High-strength marine plate resistant to marine bio-corrosion and manufacturing method

Abstract

The application belongs to the field of metal material production and specifically relates to a high-strength ship plate resistant to marine organism corrosion and a manufacturing method, wherein the composition is in percentage by weight: C: 0.030-0.120%, Si: 0.050-0.250%, Mn: 0.80-1.30%, P: 0.006-0.020%, S<=0.005%, Nb: 0.040-0.080%, V: 0.050-0.150%, N: 0.0220-0.0280%, Cu: 1.00-2.00%, Ni: 1.00-2.00%, Cr: 0.50-1.00%, Ti: 0.006-0.030%, Als: 0.020-0.050%, Sb: 0.20-0.70%, Sn: 0.20-0.70%, and the balance is Fe. The ship plate has excellent marine organism corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of metal material production technology, and in particular relates to a high-strength ship plate resistant to marine organism corrosion and its manufacturing method. Background Technology

[0002] Ships operate in the marine environment, enduring harsh conditions such as wind, waves, rain, snow, and low temperatures over extended periods, requiring marine steel to possess excellent strength and toughness. Furthermore, the corrosive effects of the marine environment significantly impact a ship's service life, particularly the corrosion caused by marine organisms. This biofouling has received increasing attention in recent years. Biofouling is primarily localized, and its occurrence and development are unpredictable in time and space, leading to increasingly prominent safety issues. For ships, marine organisms adhering to the hull surface significantly increase surface friction, resulting in increased fuel consumption and decreased speed. Therefore, developing marine steel resistant to biofouling is the optimal technical solution to address the adverse effects of marine organisms.

[0003] Currently, for ship steels resistant to marine organism corrosion, specific element combinations are often added to improve their resistance. Patent application number CN202011054693.4 discloses a corrosion-resistant and biofouling-resistant EH690 steel plate and its manufacturing method. Its chemical composition is: C: 0.09%-0.12%, Si: 0.15%-0.35%, Mn: 1.0%-1.5%, P: 0.02%-0.03%, S≤0.01%, Als: 0.01%-0.03%, Ni: 1.5%-3.0%, Cr: 0.3-0.6%, Mo: 0.3-0.5%, Cu: 0.5-1.5%, V: 0.03%-0.06%. The steel plate contains 0.005%-0.02% Ti, 0.0005%-0.001% B, 0.005%-0.3% Sb, and 0.005%-0.3% Sn, with the balance being iron and unavoidable impurities. The production process is as follows: first-stage rolling temperature 1000-1050℃, second-stage rolling temperature 900-1000℃, final rolling temperature 900-950℃, quenching temperature 830-870℃, holding time 1.0-2.0 min / mm, tempering temperature 600-630℃, holding time 2-3 min / mm, and tempering cooling rate 5-15℃ / s. This steel plate exhibits excellent resistance to marine corrosion; however, the process employs a quenching and tempering technique, which is complex and increases production costs. Patent application CN202210685312.5 discloses a 960MPa grade ultra-high strength steel plate with resistance to marine organism adhesion and its manufacturing method. Its chemical composition is: C: 0.03%-0.12%, Si: 0.05%-0.20%, Mn: 0.50-2.00%, P≤0.015%, S≤0.005%, Cu: 1.60-3.00%, Cr: 0.10%-1.00%, Ni: 2.0%-6.0%, Mo: 0.10%-1.00%, Nb≤0.10%, V≤0.10%, Ti≤0.02%, Al≤0.04%, with the balance being Fe and unavoidable impurities. This patent uses the TMCP process, eliminating the need for post-rolling reheating, resulting in steel plates with good mechanical properties and resistance to marine organism adhesion. However, the high content of precious metals such as Ni and Mo in its chemical composition inevitably increases its production cost.Patent application number CN202210139047.0 discloses a copper-containing low-alloy steel resistant to marine biological corrosion and its preparation method. Its chemical composition is: Cu: 0.9%-1.1%, Mo: 0.20-0.40, V: 0.06-0.12, Ti: 0.04-0.08, Cr: 0.7-1.2, Ni: 0.8-1.2, C: 0.03-0.08, Mn: 0.35-0.65, Si: 0.25-0.35, S≤0.010, P≤0.02, N≤0.0020, with the remainder being Fe. Its KV2 (-40℃) impact energy is greater than or equal to 100J, and its elongation is ≥25%. It has the ability to resist marine microbial corrosion, but its impact toughness is low and its resistance to marine biological corrosion is insufficient, which cannot meet the requirements of high-tech ships.

[0004] In summary, the production of high-strength ship plates resistant to marine organism corrosion currently faces the following problems.

