JP5453747B2 - Stainless cold-rolled steel sheet excellent in punching processability and manufacturing method thereof - Google Patents
Stainless cold-rolled steel sheet excellent in punching processability and manufacturing method thereof Download PDFInfo
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- 239000010960 cold rolled steel Substances 0.000 title claims description 37
- 238000004080 punching Methods 0.000 title claims description 20
- 238000004519 manufacturing process Methods 0.000 title claims description 12
- 229910000859 α-Fe Inorganic materials 0.000 claims description 23
- 239000013078 crystal Substances 0.000 claims description 20
- 238000005096 rolling process Methods 0.000 claims description 13
- 238000000137 annealing Methods 0.000 claims description 10
- 238000005098 hot rolling Methods 0.000 claims description 9
- 239000012535 impurity Substances 0.000 claims description 7
- 238000010438 heat treatment Methods 0.000 claims description 6
- 229910052717 sulfur Inorganic materials 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 229910052698 phosphorus Inorganic materials 0.000 claims description 5
- 238000004804 winding Methods 0.000 claims description 5
- 238000000034 method Methods 0.000 description 17
- 229910000831 Steel Inorganic materials 0.000 description 16
- 229910001220 stainless steel Inorganic materials 0.000 description 16
- 239000010959 steel Substances 0.000 description 16
- 229910000734 martensite Inorganic materials 0.000 description 14
- 230000007547 defect Effects 0.000 description 9
- 230000007797 corrosion Effects 0.000 description 7
- 238000005260 corrosion Methods 0.000 description 7
- 229910001566 austenite Inorganic materials 0.000 description 5
- 238000005097 cold rolling Methods 0.000 description 5
- 230000007423 decrease Effects 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 150000004767 nitrides Chemical class 0.000 description 5
- 238000001816 cooling Methods 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 238000007670 refining Methods 0.000 description 3
- 239000010935 stainless steel Substances 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 238000005554 pickling Methods 0.000 description 2
- 238000007665 sagging Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- 206010013642 Drooling Diseases 0.000 description 1
- 208000008630 Sialorrhea Diseases 0.000 description 1
- QZPSXPBJTPJTSZ-UHFFFAOYSA-N aqua regia Chemical compound Cl.O[N+]([O-])=O QZPSXPBJTPJTSZ-UHFFFAOYSA-N 0.000 description 1
- 239000012300 argon atmosphere Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000005261 decarburization Methods 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Description
本発明は、優れた打抜き加工性を有するフェライト系ステンレス冷延鋼板とその製造方法に関するものである。 The present invention relates to a ferritic stainless cold-rolled steel sheet having excellent punchability and a method for producing the same.
フェライト系ステンレス冷延鋼板は、耐食性に優れているので、建築材料，輸送機器，家庭電化製品，厨房機器，化学プラント，貯水槽，自動車部品等の様々な用途に使用されている。一方でフェライト系ステンレス冷延鋼板は、延性が乏しいという欠点を有しており、純度を高めて軟質化することによって延性を確保している。しかし、純度を高めて延性を付与したフェライト系ステンレス冷延鋼板は打抜き加工の際にだれが生じ易いので、精密な打抜き加工が困難である。 Ferritic stainless steel cold-rolled steel sheets are excellent in corrosion resistance and are used in various applications such as building materials, transportation equipment, home appliances, kitchen equipment, chemical plants, water tanks, and automobile parts. On the other hand, ferritic stainless steel cold-rolled steel sheet has a defect that ductility is poor, and the ductility is ensured by increasing the purity and softening. However, since the ferritic stainless steel cold rolled steel sheet with increased purity and imparted ductility is likely to be damaged during punching, precise punching is difficult.
