EP3872216B1 - Kryogener austenitischer stahl mit hohem mangananteil und ausgezeichneter form und verfahren zur herstellung davon - Google Patents

Kryogener austenitischer stahl mit hohem mangananteil und ausgezeichneter form und verfahren zur herstellung davon Download PDF

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EP3872216B1
EP3872216B1 EP19876795.6A EP19876795A EP3872216B1 EP 3872216 B1 EP3872216 B1 EP 3872216B1 EP 19876795 A EP19876795 A EP 19876795A EP 3872216 B1 EP3872216 B1 EP 3872216B1
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rolling
hot
tnr
steel material
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French (fr)
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EP3872216C0 (de
EP3872216A4 (de
EP3872216A1 (de
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Un-Hae LEE
Bo-Sung Kim
Jeong-Hun SEOK
Dong-Ho Lee
Sung-Kyu Kim
Sang-Deok Kang
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Posco Holdings Inc
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Posco Co Ltd
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Priority claimed from PCT/KR2019/014193 external-priority patent/WO2020085861A1/ko
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    • 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
    • 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
    • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
    • 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
    • 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
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0231—Warm 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys 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 of ferrous metals or ferrous alloys 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
    • 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
    • C22C38/06—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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • 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
    • C21D2211/001—Austenite

Definitions

  • the present invention relates to an austenitic high-manganese steel material and a method of manufacturing the same, and more particularly, to a cryogenic austenitic high-manganese steel material having excellent cryogenic toughness and an excellent shape, and a manufacturing method thereof.
  • An austenitic high-manganese steel material has high toughness because austenite is stable even in room temperature and cryogenic environment by adjusting contents of manganese (Mn) and carbon (C), which are elements increasing stability of austenite, so that it has particularly suitable properties as a material for cryogenic structures such as tanks for LNG storage, tanks for LNG transport, and the like.
  • Mn manganese
  • C carbon
  • high-manganese steel has high deformation resistance at high temperatures, and particularly, in the case of thin materials, it is difficult to secure a uniform shape in a longitudinal direction according to a rolling pass, a reduction ratio, and the like. If a shape of the hot-rolled material is poor, a cooling safety is lowered, and there is a possibility of causing equipment damage in a process such as transportation. In addition, when the shape of the hot-rolled material in the longitudinal direction is poor, a subsequent operation such as a shape correction operation, or the like, must be undertaken, which is not preferable in terms of economy and productivity.
  • CN106222554 A discloses an economic ultra-low temperature high manganese austenitic steel, having excellent low-temperature toughness.
  • an austenitic high-manganese steel material having excellent cryogenic toughness and an excellent shape, and a method of manufacturing the same.
  • FIG. 1 (a) is a view to help in understanding a crest and a trough formed in a steel material in the present disclosure
  • FIG. 1 (b) is a view is an image captured of a steel material according to an example of the present disclosure.
  • the present invention relates to a cryogenic austenitic high-manganese steel material having an excellent shape and a method of manufacturing the same, and hereinafter, preferable embodiments of the present invention will be described.
  • 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. These embodiments are provided to further describe the present invention to a person skilled in the art to which the present invention pertains.
  • % indicating a content of each element, may be based on weight, unless otherwise indicated.
  • the cryogenic austenitic high-manganese steel material having an excellent shape according to an aspect of the present disclosure includes by weight %, 0.2 to 0.5% of C, 23 to 28% of Mn, 0.05 to 0.5 % of si, 0.3 to 1% of Cu 0.03% or less of P, 0.005% or less of S, 0.05 to 0.5% of Al, 2.5 to 4.5% of Cr, 0.0005 to 0.01% of B, and a remainder of Fe and other unavoidable impurities.
  • Carbon (C) is effective in stabilizing austenite and securing strength by solid solution strengthening. Accordingly, in the present disclosure, a lower limit of the carbon (C) content is limited to 0.2% to secure low-temperature toughness and strength. That is, when the carbon (C) content is less than 0.2%, austenite stability may be insufficient such that stable austenite may not be obtained at cryogenic temperature, and processing organic transformation into ⁇ -martensite and ⁇ '-martensite may easily occur by external stress such that toughness and strength of the steel material may be reduced.
  • the carbon (C) content exceeds a certain range, toughness of the steel material may be rapidly deteriorated due to precipitation of carbides, and strength of the steel material may increase excessively such that workability of the steel material may significantly degrade.
