JP3941363B2 - Ferritic stainless cold-rolled steel sheet excellent in ductility, workability and ridging resistance, and method for producing the same - Google Patents

Description

【００６９】
【表２】

【００７０】
【表３】

【００７１】
本発明例は、いずれもＥｌ_mean：32％以上、ｒ_mean値：1.30以上、リジンググレード：Ａと、延性、ｒ値、耐リジング性ともに良好な特性を有している。一方、本発明の範囲を外れる比較例は、延性、ｒ値、耐リジング性のいずれかが低下していた。
（実施例２）
表４に示す組成の溶鋼を、転炉−２次精錬工程で溶製し、連続鋳造法でスラブとした。これらスラブを再加熱後、表５に示す仕上げ圧延温度の熱間圧延を施す熱延工程により、3.2 〜4.0 mm厚の熱延板とした。ついで、これら熱延板を酸洗後、予備圧延工程と、熱延板焼鈍工程と、酸洗工程と、冷延工程と、仕上げ焼鈍工程を順次施し板厚0.8mm の冷延焼鈍板とした。予備圧延の圧延条件、熱延板焼鈍条件を表５に示す。なお、熱延板焼鈍条件は、800 〜860 ℃×８hr保持の箱焼鈍とした。冷延工程では、冷延圧下率を調整し板厚0.8mm の冷延板とした。なお、熱延板の累積圧下率は75〜80％であった。また、仕上げ焼鈍工程における焼鈍は、連続焼鈍とし、830 ℃で30ｓ保持とした。
【００７２】
得られた冷延焼鈍板から試験片を採取し、引張試験を実施し、伸びＥｌ、ｒ値、リジンググレードを測定した。伸び、ｒ値、リジンググレードの測定方法は実施例１と同様とした。なお、ｒ₀ 、ｒ₄₅、ｒ₉₀のうちの最小値をｒ_min とした。なお、熱延板焼鈍工程を経た得られた熱延焼鈍板（冷延鋼板用原板）から試験片を採取し、圧延方向に平行な板厚断面を研摩し、王水にてエッチングしたのち、光学顕微鏡を用いて100 倍で板厚×２mmの範囲の組織を撮影した。得られた組織写真より、画像解析装置を用いた画像処理により、結晶粒の伸展度ｅを測定し、その最大値を求めた。また、冷延焼鈍板について、圧延方向に平行な板厚断面を研摩し、王水にてエッチングした後、光学顕微鏡を用いて 200倍にて板厚×１mmの範囲を撮影した。得られた組織写真により、画像解析装置を用いた画像処理により平均の結晶粒面積Ａ₀ 、および２×Ａ₀ 以上の結晶粒面積を有する粗大結晶粒が圧延方向に連続して集合した集合体である粗大コロニーのアスペクト比Ａを測定し、その最大値を求めた。
【００７３】
得られた結果を表６に示す。
【００７４】
【表４】

【００７５】
【表５】

【００７６】
【表６】

【００７７】
本発明例は、いずれもＥｌ_mean：32％以上、ｒ_mean値：1.30以上、リジンググレード：Ａと、伸び、ｒ値、耐リジング性ともに良好な特性を有している。しかも、ｒ値の最小値ｒ_min が1.00以上と高く、面内異方性が小さい。
一方、本発明の範囲を外れる比較例は、伸び、ｒ値、耐リジング性のいずれかが低下し、ｒ_min も低い。
（実施例３）
表７に示す組成の溶鋼を、転炉−２次精錬工程で溶製し、連続鋳造法でスラブとした。これらスラブを再加熱後、表８に示す仕上げ圧延温度の熱間圧延を施す熱延工程により、3.2 〜5.0 mm厚の熱延板とした。ついで、これら熱延板を酸洗後、予備圧延工程と、熱延板焼鈍工程と、酸洗工程と、冷延工程と、仕上げ焼鈍工程を順次施し板厚0.8mm の冷延焼鈍板とした。予備圧延の圧延条件、熱延板焼鈍条件を表９に示す。なお、熱延板焼鈍条件は、880 〜1000℃×２〜８hr保持の箱焼鈍とした。冷延工程では、冷延圧下率を調整し板厚0.8mm の冷延板とした。なお、熱延板の累積圧下率は75〜84％であった。また、仕上げ焼鈍工程における焼鈍は、連続焼鈍とし、830 ℃で30ｓ保持とした。
【００７８】
得られた冷延焼鈍板から試験片を採取し、引張試験を実施し、伸びＥｌ、ｒ値、リジンググレードを測定した。また、熱延焼鈍板について伸展度ｅの最大値を冷延焼鈍板について粗大コロニーのアスペクト比Ａの最大値を求めた。伸び、ｒ値、リジンググレード、伸展度ｅ、アスペクト比Ａの測定方法は実施例１と同様とした。
【００７９】
得られた結果を表９に示す。
【００８０】
【表７】

【００８１】
【表８】

【００８２】
【表９】

【００８３】
本発明例は、いずれもＥｌ_mean：34％以上、ｒ_mean値：1.40以上、リジンググレード：Ａと、伸び、ｒ値、耐リジング性ともに良好な特性を有している。
一方、本発明の範囲を外れる比較例は、耐リジング性が低下した。
（実施例４）
表10に示す組成の溶鋼を、転炉−２次精錬工程で溶製し、連続鋳造法でスラブとした。これらスラブを再加熱後、表11に示す仕上げ圧延温度の熱間圧延を施す熱延工程により、3.2 〜4.0 mm厚の熱延板とした。ついで、これら熱延板を酸洗後、予備圧延工程と、熱延板焼鈍工程と、酸洗工程と、冷延工程と、仕上げ焼鈍工程を順次施し板厚0.8mm の冷延焼鈍板とした。予備圧延の圧延条件、熱延板焼鈍条件を表11に示す。なお、熱延板焼鈍条件は、880 〜930 ℃×２〜８hr保持の箱焼鈍とした。冷延工程では、冷延圧下率を調整し板厚0.8mm の冷延板とした。なお、熱延板の累積圧下率は75〜80％であった。また、仕上げ焼鈍工程における焼鈍は、連続焼鈍とし、830 ℃で30ｓ保持とした。
【００８４】
得られた冷延焼鈍板から試験片を採取し、引張試験を実施し、伸びＥｌ、ｒ値、リジンググレードを測定した。また、熱延焼鈍板について伸展度ｅの最大値を、冷延焼鈍板について粗大コロニーのアスペクト比Ａの最大値を求めた。伸び、ｒ値、リジンググレード、伸展度ｅ、アスペクト比Ａの測定方法は実施例１と同様とした。
【００８５】
得られた結果を表12に示す。
【００８６】
【表１０】

