JP2008266696A - Ferritic stainless steel sheet having excellent weldability to austenitic stainless steel sheet, and its manufacturing method - Google Patents
Ferritic stainless steel sheet having excellent weldability to austenitic stainless steel sheet, and its manufacturing method Download PDFInfo
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- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 34
- 229910000963 austenitic stainless steel Inorganic materials 0.000 title claims abstract description 21
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 9
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 10
- 239000012535 impurity Substances 0.000 claims abstract description 8
- 239000000203 mixture Substances 0.000 claims abstract description 8
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 5
- 238000000137 annealing Methods 0.000 claims description 17
- 238000001953 recrystallisation Methods 0.000 claims description 7
- 238000004804 winding Methods 0.000 claims description 6
- 238000005097 cold rolling Methods 0.000 claims description 5
- 230000007797 corrosion Effects 0.000 abstract description 38
- 238000005260 corrosion Methods 0.000 abstract description 38
- 229910052799 carbon Inorganic materials 0.000 abstract description 7
- 229910052804 chromium Inorganic materials 0.000 abstract description 3
- 229910052802 copper Inorganic materials 0.000 abstract description 2
- 229910052758 niobium Inorganic materials 0.000 abstract description 2
- 229910000831 Steel Inorganic materials 0.000 description 22
- 239000010959 steel Substances 0.000 description 22
- 230000006866 deterioration Effects 0.000 description 9
- 239000002244 precipitate Substances 0.000 description 9
- 238000005098 hot rolling Methods 0.000 description 6
- 238000001556 precipitation Methods 0.000 description 6
- 239000010935 stainless steel Substances 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 4
- 238000005096 rolling process Methods 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 230000002542 deteriorative effect Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 229910000765 intermetallic Inorganic materials 0.000 description 3
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 3
- 239000006104 solid solution Substances 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 2
- 239000010960 cold rolled steel Substances 0.000 description 2
- 238000000151 deposition Methods 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 239000007921 spray Substances 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical class [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 239000011324 bead Substances 0.000 description 1
- 230000003749 cleanliness Effects 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 230000002250 progressing effect Effects 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000003746 surface roughness Effects 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
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Abstract
Description
本発明は、建築物、輸送機器、家庭電化製品、厨房器具などに用いるフェライト系ステンレス鋼板、特に、オーステナイト系ステンレス鋼板との溶接性に優れるフェライト系ステンレス鋼板およびその製造方法に関する。 The present invention relates to a ferritic stainless steel plate used for buildings, transportation equipment, home appliances, kitchen appliances, and the like, and more particularly to a ferritic stainless steel plate excellent in weldability with an austenitic stainless steel plate and a method for producing the same.
フェライト系ステンレス鋼板は、意匠性や耐食性に優れるため、建築物、輸送機器、家庭電化製品、厨房器具など、様々な用途に用いられている。最近、これらの用途においては、部材の形状が複雑化しており、別々に形成した複数の部品を溶接して組み立る手法が採られる機会が増えている。それにともない、フェライト系ステンレス鋼板で形成した部品にオーステナイト系ステンレス鋼板で形成した部品を溶接するようなことも行われている。 Ferritic stainless steel sheets are excellent in design and corrosion resistance, and are used in various applications such as buildings, transportation equipment, home appliances, and kitchen appliances. Recently, in these applications, the shape of the member has become complicated, and the opportunity to assemble by assembling a plurality of separately formed parts is increasing. Along with this, parts made of austenitic stainless steel plates are welded to parts made of ferritic stainless steel plates.
