JP2023539140A - Austenitic stainless steel with improved deep drawability - Google Patents

Austenitic stainless steel with improved deep drawability Download PDF

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JP2023539140A
JP2023539140A JP2023512177A JP2023512177A JP2023539140A JP 2023539140 A JP2023539140 A JP 2023539140A JP 2023512177 A JP2023512177 A JP 2023512177A JP 2023512177 A JP2023512177 A JP 2023512177A JP 2023539140 A JP2023539140 A JP 2023539140A
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stainless steel
austenitic stainless
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work hardening
deep drawability
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キョン－フン キム，
キム，ジス
ゾンジン ジョン，
ミ－ナム パク，
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ポスコ カンパニー リミテッド
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Abstract

【課題】加工硬化による強度増加を最小化することによって深絞り加工の適用時に成形加工性を確保し得るオーステナイト系ステンレス鋼を提供する。【解決手段】重量％で、Ｃ：０．０１～０．０５％、Ｎ：０．０１～０．２５％、Ｓｉ：１．５％以下（０は除外）、Ｍｎ：０．３～３．５％、Ｃｒ：１７．０～２２．０％、Ｎｉ：９．０～１４．０％、Ｍｏ：２．０％以下（０は除外）、Ｃｕ：０．２～２．５％、を含み、残りがＦｅ及び不可避な不純物からなり、下記式（１）を満足することを特徴とする。式（１）：Ｃｒ＋Ｓｉ＋２＊Ｍｏ＋３＊（Ｎｉ＋Ｃｕ）＋５０＊（Ｃ＋Ｎ）≧６３ここで、Ｃｒ、Ｓｉ、Ｍｏ、Ｎｉ、Ｃｕ、Ｃ、Ｎは、各元素の重量％を意味する。【選択図】図１The present invention provides an austenitic stainless steel that can ensure formability during deep drawing by minimizing strength increase due to work hardening. [Solution] In weight%, C: 0.01 to 0.05%, N: 0.01 to 0.25%, Si: 1.5% or less (0 is excluded), Mn: 0.3 to 3 .5%, Cr: 17.0-22.0%, Ni: 9.0-14.0%, Mo: 2.0% or less (0 is excluded), Cu: 0.2-2.5%, The remainder consists of Fe and unavoidable impurities, and satisfies the following formula (1). Formula (1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N)≧63 Here, Cr, Si, Mo, Ni, Cu, C, and N mean the weight percent of each element. [Selection diagram] Figure 1

Description

本発明は、深絞り性（Ｄｅｅｐ Ｄｒａｗｉｎｇ）が向上したオーステナイト系ステンレス鋼に係り、より詳しくは、板材を３次元部品に変換させる深絞り加工の適用時にクラックが発生しない深絞り性が向上したオーステナイト系ステンレス鋼に関する。 The present invention relates to an austenitic stainless steel with improved deep drawing properties, and more specifically, an austenitic stainless steel with improved deep drawing properties that prevents cracks from occurring when applying deep drawing processing to convert plate materials into three-dimensional parts. Regarding stainless steel.

最近、製品価格の競争が激しくなるにしたがって、部品に適用される素材の原価節減が要求されている。深絞り加工は、溶接、応力除去熱処理などのように付加的な工程を省略し得るので、製造コストの節減に効果的な方法である。一方、コップ、バッテリーなどのように円筒状の成形が伴う場合には、深絞り性に優れた素材が要求されている。
オーステナイト系ステンレス鋼材は、延伸率に優れているため複雑な形状を作るのに問題がなく、加工硬化能に優れているため深絞り加工の伴う多様な分野に適用されている鋼種である。
一般的に、オーステナイト系ステンレス鋼は、冷間加工時に加工硬化が起きながら形態が変形される。このとき、オーステナイト系ステンレス鋼が加工硬化能に優れると成形が容易であることが知られている。 Recently, as product price competition has become more intense, there is a need to reduce the cost of materials used in parts. Deep drawing is an effective method for reducing manufacturing costs because additional steps such as welding, stress relief heat treatment, etc. can be omitted. On the other hand, in cases where cylindrical molding is involved, such as in cups and batteries, materials with excellent deep drawability are required.
Austenitic stainless steel materials have an excellent elongation rate, so there is no problem in making complex shapes, and because they have excellent work hardening ability, they are a steel type that is used in a variety of fields that involve deep drawing.
In general, austenitic stainless steel undergoes work hardening and deforms during cold working. At this time, it is known that austenitic stainless steel has excellent work hardenability and is easy to form.

しかし、オーステナイト系ステンレス鋼の深絞り加工を適用する場合には、加工硬化によって持続的に強度が上昇して素材に局所的な応力集中が発生し、結局、破損されるという問題が発生する。
一方、加工硬化による強度増加問題を解決するために中間熱処理を導入する場合を考慮し得るが、工程時間的／工程費用的な側面から制約がある。
したがって、深絞り加工の適用時に、中間熱処理工程を省略し得ると共に加工硬化による強度増加を最小化し得ることによって、深絞り加工の素材として適用可能なオーステナイト系ステンレス鋼の開発が要求される。 However, when applying deep drawing to austenitic stainless steel, the problem arises that the strength continuously increases due to work hardening, causing local stress concentration in the material and eventually causing it to break.
On the other hand, it is possible to consider introducing an intermediate heat treatment to solve the problem of strength increase due to work hardening, but there are restrictions from the aspects of process time and process cost.
Therefore, there is a need to develop an austenitic stainless steel that can be used as a material for deep drawing by eliminating the intermediate heat treatment step and minimizing the increase in strength due to work hardening.

本発明の目的とするところは、加工硬化による強度増加を最小化することによって深絞り加工の適用時に成形加工性を確保し得るオーステナイト系ステンレス鋼を提供することである。 An object of the present invention is to provide an austenitic stainless steel that can ensure formability when deep drawing is applied by minimizing the increase in strength due to work hardening.

本発明による深絞り性が向上したオーステナイト系ステンレス鋼は、重量％で、Ｃ：０．０１～０．０５％、Ｎ：０．０１～０．２５％、Ｓｉ：１．５％以下（０は除外）、Ｍｎ：０．３～３．５％、Ｃｒ：１７．０～２２．０％、Ｎｉ：９．０～１４．０％、Ｍｏ：２．０％以下（０は除外）、Ｃｕ：０．２～２．５％、を含み、残りがＦｅ及び不可避な不純物からなり、下記式（１）を満足する。
式（１）：Ｃｒ＋Ｓｉ＋２＊Ｍｏ＋３＊（Ｎｉ＋Ｃｕ）＋５０＊（Ｃ＋Ｎ）≧６３
ここで、Ｃｒ、Ｓｉ、Ｍｏ、Ｎｉ、Ｃｕ、Ｃ、Ｎは、各元素の重量％を意味する。 The austenitic stainless steel with improved deep drawability according to the present invention has a weight percentage of C: 0.01 to 0.05%, N: 0.01 to 0.25%, and Si: 1.5% or less (0 are excluded), Mn: 0.3 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 2.0% or less (0 is excluded), Contains Cu: 0.2 to 2.5%, the remainder consists of Fe and unavoidable impurities, and satisfies the following formula (1).
Formula (1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N)≧63
Here, Cr, Si, Mo, Ni, Cu, C, and N mean the weight percent of each element.

