Title of Invention: Steel material for vacuum tube and manufacturing method thereof
technical field
[One]
The present invention relates to a steel material having properties particularly suitable for a vacuum tube provided in a high-speed vacuum tube train and a method for manufacturing the same.
background
[2]
Recently, as a next-generation transportation system, research on a high-speed vacuum tube train called a one-sided hyperloop is being actively conducted at home and abroad. The high-speed vacuum tube train is basically a type of transportation that moves the train in a vacuum tube. That is, it is a transportation means of the concept that the train can be operated at a high speed because the air resistance is minimized by maintaining the inside of the tube in a vacuum state.
[3]
[4]
In a vacuum tube used in a high-speed vacuum tube train, not only the structure of the tube, but also the material of the tube is a factor that greatly influences the maintenance of the vacuum inside the tube, but research and development of the tube material is insufficient at present.
[5]
[6]
Patent Document 1 also discloses a segmented tube for manufacturing a vacuum tube used in a high-speed vacuum tube train, but does not specifically mention the material of the tube.
[7]
[8]
(Prior art literature)
[9]
(Patent Document 1) US 2019/0170276 A1 (published on June 6, 2019)
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[10]
According to one aspect of the present invention, a steel material having properties particularly suitable for a vacuum tube provided in a high-speed vacuum tube train and a method for manufacturing the same may be provided.
[11]
The subject of the present invention is not limited to the above. A person of ordinary skill in the art will have no difficulty in understanding the further problems of the present invention from the general contents of the present specification.
means of solving the problem
[12]
Steel material for vacuum tube according to an aspect of the present invention, in weight %, C: 0.1 to 0.2%, Si: 0.05 to 0.5%, Mn: 1.0 to 1.6%, Ni: 0.5 to 1.0%, Cr: 1.5 to 4.0 %, including the remaining Fe and unavoidable impurities, and having a ferrite and pearlite composite structure as a microstructure, and the gas release rate of the steel may be 1.0*10 -10 mbar·l·s -1 ·cm -2 or less.
[13]
The total content of Ti, Nb and V in the impurities contained in the steel may be less than 0.01% (including 0%).
[14]
The fraction of the ferrite may be 60 to 90 area%, and the fraction of the pearlite may be 10 to 40 area%.
[15]
The fraction of martensite or bainite contained in the steel may be less than 1 area% (including 0%).
[16]
The steel may have a yield strength (YS) of 400 to 600 MPa, a yield ratio (YR) of 0.8 or less, and an elongation (El) of 19 to 30%.
[17]
The steel may have a Charpy impact energy of 30 to 50J at -20°C.
[18]
The thickness of the steel may be 15 ~ 30mm.
[19]
[20]
The manufacturing method of a steel material for a vacuum tube according to an aspect of the present invention, in weight %, C: 0.1 to 0.2%, Si: 0.05 to 0.5%, Mn: 1.0 to 1.6%, Ni: 0.5 to 1.0%, Cr: 1.5 to 4.0%, after reheating the slab containing the remaining Fe and unavoidable impurities to provide a steel material by hot rolling at a finish rolling temperature of 900 ~ 1000 ℃; First cooling the hot-rolled steel material to 550 ~ 650 ℃ at a first cooling rate of 5 ~ 50 ℃ / s; winding the steel material into a coil at a first cooling stop temperature after the first cooling is finished; and second cooling the coil to room temperature at a second cooling rate of 0.005 to 0.05° C./s.
[21]
The total content of Ti, Nb and V in the impurities contained in the slab may be less than 0.01% (including 0%).
[22]
The thickness of the hot-rolled steel may be 15 ~ 30mm.
[23]
The cooling method of the first cooling may be water cooling, and the cooling method of the second cooling may be standing cooling.
Effects of the Invention
[24]
According to one aspect of the present invention, since it has a low gas release rate and a yield ratio, it is possible to provide a steel material having properties particularly suitable for a vacuum tube of a high-speed vacuum tube train and a method for manufacturing the same.
