KR20200046831A - Low temperature austenitic high manganese steel having excellent surface quality and resistance to stress corrosion cracking, and manufacturing method for the same - Google Patents
Low temperature austenitic high manganese steel having excellent surface quality and resistance to stress corrosion cracking, and manufacturing method for the same Download PDFInfo
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- 230000007797 corrosion Effects 0.000 title claims abstract description 51
- 238000005260 corrosion Methods 0.000 title claims abstract description 51
- 238000005336 cracking Methods 0.000 title claims abstract description 41
- 229910000617 Mangalloy Inorganic materials 0.000 title claims abstract description 31
- 238000004519 manufacturing process Methods 0.000 title claims description 15
- 239000011572 manganese Substances 0.000 claims abstract description 51
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 27
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- RQCJDSANJOCRMV-UHFFFAOYSA-N [Mn].[Ag] Chemical compound [Mn].[Ag] RQCJDSANJOCRMV-UHFFFAOYSA-N 0.000 description 1
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- 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
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- 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
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- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
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- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/16—Control of thickness, width, diameter or other transverse dimensions
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
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- 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
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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- 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
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- 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
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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- C21D2211/00—Microstructure comprising significant phases
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Abstract
Description
본 발명은 액화석유가스, 액화천연가스 등의 저장 및 운반을 위한 연료탱크, 저장탱크, 선박용 멤브레인 및 수송용 파이프 등에 적합한 극저온용 오스테나이트계 고 망간 강재 및 그 제조방법에 관한 것이며, 상세하게는 표면 흠 형성을 억제하여 표면품질을 효과적으로 확보함과 동시에 응력부식균열 저항성을 효과적으로 확보한 극저온용 오스테나이트계 고 망간 강재 및 그 제조방법에 관한 것이다. The present invention relates to a cryogenic austenitic high manganese steel material and a method for manufacturing the same, suitable for fuel tanks, storage tanks, ship membranes, and transport pipes for storage and transport of liquefied petroleum gas, liquefied natural gas, and the like. The present invention relates to an austenitic high-manganese steel for cryogenic temperature and a method for manufacturing the same, which effectively suppresses the formation of surface defects and effectively secures surface corrosion cracking resistance.
환경오염에 대한 규제가 강화되고, 석유에너지의 고갈이 예상됨에 따라 대체에너지로 LNG, LPG 등의 친환경 에너지의 수요가 증가하고, 사용 기술개발에 대한 관심이 증가하는 실정이다. 저온의 액체상태로 운반되는 LNG, LPG 등의 무공해 연료의 수요가 증가함에 따라 이들의 저장 및 운송을 위한 저온 구조물용 소재개발이 증가하는 추세이다. 저온 구조물용 소재는 저온 강도 및 인성 등의 기계적 성질이 요구되며, 이와 같은 소재로는 알루미늄 합금, 오스테나이트계 스테인리스강, 35% 인바강, 9% Ni 강이 이용되고 있다. 이들 재료 중 9% Ni 강이 용접성 및 경제성 측면에서 우수한 기계적 특성을 나타내는바, 현재 저온 구조물용 소재로서 가장 널리 이용되고 있다. As regulations on environmental pollution are strengthened and petroleum energy is expected to be depleted, demand for eco-friendly energy such as LNG and LPG increases as an alternative energy, and interest in developing technology is increasing. As the demand for pollution-free fuels such as LNG and LPG transported in a low-temperature liquid state increases, the development of materials for low-temperature structures for their storage and transportation is increasing. Materials for low-temperature structures require mechanical properties such as low-temperature strength and toughness, and aluminum alloy, austenitic stainless steel, 35% invar steel, and 9% Ni steel are used as such materials. Of these materials, 9% Ni steel shows excellent mechanical properties in terms of weldability and economy, and is currently most widely used as a material for low-temperature structures.
다만, 9% Ni 강은 페라이트를 기지조직으로 구비하므로 수소의 확산속도가 커서 수소에 의한 취성, 즉 응력부식균열 저항성이 열위하며, 변형과 부식이 수반되는 환경에의 적용은 바람직하지 않다. 또한, 대표적인 오스테나이트계 강인 304 스테인리스강은, 변형이 가해지면 슬립밴드가 표층에 형성되면서 치밀한 산화층이 깨어져 국부 부식이 발생하므로, 응력부식균열저항성이 낮은 문제가 있다. 따라서, 저온 인성이 우수하면서도 응력부식균열저항성이 우수한 소재의 개발이 시급한 실정이다.However, since 9% Ni steel has ferrite as a base structure, the diffusion rate of hydrogen is large, and thus brittleness by hydrogen, that is, stress corrosion cracking resistance is inferior, and application to an environment accompanied by deformation and corrosion is undesirable. In addition, the typical austenitic steel 304 stainless steel has a problem that stress corrosion cracking resistance is low because, when strain is applied, a slip band is formed on the surface layer and the dense oxide layer is broken and local corrosion occurs. Therefore, there is an urgent need to develop a material having excellent low temperature toughness and excellent stress corrosion cracking resistance.