また、本発明によると、下記式（２）を満足することができる。
式（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
ここで、Ｃｒ、Ｍｏ、Ｓｉ、Ｎｉ、Ｍｎ、Ｃｕ、Ｃ、Ｎは、各元素の重量％を意味する。 Further, according to the present invention, the following formula (2) can be satisfied.
Formula (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
Here, Cr, Mo, Si, Ni, Mn, Cu, C, and N mean the weight percent of each element.

また、本発明によると、Ａｌ：０．０４％以下（０は除外）、Ｔｉ：０．００３％以下（０は除外）、Ｂ：０．００２５％以下（０は除外）、Ｐ：０．０３５％以下及びＳ：０．００３５％以下のうち１種以上をさらに含むことができる。
また、本発明によると、下記式（３）で、加工硬化指数が最大であるときの真ひずみ率値が０．２以下であってもよい。
式（３）：σ＝Ｋεｎ
ここで、σは、応力、Ｋは、強度係数、εは、ひずみ率、ｎは、加工硬化指数を意味する。 Further, according to the present invention, Al: 0.04% or less (0 is excluded), Ti: 0.003% or less (0 is excluded), B: 0.0025% or less (0 is excluded), P: 0. 0.035% or less and S:0.0035% or less.
Further, according to the present invention, in the following formula (3), the true strain rate value when the work hardening index is maximum may be 0.2 or less.
Formula (3): σ=Kε n
Here, σ means stress, K means strength coefficient, ε means strain rate, and n means work hardening index.

また、本発明によると、加工硬化指数が最大であるときの真ひずみ率値と加工硬化指数が０であるときの真ひずみ率値の差が０．１１以上であり、
延伸率が３５％以上であり、
引張強度が３６０ＭＰａ以上であり、
ドローイング比１．７～４．３の条件で多段成形するとき、５段成形までクラックが発生しなくてもよい。 Further, according to the present invention, the difference between the true strain rate value when the work hardening index is maximum and the true strain rate value when the work hardening index is 0 is 0.11 or more,
The stretching ratio is 35% or more,
The tensile strength is 360 MPa or more,
When performing multi-stage molding under the conditions of a drawing ratio of 1.7 to 4.3, cracks do not need to occur until the 5th stage molding.

本発明によると、深絞り加工の適用時に中間熱処理工程を省略し得ると共に加工硬化による強度増加を最小化し得ることによって、深絞り加工の素材として適用可能なオーステナイト系ステンレス鋼を提供することができる。 According to the present invention, an intermediate heat treatment step can be omitted when deep drawing is applied, and strength increase due to work hardening can be minimized, thereby providing an austenitic stainless steel that can be used as a material for deep drawing. .

素材の引張実験による応力－ひずみ率の間の関係を説明するためのグラフである。FIG. 2 is a graph for explaining the relationship between stress and strain rate based on a tensile experiment of a material. FIG. 開示した実施例によるオーステナイト系ステンレス鋼の引張実験時の応力－ひずみ率の間の関係を加工硬化指数とともに示したグラフである。1 is a graph showing the relationship between stress and strain rate during a tensile test of austenitic stainless steel according to a disclosed example, along with a work hardening index.

本発明による深絞り性が向上したオーステナイト系ステンレス鋼は、重量％で、Ｃ：０．０１～０．０５％、Ｎ：０．０１～０．２５％、Ｓｉ：１．５％以下（０は除外）、Ｍｎ：０．３～３．５％、Ｃｒ：１７．０～２２．０％、Ｎｉ：９．０～１４．０％、Ｍｏ：２．０％以下（０は除外）、Ｃｕ：０．２～２．５％、を含み、残りがＦｅ及び不可避な不純物からなり、下記式（１）を満足する。
式（１）：Ｃｒ＋Ｓｉ＋２＊Ｍｏ＋３＊（Ｎｉ＋Ｃｕ）＋５０＊（Ｃ＋Ｎ）≧６３
ここで、Ｃｒ、Ｓｉ、Ｍｏ、Ｎｉ、Ｃｕ、Ｃ、Ｎは、各元素の重量％を意味する。 The austenitic stainless steel with improved deep drawability according to the present invention has a weight percentage of C: 0.01 to 0.05%, N: 0.01 to 0.25%, and Si: 1.5% or less (0 are excluded), Mn: 0.3 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 2.0% or less (0 is excluded), Contains Cu: 0.2 to 2.5%, the remainder consists of Fe and unavoidable impurities, and satisfies the following formula (1).
Formula (1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N)≧63
Here, Cr, Si, Mo, Ni, Cu, C, and N mean the weight percent of each element.

以下では、本発明について添付図面を参照して詳しく説明する。以下の実施例は、本発明が属する技術分野において通常の知識を有した者に本発明の思想を十分に伝達するために提示するものである。本発明は、ここで提示した実施例に限定されず、他の形態で具体化できる。図面は、本発明を明確にするために、説明と関係ない部分の図示を省略し、理解を助けるために構成要素のサイズを誇張して表現することができる。
また、任意の部分がある構成要素を「含む」というとき、これは、特に反対にする記載がない限り、他の構成要素を除外するものではなく、他の構成要素をさらに含むことができることを意味する。
単数の表現は、文脈上明白に例外がない限り、複数の表現を含む。 Hereinafter, the present invention will be explained in detail with reference to the accompanying drawings. The following examples are provided so that the spirit of the invention will be fully conveyed to those skilled in the art to which the invention pertains. The invention is not limited to the embodiments presented here, but can be embodied in other forms. In the drawings, in order to clarify the present invention, parts not related to the description may be omitted, and the sizes of components may be exaggerated to facilitate understanding.
Furthermore, when we say that any part "contains" a certain component, this does not mean excluding other components, unless there is a statement to the contrary, and it does not mean that it may further include other components. means.
References to the singular include the plural unless the context clearly dictates otherwise.

