JP6421772B2 - Manufacturing method of steel sheet for cans - Google Patents
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Description
本発明は、高強度かつフランジ成形性に優れた缶用鋼板の製造方法に関するものである。 The present invention relates to a method for producing a steel plate for cans having high strength and excellent flange formability.
近年、スチール缶の需要を拡大するため、製缶コストを低減する策がとられている。 In recent years, in order to increase the demand for steel cans, measures have been taken to reduce can manufacturing costs.
製缶コストの低減策としては、素材の低コスト化が挙げられる。絞り加工により成形される２ピース缶はもとより、溶接による円筒成形が主体の３ピース缶であっても、使用する鋼板の薄肉化が進められている。 One way to reduce can manufacturing costs is to reduce the cost of materials. In addition to 2-piece cans formed by drawing, even 3-piece cans mainly made by cylindrical forming by welding, thinning of steel sheets to be used is being promoted.
ただし、単に鋼板を薄肉化すると缶体強度が低下する。したがって、再絞り缶（ＤＲＤ（ｄｒａｗ−ｒｅｄｒａｗ）缶）や溶接缶の缶胴部のような高強度材が用いられている箇所には、単に薄肉化したのみの鋼板を用いることができない。そこで、高強度で極薄の缶用鋼板が望まれている。 However, simply reducing the thickness of the steel sheet will reduce the strength of the can body. Therefore, it is not possible to use a thinned steel plate in a place where a high-strength material such as a redrawn can (DRD (draw-redraw) can) or a can body of a welded can is used. Therefore, a high strength and extremely thin steel plate for cans is desired.
鋼板を薄肉化し、かつ缶体強度を維持するためには、高い上降伏点を備えることが必要になる。缶体強度は耐圧強度で評価されるため、上降伏点の低い鋼板では低い圧力で鋼板が座屈し、缶体強度に劣る。 In order to reduce the thickness of the steel sheet and maintain the can strength, it is necessary to provide a high upper yield point. Since the can strength is evaluated by the pressure strength, the steel plate buckles at a low pressure in the steel plate having a low upper yield point, and the can strength is inferior.
一方、缶胴成形においては、蓋や底を巻き締めるために開口端の拡径加工（フランジ成形）が必要であり、優れた加工性が必要となる。 On the other hand, in can body forming, diameter expansion processing (flange forming) of the open end is necessary to wind up the lid and the bottom, and excellent workability is required.
現在、極薄で硬質な缶用鋼板は、主にＤｏｕｂｌｅ Ｒｅｄｕｃｅ法（以下、ＤＲ法と称す）により製造されている。ＤＲ法では、焼鈍後の鋼板に圧下率が２０％以上の二次冷間圧延を施す。ＤＲ法により製造した鋼板は、高強度であるが加工性に乏しく、フランジ成形時に端部の割れを生じやすい。 Currently, ultra-thin and hard steel plates for cans are mainly manufactured by the Double Reduce method (hereinafter referred to as DR method). In the DR method, secondary cold rolling with a rolling reduction of 20% or more is applied to the annealed steel sheet. A steel plate produced by the DR method has high strength but poor workability, and is liable to crack at the end during flange forming.
こうしたフランジ成形時の割れを防ぐため、溶接部のＨＡＺ（Ｈｅａｔ Ａｆｆｅｃｔｅｄ Ｚｏｎｅ）軟化による加工ひずみの集中を抑制すべく固溶Ｃおよび固溶Ｎの量を適正範囲に限定する方法、フランジ成形性の指標である穴拡げ率を改善すべく鋼板のフェライト及びマルテンサイトの分率を適正なものとする鋼板及び製造方法が下記特許文献により提案されている。 In order to prevent such cracking at the time of flange forming, a method of limiting the amount of solute C and solute N to an appropriate range in order to suppress concentration of processing strain due to HAZ (Heat Affected Zone) softening of the weld, The following patent document proposes a steel plate and a manufacturing method in which the ferrite and martensite fractions of the steel plate are appropriate in order to improve the hole expansion rate as an index.
特許文献１には、質量％で、Ｃ：０．０３０％以上０．１５０％以下、Ｓｉ：０．０１０％以上１．０００％以下、Ｍｎ：１．５０％以上２．７０％以下、Ｐ：０．００１％以上０．０６０％以下、Ｓ：０．００１％以上０．０１０％以下、Ｎ：０．０００５％以上０．０１００％以下、Ａｌ：０．０１０％以上０．０５０％以下、を含有し、選択的に、Ｂ：０．０００５％以上０．００２０％以下、Ｍｏ：０．０１％以上０．５０％以下、Ｃｒ：０．０１％以上０．５０％以下、Ｖ：０．００１％以上０．１００％以下、Ｔｉ：０．００１％以上０．１００％以下、Ｎｂ：０．００１％以上０．０５０％以下、Ｎｉ：０．０１％以上１．００％以下、Ｃｕ：０．０１％以上１．００％以下、Ｃａ：０．０００５％以上０．００５０％以下、ＲＥＭ：０．０００５％以上０．００５０％以下、の１種以上を含有する場合があり、残部がＦｅ及び不可避不純物からなり、前記Ｃ含有量、前記Ｓｉ含有量及び前記Ｍｎ含有量を、単位質量％でそれぞれ［Ｃ］、［Ｓｉ］及び［Ｍｎ］と表したとき、式（５×［Ｓｉ］＋［Ｍｎ］）／［Ｃ］＞１１の関係が成り立ち、金属組織が、面積率で、４０％以上９０％以下のフェライトと、１０％以上６０％以下のマルテンサイトとを含有し、かつ前記フェライトの面積率と前記マルテンサイトの面積率との和が６０％以上を満たし、さらに前記金属組織が、面積率で１０％以下のパーライトと、体積率で５％以下の残留オーステナイトと、面積率で４０％未満の残ベイナイトとのうち１種以上を含有する場合があり、ナノインデンターにて測定された前記マルテンサイトの硬度が、式Ｈ２／Ｈ１＜１．１０及び式σＨＭ＜２０（Ｈ１は前記ホットスタンプ後の板厚表層部の前記マルテンサイトの平均硬度であり、Ｈ２は前記ホットスタンプ後の板厚中心部、すなわち板厚中心における板厚方向に２００μｍの範囲の前記マルテンサイトの平均硬度であり、σＨＭ１は前記ホットスタンプ後の前記板厚中心部における前記マルテンサイトの前記硬度の分散値）を満足し、引張強度ＴＳと穴拡げ率λとの積であるＴＳ×λにおいて５００００ＭＰａ・％以上を満足することを特徴とする冷延鋼板が提案されている。 In Patent Document 1, in mass%, C: 0.030% or more and 0.150% or less, Si: 0.010% or more and 1.000% or less, Mn: 1.50% or more and 2.70% or less, P : 0.001% to 0.060%, S: 0.001% to 0.010%, N: 0.0005% to 0.0100%, Al: 0.010% to 0.050% B: 0.0005% or more and 0.0020% or less, Mo: 0.01% or more and 0.50% or less, Cr: 0.01% or more and 0.50% or less, V: 0.001% to 0.100%, Ti: 0.001% to 0.100%, Nb: 0.001% to 0.050%, Ni: 0.01% to 1.00%, Cu: 0.01% to 1.00%, Ca: 0.0005% to 0.0050%, EM: may contain one or more of 0.0005% or more and 0.0050% or less, and the balance consists of Fe and inevitable impurities, and the C content, the Si content, and the Mn content are expressed in units. When expressed as [C], [Si], and [Mn] in mass%, the relationship of the formula (5 × [Si] + [Mn]) / [C]> 11 holds, and the metal structure is expressed in area ratio. 40% or more and 90% or less of ferrite and 10% or more and 60% or less of martensite, and the sum of the area ratio of the ferrite and the area ratio of the martensite satisfies 60% or more, and The metal structure may contain one or more of pearlite with an area ratio of 10% or less, residual austenite with a volume ratio of 5% or less, and residual bainite with an area ratio of less than 40%. Measured in Further, the hardness of the martensite is expressed by the formula H2 / H1 <1.10 and the formula σHM <20 (H1 is the average hardness of the martensite in the surface layer portion after the hot stamping, and H2 is after the hot stamping. It is the average hardness of the martensite in the range of 200 μm in the thickness direction at the center of the plate thickness, that is, at the thickness center, and σHM1 is the dispersion value of the hardness of the martensite at the center of the plate thickness after the hot stamping) Has been proposed, and a cold-rolled steel sheet characterized by satisfying 50,000 MPa ·% or more in TS × λ, which is the product of tensile strength TS and hole expansion ratio λ, has been proposed.
