TW201510524A - Method for evaluating brittle fracture propagation arrestability of thick steel plate - Google Patents

Abstract

A simple method is provided for evaluating the brittle fracture propagation arrestability of a thick steel plate using a small-scale test. In the small-scale test, a deformed pressed-notch Charpy impact test is performed using a deformed pressed-notch Charpy impact test piece which is sampled in the center of a plate in the thickness direction and in which a pressed notch is made in a brittle-cracking propagation direction, and brittle fracture propagation arrestability is evaluated on the basis of the temperature (in DEG C; pT40J) indicating that the deformed-pressed-notch-Charpy absorbed energy determined by the Charpy impact test is 40 J.

Description

Evaluation method for brittle failure propagation stop performance of thick steel plate

The present invention relates to a method for evaluating the brittle failure propagation stop performance of a thick steel plate for a ship, a marine structure, a low temperature storage tank, and a large structure such as a building or a civil structure, in particular, a thick steel plate having a thickness of 50 mm or more.

In large structures such as ships, marine structures, cryogenic storage tanks, and buildings and civil structures, accidents caused by brittle failure have a great impact on the economy or the environment, and the safety is constantly required. Further, for the steel material to be used, it is required to have a toughness or brittleness at the use temperature to destroy the propagation stop performance.

The evaluation of the brittle failure propagation stop performance is usually carried out by a large-scale test typified by an ESSO test or a double tensile test. However, since these tests are large, it takes a large number of days or costs to carry out the test, which is a problem that is difficult to carry out easily.

Therefore, a method for predicting the brittle failure propagation stop performance according to the Fracture Appearance Transition Temperature vTrs of the V-notch Charpy test is established in WES3003-1995. However, in the case of materials having a thickness of more than 50 mm in recent years, it is in a situation where the prediction accuracy is poor and it is difficult to easily evaluate.

In order to solve this problem, a relatively small and simple evaluation method such as a Charpy impact test or a drop weight test having a designed test piece shape has been developed instead of the large-scale test. Regarding the drop weight test, Patent Document 1 proposes a method of imparting a direction along the thickness of the test piece. After the compression deformation, a test piece was produced by punching the notch to more stably test from the brittle fracture.

With regard to the Charpy impact test, Patent Document 2 proposes a method of performing a test from a brittle fracture more efficiently, that is, using a depth after filling a portion corresponding to a notch of a Charpy impact test piece with a bead. A test piece made of a saw notch of 2 mm or less was used instead of the Charpy impact test piece.

Non-Patent Document 1 describes that the Kca value obtained by the ESSO test is strongly affected by the low toughness region because the toughness has a distribution depending on the thickness of the plate and the brittle fracture propagation stop performance. The toughness value of each plate thickness position was averaged from the area of the steel plate, and the brittle fracture propagation stop performance was evaluated by the value obtained by weighting the center portion of the plate thickness.

Further, as a simple evaluation method for the brittle fracture propagation stop performance in consideration of the thickness effect, Patent Document 3 proposes a method of performing a three-point bending test on a test piece taken from the center portion and the surface portion of the sheet thickness. The Kca value is predicted as a result of the obtained. Further, Patent Document 4 proposes a technique for evaluating the brittle failure propagation stop performance using a modified Charpy impact test piece having a special shape.

Patent Document 5 discloses a technique for evaluating the brittle failure propagation stop performance of a thick steel plate having a thickness of 50 mm or more by using a punched notched Charpy impact test piece. In the above, a method for evaluating the brittle fracture propagation resistance of a thick steel plate is described, which is characterized in that the center portion of the thickness of the thick steel plate having a thickness of 50 mm or more and the position at which the surface is 1/4 of the thickness of the plate are used. The Charpy impact test piece with the punched notch was introduced, and the Charpy impact test was performed, and the brittle fracture propagation stop performance was evaluated based on the fracture transition temperature vTrs* obtained in the Charpy impact test of each test piece.

Further, Patent Document 6 discloses a method of obtaining a high precision The overall crack arrest performance of a thick steel plate with a thickness of 50 mm or more is related to the test results of a small test piece taken from a thick steel plate. In this case, it is proposed to take a plurality of small test pieces along the thickness direction, and perform a small test by using the best method corresponding to the position taken, that is, using the drop weight test for the surface layer of the steel sheet, and determining the brittle fracture rate or absorbing energy for the internal use of the steel sheet. In the small-scale test, the test results are appropriately combined, and the Kca value obtained in the large-scale test is estimated based on the combination result.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open Publication No. SHO 63-67544

Patent Document 2: Japanese Patent Laid-Open No. 62-274258

Patent Document 3: Japanese Patent Laid-Open Publication No. 2008-46106

Patent Document 4: Japanese Patent Laid-Open Publication No. 2009-47462

Patent Document 5: Japanese Patent Laid-Open Publication No. 2011-33457

Patent Document 6: Japanese Patent No. 4795487

[Non-patent literature]

