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WO2022045595A1 - Austenitic stainless steel with improved deep drawability - Google Patents

Austenitic stainless steel with improved deep drawability Download PDF

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Publication number
WO2022045595A1
WO2022045595A1 PCT/KR2021/009569 KR2021009569W WO2022045595A1 WO 2022045595 A1 WO2022045595 A1 WO 2022045595A1 KR 2021009569 W KR2021009569 W KR 2021009569W WO 2022045595 A1 WO2022045595 A1 WO 2022045595A1
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Prior art keywords
stainless steel
austenitic stainless
less
work hardening
excluding
Prior art date
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Ceased
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PCT/KR2021/009569
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French (fr)
Korean (ko)
Inventor
김경훈
김지수
전종진
박미남
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Posco Holdings Inc
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Posco Co Ltd
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Application filed by Posco Co Ltd filed Critical Posco Co Ltd
Priority to US18/019,187 priority Critical patent/US20230287549A1/en
Priority to CN202180055978.6A priority patent/CN116096934A/en
Priority to JP2023512177A priority patent/JP7624506B2/en
Priority to EP21861894.0A priority patent/EP4177368A4/en
Publication of WO2022045595A1 publication Critical patent/WO2022045595A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the 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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
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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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    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets

Definitions

  • the present invention relates to austenitic stainless steel with improved deep drawing, and more particularly, to austenitic stainless steel that does not crack when deep machining is applied to convert a plate material into a three-dimensional part. is about
  • Deep machining can omit additional processes such as welding and stress relief heat treatment, so it is an effective method for reducing manufacturing cost.
  • cylindrical molding such as a cup or a battery, a material excellent in deep workability is required.
  • Austenitic stainless steels have excellent elongation, no problem in making complex shapes, and excellent work hardenability, and are used in various fields involving deep machining.
  • austenitic stainless steel is deformed in shape while work hardening occurs during cold working. At this time, it is known that when the austenitic stainless steel has excellent work hardenability, forming is easy.
  • Embodiments of the present invention are intended to provide an austenitic stainless steel capable of securing formability when deep machining is applied by minimizing an increase in strength due to work hardening.
  • Austenitic stainless steel with improved deep workability by weight, C: 0.01 to 0.05%, N: 0.01 to 0.25%, Si: 1.5% or less (excluding 0), Mn: 0.3 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 2.0% or less (excluding 0), Cu: 0.2 to 2.5%, remaining Fe and unavoidable impurities, including the following formula (1 ) is satisfied.
  • Cr, Si, Mo, Ni, Cu, C, and N mean wt% of each element.
  • Equation (2) 0 ⁇ 2.4*Cr+1.7*Mo+3.9*Si-2.1*Ni-Mn-0.4*Cu-58*C-64*N-13 ⁇ 5.5
  • Cr, Mo, Si, Ni, Mn, Cu, C, and N mean weight% of each element.
  • Al 0.04% or less (excluding 0)
  • Ti 0.003% or less (excluding 0)
  • B 0.0025% or less (excluding 0)
  • P 0.035% or less
  • S It may further include one or more of 0.0035% or less.
  • the true strain value when the work hardening index is the maximum may be 0.2 or less.
  • ⁇ is the stress
  • K is the strength modulus
  • ⁇ is the strain rate
  • n is the work hardening index
  • the difference between the true strain value when the work hardening index is the maximum and the true strain value when the work hardening index is 0 may be 0.11 or more.
  • the elongation may be 35% or more.
  • the tensile strength may be 360 MPa or more.
  • cracks may not occur until five-stage molding.
  • an austenitic stainless steel applicable as a deep machining material because it is possible to omit an intermediate heat treatment process and minimize an increase in strength due to work hardening when deep machining is applied.
  • 1 is a graph for explaining the relationship between stress-strain according to a tensile test of a material.
  • FIG. 2 is a graph showing the relationship between stress-strain together with a work hardening index during a tensile test of austenitic stainless steel according to the disclosed embodiment.
  • Austenitic stainless steel with improved deep workability by weight, C: 0.01 to 0.05%, N: 0.01 to 0.25%, Si: 1.5% or less (excluding 0), Mn: 0.3 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 2.0% or less (excluding 0), Cu: 0.2 to 2.5%, remaining Fe and unavoidable impurities, including the following formula (1 ) is satisfied.
  • Cr, Si, Mo, Ni, Cu, C, and N mean wt% of each element.
  • Austenitic stainless steel has high elongation and excellent formability, so it is a steel grade used for products of various shapes. When austenitic stainless steel is subjected to stress, deformation occurs by transformation from an unstable austenite phase to a martensite phase at room temperature, that is, transformation induced plasticity.
  • the strength of the material also increases.
  • the austenitic stainless steel exhibits both deformation and strength increase due to work-hardening.
  • Work hardening capacity is expressed using work-hardening exponent, which changes according to strain.
  • work hardening of austenitic stainless steels is related to the degree of stabilization of the austenite phase. By increasing the degree of stabilization of the austenite phase through component control, work hardening of austenitic stainless steel can be suppressed.
  • the present inventors have obtained the following knowledge as a result of various studies in order to secure the elongation of the austenitic stainless steel and suppress the increase in strength due to work hardening when deep machining is applied.
  • Austenitic stainless steel with improved deep workability by weight, C: 0.01 to 0.05%, N: 0.01 to 0.25%, Si: 1.5% or less (excluding 0), Mn: 0.3 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 2.0% or less (excluding 0), Cu: 0.2 to 2.5%, remaining Fe and unavoidable impurities.
  • the unit is % by weight.
  • the content of C is 0.01 to 0.05%.
  • Carbon (C) is an effective element for stabilizing the austenite phase, and may be added in an amount of 0.01% or more to suppress martensite formation during deformation and secure strength.
  • the content is excessive, there is a problem in that corrosion resistance is deteriorated by inducing grain boundary precipitation of Cr carbides by bonding with Cr, so the upper limit can be limited to 0.05%.
  • the content of N is 0.01 to 0.25%.
  • the content of Si is 1.5% or less (excluding 0).
  • Silicon (Si) acts as a deoxidizer during the steelmaking process and is an element that secures the strength and corrosion resistance of austenitic stainless steel.
  • silicon which is a ferrite phase stabilizing element
  • the upper limit may be limited to 1.5%.
  • the content of Mn is 0.3 to 3.5%.
  • the upper limit may be limited to 3.5% because it may reduce the corrosion resistance and surface gloss of the austenitic stainless steel by forming an excessive amount of S-based inclusions (MnS).
  • the content of Cr is 17.0 to 22.0%.
  • Chromium (Cr) is a basic element that stabilizes ferrite and contains the most among elements for improving corrosion resistance of stainless steel. In the present invention, 17.0% or more may be added to form a passivation film to inhibit oxidation to secure corrosion resistance.
  • Ni 9.0 to 14.0%.
  • Nickel (Ni) is the most powerful austenite phase stabilizing element, and as its content increases, the austenite phase is stabilized to soften the material, and 9% or more is added to suppress work hardening caused by the occurrence of strain-induced martensite. It is essential However, since Ni is an expensive element, it causes an increase in raw material cost when a large amount is added. Accordingly, the upper limit may be limited to 14.0% in consideration of both the cost and efficiency of the steel.
  • the content of Mo is 2.0% or less (excluding 0).
  • Molybdenum (Mo) is an effective element for corrosion resistance of steel.
  • the content of molybdenum, a ferrite phase stabilizing element is excessive, the austenite phase stabilization degree decreases, making it difficult to secure deep machinability, and mechanical properties and corrosion resistance are lowered by precipitation of intermetallic compounds such as ⁇ phase.
  • the upper limit can be limited to 2.0%.
  • the content of Cu is 0.2 to 2.5%%.
  • Copper (Cu) is an austenite phase stabilizing element added instead of expensive nickel (Ni), and may be added in an amount of 0.2% or more to secure price competitiveness and deep workability. However, if the content is excessive, ⁇ -Cu precipitation phase with a low melting point may be formed, which may deteriorate the surface quality, so the upper limit may be limited to 2.5%.
  • Al 0.04% or less (excluding 0)
  • Ti 0.003% or less (excluding 0)
  • B 0.0025% or less (excluding 0)
  • P 0.035% or less
  • S It may further include one or more of 0.0035% or less.
  • the content of Al is 0.04% or less (excluding 0).
  • Aluminum (Al) is an element that lowers the oxygen content in molten steel as a strong deoxidizer. However, if the content is excessive, there is a problem that the sleeve defect of the cold-rolled strip occurs due to an increase in non-metallic inclusions, so the upper limit may be limited to 0.04%.
  • the content of Ti is 0.003% or less (excluding 0).
  • Titanium (Ti) preferentially combines with interstitial elements such as carbon (C) and nitrogen (N) to form precipitates (carbonitrides), thereby reducing the amount of solid solution C and solid solution N in steel and reducing the formation of a Cr depleted region It is an effective element for securing corrosion resistance of steel by suppressing it.
  • interstitial elements such as carbon (C) and nitrogen (N)
  • carbonitrides carbonitrides
  • the content of B is 0.0025% or less (excluding 0).
  • Boron (B) is an effective element for suppressing crack generation during casting to ensure good surface quality.
  • nitride (BN) may be formed on the surface of the product during the annealing/pickling process to deteriorate the surface quality, and thus the upper limit may be limited to 0.0025%.
  • the content of P is 0.035% or less.
  • Phosphorus (P) is an impurity that is unavoidably contained in steel and is an element that causes intergranular corrosion or inhibits hot workability.
  • the upper limit of the P content is managed as 0.035%.
  • the content of S is 0.0035% or less.
  • S is an impurity that is unavoidably contained in steel, and is an element that segregates at grain boundaries and is a major cause of inhibiting hot workability, so it is desirable to control its content as low as possible.
  • the upper limit of the S content is managed to 0.0035% or less.
  • the remaining component of the present invention is iron (Fe).
  • Fe iron
  • phase transformation increases the strength of the austenitic stainless steel until the material is damaged.
  • the following formula (1) was derived in consideration of the phase transformation caused by the deformation of the austenitic stainless steel.
  • the content of austenite stabilizing elements such as Mn, N, Cu, and Ni was increased to increase the degree of stabilization of the austenite phase. Accordingly, the phase transformation to the martensitic phase was suppressed, and work hardening of the austenitic stainless steel could be suppressed.
  • Cr, Si, Mo, Ni, Cu, C, and N mean wt% of each element.
  • Equation (1) satisfies the range of 63 or more.
  • the present inventors confirmed that the lower the value of Equation (1), the greater the change in strength during deformation due to external stress. Specifically, when the value of Equation (1) is less than 63, the austenitic stainless steel of the above alloy composition system exhibits abrupt strain-induced martensitic transformation behavior due to external deformation or plasticity non-uniformity due to twin crystal formation. . Accordingly, there is a problem in that the elongation of the austenitic stainless steel and the deep workability during multi-stage forming are reduced, so that the lower limit of Equation (1) is limited to 63.
  • 1 is a graph for explaining the relationship between stress-strain according to a tensile test of a material.
  • the increase in strength due to work hardening can be explained by the stress-strain curve of FIG. 1 .
  • the work-hardening exponent (n) indicating the degree of work-hardening ability can be expressed as follows.
  • ⁇ is the stress
  • K is the strength factor
  • ⁇ is the strain
  • the work hardening index n corresponds to the slope of the graph, and the larger the slope, the greater the increase in the strength of the material during plastic deformation.
  • Cr, Mo, Si, Ni, Mn, Cu, C, and N mean weight% of each element.
  • Equation (2) satisfies the range of 0 or more and 5.5 or less.
  • Equation (2) the higher the value of Equation (2), the easier the martensitic transformation due to external stress occurred, resulting in an excessive increase in strength and lowering of the formability.
  • the value of Equation (2) is 5.5 or more, there is a problem in that the strength increases continuously from tensile deformation to just before fracture, resulting in rapid fracture. Accordingly, there is a problem that the elongation cannot be secured, so the upper limit of Equation (2) is to be limited to 5.5.
  • Equation (2) when the value of Equation (2) was too low, it was confirmed that the cross-slip expression of the austenite phase due to external stress became difficult. Specifically, when the value of Equation (2) is less than 0, the austenitic stainless steel exhibits only planar slip behavior with respect to deformation, so that the accumulation of dislocations due to external stress proceeds, and plastic non-uniformity and high work hardening are exhibited. . Accordingly, there is a problem in that the elongation and yield ratio of the austenitic stainless steel decrease, and the lower limit of the value of Equation (2) is to be limited to 0.
  • FIG. 2 is a graph showing the relationship between stress-strain together with a work hardening index during a tensile test of austenitic stainless steel according to the disclosed embodiment.
  • the true strain value when the work hardening index is maximum may be 0.2 or less.
  • the hardening index decreases after the point A, even if the deformation proceeds. That is, it can be seen that the intensity gradually increases from point A to point B.
  • the point A in order to improve the deep workability of the austenitic stainless steel, paying attention to the point that it should be possible to secure a certain amount or more of deformation without excessive strength increase, the point A, where the increase in strength is maximum, is arranged at a relatively low amount of deformation, It was derived that it is necessary to obtain a certain amount of deformation from point A to reach point B.
  • the ferritic stainless steel with improved surface properties according to the disclosed embodiment has a true strain value of 0.2 or less when the work hardening index is maximum.
  • the difference between the true strain value when the work hardening index is maximum and the true strain value when the work hardening index is 0 is 0.11 or more.
  • the ferritic stainless steel with improved surface properties according to the disclosed embodiment satisfying the alloy element composition range and relational expression can secure an elongation of 35% or more and a tensile strength of 360 MPa or more.
  • the ferritic stainless steel with improved surface properties according to the disclosed embodiment does not crack when formed in two or more stages under the condition of a drawing ratio of 1.7 to 4.3, and cracks do not occur until forming in 5 stages.
  • Example 1 0.022 0.39 0.79 0.030 0.0011 21.4 10.3 0.5 0.8 0.206 0.003 0.002 0.0023 67.4 3.53
  • Example 2 0.020 0.40 0.70 0.032 0.0010 20.9 10.5 0.6 1.0 0.190 0.003 0.002 0.0023 67.4 3.22
  • Example 3 0.022 0.51 0.65 0.028 0.0010 21.2 10.6 0.5 0.7 0.200 0.003 0.002 0.0023 67.6 3.56
  • Example 4 0.025 0.39 0.80 0.008 0.0035 21.0 10.1 0.6 0.8 0.210 0.004 0.002 0.0022 67.1 2.71
  • Example 5 0.023 0.40 0.64 0.010 0.0005 21.3 10.3 0.6 0.9 0.210 0.004 0.002 0.0022 68.2 3.30
  • Example 6 0.029 0.38 0.81 0.034 0.0011 21.3 9.3 0.5 0.7 0.224 0.003 0.003 0.0022 65.5 3.
  • the number of multi-stage forming and work hardening index were measured. Specifically, in deep drawing forming, a blank with a diameter of 85 mm was used in 5 steps with a diameter of 1st punch 50mm, 2nd punch diameter 38mm, 3rd stage punch diameter 30mm, 4th stage punch diameter 24mm, and 5th stage punch diameter 20mm. did.
  • the drawing ratio for each stage is 1.7 in 1st stage, 2.2 in 2nd stage, 2.8 in 3rd stage, 3.5 in 4th stage, and 4.3 in 5th stage.
  • Example 1 5 0.37 0.17 0.29 0.12 450 37.4
  • Example 2 5 0.36 0.18 0.29 0.12 451 37.5
  • Example 3 5 0.36 0.18 0.29 0.12 450 37.5
  • Example 4 5 0.30 0.17 0.30 0.14 441 42.2
  • Example 5 5 0.27 0.17 0.30 0.13 467 41.0
  • Example 6 5 0.35 0.17 0.32 0.15 401 46.0
  • Example 7 5 0.35 0.18 0.32 0.15 404 46.7
  • Example 8 5 0.35 0.18 0.32 0.14 402 46.2
  • Example 9 5 0.36 0.17 0.32 0.15 386 45.6
  • Example 10 5 0.36 0.17 0.32 0.15 387 45.4
  • Example 11 5 0.36 0.17 0.32 0.15 388 45.5
  • Example 12 5 0.39 0.17 0.31 0.14 420 42.4
  • Example 13 5 0.39 0.17 0.31 0.14 421 42.5
  • Example 14 5 0.39 0.17 0.31 0.14 419 42.4
  • Example 15 5 0.38 0.15 0.30 0.15 441
  • Equation (1) was less than 63, resulting in a continuous increase in strength during work hardening, and the value of Equation (2) exceeded 5.5, resulting in martens due to deformation. Site transformation was active and cracks were frequent during multi-stage molding.
  • the alloy component and the relational expression when forming two or more stages under the condition of a drawing ratio of 1.7 to 4.3, cracks do not occur until five stages forming, an elongation of 35% or more, and a tensile strength of 360 MPa or more
  • the secured austenitic stainless steel can be manufactured.
  • the present invention can be used in various industrial fields such as fields involving deep machining.

