JP3794999B2 - Nickel-base alloy, nickel-base alloy heat treatment method, and nuclear component using nickel-base alloy - Google Patents
Nickel-base alloy, nickel-base alloy heat treatment method, and nuclear component using nickel-base alloy Download PDFInfo
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- 238000010438 heat treatment Methods 0.000 title claims description 54
- 239000000956 alloy Substances 0.000 title claims description 40
- 229910045601 alloy Inorganic materials 0.000 title claims description 40
- 238000000034 method Methods 0.000 title claims description 10
- 239000000203 mixture Substances 0.000 claims description 28
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 20
- 229910052759 nickel Inorganic materials 0.000 claims description 11
- 238000001816 cooling Methods 0.000 claims description 6
- 239000000126 substance Substances 0.000 claims description 4
- 230000032683 aging Effects 0.000 claims description 2
- 229910052804 chromium Inorganic materials 0.000 claims description 2
- 229910052802 copper Inorganic materials 0.000 claims description 2
- 239000012535 impurity Substances 0.000 claims description 2
- 229910052748 manganese Inorganic materials 0.000 claims description 2
- 229910052750 molybdenum Inorganic materials 0.000 claims description 2
- 229910052758 niobium Inorganic materials 0.000 claims description 2
- 238000003672 processing method Methods 0.000 claims 1
- 230000007797 corrosion Effects 0.000 description 21
- 238000005260 corrosion Methods 0.000 description 21
- 230000035882 stress Effects 0.000 description 17
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 15
- 239000000463 material Substances 0.000 description 12
- 238000005336 cracking Methods 0.000 description 11
- 238000009864 tensile test Methods 0.000 description 9
- 239000013078 crystal Substances 0.000 description 6
- 239000000446 fuel Substances 0.000 description 4
- 230000007774 longterm Effects 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 239000010421 standard material Substances 0.000 description 3
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 1