Non-Patent Document 1: Summary of the National Conference of the Welding Society, Episode 49, P.108 (1991)

Non-Patent Document 2: Guidelines for Design of Brittle Cracks and Cracks, Japan Maritime Association (2009)

However, the method of taking the test pieces of Patent Documents 1 to 3 is based on the size of the test piece or the case where it is processed again after welding, and the test piece is produced. Complex, hard to call a simple method. The technique of Patent Document 4 lacks versatility because the shape of the test piece is relatively special. Further, in the method of estimating the large-scale test result by considering the Kca value obtained by considering the toughness value of the thickness position in the non-patent document 1, it is confirmed that the two have a certain degree of correlation. However, the current situation is that the overall deviation is large and does not meet the extent that it can be used instead of a large-scale test.

In the technique of Patent Document 5 or Patent Document 6, it is necessary to test a test piece from a plurality of positions in the thickness direction of the thick steel plate. Therefore, the test piece is taken to be complicated, and it is difficult to say that it is a simple method.

Accordingly, it is an object of the present invention to provide a simple method for evaluating the brittle failure propagation stop performance of a thick steel plate by a small test.

The inventors of the present invention used the evaluation method of the brittle fracture propagation stop performance of the thick steel plate described in Patent Document 5, and the brittle fracture propagation stop performance evaluated by the ESSO test for a thick-walled material having a thickness of 50 mm or more The relationship between the punching notch stamping notched Charpy test piece or the modified Charpy test piece (hereinafter, as a modified punching notch Charpy test piece) was further studied, and the following findings were newly obtained. Fig. 4 is a schematic view showing the fracture of an ESSO test piece for a thick-walled material having a plate thickness of 50 mm or more. The brittle crack propagates differently in the plate thickness direction section, and the brittle crack length in the central portion of the plate thickness is shorter than the brittle crack length in the vicinity of the surface portion, and the depressed portion in the central portion of the plate thickness is formed. Further, in the fracture of the ESSO test piece of the thick-walled material having a thickness of 50 mm or more, as shown in Fig. 5, the central portion of the plate thickness is a convex portion, and a concave portion is formed between the upper and lower regions of the central portion of the plate thickness. However, such an object is not targeted in the present invention.

1. Even when the propagation behavior of brittle cracks in the thickness direction section is different (Figure 4 When the brittle crack in the surface portion is transmitted longer than the central portion of the thickness of the plate, the dynamic stress intensity factor of the mechanical surface portion is also affected if the brittle crack in the central portion of the plate thickness stops. The intensity factor is lowered, and it is easy to stop the propagation. Therefore, the brittle crack propagation stop performance at the center portion of the thickness represents the brittle crack propagation stop performance of the entire steel sheet.

2. In the punching notched Charpy impact test using a test piece taken from the central portion of the thickness of the steel sheet, the absorbed energy shows a temperature of 20 J to 100 J (preferably 25 J to 60 J) showing brittleness with the steel sheet. A good correlation between the value of the disruption of the propagation stop performance. In particular, the absorption energy indicates a temperature of 40 J (°C): pT _40J shows a very good correlation with the value of the brittle fracture propagation stop performance of the steel sheet.

3. In the stamping gap, the Charpy absorbed energy is related to the brittle fracture rate. In the case of the stamping notch Charpy absorbed energy showing 20J to 100J, the brittle fracture rate becomes 50% to 90%. When the specific absorption energy shows 25J to 60J, the brittle fracture rate becomes 60% to 90%. Especially in the case of displaying 40J, the brittle fracture rate was 63%. The brittle fracture rate of the stamped notched Charpy test piece showed that the temperature (°C) of 50% to 90% showed a good correlation with the value of the brittle fracture propagation stop performance as well as the punched notched Charpy absorbed energy. In particular, the brittle fracture rate of the stamped notched Charpy test piece shows 63% of the temperature (°C): 63% BATT (Brittle area transition temperature) shows the same brittle failure as the punched notched Charpy energy. The value of the propagation stop performance is very well correlated.

4. In addition, the deformation stamping notched Xiabi test piece which has a cross-sectional area which is perpendicular to the long side and which is larger than the normal test piece and which is more than 100 mm ^{2 from} the center portion of the thickness of the thick steel plate is also a fracture form self-brittle failure. The transition to ductile failure, so that the brittle crack propagation stops can be reproduced in the test piece. On the other hand, in the deformation stamping notch near the surface of the thick steel plate, the fracture morphology of the Xiabi test piece was changed from ductile failure to brittle fracture, and the brittle crack propagation was stopped and could not be reproduced in the test piece.

