51kg-grade BCA2 crack-arrest steel having high CTOD characteristics, and manufacturing method therefor

Abstract

The present invention belongs to the technical field of the manufacturing of low-alloy steel for ships. Disclosed are a 51kg-grade BCA2 crack-arrest steel having high CTOD characteristics, and a manufacturing method therefor. The crack-arrest steel comprises the following chemical components in percentages by weight: C: 0.05％-0.13%, Si: 0.15％-0.40%, Mn: 1.20％-1.60%, P: 0.007％-0.012%, S≤0.01%, Al: 0.01％-0.05%, Nb: 0.007％-0.050%, Ti: 0.006％-0.012%, Ni: 0.50％-1.00%, Cu: 0.35％-0.75%, V: 0.03％-0.08%, one or more of Cr, Mo and RE, wherein Cr: 0.10％-0.30%, Mo: 0.08％-0.15% and RE: 0.02％-0.05%, and the balance of Fe and inevitable impurities. By using a specific composition system and a specific production process and also regulating the phase composition and texture components of a product, a crack-arrest steel having technical features such as ultra-high strength, low-temperature resistance, good weldability, high fracture toughness and crack-arresting capability is obtained. The obtained crack-arrest steel is not only suitable for key parts such as a hatch coaming and an upper deck keel of an ultra-large container ship, but can also be used for large welded structures bearing alternating loads and having high fracture toughness requirements.

Description

A 51kg grade BCA2 crack-arresting steel with high CTOD properties and its manufacturing method Technical Field

[0001] This invention belongs to the field of low-alloy shipbuilding steel manufacturing technology, specifically relating to a 51Kg grade BCA2 crack-arresting steel with high CTOD characteristics and its manufacturing method. Background Technology

[0002] As container ships become larger, orders for 18,000-20,000 TEU container ships have been steadily increasing since 2016, currently reaching 24,000 TEU. With increasing safety requirements for large container ships, higher performance demands are being placed on the thicker steel plates used in the deck superstructure. However, as steel plate thickness and strength increase, the steel becomes more brittle, and its crack-arresting properties decrease. The International Association of Classification Societies (IACS) stipulates that container ships contracted after January 1, 2014, must adhere to the obligation to use high-crack-arresting steel in their deck superstructure, thus limiting the production of mega-container ships exceeding 16,000 TEU.

[0003] Crack-arresting steels used in critical components of container ships are generally classified into three types based on their critical properties, depending on their stress conditions: BCA type, CTOD type, and a combination of BCA and CTOD. CTOD (Crack Tip Opening Displacement) is an effective method for evaluating the fracture resistance of materials and welded joints. By calculating the opening displacement near the crack tip and using displacement extrapolation interpolation, the stress intensity factor at the crack tip is obtained, and it has become one of the important indicators for characterizing the fracture toughness of materials. A larger CTOD value indicates better crack resistance at the crack tip, i.e., better toughness; conversely, a smaller CTOD value indicates worse crack resistance at the crack tip, i.e., lower toughness. This indicator has consistently been listed as a primary evaluation indicator for the fracture toughness of steel used in hulls and offshore platforms by IACS guidelines and classification society regulations of various countries, especially for steel plates thicker than 50mm used in critical structural components, where it is a mandatory performance evaluation. BCA is an evaluation index for the brittle fracture crack arrest toughness of steel plates. In current classification society specifications, it is divided into two types: BCA1 and BCA2, with a value of 6000 N / mm². 3 / 2 and 8000N / mm 3 / 2 The higher the index, the greater its ability to inhibit brittle fracture.

