Method for evaluating brittle crack propagation stop performance of thick steel plate

Abstract

A method for evaluating the brittle crack propagation cessation performance of thick steel plates is provided. For the brittle crack propagation cessation performance of thick steel plates, the Charpy impact test, used as a small-scale test, is used to evaluate characteristic values ​​at the center of the plate thickness and at the center of the plate thickness, which exhibits a different cross-sectional shape. The temperatures (transformation temperatures) obtained, representing specified characteristic values, are combined to estimate the brittle crack propagation cessation performance of the thick steel plate obtained in a large-scale test. At the center of the plate thickness, the energy transformation temperature Ti of the notched Charpy impact test is used. ct The evaluation was conducted at the midpoint of the plate thickness, using the section transition temperature TV-notch Charpy impact test. mt To evaluate, the combined transition temperature T obtained by combining them is used. w (=T mt +B1×T ct This allows for a simple and accurate evaluation of the brittle crack propagation cessation performance of thick steel plates. Furthermore, the combined transformation temperature T... w T can also be used w =(T mt +T ct ) / 2+B2×(T ct -T mt ).

Description

Technical Field

[0001] This invention relates to an evaluation method for conveniently evaluating the brittle crack propagation stopping performance of thick steel plates with a thickness of 40 mm or more using small test specimens. Background Technology

[0002] In large structures such as ships, marine structures, cryogenic storage tanks, and building / civil engineering structures, accidents involving brittle fracture can have significant economic and environmental impacts. Therefore, enhanced safety is crucial, especially for large structures. The steel used must possess excellent toughness at operating temperatures and excellent brittle fracture propagation prevention properties.

[0003] The evaluation of brittle fracture propagation cessation performance has traditionally been conducted through large-scale tests, such as the ESSO test or the double tensile test. However, these large-scale tests require a significant number of days and are very expensive, making them difficult to perform simply. Therefore, WES 3003-1995 (Japan Welding Association Standard) established the section transition temperature based on the V-notch Charpy impact test. v T rs A method for predicting the cessation of brittle fracture propagation has been developed. However, when applied to steels with a thickness exceeding 50 mm, which have been developed in recent years, the prediction accuracy is poor, making it difficult to evaluate easily.

[0004] For example, Patent Document 1 describes an evaluation method for stopping the propagation of brittle fracture in thick steel plates, which uses Charpy impact test pieces with stamped notches collected from the center of the plate thickness and from a position 1 / 4 of the plate thickness away from the surface to conduct Charpy impact tests, and evaluates the stopping performance of brittle fracture propagation based on the section transition temperature with a brittle section ratio of 75% obtained respectively.

[0005] Furthermore, Patent Document 2 describes an evaluation method for stopping the brittle fracture propagation of thick steel plates. When evaluating the stopping performance of brittle fracture propagation of steel plates thicker than 50 mm through small-scale tests, a rectangular cross-section exceeding 100 mm, taken from the center of the steel plate's thickness, is used. 2 Charpy impact tests were conducted using deformed, stamped, notched Charpy test pieces, and the transition temperature was represented by the absorbed energy obtained. p T E The brittle fracture surface area (BRI) or brittle fracture surface area (BRI) represents a specific value of the transition temperature (BATT) and is used to evaluate the performance of stopping the propagation of brittle fracture.

[0006] In addition, Non-Patent Document 1 describes a technique that considers the distribution of toughness at various locations along the thickness direction and calculates the brittle fracture propagation stopping performance K through an ESSO test. caThe value is strongly affected by the low toughness region. The toughness value at each position in the thickness direction is set as the average area of ​​the steel plate, and the value in the central part of the plate thickness is weighted to evaluate the brittle fracture propagation stopping performance.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2011-33457

[0010] Patent Document 2: International Publication No. 2014 / 208072

[0011] Non-patent literature

[0012] Non-patent literature 1: Summary of speeches at the National Congress of the Welding Society, Volume 49, p. 108 (1991) Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] The technology described in Patent Document 1 uses notched Charpy impact test specimens taken from the center of the thickness of a thick steel plate and from a position one-quarter of the plate thickness away from the surface to evaluate the brittle fracture propagation cessation performance. However, it does not reflect the toughness value of the surface layer. In thick steel plates where the shear lip of the surface layer has a significant impact on the brittle crack propagation cessation, the toughness value K for brittle crack propagation cessation is not reflected. ca The correlation decreases. Furthermore, even with minimal shear lip formation, thick steel plates exhibiting significantly different failure modes along their thickness direction still show a correlation with the brittle crack propagation cessation toughness value K. ca The correlation decreases. Furthermore, in steel plates with high brittle fracture propagation stopping performance, brittle cracks are sometimes difficult to generate from the bottom of the notch in the Charpy impact test at the 1 / 4 position of the plate thickness, thus making it difficult to obtain appropriate Charpy impact test results.

[0015] Furthermore, in the technology described in Patent Document 2, a notched Charpy impact test piece of the same size as that used in a conventional Charpy impact test is used. Test pieces are collected from the center of the plate thickness 1 to evaluate the brittle crack propagation cessation performance of thick steel plates. However, in thick steel plates with a thickness of 60 to 80 mm, a high correlation was observed between the characteristic values ​​obtained from small-scale tests using the notched Charpy impact test and the brittle crack propagation cessation performance of the thick steel plate. On the other hand, when the plate thickness exceeds 80 mm and becomes further thicker, there is a problem of reduced accuracy.

[0016] Therefore, the object of this invention is to provide a method for evaluating the brittle crack propagation cessation performance of thick steel plates, wherein large-scale tests of the total thickness are only used to determine the test location, and the brittle crack propagation cessation performance of thick steel plates can be evaluated with high precision by using a simple method of small-scale tests. Furthermore, the thick steel plates targeted by this invention are those with a thickness of 40 mm or more, exhibiting variations in brittle crack propagation morphology at the center and middle of the plate thickness. Here, "center of the plate thickness" refers to a range from 3 / 8 to 5 / 8 of the plate thickness, centered at 1 / 2 of the plate thickness. "Middle of the plate thickness" refers to positions symmetrically separated from the center of the plate thickness at 1 / 6 to 3 / 8 of the plate thickness and at 5 / 8 to 5 / 6 of the plate thickness.

