JPH11230921A - Method for measuring austenite in steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To implement a highly accurate and simple method for quantitatively analyzing austenite in steel, by measuring the diffraction intensities of a plurality of crystalline lattice surfaces belonging to each phase as providing biaxial rotation to the steel, correcting them by P-values, and computing the amount of the austenite. SOLUTION: A P-value is an observed diffraction intensity from each crystalline surface indicated by a ratio to a diffraction intensity in a non-oriented state. A method to suppress the effects of the texture of steel at the time of measuring the amount of austenite in the steel through the use of an x-ray diffraction method is studied. The measurement of diffraction intensities under biaxial rotation steadily functions with respect to even a cold rolled steel sheet, etc., with a remarkable texture, but it is difficult to obtain diffraction intensities corresponding to a non-oriented state only by this operation. There, each P-value is computed from the balance of each diffraction intensity measured as providing biaxial rotation for a sample, and each diffraction intensity is divided by a corresponding P-value. By this, diffraction intensities corresponding to a non- oriented state is computed and is applied to theoretical computation to improve measuring accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for accurately measuring the amount of austenite in a steel having a mixed structure of a ferrite phase and an austenite phase by using an X-ray diffraction method.

[0002]

2. Description of the Related Art Since the amount of austenite in steel greatly affects the ductility and toughness of steel, it is very important to accurately measure the amount of austenite in terms of improvement of steel material and quality control. The ferrite phase (hereinafter abbreviated as α phase) and the austenite phase (hereinafter abbreviated as γ phase) are so-called “polymorphs” having substantially the same composition and different crystal structures. Therefore, elemental analysis methods such as X-ray fluorescence analysis are not suitable for these quantitative analyses.

[0003] Therefore, X-ray diffraction, which is sensitive to the type of phase, is widely used for the determination of the γ phase contained in steel (for the principle of measurement, for example, BD Cullity, Elements of
X-ray Diffraction, Addison-Wesley Publishing Co.
(1956) 388-396. ). This method is based on Cohen's theoretical calculation (B.
L. Averbach and M. Cohen, Trans.AIME, 176 (1948)
See 401; hereinafter abbreviated as theoretical calculation. ) Based on.

[0004] Measurement accuracy when the X-ray diffraction method is applied to an actual steel sheet or the like is strongly affected by the texture of the sample steel. This effect is particularly large in a cold-rolled steel sheet having a remarkable texture, and the measurement result significantly changes depending on the combination of lattice planes which should not be affected in a non-oriented state. In order to alleviate the influence of such texture, the steel plate is measured by applying an in-plane rotation to the steel plate. Even in this case, the (200) plane of the α phase (hereinafter, referred to as such The combination of a phase and a lattice plane is abbreviated as α (200).) The result of evaluating the volume ratio of 11% to the combination of γ (111) is α (200) and γ (220). 79 in combination
%, And accurate measurement cannot be performed.

[0005] From such a background, the following methods have been proposed in order to obtain a highly accurate quantitative result excluding the influence of the texture of steel.

(1) A method of calculating a diffraction intensity corresponding to a non-oriented state from a pole figure and using the calculated diffraction intensity for a theoretical calculation (SL Lo)
pata and EB Kula, Trans. AIME, 233 (1965) 288;
PR Morris, Trans. AIME, 239 (1967) 1586; CR H
ouska and V. Rao, Met. Trans, 9A (1978) 1483, etc.)

(2) A method in which a sample (or an X-ray incident angle) is given a biaxial rotation consisting of an in-plane rotation and an inclination to measure a diffraction intensity close to a non-oriented state and use this for theoretical calculation (RL Miller , Trans. ASM 57 (1964) 892; SL L
opata and EB Kula, Trans.AIME, 233 (1965) 288
other)

(3) A method of measuring the intensities of a large number of diffraction lines belonging to each phase and improving the theoretical calculation to perform a kind of averaging process to calculate a value in which the influence of texture is suppressed (R .
D. Arnell, JISI, 206 (1968) 1035; MJ Dickson,
J. Appl. Cryst. 2 (1969) 176; J. Burke and DW H
arvey, JISI, 208 (1970) 779; Fujino et al. Iron and Steel 67 (19
81) 239; JP-A-55-158545, JP-A-55-164341, etc.)

