JPS63304135A - Brittle fracture test piece for hybrid esso and hybrid double tension test - Google Patents

Abstract

PURPOSE:To surely test the brittle crack stop performance of a test plate in a brittle fracture test by using a steel plate having <=3.5kgf.m impact value at -170 deg.C and consisting of 0.1-0.3% C, 7.5-9.5% Ni and the balance Fe as an approach plate. CONSTITUTION:The steel plate having the chemical components (weight %) consisting of 0.1-0.3% carbon C, 7.5-9.5% nickel Ni, and the balance Fe and unavoidable impurities and having <=3.5kgf.m impact value at -170 deg.C is used as the approach plate 1 and the test plate 2 is butted and welded to this approach plate 1 to prepare the hybrid ESSO test piece and double tension test piece. The ramification of the brittle crack in the plate 1 is then prevented. The stepping which arises in the weld zone and the stop of the crack in the weld zone at the time of plunging-in of the test piece are thus prevented and the decrease in the brittle fracture speed is prevented.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention aims to improve the brittle fracture arresting performance of steel plates with high accuracy and accuracy in steel plates such as 9% Ni steel used in structures for cryogenic containers such as LNG. Concerning hybrid ESSO and double tensile test specimens that are reliably sought.

(Prior art) Due to the recent increase in energy demand, the consumption of LNG as a cheap and clean energy source is rapidly increasing, and as a result, the construction of low-temperature container structures necessary for storing LNG is becoming more popular. . Along with this, discussions about the safety of structures have increased, and steel plates such as 9% Nig used in these structures have come to be required to have better low-temperature toughness.

Traditionally, the requirements for low-temperature toughness for steel sheets have focused on brittle fracture initiation characteristics, mainly in Charpy tests, but with recent developments in fracture mechanics, brittle crack arrest characteristics are also attracting attention. It has become.

Generally, the well-known ESSO test and double tension test have been used as test methods for evaluating the brittle crack arrest characteristics of steel sheets.

However, like 9% Ni steel, liquid nitrogen temperature (-f
For materials that exhibit high toughness even at 96°C, normal ESS
Since brittle cracks cannot be generated and propagated in the O test etc., we conducted a run-up plate l as shown in Figure 1 for the purpose of propagating brittle cracks in the test plate.
A hybrid ESSO test in which a test plate 2 and a test plate 2 are butt welded 3 or a similar hybrid double tensile test has been conducted to date.

In other words, these test methods generate brittle cracks in the run-up plate under uniform stress and temperature to simulate brittle fracture of a structure.
The purpose of this test is to evaluate the stopping characteristics of the test plate by causing it to propagate and temporarily enter the test plate. The brittle crack is a straight brittle crack from the moment it penetrates into the test plate.
It is desirable to have a cracking velocity of 700+/s or more.

However, in reality, due to problems such as the toughness of the run-up plate,
The above conditions are often not always met.

For example, in the document ``Study on the brittle fracture characteristics of 9%N1tI!4 plate, May 1960, Japan Welding Association Iron and Steel Subcommittee LT Committee, pp. 16-18'', there is a hybrid double tensile test of 9%Ni steel. (Plate thickness: 20f1 width = 500fi) and the run-up is tentatively 0. lO%C-0,22%5i-0,86%
Mn-0,017%P-0.019%S-0.07%C
Tests are being conducted using test pieces made of U steel.

The test was conducted under the conditions of a test temperature of 16O to -196℃ and a load of 10 to 45 kgf/was, but the test temperature was -180℃ or lower and the load stress was 3
In tests of 5 kgf/ts" or higher, there have been many reports of branching brittle cracks occurring in the run-up.

When brittle cracks branch out in the run-up like this,
It is not possible to correctly evaluate the brittle crack arrest performance of the test plate, and recently, in order to avoid branching of brittle cracks in the run-up machine, the same 9%N1 as the test plate
There is a tendency to use steel that has been subjected to embrittlement treatment as the run-up plate.

However, although this method can certainly prevent the occurrence of branching within the run-up plate, depending on the embrittlement treatment conditions, that is, the toughness of the run-up plate, the brittle crack speed at the time of entry may be 70%.
At the same time, when the brittle crack enters the test plate, it does not enter straight at the welded part (on the run-up plate side), and a phenomenon occurs in which it forms steps as shown in Figure 2. However, this is not preferable for evaluating brittle crack arrest characteristics.

