Collision-resistant steel for ship hull structure and its manufacturing method

Abstract

A steel for a ship hull structure with impact breakage resistance is disclosed. In addition to Fe and inevitable impurities, the steel contains the following chemical elements by mass percentage: C: 0.06 to 0.12%, Si: 0.05 to 0.60%, Mn: 1.30 to 1.70%, Al: 0.01 to 0.06%, Ti: 0.005 to 0.012%, Mg: 0.0005 to 0.003%, and further contains 0 < Ca ≦ 0.004%, and 0.0005% ≦ Ca + Mg ≦ 0.004%. Further, a method for manufacturing a steel for a ship hull structure with impact breakage resistance, comprising: (1) a smelting and continuous casting step, (2) a heating step, (3) a controlled rolling step, (4) an air cooling step, and (5) a normalizing heat treatment step: controlling the normalizing temperature to T q (where [Equation 1] TIFF2024505962000020.tif7156, and each chemical element is replaced by the numerical value before the percentage symbol in the content of the chemical element by mass, and the unit of the normalizing temperature is °C), and controlling the holding time to T in minutes h (where T h = 1.5 × t, and t represents the thickness of the steel plate in mm), and a manufacturing method including controlling thereto is further disclosed.

Description

[Technical field]

[0001] The present invention relates to a steel product and a manufacturing method thereof, and more particularly to a steel for ship hull construction and a manufacturing method thereof. [Background technology]

[0002] In recent years, with the rapid development of the Chinese economy, the number of ships has correspondingly increased significantly. Similarly, with the increase in the number of ships, the traffic density will become higher and higher, and the possibility of collisions between ships will also become higher.

[0003] When collision accidents occur to ships, it often leads to disastrous consequences such as damage to the hull structure, cargo leakage, environmental pollution, and casualties. In general, due to the huge mass and kinetic energy of the ship during collision, the structure at the collision site can rapidly exceed the elastic deformation and enter the plastic deformation stage and tear. The collision process can only be stopped when the kinetic energy generated by the ship collision is absorbed by the deformation of the hull structure and the movement of the surrounding medium. The hull is formed by welding reinforcing steel plates. The fracture of the steel plates and the welded joint failure play an important role in the failure of the hull structure, which directly affects the failure mechanism and energy absorption capacity of the structure.

[0004] At present, the production and development of existing steels for ship hulls does not fully consider the collision resistance of steel plates, so that the ship cannot fully absorb energy during a collision or withstand damage to the passenger compartment. Based on this, the present invention hopes to obtain a collision-resistant ship hull structural steel with suitable strength properties, excellent impact toughness, and good fracture and crack resistance properties while having excellent collision resistance and breakage resistance through reasonable chemical composition design and optimization of production process.

[0005] In the prior art, some researchers have studied the crashworthiness of steel plates, but there are still some limitations.

[0006] For example, China Patent Application Publication No. 106086655 discloses a crash-resistant hot-formed martensitic steel that is beneficial for optimizing the retained austenite, and adopts a composition design of medium carbon (0.1-0.35 wt%), high manganese (1.5-3.5 wt%), and high aluminum (1.0-2.5 wt%). By adopting traditional hot-forming process, the content of retained austenite in the steel is increased, so that the retained austenite is distributed in a thin film shape at the austenite grain boundaries and between lath bundles. The material has a yield strength of more than 1000 MPa, a tensile strength of more than 1550 MPa, a yield ratio of less than or equal to 0.7, an elongation of more than 16%, and a tensile strength-elongation product of more than 26000 MPa%.

[0007] China Patent Application Publication No. 102286695 discloses an ultra-high strength steel plate with high plasticity and high toughness, which adopts a composition design of high carbon (0.14-0.18 wt%) and medium manganese (0.8-1.3 wt%), and a manufacturing method thereof. A steel plate with the target properties is obtained by TMCP and tempering process, and the structure of the steel plate is tempered sorbite with fine lamellar spacing. The material has a yield strength of 960-1080 MPa, a tensile strength of 1020-1150 MPa, an elongation of 18-25%, and an impact energy at -40℃ of more than 60 J. Summary of the Invention [Problem to be solved by the invention]

