JP4823986B2 - Deformation Charpy impact test piece for evaluating brittle fracture propagation stop property of thick steel plate and quality control method of brittle fracture propagation stop property of thick steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a deformation Charpy impact test piece and a quality control method of a brittle fracture propagation stopping characteristic of a thick steel plate, capable of evaluating easily the brittle fracture propagation stopping characteristic of the thick steel plate. <P>SOLUTION: When evaluating a brittle fracture propagation stopping performance Kca value of the thick steel plate, a Charpy impact test is performed by using a deformation Charpy impact test piece having the thickness of 10 mm, the width of 15 mm-25 mm and the length of 55 mm, preferably, a chevron notch deformation Charpy impact test piece. When a 70 J energy transition temperature vT<SB>CN70J</SB>(&deg;C) is lower than vT<SB>CN70J</SB>(&deg;C) calculated by the formula (1), it is determined that the brittle fracture propagation stopping performance Kca value determined by a brittle fracture propagation stopping test is not less than 3,900 (N/mm<SP>1.5</SP>) at T<SB>0</SB>&deg;C. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

The present invention is used for evaluating a brittle fracture propagation stop property of a thick steel plate , which is suitable for a quality control method of a thick steel plate having excellent brittle fracture propagation stop properties, which is used for a large structure such as a ship, a low temperature tank, a hydraulic iron pipe for power generation . The modified Charpy impact test piece (hereinafter, also simply referred to as “deformed Charpy impact test piece”) and the quality control method for brittle fracture propagation stop characteristics of thick steel plates.

  Brittle fracture occurs in structural materials, such as steel materials, sometimes with a low stress below the yield strength of the material without large-scale plastic deformation, and propagates over a long distance at a high speed of about 1000 m / s, causing the structure to momentarily It is a very important phenomenon for safety because it breaks down inside.

As a technique for preventing the occurrence of brittle fracture, CTOD (Crack-Tip defined in Non-Patent Document 1 is used.
Prevention methods such as Non-Patent Document 2 using an evaluation test such as an Opening Displacement test have been proposed and incorporated in various standards, and it has become possible to prevent the occurrence of brittle fracture.

On the other hand, since brittle fracture propagates at a high speed in an instant, even in the case of large-scale structures, even if brittle fracture occurs, safety can be significantly improved if crack propagation can be prevented. It becomes possible. Actually, LNG (Liquified Natural
Gas, LPG (Liquified Petrolium Gas) and other low-temperature steel, hydraulic iron pipe steel, shipbuilding steel, etc., large-scale fracture such as the brittle fracture propagation stop test specified in Non-Patent Document 3 A required value for the brittle fracture propagation stop characteristic Kca value measured in the test is specified.

  These tests have a large construction period and cost for performing the tests, and are generally not suitable as tests for quality control. Therefore, a correlation formula using the Charpy impact test method, which is a typical simple evaluation test, and the brittle fracture propagation stop characteristics is proposed as described in Non-Patent Documents 4 to 6, and the Charpy impact test is defined to determine the brittle crack propagation. It has been done in the past to expect stop characteristics.

  Furthermore, since the brittle crack propagation stop characteristic has a plate thickness dependency, Non-Patent Documents 4 and 5 also consider the plate thickness dependency.

Also, press notch Charpy impact test method described in Non-Patent Document 4, ASTM (American
Evaluation by a drop weight test method defined in Standard of Testing and Materials (E-208), a notched bending test method (TKB test method) as described in Non-Patent Document 3, and the like has also been studied.
Japan Welding Association WES1108 Standard Japan Welding Association WES2805 standard Japan Welding Association Standard "WES Steel Grade Certification Test Method" (1995) Japan Welding Association WES3003 Standard "Low Temperature Rolled Steel Sheet Criteria" (1995) Japan Steel Association "Data Sheet Series 4" (1982) Inoue et al. “Evaluation of Propagation of Brittle Crack Propagation Stopping Performance by TKB Test” National Welding Society Annual Meeting, Vol. 42, p.238 (1988)

  However, since the Charpy impact test is strongly influenced by the characteristics of the occurrence of brittle fracture, the correlation with the propagation stop characteristics of the brittle fracture includes a large variation, and there is a big problem in accuracy. Also, a method has been proposed to facilitate the occurrence of brittle fracture and evaluate the propagation stop characteristics of brittle fracture, such as the press notch Charpy impact test method, but the influence of the occurrence characteristics remains significant, and sufficient accuracy is not achieved. It was not obtained.

  On the other hand, test methods such as drop weight test method and TKB test method are classified as simple evaluation methods, and the test piece shape and test piece processing cost are large, but on the other hand, there are problems in accuracy, and it is carried out as a shipping test. It was not enough.

