JP6150830B2 - Ferritic stainless steel and brazed joint with excellent Cu grain boundary penetration resistance during Cu brazing - Google Patents
Ferritic stainless steel and brazed joint with excellent Cu grain boundary penetration resistance during Cu brazing Download PDFInfo
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- 238000005219 brazing Methods 0.000 title claims description 104
- 229910001220 stainless steel Inorganic materials 0.000 title claims description 50
- 230000035515 penetration Effects 0.000 title claims description 37
- 239000000463 material Substances 0.000 claims description 64
- 239000010935 stainless steel Substances 0.000 claims description 20
- 238000012360 testing method Methods 0.000 claims description 17
- 239000000203 mixture Substances 0.000 claims description 8
- 229910052802 copper Inorganic materials 0.000 claims description 7
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 229910052720 vanadium Inorganic materials 0.000 claims description 4
- 229910052726 zirconium Inorganic materials 0.000 claims description 4
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims description 3
- 239000011261 inert gas Substances 0.000 claims description 3
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 229910052758 niobium Inorganic materials 0.000 claims description 3
- 229910052757 nitrogen Inorganic materials 0.000 claims description 3
- 229910052742 iron Inorganic materials 0.000 claims description 2
- 229910052748 manganese Inorganic materials 0.000 claims description 2
- 229910052698 phosphorus Inorganic materials 0.000 claims description 2
- 229910052717 sulfur Inorganic materials 0.000 claims description 2
- -1 Furthermore Substances 0.000 claims 1
- 239000010949 copper Substances 0.000 description 93
- 229910000831 Steel Inorganic materials 0.000 description 22
- 239000010959 steel Substances 0.000 description 22
- 238000005260 corrosion Methods 0.000 description 14
- 230000007797 corrosion Effects 0.000 description 14
- 230000000694 effects Effects 0.000 description 8
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 7
- 239000012071 phase Substances 0.000 description 6
- 230000009467 reduction Effects 0.000 description 5
- 239000000758 substrate Substances 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- 238000011156 evaluation Methods 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 238000002844 melting Methods 0.000 description 4
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- 229910052761 rare earth metal Inorganic materials 0.000 description 3
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
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- 238000000137 annealing Methods 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
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- 229910000679 solder Inorganic materials 0.000 description 2
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- 229910000859 α-Fe Inorganic materials 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 239000005539 carbonized material Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
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Description
本発明は、Ｃｕろう付け時の耐Ｃｕ粒界浸透性に優れたフェライト系ステンレス鋼に関する。Ｃｕろう付けにより接合されたプレート式熱交換器等のような耐食性が必要とされるＣｕろう付け用途に適したフェライト系ステンレス鋼に関する。 The present invention relates to a ferritic stainless steel having excellent resistance to Cu grain boundary penetration during Cu brazing. The present invention relates to a ferritic stainless steel suitable for Cu brazing applications requiring corrosion resistance such as a plate heat exchanger joined by Cu brazing.
プレート式熱交換器等の熱交換器は、水、温水、蒸気の流体が循環し、配管や壁を介して熱交換が行われる。例えば、プレート式熱交換器は、プレス加工により流路を形成したプレートを複数枚を重ね合わせて積層された構造を備えており、プレート壁を介して液相／液相又は気相／液相の間で熱交換が行われる。このような水を含む使用環境にあるため、熱交換器の構造材として従来から耐食性や加工性に優れたオーステナイト系ステンレス鋼が使用されている。
ステンレス鋼プレートの接合には、Ｃｕろう、Ｎｉろう等の母材よりも低融点のろう材によるろう付け手段が用いられる。この接合方法は、ろう材をプレート基材の間に配置し、真空中またはＡｒや水素の雰囲気ガス中で１１２０℃程度の高温に加熱することで溶融したろう材が基材間を埋めることによりプレート基材同士が接合される。オーステナイト系ステンレス鋼としては、ＳＵＳ３０４系やＳＵＳ３１６系が用いられる。例えば、特許文献１は、ろう材で接合される構造物に用いられるオーステナイ系ステンレス鋼に関して、ろう付け性と耐食性を両立させるために、［Ｃｕ］×［Ｓｉ］、２「Ｎ］＋［Ｍｏ］の各範囲を規定している。
In a heat exchanger such as a plate heat exchanger, water, hot water, and steam fluid circulate, and heat exchange is performed through piping and walls. For example, a plate heat exchanger has a structure in which a plurality of plates in which flow paths are formed by pressing are stacked and stacked, and a liquid phase / liquid phase or a gas phase / liquid phase is interposed through the plate wall. Heat exchange between the two. Due to the use environment containing such water, austenitic stainless steel having excellent corrosion resistance and workability has been conventionally used as a structural material for heat exchangers.
For joining the stainless steel plates, brazing means using a brazing material having a melting point lower than that of a base material such as Cu brazing or Ni brazing is used. In this bonding method, a brazing material is disposed between plate base materials, and the brazing material melted by filling the space between the base materials by heating to a high temperature of about 1120 ° C. in a vacuum or an atmosphere gas of Ar or hydrogen. Plate base materials are joined together. As the austenitic stainless steel, SUS304 or SUS316 is used. For example, Patent Document 1 discloses [Cu] × [Si], 2 “N] + [Mo] in order to achieve both brazeability and corrosion resistance for an austenitic stainless steel used for a structure joined with a brazing material. ] Are specified.
