JPH0145864B2 - - Google Patents

Description

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

The cross-sectional macrostructure of a continuously cast ferritic stainless steel slab is divided into a columnar crystal part that grows inward from the surface and an equiaxed crystal part with random crystal orientation. This is shown in FIG.
In FIG. 1, when the thickness of the slab is D and the thickness of the equiaxed crystal portion is d, F=d/D is called the equiaxed crystal ratio of the slab.

The equiaxed crystallinity F has a close relationship with the quality of the stainless steel thin plate product produced by rolling the slab, and if the equiaxed crystallinity F is less than approximately 50%, the deep drawing process of the stainless steel thin plate will be difficult. It has been found that wrinkles, called ridging, sometimes occur, significantly reducing commercial value or rendering the product unusable.

Therefore, if the equiaxed crystal rate is measured early using the equiaxed crystal rate measuring method as described in Japanese Patent Application No. 55-62306, the slab can be manufactured into a thin plate even if the equiaxed crystal rate is less than 50%. It is possible to take measures to prevent ridging before it occurs.

However, in this method, the columnar crystals in the slab have a constant crystal orientation (<100>
This paper describes a method for measuring equiaxed crystallinity from the propagation time ratio of longitudinal ultrasound waves and transverse ultrasound waves in the slab thickness direction when the slab is growing in the slab thickness direction.

However, the growth direction of the columnar crystals is closely related to the temperature gradient within the slab, and the columnar crystals may not only grow substantially perpendicular to the slab surface but also grow at an angle. The situation is shown in Figure 2.

When the columnar crystals grow obliquely, the ultrasonic sound speed propagating through the columnar crystal portion is different from the ultrasonic sound speed when the columnar crystals grow perpendicular to the surface. FIG. 3 shows the results of measuring the equiaxed crystal ratio by the method described in Japanese Patent Application No. 55-62306 using the inclination angle of the columnar crystals as a parameter. In the figure, 1 indicates the case where θ is 0 to 5 degrees, and 2 indicates the case where θ is 15 to 20 degrees.
In the above method, even if the longitudinal wave/transverse wave propagation time ratio is the same, the value of equiaxed crystallinity varies depending on the inclination angle of the columnar crystal, and the lower the equiaxed crystallinity of the slab, the larger the measurement error. There is a problem that a predetermined measurement accuracy cannot be maintained.

Therefore, the present invention transmits a longitudinal electromagnetic ultrasonic wave and two transverse electromagnetic ultrasonic waves linearly polarized in the length [L] direction and width [C] direction of the slab, and propagates each ultrasonic wave in the thickness direction of the slab. To provide a highly accurate equiaxed crystal rate measurement method that is not affected by the tilt angle of the columnar crystals by measuring time and measuring the tilt angle of the columnar crystals and the equiaxed crystal rate based on the propagation time. It is something.

FIG. 4 shows a principle diagram of equiaxed crystallinity measurement according to the present invention. Magnetic cores 5-1, 5-2, 5- are placed near the surface of stainless steel slab (200 mm thick) 4.
3. Magnet coil 6-1, 6-2, 6-
3. Ultrasonic generation detection coils 7-1, 7-2, 7
-Longitudinal wave electromagnetic ultrasonic sensor 8 consisting of 3.
and two linearly polarized transverse electromagnetic ultrasonic sensors 9,
Place 10. A sensor 9 generates and detects linearly polarized transverse ultrasonic waves deflected in the longitudinal direction (L direction) of the slab, and 10 in the width direction (C direction).

When the magnet coil is connected to the magnet power source 11 and current is applied, a horizontal magnetic flux Bx is generated near the surface of the stainless steel slab by the longitudinal wave electromagnetic ultrasonic sensor 8, and the linear deflection transverse wave sensor 9,
10, a magnetic velocity Bz in the vertical direction occurs. In addition, when the pulse current generator 12 is connected to the ultrasonic generation detection coils 7-1, 7-2, and 7-3 and a high-frequency pulse current is passed, the electromagnetic ultrasonic sensor 10 An induced current Ix in the horizontal direction is generated in the electromagnetic ultrasonic sensors 8 and 9, and an induced current Iy perpendicular to the plane of the paper is generated near the surface of the stainless steel slab.