[0017] Technical solutions for solving the problem

[0018] To achieve the above objectives, the inventors first conducted an ESSO test as a large-scale experiment on 19 types of thick steel plates (100mm thick) to determine K. ca Become 8000N / mm 3 / 2 Temperature T Kca＝8000 (°C), and simultaneously, a notched Charpy impact test (test piece: 10mm square × 55mm length) was conducted as a small-scale test to determine the temperature at which 40J of energy was absorbed. p T E40J (°C). In addition, the Charpy impact test with a notched stamping used a test piece collected from the center of the plate thickness at position 1.

[0019] The results are expressed in temperature T. Kca＝8000 (°C) and temperature p T E40J The relationship between (°C) and Figure 2 As shown in the figure. Based on the obtained T... Kca＝8000 and p T E40J The correlation is obtained as the following equation (a) as a regression equation.

[0020] T Kca＝8000 =0.17× p T E40J -23.25…(a)

[0021] (Where, the regression residual u: 10.61)

[0022] Then, as temperature T Kca＝8000 The estimating formula for the upper limit of (°C) yields the following formula (b).

[0023] T Kca＝8000 =0.17× p T E40J -2.03…(b).

[0024] Then, based on this presumption, it is presumed that T will... Kca＝8000 Set to -10℃ required p T E40J hour, p T E40J = -46.9℃. According to Figure 2 , indicating more than p T E40J Nine types of thick steel plates had a value of -46.9℃. It was found that the percentage below the estimated value was 10 / 19 (53%), indicating low estimation accuracy. This shows that in this method of evaluating the brittle crack propagation cessation performance of thick steel plates using small-scale tests based on Charpy impact tests of test pieces taken from the center position 1 of the plate thickness, only evaluation results lacking correlation can be obtained for thicker steel plates. Due to the low correlation, the 2σ set in the safety-side study becomes larger, and even steel plates with the expected brittle crack propagation cessation performance if large-scale tests are conducted are evaluated as "exceeding the estimated value" in small-scale tests.

[0025] Therefore, a brittle crack propagation cessation test (CAT test, test temperature: -30℃) was conducted as a large-scale test on thick steel plates (thickness: 100mm, EH: 40~47 grade) with high brittle crack propagation cessation performance. After the test, the cross-sectional morphology of the obtained test pieces was observed. Figure 1 The cross-sectional morphology of the test piece is schematically shown.

[0026] After entering the test section, the brittle crack generated in the cut 1 and the embrittlement treatment area shows a cross-sectional shape at the center of the plate thickness where the main crack (brittle crack) 3 progresses in an inclined direction of 35° and then stops (brittle crack stop 4). Furthermore, at the end of the main crack 3 that progresses in the inclined direction, the following cross-sectional shape is shown: multiple cracks (flat sections 5) that progress relatively flatly and stop at positions from 35% to 15% of the surface along the plate thickness direction and from 65% to 85% of the surface along the plate thickness direction, and step-like steps 6 (ductile sections). The height of the crack initiation positions in these flat sections 5 is different, forming step-like steps with a considerable band.

[0027] Based on this cross-sectional morphology, it can be said that the brittle crack propagation cessation performance of thick steel plates is strongly influenced not only by the toughness of the central portion of the plate thickness but also by the toughness of the portion with a different cross-section (the middle position). Furthermore, observations of non-penetrating test specimens of this thick steel plate indicate that, in brittle crack propagation cessation tests, cracks propagated deeper in the center and middle positions of the plate thickness when propagation ceased, but their propagation was relatively shallower near the surface. Based on this failure mode, it is believed that crack propagation behavior in the center and middle positions of the plate thickness dominates the overall brittle crack propagation progression of the steel plate compared to the surface. Therefore, in this type of thick steel plate, it is observed that the area near the surface has less influence on the brittle crack propagation cessation performance.

[0028] In thickness-direction locations other than the center of the plate thickness, the cross-sectional morphology differs from that at the center. When these morphologies exhibit numerous ductile cracks and bands, the dynamic stress propagation coefficient at the crack leading edge decreases, making crack propagation easier to halt. Therefore, it is speculated that the toughness of thickness-direction locations exhibiting cross-sectional morphologies different from the center significantly influences the overall brittle crack propagation cessation performance of thick steel plates.

[0029] This leads to the idea that if we evaluate the temperatures representing specified characteristic values ​​at the center of the plate thickness and at the thickness-direction positions showing cross-sectional morphologies different from those at the center of the plate thickness through small-scale tests, and combine the temperatures representing the obtained specified characteristic values ​​to estimate the brittle crack propagation cessation performance of thick steel plates, then we can evaluate the brittle crack propagation cessation performance of thick steel plates with high precision and high reliability.

[0030] Therefore, the position showing a different cross-sectional shape from that at the center of the plate thickness is the 1 / 4 position. Thus, in addition to the Charpy impact test with a notched punch at the center of the plate thickness, Charpy impact test specimens (10mm square × 55mm long) are also collected from the 1 / 4 position (hereinafter, the 1 / 4 position is indicated by the subscript 'q' in the notation). A V-notch is also introduced into the Charpy impact test specimen from the 1 / 4 position, and a V-notch Charpy impact test is performed to determine the section transition temperature at 50% brittle fracture surface area. v T rsq (°C). The temperature at which the Charpy impact test absorbs 40 J of energy at the center of the plate thickness (hereinafter, the subscript h in the notation indicates the center of the plate thickness) is conducted. p T E40Jh (°C), the brittle fracture ratio of the V-notch Charpy impact test at 1 / 4 of the plate thickness, representing 50% of the temperature. v T rsq The (°C) combination serves as the combination transition temperature T based on small-scale experiments. w (°C), calculate the temperature T. Kca＝8000(°C) and temperature T w The correlation (°C) is also considered. Furthermore, when combining the transition temperatures at various locations along the thickness direction based on small-scale tests, the transition temperatures at each location along the thickness direction are weighted and averaged as their contribution to the brittle crack propagation stopping performance of the total thickness. The weighted average is 12:100. Therefore, the combined transition temperature T based on small-scale tests... w (°C) is represented as T w = v T rsq +0.12× p T E40Jh .

[0031] The obtained temperature T Kca＝8000 (°C) and combined transition temperature T w The relationship between (°C) and Figure 3 As shown in the figure. Temperature T Kca＝8000 (°C) and temperature T w The correlation between (°C) and (°C) is expressed as a regression equation by the following equation (c).