製品において高耐熱性が不要なステンレス鋼のろう付けにはＣｕろう材を使用することが多い。オーステナイト系ステンレス鋼の基材にＣｕろう付け処理を施すと、基材およびＣｕろうは、所定の温度と時間で保持されて、溶融したＣｕろうは、基材同士の隙間を埋めるが、その際に基材との界面から基材の粒界に浸透（侵入）する現象が発生する（図４）。粒界に浸透したＣｕは、選択的に粒界と反応を起こしやすい。これは、Ｃｕと基材界面の保護皮膜を生成できないので、粒界に浸透したＣｕが、粒界に析出した炭素（Ｃ）と結合したり、ＣｕろうによりＣを溶出させることによると考えられている。 Cu brazing material is often used for brazing stainless steel that does not require high heat resistance in the product. When Cu brazing is applied to a base material of austenitic stainless steel, the base material and Cu brazing are held at a predetermined temperature and time, and the molten Cu brazing fills the gaps between the base materials. The phenomenon of penetration (invasion) from the interface with the base material to the grain boundary of the base material occurs (FIG. 4). Cu that has permeated into the grain boundary tends to selectively react with the grain boundary. This is thought to be due to the fact that a protective film at the interface between Cu and the substrate cannot be formed, so that Cu that has penetrated the grain boundary binds to carbon (C) deposited at the grain boundary or elutes C by Cu brazing. ing.
この場合、基材粒界にＣｕろう材が混在した組織を有しているので、ろう付けされたプレート式熱交換器を組み上げた際、流路で発生する脈圧、ウォーターハンマーのような水圧変動や蒸気圧によりプレートに応力が付加されると、Ｃｕろうが混在した粒界部分で応力集中が起きて、プレート基材に亀裂が発生し易くなり、そのことにより、内容物の漏れや熱交換器の耐久性を劣化させるといった不具合が生じる原因となり得る。
そのため、オーステナイト系ステンレス鋼を基材に用いたプレート式熱交換器は、従来から使用されているが、Ｃｕろうの粒界浸透を抑制する手法については知られていなかったのが現状である。特許文献１は、ろう付け性について、Ｓｉ、Ｃｕが一定量以上で添加されると、濡れ性が過剰に良好となり、被接合材同士の隙間からろう材が流出するという問題について、銀ろうを用いたろう付け性試験により、ろう付け性の評価をしているが、ろう材の粒界浸透に関する課題は開示されていない。
このように、プレート式熱交換器のステンレス鋼基材をＣｕろう材によってろう付け接合する場合、ステンレス鋼の粒界に発生するＣｕろうの粒界浸透を抑制可能なステンレス鋼が望まれていた。
In this case, since it has a structure in which Cu brazing material is mixed in the grain boundary of the base material, when a brazed plate heat exchanger is assembled, the pulse pressure generated in the flow path, the water pressure like a water hammer, etc. When stress is applied to the plate due to fluctuations or vapor pressure, stress concentration occurs at the grain boundary part where Cu brazing is mixed, and cracks are likely to occur in the plate base material. This may cause a problem that the durability of the exchanger is deteriorated.
For this reason, plate heat exchangers using austenitic stainless steel as a base material have been used in the past, but there is no known method for suppressing the penetration of Cu braze grain boundaries. Japanese Patent Application Laid-Open No. H10-228707 discusses the problem that when brazing properties are added, Si and Cu are added in a certain amount or more, the wettability becomes excessively good and the brazing material flows out from the gaps between the joined materials. Although the brazing property is evaluated by the brazing property test used, the problem concerning the grain boundary penetration of the brazing material is not disclosed.
Thus, when brazing and joining a stainless steel base material of a plate heat exchanger with a Cu brazing material, a stainless steel capable of suppressing grain boundary penetration of Cu brazing generated at the grain boundary of stainless steel has been desired. .
本発明は、ステンレス鋼が備える耐食性レベルを確保しつつ、Ｃｕろう付け時に発生するＣｕろうの粒界浸透が抑制された耐Ｃｕ粒界浸透性に優れたＣｕろう付け用のステンレス鋼を提供することを目的とする。 The present invention provides a stainless steel for Cu brazing excellent in Cu grain boundary penetration resistance in which the grain boundary penetration of Cu brazing generated during Cu brazing is suppressed while securing the corrosion resistance level of stainless steel. For the purpose.
本発明者らは、上記の課題を解決すべく、フェライト系ステンレス鋼について検討した結果、フェライト系ステンレス鋼のＣｕろう付け時に、粒界においてＣｕろう浸透現象が発生しないことに着目し、Ｃｕろうの粒界浸透性を抑制するのに適した成分組成を知見することにより、本発明を完成するに至った。 As a result of studying ferritic stainless steel in order to solve the above-mentioned problems, the present inventors paid attention to the fact that Cu brazing penetration phenomenon does not occur at the grain boundaries when Cu brazing ferritic stainless steel. The present invention has been completed by finding out a component composition suitable for suppressing the grain boundary permeability.
