WO2020085851A1 - Cryogenic austenitic high manganese steel having excellent surface quality and manufacturing method therefor - Google Patents

Cryogenic austenitic high manganese steel having excellent surface quality and manufacturing method therefor Download PDF

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WO2020085851A1
WO2020085851A1 PCT/KR2019/014170 KR2019014170W WO2020085851A1 WO 2020085851 A1 WO2020085851 A1 WO 2020085851A1 KR 2019014170 W KR2019014170 W KR 2019014170W WO 2020085851 A1 WO2020085851 A1 WO 2020085851A1
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surface quality
manganese steel
austenite
slab
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PCT/KR2019/014170
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French (fr)
Korean (ko)
Inventor
김성규
하유미
이동호
이운해
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주식회사 포스코
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Priority claimed from KR1020190118927A external-priority patent/KR102255827B1/en
Application filed by 주식회사 포스코 filed Critical 주식회사 포스코
Priority to EP19877327.7A priority Critical patent/EP3872217A4/en
Priority to CN201980068253.3A priority patent/CN112888804A/en
Publication of WO2020085851A1 publication Critical patent/WO2020085851A1/en

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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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/16—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling wire rods, bars, merchant bars, rounds wire or material of like small cross-section
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous 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
    • 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 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
    • 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
    • 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
    • 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

Definitions

  • the present invention relates to a cryogenic austenitic high-manganese steel material for a storage tank, a storage tank, a ship membrane, and a transport pipe for storage and transportation of liquefied petroleum gas, liquefied natural gas, and a method of manufacturing the same.
  • the present invention relates to an austenitic high-manganese steel for cryogenic temperature that effectively secures surface quality by suppressing surface flaw formation and a method for manufacturing the same.
  • Austenitic high-manganese (Mn) steel has a high toughness because the austenite phase is stable even at room temperature or cryogenic temperature by adjusting the content of manganese (Mn) and carbon (C), which are elements that increase the phase stability of austenite. It can be used as a material for fuel tanks, storage tanks, ship membranes, and transport pipes for storage and transportation of liquefied petroleum gas, liquefied natural gas, etc., which require properties.
  • Patent Document 1 Republic of Korea Patent Publication No. 10-2015-0075275 (2015.07.03. Public)
  • an austenitic high-manganese steel for cryogenic temperature and a method for manufacturing the same can be provided by effectively suppressing the formation of surface defects and effectively securing the surface quality.
  • the austenite-based high-manganese steel material having excellent surface quality according to an aspect of the present invention is in weight percent, C: 0.4 to 0.5%, Mn: 23 to 26%, Si: 0.03 to 0.5%, Cr: 3 to 5%, Al: 0.05% or less, S: 0.05% or less, P: 0.5% or less, B: 0.005% or less, including residual Fe and unavoidable impurities, and containing 95% by area or more of austenite as a microstructure.
  • the number of surface flaws formed at a depth of 10 ⁇ m or more from the surface among the surface flaws observed in the area from the surface to the point t / 8 (where t stands for product thickness (mm)) is the unit area. It may be 0.0001 or less per (mm 2 ).
  • the steel material may further include less than 0.7% by weight of Cu.
  • the yield strength of the steel material is 400 MPa or more, and the Charpy impact toughness of -196 ° C may be 41 J or more.
  • the austenite-based high-manganese steel material having excellent surface quality according to an aspect of the present invention is in weight percent, C: 0.4 to 0.5%, Mn: 23 to 26%, Si: 0.03 to 0.5%, Cr: 3 to 5%, Al: 0.05% or less, S: 0.05% or less, P: 0.5% or less, B: 0.005% or less, the slab containing the residual Fe and unavoidable impurities is reheated in a temperature range of 1000 to 1300 ° C, and the reheating is performed.
  • T SR means rough rolling reduction (mm) and slab reheating temperature (°C), respectively.
  • the slab may further include less than 0.7% by weight of Cu.
  • the hot-rolled hot rolled material may be accelerated to 600 ° C. or less at a cooling rate of 10 ° C./s or more.
  • an austenitic high-manganese steel having excellent surface quality while having properties particularly suitable for cryogenic temperatures.
  • FIG 3 is a photograph of a specimen 1 cut in the thickness direction, and a cross section observed by an optical microscope.
  • the present invention relates to an austenitic high-manganese steel for cryogenic temperature and a method of manufacturing the same, hereinafter, to describe preferred embodiments of the present invention.
  • the 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. Embodiments of the present invention are provided to those having ordinary skill in the art to further describe the present invention.
  • the austenite-based high-manganese steel material having excellent surface quality according to an aspect of the present invention is in weight percent, C: 0.4 to 0.5%, Mn: 23 to 26%, Si: 0.03 to 0.5%, Cr: 3 to 5%, Al: 0.05% or less, S: 0.05% or less, P: 0.5% or less, B: 0.005% or less, balance Fe and unavoidable impurities.
  • the austenite-based high-manganese steel material having excellent surface quality according to an aspect of the present invention may further include 0.7 wt% or less of Cu.
  • Carbon (C) is an effective element for stabilizing austenite in steel and securing strength by solid solution strengthening. Therefore, the present invention can limit the lower limit of the carbon (C) content to 0.4% in order to secure low-temperature toughness and strength.
  • the lower limit of the preferred carbon (C) content may be 0.41%, and the lower limit of the more preferred carbon (C) content may be 0.43%. That is, when the carbon (C) content is less than 0.4%, the yield strength may be lowered, the austenite stability is lowered, ferrite or martensite is formed, and the low-temperature toughness may be lowered.
  • the present invention may limit the upper limit of the carbon (C) content to 0.5%.
  • the upper limit of the preferred carbon (C) content may be 0.49%, and the upper limit of the more preferred carbon (C) content may be 0.47%.
  • Manganese (Mn) is an important element that plays a role in stabilizing austenite. Therefore, the present invention can limit the lower limit of the manganese (Mn) content to 23% to achieve this effect. That is, since the present invention includes 23% or more of manganese (Mn), it is possible to effectively increase austenite stability, thereby suppressing the formation of ferrite, ⁇ -martensite, and ⁇ '-martensite, thereby effectively securing low-temperature toughness. You can.
  • the lower limit of the more preferred manganese (Mn) content may be 23.1%.
  • the manganese (Mn) content when the manganese (Mn) content is more than a certain level, the effect of increasing the austenite stability is saturated, while excessive manufacturing cost is greatly increased, and surface oxidation may be deteriorated due to excessive internal oxidation during hot rolling.
  • the upper limit of the silver manganese (Mn) content may be limited to 26%.
  • the upper limit of the more preferable manganese (Mn) content may be 25.5%.
  • Silicon (Si) is an element that is indispensably added in trace amounts as a deoxidizer, such as aluminum (Al).
  • a deoxidizer such as aluminum (Al).
  • the present invention is an upper limit of the silicon (Si) content. Can be limited to 0.5%.
  • the upper limit of the more preferable silicon (Si) content may be 0.45%.
  • an excessive cost is required to reduce the Si content in the steel, so the present invention can limit the lower limit of the silicon (Si) content to 0.03%.
  • the lower limit of the more preferable silicon (Si) content may be 0.04%.
  • Chromium (Cr) is an element that contributes to the increase in strength through solid solution strengthening in austenite.
  • Cr chromium
  • the present invention can limit the lower limit of the chromium (Cr) content to 3% to achieve this effect.
  • the lower limit of the preferred chromium (Cr) content may be 3.1%, and the lower limit of the more preferred chromium (Cr) content may be 3.3%.
  • the present invention may limit the upper limit of the chromium (Cr) content to 5%.
  • the upper limit of the preferred chromium (Cr) content may be 4.5%, and the upper limit of the more preferred chromium (Cr) content may be 4.0%.
  • Sulfur (S) is not only an inevitably introduced impurity element, but also an element that causes hot brittle defects by inclusion formation. Therefore, the present invention can actively suppress the upper limit of the sulfur (S) content, the upper limit of the preferred sulfur (S) content may be 0.05%.
  • Phosphorus (P) 0.5% or less
  • Phosphorus (P) is not only an inevitably introduced impurity element, but also an element that is easily segregated and causes cracking during casting or deteriorates weldability. Therefore, the present invention can actively suppress the upper limit of the phosphorus (P) content, the upper limit of the preferred phosphorus (P) content may be 0.5%.
  • Boron (B) is an element that contributes to the improvement of surface quality by suppressing grain boundary destruction through strengthening of grain boundaries, but is also an element that deteriorates toughness and weldability due to formation of coarse precipitates when excessively added. Therefore, the present invention may include boron (B) of 0.0005% or more to achieve the effect of improving surface quality, but the upper limit of the boron (B) content may be limited to 0.005% to prevent deterioration of weldability.
  • Copper (Cu) is an austenite stabilizing element and is an element that stabilizes austenite together with manganese (Mn) and carbon (C), and is an element contributing to the improvement of low-temperature toughness.
