Hot-rolled steel plate for vacuum train pipe and method for manufacturing the same

Abstract

According to one aspect of the present application, a hot-rolled steel plate having excellent yield strength, vibration damping ratio, electrical resistivity, and low-temperature toughness, thus having physical properties suitable for vacuum train pipes, and a method for manufacturing the same can be provided.

Description

Technical Field

[0001] This invention relates to a hot-rolled steel plate and its manufacturing method. Specifically, it relates to a hot-rolled steel plate and its manufacturing method, wherein the hot-rolled steel plate has excellent yield strength, vibration damping ratio, resistivity and low-temperature toughness, and therefore has physical properties suitable for vacuum train pipelines. Background Technology

[0002] Vacuum trains, also known as hypertube trains, are magnetically levitated trains that move within vacuum tubes. Because vacuum trains eliminate friction with air or tracks, which is a major cause of energy loss, they can operate at extremely high speeds. Due to minimal energy loss—saving up to 93% of the energy compared to airplanes—they are attracting significant attention as an environmentally friendly next-generation mode of transportation, and are being actively researched worldwide.

[0003] The structure and materials of the vacuum tubes used in ultra-high-speed vacuum trains affect the system's performance and cost. Currently, three main types of tube materials are being researched for vacuum trains. One is concrete. Concrete tubes are cost-effective, but it's difficult to join individual tubes of about 10 meters to each other. Furthermore, due to the porosity within concrete, external gases can easily invade the tube's interior when a vacuum is achieved, thus easily disrupting the vacuum level. Another material being extensively researched is composite materials, such as carbon fiber. Composite materials like carbon fiber are lightweight and have high performance, but their biggest drawback is their high cost.

[0004] Currently, steel is the most promising material for vacuum train piping. Steel is a material that can be mass-produced at low cost. It possesses high rigidity and strength, and is easy to process. Furthermore, steel is easy to assemble or weld fittings between or on pipes, and it also has a suitable degassing rate when maintaining a vacuum. However, since ultra-high-speed vacuum trains operate at significantly higher speeds than current high-speed trains, the safety of passengers and surrounding facilities is paramount. Currently, safety standards for ultra-high-speed vacuum trains have not been established, and the development of piping materials to ensure their safety is insufficient. In addition, vacuum trains also need to maintain high efficiency to keep pace with technological advancements, but the development of piping materials to maximize the energy efficiency of vacuum trains is also inadequate.

[0005] Therefore, there is an urgent need to develop a material for vacuum train pipes that has the processability and degassing rate suitable for vacuum train pipes, while ensuring safety and achieving high efficiency.

[0006] (Existing technical literature)

[0007] (Patent Document) Korean Patent Publication No. 10-2106353 (Published on May 4, 2020) Summary of the Invention

[0008] Technical problems to be solved

[0009] According to one aspect of the present invention, a hot-rolled steel plate and a method for manufacturing the same can be provided, wherein the hot-rolled steel plate has excellent yield strength, vibration damping ratio, resistivity and low-temperature toughness, and thus possesses physical properties suitable for vacuum train pipes.

[0010] The technical problems addressed by this invention are not limited to those described above. Those skilled in the art can readily understand the additional technical problems addressed by this invention based on the entire contents of this specification.

[0011] Technical solution

[0012] According to one aspect of the invention, a hot-rolled steel plate for a vacuum train pipeline may contain, by weight percent: carbon (C): 0.03-0.25%, silicon (Si): 1.5-2.5%, manganese (Mn): 0.8-1.8%, balance Fe and other unavoidable impurities, the fine structure having a composite structure of ferrite and pearlite, and the hot-rolled steel plate satisfies the following relations 1 to 3.

[0013] [Relation 1]

[0014] 350≤11+394*D (-0.5) +448*[C]+94*[Si]+69*[Mn]

[0015] [Relationship 2]

[0016] 100≤186-210*D (-0.5) -121*[C]-13.2*[Si]+13.7*[Mn]

[0017] [Relationship 3]

[0018] 30≤9.5+5.2*[C]+5.8*[Mn]+13.1*[Si]

[0019] In Equations 1 to 3, D represents the average grain size (μm) of ferrite in the hot-rolled steel plate, and [C], [Si] and [Mn] represent the carbon (C), silicon (Si) and manganese (Mn) content (wt%) of the hot-rolled steel plate, respectively.

[0020] The hot-rolled steel plate can satisfy the following relationship 4.