以下では、本発明を添付した図面を参照して詳しく説明する。
オーステナイト系ステンレス鋼は、延伸率が高く、成形性に優れているため多様な形状の製品に用いられる鋼種である。オーステナイト系ステンレス鋼は、応力を受けると常温で不安定なオーステナイト相からマルテンサイト相への変態、すなわち、塑性有機変態（Ｔｒａｎｓｆｏｒｍａｔｉｏｎ Ｉｎｄｕｃｅｄ Ｐｌａｓｔｉｃｉｔｙ）により変形が発生する。
このとき、生成されるマルテンサイト相は、強度が高いので、素材の強度も増加する。言い換えれば、オーステナイト系ステンレス鋼は、加工硬化（ｗｏｒｋ－ｈａｒｄｅｎｉｎｇ）により変形と強度増加が同時に行われる。加工硬化能は、加工硬化指数（ｗｏｒｋ－ｈａｒｄｅｎｉｎｇ ｅｘｐｏｎｅｎｔ）を用いて表示するが、加工硬化指数は、ひずみ率（ｓｔｒａｉｎ）によって変化する。
オーステナイト系ステンレス鋼の加工硬化能が優秀であると成形が容易であることが知られている。
しかし、オーステナイト系ステンレス鋼にブランク直径を減少させながら実行する深絞り加工を適用する場合には、加工硬化によって持続的に強度が上昇して素材に局所的な応力集中が発生し、結局、破損されるという問題が発生する。また、時効割れによって成形後に突然クラックが発生したりもする。
したがって、変形量が多い深絞り加工の成形では、素材全体に均一に変形が起き、変形の間強度の変化を最小化することが重要である。すなわち、オーステナイト系ステンレス鋼の深絞り性を向上させるためには、加工硬化を抑制する必要がある。 Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
Austenitic stainless steel has a high elongation rate and excellent formability, so it is a steel type used for products of various shapes. When austenitic stainless steel is subjected to stress, deformation occurs due to transformation from an austenite phase, which is unstable at room temperature, to a martensitic phase, that is, transformation induced plasticity.
At this time, the martensite phase produced has high strength, so the strength of the material also increases. In other words, austenitic stainless steel undergoes work-hardening to simultaneously deform and increase strength. The work hardening ability is expressed using a work-hardening exponent, and the work-hardening exponent changes depending on the strain rate.
It is known that austenitic stainless steel has excellent work hardening ability and is easy to form.
However, when deep drawing is applied to austenitic stainless steel while decreasing the blank diameter, the strength increases continuously due to work hardening, causing local stress concentration in the material, which eventually leads to failure. The problem arises that In addition, cracks may suddenly occur after molding due to age cracking.
Therefore, in deep drawing forming, which involves a large amount of deformation, it is important to uniformly deform the entire material and to minimize changes in strength during deformation. That is, in order to improve the deep drawability of austenitic stainless steel, it is necessary to suppress work hardening.

一方、オーステナイト系ステンレス鋼の加工硬化は、オーステナイト相の安定化度と関連がある。成分制御を通じてオーステナイト相の安定化度を増加させると、オーステナイト系ステンレス鋼の加工硬化を抑制することができる。
しかし、オーステナイト系ステンレス鋼の延伸率に代表される加工性は、塑性有機変態に起因した加工硬化から導出されたものであるので、加工硬化能の縮小はオーステナイト系ステンレス鋼の加工性を低下させるという問題がある。 On the other hand, the work hardening of austenitic stainless steel is related to the degree of stabilization of the austenite phase. Increasing the degree of stabilization of the austenite phase through component control can suppress work hardening of austenitic stainless steel.
However, the workability of austenitic stainless steel, represented by the elongation rate, is derived from work hardening caused by plastic organic transformation, so a reduction in work hardening ability reduces the workability of austenitic stainless steel. There is a problem.

本発明者らは、オーステナイト系ステンレス鋼の延伸率を確保すると共に深絞り加工の適用時に加工硬化による強度増加を抑制するために多様な検討を行った結果、以下の知見を得た。
本発明では、オーステナイト系ステンレス鋼において深絞り加工の適用時の破損の発生を防止するための要因を検討した結果、応力によるマルテンサイト相の変態を抑制して過度な加工硬化を防止すると共に、過度な強度増加なしに一定量以上の変形を確保することによって、オーステナイト系ステンレス鋼の深絞り加工を向上させ得ることを発見した。このためには、過度な強度増加なしに持続的な変形を確保し得る合金成分系を導出することによって達成することができる。
本発明の一側面による深絞り性が向上したオーステナイト系ステンレス鋼は、重量％で、Ｃ：０．０１～０．０５％、Ｎ：０．０１～０．２５％、Ｓｉ：１．５％以下（０は除外）、Ｍｎ：０．３～３．５％、Ｃｒ：１７．０～２２．０％、Ｎｉ：９．０～１４．０％、Ｍｏ：２．０％以下（０は除外）、Ｃｕ：０．２～２．５％、を含み、残りはＦｅ及び不可避な不純物からなる。 The present inventors conducted various studies in order to ensure the elongation rate of austenitic stainless steel and to suppress the increase in strength due to work hardening when deep drawing is applied, and as a result, the following findings were obtained.
In the present invention, as a result of studying the factors to prevent the occurrence of damage when deep drawing is applied to austenitic stainless steel, we found that we suppress the transformation of the martensitic phase due to stress and prevent excessive work hardening. It has been discovered that deep drawing of austenitic stainless steel can be improved by ensuring a certain amount of deformation or more without excessively increasing strength. This can be achieved by deriving an alloy component system that can ensure sustained deformation without excessively increasing strength.
The austenitic stainless steel with improved deep drawability according to one aspect of the present invention has a weight percentage of C: 0.01 to 0.05%, N: 0.01 to 0.25%, and Si: 1.5%. The following (0 is excluded), Mn: 0.3 to 3.5%, Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 2.0% or less (0 is ), Cu: 0.2 to 2.5%, and the remainder consists of Fe and unavoidable impurities.

以下、本発明の合金成分元素の含量の数値限定理由について説明する。以下では、特に言及がない限り、単位は、重量％である。
Ｃの含量は、０．０１～０．０５％である。
炭素（Ｃ）は、オーステナイト相の安定化に効果的な元素であって、変形時にマルテンサイト相の形成を抑制して強度を確保するために０．０１％以上添加できる。ただし、その含量が過度な場合、Ｃｒと結合することによってＣｒ炭化物の粒界析出を誘導して耐食性が低下する問題があるため、その上限を０．０５％に限定することができる。
Ｎの含量は、０．０１～０．２５％である。
窒素（Ｎ）は、炭素と同様にオーステナイト相の安定化に効果的な元素であって、深絞り性の確保のために０．０１％以上添加できる。ただし、その含量が過度な場合、窒化物の形成により表面品質を低下させ得るので、その上限を０．２５％に限定することができる。 The reasons for numerically limiting the content of the alloy component elements of the present invention will be explained below. In the following, the units are % by weight, unless otherwise stated.
The content of C is 0.01-0.05%.
Carbon (C) is an element effective in stabilizing the austenite phase, and can be added in an amount of 0.01% or more in order to suppress the formation of a martensitic phase during deformation and ensure strength. However, if its content is excessive, it may combine with Cr and induce grain boundary precipitation of Cr carbides, resulting in a decrease in corrosion resistance, so the upper limit can be limited to 0.05%.
The content of N is 0.01-0.25%.
Nitrogen (N), like carbon, is an element effective in stabilizing the austenite phase, and can be added in an amount of 0.01% or more to ensure deep drawability. However, if its content is excessive, it may deteriorate the surface quality due to the formation of nitrides, so its upper limit can be limited to 0.25%.

