JP2021063257A - Ferritic stainless steel, and method for producing steel sheet - Google Patents
Ferritic stainless steel, and method for producing steel sheet Download PDFInfo
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Abstract
Description
本願は、成形加工した際の成形後の表面特性に優れるフェライト系ステンレス鋼板を製造するのに適した鋼材を開示する。 The present application discloses a steel material suitable for producing a ferritic stainless steel sheet having excellent surface characteristics after molding during molding.
代表鋼種であるＳＵＳ３０４（１８Ｃｒ−８Ｎｉ）をはじめとしたオーステナイト系ステンレス鋼は、耐食性、加工性、美麗性等に優れることから家電、厨房品、建材等に広く用いられている。但し、オーステナイト系ステンレス鋼は高価かつ価格変動の激しいＮｉが多量に添加されているため、鋼板とした場合の価格も高くなってしまう。経済性の観点からはより安価な材料が望まれている。 Austenitic stainless steels such as SUS304 (18Cr-8Ni), which is a representative steel type, are widely used in home appliances, kitchen products, building materials, etc. because they are excellent in corrosion resistance, workability, and beauty. However, since austenitic stainless steel is expensive and contains a large amount of Ni, which is subject to drastic price fluctuations, the price of austenitic stainless steel is also high. From the economical point of view, cheaper materials are desired.
一方、フェライト系ステンレス鋼はＮｉを含有しないか、もしくは含有量が少ないため、コストパフォーマンスに優れる材料として、近年需要が増加している。しかしながら、成形用途として使用する場合に最大の問題となるのが、成形後に表面凹凸が形成されることによる表面特性の劣化である。 On the other hand, since ferritic stainless steel does not contain or contains a small amount of Ni, its demand has been increasing in recent years as a material having excellent cost performance. However, the biggest problem when used for molding is the deterioration of surface characteristics due to the formation of surface irregularities after molding.
「表面凹凸」とは、加工や成形を行った後に鋼板表面に生じるものであり、結晶粒複数個の大きさに対応した「肌荒れ（オレンジピール）」と、元の圧延方向に展伸した「リジング」とが重畳したものである。ＳＵＳ４３０ＬＸのようにＣ、Ｎを低減させた、いわゆる高純フェライト系ステンレス鋼は、結晶粒が粗大化しやすいため、肌荒れが大きく、顕著となる。また、高純フェライト系ステンレス鋼は、高温でオーステナイト相が生成しないため、変態を活用した細粒化ができない。したがって、リジングも大きくなる傾向がある。 "Surface unevenness" occurs on the surface of a steel sheet after processing or molding, and includes "rough skin (orange peel)" corresponding to the size of multiple crystal grains and "roughness (orange peel)" that extends in the original rolling direction. "Rising" is superimposed. The so-called high-pure ferritic stainless steel in which C and N are reduced, such as SUS430LX, tends to have coarse crystal grains, so that the rough skin becomes large and remarkable. In addition, since high-pure ferritic stainless steel does not form an austenite phase at high temperatures, it cannot be granulated by utilizing transformation. Therefore, the rigging also tends to be large.
家電製品の筺体或いは器物のように比較的厳しい成形性が要求される場合、高純フェライト系ステンレス鋼が用いられることが多い。この場合、成形後の強度を担保するために、０．６ｍｍ以上の板厚を有する鋼板を採用するのが一般的である。通常、前述の肌荒れやリジングの発生のため、成形後に研磨によって表面凹凸の除去が行われている。この研磨の際、鋼組織中に粗大な析出物或いは介在物（粗大な化合物）が存在すると、研磨後の耐食性が低下する。この原因は表面に現出した粗大な化合物が研磨で除去されて腐食起点となる孔が形成される、もしくは、母材との隙間が広がり、隙間腐食を促進するためである。したがって成形用に用いられるフェライト系ステンレス鋼は高純かつ、粗大な化合物が存在しないことが重要となる。 Highly pure ferritic stainless steel is often used when relatively strict moldability is required, such as the housing or equipment of home appliances. In this case, in order to ensure the strength after molding, it is common to use a steel plate having a plate thickness of 0.6 mm or more. Usually, due to the above-mentioned rough skin and rigging, surface irregularities are removed by polishing after molding. During this polishing, if coarse precipitates or inclusions (coarse compounds) are present in the steel structure, the corrosion resistance after polishing is lowered. The reason for this is that the coarse compound appearing on the surface is removed by polishing to form holes that serve as the starting point of corrosion, or the gap between the base material and the base material is widened to promote crevice corrosion. Therefore, it is important that the ferritic stainless steel used for molding is highly pure and free of coarse compounds.
上述した背景から、成形後の肌荒れとリジングとを同時に改善するフェライト系ステンレス鋼が求められている。リジングを改善するには凝固組織の細粒化、等軸晶化が重要であることが知られている。また肌荒れは結晶粒径を細かくすることにより抑制できることが知られている。 From the above background, there is a demand for a ferritic stainless steel that simultaneously improves rough skin and rigging after molding. It is known that fine graining and equiaxed crystallization of the solidified structure are important for improving rigging. It is also known that rough skin can be suppressed by making the crystal grain size finer.
非特許文献１には、フェライト系ステンレス鋼にＴｉ又はＣｏ−Ｂ化合物を添加することにより凝固組織の等軸晶率を増加する手法が記載されている。しかしこれらはＴｉＮ或いはＣｏ−Ｂ化合物の接種核効果（不均質核生成）を利用するものである。この場合の接種核は大きさが１０μｍを超えるものが多数存在するため、凝固組織の等軸晶率を増加することができても研磨後の耐食性低下を招く。また、本技術を採用したとしても、凝固組織の細粒化ができるとは限らない。 Non-Patent Document 1 describes a method for increasing the equiaxed crystal ratio of a solidified structure by adding a Ti or Co-B compound to a ferritic stainless steel. However, these utilize the inoculated nucleation effect (heterogeneous nucleation) of TiN or Co-B compounds. In this case, since there are many inoculated nuclei having a size exceeding 10 μm, even if the equiaxed crystal ratio of the solidified tissue can be increased, the corrosion resistance after polishing is deteriorated. Moreover, even if this technology is adopted, it is not always possible to make the solidified structure finer.
特許文献１にはＭｇ系介在物を接種核として用いてリジング性を向上させる手法が開示されている。本手法も接種核を用いる技術であり、接種核が粗大な場合には研磨後の耐食性低下を招く懸念がある。また、本技術は肌荒れ性を改善する手法については開示していない。本技術を採用したとしても、凝固組織の細粒化ができるとは限らない。 Patent Document 1 discloses a method for improving rigging property by using Mg-based inclusions as inoculation nuclei. This method is also a technique using inoculated nuclei, and if the inoculated nuclei are coarse, there is a concern that the corrosion resistance after polishing may be deteriorated. In addition, this technology does not disclose a method for improving rough skin. Even if this technology is adopted, it is not always possible to make the solidified structure finer.
この他に鋳造温度の低下や電磁撹拌の利用により凝固組織の等軸晶化が促進することが知られているが、リジング性は必ずしも改善しない場合がある。また耐肌荒れ性は改善されない。 In addition to this, it is known that equiaxed crystallization of the solidified structure is promoted by lowering the casting temperature or using electromagnetic agitation, but the rigging property may not always be improved. Moreover, the rough skin resistance is not improved.
上述の通り、高純フェライト系ステンレス鋼は、高温でオーステナイト相が生成しないことから変態を活用した細粒化が困難である。そのため、凝固段階において予め結晶粒を微細化しておくことが重要である。しかしながら、現状の技術では、高純フェライト系ステンレス鋼の凝固段階で結晶粒を十分に微細化することは難しい。すなわち、高純フェライト系ステンレス鋼を鋼板とし、当該鋼板を製品形状へ成形した場合、製品成形後の肌荒れとリジングとを低減することは難しいのが現状である。このため、現状の技術では、所定の形状への成形加工ができない、もしくは成形加工できても成形後に生じた表面凹凸が大きく、それを除去するために研磨工程を行う必要がある。研磨工程を行う場合、研磨時間がかかり製造コストがかさむ上、研磨にて生じた粉じんが多く発生するなどの環境面の問題もある。 As described above, high-pure ferritic stainless steel is difficult to be granulated by utilizing transformation because the austenite phase is not formed at high temperature. Therefore, it is important to refine the crystal grains in advance at the solidification stage. However, with the current technology, it is difficult to sufficiently refine the crystal grains at the solidification stage of the highly pure ferritic stainless steel. That is, when a high-pure ferritic stainless steel is used as a steel sheet and the steel sheet is molded into a product shape, it is difficult to reduce rough skin and rigging after product molding. For this reason, with the current technology, it is not possible to perform molding to a predetermined shape, or even if molding is possible, the surface unevenness generated after molding is large, and it is necessary to perform a polishing step to remove it. When the polishing process is performed, the polishing time is long, the manufacturing cost is high, and there are also environmental problems such as a large amount of dust generated by the polishing.
上記問題に鑑み、本願においては、製品形状へ成形後の肌荒れとリジングとを低減することが可能な、高純フェライト系ステンレス鋼からなる素材を提供することを目指す。 In view of the above problems, the present application aims to provide a material made of high-pure ferritic stainless steel capable of reducing rough skin and rigging after molding into a product shape.
本発明者らは、製品形状へ成形後の表面凹凸に及ぼす成分について鋭意検討を行った。その結果、特にＮｂ及びＢの含有量を特定の範囲に制御した際に、凝固組織が微細化するとともに、凝固組織の凝固方向への伸びを抑えることができ、製品形状への成形後の肌荒れとリジングの両欠陥が抑制されることを明らかにした。この結果は、例えば、ＮｂとＢとが微細な化合物を形成し、その化合物が凝固時の有効な晶出場所になっている、或いは、その後の凝固の進行に際して極めて有効な障害物として作用し、凝固組織の成長を抑制しているためと考えられるが、この点は形成される化合物、そのメカニズムを含めて、現在も更なる調査を継続中である。 The present inventors have diligently studied the components affecting the surface unevenness after molding into the product shape. As a result, especially when the contents of Nb and B are controlled to a specific range, the coagulated structure can be made finer and the coagulated structure can be suppressed from growing in the coagulation direction, resulting in rough skin after molding into the product shape. It was clarified that both defects of and rigging were suppressed. As a result, for example, Nb and B form a fine compound, and the compound serves as an effective crystallization site during solidification, or acts as an extremely effective obstacle in the subsequent progress of solidification. It is thought that this is because it suppresses the growth of coagulated tissue, but further investigation is still ongoing on this point, including the compounds that are formed and their mechanisms.
