of Mo, 0.10%-0.50% of Cu, 0.02%-0.04% of Nb or V, 0.05%-0.08% of Al, 0.0005%-0.0015% of B, less than or equal to 0.01% of Ti, less than or equal to 0.005% of N, less than or equal to 0.010% of P, less than or equal to 0.006% of S and the balance of Fe and inevitable impurities. According to the technical scheme, direct quenching and tempering heat treatment after hot rolling are adopted, a complex-phase structure of tempered martensite, recovered ferrite and carbide is obtained, the work hardening rate in the deformation stage from the yield strength to the tensile strength is higher than 5000 MPa, the yield ratio is lower than 0.90, the yield strength is higher than 690 MPa, and the Charpy impact energy at the temperature of 60 DEG C below zero is higher than 150 J.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material manufacturing, and relates to a high-strength and high-toughness steel for marine engineering equipment with excellent work hardening ability and a manufacturing method thereof. Background Art

[0002] In the international classification society specifications, the yield strength of ultra-high strength marine engineering steel ranges from 420 MPa to 960 MPa, using a weldable low-carbon low-alloy composition system, usually adding alloy elements such as Ni, Cr, Mo, Cu, and V. Grades of 690 MPa and above require the use of a quenching + high-temperature tempering heat treatment process. High-temperature tempering causes martensite to recover, and supersaturated C in the distorted lattice diffuses to form carbides with Cr, Mo, and V, reducing dislocation density. High-density dislocation strengthening and solid solution carbon strengthening are significantly reduced, and yield strength and tensile strength are reduced at the same time. The tensile stress-strain curve becomes flat, which significantly reduces the work hardening ability. The work hardening rate decreases immediately after over-yielding until necking fracture. Therefore, the ratio of yield strength YS to tensile strength UTS (yield ratio) of quenching + tempering heat-treated ultra-high strength steel is usually higher than 0.95, that is, the strength reserve after plastic deformation is limited, and local plastic instability failure and fracture are prone to occur after forming, increasing the service safety risk of marine engineering structures.

[0003] Therefore, the steel material specification for marine structure design specifies that the yield strength ratio of 420~960MPa grade steel is ≤0.94. However, how to reduce the yield strength ratio of ultra-high strength grade, especially 690MPa grade and above marine steel has become a technical problem. The key to regulating the yield strength ratio above 690MPa is to improve the work hardening ability after yielding, optimize the alloy composition and process to regulate the contribution of various strengthening mechanisms, and improve the tensile strength by stabilizing the high work hardening rate after yielding on the basis of ensuring the yield strength.

[0004] Chinese patent CN116516252A discloses a 1200MPa ultra-high strength plastic hot-rolled Mn-TRIP steel with a yield strength of 850-950MPa, a tensile strength of 1200-1400MPa, an elongation of 30%-35% or more, and a hole expansion rate of ≥60%, and a preparation method thereof. The steel adopts a composition design of C: 0.23%-0.33%, Si: 0.45%-1.55%, Mn: 6.8%-96%, and Al: 2.8%-4.8%. The carbon equivalent Ceq far exceeds the specification range of marine engineering steel and is not suitable for use in welding marine engineering structures.

[0005] Chinese patent CN115181886A discloses a 980MPa grade low-carbon low-alloy dual-phase steel and a rapid heat treatment manufacturing method. Through rapid heat treatment to change the recovery, recrystallization and austenite phase transformation process of the deformed structure, the prepared dual-phase steel has a yield strength of 598-749MPa, a tensile strength of 1030-1090MPa, an elongation of 10.6-16.6%, a strength-plasticity product of 109-174GPa%, and a strain hardening index n90 value greater than 0.21. However, the method provided by the patent requires hot rolling, coiling, cold rolling and rapid heat treatment, and the width and thickness of the steel plate are limited, which is not suitable for medium and thick steel plate production process equipment and cannot be applied to marine engineering structures.

