JP2015135324A - Determination method of brittle crack arrest property of high strength thick steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of determining a brittle crack arrest property of a high strength thick steel plate by a simple and rational method.SOLUTION: A determination method of a brittle crack arrest property of a high strength thick steel plate is provided that includes: a step of performing a brittle fracture arrest test and a complex miniature test using a plurality of standard steels; a step of calculating a correlation model of a Kca value actually measured by the brittle fracture arrest test and a result (NDT temperature and fracture surface transition temperature or energy transition temperature) of the complex miniature test; a step of deciding an arrest property determination criteria for each plate thickness based on the brittle fracture arrest test, a result of the complex miniature test, and the correlation model; a step of performing the complex miniature test using a sample steel; and a step of determining the arrest property of a sample plate based on the result of the complex miniature test of the sample steel and the determination criteria.

Description

  The present invention relates to a method for determining brittle crack propagation stopping characteristics of a high-strength thick steel plate, and in particular, high-strength used for construction of a structure that needs to prevent large-scale damage or damage caused by brittle crack propagation. The present invention relates to a method for judging the brittle crack propagation stop characteristic of a thick steel plate by a simple and rational method.

  Unlike tankers, container ships and bulk carriers, which are welded structures, have few partition walls in the hold and a large opening at the top of the ship. On the contrary, the tanker is finely partitioned by the oil tank, and the inner wall and upper deck also have a structure that bears the hull strength.

  For this reason, in a container ship, in order to ensure the strength of a hull structure, it is especially necessary to use a high-strength steel plate as a hull outer plate.

In recent years, container ships have become larger, and large container ships of 6000 to 20000 TEU (Twenty Fee Equivalent Unit) have been built and planned. Accordingly, the steel plate for the outer hull plate, with thickened, and high strength, with a thickness 50Mm～250mm, steel yield strength 390 N / mm ² grade, more 470N / mm ² class thick (Thick steel plate) has come to be used.

  The TEU is an index indicating the loading capacity of the container ship, and is displayed as the number of containers when converted into a container having a length of 20 feet.

As described above, in high-strength thick steel plates used in ships and the like, brittle crack propagation stopping characteristics (hereinafter sometimes referred to as “arrest performance”) are very important in evaluating the safety of high-strength thick steel plates. It becomes a characteristic.
In addition, there is an increasing demand for arrest performance even in high-strength steel materials used for hydraulic iron pipes (penstock) for hydropower generation.

  In order to improve the arrest performance, various component compositions, steel materials with manufacturing processes, various large welded structures, and the like have been developed and manufactured. To quantitatively evaluate the arrest performance of these newly developed steel materials, the ESSO test (Brittle Fracture Propagation Stop Test: evaluates the ability to artificially generate a brittle crack in a specimen and stop the brittle crack. Large-scale tests such as a double tensile test and the like. For example, in the case of the brittle fracture propagation stop test, a full-sized large-sized test piece having dimensions of about 500 mm × 500 mm × plate thickness is produced, and a V-notch is formed at the end of the test piece. A temperature gradient is applied to the test piece, and an impact load is applied to the V notch through a wedge to artificially generate a brittle crack. The Kca value (fracture) based on the stress applied to the specimen, the temperature at which the propagation of the brittle crack stopped (hereinafter also referred to as “crack stop temperature”), and the crack length. Toughness value) is calculated.

The test is performed by changing the temperature gradient condition and the load load condition, the relationship between the crack stop temperature and the Kca value is obtained, and the arrest performance at an arbitrary temperature is evaluated by the Kca value. Further, as an index of arrest performance, a limit temperature (minimum temperature) at which a predetermined Kca can be secured is called a target Kca limit temperature and expressed as “TKca”.
Specifically, for example, the target Kca limit temperature when the target Kca value is 6000 N / mm ^1.5 is expressed as TKca6000.
When a steel plate is used for a steel structure such as a container ship, a design temperature or a minimum use temperature of the steel structure is determined. If TKca6000 measured or estimated about a predetermined steel plate is the temperature below the design temperature, it will evaluate that said steel plate can ensure sufficient arrest performance in this design temperature.

  However, in order to actually measure the Kca value, a large test piece and a large test machine are required, and a lot of work and time are required until a test result is obtained. In particular, a large-scale testing machine capable of applying a tensile load of 1000 tons or more is required for a large-scale test of a thick steel plate having a thickness of 50 mm or more. Therefore, in conventional performance inspection or quality control of steel plates, it is necessary to obtain in advance a correlation between the arrest performance of the entire thick steel plate and a simple small test result using a small test piece taken from the thick steel plate. (See, for example, Patent Document 1 and Non-Patent Documents 1 to 3). Then, based on the preliminary examination results, based on the required value of the small test calculated from the required arrest performance, a small test is performed on a steel plate manufactured at a steelworks, etc. Performance inspection or quality control of steel sheets has been performed by a method for determining whether or not a required value is satisfied.

Non-Patent Document 1 describes the correlation between the arrest performance of a low-temperature steel having a thickness of about 16 mm and a small test. Non-Patent Document 2 describes a simple evaluation method for arrest performance of a steel sheet having a multi-layer structure having a special ultrafine grain structure in the steel sheet surface layer. Non-Patent Document 3 describes a fracture surface transition temperature obtained by a Charpy impact test at an extremely thick high strength 790 N / mm grade ² steel plate at the center of the plate thickness, 1/4 of the plate thickness, and 2 mm below the surface of the steel plate. Describes a method for simple evaluation of arrest performance.

JP 2007-302993 A Japanese Patent No. 4795487

Steel Society Presentation Summary, CAMP-ISIJ Vol. 4 (1991) -918, “Correlation between Kca and small arrest test method and factors controlling arrest performance” (Examination of arrest performance of steel sheet (5)) Western Shipbuilding Association Bulletin No. 106 (August 2003), P275-280, “Easy Evaluation Method for Arrest Performance of Surface Superfine-Grained Steel Sheet (Part 1) —Establishment of Arrest Performance Estimation Formula” Summary of National Welding Society Conference Lecture, No. 49 (issued on August 25, 1991), P108-109, “Effects of plate thickness and plate thickness direction toughness distribution on the arrestability of extra-thick HT790”

For safety large container ships, for example, in thickness 50mm~100mm used, yield strength 390 N / mm ² grade, the 470N / mm ² class of thick steel plate (steel plate) is, -10 ° C. arrest the performance of in the order of 6000N ^{/ mm 1.5} from 4000N ^{/ mm 1.5} has been found to be very important. Is this in order to meet the arrestability request, but steel sheet having a high arrest performance have been developed, arrest performance of about 6000 N ^{/ mm 1.5} from 4000 N ^{/ mm 1.5} is for all of the steel sheet is provided It became necessary to confirm. For this reason, it has come to be required to confirm the arrest performance by a steel sheet shipping test at a steelworks. However, as described above, it is difficult to perform a large-scale test such as a brittle fracture propagation stop test on all steel plates. In addition, there is a large variation in the correlation between the arrest performance in the large test and the small test result, and taking into account the variation, it is necessary to have extremely strict requirements for small test that cannot be stably manufactured at the steelworks. There wasn't. Therefore, in the thickness 50 to 100 mm, the yield strength 390 N / mm ² class, with respect to the steel plate of 470N / mm ² class thick, a method of assessing easily and accurately using a small test arrest performance It has been sought.
Accordingly, the present inventors have developed a method for obtaining a correlation between the arrest performance of the entire thick steel plate and a simple small test result using a small test piece collected from the thick steel plate more easily and more accurately than before. investigated.