[0032] T Kca＝8000 =0.36×T w -3.27…(c)

[0033] (Where, the regression residual u: 9.51)

[0034] Based on this regression, T will be estimated within the range of deviation. Kca＝8000 The upper limit of (°C) is estimated by the following formula (d).

[0035] T Kca＝8000 (°C) = 0.36 × T w +22.29…(d)

[0036] According to this presumption, it is presumed that in order to make T Kca＝8000 T required to reach -10℃ w At that time, T w = -89.1℃. According to Figure 3 It can be seen that this indicates exceeding T. w There are four types of thick steel plates with a temperature of -89.1℃, of which 15 / 19 (80%) are below the estimated value. Figure 2 Compared to the situation shown, the estimation error is smaller. Therefore, the 2σ set in the safety-side study is smaller, and most steel plates that can represent the expected brittle crack propagation cessation performance under large-scale tests are below the estimation value based on small-scale tests, thus allowing for reasonable estimation.

[0037] This invention was completed based on further research conducted according to the above-mentioned insights. Specifically, the key points of this invention are as follows.

[0038] [1] A method for evaluating the brittle crack propagation cessation performance of thick steel plates, wherein, when evaluating the brittle crack propagation cessation performance obtained by large-scale tests based on a temperature representing a specified characteristic value obtained using small-scale tests,

[0039] A brittle crack propagation cessation test was conducted using test specimens of the aforementioned thick steel plate. Based on the observed cross-sectional morphology, the range of locations along the plate thickness from which a cross-sectional morphology differed from the center position of the plate thickness was defined as the center position of the plate thickness.

[0040] The temperature representing the specified characteristic value obtained using the aforementioned small-scale test is designated as the combined transition temperature. This combined transition temperature is obtained by combining the transition temperature of the Charpy impact test with a notched stamp at the center of the plate thickness and the transition temperature of the Charpy impact test with a V-notch at the center of the plate thickness.

[0041] The brittle crack propagation cessation performance of the thick steel plate is evaluated based on the combined transition temperature.

[0042] [2] A method for evaluating the brittle crack propagation cessation performance of thick steel plates, wherein, when evaluating the brittle crack propagation cessation performance obtained through large-scale tests based on a temperature representing a specified characteristic value obtained using small-scale tests,

[0043] A brittle crack propagation cessation test was conducted using test specimens of the aforementioned thick steel plate. Based on the observed cross-sectional morphology, the range of locations along the plate thickness from which a cross-sectional morphology differed from the center position of the plate thickness was defined as the center position of the plate thickness.

[0044] The temperature at which the specified characteristic value is obtained using the aforementioned small-scale test is set as the combined transition temperature T. w The combination transition temperature T w The transformation temperature T of the Charpy impact test at the center of the stamping notch of the plate thickness is... ct The transition temperature T of the Charpy impact test at the V-notch position at the middle of the plate thickness. mt The combination is obtained, and the combination transition temperature T w Defined by the following equation (1), based on the combined transition temperature T w The following equation (2) is used to estimate the brittle crack propagation cessation toughness K. ca Become k1 (N / mm) 3 / 2 Temperature T Kca＝k1 (°C) was used to evaluate the brittle crack propagation cessation performance of thick steel plates.

[0045] T w =T mt +B1×T ct …(1)

[0046] T Kca＝k1 =A1×T w +C1…(2)

[0047] Among them, T w The combined transition temperatures (°C) obtained using small-scale experiments.

[0048] T mt The transition temperature (°C) of the V-notch Charpy impact test at the middle position of the plate thickness, T ct : Charpy impact test transition temperature (°C) at the center of the plate thickness where the stamping notch is located; A1, B1, C1: coefficients.

[0049] [3] A method for evaluating the brittle crack propagation cessation performance of thick steel plates, wherein, when evaluating the brittle crack propagation cessation performance obtained through large-scale tests based on a temperature representing a specified characteristic value obtained using small-scale tests,

[0050] A brittle crack propagation cessation test was conducted using test specimens of the aforementioned thick steel plate. Based on the observed cross-sectional morphology, the range of locations along the plate thickness from which a cross-sectional morphology differed from the center position of the plate thickness was defined as the center position of the plate thickness.

[0051] The temperature at which the specified characteristic value is obtained using the aforementioned small-scale test is set as the combined transition temperature T. w The combination transition temperature T w The transformation temperature T of the Charpy impact test at the center of the stamping notch of the plate thickness is... ct The transition temperature T of the Charpy impact test at the V-notch position at the middle of the plate thickness. mt The combination is obtained, and the combination transition temperature T w Defined by the following equation (3), based on the combined transition temperature T w The following equation (4) is used to estimate the brittle crack propagation cessation toughness K. ca Become k1 (N / mm) 3 / 2 Temperature T Kca＝k1 (°C) was used to evaluate the brittle crack propagation cessation performance of thick steel plates.

[0052] T w =(T mt +T ct ) / 2+B2×(T ct -T mt )…(3)

[0053] T Kca＝k1 =A2×T w +C2…(4)

[0054] Among them, T wThe combined transition temperatures (°C) obtained using small-scale experiments.

[0055] T mt The transition temperature (°C) of the V-notch Charpy impact test at the middle position of the plate thickness, T ct : Charpy impact test transition temperature (°C) at the center of the plate thickness where the stamping notch is located; A2, B2, C2: coefficients.

[0056] [4] According to the evaluation method for stopping the brittle crack propagation of thick steel plates described in [2], the middle position of the plate thickness is set as the 1 / 4 position of the plate thickness, and the transformation temperature T is set as... ct The energy absorbed in the Charpy impact test at the center of the plate thickness, representing the transition temperature at 40 J, is set as follows: p T E40Jh The transition temperature T mt The transition temperature at the V-notch Charpy impact test position at 1 / 4 of the plate thickness, where the brittle fracture ratio is 50%, is set as follows: v T rsq ,

[0057] Instead of equation (1), use equation (5) below.

[0058] Instead of equation (2), use equation (6) below.

[0059] T w = v T rsq +0.12× p T E40Jh …(5)

[0060] T Kca＝8000 =0.36×T w +22.3…(6)

[0061] v T rsq The transition temperature (°C) at which the brittle fracture ratio is 50% in the V-notch Charpy impact test at 1 / 4 of the plate thickness.

[0062] p T E40Jh The energy absorbed in the Charpy impact test at the center of the plate thickness notch represents the transition temperature (°C) of 40 J.