- 230000000712 assembly Effects 0.000 description 1
- 238000000429 assembly Methods 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005242 forging Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
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Description
【０００１】
【発明の属する技術分野】
本発明は、例えば原子炉炉内環境のように、高温高圧水中で優れた耐応力腐食割れ性を有するニッケル基合金、およびその熱処理方法に関する。更に、このようなニッケル基合金を、各種の押さえ部品、ばね、ピン、ボルトなどの高強度部材として用いることによって、高温高圧水中で長時間使用された場合であっても耐応力腐食割れ性に優れた原子力用部材に関する。
【０００２】
【従来の技術】
析出強化型ニッケル基合金のＮＣＦ７１８合金は、高強度で耐食性が優れていることから、原子炉炉内構造物のスプリング、ベローズ、燃料支持格子、ボルトなどの原子力用部材に使用されている。
【０００３】
【発明が解決しようとする課題】
しかしながら、析出強化型ニッケル基合金のＮＣＦ７１８合金は、高温高圧水中において、高引張応力が作用すると、粒界型応力腐食割れを生じることがあるということが知られている。
【０００４】
原子炉の炉内環境は、高温高圧水中であることから、ＮＣＦ７１８合金からなる原子力用部材は、高引張応力が作用すると、粒界型応力腐食割れを生じる可能性があるという問題がある。
【０００５】
本発明はこのような事情に鑑みてなされたものであり、ＮＣＦ７１８合金よりさらに高温高圧水中で優れた耐粒界型応力腐食割れ性を有し、もって、高温高圧水中の環境下で長時間の使用に耐えることが可能なニッケル基合金、ニッケル基合金の熱処理方法、およびニッケル基合金を用いた原子力用部材を提供することを目的とする。
【０００６】
【課題を解決するための手段】
上記の目的を達成するために、本発明では、以下のような手段を講じる。
【０００７】
すなわち、請求項１の発明のニッケル基合金の熱処理方法は、重量パーセントでＣ：０．０８％以下、Ｓｉ：０．３５％以下、Ｍｎ：０．３５％以下、Ｐ：０．０１５％以下、Ｓ：０．０１５％以下、Ｎｉ：５０．０％以上５５．０％以下、Ｃｒ：１７．０％以上２１．０％以下、Ｍｏ：２．８０％以上３．３０％以下、Ｃｕ：０．３０％以下、Ａｌ：０．２０％以上０．８０％以下、Ｔｉ：０．６５％以上１．１５％以下、Ｎｂ＋Ｔａ：４．７５％以上５．５０％以下、Ｂ：０．００６％以下、および残部Ｆｅならびに不可避的不純物からなる化学組成を有するニッケル基合金を、９９５℃〜１０４０℃の温度で、２時間〜２０時間加熱して空冷する固溶化熱処理を施し、前記固溶化熱処理の下記式で表わされるラルソン・ミラーのパラメータＰが２９７６９〜３０８２５の範囲とする。
Ｐ＝Ｔ（ｃ＋Ｌｏｇｔ）、
ただし、Ｔ：絶対温度（Ｋ）、ｃ＝２３（定数）、ｔ：時間（ｈｒ）。
【０００９】
請求項２の発明のニッケル基合金は、請求項１の発明のニッケル基合金の熱処理方法を実施し、かつＮｂ＋Ｔａの重量パーセントを４．９０％以上５．４０％以下としている。
【００１０】
請求項３の発明のニッケル基合金は、請求項１又は請求項２に記載のニッケル基合金の熱処理方法を実施した後、７６０℃の温度で５時間保持した後炉内冷却によって７６０℃から６５０℃まで降温し、更に６５０℃の温度で１時間保持した後冷却する時効処理を施すとしている。
【００１１】
請求項４の発明の、ニッケル基合金を用いた原子力用部材は、請求項２又は請求項３の発明のニッケル基合金を用いたものである。
【００１２】
従って、請求項１から請求項３の発明においては、以上のような手段を講じることにより、高温高圧水中で優れた耐粒界型応力腐食割れ性を有し、例えば原子炉炉内のような高温高圧水中の環境下で長時間の使用に耐えることが可能なニッケル基合金を実現することができる。
【００１３】
また、請求項４の発明では、請求項２又は請求項３のようなニッケル基合金を用いた原子力用部材を燃料集合体や炉内構造物に適用することによって、高温高圧水中であっても、優れた耐粒界型応力腐食割れ性を有し、例えば原子炉炉内のような高温高圧水中の環境下であっても長時間の使用に耐えることが可能な原子力用部材を実現することができる。
【００１４】
【発明の実施の形態】
以下に、本発明の実施の形態について図面を参照しながら説明する。
【００１５】
本発明の実施の形態を図１から図１１、および表１から表２を用いて説明する。
【００１６】
【表１】