  The inventors first manufactured high-strength thick steel plates with a plurality of compositions and manufacturing methods, and obtained the Kca value of the high-strength thick steel plates in a brittle fracture propagation stop test using the methods disclosed in Non-Patent Documents 1 and 2. Asked. Moreover, a small test piece was sampled from the above-mentioned thick steel plate, and various small tests (V-notch Charpy impact test, drop weight test, etc.) were performed on the small test piece to determine the characteristic value of the small test piece. Then, the correspondence relationship between the Kca value, which is the result of the large test obtained, and the characteristic value of the small test piece was investigated. As described above, when the correlation between the characteristic value obtained in the small test and the arrest performance is related with the existing method for obtaining the correlation related to the steel sheet having a thickness of about 20 mm, the correlation between the two varies and sufficient accuracy is obtained. It was found that no correlation was obtained.

  Therefore, the present invention was made against the background of such circumstances, greatly improved the small test method and its evaluation method, without performing a large-scale test such as a brittle fracture propagation stop test of high strength thick steel plate It is an object to provide a method for determining arrest performance by a simple method.

  In order to solve the above-mentioned problems, the present inventor examined the factors that do not provide sufficient consistency between the arrest performance in the large test and the small test result. It was found that the steel plate thickness that was not taken into account had a great influence. In other words, when the correlation between the arrest performance in the large test and the small test result was derived using the existing method, the plate thickness was not taken into account, and thus the correlation between the two was considered to have varied.

Therefore, the gist of the present invention is as follows.
[1] A method for determining brittle crack propagation stopping characteristics of a thick steel plate,
A process of performing a brittle fracture propagation stop test using a plurality of standard steels having different thicknesses;
Performing a composite compact test using the standard steel;
Calculating a correlation model between a brittle crack propagation stop characteristic Kca value measured by the brittle fracture propagation stop test and a result of the composite small test;
Based on the results of the brittle fracture propagation stop test, the composite small test and the correlation model, determining a criterion for determining the brittle crack propagation stop characteristics for each plate thickness;
Performing the composite compact test using sample steel;
Based on the result of the composite small test of the sample steel and the criterion for determining the brittle crack propagation stop property, determining the brittle crack propagation stop property of the sample steel;
Including
Both the step of performing the composite compact test using the standard steel and the step of performing the composite compact test using the sample steel,
(A) a step of collecting a surface layer small test piece including a steel sheet surface layer portion;
(B) a step of collecting internal small test pieces from one or two or more internal regions not including the steel sheet surface layer portion;
(C) A step of performing a drop weight test in accordance with the NRL drop weight test method defined in ASTM E208-06 using the surface layer small test piece, and obtaining an NDT temperature;
(D) performing a small test to measure the brittle fracture surface rate or absorbed energy using the internal small test piece, and obtaining a fracture surface transition temperature or an energy transition temperature;
Including
In the brittle crack propagation stop characteristic Kca value, the target Kca limit temperature TKca, which is the limit temperature at which a predetermined Kca value can be secured, is the objective variable, the NDT temperature of the standard steel is the first explanatory variable X, and the standard steel Where the fracture surface transition temperature or energy transition temperature is a second explanatory variable Y, the thickness of the standard steel is a third explanatory variable Z, and a, b, c, and d are coefficients, It is following formula (1),
a · X + b · Y + c · Z + d = TKca (1)
In the step of determining the brittle crack propagation stop property criteria,
The NDT temperature of the standard steel, the fracture surface transition temperature or energy transition temperature, and TKca are the above-mentioned formulas that are guaranteed temperatures that are the lowest temperatures that guarantee that the standard steel has a predetermined Kca value. A step of obtaining a correlation with (1) for each plate thickness;
Based on the correlation, a region in which the value of the TKca of the standard steel indicates the guaranteed temperature or less is determined, and the NDT temperature and the fracture surface transition temperature or energy transition temperature of the standard steel for representing the region. , The process of summarizing every thickness,
A method for determining brittle crack propagation stopping characteristics of a high-strength thick steel plate characterized by comprising:
[2] In the step of determining the criterion for determining the brittle crack propagation stop property, when determining the region where the value of the TKca of the standard steel is equal to or lower than the guaranteed temperature based on the correlation, Regardless, the NDT temperature of the standard steel for representing the region is determined with the fracture surface transition temperature or energy transition temperature for representing the region being constant. Method for determining brittle crack propagation stopping properties of high-strength thick steel plates.
[3] The above-mentioned [1] or [3], wherein the third explanatory variable Z is expressed by the following formula (2), where the thickness of the standard steel is t and n is a coefficient of 0.01 to 1. 2] The determination method of the brittle crack propagation stop characteristic of the high-strength thick steel plate according to [2].
Z = t ⁿ (2)

According to the method for determining the brittle crack propagation stop property of the high-strength thick steel plate of the present invention, a method for determining the arrest performance of the high-strength thick steel plate by a simple method without performing a large-scale test such as a brittle fracture propagation stop test. Can be provided.
In particular, according to the method for determining the brittle crack propagation stopping property of the high strength thick steel plate of the present invention, when determining the arrest performance of the high strength thick steel plate used for a large welded structure, the steel pieces of each lot to be manufactured It is not necessary to use a large-sized test piece such as a test piece for brittle fracture propagation stop test or a large-scale destructive testing machine of 1000 tons or more. That is, it is possible to quickly and accurately evaluate whether a high-strength thick steel plate can prevent a fatal large-scale damage or damage that destroys a large welded structure by a simple method.
Therefore, the method of the present invention can be effectively applied to quality control at the time of production of a high-strength thick steel plate used for a large welded structure, for example.

