JP2006291296A - Austenitic stainless steel having excellent deep drawability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an austenitic stainless steel sheet in which hardening caused by press working is suppressed, and which is free from the generation of working defects such as cracks even if being subjected to severe working. <P>SOLUTION: The austenitic stainless steel has a composition comprising, by mass, ≤0.03% C, ≤1.0% Si, ≤5.0% Mn, 5 to 15% Ni, 15 to 20% Cr, ≤5.0% Cu, ≤3.0% Mo, ≤0.03% N and 0.0001 to 0.0100% B, and satisfying Md<SB>30</SB>: -60 to -10, SFI≥30, and B/N mass ratio≥0.01: Md<SB>30</SB>=551-462(C+N)-9.2Si-8.1Mn-29(Ni+Cu)-13.7Cr-18.5Mo, and SFI=2.2Ni+6Cu-1.1Cr-13Si-1.2Mn+32. In the matrix after working, BN-based compounds are dispersedly precipitated in the ratio of ≥0.01 area%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、厚板にも拘わらずプレス加工で各種形状の部品や部材に成形できる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 that can be formed into parts and members of various shapes by press working in spite of thick plates.

水道や各種液体，ガス配管の接合部で締め付けられる部品、耐食性が必要なポンプ等の機械類用ケースに使用される部品や部材には、従来からステンレス鋼鋳物が多用されている。鋳造法によるとき鋳型キャビティで目標形状が定まり、厚肉製品や肉厚偏差の大きな製品等が容易に製造される。そのため、剛性，意匠性が要求される配管部品や騒音，振動防止用に質量が必要なケース等にステンレス鋼鋳物が適用されている。ステンレス鋼鋳物は、他にも構造部材として使用されることもある。
ステンレス鋼鋳物は、生産性が低いことが欠点であり、凝固組織で構成されるために圧延法で製造されるステンレス鋼製品に比較して強度や靭性にも劣る。 Conventionally, stainless steel castings have been widely used for parts and members used in mechanical cases such as pumps that require corrosion resistance, parts that are tightened at joints of water supply, various liquids, and gas pipes. When the casting method is used, a target shape is determined in the mold cavity, and a thick product or a product with a large thickness deviation is easily manufactured. Therefore, stainless steel castings are applied to piping parts that require rigidity and design, and cases that require mass to prevent noise and vibration. Stainless steel castings may also be used as structural members.
Stainless steel castings have the disadvantage of low productivity, and are inferior in strength and toughness compared to stainless steel products manufactured by a rolling method because they are composed of a solidified structure.

そこで、量産性，経済性を兼ね備えたプレス加工で製造された部品で、従来の鋳物製品を置き換える検討が重ねられてきた。しかし、SUS304に代表されるオーステナイト系ステンレス鋼をプレス加工すると、加工硬化に起因して成形荷重が増大し、二次加工性も低下する。そのため、厚肉形状や肉厚偏差の大きな形状の製品は、厚板オーステナイト系ステンレス鋼板のプレス加工では得られ難い。   Therefore, studies have been made to replace conventional casting products with parts manufactured by press working that have both mass productivity and economy. However, when austenitic stainless steel typified by SUS304 is pressed, the forming load increases due to work hardening, and the secondary workability also decreases. Therefore, it is difficult to obtain a product having a thick wall shape or a shape having a large wall thickness deviation by pressing a thick austenitic stainless steel sheet.

本発明者等は、オーステナイト系ステンレス鋼のプレス加工性を改善し、割れ等の加工欠陥を抑えて目標形状に成形可能なステンレス鋼を調査・検討した。その結果、加工誘起マルテンサイト生成指標Ｍd₃₀や積層欠陥難易度指数SFIがプレス加工性に大きな影響を及ぼしており、特定成分系でＭd₃₀≦-１０，SFI≧３０の成分設計を採用することにより深絞り性等を初めとする加工性に優れたオーステナイト系ステンレス鋼が得られることを解明した（特許文献１〜３）。しかし、厚肉製品の製造には厚鋼板を素材に用いたプレス加工が必要とされ、指標Ｍd₃₀，指数SFIの管理だけでは厚鋼板のプレス加工時に発生しがちな加工欠陥を十分に抑制できない。
特開平9-263905号公報 特開2002-371339号公報 特開2003-113450号公報 The present inventors investigated and examined a stainless steel that can improve the press workability of austenitic stainless steel and can be formed into a target shape while suppressing processing defects such as cracks. As a result, the processing-induced martensite generation index Md ₃₀ and the stacking fault difficulty index SFI have a great influence on the press workability, and a component design of Md ₃₀ ≦ −10 and SFI ≧ 30 should be adopted in a specific component system. It has been clarified that an austenitic stainless steel excellent in workability such as deep drawability can be obtained (Patent Documents 1 to 3). However, thick-walled products require press working using thick steel plates as raw materials. Management of the index Md ₃₀ and index SFI alone cannot sufficiently suppress processing defects that tend to occur during thick steel plate pressing. .
JP-A-9-263905 JP 2002-371339 A Japanese Patent Laid-Open No. 2003-113450

