High-strength corrosion-resistant marine steel plate with good strain aging performance and manufacturing method thereof

Abstract

The application relates to the technical field of steel material manufacturing, in particular to a high-strength corrosion-resistant marine steel plate with good strain aging performance and a manufacturing method thereof. The steel plate is compounded with rare earth elements, the rare earth elements purify the steel, refine the grains and spheroidize the inclusions so as to reduce stress concentration, improve toughness and corrosion resistance, and meanwhile, the steel plate has low aging sensitivity. The comprehensive mechanical properties of the steel plate are as follows: yield strength 490-550 MPa, tensile strength 560-650 MPa, elongation greater than or equal to 28%, impact energy at-60 DEG C greater than or equal to 220 J, and corrosion rate less than or equal to 0.08 mm / a. After 12% pre-strain + 250 DEG C heat preservation for 1 hour, the impact energy at-60 DEG C is greater than or equal to 190 J, and the strain aging sensitivity coefficient C is less than or equal to 15%.

Description

Technical Field

[0001] This invention belongs to the field of steel material manufacturing technology, and specifically relates to a high-strength corrosion-resistant marine steel plate with good strain aging properties and its manufacturing method. Background Technology

[0002] With the booming development of marine oil and gas, wind power, and fishery resources, higher demands are being placed on steel used in marine engineering equipment. For example, in the construction of ship structures and marine engineering equipment, cold bending and edge rolling are required for marine engineering steel. This induces strain aging, leading to increased strength and hardness, but decreased plasticity and toughness, affecting the performance and safety of the equipment. Therefore, to ensure the low-temperature toughness and safety of steel after cold deformation, marine engineering steel must possess excellent strain aging properties. As marine resource development expands into polar and other low-temperature sea areas, the harsh polar environment presents challenges such as low temperatures and sea ice. This necessitates that marine engineering steel not only possess good strength-toughness matching under low-temperature conditions but also excellent strain aging properties and corrosion resistance to ensure personnel safety and extend the service life of engineering equipment after cold working. Currently, high-strength marine engineering steels often employ quenching and tempering processes to form tempered martensite structures. However, these steels suffer from poor strain-aged impact toughness, high yield strength ratio, and low plasticity, failing to meet the safety requirements for ships and marine engineering in low-temperature sea areas. Therefore, improving the strain-aged impact toughness of ultra-high strength marine engineering steel is one of the main directions for developing a new generation of high-performance marine engineering steel. Because excessively high levels of certain elements in steel, such as carbon and nitrogen, can enhance aging sensitivity, affecting the low-temperature toughness and overall performance of marine engineering steel. By rationally designing the alloy composition and adding elements such as hafnium and cerium, the aging sensitivity of the steel can be reduced, improving its strain-aged performance and corrosion resistance, thus meeting the requirements for use in marine environments.

[0003] Patent CN103031498B describes a method for manufacturing low-compression, thick, ultra-high-strength strain-aged marine engineering steel plates. This method employs low-carbon control (C: 0.05-0.09%) combined with multi-element microalloying (Ni: 0.7-1.3%, Cr: 0.25-0.50%, Mo: 0.40-0.60%, Nb: 0.030-0.050%, Ti: 0.005-0.020%), significantly reducing the carbon equivalent and improving weldability. It also controls ultra-low impurities (P≤0.010%, S≤0.0020%), reducing the risk of segregation and low-temperature brittleness. A two-stage rolling process (roughing and finishing at 1030-1080℃ + finishing at 830-850℃) with a final cooling and red-heating temperature of 600-640℃ is used to obtain a bainitic matrix. The process employs post-rolling quenching and tempering: quenching at 890-910℃ followed by tempering at 590-630℃. This process transforms the microstructure from bainite to martensite to tempered sorbite, refining the grains and fixing free C / N atoms. The final product exhibits a yield strength of 720-800 MPa, an impact energy ≥100 J at -40℃, and a reduction in aging sensitivity of over 30%, making it suitable for 60-80 mm thick plates. However, its high alloy content increases costs and processing time with offline heat treatment, and corrosion performance evaluation is lacking.

[0004] Patent CN119956209A describes a low-aging-sensitivity, high-strength, extra-thick ship plate and its manufacturing method. It involves VN microalloying (V: 0.060-0.200%, N: 0.0190-0.0250%) + rare earth Y (0.0330-0.0390%) to form VN precipitates for strengthening, while Y simultaneously purifies grain boundaries. Slow cooling of the cast billet (72-240 hours) followed by multi-stage heated rolling (1180-1200℃) reduces segregation. The impact energy at -80℃ is ≥280J, and after strain aging, it is ≥240J, with an aging sensitivity coefficient ≤17%. This method is suitable for thick plates (≥80mm) used in polar vessels. However, its strength is insufficient, and its corrosion performance has not been evaluated.

[0005] Patent CN109161791B discloses a 690MPa grade steel for shipbuilding and marine engineering with excellent low-temperature toughness and its manufacturing method. The patented alloy composition contains 1.0-2.5% Ni and employs quenching + tempering, or normalizing + quenching + tempering, or tempering + quenching + tempering. The steel plate developed using this process has a yield strength of 690MPa. However, the alloy cost is high, the heat treatment process is lengthy and costly, and no evaluation of its corrosion resistance has been provided.

[0006] Patent CN112899558A describes a 550MPa grade weathering steel plate with excellent weldability and its manufacturing method. It employs an optimized TMCP process, achieving a yield strength ≥460MPa, tensile strength ≥570MPa, Charpy impact energy (single value) ≥120J at -40℃, impact toughness KV2 ≥100J at -40℃, and weld heat-affected zone (HAZ) Akv ≥100J at -40℃. However, its strength is relatively low, its low-temperature toughness is only at -40℃, and the aging performance issue remains unresolved.