[0063] [5] According to the evaluation method for the brittle crack propagation cessation performance of thick steel plates described in [3], the middle position of the plate thickness is set as the 1 / 4 position of the plate thickness, and the transformation temperature T is set as... ct The energy absorbed in the Charpy impact test at the center of the plate thickness, representing the transition temperature at 40 J, is set as follows: p T E40JhThe transition temperature T mt The transition temperature at the V-notch Charpy impact test position at 1 / 4 of the plate thickness, where the brittle fracture ratio is 50%, is set as follows: v T rsq ,

[0064] Instead of equation (3), use equation (7) below.

[0065] Instead of equation (4), use equation (8) below.

[0066] T w =1.12×( p T E40Jh + v T rsq ) / 2+0.44×( p T E40Jh - v T rsq )…(7)

[0067] T Kca＝8000 =0.40×( p T E40Jh + v T rsq ) / 2+0.16×( p T E40Jh - v T rsq )+22.3…(8)

[0068] v T rsq The transition temperature (°C) at which the brittle fracture ratio is 50% in the V-notch Charpy impact test at 1 / 4 of the plate thickness.

[0069] p T E40Jh The energy absorbed in the Charpy impact test at the center of the plate thickness notch represents the transition temperature (°C) of 40 J.

[0070] [6] A method for evaluating the brittle crack propagation cessation performance of thick steel plates, wherein, when evaluating the brittle crack propagation cessation performance obtained through large-scale tests based on a temperature representing a specified characteristic value obtained using small-scale tests,

[0071] A brittle crack propagation cessation test was conducted using test specimens of the aforementioned thick steel plate. Based on the observed cross-sectional morphology, the range of locations along the plate thickness from which a cross-sectional morphology differed from the center position of the plate thickness was defined as the center position of the plate thickness.

[0072] The temperature at which the specified characteristic value is obtained using the aforementioned small-scale test is set as the combined transition temperature T. w The combination transition temperature Tw Defined by the following equation (1a) and by the transition temperature T ct and transition temperature T mt The transition temperature T obtained by combination ct The transition temperature T of the Charpy impact test at the center of the stamping notch of the plate thickness is... ct The transition temperature T mt The transition temperature T of the V-notch Charpy impact test at the midpoint of the plate thickness is... mt According to the combined transition temperature T w Using the following equation (2a), the temperature at which brittle crack propagation does not occur in the CAT test is estimated, and the brittle crack propagation cessation performance of thick steel plates is evaluated.

[0073] T w =T mt +E1×T ct …(1a)

[0074] CAT = D1 × T w +F1…(2a)

[0075] Where D1, E1, and F1 are coefficients.

[0076] [7] A method for evaluating the brittle crack propagation cessation performance of thick steel plates, wherein, when evaluating the brittle crack propagation cessation performance obtained through large-scale tests based on a temperature representing a specified characteristic value obtained using small-scale tests,

[0077] A brittle crack propagation cessation test was conducted using test specimens of the aforementioned thick steel plate. Based on the observed cross-sectional morphology, the range of locations along the plate thickness from which a cross-sectional morphology differed from the center position of the plate thickness was defined as the center position of the plate thickness.

[0078] The temperature at which the specified characteristic value is obtained using the aforementioned small-scale test is set as the combined transition temperature T. w The combination transition temperature T w Defined by the following equation (3a) and by the transition temperature T ct and transition temperature T mt The transition temperature T obtained by combination ct The transition temperature T of the Charpy impact test at the center of the stamping notch of the plate thickness is... ct The transition temperature T mt The transition temperature T of the V-notch Charpy impact test at the midpoint of the plate thickness is... mt According to the combined transition temperature T w Using the following formula (4a), the temperature at which brittle crack propagation does not occur in the CAT test is estimated, and the brittle crack propagation cessation performance of thick steel plates is evaluated.

[0079] T w =(T mt +T ct ) / 2+E2×(T ct -T mt ...(3a)

[0080] CAT = D² × T w +F2…(4a)

[0081] Among them, T mt The transition temperature (°C) of the V-notch Charpy impact test at the middle position of the plate thickness.

[0082] T ct : Charpy impact transition temperature (°C) at the center of the plate thickness where the stamping notch is located; D2, E2, F2: coefficients.

[0083] Invention Effects

[0084] According to the present invention, large-scale brittle crack propagation cessation tests with total thickness, such as the ESSO test, are only used to determine the test location. Based on the toughness evaluation results of small-scale tests using test pieces of the same size as those in the Charpy impact test, the brittle crack propagation cessation performance of thick steel plates can be evaluated simply and with high precision, which has a significant effect on industry. Attached Figure Description

[0085] Figure 1 This is an illustrative diagram showing an example of the cross-sectional morphology of a CAT total thickness test specimen after a brittle crack propagation cessation test (CAT test).

[0086] Figure 2 It represents the temperature T obtained through the ESSO test. Kca＝8000 The energy transition temperature of the Charpy impact test at the center of the plate thickness. p T E40J A diagram showing the relationships between them.

[0087] Figure 3 It represents the temperature T obtained through the ESSO test. Kca＝8000 A graph showing the relationship between the combined transformation temperature Tw and the energy transformation temperature of the Charpy impact test at the center of the plate thickness notch. p T E40Jh Section transition temperature of Charpy impact test at 1 / 4 of plate thickness and V-notch v T rsq The combination yields the result.

[0088] Figure 4 It represents the temperature T obtained through the ESSO test. Kca＝8000The predicted temperature (estimated temperature) T derived from the results of small-scale experiments Kca＝8000 ＊ A diagram showing the relationships between them. Detailed Implementation

[0089] This invention relates to an evaluation method for stopping brittle crack propagation in thick steel plates with a thickness of 40 mm or more, preferably 50 mm or more, using a temperature at which a specified characteristic value is obtained from a small-scale test. Furthermore, the upper limit for the plate thickness in this invention is preferably 120 mm or less.