そこでフェライト系ステンレス冷延鋼板の打抜き加工性を向上させる技術が種々検討されている。
たとえば特許文献１には、Ｃ，Si，Mn，Ｓ，Cr，Ｎ，Al，Ti，Ｖ，Ｂ，Ｏの含有量を規定し、かつ各元素の含有量から算出されるTi／（Ｃ＋Ｎ）値およびＶ／Ｂ値を規定することによって、打抜き性と成形性を改善したフェライト系ステンレス冷延鋼板が開示されている。しかしこの技術はTiを添加するので、フェライト系ステンレス冷延鋼板を製造する過程にて、そのTiがＣやＮ，Ｏと結合してTi炭化物，Ti窒化物，Ti酸化物を形成し、表面欠陥を誘起する。
For example, Patent Document 1 defines the content of C, Si, Mn, S, Cr, N, Al, Ti, V, B, and O, and is calculated from the content of each element Ti / (C + N). Ferritic stainless steel cold-rolled steel sheets with improved punchability and formability by specifying the value and the V / B value are disclosed. However, since this technology adds Ti, in the process of manufacturing a ferritic stainless steel cold-rolled steel sheet, Ti combines with C, N, and O to form Ti carbide, Ti nitride, and Ti oxide. Induces defects.
本発明は、製造工程で表面欠陥を発生せず、かつ加工工程で優れた打抜き加工性を有するフェライト系ステンレス冷延鋼板とその製造方法を提供することを目的とする。 An object of this invention is to provide the ferritic stainless steel cold-rolled steel plate which does not produce a surface defect at a manufacturing process, and has the outstanding punching workability at a manufacturing process, and its manufacturing method.
発明者らは、フェライト系ステンレス冷延鋼板（以下、ステンレス冷延鋼板という）の表面欠陥を防止し、かつ打抜き加工性を向上する技術について検討した。その結果、表面欠陥の防止については、
(A)Tiを添加せず成分を設計する、
ことによって表面欠陥を防止でき、打抜き加工性の向上については、
(a)ステンレス冷延鋼板の成分を規定するとともに、熱間圧延の仕上げ温度と巻取り温度，冷間圧延した後の焼鈍の加熱温度と保持時間を規定することによって、冷延焼鈍板の固溶Ｎが増加し、結晶粒内の応力が増加する。この内部応力が打抜き加工時の亀裂の伝播を容易にし、ダレの発生を抑制する、
(b)冷間圧延した後の焼鈍（以下、冷延板焼鈍という）による板厚方向のフェライト結晶粒の成長を、熱延板におけるフェライト−マルテンサイト界面に析出したCr炭化物が抑制することによって、板厚方向の変形に対する抵抗力が増加し、さらにダレの発生が抑制される
ことによって打抜き加工性を向上できるという知見を得た。
The inventors examined a technique for preventing surface defects of a ferritic stainless steel cold-rolled steel sheet (hereinafter referred to as a stainless steel cold-rolled steel sheet) and improving punching workability. As a result, for the prevention of surface defects,
(A) Design components without adding Ti,
Can prevent surface defects and improve punchability.
(a) In addition to defining the components of the stainless cold-rolled steel sheet, by specifying the finishing temperature and winding temperature of hot rolling, and the heating temperature and holding time of annealing after cold rolling, Molten N increases and stress in the crystal grains increases. This internal stress facilitates the propagation of cracks during punching and suppresses the occurrence of sagging.
(b) The growth of ferrite crystal grains in the thickness direction by annealing after cold rolling (hereinafter referred to as cold rolling annealing) is suppressed by Cr carbide precipitated at the ferrite-martensite interface in the hot rolled sheet. The inventors have found that the punching processability can be improved by increasing the resistance to deformation in the plate thickness direction and further suppressing the occurrence of sagging.
本発明は、これらの知見に基づいてなされたものである。
すなわち本発明は、Ｃ：0.01〜0.06質量％，Si：0.02〜0.40質量％，Mn：0.30〜1.0質量％，Ｐ：0.05質量％以下，Ｓ：0.01質量％以下，Al：0.001〜0.02質量％，Ｎ：0.01〜0.08質量％，Cr：16.0〜18.0質量％を含有し、残部がFeおよび不可避的不純物からなる組成と、圧延方向に平行でかつ圧延面に垂直な断面の板厚方向のフェライト結晶粒径の平均値が10μｍ以下である組織と、を有する打抜き加工性に優れたステンレス冷延鋼板である。
The present invention has been made based on these findings.