[0005] 1) The production process of steel plates is complex, the production cycle is long, and the production cost is relatively high;

[0006] 2) The steel plate contains expensive alloying elements, resulting in higher production costs;

[0007] 3) The mechanical properties and resistance to marine biological corrosion of the steel plates are insufficient, which cannot meet the requirements for use in high-tech ships. Summary of the Invention

[0008] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a high-strength ship plate with reasonable composition design and simple manufacturing process, as well as a method for manufacturing it. The invention improves the low-temperature toughness of the steel by designing the chemical composition, thereby enhancing its resistance to marine environments and marine biological corrosion. Optimizing continuous casting, rolling and other processes improves the mechanical properties and resistance to marine biological corrosion of the steel plate.

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

[0010] A high-strength ship plate resistant to marine organism corrosion, the composition of which is as follows by weight percentage:

[0011] C: 0.030%~0.120%, Si: 0.050%~0.250%, Mn: 0.80%~1.30%, P: 0.006%~0.020%, S≤0.005%, Nb: 0.040%~0.080%, V: 0.050%~0.150%, N: 0.0220%~0.0280%, Cu: 1.00%~2.00%, Ni: 1.00%~2.00%, Cr: 0.50%~1.00%, Ti: 0.006%~0.030%, Als: 0.020%~0.050%, Sb: 0.20%~0.70%, Sn: 0.20%~0.70%, balance Fe and unavoidable impurities.

[0012] The metallographic structure of the ship plate is ferrite + bainite, and the proportion of ferrite is ≤10% by area ratio.

[0013] The role of each chemical component in this invention will be described in detail below.

[0014] C: An important strengthening element in steel, in this invention it is the main element for controlling the microstructure of the steel plate, optimizing the precipitation of microalloying elements, and ensuring the strength and hardness of the rolled steel plate. A low content will reduce the formation of carbides, affecting the grain refinement effect during rolling. A high content will increase the cementite content in the steel, which is detrimental to the low-temperature toughness, corrosion resistance, and weldability of the steel plate. Therefore, considering factors such as cost and performance, the range of C is controlled to be 0.030%~0.120%.

[0015] Si (Si): It can improve the strength and hardness of steel and plays a deoxidizing role in the steelmaking process. However, excessive Si content can increase the ductile-brittle transition temperature, reduce the low-temperature toughness of the steel plate, and affect its surface quality. Considering factors such as cost and performance, the Si content is controlled within the range of 0.050% to 0.250%.

[0016] Mn (Mn): An element that expands the austenite phase region, forming substitutional solid solutions in steel. It can dissolve extensively in the Fe matrix, improving steel strength through solid solution strengthening and positively impacting grain refinement. It can also delay the ferrite-pearlite transformation in steel, significantly increasing hardenability, lowering the ductile-brittle transition temperature, altering impact toughness, eliminating the influence of sulfur (S), and improving hot workability. However, excessive Mn content can easily lead to segregation in steel, negatively affecting both plasticity and toughness. Considering all factors, the Mn content should be controlled within the range of 0.80% to 1.30%.

[0017] P: Improves the corrosion resistance of steel in marine environments. When coexisting with Cu, it can form various complex salts, resulting in finer and denser grains in the inner rust layer, which can resist the damage of Cl- and reduce the corrosion rate of the steel. However, excessive P content is detrimental to the low-temperature toughness and weldability of the steel. Therefore, the range of P should be controlled between 0.006% and 0.020%.

[0018] Nitrogen (Nb): A grain-refining element. When heated, undissolved Nb carbon and nitride particles are distributed along the austenite grain boundaries, hindering austenite grain growth during heating. Upon cooling, it effectively delays the recrystallization of deformed austenite, preventing austenite grain growth and refining ferrite grains, thus improving both the strength and toughness of the steel. Therefore, the range of Nb content should be controlled between 0.040% and 0.080%.

[0019] Vanadium (V): A key strengthening and toughening element in this invention, it has a strong affinity for nitrogen and carbon, and is a potent carbide and nitride forming element, capable of forming extremely stable carbonitrides. In steel, it improves strength through grain refinement, precipitation strengthening, and solid solution strengthening. As the V content increases, the ductile-brittle transition temperature of the steel decreases. However, excessively high V content can actually increase the ductile-brittle transition temperature. Vanadium carbonitrides can precipitate at relatively low temperatures, hindering dislocation movement and thus playing a strengthening and toughening role, significantly improving the overall mechanical properties of the steel plate. Considering all factors, the V content is controlled within the range of 0.050% to 0.150%.