Further, in the deformation punching notched Charpy impact test by the test piece taken from the central portion of the thickness of the steel sheet, the temperature of the absorption energy is 20 J to 225 J, and the brittle fracture propagation stop of the steel sheet is stopped. A good correlation between the values of performance. Further, in the case of the deformation punching notch Charpy impact test, when the absorbed energy shows 20 J to 225 J, the brittle fracture rate becomes 50% to 90%.

5. In the deformation of the stamping notched Charpy impact test using a test piece having a cross-sectional area (rectangular cross-sectional area) in which the long side is a direction perpendicular to the longitudinal direction of the thick steel plate is more than 100 mm ² When the longitudinal section of the punched notched Charpy test piece is 15 mm square in the longitudinal direction, the absorbed energy is the temperature of ₁₀₀ J (referred to as pT _100J ), and the absorption energy shows a temperature of 68 J in the case of 13 mm square (referred to as pT _68J). The temperature transition temperature (°C) of 20 to 225 J shows a good correlation with the value of the brittle fracture propagation stop performance of the steel sheet.

6. In the case of a deformed stamping notched Xiabi test piece with a rectangular cross-sectional area exceeding 100 mm ² , as shown in Fig. 3, the Charpy absorbed energy in the deformed stamping notch is related to the brittle fracture rate, and the longitudinal direction cross section of the longitudinal direction is 15 mm square. When the deformation of the stamping notch Charpy absorbed energy shows 100J, and the deformation of the longitudinal direction of the longitudinal direction is 13mm square, the deformation of the stamping notch Charpy absorbed energy shows 68J, and the brittle fracture rate of the deformed stamping notched Charpy test piece Both show 63%. The brittle fracture rate of the deformed stamping notched Charpy test piece shows 63% of the temperature (°C): 63% fracture transition temperature BATT system and deformation stamping notch Charpy absorbed energy shows good correlation with the value of brittle failure propagation stop performance Therefore, it can be converted into a 20-225J energy transition temperature of Charpy absorbed energy: pT _E , which is used for evaluation of brittle failure propagation stop performance.

The present invention has been completed based on the above findings, and the gist thereof is as follows.

[1] A method for evaluating the brittle failure propagation stop performance of a thick steel plate, characterized in that a punched notched Charpy impact test is performed using a stamped notched Charpy impact test piece, and the punched notched Charpy impact test piece is 50 mm. The above thick steel plate is taken from the center of the plate thickness (40% to 60% of the plate thickness) and is introduced with a stamping notch, and according to the 20J~100J energy obtained in the Charpy impact test of each test piece. The transition temperature pT _{E is used} , or the brittle failure propagation stop performance is evaluated based on the fracture transition temperature BATT of 50 to 90%.

[2] The method for evaluating the brittle failure propagation stop performance of the thick steel sheet according to claim 1, characterized in that Tk is calculated according to the energy conversion temperature pT _E or the fracture transition temperature BATT according to the following formula (1-1) From this, it is presumed that the brittle failure propagation stop performance (Kca value) becomes a certain temperature: Tk = a × (pT _E or BATT) + b (1-1)

Among them, pT _E : 20~100J energy transition temperature (°C) of the Charging notch Charpy energy; BATT: 50~90% fracture transition temperature (°C); a and b are coefficients.

[3] A method for evaluating the brittle failure propagation stop performance of a thick steel plate, which is a small test for estimating the brittle failure propagation stop performance of a thick steel plate, characterized in that the small test system is based on the use of a punching gap Charpy impact The stamping notched Charpy impact test conducted by the test piece, in the Charpy impact test, the temperature of the stamping notch Charpy absorbed energy is 40 J (°C): pT _40J , and the brittle failure propagation stop performance is evaluated. On the other hand, the punched notched Charpy impact test piece was taken at a position centered at the thickness of the plate and introduced with a punched notch in the propagation direction of the brittle crack.

[4] A method for evaluating the brittle failure propagation stop performance of a thick steel plate according to [3], characterized in that Tk calculated according to the above pT _40J and according to the formula (1-2) is used as a brittle failure propagation stop performance (Kca) The value becomes a temperature of 6000 N/mm ^1.5 , and the brittle failure propagation stop performance is evaluated: Tk=a×pT _40J +b...(1-2)

Among them, pT _40J : shows the stamping notch Charpy absorbed energy is 40J temperature; a, b is the coefficient.

[5] A method for evaluating the brittle failure propagation stop performance of a thick steel plate according to [3] or [4], characterized in that a temperature at which a brittle fracture rate of a stamped notched Charpy test piece is 63% is used: 63% BATT, Instead of pT _40J .