上記知見に基づき、本願は上記課題を解決するための手段の一つとして以下の技術を開示する。
［１］質量％で、Ｃ：０．００１％以上０．０１５％以下、Ｓｉ：０．０１％以上１．００％以下、Ｍｎ：０．０１％以上１．００％以下、Ｃｒ：１１．０％以上２５．０％以下、Ｎ：０．００２％以上０．０２０％以下、Ａｌ：０％以上０．３０％以下、Ｎｂ：０．０５％以上０．２０％以下、Ｂ：０．００１０％以上０．０１００％以下、Ｐ：０％以上０．０４０％以下、Ｓ：０％以上０．０１００％以下、Ｔｉ：０％以上０．２０％以下、Ｍｏ：０％以上０．３０％以下、Ｖ：０％以上０．３０％以下、Ｓｎ：０％以上０．５０％以下、Ｎｉ：０％以上１．００％以下、Ｃｕ：０％以上１．００％以下、Ｗ：０％以上１．００％以下、Ｃｏ：０％以上０．５０％以下、Ｚｒ：０％以上０．５０％以下、Ｃａ：０％以上０．００５０％以下、Ｍｇ：０％以上０．００５０％以下、Ｙ：０％以上０．２０％以下、Ｈｆ：０％以上０．２０％以下、ＲＥＭ：０％以上０．１０％以下、Ｓｂ：０％以上０．５０％以下を含み、残部がＦｅ及び不純物からなり、下記（１）式を満足し、等軸晶率が７０％以上のフェライト単相組織よりなり、厚さが１５０ｍｍ以上である、フェライト系ステンレス鋼材。
Ｎｂ＋５０Ｂ≧０．２００・・・（１）
［２］平均結晶粒径が５ｍｍ以下である、［１］に記載のフェライト系ステンレス鋼材。
［３］厚さの１／４位置において厚さ方向の｛００１｝面ランダム強度比が２．０未満である、［１］又は［２］に記載のフェライト系ステンレス鋼材。
［４］［１］〜［３］のいずれかに記載のフェライト系ステンレス鋼材に対して、熱間加工及び／又は冷間加工を行う工程を含む、鋼板の製造方法。
Based on the above findings, the present application discloses the following techniques as one of the means for solving the above problems.
[1] In terms of mass%, C: 0.001% or more and 0.015% or less, Si: 0.01% or more and 1.00% or less, Mn: 0.01% or more and 1.00% or less, Cr: 11. 0% or more and 25.0% or less, N: 0.002% or more and 0.020% or less, Al: 0% or more and 0.30% or less, Nb: 0.05% or more and 0.20% or less, B: 0. 0010% or more and 0.0100% or less, P: 0% or more and 0.040% or less, S: 0% or more and 0.0100% or less, Ti: 0% or more and 0.20% or less, Mo: 0% or more and 0.30 % Or less, V: 0% or more and 0.30% or less, Sn: 0% or more and 0.50% or less, Ni: 0% or more and 1.00% or less, Cu: 0% or more and 1.00% or less, W: 0 % Or more and 1.00% or less, Co: 0% or more and 0.50% or less, Zr: 0% or more and 0.50% or less, Ca: 0% or more and 0.0050% or less, Mg: 0% or more and 0.0050% Below, Y: 0% or more and 0.20% or less, Hf: 0% or more and 0.20% or less, REM: 0% or more and 0.10% or less, Sb: 0% or more and 0.50% or less, and the balance is A ferrite-based stainless steel material composed of Fe and impurities, satisfying the following equation (1), having a ferrite single-phase structure having an equiaxed crystal ratio of 70% or more, and having a thickness of 150 mm or more.
Nb + 50B ≧ 0.200 ・ ・ ・ (1)
[2] The ferritic stainless steel material according to [1], which has an average crystal grain size of 5 mm or less.
[3] The ferrite-based stainless steel material according to [1] or [2], wherein the {001} plane random strength ratio in the thickness direction is less than 2.0 at the 1/4 position of the thickness.
[4] A method for producing a steel sheet, which comprises a step of performing hot working and / or cold working on the ferritic stainless steel material according to any one of [1] to [3].
本開示の技術によれば、製品形状へ成形後の肌荒れとリジングとを低減することが可能な、高純フェライト系ステンレス鋼からなる素材を提供することができる。 According to the technique of the present disclosure, it is possible to provide a material made of high-pure ferritic stainless steel, which can reduce rough skin and rigging after molding into a product shape.
１．フェライト系ステンレス鋼材
本開示のフェライト系ステンレス鋼材は、以下に説明するように所定の成分を所定の量含み、上記式（１）を満足し、等軸晶率が７０％以上のフェライト単相組織よりなり、厚さが１５０ｍｍ以上である。以下、本開示のフェライト系ステンレス鋼材の要件について詳しく説明する。
1. 1. Ferritic stainless steel material The ferritic stainless steel material of the present disclosure contains a predetermined amount of a predetermined component as described below, satisfies the above formula (1), and has a ferrite single-phase structure having an equiaxed crystal ratio of 70% or more. It is made of stainless steel and has a thickness of 150 mm or more. Hereinafter, the requirements of the ferritic stainless steel material of the present disclosure will be described in detail.
１．１ 成分
まず、本開示のフェライト系ステンレス鋼材に含まれる成分について説明する。なお、各元素の含有量の「％」表示は「質量％」を意味する。
1.1 Components First, the components contained in the ferrite-based stainless steel material of the present disclosure will be described. The "%" indication of the content of each element means "mass%".
（Ｃ：０．００１％以上０．０１５％以下）
Ｃは、Ｃｒと析出物を作るときに耐食性を低下させる。このためＣ含有量は低い方が好ましいが、極低炭素成分にするには精錬時間が長くなるため、０．００１％を下限とする。また過度の添加は成形性を低下させるため、上限を０．０１５％とする。精錬コスト及び成形性の両方を考慮した場合、Ｃ含有量は、０．００２％以上であってもよいし、０．００４％以上であってもよく、０．０１１％以下であってもよいし、０．００８％以下であってもよい。
(C: 0.001% or more and 0.015% or less)
C lowers the corrosion resistance when forming a precipitate with Cr. Therefore, it is preferable that the C content is low, but since the refining time is long to obtain an extremely low carbon component, the lower limit is 0.001%. Further, since excessive addition lowers moldability, the upper limit is set to 0.015%. Considering both refining cost and moldability, the C content may be 0.002% or more, 0.004% or more, or 0.011% or less. However, it may be 0.008% or less.
（Ｓｉ：０．０１％以上１．００％以下）
Ｓｉは、耐酸化性向上元素であるが過剰な添加は成形性の低下を招くため、１．００％を上限とする。成形性の点からＳｉ含有量は低い方が好ましいが、過度の低下はコストの増加を招くため、０．０１％を下限とする。製造性の観点から、Ｓｉ含有量は、０．０５％以上であってもよいし、０．１１％以上であってもよく、０．６０％以下であってもよいし、０．４０％以下であってもよいし、０．３０％以下であってもよい。
(Si: 0.01% or more and 1.00% or less)
Si is an element for improving oxidation resistance, but excessive addition causes deterioration of moldability, so the upper limit is 1.00%. From the viewpoint of moldability, it is preferable that the Si content is low, but since an excessive decrease causes an increase in cost, 0.01% is set as the lower limit. From the viewpoint of manufacturability, the Si content may be 0.05% or more, 0.11% or more, 0.60% or less, or 0.40%. It may be less than or equal to or less than or equal to 0.30%.
（Ｍｎ：０．０１％以上１．００％以下）
ＭｎもＳｉ同様に、多量の添加は成形性の低下を招くため、上限を１．０％とする。成形性の点からＭｎ含有量が低い方が好ましいが、過度の低下はコストの増加を招くため、０．０１％を下限とする。製造性の観点から、Ｍｎ含有量は、０．０５％以上であってもよいし、０．１０％以上であってもよく、０．４０％以下であってもよいし、０．３０％以下であってもよい。
(Mn: 0.01% or more and 1.00% or less)
As with Si, the upper limit of Mn is set to 1.0% because adding a large amount of Mn causes a decrease in moldability. From the viewpoint of moldability, it is preferable that the Mn content is low, but since an excessive decrease causes an increase in cost, 0.01% is set as the lower limit. From the viewpoint of manufacturability, the Mn content may be 0.05% or more, 0.10% or more, 0.40% or less, or 0.30%. It may be as follows.
（Ｃｒ：１１．０％以上２５．０％以下）
Ｃｒは、ステンレス鋼の基本特性である耐食性を向上する元素である。１１．０％未満では十分な耐食性は得られないため、下限を１１．０％とする。一方、過度な添加はσ相（Ｆｅ−Ｃｒの金属間化合物）相当の金属間化合物の生成を促進して製造時の割れを助長するため、上限を２５．０％とする。安定製造性（歩留まり、圧延疵等）の点から、Ｃｒ含有量は、１４．０％以上であってもよいし、１６．０％以上であってもよく、２２．０％以下であってもよいし、２１．０％以下であってもよい。
(Cr: 11.0% or more and 25.0% or less)
Cr is an element that improves corrosion resistance, which is a basic property of stainless steel. If it is less than 11.0%, sufficient corrosion resistance cannot be obtained, so the lower limit is set to 11.0%. On the other hand, excessive addition promotes the formation of an intermetallic compound equivalent to the σ phase (an intermetallic compound of Fe-Cr) and promotes cracking during production, so the upper limit is set to 25.0%. From the viewpoint of stable manufacturability (yield, rolling defects, etc.), the Cr content may be 14.0% or more, 16.0% or more, or 22.0% or less. It may be 21.0% or less.
