JPH0658356B2 - Measuring method for quench hardening of columnar material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for nondestructively measuring the thickness of a hardened layer from the outer surface of a cylindrical material by utilizing the change in the sound velocity of ultrasonic waves.

The sound velocity of ultrasonic waves changes depending on factors such as internal defects, materials, tissues, pressure, temperature, etc., but this application detects changes in tissues due to heat treatment as changes in ultrasonic sound velocity, and detects changes in hardness of ultrasonic propagation paths. Regarding how to measure.

(Prior Art) A steel material used by quenching only the surface layer of the material often wears its quenched surface due to contact with another material. Therefore, not only the hardness of the surface but also the hardness distribution inside is important. For example, in a rolling roll for steel sheet production, the outer surface is thinned by abrasion and grinding to remove surface defects that occur during use, so the internal hardness is maintained so that it can be used to a certain depth. Need to be The deeper the hardened range, the longer the life of the rolling roll.

Conventionally, as a method of nondestructively measuring the hardening depth, Japanese Patent Publication No. 45-28274 discloses a method of detecting a structural change due to quenching as a change in magnetic properties.

Further, as another method, a method utilizing the sound velocity of ultrasonic wave propagation is disclosed in JP-A-53-32054. As an example of this method, as shown in FIG. 8, an ultrasonic pulse signal from an ultrasonic wave transmitter / receiver 24 is transmitted to the surface of a specimen 21 having a surface hardened layer 21-1 by quenching or the like on its surface to transmit a probe 22. Specimen 21
Propagate ultrasonic waves inside the. This propagated ultrasonic wave reaches the surface on the opposite side, and then part of it is reflected back. This return ultrasonic wave is received by the reception probe 23, converted into an ultrasonic pulse signal again, and received by the ultrasonic wave transmitter / receiver 24, and the time Th from transmission to reception is measured. Separately from this, the ultrasonic wave is propagated in the same way to the specimen 21 'of the same material and the same size that does not have a hardened layer, and in this case the time from transmission to reception
Measure Tn. Based on these two data, the depth d of the surface-hardened layer was calculated from the following equation.

Ed: Young's modulus of hardened layer Et: Young's modulus of non-hardened layer T: Overall thickness (Problems to be solved by the invention) The above-mentioned conventional example has the following drawbacks.

1) The magnetic method only measures near the surface, and the depth is 90 mm.
It is difficult to measure to a deep position (30% of radius).

2) The ultrasonic wave propagation method is an effective method for a plate material or the like, but requires another specimen of the same material and having the same size. In the case of a thick plate or the like, the hardened layer is thinner than the non-hardened layer, Since the rate of change is small, there is a drawback that the measurement accuracy is reduced.

The present invention solves the above-mentioned drawbacks, and a method of nondestructively measuring the hardness distribution state by quenching of a material having a cylindrical surface layer portion from the outer surface to a depth of about 30% of the radius. The purpose is to provide.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides a method for nondestructively measuring the thickness of a hardened layer by quenching of a cylindrical column 1 whose surface is quenched. From one point of columnar material 1
The ultrasonic pulse is sequentially incident in the arc direction, which is one side of various regular polygons inscribed in the cross section of, and the ultrasonic pulse propagated along the sides of the various polygons is sequentially incident at the incident point. The ultrasonic wave velocity of each layer is received, and the hardness of each layer is measured by utilizing the fact that this ultrasonic wave velocity correlates with the hardness of the columnar material 1 which is a propagation medium. It is a method of measuring the curing depth of 1.

(Function) The main cause of the increase in hardness due to quenching of steel is the fact that the steel is rapidly cooled from the austenite region, causing a large amount of carbon that was solid-solved in γ-iron (fcc) to form solid-solution in α-iron (bcc). It is believed that carbon is dissolved in the octahedral center called the martensite transformation, which is a solid solution of carbon without releasing carbon up to a certain amount, and carbon atoms distort the crystal lattice up and down. This strain results in a change in elastic constant, which is the basic equation of the wave equation. As shown in equation (1), it appears as a change in sound velocity.

As shown in FIG. 2, the structure of the hardened columnar material has a higher morphology as the martensite content is closer to the outer surface, and its hardness is proportional to the martensite content.
In the figure, the martensite structure, the bainite structure,
Is a pearlite structure, is a gamma-ized pearlite structure,
Is the structure before quenching.

Since the sound velocity of a material greatly changes depending on the content of martensite, the sound velocity changes in proportion to its content, and the relationship between the sound velocity and hardness is determined by the content of martensite. The relationship between the Charpy hardness (Hs) of the hardened roll and the depth (mm) from the outer surface is shown in FIG. or,
Fig. 4 shows the relationship between the speed of sound propagating in the roll (m / sec) and the depth from the outer surface (mm) at that time. Figures 3 and 4
Charpy hardness (Hs) and sound velocity (m / sec) obtained from the figure
As shown in FIG. 5, the relationship with and is proportional between Hs = 70 to 100, and from this relationship, the hardness distribution can be estimated from the ultrasonic sound velocity distribution.