[0020] Nitrogen (N): Another important strengthening and toughening element in this invention. The addition of nitrogen promotes the formation of a large amount of vanadium (CN) in the steel, thereby refining its grains and improving its plasticity and toughness. Nitrogen-containing steel not only eliminates the cost increase caused by degassing and refining denitrification during steelmaking, but also allows the addition of nitrogen to fully utilize the role of microalloying elements, saving the amount of alloying elements used, thus greatly reducing production costs. The addition of nitrogen can partially replace the role of carbon (C), reducing the carbon equivalent of the steel and thus improving its weldability. Considering both performance and cost, the range of nitrogen is controlled at 0.0220%~0.0280%.

[0021] Cu (Cu) can improve the stability of austenite in steel, increase its hardenability, and, when added in appropriate amounts, enhance its strength, plasticity, and low-temperature toughness. During low-temperature treatment, it can produce ε-Cu precipitation, thereby increasing the steel's strength. Cu can effectively improve the corrosion resistance of steel under reducing atmospheres and also effectively inhibit the growth and adhesion of microorganisms. However, excessively high content can worsen the hot brittleness of steel and easily lead to hot cracking. Therefore, the Cu content should be controlled within the range of 1.00% to 2.00%.

[0022] Ni has no adverse effects on the hardening and toughness of the weld heat-affected zone of steel, and can improve the plasticity and low-temperature toughness of steel. In addition, the addition of Ni can reduce the tendency of hot cracking when the Cu content is high, and also has a beneficial effect on the corrosion resistance of steel plates in marine environments. Taking into account factors such as cost and performance, the range of Ni is controlled at 1.00%~2.00%.

[0023] Cr: increases the hardenability of steel and has a secondary hardening effect. It can improve the strength, hardness and wear resistance of steel. It can form a dense oxide film on the steel surface and has a positive effect on the seawater corrosion resistance of steel plates. However, if the content is too high, it will be detrimental to the low temperature toughness and weldability of steel plates. The range of Cr should be controlled at 0.50%~1.00%.

[0024] Ti (TiO2) exhibits strong precipitation strengthening, increasing the strength of steel and preventing austenite recrystallization. Simultaneously, it refines the grain size, improving the yield strength of the steel. The high dissolution temperature of Ti carbides and nitrides inhibits austenite grain growth during heating, thus refining the grain size of the steel plate, improving its strength and toughness, and promoting the overall mechanical properties of the steel plate. Considering all factors, the Ti content should be controlled within the range of 0.006% to 0.030%.

[0025] Al: A strong deoxidizer in steel. Adding a small amount can generate highly fine, ultramicroscopic oxides, which has a beneficial effect on improving the purity of the steel. Therefore, the range of Al is controlled to be 0.020%~0.050%.

[0026] Sb generally has a negative impact on the mechanical properties of steel, reducing its strength and increasing its brittleness. However, adding a certain amount of antimony to steel can improve its corrosion resistance and wear resistance to varying degrees. When added in combination with Sn, Sn accumulates and Sb is evenly distributed in the rust layer of the steel, forming a SnO2-Sb2O5 corrosion-resistant oxide film on the steel surface. This film can enhance the ability to block Cl- penetration, thereby further improving the corrosion resistance of the steel. Therefore, the range of Sb should be controlled between 0.20% and 0.70%.

[0027] Sn: Similar to Sb, adding an appropriate amount can improve the corrosion resistance of steel and inhibit the attachment of marine organisms. When added in combination with Sb, it can further improve the corrosion resistance of steel. Therefore, the range of Sn should be controlled at 0.20%~0.70%.

[0028] The ship plate has a yield strength of 570~620MPa, a tensile strength of 630~710MPa, an elongation after fracture of ≥24.0%, and an impact absorption energy of ≥200J at -60℃; the bio-attachment rate of the steel plate is ≤8.0% after 12 months and ≤11.5% after 24 months.

[0029] A method for manufacturing high-strength ship plates resistant to marine organism corrosion includes smelting, continuous casting, furnace heating, rolling, online accelerated cooling, and tempering heat treatment, as detailed below:

[0030] 1) Smelting:

[0031] a) Adjust the content of C, Si, Mn, P and S elements during converter smelting and add other alloying components for melting;

[0032] b) Refine the molten steel and adjust the content of other alloying elements;

[0033] c) The refined molten steel is subjected to RH treatment for 40-60 minutes. Nitrogen is blown throughout the RH treatment process at a pressure of 600-620 Pa to ensure that the final N content is within the set range and to control [H] ≤ 1.5 ppm and [O] ≤ 10 ppm in the steel.

