JP2005292025A - Method of determining plane strain fracture toughness value - Google Patents

Method of determining plane strain fracture toughness value Download PDF

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JP2005292025A
JP2005292025A JP2004109899A JP2004109899A JP2005292025A JP 2005292025 A JP2005292025 A JP 2005292025A JP 2004109899 A JP2004109899 A JP 2004109899A JP 2004109899 A JP2004109899 A JP 2004109899A JP 2005292025 A JP2005292025 A JP 2005292025A
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fracture toughness
plane strain
toughness value
value
test
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Hiromi Uemura
啓美 植村
Akira Kiuchi
晃 木内
Takao Inoue
隆夫 井上
Atsushi Wakami
淳 若三
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Kansai Electric Power Co Inc
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<P>PROBLEM TO BE SOLVED: To provide a method of finding an accurate plane strain fracture toughness value of low alloy steel such as that in a turbine rotor, using a test piece remarkably smaller than a conventional specification. <P>SOLUTION: In this plane strain fracture toughness value determining method of finding the plane strain fracture toughness value by a fracture toughness test, a measured value K<SB>C</SB>is a value equivalent to the plane strain fracture toughness value, when a test result satisfies B≥1.0(K<SB>C</SB>/σ<SB>Y</SB>)<SP>2</SP>, where B is a thickness of the test piece, K<SB>C</SB>is the fracture toughness value measured by the fracture toughness test, and σ<SB>Y</SB>represents a yield stress or 0.2% proof stress. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

この発明は、ＣｒＭｏＶ鋼などの低合金耐熱鋼により構成されたタービンロータなどの平面ひずみ破壊靭性値の判定方法に関する。   The present invention relates to a method for determining a plane strain fracture toughness value of a turbine rotor made of a low alloy heat resistant steel such as CrMoV steel.

脆性破壊による使用限度を定量的に評価する上で破壊靭性値を求めることが重要であるが、一般に破壊靭性は材料の厚さに依存し、材料の厚さが薄い場合は大きく、材料が厚くなるに従って小さくなり、ある程度以上の厚さになると下限値に収束する。この下限値は平面ひずみ破壊靭性値と呼ばれ、通常ＫICと表記される。発電用タービンロータのような大型設備の破壊に対する評価には、この下限値である平面ひずみ破壊靭性値による評価が必要である。 It is important to obtain the fracture toughness value to quantitatively evaluate the limit of use due to brittle fracture, but generally the fracture toughness depends on the thickness of the material, and when the thickness of the material is thin, it is large, and the material is thick. As the thickness becomes smaller, it converges to the lower limit when the thickness reaches a certain level. This lower limit is called the plane strain fracture toughness value and is usually expressed as K IC . For the evaluation of the destruction of a large-scale facility such as a turbine rotor for power generation, an evaluation based on the plane strain fracture toughness value which is this lower limit value is required.

破壊靭性値は通常ＡＳＴＭ（アメリカ材料試験協会規格）Ｅ３９９−９０に規定される条件にしたがって求められるが、上記のＡＳＴＭ Ｅ３９９−９０に従ってタービンロータ材のような低合金鋼の破壊靭性値を求めるためには、試験片厚さについて必要とされる条件が非常に厳しく、板厚の大きな巨大な試験片を準備して、大型試験機を用いた大規模な試験が必要となる。このため、同等の結果を得ることが可能な、より簡便な試験条件の検討がなされている。これに関するものとして、非特許文献１がある。
池田 一夫、外４名，「タービンロータ材の破壊じん性およびＫＩＣ値の判定条件」，神戸製鋼技報，株式会社神戸製鋼所，１９７９年，Ｖｏｌ．２９，Ｎｏ．４ Fracture toughness values are usually determined according to the conditions specified in ASTM (American Society for Testing and Materials) E399-90, but in order to determine the fracture toughness values of low alloy steels such as turbine rotor materials according to the above ASTM E399-90 In this case, the conditions required for the thickness of the test piece are very strict, and a large-scale test using a large test machine is required by preparing a huge test piece having a large plate thickness. For this reason, examination of simpler test conditions that can obtain equivalent results has been made. Regarding this, there is Non-Patent Document 1.
Kazuo Ikeda and 4 others, “Judgment conditions for fracture toughness and KIC value of turbine rotor materials”, Kobe Steel Technical Report, Kobe Steel, 1979, Vol. 29, no. 4

上記のように、タービンロータ材のような低合金鋼に対する平面ひずみ破壊靭性値を求めるために、上記のＡＳＴＭ Ｅ３９９−９０の規定に従って求められる値と、同等の結果を得ることが可能な、より簡便な条件の確立が求められている。   As described above, in order to obtain a plane strain fracture toughness value for a low alloy steel such as a turbine rotor material, it is possible to obtain a result equivalent to the value obtained in accordance with the above-mentioned ASTM E399-90. Establishment of simple conditions is required.

