JP2004137515A - Square vessel made of ferritic stainless steel - Google Patents
Square vessel made of ferritic stainless steel Download PDFInfo
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Abstract
Description
【0001】
【産業上の利用分野】
本発明は、壁割れ(ウォールブレーク)がなく形状精度の良好なフェライト系ステンレス鋼製角筒容器に関する。
【0002】
【従来の技術】
SUS430,SUS430LX等のフェライト系ステンレス鋼は、良好な耐食性を呈し、高価なNiを含まないためオーステナイト系ステンレス鋼に比較して安価であるため、耐久消費財を中心に広範な用途で使用されている。フェライト系ステンレス鋼の用途展開に伴い、製品形状に成形するプレス加工条件が一段と過酷になることから、一層優れた深絞り加工性を呈するフェライト系ステンレス鋼が望まれている。
【0003】
深絞り加工性の向上を狙った数多くの研究が報告されており、Ti,Nbの複合添加が代表的である。複合添加したTi,Nbは、マトリックスに固溶しているC,Nを炭窒化物として析出させ、マトリックスのC,N濃度を低減させることにより深絞り加工性を向上させる。更に、Mg系介在物によるリジング特性の向上(特開2000−192199号公報),Ti,Nbの複合添加と熱延条件との組合せによるランクフォード値の向上(特公平8−26436号公報)等も知られている。
【0004】
種々の用途にフェライト系ステンレス鋼を使用する場合、ランクフォード値,リジング特性だけでなく最終製品形状に成形する際の形状対称性も重要な要求特性である。たとえば、角筒形状に成形する角筒絞りでは、素材各部に均一な変形が生じがたく、壁割れや肉厚変動が発生しやすい。場合によっては、角筒絞り後の二次加工で最終製品形状に成形する場合があり、二次加工時に割れ,破断等の加工欠陥が生じないことも要求特性である。
【0005】
一般的にオーステナイト系ステンレス鋼板よりも加工性が劣るフェライト系ステンレス鋼板を角筒絞りすると、オーステナイト系ステンレス鋼板に比較して大きな減肉が生じやすい。大きな減肉部のある角筒容器に型寸法最終調整のためのプレス(リストライク)を施すと、減肉部を起点とする壁割れ(ウォールブレーク)が発生する。壁割れは、穴拡げ加工,曲げ,扁平化,張出し等の二次加工によっても発生しがちである。
【0006】
【発明が解決しようとする課題】
角筒絞り後に角筒容器を600〜800℃で軟化焼鈍することにより壁割れをある程度抑制できるが、二次加工条件が過酷になるに従い軟化焼鈍だけでは壁割れの発生を完全に抑制できない。壁割れを完全に防止できない現状では、壁割れの発生率を予測することが困難であり、角筒絞りや二次加工の際に壁割れが急に頻発する事態もある。
【0007】
壁割れ対策が十分でないことは、壁割れに及ぼす合金設計や金属組織が解明されていないことに原因がある。そこで、本発明者等は、耐壁割れ性と合金設計,金属組織との関係を調査・検討した。その結果、成分・組成を適正に管理し、深絞り加工性の指標であるランクフォード値の面内異方性を小さくするとき、過酷な条件下で二次加工しても壁割れを抑制できることを見出した。
【0008】
【課題を解決するための手段】
本発明は、新規な知見をベースに完成されたものであり、合金設計,ランクフォード値の最小値及び平均偏差Δr*を総合的に調整することにより、壁割れがなく高精度の最終製品形状に加工できる角筒容器を提供することを目的とする。
【0009】
本発明の角筒容器は、その目的を達成するため、C:0.10質量%以下,Si:2.0質量%以下,Mn:2.0質量%以下,P:0.050質量%以下,S:0.020質量%以下,Cr:11.0〜35.0質量%,N:0.05質量%以下,Ti:0.05〜0.5質量%,Nb:0.10〜0.50質量%を含み、面内全方向に沿って測定したランクフォード値の最小値rminが1.4以上,Δr*=(|rL−rD|+|rT−rD|)/2(ただし、rL,rT,rDはそれぞれ圧延方向,圧延方向に直交する方向,圧延方向に対して45度傾斜する方向に沿って測定したランクフォード値)で定義される平均偏差Δr*が0.8以下のフェライト系ステンレス鋼板を素材とし、深絞り加工によって角筒状に成形されていることを特徴とする。
【0010】