Ｓｉの含量は、１．５％以下（０は除外）である。
シリコーン（Ｓｉ）は、製鋼工程中に脱酸剤の役目をし、オーステナイト系ステンレス鋼の強度と耐食性を確保する元素である。ただし、フェライト相の安定化元素であるシリコーンの含量が過多な場合、マルテンサイト相の変態を促進させ、σ相など金属間化合物（Ｉｎｔｅｒｍｅｔａｌｌｉｃ Ｃｏｍｐｏｕｎｄ）を析出して機械的特性及び耐食性が低下する問題があるので、本発明では、その上限を１．５％に限定することができる。
Ｍｎの含量は、０．３～３．５％である。
マンガン（Ｍｎ）は、炭素（Ｃ）、窒素（Ｎ）と同様にオーステナイトを安定化する元素であって、成形加工時に発生する強度増加を抑制する効果があるので、０．３％以上添加できる。ただし、その含量が過度な場合、Ｓ系介在物（ＭｎＳ）を過量形成してオーステナイト系ステンレス鋼の耐食性及び表面光沢を低下させ得るので、その上限を３．５％に限定することができる。
Ｃｒの含量は、１７．０～２２．０％である。
クロム（Ｃｒ）は、フェライトを安定化し、ステンレス鋼の耐食性を向上させる元素のうち最も多く含有されて基本となる元素である。本発明では、酸化を抑制する不動態皮膜を形成して耐食性を確保するために１７．０％以上添加することができる。
ただし、フェライト相の安定化元素であるクロムの含量が過多な場合、オーステナイト相の安定化度が減少してマルテンサイトの変態を促進させ、これによって、ニッケル含量の増加を伴うので製造コストが上昇し、σ相など金属間化合物（Ｉｎｔｅｒｍｅｔａｌｌｉｃ Ｃｏｍｐｏｕｎｄ）を析出して機械的特性及び耐食性が低下する問題があるので、本発明では、その上限を２２．０％に限定することができる。 The Si content is 1.5% or less (0 is excluded).
Silicone (Si) is an element that acts as a deoxidizer during the steelmaking process and ensures the strength and corrosion resistance of austenitic stainless steel. However, if the content of silicone, which is a stabilizing element for the ferrite phase, is excessive, it will accelerate the transformation of the martensitic phase and precipitate intermetallic compounds such as the σ phase, resulting in a decrease in mechanical properties and corrosion resistance. Therefore, in the present invention, the upper limit can be limited to 1.5%.
The content of Mn is 0.3-3.5%.
Manganese (Mn) is an element that stabilizes austenite like carbon (C) and nitrogen (N), and has the effect of suppressing the increase in strength that occurs during forming processing, so it can be added in an amount of 0.3% or more. . However, if the content is excessive, S-based inclusions (MnS) may be formed in an excessive amount and deteriorate the corrosion resistance and surface gloss of the austenitic stainless steel, so the upper limit can be limited to 3.5%.
The content of Cr is 17.0 to 22.0%.
Chromium (Cr) is the most abundant and basic element among the elements that stabilize ferrite and improve the corrosion resistance of stainless steel. In the present invention, it can be added in an amount of 17.0% or more in order to form a passive film that suppresses oxidation and to ensure corrosion resistance.
However, if the content of chromium, which is a stabilizing element of the ferrite phase, is excessive, the degree of stabilization of the austenite phase decreases and promotes the transformation of martensite, which is accompanied by an increase in the nickel content and increases manufacturing costs. However, there is a problem that intermetallic compounds such as σ phase are precipitated and the mechanical properties and corrosion resistance are deteriorated, so in the present invention, the upper limit can be limited to 22.0%.

Ｎｉの含量は、９．０～１４．０％である。
ニッケル（Ｎｉ）は、最も強力なオーステナイト相の安定化元素であって、その含量が増加するほどオーステナイト相が安定化して素材を軟質化し、変形有機マルテンサイトの発生に起因する加工硬化を抑制するために９％以上を添加することが必須的である。しかし、Ｎｉは、高価の元素であるので、多量の添加時に原料費用の上昇をもたらす。そこで、鋼材の費用及び効率性を全て考慮して、その上限を１４．０％に限定することができる。
Ｍｏの含量は、２．０％以下（０は除外）である。
モリブデン（Ｍｏ）は、鋼の耐食性に効果的な元素である。ただし、フェライト相の安定化元素であるモリブデンの含量が過多な場合、オーステナイト相の安定化度が減少して深絞り性を確保しにくく、σ相など金属間化合物（Ｉｎｔｅｒｍｅｔａｌｌｉｃ Ｃｏｍｐｏｕｎｄ）を析出して機械的特性及び耐食性が低下する問題があるので、本発明では、その上限を２．０％に限定することができる。 The Ni content is 9.0 to 14.0%.
Nickel (Ni) is the strongest stabilizing element for the austenite phase, and as its content increases, the austenite phase becomes more stable, softening the material, and suppressing work hardening caused by the generation of deformed organic martensite. Therefore, it is essential to add 9% or more. However, since Ni is an expensive element, adding a large amount increases raw material costs. Therefore, the upper limit can be limited to 14.0%, taking into consideration the cost and efficiency of steel materials.
The Mo content is 2.0% or less (0 is excluded).
Molybdenum (Mo) is an element effective in improving the corrosion resistance of steel. However, if the content of molybdenum, which is a stabilizing element for the ferrite phase, is excessive, the degree of stabilization of the austenite phase decreases, making it difficult to ensure deep drawability, and intermetallic compounds such as σ phase may precipitate. Since there is a problem of deterioration of mechanical properties and corrosion resistance, the upper limit can be limited to 2.0% in the present invention.

Ｃｕの含量は、０．２～２．５％である。
銅（Ｃｕ）は、高価のニッケル（Ｎｉ）の代わりに添加されるオーステナイト相の安定化元素であって、価格競争力及び深絞り性を確保するために０．２％以上添加できる。ただし、その含量が過度な場合、低融点のε－Ｃｕ析出相が形成されて表面品質を低下させ得るので、その上限を２．５％に限定することができる。
また、本発明の一実施例によると、Ａｌ：０．０４％以下（０は除外）、Ｔｉ：０．００３％以下（０は除外）、Ｂ：０．００２５％以下（０は除外）、Ｐ：０．０３５％以下及びＳ：０．００３５％以下のうち１種以上をさらに含むことができる。
Ａｌの含量は、０．０４％以下（０は除外）である。
アルミニウム（Ａｌ）は、強力な脱酸剤として溶鋼中の酸素の含量を下げる役目をする元素である。ただし、その含量が過多な場合、非金属介在物の増加によって冷延ストリップのスリーブ欠陥が発生する問題があるので、その上限を０．０４％に限定することができる。
Ｔｉの含量は、０．００３％以下（０は除外）である。
チタン（Ｔｉ）は、炭素（Ｃ）と窒素（Ｎ）のような侵入型元素と優先的に結合して析出物（炭窒化物）を形成することによって、鋼中の固溶Ｃ及び固溶Ｎの量を低減してＣｒ枯渇領域の形成を抑制して鋼の耐食性の確保に効果的な元素である。ただし、その含量が過多な場合、Ｔｉ系介在物を形成して製造上に困難があり、スキャブ（ｓｃａｂ）のような表面欠陥が発生する問題があるので、その上限を０．００３％に限定することができる。 The content of Cu is 0.2-2.5%.
Copper (Cu) is an austenite phase stabilizing element added in place of expensive nickel (Ni), and can be added in an amount of 0.2% or more to ensure price competitiveness and deep drawability. However, if the content is excessive, a low melting point ε-Cu precipitate phase may be formed and the surface quality may deteriorate, so the upper limit can be limited to 2.5%.
Further, according to an embodiment of the present invention, Al: 0.04% or less (0 is excluded), Ti: 0.003% or less (0 is excluded), B: 0.0025% or less (0 is excluded), It may further contain one or more of P: 0.035% or less and S: 0.0035% or less.
The Al content is 0.04% or less (0 is excluded).
Aluminum (Al) is an element that serves as a strong deoxidizer to lower the oxygen content in molten steel. However, if the content is too large, sleeve defects may occur in the cold-rolled strip due to an increase in nonmetallic inclusions, so the upper limit can be limited to 0.04%.
The Ti content is 0.003% or less (0 is excluded).
Titanium (Ti) preferentially combines with interstitial elements such as carbon (C) and nitrogen (N) to form precipitates (carbonitrides), thereby reducing solid solution C and solid solution in steel. It is an effective element for ensuring the corrosion resistance of steel by reducing the amount of N and suppressing the formation of Cr-depleted regions. However, if its content is too large, Ti-based inclusions will form, creating manufacturing difficulties and surface defects such as scabs, so the upper limit is limited to 0.003%. can do.

