JP2013204059A - Heat-resistant ferritic stainless steel sheet with high weldability - Google Patents
Heat-resistant ferritic stainless steel sheet with high weldability Download PDFInfo
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- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 22
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 12
- 239000012535 impurity Substances 0.000 claims abstract description 4
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 4
- 229910052721 tungsten Inorganic materials 0.000 claims abstract description 4
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 4
- 229910052726 zirconium Inorganic materials 0.000 claims abstract description 4
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 229910052718 tin Inorganic materials 0.000 claims description 3
- 229910052758 niobium Inorganic materials 0.000 abstract description 12
- 229910052757 nitrogen Inorganic materials 0.000 abstract description 2
- 229910052802 copper Inorganic materials 0.000 abstract 1
- 229910052748 manganese Inorganic materials 0.000 abstract 1
- 229910000831 Steel Inorganic materials 0.000 description 24
- 239000010959 steel Substances 0.000 description 24
- 238000005336 cracking Methods 0.000 description 19
- 230000000694 effects Effects 0.000 description 16
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- 238000007254 oxidation reaction Methods 0.000 description 14
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- 238000005260 corrosion Methods 0.000 description 11
- 238000005728 strengthening Methods 0.000 description 11
- 238000004519 manufacturing process Methods 0.000 description 10
- 238000012360 testing method Methods 0.000 description 10
- 238000003466 welding Methods 0.000 description 9
- 238000000137 annealing Methods 0.000 description 8
- 238000000034 method Methods 0.000 description 8
- 238000001556 precipitation Methods 0.000 description 8
- 230000007423 decrease Effects 0.000 description 6
- 238000005204 segregation Methods 0.000 description 6
- 238000005098 hot rolling Methods 0.000 description 5
- 238000005096 rolling process Methods 0.000 description 5
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000006104 solid solution Substances 0.000 description 4
- 238000005097 cold rolling Methods 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 238000007670 refining Methods 0.000 description 3
- 239000010935 stainless steel Substances 0.000 description 3
- 238000009628 steelmaking Methods 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 229910000765 intermetallic Inorganic materials 0.000 description 2
- 229910001068 laves phase Inorganic materials 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- 229910001018 Cast iron Inorganic materials 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000005496 eutectics Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
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- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
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Abstract
Description
本発明は、特に高温強度や耐酸化性が必要な排気系部材などの使用に最適な溶接性に優れた耐熱フェライト系ステンレス鋼板に関するものである。 The present invention relates to a heat-resistant ferritic stainless steel sheet having excellent weldability that is optimal for use in exhaust system members that require particularly high-temperature strength and oxidation resistance.
自動車の排気マニホールド、フロントパイプおよびセンターパイプなどの排気系部材は、エンジンから排出される高温の排気ガスを通すため、排気部材を構成する材料には耐酸化性、高温強度、熱疲労特性など多様な特性が要求される。 Exhaust system members such as automobile exhaust manifolds, front pipes, and center pipes pass high-temperature exhaust gas exhausted from the engine, so the materials that make up the exhaust members have various characteristics such as oxidation resistance, high-temperature strength, and thermal fatigue characteristics. Is required.
従来、自動車排気部材には鋳鉄が使用されるのが一般的であったが、排ガス規制の強化、エンジン性能の向上、車体軽量化などの観点から、ステンレス鋼製の排気マニホールドが使用されるようになった。排ガス温度は車種やエンジン構造によって異なるが、６００〜８００℃程度が多く、このような温度域で長時間使用される環境において高い高温強度、耐酸化性を有する材料が要望されている。 Conventionally, cast iron is generally used for automobile exhaust members, but stainless steel exhaust manifolds are likely to be used from the viewpoints of strengthening exhaust gas regulations, improving engine performance, and reducing vehicle weight. Became. Although the exhaust gas temperature varies depending on the vehicle type and engine structure, it is often about 600 to 800 ° C., and a material having high high-temperature strength and oxidation resistance in an environment used for a long time in such a temperature range is desired.
ステンレス鋼の中でオーステナイト系ステンレス鋼は、耐熱性や加工性に優れているが、熱膨張係数が大きいために、排気マニホールドのように加熱・冷却を繰り返し受ける部材に適用した場合、熱疲労破壊が生じやすい。 Among stainless steels, austenitic stainless steel has excellent heat resistance and workability, but due to its large thermal expansion coefficient, thermal fatigue failure occurs when applied to a member that repeatedly receives heating and cooling, such as an exhaust manifold. Is likely to occur.
一方、フェライト系ステンレス鋼は、オーステナイト系ステンレス鋼に比べて熱膨張係数が小さいため、熱疲労特性や耐スケール剥離性に優れている。また、オーステナイト系ステンレス鋼に比べて、Ｎｉを含有しないため材料コストも安く、汎用的に使用されている。但し、フェライト系ステンレス鋼は、オーステナイト系ステンレス鋼に比べて、高温強度が低いために、高温強度を向上させる技術が開発されてきた。例えば、ＳＵＳ４３０Ｊ１（Ｎｂ添加鋼）、Ｎｂ−Ｓｉ添加鋼、ＳＵＳ４４４（Ｎｂ−Ｍｏ添加鋼）があり、いずれもＮｂ添加が前提となっている。これは、Ｎｂによる固溶強化あるいは析出強化によって高温強度を高くするものであった。 On the other hand, since ferritic stainless steel has a smaller thermal expansion coefficient than austenitic stainless steel, it is excellent in thermal fatigue characteristics and scale peel resistance. Further, compared with austenitic stainless steel, it does not contain Ni, so the material cost is low and it is used for general purposes. However, since ferritic stainless steel has lower high-temperature strength than austenitic stainless steel, a technique for improving high-temperature strength has been developed. For example, there are SUS430J1 (Nb-added steel), Nb-Si-added steel, and SUS444 (Nb-Mo-added steel), all of which are premised on Nb addition. This increased the high-temperature strength by solid solution strengthening or precipitation strengthening with Nb.
