A marine crack-arresting steel EH47 and its preparation method

Abstract

This invention relates to the field of metallurgical materials technology, specifically to a marine crack-arresting steel EH47 and its preparation method. This invention employs a low-C and Mg-Ca-Ti-Al composite microalloying design, precisely controlling the elemental ratio to generate spherical composite inclusions of TiO₂. X The resulting material is MgO-Al₂O₃-TiN-(Mn,Ca)S with an average particle size of 1~3μm. This method involves composite refining, inclusion modification, two-stage controlled rolling, and ultra-rapid cooling, eliminating the need for heat treatment and resulting in a short process flow. The thick steel plate produced by this invention exhibits a yield strength ≥460MPa, a low-temperature impact energy ≥200J at -40℃, and a crack-arresting toughness Kca ≥8800N / mm at -10℃. 3 / 2 After welding at 600kJ / cm, the performance of the heat-affected zone does not decrease significantly, which can greatly improve the welding efficiency; the EH47 has a uniform microstructure throughout its thickness, excellent welding performance, and low cost, making it suitable for the construction of high-end marine equipment such as ultra-large container ships.

Description

Technical Field

[0001] This invention relates to the field of metallurgical materials technology, specifically to a marine crack-arresting steel EH47 and its preparation method. Background Technology

[0002] As the global shipping industry moves towards larger, lighter, and safer vessels, ultra-large container ships (18,000 TEU and above) face extremely high comprehensive performance requirements for their steel plates, particularly in key areas such as the main deck, top deck, and hatch coamings. These steels must possess yield strength exceeding 460 MPa, excellent low-temperature impact toughness, and outstanding crack arrest properties to prevent rapid crack propagation and major safety accidents during ship operation. EH47 steel, a high-strength marine structural steel specified in the IACS standard, is currently a core material used in the construction of large container ships. Its standard thickness is typically 40-85 mm, with some special sections requiring up to 100 mm. Welding of medium-thick steel plates currently employs high heat input welding, generally exceeding 400 kJ / cm. With increasing welding heat input, the heat-affected zone (HAZ) endures higher temperatures for longer periods, leading to severe austenite grain coarsening, especially in the coarse-grained region. This significantly reduces the strength and toughness of this area, making it a weak point in the weld joint.

[0003] Chinese patent application CN202511683975.3 does not mention the crack-arresting properties of steel for high heat input welding. Chinese patents CN201110172661.9 and CN201510700964.1 both rely on boron (B) for microalloying of the steel; however, adding boron during smelting is difficult, and it is prone to segregation during subsequent production, resulting in high production difficulty and cost. Chinese patents CN202511047808.X and CN202411743684.4 research steel for high heat input welding, but their manufacturing methods require subsequent quenching and tempering heat treatments, resulting in lengthy processes, high energy consumption, and high production costs. Summary of the Invention

[0004] The purpose of this invention is to provide a marine crack-arresting steel EH47 and its preparation method to solve the problems mentioned in the background art.

[0005] To address the aforementioned technical problems, this invention provides a marine crack-arresting steel, EH47, with the following chemical composition by weight percentage: C: 0.05%~0.8%, Si: 0.10%~0.30%, S: 0.002%~0.0058%, Mn: 1.5%~2.0%, Ti: 0.01%~0.06%, P≤0.012%, Cu≤0.30%, Ni: 0.05%~0.55%, Cr≤0.25%, Ca: 0.0015%~0.0040%, N: 0.004%~0.015%, O≤0.002%, Al: 0.02%~0.05%, Mg: 0.01%~0.06%, Nb≤0.05%, V≤0.02%, H≤0.00015%, with the balance being Fe and unavoidable impurities.

[0006] Furthermore, the inclusions in the marine crack-arresting steel EH47 are TiO2. X -MgO-Al2O3-TiN-(Mn,Ca)S spherical composite inclusions with an average particle size of 1~3μm and a microstructure of bainite + ferrite + pearlite.

[0007] Furthermore, the marine crack-arresting steel EH47 has a yield strength ≥460MPa, a tensile strength of 570~720MPa, and an elongation after fracture ≥17%; a core low-temperature impact energy at -40℃ ≥200J; and a crack arrest coefficient Kca at -10℃ ≥8800N / mm. 3 / 2 .