しかし、フェライト系ステンレス鋼板とオーステナイト系ステンレス鋼板とを溶接すると、溶接部の耐食性が著しく劣化する。フェライト系ステンレス鋼板とオーステナイト系ステンレス鋼板の溶接部は、Niの希釈によりフェライト系ステンレス鋼となるが、こうしたフェライト系ステンレス鋼の溶接性を改善させる技術として、例えば、特許文献1には、質量%で、0.0005%≦C≦0.08%、0.01%≦Si≦1%、0.01%≦Mn≦1%、P<0.04%、0.0001%≦S≦0.01%、10%≦Cr≦25%、0.005%≦N≦0.08%、0.0005%≦Mg≦0.01%を含有し、さらに0.01%≦Ti≦0.8%および0.005%≦Al≦0.2%のうち少なくとも1種を含有し、残部がFeおよび不可避的不純物からなり、かつ、TiおよびAlのうち少なくとも1種とMgを含み、2種類以上の組成からなる層構造を有し、最大径が0.05μm以上5μmである酸化物を、3個/mm2以上の分布密度で鋼中に含有することを特徴とする溶接性、特に、溶接部の加工性に優れたフェライト系ステンレス鋼が開示されている。また、特許文献2には、質量%で、0.001%≦C≦0.08%、0.01%≦Si≦1.0%、0.01%≦Mn≦2.0%、10.5%≦Cr≦32.0%、0.001%≦N≦0.04%、0.005%≦Al≦0.2%、0.001%≦Mg≦0.02%、0.001%≦O≦0.02%を含有し、残部がFeおよび不可避的不純物からなることを特徴とする溶接性、特に、溶接部の延性と靭性に優れたフェライト系ステンレス鋼が開示されている。
しかしながら、特許文献1および2に記載されたフェライト系ステンレス鋼では、フェライト系ステンレス鋼同士の溶接を前提としており、オーステナイト系ステンレス鋼との溶接を行うと、溶接部の耐食性が著しく劣化する。 However, the ferritic stainless steels described in Patent Documents 1 and 2 are premised on welding between ferritic stainless steels, and when welded with austenitic stainless steel, the corrosion resistance of the welded portion is significantly deteriorated.
本発明は、オーステナイト系ステンレス鋼板との溶接性、特に、溶接部の耐食性に優れるフェライト系ステンレス鋼板およびその製造方法を提供することを目的とする。 An object of the present invention is to provide a ferritic stainless steel sheet excellent in weldability with an austenitic stainless steel sheet, in particular, corrosion resistance of a welded part, and a method for producing the same.
本発明者等は、フェライト系ステンレス鋼板とオーステナイト系ステンレス鋼板の代表であるSUS304鋼板との溶接部の耐食性について詳細に検討を行ったところ、以下の知見を得た。 The inventors of the present invention have examined in detail the corrosion resistance of a welded portion between a ferritic stainless steel plate and a SUS304 steel plate, which is representative of an austenitic stainless steel plate, and obtained the following knowledge.
i)溶接部のうち熱影響部は、オーステナイト系ステンレス鋼板からフェライト系ステンレス鋼板へC、N、Niが拡散して、C、N量の高く、Ni量の低いフェライト系ステンレス鋼板となり、Cr炭窒化物が析出して、耐食性を劣化させる。 i) The heat-affected zone in the weld zone is a ferritic stainless steel plate with high C, N content and low Ni content, with C, N and Ni diffusing from the austenitic stainless steel plate to the ferritic stainless steel plate. Nitride precipitates and deteriorates the corrosion resistance.
ii)熱影響部に存在するMnSやTiSなどの硫化物が発錆起点となり、耐食性を劣化させる。 ii) Sulfides such as MnS and TiS present in the heat-affected zone become rusting origins and degrade the corrosion resistance.
iii)Nb量を多くしてCr炭窒化物の生成を抑制し、Ti量を低減してTiSの生成を抑制し、かつCuSを1μm以下の大きさのMnSの周辺に析出させることが、耐食性の向上に効果的である。 iii) It is possible to suppress the formation of Cr carbonitride by increasing the amount of Nb, to suppress the formation of TiS by reducing the amount of Ti, and to precipitate CuS around MnS having a size of 1 μm or less. It is effective for improvement.