[0090] For thick steel plates with high brittle crack propagation cessation properties, when brittle crack propagation cessation tests are conducted and the cross-sectional morphology is observed, the following results appear: Figure 1 The cross-sectional morphology is schematically shown in the diagram. In the central part of the plate thickness, the main crack (brittle crack) 3 propagates from the embrittled portion 2 adjacent to the cut 1 in a 35° inclined direction and then stops (brittle crack stop 4). In addition, at the end of the main crack 3 that propagates in the inclined direction, the following cross-sectional morphology is shown: multiple flat cracks (flat section 5) are formed at intervals of 35% to 15% of the distance from the surface along the plate thickness direction and 65% to 85% of the distance from the surface along the plate thickness direction, which propagate relatively flatly and then stop. A stepped step 6 (ductile section) is also shown.

[0091] These flat sections 5 arise from different locations of the obliquely advancing main crack 3, and between these flat sections 5, step-like steps 6 (ductile sections) with considerable bands are formed.

[0092] Based on this cross-sectional morphology, it is inferred that, in addition to the toughness at the center of the plate thickness, the toughness at the thickness-direction position (hereinafter referred to as the middle position of the plate thickness) which forms a cross-section different from that at the center of the plate thickness has a significant impact on the overall brittle crack propagation cessation performance of the thick steel plate.

[0093] Furthermore, observations of non-penetrating test specimens of this thick steel plate revealed that, in brittle crack propagation cessation tests, cracks progressed deeper in the center and middle of the plate thickness when propagation ceased, but their progression was relatively shallower near the surface. Based on this failure mode, it is believed that crack propagation behavior in the center and middle of the plate thickness, compared to the surface, dominates the overall brittle crack propagation progression of the steel plate. Therefore, in this type of thick steel plate, it can be said that the area near the surface has little influence on the brittle crack propagation cessation performance.

[0094] Therefore, in this invention, firstly, for the thick steel plate being tested, several test pieces, preferably 3 to 5 pieces with a total thickness, are used to conduct a large-scale brittle crack propagation cessation test at an appropriate test temperature. Then, the cross-sectional morphology of the obtained test pieces is observed, and the range of positions in the thickness direction showing a cross-sectional morphology different from the central position of the plate thickness is determined as the central position of the plate thickness. Furthermore, in such thick steel plates, the central position of the plate thickness is mostly a position within a range of (1 / 6 to 3 / 8)t from the back of the plate, and in most cases, it can also be represented by a position t / 4 from the back of the plate. Furthermore, the terms "central position of the plate thickness" and "1 / 4 position of the plate thickness" allow for a range of ±5% of the plate thickness. (That is, "1 / 4 position of the plate thickness" includes a range of (1.05t / 4) to (0.95t / 4).) Additionally, in this invention, for example, the plate thickness is sometimes replaced with t, such as using "t / 2" for 1 / 2 of the plate thickness and "t / 4" for 1 / 4 of the plate thickness.

[0095] Examples of large-scale tests involving total thickness include the ESSO test, CAT test, and stamping notch bending test, but the present invention is not limited to these. For example, the ESSO test, CAT test, and stamping notch bending test using a thickness-reduced test piece can also be used. However, in such cases, it is important to consider the test piece thickness at the middle position of the sheet thickness, which represents a region of characteristic variation showing a cross-sectional shape different from the center position of the sheet thickness. Furthermore, if small-scale tests can be performed at multiple sheet thickness positions to identify the region of characteristic variation, cross-sectional observation based on a large test piece can be omitted.

[0096] Furthermore, the small-scale test used in this invention is the Charpy impact test, and the test piece size used is a commonly used size (e.g., 10 mm square). Additionally, the notch on the test piece is a V-notch or a stamped notch.

[0097] Furthermore, in this invention, it is believed that the brittle crack propagation cessation performance of thick steel plates is greatly affected by the temperature at the center of the plate thickness, which represents a specified characteristic value, and the temperature at the middle of the plate thickness, which shows a cross-sectional shape different from that at the center of the plate thickness, which represents a specified characteristic value. Small-scale tests are conducted at the center of the plate thickness and the middle of the plate thickness of the thick steel plates.

[0098] A Charpy impact test was performed at the center of the thickness of a thick steel plate, and the energy transformation temperature or section transformation temperature T was obtained. ct The temperature (transition temperature) representing the specified characteristic value is set at the center of the plate thickness. Furthermore, a notched Charpy impact test, which has been performed consistently, is conducted at the center of the plate thickness. This is because, in the notched Charpy impact test, brittle cracks can be generated from the embrittled area due to the notch, and the phenomenon of crack propagation cessation can be reproduced; this phenomenon is the same as the actual brittle crack propagation cessation behavior. Furthermore, the transition temperature T at the center of the plate thickness... ctPreferably, the absorbed energy of the Charpy impact test with a notched stamping, representing a high correlation with the brittle crack propagation cessation performance when the steel plate thickness is relatively thin, indicates a temperature of 40 J. p T E40J (°C).

[0099] In addition, the energy transformation temperature or section transformation temperature T obtained by performing a Charpy impact test at the middle of the thickness of the thick steel plate will be measured. mt The temperature (transformation temperature) representing the specified characteristic value is set at the midpoint of the plate thickness. Furthermore, at the midpoint of the thickness of a thick steel plate, the crack stops due to the load causing it to regenerate from the ductile failure end into a brittle crack. Therefore, in this invention, a V-notch Charpy impact test exhibiting the same failure mode, which generates a brittle crack from a ductile crack, is conducted as a small-scale test.

[0100] Furthermore, V-notched Charpy impact test specimens are easy to process and can be tested immediately after processing, thus simplifying the testing process. Stamped-notched Charpy impact test specimens require stamping, necessitating additional labor and time. In high-toughness steel plates, when the area directly below the notch is embrittled by introducing a stamped notch, brittle cracks do not consistently develop during testing. Moreover, even at the temperature at which brittle cracks stably develop, the cracks may not stop, resulting in the inability to conduct stable tests. Therefore, the transition temperature T at the midpoint of the plate thickness is crucial. mt The section transition temperature with a brittle fracture ratio of 50% was used in the V-notch Charpy impact test, where stable test results are easily obtained. v T rs (°C) is simple and preferred.

[0101] In this invention, the combined transition temperature T is used as the temperature (transition temperature) representing the specified characteristic value obtained using small-scale tests. w The combined transition temperature T w The transition temperature T at the center of the plate thickness, calculated from two locations along the plate thickness direction. ct The transition temperature T at the midpoint of the plate thickness mentioned above. mt It is obtained by combining. T w It is represented by the following equations (1) and (1a).

