Method for evaluating relation between impact absorption energy and lateral expansion value of low-temperature steel

Abstract

The invention provides a method for evaluating the relationship between the impact absorption energy and the lateral expansion value of low-temperature steel, which comprises the following steps of: S1, establishing an impact lateral expansion value prediction model by analyzing the correlation between the impact absorption energy and the lateral expansion value of austenite low-temperature steel; s2, carrying out an impact test on the typical thickness sample of the austenite low-temperature steel at the typical temperature to obtain impact absorption energy and a lateral expansion value; and S3, substituting the data obtained in the step S2 into the prediction model in the step S1 to obtain undetermined coefficients alpha and beta. Starting from the correlation between the impact absorption energy and the lateral expansion value of the austenite low-temperature steel, a prediction model of the lateral expansion value, the impact absorption energy and the sample thickness is established by analyzing the correlation between the lateral expansion value, the impact absorption energy and the sample thickness, and the model has the advantages of being simple to construct, rapid to use and the like; and the establishment of the model has important significance on fracture performance evaluation and quality consistency inspection of the high manganese steel.

Description

Technical Field

[0001] The present invention relates to the technical field of material fracture failure research, and in particular to a method for evaluating the relationship between impact absorption energy and lateral expansion value of low-temperature steel. Background Art

[0002] With the rapid development of the global economy and the increasing emphasis on environmental protection worldwide, the demand for natural gas (LNG) is increasing rapidly. This has also fueled the rapid development of the LNG storage and transportation industries. High-manganese steel, due to its excellent performance and relatively low price, is gaining increasing popularity in marine LNG storage tanks. To ensure the safety of high-manganese austenitic low-temperature steel tanks during service, the material must exhibit excellent fracture properties at service temperatures.

[0003] For large welded structures such as ships and pressure vessels, how to design materials and structural fracture control to prevent fracture accidents has always been a research area of ​​great interest. The Charpy impact test is a commonly used test method for evaluating the fracture performance of materials. It has the advantage of being more sensitive than other mechanical property testing methods in terms of testing material quality, internal defects, and process quality. For the parent material and weld quality of large steel structures such as pressure vessels and ships, the impact absorption energy and lateral expansion value are the reference basis for their evaluation. When evaluating nuclear container materials in the United States, the temperature scale for toughness evaluation, RTNDT, is determined based on the Charpy impact test. That is, at a temperature of (DWT-NDTT+16℃), when the lateral expansion of the Charpy impact specimen is not less than 0.89mm and the impact absorption energy is not less than 68J, DWT-NDTT is RTNDT. Impact testing is also commonly used to assess fracture performance in oil and natural gas pipelines. As pipe diameters increase and stress levels rise, brittle fractures are often accompanied by ductile fractures. Their common characteristic is that the impact absorption energy of these pipes is relatively low, and the inherent toughness of the material is insufficient to arrest the cracks. To determine the technical indicators of impact absorption energy and lateral expansion, various countries have conducted extensive theoretical research and experimental work.

[0004] High manganese austenitic low-temperature steel is a new type of low-temperature steel for LNG storage tanks. To ensure product quality consistency and service safety during the use of the material, technical indicators for its impact absorption energy and lateral expansion are specified. GB / T 713.5-2023 "Steel Plate and Strip for Pressure Equipment Part 5: High Manganese Steel with Specifying Low-Temperature Properties" stipulates that its lateral impact absorption energy at -196°C must be ≥60J, the lateral expansion value must be ≥0.53mm, and the plate thickness specification must be 5 to 60mm; T / SSEA 0060-2020 "High Manganese Austenitic Steel Plate for Low-Temperature Pressure Vessels" stipulates that its -196℃ lateral impact absorption energy is ≥80J, the lateral expansion value is ≥0.64mm, and the plate thickness specification is 6~63.5mm. The specimen size and impact absorption energy of steel plates of different thicknesses are specified. The impact specimen of 6~8mm steel plate is 10×5×55mm, and the impact absorption energy is not less than 50% of the standard specimen. The impact specimen of 8~12mm steel plate is 10×7.5×55mm, and the impact absorption energy is not less than 75% of the standard specimen. However, the lateral expansion is only specified to be ≥0.64mm, and it is not graded by size. China Classification Society's guidance document, GD 28-2021, "Guidelines for the Application of High-Manganese Austenitic Low-Temperature Steel," stipulates that the impact absorbed energy at -196°C must be ≥ 27J for transverse impact and ≥ 41J for transverse impact, for plate thicknesses of 6 to 40mm. The impact absorbed energy for 10×5×55mm specimens must be no less than 2 / 3 (67%) of the standard specimen, and for 10×7.5×55mm specimens must be no less than 5 / 6 (83%) of the standard specimen. It only requires recording lateral expansion, without specifying its value. In summary, GB / T 713.5-2023, T / SSEA 0060-2020, and GD 28-2021 all provide technical indicators for high-manganese steel's impact absorbed energy at -196°C, but neither GB / T 713.5-2023 or GD 28-2021 specifies lateral expansion, and the T / SSEA 0060-2020 specification is also not entirely reasonable.

