Property simulation material and method for manufacturing the same
The property simulation material and method address the challenge of simulating complex material property changes by combining cold rolling and second phase introduction, enabling accurate simulation of ductility and toughness for precise material evaluation.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- KK TOSHIBA
- Filing Date
- 2021-04-26
- Publication Date
- 2026-07-01
- Estimated Expiration
- Not applicable · inactive patent
AI Technical Summary
Existing methods struggle to accurately simulate the complex balance between changes in strength, ductility, and toughness of structural materials due to neutron irradiation and thermal aging, making it difficult to evaluate the degradation of properties in power generation equipment effectively.
A property simulation material and method that combines cold rolling and introduction of a second phase to simulate multiple properties such as ductility and toughness, adjusting chemical composition and mechanical processing to achieve desired material characteristics.
Enables simultaneous and accurate simulation of material properties like ductility and toughness, facilitating precise evaluation of material degradation in power generation equipment.
Smart Images
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Abstract
Description
Technical Field
[0001] Embodiments of the present invention relate to characteristic simulation materials and a method for manufacturing the same.
Background Art
[0002] With the aging of power generation equipment, improving the accuracy and reliability of soundness evaluation is important for the effective utilization and safety improvement of the entire power generation equipment.
[0003] In order to ensure the soundness of equipment during the operation period, design and manufacturing are carried out considering the aging deterioration events assumed for equipment and structures, and inspection and maintenance measures are taken within an appropriate period after the start of operation. In the soundness evaluation of equipment, an analysis of the progress of assumed aging deterioration events is performed, and the soundness is evaluated using as an index the occurrence or probability of damage leading to destruction or loss of function during the evaluation period. The evaluation methods and criteria used for such soundness evaluation are set based on obtaining material property data such as strength, toughness, and progress rate required for evaluating deterioration events.
[0004] It is known that structural materials of power generation equipment typified by nuclear power equipment exhibit characteristic changes such as hardening, ductility reduction, and embrittlement due to neutron irradiation accompanying nuclear reactions and thermal aging in a high-temperature environment. Conventionally, materials treated by irradiation or thermal aging under accelerated conditions have been used for the evaluation of materials with such deteriorated characteristics, but this takes time and cost, and in particular, in the case of neutron irradiation, there is also a problem of material activation, resulting in significant limitations in terms of quantity and management.
[0005] Due to such limitations, it is generally extremely difficult to obtain a sufficient number of material data required for the development, expansion, high-precision improvement, and appropriateness confirmation of evaluation methods and criteria. This is particularly important in the study of new evaluation methods that replace conventional evaluation methods studied based on limited data, the study using precious materials with limited quantities collected from actual in-service equipment, decommissioning equipment, etc., and the study of evaluation considering variations in material characteristics, in order to efficiently and effectively advance preliminary verification tests and studies.
[0006] It is known that neutron irradiation and thermal aging increase material strength, decrease ductility, and decrease toughness. Methods to simulate such degradation of material properties include applying cold working and introducing a second phase such as precipitates or inclusions. However, the way and degree to which each method contributes to the simulated properties differs. For this reason, in materials where the fracture mode gradually transitions from ductile to brittle over time, the balance between changes in strength such as decreased ductility and hardening and changes in toughness due to embrittlement becomes complex, and it is often difficult to simulate them appropriately. [Prior art documents] [Patent Documents]
[0007] [Patent Document 1] Japanese Patent Application Publication No. 2-236139 [Patent Document 2] Japanese Patent Application Publication No. 1-167633 [Overview of the project] [Problems that the invention aims to solve]
[0008] As mentioned above, in order to evaluate the degradation of properties such as hardening and embrittlement of structural materials of power generation equipment, such as nuclear power plants, due to neutron irradiation or thermal aging in high-temperature environments, methods other than using materials that have actually undergone neutron irradiation or thermal aging under accelerated conditions include methods of applying cold working and methods of introducing second phases such as precipitates and inclusions. However, the way and degree of contribution to the simulated properties differ depending on the method. For this reason, in materials whose properties gradually change over time during their service life, the balance between changes in strength such as ductility reduction and hardening and changes in toughness due to embrittlement becomes complex, making it difficult to simulate them appropriately.