本発明は、このような知見に基づきなされたもので、質量%で、C≦0.012%、Si≦0.3%、0.1%≦Mn≦0.3%、P≦0.04%、S≦0.01%、Al≦0.08%、N≦0.012%、Ti≦0.01%、0.35%≦Nb≦0.7%、20.5%≦Cr≦23.5%、0.3%≦Cu≦0.8%を含み、残部がFeおよび不可避的不純物からなる成分組成を有し、かつCuSが1μm以下の大きさのMnSを核として、あるいは1μm以下の大きさのMnSに隣接して析出していることを特徴とするオーステナイト系ステンレス鋼板との溶接性に優れるフェライト系ステンレス鋼板を提供する。 The present invention has been made based on such knowledge, and in mass%, C ≦ 0.012%, Si ≦ 0.3%, 0.1% ≦ Mn ≦ 0.3%, P ≦ 0.04%, S ≦ 0.01%, Al ≦ 0.08. %, N ≦ 0.012%, Ti ≦ 0.01%, 0.35% ≦ Nb ≦ 0.7%, 20.5% ≦ Cr ≦ 23.5%, 0.3% ≦ Cu ≦ 0.8%, with the balance being composed of Fe and inevitable impurities Ferritic alloy with excellent weldability with austenitic stainless steel sheet, characterized by having CuS deposited as a core with MnS of 1 μm or less or adjacent to MnS of 1 μm or less Provide stainless steel sheet.
本発明のフェライト系ステンレス鋼板では、1μm以下の大きさのMnSのうち、50%以上のMnSにCuが検出されることと、CuSが1μm以下の大きさのMnSを核として、あるいは1μm以下の大きさのMnSに隣接して析出していることがほぼ等価である。 In the ferritic stainless steel sheet of the present invention, Cu is detected in 50% or more of MnS of MnS having a size of 1 μm or less, and CuS is a core of MnS having a size of 1 μm or less, or 1 μm or less. It is almost equivalent to depositing adjacent to the size of MnS.
本発明のフェライト系ステンレス鋼板は、上記の成分組成を有するスラブを、1000℃以上に加熱後、仕上温度800℃以上1000℃未満で熱間圧延を行い、巻取温度400℃以上で巻取った後、熱延板焼鈍を行うことを特徴とする方法により製造できる。 The ferritic stainless steel sheet of the present invention was heated at a finishing temperature of 800 ° C. or higher and lower than 1000 ° C. after being heated to 1000 ° C. or higher after the slab having the above component composition, and wound at a winding temperature of 400 ° C. or higher. Then, it can manufacture by the method characterized by performing a hot-rolled sheet annealing.
なお、熱延板焼鈍後、さらに冷間圧延、再結晶焼鈍を行って冷延鋼板とすることもできる。 In addition, after hot-rolled sheet annealing, cold rolling and recrystallization annealing can be further performed to obtain a cold-rolled steel sheet.
本発明により、オーステナイト系ステンレス鋼板との溶接性、特に、溶接部の耐食性に優れるフェライト系ステンレス鋼板を製造できるようになった。 According to the present invention, it is possible to produce a ferritic stainless steel sheet having excellent weldability with an austenitic stainless steel sheet, in particular, excellent corrosion resistance of a welded portion.
以下に、本発明であるオーステナイト系ステンレス鋼板との溶接部の耐食性に優れるフェライト系ステンレス鋼板およびその製造方法について詳述する。 Below, the ferritic stainless steel plate which is excellent in the corrosion resistance of a welded part with the austenitic stainless steel plate which is this invention, and its manufacturing method are explained in full detail.
1)成分組成(以下の「%」は、「質量%」を表す。)
C≦0.012%
Cは、Crと結合して固溶Cr量を減じるため、耐食性を劣化させる。そのため、本願発明では、Nbを添加してCを炭窒化物として析出させるが、C量が0.012%を超えると、Nbの多量添加が必要になり、脆いCrとの金属間化合物などの硬質相が生成するため、C量は0.012%以下とする。
1) Component composition ("%" below represents "% by mass")
C ≦ 0.012%
C combines with Cr to reduce the amount of solid solution Cr, thus deteriorating corrosion resistance. Therefore, in the present invention, Nb is added to precipitate C as carbonitride, but if the amount of C exceeds 0.012%, a large amount of Nb is required and a hard phase such as an intermetallic compound with brittle Cr is required. Therefore, the C content is 0.012% or less.
Si≦0.3%
Siは、鋼の固溶強化元素であり、その量が0.3%を超えると、鋼が硬質低延性化するので、Si量は0.3％以下とする。
Si ≦ 0.3%
Si is a solid solution strengthening element of steel, and if its amount exceeds 0.3%, the steel becomes hard and ductile, so the Si amount is 0.3% or less.