[0008] On the other hand, the present invention provides a method for preparing the marine crack-arresting steel EH47, comprising the following steps: Step 1: S1: The steel is smelted in a converter, and the C content is precisely controlled to be ≤0.05wt.% and the P content to be ≤0.008wt.%. The steel is deoxidized and alloyed simultaneously during the tapping process, and then it enters the LF furnace for refining. Argon gas is used for stirring throughout the process to create white slag for deep deoxidation and desulfurization. The white slag is maintained for ≥20 minutes to ensure the deoxidation and desulfurization effect. Furthermore, during the tapping process, a double slag-blocking system using a slag-blocking cap and a slag-blocking plug is employed. Simultaneously, silicon-manganese alloy and aluminum-iron are added for initial deoxidation. Subsequently, Cr, Nb, Cu, Ti, V, and Ni are added in batches to prevent alloy agglomeration. Immediately after tapping, the ladle is purged with argon for weak stirring to remove large particle inclusions in the initial stage. S2: The ladle is transferred to the LF furnace, and argon blowing and stirring are carried out in a closed system throughout the process. The argon flow rate is controlled at 30L / min to avoid secondary oxidation of the molten steel. Alkaline white slag is quickly formed. The slag material mass ratio is lime:fluorite:bauxite = 5:2:1. The white slag is maintained for ≥25min after formation to further reduce the S content in the steel to 0.002~0.0058wt.%. The temperature of the molten steel is monitored throughout the process, and the temperature at the end of refining is 1570~1580℃. S3: After LF refining, the steel is transferred to an RH vacuum furnace and evacuated to a vacuum level ≤0.5mbar. The vacuum time is maintained for ≥20min, and the entire process is used for degassing to efficiently remove harmful gases such as hydrogen, nitrogen, and oxygen from the steel, ensuring that the H content is ≤0.00015wt.% and the O content is ≤0.004wt.%. After maintaining the vacuum for 10min, magnesium-calcium composite cored wire is precisely added through a vacuum feeding device at a feeding speed of 1.5m / s to complete the composite modification treatment of inclusions, ensuring that Mg and Ca elements are uniformly dissolved and directionally generated into spherical composite inclusions. After RH treatment, the steel is transferred to a VD furnace for deep vacuum degassing to further improve the purity of the molten steel. After maintaining the vacuum for 5min, the vacuum is broken, and soft argon is blown for 8min to promote the full flotation and removal of fine inclusions. The soft argon flow rate is controlled at 10L / min to avoid exposing the molten steel. Step 2: Use 300~350mm thick slabs for full-process protective continuous casting, implement protective casting throughout the process to prevent secondary oxidation of molten steel; control the continuous casting temperature at 1550~1570℃, the casting speed at 0.7~1.6m / min, and perform slow cooling treatment after the slab is cast to reduce internal residual stress. Step 3: Heat the continuously cast billet uniformly to 1150~1180℃ for ≥35min to ensure that the microalloying elements are fully dissolved and to avoid excessive coarsening of austenite grains, thus laying the foundation for subsequent rolling to refine the microstructure. Step 4: A two-stage rolling process is adopted. The first stage is the recrystallization zone rolling, with an initial rolling temperature of 1020~1160℃ and a large reduction rolling mode to fully break down the original coarse structure of the billet. The single-pass reduction rate is ≥15%, the intermediate billet thickness is controlled at ≥2.2 times the finished product thickness, and the final rolling temperature is controlled at ≥980℃. The second stage is the non-recrystallization zone rolling, with an initial rolling temperature of 710~820℃, a single-pass reduction rate of ≥10%, a cumulative reduction rate of ≥60%, and a final rolling temperature controlled at 20~50℃ above Ar3. This allows the austenite grains to be fully deformed, forming a large number of deformation bands, creating conditions for the nucleation of acicular ferrite. The calculation method for Ar3 is: Ar3 = 910 - 310 × ω C -80×ω Mn -20×ω Cu -15×ω Cr -55×ω Ni -0.35×(h-8); Where, ω C ω Mn ω Cu ω Cr ω Ni These represent the mass percentage of each element in the steel; h represents the thickness of the steel plate, in mm.