  Therefore, the present invention advantageously solves the above-mentioned problems and can easily evaluate the brittle fracture propagation stop characteristic of the thick steel sheet, and a quality control method for the brittle fracture propagation stop characteristic of the deformed Charpy impact test piece and the thick steel sheet. Is intended to provide.

  As a condition of a simple evaluation method that can be used for shipping tests, etc., the present inventors can evaluate with existing widely used testing machines, and the production cost of the test piece is within several times that of Charpy impact test piece. We examined on the assumption that there is.

In order to accurately evaluate the brittle fracture propagation stop characteristics, it is necessary to facilitate the occurrence of brittle cracks. Therefore, in order to facilitate the generation of brittle cracks, a modified Charpy impact test piece with an increased notch ratio of the Charpy impact test piece was conceived. However, simply adding the above improvements to a Charpy impact test piece reduces the cross-sectional area at the notch position and is not suitable for evaluating brittle fracture propagation stop characteristics. It has been found that it is preferable to have a shape that matches the area and that can be tested with an existing Charpy impact tester.
The present invention has been made for the first time as a result of the above studies, and the gist thereof is as follows.
(1) A test piece used in the Charpy impact test specified in JIS Z 2242, and has a notch with a predetermined shape at the center in the length direction of the front surface when attached to the Charpy impact tester. in the 55 ± 0.6 mm in length, a is 10 ± 0.05 mm height, both side portions of at least notches have a width Ri 15~25mm der until 8~20mm from both ends in the longitudinal direction part, width and wherein 10 ± 0.05 mm der Rukoto, thickness variations Charpy impact test specimens brittle fracture propagation stop characteristics for evaluation of the steel sheet.
(2) For evaluating the brittle fracture propagation stop characteristics of a thick steel plate according to (1) , wherein the notch is a chevron notch having a shallow chevron shape at the center in the height direction and shallow at the upper and lower ends . modified Charpy impact test specimens.
(3) The modified Charpy for evaluation of brittle fracture propagation stop characteristics of a thick steel plate according to claim (1) or (2) , wherein the remaining cross-sectional area at the position of the notch is 80 mm ^2. Impact test piece.
(4) Using the deformed Charpy impact test piece described in any one of (1) to (3 ) above, in accordance with the Charpy impact test specified in JIS Z 2242, the brittle fracture propagation stop property of the thick steel plate A quality control method for brittle fracture propagation stop characteristics of a thick steel plate, characterized by evaluating (arrest characteristics).
(5) When the _70J energy transition temperature vT _CN70J (° C) of the deformed Charpy impact test piece having the chevron notch described in (2) is equal to or lower than vT _CN70J (° C) calculated by the following equation (1) The brittle fracture propagation stop performance Kca value determined by the brittle fracture propagation stop test specified in the Japan Welding Association Standard “WES Steel Grade Certification Test Method” (1995) is 3900 (N / mm ^1.5 ) or more at T ₀ ° C. The quality control method for brittle fracture propagation stop characteristics of a thick steel plate according to (4) , characterized in that it is present.

  According to the present invention, when the brittle fracture propagation stop characteristic Kca value is guaranteed, a simple and accurate determination can be performed without using a large-scale test such as the brittle fracture propagation stop test defined in Non-Patent Document 3.

The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a plan view (a) of a modified Charpy impact test piece 1 according to the first embodiment of the present invention and a cross-sectional view (b) at the position of a notch 10. FIG. 2A is a plan view of a modified Charpy impact test piece 2 according to the second embodiment of the present invention, and FIG. 2B is a cross-sectional view at the position of the notch 20. These deformed Charpy impact test pieces 1 and 2 are attached to the Charpy impact tester with the notches 10 and 20 facing forward. And the Charpy impact test prescribed | regulated to JISZ2242 is performed by hitting with the hammer and breaking the side surface (back surface 12,22) opposite to the front surface 11,21 in which the notch parts 10 and 20 were formed. . In the present invention, for the sake of explanation, the thickness direction of the front surfaces 11 and 21 and the rear surfaces 12 and 22 is the width direction (the vertical direction in FIGS. 1 and 2), and the direction parallel to the front surfaces 11 and 21 and the rear surfaces 12 and 22 is. The length direction (the left-right direction in FIGS. 1 and 2) and the direction perpendicular to the width direction and the length direction are defined as the height direction (the direction perpendicular to the paper surface in FIGS. 1 and 2).