[0007] The aforementioned patents achieved good aging performance through alloy design and process control, but they also have problems such as excessive alloy content, use of offline heat treatment process, high production cost, long process, and failure to simultaneously solve aging performance and corrosion performance. Summary of the Invention

[0008] The technical problem to be solved by this invention is to provide a high-strength, corrosion-resistant marine engineering steel plate with excellent strain-aging properties and its manufacturing method. The invention is characterized by low-carbon microalloying and the addition of rare earth elements. These rare earth elements purify the steel, refine the grains, and spheroidize inclusions to reduce stress concentration and improve toughness and corrosion resistance, while also exhibiting low aging sensitivity. This addresses the problems of low strength, high aging sensitivity, poor low-temperature impact toughness, and insufficient corrosion resistance in existing marine engineering steel plates.

[0009] To achieve the above objectives, the present invention employs the following technical solution:

[0010] A high-strength, corrosion-resistant marine engineering steel plate with excellent strain-aging properties, the chemical composition of which is as follows by weight percentage: C: 0.02%-0.05%, Si: 0.10%-0.25%, Mn: 1.35%-1.55%, Nb: 0.035%-0.040%, V: 0.045%-0.055%, Ti: 0.025%-0.035%, Cu: 0.35%-0.40%, Zr: 0.10%-0.14%, Co: 0.05%-0.08%, Sn: 0.03%-0.05%, Sb: 0.03%-0.05%, B: 0.001 2%-0.0020%, Als: 0.025%-0.030%, Hf: 0.03%-0.05%, Ce: 0.035%-0.045%, S≤0.003%, P≤0.01%, N≤0.004%, 4≤Si / Al≤9, (Nb+V+Ti+Als) / N≥35, (Nb+V+Ti) / Mn≥0.06, Ti / N≥6.5, (Ti+Zr) / C≥2, 180<Cu / B<300, 15<Nb / B<35, 20<(Hf+Ce+Ti) / N<40, the remainder being iron and unavoidable impurities.

[0011] A high-strength, corrosion-resistant marine steel plate with good strain aging properties, the finished steel plate thickness is 20-100mm.

[0012] The content range and functions of various elements:

[0013] Carbon (C) significantly affects the strength, low-temperature toughness, elongation, and weldability of ultra-high strength quenched and tempered steel plates. From the perspective of improving the intrinsic ductility, toughness, corrosion resistance, and strain aging of ultra-high strength steel plates, the C content should be controlled to a relatively low level. However, from the perspective of hardenability, strength-toughness balance, weldability, microstructure control, and alloy cost control, the C content should not be controlled too low. Carbon can form strong carbides with elements such as niobium, vanadium, titanium, and zirconium, including VC, NbC, and TiC, which have the highest stability, melting point, hardness, and wear resistance. Carbon is a key element affecting the microstructure and properties of steel plates, and its variation is significant. Different carbon contents result in different balances of hardness and toughness. Carbon is the most effective element for improving the strength of steel plates; when its content is below 0.02%, the strength of the steel plate will be significantly reduced, but it will be beneficial to the corrosion resistance and low-temperature impact toughness. Therefore, the C content in this invention is selected to be between 0.02% and 0.05%.

[0014] Silicon (Si): Silicon is an essential element for deoxidation in steelmaking and has a certain solid solution strengthening effect. However, Si reduces the critical cooling rate of martensitic transformation, severely impairing the low-temperature toughness, crack arrest properties, elongation, and weldability of ultra-high-strength steel plates. Silicon can promote the growth of columnar crystals in cast steel and reduce plasticity. Therefore, the Si content in steel should be controlled as low as possible. However, a certain Si content can effectively improve the steel's resistance to marine corrosion. Adding a certain amount of silicon when deoxidizing aluminum can significantly improve the deoxidation capacity of aluminum. When silicon-containing steel is heated in an oxidizing atmosphere, a SiO2 film will form on the surface, thereby improving the steel's oxidation resistance at high temperatures. In this invention, the Si content is controlled at 0.10%-0.25%, and 4≤Si / Al≤9.

[0015] Manganese (Mn) is a key element for improving strength and toughness, significantly enhancing the hardenability of steel, and is very inexpensive. It is a major additive element in steel, eliminating or reducing hot brittleness caused by sulfur, thus improving the hot workability of steel. The solid solution formed by manganese and iron increases the hardness and strength of ferrite and austenite in steel; simultaneously, it is a carbide-forming element, entering cementite to replace some iron atoms. Manganese in steel lowers the critical transformation temperature, refining pearlite and indirectly increasing the strength of pearlitic steel. Manganese reacts with sulfur to form MnS, which has a high melting point and can prevent hot brittleness caused by FeS. However, excessively high levels of Mn can reduce the ductility of steel. When the carbon (C) content is low, a higher manganese (Mn) content can effectively improve the hardenability of the steel and increase the strength of the steel plate by refining the microstructure and promoting bainite transformation. However, excessively high Mn content is detrimental to the weldability of the steel and may worsen center segregation. With the increase of manganese content, the thermal conductivity of the steel decreases sharply, and the coefficient of linear expansion increases, resulting in greater internal stress during rapid heating or cooling, and increasing the tendency of the workpiece to crack. Manganese expands the austenite region and promotes grain enlargement, requiring the use of grain-refining elements. In this invention, the Mn content is selected to be between 1.35% and 1.55%.