0.1%≦Mn≦0.3%
Mnは、MnSを形成して発錆の起点となって溶接部の耐食性を劣化させる。そのため、本願発明では、1μm以下の大きさのMnSの周辺にCuSを析出させて、MnSを起点とした発錆に起因する溶接部の耐食性の劣化を防止する。Mn量が0.1%未満では、FeSの生成による熱間脆性を回避できず、表面性状が劣化する。また、Mn量が0.3%を超えると、CuSの析出量が少なくなり、溶接部の耐食性の劣化を防止できない。このため、Mn量は0.1%以上0.3%以下とする。
0.1% ≦ Mn ≦ 0.3%
Mn forms MnS and becomes a starting point of rusting, thereby deteriorating the corrosion resistance of the weld. Therefore, in the present invention, CuS is deposited around MnS having a size of 1 μm or less to prevent deterioration of the corrosion resistance of the weld due to rusting starting from MnS. If the Mn content is less than 0.1%, hot brittleness due to the formation of FeS cannot be avoided, and the surface properties deteriorate. On the other hand, if the Mn content exceeds 0.3%, the amount of CuS deposited decreases, and deterioration of the corrosion resistance of the weld cannot be prevented. For this reason, the amount of Mn shall be 0.1% or more and 0.3% or less.
P≦0.04%
Pは、鋼を固溶強化するとともに、粒界に偏析して鋼を脆化する。P量が0.04%を超えると、鋼の脆化が顕著に現れるので、P量の上限は0.04%とする。
P ≦ 0.04%
P solidifies and strengthens the steel and segregates at the grain boundaries to embrittle the steel. If the P content exceeds 0.04%, the embrittlement of the steel appears remarkably, so the upper limit of the P content is 0.04%.
S≦0.01%
Sは、耐食性を劣化させるMnSとそれを防止するCuSとして析出し、両者のバランスにより溶接部の耐食性の劣化が防止される。S量が0.01%を超えると、1μmを超える大きさの粗大なMnSの析出量が多くなり、CuSによる耐食性の劣化を防止できなくなる。このため、S量は0.01%以下とする。
S ≦ 0.01%
S precipitates as MnS that degrades corrosion resistance and CuS that prevents it, and the balance between both prevents deterioration of the corrosion resistance of the weld. When the amount of S exceeds 0.01%, the amount of coarse MnS having a size exceeding 1 μm increases, and it becomes impossible to prevent the corrosion resistance from being deteriorated by CuS. Therefore, the S content is 0.01% or less.
Al≦0.08%
Alは脱酸剤として働き、鋼の清浄度を向上させる。そのため、Al量は0.02%以上含有させることが望ましい。しかし、Al量が0.08%を超えると、AlNが微細に析出して鋼を硬質低延性化する。このため、Al量は0.08%以下とする。
Al ≦ 0.08%
Al acts as a deoxidizer and improves the cleanliness of the steel. Therefore, the Al content is desirably 0.02% or more. However, when the Al content exceeds 0.08%, AlN precipitates finely and makes the steel hard and ductile. For this reason, the Al content is 0.08% or less.
N≦0.012%
Nは、Crと結合して固溶Cr量を減じるため、耐食性を劣化させる。そのため、本願発明では、Nbを添加してNを炭窒化物として析出させるが、N量が0.012%を超えると、Nbの添加量の増大や多量のAlNの析出を避けられず、鋼が硬質化する。このため、N量の上限は0.012%以下とする。
N ≦ 0.012%
N combines with Cr to reduce the amount of solid solution Cr, thus deteriorating corrosion resistance. Therefore, in the present invention, Nb is added to precipitate N as carbonitride, but if the amount of N exceeds 0.012%, an increase in the amount of Nb added or precipitation of a large amount of AlN cannot be avoided, and the steel is hard. Turn into. For this reason, the upper limit of the N amount is set to 0.012% or less.
Ti≦0.01%
Tiは、TiSとして析出し、発錆起点となる。発錆が問題とならないようにするには、Ti量を0.01%以下とする必要がある。
Ti ≦ 0.01%
Ti precipitates as TiS and becomes a starting point for rusting. In order to prevent rusting from becoming a problem, the Ti content needs to be 0.01% or less.