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Abstract

An austenitic stainless steel with improved deep drawability is disclosed. The austenitic stainless steel with improved deep drawability, of the present invention, comprises, by wt%, 0.01-0.05% of C, 0.01-0.25% of N, 1.5% or less of Si (excluding 0), 0.3-3.5% of Mn, 17.0-22.0% of Cr, 9.0-14.0% of Ni, 2.0% or less of Mo (excluding 0), 0.2-2.5% of Cu, and the balance of Fe and inevitable impurities, and satisfies formula (1). Formula (1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N) ≥ 63, wherein Cr, Si, Mo, Ni, Cu, C and N mean the wt% of each element.

Description

심가공성이 향상된 오스테나이트계 스테인리스강Austenitic stainless steel with improved deep machinability

본 발명은 심(深)가공성(Deep Drawing)이 향상된 오스테나이트계 스테인리스강에 관한 것으로, 보다 상세하게는 판재를 3차원 부품으로 변환시키는 심가공 적용 시, 크랙이 발생하지 않는 오스테나이트계 스테인리스강에 관한 것이다.The present invention relates to austenitic stainless steel with improved deep drawing, and more particularly, to austenitic stainless steel that does not crack when deep machining is applied to convert a plate material into a three-dimensional part. is about

최근 제품 가격 경쟁이 심화됨에 따라, 부품에 적용되는 소재의 원가 절감이 요구되고 있다. 심가공은 용접, 응력 제거 열처리 등과 같이 부가적인 공정을 생략할 수 있어, 제조 비용 절감에 효과적인 방법이다. 한편, 컵, 배터리 등과 같이 원통형 성형이 수반되는 경우에는, 심가공성이 우수한 소재가 요구되고 있다.Recently, as product price competition intensifies, cost reduction of materials applied to parts is required. Deep machining can omit additional processes such as welding and stress relief heat treatment, so it is an effective method for reducing manufacturing cost. On the other hand, when cylindrical molding is involved, such as a cup or a battery, a material excellent in deep workability is required.

오스테나이트계 스테인리스 강재는 연신율이 뛰어나 복잡한 형상을 만드는데 문제가 없고, 가공경화능이 우수하여, 심가공이 수반되는 다양한 분야에 적용되고 있는 강종이다. Austenitic stainless steels have excellent elongation, no problem in making complex shapes, and excellent work hardenability, and are used in various fields involving deep machining.

일반적으로, 오스테나이트계 스테인리스강은 냉간가공시 가공경화가 일어나면서 형태가 변형된다. 이 때, 오스테나이트계 스테인리스강의 가공경화능이 우수하면 성형이 용이한 것으로 알려져 있다. In general, austenitic stainless steel is deformed in shape while work hardening occurs during cold working. At this time, it is known that when the austenitic stainless steel has excellent work hardenability, forming is easy.

그러나, 오스테나이트계 스테인리스강의 심가공을 적용하는 경우에는, 가공경화에 따라 지속적으로 강도가 상승하여, 소재에 국부적인 응력집중이 발생하고, 결국 파손되는 문제가 발생한다. However, when deep processing of austenitic stainless steel is applied, the strength is continuously increased according to work hardening, and local stress concentration occurs in the material, resulting in a problem of breakage.

한편, 가공 경화에 따른 강도 증가 문제를 해결하기 위해, 중간 열처리를 도입하는 경우를 고려할 수 있으나, 공정 시간적/공정 비용적 측면에서 제약이 있다. On the other hand, in order to solve the problem of strength increase due to work hardening, a case of introducing an intermediate heat treatment may be considered, but there is a limitation in terms of process time/process cost.

따라서, 심가공 적용 시, 중간 열처리 공정을 생략할 수 있으면서도, 가공 경화에 따른 강도 증가를 최소화할 수 있어 심가공 소재로 적용 가능한 오스테나이트계 스테인리스강의 개발이 요구된다.Therefore, when applying deep machining, it is possible to omit the intermediate heat treatment process, and it is possible to minimize the increase in strength due to work hardening, so the development of austenitic stainless steel applicable as a deep machining material is required.

본 발명의 실시예들은 가공 경화에 따른 강도 증가를 최소화함으로써 심가공 적용 시, 성형 가공성을 확보할 수 있는 오스테나이트계 스테인리스강을 제공하고자 한다.Embodiments of the present invention are intended to provide an austenitic stainless steel capable of securing formability when deep machining is applied by minimizing an increase in strength due to work hardening.

본 발명의 일 실시예에 따른 심가공성이 향상된 오스테나이트계 스테인리스강은, 중량%로, C: 0.01 내지 0.05%, N: 0.01 내지 0.25%, Si: 1.5% 이하(0은 제외), Mn: 0.3 내지 3.5%, Cr: 17.0 내지 22.0%, Ni: 9.0 내지 14.0%, Mo: 2.0% 이하(0은 제외), Cu: 0.2 내지 2.5%, 나머지 Fe 및 불가피한 불순물을 포함하고, 하기 식(1)을 만족한다.Austenitic stainless steel with improved deep workability according to an embodiment of the present invention, by weight, C: 0.01 to 0.05%, N: 0.01 to 0.25%, Si: 1.5% or less (excluding 0), Mn: 0.3 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 2.0% or less (excluding 0), Cu: 0.2 to 2.5%, remaining Fe and unavoidable impurities, including the following formula (1 ) is satisfied.

식(1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N) ≥ 63Formula (1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N) ≥ 63

여기서, Cr, Si, Mo, Ni, Cu, C, N는 각 원소의 중량%를 의미한다.Here, Cr, Si, Mo, Ni, Cu, C, and N mean wt% of each element.

또한, 본 발명의 일 실시예에 따르면, 하기 식(2)를 만족할 수 있다.In addition, according to an embodiment of the present invention, the following formula (2) may be satisfied.