特許文献２には、質量％で、Ｃ：０．０２％以上０．２０％以下、Ｓｉ：０．００１％以上２．０％以下、Ｍｎ：１．２％以上５．０％以下、Ｐ：０．１％以下、Ｓ：０．０１％以下、ｓｏｌ．Ａｌ：０．００１％以上２．０％以下、Ｎ：０．０１％以下、Ｏ：０．０１％以下およびＢｉ：０．０００１％以上０．０５％以下を含有し、さらに、ＴｉおよびＮｂの１種または２種を０．０５≦Ｔｉ＋Ｎｂ／２≦０．３０を満たす範囲で含有し、残部がＦｅおよび不純物からなる化学組成を有し、引張強度が５９０ＭＰａ以上である機械特性を有することを特徴とする鋼板が提案されている。 Patent Document 2 includes mass%, C: 0.02% to 0.20%, Si: 0.001% to 2.0%, Mn: 1.2% to 5.0%, P : 0.1% or less, S: 0.01% or less, sol. Al: 0.001% or more and 2.0% or less, N: 0.01% or less, O: 0.01% or less and Bi: 0.0001% or more and 0.05% or less, and Ti and Nb One or two of the above are contained in a range satisfying 0.05 ≦ Ti + Nb / 2 ≦ 0.30, the remainder has a chemical composition composed of Fe and impurities, and has mechanical properties of a tensile strength of 590 MPa or more. A steel sheet characterized by the following has been proposed.
特許文献３には、ｍａｓｓ％で、Ｃ：０．０４％超０．０８％以下、Ｓｉ：０．０２％以下、Ｍｎ：１．０％以下、Ｐ：０．０４％以下、Ｓ：０．０５％以下、Ａｌ：０．１％以下、Ｎ：０．００５〜０．０２％以下を含有し、かつ、鋼板中に固溶するＣおよび固溶Ｎの合計が、５０ｐｐｍ≦固溶Ｃ＋固溶Ｎ≦２００ｐｐｍ、かつ鋼板中の固溶Ｃが５０ｐｐｍ以下かつ、鋼板中の固溶Ｎが５０ｐｐｍ以上の範囲からなり、残部をＦｅおよび不可避不純物からなることを特徴とするフランジ成形性に優れた高強度溶接缶用薄鋼板が提案されている。 In Patent Document 3, mass%, C: more than 0.04% and 0.08% or less, Si: 0.02% or less, Mn: 1.0% or less, P: 0.04% or less, S: 0 0.05% or less, Al: 0.1% or less, N: 0.005 to 0.02% or less, and the total of C and solid solution N dissolved in the steel sheet is 50 ppm ≦ solid solution C + Excellent in flange formability characterized by solid solution N ≦ 200 ppm, solid solution C in steel plate is 50 ppm or less, and solid solution N in steel plate is in the range of 50 ppm or more, with the balance being Fe and inevitable impurities. In addition, a thin steel plate for a high-strength weld can has been proposed.
高強度鋼板の薄肉化により、フランジ成形時に介在物起因のクラック発生やクラックの伝播・貫通などが生じやすくなる。 By thinning the high-strength steel sheet, cracks due to inclusions and crack propagation / penetration tend to occur during flange forming.
缶用鋼板の場合、腐食性を有する内容物への適用を考慮すると、良好な耐食性を備える必要があるため、耐食性を阻害する過剰な元素添加は行うことができない。 In the case of steel plates for cans, considering application to corrosive contents, it is necessary to provide good corrosion resistance, so that excessive addition of elements that inhibit corrosion resistance cannot be performed.
上記特性について、前述の従来技術では、フランジ成形性または耐食性のいずれかを満足する鋼板を製造することは可能であるが、両者を満足する鋼板は製造できない。 With respect to the above characteristics, the above-described conventional technology can produce a steel sheet that satisfies either flange formability or corrosion resistance, but cannot produce a steel sheet that satisfies both.
特許文献１に記載の方法は、強度上昇には有効な方法ではあるが、鋼中のＭｎ量が多く、焼鈍時に表面にＭｎが濃化して耐食性を阻害する可能性が高いため缶用鋼板に用いることはできない。また、鋼中のＭｎ量が多くなると、ＭｎＳの析出量が増加するとともにＭｎＳが粗大に成長し、板厚の薄い缶用鋼板においてはＭｎＳがフランジ成形時におけるクラックの起点となる。さらに、硬質相としてマルテンサイトを１０％以上６０％以下含むため、板厚の薄い缶用鋼板ではクラックの伝播や貫通などに対し不利である。 Although the method described in Patent Document 1 is an effective method for increasing the strength, the amount of Mn in the steel is large, and Mn is concentrated on the surface during annealing, so there is a high possibility of inhibiting corrosion resistance. Cannot be used. In addition, when the amount of Mn in the steel increases, the amount of MnS precipitated increases and MnS grows coarsely. In thin steel plates for cans, MnS becomes the starting point of cracks during flange forming. Furthermore, since martensite is contained in the hard phase in an amount of 10% to 60%, a thin steel plate for cans is disadvantageous for crack propagation and penetration.
特許文献２に記載の方法もまた、鋼中のＭｎ量が多く、焼鈍時に表面にＭｎが濃化して耐食性を阻害する可能性が高いため缶用鋼板に用いることはできない。 The method described in Patent Document 2 cannot be used for a steel plate for cans because the amount of Mn in the steel is large and there is a high possibility that Mn will concentrate on the surface during annealing and inhibit corrosion resistance.
特許文献３に記載の方法は、固溶強化による高強度化を提案しているが、固溶強化に有効な固溶Ｃを過時効処理により低減させて軟質化させているうえに、Ｃ：０．０４％超０．０８％以下とＣ量が高いために粗大炭化物が形成しやすく、クラックの起点となるためにフランジ成形性には不利である。 The method described in Patent Document 3 proposes high strength by solid solution strengthening, but solid solution C effective for solid solution strengthening is reduced by overaging treatment and softened, and C: Since the amount of C is more than 0.04% and 0.08% or less, coarse carbides are easily formed, and since it becomes a starting point of cracks, it is disadvantageous for flange formability.
本発明は、かかる事情に鑑みなされたものであり、薄肉化してもフランジ成形において割れを生じず、かつ腐食性の強い内容物に対しても耐食性が良好な高強度缶用鋼板の製造方法を提供することを目的とする。 The present invention has been made in view of such circumstances, and there is provided a method for producing a steel plate for high-strength cans that does not crack in flange molding even when it is thinned, and has good corrosion resistance against highly corrosive contents. The purpose is to provide.
本発明者らは、上記課題を解決するために鋭意研究を行った。その結果、以下の知見を得た。 The inventors of the present invention have intensively studied to solve the above problems. As a result, the following knowledge was obtained.
フランジ成形において、硬度差が存在する部分にひずみが集中するのを防ぐために、母材部硬度と溶接部硬度の比が小さい鋼板を用いることが有効であることがわかった。 In flange forming, it was found that it is effective to use a steel sheet having a small ratio of the base material hardness and the weld hardness in order to prevent strain from concentrating on the portion where the hardness difference exists.
また、３ピース缶におけるフランジ成形時に発生するクラックは、従来は溶接のＨＡＺ部又はＨＡＺ／母材界面で発生していたが、薄肉化した鋼板を用いたフランジ成形のクラックは、ＨＡＺ部より数ミリ離れた領域で発生しており、この領域にひずみが集中してクラックが発生する。これは、薄肉化した鋼板を用いると、ネック（縮径）成形時にシワが発生しやすくなり、そのシワがＨＡＺ部より数ミリ離れた領域で発生するためである。ＨＡＺ部より数ミリ離れた領域の材料特性は母材とほぼ等しく、フランジ成形性は母材の穴拡げ率と相関することもわかった。 Also, cracks that occur during flange forming in a three-piece can have conventionally occurred at the welded HAZ part or at the HAZ / base metal interface. It occurs in a region separated by millimeters, and strain concentrates in this region and cracks occur. This is because when a thin steel plate is used, wrinkles are likely to occur during neck (reduced diameter) forming, and the wrinkles occur in a region several millimeters away from the HAZ portion. It was also found that the material properties in the region several millimeters away from the HAZ part are almost equal to the base material, and the flange formability correlates with the hole expansion rate of the base material.