[0102] T w =T mt +B1×T ct …(1)

[0103] (Where, B1: coefficient)

[0104] T w =T mt +E1×Tct …(1a)

[0105] (Where, E1: coefficient)

[0106] This is based on the observation of the cross-sectional morphology of the aforementioned thick steel plates, which shows that the toughness at the center of the plate thickness and the toughness in the middle of the plate thickness strongly affect the brittle crack propagation cessation performance of the thick steel plate. Furthermore, the degree of influence of the total thickness on the brittle crack propagation cessation performance can also be used as a metric for T. mt and T ct The weighted average. Specifically, when the middle position of the plate thickness is set as the 1 / 4 position of the plate thickness, it is taken as T. ct Using transition temperature p T E40Jh As T mt Using transition temperature v T rsq As a weighted average ratio, 12:100 is applied, preferably set as the following formula (5).

[0107] T w = v T rsq +0.12× p T E40Jh …(5)

[0108] Furthermore, the application of a 12:100 weighted average ratio is based on the following: the stepped cross-sectional morphology obtained at the midpoint of the plate thickness significantly improves the brittle crack propagation cessation performance; and by using this weighted average allocation, the correlation between large-scale and small-scale test results becomes higher. However, this invention is not limited to the aforementioned weighted average.

[0109] Alternatively, the temperature representing the specified characteristic value obtained from small-scale tests can also be the temperature representing the overall toughness of the plate thickness. Preferably, the temperature representing the overall toughness of the plate thickness is the temperature obtained by combining the average toughness at each location of the plate thickness (toughness average) with the difference in toughness at each location of the plate thickness (toughness difference). When the representative locations in the plate thickness direction are set as the center location and the middle location of the plate thickness, the Charpy impact test transition temperature T at the center location of the plate thickness is used. ct The Charpy impact transition temperature T at the midpoint of the plate thickness. mt Preferably, the combined transition temperature T is defined by the following equation (3). w .

[0110] T w =(T mt +T ct ) / 2+B2×(T ct -T mt )…(3)

[0111] (Where, B2: coefficient)

[0112] This is because it is assumed that the overall toughness of the plate thickness is the average toughness at various locations along the plate thickness (average toughness), i.e., (T). mt +T ct In addition to ) / 2, for Figure 1 The stepped structure mentioned above affects the toughness of the plate at different locations, specifically the difference in toughness (toughness difference), i.e., (T). ct -T mt They also made significant contributions.

[0113] Furthermore, the combined transition temperature T, obtained from small-scale experiments, is calculated in advance. w The correlation between the brittle fracture propagation stopping performance of thick steel plates obtained through large-scale tests and the relationship between the two.

[0114] As a large-scale test, using the ESSO test, the brittle crack propagation stopping toughness K was used as the brittle fracture propagation stopping performance of thick steel plates. ca Become k1 (N / mm) 3 / 2 Temperature T Kca＝k1 (°C).

[0115] Such a correlation is represented by the following equation (2) and equation (4).

[0116] T Kca＝k1 =A1×T w +C1…(2)

[0117] (Where A1 and C1 are coefficients)

[0118] T Kca＝k1 =A2×T w +C2…(4)

[0119] (Where, A2 and C2 are coefficients)

[0120] Based on the combined transition temperature T obtained using small-scale experiments w Using equation (2) or (4), the brittle crack propagation cessation toughness K is estimated. ca The temperature T that becomes k1 Kca＝k1 .

[0121] Furthermore, when set to T w = v T rsq +0.12× p T E40Jh In the case of T w and T Kca＝8000 The relationship is specifically represented by the following formula.

[0122] T Kca＝8000=0.36×( v T rsq +0.12× p T E40Jh +22.3

[0123] Or the following formula (6)

[0124] T Kca＝8000 =0.36×T w +22.3…(6)

[0125] Alternatively, instead of equation (3), in the case of equation (7) below,

[0126] T w =1.12×( p T E40Jh + v T rsq ) / 2+0.44×( p T E40Jh - v T rsq )…(7)

[0127] It is represented by the following equation (8).

[0128] T Kca＝8000 =0.40×( p T E40Jh + v T rsq ) / 2+0.16×( p T E40Jh - v T rsq )+22.3…(8)

[0129] In addition, the CAT test can also be used as a large-scale test. In this case, the temperature at which brittle crack propagation does not occur is preferably used as the CAT (°C) to measure the brittle fracture propagation cessation performance of thick steel plates.

[0130] Such a correlation is represented by equations (2a) and (4a) below.

[0131] CAT = D1 × T w +F1…(2a)

[0132] (Where, D1 and F1 are coefficients)

[0133] CAT = D² × T w +F2…(4a)

[0134] (Where, D2 and F2 are coefficients)

[0135] Based on the combined transition temperature Tw obtained from small-scale tests, the temperature at which brittle cracks do not propagate in the CAT test is estimated using equation (2a) (°C).

[0136] In equation (2a), the transition temperature T is made... w To represent the overall toughness of the plate thickness, the following formula (3a) is derived by combining the average toughness at each plate thickness location (toughness average) and the difference in toughness at each plate thickness location (toughness difference).

[0137] T w =(T mt +T ct ) / 2+E2×(T ct -T mt ...(3a)

[0138] (Where, E2: coefficient)

[0139] In this case, the temperature at which brittle cracks do not propagate in the CAT test is estimated using the above formula (4a) CAT (°C).

[0140] The present invention will be further described below using examples.

[0141] Example

[0142] For thick steel plates (EH40-47 grade) with a thickness of 70-100 mm, a temperature gradient ESSO test was conducted using total thickness test specimens to determine the brittle crack propagation arrest performance and calculate the brittle crack propagation arrest toughness K. ca Indicates 8000 N / mm 3 / 2 Temperature T Kca＝8000 Furthermore, after the experiment, the cross-sectional morphology was observed, and the range of plate thickness positions showing a cross-sectional morphology different from that at the center of the plate thickness was determined as the center of the plate thickness. Moreover, in the thick steel plates tested, it was confirmed that the center of the plate thickness can also be represented by the t / 4 position of the plate thickness.

[0143] On the other hand, Charpy impact test pieces (10 mm square) are collected from the L direction at the position of t / 4 of the plate thickness, which is the center position of the plate thickness and the middle position of the plate thickness. Charpy impact tests are carried out as a small-scale test, and the temperature at which the specified characteristic value is indicated by the small-scale test is determined.