[0008] One of the objectives of the present invention is to provide a collision-resistant ship hull structural steel, which not only has excellent strength and toughness, but also has good fracture and crack resistance properties, as well as collision resistance and breakage resistance, can be used to produce steel plates for ship hull construction and ultra-large ship hull construction, meets the current development requirements of steel for ships and marine engineering equipment in China, and has a very wide application prospect. [Means for solving the problem]

[0009] To achieve the above object, the present invention provides a steel for impact-resistant and fracture-resistant hull structures. In addition to Fe and inevitable impurities, the steel contains the following chemical elements by mass percentage: C: 0.06 - 0.12%, Si: 0.05 - 0.60%, Mn: 1.30 - 1.70%, Al: 0.01 - 0.06%, Ti: 0.005 - 0.012%, Mg: 0.0005 - 0.003%, and 0 < Ca ≤ 0.004% and further contains 0.0005% ≤ Ca + Mg ≤ 0.004%.

[0010] Preferably, the steel for impact-resistant and fracture-resistant hull structures in the present invention contains the following chemical elements by mass percentage: C: 0.06 - 0.12%, Si: 0.05 - 0.60%, Mn: 1.30 - 1.70%, Al: 0.01 - 0.06%, Ti: 0.005 - 0.012%, Mg: 0.0005 - 0.003%, 0 < Ca ≤ 0.004%, and the balance Fe and inevitable impurities and has 0.0005% ≤ Ca + Mg ≤ 0.004%.

[0011] In the steel for impact-resistant and fracture-resistant hull structures in the present invention, the design principles of all chemical elements are specifically shown as follows. C: The steel for hull structures in the present invention adopts an ultra-low C design. Therefore, it can ensure that the steel plate achieves appropriate strength due to the interstitial strengthening effect of C. Furthermore, the ultra-low C design can prevent the precipitation of excessive carbides, thereby avoiding the reduction of the low-temperature toughness and weldability of the steel plate. Therefore, in the present invention, the mass percentage content of C is controlled to be 0.06 - 0.12%.

[0012] Si: Si is a common light deoxidizing element in steelmaking and has a specific solid solution strengthening effect. In the steel for hull structures in the present invention, the mass percentage content of Si is controlled to be 0.05 - 0.60%.

[0013] Mn: Mn is the most basic alloying element in low alloy and high strength type steels, which can improve the strength of steel by solid solution strengthening, thereby compensating for the strength loss caused by the decrease in the content of element C. However, it should be noted that the content of element Mn in steel should not be too high. If the content of element Mn in steel is too high, it is easy to cause segregation at the center position of the steel plate and a decrease in the low temperature toughness of the steel. Based on this, in the ship structural steel in the present invention, the mass percentage content of Mn is controlled to 1.30-1.70%.

[0014] Al: Al is an element added to steel for deoxidation, which can reduce the content of O in the material and improve the aging property. In addition, the moderate addition of element Al in steel is further beneficial to refine the crystal grains, thereby improving the strength and toughness. Therefore, in the ship structural steel in the present invention, the mass percentage content of Al is controlled to 0.01-0.06%.

[0015] Ti: Ti is a strong N-fixing element that can effectively suppress the content of N element in steel to avoid the adverse effect on the properties of steel caused by excessively high N content. At the same time, the TiN precipitation phase formed by Ti and N can suppress excessive grain growth during heating of slabs and steel plates. Therefore, in the hull structural steel in the present invention, the mass percentage content of Ti is controlled to 0.005-0.012%.

[0016] Mg: Mg can effectively improve the sulfide morphology, refine inclusions, and improve the corrosion resistance of steel plate. If the Mg content in steel is too low, the effect of modifying inclusions cannot be achieved, and if the Mg content in steel is too high, it is easy to form substances such as MgO and MgS, which have higher melting points and are deposited on the inner wall of the tundish nozzle, causing nozzle clogging. Therefore, in the hull structural steel of the present invention, the mass percentage content of Mg is controlled to 0.0005-0.003%.

[0017] Ca: In the steel for ship hull structures in the present invention, by Ca treatment, the morphology of sulfides in the steel can be controlled, the anisotropy of the steel plate can be improved, and the low-temperature toughness can be improved. Furthermore, Ca is also an important element in the present invention, and it is necessary to match its content with the content of Mg. Therefore, in the steel for ship hull structures in the present invention, the mass percentage content of Ca is controlled to be 0 < Ca ≦ 0.004%.

