JPH03130658A - Hardening-depth measuring method - Google Patents

Abstract

PURPOSE:To perform precise hardening depth control by detecting backward scattersed waves based on the directivity of an ultrasonic wave beam, and reproducing the mea sured scattering pattern obtained by averaging the scattering wave. CONSTITUTION:A cylindrical sample 2 is mounted on a rotary table 1, and the entire body is submerged into the water. Under this state, the sample is rotated together with the table 1. As a probe 2, a contact piece having a converged structure wherein the thickness of the beam is approximately uniform is used. The probe is applied on the outer surface of the sample 2 under the state wherein the probe is inclined at a specified angle theta with respect to the axis of an axially symmetrical object 2. The probe 3 is moved in the axial direction of the object 2. The position of the probe 3 is shifted in the circumferential direction and the axial direction of the object 2. An ultrasonic wave is inputted into the object 2 through the probe 3 from an ultrasonic wave transceiver 4. Then, the backward scattering waves generated in the object 2 are detected in the receiver 4 and inputted into an operating and controlling device 6 through an A/D converter 5. The backward scattered waves are averaged for every specified number, and the counted scattering pattern is computed. The counted scatter ing pattern is operated, and the reproduced scattering pattern is obtained. Thus, the precise hardening depth control can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for nondestructively measuring the hardening depth of axially symmetrical objects such as wheel sets, rolling rolls, and various other parts.

[Prior art]

In general, for metal axially symmetrical objects that undergo severe wear during use, such as wheel sets and rolling rolls, induction hardening is performed on the surface to form a hardened layer near the surface in order to reduce wear as much as possible. However, accurately grasping the depth of this hardened layer is an extremely important control item from the viewpoint of quality assurance of the axially symmetrical object itself and estimation of life.

By the way, in the conventional measurement of hardening depth, for example, an axially symmetrical product is cut in the radial direction, the cut surface is polished, etched, and macroscopically observed, and the hardness is detected at each part on the cut surface. The most common method is to measure the depth of hardening, but this method requires a lot of effort and
Moreover, since it is a destructive test, it has the disadvantage that only sampling tests can be performed.

As a countermeasure to this problem, the present inventors focused on the fact that the backscattered wave intensity of ultrasonic waves incident on an axially symmetric object changes stepwise at the boundary between the hardened region and the non-hardened region such as the heat-affected zone. Ultrasonic waves are incident on the outer circumferential surface of an object at multiple locations in the axial direction and circumferential direction obliquely with respect to the axial center line, each backscattered wave is detected, and the backscattered waves are averaged to create a backscattering pattern (measured scattering pattern). ) and have already proposed a method for measuring the hardening depth based on the stepwise increasing points of this measured scattering pattern. (Unexamined Japanese Patent Publication No. 60-205353.

Nonstructural Testing Co
(Problems to be Solved by the Invention) However, in such conventional methods, when the tissue is clearly divided in the depth direction, in other words, when the boundary surface is parallel to the surface, Even in this case, the backscattering pattern does not become a linearly angular pattern but shows a curved change. However, such a curved pattern has the disadvantage that it is difficult to specify the structure in the depth direction of the boundary surface.

Figure 5 shows a schematic cross-sectional view of an axially symmetrical object in which the interface between A and B tissues, which are formed overlapping in the depth direction, is parallel to the surface. When an ultrasonic beam with a predetermined diameter is incident on the surface of an axially symmetrical object at an angle θ, ideally it should form a linear and angular pattern as shown in Figure 6 (a), but in reality it It exhibits a curvilinear and gentle pattern as shown in FIG. 6(b).

The main reason for this is thought to be that the incident ultrasonic beam has a certain thickness, and its wavefront is non-parallel to the boundary between the sets iA and B.

Figure 7.8 shows an example of a measured scattering pattern obtained using the method proposed by the present inventors as described above, in which the horizontal axis represents the depth (the time from the time when the ultrasonic wave was incident on the axially symmetrical object). The vertical axis shows the intensity of the measured scattered waves.

Figures 7 and 8 specifically show measured scattering patterns obtained by performing different heat treatments on two types of metals and detecting four samples using the method proposed by the inventors as described above. .

Figures 7 (a) and 8 (a) show the measured scattering patterns when two types of samples were heat-treated so that the hardened zone and the heat-affected zone approximately coincided. As shown, the boundaries of the tissue clearly show points of gradual increase in intensity, as shown by arrows.