本発明の要旨は、次のとおりである。
（１）重量％で、Ｃ：０．０３％以下、Ｓｉ：０．１〜３．０％、Ｍｎ：０．１〜２．０％、Ｐ：０．０４％以下、Ｓ：０．００３％以下、Ｃｒ：１０．０〜３０．０％、Ｎｂ：０．３〜０．８％、Ｎ：０．０３％以下を含有し、残部はＦｅ及び不可避的不純物からなる成分組成であり、Ｃｕろうの粒界浸透深さを厚み方向で界面から５μｍ以下に抑制する、Ｃｕろう付け時の耐Ｃｕ粒界浸透性に優れたフェライト系ステンレス鋼。
The gist of the present invention is as follows.
(1) By weight, C: 0.03% or less, Si: 0.1-3.0%, Mn: 0.1-2.0%, P: 0.04% or less, S: 0.003 %, Cr: 10.0 to 30.0%, Nb: 0.3 to 0.8%, N: 0.03% or less, the balance is a component composition consisting of Fe and inevitable impurities, Ferritic stainless steel excellent in Cu grain boundary penetration resistance during Cu brazing, in which the grain boundary penetration depth of Cu brazing is controlled to 5 μm or less from the interface in the thickness direction.
（２）さらに、重量％で、Ｍｏ、Ｃｕ、Ｖ、Ｗの１種または２種以上を合計で０．０５〜４．０％を含む、上記（１）に記載のフェライト系ステンレス鋼。 (2) The ferritic stainless steel according to (1), further including 0.05 to 4.0% in total by weight percent of one or more of Mo, Cu, V, and W.
（３）さらに、重量％で、Ｔｉ、Ｚｒ、Ａｌの１種または２種以上を合計で０．０５％以下を含む、上記（１）または（２）に記載のフェライト系ステンレス鋼。 (3) The ferritic stainless steel according to the above (1) or (2), further containing 0.05% or less of one or more of Ti, Zr, and Al in total by weight.
（４）さらに、重量％で、Ｎｉ、Ｃｏの１種または２種を合計で０．５〜５．０％を含む、上記（１）〜（３）のいずれかに記載のフェライト系ステンレス鋼。 (4) The ferritic stainless steel according to any one of (1) to (3), further including 0.5 to 5.0% in total by weight percent of one or two of Ni and Co. .
（５）さらに、重量％で、ＲＥＭ、Ｃａの１種または２種を合計で０．０１〜０．２％を含む、上記（１）〜（４）のいずれかに記載のフェライト系ステンレス鋼。 (5) The ferritic stainless steel according to any one of (1) to (4), further including 0.01 to 0.2% in total by weight percent of one or two of REM and Ca. .
（６）上記（１）〜（５）のいずれかに記載されたフェライト系ステンレス鋼を基材とするフェライト系ステンレス鋼ろう継手。 (6) A ferritic stainless steel brazed joint using the ferritic stainless steel described in any one of (1) to (5) as a base material.
（７）前記基材の体積の１／３以下となる量のＣｕろうで接合されてなる、上記（６）に記載のフェライト系ステンレス鋼ろう継手。 (7) The ferritic stainless steel brazed joint according to (6), which is joined with Cu brazing in an amount that is 1/3 or less of the volume of the base material.
本発明によれば、Ｃｕろう付け時の耐Ｃｕ粒界浸透性に優れるフェライト系ステンレス鋼が提供された。このステンレス鋼材を用いることにより、Ｃｕろう付け時に、ステンレス鋼基材の粒界に対するＣｕろうの浸透が抑制されるので、Ｃｕ粒界浸透に起因する亀裂発生を防止することができる。エコキュート等に使用される熱交換器等のようにＣｕろう付け接合される製品のろう継手として広く適用できるものであり、製品の耐久性向上に寄与する。 ADVANTAGE OF THE INVENTION According to this invention, the ferritic stainless steel which is excellent in Cu grain boundary permeability at the time of Cu brazing was provided. By using this stainless steel material, the penetration of Cu brazing into the grain boundaries of the stainless steel base material is suppressed during Cu brazing, so that the occurrence of cracks due to the penetration of Cu grain boundaries can be prevented. It can be widely applied as a brazed joint for Cu brazed products such as heat exchangers used for Ecocute etc., and contributes to improving the durability of the product.
Ｃｕろう付け時に、従来のオーステナイト系ステンレス鋼で発生するＣｕろうの粒界浸透が、本発明のフェライト系ステンレス鋼では、十分に抑止されるため、Ｃｕろうの粒界浸透深さを厚み方向で界面から５μｍ以下に抑制することが可能である。 Since the grain boundary penetration of Cu brazing that occurs in conventional austenitic stainless steel during Cu brazing is sufficiently suppressed in the ferritic stainless steel of the present invention, the grain boundary penetration depth of Cu brazing is reduced in the thickness direction. It can be suppressed to 5 μm or less from the interface.
本発明のフェライト系ステンレス鋼が含有する各元素について説明する。各元素の含有量の「％」は、特に断らない限り「重量％」を意味する。 Each element contained in the ferritic stainless steel of the present invention will be described. “%” Of the content of each element means “% by weight” unless otherwise specified.