[0018] Furthermore, it should be noted that in order to ensure the properties of the steel for ship hull structures in the present invention, while controlling the content of each chemical element, it is necessary to further control the mass percentage contents of Mg and Ca so that 0.0005% ≦ Ca + Mg ≦ 0.004%. In the present invention, a combined treatment of calcium and magnesium is adopted. Therefore, inclusions in the steel are modified, so the possibility of stress concentration and microcrack generation is reduced, which is beneficial to the improvement of the properties of the steel.

[0019] Preferably, the steel for ship hull structures in the present invention is, by mass percentage: 0 < Nb ≦ 0.04%, 0 < V ≦ 0.05%, and 0 < B ≦ 0.0005% and further contains at least one of Nb, V, and B that satisfies the above.

[0020] In order to further improve the properties of the steel, at least one of the three elements Nb, V, and B can also be added to the steel, and these elements have the following effects in the steel.

[0021] Nb: Nb is a strong carbide and nitride forming element and has a strong grain refinement effect. By adding an appropriate amount of Nb to the steel, a uniform crystal grain size can be obtained, and the formation of a mixed crystal structure due to excessive growth of some crystal grains during the heating process, as well as the deterioration of strength, toughness, and corrosion resistance, can be avoided. Therefore, in the steel for ship hull structures in the present invention, the mass percentage content of Nb can be controlled to be 0 < Nb ≦ 0.04%.

[0022] V: V can form fine VN or V(CN) precipitation crystal grains together with C and N, thereby contributing to the strengthening of the steel. However, it should be noted that the content of V in the steel should not be too high. If the content of V in the steel is too high, the manufacturing cost will increase significantly. Therefore, in the steel for ship hull structures in the present invention, the mass percentage content of V can be controlled to 0 < V ≤ 0.05%.

[0023] B: B can improve the hardenability of the steel and affect the low-temperature cracking characteristics of the steel. In the steel for ship hull structures in the present invention, the mass percentage content of B can be controlled to 0 < B ≤ 0.0005%.

[0024] It should be noted that the addition of the above elements Nb, V, and B increases the cost of the material. By comprehensively considering the properties and cost management, in the technical solution of the present invention, preferably, one or more of these elements can be added.

[0025] Preferably, the steel for ship hull structures in the present invention is, by mass percentage: Cr + Ni + Mo + Cu ≤ 0.5% and further contains at least one of Cr, Ni, Mo, and Cu that satisfies the above.

[0026] In the above technical solution of the present invention, all of the above four alloy elements Cr, Ni, Mo, and Cu can effectively play a role in solid solution strengthening. In the case of thick steel plates, the strength and toughness of the steel can be effectively improved by appropriately adding the elements Cr, Ni, Mo, and Cu to the steel. Therefore, in the technical solution of the present invention, preferably, at least one of the above elements can be added, and its mass percentage content satisfies Cr + Ni + Mo + Cu ≤ 0.5%.

[0027] Preferably, in the steel for ship hull structures with impact fracture resistance in the present invention, the content in terms of mass percentage of P and S in unavoidable impurities is as follows: P≦0.015% and S≦0.0040% Satisfy at least one of the following:

[0028] Both P and S are inevitable impurity elements in steel, and if the content of elements P and S in steel is too high, it is easy to cause defects such as segregation and inclusions, and is easy to deteriorate weldability and impact toughness. In order to obtain steel with better properties and higher quality, the content of impurity elements in steel should be reduced as much as possible under acceptable technical conditions. Therefore, in the ship structural steel in the present invention, it is preferable to control P≦0.015% and S≦0.0040%, and it is necessary to spheroidize the inclusions, refine their size, and achieve their uniform distribution by the beneficial modification technology of inclusions, so that the strength and toughness of the steel plate are improved.

[0029] Preferably, in the collision-resistant ship hull structural steel of the present invention, the content of chemical elements in mass percentages satisfies the following conditions: 1.9≦α≦2.1 (where α=6.1C+0.9Mn+1.5V); 4.1≦β≦6.8 (where,

[0030]

number

[0031] In the collision-resistant and crashworthy ship hull structural steel of the present invention, the mass percentage content of each chemical element is preferably controlled, and the mass percentage content of the chemical elements in the steel is set to the following conditions: 1.9≦α≦2.1 and 4.1≦β≦6.8 By setting the value of α within the above range, the solid solution strengthening effect and precipitation strengthening effect of C, Mn, and V can be fully utilized, so that the steel has good strength and plasticity. By setting the value of β within the above range, it can be ensured that the grain size of ferrite is sufficiently refined, so that the steel has good strength, toughness, and plasticity, as well as impact resistance and fracture resistance.