【００８７】
【表１１】

【００８８】
【表１２】

【００８９】
本発明例は、いずれも伸び、ｒ値、耐リジング性ともに良好な特性を有している。これに対し、本発明の範囲を外れる比較例は、伸び、ｒ値、耐リジング性のいずれかが劣化していた。
一方、本発明の範囲を外れる比較例は、耐リジング性が低下した。
【００９０】
【発明の効果】
本発明によれば、延性、加工性、および耐リジング性がともに優れ、あるいはさらにｒ値の面内異方性も小さくプレス加工性に優れるフェライト系ステンレス鋼板を能率よくしかも安価に、提供でき、産業上格段の効果を奏する。
【図面の簡単な説明】
【図１】予備圧延圧下率と、平均伸びＥｌ_mean（ａ）、平均ｒ値ｒ_mean（ｂ）、リジンググレード（ｃ）との関係を示すグラフである。
【図２】ｒ_mean、ｒ_min 値と熱間圧延仕上げ温度ＦＤＴとの関係を示すグラフである。
【図３】熱延板焼鈍時の徐冷パターンの例を示す模式図である。
【図４】（ａ）は熱延焼鈍板の圧延方向に平行な板厚断面の結晶粒組織の一例を示す模式図であり、（ｂ）は結晶粒の伸展度ｅの定義を説明する模式図である。
【図５】熱延焼鈍板の結晶粒伸展度の分布の一例を示すグラフである。
【図６】（ａ）は冷延焼鈍板の圧延方向に平行な板厚断面の結晶粒組織の一例を示す模式図であり、（ｂ）は粗大粒コロニーのアスペクト比Ａの定義を説明する模式図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ferritic stainless steel sheet suitable for use in building exterior materials, kitchen appliances, chemical plants, water tanks, heat resistant members for automobiles, etc., and in particular, ferrite excellent in ductility, workability and ridging resistance. The present invention relates to a stainless steel cold-rolled steel sheet and a manufacturing method thereof. In addition, the steel plate as used in the field of this invention shall contain a steel plate and a steel strip.
[0002]
[Prior art]
Stainless steel sheets have a beautiful surface and excellent corrosion resistance, so they are widely used for building exterior materials, kitchen appliances, chemical plants, water storage tanks, and the like. In particular, austenitic stainless steel sheets have been widely used in the above applications because they are excellent in ductility, have no ridging and are excellent in press formability.
[0003]
Ferritic stainless steel sheets, on the other hand, have improved formability due to advances in steel purification technology. Recently, application to the above-mentioned applications has been examined in place of austenitic stainless steel sheets such as SUS 304 and SUS 316. Yes. This is because the features of ferritic stainless steel, such as the low thermal expansion coefficient, low stress corrosion cracking susceptibility, and low price because it does not contain expensive Ni, have become widely known. is there.
[0004]
However, when considering application to molded products, this ferritic stainless steel sheet has poor ductility compared to austenitic stainless steel sheets, and irregularities on the surface of the processed product called ridging occur, resulting in There was a problem that the aesthetic appearance was impaired and the load of surface polishing was increased. For this reason, in order to further expand the applications of ferritic stainless steel sheets, improvements in ductility, workability, and ridging resistance have been required.
[0005]
In response to such a requirement, for example, JP-A-52-24913 contains C: 0.03 to 0.08%, N: 0.01% or less, and Al: 2 × N% or more and 0.2% or less by weight%. Ferritic stainless steel with excellent workability has been proposed. In the technique described in Japanese Patent Application Laid-Open No. 52-24913, the content of C and N is reduced, and further, the amount of solid solution N is reduced by adding Al more than twice the N content. It is said that it is possible to improve the ductility, ridging resistance and secondary workability.
[0006]
JP-A-54-112319 discloses (C + N): 0.02 to 0.06%, Zr: 0.2 to 0.6% by weight%, Zr: 10 (C + N) ± 0.15%, ductility, r A heat-resistant ferritic stainless steel with improved value and improved press formability has been proposed. JP-A-57-70223 discloses a ferritic stainless steel slab containing, by weight%, sol Al: 0.08 to 0.5% and one or more of B, Ti, Nb, V, and Zr. A method for manufacturing a ferritic stainless steel sheet having excellent workability has been proposed in which the steel is hot-rolled, cold-rolled and then finally annealed.
[0007]
However, with the techniques described in JP-A-52-24913, JP-A-54-112319, and JP-A-57-70223, although a significant improvement in workability is observed, ridging resistance is improved. However, when processing such as press molding is performed, there is a problem that polishing for improving aesthetics is required, and the polishing load increases and the cost increases.
[0008]
On the other hand, for improving the ridging resistance, for example, in JP-A-51-123720, after hot rolling, rolling is performed at a reduction rate of 15% or more in a temperature range of 450 to 700 ° C., and further annealing and cooling are performed. A method for producing a ferritic stainless steel sheet with less ridging generated by hot rolling and final annealing is disclosed.
Japanese Patent Laid-Open No. 53-40625 discloses that a hot-rolled stainless steel sheet containing Al so that the weight percentage is Al: 0.01% or more and Al / N: 2 or more is 900 ° C. or more. Has disclosed a method for producing a ferritic stainless steel sheet that is excellent in ridging properties and is subjected to continuous annealing at a temperature of 5 ° C.
[0009]
JP-A-1-111816 discloses hot rolling at a finishing temperature of 850 ° C. or higher, quenching immediately after rolling at a rate of 10 ° C./s or higher, winding at a temperature of 550 ° C. or lower, and then cumulative reduction ratio. A method for producing a ferritic stainless cold-rolled steel sheet having excellent ridging resistance that is annealed after cold rolling of 50% or more is disclosed.
However, the techniques described in JP-A-51-123720, JP-A-53-40625, and JP-A-1-111816 have improved ridging resistance, but both ductility and workability are achieved. It has not been improved enough. Then, as an attempt to make ductility, workability, and ridging resistance compatible, there are the following.
[0010]
In Japanese Patent Laid-Open No. 2-170923, preliminary cold rolling with a rolling reduction of 2 to 30% is applied to a hot rolled sheet obtained by hot rolling a chromium-based stainless steel piece containing 13.0 to 20.0 wt% of chromium. A method for producing a chrome-based stainless steel cold-rolled sheet excellent in ridging resistance and press workability by applying, followed by continuous annealing, descaling, cold rolling, and finish annealing is disclosed. In the technique described in Japanese Patent Laid-Open No. 2-170923, cold rolling is applied before annealing to promote recrystallization behavior during annealing, enabling continuous annealing, and improving workability and ridging resistance. It is said.
[0011]
JP-A-9-111354 discloses a steel slab containing, by weight, C: 0.02 to 0.05%, N: 0.02 to 0.05%, Cr: 15 to 18%, Al: 0.10 to 0.30%. Pass exit temperature: hot rolled at 950 ° C or higher, then cooled to 500-650 ° C at a cooling rate of 20-80 ° C / s to obtain a hot-rolled sheet having a composite structure of ferrite and martensite, Annealing is performed for 180 to 300 s in the temperature range of 850 to 980 ° C, followed by quenching at a cooling rate of 15 ° C / s or more, followed by cold rolling and finish annealing. Excellent ridging resistance and press formability. A method for producing a ferritic stainless steel sheet having good surface properties is disclosed.
[0012]
JP-A-10-53817 discloses that wt%, Cr: 11 to 25%, C: 0.005% or less, N: 0.008 to 0.03%, Ti is Ti / 48 is (C / 12 + N / 14) to 5 (C / 12 + N / 14) containing a ferritic stainless steel slab having a total rolling reduction of 50% or more over one pass or two passes in a temperature range of 1100 to 950 ° C. In addition, rough rolling is performed at an end temperature of 950 ° C. or higher, and after 10 s or more after rough rolling, final rolling at the final two passes: 40% or higher and finishing temperature: 850 ° C. or higher is performed, and for 5 s immediately after rolling. A method for producing a ferritic stainless steel sheet having an average cooling rate of 25 ° C./s or less and excellent in roping resistance, ridging resistance and formability is disclosed. According to the technique described in Japanese Patent Laid-Open No. 10-53817, strong reduction in hot rolling is effective in improving ridging resistance.
[0013]
[Problems to be solved by the invention]
However, there is still room for further improvement in the techniques described in JP-A-2-170923, JP-A-9-111354, and JP-A-10-53817. In the technique described in Japanese Patent Laid-Open No. 2-170923, there remains a problem that it is not improved until it has both good ridging resistance and a high r value.
[0014]
In addition, in the technique described in JP-A-9-111354, in addition to the problem that a large amount of Al needs to be added, the amount of inclusions in the steel increases and the occurrence of surface defects due to this is unavoidable. However, the problem of improvement in ductility and ridging resistance was still insufficient.
In addition, in the technique described in Japanese Patent Laid-Open No. 10-53817, even if the rating of ridging is the highest rank 1, the ridging resistance is still insufficient because it includes a maximum of 20 μm. The problem was left. In addition to the extremely low carbon content, it is necessary to add a sufficient amount of Ti to fix C and N, and in addition to the problem that the manufacturing cost increases, the occurrence of surface defects due to the addition of a large amount of Ti is unavoidable. There was a problem.
[0015]
The generation of ridging is an essential problem of ferritic stainless steel, and a fundamental solution has been demanded. In response to such demands, Japanese Patent Application Laid-Open Nos. 9-263900 and 10-330887 propose techniques for improving ridging resistance by controlling the orientation colonies of crystal grains. In the technique described in Japanese Patent Laid-Open No. 9-263900, adjusting the rolling temperature, friction coefficient, reduction ratio, rolling speed, and rolling pass time during hot rolling of a hot rolled steel sheet as a cold rolling original sheet. Thus, the distribution in the plate width direction is controlled in {111} -oriented colonies to improve the ridging characteristics.
[0016]
JP-A-10-330887 discloses adjusting the basicity in the steel melting stage, the time from the slab extraction in the hot rolling process to the end of the rough rolling process, the rolling temperature in the rough rolling process, and the friction coefficient. There has been proposed a technique for improving ridging characteristics by adjusting the rolling reduction so that the thickness of the azimuth colony in the plate thickness section parallel to the rolling direction is 30% or less of the plate thickness.
[0017]
[Problems to be solved by the invention]
However, the techniques described in JP-A-9-263900 and JP-A-10-330887 cannot completely prevent the generation of ridging even if the generation of orientation colonies is suppressed. The problem was that the surface quality after molding was inferior compared to not SUS 304 steel.
[0018]