[0006] Chinese patent CN111448332B discloses a method for manufacturing high-strength steel plates with a tensile strength of 780 MPa or above, low yield ratio, excellent ductility and work hardening index, and excellent processing performance. However, the document technology is aimed at high-strength steel plates for automotive structural parts, using high Si, high Mn and high Al alloy components, and is produced through hot rolling coiling, cold rolling and continuous annealing processes, which does not meet the requirements for use in marine engineering structures. Summary of the invention

[0007] The present invention aims to provide a high-strength and high-toughness steel for marine engineering equipment with excellent work hardening ability and a method for manufacturing the same. By optimizing the alloy composition, controlling rolling and controlled cooling, and high-temperature tempering process methods, the proportion of multiphase structures of bainite, martensite, and alloy carbide is regulated, the work hardening rate in the post-yield deformation stage is improved, and the technical problems of formability and local plastic failure of ultra-high-strength marine engineering steel are solved.

[0008] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions: A high-strength and high-toughness steel for marine engineering equipment with excellent work hardening ability, the chemical composition of the steel is C=0.08%~0.15%, Si=0.10%~0.20%, Mn=0.50%~1.00%, Ni=0.30%~0.80%, Cr=0.50%~1.50%, Mo=0.10%~0.50%, Cu=0.10%~0.50%, Nb or V= 0.02%~0.04%, Al=0.05%~0.08%, B=0.0005%~0.0015%, Ti≤ 0.01%, N≤ 0.005%, P≤0.010%, S≤0.006%, the rest is Fe and unavoidable impurities; the volume percentage of tempered martensite in the steel plate microstructure is 75%~85%, the volume percentage of recovered polygonal ferrite is 13.5%~23.5%, and the volume percentage of carbide is 0.5%~1.5%.

[0009] A method for manufacturing high-strength and high-toughness steel for marine engineering equipment with excellent work hardening ability, the process steps are: 1) Hot metal pretreatment: First, the hot metal is pretreated with desulfurization, and the magnesium desulfurizer is fully mixed with hot metal at a temperature not lower than 1300°C to make the sulfur content of the hot metal not higher than 0.002%; 2) Converter refining: The pretreated molten iron is poured into the converter for smelting. The treatment time is 25 to 30 minutes. The excess carbon, phosphorus and sulfur in the molten iron are removed to make C≤0.12%, P≤0.010%, S≤0.008%. The temperature reaches 1650±30℃ for steelmaking. 3) Ladle refining: FeMn, FeSi, FeNi, FeAl, FeCr, Cu, and Mo alloys calculated in advance are added to the converter during the steel tapping process; the ladle is transported to the LF furnace refining station, bottom blowing of argon is turned on, graphite electrodes are used for electrical heating, lime and aluminum are added to adjust the slag and further deoxidize, and after 25 to 30 minutes of treatment, the temperature of the molten steel is adjusted to 1600±10℃; 4) Vacuum degassing: The molten steel after refining in the LF furnace is sent to the RH / VD vacuum treatment station and ferroboron is added to the molten steel. After that, vacuum degassing is carried out for no less than 10 minutes in a vacuum environment of no more than 0.5tor. When the temperature of the molten steel reaches 1560±10℃, a heat preservation agent is added; 5) Tundish casting: The ladle after vacuum treatment is lifted to the continuous casting station, and the liquid steel is drained from the bottom of the ladle to the casting tundish. The flow rate and temperature of the molten steel are controlled. The temperature of the molten steel in the tundish is controlled at 1535-1550°C. The argon sealing and covering agent protection casting are carried out throughout the process, and the liquid steel flows into the crystallizer through the submerged nozzle; 6) Slab continuous casting: The tundish molten steel is poured into the cooling rectangular copper plate crystallizer through the immersion nozzle. The casting superheat is controlled at 15-25°C. The molten steel in contact with the copper wall of the crystallizer solidifies into a billet shell. The billet is separated from the crystallizer by the crystallizer vibration and the dummy rod, and enters the clamping roller in the foot roller area, the roller in the secondary cooling area, the fan-shaped segment bending roller and the straightening roller. The continuous casting slabs of various lengths and thicknesses of 200-320 mm are obtained by flame cutting; 7) Slab heating: The continuous casting slab is sent to the stepping furnace and heated to 1150-1230°C in stages, and kept in the soaking section for 1-3 hours, and the austenite grain size is controlled at 50-100μm; 8) Controlled rolling: The continuous casting slab is pushed out of the heating furnace and sent to the descaling machine through the conveyor roller. The surface oxide scale is removed by high-pressure water, and then sent to the four-roll mill for the first stage of controlled rolling in the high temperature zone of 1050~950℃. The intermediate slab is cooled to 850~900℃ on the warm roller for the second stage of controlled rolling. 9) Online linear quenching: After final rolling, the steel plate is conveyed by rollers and enters the laminar cooling zone for two-stage accelerated cooling; 10) Tempering heat treatment: The steel plate after direct quenching is transported to the tempering furnace for high-temperature tempering heat treatment. The tempering temperature is 550~650℃ and the holding time is 2.5 times the plate thickness mm×min / mm; Further, step 8) controlled rolling: in the first stage of controlled rolling, the average single-pass reduction in the high temperature section above 950°C is above 30mm, and the intermediate billet thickness is rolled to 2 to 5 times the target thickness of the finished product; in the second stage of controlled rolling, the cumulative reduction reaches 50% to 80%, and the steel plate is rolled to the target size and shape requirements of the finished product; Furthermore, step 9) online linear quenching: in the first stage, in the first 1 / 3 of the length of the cooling zone, a weak cooling mode is adopted to control the cooling rate of the steel plate to 5-10°C / s, and the temperature of the steel plate is brought to 620-660°C, so that the portion with a volume percentage not exceeding 25% undergoes a pro-eutectoid ferrite phase transformation; in the second stage, in the last 2 / 3 of the length of the cooling zone, a strong cooling direct quenching mode is adopted to control the cooling rate of the steel plate to 15-30°C / s, to a final cooling temperature below 300°C, to ensure that the remaining austenite undergoes a martensitic phase transformation, with a content of more than 75%.

