JPH01170849A - Method for measuring strength of spheroidal graphite cast iron - Google Patents

Abstract

PURPOSE:To improve accuracy by projecting ultrasonic waves of a wide frequency band into a spheroidal graphite cast iron and measuring the upper limit value of the frequencies of the ultrasonic waves transmitted through the cast iron, then determining the fracture toughness of an object to be measured from the upper limit value of the frequencies. CONSTITUTION:The ultrasonic waves X of, for example, an about 0.5-10MHz frequency band are projected from an ultrasonic probe 2 into the spheroidal graphite cast iron which is the object 1 to be measured. Only the high frequency bands of the ultrasonic waves transmitted through and reflected by the object 1 to be measured scatter and attenuate according to the grain sizes of the graphite 3 and the distance between the graphite 3 particles and, therefore, the fracture toughness is determined as a relative value by measuring the upper limit value of the frequencies and the normal fracture toughness is obtd. by a suitable calibration curve. The fracture toughness is, therefore, measured with good accuracy by a non-destructive method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method capable of measuring the fracture toughness of spheroidal graphite cast iron by a non-destructive method.

[Conventional technology and its problems]

Conventionally, the fracture toughness value of a metal material has been measured by cutting out a part of the material, processing it into a compact tensile test piece, and fracturing this using a fatigue testing machine. In the conventional fracture toughness measurement method, such a fracture test is the only method, and therefore, the measured value is only considered to be a representative value for the metal material concerned.

Incidentally, spheroidal graphite cast iron is used as nuclear power related components (for example, casks, etc.), and in such cases it is necessary to strictly check the fracture toughness of the product. However, conventionally, the fracture toughness has to be measured by the above-mentioned fracture test, which has the disadvantage that it cannot be checked sufficiently.

Regarding spheroidal graphite cast iron, there are methods to measure the graphite nodularity using an attenuation method using ultrasonic waves, a sonic method, etc., but it may not be possible to measure it depending on the shape of the product. Although graphite nodularity is considered to have a certain correlation with the fracture toughness value, it is practically difficult to measure the fracture toughness value by such a measurement method. In other words, when trying to measure the fracture toughness value using a non-destructive method, it is thought that the value is affected not only by the graphite particle size but also by various factors such as the distance between graphite particles. Just looking at it alone makes no sense.

[Means to solve the problem]

In view of such conventional problems, the present inventors investigated a method for measuring the fracture toughness of spheroidal graphite cast iron using a non-destructive method. As a result, there is a very high correlation between the upper end of the frequency of ultrasonic waves transmitted through cast iron and the fracture toughness of the cast iron, and by measuring the two end values, the relative value of the fracture toughness can be determined. I discovered that.

The present invention was made based on such knowledge, and its characteristics are that broadband ultrasonic waves are incident on the spheroidal graphite cast iron that is the object to be measured, and the upper end value of the frequency of the transmitted ultrasonic waves is measured. However, the fracture toughness value of the object to be measured is determined from the upper end value of the frequency.

The principle and specific measurement method of the present invention will be explained below.

As mentioned above, the fracture toughness value of spheroidal graphite cast iron is influenced by factors such as graphite particle size and distance between graphite. Figure 1 (Ia)
As shown in (na), when a broadband ultrasonic wave X is incident from the ultrasonic probe 2 into the spheroidal graphite cast iron that is the object to be measured 1, a part of the ultrasonic wave is scattered by the graphite 3. Such scattering of incident waves occurs first at high frequencies and gradually moves to lower frequencies. In this case, as shown in Fig. 1 (1a), if the graphite particle size is small and the distance between graphites is large, only the high frequency band is scattered and attenuated, and as shown in Fig. 1 ([la)] The larger the particle size and the smaller the distance between graphites,
Attenuates down to low frequency bands.

Therefore, in the case of Figures 1 (1a) and (Ila), the two extreme values of the frequencies of the ultrasonic waves transmitted (including reflection) through the spheroidal graphite cast iron are Figure 1 (Ib) (fi
b) By measuring the upper end of the frequency of the transmitted wave, which is affected by the graphite particle size and distance between graphite, it is possible to determine the fracture toughness value, which is correlated with graphite particle size and distance between graphite, as a relative value. can.

Figure 2 shows the upper frequency value of ultrasonic waves transmitted through spheroidal graphite cast iron and its fracture toughness value (actually measured value from a fracture test of a test piece).
It was found that there is a very clear correlation between the two-end value of the frequency and the fracture toughness value.

Note that the fracture toughness value from the upper frequency limit value is determined as a relative value, and a regular fracture toughness value can be obtained using an appropriate calibration curve.

Furthermore, the wider the frequency band of the ultrasonic waves that should be incident on the cast iron, the more clearly the difference in attenuation depending on the frequency will appear, allowing for more accurate measurements. Although the range of the band is not particularly limited, it is preferable to secure a range of at least 0.7 to 7 Mt+z from the viewpoint of measurement accuracy. Usually, ultrasonic waves having a frequency band of about 0.5 to 10 Mt (z) are incident.

FIG. 3 shows a state of implementation of the present invention, in which an ultrasonic pulse is introduced into the object to be measured 1 from the probe 2, and its reflected echo is detected. From the detected echoes, only the first bottom echo is extracted by a gate device 4 as shown in FIG. 4(A), and then passed through a spectrum analyzer 5.
The upper end value of the frequency is determined as shown in FIG. 4(B).

In addition to the method of capturing reflected waves as shown in FIG. 3, the measurement of transmitted waves may be performed by a so-called transmission method in which a transmitter and a receiver are provided on both sides of the object to be measured 1.

〔Example〕

Spheroidal graphite cast iron cask (330 x 500 x 3
Fracture toughness was measured using the method of the present invention (measuring location: central portion) for 60 strokes). In addition, a test piece was taken from the same object, and the fracture toughness value was measured using a fatigue tester. The results are shown in Table 1.

As is clear from Table 1, the fracture toughness of spheroidal graphite cast iron can be accurately measured by the method of the present invention (measurement accuracy: approximately ±10%).

〔Effect of the invention〕

According to the present invention described above, the fracture toughness of spheroidal graphite cast iron can be measured with high precision using a non-destructive method, and thereby the fracture toughness of each product can be strictly checked. Further, according to the present invention, it is possible to easily measure the fracture toughness of any part of a product.

[Brief explanation of the drawing]

Figure 1 (la) (lb) and (Da) (Ilb) show the measurement principle of the present invention, among which (Ia) (D
a) is an explanatory diagram showing the state of scattering of ultrasonic waves within the material;
Also, (Ib) (llb) are (la) (na) respectively
) indicates the upper limit value of the frequency of the transmitted wave corresponding to FIG. 2 shows the relationship between the upper frequency limit of transmitted waves in a material and fracture toughness. FIG. 3 is an explanatory diagram showing a measuring device used in the present invention and a measurement situation using the measuring device. Fourth
Figures (A) and (B) show the ultrasonic oscilloscope waveform and spectrum analyzer display when the present invention is implemented. In the figure, 1 is an object to be measured, 2 is a probe, and 5 is a spectrum analyzer. Figure 1 (I[a) (Ib) (nb)

Claims (1)

[Claims] A spherical device characterized by injecting broadband ultrasonic waves into spheroidal graphite cast iron as the object to be measured, measuring the upper end of the frequency of the transmitted ultrasonic waves, and determining the fracture toughness value of the object to be measured from the upper end of the frequency. How to measure the strength of graphite cast iron.