[0005] The prior art, publication number CN118500939 A, discloses a method for predicting the impact absorption energy of a small-sized specimen of austenitic low-temperature steel, comprising the following steps: Step S1: Establishing a prediction model for impact absorption energy by analyzing the correlation between impact absorption energy, specimen thickness, and test temperature; Step S2: Conducting impact tests on austenitic low-temperature steel at different temperatures and thicknesses to obtain the impact absorption energy of the specimens; Step S3: Substituting the test data obtained in Step S2 into equations (1) and (2) to determine the values ​​of the unknown coefficients δ, γ, μ, and θ. This prior art can only determine the equivalent ratio of the impact absorption energy of a small-sized specimen to that of a standard specimen and cannot evaluate the relationship between the impact absorption energy of low-temperature steel and the lateral expansion.

[0006] Based on this, the present invention is proposed. Summary of the Invention

[0007] In view of this, the present invention aims to propose a method for evaluating the relationship between the impact absorption energy and lateral expansion of low-temperature steel. By impact tests on samples of different thicknesses at different temperatures, the relationship between the impact absorption energy and lateral expansion of samples of different thicknesses is established, and then the lateral expansion index is determined according to the impact absorption energy index of the standard sample, providing a technical basis for the low-temperature fracture performance evaluation and quality consistency inspection of austenitic low-temperature steel.

[0008] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0009] A method for evaluating the relationship between impact absorption energy and lateral expansion value of low-temperature steel comprises the following steps:

[0010] Step S1: establishing an impact lateral expansion value prediction model by analyzing the correlation between the impact absorption energy and lateral expansion value of austenitic low-temperature steel;

[0011] Wherein, step S1 includes:

[0012] Step S11: performing impact tests on austenitic low-temperature steel of different test temperatures and sample thickness specifications on the same material to obtain the impact absorption energy and lateral expansion value of the sample;

[0013] Step S12: analyzing the correlation between the impact absorption energy and the lateral expansion value under multiple sample thicknesses, and establishing a relationship between the impact absorption energy and the lateral expansion value corresponding to the sample thickness;

[0014] Step S13: Analyze the relationship in step S12, convert the relationship between the impact absorption energy of the same material and different thicknesses according to the existing technology, and uniformly fit the impact absorption energy of multiple thickness samples to a certain sample thickness, thereby obtaining a prediction model for the relationship between the lateral expansion value, the impact absorption energy, and the sample thickness;

[0015]

[0016] Where, KV2 is the impact absorption energy, J; LE is the lateral expansion value, mm; t is the thickness of the sample, mm; α, β are parameters to be determined;

[0017] Step S2: performing an impact test on a sample of austenitic low-temperature steel of typical thickness at a typical temperature to obtain impact absorption energy and lateral expansion value;

[0018] Step S3: bring the data obtained in step S2 into the prediction model in step S13 to obtain the undetermined coefficients α and β.

[0019] Further, in step S11, the sample thickness includes two of 5 mm, 7.5 mm, 10 mm, 12.5 mm, and 15 mm.

[0020] Further, in step S11, the test temperature is room temperature, -100°C, -165°C and -196°C.

[0021] Furthermore, in step S11, the impact test is from GB / T 2209-2020 "Charpy Pendulum Impact Test Method for Metallic Materials".

[0022] Furthermore, during the impact test, the length L of the standard specimen is 55 mm, and the cross-sectional area is rectangular with dimensions of 10 mm×10 mm×8 mm.

[0023] Furthermore, in step S11, the number of the temperatures is no less than 3.

[0024] Furthermore, in step S13 , the certain sample thickness refers to 10 mm.

[0025] Furthermore, in step S3, the least square method is used for fitting to obtain the undetermined coefficients α and β.

[0026] Furthermore, the austenitic low-temperature steel is high-manganese austenitic low-temperature steel.

[0027] Further, in step S3, the typical temperature refers to one of room temperature, -100°C, -165°C and -196°C, and the typical thickness refers to one of 5 mm, 7.5 mm, 10 mm, 12.5 mm and 15 mm.