素材フェライト系ステンレス鋼は、更にNi:2.0質量%以下,Mo:3.0質量%以下,Cu:2.0質量%以下,V:0.30質量%以下,Al:4.0質量%以下,B:0.0100質量%以下の1種又は2種以上を含むことができる。
【0011】
【作用】
本発明者等は、角筒絞りによって素材フェライト系ステンレス鋼から作製された角筒容器に発生する壁割れを素材の材質,物性との関係で詳細に調査・検討した。その結果、ランクフォード値の最小値rmin及び平均偏差Δr*に壁割れが大きく依存しており、最小値rmin及び平均偏差Δr*を適正に管理することにより耐壁割れ性を改善できることを解明した。
【0012】
フェライト系ステンレス鋼は、普通鋼に比較してCr含有量が高いため硬質化しており、伸びも低い。素材の延性に基づく張出し要素による加工性の向上が期待できないことから、板厚収縮又は幅方向に沿った材料流入の指標としてランクフォード値(r値)に着目し、最終製品形状への成形に耐え得るフェライト系ステンレス鋼を調査した。ランクフォード値としても、従来から汎用されている圧延方向(L方向),圧延方向に直交する方向(T方向),圧延方向に対して45度傾斜した方向(D方向)の三方向に限らず、面内全方向に沿って測定し、最小のランクフォード値rmin及びΔr*=(|rL−rD|+|rT−rD|)/2で定義される平均偏差Δr*評価指標に使用している。
ランクフォード値の最小値rmin及び平均偏差Δr*は角筒絞り加工性,二次加工性を的確に表す指標であり、rmin≧1.4,Δr*≦0.8に管理することにより角筒絞り時や二次加工時に割れ等の欠陥発生が抑制され、形状精度の良好な角筒容器が得られる。
【0013】
以下、素材に使用するフェライト系ステンレス鋼の合金成分,含有量等を説明する。
C:0.10質量%以下
最終焼鈍時に再結晶フェライトのランダム化に有効な再結晶核となる炭化物を形成する。しかし、過剰量のC含有は、冷延焼鈍板の強度を上昇させ延性の低下を招くことから、上限を0.10質量%に規制した。
Si:2.0質量%以下
溶鋼段階で脱酸剤として使用される合金成分である。しかし、固溶強化能が高く、過剰量のSi含有は材質硬化,延性低下を引き起こすので、Si含有量の上限を2.0質量%に規制した。
【0014】
Mn:2.0質量%以下
オーステナイト形成元素であり、固溶強化能が小さく材質への悪影響が小さい。しかし、2.0質量%を超える過剰量のMnが含まれると、溶製時にヒュームが発生しやすく、製造性が低下する。
P:0.050質量%以下
熱間加工性に悪影響を及ぼす有害成分であるが、0.05質量%以下にP含有量を抑えることによりP起因の悪影響がなくなる。
【0015】
S:0.020質量%以下
結晶粒界に偏析しやすく、粒界脆化によって熱間加工性を劣化させる有害成分であるが、0.020質量%以下に規制することによりS起因の悪影響がなくなる。
Cr:11.0〜35.0質量%
ステンレス鋼に要求される耐食性の向上に有効な不動態皮膜を形成する合金成分であり、11.0質量%以上でCr添加の効果がみられる。しかし、Cr含有量が高くなると靭性,加工性が低下するので、上限を35.0質量%に規制した。
【0016】
N:0.05質量%以下
最終焼鈍時に再結晶フェライトのランダム化に有効な再結晶核となる窒化物を形成する。しかし、過剰量のN含有は、冷延焼鈍板の強度を上昇させ延性の低下を招くことから、上限を0.05質量%に規制した。
Ti:0.05〜0.5質量%
C,Nの固定及びフェライト結晶粒の微細化よって加工性,耐食性,耐壁割れ性を向上させる合金成分であり、0.05質量%以上でTi添加の効果がみられる。しかし、0.50質量%を超える過剰量のTiを添加すると、鋼材コストが上昇するばかりでなくTi系介在物起因の表面欠陥が発生しやすくなる。
【0017】
Nb:0.10〜0.50質量
Tiと同様にC,Nの固定及びフェライト結晶粒の微細化よって加工性,耐壁割れ性を向上させる合金成分であり、0.10質量%以上で添加効果がみられる。Nbに由来するNb系炭化物やFe2Nbは、フェライトの再結晶核として働き、ランクフォード値の最小値rmin及び平均偏差Δr*を改善する上でも有効である。しかし、0.50質量%を超える過剰量のNbを添加すると、鋼材が硬質化し加工性に悪影響が現れやすくなる。Nbの過剰添加は、再結晶温度を上げる点でも不利である。
【0018】
Ni:2.0質量%以下
必要に応じて添加される合金成分であり、オーステナイト形成元素であって過剰添加は鋼材の硬質化,コスト上昇の原因となるので、Ni添加量を2.0質量%以下に定める。
Mo:3.0質量%以下
