A 440mpa grade hull structure steel with high ductility and excellent toughness and a preparation method thereof

Abstract

This invention relates to a 440MPa grade ship hull structural steel with high ductility and excellent toughness, and its preparation method, belonging to the field of ship hull structural steel. The 440MPa grade ship hull structural steel with high ductility and excellent toughness has the following composition by mass percentage: C: 0.03–0.05%, Si: 0.10–0.25%, Mn: 1.0–2.0%, Cu: 0.1–0.2%, Ni: 0.8–1.2%; Cr ≤ 0.2%, Ti: 0.005–0.015%; Nb: 0.020–0.045%; V: 0.03–0.06%, Als ≥ 0.015%, with the remainder being Fe and unavoidable impurity elements. The steel of this invention exhibits high elongation and excellent low-temperature toughness, making it suitable for ship hull structures requiring high impact resistance and excellent low-temperature toughness.

Description

Technical Field

[0001] This invention relates to the field of special steel technology with special requirements for anti-collision performance and low-temperature toughness, and in particular to a 440MPa grade ship hull structural steel with high ductility and excellent toughness and its preparation method. Background Technology

[0002] The collision resistance of ships is crucial to the safety of vessels, personnel, and the environment, and has received widespread attention and importance. Ships are inevitably subject to collisions during navigation due to the ever-changing marine environment, including strong winds, waves, currents, and fog, as well as human factors such as not using safe speeds, improper avoidance, and negligence in lookout. For vessels transporting oil, LPG, LNG, and chemicals, a collision often results in damage or even fracture of the hull structure under immense loads, leading to catastrophic consequences such as fuel leaks, environmental pollution, and casualties. Ship collisions involve a complex deformation and stress process. Common methods to improve impact resistance in strong structural designs include double-hull structures, "sandwich" designs, longitudinal steel plate sandwich strips, and elastic glass infill. However, these structural changes increase the weight of the hull structure and complicate construction and inspection. Using high-ductility hull structural steel in ship construction significantly improves the ship's ability to absorb collision energy, effectively enhancing its safety.

[0003] As service temperatures decrease, the requirements for low-temperature toughness of steel used in ship hull structures are becoming increasingly stringent. With the depletion of oil and gas resources in conventional sea areas, the development of marine oil and gas resources will become increasingly challenging, exhibiting characteristics of harsher and more extreme extraction environments. Specifically, this manifests as a shift from shallow to deep water areas and from conventional sea areas to extremely cold sea areas, demanding that the materials used possess both high strength and high toughness.

[0004] In conclusion, existing Class E steel plates cannot meet the collision resistance requirements of polar ship hulls, and it is necessary to develop hull structural steel with high ductility and excellent toughness. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a 440MPa grade hull structural steel with high ductility and excellent toughness and its preparation method, which can simultaneously meet the two performance requirements of high collision resistance and excellent low-temperature toughness of ships.

[0006] The objective of this invention is mainly achieved through the following technical solutions:

[0007] This invention provides a 440MPa grade ship hull structural steel with high ductility and excellent toughness. The chemical composition by mass percentage is as follows: C: 0.03-0.05%, Si: 0.10-0.25%, Mn: 1.0-2.0%, Cu: 0.1-0.2%, Ni: 0.8-1.2%; Cr≤0.2%, Ti: 0.005-0.015%; Nb: 0.020-0.045%; V: 0.03-0.06%, Als≥0.015%, with the remainder being Fe and unavoidable impurity elements.

[0008] Furthermore, the chemical composition of the steel must meet the following requirements: 16 ≤ Ni / C ≤ 40.

[0009] Furthermore, the microstructure of the steel consists of polygonal ferrite, granular bainite, and mausoleum, wherein the polygonal ferrite content is ≥60% and the size is ≤5μm.

[0010] Furthermore, the content of marugroup elements in the 440MPa grade hull structural steel with high ductility and excellent toughness is ≤5%.

[0011] Furthermore, the 440MPa grade ship structural steel with high ductility and excellent toughness has a yield strength ≥440MPa, tensile strength ≥550MPa, impact energy at -80℃ ≥100J, and elongation ≥30%.

