JPH08262009A - Evaluation method of remaining life of high-temperature member - Google Patents

Abstract

PURPOSE: To evaluate the remaining life of a high-temperature member with high accuracy by a method wherein the relationship between the quantified value of a shape and the damage amount of the high-temperature member is found in advance and the shape of a eutectic structure is quantified by an image processing method. CONSTITUTION: The creep rupture test of a creep-damaged material by using an unused material which is the same as an actual-machine material is executed under several conditions of different stresses. In addition, a sample whose rupture time has been interrupted at 10 to 90% of the time is prepared. Samples, for structure observation, which have been sampled from interrupted materials and ruptured materials are observed with a scanning electron microscope, and their eutectic structure shape is quantified at an aspect ratio by using an image analyzer. Then, the relationship between the aspect ratio and a damage amount is registered as a master curve 7 in a database 6. Then, a sample actual-machine observation is sampled from an actual machine in which the main damage of a moving blade is creep damage due to the result of an investigation, and it is observed in the same manner as the creation of the curve 7 so as to be quantified. this quantified value is applied to the curve 7, and the damage amount of the actual-machine material is found. Thereby, a remaining life can be evaluated with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the remaining life of a high temperature member used in a state having a eutectic structure.

[0002]

2. Description of the Related Art A high temperature member of a high temperature equipment such as a gas turbine which is used for a long time under a high temperature causes cracks during use due to accumulation of damage such as creep, which eventually progresses to damage. There is a danger of reaching. Therefore, it is necessary to quantify the damage amount of the material with high accuracy in the periodic inspection of the high temperature member. Therefore, in recent years, a method of quantifying the amount of damage of a material from a structural change of the material has come to be used as a method replacing classical visual appearance or hardness measurement. For example, γ'phase precipitation-strengthened Ni-based superalloys, which are widely used for high-temperature members such as rotor blades or stationary blades of gas turbines because of their excellent high-temperature strength, are characterized by γ'phase which is a precipitation-strengthened phase. Depends on the shape of. Therefore, as a method for quantitatively estimating the relationship between the structural change of the γ'phase and the degree of damage to the material, Japanese Patent Laid-Open Nos. 3-209162 and 4-25
The publicly known examples of 745 and JP-A-5-223809 are shown.

[0003]

A casting material is often used as a high temperature member of a high temperature equipment such as a gas turbine. However, segregation of alloying elements is present in the casting material. The solidified material has a large solidification segregation inside,
It is difficult to completely homogenize this by heat treatment. Therefore, a eutectic structure generated by solidification segregation exists in the high temperature member. Since the interface between the eutectic structure and the matrix that is almost homogenized by the heat treatment has a small compatibility, local stress concentration is likely to occur. However, in all of the above-mentioned three known examples, since attention is paid only to the structural change of the homogenized portion in which the γ ′ phase and the γ phase are coherently precipitated, stress concentration actually occurs, It is difficult to accurately quantify the amount of damage at the site where the most damage is accumulated in the material.

Therefore, the object of the present invention is to quantify the damage of the local region that most affects the life of the material, and to provide a highly accurate residual life of a high temperature member suitable for a material in which different structures due to solidification segregation coexist. To provide an evaluation method.

[0005]

As a result of studies to solve the above-mentioned problems, in the cast material, the stress concentration is most likely to occur in the eutectic structure and at the interface between the eutectic structure and the matrix. It became clear. Therefore, the present invention provides a method for evaluating the remaining life of a high-temperature member used in a state where a eutectic structure is formed during solidification, and the eutectic structure remains even after heat treatment, and the eutectic structure is used. And a step of quantifying the morphology of the crystal structure by an image processing method and a step of calculating the degree of damage and the remaining life of the material from the relationship between the quantitative value of the morphology and the amount of damage of the high temperature member which is obtained in advance. This is a characteristic method for evaluating the remaining life of high temperature members.
Furthermore, in addition to the morphology of the eutectic structure, the concentration ratio of the specific element in the eutectic structure and the dendrite core portion and the concentration of the specific element in the eutectic structure also indicate the local damage amount of the high temperature member. Quantification is possible. In the case of a γ'-phase precipitation strengthened Ni-base superalloy, it is effective to evaluate the remaining life by using a eutectic of the γ'-γ phase. Particularly in the case of unidirectionally solidified γ'-phase precipitation strengthened Ni-base superalloy, the tendency that local damage is accumulated in the eutectic of the γ'-γ phase is remarkable. Further, in the case of a carbide precipitation strengthening type Co-based alloy, highly accurate residual life evaluation can be performed with a eutectic carbide. In the case of a γ'phase precipitation strengthened Ni-based superalloy, the specific element is A which is a γ'phase forming element.
It is effective to use 1, Ti, Hf, Zr, Ta and Nb, but W, Mo, Cr and R which are γ phase forming elements.
It is also possible to use e or the base Ni or Co. Further, C or B that segregates toward the final solidified portion side of the eutectic structure can also be used. By quantifying the above concentration and morphology, it becomes possible to quantify damage such as creep damage, low cycle fatigue damage or high cycle fatigue damage.
Further, even when these damages are superposed, the remaining life can be evaluated by preparing an appropriate master curve. The present invention is mainly effective as a residual life evaluation method for moving blades or stationary blades of a gas turbine, but can also be used as a residual life evaluation method for other high temperature members using the same material.