It is a figure which shows the position which extract | collects a small test piece from a thick steel plate. It is a figure which shows the position which extract | collects a small test piece from a thick steel plate. It is a schematic diagram for demonstrating the position and direction which extract | collect an internal small test piece and a surface layer small test piece from a high strength thick steel plate. It is a schematic diagram which shows arrangement | positioning of the test machine of a drop weight test, and a small test piece. It is a schematic diagram which shows the determination method of the test result of a drop weight test. It is a figure which shows the shape of a small test piece, and shows a falling weight test piece. The numerical value in a figure shows a dimension (unit: mm). It is a figure which shows the shape of a small test piece, and is a schematic side view and front view showing a V-notch Charpy impact test piece. It is a figure which shows the shape of a small test piece, and shows a 1-side sharp notch Charpy impact test piece. The numerical value in a figure shows a dimension (unit: mm). It is a figure which shows the shape of a small test piece, and shows a 3 surface sharp notch Charpy impact test piece. The numerical value in a figure shows a dimension (unit: mm). It is a figure which shows the shape of a small test piece, and shows the shape of a chevron notch Charpy impact test piece. It is a schematic diagram of the fracture surface of the drop weight test of surface superfine-grained steel. It is a schematic diagram of the fracture surface of the drop weight test of general steel. It is a graph which shows the relationship between the actual value of TKca6000 in a brittle fracture propagation stop test in a present Example, and the estimated value of TKca6000 by the formula of a correlation model. It is a graph which shows the relationship between NDT temperature and vTrs in plate | board thickness 65mm from the result of a drop weight test and a V notch Charpy impact test by a present Example. It is a graph which shows the relationship between NDT temperature and vTrs in plate | board thickness 70mm from the result of a drop weight test and a V notch Charpy impact test by a present Example. It is a graph which shows the relationship between NDT temperature and vTrs in plate | board thickness 80mm from the result of a drop weight test and a V notch Charpy impact test by a present Example. It is a graph which shows the relationship between NDT temperature and vTrs in plate | board thickness 100mm from the result of a drop weight test and a V notch Charpy impact test by a present Example. It is a graph which shows the relationship between NDT temperature and vTrs in plate | board thickness 150mm from the result of a drop weight test and a V notch Charpy impact test by a present Example. It is a graph which shows the relationship between NDT temperature and vTrs in plate | board thickness 200mm from the result of a drop weight test and a V notch Charpy impact test by a present Example. It is a graph which shows the relationship between NDT temperature and vTrs in plate | board thickness 250mm from the result of a drop weight test and a V notch Charpy impact test by a present Example.

  Hereinafter, a method for determining brittle crack propagation stopping characteristics of a high-strength thick steel plate according to a first embodiment of the present invention will be described with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features of the present invention easier to understand, the portions that become the features may be shown in an enlarged manner for convenience, and the dimensional ratios of the respective components are the same as the actual ones Not necessarily.

The method for determining the brittle crack propagation stop property of the high-strength thick steel plate according to the present embodiment includes a step of performing a brittle fracture propagation stop test using a plurality of standard steels having different thicknesses, and a composite using the standard steel. A step of performing a small test, a step of calculating a correlation model between a brittle crack propagation stop characteristic Kca value measured by the brittle fracture propagation stop test and a result of the composite small test, the brittle fracture propagation stop test, Based on the result of the composite small test and the correlation model, a step of determining a brittle crack propagation stop property judgment criterion for each plate thickness, a step of performing the composite small test using sample steel, and the composite of the sample steel A step of determining the brittle crack propagation stop property of the sample steel based on a result of a small test and the criteria for determining the brittle crack propagation stop property, and
Both the step of performing the composite compact test using the standard steel and the step of performing the composite compact test using the sample steel,
(A) a step of collecting a surface layer small test piece including a steel sheet surface layer portion;
(B) a step of collecting internal small test pieces from one or two or more internal regions not including the steel sheet surface layer portion;
(C) A step of performing a drop weight test in accordance with the NRL drop weight test method defined in ASTM E208-06 using the surface layer small test piece, and obtaining an NDT temperature;
(D) performing a small test to measure the brittle fracture surface rate or absorbed energy using the internal small test piece, and obtaining a fracture surface transition temperature or an energy transition temperature;
Including
In the brittle crack propagation stop characteristic Kca value, the target Kca limit temperature TKca, which is the limit temperature at which a predetermined Kca value can be secured, is the objective variable, the NDT temperature of the standard steel is the first explanatory variable X, and the standard steel Where the fracture surface transition temperature or energy transition temperature is a second explanatory variable Y, the thickness of the standard steel is a third explanatory variable Z, and a, b, c, and d are coefficients, It is following formula (1),
a · X + b · Y + c · Z + d = TKca (1)
In the step of determining the brittle crack propagation stop property criteria,
The NDT temperature of the standard steel, the fracture surface transition temperature or energy transition temperature, and TKca are the above-mentioned formulas that are guaranteed temperatures that are the lowest temperatures that guarantee that the standard steel has a predetermined Kca value. The step of obtaining the correlation with (1) for each plate thickness, and determining the region where the value of the TKca of the standard steel indicates the guaranteed temperature or less based on the correlation, and representing the region The NDT temperature of the standard steel and the fracture surface transition temperature or the energy transition temperature are summarized for each plate thickness.
Hereinafter, each step will be described in detail.

First, a description will be given of a step of performing a brittle fracture propagation stop test using a plurality of standard steels having different thicknesses and setting a guaranteed temperature of the steel plate, and a step of performing a composite compact test using the standard steel. In addition, the high-strength thick steel plate which is the object of the determination method of the present embodiment is, for example, a thick steel plate for building a structure such as a large hull or a hydraulic iron pipe, and has a thickness of 50 mm or more and a yield strength of 240 to 240. What is 1000 N / mm < ² > is preferable.
First, a plurality of standard steels (high-strength thick steel plates) with different thicknesses are manufactured by a predetermined composition and manufacturing method (for example, 10 to 100 sheets), and by the methods disclosed in Non-Patent Documents 1 and 2, The Kca value of a high-strength thick steel plate is determined by a brittle crack propagation stop test.

Moreover, a small test piece is sampled from the above-described standard steel thick steel plate, and various small tests described later are performed on the small test piece to obtain the characteristic value of the small test piece.
In this specification, the “small test” refers to a test performed by cutting out a part of each test material prepared as described above, collecting a small test piece, and using the small test piece. As will be described in detail later, various small test pieces may be collected from one place in the test material or from a plurality of places. The small test can also be called a partial test.
In this embodiment, among a plurality of regions obtained by dividing a small test piece to be subjected to a small test in the thickness direction of a high-strength thick steel plate, a region including a steel plate surface layer portion, and one or two locations not including a steel plate surface layer portion Collect from each of the above internal areas.

  Here, the reason why the crack propagation behavior in the central portion of the plate thickness in the thick steel plate having a thickness of 50 mm or more and the crack propagation behavior in the vicinity of the steel plate surface layer portion will be described.

