Method for determining the initial test temperature of ferritic steel fracture toughness test

Abstract

An embodiment of the present invention discloses a method for determining the initial test temperature of a fracture toughness test of ferritic steel. The fracture toughness test is used to determine the ductile-brittle transition reference temperature of the ferritic steel. The method comprises: obtaining the ductile-brittle transition temperature of the sample based on an impact test of the sample of the ferritic steel; calculating the minimum temperature and the maximum temperature of the initial test temperature according to the ductile-brittle transition temperature, the size of the sample and the temperature characteristic factor; determining the initial test temperature according to the minimum temperature and the maximum temperature. The samples of different shapes and sizes have corresponding temperature characteristic factors, and the temperature characteristic factors are determined based on the shape and size of the sample. The method of the present invention can reduce the deviation between the initial test temperature and the reference temperature, so that an accurate reference temperature can be obtained by using fewer samples in the fracture toughness test.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of ferritic steel, and in particular to a method for determining an initial test temperature of a ferritic steel fracture toughness test. Background Art

[0002] When conducting a fracture toughness test to determine the reference temperature of the ductile-brittle transition of ferrite steel, it is necessary to first determine the initial test temperature of the fracture toughness test. At present, when determining the initial test temperature, a group of pilot samples are usually used for testing, and the initial test temperature is adjusted according to the test results. After repeated tests and adjustments, an initial test temperature that meets the requirements is obtained. For nuclear power plant irradiation supervision tube tests with a limited number of samples, there will be a problem of insufficient number of samples, and it is impossible to determine an initial test temperature that meets the requirements. Summary of the invention

[0003] According to one aspect of the present invention, a method for determining the initial test temperature of a fracture toughness test of ferritic steel is provided. The fracture toughness test is used to determine the ductile-brittle transition reference temperature of the ferritic steel. The method comprises: obtaining the ductile-brittle transition temperature of the sample based on an impact test of the sample of the ferritic steel; calculating the minimum and maximum temperatures of the initial test temperature according to the ductile-brittle transition temperature, the size of the sample and the temperature characteristic factor of the sample; determining the initial test temperature according to the minimum and maximum temperatures of the initial test temperature; the samples of different shapes and sizes have corresponding temperature characteristic factors, and the temperature characteristic factors are determined based on the shape and size of the sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Other objects and advantages of the present invention will become apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, which will help to provide a comprehensive understanding of the present invention.

[0005] Figure 1 The present invention is a flowchart of a method for determining an initial test temperature of a ferritic steel fracture toughness test according to an embodiment of the present invention.

[0006] Figure 2 is a schematic structural diagram of a sample according to an embodiment of the present invention.

[0007] Figure 3 yes Figure 2 Schematic diagram of the structure of the sample from another perspective.

[0008] Figure 4 is a schematic structural diagram of a sample according to another embodiment of the present invention.

[0009] Figure 5is a flow chart of a single temperature point method according to an embodiment of the present invention.

[0010] Figure 6 is a flow chart of a multi-temperature point method according to an embodiment of the present invention.

[0011] It should be noted that the drawings are not necessarily drawn to scale, but are merely shown in a schematic manner that does not affect the reader's understanding. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in conjunction with the drawings of the embodiments of the present application. Obviously, the described embodiment is one embodiment of the present application, not all embodiments. Based on the described embodiments of the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0013] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in this application should be the usual meanings understood by people with general skills in the field to which this application belongs. If the full text involves descriptions such as "first" and "second", the descriptions such as "first" and "second" are only used to distinguish similar objects, and cannot be understood as indicating or implying their relative importance, order of precedence, or implicitly indicating the number of technical features indicated. It should be understood that the data described by "first" and "second" can be interchangeable under appropriate circumstances. If "and / or" appears in the full text, its meaning is to include three parallel schemes, taking "A and / or B" as an example, including scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, for the convenience of description, spatial relative terms such as "above", "below", "top", "bottom", etc. can be used here, which are only used to describe the spatial position relationship between a device or feature as shown in the figure and other devices or features, and should be understood to also include different orientations in use or operation except for the orientation shown in the figure.