[0006]

According to the residual life evaluation method of the present invention, it is possible to evaluate the residual life of a high temperature member used in a state having a eutectic structure with a higher accuracy than ever before. Further, the reliability of the high-temperature equipment maintained by the residual life diagnosis method of the present invention is much higher than the conventional one.

[0007]

【Example】

(Example 1) An example in which the amount of damage to the first-stage turbine rotor blade of a gas turbine used for a certain period of time was evaluated by the method of the present invention is shown below. This blade is a unidirectionally solidified γ'phase precipitation-strengthened N
Made of i-base superalloy.

FIG. 1 shows a flowchart of the present invention. According to this flowchart, a database is created prior to the evaluation of actual material. First, we show how to create a database for creep damage. First, a creep damage material is manufactured using an unused material that is the same as the material used in the actual machine (2). The creep rupture test was conducted under several conditions of different temperature and stress, and the rupture time was 10, 20, 30, 40, 50, 6 under the same conditions as the creep rupture test.
Samples that were interrupted at 0, 70, 80, 90% time were made. Here, each interrupted material is considered as a 50% damaged material when interrupted, for example, at 50% of the breaking time.
With respect to these interrupted materials and fractured materials, samples for microstructure observation were taken so that the observation surface was parallel to the stress loading direction (3b), and the morphology of the eutectic structure was observed (4b). Here, a scanning electron microscope was used for observation, and the morphology of the eutectic structure was quantified by the aspect ratio using an image analyzer.
(5b). FIG. 2 shows an observation example of a 40% damaged material. As shown in FIG. 2, the aspect ratio is as follows: b /
It was defined in a. When the 90% damaged material is observed, the aspect ratio of the eutectic structure is further increased, and cracks are generated starting from the interface between the eutectic structure and the matrix. From this, it is understood that there is a close relationship between the morphological change of the eutectic structure and the local damage of the region. The material used in this example is a unidirectionally solidified material that is solidified so that the principal stress axis direction and the solidification direction coincide with each other, and the eutectic structure is parallel to the principal stress axis direction. Therefore, the aspect ratio of the eutectic structure is less likely to be affected by differences in solidification conditions and crystal grains,
It is possible to evaluate the damage amount with high accuracy. The above result is
The horizontal axis shows the damage amount and the vertical axis shows the aspect ratio of the eutectic structure.

FIG. 3 shows the relationship between the aspect ratio and the damage amount. As shown in the drawing, there is a high correlation between the damage amount and the aspect ratio of the eutectic structure even under different test conditions. I understand. This relationship is registered in the database (6) as the master curve (7) for creep damage of this material.

Next, an example of creating a database of low cycle fatigue damage will be shown. Similar to the case of creep damage, first, a low cycle fatigue damage material is created using an unused material which is the same material as the material used in the actual machine (2). Under several conditions with different temperature and strain range, the low cycle fatigue life until the sample breaks is obtained. Then, under the same conditions as the fractured material, the number of fractures is 10, 20, 30, 40, 50, 60, 70, 8
A sample interrupted at a frequency of 0.90% was prepared. here,
Each interrupted material is considered to be 50% damaged if interrupted, for example, at 50% of the number of breaks. The morphology of the eutectic structure of these interrupted materials and fracture materials was quantified by the same method as the creep damage material (3b, 4b, 5b). As a result, it was found that even in low cycle fatigue damage, there is a high correlation between the damage amount and the aspect ratio of the eutectic structure, similar to creep damage. This relationship is registered in the database (6) as the master curve (7) for low cycle fatigue damage of the material.

Next, the evaluation method of the actual material will be described.
According to the flowchart of FIG. 1, first, the main damage forms of this rotor blade are investigated (1). The investigation revealed that the major damage to this blade was creep damage. Next, a sample for observing the actual device was taken from the actual device by the replica transfer method (3a) and observed with a transmission electron microscope (4).
a). This observation result was quantified by the same method as when creating the master curve (5a), and the quantitative value (42) was applied to the master curve for creep damage (7) in the database (6). The amount of damage (43) is calculated (8).

(Embodiment 2) An example in which the same blade as in Embodiment 1 is evaluated by another method will be described.

The eutectic structure of the sample used for preparing the master curve in Example 1 and the Al concentration in the dendrite core were measured using an energy dispersive X-ray spectroscopic analyzer attached to a scanning electron microscope. This result can be summarized by using the damage amount on the horizontal axis and the ratio of the Al concentration of the eutectic structure to the Al concentration of the dendrite core on the vertical axis.