必要に応じて添加される合金成分であり、耐食性を改善する作用を呈する。しかし、3.0質量%を超える過剰量のMoを添加すると高温での固溶強化や動的再結晶の遅滞により熱間加工性が低下する。
【0019】
Cu:2.0質量%以下
製鋼段階でスクラップ等の原料から不可避的に混入する成分であるが、Cu含有量を2.0質量%以下に規制するときCu起因の熱間加工性,耐食性低下が抑えられる。
V,Zr:0.30質量%以下
Vは固溶Cを炭化物として析出させることにより、Zrは鋼中酸素を酸化物として捕捉することにより加工性,靭性の向上に寄与する任意成分である。しかし、過剰添加は製造性の低下を招くので、V,Zrを添加する場合には0.01〜0.30質量%の範囲で含有量を選定することが好ましい。
【0020】
Al:4.0質量%以下
必要に応じて添加される合金成分であり、製鋼段階で脱酸剤として添加され、耐酸化性を向上させる作用も呈する。しかし、Alを過剰添加すると表面欠陥が発生しやすくなるので、4.0質量%にAl含有量の上限を設定した。
B:0.0100質量%以下
必要に応じて添加される合金成分であり、Nを固定し耐食性,加工性を改善する。0.0005質量%以上で添加効果がみられるが、0.0050質量%を超える過剰添加は熱間加工性に悪影響を及ぼす。
以上に掲げた成分の他、Ca,Mg,Co,REM等もあるが、過剰に含まれない限り角筒容器の耐壁割れ性に影響を及ぼさない。
【0021】
ランクフォード値の最小値の最小値:rmin≧1.4
ランクフォード値が高い材料は、プレス成形,角筒絞り加工時に板厚方向の歪みが小さく平面方向の歪みが大きくなる。板厚方向に優先して平面方向に歪みが進行することは、プレス成形,角筒絞り加工で得られる角筒容器の減肉が少なくなることを意味する。逆にランクフォード値の低い材料から得られる角筒容器では大きな減肉部が生じやすく、壁割れや二次加工の際に割れ発生の起点となる。
【0022】
プレス成形,角筒絞り加工で角筒容器を作製するとき、素材形状に応じてコーナ部分が種々の方向に変わるので、L,T,Dの三方向に沿った従来のランクフォード値だけでは角筒容器の耐壁割れ性を適正に評価できない。そこで、鋼板の面内全方向においてランクフォード値を測定し、ランクフォード値の最小値rminで耐壁割れ性を評価することが必要である。最小値rminを1.4以上と管理することにより、角筒容器の板厚が均等化され、後述の実施例にみられるように壁割れのない角筒容器が得られ、穴拡げ加工,曲げ,扁平化,張出し等の二次加工の際にも加工欠陥の発生が抑制される。
【0023】
ランクフォード値の最小値の平均偏差:Δr*≦0.8
素材ステンレス鋼板は、直辺部12,コーナ部13のあるフランジ11をもつ角筒容器10(図1)に角筒絞り加工される。直辺部12,コーナ部13が不均一変形した素材を更に角筒絞りすると、コーナ部13が局部的に増肉する。増肉したコーナ部13は、大きく加工硬化しており、壁部14に壁割れ15が発生しやすくなる。
【0024】
壁割れの発生原因になるコーナ部の局部的増肉は、L,T,Dの三方向に沿ったランクフォード値の最小値から式Δr*=(|rL−rD|+|rT−rD|)/2で求められる平均偏差Δr*を0.8以下に調整することにより抑制される。すなわち、Δr*≦0.8に平均偏差Δr*を調整することにより、フランジ部を構成する直辺部とコーナ部の変形が均一化され、二次加工時にも壁割れが生じがたい角筒容器が得られる。rmin≧1.4,Δr*≦0.8は、Nb系析出物が析出する温度での熱延板焼鈍及びフェライト再結晶が完了し且つ粗粒化しない中間焼鈍を適正に組み合わせることにより達成される。
【0025】
この点、D方向に沿ったランクフォード値rDが最も低いとする前提でΔr=(rL−2rD+rT)/2が異方性の指標に従来から使用されているが、D方向に沿ったランクフォード値rDが最小でない場合が多い角筒絞りではΔrは意味をもたない。
特定された成分系においてrmin≧1.4,Δr≦0.8に調整されたフェライト系ステンレス鋼板から作製された角筒容器は、耐壁割れ製に優れていると共に伸びフランジ部の割れも抑制され、フランジ部,ダイアール部で板厚減少が小さく良好な形状をもつ製品となる。また、二軸引張り応力下での側壁破断も抑制されるので、穴拡げ加工,曲げ,扁平化,張出し等の二次加工性も優れている。
【0026】
【実施例】
表1に示した成分・組成のステンレス鋼を真空溶解炉で溶製し、鋳造,鍛造を経て板厚4.0mmに熱間圧延した。表中、鋼種A〜Fは本発明で規定した成分・組成を満足し、鋼種G〜Iは本発明の規定を外れる成分・組成をもつ。