（Ｎ：０．００２％以上０．０２０％以下）
Ｎは、Ｃ同様、Ｃｒとの化合物を作るときに耐食性を低下させる。また過度の添加は成形性を低下させるため低い方が好ましい。低窒素化は精錬コストの上昇を招くため下限を０．００２％とする。一方で、成形性、耐食性の観点から、上限を０．０２０％とする。成形性と製造性と耐食性との点から、Ｎ含有量は、０．００５％以上であってもよいし、０．００８％以上であってもよく、０．０１５％以下であってもよいし、０．０１２％以下であってもよい。
(N: 0.002% or more and 0.020% or less)
Like C, N lowers the corrosion resistance when forming a compound with Cr. Further, excessive addition lowers the moldability, so a lower value is preferable. The lower limit is set to 0.002% because lowering nitrogen causes an increase in refining cost. On the other hand, from the viewpoint of moldability and corrosion resistance, the upper limit is set to 0.020%. From the viewpoint of moldability, manufacturability, and corrosion resistance, the N content may be 0.005% or more, 0.008% or more, or 0.015% or less. However, it may be 0.012% or less.
（Ａｌ：０％以上０．３０％以下）
Ａｌは脱酸元素として使用されることが多い。ただし、本発明者らの新たな知見によれば、フェライト系ステンレス鋼においてＡｌを多量に添加すると、リジング性及び肌荒れ性を共に低下させるとともに、研磨後の耐食性も低下させることが明らかとなった。この点、Ａｌ含有量は低い方が好ましく、上限を０．３０％とする。特性上は添加する必要がないため下限は０％であってもよい。ただし、不可避的に混入する場合や製造性を考慮すると、Ａｌ含有量は０．００３％以上であってもよいし、０．０１％以上であってもよく、０．２０％以下であってもよいし、０．０９％以下であってもよい。
(Al: 0% or more and 0.30% or less)
Al is often used as a deoxidizing element. However, according to the new findings of the present inventors, it has been clarified that when a large amount of Al is added to the ferritic stainless steel, both the rigging property and the rough skin property are lowered, and the corrosion resistance after polishing is also lowered. .. In this respect, the Al content is preferably low, and the upper limit is 0.30%. Since it is not necessary to add it due to its characteristics, the lower limit may be 0%. However, in the case of unavoidable mixing or in consideration of manufacturability, the Al content may be 0.003% or more, 0.01% or more, or 0.20% or less. It may be 0.09% or less.
（Ｎｂ：０．０５％以上０．２０％以下）
ＮｂはＢと複合で添加した場合にリジング性、耐肌荒れ性を改善する重要な元素である。後述するようにＮｂ含有量には適正な範囲が存在する。０．０５％未満であるとリジング及び肌荒れが顕著に発生するため、下限を０．０５％とする。凝固組織の微細化にはＮｂ添加量が多いほど好ましいが、過度の添加は肌荒れ性の劣化を招く。また、本発明者の知見によれば、Ｎｂを過度に添加した場合、鋼材における等軸晶率が低下する傾向にある。これは、過剰なＮｂによってＮｂ含有化合物が晶出し、固溶Ｎｂ量が実質的に減少したためと推定される。このためＮｂの上限を０．２０％とする。リジング、肌荒れの両特性を安定的に確保する観点から、Ｎｂ含有量は、０．０８％以上であってもよいし、０．１０％以上であってもよく、０．１９％以下であってもよいし、０．１５％以下であってもよい。
(Nb: 0.05% or more and 0.20% or less)
Nb is an important element that improves rigging property and rough skin resistance when added in combination with B. As will be described later, there is an appropriate range for the Nb content. If it is less than 0.05%, rigging and rough skin will occur remarkably, so the lower limit is set to 0.05%. The larger the amount of Nb added, the more preferable it is for the miniaturization of the solidified structure, but excessive addition causes deterioration of rough skin. Further, according to the knowledge of the present inventor, when Nb is excessively added, the equiaxed crystal ratio in the steel material tends to decrease. It is presumed that this is because the Nb-containing compound crystallized due to the excess Nb and the amount of solid solution Nb was substantially reduced. Therefore, the upper limit of Nb is set to 0.20%. From the viewpoint of stably ensuring both rigging and rough skin characteristics, the Nb content may be 0.08% or more, 0.10% or more, or 0.19% or less. It may be 0.15% or less.
（Ｂ：０．００１０％以上０．０１００％以下）
ＢはＮｂと複合添加した場合に前述のようにリジング及び肌荒れ性が向上する。Ｎｂと同様にリジング性に対して適正な範囲が存在する。０．００１０％未満ではリジング性の改善が不十分であるため、下限を０．００１０％とする。また、凝固組織の微細化にはＢ添加量が多いほど好ましいが、過度の添加は製造時の凝固割れを招く場合がある。このため上限を０．０１００％とする。製造時の凝固割れを一層抑制する観点から、上限は０．００５０％であってもよい。製造安定性を考慮すると、Ｂ含有量は、０．００１２％以上であってもよいし、０．００１９％以上であってもよく、０．００５０％以下であってもよいし、０．００３０％以下であってもよい。
(B: 0.0010% or more and 0.0100% or less)
When B is added in combination with Nb, rigging and rough skin are improved as described above. Similar to Nb, there is an appropriate range for rigging. If it is less than 0.0010%, the improvement of rigging property is insufficient, so the lower limit is set to 0.0010%. Further, it is preferable that the amount of B added is large for the miniaturization of the solidified structure, but excessive addition may cause solidification cracking during production. Therefore, the upper limit is set to 0.0100%. From the viewpoint of further suppressing solidification cracking during production, the upper limit may be 0.0050%. Considering the production stability, the B content may be 0.0012% or more, 0.0019% or more, 0.0050% or less, or 0.0030. It may be less than or equal to%.
（式（１）：Ｎｂ＋５０Ｂ≧０．２００）
本開示のフェライト系ステンレス鋼材においては、Ｎｂ＋５０Ｂが０．２００％以上であることが重要である。上述のようにＮｂ及びＢの両者を複合添加した際に凝固組織が微細化するとともに、凝固組織の凝固方向への伸びを抑制してリジング性及び肌荒れ性が改善される。具体的には、本開示のフェライト系ステンレス鋼材においては、Ｎｂ及びＢの両者が複合添加されることで、Ｎｂ−Ｂ系の微細な晶出物が核となって等軸晶化が促進されて凝固組織が微細化し、製品形状への成形後のリジング性が向上するものと考えられる。或いは、Ｎｂ及びＢが結晶粒界に偏析することにより、再結晶時の結晶粒の成長が抑制され、製品形状への成形後の肌荒れ性が低減されるものと考えられる。Ｎｂ＋５０Ｂが０．２００％未満であるとこの効果を発揮しない。Ｎｂ＋５０Ｂは０．２１０％以上であってもよいし、０．２３０％以上であってもよい。上限は特に限定されないが、製造時の割れ、靱性低下を考慮した場合、０．６００％以下であってもよいし、０．４００％以下であってもよい。
(Equation (1): Nb + 50B ≧ 0.200)
In the ferrite-based stainless steel material of the present disclosure, it is important that Nb + 50B is 0.200% or more. When both Nb and B are added in combination as described above, the coagulated structure becomes finer and the coagulation structure is suppressed from growing in the coagulation direction to improve the rigging property and the rough skin property. Specifically, in the ferrite-based stainless steel material of the present disclosure, by adding both Nb and B in a composite manner, equiaxed crystallization is promoted with fine Nb-B-based crystallization as nuclei. It is considered that the solidified structure becomes finer and the rigging property after molding into the product shape is improved. Alternatively, it is considered that the segregation of Nb and B at the grain boundaries suppresses the growth of crystal grains during recrystallization and reduces the rough skin after molding into the product shape. If Nb + 50B is less than 0.200%, this effect will not be exhibited. Nb + 50B may be 0.210% or more, or 0.230% or more. The upper limit is not particularly limited, but may be 0.600% or less, or 0.400% or less in consideration of cracking during manufacturing and a decrease in toughness.
（Ｐ：０％以上０．０４０％以下）
Ｐは、成形性及び耐食性を低下させる元素であるため、Ｐ含有量は低い方が好ましく、上限を０．０４０％とする。下限は特に限定されず０％であってもよい。但し、コストを抑える観点から、０．００５％以上であってもよい。成形性と製造コストの両者を考慮した場合、Ｐ含有量は、０．００７％以上であってもよいし、０．０１０％以上であってもよく、０．０３０％以下であってもよいし、０．０２５％以下であってもよい。
(P: 0% or more and 0.040% or less)
Since P is an element that lowers moldability and corrosion resistance, it is preferable that the P content is low, and the upper limit is 0.040%. The lower limit is not particularly limited and may be 0%. However, from the viewpoint of suppressing the cost, it may be 0.005% or more. When both moldability and manufacturing cost are taken into consideration, the P content may be 0.007% or more, 0.010% or more, or 0.030% or less. However, it may be 0.025% or less.
（Ｓ：０％以上０．０１００％以下）
Ｓは不可避的不純物元素であり、製造時の割れを助長するため、上限を０．０１００％とする。Ｓ含有量は低いほど好ましく、０．００３０％以下であってもよいし、０．００２０％以下であってもよい。下限は特に限定されず０％であってもよい。一方、Ｓ含有量を過度の低下させるためにはコストの上昇を招く。この観点から、Ｓ含有量は、０．０００３％以上であってもよい。
(S: 0% or more and 0.0100% or less)
S is an unavoidable impurity element, and the upper limit is set to 0.0100% in order to promote cracking during manufacturing. The lower the S content, the more preferable, and it may be 0.0030% or less, or 0.0020% or less. The lower limit is not particularly limited and may be 0%. On the other hand, in order to excessively reduce the S content, the cost increases. From this point of view, the S content may be 0.0003% or more.
本開示のフェライト系ステンレス鋼材は、上記の基本組成に加えて下記の元素群のうち１種又は２種以上を選択的に含有させてもよい。 The ferrite-based stainless steel material of the present disclosure may selectively contain one or more of the following element groups in addition to the above basic composition.