Ｂの含量は、０．００２５％以下（０は除外）である。
ホウ素（Ｂ）は、鋳造中のクラック発生を抑制して良好な表面品質を確保するのに効果的な元素である。ただし、その含量が過度な場合、焼鈍／酸洗工程中に製品表面に窒化物（ＢＮ）を形成させて表面品質を低下させ得るので、その上限を０．００２５％に限定することができる。
Ｐの含量は、０．０３５％以下である。
リン（Ｐ）は、鋼中に不可避に含有される不純物であって、粒界腐食を起こすか熱間加工性を阻害する主要原因となる元素であるので、その含量をできるだけ低く制御することが好ましい。本発明では、前記Ｐ含量の上限を０．０３５％に管理する。
Ｓの含量は、０．００３５％以下である。
硫黄（Ｓ）は、鋼中の不可避に含有される不純物であって、結晶粒界に偏析して熱間加工性を阻害する主要原因となる元素であるので、その含量をできるだけ低く制御することが好ましい。本発明では、前記Ｓ含量の上限を０．００３５％以下に管理する。
本発明の残り成分は、鉄（Ｆｅ）である。ただし、通常の製造過程では、原料又は周囲環境から意図しない不純物が不可避に混入することがあるので、これを排除することはできない。これらの不純物は、通常の製造過程の技術者であれば、誰でも知ることができるので、その全ての内容を特に本明細書で言及しない。 The content of B is 0.0025% or less (0 is excluded).
Boron (B) is an effective element for suppressing the occurrence of cracks during casting and ensuring good surface quality. However, if its content is excessive, it may form nitrides (BN) on the product surface during the annealing/pickling process, degrading the surface quality, so the upper limit can 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 the main element that causes intergranular corrosion or inhibits hot workability, so it is important to control its content as low as possible. preferable. In the present invention, the upper limit of the P content is controlled to 0.035%.
The content of S is 0.0035% or less.
Sulfur (S) is an impurity that is unavoidably contained in steel, and is the main element that segregates at grain boundaries and inhibits hot workability, so its content should be controlled as low as possible. is preferred. In the present invention, the upper limit of the S content is controlled to be 0.0035% or less.
The remaining component of the present invention is iron (Fe). However, in normal manufacturing processes, unintended impurities may inevitably be mixed in from raw materials or the surrounding environment, and this cannot be eliminated. These impurities are known to anyone skilled in the art of ordinary manufacturing processes, and therefore their full contents will not be specifically mentioned herein.

上述したように、オーステナイト系ステンレス鋼の加工硬化は、常温で不安定なオーステナイト相が塑性変形に起因した応力によりマルテンサイト相に変態することから発生する。
変形が持続するによって持続的な相変態が行われ、このような相変態は、オーステナイト系ステンレス鋼の材料が破損される前まで強度を増加させるところ、深絞り性の確保のためには、マルテンサイト相の変態を抑制する必要がある。
本発明では、オーステナイト系ステンレス鋼の変形により発生する相変態を考慮して、下記式（１）を導出した。
具体的に、本発明では、Ｍｎ、Ｎ、Ｃｕ、Ｎｉなどオーステナイトの安定化元素の含量を上向制御してオーステナイト相の安定化度を高めようとした。これによって、マルテンサイト相への相変態が抑制され、オーステナイト系ステンレス鋼の加工硬化を抑制することができた。
式（１）：Ｃｒ＋Ｓｉ＋２＊Ｍｏ＋３＊（Ｎｉ＋Ｃｕ）＋５０＊（Ｃ＋Ｎ）
ここで、Ｃｒ、Ｓｉ、Ｍｏ、Ｎｉ、Ｃｕ、Ｃ、Ｎは、各元素の重量％を意味する。 As described above, work hardening of austenitic stainless steel occurs because the austenite phase, which is unstable at room temperature, transforms into the martensitic phase due to stress caused by plastic deformation.
Continuous phase transformation occurs due to sustained deformation, and this phase transformation increases the strength of the austenitic stainless steel material before it breaks. However, in order to ensure deep drawability, marten It is necessary to suppress the metamorphosis of the site phase.
In the present invention, the following formula (1) was derived in consideration of the phase transformation that occurs due to deformation of austenitic stainless steel.
Specifically, the present invention attempts to increase the degree of stabilization of the austenite phase by upwardly controlling the content of austenite stabilizing elements such as Mn, N, Cu, and Ni. As a result, phase transformation to the martensitic phase was suppressed, and work hardening of the austenitic stainless steel could be suppressed.
Formula (1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N)
Here, Cr, Si, Mo, Ni, Cu, C, and N mean the weight percent of each element.

本発明による深絞り性が向上したオーステナイト系ステンレス鋼は、式（１）で表現される値が６３以上の範囲を満足する。
本発明者らは、式（１）の値が低いほど、外部応力による変形時に強度変化が大きく現われることを確認した。具体的に、式（１）の値が６３未満である場合、外部変形により上述した合金成分系のオーステナイト系ステンレス鋼は、急激な変形有機マルテンサイト変態挙動を示すか、双晶形成による塑性ばらつきが発生した。これによって、オーステナイト系ステンレス鋼の延伸率及び多段成形時に深絞り性が減少する問題があるので、式（１）の下限値を６３に限定しようとする。
図１は、素材の引張実験による応力－ひずみ率の間の関係を説明するためのグラフである。
加工硬化による強度増加は、図１の応力－ひずみ率曲線で説明できる。図１で、加工硬化能の程度を示す加工硬化指数（ｗｏｒｋ－ｈａｒｄｅｎｉｎｇ ｅｘｐｏｎｅｎｔ、ｎ）は、次のように示すことができる。
σ＝Ｋεｎ
ここで、σは、応力、Ｋは、強度係数、εは、ひずみ率を意味する。 The austenitic stainless steel with improved deep drawability according to the present invention satisfies the range in which the value expressed by formula (1) is 63 or more.
The present inventors have confirmed that the lower the value of formula (1), the greater the change in strength appears during deformation due to external stress. Specifically, when the value of formula (1) is less than 63, the austenitic stainless steel of the alloy composition system described above will exhibit rapid deformation organic martensitic transformation behavior due to external deformation, or plasticity variation due to twin formation. There has occurred. As a result, there is a problem that the drawing ratio of the austenitic stainless steel and the deep drawability during multi-stage forming are reduced, so the lower limit value of formula (1) is limited to 63.
FIG. 1 is a graph for explaining the relationship between stress and strain rate based on tensile experiments of materials.
The increase in strength due to work hardening can be explained by the stress-strain rate curve shown in FIG. In FIG. 1, the work-hardening exponent (n), which indicates the degree of work-hardening ability, can be expressed as follows.
σ=Kε n
Here, σ means stress, K means strength coefficient, and ε means strain rate.

