EP4261304A1 - Matériau d'acier pour amortisseur sismique présentant une grande résistance au choc et son procédé de fabrication - Google Patents

Matériau d'acier pour amortisseur sismique présentant une grande résistance au choc et son procédé de fabrication Download PDF

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EP4261304A1
EP4261304A1 EP21903728.0A EP21903728A EP4261304A1 EP 4261304 A1 EP4261304 A1 EP 4261304A1 EP 21903728 A EP21903728 A EP 21903728A EP 4261304 A1 EP4261304 A1 EP 4261304A1
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Prior art keywords
steel material
less
steel
seismic damper
content
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German (de)
English (en)
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Jae-Young Cho
Sang-Deok Kang
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Posco Holdings Inc
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Posco Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
    • C21D7/04—Modifying the physical properties of iron or steel by deformation by cold working of the surface
    • C21D7/06—Modifying the physical properties of iron or steel by deformation by cold working of the surface by shot-peening or the like
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04H—BUILDINGS OR LIKE STRUCTURES FOR PARTICULAR PURPOSES; SWIMMING OR SPLASH BATHS OR POOLS; MASTS; FENCING; TENTS OR CANOPIES, IN GENERAL
    • E04H9/00—Buildings, groups of buildings or shelters adapted to withstand or provide protection against abnormal external influences, e.g. war-like action, earthquake or extreme climate
    • E04H9/02—Buildings, groups of buildings or shelters adapted to withstand or provide protection against abnormal external influences, e.g. war-like action, earthquake or extreme climate withstanding earthquake or sinking of ground
    • E04H9/021—Bearing, supporting or connecting constructions specially adapted for such buildings
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • the present invention relates to a steel material for a seismic damper used to secure seismic resistance of a structure against an earthquake and a manufacturing method for the same.
  • a seismic damper is used as a device for absorbing such seismic energy, and a steel material for the seismic damper has an ultra-low yield point characteristic.
  • Patent Document 1 Patent Publication No. 2008-0088605
  • An aspect of the present disclosure is to provide a steel material for a seismic damper, which has low yield strength and can be used to secure seismic resistance of a structure against an earthquake, and a manufacturing method for the same.
  • another aspect of the present disclosure is to provide a steel material for a seismic damper having low yield strength and excellent low-temperature impact toughness simultaneously, and a manufacturing method for the same.
  • An object of the present disclosure is not limited to the above description.
  • the object of the present disclosure will be understood from the entire content of the present specification, and a person skilled in the art to which the present disclosure pertains will understand an additional object of the present disclosure without difficulty.
  • a steel material that can be suitably used for a seismic damper used to secure seismic resistance of a structure against an earthquake and a manufacturing method for the same may be provided.
  • a steel material for a seismic damper having low yield strength and excellent low-temperature impact toughness and a manufacturing method for the same may be provided.
  • the present inventors have developed that it is possible to provide a steel material having a yield strength as low as 120 MPa or less and excellent low-impact toughness, and thus the present disclosure was provided.
  • the steel material for a seismic damper has a composition including by weight: 0.006% or less of C, 0.05% or less of Si, 0.3% or less of Mn, 0.02% or less of P, 0.01% or less of S, 0.005 to 0.05% of Al, 0.005% or less of N, 48/14 ⁇ [N] to 0.05% of Ti, with a balance of Fe and other unavoidable impurities.
  • a reason for adding each alloy component constituting the composition of steel which is one of the main characteristics of the present disclosure, and an appropriate content range thereof will first be described.
  • C is an element causing solid solution strengthening and is fixed to dislocations in a free state to increase yield strength and decrease elongation.
  • a case in which a C content is 0% is excluded (i.e., the C content exceeds 0%). Therefore, in order to be suitably used as a steel material for a seismic damper, the lower the C content, the better, so the C content is controlled to be 0.006% or less, and more preferably is controlled to be 0.0045% or less. In addition, more preferably, the C content may be 0.0005% or more.
  • Si 0.05% or less (excluding 0%)
  • Si like C
  • Si is an element causing solid solution strengthening, to increase yield strength and lower elongation.
  • the Si content can be controlled to be 0.03% or less, more preferably be controlled to be 0.013% or less, in terms of securing low yield strength.
  • the Si content may be 0.001% or more.
  • Mn is an element causing solid solution strengthening, to increase yield strength and lower elongation.
  • the Mn content may be controlled to be 0.3% or less, more preferably may be controlled to be 0.2% or less, in terms of securing low yield strength.
  • the Mn content may be 0.06% or more, and more preferably may be 0.1% or more.