0.35%≦Nb≦0.7%
上述したように、Nbは、C、Nと結合し炭窒化物を形成する。Nb量が0.35%未満だと、オーステナイト系ステンレス鋼板から拡散してくる多量のC、NをNbの炭窒化物として析出できず、Crの炭窒化物が生成して、耐食性が著しく劣化する。一方、Nb量が0.7%を超えると、Crとの金属間化合物が生成しやすくなり、鋼の脆化を招く。このため、Nb量は0.35%以上0.7%以下とする。
0.35% ≦ Nb ≦ 0.7%
As described above, Nb combines with C and N to form carbonitride. If the Nb content is less than 0.35%, a large amount of C and N diffusing from the austenitic stainless steel sheet cannot be precipitated as Nb carbonitrides, and Cr carbonitrides are formed, resulting in a significant deterioration in corrosion resistance. On the other hand, when the Nb content exceeds 0.7%, an intermetallic compound with Cr is likely to be generated, which causes embrittlement of the steel. Therefore, the Nb content is set to 0.35% or more and 0.7% or less.
20.5%≦Cr≦23.5%
Crは、ステンレス鋼表面に不動態被膜を形成し、ステンレス鋼特有の耐食性を付与する元素である。例えば、SUS430に代表される通常のフェライト系ステンレス鋼板には、18%程度のCrが含有されるが、オーステナイト系ステンレス鋼板との溶接部では、多量のC、Nが存在するので、Cr量は20.5%以上とする必要がある。一方、Cr量が23.5%を超えると、NbとCrの金属間化合物が生成しやすくなり、鋼の脆化を招く。このため、Cr量は20.5%以上23.5%以下とする。
20.5% ≦ Cr ≦ 23.5%
Cr is an element that forms a passive film on the surface of stainless steel and imparts corrosion resistance unique to stainless steel. For example, a normal ferritic stainless steel sheet represented by SUS430 contains about 18% of Cr, but a large amount of C and N exist in the welded part with an austenitic stainless steel sheet, so the Cr amount is It needs to be 20.5% or more. On the other hand, if the Cr content exceeds 23.5%, an intermetallic compound of Nb and Cr is likely to be formed, resulting in embrittlement of the steel. Therefore, the Cr content is 20.5% or more and 23.5% or less.
0.3%≦Cu≦0.8%
上述したように、Cuは、1μm以下の大きさのMnSの周辺にCuSとして析出し、MnSを起点とした発錆に起因する溶接部の耐食性の劣化を防止する。Cu量が0.3%未満だと、CuSの析出が起こりにくくなり、0.8%を超えると、鋼中にCuが析出して、鋼板を著しく硬質化する。このため、Cu量は0.3%以上0.8%以下とする。
0.3% ≦ Cu ≦ 0.8%
As described above, Cu precipitates as CuS around MnS having a size of 1 μm or less, and prevents deterioration of the corrosion resistance of the weld due to rusting starting from MnS. If the amount of Cu is less than 0.3%, CuS hardly precipitates, and if it exceeds 0.8%, Cu precipitates in the steel, and the steel sheet is remarkably hardened. For this reason, the amount of Cu shall be 0.3% or more and 0.8% or less.
残部は、Feおよび不可避的不純物である。不可避的不純物として、Ni≦0.5%、B≦0.001%、Mo≦0.1%、V≦0.05%、Mg<0.005%、Ca≦0.01%などが混入しても、本発明の効果が妨げられることはない。なお、これらの元素は少ないほど好ましい。 The balance is Fe and inevitable impurities. Even if Ni ≦ 0.5%, B ≦ 0.001%, Mo ≦ 0.1%, V ≦ 0.05%, Mg <0.005%, Ca ≦ 0.01%, etc. are mixed as unavoidable impurities, the effect of the present invention may be hindered. Absent. In addition, these elements are so preferable that there are few.