本発明の実施の形態では、表１に化学成分（重量％）を示す試験組成１〜試験組成６の試作鍛造材を対象として、９５０℃から１０７０℃の温度で３時間保持した後空冷する固溶化熱処理を施した後、７６０℃の温度で５時間保持した後炉内冷却によって７６０℃から６５０℃まで降温し、更に６５０℃の温度で１時間保持した後空冷する時効処理を施した。
【００１８】
その後、１）低歪速度引張試験、２）粒界腐食試験、３）引張試験、４）結晶粒度測定を行った。なお、試験組成１はＪＩＳ規格に適合する標準材（ＮＣＦ７１８合金）、試験組成２は試験組成１よりもＮｂ＋Ｔａ量が少ない低Ｎｂ材、試験組成３はＮｂ＋Ｔａ量が試験組成２よりも多く試験組成４よりも少ない中Ｎｂ材、試験組成４は試験組成３よりもＮｂ＋Ｔａ量が多い高Ｎｂ材、試験組成５は試験組成１よりもＣｒ量が少ない低Ｃｒ材、試験組成６は試験組成１よりもＣｒ量が多い高Ｃｒ材である。
【００１９】
１）低歪速度引張試験
図１（ａ）に正面図を、図１（ｂ）に側面図を示すようなノッチ付きの試験片１２を用いて、軽水炉模擬環境下の高温高圧純水中（３６０℃、≦２１４ｋｇ／ｃｍ２Ｇ）で低歪速度引張試験（引張速度：０．１μｍ／ｍｉｎ）を行った。その結果、図２および図３に示すように試験片１２の粒界破面率は、固溶化熱処理温度が高くなると減少するという傾向が認められた。また、固溶化熱処理温度が１０２５℃以上では、試験組成４（高Ｎｂ材）と試験組成５（低Ｃｒ材）とを除く何れの材料とも粒界破面率がほぼゼロとなった。一方、粒界破面率は、Ｎｂ＋Ｔａ量が増加するほど、またＣｒ量が減少するほど増大する傾向が認められた。
【００２０】
図１に示すようなノッチ付きの試験片１２を用いた低歪速度引張試験は、応力腐食割れ（以下、「ＳＣＣ」と称する。）に対する感受性を評価するための過酷な試験方法である。そこで、低歪速度引張試験でのＳＣＣ感受性のしきい値を粒界破面率で１０％以下と仮定すると、固溶化熱処理温度は９９５℃以上で、Ｃｒ量は重量割合で１９．０％以上２１．０％以下が、Ｎｂ＋Ｔａ量は重量割合で５．４０％以下が望ましいことがわかる。
【００２１】
２）粒界腐食（コリオ）試験
粒界腐食（コリオ）試験（５Ｋｍｏｌ／ｍ３ＨＮＯ３＋０．０７７Ｋｍｏｌ／ｍ３Ｃｒ２Ｏ７ ２−溶液中で３時間の沸騰試験）を行った結果、得られた固溶化熱処理温度と腐食速度との関係を図４および図５に示す。図４および図５に示すように、腐食速度は、試験組成４（高Ｎｂ材）が、固溶化熱処理温度に関わらず他の試験組成の場合に比べて大きな値を示すことが認められた。その他の試験組成の腐食速度は、固溶化熱処理温度９８０℃の場合が大きく、固溶化熱処理温度が９９５℃から１０２５℃では９８０℃に比べて小さな値を示している。したがって、耐粒界腐食性の観点からは、固溶化熱処理温度は９９５℃以上で、Ｎｂ＋Ｔａ量は重量割合で５．４０％以下が望ましいことがわかる。
【００２２】
３）引張試験
引張試験の結果を、固溶化熱処理温度と０．２％耐力との関係にまとめたグラフを図６および図７に、固溶化熱処理温度と引張強さとの関係にまとめたグラフを図８および図９にそれぞれ示す。
【００２３】
図６および図７に示すように、０．２％耐力は、固溶化熱処理温度が高くなると若干低下する傾向が認められるものの、図７に示すように、Ｃｒ量の変化に対してはほぼ同等で有意差が認められないが、図６に示すように、試験組成２（低Ｎｂ材）では試験組成１（標準材）よりも低強度で、ＪＩＳ規格を下回っている。また、図８および図９に示すように、引張強さは、固溶化熱処理温度が高くなると若干低下する傾向が認められるものの、図９に示すように、Ｃｒ量の変化に対してはほぼ同等で有意差が認められないが、図８に示すように、試験組成２（低Ｎｂ材）では試験組成１（標準材）よりも低強度で、ＪＩＳ規格を下回っている。したがって、引張試験の結果からは、固溶化熱処理温度は９８０℃以上で、Ｎｂ＋Ｔａ量は重量割合で４．９０％以上が望ましいことがわかる。
【００２４】
４）結晶粒度測定
結晶粒度測定の結果を、固溶化熱処理温度と結晶粒度番号との関係にまとめたグラフを図１０および図１１にそれぞれ示す。結晶粒度番号は、何れの試験組成に対しても、固溶化熱処理温度が高くなると共に小さくなる傾向を示している。固溶化熱処理温度が１０７０℃以上では、いずれの試験組成も結晶粒度番号が５以下となっている。結晶粒度番号が小さいことは望ましくないため、固溶化熱処理温度としては１０４０℃以下が望ましいことがわかる。
【００２５】
５）固溶化熱処理
以上のことから、固溶化熱処理温度としては、９９５℃〜１０４０℃が望ましいことがわかる。一方、固溶化熱処理時間は、ここでは一例として３時間としている。
【００２６】
そこで、固溶化熱処理温度が９９５℃〜１０４０℃の場合の固溶化熱処理時間を以下に示すようなラルソン・ミラーのパラメータＰを用いて検討した。
【００２７】
Ｐ＝Ｔ（ｃ＋Ｌｏｇｔ）