板厚が厚い材料の穴拡げ試験では、加工度の大きいパンチ非接触面でクラックが発生して伝播するが、板厚が薄い缶用鋼板では表裏の加工度の差が小さくなるのでパンチ接触面でもクラックが発生する。このため、穴拡げ試験は両面に対して実施することが必要で、クラックの起点を少なくするために鋼板表面の材質の差を小さくすることが望ましいことがわかった。そして、これらの知見をもとに、フランジ成形性の優れる缶を評価できる試験方法を確立した。すなわち、溶接部平均ビッカース硬度／母材部平均ビッカース硬度≦３．４、穴拡げ率（％）≧３０であれば、フランジ成形性が優れる缶とできることを見出した。 In a hole expansion test for a material with a large plate thickness, cracks are generated and propagated on the non-contact surface of the punch with a large degree of processing. But cracks occur. For this reason, it has been found that the hole expansion test needs to be performed on both sides, and it is desirable to reduce the difference in the material on the steel sheet surface in order to reduce the starting point of cracks. And based on these knowledge, the test method which can evaluate the can excellent in flange formability was established. That is, it has been found that if the welded part average Vickers hardness / base material part average Vickers hardness ≦ 3.4 and the hole expansion ratio (%) ≧ 30, the can can be made excellent in flange formability.
発明者らは、缶成形後にこのような特性となる缶用鋼板の製造方法を鋭意検討した。その結果、板厚を薄くした場合でも穴拡げ性を損なわずに高強度化するためには、析出強化および固溶強化を適切なバランスで適用することが必要であることを見出した。すなわち、窒素の析出物は粗大になりやすく、析出強化に効果が見られないだけでなく、粗大な窒化物は穴拡げ（フランジ）成形時にクラックの起点となり好ましくないため、Ｎ含有量を０．０２００％以下として、窒素は固溶させて粗大な窒化物の生成を抑制しつつ、固溶強化に利用した。また、ＮｂとＣを適正量とすることで、微細なＮｂＣを析出させ、析出強化に利用した。
さらに、耐食性に支障のない範囲の元素添加量（特に、Ｍｎ，Ｐの含有量範囲を制限）で成分設計を行うことにより、腐食性の強い内容物に対しても良好な耐食性を示すことを確認した。
加えて、従来の二次冷間圧延における圧下率に比べ低い圧下率での加工強化を施すことも有効である。
本発明は、以上の知見に基づきなされたもので、その要旨は以下の通りである。
Inventors earnestly examined the manufacturing method of the steel plate for cans which becomes such a characteristic after can molding. As a result, it was found that precipitation strengthening and solid solution strengthening must be applied in an appropriate balance in order to increase the strength without impairing the hole expandability even when the plate thickness is reduced. That is, nitrogen precipitates tend to be coarse and not only have no effect on precipitation strengthening, but coarse nitrides are not preferable because they are the starting point of cracks during hole expansion (flange) molding, and therefore the N content is set to a value of 0.1. Nitrogen was used as a solid solution strengthening while suppressing the formation of coarse nitrides by setting the nitrogen content to 0200% or less. Moreover, by making Nb and C into appropriate amounts, fine NbC was precipitated and used for precipitation strengthening.
In addition, by designing the components with an element addition amount that does not interfere with corrosion resistance (especially, limiting the content range of Mn and P), it shows good corrosion resistance even for highly corrosive contents. confirmed.
In addition, it is also effective to perform work strengthening at a reduction rate that is lower than the reduction rate in conventional secondary cold rolling.
The present invention has been made based on the above findings, and the gist thereof is as follows.
質量％で、Ｃ：０．０２０％超え０．０４０％以下、Ｓｉ：０．０４％以下、Ｍｎ：０．１０％以上１．００％以下、Ｐ：０．１００％以下、Ｓ：０．０３０％以下、Ａｌ：０．１０％以下、Ｎ：０．０１２０％超え０．０２００％以下、Ｎｂ：０．００４％以上０．０４０％以下を含有し、残部がＦｅおよび不可避的不純物からなる成分組成を有する鋼スラブを、仕上げ圧延温度がＡｒ３変態点以上９９０℃以下の条件で圧延し、巻き取り温度が４００℃以上６００℃未満の条件で巻き取る熱間圧延工程と、前記熱間圧延工程後に、酸洗し、圧下率が８０％以上の条件で圧延する一次冷間圧延工程と、前記一次冷間圧延工程後に、均熱温度が６５０℃以上７８０℃以下、均熱時間が１０ｓ以上５５ｓ以下の条件で連続焼鈍する焼鈍工程と、前記焼鈍工程後に、少なくとも２基の圧延機スタンドを用い、うち少なくとも１基の圧延機スタンドにおいて表面粗さＲａが０．９μｍ以上３．０μｍ以下かつＰＰＩが１５０以上４００以下の圧延ロールを用い、１．０％以上１９％以下の圧下率で圧延する二次冷間圧延工程を有することを特徴とする缶用鋼板の製造方法。 In mass%, C: more than 0.020% and 0.040% or less, Si: 0.04% or less, Mn: 0.10% or more and 1.00% or less, P: 0.100% or less, S: 0.00. 030% or less, Al: 0.10% or less, N: 0.0120% to 0.0200% or less, Nb: 0.004% or more and 0.040% or less, with the balance being Fe and inevitable impurities A hot rolling step in which a steel slab having a component composition is rolled under a condition where the finish rolling temperature is Ar 3 transformation point or higher and 990 ° C. or lower and the winding temperature is 400 ° C. or higher and lower than 600 ° C., and the hot After the rolling step, pickling and rolling in a primary cold rolling step in which the rolling reduction is 80% or more, and after the primary cold rolling step, the soaking temperature is 650 ° C. or more and 780 ° C. or less and the soaking time is 10 seconds. An annealing process for continuous annealing under the condition of 55 s or less, After the annealing step, at least two rolling mill stands are used, of which at least one rolling mill stand uses a rolling roll having a surface roughness Ra of 0.9 μm to 3.0 μm and a PPI of 150 to 400, A method for producing a steel plate for cans, comprising a secondary cold rolling step of rolling at a rolling reduction of 1.0% or more and 19% or less.
本発明の製造方法によれば、溶接部平均ビッカース硬度／母材部平均ビッカース硬度≦３．４、穴拡げ率（％）≧３０を示すフランジ成形性に優れる高強度缶用鋼板が得られる。詳細には、本発明では、溶接部硬度を上昇させるＣ量を０．０２０％超え０．０４０％以下に限定し、微細ＮｂＣによる析出強化、Ｎによる固溶強化および焼鈍後に１．０％以上１９％以下の低圧下率で二次冷間圧延を行うことによる加工強化により、複合強化し強度を上昇させる。その結果、溶接部平均ビッカース硬度／母材部平均ビッカース硬度≦３．４、穴拡げ率（％）≧３０を示す缶用鋼板が得られ、割れを生じることなく缶体のフランジ成形が可能となる。本発明の鋼板は溶接部の無い２ピース缶用途に適用することも可能である。さらに、本発明の成分組成であれば、耐食性に支障が生じない。その結果、本発明の缶用鋼板の製造方法で製造された缶用鋼板は、強度、フランジ成形性、耐食性いずれにおいても優れる。 According to the production method of the present invention, a steel plate for a high-strength can that is excellent in flange formability and exhibits a weld zone average Vickers hardness / base material average Vickers hardness ≦ 3.4 and a hole expansion ratio (%) ≧ 30 is obtained. Specifically, in the present invention, the amount of C for increasing the hardness of the weld zone is limited to 0.020% and 0.040% or less, 1.0% or more after precipitation strengthening with fine NbC, solid solution strengthening with N, and annealing. By strengthening the work by performing secondary cold rolling at a low pressure reduction rate of 19% or less, the composite strength is increased and the strength is increased. As a result, a steel plate for a can having a welded portion average Vickers hardness / base material portion average Vickers hardness ≦ 3.4 and a hole expansion ratio (%) ≧ 30 can be obtained, and the can body can be flange-formed without causing cracks. Become. The steel plate of the present invention can also be applied to a two-piece can used without a weld. Furthermore, if it is a component composition of this invention, a trouble will not arise in corrosion resistance. As a result, the steel plate for cans produced by the method for producing a steel plate for cans of the present invention is excellent in any of strength, flange formability, and corrosion resistance.
以下、本発明の実施形態について説明する。 Hereinafter, embodiments of the present invention will be described.