Best mode for carrying out the invention
[25]
The present invention relates to a steel material for a vacuum tube and a method for manufacturing the same, and preferred embodiments of the present invention will be described below. Embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The present embodiments are provided in order to further detailed the present invention to those of ordinary skill in the art to which the present invention pertains.
[26]
[27]
Hereinafter, a steel material for a vacuum tube according to an aspect of the present invention will be described in more detail.
[28]
[29]
Steel material for vacuum tube according to an aspect of the present invention, in weight %, C: 0.1 to 0.2%, Si: 0.05 to 0.5%, Mn: 1.0 to 1.6%, Ni: 0.5 to 1.0%, Cr: 1.5 to 4.0 %, including the remaining Fe and unavoidable impurities, and having a ferrite and pearlite composite structure as a microstructure, and the gas release rate of the steel may be 1.0*10 -10 mbar·l·s -1 ·cm -2 or less.
[30]
[31]
Hereinafter, the alloy composition of the present invention will be described in more detail. Hereinafter, unless otherwise specified, % and ppm related to the content of the alloy composition are based on weight.
[32]
[33]
Steel material for vacuum tube according to an aspect of the present invention, in weight %, C: 0.1 to 0.2%, Si: 0.05 to 0.5%, Mn: 1.0 to 1.6%, Ni: 0.5 to 1.0%, Cr: 1.5 to 4.0 %, including the remaining Fe and unavoidable impurities, the total content of Ti, Nb and V in the impurities can be actively suppressed to less than 0.01% (including 0%).
[34]
[35]
Carbon (C): 0.1~0.2%
[36]
Carbon (C) is a representative hardenability improving element, and is an element that effectively contributes to securing the strength of steel materials. Accordingly, the present invention may contain 0.1% or more of carbon (C) in terms of securing the strength of the vacuum tube structure. A preferred carbon (C) content may be greater than 0.1%, and a more preferred carbon (C) content may be 0.12% or higher. On the other hand, when the carbon (C) content is excessive, the toughness of the steel is reduced, weldability is poor, and the yield ratio is increased, so the present invention can limit the upper limit of the carbon (C) content to 2.0% . A preferred carbon (C) content may be less than 0.2%, and a more preferred carbon (C) content may be 0.18% or less.
[37]
[38]
Silicon (Si): 0.05-0.5%
[39]
Silicon (Si) is an element that contributes to deoxidation of steel. Therefore, the present invention may contain 0.05% or more of silicon (Si) in order to secure the cleanliness of the steel. A preferable silicon (Si) content may be 0.06% or more, and a more preferable silicon (Si) content may be 0.08%. On the other hand, when silicon (Si) is excessively added, the product surface quality may be deteriorated by preventing the surface scale from falling off, and the formation of a target microstructure may be prevented by preventing the precipitation of carbides. Accordingly, the present invention may limit the upper limit of the silicon (Si) content to 0.5%. A preferable silicon (Si) content may be 0.4% or less, and a more preferable silicon (Si) content may be 0.3% or less.
[40]
[41]
Manganese (Mn): 1.0~1.6%
[42]
Since manganese (Mn) is an element that contributes to the improvement of the hardenability of steel, the present invention may include 1.0% or more of manganese (Mn) in order to secure the strength of the steel. A preferable manganese (Mn) content may be 1.1% or more, and a more preferable manganese (Mn) content may be 1.2% or more. On the other hand, when manganese (Mn) is added excessively, the toughness of the steel decreases, crack resistance becomes inferior, and there is a concern about material deviation due to cast segregation, so the present invention sets the upper limit of the manganese (Mn) content to 1.6 % can be limited. A preferable manganese (Mn) content may be 1.5% or less, and a more preferable manganese (Mn) content may be 1.4% or less.