In a thick steel plate having a plate thickness of 50 mm or more, the temperature history in the plate thickness direction differs during production, and the strain acting on the inside of the steel plate during rolling may also vary in the plate thickness direction. For this reason, the crystal grain size and texture of the steel sheet structure often differ greatly in the thickness direction.
Therefore, when a small test piece is collected from a thick steel plate with a thickness of 50 mm or more at any position and a small test is performed, the test results are greatly dispersed due to the influence of the sampling position of the small test piece. It does not represent the brittle crack propagation characteristics of the entire thick steel plate having a thickness of 50 mm or more.

  Furthermore, the brittle crack propagation behavior differs in the thickness direction of thick steel plates having a thickness of 50 mm or more. This is related to the fact that the crack tip is in a plane strain state inside the plate thickness and in a plane stress state near the surface. That is, since the crack tip is in a plane strain state within the plate thickness of the thick steel plate, the size of the plastic zone formed at the crack tip is larger than that of the crack tip existing near the plate thickness surface. As a result, the resistance to propagation of cracks is reduced, and brittle cracks are likely to progress.

  On the other hand, in the vicinity of the surface of the thick steel plate (surface layer), the crack tip is in a plane stress state, so the dimension of the plastic zone formed at the crack tip is the plastic zone of the crack tip existing inside the plate thickness. As a result, the brittle crack is harder to propagate than inside the plate thickness. For this reason, it is well known that a shear lip is formed in the vicinity of the surface layer portion and contributes greatly to the improvement of brittle crack propagation stopping performance. Thus, a phenomenon completely different from the inside of the plate thickness occurs in the surface layer portion of the steel plate.

  Therefore, in the present embodiment, based on the fact that the brittle crack propagation behavior of a thick steel plate having a thickness of 50 mm or more differs in the plate thickness direction, the small test piece used for the composite small test is changed to the plate thickness direction of the high-strength thick steel plate. Collected from a plurality of areas divided in.

In the following description, a test piece collected so as to include at least the surface of the thick steel plate or a position up to about 2 mm below the surface is referred to as a small surface test piece (falling weight test piece).
Furthermore, in this embodiment, in addition to the surface layer small test piece, the test piece is collected from one position inside the thickness direction of the thick steel plate. Thus, the test piece collected from the inside 10 mm or more below the surface in the thickness direction of the thick steel plate without including the surface portion of the thick steel plate is referred to as an internal small test piece.

  When collecting an internal small-sized test piece, it is preferable to avoid the central portion (center segregation portion) a of the thick steel plate as the collection position. As shown in FIG. 1A, if an internal small test piece 8 is taken from the thickness center portion a of the thick steel plate 7, it is usually considered that the test result shows a brittle crack propagation behavior at the thickness center portion. However, steel sheets manufactured by a continuous casting process often have an alloy element enrichment zone called a center segregation part at the center of the plate thickness, and when the center segregation is remarkable, the center segregation part is not brittle. It can cause a significant decrease in crack initiation characteristics. Therefore, when the center segregation is remarkable in the thick steel plate, as shown in FIG. 1A, it is preferable to collect the small internal test piece 9 in a region b where the brittle crack propagation surface does not include the center segregation portion. If center segregation is not remarkable inside the thick steel plate, an internal small test piece 8 including the center portion of the plate thickness may be collected.

  When collecting an internal small test piece that does not include the plate thickness center portion in the vicinity of the plate thickness center portion of the thick steel plate, it is separated from the plate thickness center portion by 0.1 mm or more (more preferably 1 mm or more). It is preferable to collect a region, and it is preferable to collect a region including a position within 5 mm from the center of the plate thickness. For example, as shown in FIG. 1A, the test result relating to the internal small test piece 9 collected so as not to include the plate thickness center portion a of the thick steel plate but to include a position within 5 mm from the plate thickness center portion is the center segregation portion. Therefore, the brittle crack propagation characteristics at the center of the plate thickness are accurately shown.

  As shown in FIG. 1A, when a small test piece 10 is taken from the vicinity of the steel plate surface (surface layer portion) where the crack tip is in a plane stress state and a brittle crack is difficult to propagate, the test piece including the steel plate surface (small surface layer) It is preferable to collect a test piece). After the steel plate is manufactured, if there are layers with significantly different characteristics compared to the inside of the steel plate, such as scales and decarburized parts, remove these layers by cutting them as thin as possible before collecting the specimen. May be. Even when the surface is cut, if it is cut greatly beyond 2 mm from the surface of the steel sheet, there is a possibility that a test piece representative of crack propagation characteristics on the surface of the steel sheet cannot be obtained. Even when the steel sheet surface is cut for reasons such as avoiding the effects of scale, decarburized parts, etc., it is necessary to keep the steel sheet surface within 2 mm.

FIG. 1B shows an aspect of collecting small test pieces. The small test piece 9a is a small test piece including a position within 5 mm from the plate thickness center portion a. The small test piece 10a is a small test piece including a position 2 mm below the surface of the steel plate. The small test piece 11 is a mode in which a small test piece including a position of a thickness ¼ of a thick steel plate is collected. The small test piece 8a is a small test piece including a plate thickness center portion a. The small test piece 12 includes a position 2 mm below the steel plate surface and the steel plate surface.
In the present embodiment, the surface small test piece 12 is taken from the position shown in FIG. 1B (including the surface of the steel plate), and the internal small test piece 11 has a depth position (position shown in FIG. 1B) of a thickness of 1/4. Most preferably, it is collected so that it contains.

  The internal small test piece 11 is collected so as to be separated from the steel plate surface by 7 mm or more, preferably 10 mm or more in order to avoid the effect of shear lip. As an internal small test piece, a test piece including a plate thickness center portion, a test piece collected so as to include a position within 5 mm from the plate thickness center portion, and a position of a plate thickness 1/4 of a thick steel plate are included. The collected small test pieces can be used.

  In this way, by collecting the small internal test piece and the small surface test piece and performing the small test respectively, it is possible to obtain test results corresponding to different brittle crack propagation behaviors in the plate thickness direction. Based on this test result, the arrest performance of the thick steel plate can be accurately estimated even when the plate thickness is 50 mm or more. Details of this estimation method will be described later.