[0034] 2) Continuous casting:

[0035] Step 1) The obtained molten steel is continuously cast to obtain the required billet. During continuous casting, a high superheat is used in the tundish, and the superheat is controlled at 40~60℃. Superheat protection is maintained throughout the casting process. The billet pulling speed is controlled at 0.50~1.00m / min, and the secondary cooling water ratio is 0.50~0.80m³. 3 / t, electromagnetic stirring is used during continuous casting with a stirring current of 450~550A, and a light reduction process is used at the end of continuous casting with a reduction of 10.0~15.0mm;

[0036] To control the grain size of the continuously cast billet, the billet is rapidly cooled with a starting temperature of 950~1050℃ and a final cooling temperature of 800~850℃, followed by slow cooling by stacking with a starting temperature of 750~780℃ and a slow cooling time of ≥36h.

[0037] 3) Heating in a heating furnace:

[0038] The billet is heated to 1100~1250℃ and held for 0.5~1.5h, with a total furnace time of 4.0~6.0h;

[0039] 4) Rolling:

[0040] The cast billet is rolled into hot-rolled steel plate in two stages:

[0041] In order to fully break down the columnar crystals of the continuously cast billet and prepare for subsequent grain refinement, the first stage adopts high-temperature fast rolling + large reduction. After the billet is descaled after exiting the furnace, it is heated to 950~1000℃ and then rolled. The roll speed is controlled at 1.00~2.00m / s, the first reduction is 40~50mm, the final rolling temperature is 880~920℃, and the thickness of the billet after heating is (1.5~2.5)t, where t is the final product thickness.

[0042] The second stage rolling temperature is 770~820℃, and the final rolling temperature is 700~750℃.

[0043] 5) Online accelerated cooling:

[0044] To maintain fine grains after rolling and prevent grain growth, the rolled steel plate is subjected to ultra-fast cooling (UFC cooling) with a cooling rate of 10.0~25.0℃ / s and a reddening temperature of 350~450℃.

[0045] 6) Slow cooling:

[0046] In order to release the internal stress formed during the rolling and cooling process of steel plates and to further form fine precipitates, the cooled steel plates are stacked for slow cooling at a stacking temperature of 200~300℃ and a stacking time of ≥20h.

[0047] 7) Tempering heat treatment:

[0048] The stacked steel plates are then tempered at a temperature of 400-600℃ for 2.5-5.0 min / mm.

[0049] Compared with the prior art, the beneficial effects of the present invention are:

[0050] This invention employs a low-carbon chemical composition system to improve the low-temperature toughness of steel, and adds grain-refining elements such as Nb, VN, and Ti to promote the formation of ferrite in the steel. Ni, Cr, Sb, Sn, and P are used to enhance corrosion resistance in marine environments, and Cu is added to improve the steel plate's resistance to marine organism adhesion, further enhancing its resistance to marine bio-corrosion. The continuous casting process uses high superheat + strong secondary cooling water + electromagnetic stirring + light pressure to control center segregation in the billet and obtain fine initial austenite grains. The continuously cast billet uses a rapid cooling + stacking slow cooling process to control grain growth and adjust the precipitated phases. The rolling process employs a two-stage controlled rolling TMCP process + offline tempering process, resulting in a steel plate with excellent mechanical properties and resistance to marine bio-corrosion. The metallographic structure of the steel plate is ferrite + bainite, with ferrite content ≤10%, yield strength of 570-620MPa, tensile strength of 630~710MPa, elongation after fracture ≥24.0%, and impact absorption energy at -60℃ ≥200J; the bio-adhesion rate of the steel plate is ≤8.0% after 12 months and ≤11.5% after 24 months. Attached Figure Description

[0051] Figure 1 This is a metallographic diagram of a high-strength ship plate resistant to marine organism corrosion. Detailed Implementation

[0052] The present invention will be described in more detail below through embodiments. These embodiments are merely descriptions of the best implementation of the present invention and do not limit the scope of the present invention in any way.

[0053] Smelting was carried out according to the chemical composition range designed according to the present invention. The chemical composition is shown in Table 1. The metallographic structure of the ship plate is shown in Table 1. Figure 1 The molten steel obtained is continuously cast, heated, rolled and cooled to obtain the steel plate of the present invention. The smelting process is shown in Table 2, the heating process is shown in Table 3, the rolling process is shown in Table 4 and the cooling process is shown in Table 5.