ただし、Ｐ：パラメータ、Ｔ：絶対温度（Ｋ）、ｃ＝定数（ここでは２３）、ｔ：時間（ｈｒ）である。ここで行なった固溶化熱処理条件および加熱時間を変化させた場合について下式のラルソン・ミラーのパラメータで整理した結果を表２に示す。
【００２８】
【表２】
表２に示すように、１０４０℃の温度で３時間加熱した場合のパラメータは３０８２５で、９９５℃の温度で３時間加熱した場合のパラメータは２９７６９である。９９５℃の温度で２０時間加熱した場合のパラメータは３０８１４で、１０４０℃の温度で３時間加熱した場合のパラメータ（３０８２５）とほぼ同等である。一方、１０４０℃の温度で３０分間加熱した場合のパラメータは２９８０４で、９９５℃の温度で３時間加熱した場合のパラメータ（２９７６９）とほぼ同等である。
【００３０】
したがって、固溶化熱処理時間としては、２時間〜２０時間が望ましいことがわかる。
【００３１】
以上のことから、耐粒界型応力腐食割れ性に優れた析出強化型のニッケル基合金としては、Ｃｒの重量パーセントが１９．０％以上２１．０％以下、Ｎｂ＋Ｔａの重量パーセントが４．９０％以上５．４０％以下であり、その他はＮＣＦ７１８合金と同等の化学組成を有するものがよい。
【００３２】
また、このようなニッケル基合金の熱処理方法としては、９９５℃〜１０４０℃の温度で、２時間〜２０時間加熱して空冷する固溶化熱処理を施し、前記固溶化熱処理の下記式で表わされるラルソン・ミラーのパラメータＰが２９７６９〜３０８２５の範囲とすればよい。
Ｐ＝Ｔ（ｃ＋Ｌｏｇｔ）、
ただし、Ｔ：絶対温度（Ｋ）、ｃ＝２３（定数）、ｔ：時間（ｈｒ）。
【００３３】
したがって、このようなニッケル基合金によって製造されたスプリング、ベローズ、燃料支持格子、ボルトなどの原子力用部材を、燃料集合体や原子炉炉内構造物に用いることによって、高温高圧水中であっても、優れた耐粒界型応力腐食割れ性を有し、原子炉炉内の高温高圧水中の環境下で長時間の使用に耐えることが可能となる。
【００３４】
以上、本発明の好適な実施の形態について、添付図面を参照しながら説明したが、本発明はかかる構成に限定されない。特許請求の範囲の発明された技術的思想の範疇において、当業者であれば、各種の変更例及び修正例に想到し得るものであり、それら変更例及び修正例についても本発明の技術的範囲に属するものと了解される。
【００３５】
【発明の効果】
以上説明したように、本発明によれば、ＮＣＦ７１８合金よりもさらに高温高圧水中で優れた耐粒界型応力腐食割れ性を有し、もって、高温高圧水中の環境下で長時間の使用に耐えることが可能なニッケル基合金、ニッケル基合金の熱処理方法、およびニッケル基合金を用いた原子力用部材を実現することができる。
【図面の簡単な説明】
【図１】試験片の形状を示す正面図および側面図
【図２】固溶化熱処理温度と粒界破面率との関係を示す図（Ｎｂ量に対する傾向）
【図３】固溶化熱処理温度と粒界破面率との関係を示す図（Ｃｒ量に対する傾向）
【図４】固溶化熱処理温度と腐食速度との関係を示す図（Ｎｂ量に対する傾向）
【図５】固溶化熱処理温度と腐食速度との関係を示す図（Ｃｒ量に対する傾向）
【図６】固溶化熱処理温度と０．２％耐力との関係を示す図（Ｎｂ量に対する傾向）
【図７】固溶化熱処理温度と０．２％耐力との関係を示す図（Ｃｒ量に対する傾向）
【図８】固溶化熱処理温度と引張強さとの関係を示す図（Ｎｂ量に対する傾向）
【図９】固溶化熱処理温度と引張強さとの関係を示す図（Ｃｒ量に対する傾向）
【図１０】固溶化熱処理温度と結晶粒度番号との関係を示す図（Ｎｂ量に対する傾向）
【図１１】固溶化熱処理温度と結晶粒度番号との関係を示す図（Ｃｒ量に対する傾向）
【符号の説明】
１２…試験片[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nickel-based alloy having excellent stress corrosion cracking resistance in high-temperature and high-pressure water, such as a reactor internal environment, and a heat treatment method thereof. Furthermore, by using such a nickel-based alloy as a high-strength member such as various holding parts, springs, pins, bolts, etc., even when used for a long time in high-temperature and high-pressure water, it becomes stress corrosion cracking resistant. It relates to excellent nuclear components.