しかし、Ｎｂ添加により製造コストも上昇するため、Ｎｂ以外の添加元素によって高温特性を確保できればＮｂ添加量を抑えることができ、低コストで加工性に優れた耐熱フェライト系ステンレス鋼板を提供することが可能になる。ＳＵＳ４４４に添加されているＭｏも合金コストが高いため、部品コストが著しく上昇する課題も生じる。 However, since the manufacturing cost also increases due to the addition of Nb, the amount of Nb added can be suppressed if high temperature characteristics can be secured by an additive element other than Nb, and a heat-resistant ferritic stainless steel sheet having excellent workability at low cost can be provided. It becomes possible. Since Mo added to SUS444 also has a high alloy cost, there is a problem that the component cost is significantly increased.
ＮｂやＭｏ以外に高温強度向上に寄与する合金として、特許文献１〜４では、Ｎｂの他にＣｕを添加し、Ｃｕ析出物による析出強化を利用して６００℃あるいは７００〜８００℃の温度域における高温強度を向上させる技術が開示されている。 In addition to Nb and Mo, in Patent Documents 1 to 4, Cu is added in addition to Nb as an alloy that contributes to improving high-temperature strength, and a temperature range of 600 ° C. or 700 to 800 ° C. is utilized by precipitation strengthening by Cu precipitates. A technique for improving the high-temperature strength is disclosed.
Ｎｂ含有鋼は耐熱性に優れた鋼であるが、溶接において、ときどき、高温割れを引き起こすことがあった。また、ＥＲＷ管造管時においても高温割れが発生することがあり、解決策の提案が期待されていた。 Nb-containing steel is a steel excellent in heat resistance, but sometimes causes hot cracking during welding. In addition, hot cracking may occur even during ERW pipe making, and a proposal for a solution has been expected.
本発明は、特に高温強度や耐酸化性が必要な排気系部材などの使用に最適な、溶接性に優れたフェライト系ステンレス鋼を提供するものである。 The present invention provides a ferritic stainless steel excellent in weldability, which is most suitable for use in exhaust system members that particularly require high-temperature strength and oxidation resistance.
本発明では、Ｎｂ添加鋼の耐高温割れ性を改善することを目的とし、種々に検討を行った結果、高温割れは液化割れであり、粒界で割れが発生しており、その粒界部には、ＮｂとＰの偏析が見られる等の知見を得た。つまり、ＮｂとＰの影響で高温割れが発生していると考えられる。このメカニズムは明らかでないが、以下のように考えている。 In the present invention, for the purpose of improving the hot cracking resistance of the Nb-added steel, various investigations have been made. As a result, the hot crack is a liquefied crack, and cracks are generated at the grain boundaries. Obtained the knowledge that segregation of Nb and P was observed. That is, it is considered that hot cracking has occurred under the influence of Nb and P. This mechanism is not clear, but I think as follows.
鋼中にＮｂとＰが共存すると、溶接時に高温に曝された時に、相互の粒界偏析を助長し、その結果、粒界に低融点のリン化物が生成され、このリン化物と母相の共晶融解により粒界に液相が生成し、溶接時に負荷された応力により液化割れが発生する。 The coexistence of Nb and P in the steel promotes mutual grain boundary segregation when exposed to high temperatures during welding, resulting in the formation of low melting point phosphides at the grain boundaries. A liquid phase is generated at the grain boundary due to eutectic melting, and liquefaction cracking occurs due to stress applied during welding.
また、Ｓがこの偏析を助長する傾向にあること、および、Ｂがこの偏析を抑制する方向にあることが判明した。さらには、Ｙ、希土類元素もこの偏析を助長する傾向にあることは分かった。 It has also been found that S tends to promote this segregation and that B tends to suppress this segregation. Furthermore, it was found that Y and rare earth elements also tend to promote this segregation.
しかしながら、Ｎｂは耐熱性を向上させる重要な元素であり、単純にＮｂ添加量を低減することは耐熱性を低下させることになる。したがって、発明者らは、Ｎｂを出来るだけ低減しない方法を検討するとともに、耐熱性の観点から、Ｎｂを代替できる元素として析出強化により耐熱性を向上させるＣｕを選択した。 However, Nb is an important element for improving the heat resistance, and simply reducing the amount of Nb added decreases the heat resistance. Therefore, the inventors examined a method that does not reduce Nb as much as possible, and selected Cu that improves heat resistance by precipitation strengthening as an element that can replace Nb from the viewpoint of heat resistance.