  • an upper limit of the carbon (C) content is limited to 0.5%. Therefore, the carbon (C) content in the present disclosure may be 0.2 to 0.5%.
  • a preferable carbon (C) content is 0.3 to 0.5%, and a more preferable carbon (C) content may be 0.3 to 0.45%.
  • Manganese (Mn) is an element effectively contributing to austenite stabilization, and thus, in the present disclosure, a lower limit of the manganese (Mn) content is limited to 23% to achieve such an effect. In other words, since 23% or more of manganese (Mn) is included in the present disclosure, stability of austenite may effectively increase, such that the formation of ferrite, ⁇ -martensite, and ⁇ '-martensite may be inhibited, thereby effectively securing low-temperature toughness of the steel material.
  • the manganese (Mn) content exceeds a certain level, an effect of increasing stability of austenite may be saturated, but manufacturing costs may greatly increase, and internal oxidation may excessively occur during hot-rolling, such that surface quality may be deteriorated.
  • an upper limit of the manganese (Mn) content is limited to 28%. Accordingly, the manganese (Mn) content in the present disclosure is 23 to 28%, and a more preferable manganese (Mn) content may be 23 to 25%.
  • Silicon (Si) is a deoxidizing agent as aluminum (Al) and is inevitably added in a small amount.
  • silicon (Si) is excessively added, an oxide may be formed on a grain boundary such that high-temperature ductility may be reduced, and cracks may be created such that surface quality may be deteriorated.
  • an upper limit of the silicon (Si) content is limited to 0.5%. Since excessive costs may be required to reduce the silicon (Si) content in steel, a lower limit of the silicon (Si) content is limited to 0.05% in the present disclosure. Therefore, the silicon (Si) content in the present disclosure is 0.05 to 0.5%.
  • Copper (Cu) is an element stabilizing austenite together with manganese (Mn) and carbon (C), and effectively contributes to improving low-temperature toughness. Also, copper (Cu) has an extremely low solubility in carbides and is slowly diffused in austenite, such that copper (Cu) may be concentrated on an interfacial surface between austenite and carbide and may surround a nuclei of fine carbide, thereby effectively inhibiting formation and growth of carbides caused by additional diffusion of carbon (C). Thus, in the present disclosure, copper (Cu) is essentially added to secure low-temperature toughness, and a lower limit of the copper (Cu) content is 0.3%.
  • an upper limit of the copper (Cu) content is limited to 1%.
  • a more preferable upper limit of the copper (Cu) content may be 0.8%.
  • Phosphorus (P) is not only an impurity element that is unavoidably introduced, but is also an element that easily segregates and causes cracking during casting, or an element that deteriorates weldability. Accordingly, in the present disclosure, an upper limit of the phosphorus (P) content is limited to 0.03% to prevent deterioration of castability and weldability.
  • Sulfur (S) is not only an impurity element that is unavoidably introduced, but is also an element that causes a hot brittleness defect by forming inclusions. Accordingly, in the present disclosure, an upper limit of the sulfur (S) content is limited to 0.005% to inhibit hot brittleness.
  • Aluminum (Al) is a representative element added as a deoxidizer. However, aluminum (Al) may form precipitates by reacting with carbon (C) and nitrogen (N), and hot workability may be deteriorated by the precipitates. Thus, in the present disclosure, an upper limit of the aluminum (Al) content is limited to 0.5%. The aluminum (Al) content is 0.05 to 0.5%.
  • Chromium (Cr) may stabilize austenite in a range of an appropriate amount such that chromium (Cr) may contribute to improving impact toughness at low temperature, and may be solid-solute in austenite and may increase strength of the steel material. Also, chromium may improve corrosion resistance of the steel material. Therefore, in the present disclosure, 2.5% or more of chromium (Cr) is added to obtain the effect as above. However, chromium (Cr) may be a carbide-forming element and may form carbides on an austenite grain boundary, such that low-temperature impact toughness may be reduced. Thus, an upper limit of the chromium (Cr) content is limited to 4.5% in consideration of content relationship between carbon (C) and other elements added together. Accordingly, the chromium (Cr) content in the present disclosure is 2.5 to 4.5%, and a more preferable chromium (Cr) content may be 3 to 4%.
  • Boron (B) is a grain boundary strengthening element which may strengthen an austenite grain boundary, and by even adding boron (B) in a small amount, an austenite grain boundary may be strengthened such that high-temperature cracking sensitivity may be effectively reduced.