  • copper (Cu) is a very low solid solution in carbide and has a slow diffusion in austenite, it is concentrated at the interface between austenite and carbide to surround the nucleus of fine carbide to further diffuse carbon (C). It is an element that effectively suppresses the formation and growth of carbides. Therefore, the present invention can additionally add a certain amount of copper (Cu) to achieve this effect.
  • the lower limit of the copper (Cu) content may be 0.3%, the lower limit of the preferred copper (Cu) content may be 0.35%, and the lower limit of the more preferred copper (Cu) content may be 0.4%.
  • the present invention may limit the upper limit of the copper (Cu) content to 0.7%.
  • the upper limit of the preferred copper (Cu) content may be 0.65%, and the upper limit of the more preferred copper (Cu) content may be 0.6%.
  • the austenite-based high-manganese steel material having excellent surface quality according to an aspect of the present invention may contain the remaining Fe and other unavoidable impurities in addition to the above-described components.
  • unintended impurities may be inevitably mixed from the raw material or the surrounding environment, and thus cannot be entirely excluded. Since these impurities are known to anyone skilled in the art, they are not specifically mentioned in this specification.
  • addition of effective ingredients other than the above composition is not excluded.
  • the austenite-based high-manganese steel material having excellent surface quality contains 95% by area or more of austenite as a microstructure, and when observed through a cross section using an optical microscope, t / 8 (where t (Meaning the product thickness (mm)) may be 0.0001 or less per unit area (mm 2 ) of the number of surface defects formed at a depth of 10 ⁇ m or more from the surface among the surface defects observed in the region up to the point.
  • the observation area means an arbitrary rectangular area formed on a steel section, and one surface of the observation area may be located adjacent to the surface of the steel material. That is, the height of the observation area is t / 8 (t: product thickness, mm), and the density of surface defects can be calculated using the number of surface defects having a depth of a predetermined level or more among the defects formed in the observation area.
  • the austenite-based high-manganese steel material having excellent surface quality actively suppresses surface defect formation on the product surface through strict process condition control as described below, effectively improving surface quality It is possible to omit subsequent processes such as a grinding process, thereby effectively securing the economics and productivity of the product.
  • the austenite-based high-manganese steel for cryogenic properties with excellent surface quality has a yield strength of 400 MPa or more and a Charpy impact toughness of 41 J or more at -196 ° C, so liquefied petroleum gas, liquefaction requiring cryogenic properties It is possible to provide austenite-based high-manganese steel materials particularly suitable as materials for fuel tanks, storage tanks, ship membranes, and transport pipes for storage and transportation of natural gas.
  • the austenite-based high-manganese steel material having excellent surface quality re-heats a slab provided with the above-described composition in a temperature range of 1000 to 1300 ° C, and rough-rolls the re-heated slab.
  • a bar is provided, and finish rolled in a temperature range of 750 to 1000 ° C to provide a hot rolled material, but the reheating temperature of the slab (T SR , ° C) and the rolling reduction amount of the rough rolling (R RM , mm).
  • the steel composition of the slab corresponds to the steel composition of the austenitic high-manganese steel described above
  • the steel composition of the austenitic high-manganese steel described above is replaced with the description of the steel composition of the austenitic high-manganese steel.
  • Slabs provided with the above-described steel composition can be uniformly heated in a temperature range of 1000 to 1300 ° C.
  • the thickness of the slab provided in the slab reheating step may be about 250 mm, but the scope of the present invention is not necessarily limited thereto.
  • the lower limit of the slab reheating temperature may be limited to 1000 ° C in order to prevent excessive rolling loads in subsequent hot rolling.
  • the higher the heating temperature the easier the hot rolling is secured, but the higher the manganese (Mn) content, the higher the temperature may cause grain boundary oxidation during high-temperature heating, and the present invention limits the upper limit of the slab reheating temperature to 1300 ° C. You can.
  • a re-heated slab may be roughly rolled with a rough rolling bar, and the hot rolling process may be performed by finishing rolling the rough rolling bar at a temperature range of 750 to 1000 ° C to provide a hot rolled material.
  • the high temperature of the hot rolling finish rolling also lowers the deformation resistance, so that the ease of rolling is secured, but the higher the finish rolling temperature causes the surface quality to decrease due to grain boundary oxidation, so the finish rolling temperature of the present invention is 750 to 1000 ° C. Can be limited.
  • the austenitic high-manganese steel of the present invention contains a large amount of manganese (Mn) having strong oxidizing properties, intergranular oxidation is inevitably caused by temperature limitations of the heating furnace. Even if some of the grain boundary oxidation formed during slab reheating is removed by scale, the remaining part grows as a crack during hot rolling to form a surface defect on the surface of the product, thereby deteriorating the surface quality of the product.
  • Mn manganese
  • the inventors of the present invention have reached the conclusion that it is effective to refine the tissue by heating the slab as quickly as possible to minimize re-crystallization to minimize the growth of grain boundary oxidation remaining on the slab surface during hot rolling.
  • an increase in the strain rate is most effective, and an increase in the strain rate is a factor that can be reached through an increase in the rolling amount of the rough rolling, but minimizes the growth of grain boundary oxidation into cracks when the rolling amount is excessively increased.
  • equipment damage due to excessive rolling load may be a problem.
  • the inventor of the present invention has derived the following relational expression 1, which controls the rolling load of hot rolling to a threshold value or less while actively suppressing the formation of surface flaws in the product through repeated experiments.
  • the present invention controls the amount of rough rolling against the furnace temperature to a certain range, as in the relational expression 1 above, so that when the temperature of the furnace is high, the amount of rolling reduction of the rough rolling is relatively increased, thereby intergranular oxidation during hot rolling surface flaws. Growth can be suppressed, and when the furnace temperature is low, the rolling load applied to the rolling mill during hot rolling can be reduced by relatively reducing the rolling amount of rough rolling, so that the optimum slab heating conditions and hot rolling conditions Can provide
  • the hot-rolled hot rolled material may be accelerated to 600 ° C. or less at a cooling rate of 10 ° C./s or more. Since the austenitic high manganese steel of the present invention contains 3 to 5% of chromium (Cr) and C, the cooling rate of the hot rolled material is controlled to 10 ° C./s or more to effectively prevent low-temperature toughness degradation due to carbide precipitation. You can. In addition, in normal accelerated cooling, a cooling rate exceeding 100 ° C / s is difficult to implement due to the characteristics of the equipment, and the present invention can limit the upper limit of the cooling rate to 100 ° C / s.
  • Cr chromium
  • the present invention can limit the cooling stop temperature to 600 ° C. have.
  • the austenitic high-manganese steel material prepared as described above contains 95% by area or more of austenite as a microstructure, but when observing a cross section using an optical microscope, t / 8 from the surface (where t is the product thickness (mm))
  • the number of surface flaws formed at a depth of 10 ⁇ m or more from the surface with respect to the cross-sectional area up to the point may be 0.0001 or less per unit area (mm 2 ), and yield strength of 400 MPa or more and Charpy impact toughness of 41 J or more at -196 ° C can do.
  • a slab having a thickness of 250 mm was manufactured using a steel material having the composition of Table 1 below, and a specimen was prepared by preparing through the process conditions of Table 2 below. Each specimen was prepared by finish rolling in a temperature range of 750 to 1000 ° C, and accelerated cooling to 600 ° C or less at a cooling rate of 10 ° C / s or higher. Impact absorption energy, yield strength, and surface flaw formation were evaluated for each specimen, and the results are shown in Table 2 below. The shock absorption energy was evaluated at -196 ° C using a plate-shaped specimen having a notch of 2 mm according to the standard test method ASTM E23.
  • the tensile test was performed by processing a plate specimen according to the standard test method ASTM E8 / E8M and evaluated by a one-way tensile tester. Depth and number of surface flaws are prepared by cutting specimens in the thickness direction to prepare specimens according to ASTM E112, and then using an optical microscope, the depth of the largest surface flaw in the viewing area and the number of surface flaws greater than 10 ⁇ m per unit area in the viewing area was measured and evaluated.
  • FIG. 1 is a photograph of the surface of the specimen 1
  • FIG. 2 is a photograph of the surface of the specimen 3.
  • FIG. 3 is a photograph obtained by cutting the specimen 1 in the thickness direction and observing the cross section with an optical microscope, and it can be seen that a surface defect was formed on the surface side of the specimen 1 in a direction inclined with respect to the thickness direction of the specimen.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
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  • Metallurgy (AREA)
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Abstract

A cryogenic austenitic high manganese steel having excellent surface quality according to an aspect of the present invention comprises: in weight%, 0.4-0.5% of C; 23-26% of Mn; 0.03-0.5% of Si; 3-5% of Cr; 0.05% or less of Al; 0.05% or less of S; 0.5% or less of P; and 0.005% or less of B; and the balance being Fe and unavoidable impurities, and contains 95 area% or more of austenite as a microstructure, wherein under cross-sectional observation using a microscope, the number of surface flaws formed at a depth of 10 μm or more from the surface may be 0.0001 or less per unit area (mm 2 ) from among the surface flaws observed in an area from the surface to a t/8 (where t means product thickness (mm)) point.