（Ｔｉ：０％以上０．２０％以下）
Ｔｉは成形性及び耐食性を向上させる元素である。フェライト系ステンレス鋼の用途に応じて添加することができる。ただし、Ｔｉの過度の添加は研磨後の耐食性低下、製造性低下を招くため、上限を０．２０％とする。下限は特に限定されず０％であってもよい。Ｔｉ含有量は、０．０５％以上であってもよく、０．１６％以下であってもよいし、０．１４％以下であってもよい。
(Ti: 0% or more and 0.20% or less)
Ti is an element that improves moldability and corrosion resistance. It can be added depending on the application of ferritic stainless steel. However, since excessive addition of Ti causes a decrease in corrosion resistance and a decrease in manufacturability after polishing, the upper limit is set to 0.20%. The lower limit is not particularly limited and may be 0%. The Ti content may be 0.05% or more, 0.16% or less, or 0.14% or less.
（Ｍｏ：０％以上０．３０％以下）
Ｍｏは耐食性を向上させる元素であり、必要に応じて添加してもよい。ただし、過度の添加はリジング性及び肌荒れ性を低下させるため、上限を０．３０％とする。下限は特に限定されず０％であってもよい。製造性を考慮すると、Ｍｏ含有量は、０．０２％以上であってもよいし、０．０４％以上であってもよく、０．２４％以下であってもよいし、０．１２％以下であってもよい。
(Mo: 0% or more and 0.30% or less)
Mo is an element that improves corrosion resistance and may be added if necessary. However, since excessive addition reduces rigging and rough skin, the upper limit is set to 0.30%. The lower limit is not particularly limited and may be 0%. Considering the manufacturability, the Mo content may be 0.02% or more, 0.04% or more, 0.24% or less, or 0.12%. It may be as follows.
（Ｖ：０％以上０．３０％以下）
ＶもＭｏ同様に耐食性を向上させるため、必要に応じて添加してもよい。一層良好な耐食性を発揮させる観点から、下限を０．０３％としてもよい。一方で、０．３０％超の添加はリジング性の低下を招くためこれを上限とする。Ｖ含有量は、０％以上であってもよいし、０．０３％以上であってもよいし、０．０８％以上であってもよく、０．３０％以下であってもよいし、０．２２％以下であってもよい。
(V: 0% or more and 0.30% or less)
Like Mo, V may be added as needed in order to improve corrosion resistance. From the viewpoint of exhibiting better corrosion resistance, the lower limit may be 0.03%. On the other hand, addition of more than 0.30% causes a decrease in rigging property, so this is the upper limit. The V content may be 0% or more, 0.03% or more, 0.08% or more, 0.30% or less, or It may be 0.22% or less.
（Ｓｎ：０％以上０．５０％以下）
Ｓｎは耐食性を向上させる効果を有する元素であるため、必要に応じて添加してもよい。一層良好な耐食性を発揮させる観点から、下限を０．００５％としてもよい。一方、多量の添加は製造性の劣化を招くため、０．５０％を上限とする。製造性も考慮すると、Ｓｎ含有量は、０％以上であってもよいし、０．００５％以上であってもよいし、０．０１％以上であってもよいし、０．０２％以上であってもよく、０．５０％以下であってもよいし、０．２０％以下であってもよいし、０．１０％以下であってもよい。
(Sn: 0% or more and 0.50% or less)
Since Sn is an element having an effect of improving corrosion resistance, it may be added if necessary. From the viewpoint of exhibiting even better corrosion resistance, the lower limit may be set to 0.005%. On the other hand, since a large amount of addition causes deterioration of manufacturability, the upper limit is 0.50%. Considering the manufacturability, the Sn content may be 0% or more, 0.005% or more, 0.01% or more, or 0.02% or more. It may be 0.50% or less, 0.20% or less, or 0.10% or less.
（Ｎｉ：０％以上１．００％以下、Ｃｕ：０％以上１．００％以下、Ｗ：０％以上１．００％以下、Ｃｏ：０％以上０．５０％以下、Ｚｒ：０％以上０．５０％以下）
Ｎｉ、Ｃｕ、Ｗ、Ｃｏ、Ｚｒは、耐食性或いは耐酸化性を高めるのに有効な元素であり、必要に応じて添加してもよい。但し、これらの元素の過度な添加は成形性の低下を招くばかりでなく合金コストの上昇や製造性を阻害することに繋がる虞がある。そのため、Ｎｉ、Ｃｕ、Ｗの各々の含有量の上限は１．００％とする。Ｎｉ、Ｃｕ、Ｗの各々の含有量は、０．８０％以下であってもよいし、０．５０％以下であってもよい。一方で、Ｃｏ、Ｚｒの各々の含有量の上限は０．５０％とする。Ｃｏ、Ｚｒの各々の含有量は、０．４０％以下であってもよいし、０．３５％以下であってもよい。いずれの元素についても、その含有量は、０％以上であってもよいし、０．０５％以上であってもよいし、０．１０％以上であってもよい。
(Ni: 0% or more and 1.00% or less, Cu: 0% or more and 1.00% or less, W: 0% or more and 1.00% or less, Co: 0% or more and 0.50% or less, Zr: 0% or more 0.50% or less)
Ni, Cu, W, Co, and Zr are elements effective for enhancing corrosion resistance or oxidation resistance, and may be added if necessary. However, excessive addition of these elements may not only reduce the moldability but also increase the alloy cost and hinder the manufacturability. Therefore, the upper limit of the content of each of Ni, Cu, and W is set to 1.00%. The content of each of Ni, Cu, and W may be 0.80% or less, or 0.50% or less. On the other hand, the upper limit of the content of each of Co and Zr is 0.50%. The content of each of Co and Zr may be 0.40% or less, or may be 0.35% or less. The content of any of the elements may be 0% or more, 0.05% or more, or 0.10% or more.
（Ｃａ：０％以上０．００５０％以下、Ｍｇ：０％以上０．００５０％以下）
Ｃａ、Ｍｇは、熱間加工性や２次加工性を向上させる元素であり、必要に応じて添加してもよい。但し、これら元素の過度な添加は製造性を阻害することに繋がる。また粗大な介在物を形成して研磨後の耐食性低下に繋がるため、Ｃａ、Ｍｇの各々の含有量の上限は０．００５０％とする。下限については、０％以上であってもよいし、０．０００１％以上であってもよい。製造性と熱間加工性を考慮した場合、Ｃａ、Ｍｇともに、その含有量は、０．０００２％以上であってもよく、０．００２０％以下であってもよいし、０．００１０％以下であってもよい。
(Ca: 0% or more and 0.0050% or less, Mg: 0% or more and 0.0050% or less)
Ca and Mg are elements that improve hot workability and secondary workability, and may be added if necessary. However, excessive addition of these elements leads to inhibition of manufacturability. Further, since coarse inclusions are formed and lead to a decrease in corrosion resistance after polishing, the upper limit of the content of each of Ca and Mg is set to 0.0050%. The lower limit may be 0% or more, or 0.0001% or more. Considering manufacturability and hot workability, the content of both Ca and Mg may be 0.0002% or more, 0.0020% or less, or 0.0010% or less. It may be.
（Ｙ：０％以上０．２０％以下、Ｈｆ：０％以上０．２０％以下、ＲＥＭ：０％以上０．１０％以下）
Ｙ、Ｈｆ、ＲＥＭは、熱間加工性や鋼の清浄度の向上並びに耐酸化性の改善に対して有効な元素であり、必要に応じて添加してもよい。添加する場合、含有量の上限は、Ｙ及びＨｆはそれぞれ０．２０％、ＲＥＭは０．１０％とする。Ｙ及びＨｆの各々の含有量は０．１５％以下であってもよいし、０．１０％以下であってもよい。ＲＥＭの含有量は０．０８％以下であってもよいし、０．０５％以下であってもよい。Ｙ、Ｈｆ、ＲＥＭともに、各々の含有量は０％以上であってもよいし、０．００１％以上であってもよいし、０．００５％以上であってもよい。尚、本願において「ＲＥＭ」とは、原子番号５７〜７１に帰属する元素（ランタノイド）を指し、例えば、Ｃｅ、Ｐｒ、Ｎｄ等である。
(Y: 0% or more and 0.20% or less, Hf: 0% or more and 0.20% or less, REM: 0% or more and 0.10% or less)
Y, Hf, and REM are elements effective for improving hot workability, steel cleanliness, and oxidation resistance, and may be added as necessary. When added, the upper limit of the content is 0.20% for Y and Hf, and 0.10% for REM, respectively. The respective contents of Y and Hf may be 0.15% or less, or may be 0.10% or less. The content of REM may be 0.08% or less, or may be 0.05% or less. The content of each of Y, Hf, and REM may be 0% or more, 0.001% or more, or 0.005% or more. In the present application, "REM" refers to an element (lanthanoid) belonging to atomic numbers 57 to 71, and is, for example, Ce, Pr, Nd, or the like.
（Ｓｂ：０％以上０．５０％以下）
ＳｂはＳｎと同様に耐食性向上効果を持つ元素であり、必要に応じて添加してもよい。ただし、Ｓｂの多量の添加は製造性の劣化を招くため、０．５０％を上限とする。一方、耐食性向上の効果は０．００５％以上で発揮されるためこれを下限とする。Ｓｂ含有量は、０％以上であってもよいし、０．００５％以上であってもよいし、０．０１％以上であってもよく、０．３０％以下であってもよいし、０．１０％以下であってもよい。
(Sb: 0% or more and 0.50% or less)
Sb is an element having an effect of improving corrosion resistance like Sn, and may be added if necessary. However, since the addition of a large amount of Sb causes deterioration of manufacturability, the upper limit is 0.50%. On the other hand, since the effect of improving corrosion resistance is exhibited at 0.005% or more, this is set as the lower limit. The Sb content may be 0% or more, 0.005% or more, 0.01% or more, 0.30% or less, or It may be 0.10% or less.