そこで、発明者らは、Ｃｕを添加し、Ｓ量を抑制し、Ｂを添加した種々のＮｂ添加鋼について、高温割れ性を、その評価試験方法であるトランスバレストレイン試験で評価した。図１は、１５Ｃｒ−１．２Ｃｕ−０．００１Ｓ−０．００１ＢをベースにＮｂとＰ量を変えた鋼をバレストレイン試験を行った結果をＮｂ量とＰ量で整理したものである。図中の「○」「×」の評価条件は、実施例の記述で詳述するが、本実験では付加歪量を１．６％の試験で発生した割れの、最大割れ長さ１ｍｍ以下、かつ、総割れ長さ５ｍｍ以下を、耐高温割れ性が良好（○）、それ以外を不良（×）とした。Ｎｂ量とＰ量の総量が多いほど、耐高温割れ性は低位にあることが分かった。また、大凡であるが、Ｐ［％］が、−０．０５×Ｎｂ［％］＋０．０４より小さければ、即ち、
Ｐ［％］≦−０．０５×Ｎｂ［％］＋０．０４ 式（１）
を満足すれば、耐高温割れ性は向上し、溶接時の高温割れがほぼ防止できることが判明した。
Therefore, the inventors evaluated the hot cracking property of various Nb-added steels to which Cu was added, the amount of S was suppressed, and B was added by a transbaretrain test, which is an evaluation test method thereof. FIG. 1 is a summary of the results of a ballast train test performed on steels with Nb and P contents varied based on 15Cr-1.2Cu-0.001S-0.001B based on Nb contents and P contents. The evaluation conditions of “O” and “X” in the figure are described in detail in the description of the examples, but in this experiment, the maximum crack length of 1 mm or less of the crack generated in the test with an additional strain amount of 1.6%, In addition, the total crack length of 5 mm or less was defined as good hot cracking resistance (◯), and the other was regarded as defective (x). It was found that the higher the total amount of Nb and P, the lower the hot crack resistance. In general, if P [%] is smaller than −0.05 × Nb [%] + 0.04, that is,
P [%] ≦ −0.05 × Nb [%] + 0.04 Formula (1)
If it satisfies, it has been found that the resistance to hot cracking is improved and hot cracking during welding can be substantially prevented.
発明者らは、この知見をさらに発展させて、耐高温割れ性を向上させた溶接性に優れた耐熱フェライト系ステンレス鋼を発明した。 The inventors further developed this knowledge and invented a heat-resistant ferritic stainless steel with improved hot cracking resistance and excellent weldability.
上記課題を解決する本発明の要旨は、以下のとおりである。
（１） 質量％にて、
Ｃ：０．０２％以下、
Ｎ：０．０２％以下、
Ｓｉ：２％以下、
Ｍｎ：２％以下、
Ｐ：０．００５以上０．０２５％以下
かつ、Ｐ［％］≦−０．０５×Ｎｂ［％］＋０．０４
Ｓ：０．００２％未満
Ｃｒ：１０超〜２０％、
Ｃｕ：０．４〜３％、
Ｎｂ：０．０５〜０．６％
Ｔｉ：０．００５〜０．２５％、
Ａｌ：０．２％以下
Ｂ：０．０００２〜０．００３０％
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に優れた耐熱フェライト系ステンレス鋼板。
（２） 質量％にて、Ｍｏ：０．０１〜１％、Ｗ：１％以下、Ｖ：１％以下、Ｃｏ：１％以下、Ｎｉ：０．５％以下、Ｚｒ：１％以下、Ｓｎ：０．３％以下の１種または２種以上を含有することを特徴とする（１）の耐熱性と加工性に優れたフェライト系ステンレス鋼板。
The gist of the present invention for solving the above problems is as follows.
(1) In mass%
C: 0.02% or less,
N: 0.02% or less,
Si: 2% or less,
Mn: 2% or less,
P: 0.005 to 0.025% and P [%] ≦ −0.05 × Nb [%] + 0.04
S: less than 0.002% Cr: more than 10 to 20%,
Cu: 0.4-3%,
Nb: 0.05 to 0.6%
Ti: 0.005 to 0.25%,
Al: 0.2% or less B: 0.0002 to 0.0030%
A heat-resistant ferritic stainless steel sheet excellent in weldability, characterized in that the balance is made of Fe and inevitable impurities.
(2) In mass%, Mo: 0.01 to 1%, W: 1% or less, V: 1% or less, Co: 1% or less, Ni: 0.5% or less, Zr: 1% or less, Sn : Ferritic stainless steel sheet excellent in heat resistance and workability of (1), characterized by containing one or more of 0.3% or less.
本発明によれば、溶接性に優れた耐熱フェライト系ステンレス鋼板が得られ、部品加工における溶接時のトラブルを回避できる。 According to the present invention, a heat-resistant ferritic stainless steel sheet having excellent weldability can be obtained, and troubles during welding in parts processing can be avoided.
ここで、下限の規定がないものについては、不可避的不純物レベルまで含むことを示す。 Here, for the case where the lower limit is not specified, it indicates that an inevitable impurity level is included.
以下に本発明の限定理由について説明する。 The reason for limitation of the present invention will be described below.
Ｃは、成形性と耐食性を劣化させ、高温強度の低下をもたらすため、その含有量は少ないほど良いため、０．０２％以下とした。但し、過度の低減は精錬コストの増加に繋がるため、０．００１〜０．００９％が望ましい。 C deteriorates moldability and corrosion resistance and causes a decrease in high-temperature strength. Therefore, the smaller the content, the better. Therefore, the C content is set to 0.02% or less. However, excessive reduction leads to an increase in refining costs, so 0.001 to 0.009% is desirable.
ＮはＣと同様、成形性と耐食性を劣化させ、高温強度の低下をもたらすため、その含有量は少ないほど良いため、０．０２％以下とした。但し、過度の低減は精錬コストの増加に繋がるため、０．００３〜０．０１５％が望ましい。 N, like C, deteriorates moldability and corrosion resistance and brings about a decrease in high-temperature strength. Therefore, the smaller the content, the better. Therefore, the N content is set to 0.02% or less. However, excessive reduction leads to an increase in refining costs, so 0.003 to 0.015% is desirable.
Ｓｉは、脱酸剤としても有用な元素であるとともに、高温強度と耐酸化性を改善する元素である。しかし、過度な添加は常温延性を低下させるためその上限を２％とする。また、耐酸化性を考慮すると０．２〜１．０％が望ましい。 Si is an element that is also useful as a deoxidizer and is an element that improves high-temperature strength and oxidation resistance. However, excessive addition lowers the room temperature ductility, so the upper limit is made 2%. Further, considering oxidation resistance, 0.2 to 1.0% is desirable.