そこで、本発明者等は、厚板ステンレス鋼板をプレス加工する際に鋼組成及び組織がプレス加工性に及ぼす影響を検討した。その結果、Ｍd₃₀値，SFI値に加えＢＮの分散量を適正管理すると、板厚が２ｍｍ以上のステンレス鋼板であっても加工欠陥なく良好な形状にプレス加工できることを解明した。
本発明は、かかる知見をベースに完成されたものであり、特定成分系においてＭd₃₀値，SFI値，Ｂ／Ｎ質量比が所定範囲に収まる成分設計を採用することにより、厚板にも拘わらず加工欠陥なく目標形状にプレス加工でき、二次加工性も良好なオーステナイト系ステンレス鋼を提供することを目的とする。 Therefore, the present inventors examined the influence of the steel composition and structure on the press workability when pressing a thick stainless steel plate. As a result, it has been clarified that if the dispersion amount of BN is appropriately controlled in addition to the Md ₃₀ value and the SFI value, even a stainless steel plate having a thickness of 2 mm or more can be pressed into a good shape without any processing defects.
The present invention has been completed on the basis of such knowledge, and by adopting a component design in which the Md ₃₀ value, the SFI value, and the B / N mass ratio are within a predetermined range in a specific component system, the present invention is also related to a thick plate. It is an object of the present invention to provide an austenitic stainless steel that can be pressed into a target shape without any processing defects and has good secondary workability.

本発明のオーステナイト系ステンレス鋼は、鋼組成及び金属組織で特徴付けられる。
鋼組成は、Ｃ：０.０３質量％以下，Ｓｉ：１.０質量％以下，Ｍｎ：５.０質量％以下，Ｎｉ：５〜１５質量％，Ｃｒ：１５〜２０質量％，Ｃｕ：５.０質量％以下，Ｍｏ：３.０質量％以下，Ｎ：０.０３質量％以下，Ｂ：０.０００１〜０.０１００質量％を含み、Ｍd₃₀：-６０〜-１０，SFI≧３０，Ｂ／Ｎ≧０.０１を満足するよう成分調整されている。 The austenitic stainless steel of the present invention is characterized by a steel composition and a metal structure.
Steel composition: C: 0.03 mass% or less, Si: 1.0 mass% or less, Mn: 5.0 mass% or less, Ni: 5-15 mass%, Cr: 15-20 mass%, Cu: 5 0.0 mass% or less, Mo: 3.0 mass% or less, N: 0.03 mass% or less, B: 0.0001 to 0.0100 mass%, Md ₃₀ : −60 to −10, SFI ≧ 30 , B / N ≧ 0.01 so that the components are adjusted.

Ｍd₃₀は式(１)で定義され、オーステナイト安定度（換言すれば、加工誘起マルテンサイトの生成量）を表す。SFIは式(２)で定義され、プレス加工時の積層欠陥の生成難易度を表す。
Md₃₀=551-462(Ｃ+Ｎ)-9.2Ｓｉ-8.1Ｍｎ-29(Ｎｉ+Ｃｕ)-13.7Ｃｒ-18.5Ｍｏ
・・・・(１)
SFI=2.2Ｎｉ+6Ｃｕ-1.1Ｃｒ-13Ｓｉ-1.2Ｍｎ+32 ・・・・(２)
該オーステナイト系ステンレス鋼は、マトリックスにＢＮが分散した組織をもち、ＢＮ分散量は０.００１面積％以上に調整されている。 Md ₃₀ is defined by the formula (1) and represents austenite stability (in other words, the amount of processing-induced martensite generated). SFI is defined by equation (2) and represents the difficulty in generating stacking faults during press working.
Md ₃₀ = 551-462 (C + N) -9.2Si-8.1Mn-29 (Ni + Cu) -13.7Cr-18.5Mo
・ ・ ・ ・ (1)
SFI = 2.2Ni + 6Cu-1.1Cr-13Si-1.2Mn + 32 (2)
The austenitic stainless steel has a structure in which BN is dispersed in a matrix, and the amount of BN dispersion is adjusted to 0.001 area% or more.