[43]
[44]
Nickel (Ni): 0.5 to 1.0%
[45]
Nickel (Ni) is not only an element contributing to an increase in strength of steel, but also an element that effectively contributes to an increase in impact toughness of steel. Accordingly, the present invention may contain 0.5% or more of nickel (Ni) for this effect. A preferred nickel (Ni) content may be greater than 0.5%, and a more preferred nickel (Ni) content may be 0.6% or more. However, when the content of nickel (Ni) exceeds a certain level, the above-described effect is saturated, but it is not desirable in terms of economical efficiency, so the present invention may limit the upper limit of the nickel (Ni) content to 1.0%. A preferred nickel (Ni) content may be less than 1.0%, and a more preferred nickel (Ni) content may be 0.9% or less.
[46]
[47]
Chromium (Cr): 1.5~4.0%
[48]
Chromium (Cr) is an element that effectively contributes to the reduction of the gas release rate targeted by the present invention. Since chromium (Cr) has a lower reduction potential (-0.73V) than iron (-0.44V), a very thin and dense chromium oxide film can be formed on the steel surface. Since the dense oxide film acts as a barrier to the gas emitted from the material, the gas release rate of the material can be effectively reduced. Accordingly, the present invention may include 1.5% or more of chromium (Cr) for this effect. A preferred chromium (Cr) content may be greater than 1.5%, and a more preferred chromium (Cr) content may be 1.7% or more. As the chromium (Cr) content increases, the gas release rate reduction effect is improved, but considering that chromium (Cr) is an expensive component, it is not desirable to add more than a certain level from an economic point of view. In addition, when chromium (Cr) is excessively added, the hardenability may be excessively increased to cause the formation of a low-temperature structure in the surface layer, which is undesirable in view of the deviation of the physical properties of the material. Accordingly, the present invention may limit the upper limit of the chromium (Cr) content to 4.0%. A preferred chromium (Cr) content may be 3.6% or less, and a more preferred chromium (Cr) content may be 3.3% or less.
[49]
[50]
The steel material for a vacuum tube according to an aspect of the present invention may include the remainder Fe and other unavoidable impurities in addition to the above components. However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in the normal manufacturing process, it cannot be entirely excluded. Since these impurities are known to those of ordinary skill in the art, all contents thereof are not specifically mentioned in the present specification. In addition, addition of effective ingredients other than the above composition is not excluded.
[51]
[52]
In addition, the steel material of the present invention may actively limit the total content of titanium (Ti), niobium (Nb) and vanadium (V) included as impurities to less than 0.01% (including 0%). These, titanium (Ti), niobium (Nb), and vanadium (V) are representative precipitation strengthening elements, and are elements that effectively contribute to the improvement of strength of steel materials by forming fine carbonitrides with only a small amount of addition. Since the object to which the steel of the present invention is finally applied is a vacuum tube for a high-speed train, which is a large structure, an increase in the yield ratio is undesirable in terms of workability and workability. Therefore, the present invention positively limits the intentional addition of titanium (Ti), niobium (Nb) and vanadium (V) in order to secure a desired yield ratio, and even if these components are unavoidably introduced, the total content is less than 0.01% (including 0%) can be limited.
[53]
[54]
The steel material for a vacuum tube according to an aspect of the present invention may have a ferrite and pearlite composite structure as a microstructure, and may actively suppress the formation of a hard structure. The fraction of ferrite may be 60 to 90 area%, the fraction of pearlite may be 10 to 40 area%, and the total fraction of martensite or bainite, which is a hard structure, may be less than 1 area% (including 0%).
[55]
[56]
Low-temperature structures such as martensite or bainite exhibit excellent properties as structural materials due to their high strength and low yield ratio. However, since the thickness of the steel for vacuum tube of the present invention is at a level of 5 to 30 mm, there is a high possibility that a hard structure is introduced only on the surface of the steel material even through control of the cooling conditions. That is, the hard structure is not formed in the center of the steel, whereas the formation of the hard structure is concentrated only on the surface of the steel, and there is a high possibility that material deviation occurs in the steel material thickness direction. Therefore, the present invention can actively control the total fraction of martensite and bainite in order to reduce such material deviation.