[0004] The invention patent CN113242910A, entitled "Ultra-thick Structural Steel with Excellent Resistance to Brittle Crack Initiation and its Manufacturing Method," discloses a steel plate for welded structures with a strength grade of only 47 kg / m². Only CTOD performance evaluation was completed; brittle crack arrest toughness testing was not conducted, thus failing to prove its ability to meet design requirements for higher strength and crack arrest toughness grades. The invention patent CN109311126B, entitled "Welded Structure with Excellent Brittle Crack Propagation Stopping Characteristics," proposes a structural steel that inhibits brittle crack propagation, with a maximum thickness of 50 mm. Its refined microstructure improves crack propagation energy, giving it high crack propagation inhibition capability. However, this material only has a high-strength grade strength grade, lacks CTOD and low-temperature toughness evaluations, and is relatively thin, making it unsuitable for structural components requiring large thickness and multiple key properties, such as the side panels of large container ships. The invention patent CN110616300B, entitled "A Low-Temperature Steel with Excellent CTOD Properties and Its Manufacturing Method," discloses a low-temperature steel with excellent CTOD properties and a strength grade of 420 MPa. While it possesses good CTOD properties, it lacks an evaluation of brittle fracture arrest toughness, failing to meet the material selection requirements for key structural components such as hatch coamings and upper decks of ultra-large container ships. Therefore, researching and developing a crack-arresting steel with a strength of 50 kg or higher, suitable for critical components of ultra-large container ships, and possessing high CTOD values ​​and BCA2-type brittle fracture arrest toughness, has become an important and urgent research topic.

[0005] Summary of the Invention

[0006] Addressing the upgrading and comprehensive performance requirements of core materials, particularly in the critical structures of ultra-large container ships, and to solve the problem of deteriorated crack arrest toughness due to plane strain in thick materials during brittle fracture, as well as the high standards required for various key material properties under mandatory specifications, this invention aims to provide a 51kg grade BCA2 crack arresting steel with high CTOD characteristics and its manufacturing method. This invention employs a specific composition system and production process, simultaneously controlling the phase composition and texture composition of the product to obtain a crack arresting steel with technical characteristics such as ultra-high strength, low-temperature resistance, easy weldability, high fracture toughness, and crack suppression capability. It is suitable not only for critical components such as hatch coamings and upper deck keels of ultra-large container ships, but also for large welded structural components subjected to alternating loads and requiring high fracture toughness.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a 51kg grade BCA2 crack-arresting steel with high CTOD properties, the chemical composition and weight percentage of which are: C: 0.05%~0.13%, Si: 0.15%~0.40%, Mn: 1.20%~1.60%, P: 0.007%~0.012%, S≤0.01%, Al: 0.01%~0.05%, Nb: 0.007%~0.050%, Ti: 0.006%~0.012%, Ni: 0.50%~1.00%, Cu: 0.35%~0.75%, V: 0.03%~0.08%, and one or more of Cr, Mo and RE, Cr: 0.10%~0.30%, Mo: 0.08%~0.15%, RE: 0.02%~0.05%, with the balance being Fe and unavoidable impurities.

[0009] Based on the above technical solution, the 51Kg grade BCA2 grade crack-arresting steel with high CTOD characteristics has a thickness of 60-100mm, a bainite content of over 60%, a yield strength ≥500MPa, a tensile strength of 600-770MPa, an elongation after fracture ≥20%, a low-temperature impact energy of -40℃ ≥200J, and a CTOD... (-10℃) ≥0.8mm, NDT≤-60℃, crack arrest toughness Kca≥8000N / mm 3 / 2 .

[0010] The following details the mechanism of action of each alloy component in the crack-arresting steel of this invention, where the percentage symbol % represents a weight percentage:

[0011] Carbon (C) is an essential element for ensuring the strength of steel, especially for TMCP steel plates, where its content should be above 0.05%. However, when the content exceeds a certain level, it significantly worsens the material's low-temperature toughness, crack-arresting toughness, and weldability. Furthermore, increasing the C content also increases the tendency for retained austenite to form during cooling, further deteriorating weldability and low-temperature toughness. Therefore, the upper limit is 0.13%. The preferred C content is controlled between 0.06% and 0.13%.

[0012] Si is the main deoxidizing component in steelmaking. To achieve sufficient deoxidation, it must contain more than 0.10%. However, if it exceeds the upper limit, it will reduce the toughness of the base material and the weld. Si in solid solution form can increase strength and also increase the ductile-brittle transition temperature. Therefore, the Si content should be 0.15% to 0.30%.

[0013] Mn (manganese) is an essential element for ensuring the strength and toughness of steel. Mn combines with sulfur (S) to form MnS, preventing hot cracking caused by FeS formation at grain boundaries. Mn is also a good deoxidizer. While manganese is a low-cost strengthening and toughening element, its content is too low to guarantee material strength. However, when the Mn content exceeds 1.60%, it exacerbates segregation in the cast billet and worsens the low-temperature toughness of the coarse-grained heat-affected zone (CGHAZ). Therefore, the optimal Mn content should be controlled between 1.20% and 1.60%.