[0010] The mechanism of action of each alloy component of the ultra-high strength marine engineering steel with excellent work hardening ability manufactured by the present invention is as follows: C is an essential element for controlling quenching phase transformation and improving strength. It maintains a solid solution state in austenite and forms high dislocation density martensite with severe lattice distortion after direct quenching, providing strong dislocation strengthening. During the tempering process, it precipitates carbide particles together with Fe, Cr, Mo, and V to ensure strength stability. However, too high C content is not only easy to form banded structure, which is not conducive to plasticity and toughness, but also high C content is easy to form martensite in the heat affected zone of welding and reduce the toughness of the welding part. From the perspective of comprehensive performance, it is preferred that the C content be controlled at 0.08-0.15%.

[0011] Si is a deoxidizing element in the ladle after converter refining, and can also play a certain role in solid solution strengthening. At the same time, Si can inhibit the precipitation and coarsening of cementite, thereby improving toughness. However, it is easy to enrich in the surface layer to form fayalite during the heating process of the slab, affecting the descaling effect of the oxide scale. Therefore, the preferred Si content is 0.10-0.20%.

[0012] Mn is the main element that ensures the ability to form martensite and exerts solid solution strengthening. If the content is too high, it will inhibit the phase transformation of austenite to ferrite, which is not conducive to the formation of proeutectoid ferrite in the first stage of online accelerated cooling after rolling. If the content is too low, sufficient martensite cannot be formed in the second stage of cooling, the strong cooling direct quenching stage. Therefore, the Mn content range is 0.50-1.20%, and the preferred range is 0.70-1.00%.

[0013] Ni is the main element that improves the toughness and hardenability of steel, and also plays a role in solid solution strengthening. Ni in steel reduces the activation energy of dislocation movement, enhances the dislocation mobility during deformation, and thus improves the plasticity and low-temperature toughness of steel. However, Ni is also a high-cost alloy, therefore, the Ni content of the present invention is not higher than 0.30-0.80%, and the preferred range is 0.50-0.70%.

[0014] Cr is the main element to improve the hardenability of steel and promote the formation of martensite during the quenching process. At the same time, Cr is also an austenite fine grain element and a strong carbide forming element, which can significantly improve the temper brittleness resistance and improve the low temperature toughness of the steel plate after tempering. Therefore, the Cr content of the present invention is in the range of 0.50-1.50%, and the preferred range is 0.80-1.20%.

[0015] Mo is a main element for improving the hardenability of steel, and forms nano-sized carbides MoC together with C, which has a significant precipitation strengthening effect. Therefore, the Mo content of the present invention is in the range of 0.10-0.50%, preferably in the range of 0.20-0.40%.