However, when the hardened zone and the heat-affected zone of the sample appear differently in the depth direction (the position indicated by the arrow is the hardened layer, and the position indicated by the open arrow is the heated V layer), the measurement scattering It can be seen that the pattern as a whole changes gradually, making it extremely difficult to distinguish between them.

The hardening depth is defined as T, which is the time from the time when a flat wave is incident on the surface of an axially symmetrical object until the measured scattering pattern rapidly increases, and θ, which is the refraction angle when the ultrasonic wave is incident.

Then, it can be obtained by the following formula.

D=%T-Vt cos a.

However, (2) the speed of sound in biaxially symmetrical objects.The present invention was made in view of the above circumstances, and its purpose is to eliminate the influence of the thickness of the ultrasonic beam and to produce a clear scattering pattern. It is an object of the present invention to provide a curing depth measuring method capable of accurately detecting the curing depth.

[Means to solve the problem]

The hardening depth measuring method according to the present invention involves injecting ultrasonic waves from a probe obliquely to the axial direction into multiple locations of an axially symmetrical object, and detecting the intensity of backscattered waves generated in the internal tissue of the axially symmetrical object. , a method in which a measured scattering pattern is obtained by averaging a plurality of detected measured values, and the curing depth is measured based on the stepwise increasing points of the measured scattering pattern, using a focusing probe as the probe, A measured scattering pattern is obtained in a depth range in which the thickness of the ultrasonic beam by the focusing probe can be considered to be approximately constant, and the measured scattering pattern and the directional characteristic of the ultrasonic beam obtained in advance in the material depth direction are calculated. The method is characterized in that it includes a process of obtaining a reproduced scattering pattern based on the method.

[Effect]

According to the present invention, it is thereby possible to clearly distinguish between the hardened layer and the heat-affected zone even when the positions of the hardened layer and the heat-affected zone are different in the depth direction.

〔Example〕

The present invention will be specifically explained below based on the drawings.

FIG. 1 is a schematic diagram showing the implementation state of the method of the present invention, in which reference numeral 1 indicates a rotary table, 2 indicates an axially symmetrical object as a sample, and 3 indicates a probe for transmitting and receiving ultrasonic waves. A cylindrical sample 2 is placed upright concentrically on a rotary table 1, and can be rotated together with the rotary table 1 while being entirely submerged in water. For the probe 3, a probe with a focusing type structure whose beam thickness can be regarded as approximately -like within a predetermined range is used, and the probe is tilted by a predetermined angle θ with respect to the axis of the axially symmetrical object 2. It faces the circumferential surface of the sample 2 and can be moved in the axial direction of the axially symmetrical object 2.

4 is an ultrasonic transmitter and receiver, and the circumferential direction of the axially symmetrical object 2;
While shifting the position in the axial direction, an ultrasonic oscillation signal is output to the probe 3 at a predetermined timing, causing the probe 3 to oscillate an ultrasonic wave to the axially symmetrical object 2, while detecting backscattered waves each time, The backscattered waves are taken into the arithmetic and control unit 6 via the D converter 5, and the detected backscattered waves are averaged every predetermined number to calculate a backscattering pattern (referred to as a measured scattering pattern).
Next, this measured scattering pattern is subjected to arithmetic processing to obtain a reproduced scattering pattern, which is then output.

The arithmetic and control unit 6 also outputs a control signal to the scan controller 7, which controls the drive source for the rotary table 1 and the drive source for moving the probe 3 in the axial direction, and controls the rotation angle φ of the rotary table. , the axial position Y of the probe 3 is set and adjusted.

The process of obtaining a reproduced scattering pattern from a measured scattering pattern is performed as follows.

The backscattering pattern obtained using an infinitely narrow ultrasound beam at the refraction angle θ (referred to as the reproduced scattering pattern)
s (z) and the backscattering pattern obtained using an ultrasound beam with a constant thickness at a refraction angle θ is i
(z), the following relationship (Equation 11) holds true.

However, b'' (y·): Directivity of the ultrasonic beam in the depth direction, expressed as a function of the value y· (see FIG. 5) in the direction orthogonal to the ultrasonic beam.