本発明の缶用鋼板の製造方法で製造された缶用鋼板は、溶接部平均ビッカース硬度／母材部平均ビッカース硬度≦３．４、穴拡げ率（％）≧３０であり、優れたフランジ成形性を有する。
本発明では、Ｎｂを析出強化元素として添加し、Ｎを固溶強化元素として添加し、焼鈍後に圧下率１．０％以上１９％以下の二次冷間圧延を行うことによる加工強化で高強度を達成する。析出強化元素、固溶強化元素を添加しつつ、成分組成、製造条件を適正化することで、溶接部平均ビッカース硬度／母材部平均ビッカース硬度≦３．４、穴拡げ率（％）≧３０である缶用鋼板が得られる。
The steel plate for cans produced by the method for producing a steel plate for cans according to the present invention has an average flanged Vickers hardness / average base Vickers hardness ≦ 3.4, hole expansion rate (%) ≧ 30, and excellent flange forming Have sex.
In the present invention, Nb is added as a precipitation strengthening element, N is added as a solid solution strengthening element, and high strength is achieved by work strengthening by performing secondary cold rolling with a rolling reduction of 1.0% to 19% after annealing. To achieve. By adding the precipitation strengthening element and the solid solution strengthening element and optimizing the component composition and manufacturing conditions, the welded part average Vickers hardness / base material part average Vickers hardness ≦ 3.4, hole expansion rate (%) ≧ 30 A steel plate for cans is obtained.
次に、本発明の缶用鋼板の製造方法における成分組成について説明する。本発明の缶用鋼板は、Ｃ：０．０２０％超え０．０４０％以下、Ｓｉ：０．０４％以下、Ｍｎ：０．１０％以上１．００％以下、Ｐ：０．１００％以下、Ｓ：０．０３０％以下、Ａｌ：０．１０％以下、Ｎ：０．０１２０％超え０．０２００％以下、Ｎｂ：０．００４％以上０．０４０％以下を含有し、残部がＦｅおよび不可避的不純物からなる成分組成とする。以下、各成分について説明する。なお、本明細書において、成分組成の説明における「％」は「質量％」を意味する。 Next, the component composition in the manufacturing method of the steel plate for cans of this invention is demonstrated. The steel plate for cans of the present invention is C: more than 0.020% and 0.040% or less, Si: 0.04% or less, Mn: 0.10% or more and 1.00% or less, P: 0.100% or less, S: 0.030% or less, Al: 0.10% or less, N: 0.0120% to 0.0200% or less, Nb: 0.004% or more and 0.040% or less, the balance being Fe and inevitable The component composition consists of mechanical impurities. Hereinafter, each component will be described. In the present specification, “%” in the description of the component composition means “% by mass”.
Ｃ：０．０２０％超え０．０４０％以下
本発明の缶用鋼板においては、二次冷間圧延工程に所定値以上の上降伏点（４５０〜６００ＭＰａ）を達成することが必要であり、Ｎｂ添加で生成するＮｂＣによる析出強化を利用することが重要となる。ＮｂＣによる析出強化を利用するためには、Ｃ含有量を０．０２０％超えとすることが必要である。一方、Ｃ含有量が０．０４０％を超えるとセメンタイトが粗大に成長して析出し、穴拡げ加工時に、粗大なセメンタイトを起点として割れ（クラック）が発生し、フランジ加工性が劣化する。このためＣ含有量は０．０４０％以下とする。
C: 0.020% to 0.040% or less In the steel sheet for cans of the present invention, it is necessary to achieve an upper yield point (450 to 600 MPa) of a predetermined value or more in the secondary cold rolling step, and Nb It is important to use precipitation strengthening due to NbC produced by addition. In order to utilize precipitation strengthening by NbC, it is necessary to make the C content exceed 0.020%. On the other hand, when the C content exceeds 0.040%, cementite grows coarsely and precipitates, and cracks are generated from the coarse cementite as a starting point during hole expansion processing, and flange workability deteriorates. For this reason, C content shall be 0.040% or less.
Ｓｉ：０．０４％以下
Ｓｉは固溶強化により鋼を高強度化させる元素である。しかし、Ｓｉ含有量が０．０４％を超えると耐食性が著しく損なわれる。よって、Ｓｉ含有量は０．０４％以下とする。
Si: 0.04% or less Si is an element that increases the strength of steel by solid solution strengthening. However, if the Si content exceeds 0.04%, the corrosion resistance is significantly impaired. Therefore, the Si content is set to 0.04% or less.
Ｍｎ：０．１０％以上１．００％以下
Ｍｎは固溶強化により鋼の強度を増加させる元素である。この効果を得るためには、０．１０％以上の含有を必要とする。また、目標の降伏強度を確保するには０．１０％以上にする必要がある。一方、Ｍｎ含有量が１．００％を超えると耐食性が劣る。また、フランジ成形におけるクラックの起点となるＭｎＳ介在物の生成量が増加し、フランジ成形性を劣化させる。よって、Ｍｎ含有量の上限を１．００％以下とする。
Mn: 0.10% or more and 1.00% or less Mn is an element that increases the strength of steel by solid solution strengthening. In order to obtain this effect, a content of 0.10% or more is required. Moreover, in order to ensure the target yield strength, it is necessary to make it 0.10% or more. On the other hand, if the Mn content exceeds 1.00%, the corrosion resistance is poor. In addition, the amount of MnS inclusions that become the starting point of cracks in flange molding increases, and the flange moldability deteriorates. Therefore, the upper limit of the Mn content is 1.00% or less.
Ｐ：０．１００％以下
Ｐは固溶強化能が大きい元素である。しかし、Ｐの含有量が０．１００％を超えると耐食性が劣る。このため、Ｐ含有量は０．１００％以下とする。
P: 0.100% or less P is an element having a large solid solution strengthening ability. However, if the P content exceeds 0.100%, the corrosion resistance is poor. For this reason, the P content is 0.100% or less.
Ｓ：０．０３０％以下
本発明の缶用鋼板はＮｂ、Ｃ、Ｎ含有量が多いため、連続鋳造時に矯正帯でスラブエッジが割れやすくなる。Ｓの含有量が０．０３０％を超えると、連続鋳造時に温度が低下する矯正帯でひずみ誘起により多量のＭｎＳが生じ、スラブ割れが多発する。スラブ割れを防止する観点からＳ含有量は０．０３０％以下にする。また、Ｓ含有量が多くなると、フランジ成形におけるクラックの起点となるＭｎＳ介在物の生成量が増加し、フランジ成形性を劣化させる。好ましくは、Ｓ含有量は０．０２０％以下である。より好ましくは、Ｓ含有量は０．０１０％以下である。
S: 0.030% or less Since the steel plate for cans of the present invention has a high Nb, C, and N content, the slab edge is easily broken in the straightening band during continuous casting. If the S content exceeds 0.030%, a large amount of MnS is generated by strain induction in the straightening zone where the temperature decreases during continuous casting, and slab cracks occur frequently. From the viewpoint of preventing slab cracking, the S content is 0.030% or less. Moreover, when S content increases, the production amount of the MnS inclusion used as the starting point of the crack in flange molding will increase, and flange moldability will deteriorate. Preferably, the S content is 0.020% or less. More preferably, the S content is 0.010% or less.
Ａｌ：０．１０％以下
Ａｌ含有量を増加すると、再結晶温度の上昇がもたらされるため、焼鈍温度を高く設定する必要がある。本発明においては、上降伏点を上昇させるために添加する他の元素の影響で再結晶温度が上昇し、焼鈍温度を高く設定しなければならない。そこで、Ａｌ添加による再結晶温度の上昇を極力回避することが必要であり、Ａｌ含有量を０．１０％以下とする。なお、Ａｌは鋼の精錬において脱酸剤として用いられる元素であり、この効果を得るためにはＡｌ含有量を０．０１０％以上とすることが好ましい。
Al: 0.10% or less Increasing the Al content results in an increase in the recrystallization temperature, so the annealing temperature must be set high. In the present invention, the recrystallization temperature rises due to the influence of other elements added to raise the upper yield point, and the annealing temperature must be set high. Therefore, it is necessary to avoid the increase in the recrystallization temperature due to the addition of Al as much as possible, and the Al content is set to 0.10% or less. Al is an element used as a deoxidizer in steel refining. In order to obtain this effect, the Al content is preferably 0.010% or more.