A small test using a small test piece (internal small test piece) taken from a region other than the surface layer part of a thick steel plate is to measure the brittle fracture surface rate or absorbed energy and obtain the fracture surface transition temperature or energy transition temperature. Is not limited to a specific test, as long as it is a small test that can be performed. In the case of such a test, the behavior when a crack progresses inside a small test piece can be sufficiently evaluated.
For example, various Charpy type impact test specimens, specifically, V-notch Charpy impact test specimens, sharp notch Charpy impact test specimens, press notch Charpy impact test specimens, pre-crack Charpy impact test specimens, and three-face sharp notch Charpy impact test specimens Chevron notch Charpy impact test pieces and U-notch Charpy impact test pieces can be used. In any test piece, the absorbed energy during the impact test can be measured. Moreover, the ductile fracture surface ratio or brittle fracture surface ratio of a fracture surface can be measured.
There is usually a positive correlation between the ductile fracture surface rate and the absorbed energy in small tests of certain steel materials. In the measurement of the brittle fracture surface ratio and the absorbed energy, the results of stress acting on the entire cross section of the specimen including the inside of the specimen as well as the surface part of the small specimen are integrated and accumulated. Is fully reflected in the test results. For this reason, as an evaluation method for small internal test specimens, the brittle crack propagation characteristics inside a thick steel plate can be evaluated with high accuracy by measuring the brittle fracture surface ratio (or ductile fracture surface ratio) or absorbed energy. it is conceivable that. Since the ductile fracture surface ratio and the brittle fracture surface ratio are 100%, the ductile fracture surface ratio may be used instead of the brittle fracture surface ratio.

  The V-notch Charpy impact test and drop weight test may be performed using a test method based on the ASTM standard or JIS standard. In addition, when using the chevron notch Charpy impact test or sharp notch Charpy impact test, test pieces are designed so that the contribution of brittle crack propagation characteristics can be greatly extracted by devising the notch shape so that brittle cracks are likely to occur. It is desirable to adjust the shape. A preferable shape of the test piece will be described later.

In FIG. 2, the schematic diagram for demonstrating the position and direction which extract | collect the internal small test piece 102 and the surface layer small test piece 101 from a high strength thick steel plate is shown. FIG. 3A is a schematic diagram showing the arrangement of a drop weight tester and a surface layer small test piece, and FIG. 3B is a schematic diagram of a surface layer small test piece for explaining a method for judging the test result of the drop weight test. Show. 2 shows a V-notch Charpy impact test piece, and “N” in the figure indicates a notch.
4A to 4E show shapes of suitable small test pieces. 4A is a drop weight test piece, FIG. 4B is a V-notch Charpy impact test piece, FIG. 4C is a (one side) sharp notch Charpy impact test piece, FIG. 4D is a three-side sharp notch Charpy impact test piece, and FIG. 4E is a chevron notch Charpy. Representative shapes of impact test pieces are shown respectively.

  When the drop weight test is used as the surface layer small test according to the method of the present embodiment, the brittle crack propagation characteristics of the outermost surface portion of the thick steel plate can be directly evaluated. For this reason, the arrest performance of a thick steel plate can be evaluated with high accuracy as compared with the case where the surface layer small test is tested by other methods such as a V-notch Charpy impact test.

Next, the drop weight test piece will be described.
As shown in FIGS. 2 and 4A, a welded portion (weld bead, 101b in FIG. 2) is formed on the surface of the drop test piece 101, and a notch (slit) is formed in the welded portion. The drop weight test piece 101 is collected so as to include a surface layer portion of a thick steel plate as shown in FIG. That is, one surface 101a of the drop weight test piece 101 is collected so as to correspond to the surface of the thick steel plate. As schematically shown in FIG. 2, the weld bead 101b is formed on the surface 101a. The table in FIG. 4A shows the types of dimensions (P-1 to P-3), where “T” represents height (thickness), “L” represents length, and “W” represents width. Yes.

Next, the drop weight test method will be described.
Using the obtained drop weight test piece 101, an NRL (Naval Research Laboratory) drop test specified in E208-06 of ASTM (Standards of American Society for Testing and Materials) is conducted. A welding bead 101b having a length of about 64 mm is attached to one surface 101a of the drop weight test piece 101 in the longitudinal direction with a welding material in accordance with the above-mentioned regulations (FIG. 4A). This bead acts as a crack start weld. Further, a slit having a width of 1.5 mm or less is formed in the weld bead 101b.

Next, as shown in FIG. 3A, the drop test piece 101 is installed on the test piece installation base 200 b of the drop test machine 200. At this time, it is installed so that the surface 101a on which the weld bead 101b is formed faces downward. In the drop weight test, a weight 200 a having a specified shape and mass falls on the test piece 101. When the toughness of the steel material of the test piece 101 is low, a brittle crack generated from the notch (slit) of the weld bead 101b propagates into the test piece 101 depending on conditions such as a drop weight test temperature.
When a crack that has started from the notch propagates on the surface 101a of the test piece in the width direction of the test piece 101 and progresses to its end (state in FIG. 3B), the test result is determined to be Break (with crack propagation). . When a crack does not reach the end in the width direction, the test result is determined as No Break (no crack propagation). The above test operation was repeated for each of the two test pieces while changing the drop test temperature in 5 ° C increments (5 ° C decrease for No Break, 5 ° C increase for Break). The NDT temperature is defined as a temperature 5 ° C. lower than the lowest drop weight test temperature at which No break was obtained for both test pieces.
In some cases, the crack penetrates the test piece and proceeds to the surface opposite to the weld bead installation surface 101a. However, in the drop weight test employed in this embodiment, the presence or absence of this penetration is not included in the evaluation. .

  As an example of using the NDT temperature in the drop weight test for the simple evaluation of the arrest toughness value Kca, there is an example used for the fracture evaluation of a special steel plate called a super-fine grain steel (Non-Patent Document 2). In the super-fine-grain steel, a layer having a substantially uniform ultra-fine grain structure that is difficult to brittle fracture exists in the super-fine grain steel. In Non-Patent Document 2, a drop weight test is used for evaluation of super-fine grain steel. However, in this document, test conditions, correlation equations, etc. are used so that the main evaluation criterion is whether or not the brittle cracks generated in the drop weight test penetrate the surface ultrafine-grained steel and reach the back surface. Optimized. For this reason, the usage of the entire test, interpretation of the results, correlation equations, and the like are greatly different from the general operation method of the drop weight test of the ASTM standard. That is, with this prior art, although a special correlation formula dedicated to the evaluation of the characteristics of the superfine particle layer can be obtained, it is difficult to use test conditions such as the correlation formula for general steel materials. Moreover, in the test of the said literature, the propagation of the crack of the aspect along a bead installation surface does not necessarily have a decisive influence directly on a test result. This is because in super-fine-grain steel, the crack propagates vertically through the super-fine grain part, and then the crack propagates inside (under) the super-fine grain part. This is because it occurs. FIG. 5A shows the state of the fracture surface in the drop test of the surface ultrafine-grained steel, and FIG. 5B shows the state of the fracture surface in the drop test of the general steel material. In the drop test of the super-fine grain steel, a brittle crack penetrates the super-fine grained surface layer portion, and when the area P in FIG. If the crack does not penetrate to the region P, the operation is stopped. That is, if the crack reaches the boundary of the substantially ultrafine grain region, it is determined as Go (propagation). That is, in the drop weight test of the superfine grain steel, it is equivalent to evaluating only the superficial part composed of the superfine grain structure. On the other hand, in a drop test of a general steel material, a brittle crack propagates in both the plate thickness direction and the specimen width direction (arrow in FIG. 5B), and is judged as Break (with crack propagation) by penetration in the width direction. . As described above, the drop test of the general steel material is greatly different from the drop test of the super-fine grain steel in that the propagation characteristic of the brittle crack parallel to the plate surface in the vicinity of the plate surface is evaluated. For this reason, the test method of Non-Patent Document 2 is set to a condition that can be applied only to the super-fine grain steel, and cannot be applied to the test of general steel.