(4) A calculation method based on an empirical rule that the influence of texture can be suppressed by using a combination of the intensity of a specific diffraction line belonging to each phase in a theoretical calculation (J. Durni
n andK. A. Ridal, JISI. 206 (1968) 669; CJ Ball
and PM Kelly, Metal Sci. 16 (1982) 332 and others)

[0010]

SUMMARY OF THE INVENTION
The methods (1) to (4) have the following problems, respectively. (1) is a highly complete method, but has a problem that it is difficult to implement easily. That is, in order to calculate the diffraction intensity corresponding to the non-oriented state using this method, a complete pole figure must be measured in principle. In order to measure a complete pole figure, the sample needs to be thinned to about several tens of μm for the sake of measuring the diffraction intensity during transmission measurement. Bonarski et al. (J. Bonarski, M. Wrobel and K. Pawl
ik, Scr. Metall. Mater 25 (1991) 1401) uses ODF (azimuth distribution function) from incomplete pole figure measured only by reflection method.
This paper describes a method to save the labor of sample preparation by reproducing a complete pole figure by analysis. However, even with this method, at least two types of pole figures must be measured in order to calculate the diffraction intensities corresponding to the α and γ phases, so that the problem that the measurement takes a long time has not been solved.

The method (2) can be easily carried out using a commercially available attachment (for example, a rotary vibration sample table manufactured by Rigaku Denki) and the measurement time is almost the same as that of a normal X-ray diffraction pattern measurement. It is simple and short. Also,
Since the sample is mechanically rotated to approach a non-oriented state in units of individual crystal grains in the sample, a steady effect can be obtained. Therefore, this method is very effective for the determination of the γ phase in steel having only a relatively mild texture such as steel.

However, it is difficult to rotate the sample uniformly in all directions by this mechanical method.
Sufficient measurement accuracy cannot be obtained for cold rolled steel sheets with a remarkable texture. For example, according to this method, even if the combination of α (200) and γ (200) is evaluated as 11%, if the combination of surfaces is changed to α (220) and γ (222), 15%
It is unavoidable that the measurement result changes by about 30% depending on the combination of surfaces, such as changing to.

The method (3) is a method of calculating based on the assumption that all diffraction intensities are preserved. This method
It is very effective for steel having only a relatively mild texture, but exhibits only a certain suppression effect on cold-rolled steel sheets and the like that have a remarkable texture. The reason is that the content assumed in this method breaks down when the texture is significant. For example, when measuring a single crystal which is the limit of the texture, an extreme difference occurs in the total diffraction intensity depending on whether the single crystal is arranged so as to satisfy the diffraction condition. As can be inferred from this, if the texture is significant, the assumption that the total diffraction intensity is preserved no longer holds.

The method (4) is based mainly on empirical rules, and it has been reported that large errors occur when the texture is significant (for example, MJ Dickson, J. Ap.
pl. Cryst. 2 (1969) 176). There has been a proposal to select a combination of surfaces based on the assumption that the orientation relationship during α-γ transformation is maintained (CJ Ball and PM Kel
ly, Metal Sci. 16 (1982) 332), and this method is not sufficient, as will be shown in the examples below.

As described above, at present, there is no known method for accurately measuring the amount of austenite in a steel sheet or a steel material exhibiting a remarkable texture by using an X-ray diffraction method. The present invention has been made in view of such circumstances, and even for a steel sheet or a steel material having a remarkable texture such as a cold-rolled steel sheet, an austenitic steel in steel that can easily obtain a highly accurate measurement result. An object of the present invention is to provide a quantitative analysis method.