本開示のフェライト系ステンレス鋼材は、上述の各元素に加えて、Ｆｅ及び不純物（不可避的不純物を含む）からなるが、上記課題を解決できる範囲で、上述の各元素以外の元素を含有していてもよい。例えば、Ｂｉ、Ｐｂ、Ｓｅ、Ｈ、Ｔａ等を含有させてもよいが、これらの元素の含有量は可能な限り低減することが好ましい。これらの元素は、上記課題を解決できる限度において、その含有割合が制御され、例えば、Ｂｉ≦１００ｐｐｍ、Ｐｂ≦１００ｐｐｍ、Ｓｅ≦１００ｐｐｍ、Ｈ≦１００ｐｐｍ、Ｔａ≦５００ｐｐｍの１種以上を含有してもよい。 The ferritic stainless steel material of the present disclosure is composed of Fe and impurities (including unavoidable impurities) in addition to the above-mentioned elements, but contains elements other than the above-mentioned elements as long as the above problems can be solved. You may. For example, Bi, Pb, Se, H, Ta and the like may be contained, but it is preferable to reduce the content of these elements as much as possible. The content ratio of these elements is controlled to the extent that the above problems can be solved, and even if one or more of these elements are contained, for example, Bi ≦ 100 ppm, Pb ≦ 100 ppm, Se ≦ 100 ppm, H ≦ 100 ppm, and Ta ≦ 500 ppm. Good.
１．２ 形状及び組織
次に本開示のフェライト系ステンレス鋼材の形状及び金属組織について述べる。
1.2 Shape and structure Next, the shape and metal structure of the ferrite stainless steel material of the present disclosure will be described.
１．２．１ 鋼材の形状
本願にいう「鋼材」とは、精錬後に凝固工程を通ったままの状態の素材を指す。凝固後に再加熱したものや、また分解（圧延）などの加工をしたものは含まない。尚、表面疵抑制を目的に表面手入れを行うことは構わない。本開示のフェライト系ステンレス鋼材は、凝固ままで後述の細粒組織を得ることができる。鋼材の厚さは１５０ｍｍ以上とする。厚さが１５０ｍｍ未満の場合、鋼板製造時の加工率(圧延率)が少なく、肌荒れを抑制することが難しくなる場合がある。鋼材の具体例としてはスラブのような扁平厚板素材が挙げられる。
1.2.1 Shape of steel material The term "steel material" as used in the present application refers to a material that has undergone a solidification process after refining. It does not include those that have been reheated after solidification and those that have been processed such as decomposition (rolling). It is permissible to perform surface maintenance for the purpose of suppressing surface defects. In the ferrite-based stainless steel material of the present disclosure, the fine-grained structure described later can be obtained as it is solidified. The thickness of the steel material shall be 150 mm or more. If the thickness is less than 150 mm, the processing rate (rolling rate) at the time of manufacturing the steel sheet is small, and it may be difficult to suppress rough skin. Specific examples of the steel material include a flat plate material such as a slab.
１．２．２ 金属組織
本開示のフェライト系ステンレス鋼材はフェライト単相組織よりなる。これは、母材の金属組織において、オーステナイト相やマルテンサイトを実質的に含まないことを意味する。母材の金属組織においてオーステナイト相やマルテンサイトが含まれる場合は、変態の活用により結晶粒径を細かくすることが可能である。また、これらは製造時に耳割れ等の歩留まり低下を招く。この点、母材の金属組織はフェライト単相組織が好ましいが、工業生産上許容できる範囲で不可避的に異相が含まれていてもよい。なお、鋼中には炭窒化物等の析出物が存在する場合があるが、本開示の鋼材においてもこのような析出物が存在していてもよい。
1.2.2 Metal structure The ferritic stainless steel material disclosed in the present disclosure has a ferrite single-phase structure. This means that the metallographic structure of the base metal is substantially free of the austenite phase and martensite. When the metallographic structure of the base metal contains an austenite phase or martensite, it is possible to make the crystal grain size finer by utilizing transformation. In addition, these cause a decrease in yield such as ear cracking during manufacturing. In this respect, the metal structure of the base metal is preferably a ferrite single-phase structure, but different phases may be unavoidably contained within an acceptable range in industrial production. Precipitates such as carbonitrides may be present in the steel, but such precipitates may also be present in the steel materials of the present disclosure.
１．２．３ 等軸晶率
本開示のフェライト系ステンレス鋼材は、上述したように、Ｎｂ及びＢの含有量を所定の範囲に制限することによってＮｂ及びＢの晶出物が核となって等軸晶化が促進されるものと考えられ、等軸晶率が７０％以上の組織が得られる。等軸晶は粒形状アスペクト比（短径／長径）が０．５〜１．０の範囲の結晶粒を示す。結晶粒のアスペクト比はＳＥＭにより鋼材の表面や断面の二次画像を取得することにより特定する。すなわち、断面光学顕微鏡画像において結晶粒の最長径を特定し、当該最長径と直交する最短径を特定し、特定した最長径と最短径とからアスペクト比を特定する。等軸晶率を特定する場合は、鋼材における任意の５つの断面について測定を実施し、その平均値を持って等軸晶率とする。ただし、鋳造方向で等軸晶率が２倍以上に大きく変化する場合には、更に５断面以上で測定し、その平均値を算出する。等軸晶率は断面組織を観察した際に全面積に対する等軸晶組織の占める割合（面積率）であるが、測定は板厚長さに対する等軸晶組織が占める長さを持って算出する。等軸晶率は、研磨、腐食によって金属組織を現出させた後に測定する。具体的には、鋼材全厚みを含む断面において、金属組織を現出させた後で、鋼材厚さ方向の全長さに対する等軸晶が占める長さを算出して、鋼材厚さ方向における等軸晶率を測定・算出する。なお測定位置によるばらつきが生じるため、５か所以上を測定し、その平均値を持って等軸晶率とすることとする。
1.2.3 Equiaxial crystal ratio As described above, the ferrite-based stainless steel material of the present disclosure has Nb and B crystals as nuclei by limiting the Nb and B contents to a predetermined range. It is considered that equiaxed crystallization is promoted, and a structure having an equiaxed crystal ratio of 70% or more can be obtained. Equiaxial crystals show crystal grains having a grain shape aspect ratio (minor axis / major axis) in the range of 0.5 to 1.0. The aspect ratio of the crystal grains is specified by acquiring a secondary image of the surface or cross section of the steel material by SEM. That is, the longest diameter of the crystal grain is specified in the cross-sectional optical microscope image, the shortest diameter orthogonal to the longest diameter is specified, and the aspect ratio is specified from the specified longest diameter and the shortest diameter. When specifying the equiaxed crystal ratio, measurement is performed on any five cross sections of the steel material, and the average value thereof is used as the equiaxed crystal ratio. However, if the equiaxed crystal ratio changes significantly more than twice in the casting direction, the measurement is performed on five or more cross sections, and the average value is calculated. The equiaxed crystal ratio is the ratio (area ratio) of the equiaxed crystal structure to the total area when observing the cross-sectional structure, but the measurement is calculated by taking the length occupied by the equiaxed crystal structure to the plate thickness length. .. The equiaxed crystal ratio is measured after the metallographic structure is exposed by polishing and corrosion. Specifically, after the metallographic structure is exposed in the cross section including the total thickness of the steel material, the length occupied by the equiaxed crystals with respect to the total length in the steel material thickness direction is calculated, and the equiaxed axis in the steel material thickness direction is calculated. Measure and calculate the crystallinity. Since variations occur depending on the measurement position, 5 or more points are measured, and the average value is used as the equiaxed crystal ratio.
尚、例えば、冷延焼鈍板を成形した際に生じる肌荒れの程度は、冷延焼鈍板の結晶粒径の影響を受ける。本発明者の知見では、冷延焼鈍板における結晶粒度番号が９．０以上のときに肌荒れが抑制されやすい。冷延焼鈍後の鋼板における結晶粒度番号を９．０以上とするためには、再結晶による細粒化を製造工程内で行う必要がある。このため、元の素材（鋼材）を再結晶しやすい組織とし、必要な圧下を加える。ここで、鋼材（例えばスラブ）において柱状晶粒は再結晶しにくい、或いは再結晶したとしても結晶粒径が大きくなりやすい。そのため、上述の通り、鋼材における等軸晶率を７０％以上とする必要がある。加えて、総圧下率が大きいほど好ましい。そのため、上述の通り、鋼材の厚みを１５０ｍｍ以上とする必要がある。これらの条件を満足することで、冷延焼鈍後に結晶粒度番号９．０以上の鋼板が得られやすくなり、肌荒れが一層抑制されやすくなる。 For example, the degree of rough skin generated when the cold-rolled annealed plate is molded is affected by the crystal grain size of the cold-rolled annealed plate. According to the findings of the present inventor, rough skin is likely to be suppressed when the crystal grain size number of the cold-spread annealed plate is 9.0 or more. In order to set the crystal grain size number of the steel sheet after cold annealing to 9.0 or more, it is necessary to perform fine graining by recrystallization in the manufacturing process. Therefore, the original material (steel material) is made into a structure that is easy to recrystallize, and the necessary reduction is applied. Here, in a steel material (for example, a slab), columnar crystal grains are difficult to recrystallize, or even if they are recrystallized, the crystal grain size tends to be large. Therefore, as described above, it is necessary to set the equiaxed crystal ratio in the steel material to 70% or more. In addition, the larger the total reduction rate, the more preferable. Therefore, as described above, the thickness of the steel material needs to be 150 mm or more. By satisfying these conditions, a steel sheet having a crystal grain size of 9.0 or more can be easily obtained after cold annealing and annealing, and rough skin can be further suppressed.
１．２．４ 結晶粒径
上述の通り、本開示のフェライト系ステンレス鋼材はＮｂ及びＢ等の含有量を特定の範囲に制御されており、且つ、凝固組織中の等軸晶率が増加している。すなわち、平均結晶粒径が小さい。例えば、本開示のフェライト系ステンレス鋼材は、平均結晶粒径が５ｍｍ以下であってもよい。結晶粒径は、研磨及び腐食により金属組織を現出させた後に測定すればよい。平均結晶粒径の測定は、線分法で測定する。すなわち、圧延方向と垂直な断面について光学顕微鏡画像を取得し、当該画像に含まれる等軸晶部において、板厚方向に２５０ｍｍ以上、板幅方向に２５０ｍｍ以上となるように直線を引き、測定長さを交差する結晶粒回数で除することで算出する。平均結晶粒径が５ｍｍ以下であることで、後工程において再結晶を活用した細粒化がより容易となる。
1.2.4 Crystal grain size As described above, in the ferrite stainless steel material of the present disclosure, the content of Nb, B, etc. is controlled within a specific range, and the equiaxed crystal ratio in the solidified structure increases. ing. That is, the average crystal grain size is small. For example, the ferrite-based stainless steel material of the present disclosure may have an average crystal grain size of 5 mm or less. The crystal grain size may be measured after the metal structure is exposed by polishing and corrosion. The average crystal grain size is measured by the line segment method. That is, an optical microscope image is acquired for a cross section perpendicular to the rolling direction, and a straight line is drawn so that the equiaxed crystal portion included in the image is 250 mm or more in the plate thickness direction and 250 mm or more in the plate width direction, and the measurement length is measured. It is calculated by dividing the number of grains by the number of intersecting crystal grains. When the average crystal grain size is 5 mm or less, it becomes easier to refine the particles by utilizing recrystallization in the subsequent step.