  • the P content may be controlled to be 0.02% or less, more preferably 0.013% or less.
  • the P content may be 0.001% or more, and more preferably 0.004% or more.
  • the S content may be controlled to be 0.01% or less, more preferably 0.004% or less.
  • the S content may be 0.0005% or more, more preferably 0.001% or more.
  • Al is an element capable of inexpensively deoxidizing molten steel, and an upper limit of an Al content is controlled to be 0.05% in terms of securing impact toughness while sufficiently lowering yield strength.
  • the upper limit of the Al content may be controlled to 0.035%, and a lower limit of the Al content may be controlled to 0.005%, and more preferably 0.023%, in terms of securing the minimum deoxidation performance.
  • N is an element causing solid solution strengthening and is fixed to dislocations in a free state to increase yield strength and decrease elongation.
  • a case in which a N content is 0% is excluded (i.e., the N content exceeds 0%).
  • the N content is controlled to be 0.005% or less in terms of securing low yield strength.
  • the N content may be 0.001% or more.
  • Nb is an important element in manufacturing TMCP steel, and is a very important element which prevents C from being fixed to dislocations by being precipitated in a form of NbC or NbCN.
  • Nb dissolved during reheating to a high temperature suppresses recrystallization of austenite, thereby exhibiting an effect of refining the structure.
  • Nb in order to introduce deformed organic precipitates, it is necessary to secure a wide non-recrystallization region. As can be seen in FIG. 2 , it is preferable to add 0.04% or more of Nb in terms of securing a temperature range of 50°C or higher between Ar3 and Tnr. In addition, in order to prevent deterioration of impact toughness due to coarsening of precipitates, it is preferable to add Nb to 0.15% or less.
  • FIG. 2 illustrates a graph of a change in recrystallization stop temperature (Tnr) according to an amount of Nb added to the steel material of the present disclosure. That is, in the case of ultra-low carbon steel in which the carbon content is controlled to be an ultra-low amount as in the present disclosure, Ar3 is very high at about 890°C, and the change in Ar3 is insignificant. Therefore, since the change value of Ar3 becomes a negligible level, it can be expressed by fixing Ar3 to about 890°C as shown in FIG. 2 , and the recrystallization stop temperature (Tnr) of ultra-low carbon steel can be controlled to be high only when the Nb content is added at 0.04 to 0.15%.
  • Tnr recrystallization stop temperature
  • a lower limit of the Nb content may be 0.07%, or an upper limit of the Nb content may be 0.1%.
  • Ti is an element that precipitates in a form of TiN, serving to prevent N from being fixed to dislocations. Therefore, in order to adhere N in steel in an appropriate range, considering the added N content (weight %), Ti should be added in an amount of 48/14 ⁇ [N]% or more, where [N] refers to a content of nitrogen (weight %), or Ti should be added in an amount of 0.02% or more. Meanwhile, when Ti is excessively added, there is a concern that impact toughness may deteriorate due to coarsening of precipitates, so Ti may be controlled to be 0.05% or less in terms of securing impact toughness, and more particularly, Ti may be controlled to be 0.04% or less.
  • N in steel may be fixed to as precipitates by controlling the Ti content to be within a range of 48/14 ⁇ [N] to 0.05%
  • C in steel may be fixed to as precipitates by controlling the Nb content to be within a range of 0.04 to 0.15%. Therefore, in the present disclosure, by optimizing the Ti and Nb contents, it is possible to control the deformed organic precipitates to be finely formed in an appropriate size, thereby effectively providing a steel material for a seismic damper having excellent low-temperature impact toughness while having low yield strength.
  • the steel material for a seismic damper may have an R1 value defined by the following Relational Expression 1 of 0.8 or more, or more preferably, the R1 value have a range within 0.8 to 150.
  • R1 value 0.8 or more
  • a steel material having an ultra-low yield strength of 120MPa or less may be more effectively provided.
  • Nb precipitates may be finely formed, so that more excellent impact toughness can be secured.
  • R 1 Nb / Si
  • a lower limit of the R1 value defined by the Relational Expression 1 may be 3.33, or an upper limit of the R1 value may be 90.
  • an R2 value defined by the following Relational Expression 2 of the steel material for a seismic damper may satisfy 0.8 or more.
  • the R2 value may be within a range of 0.8 to 200, and most preferably within a range of 4 to 200.
  • the R2 value is 0.8 or more, a steel material having a low yield strength of 120MPa or less may be more effectively provided.
  • Nb precipitates may be formed finely, so that better impact toughness may be secured.
  • a lower limit of the R2 value defined by the Relational Expression 2 may be 4.33, and an upper limit of the R2 value may be 130.