[0014] Phosphorus (P): An unavoidable impurity element in steel, it deteriorates the steel's toughness and weldability. Studies have shown that when the P content is too high, its embrittlement properties increase significantly; therefore, the upper limit is preferably 0.012%.

[0015] If the sulfur (S) content exceeds 0.02%, it will form a large number of MnS inclusions in the steel. The formation of MnS inclusions and the resulting anisotropy severely reduce the toughness, plasticity, and weldability of the steel plate. Simultaneously, increasing the S content will increase the tendency of hot-rolled steel plates to hot crack. Therefore, measures are taken during the smelting process to minimize the S content in the steel. In this invention, the upper limit of the S content is determined to be 0.01%.

[0016] Al: As a deoxidizing and grain refining element, the content is generally above 0.01%, but when it exceeds 0.05%, it is easy to cause hot cracks in the billet, forming a large number of inclusions, and at the same time, the toughness of the steel is reduced. Therefore, the upper limit of Al content is 0.05%, and the preferred content range is 0.01% to 0.05%.

[0017] Ni: As an austenite stabilizing element, the increase of Ni can improve the solid solution strengthening effect. Nickel can reduce the critical cooling rate and delay the pearlite transformation, which is beneficial to the microstructure control, grain refinement and homogenization of the high CTOD characteristic crack-arresting steel plate of the present invention. However, excessively high content will significantly increase the cost, and its content should be controlled between 0.50% and 1.00%.

[0018] Cu (Cu) significantly improves the hardenability and corrosion resistance of steel plates and is also a stabilizing element for austenite in steel. Appropriate addition can refine the microstructure of TMCP steel plates and improve low-temperature toughness; however, excessive addition can lead to "copper embrittlement," causing cracks to easily appear on the surface and inside of the cast billet, reducing the mechanical properties of the rolled steel plate, decreasing toughness, and causing embrittlement. This invention employs a TMCP + tempering process, utilizing the dispersed precipitation of Cu to obtain high strength without compromising toughness. Therefore, the Cu content in this invention is preferably controlled between 0.45% and 0.75%.

[0019] Cr: Chromium is a weak carbide-forming element. Adding a certain amount of Cr can improve the hardenability of steel plates and promote the formation of strengthening structures represented by bainite. It can replace some of the strengthening elements such as C and Mn, reducing the toughness deterioration caused by the former's increased strength. However, adding too much Cr can also lead to a deterioration in weldability. Therefore, under the TMCP process, the preferred Cr content range is between 0.10% and 0.30%.

[0020] Mo: As an element that significantly improves hardenability and bainitrification tendency, appropriate addition of Mo to steel can inhibit the formation of pearlite. Its effect on improving the strengthening of steel is similar to that of Cr. It improves the strength of steel through the formation of carbides. However, excessive addition will also cause deterioration of weldability and low-temperature toughness. Therefore, the preferred Mo content range is between 0.08% and 0.15%.

[0021] Nitrogen (Nb) is one of the key elements for grain refinement and strengthening. Its grain refinement effect manifests in two ways: firstly, it significantly delays austenite recrystallization, increasing the recrystallization temperature and preventing the growth of recrystallized austenite; secondly, as the rolling temperature decreases, Nb's C and N compounds disperse and precipitate before the austenite transforms into ferrite, becoming ferrite nucleation sites. This allows ferrite to form under low supercooling, making it less prone to growth and refining the ferrite grain size. As an element with an extended non-recrystallization temperature range, Nb can improve crack arrest toughness by increasing high-angle grain boundaries through grain refinement.

[0022] Ti: Trace amounts of titanium combine with C and N in steel to form fine and stable C and N compound particles. During the slab heating process, it can effectively prevent austenite grain coarsening. During welding, it can suppress the coarsening of weld heat-affected grains and improve the low-temperature toughness of the matrix structure and the heat-affected zone of the weld.

[0023] N can form fine precipitates with Nb, Ti, and V, which can strengthen and refine the grains, improving strength and toughness. However, excessive N content can deteriorate weldability and easily cause strain aging, which can worsen low-temperature toughness. The N content should be controlled between 0.001% and 0.004%.