１．２．５ 板厚方向の｛００１｝面ランダム強度比
本開示のフェライト系ステンレス鋼材は、厚さの１／４位置において厚さ方向の｛００１｝面ランダム強度比が２．０未満であってもよい。凝固組織に粗大な結晶粒（柱状晶）が残存してリジング特性が劣化する場合、粗大柱状晶は板厚の１／４に残存することが多い。このため、１／４位置を組織調査位置とする。また板厚方向の｛００１｝面ランダム強度比が２．０未満であることにより、リジング特性がさらに向上する。ランダム強度比は、板厚１／４位置の板厚方向と垂直をなす断面においてＸ線回折を行い、粉末焼結で作製し、特定方位への結晶配向を持たない標準サンプルの強度との比を算出することで求める。
1.2.5 {001} plane random strength ratio in the plate thickness direction The ferritic stainless steel material of the present disclosure has a {001} plane random strength ratio in the thickness direction of less than 2.0 at the 1/4 position of the thickness. There may be. When coarse crystal grains (columnar crystals) remain in the solidified structure and the rigging characteristics deteriorate, the coarse columnar crystals often remain at 1/4 of the plate thickness. Therefore, the 1/4 position is set as the tissue survey position. Further, when the {001} plane random strength ratio in the plate thickness direction is less than 2.0, the rigging characteristics are further improved. The random intensity ratio is the ratio to the intensity of a standard sample that is manufactured by powder sintering by performing X-ray diffraction on a cross section perpendicular to the plate thickness direction at the plate thickness 1/4 position and does not have crystal orientation in a specific orientation. It is calculated by calculating.
１．３ その他の条件
本開示のフェライト系ステンレス鋼材は鋳造により得ることができる。具体的には、上記の鋼組成を有する溶鋼を用いてインゴット鋳造や連続鋳造を行うことで、厚みが１５０ｍｍ以上の鋼材を得る。ここで、鋳造後に得られる鋼材が目的とする組織を有するように、鋳造時の温度や冷却速度等を制御してもよい。本開示のフェライト系ステンレス鋼材を得るにあたって、鋳造時の条件は特に限定されるものではないが、安定鋳造のために次の条件としてもよい。すなわち、鋳造温度は凝固開始温度より２５℃以上１００℃以下高くしてもよい。また、鋼材における等軸晶率を一層高めるために、鋳造時に鋳造速度を低めて溶鋼の温度勾配を低くしてもよい。尚、鋳造時における電磁撹拌有無等がリジング性及び肌荒れ性に与える影響は小さいものと考えられる。
1.3 Other conditions The ferritic stainless steel material of the present disclosure can be obtained by casting. Specifically, a steel material having a thickness of 150 mm or more can be obtained by performing ingot casting or continuous casting using the molten steel having the above steel composition. Here, the temperature, cooling rate, etc. at the time of casting may be controlled so that the steel material obtained after casting has a desired structure. In obtaining the ferrite-based stainless steel material of the present disclosure, the conditions at the time of casting are not particularly limited, but the following conditions may be used for stable casting. That is, the casting temperature may be 25 ° C. or higher and 100 ° C. or lower higher than the solidification start temperature. Further, in order to further increase the equiaxed crystal ratio in the steel material, the casting speed may be lowered at the time of casting to lower the temperature gradient of the molten steel. It is considered that the presence or absence of electromagnetic agitation during casting has little effect on the rigging property and the rough skin property.
以上の通り、本開示のフェライト系ステンレス鋼材は、Ｎｂ及びＢの含有量等が特定の範囲に制御される。これにより、当該鋼材を鋼板に加工し、その後、製品形状へと成形する場合においても、製品形状への成形性を確保しつつ、製品形状へ成形後の肌荒れとリジングとを同時に低減するとともに、研磨後の耐腐食性も確保することが可能である。 As described above, in the ferrite-based stainless steel material of the present disclosure, the contents of Nb and B and the like are controlled within a specific range. As a result, even when the steel material is processed into a steel plate and then molded into a product shape, while ensuring moldability into the product shape, rough skin and rigging after molding into the product shape are simultaneously reduced. It is also possible to ensure corrosion resistance after polishing.
２．鋼板の製造方法
本開示の技術は、鋼板の製造方法としての側面も有する。すなわち、上述のフェライト系ステンレス鋼材に対して、熱間加工及び／又は冷間加工を行う工程を含む、鋼板の製造方法である。
2. Steel Sheet Manufacturing Method The technique disclosed in the present disclosure also has an aspect as a steel sheet manufacturing method. That is, it is a method for manufacturing a steel sheet, which includes a step of performing hot working and / or cold working on the above-mentioned ferritic stainless steel material.
鋼材は板厚が厚いため、製品へと成形加工し得る板厚（一般的には１ｍｍ以下）まで薄くする必要がある。これには熱間加工や冷間加工を行う。板状の形状を得るには熱間圧延及び冷間圧延を行うことが好ましい。また必要に応じて適宜熱処理を加えても良い。鋼板の製造方法の一例として、例えば、溶解、精錬、鋳造による鋼材の製造−熱間圧延−熱延板焼鈍−冷間圧延−冷延板焼鈍の各工程からなる製法を採用できる。熱間圧延により、例えば、板厚３ｍｍ〜１０ｍｍの熱延板とする。冷間圧延率は、例えば、７０％以上とすることが好ましい。また冷間圧延後の熱処理（冷延板焼鈍、最終焼鈍）における最高到達温度は、冷延板の再結晶温度をＴ（℃）とすると、例えば、（Ｔ−１０）〜（Ｔ２＋５０）℃の範囲に制御することが好ましい。冷延板焼鈍の最高到達温度が（Ｔ２−１０）未満であると材料が硬質化して成形割れが生じ易くなるためである。一方、最高到達温度が（Ｔ２＋５０）超であると結晶粒径が大きくなり、成形後の肌荒れが生じ易くなるためである。 Since the steel material has a large plate thickness, it is necessary to reduce the plate thickness to a plate thickness (generally 1 mm or less) that can be formed into a product. This is done by hot or cold working. Hot rolling and cold rolling are preferable to obtain a plate-like shape. Moreover, heat treatment may be added as needed. As an example of the method for manufacturing a steel sheet, for example, a manufacturing method including each step of manufacturing a steel material by melting, refining, and casting-hot rolling-annealing a hot-rolled sheet-cold rolling-annealing a cold-rolled sheet can be adopted. By hot rolling, for example, a hot-rolled plate having a plate thickness of 3 mm to 10 mm is obtained. The cold rolling ratio is preferably 70% or more, for example. The heat treatment after cold rolling (cold-rolled sheet annealing, final annealing) maximum temperature in, when the recrystallization temperature of the cold-rolled sheet to T (° C.), for example, (T-10) ~ ( T 2 +50) It is preferable to control the temperature in the range of ° C. Material maximum temperature of the cold-rolled sheet annealing is less than (T 2 -10) is because the easily occurs molding cracks in hardening. On the other hand, if the maximum temperature reached exceeds (T 2 +50), the crystal grain size becomes large and rough skin after molding is likely to occur.
３．推定メカニズム及び効果
本開示のフェライト系ステンレス鋼材を用いて鋼板を製造し、当該鋼板を成形して製品を得た場合に、製品成形後の表面凹凸（リジングと肌荒れ）が低減される理由については鋭意調査中ではあるが、現時点では次のように推測される。
3. 3. Estimating mechanism and effect When a steel sheet is manufactured using the ferritic stainless steel material of the present disclosure and the steel sheet is molded to obtain a product, the reason why the surface unevenness (rigging and rough skin) after product molding is reduced is as follows. Although it is under intensive investigation, it is presumed as follows at this time.
一般的にフェライト系ステンレス鋼は凝固時に粗大な柱状晶組織を形成しやすい。この粗大柱状結晶粒がリジングの原因となり得る。また高純フェライト系ステンレス鋼においては、一旦形成した結晶粒を微細にする方法としては再結晶現象を活用するしかない。したがって、上述した各成分は凝固組織或いは製造時の再結晶挙動に寄与していると考えられる。今回の知見では、Ｎｂ及びＢを複合的に添加することが重要である。Ｎｂ及びＢの添加は凝固組織の等軸晶率増加をもたらす。スラブ観察ではＮｂ−Ｂの粗大な介在物は観察できなかったため、微細な化合物を生成したか、組成的過冷現象により細粒化したと考えられる。実際に冷延焼鈍後においても粗大な析出物は認められなかった。Ａｌは再結晶への影響は小さいが、凝固組織を粗大化する傾向があるため、このことを通して圧延時の再結晶が遅延し、結果として製品のリジング性へ影響を及ぼすと推察される。また、肌荒れ性が低減される原因としては、ＮｂとＢは粒界偏析元素であるため、結晶粒界に偏析して結晶粒成長を抑制する効果があると考えられる。すなわち、本開示の技術は、凝固組織微細化と熱間再結晶促進を両立するために、凝固組織を微細化し、かつ再結晶後の粒成長を抑える元素の添加量を適正化することで、リジングの発生並びに肌荒れ性に影響する粒成長性を制御した新たな技術と言える。これまでにおいて、これらの元素の全てを適正範囲に制御した組成、またそれを示唆する指針は存在しない。 Generally, ferritic stainless steel tends to form a coarse columnar crystal structure during solidification. These coarse columnar crystal grains can cause rigging. Further, in high-pure ferritic stainless steel, the only way to make the crystal grains once formed finer is to utilize the recrystallization phenomenon. Therefore, it is considered that each of the above-mentioned components contributes to the solidified structure or the recrystallization behavior during production. In this finding, it is important to add Nb and B in a complex manner. The addition of Nb and B results in an increase in equiaxed crystal ratio of the solidified structure. Since no coarse inclusions of Nb-B could be observed in the slab observation, it is considered that a fine compound was produced or the particles were finely divided by the compositional supercooling phenomenon. No coarse precipitates were actually observed even after cold annealing. Although Al has a small effect on recrystallization, it tends to coarsen the solidified structure, which delays recrystallization during rolling, and as a result, it is presumed that it affects the rigging property of the product. Further, it is considered that the reason why the rough skin property is reduced is that since Nb and B are intergranular segregation elements, they have an effect of segregating at the grain boundaries and suppressing crystal grain growth. That is, in the technique of the present disclosure, in order to achieve both the refinement of the solidified structure and the promotion of hot recrystallization, the solidified structure is refined and the amount of the element that suppresses the grain growth after recrystallization is optimized. It can be said that this is a new technology that controls the grain growth that affects the occurrence of rigging and rough skin. So far, there is no composition that controls all of these elements within an appropriate range, and no guideline that suggests it.