  • remainder is Fe. That is, in a steel material for a seismic damper, since in the common manufacturing process, unintended impurities may be inevitably incorporated from raw materials or the surrounding environment, the component may not be excluded. Since these impurities are known to any person skilled in the common manufacturing process, the entire contents thereof are not particularly mentioned in the present specification.
  • the steel material for a seismic damper has a ferrite single structure.
  • the steel material may serve as an earthquake damper by effectively adsorbing energy when an earthquake occurs.
  • an average ferrite grain size in a surface layer portion may be 150 to 500 um.
  • the average ferrite grain size in the surface layer portion is less than 150 um, a problem in that the yield strength exceeds a target yield strength may occur, and when average ferrite grain size exceeds 500 ⁇ m, a problem in that the yield strength of steel material for the damper is lower than the target strength may occur.
  • a lower limit of the average ferrite grain size in the surface layer portion may be more preferably 175 ⁇ m, and most preferably 200 um.
  • an upper limit of the average ferrite grain size in the surface layer portion may be more preferably 310 ⁇ m, and most preferably 300 ⁇ m.
  • the surface layer portion refers to a region from a surface of the steel material to a region corresponding to 30% of a total thickness. Therefore, an inner region, other than the surface layer portion described later refers to a region excluding surface layer portions (upper surface layer portion and lower surface layer portion) respectively disposed in upper and lower portions in the thickness direction of the steel material.
  • the average ferrite grain size in the surface layer portion may be greater than an average ferrite grain size in an inner region, other than the surface layer portion, and more particularly, the average ferrite grain size may be 150 um or more greater than the average ferrite grain size in the inner region.
  • the average ferrite grain size in the inner region may be within a range of 10 to 50 um, more preferably within a range of 30 to 50 um.
  • the average ferrite grain size in the inner region is less than 10 um, a problem of exceeding the target yield strength may occur, and when the average ferrite grain size in the inner region exceeds 50 ⁇ m, a problem that the yield strength of the entire damper is lower than the target strength may occur.
  • the average ferrite grain size described above refers to an average value of values obtained by measuring an equivalent circle diameter of the crystal grains, and assuming that a spherical particle drawn with the longest length penetrating an inside of the crystal grain as a particle diameter, the average ferrite grain size described above is an average value of the measured grain sizes.
  • FIG. 1 For a steel material of Inventive Example 1-2 to be described later, corresponding to an example of the present disclosure, an optical photograph of a microstructure captured with an optical microscope was shown in FIG. 1 . As can be seen in FIG. 1 , it can be confirmed that a ferrite grain size in the surface layer portion is greater than a ferrite grain size in an inner region other than the surface layer portion.
  • a ratio (Ds/Dt) of a thickness Ds of the surface layer portion to a total thickness Dt of the steel material may be within a range of 0.1 to 0.3.
  • the ratio (Ds/Dt) of the surface layer portion of the total thickness of the steel material satisfies the range of 0.1 to 0.3, so as can be seen in FIG. 5 , the steel material for a seismic damper having a very low yield strength of 120 MPa or less targeted in the present disclosure may be effectively provided.
  • the ratio (Ds/Dt) when the ratio (Ds/Dt) is less than 0.1, a problem in that sufficient energy as a damper may not be absorbed exceeding the target yield strength, may occur, and when the ratio (Ds/Dt) exceeds 0.3, as shown in FIG. 3 , the yield strength is too low, so that a problem of performing safe support for a structure may occur.
  • a lower limit of the ratio (Ds/Dt) may be 0.14, or an upper limit of the ratio (Ds/Dt) may be 0.25.
  • the surface layer portion is a concept including all of the surface layer portions formed on each of the upper and lower portions of the steel material.
  • a yield strength (YS) of the steel material for a seismic damper described above may be 120 MPa or less, and is not particularly limited, but may be more preferably in a range of 80 to 120 MPa.
  • the yield strength of the steel material exceeds 120 MPa, a problem in which energy may not be sufficiently absorbed when an earthquake occurs may occur, and when the yield strength of the steel material is less than 80MPa, a problem for stably maintaining a structure may occur.
  • a manufacturing method for a steel material for a seismic damper may include an operation of reheating a steel slab satisfying the above-described composition, and the reheating may be performed to a temperature within a range of 1050 to 1250°C.
  • a heating temperature of the steel slab is controlled to 1050°C or higher in order to sufficiently dissolve the carbonitride of Ti and/or Nb formed during casting.
  • the slab may be preferably heated at 1250 °C or lower.