[0002]
[Prior art]
The precipitation-strengthened nickel-base alloy NCF718 alloy is used for nuclear components such as springs, bellows, fuel support grids, and bolts of reactor internal structures because of its high strength and excellent corrosion resistance.
[0003]
[Problems to be solved by the invention]
However, it is known that the precipitation-strengthened nickel base alloy NCF718 alloy may cause intergranular stress corrosion cracking when subjected to high tensile stress in high temperature and high pressure water.
[0004]
Since the in-reactor environment of the nuclear reactor is high-temperature and high-pressure water, a nuclear member made of NCF718 alloy has a problem that, when a high tensile stress is applied, there is a possibility of causing grain boundary type stress corrosion cracking.
[0005]
The present invention has been made in view of such circumstances, and has an intergranular stress corrosion cracking resistance superior to that of NCF718 alloy in high-temperature and high-pressure water. An object of the present invention is to provide a nickel-base alloy that can withstand use, a heat treatment method for the nickel-base alloy, and a nuclear member using the nickel-base alloy.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention takes the following measures.
[0007]
That is, the heat treatment method of the nickel-base alloy according to the first aspect of the present invention is C: 0.08% or less, Si: 0.35% or less, Mn: 0.35% or less, P: 0.015% or less in weight percent. S: 0.015% or less, Ni: 50.0% or more and 55.0% or less, Cr: 17.0% or more and 21.0% or less, Mo: 2.80% or more and 3.30% or less, Cu: 0.30% or less, Al: 0.20% to 0.80%, Ti: 0.65% to 1.15%, Nb + Ta: 4.75% to 5.50%, B: 0.006 %, And a nickel-base alloy having a chemical composition consisting of Fe and the balance Fe and inevitable impurities is subjected to a solution heat treatment by heating at a temperature of 995 ° C. to 1040 ° C. for 2 hours to 20 hours and air-cooling, and the solution heat treatment parameters of the Larson-Miller represented by the following formula Data P is in the range of 29,769 to 30,825.
P = T (c + Logt),
However, T: Absolute temperature (K), c = 23 (constant), t: Time (hr).
[0009]
The nickel-base alloy of the invention of
[0010]
Nickel-based alloy of the invention 請 Motomeko 3, after performing the heat treatment method of the nickel-base alloy according to claim 1 or claim 2, from 760 ° C. by furnace cooling after maintaining for 5 hours at a temperature of 760 ° C. An aging treatment is performed in which the temperature is lowered to 650 ° C., and further maintained at a temperature of 650 ° C. for 1 hour and then cooled.
[0011]
The nuclear power member using the nickel base alloy according to the invention of claim 4 uses the nickel base alloy of the invention of
[0012]
Therefore, in the inventions according to claims 1 to 3 , by taking the above-described means, the steel has excellent intergranular stress corrosion cracking resistance in high-temperature and high-pressure water, such as in a nuclear reactor. A nickel-base alloy that can withstand long-time use in an environment of high-temperature and high-pressure water can be realized.
[0013]
Further, in the invention of claim 4 , by applying the nuclear member using the nickel base alloy as in
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0015]
Embodiments of the present invention will be described with reference to FIGS. 1 to 11 and Tables 1 to 2. FIG.