Description

표면품질이 우수한 극저온용 오스테나이트계 고망간 강재 및 그 제조방법Austenitic high-manganese steel with excellent surface quality and its manufacturing method
본 발명은 액화석유가스, 액화천연가스 등의 저장 및 운반을 위한 연료탱크, 저장탱크, 선박용 멤브레인 및 수송용 파이프 등에 적합한 극저온용 오스테나이트계 고망간 강재 및 그 제조방법에 관한 것이며, 상세하게는 표면 흠 형성을 억제하여 표면품질을 효과적으로 확보한 극저온용 오스테나이트계 고망간 강재 및 그 제조방법에 관한 것이다. The present invention relates to a cryogenic austenitic high-manganese steel material for a storage tank, a storage tank, a ship membrane, and a transport pipe for storage and transportation of liquefied petroleum gas, liquefied natural gas, and a method of manufacturing the same. The present invention relates to an austenitic high-manganese steel for cryogenic temperature that effectively secures surface quality by suppressing surface flaw formation and a method for manufacturing the same.
오스테나이트계 고망간(Mn) 강은 오스테나이트의 상 안정성을 높여주는 원소인 망간(Mn)과 탄소(C)의 함량을 조율하여 상온 또는 극저온에서도 오스테나이트 상이 안정하여 높은 인성을 가지므로, 극저온 특성이 요구되는 액화석유가스, 액화천연가스 등의 저장 및 운반을 위한 연료탱크, 저장탱크, 선박용 멤브레인 및 수송용 파이프 등의 소재로 사용될 수 있다. Austenitic high-manganese (Mn) steel has a high toughness because the austenite phase is stable even at room temperature or cryogenic temperature by adjusting the content of manganese (Mn) and carbon (C), which are elements that increase the phase stability of austenite. It can be used as a material for fuel tanks, storage tanks, ship membranes, and transport pipes for storage and transportation of liquefied petroleum gas, liquefied natural gas, etc., which require properties.
다만, 고망간(Mn) 강은 산화 경향이 강한 망간(Mn)을 다량 포함하므로, 슬라브 재가열 시 형성된 입계산화 중 일부는 스케일로 제거되지만, 일부는 열간압연 시 크랙으로 성장하여 제품의 표면에 표면 흠으로 잔존할 수 있다. 따라서, 고망간(Mn) 강의 제조 시 제품 표면의 그라인딩 공정이 필수적으로 수반되는바, 경제성 및 생산성 측면에서 바람직하지 않다. However, since high-manganese (Mn) steel contains a large amount of manganese (Mn), which has a strong oxidation tendency, some of the intergranular oxidation formed during slab reheating is removed on a scale, but some of it grows as a crack during hot rolling, resulting in the surface of the product. It may remain as a surface flaw. Therefore, since the grinding process of the product surface is essential when manufacturing high-manganese (Mn) steel, it is not preferable in terms of economy and productivity.
(선행기술문헌)(Advanced technical literature)
(특허문헌 1) 대한민국 공개특허공보 제10-2015-0075275호 (2015.07.03. 공개)(Patent Document 1) Republic of Korea Patent Publication No. 10-2015-0075275 (2015.07.03. Public)
본 발명의 한 가지 측면에 따르면 표면 흠 형성을 억제하여 표면품질을 효과적으로 확보한 극저온용 오스테나이트계 고망간 강재 및 그 제조방법이 제공될 수 있다According to one aspect of the present invention, an austenitic high-manganese steel for cryogenic temperature and a method for manufacturing the same can be provided by effectively suppressing the formation of surface defects and effectively securing the surface quality.
본 발명의 과제는 상술한 내용에 한정되지 않는다. 통상의 기술자라면 본 명세서의 전반적인 내용으로부터 본 발명의 추가적인 과제를 이해하는데 아무런 어려움이 없을 것이다.The subject of this invention is not limited to the above-mentioned content. Those skilled in the art will have no difficulty in understanding the additional subject matter of the present invention from the general contents of this specification.
본 발명의 일 측면에 따른 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재는, 중량%로, C: 0.4~0.5%, Mn: 23~26%, Si: 0.03~0.5%, Cr: 3~5%, Al: 0.05% 이하, S: 0.05% 이하, P: 0.5% 이하, B: 0.005% 이하, 잔부 Fe 및 불가피한 불순물을 포함하고, 95면적% 이상의 오스테나이트를 미세조직으로 포함하되, 광학현미경을 이용한 단면 관찰 시, 표면으로부터 t/8(여기서 t는 제품 두께(mm)를 의미함) 지점까지의 영역에서 관찰되는 표면 흠 중 표면으로부터 10㎛ 이상의 깊이로 형성된 표면 흠의 개수가 단위 면적(mm 2)당 0.0001개 이하일 수 있다.The austenite-based high-manganese steel material having excellent surface quality according to an aspect of the present invention is in weight percent, C: 0.4 to 0.5%, Mn: 23 to 26%, Si: 0.03 to 0.5%, Cr: 3 to 5%, Al: 0.05% or less, S: 0.05% or less, P: 0.5% or less, B: 0.005% or less, including residual Fe and unavoidable impurities, and containing 95% by area or more of austenite as a microstructure. When observing a cross section using a microscope, the number of surface flaws formed at a depth of 10 µm or more from the surface among the surface flaws observed in the area from the surface to the point t / 8 (where t stands for product thickness (mm)) is the unit area. It may be 0.0001 or less per (mm 2 ).
상기 강재는 0.7중량% 이하의 Cu를 더 포함할 수 있다.The steel material may further include less than 0.7% by weight of Cu.
상기 강재의 항복강도는 400MPa 이상이고, -196℃의 샤르피 충격인성은 41J 이상일 수 있다.The yield strength of the steel material is 400 MPa or more, and the Charpy impact toughness of -196 ° C may be 41 J or more.
본 발명의 일 측면에 따른 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재는, 중량%로, C: 0.4~0.5%, Mn: 23~26%, Si: 0.03~0.5%, Cr: 3~5%, Al: 0.05% 이하, S: 0.05% 이하, P: 0.5% 이하, B: 0.005% 이하, 잔부 Fe 및 불가피한 불순물을 포함하는 슬라브를 1000~1300℃의 온도범위에서 재가열하고, 상기 재가열된 슬라브를 조압연하여 조압연바를 제공하고, 상기 조압연바를 750~1000℃의 온도범위에서 마무리 압연하여 열연재를 제공하되, 하기의 관계식 1을 만족하도록 상기 슬라브의 재가열 온도(T SR)와 상기 조압연의 압하량(R RM)을 제어하여 제조될 수 있다.The austenite-based high-manganese steel material having excellent surface quality according to an aspect of the present invention is in weight percent, C: 0.4 to 0.5%, Mn: 23 to 26%, Si: 0.03 to 0.5%, Cr: 3 to 5%, Al: 0.05% or less, S: 0.05% or less, P: 0.5% or less, B: 0.005% or less, the slab containing the residual Fe and unavoidable impurities is reheated in a temperature range of 1000 to 1300 ° C, and the reheating is performed. Roughly rolling the slab to provide a rough rolling bar, and finishing rolling the rough rolling bar in a temperature range of 750 to 1000 ° C to provide a hot rolled material, but with the reheating temperature (T SR ) of the slab to satisfy the following relational expression 1 It can be produced by controlling the rolling reduction (R RM ) of the rough rolling.
[관계식 1][Relationship 1]
R RM/T SR > 0.15R RM / T SR > 0.15
(관계식 1에서 R RM 및 T SR는 각각 조압연 압하량(mm) 및 슬라브 재가열 온도(℃)를 의미함)(R RM in relation 1 And T SR means rough rolling reduction (mm) and slab reheating temperature (℃), respectively.
상기 슬라브는 0.7중량% 이하의 Cu를 더 포함할 수 있다.The slab may further include less than 0.7% by weight of Cu.
상기 마무리 압연 된 열연재를 10℃/s 이상의 냉각속도로 600℃ 이하까지 가속냉각할 수 있다.The hot-rolled hot rolled material may be accelerated to 600 ° C. or less at a cooling rate of 10 ° C./s or more.
상기 과제의 해결 수단은 본 발명의 특징을 모두 열거한 것은 아니며, 본 발명의 다양한 특징과 그에 따른 장점과 효과는 아래의 구체적인 실시예를 참조하여 보다 상세하게 이해될 수 있을 것이다.The solving means of the above problems does not list all the features of the present invention, and various features of the present invention and the advantages and effects thereof may be understood in more detail with reference to specific embodiments below.
본 발명의 일 측면에 따르면 극저온용으로 특히 적합한 물성을 가지면서도 우수한 표면품질을 가지 오스테나이트계 고망간 강재를 제공할 수 있다.According to one aspect of the present invention, it is possible to provide an austenitic high-manganese steel having excellent surface quality while having properties particularly suitable for cryogenic temperatures.
또한, 본 발명의 일 측면에 따르면, 그라인딩 등의 후속 공정을 수반하지 않고서도 우수한 표면품질을 확보하여, 생산성 및 경제성을 효과적으로 확보 가능한 오스테나이트계 고망간 강재의 제조방법을 제공할 수 있다.In addition, according to an aspect of the present invention, it is possible to provide a method for manufacturing austenitic high-manganese steel materials that can secure an excellent surface quality without effectively carrying out subsequent processes such as grinding, thereby effectively securing productivity and economy.