Ｎ：０．０１２０％超え０．０２００％以下
Ｎは固溶強化に必要な元素である。固溶強化の効果を発揮させるためには、Ｎ含有量を０．０１２０％超えとする必要がある。一方、Ｎ含有量が０．０２００％を超えると連続鋳造時の温度が低下する下部矯正帯で高ＮによりＮｂ窒化物の析出が促進されて硬化することにより、スラブ割れが生じやすくなる。よって、Ｎ含有量は０．０２００％以下とする。好ましくは、０．０１３０％以上０．０１７０％以下である。
N: 0.0120% to 0.0200% or less N is an element necessary for solid solution strengthening. In order to exert the effect of solid solution strengthening, the N content needs to be over 0.0120%. On the other hand, when the N content exceeds 0.0200%, the precipitation of Nb nitride is promoted and hardened by the high N in the lower straightening zone where the temperature at the time of continuous casting decreases, so that slab cracking is likely to occur. Therefore, the N content is 0.0200% or less. Preferably, it is 0.0130% or more and 0.0170% or less.
Ｎｂ：０．００４％以上０．０４０％以下
本発明において、Ｎｂは重要な添加元素である。Ｎｂは炭化物生成能の高い元素であり、微細な炭化物を形成する。これにより、鋼板の上降伏点が上昇する。Ｎｂ含有量が０．００４％以上の場合にこの効果が生じるため、Ｎｂ含有量の下限は０．００４％に限定する。一方、Ｎｂは再結晶温度の上昇をもたらす。Ｎｂ含有量が０．０４０％を超えると、６５０℃以上７８０℃以下の均熱温度、１０ｓ以上５５ｓ以下の均熱時間での連続焼鈍（均熱温度、均熱時間については後述）では未再結晶粒が一部残存するなど、焼鈍し難くなる。このため、Ｎｂ含有量の上限を０．０４０％に限定する。好ましくは、０．００６％以上０．０２５％以下である。
Nb: 0.004% or more and 0.040% or less In the present invention, Nb is an important additive element. Nb is an element with high carbide generating ability and forms fine carbides. Thereby, the upper yield point of a steel plate rises. Since this effect occurs when the Nb content is 0.004% or more, the lower limit of the Nb content is limited to 0.004%. On the other hand, Nb increases the recrystallization temperature. If the Nb content exceeds 0.040%, it is not re-applied in continuous annealing at a soaking temperature of 650 ° C. or more and 780 ° C. or less and a soaking time of 10 s or more and 55 s or less (soaking temperature and soaking time will be described later). It becomes difficult to anneal because some crystal grains remain. For this reason, the upper limit of Nb content is limited to 0.040%. Preferably, it is 0.006% or more and 0.025% or less.
上記成分以外の残部はＦｅおよび不可避的不純物とする。 The balance other than the above components is Fe and inevitable impurities.
次に本発明の缶用鋼板の製造方法で製造された缶用鋼板の特性について説明する。 Next, the characteristic of the steel plate for cans manufactured with the manufacturing method of the steel plate for cans of this invention is demonstrated.
母材部硬度と溶接部硬度の比（溶接部平均ビッカース硬度／母材部平均ビッカース硬度≦３．４）
母材部硬度と溶接部硬度の比率は、フランジ成形性に大きな影響を及ぼす。溶接部硬度が上昇して母材部硬度と差が生じると、フランジ成形時に硬度差が生じている領域にひずみが集中して、割れが発生する。このため、硬度比を出来るだけ小さくすることで、ひずみの集中を抑制し、フランジ成形時の割れを防ぐことが出来る。フランジ成形性で割れの発生しない硬度比を具体的に検討したところ、母材部平均ビッカース硬度に対する溶接部平均ビッカース硬度の比を３．４以下とすればよいことがわかった。硬度はビッカース硬度を用い、断面を研磨した面に対して測定する。ビッカース硬度は微小領域を測定する試験方法であり、測定値にバラツキが生じるのを防ぐため、複数個所を測定して平均値を求めることが好ましい。本願の実施例では、３０点測定した平均値を用いた。溶接部硬度は加熱により熱影響を受けているナゲットの部分を測定し、母材部硬度は溶接部から10mm以上離れた熱影響受けていない部分を測定する。溶接はシーム溶接方式により行い、チリ発生の電流を上限電流とし、溶接部の剥がれが生じなくなる電流を下限電流とし、その中間の電流で溶接する。母材部硬度と溶接部硬度の比は、Ｃ量を適正範囲とすることにより制御できる。
Ratio of base metal part hardness to weld part hardness (welded part average Vickers hardness / base metal part average Vickers hardness ≦ 3.4)
The ratio between the base material hardness and the weld hardness has a significant effect on flange formability. When the welded portion hardness increases and a difference from the base metal portion hardness occurs, strain concentrates in a region where the hardness difference is generated during flange forming, and cracks are generated. For this reason, by making the hardness ratio as small as possible, it is possible to suppress the concentration of strain and prevent cracks during flange molding. When the hardness ratio at which cracks do not occur due to flange formability was specifically examined, it was found that the ratio of the welded portion average Vickers hardness to the base metal portion average Vickers hardness should be 3.4 or less. The hardness is measured with respect to the surface whose cross section is polished using Vickers hardness. Vickers hardness is a test method for measuring a minute region, and it is preferable to determine an average value by measuring a plurality of locations in order to prevent variation in the measured value. In the examples of the present application, an average value measured at 30 points was used. The weld hardness is measured on the nugget part that is thermally affected by heating, and the base metal part hardness is measured on a part that is 10 mm or more away from the weld and not affected by heat. Welding is performed by a seam welding method, where the current generated when dust occurs is set as the upper limit current, and the current at which peeling of the weld does not occur is set as the lower limit current. The ratio between the base material hardness and the weld hardness can be controlled by adjusting the C content within an appropriate range.
各片面（表面と裏面）の穴拡げ性（各面の穴拡げ率３０％以上）
フランジ成形時のクラックは溶接部のＨＡＺ部より数ミリ離れた箇所で発生する。このため、母材の穴拡げ率を大きくすることで、フランジ成形時の割れを防ぐことが可能となり、穴拡げ率が両面（表面と裏面）ともに３０％以上の場合にはフランジ割れは発生しない。
穴拡げ率は、Ｍｎ量を０．１０％以上１．００％以下とし、圧延機スタンドにおいて表面粗さＲａが０．９μｍ以上３．０μｍ以下かつＰＰＩが１５０以上４００以下の圧延ロールで圧延することにより制御できる。Ｍｎ量を少なくするとＭｎＳ析出量が減少するので穴拡げ率は大きくなり、Ｍｎ量を多くするとＭｎＳ析出量が増加するので穴拡げ率は小さくなる。圧延ロールのRaを小さくすると表層が均一に硬化するので穴拡げ率は小さくなり、Raを大きくすると鋼板の表層の一部に軟質部ができるため穴拡げ率は大きくなる。ロールPPIを小さくすると表層が均一に硬化するので穴拡げ率は小さくなり、PPIを大きくすると鋼板の表層の一部に軟質部ができるため穴拡げ率は大きくなる。
ここで、穴拡げ率λ（％）は初期穴径：ｄ０、割れ直後穴径：ｄ１のとき
λ＝｛（ｄ１−ｄ０）／ｄ０｝×１００
で表すことができる。
また、試験片の穴の端面性状が穴拡げ性に影響するため、バリ等が発生しにくい研削加工により穴開け加工の仕上げを行い、穴拡げ性の評価に供する。なお、穴拡げ率は、ＪＩＳ Ｚ ２２５６に規定された方法で測定することができる。本願では、表裏それぞれの穴拡げ率を測定し、表裏両方の面とも３０％以上であることが好ましい。
Hole expandability on each side (front and back) (hole expansion rate of 30% or more on each side)
Cracks at the time of flange forming occur at a location several millimeters away from the HAZ portion of the weld. For this reason, it is possible to prevent cracking during flange molding by increasing the hole expansion rate of the base material, and if the hole expansion rate is 30% or more on both sides (front and back), flange cracking will not occur. .
The hole expansion ratio is Mn amount of 0.10% to 1.00%, and rolling is performed with a rolling roll having a surface roughness Ra of 0.9 μm to 3.0 μm and a PPI of 150 to 400 in a rolling mill stand. Can be controlled. When the amount of Mn is decreased, the amount of MnS precipitation decreases, so the hole expansion rate increases. When the amount of Mn is increased, the amount of MnS precipitation increases, so the hole expansion rate decreases. When Ra of the rolling roll is reduced, the surface layer is uniformly cured, so the hole expansion rate is reduced. When Ra is increased, a soft part is formed in a part of the surface layer of the steel sheet, so that the hole expansion rate is increased. When the roll PPI is reduced, the surface layer is uniformly cured, so the hole expansion rate is reduced. When the roll PPI is increased, a soft part is formed on a part of the surface layer of the steel sheet, so the hole expansion rate is increased.