[0009] This invention addresses the aforementioned conventional circumstances and aims to provide a property simulation material and a method for manufacturing the same that can simultaneously and accurately simulate two or more properties from among multiple properties of a material, such as ductility and toughness. [Means for solving the problem]
[0010] The property simulation material of the embodiment is a property simulation material that simulates the property degradation of a material that undergoes neutron irradiation during the operation of a power generation facility, resulting in an increase in material strength, a decrease in ductility, and a decrease in toughness, and the chemical composition of the material is adjusted compared to the material before the neutron irradiation. and heat This method is characterized by simultaneously simulating two or more properties from among multiple properties such as strength, ductility, and toughness, by combining the introduction of a second phase through processing with cold rolling. [Effects of the Invention]
[0011] According to embodiments of the present invention, it is possible to provide a property simulation material and a method for manufacturing the same that can simultaneously and accurately simulate two or more properties from among multiple properties of a material, such as ductility and toughness. [Brief explanation of the drawing]
[0012] [Figure 1] A diagram illustrating a property simulation material and its manufacturing method according to an embodiment. [Figure 2] A figure showing the properties and target values of a property simulation material according to the embodiment. [Figure 3] A diagram showing the properties and target values of the property simulation material related to the comparative example. [Modes for carrying out the invention]
[0013] The following describes the properties of the simulated material according to the embodiment and the method for manufacturing the same with reference to the drawings.
[0014] In this embodiment, as an example of a material whose properties change during the operation of a power generation facility, we will describe a property simulation material and its manufacturing method for stainless steel used in the in-reactor structures of a nuclear reactor. In stainless steel used in a reactor, exposure to fast neutron irradiation during the operation period leads to the accumulation of irradiation defects as the irradiation dose increases, resulting in an increase in material strength and hardness, and a decrease in ductility and fracture toughness.
[0015] These changes in strength properties and fracture toughness depend on the material properties before neutron irradiation, as well as the environmental conditions to which the material is exposed, such as temperature and neutron flux (the amount of neutrons received per unit time). Furthermore, although these properties are known to show the strong correlations mentioned above, the degree of change is not necessarily fixed, and the properties being simulated may be in a complex balance.
[0016] Figure 1 is a diagram illustrating the properties of a simulated material and its manufacturing method according to this embodiment. In Figure 1, the leftmost part shows the change in properties of the simulated material due to cold working as a mechanical process, with the left side showing stress and the right side showing toughness, the dashed line representing the original properties, the dotted line representing the target properties, and the solid line representing the simulated properties. Also in Figure 1, the central part shows the change in properties of the simulated material due to the introduction of a second phase, with the left side showing stress and the right side showing toughness, the dashed line representing the original properties, the dotted line representing the target properties, and the solid line representing the simulated properties. Furthermore, the rightmost part of Figure 1 shows the change in properties of the simulated material when cold working and the introduction of a second phase are combined, with the left side showing stress and the right side showing toughness, the dashed line representing the original properties, the dotted line representing the target properties, and the solid line representing the simulated properties. As shown in Figure 1, in this embodiment, by combining multiple simulation methods such as cold working and the introduction of a second phase, it is possible to accurately simulate neutron-irradiated stainless steel with desired properties.
[0017] Since dislocation density and mobility strongly contribute to the simulation of strength and ductility, mechanical processing such as rolling and forging can be used as the simplest method for controlling them. Other methods include introducing relatively small precipitates and lattice defects, and adjusting the chemical composition to inhibit cross-slip.
[0018] Toughness is strongly influenced by the ease of generation and growth of voids and the ease of cleavage fracture accompanying the progress of plastic deformation at the crack tip. Therefore, its control can use the introduction of the second phase (precipitates and inclusions) that serves as the starting point of fracture as the simplest method. Other methods include adjusting chemical components and heat treatment conditions that promote the generation and growth of voids and cleavage fracture, and further adjusting chemical components and structures that inhibit dislocation movement and cross-slip or promote the localization of deformation. As a result, it is possible to manufacture a test material that simulates the strength characteristics and fracture toughness in a desired balance.
[0019] Figure 2 shows the characteristics of a simulated material manufactured by subjecting a material obtained by intentionally adding 0.015 mass% of sulfur element (S) to 316L austenitic stainless steel used for in-reactor structures of nuclear reactors to cold rolling as a mechanical process.
[0020] The addition of sulfur element promotes the formation of sulfides in steel, and this is mainly intended to reduce toughness. Since the formation of sulfides occurs in the solution treatment at about 1000°C to 1200°C commonly used in the steelmaking process for heat treatment, only the solution treatment was performed. The target values of the characteristics of the simulated material were set according to the irradiation level based on the fact that the material characteristics of irradiated stainless steel change with the increase in neutron irradiation dose and tend to saturate above a certain irradiation dose. Irradiation dose level A is the irradiation dose at which significant changes occur in material characteristics due to neutron irradiation, irradiation dose level C is the irradiation dose at which material characteristics due to neutron irradiation are close to saturation, and irradiation dose level B is the intermediate irradiation dose.
[0021] For each such irradiation dose level, cold working rates of 10%, 15%, and 20% were imparted step by step. As shown in Figure 2, by combining the introduction of the second phase by adjusting chemical components and mechanical processing by cold rolling, the characteristics of strength (0.2% proof stress), ductility (elongation), and fracture toughness can be accurately simulated for the target characteristic values of the irradiated material.