発明の効果及び実施の形態Effects and embodiments of the invention

本発明者等は、製品寸法に比較して厚いオーステナイト系ステンレス鋼板を素材に用いたプレス加工において、加工性に及ぼす材質面の影響を調査・検討した。
オーステナイト系ステンレス鋼板をプレス加工するとき、加工誘起マルテンサイト相が生成すると加工硬化が進行する。加工誘起マルテンサイト変態は、加工時に導入される歪で生じるオーステナイト相の結晶格子の変形が原因である。加工誘起マルテンサイトの生成は、式(１)で定義されるオーステナイト安定指標Ｍd₃₀の上限が-１０以下になる成分設計によって規制される。加工誘起マルテンサイトが生成し難い成分設計，ひいては加工硬化し難い成分設計のため、プレス加工時に皺押え部の流入抵抗が抑制され、深絞り性が向上する。 The present inventors investigated and examined the influence of the material surface on workability in press working using a thick austenitic stainless steel plate as a raw material compared to the product dimensions.
When the austenitic stainless steel plate is pressed, work hardening proceeds when a work-induced martensite phase is generated. The processing-induced martensitic transformation is caused by deformation of the austenite crystal lattice caused by strain introduced during processing. The formation of work-induced martensite is regulated by the component design in which the upper limit of the austenite stability index Md ₃₀ defined by the equation (1) is −10 or less. The component design that does not easily generate work-induced martensite, and therefore the component design that does not easily work harden, suppresses the inflow resistance of the presser foot during pressing and improves deep drawability.

オーステナイト安定指標Ｍd₃₀がある程度大きくなると、加工誘起マルテンサイトが生成しやすくなる。特に、絞り加工時に加工歪みが導入される個所である金型に接する面で加工誘起マルテンサイトが生成する。加工誘起マルテンサイト相のＮ固溶度はオーステナイト相より低いので、Ｂを含む成分系では、鋼板表面に生成する加工誘起マルテンサイト相にＢＮ化合物相が析出しやすくなる。潤滑作用のあるＢＮ化合物相が鋼板表面に析出すると、プレス加工時の金型に対するステンレス鋼板の滑り性，ひいては加工性が改善される。ＢＮ化合物相の効果を確実にするため、一定量以上の加工誘起マルテンサイト相の生成が必要であり、この点からＭd₃₀値の下限が-６０と定められる。 When austenite stability index Md ₃₀ increases to some extent, deformation-induced martensite is easily generated. In particular, machining-induced martensite is generated on the surface in contact with the mold, which is a place where machining distortion is introduced during drawing. Since the N solid solubility of the work-induced martensite phase is lower than that of the austenite phase, in the component system containing B, the BN compound phase tends to precipitate in the work-induced martensite phase generated on the steel sheet surface. When the BN compound phase having a lubricating action precipitates on the surface of the steel sheet, the slipperiness of the stainless steel sheet with respect to the mold during press working, and hence the workability is improved. In order to ensure the effect of the BN compound phase, it is necessary to generate a certain amount of processing-induced martensite phase. From this point, the lower limit of the Md ₃₀ value is set to -60.

過酷なプレス加工で製品化される用途では、Ｍd₃₀値の管理だけでは依然として加工割れや硬質化を防止できず、未変態のオーステナイト相であっても加工硬化する。オーステナイト相の加工硬化挙動は、f.c.c.構造を採るオーステナイト相における転移の増殖形態に影響され、積層欠陥の生成難易度によって加工硬化量が決まってくる。
積層欠陥の生成傾向は、前掲の式(２)で定義される積層欠陥難易度指数SFIで表すことができる。積層欠陥難易度指数SFIが小さいと僅かなエネルギーにより積層欠陥が生成し、転移の伝播が積層欠陥によって抑えられる。その結果、転移が蓄積し、加工硬化が進行する。プレス加工性に悪影響を及ぼさない程度に加工硬化の進行を抑える上で、積層欠陥難易度指数SFIの下限値を３０とし、積層欠陥エネルギーを高い状態に維持する必要がある。鋼成分のうち、Ｃｕは、積層欠陥難易度指数SFIを大きく上昇させる作用を呈し、Ｎｉ代替による原料費の低減に留まらず、加工硬化を一層抑制する有効成分である。 In applications that are commercialized by severe press work, it is still impossible to prevent work cracking and hardening by controlling the Md ₃₀ value alone, and even an untransformed austenite phase is work hardened. The work hardening behavior of the austenite phase is affected by the growth form of the transition in the austenite phase adopting the fcc structure, and the work hardening amount is determined depending on the difficulty in generating stacking faults.
The generation tendency of stacking faults can be represented by the stacking fault difficulty index SFI defined by the above formula (2). When the stacking fault difficulty index SFI is small, stacking faults are generated by a small amount of energy, and propagation of transition is suppressed by the stacking faults. As a result, transition accumulates and work hardening proceeds. In order to suppress the progress of work hardening so as not to adversely affect the press workability, it is necessary to set the lower limit value of the stacking fault difficulty index SFI to 30 and maintain the stacking fault energy at a high level. Of the steel components, Cu exhibits an effect of greatly increasing the stacking fault difficulty index SFI, and is an effective component that further suppresses work hardening as well as reducing raw material costs by replacing Ni.