[0014] An embodiment of the present invention provides a method for determining the initial test temperature of a fracture toughness test of ferritic steel. The fracture toughness test is used to determine the ductile-brittle transition reference temperature T0 of the ferritic steel. In the fracture toughness test of ferritic steel, it is first necessary to select the initial test temperature of the fracture toughness test. The initial test temperature has a great influence on the test results of the fracture toughness test and the amount of ferritic steel samples required for the test. The closer the selected initial test temperature is to the reference temperature T0 of the sample, the more accurate the result obtained from the fracture toughness test, and the fewer the number of samples required for the test.

[0015] At present, technicians mostly determine the reference temperature T0 of ferritic steel by the test method in the American standard ASTM E1921. In this method, the initial test temperature is determined according to the Charpy impact test, and the initial test temperature T0′ is calculated using the following formula (1):

[0016] T′0=T CVN +C (1);

[0017] Where, T CVN =T 41J , T CVN is the ductile-brittle transition temperature obtained from the Charpy impact test, T 41J It is the ductile-brittle transition temperature of the Charpy impact with an absorbed energy of 41 J. C is a constant, and the value of C corresponds to the size of the sample used. The corresponding constant C can be selected according to the size of the sample. Among them, when the sample is a 1-inch thick sample, C is -24°C; when the sample is a 0.5-inch thick sample, C is -34°C.

[0018] The initial test temperature T0′ calculated by this method may have a large deviation from the actual reference temperature T0. When conducting a test at an initial test temperature T0′ with a large deviation, more samples are needed to obtain an accurate reference temperature T0. For tests such as the tube fracture toughness test in the irradiation supervision of reactor pressure vessels, where the number of samples is limited, the uncertainty of the reference temperature T0 obtained is increased. The method for determining the initial test temperature of a ferritic steel fracture toughness test provided by the present invention can significantly reduce the deviation between the initial test temperature and the actual reference temperature, compared with the above-mentioned determination of the initial test temperature based only on the Charpy impact test.

[0019] Figure 1 FIG. 1 is a flow chart showing a method for determining the initial test temperature of a ferritic steel fracture toughness test according to an embodiment of the present invention. Figure 1 As shown, the determination method in this embodiment includes the following steps.

[0020] Step S11, based on the impact test of the ferrite steel sample, obtaining the ductile-brittle transition temperature T of the sample K .

[0021] Wherein, the specimen includes a compact tensile specimen or a three-point bending specimen. In the present embodiment, the specimen is a compact tensile specimen, represented by the symbol C(T). Optionally, the C(T) specimen can be a straight-through notch compact tensile specimen or a step-notch compact tensile specimen. In the present embodiment, C(T) specimens of different sizes can be selected. Exemplarily, C(T) specimens of different thicknesses can be selected, represented by the symbol nC(T), where n represents a multiple of 1 inch. For example, 1C(T) represents a compact tensile specimen with a thickness of 1 inch, and 0.5C(T) represents a compact tensile specimen with a thickness of 0.5 inches.

[0022] Step S12, according to the ductile-brittle transition temperature, the size of the sample and the temperature characteristic factor δT of the sample type , calculate the minimum temperature T of the initial test temperature min and the maximum temperature T max .

[0023] Among them, the temperature characteristic factor δT type It is a structural parameter of the sample, which characterizes the structural characteristics of the sample. The samples of different shapes and sizes have corresponding temperature characteristic factors δT type The temperature characteristic factor δT can be determined based on the shape and size of the sample type For example, when using a 0.5C(T) sample, the corresponding temperature characteristic factor δT type =0℃.

[0024] Step S13, according to the lowest temperature T of the initial test temperature min and the maximum temperature T max , determine the initial test temperature T0′.

[0025] By adopting the determination method in this embodiment, the deviation between the initial test temperature and the reference temperature can be reduced, so that an accurate reference temperature T0 can be obtained by using fewer specimens in the fracture toughness test. For tests with a limited number of specimens, the test accuracy and effectiveness can be increased and the test difficulty can be reduced.

[0026] In this embodiment, an impact test, such as a Charpy impact test, can be performed on the sample, and the ductile-brittle transition temperature T can be obtained based on the test results. K For example, when the ductile-brittle transition temperature obtained based on the Charpy impact test is T CVN When T K Equal to T CVN .