오스테나이트계 고 망간(Mn) 강은 오스테나이트의 안정성을 높여주는 원소인 망간(Mn)과 탄소(C)의 함량을 조율하여 상온 또는 극저온에서도 오스테나이트가 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 high toughness because it has high toughness by stabilizing austenite even at room temperature or cryogenic temperature by adjusting the content of manganese (Mn) and carbon (C), which are elements that increase the 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, and the like.
다만, 고 망간(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, 고 망간(Mn) 강 제조 시 제품 표면의 그라인딩 공정이 후속되는바, 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 grain boundary oxidation formed during slab reheating is removed by scale, but some of it grows as a crack during hot rolling, so that it forms on the product surface. It may remain as a surface flaw. Therefore, since the grinding process of the product surface is followed when manufacturing high manganese (Mn) steel, it is not preferable in terms of economy and productivity.
본 발명의 한 가지 측면에 따르면 부식 및 변형의 복합 환경에서 쌍정 형성을 유도하여 응력부식균열 저항성을 효과적으로 확보하되, 강재의 표면 흠 형성을 억제하여 표면품질을 효과적으로 확보한 극저온용 오스테나이트계 고 망간 강재 및 그 제조방법이 제공될 수 있다.According to one aspect of the present invention, by inducing twin formation in a complex environment of corrosion and deformation, it effectively secures stress corrosion cracking resistance, but suppresses the formation of surface flaws in steel to effectively secure the surface quality by cryogenic austenitic high manganese. Steel and a method of manufacturing the same can be provided.
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 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 강재는, 중량%로, C: 0.4~0.5%, Mn: 23~26%, Cr: 3~5%, Cu: 0.3~0.7%, S: 0.05% 이하, P: 0.5% 이하, B: 0.005% 이하, 잔부 Fe 및 불가피한 불순물을 포함하고, 95면적% 이상의 오스테나이트를 미세조직으로 포함하되, 하기 관계식 1로 표시되는 적층결함에너지(SFE)가 45mJ/m2 이하의 범위를 만족하며, 광학현미경을 이용하여 단면 관찰 시, 표면으로부터 t/8(여기서 t는 제품 두께를 의미함) 지점까지의 단면적에 대해 표면으로부터 10㎛ 이상의 깊이로 형성된 표면 흠의 개수가 단위 면적(mm2)당 0.0001개 이하일 수 있다.Austenitic high manganese steel for cryogenic properties, which has excellent surface quality and stress corrosion cracking resistance according to one aspect of the present invention, in weight percent, C: 0.4 to 0.5%, Mn: 23 to 26%, Cr: 3 to 5% , Cu: 0.3 ~ 0.7%, S: 0.05% or less, P: 0.5% or less, B: 0.005% or less, including residual Fe and unavoidable impurities, and 95% by area or more of austenite as a microstructure. The stacked defect energy (SFE) indicated by 1 satisfies the range of 45 mJ / m 2 or less, and the cross-sectional area from the surface to the point t / 8 (where t is the product thickness) when observing the cross section using an optical microscope For the number of surface flaws formed to a depth of 10 μm or more from the surface may be 0.0001 or less per unit area (mm 2 ).
[관계식 1] [Relationship 1]
적층결함에너지(SFE) = 25.7 + 2*Ni - 0.9*Cr + 410*C - 77*N - 13*Si -1.2*MnStacked Fault Energy (SFE) = 25.7 + 2 * Ni-0.9 * Cr + 410 * C-77 * N-13 * Si -1.2 * Mn
(관계식 1에서 Ni, Cr, C, N, Si, Mn은 각 성분의 중량%를 의미하며, 해당 성분이 포함되지 않는 경우 그 값은 0을 의미함)(In relational expression 1, Ni, Cr, C, N, Si, and Mn mean the weight percent of each component, and if the component is not included, the value means 0)
상기 강재에 항복강도 수준의 응력을 가한 후 100℃의 25% NaCl 용액에 침지시키는 경우 응력부식균열 발생시간이 900시간 이상일 수 있다.When the stress of the yield strength level is applied to the steel material, when it is immersed in a 25% NaCl solution at 100 ° C, the stress corrosion cracking generation time may be 900 hours or more.
상기 강재의 항복강도는 400MPa 이상이고, -196℃에서의 샤르피 충격인성은 41J 이상일 수 있다.The yield strength of the steel material is 400 MPa or more, and Charpy impact toughness at -196 ° C may be 41 J or more.