도 1은 시편 1의 표면을 촬영한 사진이다.1 is a photograph of the surface of the specimen 1.
도 2는 시편 3의 표면을 촬영한 사진이다. 2 is a photograph of the surface of the specimen 3.
도 3은 시편 1을 두께 방향으로 절단한 후 단면을 광학현미경으로 관찰한 사진이다.3 is a photograph of a specimen 1 cut in the thickness direction, and a cross section observed by an optical microscope.
본 발명은 극저온용 오스테나이트계 고망간 강재 및 그 제조방법에 관한 것으로, 이하에서는 본 발명의 바람직한 구현예들을 설명하고자 한다. 본 발명의 구현예들은 여러 가지 형태로 변형될 수 있으며, 본 발명의 범위가 아래에서 설명되는 구현예들에 한정되는 것으로 해석되어서는 안된다. 본 발명의 구현예들은 당해 발명이 속하는 기술분야에서 통상의 지식을 가지는 자에게 본 발명을 더욱 상세하기 위하여 제공되는 것이다.The present invention relates to an austenitic high-manganese steel for cryogenic temperature and a method of manufacturing the same, hereinafter, to describe preferred embodiments of the present invention. The 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. Embodiments of the present invention are provided to those having ordinary skill in the art to further describe the present invention.
이하, 본 발명의 강 조성에 대하여 보다 상세히 설명한다. 이하, 특별히 달리 표시하지 않는 한 각 원소의 함량을 나타내는 %는 중량을 기준으로 한다.Hereinafter, the steel composition of the present invention will be described in more detail. Hereinafter, unless otherwise indicated,% representing the content of each element is based on weight.
본 발명의 일 측면에 따른 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재는, 중량%로, C: 0.4~0.5%, Mn: 23~26%, Si: 0.03~0.5%, Cr: 3~5%, Al: 0.05% 이하, S: 0.05% 이하, P: 0.5% 이하, B: 0.005% 이하, 잔부 Fe 및 불가피한 불순물을 포함할 수 있다. 또한, 본 발명의 일 측면에 따른 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재는 0.7중량% 이하의 Cu를 더 포함할 수 있다.The austenite-based high-manganese steel material having excellent surface quality according to an aspect of the present invention is in weight percent, C: 0.4 to 0.5%, Mn: 23 to 26%, Si: 0.03 to 0.5%, Cr: 3 to 5%, Al: 0.05% or less, S: 0.05% or less, P: 0.5% or less, B: 0.005% or less, balance Fe and unavoidable impurities. In addition, the austenite-based high-manganese steel material having excellent surface quality according to an aspect of the present invention may further include 0.7 wt% or less of Cu.
탄소(C): 0.4~0.5%Carbon (C): 0.4 ~ 0.5%
탄소(C)는 강 내에 오스테나이트를 안정화시키고, 고용강화에 의해 강도를 확보하는데 효과적인 원소이다. 따라서, 본 발명은 저온인성 및 강도 확보를 위하여 탄소(C) 함량의 하한을 0.4%로 제한할 수 있다. 바람직한 탄소(C) 함량의 하한은 0.41% 일 수 있으며, 보다 바람직한 탄소(C) 함량의 하한은 0.43% 일 수 있다. 즉, 탄소(C) 함량이 0.4% 미만인 경우, 항복강도가 저하될 수 있으며, 오스테나이트 안정도가 저하되어 페라이트 또는 마르텐사이트가 형성되며, 저온인성이 저하될 수 있기 때문이다. 반면, 탄소(C) 함량이 일정 범위를 초과하는 경우 압연 후 냉각 시 과다한 탄화물이 형성될 수 있는바, 본 발명은 탄소(C) 함량의 상한을 0.5%로 제한할 수 있다. 바람직한 탄소(C) 함량의 상한은 0.49%일 수 있으며, 보다 바람직한 탄소(C) 함량의 상한은 0.47% 일 수 있다.Carbon (C) is an effective element for stabilizing austenite in steel and securing strength by solid solution strengthening. Therefore, the present invention can limit the lower limit of the carbon (C) content to 0.4% in order to secure low-temperature toughness and strength. The lower limit of the preferred carbon (C) content may be 0.41%, and the lower limit of the more preferred carbon (C) content may be 0.43%. That is, when the carbon (C) content is less than 0.4%, the yield strength may be lowered, the austenite stability is lowered, ferrite or martensite is formed, and the low-temperature toughness may be lowered. On the other hand, when the carbon (C) content exceeds a certain range, excessive carbide may be formed upon cooling after rolling, and the present invention may limit the upper limit of the carbon (C) content to 0.5%. The upper limit of the preferred carbon (C) content may be 0.49%, and the upper limit of the more preferred carbon (C) content may be 0.47%.
망간(Mn): 23~26%Manganese (Mn): 23-26%
망간(Mn)은 오스테나이트를 안정화시키는 역할을 하는 중요한 원소이다. 따라서, 본 발명은 이와 같은 효과 달성을 위해 망간(Mn) 함량의 하한을 23%로 제한할 수 있다. 즉, 본 발명은 23% 이상의 망간(Mn)을 포함하므로 오스테나이트 안정도를 효과적으로 증가시킬 수 있으며, 그에 따라 페라이트, ε-마르텐사이트 및 α'-마르텐사이트의 형성을 억제하여 저온인성을 효과적으로 확보할 수 있다. 보다 바람직한 망간(Mn) 함량의 하한은 23.1%일 수 있다. 반면, 망간(Mn) 함량이 일정 수준 이상인 경우, 오스테나이트 안정도 증가 효과는 포화되는 반면 과다한 제조원가가 크게 증가하고, 열간압연 중 내부산화가 과도하게 발생하여 표면품질이 열위해질 수 있는바, 본 발명은 망간(Mn) 함량의 상한을 26%로 제한할 수 있다. 보다 바람직한 망간(Mn) 함량의 상한은 25.5%일 수 있다.Manganese (Mn) is an important element that plays a role in stabilizing austenite. Therefore, the present invention can limit the lower limit of the manganese (Mn) content to 23% to achieve this effect. That is, since the present invention includes 23% or more of manganese (Mn), it is possible to effectively increase austenite stability, thereby suppressing the formation of ferrite, ε-martensite, and α'-martensite, thereby effectively securing low-temperature toughness. You can. The lower limit of the more preferred manganese (Mn) content may be 23.1%. On the other hand, when the manganese (Mn) content is more than a certain level, the effect of increasing the austenite stability is saturated, while excessive manufacturing cost is greatly increased, and surface oxidation may be deteriorated due to excessive internal oxidation during hot rolling. The upper limit of the silver manganese (Mn) content may be limited to 26%. The upper limit of the more preferable manganese (Mn) content may be 25.5%.
실리콘(Si): 0.03~0.5%Silicon (Si): 0.03 ~ 0.5%
실리콘(Si)은 알루미늄(Al)과 같이 탈산제로서 필수불가결하게 미량 첨가되는 원소이다. 다만, 실리콘(Si)이 과도하게 첨가되는 경우, 입계에 산화물을 형성하여 고온연성을 감소시키고, 크랙 등을 유발하여 표면품질을 저하시킬 우려가 있는바, 본 발명은 실리콘(Si) 함량의 상한을 0.5%로 제한할 수 있다. 보다 바람직한 실리콘(Si) 함량의 상한은 0.45%일 수 있다. 반면, 강 중에서 Si 함량을 줄이기 위해서는 과도한 비용이 소요되는바, 본 발명은 실리콘(Si) 함량의 하한을 0.03%로 제한할 수 있다. 보다 바람직한 실리콘(Si) 함량의 하한은 0.04%일 수 있다.Silicon (Si) is an element that is indispensably added in trace amounts as a deoxidizer, such as aluminum (Al). However, when silicon (Si) is excessively added, there is a possibility of reducing the high temperature ductility by forming an oxide at the grain boundary, and causing cracks, etc., thereby reducing the surface quality. The present invention is an upper limit of the silicon (Si) content. Can be limited to 0.5%. The upper limit of the more preferable silicon (Si) content may be 0.45%. On the other hand, an excessive cost is required to reduce the Si content in the steel, so the present invention can limit the lower limit of the silicon (Si) content to 0.03%. The lower limit of the more preferable silicon (Si) content may be 0.04%.