[0016] P: Phosphorus is used as an impurity element in this invention. A content greater than 0.04% will adversely affect the low-temperature toughness of the base material and the toughness of the weld heat-affected zone. Therefore, its content should be controlled to a low level as much as possible. In this invention, its content is controlled to ≤0.01%.

[0017] S: Sulfur segregates severely in steel, deteriorating its quality. As an inclusion-forming element, it forms inclusions such as FeS and MnS, reducing the ductility of the steel. Furthermore, the vicinity of these inclusions becomes a source of corrosion and impact fracture, negatively impacting the corrosion resistance and strain aging properties of the steel plate. In this invention, its content is controlled at ≤0.003%.

[0018] N: In this invention, nitrogen is a residual element. Excessive residual nitrogen can lead to a loose macrostructure or porosity, affecting the performance of the steel. Furthermore, after plastic deformation and isothermal aging treatment, C and N atoms dissolved in the steel diffuse towards the vicinity of dislocation lines, forming Cottrell atmospheres through elastic interaction with these lines. These atmospheres pin dislocation movement, hindering slip and resulting in a decrease in plastic deformation capacity and impact performance due to strain aging. Therefore, it is necessary to add certain nitride-forming elements such as Nb, V, Ti, and Al to form stable nitrides. In this invention, the N content is controlled at ≤0.004%, and (Nb+V+Ti+Als) / N≥35.

[0019] Niobium (Nb) is an important element in controlled-rolled and controlled-cooled steel. As a strong carbide-forming element, niobium forms NbC and NbN two-phase particles with C and N, which are crucial elements in controlled-rolled and controlled-cooled steel, effectively refining grains and thus simultaneously improving strength and low-temperature impact toughness. The combined addition of Nb and Mn effectively suppresses austenite recovery and recrystallization during rolling. On one hand, it increases the austenite recrystallization temperature, thereby increasing the rolling temperature and reducing the load on the rolling mill; on the other hand, it effectively refines the phase transformation structure of the steel plate, thus simultaneously improving strength and low-temperature impact toughness. Nb can increase the solid solution content of rare earth elements in steel, thereby improving the corrosion resistance of the steel. In this invention, its content is controlled at 0.035%-0.040%, and (Nb+V+Ti) / Mn≥0.06.

[0020] V: V has a strong affinity for both O and N, and is a strong carbide-forming element. Generally, V(CN) has a high dispersion and is extremely stable, so it is beneficial for deoxidation and degassing to obtain a dense and fine-grained structure, improving plasticity, toughness and high strength. Its impact performance and aging performance are higher than those of vanadium-free steel. V can increase the solid solution content of rare earth elements in steel, thereby improving the corrosion resistance of steel. In this invention, its content is controlled at 0.045%-0.055%.

[0021] Ti: Titanium has a strong affinity for nitrogen, oxygen, and carbon, and its affinity for sulfur is stronger than that for iron. Therefore, it is an excellent deoxidizer and degassing agent, and an effective element for fixing nitrogen and carbon. Trace amounts of Ti can combine with nitrogen in steel to form TiN, preventing the growth of austenite grains during homogenization. Titanium carbide and titanium nitride have strong, stable, and non-decomposing bonds, and only slowly dissolve into the solid solution in steel when heated to above 1000℃, thus significantly controlling the strain aging sensitivity of steel. Before dissolving, titanium carbide particles inhibit grain growth. Because titanium fixes nitrogen and sulfur and forms titanium nitride, the plasticity and impact toughness of steel are significantly improved. Ti can increase the solid solution content of rare earth elements in steel, thereby improving the corrosion resistance of steel. Ti has a nitrogen-fixing effect, eliminating free nitrogen in steel and ensuring that boron exists in solid solution form. When the content of strong carbide elements (such as Ti and Zr) is more than 8 times the carbon content, almost all the carbon in the steel can be fixed, giving the steel excellent resistance to strain aging. The content of the present invention is controlled at 0.025%-0.035%, Ti / N≥6.5, (Ti+Zr) / C≥2.

[0022] Cu: Copper is the most important and widely used alloying element in corrosion-resistant steel. Copper can activate the cathode, promote anodic passivation, and slow down corrosion. During corrosion, a copper-rich phase forms on the surface of the steel. Between the corrosion layer and the copper-rich layer, there is a dense and strongly adherent intermediate layer, which further alleviates corrosion. In particular, when used in combination with phosphorus, it can significantly improve the resistance to marine atmospheric corrosion and seawater corrosion. Copper can significantly synergistically interact with boron to further inhibit the formation of ferrite before bainite transformation. At the same time, copper can accelerate the high-temperature strain-induced precipitation of niobium carbonitride and raise the recrystallization stopping temperature, which is beneficial for controlled rolling in the non-recrystallization zone to refine the phase transformation products. Therefore, the range of Cu controlled in this invention is 0.35%-0.40%, and 180 < Cu / B < 300.

[0023] Zirconium (Zr) is a strong carbide-forming element that can form stable zirconium carbide (ZrC), inhibiting grain growth and refining the grain structure of steel. This helps improve the strength, toughness, and low-temperature performance of steel. Zirconium can effectively remove gaseous impurities such as hydrogen and nitrogen from steel, reducing porosity and inclusions, improving the purity of steel, and enhancing its mechanical properties and strain-aging properties. The grain-refining and impurity-reducing effects of zirconium allow steel to maintain good toughness at low temperatures, lower the brittle transition temperature, and improve corrosion resistance, making it suitable for low-temperature engineering structural materials in marine environments. The addition of zirconium also improves the plasticity and work-hardening properties of steel, making it less prone to cracking during stamping and improving the quality and production efficiency of stamped parts. In this invention, its content is controlled at 0.10%-0.14%.