一方、前記関係式で両辺に常用ログを適用してｌｏｇ関係式で示すと、次のように示すことができる。
ｌｏｇσ＝ｌｏｇＫ＋ｎ＊ｌｏｇε
言い換えれば、応力－ひずみ率のｌｏｇ関係で、加工硬化指数ｎは、グラフの傾きに該当し、傾きが大きいほど塑性変形時に素材の強度増加が激しいことを意味する。
本発明では、オーステナイト系ステンレス鋼の深絞り性を向上させるためには、過度な強度増加なしに持続的な変形を確保するべきであるという点に着眼して、下記式（２）を導出した。
式（２）：２．４＊Ｃｒ＋１．７＊Ｍｏ＋３．９＊Ｓｉ－２．１＊Ｎｉ－Ｍｎ－０．４＊Ｃｕ－５８＊Ｃ－６４＊Ｎ－１３
ここで、Ｃｒ、Ｍｏ、Ｓｉ、Ｎｉ、Ｍｎ、Ｃｕ、Ｃ、Ｎは、各元素の重量％を意味する。
本発明の一実施例による深絞り性が向上したオーステナイト系ステンレス鋼は、前記式（２）で表現される値が０以上５．５以下の範囲を満足する。 On the other hand, if the above relational expression is expressed as a log relational expression by applying the common log to both sides, it can be expressed as follows.
logσ=logK+n*logε
In other words, in the stress-strain rate logarithm relationship, the work hardening index n corresponds to the slope of the graph, and the larger the slope, the greater the strength increase of the material during plastic deformation.
In the present invention, in order to improve the deep drawability of austenitic stainless steel, we focused on the point that sustained deformation should be ensured without excessively increasing strength, and we derived the following formula (2). .
Formula (2): 2.4*Cr+1.7*Mo+3.9*Si-2.1*Ni-Mn-0.4*Cu-58*C-64*N-13
Here, Cr, Mo, Si, Ni, Mn, Cu, C, and N mean the weight percent of each element.
The austenitic stainless steel with improved deep drawability according to an embodiment of the present invention satisfies the value expressed by the above formula (2) in the range of 0 to 5.5.

本発明者らは、式（２）の値が高いほど、外部応力によるマルテンサイト変態が容易に起き、それから過度な強度増加が発生して成形性が低下することを確認した。具体的に、式（２）の値が５．５以上である場合、引張変形で破断直前まで持続的な強度増加が起きて急激な破断が発生する問題がある。これによって、延伸率を確保できないという問題があるので、式（２）の上限を５．５に限定しようとする。
一方、式（２）の値が過度に低いと、外部応力によるオーステナイト相のクロススリップの発現が難しくなることを確認した。具体的に、式（２）の値が０未満である場合、オーステナイト系ステンレス鋼は、変形に対してプラナー（ｐｌａｎａｒ）スリップ挙動のみを示して外部応力による電位の蓄積が進行され、塑性ばらつき及び高い加工硬化を示す。これによって、オーステナイト系ステンレス鋼の延伸率及び降伏比が減少する問題があるので、式（２）の値の下限を０に限定しようとする。
図２は、開示した実施例によるオーステナイト系ステンレス鋼の引張実験時の応力－ひずみ率の間の関係を加工硬化指数とともに示したグラフである。 The present inventors have confirmed that the higher the value of formula (2), the more easily martensitic transformation occurs due to external stress, which leads to an excessive increase in strength and a decrease in formability. Specifically, when the value of formula (2) is 5.5 or more, there is a problem that a continuous increase in strength occurs due to tensile deformation until immediately before breakage, resulting in sudden breakage. As a result, there is a problem that the stretching ratio cannot be ensured, so the upper limit of formula (2) is limited to 5.5.
On the other hand, it was confirmed that if the value of equation (2) is too low, it becomes difficult for the austenite phase to develop cross-slip due to external stress. Specifically, when the value of equation (2) is less than 0, the austenitic stainless steel exhibits only planar slip behavior in response to deformation, and the accumulation of potential due to external stress progresses, leading to plasticity variations and Shows high work hardening. As a result, there is a problem that the elongation ratio and yield ratio of the austenitic stainless steel decrease, so the lower limit of the value of equation (2) is set to zero.
FIG. 2 is a graph showing the relationship between stress and strain rate during a tensile experiment of austenitic stainless steel according to the disclosed example, along with a work hardening index.

一方、本発明による深絞り性が向上したオーステナイト系ステンレス鋼は、加工硬化指数が最大であるときの真ひずみ率の値が０．２以下であってもよい。
図２で、加工硬化指数が最大となる地点をＡで示し、加工硬化指数が０となる地点をＢで示した。
図２を参照すると、Ａ地点以後では、変形が進行しても加工硬化指数が減少することが確認できる。すなわち、Ａ地点以後では、Ｂ地点まで強度が緩やかに増加することが確認できる。
本発明では、オーステナイト系ステンレス鋼の深絞り性を向上させるために、過度な強度増加なしに一定量以上の変形を確保するべきであるという点に着眼して、強度の増加が最大となる地点Ａを比較的低い変形量に配置し、地点Ａから一定量の変形量を確保して地点Ｂに至ることが必要であるということを導出した。
開示した実施例による深絞り性が向上したオーステナイト系ステンレス鋼は、加工硬化指数が最大であるときの真ひずみ率の値が０．２以下である。 On the other hand, the austenitic stainless steel with improved deep drawability according to the present invention may have a true strain rate value of 0.2 or less when the work hardening index is maximum.
In FIG. 2, the point where the work hardening index becomes maximum is indicated by A, and the point where the work hardening index becomes 0 is indicated by B.
Referring to FIG. 2, it can be confirmed that after point A, the work hardening index decreases even if the deformation progresses. That is, it can be confirmed that the intensity gradually increases after point A until point B.
In the present invention, in order to improve the deep drawability of austenitic stainless steel, we focus on the point that a certain amount or more of deformation should be ensured without an excessive increase in strength, and we focus on the point where the increase in strength is maximum. It was derived that it is necessary to arrange A at a relatively low amount of deformation and to reach point B by securing a certain amount of deformation from point A.
The austenitic stainless steel with improved deep drawability according to the disclosed embodiments has a true strain rate value of 0.2 or less when the work hardening index is at its maximum.

