JPS584298B2 - Delayed fracture test method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION When determining the delayed fracture strength of metal materials such as high-strength steel and high-strength alloys using a cantilever bending weight method or a tensile method using a test piece with cracks, the present invention provides a method for determining the composition of a test solution. The present invention relates to a test method and apparatus for measuring delayed fracture strength while keeping the pH constant at all times.

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, in increasing the tensile strength of steel, there is a problem in that delayed fracture occurs due to hydrogen entering 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 eventually rapidly break.

Although it is desirable to conduct tests 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 performed by comparing the relative delayed fracture behavior. An accelerated testing method is used.

The currently adopted test methods are the cantilever bending weight method using a rectangular bar or round bar test piece with cracks such as notches and fatigue cracks, and the tensile weight method using a round bar test piece 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 a 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 a test piece is immersed in a constant volume of a test solution.

The test solution used at this time is generally 0.1N hydrochloric acid or a 3-3.5% sodium chloride solution, 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. However, it has been difficult to prevent fluctuations in the pH and composition of the test solution due to the increased pH of the test solution and the dissolution of iron and the like from the test piece.

In particular, it is known that when the pH of the test solution rises above about 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.

Based on the purpose explained above, the present invention removes metal ions such as iron ions dissolved in the test liquid using an ion exchange resin, then adds an acidic solution and circulates the test liquid. The purpose of the present invention is to provide a new simple and practical delayed fracture test method and apparatus, which are characterized by automatically controlling the pH to be kept constant.

FIG. 2 is an explanatory diagram of an apparatus according to an embodiment of the present invention.

1 is a test piece, and 2 is a cell in which the test piece is immersed in the test liquid. 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. Ta.

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;
11 is a test liquid tank, 11 is an inert gas injection pipe such as argon gas or nitrogen gas for expelling dissolved oxygen in the test liquid, and 12 is a filler such as chelate resin for removing metal ions, etc. from the test liquid. 13 is a removal tank filled with 13, 14 is a pH adjustment tank equipped with a stirrer 18 and a pH measurement electrode 19, 15 is an acidic solution tank, 20 is a pH meter, 21 is a pH controller, and 22 is a pump for circulating the test liquid.

During the delayed fracture test, the test solution is circulated in the flow path indicated by the arrow in FIG. 2, during which metal ions are automatically removed and the pH is maintained at a constant value.

The test liquid adjusted to a constant pH in the pH adjustment tank 14 is transferred by a pump 22 to a test liquid tank 10 installed at a higher position than the cell, and the test liquid in this tank is fed at a constant flow rate through a flow meter 8. Supply to cell 2.

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

Therefore, the number of cells is usually plural, and the test liquid tank 10
A 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 22 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 the cell 2 at a flow rate that does not affect the test due to changes in the composition such as the pH and metal ion concentration of the test liquid in the cell, but if the internal volume is approx. 2
When using a 00ml cell, the flow rate of the test solution is approximately 1m
It is sufficient to supply the gas at a relatively low flow rate of about 1/min.

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 23 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 is flowed from the top to the bottom of the cell as described above. is the most suitable.

Similar to this reason, in a tensile weight type delayed fracture testing device that uses a round bar with a crack on its circumference as a test specimen, the test liquid is applied to the cracked part of the round bar's circumference. It is effective to supply the test liquid from the vertical direction, ie from the side.

The test liquid discharged from the cell 2 enters the metal ion removal tank 12.

The tank 12 is filled with a filler such as a chelate resin, an anion exchange resin, or a cation exchange resin.

200ml of IN sodium acetate solution, 18ml of 1N hydrochloric acid solution
pH 3.5 prepared by mixing 5 ml and 615 ml of water
When the test liquid is supplied at a flow rate of 1 ml/min and a 10 x 10 x 50 ml (surface area 22 cm2) square rod of high-tensile steel is used as the test piece, the test liquid discharged from the cell contains approximately 65 μg/ml of iron was leached out.

When this test solution is passed through the tank 12 filled with chelate resin, all iron ions are adsorbed and captured by the chelate resin, and metal ions such as iron ions are not removed from the test solution discharged from the tank 12. Ta.

Chelate resin easily adsorbs and captures metal ions in solutions with a pH of approximately 3 or higher, and does not capture other ions such as sodium ions and chloride ions in the test solution.
The test liquid composition hardly changes.

Both Na-type and H-type chelate resins can be used, but the Na-type generally has a stronger ability to adsorb and capture metal ions.

