JPS6367544A - Press notch dwtt testing method - Google Patents

Abstract

PURPOSE:To accurately test brittle fracture propagation stop characteristics by an easy method that tests a test-piece which is compressed and deformed to 25-40% in the plate thickness direction at the press notch part of the test- piece. CONSTITUTION:The test-piece which is compressed and deformed to 25-40% in the plate thickness direction its press notch part is prepared and used to take the test. For the purpose one edge of the intermediate of the test-piece 1 is compressed on both front and rear surfaces with press punches 2 and 2 to deform in the plate thickness directions, and a V press notch is formed with a tool 4 at the press notch parts where compressive deformation parts 3 are formed. Thus, the compressive deformation is caused at the press notch parts in the plate thickness direction to suppress fracture generating energy.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION Field of Industrial Application The present invention relates to press-notched DWTT test specimens and test methods for evaluating brittle crack propagation properties of line pipe steels and the like.

Due to the occurrence of unstable ductile fracture accidents in conventional technology pipelines, real pipe pipeline burst tests have been conducted, but instead of this real pipe test, which is burdensome in terms of cost and labor, this test corresponds well to the burst test results. DWTT test (Drop
Weight Tear Te5t) has become the mainstream. This DWTT test is a test method that specifies the temperature at which a ductile fracture ratio of 85% is obtained, and is specified as ASTM standard E436-71T and is put into practical use, and the notch is a press notch. However, as steel for line pipes has become more tough, a problem has arisen that cannot be addressed by the conventional DWT test method. That is, it is a reverse fracture surface in which a ductile fracture surface appears from the bottom of the press notch and then transitions to a brittle fracture surface. This is due to the increased toughness,
This is thought to be due to the insufficient plastic restraint necessary for the formation of brittle fracture surfaces in press notches.

Therefore, the following measures have been announced as countermeasures against this problem.

■ DWTT test method with embrittlement welded bead is 1) Kobayashi, Taira, Yamaguchi, Iwasaki 2 Nippon Steel Tube Technical Report Th72. 2) Nosari, Kaisho, Sumitomo et al.: Sumitomo Metals Vol. 1.33, Takashi I June 19
8L3) Nakano, Kudo, Funakoshi et al.: Yozaki Steel Technical Report, Vol.
8.11kL40ct Published in 1976, etc. Also, ■ Pre-Crack DWT
The T test method was developed by G, M, Wilkowski & R,
J, Eiber: DRAFT.

Procedure for conducting
the 5tatic Precrack Drop
Weight Tear Te5t on Line
Pipe”.

It was announced in 1978. Namely, method (2) is a method in which cracking is facilitated by placing an embrittled weld bead in the press notch area, and (2) is a method in which a fibrous fracture surface is grown several mm from the tip of the press notch by static loading, and then impact bending is applied. This is a method of applying

Problems to be Solved by the Invention However, the DWTT test method with an embrittled welded bead (2) involves a step of welding an embrittled bead, and it is difficult to produce a defect-free bead and is not practical. Also ■ pre-crack DWT
In the T test method, plastic deformation is also applied to the ligament part during static loading, and the influence of the pre-strain is particularly significant on QT-treated steel types, resulting in the situation shown below.

(a) Temperature showing 85% ductile fracture ratio (85% 5ATT)
increases compared to presnotch. For QT materials, the higher the energy, the greater the difference (QT material with vEs of 35 kg-m
As shown in FIG. 6, the temperature of T material increases by as much as 60°C.

(b) Removes the energy required to deform the ligament under static loads. The deformation energy of the ligament should be considered as part of the propagated energy, which results in an underestimate of the propagated energy.

"Structure of the Invention" Means for Solving the Problems: Prepare a test piece to which a compressive deformation of 25% or more and 40% or less is applied in the thickness direction at the press notch portion of the test piece, and conduct a test using the test piece. Press Notsuchi DW featuring
TT test method.

Crack generation energy is suppressed by applying compressive deformation in the plate thickness direction at the action press notch.

By setting the compressive deformation to 25% or more, the propagation energy becomes approximately equal to the total energy.

By setting the compressive deformation to 40% or less, it can be easily processed using a push punch or the like.

A press notch is appropriately formed in the compressively deformed portion and an impact bending test is performed.

EXAMPLE To explain the present invention as described above in more detail, the present inventors have conducted various studies in view of the problems of the prior art as described above, and as a result of intensive consideration, the brittleness of steel for line pipes has been determined. In order to appropriately evaluate crack propagation characteristics, it is necessary to develop a test method that does not apply plastic deformation to the ligament, suppresses crack initiation energy, and is simple in practical terms. As a test method, a test method that uses a test piece that has been subjected to compressive deformation in the thickness direction of the press notch portion of the test piece before the test, that is, lateral compression
We have developed a test method that can also be called the DWTT method.

That is, the procedure for preparing a test piece used in the test according to the present invention is as follows.