  • a lower limit of the boron (B) content is limited to 0.0005%.
  • the boron (B) content exceeds a certain range, segregation may occur on an austenite grain boundary such that high-temperature cracking sensitivity of the steel material may increase, and surface quality of the steel material may be degraded.
  • an upper limit of the boron (B) content is limited to 0.01%.
  • the boron (B) content of the present disclosure is 0.0005 to 0.01%, and a more preferable boron (B) content may be 0.002 to 0.006%.
  • the cryogenic austenitic high-manganese steel having an excellent shape of the present disclosure has a remainder of Fe and other unavoidable impurities in addition to the above components.
  • inevitable impurities may be inevitably added from raw materials or an ambient environment, and thus, impurities may not be excluded.
  • a person skilled in the art of a general manufacturing process may be aware of the impurities, and thus, the descriptions of the impurities may not be provided in the present disclosure.
  • the cryogenic austenitic high-manganese steel material having an excellent shape according to an aspect of the present disclosure may include 95 area% or more of austenite as a microstructure, thereby effectively securing cryogenic toughness of the steel material.
  • An average grain size of austenite may be 5-150 ⁇ m.
  • An average grain size of austenite implementable in the manufacturing process may be 5 ⁇ m or more, and when the average grain size increases significantly, strength of the steel material may be reduced. Thus, the grain size of austenite may be limited to 150 ⁇ m or less.
  • the cryogenic austenitic high-manganese steel material having an excellent shape according to an aspect of the present disclosure may include a carbide and/or ⁇ -martensite as a possible structure other than austenite.
  • a fraction of carbide and/or ⁇ -martensite exceeds a certain level, toughness and ductility of the steel material may be rapidly deteriorated.
  • the fraction of carbide and/or ⁇ -martensite may be limited to 5 area% or less.
  • the cryogenic austenitic high-manganese steel material having an excellent shape according to the present invention has a yield strength of 350 MPa or more, a tensile strength of 700 MPa or more, and an elongation of 40% or more.
  • the cryogenic austenitic high-manganese steel material having an excellent shape according to the present invention has a Charpy impact toughness of -196°C of 30J or more (based on a thickness of 5mm), and thus can have excellent cryogenic properties.
  • cryogenic austenitic high-manganese steel material having an excellent shape has a maximum height difference within 10 mm between the a crest and a trough formed in the steel material in a region within 2m of the rolling direction even without performing a separate correction operation after the steel material is manufactured, excellent shape uniformity may be secured.
  • FIG. 1 (a) is a view to help in understanding a crest and a trough formed in a steel material in the present disclosure
  • FIG. 1 (b) is an image captured of a steel material according to an example of the present disclosure.
  • a method of manufacturing a cryogenic austenitic high-manganese steel material having an excellent shape includes: primarily heating a slab including, by weight%, 0.2 to 0.5% of C, 23 to 28% of Mn, 0.05 to 0.5% of Si, 0.3 to 1% of Cu, 0.03% or less of P, 0.005% or less of S, 0.05 to 0.5% of Al, 2.5 to 4.5% of Cr, 0.0005 to 0.01% of B, and a remainder of Fe and unavoidable impurities, to a temperature range of 1050 to 1300°C; primarily hot-rolling the heated slab at a finishing rolling temperature of 800 to 1100°C at a total rolling reduction ratio of 35 to 80% to provide an intermediate material; cutting the intermediate material into a length of 1500 to 4000 mm; secondarily heating the intermediate material to a temperature range of 1050 to 1300°C; secondarily hot-rolling the secondarily-heated intermediate material at a finishing rolling temperature of (Tnr-120
  • composition of the slab provided in the manufacturing method in the present disclosure corresponds to the steel composition of the austenitic high-manganese steel material described above
  • description of the steel composition of the slab is replaced with the description of the steel composition of the austenitic high-manganese steel material described above.
  • the slab provided in the above-described steel composition is primarily heated in a temperature range of 1050 to 1300°C.
  • a primary heating temperature is lower than a certain range, there may be a problem in which an excessive rolling load may be applied during primary hot-rolling, or an alloy component may not be sufficiently solid solute. Therefore, in the present disclosure, a lower limit of the primary heating temperature range is limited to 1050°C.
