JPS59147253A - On-line hardness measurement of steel plate - Google Patents

Abstract

PURPOSE:To measure the hardness of a steel plate with high accuracy, by correcting the thickness of the steel plate by measuring the intensity of the residual magnetism of the steel plate subjected to saturation magnetization. CONSTITUTION:A DC exciting electromagnet 2 is arranged in opposed relation to the surface of a continuously running steel plate 1 while the N-pole and the S-pole of the electromagnet 2 are arranged so as to be spaced apart to each other in the running direction of the steel plate 1 and the steel plate 1 is successively magnetized at the positions A-E thereof. By this constitution, even if the steel plate has been magnetized prior to advancing to the position A, it is subjected to saturation magnetization at the position B by the N-pole and demagnetized. Thereafter, said steel plate 1 is subjected to saturation magnetization in the reverse direction at the position D by the S-pole and finally possesses residual magnetization at the position E. The intensity of the residual magnetization is detected by a detector 4 and amplified by a converter 5 while the amplified magnetism is converted to hardness by performing the correction of the plate thickness to be recorded by a recorder 6.

Description

[Detailed description of the invention] The present invention relates to an online hardness measurement method for steel plates.

In general, the hardness of cold-rolled steel sheets and the like is often used as a control factor for its mechanical properties because it is related to its magnetic properties and the like.

In the past, various hardness measurement methods have been proposed that focus on the correlation between the magnetic properties of steel plates and hardness, in order to be able to continuously measure the hardness of steel plates online and non-destructively over their entire length. There is.

In the specification and drawings attached to Japanese Patent Application No. 56-200135, the applicant states that ``a steel plate and a DC-excited electromagnet are arranged facing each other in a state of relative movement, and both the positive and negative magnetic poles of the electromagnet are moved relative to each other. A steel plate part that is spaced apart in the same direction and saturated magnetized by one magnetic pole of the electromagnet is saturated in the opposite direction by the other magnetic pole of the electromagnet, and the strength of residual magnetism in the saturated magnetized part is measured. We have already proposed a method for measuring the hardness of G18 on-line, which determines the hardness of the part based on the strength of residual magnetism.

According to the hardness measuring method already proposed by the applicant, the method does not involve sandwiching the steel plate.

It becomes possible to dispose a steel plate pressure measuring device that passes the steel plate in close contact with a conveyance roller or the like, and there is no variation in measurement accuracy due to fluctuations in the steel plate pass line. Further, instead of magnetizing the steel plate by sandwiching it, it becomes possible to saturate the steel plate.

The correlation between the hardness meter output and Rockwell hardness according to the hardness measurement method already proposed by the applicant is as shown in FIG. It is 5.

However, the hardness measuring method already proposed by the applicant cannot be used for standard determination of products of annealing furnaces, which require a measurement accuracy of ±2 in terms of Rockwell hardness, for example.

An object of the present invention is to provide an online hardness measurement method that enables the hardness of a steel plate to be measured with higher precision.

In order to achieve the above object, the online hardness measurement method for a steel plate according to the present invention involves arranging a steel plate and a DC-excited electromagnet to face each other in a state of relative movement, and aligning both the positive and negative magnetic poles of the electromagnet in the direction of the relative movement. A steel plate portion that is spaced apart and saturated magnetized by one magnetic pole of the 'flE stone is trap saturated magnetized in the opposite direction by the other magnetic pole of the electromagnet, and the strength of residual magnetism of the saturated magnetized steel plate portion is measured, The hardness of the steel plate portion is determined based on the correlation between the predetermined thickness of the steel plate, the strength of the residual magnetism, and the hardness of the steel plate.

The present invention will be explained in more detail below.

FIG. 2 is an explanatory diagram showing a measuring device used in carrying out the present invention. For the surface of the continuously running steel plate 10,
Direct-current excited electromagnets 2 are disposed to face each other, and the positive magnetic pole (N'Wi,) and negative magnetic pole (S pole) of the electromagnets are spaced apart in the running direction of the steel plate 10.

Therefore, any measurement point P on the steel plate 1 moves under the influence of the magnetic field lines 3 generated from the positive magnetic pole to the negative magnetic pole of the electromagnet 2, and arrives at one position A to one position E in sequence according to the history shown in FIG. be magnetized. In Figure 3, the horizontal axis shows the strength of the magnetic field X for magnetization, and the vertical axis shows the density Y of the magnetic field remaining in the steel plate 1 after being magnetized. Even if it is magnetized before entering, it is demagnetized and demagnetized by the positive magnetic pole at position B, then saturated magnetized in the opposite direction by the negative magnetic pole at position B, and finally loses residual magnetism at position E. Possess.

In this way, the steel plate 1 that passes under the influence of the magnetic field lines of the electromagnet 2 and has residual magnetism has the strength of the residual magnetism detected by the detector 4.