In addition, when the latter phenomenon becomes severe, the crack may stop at the weld before entering the test plate, and this phenomenon is difficult to accurately evaluate the stopping characteristics of the steel plate when performing brittle fracture tests. This not only impairs the quality of the test, but also causes an economic disadvantage due to the increase in the number of time-consuming retests.

(Problems to be solved by the invention) To summarize the above, hybrid ESSO such as 9% Ni steel
As problems in the test and hybrid double tensile test, 1.
) Branching of brittle cracks in the run-up machine, 2) Stepping and stopping at the welded part (on the run-up plate side) when entering the test plate, and 3) Decrease in the brittle crack speed.

The present invention solves these problems and provides a test piece for achieving reliable and accurate tests in the hybrid ESSO test and the hybrid double tensile test.

(Means for Solving the Problems) The means for the present invention to solve the above problems is as described below, in which C:0.
1-0.3% Ni: 7.5-9.5% and the balance is F
The brittle crack arresting performance of the test plate in the brittle fracture test was improved by butt welding a steel plate containing e and unavoidable impurities and having an impact value of 3.5 kgf-2 or less at -170°C as a run-up plate to the test plate. It is an object of the present invention to provide a brittle fracture test piece which is characterized in that the following properties can be determined reliably and accurately.

Hereinafter, the present invention will be explained in detail in conjunction with solutions to the three problems mentioned above.

The phenomenon in which brittle cracks branch out in the run-up plane is caused by the toughness of the steel plate used as the run-up plate at the test temperature.

In other words, if the surface energy that forms the brittle fracture surface of a steel plate is significantly lower than the energy of a brittle crack, it is thought that branching will occur more easily. There is a need to.

Therefore, the present inventors focused on the fact that in the run-up plate made by embrittling 9zNi steel, the branching phenomenon was not observed at all. It was found that the addition of Ni was effective.

In other words, if the content is less than 7.5%, brittle cracks are likely to branch in the run-up machine, and if the content is more than 9.5%, the effect becomes saturated, and the effectiveness of addition can be seen economically. Therefore, the range was set at 7.5% to 9.5%.

The second problem to be solved by the present invention is to increase the speed of brittle cracks entering the test plate to 700 mb or more.

Figure 3 shows the brittle crack velocity (Crack Ve
locity) and run-up plate (0.05%C-9.1~9.
2%Ni) at -170°C.

That is, it can be seen that as the impact value of the run-up plate decreases, the brittle crack speed increases. Therefore, in order to achieve a brittle crack speed of 700 m/s or more in the run-up machine,
It is necessary to keep the impact value of the run-up plate at -170°C to 3.5 kgf·- or less.

The reason why the temperature of -170°C was selected is as follows.

Normally, low-temperature steel such as 9% Ni steel is evaluated for service performance at its lowest service temperature, so tests such as brittle crack stopping performance are also conducted near the LNG temperature (-162°C). Therefore, it is most appropriate to evaluate the toughness of the run-up plate at the temperature at which the destructive test is actually performed.

By solving the above two problems, it becomes possible to cause a brittle crack without branches to enter the run-up machine at a speed of 700 m/s or more, but as shown in Fig. The phenomenon of sticking and stopping of the weld occurs regardless of the impact value of the run-up plate.

That is, it is necessary to prevent the phenomena of stepping occurring at the welded portion and stopping of the cracking at the welded portion when the brittle crack enters the test plate as described in the third problem.

This phenomenon occurs because the toughness of the run-up plate, which has been subjected to brittle treatment and whose impact value at -170°C has decreased to 3.5 kgf or less, is reheated by the welding heat during welding of the run-up plate and the test plate. This is due to the fact that a significant recovery of toughness occurs.

In other words, even if a brittle crack propagates at high speed in the run-up machine, when it enters the test plate, it is affected by this toughness recovery part,
Stepping or stoppage inside the run-up machine may occur.

Therefore, it is essential to lower the toughness of the weld heat-affected zone, but the present inventors have so far attempted to reduce the toughness of the heat-affected zone by localized re-embrittlement treatment, etc. of the heat-affected zone. However, these methods not only impede the efficiency of the test, but the re-embrittlement treatment may also affect the toughness of the test plate, so a simple and reliable method is desired. was.