크롬(Cr): 3~5%Chromium (Cr): 3-5%
크롬(Cr)은 오스테나이트 내에서 고용강화를 통해 강도 상향에 기여하는 원소이다. 또한, 크롬(Cr)은 우수한 내식성을 가지므로, 고온산화에 의한 표면품질 저하 방지에 효과적으로 기여하는 원소이다. 따라서, 본 발명은 이와 같은 효과 달성을 위해 크롬(Cr) 함량의 하한을 3%로 제한할 수 있다. 바람직한 크롬(Cr) 함량의 하한은 3.1%일 수 있으며, 보다 바람직한 크롬(Cr) 함량의 하한은 3.3%일 수 있다. 반면, 크롬(Cr) 함량이 일정 수준 이상인 경우, 탄화물 생성에 따른 극저온인성 저하가 문제되는바, 본 발명은 크롬(Cr) 함량의 상한을 5%로 제한할 수 있다. 바람직한 크롬(Cr) 함량의 상한은 4.5%일 수 있으며, 보다 바람직한 크롬(Cr) 함량의 상한은 4.0%일 수 있다.Chromium (Cr) is an element that contributes to the increase in strength through solid solution strengthening in austenite. In addition, since chromium (Cr) has excellent corrosion resistance, it is an element that effectively contributes to prevention of surface quality degradation due to high temperature oxidation. Therefore, the present invention can limit the lower limit of the chromium (Cr) content to 3% to achieve this effect. The lower limit of the preferred chromium (Cr) content may be 3.1%, and the lower limit of the more preferred chromium (Cr) content may be 3.3%. On the other hand, when the chromium (Cr) content is more than a certain level, a decrease in cryogenic toughness due to carbide formation is a problem, and the present invention may limit the upper limit of the chromium (Cr) content to 5%. The upper limit of the preferred chromium (Cr) content may be 4.5%, and the upper limit of the more preferred chromium (Cr) content may be 4.0%.
황(S): 0.05% 이하Sulfur (S): 0.05% or less
황(S)은 불가피하게 유입되는 불순물 원소일 뿐만 아니라, 개재물 형성에 의해 열간취성 결함을 유발하는 원소이기도 하다. 따라서, 본 발명은 황(S) 함량의 상한을 적극 억제할 수 있으며, 바람직한 황(S) 함량의 상한은 0.05%일 수 있다.Sulfur (S) is not only an inevitably introduced impurity element, but also an element that causes hot brittle defects by inclusion formation. Therefore, the present invention can actively suppress the upper limit of the sulfur (S) content, the upper limit of the preferred sulfur (S) content may be 0.05%.
인(P): 0.5% 이하Phosphorus (P): 0.5% or less
인(P)은 불가피하게 유입되는 불순물 원소일 뿐만 아니라, 쉽게 편석되는 원소로서 주조 시 균열발생을 유발하거나, 용접성을 저하시키는 원소이기도 하다. 따라서, 본 발명은 인(P) 함량의 상한을 적극 억제할 수 있으며, 바람직한 인(P) 함량의 상한은 0.5%일 수 있다. Phosphorus (P) is not only an inevitably introduced impurity element, but also an element that is easily segregated and causes cracking during casting or deteriorates weldability. Therefore, the present invention can actively suppress the upper limit of the phosphorus (P) content, the upper limit of the preferred phosphorus (P) content may be 0.5%.
보론(B): 0.005% 이하Boron (B): 0.005% or less
보론(B)은 결정입계 강화를 통한 입계파괴의 억제 효과로 표면품질 향상에 기여하는 원소이나, 과도한 첨가 시 조대 석출물의 형성 등에 의해 인성 및 용접성을 저하시키는 원소이기도 하다. 따라서 본 발명은 표면품질 향상의 효과 달성을 위해 0.0005% 이상의 보론(B)을 포함할 수 있으나, 용접성 저하를 방지하기 위하여 보론(B) 함량의 상한을 0.005%로 제한할 수 있다.Boron (B) is an element that contributes to the improvement of surface quality by suppressing grain boundary destruction through strengthening of grain boundaries, but is also an element that deteriorates toughness and weldability due to formation of coarse precipitates when excessively added. Therefore, the present invention may include boron (B) of 0.0005% or more to achieve the effect of improving surface quality, but the upper limit of the boron (B) content may be limited to 0.005% to prevent deterioration of weldability.
구리(Cu): 0.7% 이하Copper (Cu): 0.7% or less
구리(Cu)는 오스테나이트 안정화 원소로 망간(Mn) 및 탄소(C)와 더불어 오스테나이트를 안정화시키는 원소로서, 저온인성 향상에 기여하는 원소이다. 또한, 구리(Cu)는 탄화물 내 고용도가 매우 낮고 오스테나이트 내에서의 확산이 느린 원소이므로, 오스테나이트와 탄화물의 계면에 농축되어 미세한 탄화물의 핵 주위를 둘러싸게 됨으로써 탄소(C)의 추가적인 확산에 따른 탄화물의 생성 및 성장을 효과적으로 억제하는 원소이다. 따라서, 본 발명은 이와 같은 효과 달성을 위해 일정 함량의 구리(Cu)를 추가적으로 첨가할 수 있다. 구리(Cu) 함량의 하한은 0.3%일 수 있으며, 바람직한 구리(Cu) 함량의 하한은 0.35%일 수 있으며, 보다 바람직한 구리(Cu) 함량의 하한은 0.4%일 수 있다. 다만, 구리(Cu) 함량이 일정 수준 이상인 경우 열간취성(hot shortness)에 의한 표면품질이 저하가 문제되는바, 본 발명은 구리(Cu) 함량의 상한을 0.7%로 제한할 수 있다. 바람직한 구리(Cu) 함량의 상한은 0.65%일 수 있으며, 보다 바람직한 구리(Cu) 함량의 상한은 0.6%일 수 있다.Copper (Cu) is an austenite stabilizing element and is an element that stabilizes austenite together with manganese (Mn) and carbon (C), and is an element contributing to the improvement of low-temperature toughness. In addition, since copper (Cu) is a very low solid solution in carbide and has a slow diffusion in austenite, it is concentrated at the interface between austenite and carbide to surround the nucleus of fine carbide to further diffuse carbon (C). It is an element that effectively suppresses the formation and growth of carbides. Therefore, the present invention can additionally add a certain amount of copper (Cu) to achieve this effect. The lower limit of the copper (Cu) content may be 0.3%, the lower limit of the preferred copper (Cu) content may be 0.35%, and the lower limit of the more preferred copper (Cu) content may be 0.4%. However, when the copper (Cu) content is above a certain level, the surface quality is deteriorated due to hot shortness, and the present invention may limit the upper limit of the copper (Cu) content to 0.7%. The upper limit of the preferred copper (Cu) content may be 0.65%, and the upper limit of the more preferred copper (Cu) content may be 0.6%.
본 발명의 일 측면에 따른 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재는 상기한 성분 이외에 잔부 Fe 및 기타 불가피한 불순물을 포함할 수 있다. 다만, 통상의 제조과정에서는 원료 또는 주위 환경으로부터 의도되지 않는 불순물이 불가피하게 혼입될 수 있으므로, 이를 전면적으로 배제할 수는 없다. 이들 불순물은 본 기술분야에서 통상의 지식을 가진 자라면 누구라도 알 수 있는 것이기 때문에 그 모든 내용을 본 명세서에서 특별히 언급하지는 않는다. 더불어, 상기 조성 이외에 유효한 성분의 첨가가 배제되는 것은 아니다.The austenite-based high-manganese steel material having excellent surface quality according to an aspect of the present invention may contain the remaining Fe and other unavoidable impurities in addition to the above-described components. However, in the normal manufacturing process, unintended impurities may be inevitably mixed from the raw material or the surrounding environment, and thus cannot be entirely excluded. Since these impurities are known to anyone skilled in the art, they are not specifically mentioned in this specification. In addition, addition of effective ingredients other than the above composition is not excluded.
본 발명의 일 측면에 따른 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재는, 95면적% 이상의 오스테나이트를 미세조직으로 포함하되, 광학현미경을 이용한 단면 관찰 시, 표면으로부터 t/8(여기서 t는 제품 두께(mm)를 의미함) 지점까지의 영역에서 관찰되는 표면 흠 중 표면으로부터 10㎛ 이상의 깊이로 형성된 표면 흠의 개수가 단위 면적(mm 2)당 0.0001개 이하일 수 있다. 여기서, 관찰 영역은 강재 단면상 형성되는 임의의 직사각형 영역을 의미하며, 관찰 영역의 일면은 강재의 표면에 인접하여 위치할 수 있다. 즉, 관찰 영역의 높이는 t/8(t: 제품 두께, mm)이며, 관찰영역 내에 형성된 흠 중 깊이가 일정 수준 이상인 표면 흠 개수를 이용하여 표면 흠 개수 밀도를 산출할 수 있다.The austenite-based high-manganese steel material having excellent surface quality according to an aspect of the present invention contains 95% by area or more of austenite as a microstructure, and when observed through a cross section using an optical microscope, t / 8 (where t (Meaning the product thickness (mm)) may be 0.0001 or less per unit area (mm 2 ) of the number of surface defects formed at a depth of 10 μm or more from the surface among the surface defects observed in the region up to the point. Here, the observation area means an arbitrary rectangular area formed on a steel section, and one surface of the observation area may be located adjacent to the surface of the steel material. That is, the height of the observation area is t / 8 (t: product thickness, mm), and the density of surface defects can be calculated using the number of surface defects having a depth of a predetermined level or more among the defects formed in the observation area.