[0009] Step 5: Immediately after rolling, ultra-fast forced cooling is performed, with the cooling rate of the steel plate core controlled at 6~12℃ / s and the final cooling temperature set at 220~380℃. Subsequently, air cooling is performed to the red-hot temperature of 420~460℃. The latent heat of phase transformation of the steel itself is used to achieve uniform transformation of the microstructure, and finally a uniform and dense microstructure is formed with fine needle-like ferrite as the matrix and a small amount of degenerate pearlite dispersedly, thus completely avoiding the formation of brittle microstructure.

[0010] Compared with the prior art, the beneficial effects achieved by the present invention are: To address the shortcomings of existing EH47 steel, such as embrittlement of the heat-affected zone during high heat input welding, poor crack arrest performance, undesirable inclusion morphology, and complex and costly production processes, this invention aims to provide a method for preparing marine crack arrest steel EH47. This method employs a low-carbon, low-alloy, and Mg-Ca-Ti-Al composite microalloying composition design. The control of each element's composition and its working principle are as follows: C employs a low-carbon design to reduce sensitivity to cold cracking during welding, suppress grain coarsening in the weld heat-affected zone, and balance the basic strength requirements of the steel. Si is the main deoxidizing element, moderately refining the ferrite structure, with strict control over the upper limit to avoid increased inclusions and reduced toughness. Mn is the core solid solution strengthening element, lowering the austenite phase transformation temperature, refining the matrix structure, and simultaneously improving strength and low-temperature toughness. Ti forms stable TiN and TiO particles at high temperatures, refining the billet structure, and forms composite inclusions with Mg and Ca, inducing acicular ferrite nucleation and improving the low-temperature toughness of the weld heat-affected zone. Cu is added in trace amounts to achieve solid solution strengthening, improving the steel's strength and corrosion resistance in marine environments, with strict control over the content to avoid copper embrittlement. Ni improves the hardenability and low-temperature toughness of the steel, but Ni is expensive, and adding more Ni will increase the cost of the steel. Cr assists in improving the hardenability of the steel. Ca, added in trace amounts, modifies sulfide and oxide inclusions in steel, transforming elongated, angular, brittle inclusions into fine, dispersed, spherical calcium-sulfur composite inclusions and calcium aluminate inclusions. Mg is the core innovative modifying element of this invention, synergistically forming TiOx-MgO-Al2O3-TiN-(Mn,Ca)S spherical composite inclusions with Ca, Ti, and Al. Nb forms dispersed carbonitrides, pinning austenite grain boundaries, inhibiting grain growth during rolling and welding, and refining the microstructure of the base metal and the weld heat-affected zone. V assists in precipitation strengthening, synergistically refining grains with Nb and Ti, improving the high-temperature stability of the steel and the performance of welded joints. In addition, the content of impurities such as P, S, O, N, and H is controlled to ultra-low levels, reducing grain boundary segregation and brittle inclusions, purifying the steel, and improving low-temperature toughness and crack resistance.

[0011] After smelting using the process described in this invention, spherical composite inclusion TiO is obtained. X The -MgO-Al2O3-TiN-(Mn,Ca)S inclusion has a microstructure of bainite, ferrite, and pearlite, with an average grain size of 1~3μm. This inclusion can, on the one hand, pin austenite grain boundaries, inhibiting austenite grain growth; on the other hand, it can act as an effective nucleation site, inducing the formation of acicular ferrite within the grains, refining the grains in the heat-affected zone (HAZ), and solving the problem of reduced strength and toughness in the HAZ due to severe grain coarsening caused by prolonged high-temperature residence time. Attached Figure Description