Ｍｎは、脱酸剤として添加される元素であるとともに、中温域での高温強度上昇に寄与する。また、長時間使用中にＭｎ系酸化物を表層に形成し、スケール密着性や異常酸化抑制効果に寄与する。一方、２％超の過度な添加は、常温延性を低下させる他、ＭｎＳを形成して耐食性を低下させるため、上限を２％とした。更に、高温延性やスケール密着性を考慮すると、０．１〜１．０％が望ましい。 Mn is an element added as a deoxidizer and contributes to an increase in high-temperature strength in the middle temperature range. In addition, during use for a long time, a Mn-based oxide is formed on the surface layer, contributing to the scale adhesion and the effect of suppressing abnormal oxidation. On the other hand, excessive addition of more than 2% lowers ordinary temperature ductility and also forms MnS to lower corrosion resistance, so the upper limit was made 2%. Furthermore, if considering high temperature ductility and scale adhesion, 0.1 to 1.0% is desirable.
Ｐは、鋼中に不可避的に０．０３〜０．０４％程度含まれる成分であるが、本発明では、その存在が非常に重要な元素である。鋼中にＮｂが含まれていると、鋼板が高温に曝されると、ＮｂとＰが粒界に偏析しやすくなる傾向にある。そのため、Ｐ量をできるだけ、低減する必要がある。従って、Ｐ量の上限を０．０２５％とする。好ましくは０．０１５％である。また、過度の低減は製鋼プロセスの過大の負荷を与えるため、０．００５％を下限とするのが良い。好ましくは、０．００５％〜０．０１５％である。また、図１から明らかなように、高温割れに関してＰ量とＮｂ量には一定の相関があり、
Ｐ［％］≦−０．０５×Ｎｂ［％］＋０．０４ 式（１）
となるようにＰ量を調整すれば、耐高温割れ性を向上できる。
P is a component that is unavoidably contained in steel in an amount of about 0.03 to 0.04%. In the present invention, P is an extremely important element. When Nb is contained in steel, Nb and P tend to segregate at grain boundaries when the steel sheet is exposed to high temperatures. Therefore, it is necessary to reduce the P amount as much as possible. Therefore, the upper limit of the P content is 0.025%. Preferably it is 0.015%. Moreover, since excessive reduction gives an excessive load of the steelmaking process, 0.005% is a lower limit. Preferably, it is 0.005% to 0.015%. Further, as apparent from FIG. 1, there is a certain correlation between the P amount and the Nb amount with respect to hot cracking,
P [%] ≦ −0.05 × Nb [%] + 0.04 Formula (1)
If the amount of P is adjusted so that, the hot cracking resistance can be improved.
Ｓは、鋼中に不可避的に含まれる成分であるが、耐食性を低下させるＣａＳが生成しやすい。また、本発明において重要なことは、Ｓは粒界に偏析しやすい元素であり、耐高温割れ性を低下させる元素である。したがって、本発明ではＳを極力抑制することとし、その上限を０．００２％未満とする。しかし、Ｓを０．０００５％未満とすることは製鋼コストの非常な増大を招くため、０．０００５％を下限とすることが好ましい。 S is a component inevitably contained in the steel, but CaS that tends to reduce corrosion resistance is likely to be generated. In addition, what is important in the present invention is that S is an element that easily segregates at grain boundaries, and is an element that lowers hot cracking resistance. Therefore, in the present invention, S is suppressed as much as possible, and the upper limit is made less than 0.002%. However, if S is less than 0.0005%, the steelmaking cost is greatly increased, so 0.0005% is preferably set as the lower limit.
Ｃｒは、本発明において、耐酸化性や耐食性確保のために必須な元素である。１０％未満では、その効果は発現せず、２０％超では加工性の低下や靭性の劣化をもたらすため、１０〜２０％とした。更に、製造性や高温延性を考慮すると１０〜１８％が望ましい。耐酸化性や耐食性向上のためには、Ｃｒは１２．７％超、あるいは１３．７％超が好ましい。 In the present invention, Cr is an essential element for ensuring oxidation resistance and corrosion resistance. If it is less than 10%, the effect is not exhibited, and if it exceeds 20%, the workability is deteriorated and the toughness is deteriorated. Furthermore, considering the manufacturability and high temperature ductility, 10 to 18% is desirable. In order to improve oxidation resistance and corrosion resistance, Cr is preferably more than 12.7% or more than 13.7%.
Ｃｕは、高温強度向上に有効な元素である。特に、６００〜８００℃程度の中温度域における強化能が高い。これは、該温度域におけるＣｕ析出物の生成による析出強化が主な要因である。本発明では、高温強度を担保するＮｂ量を制限するため、それを補うために、Ｃｕを積極的に添加する。その高温強化能は、０．４％以上の添加により発現する。一方、過度な添加は、常温延性および耐酸化性支障が生じる。また、３％超添加すると熱延工程での耳割れが顕著になり製造性に問題が生じるとともに、Ｃｕ添加により溶接性も低下するため上限を３％とした。製造性、スケール密着性などを考慮すると、０．５〜２．５％が望ましい。 Cu is an element effective for improving high-temperature strength. In particular, the strengthening ability in the middle temperature range of about 600 to 800 ° C. is high. This is mainly due to precipitation strengthening due to the formation of Cu precipitates in the temperature range. In this invention, in order to restrict | limit the amount of Nb which ensures high temperature strength, in order to supplement it, Cu is added positively. The high-temperature strengthening ability is manifested by addition of 0.4% or more. On the other hand, excessive addition causes cold ductility and oxidation resistance. Further, if added over 3%, ear cracks in the hot rolling process become prominent, causing problems in manufacturability, and weldability is also lowered by adding Cu, so the upper limit was made 3%. Considering manufacturability and scale adhesion, 0.5 to 2.5% is desirable.