【0027】
【0028】
各熱延鋼帯を焼鈍した後、中間板厚2mmに冷間圧延し、中間焼鈍を経て最終板厚0.6mmに仕上げ圧延し、最終的に仕上げ焼鈍した。熱延板焼鈍から仕上げ焼鈍までの熱処理条件を表2に示す。
【0029】
【0030】
圧延方向(L方向)から直交方向(T方向)に至る90度の範囲を5度刻みした各方向に沿って焼鈍仕上げ材からJIS 13B号試験片を切り出し、引張試験に供した。引張試験では、15%の引張り歪みを試験片に与えた後、ランクフォード値を測定し、ランクフォード値の最小値rminを求め、式Δr*=(|rL−rD|+|rT−rD|)/2に従って平均偏差Δr*を算出した。
次いで、焼鈍仕上げ材を角筒形状(図1)に一段絞りし、更にリストライクした各焼鈍仕上げ材につき5個の角筒容器を作製した。角筒容器の各部寸法を図2に示す。個々の角筒容器を観察し、一段絞り又はリストライク後に壁割れが発生していない角筒容器を○,1個でも壁割れが検出された角筒容器を×として耐壁割れ性を評価した。
【0031】
表3の調査結果にみられるように、成分・組成,ランクフォード値の最小値rmin及び平均偏差Δr*が本発明条件を満足する角筒容器では、壁割れが皆無であった。また、リストライクで型寸法を最終調整しても壁割れが発生せず、二次加工性に優れていた。
他方、成分・組成が本発明条件を満足していても、rmin<1.4又はΔr*>0.8の試験番号A2,B2,C2,D2,E2では、角筒絞りによる割れが壁部に検出された。過剰のN,Nbを含む素材GやNbが過剰な素材Iから作製された角筒容器は、素材強度が高いため大きな壁割れが発生していた。逆にNbが少なすぎる素材Hから作製された角筒容器にも壁割れが発生しており、Nb系析出物が不足してランクフォード値の低下が壁割れ発生に至ったことが窺われる。
【0032】
【0033】
【発明の効果】
以上に説明したように、成分・組成が特定されたフェライト系ステンレス鋼板においてrmin≧1.4,Δr*≦0.8とランクフォード値の最小値rmin及び平均偏差Δr*が管理された素材から得られた角筒容器は、壁部に割れがなく、フランジの直辺部及びコーナ部が均一変形している。そのため、各種流体の容器に使用した場合に液漏れが生じる虞がない。また、穴拡げ加工,曲げ,扁平化,張出し等の二次加工を施す場合でも、加工欠陥がなく形状精度の良好な製品形状となる。しかも、オーステナイト系ステンレス鋼に比較して安価な素材を使用しているにも拘らず、優れた耐食性を呈する容器が得られる。このような長所を活用し、高精度で且つ複雑形状が要求される車載用燃料タンク,シンク,角バット,各種器物,電磁調理器鍋等の家庭用機器の部品,モータケース,電池ケース,カバー,センサー,インジェクタ,サーモスタットバルブ,ベアリングシール,フランジ等の産業用機器部品に適した角筒容器が提供される。
【図面の簡単な説明】
【図1】実施例で作製した角筒容器を示す斜視図
【図2】角筒容器の各部寸法を示す平面図(a)及び断面図(b)
【符号の説明】
10:角筒容器 11:フランジ 12:フランジの直辺部 13:フランジのコーナ部 14:壁部 15:壁割れ[0001]
[Industrial application fields]
The present invention relates to a square tube container made of ferritic stainless steel having no wall cracks and good shape accuracy.
[0002]
[Prior art]
Ferritic stainless steels such as SUS430 and SUS430LX exhibit good corrosion resistance and are inexpensive compared to austenitic stainless steels because they do not contain expensive Ni. Yes. With the development of applications of ferritic stainless steel, the press working conditions for forming into a product shape become more severe, so a ferritic stainless steel exhibiting further excellent deep drawing workability is desired.