[0027] Furthermore, the inverse hyperbolic cotangent function can be used to calculate the maximum temperature and the minimum temperature of the initial test temperature. The independent variables of the inverse hyperbolic cotangent function include the size of the sample and the ductile-brittle transition temperature T K Specifically, in the independent variables of the inverse hyperbolic cotangent function, the size of the sample includes the reference sample thickness B0 and the net thickness B of the sample. N .

[0028] Figure 2 and Figure 3 FIG. 2 shows a schematic diagram of the structure of a sample according to an embodiment of the present invention. Figure 2 and Figure 3 As shown, the side of the sample 10 has no grooves. For the sample 10 without grooves on the side, the net thickness B of the sample N That is the thickness B of the sample, that is, B N =B.

[0029] Figure 4 FIG. 2 shows a schematic diagram of the structure of a sample according to another embodiment of the present invention. Figure 4 As shown, the side of the sample 20 is provided with a groove 21. For the sample 20 with the groove 21 on the side, the net thickness B of the sample is N is the distance between the bottoms of the two grooves 21 in the sample 20.

[0030] In step S12, the lowest temperature T of the initial test temperature can be calculated using the first inverse hyperbolic cotangent function. min , the minimum temperature T min is the first inverse hyperbolic cotangent function and the temperature characteristic factor δT type In this embodiment, the first inverse hyperbolic cotangent function can be represented by A·arcth(X1)+B, where A and B are both constants. The independent variables of the first inverse hyperbolic cotangent function include: the size of the sample, such as the net thickness B N , and the ductile-brittle transition temperature T K .

[0031] Specifically, the minimum temperature T can be calculated using the following formula (2): min :

[0032]

[0033] In formula (2), arcth(x) represents the inverse hyperbolic cotangent function, and th(x) represents the hyperbolic tangent function. In the inverse hyperbolic cotangent function, the independent variable is B N and T K Among them, B N is the net thickness of the specimen. For specimens without grooves on the side, BN =B. B0 is the reference sample thickness, B0 = 25mm. T K δT is the ductile-brittle transition temperature obtained from the impact test. type is the temperature characteristic factor. For the 0.5C(T) sample, δT type =0℃.

[0034] In addition, the remaining parameters in formula (2) are empirical coefficients and are all constants. K min is the threshold fracture toughness, K1=0.52;

[0035] In step S12, the maximum limit value K of the fracture toughness of the sample can be used to determine the fracture toughness of the sample. JC(lim) , the ductile-brittle transition temperature T K , the size of the sample and the temperature characteristic factor δT of the sample type , to calculate the maximum temperature T of the initial test temperature max .

[0036] In this embodiment, the maximum temperature T of the initial test temperature can be calculated using the second inverse hyperbolic cotangent function. max , the maximum temperature T max is the second inverse hyperbolic cotangent function and the temperature characteristic factor δT type The second inverse hyperbolic cotangent function can be represented by A·arcth(X2)+B, where A and B are both constants. The independent variables of the second inverse hyperbolic cotangent function include: the maximum limit value K of the fracture toughness of the sample JC(lim) , the dimensions of the specimen, such as the net thickness B N , and the ductile-brittle transition temperature T K .

[0037] Specifically, the maximum temperature T can be calculated using the following formula (3): max :

[0038]

[0039] In formula (3), in the inverse hyperbolic cotangent function, the independent variable is K JC(lim) , B N and T K Among them, K JC(lim) It is the maximum limit value of the fracture toughness of the sample. N is the net thickness of the specimen. For specimens without grooves on the side, B N =B. B0 is the reference sample thickness, B0 = 25mm. T KδT is the ductile-brittle transition temperature obtained from the impact test. type is the temperature characteristic factor. For the 0.5C(T) sample, δT type =0℃.

[0040] In addition, the remaining parameters in formula (3) are empirical coefficients and are all constants. min is the threshold fracture toughness, K2=1.44;

[0041] Among them, the maximum limit value K of the fracture toughness of the sample is JC(lim) It can be calculated based on the size of the specimen and the estimated test temperature T.