図２で、最大加工硬化指数を示す地点ＡのＸ座標である変形量値が０．２以下で導出されると、深絞り加工時に過度な加工硬化の発生を抑制することができる。
開示した実施例による深絞り性が向上したオーステナイト系ステンレス鋼は、加工硬化指数が最大であるときの真ひずみ率値と加工硬化指数が０であるときの真ひずみ率値の差が０．１１以上である。
言い換えれば、小さい変形量で最大加工硬化指数を示し、過度な強度増加なしに持続的な変形を確保することが可能であれば、オーステナイト系ステンレス鋼の延伸率を確保すると共に２段以上の多段加工適用時にクラックの発生を防止することができる。
前記合金元素の組成範囲及び関係式を満足する開示した実施例による深絞り性が向上したオーステナイト系ステンレス鋼は、３５％以上の延伸率、３６０ＭＰａ以上の引張強度を確保することができる。
また、満足する開示した実施例による深絞り性が向上したオーステナイト系ステンレス鋼は、ドローイング比１．７～４．３の条件で２段以上の成形時に５段成形までクラックが発生しない。 In FIG. 2, if the deformation amount value, which is the X coordinate of point A indicating the maximum work hardening index, is derived to be 0.2 or less, it is possible to suppress the occurrence of excessive work hardening during deep drawing.
In the austenitic stainless steel with improved deep drawability according to the disclosed embodiments, the difference between the true strain rate value when the work hardening index is maximum and the true strain rate value when the work hardening index is 0 is 0.11. That's all.
In other words, if it is possible to show the maximum work hardening index with a small amount of deformation and to ensure sustained deformation without excessive strength increase, it is possible to ensure the elongation rate of austenitic stainless steel and to It is possible to prevent cracks from occurring during processing.
The austenitic stainless steel with improved deep drawability according to the disclosed embodiments that satisfies the composition range of the alloying elements and the relational expression can secure a stretching ratio of 35% or more and a tensile strength of 360 MPa or more.
In addition, the austenitic stainless steel with improved deep drawability according to the disclosed embodiments satisfactorily does not generate cracks up to 5th stage forming when forming two or more stages under the condition of a drawing ratio of 1.7 to 4.3.

以下、本発明の好ましい実施例を通じてより詳しく説明する。
実施例
下記表１の成分範囲に対して、連続鋳造工程を通じて２００ｍｍ厚さのスラブを製造し、１，２５０℃で２時間加熱した後、６ｍｍ厚さまで熱間圧延を進行し、熱間圧延以後に１，１５０℃で熱延焼鈍を進行して巻き取った。次に、熱延コイルは、２回にわたって１ｍｍ厚さまで冷間圧延及び冷延焼鈍を進行した。冷間圧延は、パス当たり圧下率３０～７０％範囲で実施し、冷延焼鈍は、１１００～１２００℃温度の加熱炉で５分以内で実施した。
下記表１で、式（１）及び式（２）値は、各合金元素の重量％を下記式（１）及び式（２）に代入して導出した値である。
式（１）：Ｃｒ＋Ｓｉ＋２＊Ｍｏ＋３＊（Ｎｉ＋Ｃｕ）＋５０＊（Ｃ＋Ｎ）
式（２）：２．４＊Ｃｒ＋１．７＊Ｍｏ＋３．９＊Ｓｉ－２．１＊Ｎｉ－Ｍｎ－０．４＊Ｃｕ－５８＊Ｃ－６４＊Ｎ－１３ Hereinafter, the present invention will be described in more detail through preferred embodiments.
Example
A slab with a thickness of 200 mm was manufactured through a continuous casting process according to the component range shown in Table 1 below, heated at 1,250°C for 2 hours, and then hot rolled to a thickness of 6 mm. , hot rolling annealing was performed at 150° C. and the material was rolled up. Next, the hot rolled coil was cold rolled and cold rolled annealed twice to a thickness of 1 mm. Cold rolling was performed at a rolling reduction rate of 30 to 70% per pass, and cold rolling annealing was performed within 5 minutes in a heating furnace at a temperature of 1100 to 1200°C.
In Table 1 below, the values of formula (1) and formula (2) are values derived by substituting the weight percent of each alloying element into formula (1) and formula (2) below.
Formula (1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N)
Formula (2): 2.4*Cr+1.7*Mo+3.9*Si-2.1*Ni-Mn-0.4*Cu-58*C-64*N-13

Figure 2023539140000002
Figure 2023539140000002

各鋼板に対して、多段成形回数及び加工硬化指数を測定した。具体的に、ディープドローイング成形は、直径８５ｍｍのブランク（Ｂｌａｎｋ）を１段パンチ直径５０ｍｍ、２段パンチ直径３８ｍｍ、３段パンチ直径３０ｍｍ、４段パンチ直径２４ｍｍ、５段パンチ直径２０ｍｍで５段階にわたって実施した。各段階別ドローイング比は、１段で１．７、２段で２．２、３段で２．８、４段で３．５、５段で４．３である。
各段階で、加工品の成形後に４８時間が経過するまでクラック発生がない場合を基準として、最大成形回数を下記表２に記載した。
次に、ＪＩＳ１３Ｂ号引張試験片の規格によって引張実験を進行し、実験結果として得られた応力－ひずみ率値から真応力－真ひずみ率を計算し、最大加工硬化指数（ａ）、加工硬化指数が最大であるときの真ひずみ率値（ｂ）、加工硬化指数が０であるときの真ひずみ率値（ｃ）及び、加工硬化指数が最大であるときの真ひずみ率値（ｂ）と加工硬化指数が０であるときの真ひずみ率値（ｃ）の差を導出して下記表２に記載した。
また、引張実験の結果より測定された引張強度（Ｔｅｎｓｉｌｅ Ｓｔｒｅｎｇｔｈ、ＭＰａ）延伸率（Ｅｌｏｎｇａｔｉｏｎ、％）を下記表２に記載した。 For each steel plate, the number of times of multistage forming and the work hardening index were measured. Specifically, deep drawing molding involves forming a blank with a diameter of 85 mm in 5 stages using a 1st stage punch diameter of 50mm, a 2nd stage punch diameter of 38mm, a 3rd stage punch diameter of 30mm, a 4th stage punch diameter of 24mm, and a 5th stage punch diameter of 20mm. carried out. The drawing ratio for each stage is 1.7 for 1 stage, 2.2 for 2 stages, 2.8 for 3 stages, 3.5 for 4 stages, and 4.3 for 5 stages.
At each stage, the maximum number of times of molding is listed in Table 2 below, based on the case where no cracks occur until 48 hours have passed after molding of the processed product.
Next, a tensile experiment was performed according to the standard of JIS No. 13B tensile test piece, and the true stress-true strain rate was calculated from the stress-strain rate value obtained as the experimental result, and the maximum work hardening index (a) and work hardening index The true strain rate value (b) when the work hardening index is the maximum, the true strain rate value (c) when the work hardening index is 0, and the true strain rate value (b) when the work hardening index is the maximum and processing The difference in true strain rate values (c) when the hardening index is 0 was calculated and is listed in Table 2 below.
Further, the tensile strength (MPa) and elongation (%) measured from the results of the tensile experiment are listed in Table 2 below.