  • the primary heating temperature exceeds a certain range, grains may grow excessively such that strength of the steel material may be deteriorated, or the steel material may be heated by exceeding a solidus temperature of the steel material such that hot-rolling properties of the steel material may be deteriorated.
  • an upper limit of the primary heating temperature range of slab is limited to 1300°C.
  • a primary hot-rolling process may include a rough-rolling process and a finishing rolling process, and the primarily-heated slab may be size-rolled during the first hot-rolling and may be provided as an intermediate material.
  • a total reduction ratio of the primary hot-rolling is 35 to 80%, and the finishing rolling of the primary hot-rolling is performed in a temperature range of 800 tc 1100°C.
  • the finishing hot-rolling temperature of the primary hot-rolling is less than a certain range, an excessive rolling load due to an increase in rolling load may be a problem, and when the finishing hot-rolling temperature of the primary hot-rolling exceeds a certain range, grains may grow coarse and the target strength cannot be obtained.
  • the intermediate material In order to load an intermediate material into a heating furnace, the intermediate material is cut to a length of 1500 to 4000 mm.
  • the length of the intermediate material is less than 1500mm, tracking in the heating furnace is difficult, and when the length of the intermediate material exceeds 4000mm, there may be a risk of bending in a longitudinal direction.
  • the intermediate material is secondarily heated in a temperature range of 1050 to 1300°C.
  • a secondary heating temperature is lower than a certain range, there may be a problem in which an excessive rolling load may occur during the secondary hot-rolling, or a problem in that the alloy component is not sufficiently dissolved may occur.
  • a lower limit of the secondary heating temperature range is limited to 1050°C.
  • the secondary heating temperature exceeds a certain range, grains may grow excessively such that strength of the steel material may be deteriorated, or the steel material may be heated by exceeding a solidus temperature of the steel material such that hot-rolling properties of the steel material may be deteriorated.
  • an upper limit of the secondary heating temperature range of the intermediate material is limited to 1300°C.
  • a secondary hot-rolling process may include a rough-rolling process and a finishing-rolling process, and the secondarily-reheated intermediate material is provided as an intermediate material by secondary hot-rolling.
  • the finishing rolling is performed in a temperature range of (Tnr-120) to Tnr°C.
  • Tnr can be derived by Equation 1 below.
  • Tnr ° C 840 + 150 * C + 2.5 * Mn + 5 * Cu + 3.5 * Cr ⁇ 50 * Si (where, C, Mn, Cu, Cr, and Si are weight percentages of each component).
  • a total rolling reduction amount of the intermediate material in the temperature range of (Tnr-120) to Tnr°C during the secondary hot rolling is controlled to 5 to 25%.
  • the total rolling reduction amount of the intermediate material in the temperature range of (Tnr-120) to Tnr°C is less than 5%, the desired shape correction effect cannot be achieved, and when the total rolling reduction amount of the intermediate material in the temperature range of (Tnr-120) to Tnr°C exceeds 25%, there is a concern about a decrease in impact toughness due to excessive reduction.
  • the secondarily hot-rolled material is cooled to a cooling stop temperature of 600°C or less at a cooling rate of 1 to 100°C/s.
  • the cooling rate is less than a certain range, a decrease in ductility of the steel material and deterioration of abrasion resistance may become problems due to carbides precipitated on a grain boundary during cooling, and thus, in the present disclosure, the cooling rate the hot-rolled material is limited to 1°C/s or more.
  • a lower limit of the preferred cooling rate may be 10°C/s, and a cooling method may be accelerated cooling.
  • an upper limit of the cooling rate is limited to 100°C/s in the present disclosure.
  • the cooling stop temperature is limited to 600°C or less.
  • the austenitic high-manganese steel material manufactured as above may include 95 area% or more of austenite.
  • the austenitic high-manganese steel material has yield strength of 350 MPa or more, tensile strength of 700 MPa or more, elongation of 40% or more, and Charpy impact toughness of 30 J or more (based on a thickness of 5 mm) at -196°C.
  • the austenitic high-manganese steel material manufactured as described above has a maximum height difference of within 10 mm or less between a crest and a trough formed in the steel material in an area within 2 m in the longitudinal direction of the steel material, so that excellent shape uniformity can be ensured.