[0042] It should be noted that, in this embodiment, K JC By J c The converted elastic-plastic equivalent stress intensity factor characterizes the fracture toughness of the specimen. c It is the J integral value, which represents the line integral or surface integral from one surface of the crack to the other surface around the crack front of the specimen, and is used to characterize the intensity of the local stress and strain field in the crack front area. JC(lim) It represents the fracture toughness K JC In addition, the reference temperature T0 in the present invention represents the median fracture toughness K of a sample with a thickness of 1 inch. JC(med) equal The test temperature at .

[0043] In this embodiment, when determining the maximum limit value of the fracture toughness of the sample according to the size of the sample and the estimated value of the test temperature, the elastic modulus E(T) and the yield strength σ at the test temperature can be calculated according to the estimated value of the test temperature T. 0.2 , and then according to the ligament size, elastic modulus E(T) and yield strength σ of the sample 0.2 , to calculate the maximum limit value K of the fracture toughness of the sample JC(lim) .

[0044] Specifically, the following formula (4) is used to calculate K JC(lim) :

[0045]

[0046] Where E(T) is the elastic modulus at the test temperature, b is the ligament size of the specimen, and σ 0.2 is the yield strength at the test temperature, and μ is the Poisson's ratio.

[0047] In this embodiment, the ligament size b of the sample can be determined according to the thickness B, width W and initial crack length a0 of the sample. Optionally, the ligament size b is calculated according to the following formula (5):

[0048] b = min(B, W - a0, a0) (5).

[0049] Wherein, b is the ligament size of the sample, B is the thickness of the sample, W is the width of the sample, and a0 is the initial crack length of the sample. In this embodiment, before the test, the sample is prefabricated with a fatigue crack, and the length of the prefabricated fatigue crack is measured, which is the initial crack length a0.

[0050] In this embodiment, the elastic modulus E and the yield strength σ at the test temperature are 0.2 , can be calculated based on the estimated test temperature T. That is, the test temperature can be selected as the estimated test temperature T, thereby calculating the elastic modulus E(T) and the yield strength σ at the test temperature 0.2 .

[0051] Specifically, the elastic modulus E(T) at the test temperature can be calculated using the following formula (6), and the yield strength σ at the test temperature can be calculated using formula (7): 0.2 .

[0052]

[0053] σ ys =4×10 -8 T 4 -2 -5 T 3 +3.6×10 -3 T 2 -0.543×T+490 (7); where E(T) is the elastic modulus at the test temperature; E is the elastic modulus at room temperature; T is the estimated value of the test temperature; σ ys is the yield strength. At the test temperature, the yield strength is expressed as σ 0.2 express.

[0054] In this embodiment, the test temperature estimate value T is selected as the test temperature to calculate the elastic modulus and yield strength. Optionally, the test temperature estimate value may be a ductile-brittle transition temperature obtained based on an impact test of the sample. For example, a Charpy impact test is performed on the sample, and the ductile-brittle transition temperature obtained from the Charpy impact test is T CVN , then the estimated test temperature T = T CVN .

[0055] After calculating the maximum temperature and the minimum temperature of the initial test temperature, the initial test temperature can be determined based on the maximum temperature and the minimum temperature.

[0056] like Figure 5 As shown, when the single temperature point method is used to perform the fracture toughness test, the method for determining the initial test temperature of the ferritic steel fracture toughness test in this embodiment specifically includes the following steps.

[0057] Step S21, based on the impact test of the ferritic steel sample, obtaining the ductile-brittle transition temperature of the sample.

[0058] Step S22, calculating the minimum temperature and the maximum temperature of the initial test temperature according to the ductile-brittle transition temperature, the size of the sample and the temperature characteristic factor of the sample. The samples of different shapes and sizes have corresponding temperature characteristic factors, and the temperature characteristic factors are determined based on the shape and size of the sample.

[0059] Step S23, determining an average value of the initial test temperature according to the maximum temperature and the minimum temperature.

[0060] Step S24, determining the initial test temperature according to the average value of the initial test temperature and the ductile-brittle transition temperature.

