JPH05281133A - Method for evaluating environmental embrittlement of metal material - Google Patents

Abstract

PURPOSE:To evaluate the environmental embrittlement of metal material safely and simply by performing the deep drawing of the metal material having the circular or polygonal plate shape, applying strain, holding the material in the gaseous or liquid environment, and measuring the degree of the cracking of the metal material. CONSTITUTION:A metal material is machined into the disk shape or into the polygonal plate shape. Strain is applied by deep drawing, and micro-cracks are formed. When embrittlement material in environment comes into contact with the tip of a crack, the crack develops by the decrease in surface energy, generation and intrusion of hydrogen due to chemical reaction and the like, and the material is broken. At this time, the crack generating reference is set by dividing, e.g. the drawing rate of the deep drawing into several stages. What environment the metal material can resist is relatively evaluated without using a special jig. For example, when the cylindrical material, which is obtained by the deep drawing of SUS-304 steel having a diameter of 96mm and a thickness of 0.7mm at the drawing ratio of 2.8, is exposed in hydrogen sulfide at normal temperature for one day, a large crack is generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the degree of embrittlement of a metallic material in the environment of various gases or liquids.

[0002]

2. Description of the Related Art Generally, a metal material becomes brittle in various environments due to factors such as corrosion, and particularly in a stressed state or a site where a defect such as a scratch is generated, the brittleness is accelerated. As a means to evaluate the degree of embrittlement of a metallic material in a specific environment, generally, a tensile test at a low strain rate in a state of being exposed or immersed in the environment (Metal Handbook: Revised 4th Edition: The Japan Institute of Metals) : P13
38) was carried out, and the embrittlement was evaluated by the comparison value of the cross-sectional shrinkage rate or elongation value with the atmosphere or pure water.

[0003]

However, in the conventional method, when the environmental condition is hydrogen sulfide, the exposed portion of the tensile tester (for example, the jig holding the test material and its periphery) is corroded by hydrogen sulfide. Alternatively, the tester must be configured so that it will not be embrittled, and this harmful gas must never be released into the surrounding environment to ensure safety and safety in carrying out such tests. There is a problem in simplicity. In addition, it is necessary to use a matching jig that is not affected by the environment each time in the evaluation test of the degree of embrittlement in various environments, and there is a problem in simplicity. An object of the present invention is to provide a method for evaluating environmental embrittlement of a metal material that solves the above problems and is safe and simple.

[0004]

DISCLOSURE OF THE INVENTION According to the present invention, a plate-shaped metal material having a circular or polygonal shape is deep-drawn, held at a predetermined temperature in a gas or liquid environment, and then the metal material is cracked. It is characterized by measuring and evaluating the degree of. Further, according to the present invention, when deep-drawing a plate-shaped metal material having a circle or a polygon, the extent of the deep-drawing processing is set in advance in several stages, and after deep-drawing, the environment is changed to a gas or liquid. After being kept at a predetermined temperature, the degree of cracking of the metal material is measured and evaluated.

[0005]

In general, metallic materials become brittle due to corrosion or the like in various environments, and particularly in a stressed state or a site where a defect such as a scratch occurs, the brittleness is accelerated. In the method of the present invention, a microcrack can be generated on the surface of the metal material by applying a strain to the metal material by disk-shaped or polygonal plate-shaped processing and deep drawing. Therefore, when an embrittlement substance in the environment comes into contact with the tip of the crack, the surface energy of the contact interface is reduced, hydrogen is generated due to a chemical reaction and the cracks are promoted due to invasion or corrosion, which leads to embrittlement and destruction. You can do it. Further, in the present invention, by setting the degree of processing amount during deep drawing in several stages, various kinds of micro crack generation levels on the surface of the metal material are set, and the material strain of the metal material is determined. It is possible to evaluate the adaptability of a metal material safely, simply, quickly and sufficiently as to whether it can withstand the environment. The kind of gas or liquid which is the environmental condition in the method of the present invention may be appropriately selected. Regarding the temperature, the temperature from the freezing point to the boiling point may be appropriately selected, and normally room temperature is sufficient. The dipping time may be appropriately selected, and usually about 3 days is sufficient.

[0006]

【Example】

Example 1 FIG. 1 shows a cylindrical test material obtained by deep-drawing SUS-304 steel having a diameter of 96 mm and a thickness of 0.7 mm at a drawing ratio of 2.8. Even if this cylindrical test material is left as it is at room temperature and in the atmosphere, no cracks occur. This cylindrical test material was exposed to hydrogen sulfide at room temperature for one day and then visually observed, and as a result, large cracks as shown in FIG. 2 were generated. On the other hand, the test material of the same shape was immersed in liquid paraffin for one day at room temperature, and the result of visual observation showed that no crack was generated as shown in FIG. Furthermore, the test material is at room temperature and the surfactant is 1%.
As a result of immersing in the added liquid paraffin for one day, large cracks were generated as shown in FIG. As described above, according to the method of the present invention, the degree of embrittlement can be easily measured and evaluated simply by exposing or immersing the deep-drawn material to a certain environment. In addition,
For comparison, when the same material was simply processed into a disk shape without deep drawing and left to stand for several days at the same various temperatures and various brittle environments as in Example 1 of the present invention, cracking occurred at all. Without it, the brittleness could not be evaluated.