[0016]

The gist of the present invention is to measure (i) a diffraction intensity close to a non-oriented state while giving a sample a biaxial rotation consisting of an in-plane rotation and an inclination, and (ii) to measure the diffraction intensity. The effect of the remaining texture was evaluated by the P value (MJ Dickson: J. Appl.
yst. 2 (1969) 176) and apply it to the theoretical calculation to easily obtain high-precision measurement results even for steel sheets or steel materials showing a remarkable texture. .

[0017] That is, the object is to measure the amount of austenite in a steel having a mixed structure of a ferrite phase and an austenite phase by using an X-ray diffraction method. This problem is solved by a method for measuring austenite in steel, characterized in that, after measuring the diffraction intensity of the crystal lattice plane, the austenite amount is calculated by correcting each diffraction intensity with a P value.

At this time, the most accurate measurement result can be obtained by performing measurement using characteristic X-rays of cobalt.

Here, the P value refers to the MJ D
ickson: As described in J. Appl. Cryst. 2 (1969) 176, the measured diffraction intensity from each crystal plane is expressed as a ratio to the diffraction intensity with respect to the non-oriented state. If P = 1, it corresponds to non-orientation, and if P> 1, the crystal plane is P
It is preferentially oriented by a factor of two, and if P <1, it means that it is preferentially avoided.

The present inventors have conducted a detailed study on a method for suppressing the influence of the texture of steel when measuring the amount of austenite in steel by X-ray diffraction. "Measurement of diffraction intensity under biaxial rotation" shown in (i) of the feature of the present invention
Is the same as the above-mentioned method of the prior art (2). As described above, this method functions steadily even for a cold-rolled steel sheet having a remarkable texture, but it is difficult to obtain a diffraction intensity corresponding to a non-oriented state only by this operation. Therefore, the present inventors calculate each P value from the balance of each diffraction intensity obtained through the operation (i), and divide each diffraction intensity by the corresponding P value to correspond to the non-oriented state. By calculating the diffraction intensity and applying it to the theoretical calculation, it has been found that the measurement accuracy is improved. According to the present invention, the amount of austenite is uniquely determined irrespective of the combination of surfaces.

According to the results of calculation by the present inventors, the correction based on the P value is mathematically equivalent to the calculation formula of Arnell (RD Arnell: JISI, 206 (1968) 1035) which is relatively frequently used today. Are equivalent. However, even in Arnell's method, there is a limit to the degree of orientation that can be corrected as described above, and if the orientation is strong, the accuracy becomes poor. In the present invention, the normal Arnell method is applied in that a correction by a P value equivalent to the Arnell method is applied to remove the influence of a relatively small texture remaining on the diffraction intensity measured under biaxial rotation. Method is very different,
Very accurate measurement results can be obtained compared to the case where Arnell's method is used alone. It is also possible to apply the P-value correction to the diffraction intensity measured by a normal method, but in this case, it is equivalent to the method of Arnell, and a highly accurate measurement result as obtained by the present invention is obtained. I can't.

The present inventors have conducted detailed studies on the types of X-rays to be used in operating the quantitative method according to the first aspect. As a result, it has been found that utilization of characteristic X-rays of cobalt is most preferable.

In the field of thin plates, several vol% of retained austenite is often measured, and it is important to maintain the measurement accuracy of diffraction intensity. In particular, in the quantitative method according to the first aspect, since it is necessary to measure the diffraction intensity while rotating in two axes, it is desirable to consider the following points in order to perform accurate measurement. (i) Since the sample is biaxially rotated, the width of the diffraction peaks is systematically widened, the separation of adjacent α-phase and γ-phase peaks becomes poor, and the measurement accuracy of the respective diffraction intensities tends to deteriorate. (ii) Since the measurement area satisfying the diffraction condition is narrower than the case where the two-axis rotation is not performed, the S / N ratio of the diffraction pattern is likely to be deteriorated. (iii) If accurate P-value measurement cannot be performed in a state where the influence of the texture is reduced by biaxial rotation, the validity of the quantitative result will be impaired.