In Non-Patent Document 2, the inside of the plate thickness is also evaluated by the drop weight test. The main mechanism by which the inside of the plate thickness contributes to arrestability is the energy of brittle crack propagation resistance, not the energy of shear lip formation. For this reason, it is considered that evaluating the internal test piece by the drop weight test causes an evaluation error due to the deviation of the steel properties generated for each production batch and production method of the test steel. In the steel sheet, since the contribution to the arrest characteristics of the super-fine grain region is too large, such an error does not increase and is put into practical use. For this reason, the said evaluation formula cannot be applied to general steel materials.
On the other hand, regarding the evaluation of the plate thickness surface layer of a general steel material, it is important to use different optimum methods separately for the outermost surface evaluation and the internal evaluation. In the drop weight test used in this embodiment, whether or not a crack has reached the back layer of the test piece is not included in the evaluation. This drop weight test is a test method in which the contribution on the surface layer side is the largest and the contribution on the back surface side is small, and is suitable for evaluating the shear lip effect of the steel material surface layer.

  The present embodiment is based on the basic idea of determining the arrest performance of a thick steel plate based on the results of the brittle fracture propagation stop test (ESSO test) and the composite compact test described above, and the characteristics based on the component composition are as follows. Appears in test results. For this reason, the method of this embodiment is applicable with respect to the thick steel plate of a wide component composition. The thick steel plate used in the present embodiment may be manufactured from a structural steel having a known component composition. That is, the thick steel plate used in the present embodiment may be a thick steel plate having a known component composition.

  In addition, as a thick steel plate used as determination object in this embodiment, for example, in mass%, C: 0.02 to 0.20%, Si: 0.01 to 1.0%, Mn: 0.3 to 2 0.0%, Al: 0.001 to 0.20%, N: 0.02% or less, P: 0.01% or less, and S: 0.01% or less. Further, according to required properties such as improvement of base material strength and joint toughness, Ni: 2.0% or less, Cr: 1.5% or less, Mo: 1.0% or less, Cu: 1. 0% or less, W: 1.0% or less, Co: 1.0% or less, V: 0.1% or less, Nb: 0.1 or less, Ti: 0.05 or less, Zr: 0.05% or less, Ta: 0.05% or less, Hf: 0.005% or less, REM: 0.005% or less, Y: 0.005% or less, Ca: 0.01% or less, Mg: 0.01% or less, Te: A thick steel plate containing one or more of 0.01% or less, Se: 0.005% or less, and B: 0.005% or less may be used.

  In the determination method of arrest performance according to the present embodiment, a plurality of small tests (V-notch Charpy impact test, drop weight test, etc.) are performed on the small test pieces collected from a plurality of locations of the various standard steels. Next, the correlation model between the results of the composite compact test obtained and the results of the brittle fracture propagation stop test of the above-mentioned various standard steels is calculated as follows: .

  The correlation model according to the present embodiment uses TKca, which is a temperature at which the brittle crack propagation stop characteristic Kca value is a predetermined required value, measured by a brittle fracture stop test of standard steel, as an objective variable, and the surface layer of standard steel. NDT temperature as a result of drop test of small test piece is first explanatory variable X, fracture surface transition temperature as a result of small test (V notch Charpy impact test) using internal small test piece of standard steel (Or energy transition temperature) is the second explanatory variable Y, and the thickness t of the standard steel is the third explanatory variable Z. Specifically, the correlation model equation represented by the following equation (1) can be calculated.

a · X + b · Y + c · Z + d = TKca (1)
Note that a, b, c, and d are coefficients.

  Conventionally, the correspondence between the Kca value, which is the result of the large test, and the characteristic value of the small test piece has been investigated from the viewpoint of arrest performance, but a correlation with sufficient accuracy could not be obtained. However, in the above correlation model formula according to the present embodiment, the arrest performance in the large test and the small test are added to the arrest performance of the thick steel plate by adding a plate thickness that has not been considered in the past as a new factor. In relation to the result, a highly accurate correlation can be derived.

Next, based on the results of the brittle fracture propagation stop test and the composite compact test, and the above-mentioned correlation model formula, criteria for determining the arrest performance of the thick steel plate for each plate thickness are determined.
Specifically, first, the NDT temperature, fracture surface transition temperature (or energy transition temperature) of the standard steel obtained by the composite compact test, and the TKca on the left side in the above correlation model formula are the guaranteed temperature of the standard steel. Correlation (graph) with the calculated formula is obtained for each plate thickness. The guaranteed temperature is the lowest temperature that guarantees that the steel plate has a predetermined Kca value.
Next, based on the obtained correlation (graph) for each sheet thickness, a region where the TKca value of the standard steel shows a guaranteed temperature or less is determined, and the NDT temperature and fracture surface transition of the standard steel for representing the region. For example, as shown in Table 2, the temperature or energy transition temperature is summarized as a criterion for determining the arrest performance of a thick steel plate for each plate thickness.
Using the determination criteria thus obtained, it is possible to easily determine whether the arrest performance of the sample steel is acceptable or not from the result of the composite small test of the sample steel. In addition, any number of sample steels can be obtained from the production line, and from each sample steel, a small surface specimen (for drop weight test) and a small internal specimen (in the same way as for standard steel) Get brittle fracture surface ratio or absorbed energy measurement). Then, similarly to the standard steel, each small test is performed on the small test piece, and the composite small test result of the sample steel can be obtained.

  As described above, the arrest performance of the thick steel plate is greatly affected by the plate thickness. That is, the arrest performance tends to be severer as the plate thickness increases, and the crack propagation becomes more difficult to stop as the plate thickness of the thick steel plate increases. Therefore, the correlation (graph) between the NDT temperature of the standard steel, the fracture surface transition temperature or the energy transition temperature, and the formula where TKca is the guaranteed temperature of the standard steel in the above correlation model is obtained for each plate thickness. It is possible to create a highly accurate and simple determination criterion for arrest performance by collecting, for each plate thickness, a region where the value of TKca is equal to or lower than the guaranteed temperature, that is, an acceptable region where the arrest performance is good.