Ｃは、その含有量が多くなると、ろう付け温度やろう付け温度からの冷却速度によってはＣｒ炭化物の生成を招き、粒界にＣｒ欠乏層を形成して粒界腐食の原因となることがある。また、粒界に浸透したＣｕろうとの反応により炭化物を生成して亀裂の原因となることがある。そのため、Ｃ含有量を０．０３％以下に低減させる必要がある。 When the content of C increases, depending on the brazing temperature and the cooling rate from the brazing temperature, Cr carbide may be generated, and a Cr-deficient layer may be formed at the grain boundary, causing intergranular corrosion. . Moreover, a carbide | carbonized_material may be produced | generated by reaction with the Cu wax which osmose | permeated the grain boundary, and it may cause a crack. Therefore, it is necessary to reduce the C content to 0.03% or less.
Ｓｉは、Ｃｕろうの濡れ性の改善のために添加される。また、高温酸化特性を改善する作用を有する。０．１％未満であると、それら効果が十分に得られない。３．０％を超えると、濡れ性が過剰に発現されて流動が過多になるので、ろう付け性が低下する。そのため、Ｓｉ含有量は、０．１〜３．０％が好ましい。 Si is added to improve the wettability of Cu brazing. Moreover, it has the effect | action which improves a high temperature oxidation characteristic. If it is less than 0.1%, these effects cannot be obtained sufficiently. If it exceeds 3.0%, the wettability is excessively expressed and the flow becomes excessive, so that the brazing property is lowered. Therefore, the Si content is preferably 0.1 to 3.0%.
Ｍｎは、脱酸に有効な元素であるが、過剰に添加するとＭｎ化合物を形成して耐食性を低下させる。けるフェライト相形成を阻害する。そのため、Ｍｎ含有量は、１．０％以下とする。 Mn is an element effective for deoxidation, but if added excessively, a Mn compound is formed and the corrosion resistance is lowered. Inhibits ferrite phase formation. Therefore, the Mn content is 1.0% or less.
Ｐは、鋼の靭性の低下や加工性の低下を招く元素である。Ｐ含有量は、０．０４％以下に制限される。 P is an element that causes a reduction in toughness and workability of steel. The P content is limited to 0.04% or less.
Ｓは、孔食の原因となりやすいＭｎＳを生成して耐食性を阻害する元素である。また、ろう付け部の高温割れの要因にもなりやすい。Ｓ含有量は、０．００３％以下に制限される。 S is an element that generates MnS that easily causes pitting corrosion and inhibits corrosion resistance. In addition, it tends to cause hot cracking in the brazed part. The S content is limited to 0.003% or less.
Ｃｒは、不働態被膜を形成して耐食性を付与する元素である。また、フェライト相を生成する作用を有する。１０．０％未満では、それらの効果が十分でない。また、３０．０％を超えると、加工性、靭性の低下を招くことから、Ｃｒ含有量は、１６．０〜３０．０％とした。 Cr is an element that forms a passive film and imparts corrosion resistance. Moreover, it has the effect | action which produces | generates a ferrite phase. If it is less than 10.0%, those effects are not sufficient. Further, if it exceeds 30.0%, workability and toughness are reduced, so the Cr content is set to 16.0 to 30.0%.
Ｎｂは、炭窒化物を形成してＣｒ炭化物の形成を抑制するので、Ｃｒ固溶量がより低減するのを抑制し耐粒界腐食性に有効な元素である。過剰に含有すると、粒界からＣｒ系炭窒化物の析出を促進して耐粒界腐食性や加工性に悪影響を招くことがある。そのため，Ｎｂ含有量は、０．３〜０．８％とした。 Since Nb forms carbonitride and suppresses the formation of Cr carbide, Nb is an element that suppresses further reduction in the amount of Cr solid solution and is effective for intergranular corrosion resistance. If contained excessively, precipitation of Cr-based carbonitrides from the grain boundaries may be promoted, which may adversely affect intergranular corrosion resistance and workability. Therefore, the Nb content is set to 0.3 to 0.8%.
Ｎは、Ｃｒ窒化物を粒界に析出させて、粒界近傍のＣｒ固溶量の低減を招き、耐粒界腐食性を低下させることから、０．０３％以下が好ましい。 N is preferably 0.03% or less because it causes Cr nitride to precipitate at the grain boundaries, leading to a reduction in the amount of Cr solid solution in the vicinity of the grain boundaries and lowering the intergranular corrosion resistance.
Ｍｏ、Ｃｕ、Ｖ、Ｗは、ステンレス鋼の耐酸性を向上させ、耐食性を改善する。さらに、ろう付け温度でのフィライト粒の結晶粒粗大化の防止に効果がある。Ｍｏ、Ｖ、Ｗについては固溶によるドラック効果と析出物によるピン止め効果がある。ＣｕについてはεＣｕ相の析出によるピン止め効果がある。そのため、これらの元素の１種または２種以上を合計で０．０５％以上添加することが好ましい。他方、これらの元素を過多に添加すると、熱間加工性に悪影響を及ぼす場合があるので、合計で４．０％以下とすることが好ましい。 Mo, Cu, V, and W improve the acid resistance of stainless steel and improve the corrosion resistance. Furthermore, it is effective in preventing coarsening of the phylite grains at the brazing temperature. Mo, V, and W have a drag effect due to solid solution and a pinning effect due to precipitates. Cu has a pinning effect due to precipitation of εCu phase. Therefore, it is preferable to add one or more of these elements in a total of 0.05% or more. On the other hand, since excessive addition of these elements may adversely affect hot workability, the total content is preferably 4.0% or less.