즉, 본 발명의 일 측면에 따른 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재는, 후술하는 바와 같이 엄격한 공정 조건 제어를 통해 제품 표면에서의 표면 흠 형성을 적극 억제하는바, 표면 품질을 효과적으로 확보하여 그라인딩 공정 등의 후속 공정의 생략이 가능하며, 그에 따라 제품의 경제성 및 생산성을 효과적으로 확보할 수 있다.That is, the austenite-based high-manganese steel material having excellent surface quality according to an aspect of the present invention actively suppresses surface defect formation on the product surface through strict process condition control as described below, effectively improving surface quality It is possible to omit subsequent processes such as a grinding process, thereby effectively securing the economics and productivity of the product.
또한, 본 발명의 일 측면에 따른 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재는 400MPa 이상의 항복강도 및 -196℃에서 41J 이상의 샤르피 충격인성을 구비하므로, 극저온 특성이 요구되는 액화석유가스, 액화천연가스 등의 저장 및 운반을 위한 연료탱크, 저장탱크, 선박용 멤브레인 및 수송용 파이프 등의 소재로 특히 적합한 오스테나이트계 고망간 강재를 제공할 수 있다.In addition, the austenite-based high-manganese steel for cryogenic properties with excellent surface quality according to an aspect of the present invention has a yield strength of 400 MPa or more and a Charpy impact toughness of 41 J or more at -196 ° C, so liquefied petroleum gas, liquefaction requiring cryogenic properties It is possible to provide austenite-based high-manganese steel materials particularly suitable as materials for fuel tanks, storage tanks, ship membranes, and transport pipes for storage and transportation of natural gas.
이하, 본 발명의 제조방법에 대해 보다 상세히 설명한다.Hereinafter, the manufacturing method of the present invention will be described in more detail.
본 발명의 일 측면에 따른 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재는, 상술한 조성으로 구비되는 슬라브를 1000~1300℃의 온도범위에서 재가열하고, 상기 재가열된 슬라브를 조압연하여 조압연바를 제공하고, 750~1000℃의 온도범위에서 마무리 압연하여 열연재를 제공하되, 하기의 관계식 1을 만족하도록 상기 슬라브의 재가열 온도(T SR, ℃)와 상기 조압연의 압하량(R RM, mm)을 제어하여 제조될 수 있다.The austenite-based high-manganese steel material having excellent surface quality according to an aspect of the present invention, re-heats a slab provided with the above-described composition in a temperature range of 1000 to 1300 ° C, and rough-rolls the re-heated slab. A bar is provided, and finish rolled in a temperature range of 750 to 1000 ° C to provide a hot rolled material, but the reheating temperature of the slab (T SR , ° C) and the rolling reduction amount of the rough rolling (R RM , mm).
[관계식 1][Relationship 1]
R RM/T SR > 0.15R RM / T SR > 0.15
슬라브 재가열Slab reheating
슬라브의 강 조성은 전술한 오스테나이트계 고망간 강재의 강 조성과 대응하므로, 슬라브의 강 조성에 대한 전술한 오스테나이트계 고망간 강재의 강 조성에 대한 설명으로 대신한다.Since the steel composition of the slab corresponds to the steel composition of the austenitic high-manganese steel described above, the steel composition of the austenitic high-manganese steel described above is replaced with the description of the steel composition of the austenitic high-manganese steel.
전술한 강 조성으로 구비되는 슬라브를 1000~1300℃의 온도범위에서 균일하게 가열할 수 있다. 슬라브 재가열 단계에 제공되는 슬라브의 두께는 약 250mm일 수 있으나, 본 발명의 범위가 반드시 이에 국한되는 것은 아니다.Slabs provided with the above-described steel composition can be uniformly heated in a temperature range of 1000 to 1300 ° C. The thickness of the slab provided in the slab reheating step may be about 250 mm, but the scope of the present invention is not necessarily limited thereto.
후속되는 열간압연에서 압연하중이 과도하게 걸리는 것을 방지하기 위하여 슬라브 재가열 온도의 하한은 1000℃로 제한할 수 있다. 또한, 가열온도가 높을수록 열간압연의 용이성이 확보되지만, 망간(Mn) 함량이 높은 강은 고온 가열 시 입계산화가 심하게 발생할 수 있는바, 본 발명은 슬라브 재가열 온도의 상한을 1300℃로 제한할 수 있다.The lower limit of the slab reheating temperature may be limited to 1000 ° C in order to prevent excessive rolling loads in subsequent hot rolling. In addition, the higher the heating temperature, the easier the hot rolling is secured, but the higher the manganese (Mn) content, the higher the temperature may cause grain boundary oxidation during high-temperature heating, and the present invention limits the upper limit of the slab reheating temperature to 1300 ° C. You can.
열간압연Hot rolled
슬라브 재가열 공정 이후 재가열된 슬라브를 조압연바로 조압연하고, 조압연바를 750~1000℃의 온도범위에서 마무리 압연하여 열연재를 제공하는 열간압연 공정이 수반될 수 있다. 열간압연의 마무리 압연 온도 역시 고온일수록 변형저항이 낮아져 압연의 용이성이 확보되지만, 마무리 압연 온도가 높을수록 입계산화에 따른 표면품질 저하가 유발되므로, 본 발명의 마무리 압연 온도는 750~1000℃로 제한될 수 있다.After the slab reheating process, a re-heated slab may be roughly rolled with a rough rolling bar, and the hot rolling process may be performed by finishing rolling the rough rolling bar at a temperature range of 750 to 1000 ° C to provide a hot rolled material. The high temperature of the hot rolling finish rolling also lowers the deformation resistance, so that the ease of rolling is secured, but the higher the finish rolling temperature causes the surface quality to decrease due to grain boundary oxidation, so the finish rolling temperature of the present invention is 750 to 1000 ° C. Can be limited.
본 발명의 오스테나이트계 고망간 강은 산화성이 강한 망간(Mn)을 다량 포함하므로, 가열로의 온도 제한에 의하더라도 필연적으로 입계산화가 발생하게 된다. 슬라브 재가열 중에 형성된 입계산화 중 일부는 스케일로 제거되더라도, 잔존하는 일부는 열간압연 중 크랙으로 성장하여 제품의 표면에 표면 흠을 형성하며, 그에 따라 제품의 표면품질이 악화된다. Since the austenitic high-manganese steel of the present invention contains a large amount of manganese (Mn) having strong oxidizing properties, intergranular oxidation is inevitably caused by temperature limitations of the heating furnace. Even if some of the grain boundary oxidation formed during slab reheating is removed by scale, the remaining part grows as a crack during hot rolling to form a surface defect on the surface of the product, thereby deteriorating the surface quality of the product.
본 발명의 발명자는 심도 있는 연구를 통해 열간압연 중 슬라브 표면에 잔존하는 입계산화가 크랙으로 성장하는 것을 최소화하기 위해서는 슬라브 가열 후 가급적 신속하게 재결정이 발생하도록 하여 조직을 미세화하는 것이 효과적이라는 결론에 도달하였다. 다만, 재결정 촉진을 위해서는 변형속도의 증가가 가장 효과적이며, 변형속도의 증가는 조압연의 압하량 증가를 통해 도달 가능한 요소이나, 압하량이 과다하게 증가하는 경우 입계산화가 크랙으로 성장하는 것을 최소화하는 것은 별론, 과다한 압연부하에 의한 설비 파손 등이 문제될 수 있다.Through the in-depth study, the inventors of the present invention have reached the conclusion that it is effective to refine the tissue by heating the slab as quickly as possible to minimize re-crystallization to minimize the growth of grain boundary oxidation remaining on the slab surface during hot rolling. Did. However, in order to promote recrystallization, an increase in the strain rate is most effective, and an increase in the strain rate is a factor that can be reached through an increase in the rolling amount of the rough rolling, but minimizes the growth of grain boundary oxidation into cracks when the rolling amount is excessively increased. Apart from this, equipment damage due to excessive rolling load may be a problem.
따라서, 본 발명의 발명자는 거듭된 실험을 통해 제품의 표면 흠 형성을 적극 억제하면서도 열간압연의 압연부하를 임계치 이하로 제어하는 아래의 관계식 1을 도출하였다.Therefore, the inventor of the present invention has derived the following relational expression 1, which controls the rolling load of hot rolling to a threshold value or less while actively suppressing the formation of surface flaws in the product through repeated experiments.