[57]
[58]
The gas release rate of the steel for vacuum tube according to an aspect of the present invention may be 1.0*10 -10 mbar·l·s -1 ·cm -2 or less. Here, the gas release rate refers to the amount of gas per area per hour that is released from the material into a vacuum when the vacuum chamber is configured using the material. That is, when a chamber is constructed using a material, exhausted using a pump, and then the pump is isolated from the chamber, the pressure in the chamber rises as a certain period of time cures. The gas release rate can be calculated by measuring the pressure rise value in the chamber and substituting it in [Relational Expression 1] below.
[59]
[60]
[Relational Expression 1]
[61]
q = (V/A)·(ΔP/t)
[62]
In Relation 1, q is the gas release rate (mbar·l·s -1 ·cm -2 ), V is the chamber volume (liter), A is the chamber surface area (cm 2 ), P is the pressure in the chamber (mbar), t is the time (s).
[63]
[64]
In addition, the steel material for a vacuum tube according to an aspect of the present invention may have a yield strength (YS) of 400 to 600 MPa, a yield ratio (YR) of 0.8 or less, and an elongation (El) of 19 to 30%, -20 Charpy impact energy at ℃ can satisfy the range of 30 ~ 50J.
[65]
[66]
Since the steel material according to an aspect of the present invention has a low gas release rate and a low yield ratio characteristic, it can provide properties particularly suitable as a vacuum tube for a high-speed train, which is a large vacuum structure. In particular, the vacuum tube manufactured using the steel material according to an aspect of the present invention can effectively maintain the vacuum state inside the vacuum tube by having a low gas release rate, and has excellent seismic resistance properties by having a low yield ratio can do.
[67]
[68]
The steel material for a vacuum tube according to an aspect of the present invention may have a thickness of 5 to 30 mm, and the thickness of the steel material applied to the manufacture of the vacuum tube to be applied may be selectively determined according to the diameter of the vacuum tube. As a non-limiting example, when the diameter of the vacuum tube is about 1 to 3 m, a steel material having a thickness of 5 to 15 mm may be applied, and when the diameter of the vacuum tube is about 3 to 5 m, having a thickness of 15 to 30 mm Steel may be applied.
[69]
[70]
Hereinafter, a method for manufacturing a steel material for a vacuum tube according to an aspect of the present invention will be described in more detail.
[71]
[72]
The manufacturing method of a steel material for a vacuum tube according to an aspect of the present invention, in weight %, C: 0.1 to 0.2%, Si: 0.05 to 0.5%, Mn: 1.0 to 1.6%, Ni: 0.5 to 1.0%, Cr: 1.5 to 4.0%, after reheating the slab containing the remaining Fe and unavoidable impurities to provide a steel material by hot rolling at a finish rolling temperature of 900 ~ 1000 ℃; First cooling the hot-rolled steel material to 550 ~ 650 ℃ at a first cooling rate of 5 ~ 50 ℃ / s; winding the steel material into a coil at a first cooling stop temperature after the first cooling is finished; and second cooling the coil to room temperature at a second cooling rate of 0.005 to 0.05° C./s.
[73]
[74]
slab reheat
[75]
After preparing a slab provided with a predetermined component, it can be reheated. Since the slab alloy composition of the present invention corresponds to the alloy composition of the above-described steel, the description of the slab alloy composition of the present invention is replaced with the description of the above-described steel alloy composition. The slab heating conditions of the present invention may be applied to the normal slab heating conditions, but as a non-limiting example, the slab reheating may be carried out in a temperature range of 1200 to 1350 ℃.
[76]
[77]
hot rolled
[78]
A hot rolled steel may be provided by hot rolling the reheated slab. Finish hot rolling may be carried out in a temperature range of 900 ~ 1000 ℃. In order to prevent deterioration of the resistance yield ratio characteristic due to the refining of the structure, the finish hot rolling may be performed in a temperature range of 900° C. or higher. In addition, in order to prevent excessive scale, it is preferable that the finish hot rolling is performed in a temperature range of 1000° C. or less.