2)CuSの析出状態
上述したように、1μm以下の大きさのMnSの周辺にCuSを析出させると、MnSを起点とした発錆に起因する溶接部の耐食性の劣化が防止される。これは、次のように考えられる。すなわち、溶接部が腐食環境下に置かれると、そこに存在するMnSが最初に溶解し、発錆の起点となって、そこから孔食が生じ、不動態被膜の破壊へと進行し、耐食性の劣化を引き起こす。しかし、MnSの周辺にCuSが存在すると、CuSも腐食環境下で溶解し、Cuイオンを排出して、電気化学的に腐食の進行を食い止めることができる。なお、CuSを析出させるMnSの大きさが1μmを超えると、MnSを核としたCuSの析出が生じにくくなるばかりか、MnSを核として析出したCuSからのCuイオン排出による腐食進行の防止効果がなくなる。このため、溶接部の耐食性の劣化を防止できなくなるので、1μm以下とする必要がある。
2) Precipitation state of CuS As described above, when CuS is deposited around MnS having a size of 1 μm or less, deterioration of the corrosion resistance of the weld due to rusting starting from MnS is prevented. This is considered as follows. That is, when the weld is placed in a corrosive environment, the MnS present there dissolves first and becomes the starting point of rusting, resulting in pitting corrosion, progressing to the destruction of the passive film, and corrosion resistance. Cause deterioration. However, if CuS is present in the vicinity of MnS, CuS can also be dissolved in a corrosive environment, and Cu ions can be discharged to electrochemically stop the progress of corrosion. In addition, when the size of MnS for depositing CuS exceeds 1 μm, not only CuS precipitation with MnS as a nucleus is difficult to occur, but also the effect of preventing the progress of corrosion due to Cu ion discharge from CuS deposited with MnS as a nucleus. Disappear. For this reason, it becomes impossible to prevent the deterioration of the corrosion resistance of the welded portion, so it is necessary to make it 1 μm or less.
MnSの周辺にCuSを析出させるには、MnSを核として、CuSを析出させてもよいし、あるいはMnSに隣接してCuSを析出させてもよい。なお、透過電子顕微鏡で観察して、観測される1μm以下のMnSの50%以上にCuSが接して析出していれば、本発明の効果が得られることを確認している。 In order to deposit CuS around MnS, CuS may be deposited using MnS as a nucleus, or CuS may be deposited adjacent to MnS. It has been confirmed by observation with a transmission electron microscope that the effect of the present invention can be obtained if CuS is deposited in contact with 50% or more of MnS of 1 μm or less observed.
3)製造条件
上述したように、本発明のフェライト系ステンレス鋼板は、例えば、上記の成分組成を有するスラブを、1000℃以上に加熱後、仕上温度800℃以上1000℃未満で熱間圧延を行い、巻取温度400℃以上で巻取った後、熱延板焼鈍を行う、あるいは、その後さらに冷間圧延、再結晶焼鈍を行うことにより製造できる。
3) Manufacturing conditions As described above, the ferritic stainless steel sheet of the present invention is, for example, hot-rolled at a finishing temperature of 800 ° C. or more and less than 1000 ° C. after heating a slab having the above component composition to 1000 ° C. or more. It can be produced by winding at a coiling temperature of 400 ° C. or higher and then performing hot-rolled sheet annealing, or further performing cold rolling and recrystallization annealing.
スラブの加熱温度
熱間圧延に先立つスラブの加熱温度が1000℃を下回ると、MnSが溶解しないまま熱間圧延されて、粗大に展伸したMnSが形成され、CuSが隣接しないMnSの部分が多くなり、耐食性の劣化を招く。このため、スラブの加熱温度は1000℃以上とする。
Slab heating temperature When the slab heating temperature prior to hot rolling falls below 1000 ° C, MnS is hot-rolled without melting, forming coarsely expanded MnS, and there are many parts of MnS where CuS is not adjacent Thus, the corrosion resistance is deteriorated. For this reason, the heating temperature of a slab shall be 1000 degreeC or more.