Ｔｉは、Ｃ，Ｎ，Ｓと結合して耐食性、耐粒界腐食性、常温延性や深絞り性を向上させる元素である。これらの効果は、０．００５％以上から発現するが、０．２５％超の添加により、固溶Ｔｉ量が増加して常温延性が低下するため、Ｔｉ添加量の上限は０．２５％とした。更に、表面疵の発生や靭性を考慮すると０．０５〜０．２０％が望ましい。 Ti is an element that combines with C, N, and S to improve corrosion resistance, intergranular corrosion resistance, room temperature ductility and deep drawability. These effects are manifested from 0.005% or more, but addition of more than 0.25% increases the amount of dissolved Ti and lowers the room temperature ductility, so the upper limit of Ti addition amount is 0.25% did. Furthermore, if considering the occurrence of surface flaws and toughness, 0.05 to 0.20% is desirable.
Ｎｂは、本発明で重要な元素である。高温強度や熱疲労特性を向上させる必須元素であり、０．０５％以上の添加でその効果が発現する。下限を０．０５％とした。しかし、本発明者らが明らかにしたように、Ｎｂを過剰に添加すると耐高温割れ性を低下させるので、その上限を０．６％とする。０．１％以上のＮｂの添加で、効果の発現が顕著になる。好ましくは０．３％以上０．６％以下である。なお、生産性や製造性の観点からは、０．０５〜０．３％が望ましい。 Nb is an important element in the present invention. It is an essential element that improves high-temperature strength and thermal fatigue characteristics, and its effect is manifested when added in an amount of 0.05% or more. The lower limit was set to 0.05%. However, as the present inventors have clarified, when Nb is added excessively, the hot cracking resistance is lowered, so the upper limit is made 0.6%. Addition of 0.1% or more of Nb makes the effect manifest significantly. Preferably they are 0.3% or more and 0.6% or less. From the viewpoint of productivity and manufacturability, 0.05 to 0.3% is desirable.
Ａｌは、脱酸元素として添加される他、固溶強化元素として６００〜７００℃の強度向上に有用である。また、耐酸化性を向上させるために添加する。しかし、過度の添加は硬質化するほか、溶接性を低下させるため、その上限を０．２％とする。０．０１％以下にするにはコスト増加を招くため、０．０１〜０．２％が望ましい。 In addition to being added as a deoxidizing element, Al is useful for improving the strength at 600 to 700 ° C. as a solid solution strengthening element. Moreover, it adds in order to improve oxidation resistance. However, excessive addition hardens and reduces weldability, so the upper limit is made 0.2%. If it is 0.01% or less, it causes an increase in cost, so 0.01 to 0.2% is desirable.
Ｂは、高温強度を向上させる元素であるともに、本発明における重要な効果であるＮｂおよびＰの粒界偏析を抑制する元素である。これはＢは拡散が速く、粒界偏析しやすい元素であり、特に、Ｃｕ添加鋼で顕著である。これは、Ｃｕの微細析出を促進させるためであると考えられている。これらの効果は、０．０００２％以上で発現するが、過度な添加は硬質化や粒界腐食性と耐酸化性を劣化させる他、溶接割れが生じるため、０．０００２〜０．００３０％とした。耐食性や製造コストを考慮すると、０．０００３〜０．００１５％が望ましい。 B is an element that improves the high-temperature strength and suppresses the grain boundary segregation of Nb and P, which is an important effect in the present invention. This is an element in which B diffuses quickly and easily segregates at grain boundaries, and is particularly remarkable in Cu-added steel. This is considered to promote the fine precipitation of Cu. These effects are manifested at 0.0002% or more, but excessive addition deteriorates the hardness, intergranular corrosion and oxidation resistance, and also causes weld cracks, so 0.0002 to 0.0030%. did. In consideration of corrosion resistance and manufacturing cost, 0.0003 to 0.0015% is desirable.
以上の元素に加えて、必要に応じて、Ｍｏ、Ｖ、Ｗ、Ｃｏ、Ｎｉ、Ｚｒ、Ｓｎを添加しても良い。 In addition to the above elements, Mo, V, W, Co, Ni, Zr, and Sn may be added as necessary.
Ｍｏは高温強度や熱疲労特性を向上させる元素である。その効果は０．０１％以上の添加で発現する。しかしながら、多量に添加すると、Ｌａｖｅｓ相等の金属間化合物の析出が起こり、高温強度向上効果が低下するため、好ましくない。そのため、添加する上限を１％とする。 Mo is an element that improves high temperature strength and thermal fatigue characteristics. The effect is manifested when 0.01% or more is added. However, when added in a large amount, precipitation of an intermetallic compound such as a Laves phase occurs, and the effect of improving the high temperature strength is lowered, which is not preferable. Therefore, the upper limit of addition is set to 1%.
Ｗは、Ｍｏと同じく、高温強度や熱疲労特性を向上させる元素である。その効果は０．０１％以上の添加で発現する。しかしながら、多量に添加すると、やはり、Ｌａｖｅｓ相等の金属間化合物の析出が起こり、高温強度向上効果が低下するため、好ましくない。そのため、添加する上限を１％とする。 W, like Mo, is an element that improves high-temperature strength and thermal fatigue characteristics. The effect is manifested when 0.01% or more is added. However, if added in a large amount, precipitation of an intermetallic compound such as a Laves phase occurs and the effect of improving the high-temperature strength decreases, which is not preferable. Therefore, the upper limit of addition is set to 1%.