[0061] In this embodiment, the specific methods and processes of step S21 and step S22 are the same as those in the above embodiments, and are not described again here.

[0062] In step S23, the average value T of the initial test temperature can be calculated using the following formula (8): mean :

[0063]

[0064] In step S24, the average values ​​of the initial test temperatures T mean The ductile-brittle transition temperature obtained by the impact test is compared with the ductile-brittle transition temperature obtained by the impact test, and a corresponding calculation method is selected according to the comparison result to calculate the initial test temperature T0′. Optionally, in this embodiment, the sample is subjected to an impact test when the absorbed energy is 41J, and the ductile-brittle transition temperature obtained according to the test result is T 41J .

[0065] When the average value of the initial test temperature T mean When the deviation from the ductile-brittle transition temperature is less than or equal to a preset threshold, the initial test temperature T0′ is calculated according to the ductile-brittle transition temperature. mean When the deviation from the ductile-brittle transition temperature exceeds the preset threshold, the average value T of the initial test temperature is calculated based on the average value T of the initial test temperature.mean and the ductile-brittle transition temperature, and calculate the initial test temperature T0′. The preset threshold value can be set according to actual needs. Optionally, the preset threshold value in this embodiment is 10°C.

[0066] Specifically, if the ductile-brittle transition temperature obtained by the impact test is T 41J When T 41J With T mean size.

[0067] When T 41J With T mean When the deviation between is within a preset threshold, for example, not exceeding 10°C, the following formula (9) can be used to calculate the initial test temperature T0′:

[0068] T′0=T 41J +C (9).

[0069] When T 41J With T mean When the deviation between the values ​​exceeds the preset threshold, for example, exceeds 10°C, the following formula (10) is used to calculate the initial test temperature T0′:

[0070] T′0=(T 41J +C+T mean ) / 2 (10).

[0071] Among them, T 41J is the ductile-brittle transition temperature obtained based on an impact test when the absorbed energy is 41 J; C is a constant corresponding to the size of the sample, for example, when the sample is a 0.5C (T) sample, C = -34°C.

[0072] like Figure 6 As shown, when the fracture toughness test is performed using the multi-temperature point method, the method for determining the initial test temperature of the ferritic steel fracture toughness test in this embodiment specifically includes the following steps.

[0073] Step S31, based on the impact test of the ferritic steel sample, obtaining the ductile-brittle transition temperature of the sample.

[0074] Step S32, calculating the minimum temperature and the maximum temperature of the initial test temperature according to the ductile-brittle transition temperature, the size of the sample and the temperature characteristic factor of the sample. The samples of different shapes and sizes have corresponding temperature characteristic factors, and the temperature characteristic factors are determined based on the shape and size of the sample.

[0075] Step S33, at the minimum temperature T min and the maximum temperature T maxA plurality of temperatures are selected as the initial test temperatures.

[0076] Specifically, the selected multiple temperatures can be at the lowest temperature T min and the maximum temperature T max The temperature is evenly distributed between them, that is, the difference between the selected multiple temperatures is the same. In addition, at the lowest temperature T min and the maximum temperature T max The number of the selected multiple temperatures can be set according to actual needs.

[0077] In addition, in this embodiment, the specific methods and processes of step S31 and step S32 are the same as those in the above embodiments, and are not described again here.

[0078] By using the method in the embodiment of the present invention to determine the initial test temperature of the fracture toughness test of ferritic steel, the deviation between the initial test temperature and the reference temperature can be controlled within ±20°C, which is much better than the method in the ASTM E1921 standard with a deviation within ±50°C. The method in the embodiment of the present invention can select a reasonable and accurate initial test temperature, so that a reference temperature with higher accuracy can be obtained by using fewer specimens in the fracture toughness test.

[0079] In addition, the method in the embodiment of the present invention can be applied to the test of fracture toughness samples in the irradiation monitoring tube of a nuclear power plant. After determining the initial test temperature using the method in this embodiment, the fracture toughness test is carried out, which can save approximately half of the fracture toughness samples in the irradiation monitoring tube, and the obtained reference temperature has a higher accuracy.

[0080] Regarding the embodiments of the present invention, it should also be noted that, in the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other to obtain new embodiments.