Furthermore, when deep drawing is performed by press forming or the like using a ferritic stainless steel plate, the in-plane anisotropy of the r value of the material steel plate becomes a problem. Even if the average r value that is the average value in each direction of the material steel plate is high, if the minimum r value is too low, sufficient deep drawing cannot be performed. All of the steel sheets produced by the above-described conventional techniques have improved average r value, but have a problem that the minimum r value is low and the in-plane anisotropy of the r value is large.
[0019]
As described above, in the above-described conventional technology, although a significant improvement in workability is recognized, since the improvement in ridging resistance is insufficient, the surface appearance of the molded product is improved in applications where processing such as press molding is performed. Therefore, the polishing load in the manufacturing process increases. In addition, although the improvement of the average r value is recognized, there is a problem that sufficient workability cannot be obtained in actual press molding or the like because the in-plane anisotropy of the r value is large, and ductility, workability and ridging resistance It was very difficult to produce a steel sheet having both properties at a sufficient level at a low cost.
[0020]
The present invention solves the above-mentioned problems of the prior art, has both good ductility, workability, and excellent ridging resistance, particularly has ridging resistance comparable to that of SUS 304 steel, and excellent after molding. An object of the present invention is to provide a ferritic stainless steel cold-rolled steel sheet having a surface quality and a small r value in-plane anisotropy and a method for producing the same. Also, a ferritic stainless cold-rolled steel sheet for producing a ferritic stainless cold-rolled steel sheet having good ductility, workability, and excellent ridging resistance, and capable of producing a ferritic stainless cold-rolled steel sheet having a small in-plane anisotropy of r value and Another object of the present invention is to provide a manufacturing method thereof.
[0021]
[Means for Solving the Problems]
As a result of repeating various studies to achieve the above-mentioned problems, the present inventors have adjusted the chemical components, and after hot rolling, prior to hot-rolled sheet annealing, warm rolling or cold rolling with a relatively low reduction rate It has been found that ductility, workability and ridging resistance are improved by applying pre-rolling according to, and further maintaining the subsequent hot-rolled sheet annealing for a long period of time and gradually cooling box annealing. Furthermore, the minimum r value r can be reduced by lowering the hot rolling finishing temperature FDT to 850 ° C. or lower._minIt has been found that the in-plane anisotropy of the r value is improved by increasing.
[0022]
In addition, the inventors of the present invention focused on the crystal grain structure of the steel sheet in order to obtain a fundamental solution regarding the generation of ridging, which is an essential problem of the ferritic stainless steel sheet. As a result, it has been found that ridging resistance is remarkably improved by reducing the degree of extension of crystal grains after hot rolling annealing throughout the entire plate thickness. Here, the degree of crystal grain extension means the ratio of the length of the crystal grains in the rolling direction to the length of the crystal grains in the plate thickness direction.
[0023]
Moreover, by suppressing the formation of coarse-grained colonies present in the steel sheet after cold rolling annealing, the generation of ridging is remarkably suppressed, and it has both good ductility, workability and excellent ridging resistance. It has been found that ridging resistance similar to that of steel can be obtained. The coarse colony referred to here is the average crystal grain area A.₀Means an aggregate in which coarse crystal grains having a crystal grain area twice or more of the above are continuously arranged in the rolling direction.
[0024]
First, a description will be given of experimental results performed by the present inventors and serving as the basis of the present invention.
First, the present inventors investigated the influence of rolling strain addition prior to hot-rolled sheet annealing after hot rolling.
  Ferritic stainless hot-rolled steel sheet with a composition containing 0.063 mass% C-0.033 mass% N-0.27 mass% Si-0.60 mass% Mn-16.3 mass% Cr-0.33 mass% Ni-0.001 mass% Al-0.061 mass% V (Hot rolling finish temperature FDT: 950 ° C.) After cold rolling at a reduction rate of 0 to 20%, hold at 860 ° C. for 8 hours and then average cooling rate to 600 ° C. becomes 7.2 ° C./h The steel sheet is annealed in such a manner that it is gradually cooled, and after the cold rolling is performed so that the cumulative reduction ratio to the hot-rolled sheet after hot rolling is 75%, the finish annealing is maintained at 830 ° C for 30 seconds. A ferritic stainless steel cold rolled steel sheet was obtained. For these ferritic stainless steel cold rolled steel sheets, the average elongation El_mean, Average r value (Rankford value) r_mean, And changes in ridging grade were investigated. The result is shown in FIG.
[0025]
From FIG. 1, by performing cold rolling with a rolling reduction of 2 to 15% before hot-rolled sheet annealing, the elongation El_mean: 32% or more, r value r_mean: 1.3 or more, ridging grade: A (waviness height of 5 μm or less), elongation El, r value, and ridging resistance are all improved. According to other experiments conducted by the present inventors, such a remarkable improvement in characteristics is achieved by adjusting Al to 0.03 mass% or less of the chemical components in addition to adding strain by pre-rolling before hot-rolled sheet annealing. It has been found that this is a composite result of performing annealing and holding at an annealing temperature for 1 h or more by hot-rolled sheet annealing and further cooling gradually after holding. Although the mechanism for improving the properties is not clear at present, the solid solution N is increased by reducing Al, and further the rolling distortion by pre-rolling is applied to the heating process of the hot-rolled sheet annealing. This is considered to be related to the fact that the precipitation of carbonitride on the dislocation is promoted and recrystallization is likely to occur. In addition, the annealing temperature of hot-rolled sheet annealing is (A₁It has been found that the above-described effect becomes remarkable by setting the transformation point to 30 ° C. or higher and lower than 1000 ° C. Where A₁The transformation point is
A₁Transformation point (℃) = 35 (Cr + 1.72Mo + 2.09Si + 4.86Nb + 8.29V + 1.77Ti + 21.4Al + 40B-7 .14C-8.0N-3.28Ni-1.89Mn-0.51Cu) +310 …… (2)
(Here, Cr, Mo, Si, Nb, V, Ti, Al, B, C, N, Ni, Mn, Cu: content of each alloy element (mass%))
Defined by In the calculation of equation (2), the component (alloy element) not included in the steel sheet is calculated as 0.
[0026]
Next, the present inventors investigated the influence of the finishing temperature on the r value in hot rolling in order to further improve the workability.
1000% to 700% ferritic stainless steel material with a composition containing 0.063% C-0.033% N-0.27% Si-0.60% Mn-16.3% Cr-0.3% Ni-0.001% Al-0.61% V at mass% Hot rolled to a finish temperature (FDT) between ℃ and made into hot rolled sheet, then cold rolled with a rolling reduction of 10%, held at 860 ℃ for 8h, then averaged up to 600 ℃ After subjecting hot-rolled sheet annealing to slowly cool so that the cooling rate becomes 7.2 ° C./h, and after cold rolling so that the cumulative reduction ratio to the hot-rolled sheet after hot rolling is 75%, Finish annealing was performed at 830 ° C. for 30 seconds to obtain a ferritic stainless steel cold-rolled steel sheet.
[0027]
For these ferritic stainless steel cold-rolled steel sheets, r values were investigated in the rolling direction, rolling direction and 45 ° direction, rolling direction and 90 ° direction, and the average r value (r_mean), Minimum r value (r_min) The result is shown in FIG.
From FIG. 2, by setting the FDT to 850 ° C. or less, r_minThe value was improved, in-plane anisotropy was improved, and the press formability was further improved.
[0028]
The present invention has been completed based on the above findings and further studies.
  That is, 1st this invention is mass%, C: 0.01-0.12%, N: 0.01-0.12%, Cr: 11-18%, Al: 0.03% or lessContainsSi: 1.0% or less, Mn: 1.0% or less, P: 0.05% or less, S: 0.01% or less, V: 0.15% or less, Ni: 1.0% or less, or Mo, Cu Less than or equal to 2.5% and / or 1 or 2 of themIs Mg: 0.0002 to 0.0050%Contains, balance Fe and inevitable impuritiesKaraAnd the following formula (1)
                        e = L1 / L2 (1)
(Where e: degree of extension, L1: length of crystal grain in rolling direction (μm), L2: length of crystal grain in thickness direction (μm))
The base plate for a ferritic stainless steel cold-rolled steel sheet, characterized in that it has a structure in which the maximum value of the degree of extension e defined by (1) is 5 or less.
[0029]
  Moreover, 2nd this invention is mass%, C: 0.01-0.12%, N: 0.01-0.12%, Cr: 11-18%, Al: 0.03% or lessContainsAndSi : 1.0 %Less than, Mn : 1.0 % Or less, and P: 0.05 %, S: 0.01 % Or less, V: 0.15 %Less than, Ni : 1.0 % Adjusted to includeOr, in addition, one or two of Mo and Cu in total less than 2.5% and / orIs Mg: 0.0002 to 0.0050%ContainsAnd the rest Fe And from inevitable impuritiesAfter subjecting the steel material to a hot rolling process by hot rolling to a hot rolled sheet, the hot rolled sheet is subjected to a pre-rolling process in which rolling is performed at a reduction ratio of 2 to 15% cold or warm. Next, it is a manufacturing method of a ferritic stainless steel cold-rolled steel sheet, characterized by performing a hot-rolled sheet annealing process in which the hot-rolled sheet subjected to the pre-rolling process is subjected to box annealing, and in the second aspect of the present invention, The box annealing is preferably performed at a predetermined annealing temperature for 1 hour or more, and after the holding at an average cooling rate of up to 600 ° C., it is gradually cooled at 25 ° C./h or less. In the second aspect of the present invention, The predetermined annealing temperature is 700 ° C. or higher, or 750 ° C. or higher and lower than 1000 ° C., or the following formula (2)
  A₁Transformation point (℃) = 35 (Cr + 1.72Mo + 2.09Si + 4.86Nb + 8.29V + 1.77Ti + 21.4Al + 40B-7 .14C-8.0N-3.28Ni-1.89Mn-0.51Cu) +310 …… (2)