본 발명의 일 측면에 따른 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 강재는, 중량%로, C: 0.4~0.5%, Mn: 23~26%, Cr: 3~5%, Cu: 0.3~0.7%, S: 0.05% 이하, P: 0.5% 이하, B: 0.005% 이하, 잔부 Fe 및 불가피한 불순물을 포함하는 슬라브를 1000~1150℃의 온도범위에서 재가열하고, 상기 재가열된 슬라브를 조압연하여 조압연바를 제공하고, 상기 조압연바를 750~1000℃의 온도범위에서 마무리 압연하여 열연재를 제공하되, 상기 조압연바의 두께(t2)와 상기 슬라브의 두께(t1)의 비(t2/t1)가 0,3 이하를 만족하도록 상기 슬라브를 조압연하고, 상기 슬라브는 하기 관계식 1로 표시되는 적층결함에너지(SFE)가 45mJ/m2 이하의 범위를 만족하도록 제어하여 제조될 수 있다. [관계식 1]Austenitic high manganese steel for cryogenic properties, which has excellent surface quality and stress corrosion cracking resistance according to one aspect of the present invention, in weight percent, C: 0.4 to 0.5%, Mn: 23 to 26%, Cr: 3 to 5% , Cu: 0.3 to 0.7%, 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 1150 ° C, and the reheated Roughly rolling the slab to provide a rough rolling bar, and finish rolling the temperature of the rough rolling bar at a temperature range of 750 to 1000 ° C to provide hot rolling material, but the thickness of the rough rolling bar (t 2 ) and the thickness of the slab (t 1) ), The slab is roughly rolled so that the ratio (t 2 / t 1 ) satisfies 0,3 or less, and the slab satisfies the range of 45 mJ / m 2 or less of the stacked defect energy (SFE) represented by the following relational expression 1 Control. [Relationship 1]
적층결함에너지(SFE) = 25.7 + 2*Ni - 0.9*Cr + 410*C - 77*N - 13*Si -1.2*MnStacked Fault Energy (SFE) = 25.7 + 2 * Ni-0.9 * Cr + 410 * C-77 * N-13 * Si -1.2 * Mn
(관계식 1에서 Ni, Cr, C, N, Si, Mn은 각 성분의 중량%를 의미하며, 해당 성분이 포함되지 않는 경우 그 값은 0을 의미함)(In relational expression 1, Ni, Cr, C, N, Si, and Mn mean the weight percent of each component, and if the component is not included, the value means 0)
상기 마무리 압연 된 열연재를 10℃/s 이상의 냉각속도로 600℃ 이하까지 가속냉각할 수 있다.The finish 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, 부식 및 변형의 복합 환경에서 쌍정 형성을 유도하여 응력부식균열 저항성을 효과적으로 확보한 극저온용 오스테나이트계 고 망간 강재 및 그 제조방법을 제공할 수 있다.According to one aspect of the present invention, it is possible to provide a cryogenic austenitic high-manganese steel material and a method of manufacturing the same, which effectively secures stress corrosion cracking resistance by inducing twin formation in a complex environment of corrosion and deformation.
또한, 본 발명의 일 측면에 따르면, 강재의 표면 흠 형성을 억제하여 표면품질을 효과적으로 확보한 극저온용 오스테나이트계 고 망간 강재 및 그 제조방법을 제공할 수 있다.In addition, according to an aspect of the present invention, it is possible to provide a cryogenic austenitic high manganese steel material and a method for manufacturing the same, which effectively secures the surface quality by suppressing the formation of surface flaws in the steel material.
도 1은 304 스테인리스강의 응력부식균열 발생 메커니즘을 개략적으로 나타낸 도면이다.
도 2는 응력부식균열 특성 평가 시험의 예를 개략적으로 나타낸 도면이다.
도 3 및 도 4는 시편 1 및 시편 4의 응력부식균열 실험 결과를 촬영한 사진이다.1 is a view schematically showing a mechanism for generating stress corrosion cracking in 304 stainless steel.
2 is a view schematically showing an example of a stress corrosion cracking property evaluation test.
3 and 4 are photographs of stress corrosion cracking test results of specimens 1 and 4.
본 발명은 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 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 low temperature and a method for manufacturing the same, which is excellent in surface quality and stress corrosion cracking resistance. Hereinafter, preferred embodiments of the present invention will be described. 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 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 강재는, 중량%로, C: 0.4~0.5%, Mn: 23~26%, Cr: 3~5%, Cu: 0.3~0.7%, S: 0.05% 이하, P: 0.5% 이하, B: 0.005% 이하, 잔부 Fe 및 불가피한 불순물을 포함할 수 있다.Austenitic high manganese steel for cryogenic properties, which has excellent surface quality and stress corrosion cracking resistance according to one aspect of the present invention, in weight percent, C: 0.4 to 0.5%, Mn: 23 to 26%, Cr: 3 to 5% , Cu: 0.3 to 0.7%, S: 0.05% or less, P: 0.5% or less, B: 0.005% or less, residual Fe and unavoidable impurities.
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. 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. 따라서, 본 발명의 탄소(C) 함량은 0.4~0.5%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. 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%. Therefore, the carbon (C) content of the present invention may be 0.4 to 0.5%.
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. 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. 따라서, 본 발명의 망간(Mn) 함량은 23~26%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. 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%. Therefore, the manganese (Mn) content of the present invention may be 23 to 26%.
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. 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. 따라서, 본 발명의 크롬(Cr) 함량은 3~5%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. 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%. Therefore, the chromium (Cr) content of the present invention may be 3 to 5%.
구리(Cu): 0.3~0.7%Copper (Cu): 0.3 ~ 0.7%
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 구리(Cu) 함량의 하한을 0.3%로 제한할 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. 따라서, 본 발명의 구리(Cu) 함량은 0.3~0.7%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, copper (Cu) is a very low solid solution in carbide and is a slow diffusion element in austenite, so 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 limit the lower limit of the copper (Cu) content to 0.3% to achieve this effect. 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%. Therefore, the copper (Cu) content of the present invention may be 0.3 to 0.7%.