[0016]
[Table 1]
In the embodiment of the present invention, a trial forging material of Test Composition 1 to
[0018]
Thereafter, 1) low strain rate tensile test, 2) intergranular corrosion test, 3) tensile test, and 4) crystal grain size measurement were performed. Test composition 1 is a standard material (NCF718 alloy) conforming to the JIS standard,
[0019]
1) Low Strain Rate Tensile Test Using a
[0020]
The low strain rate tensile test using the
[0021]
2) Intergranular corrosion (corio) test Intergranular corrosion (corio) test (5 Kmol / m 3 HNO 3 +0.077 Kmol / m 3 Cr 2 O 7 2 -boiling test in solution for 3 hours) FIG. 4 and FIG. 5 show the relationship between the solution heat treatment temperature and the corrosion rate. As shown in FIGS. 4 and 5, it was confirmed that the corrosion rate of the test composition 4 (high Nb material) was larger than that of other test compositions regardless of the solution heat treatment temperature. The corrosion rate of other test compositions is large when the solution heat treatment temperature is 980 ° C., and the solution heat treatment temperature is 995 ° C. to 1025 ° C., which is smaller than 980 ° C. Therefore, from the viewpoint of intergranular corrosion resistance, it is understood that the solution heat treatment temperature is preferably 995 ° C. or more and the Nb + Ta amount is preferably 5.40% or less by weight.
[0022]
3) Tensile test A graph summarizing the results of the tensile test in relation to the solution heat treatment temperature and the 0.2% proof stress is shown in FIGS. 6 and 7, and a graph summarizing the relationship between the solution heat treatment temperature and the tensile strength. It shows in FIG. 8 and FIG. 9, respectively.
[0023]
As shown in FIGS. 6 and 7, the 0.2% proof stress tends to decrease slightly as the solution heat treatment temperature increases, but as shown in FIG. 7, it is almost equal to the change in Cr content. However, as shown in FIG. 6, the test composition 2 (low Nb material) has lower strength than the test composition 1 (standard material) and is lower than the JIS standard. Further, as shown in FIG. 8 and FIG. 9, the tensile strength tends to decrease slightly as the solution heat treatment temperature increases, but as shown in FIG. However, as shown in FIG. 8, the test composition 2 (low Nb material) has lower strength than the test composition 1 (standard material) and is below the JIS standard. Therefore, from the results of the tensile test, it is understood that the solution heat treatment temperature is preferably 980 ° C. or higher and the Nb + Ta amount is preferably 4.90% or higher by weight.
[0024]
4) Grain size measurement Graphs summarizing the results of the crystal grain size measurement in relation to the solution heat treatment temperature and the crystal grain size number are shown in FIGS. 10 and 11, respectively. The grain size number shows a tendency to decrease as the solution heat treatment temperature increases for any test composition. When the solution heat treatment temperature is 1070 ° C. or higher, the crystal grain size number of each test composition is 5 or less. Since it is not desirable that the crystal grain size number is small, it is understood that the solution heat treatment temperature is preferably 1040 ° C. or lower.
[0025]
5) From the above solution heat treatment, it can be seen that the solution heat treatment temperature is preferably 995 ° C. to 1040 ° C. On the other hand, the solution heat treatment time is 3 hours as an example here.
[0026]
Therefore, the solution heat treatment time when the solution heat treatment temperature was 995 ° C. to 1040 ° C. was examined using the parameter P of Larson Miller as shown below.
[0027]
P = T (c + Logt)
Here, P: parameter, T: absolute temperature (K), c = constant (23 here), t: time (hr). Table 2 shows the results of arranging the solution heat treatment conditions and the heating time performed here with the parameters of the Larson Miller of the following equation.
[0028]
[Table 2]
As shown in Table 2, the parameter when heated at a temperature of 1040 ° C. for 3 hours is 30825, and the parameter when heated at a temperature of 995 ° C. for 3 hours is 29769. The parameter when heated at a temperature of 995 ° C. for 20 hours is 30814, which is almost the same as the parameter (30825) when heated at a temperature of 1040 ° C. for 3 hours. On the other hand, the parameter when heated at a temperature of 1040 ° C. for 30 minutes is 29804, which is almost the same as the parameter when heated at a temperature of 995 ° C. for 3 hours (29769).
[0030]
Therefore, it can be seen that the solution heat treatment time is preferably 2 to 20 hours.
[0031]
From the above, the precipitation-strengthened nickel-base alloy having excellent intergranular stress corrosion cracking resistance has a Cr weight percentage of 19.0% to 21.0% and a Nb + Ta weight percentage of 4. It is 90% or more and 5.40% or less, and others have the same chemical composition as the NCF718 alloy.