[0016] Cu precipitates a nano-scale Cu-rich phase during the tempering process, which plays a precipitation strengthening role. Therefore, the Cu content of the present invention is in the range of 0.15-0.50%, preferably in the range of 0.20-0.30%.

[0017] Nb or V: a strong carbide-forming microalloying element, which precipitates nano-sized NbC or VC during tempering and provides effective precipitation strengthening contribution. Therefore, the content of either Nb or V in the present invention is in the range of 0.02-0.04%.

[0018] V has the effects of precipitation strengthening, grain refinement, and improving resistance to HIC and sulfide stress cracking. It forms nano-sized VC and V (C, N) particles with C and N in steel to improve strength, and hinder the transformation of austenite to ferrite, achieving fine grain strengthening and toughening effects. At the same time, it acts as a hydrogen trap to improve resistance to hydrogen-induced cracking and sulfide stress cracking in an acid environment. Therefore, the V content of the present invention is in the range of 0.005-0.04%, preferably in the range of 0.01-0.03%.

[0019] Ti has the function of refining the austenite grain size and improving the welding performance. During the high-temperature refining process, it forms TiN particles with free N in the molten steel, plays a role in fixing N, protects the added B in a solid solution state, and improves the hardenability. It effectively inhibits the growth of austenite grains during the slab heating process, organizes the grain coarsening of the heat-affected zone during the welding process, and improves the toughness of the welding part. Therefore, the Ti content of the present invention is in the range of 0.008-0.020%, and the preferred range is 0.010-0.015%.

[0020] Al plays a strong role in deoxidation and denitrification during the refining process, forming Al2 O 3 and AlN inclusions, ensuring that the free oxygen content in the molten steel is not higher than 10ppm, the free nitrogen content is not higher than 40ppm, and ensuring that the added B does not form BN in the steel but maintains a solid solution state. Therefore, the Al content in the present invention is in the range of 0.05-0.08%, preferably in the range of 0.055-0.065%.

[0021] B is a strong hardenability element. When it is dissolved in a small amount in steel and concentrated at the austenite grain boundary, it can effectively improve the martensite forming ability during the quenching process. B is also a strong nitride forming element. Therefore, it must be used in combination with Al in the present invention. The content range is 0.0005-0.0015%, and the preferred range is 0.0008-0.0012%.

[0022] N is an inevitable gas element in steel. During the steelmaking process, it is very easy to form sharp-angle nitride particles with Ti, Al, and B, which are concentrated at the austenite grain boundary and are not conducive to the toughness of the steel. Therefore, the N content of the present invention is not higher than 0.005%, preferably not higher than 0.003%.

[0023] P is an element harmful to the low-temperature toughness and ductility of ultra-high-strength marine engineering steel. It is easy to be concentrated in the center of the slab during continuous casting and segregated at the original austenite grain boundaries, which reduces the crystal bonding strength and damages the toughness. In the present invention, P is controlled to be no higher than 0.010%, preferably no higher than 0.005%.

[0024] S is a harmful element that is detrimental to toughness and plasticity. It segregates in the core of the ingot and forms large-sized MnS inclusions in the Mn segregation zone. It is deformed into long strips with sharp ends during the rolling stage and becomes a crack source. Therefore, the S content in the material of the present invention is controlled to be no higher than 0.006%, and preferably no higher than 0.003%.

[0025] The beneficial effects of the present invention are as follows: 1) Low-cost and simple alloy composition: the two main alloys of low C and Mn+Cr and a single micro-alloying element of Nb or V are used, which has the advantages of low carbon equivalent, simple composition and low cost, and reduces the difficulty of executing processes such as refining; 2) High-efficiency preparation process: the controlled rolling and online direct quenching process are adopted, which eliminates the process link of offline reheating and quenching of traditional tempered ultra-high strength marine engineering steel, improves production efficiency, and reduces energy consumption in the production process; 3) Effectively improves the work hardening ability: the two-stage controlled cooling process of weak cooling at the beginning and strong cooling at the end is adopted to obtain a dual-phase structure of a small amount of proeutectoid ferrite soft phase and main martensite hard phase in the wide and thick plate, which effectively improves the work hardening ability during plastic deformation and its stability after over-yielding, and obtains a low yield strength ratio that is difficult to achieve with traditional offline quenching + tempering ultra-high strength marine engineering steel, thereby improving the service safety of marine engineering structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1Schematic diagram of the online direct quenching process with controlled rolling and two-stage controlled cooling.