次に実施例を示しつつ本開示のフェライト系ステンレス鋼材による効果についてさらに詳細に説明するが、実施例での条件は、本開示の技術の実施可能性及び効果を確認するために採用した一条件例に過ぎず、本開示の技術は、以下の実施例に限定されるものではない。以下の実施例に示す条件以外にも、上記課題を解決できる限りにおいて、種々の条件を採用し得る。 Next, the effect of the ferritic stainless steel material of the present disclosure will be described in more detail with reference to Examples, but the conditions in the Examples are one condition adopted for confirming the feasibility and effect of the technique of the present disclosure. By way of example only, the techniques of the present disclosure are not limited to the following examples. In addition to the conditions shown in the following examples, various conditions can be adopted as long as the above problems can be solved.
１．スラブの製造及び評価
鋼材としてスラブを製造して各種評価を行った。具体的には、下記表１、２に示す成分組成のステンレス溶鋼を球状黒鉛鋳鉄よりなる鋳型に流し込むことで溶製して２００ｍｍ厚のスラブを製造し、スラブ断面より金属組織を調査した。金属組織に対して、その等軸晶率（全板厚に占める等軸粒の割合）及び平均結晶粒径（測定長さを交差した結晶粒回数で除した値）を求めた。また厚み１／４の厚さ方向に垂直な断面よりＸ線測定を実施し、厚さの１／４位置における厚さ方向の｛００１｝面ランダム強度比を測定した。Ｘ線測定は５か所測定し、その平均値を用いた。
1. 1. Manufacture and evaluation of slabs Slabs were manufactured as steel materials and evaluated in various ways. Specifically, stainless molten steel having the composition shown in Tables 1 and 2 below was melted by pouring it into a mold made of spheroidal graphite cast iron to produce a slab having a thickness of 200 mm, and the metallographic structure was investigated from the cross section of the slab. The equiaxed crystal ratio (ratio of equiaxed grains to the total plate thickness) and average crystal grain size (value obtained by dividing the measured length by the number of crossed crystal grains) were determined for the metal structure. Further, X-ray measurement was performed from a cross section perpendicular to the thickness direction of 1/4 of the thickness, and the {001} plane random intensity ratio in the thickness direction at the 1/4 position of the thickness was measured. X-ray measurement was performed at 5 points, and the average value was used.
２．ステンレス鋼板の製造
上述のようにして得られたスラブを熱間圧延にて圧延した（ここで、鋼種Ａについてのみ、２００ｍｍ厚のスラブをそのまま熱間圧延した場合（下記実施例１）と、スラブの板厚中心１００ｍｍ厚を切断して熱間圧延した場合（下記比較例６）との２つの場合について検討を行うこととした。）。その後、熱延板焼鈍、冷間圧延、冷延板焼鈍を施して０．６ｍｍ厚のステンレス鋼板を製造した。熱延板焼鈍、冷延板焼鈍においては再結晶温度Ｔを測定してから焼鈍温度を決定した。熱延板焼鈍はＴ＋１０(℃)、冷延板焼鈍はＴ(℃)とした。なお熱延板焼鈍及び冷延板焼鈍における焼鈍時間（保持時間）はそれぞれ、３０秒とし、かつ本実施例において中間焼鈍は省略した。冷間圧延率は８５％とした。
2. Manufacture of Stainless Steel Sheet The slab obtained as described above was rolled by hot rolling (here, only for steel type A, when a slab having a thickness of 200 mm is hot rolled as it is (Example 1 below), the slab It was decided to examine two cases, that is, the case where the plate thickness center of 100 mm was cut and hot-rolled (Comparative Example 6 below). Then, hot-rolled sheet annealing, cold rolling, and cold-rolled sheet annealing were performed to produce a stainless steel sheet having a thickness of 0.6 mm. In the hot-rolled plate annealing and the cold-rolled plate annealing, the recrystallization temperature T was measured before determining the annealing temperature. The hot-rolled plate was annealed at T + 10 (° C.), and the cold-rolled plate was annealed at T (° C.). The annealing time (holding time) in the hot-rolled plate annealing and the cold-rolled plate annealing was 30 seconds, respectively, and the intermediate annealing was omitted in this example. The cold rolling ratio was 85%.
３．ステンレス鋼板の成形
得られたステンレス鋼板より、φ１１０ｍｍの試料を切り出し、限界絞り比２．２のカップ成形試験を行った。今回実施したカップ成形試験条件は、ポンチ径が５０ｍｍ、ポンチ肩Ｒが５ｍｍ、ダイス径が５３ｍｍ、ダイス肩Ｒが８ｍｍ、しわ押さえ圧が１０トンであり、試料とポンチ間の潤滑のために、出光興産株式会社製の防錆油「ダフニーオイルコートＺ３（登録商標）」を塗布後に潤滑シート「ニチアス株式会社製ナフロンテープＴＯＭＢＯ９００１」を貼り付けた。
3. 3. Molding of Stainless Steel Sheet A sample having a diameter of 110 mm was cut out from the obtained stainless steel sheet and subjected to a cup forming test with a limit drawing ratio of 2.2. The cup forming test conditions carried out this time were a punch diameter of 50 mm, a punch shoulder R of 5 mm, a die diameter of 53 mm, a die shoulder R of 8 mm, and a wrinkle pressing pressure of 10 tons. After applying the rust preventive oil "Daphne Oil Coat Z3 (registered trademark)" manufactured by Idemitsu Kosan Co., Ltd., the lubricating sheet "Naflon Tape TOMBO9001 manufactured by Nichias Co., Ltd." was attached.
４．成形品の評価
４．１．肌荒れ
カップ成形後の肌荒れを評価した。具体的には、カップ成形後の試料の縦壁部の高さ中央部において、圧延方向と平行方向に５ｍｍ長さについて二次元接触式の表面粗さ測定機を用いて表面粗さ測定を行った。ＪＩＳ Ｂ ００３１（２００３）に記述される算術平均粗さＲａが２．０μｍを基準とし、それ以下の場合に表面肌荒れ評価を良好（○）、Ｒａが２．０μｍ超の場合に表面肌荒れ評価を不良（×）と判断した。
4. Evaluation of articles 4.1. Rough skin Rough skin after cup molding was evaluated. Specifically, at the center of the height of the vertical wall of the sample after cup forming, the surface roughness is measured using a two-dimensional contact type surface roughness measuring machine for a length of 5 mm in the direction parallel to the rolling direction. It was. The arithmetic mean roughness Ra described in JIS B 0031 (2003) is based on 2.0 μm, and when it is less than that, the surface roughness evaluation is good (○), and when Ra is more than 2.0 μm, the surface roughness evaluation is evaluated. It was judged to be defective (x).
４．２．リジング性
カップ成形後のリジングは縦壁部を圧延方向と垂直方向に測定した。すなわち、前述の肌荒れを測定した方向と９０°ずらした方向の縦壁部で測定した。測定は二次元接触式の表面粗さ測定機で実施し、測定長さは１０ｍｍとした測定範囲内で最も高い部分と低い部分の高さの差をリジングと定義し、これが５μｍ未満の場合にリジング性良好（〇）、５μｍ以上の場合にリジング性不良（×）と判断した。
4.2. Rigging property For rigging after cup molding, the vertical wall portion was measured in the direction perpendicular to the rolling direction. That is, the measurement was performed on the vertical wall portion in the direction deviated by 90 ° from the direction in which the above-mentioned rough skin was measured. The measurement is carried out with a two-dimensional contact type surface roughness measuring machine, and the difference in height between the highest part and the lowest part within the measurement range with a measurement length of 10 mm is defined as rigging, and when this is less than 5 μm. When the rigging property was good (◯) and 5 μm or more, it was judged to be poor rigging property (×).
４．３．研磨後耐食性
カップ外面の凹凸部を＃１５０に相当するグラインダで研削した後、耐食性を調査した。耐食性はカップ外側から塩水を噴霧する試験とした。ＮａＣｌ濃度は５％、試験温度は５０℃とし、その他の試験片形状及び試験条件はＪＩＳ Ｚ ２３７１に準拠した。耐食性の評価は、４８試験後の外観で赤錆が認められたものを不良（×）、赤錆が認められないものを良好（〇）とした。
4.3. Corrosion resistance after polishing After grinding the uneven portion of the outer surface of the cup with a grinder corresponding to # 150, the corrosion resistance was investigated. Corrosion resistance was tested by spraying salt water from the outside of the cup. The NaCl concentration was 5%, the test temperature was 50 ° C., and other test piece shapes and test conditions were in accordance with JIS Z 2371. In the evaluation of corrosion resistance, those in which red rust was observed in the appearance after 48 tests were evaluated as defective (x), and those in which no red rust was observed were evaluated as good (〇).
下記表３に、上記特性評価の結果を示す。なお、実施例においてステンレス鋼板は全てフェライト単相（オーステナイト相やマルテンサイト組織を含まない）であった。 Table 3 below shows the results of the above characteristic evaluation. In the examples, all the stainless steel sheets were ferrite single phases (excluding the austenite phase and the martensite structure).