Here, hole expansion ratio lambda (%) Initial hole diameter: d 0, immediately after cracking hole diameter: lambda = When d 1 {(d 1 -d 0 ) / d 0} × 100
Can be expressed as
Moreover, since the end face property of the hole of the test piece affects the hole expandability, the drilling process is finished by a grinding process in which burrs and the like are not easily generated, and the hole expandability is evaluated. In addition, a hole expansion rate can be measured by the method prescribed | regulated to JISZ2256. In the present application, the hole expansion rate of each of the front and back surfaces is measured, and it is preferable that both the front and back surfaces are 30% or more.
鋼板両面の穴拡げ率の差（１０パーセンテージポイント以下）
板厚が薄い缶用鋼板では表裏の加工度の差が小さくなるのでパンチ接触面でもクラックが発生する。このため、穴拡げ試験は両面に対して実施することが必要であり、両面の穴拡げ率の差が大きい場合には表裏を貫通する大きなクラックの発生頻度が多くなることがあるため好ましくない。具体的には、鋼板両面の穴拡げ率の差は１０パーセンテージポイント以下であることが好ましい。
Difference in hole expansion ratio on both sides of steel sheet (10 percentage points or less)
In a steel plate for cans with a small plate thickness, the difference in the degree of processing between the front and back surfaces is small, so cracks are generated even on the punch contact surface. For this reason, it is necessary to carry out the hole expansion test on both surfaces, and when the difference in the hole expansion ratio between both surfaces is large, the occurrence frequency of large cracks penetrating the front and back may increase, which is not preferable. Specifically, it is preferable that the difference between the hole expansion ratios on both surfaces of the steel sheet is 10 percentage points or less.
上降伏強度：４５０〜６００ＭＰａ
缶の耐圧強度等を確保するために、上降伏強度を４５０ＭＰａ以上とすることが好ましい。一方、６００ＭＰａ超えの上降伏強度を得ようとすると多量の元素含有が必要となる。多量の元素含有は本発明の缶用鋼板の耐食性を阻害するおそれがある。そこで、上降伏強度は６００ＭＰａ以下とすることが好ましい。上記成分組成を採用するとともに、後述する製造条件を採用することで、缶用鋼板の上降伏強度を４５０〜６００ＭＰａに制御することができる。
Upper yield strength: 450-600 MPa
In order to secure the pressure resistance of the can, the upper yield strength is preferably set to 450 MPa or more. On the other hand, in order to obtain an upper yield strength exceeding 600 MPa, a large amount of element is required. If a large amount of elements are contained, the corrosion resistance of the steel sheet for cans of the present invention may be impaired. Therefore, the upper yield strength is preferably 600 MPa or less. The upper yield strength of the steel plate for cans can be controlled to 450 to 600 MPa by adopting the above component composition and the production conditions described later.
板厚
フランジ割れの発生には板厚も影響する。板厚が薄い場合には、割れの起点となるクラックが板厚方向に貫通しやすく、割れが生じやすい。缶用鋼板でフランジ成形が行われている鋼板の板厚は０．２６ｍｍ以下であり、本発明はこの範囲の板厚を主な対象とする。
Plate thickness Plate thickness also affects the occurrence of flange cracks. When the plate thickness is thin, the crack that becomes the starting point of the crack is likely to penetrate in the plate thickness direction, and the crack is likely to occur. The plate thickness of the steel plate that is flange-formed with the steel plate for cans is 0.26 mm or less, and the present invention mainly covers the plate thickness in this range.
次に本発明の缶用鋼板の製造方法について説明する。本発明の缶用鋼板は、熱間圧延工程と、一次冷間圧延工程と、焼鈍工程と、二次冷間圧延工程とを有する方法で製造される。以下、各製造工程について説明する。 Next, the manufacturing method of the steel plate for cans of this invention is demonstrated. The steel plate for cans of this invention is manufactured by the method which has a hot rolling process, a primary cold rolling process, an annealing process, and a secondary cold rolling process. Hereinafter, each manufacturing process will be described.
熱間圧延工程
原料となる鋼スラブは、上記成分組成に調整された溶鋼を、転炉等を用いた通常公知の方法により溶製し、次いで連続鋳造法等の通常用いられる鋳造方法で得られる。
Hot rolling process Steel slab as a raw material is obtained by melting a molten steel adjusted to the above component composition by a generally known method using a converter or the like, and then by a commonly used casting method such as a continuous casting method. .
上記により得られた鋼スラブに対して熱間圧延を施し、熱延板を製造する。熱間圧延の圧延開始時には、鋼スラブの温度を１２３０℃以上にするのが好ましい。 Hot rolling is performed with respect to the steel slab obtained by the above, and a hot-rolled sheet is manufactured. At the start of hot rolling, the temperature of the steel slab is preferably 1230 ° C or higher.
また、熱間圧延における仕上げ温度はＡｒ３変態点以上とする。熱間圧延における仕上げ圧延温度は、所望の上降伏点を確保する上で重要因子となる。仕上げ温度がＡｒ３変態点未満の場合はオーステナイト＋フェライトの２相域圧延となり、圧延直後にフェライト粒の粒成長が生じるため、上降伏点が低下し、缶体強度が不足する。よって、熱間圧延仕上げ温度は、Ａｒ３変態点以上に限定する。一方、仕上げ圧延温度を９９０℃超とした場合、動的再結晶した結晶粒が高温のため粗大に成長するため上降伏点が低下する。また、高温での表層スケール発生を抑制する観点からも、仕上げ圧延温度は９９０℃を上限とする。 Further, the finishing temperature in hot rolling is set to Ar 3 transformation point or more. The finish rolling temperature in hot rolling is an important factor in securing a desired upper yield point. If the finishing temperature is lower than Ar 3 transformation point becomes two-phase region rolling austenite + ferrite, because the grain growth of ferrite grains after rolling occurs, the upper yield point is lowered, the can body strength is insufficient. Therefore, the hot rolling finishing temperature is limited to the Ar 3 transformation point or higher. On the other hand, when the finish rolling temperature is higher than 990 ° C., the dynamically yielded crystal grains grow coarsely due to the high temperature, so that the upper yield point decreases. Also, from the viewpoint of suppressing the generation of surface scale at high temperatures, the finish rolling temperature is 990 ° C. as the upper limit.
熱間圧延工程における巻取り温度は、本発明で重要となる上降伏点を目標値に制御する上で重要な因子である。巻取り温度を６００℃以上にすると、ＮがＡｌＮとなって析出するため固溶Ｎ量が減少し、固溶強化量が低下する。その結果として上降伏点が低下する。このため、巻取り温度を６００℃未満とする。また、巻取り温度を４００℃未満にすると、コイル内の冷却が不均一になり、コイル長手方向の冷却も不均一になり、コイル長手方向の材質にバラツキが生じ、成形性が劣化するため巻取り温度は４００℃以上とする。原因は定かではないが、この材質のバラツキが穴拡げ率の差を大きくし、成形性が劣化する。なお、巻取り温度を下げるために急冷した場合、冷却が不均一になり板形状が劣化するため、製造効率の観点からも、４００℃を下限とする。また、Ｎｂ析出物制御の観点から、巻き取り後の冷却速度は徐冷となることが好ましく、１１．５℃／ｈ以下での冷却が好ましく、６．３℃／ｈ以下での冷却がさらに好ましく、１．７℃／ｈ以下での冷却がより一層好ましい。このような冷却後に、鋼板の表面温度が２００℃以下になってから次工程である一次冷間圧延工程の処理を行うことが好ましく、１００℃以下がさらに好ましく、５０℃以下がさらに好ましい。 The coiling temperature in the hot rolling process is an important factor in controlling the upper yield point, which is important in the present invention, to the target value. When the coiling temperature is 600 ° C. or higher, N precipitates as AlN, so the amount of solid solution N decreases and the amount of solid solution strengthening decreases. As a result, the upper yield point decreases. For this reason, winding temperature shall be less than 600 degreeC. If the coiling temperature is less than 400 ° C., the cooling in the coil becomes non-uniform, the cooling in the coil longitudinal direction becomes non-uniform, the material in the coil longitudinal direction varies, and the formability deteriorates. The taking temperature is 400 ° C. or higher. The cause is not clear, but the variation in this material increases the difference in the hole expansion rate and deteriorates the moldability. In addition, when it cools rapidly in order to lower coiling temperature, since cooling will become non-uniform | heterogenous and plate shape will deteriorate, 400 degreeC is made into a minimum from a viewpoint of manufacturing efficiency. Further, from the viewpoint of Nb precipitate control, the cooling rate after winding is preferably slow cooling, cooling at 11.5 ° C./h or less is preferable, and cooling at 6.3 ° C./h or less is further performed. Preferably, cooling at 1.7 ° C./h or less is even more preferable. After such cooling, after the surface temperature of the steel sheet reaches 200 ° C. or lower, it is preferable to perform the next cold rolling process, more preferably 100 ° C. or lower, and further preferably 50 ° C. or lower.