[0003]
Numerous studies aimed at improving deep drawing workability have been reported, and the combined addition of Ti and Nb is typical. The combined addition of Ti and Nb precipitates C and N dissolved in the matrix as carbonitrides, and improves the deep drawability by reducing the C and N concentration of the matrix. Further, improvement of ridging characteristics by Mg inclusions (Japanese Patent Laid-Open No. 2000-192199), improvement of Rankford value by combination of combined addition of Ti and Nb and hot rolling conditions (Japanese Patent Publication No. 8-26436), etc. Is also known.
[0004]
When ferritic stainless steel is used for various applications, not only the Rankford value and ridging characteristics, but also the shape symmetry when forming the final product shape are important required characteristics. For example, in a rectangular tube shaper formed into a rectangular tube shape, uniform deformation is unlikely to occur in each part of the material, and wall cracks and wall thickness variations are likely to occur. Depending on the case, it may be formed into a final product shape by secondary processing after rectangular tube drawing, and it is also a required characteristic that processing defects such as cracking and fracture do not occur during secondary processing.
[0005]
In general, when a ferritic stainless steel plate having a workability inferior to that of an austenitic stainless steel plate is square-drawn, a large thickness reduction is likely to occur compared to an austenitic stainless steel plate. When a square tube container having a large thickness reduction part is subjected to a press (restriction) for final adjustment of the mold size, a wall break (wall break) starting from the thickness reduction part occurs. Wall cracks tend to occur by secondary processing such as hole expansion, bending, flattening, and overhanging.
[0006]
[Problems to be solved by the invention]
Wall cracking can be suppressed to some extent by softening and annealing the rectangular tube container at 600 to 800 ° C. after the rectangular tube is drawn. However, the occurrence of wall cracking cannot be completely suppressed only by softening annealing as the secondary processing conditions become severe. In the present situation where wall cracks cannot be completely prevented, it is difficult to predict the rate of occurrence of wall cracks, and there are situations in which wall cracks suddenly occur frequently during square tube drawing or secondary processing.
[0007]
The lack of countermeasures against wall cracks is due to the fact that the alloy design and metal structure that affect wall cracks have not been elucidated. Therefore, the present inventors investigated and examined the relationship between wall crack resistance, alloy design, and metal structure. As a result, it is possible to control wall cracking even under secondary conditions under severe conditions when properly controlling the ingredients and composition and reducing the in-plane anisotropy of the Rankford value, which is an index of deep drawability. I found.
[0008]
[Means for Solving the Problems]
The present invention has been completed on the basis of novel knowledge, and by comprehensively adjusting the alloy design, the minimum value of the Rankford value and the average deviation Δr *, there is no wall cracking and the final product shape is highly accurate. An object of the present invention is to provide a rectangular tube container that can be processed into a rectangular shape.
[0009]
In order to achieve the object, the rectangular tube container of the present invention has C: 0.10% by mass or less, Si: 2.0% by mass or less, Mn: 2.0% by mass or less, P: 0.050% by mass or less. , S: 0.020 mass% or less, Cr: 11.0-35.0 mass%, N: 0.05 mass% or less, Ti: 0.05-0.5 mass%, Nb: 0.10-0 The minimum value r min of the Rankford value measured along all in-plane directions including 50 mass% is 1.4 or more, Δr * = (| r L −r D | + | r T −r D |) / 2, where r L , r T , and r D are the average deviation defined by the rolling direction, the direction orthogonal to the rolling direction, and the Rankford value measured along the direction inclined 45 degrees with respect to the rolling direction, respectively. Made from a ferritic stainless steel plate with a Δr * of 0.8 or less and formed into a square tube by deep drawing. And wherein the are.
[0010]
The material ferritic stainless steel further includes Ni: 2.0 mass% or less, Mo: 3.0 mass% or less, Cu: 2.0 mass% or less, V: 0.30 mass% or less, Al: 4.0 mass% % Or less, B: 0.0100% by mass or less can be included.
[0011]
[Action]
The present inventors investigated and examined in detail the wall cracks generated in a rectangular tube container made of ferritic stainless steel by a rectangular tube restriction in relation to the material and physical properties of the material. As a result, we rely wall cracks larger the minimum value r min and the average deviation [Delta] r of Lankford value *, can improve the耐壁cracking resistance by properly managing the minimum value r min and a mean deviation [Delta] r * Elucidated.