[관계식 1] [Relationship 1]
R RM/T SR > 0.15R RM / T SR > 0.15
(관계식 1에서 R RM 및 T SR은 각각 조압연 압하량(mm) 및 슬라브 재가열 온도(℃)를 의미함)(R RM in relation 1 And T SR means rough rolling reduction (mm) and slab reheating temperature (℃), respectively)
즉, 본 발명은 상기 관계식 1과 같이 가열로 온도에 대한 조압연 압하량을 일정 범위로 제어하므로, 가열로 온도가 높은 경우 상대적으로 조압연의 압하량을 증가시켜 열간압연 중 입계산화가 표면 흠으로 성장하는 것을 억제할 수 있으며, 가열로 온도가 낮은 경우 상대적으로 조압연의 압연량을 감소시켜 열간압연 중 압연기에 가해지는 압연부하를 감소시킬 수 있는바, 최적의 슬라브 가열 조건 및 열간 압연 조건을 제공할 수 있다.That is, the present invention controls the amount of rough rolling against the furnace temperature to a certain range, as in the relational expression 1 above, so that when the temperature of the furnace is high, the amount of rolling reduction of the rough rolling is relatively increased, thereby intergranular oxidation during hot rolling surface flaws. Growth can be suppressed, and when the furnace temperature is low, the rolling load applied to the rolling mill during hot rolling can be reduced by relatively reducing the rolling amount of rough rolling, so that the optimum slab heating conditions and hot rolling conditions Can provide
가속냉각Accelerated cooling
열간압연 공정 이후 마무리 압연된 열연재를 10℃/s 이상의 냉각속도로 600℃ 이하까지 가속냉각할 수 있다. 본 발명의 오스테나이트계 고 망간 강재는 3~5%의 크롬(Cr) 및 C를 포함하므로, 열연재의 냉각속도를 10℃/s 이상으로 제어하여 탄화물 석출에 의한 저온인성 저하를 효과적으로 방지할 수 있다. 또한, 통상의 가속냉각에 있어서 100℃/s를 초과하는 냉각속도는 설비 특성상 구현하기 어려운바, 본 발명은 냉각속도의 상한을 100℃/s로 제한할 수 있다.After the hot rolling process, the hot-rolled hot rolled material may be accelerated to 600 ° C. or less at a cooling rate of 10 ° C./s or more. Since the austenitic high manganese steel of the present invention contains 3 to 5% of chromium (Cr) and C, the cooling rate of the hot rolled material is controlled to 10 ° C./s or more to effectively prevent low-temperature toughness degradation due to carbide precipitation. You can. In addition, in normal accelerated cooling, a cooling rate exceeding 100 ° C / s is difficult to implement due to the characteristics of the equipment, and the present invention can limit the upper limit of the cooling rate to 100 ° C / s.
또한, 10℃/s 이상의 냉각속도를 적용하여 열연재를 냉각하더라도, 높은 온도에서 냉각이 정지되는 경우 탄화물이 생성 및 성장할 가능성이 높으므로, 본 발명은 냉각 정지 온도를 600℃ 이하로 제한할 수 있다.In addition, even if the hot-rolled material is cooled by applying a cooling rate of 10 ° C./s or more, when the cooling is stopped at a high temperature, there is a high possibility that carbides are generated and grown, so the present invention can limit the cooling stop temperature to 600 ° C. have.
상기와 같이 제조된 오스테나이트계 고망간 강재는, 95면적% 이상의 오스테나이트를 미세조직으로 포함하되, 광학현미경을 이용한 단면 관찰 시, 표면으로부터 t/8(여기서 t는 제품 두께(mm)를 의미함) 지점까지의 단면적에 대해 표면으로부터 10㎛ 이상의 깊이로 형성된 표면 흠의 개수가 단위 면적(mm 2)당 0.0001개 이하일 수 있으며, 400MPa 이상의 항복강도 및 -196℃에서 41J 이상의 샤르피 충격인성은 구비할 수 있다.The austenitic high-manganese steel material prepared as described above contains 95% by area or more of austenite as a microstructure, but when observing a cross section using an optical microscope, t / 8 from the surface (where t is the product thickness (mm)) The number of surface flaws formed at a depth of 10 μm or more from the surface with respect to the cross-sectional area up to the point may be 0.0001 or less per unit area (mm 2 ), and yield strength of 400 MPa or more and Charpy impact toughness of 41 J or more at -196 ° C can do.
이하, 실시예를 통하여 본 발명을 보다 구체적으로 설명한다. 다만, 후술하는 실시예는 본 발명을 예시하여 보다 구체화하기 위한 것일 뿐, 본 발명의 권리범위를 제한하기 위한 것은 아니라는 점에 유의할 필요가 있다.Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the embodiments described below are only intended to further illustrate the present invention and are not intended to limit the scope of the present invention.
(실시예)(Example)
하기 표 1의 조성을 가지는 강재를 이용하여 250mm 두께의 슬라브를 제작하였으며, 하기 표 2의 공정 조건을 통해 제조하여 시편을 준비하였다. 각각의 시편은 750~1000℃의 온도범위에서 마무리 압연하고, 10℃/s 이상의 냉각속도로 600℃ 이하까지 가속냉각하여 제조되었다. 각각의 시편에 대해 충격흡수에너지, 항복강도 및 표면 흠 형성 여부를 평가하여 그 결과를 하기 표 2에 함께 나타내었다. 충격흡수에너지는 표준 시험법인 ASTM E23에 준하여 2mm의 노치를 가지는 판상시편을 이용하여 -196℃에서 평가하였다. 인장시험은 표준 시험법인 ASTM E8/E8M에 준하는 판상시편을 가공하여 일방향 인장시험기로 평가하였다. 표면 흠의 깊이 및 개수는 시편을 두께방향으로 절단하여 ASTM E112에 따라 시편을 준비한 후 광학현미경을 이용하여 관찰 영역 내의 가장 큰 표면 흠의 깊이 및 관찰 영역 내의 단위면적당 깊이 10㎛ 이상인 표면 흠의 개수를 측정하여 평가하였다. A slab having a thickness of 250 mm was manufactured using a steel material having the composition of Table 1 below, and a specimen was prepared by preparing through the process conditions of Table 2 below. Each specimen was prepared by finish rolling in a temperature range of 750 to 1000 ° C, and accelerated cooling to 600 ° C or less at a cooling rate of 10 ° C / s or higher. Impact absorption energy, yield strength, and surface flaw formation were evaluated for each specimen, and the results are shown in Table 2 below. The shock absorption energy was evaluated at -196 ° C using a plate-shaped specimen having a notch of 2 mm according to the standard test method ASTM E23. The tensile test was performed by processing a plate specimen according to the standard test method ASTM E8 / E8M and evaluated by a one-way tensile tester. Depth and number of surface flaws are prepared by cutting specimens in the thickness direction to prepare specimens according to ASTM E112, and then using an optical microscope, the depth of the largest surface flaw in the viewing area and the number of surface flaws greater than 10 μm per unit area in the viewing area Was measured and evaluated.
구분division MnMn CrCr CC CuCu BB SiSi PP S.AlS.Al SS
1One 23.223.2 3.53.5 0.440.44 0.500.50 0.00120.0012 0.0410.041 0.0270.027 0.0360.036 0.00140.0014
22 24.624.6 3.43.4 0.460.46 0.520.52 0.00280.0028 0.3110.311 0.0140.014 0.0390.039 0.00130.0013
33 25.225.2 3.43.4 0.450.45 0.490.49 0.00260.0026 0.3180.318 0.0170.017 0.0430.043 0.00150.0015
44 24.824.8 3.43.4 0.450.45 0.480.48 0.00290.0029 0.3000.300 0.0170.017 0.0330.033 0.00130.0013
55 24.824.8 3.43.4 0.450.45 0.480.48 0.00290.0029 0.3000.300 0.0170.017 0.0330.033 0.00140.0014
66 24.824.8 3.43.4 0.450.45 0.480.48 0.00290.0029 0.3000.300 0.0170.017 0.0330.033 0.00150.0015
77 24.824.8 3.43.4 0.450.45 0.480.48 0.00290.0029 0.3000.300 0.0170.017 0.0330.033 0.00130.0013
88 24.024.0 3.43.4 0.440.44 0.430.43 0.00300.0030 0.2700.270 0.0130.013 0.0230.023 0.00140.0014
99 24.024.0 3.43.4 0.440.44 0.430.43 0.00300.0030 0.2700.270 0.0130.013 0.0230.023 0.00150.0015
구분division 재가열온도(℃)Reheating temperature (℃) 조압연압하량(mm)Rough rolling load (mm) 관계식 1(R RM/T SR)Relation 1 (R RM / T SR ) 충격흡수에너지(J, @-196℃)Shock absorption energy (J, @ -196 ℃) 항복강도(MPa)Yield strength (MPa) 최대표면 흠깊이(㎛)Maximum surface depth (㎛) 표면 흠개수(개/mm 2)Surface defects (pcs / mm 2 ) 비고Remark
1One 13001300 132132 0.1020.102 123123 458458 3030 0.030.03 비교예Comparative example
22 11741174 130130 0.1110.111 9090 464464 2828 0.020.02 비교예Comparative example
33 11201120 180180 0.1610.161 9696 465465 00 00 발명예Inventive Example
44 11501150 105105 0.0910.091 8686 486486 3232 0.030.03 비교예Comparative example
55 11621162 135135 0.1160.116 8484 514514 3030 0.030.03 비교예Comparative example
66 11551155 175175 0.1520.152 8484 514514 00 00 발명예Inventive Example
77 11991199 203203 0.1700.170 8484 495495 00 00 발명예Inventive Example
88 11981198 207207 0.1730.173 7171 529529 00 00 발명예Inventive Example
99 11301130 207207 0.1840.184 7070 531531 00 00 발명예Inventive Example
관계식 1을 만족하는 시편 3, 6 내지 9의 경우, 표면 흠이 발생하지 않아 표면품질이 우수한 반면, 관계식 1을 만족하지 않는 시편 1, 2, 4 및 5의 경우, 표면 흠이 발생하여 표면품질이 열위하며, 표면품질 확보를 위해 그라인딩 등의 후속 공정 필수적으로 수반되어야 함을 확인할 수 있다.In the case of specimens 3, 6 to 9 satisfying relational expression 1, surface defects do not occur, and thus the surface quality is excellent, whereas in the case of specimens 1, 2, 4 and 5 that do not satisfy relational expression 1, surface defects occur and surface quality This is inferior, and it can be confirmed that the subsequent processes such as grinding are essential to secure the surface quality.