[6] A method for evaluating the brittle failure propagation stop performance of a thick steel plate, which is a method for estimating the brittle failure propagation stop performance of a thick steel plate by a small test, characterized in that the small test system is based on the use of a deformation stamping gap The deformation stamping notch Charpy impact test carried out by the impact test piece, the 20-225J energy transition temperature of the deformation punching notch Charpy's energy obtained in the above Charpy impact test: pT _E (°C), and the evaluation of brittleness The propagation stop performance (Kca value) is broken, and the deformation stamping notch Charpy impact test piece takes the position of the center portion of the plate thickness, and the punching notch is introduced in the propagation direction of the brittle crack, and the rectangular cross-sectional area is more than 100 mm ² .

[7] A method for evaluating the brittle failure propagation stop performance of a thick steel plate according to [6], characterized in that Tk (°C) calculated according to the above pT _E (°C) according to the formula (3) is used as brittle failure propagation. The stop performance (Kca value) becomes the stop temperature of the target value, and the stop temperature is compared with the set temperature set by the target value of the brittle fracture propagation stop performance (Kca value), and the brittle fracture propagation stop performance is evaluated: Tk= a×pT _E +b...(3)

Among them, pT _E : deformation stamping notch Charpy absorbed energy 20~225J energy transition temperature (°C); a, b is the coefficient.

[8] A method for evaluating the brittle failure propagation stop performance of a thick steel plate according to [6] or [7], characterized in that a fracture transition temperature BATT (°C) of 50 to 90% is used instead of pT _E (°C), The 50-90% fracture transition temperature BATT (°C) shows the fracture transition of the deformed stamping notch Charpy impact test piece with a brittle fracture rate of 50-90%.

According to the present invention, it is possible to evaluate the thickness of the test piece of the same size as the normal Charpy impact test without using a large-scale brittle crack propagation test such as the ESSO test. The thick steel plate of 50 mm or more has extremely brittleness and propagation stop performance, so it is extremely useful in the industry.

1‧‧‧ Stamping Notch Charpy Test Piece or Deformed Stamping Notch Charpy Impact Test

2‧‧‧2mm V-shaped stamping gap

Fig. 1 is a view showing the position (50% of the plate thickness) of the punched notched Charpy test piece or the deformed punched notched Charpy test piece.

Fig. 2(a) is a view showing a stamped notched Charpy test piece, and Fig. 2(b) is a view showing a deformed punched notched Xiabi test piece.

Fig. 3 is a graph showing the relationship between the Charpy absorbed energy (J) and the brittle fracture rate (%) in the deformation stamping notch Charpy impact test using a deformed stamping notched Charpy test piece having a rectangular cross-sectional area of more than 100 mm ² . (The deformation of the stamping notch Charpy test piece has a long-side orthogonal direction section of 13 mm square and 15 mm square).

Fig. 4 is a schematic view showing the fracture of an ESSO test piece of a thick-walled material having a plate thickness of 50 mm or more.

Fig. 5 is a schematic view showing another fracture of an ESSO test piece of a thick-walled material having a plate thickness of 50 mm or more.

Fig. 6 is a graph showing the relationship between the Charpy absorbed energy and the brittle fracture rate of the punched notch.

The present invention is an evaluation method in which a thick steel plate having a plate thickness of 50 mm or more and a fracture of the ESSO test piece has a shape shown in the schematic view of Fig. 4, using a stamping notched Charpy test result or a deformation punching notch Charpy test result. The brittle failure propagation stop performance is presumed.

The Charpy test was carried out by using a punched notched Charpy test piece or a deformed punched notched Charpy test piece in which the position of the center portion of the plate thickness was introduced and the punched notch was introduced in the propagation direction of the brittle crack. In the case where the cross-sectional area (rectangular cross-sectional area) in the direction perpendicular to the longitudinal direction exceeds 100 mm ^2, the test piece of 100 mm ² to 225 mm ² is used. The position at which the position is the center portion of the plate thickness is taken so that the center width of the test piece of the punched notch Charpy test or the deformed punched Charpy test piece coincides with the position of 40% to 60% of the thickness of the steel plate. Figure 1 is a schematic illustration of the situation taken in accordance with the 50% position of the sheet thickness.

The Charpy test results show a good correlation with the results of the brittle crack propagation performance test when using a Charpy test piece in which a notched gap is introduced instead of a notched gap, so it is set as a stamping gap. Xiabi test piece.

The punching notch is preferably introduced in the following manner. After considering the direction of the test piece, the material to be subjected to the test piece is divided and cut, and then the shape finishing process is performed, and the notched portion is pressed by the die for the rectangular steel piece thus obtained. In the present invention, the following stamped notched Charpy test piece or the deformed stamped notched Charpy test piece is used: as shown in Fig. 2(a), the dimension of the main body is 55 mm in the longitudinal direction and the cross section in the longitudinal direction of the long side is 10 ×. 10mm, or as shown in Fig. 2(b), the length of the main body is 50~60mm, and the dimension of the long-side orthogonal direction is (10~15)×(10~15)mm, and it becomes depth. 2mm V-notch with 2mm angle and 45 degree angle.