Therefore, it is important to select an X-ray source in consideration of these three points in measurement. The present inventors have studied characteristic X-rays of Mo, Cu, Co, Fe, and Cr from such a viewpoint, and as a result, have found that characteristic X-rays of Co are most preferable.

[0025]

EXAMPLES The effects of the present invention will be described below based on examples. (Example 1) Comparison of measurement results for hot-rolled steel sheets with relatively moderate texture Table 1 shows the results of studies on hot-rolled steel sheets with relatively mild texture. This steel plate has an α phase (200) and a γ phase (200)
Is slightly higher, and the P-value
The values are 1.81 and 1.62. The results in the table were obtained by combining Rigaku's X-ray diffractometer RINT2100 with the company's rotary vibration sample table. For the measurement, Co Kα radiation was used under the conditions of a tube voltage of 40 kV and a tube current of 50 mA. The measured diffraction angle was set to 10 to 130 ° in consideration of the reliability of the temperature factor in the theoretical calculation described above.

The amount of austenite and P value are determined by the diffraction peak of each phase appearing in this angle range, specifically, α (110),
α (200), α (211), α (220), γ (111), γ (200), γ (22
0), γ (311), and γ (222) were obtained from integrated measurements, and then applied to theoretical calculations. Among the parameters required when calculating the amount of austenite, the lattice constant of the α phase 2.87 based on the actual measurement from the diffraction pattern
01A (Ogstrom), γ-phase 3.626A. Atomic scattering factor and temperature factor are listed in International Tables for
The values described in X-ray Crystallography were used. Regarding the atomic scattering factor, the composition of the steel sheet and the
The effect of extraordinary Kα ray scattering was considered.

In comparison with the existing method, calculation was performed for each combination of 4 peaks of α phase and 5 peaks of γ phase by the method (2) (Choen's method in the table (with biaxial rotation)). Those that fall within the range of the results obtained were considered appropriate, and those that fell outside this range were evaluated as inappropriate. This method was based because it is most commonly used as an X-ray diffraction method for oriented steel.

As can be seen from the quantitative results and the above description, the effect of the texture cannot be completely removed by the method (2), so that the result varies depending on the combination of peaks. Therefore, the method of (2) itself as a criterion is
It is insufficient that it is impossible to judge which combination is appropriate.

As comparative examples, the above-mentioned method (3) (Arnell's method) and the method of Ball & Kelly, which is reported to be highly relevant among the methods of (4), were mentioned. In order to show the effect of reducing the influence of the texture by the sample rotation, the table also shows the evaluation results by the Choen method when the method of the sample rotation was changed. The method (1), which takes a long time to evaluate (a method of calculating a diffraction intensity corresponding to a non-oriented state from a pole figure and using it for a theoretical calculation) is out of the scope of the present invention because it is out of the object of the present invention. As can be seen from the table, the invention and the Arne
The method is inappropriate except for the method of II.

[0030]

[Table 1]

(Example 2) Comparison of measurement results for alloy steel sheets with remarkable textures Table 2 shows the results of studies on alloy steel sheets with remarkable textures. This steel sheet has a remarkably high degree of accumulation of (220) in the γ phase, and the corresponding P value is 3.35. The measurement conditions and the determination of the result are the same as in the first embodiment. For this material, 2
Even when the shaft is rotated, the influence of the texture of the γ phase remains strong (the P value of γ (220) is improved only up to 1.37). As can be seen, Arnell's method is also unsuitable for such materials. As described above, the present invention provides highly reliable evaluation results even for steel sheets and steel materials having a remarkable texture.

[0032]

[Table 2]

(Example 3) Comparison of source with respect to accuracy of diffraction intensity measurement Table 3 shows the operation of the quantitative method according to claim 1.
The result of examining the type of X-ray source to be used is shown. As described above, in the quantitative method according to the first aspect, the measurement accuracy of the diffraction intensity tends to deteriorate with the rotation of the two axes. Therefore, it is desirable to consider the selection of the radiation source.