Ｖは、微細な炭窒化物を形成し、析出強化作用が生じて高温強度向上に寄与するため必要に応じて添加する元素である。この効果は０．０１％以上の添加で安定して発現するが、１％超添加すると析出物が粗大化して高温強度が低下し、熱疲労寿命は低下してしまうため、上限を１％とした。更に、製造コストや製造性を考慮すると、０．０８〜０．５％が望ましい。 V is an element which is added as necessary because it forms fine carbonitrides and a precipitation strengthening effect is generated, contributing to the improvement of high temperature strength. This effect is stably exhibited by addition of 0.01% or more. However, if added over 1%, the precipitate becomes coarse and the high-temperature strength decreases and the thermal fatigue life decreases, so the upper limit is set to 1%. did. Furthermore, if considering the manufacturing cost and manufacturability, 0.08 to 0.5% is desirable.
Ｃｏは、高温強度を向上させる元素である。その効果は０．０１％以上の添加で発現する。しかしながら、多量に添加すると、加工性を低下させるため、好ましくない。そのため、添加する上限を１％とする。 Co is an element that improves high-temperature strength. The effect is manifested when 0.01% or more is added. However, addition in a large amount is not preferable because processability is lowered. Therefore, the upper limit of addition is set to 1%.
Ｎｉは耐食性を向上させる元素である。その効果は０．０１％以上の添加で発現する。しかしながら、多量に添加すると、相安定性を低下させるため、常温延性等が低下する。そのため、添加する上限を０．５％とする。 Ni is an element that improves the corrosion resistance. The effect is manifested when 0.01% or more is added. However, when added in a large amount, the phase stability is lowered, so the room temperature ductility and the like are lowered. Therefore, the upper limit to be added is 0.5%.
ＺｒはＴｉやＮｂ同様に炭窒化物形成元素であり、固溶Ｔｉ，Ｎｂ量の増加による高温強度向上、耐酸化性の向上に寄与し、０．１％以上の添加により安定して効果を発揮するため必要に応じて添加しても良い。しかしながら、１％超の添加により製造性の劣化が著しいため、０．２〜１％とした。コストや表面品位を考慮すると、０．２〜０．６％が望ましい。 Zr is a carbonitride-forming element like Ti and Nb, contributes to improving high-temperature strength and oxidation resistance by increasing the amount of solid solution Ti and Nb, and is stable by adding 0.1% or more. You may add as needed in order to exhibit. However, since the deterioration of manufacturability due to the addition of more than 1% is remarkable, the content is set to 0.2 to 1%. In consideration of cost and surface quality, 0.2 to 0.6% is desirable.
Ｓｎは、原子半径が大きく固溶強化に有効な元素であり、高温強度向上に寄与する。常温の機械的特性を大きく劣化させないため程度に、必要に応じて添加できる。高温強度への寄与は０．０１％以上で安定して発現するが、０．３％超添加すると製造性や溶接性が著しく劣化するため、０．３％を上限とした。更に、耐酸化性等を考慮すると、０．０５〜０．１％が望ましい。 Sn is an element having a large atomic radius and effective for solid solution strengthening, and contributes to improvement of high-temperature strength. It can be added as needed to the extent that it does not significantly degrade the mechanical properties at room temperature. The contribution to high-temperature strength is stable at 0.01% or more, but if added over 0.3%, manufacturability and weldability deteriorate significantly, so 0.3% was made the upper limit. Furthermore, if considering oxidation resistance and the like, 0.05 to 0.1% is desirable.
次に製造方法について説明する。本発明の製造に関しては、特段の規定するものではなく、通常のフェライト系ステンレス鋼の製造方法である、製鋼−熱間圧延−酸洗−冷間圧延−焼鈍・酸洗の各工程を経て製造させることが好ましい。各プロセスの製造条件は適宜選択することで製造できる。 Next, a manufacturing method will be described. With respect to the production of the present invention, it is not particularly specified, and is produced through each process of steelmaking-hot rolling-pickling-cold rolling-annealing / pickling, which is a method for producing ordinary ferritic stainless steel. It is preferable to make it. Manufacturing can be performed by appropriately selecting the manufacturing conditions for each process.
製鋼においては、前記必須成分および必要に応じて添加される成分を含有する鋼を、転炉溶製し続いて２次精錬を行う方法が好適である。溶製した溶鋼は、公知の鋳造方法（連続鋳造）に従ってスラブとする。スラブの厚さは、特に定めないが、１００〜３００ｍｍが好適である。スラブは、所定の温度に加熱され、所定の板厚に連続圧延で熱間圧延される。熱間圧延については、熱延条件、熱延板厚を適宜選択すればよい。特に条件を定めないが、スラブ加熱温度は１０００〜１３００℃、熱延終了温度は、６００〜１０００℃、巻き取り温度は、５００℃以下が好適である。熱延後の板厚は、２〜１０ｍｍが好適である。冷間圧延条件について、ステンレス鋼板の冷間圧延は、通常ロール径が６０〜１００ｍｍ程度のゼンジミア圧延機でリバース圧延されるか、ロール径が４００ｍｍ以上のタンデム式圧延機で一方向圧延されるかである。いずれも、複数パスで圧延される。 In steelmaking, a method in which the steel containing the above essential components and components added as necessary is subjected to furnace melting followed by secondary refining. The molten steel is made into a slab according to a known casting method (continuous casting). The thickness of the slab is not particularly defined but is preferably 100 to 300 mm. The slab is heated to a predetermined temperature and hot-rolled to a predetermined plate thickness by continuous rolling. About hot rolling, what is necessary is just to select hot-rolling conditions and hot-rolled sheet thickness suitably. Although no particular conditions are set, it is preferable that the slab heating temperature is 1000 to 1300 ° C, the hot rolling end temperature is 600 to 1000 ° C, and the winding temperature is 500 ° C or less. The plate thickness after hot rolling is preferably 2 to 10 mm. Regarding cold rolling conditions, is cold rolling of stainless steel sheet usually reverse rolled with a Sendzimir rolling mill with a roll diameter of about 60 to 100 mm or unidirectionally rolled with a tandem rolling mill with a roll diameter of 400 mm or more? It is. Both are rolled in multiple passes.