In the stamping notched Charpy test or the deformed stamping notched Charpy test, the influence of brittle fracture generation characteristics must be excluded from the obtained test results. Therefore, after the test, the punching notch Charpy test or the deformation stamping notched Charpy test piece is observed, and the test piece which is not damaged by the brittle crack is regarded as the evaluation of the brittle crack propagation stop performance, and is removed from the test result. . The impact test result obtained by arranging only the test piece which has been damaged by the brittle crack is an influence of eliminating the characteristic of the brittle fracture generation, and only reflects the brittle fracture propagation stop performance.

In the present invention, the brittle failure propagation stop performance is evaluated based on the 20J~100J energy transition temperature (°C): pT _E based on the energy absorbed in the punching notch Charpy test. In particular, in the present invention, the brittle fracture propagation stop performance was evaluated based on the absorption energy obtained in the punching notch Charpy test showing a temperature of _{40 J} : pT _40J . Hereinafter, a case where the brittle fracture propagation stop performance is evaluated by estimating the temperature at which the brittle fracture propagation stop performance Kca value becomes 6000 N/mm ^{1.5 will} be described.

In the case of a steel sheet having a thickness of 75 mm or less, if the Kca value at -10 ° C is 6000 N/mm ^1.5 or more, brittle cracking stops at -10 ° C (Non-Patent Document 2). According to the Charging Notch Charpy Ratio Test, the absorbed energy becomes 20J to 100J 20J~100J energy transition temperature: pT _E (°C), or the absorbed energy shows 40J 40J energy transition temperature pT _40J , and the Kca value is determined to be 6000N. The temperature of /mm ^1.5 was evaluated based on the temperature below or above -10 ° C to evaluate the brittle failure propagation stop performance.

[step 1]

For thick steel plates with a thickness of 50 mm or more, punched notched Charpy impact test pieces are taken from the center of the plate thickness, and introduced into the punched notches, and then subjected to various test temperatures. Charpy impact test. Since it should be taken in the direction in which the crack propagates, the direction in which the stamping notch is introduced coincides with the direction of the notch in the ESSO test, specifically, in the rolling direction or the rolling width direction.

[Step 2]

According to the result of the punching notch Charpy impact test, the temperature at which the absorbed energy becomes 20J~100J is set to pT _E , or the temperature at which the absorbed energy is displayed is 40J is set to pT _40J , and the above value is substituted into (1-1) or Tk* is obtained by the formula (1-2). The Tk* determined here shows a relationship between the brittle fracture propagation stop performance Kca value measured by the ESSO test and the temperature of 6000 N/mm ^1.5 : Tk (6000) is extremely good. The evaluation of the brittle fracture propagation stop performance can be performed with Tk* calculated as described above.

Tk=a×(pT _E or BATT)+b...(1-1)

Among them, pT _E : 20~100J energy transition temperature (°C) of the Charging notch Charpy energy; BATT: 50~90% fracture transition temperature (°C); a and b are coefficients.

Tk=a×pT _40J +b...(1-2)

Among them, pT _40J : stamping notch Charpy absorbed energy shows 40J temperature; a, b is the coefficient.

When the lodging strength of the steel sheet for which the brittle failure propagation stop performance is to be evaluated is 360 MPa or more, a good correlation can be obtained in the range of 0.4 < a < 1.5 and 0 < b < 40.

Formula (1-2) is an experimental formula in which pT _{40J at the} center of the thickness of the test piece is measured for each test piece, and an ESSO test is performed on the test piece common to the test pieces to obtain a temperature: Tk (6000). As a result of these measurements, the correlation between pT _{40J at the} center portion of the thickness and temperature: Tk (6000) was obtained.

It is known that the punching notch Charpy absorbed energy is related to the brittle fracture rate. When the punched notched Charpy absorbed energy shows 20J to 100J, the brittle fracture rate becomes 50% to 90%, and when the absorbed energy shows 25J to 60J, the brittle fracture rate becomes 60% to 90%. In particular, at a temperature at which the stamping notch Charpy absorbed energy is displayed at 40 J, it is possible to obtain a fracture rate at which brittle cracks generated from the punched notch are stopped due to the characteristics of the steel sheet (in the present invention, the brittle fracture rate is 63%).

Fig. 6 shows the relationship between the Charpy notched absorption energy and the brittle fracture rate. That is, even if the pT _E (°C) of the formula (1-1) is replaced with the fracture transition temperature BATT (° C.) of 50 to 90%, a good correlation with the temperature: Tk (6000) (° C.) can be obtained.