Ｔｉ、Ｚｒ、Ａｌは、ＣやＮと結合して微細析出物を形成し、鋼中に分散することにより高温強度を向上させる作用を呈するため、これらの元素の１種以上を添加することが好ましい。他方、これらの元素は、過多に含有させると、熱間加工性や表面品質特性の低下を招く要因となる。また、鋼材表面に強固な酸化皮膜を形成する元素であるから、その酸化皮膜によってろう材の流れが悪くなる。そのため、合計量を０．０５％以下とすることが好ましい。 Since Ti, Zr, and Al combine with C and N to form fine precipitates and exhibit an action of improving high temperature strength by being dispersed in steel, it is possible to add one or more of these elements. preferable. On the other hand, if these elements are contained excessively, they cause a decrease in hot workability and surface quality characteristics. Moreover, since it is an element which forms a strong oxide film on the steel material surface, the flow of the brazing material is deteriorated by the oxide film. Therefore, the total amount is preferably 0.05% or less.
Ｎｉ、Ｃｏは、高温ろう付けよって結晶粒が若干粗大化した場合において、靭性低下の抑制を著しく効果がある。また、これらの元素は、高温強度の向上にも有利である。これらの元素の１種または２種以上を合計で０．５％以上添加することが好ましい。他方、これらの元素を過多に含有させると、高温域でオーステナイト相の生成を招く。そのため、合計量を５．０％以下とすることが好ましい。 Ni and Co are remarkably effective in suppressing toughness reduction when crystal grains are slightly coarsened by high-temperature brazing. These elements are also advantageous for improving the high temperature strength. It is preferable to add one or more of these elements in a total amount of 0.5% or more. On the other hand, if these elements are contained excessively, an austenite phase is generated in a high temperature range. Therefore, the total amount is preferably 5.0% or less.
ＲＥＭ（希土類元素）、Ｃａは、高温酸化特性を向上させる作用を呈するため、これらの元素を１種または２種を合計で０．０１％以上を添加することが好ましい。他方、これらの元素を過多に含有させると、靭性低下等により製造性の低下を招く。そのため、合計量で０．２％以下とすることが好ましい。 Since REM (rare earth element) and Ca exhibit an effect of improving high-temperature oxidation characteristics, it is preferable to add one or two of these elements in a total of 0.01% or more. On the other hand, when these elements are contained excessively, productivity is lowered due to toughness reduction or the like. Therefore, the total amount is preferably 0.2% or less.
本発明のフェライト系ステンレス鋼は、公知の製造方法により、溶製、熱間圧延、冷間圧延、焼鈍等の各処理を行って、所定の形状および寸法の鋼材を製造することができる。 The ferritic stainless steel of the present invention can be manufactured by a known manufacturing method to produce a steel material having a predetermined shape and size by performing various processes such as melting, hot rolling, cold rolling, and annealing.
ろう付け時のＣｕろう材は、Ｃｕを主成分とするろう材であればよく、無酸化銅（Ｃｕ濃度：約１００ｍａｓｓ％、固相温度１０８３℃）からなるものを使用できる。Ｃｕろう材の形態としては、ペ一スト状のもの、シート箔状のものを使用できる。 The brazing material used for brazing may be a brazing material containing Cu as a main component, and may be made of copper oxide-free (Cu concentration: about 100 mass%, solid phase temperature 1083 ° C.). As the form of the Cu brazing material, a paste shape or a sheet foil shape can be used.
以下、本発明の実施例について説明するが、本発明は、以下の実施例に限定されるものではなく、発明の要旨の範囲内で適宜変更して実施できる。 Examples of the present invention will be described below, but the present invention is not limited to the following examples, and can be implemented with appropriate modifications within the scope of the gist of the invention.
表１に示す成分を有するフェライト系ステンレス鋼について、３０ｋｇの真空溶解で溶製し、得られた鋼塊を３０ｍｍ厚の板に鍛造した後、熱間圧延を行って４ｍｍ厚の熱延板を得た。次いで、焼鈍、酸洗および冷間圧延を行って０．３ｍｍ厚の冷延板を得た。その後、該冷延板に１０５０℃の焼鈍処理を施して冷延焼鈍板を製造し、これを供試材とした。 About ferritic stainless steel having the components shown in Table 1, it was melted by 30 kg of vacuum melting, and the obtained steel ingot was forged into a 30 mm thick plate, and then hot rolled to obtain a 4 mm thick hot rolled plate. Obtained. Next, annealing, pickling and cold rolling were performed to obtain a cold rolled sheet having a thickness of 0.3 mm. Thereafter, the cold-rolled sheet was annealed at 1050 ° C. to produce a cold-rolled annealed sheet, which was used as a test material.