[0024] Co (Co) is a weak carbide-forming element, primarily acting as a solid solution strengthening element in steel, imparting hardness and improving its high-temperature performance, oxidation resistance, and corrosion resistance. Co can make the distribution of precipitates more dispersed, thereby enhancing the precipitation strengthening effect. Co strengthens ferrite; its addition to carbon steel increases hardness, yield point, and tensile strength, but negatively impacts elongation and reduction of area. Impact toughness also decreases with increasing cobalt content; therefore, excessive cobalt should be avoided. In this invention, its content is controlled at 0.05%-0.08%.

[0025] B: Boron strengthens grain boundaries because its segregation at these boundaries reduces lattice vacancies and voids, lowering the grain boundary free energy. Boron also slows the diffusion of alloying elements along grain boundaries. It reduces precipitates along grain boundaries, improving the grain boundary condition. Adding trace amounts of boron, zirconium, or a combination of boron and zirconium can delay crack formation at grain boundaries. Nb, Cu, and B have strong interactions; their combined addition can raise the recrystallization temperature of steel to over 950°C, significantly altering the bainitic transformation temperature and ensuring a more complete bainitic transformation. Due to size effects, Nb and B atoms tend to segregate at grain boundaries, greatly hindering the nucleation of new phases at these boundaries. This causes a significant rightward shift of the proeutectoid ferrite region, ensuring a uniform bainitic structure over a wide temperature range. Ti is used to fix N in the steel, allowing B to dissolve in the steel. In this invention, B is controlled within the range of 0.0012%-0.0020%, with 15 < Nb / B < 35.

[0026] Al: Aluminum is mainly used for deoxidation and grain refinement. Aluminum reacts with nitrogen or oxygen to form effective fine dispersions, inhibiting grain growth and thus improving the strength and toughness of steel. Aluminum can inhibit the aging of low-carbon steel, allowing it to be stored for a long time after precision rolling without strain aging. Aluminum enhances the corrosion resistance of steel by forming a strong alumina layer on the surface, improving its oxidation resistance and resistance to corrosion in oxidizing acids and H2S gas. However, excessive aluminum content can lead to abnormal structures and promote graphitization. In ferritic and pearlitic steels, high aluminum content reduces their high-temperature strength and toughness. In this invention, the Al content is controlled at 0.025%-0.030%.

[0027] Hf: Hf is one of the more important elements for improving the low-temperature toughness and aging properties of steel. Compared with other microalloying elements, Hf has a stronger affinity for C and N, forming stable and insoluble fine HfC and HfN dispersed precipitates at high temperatures. These precipitates are distributed as dispersed particles within the grains, achieving ultrafine second-phase strengthening, thereby improving the strength and low-temperature toughness of the steel. The combined addition of Hf with Ce, B, and Ti elements better inhibits austenite grain growth and promotes the formation of ultrafine grains than adding them alone. The combination of Hf+Ce+Ti can remove all free N elements from the solid solution, further reducing the ductile-brittle transition temperature and improving the low-temperature strain-aging toughness of the steel plate. In this invention, the range of Hf is controlled to be 0.03%-0.05%, and 20 < (Hf+Ce+Ti) / N < 40.

[0028] Sn and Sb: At austenitic temperatures, antimony (Sb) in steel precipitates at MnS inclusions and along the original austenite grain boundaries, thus inhibiting the enrichment and precipitation of MnS inclusions at the grain boundaries. Antimony can also refine the grain size of secondary recrystallization, refining the steel's microstructure and improving its toughness, thereby enhancing the steel's corrosion resistance. Sn and Sb contribute to improving the corrosion resistance of materials; both adding Sn alone and adding Sn and Sb in combination significantly improve the corrosion resistance of the material. Sn and Sb form a corrosion-resistant oxide film of SnO2 and Sb2O5 on the steel surface, which effectively prevents the interaction between the matrix and the corrosive medium, inhibiting the corrosion of the steel in the corrosive medium. Sn and Sb are further hydrated to obtain Sn... 2+ Sb 3+ The precipitates formed in the anodic micro-regions fill corrosion cracks or cavities, enhancing the resistance to corrosion. - The ability to penetrate. Sn and Sb can also penetrate through Cl. - Hydration under environmental media inhibits Fe 3+ Hydrolysis produces H + The process improves the pH value of the corrosion micro-area and alleviates the anodic dissolution process. Sn and Sb act as corrosion inhibitors, altering the anode and cathode reaction processes. In this invention, their contents are controlled at 0.03%-0.05%.

[0029] Cerium (Ce): Forms CeC2 with carbon and CeN with nitrogen, reducing the brittle effects of free carbon and nitrogen on steel, improving the strain aging properties of steel, and preferentially reacting with residual oxygen and sulfur in steel (purifying the molten steel), thus improving the corrosion resistance of steel. Ce compounds (such as Ce2O2S) can act as heterogeneous nucleation sites, inhibiting grain boundary migration, hindering grain growth, promoting austenite grain refinement, and improving the strength and toughness of steel. In this invention, its content is controlled at 0.035%-0.045%.