[0021] [Relationship 4]

[0022] 303.78-85.22*ln(D)>27

[0023] In Equation 4, D represents the average grain size (μm) of ferrite in the hot-rolled steel sheet.

[0024] The microstructure of the hot-rolled steel sheet may consist of 60-90% ferrite, 10-40% pearlite, and other unavoidable microstructures.

[0025] The total amount of titanium (Ti), niobium (Nb), and vanadium (V) inevitably contained in the hot-rolled steel plate may be less than 0.01% (inclusive).

[0026] The average grain size (D) of the ferrite can be 10-30 μm.

[0027] The yield strength of the hot-rolled steel plate can be above 350 MPa, and the Charpy impact energy based on -20℃ can be above 27 J. After processing the hot-rolled steel plate into a specimen with a length*width*thickness of 80*20*2 mm, the vibration damping ratio measured at a frequency of 1650 Hz in flexural vibration mode can be 100*10. -6 The resistivity can be 30*10. -8 Ωm or above.

[0028] The thickness of the hot-rolled steel plate can be 10 mm or more.

[0029] A method for manufacturing hot-rolled steel sheet for vacuum train pipes according to one aspect of the present invention comprises the following steps: heating a slab at a heating temperature (T1) of 1100-1300°C, the slab comprising, by weight %,: carbon (C): 0.15-0.25%, silicon (Si): 0.3-1.3%, manganese (Mn): 1.0-2.0%, the balance being Fe and other unavoidable impurities; hot-rolling the heated slab at a finishing rolling temperature (T2) of 900-1000°C to provide a hot-rolled steel sheet; and coiling the hot-rolled steel sheet at a coiling temperature (T3) of 600-700°C, wherein the heating temperature (T1), finishing rolling temperature (T2) and coiling temperature (T3) can satisfy the following relationship 5.

[0030] [Relation 5]

[0031] 1≤0.0284*[T1]+0.071*[T2]+0.045*[T3]-131≤3

[0032] In the above relation 5, [T1], [T2] and [T3] represent the slab heating temperature (T1, °C), finishing rolling temperature (T2, °C) and coiling temperature (T3, °C), respectively.

[0033] The total amount of titanium (Ti), niobium (Nb) and vanadium (V) inevitably contained in the slab may be less than 0.01% (inclusive).

[0034] The slab can satisfy the following relationship 3.

[0035] [Relationship 3]

[0036] 30≤9.5+5.2*[C]+5.8*[Mn]+13.1*[Si]

[0037] In Equation 3, [C], [Si] and [Mn] represent the carbon (C), silicon (Si) and manganese (Mn) content (wt%) of the hot-rolled steel plate, respectively.

[0038] The solutions to the above-mentioned technical problems do not list all the features of the present invention. The various features, advantages and effects of the present invention can be understood in more detail by referring to the following specific implementation schemes and embodiments.

[0039] Beneficial effects

[0040] According to one aspect of the present invention, a hot-rolled steel plate and a method for manufacturing the same can be provided, wherein the hot-rolled steel plate has excellent yield strength, vibration damping ratio, resistivity and low-temperature toughness, and thus possesses physical properties suitable for vacuum train pipes.

[0041] The effects of this invention are not limited to the above description, but can be interpreted as including the contents that can be reasonably deduced by those skilled in the art from the contents described in this specification. Attached Figure Description

[0042] Figure 1 These are optical microscope photographs used to observe the fine tissues of specimen 1.

[0043] Figure 2 This is an optical microscope photograph of EN-S355 steel, which is used as an existing structural material.

[0044] Best practice

[0045] This invention relates to a hot-rolled steel plate for vacuum train pipes and its manufacturing method. Preferred embodiments of the invention are described below. These embodiments can be modified in various ways and should not be construed as limiting the scope of the invention to the specific embodiments described below. These specific embodiments are provided to illustrate the invention in more detail to those skilled in the art.

[0046] Vacuum trains, which run in tubes under vacuum or near-vacuum conditions, are a next-generation mode of transportation currently in the early stages of development. Vacuum trains eliminate frictional resistance between wheels and rails and minimize air resistance, thus enabling efficient and high-speed transportation. However, due to the characteristics of ultra-high-speed operation, large-scale accidents can occur if the safety of vacuum trains is not adequately ensured. In particular, not only structural damage or collapse of the vacuum tube, but also deformation of a portion of the tube's shape, can trigger catastrophic events, thus requiring more stringent safety standards for the tube materials used in vacuum trains. Through in-depth research, the inventors of this invention have discovered that the following physical properties are crucial for materials used in vacuum tubes to ensure the safety of vacuum trains.