[0012] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a metallographic diagram of the weld heat-affected zone in Embodiment 1 of the present invention; Figure 2 This is a metallographic diagram of the weld heat-affected zone in Embodiment 2 of the present invention; Figure 3This is a metallographic diagram of the weld heat-affected zone in Embodiment 3 of the present invention; Figure 4 This is a metallographic diagram of the weld heat-affected zone in Embodiment 4 of the present invention; Figure 5 These are morphological images and elemental distribution diagrams of typical spherical composite inclusions in Embodiment 1 of the present invention; Figure 6 These are typical spherical composite inclusion morphology diagrams and elemental distribution diagrams in Embodiment 2 of the present invention. Detailed Implementation

[0013] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] The following production process was adopted in embodiments 1 to 4 of the present invention (all with a plate thickness of 80 mm), wherein the content of each element is a weight percentage; A method for preparing marine crack-arresting steel EH47 includes the following steps: Step 1: Converter smelting and primary deoxidation alloying: S1: A 100t top-and-bottom blown converter is used for smelting. The sulfur and phosphorus content of the molten iron is strictly controlled. The molten iron is pre-desulfurized to S≤0.005%, and the temperature of the molten iron entering the furnace is ≥1350℃. The carbon and temperature are precisely controlled during the converter blowing process. The final control is C≤0.05% and P≤0.008%. The tapping temperature is controlled at 1600~1620℃ to prevent slag discharge and dryness. During the tapping process, a double slag blocking method of slag cap + slag plug is used. Silicon manganese alloy and aluminum iron are added simultaneously for initial deoxidation. Cr, Nb, Cu, Ti, V and Ni are added in batches to avoid alloy agglomeration. After tapping, the ladle is immediately blown with argon for weak stirring to remove large particle inclusions in the early stage. S2: The ladle is transferred to the LF furnace station, where it is stirred with argon gas in a closed system throughout the process. The argon gas flow rate is controlled at 30L / min to prevent secondary oxidation of the molten steel. Alkaline white slag is quickly formed with a slag ratio of lime:fluorite:bauxite = 5:2:1. The white slag is maintained for ≥25min after formation to achieve deep deoxidation and desulfurization, further reducing the S content in the steel to 0.002~0.0058wt.%. The alloy content is finely adjusted in real time according to the steel composition to ensure that each element accurately hits the target range. The steel temperature is monitored throughout the process, and the refining end temperature is controlled at 1570-1580℃. S3: After LF refining, the steel is transferred to an RH vacuum furnace and evacuated to a vacuum level ≤0.5mbar. The pure vacuum is maintained for ≥20min, with full-process circulation degassing to efficiently remove harmful gases such as hydrogen, nitrogen, and oxygen from the steel, controlling the H content below 0.00015% and the O content ≤0.004%. After maintaining the vacuum for 10min, magnesium-calcium composite cored wire is precisely added through a vacuum feeding device, with the wire feeding speed controlled at 1.5m / s, to complete the composite modification treatment of inclusions, ensuring uniform dissolution of Mg and Ca elements and the directional formation of spherical composite inclusions. After RH treatment, the steel is transferred to a VD furnace for deep vacuum treatment to further improve the purity of the molten steel. After maintaining the vacuum for 5min, the vacuum is broken, and soft argon is blown for 8min to promote the full flotation and removal of fine inclusions. The soft argon flow rate is controlled at 10L / min to avoid exposing the molten steel. Step 2: A 325mm thick slab continuous casting machine is used, with full-process protective casting. The ladle-tundish-crystallizer system employs triple protection: long nozzle, argon seal, and submerged entry nozzle to prevent secondary oxidation by air. The superheat of the molten steel in the tundish is controlled at 20~30℃, the casting speed is stabilized at 0.9m / min, and the cooling water flow rate in the crystallizer is controlled at 120~130m³. 3 The vibration frequency is 120~130 times / min. A weak cooling regime is adopted to reduce surface cracks and center segregation of the billet. After the billet is cut, it is immediately transferred to the slow cooling pit. The slow cooling time is 12 hours to slowly release the residual stress inside the billet and avoid cracking. The slow cooling temperature is controlled above 600℃ when entering the pit and below 200℃ when leaving the pit. Step 3: Billet Heating and Homogenization: After slow cooling, the billet is pushed into a walking beam furnace and a segmented heating system is adopted: the preheating section temperature is 800~900℃, the heating section temperature is 1120~1160℃, and the homogenization section temperature is 1165℃. The total heating time is controlled at 240~270min according to the billet thickness, and the homogenization time is ≥40min to ensure that the microalloying elements Nb, Ti, and V are fully dissolved, while avoiding excessive coarsening of austenite grains. The air-fuel ratio of the furnace is controlled at 1.05~1.1 to prevent decarburization of the billet surface.