この発明は、上記課題を解決するためになされたものであり、タービンロータなどの低合金鋼の正確な平面ひずみ破壊靭性値を、従来の規格よりも相当小さな試験片により求める方法を提供することを目的とする。   The present invention has been made to solve the above problems, and provides a method for obtaining an accurate plane strain fracture toughness value of a low alloy steel such as a turbine rotor by using a test piece considerably smaller than a conventional standard. With the goal.

この発明に基づいた平面ひずみ破壊靭性値の判定方法に従えば、破壊靭性試験により平面ひずみ破壊靭性値を求める平面ひずみ破壊靭性値の判定方法において、破壊靭性試験に用いられる試験片が、試験片厚をＢ、破壊靭性試験により測定された破壊靭性値をＫC、降伏応力または０.２％耐力をσYとすると、１．０（ＫC／σY）２≦Ｂを満たす試験片厚Ｂにより平面ひずみ破壊靭性値と同等の値が得られる。 According to the method for determining the plane strain fracture toughness value based on the present invention, in the method for determining the plane strain fracture toughness value for obtaining the plane strain fracture toughness value by the fracture toughness test, the test piece used for the fracture toughness test is a test piece. Specimen thickness satisfying 1.0 (K C / σ Y ) 2 ≦ B, where B is the thickness, K C is the fracture toughness value measured by the fracture toughness test, and σ Y is the yield stress or 0.2% proof stress. By B, a value equivalent to the plane strain fracture toughness value is obtained.

上述のように、脆性破壊靭性は、図１に示すように、薄い試験片では大きく、試験片が厚くなるに従って小さくなり、ある程度以上の厚さになると下限値に収束するという寸法依存性があり、この下限値は平面ひずみ破壊靭性値と呼ばれ、通常ＫICと表記される。 As described above, as shown in FIG. 1, the brittle fracture toughness is large for a thin test piece, decreases as the test piece becomes thicker, and has a dimensional dependence that converges to a lower limit when the thickness exceeds a certain level. This lower limit is called the plane strain fracture toughness value and is usually expressed as K IC .

発電用タービンロータのような大型設備の破壊に対する評価には、この下限値である平面ひずみ破壊靭性値による評価が必要であるが、図１に示すように高温域における正確な平面ひずみ破壊靭性を求めるためには、板厚の厚い大きな試験片が必要となる。   For the evaluation of the destruction of large equipment such as a turbine rotor for power generation, it is necessary to evaluate by the plane strain fracture toughness value which is this lower limit value, but as shown in FIG. In order to obtain it, a large test piece having a large plate thickness is required.

そのためタービンロータの強度評価において重要な、図２に示す脆性破壊高温域における平面ひずみ破壊靭性値を正確に求めるためには、ある程度以上の厚みの試験体が必要となる。この平面ひずみ破壊靭性値を求めるための規格として、上述のＡＳＴＭ Ｅ３９９−９０がある。発明者らは、長期間使用後に取り外された低合金製タービンロータを輪切りにし、この規格に準拠するように、図３に示すような試験片の厚さが２００ｍｍの大型試験体を製作して、脆性破壊高温域での正確な平面ひずみ破壊靭性値を求めることができることを確認している。   Therefore, in order to accurately obtain the plane strain fracture toughness value in the brittle fracture high temperature region shown in FIG. 2, which is important in the strength evaluation of the turbine rotor, a specimen having a thickness of a certain level or more is required. As a standard for obtaining the plane strain fracture toughness value, there is the above-mentioned ASTM E399-90. The inventors cut a low-alloy turbine rotor removed after long-term use, and manufactured a large specimen having a test piece thickness of 200 mm as shown in FIG. 3 so as to comply with this standard. It has been confirmed that an accurate plane strain fracture toughness value in a brittle fracture high temperature range can be obtained.