[0012]
Ferritic stainless steel is hardened because of its high Cr content compared to ordinary steel, and its elongation is low. Since it is not possible to expect improvement in workability due to the overhanging element based on the ductility of the material, attention is paid to the Lankford value (r value) as an index of material thickness shrinkage or material inflow along the width direction. We investigated ferritic stainless steels that can withstand. The Rankford value is not limited to the three directions of the rolling direction (L direction), the direction orthogonal to the rolling direction (T direction), and the direction inclined 45 degrees with respect to the rolling direction (D direction). , Measured along all in-plane directions, and averaged deviation Δr * evaluation defined by the minimum Rankford value r min and Δr * = (| r L −r D | + | r T −r D |) / 2 Used for indicators.
The minimum value r min and the average deviation Δr * of the Rankford value are indexes that accurately represent the square tube drawing workability and the secondary workability, and are managed so that r min ≧ 1.4 and Δr * ≦ 0.8. Defects such as cracks are suppressed during square tube drawing or secondary processing, and a square tube container with good shape accuracy is obtained.
[0013]
Hereinafter, the alloy components, contents, and the like of the ferritic stainless steel used for the material will be described.
C: 0.10% by mass or less Forms carbides as recrystallization nuclei effective for randomizing recrystallized ferrite during final annealing. However, since excessive C content increases the strength of the cold-rolled annealed plate and causes a decrease in ductility, the upper limit is regulated to 0.10% by mass.
Si: 2.0% by mass or less Si is an alloy component used as a deoxidizer in the molten steel stage. However, since the solid solution strengthening ability is high and excessive Si content causes material hardening and ductility reduction, the upper limit of Si content is regulated to 2.0 mass%.
[0014]
Mn: 2.0% by mass or less An austenite forming element having a small solid solution strengthening ability and a small adverse effect on the material. However, when an excessive amount of Mn exceeding 2.0% by mass is contained, fumes are likely to be generated during melting, and productivity is lowered.
P: 0.050% by mass or less Although it is a harmful component that adversely affects hot workability, by suppressing the P content to 0.05% by mass or less, there is no adverse effect due to P.
[0015]
S: 0.020% by mass or less It is a harmful component that easily segregates at grain boundaries and deteriorates hot workability due to grain boundary embrittlement, but by controlling to 0.020% by mass or less, there is an adverse effect due to S. Disappear.
Cr: 11.0-35.0 mass%
It is an alloy component that forms a passive film effective for improving the corrosion resistance required for stainless steel, and the effect of Cr addition is seen at 11.0% by mass or more. However, as the Cr content increases, the toughness and workability deteriorate, so the upper limit was regulated to 35.0 mass%.
[0016]
N: 0.05% by mass or less A nitride serving as a recrystallization nucleus effective for randomizing recrystallized ferrite is formed during the final annealing. However, an excessive amount of N contained increases the strength of the cold-rolled annealed plate and causes a decrease in ductility, so the upper limit was regulated to 0.05% by mass.
Ti: 0.05 to 0.5% by mass
It is an alloy component that improves workability, corrosion resistance, and wall cracking resistance by fixing C and N and making ferrite crystal grains finer. The effect of adding Ti is seen at 0.05% by mass or more. However, when an excessive amount of Ti exceeding 0.50% by mass is added, not only the cost of the steel material increases, but also surface defects caused by Ti inclusions tend to occur.
[0017]
Nb: Similar to 0.10 to 0.50 mass Ti, it is an alloy component that improves workability and wall cracking resistance by fixing C and N and refining ferrite crystal grains, added at 0.10 mass% or more The effect is seen. Nb-based carbides derived from Nb and Fe 2 Nb act as recrystallization nuclei of ferrite and are effective in improving the minimum value r min and the average deviation Δr * of the Rankford value. However, when an excessive amount of Nb exceeding 0.50% by mass is added, the steel material becomes hard and adversely affects the workability. The excessive addition of Nb is also disadvantageous in increasing the recrystallization temperature.
[0018]
Ni: 2.0% by mass or less Ni is an alloy component added as necessary, and is an austenite forming element. Excessive addition causes hardening of the steel material and cost increase. % Or less.
Mo: 3.0% by mass or less Mo is an alloy component added as necessary, and exhibits an effect of improving corrosion resistance. However, when an excessive amount of Mo exceeding 3.0% by mass is added, hot workability deteriorates due to solid solution strengthening at a high temperature and delay of dynamic recrystallization.
[0019]
Cu: 2.0% by mass or less Although it is a component inevitably mixed from raw materials such as scrap in the steelmaking stage, when Cu content is regulated to 2.0% by mass or less, hot workability and corrosion resistance decrease due to Cu Is suppressed.
