JPH0216874B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for non-destructively measuring the crystal transformation rate of steel materials using electromagnetic ultrasound.

When rolling thick steel plates for shipbuilding materials, construction materials, etc., when rolling is performed when the austenite phase and ferrite phase near the transformation temperature of the steel material are mixed together (two-phase region rolling), the strength of the rolled plate will decrease. , the toughness improves, but in this case, the ratio of α phase (ferrite phase) to γ phase (austenite phase) is 40 to 60.
It has been found that the effect is most enhanced when rolling is performed within the range of %. Therefore, it is meaningful to measure the crystal transformation rate of steel materials.

However, this method has many difficulties because it must be measured at high temperatures (approximately 700°C), and conventional methods use the relationship between the ratio of α and γ phases and magnetism. This is shown in FIG. In the figure, magnetic poles 1 are provided on the top and bottom of a thick plate 2 being rolled, and magnetic flux density measuring sensors 3 are interposed therebetween. 4 indicates the magnetic flux flowing through the center, and 5 indicates the magnetic flux along the surface of the plank. Magnetic flux (N
This method takes advantage of the fact that the magnetic flux density changes depending on the magnetism of the steel material (i.e., the ratio of α phase and γ phase) that passes through the magnetic flux (pole, south pole), and the magnetic flux density can be measured by a sensor such as a Hall element. Measuring.

However, with this method, the steel surface temperature first decreases and the ratio of the α phase in the surface layer increases, and as the magnetic permeability of the surface layer increases, the magnetic flux begins to flow along the surface, so it cannot penetrate sufficiently into the interior. Instead, the transformation rate of only the surface is measured;
There were some points where it was difficult to say that it was fully fulfilling its role. Therefore, the present inventors measured the transformation rate of a thick plate during rolling using the transformation rate measurement method described in JP-A-56-158941, and as a result of rolling when the transformation rate was optimal, the strength, It was possible to improve toughness, etc.

However, in this method, the longitudinal and transverse ultrasonic propagation velocities of the α and γ phases are constant regardless of temperature, but these propagation velocities change depending on the temperature. Since it is thought that there is a temperature distribution inside the thick steel plate in the middle, it was insufficient in terms of measuring the transformation rate in a precise sense.

The present invention describes a method for non-destructively measuring the crystal transformation rate of steel materials using electromagnetic ultrasonic waves (Japanese Patent Application Laid-Open No.
158941), with the aim of obtaining a means to more accurately measure the transformation rate and temperature distribution of steel materials by taking into account temperature changes in the ultrasonic propagation velocity.

FIG. 2 shows temperature change curves of the ultrasonic longitudinal sound velocity v ₁ and the ultrasonic shear wave sound velocity V _s inside the thick steel plate. The values of both sound velocities decrease as the temperature rises, but the rate of decrease is not proportional and changes independently. Points where the speed of sound changes significantly are points where transformation occurs, and according to this, if you measure the speed of sound, you can determine the temperature and, in turn, measure the transformation point.

Furthermore, when the temperature distribution in the thickness direction inside a thick steel plate was measured in various cases, it was found that it can be approximated as approximately quadratic and approximately symmetrical with respect to the center of the plate. A diagram based on this approximation is shown in FIG. 3, and when this is expressed as an equation, equation (1) is obtained.

θ (x) = 4 (θ _s - θ _c ) / D ² (x - D / 2) ² + θ _c ... (1) where, θ (x): From the metal plate (thick steel plate) surface to the thickness direction _Temperature at _distance x to Thick steel plate) Distance from the surface in the thickness direction.

Therefore, as shown in FIG. 2, it is known that the sound velocities v ₁ and v _s of ultrasonic longitudinal waves and transverse waves are given as a function of temperature for each steel type as shown in the following equation.

v ₁ = v ₁ (θ(x)) ...(2) v _s = v _s (θ(x)) ...(3) Longitudinal wave electromagnetic ultrasonic transducer 12 as shown in Fig. 4
And the longitudinal waves 14 and transverse waves 15 emitted from the transverse electromagnetic ultrasonic transducer 13 are α inside the thick steel plate 11.
The time it takes to pass through phase 16, γ phase 17, and α phase 18 in order, be reflected at the lower surface of the steel material, and return to the surface of the steel material.
T ₁ and T _s can be expressed by equations (4) and (5), respectively.

T ₁ =2∫ ^D ₀ d _x /v ₁ (θ(x)) ...(4) T _s =2∫ ^D ₀ d _x /v _s (θ(x)) ...(5) (4), In equation (5), if T ₁ and T _s are measured, the unknowns are θ included in v ₁ (θ(x)) and v _s (θ(x)).
_c ,
Since there is only θ _s , this can be found.

If θ _c and θ _s are known, the temperature distribution inside the thick steel plate can be determined from equation (1), and the transformation rate can also be easily estimated.