  • a lower limit of a reheating temperature of the slab may be 1075°C, or an upper limit of the reheating temperature of the slab may be 1125°C.
  • the heated steel slab may include an operation of performing rough rolling to adjust a shape of the slab, and a temperature during rough rolling may be controlled to be higher than a temperature (Tnr) at which recrystallization of austenite stops. It is possible to obtain an effect of destroying structural structures such as dentrite, or the like, formed during casting by rough rolling, and it is also possible to obtain an effect of reducing a size of austenite. Meanwhile, although not particularly limited, in terms of improving the effects described above, more preferably, a lower limit of the rough rolling end temperature may be 995°C, or an upper limit of the rough rolling end temperature may be 1035°C.
  • An operation in which the heated steel slab described above (or rough-rolled bar) is finish rolled in a temperature range of Ar3 to 80°C or higher and Ar3 or lower is included. Subsequently, an operation of cooling, if necessary, after finish rolling may be included, and the cooling may be air cooling. Meanwhile, when the finish rolling temperature is lower than Ar3 to 80°C, a problem that a ferrite grain size inside the steel material becomes too fine may occur. In addition, when the finish rolling temperature exceeds Ar3, a problem in that the ferrite grain size inside the steel material become coarse may occur.
  • a lower limit of the finish rolling start temperature may be 955°C, or an upper limit of the finish rolling start temperature may be 980°C.
  • a lower limit of the finish rolling end temperature may be 860°C, or an upper limit of the finish rolling end temperature may be 905°C.
  • An operation of performing a shot blasting treatment on a surface of the finish-rolled steel material described above is included, wherein the shot blasting treatment may be performed so that a metallic ball or a non-metallic ball is rotated at a rate of 1,500 to 2,500 rpm, and sprayed on a surface of the plate material at a rate of 60 to 100 m/s.
  • the shot blasting treatment By performing the shot blasting treatment, coarse ferrite crystal grains may grow on the surface layer portion of the steel material, and a ratio of the thickness of the surface layer portion to the total thickness of the steel material can be increased to lower the yield strength.
  • a rotational speed of the metallic ball or non-metallic ball when a rotational speed of the metallic ball or non-metallic ball is less than 1,500 rpm, a sufficient speed may not be secured, resulting in a problem of not securing the size of the ferrite grains on the surface layer portion, and when a rotational speed of the metallic ball or non-metallic ball exceeds 2,500 rpm, a problem may occur in a stable operation of a machine.
  • a lower limit of the rotational speed may be 1,550 rpm, or an upper limit of the rotational speed may be 2,350 rpm.
  • a lower limit of the spraying speed may be 62 m/s, or an upper limit of the spraying speed may be 94 m/s.
  • a metallic ball or a non-metallic ball having an average diameter of 0.8 to 1.2 mm may be used.
  • a diameter of the ball is less than 0.8 mm, a problem of insufficient energy transmitted to a surface of the steel material may be caused, and when the diameter of the ball exceeds 1.2 mm, a problem of not uniformly transmitting energy to the surface of the steel material may be caused.
  • a lower limit of the average diameter of the metallic ball (or non-metallic ball) may be 0.9 mm, or an upper limit of the average diameter of the metallic ball (or non-metallic ball) may be 1.1 mm.
  • the shot blasting treatment may be performed for 10 to 30 minutes.
  • the shot blasting treatment time is less than 10 minutes, a problem of insufficient energy transmitted to a surface of the steel material may be caused, and when the shot blasting treatment time exceeds 30 minutes, a problem of causing defects in the surface quality of the steel material may be caused.
  • a lower limit of the shot blasting treatment time may be 15 minutes, or an upper limit of the shot blasting treatment time may be 25 minutes.
  • a heat treatment operation so that an LMP value defined by the following Relational Expression 3 satisfies a range of 23.5 to 24.5, may be further included.
  • LMP T ⁇ log t + 20 / 1000
  • T represents a heat treatment temperature, a unit thereof is °C
  • t represents a heat treatment temperature, a unit thereof is minutes.
  • Relational Expression 3 is a numerical value obtained empirically, a unit may not be particularly determined. That is, in the Relational Expression 3, it is sufficient when each unit of T and t described later is satisfied.
  • the LMP value defined by the Relational Expression 3 described above may satisfy a range of 23.5 to 24. 5, so, as can be shown in FIG. 4 , a thickness ratio of the surface layer portion with respect to the total thickness of the steel material may be controlled to be within a range of 0.1 to 0.3, so that a steel material having a target yield strength of 120 MPa or less (more preferably, within a range of 80 to 120 MPa) may be obtained.