When the brittle fracture rate indicates that 63% of the temperature is 63% BATT, 63% BATT and pT _40J are substantially the same temperature.

[Step 3]

When the temperature: Tk (6000) is less than -10 ° C, it is judged that the brittle fracture propagation stop performance is excellent.

The present invention can also be applied to the case where the brittle failure propagation stop performance (Kca value) is a value other than 6000 N/mm ^1.5 , for example, 4000 N/mm ^1.5 or 8000 N/mm ^1.5, etc., and the correlation can be derived from the experimental results, respectively. The same evaluation as above was performed.

In the case where the thick steel plate of the same steel type to evaluate the brittle failure propagation stop performance has a plurality of sheets, the invention can be preliminarily implemented for one of the sheets, and the brittle fracture propagation stop performance of the steel sheet can be evaluated. For other steel sheets, the test temperature is determined under pT _40J . The punched notch Charpy absorbed energy (J), and the brittle crack propagation stop performance at -10 ° C was judged according to the following formula. When the steel sheet of the formula (2) is satisfied, the brittle crack propagation stop performance is excellent.

pE≧40(J)...(2)

pE: absorbed energy of stamping notch Charpy (J)

Then, in the present invention, in the case of a deformed stamping notched Xiabi test piece having a rectangular cross-sectional area exceeding 100 mm ² , the absorbed energy obtained in the Xiaby test based on the deformation stamping notch becomes an energy transition temperature of 20 to 225 J of 20 to 225 J. (°C): pT _E was used to evaluate the brittle failure propagation stop performance. Hereinafter, a case where the brittle fracture propagation stop performance is evaluated by estimating the temperature at which the brittle fracture propagation stop performance Kca value becomes 6000 N/mm ^{1.5 will} be described.

In the case of a steel sheet having a thickness of 75 mm or less, if the Kca value at -10 ° C is 6000 N/mm ^1.5 or more, brittle cracking stops at -10 ° C (Non-Patent Document 2). The energy transfer temperature obtained by the Charpy test using the deformed stamping notched Charpy test piece is 20 to 225 J: pT _E (°C), and the Kca value is determined to be 6000 N/mm ^1.5 , which is low according to the temperature. The brittle failure propagation stop performance was evaluated at or above -10 °C.

[step 1]

For thick steel plates with a thickness of 50 mm or more, a Charpy notched Charpy impact test piece was taken from the center of the plate thickness, and a Charpy impact test piece was introduced, and a Charpy impact test was performed at various test temperatures. Since it should be taken in the direction in which the crack propagates, the direction in which the stamping notch is introduced coincides with the direction of the notch in the ESSO test, specifically, in the rolling direction or the rolling width direction.

[Step 2]

According to the results of the Charpy impact test, the absorbed energy is determined to be 20 to 225 J and the energy transition temperature is 20 to 225 J: pT _E (°C), and the above value is substituted into the equation (3) to obtain Tk (°C). . The Tk (°C) determined here shows a relationship between the brittle fracture propagation stop performance Kca value measured by the ESSO test and the temperature of 6000 N/mm ^1.5 : Tk (6000) (° C.) is extremely good. The evaluation of the brittle failure propagation stop performance can be performed at Tk (° C.) calculated as described above.

Tk=a×pT _E +b...(3)

Among them, pT _E : 20~225J energy transition temperature (the deformation of the stamping notch Xiabi absorption energy shows 100J when 15mm square, and 68J when 13mm square); a, b is the coefficient.

When the lodging strength of the steel sheet for which the brittle failure propagation stop performance is to be evaluated is 360 MPa or more, a good correlation can be obtained in the range of 0.4 < a < 1.5 and 0 < b < 40.

Formula (3) is an experimental formula in which the deformation punching notch at the center portion of the thickness of the plate is measured for 100 J at a center portion of the thickness of the plate, and the pT _E (° C) at a time of displaying 68 J at a square of 13 mm is obtained. Further, an ESSO test was performed on the test piece common to the test pieces to obtain a temperature: Tk (6000) (° C.), and the measurement results were collected to obtain pT _E (° C.) and temperature: Tk (6000) (° C.). The association.

It is known that the deformation stamping notch Charpy absorbed energy is related to the brittle fracture rate. In the deformation stamping notch, the Charpy absorbed energy shows 100J at 15mm square, and at a temperature of 68J at 13mm square, it is possible to obtain a fracture rate that can be recognized by the characteristics of the steel plate due to the characteristics of the steel plate. In the invention, the brittle fracture rate was 63%). When the brittle fracture rate is 63% of the temperature is specified as 63% BATT (°C), the display is 100 J when the energy is absorbed at 15 mm square and the display is at 13 mm square. The temperature of 68J is approximately the same temperature, so even if pT _E (°C) of formula (3) is replaced by 63% BATT (50~90% fracture transition temperature BATT) (°C), temperature and Tk can be obtained (Tk). 6000) (°C) Good correlation.