プレス加工されたオーステナイト系ステンレス鋼板の表面には、加工誘起マルテンサイト相の外にオーステナイト相も存在する。金型に対する摺動面における積層欠陥とオーステナイト相の摺動性との関係を調査した結果、多量の積層欠陥が生成するオーステナイト相では摺動性が低下することが判った。この点、摺動性を低下させないためにも積層欠陥難易度指数SFIを３０以上とし、積層欠陥エネルギーを高く設定する必要がある。   In addition to the processing-induced martensite phase, an austenitic phase is also present on the surface of the pressed austenitic stainless steel plate. As a result of investigating the relationship between the stacking faults on the sliding surface with respect to the mold and the slidability of the austenite phase, it was found that the slidability decreases in the austenite phase where a large number of stacking faults are generated. In this respect, in order not to lower the slidability, it is necessary to set the stacking fault difficulty index SFI to 30 or more and set the stacking fault energy high.

プレス加工されるオーステナイト系ステンレス鋼板が厚板であるほど、金型に摺動する面に大きな圧力が発生し、割れが発生しやすくなる。特に、素材板厚ｔに対する肩半径ｒ_dの比ｒ_d／ｔが２以下となる金型を用いて厚板を絞り加工する場合、限界絞り比が極端に低下する。限界絞り比の低下は、ダイス肩部での厳しい曲げ-曲げ戻し変形によって割れが発生しやすくなることが原因である。 The thicker the austenitic stainless steel sheet to be pressed, the more pressure is generated on the surface that slides on the mold, and cracks are more likely to occur. In particular, when a thick plate is drawn using a mold in which the ratio r _d / t of the shoulder radius r _d to the material plate thickness t is 2 or less, the limit drawing ratio is extremely reduced. The reduction in the limit drawing ratio is caused by the fact that cracks are likely to occur due to severe bending-bending deformation at the die shoulder.

本成分系では、対板厚比ｒ_d／ｔ≦２の条件下でプレス加工する際にみられる割れの発生を抑制するため、Ｂ／Ｎ質量比を０.０１以上としマトリックスにＢＮが０.００１面積％以上の割合で分散した金属組織に調整している。ＢＮは耐熱性に優れ、ステンレス鋼に近い熱伝導率を呈する潤滑剤であり、マトリックスに分散することにより鋼板表面の潤滑性を向上させる。そのため、金型に対する摺動面の昇温が顕著な厚板のオーステナイト系ステンレス鋼板をプレス加工する際にも良好な潤滑効果が発揮され、割れの発生なく目標形状にプレス加工できる。
以下、本発明オーステナイト系ステンレス鋼の合金成分，含有量等を説明する。 In this component system, the B / N mass ratio is set to 0.01 or more and BN is 0 in the matrix in order to suppress the occurrence of cracks observed during press working under the condition of the thickness ratio r _d / t ≦ 2. It is adjusted to a metal structure dispersed at a ratio of 0.001 area% or more. BN is a lubricant having excellent heat resistance and a thermal conductivity close to that of stainless steel, and improves the lubricity of the steel sheet surface by being dispersed in a matrix. Therefore, a good lubrication effect is exerted even when a thick austenitic stainless steel plate with a remarkable temperature rise on the sliding surface with respect to the mold is pressed, and the target shape can be pressed without cracking.
Hereinafter, alloy components, contents, and the like of the austenitic stainless steel of the present invention will be described.