식(2): 0 < 2.4*Cr+1.7*Mo+3.9*Si-2.1*Ni-Mn-0.4*Cu-58*C-64*N-13 < 5.5Equation (2): 0 < 2.4*Cr+1.7*Mo+3.9*Si-2.1*Ni-Mn-0.4*Cu-58*C-64*N-13 < 5.5

여기서, Cr, Mo, Si, Ni, Mn, Cu, C, N는 각 원소의 중량%를 의미한다.Here, Cr, Mo, Si, Ni, Mn, Cu, C, and N mean weight% of each element.

또한, 본 발명의 일 실시예에 따르면, Al: 0.04% 이하(0은 제외), Ti: 0.003% 이하(0은 제외), B: 0.0025% 이하(0은 제외), P: 0.035% 이하 및 S: 0.0035% 이하 중 1종 이상을 더 포함할 수 있다. In addition, according to an embodiment of the present invention, Al: 0.04% or less (excluding 0), Ti: 0.003% or less (excluding 0), B: 0.0025% or less (excluding 0), P: 0.035% or less, and S: It may further include one or more of 0.0035% or less.

또한, 본 발명의 일 실시예에 따르면, 하기 식(3)에서, 가공경화지수가 최대일 때의 진변형율 값이 0.2 이하일 수 있다.In addition, according to an embodiment of the present invention, in the following formula (3), the true strain value when the work hardening index is the maximum may be 0.2 or less.

식(3): σ = Kεn Equation (3): σ = Kε n

여기서, σ는 응력, K는 강도계수, ε는 변형율, n은 가공경화지수를 의미한다.Here, σ is the stress, K is the strength modulus, ε is the strain rate, and n is the work hardening index.

또한, 본 발명의 일 실시예에 따르면, 가공경화지수가 최대일 때의 진변형율 값과 가공경화지수가 0일 때의 진변형율 값의 차이가 0.11 이상일 수 있다.Further, according to an embodiment of the present invention, the difference between the true strain value when the work hardening index is the maximum and the true strain value when the work hardening index is 0 may be 0.11 or more.

또한, 본 발명의 일 실시예에 따르면, 연신율이 35% 이상일 수 있다.In addition, according to an embodiment of the present invention, the elongation may be 35% or more.

또한, 본 발명의 일 실시예에 따르면, 인장강도가 360MPa 이상일 수 있다.In addition, according to an embodiment of the present invention, the tensile strength may be 360 MPa or more.

또한, 본 발명의 일 실시예에 따르면, 드로잉비 1.7 내지 4.3 조건으로 다단 성형시, 5단 성형까지 균열이 발생하지 않을 수 있다.In addition, according to an embodiment of the present invention, during multi-stage molding with a drawing ratio of 1.7 to 4.3, cracks may not occur until five-stage molding.

본 발명의 실시예에 따르면, 심가공 적용 시, 중간 열처리 공정을 생략할 수 있으면서도, 가공 경화에 따른 강도 증가를 최소화할 수 있어 심가공 소재로 적용 가능한 오스테나이트계 스테인리스강을 제공할 수 있다.According to an embodiment of the present invention, it is possible to provide an austenitic stainless steel applicable as a deep machining material because it is possible to omit an intermediate heat treatment process and minimize an increase in strength due to work hardening when deep machining is applied.

도 1은 소재의 인장실험에 따른 응력- 변형률 사이의 관계를 설명하기 위한 그래프이다.1 is a graph for explaining the relationship between stress-strain according to a tensile test of a material.

도 2는 개시된 실시예에 따른 오스테나이트계 스테인리스강의 인장실험 시, 응력- 변형률 사이의 관계를 가공경화지수와 함께 나타낸 그래프이다.2 is a graph showing the relationship between stress-strain together with a work hardening index during a tensile test of austenitic stainless steel according to the disclosed embodiment.

본 발명의 일 실시예에 따른 심가공성이 향상된 오스테나이트계 스테인리스강은, 중량%로, C: 0.01 내지 0.05%, N: 0.01 내지 0.25%, Si: 1.5% 이하(0은 제외), Mn: 0.3 내지 3.5%, Cr: 17.0 내지 22.0%, Ni: 9.0 내지 14.0%, Mo: 2.0% 이하(0은 제외), Cu: 0.2 내지 2.5%, 나머지 Fe 및 불가피한 불순물을 포함하고, 하기 식(1)을 만족한다.Austenitic stainless steel with improved deep workability according to an embodiment of the present invention, by weight, C: 0.01 to 0.05%, N: 0.01 to 0.25%, Si: 1.5% or less (excluding 0), Mn: 0.3 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 2.0% or less (excluding 0), Cu: 0.2 to 2.5%, remaining Fe and unavoidable impurities, including the following formula (1 ) is satisfied.

식(1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N) ≥ 63Formula (1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N) ≥ 63

여기서, Cr, Si, Mo, Ni, Cu, C, N는 각 원소의 중량%를 의미한다.Here, Cr, Si, Mo, Ni, Cu, C, and N mean wt% of each element.

이하에서는 본 발명의 실시예를 첨부 도면을 참조하여 상세히 설명한다. 이하의 실시예는 본 발명이 속하는 기술분야에서 통상의 지식을 가진 자에게 본 발명의 사상을 충분히 전달하기 위해 제시하는 것이다. 본 발명은 여기서 제시한 실시예만으로 한정되지 않고 다른 형태로 구체화될 수도 있다. 도면은 본 발명을 명확히 하기 위해 설명과 관계없는 부분의 도시를 생략하고, 이해를 돕기 위해 구성요소의 크기를 다소 과장하여 표현할 수 있다.Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are presented in order to sufficiently convey the spirit of the present invention to those of ordinary skill in the art to which the present invention pertains. The present invention is not limited to the embodiments presented herein, and may be embodied in other forms. The drawings may omit illustration of parts irrelevant to the description in order to clarify the present invention, and slightly exaggerate the size of the components to help understanding.

또한 어떤 부분이 어떤 구성요소를 "포함"한다고 할 때, 이는 특별히 반대되는 기재가 없는 한 다른 구성요소를 제외하는 것이 아니라 다른 구성요소를 더 포함할 수 있는 것을 의미한다.Also, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

단수의 표현은 문맥상 명백하게 예외가 있지 않는 한, 복수의 표현을 포함한다.The singular expression includes the plural expression unless the context clearly dictates otherwise.

이하에서는 본 발명에 따른 실시예를 첨부된 도면을 참조하여 상세히 설명한다. Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

오스테나이트계 스테인리스강은 연신율이 높고, 성형성이 우수하여 다양한 형상의 제품에 사용되는 강종이다. 오스테나이트계 스테인리스강은 응력을 받으면 상온에서 불안정한 오스테나이트상에서 마르텐사이트상으로의 변태, 즉 소성유기변태(Transformation Induced Plasticity)에 의해 변형이 발생한다. Austenitic stainless steel has high elongation and excellent formability, so it is a steel grade used for products of various shapes. When austenitic stainless steel is subjected to stress, deformation occurs by transformation from an unstable austenite phase to a martensite phase at room temperature, that is, transformation induced plasticity.

이 때, 생성되는 마르텐사이트상은 강도가 높으므로 소재의 강도 또한 증가하는 것이다. 다시 말해, 오스테나이트계 스테인리스강은 가공경화(work-hardening)로 인해 변형과 강도 증가가 동시에 나타난다. 가공경화능은 가공경화지수(work-hardening exponent)를 사용하여 표시하는데, 가공경화지수는 변형율(strain)에 따라 변화한다.At this time, since the generated martensite phase has high strength, the strength of the material also increases. In other words, the austenitic stainless steel exhibits both deformation and strength increase due to work-hardening. Work hardening capacity is expressed using work-hardening exponent, which changes according to strain.

오스테나이트계 스테인리스강의 가공경화능이 우수하면 성형이 용이한 것으로 알려져 있다. It is known that when the austenitic stainless steel has excellent work hardenability, it is easy to form.

그러나, 오스테나이트계 스테인리스강에 블랭크 직경을 감소시키면서 수행하는 심가공을 적용하는 경우에는, 가공경화에 따라 지속적으로 강도가 상승하여, 소재에 국부적인 응력집중이 발생하고, 결국 파손되는 문제가 발생한다. 또한, 시효균열로 인해 성형 후 갑작스럽게 크랙이 발생하기도 한다.However, when deep machining performed while reducing the blank diameter is applied to austenitic stainless steel, the strength continuously increases according to work hardening, resulting in local stress concentration in the material, resulting in breakage. do. In addition, cracks may occur suddenly after molding due to aging cracks.

따라서, 변형량이 많은 심가공 성형에서는 소재 전체에 고르게 변형이 일어나고, 변형 동안의 강도의 변화를 최소화하는 것이 중요하다. 즉, 오스테나이트계 스테인리스강의 심가공성을 향상시키기 위해서는 가공경화를 억제할 필요가 있다. Therefore, in deep machining molding with a large amount of deformation, it is important to uniformly deform the entire material and to minimize the change in strength during deformation. That is, in order to improve the deep workability of the austenitic stainless steel, it is necessary to suppress work hardening.

한편, 오스테나이트 스테인리스강의 가공경화는 오스테나이트상의 안정화도와 관련이 있다. 성분 제어를 통해 오스테나이트상의 안정화도를 증가시키면, 오스테나이트 스테인리스강의 가공경화를 억제할 수 있다.On the other hand, work hardening of austenitic stainless steels is related to the degree of stabilization of the austenite phase. By increasing the degree of stabilization of the austenite phase through component control, work hardening of austenitic stainless steel can be suppressed.

하지만, 오스테나이트계 스테인리스강의 연신율로 대표되는 가공성은 소성유기변태에 기인한 가공경화로부터 도출된 것이므로, 가공경화능의 축소는 오스테나이트계 스테인리스강의 가공성을 저하시키는 문제가 있다.However, since the workability represented by the elongation of the austenitic stainless steel is derived from work hardening caused by plastic induced transformation, the reduction in work hardenability has a problem of lowering the workability of the austenitic stainless steel.

본 발명자들은 오스테나이트계 스테인리스강의 연신율을 확보하면서도 심가공 적용 시, 가공경화에 따른 강도 증가를 억제하기 위하여 다양한 검토를 행한 결과, 이하의 지견을 얻을 수 있었다.The present inventors have obtained the following knowledge as a result of various studies in order to secure the elongation of the austenitic stainless steel and suppress the increase in strength due to work hardening when deep machining is applied.

본 발명에서는, 오스테나이트계 스테인리스강에 있어서 심가공 적용 시, 파손 발생을 방지하기 위한 요인들을 검토한 결과, 응력에 의한 마르텐사이트상 변태를 억제하여 과도한 가공 경화를 방지하면서도, 과도한 강도 증가없이 일정량 이상의 변형을 확보함으로써 오스테나이트계 스테인리스강의 심가공성을 향상시킬 수 있음을 발견하였다. 이를 위해서는 과도한 강도 증가없이 지속적인 변형을 확보할 수 있는 합금 성분계를 도출함으로써 달성할 수 있다.In the present invention, as a result of examining factors for preventing the occurrence of breakage when deep machining is applied to austenitic stainless steel, a certain amount without excessive strength increase while preventing excessive work hardening by suppressing martensitic phase transformation due to stress It has been found that the deep workability of austenitic stainless steel can be improved by securing the above deformation. To this end, it can be achieved by deriving an alloy composition system that can ensure continuous deformation without excessive strength increase.

