JPS5836055Y2 - Delayed fracture test equipment - Google Patents

Description

[Detailed description of the invention] This invention uses a cantilever bending weight method using a cracked test piece or a tension method to determine the delayed fracture strength of metal materials such as high-strength steel and high-strength alloys, while keeping the pH constant at all times. This relates to a test device that measures delayed fracture strength while maintaining

In recent years, there has been an increasing demand for lighter steel structures, and as a result, it has become necessary to increase the tensile strength of steel.

However, when steel is made to have a high tensile strength, there is a problem in that delayed fracture occurs due to hydrogen that enters from the environment during manufacturing or use.

Delayed fracture is a phenomenon in which metal materials such as steel suddenly break brittle with almost no apparent plastic deformation after a certain period of time has passed under static load. In reality, cracks occur during static loading from stress concentration areas such as notches, fatigue cracks, and corrosion pits in the material, progress over time, and finally rapidly break.

Although it is desirable to conduct a test to measure the delayed fracture strength of metal materials under the conditions in which the material is used, it requires a very long period of time and is therefore impractical, so it is generally a comparison of relative delayed fracture behavior. An accelerated testing method has been adopted.

The currently adopted testing methods are the cantilever bending weight method using square bar or round bar test pieces with cracks such as notches and fatigue cracks, and the tensile weight method using round bar test pieces with cracks. There is.

These methods are distinguished by the way static loads are applied to the test piece, but in delayed fracture testing, the test environment for the test piece is also an important requirement.

Although it would be ideal to conduct the test under the natural conditions in which metal materials such as high-strength steel are used, it requires a long period of time, so conventionally, the test method shown in Figure 1 was generally used. A method is adopted in which the test piece 1 is passed through a cell 2 filled with a test liquid to promote hydrogen penetration into the test piece.

That is, conventionally, a method has been adopted in which the delayed fracture strength is measured by applying a load of 3 under a test environment in which the test piece is immersed in a fixed volume of test liquid.

The test liquid used at this time is generally 0. IN hydrochloric acid or 3-3.5% sodium chloride solution is used, but
This test method has a problem in that the composition and pH of the test solution have a large effect on the measurement results.

Therefore, tests are carried out using test specimens of the same shape and test liquid of the same composition, but the test usually takes a long period of time, about three weeks, and the dissolution of the test specimen by the test liquid progresses. , it was difficult to prevent pH fluctuations in the test solution.

In particular, it is known that when the pH of the test solution rises from around 4, the penetration of hydrogen into the test piece is significantly reduced, and maintaining the pH of the test solution constant is very important in delayed fracture tests.

For these reasons, in the field of materials testing, there is a strong demand for the development of testing methods and equipment that can measure the delayed fracture strength of metal materials such as high-strength steel while maintaining a stable test solution composition and pH using a simple method. was.

The present invention is based on the purpose explained above, and is a simple and simple method characterized by adding an acidic solution to a test solution and automatically controlling the pH of the test solution to be kept constant without circulating the test solution. This provides a new and practical delayed fracture testing device.

FIG. 2 is an explanatory diagram of an embodiment of the device of the present invention.

1 is a test piece, and 2 is a cell in which the test piece is immersed in a test solution.The position of this part in relation to the entire delayed fracture test apparatus is shown in Figure 1, and the details of the structure of this part are shown in Figure 3. Indicated.

4 is a thin tube for supplying the test liquid to the cell, 5 is a discharge pipe for hydrogen gas etc. generated from the cell, 6 is a discharge pipe from which the test liquid flows out from the cell, and 7 is a flow for filling and discharging the test liquid into the cell. A cock for switching the flow, 8, a flow meter with a flow rate adjustment valve 9 for keeping the amount of test liquid flowing into the cell constant; 10;
is a test liquid tank; 11 is a pipe for blowing inert gas such as argon gas or nitrogen gas to expel dissolved oxygen in the test liquid; 12 is a pH adjustment tank equipped with a stirrer 16 and a pH measurement electrode 17; 13 is an acidic solution tank; 18 is a pH meter, 1
9 is a pH controller, and 20 is a pump for circulating the test liquid.