[0022] In the manufacturing of this simulated material, the aim is to simulate the properties of stainless steel hardened by neutron irradiation. Therefore, mechanical processing by cold rolling is performed after heat treatment to effectively impart strain to the steel material and simulate its strength and ductility. However, the simulation method is not limited to this sequence of heat treatment and mechanical processing. Depending on the properties to be simulated, for example, mechanical processing can be performed before heat treatment to more effectively promote the formation of the second phase during heat treatment by pre-straining in the material. Furthermore, by using hot working or warm working for the mechanical processing, it is possible to achieve an appropriate balance between the formation of the second phase and the application of strain simultaneously.
[0023] Here, Figure 3 shows an example of a case that does not rely on a simulation method combining mechanical processing and second-phase introduction, as a comparative example. Figure 3 shows the properties of a simulated material that has been subjected to 25% cold working on commercially available stainless steel, which generally has a low sulfur content. The sulfur content of this stainless steel was 0.0004 mass% or less. While the strength (0.2% yield strength) and ductility (elongation) are accurately simulated against the target properties, there is a discrepancy in fracture toughness. As mentioned above, cold working is an effective method for simulating unique deformation behaviors such as an increase in material strength, a decrease in ductility, and the localization of sliding deformation due to an increase in irradiation dose, but it can be difficult to simulate properties, including the accumulation of irradiation defects and changes in fracture toughness due to irradiation-induced segregation, in a balanced manner using cold working alone. This result demonstrates that point and also shows the effectiveness of the property simulation method of the embodiment.
[0024] In the above embodiment, the method for introducing the second phase involved the addition of sulfur to stainless steel, but the method for introducing the second phase is not limited to the addition of sulfur to stainless steel. Impurity elements such as P, Sn, Sb, and As, which are known to cause tempering brittleness in steel, can also be used as additive elements to simulate a decrease in toughness due to grain boundary segregation. In the case of stainless steel, elements such as Si, Mo, V, and Nb promote the formation of a second phase that causes embrittlement, such as the σ phase. There is also a method of adjusting the toughness to the desired level by adding these elements and performing heat treatment that causes grain boundary segregation and precipitation of the second phase. In this case, two or more elements may be added.
[0025] Furthermore, properties altered by mechanical processing exhibit anisotropy corresponding to the direction of mechanical processing. By considering such anisotropy in the mechanical processing method and the setting of the test specimen sampling direction, detailed adjustment of properties becomes possible. Moreover, beyond mechanical properties such as strength and fracture toughness, methods for simulating a decrease in corrosion resistance can be used. For example, chromium deficiency at the grain boundaries of materials that causes a decrease in stress corrosion cracking resistance can be simulated by applying sensitization heat treatment at around 400°C to 900°C, which causes the formation of grain boundary carbides and the resulting chromium deficiency, or by applying an alloy with a lower chromium concentration in the base material. By combining these methods, it is possible to manufacture materials that simulate the changes in material properties during their service life with desired properties.
[0026] By using the simulated material fabricated by the method described above, and conducting strength and fracture tests with parameters such as strength characteristics, fracture toughness, and their balance, it is possible to quantitatively evaluate the changes in properties and behavior of structural materials due to aging.
[0027] Although several embodiments of the present invention have been described above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.
Claims
1. A property simulation material that simulates the property degradation of a material that undergoes neutron irradiation during operation of a power generation facility, resulting in an increase in material strength, a decrease in ductility, and a decrease in toughness. A property-simulating material characterized by simultaneously simulating two or more properties from among multiple properties of strength, ductility, and toughness by combining the introduction of a second phase through chemical composition adjustment and heat treatment with cold rolling of the material before it is subjected to neutron irradiation.
2. In the property simulation material described in claim 1, A property-simulating material characterized by adding at least one element from among S, P, Sn, Sb, As, Si, Mo, V, and Nb to adjust the aforementioned chemical composition.
3. A method for manufacturing a property-simulating material that simulates the property degradation of a material that undergoes property degradation due to neutron irradiation during operation of a power generation facility, resulting in an increase in material strength, a decrease in ductility, and a decrease in toughness. A method for manufacturing a material with simulated properties, characterized by simultaneously simulating two or more properties from among several properties such as strength, ductility, and toughness, by combining the introduction of a second phase through chemical composition adjustment and heat treatment with cold rolling of the material of the material before it is subjected to neutron irradiation.
4. In the method for manufacturing a property-simulating material according to claim 3, A method for producing a property-simulating material, characterized by adding at least one element from among S, P, Sn, Sb, As, Si, Mo, V, and Nb to adjust the aforementioned chemical composition.