（ろう付け性試験）
板厚０．３ｍｍの当該供試材から４０ｍｍ×４０ｍｍろう付け試験片を各鋼種２枚ずつ切り出した。２枚の試験片の間に、７０μｍ厚で２００ｍｍ２の初期面積のシート箔からなるＣｕろう材を挟んで、試験片／Ｃｕろう材／試験片の３層からなる試験体を構成し、これを水平に保ったまま０．０１ＭＰａ程度の面圧をかけて真空炉に装入した。そして、メカニカルブースターで真空引きし、初期真空度を１×１０−２Ｐａ以下に保持した。次いで、炉内に不活性ガスを１００Ｐａ程度充填させた後、加熱して昇温を開始した。昇温は、Ｃｕろう材の固相温度（１０８３℃）に達する前の１０５０℃で一旦５分保持した。次いで、ろう付け温度の１１２０℃に昇温し、その温度で１５分保持した。その後、炉内に不活性ガスを９０ｋＰａ程度に充填して冷却を行った後、炉内から取り出すことで、Ｃｕろう付けを施した試験体を作製した。なお、Ｃｕろう材として無酸素銅（ＪＩＳＺ３２６３の１００ｍａｓｓ％Ｃｕ）を使用した。
(Brassability test)
Two 40 mm × 40 mm brazing specimens were cut out from each specimen having a thickness of 0.3 mm. A test piece consisting of three layers of test piece / Cu brazing material / test piece is formed by sandwiching a Cu brazing material consisting of a sheet foil of 70 μm thickness and an initial area of 200 mm 2 between two test pieces. Was kept horizontal and charged with a surface pressure of about 0.01 MPa in a vacuum furnace. And it evacuated with the mechanical booster and kept the initial stage vacuum degree below 1 * 10 <-2 > Pa. Next, the furnace was filled with about 100 Pa of an inert gas, and then heated to start heating. The temperature was raised once at 1050 ° C. for 5 minutes before reaching the solid phase temperature (1083 ° C.) of the Cu brazing material. Next, the temperature was raised to the brazing temperature of 1120 ° C. and held at that temperature for 15 minutes. Thereafter, the furnace was filled with an inert gas at about 90 kPa, cooled, and then taken out of the furnace to prepare a test body subjected to Cu brazing. In addition, oxygen free copper (100 mass% Cu of JISZ3263) was used as the Cu brazing material.
（耐Ｃｕ粒界浸透性の評価）
Ｃｕろう付け後の当該試験体は、板厚方向に切断し、樹脂に埋め込み、その断面を鏡面研磨した後、光学顕微鏡により５視野観察を行い、ステンレス鋼基材の粒界におけるＣｕろうの浸透深さを測定し、最大浸透深さを求めた。この最大浸透深さを平均化した数値に基づいて、Ｃｕろうに関する耐粒界浸透性を評価した。評価基準は、浸透深さが１０μｍ以下のものを合格と判定し、１０μｍを超えるものを不合格と判定した。測定結果を表２に示す。
(Evaluation of Cu grain boundary penetration resistance)
The test body after Cu brazing is cut in the thickness direction, embedded in resin, and the cross section is mirror-polished, followed by observation with five fields of view with an optical microscope, and penetration of Cu brazing into the grain boundary of the stainless steel substrate. The depth was measured to determine the maximum penetration depth. Based on a value obtained by averaging the maximum penetration depth, the intergranular penetration resistance with respect to Cu brazing was evaluated. Evaluation criteria determined that the penetration depth was 10 μm or less as acceptable, and those exceeding 10 μm were determined as unacceptable. The measurement results are shown in Table 2.
（ろう流れ性（ろう広がり性）の評価）
Ｃｕろうの流れ性に関しては、Ｃｕろう付けされた上記試験体の表面を観察し、表面のうちＣｕろう材で濡れ広がった面積を測定した。具体的には、板厚０．３ｍｍの当該供試材から４０ｍｍ×４０ｍｍろう付け試験片を作製し、当該試験片の表面に初期面積０．４ｃｍ２のＣｕろうを置いて、加熱処理後に広がったＣｕろうの面積を測定した。この測定面積を加熱前のＣｕろう初期面積で除して、ろう広がり率（％）を求めた。ろう広がり率が３００％以上のものを合格と判定し、３００％未満のものを不合格と判定した。測定結果を表２に示す。
(Evaluation of wax flowability (wax spreadability))
Regarding the flowability of the Cu brazing, the surface of the above-mentioned specimen that was brazed with Cu was observed, and the area of the surface that was wet and spread with the Cu brazing material was measured. Specifically, a 40 mm × 40 mm brazing test piece is prepared from the test material having a thickness of 0.3 mm, a Cu brazing having an initial area of 0.4 cm 2 is placed on the surface of the test piece, and spreads after the heat treatment. The area of Cu solder was measured. This measured area was divided by the initial Cu brazing area before heating to obtain a brazing spreading rate (%). Those having a wax spreading rate of 300% or more were judged as acceptable, and those less than 300% were judged as unacceptable. The measurement results are shown in Table 2.