熱間圧延の仕上温度
熱間圧延の仕上温度が800℃を下回ると、MnSが圧延方向に長く展伸しやすくなり、上記の場合と同様に、CuSが隣接しないMnSが多くなり、耐食性の劣化を招く。また、ロールと鋼板の摩擦力が大きくなり、表面性状も劣化して、ステンレス鋼特有の光沢と耐食性を具備する表面が得られにくくなる。一方、仕上温度が1000℃以上だと、熱間圧延中にMnSが粗大化しやすくなり、1μm以下のMnSが得られなくなる。このため、熱間圧延の仕上温度は800℃以上1000℃未満とする。
Finishing temperature of hot rolling When the finishing temperature of hot rolling is below 800 ° C, MnS tends to extend in the rolling direction for a long time, and as in the case above, there is more MnS that is not adjacent to CuS, resulting in degraded corrosion resistance. Invite. In addition, the frictional force between the roll and the steel sheet is increased, the surface properties are deteriorated, and it becomes difficult to obtain a surface having gloss and corrosion resistance peculiar to stainless steel. On the other hand, if the finishing temperature is 1000 ° C. or higher, MnS tends to be coarsened during hot rolling, and MnS of 1 μm or less cannot be obtained. For this reason, the finishing temperature of hot rolling shall be 800 degreeC or more and less than 1000 degreeC.
巻取温度
巻取温度は、CuSの析出制御に重要である。巻取温度が400℃を下回ると、CuSが析出しなくなり、CuSが核にしてまたは隣接して析出している1μm以下のMnS量が50%を下回り、耐食性の劣化を防止できなくなる。このため、巻取温度は400℃以上とする。なお、熱延板の形状が劣化しないように、巻取温度は450℃以上とすることが好ましい。
Winding temperature Winding temperature is important for CuS precipitation control. When the coiling temperature is lower than 400 ° C., CuS does not precipitate, and the amount of MnS of 1 μm or less deposited in or adjacent to the nucleus is less than 50%, and deterioration of corrosion resistance cannot be prevented. For this reason, the coiling temperature is set to 400 ° C. or higher. The coiling temperature is preferably 450 ° C. or higher so that the shape of the hot-rolled plate does not deteriorate.
巻取り後の熱延板には、熱延板焼鈍を行い、さらに通常のステンレス鋼板に対する酸洗によりスケールを除去して熱延鋼板の製品とすることができる。また、熱延板焼鈍後、さらに冷間圧延、再結晶焼鈍が行って、冷延鋼板の製品とすることもできる。なお、熱延板焼鈍、冷間圧延、再結晶焼鈍の条件は、通常のステンレス鋼板に適用される条件と同じでよい。熱延板焼鈍後あるいは再結晶焼鈍後は、鋼板形状や表面粗さを整えることを目的として調質圧延を行うことが好ましい。調質圧延の伸長率は0.5%以上1.5%以下とすることが望ましい。 The hot-rolled sheet after winding can be subjected to hot-rolled sheet annealing, and the scale can be removed by pickling a normal stainless steel sheet to obtain a hot-rolled sheet product. Further, after hot-rolled sheet annealing, cold rolling and recrystallization annealing can be further performed to obtain a cold-rolled steel sheet product. In addition, the conditions of hot-rolled sheet annealing, cold rolling, and recrystallization annealing may be the same as the conditions applied to a normal stainless steel plate. After hot-rolled sheet annealing or after recrystallization annealing, temper rolling is preferably performed for the purpose of adjusting the shape of the steel sheet and the surface roughness. The elongation of temper rolling is preferably 0.5% or more and 1.5% or less.