황(S): 0.05% 이하Sulfur (S): 0.05% or less
개재물 형성에 따른 열간취성 억제를 위해, 본 발명은 황(S) 함량의 상한을 적극 억제할 수 있으며, 바람직한 황(S) 함량의 상한을 0.05%일 수 있다.In order to suppress hot brittleness due to inclusion formation, 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 쉽게 편석되는 원소로서 주조 시 균열발생을 유발하거나, 용접성을 저하시키는 원소이다. 따라서, 본 발명은 인(P) 함량의 상한을 적극 억제할 수 있으며, 바람직한 인(P) 함량의 상한은 0.5%일 수 있다. Phosphorus (P) is an element that is easily segregated and causes cracking during casting or degrades 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 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 can limit the upper limit of the boron (B) content to 0.005%.
본 발명의 일 측면에 따른 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 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 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 for cryogenic properties, which has excellent surface quality and stress corrosion cracking resistance according to an aspect of the present invention, may contain residual Fe and other unavoidable impurities. However, in the normal manufacturing process, unintended impurities may be inevitably mixed from the raw material or the surrounding environment, and thus cannot be 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 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 강재는, 하기 관계식 1로 표시되는 적층결함에너지(SFE)가 45mJ/m2 이하의 범위를 만족하도록 합금 성분의 함량이 제어될 수 있다. The austenite-based high-manganese steel for cryogenic properties, which has excellent surface quality and stress corrosion cracking resistance according to an aspect of the present invention, has an alloy having a stacking fault energy (SFE) represented by the following relational expression 1 satisfying a range of 45 mJ / m 2 or less The content of the ingredients can be controlled.
[관계식 1][Relationship 1]
적층결함에너지(SFE) = 25.7 + 2*Ni - 0.9*Cr + 410*C - 77*N - 13*Si -1.2*MnStacked Fault Energy (SFE) = 25.7 + 2 * Ni-0.9 * Cr + 410 * C-77 * N-13 * Si -1.2 * Mn
(관계식 1에서 Ni, Cr, C, N, Si, Mn은 각 성분의 중량%를 의미하며, 해당 성분이 포함되지 않는 경우 그 값은 0을 의미함)(In relational expression 1, Ni, Cr, C, N, Si, and Mn mean the weight percent of each component, and if the component is not included, the value means 0)
본 발명의 발명자는 응력부식균열의 발생 메커니즘에 대해 심도 있는 연구를 수행한 결과, 상기 관계식 1에 의해 정의되는 적층결함에너지(SFE)를 일정 수준 이하로 제어하는 경우, 응력 및 부식 환경에서 쌍정 형성을 유도하여 응력부식균열 저항성을 효과적으로 향상시킬 수 있음을 알게 되었다. 도 1에 도시된 바와 같이, 304 스테인리스강의 경우, 전위가 작용하여 변형이 발생하므로 표면에 slip band 또는 Slip step이 형성되고, 국부 부식이 가속화되어 크랙으로 발전하는 응력부식 균열이 발생하는 반면, 본 발명의 고 망간 강재는 관계식 1로 표시되는 적층결함에너지(SFE)를 45mJ/m2 이상으로 제어하므로 응력 및 부식 환경에서 쌍정이 형성되어 우수한 응력부식균열 저항성을 확보함을 알 수 있다. 즉, 본 발명의 일 측면에 따른 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 강재는, 항복강도 수준의 응력을 가한 후 100℃의 25% NaCl 용액에 침지시키는 경우 응력부식균열 발생시간이 900시간 이상으로 우수한 응력부식균열 저항성을 확보할 수 있다.The inventors of the present invention have conducted an in-depth study of the mechanism for generating stress corrosion cracking, and when controlling the stacking fault energy (SFE) defined by the relational expression 1 to a certain level or less, twin formation in a stress and corrosion environment It was found that the resistance to stress corrosion cracking can be effectively improved by inducing. As shown in FIG. 1, in the case of 304 stainless steel, since a deformation occurs due to the action of a dislocation, a slip band or slip step is formed on the surface, and stress corrosion cracking, which develops into cracks by accelerating local corrosion, occurs. It can be seen that the high-manganese steel of the invention controls the stacking fault energy (SFE) represented by the relational expression 1 to 45 mJ / m 2 or more, so that twins are formed in a stress and corrosion environment to secure excellent stress corrosion cracking resistance. That is, the austenitic high manganese steel for cryogenic properties, which has excellent surface quality and stress corrosion cracking resistance according to one aspect of the present invention, is subjected to stress corrosion cracking when immersed in a 25% NaCl solution at 100 ° C after applying stress at the level of yield strength. It is possible to secure excellent stress corrosion cracking resistance with an occurrence time of 900 hours or more.
또한, 본 발명의 일 측면에 따른 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 강재는, 95면적% 이상의 오스테나이트를 미세조직으로 포함하되, 광학현미경을 이용하여 단면 관찰 시, 표면으로부터 t/8(여기서 t는 제품 두께를 의미함) 지점까지의 단면적에 대해 표면으로부터 10㎛ 이상의 깊이로 형성된 표면 흠의 개수가 단위 면적(mm2)당 0.0001개 이하일 수 있다.In addition, the austenite-based high-manganese steel for cryogenic properties, which has excellent surface quality and stress corrosion cracking resistance according to an aspect of the present invention, contains 95% by area or more of austenite as a microstructure, and when sectional observation is performed using an optical 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 ) with respect to the cross-sectional area from the surface to the point t / 8 (where t means product thickness).