FIG. 4 is an explanatory diagram showing the actual magnetization state of the steel plate 1. As shown in FIG. In FIG. 4, the spin (direction of magnetization) of the steel plate 1 at position A is completely random.

When this steel plate 1 comes to position C, it becomes intermediate between the positive magnetic pole and the negative magnetic pole, and a strong external magnetic field is applied to the traveling direction of the steel plate 1, so that the spins of the steel plate 1 are aligned in one direction.

After that, when the steel plate 1 comes to the position, the spin of the steel plate 1 is all upward.9. Furthermore, when the steel plate 1 comes to position E, the upward spin tries to return to a random direction. Soft material (
For the annealed material IA, the direction of this spin changes easily, and for the hard material (unannealed material) 1B, the spin direction does not change easily. If this magnetization state is shown by plotting the strength X of the magnetizing magnetic field on the horizontal axis and the density Y of the magnetic field remaining in the steel plates iA and 1B on the vertical axis, the result will be as shown in FIG. Detector 4 is connected to Y in FIG. 5 for steel plates IA and 18, respectively.
Detect the strength of residual magnetism shown at point A + point YB.

The curve L formed by the magnetizing magnetic field strength X and the residual magnetic field density Y shown in FIG. Accordingly, the third
The curve shown in the figure tends to be sloped. In other words, this demagnetizing field is related to the size of the object to be examined, and in particular, since the apparatus used to implement the present invention aims to direct the magnetization of the steel plate in the thickness direction, the magnitude of the demagnetizing field is related to the thickness of the steel plate. The quality will be different. The thicker the plate (the thicker it is, the more it requires a strong external magnetic field to magnetize the steel plate. Since the demagnetizing field is proportional to the strength of one magnetic pole, it is natural that the thicker the plate, the more the demagnetizing field will increase by 5). As the demagnetizing field increases, the slope of the curve formed by the magnetizing magnetic field strength X and the residual magnetic field density Y becomes more sloped. In contrast, the curve shown in Figure 5 shows the magnetization state actually measured by this device (the magnetizer, detector, and object are fixed). Only the subject moves.The reverse is also possible)
in a dynamic magnetic field. This is a history curve diagram showing the course of magnetization of a steel plate, and shows history curves for a soft material and a hard material with the same plate thickness (*i4 plate 1A is a soft material, 1B is a hard material).

That is, the magnetizing magnetic field strength X and the residual magnetic field density Y of the thin annealed material 1C and the thick annealed material 1D.
The curves formed by Y and Y in FIG. 6 are shown as shown in FIG.
The strength of residual magnetism shown at point c and point YD is detected. As shown in Figure 6, as the plate thickness increases, the strength of the magnetic field that magnetizes
The slope of the curve formed by Y and the density Y of the residual magnetic field becomes larger, and the strength of the detected residual magnetism becomes smaller. therefore.

As the plate thickness becomes thicker, the detected residual magnetism becomes smaller.
The residual magnetism is inversely proportional to the plate thickness.

As shown in Fig. 2, the detector 4 has sensors for detecting N and S poles, and both sensors are balanced when there is no magnetic field around them, and their output is It's almost zero. Since the steel plate 1 is magnetized to the north pole as described above, when this steel plate 1 approaches both of the above sensors,
The coil of the N-pole detection sensor is excited by the N-pole of the steel plate 1, the balance between the coils of both sensors is disrupted, a current flows through the excitation side coil, and this current value is displayed on the Gauss Make 4A. The strength of the residual magnetism thus detected by the detector 4 is amplified by the converter 5, corrected for the plate thickness, converted into hardness, and recorded in the recorder 6.

Here, since the strength of the residual magnetism of the steel plate 1 is correlated with the hardness of the steel plate 1 as shown below, it is possible to determine the hardness of the steel plate 1 from the recording results of the recorder 6. Become. That is, the relationship between residual magnetism and hardness can be considered by considering the stage of crystal grains between the two.

Petch states that there is the following relationship between the yield point of steel and the grain size.

(yLYP = ao+f(I-%
(1) However, σLYP is the lower yield point, σ0 is the lower yield point of the single crystal, ■ is the diameter of the single crystal, and K is a constant. Moreover, since the rolling hardness measures plastic deformation resistance, the yield point in the above equation (1,) can be replaced with accuracy. In other words, there is a correlation between hardness and crystal grain size. Next trap.

Considering the relationship between residual magnetism and crystal grains, larger crystal grains are more easily magnetized, and smaller crystal grains are less likely to be magnetized. Since the number of crystal grains per unit area is small, residual magnetism is small. On the other hand, when the crystal grains are small, the number of crystal grains per unit area is large, so the residual magnetism becomes large. That is, the larger the residual magnetism, the higher the hardness, and the smaller the residual magnetism, the lower the hardness. Hardness can be measured by measuring residual magnetism in this manner.