[0024] RE: Rare earth elements can significantly reduce the deteriorating behavior caused by the segregation of low-melting-point elements at grain boundaries in steel, thereby improving strength and toughness by purifying grain boundaries. They also alter the distribution and morphology of sulfides in steel, particularly MnS inclusions which tend to form fine stripes during hot rolling, resulting in significant directionality and severely deteriorating transverse properties. Simultaneously, a certain amount of rare earth elements can also improve the weldability and corrosion resistance of steel, with a preferred content of 0.02%–0.05%.

[0025] This invention also provides a method for manufacturing the aforementioned 51kg grade BCA2 grade crack-arresting steel with high CTOD properties, mainly including smelting, refining, continuous casting, heating, rolling, cooling, and tempering processes; wherein,

[0026] The heating temperature during the heating process is 1100~1150℃, and the holding time is 0.8~1.5min / mm. This temperature setting is because temperatures below 1100℃ are insufficient to allow alloying elements such as Nb to completely dissolve into the austenite, which cannot guarantee the final rolling temperature required for hot rolling. Temperatures above 1150℃ will cause significant coarsening of the original austenite grains, which will reduce the low-temperature toughness of the steel plate.

[0027] The rolling process is divided into two stages: the first stage rolling is carried out in the austenite recrystallization zone, and the second stage rolling is carried out in the non-recrystallization zone.

[0028] The cooling process is laminar flow cooling, with an initial cooling temperature above 730℃ and a final cooling temperature below 550℃, and the cooling rate is controlled at 1-4℃ / s.

[0029] The tempering process involves a tempering temperature of 580-630℃ and a tempering time of 1.5-2.3 min / mm. After exiting the furnace, the furnace is air-cooled to room temperature.

[0030] Based on the above technical solution, further, the heating temperature during the heating process is 1100~1140℃, and the holding time is 1~1.2min / mm.

[0031] Based on the above technical solution, further, the initial rolling temperature of the first stage rolling is 930℃~1105℃, and the cumulative reduction is not less than 45%; the initial rolling temperature of the second stage rolling is 800℃~840℃, the final rolling temperature is 750℃~790℃, and the cumulative reduction is not less than 45%.

[0032] Based on the above technical solution, the initial cooling temperature is 690–730℃, and the final cooling temperature is 500–550℃.

[0033] Based on the above technical solution, the smelting process further adopts deep desulfurized molten iron with S≤0.02%. After the molten iron arrives at the converter, it is smelted by a combination of "double slag" dephosphorization and "slag removal" of molten steel after the furnace. The final slag basicity is controlled between R=3.0±0.1. The slag blocking operation and the steel discharge time are not less than 6 minutes.

[0034] Based on the above technical solution, the smelting process further adopts a high-pulling carbon single-point blowing method for production.

[0035] Based on the above technical solution, the refining is further described as LF refining, which uses aluminum granules, silicon carbide, and calcium carbide to adjust the slag, thereby further reducing the content of harmful impurities such as O, S, and non-metallic inclusions.

[0036] Based on the above technical solution, further, the superheat during the continuous casting process is ≤20℃, heavy pressure is applied and electromagnetic stirring is carried out at the end of the billet solidification. The heavy pressure is 15-25mm, and the secondary cooling adopts segmented cooling. The first segment is strong cooling with a cooling rate of 10-30℃ / s, and the second segment is weak cooling with a cooling rate of 5-15℃ / s. The continuous casting billet pulling speed is 1.0-1.3m / min, and the thickness of the cast slab is 280-320mm.

[0037] The advantages of this invention over the prior art are as follows:

[0038] (1) The present invention provides a 51kg grade, BCA2 type brittle-tough crack-arresting steel with high CTOD characteristic value, suitable for key parts of ultra-large container ships, with CTOD≥0.8mm, low-temperature impact energy at -40℃≥200J, and Kca≥8000N / mm 3 / 2 This meets the requirements of ultra-large container ships for improved steel strength and fracture toughness.

[0039] (2) Since crack-arresting steel requires welding and post-weld stress relief during manufacturing to reduce fractures caused by stress concentration at weld joints, steel plates produced using only the TMCP process often fail to meet tempering stability requirements and are prone to performance degradation. However, this invention, through TMCP + tempering, ensures both strength and improved material toughness, while also guaranteeing good tempering stability in the steel plate, which is beneficial for engineering applications.