また、フェライト系ステンレス鋼板の製造において通常実施される熱延板焼鈍を施して
も良いが、省略して良い。その焼鈍条件は特に定めないが、８００℃〜１１００℃、１時間以内が好適である。冷延板の焼鈍条件も焼鈍温度、雰囲気などは適宜選択すれば良い。冷延板の焼鈍温度は、結晶粒度を調整し材質を整えるために適宜選択する。また、冷延・焼鈍後に調質圧延やテンションレベラーによる矯正を付与しても構わない。更に、製品板厚についても、要求部材厚に応じて選択すれば良い。
Moreover, although hot-rolled sheet annealing normally performed in manufacture of a ferritic stainless steel plate may be given, you may abbreviate | omit. The annealing conditions are not particularly defined, but 800 ° C. to 1100 ° C. and 1 hour or less are suitable. As for the annealing conditions of the cold rolled sheet, the annealing temperature, atmosphere, etc. may be appropriately selected. The annealing temperature of the cold-rolled sheet is appropriately selected in order to adjust the crystal grain size and adjust the material. Further, temper rolling or correction by a tension leveler may be applied after cold rolling and annealing. Further, the product plate thickness may be selected according to the required member thickness.
さらに、本発明について、実施例で詳しく説明する。 Further, the present invention will be described in detail in Examples.
表１に示す成分組成の鋼を溶製してスラブに鋳造し、スラブを熱間圧延して５ｍｍ厚の熱延コイルとした。その後、熱延コイルを焼鈍せずに酸洗し、２ｍｍ厚まで冷間圧延し、焼鈍・酸洗を施して製品板とした。冷延板の焼鈍温度は、結晶粒度番号を６〜８程度にするために、１０００〜１１００℃とした。表中のＮｏ．１〜１５は本発明鋼、Ｎｏ．１６〜４１は比較鋼である。 Steel having the component composition shown in Table 1 was melted and cast into a slab, and the slab was hot-rolled to form a hot rolled coil having a thickness of 5 mm. Thereafter, the hot rolled coil was pickled without being annealed, cold-rolled to a thickness of 2 mm, annealed and pickled to obtain a product plate. The annealing temperature of the cold-rolled sheet was set to 1000 to 1100 ° C. in order to make the grain size number about 6 to 8. No. in the table. 1-15 are steels of the present invention, No. 16 to 41 are comparative steels.
このようにして得られた製品板から、高温引張試験片を採取し、８００℃で引張試験を実施し、０．２％耐力を測定した（ＪＩＳＧ０５６７に準拠）。８００℃耐力が３０ＭＰａ以上を合格とした。 A high-temperature tensile test piece was collected from the product plate thus obtained, a tensile test was performed at 800 ° C., and a 0.2% yield strength was measured (in accordance with JISG0567). An 800 ° C. proof stress of 30 MPa or more was regarded as acceptable.
常温の加工性として、ＪＩＳ１３号Ｂ試験片を作製して圧延方向破断伸びを測定した。常温での破断伸びは３０％以上あれば、複雑な部品への加工が可能となるため、破断伸び３０％以上を合格とした。 As workability at room temperature, a JIS No. 13 B test piece was prepared, and the elongation at break in the rolling direction was measured. If the elongation at break at room temperature is 30% or more, it becomes possible to process a complex part.
耐高温割れ性の評価は、トランスバレストレイン試験で評価した。バレストレイン試験とは、溶接割れ試験方法の一つである。溶接を行いながら歪みを強制的にかけることによって溶接高温割れを再現し、発生した割れ数・長さなどを測定して、溶接高温割れ感受性を定量的に行うものである。溶接方向と垂直に歪みをかけるものがトランス・バレストレイン試験である。本試験では、付加歪量を１．６％として評価した。試験で発生した割れの長さを測定し、その結果から最大割れ長さと総割れ長さを求め、評価項目とし、最大割れ長さ１ｍｍ以下、かつ、総割れ長さ５ｍｍ以下を合格とて○とし、さらに、最大割れ長さ０．５ｍｍ以下、かつ、総割れ長さ３ｍｍ以下を◎とた。 The evaluation of hot cracking resistance was evaluated by a transbalance train test. The ballast train test is one of the weld cracking test methods. The welding hot cracking is reproduced by forcibly applying strain while welding, and the number and length of cracks generated are measured to quantitatively determine the welding hot cracking susceptibility. The transformer / ballest rain test applies a strain perpendicular to the welding direction. In this test, the additional strain was evaluated as 1.6%. The length of cracks generated in the test was measured, and the maximum crack length and the total crack length were obtained from the results. The evaluation items were taken, and the maximum crack length was 1 mm or less and the total crack length was 5 mm or less. Furthermore, the maximum crack length of 0.5 mm or less and the total crack length of 3 mm or less were evaluated as ◎.
表１において、成分は質量％を意味する。また本発明範囲から外れる数値にアンダーラインを付している。表１から明らかなように、Ｎｏ．１〜１５の本発明で規定する成分組成を有する鋼は、バレストレイン試験で良好な結果を示し、溶接性が合格である。加えて、８００℃における高温耐力が３５ＭＰａ以上と高く、常温での機械的性質において破断延性が３０％以上と良好である。 In Table 1, a component means mass%. In addition, numerical values outside the scope of the present invention are underlined. As is apparent from Table 1, No. Steel having a component composition defined in the present invention of 1 to 15 shows good results in the ballast train test, and the weldability is acceptable. In addition, the high-temperature proof stress at 800 ° C. is as high as 35 MPa or more, and the fracture ductility is good at 30% or more in the mechanical properties at room temperature.