[0027] Figure 2 The following is a scanning electron microscope micrograph of the complete martensitic structure of the steel plate for comparison.

[0028] Figure 3 This is a microstructure photograph of the steel plate in Example 1.

[0029] Figure 4 This is a microstructure photograph of the steel plate of Example 2.

[0030] Figure 5 Microstructure photograph of the steel plate of Example 3.

[0031] In the figure: 1-heating furnace; 2-slab; 3-high-pressure water descaling; 4-four-roller reversible hot rolling; 5-laminar weak cooling; 6-strong cooling direct quenching; 7-multi-roller straightening; 8-finished steel plate. DETAILED DESCRIPTION

[0032] The following is an explanation using examples and comparative steel.

[0033] The mass percentages of the chemical components of the example and comparative steels are shown in Table 1; the controlled rolling and controlled cooling direct quenching or processes of the example and comparative steels are shown in Table 2.

[0034] The test results of mechanical properties and HIC resistance of the example and comparative steels are shown in Table 3.

[0035] Contrast Steel: A method for manufacturing steel for marine engineering equipment, the production process steps are: after being treated in an LF furnace and an RH furnace for 25 minutes and 15 minutes respectively, the superheat degree during casting in the tundish is 24°C, and continuous casting is used to form a 260mm thick slab. The slab is heated at 1210°C and then kept warm for 120 minutes. After being removed from the furnace, it is descaled by high-pressure water. The starting rolling temperature is 1080°C, and the rough rolling is carried out to a 130mm thick intermediate slab. The average single-pass reduction is 22mm. The second stage of finishing rolling is carried out when the temperature reaches 880°C, and the cumulative reduction is 92mm. The final rolling temperature is 850°C, and it is cooled to 260°C at a rate of 25°C / s through ACC accelerated cooling, and then transported to the cooling bed after straightening. After cooling, the steel plate is sent to the heating furnace for tempering heat treatment at 600°C±10°C for 95 minutes. Figure 2 and Figure 3 For comparison of the microstructure of the steel plates, the volume percentage of martensite is 100%. Example 1

[0036] A high-strength and high-toughness steel for marine engineering equipment with excellent work hardening ability and a manufacturing method thereof, the production process steps are: after being treated in the LF furnace and the RH furnace for 22 minutes and 16 minutes respectively, the superheat degree during casting in the tundish is 23°C, and continuous casting is used to form a 260mm thick slab. The slab is heated at 1210°C and then kept warm for 120 minutes. After being removed from the furnace, it is descaled by high-pressure water. The starting rolling temperature is 1080°C, and the rough rolling is to 80 mm thick intermediate slab. The average single-pass reduction is 25mm. The second stage of finishing rolling is carried out when the temperature reaches 820°C, and the cumulative reduction is 65mm. The final rolling temperature is 780°C, and it is cooled to 270°C at a rate of 36°C / s through ACC accelerated cooling, and then transported to the cooling bed after straightening. After cooling, the steel plate is sent to the heating furnace for tempering heat treatment at 600°C±10°C for 40 minutes. Figure 4 The microstructure of the core of Example 1 is shown, in which the proportion of tempered martensite reaches 84%, the proportion of ferrite is 15.5%, and the proportion of carbide is 0.5%.

[0037] Figure 1 As shown: Example 1 steel plate structure 84% martensite + 15.5% polygonal ferrite. Example 2