[0015] Step 4: Using a 4300mm wide and thick plate rolling mill, the rolling process is controlled in two stages, with strict control over the reduction rate and temperature parameters: The first stage is the recrystallization zone rolling: the initial rolling temperature is 1080℃, the single-pass reduction rate is 15%, and the rolling is carried out three times to fully break down the original coarse austenite structure of the billet and refine the grains. The second stage is rolling in the non-recrystallization zone: the single-pass reduction rate is 12%, and 5 passes are rolled. The final rolling temperature is strictly controlled at 30°C above the corresponding Ar3 phase transformation temperature in each embodiment. Finally, it is rolled into an 80mm finished steel plate, which causes the austenite grains to form a large number of flat deformation bands, providing core sites for the subsequent nucleation of acicular ferrite. The calculation method for Ar3 is: Ar3 = 910 - 310 × ω C -80×ω Mn -20×ω Cu -15×ω Cr -55×ω Ni -0.35×(h-8); Where, ω C ω Mn ω Cu ω Cr ω Ni These represent the mass percentage of each element in the steel; h represents the thickness of the steel plate, in mm. Step 5: Immediately after rolling, the steel plate enters an ultra-fast cooling system, employing symmetrical cooling of the upper and lower surfaces. The cooling rate of the steel plate's core is stabilized at 9℃ / s, with pure water as the cooling medium and water pressure controlled at 0.8~1.0MPa. Rapid cooling is achieved to a final cooling temperature of 260℃, instantly inhibiting austenite grain growth. After cooling is terminated, the steel plate is removed from the cooling bed and air-cooled for natural reheating. Utilizing the latent heat of phase transformation within the steel plate, the temperature rises to 440℃, completing the uniform transformation of austenite to fine-grained ferrite. Throughout the process, excessively rapid water cooling is avoided to prevent excessive internal stress, ensuring uniform microstructure across the entire thickness of the 80mm thick plate, with no surface-to-core gradient difference. Sample preparation using a high heat input of 600KJ / cm: After the steel plate is air-cooled to room temperature, welding samples are cut according to the CCS "Materials and Welding" specifications. Gas-electric vertical welding is employed, with the welding heat input strictly set to 600KJ / cm.

[0016] Example 1: The chemical composition of the marine crack-arresting steel EH47 provided in this example is as follows (mass percentage, balance being Fe and unavoidable impurities): C: 0.055%, Si: 0.15%, Mn: 1.6%, P: 0.009%, S: 0.0035%, Ti: 0.02%, Nb: 0.03%, V: 0.008%, Cu: 0.15%, Ni: 0.25%, Cr: 0.12%, Al: 0.03%, Ca: 0.0020%, Mg: 0.02%, N: 0.008%, O: 0.0015%, H: 0.00012%; carbon equivalent is 0.374%, and Ar3 temperature is 721.2℃; CCS standard performance test results: Yield strength 465MPa, tensile strength 585MPa, elongation after fracture 21.5%; base metal -40℃ impact energy (1 / 2 thickness) 228J, weld heat-affected zone -40℃ impact energy 62J; -10℃ brittle crack arrest toughness Kca=9035N / mm 3 / 2 All indicators meet the requirements of CCS specifications and EH47 ship plate requirements.

[0017] Figure 1The image shows the metallographic structure of the heat-affected zone after actual welding. It can be seen that acicular ferrite is formed in the steel, and the grains are refined to a certain extent.