By setting y'si = Y, equation (1) can be rewritten as equation (2) below.Fourier transform equation T (f) of measured scattering pattern 1(z)
is a function b (
y) divided by the Fourier transform formula B (f) and S (f)
is obtained, and the desired reproduced scattering pattern s (2) is obtained by its inverse Fourier transform.

Note that in the actual calculation, FFT is used, and B (f)=
To avoid 0, use the following (5) instead of formula (4).
Use the formula.

(2) The Fourier transform formula of i (zLs (zLb (z)) is I (f), S (f), B (f
), the following relationships (3) and (412) hold true.

However, ε: constant, B(f) ”＞＞εB”
Cf): common complex number of B(f) Next, simulation results for the above-mentioned method of the present invention will be explained.

Figure 2.3 shows the ideal scattering pattern (Figure 2 (Illustrated)) obtained using an infinitely thin ultrasonic beam when the boundary between tissues is parallel to the surface as shown in Figure 5. )
, Fig. 3 (a)), each thickness 0.5 m (-6aB)
, 1. Measured scattering pattern when using an On (-6 dB) ultrasound beam (Fig. 2 (b), Fig. 3 (b)),
The reproduced scattering patterns (FIGS. 2(C) and 3(C)) in each case of the above method are shown.

As is clear from Figures 2 and 3, the smaller the thickness of the ultrasonic beam used, the more closely the ideal scattering pattern is obtained for both the measured scattering pattern and the reproduced scattering pattern. The reproduced scattering patterns shown in Figures 2 (C) and 3 (C) are better than the measured scattering patterns (Figures 2 (B) and 3 (B)) shown in Figures 2 (B) and 3 (B). It can be seen that the shape that is used is closer to the ideal scattering pattern shown in FIGS. 2(A) and 3(A).

Next, a description will be given of the test results in which the measured scattering pattern and the reproduced scattering pattern were obtained by the method of the present invention using the same sample as that used to obtain FIG. 7(b).

The test conditions are as shown in Table 1.

(Space below) Table 1 The directivity b (z) of the ultrasonic beam measured at a depth of 4n with the measured scattering pattern i (z) as shown in Figure 4 (a) obtained under the test conditions shown in Table 1. FIG. 4 shows the scattering pattern reproduced according to equation (2).

Both figures 4(a) and 4(b) show the depth (100) on the horizontal axis and the intensity on the vertical axis. Figure 4 (b) shows the reproduced scattering pattern.

Note that the dotted line shown in FIG. 4(a) is a waveform near the surface echo used to maintain continuity in FFT.

As is clear from comparing the patterns shown in Figure 4 (a) and (b), the rise characteristics have been improved, and the gradual increase points of the scattering pattern have become clearer in Figure 4 (b). I understand that there is.

[Effect] As described above, in the method of the present invention, by using the directivity of the ultrasonic beam to reproduce the measured scattering pattern obtained by averaging the detected backscattered waves, a more gradual increase in points can be achieved. The present invention has excellent effects such as clarity, making it possible to measure the hardening depth more accurately, and enabling precise hardening depth management.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the implementation state of the method of the present invention, Figures 2 and 3
The figure is an ideal, measurement, and reproduction backscattering pattern diagram showing the simulation results of the method of the present invention, and Figures 4 (a) and (b) are measurement and reproduction backscattering pattern diagrams showing the test results of the method of the present invention. , Fig. 5 is a schematic diagram when the interface between fibers is parallel to the surface, and Fig. 6 (a) and (b) show the ideal scattering pattern and measured scattering pattern for the sample shown in Fig. 5. 7.8 is a diagram showing a measured scattering pattern obtained by the conventional method. 1... Rotary table 2... Sample 3... Probe 4... Ultrasonic transmission, receiver 6... Arithmetic control device

Claims (1)

[Claims] 1. Ultrasonic waves are incident on multiple locations of an axially symmetrical object from a probe obliquely with respect to the axial direction, and the intensity of backscattered waves generated in the internal tissue of the axially symmetrical object is detected. In this method, a measured scattering pattern is obtained by averaging a plurality of measured values, and the curing depth is measured based on the stepwise increasing points of the measured scattering pattern. Obtain a measured scattering pattern in a depth range in which the thickness of the ultrasonic beam from the probe can be considered to be approximately constant, and combine the measured scattering pattern with
1. A hardening depth measuring method comprising the step of obtaining a reproduced scattering pattern based on a predetermined directivity characteristic of an ultrasonic beam in the material depth direction.