一次冷間圧延工程
熱間圧延工程の後に酸洗を行う。酸洗は表層スケールが除去できればよく、特に条件は規定しない。公知の方法により、実施することができる。なお、酸洗以外の方法でスケールを除去することもできる。
Primary cold rolling process Pickling is performed after the hot rolling process. Pickling is not particularly limited as long as the surface scale can be removed. It can implement by a well-known method. The scale can be removed by a method other than pickling.
酸洗後の鋼板に一次冷間圧延を施す。一次冷間圧延での圧下率を８０％未満とした場合、従来ＤＲ材並みの板厚（０．１７ｍｍ程度）を得るためには、少なくとも熱延後の板厚を１ｍｍ以下にする必要がある。しかし、操業上、熱延の圧延ロール径等、設備の大幅な変更なしに熱延後の板厚を１ｍｍ以下とするためには、熱延時に強圧下とする必要があり、安定製造が難しくなる問題がある。強圧下とするために圧延機の荷重負荷が増加しロールの交換頻度が増えるのと、板厚が薄くなることで急冷されるため仕上げ圧延温度をＡｒ３変態点以上にすることが困難になる。従って、本工程での圧下率は８０％以上とする。 The cold-rolled steel sheet is subjected to primary cold rolling. When the reduction ratio in the primary cold rolling is less than 80%, in order to obtain a plate thickness (about 0.17 mm) comparable to that of a conventional DR material, at least the plate thickness after hot rolling needs to be 1 mm or less. . However, in order to reduce the sheet thickness after hot rolling to 1 mm or less without significant changes in equipment such as hot rolling mill roll diameter, it is necessary to use a strong reduction during hot rolling, making stable production difficult. There is a problem. If the rolling load is increased and the roll replacement frequency is increased in order to achieve a high pressure, it is difficult to make the finish rolling temperature equal to or higher than the Ar 3 transformation point because the sheet is thinned and rapidly cooled. . Therefore, the rolling reduction in this step is 80% or more.
焼鈍工程
一次冷間圧延工程の後に、連続焼鈍を施す。均一な組織と良好な伸びを得るため、均熱温度は６５０℃以上とする。一方、均熱温度が７８０℃超えの場合、上降伏点が低下し、缶体強度が不足する。また、７８０℃超えの条件で連続焼鈍するためには、鋼板の破断を防止するために搬送速度を落とす必要があり、生産性が低下する。このため、均熱温度は７８０℃以下とする。
Annealing process Continuous annealing is performed after the primary cold rolling process. In order to obtain a uniform structure and good elongation, the soaking temperature is set to 650 ° C. or higher. On the other hand, when the soaking temperature exceeds 780 ° C., the upper yield point decreases and the strength of the can body is insufficient. Moreover, in order to perform continuous annealing on conditions exceeding 780 degreeC, it is necessary to reduce a conveyance speed in order to prevent the fracture | rupture of a steel plate, and productivity falls. For this reason, the soaking temperature is set to 780 ° C. or lower.
均熱時間が５５ｓ超えになるような処理では、ＮｂＣ粒径が大きくなりすぎて上降伏点が低下し、缶体強度が不足する。また、生産性も損なわれる。よって、均熱時間は５５ｓ以下とする。均熱時間１０ｓ未満では、高速通板による加熱不均一が生じ、ＮｂＣ析出物の粒径分布が大きくなり缶体強度のばらつきが発生する。また炉内での鋼板張力が不安定になり鋼板が破断するおそれがあるため、均熱時間は１０ｓ以上とする。 In the treatment where the soaking time exceeds 55 s, the NbC particle size becomes too large, the upper yield point is lowered, and the can body strength is insufficient. Moreover, productivity is also impaired. Therefore, the soaking time is 55 s or less. If the soaking time is less than 10 s, nonuniform heating due to high-speed sheeting occurs, and the particle size distribution of NbC precipitates increases, resulting in variation in can strength. Further, since the steel plate tension in the furnace becomes unstable and the steel plate may be broken, the soaking time is set to 10 s or more.
二次冷間圧延工程
焼鈍工程の後に、二次冷間圧延を施す。本発明では、少なくとも２基のスタンドを有する圧延機を用い、うち少なくとも１基のスタンドにおいては表面粗さＲａ（算術平均粗さ）が０．９μｍ以上３．０μｍ以下かつＰＰＩ（Ｐｅａｋ Ｐｅｒ Ｉｎｃｈ）が１５０以上４００以下の圧延ロールを用いる。用いる圧延スタンドが１基のみでは、圧延時に十分な張力を得ることが困難であり、少なくとも２基とする。このようなロールを用いて二次冷間圧延を施すことにより、鋼板の最表層の一部に軟質部が生じ、穴拡げ加工時に応力が軟質部分で緩和されて、クラックが発生しにくくなり、鋼板表裏の穴拡げ率の差を小さくすることができる。Ｒａが０．９μm未満またはＰＰＩが１５０未満では、最表層が均一に硬化し、穴拡げ加工時に最表層への応力が高くなり、クラックが発生しやすくなり、好ましくない。一方、Ｒａが３．０μm超またはＰＰＩが４００超では、ロール凸部により押込まれて生成した硬質相の硬度が高くなり、穴拡げ加工時に最表層の硬質相への応力がより一層高くなるので、クラックが発生しやすくなり好ましくない。上記のような圧延ロールは少なくとも１基のスタンドに適用する。なお、Ｒａとは、ＪＩＳ Ｂ ０６０１の算術平均粗さのことであり、ＰＰＩとは、Ｐｅａｋ Ｐｅｒ Ｉｎｃｈであり１インチあたりに観察される山の数を表す。
Secondary cold rolling process Secondary cold rolling is performed after the annealing process. In the present invention, a rolling mill having at least two stands is used, of which at least one stand has a surface roughness Ra (arithmetic average roughness) of 0.9 μm or more and 3.0 μm or less and PPI (Peak Per Inch). However, a rolling roll having 150 to 400 is used. If only one rolling stand is used, it is difficult to obtain sufficient tension during rolling, and at least two rolling stands are used. By performing secondary cold rolling using such a roll, a soft part occurs in a part of the outermost layer of the steel sheet, stress is relaxed in the soft part during hole expansion processing, and cracks are less likely to occur, The difference in the hole expansion rate between the front and back of the steel sheet can be reduced. When Ra is less than 0.9 μm or PPI is less than 150, the outermost layer is hardened uniformly, the stress on the outermost layer is increased during hole expansion processing, and cracks are likely to occur, which is not preferable. On the other hand, when Ra is more than 3.0 μm or PPI is more than 400, the hardness of the hard phase generated by being pushed by the roll convex portion is increased, and the stress to the hard phase of the outermost layer is further increased during hole expansion processing. , Cracks tend to occur, which is not preferable. The rolling roll as described above is applied to at least one stand. Ra is the arithmetic average roughness of JIS B 0601, and PPI is Peak Per Inch, which represents the number of peaks observed per inch.
極薄材の二次冷間圧延での圧下率を通常の板厚のＤＲ材製造条件と同様の２０％以上とすると、十分な穴拡げ性が得られない。本発明では極薄材で穴拡げ率３０％以上を確保する必要があるため、二次冷間圧延での圧下率は１９％以下とする。また、二次冷間圧延率を１．０％未満とすると、ロール表面の凹凸が鋼板に転写されにくくなり、鋼板の表面粗さ調整が困難となる。よって、二次冷間圧延の圧下率は１．０％以上にする必要がある。また、理由は定かではないが、極薄材で圧下率を１．０％未満とすると長手方向の圧下率がばらつくため、安定的に表面粗さを制御することが困難になる。 If the reduction ratio in the secondary cold rolling of the ultra-thin material is 20% or more, which is the same as the production conditions of the DR material having a normal plate thickness, sufficient hole expandability cannot be obtained. In the present invention, it is necessary to secure a hole expansion ratio of 30% or more with an ultrathin material, and therefore the reduction ratio in secondary cold rolling is set to 19% or less. Moreover, when the secondary cold rolling rate is less than 1.0%, the unevenness on the roll surface becomes difficult to be transferred to the steel sheet, and it becomes difficult to adjust the surface roughness of the steel sheet. Therefore, the reduction ratio of secondary cold rolling needs to be 1.0% or more. Although the reason is not clear, if the rolling reduction is less than 1.0% with an extremely thin material, the rolling reduction in the longitudinal direction varies, and it becomes difficult to stably control the surface roughness.