[0028] Furthermore, the method further includes step S4, performing an impact test at a specific sample thickness to obtain actual values ​​of impact absorption energy and lateral expansion value, and determining a predicted value of lateral expansion value based on the test thickness and the actual values ​​of impact absorption energy.

[0029] Furthermore, the difference between the predicted value of the lateral expansion value and the measured value of the lateral expansion value is -0.13 to 0.1 mm.

[0030] Compared with the prior art, the method for evaluating the relationship between the impact absorption energy and lateral expansion value of low-temperature steel described in the present invention has the following advantages:

[0031] 1) Based on the correlation between the impact absorption energy and lateral expansion value of austenitic low-temperature steel, the present invention establishes a prediction model for lateral expansion value, impact absorption energy, and sample thickness through correlation analysis of lateral expansion value, impact absorption energy, and sample thickness. This model has the advantages of being simple to construct and quick to use. By determining the corresponding relationship between the impact absorption energy and lateral expansion of high-manganese steel, it has important significance for the fracture performance evaluation and quality consistency inspection of high-manganese steel.

[0032] 2) When predicting the lateral expansion value of austenitic low-temperature steel, the present invention conducts impact tests on samples of austenitic low-temperature steel of typical thickness at typical temperatures to obtain impact absorption energy and lateral expansion value. Substituting these into the prediction model can determine the parameters α and β, and establish a correlation model between the lateral expansion value, the impact absorption energy, and the sample thickness. When subsequently evaluating the fracture performance and quality consistency of austenitic low-temperature steel, the correlation model between the lateral expansion value, the impact absorption energy, and the sample thickness can be used to obtain the corresponding relationship between the impact absorption energy and the lateral expansion value, thereby enabling the evaluation of the fracture performance of austenitic low-temperature steel with small plate thickness. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the standard impact specimen of the present invention;

[0034] Figure 2 is a graph showing the relationship between the impact absorption energy and the lateral expansion value of different thicknesses in the embodiment of the present invention, wherein Figure 2 (a) Relationship diagram for thickness of 7.5 mm, Figure 2 (b) Relationship diagram for thickness of 10 mm, Figure 2 (c) Relationship diagram for thicknesses of 7.5 mm and 10 mm;

[0035] Figure 3 This is a linear relationship diagram between the impact absorption energy and the lateral expansion value of different thickness fittings in the embodiment of the present invention; wherein, Figure 3 (a) Fitting relationship diagram for thickness of 7.5 mm, Figure 2 (b) Fitting relationship diagram with a thickness of 10 mm;

[0036] Figure 4 This is the relationship between the impact absorption energy and the lateral expansion value considering the plate thickness factor in the embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0038] The present invention provides a method for evaluating the relationship between the impact absorption energy and the lateral expansion value of low-temperature steel, comprising the following steps:

[0039] Step S1: establishing an impact lateral expansion value prediction model by analyzing the correlation between the impact absorption energy and lateral expansion value of austenitic low-temperature steel;

[0040] Wherein, step S1 includes:

[0041] Step S11: performing impact tests on austenitic low-temperature steel of different test temperatures and sample thickness specifications on the same material to obtain the impact absorption energy and lateral expansion value of the sample;

[0042] Step S12: analyzing the correlation between the impact absorption energy and the lateral expansion value under multiple sample thicknesses, and establishing a relationship between the impact absorption energy and the lateral expansion value corresponding to the sample thickness;

[0043] Step S13: Analyze the relationship in step S12, convert the relationship between the impact absorption energy of the same material and different thicknesses according to the existing technology, and uniformly fit the impact absorption energy of multiple thickness samples to a certain sample thickness, thereby obtaining a prediction model for the relationship between the lateral expansion value, the impact absorption energy, and the sample thickness;

[0044]

[0045] Where, KV2 is the impact absorption energy, J; LE is the lateral expansion value, mm; t is the thickness of the sample, mm; α, β are parameters to be determined;

[0046] Step S2: performing an impact test on a sample of austenitic low-temperature steel of typical thickness at a typical temperature to obtain impact absorption energy and lateral expansion value;

[0047] Step S3: bring the data obtained in step S2 into the prediction model in step S13 to obtain the undetermined coefficients α and β.

[0048] Specifically, in step S11, the sample thickness includes two of 5 mm, 7.5 mm, 10 mm, 12.5 mm, and 15 mm.

[0049] Specifically, in step S11, the test temperatures are room temperature, -100°C, -165°C and -196°C.

[0050] Specifically, in step S11, the impact test comes from GB / T 2209-2020 "Charpy Pendulum Impact Test Method for Metallic Materials".