즉, 본 발명의 일 측면에 따른 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 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 경제성 및 생산성을 효과적으로 확보할 수 있다.That is, the austenite-based high manganese steel for cryogenic properties, which has excellent surface quality and stress corrosion cracking resistance 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. , By effectively securing the surface quality, it is possible to omit subsequent processes such as a grinding process, thereby effectively securing economic efficiency and productivity.
또한, 본 발명의 일 측면에 따른 표면품질이 우수한 극저온용 오스테나이트계 고 망간 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 소재르 특히 적합한 오스테나이트계 고 망간 강재를 제공할 수 있다.In addition, 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 Charpy impact toughness of 41 J or more at -196 ° C, so liquefied petroleum gas, liquefaction requiring cryogenic properties It is possible to provide an austenitic high manganese steel material particularly suitable for materials such as fuel tanks for storage and transportation of natural gas, storage tanks, ship membranes, and transport pipes.
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 1000~1150℃의 온도범위에서 재가열하고, 상기 재가열된 슬라브를 조압연하여 조압연바를 제공하고, 750~1000℃의 온도범위에서 마무리 압연하여 열연재를 제공하되, 상기 조압연바의 두께(t2)와 상기 슬라브의 두께(t1)의 비(t2/t1)가 0,3 이하를 만족하도록 상기 슬라브를 조압연하고, 상기 슬라브는 하기 관계식 1로 표시되는 적층결함에너지(SFE)가 45mJ/m2 이하의 범위를 만족하도록 제어하여 제조될 수 있다.The austenitic high-manganese steel for cryogenic properties with excellent surface quality according to one aspect of the present invention re-heats a slab provided with the above-described composition in a temperature range of 1000 to 1150 ° C and roughly rolls the reheated slab. Providing a bar and finishing rolling in a temperature range of 750 to 1000 ° C to provide a hot rolled material, the ratio (t 2 / t 1 ) of the thickness (t 2 ) of the rough rolling bar and the thickness (t 1 ) of the slab The slabs may be roughly rolled to satisfy 0,3 or less, and the slabs may be manufactured by controlling the stacking defect energy (SFE) represented by the following relational expression 1 to satisfy a range of 45 mJ / m 2 or less.
[관계식 1] [Relationship 1]
적층결함에너지(SFE) = 25.7 + 2*Ni - 0.9*Cr + 410*C - 77*N - 13*Si -1.2*MnStacked Fault Energy (SFE) = 25.7 + 2 * Ni-0.9 * Cr + 410 * C-77 * N-13 * Si -1.2 * Mn
(관계식 1에서 Ni, Cr, C, N, Si, Mn은 각 성분의 중량%를 의미하며, 해당 성분이 포함되지 않는 경우 그 값은 0을 의미함)(In relational expression 1, Ni, Cr, C, N, Si, and Mn mean the weight percent of each component, and if the component is not included, the value means 0)
슬라브 재가열Slab reheating
슬라브의 강 조성은 전술한 오스테나이트계 고 망간 강재의 강 조성과 대응하므로, 슬라브의 강 조성에 대한 설명은 전술한 오스테나이트계 고망간 강재의 강 조성에 대한 설명으로 대신하도록 한다. 더불어, 슬라브의 적층결함에너지(SFE)에 대한 설명 역시 전술한 오스테나이트계 고 망간 강재의 적층결함에너지(SFE)에 대한 설명으로 대신하도록 한다. Since the steel composition of the slab corresponds to the steel composition of the austenitic high manganese steel described above, the description of the steel composition of the slab will be replaced by the description of the steel composition of the austenitic high manganese steel described above. In addition, the description of the stacking fault energy (SFE) of the slab is also replaced by the description of the stacking fault energy (SFE) of the austenitic high manganese steel described above.
전술한 강 조성으로 구비되는 슬라브를 1000~1150℃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 1150 ° 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 제한될 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 1150℃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 when heated at high temperatures, and the present invention limits the upper limit of the slab reheating temperature to 1150 ° 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 a decrease in surface quality 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 고 망간 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 가열로 온도 상승 및 조압연의 압하량 증가를 통해 도달 가능한 요소이나, 과도한 가열로 온도 상승은 입계 산화량을 증가시키는바 오히려 표면 품질의 저하를 유발하는 요인이 될 수 있는바, 이들을 최적의 범위에서 이들 공정 조건을 제어하는 것이 주요하다.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 in order 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 temperature of the heating furnace and an increase in the rolling reduction of the rough rolling, but an increase in the temperature of the heating furnace increases the amount of grain boundary oxidation Rather, it can be a factor that causes a decrease in surface quality, so it is important to control these process conditions in an optimal range.