[0047] To ensure safety, the first required physical property of materials used in vacuum pipelines is high strength. Vacuum trains move through the interior of vacuum pipelines, therefore the materials used in these pipelines need sufficient strength as a structural element. Furthermore, the interior of the vacuum pipeline needs to be maintained in a vacuum or near-vacuum state, thus requiring sufficiently high strength to prevent deformation of the pipeline due to the pressure difference between the internal and external surfaces.

[0048] To ensure safety, the second required physical property of materials used in vacuum tubes is vibration damping. Vacuum trains consist of pods carrying several to dozens of people passing through the interior of a vacuum tube at intervals of tens of seconds to minutes. As one pod passes, the vibrations within the vacuum tube are amplified, potentially causing resonance and, in severe cases, damage to the tube. Therefore, when materials with a vibration damping ratio exceeding a certain level are applied to vacuum tubes, vibrations within the tube can be effectively reduced after the previous pod passes, significantly improving the safety of the vacuum train.

[0049] To ensure safety, the third required physical property for materials used in vacuum pipelines is low-temperature toughness. Vacuum trains can also operate in polar regions or the deep sea. Because steel materials are more susceptible to damage in low or extremely low temperature environments, when steel materials are used in vacuum pipelines, they need to possess a certain level of low-temperature toughness to ensure safety.

[0050] Furthermore, due to the rapidly increasing global demand for environmentally friendly transportation in recent years, vacuum tube trains also need to maximize energy efficiency. The conventional electromagnetic suspension (EMS) method uses the attraction between electromagnets to levitate the train, while the superconducting electrodynamic suspension (EDS) method uses the repulsive force between a superconductor and a magnet. When using the EDS method, a strong magnetic field can be generated in the surrounding environment compared to the EMS method. When the train passes through the tube, the magnetic field changes, inducing a current in the tube, which may result in energy loss. Therefore, it is necessary to reduce the energy loss mentioned above by increasing the resistance of the tube material, and a certain level of resistivity (ρ) is required to ensure energy efficiency.

[0051] Through in-depth research, the inventors of this invention have realized that excellent yield strength, vibration damping ratio, resistivity, and low-temperature toughness can be achieved by strictly controlling the alloy composition and microstructure of the steel plate, thereby obtaining this invention.

[0052] The following is a more detailed description of a hot-rolled steel sheet for a vacuum train pipeline according to one aspect of the present invention.

[0053] According to one aspect of the present invention, a hot-rolled steel plate for a vacuum train pipeline may, by weight percent, contain: carbon (C): 0.03-0.25%, silicon (Si): 1.5-2.5%, manganese (Mn): 0.8-1.8%, balance Fe and other unavoidable impurities, and the fine structure may have a composite structure of ferrite and pearlite. The hot-rolled steel plate may satisfy the following relations 1 to 3, and may further satisfy the following relation 4.

[0054] [Relation 1]

[0055] 350≤11+394*D (-0.5) +448*[C]+94*[Si]+69*[Mn]

[0056] [Relationship 2]

[0057] 100≤186-210*D (-0.5) -121*[C]-13.2*[Si]+13.7*[Mn]

[0058] [Relationship 3]

[0059] 30≤9.5+5.2*[C]+5.8*[Mn]+13.1*[Si]

[0060] [Relationship 4]

[0061] 303.78-85.22*ln(D)>27

[0062] In Equations 1 to 4, D represents the average grain size (μm) of ferrite in the hot-rolled steel plate, and [C], [Si] and [Mn] represent the carbon (C), silicon (Si) and manganese (Mn) content (wt%) of the hot-rolled steel plate, respectively.

[0063] The composition of the steel contained in the hot-rolled steel sheet of the present invention will be described in more detail below. Unless otherwise specified, the percentage of each element is expressed by weight.

[0064] Carbon (C): 0.03-0.25%

[0065] Carbon (C) is a component that has a very significant impact on the strength of steel plates. In this invention, more than 0.03% carbon (C) can be included to ensure the required strength of the structure. Preferably, the lower limit of the carbon (C) content is 0.05%, and more preferably, it is 0.07%. On the other hand, when the carbon (C) content is too high, the toughness and weldability of the material decrease, and the yield strength ratio may increase. Furthermore, when the carbon (C) content is too high, it is difficult to achieve grain coarsening; therefore, in this invention, the upper limit of the carbon (C) content can be limited to 0.25%. Preferably, the upper limit of the carbon (C) content is 0.2%, and more preferably, it is 0.15%.