〔Ｃ，Ｎ：０.０３質量％以下〕
何れも固溶強化能のある成分であり、多量に含まれると０.２％耐力や硬さを上昇させる。また、加工誘起マルテンサイト相を過度に硬質化し、成形性，二次加工性に悪影響を及ぼすので、Ｃ，Ｎの上限を０.０３質量％（好ましくは、０.０２質量％）と規制する。
〔Ｓｉ：１.０質量％以下〕
製鋼段階で脱酸剤として添加される成分であるが、加工硬化能が強く二次加工性を低下させる。加工硬化はＳｉの増量に伴い顕著になるが、１.０質量％以下（好ましくは、０.５質量％以下）にＳｉ量を抑えることによって加工硬化、二次加工性の低下を支障ない程度に防止できる。 [C, N: 0.03 mass% or less]
All are components having a solid solution strengthening ability, and if contained in a large amount, the yield strength and hardness are increased by 0.2%. Further, since the work-induced martensite phase is excessively hardened and adversely affects the formability and secondary workability, the upper limit of C and N is regulated to 0.03 mass% (preferably 0.02 mass%). .
[Si: 1.0 mass% or less]
Although it is a component added as a deoxidizer in the steelmaking stage, it has strong work hardening ability and lowers secondary workability. Work hardening becomes significant as the amount of Si increases, but the degree to which work hardening and deterioration of secondary workability are not hindered by suppressing the Si amount to 1.0% by mass or less (preferably 0.5% by mass or less). Can be prevented.

〔Ｍｎ：５.０質量％以下〕
オーステナイト安定化元素であり、Ｍｎの増量に伴い加工誘起マルテンサイト相が生成し難くなり、０.２％耐力、加工硬化率が低下する。このような効果は、１.０質量％以上のＭｎ添加で顕著になる。しかし、過剰量のＭｎ含有は、製鋼時に耐火物の損傷を促進させ、加工割れの起点となるＭｎ系介在物を増加させるので上限を５.０質量％（好ましくは、４.０質量％）とした。
〔Ｃｒ：１５〜２０質量％〕
ステンレス鋼の耐食性を向上させる上で必須の合金成分であり、１５質量％以上でＣｒの添加効果が顕著になる。耐食性向上に及ぼすＣｒの効果は、Ｎｉとの共存によって一層顕著になる。しかし、Ｃｒ含有量の増加に従ってステンレス鋼板が硬質化し、曲げ性や伸縮性が損なわれるので、上限を２０質量％（好ましくは、１９質量％）とした。 [Mn: 5.0% by mass or less]
It is an austenite stabilizing element, and it becomes difficult to produce a work-induced martensite phase with an increase in Mn, and the 0.2% yield strength and work hardening rate are lowered. Such an effect becomes remarkable when Mn is added in an amount of 1.0% by mass or more. However, excessive Mn content promotes damage to the refractory during steelmaking and increases the Mn-based inclusions that are the starting point of work cracks, so the upper limit is 5.0 mass% (preferably 4.0 mass%). It was.
[Cr: 15-20% by mass]
It is an essential alloy component for improving the corrosion resistance of stainless steel, and the effect of adding Cr becomes remarkable at 15% by mass or more. The effect of Cr on the corrosion resistance improvement becomes more prominent by coexistence with Ni. However, as the Cr content increases, the stainless steel plate hardens and the bendability and stretchability are impaired, so the upper limit was set to 20% by mass (preferably 19% by mass).

〔Ｎｉ：５〜１５質量％〕
Ｃｒとの複合添加で耐孔食性等の耐食性改善に寄与し、５質量％以上で添加効果が顕著になる。Ｎｉの増量に伴い軟質化し、加工誘起マルテンサイト相の生成に起因する加工硬化が抑えられ、変形抵抗の増大が抑制される。しかし、高価な元素であるので、改善効果を経済性と照らし合わせ、上限を１５質量％（好ましくは、１３質量％）とした。 [Ni: 5 to 15% by mass]
The combined addition with Cr contributes to improvement of corrosion resistance such as pitting corrosion resistance, and the addition effect becomes remarkable at 5% by mass or more. As the amount of Ni increases, softening occurs, work hardening resulting from the formation of a work-induced martensite phase is suppressed, and an increase in deformation resistance is suppressed. However, since it is an expensive element, the improvement effect is compared with economic efficiency, and the upper limit is set to 15% by mass (preferably 13% by mass).