  A normal Charpy impact test piece used for the Charpy impact test specified in JIS Z 2242 is 55 mm ± 0.6 mm in length and 10 mm ± 0.05 mm on one side as specified in JIS Z 2202. The front surface is formed with a V-notch-shaped or U-notched notch at the center in the length direction. On the other hand, the modified Charpy impact test pieces 1 and 2 according to the present invention are characterized in that the widths of both side portions of the notches 10 and 20 are 15 to 25 mm. That is, if the widths of both side portions of the notches 10 and 20 are 10 + X mm, both sides of the notches 10 and 20 are constant in a range of X = 5 to 15 mm in a predetermined length portion. Further, a portion (Y) from 8 to 20 mm from both ends in the length direction has a constant width of 10 ± 0.05 mm. Therefore, the deformed Charpy impact test pieces 1 and 2 according to the present invention can be attached to the Charpy impact test defined in JIS Z 2242 and the Charpy impact test can be performed in the same manner as a normal Charpy impact test piece.

  The portion (Y) from both ends in the length direction to 8 to 20 mm and the front surfaces 11 and 21 are inclined surfaces 13 between both side portions (portions having a width of 15 to 25 mm) of the notches 10 and 20. 23. An angle A with respect to the length direction of the slopes 13 and 23 is 20 ° or more.

  In the modified Charpy impact test piece 1 according to the first embodiment of the present invention shown in FIG. 1, the notch 10 is a chevron notch having a chevron shape that is shallow at the center in the height direction and deep at the upper and lower ends. . The angle B of the top of the chevron shape that appears on the bottom surface of the notch 10 is 60 to 150 °.

  In the modified Charpy impact test piece 2 according to the second embodiment of the present invention shown in FIG. 2, the width of the notch 10 is substantially constant (the normal Charpy impact test defined in JIS Z 2202). It is 8 ± 0.05 mm similarly to the piece.

In these modified Charpy impact test pieces 1 and 2, the remaining cross-sectional area (ligament area) at the positions of the notches 10 and 20 is about 80 mm ² . The notches 10 and 20 have a V-notch shape or a U-notch shape, the width (interval in the length direction) of the notches 10 and 20 is 5 mm or less, and the bottom (tip) of the notches 10 and 20. The curvature radius is 1 mm or less.

  To evaluate the brittle crack arrest properties, it is very important to eliminate the influence of the brittle crack initiation properties. For this reason, an embrittlement treatment for easily occurring is sometimes used, but the degree of embrittlement varies depending on the steel material, and the cost is large and many are not suitable for simple evaluation. A method that requires less cost as in the existing press notch Charpy test is insufficient in embrittlement as described in the examples. In the modified Charpy test pieces 1 and 2 configured as described above, the notch ratio was increased and a notch bottom cross-sectional area equal to that of the standard test was secured, thereby eliminating the influence of the brittle fracture occurrence characteristics.

  On the other hand, if the above deformation is performed with the outer shape being rectangular, the test with the existing test equipment cannot be performed and the test machine needs to be modified. The width was wide only on both sides of the part, and the cross-sectional shape was the same as the standard Charpy test piece at both ends of the test piece.

  The modified Charpy impact test pieces 1 and 2 configured as described above are attached to the Charpy impact tester with the notches 10 and 20 facing forward. And the Charpy impact test prescribed | regulated to JISZ2242 is performed by striking and breaking with the hammer the side surface (back surface 12,22) opposite to the front surface 11,21 in which the notch parts 10 and 20 were formed. In this way, the absorbed energy, impact value, fracture rate, and transition temperature required for fracture can be measured, and the brittle fracture propagation stop characteristic (arrest characteristic) Kca value of the thick steel plate can be evaluated.

In particular, as shown in FIG. 1, when the modified Charpy impact test piece 1 in which the notch 10 is a chevron-shaped chevron notch is used, as a result of the Charpy impact test, the 70 J energy transition temperature of the deformed Charpy impact test piece 1 is obtained. When vT _CN70J (° C) is equal to or lower than vT _CN70J (° C) calculated by the following equation (1), the brittle fracture propagation stop test specified in the Japan Welding Association Standard "WES Steel _Grade Certification Test Method" (1995) It can be determined that the brittle fracture propagation stop performance Kca value obtained in ( ¹ ) is 3900 (N / mm ^1.5 ) or more at T ₀ ° C.

  The present invention was examined using steel materials conforming to the Standards of the Japan Maritime Association shown in Table 1 “Keeling Rules K”.

  The chevron notch deformation Charpy impact test piece of FIG. 1 and the deep notch deformation Charpy impact test piece of FIG. 2 were sampled from steels A to G of Table 1 and tested with a Charpy impact tester in accordance with JIS Z 2242. In addition, a standard Charpy impact test and a press notch Charpy impact test based on JIS Z 2242 were also carried out for comparison. The transition curves are compared with FIGS.