[0038] A high-strength and high-toughness steel for marine engineering equipment with excellent work hardening ability and a manufacturing method thereof, the production process steps: after being treated in an LF furnace and an RH furnace for 21 minutes and 23 minutes respectively, the superheat degree during casting in the tundish is 21°C, and continuous casting is adopted to form a 360mm thick slab, and the core macro-segregation level is Class B 0.5. The slab is heated at 1220℃ and then kept warm for 210min. After being taken out of the furnace, it is descaled by high-pressure water. The starting rolling temperature is 1082℃. It is roughly rolled to an intermediate slab with a thickness of 180mm. The average single-pass reduction is 38mm. When the temperature reaches 790℃, the second stage of finishing rolling is carried out with a cumulative reduction of 120mm and a final rolling temperature of 780℃. It is cooled to 310℃ at a rate of 18℃ / s through ACC accelerated cooling, and then transported to the cooling bed after straightening. After cooling, the steel plate is sent to the heating furnace for tempering heat treatment at 630℃±10℃ for 100min. Figure 4 The microstructure of the core of Example 2 is shown, in which the proportion of tempered martensite reaches 76%, the proportion of ferrite is 22.5%, and the proportion of carbide is 1.5%.

[0039] Figure 2 As shown: The structure of the steel plate in Example 2 is 76% martensite + 22.5% polygonal ferrite. Example 3

[0040] A high-strength and high-toughness steel for marine engineering equipment with excellent work hardening ability and a manufacturing method thereof, the production process steps are: after being treated in LF furnace and RH furnace for 23 min and 24 min respectively, the superheat degree during casting in the tundish is 18°C, and continuous casting is used to form a 300mm thick slab, and the core macro segregation level is Class B 0.5. The slab is heated at 1210°C and then kept warm for 160min, and then descaled by high-pressure water after being taken out of the furnace, and the starting rolling temperature is 1078°C, and the rough rolling is to 150 mm thick intermediate slab, the average single pass reduction is 30mm, and the second stage finishing rolling is carried out when the temperature reaches 792°C, the cumulative reduction is 120mm, the final rolling temperature is 780°C, and the ACC is accelerated to cool to 270°C at a rate of 26°C / s, and then transported to the cooling bed after straightening. After cooling, the steel plate is sent to the heating furnace for tempering heat treatment at 610°C±10°C for 75min. Figure 4 The microstructure of the core of Example 3 is shown, in which the proportion of tempered martensite reaches 79%, the proportion of ferrite is 20%, and the proportion of carbide is 1.0%.

[0041] Figure 3 As shown: The microstructure of the steel plate in Example 3 is 79% martensite + 20% polygonal ferrite.

[0042] Table 3 lists the mechanical property test results of the comparative steel and the steel produced by Examples 1 to 3 of the present invention. Table 3 shows that after adopting the alloy composition, steelmaking and controlled rolling and controlled cooling direct quenching and tempering process of the present invention, the microstructure of the embodiment with martensite as the main and polygonal ferrite as the auxiliary has a higher work hardening rate, and has obvious advantages in tensile properties, low yield strength ratio and -60℃ Charpy impact energy, meeting the safe service requirements of marine engineering equipment.

[0043] Table 1 Chemical composition of the embodiments of the present invention and the comparative steel (mass percentage) .

[0044] Table 2 Controlled rolling and controlled cooling direct quenching or process of the embodiment of the present invention .

[0045] Table 3 Mechanical properties and HIC resistance test results of steel according to the present invention .

Claims

1. A high-strength and high-toughness steel for marine engineering equipment with excellent work hardening ability, characterized by: The chemical composition of the steel is C=0.08%~0.15%, Si=0.10%~0.20%, Mn=0.50%~1.00%, Ni=0.30%~0.80%, Cr=0.50%~1.50%, Mo=0.10%~0.50%, Cu=0.10%~0.50%, Nb or V= 0.02%~0.04%, Al=0.05%~0.08%, B=0.0005%~0.0015%, Ti≤ 0.01%, N≤ 0.005%, P≤0.010%, S≤0.006%, and the rest are Fe and unavoidable impurities; the volume percentage of tempered martensite in the steel plate microstructure is 75%~85%, the volume percentage of recovered polygonal ferrite is 13.5%~23.5%, and the volume percentage of carbide is 0.5%~1.5%.