[0012] Furthermore, this invention also provides a method for preparing 440MPa grade ship hull structural steel with high ductility and excellent toughness, used to prepare the 440MPa grade ship hull structural steel. The method includes the following steps: hot metal pretreatment, converter smelting, LF refining, RH refining, continuous casting, and controlled rolling and cooling. The hot metal pretreatment includes KR desulfurization, with an S content ≤0.008%, and slag thickness meeting the requirements of slag removal grade 1.

[0013] Furthermore, during the LF refining process, the slag-forming materials and deoxidizers added must be dried and kept in the silo for ≤24 hours; the white slag retention time must be ≥10 minutes.

[0014] During the RH refining process, calcium treatment is performed before tapping, and argon blowing time is ≥10 min after wire feeding to ensure that the Ca content in the molten steel is not higher than 0.0015%.

[0015] Furthermore, the continuous casting process adopts full-process protective casting, the heating temperature of the continuous casting billet is ≤1150℃, the target superheat of the molten steel in the tundish is ≤30℃, and after continuous casting, it enters the slow cooling pit for treatment.

[0016] Furthermore, the controlled rolling and cooling adopts a two-stage rolling process. The first stage rolling is rough rolling, with a final rolling temperature ≥950℃, a single-pass deformation of 10-15%, and a cumulative deformation of ≤50% in the first stage rolling.

[0017] Furthermore, in the two-stage rolling process, the second stage rolling is a finishing rolling process with a rolling temperature of ≤890℃, a final rolling temperature of 750℃~800℃, a deformation pass of no less than 3 passes in the two-phase region, a cumulative deformation amount of no less than ≥15%, and a cumulative deformation amount of ≥60% in the second stage rolling process.

[0018] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0019] 1. This invention achieves stable austenitic structure while promoting the formation of bainite structure by adding Ni element at ultra-low C, especially by controlling 16≤Ni / C≤40. The steel plate prepared according to the composition ratio of this invention has a multiphase multi-component composite structure composed of polygonal ferrite, granular bainite and mausoleum, with polygonal ferrite structure as the main component, its content ≥60% and size ≤5μm, thus achieving a good match between strength and low temperature toughness.

[0020] 2. By controlling the C content to an ultra-low range, this invention achieves a Maurice component of ≤5%, which reduces the brittleness of the steel plate and improves its toughness and plasticity, resulting in an elongation of ≥30%. This significantly enhances the uniform plastic deformation capacity of the hull structural steel, playing a crucial role in ensuring the collision resistance performance of ships.

[0021] 3. By controlling the types and contents of elements, especially the contents of Ni and C, and particularly controlling 16≤Ni / C≤40, and combining this with controlled rolling and cooling processes, this invention achieves excellent mechanical properties of steel plates: yield strength ≥440MPa, tensile strength ≥550MPa, and impact energy of the steel plate at -80℃ not less than 100J. The polar hull structural steel produced by this invention can be used in the construction of ships serving in polar regions, meeting the usage conditions of polar service environments, and helping to improve the safety performance of ships in collision situations with ice.

[0022] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0023] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0024] Figure 1 A metallographic image of a quarter section of the No. 1 rolled steel plate provided in Embodiment 1 of the present invention.

[0025] Figure 2 A scanning electron microscope (SEM) image of the microstructure of a quarter section of a No. 1 rolled steel plate provided in Embodiment 1 of the present invention. Detailed Implementation

[0026] Currently, my country's ship steel that meets the requirements of polar service environments is still in its initial stage. Existing E-series steel plates cannot fully meet the temperature requirements of polar environments. This invention provides a 440MPa grade hull structural steel with high ductility and excellent toughness. This ship steel has the characteristics of high strength, excellent low-temperature toughness, and high elongation, which solves the problem that existing steel plates cannot meet the temperature requirements of polar environments.

[0027] The chemical composition of the 440MPa grade ship hull structural steel with high ductility and excellent toughness provided by this invention, by mass percentage, is as follows: C: 0.03-0.05%, Si: 0.10-0.25%, Mn: 1.0-2.0%, Cu: 0.1-0.2%, Ni: 0.8-1.2%; Cr≤0.2%, Ti: 0.005-0.015%; Nb: 0.020-0.045%; V: 0.03-0.06%; Als≥0.015%; the remainder is Fe and unavoidable impurity elements.