[0030] A method for manufacturing a high-strength, corrosion-resistant marine engineering steel plate with good strain aging properties, comprising the following steps: steelmaking, continuous casting, rolling, and slow cooling by stacking. Specific steps include:

[0031] I. Steelmaking process: Converter + LF + RH;

[0032] 2. The tundish superheating temperature is 25-35℃, the billet pulling speed of continuous casting is controlled at 1.1-1.3 m / min, and the secondary cooling water ratio is 0.90-1.00 m³ / min. 3 / t, ensuring the equiaxed grain ratio of the continuously cast billet is >26.0%, electromagnetic stirring is used at the end of solidification, heavy pressure is applied during continuous casting with a reduction of 12.0-16.0 mm, the continuously cast billet is rapidly cooled, with an initial cooling temperature of 980-1000℃ and a cooling rate of 6.0-9.0℃ / s, after cooling to 620-650℃, it is transferred to a slow cooling pit for slow cooling, and then cooled to below 200℃ at a cooling rate of 25.0-35.0℃ / h; the grain size of the continuously cast billet is not greater than 450μm;

[0033] III. Rolling process:

[0034] 1) Heating: When the furnace temperature is 650-700℃, the billet is preheated in the furnace and held for 1.5-2.5 hours. The first stage heating rate is 6-8℃ / min, and the billet is heated to 950-1000℃ and held for 20-40 minutes. The second stage is rapid heating, with the heating rate controlled at 15-20℃ / min, and the billet is heated to 1180-1200℃ for homogenization and held for 2.0-2.5 hours.

[0035] 2) Rolling: A two-stage rolling process is adopted. After descaling, the billet is rolled directly after exiting the furnace. The first stage rolling temperature is 1120-1160℃, the rolling speed is 0.8-1.2m / s, the reduction per pass of the first three passes is >40mm, and the final rolling temperature is 980-1050℃. During the rolling process, the billet is cooled with mill cooling water between each pass, with a cooling time of 5-8s. The thickness of the billet waiting to be heated is 2.0-2.5 times the thickness of the finished product. The billet waiting to be heated is cooled by water spraying at a cooling rate of 10.0-12.0℃ / s. The second stage rolling temperature is 860-880℃, the rolling speed is 1.8-2.5m / s, and the final rolling temperature is 720-750℃.

[0036] 3) The rolled steel plate adopts the rapid cooling ACC process, with a cooling rate of 12.0-14.0℃ / s and a steel plate reddening temperature of 560-600℃;

[0037] IV. Stacking and slow cooling: After rolling, the product is placed in a slow cooling tank for slow cooling. The temperature of the product entering the tank is not lower than 340℃, and the slow cooling time is not less than 24 hours.

[0038] The steelmaking process described above:

[0039] 1) During the smelting process, the molten iron is first desulfurized and pretreated. After desulfurization, the S content in the molten iron is ≤0.0020%. The furnace top and bottom combined blowing process is adopted. 2-3 minutes before the end of blowing and before tapping, the bottom blowing gas is switched from nitrogen to argon. The entry of converter slag into the ladle is strictly controlled. During the tapping process, the steel is tapped with a long nozzle and sealed with argon. The tapping temperature of the converter is 1630-1640℃. After that, the Si-Ca wire is fed.

[0040] 2) During the process of steel ladle entering the station, handling and waiting for casting, argon gas is introduced into the top of the steel ladle for sealing protection, and nitrogen is added to isolate it from the air. The FeO+MnO content of the refined steel slag is <1%. When the electrode is heated, the steel slag is ensured to completely cover the electric arc.

[0041] 3) 10-12 minutes before the end of vacuum treatment in the LF furnace, add 20% Ce rare earth alloy 2.25-3.55 kg / t steel to the LF furnace, and then purge with argon for 8-10 minutes; then perform RH treatment for 20-30 minutes, purging with argon throughout the RH treatment, controlling [H] ≤ 1.0 ppm, [O] ≤ 20 ppm, and [N] ≤ 40 ppm in the steel, with a net circulation time of 8-10 minutes before removal. Before the end of RH treatment, add Sb and Sn elements, ensuring that the amount added is 1.25-1.35 times the target control amount.

[0042] Compared with existing technologies, the beneficial effects of this invention are:

[0043] 1) In terms of composition design, low-carbon microalloying is the basic feature. It contains no Ni, Cr, or Mo, but contains small amounts of Zr and Cu. Nb, Ti, and V are microalloyed, and small amounts of rare earth elements Ce and Hf are added in combination. The NbC and NbN two-phase particles formed by Nb with C and N are important elements in controlled-rolling and controlled-cooling steel, effectively refining the grain size and thus simultaneously improving strength and low-temperature impact toughness. The combined addition of Nb and Mn effectively suppresses austenite recovery and recrystallization during rolling. On the one hand, it increases the austenite recrystallization temperature, thereby increasing the rolling temperature and reducing the load on the rolling mill; on the other hand, it effectively refines the phase transformation structure of the steel plate, thus simultaneously improving strength and low-temperature impact toughness. Nb can increase the solid solution content of rare earth elements in the steel, thereby improving the steel's corrosion resistance. C can form strong carbide elements with Nb, V, Ti, and Zr, such as VC, NiC, and TiC, exhibiting the highest stability, melting point, hardness, and wear resistance. Hf has a stronger affinity for C and N, forming stable, insoluble, fine HfC and HfN dispersed precipitates at high temperatures. These precipitates are distributed as dispersed particles within the grains, achieving ultrafine second-phase strengthening and thus improving the steel's strength and low-temperature toughness. The combined addition of Hf with Ce, B, and Ti elements better inhibits austenite grain growth and promotes the formation of ultrafine grains. The combination of Hf+Ce+Ti can remove all free N elements from the solid solution, further reducing the ductile-brittle transition temperature and improving the low-temperature strain-aging toughness of the steel plate.

