JPS62255846A - Measuring method for fracture toughness value - Google Patents

Abstract

PURPOSE:To exactly grasp a fracture toughness value of a material by a small amount of test pieces, by deriving by an experiment one of a compressive yield stress and a modulus of longitudinal elasticity which can obtain a data from a minute test piece and the breakdown energy amount. CONSTITUTION:A test piece 4 is placed between a pedestal 5 and the upper cover 6, and fixed firmly with a set-screw 2. Subsequently, it is placed on a steel ball 3 and set through a hole 6a of the center of the upper cover 6. A punching test is executed by fixing the test piece 4 to a jig, and thereafter, applying a compressive force until the test piece 4 is broken down by the pedestal 5 and a push rod 1 by a tension tester in a state that the whole jig is in an extremely low temperature. A relation of a load and a displacement in this case is recorded. In this case, there is a strong correlation between impact absorbing energies of 100 deg.C and 200 deg.C of a breakdown energy of a punching test at -196 deg.C, and a fracture toughness value of 100 deg.C and 200 deg.C can be calculated by using each different experiential expression with regard to the upper shelf area and the transition temperature area.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to steam turbine rotors, casings, valve chambers, boiler tubes, steel plates, and other components of thermal power and nuclear power plants that are used at high temperatures and those that are used for long periods of time. This paper relates to a method for measuring the fracture toughness of general structural materials that become brittle.

[Conventional technology]

Conventionally, ASTM E399 or ASTM
Fracture toughness values KIC or Jrc are determined using test pieces with dimensions and methods specified in E813.

[Problem that the invention seeks to solve]

However, in the past, fracture toughness value) (IC or Jr.
When determining c, ASTM E399 or E813
Relatively large specimens are required, as specified in However, in many cases, it is practically impossible to collect test pieces as specified in ASTM E399 or E813 in order to measure the fracture toughness values of various parts of various plants in operation, such as heat exchanger tubes. Therefore, it was difficult to collect test pieces for measuring the fracture toughness value from the limited number of specimens, and there was a problem in that the fracture toughness value could not be measured in practice.

The present invention was made in view of the above-mentioned disadvantages of the conventional method, and an object of the present invention is to provide a method for measuring a fracture toughness value that can obtain a fracture toughness value by collecting a minute test piece.

[Means for solving problems]

In order to measure all the fracture toughness values of each member of a plant in operation, the present invention is carried out at a distance of, for example, 3 mm x 3 mm from the specimen.
In the first step, one or two rectangular parallelepiped specimens of 5 mm x 5 mm are usually taken and subjected to a micro compression test to determine the yield stress or longitudinal modulus.
0 + nm X O,5ynx thin piece 1 usually 1-2
Take a piece as a test piece.

A punching test was conducted at a cryogenic temperature, and the amount of fracture energy required for fracture was calculated from the load-displacement curve obtained in the punching test, and the amount of fracture energy was calculated from a predetermined evaluation standard curve. a second step of converting into a value; a second step of substituting the yield stress or modulus of longitudinal elasticity and 7 Jarby impact characteristic values obtained from the first step and the second step into the conversion formula;
This is a method for measuring fracture toughness value KIC, which is characterized by comprising:

[For production]

With the above-mentioned configuration, the present invention first determines either the compressive yield stress or the modulus of longitudinal elasticity from which data can be obtained from a micro test piece, and the amount of fracture energy through an experiment, and then uses a previously obtained correlation straight line to determine an extremely high correlation with the fracture energy. The fracture toughness value is calculated from the shock absorption energy and the yield stress or longitudinal elastic modulus using a conversion formula after obtaining the shock absorption energy value at the relevant test temperature. 2. Appropriate fracture toughness values can be obtained even when large test pieces cannot be cut.

By applying the present invention, it is also possible to diagnose the remaining life of an existing plant from the fracture toughness value.

〔Example〕

One embodiment of the present invention will be described in more detail.

The test material is CrMoV steel, which is a steam turbine rotor material that has actually been used for approximately 100,000 hours of operation, and its chemical composition is shown in Table 1.

The yield stress and longitudinal elastic modulus were measured by the micro compression test in the first step as follows. First, prepare a test piece of approximately 3 x 3
Cut out 5 friends.