(11 Process the test piece into the same rectangular size as the press notch DWTT.

(2) Apply compressive deformation in the thickness direction from both sides of the thickness of the notch.

(3) ■Make a press notch.

The test piece shape and test method were the same as the conventional DWTT test. A feature of the test method of the present invention is to suppress crack generation energy by applying compressive deformation in the plate thickness direction as described in (2) above.

Further, the test piece and test method according to the present invention will be described below with reference to the drawings. That is,
Figure 1 shows the lateral compression DW as described above.
This shows the procedure for creating a TT test piece, in which a rectangular test piece 1 as shown in Figure (a) is prepared, and the middle part to the side edge of the test piece 1 is inserted as shown in Figure (b). A press punch 2.2 is used to apply compressive deformation to the plate from both the front and back surfaces, and the press notch portion in which the compressively deformed portion 3 is formed is then punched with a tool 4 as shown in FIG. 1(C). This is to form a press notch.

FIG. 2 shows a method for simultaneously processing two specimens 1.1 in order to give the compressive deformation in fb) of FIG. 1 described above. That is, the test piece 1.1 is accommodated between the receiving portions 6.6 formed in the two jig members 5.5, and held tightly by the tightening means 7, and the jig members 5.5 as described above are held tightly. The push punches 2a, 2a are inserted from above and below into the elongated insertion hole 8 formed in the center of the two test specimens 1.1 on opposite side edges as described above. The test piece 1.1 is subjected to compressive deformation at the same time.

The dimensions of the compressive deformation obtained as described above are as shown in FIG.
The depth is 5mm, and the length (100%) is 1
As an example, it was set to 30%. ■For the press notch, after applying compression deformation as shown on the right side of Fig. 3, ■Notch 9 can be applied using the same testing machine, and the impact bending test is performed at 3t.
It can be performed using an on-m impact tester.

In Fig. 4, the fracture transition temperature and absorbed energy transition curve of X70 are shown, and the absorbed energy is shown by the press notch DWTT indicated by the X mark, and the 30% lateral compression D shown by the square mark. The pre-crack DWTT becomes smaller in the order of W T T and pre-crack DWTT indicated by *. i.e. 30% lateral compression D W 'T'T
Since the generated energy is suppressed by compressive deformation as described above, the energy is smaller than that of the press-notched DWTT, and the absorbed energy is larger than that of the pre-cracked DWTT because the ligament is not deformed.

Further, it has been found from the test results that the relationship between Et (total energy) and Ep (propagation energy) in the press notch DWTT test for five mesh types in the intensity level range of X65 to X80 is expressed by the following equation.

BpPN = 0.7Et" The propagation energy Ep is considered to be approximately equal in the press notch DWTT and the lateral compression DWTT. Therefore, the propagation energy Ep in the lateral compression DWTT is
The ratio between t and Ep is expressed by the following formula.

E tLcE L" Figure 5 summarizes the relationship between EpLc/EtLc and the compression ratio. From this figure, some variation can be seen, but when the compression ratio exceeds 25%, the propagation energy is almost the total. It turns out that the energy is equal to
Furthermore, if the compression rate exceeds 40%, it becomes difficult to compress and deform using a push punch, so it is desirable that the compression rate is 25 to 40%.

As the toughness of steel increases, the crack initiation energy in the press notch DWTT test cannot be ignored, but the lateral compression DWTT test method is a simple test method that evaluates the propagation energy without pre-deforming the ligament part.

"Effects of the Invention" As explained above, according to the present invention, the brittle crack propagation arresting properties of steel for line pipes and steel for low-temperature use can be accurately tested using a simple method even under highly toughened conditions. This invention can be evaluated and has great industrial effects.

[Brief explanation of drawings]

The drawings show the technical content of the present invention, and Fig. 1 is an explanatory diagram showing step-by-step the test piece preparation method according to the present invention, and Fig. 2 is an explanatory diagram showing the jig for performing the compression deformation. Slope view, Figure 3 is an explanatory diagram of the main part of the test piece, Figure 4
The figure is a chart summarizing the fracture transition temperature and absorption energy transition curve of various test pieces for X70.
The figure is a diagram summarizing the relationship between compression ratio and EpLc/EtLc, and Figure 6 is 85% in the pre-crack test method.
It is a chart showing the relationship between the temperature (85% 5ATT) showing the ductile fracture ratio and vEs for a ferrite + pearlite structure, a ferrite + bainite structure, and a QT material. In FIGS. 1 to 3, the symbol (■) represents the test piece, 2.2a represents the press punch, and 3 represents the compressive deformation portion. Warm L('e) Node 5 Fig.

Claims (1)

[Claims] A press notch DW characterized in that a test piece is prepared which has been subjected to compressive deformation of 25% or more and 40% or less in the plate thickness direction at the press notch portion of the test piece, and the test is performed using the test piece.
TT test method.