[0018] Example 2: The chemical composition of the marine crack-arresting steel EH47 provided in this example is as follows (mass percentage, balance being Fe and unavoidable impurities): C: 0.065%, Si: 0.20%, Mn: 1.7%, P: 0.008%, S: 0.0030%, Ti: 0.03%, Nb: 0.035%, V: 0.01%, Cu: 0.20%, Ni: 0.45%, Cr: 0.18%, Al: 0.035%, Ca: 0.0028%, Mg: 0.03%, N: 0.007%, O: 0.0012%, H: 0.00011%, carbon equivalent is 0.43%, and Ar3 temperature is 697.2℃; CCS standard performance test results: Yield strength 480MPa, tensile strength 615MPa, elongation after fracture 20.5%; base metal -40℃ impact energy (1 / 2 thickness) 246J, weld heat-affected zone -40℃ impact energy 70J; -10℃ brittle crack arrest toughness Kca=9528N / mm 3 / 2 Its toughness and crack arrest performance are superior to those of Example 1, making it suitable for welding conditions with higher requirements.

[0019] Figure 2 The images show metallographic images of the weld heat-affected zone after actual welding. In Example 2, a large number of intragranular needle-like ferrites were generated in the weld heat-affected zone, and the grains were significantly refined.

[0020] Example 3: The chemical composition of the marine crack-arresting steel EH47 provided in this example is as follows (mass percentage, balance is Fe and unavoidable impurities): C: 0.05%, Si: 0.25%, Mn: 1.8%, P: 0.007%, S: 0.0025%, Ti: 0.025%, Nb: 0.028%, V: 0.009%, Cu: 0.18%, Ni: 0.30%, Cr: 0.15%, Al: 0.04%, Ca: 0.0035%, Mg: 0.045%, N: 0.006%, O: 0.0010%, H: 0.00010%, carbon equivalent is 0.414%, Ar3 temperature is 702.9℃; CCS standard performance test results: Yield strength 480MPa, tensile strength 580MPa, elongation after fracture 22.0%; base metal -40℃ impact energy (1 / 2 thickness) 235J, weld heat-affected zone -40℃ impact energy 75J; -10℃ brittle crack arrest toughness Kca=9973N / mm 3 / 2 With a low carbon equivalent, it has extremely low sensitivity to cold cracking during welding and is suitable for welding with ultra-high heat input of 600KJ / cm.

[0021] Figure 3 The images show metallographic images of the weld heat-affected zone after actual welding. In Example 3, a large number of intragranular needle-like ferrites were generated in the weld heat-affected zone, and the grains were significantly refined.

[0022] Example 4: The chemical composition of the marine crack-arresting steel EH47 provided in this example is as follows (mass percentage, balance being Fe and unavoidable impurities): C: 0.07%, Si: 0.30%, Mn: 2.0%, P: 0.008%, S: 0.0032%, Ti: 0.04%, Nb: 0.04%, V: 0.012%, Cu: 0.25%, Ni: 0.50%, Cr: 0.20%, Al: 0.045%, Ca: 0.0030%, Mg: 0.035%, N: 0.0075%, O: 0.0013%, H: 0.00011%. The carbon equivalent is 0.496%, and the Ar3 temperature is 667.6℃. CCS standard performance test results: Yield strength 490MPa, tensile strength 630MPa, elongation after fracture 19.5%; base metal -40℃ impact energy (1 / 2 thickness) 240J, weld heat-affected zone -40℃ impact energy 68J; -10℃ brittle crack arrest toughness Kca=11765N / mm 3 / 2 It boasts both superior strength and crack arrest performance, meeting the most stringent requirements for load-bearing components of ultra-large container ships.

[0023] Figure 4 The image shows a metallographic image of the heat-affected zone after actual welding. In Example 4, a large number of acicular ferrites are generated, and the acicular ferrites interlock with each other to form an interlocking mechanism, which can effectively prevent crack propagation. This causes the crack to deflect during the propagation process, increasing the work required for crack propagation, thus effectively preventing crack propagation.

[0024] Figure 5 and Figure 6 These are typical composite inclusions in the steels of Examples 1 and 2, respectively. The inclusions induce the formation of acicular ferrite, which can effectively refine the grains in the heat-affected zone.