Note that, in the step of determining the determination criterion for arrest performance, based on the correlation (graph), a region where the value of TKca of the standard steel is equal to or lower than the guaranteed temperature (region where the arrest performance is determined to be good) is determined. At this time, the NDT temperature of the standard steel for representing the region may be determined with the fracture surface transition temperature (or energy transition temperature) for representing the region constant, regardless of the difference in the plate thickness.
As described above, the arrest performance tends to be severer as the plate thickness increases, and the acceptance criteria (fracture surface transition temperature or energy transition temperature, and NDT temperature) at which the arrest performance is good become severe. Therefore, although the value indicating the acceptance criteria varies depending on the plate thickness, it is simpler by fixing the fracture surface transition temperature or energy transition temperature to a constant value and determining the acceptance criteria for the NDT temperature for each plate thickness. It is possible to determine the arrest performance.

As described above, the arrest performance tends to become severer as the plate thickness increases. That is, when the NDT temperature and the fracture surface transition temperature (or energy transition temperature) are the same, the value of TKca increases (high temperature) as the plate thickness increases. Moreover, as the plate thickness increases, the plate thickness dependency of TKca gradually decreases. For example, the change in TKca with respect to the increase in plate thickness in the range of more than 100 to 250 mm is smaller than the change in TKca with the increase in plate thickness in the range of 50 to 100 mm. Therefore, it is preferable that the third explanatory variable Z is represented by the following formula (2). In addition, t in following formula (2) is a plate | board thickness of the said standard steel, and is a coefficient which set n to 0.01-1. This improves the accuracy of the correlation model.
Z = t ⁿ (2)

  At this time, as the value of n in the model formula (2), any value within the range of 0.01 to 1 has no practical problem. However, when a steel sheet having a thickness exceeding 100 mm is included, the value of n is less than 1, and the smaller the value of n, that is, the closer to 0.01, the more accurate the correlation model is. It is preferable because it improves. However, even if it is less than 0.01, further improvement in accuracy cannot be expected, and the value of the coefficient c in the above equation (1) becomes large, so that the correlation model equation becomes complicated. Therefore, the lower limit of n is preferably 0.01. On the other hand, if the plate thickness does not include a steel plate having a thickness exceeding 100 mm, for example, and is made of a thin steel plate in the region of 50 to 100 mm, using 1 as the value of n makes the correlation model equation simple. Easy to handle. Therefore, n is preferably set to 1 when a steel plate having a thickness exceeding 100 mm is not included.

  Next, examples of each embodiment of the present invention will be described. The conditions of the examples are examples of conditions adopted to confirm the feasibility and effects of the present invention, and the scope of application of the present invention is not limited to this one condition example. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

Example 1
Table 1 shows the composition of the thick steel plates (steel types Nos. 1 to 14) used in this example, the plate thickness, the strength category YP, and the number of prepared steel plates (105 in total). Moreover, these steel types No.1. Table 1 also shows the results (Kca- _{10 ° C} [N / mm ^1.5 ], TKca6000 [° C]) of -14 brittle fracture propagation stop test (guaranteed temperature of steel: -10 ° C).
As for the strength classification, for example, “YP40” means “yield point 40 kgf / mm ² class”.

From the thick steel plate (steel types No. 1 to 14) shown in Table 1, among the sampling modes shown in FIG. 1B, a small test piece 12 obtained by sampling a small test piece for drop weight test from a position including the surface layer was used. A small test piece 11 obtained by collecting a small test piece for the Charpy test from a position including a quarter of the plate thickness was used. The dimensions and shape of each test piece are as shown in FIGS. 2, 4A, and 4B, and the drop weight test piece dimensions are “P-3 (T: 16 mm, L: 130 mm, W: 50 mm” in FIG. 4A. It was.
Next, NRL drop weight test (according to ASTM E208-06) and V-notch Charpy impact test (according to JIS Z 2242) are performed on each sampled small test piece, and NDT temperature and vTrs (fracture surface transition temperature) are measured. Asked.

Next, based on the results of the above test, a multiple regression analysis was performed using TKca 6000 [° C.] as an objective variable, NDT temperature [° C.], vTrs [° C.], and plate thickness t [mm] to the (1/13) th power. As a result, the coefficients a, b, c and d of the above formula (1) were obtained as follows: a = 0.4033, b = 0.882, c = 144.1, d = −162.5. From this, the correlation model in a present Example became following formula (3).
TKca6000 = 0.4033 × NDT temperature + 0.2882 × vTrs + 144.1 × t ^1/13 −162.5 (3)

FIG. 6 shows the relationship between the estimated value of TKca6000 according to equation (3) of the correlation model and the measured value of TKca6000 shown in Table 1 when the plate thickness is 50 to 250 mm.
As can be seen from the graph of FIG. 6, the estimated value of TKca6000 and the actually measured value almost coincide with each other, but a slight error occurs. Even if the same steel plate is used in various tests, a certain degree of error cannot be avoided because test results vary. Therefore, in this example, the criterion for simple determination that the arrestability satisfies Kca- _{10 ° C.} ≧ 6000 N / mm ^1.5 was set to estimated TKca 6000 ≦ − (10 + e) ° C. For example, the standard deviation σ of the error between the estimated value of TKca6000 and the actually measured value can be used as the value of e. In this example, σ = 6.3 ° C. according to the graph of FIG. 6, so that the criterion for simple determination of arrestability was estimated TKca6000 ≦ −16.3 ° C. By doing in this way, it is prevented that the sample whose measured value of TKca6000 exceeds the guaranteed temperature (−10 ° C.) and is rejected is erroneously determined to be acceptable due to an error between the estimated value of TKca6000 and the measured value. be able to. The value of e need not be σ, and may be 2σ, for example.

Further, according to the study by the present inventors, most of the steel sheets having arrestability satisfying Kca _{−10 ° C.} ≧ 6000 N / mm ^1.5 had vTrs of −80 ° C. or lower. The passing condition was fixed at -80 ° C.
Thus, by substituting TKca6000 = −16.3 ° C. and vTrs = −80 ° C. into equation (3) of the correlation model, it is possible to determine the NDT temperature pass condition for each plate thickness. Table 2 shows a determination criterion table that summarizes the drop weight test temperature, NDT temperature, and vTrs determined for each plate thickness.

Next, in order to confirm that the pass / fail determination of arrestability can be reliably performed according to the determination reference table of Table 2, NDT is performed on samples having plate thicknesses of 65 mm, 70 mm, 80 mm, 100 mm, 150 mm, 200 mm, and 250 mm. 7A to 7G show the results of summarizing the relationship between the temperature and the vTrs together with the pass areas according to the determination criterion table of Table 2.
7A to 7G, the NDT temperature values in Table 2 are plotted on the vertical axis in FIGS. 7A to 7G, and the vTrs values in Table 2 are plotted on the horizontal axis in FIGS. 7A to 7G. The lower side of the line connecting the two (temperature range lower than both temperatures) is set as the pass range.
Moreover, in FIG. 7A-FIG. 7G, what passed TKca6000 (actual value) below guarantee temperature (-10 degreeC) is "(circle)", and TKca6000 (actual value) is over guarantee temperature (-10 degreeC). Those which were not accepted were evaluated as “x”.
As can be seen from FIG. 7A to FIG. 7G, only “◯” is present in the pass region at each plate thickness, and only the steel plate whose arrestability satisfies Kca _{−10 ° C.} ≧ 6000 N / mm ^1.5 is surely determined. I can prove that it is done.