表１に示す成分組成を含有し、残部がＦｅ及び不可避的不純物からなる鋼を実機転炉で溶製し、連続鋳造により鋼スラブを得た。得られた鋼スラブを再加熱した後、熱間圧延し、巻取った。次いで、酸洗後、一次冷間圧延し、薄鋼板を製造した。なお、酸洗前の鋼板温度はコイルの全長で２５〜６０℃での範囲であった。得られた薄鋼板を、加熱速度１５℃／ｓで加熱した。その後、連続焼鈍を行った。次いで、冷却後、２基の圧延スタンドを有する圧延機を用いて二次冷間圧延を施し、通常のＳｎめっきを連続的に施して、ぶりきを得た。詳細な製造条件を表２に示す。なお、Ａｒ３変態点は冷却時のオーステナイト→フェライト変態による体積変化が最も大きくなる温度を測定して求めた。また、上記２基の圧延スタンドのうち、一つ目のロールは表２に示すＲａ、ＰＰＩとし、二つ目のロールは、Ｒａを０．６μm、ＰＰＩを１４０で固定した。 Steel containing the composition shown in Table 1 and the balance being Fe and inevitable impurities was melted in an actual converter, and a steel slab was obtained by continuous casting. The obtained steel slab was reheated, then hot rolled and wound up. Next, after pickling, primary cold rolling was performed to produce a thin steel plate. In addition, the steel plate temperature before pickling was the range in 25-60 degreeC with the full length of a coil. The obtained thin steel plate was heated at a heating rate of 15 ° C./s. Then, continuous annealing was performed. Next, after cooling, secondary cold rolling was performed using a rolling mill having two rolling stands, and normal Sn plating was continuously performed to obtain a tinplate. Detailed manufacturing conditions are shown in Table 2. The Ar 3 transformation point was obtained by measuring the temperature at which the volume change due to the austenite → ferrite transformation during cooling was greatest. Of the two rolling stands, the first roll had Ra and PPI shown in Table 2, and the second roll had Ra fixed at 0.6 μm and PPI fixed at 140.
以上により得られたＳｎめっき鋼板（ぶりき）に対して、圧延方向に対して平行方向を引張方向とするJIS 5号引張試験片（ＪＩＳ Ｚ ２２０１）を採取し、２１０℃で２０分間の塗装焼付相当処理を施した後、ＪＩＳ Ｚ ２２４１の規定に準拠した引張試験を引張速度１０ｍｍ／分で行って、上降伏点（Ｕ−ＹＰ：ｕｐｐｅｒ ｙｉｅｌｄ ｐｏｉｎｔ）を測定した。 JIS No. 5 tensile test piece (JIS Z 2201) having a tensile direction parallel to the rolling direction is collected from the Sn-plated steel sheet (cover) obtained as described above and coated at 210 ° C. for 20 minutes. After performing the baking equivalent treatment, a tensile test in accordance with the provisions of JIS Z 2241 was performed at a tensile speed of 10 mm / min, and an upper yield point (U-YP) was measured.
また、得られたＳｎめっき鋼板（ぶりき）を用いて缶胴の溶接を行った。溶接はシーム溶接方式により行い、チリ発生の電流を上限電流とし、溶接部の剥がれが生じなくなる電流を下限電流とし、その中間の電流で溶接した。溶接部と母材部のそれぞれの断面を研磨した面について、ビッカース硬度を測定した。硬度測定は５０ｇの荷重を負荷する条件で行い、３０点測定の平均値を求めた。 Moreover, the can body was welded using the obtained Sn-plated steel sheet (cover). Welding was performed by a seam welding method. The current generated when dust occurred was set as the upper limit current, and the current at which peeling of the weld did not occur was set as the lower limit current. The Vickers hardness was measured on the surface of each welded part and base metal part polished. The hardness measurement was performed under the condition of applying a load of 50 g, and an average value of 30 points was obtained.
ＪＩＳ Ｚ ２２５６に規定された方法に基づいて、鋼板の表面および裏面のそれぞれの穴拡げ率を測定した。両面の穴拡げ性としては、表面と裏面の穴拡げ率の差が１０パーセンテージポイント以下を「○」、１０パーセンテージポイント超えを「×」とした。また、各片面（表面と裏面）の穴拡げ性は、各々の面の穴拡げ率が３０％以上を「○」、３０％未満を「×」とした。
得られた結果を表３に示す。
Based on the method defined in JIS Z 2256, the respective hole expansion rates of the front and back surfaces of the steel sheet were measured. As for the hole expandability on both sides, the difference between the hole expansion ratios on the front surface and the back surface was 10 percentage points or less, “◯”, and 10 percent points exceeded “×”. In addition, regarding the hole expandability of each side (front and back surfaces), the hole expansion ratio of each surface was 30% or more as “◯”, and less than 30% as “X”.
The obtained results are shown in Table 3.
表３より、本発明例は上降伏点が４５０ＭＰａ以上と大きく、母材部硬度と溶接部硬度の比が小さい。また、穴拡げ性が良好であり、穴拡げ率の表裏差が小さいことが認められる。なお、表１に示すように、本発明例では耐食性に悪影響をおよぼす可能性のある元素を適切な含有量に制限しているため、耐食性にも優れる。 From Table 3, the present invention example has a large upper yield point of 450 MPa or more, and the ratio of the base material hardness and the weld hardness is small. Moreover, it is recognized that the hole expandability is good and the difference in front and back of the hole expansion rate is small. In addition, as shown in Table 1, in the example of the present invention, an element that may adversely affect the corrosion resistance is limited to an appropriate content, so that the corrosion resistance is also excellent.
また、比較例では、本発明の請求範囲のいずれかの条件が外れているため、本発明の所望の特性が得られない。 Further, in the comparative example, since any of the conditions of the claims of the present invention is not satisfied, the desired characteristics of the present invention cannot be obtained.
本発明によれば、母材部硬度と溶接部硬度の比が小さく、穴拡げ性、耐食性いずれの特性にも優れた鋼板の製造方法が得られ、フランジ成形が施される３ピース缶や２ピース缶向けの缶用鋼板の製造方法として最適である。 According to the present invention, a method for producing a steel sheet having a small ratio between the base material hardness and the weld hardness and excellent in both hole expansibility and corrosion resistance can be obtained, and a three-piece can or 2 which is subjected to flange forming. It is the most suitable method for manufacturing steel plates for cans for peace cans.
Claims (1)
前記熱間圧延工程後に、酸洗し、圧下率が８０％以上の条件で圧延する一次冷間圧延工程と、
前記一次冷間圧延工程後に、均熱温度が６５０℃以上７８０℃以下、均熱時間が１０ｓ以上５５ｓ以下の条件で連続焼鈍する焼鈍工程と、
前記焼鈍工程後に、少なくとも２基の圧延機スタンドを用い、うち少なくとも１基の圧延機スタンドにおいて表面粗さＲａが０．９μｍ以上３．０μｍ以下かつＰＰＩが１５０以上４００以下の圧延ロールを用い、１．０％以上１９％以下の圧下率で圧延する二次冷間圧延工程を有することを特徴とする缶用鋼板の製造方法。 In mass%, C: more than 0.020% and 0.040% or less, Si: 0.04% or less, Mn: 0.10% or more and 1.00% or less, P: 0.100% or less, S: 0.00. 030% or less, Al: 0.10% or less, N: 0.0120% to 0.0200% or less, Nb: 0.004% or more and 0.040% or less, with the balance being Fe and inevitable impurities A hot rolling step in which a steel slab having a component composition is rolled under a condition where the finish rolling temperature is Ar 3 transformation point or higher and 990 ° C. or lower and the winding temperature is 400 ° C. or higher and lower than 600 ° C .;
After the hot rolling step, pickling, and a primary cold rolling step of rolling under a condition where the rolling reduction is 80% or more,
After the primary cold rolling step, an annealing step in which the soaking temperature is 650 ° C. or higher and 780 ° C. or lower, and the soaking time is 10 s or longer and 55 s or shorter.
After the annealing step, at least two rolling mill stands are used, of which at least one rolling mill stand uses a rolling roll having a surface roughness Ra of 0.9 μm to 3.0 μm and a PPI of 150 to 400, A method for producing a steel plate for cans, comprising a secondary cold rolling step of rolling at a rolling reduction of 1.0% or more and 19% or less.
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