To remove the processed layer on the surface, use a 5% perchloric acid + 95% acetic acid solution cooled to around 1080 ℃ and use a current condition of 40 to 6 ft.
Electrolytic polishing was performed at 0 V and 0.8 to 1.2 A for about 8 minutes. The thus obtained test piece was subjected to a compression test using a tension compression tester (not shown) to determine the yield stress. As a result e
As shown in Figures 1 to 3 and Table 2, the yield stress results from the micro compression test are slightly lower than the tensile test results compared to the test results obtained from the tensile test of JIS Z2204 test pieces. As shown, the values are almost the same.

Further, the impact ≦ characteristic in the punching test in the second step was measured as follows.

Figure 4 shows the jig used in the punching test.

FIG. 5 is a perspective view showing a test piece to be subjected to a punch-out test. In this embodiment, first, as shown in FIG.
A test piece 4 is sandwiched between a pedestal 5 and an upper lid 6, and firmly fixed with a set screw 2. Next, the steel ball 3 is placed on the test piece 4 through the center hole 6a of the upper lid 6, and the push rod 1 is inserted into the steel ball 3.
Place it on top of the cent. In the push-out test, as shown in Fig. 4, after fixing the test piece 4 to the test jig, the entire jig is placed in a cryogenic state, for example, in liquid nitrogen (-196°C), using a tension-compression tester (not shown). A compressive force is applied using the pedestal 5 and the push rod 1 until the test piece 4 breaks. Record the relationship between load and displacement at this time. Figure 6 shows an example of a load-displacement curve. From this load-displacement curve, the amount of fracture energy Jt required for generating a crack in each test piece was calculated.

This fracture energy iJ and the results of a 2 mmV nonochinyalpy impact test conducted separately are shown in FIGS. 7 and 8. Figures 7 and 8 show the fracture energy J required to generate a crack in a punch-out test conducted at a temperature of 196°C and the values obtained by a 2-hv notch 7-year-old impact test at 100°C and 200°C. It is a figure which shows the relationship of impact absorption energy (kgf-m) of degreeC. The solid line in the figure was determined from these experimental values. As is clear from this figure, there is a strong correlation between the fracture energy of the punching test at -196°C and the impact absorption energy of 100°C and 200°C.

Here, the fracture toughness values at 100°C and 200°C for material numbers 5 and 8 are calculated as follows.

The following empirical formula is used as a conversion formula for the fracture toughness value (1 (tc)).

(11 upper shelf area (1(IC/δy)” = 646(vE/δy) −
6,35----, a(1) formula 1 formula % krc = 0.833α (VE)3/4
Equation (2) where δy: Yield stress Ckgf/myn)vE: 2nmv Hatenjarby impact absorption energy (kgf-yn) E: Longitudinal elastic modulus (kgf/mf).

In addition, Fig. 9 shows the results of a 2mmV7.7-chip impact test of CrMoV steel, and also shows the results of the upper shelf area,
The transition temperature range and lower column region 50% FATT have been explained. What is 50% FATT? 50% Fracture App
earance Transition Teuoer
Abbreviation for ature, which refers to the temperature at which the areas of brittle and ductile fractures are equal in the 2Ryu vs. Notchiru Ruby impact test. There is a question of whether to use equation (1) or equation (2) when calculating the fracture toughness value, but as is clear from FIG. 9, the value of 50% FATT is an effective guideline.

Figure 10 shows the fracture energy values of the punching test at -196°C and the
Although the relationship of 0% FATT is shown.

There is a strong correlation between the two values, and they are summarized in one curve as shown in FIG. Therefore, 50% FAT from the fracture energy of the punching test at -196℃
T can be specified, and it can be determined whether to use equation (1) or equation (2).

In the case of material number 8, the 50% FATT is approximately 100°C, the fracture toughness value at 100°C is given by equation (2), and the fracture toughness value at 200°C is given by equation (11). Although 50% FATT is slightly higher than 100°C, it is the same as material number 8. Formula (2) is used for the fracture toughness value of <100°C, and Formula (11) is used for the fracture toughness value of 200°C.

First, the fracture toughness value is determined using material number 5.