That is, the present invention includes C: 0.01 to 0.06 mass%, Si: 0.02 to 0.40 mass%, Mn: 0.30 to 1.0 mass%, P: 0.05 mass% or less, S: 0.01 mass% or less, Al: 0.001 to 0.02 mass %. , N: 0.01 to 0.08% by mass, Cr: 16.0 to 18.0% by mass, the balance being Fe and inevitable impurities, and ferrite in the thickness direction of the cross section parallel to the rolling direction and perpendicular to the rolling surface A stainless cold-rolled steel sheet having a structure having an average grain size of 10 μm or less and excellent punching workability .
また本発明は、Ｃ：0.01〜0.06質量％，Si：0.02〜0.40質量％，Mn：0.30〜1.0質量％，Ｐ：0.05質量％以下，Ｓ：0.01質量％以下，Al：0.02質量％以下，Ｎ：0.01〜0.08質量％，Cr：16.0〜18.0質量％を含有し、残部がFeおよび不可避的不純物からなる組成と、圧延方向に平行でかつ圧延面に垂直な断面の板厚方向のフェライト結晶粒径の平均値が10μｍ以下で、かつフェライト結晶粒のアスペクト比が４以下である組織と、を有するステンレス冷延鋼板である。 In the present invention, C: 0.01 to 0.06 mass%, Si: 0.02 to 0.40 mass%, Mn: 0.30 to 1.0 mass%, P: 0.05 mass% or less, S: 0.01 mass% or less, Al: 0.02 mass% or less, N: 0.01 to 0.08% by mass, Cr: 16.0 to 18.0% by mass, with the balance consisting of Fe and inevitable impurities, and ferrite crystals in the thickness direction of the cross section parallel to the rolling direction and perpendicular to the rolling surface A stainless cold-rolled steel sheet having a structure having an average grain size of 10 μm or less and a ferrite crystal grain having an aspect ratio of 4 or less.
また本発明は、Ｃ：0.01〜0.06質量％，Si：0.02〜0.40質量％，Mn：0.30〜1.0質量％，Ｐ：0.05質量％以下，Ｓ：0.01質量％以下，Al：0.001〜0.02質量％，Ｎ：0.01〜0.08質量％，Cr：16.0〜18.0質量％を含有し、残部がFeおよび不可避的不純物からなるスラブの熱間圧延を仕上げ温度800〜1000℃で行ない、巻取り温度700℃以下で巻取って冷却した後、必要に応じて酸洗し、さらに冷間圧延を行ない、次いで加熱温度750〜850℃かつ保持時間20〜240秒で冷延板焼鈍を行なう打抜き加工性に優れたステンレス冷延鋼板の製造方法である。 In the present invention, C: 0.01 to 0.06 mass%, Si: 0.02 to 0.40 mass%, Mn: 0.30 to 1.0 mass%, P: 0.05 mass% or less, S: 0.01 mass% or less, Al: 0.001 to 0.02 mass % , N: 0.01 ~ 0.08 mass%, Cr: 16.0 ~ 18.0 mass%, the remainder of the slab consisting of Fe and inevitable impurities is hot rolled at a finishing temperature of 800 ~ 1000 ℃, winding temperature of 700 ℃ or less After coiling and cooling, pickling as necessary, cold rolling is performed, and then cold rolled sheet annealing is performed at a heating temperature of 750 to 850 ° C. and a holding time of 20 to 240 seconds . It is a manufacturing method of a stainless cold-rolled steel sheet.
本発明によれば、製造工程で表面欠陥を発生せず、かつ加工工程で優れた打抜き加工性を発揮するフェライト系ステンレス冷延鋼板を得ることができる。 ADVANTAGE OF THE INVENTION According to this invention, the ferritic stainless steel cold-rolled steel plate which does not generate | occur | produce a surface defect in a manufacturing process, and exhibits the punching workability excellent in the manufacturing process can be obtained.