As described above, a determination criterion for arrestability can be created. As a result, it is possible to easily determine whether or not the arrestability of the sample steel is acceptable by performing a small test without performing a large test (brittle fracture propagation stop test) of the sample steel based on the determination criteria. .
In this example, the guaranteed temperature of steel: −10 ° C. and the required value of brittle crack propagation stop characteristic Kca: 6000 N / mm ^1.5 are the conditions. When the surface transition temperature vTrs (or energy transition temperature vTre) is −80 ° C. or lower and the NDT temperature is lower than the value shown in Table 2, it can be determined that the brittle crack propagation stop characteristic of the sample steel satisfies the required value. In other words, in the case of a sample steel having a thickness of 50 mm, for example, “In the NRL drop weight test, it passed 5 ° C., which is 5 ° C. higher than −63 ° C., which is the NDT temperature in Table 2, and in the V-notch Charpy impact test. If it passes at −80 ° C. or lower, which is the vTrs in Table 2, it can be determined that the brittle crack propagation stop characteristic of the sample steel satisfies the required value. ”Note that the pass criterion for the NRL drop weight test starts from a notch. If the crack propagated on the surface of the sample steel specimen in the width direction of the specimen and progressed to the end, the test result was judged as “Break (with crack propagation)” and failed, When the crack does not reach the end, the test result is determined as “No Break (no crack propagation)”. The above test operation is repeated with two test pieces at the same test temperature, and when “No break” is obtained for both of the two test pieces, the test is accepted at this temperature. The acceptance criteria for the V-notch Charpy impact test are to measure the brittle fracture surface ratio of three tests, and when the average value is 50% or less, the test temperature at this time is passed.

  As explained above, by adding a plate thickness element that greatly affects the arrestability as a criterion for determining the arrestability of the sample steel, it is possible to improve the determination accuracy and to determine the determination criterion for each plate thickness. By making it, the arrestability of the sample steel can be easily determined.

  In addition, when the required values of the guaranteed temperature of steel and the brittle crack propagation stop characteristic Kca are different, a criterion based on the condition can be created by deriving a correlation model along the condition in that case. .

  According to the method of the present invention, a large-sized test apparatus is required as in the brittle fracture propagation stop test, and a high-cost large-scale test can be omitted. That is, a sample steel material is selected from the product steel materials of each batch, a small test is performed using a small test piece cut out from the sample steel material, and the arrest performance of the actual product can be estimated with the same high accuracy as the large test. By using the method of the present invention, it is possible to provide quality assurance at the level of product steel of each batch based on a small test, instead of quality assurance at the component / process level.

7 ・ ・ ・ Thick steel plate,
8, 8a, 9, 9a, 10, 10a, 11, 12 ... small test pieces,
101... Small surface layer test piece (falling weight test piece),
101a ... one surface (weld bead installation surface),
101b ... weld bead,
102 ... Internal small test piece,
N ... notch,
200: Drop weight tester,
200a: weight,
200b ... Test specimen mounting table

Claims (3)

A method for determining brittle crack propagation stopping characteristics of a thick steel plate,
A process of performing a brittle fracture propagation stop test using a plurality of standard steels having different thicknesses;
Performing a composite compact test using the standard steel;
Calculating a correlation model between a brittle crack propagation stop characteristic Kca value measured by the brittle fracture propagation stop test and a result of the composite small test;
Based on the results of the brittle fracture propagation stop test, the composite small test and the correlation model, determining a criterion for determining the brittle crack propagation stop characteristics for each plate thickness;
Performing the composite compact test using sample steel;
Based on the result of the composite small test of the sample steel and the criterion for determining the brittle crack propagation stop property, determining the brittle crack propagation stop property of the sample steel;
Including
Both the step of performing the composite compact test using the standard steel and the step of performing the composite compact test using the sample steel,
(A) a step of collecting a surface layer small test piece including a steel sheet surface layer portion;
(B) a step of collecting internal small test pieces from one or two or more internal regions not including the steel sheet surface layer portion;
(C) A step of performing a drop weight test in accordance with the NRL drop weight test method defined in ASTM E208-06 using the surface layer small test piece, and obtaining an NDT temperature;
(D) performing a small test to measure the brittle fracture surface rate or absorbed energy using the internal small test piece, and obtaining a fracture surface transition temperature or an energy transition temperature;
Including
In the brittle crack propagation stop characteristic Kca value, the target Kca limit temperature TKca, which is the limit temperature at which a predetermined Kca value can be secured, is the objective variable, the NDT temperature of the standard steel is the first explanatory variable X, and the standard steel Where the fracture surface transition temperature or energy transition temperature is a second explanatory variable Y, the thickness of the standard steel is a third explanatory variable Z, and a, b, c, and d are coefficients, It is following formula (1),
a · X + b · Y + c · Z + d = TKca (1)
In the step of determining the brittle crack propagation stop property criteria,
The NDT temperature of the standard steel, the fracture surface transition temperature or energy transition temperature, and TKca are the above-mentioned formulas that are guaranteed temperatures that are the lowest temperatures that guarantee that the standard steel has a predetermined Kca value. A step of obtaining a correlation with (1) for each plate thickness;
Based on the correlation, a region in which the value of the TKca of the standard steel indicates the guaranteed temperature or less is determined, and the NDT temperature and the fracture surface transition temperature or energy transition temperature of the standard steel for representing the region. , The process of summarizing every thickness,
A method for determining brittle crack propagation stopping characteristics of a high-strength thick steel plate characterized by comprising:   In the step of determining the criterion for determining the brittle crack propagation stop property, when determining the region where the value of the TKca of the standard steel shows the guaranteed temperature or less based on the correlation, regardless of the difference in the plate thickness The high strength thickness according to claim 1, wherein the NDT temperature of the standard steel for representing the region is determined with the fracture surface transition temperature or energy transition temperature for representing the region being constant. Judgment method of brittle crack propagation stop property of steel sheet. 3. The high value according to claim 1, wherein the third explanatory variable Z is defined by the following formula (2), wherein the thickness of the standard steel is t and n is a coefficient of 0.01 to 1. Judgment method of brittle crack propagation stop property of high strength steel plate.
Z = t ⁿ (2)

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