[79]
[80]
First cooling and winding
[81]
After the hot rolling is completed, the hot-rolled steel may be cooled to 550 to 650°C at a first cooling rate of 5 to 50°C/s, and then wound into a hot-rolled coil.
[82]
[83]
When the first cooling rate is excessively low, transformation occurs after winding, and scale formation by recuperative heat may be a problem. Therefore, in the present invention, the first cooling can be performed at a cooling rate of 5° C./s or more. On the other hand, when the first cooling rate is too fast, the shape of the product is deteriorated or there is a possibility that a low-temperature structure is generated. Therefore, the present invention may limit the upper limit of the first cooling rate to 50°C/s.
[84]
[85]
Since the steel material provided with the alloy composition of the present invention exhibits the fastest transformation rate within about 600°C, cooling is terminated in a temperature range of 550 to 650°C in order to introduce all the microstructures of the final steel into a ferrite and pearlite composite structure. It is preferable to wind it in the corresponding temperature section after
[86]
[87]
second cooling
[88]
The winding coil may be cooled to room temperature at a second cooling rate of 0.005 to 0.05°C/s. In the steel material of the present invention, the transformation of ferrite and pearlite is completed in a section of about 600° C., but it is preferable to perform the second cooling under slow cooling conditions in order to prevent low-temperature organization of some untransformed structures. In addition, when the winding coil is cooled by applying a fast cooling rate, shape defects such as product distortion and curvature may occur, and the present invention may limit the upper limit of the second cooling rate to 0.05°C/s. On the other hand, the present invention does not specifically limit the lower limit of the second cooling rate, but may limit the lower limit of the second cooling rate to 0.005 °C/s in the sense of excluding the cooling rate of 0 °C/s. The cooling condition of the second cooling may be standing cooling.
[89]
[90]
The steel material manufactured through the above-described manufacturing process may not only have a composite structure of ferrite and pearlite, but also actively suppress the formation of a hard structure such as martensite or bainite. Preferably, the fraction of ferrite is 60 to 90%, the fraction of pearlite is 10 to 40 area%, and the fraction of hard tissue may be less than 1 area% (including 0%).
[91]
[92]
In addition, the steel material manufactured through the above-described manufacturing process has a gas release rate of 1.0*10 -10 mbar·l·s -1 ·cm -2 or less, a yield strength (YS) of 400 to 600 MPa, and a yield ratio of 0.8 or less ( YR), an elongation (El) of 19-30% and a Charpy impact energy at -20°C of 30-50J.
[93]
Modes for carrying out the invention
[94]
Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the examples described below are for illustrative purposes only and not for limiting the scope of the present invention.
[95]
[96]
(Example)
[97]
After heating the slab provided with the alloy composition of Table 1 in a temperature range of 1250 ° C., the finish hot rolling was performed in a temperature range of 950 ° C. to prepare a hot steel material having a thickness of 25 mm. Thereafter, cooling was terminated by cooling to 600°C at a cooling rate of 25°C/s, and the hot-rolled steel was wound at the cooling termination temperature. Thereafter, it was cooled to room temperature by applying a cooling rate of 0.03° C./s, and the microstructure, yield ratio, and gas release rate for each specimen were measured and described together in Table 1.
[98]
[99]
The microstructure was measured using an optical microscope at 500 magnification after etching each specimen by the nital etching method. In the microstructure of Table 1, F means ferrite, and P means pearlite. The tensile test was conducted by taking a specimen of JIS 5 standard along the rolling direction, and the yield ratio was calculated by dividing the 0.2% off-set yield strength by the tensile strength. The gas release rate was measured using [Relational Expression 1] described above after constructing a vacuum chamber with a length of 500 mm, a diameter of 150 mm, and a thickness of 20 mm.