[0081] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for determining the initial test temperature of a ferritic steel fracture toughness test, characterized in that: The fracture toughness test is used to determine the ductile-brittle transition reference temperature of the ferrite steel, and the method comprises: Based on the impact test of the sample of the ferritic steel, obtaining the ductile-brittle transition temperature of the sample; Calculating the minimum temperature and the maximum temperature of the initial test temperature according to the ductile-brittle transition temperature, the size of the sample and the temperature characteristic factor of the sample; Determining the initial test temperature according to the lowest temperature and the highest temperature of the initial test temperature; Wherein, the samples of different shapes and sizes have corresponding temperature characteristic factors, and the temperature characteristic factors are determined based on the shape and size of the sample; Calculating the lowest temperature of the initial test temperature by using the first inverse hyperbolic cotangent function, wherein the lowest temperature is the difference between the first inverse hyperbolic cotangent function and the temperature characteristic factor; Wherein, the independent variables of the first inverse hyperbolic cotangent function include the size of the sample and the ductile-brittle transition temperature; Calculate the maximum limit value of the fracture toughness of the sample according to the size of the sample and the estimated value of the test temperature; Calculating the maximum temperature of the initial test temperature according to the maximum limit value of the fracture toughness, the ductile-brittle transition temperature, the size of the sample and the temperature characteristic factor of the sample; When the single temperature point method is used, the method further comprises: According to the maximum temperature and the minimum temperature, determine the average value of the initial test temperature, The initial test temperature is determined according to the average value of the initial test temperature and the ductile-brittle transition temperature.

2. The method according to claim 1, characterized in that Among the independent variables of the first inverse hyperbolic cotangent function, the size of the sample includes: a reference sample thickness and a net thickness of the sample; Wherein, for a specimen with grooves on the side, the net thickness is the distance between the bottoms of two grooves in the specimen; For a specimen without grooves on the side, the net thickness is the thickness of the specimen.

3. The method according to claim 1, characterized in that Determining the maximum limit value of the fracture toughness of the sample according to the size of the sample and the estimated value of the test temperature includes: Calculating the elastic modulus and yield strength of the sample according to the estimated value of the test temperature; The maximum limit value of the fracture toughness of the sample is calculated according to the ligament size, elastic modulus and yield strength of the sample.

4. The method according to claim 3, characterized in that Also includes: The ligament size of the sample is determined according to the thickness, width and initial crack length of the sample.

5. The method according to claim 1, characterized in that The test temperature estimation value is a ductile-brittle transition temperature obtained based on an impact test of the sample.

6. The method according to claim 1, characterized in that Also includes: Calculating the maximum temperature of the initial test temperature using the second inverse hyperbolic cotangent function, wherein the maximum temperature is the difference between the second inverse hyperbolic cotangent function and the temperature characteristic factor; The independent variables of the second inverse hyperbolic cotangent function include: the maximum limit value of the fracture toughness of the sample, the size of the sample and the ductile-brittle transition temperature.

7. The method according to claim 6, characterized in that: Among the independent variables of the second inverse hyperbolic cotangent function, the size of the sample includes: a reference sample thickness and a net thickness of the sample; Wherein, for a specimen with grooves on the side, the net thickness is the distance between the bottoms of two grooves in the specimen; For a specimen without grooves on the side, the net thickness is the thickness of the specimen.

8. The method according to claim 1, characterized in that Determining the initial test temperature includes: comparing an average value of the initial test temperature and the ductile-brittle transition temperature; When the deviation between the average value of the initial test temperature and the ductile-brittle transition temperature is less than or equal to a preset threshold, calculating the initial test temperature according to the ductile-brittle transition temperature; When the deviation between the average value of the initial test temperature and the ductile-brittle transition temperature exceeds the preset threshold, the initial test temperature is calculated according to the average value of the initial test temperature and the ductile-brittle transition temperature.

9. The method according to claim 1, characterized in that: When the multi-temperature point method is used, the method further comprises: Between the lowest temperature and the highest temperature, a plurality of temperatures are selected as the initial test temperatures.

10. The method according to any one of claims 1 to 9, characterized in that: The specimens include compact tension specimens.

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