[0032] Preferably, the microstructure of the collision-resistant ship hull structural steel in the present invention is ferrite + pearlite, where the volume fraction of the ferrite phase is 90% or more to ensure that the steel has good strength and toughness, as well as collision resistance and fracture resistance.

[0033] Preferably, the collision-resistant, fracture-resistant steel for ship hull structures in the present invention has a yield strength of 315 MPa or more, a tensile strength of 440 to 570 MPa, an impact energy at -60°C of 200 J or more, a CTOD (crack tip opening displacement) at -60°C of 1.5 mm or more, a NDTT (non-ductile transition temperature) of -70°C or less, a uniform elongation Ag of 18% or more, and a total elongation A5 of 38% or more.

[0034] Another object of the present invention is to provide a method for producing a crash-resistant steel for ship hull construction. This method has a simple production process, and the resulting steel for ship hull construction not only has excellent strength and toughness, but also has good crash resistance and crash resistance, as well as fracture and crack resistance properties. This steel has a yield strength of 315 MPa or more, a tensile strength of 440-570 MPa, an impact energy at -60°C of 200 J or more, a CTOD at -60°C of 1.5 mm or more, an NDTT at -70°C or less, a uniform elongation Ag of 18% or more, and a total elongation A5 of 38% or more, and has good application prospects and high application value.

[0035] In order to achieve the above object, the present invention provides: (1) Smelting and continuous casting steps; (2) a heating step; (3) a controlled rolling step; (4) an air-cooling step, and (5) Normalizing heat treatment step: Normalizing temperature T in °C q teeth,

[0036]

number

[0037] In step (5) of the manufacturing method of the present invention, the normalizing temperature is:

[0038]

number

[0039] Correspondingly, in the above step (5) of the present invention, the retention time T h = 1.5 × t, which is mainly for the purpose of sufficiently austenitizing the steel sheet and homogenizing the element C and the microalloying elements in the steel.

[0040] Preferably, in step (1) of the present invention, hot metal pretreatment, converter smelting, LF refining, RH refining, beneficial treatment of inclusions, and continuous casting are carried out in sequence, and in the stage of beneficial treatment of inclusions, composite inclusions with a size of 0.2-2.5 μm and having MgO+Al2O3 as a core coated with CaS and MnS are formed, and the number of composite inclusions within this size range accounts for more than 95% of the total number of inclusions.

[0041] Preferably, in step (1), in the converter smelting stage, slag cut-off tapping is carried out when the slag layer thickness is less than 35 mm, in the LF refining stage, the sum of the contents of FeO and MnO in mass percentage in the slag is less than 1%, (CaO+MgO+MnO) / (SiO2+P2O5) is greater than 9, where each substance represents its corresponding mass percentage, and in the inclusion beneficial treatment stage, Mg and Ca are fed simultaneously at a wire feeding speed of 160-300 m / min.

[0042] In step (1) of the manufacturing method of the present invention, slag cut-off tapping is carried out in the converter smelting stage to control the thickness of the slag layer to be less than 35 mm, so that the oxidizing property of the slag in the steel ladle can be reduced, the increase in oxygen activity and the re-phosphorization of molten steel can be prevented, and the subsequent generation of white slag and the modification of inclusions can be promoted.

[0043] Correspondingly, in the stage of LF refining, (CaO+MgO+MnO) / (SiO2+P2O5), where each substance is replaced by its mass percentage, is controlled to be greater than 9, so as to ensure that the slag has good dephosphorization and desulfurization ability. In the production of white slag in the steel ladle, the sum of the content of FeO and MnO by mass in the slag is controlled to be less than 1%, so as to ensure the reducibility and complete desulfurization of the molten slag, thereby reducing the content of inclusions in the molten steel, and improving the strength and toughness of the steel, as well as the corrosion resistance.

[0044] Preferably, in step (2), the slab heating temperature is

[0045]

number

[0046] In step (2), in order to ensure sufficient solid solution of the microalloy carbonitride, the slab heating temperature T h is set to the above-mentioned value, thereby promoting the homogenization of alloying elements, mitigating macroscopic and microscopic segregation in the steel, reducing the formation of corrosion primary cells due to the difference in potential difference between different phases and components, and thus improving the corrosion resistance of the steel plate.