[Step 3]

When the temperature: Tk (6000) (° C.) is lower than -10 ° C, it is judged that the brittle fracture propagation stop performance is excellent.

The present invention can also be applied to the case where the brittle failure propagation stop performance (Kca value) is a value other than 6000 N/mm ^1.5 , for example, 4000 N/mm ^1.5 or 8000 N/mm ^1.5, etc., and the correlation can be derived from the experimental results, respectively. The same evaluation as above was performed.

In the case where the thick steel plate of the same steel type to evaluate the brittle failure propagation stop performance has a plurality of sheets, the invention can be preliminarily implemented for one of the sheets, and the brittle fracture propagation stop performance of the steel sheet can be evaluated, and the test temperature pT _E is obtained for the other steel sheets. The absorbing energy (J) of the stamped notched Charpy test piece was determined, and the brittle crack propagation stop performance at -10 ° C was judged according to the following formula. When the steel sheet of the formula (4) is satisfied at a test temperature pT ₁₀₀ (° C.) with a deformation of a 15 mm square, the brittle crack propagation stop performance is excellent.

pE≧100(J)...(4)

pE: the absorbed energy of the deformation stamping notch Charpy at the test temperature pT _E (°C) (J)

[Example 1]

For the thick steel plate with a thickness of 50 mm or more, the Charpy impact test piece material was taken from the center portion of the plate thickness, and the deformation stamping gap was introduced into the test piece material using a die made of hard steel, and was supplied to the Charpy impact test. The composition of the thick steel plate is shown in Table 1, and the manufacturing conditions are shown in Table 2. Further, the rectangular cross-sectional area of the punched notched Charpy impact test piece was set to 100 mm ² (10 mm square).

The Charpy impact test was carried out at various temperatures to determine the temperature at which the stamping notch Charpy absorbed energy showed 40 J: pT _40J . In the punching notched Charpy impact test, the punched notched Charpy impact test piece was observed after the test, and the test piece which was not damaged by the brittle crack was regarded as the one who did not evaluate the brittle crack propagation stop performance, and was excluded. The average value of 5 test pieces which were destroyed from the brittle crack at each test temperature. Thereafter, the value of pT _40J is substituted into the above formula (1-2), and the temperature Tk* is obtained. Further, in the above formula (1-2), 63% BATT was substituted for the value of pT _40J , and the temperature Tk** was obtained.

On the other hand, for the same thick steel plate, the ESSO test was carried out together with the punched notch Charpy impact test as a large-scale brittle crack propagation test, and the temperature at which the Kca value became 6000 N/mm ^1.5 was determined: Tk6000. Tk*, Tk** and Tk6000 are shown in Table 3. The comparative example is based on the predicted results of the ductile brittle fracture transition temperature vTrs of the V-notch Charpy test piece used in the conventional prediction.

In the comparative example, the prediction error is large and the error is 30 ° C or more. On the other hand, in the present invention, the prediction error is within 10 ° C, and the accuracy is very good, and the usefulness of the evaluation method of the brittle crack propagation stop performance of the present invention is confirmed.

[Embodiment 2]

For the thick steel plate with a thickness of 50 mm or more, the Charpy impact test piece material was taken from the center portion of the plate thickness, and the deformation stamping gap was introduced into the test piece material using a die made of hard steel, and was supplied to the Charpy impact test. A deformation stamping notched Xiabi test piece having a right-angled right-angled section of 15 mm square and 13 mm square was produced. The composition of the thick steel plate is shown in Table 4, and the manufacturing conditions are shown in Table 5.

The Charpy impact test is carried out at various temperatures to determine the deformation of the stamping notch. The Charpy absorbed energy shows a temperature of ₁₀₀ J at 15 mm square: pT _100J (°C), and a temperature of 68 J at 13 mm square: pT _68J (°C) . In the Charpy impact test of the deformation stamping notch, the deformation stamping notched Charpy impact test piece was observed after the test, and the test piece which was not damaged by the brittle crack was regarded as the evaluation of the brittle crack propagation stop performance. Except for the average of 5 pieces of test pieces which were destroyed by brittle fracture at each test temperature. Thereafter, the value of pT _100J (°C) or pT _68J (°C) is substituted into the above formula (3), and the temperature Tk* (° C.) of each of 15 mm square and 13 mm square is obtained. Further, the temperature Tk** of each of 15 mm square and 13 mm square obtained from the brittle fracture rate was also obtained in the same manner.