（試験結果）
表２に示すように、本発明例の鋼Ａ〜Ｋは、基材界面からのＣｕろうの浸透深さが５μｍ以下であり、また、ろう広がり率が３００％以上を示していた。このように、本発明の成分組成を有する本発明例は、耐Ｃｕ粒界浸透性及びろう流れ性の両方において優れていることを確認した。
(Test results)
As shown in Table 2, in the steels A to K of the present invention, the penetration depth of Cu brazing from the base material interface was 5 μm or less, and the brazing spread rate was 300% or more. As described above, it was confirmed that the inventive examples having the component composition of the present invention were excellent in both Cu grain boundary penetration resistance and wax flowability.
それに対し、比較例の鋼Ｌ〜Ｏは、ろう付け時にオーステナイト相を生成してＣｕの粒界浸透が起きたため、Ｃｕろうの浸透深さが５μｍを大きく超えており、耐粒界浸透性が本発明よりも劣っていた。比較例の鋼Ｌは、ＳＵＳ３０４の組成に相当し、また、比較例の鋼Ｍは、ＳＵＳ３１６Ｌの組成に相当し、いずれもＮｉを相当量含有するオーステナイト系ステンレス鋼である。そのため、Ｃｕろうの粒界浸透を抑止できなかった。比較例の鋼Ｎは、従来のフェライト系ステンレス鋼であるＳＵＳ４３０の組成に相当するが、Ｃを本発明の範囲よりも多く含有している。そのため、Ｃｕろうの粒浸透性が低下した。
また、比較例の鋼Ｏは、普通鋼の組成に相当し、Ｃ含有量が本発明よりも高く、Ｃｒ、Ｎｂ含有量が本発明よりも低く、耐食性に乏しい。Ｃｕろう付け時に酸化膜が形成されやすく、ろう材の流れが悪くなった。
On the other hand, the steels L to O of the comparative example produced an austenite phase during brazing, and Cu intergranular penetration occurred. Therefore, the penetration depth of Cu brazing greatly exceeded 5 μm, and the intergranular penetration resistance was high. It was inferior to the present invention. The steel L of the comparative example corresponds to the composition of SUS304, and the steel M of the comparative example corresponds to the composition of SUS316L, both of which are austenitic stainless steels containing a considerable amount of Ni. For this reason, the penetration of the Cu solder grain boundaries could not be suppressed. Steel N of the comparative example corresponds to the composition of SUS430, which is a conventional ferritic stainless steel, but contains more C than the range of the present invention. Therefore, the grain permeability of Cu wax was lowered.
Moreover, the steel O of the comparative example corresponds to the composition of ordinary steel, has a C content higher than that of the present invention, Cr and Nb contents lower than those of the present invention, and has poor corrosion resistance. An oxide film was easily formed during Cu brazing, and the flow of the brazing material deteriorated.
比較例の鋼Ｐ、Ｑは、浸透深さが５μｍ以下であったが、ろう広がり率が３００％未満を示し、Ｃｕろう濡れ性の点で本発明のステンレス鋼よりも劣っていた。当該鋼Ｐ、Ｑは、Ｔｉ、ＡｌまたはＺｒの含有量が高く、本発明における不可避的不純物の範囲を超える程度であったため、強固な酸化皮膜が形成されて、ろう材の流れが悪くなった。
比較例の鋼Ｏ〜Ｑのように、Ｃｕろうの流れ性（ろう広がり性）が悪いステンレス鋼基材は、ろう接合が不十分であるため、Ｃｕろう付けされた製品に不適合であると評価される。
The steels P and Q of the comparative examples had a penetration depth of 5 μm or less, but the brazing spread ratio was less than 300%, which was inferior to the stainless steel of the present invention in terms of Cu brazing wettability. Since the steels P and Q have a high content of Ti, Al or Zr and exceeded the range of inevitable impurities in the present invention, a strong oxide film was formed and the flow of the brazing material was deteriorated. .
Stainless steel base materials with poor Cu braze flowability (brazing spreadability), such as comparative steels O to Q, are evaluated as being incompatible with Cu brazed products due to insufficient brazing. Is done.
（界面組織）
図１に、本発明例１（鋼Ａ）の鋼材について観察した界面組織を示す。図１に示すように、Ｃｕろうとプレート基材（ステンレス鋼）との界面において、Ｃｕろうの基材粒界浸透の発生が認められなかった。
(Interface structure)
In FIG. 1, the interface structure observed about the steel material of this invention example 1 (steel A) is shown. As shown in FIG. 1, the occurrence of penetration of the base material grain boundary of the Cu brazing was not observed at the interface between the Cu brazing and the plate base material (stainless steel).