Furthermore, when a strong acid such as 0.1N hydrochloric acid is used as the test liquid, a chelate resin is unsuitable because its adsorption/trapping property deteriorates, so it is more appropriate to use an anion exchange resin.

When metal ions such as iron ions are not removed in the tank 12 filled with chelate resin etc., the pH adjustment tank 14 is used.
Alternatively, iron ions or the like may undergo hydrolysis in the test liquid tank 10 to produce hydroxide precipitates, and these precipitate particles may clog the flowmeter 8 or adhere to cracks in the test piece in the cell 2. This may interfere with measurement.

For pH control, the pH of the solution in the pH adjustment tank is read by the pH meter 20, and if it deviates from the value set in the pH controller 21, the solenoid valve 16 is opened and closed, and the pH of the solution prepared in the acidic solution tank 15 is prepared in advance. The pH is adjusted by continuously pouring a solution that is thicker than the previously prepared test solution into the pH adjustment tank.

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

Thereafter, the three-way cock is closed, the flow rate is adjusted to a predetermined level 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 metal ion removal tank through the discharge pipe 25 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 quickly discharged from the lower part of the test liquid discharge pipe 6 through a three-way cock into the metal ion removal tank.

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

For example, when low alloy steel with a surface area of 22 cm2 is immersed in 200 ml of a buffer solution adjusted to pH 3.5, the result is 3.62 after 1 hour, 3.70 after 4 hours, 4.20 after 24 hours, and 7
After 2 hours, it changes to 4.80.

On the other hand, in the case of the present invention, the pH fluctuation is as shown in Figure 4, which shows 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. , the pH hardly changes and remains almost constant.

Furthermore, about 60 μg/ml of iron was dissolved in the discharged test solution, but since a chelate resin was used, there was no staining of the solution and almost no change in composition was observed.

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

That is, when the test is conducted for 21 days using the drip method at 1 ml/min, 30 liters of the test liquid is required for one testing machine.

This type of test typically uses multiple test machines, but assuming five machines are in operation, it will consume 7.2 liters 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 content of the present invention has been explained mainly using steel as an example, it goes without saying that the method and apparatus of the present invention can be applied to metal materials in general.

Examples will be described below.

Example 1 Low alloy steel (composition C0.20%, Si0.21%, Mn0
．． 75%, P0.013%, S0.010%, Cr1.
03%) test piece (10 x 10 x 50 mm, surface area 22
cm2) was set on this device, a load of 100 kg was applied, and a test solution (pH 3.5) containing sodium acetate and hydrochloric acid was flowed into the cell at a flow rate of 1 ml/min to conduct a delayed fracture test.

Figure 4 shows the results of investigating the relationship between the immersion time of the test piece and the pH change in the cell during the test process.

The low-alloy steel specimen used in the test broke on the seventh day after the start of the test, but almost no pH fluctuation was observed during this period.

[Brief explanation of drawings]

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, total...
... Weight, 4 ... Test liquid supply pipe, 5 ...
・Gas discharge pipe, 6...Test liquid discharge pipe, 7...
...Liquid path switching cock, 8...Flowmeter, 9...
...Flow rate adjustment valve, 10...Test liquid tank, 11...Inert gas blowing pipe, 12...
...metal ion removal tank, 13... filler,
14: pH adjustment tank, 15: acidic solution tank, 16: solenoid valve, 17: addition tube, 18: stirrer , 19... pH measurement electrode, 20... pH meter, 21...
pH controller, 22...Pump, 23.
...Crack, 24...Liquid level gauge, 25...
...Discharge pipe, → mark...Test liquid circulation channel.

Claims (1)

[Claims] 1. A test liquid is supplied from a vertical direction to the cracked part of a cracked test piece set in a cell, and the test liquid discharged from the cell is dissolved from the test piece through a metal ion removal tank. A delayed fracture testing method for metal materials, which comprises removing metal ions, adjusting the pH, and circulating the metal ions into the cell again. 2 Test liquid supply port in the direction perpendicular to the crack part of the test piece,
It has a cracked test piece setting cell with a gas outlet above the test piece and a test solution outlet below the test piece, and from the test solution outlet of the cell, a metal ion removal tank, a pH adjustment solution addition device, and a pH adjustment solution addition device are connected. A metal material characterized by a configuration in which a pH controller, a pH measuring electrode, a pH adjusting tank equipped with a stirrer, and a test liquid circulation pump are sequentially connected by a thin tube, and the end of the thin tube is connected to the test liquid supply port of the cell. Delayed fracture testing equipment.