(Here, Cr, Mo, Si, Nb, V, Ti, Al, B, C, N, Ni, Mn, Cu: content of each alloy element (mass%))
A defined by₁Based on the transformation point, (A₁(Transformation point + 30 ° C.) or more and less than 1000 ° C. In the second aspect of the present invention, it is preferable that the hot rolling in the hot rolling step has a finishing temperature of 850 ° C. or lower.
[0030]
  Moreover, 3rd this invention is mass%, C: 0.01-0.12%, N: 0.01-0.12%, Cr: 11-18%, Al: 0.03% or lessContainsSi: 1.0% or less, Mn: 1.0% or less, P: 0.05% or less, S: 0.01% or less, V: 0.15% or less, Ni: 1.0% or less, or Mo, Cu Less than or equal to 2.5% and / or 1 or 2 of themIs Mg: 0.0002 to 0.0050%Contains, balance Fe and inevitable impuritiesKaraThe average grain area A with the composition and the plate thickness section parallel to the rolling direction₀The following formula (3) of a coarse-grained colony that is an aggregate in which crystal grains having a crystal grain area twice or more of the above are continuously arranged in the rolling direction
                        A = L3 / L4 (3)
(Here, A: aspect ratio of coarse-grained colonies, L3: length of coarse-colony colonies in the rolling direction (μm), L4: length of coarse-grained colonies in the plate thickness direction (μm))
A ferritic stainless steel cold-rolled steel sheet excellent in ductility, workability and ridging resistance, characterized by having a structure having a maximum aspect ratio A defined by
[0031]
  Moreover, 4th this invention is mass%, C: 0.01-0.12%, N: 0.01-0.12%, Cr: 11-18%, Al: 0.03% or lessContainsAndSi : 1.0 %Less than, Mn : 1.0 % Or less, and P: 0.05 %, S: 0.01 % Or less, V: 0.15 %Less than, Ni : 1.0 % Adjusted to includeOr, in addition, one or two of Mo and Cu in total less than 2.5% and / orIs Mg: 0.0002 to 0.0050%ContainsAnd the rest Fe And from inevitable impuritiesA hot-rolled sheet that is a hot-rolled sheet by hot rolling, a hot-rolled sheet annealing process that anneals the hot-rolled sheet, and a hot-rolled sheet that has undergone the hot-rolled sheet annealing process as a cold-rolled steel sheet In the method for producing a ferritic stainless steel sheet, comprising a cold rolling step of cold rolling the cold rolled steel sheet into a cold rolled sheet, and a finish annealing step of finish annealing the cold rolled sheet, the hot rolling step Later, before the hot-rolled sheet annealing step, it is subjected to a pre-rolling step of rolling at a cold or warm reduction ratio of 2 to 15%, and further, annealing in the hot-rolled plate annealing step,Hold for 1 h or more at the specified annealing temperatureIt is a method for producing a ferritic stainless cold-rolled steel sheet having excellent ductility, workability and ridging resistance, characterized by box annealing. Further, in the fourth aspect of the present invention, the box annealing is a treatment in which holding at a predetermined annealing temperature for 1 h or more and slow cooling at 25 ° C./h or less at an average cooling rate up to 600 ° C. after holding. Preferably, in the fourth aspect of the present invention, the predetermined annealing temperature is preferably 700 ° C. or higher, or 750 ° C. or higher and lower than 1000 ° C., but in particular, A defined by the formula (2)₁Based on the transformation point, (A₁(Transformation point + 30 ° C.) or higher and preferably lower than 1000 ° C. In the fourth aspect of the present invention, the hot rolling in the hot rolling step may have a finishing temperature of 850 ° C. or lower. This is preferable from the viewpoint of reducing the anisotropy.
[0032]
In the fifth aspect of the present invention, the ferritic stainless steel cold-rolled steel plate is cold-rolled using the ferritic stainless steel cold-rolled steel plate of the first aspect of the present invention, and then finish annealing is performed. It is a method for producing a ferritic stainless steel cold-rolled steel sheet having excellent ductility, workability and ridging resistance, and in the fifth aspect of the present invention, the rolling reduction of the cold rolling is 30% or more, It is preferable that the annealing temperature of finish annealing is 700 ° C. or higher.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
  First, the composition of the ferritic stainless steel cold rolled steel sheet according to the present invention and the reason for limiting the structure will be described. The original sheet for cold-rolled steel sheet as used in the present invention means a hot-rolled annealed sheet.
  The ferritic stainless steel cold rolled steel sheet (hot rolled annealed sheet) of the present invention is mass%, C: 0.01 to 0.12%, N: 0.01 to 0.12%, Cr: 11 to 18%, Al: 0.03% or less, Si: 1.0% or less, Mn: 1.0% or lessTo P: 0.05% or less, S: 0.01% or less, V: 0.15% or less, Ni: adjusted to 1.0% or less, or one or two of Mo and Cu in total 2.5% or less and / orIs Mg: 0.0002 to 0.0050%Contains, balance Fe and inevitable impuritiesKaraThe Hereinafter, mass% is simply written as%.
[0034]
C: 0.01 to 0.12%
In the present invention, C is preferably reduced as much as possible to improve ductility. However, if the C content is reduced too much, the ridging resistance is deteriorated, and irregularities are produced in the processed part during processing such as press molding, and the aesthetic appearance of the product is impaired. For this reason, the lower limit of the C content is set to 0.01%. On the other hand, if the content exceeds 0.12%, the ductility is lowered, and the Cr removal layer, coarse precipitates, and inclusions that start rusting increase. For this reason, the upper limit of the C content is set to 0.12%.
[0035]
N: 0.01 to 0.12%
N, like C, is preferably reduced as much as possible to improve ductility. However, if the N content is reduced too much, the ridging resistance is deteriorated, and irregularities are produced in the processed part during processing such as press molding, and the aesthetic appearance of the product is impaired. For this reason, the lower limit of the N content is set to 0.01%. On the other hand, if it exceeds 0.12%, the ductility is lowered and the Cr removal layer, coarse precipitates, and inclusions that are the starting point of rusting increase. For this reason, the upper limit of N content was made into 0.12%.
[0036]
Cr: 11-18%
Cr is an element effective in improving the corrosion resistance, and in order to have corrosion resistance in various corrosive environments, it is necessary to contain at least 11%. On the other hand, when it contains exceeding 18%, workability will fall. For this reason, Cr was limited to the range of 11 to 18%.
Al: 0.03% or less
Al is an element that acts as a deoxidizer, but is reduced as much as possible in the present invention. By reducing Al, solid solution N increases, and precipitation of carbonitride during hot-rolled sheet annealing heating on dislocations introduced in the preliminary rolling process is promoted. On the other hand, when Al is contained in a large amount, oxide inclusions increase and surface defects such as dents occur frequently. For this reason, Al is adjusted to 0.03% or less. In addition, Preferably, Al is 0.01% or less.
[0037]
Si: 1.0% or less
Si is an element that acts as a deoxidizer, but if contained in a large amount, Si is accompanied by a decrease in ductility and cold workability. For this reason, Si is preferably 1.0% or less. In addition, More preferably, it is 0.03 to 0.50%.
Mn: 1.0% or less
Mn is an effective element that combines with S and reduces the solid solution S to suppress grain boundary segregation of S and prevent cracking during hot rolling, but excessive content is cold workability, Corrosion resistance is reduced. For this reason, it is preferable to limit Mn to 1.0% or less. In addition, More preferably, it is 0.05 to 0.8%.
[0038]
Ni: 1.0% or less
Ni is an element that improves the corrosion resistance. However, it is preferable to limit the content to 1.0% or less because a large amount decreases the cold workability. From the viewpoint of workability, it is more preferably 0.7% or less.
V: 0.15% or less
V is an element that combines with C and N to form carbides and nitrides and suppresses the coarsening of crystal grains. However, since a large amount reduces cold workability, it is limited to 0.15% or less. It is preferable to do this.
[0039]
P: 0.05% or less
P is an element that deteriorates hot workability and generates pits, and is preferably reduced as much as possible. Up to 0.05%, the adverse effect is not noticeable, so 0.05% is acceptable.
S: 0.01% or less
S is an element that forms sulfides and lowers the cleanliness of the steel, and also serves as a starting point for rusting as MnS, and further segregates at the grain boundaries to promote grain boundary embrittlement, and is preferably reduced as much as possible. Up to 0.01%, the adverse effect is not significant and is acceptable.
[0040]
Less than 2.5% in total of one or two of Mo and Cu
Mo and Cu are both elements that improve the corrosion resistance, and can be contained alone or in combination as required. In particular, it is effective to contain it when high corrosion resistance is required. Such an effect becomes remarkable when the total content is 0.5% or more. However, excessive content impairs processability. Therefore, the content of one or two of Mo and Cu is preferably limited to 2.5% or less in total. In addition, Preferably it is 0.5 to 2.0%.
Ca: One or two selected from 0.0005 to 0.010%, Mg: 0.0002 to 0.0050%
Both Ca and Mg have an effect of improving processability, and can be selected as necessary and contained alone or in combination. Ca improves the workability through the control of the form of inclusions, but no effect is observed at less than 0.0005%. On the other hand, if the content exceeds 0.010%, surface defects due to oxides frequently occur and the surface quality deteriorates. For this reason, Ca is preferably limited to a range of 0.0005 to 0.010%. Mg has the effect of improving hot workability, but its effect is recognized when the content is 0.0002% or more. On the other hand, when it contains exceeding 0.0050%, surface quality will fall. For this reason, Mg is preferably limited to a range of 0.0002 to 0.0050%.
[0041]
Remaining Fe and inevitable impurities
The balance other than the above components is Fe and inevitable impurities. In addition to the above unavoidable impurities, Nb: 0.05% or less, Ti: 0.05% or less, Co: 0.5% or less, W: 0.01% or less, Zr: 0.01% or less, Ta: 0.01% or less are acceptable. In addition to the above composition, the original sheet for cold-rolled steel sheet according to the present invention is a sheet thickness section parallel to the rolling direction,
e = L1 / L2 (1)