Figure 2023539140000003
Figure 2023539140000004
Figure 2023539140000003
Figure 2023539140000004

表２を参照すると、本発明が提示する合金組成と式（１）の値及び式（２）の値の範囲を満足する実施例１～２３の場合、３５０ＭＰａ以上の引張強度の確保が可能であるだけでなく、３５％以上の優れた延伸率を確保し得ることを確認した。また、ドローイング比１．７～４．３の条件で２段以上の成形時、５段成形までクラックが発生しないので複雑な形状のディープドローイング成形が要求される分野に適用が可能である。
比較例１～６、比較例１７～２１は、式（１）の値が６３に未達で加工硬化の時に継続的な強度増加を示すだけでなく、式（２）の値が５．５を超過して変形によるマルテンサイト変態が活発に起きるので、多段成形時にクラックの発生が頻繁であった。
比較例７～１６は、式（１）の値が６３に未達で、式（２）の値が０に未達であり、加工時に双晶形成による急激な強度増加が発生した。双晶形成による強度増加が変形量によって持続的に起き、これによって、深絞り加工時に応力ばらつきが発生して十分な深さの成形量を確保することができなかった。
このように、開示した実施例によると、合金成分と関係式を制御することによって、ドローイング比１．７～４．３の条件で２段以上の成形時に、５段成形までクラックが発生せず、３５％以上の延伸率、３６０ＭＰａ以上の引張強度を確保したオーステナイト系ステンレス鋼を製造することができる。 Referring to Table 2, it is possible to secure a tensile strength of 350 MPa or more in the case of Examples 1 to 23 that satisfy the alloy composition and the range of values of formula (1) and formula (2) proposed by the present invention. It was confirmed that not only that, but also that an excellent stretching ratio of 35% or more could be secured. In addition, when forming two or more stages under the conditions of a drawing ratio of 1.7 to 4.3, cracks do not occur up to five stages, so it can be applied to fields where deep drawing molding of complex shapes is required.
Comparative Examples 1 to 6 and Comparative Examples 17 to 21 not only show a continuous increase in strength during work hardening with the value of formula (1) below 63, but also the value of formula (2) of 5.5. Since martensitic transformation occurs actively due to deformation when the temperature is exceeded, cracks frequently occur during multi-stage molding.
In Comparative Examples 7 to 16, the value of formula (1) did not reach 63, the value of formula (2) did not reach 0, and a rapid increase in strength occurred due to twin formation during processing. Strength increases due to twin crystal formation occur continuously depending on the amount of deformation, and this causes stress variations during deep drawing, making it impossible to secure a sufficient amount of forming depth.
As described above, according to the disclosed example, by controlling the alloy components and the relational expression, cracks did not occur up to 5 stages of forming when forming two or more stages under the conditions of a drawing ratio of 1.7 to 4.3. It is possible to produce an austenitic stainless steel having a stretching ratio of 35% or more and a tensile strength of 360 MPa or more.

以上、本発明の例示的な実施例を説明したが、本発明はこれに限定されず、該当技術分野において通常の知識を有した者であれば、次に記載する特許請求の範囲の概念と範囲を脱しない範囲内で多様に変更及び変形が可能であることを理解すべきである。 Although the exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and a person having ordinary knowledge in the relevant technical field will understand the concept of the following claims. It should be understood that various changes and modifications can be made without departing from the scope.

本発明は、深絞り加工が伴う分野など多様な産業分野に利用が可能である。 The present invention can be used in various industrial fields including fields involving deep drawing.

Claims (8)

重量％で、Ｃ：０．０１～０．０５％、Ｎ：０．０１～０．２５％、Ｓｉ：１．５％以下（０は除外）、Ｍｎ：０．３～３．５％、Ｃｒ：１７．０～２２．０％、Ｎｉ：９．０～１４．０％、Ｍｏ：２．０％以下（０は除外）、Ｃｕ：０．２～２．５％、を含み、残りがＦｅ及び不可避な不純物からなり、
下記式（１）を満足することを特徴とする深絞り性が向上したオーステナイト系ステンレス鋼。
式（１）：Ｃｒ＋Ｓｉ＋２＊Ｍｏ＋３＊（Ｎｉ＋Ｃｕ）＋５０＊（Ｃ＋Ｎ）≧６３
（ここで、Ｃｒ、Ｓｉ、Ｍｏ、Ｎｉ、Ｃｕ、Ｃ、Ｎは、各元素の重量％を意味する。） In weight%, C: 0.01 to 0.05%, N: 0.01 to 0.25%, Si: 1.5% or less (0 is excluded), Mn: 0.3 to 3.5%, Contains Cr: 17.0 to 22.0%, Ni: 9.0 to 14.0%, Mo: 2.0% or less (0 is excluded), Cu: 0.2 to 2.5%, and the rest consists of Fe and unavoidable impurities,
An austenitic stainless steel with improved deep drawability, characterized by satisfying the following formula (1).
Formula (1): Cr+Si+2*Mo+3*(Ni+Cu)+50*(C+N)≧63
(Here, Cr, Si, Mo, Ni, Cu, C, and N mean the weight percent of each element.) 下記式（２）を満足することを特徴とする請求項１に記載の深絞り性が向上したオーステナイト系ステンレス鋼。
式（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
（ここで、Ｃｒ、Ｍｏ、Ｓｉ、Ｎｉ、Ｍｎ、Ｃｕ、Ｃ、Ｎは、各元素の重量％を意味する。） The austenitic stainless steel with improved deep drawability according to claim 1, which satisfies the following formula (2).
Formula (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
(Here, Cr, Mo, Si, Ni, Mn, Cu, C, and N mean the weight percent of each element.) Ａｌ：０．０４％以下（０は除外）、Ｔｉ：０．００３％以下（０は除外）、Ｂ：０．００２５％以下（０は除外）、Ｐ：０．０３５％以下及びＳ：０．００３５％以下のうち１種以上をさらに含むことを特徴とする請求項１に記載の深絞り性が向上したオーステナイト系ステンレス鋼。 Al: 0.04% or less (0 is excluded), Ti: 0.003% or less (0 is excluded), B: 0.0025% or less (0 is excluded), P: 0.035% or less, and S: 0 The austenitic stainless steel with improved deep drawability according to claim 1, further comprising at least one of .0035% or less. 下記式（３）で、加工硬化指数が最大であるときの真ひずみ率値が０．２以下であることを特徴とする、請求項１に記載の深絞り性が向上したオーステナイト系ステンレス鋼。
式（３）：σ＝Ｋεｎ
（ここで、σは、応力、Ｋは、強度係数、εは、ひずみ率、ｎは、加工硬化指数を意味する。） The austenitic stainless steel with improved deep drawability according to claim 1, characterized in that the true strain rate value when the work hardening index is maximum is 0.2 or less in the following formula (3).
Formula (3): σ=Kε n
(Here, σ means stress, K means strength coefficient, ε means strain rate, and n means work hardening index.) 加工硬化指数が最大であるときの真ひずみ率値と加工硬化指数が０であるときの真ひずみ率値の差が０．１１以上であることを特徴とする請求項４に記載の深絞り性が向上したオーステナイト系ステンレス鋼。 Deep drawability according to claim 4, characterized in that the difference between the true strain rate value when the work hardening index is maximum and the true strain rate value when the work hardening index is 0 is 0.11 or more. Austenitic stainless steel with improved properties. 延伸率が３５％以上であることを特徴とする請求項１に記載の深絞り性が向上したオーステナイト系ステンレス鋼。 The austenitic stainless steel with improved deep drawability according to claim 1, characterized in that the drawing ratio is 35% or more. 引張強度が３６０ＭＰａ以上であることを特徴とする請求項１に記載の深絞り性が向上したオーステナイト系ステンレス鋼。 The austenitic stainless steel with improved deep drawability according to claim 1, having a tensile strength of 360 MPa or more. ドローイング比１．７～４．３の条件で多段成形するとき、５段成形までクラックが発生しないことを特徴とする、請求項１に記載の深絞り性が向上したオーステナイト系ステンレス鋼。 The austenitic stainless steel with improved deep drawability according to claim 1, characterized in that no cracks occur until the fifth stage of forming when multistage forming is performed under conditions of a drawing ratio of 1.7 to 4.3.
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