These induced currents Ix and Iy interact with magnetic fluxes Bz and Bx, respectively, to generate Lorentz forces Fy, Fx, and Fz. The Lorentz force Fy produces a linearly polarized transverse ultrasonic wave W _sc deflected in the C direction, and Fx produces a linearly polarized transverse ultrasonic wave W _SL deflected in the L direction. Further, Fz generates a longitudinal ultrasonic wave W _L. W _L , W _SL , and W _SC travel in the direction of the arrows, pass through the columnar crystal portion and the equiaxed crystal portion, are reflected at the bottom surface of the slab, and return to the slab surface.

The ultrasonic waves are detected by the ultrasonic generation detection coil and turned into electrical signals based on the completely opposite principle to that used when they are generated.

The detected electrical signal is amplified by an amplifier 13, converted into a digital signal by a wave memory 14, and then taken into a minicomputer 17 via an interface 16.

On the other hand, the digital signal is converted back into an analog signal within the wave memory, and the oscilloscope 1
5 can also display the signal waveform. The minicomputer 17 calculates the propagation time of the longitudinal wave and the two linearly polarized transverse ultrasonic waves within the slab based on the signal waveforms, and calculates the tilt angle of the columnar crystal using the method described below based on the propagation time. It is possible to determine the equiaxed crystallinity corresponding to the tilt angle.

In the oscilloscope display in Fig. 4, P is the transmission waveform corresponding to the pulse current passed from the pulse current generator to the ultrasonic generation detection coil in order to generate ultrasonic waves, and L is the waveform reflected from the bottom surface of the slab. Longitudinal waves detected by ultrasonic generation detection coil
This is the waveform of _WL . Similarly, SL is the waveform of a linearly polarized transverse wave W _SL deflected in the L direction, and SC is a waveform of a linearly polarized transverse wave W _SC deflected in the C direction.

In addition, 2T _L is the propagation time required for a longitudinal wave to travel back and forth within the stainless steel slab, and similarly, 2T _SL
is the propagation time of a linearly polarized transverse wave polarized in the L direction,
2T _SC is the propagation time of a linearly polarized shear wave polarized in the C direction.

Here, the inclination angle of the columnar crystals of the stainless steel slab is θ, the sound velocity of longitudinal waves propagating through the columnar crystals, the sound velocity of linearly polarized transverse waves deflected in the L direction, and the sound velocity of linearly polarized transverse waves deflected in the C direction are respectively V _DL (θ ), V _DSL (θ),
Let V _DSC (θ) be _the longitudinal wave sound velocity propagating through the equiaxed crystal part. In addition, since the crystal orientation of the equiaxed crystal is random, the sound speed of linearly polarized transverse waves deflected in the L direction and the C direction propagating through the equiaxed crystal part is equal,
If the speed of sound is V _FS , the following formula holds true.

2T _L = 2 (D-d/V _DL (θ) + d/V _FL ) ...(1) 2T _SL = 2 (D-d/V _DSL (θ) + d/V _FS ) ...(2) 2T _SC = 2 (D-d/V _DSC (θ) + d/V _FS )...(3) Figure 5 shows the tilt angle θ of the columnar crystal and the linearly polarized transverse waves deflected in the L and C directions propagating through the columnar crystal part. speed of sound
It shows the relationship between V _DSL (θ) and V _DSC (θ).

The ultrasonic sound speed in both directions can be determined by cutting out columnar crystal parts with various inclinations from a slab with a predetermined thickness D', and then calculating the propagation time of linearly polarized transverse waves in the L and C directions based on the principle explained using Fig. 4. T _DSL ,
Measure T _DSC , V _DSL (θ) = D′/T _DSL (θ), V _DSC
It is calculated from the relationship (θ)=D′/T _DSC (θ).

Further, FIG. 6 shows the relationship between the inclination angle θ of the columnar crystal and the longitudinal wave sound velocity V _DL (θ) propagating through the columnar crystal portion.
V _DL (θ) is calculated using the same method as the transverse wave sound velocity: V _DL (θ) =
It was obtained from the relationship D′/T _DL (θ).

From FIGS. 5 and 6, it can be seen that there is a linear correlation between V _DL (θ), V _DSL (θ), and V _DSC (θ) and θ. Each of these relationships can be expressed by the following equations.