(Where e: degree of extension, L1: length of crystal grain in rolling direction (μm), L2: length of crystal grain in thickness direction (μm))
And a structure having a maximum value of the degree of extension e defined by ≦ 5.
[0042]
The grain structure in the thickness section parallel to the rolling direction of the hot-rolled annealed steel sheet, which is a ferritic stainless cold-rolled steel sheet, is usually larger in the rolling direction than in the vicinity of the surface. There are many grains that have been extended for a long time. An example thereof is schematically shown in FIG. In the present invention, the length L1 in the rolling direction and the length L2 in the thickness direction are measured for each crystal grain in the thickness cross section parallel to the rolling direction, and as shown by the above formula (1), The ratio L1 / L2 is defined as the degree of extension e of the crystal grains (FIG. 4 (b)).
[0043]
In the present invention, the crystal grain structure in the thickness cross section parallel to the rolling direction of the cold-rolled steel sheet is set to a structure in which the maximum value of the degree of extension e is 5 or less.
FIG. 5 shows an example of the distribution of the degree of extension e in the thickness cross section parallel to the rolling direction for various ferritic stainless steel cold-rolled steel sheets (hot-rolled annealed sheets). Each ridging grade is displayed on each curve in FIG. 5, and this ridging grade is obtained by subjecting these hot-rolled annealed plates to normal cold rolling-finish annealing to form cold-rolled annealed plates. . In the hot-rolled annealed sheet in which the ridging grades of the steel sheet after cold-rolled annealing are D and B, the maximum value of the degree of extension e is higher than 5 near the center. In order to improve the ridging resistance of the ridging grade A and the cold-rolled annealed sheet, the crystal structure of the hot-rolled annealed sheet (cold-rolled steel sheet original plate) needs to be a structure in which the maximum value of the degree of extension e is 5 or less. I understand that there is.
[0044]
The stretched grains present in the hot-rolled annealed plate are sufficiently recrystallized by ordinary cold rolling / finish annealing to become substantially equiaxed grains. However, stretched grains with a degree of stretch e exceeding 5 in the hot-rolled annealed plate are orientation colonies (aggregates with similar crystal orientation) or coarse-grained colonies that are one of the causes of ridging of the cold-rolled annealed plate. It is considered that it promotes the formation of (aggregate of coarse crystal grains continuously arranged in the rolling direction), thereby reducing the ridging resistance of the cold-rolled annealed plate.
[0045]
In order to obtain a crystal grain structure with a degree of extension e of 5 or less, in the present invention, as described later, it is preferable to pre-roll the hot-rolled sheet at a reduction rate of 2 to 15% in a cold or warm state. The strain introduced by this pre-rolling promotes recrystallization and equiaxing during hot-rolled sheet annealing, and particularly reduces the degree of extension of crystal grains in the vicinity of the center part of the sheet thickness. In the present invention, the method of making the crystal structure of the hot-rolled annealed sheet a structure having an extension degree e of 5 or less is not limited to the method of pre-rolling the hot-rolled sheet. Conditions such as a method of accumulating energy due to strain before hot-rolled sheet annealing at a low rolling finish temperature of less than 450 ° C or a method of using the strain associated with transformation by quenching before hot-rolled sheet annealing It is considered effective if selected.
[0046]
  Next, the ferritic stainless steel cold rolled steel sheet of the present invention will be described.
  The ferritic stainless steel cold-rolled steel sheet of the present invention is obtained by subjecting the above-described ferritic stainless steel cold-rolled steel sheet to cold rolling and subsequent annealing, and has the same composition as the cold-rolled steel sheet, In mass%, C: 0.01 to 0.12%, N: 0.01 to 0.12%, Cr: 11 to 18%, Al: 0.03% or less, Si: 1.0% or less, Mn: 1.0% or less, and P: 0.05% In the following, S: 0.01% or less, V: 0.15% or less, Ni: 1.0% or less are included, or one or two of Mo and Cu are added to 2.5% or less in total and / orIs Mg: 0.0002 to 0.0050%Contains, balance Fe and inevitable impuritiesKaraThe
[0047]
Furthermore, the cold-rolled steel sheet of the present invention has a thickness cross section parallel to the rolling direction and an average grain area A₀The following formula (3) of a coarse-grained colony that is an aggregate of crystal grains having a grain area twice or more of the above, that is, coarse grains continuously arranged in the rolling direction:
A = L3 / L4 (3)
(Here, A: aspect ratio of coarse-grained colonies, L3: length of coarse-colony colonies in the rolling direction (μm), L4: length of coarse-grained colonies in the plate thickness direction (μm))
The maximum aspect ratio A defined in (1) is a structure having 5 or less.
[0048]
In the present invention, the average crystal grain area A is a plate thickness section parallel to the rolling direction.₀A crystal grain having a crystal grain area twice or more of the above is called a coarse grain. Here, average grain area A₀Means the average area of crystal grains in a plate thickness section parallel to the rolling direction. In the present invention, an aggregate in which these coarse grains are continuously arranged in the rolling direction is called a coarse colony.
FIG. 6A schematically shows an example of the crystal grain structure of the cold-rolled annealed steel sheet in the thickness cross section parallel to the rolling direction of the cold-rolled annealed steel sheet. In Fig.6 (a), a coarse-grained colony exists in the plate | board thickness center part vicinity. Coarse grain colonies have an average grain area A₀Is an aggregate of coarse grains in which coarse grains having a crystal grain area twice or more of the above are continuously arranged in the rolling direction (in FIG. 6, six coarse grains are continuous). Moreover, in FIG. 6, although only one coarse grain colony is illustrated, a coarse grain colony is not limited to one. Further, the position of the coarse colony is not limited to the vicinity of the central portion of the plate thickness.
[0049]
In the present invention, the length L3 of the coarse colony in the rolling direction and the length L4 in the thickness direction of the coarse-grained colony are measured in the thickness cross section parallel to the rolling direction, and as shown by the above formula (3), The ratio, L3 / L4, is defined as the aspect ratio A of the coarse-grained colonies. (FIG. 6B). The aspect ratio A is measured for each coarse grain colony present in a plate thickness section parallel to the rolling direction, and the maximum value is obtained. In the cold-rolled steel sheet of the present invention, the maximum aspect ratio of such a coarse grain colony is set to 5 or less. When the aspect ratio exceeds 5, ridging resistance is lowered, and ridging resistance comparable to that of SUS 304 cannot be secured.
[0050]
The detailed mechanism of ridging due to the presence of coarse colonies is not clear at present, but is thought to be as follows. In ferritic steel, a yield phenomenon appears during deformation, and non-uniform deformation called Lueders band occurs, but the yield stress depends on the crystal grain size, and the coarser grain yields with lower stress, so the aspect ratio exceeds 5. If a coarse colony exists, yielding occurs in a fine region in the coarse colony portion in the early stage of deformation, which influences the surrounding deformation and causes ridging on the steel sheet surface.
[0051]
By suppressing the formation of coarse colonies having an aspect ratio exceeding 5, and making a uniform crystal grain structure, ridging resistance is remarkably improved. In order to suppress the formation of coarse colonies having an aspect ratio exceeding 5, as described above, the maximum value of the degree of extension e of the crystal grain structure in the cold rolled steel sheet original plate (hot rolled annealed plate) is 5 or less. An organization is preferred.
[0052]
  Next, a preferred method for producing a ferritic stainless steel cold rolled steel sheet having the above-described structure and a ferritic stainless steel cold rolled steel sheet will be described.
  First, chemical components of steel materials suitable for the present invention will be described.
  Steel materials suitable for the present invention include C: 0.01 to 0.12%, N: 0.01 to 0.12%, Cr: 11 to 18%, and Al: 0.03% or less,Si : 1.0 %Less than, Mn : 1.0 % Or less, and Ni : 1.0 % Or less, V: 0.15 % Or less, P: 0.05 %, S: 0.01 % Or less,Or in addition one or two of Mo and Cu in total less than 2.5%, and / orIs Mg: 0.0002 to 0.0050%ContainsThe rest Fe And from inevitable impuritiesRu. NaThe reason for limitation of each component is the same as the reason for limitation in the cold rolled steel sheet or cold rolled steel sheet.
[0053]
After the molten steel having the above composition is melted in a generally known melting furnace such as a converter or an electric furnace, it is further refined by a known refining method such as vacuum degassing (RH method), VOD method, AOD method, Then, it is preferable to cast it into a slab or the like by a continuous casting method or an ingot-making method to obtain a steel material.
The steel material was then heated and subjected to a hot rolling step to form a hot-rolled sheet by hot rolling, a pre-rolling step for performing rolling to impart a rolling strain to the hot-rolled plate cold or warm, and a pre-rolling step. A hot-rolled sheet annealing step for annealing the hot-rolled sheet is sequentially performed to obtain a cold-rolled steel sheet. Next, a cold rolling process in which the cold-rolled steel sheet is cold-rolled into a cold-rolled sheet and a finish annealing process for finish-annealing the cold-rolled sheet are sequentially performed on the cold-rolled steel sheet. If necessary, the descaling process may be performed after the hot rolling process, before the pre-rolling process, after the hot-rolled sheet annealing process, or after finish annealing.
[0054]
In the hot rolling process of the present invention, it is only necessary to obtain a hot rolled sheet having a desired thickness, and the hot rolling conditions are not particularly limited. When further improvement of workability, particularly improvement of the in-plane anisotropy of the r value, is required, the hot rolling finishing temperature FDT is preferably set to 850 ° C. or lower. When the finishing temperature of hot rolling exceeds 850 ° C., the in-plane anisotropy of r value increases.