表1に示す化学成分の鋼1〜24を溶製し、表1に示す熱延条件で熱間圧延を行い、板厚5mmの熱延板を作製した。この熱延板を950℃で熱延板焼鈍し、酸洗後、冷間圧延を行い、板厚1.2mmの冷延板とし、この冷延板を910℃で再結晶焼鈍した。そして、焼鈍後の冷延板を片面0.5mm研削を行い、板厚中央より抽出レプリカで析出物を抽出し、分析機能付き透過電子顕微鏡で観察し、100個以上の1μm以下のMnSのうちCuの検出されたMnSの割合を求めた。また、圧延方向に沿ってJIS 13号B引張試験片を採取し、引張試験を行って、機械的性質(引張強度TSと伸びEl)を求めた。ここで、Elが30%未満の場合は、次の試験で耐食性が良好であっても本発明外(比較例)とした。さらに、オーステナイト系ステンレス鋼板SUS304(C:0.05%、S:0.005%、N:0.05%、Cr:18%、Ni:8%)と突き合わせてTIG溶接し、溶接部(ビード部)の片面を＃600研磨後、10サイクル塩水噴霧と乾燥を繰り返すJASO-CCTサイクル腐食試験(1CCTサイクル：5%NaCl塩水噴霧、35℃×2hr→乾燥、60℃×4hr→RH95%湿潤雰囲気、50℃×2hr)を行い、発錆の有無を目視で観察した。そして、顕著な赤錆が認められない場合を耐食性が良好(○)、著しい赤錆が認めらる場合を耐食性が劣る(×)の2段階の評価を行った。 Steels 1 to 24 having chemical components shown in Table 1 were melted and hot-rolled under the hot rolling conditions shown in Table 1 to produce hot-rolled sheets having a thickness of 5 mm. This hot-rolled sheet was subjected to hot-rolled sheet annealing at 950 ° C., pickled and cold-rolled to obtain a cold-rolled sheet having a thickness of 1.2 mm, and this cold-rolled sheet was subjected to recrystallization annealing at 910 ° C. Then, the annealed cold-rolled plate is ground 0.5 mm on one side, the precipitate is extracted with an extraction replica from the center of the plate thickness, and observed with a transmission electron microscope with an analytical function. Of 100 MnS of 1 μm or less, Cu The percentage of MnS detected was determined. In addition, JIS 13B tensile test pieces were collected along the rolling direction and subjected to a tensile test to obtain mechanical properties (tensile strength TS and elongation El). Here, when El was less than 30%, it was regarded as outside of the present invention (comparative example) even if the corrosion resistance was good in the next test. Furthermore, austenitic stainless steel plate SUS304 (C: 0.05%, S: 0.005%, N: 0.05%, Cr: 18%, Ni: 8%) was butted and TIG welded, and one side of the welded part (bead part) was # JASO-CCT cycle corrosion test that repeats 10 cycles of salt spray and drying after 600 polishing (1CCT cycle: 5% NaCl salt spray, 35 ℃ × 2hr → dry, 60 ℃ × 4hr → RH95% wet atmosphere, 50 ℃ × 2hr) And the presence or absence of rusting was visually observed. Then, a two-stage evaluation was performed, in which corrosion resistance was good (◯) when significant red rust was not observed, and corrosion resistance was poor (x) when significant red rust was observed.
結果を表2に示す。本発明の成分組成を有し、かつCuSのMnSに対する析出状態が本発明の条件を満足する鋼1〜4、6〜8、11〜13、16、17、19、20、22では、赤錆が認められず、溶接部の耐食性が良好であり、かつ30%以上のElが得られることがわかる。なお、鋼14、18は、いずれも優れた溶接部の耐食性を有するが、鋼14では、Cu量が本発明範囲を超えているため、鋼18では、Nb量が本発明範囲を超えているため、30%未満のElしか得られない。また、鋼15では、CuSのMnSに対する析出状態は本発明の条件を満足しているが、Nb量が本発明範囲を下回るため、Crの炭窒化物が生成して、耐食性に劣っている。 The results are shown in Table 2. In steels 1-4, 6-8, 11-13, 16, 17, 19, 20, 22 having the composition of the present invention and the precipitation state of CuS with respect to MnS satisfying the conditions of the present invention, red rust is present. It is not recognized that the corrosion resistance of the welded portion is good and El of 30% or more is obtained. Steels 14 and 18 both have excellent corrosion resistance of the welded portion. However, in Steel 14, the amount of Cu exceeds the range of the present invention, so in Steel 18, the amount of Nb exceeds the range of the present invention. Therefore, only less than 30% El can be obtained. In Steel 15, the precipitation state of CuS with respect to MnS satisfies the conditions of the present invention. However, since the Nb content is below the range of the present invention, Cr carbonitrides are formed and the corrosion resistance is poor.
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| KR101663207B1 (en) | 2013-03-27 | 2016-10-06 | 닛폰 스틸 앤드 스미킨 스테인레스 스틸 코포레이션 | Ferritic stainless steel with excellent surface corrosion resistance after polishing, and process for producing same |
| JP2017186665A (en) * | 2016-03-30 | 2017-10-12 | 日新製鋼株式会社 | Nb-CONTAINING FERRITIC STAINLESS STEEL SHEET AND MANUFACTURING METHOD THEREFOR |
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