24 is a filter for removing precipitates generated in the test solution.

This may be a general filter using filter paper, filter cloth, etc.

The test piece is partially dissolved by the test liquid, and precipitated residues such as cementite in the test piece become suspended in the test liquid.

In addition, the pH of the test solution in the cell increases until it is drained and the pH is adjusted, so metal ions such as iron dissolved from the test piece into the test solution undergo hydrolysis and become hydroxylated. Causes precipitation of substances.

These residues and precipitates may clog the flow meter 8 or accumulate in the cracks of the test piece, causing trouble in the test.

Therefore, it is necessary to install the filter 24 as described above.

During the delayed destruction test, the test solution is circulated in the flow path indicated by the arrow in FIG. 2, during which time the pH is automatically maintained at a constant value.

The test liquid adjusted to a constant pH in the pH adjustment tank 12 is transferred by a pump 20 to a test liquid tank 10 installed at a higher position than the cell, and the test liquid in this tank is fed through a flow meter 8 at a constant flow rate. Supply to cell 2.

Figure 2 shows only one cell 2 to make the drawing easier to understand, but since the delayed fracture test usually requires a long period of time of about 3 weeks for one sample, it is generally shown in Figure 1. Several test devices as shown are lined up and multiple test pieces are tested in parallel at the same time.

Therefore, the number of cell cylinders is usually plural, and the test liquid tank 10
The test liquid supply pipe is branched from the flowmeter, and the test liquid is supplied to each cell through each flowmeter.

When there is only one cell 2, a method can be used in which the flow rate of the pump 20 is kept constant and the test liquid is directly supplied to the cell 2 without using the tank 10 or the flow meter 8.

The test liquid can be supplied to cell 2 at a flow rate within a range where fluctuations in the pH composition of the test liquid in the cell do not affect the test, but a cell with an internal volume of approximately 200 WLe is used. In this case, the test liquid may be supplied at a relatively low flow rate of about 1 degree.

Reducing the flow rate of the test liquid in this way is effective for downsizing the entire device and for manufacturing purposes, but on the other hand, it reduces the diffusion of the test liquid within the cell, making it difficult to conduct tests under certain conditions. There is a problem that makes it impossible.

We investigated various supply and discharge positions of the test liquid using a colored liquid, and found that it is important to supply the test liquid from a direction perpendicular to the crack in the test piece.

That is, the crack part 21 of the square test piece as shown in FIG.
In contrast, the test liquid is supplied perpendicularly to the crack through the test liquid introduction pipe No. 4.

On the other hand, hydrogen gas is generated due to the reaction between the surface of the test piece and the test liquid, and although some of it enters the test piece, most of it rises to the top of the cell.

This is discharged outside the cell through the pipe 5.

When the test liquid is supplied from the tube 6 in FIG. 3, the flow of the test liquid is stagnant at the cracked portion.

This becomes obvious when colored liquid is added, and the exchange of liquid in the cracks becomes incomplete.

That is, in order to constantly supply a new test liquid to the crack, the most suitable method is to supply the test liquid from a direction perpendicular to the crack.

As shown in Figure 1, in the case of the cantilever bending weight method using a rectangular test piece, the crack part of the test piece is located on the upper side, so the test liquid flows from the top to the bottom of the cell as described above. It is best to let it flow.

Similar to this reason, in a tensile weight type delayed fracture testing device that uses a round bar with cracks on its circumference as a test specimen, the test liquid is applied perpendicular to the crack notched on the circumference of the round bar. It is effective to supply the test liquid from the lateral direction.

The test liquid discharged from the cell 2 enters the pH adjustment tank 12.

pH control adjusts the pH of the solution in the pH adjustment tank.
If the value read by the meter 18 deviates from the value set in the pH controller 19, the electromagnetic valve 14 is opened and closed, and a solution that is thicker than the test solution prepared in advance is added to the acidic solution tank 13 intermittently to adjust the pH. Pour into the adjustment tank and adjust the pH.