[0047] Preferably, in step (3), the initial rolling temperature is T sr =0.92T h ~0.96T h Meet T sr and the final rolling temperature is

[0048]

number

[0049] In the above technical solution, the initial rolling temperature T sr =0.92T h ~0.96T h The main reason for controlling the final rolling temperature is to ensure that the steel sheet is rolled at a higher temperature in the recrystallization region to fully recrystallize and form uniform and equiaxed austenite grains.

[0050]

number

[0051] Preferably, in step (3), the single pass rolling reduction is 8 to 12%, and the cumulative rolling reduction is 60% or more.

[0052] The single pass rolling reduction is controlled to 8-12%, mainly to ensure that the steel plate has sufficient recrystallization driving force in each pass and that there are enough rolling passes to homogenize the grains of the steel plate and keep the original austenite grain size at 25-30 μm after rolling. In the above step (3), the cumulative rolling reduction is controlled to be 60% or more, mainly to ensure that sufficient recrystallization occurs in the core of the steel plate to achieve sufficient homogenization, thereby ensuring the strength and toughness of the core, as well as the fracture and crack resistance properties.

[0053] Preferably, in the above step (5), air cooling is performed after holding, and the cooling rate of the air cooling is 0.2 to 0.5°C / sec. This is mainly for forming a microstructure having a ferrite phase ratio of more than 90% in the steel sheet.

[0054] Compared with the prior art, the collision-resistant ship hull structural steel and its manufacturing method in the present invention have the following advantages and beneficial effects:

[0055] The present invention is designed in terms of composition design, structure control, production process, etc., so that the steel plate has suitable strength properties, excellent impact toughness, and good fracture and crack resistance properties, while also having excellent impact resistance and breakage resistance.

[0056] Compared with the prior art, the collision-resistant ship hull structural steel in the present invention adopts unique composition design technology, pure steel smelting technology, inclusion beneficial control technology, steel homogenization technology, as well as grain size control and microstructure control technology, which can produce a steel that meets the strength requirement of 315 MPa, good low-temperature impact toughness, fracture and crack resistance properties, and excellent collision fracture resistance, and the steel is significantly different from the prior art in structure, composition, and process design.

[0057] The produced collision-resistant hull structural steel in the present invention has a yield strength of not less than 315 MPa, a tensile strength of 440-570 MPa, an impact energy at -60°C not less than 200 J, a CTOD at -60°C not less than 1.5 mm, an NDTT not more than -70°C, a uniform elongation Ag not less than 18%, and a total elongation A5 not less than 38%, and can be used to construct the hulls of ultra-large ships such as super tankers, liquefied petroleum gas carriers, liquefied natural gas carriers, chemical tankers, and container ships, so as to ensure the safe operation of ships and reduce the pollution caused by the leakage of crude oil and chemicals, and has a very wide application prospects. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] The following will further explain and describe the collision-resistant ship hull structural steel and its manufacturing method in the present invention in combination with specific embodiments. However, the explanation and description do not constitute an inappropriate limitation on the technical solution of the present invention.

[0059] Embodiments 1 to 6 and Comparative Example 1 The collision-resistant and crash-resistant ship hull structural steels of the first to sixth embodiments and the comparative steel of the comparative example 1 are both manufactured by the following steps. (1) The steps of carrying out smelting and casting according to the chemical compositions shown in the following Tables 1-1 and 1-2: sequentially carrying out hot metal pretreatment, converter smelting, LF refining, RH refining, beneficial treatment of inclusions, and continuous casting, and in the stage of beneficial treatment of inclusions, forming composite inclusions with a size of 0.2-2.5 μm having MgO+Al2O3 as the core coated with CaS and MnS, and the number of composite inclusions within this size range accounts for more than 95% of the total number of inclusions. In the converter smelting stage, slag cut-off tapping is carried out when the slag layer thickness is less than 35 mm; in the LF refining stage, the sum of the contents of FeO and MnO in the slag by mass is controlled to be less than 1%, and (CaO+MgO+MnO) / (SiO2+P2O5) is greater than 9, in which each substance is replaced by its mass percentage; in the stage of beneficial treatment of inclusions, Mg and Ca are fed simultaneously with a wire feeding speed of 160-300 m / min. (2) Heating step: Slab heating temperature in °C

[0060]

number

[0061]

number

[0062]

number

[0063] It should be noted that the chemical composition designs and related processes of the collision-resistant ship hull structural steels of the first to sixth embodiments of the present invention all meet the design criteria requirements of the present invention. However, the comparative steel of the comparative example 1 has parameters in its chemical composition design that do not meet the design criteria requirements of the present invention.