まず、本発明のステンレス冷延鋼板の成分の限定理由を説明する。
Ｃ：0.01〜0.06質量％
Ｃは、素材となるスラブを熱間圧延する際にマルテンサイト相を生成させ、かつCrと結合してCr炭化物をフェライト結晶粒の粒界に析出させる元素である。Ｃ含有量が0.01質量％未満では、この効果が十分に得られない。粒界に析出するCr炭化物が不足すると、板厚方向のフェライト結晶粒の成長を抑制できないので、打抜き加工におけるだれの発生を防止できない。一方、0.06質量％を超えると、スラブの熱間圧延によってマルテンサイトが多量に生成され、熱延鋼板が硬質化するので、冷間圧延に支障を来たす。したがって、Ｃは0.01〜0.06質量％の範囲内とする。
First, the reasons for limiting the components of the stainless cold-rolled steel sheet of the present invention will be described.
C: 0.01-0.06 mass%
C is an element that forms a martensite phase when hot-rolling a slab as a raw material, and combines with Cr to precipitate Cr carbide at the grain boundaries of ferrite crystal grains. If the C content is less than 0.01% by mass, this effect cannot be obtained sufficiently. If the Cr carbide precipitated at the grain boundary is insufficient, the growth of ferrite crystal grains in the thickness direction cannot be suppressed, so that no dripping can be prevented in the punching process. On the other hand, if it exceeds 0.06 mass%, a large amount of martensite is generated by hot rolling of the slab, and the hot-rolled steel sheet is hardened, which hinders cold rolling. Therefore, C is in the range of 0.01 to 0.06 mass%.
Si：0.02〜0.40質量％
Siは、フェライト系ステンレス鋼の溶製段階で脱酸剤として用いられる元素であるが、マルテンサイト相の生成量を減少させる。Si含有量が0.02質量％未満では、脱酸の効果が十分に得られない。一方、0.40質量％を超えると、マルテンサイト相の生成が減少するので板厚方向のフェライト結晶粒の成長を抑制できず、打抜き加工におけるだれの発生を防止できない。したがって、Siは0.02〜0.40質量％の範囲内とする。
Si: 0.02-0.40 mass%
Si is an element used as a deoxidizer in the melting stage of ferritic stainless steel, but reduces the amount of martensite phase generated. When the Si content is less than 0.02% by mass, the effect of deoxidation cannot be obtained sufficiently. On the other hand, if it exceeds 0.40 mass%, the formation of martensite phase decreases, so that the growth of ferrite crystal grains in the thickness direction cannot be suppressed, and the occurrence of drooling in the punching process cannot be prevented. Therefore, Si is within the range of 0.02 to 0.40 mass%.
Mn：0.30〜1.0質量％
Mnは、熱間圧延にて熱延鋼板にマルテンサイト相を生成させる元素である。Mn含有量が0.30質量％未満では、マルテンサイト相が十分に生成されないので板厚方向のフェライト結晶粒の成長を抑制できず、打抜き加工におけるだれの発生を防止できない。一方、1.0質量％を超えると、後述するＳと結合してMnＳの析出が促進され、ステンレス冷延鋼板の耐食性が低下する。したがって、Mnは0.30〜1.0質量％の範囲内とする。
Mn: 0.30 to 1.0 mass%
Mn is an element that generates a martensite phase in a hot-rolled steel sheet by hot rolling. If the Mn content is less than 0.30% by mass, the martensite phase is not sufficiently generated, so that the growth of ferrite crystal grains in the thickness direction cannot be suppressed, and the occurrence of dripping in the punching process cannot be prevented. On the other hand, when it exceeds 1.0 mass%, it will combine with S mentioned later and precipitation of MnS will be accelerated | stimulated and the corrosion resistance of a stainless cold-rolled steel plate will fall. Therefore, Mn is in the range of 0.30 to 1.0 mass%.