[0040] (3) This invention utilizes Nb and Ti elements to inhibit austenite grain growth and promote nucleation during austenite transformation to refine grains, control the thickness of the core structure, and improve the uniformity of the structure; coupled with a corresponding unique production process, it solves the problem of matching technical indicators for thick, high-CTOD type crack-arresting steel.

[0041] (4) This invention achieves the combined effects of fine grain, precipitation and phase transformation strengthening by adding appropriate amounts of toughening elements and using precise smelting and TMCP+ tempering processes; for example, by adding appropriate amounts of Cu, precipitation strengthening is ensured to guarantee strength, while the addition of Mo improves tempering stability, and the addition of Ni avoids the deterioration of low-temperature toughness, crack arrest performance and weldability.

[0042] (5) This invention achieves high fracture toughness and crack arrest toughness by controlling the phase composition and texture configuration, while also possessing ultra-high strength, especially obtaining bainite with a certain composition and {112} <110> Texture can improve the ability to coordinate deformation and the resistance to crack propagation, thereby generating higher crack initiation energy and crack propagation energy, and achieving good fracture toughness.

[0043] (6) The preparation process of the present invention is complete and economical, and can meet the needs of batch stable production. Attached Figure Description

[0044] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0045] Figure 1 is a microstructure of the crack-arresting steel plate prepared in Example 4.

[0046] Figure 2 shows the evaluation results of the crack arrest toughness of the crack-arresting steel plate prepared in Example 2. Detailed Implementation

[0047] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0048] Examples 1-7

[0049] This embodiment provides a method for manufacturing a 51Kg grade BCA2 crack arresting steel with high CTOD properties. The chemical composition and weight percentage of the crack arresting steel are shown in Table 1.

[0050] Table 1. Chemical composition and weight percentage (%) of the crack-arresting steels in Examples 1-7

[0051] Includes the following steps:

[0052] (1) Smelting: Deep desulfurized molten iron (S≤0.02%) is used. After the molten iron is delivered to the converter, the process of "double slag" dephosphorization and "slag removal" of molten steel after the furnace is adopted. The final slag basicity is controlled between R=3.0±0.1. Through effective slag blocking operation, a large amount of slag is prevented from being discharged. The steel discharge time is not less than 6 minutes. The smelting process adopts the high carbon pulling one-time blowing method. The main elements of the steel are adjusted to the range of Table 1 in the converter, and alloy components are added for smelting as required.

[0053] (2) LF refining: The molten steel from the converter is refined a second time to further reduce the content of harmful impurities such as O, S, and non-metallic inclusions; aluminum particles, silicon carbide and calcium carbide are used to adjust the slag during the LF refining process.

[0054] (3) Continuous casting: The superheat during continuous casting is ≤20℃. Heavy pressure (15~25mm) and electromagnetic stirring at the end of the solidification of the billet are adopted. The secondary cooling adopts segmented cooling. The first stage is strong cooling with a cooling rate of 10~30℃ / s, and the second stage is weak cooling with a cooling rate of 5~15℃ / s. The continuous casting billet pulling speed is 1.0-1.3m / min, and the thickness of the cast slab is 300mm.

[0055] (4) Heating: The above steel slab is heated. The heating temperature and holding time are shown in Table 2.

[0056] (5) Rolling: First, roll in the austenite recrystallization zone, and then roll in the non-recrystallization zone in two stages. The initial rolling temperature, the second initial rolling temperature and the final rolling temperature are shown in Table 2. Ensure that the cumulative reduction of each stage of rolling is not less than 45%.

[0057] (6) Cooling: The cooling method is laminar flow cooling. The start-up cooling temperature, final cooling temperature and cooling rate are shown in Table 2.

[0058] (7) Tempering treatment: The cooled steel plate is tempered. The tempering temperature and tempering time are shown in Table 2. The steel plate is air-cooled to room temperature after being taken out of the furnace.

[0059] Table 2. Process parameters for preparing crack-arresting steel in Examples 1-7

[0060] The mechanical properties of the crack-arresting steel plates prepared in each embodiment are shown in Table 3; wherein the CTOD of the base material of the crack-arresting steel plates is... (-10℃) For values ​​greater than 0.8 mm, after welding with a heat input of 50 KJ / cm, the CTOD of the welded joint... (-10℃) The values ​​are greater than 0.60 mm, all of which are far higher than the requirements of international classification society standards.