  • a lower limit of the LMP value defined by the Relational Expression 3 may be 23.7, or an upper limit of the LMP value defined by the Relational Expression 3 may be 24.3.
  • the heat treatment operation may be performed in a range of 850 to 900°C.
  • the heat treatment temperature is lower than 850°C, a problem of not securing sufficiently coarse ferrite growth may occur, and when the heat treatment temperature is higher than 900°C, a problem in that ferrite grains that are too more coarse than target ferrite grains are formed may occur.
  • a lower limit of the heat treatment temperature may be 855°C, or an upper limit of the heat treatment temperature may be 880°C.
  • the heat treatment time may be in a range of 5 to 30 minutes. Meanwhile, more preferably, a lower limit of the heat treatment time may be 10 minutes, or an upper limit of the heat treatment time may be 25 minutes.
  • a steel slab having the alloy composition and properties illustrated in Table 1 below was prepared.
  • a content of each component in Table 1 below is % by weight, and a balance thereof is Fe and inevitable impurities. That is, in the steel slabs (the balance being Fe) described in Table 1 below, Inventive Steels A to D illustrate an example matching a range of alloy compositions defined by the present disclosure, and Comparative Steels E to I illustrate an example deviating from the range of alloy compositions defined by the present disclosure.
  • slab reheating - rough rolling -finish rolling was performed under the conditions illustrated in Table 2 below. Subsequently, after performing a shot blasting treatment for 15 minutes under the conditions of Table 3 using a metallic ball having an average diameter of 1.0 m, a heat treatment was performed to manufacture a steel material.
  • the steel sheet thus obtained was polishing-etched and then observed with an optical microscope, so that it was confirmed that the steel material has a ferrite single structure.
  • the average grain size was measured using a line measurement method, and a point at which yielding occurs using a tensile tester according to the ASTM standard was set to be a yield strength and a strength when necking occurs was set to be a tensile strength.
  • a Charpy impact transition temperature an impact absorption energy was measured using a Charpy impact tester and a temperature at which fracture transitions from ductility to brittleness was shown.
  • Example 1-1 210 37 0.2 98 247 -45 Example 1-2 275 42 0.25 89 257 -50 Reference Example 1 730 65 0.45 65 235 -35 Inventi ve Steel B Example 2-1 175 25 0.14 112 289 -38 Example 2-2 310 40 0.22 95 250 -37 Reference Example 2 750 55 0.08 68 275 -40 Inventi ve Steel C Example 3-1 182 32 0.16 107 285 -37 Example 3-2 305 41 0.22 95 260 -41 Reference Example 3 820 75 0.47 64 225 -28 Inventi ve Steel D Example 4-1
  • a thickness ratio of the upper and lower surface layer portions to the total thickness of the steel material was in a range of 0.1 to 0.3, and the physical properties of the steel material all satisfied the yield strength of 80 to 120 MPa and the Charpy impact transition temperature of -20 °C or lower.
  • Reference Examples 1 to 4 illustrate a case of satisfying the steel composition of the present disclosure, but deviating from the manufacturing conditions. Thereamong, Reference Examples 1 to 4 illustrate a case in which the LMP exceeds 24.5. Reference Examples 1 to 4 illustrate a case of deviating from the range of 0.1 to 0.3, which is the thickness ratio of the surface layer portion, and the yield ratios were all less than 80 MPa.
  • Comparative Example 1 exceeded the upper limit of the content specified in the present disclosure, and the yield strength exceeded 120 MPa.
  • Comparative Example 2 Si, a solid solution strengthening element, exceeds the upper limit of the content specified in the present disclosure, and the yield strength exceeded 120 MPa.
  • Comparative Example 3 when Nb was added excessively, the impact toughness was deteriorated due to the formation of coarse precipitates, and the Sharpie impact transition temperature exceeded -20°C.
  • Comparative Example 4 illustrates a case of satisfying all the manufacturing conditions of the present disclosure, but a content of Ti exceeded the upper limit specified in the present disclosure, and the Charpy impact transition temperature exceeded -20°C due to the formation of coarse precipitates.
  • Comparative Example 5 illustrates a case of satisfying all the manufacturing conditions of the present disclosure, but the content of Ti was less than the lower limit specified in the present disclosure, and in Comparative Example 5, it was insufficient to precipitate free N as a nitride due to the insufficient Ti content, and a yield point phenomenon was expressed, and the yield strength exceeded 120 MPa.

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EP21903728.0A 2020-12-10 2021-12-01 Matériau d'acier pour amortisseur sismique présentant une grande résistance au choc et son procédé de fabrication Pending EP4261304A1 (fr)

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