Ｐ：0.05質量％以下
Ｐは、フェライト結晶粒の粒界に偏析して脆性破壊を誘起する。Ｐ含有量が0.05質量％を超えると、粒界における偏析の問題に加えて、固溶強化によって熱延鋼板が硬質化して、延性が著しく低下する。したがって、Ｐは0.05質量％以下とする。
Ｓ：0.01質量％以下
Ｓは、ステンレス冷延鋼板の耐食性を低下させる元素である。Ｓ含有量が0.01質量％を超えると、耐食性が著しく低下する。したがって、Ｓは0.01質量％以下とする。
P: 0.05 mass% or less P segregates at the grain boundary of ferrite crystal grains and induces brittle fracture. If the P content exceeds 0.05% by mass, in addition to the problem of segregation at the grain boundaries, the hot-rolled steel sheet is hardened by solid solution strengthening, and the ductility is significantly reduced. Therefore, P is 0.05 mass% or less.
S: 0.01% by mass or less S is an element that lowers the corrosion resistance of the stainless cold-rolled steel sheet. When S content exceeds 0.01 mass%, corrosion resistance will fall remarkably. Therefore, S is set to 0.01% by mass or less.
Al：0.02質量％以下
Alは、フェライト系ステンレス鋼の溶製段階で脱酸剤として用いられる元素であるが、マルテンサイト相の生成量を減少させる。Al含有量が0.02質量％を超えると、マルテンサイト相の生成が減少するので板厚方向のフェライト結晶粒の成長を抑制できず、打抜き加工におけるだれの発生を防止できない。したがって、Alは0.02質量％以下とする。
Al: 0.02 mass% or less
Al is an element used as a deoxidizer in the melting stage of ferritic stainless steel, but reduces the amount of martensite phase produced. If the Al content exceeds 0.02% by mass, the formation of martensite phase decreases, so the growth of ferrite crystal grains in the plate thickness direction cannot be suppressed, and the occurrence of dripping in the punching process cannot be prevented. Therefore, Al is 0.02 mass% or less.
Ｎ：0.01〜0.08質量％
Ｎは、フェライト結晶粒の粒内に固溶して、冷延板焼鈍した後のステンレス冷延鋼板のフェライト結晶粒に内部応力を蓄積する作用を有する。Ｎ含有量が0.01質量％未満では、その効果が十分に得られない。一方、0.08質量％を超えると、後述するCrと結合してCr窒化物を生成し、ステンレス冷延鋼板の耐食性向上に寄与するCrが減少する。したがって、Ｎは0.01〜0.08質量％の範囲内とする。
N: 0.01 to 0.08 mass%
N has a function of accumulating internal stress in the ferrite crystal grains of the stainless cold-rolled steel sheet after being solid-solved in the ferrite crystal grains and annealed in the cold-rolled sheet. If the N content is less than 0.01% by mass, the effect cannot be obtained sufficiently. On the other hand, if it exceeds 0.08% by mass, it combines with Cr to be described later to produce Cr nitride, and Cr that contributes to improving the corrosion resistance of the stainless cold-rolled steel sheet decreases. Therefore, N is in the range of 0.01 to 0.08 mass%.
Cr：16.0〜18.0質量％
Crは、ステンレス冷延鋼板の表面に不動態皮膜を形成して耐食性を高める元素である。Cr含有量が16.0質量％未満では、十分な耐食性が得られない。一方、18.0質量％を超えると、ステンレス冷延鋼板のフェライト相が増加し、マルテンサイト相が十分に生成されないので板厚方向のフェライト結晶粒の成長を抑制できず、打抜き加工におけるだれの発生を防止できない。したがって、Crは16.0〜18.0質量％の範囲内とする。
Cr: 16.0-18.0% by mass
Cr is an element that improves the corrosion resistance by forming a passive film on the surface of a stainless cold-rolled steel sheet. If the Cr content is less than 16.0% by mass, sufficient corrosion resistance cannot be obtained. On the other hand, if it exceeds 18.0% by mass, the ferrite phase of the stainless cold-rolled steel sheet will increase, and the martensite phase will not be generated sufficiently, so it will not be possible to suppress the growth of ferrite crystal grains in the plate thickness direction, and dripping will occur in the punching process. It cannot be prevented. Therefore, Cr is in the range of 16.0 to 18.0 mass%.