[0066] Silicon (Si): 1.5-2.5%

[0067] Silicon (Si) combines with oxygen during the steelmaking process to form slag, and is therefore typically removed along with oxygen. Furthermore, silicon (Si) is also a component that effectively promotes increased strength and resistivity of materials. Therefore, in this invention, to achieve the effects described above, it may contain 1.5% or more silicon (Si). A preferred lower limit for the silicon (Si) content is 1.6%, and a more preferred lower limit is 1.8%. On the other hand, when the silicon (Si) content is too high, it interferes with the removal of surface oxide scale, thus potentially reducing the surface quality of the product. Furthermore, when the silicon (Si) content is too high, the low-temperature toughness of the base material and welded parts decreases, increasing the risk of fracture during material use. Therefore, in this invention, the silicon (Si) content may be limited to 2.5% or less. A preferred upper limit for the silicon (Si) content is 2.3%, and a more preferred upper limit is 2.0%.

[0068] Manganese (Mn): 0.8-1.8%

[0069] Manganese (Mn) is a component that improves the strength and hardenability of steel. Therefore, the present invention may contain more than 0.8% manganese (Mn) to ensure the effects described above. Preferably, the lower limit of the manganese (Mn) content is 1.0%, and more preferably, the lower limit is 1.1%. On the other hand, when the manganese (Mn) content is too high, material deviation may occur due to central segregation, and the resistance to crack propagation may deteriorate. Furthermore, when the manganese (Mn) content is too high, the toughness of the steel may decrease; therefore, the manganese (Mn) content is limited to 1.8% or less in the present invention. Preferably, the upper limit of the manganese (Mn) content is 1.6%, and more preferably, the upper limit is 1.5%.

[0070] In addition to the above-described components, the hot-rolled steel sheet of the present invention may contain the balance of Fe and other unavoidable impurities. However, undesirable impurities may inevitably be introduced from raw materials or the surrounding environment during normal manufacturing processes, and therefore cannot be completely eliminated. These impurities are well known to those skilled in the art, and therefore their contents are not specifically mentioned in this specification. Furthermore, the further addition of effective components other than those described above is not entirely excluded.

[0071] The hot-rolled steel sheet of the present invention actively suppresses the addition of titanium (Ti), niobium (Nb), and vanadium (V), and even if these components are unavoidably present, their total content can be limited to less than 0.01% (including 0%). Titanium (Ti), niobium (Nb), and vanadium (V) are representative precipitation strengthening elements and are components that effectively promote the improvement of steel strength by forming fine carbonitrides. However, titanium (Ti), niobium (Nb), and vanadium (V) cause excessive refinement of the steel's microstructure, which is detrimental to ensuring vibration damping capacity; therefore, the present invention attempts to actively suppress these components. Furthermore, titanium (Ti), niobium (Nb), and vanadium (V) are expensive components and are not preferred from an economic perspective. In the present invention, these components are not added intentionally, and even in the case of unavoidable addition, the total content of these components can be actively suppressed to less than 0.01%. Preferably, the total content of these components can be less than 0.005%, and more preferably, the total content of these components can be 0%.

[0072] According to one aspect of the invention, the microstructure of the hot-rolled steel sheet can have a composite structure composed of ferrite and pearlite. The formation of low-temperature structures such as bainite and martensite can be actively suppressed in this invention. Low-temperature structures such as bainite and martensite have high strength and low yield strength ratio, and can exhibit excellent physical properties as structural materials. However, according to one example of the invention, the thickness of the hot-rolled steel sheet for vacuum train pipes is at a level of 10 mm or more, so even if low-temperature structures are introduced, deviations in physical properties may occur in the thickness direction of the steel sheet. This is because low-temperature structures are formed only on the surface of the steel sheet, and it is difficult for them to fully form in the center of the steel sheet.

[0073] Therefore, in this invention, the microstructure of the steel plate is configured as a composite structure consisting of ferrite and pearlite to reduce deviations in physical properties. Even if low-temperature structures such as bainite and martensite are unavoidably formed, the fraction of such low-temperature structures can be actively suppressed to 1% by area or less (including 0%). To ensure physical properties, the fraction of ferrite can be 60-90% by area, and the fraction of pearlite can be 10-40% by area.