V _DL (θ) = αθ + β ... (4) V _DSL (θ) = aθ + b ... (5) V _DSC (θ) = pθ + q ... (6) Expressions (4), (5), and (6) Substituting into (1), (2), and (3), θ,
A three-dimensional simultaneous equation with D and d as unknowns is obtained,
By solving this equation, all unknowns can be derived. Note that since the equiaxed crystallinity F to be determined is F=d/D, the results of deriving θ and F are shown in equations (7) and (8).

θ−{(αq+pβ)X+(aβ+αb)Y+(aq+bp)Z
}/2 (αpX+aαY+apZ) ±[{αq+pβ)X+(aβ+αb)Y+(aq+bp)Z
} ² / -4 (αpX + aαY + apZ) (βqX + bβY + bqZ)] ^1
/2 /2 (αpX+aαY+apZ)...(7) However, X=T _L・V _FL −T _SC V _FS Y=T _SL V _FS −T _L V _FL Z=V _FL (T _SC −T _SL ) F= {1/αθ+β−1/aθ+b(T _L /(T _SL )}/
{(1/V _FS −1/aθ+b) (T _L /T _SL ) − (1/V _FL −
1/αθ+β)}...(8) Although θ is calculated as a binary value, it is assumed that θ>0.

α, β, a, b, p, q and in formulas (7) and (8)
V _FL and V _FS are constants determined experimentally.

Therefore, by measuring T _L , T _SL , and T _SC in a slab whose equiaxed crystal ratio is unknown, the tilt angle θ of the columnar crystals and the equiaxed crystal ratio F can be determined.

As described above, according to the present invention, it is possible to nondestructively measure the equiaxed crystallinity of a stainless steel slab on-line with a good measurement accuracy of about ±11 (%) without being affected by the tilt angle of columnar crystals. It becomes possible. Therefore, even if the equiaxed crystallinity of the slab is low (usually less than 50%), by early detection, it is possible to take measures to prevent ridging.
It has become clear that this method is extremely effective industrially.

In addition, in the example, a method for measuring equiaxed crystallinity is explained based on measuring the propagation time of ultrasonic waves reciprocating within the slab (i.e., reflection method), but it is not necessary to use a sensor for generating ultrasonic waves. On one side of the slab,
The purpose can also be achieved by placing a detection sensor on the opposite surface and measuring the one-way propagation time (ie, the transmission method).

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the macroetch structure of a slab cross section, Figure 2 is a macroetch diagram of a slab cross section with tilted columnar crystals, and Figure 3 is the equiaxed crystal ratio and longitudinal and transverse waves using the tilt angle of the columnar crystals as a parameter. Figure 4 is a diagram of the relationship between the propagation time ratio, and Figure 4 is a diagram of the principle of equiaxed crystallinity measurement using electromagnetic ultrasonic waves. Figure 5 is a diagram of the inclination angle of columnar crystals and the sound speed of linearly polarized transverse waves in the L and C directions propagating through the columnar crystals. FIG. 6 shows a relationship diagram between the inclination angle of a columnar crystal and the longitudinal sound velocity propagating through the columnar crystal portion. DESCRIPTION OF SYMBOLS 1... Column crystal part, 2... Equiaxed crystal part, 3... Column crystal part, 4... Stainless steel slab surface, 5... Magnet core, 6... Coil for magnet, 7...
Coil for ultrasonic generation detection, 8...Longitudinal wave electromagnetic ultrasonic sensor, 9...L direction linear polarization transverse wave electromagnetic ultrasonic sensor, 10...C direction linear polarization transverse wave electromagnetic ultrasonic sensor, 11...Pulse current generator , 12
... Magnetic power supply, 13 ... Multiplier, 14 ...
Wave memory, 15...Oscilloscope, 16
...Interface, 17...Mini computer.

Claims (1)

[Claims] 1. A longitudinal wave electromagnetic ultrasound wave and two transverse wave electromagnetic ultrasound waves linearly polarized in the length direction and the width direction of the metal material are penetrated into a metal material having two different types of structures including a columnar crystal structure, and these waves are The propagation time of each ultrasonic wave in the thickness direction of the metal material is measured, and the angle (θ) between the crystal axis of the columnar crystal in the metal material and the axis perpendicular to the surface of the metal material measured in advance is determined.
Based on the correlation between the velocity of the longitudinal ultrasound transmitted through the columnar crystal part and the structured ultrasound linearly polarized in the length direction and the width direction of the metal material, and the propagation time measurement results, the above two types are determined. A method for measuring the content ratio of two types of structures in a metal material, the method comprising measuring the content ratio of the structures.