[0028] The rationale for limiting the composition of the steel plate for the 440MPa grade polar ship hull steel and its preparation method in this invention will be explained. Hereinafter, only the percentage of mass in the composition will be used.

[0029] C: Carbon has a significant impact on the strength and toughness of materials. To achieve excellent low-temperature toughness, the C content needs to be below 0.06%. When the C content is <0.03%, the microstructure of the steel plate is ferrite + pearlite, and the strength of the steel plate will not meet the requirements; that is, it is impossible to obtain a strength of 440 MPa under the ferrite + pearlite microstructure conditions. Therefore, the C content is controlled between 0.03% and 0.05%.

[0030] Meanwhile, carbon (C) is an alloying element that degrades toughness, while nickel (Ni) is an alloying element that improves toughness. To ensure that the material has excellent low-temperature toughness, the amount of Ni added should be increased accordingly as the C content increases. By adding Ni with ultra-low C content, especially by controlling 16 ≤ Ni / C ≤ 40, the microstructure of the steel plate can be made into a multiphase multi-component composite microstructure composed of polygonal ferrite, granular bainite, and mausoleum, with polygonal ferrite as the main component, its content ≥ 60%, and its size ≤ 5 μm, thus achieving a balance between strength and low-temperature toughness.

[0031] Mn: Mn dissolved in steel increases its strength. The Mn content should be controlled above 1.0% to ensure the steel's strength. When the Mn content exceeds 2.0%, it alters the phase transformation behavior of the material, inhibits ferrite formation, and negatively impacts low-temperature toughness and elongation. Therefore, the Mn content should be controlled between 1.0% and 2.0%.

[0032] Si: Si is a solid solution strengthening element in materials. If the Si content is less than 0.1%, the strength of the material will be insufficient; however, excessive Si is detrimental to low-temperature toughness and should be controlled to less than 0.25%. Therefore, the Si content should be controlled between 0.1% and 0.25%.

[0033] Ti: When the Ti content is below 0.005%, TiN particles precipitate insufficiently; excessive Ti promotes premature TiN precipitation, forming coarse TiN particles that reduce toughness. In this case, the Ti content should not exceed 0.015%. Therefore, the Ti content should be controlled between 0.005% and 0.015%.

[0034] Als: Als is an important deoxidizing element. When the Als content is less than 0.015%, it is difficult to control the oxygen content below 0.005%, which affects the low-temperature toughness of the material.

[0035] Niobium (Nb) typically forms Nb(C,N) precipitates, which refine the grain size and improve material strength. However, concentrations below 0.02% or above 0.045% are ineffective. Therefore, the Nb content is controlled between 0.020% and 0.045%.

[0036] Vanadium (V): Vanadium typically forms V(C,N) precipitates, which improve material strength. However, its contribution to strength is insufficient when its content is less than 0.03%. A vanadium content greater than 0.06% increases the carbon equivalent of the material, affecting the low-temperature toughness of the weld heat-affected zone. Therefore, the V content should be controlled between 0.03% and 0.06%.

[0037] Cr: Cr can improve the hardenability and corrosion resistance of materials, but if the Cr content exceeds 0.2%, it will reduce the low-temperature toughness of the base material and increase the manufacturing cost of the material. Therefore, Cr should be controlled to be less than 0.2%.

[0038] Cu: Cu and Ni are often added in combination. The aging precipitation of Cu particles can improve the strength of high-strength steel plates, compensating for the strength reduction caused by low carbon content. However, excessive Cu content will affect the weldability and low-temperature toughness of the material. Therefore, the Cu content is controlled between 0.1% and 0.2%.

[0039] Ni: Ni can improve the low-temperature toughness of materials and affect their phase transformation characteristics, playing a significant role in the preparation of multiphase, multi-scale microstructures. Low Ni content is detrimental to improving low-temperature toughness; therefore, the Ni content should not be lower than 0.8%. Excessive Ni content will further stabilize austenite, promoting the formation of hard phase structures during cooling, particularly bainite and martensite, which are crucial for improving strength. Furthermore, excessive Ni content will further strengthen austenite stability, leading to the formation of martensite, which is detrimental to strength control. Therefore, the Ni content should not exceed 1.2%, and should be controlled between 0.8% and 1.2%.