[0074] To simultaneously ensure the desired yield strength, vibration damping ratio, and low-temperature toughness, the average grain size of ferrite in this invention can be limited to a certain range. Increasing the grain size is beneficial for ensuring the vibration damping ratio; therefore, the average grain size of ferrite in this invention can be limited to 10 μm or more. Preferably, the average grain size can exceed 10 μm, and more preferably, it can be 15 μm or more. On the other hand, when the grain size is too large, the strength and low-temperature toughness of the material deteriorate; therefore, the average grain size of ferrite in this invention can be limited to 30 μm or less. Preferably, the upper limit of the average grain size can be 25 μm.

[0075] The inventors of this invention conducted in-depth research on methods to ensure the stability and energy efficiency of materials used in vacuum train pipelines. They realized that by controlling the content of carbon (C), silicon (Si), and manganese (Mn) and the average grain size of ferrite within a certain range in low-alloy steel plates like those of this invention, yield strength, vibration damping ratio, and resistivity can be ensured simultaneously. This led to the following relationships 1 to 3.

[0076] [Relation 1]

[0077] 350≤11+394*D (-0.5) +448*[C]+94*[Si]+69*[Mn]

[0078] [Relationship 2]

[0079] 100≤186-210*D (-0.5)-121*[C]-13.2*[Si]+13.7*[Mn]

[0080] [Relationship 3]

[0081] 30≤9.5+5.2*[C]+5.8*[Mn]+13.1*[Si]

[0082] In Equations 1 to 3, D represents the average grain size (μm) of ferrite in the hot-rolled steel plate, and [C], [Si] and [Mn] represent the carbon (C), silicon (Si) and manganese (Mn) content (wt%) of the hot-rolled steel plate, respectively.

[0083] The hot-rolled steel plate for vacuum train pipes of the present invention satisfies Equations 1 to 3 simultaneously, thus ensuring the desired yield strength, vibration damping ratio and resistivity at the same time.

[0084] Furthermore, the inventors of this invention recognized that low-temperature toughness could be ensured when the average grain size of ferrite was controlled within a certain range in a steel sheet having the composition system of this invention, thereby further deriving the following relationship 4.

[0085] [Relationship 4]

[0086] 303.78-85.22*ln(D)>27

[0087] In Equation 4, D represents the average grain size (μm) of ferrite in the hot-rolled steel sheet.

[0088] The hot-rolled steel plate for vacuum train pipes of the present invention further satisfies relation 4, thus effectively ensuring the desired low-temperature toughness.

[0089] The hot-rolled steel plate for vacuum train pipelines of the present invention can have a yield strength of 350 MPa or more and a Charpy impact energy of 27 J or more at -20°C. Therefore, the hot-rolled steel plate for vacuum train pipelines of the present invention ensures suitable strength and low-temperature toughness as a structural material, thereby effectively ensuring the structural safety of the pipeline for vacuum trains.

[0090] The hot-rolled steel plate for the vacuum train pipeline of the present invention can have a diameter of 100*10. -6 The above refers to the vibration damping ratio. The vibration damping ratio is the ratio measured at a frequency of 1650Hz after striking a specimen with a length*width*thickness of 80*20*2mm in flexural vibration mode. The hot-rolled steel plate for the vacuum train pipe of this invention can have a diameter of 100*10... -6The above vibration damping ratio can effectively suppress vibration amplification in vacuum pipes and effectively prevent damage to vacuum train pipes caused by vibration.

[0091] The hot-rolled steel plate for the vacuum train pipeline of the present invention can have a diameter of 30*10 mm. -8 With a resistivity of over Ωm, the energy efficiency of the vacuum train can be effectively ensured during operation.

[0092] Therefore, according to one aspect of the invention, a hot-rolled steel sheet can be provided, which has excellent yield strength, vibration damping ratio, resistivity and low-temperature toughness, and thus possesses physical properties suitable for vacuum train pipes.

[0093] The following describes in more detail a method for manufacturing hot-rolled steel plates for vacuum train pipes according to one aspect of the present invention.

[0094] A method for manufacturing hot-rolled steel sheet for vacuum train pipes according to one aspect of the present invention may include the following steps: heating a slab at a heating temperature (T1) of 1100-1300°C, the slab comprising, by weight %,: carbon (C): 0.03-0.25%, silicon (Si): 1.5-2.5%, manganese (Mn): 0.8-1.8%, the balance being Fe and other unavoidable impurities; hot-rolling the heated slab at a finishing rolling temperature (T2) of 900-1000°C to provide a hot-rolled steel sheet; and coiling the hot-rolled steel sheet at a coiling temperature (T3) of 600-700°C, wherein the heating temperature (T1), finishing rolling temperature (T2) and coiling temperature (T3) may satisfy the following relationship 5.