〔Ｃｕ：５.０質量％以下〕
加工誘起マルテンサイト相の生成に起因する加工硬化を抑制し、ステンレス鋼を軟質化することにより金型負荷を低減する合金成分である。好ましくは０.８質量％以上で、Ｃｕの添加効果が顕著になる。オーステナイト生成元素であるため、Ｃｕ含有量の増加に応じてＮｉ含有量の設定自由度も高くなる。具体的には、２.０質量％以上のＣｕを含有させることにより、Ｎｉ含有量を下限値：５質量％近くまで低減できる。Ｃｕは、積層欠陥難易度指数SFIを高める上でも有効な成分であり、オーステナイト相の加工硬化を抑え、積層欠陥の生成抑制による表面摺動性を改善すること等、非常に有用な特性を付与する。しかし、５.０質量％を超える過剰量のＣｕが含まれると、熱間加工性に悪影響が現れる。 [Cu: 5.0% by mass or less]
It is an alloy component that suppresses work hardening resulting from the formation of a work-induced martensite phase and softens stainless steel to reduce the mold load. Preferably, the addition effect of Cu becomes remarkable at 0.8 mass% or more. Since it is an austenite generating element, the degree of freedom in setting the Ni content increases as the Cu content increases. Specifically, the Ni content can be reduced to near the lower limit of 5% by mass by containing 2.0% by mass or more of Cu. Cu is an effective component in increasing the stacking fault difficulty index SFI, and provides very useful properties such as suppressing the work hardening of the austenite phase and improving the surface slidability by suppressing the generation of stacking faults. To do. However, when an excessive amount of Cu exceeding 5.0% by mass is included, an adverse effect on hot workability appears.

〔Ｂ：０.０００１〜０.０１００質量％〕
本成分系では必須の成分であり、加工摺動面に窒化物を主体とする析出物を形成し、表面の摺動性を改善し深絞り性を著しく向上させる。０.０００１質量％以上で且つＢ／Ｎ質量比を０.０１以上とすることにより、加工誘起マルテンサイト相からＢＮの析出が促進され、０.００１面積％以上の割合でＢＮが析出した金属組織となり鋼板表面の潤滑性が改善される。しかし、０.０１００質量％を超える過剰量のＢ含有は、却って加工性を低下させる。また、０.０１未満のＢ／Ｎ質量比や０.００１面積％未満のＢＮ分散量では、ＢＮの潤滑作用が十分に発現しない。 [B: 0.0001-0.0100 mass%]
It is an essential component in this component system, and precipitates mainly composed of nitride are formed on the processing sliding surface, improving the sliding property of the surface and remarkably improving the deep drawability. By setting the B / N mass ratio to 0.001% or more and a B / N mass ratio of 0.01 or more, the precipitation of BN from the work-induced martensite phase is promoted, and BN is precipitated at a rate of 0.001 area% or more. It becomes a structure and the lubricity of the steel sheet surface is improved. However, excessive B content exceeding 0.0100% by mass reduces the workability. Further, when the B / N mass ratio is less than 0.01 or the BN dispersion amount is less than 0.001 area%, the lubricating action of BN is not sufficiently exhibited.

表１の組成をもつステンレス鋼Ａ〜Ｆを溶製し、連続鋳造後、抽出温度：１２３０℃で熱間圧延することにより板厚：９ｍｍの熱延鋼帯を製造した。熱延鋼帯を１１００℃×均熱１分で焼鈍した後、板厚：６ｍｍまで冷間圧延した。更に、１０５０℃×均熱１分で焼鈍し酸洗することにより、焼鈍・酸洗鋼帯を用意した。   Stainless steels A to F having the composition shown in Table 1 were melted, and after continuous casting, hot rolling was performed at an extraction temperature of 1230 ° C. to produce a hot rolled steel strip having a thickness of 9 mm. The hot-rolled steel strip was annealed at 1100 ° C. × 1 minute soaking and then cold-rolled to a thickness of 6 mm. Furthermore, an annealing / pickling steel strip was prepared by annealing and pickling at 1050 ° C. × soaking for 1 minute.