[0054] Table 1. Smelting process and chemical composition (wt%) of the steel in the examples

[0055]

[0056] Table 2. Steelmaking process in the examples

[0057]

[0058] Table 3. Casting billet cooling and reheating process

[0059]

[0060] Table 4. Rolling process of steel in the examples

[0061]

[0062] Table 5. Cooling and heat treatment processes for the steel in the examples.

[0063]

[0064] Mechanical properties and resistance to marine biological corrosion of the steel in the embodiments of the present invention were tested, and the results are shown in Table 6.

[0065] Table 6 Mechanical properties and resistance to marine bio-corrosion of the steels in the examples.

[0066] .

Claims

1. A high-strength ship plate resistant to marine organism corrosion, characterized in that, The composition of the ship plate, by weight percentage, is as follows: C: 0.030%~0.120%, Si: 0.050%~0.250%, Mn: 0.80%~1.30%, P: 0.006%~0.020%, S≤0.005%, Nb: 0.040%~0.080%, V: 0.050%~0.150%, N: 0.0220%~0.0280%, Cu: 1.00%~2.00%, Ni: 1.00%~2.00%, Cr: 0.50%~1.00%, Ti: 0.006%~0.030%, Als: 0.020%~0.050%, Sb: 0.20%~0.70%, Sn: 0.20%~0.70%, balance Fe and unavoidable impurities.

2. The high-strength ship plate resistant to marine organism corrosion according to claim 1, characterized in that, The metallographic structure of the ship plate is ferrite + bainite, and the proportion of ferrite is ≤10% by area ratio.

3. The high-strength ship plate resistant to marine organism corrosion according to claim 1, characterized in that, The ship plate has a yield strength of 570~620MPa, a tensile strength of 630~710MPa, an elongation after fracture of ≥24.0%, and an impact absorption energy of ≥200J at -60℃; the bio-attachment rate of the steel plate is ≤8.0% after 12 months and ≤11.5% after 24 months.

4. A method for manufacturing a high-strength ship plate resistant to marine organism corrosion as described in any one of claims 1-3, characterized in that, This includes smelting, continuous casting, furnace heating, rolling, online accelerated cooling, and tempering heat treatment, as detailed below: 1) Smelting: To obtain molten steel with a chemical composition within a specified range; 2) Continuous casting: Step 1) The molten steel obtained is continuously cast to obtain the required billet. During continuous casting, the superheat of the tundish is controlled at 40~60℃, and the superheat is maintained throughout the casting process. The billet pulling speed is controlled at 0.50~1.00m / min, and the secondary cooling water ratio is 0.50~0.80m³. 3 / t, electromagnetic stirring is used during continuous casting with a stirring current of 450~550A, and a light reduction process is used at the end of continuous casting with a reduction of 10.0~15.0mm; The continuously cast billet is rapidly cooled at a starting temperature of 950~1050℃ and a final cooling temperature of 800~850℃. It is then stacked for slow cooling at a starting temperature of 750~780℃ and a slow cooling time of ≥36h. 3) Heating in a heating furnace: The billet is heated to 1100~1250℃ and held for 0.5~1.5h, with a total furnace time of 4.0~6.0h; 4) Rolling: The cast billet is rolled into hot-rolled steel plate in two stages: The first stage adopts a high-temperature fast rolling + large reduction method. After the billet is descaled after being taken out of the furnace, it is heated to 950~1000℃ and then rolled. The roll speed is controlled at 1.00~2.00m / s, the first reduction is 40~50mm, the final rolling temperature is 880~920℃, and the thickness of the billet after heating is (1.5~2.5)t, where t is the final product thickness. The second stage rolling temperature is 770~820℃, and the final rolling temperature is 700~750℃. 5) Online accelerated cooling: The rolled steel plate is cooled by ultra-fast cooling at a rate of 10.0~25.0℃ / s, and the red-hot temperature is 350~450℃. 6) Slow cooling: After cooling, the steel plates are stacked for slow cooling at a temperature of 200~300℃ for a time of ≥20h. 7) Tempering heat treatment: The stacked steel plates are then tempered at a temperature of 400-600℃ for 2.5-5.0 min / mm.

5. The method for manufacturing a high-strength ship plate resistant to marine organism corrosion according to claim 4, characterized in that, The specific smelting process in step 1) is as follows: a) Adjust the content of C, Si, Mn, P and S elements during converter smelting and add other alloying components for melting; b) Refine the molten steel and adjust the content of other alloying elements; c) The refined molten steel is subjected to RH treatment for 40-60 minutes. Nitrogen is blown throughout the RH treatment process at a pressure of 600-620 Pa to ensure that the final N content is within the set range and to control [H] ≤ 1.5 ppm and [O] ≤ 10 ppm in the steel.

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