本発明鋼に対し、比較鋼では、溶接性が不合格であったり、高温耐力が小さい、常温加工性が低い等の結果となっている。 In contrast to the steel of the present invention, the comparative steel has poor weldability, low high-temperature proof stress, low normal temperature workability, and the like.
以上から、本発明鋼は、比較鋼に比べ、溶接性に優れた耐熱フェライト系ステンレス鋼と言える。 From the above, it can be said that the steel of the present invention is a heat-resistant ferritic stainless steel superior in weldability compared to the comparative steel.
以上の説明から明らかなように、本発明によれば溶接性に優れた耐熱ステンレス鋼を提供することができ、特に排気部材に適用することにより、部品コストの低減や製造安定性に寄与でき、社会に対して格段の貢献が可能である。 As is clear from the above description, according to the present invention, it is possible to provide heat resistant stainless steel excellent in weldability, and in particular, by applying it to the exhaust member, it can contribute to the reduction of parts cost and manufacturing stability, It can make a significant contribution to society.
Claims (2)
Ｃ：０．０２％以下、
Ｎ：０．０２％以下、
Ｓｉ：２％以下、
Ｍｎ：２％以下、
Ｐ：０．００５以上０．０２５％以下
かつ、Ｐ［％］≦−０．０５×Ｎｂ［％］＋０．０４
Ｓ：０．００２％未満
Ｃｒ：１０〜２０％、
Ｃｕ：０．４〜３％、
Ｎｂ：０．０５〜０．６％
Ｔｉ：０．００５〜０．２５％、
Ａｌ：０．２％以下
Ｂ：０．０００２〜０．００３０％
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に優れた耐熱フェライト系ステンレス鋼板。 In mass%
C: 0.02% or less,
N: 0.02% or less,
Si: 2% or less,
Mn: 2% or less,
P: 0.005 to 0.025% and P [%] ≦ −0.05 × Nb [%] + 0.04
S: less than 0.002% Cr: 10-20%,
Cu: 0.4-3%,
Nb: 0.05 to 0.6%
Ti: 0.005 to 0.25%,
Al: 0.2% or less B: 0.0002 to 0.0030%
Containing
A heat-resistant ferritic stainless steel sheet excellent in weldability, characterized in that the balance consists of Fe and inevitable impurities.
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| JP5904306B2 (en) * | 2014-02-05 | 2016-04-13 | Ｊｆｅスチール株式会社 | Ferritic stainless steel hot-rolled annealed steel sheet, manufacturing method thereof, and ferritic stainless steel cold-rolled annealed steel sheet |
| WO2016117458A1 (en) * | 2015-01-19 | 2016-07-28 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel for exhaust system member having excellent corrosion resistance after heating |
| JPWO2014069543A1 (en) * | 2012-10-30 | 2016-09-08 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel plate with excellent heat resistance |
| JP2017101267A (en) * | 2015-11-30 | 2017-06-08 | Ｊｆｅスチール株式会社 | Ferritic stainless steel |
| JP2018199867A (en) * | 2018-08-24 | 2018-12-20 | Ｊｆｅスチール株式会社 | Ferritic stainless steel |
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| JP2005307324A (en) * | 2004-04-26 | 2005-11-04 | Nippon Steel & Sumikin Stainless Steel Corp | Method for manufacturing ferritic stainless steel having excellent deep drawability |
| WO2012036313A1 (en) * | 2010-09-16 | 2012-03-22 | 新日鐵住金ステンレス株式会社 | Heat-resistant ferrite-type stainless steel plate having excellent oxidation resistance |
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| JP2005307324A (en) * | 2004-04-26 | 2005-11-04 | Nippon Steel & Sumikin Stainless Steel Corp | Method for manufacturing ferritic stainless steel having excellent deep drawability |
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| JPWO2014069543A1 (en) * | 2012-10-30 | 2016-09-08 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel plate with excellent heat resistance |
| JP5904306B2 (en) * | 2014-02-05 | 2016-04-13 | Ｊｆｅスチール株式会社 | Ferritic stainless steel hot-rolled annealed steel sheet, manufacturing method thereof, and ferritic stainless steel cold-rolled annealed steel sheet |
| CN105960476A (en) * | 2014-02-05 | 2016-09-21 | 杰富意钢铁株式会社 | Hot-rolled and annealed ferritic stainless steel sheet, method for producing same, and cold-rolled and annealed ferritic stainless steel sheet |
| US10837075B2 (en) | 2014-02-05 | 2020-11-17 | Jfe Steel Corporation | Hot rolled and annealed ferritic stainless steel sheet, method of producing same, and cold rolled and annealed ferritic stainless steel sheet |
| WO2016117458A1 (en) * | 2015-01-19 | 2016-07-28 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel for exhaust system member having excellent corrosion resistance after heating |
| US20180016655A1 (en) * | 2015-01-19 | 2018-01-18 | Nippon Steel & Sumikin Stainless Steel Corporation | Ferritic stainless steel for exhaust system member having excellent corrosion resistance after heating |
| EP3249067A4 (en) * | 2015-01-19 | 2018-07-04 | Nippon Steel & Sumikin Stainless Steel Corporation | Ferritic stainless steel for exhaust system member having excellent corrosion resistance after heating |
| JP2017101267A (en) * | 2015-11-30 | 2017-06-08 | Ｊｆｅスチール株式会社 | Ferritic stainless steel |
| JP2018199867A (en) * | 2018-08-24 | 2018-12-20 | Ｊｆｅスチール株式会社 | Ferritic stainless steel |
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