[0064] The mass percentages of all chemical elements in the collision-resistant ship hull structural steels of the embodiments 1 to 6 and the comparative steel of the comparative example 1 are listed in Tables 1-1 and 1-2.

[0065] [Table 1-1]

[0066] [Table 1-2]

[0067] In Table 1-2, α = 6.1C + 0.9Mn + 1.5V, and

[0068]

number

[0069] Table 2 lists specific process parameters for the collision-resistant ship structural steels of the first to sixth embodiments and the comparative steel of the first comparative example in the above-mentioned process steps.

[0070] [Table 2]

[0071] The obtained collision-resistant and fracture-resistant hull structural steels of the embodiments 1 to 6 and the comparative steel of the comparative example 1 are sampled. The completed product plates of the embodiments and the comparative example are subjected to a tensile test, a Charpy V-notch impact test, a CTOD test (an index for testing the fracture toughness of the steel plate), and a NDTT property confirmation test (an important index for measuring the crack resistance property of the steel plate), and the test results of the embodiments and the comparative example are listed in Table 3.

[0072] The relevant measurement method is shown as follows: Tensile test: Based on GB / T228.1, full thickness plate tensile test specimens are used for steel plates with a thickness of less than 50mm, and bar tensile test specimens are used for steel plates with a thickness of more than 50mm to test the room temperature tensile properties. Charpy V-notch impact test: Based on GB / T229, the Charpy V-notch impact test specimen is adopted to test the impact properties at -60℃ at the t / 4 position of the plate thickness. CTOD Test: Based on BS7448-1, the fracture toughness of the material is tested at -60℃ by adopting full thickness CTOD specimen. NDTT property verification test: Based on GB / T6803-2008, the non-ductile transition temperature of the material is tested by adopting specimen P3.

[0073] Table 3 lists the test results of the collision-resistant and crash-resistant ship hull structural steels of the first to sixth embodiments and the comparative steel of the first comparative example.

[0074] [Table 3]

[0075] From Table 3, it can be seen that the overall properties of the collision-resistant and fracture-resistant ship hull structural steels of Embodiments 1 to 6 are clearly superior to the overall properties of the comparative steel of Comparative Example 1. Compared to the comparative steel, the collision-resistant and fracture-resistant ship hull structural steels of Embodiments 1 to 6 have significantly increased uniform elongation Ag and total elongation A5 by 50% or more.

[0076] As shown in Table 3, compared with the comparative steel of Comparative Example 1, the collision-resistant and fracture-resistant ship structural steels of Embodiments 1 to 6 have good strength and toughness, fracture and crack resistance properties, and collision resistance and breakage resistance, and the collision-resistant and fracture-resistant ship structural steels of Embodiments 1 to 6 have a yield strength of 330 to 360 MPa, a tensile strength of 460 to 470 MPa, an impact energy at -60°C of 205 J or more, a CTOD at -60°C of 1.51 mm or more, an NDTT of -75°C or less, a uniform elongation Ag of 18.5% or more, and a total elongation A5 of 38.4% or more.

[0077] From the above, it can be seen that through reasonable chemical composition design and process optimization, the collision-resistant and fracture-resistant steel for ship hull construction in the present invention can simultaneously have suitable strength properties, excellent impact toughness, good fracture and crack resistance properties, and excellent collision resistance and breakage resistance. The collision-resistant and fracture-resistant steel for ship hull construction can be effectively applied to the construction of super-large ships such as super-tankers, liquefied petroleum gas carriers, liquefied natural gas carriers, chemical tankers, and container ships, and has a very wide application prospect.

[0078] It should be noted that the combination of technical features in the present invention is not limited to the combinations described in the claims of the present invention or the combinations described in the specific embodiments, and all technical features described in the present invention can be freely combined or incorporated in any manner as long as there is no contradiction between them.