各ステンレス鋼板を打抜き加工し、外径：８０〜１１０ｍｍのブランクを作製した。内径Ｄ_d：６２.６ｍｍ，肩半径ｒ_d：１２ｍｍのダイス１と先端径Ｄ_p：５０ｍｍ，肩半径ｒ_p：１２ｍｍのポンチ２との間にブランク３をセットし、ダイス側面に当るブランク３に粘度：６０ｍｍ²／秒の潤滑油を塗布し、絞り抜くまでブランクを絞り加工した〔図１〕。
絞り加工されたブランクを観察して割れの有無を調査し、割れなく絞り抜きできた最大ブランク径Ｄ_bmaxのパンチ径Ｄ_pに対する比率Ｄ_bmax／Ｄ_pとして限界絞り比LDRを算出した。限界絞り比LDRの測定結果をＭd₃₀，SFI，Ｂ／Ｎ質量比と共に表２に示す。なお、倍率：１０００倍のSEM画像から１０視野を任意に選定し、SEM画像に観察されるＢＮ析出物の面積率測定値を１０視野で平均化し、ＢＮの面積率として表２に併せ示す。 Each stainless steel plate was punched into a blank having an outer diameter of 80 to 110 mm. Blank 3 is set between a die 1 having an inner diameter D _{d of} 62.6 mm and a shoulder radius r _{d of} 12 mm and a punch 2 having a tip diameter D _{p of} 50 mm and a shoulder radius r _{p of} 12 mm, and hits the side of the die 3 A lubricant having a viscosity of 60 mm ² / sec was applied to the blank, and the blank was drawn until it was drawn (FIG. 1).
Observe the drawn blank investigated the existence of cracks was calculated limit drawing ratio LDR as the ratio D _b max / D _p for punch diameter D _p of the maximum blank diameter D _b max made punching aperture not crack. The measurement results of the limit drawing ratio LDR are shown in Table 2 together with Md ₃₀ , SFI, and B / N mass ratio. In addition, 10 visual fields are arbitrarily selected from the SEM image of 1000 times magnification, and the area ratio measured values of BN precipitates observed in the SEM image are averaged over 10 visual fields, and are also shown in Table 2 as the BN area ratio.

表２から明らかなように、Ｍd₃₀，SFI，Ｂ／Ｎ質量比共に本発明で規定する条件を満足する鋼種Ｅは、限界絞り比ＬＤＲが２.２と高く最も優れた深絞り性を示した。
他方、Ｂ／Ｎ質量比が本発明で規定した条件を満足していない鋼種Ｆ，Ｍd₃₀が低すぎる鋼種Ｃ，Ｍd₃₀，Ｂ／Ｎ質量比共に低すぎる鋼種Ｄ，Ｍd₃₀，SFI，Ｂ／Ｎ質量比何れも本発明で期待した条件を満足していない鋼種Ａ，Ｍd₃₀が低くSFIが高い鋼種Ｂでは、限界絞り比LDRが２.１以下になっており鋼種Ｅに比較して深絞り性に劣っていた。 As is clear from Table 2, steel type E that satisfies the conditions specified in the present invention for Md ₃₀ , SFI, and B / N mass ratio has the highest drawing ratio LDR of 2.2 and exhibits the best deep drawability. It was.
On the other hand, steel types F and Md ₃₀ whose B / N mass ratio does not satisfy the conditions specified in the present invention are too low. Steel types C, Md ₃₀ and B / N mass ratios are too low. Steel types D, Md ₃₀ , SFI, B N / N mass ratio does not satisfy the conditions expected in the present invention. Steel type A, Md ₃₀ is low and steel type B is high and SFI is high, and the limit drawing ratio LDR is 2.1 or less, compared to steel type E. The deep drawability was poor.

表３の組成をもつステンレス鋼Ｇ〜Ｊを溶製し、実施例１と同様な工程で作り込み、板厚：６ｍｍの冷延焼鈍鋼帯を製造した。   Stainless steels G to J having the compositions shown in Table 3 were melted and manufactured in the same process as in Example 1 to produce a cold-rolled annealed steel strip having a thickness of 6 mm.

得られた冷延焼鈍鋼帯から径：９０ｍｍのブランク５０００個を採取し、実施例１と同じ条件の深絞り加工に供し、加工の繰返し（連続プレス）が製品形状，金型性状に及ぼす影響を調査した。比較のため、表１の鋼種Ｂ，Ｄについても、同じ条件下で成形性を評価した。   From the obtained cold-rolled annealed steel strip, 5000 blanks having a diameter of 90 mm were collected and subjected to deep drawing under the same conditions as in Example 1, and the effect of repeated processing (continuous press) on the product shape and mold properties investigated. For comparison, the formability of steel types B and D in Table 1 was also evaluated under the same conditions.

表４の連続プレス結果にみられるように、Ｍd₃₀，SFI，Ｂ／Ｎ質量比，ＢＮ析出量の何れも本発明で規定した条件を満足する鋼種Ｈ、Ｉ，Ｊは、５０００個まで良好にプレス加工できた。プレス加工品に更に穴開け，穴拡げ等の二次加工を施しても、亀裂，破断なく目標形状に加工できた。 As seen in the continuous press results in Table 4, Md ₃₀ , SFI, B / N mass ratio, and BN precipitation amount satisfy all the conditions specified in the present invention. We were able to press work. Even if the stamped product was further subjected to secondary processing such as drilling or expanding, it could be processed into the target shape without cracking or breaking.