[0032]
In addition, as a heat treatment method for such a nickel-base alloy, a solution heat treatment that is air-cooled by heating for 2 hours to 20 hours at a temperature of 995 ° C. to 1040 ° C. is performed, and Larson represented by the following formula of the solution heat treatment: The mirror parameter P may be in the range of 29769-30825.
P = T (c + Logt),
However, T: Absolute temperature (K), c = 23 (constant), t: Time (hr).
[0033]
Therefore, by using nuclear members such as springs, bellows, fuel support grids, and bolts manufactured with such nickel-based alloys for fuel assemblies and reactor internal structures, even in high-temperature and high-pressure water. It has excellent intergranular stress corrosion cracking resistance and can withstand long-term use in an environment of high temperature and high pressure water in a nuclear reactor.
[0034]
As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, this invention is not limited to this structure. Within the scope of the invented technical idea of the scope of claims, a person skilled in the art can conceive of various changes and modifications. The technical scope of the present invention is also applicable to these changes and modifications. It is understood that it belongs to.
[0035]
【The invention's effect】
As described above, according to the present invention, it has superior intergranular stress corrosion cracking resistance in high-temperature and high-pressure water as compared with NCF718 alloy, and thus can withstand long-term use in an environment of high-temperature and high-pressure water. It is possible to realize a nickel-base alloy, a heat treatment method for the nickel-base alloy, and a nuclear member using the nickel-base alloy.
[Brief description of the drawings]
FIG. 1 is a front view and a side view showing the shape of a test piece. FIG. 2 is a view showing a relationship between a solution heat treatment temperature and a grain boundary fracture surface ratio (trend with respect to Nb content).
FIG. 3 is a graph showing the relationship between the solution heat treatment temperature and the grain boundary fracture surface ratio (trend with respect to Cr content).
FIG. 4 is a graph showing the relationship between the solution heat treatment temperature and the corrosion rate (trend with respect to Nb content).
FIG. 5 is a graph showing the relationship between the solution heat treatment temperature and the corrosion rate (trend with respect to Cr content).
FIG. 6 is a graph showing the relationship between solution heat treatment temperature and 0.2% proof stress (trend with respect to Nb content).
FIG. 7 is a graph showing the relationship between solution heat treatment temperature and 0.2% proof stress (trend with respect to Cr content).
FIG. 8 is a graph showing the relationship between the solution heat treatment temperature and the tensile strength (trend with respect to the amount of Nb).
FIG. 9 is a graph showing the relationship between solution heat treatment temperature and tensile strength (trend with respect to Cr content).
FIG. 10 is a graph showing the relationship between the solution heat treatment temperature and the crystal grain size number (trend with respect to Nb content).
FIG. 11 is a graph showing the relationship between the solution heat treatment temperature and the grain size number (trend with respect to Cr content).
[Explanation of symbols]
12 ... Test piece
Claims (4)
Ｐ＝Ｔ（ｃ＋Ｌｏｇｔ）、
ただし、Ｔ：絶対温度（Ｋ）、ｃ＝２３（定数）、ｔ：時間（ｈｒ）。 C: 0.08% or less in weight percent, Si: 0.35% or less, Mn: 0.35% or less, P: 0.015% or less, S: 0.015% or less, Ni: 50.0% or more 55.0% or less, Cr: 17.0% or more and 21.0% or less, Mo: 2.80% or more and 3.30% or less, Cu: 0.30% or less, Al: 0.20% or more and 0.80 %, Ti: 0.65% or more and 1.15% or less, Nb + Ta: 4.75% or more and 5.50% or less, B: 0.006% or less, and the balance Fe and a chemical composition consisting of inevitable impurities the nickel-base alloy at a temperature of 995 ℃ ~1040 ℃, subjected to a solution heat treatment for cooling and heating for 2 hours to 20 hours, the parameter P of Larsson mirror represented by the following formula of the solution treatment is from 29,769 to 30,825 The range of Ni Heat treatment method of the Le-based alloy.
P = T (c + Logt),
However, T: Absolute temperature (K), c = 23 (constant), t: Time (hr).
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