[100]
[101]
[Table 1]
Psalm
No. Alloy composition (wt%) microstructure
_ Yield ratio
(%) Outgassing rate
(mbar·l·s -1 ·cm -2 )
C Si Mn Ni Cr Nb
One 0.15 0.1 1.3 0.8 1.5 - F+P 0.74 8.6*10 -11
2 0.15 0.1 1.3 0.8 2.5 - F+P 0.75 6.0*10 -11
3 0.15 0.1 1.3 0.8 2.5 0.02 F+P 0.82 5.1*10 -11
4 0.15 0.1 1.3 0.8 0.8 - F+P 0.71 5.7*10 -10
[102]
[103]
In the case of specimens 1 and 2 that satisfy the conditions limited by the present invention, it can be confirmed that a gas release rate of 1.0*10 -10 mbar·l·s -1 ·cm -2 or less and a yield ratio of 0.8 or less are simultaneously satisfied. . On the other hand, in the case of specimens 3 and 4, which do not satisfy the conditions limited by the present invention, it can be confirmed that the present invention does not simultaneously satisfy the desired yield ratio and gas release rate.
[104]
[105]
Therefore, it can be confirmed that the steel material according to an aspect of the present invention has properties particularly suitable as a vacuum tube for a high-speed train, which is a large vacuum structure, since it has both a low gas release rate and a low yield ratio characteristic.
[106]
[107]
Although the present invention has been described in detail through examples above, other embodiments are also possible. Therefore, the spirit and scope of the claims set forth below are not limited to the embodiments.
Claims
[Claim 1]
By weight %, C: 0.1 to 0.2%, Si: 0.05 to 0.5%, Mn: 1.0 to 1.6%, Ni: 0.5 to 1.0%, Cr: 1.5 to 4.0%, including the remaining Fe and unavoidable impurities, microstructure With a ferrite and pearlite composite structure, the gas release rate of the steel is 1.0 * 10 -10 mbar · l · s -1 · cm -2 or less, a steel for a vacuum tube.
[Claim 2]
According to claim 1, wherein the total content of Ti, Nb and V in the impurities contained in the steel is less than 0.01% (including 0%), vacuum tube steel.
[Claim 3]
According to claim 1, The fraction of the ferrite is 60 to 90 area%, the fraction of the pearlite is 10 to 40 area%, the vacuum tube steel.
[Claim 4]
According to claim 1, wherein the fraction of martensite or bainite contained in the steel is less than 1 area% (including 0%), vacuum tube steel.
[Claim 5]
According to claim 1, wherein the steel has a yield strength (YS) of 400 to 600 MPa, a yield ratio (YR) of 0.8 or less and an elongation (El) of 19 to 30%, the steel for vacuum tube.
[Claim 6]
According to claim 1, wherein the steel material is a Charpy impact energy at -20 ℃ 30 ~ 50J, vacuum tube steel.
[Claim 7]
According to claim 1, The thickness of the steel is 5 ~ 30mm, vacuum tube steel.
[Claim 8]
By weight%, C: 0.1-0.2%, Si: 0.05-0.5%, Mn: 1.0-1.6%, Ni: 0.5-1.0%, Cr: 1.5-4.0%, reheating the slab containing the remainder Fe and unavoidable impurities After hot rolling at a finish rolling temperature of 900 ~ 1000 ℃ to provide a steel; first cooling the hot-rolled steel to a temperature range of 550 to 650° C. at a first cooling rate of 5 to 50° C./s; winding the steel material into a coil at a first cooling stop temperature after the first cooling is finished; and second cooling the coil to room temperature at a second cooling rate of 0.005 to 0.05° C./s.
[Claim 9]
According to claim 8, wherein the total content of Ti, Nb and V in the impurities contained in the slab is less than 0.01% (including 0%), the method for manufacturing a steel material for a vacuum tube.
[Claim 10]
The method of claim 8, wherein the hot-rolled steel has a thickness of 5 to 30 mm.
[Claim 11]
The method of claim 8, wherein the cooling method of the first cooling is water cooling, and the cooling method of the second cooling is standing cooling.