（参考例）
ところで、図３に、本発明鋼Ｂ（ＳＵＳ４３０Ｊ１Ｌ系）を用いて、Ｃｕろう材を通常の約４倍も多い量で使用し、ろう付けした場合の界面組織を示す。図３に示すように、ステンレス鋼基材とＣｕろうとの界面には、Ｃｕろうが基材を浸食した現象が生じていた。
そこで、表１に示す鋼Ａ、鋼Ｂ、鋼Ｅ、鋼Ｆを用いて、Ｃｕろう材の使用量を通常よりも多くして、耐Ｃｕ粒界浸透性の評価試験を行った。具体的には、２８０μｍのシート箔からなるＣｕろう材を使用した以外は、本発明例と同様の条件でろう付けされた試験体を作製し、本発明例と同様の方法で浸透深さを測定した。その試験結果を表３に示す。
(Reference example)
By the way, FIG. 3 shows the interfacial structure when the brazing material of the present invention B (SUS430J1L system) is used and brazed in an amount about four times as large as usual. As shown in FIG. 3, the phenomenon that Cu brazing eroded the base material occurred at the interface between the stainless steel base material and Cu brazing.
Therefore, using the steel A, steel B, steel E, and steel F shown in Table 1, the amount of Cu brazing material used was increased more than usual, and an evaluation test for Cu grain boundary penetration resistance was performed. Specifically, except that a Cu brazing material made of 280 μm sheet foil was used, a test specimen brazed under the same conditions as in the present invention example was prepared, and the penetration depth was adjusted in the same manner as in the present invention example. It was measured. The test results are shown in Table 3.
表３に示すように、本発明鋼Ａ、Ｂ、Ｅ、Ｆは、浸透深さが１０μｍを超えていた。当該参考例の鋼材は、実施例の本発明例Ｎｏ．１、Ｎｏ．２、Ｎｏ．５、Ｎｏ．６と同じ鋼材であって、Ｃｕろうによる粒界浸透の抑制が可能なフェライト系ステンレス鋼であるが、過多のＣｕろう材を使用した場合には、５μｍを超える浸透が起きた。界面組織を観察したところ、図３に示したものと同様の浸食現象が生じていた。
これは、Ｃｕろう材の使用量が多いと、Ｃｕろうが濡れ広がる前にその場で溜まって対流が起きると推測され、この対流によりステンレス鋼基材に溶融（エロージョン）が生じて、実施例の拡散層が浸食される結果、Ｃｕろうの浸透を抑制する機能が低下したものと推測される。
それに対し、実施例の本発明例で使用されたＣｕろう材（７０μｍ厚）は、ステンレス鋼基材（０．３ｍｍ厚）に比べて１／３程度の厚みである。そのため、本発明のフェライト系ステンレス鋼を、例えば熱交換器の構造材に使用してＣｕろうで接合する場合は、Ｃｕろう材の厚みをステンレス鋼基材の厚みの１／３以下にすることが好ましい。
As shown in Table 3, the penetration depths of the inventive steels A, B, E, and F exceeded 10 μm. The steel material of the reference example is the invention example No. of the example. 1, no. 2, No. 5, no. 6 is a ferritic stainless steel that can suppress grain boundary penetration by Cu brazing, but when excessive Cu brazing material was used, penetration exceeding 5 μm occurred. When the interface structure was observed, an erosion phenomenon similar to that shown in FIG. 3 occurred.
This is because if the amount of Cu brazing material used is large, it is presumed that Cu brazing accumulates in place before wetting and spreading, and convection occurs, and this convection causes melting (erosion) in the stainless steel substrate. As a result of erosion of the diffusion layer, it is presumed that the function of suppressing the penetration of the Cu brazing is lowered.
On the other hand, the Cu brazing material (70 μm thickness) used in the examples of the present invention of the example is about 1/3 of the thickness of the stainless steel substrate (0.3 mm thickness). Therefore, the ferritic stainless steel of the present invention, for example, when using the structural material of the heat exchanger is joined with Cu brazing is to the thickness of the Cu brazing material less than 1/3 of the thickness of the stainless steel substrate Is preferred.
Claims (6)
さらに、ＴｉおよびＡｌを合計で０．０５％以下、ＮｉおよびＣｏを合計で０．１５〜５．０％を含み、
板厚０．３ｍｍの２枚のステンレス鋼板の間に、７０μｍ厚のＣｕろう材を挟んだ試験体を、不活性ガス雰囲気において、１０５０℃で５分保持した後、１１２０℃で１５分のろう付けをした後に測定されたＣｕろうの粒界浸透深さを厚み方向で界面から５μｍ以下に抑制する、Ｃｕろう付け時の耐Ｃｕ粒界浸透性に優れたフェライト系ステンレス鋼。 % By weight, C: 0.03% or less, Si: 0.1-3.0%, Mn: 0.1-2.0%, P: 0.04% or less, S: 0.003% or less, Cr: 10.0 to 30.0%, Nb: 0.3 to 0.8%, N: 0.03% or less, the balance is a component composition consisting of Fe and unavoidable impurities,
Furthermore, Ti and Al in total include 0.05% or less, Ni and Co include 0.15 to 5.0% in total,
A test specimen in which a 70 μm thick Cu brazing material is sandwiched between two stainless steel plates having a thickness of 0.3 mm is held at 1050 ° C. for 5 minutes in an inert gas atmosphere, and then soldered at 1120 ° C. for 15 minutes. Ferritic stainless steel excellent in Cu grain boundary penetration resistance during Cu brazing, which suppresses the grain boundary penetration depth of Cu brazing measured after brazing to 5 μm or less from the interface in the thickness direction.
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