[0040] By adding Ni to ultra-low C, especially by controlling 16≤Ni / C≤40, the microstructure of the steel plate can be made into a multiphase multi-component composite microstructure composed of polygonal ferrite, granular bainite and mausoleum, with polygonal ferrite as the main microstructure, its content ≥60% and size ≤5μm, thus achieving a balance between strength and low-temperature toughness.

[0041] The 440MPa grade ship hull structural steel provided by this invention has a yield strength ≥440MPa, tensile strength ≥550MPa, impact energy at -80℃ ≥100J, and elongation ≥30%.

[0042] Specifically, the microstructure of the steel consists of polygonal ferrite, granular bainite, and Maussian components, wherein the polygonal ferrite content is ≥60% with a size ≤5μm, and the Maussian components are ≤5%.

[0043] It should be noted that the ferrite matrix has good toughness and a large plastic deformation capacity; granular bainite is a medium-temperature transformation structure, composed of blocky ferrite and carbides or mausoleum components. Since the microhardness of mausoleum components is higher than that of the matrix structure, they are generally used as the initiation site of microcracks. Therefore, mausoleum components and granular bainite structures have adverse effects on plasticity and toughness. The microstructure ratio and morphology obtained by this invention can achieve a good match between strength and low-temperature toughness.

[0044] On the other hand, the present invention also provides a method for preparing the above-mentioned 440MPa grade ship structural steel with high ductility and excellent toughness, comprising the following steps:

[0045] Step 1: Hot metal pretreatment: Hot metal pretreatment reduces impurity elements in steel, ensuring that after KR desulfurization, the S content is ≤0.008% and the slag thickness meets the requirements of slag removal level 1.

[0046] Step 2: Converter smelting: When tapping steel, the slag layer thickness should be ≤100mm. The added alloy materials and auxiliary materials such as lime, sintered ore, and dolomite must be dry. The alloying and deoxidation sequence in the ladle should be from strong to weak.

[0047] Step 3: LF Refining: In the LF furnace process, the added slag-forming materials and deoxidizers must be dried and kept in the silo for ≤24 hours to ensure that the slag has good fluidity; the white slag holding time is ≥10 minutes.

[0048] Step 4: RH refining: In the RH furnace process, calcium treatment is carried out before tapping, and the static argon blowing time after wire feeding is ≥10min to ensure that the Ca content in the molten steel is not higher than 0.0015%.

[0049] Step 5: Continuous casting: The continuous casting process adopts full-process protective casting, electromagnetic stirring and light pressure, the superheat of the tundish is ≤30℃, and after continuous casting, it enters the slow cooling pit for treatment to obtain the continuously cast billet;

[0050] Step 6: Controlled rolling and cooling: The continuously cast billet is heated and then subjected to controlled rolling and cooling.

[0051] Specifically, in step 5, the thickness ratio of the continuously cast billet to the steel plate is controlled to be greater than 8, and the heating temperature of the continuously cast billet is ≤1150℃ to ensure that the austenite grains do not grow.

[0052] Specifically, in step 6, the controlled rolling adopts a two-stage rolling method: the two-stage rolling can fully utilize the grain refinement effect of the controlled rolling process on the material. The first stage rolling is rough rolling, which involves rapid deformation within the austenite recrystallization temperature range, with a final rolling temperature ≥950℃, a single-pass deformation amount of 10-15%, and a cumulative deformation amount of ≤50% in the first stage rolling. Through alternating deformation and recrystallization, the γ grains are refined, providing the prerequisite for the formation of fine ferrite grains after phase transformation. The second stage of rolling is finishing rolling, which is rolled in the non-recrystallized austenite region. The rolling temperature is ≤890℃, and the final rolling temperature is 750℃~800℃. There are no less than 3 deformation passes in the two-phase region, and the cumulative deformation is no less than ≥15%. The cumulative deformation in the second stage of rolling is ≥60%. The austenite grains elongate along the rolling direction, the grain boundary area increases, and the nucleation density of ferrite increases. At the same time, due to deformation, a large number of deformation bands are introduced into the grains, increasing the number of nucleation points when austenite transforms into ferrite. After transformation, fine ferrite is obtained, and the number of transformed ferrite increases with the increase of deformation.