[0055]
The obtained hot-rolled sheet is subjected to descaling treatment as necessary, and then subjected to a pre-rolling step before being subjected to hot-rolled sheet annealing.
In the preliminary rolling process, rolling is performed at a reduction rate of 2 to 15% in a cold or warm state. This rolling introduces rolling strain, and the elongation, r value, and ridging resistance are all improved by the combination with subsequent annealing. When the rolling reduction is less than 2%, the elongation, r value, and ridging resistance are hardly improved. On the other hand, when it exceeds 15%, both the elongation, r value, and ridging resistance are deteriorated. For this reason, the rolling reduction in the preliminary rolling process is limited to a range of 2 to 15%. Rolling in the pre-rolling step is performed in the cold region or in a warm region of less than 450 ° C. When the rolling temperature is 450 ° C. or higher, the rolling strain introduced by rolling is recovered and the effect of pre-rolling is reduced.
[0056]
The preliminary rolling may be performed after the hot rolling process and before the hot rolled sheet annealing process. For example, while the coil is cooled to less than 450 ° C. to room temperature after hot rolling, the coil is still The rolling may be performed at a temperature higher than room temperature.
The pre-rolled hot rolled sheet is then annealed in a hot rolled sheet annealing process. The annealing in the hot rolled sheet annealing step is box annealing. In the box annealing, the heating rate up to a predetermined annealing temperature is not particularly limited, but it is preferable that the average from 500 ° C. to a predetermined temperature is 50 ° C./h or less. In box annealing, after heating to a predetermined annealing temperature, hold for 1 h or more at that temperature, and then gradually cool at 25 ° C / h or less at an average cooling rate up to 600 ° C. It is preferable that the annealing is performed. The predetermined annealing temperature in the present invention is 700 ° C. or higher, preferably 750 ° C. or higher and lower than 1000 ° C. from the viewpoint of improving ductility.
[0057]
A more preferable annealing temperature is (A₁Transformation point + 30 ° C) or higher and lower than 1000 ° C. A₁The transformation point is the following equation (2)
A₁Transformation point (℃) = 35 (Cr + 1.72Mo + 2.09Si + 4.86Nb + 8.29V + 1.77Ti + 21.4Al + 40B-7 .14C-8.0N-3.28Ni-1.89Mn-0.51Cu) +310 …… (2)
(Here, Cr, Mo, Si, Nb, V, Ti, Al, B, C, N, Ni, Mn, Cu: content of each alloy element (mass%))
Defined by In the calculation of equation (2), the component (alloy element) not included in the steel sheet is calculated as 0.
[0058]
The annealing temperature of hot-rolled sheet annealing is particularly (A₁(Alternative transformation temperature + 30 ° C) or higher, (α + γ) two-phase structure is formed during hot-rolled sheet annealing, partially re-solidifying carbonitrides, recrystallization and equiaxing of ferrite grains, and crystals accompanying transformation It is considered that orientation randomization or the like occurs, and the ductility and ridging resistance of the cold-rolled steel sheet are remarkably improved through subsequent processing. When the annealing temperature is 1000 ° C. or more, the crystal grains after hot-rolled sheet annealing or after finish annealing become coarse, and the ridging resistance is lowered, and the surface roughness is deteriorated due to remarkable skin roughness. In the present invention, in addition to this high temperature holding, slow cooling as a precipitation treatment is effective for improving the characteristics. In place of the slow cooling after the holding, an isothermal holding treatment may be added in the temperature range of 600 to 850 ° C. during the slow cooling.
[0059]
Here, the average cooling rate from the holding temperature to 600 ° C. in the present invention means a value obtained by dividing the temperature drop ΔT from the holding temperature to 600 ° C. by the time t required for the temperature drop.
As shown in FIG. 3, the cooling pattern after hot-rolled sheet annealing is roughly divided into (a) a linear pattern, (b) a pattern with isothermal holding in the middle, and (c) a pattern in which the cooling rate gradually decreases. Considering the pattern illustrated in FIG. 2B, T = 860 ° C., T ′ = 700 ° C., t_a= 16h, t_b= 10h, t_c= 10h, the average cooling rate (CR) up to 600 ° C after holding is 7.2 ° C / h.
[0060]
The hot-rolled sheet that has undergone the hot-rolled sheet annealing step is used as a cold-rolled steel sheet. The cold-rolled steel sheet produced by the above-described process has a crystal structure in which the above-described composition and the maximum value of the degree of extension e described above are 5 or less.
In the present invention, the method of making the crystal structure of the hot-rolled annealed sheet a structure having an extension degree e of 5 or less is not limited to the method of pre-rolling the hot-rolled sheet. Conditions such as a method of accumulating energy due to strain before hot-rolled sheet annealing at a low rolling finish temperature of less than 450 ° C or a method of using the strain associated with transformation by quenching before hot-rolled sheet annealing It is considered effective if selected.
[0061]
Such an original sheet for cold-rolled steel sheet is then descaled and then made into a cold-rolled sheet by cold rolling in a cold rolling process.
In the cold rolling in the cold rolling process, the rolling reduction is preferably 30% or more. In addition, More preferably, it is 50 to 95%. If the rolling reduction is less than 30%, the r value and ridging resistance may be insufficient.
[0062]
After the cold rolling process, the cold rolled sheet is subjected to finish annealing in the finish annealing process.
The finish annealing is preferably performed at a temperature of 600 ° C. or higher at which recrystallization occurs in order to improve workability. In addition, the more preferable temperature range of finish annealing is 700-900 degreeC. The finish annealing is preferably continuous annealing in consideration of productivity. The cold rolled steel sheet having a crystal structure with the above composition and the maximum degree of extension e of 5 or less is subjected to cold rolling with a rolling reduction of 30% or more, and then the annealing temperature is 700 ° C. or more. It is more preferable to perform the final annealing.
[0063]
In the present invention, the cold rolling process and the finish annealing process may be repeated twice or more. By repeating the cold rolling process and the finish annealing process, the r value, ductility, and ridging resistance are further improved.
Needless to say, the finish of the cold-rolled sheet can be various finishes such as 2D finish, 2B finish, and BA finish depending on the application.
[0064]
【Example】
Example 1
Molten steel having the composition shown in Table 1 was melted in the converter-secondary refining process and made into a slab by a continuous casting method. After these slabs were reheated, they were formed into hot rolled sheets by a hot rolling process in which hot rolling at a finish rolling temperature of 950 to 1000 ° C. was performed. Then, after pickling these hot-rolled sheets, a preliminary rolling process, a hot-rolled sheet annealing process, a pickling process, a cold-rolling process, and a finish annealing process were sequentially performed to obtain a cold-rolled annealed sheet having a thickness of 0.8 mm. . Table 2 shows the rolling conditions and hot-rolled sheet annealing conditions in the preliminary rolling process. In the cold rolling process, the cold rolling reduction ratio was adjusted so that the cumulative rolling reduction ratio to the hot rolled sheet was 75%. The annealing in the final annealing process was continuous annealing and held at 830 ° C. for 30 seconds.
[0065]
A test piece was taken from the obtained cold-rolled annealed plate, a tensile test was performed, and the elongation El, r value, and ridging grade were measured. The measuring method of elongation El, r value, and ridging grade is as follows.
(1) Elongation
JIS 13B test specimens were taken from each direction of each cold-rolled annealed plate (rolling direction, 45 ° direction to the rolling direction and perpendicular direction to the rolling direction), subjected to a tensile test, and the elongation El in each direction ( El₀, El₄₅, El₉₀) Was measured. From the elongation El in each direction, the average elongation El_meanAsked.
[0066]
El_mean= (El₀+2 El₄₅+ El₉₀) / 4
(Where El₀Is the elongation in the rolling direction, El₄₅Is the 45 ° elongation relative to the rolling direction, El₉₀Is the elongation in the 90 ° (right angle) direction with respect to the rolling direction. )
(2) r value
JIS 13 B test specimens were collected from each direction (rolling direction, 45 ° direction with respect to the rolling direction, and perpendicular direction to the rolling direction) of each cold-rolled annealed sheet. These test pieces (width w₀, Gauge length l₀ ) Was used to determine the r value at 15% strain based on JIS Z 2254. That is, the width w and gauge length l of each test piece after applying 15% uniaxial tensile pre-strain is obtained by the following formula:
r = ln (w₀/ W) / ln (lw / l₀w₀)
(Where₀, L₀Is the width and gauge length of each test piece before the tensile test, and w and l are the width and gauge length after the tensile test piece, respectively. )
To obtain the r value in each direction,
r_mean= (R₀+ 2r₄₅+ R₉₀) / 4
(Where r₀Is the r value in the rolling direction, r₄₅Is the r value in the 45 ° direction relative to the rolling direction, r₉₀Is the r value in the 90 ° (right angle) direction with respect to the rolling direction. )
The average r value r_meanAsked.
(3) Ridging grade
A JIS No. 5 test piece was taken from the rolling direction of each cold-rolled annealed plate, and one side of this test piece was finished and polished with # 600 abrasive paper. Then, after applying 20% uniaxial tensile pre-strain to these test pieces, the height of waviness (riding unevenness) generated in the test pieces was measured by a roughness meter at the center of the test pieces. The degree of ridging was evaluated from the height of this swell.
[0067]
The degree of ridging was evaluated on a four-point scale. A swell height of 5 μm or less was A, 5 μm to 10 μm B, 10 μm to 20 μm C, and 20 μm D. In the case of A and B based on this evaluation standard, the ridging resistance during press molding is good.
The obtained results are shown in Table 3.
[0068]
[Table 1]