따라서, 본 발명은 슬라브 재가열 온도의 상한을 1150℃로 제한하되, 조압연 압하량을 일정 수준 이항으로 유지하여 입계산화가 크랙으로 성장하는 것을 최소화하고자 한다. 즉, 본 발명은 조압연 단계에서 슬라브의 두께(t1)에 대한 조압연바의 두께(t2)의 비(t1/t2)가 0.3 이하를 만족하도록 조압연하여, 입계산화가 크랙으로 성장하는 것을 최소화하며, 그에 따라 최종 제품의 표면 흠 발생을 효과적으로 억제할 수 있다.Accordingly, the present invention intends to limit the upper limit of the slab reheating temperature to 1150 ° C, but minimize the growth of grain boundary oxidation into cracks by maintaining the rough rolling reduction at a certain level. That is, the present invention is found in so as to satisfy a ratio (t 1 / t 2) of the rough rolling bar thickness (t 2) of about the thickness of the slab (t 1) of 0.3 or less in the rough rolling step rolling, mouth calculated upset crack It minimizes the growth, thereby effectively suppressing the occurrence of surface flaws in the final product.
가속냉각Accelerated cooling
열간압연 공정 이후 마무리 압연된 열연재를 10℃/s 이상의 냉각속도로 600℃ 이하까지 가속냉각할 수 있다. 본 발명의 오스테나이트계 고 망간 강은 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 성장될 가능성이 높은바, 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 higher, when cooling is stopped at a high temperature, there is a high possibility that carbides are generated and grown. In the present invention, the cooling stop temperature is limited to 600 ° C. or less. You can.
상기와 같이 제조된 오스테나이트계 고 망간 강재는, 95면적% 이상의 오스테나이트를 미세조직으로 포함하되, 광학현미경을 이용하여 단면 관찰 시, 표면으로부터 t/8(여기서 t는 제품 두께를 의미함) 지점까지의 단면적에 대해 표면으로부터 10㎛ 이상의 깊이로 형성된 표면 흠의 개수가 단위 면적(mm2)당 0.0001개 이하일 수 있으며, 400MPa 이상의 항복강도 및 -196℃에서 41J 이상의 샤르피 충격인성을 구비할 수 있다.The austenitic high manganese steel produced as described above contains 95% by area or more of austenite as a microstructure, but when observed in cross section using an optical microscope, t / 8 from the surface (where t means product thickness) 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 may have a yield strength of 400 MPa or more and a Charpy impact toughness of 41 J or more at -196 ° C. have.
또한, 상기와 같이 제조된 오스테나이트계 고 망간 강재에 항복강도 수준의 응력을 가한 후 100℃의 25% NaCl 용액에 침지시키는 경우 응력부식균열 발생시간이 900시간 이상으로 우수한 응력부식균열 저항성을 확보할 수 있다.In addition, when the stress of the yield strength level is applied to the austenitic high-manganese steel prepared as described above and immersed in a 25% NaCl solution at 100 ° C., the stress corrosion cracking generation time is 900 hours or more, ensuring excellent stress corrosion cracking resistance 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.
(( 실시예Example 1) One)
하기 표 1의 조성을 가지는 슬라브를 250mm 두께로 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, 표면 흠 형성 여부, slip 발생 여부 및 응력부식균열 특성을 평가하여 그 결과를 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. 응력부식균열 특성은 도 2와 같이 ASTM G123 표준 방법으로 평가하였으며, 시험을 위해 시편에 항복강도 수준의 응력을 가한 후 100℃의 25% NaCl 용액에 침지하여 파괴가 발생하는 시간을 측정하여 평가하였다. A slab having the composition of Table 1 was prepared to a thickness of 250 mm, and prepared through the process conditions of Table 2 to prepare a specimen. 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, surface flaw formation, slip occurrence, and stress corrosion cracking properties were evaluated for each specimen, and the results are shown in Table 2. 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. The stress corrosion cracking properties were evaluated by the ASTM G123 standard method as shown in FIG. 2, and the stress was measured by measuring the time at which fracture occurred by immersing in a 25% NaCl solution at 100 ° C after applying stress at the yield strength level to the specimen for testing. .
(mJ/m2)SFE
(mJ / m 2 )
온도
(℃)Reheat
Temperature
(℃)
두께
(t1, mm)Slavic
thickness
(t1, mm)
연바
두께
(t2, mm)Pressure
Yeonba
thickness
(t2, mm)
(t2/t1)Thickness ratio
(t2 / t1)
표면 흠
깊이
(㎛)maximum
Surface flaw
depth
(㎛)
(개/mm2)Number of surface flaws
(Pcs / mm 2 )
흡수
에너지
(J, @-196℃)Shock
absorption
energy
(J, @ -196 ℃)
강도
(MPa)surrender
burglar
(MPa)
부식
균열
발생
시간
(hr)Stress
corrosion
crack
Occur
time
(hr)
시편 1은 304 스테인리스강 시편으로, 응력 및 부식 환경 하에서 slip band가 형성되어 응력부식균열 저항성이 현저히 열위한 것을 할 수 있다. 반면 시편 2 내지 5의 경우 본원발명의 제한하는 적층결함에너지(SFE) 범위를 만족하는바, 응력 및 부식 환경 하에서 쌍정이 형성되며, 그에 따라 우수한 응력부식균열 저항성을 확보하는 것을 알 수 있다. 도 3 및 도 4는 시편 1 및 시편 4의 응력부식균열 실험 결과를 촬영한 사진으로, 시편 1의 경우 크랙이 발생한 반면, 시편 4의 경우 크랙이 발생하지 않은 것을 확인할 수 있다. Specimen 1 is a 304 stainless steel specimen, and a slip band is formed under a stress and corrosion environment, so that the stress corrosion cracking resistance can be significantly deteriorated. On the other hand, in the case of the specimens 2 to 5, since it satisfies the limited stacking defect energy (SFE) range of the present invention, it can be seen that twins are formed under a stress and corrosion environment, thereby securing excellent stress corrosion cracking resistance. 3 and 4 is a photograph of the stress corrosion cracking test results of the specimen 1 and specimen 4, it can be seen that the crack occurred in the case of the specimen 1, the crack did not occur in the case of the specimen 4.