上記した成分以外の残部は、Feおよび不可避的不純物である。不可避的不純物は可能な限り低減することが望ましい。
本発明のステンレス冷延鋼板はTiを含有しないので、Ti炭化物やTi窒化物に起因する表面欠陥を防止できる。さらに、後述するようにステンレス冷延鋼板の製造方法を規定することによって、その他の表面欠陥を防止する効果も得られる。
The balance other than the above components is Fe and inevitable impurities. It is desirable to reduce inevitable impurities as much as possible.
Since the stainless cold-rolled steel sheet of the present invention does not contain Ti, surface defects caused by Ti carbide or Ti nitride can be prevented. Furthermore, the effect of preventing other surface defects can also be obtained by defining a method for producing a stainless cold-rolled steel sheet as will be described later.
次に、ステンレス冷延鋼板用素材の組織を説明する。
板厚方向のフェライト結晶粒の平均粒径：10μｍ以下
ここで板厚方向とは、ステンレス冷延鋼板の圧延方向に平行でかつ圧延面に垂直な断面における板厚方向を指す。板厚方向に測定したフェライト結晶粒の粒径の平均値が10μｍを超えると、板厚方向の変形に対する抵抗力が小さく、打抜き加工におけるだれの発生を防止できない。したがって、ステンレス冷延鋼板の打抜き加工性を確保するために、板厚方向のフェライト結晶粒の平均粒径を10μｍ以下とする。
Next, the structure of the stainless steel cold rolled steel sheet material will be described.
Average grain size of ferrite crystal grains in the plate thickness direction: 10 μm or less Here, the plate thickness direction refers to the plate thickness direction in a cross section parallel to the rolling direction of the stainless cold-rolled steel plate and perpendicular to the rolling surface. If the average value of the ferrite crystal grain size measured in the plate thickness direction exceeds 10 μm, the resistance to deformation in the plate thickness direction is small, and it is impossible to prevent the occurrence of dripping in the punching process. Therefore, in order to ensure the punchability of the stainless cold-rolled steel sheet, the average grain size of the ferrite crystal grains in the thickness direction is set to 10 μm or less.
次に、ステンレス冷延鋼板の製造方法を説明する。
転炉，電気炉等を用いて所定の成分を有するフェライト系ステンレス鋼を溶製（いわゆる１次精錬）し、さらに脱炭処理（いわゆる２次精錬）を施す。２次精錬は、強攪拌真空酸素脱炭法（いわゆるＶＯＤ法）を採用することが好ましい。
得られた溶鋼を連続鋳造法あるいは造塊法によってスラブとする。ただし、生産性の高い連続鋳造法を採用することが好ましい。
Next, a method for producing a stainless cold-rolled steel sheet will be described.
Using a converter, electric furnace, etc., ferritic stainless steel having a predetermined component is melted (so-called primary refining) and further decarburized (so-called secondary refining). The secondary refining preferably employs a strong stirring vacuum oxygen decarburization method (so-called VOD method).
The obtained molten steel is made into a slab by a continuous casting method or an ingot-making method. However, it is preferable to employ a continuous casting method with high productivity.