본 발명의 일 측면에 따른 심가공성이 향상된 오스테나이트계 스테인리스강은, 중량%로, C: 0.01 내지 0.05%, N: 0.01 내지 0.25%, Si: 1.5% 이하(0은 제외), Mn: 0.3 내지 3.5%, Cr: 17.0 내지 22.0%, Ni: 9.0 내지 14.0%, Mo: 2.0% 이하(0은 제외), Cu: 0.2 내지 2.5%, 나머지 Fe 및 불가피한 불순물을 포함한다.Austenitic stainless steel with improved deep workability according to an aspect of the present invention, by weight, C: 0.01 to 0.05%, N: 0.01 to 0.25%, Si: 1.5% or less (excluding 0), Mn: 0.3 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 2.0% or less (excluding 0), Cu: 0.2 to 2.5%, remaining Fe and unavoidable impurities.

이하, 본 발명의 실시예에서의 합금성분 원소 함량의 수치한정 이유에 대하여 설명한다. 이하에서는 특별한 언급이 없는 한 단위는 중량%이다.Hereinafter, the reason for numerical limitation of the alloying element content in the embodiment of the present invention will be described. Hereinafter, unless otherwise specified, the unit is % by weight.

C의 함량은 0.01 내지 0.05%이다.The content of C is 0.01 to 0.05%.

탄소(C)는 오스테나이트상 안정화에 효과적인 원소로, 변형시 마르텐사이트 형성을 억제하고 강도를 확보하기 위해 0.01% 이상 첨가할 수 있다. 다만 그 함량이 과도할 경우, Cr과 결합함으로써 Cr탄화물의 입계 석출을 유도하여 내식성이 저하되는 문제가 있는 바, 그 상한을 0.05%로 한정할 수 있다.Carbon (C) is an effective element for stabilizing the austenite phase, and may be added in an amount of 0.01% or more to suppress martensite formation during deformation and secure strength. However, when the content is excessive, there is a problem in that corrosion resistance is deteriorated by inducing grain boundary precipitation of Cr carbides by bonding with Cr, so the upper limit can be limited to 0.05%.

N의 함량은 0.01 내지 0.25%이다.The content of N is 0.01 to 0.25%.

질소(N)는 탄소와 마찬가지로 오스테나이트상 안정화에 효과적인 원소로, 심가공성 확보를 위해 0.01% 이상 첨가할 수 있다. 다만 그 함량이 과도할 경우, 질화물 형성에 의해 표면 품질을 저하시킬 수 있으므로 그 상한을 0.25%로 한정할 수 있다.Nitrogen (N), like carbon, is an effective element for stabilizing the austenite phase, and may be added in an amount of 0.01% or more to secure deep workability. However, when the content is excessive, the upper limit may be limited to 0.25% because the surface quality may be deteriorated by the formation of nitride.

Si의 함량은 1.5% 이하(0은 제외)이다.The content of Si is 1.5% or less (excluding 0).

실리콘(Si)은 제강공정 중 탈산제의 역할을 하고, 오스테나이트계 스테인리스강의 강도와 내식성을 확보하는 원소이다. 다만, 페라이트상 안정화 원소인 실리콘의 함량이 과다할 경우, 마르텐사이트 변태를 촉진시키고, σ상 등 금속간 화합물(Intermetallic Compound)을 석출하여 기계적 특성 및 내식성이 저하되는 문제가 있어, 본 발명에서는 그 상한을 1.5%로 한정할 수 있다.Silicon (Si) acts as a deoxidizer during the steelmaking process and is an element that secures the strength and corrosion resistance of austenitic stainless steel. However, when the content of silicon, which is a ferrite phase stabilizing element, is excessive, there is a problem in that the martensite transformation is accelerated and intermetallic compounds such as σ phase are precipitated to decrease mechanical properties and corrosion resistance, and in the present invention, The upper limit may be limited to 1.5%.

Mn의 함량은 0.3 내지 3.5%이다.The content of Mn is 0.3 to 3.5%.

망간(Mn)은 탄소(C), 질소(N) 와 마찬가지로 오스테나이트 안정화하는 원소로, 성형 가공시 발생하는 강도 증가를 억제하는 효과가 있어, 0.3% 이상 첨가할 수 있다. 다만 그 함량이 과도할 경우, S계 개재물(MnS)을 과량 형성하여 오스테나이트계 스테인리스강의 내식성 및 표면광택을 저하시킬 수 있으므로 그 상한을 3.5%로 한정할 수 있다.Manganese (Mn), like carbon (C) and nitrogen (N), is an austenite stabilizing element, has an effect of suppressing an increase in strength that occurs during molding, and can be added in an amount of 0.3% or more. However, if the content is excessive, the upper limit may be limited to 3.5% because it may reduce the corrosion resistance and surface gloss of the austenitic stainless steel by forming an excessive amount of S-based inclusions (MnS).

Cr의 함량은 17.0 내지 22.0%이다. The content of Cr is 17.0 to 22.0%.

크롬(Cr)은 페라이트를 안정화하고, 스테인리스강의 내식성 향상 원소 중 가장 많이 함유되어 기본이 되는 원소이다. 본 발명에서는 산화를 억제하는 부동태피막 형성하여 내식성을 확보하기 위해 17.0% 이상 첨가할 수 있다.Chromium (Cr) is a basic element that stabilizes ferrite and contains the most among elements for improving corrosion resistance of stainless steel. In the present invention, 17.0% or more may be added to form a passivation film to inhibit oxidation to secure corrosion resistance.

다만, 페라이트상 안정화 원소인 크롬의 함량이 과다할 경우, 오스테나이트상 안정화도가 감소하여 마르텐사이트 변태를 촉진시키고, 이에 따라 니켈 함량의 증가를 수반하므로 제조비용이 상승하며, σ상 등 금속간 화합물(Intermetallic Compound)을 석출하여 기계적 특성 및 내식성이 저하되는 문제가 있어, 본 발명에서는 그 상한을 22.0%로 한정할 수 있다.However, when the content of chromium, which is a ferrite phase stabilization element, is excessive, the degree of stabilization of the austenite phase decreases and promotes martensite transformation, which accompanies an increase in the nickel content, thereby increasing the manufacturing cost, and intermetallics such as σ phase. There is a problem in that mechanical properties and corrosion resistance are lowered by precipitation of an intermetallic compound, and thus the upper limit thereof may be limited to 22.0% in the present invention.

Ni의 함량은 9.0 내지 14.0%이다.The content of Ni is 9.0 to 14.0%.

니켈(Ni)은 가장 강력한 오스테나이트상 안정화 원소로써 그 함량이 증가할수록 오스테나이트상이 안정화되어 소재를 연질화하고, 변형유기 마르텐사이트의 발생에 기인하는 가공경화를 억제하기 위하여 9% 이상을 첨가하는 것이 필수적이다. 그러나, Ni은 고가의 원소임에 따라 다량의 첨가 시 원료비용의 상승을 초래한다. 이에, 강재의 비용 및 효율성을 모두 고려하여 그 상한을 14.0%로 한정할 수 있다.Nickel (Ni) is the most powerful austenite phase stabilizing element, and as its content increases, the austenite phase is stabilized to soften the material, and 9% or more is added to suppress work hardening caused by the occurrence of strain-induced martensite. it is essential However, since Ni is an expensive element, it causes an increase in raw material cost when a large amount is added. Accordingly, the upper limit may be limited to 14.0% in consideration of both the cost and efficiency of the steel.

Mo의 함량은 2.0% 이하(0은 제외)이다.The content of Mo is 2.0% or less (excluding 0).

몰리브덴(Mo)은 강의 내식성에 효과적인 원소이다. 다만, 페라이트상 안정화 원소인 몰리브덴의 함량이 과다할 경우, 오스테나이트상 안정화도가 감소하여 심가공성을 확보하기 어렵고, σ상 등 금속간 화합물(Intermetallic Compound)을 석출하여 기계적 특성 및 내식성이 저하되는 문제가 있어, 본 발명에서는 그 상한을 2.0%로 한정할 수 있다.Molybdenum (Mo) is an effective element for corrosion resistance of steel. However, if the content of molybdenum, a ferrite phase stabilizing element, is excessive, the austenite phase stabilization degree decreases, making it difficult to secure deep machinability, and mechanical properties and corrosion resistance are lowered by precipitation of intermetallic compounds such as σ phase. There is a problem, and in the present invention, the upper limit can be limited to 2.0%.

Cu의 함량은 0.2 내지 2.5%%이다.The content of Cu is 0.2 to 2.5%%.

구리(Cu)는 고가의 니켈(Ni) 대신 첨가되는 오스테나이트상 안정화 원소로, 가격 경쟁력 및 심가공성을 확보하기 위해 0.2% 이상 첨가할 수 있다. 다만 그 함량이 과도할 경우, 저융점의 ε-Cu 석출상이 형성되어 표면 품질을 저하시킬 수 있으므로 그 상한을 2.5%로 한정할 수 있다.Copper (Cu) is an austenite phase stabilizing element added instead of expensive nickel (Ni), and may be added in an amount of 0.2% or more to secure price competitiveness and deep workability. However, if the content is excessive, ε-Cu precipitation phase with a low melting point may be formed, which may deteriorate the surface quality, so the upper limit may be limited to 2.5%.

또한, 본 발명의 일 실시예에 따르면, Al: 0.04% 이하(0은 제외), Ti: 0.003% 이하(0은 제외), B: 0.0025% 이하(0은 제외), P: 0.035% 이하 및 S: 0.0035% 이하 중 1종 이상을 더 포함할 수 있다.In addition, according to an embodiment of the present invention, Al: 0.04% or less (excluding 0), Ti: 0.003% or less (excluding 0), B: 0.0025% or less (excluding 0), P: 0.035% or less, and S: It may further include one or more of 0.0035% or less.

Al의 함량은 0.04% 이하(0은 제외)이다.The content of Al is 0.04% or less (excluding 0).

알루미늄(Al)은 강력한 탈산제로써 용강 중 산소의 함량을 낮추는 역할을 하는 원소이다. 다만, 그 함량이 과다할 경우 비금속 개재물 증가로 인해 냉연 스트립의 슬리브 결함이 발생하는 문제가 있어 그 상한을 0.04%로 한정할 수 있다.Aluminum (Al) is an element that lowers the oxygen content in molten steel as a strong deoxidizer. However, if the content is excessive, there is a problem that the sleeve defect of the cold-rolled strip occurs due to an increase in non-metallic inclusions, so the upper limit may be limited to 0.04%.

Ti의 함량은 0.003% 이하(0은 제외)이다.The content of Ti is 0.003% or less (excluding 0).

티타늄(Ti)은 탄소(C)와 질소(N)와 같은 침입형 원소와 우선적으로 결합하여 석출물(탄질화물)을 형성함으로써, 강 중 고용 C 및 고용 N의 양을 저감하고 Cr 고갈영역 형성을 억제하여 강의 내식성 확보에 효과적인 원소이다. 다만, 그 함량이 과다할 경우, Ti계 개재물을 형성하여 제조상에 어려움이 있고, 스캡(scab)과 같은 표면결함이 발생하는 문제가 있어, 그 상한을 0.003%로 한정할 수 있다.Titanium (Ti) preferentially combines with interstitial elements such as carbon (C) and nitrogen (N) to form precipitates (carbonitrides), thereby reducing the amount of solid solution C and solid solution N in steel and reducing the formation of a Cr depleted region It is an effective element for securing corrosion resistance of steel by suppressing it. However, when the content is excessive, there is a problem in manufacturing by forming Ti-based inclusions, and there is a problem in that surface defects such as scabs occur, and the upper limit thereof may be limited to 0.003%.

B의 함량은 0.0025% 이하(0은 제외)이다.The content of B is 0.0025% or less (excluding 0).