Based on this background, the present inventors focused on the components of the run-up plate as a means of degrading the toughness of the weld, and as a result of repeated experiments, as shown in Figure 4 (a), the addition of C was found to be effective. I discovered something.

At 0.05% C@, which is the C content of ordinary 9% Ni steel, as shown in the figure, even after embrittlement treatment, the steel is reheated by welding heat, so a remarkable recovery in toughness is observed. In contrast,
In steel containing 0.1% or more of C, the toughness recovery of the weld is reduced as the amount of C increases, and the impact value at -170°C also decreases to 3.
．． Since the pressure can be lowered to 5 kgF or less, it is possible to prevent phenomena such as step formation and stoppage of run-up plate thickness that have an unfavorable effect on the test.

Run-up plate: 8.0-9.2% Ni, welding material: 3.5% Ni
, the heat input was 30 kj/cn, and the groove shape is shown in FIG. 4(b).

However, if a large amount is added, it may actually impair weldability and adversely affect the test due to weld cracking, etc.
The upper limit was 3%, and the ct was in the range of 0.1 to 0.3%.

Table 1 shows the maximum impact value of the welded part of the run-up plate and the test plate (run-up plate side) and the step impact etc. after performing a hybrid ESSO test using 0.11%C-8,28%Ni as the run-up plate. This study investigated the incidence of abnormalities when entering the test plate.

Table 1 As can be seen from the results, those with an impact value of 3.5 kgf·- or less at -170°C do not exhibit any abnormality during brittle crack propagation, whereas those with an impact value of 3.5 kgf. 5k
If the value exceeds gf.-, the incidence of abnormality tends to be as high as 25%.

Therefore, in order to prevent the recovery of the toughness of the weld and to prevent abnormalities such as stepping, the CM of the steel used as the run-up plate should be set to 0.1
% or more was confirmed to be very effective.

By the way, as a method for manufacturing a run-up plate to meet such requirements for low-temperature toughness, for example, 650 to 800°C
Possible methods include water cooling, air cooling, and gradual cooling after heating.

The run-up plates manufactured in this way were temporarily butt-welded for testing and used as hybrid ESSO test specimens and hybrid double tension test specimens, which have been conventionally conducted. In addition, when welding at this time, it is necessary to use a welding material that does not break brittle even at -170°C, and generally, 3.5
%Ni-based material is used.

(Example) A steel plate having the composition shown in Table 2 and made embrittled under the heat treatment conditions shown in Table 3 was used as the run-up plate. :150mX50Q
The relationship between the toughness of the run-up plate and the hybrid ESSO test results was investigated by conducting a test using a test plate with dimensions of 350 m x 50 Q m.

Hybrid ESS using a run-up plate manufactured based on the present invention
In the O test, brittle cracks, which are preferable in any case, propagate from the run-up plate to the test plate, whereas those that deviate from the present invention result in branching, stepping, stopping in the run-up, etc. It is an uncertain test in which the brittle crack speed when entering the test plate is less than the predetermined 700 mm.

(The following margins continue on the next page) (Effects of the invention) As described above, according to the present invention, the brittle fracture arresting performance of 9%Nl steel etc. can be determined reliably and accurately, increasing the number of re-tests, etc. This method is useful as an economic evaluation method for low-temperature steel materials.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the specimen shape of a standard hybrid ESSO test, and Figure 2 is an explanatory diagram showing a situation where brittle cracks propagating in the run-up machine are stepped at the welded joint in a hybrid ESSO test. Figure 3 is a chart showing the relationship between the brittle crack velocity immediately before entering the test plate and the impact value of the run-up plate at 170°C, and Figure 4 (a) is the heat-affected zone of the weld between the run-up plate and the test plate. Figure 4 (
b) is an explanatory diagram of the groove shape. Agent Patent Attorney Tatsuo Chanoki Figure 1 Figure 2 Figure 3 vE470 (K9f-yn) Figure 41 (d) (b) (Tsubasa) Procedural amendment (voluntary) November 6, 1988

Claims (1)

[Claims] The impact value at -170℃ is 3.5kgf・m or less,
And a steel plate consisting of C: 0.1 to 0.3%, Ni: 7.5 to 9.5%, and the balance is Fe and inevitable impurities,
A brittle fracture test piece for hybrid ESSO and hybrid double tensile tests, characterized in that it is butt-welded to a test plate as a run-up plate.