FIG. 4 shows the relationship between the Al concentration and the amount of damage, and the master curve (51) shown in the figure is obtained.
Next, a test piece for scanning electron microscope observation was sampled from the rotor blade, and the Al concentration ratio was measured by the same method as when the master curve was created. This result (52) is the master curve (51)
Then, the actual machine damage amount (53) is obtained.

Further, the Hf concentration in the eutectic structure can be measured by the same method, and the master curve (61) shown in FIG. 5 can be obtained. If the Hf concentration (62) of the actual machine blade is obtained using this master curve, the actual machine damage amount (6
3) can be obtained.

[0016]

As described above, according to the present invention, it is possible to quantify the damage amount and evaluate the life with higher accuracy than ever before. Therefore, the reliability of the high temperature device is improved. In a gas turbine, which is a typical high-temperature device, according to the present invention,
It enables stable power supply, prevents unnecessary material replacement during regular inspections, and prolongs the period of regular inspections.

[Brief description of drawings]

FIG. 1 is a flowchart showing a process of evaluating a remaining life in the present invention.

FIG. 2 is a conceptual diagram showing a method for quantifying the morphology of a eutectic structure in Example 1.

FIG. 3 is a diagram showing the relationship between the amount of damage and the aspect ratio of a eutectic structure in Example 1.

FIG. 4 is a diagram showing the relationship between the damage amount and the ratio of the Al concentration of the eutectic structure to the Al concentration of the dendrite core in Example 2.

5 is a graph showing the relationship between the amount of damage and the Hf concentration of a eutectic structure in Example 2. FIG.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noriyuki Watanabe 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (17)

[Claims] 1. A method for evaluating the remaining life of a high temperature member having a eutectic structure, the step of quantifying the morphology of the eutectic structure by an image processing method, and the quantitative value of the morphology obtained in advance and the high temperature member. A method for evaluating the remaining life of a high temperature member, comprising the step of calculating the degree of damage or the remaining life of the material from the relationship with the amount of damage. 2. A method of evaluating the remaining life of a high temperature member having a eutectic structure, the step of quantifying the concentration ratio of the specific element in the eutectic structure and the dendrite core portion, and the previously determined specific element A method for evaluating the remaining life of a high temperature member, comprising the step of calculating the degree of damage or remaining life of the material from the relationship between the quantitative value of the concentration ratio and the amount of damage to the high temperature member. 3. A method for evaluating the remaining life of a high temperature member having a eutectic structure, the step of measuring the concentration of a specific element in the eutectic structure, and the concentration of the specific element previously obtained and the high temperature member. A method for evaluating the remaining life of a high-temperature member, comprising the step of calculating the degree of damage or the remaining life of the material in relation to the amount of damage. 4. The residual life evaluation method for a high temperature member according to claim 1, wherein the eutectic structure is a γ′-γ phase eutectic of a γ ′ phase precipitation strengthened Ni-base superalloy. 5. The high temperature member according to claim 1, wherein the eutectic structure is a γ'-γ phase eutectic of a γ'phase precipitation strengthened Ni-base superalloy having a unidirectionally solidified structure. Remaining life assessment method. 6. The residual life evaluation method for a high temperature member according to claim 1, wherein the eutectic structure is a eutectic carbide of a carbide precipitation strengthened Co-based alloy. 7. The concentration of the specific element according to claim 2 or 3 is one of Al, Ti, Hf, Zr, Ta and Nb or 2 of Al, Ti, Hf, Zr, Ta and Nb.
A method for evaluating the remaining life of high-temperature members, which is the sum of the concentrations of at least one element. 8. The concentration of the specific element according to claim 2 or 3 is one of Ni, Co, W, Mo, Cr and Re or 2 of Ni, Co, W, Mo, Cr and Re. A method for evaluating the remaining life of high-temperature members, which is the sum of the concentrations of at least one element. 9. A residual life evaluation of a high temperature member, wherein the concentration of the specific element according to claim 2 or 3 is the concentration of one of C or B or the concentration of two or more of the elements of C or B. Law. 10. The residual life evaluation method for a high temperature member according to claim 1, wherein the damage to the high temperature member is creep damage. 11. The method for evaluating the remaining life of a high temperature member according to claim 1, wherein the damage to the high temperature member is low cycle fatigue damage. 12. The method of evaluating the remaining life of a high temperature member according to claim 1, wherein the damage of the high temperature member is high cycle fatigue damage. 13. The residual life of the high temperature member according to claim 1, wherein the damage of the high temperature member is a damage in which two or more of creep damage, low cycle fatigue damage and high cycle fatigue damage are superposed. Evaluation method. 14. A method for evaluating the remaining life of a high temperature member according to any one of claims 1 to 13, which is a moving blade of a gas turbine. 15. A method for evaluating a remaining life of a high temperature member according to claim 1, which is a stationary blade of a gas turbine. 16. A high temperature device having the damage degree or remaining life display means according to the remaining life evaluation method for a high temperature member according to claim 1. 17. A gas turbine having the damage degree or remaining life display means according to the remaining life evaluation method for a high temperature member according to claim 1.