2. A method for manufacturing high-strength and high-toughness steel for marine engineering equipment with excellent work hardening ability, characterized in that The process steps are: 1) Hot metal pretreatment: First, the hot metal is pretreated with desulfurization, and the magnesium desulfurizer is fully mixed with hot metal at a temperature not lower than 1300°C to make the sulfur content of the hot metal not higher than 0.002%; 2) Converter refining: The pretreated molten iron is poured into the converter for smelting for 25 to 30 minutes to remove excess carbon, phosphorus and sulfur in the molten iron, so that C≤0.12%, P≤0.010%, S≤0.008%, and the temperature reaches 1650±30℃ for steelmaking; 3) Ladle refining: The pre-calculated FeMn, FeSi, FeNi, FeAl, FeCr, Cu, and Mo alloys are added to the converter during the steel tapping process; the ladle is transported to the LF furnace refining station, the bottom blowing of argon is turned on, the graphite electrode is electrically heated, lime and aluminum are added to adjust the slag and further deoxidize, and after 25 to 30 minutes of treatment, the molten steel temperature is adjusted to 1600±10 ℃; 4) Vacuum degassing: The molten steel after LF furnace refining is sent to the RH / VD vacuum treatment station and ferroboron is added to the molten steel. After that, vacuum degassing is carried out for no less than 10 minutes in a vacuum environment of no more than 0.5tor. When the temperature of the molten steel reaches 1560±10℃, a heat preservation agent is added; 5) Tundish casting: The ladle after vacuum treatment is lifted to the continuous casting station, and the liquid steel is drained from the bottom of the ladle to the casting tundish. The flow rate and temperature of the molten steel are controlled. The temperature of the molten steel in the tundish is controlled at 1535-1550°C. The argon sealing and covering agent protection casting are carried out throughout the process, and the liquid steel flows into the crystallizer through the submerged nozzle; 6) Slab continuous casting: The tundish molten steel is poured into the cooling rectangular copper plate crystallizer through the immersion nozzle. The casting superheat is controlled at 15-25°C. The molten steel in contact with the copper wall of the crystallizer solidifies into a billet shell. The billet is separated from the crystallizer by the crystallizer vibration and the dummy rod, and enters the clamping roller in the foot roller area, the roller in the secondary cooling area, the fan-shaped segment bending roller and the straightening roller. The continuous casting slabs of various lengths and thicknesses of 200-320 mm are obtained by flame cutting; 7) Slab heating: The continuous casting slab is sent to the stepping furnace and heated to 1150-1230°C in stages, and kept in the soaking section for 1-3 hours, and the austenite grain size is controlled at 50-100μm; 8) Controlled rolling: The continuous casting slab is pushed out of the heating furnace and sent to the descaling machine through the conveyor roller. The surface oxide scale is removed by high-pressure water, and then sent to the four-roll mill for the first stage of controlled rolling in the high temperature zone of 1050~950℃. The intermediate slab is cooled to 850~900℃ on the warm roller for the second stage of controlled rolling. 9) Online linear quenching: After final rolling, the steel plate is conveyed by rollers and enters the laminar cooling zone for two-stage accelerated cooling; 10) Tempering heat treatment: The steel plate after direct quenching is transported to the tempering furnace for high-temperature tempering heat treatment. The tempering temperature is 550~650℃ and the holding time is 2.5 times the plate thickness (mm×min / mm).

3. The method for manufacturing a high-strength and high-toughness marine engineering equipment steel with excellent work hardening ability according to claim 2, characterized in that Step 8) Controlled rolling: In the first stage of controlled rolling, the average single-pass reduction in the high-temperature section above 950°C is above 30mm, and the intermediate billet thickness is rolled to 2 to 5 times the target thickness of the finished product; in the second stage of controlled rolling, the cumulative reduction reaches 50% to 80%, and the steel plate is rolled to the target size and shape requirements of the finished product.

4. The method for manufacturing the high-strength and high-toughness steel for marine engineering equipment with excellent work hardening ability as claimed in claim 2, characterized in that Step 9) Online linear quenching: In the first stage, the steel plate cooling rate is controlled at 5-10°C / s in the weak cooling mode in the first 1 / 3 of the cooling zone, and the steel plate temperature is raised to 620-660°C, so that the portion with a volume percentage not exceeding 25% undergoes a pro-eutectoid ferrite phase transformation; in the second stage, the steel plate cooling rate is controlled at 15-30°C / s in the strong cooling direct quenching mode in the last 2 / 3 of the cooling zone, until the final cooling temperature is below 300°C, to ensure that the remaining austenite undergoes a martensitic phase transformation, with a content of more than 75%.

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