表３に示すように、実施例１〜８については、耐肌荒れ性及びリジング性成形性に優れたフェライト系ステンレス鋼板を得ることができた。 As shown in Table 3, for Examples 1 to 8, ferrite stainless steel sheets having excellent rough skin resistance and rigging formability could be obtained.
一方、比較例１については、鋼種ＫのＢ量が低く、Ｎｂ量及びＢ量の合計量も低い。また、スラブでの等軸晶率が低く、｛００１｝面強度比が高い。このため、製品板のリジング特性が不良となる。 On the other hand, in Comparative Example 1, the B amount of the steel type K is low, and the total amount of the Nb amount and the B amount is also low. In addition, the equiaxed crystal ratio in the slab is low, and the {001} plane strength ratio is high. Therefore, the rigging characteristics of the product plate become poor.
比較例２については、鋼種ＬのＮｂ量及びＢ量の合計量が低い。また、スラブでの等軸晶率が低く、｛００１｝面強度比が高い。加えて製品の結晶粒径が大きく、肌荒れ性が不良となる。 In Comparative Example 2, the total amount of Nb amount and B amount of steel type L is low. In addition, the equiaxed crystal ratio in the slab is low, and the {001} plane strength ratio is high. In addition, the crystal grain size of the product is large, resulting in poor rough skin.
比較例３については、鋼種ＭのＡｌ量及びＴｉ量が高い。また、スラブでの等軸晶率が低く、｛００１｝面強度比が高い。このため、製品板のリジング特性が不良となる。また研磨後の耐食性も不良となる。 In Comparative Example 3, the Al amount and Ti amount of the steel type M are high. In addition, the equiaxed crystal ratio in the slab is low, and the {001} plane strength ratio is high. Therefore, the rigging characteristics of the product plate become poor. In addition, the corrosion resistance after polishing is also poor.
比較例４については、鋼種ＮのＮｂ量が高い。また、スラブでの等軸晶率が低く、｛００１｝面強度比が高い。このため、製品板のリジング特性が不良となる。 In Comparative Example 4, the amount of Nb of the steel type N is high. In addition, the equiaxed crystal ratio in the slab is low, and the {001} plane strength ratio is high. Therefore, the rigging characteristics of the product plate become poor.
比較例５については、鋼種ＯのＮｂ量が低い。また、スラブの等軸晶率が低い。このため、製品板の肌荒れ性とリジング性とがともに不良となる。 In Comparative Example 5, the amount of Nb of steel type O is low. In addition, the equiaxed crystal ratio of the slab is low. Therefore, both the rough skin property and the rigging property of the product board are poor.
比較例６については、スラブ厚が１５０ｍｍ未満であるため、製造時の圧下率が少なくなり、製品板の肌荒れ性が不良となる。 In Comparative Example 6, since the slab thickness is less than 150 mm, the reduction rate at the time of manufacturing is reduced, and the rough skin of the product plate becomes poor.
以上の通り、実施例１〜８に係るフェライト系ステンレス鋼スラブのように、Ｎｂ及びＢの含有量等を特定の範囲に制御し、等軸晶率を所定以上とし、且つ、厚みを１５０ｍｍ以上とすることで、当該スラブを鋼板に加工し、その後、製品形状へと成形する場合においても、製品形状への成形性を確保しつつ、製品形状へ成形後の肌荒れとリジングとを同時に低減するとともに、研磨後の耐腐食性も確保することが可能であることが分かる。 As described above, like the ferritic stainless steel slabs according to Examples 1 to 8, the contents of Nb and B are controlled within a specific range, the equiaxed crystal ratio is set to a predetermined value or more, and the thickness is 150 mm or more. By doing so, even when the slab is processed into a steel plate and then molded into a product shape, the rough skin and rigging after molding into the product shape are simultaneously reduced while ensuring the moldability into the product shape. At the same time, it can be seen that it is possible to secure corrosion resistance after polishing.
本開示のフェライト系ステンレス鋼板は、成形加工後の表面特性に優れているので、従来行われていた表面凹凸除去を目的とした成形加工後の研磨工程を省略することができるため、製造コストの面でも効果を十分に享受できる。本開示のフェライト系ステンレス鋼板は、例えば、家電製品の筺体或いは器物のように、比較的厳しい成形性が要求される用途においても採用することができる。 Since the ferritic stainless steel sheet of the present disclosure has excellent surface characteristics after molding, it is possible to omit the polishing step after molding for the purpose of removing surface irregularities, which is a manufacturing cost. In terms of aspects, you can fully enjoy the effect. The ferritic stainless steel sheet of the present disclosure can also be used in applications that require relatively strict moldability, such as housings or utensils of home appliances.
Claims (4)
Ｃ：０．００１％以上０．０１５％以下、
Ｓｉ：０．０１％以上１．００％以下、
Ｍｎ：０．０１％以上１．００％以下、
Ｃｒ：１１．０％以上２５．０％以下、
Ｎ：０．００２％以上０．０２０％以下、
Ａｌ：０％以上０．３０％以下、
Ｎｂ：０．０５％以上０．２０％以下、
Ｂ：０．００１０％以上０．０１００％以下、
Ｐ：０％以上０．０４０％以下、
Ｓ：０％以上０．０１００％以下、
Ｔｉ：０％以上０．２０％以下、
Ｍｏ：０％以上０．３０％以下、
Ｖ：０％以上０．３０％以下、
Ｓｎ：０％以上０．５０％以下、
Ｎｉ：０％以上１．００％以下、
Ｃｕ：０％以上１．００％以下、
Ｗ：０％以上１．００％以下、
Ｃｏ：０％以上０．５０％以下、
Ｚｒ：０％以上０．５０％以下、
Ｃａ：０％以上０．００５０％以下、
Ｍｇ：０％以上０．００５０％以下、
Ｙ：０％以上０．２０％以下、
Ｈｆ：０％以上０．２０％以下、
ＲＥＭ：０％以上０．１０％以下、
Ｓｂ：０％以上０．５０％以下
を含み、
残部がＦｅ及び不純物からなり、
下記（１）式を満足し、
等軸晶率が７０％以上のフェライト単相組織よりなり、
厚さが１５０ｍｍ以上である、
フェライト系ステンレス鋼材。
Ｎｂ＋５０Ｂ≧０．２００・・・（１） By mass%
C: 0.001% or more and 0.015% or less,
Si: 0.01% or more and 1.00% or less,
Mn: 0.01% or more and 1.00% or less,
Cr: 11.0% or more and 25.0% or less,
N: 0.002% or more and 0.020% or less,
Al: 0% or more and 0.30% or less,
Nb: 0.05% or more and 0.20% or less,
B: 0.0010% or more and 0.0100% or less,
P: 0% or more and 0.040% or less,
S: 0% or more and 0.0100% or less,
Ti: 0% or more and 0.20% or less,
Mo: 0% or more and 0.30% or less,
V: 0% or more and 0.30% or less,
Sn: 0% or more and 0.50% or less,
Ni: 0% or more and 1.00% or less,
Cu: 0% or more and 1.00% or less,
W: 0% or more and 1.00% or less,
Co: 0% or more and 0.50% or less,
Zr: 0% or more and 0.50% or less,
Ca: 0% or more and 0.0050% or less,
Mg: 0% or more and 0.0050% or less,
Y: 0% or more and 0.20% or less,
Hf: 0% or more and 0.20% or less,
REM: 0% or more and 0.10% or less,
Sb: Including 0% or more and 0.50% or less
The rest consists of Fe and impurities
Satisfy the following formula (1)
It consists of a ferrite single-phase structure with an equiaxed crystal ratio of 70% or more.
The thickness is 150 mm or more,
Ferritic stainless steel material.
Nb + 50B ≧ 0.200 ・ ・ ・ (1)
請求項１に記載のフェライト系ステンレス鋼材。 The average crystal grain size is 5 mm or less.
The ferrite-based stainless steel material according to claim 1.
請求項１又は２に記載のフェライト系ステンレス鋼材。 The {001} plane random intensity ratio in the thickness direction is less than 2.0 at the 1/4 position of the thickness.
The ferrite-based stainless steel material according to claim 1 or 2.
鋼板の製造方法。 A step of performing hot working and / or cold working on the ferritic stainless steel material according to any one of claims 1 to 3 is included.
Steel sheet manufacturing method.
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|---|---|---|---|---|
| JP2001020046A (en) * | 1999-07-07 | 2001-01-23 | Sumitomo Metal Ind Ltd | Ferritic stainless steel excellent in workability and toughness, ferritic stainless steel ingot and production thereof |
| JP2001028544A (en) * | 1999-07-12 | 2001-01-30 | Yokogawa Electric Corp | Multichannel pwm digital/analog converter |
| JP2004002974A (en) * | 2002-03-27 | 2004-01-08 | Nippon Steel Corp | Cast slab and steel sheet of ferritic stainless steel and production method for the same |
| JP2004043838A (en) * | 2002-07-09 | 2004-02-12 | Nisshin Steel Co Ltd | Method for melting ferritic stainless steel with excellent ridging resistance/workability, and steel sheet |
| JP2005307234A (en) * | 2004-04-19 | 2005-11-04 | Nisshin Steel Co Ltd | Ferritic stainless steel sheet having excellent ridging resistance and surface characteristic and method for manufacturing the same |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2001020046A (en) * | 1999-07-07 | 2001-01-23 | Sumitomo Metal Ind Ltd | Ferritic stainless steel excellent in workability and toughness, ferritic stainless steel ingot and production thereof |
| JP2001028544A (en) * | 1999-07-12 | 2001-01-30 | Yokogawa Electric Corp | Multichannel pwm digital/analog converter |
| JP2004002974A (en) * | 2002-03-27 | 2004-01-08 | Nippon Steel Corp | Cast slab and steel sheet of ferritic stainless steel and production method for the same |
| JP2004043838A (en) * | 2002-07-09 | 2004-02-12 | Nisshin Steel Co Ltd | Method for melting ferritic stainless steel with excellent ridging resistance/workability, and steel sheet |
| JP2005307234A (en) * | 2004-04-19 | 2005-11-04 | Nisshin Steel Co Ltd | Ferritic stainless steel sheet having excellent ridging resistance and surface characteristic and method for manufacturing the same |
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