도 1은 시편 1의 표면을 촬영한 사진이며, 도 2는 시편 3의 표면을 촬영한 사진이다. 육안 관찰 결과 시편 1에는 미세한 표면 흠이 다량 형성된 반면, 시편 3에는 표면 흠이 형성되지 않아 우수한 표면품질을 확보함을 알 수 있다. 또한, 도 3은 시편 1을 두께 방향으로 절단한 후 단면을 광학현미경으로 관찰한 사진으로, 시편 1의 표면측에는 시편의 두께방향에 대해 경사진 방향으로 표면 흠이 형성된 것을 확인할 수 있다.1 is a photograph of the surface of the specimen 1, and FIG. 2 is a photograph of the surface of the specimen 3. As a result of visual observation, it can be seen that while a large amount of fine surface defects were formed in the specimen 1, a surface defect was not formed in the specimen 3, thereby ensuring excellent surface quality. In addition, FIG. 3 is a photograph obtained by cutting the specimen 1 in the thickness direction and observing the cross section with an optical microscope, and it can be seen that a surface defect was formed on the surface side of the specimen 1 in a direction inclined with respect to the thickness direction of the specimen.
이상에서 실시예를 통하여 본 발명을 상세하게 설명하였으나, 이와 다른 형태의 실시예들도 가능하다. 그러므로, 이하에 기재된 청구항들의 기술적 사상과 범위는 실시예들에 한정되지 않는다.Although the present invention has been described in detail through the above embodiments, other types of embodiments are possible. Therefore, the technical spirit and scope of the claims set forth below are not limited to the embodiments.

Claims (6)

  1. 중량%로, C: 0.4~0.5%, Mn: 23~26%, Si: 0.03~0.5%, Cr: 3~5%, Al: 0.05% 이하, S: 0.05% 이하, P: 0.5% 이하, B: 0.005% 이하, 잔부 Fe 및 불가피한 불순물을 포함하고,In weight percent, C: 0.4 to 0.5%, Mn: 23 to 26%, Si: 0.03 to 0.5%, Cr: 3 to 5%, Al: 0.05% or less, S: 0.05% or less, P: 0.5% or less, B: 0.005% or less, containing residual Fe and unavoidable impurities,
    95면적% 이상의 오스테나이트를 미세조직으로 포함하되,It contains at least 95% by area of austenite as a microstructure,
    광학현미경을 이용한 단면 관찰 시, 표면으로부터 t/8(여기서 t는 제품 두께(mm)를 의미함) 지점까지의 영역에서 관찰되는 표면 흠 중 표면으로부터 10㎛ 이상의 깊이로 형성된 표면 흠의 개수가 단위 면적(mm 2)당 0.0001개 이하인, 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재. When observing a cross section using an optical microscope, the number of surface flaws formed at a depth of 10 µm or more from the surface among the surface flaws observed in the region from the surface to the point t / 8 (where t stands for product thickness (mm)) is the unit. Austenitic high manganese steel for cryogenics with excellent surface quality, less than 0.0001 per area (mm 2 ).
  2. 제1항에 있어서,According to claim 1,
    상기 강재는 0.7중량% 이하의 Cu를 더 포함하는, 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재.The steel material further comprises Cu of less than 0.7% by weight, an austenitic high-manganese steel material for cryogenic properties having excellent surface quality.
  3. 제1항에 있어서,According to claim 1,
    상기 강재의 항복강도는 400MPa 이상이고, -196℃의 샤르피 충격인성은 41J 이상인, 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재. The yield strength of the steel is 400MPa or more, and the Charpy impact toughness of -196 ° C is 41J or more, and an austenite-based high-manganese steel material having excellent surface quality.
  4. 중량%로, C: 0.4~0.5%, Mn: 23~26%, Si: 0.03~0.5%, Cr: 3~5%, Al: 0.05% 이하, S: 0.05% 이하, P: 0.5% 이하, B: 0.005% 이하, 잔부 Fe 및 불가피한 불순물을 포함하는 슬라브를 1000~1300℃의 온도범위에서 재가열하고,In weight percent, C: 0.4 to 0.5%, Mn: 23 to 26%, Si: 0.03 to 0.5%, Cr: 3 to 5%, Al: 0.05% or less, S: 0.05% or less, P: 0.5% or less, B: 0.005% or less, the slab containing the residual Fe and unavoidable impurities is reheated in a temperature range of 1000 to 1300 ° C,
    상기 재가열된 슬라브를 조압연하여 조압연바를 제공하고,Roughly rolling the reheated slab to provide a rough rolling bar,
    상기 조압연바를 750~1000℃의 온도범위에서 마무리 압연하여 열연재를 제공하되,The rough rolling bar is finished rolling in a temperature range of 750 ~ 1000 ℃ to provide a hot rolled material,
    하기의 관계식 1을 만족하도록 상기 슬라브의 재가열 온도(T SR)와 상기 조압연의 압하량(R RM)를 제어하는, 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재의 제조방법.A method for manufacturing austenite-based high-manganese steel having excellent surface quality, which controls the reheating temperature (T SR ) of the slab and the rolling reduction (R RM ) of the rough rolling to satisfy the following relational expression 1.
    [관계식 1][Relationship 1]
    R RM/T SR > 0.15R RM / T SR > 0.15
    (관계식 1에서 R RM 및 T SR은 각각 조압연 압하량(mm) 및 슬라브 재가열 온도(℃)를 의미함)(In relation 1, R RM and T SR mean rough rolling reduction (mm) and slab reheating temperature (℃), respectively.
  5. 제4항에 있어서,According to claim 4,
    상기 슬라브는 0.7중량% 이하의 Cu를 더 포함하는, 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재의 제조방법.The slab further comprises less than 0.7% by weight of Cu, a method of manufacturing austenite-based high-manganese steel for cryogenic superior in surface quality.
  6. 제4항에 있어서,According to claim 4,
    상기 마무리 압연 된 열연재를 10℃/s 이상의 냉각속도로 600℃ 이하까지 가속냉각하는, 표면품질이 우수한 극저온용 오스테나이트계 고망간 강재의 제조방법.A method of manufacturing an austenitic high-manganese steel material having excellent surface quality for accelerated cooling of the finished rolled hot rolled material to 600 ° C or less at a cooling rate of 10 ° C / s or more.
PCT/KR2019/014170 2018-10-25 2019-10-25 Cryogenic austenitic high manganese steel having excellent surface quality and manufacturing method therefor WO2020085851A1 (en)

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20000041265A (en) * 1998-12-22 2000-07-15 이구택 Method for producing high manganese hot rolled metal strip by mini mill process and for preventing surface scab defect and crack defect
JP2011246817A (en) * 2003-07-22 2011-12-08 Arcelormittal France Method of producing austenitic iron/carbon/manganese steel sheet having high strength and excellent toughness and being suitable for cold forming, and the steel sheet thus produced
KR20150075275A (en) 2013-12-25 2015-07-03 주식회사 포스코 A high manganese steel having superior toughness at low temperature, and manufacturing method
KR20170075657A (en) * 2015-12-23 2017-07-03 주식회사 포스코 Nonmagnetic steel having superior hot workability and method for manufacturing the same
KR20180070383A (en) * 2016-12-16 2018-06-26 주식회사 포스코 High strength clad steel having good delayed fracture resistance
US10041156B2 (en) * 2012-12-26 2018-08-07 Posco High strength austenitic-based steel with remarkable toughness of welding heat-affected zone and preparation method therefor

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20000041265A (en) * 1998-12-22 2000-07-15 이구택 Method for producing high manganese hot rolled metal strip by mini mill process and for preventing surface scab defect and crack defect
JP2011246817A (en) * 2003-07-22 2011-12-08 Arcelormittal France Method of producing austenitic iron/carbon/manganese steel sheet having high strength and excellent toughness and being suitable for cold forming, and the steel sheet thus produced
US10041156B2 (en) * 2012-12-26 2018-08-07 Posco High strength austenitic-based steel with remarkable toughness of welding heat-affected zone and preparation method therefor
KR20150075275A (en) 2013-12-25 2015-07-03 주식회사 포스코 A high manganese steel having superior toughness at low temperature, and manufacturing method
KR20170075657A (en) * 2015-12-23 2017-07-03 주식회사 포스코 Nonmagnetic steel having superior hot workability and method for manufacturing the same
KR20180070383A (en) * 2016-12-16 2018-06-26 주식회사 포스코 High strength clad steel having good delayed fracture resistance

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