Therefore, the strength of the residual magnetism imparted to the steel plate by the measuring device used in the implementation of the present invention, that is, the uncorrected output V (V) of the measuring device, is determined by the plate thickness t (, m
Since it is inversely proportional to m), let C be a constant and α−
a, , [(If +b is a constant determined by the hardness H (HR30'f') of the steel plate, the following equation (2) holds true.

■−♀+α=presentation+al(+b
- (2) When an experimental formula for the relationship between the strength of the residual magnetism and the thickness and hardness of the steel plate was determined using actual experimental data, the following formula (8) was obtained.

V Engineering ■ Todan-1 L 3 (1””””””) (8) Figure 7 shows the strength of residual magnetism imparted to the steel plate by the measuring device used in implementing the present invention based on (8) 2 above. In other words, it shows the correspondence between the uncorrected output of the measuring device and the thickness of the steel plate. For example, if the plate thickness is 0.24 and the hardness meter output is 2.
．． In the case of OV, the hardness is 64 when read on the HR30T scale from the intersection of the two.

That is, it is possible to obtain a certain correlation among the thickness of the W4 plate, the strength of residual magnetism, and the hardness of the steel plate.

Therefore, in the present invention, the strength of the residual magnetism measured by the detector 4 of the measuring device, that is, the uncorrected output V of the measuring device, is By correcting the plate thickness t, it is possible to obtain a more reliable and accurate hardness meter output H.

H=30 (V+LO-4y, 0.21)
・・・・・・・・・(4) Figure 8 shows plate thickness of 0.24m.
a hardness meter output corrected by the present invention at x;
It is a diagram showing the relationship with Rockwell hardness. This eighth
According to the diagram.

The correspondence between the hardness meter output and the Rockwell hardness is very good, and the Rockwell hardness value is within the range of ±1 with respect to the calibration curve. That is, according to this hardness measurement method,
It becomes possible to measure the hardness of a steel plate with higher accuracy online, and it can be used, for example, to determine the standards for products in annealing furnaces.

As described above, the online hardness measurement method of a steel plate according to the present invention involves arranging a steel plate and a DC-excited electromagnet to face each other in a state of relative movement, and placing both the positive and negative magnetic poles of the electromagnet apart in the direction of the relative movement. , one plate part that is saturated magnetized by one magnetic pole of the electromagnet is saturated in the opposite direction by the other magnetic pole of the electromagnet, and the strength of residual magnetism of the saturation magnetized steel plate part is measured, and the strength of the residual magnetism is measured. The hardness of the steel plate portion is determined based on the correlation between the thickness of the steel plate, the strength of the residual magnetism, and the hardness of the steel plate.

Therefore, according to the present invention, it is possible to measure the hardness of a 1gA plate online with high precision.

[Brief explanation of drawings]

FIG. 1 is a diagram showing hardness measurement results by a hardness measurement method already proposed by the applicant, and FIG. 2 is an explanatory diagram showing a measuring device used in implementing the present invention. Fig. 3 is a history diagram showing the progress of magnetization of the steel plate by the measuring device shown in Fig. 2, Fig. 4 is an explanatory diagram showing the actual magnetization state of the steel plate measured by the measuring device shown in Fig. 2, and Fig. 5 is a history diagram showing the progress of magnetization of the steel plate by the measuring device shown in Fig. A history diagram showing the progress of magnetization of soft and hard materials using the measuring device shown in the figure.
Fig. 6 is a history diagram showing the course of magnetization of thick plate and thin plate material by the measuring device of Fig. 2, and Fig. 7 is the relationship between the thickness and hardness of steel plate and the uncorrected output of the hardness meter in the present invention. Figure 8 is a diagram showing the relationship between the hardness meter output and Rockwell hardness according to the present invention (& for thickness 0.24 m)
It is. i, IA, 1B, ic, i・0... steel plate, 2
...electromagnet, 3...magnetic field lines, 4...detector. Agent Patent Attorney Osamu Shiokawa Fig. 2 Fig. 4 Fig. 5 Fig. 7 Single Nucleus [mm] Fig. 8 Hardness Pulling Force (HR-307)

Claims (1)

[Claims] (The 11e plate and the DC-excited electromagnet are arranged facing each other in a state of relative movement, and the positive and negative magnetic poles of the electromagnet are spaced apart in the direction of relative movement, and the steel plate portion that is saturated magnetized by one of the magnetic poles of the electromagnet is The other magnetic pole of the electromagnet saturates the steel plate in the opposite direction, measures the strength of the residual magnetism in the saturated magnetized steel plate, and determines the correlation between the predetermined thickness of the steel plate, the strength of the residual magnetism, and the hardness of the steel plate. A steel plate online hardness measurement method for determining the hardness of a steel plate portion based on a relationship.