[0144] Charpy impact test with a stamped notch was performed at the center of the plate thickness as the transition temperature T. ct (°C), calculate the temperature at which the absorbed energy represents 40 J. p T E40Jh Additionally, a V-notch Charpy impact test was performed at the midpoint of the plate thickness (1 / 4 of the plate thickness) to determine the transition temperature T. mt(°C), calculate the section transition temperature when the brittle fracture surface area is 50%. v T rsq .

[0145] Then, the obtained T ct and T mt The combination, as determined by small-scale experiments, refers to the combination transition temperature T. w The temperature T is calculated based on the pre-determined correlation formula. Kca＝8000 .

[0146] In addition, the combined transition temperature T obtained through small-scale experiments will be... w (°C) is set to T w =1.12×( p T E40Jh + v T rsq ) / 2+0.44×( p T E40Jh - v T rsq Use the following formula to predict (estimate) the temperature T. Kca＝8000 ＊ .

[0147] T Kca＝8000 ＊ =0.40×( p T E40Jh + v T rsq ) / 2+0.16×( p T E40Jh - v T rsq +22.3

[0148] The results obtained are expressed in terms of temperature T. Kca＝8000 and the estimated (predicted) temperature T Kca＝8000 ＊ The relationship is Figure 4 As shown in the image.

[0149] Depend on Figure 4 It can be seen that the estimated temperature T in the evaluation method of the present invention Kca＝8000 ＊ With T Kca＝8000 The correlation is also high, with 2σ below 20℃, enabling the estimation of temperature T with a small estimation error. Kca＝8000 .

[0150] Thus, according to the evaluation method of the present invention, large-scale tests are only used to determine the test location. Based on the results of small-scale tests at two locations—the central location of the plate thickness and the intermediate location of the plate thickness with a cross-sectional shape different from that of the central location—the brittle crack propagation cessation performance of thick steel plates can be evaluated simply and with high precision, thus confirming the usefulness of the evaluation method of the present invention.

[0151] Label Explanation

[0152] 1: Incision

[0153] 2: Embrittlement part

[0154] 3: Main crack (brittle crack)

[0155] 4: Brittle cracking stops

[0156] 5: Flat cross-section

[0157] 6: Step-like steps

[0158] s: Direction of brittle crack propagation.

Claims

1. A method for evaluating the brittle crack propagation cessation performance of thick steel plates, wherein, When evaluating the brittle crack propagation cessation performance obtained from large-scale tests based on the temperature representing the specified characteristic values ​​obtained using small-scale tests, A brittle crack propagation cessation test was conducted using test specimens of the aforementioned thick steel plate. Based on the observed cross-sectional morphology, the range of positions along the thickness direction that exhibit a cross-sectional morphology different from the central position of the plate thickness was defined as the central position of the plate thickness. The central position of the plate thickness is defined as the range from 3 / 8 to 5 / 8 of the plate thickness, centered at the 1 / 2 position. The central positions of the plate thickness are symmetrically separated from the central position at the 1 / 6 to 3 / 8 and 5 / 8 to 5 / 6 positions. The temperature representing the specified characteristic value obtained using the aforementioned small-scale test is designated as the combined transition temperature. This combined transition temperature is obtained by combining the transition temperature of the Charpy impact test with a notched stamp at the center of the plate thickness and the transition temperature of the Charpy impact test with a V-notch at the center of the plate thickness. The brittle crack propagation cessation performance of the thick steel plate is evaluated based on the combined transition temperature.

2. A method for evaluating the brittle crack propagation cessation performance of thick steel plates, wherein, When evaluating the brittle crack propagation cessation performance obtained from large-scale tests based on the temperature representing the specified characteristic values ​​obtained using small-scale tests, A brittle crack propagation cessation test was conducted using test specimens of the aforementioned thick steel plate. Based on the observed cross-sectional morphology, the range of positions along the thickness direction that exhibit a cross-sectional morphology different from the central position of the plate thickness was defined as the central position of the plate thickness. The central position of the plate thickness is defined as the range from 3 / 8 to 5 / 8 of the plate thickness, centered at the 1 / 2 position. The central positions of the plate thickness are symmetrically separated from the central position at the 1 / 6 to 3 / 8 and 5 / 8 to 5 / 6 positions. The temperature at which the specified characteristic value is obtained using the aforementioned small-scale test is set as the combined transition temperature T. w The combination transition temperature T w The transformation temperature T of the Charpy impact test at the center of the stamping notch of the plate thickness is... ct The transition temperature T of the Charpy impact test at the V-notch position at the middle of the plate thickness. mt The combination is obtained, and the combination transition temperature T w Defined by the following equation (1), based on the combined transition temperature T w The following equation (2) is used to estimate the brittle crack propagation cessation toughness K. ca Become k1 (N / mm) 3 / 2 Temperature T Kca＝k1 (°C) to evaluate the brittle crack propagation cessation performance of thick steel plates. T w =T mt +B1×T ct …(1) T Kca＝k1 =A1×T w +C1…(2) Among them, T w Combined transition temperatures (°C) obtained using small-scale experiments. T mt Transition temperature (°C) of Charpy impact test at the V-notch position in the middle of the plate thickness. T ct : Charpy impact test transition temperature (°C) at the center of the plate thickness where the stamping notch is located. A1, B1, C1: Coefficients.

3. A method for evaluating the brittle crack propagation cessation performance of thick steel plates, wherein, When evaluating the brittle crack propagation cessation performance obtained from large-scale tests based on the temperature representing the specified characteristic values ​​obtained using small-scale tests, A brittle crack propagation cessation test was conducted using test specimens of the aforementioned thick steel plate. Based on the observed cross-sectional morphology, the range of positions along the thickness direction that exhibit a cross-sectional morphology different from the central position of the plate thickness was defined as the central position of the plate thickness. The central position of the plate thickness is defined as the range from 3 / 8 to 5 / 8 of the plate thickness, centered at the 1 / 2 position. The central positions of the plate thickness are symmetrically separated from the central position at the 1 / 6 to 3 / 8 and 5 / 8 to 5 / 6 positions. The temperature at which the specified characteristic value is obtained using the aforementioned small-scale test is set as the combined transition temperature T. w The combination transition temperature T w The transformation temperature T of the Charpy impact test at the center of the stamping notch of the plate thickness is... ct The transition temperature T of the Charpy impact test at the V-notch position at the middle of the plate thickness. mt The combination is obtained, and the combination transition temperature T w Defined by the following equation (3), based on the combined transition temperature T w The following equation (4) is used to estimate the brittle crack propagation cessation toughness K. ca Become k1 (N / mm) 3 / 2 Temperature T Kca＝k1 (°C) to evaluate the brittle crack propagation cessation performance of thick steel plates. T w =(T mt +T ct ) / 2+B2×(T ct -T mt )…(3) T Kca＝k1 =A2×T w +C2…(4) Among them, T w Combined transition temperatures (°C) obtained using small-scale experiments. T mt Transition temperature (°C) of Charpy impact test at the V-notch position in the middle of the plate thickness. T ct : Charpy impact test transition temperature (°C) at the center of the plate thickness where the stamping notch is located. A2, B2, C2: coefficients.