붕소(B)는 주조 중의 크랙 발생을 억제하여 양호한 표면 품질을 확보하는데 효과적인 원소이다. 다만, 그 함량이 과도할 경우, 소둔/산세 공정 중 제품 표면에 질화물(BN)을 형성시켜 표면품질을 저하시킬 수 있어 그 상한을 0.0025%로 한정할 수 있다.Boron (B) is an effective element for suppressing crack generation during casting to ensure good surface quality. However, if the content is excessive, nitride (BN) may be formed on the surface of the product during the annealing/pickling process to deteriorate the surface quality, and thus the upper limit may be limited to 0.0025%.

P의 함량은 0.035% 이하이다.The content of P is 0.035% or less.

인(P)은 강 중 불가피하게 함유되는 불순물로, 입계 부식을 일으키거나 열간가공성을 저해하는 주요 원인이 되는 원소이므로, 그 함량을 가능한 낮게 제어하는 것이 바람직하다. 본 발명에서는 상기 P 함량의 상한을 0.035%로 관리한다.Phosphorus (P) is an impurity that is unavoidably contained in steel and is an element that causes intergranular corrosion or inhibits hot workability. In the present invention, the upper limit of the P content is managed as 0.035%.

S의 함량은 0.0035% 이하이다.The content of S is 0.0035% or less.

황(S)은 강 중 불가피하게 함유되는 불순물로, 결정립계에 편석되어 열간가공성을 저해하는 주요 원인이 되는 원소이므로, 그 함량을 가능한 낮게 제어하는 것이 바람직하다. 본 발명에서는 상기 S 함량의 상한을 0.0035% 이하로 관리한다.Sulfur (S) is an impurity that is unavoidably contained in steel, and is an element that segregates at grain boundaries and is a major cause of inhibiting hot workability, so it is desirable to control its content as low as possible. In the present invention, the upper limit of the S content is managed to 0.0035% or less.

본 발명의 나머지 성분은 철(Fe)이다. 다만, 통상의 제조과정에서는 원료 또는 주위 환경으로부터 의도되지 않는 불순물들이 불가피하게 혼입될 수 있으므로, 이를 배제할 수는 없다. 이들 불순물들은 통상의 제조과정의 기술자라면 누구라도 알 수 있는 것이기 때문에 그 모든 내용을 특별히 본 명세서에서 언급하지는 않는다. The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in the normal manufacturing process, this cannot be excluded. Since these impurities are known to any person skilled in the art of manufacturing processes, all details thereof are not specifically mentioned in the present specification.

전술한 바와 같이, 오스테나이트계 스테인리스강의 가공경화는, 상온에서 불안정한 오스테나이트상이 소성변형에서 기인한 응력에 의하여 마르텐사이트상으로 변태되는 것으로부터 발생한다. As described above, work hardening of austenitic stainless steels occurs from the transformation of an unstable austenite phase into a martensitic phase by stress resulting from plastic deformation at room temperature.

변형이 지속됨에 따라 지속적인 상변태가 일어나고, 이러한 상변태는 오스테나이트계 스테인리스강이 재료가 파손되기 전까지 강도를 증가시키는 바, 심가공성 확보를 위해서는 마르텐사이트상의 변태를 억제할 필요가 있다.As the deformation continues, a continuous phase transformation occurs, and this phase transformation increases the strength of the austenitic stainless steel until the material is damaged.

본 발명에서는 오스테나이트계 스테인리스강의 변형에 의해 발생하는 상변태를 고려하여, 하기 식(1)을 도출하였다. In the present invention, the following formula (1) was derived in consideration of the phase transformation caused by the deformation of the austenitic stainless steel.

구체적으로, 본 발명에서는 Mn, N, Cu, Ni 등 오스테나이트 안정화 원소의 함량을 상향 제어하여 오스테나이트상의 안정화도를 높이고자 하였다. 이에 따라, 마르텐사이트상으로의 상변태가 억제되고, 오스테나이트계 스테인리스강의 가공경화를 억제할 수 있었다.Specifically, in the present invention, the content of austenite stabilizing elements such as Mn, N, Cu, and Ni was increased to increase the degree of stabilization of the austenite phase. Accordingly, the phase transformation to the martensitic phase was suppressed, and work hardening of the austenitic stainless steel could be suppressed.

식(1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N) Formula (1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N)

여기서, Cr, Si, Mo, Ni, Cu, C, N는 각 원소의 중량%를 의미한다.Here, Cr, Si, Mo, Ni, Cu, C, and N mean wt% of each element.

본 발명의 일 실시예에 따른 심가공성이 향상된 오스테나이트계 스테인리스강은 상기 식(1) 로 표현되는 값이 63 이상의 범위를 만족한다.In the austenitic stainless steel with improved deep workability according to an embodiment of the present invention, the value expressed by Equation (1) satisfies the range of 63 or more.

본 발명자들은 식(1)의 값이 낮을수록, 외부 응력에 의한 변형시 강도변화가 크게 나타남을 확인하였다. 구체적으로, 식(1)의 값이 63 미만인 경우, 외부 변형에 의해 전술한 합금성분계의 오스테나이트계 스테인리스강은 급격한 변형유기 마르텐사이트 변태거동을 나타내거나, 쌍정 형성에 의한, 소성불균일이 발생하였다. 이에 따라, 오스테나이트계 스테인리스강의 연신율 및 다단 성형시 심가공성이 감소하는 문제가 있어, 식(1)의 하한값을 63으로 한정하고자 한다.The present inventors confirmed that the lower the value of Equation (1), the greater the change in strength during deformation due to external stress. Specifically, when the value of Equation (1) is less than 63, the austenitic stainless steel of the above alloy composition system exhibits abrupt strain-induced martensitic transformation behavior due to external deformation or plasticity non-uniformity due to twin crystal formation. . Accordingly, there is a problem in that the elongation of the austenitic stainless steel and the deep workability during multi-stage forming are reduced, so that the lower limit of Equation (1) is limited to 63.

도 1은 소재의 인장실험에 따른 응력-변형률 사이의 관계를 설명하기 위한 그래프이다. 1 is a graph for explaining the relationship between stress-strain according to a tensile test of a material.

가공경화에 의한 강도 증가는, 도 1의 응력-변형율 곡선으로 설명할 수 있다. 도 1에서, 가공경화능의 정도를 나타내는 가공경화지수(work-hardening exponent, n)는 다음과 같이 나타낼 수 있다. The increase in strength due to work hardening can be explained by the stress-strain curve of FIG. 1 . In FIG. 1, the work-hardening exponent (n) indicating the degree of work-hardening ability can be expressed as follows.

σ = Kεn σ = Kε n

여기서, σ는 응력, K는 강도계수, ε는 변형율을 의미한다.Here, σ is the stress, K is the strength factor, and ε is the strain.

한편, 상기 관계식에서 양변에 상용로그를 적용하여 log 관계식으로 나타내면, 다음과 같이 나타낼 수 있다.On the other hand, when a log relational expression is expressed by applying a common logarithm to both sides in the above relational expression, it can be expressed as follows.

log σ = log K + n* log εlog σ = log K + n* log ε

다시 말해, 응력-변형률 log 관계에서, 가공경화지수 n은 그래프의 기울기에 해당하고, 기울기가 클수록 소성 변형시 소재의 강도 증가가 심하다는 것을 의미한다.In other words, in the stress-strain log relationship, the work hardening index n corresponds to the slope of the graph, and the larger the slope, the greater the increase in the strength of the material during plastic deformation.

본 발명에서는 오스테나이트계 스테인리스강의 심가공성을 향상시키기 위해서는, 과도한 강도 증가없이 지속적인 변형을 확보할 수 있어야 한다는 점에 착안하여 하기 식(2)를 도출하였다.In the present invention, in order to improve the deep workability of the austenitic stainless steel, the following formula (2) was derived by paying attention to the point that continuous deformation should be secured without excessive strength increase.

식(2): 2.4*Cr+1.7*Mo+3.9*Si-2.1*Ni-Mn-0.4*Cu-58*C-64*N-13 Formula (2): 2.4*Cr+1.7*Mo+3.9*Si-2.1*Ni-Mn-0.4*Cu-58*C-64*N-13

여기서, Cr, Mo, Si, Ni, Mn, Cu, C, N는 각 원소의 중량%를 의미한다.Here, Cr, Mo, Si, Ni, Mn, Cu, C, and N mean weight% of each element.

본 발명의 일 실시예에 따른 심가공성이 향상된 오스테나이트계 스테인리스강은 상기 식(2) 로 표현되는 값이 0 이상 5.5 이하의 범위를 만족한다.In the austenitic stainless steel with improved deep workability according to an embodiment of the present invention, the value expressed by Equation (2) satisfies the range of 0 or more and 5.5 or less.

본 발명자들은 식 (2)의 값이 높을수록, 외부 응력에 의한 마르텐사이트 변태가 쉽게 일어나고, 이로부터 과도한 강도 증가가 발생하여, 성형성이 저하되는 것을 확인하였다. 구체적으로 식 (2)의 값이 5.5 이상인 경우 인장 변형에 서 파단 직전까지 지속적인 강도 증가가 일어나 급격한 파단이 발생하는 문제가 있다. 이에 따라 연신율을 확보할 수 없는 문제가 있어 식(2)의 상한을 5.5로 한정하고자 한다.The present inventors confirmed that the higher the value of Equation (2), the easier the martensitic transformation due to external stress occurred, resulting in an excessive increase in strength and lowering of the formability. Specifically, when the value of Equation (2) is 5.5 or more, there is a problem in that the strength increases continuously from tensile deformation to just before fracture, resulting in rapid fracture. Accordingly, there is a problem that the elongation cannot be secured, so the upper limit of Equation (2) is to be limited to 5.5.

반면, 식 (2)의 값이 지나치게 낮으면, 외부 응력에 의한 오스테나이트상의 크로스 슬립 발현이 어려워 지는 것을 확인하였다. 구체적으로, 식 (2)의 값이 0 미만인 경우, 오스테나이트계 스테인리스강은 변형에 대해서 플래너(planar) 슬립거동만을 나타내어 외부 응력에 의한 전위의 축적이 진행되고, 소성 불균일 및 높은 가공경화를 나타낸다. 이에 따라, 오스테나이트계 스테인리스 강의 연신율 및 항복비가 감소하는 문제가 있어, 식 (2)의 값 하한을 0으로 한정하고자 한다.On the other hand, when the value of Equation (2) was too low, it was confirmed that the cross-slip expression of the austenite phase due to external stress became difficult. Specifically, when the value of Equation (2) is less than 0, the austenitic stainless steel exhibits only planar slip behavior with respect to deformation, so that the accumulation of dislocations due to external stress proceeds, and plastic non-uniformity and high work hardening are exhibited. . Accordingly, there is a problem in that the elongation and yield ratio of the austenitic stainless steel decrease, and the lower limit of the value of Equation (2) is to be limited to 0.

도 2는 개시된 실시예에 따른 오스테나이트계 스테인리스강의 인장실험 시, 응력- 변형률 사이의 관계를 가공경화지수와 함께 나타낸 그래프이다. 2 is a graph showing the relationship between stress-strain together with a work hardening index during a tensile test of austenitic stainless steel according to the disclosed embodiment.

한편, 본 발명의 일 실시예에 따른 심가공성이 향상된 오스테나이트계 스테인리스강은, 가공경화지수가 최대일 때의 진변형율 값이 0.2 이하일 수 있다. On the other hand, in the austenitic stainless steel with improved deep workability according to an embodiment of the present invention, the true strain value when the work hardening index is maximum may be 0.2 or less.