一方、ＡＳＴＭ Ｅ３９９−９０は、元来高強度鋼、高力アルミニウム、チタン合金などの高強度低靭性材を主な対象として開発されたものであった。そのため、これらの延性の低い材料については、簡易に破壊靭性値の下限値である平面ひずみ破壊靭性値が求められる試験方法があるが、タービンロータ材のような強度に比べて靭性の高い低中強度鋼に対して適用し正確な平面ひずみ破壊靭性値を求めようとする場合には、その判定条件を満足するために、非常に板厚の厚い大きな試験片が必要となる。   On the other hand, ASTM E399-90 was originally developed mainly for high-strength low-toughness materials such as high-strength steel, high-strength aluminum, and titanium alloys. Therefore, for these materials with low ductility, there is a test method in which the plane strain fracture toughness value, which is the lower limit value of the fracture toughness value, can be easily obtained. When applying to high-strength steel and obtaining an accurate plane strain fracture toughness value, a large specimen having a very large plate thickness is required to satisfy the judgment condition.

しかし、これまでの実験結果から、タービンロータ材のような低合金鋼においては、ＡＳＴＭ Ｅ３９９−９０で要求される試験片厚さを厳密には満たさない薄い試験片厚で実施した試験でも、破壊靭性値の下限値である平面ひずみ破壊靭性値に相当する結果の得られることが経験的に知られている。   However, based on the results of previous experiments, even in tests conducted with a thin specimen thickness that does not strictly satisfy the specimen thickness required by ASTM E399-90, the fracture of low alloy steels such as turbine rotor materials It is empirically known that a result corresponding to the plane strain fracture toughness value which is the lower limit value of the toughness value can be obtained.

破壊靭性試験実施時の負荷荷重の変化と、その際の亀裂の開口変位の関係、すなわち、荷重−開口変位曲線の試験時に現れる代表的な形態を模式図として図４に示す。図４において、Ｐmaxは荷重の極大値、Ｐ5は原点における、荷重−開口変位曲線の傾きより、５％少ない傾きを有する直線（５％ Secant Line）を、原点を通るように引いたときのその直線と荷重−開口変位曲線との交点である。ＡＳＴＭ Ｅ３９９−９０においては、ＰQは、図４のタイプ（ａ）のように、Ｐ5より先に荷重の極大値Ｐmaxが現れる場合には、Ｐmax＝ＰQ、タイプ（ｂ）および（ｃ）のように、ＰmaxがＰ5より後に生じる場合には、Ｐ5＝ＰQと表される。 FIG. 4 is a schematic diagram showing a typical form appearing during the test of the load-to-opening displacement curve, that is, the relationship between the change in the load applied during the fracture toughness test and the crack opening displacement at that time. In FIG. 4, P max is the maximum value of the load, and P 5 is a straight line (5% Secant Line) having an inclination of 5% less than the inclination of the load-opening displacement curve at the origin, passing through the origin. Is the intersection of the straight line and the load-opening displacement curve. In ASTM E399-90, P Q is equal to P max = P Q , type (b) and P max when the maximum load value P max appears before P 5 as shown in FIG. 4 type (a). When P max occurs after P 5 as shown in (c), P 5 = P Q is expressed.

上述のタービンロータ材のような低合金鋼についてＡＳＴＭ Ｅ３９９−９０の要求を厳密に満たさない薄い試験片厚さで平面ひずみ破壊靭性値に相当する結果の得られる例として、非特許文献１においては、2.8Ni-Cr-Mo-Vロータ材を用いた実験結果をもとに、破壊靭性試験時の荷重−開口変位曲線が原点を通る５％ Secant Lineと荷重−開口変位曲線との交点（Ｐ5）と交わる以前に不安定破壊すれば、すなわち図４のタイプ（ａ）での破壊形態の場合なら、ＡＳＴＭ Ｅ３９９−９０の試験片厚さの要求である、Ｂ≧２.５（ＫC／σY）２（ここで、σYは降伏応力または０．２％耐力）の条件を満足していなくても試験により得られた破壊靭性値ＫQは平面ひずみ破壊靭性値ＫICとみなせると報告している。 As an example of obtaining a result corresponding to the plane strain fracture toughness value with a thin specimen thickness that does not strictly meet the requirements of ASTM E399-90 for the low alloy steel such as the above-described turbine rotor material, Based on the experimental results using 2.8Ni-Cr-Mo-V rotor material, the intersection of the load-opening displacement curve with the 5% secant line through which the load-opening displacement curve during the fracture toughness test passes the origin (P 5 ) If unstable fracture occurs before crossing with (i.e., in the case of the fracture mode of type (a) in FIG. 4), the test piece thickness requirement of ASTM E399-90, B ≧ 2.5 (K C / Σ Y ) 2 (where σ Y is the yield stress or 0.2% proof stress) The fracture toughness value K Q obtained by the test can be regarded as the plane strain fracture toughness value K IC even if the condition is not satisfied. It is reported.