[0025] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0026] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing marine crack-arresting steel EH47, characterized in that: Includes the following steps: Step 1: Converter smelting and compound refining: S1: Smelting is carried out in a converter, and the carbon content of the tapped steel is controlled to be ≤0.05wt.% and the phosphorus content to be ≤0.008wt.%; deoxidation and alloying are completed simultaneously during the tapping process; S2: Enters the LF furnace for refining, and uses argon gas stirring throughout the process to create white slag for deoxidation and desulfurization; S3: Enter RH-VD composite refining, add magnesium-calcium cored wire in RH furnace to complete the modification of Mg-Ca composite inclusions, and then transfer to VD vacuum degassing treatment; Step 2: Continuous casting with full protection of molten steel. After the billet is cut, it is immediately transferred to a slow cooling pit. It is placed in the pit at a temperature above 600°C and removed from the pit at a temperature below 200°C to obtain a continuously cast billet. Step 3: The continuously cast billet is uniformly heated and rolled in two stages using a plate mill. The first stage is rolling in the recrystallization zone, with an initial rolling temperature of 1150~1180℃, a single-pass reduction rate of 15%, and three rolling passes. The second stage is rolling in the non-recrystallization zone, with a single-pass reduction rate of 12%, and five rolling passes. The final rolling temperature is strictly controlled at 30℃ above the Ar3 phase transformation temperature. Step 4: After rolling, the upper and lower surfaces are cooled symmetrically. The cooling rate of the core of the steel plate is controlled at 6~12℃ / s, and the final cooling temperature is 220~380℃. After cooling is terminated, the steel plate is removed from the cooling bed and air-cooled to the red-hot temperature of 420~460℃ to finally obtain the finished steel.

2. The preparation method according to claim 1, characterized in that: In S2, the white residue retention time is ≥25 min.

3. The preparation method according to claim 1, characterized in that: In S3, during the VD vacuum degassing process, the vacuum level is controlled to be ≤0.5mbar, and the vacuum holding time is 18~25min.

4. The preparation method according to claim 1, characterized in that: In step 2, the continuous casting temperature is 1550~1570℃ and the casting speed is 0.7~1.6m / min.

5. The preparation method according to claim 1, characterized in that: In step 3, the Ar3 phase transition temperature is calculated as follows: Ar3 = 910 - 310 × ω C -80×ω Mn -20×ω Cu -15×ω Cr -55×ω Ni -0.35×(h-8); Where, ω C ω Mn ω Cu ω Cr ω Ni These represent the mass percentage of each element in the steel; h represents the thickness of the steel plate, which is 50~100mm.

6. The preparation method according to claim 1, characterized in that: In step 4, the chemical composition by weight percentage in the finished steel is as follows: C: 0.05%~0.8%, Si: 0.10%~0.30%, S: 0.002%~0.0058%, Mn: 1.5%~2.0%, Ti: 0.01%~0.06%, P≤0.012%, Cu≤0.30%, Ni: 0.05%~0.55%, Cr≤0.25%, Ca: 0.0015%~0.0040%, N: 0.004%~0.015%, O≤0.002%, Al: 0.02%~0.05%, Mg: 0.01%~0.06%, Nb≤0.05%, V≤0.02%, H≤0.00015%, with the balance being Fe and unavoidable impurities.

7. Marine crack-arresting steel EH47 prepared by the method according to any one of claims 1 to 6.

8. The marine crack-arresting steel EH47 according to claim 7, characterized in that: The chemical composition by weight percentage in the finished steel is as follows: C: 0.05%~0.8%, Si: 0.10%~0.30%, S: 0.002%~0.0058%, Mn: 1.5%~2.0%, Ti: 0.01%~0.06%, P≤0.012%, Cu≤0.30%, Ni: 0.05%~0.55%, Cr≤0.25%, Ca: 0.0015%~0.0040%, N: 0.004%~0.015%, O≤0.002%, Al: 0.02%~0.05%, Mg: 0.01%~0.06%, Nb≤0.05%, V≤0.02%, H≤0.00015%, with the balance being Fe and unavoidable impurities.

9. The marine crack-arresting steel EH47 according to claim 7, characterized in that: The inclusions in the finished steel are TiO X -MgO-Al2O3-TiN-(Mn,Ca)S spherical composite inclusions with an average particle size of 1~3μm and a microstructure of bainite + ferrite + pearlite.

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