The point at that time is as follows: (i) The adjacent α (11
0), degree of separation of γ (111) peak, (ii) P / B of diffraction intensity
(Peak to Background) ratio, (iii) α that can be used for accurate P value measurement with the influence of texture reduced by biaxial rotation
Phase peak number.

(I) directly affects the accuracy in measuring the diffraction intensity of α (110) and γ (111). In recent years, with the development of the peak separation method, the measurement accuracy of the diffraction intensity when the peak overlap occurs has also been improved. However, considering the asymmetry of the low angle peak caused by the umbrella effect and the calculation error caused by the calculation restriction on the peak shape, it is desirable to reduce the influence of the overlap at the stage of the original data as much as possible. Then, α (1
10), when the difference in diffraction angle of γ (111) is 1.2 ° or more and the influence of the overlap is small or negligible, の も の indicates that the influence of peak separation is somewhat expected from 1.0 to 1.2 °, Those having a result of less than 1.0 °, which tends to vary depending on the method of peak separation, were evaluated as x.

(Ii) affects the statistical accuracy in measuring the integrated intensity. Here, when the (111) diffraction peak of SUS304 was measured without a monochromator, the one with a P / B ratio of 2.0 or more was evaluated as ○, and the one less than that was evaluated as ×.

(Iii) is an item in consideration of the accuracy of the P value correction calculation. Here, the number of peaks of the α phase having a relative intensity of 10 or more in each phase, which appears up to a diffraction angle of 130 °. Compared. (Since the number of peaks in the γ-phase always exceeds the number of α-phases, only the peak number in the α-phase was evaluated.) It is expected that the greater the number of such peaks, the higher the accuracy of P value measurement.
The case of the book was evaluated by Δ, and the case of 2 or less was evaluated by ×. The reason for limiting the upper limit of the diffraction angle to 130 ° here is that the effect of the temperature factor error assumed in the theoretical calculation (the higher the angle, the more likely it appears) causes an error of several percent or more in the diffraction intensity at the 130 ° diffraction angle. This is because there is a possibility. The reason why the peak having a relative intensity of 10 or less is not counted is that the diffraction intensity of a peak having a low relative intensity (that is, poor statistical accuracy) is taken into account in a situation in which a biaxial rotation is likely to cause the measurement accuracy of diffraction intensity to deteriorate. This causes a large error in the calculation of the P value.

The sources examined were Mo, Cu, Co, Fe, and Cr.
Kind. As can be seen from the table, when quantifying austenite, the P / B ratio of Mo, which is relatively frequently used in the literature, is worse than that of Co or Cr. When Mo is used, the absolute number of diffraction peaks detected in the measurement angle range is increased, but P
The number of diffraction peaks having a relative intensity of 10 or more, which is effective for value calculation accuracy, is reduced. Peak separation, P / B ratio, accurate P
Co is the most excellent among the three points of the peak number of the α phase that can be used for the value measurement. From this, it can be said that the use of a Co source is most desirable when operating the quantification method according to the first aspect.

[0039]

[Table 3]

[0040]

As described above, in the present invention, when the amount of austenite in a steel having a mixed structure of a ferrite phase and an austenite phase is measured by the X-ray diffraction method, the steel is given a biaxial rotation. After measuring the diffraction intensities of a plurality of crystal lattice planes belonging to each phase, the amount of austenite is calculated by correcting each diffraction intensity with the P value. In addition, it is possible to accurately evaluate the amount of austenite.

Further, by using characteristic X-rays of cobalt as X-rays, particularly accurate measurement can be performed.

Claims (2)

[Claims] When measuring the amount of austenite in a steel having a mixed structure of a ferrite phase and an austenite phase using an X-ray diffraction method, a plurality of crystal lattice planes belonging to each phase while giving biaxial rotation to the steel. After measuring the diffraction intensity of
A method for measuring austenite in steel, wherein each diffraction intensity is corrected by a P value to calculate an austenite amount. 2. The method for measuring austenite in steel according to claim 1, wherein the measurement is performed using characteristic X-rays of cobalt.