このため、破壊靭性値の試験片厚依存性を評価するため、上述の規格に基づいて平面ひずみ破壊靭性値の得られた試験後の大型試験体から、試験片厚さを変えた小型の試験片を採取し、破壊靭性試験を実施して試験片厚さと破壊靭性値との関係を検討した。評価のために用いた小型の試験片の形状は、図５に示すＣＴ試験片（Compact Tension試験片）で試験片厚をＢ、亀裂長さをａ、試験片幅をＷとすると、Ｂ＝ａ＝Ｗ−ａである標準ＣＴ試験片とした。また、図６に示すように、２５ｍｍ厚試験片（１ＣＴ）、５０ｍｍ厚試験片（２ＣＴ）を各試験片の亀裂先端部が、大型試験体の亀裂先端を通る同心円に一致するように採取して加工し、これらの試験片により大型試験体と同一温度にて破壊靭性試験を実施し、破壊靭性値を求めた。   For this reason, in order to evaluate the dependence of the fracture toughness value on the specimen thickness, a small test with the specimen thickness changed from the large specimen after the test in which the plane strain fracture toughness value was obtained based on the above-mentioned standard. Pieces were collected and subjected to a fracture toughness test to examine the relationship between the specimen thickness and the fracture toughness value. The shape of the small test piece used for the evaluation is as follows. The CT test piece (Compact Tension test piece) shown in FIG. 5 has a test piece thickness of B, a crack length of a, and a test piece width of W. It was set as the standard CT test piece which is a = W-a. In addition, as shown in FIG. 6, 25 mm-thick specimens (1CT) and 50-mm specimens (2CT) were sampled so that the crack tip of each specimen coincides with a concentric circle passing through the crack tip of the large specimen. These samples were subjected to fracture toughness tests at the same temperature as the large specimens, and the fracture toughness values were determined.

併せて、破壊靭性値の試験片厚依存性について、ＡＳＴＭ Ｅ３９９−９０の標準ＣＴ試験片を対象として３次元弾塑性有限要素法解析による解析検討も行なった。解析的検討においては、３次元ソリッド要素を用い、境界条件は、図７に示すとおりとした。   In addition, the specimen thickness dependence of the fracture toughness value was also analyzed by three-dimensional elastoplastic finite element method analysis for standard CT specimens of ASTM E399-90. In the analytical study, a three-dimensional solid element was used, and the boundary conditions were as shown in FIG.

この結果、標準ＣＴ試験片の試験片厚さを変えて実施した試験結果と、上述の解析結果を併記した図８に示すような破壊靭性Ｋｃ（ＭＰａ・ｍ１／２）と試験片厚Ｂ（ｍｍ）との関係を求めることができた。図８において黒丸印（●）は、ＡＳＴＭ Ｅ３９９−９０の平面ひずみ破壊靭性値の条件を満たした試験結果、白丸印（○）は、平面ひずみ破壊靭性値の条件は満たさなかったが、図４のタイプ（ａ）の破壊形態を示した試験結果、ばつ印（×）は、図４のタイプ（ｂ）または（ｃ）の破壊形態を示した試験結果、黒三角印は、解析結果である。図８によると、試験片厚Ｂが小さくなるに従い、破壊靭性Ｋcは大きくなるが、ＡＳＴＭ Ｅ３９９−９０に準拠する試験片厚より相当小さくなっても、それと同等の破壊靭性値ＫCが得られることがわかる。ＡＳＴＭ Ｅ３９９と同等の結果が得られる限界は、降伏応力または０.２％耐力をσY（ＭＰａ）とすると、次のように表すことができる。 As a result, the fracture toughness Kc (MPa · m 1/2 ) and the specimen thickness B as shown in FIG. 8 in which the test results obtained by changing the specimen thickness of the standard CT specimen and the above analysis results are shown. The relationship with (mm) could be obtained. In FIG. 8, black circles (●) indicate test results that satisfy the conditions of the plane strain fracture toughness value of ASTM E399-90, while white circles (◯) do not satisfy the conditions of the plane strain fracture toughness value. 4 is a test result showing a type of fracture (a), a cross mark (×) is a test result showing a type (b) or (c) of FIG. 4, and a black triangle is an analysis result. . According to FIG. 8, as the specimen thickness B decreases, the fracture toughness K c increases, but even when the specimen thickness in accordance with ASTM E399-90 is considerably smaller, the equivalent fracture toughness value K C is obtained. I understand that The limit at which results equivalent to ASTM E399 can be obtained can be expressed as follows, assuming that yield stress or 0.2% yield strength is σ Y (MPa).