1) From Table 2 at 100°C, E = 2. I x 10'kgf/m
m' 7th drawing vE = 1.7 kgf・m krc = 0.833X421000X1.74=
180 kgf/lm2 ii) At 200℃ From Figure 3 δy = 60.7 kgf/art No. 8
From the figure, vE = 5.9 kgf-m yacht kIc
= 60.7x/646X(5,9/60.7)-6
, 35 = 456 kgf〆i2 Next, the fracture resistance value of material number 8 is determined as follows.

i) From Table 2 at 100°C E == 2. I x 10'kgfA
m' From Figure 7, vE = 3.3 kgf-m, so kxc = o, 533xC21ooox3. Door = 2
95kg theory 1i) At 200℃, from Figure 3, δy = 58.5 kgf/Ia From Figure 8, δy -7,4kgf °m Therefore, kr c=5
8.7 X convex 46X (7,4158,5)-6,35=
510 kgf/+++” These results and 1 (I
I or JrC determined by ASTM E813 is kIC=
-J! Table 3 shows a comparison with krc obtained by substituting it into the formula - C E - (E: longitudinal elastic modulus, C: bore 1-V'Son's ratio).

From Table 3, it can be seen that the I(rC value determined by the method of the present invention agrees well with the value of the conventional method.

Note that in this embodiment, equations (1) and (2) were used, but depending on the material, it may be better to use the following conversion equation. For example, all temperature ranges such as welding parts) (kxc
/δy)' = 300(vF7δy) −・−・th(
3) Formula (total temperature range) kIc'/δy = 900'vE-...
Equation (4) δy=yield stress (kg f/I) VE=2 positive V notch Charpy impact absorption energy (kgf-□): ka-,,~! , I'll:, W l-~-knee: to Table 3 Fracture toughness value KIC 脣JrC was determined according to ASTM E813, and KIC was calculated by substituting it into the following formula.

KIC='J to'X-Si-(commonly used conversion formula)%
Formula % r: Poisson's ratio (here assumed to be 0.3) [Effects of the invention] The method of the present invention reduces the fracture toughness value of materials in parts exposed to high temperatures in currently operating plants, especially thermal nuclear power plants. It can be accurately determined with a test piece, and it is of great help in diagnosing remaining life, making a major contribution to the development of industry.

[Brief explanation of drawings]

Figure 1 shows the relationship between the yield stress determined from the microcompression test at room temperature and the yield stress determined from the tensile test of a J Is z2201.4 test piece, and Figure 2 shows the relationship between the yield stress determined from the microcompression test at 100°C. Yield stress and Jts z220
Figure 3 shows the relationship between the yield stress determined from the micro compression test at 200°C and the yield stress determined from the tensile test of the JTS Z2201, No. 4 test piece. A diagram showing the relationship between yield stress, FIG. 4 is a cross-sectional view showing the configuration of a jig (including a test piece) for a push-out test according to the present invention, and FIG. 5 shows the shape of a test piece to be subjected to a push-out test. A perspective view, Figure 6 is a diagram showing an example of a load-displacement curve obtained in a punching test and the definition of fracture energy, and Figure 7 is a diagram showing a crack in the test material in a punching test at a temperature of -196°C. Experimental value of fracture energy required to generate and 100℃
Figure 8 shows the relationship between the impact energy absorbed by a 2mm V notch/Yalpi T# at 200°C and the experimental value of the fracture energy required to generate a crack in the test material in a punching test at a temperature of -196°C. Figure 9 is a diagram showing an example of the results of a 2-way V-notch jarby impact absorption test, where the horizontal axis shows the test temperature, and the vertical axis shows the impact absorption energy and the brittle fracture ratio. This figure also shows the definitions of the lower column region, transition temperature region, upper shelf region, and 50% FATT. 1st
Figure 0 shows the experimental value of the fracture energy required to generate cracks in the test material during a punching test at a temperature of -196°C, and
50%F obtained in 2mm V notch 7 jarby impact test
It is a figure showing the relationship with ATT. 1... Push rod, 2... Set screw, 3... Steel ball, 4
...Test piece, 5...Pedestal, 6...Top lid, 6a
···hole. Load (kqf) 12-Hot

Claims (1)

[Claims] The first step is to determine the yield stress or modulus of longitudinal elasticity of the test piece through a micro compression test.The thin plate-shaped test piece is fixed to a jig, the test piece is pushed with a steel ball, and the load-displacement curve at that time is calculated. A second step of performing the desired push-out test at a cryogenic temperature, calculating the amount of fracture energy from the load-displacement curve, and converting the amount of fracture energy into a predetermined Charpy impact characteristic value; A method for measuring a fracture toughness value, comprising a third step of substituting the yield stress or modulus of longitudinal elasticity obtained in the two steps and the Charpy impact property value into a conversion formula.