The test liquid is introduced into the cell 2 in Fig. 2 using the test liquid tank 10.
The liquid flows from the bottom of the cell through the three-way cock 7 to quickly fill the cell.

Thereafter, the three-way cock is closed, the flow rate is adjusted to a predetermined value through a flow meter 8, and the test liquid is allowed to flow into the upper part of the cell from the supply pipe 4.

Drainage liquid during the test is taken out from the middle of the test liquid discharge pipe 6 and enters the pH adjustment tank 12 through a discharge pipe 23 provided at a location higher than the cell liquid level and lower than the upper tip of the gas discharge pipe.

After the test is completed, the test liquid is discharged from the lower part of the test liquid discharge pipe 6 through a three-way cock and promptly discharged into the pH adjustment tank.

In addition, even if a buffer solution is used for the test solution, in the case of a batch method, the pH
varies greatly.

For example, when low-alloy steel with a surface area of 22C1it is immersed in 200w1l of a buffer solution adjusted to pH 3.5, after 1 hour it becomes 3.62.4 hours after 3.70 after 24 hours.4.20 after 24 hours.
．． After 72 hours, it changes to 4.80.

On the other hand, when using the device of the present invention, pH fluctuations can be measured using the results of a delayed fracture test of high-strength steel in a test solution of pH 3.5 consisting of sodium acetate and hydrochloric acid.
As shown in the figure, the pH hardly changes and remains constant.

Furthermore, in the present invention, the test liquid is circulated, which is more economical than the dripping method.

That is, when a test is conducted for 21 days at 1 rttl/mVl using a dripping method, 307 test liquids are required for one testing machine.

This type of test typically uses multiple test machines, but assuming 5 machines are in operation, it consumes 7.2 hours each day.

In addition, preparing the solutions used every day requires not only reagent costs but also a large amount of labor and time.

On the other hand, if such a large amount of test fluid is to be discharged, the discharged fluid must be neutralized from the viewpoint of environmental pollution.

All of these points can be solved by using a circulating system for the test liquid as in the present invention.

Although the contents of the present invention have been mainly explained using steel as an example, it goes without saying that the apparatus of the present invention can be applied to metal materials in general.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the cantilever beam bending test, Fig. 2 is an explanatory diagram of the apparatus according to the embodiment of the present invention, Fig. 3 is an explanatory diagram of the cell portion of the apparatus according to the embodiment, and Fig. 4 is an explanatory diagram of the apparatus according to the present invention. It is an explanatory diagram showing a measurement result. 1...Test piece, 2...Cell, 3...
... Weight, 4 ... Test liquid supply pipe, 5 ...
...Gas discharge pipe, 6...Test liquid discharge pipe, 7...
...Flow path switching cock, 8...Flowmeter, 9.
...Flow rate adjustment valve, 10...Test liquid tank, 11...Inert gas blowing pipe, 12.
...pH adjustment tank, 13...acidic solution tank,
14... Solenoid valve, 15... Addition pipe, 1
6... Stirrer, 17... pH measurement electrode, 18 = pH meter, 19... pH controller, 20... Pump, 21... - Crack, 22...Liquid level gauge, 23...Discharge pipe, 24...Filter → mark...Test liquid circulation channel.

Claims (1)

[Scope of utility model registration request] It has a cracked test piece setting cell with a test liquid supply port perpendicular to the crack part of the test piece, a gas discharge port above the test piece, and a test liquid discharge port below the test piece, and the test liquid in the cell is From the outlet, a pH controller equipped with a p)I adjustment solution addition device, an interlocking pH controller, a pH measuring electrode, and a stirrer is installed.
1. A delayed fracture testing device for metal materials, characterized in that a regulating tank, a filter for removing sediment, and a test liquid circulation pump are sequentially connected by a thin tube, and the thin tube is connected to a test liquid supply port of the cell.