더불어, 본원발명의 제조조건을 만족하는 시편 3 내지 5의 경우, 표면 흠의 발생이 억제되어 우수한 표면품질을 가지는 반면, 본원발명의 제조조건을 만족하지 않는 시편 2의 경우, 표면 흠이 발생되어 표면품질을 가짐을 알 수 있다.In addition, in the case of specimens 3 to 5 satisfying the manufacturing conditions of the present invention, the occurrence of surface defects is suppressed to have excellent surface quality, whereas in the case of the specimen 2 not meeting the manufacturing conditions of the present invention, surface defects are generated It can be seen that it has a surface quality.
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 forms of embodiments are possible. Therefore, the technical spirit and scope of the claims set forth below are not limited to the embodiments.
Claims (5)
95면적% 이상의 오스테나이트를 미세조직으로 포함하되,
하기 관계식 1로 표시되는 적층결함에너지(SFE)가 45mJ/m2 이하의 범위를 만족하며,
광학현미경을 이용하여 단면 관찰 시, 표면으로부터 t/8(여기서 t는 제품 두께를 의미함) 지점까지의 단면적에 대해 표면으로부터 10㎛ 이상의 깊이로 형성된 표면 흠의 개수가 단위 면적(mm2)당 0.0001개 이하인, 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 강재.
[관계식 1]
적층결함에너지(SFE) = 25.7 + 2*Ni - 0.9*Cr + 410*C - 77*N - 13*Si -1.2*Mn
(관계식 1에서 Ni, Cr, C, N, Si, Mn은 각 성분의 중량%를 의미하며, 해당 성분이 포함되지 않는 경우 그 값은 0을 의미함)In weight percent, C: 0.4 to 0.5%, Mn: 23 to 26%, Cr: 3 to 5%, Cu: 0.3 to 0.7%, S: 0.05% or less, P: 0.5% or less, B: 0.005% or less, The balance contains Fe and unavoidable impurities,
It contains at least 95% by area of austenite as a microstructure,
The stacked defect energy (SFE) represented by the following relational expression 1 satisfies the range of 45 mJ / m 2 or less,
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 per unit area (mm 2 ) for the cross-sectional area from the surface to the point t / 8 (where t denotes the product thickness) Austenitic high-manganese steel for cryogenics with less than 0.0001 pieces and excellent surface quality and stress corrosion cracking resistance.
[Relationship 1]
Stacked Fault Energy (SFE) = 25.7 + 2 * Ni-0.9 * Cr + 410 * C-77 * N-13 * Si -1.2 * Mn
(In Relational Formula 1, Ni, Cr, C, N, Si, and Mn mean the weight percent of each component, and if the component is not included, the value means 0)
상기 강재에 항복강도 수준의 응력을 가한 후 100℃의 25% NaCl 용액에 침지시키는 경우 응력부식균열 발생시간이 900시간 이상인, 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 강재. According to claim 1,
When the stress of the yield strength level is applied to the steel material and immersed in a 25% NaCl solution at 100 ° C, the stress corrosion cracking generation time is 900 hours or more, and the cryogenic austenitic high manganese steel material having excellent surface quality and stress corrosion cracking resistance.
항복강도는 400MPa 이상이고, -196℃에서의 샤르피 충격인성은 41J 이상인, 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 강재. According to claim 1,
An austenitic, high-manganese steel for cryogenic properties with a yield strength of 400 MPa or higher and a Charpy impact toughness of -41 ° C or higher, superior in surface quality and stress corrosion cracking resistance.
상기 재가열된 슬라브를 조압연하여 조압연바를 제공하고,
상기 조압연바를 750~1000℃의 온도범위에서 마무리 압연하여 열연재를 제공하되,
상기 조압연바의 두께(t2)와 상기 슬라브의 두께(t1)의 비(t2/t1)가 0,3 이하를 만족하도록 상기 슬라브를 조압연하고,
상기 슬라브는 하기 관계식 1로 표시되는 적층결함에너지(SFE)가 45mJ/m2 이하의 범위를 만족하는, 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 강재의 제조방법.