[0044] 2) In terms of production process, to control the content of equiaxed crystals in the continuously cast billet, the superheating temperature of the tundish is 25-35℃. Lower superheating can reduce the solidification time of the molten steel and decrease the segregation of elements such as carbon and manganese in the center of the billet, thus reducing defects such as porosity and shrinkage cavities. The billet casting speed is controlled at 1.1-1.3 m / min, and the secondary cooling water ratio is 0.90-1.00 m³ / min.3 / t, to ensure the equiaxed grain ratio of the continuously cast billet is >26.0%, electromagnetic stirring is used at the end of solidification to ensure uniform mixing of the molten steel and achieve high-strength, high-density solidification as quickly as possible. To control the grain size of the continuously cast billet to be no greater than 450μm, the billet is rapidly cooled.

[0045] The heating process employs a three-stage heating method: preheating to release the internal stress of the billet; the first stage involves heating to 950-1000℃; and the second stage involves rapid heating and appropriately extended holding time. This process prevents austenite grain coarsening while allowing alloying elements in the billet to fully diffuse and dissolve, further reducing element segregation.

[0046] The cast billet is rolled into finished steel plate in two stages. In the first stage, a high-temperature, slow-rolling process with a large reduction is used to fully break down the columnar crystals of the continuously cast billet. To suppress grain growth in the intermediate billet, water spray cooling is used on the underheated billet. The second stage has a final rolling temperature of 720-750℃. The relatively low final rolling temperature hinders dislocation movement and prevents them from reorganizing. More dislocations generated during plastic deformation are retained, resulting in a larger number and density of dislocations. This hinders the movement of carbon and nitrogen atoms, reducing their precipitation and aggregation at grain boundaries, thereby reducing the strain aging sensitivity of the steel.

[0047] The rolled steel plate adopts the rapid cooling ACC process with a cooling rate of 12.0-14.0℃ / s and a reddening temperature of 560-600℃. This process not only effectively precipitates carbon and nitrogen compounds of Nb / Ti in the steel, but also inhibits the growth of precipitated phases. While reducing the solid solution content of carbon and nitrogen interstitial atoms, it also fully refines the grains and increases the grain boundary area, avoiding the aggregation of carbon and nitrogen due to aging precipitation. As a result, good low-temperature toughness and low strain aging sensitivity are obtained.

[0048] 3) The comprehensive mechanical properties of the steel plate of this invention are as follows: yield strength 490-550MPa, tensile strength 560-650MPa, elongation ≥28%, impact energy at -60℃ ≥220J, and corrosion rate ≤0.08mm / a. After aging treatment with 12% pre-strain and 250℃ for 1 hour, the impact energy at -60℃ ≥190J, and the strain aging sensitivity coefficient C ≤15%. 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] A high-strength, corrosion-resistant marine engineering steel plate with excellent strain-aging properties, the chemical composition of which is as follows by weight percentage: C: 0.02%-0.05%, Si: 0.10%-0.25%, Mn: 1.35%-1.55%, Nb: 0.035%-0.040%, V: 0.045%-0.055%, Ti: 0.025%-0.035%, Cu: 0.35%-0.40%, Zr: 0.10%-0.14%, Co: 0.05%-0.08%, Sn: 0.03%-0.05%, Sb: 0.03%-0.05%, B: 0.001 2%-0.0020%, Als: 0.025%-0.030%, Hf: 0.03%-0.05%, Ce: 0.035%-0.045%, S≤0.003%, P≤0.01%, N≤0.004%, 4≤Si / Al≤9, (Nb+V+Ti+Als) / N≥35, (Nb+V+Ti) / Mn≥0.06, Ti / N≥6.5, (Ti+Zr) / C≥2, 180<Cu / B<300, 15<Nb / B<35, 20<(Hf+Ce+Ti) / N<40, the remainder being iron and unavoidable impurities.

[0051] A method for manufacturing a high-strength, corrosion-resistant marine engineering steel plate with good strain aging properties, comprising the following steps: steelmaking, continuous casting, rolling, and slow cooling by stacking. Specific steps include:

[0052] 1. Steelmaking process:

[0053] 1) During converter smelting, the content of elements such as Si, O, P, S, and N is adjusted to be within the range of this invention. The molten iron is pre-treated for desulfurization during the smelting process, resulting in S ≤ 0.0020% in the desulfurized iron. A combined top-bottom blowing process is adopted. In the later stages of blowing (2-3 minutes before the end point) and before tapping, the bottom blowing gas is switched from nitrogen to argon. The tapping spout is kept smooth and round to reduce steel flow dispersion and gas absorption during tapping. Strict control is exercised over converter slag entering the ladle, as a large amount of slag significantly increases the risk of nitrogen absorption in subsequent refining processes (FeO and MnO in the slag promote nitrogen absorption). During tapping, a long nozzle with argon sealing is used to prevent nitrogen accumulation. The converter tapping temperature is 1630-1640℃, followed by Si-Ca wire feeding treatment, with the Ca content controlled at 0.0015%-0.0025%.

[0054] 2) During the refining of molten steel, the ladle must be sealed with a sufficient and stable amount of argon gas during its entry into the station, processing, and while awaiting casting, to prevent nitrogen addition. A low-oxidizing (FeO+MnO content <1%), high-basicity, and well-flowing refining slag should be quickly prepared to cover the molten steel and reduce its contact with air. During electrode heating, the slag must completely cover the electric arc to prevent nitrogen absorption by the arc ionization. Alloys should be added after the reducing atmosphere has stabilized, avoiding the addition of large amounts of moist or nitrogen-containing alloys (such as nitrogen-added ferrochrome or nitrogen-containing ferromanganese). The content of other alloying elements such as Co and Zr should be adjusted to within the range specified in this invention.