Therefore, the method for measuring the propagation time of longitudinal waves and transverse waves inside a steel material using electromagnetic ultrasonic waves described by the present inventors in JP-A-56-158941 will be explained in detail based on an example. As shown in FIG. 5, a magnetic core 30, a magnetic coil 31,
An electromagnetic ultrasonic sensor 35 composed of an ultrasonic generation/detection coil 32 is placed. The ultrasonic generation/detection coil 32 is electrically connected to a pulse current generator 37 . When a magnet power source 36 is connected to the magnet coil 31 and a current (20 A) is applied, the magnet core 30 is magnetized and a magnetic flux B (5 KG) is generated near the surface of the thick plate 21. In addition, when a pulse current generator 37 is connected to the ultrasonic generation/detection coil 32 and a pulse current (center frequency 500 KHz, peak value 1000 A) is applied, a pulse current (center frequency 500 KHz, peak value 1000 A) is applied near the surface of the thick plate 21 due to the law of electromagnetic induction. An induced current I flows in the direction.

This induced current I interacts with the vertical component _Bv of the magnetic flux B to generate a horizontal Lorentz force _FH . In addition, a vertical Lorentz force _Fv is generated by interaction with the horizontal component _BH . The horizontal force F _H produces a transverse ultrasound wave W _s and the vertical force
F _v produces longitudinal ultrasound W ₁ . W _s and W ₁ advance in the direction of the arrows, respectively, α phase 22, γ phase 23, α
Passing through the phase 24 in order, the waves are reflected by the lower surface of the slab, and the longitudinal waves with high sound speeds first return to the slab surface, followed by the transverse waves. The returning ultrasonic waves are detected by the ultrasonic wave generation/detection coil using a principle completely opposite to that used when they were generated, and become an electrical signal.

Since ultrasonic waves are transmitted and received based on this principle, surface irregularities do not pose any particular problem. The detected electrical signal is amplified by an amplifier 45,
displayed on the oscilloscope 40. In the figure, 41 is a wave memory, 42 is a computer, and 43 is a display. In the oscilloscope display in Fig. 5, P is the waveform of the pulsed current passed from the pulsed current generator to the ultrasonic generation detection coil 32 to generate ultrasonic waves, and L is the waveform of the pulsed current that is reflected from the bottom surface and returns. This is the waveform of the longitudinal wave _W1 detected by the ultrasonic generation detection coil 32. Similarly, S is the waveform of the transverse wave _Ws . T ₁ is the propagation time required for the longitudinal wave to reciprocate inside the stainless steel rub 21, and T _s is the propagation time of the transverse wave. Therefore, by measuring T ₁ and T _s using this method and measuring the plate thickness D using an can also be easily specified.

However, v ₁ and v _s in equations (2) and (3) are complex functions, and since they are integrated, (1) ~
It is not easy to find the unknowns θ _s and θ _c using equation (5). Therefore, since it was actually determined by trial and error using a computer, the method will be explained using an example using a thick plate.

FIG. 6 is a diagram showing the logic for obtaining θ _s and θ _c and determining the transformation rate, and 50 indicates a computer section. The relationship between temperature, ultrasonic longitudinal wave sound velocity, and transverse wave sound velocity is stored in the storage device 51 for each type of steel. By the electromagnetic ultrasonic longitudinal wave and transverse wave propagation time measurement device 52,
Measure the round trip propagation time (T ₁ , T _s ) inside the thick plate,
The data is input to the comparison section 55. Further, the plate thickness is measured using an X-ray thickness meter 53 and inputted to the calculation section 54. Therefore, the initial values (θ _s , θ _c ) are given to the calculation unit 54, which calculates (T ₁ , T _s ) using equations (4) and (5), and the comparison unit 55 calculates the previous values (T ₁ , T _s ) is compared with the measured value, and if it is within the setting error range, (θ _s , θ _c ) is determined. However, if it is outside the setting error range, (θ _s , θ _c ) is changed and fed back to the calculation unit 54, and the same operation is repeated again until (T ₁ , T _s ) falls within the setting error range, and (θ _s , θ _c ) Determine.

The determined (θ _s , θ _c ) are entered into the transformation rate calculation section 56 . Here, first, the temperature distribution in the thickness direction of the thick plate is calculated using equation (1) and displayed on the display device 57. In addition, by memorizing the transformation temperature θ _p for each type of steel in advance and setting θ (x) = θ _p in equation (1), the thickness x _p of the α phase shown in Fig. 4 can be obtained using the following equation. The metamorphosis rate is determined and displayed on the display device 57.

(Transformation rate) = 2x _p /D This transformation rate is the transformation rate in the thickness direction only in the area where the electromagnetic ultrasonic sensor is located on the top surface of the plate, but it can be measured by scanning the sensor in the width direction. The transformation status of the cross section of a thick steel plate as shown in the figure can be seen two-dimensionally. This makes it possible to measure the transformation rate based on the area ratio. This result is also displayed on the display device 57.
can be displayed.

As described above, according to the present method, the temperature distribution and transformation rate inside the steel material can be measured. It goes without saying that the temperature distribution can be similarly measured by this method regardless of whether the internal temperatures of the steel material are all below or above the transformation point.