[0051] Specifically, during the impact test, the length L of the standard specimen is 55 mm, and the cross-sectional area is rectangular with dimensions of 10 mm×10 mm×8 mm.

[0052] Specifically, in step S13 , the certain sample thickness refers to 10 mm.

[0053] Specifically, in step S3, the least square method is used for fitting to obtain the undetermined coefficients α and β.

[0054] Specifically, in step S2, the typical temperature refers to one of room temperature, -100°C, -165°C and -196°C, and the typical thickness refers to one of 5 mm, 7.5 mm, 10 mm, 12.5 mm and 15 mm.

[0055] Specifically, the austenitic low-temperature steel is high-manganese austenitic low-temperature steel.

[0056] Specifically, it also includes step S4, performing an impact test at a specific sample thickness to obtain actual values ​​of impact absorption energy and lateral expansion value, and determining a predicted value of lateral expansion value based on the test thickness and the actual values ​​of impact absorption energy.

[0057] Specifically, the difference between the predicted value of the lateral expansion value and the measured value of the lateral expansion value is -0.13 to 0.1 mm.

[0058] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0059] This embodiment is based on GB / T 2209-2020 "Charpy Pendulum Impact Test Method for Metallic Materials". The sample material is high manganese austenitic low-temperature steel. The impact absorption energy and lateral expansion values ​​of two specifications of samples with sample thicknesses of 7.5mm and 10mm are tested. The test temperatures are room temperature, -100℃, 165℃ and -196℃. A total of 24 7.5mm impact tests and 92 10mm impact tests are conducted.

[0060] (1) Correlation analysis between impact absorption energy and lateral expansion value

[0061] Figure 2 (a) shows the relationship between the impact absorption energy and lateral expansion value of a 7.5mm thick austenitic low-temperature steel specimen. The test temperatures include room temperature, -100℃, -165℃ and -196℃. It can be seen that there is an obvious linear relationship between the impact absorption energy and lateral expansion value of the 7.5mm thick specimen, as shown in Figure 2. Figure 3 (a), the correlation equation is shown in formula (1), and the correlation coefficient r is 0.988. Figure 2 (b) shows the relationship between the impact absorption energy and lateral expansion value of a 10mm thick austenitic low-temperature steel specimen. The test temperatures include room temperature, -100℃, -165℃ and -196℃. It can be seen that there is an obvious linear relationship between the impact absorption energy and lateral expansion value of the 10mm thick specimen, such as Figure 3 (b) shows the correlation equation as shown in formula (2), and the correlation coefficient r is 0.961. The impact absorption energy and lateral expansion value of the 7.5mm and 10mm thick specimens both show an obvious linear relationship, but the slopes between the impact absorption energy and lateral expansion value of the two thickness specimens are significantly different, as shown in Figure 2. Figure 2 As shown in (c), under the same lateral expansion, the impact absorption energy of the 10mm thick sample is greater than that of the 7.5mm thick sample.

[0062] 7.5mm sample: LE = 0.01·KV2 + 0.27 (1)

[0063] 10mm sample: LE = 0.008·KV2 + 0.33 (2)

[0064] (2) Establishment of the impact side expansion value prediction model

[0065] Based on the above analysis, the impact absorption energy and lateral expansion of samples of different thicknesses show different linear relationships. According to the patent "A method for predicting the impact absorption energy of small-size samples of austenitic low-temperature steel (patent number: 202410586313.3)", for the same material, the ratio of the impact absorption energy of 7.5mm thick samples to 10mm thick samples is 0.74, which is basically consistent with their thickness ratio. The present invention uses the sample thickness ratio as a parameter. Figure 2 The impact absorption energy of the 7.5 mm sample in (a) is divided by 0.75 to convert it to the impact absorption energy of the 10 mm sample. The relationship between the impact absorption energy and the lateral expansion is as follows: Figure 4 As shown, the overall relationship shows a clear linear relationship. That is, after normalizing austenitic low-temperature steel specimens of varying thickness to a 10 mm thick standard specimen, their impact absorption energy and lateral expansion exhibit a linear relationship. Based on this, a relationship between lateral expansion, impact absorption energy, and specimen thickness can be established, as shown in Equation (3).

[0066]

[0067] Where, KV2 is the impact absorption energy, J; LE is the lateral expansion value, mm; t is the specimen thickness, mm; α and β are parameters to be determined.