[0095] [Relation 5]

[0096] 1≤0.0284*[T1]+0.071*[T2]+0.045*[T3]-131≤3

[0097] In the above relation 5, [T1], [T2] and [T3] represent the slab heating temperature (T1, °C), finishing rolling temperature (T2, °C) and coiling temperature (T3, °C), respectively.

[0098] Preparation and heating of steel billets

[0099] Prepare a steel billet having a predetermined alloy composition. Since the steel billet of the present invention has an alloy composition corresponding to the above-described hot-rolled steel sheet, the description of the alloy composition of the hot-rolled steel sheet is used instead of the description of the alloy composition of the steel billet.

[0100] The prepared steel billet can be heated at a heating temperature (T1) of 1100-1300°C. Considering the rolling load during hot rolling, the steel billet can be heated in a temperature range above 1100°C. In particular, this invention aims to introduce a fine microstructure of a certain size or larger; therefore, a preferred heating temperature for the steel billet is 1200°C or higher. A more preferred heating temperature is 1250°C or higher. On the other hand, when the heating temperature of the steel billet is too high, the surface quality may decrease due to the formation of oxide scale; therefore, in this invention, the heating temperature of the steel billet can be limited to below 1300°C.

[0101] Hot rolling

[0102] Heated steel billets can be hot-rolled at a finishing rolling temperature (T2) of 900-1000°C to provide hot-rolled steel sheets. The steel sheets provided by hot rolling according to the present invention can have a thickness of 10 μm or more.

[0103] During hot rolling, the grains of the rolled material deform simultaneously but recrystallize rapidly. Through the process described above, the coarse and inhomogeneous microstructure becomes finer and more homogeneous. An important process variable during hot rolling is the finishing delivery temperature (FDT), which is the temperature at the end of rolling. This is because the grain size and other parameters of the final microstructure can be controlled according to the finishing temperature. The objective of this invention is to control the final microstructure to a level above a certain size; therefore, hot rolling can be performed at a finishing temperature of 900°C or higher. A preferred finishing temperature is 950°C or higher. On the other hand, if the finishing temperature is too high, the final microstructure may become too coarse; therefore, in this invention, the upper limit of the finishing temperature can be limited to 1000°C.

[0104] Collect

[0105] Hot-rolled steel sheets supplied by hot rolling can be coiled at a coiling temperature (T3) of 600-700°C after water cooling. The objective of this invention is to achieve a composite microstructure of ferrite and pearlite as the final microstructure; therefore, coiling can be performed at a temperature range above 600°C. The objective of this invention is to achieve a final fine microstructure of a certain size; therefore, coiling is more preferably performed at a temperature range above 650°C. However, when the coiling temperature is too high, coarse fine microstructures may form, or the surface quality may deteriorate; therefore, the upper limit of the coiling temperature in this invention is limited to 700°C.

[0106] The inventors of this invention have conducted in-depth research on the technical solutions for controlling the grain size of the final microstructure and have confirmed that in order to control the grain size of the final microstructure in the composition system of this invention, the heating temperature (T1) when heating the billet, the finishing temperature (T2) during hot rolling, and the coiling temperature (T3) when coiling the hot-rolled steel sheet should be controlled so that they independently meet a certain range. Moreover, these billet heating temperatures (T1), finishing temperatures (T2), and coiling temperatures (T3) should be correlated with each other and controlled within a certain range, thereby deriving the following relationship 5.

[0107] [Relation 5]

[0108] 1481≤0.0284*[T1]+0.071*[T2]+0.045*[T3]-131≤3

[0109] In the above relation 5, [T1], [T2] and [T3] represent the slab heating temperature (T1, °C), finishing rolling temperature (T2, °C) and coiling temperature (T3, °C), respectively.

[0110] Therefore, in the method for manufacturing hot-rolled steel sheet for vacuum train pipes according to one aspect of the present invention, the slab is heated at a heating temperature (T1) of 1100-1300°C, hot-rolled at a finishing temperature (T2) of 900-1000°C, and coiled at a coiling temperature (T3) of 600-700°C. Moreover, the process conditions are controlled so that the slab heating temperature (T1), finishing temperature (T2) and coiling temperature (T3) satisfy Equation 4, thereby effectively achieving the fine microstructure of the target hot-rolled steel sheet.

[0111] Hot-rolled steel sheets manufactured by the above manufacturing method can satisfy the following relations 1 to 3, and can also satisfy the following relation 4.