Ｂ≧１.０（ＫC／σY）２
ＡＳＴＭ Ｅ３９９においては、試験により得られた破壊靭性値ＫQが、平面ひずみ破壊靭性値ＫICであるための、試験片厚に対する判定条件は、Ｂ≧２.５（ＫC／σY）２であるので、上記の判定条件は、ＡＳＴＭ Ｅ３９９で要求される試験片厚の４０％程度の厚さの試験片により、平面ひずみ破壊靭性値と同等の値が得られることとなり、供試材の確保、試験実施に際しての費用および試験の手間の面での制約が格段に小さくなる。 B ≧ 1.0 (K C / σ Y ) 2
In ASTM E399, since the fracture toughness value K Q obtained by the test is the plane strain fracture toughness value K IC , the judgment condition for the specimen thickness is B ≧ 2.5 (K C / σ Y ) 2 Therefore, the above judgment condition is that a test piece having a thickness of about 40% of the test piece thickness required by ASTM E399 can obtain a value equivalent to the plane strain fracture toughness value. Costs for securing and conducting tests and constraints on the labor of testing are greatly reduced.

破壊靭性と材料の厚さの関係を示すグラフである。It is a graph which shows the relationship between fracture toughness and material thickness. 破壊靭性と試験温度の関係を示すグラフである。It is a graph which shows the relationship between fracture toughness and test temperature. 破壊靭性試験の試験体の形状を示す、（ａ）は正面図、（ｂ）は右側面図である。The shape of the test body of a fracture toughness test is shown, (a) is a front view, (b) is a right side view. 荷重−開口変位曲線の試験時に現れる代表的な形態を示す模式図である。It is a schematic diagram which shows the typical form which appears at the time of the test of a load-opening displacement curve. ＣＴ試験片の形状を示す斜視図である。It is a perspective view which shows the shape of CT test piece. ＣＴ試験片の採取位置を示す、（ａ）は正面図、（ｂ）は右側面図である。The sampling position of a CT test piece is shown, (a) is a front view, and (b) is a right side view. ３次元弾塑性解析における境界条件を示す図である。It is a figure which shows the boundary conditions in a three-dimensional elastic-plastic analysis. 標準ＣＴ試験片による試験結果と３次元弾塑性解析の解析結果を示すグラフである。It is a graph which shows the test result by a standard CT test piece, and the analysis result of a three-dimensional elastic-plastic analysis.

Claims (1)

破壊靭性試験により平面ひずみ破壊靭性値を求める平面ひずみ破壊靭性値の判定方法であって、
前記破壊靭性試験に用いられる試験片の、試験片厚をＢ、破壊靭性試験により測定された破壊靭性値をＫC、降伏応力または０.２％耐力をσYとすると、１．０（ＫC／σY）２≦Ｂの判定条件により、求められた破壊靭性値ＫCは、平面ひずみ破壊靭性値と同様の値が得られる、平面ひずみ破壊靭性値の判定方法。 A method for determining a plane strain fracture toughness value by obtaining a plane strain fracture toughness value by a fracture toughness test,
When the specimen thickness used in the fracture toughness test is B, the fracture toughness value measured by the fracture toughness test is K C , and the yield stress or 0.2% proof stress is σ Y , 1.0 (K C / σ Y ) 2 ≦ B The determination method of the plane strain fracture toughness value in which the obtained fracture toughness value K C is the same value as the plane strain fracture toughness value.
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CN103926136A (en) * 2013-01-10 2014-07-16 中国石油天然气集团公司 Determination method for plane strain fracture toughness and safety critical wall thickness of pipeline steel

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103926136A (en) * 2013-01-10 2014-07-16 中国石油天然气集团公司 Determination method for plane strain fracture toughness and safety critical wall thickness of pipeline steel
CN103926136B (en) * 2013-01-10 2016-01-06 中国石油天然气集团公司 The defining method of pipe line steel plane strain fracture toughness and safety critical wall thickness

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