[0061] Table 3 Mechanical properties of crack-arresting steels in Examples 1-7

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A 51kg grade BCA2 crack-arresting steel with high CTOD properties, characterized in that, The chemical composition and weight percentage are as follows: C: 0.05%–0.13%, Si: 0.15%–0.40%, Mn: 1.20%–1.60%, P: 0.007%–0.012%, S≤0.01%, Al: 0.01%–0.05%, Nb: 0.007%–0.050%, Ti: 0.006%–0.012%, Ni: 0.50%–1.00%, Cu: 0.35%–0.75%, V: 0.03%–0.08%, and one or more of Cr, Mo, and RE, with Cr: 0.10%–0.30%, Mo: 0.08%–0.15%, RE: 0.02%–0.05%, and the balance being Fe and unavoidable impurities.

2. The 51kg grade BCA2 grade crack-arresting steel with high CTOD properties according to claim 1, characterized in that, The 51kg grade BCA2 crack-arresting steel with high CTOD properties has a thickness of 60-100mm, a bainite content of over 60%, a yield strength ≥500MPa, a tensile strength of 600-770MPa, an elongation after fracture ≥20%, and a low-temperature impact energy of -40℃ ≥200J. CTOD (-10℃) ≥0.8mm, NDT≤-60℃, crack arrest toughness Kca≥8000N / mm 3 / 2 .

3. The method for manufacturing 51Kg grade BCA2 grade crack-arresting steel with high CTOD properties as described in claim 1 or 2, characterized in that, It mainly includes the processes of smelting, refining, continuous casting, heating, rolling, cooling, and tempering; among which, The heating temperature during the heating process is 1100~1150℃, and the holding time is 0.8~1.5min / mm; The rolling process is divided into two stages: the first stage rolling is carried out in the austenite recrystallization zone, and the second stage rolling is carried out in the non-recrystallization zone. The cooling process is laminar flow cooling, with an initial cooling temperature above 730℃ and a final cooling temperature below 550℃, and the cooling rate is controlled at 1-4℃ / s. The tempering process involves a tempering temperature of 580-630℃ and a tempering time of 1.5-2.3 min / mm. After exiting the furnace, the furnace is air-cooled to room temperature.

4. The manufacturing method according to claim 3, characterized in that, The heating temperature during the heating process is 1100~1140℃, and the holding time is 1.0~1.2min / mm.

5. The manufacturing method according to claim 3, characterized in that, The initial rolling temperature of the first stage is 930℃~1105℃, and the cumulative reduction is not less than 45%. The initial rolling temperature of the second stage is 800℃~840℃, and the final rolling temperature is 750℃~790℃, with a cumulative reduction of not less than 45%.

6. The manufacturing method according to claim 3, characterized in that, The initial cooling temperature is 690–730℃, and the final cooling temperature is 500–550℃.

7. The manufacturing method according to claim 3, characterized in that, The smelting process uses deep desulfurized molten iron with S≤0.02%. After the molten iron reaches the converter, it is smelted using a process that combines "double slag" dephosphorization with "slag removal" of the molten steel after the furnace. The final slag basicity is controlled between R=3.0±0.

1. Slag blocking operation is carried out, and the steel discharge time is not less than 6 minutes.

8. The manufacturing method according to claim 7, characterized in that, The smelting process adopts a high-pulling carbon single-point blowing method for production.

9. The manufacturing method according to claim 3, characterized in that, The refining process described is LF refining, which uses aluminum granules, silicon carbide, and calcium carbide to adjust the slag.

10. The manufacturing method according to claim 3, characterized in that, During the continuous casting process, the superheat is ≤20℃. Heavy pressure reduction and electromagnetic stirring at the end of the billet solidification are adopted. The heavy pressure reduction is 10-30mm. The secondary cooling adopts segmented cooling, with strong cooling in the first segment at a cooling rate of 10-30℃ / s and weak cooling in the second segment at a cooling rate of 5-15℃ / s. The continuous casting billet pulling speed is 1.0-1.3m / min, and the thickness of the cast slab is 280-320mm.

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