도 2에서, 가공경화지수가 최대가 되는 지점을 A로, 가공 경화지수가 0이 되는 지점을 B로 나타내었다. In FIG. 2, the point at which the work hardening index becomes the maximum is indicated by A, and the point at which the work hardening index becomes 0 is indicated by B.

도 2를 참조하면, A 지점 이후에는 변형이 진행 되더라도 가경경화지수가 감소하는 것을 확인할 수 있다. 즉, A 지점 이후에는 B 지점까지 강도가 완만하게 증가하는 것을 확인할 수 있다. Referring to FIG. 2 , it can be confirmed that the hardening index decreases after the point A, even if the deformation proceeds. That is, it can be seen that the intensity gradually increases from point A to point B.

본 발명에서는 오스테나이트계 스테인리스강의 심가공성을 향상시키기 위해, 과도한 강도 증가 없이 일정량 이상의 변형을 확보할 수 있어야 한다는 점에 착안하여, 강도의 증가가 최대가 되는 지점 A를 비교적 낮은 변형량에 배치하고, 지점 A로부터 일정량의 변형량을 확보하여 지점 B에 이르는 것이 필요하다는 것을 도출하였다. In the present invention, in order to improve the deep workability of the austenitic stainless steel, paying attention to the point that it should be possible to secure a certain amount or more of deformation without excessive strength increase, the point A, where the increase in strength is maximum, is arranged at a relatively low amount of deformation, It was derived that it is necessary to obtain a certain amount of deformation from point A to reach point B.

개시된 실시예에 따른 표면 특성이 향상된 페라이트계 스테인리스강은 가공경화지수가 최대일 때의 진변형율 값이 0.2 이하이다. The ferritic stainless steel with improved surface properties according to the disclosed embodiment has a true strain value of 0.2 or less when the work hardening index is maximum.

도 2에서, 최대 가공경화지수를 나타내는 지점 A의 x 좌표인 변형량 값이 0.2 이하로 도출되면, 심가공 시 과도한　가공경화 발생을 억제할 수 있다.In FIG. 2 , when the value of the deformation amount, which is the x-coordinate of the point A representing the maximum work hardening index, is derived to be 0.2 or less, excessive work hardening during deep machining can be suppressed.

개시된 실시예에 따른 표면 특성이 향상된 페라이트계 스테인리스강은 가공경화지수가 최대일 때의 진변형율 값과 가공경화지수가 0일 때의 진변형율 값의 차이가 0.11 이상이다. In the ferritic stainless steel with improved surface properties according to the disclosed embodiment, the difference between the true strain value when the work hardening index is maximum and the true strain value when the work hardening index is 0 is 0.11 or more.

다시 말해, 작은 변형량에서 최대 가공경화 지수를 나타내고, 과도한 강도 증가없이 지속적인 변형을 확보할 수 있다면, 오스테나이트계 스테인리스강의 연신율을 확보하면서도 2단 이상의 다단 가공 적용 시, 크랙 발생을 방지할 수 있다.In other words, if the maximum work hardening index is exhibited at a small amount of deformation and continuous deformation can be secured without excessive strength increase, cracks can be prevented when applying two or more stages of multi-stage machining while securing the elongation of the austenitic stainless steel.

상기 합금원소 조성 범위 및 관계식을 만족하는 개시된 실시예에 따른 표면 특성이 향상된 페라이트계 스테인리스강은 35% 이상의 연신율, 360MPa 이상 의 인장강도를 확보할 수 있다.The ferritic stainless steel with improved surface properties according to the disclosed embodiment satisfying the alloy element composition range and relational expression can secure an elongation of 35% or more and a tensile strength of 360 MPa or more.

뿐만 아니라, 만족하는 개시된 실시예에 따른 표면 특성이 향상된 페라이트계 스테인리스강은 드로잉비 1.7 내지 4.3 조건으로 2단 이상의 성형시, 5단 성형까지 균열이 발생하지 않는다. In addition, the ferritic stainless steel with improved surface properties according to the disclosed embodiment does not crack when formed in two or more stages under the condition of a drawing ratio of 1.7 to 4.3, and cracks do not occur until forming in 5 stages.

이하 본 발명의 바람직한 실시예를 통해 보다 상세히 설명하기로 한다.Hereinafter, it will be described in more detail through preferred embodiments of the present invention.

실시예Example

하기 [표 1]의 성분범위에 대하여, 연속주조공정을 통해 200mm 두께의 슬라브를 제조하고, 1,250℃에서 2시간 가열한 후 6mm 두께까지 열간압연을 진행 하였으며, 열간압연 이후 1,150℃에서 열연소둔을 진행하고 권취하였다. 다음으로, 열연코일은 2회에 걸쳐 1mm 두께까지 냉간압연 및 냉연소둔을 진행하였다. 냉간압연은 패스당 압하율 30~70% 범위에서 실시하였으며, 냉연 소둔은 1100~1200℃ 온도의 가열로에서 5분 이내로 실시하였다.With respect to the component ranges shown in Table 1 below, 200 mm thick slabs were manufactured through a continuous casting process, heated at 1,250 ° C for 2 hours, and then hot rolled to a thickness of 6 mm was performed. After hot rolling, hot rolling annealing was performed at 1,150 ° C. proceeded and wound up. Next, the hot rolled coil was subjected to cold rolling and cold annealing to a thickness of 1 mm over two times. Cold rolling was carried out at a reduction ratio of 30 to 70% per pass, and cold rolling annealing was carried out within 5 minutes in a heating furnace at a temperature of 1100 to 1200 °C.

하기 표 1에서, 식(1) 및 식(2) 값은, 각 합금원소의 중량%를 하기 식 (1) 및 식(2)에 대입하여 도출한 값이다. In Table 1, the values of formulas (1) and (2) are values derived by substituting the weight % of each alloying element into the following formulas (1) and (2).

식(1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N) Formula (1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N)

식(2): 2.4*Cr+1.7*Mo+3.9*Si-2.1*Ni-Mn-0.4*Cu-58*C-64*N-13Formula (2): 2.4*Cr+1.7*Mo+3.9*Si-2.1*Ni-Mn-0.4*Cu-58*C-64*N-13