[0053] The above rolling method can further refine the ferrite grains, ensuring that the ferrite size is ≤5μm, so that the steel has a better strength and toughness match.

[0054] The advantages of this invention in precisely controlling the elemental chemical composition, content, and preparation process parameters will be demonstrated below with specific examples.

[0055] Example 1

[0056] This embodiment discloses eight types of 440MPa grade ship hull structural steels (Example 1#-4# steel and Comparative Example 5#-8# steel).

[0057] The controlled rolling process for steel #1-#6 conforms to the requirements of this invention, and all adopt the same process:

[0058] (1) After hot metal pretreatment and KR desulfurization, the S content is ≤0.008% and the slag thickness meets the requirements of slag removal level 1;

[0059] (2) Converter smelting; when tapping steel, the slag layer thickness is required to be ≤100mm, and alloy materials are added in sequence; slag-forming agent, including lime and dolomite; coolant, including sintered ore; among which, fresh roasted lime stored for no more than 2 days is used to ensure a low moisture content, and the requirements for dolomite are wMgO≥35%, wCaO≥50%, wSiO2≤3.0%, loss on ignition≤10%, and block size of 5~40mm.

[0060] (3) LF refining; add dry slag-forming materials and deoxidizer, and keep it in the silo for ≤24 hours. The slag has good fluidity; the white slag holding time is ≥10min.

[0061] (4) RH refining; In the RH furnace process, calcium treatment is carried out before tapping, and the static argon blowing time after wire feeding is ≥10min to ensure that the Ca content in the molten steel is not higher than 0.0015%;

[0062] (5) Continuous casting: The continuous casting process adopts full-process protective casting. The heating temperature of the continuous casting billet is ≤1150℃, the target superheat of the molten steel in the tundish is ≤30℃, and after continuous casting, it enters the slow cooling pit for treatment to obtain the continuous casting billet.

[0063] (6) Controlled rolling and controlled cooling: Controlled rolling adopts a two-stage rolling method: The first stage rolling is rough rolling, which is carried out by rapid deformation in the austenite recrystallization temperature range, with a final rolling temperature ≥950℃, a single-pass deformation amount of 10~15%, and a cumulative deformation amount of ≤50% in the first stage rolling; The second stage rolling is finish rolling, with a rolling temperature ≤890℃, a final rolling temperature of 750℃~800℃, no less than 3 deformation passes in the two-phase region, and a cumulative deformation amount of no less than ≥15%, with a cumulative deformation amount of ≥60% in the second stage rolling;

[0064] The elemental composition of steels #1-#4 in Examples 1 all meet the requirements of this invention in terms of mass percentage. The Ni content and Ni / C ratio of steel #5 in Comparative Example 5 do not meet the requirements of this invention. The C content and Ni / C ratio of steel #6 in Comparative Example 6 do not meet the requirements of this invention. The differences in their elemental composition are shown in Table 1.

[0065] The controlled rolling process parameters of the comparative examples 7# and 8# steel do not meet the requirements of this invention. The specific differences in process parameters are shown in Table 2.

[0066] Metallographic image of steel #1 as shown Figure 1 As shown, the scanning electron microscope image of steel #1 is as follows: Figure 2As shown.

[0067] Table 11#-8# Steel Chemical Composition (wt, %)

[0068] Steel grade C Si Mn Nb V Ti Ni Cr Cu Ni / C 1# - Example 0.05 0.10 1.5 0.025 0.04 0.008 0.8 0.2 0.18 16 2# - Example 0.04 0.15 1.4 0.030 0.05 0.010 1.0 0.2 0.10 25 3# - Example 0.04 0.15 1.3 0.020 0.04 0.010 1.2 0.2 0.15 30 4# - Example 0.03 0.15 1.5 0.021 0.05 0.010 0.9 0.2 0.20 30 5# - Comparative Example 0.04 0.20 1.4 0.030 0.05 0.015 2.0 0.2 0.12 50 6# - Comparative Example 0.10 0.25 1.2 0.025 0.06 0.015 1.0 0.2 0.15 10 7# - Comparative Example 0.03 0.11 1.5 0.025 0.03 0.013 1.1 0.2 0.18 37 8# - Comparative Example 0.04 0.12 1.3 0.021 0.03 0.014 0.8 0.2 0.16 20

[0069] Table 2 Controlled rolling process for #1-#8 steel

[0070]

[0071] The main mechanical properties, elongation, ferrite content, ferrite grain size and mausoleum components of Example 1#-4# steel and Comparative Example 5#-8# steel are shown in Table 3.