次いでスラブを、必要に応じて再加熱し、さらに仕上げ温度800〜1000℃で熱間圧延して熱延鋼板とし、その熱延鋼板を巻取り温度700℃以下で巻取って熱延コイルとする。本発明の成分では800〜1000℃の温度範囲で熱間圧延を終了させると、オーステナイト相の生成量が増加する。したがってこの温度範囲で熱間圧延を終了して、熱延鋼板に多量のオーステナイト相を生成させる。その後、熱延鋼板を700℃以下まで冷却して巻取ることによって、オーステナイト相からフェライト相への変態を抑制し、十分な量のマルテンサイト相を生成させる。そして、上記の温度で巻取ることにより、Cr窒化物の析出が抑制され、固溶Ｎ量を確保することが可能となる。 Next, the slab is reheated as necessary, and further hot rolled at a finishing temperature of 800 to 1000 ° C. to form a hot rolled steel sheet, and the hot rolled steel sheet is wound at a winding temperature of 700 ° C. or less to obtain a hot rolled coil. . In the component of the present invention, when hot rolling is terminated in the temperature range of 800 to 1000 ° C., the amount of austenite phase generated increases. Therefore, hot rolling is finished in this temperature range, and a large amount of austenite phase is generated in the hot-rolled steel sheet. Thereafter, the hot-rolled steel sheet is cooled to 700 ° C. or lower and wound to suppress the transformation from the austenite phase to the ferrite phase, thereby generating a sufficient amount of martensite phase. And by winding up at said temperature, precipitation of Cr nitride is suppressed and it becomes possible to ensure the amount of solute N.
熱間圧延の仕上げ温度が800〜1000℃の範囲を外れると、熱延鋼板のオーステナイト相が減少するので、熱延コイルのマルテンサイト相が減少する。また、熱延鋼板の巻取り温度が700℃を超えると、オーステナイト相からフェライト相への変態が進行し、マルテンサイト相の生成量が減少する上、Cr窒化物の析出が促進され、固溶Ｎ量の確保が困難となる。 When the finishing temperature of hot rolling is out of the range of 800 to 1000 ° C., the austenite phase of the hot-rolled steel sheet is reduced, so that the martensite phase of the hot-rolled coil is reduced. In addition, when the coiling temperature of the hot-rolled steel sheet exceeds 700 ° C., the transformation from the austenite phase to the ferrite phase proceeds, the amount of martensite phase generated decreases, and precipitation of Cr nitride is promoted, resulting in solid solution. It is difficult to secure the amount of N.
このようにして製造した熱延コイルを室温まで冷却した後、冷間圧延を行ない、さらに冷延板焼鈍（加熱温度：750〜850℃，保持時間：20〜240秒）を行なってステンレス冷延鋼板を得る。なお熱延コイルに、必要に応じて酸洗を施した後、冷間圧延を行なっても良い。冷延板焼鈍の加熱温度が750℃未満，保持時間が20秒未満では、フェライト結晶粒の再結晶が進行せず、ステンレス冷延鋼板の機械的性質が低下する。一方、加熱温度が850℃を超えると、冷延板焼鈍した後の冷却によってマルテンサイト相が生成するので、ステンレス冷延鋼板の機械的性質が低下する。保持時間が240秒を超えると、フェライト結晶粒の粒内に固溶するＮが減少するので、打抜き加工の際にだれが発生し易くなる。 After cooling the hot-rolled coil thus manufactured to room temperature, it is cold-rolled and further cold-rolled sheet annealed (heating temperature: 750 to 850 ° C., holding time: 20 to 240 seconds) to cold-roll stainless steel Get a steel plate. Note that the hot-rolled coil may be pickled as necessary, and then cold-rolled. If the heating temperature for cold-rolled sheet annealing is less than 750 ° C. and the holding time is less than 20 seconds, recrystallization of ferrite crystal grains does not proceed, and the mechanical properties of the stainless cold-rolled steel sheet deteriorate. On the other hand, when the heating temperature exceeds 850 ° C., the martensitic phase is generated by cooling after the cold-rolled sheet annealing, so that the mechanical properties of the stainless cold-rolled steel sheet are deteriorated. If the holding time exceeds 240 seconds, the amount of N that dissolves in the ferrite crystal grains decreases, so that dripping easily occurs during the punching process.
また、降伏点の伸びを消失させるため、ステンレス冷延鋼板にスキンパス圧延を施しても良い。スキンパス圧延の圧下率は、0.5〜1.5％の範囲内が好ましい。 Further, in order to eliminate the elongation of the yield point, skin pass rolling may be applied to the stainless cold-rolled steel sheet. The rolling reduction of the skin pass rolling is preferably in the range of 0.5 to 1.5%.