구분division CC SiSi MnMn PP SS CrCr NiNi MoMo CuCu NN AlAl TiTi BB 식(1)Formula (1) 식(2)Equation (2) 실시예 1Example 1 0.0220.022 0.390.39 0.790.79 0.0300.030 0.00110.0011 21.421.4 10.310.3 0.50.5 0.80.8 0.2060.206 0.0030.003 0.0020.002 0.00230.0023 67.467.4 3.533.53 실시예 2Example 2 0.0200.020 0.400.40 0.700.70 0.0320.032 0.00100.0010 20.920.9 10.510.5 0.60.6 1.01.0 0.1900.190 0.0030.003 0.0020.002 0.00230.0023 67.467.4 3.223.22 실시예 3Example 3 0.0220.022 0.510.51 0.650.65 0.0280.028 0.00100.0010 21.221.2 10.610.6 0.50.5 0.70.7 0.2000.200 0.0030.003 0.0020.002 0.00230.0023 67.667.6 3.563.56 실시예 4Example 4 0.0250.025 0.390.39 0.800.80 0.0080.008 0.00350.0035 21.021.0 10.110.1 0.60.6 0.80.8 0.2100.210 0.0040.004 0.0020.002 0.00220.0022 67.167.1 2.712.71 실시예 5Example 5 0.0230.023 0.400.40 0.640.64 0.0100.010 0.00050.0005 21.321.3 10.310.3 0.60.6 0.90.9 0.2100.210 0.0040.004 0.0020.002 0.00220.0022 68.268.2 3.303.30 실시예 6Example 6 0.0290.029 0.380.38 0.810.81 0.0340.034 0.00110.0011 21.321.3 9.39.3 0.50.5 0.70.7 0.2240.224 0.0030.003 0.0030.003 0.00220.0022 65.565.5 3.963.96 실시예 7Example 7 0.0420.042 0.360.36 0.710.71 0.0300.030 0.00070.0007 21.021.0 9.49.4 0.20.2 2.42.4 0.1920.192 0.0030.003 0.0030.003 0.00220.0022 69.069.0 2.932.93 실시예 8Example 8 0.0480.048 0.910.91 0.620.62 0.0300.030 0.00080.0008 21.321.3 9.69.6 0.50.5 0.70.7 0.2240.224 0.0030.003 0.0030.003 0.00220.0022 67.967.9 4.454.45 실시예 9Example 9 0.0180.018 0.440.44 0.740.74 0.0290.029 0.00120.0012 21.521.5 10.510.5 0.60.6 0.70.7 0.2150.215 0.0040.004 0.0020.002 0.00250.0025 68.468.4 3.443.44 실시예 10Example 10 0.0100.010 0.400.40 0.830.83 0.0250.025 0.00090.0009 21.221.2 9.39.3 0.70.7 0.80.8 0.2450.245 0.0040.004 0.0020.002 0.00250.0025 65.965.9 3.623.62 실시예 11Example 11 0.0180.018 0.490.49 0.760.76 0.0220.022 0.00120.0012 22.022.0 11.011.0 0.80.8 0.60.6 0.2150.215 0.0040.004 0.0020.002 0.00250.0025 70.670.6 4.144.14 실시예 12Example 12 0.0270.027 0.390.39 0.860.86 0.0320.032 0.00110.0011 21.421.4 10.010.0 0.60.6 0.70.7 0.2380.238 0.0030.003 0.0020.002 0.00230.0023 68.368.3 1.861.86 실시예 13Example 13 0.0260.026 1.181.18 0.760.76 0.0300.030 0.00100.0010 21.121.1 10.210.2 0.50.5 0.60.6 0.2300.230 0.0030.003 0.0020.002 0.00230.0023 68.668.6 4.364.36 실시예 14Example 14 0.0120.012 1.391.39 0.720.72 0.0320.032 0.00070.0007 20.420.4 12.312.3 0.60.6 0.70.7 0.1800.180 0.0030.003 0.0020.002 0.00230.0023 71.671.6 3.313.31 실시예 15Example 15 0.0150.015 1.431.43 0.860.86 0.0290.029 0.00110.0011 19.519.5 10.210.2 0.50.5 0.80.8 0.2380.238 0.0030.003 0.0020.002 0.00230.0023 67.767.7 1.441.44 실시예 16Example 16 0.0420.042 1.461.46 1.501.50 0.0320.032 0.00090.0009 19.219.2 10.710.7 0.70.7 0.70.7 0.1800.180 0.0030.003 0.0020.002 0.00230.0023 67.467.4 1.751.75 실시예 17Example 17 0.0260.026 0.390.39 3.403.40 0.0320.032 0.00110.0011 21.421.4 9.29.2 0.60.6 0.70.7 0.2360.236 0.0030.003 0.0020.002 0.00230.0023 65.865.8 1.181.18 실시예 18Example 18 0.0110.011 1.201.20 0.860.86 0.0340.034 0.00110.0011 17.617.6 10.210.2 1.61.6 1.51.5 0.1820.182 0.0030.003 0.0020.002 0.00230.0023 66.866.8 1.481.48 실시예 19Example 19 0.0270.027 0.890.89 0.920.92 0.0320.032 0.00120.0012 17.217.2 9.29.2 1.91.9 1.81.8 0.1800.180 0.0030.003 0.0020.002 0.00230.0023 65.265.2 0.940.94 실시예 20Example 20 0.0110.011 0.200.20 0.320.32 0.0330.033 0.00220.0022 20.720.7 13.713.7 0.80.8 0.20.2 0.1100.110 0.0030.003 0.0020.002 0.00230.0023 70.370.3 1.971.97 실시예 21Example 21 0.0290.029 0.370.37 0.970.97 0.0350.035 0.00090.0009 21.221.2 9.59.5 0.50.5 0.70.7 0.2100.210 0.0040.004 0.0030.003 0.00190.0019 65.065.0 3.803.80 실시예 22Example 22 0.0360.036 0.410.41 1.261.26 0.0310.031 0.00190.0019 21.021.0 9.49.4 0.60.6 0.80.8 0.2090.209 0.0040.004 0.0030.003 0.00190.0019 65.365.3 3.283.28 실시예 23Example 23 0.0250.025 0.290.29 1.821.82 0.0200.020 0.00310.0031 21.321.3 9.69.6 0.50.5 2.02.0 0.1700.170 0.0040.004 0.0030.003 0.0020.002 67.267.2 5.015.01 비교예 1Comparative Example 1 0.0240.024 0.670.67 0.670.67 0.0340.034 0.00110.0011 17.517.5 12.012.0 1.91.9 0.20.2 0.0210.021 0.0020.002 0.0030.003 0.0020.002 60.860.8 6.186.18 비교예 2Comparative Example 2 0.0220.022 0.660.66 0.770.77 0.0300.030 0.00080.0008 17.317.3 12.112.1 2.02.0 0.30.3 0.0200.020 0.0030.003 0.0020.002 0.00210.0021 61.261.2 5.825.82 비교예 3Comparative Example 3 0.0200.020 0.600.60 0.680.68 0.0250.025 0.00060.0006 17.717.7 12.312.3 1.91.9 0.30.3 0.0220.022 0.0040.004 0.0020.002 0.00190.0019 62.062.0 5.885.88 비교예 4Comparative Example 4 0.0190.019 0.470.47 1.061.06 0.0300.030 0.00120.0012 16.216.2 10.110.1 2.02.0 0.40.4 0.0150.015 0.0040.004 0.0020.002 0.00190.0019 53.853.8 6.696.69 비교예 5Comparative Example 5 0.0110.011 0.480.48 1.001.00 0.0290.029 0.00110.0011 16.516.5 10.510.5 1.81.8 0.20.2 0.0160.016 0.0030.003 0.0020.002 0.00190.0019 54.054.0 6.746.74 비교예 6Comparative Example 6 0.0200.020 0.420.42 1.101.10 0.0340.034 0.00210.0021 16.116.1 10.010.0 2.02.0 0.30.3 0.0140.014 0.0030.003 0.0030.003 0.00190.0019 53.253.2 6.526.52 비교예 7Comparative Example 7 0.0970.097 0.400.40 11.2011.20 0.0320.032 0.00070.0007 18.718.7 6.06.0 0.10.1 0.10.1 0.3560.356 0.0030.003 0.0030.003 0.0020.002 60.360.3 -18.6-18.6 비교예 8Comparative Example 8 0.0950.095 0.470.47 11.0011.00 0.0330.033 0.00120.0012 18.918.9 6.16.1 0.20.2 0.20.2 0.3600.360 0.0040.004 0.0030.003 0.0020.002 61.461.4 -17.9-17.9 비교예 9Comparative Example 9 0.0410.041 0.710.71 9.109.10 0.0310.031 0.00110.0011 20.220.2 6.66.6 0.10.1 0.10.1 0.3170.317 0.0040.004 0.0030.003 0.00210.0021 59.159.1 -7.3-7.3 비교예 10Comparative Example 10 0.0400.040 1.221.22 9.419.41 0.0200.020 0.00180.0018 21.721.7 5.85.8 0.20.2 0.10.1 0.3200.320 0.0020.002 0.0020.002 0.00230.0023 59.059.0 -0.3-0.3 비교예 11Comparative Example 11 0.0980.098 0.700.70 15.1015.10 0.0180.018 0.00110.0011 17.617.6 5.35.3 0.30.3 0.10.1 0.4380.438 0.0030.003 0.0020.002 0.00230.0023 61.961.9 -27.5-27.5 비교예 12Comparative Example 12 0.0920.092 0.680.68 14.8214.82 0.0340.034 0.00280.0028 17.817.8 5.65.6 0.20.2 0.20.2 0.4400.440 0.0030.003 0.0020.002 0.00190.0019 62.962.9 -27.4-27.4 비교예 13Comparative Example 13 0.2000.200 0.420.42 14.5014.50 0.0240.024 0.00160.0016 17.017.0 1.51.5 0.10.1 0.20.2 0.3870.387 0.0030.003 0.0030.003 0.00190.0019 51.951.9 -24.5-24.5 비교예 14Comparative Example 14 0.1930.193 0.400.40 14.4414.44 0.0290.029 0.00240.0024 17.217.2 1.31.3 0.10.1 0.30.3 0.3900.390 0.0040.004 0.0030.003 0.00190.0019 51.651.6 -23.4-23.4 비교예 15Comparative Example 15 0.0580.058 0.330.33 14.0114.01 0.0300.030 0.00150.0015 17.317.3 4.54.5 0.20.2 0.10.1 0.3620.362 0.0040.004 0.0030.003 0.00220.0022 52.852.8 -19.9-19.9 비교예 16Comparative Example 16 0.0610.061 0.360.36 14.1014.10 0.0300.030 0.00100.0010 17.117.1 4.44.4 0.30.3 0.20.2 0.3600.360 0.0020.002 0.0040.004 0.00220.0022 52.952.9 -20.0-20.0 비교예 17Comparative Example 17 0.0600.060 0.410.41 1.101.10 0.0290.029 0.00320.0032 18.118.1 5.05.0 0.30.3 0.20.2 0.0410.041 0.0040.004 0.0030.003 0.00220.0022 39.839.8 14.7714.77 비교예 18Comparative Example 18 0.0650.065 0.390.39 0.540.54 0.0320.032 0.00170.0017 18.018.0 5.15.1 0.20.2 0.10.1 0.0400.040 0.0040.004 0.0030.003 0.00230.0023 39.639.6 14.4414.44 비교예 19Comparative Example 19 0.0660.066 0.400.40 0.330.33 0.0290.029 0.00080.0008 18.218.2 5.25.2 0.20.2 0.10.1 0.0450.045 0.0040.004 0.0030.003 0.00190.0019 40.340.3 14.6914.69 비교예 20Comparative Example 20 0.0470.047 0.420.42 1.021.02 0.0200.020 0.00240.0024 18.318.3 5.45.4 0.10.1 0.20.2 0.0380.038 0.0040.004 0.0030.003 0.00190.0019 40.040.0 15.1315.13 비교예 21Comparative Example 21 0.0720.072 0.400.40 1.101.10 0.0100.010 0.00110.0011 18.018.0 5.25.2 0.10.1 0.20.2 0.0360.036 0.0040.004 0.0020.002 0.00240.0024 40.140.1 13.4613.46

각 강판에 대하여, 다단 성형 횟수 및 가공경화지수를 측정하였다. 구체적으로, 딥 드로잉 성형은 직경 85mm의 블랭크(Blank)를 1단 펀치 직경 50mm, 2단 펀치 직경 38mm, 3단 펀치 직경 30mm, 4단 펀치 직경 24mm, 5단 펀치 직경 20mm로 5단계에 걸쳐 실시하였다. 각 단계별 드로잉비는 1단에서 1.7, 2단에서 2.2, 3단에서 2.8, 4단에서 3.5, 5단에서 4.3이다. For each steel sheet, the number of multi-stage forming and work hardening index were measured. Specifically, in deep drawing forming, a blank with a diameter of 85 mm was used in 5 steps with a diameter of 1st punch 50mm, 2nd punch diameter 38mm, 3rd stage punch diameter 30mm, 4th stage punch diameter 24mm, and 5th stage punch diameter 20mm. did. The drawing ratio for each stage is 1.7 in 1st stage, 2.2 in 2nd stage, 2.8 in 3rd stage, 3.5 in 4th stage, and 4.3 in 5th stage.

각 단계에서, 가공품의 성형 후 48시간 경과할 때까지 크랙 발생이 없는 경우를 기준으로 하여, 최대 성형 횟수를 하기 [표 2]에 기재하였다. In each step, the maximum number of moldings is described in [Table 2] below on the basis of the case in which no cracks occur until 48 hours have elapsed after the molding of the processed product.

다음으로, JIS13B호 인장 시험편 규격으로 인장 실험을 진행하였으며, 실험 결과 얻어진 응력-변형률 값으로부터 진응력-진변형율을 계산하고, 최대 가공경화지수(a), 가공경화지수가 최대일 때의 진변형율 값(b), 가공경화지수가 0일 때의 진변형율 값(c) 및 가공경화지수가 최대일 때의 진변형율 값(b)과 가공경화지수가 0일 때의 진변형율 값(c)의 차이를 도출하여 하기 [표 2]에 기재하였다.Next, a tensile test was carried out according to the JIS13B tensile test specimen standard, and the true stress-true strain was calculated from the stress-strain value obtained as a result of the test, and the maximum work hardening index (a) and the true strain rate when the work hardening index was the maximum. Value (b), true strain value (c) when work hardening index is 0, true strain value (b) when work hardening index is maximum, and true strain value (c) when work hardening index is 0 The difference was derived and described in [Table 2] below.

또한, 인장실험 결과 측정된 인장강도(Tensile Strength, MPa) 및 연신율(Elongation, %)을 하기 [표 2]에 기재하였다.In addition, the measured tensile strength (Tensile Strength, MPa) and elongation (Elongation, %) as a result of the tensile test are described in [Table 2] below.