[관계식 1]
적층결함에너지(SFE) = 25.7 + 2*Ni - 0.9*Cr + 410*C - 77*N - 13*Si -1.2*Mn
(관계식 1에서 Ni, Cr, C, N, Si, Mn은 각 성분의 중량%를 의미하며, 해당 성분이 포함되지 않는 경우 그 값은 0을 의미함)In weight percent, C: 0.4 to 0.5%, Mn: 23 to 26%, Cr: 3 to 5%, Cu: 0.3 to 0.7%, 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 1150 ° C,
Roughly rolling the reheated slab to provide a rough rolling bar,
The rough rolling bar is finished rolling in a temperature range of 750 ~ 1000 ℃ to provide a hot rolled material,
The slab is roughly rolled so that the ratio (t 2 / t 1 ) of the thickness t 2 of the rough rolling bar and the thickness t 1 of the slab satisfies 0,3 or less,
The slab is a method for manufacturing a cryogenic austenitic high manganese steel having excellent surface quality and stress corrosion cracking resistance, which satisfies a range of 45 mJ / m 2 or less of a stacked defect energy (SFE) represented by the following relational expression 1.
[Relationship 1]
Stacked Fault Energy (SFE) = 25.7 + 2 * Ni-0.9 * Cr + 410 * C-77 * N-13 * Si -1.2 * Mn
(In Relational Formula 1, Ni, Cr, C, N, Si, and Mn mean the weight percent of each component, and if the component is not included, the value means 0)
상기 마무리 압연 된 열연재를 10℃/s 이상의 냉각속도로 600℃ 이하까지 가속냉각하는, 표면품질 및 응력부식균열 저항성이 우수한 극저온용 오스테나이트계 고 망간 강재의 제조방법.
According to claim 4,
A method of manufacturing an austenitic high-manganese steel for cryogenic temperature, which accelerates and cools the finished rolled hot rolled material to 600 ° C. or less at a cooling rate of 10 ° C./s or higher, and has excellent surface quality and stress corrosion cracking resistance.
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| CN201980069177.8A CN112888805A (en) | 2018-10-25 | 2019-10-25 | Austenitic high manganese steel for ultralow temperature use excellent in surface quality and stress corrosion cracking resistance, and method for producing same |
| PCT/KR2019/014156 WO2020085847A1 (en) | 2018-10-25 | 2019-10-25 | Austenitic high manganese steel for cryogenic applications having excellent surface quality and resistance to stress corrosion cracking, and manufacturing method for same |
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| GB9922757D0 (en) * | 1999-09-27 | 1999-11-24 | Heymark Metals Ltd | Improved steel composition |
| FR2857980B1 (en) * | 2003-07-22 | 2006-01-13 | Usinor | PROCESS FOR MANUFACTURING HIGH-STRENGTH FERRO-CARBON-MANGANESE AUSTENITIC STEEL SHEET, EXCELLENT TENACITY AND COLD SHAPINGABILITY, AND SHEETS THUS PRODUCED |
| EP1878811A1 (en) * | 2006-07-11 | 2008-01-16 | ARCELOR France | Process for manufacturing iron-carbon-manganese austenitic steel sheet with excellent resistance to delayed cracking, and sheet thus produced |
| JP6377745B2 (en) * | 2013-08-14 | 2018-08-22 | ポスコＰｏｓｃｏ | Ultra-high strength steel sheet and method for manufacturing the same |
| WO2017111510A1 (en) * | 2015-12-23 | 2017-06-29 | 주식회사 포스코 | Non-magnetic steel material having excellent hot workability and manufacturing method therefor |
| KR101889187B1 (en) * | 2015-12-23 | 2018-08-16 | 주식회사 포스코 | Nonmagnetic steel having superior hot workability and method for manufacturing the same |
| CN106222554A (en) * | 2016-08-23 | 2016-12-14 | 南京钢铁股份有限公司 | A kind of economical steel used at ultra-low temperature and preparation method thereof |
| KR101940874B1 (en) * | 2016-12-22 | 2019-01-21 | 주식회사 포스코 | High manganese steel with superior low temperature toughness and yield strength and method for manufacturing the same |
| KR101899692B1 (en) * | 2016-12-23 | 2018-09-17 | 주식회사 포스코 | Low temperature austenitic high manganese steel and method for manufacturing the same |
| CN107177786B (en) * | 2017-05-19 | 2018-12-21 | 东北大学 | A kind of design and its manufacturing method of the high manganese cut deal of LNG storage tank |
| CN108570541B (en) * | 2018-05-14 | 2020-07-10 | 东北大学 | High-temperature heat treatment method of high-manganese medium plate for L NG storage tank |
-
2018
- 2018-10-25 KR KR1020180128503A patent/KR20200046831A/en not_active Application Discontinuation
-
2019
- 2019-10-25 EP EP19876375.7A patent/EP3872213A1/en not_active Withdrawn
- 2019-10-25 WO PCT/KR2019/014156 patent/WO2020085847A1/en unknown
- 2019-10-25 CN CN201980069177.8A patent/CN112888805A/en active Pending
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20150075275A (en) | 2013-12-25 | 2015-07-03 | 주식회사 포스코 | A high manganese steel having superior toughness at low temperature, and manufacturing method |
Also Published As
| Publication number | Publication date |
|---|---|
| WO2020085847A1 (en) | 2020-04-30 |
| EP3872213A4 (en) | 2021-09-01 |
| CN112888805A (en) | 2021-06-01 |
| EP3872213A1 (en) | 2021-09-01 |
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