[0068] Utilize the working process of the present invention:

[0069] 1. According to GB / T229 "Metallic Materials Charpy Pendulum Impact Test Method", the impact tests of the four temperatures and two thickness specifications of the present invention were carried out to obtain the impact absorption energy KV2 and lateral expansion value. The corresponding data are as follows: Figure 2 The corresponding result range is shown in Table 1.

[0070] Table 1 Material thickness and impact absorption energy

[0071]

[0072] 2. Substitute the data in Table 2 into formula (3) and use the least squares method for fitting. The obtained undetermined parameters are shown in Table 2. The prediction model is shown in formula (4). According to the above model, the corresponding relationship between the impact absorption energy and the lateral expansion value can be determined. Then, the lateral expansion value index value can be determined according to the impact absorption energy index value, and the technical indicators of austenitic low-temperature steel can be improved.

[0073] Table 2 Undetermined parameter values ​​in the prediction model

[0074] parameter α β Numerical 0.008 0.30

[0075]

[0076] 3. By conducting an impact test at a specific sample thickness, the measured values ​​of impact absorption energy and lateral expansion value are obtained. Based on the test thickness and the measured values ​​of impact absorption energy, the predicted value of lateral expansion value is determined, as shown in Table 3 below: the impact absorption energy, predicted value of lateral expansion value, measured value of lateral expansion value, and the difference between the measured value and the predicted value corresponding to the specific sample thickness.

[0077] Table 3 Measured and predicted values ​​of lateral expansion values ​​of typical materials

[0078]

[0079] It can be concluded from Table 3 that the prediction model of the present invention does not require a specified test temperature. The predicted value of the lateral expansion value can be obtained by the sample thickness and the impact absorption energy under the sample thickness. The difference between the predicted value and the measured value is small, which can realize the evaluation of the fracture performance of austenitic low-temperature steel with small plate thickness.

[0080] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A method for evaluating the relationship between impact absorption energy and lateral expansion value of low-temperature steel, characterized in that: The steps include: Step S1: establishing an impact lateral expansion value prediction model by analyzing the correlation between the impact absorption energy and lateral expansion value of austenitic low-temperature steel; Wherein, step S1 includes: Step S11: performing impact tests on austenitic low-temperature steel of different test temperatures and sample thickness specifications on the same material to obtain the impact absorption energy and lateral expansion value of the sample; Step S12: analyzing the correlation between the impact absorption energy and the lateral expansion value under multiple sample thicknesses, and establishing a relationship between the impact absorption energy and the lateral expansion value corresponding to the sample thickness; Step S13: Analyze the relationship in step S12, convert the relationship between the impact absorption energy of the same material and different thicknesses according to the existing technology, and uniformly fit the impact absorption energy of multiple thickness samples to a certain sample thickness, thereby obtaining a prediction model for the relationship between the lateral expansion value, the impact absorption energy, and the sample thickness; Where, KV2 is the impact absorption energy, J; LE is the lateral expansion value, mm; t is the thickness of the sample, mm; α, β are parameters to be determined; Step S2: performing an impact test on a sample of austenitic low-temperature steel of typical thickness at a typical temperature to obtain impact absorption energy and lateral expansion value; Step S3: bring the data obtained in step S2 into the prediction model in step S13 to obtain the undetermined coefficients α and β.

2. The method according to claim 1, characterized in that In step S11 , the sample thickness includes two of 5 mm, 7.5 mm, 10 mm, 12.5 mm, and 15 mm.

3. The method according to claim 1, characterized in that In step S11, the number of the test temperatures is no less than 3.

4. The method according to claim 1, wherein In step S11, the test temperatures are room temperature, -100°C, -165°C and -196°C.

5. The method according to claim 1, wherein In step S11, the impact test is based on GB / T 2209-2020 "Charpy Pendulum Impact Test Method for Metallic Materials".

6. The method according to claim 1, characterized in that During the impact test, the length L of the standard specimen is 55 mm, the cross-sectional area is rectangular, and the dimensions are 10 mm × 10 mm × 8 mm.

7. The method according to claim 1, characterized in that In step S3, the least square method is used for fitting to obtain the unknown coefficients α and β.

8. The method according to claim 1, characterized in that The austenitic low-temperature steel is high-manganese austenitic low-temperature steel.

9. The method according to claim 1, characterized in that The method further includes step S4, performing an impact test at a specific sample thickness to obtain actual values ​​of impact absorption energy and lateral expansion value, and determining a predicted value of lateral expansion value based on the sample thickness and the actual values ​​of impact absorption energy.

10. The method according to claim 9, characterized in that The difference between the predicted value of the lateral expansion value and the measured value of the lateral expansion value is -0.13 to 0.1 mm.

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