V, Zr: 0.30% by mass or less V is an optional component that contributes to improving workability and toughness by precipitating solid solution C as a carbide and capturing oxygen in the steel as an oxide. However, excessive addition causes a decrease in manufacturability, so when adding V and Zr, it is preferable to select the content in the range of 0.01 to 0.30 mass%.
[0020]
Al: 4.0% by mass or less Al is an alloy component that is added as necessary. It is added as a deoxidizer in the steelmaking stage, and also exhibits an effect of improving oxidation resistance. However, since an excessive addition of Al tends to cause surface defects, the upper limit of the Al content is set to 4.0% by mass.
B: 0.0100% by mass or less An alloy component added as necessary, fixing N and improving corrosion resistance and workability. The effect of addition is observed at 0.0005% by mass or more, but excessive addition exceeding 0.0050% by mass adversely affects hot workability.
In addition to the components listed above, there are Ca, Mg, Co, REM, etc., but they do not affect the wall crack resistance of the rectangular tube container unless it is excessively contained.
[0021]
Minimum value of the minimum value of the Rankford value: r min ≧ 1.4
A material with a high Rankford value has a small distortion in the plate thickness direction and a large distortion in the plane direction during press molding and rectangular tube drawing. If the distortion progresses in the plane direction in preference to the plate thickness direction, it means that the thickness reduction of the rectangular tube container obtained by press molding and rectangular tube drawing processing is reduced. On the other hand, in a rectangular tube container obtained from a material having a low Rankford value, a large thinned portion is likely to occur, which becomes a starting point of crack generation during wall cracking or secondary processing.
[0022]
When a rectangular tube container is manufactured by press molding or rectangular tube drawing, the corner portion changes in various directions depending on the material shape. Therefore, only the conventional Rankford value along the three directions L, T, and D The wall crack resistance of the tube container cannot be evaluated properly. Therefore, it is necessary to measure the Rankford value in all in-plane directions of the steel sheet and evaluate the wall crack resistance with the minimum value r min of the Rankford value. By managing the minimum value r min to be 1.4 or more, the plate thickness of the rectangular tube container is equalized, and a rectangular tube container without a wall crack is obtained as seen in the examples described later, The occurrence of processing defects is also suppressed during secondary processing such as bending, flattening, and overhanging.
[0023]
Average deviation of the minimum value of the Rankford value: Δr * ≦ 0.8
The material stainless steel plate is drawn into a rectangular tube container 10 (FIG. 1) having a
[0024]
The local thickening of the corner portion that causes the occurrence of wall cracking is expressed by the formula Δr * = (| r L −r D | + | r T from the minimum value of the Rankford value along the three directions L, T, and D. It is suppressed by adjusting the average deviation Δr * obtained by −r D |) / 2 to 0.8 or less. That is, by adjusting the average deviation Δr * so that Δr * ≦ 0.8, the deformation of the straight side portion and the corner portion constituting the flange portion is made uniform, and the square tube is less likely to cause wall cracking even during secondary processing. A container is obtained. r min ≧ 1.4 and Δr * ≦ 0.8 are achieved by appropriately combining hot-rolled sheet annealing at a temperature at which Nb-based precipitates precipitate and ferrite recrystallization is completed and intermediate annealing without coarsening is performed. Is done.
[0025]
In this respect, Δr = (r L −2r D + r T ) / 2 is conventionally used as an anisotropy index on the assumption that the Rankford value r D along the D direction is the lowest. is a diaphragm is often rectangular tube not have minimum Lankford value r D along the Δr is meaningless.
A rectangular tube container made of a ferritic stainless steel plate adjusted to r min ≧ 1.4 and Δr ≦ 0.8 in the specified component system is excellent in resistance to wall cracking and cracks in the stretch flange portion. Suppressed, and the product has a good shape with a small reduction in thickness at the flange and dial sections. In addition, since the side wall breakage under biaxial tensile stress is also suppressed, secondary workability such as hole expansion, bending, flattening, and overhanging is excellent.
[0026]
【Example】
Stainless steels having the components and compositions shown in Table 1 were melted in a vacuum melting furnace, and hot rolled to a plate thickness of 4.0 mm through casting and forging. In the table, steel types A to F satisfy the components and compositions defined in the present invention, and steel types G to I have components and compositions that deviate from the definitions of the present invention.
[0027]
[0028]
After each hot-rolled steel strip was annealed, it was cold-rolled to an intermediate sheet thickness of 2 mm, subjected to an intermediate annealing and finished to a final sheet thickness of 0.6 mm, and finally finished annealed. Table 2 shows heat treatment conditions from hot-rolled sheet annealing to finish annealing.