구분division 최대 가공횟수Maximum number of machining (a)(a) (b)(b) (c)(c) (b)-(c)(b)-(c) 인장강도tensile strength 연신율elongation 실시예 1Example 1 55 0.370.37 0.170.17 0.290.29 0.120.12 450450 37.437.4 실시예 2Example 2 55 0.360.36 0.180.18 0.290.29 0.120.12 451451 37.537.5 실시예 3Example 3 55 0.360.36 0.180.18 0.290.29 0.120.12 450450 37.537.5 실시예 4Example 4 55 0.300.30 0.170.17 0.300.30 0.140.14 441441 42.242.2 실시예 5Example 5 55 0.270.27 0.170.17 0.300.30 0.130.13 467467 41.041.0 실시예 6Example 6 55 0.350.35 0.170.17 0.320.32 0.150.15 401401 46.046.0 실시예 7Example 7 55 0.350.35 0.180.18 0.320.32 0.150.15 404404 46.746.7 실시예 8Example 8 55 0.350.35 0.180.18 0.320.32 0.140.14 402402 46.246.2 실시예 9Example 9 55 0.360.36 0.170.17 0.320.32 0.150.15 386386 45.645.6 실시예 10Example 10 55 0.360.36 0.170.17 0.320.32 0.150.15 387387 45.445.4 실시예 11Example 11 55 0.360.36 0.170.17 0.320.32 0.150.15 388388 45.545.5 실시예 12Example 12 55 0.390.39 0.170.17 0.310.31 0.140.14 420420 42.442.4 실시예 13Example 13 55 0.390.39 0.170.17 0.310.31 0.140.14 421421 42.542.5 실시예 14Example 14 55 0.390.39 0.170.17 0.310.31 0.140.14 419419 42.442.4 실시예 15Example 15 55 0.380.38 0.150.15 0.300.30 0.150.15 441441 39.539.5 실시예 16Example 16 55 0.380.38 0.160.16 0.310.31 0.150.15 422422 40.440.4 실시예 17Example 17 55 0.380.38 0.160.16 0.300.30 0.150.15 436436 40.040.0 실시예 18Example 18 55 0.410.41 0.160.16 0.330.33 0.170.17 402402 42.542.5 실시예 19Example 19 55 0.410.41 0.160.16 0.330.33 0.170.17 405405 42.842.8 실시예 20Example 20 55 0.410.41 0.160.16 0.330.33 0.170.17 399399 42.942.9 실시예 21Example 21 55 0.360.36 0.170.17 0.330.33 0.160.16 366366 46.946.9 실시예 22Example 22 55 0.370.37 0.150.15 0.330.33 0.180.18 373373 47.147.1 실시예 23Example 23 55 0.370.37 0.170.17 0.330.33 0.160.16 374374 47.147.1 비교예 1Comparative Example 1 33 0.330.33 0.270.27 0.340.34 0.070.07 386386 39.539.5 비교예 2Comparative Example 2 33 0.330.33 0.260.26 0.340.34 0.080.08 391391 40.240.2 비교예 3Comparative Example 3 22 0.320.32 0.270.27 0.330.33 0.060.06 379379 41.141.1 비교예 4Comparative Example 4 33 0.380.38 0.280.28 0.370.37 0.090.09 334334 47.847.8 비교예 5Comparative Example 5 33 0.370.37 0.270.27 0.370.37 0.100.10 335335 47.747.7 비교예 6Comparative Example 6 33 0.390.39 0.240.24 0.370.37 0.130.13 320320 48.048.0 비교예 7Comparative Example 7 44 0.280.28 0.240.24 0.310.31 0.070.07 556556 42.442.4 비교예 8Comparative Example 8 44 0.320.32 0.240.24 0.340.34 0.110.11 522522 46.946.9 비교예 9Comparative Example 9 44 0.300.30 0.220.22 0.330.33 0.110.11 500500 44.744.7 비교예 10Comparative Example 10 33 0.280.28 0.210.21 0.310.31 0.100.10 532532 42.142.1 비교예 11Comparative Example 11 44 0.330.33 0.210.21 0.350.35 0.140.14 516516 47.147.1 비교예 12Comparative Example 12 44 0.290.29 0.230.23 0.320.32 0.090.09 587587 44.044.0 비교예 13Comparative Example 13 1One 0.380.38 0.310.31 0.380.38 0.060.06 531531 50.850.8 비교예 14Comparative Example 14 22 0.350.35 0.300.30 0.370.37 0.070.07 598598 49.149.1 비교예 15Comparative Example 15 33 0.300.30 0.240.24 0.320.32 0.070.07 544544 42.742.7 비교예 16Comparative Example 16 33 0.320.32 0.230.23 0.340.34 0.110.11 499499 45.645.6 비교예 17Comparative Example 17 1One 0.330.33 0.280.28 0.320.32 0.030.03 687687 38.838.8 비교예 18Comparative Example 18 22 0.340.34 0.270.27 0.320.32 0.050.05 698698 39.339.3 비교예 19Comparative Example 19 33 0.320.32 0.280.28 0.310.31 0.030.03 695695 38.038.0 비교예 20Comparative Example 20 22 0.330.33 0.270.27 0.320.32 0.050.05 691691 38.838.8 비교예 21Comparative Example 21 1One 0.340.34 0.270.27 0.320.32 0.050.05 689689 39.339.3

표 2를 참조하면, 본 발명이 제시하는 합금 조성과 식(1)의 값 및 식(2)의 값의 범위를 만족하는 실시예 1 내지 23의 경우, 350 MPa 이상의 인장강도 확보가 가능할 뿐만 아니라, 35% 이상의 우수한 연신율을 확보할 수 있음을 확인하였다. 또한, 드로잉비 1.7 내지 4.3 조건으로 2단 이상의 성형시, 5단 성형까지 균열이 발생하지 않아 복잡한 형상의 딥 드로잉 성형이 요구되는 분야에 적용이 가능하다.Referring to Table 2, in the case of Examples 1 to 23 that satisfy the alloy composition and the values of Equation (1) and the ranges of values of Equation (2) presented by the present invention, it is possible to secure a tensile strength of 350 MPa or more, as well as , it was confirmed that an excellent elongation of 35% or more could be secured. In addition, when forming two or more stages with a drawing ratio of 1.7 to 4.3, cracks do not occur until five stages of forming, so it can be applied to fields requiring deep drawing forming of complex shapes.

비교예 1 내지 6, 비교예 17 내지 21은 식 (1)의 값이 63에 미달하여 가공 경화시 계속적인 강도 증가가 나타날 뿐만 아니라, 식 (2)의 값이 5.5를 초과하여 변형에 의한 마르텐사이트 변태가 활발하게 일어나 다단 성형시 크랙발생이 빈번하였다.In Comparative Examples 1 to 6 and Comparative Examples 17 to 21, the value of Equation (1) was less than 63, resulting in a continuous increase in strength during work hardening, and the value of Equation (2) exceeded 5.5, resulting in martens due to deformation. Site transformation was active and cracks were frequent during multi-stage molding.

비교예 7 내지 16은 식 (1)의 값이 63에 미달하고, 식 (2)의 값이 0에 미달하여 가공시 쌍정 형성에 의한 급격한 강도 증가가 발생하였다. 쌍정 형성에 의한 강도 증가가 변형량에 따라 지속적으로 일어나고, 이로 인하여 심가공시 응력 불균일이 발생하여 충분한 깊이의 성형량을 확보할 수 없었다.In Comparative Examples 7 to 16, the value of Equation (1) was less than 63, and the value of Equation (2) was less than 0, so a sharp increase in strength occurred due to twin crystal formation during processing. The increase in strength due to twin crystal formation continuously occurred according to the amount of deformation, which caused stress non-uniformity during deep machining, so that it was not possible to secure a forming amount of sufficient depth.

이와 같이, 개시된 실시예에 따르면, 합금성분과 관계식을 제어함으로써, 드로잉비 1.7 내지 4.3 조건으로 2단 이상의 성형시, 5단 성형까지 균열이 발생하지 않고, 35% 이상의 연신율, 360MPa 이상의 인장강도를 확보한 오스테나이트계 스테인리스강을 제조할 수 있다.As such, according to the disclosed embodiment, by controlling the alloy component and the relational expression, when forming two or more stages under the condition of a drawing ratio of 1.7 to 4.3, cracks do not occur until five stages forming, an elongation of 35% or more, and a tensile strength of 360 MPa or more The secured austenitic stainless steel can be manufactured.

상술한 바에 있어서, 본 발명의 예시적인 실시예들을 설명하였지만, 본 발명은 이에 한정되지 않으며 해당 기술 분야에서 통상의 지식을 가진 자라면 다음에 기재하는 특허청구범위의 개념과 범위를 벗어나지 않는 범위 내에서 다양한 변경 및 변형이 가능함을 이해할 수 있을 것이다.In the foregoing, exemplary embodiments of the present invention have been described, but the present invention is not limited thereto, and those of ordinary skill in the art are within the scope not departing from the concept and scope of the claims described below. It will be understood that various changes and modifications are possible.

본 발명은 심가공이 수반되는 분야 등 다양한 산업분야에 이용가능하다.The present invention can be used in various industrial fields such as fields involving deep machining.

Claims (8)

중량%로, C: 0.01 내지 0.05%, N: 0.01 내지 0.25%, Si: 1.5% 이하(0은 제외), Mn: 0.3 내지 3.5%, Cr: 17.0 내지 22.0%, Ni: 9.0 내지 14.0%, Mo: 2.0% 이하(0은 제외), Cu: 0.2 내지 2.5%, 나머지 Fe 및 불가피한 불순물을 포함하고, By weight%, C: 0.01 to 0.05%, N: 0.01 to 0.25%, Si: 1.5% or less (excluding 0), Mn: 0.3 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 2.0% or less (excluding 0), Cu: 0.2 to 2.5%, remaining Fe and unavoidable impurities, 하기 식(1)을 만족하는 심가공성이 향상된 오스테나이트계 스테인리스강.Austenitic stainless steel with improved deep workability satisfying the following formula (1). 식(1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N) ≥ 63Equation (1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N) ≥ 63 (여기서, Cr, Si, Mo, Ni, Cu, C, N는 각 원소의 중량%를 의미한다.)(Here, Cr, Si, Mo, Ni, Cu, C, and N mean weight% of each element.) 제 1항에 있어서,The method of claim 1, 하기 식(2)를 만족하는 심가공성이 향상된 오스테나이트계 스테인리스강.Austenitic stainless steel with improved deep workability satisfying the following formula (2). 식(2): 0 < 2.4*Cr+1.7*Mo+3.9*Si-2.1*Ni-Mn-0.4*Cu-58*C-64*N-13 < 5.5Equation (2): 0 < 2.4*Cr+1.7*Mo+3.9*Si-2.1*Ni-Mn-0.4*Cu-58*C-64*N-13 < 5.5 (여기서, Cr, Mo, Si, Ni, Mn, Cu, C, N는 각 원소의 중량%를 의미한다.)(Here, Cr, Mo, Si, Ni, Mn, Cu, C, and N mean weight% of each element.) 제 1항에 있어서,The method of claim 1, Al: 0.04% 이하(0은 제외), Ti: 0.003% 이하(0은 제외), B: 0.0025% 이하(0은 제외), P: 0.035% 이하 및 S: 0.0035% 이하 중 1종 이상을 더 포함하는 심가공성이 향상된 오스테나이트계 스테인리스강.Al: 0.04% or less (excluding 0), Ti: 0.003% or less (excluding 0), B: 0.0025% or less (excluding 0), P: 0.035% or less, and S: 0.0035% or less Austenitic stainless steel with improved deep machinability. 제 1항에 있어서,The method of claim 1, 하기 식(3)에서, 가공경화지수가 최대일 때의 진변형율 값이 0.2 이하인 심가공성이 향상된 오스테나이트계 스테인리스강.In the following formula (3), the true strain value at the maximum work hardening index is 0.2 or less, austenitic stainless steel with improved deep workability. 식(3): σ = Kεn Equation (3): σ = Kε n (여기서, σ는 응력, K는 강도계수, ε는 변형율, n은 가공경화지수를 의미한다.)(Where σ is the stress, K is the strength modulus, ε is the strain rate, and n is the work hardening index.) 제4항에 있어서,5. The method of claim 4, 가공경화지수가 최대일 때의 진변형율 값과 가공경화지수가 0일 때의 진변형율 값의 차이가 0.11 이상인 심가공성이 향상된 오스테나이트계 스테인리스강.Austenitic stainless steel with improved deep workability with a difference of 0.11 or more between the true strain value when the work hardening index is maximum and the true strain value when the work hardening index is 0. 제 1항에 있어서,The method of claim 1, 연신율이 35% 이상인 심가공성이 향상된 오스테나이트계 스테인리스강.Austenitic stainless steel with improved deep workability with an elongation of 35% or more. 제1항에 있어서, The method of claim 1, 인장강도가 360MPa 이상인 심가공성이 향상된 오스테나이트계 스테인리스강.Austenitic stainless steel with improved deep machinability with a tensile strength of 360 MPa or more. 제1항에 있어서, The method of claim 1, 드로잉비 1.7 내지 4.3 조건으로 다단 성형시,During multi-stage molding with a drawing ratio of 1.7 to 4.3, 5단 성형까지 균열이 발생하지 않는 것을 특징으로 하는 심가공성이 향상된 오스테나이트계 스테인리스강.Austenitic stainless steel with improved deep workability, characterized in that no cracks occur until five-step forming.
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