  • a slab having an alloy composition of Table 1 below and a thickness of 250mm was manufactured. Each slab was primarily heated in a temperature range of 1200°C and then primarily hot-rolled at a finishing rolling temperature of 1000°C with a total rolling reduction ratio of 50 to 60% to prepare an intermediate material. Each intermediate material was subjected to secondary heating and secondary hot-rolling under the conditions of Table 2 to prepare a hot-rolled material specimen, and yield strength, tensile strength, elongation, Charpy impact toughness, and shape uniformity for each specimen were measured and shown in Table 3 below. In this case, shape uniformity was described by measuring a maximum height difference between a crest and a trough formed in an area within 2mm in a rolling direction of a specimen.
  • the alloy composition and manufacturing process of the disclosure secures the desired physical properties and shape uniformity of the present disclosure in the case of a satisfactory invention example, but does not satisfy the alloy composition or manufacturing process of the present invention in the case of a comparative example.

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Claims (3)

  1. Kryogener austenitischer Stahl mit hohem Mangananteil und ausgezeichneter Form, umfassend in Gewichts-% 0,2 bis 0,5 % C, 23 bis 28 % Mn, 0,05 bis 0,5 % Si, 0,3 bis 1 % Cu, 0,03 % oder weniger P, 0,005 % oder weniger S, 0,05 bis 0,5 % Al, 2,5 bis 4,5 % Cr und 0,0005 bis 0,01 % B, mit einem Rest aus Fe und anderen unvermeidbaren Verunreinigungen,
    wobei die Charpy-Kerbschlagzähigkeit bei -196 °C, gemessen nach dem Standard ASTM A370, basierend auf einer Dicke von 5 mm, einer Streckgrenze von 350 MPa oder mehr, einer Zugfestigkeit von 700 MPa oder mehr und einer Dehnung von 40 % oder mehr mindestens 30 J beträgt, wobei die Streckgrenze, die Zugfestigkeit und die Dehnung nach dem Standard ASTM A370 gemessen werden und ein maximaler Höhenunterschied zwischen einem Scheitel und einem Tal, die innerhalb eines Bereichs von 2 m in einer Walzrichtung gebildet werden, höchstens 10 mm beträgt.
  2. Kryogener austenitischer Stahl mit hohem Mangananteil und ausgezeichneter Form nach Anspruch 1, wobei eine Korngröße des Austenits 5 bis 150 µm beträgt.
  3. Verfahren zur Herstellung eines kryogenen austenitischen Stahls mit hohem Mangananteil und ausgezeichneter Form nach Anspruch 1, umfassend:
    primäres Erwärmen einer Bramme, enthaltend in Gewichts-% 0,2 bis 0,5 % C, 23 bis 28 % Mn, 0,05 bis 0,5 % Si, 0,3 bis 1 % Cu, 0,03 % oder weniger P, 0,005 % oder weniger S, 0,05 bis 0,5 % Al, 2,5 bis 4,5 % Cr und 0,0005 bis 0,01 % B, mit einem Rest aus Fe und anderen unvermeidbaren Verunreinigungen, auf einen Temperaturbereich von 1050 bis 1300 °C;
    primäres Warmwalzen der erwärmten Bramme bei einer Fertigwalztemperatur von 800 bis 1100 °C mit einem Gesamtwalzreduktionsverhältnis von 35 bis 80 %, um ein Zwischenmaterial bereitzustellen;
    Schneiden des Zwischenmaterials auf eine Länge von 1500 bis 4000 mm;
    sekundäres Erwärmen des geschnittenen Zwischenmaterials auf einen Temperaturbereich von 1050 bis 1300 °C;
    sekundäres Warmwalzen des sekundär erwärmten Zwischenmaterials bei einer Fertigwalztemperatur von (Tnr-120) bis Tnr°C, um ein warmgewalztes Material bereitzustellen;
    Abkühlen des warmgewalzten Materials auf einen Temperaturbereich von 600 °C oder weniger mit einer Abkühlgeschwindigkeit von 1 bis 100 °C/s,
    wobei während des sekundären Warmwalzens das Gesamtwalzreduktionsausmaß des Zwischenmaterials im Temperaturbereich von (Tnr-120) bis Tnr°C 5 bis 25 % beträgt, und
    wobei Tnr durch die folgende Gleichung 1 abgeleitet wird: Tnr ° C = 840 + 150 * C + 2,5 * Mn + 5 * Cu + 3,5 * Cr − 50 * Si
    Figure imgb0003
    wobei C, Mn, Cu, Cr und Si Gewichtsprozente jeder Komponente sind.
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