Example 2 S having a diameter of 98 mm and a thickness of 0.7 mm and varying the amount of Ni
Drawing ratio of US-304 steel is 1.6, 2.1, 2.5, 2.
Cracking sensitivity when a cylindrical test material deep-drawn with 4 types of No. 8 was immersed in liquid paraffin containing 1% of a surfactant at room temperature (○ indicates no cracking, △ indicates some Table 1 shows the occurrence of cracks, x indicates the occurrence of cracks on the entire surface, and the degree of embrittlement is mild in the order of x.

[0008]

[Table 1]

The 18Cr-7Ni system has a drawing ratio of 2.1 and is 1
The 8Cr-8Ni system cracked at a drawing ratio of 2.5, whereas the 18Cr-10Ni system did not crack even at a drawing ratio of 2.8. All of the SUS304 steels do not crack at the drawing ratio of 1.6 where the working ratio is light, but when the working ratio (drawing ratio) is increased, cracking occurs in the low Ni system and does not break by making the high Ni system. Thus, according to the method of the present invention, the degree of embrittlement can be easily measured and evaluated simply by immersing the processed material in which the degree of deep drawing is set in several stages.

Example 3 SUS-304 steel (18Cr-8Ni) having a diameter of 96 m
m, 0.7 mm thick disc or 96 mm x 96 m
Deterioration of a cylindrical or square tube-shaped test material deep-drawn at a drawing ratio of 2.8 from a plate having a thickness of 0.7 mm and a thickness of 0.7 mm when exposed or immersed in various environments at room temperature for 3 days (○ indicates Table 2 shows that no cracking occurs at all, Δ indicates partial cracking, X indicates cracking on the entire surface, and the degree of embrittlement is mild in the order of × Δ. In the example of the environment, the environment in which the material is actually exposed or immersed is shown, and the shape is indicated as a circle for the cylindrical deep-drawing cup test material and as a corner for the square tubular deep-drawing cup test material. As described above, the degree of embrittlement varies greatly depending on the type of environment. Thus, according to the method of the present invention, the degree of embrittlement associated with the type of environment can be easily measured and evaluated simply by exposing or immersing the deep-drawn material in an environment.

[0011]

[Table 2]

COMPARATIVE EXAMPLE Table 3 shows the results of immersing the SUS-304 steel plate in various environments for 1 day and 7 days as it was without the deep drawing. As a result, the occurrence of cracks was not observed in any environment, and the embrittlement of the material could not be evaluated. In this embodiment, the diameter of the test material before deep drawing was 96 mm. However, in the present invention, the diameter may be appropriately selected according to the purpose, and usually 10 mm to 20 mm. Further, in the present example, the drawing ratio of the test material at the time of deep drawing was selected in the range of 1.6 to 2.8, but in the present invention, it may be appropriately selected according to the purpose and is usually 1.01.
It may be in the range of up to 10.0.

[0013]

[Table 3]

[0014]

The method of the present invention does not require a special jig unlike the conventional method, and the metal produced by exposing or immersing the deep-drawn cylindrical material to a specific temperature or environment of liquid or gas. It is possible to evaluate the phenomenon of material destruction very safely. The method of the present invention can easily evaluate the embrittlement of a metal material under various environments, can be an index such as what kind of material should be selected according to the type of environment, and its usefulness is widely used in the industrial field. ..

[Brief description of drawings]

FIG. 1 is a diagram showing a cylindrical test material deep-drawn at a drawing ratio of 2.8 in this example,

FIG. 2 is a diagram showing a state of being left in hydrogen sulfide for 1 day by the method of the present invention,

FIG. 3 is a view showing a state of being left in liquid paraffin for 1 day by the method of the present invention,

FIG. 4 is a diagram showing a state of being left in liquid paraffin containing 1% of a surfactant for 1 day according to the method of the present invention.

Claims (2)

[Claims] 1. A method of deep-drawing a circular or polygonal plate-shaped metal material, holding it in a gas or liquid environment at a predetermined temperature, and then measuring and evaluating the degree of cracking of the metal material. A method for evaluating environmental embrittlement of a metal material, characterized by: 2. When deep-drawing a circular or polygonal plate-shaped metal material, the extent of the deep-drawing is set to several stages in advance, and after deep-drawing, in a gas or liquid environment. A method for evaluating environmental embrittlement of a metal material, which comprises measuring and evaluating the degree of cracking of the metal material after holding at a predetermined temperature.