[0112] [Relation 1]

[0113] 350≤11+394*D (-0.5) +448*[C]+94*[Si]+69*[Mn]

[0114] [Relationship 2]

[0115] 100≤186-210*D (-0.5) -121*[C]-13.2*[Si]+13.7*[Mn]

[0116] [Relationship 3]

[0117] 30≤9.5+5.2*[C]+5.8*[Mn]+13.1*[Si]

[0118] [Relationship 4]

[0119] 303.78-85.22*ln(D)>27

[0120] In Equations 1 to 4, D represents the average grain size (μm) of ferrite in the hot-rolled steel plate, and [C], [Si] and [Mn] represent the carbon (C), silicon (Si) and manganese (Mn) content (wt%) of the hot-rolled steel plate, respectively.

[0121] Furthermore, hot-rolled steel sheets manufactured using the above method can possess a yield strength of over 350 MPa and a Charpy impact energy of over 27 J at -20°C. Test pieces with a length*width*thickness of 80*20*2 mm were prepared, and the vibration damping ratio measured at a frequency of 1650 Hz in bending vibration mode met the requirement of 100*10. -6 At the above levels, the resistivity can meet 30*10. -8 Levels above Ωm.

[0122] Therefore, according to one aspect of the invention, a method for manufacturing a hot-rolled steel sheet can be provided, the hot-rolled steel sheet having excellent yield strength, vibration damping ratio, resistivity and low-temperature toughness, and thus possessing physical properties suitable for vacuum train pipes. Detailed Implementation

[0123] The following detailed description, through specific embodiments, illustrates the hot-rolled steel plate for vacuum train pipes and its manufacturing method according to the present invention. It should be noted that the following embodiments are for understanding the present invention only and are not intended to define the specific scope of the invention. The scope of the invention can be determined by the contents recorded in the claims and the contents reasonably inferred therefrom.

[0124] (Example)

[0125] After preparing a 250 mm thick steel billet with the alloy composition shown in Table 1 below, the process conditions in Table 2 are applied to manufacture a 15 mm thick hot-rolled steel sheet. Alloy compositions not listed in Table 1 below indicate impurities and the balance of Fe; "-" indicates a value close to 0% by weight within the tolerance range.

[0126] [Table 1]

[0127]

[0128] [Table 2]

[0129]

[0130] The microstructure and mechanical-physical properties of each specimen were analyzed and recorded in Table 3. The results regarding whether each specimen satisfied Equations 1 to 4 are also recorded in Table 3. The microstructure was measured using a 500x optical microscope after etching each specimen with nitric acid etching solution (Nital). The ferrite grain size was measured according to ASTM E112. Figure 1 These are optical microscope photographs used to observe the fine tissues of specimen 1.

[0131] Mechanical and physical properties were measured according to KS B 0802 and KS B 0810. The measured yield strength, yield ratio, and Charpy impact toughness at -21°C are recorded together in Table 3. Resistivity was measured according to KS C IEC 60404, and its values ​​are also recorded in Table 3.

[0132] The vibration damping ratio was measured at room temperature using an IMCE RFDA LTV800 after preparing a specimen with a length*width*thickness of 80*20*2mm. After being struck in the bending vibration mode, the damping ratio was measured in the corresponding vibration mode of the specimen, corresponding to the first (1) st The vibration damping ratio in the 1650Hz region of the mode was analyzed, and the results are recorded in Table 3.

[0133] [Table 3]

[0134]

[0135] As shown in Tables 1 to 3, it can be seen that the specimens that meet the alloy composition, process conditions, and Equations 1 to 4 of this invention simultaneously meet the following requirements: yield strength of 350 MPa or more, Charpy impact energy of 27 J or more at -20°C, and 30*10 -8 Resistivity above Ωm and 100*10 -6 The above vibration damping ratios, but not meeting any of the conditions limited by this invention, do not simultaneously satisfy a yield strength of 350 MPa or more, a Charpy impact energy of -20°C or more of 27 J or more, or a vibration damping ratio of 30*10. -8 Resistivity above Ωm and 100*10 -6 The above are vibration damping ratios.

[0136] Furthermore, to compare with conventional materials, tests were conducted on EN-S355, an existing structural steel, under the same conditions. With EN-S355, it was confirmed that the vibration damping ratio measured under the same conditions was only 60*10. -6 The level. Figure 2 These are photographs of the fine tissues of EN-S355 taken using an optical microscope.