4. The evaluation method for stopping brittle crack propagation in thick steel plates according to claim 2, wherein, Set the middle position of the plate thickness as the 1 / 4 position, and set the transition temperature T ct The energy absorbed in the Charpy impact test at the center of the plate thickness, representing the transition temperature at 40 J, is set as follows: p T E40Jh The transition temperature T mt The transition temperature at the V-notch Charpy impact test position at 1 / 4 of the plate thickness, where the brittle fracture ratio is 50%, is set as the transition temperature. v T rsq , Instead of equation (1), use equation (5) below. Instead of equation (2), use equation (6) below. T w = v T rsq +0.12× p T E40Jh …(5) T Kca＝8000 =0.36×T w +22.3…(6) v T rsq The transition temperature (°C) at which the brittle fracture ratio is 50% in the V-notch Charpy impact test at 1 / 4 of the plate thickness. p T E40Jh The energy absorbed in the Charpy impact test at the center of the plate thickness notch represents the transition temperature (°C) of 40 J.

5. The evaluation method for stopping brittle crack propagation in thick steel plates according to claim 3, wherein, Set the middle position of the plate thickness as the 1 / 4 position, and set the transition temperature T ct The energy absorbed in the Charpy impact test at the center of the plate thickness, representing the transition temperature at 40 J, is set as follows: p T E40Jh The transition temperature T mt The transition temperature at the V-notch Charpy impact test position at 1 / 4 of the plate thickness, where the brittle fracture ratio is 50%, is set as the transition temperature. v T rsq , Instead of equation (3), use equation (7) below. Instead of equation (4), use equation (8) below. T w =1.12×( p T E40Jh + v T rsq ) / 2+0.44×( p T E40Jh - v T rsq )…(7) T Kca＝8000 =0.40×( p T E40Jh + v T rsq ) / 2+0.16×( p T E40Jh - v T rsq )+22.3…(8) v T rsq The transition temperature (°C) at which the brittle fracture ratio is 50% in the V-notch Charpy impact test at 1 / 4 of the plate thickness. p T E40Jh The energy absorbed in the Charpy impact test at the center of the plate thickness notch represents the transition temperature (°C) of 40 J.

6. A method for evaluating the brittle crack propagation cessation performance of thick steel plates, wherein, When evaluating the brittle crack propagation cessation performance obtained from large-scale tests based on the temperature representing the specified characteristic values ​​obtained using small-scale tests, A brittle crack propagation cessation test was conducted using test specimens of the aforementioned thick steel plate. Based on the observed cross-sectional morphology, the range of positions along the thickness direction that exhibit a cross-sectional morphology different from the central position of the plate thickness was defined as the central position of the plate thickness. The central position of the plate thickness is defined as the range from 3 / 8 to 5 / 8 of the plate thickness, centered at the 1 / 2 position. The central positions of the plate thickness are symmetrically separated from the central position at the 1 / 6 to 3 / 8 and 5 / 8 to 5 / 6 positions. The temperature at which the specified characteristic value is obtained using the aforementioned small-scale test is set as the combined transition temperature T. w The combination transition temperature T w Defined by the following equation (1a) and by the transition temperature T ct and transition temperature T mt The transition temperature T obtained by combining the two is... ct The transition temperature T of the Charpy impact test at the center of the stamping notch of the plate thickness is... ct The transition temperature T mt The transition temperature T of the V-notch Charpy impact test at the midpoint of the plate thickness is... mt According to the combined transition temperature T w Using the following formula (2a), the temperature at which brittle crack propagation does not occur in the CAT test, CAT (°C), is estimated to evaluate the brittle crack propagation cessation performance of thick steel plates. T w =T mt +E1×T ct …(1a) CAT=D1×T w +F1…(2a) Where D1, E1, and F1 are coefficients.

7. A method for evaluating the brittle crack propagation cessation performance of thick steel plates, wherein, When evaluating the brittle crack propagation cessation performance obtained from large-scale tests based on the temperature representing the specified characteristic values ​​obtained using small-scale tests, A brittle crack propagation cessation test was conducted using test specimens of the aforementioned thick steel plate. Based on the observed cross-sectional morphology, the range of positions along the thickness direction that exhibit a cross-sectional morphology different from the central position of the plate thickness was defined as the central position of the plate thickness. The central position of the plate thickness is defined as the range from 3 / 8 to 5 / 8 of the plate thickness, centered at the 1 / 2 position. The central positions of the plate thickness are symmetrically separated from the central position at the 1 / 6 to 3 / 8 and 5 / 8 to 5 / 6 positions. The temperature at which the specified characteristic value is obtained using the aforementioned small-scale test is set as the combined transition temperature T. w The combination transition temperature T w Defined by the following equation (3a) and by the transition temperature T ct and transition temperature T mt The transition temperature T obtained by combining the two is... ct The transition temperature T of the Charpy impact test at the center of the stamping notch of the plate thickness is... ct The transition temperature T mt The transition temperature T of the V-notch Charpy impact test at the midpoint of the plate thickness is... mt According to the combined transition temperature T w Using the following formula (4a), the temperature at which brittle crack propagation does not occur in the CAT test, CAT (°C), is estimated to evaluate the brittle crack propagation cessation performance of thick steel plates. T w =(T mt +T ct ) / 2+E2×(T ct -T mt )…(3a) CAT=D2×T w +F2…(4a) Among them, T mt Transition temperature (°C) of Charpy impact test at the V-notch position in the middle of the plate thickness. T ct : Charpy impact test transition temperature (°C) at the center of the plate thickness where the stamping notch is located. D2, E2, F2: coefficients.

Images