[0069]
[Table 2]

[0070]
[Table 3]

[0071]
In all of the examples of the present invention, El_mean: 32% or more, r_meanValue: 1.30 or more, ridging grade: A, and excellent properties in ductility, r value, and ridging resistance. On the other hand, in the comparative examples that are out of the scope of the present invention, any of ductility, r value, and ridging resistance was lowered.
(Example 2)
Molten steel having the composition shown in Table 4 was melted in the converter-secondary refining process and made into a slab by a continuous casting method. After reheating these slabs, hot rolled sheets having a thickness of 3.2 to 4.0 mm were formed by a hot rolling process in which hot rolling at the finish rolling temperature shown in Table 5 was performed. Then, after pickling these hot-rolled sheets, a preliminary rolling process, a hot-rolled sheet annealing process, a pickling process, a cold-rolling process, and a finish annealing process were sequentially performed to obtain a cold-rolled annealed sheet having a thickness of 0.8 mm. . Table 5 shows the pre-rolling rolling conditions and hot-rolled sheet annealing conditions. In addition, the hot-rolled sheet annealing conditions were set to 800-860 ° C. × 8 hr holding box annealing. In the cold rolling process, the cold rolling ratio was adjusted to obtain a cold rolled sheet having a thickness of 0.8 mm. The cumulative rolling reduction of the hot rolled sheet was 75 to 80%. The annealing in the final annealing process was continuous annealing and held at 830 ° C. for 30 seconds.
[0072]
A test piece was taken from the obtained cold-rolled annealed plate, a tensile test was performed, and the elongation El, r value, and ridging grade were measured. The measuring method of elongation, r value, and ridging grade was the same as in Example 1. R₀, R₄₅, R₉₀The minimum value of r_minIt was. In addition, after collecting a test piece from the obtained hot-rolled annealed plate (cold-rolled steel plate) obtained through the hot-rolled sheet annealing step, polishing the plate thickness section parallel to the rolling direction, and etching with aqua regia, The structure | tissue of the range of plate | board thickness x2mm was image | photographed 100 times using the optical microscope. From the obtained tissue photograph, the degree of extension e of the crystal grains was measured by image processing using an image analyzer, and the maximum value was obtained. Further, with respect to the cold-rolled annealed plate, a plate thickness cross section parallel to the rolling direction was polished, etched with aqua regia, and then a range of plate thickness × 1 mm was photographed at 200 times using an optical microscope. Based on the obtained structure photograph, the average crystal grain area A is obtained by image processing using an image analyzer.₀And 2 × A₀The aspect ratio A of the coarse colony, which is an aggregate in which the coarse crystal grains having the above crystal grain area continuously gather in the rolling direction, was measured, and the maximum value was obtained.
[0073]
The results obtained are shown in Table 6.
[0074]
[Table 4]

[0075]
[Table 5]

[0076]
[Table 6]

[0077]
In all of the examples of the present invention, El_mean: 32% or more, r_meanValue: 1.30 or more, Ridging grade: A, Elongation, r value, Ridging resistance In addition, the minimum r value r_minIs as high as 1.00 or more and the in-plane anisotropy is small.
On the other hand, in the comparative example out of the scope of the present invention, any of elongation, r value, and ridging resistance decreases, and r_minIs also low.
(Example 3)
Molten steel having the composition shown in Table 7 was melted in the converter-secondary refining process and made into a slab by a continuous casting method. After reheating these slabs, hot rolled sheets having a thickness of 3.2 to 5.0 mm were formed by a hot rolling process in which hot rolling at the finish rolling temperature shown in Table 8 was performed. Then, after pickling these hot-rolled sheets, a preliminary rolling process, a hot-rolled sheet annealing process, a pickling process, a cold-rolling process, and a finish annealing process were sequentially performed to obtain a cold-rolled annealed sheet having a thickness of 0.8 mm. . Table 9 shows pre-rolling rolling conditions and hot-rolled sheet annealing conditions. The hot-rolled sheet annealing conditions were 880-1000 ° C. × 2-8 hr holding box annealing. In the cold rolling process, the cold rolling ratio was adjusted to obtain a cold rolled sheet having a thickness of 0.8 mm. The cumulative rolling reduction of the hot rolled sheet was 75 to 84%. The annealing in the final annealing process was continuous annealing and held at 830 ° C. for 30 s.
[0078]
A test piece was taken from the obtained cold-rolled annealed plate, a tensile test was performed, and the elongation El, r value, and ridging grade were measured. Further, the maximum value of the degree of extension e was determined for the hot-rolled annealed plate, and the maximum value of the aspect ratio A of the coarse colony was determined for the cold-rolled annealed plate. The measuring methods of elongation, r value, ridging grade, degree of extension e, and aspect ratio A were the same as in Example 1.
[0079]
Table 9 shows the obtained results.
[0080]
[Table 7]

[0081]
[Table 8]

[0082]
[Table 9]

[0083]
In all of the examples of the present invention, El_mean: 34% or more, r_meanValue: 1.40 or more, Ridging grade: A, Elongation, r value, Ridging resistance
On the other hand, the comparative example outside the scope of the present invention has reduced ridging resistance.
(Example 4)
Molten steel having the composition shown in Table 10 was melted in the converter-secondary refining process and made into a slab by a continuous casting method. These slabs were reheated and then hot rolled into 3.2 to 4.0 mm thick by a hot rolling process in which hot rolling at the finish rolling temperature shown in Table 11 was performed. Then, after pickling these hot-rolled sheets, a preliminary rolling process, a hot-rolled sheet annealing process, a pickling process, a cold-rolling process, and a finish annealing process were sequentially performed to obtain a cold-rolled annealed sheet having a thickness of 0.8 mm. . Table 11 shows pre-rolling rolling conditions and hot-rolled sheet annealing conditions. The hot-rolled sheet annealing conditions were 880-930 ° C. × 2-8 hr holding box annealing. In the cold rolling process, the cold rolling ratio was adjusted to obtain a cold rolled sheet having a thickness of 0.8 mm. The cumulative rolling reduction of the hot rolled sheet was 75 to 80%. The annealing in the final annealing process was continuous annealing and held at 830 ° C. for 30 seconds.
[0084]
A test piece was taken from the obtained cold-rolled annealed plate, a tensile test was performed, and the elongation El, r value, and ridging grade were measured. Moreover, the maximum value of the degree of extension e was determined for the hot-rolled annealed sheet, and the maximum value of the aspect ratio A of the coarse colony was determined for the cold-rolled annealed sheet. The measuring methods of elongation, r value, ridging grade, degree of extension e, and aspect ratio A were the same as in Example 1.
[0085]
The results obtained are shown in Table 12.
[0086]
[Table 10]