[0072] Table 3 Mechanical properties and characteristics of the steels in the examples and comparative examples

[0073]

[0074]

[0075] Comparison reveals that the smelting methods and process parameters of steels #1 to #6 are the same or similar. However, the elemental composition mass percentages of steels #1 to #4 in Examples all meet the requirements of this invention. The Ni content and Ni / C ratio of steel #5 in Comparative Example do not meet the requirements of this invention. The C content and Ni / C ratio of steel #6 in Comparative Example do not meet the requirements of this invention. The mechanical properties, ferrite content, ferrite grain size, and Maurice component of steels #1 to #4 in Examples all meet the requirements of this invention. The elongation, -80℃ impact energy, ferrite grain size and content, and Maurice component content of steels #5 to #6 in Comparative Example do not meet the requirements of this invention. The elemental composition mass percentages of steels #1 to #4 in Examples and steels #7 to #8 in Comparative Example do not meet the requirements of this invention. The controlled rolling process parameters of steels #7 to #8 in Comparative Example do not meet the requirements of this invention. The elongation, -80℃ impact energy, and ferrite grain size of steels #7 to #8 in Comparative Example do not meet the requirements of this invention. Specific details are shown in Table 3.

[0076] Comparison shows that this invention achieves excellent mechanical properties of steel plates based on special steel element composition and rolling process, with yield strength ≥440MPa, tensile strength ≥550MPa, elongation ≥33%, and impact energy of steel plates at -80℃ ≥150J.

[0077] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing 440MPa grade ship hull structural steel with high ductility and excellent toughness, characterized in that, The process includes hot metal pretreatment, converter smelting, LF refining, RH refining, continuous casting, and controlled rolling and cooling. The hot metal pretreatment includes KR desulfurization, with an S content ≤0.008% and slag thickness meeting the requirements of slag removal level 1. The heating temperature of the continuously cast billet during the continuous casting process is ≤1150℃; The controlled rolling and cooling process employs a two-stage rolling method. The first stage is roughing, with a final rolling temperature ≥950℃, a single-pass deformation of 10-15%, and a cumulative deformation of 30-33%. The second stage is finishing, with a rolling temperature of 850-860℃, a final rolling temperature of 750℃-800℃, at least three deformation passes in the two-phase region, and a cumulative deformation of ≥15%. The cumulative deformation of the second stage is ≥60%. The chemical composition of the steel, by mass percentage, is as follows: C: 0.03–0.04%, Si: 0.10–0.25%, Mn: 1.3–1.5%, Cu: 0.15–0.2%, Ni: 0.8–0.9%, Cr: 0–0.2%, Ti: 0.008–0.015%, Nb: 0.020–0.03%, V: 0.03–0.06%, Als ≥ 0.015%, with the remainder being Fe and unavoidable impurity elements; The microstructure of the steel consists of polygonal ferrite, granular bainite, and Mausoleum, wherein the polygonal ferrite content is ≥60% with a size ≤5μm, and the Mausoleum content is ≤5%. The steel has a yield strength ≥440MPa, tensile strength ≥550MPa, impact energy at -80℃ ≥100J, and elongation ≥30%.

2. The method for preparing the 440MPa grade ship hull structural steel with high ductility and excellent toughness according to claim 1, characterized in that, During the LF refining process, dry slag-forming materials and deoxidizers are added, and the storage time in the silo is ≤24 hours; the white slag retention time is ≥10 minutes.

3. The method for preparing the 440MPa grade ship hull structural steel with high ductility and excellent toughness according to claim 1, characterized in that, During the RH refining process, calcium treatment is performed before tapping, and argon blowing time is ≥10 min after wire feeding to ensure that the Ca content in the molten steel is not higher than 0.0015%.

4. The method for preparing the 440MPa grade ship hull structural steel with high ductility and excellent toughness according to claim 1, characterized in that, The continuous casting process adopts full-process protective casting, with the target superheat of the molten steel in the tundish ≤30℃, and after continuous casting, it enters the slow cooling pit for treatment.

Images