実験炉を用いて表１に示す成分のフェライト系ステンレス鋼（30kg）をアルゴン雰囲気で溶製し、さらにスラブとした。そのスラブを1200℃に加熱して熱間圧延を行ない、板厚５mm，幅150mmの熱延鋼板とした。得られた熱延鋼板を550℃で１時間保持した後、冷却した。この熱延鋼板を550℃で１時間保持する処理は、実際の操業における熱延鋼帯を巻取って熱延コイルとしたときの保熱効果を想定した処理である。なお、熱間圧延の条件は表２に示す通りである。 Using an experimental furnace, ferritic stainless steel (30 kg) having the components shown in Table 1 was melted in an argon atmosphere to obtain a slab. The slab was heated to 1200 ° C. and hot-rolled to obtain a hot-rolled steel sheet having a thickness of 5 mm and a width of 150 mm. The obtained hot-rolled steel sheet was kept at 550 ° C. for 1 hour and then cooled. The process of holding the hot-rolled steel sheet at 550 ° C. for 1 hour is a process assuming a heat-retaining effect when the hot-rolled steel strip in actual operation is wound into a hot-rolled coil. The conditions for hot rolling are as shown in Table 2.
得られた熱延鋼板を酸洗した後、冷間圧延を行なって板厚1.2mmの冷延鋼板とし、さらに750〜820℃で焼鈍（すなわち冷延板焼鈍）を施してステンレス冷延鋼板とした。冷延板焼鈍の保持時間は表２に示す通りである。 After pickling the obtained hot-rolled steel sheet, it is cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1.2 mm, and further subjected to annealing (ie, cold-rolled sheet annealing) at 750 to 820 ° C. did. The holding time for cold-rolled sheet annealing is as shown in Table 2.
ステンレス冷延鋼板の幅方向中央部から組織観察用試験片（幅10mm，長さ15mm）を切り出した。この組織観察用試験片の圧延方向に平行でかつ圧延面に垂直な断面の板厚方向中央部（１mm×１mm）を王水で腐食し、光学顕微鏡で100倍の写真を撮影した。その写真に組織観察用試験片を板厚方向に垂直に貫く線分を描き、その線分と交わるフェライト結晶粒の数で板厚を除した値を平均粒径として算出した。その結果を表２に示す。 A specimen for structure observation (width 10 mm, length 15 mm) was cut out from the center in the width direction of the stainless cold-rolled steel sheet. The central part (1 mm × 1 mm) in the plate thickness direction of the cross section parallel to the rolling direction and perpendicular to the rolling surface of the test specimen for structure observation was corroded with aqua regia, and a 100 times photograph was taken with an optical microscope. In the photograph, a line segment perpendicular to the thickness direction of the test piece for structure observation was drawn, and a value obtained by dividing the thickness by the number of ferrite crystal grains intersecting with the line segment was calculated as an average particle diameter. The results are shown in Table 2.
組織観察用試験片を切り出した残りのステンレス冷延鋼板を打抜き試験に供した。打抜き試験は、ポンチ径10mm，クリアランス10％で円形状に打抜いて、刃がえりを含めた反りの高さを測定し、その最大値をだれ高さとした。だれ高さが0.02mm以下を良（○）とし、0.02mm超えを不良（×）として評価した結果を表２に示す。
表２から明らかなように、発明例は、だれ高さが0.02mm以下であったのに対して、比較例は、だれ高さが0.02mmを超えた。つまり発明例は、いずれも優れた打抜き加工性を有することが確かめられた。
The remaining stainless cold-rolled steel sheet from which the tissue observation specimen was cut was subjected to a punching test. In the punching test, a punch was punched into a circular shape with a punch diameter of 10 mm and a clearance of 10%, and the height of the warp including the edge of the blade was measured. Table 2 shows the results of evaluation where the height is 0.02 mm or less as good (◯) and the height exceeding 0.02 mm as defective (×).
As is apparent from Table 2, the height of the invention example was 0.02 mm or less, whereas the height of the comparative example exceeded 0.02 mm. That is, it was confirmed that all the inventive examples have excellent punching workability.
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