On the other hand, for the same thick steel plate, the ESSO test was carried out together with the deformation punching notch Charpy impact test as a large-scale brittle crack propagation test, and the temperature at which the Kca value became 6000 N/mm ^1.5 was determined: Tk6000 (° C.). Tk (°C) and Tk6000 (°C) are shown in Tables 6 and 7. The comparative example is based on the predicted results of the ductile brittle fracture transition temperature vTrs of the V-notch Charpy test piece used in the conventional prediction.

In the comparative example, the prediction error is large and the error is 30 ° C or more. On the other hand, in the present invention, the prediction error is within 10 ° C, and the accuracy is very good, and the usefulness of the evaluation method of the brittle crack propagation stop performance of the present invention is confirmed.

Claims (8)

A method for evaluating brittle failure propagation stop performance of a thick steel plate, characterized in that a punched notched Charpy impact test is performed using a stamped notched Charpy impact test piece, and the punched notched Charpy impact test piece is thicker than 50 mm The steel plate is taken from the center of the plate thickness (40% to 60% of the plate thickness) and is introduced with a stamping notch, and according to the 20J~100J energy transition temperature obtained in the Charpy impact test of each test piece. pT _E , or the brittle failure propagation stop performance is evaluated based on the 50 to 90% fracture transition temperature BATT. A method for evaluating the brittle failure propagation stop performance of a thick steel plate according to the first aspect of the patent application, wherein Tk is calculated according to the energy conversion temperature pT _E or the fracture transition temperature BATT according to the following formula (1-1). This presumed brittle failure propagation stop performance (Kca value) becomes a certain value of temperature: Tk = a × (pT _E or BATT) + b ... (1-1) where pT _E : stamping notch Charpy absorbed energy 20~100J Energy transition temperature (°C); BATT: 50~90% fracture transition temperature (°C); a and b are coefficients. A method for evaluating the brittle failure propagation stop performance of a thick steel plate, which is a method for estimating the brittle failure propagation stop performance of a thick steel plate by a small test, characterized in that the small-scale test is based on using a punched notch Charpy impact test piece The punched notched Charpy impact test was carried out, and the temperature of the stamping notch Charpy absorbed energy was 40 J (°C): pT _40J , which was obtained in the above Charpy impact test, and the brittle failure propagation stop performance was evaluated, and the punching was performed. The notched Charpy impact test piece was taken at a position centered at the thickness of the plate and introduced with a punched notch in the propagation direction of the brittle crack. A method for evaluating brittle failure propagation stop performance of a thick steel plate according to item 3 of the patent application, wherein Tk calculated according to the above pT _40J and according to the formula (1-2) is used as a brittle failure propagation stop performance (Kca value) Become a temperature of 6000 N/mm ^1.5 , and evaluate the brittle failure propagation stop performance: Tk = a × pT _40J + b (1-2) where pT _40J : shows the stamping notch Charpy absorbed energy is 40 J; a, b is the coefficient. For example, the method for evaluating the brittle failure propagation stop performance of a thick steel plate of the third or fourth aspect of the patent application, wherein a brittle fracture rate of 63% of the stamping notched Charpy test piece is used: 63% BATT instead of pT _40J . A method for evaluating the brittle failure propagation stop performance of a thick steel plate, which is a method for estimating the brittle failure propagation stop performance of a thick steel plate by a small-scale test, characterized in that the small-sized test is based on a stamping notched Charpy impact test piece using deformation The deformation stamping notch Charpy impact test was carried out, and the energy conversion temperature of the Charpy absorbed energy obtained in the above Charpy impact test was 20 to 225 J: pT _E (°C), and the brittle failure propagation stop performance was evaluated (Kca). The deformation stamping notch Charpy impact test piece takes the position of the center portion of the plate thickness, and introduces a punched notch in the propagation direction of the brittle crack, and the rectangular cross-sectional area is more than 100 mm ² . A method for evaluating the brittle failure propagation stop performance of a thick steel plate according to item 6 of the patent application, wherein Tk (°C) calculated according to the above pT _E (°C) and according to the formula (3) is used as a brittle failure propagation stop performance. (Kca value) becomes the stop temperature of the target value, and the above-described stop temperature is compared with the set temperature set by the target value of the brittle fracture propagation stop performance (Kca value), and the brittle fracture propagation stop performance is evaluated: Tk=a ×pT _E +b...(3) where pT _{E is the} energy transition temperature (°C) of the 20 to 225 J energy absorbed by the deformation stamping notch Charpy; a and b are coefficients. For example, the method for evaluating the brittle failure propagation stop performance of a thick steel plate according to the sixth or seventh aspect of the patent application, wherein 50 to 90% of the fracture transition temperature BATT (°C) is used instead of pT _E (°C), the 50 to 90 The fracture transition temperature of BATT (°C) shows the fracture transition of the brittle fracture rate of the deformation stamping notched Charpy impact test piece of 50 to 90%.