Since the measured sound velocity value is the average sound velocity in each propagation path, the sound velocity value at each point is obtained by an approximate method of a linear expression by comparing the average sound velocity of a regular n-gon and a regular n-1 polygon. In FIG. 6, the sound velocity at the center point BP of the distance B is almost equal to the average sound velocity (VM) of the regular n-gon passing through the distance M. The sound velocity at the center point AP of the distance A is obtained by subtracting the mean sound velocity (VM) of the regular n-gon at the distance B from the mean sound velocity (VL) of the regular n-1 polygon at the distance L, and the sound velocity at the point P (VPP ) Is based on the sound velocity and positional relationship in BP and AP.
It is calculated by the equation (2).

VP = VM + [A / ((L / VL)-(B / VM))-VM] [(L + A) / L] (2) The sound speeds VP and VB of each path calculated are By performing an approximate averaging process on the positions and sound velocities of all the measured paths, the sound velocity distribution chart shown in FIG. 4 can be obtained.

As a result, the hardness distribution of each layer can be obtained from FIG.

(Example) As shown in FIG. 1, ultrasonic waves are transmitted from a point on the outer circumference of a cylindrical material in an arc direction which is the first side of a regular n-gon (n is 4 or more) inscribed in the cross section of the cylindrical material. A sound wave pulse is incident on the transmission probe 7. This ultrasonic pulse travels along the regular n-side and repeats internal reflection on the cylindrical surface, and returns to the original incident point through the n-th side. The ultrasonic pulse is received at the incident point by the reception probe 9 provided in the n-th side direction of the regular n-sided polygon, and the propagation time during this time is detected by a measuring device (not shown).

This operation is performed by measuring the required number of times such that the regular n-sided polygon n is 4, 5, 6, ..., And displaying the measured data by calculation processing by a microcomputer (not shown).

The transmitting probe 7 and the receiving probe 9 are held by a holding device having the structure shown in FIG. That is, the medium tank 4 for containing the liquid medium 5 such as water in the center of the frame 2 is
Is provided to penetrate. The frame 2 is held by legs 2-1 such that the center of the bottom of the medium tank 4 slightly contacts the surface of the columnar material 1. The frame 2 is provided with legs 2-1 and is fixed on both sides, and the columnar shape 1 of the medium tank 4 is provided.
A circular follower plate 3 having a contact point with the center is provided. This holding plate 3 is provided with two holding members 8, 8 slidably on both sides thereof. The holding member 8 has a transmitting probe 7 on one side and a receiving probe on the other side. 9 is fixed toward the contact point with the columnar material 1. A notch 8-1 is provided at the upper end of the holding member 8 and engages with a pin planted on a slider 11 screwed to an angle adjusting screw 6 driven by a motor 19. The angle adjusting screw 6 is a screw whose left and right are opposite to each other with the center as a boundary.
Due to the rotation, both holding members 8 and 8 approach or separate at the same angle. Further, an angle detector 10 is provided at the other end so that the tilt angles of the transmission probe 7 and the reception probe 9 with respect to the columnar shape 1 can be detected.

Next, the operation of this device will be described.

First, the inclination angle θ (°) of each of the probes 7 and 9 with respect to the radial direction of the cylindrical member 1 passing through the contact point is adjusted as follows by the numerical value of n of the n-sided polygon.

However, the angle is rounded when n = 7.

When the ultrasonic pulse is incident after adjusting the respective angles described above, the sound velocity of each n-gonal path is measured, and the sound velocity distribution chart of FIG. 4 is created.

Based on this sound velocity distribution chart, the hardness distribution from the outer surface can be obtained from FIG.

(Effects of the Invention) As described above, the present invention can measure the hardness distribution from the surface to the central direction only with the quenched columnar shape, so that a specimen before quenching is not required unlike the conventional example.

Further, since the measurable depth can be up to about 30% of the radius of the columnar material, the depth can be remarkably deeper than that of the conventional example.

[Brief description of drawings]

FIG. 1 is an explanatory view of a propagation path of ultrasonic waves, FIG. 2 is an explanatory view of a microstructure change due to quenching, FIG. 3 is a hardness distribution diagram after quenching, FIG. 4 is a sound velocity distribution diagram after quenching, and FIG. Fig. 6 is a characteristic diagram of sound velocity and hardness, Fig. 6 is a sound velocity relationship diagram, Fig. 7 is a configuration diagram of a probe holding device, and Fig. 8 is an explanatory diagram of a conventional ultrasonic hardening quench hardening depth measuring method. is there. 1: Cylindrical material, 7: Transmission probe, 9: Reception probe.

Claims (1)

[Claims] 1. A method of nondestructively measuring the thickness of a hardened layer formed by quenching a columnar surface having a quenching applied thereto, comprising: The ultrasonic pulse is sequentially incident in the arc direction which is one side of the polygon, and the ultrasonic pulse propagated along the sides of the various polygons is sequentially received at the incident point to determine the ultrasonic velocity of each layer. A method for measuring the depth of quench hardening of a cylindrical material, characterized in that the hardness of each layer is measured by utilizing the fact that the ultrasonic velocity of sound is correlated with the hardness of the cylindrical material that is the propagation medium.