  In the press notch Charpy impact test, the temperature dependence of energy and fracture surface ratio is steep. Looking at the transition of the fracture surface ratio in particular, the brittle fracture surface ratio varies from 0% to 80% between 20 ° C, and 0% and 80% are mixed at the same temperature. This indicates that when a brittle crack occurs, the fracture surface ratio is high and is greatly affected by the generation characteristics.In other words, whether or not a brittle crack occurs is the controlling factor of the transition. ing.

  On the other hand, the transition is gentle in the standard Charpy impact test and the two modified Charpy impact tests of the present invention. In the case of the standard Charpy impact test, the amount of deformation until the occurrence of a brittle crack gradually changes with temperature. In the modified Charpy impact test of the present invention, it is one of the dominant factors of the brittle fracture propagation resistance. This is due to the gradual change in plastic deformation after shear and crack arrest with temperature. In other words, it is considered that the test can eliminate the influence of brittle crack initiation characteristics and evaluate only the arrest characteristics.

  Comparing the results of the deep notch deformed Charpy test piece and the chevron notch deformed Charpy test piece of the present invention, the chevron notch deformed Charpy test piece has a smoother transition curve and higher fiber temperature, eliminating the influence of brittle fracture occurrence characteristics more You can see that From this, it seems that the chevron notch deformed Charpy test piece is capable of evaluating the arrest characteristics with higher accuracy.

FIG. 7 shows a comparison between a chevron notch deformation Charpy impact test and a temperature TKca400 at which a brittle fracture propagation stop performance Kca value is 3900 N / mm ^1.5 for a steel material BG having a thickness of 70 mm. It is confirmed that the result of the Chabron notch deformation Charpy impact test shows a very good correlation with the arrest characteristics. From this correlation, the 70J transition temperature vT _CN70J of the chevron notch deformation Charpy impact test for setting Kca = 3900 N / mm ^1.5 at T ₀ ° C. with respect to the plate thickness of 70 mm may satisfy the following expression (2).

Furthermore, if the variation is taken into consideration, Kca ≧ 3900 N / mm ^1.5 can be satisfied by satisfying the following expression (1).

  The present invention can be applied to an impact test of a metal material.

It is a top view of a chevron notch deformation Charpy impact test piece. It is a top view of a deep notch deformation Charpy impact test piece. It is a standard Charpy impact test result of steel A. It is a press notch Charpy impact test result of steel A. It is a deep notch deformation Charpy impact test result of steel A. It is a chevron notch deformation Charpy impact test result of steel A. It is a relationship between a chevron notch deformation Charpy impact test and Kca.

Explanation of symbols

1, 2 Deformed Charpy impact test piece 10, 20 Notch 11, 21 Front surface 12, 22 Rear surface 13, 23 Slope

Claims (5)

A test piece used in the Charpy impact test specified in JIS Z 2242, having a notch with a predetermined shape at the center in the longitudinal direction of the front surface when attached to the Charpy impact tester. in but 55 ± 0.6 mm, a is 10 ± 0.05 mm height, both side portions of the at least cut-outs, Ri width 15~25mm der, portions from both ends to 8~20mm length direction , width and wherein 10 ± 0.05 mm der Rukoto, thickness variations Charpy impact test specimens brittle fracture propagation stop characteristics for evaluation of the steel sheet.   2. The modified Charpy impact for evaluating brittle fracture propagation stop characteristics of a thick steel plate according to claim 1, wherein the notch is a chevron notch that is shallow at the center in the height direction and deep at the upper and lower ends. Test pieces.   The remaining cross-sectional area at the position of the notch is 80 mm. ² The modified Charpy impact test piece for evaluating the brittle fracture propagation stop property of a thick steel plate according to claim 1 or 2, characterized in that:   Using the deformed Charpy impact test piece according to any one of claims 1 to 3, the brittle fracture propagation stop property (arrest property) of a thick steel plate is evaluated based on the Charpy impact test specified in JIS Z 2242. A quality control method for brittle fracture propagation stop characteristics of a thick steel plate.   70 J energy transition temperature vT of a deformed Charpy impact specimen having a chevron notch according to claim 2. _CN70J (° C.) is calculated by the following equation (1) _CN70J When the temperature is below (° C.), the brittle fracture propagation stop performance Kca value obtained in the brittle fracture propagation stop test specified in the Japan Welding Association Standard “WES Steel Grade Certification Test Method” (1995) is T ₀ 3900 at N ° C (N / mm ^1.5 5) The quality control method for brittle fracture propagation stop characteristics of a thick steel plate according to claim 4, characterized in that it is determined as above.

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