[0137] Therefore, according to one aspect of the present invention, a hot-rolled steel plate and a method for manufacturing the same can be provided, wherein the hot-rolled steel plate has excellent yield strength, vibration damping ratio, resistivity and low-temperature toughness, and thus possesses physical properties suitable for vacuum train pipes.

[0138] The present invention has been described in detail above through embodiments, but other embodiments may also be included. Therefore, the technical concept and scope of the claims are not limited to the embodiments.

Claims

1. A hot-rolled steel plate for vacuum train pipes, comprising, by weight percent: carbon (C): 0.03-0.25%, silicon (Si): 1.6-2.5%, manganese (Mn): 0.8-1.8%, with the balance being Fe and other unavoidable impurities, having a fine microstructure of ferrite and pearlite composite, and satisfying the following equations 1 to 3, wherein the average grain size D of the ferrite is 10-30 μm. [Relation 1] 350≤11+394 D (-0.5) +448 [C]+94 [Si]+69 [Mn] [Relation 2] 100≤186-210 D (-0.5) -121 [C]-13.2 [Si]+13.7 [Mn] [Relationship 3] 30≤9.5+5.2 [C]+5.8 [Mn]+13.1 [Si] In equations 1 to 3, D represents the average grain size of ferrite in the hot-rolled steel sheet, where, The unit of size is μm, and [C], [Si] and [Mn] represent the carbon (C), silicon (Si) and manganese (Mn) content of the hot-rolled steel plate, respectively, where the unit of content is by weight.

2. The hot-rolled steel plate for vacuum train pipelines according to claim 1, wherein, The hot-rolled steel plate satisfies the following relationship 4. [Relation 4] 303.78-85.22 ln(D)>27 In Equation 4, D represents the average grain size of ferrite in the hot-rolled steel sheet, where the unit of size is μm.

3. The hot-rolled steel plate for vacuum train pipelines according to claim 1, wherein, The microstructure of the hot-rolled steel sheet consists of 60-90% ferrite, 10-40% pearlite, and other unavoidable microstructures.

4. The hot-rolled steel plate for vacuum train pipelines according to claim 1, wherein, The total amount of titanium (Ti), niobium (Nb), and vanadium (V) inevitably contained in the hot-rolled steel plate is less than 0.01% and includes 0%.

5. The hot-rolled steel plate for vacuum train pipelines according to claim 1, wherein, The hot-rolled steel plate has a yield strength of 350 MPa or higher, and a Charpy impact energy of 27 J or higher based on -20°C. The hot-rolled steel plate is then processed into a certain length. width Thickness 80 20 After inserting a 2mm specimen, the vibration damping ratio measured at a frequency of 1650Hz in bending vibration mode was 100. 10 -6 The resistivity is 30. 10 -8 m or more.

6. The hot-rolled steel plate for vacuum train pipelines according to claim 1, wherein, The thickness of the hot-rolled steel plate is 10 mm or more.

7. A method for manufacturing hot-rolled steel plates for vacuum train pipes, comprising the following steps: The slab is heated at a heating temperature T1 of 1100-1300℃, and the slab contains, by weight %: carbon (C): 0.03-0.25%, silicon (Si): 1.6-2.5%, manganese (Mn): 0.8-1.8%, balance Fe and other unavoidable impurities; The heated slab is hot-rolled at a finishing rolling temperature T2 of 900-1000°C to provide hot-rolled steel sheet; as well as The hot-rolled steel sheet is wound up at a winding temperature T3 of 600-700℃. The heating temperature T1, the finishing rolling temperature T2, and the winding temperature T3 satisfy the following relationship: Equation 5. [Relationship 5] 1≤0.0284 [T1]+0.071 [T2]+0.045 [T3]-131≤3 In the above relation 5, [T1], [T2] and [T3] represent the slab heating temperature T1, the finishing rolling temperature T2 and the coiling temperature T3, respectively, where the unit of temperature is ℃.

8. The method for manufacturing hot-rolled steel plates for vacuum train pipes according to claim 7, wherein, The total amount of titanium (Ti), niobium (Nb), and vanadium (V) inevitably contained in the slab is less than 0.01% and includes 0%.

9. The method for manufacturing hot-rolled steel plates for vacuum train pipes according to claim 7, wherein, The slab satisfies the following relationship 3. [Relationship 3] 30≤9.5+5.2 [C]+5.8 [Mn]+13.1 [Si] In Equation 3, [C], [Si], and [Mn] represent the carbon (C), silicon (Si), and manganese (Mn) content of the hot-rolled steel plate, respectively, where the unit of content is by weight.

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