[0087]
[Table 11]

[0088]
[Table 12]

[0089]
The examples of the present invention all have good properties in terms of elongation, r value, and ridging resistance. On the other hand, in the comparative example outside the scope of the present invention, any of elongation, r value, and ridging resistance was deteriorated.
On the other hand, the comparative example outside the scope of the present invention has reduced ridging resistance.
[0090]
【The invention's effect】
According to the present invention, it is possible to provide a ferritic stainless steel sheet that is excellent in ductility, workability, and ridging resistance, or has a small r-value in-plane anisotropy and excellent press workability, at a low cost, There are remarkable effects in the industry.
[Brief description of the drawings]
FIG. 1 Pre-rolling reduction ratio and average elongation El_mean(A), average r value r_meanIt is a graph which shows the relationship with (b) and ridging grade (c).
FIG. 2 r_mean, R_minIt is a graph which shows the relationship between a value and hot rolling finishing temperature FDT.
FIG. 3 is a schematic diagram showing an example of a slow cooling pattern during hot-rolled sheet annealing.
FIG. 4A is a schematic diagram showing an example of a crystal grain structure of a plate thickness section parallel to the rolling direction of a hot-rolled annealed sheet, and FIG. 4B is a schematic diagram for explaining the definition of the degree of extension e of crystal grains. FIG.
FIG. 5 is a graph showing an example of the distribution of crystal grain extension of the hot-rolled annealing plate.
6A is a schematic diagram showing an example of a crystal grain structure of a plate thickness cross section parallel to the rolling direction of a cold-rolled annealed plate, and FIG. 6B illustrates the definition of the aspect ratio A of coarse-grained colonies. It is a schematic diagram.

Claims (14)

mass%
C: 0.01 to 0.12%, N: 0.01 to 0.12%,
Cr: 11-18%, Al: 0.03% or less,
Si: 1.0% or less, Mn: 1.0% or less, P: 0.05% or less, S: 0.01% or less,
V: 0.15% or less, Ni: wherein is adjusted to 1.0% or less, the composition Ru balance of Fe and unavoidable impurities Tona, plate thickness cross section parallel to the rolling direction, the following (1) extension of which is defined by the formula A base plate for a ferritic stainless steel cold-rolled steel sheet, having a structure in which the maximum value of e is 5 or less.
Record
e = L1 / L2 (1)
Where e: degree of extension
L1: Length of crystal grain in rolling direction (μm)
L2: Length of crystal grain in the plate thickness direction (μm) In addition to the composition, in mass%, Mo, the one or total 2.5% or less and / or a of the Cu Mg: claim 1, wherein the containing 0.0002 to 0.0050% Of ferritic stainless cold rolled steel sheet. In mass%, C: 0.01~0.12%, N: 0.01~0.12%, Cr: 11~18%, Al: 0.03% or less, Si: 1.0% or less, Mn: includes 1.0% or less, further P : 0.05 % or less, S: 0.01 % or less, V: 0.15 % or less, Ni : 1.0 % or less
Or even Mo, 1 kind or 2.5% of two or a total of less and / or Mg of Cu: containing from 0.0002 to 0.0050%, the steel material balance of Fe and unavoidable impurities ing, the hot rolling After performing the hot rolling step to make a hot rolled plate, the hot rolled plate is subjected to a pre-rolling step of rolling at a reduction ratio of 2 to 15% cold or warm, and then the heat subjected to the pre-rolling step A method for producing an original sheet for a ferritic stainless steel cold-rolled steel sheet, characterized by performing a hot-rolled sheet annealing process for box annealing of a rolled sheet.   4. The ferritic stainless steel according to claim 3, wherein the box annealing is performed by holding at a predetermined annealing temperature for 1 h or more and gradually cooling at 25 ° C./h or less at an average cooling rate up to 600 ° C. after holding. A method for producing a cold rolled steel sheet. The predetermined annealing temperature is set to (A ₁ transformation point + 30 ° C.) or more and less than 1000 ° C. based on the A ₁ transformation point defined by the following formula (2). A method for producing a base plate for a ferritic stainless steel cold-rolled steel sheet.
A ₁ Transformation point (℃) = 35 (Cr + 1.72Mo + 2.09Si + 4.86Nb + 8.29V + 1.77Ti + 21.4Al + 40B-7 .14C-8.0N-3.28Ni-1.89Mn-0.51Cu) + 310 …… (2)
Here, Cr, Mo, Si, Nb, V, Ti, Al, B, C, N, Ni, Mn, Cu: Content of each alloy element (mass%)   The method for manufacturing a ferritic stainless steel cold-rolled steel sheet according to any one of claims 3 to 5, wherein the hot rolling in the hot rolling step sets a finishing temperature to 850 ° C or lower. mass%
C: 0.01 to 0.12%, N: 0.01 to 0.12%,
Cr: 11-18%, Al: 0.03% or less,
Si: 1.0% or less, Mn: 1.0% or less, P: 0.05% or less, S: 0.01% or less,
V: 0.15% or less, Ni: wherein is adjusted to 1.0% or less, the composition Ru balance of Fe and unavoidable impurities Tona, plate thickness cross section parallel to the rolling direction, an average of more than twice the grain area A ₀ It is characterized by having a structure in which the maximum value of the aspect ratio A defined by the following formula (3) is 5 or less of a coarse-grained colony in which crystal grains having a crystal grain area are continuous aggregates in the rolling direction. Ferritic stainless cold-rolled steel sheet with excellent ductility, workability and ridging resistance.
Record
A = L3 / L4 (3)
Here, A: aspect ratio of coarse-grained colony
L3: Length of coarse colony in the rolling direction (μm)
L2: Length of coarse colony in the plate thickness direction (μm) In addition to the composition, in mass%, Mo, the one or total 2.5% or less and / or a of the Cu Mg: according to claim 7, characterized in that it contains 0.0002 to 0.0050% Ferritic stainless steel cold rolled steel sheet. In mass%, C: 0.01~0.12%, N: 0.01~0.12%, Cr: 11~18%, Al: 0.03% or less, Si: 1.0% or less, Mn: includes 1.0% or less, further P : 0.05 % or less, S: 0.01 % or less, V: 0.15 % or less, Ni : 1.0 % or less
Or even Mo, the one or more than 2.5% and / or two in total of Cu Mg: containing 0.0002 to 0.0050%, the steel material balance of Fe and unavoidable impurities ing, the hot rolling A hot-rolled sheet as a hot-rolled sheet, a hot-rolled sheet annealing process for annealing the hot-rolled sheet, and a hot-rolled sheet that has undergone the hot-rolled sheet annealing process as a cold-rolled steel sheet, In the method for producing a ferritic stainless steel sheet, which has a cold rolling step of cold rolling to make a cold rolled plate and a finish annealing step of finish annealing the cold rolled plate, after the hot rolling step and before the hot rolled plate annealing step In addition, a pre-rolling process is performed to perform rolling at a reduction ratio of 2 to 15% in a cold or warm condition, and the annealing in the hot-rolled sheet annealing process is to be box annealing that maintains 1 h or more at a predetermined annealing temperature. Ferritic steel with excellent ductility, workability and ridging resistance A method for producing a cold-rolled steel sheet. 10. The ferritic stainless steel according to claim 9, wherein the box annealing is performed by holding at a predetermined annealing temperature for 1 h or more and gradually cooling at 25 ° C./h or less at an average cooling rate up to 600 ° C. after the holding. A method for producing a cold-rolled steel sheet. 11. The predetermined annealing temperature is set to (A ₁ transformation point + 30 ° C.) or more and less than 1000 ° C. based on the A ₁ transformation point defined by the following formula (2). Manufacturing method of ferritic stainless steel cold-rolled steel sheet.
A ₁ Transformation point (℃) = 35 (Cr + 1.72Mo + 2.09Si + 4.86Nb + 8.29V + 1.77Ti + 21.4Al + 40B-7 .14C-8.0N-3.28Ni-1.89Mn-0.51Cu) + 310 …… (2)
Here, Cr, Mo, Si, Nb, V, Ti, Al, B, C, N, Ni, Mn, Cu: Content of each alloy element (mass%)   12. The method for producing a ferritic stainless cold-rolled steel sheet according to claim 9, wherein the hot rolling in the hot rolling step sets a finishing temperature to 850 ° C. or less.   Ductility characterized by using the ferritic stainless steel cold-rolled steel sheet according to claim 1 or 2, performing cold rolling on the ferritic stainless steel cold-rolled steel sheet, and then performing finish annealing. A method for producing a ferritic stainless cold-rolled steel sheet having excellent workability and ridging resistance.   14. The method for producing a ferritic stainless cold-rolled steel sheet according to claim 13, wherein the rolling reduction of the cold rolling is 30% or more, and the annealing temperature of the finish annealing is 700 ° C. or more.

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