[0055] 3) 10-12 minutes before the end of vacuum treatment in the LF furnace, add 20% cerium rare earth alloy 2.25-3.55 kg / t steel to the LF furnace, and then purge with argon for 8-10 minutes; then perform RH treatment for 20-30 minutes. During RH treatment, purge with argon throughout, and control the [H] in the steel to ≤1.0 ppm, [O] to ≤20 ppm, and [N] to ≤40 ppm. The net circulation time before removal is 8-10 minutes.

[0056] 4) Add Sb and Sn elements before the RH treatment is completed, ensuring that the amount added is 1.25-1.35 times the target control amount, so as to ensure that the endpoint content can be controlled within the target range.

[0057] 2. Continuous casting: Ensure a tight seal at the connection between the long nozzle and the ladle's bottom nozzle (using sealing gaskets and argon gas for sealing). Sufficient argon flow in the long nozzle prevents air intake and nitrogen enrichment. To control the equiaxed crystal content in the continuously cast billet, the tundish superheat is 25-35℃. Lower superheat reduces the solidification time of the molten steel and decreases the segregation of carbon, manganese, and other elements in the center of the billet, reducing defects such as porosity and shrinkage cavities. The billet drawing speed is controlled at 1.1-1.3 m / min, and the secondary cooling water ratio is 0.90-1.00 m³ / t, ensuring the equiaxed crystal ratio of the billet is >26.0%. Electromagnetic stirring is used at the end of solidification to ensure uniform mixing of the molten steel and achieve high-strength, high-density solidification as quickly as possible. Heavy reduction is applied during continuous casting, with a reduction of 12.0-16.0 mm. 3. In order to control the grain size of the continuously cast billet to be no more than 450μm, the continuously cast billet is rapidly cooled. The initial cooling temperature is 980-1000℃, the cooling rate is 6.0-9.0℃ / s, and after cooling to 620-650℃, it is placed in a slow cooling pit for slow cooling, and then cooled to below 200℃ at a cooling rate of 25.0-35.0℃ / h.

[0058] 3. Rolling process characteristics

[0059] 1) The continuously cast billet obtained in step 3 is fed into a heating furnace for heating. The heating adopts a three-stage heating process. The billet is preheated in the furnace at a temperature of 650-700℃ and held for 1.5-2.5 hours to release the internal stress of the billet. The first stage heating rate is 6-8℃ / min to heat to 950-1000℃ and held for 20-40 minutes. Then, a rapid heating process with an appropriate extension of the holding time is adopted to prevent the coarsening of austenite grains and to allow the alloying elements in the billet to fully diffuse and dissolve, further reducing element segregation. The second stage heating rate is controlled at 15-20℃ / min and heated to 1180-1200℃ for homogenization and held for 2.0-2.5 hours.

[0060] 2) The billet is rolled into finished steel plate in two stages. In the first stage, to fully break up the columnar crystals of the continuously cast billet, a high-temperature slow rolling process with a large reduction is adopted. After descaling, the billet is directly rolled after exiting the furnace. The initial rolling temperature is 1120-1160℃, the rolling speed is 0.8-1.2m / s, and the reduction in each of the first three passes is >40mm. The final rolling temperature is 980-1050℃. During the rolling process, the billet is cooled with mill cooling water between each pass for 5-8 seconds. The thickness of the billet after cooling is 2.0-2.5 times the thickness of the finished product. To suppress grain growth in the intermediate billet, water spray cooling is used for the underheated billet at a rate of 10.0-12.0℃ / s. The second stage rolling temperature is 860-880℃, the rolling speed is 1.8-2.5m / s, and the final rolling temperature is 720-750℃. The lower final rolling temperature hinders dislocation movement and prevents them from reorganizing. As a result, more dislocations generated during plastic deformation are retained, leading to a larger number and density of dislocations. This hinders the movement of carbon and nitrogen atoms, reducing their precipitation and aggregation at grain boundaries, thereby reducing the strain aging sensitivity of the steel.

[0061] 3) The rolled steel plate adopts the rapid cooling (ACC) process with a cooling rate of 12.0-14.0℃ / s and a steel plate reddening temperature of 560-600℃. This not only effectively precipitates the carbon and nitrogen compounds of Nb / Ti in the steel, but also inhibits the growth of the precipitated phase. While reducing the solid solution content of carbon and nitrogen interstitial atoms, it also fully refines the grains, increases the grain boundary area, and avoids the aggregation of carbon and nitrogen due to aging precipitation. As a result, good low-temperature toughness and low strain aging sensitivity are obtained.

[0062] 4. Stacking and slow cooling: After rolling, the product is placed in a slow cooling tank for slow cooling. The temperature of the product entering the tank is not lower than 340℃, and the slow cooling time is not less than 24 hours.

[0063] To make the objectives, technical solutions, and technical effects of this invention clearer, the technical solutions in the embodiments of this invention are now described clearly and completely. However, the embodiments described below are only some embodiments of this invention, not all embodiments. All other embodiments obtained by those skilled in the art in conjunction with the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0064] The chemical composition of the embodiments is shown in Tables 1-1 and 1-2, the rolling process parameters of the present invention are shown in Tables 2-5, and the steel plate properties are shown in Table 6.