[0029]
[0030]
A JIS 13B test piece was cut out from the annealed finished material along each direction in which a 90 degree range from the rolling direction (L direction) to the orthogonal direction (T direction) was cut by 5 degrees and subjected to a tensile test. In the tensile test, a tensile strain of 15% was applied to the test piece, and then the Rankford value was measured to obtain the minimum value r min of the Rankford value, and the equation Δr * = (| r L −r D | + | r The average deviation Δr * was calculated according to T −r D |) / 2.
Next, the annealed finished material was narrowed down to a square tube shape (FIG. 1), and five square tube containers were produced for each annealed finished material. The dimensions of each part of the rectangular tube container are shown in FIG. Individual square tube containers were observed, and the wall crack resistance was evaluated with ○ as a square tube container in which wall cracking did not occur after one-stage squeezing or restructuring, and x as a square tube container in which even one wall crack was detected. .
[0031]
As can be seen from the investigation results in Table 3, there was no wall cracking in the rectangular tube container in which the component / composition, the minimum value r min of the Rankford value and the average deviation Δr * satisfied the conditions of the present invention. Moreover, even when the mold dimensions were finally adjusted with the wrist-like, wall cracking did not occur and the secondary workability was excellent.
On the other hand, even if the component / composition satisfies the conditions of the present invention, cracks due to rectangular tube drawing are not observed in test numbers A2, B2, C2, D2, and E2 with r min <1.4 or Δr *> 0.8. Detected. In the rectangular tube container made of the material G containing excess N and Nb and the material I containing excessive Nb, the material strength is high, so that a large wall crack occurs. On the contrary, the square container made from the material H having too little Nb also has a wall crack, which suggests that the Nb-based precipitates are insufficient and the Lankford value is lowered.
[0032]
[0033]
【The invention's effect】
As described above, r min ≧ 1.4, Δr * ≦ 0.8, the minimum value r min of the Rankford value, and the average deviation Δr * were controlled in the ferritic stainless steel sheet whose components and compositions were specified. The rectangular tube container obtained from the raw material has no cracks in the wall portion, and the straight side portion and the corner portion of the flange are uniformly deformed. Therefore, there is no possibility of liquid leakage when used for various fluid containers. In addition, even when secondary processing such as hole expansion, bending, flattening, and overhanging is performed, the product shape has no processing defects and good shape accuracy. In addition, a container exhibiting excellent corrosion resistance can be obtained in spite of using an inexpensive material compared to austenitic stainless steel. Taking advantage of these advantages, parts for household equipment such as in-vehicle fuel tanks, sinks, square bats, various items, electromagnetic cooker pans, motor cases, battery cases, covers that require high precision and complex shapes A rectangular tube container suitable for industrial equipment parts such as sensors, injectors, thermostat valves, bearing seals, and flanges is provided.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a rectangular tube container manufactured in an embodiment. FIG. 2 is a plan view (a) and a sectional view (b) showing dimensions of each part of the rectangular tube container.
[Explanation of symbols]
10: Square tube container 11: Flange 12: Right side of flange 13: Corner part of flange 14: Wall part 15: Wall crack
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Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
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JP2010248625A (en) * | 2009-03-27 | 2010-11-04 | Nippon Steel & Sumikin Stainless Steel Corp | Ferritic stainless steel having excellent local corrosion resistance |
JP2011184731A (en) * | 2010-03-08 | 2011-09-22 | Nippon Steel & Sumikin Stainless Steel Corp | Ferritic stainless steel having excellent corrosion resistance in condensed water environment generated from hydrocarbon combustion exhaust gas |
WO2024070493A1 (en) * | 2022-09-26 | 2024-04-04 | 日鉄ステンレス株式会社 | Ferritic stainless steel material for battery components, method for producing same, and battery component |
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2002
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Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
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JP2010248625A (en) * | 2009-03-27 | 2010-11-04 | Nippon Steel & Sumikin Stainless Steel Corp | Ferritic stainless steel having excellent local corrosion resistance |
JP2011184731A (en) * | 2010-03-08 | 2011-09-22 | Nippon Steel & Sumikin Stainless Steel Corp | Ferritic stainless steel having excellent corrosion resistance in condensed water environment generated from hydrocarbon combustion exhaust gas |
WO2024070493A1 (en) * | 2022-09-26 | 2024-04-04 | 日鉄ステンレス株式会社 | Ferritic stainless steel material for battery components, method for producing same, and battery component |
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