他方、Ｂ／Ｎ質量比が低すぎＢＮ析出量が不足する鋼種ＧやＢ／Ｎ質量比，ＢＮ析出量が小さすぎSFIが低すぎる鋼種Ｄでは、３００個以下のプレスでカジリが生じたため成形を中止した。また、Ｍd₃₀が高くSFIが低い鋼種Ｂでは、５１プレスでパンチが欠損したため成形を中止した。プレス加工品に二次加工を施しても、穴拡げ個所に亀裂，破断が多発した。 On the other hand, in steel type G in which the B / N mass ratio is too low and the BN precipitation amount is insufficient, and in the steel type D in which the B / N mass ratio and the BN precipitation amount are too low and the SFI is too low, forming is caused by galling in 300 or less presses. Canceled. Further, the Md ₃₀ is high SFI lower steel grade B, the punch has ceased molded due to deficient 51 press. Even when the pressed product was subjected to secondary processing, cracks and fractures frequently occurred at the hole expansion sites.

以上に説明したように、特定された成分系においてＭd₃₀，SFI，Ｂ／Ｎ質量比を適正管理した成分設計を採用することにより、過酷な条件下でプレス加工した場合でも加工誘起マルテンサイトや積層欠陥に起因する材質硬化が抑えられ、しかもＢＮ系析出物の潤滑作用も期待できる。そのため、板厚：２ｍｍ以上のオーステナイト系ステンレス鋼板であっても、割れ等の加工欠陥なく良好な形状に加工できる。 As described above, by adopting a component design in which the Md ₃₀ , SFI, and B / N mass ratios are appropriately controlled in the specified component system, even when pressed under harsh conditions, processing-induced martensite and Curing of the material due to stacking faults can be suppressed, and the lubricating effect of BN-based precipitates can be expected. Therefore, even an austenitic stainless steel plate having a thickness of 2 mm or more can be processed into a good shape without processing defects such as cracks.

実施例で使用したダイス，ポンチとステンレス鋼板ブランクとの関係を示す図The figure which shows the relationship between the die | dye and punch used in the Example, and a stainless steel plate blank

符号の説明Explanation of symbols

１：ダイス ２：ポンチ ３：ステンレス鋼板
Ｄ_d：ダイス内径 ｒ_d：ダイス肩半径 Ｄ_p：ポンチ先端径 ｒ_p：ポンチ肩半径 1: Die 2: Punch 3: Stainless steel plate D _d : Die inner diameter r _d : Die shoulder radius D _p : Punch tip diameter r _p : Punch shoulder radius

Claims (1)

Ｃ：０.０３質量％以下，Ｓｉ：１.０質量％以下，Ｍｎ：５.０質量％以下，Ｎｉ：５〜１５質量％，Ｃｒ：１５〜２０質量％，Ｃｕ：５.０質量％以下，Ｍｏ：３.０質量％以下，Ｎ：０.０３質量％以下，Ｂ：０.０００１〜０.０１００質量％，残部が不可避的不純物を除きＦｅで、式(１)で定義されるＭd₃₀値：-６０〜-１０，式(２)で定義されるSFI値：３０以上，Ｂ／Ｎ質量比：０.０１以上に成分調整された組成をもち、マトリックスにＢＮが０.００１面積％以上の割合で分散していることを特徴とする深絞り性に優れたオーステナイト系ステンレス鋼。
Md₃₀=551-462(Ｃ+Ｎ)-9.2Ｓｉ-8.1Ｍｎ-29(Ｎｉ+Ｃｕ)-13.7Ｃｒ-18.5Ｍｏ
・・・・(１)
SFI=2.2Ｎｉ+6Ｃｕ-1.1Ｃｒ-13Ｓｉ-1.2Ｍｎ+32 ・・・・(２) C: 0.03 mass% or less, Si: 1.0 mass% or less, Mn: 5.0 mass% or less, Ni: 5-15 mass%, Cr: 15-20 mass%, Cu: 5.0 mass% Hereinafter, Mo: 3.0% by mass or less, N: 0.03% by mass or less, B: 0.0001 to 0.0100% by mass, the balance is Fe except for inevitable impurities, and is defined by the formula (1) Md ₃₀ value: −60 to −10, SFI value defined by the formula (2): 30 or more, B / N mass ratio: having a composition adjusted to 0.01 or more, and BN of 0.001 in the matrix An austenitic stainless steel excellent in deep drawability characterized by being dispersed at a ratio of area% or more.
Md ₃₀ = 551-462 (C + N) -9.2Si-8.1Mn-29 (Ni + Cu) -13.7Cr-18.5Mo
・ ・ ・ ・ (1)
SFI = 2.2Ni + 6Cu-1.1Cr-13Si-1.2Mn + 32 (2)

Images