[0079] In addition, it should be noted that the above listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above-mentioned embodiments, and those skilled in the art can directly obtain or easily conceive of similar modifications or variations that fall within the protection scope of the present invention from the contents disclosed by the present invention.

Claims

1. A steel plate for ship hull construction having crashworthiness, said steel plate comprising the following chemical elements in mass percentages: C: 0.06-0.12%, Si: 0.05-0.60%, Mn: 1.30-1.70%, Al: 0.01-0.06%, Ti: 0.005-0.012%, Mg: 0.0005-0.003%, 0<Ca≦0.004%, and the balance being Fe and unavoidable impurities, and 0.0005%≦Ca+Mg≦0.004%, It has a ferrite + pearlite microstructure, and the volume fraction of the ferrite phase is 90% or more; having an impact energy at -60°C of 200J or more, a CTOD at -60°C of 1.5mm or more, and an NDTT of -70°C or less; Steel plate for ship hull structure.

2. The steel plate has the following mass percentages: 0<Nb≦0.04%, 0<V≦0.05%, and 0<B≦0.0005% The steel plate for ship hull structure according to claim 1 , further comprising at least one of Nb, V, and B satisfying the following formula:

3. The steel plate has the following mass percentages: Cr+Ni+Mo+Cu≦0.5% The steel plate for ship hull structure according to claim 1 , further comprising at least one of Cr, Ni, Mo, and Cu satisfying the following formula:

4. The content of P and S in the unavoidable impurities in terms of mass percentage is as follows: P≦0.015% and S≦0.0040% The steel plate for ship hull structure according to claim 1 , which satisfies at least one of the following:

5. The content of the above chemical elements in mass percentages is as follows: 1.9≦α≦2.1, where α=6.1C+0.9Mn+1.5V; 4.1≦β≦6.8 (where [0010] 3. The steel plate for ship hull construction according to claim 2, further satisfying at least one of the following formulas:

6. 2. The steel plate for ship hull construction according to claim 1, wherein the steel plate has a yield strength of 315 MPa or more, a tensile strength of 440 to 570 MPa, a uniform elongation Ag of 18% or more, and a total elongation A5 of 38% or more.

7. A method for manufacturing a steel plate for a ship hull structure according to claim 1, (1) smelting and continuous casting step; (2) a heating step; (3) a controlled rolling step; (4) an air cooling step; and (5) Normalizing heat treatment step: normalizing temperature T in °C ｑ teeth, [0025] where each chemical element represents the number preceding the percent sign in mass percentage of the corresponding chemical element, and the retention time T ｈ , T ｈ = 1.5 × t (where t represents the thickness of the steel plate in mm) A manufacturing method comprising:

8. In step (1), hot metal pretreatment, converter smelting, LF refining, RH refining, beneficial treatment of inclusions, and continuous casting are sequentially carried out, and in the beneficial treatment of inclusions, MgO+Al is formed as a core coated with CaS and MnS. ２ O ３ 8. The method of claim 7, wherein composite inclusions having a size of 0.2 to 2.5 μm are formed, the number of composite inclusions within this size range being 95% or more of the total number of inclusions.

9. In step (1), in the converter smelting stage, slag cut-off tapping is performed when the slag layer thickness is less than 35 mm, and in the LF refining stage, the total content of FeO and MnO in the slag in terms of mass percentage is less than 1%, and (CaO + MgO + MnO) / (SiO ２ +P ２ O ５ 9), where each material represents its corresponding mass percentage, and wherein, during said beneficial processing of inclusions, Mg and Ca are fed simultaneously at a wire feed speed of 160-300 m / min.

10. In step (2), the slab heating temperature is [0030] 8. The process according to claim 7, wherein Ttemp in °C satisfies:

11. In step (3), the initial rolling temperature is T ｓｒ = T that satisfies 0.92Ttemp to 0.96Ttemp ｓｒ and the final rolling temperature is [0045] Satisfying T ｆｒ 8. The method of claim 7, wherein each chemical element represents the numerical value before the percent sign in mass percentage of the corresponding chemical element, and the units of the initial rolling temperature and the final rolling temperature are both in °C.

12. The method according to claim 7 or 11, wherein in step (3), the single-pass rolling reduction is 8 to 12%, and the cumulative rolling reduction is 60% or more.

13. The method according to claim 7, wherein in step (5), after the holding, air cooling is performed at a cooling rate of 0.2 to 0.5 ° C. / sec.

Images