In the above method, calculations were performed by trial and error during actual operation, but (T ₁ , T _s ) were measured in advance with various combinations of steel type, temperature, and plate thickness, and (θ _s ) was calculated using the same logic as above. , θ _c ) and (T ₁ , T _s )
The relationship between and (θ _s , θ _c ) is memorized in the computer, and
(T ₁ , T _s ) was measured during actual operation, and the steel type at that time,
A method may also be used in which (θ _s , θ _c ) corresponding to the measured values of (T ₁ , T _s ) are selected from a file that matches the plate thickness.

In Fig. 5, as a typical example, we have described the case where one electromagnetic ultrasonic sensor generates and detects longitudinal and transverse ultrasonic waves. The purpose can also be achieved using two sensors.

Furthermore, in Figure 5, the time taken for the ultrasonic wave to travel back and forth was measured, but the one-way propagation time could also be measured by placing a sensor dedicated to ultrasonic generation on the top surface and a sensor dedicated to detection on the bottom surface (4), (5) ) can be changed to equations (6) and (7), respectively, to achieve the objective.

T ₁ =∫ ^D ₀ d _x /v ₁ (θ(x)) ...(6) T _s =∫ ^D ₀ d _x /v _s (θ(x)) ...(7) In this case, each The sensor may be of a dual type for both longitudinal and transverse waves, or two sensors dedicated to each type may be used.
The purpose can be achieved even if used in combination.

The present inventors measured the transformation rate of a thick steel plate during rolling using the transformation rate measuring method described above, and performed rolling when the transformation rate was optimal.
The strength, toughness, etc. were further improved compared to the results obtained when rolling was controlled using the transformation rate measurement method described in No. 158941.

[Brief explanation of drawings]

Figure 1 is a diagram explaining measurement using the conventional method, Figure 2 is a diagram showing the relationship between ultrasonic longitudinal waves and transverse sound waves with temperature, Figure 3 is an approximate diagram of the temperature distribution in the thickness direction of a thick steel plate, and Figure 4 Figure 5 is a diagram showing the propagation of electromagnetic ultrasonic waves in a thick steel plate in the process of transformation, Figure 5 is a diagram showing longitudinal wave and transverse wave propagation time measurements, Figure 6 is a diagram showing the method of implementing the present invention, and Figure 7 is a cross-sectional view of a thick steel plate. be. 1: Magnetic pole, 2: Thick plate, 3: Sensor, 4: Magnetic flux, 5: Magnetic flux, 11: Thick steel plate, 12: Longitudinal wave electromagnetic ultrasonic transducer, 13: Transverse wave electromagnetic ultrasonic transducer, 1
4: Longitudinal wave, 15: Transverse wave, 16: α phase, 17: β
Phase, 18: α phase, 21: Thick plate, 22: α phase, 2
3: γ phase, 24: α phase, 30: magnetic core,
31: Magnetic coil, 32: Ultrasonic generation/detection coil, 35: Electromagnetic ultrasonic sensor, 36: Power supply, 37: Pulse current generator, 40: Oscilloscope, 41: Wave memory, 43: Display, 4
5: Amplifier, 50: Computer, 52: Ultrasonic longitudinal wave
Transverse wave propagation time measuring device, 53: X-ray thickness meter, 5
7: Display device.

Claims (1)

[Claims] 1. Transmitting longitudinal ultrasound waves and transverse ultrasound waves in the thickness direction of a metal material having multiple types of structures, and propagating the longitudinal ultrasound waves and shear wave ultrasound waves in the thickness direction of the metal material. Detect the times T ₁ and T _s and the propagation time
T ₁ , T _s and the relationship between temperature and ultrasonic longitudinal sound velocity v ₁ and ultrasonic transverse sound velocity V _s for each type of steel, and the separately measured thickness D of the metal material and metal From the material surface temperature θ _s and the initial value of the temperature θ _c at the center in the thickness direction, calculate the metal material surface temperature θ _s , the temperature θ _c at the center in the thickness direction, and the temperature distribution in the thickness direction using the following formula, and calculate the temperature distribution. The internal temperature and structure of the metal material are characterized in that the thickness x _p of the structure after transformation is determined from the transformation temperature θ _p of each steel type stored in a storage device separately, and the transformation rate is determined from this. How to measure. T ₁ =2∫ ^D ₀ dx/{v ₁ (θ(x))} T _s =2∫ ^D ₀ dx/{v _s (θ(x))} θ(x) = [4(θ _s −θ _c )]/D ²・(x-D/2)
² +
θ _c where, T ₁ : Propagation time of longitudinal ultrasonic wave in the thickness direction of metal material T _s : Propagation time of shear wave ultrasonic wave in the thickness direction of metal material V ₁ : Ultrasonic longitudinal wave sound velocity V _s : Ultrasonic shear wave Speed of sound x: Distance in the thickness direction from the metal material surface θ(x): Temperature at distance x in the thickness direction from the metal material surface θ _s : Metal material surface temperature θ _c : Temperature at the center of the metal material in the thickness direction D: Metal material thickness