[0065] Table 1-1 Components (%) of each embodiment

[0066]

[0067] Table 1-2 Components (%) of Each Example

[0068]

[0069] Table 2 Steelmaking Process Parameters

[0070]

[0071] Table 3 Continuous Casting Process Parameters

[0072]

[0073] Table 4 Heating process parameters

[0074]

[0075] Table 5-1 Rolling process parameters

[0076]

[0077] Table 5-2 Rolling process parameters

[0078]

[0079] Table 6 Steel Plate Properties

[0080]

[0081] 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, corrosion-resistant marine steel plate with good strain aging properties, characterized in that, The chemical composition of the steel plate, by weight percentage, is as follows: C: 0.02%-0.05%, Si: 0.10%-0.25%, Mn: 1.35%-1.55%, Nb: 0.035%-0.040%, V: 0.045%-0.055%, Ti: 0.025%-0.035%, Cu: 0.35%-0.40%, Zr: 0.10%-0.14%, Co: 0.05%-0.08%, Sn: 0.03%-0.05%, Sb: 0.03%-0.05%, B: 0.0012%-0.0020%. Als: 0.025%-0.030%, Hf: 0.03%-0.05%, Ce: 0.035%-0.045%, S≤0.003%, P≤0.01%, N≤0.004%, 4≤Si / Al≤9, (Nb+V+Ti+Als) / N≥35, (Nb+V+Ti) / Mn≥0.06, Ti / N≥6.5, (Ti+Zr) / C≥2, 180<Cu / B<300, 15<Nb / B<35, 20<(Hf+Ce+Ti) / N<40, the remainder being iron and unavoidable impurities; The comprehensive mechanical properties of the steel plate are as follows: yield strength 490-550MPa, tensile strength 560-650MPa, elongation ≥28%, impact energy at -60℃ ≥220J, and corrosion rate ≤0.08mm / a.

2. The high-strength corrosion-resistant marine steel plate with good strain aging properties according to claim 1, characterized in that, The thickness of the finished steel plate is 20-100mm.

3. The method for manufacturing a high-strength corrosion-resistant marine steel plate with good strain aging properties according to claim 1, characterized in that, The process steps include steelmaking, continuous casting, rolling, and slow cooling by stacking. Specific steps include: I. Steelmaking process: Converter + LF + RH; 2. The tundish superheating temperature is 25-35℃, the billet pulling speed of continuous casting is controlled at 1.1-1.3 m / min, and the secondary cooling water ratio is 0.90-1.00 m³ / min. 3 / t, ensuring the equiaxed grain ratio of the continuously cast billet is >26.0%, electromagnetic stirring is used at the end of solidification, heavy pressure is applied during continuous casting with a reduction of 12.0-16.0 mm, the continuously cast billet is rapidly cooled, with an initial cooling temperature of 980-1000℃ and a cooling rate of 6.0-9.0℃ / s, after cooling to 620-650℃, it is transferred to a slow cooling pit for slow cooling, and then cooled to below 200℃ at a cooling rate of 25.0-35.0℃ / h; the grain size of the continuously cast billet is not greater than 450μm; III. Rolling process: 1) Heating: When the furnace temperature is 650-700℃, the billet is preheated in the furnace and held for 1.5-2.5 hours. The first stage heating rate is 6-8℃ / min, and the billet is heated to 950-1000℃ and held for 20-40 minutes. The second stage is rapid heating, with the heating rate controlled at 15-20℃ / min, and the billet is heated to 1180-1200℃ for homogenization and held for 2.0-2.5 hours. 2) Rolling: A two-stage rolling process is adopted. After descaling, the billet is rolled directly after exiting the furnace. The first stage rolling temperature is 1120-1160℃, the rolling speed is 0.8-1.2m / s, the reduction per pass of the first three passes is >40mm, and the final rolling temperature is 980-1050℃. During the rolling process, the billet is cooled with mill cooling water between each pass, with a cooling time of 5-8s. The thickness of the billet waiting to be heated is 2.0-2.5 times the thickness of the finished product. The billet waiting to be heated is cooled by water spraying at a cooling rate of 10.0-12.0℃ / s. The second stage rolling temperature is 860-880℃, the rolling speed is 1.8-2.5m / s, and the final rolling temperature is 720-750℃. 3) The rolled steel plate adopts the rapid cooling ACC process, with a cooling rate of 12.0-14.0℃ / s and a steel plate reddening temperature of 560-600℃; IV. Stacking and slow cooling: After rolling, the product is placed in a slow cooling tank for slow cooling. The temperature of the product entering the tank is not lower than 340℃, and the slow cooling time is not less than 24 hours.

4. The method for manufacturing a high-strength corrosion-resistant marine steel plate with good strain aging properties according to claim 3, characterized in that, The steelmaking process described above: 1) During the smelting process, the molten iron is first desulfurized and pretreated. After desulfurization, the S content in the molten iron is ≤0.0020%. The furnace top and bottom combined blowing process is adopted. 2-3 minutes before the end of blowing and before tapping, the bottom blowing gas is switched from nitrogen to argon. The entry of converter slag into the ladle is strictly controlled. During the tapping process, the steel is tapped with a long nozzle and sealed with argon. The tapping temperature of the converter is 1630-1640℃. After that, the Si-Ca wire is fed. 2) During the process of steel ladle entering the station, handling and waiting for casting, argon gas is introduced into the top of the steel ladle for sealing protection, and nitrogen is added to isolate it from the air. The FeO+MnO content of the refined steel slag is <1%. When the electrode is heated, the steel slag is ensured to completely cover the electric arc. 3) 10-12 minutes before the end of vacuum treatment in the LF furnace, add 20% Ce rare earth alloy 2.25-3.55 kg / t steel to the LF furnace, and then purge with argon for 8-10 minutes; then perform RH treatment for 20-30 minutes, purging with argon throughout the RH treatment, controlling [H] ≤ 1.0 ppm, [O] ≤ 20 ppm, and [N] ≤ 40 ppm in the steel, with a net circulation time of 8-10 minutes before removal. Before the end of RH treatment, add Sb and Sn elements, ensuring that the amount added is 1.25-1.35 times the target control amount.

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