JP5962615B2 - Method for measuring the degree of alloying of galvannealed steel sheets - Google Patents

Description

  The present invention relates to a method for measuring the degree of alloying of an alloyed hot-dip galvanized steel sheet, which measures the average Fe concentration in the plated layer of the alloyed hot-dip galvanized steel sheet.

Alloyed hot-dip galvanized steel sheets (hereinafter referred to as GA steel sheets) are widely used because they are excellent in quality characteristics such as weldability, workability, post-coating corrosion resistance, and coating film adhesion. In the plated layer of the GA steel sheet, a concentration distribution of Fe or Zn is generated in the thickness direction by the thermal diffusion treatment. That is, in the plating layer, the Fe concentration increases from the surface toward the base steel plate, and a plurality of Fe—Zn alloy phases are formed. Generally, the plating layer has a ζ phase (FeZn ₁₃ ), a δ ₁ phase (FeZn _7-10 ), a Γ phase and a Γ ₁ phase (Fe ₃ Zn ₁₀ and Fe ₁₁ Zn ₄₀ , Hereinafter, the Γ phase and the Γ ₁ phase are simply referred to as a Γ phase). This is because as the alloying of the plating layer proceeds, Fe diffuses from the underlying steel sheet, so that the metallic zinc, that is, the η phase disappears, and the ζ phase, δ ₁ phase, and Γ phase are sequentially generated and grown.

The plating layer is formed mainly of the δ ₁ phase of these alloy phases, and a small amount of Γ phase and ζ phase are formed. The Fe concentration in the plating layer is usually controlled to around 10% by weight. However, when the heat treatment is excessive or insufficient, the Fe concentration fluctuates, and the ratio of the Γ phase and the ζ phase increases. Metal zinc, that is, the η phase remains.

  Since the quality characteristics of the plating layer vary significantly depending on the ratio of each alloy phase in the plating layer, the degree of alloying of the plating layer (the average Fe concentration in the plating layer) is necessary to produce a high-quality GA steel sheet. ) Is accurately measured, and heat treatment conditions such as heating temperature or heating time are controlled, and the degree of alloying needs to be managed within an appropriate range.

  Conventionally, as a technique for evaluating the degree of alloying of a GA steel sheet, the simplest method is a method for judging the color change of the plating layer surface immediately after alloying by visual observation or a photometer, or a part of the GA steel sheet after production. A chemical analysis method is known in which a sample layer is collected, the plating layer is dissolved with acid or alkali, and the average Fe concentration in the plating layer is measured.

  Further, in order to measure the alloying degree of the GA steel sheet, that is, the alloying degree of the plating layer in a non-destructive manner in a short time and accurately, an X-ray diffraction method (hereinafter referred to as XRD method) is used, and each Fe-Zn alloy is used. Many methods for evaluating the degree of alloying have been proposed from the relationship between the diffraction intensity of the phase, α-Fe, and η phase and the degree of alloying. For example, in Patent Document 1 and Non-Patent Document 1, there is a method in which a relational expression between a diffraction intensity of a Γ phase or a ζ phase existing in the vicinity of an interface between a plating layer and a base steel plate and a background is used as an index for calculating Fe concentration. Have been described. Patent Documents 2 to 5 describe a method in which a relational expression obtained from the diffraction intensities of a plurality of Fe—Zn alloy phases is used as an index for calculating Fe concentration. Patent Document 6 also describes a method of using the diffraction peak angle of the alloy phase as an index for alloying, in addition to the relational expression composed of the diffraction intensity and the half width of the Fe—Zn alloy phase.

Japanese Patent No. 2542906 Japanese Patent No. 2707865 Japanese Examined Patent Publication No. 56-12314 Japanese Patent No. 2534834 JP-A-9-33455 JP-A-52-21887

Kawasaki Steel Technical Report, 18 (1986) 2, p. 31

  However, according to the method of judging the color tone change of the plating layer surface immediately after alloying by visual observation or a photometer, or the chemical analysis method for measuring the average Fe concentration in the plating layer, it is inaccurate or measured from sampling. Since it takes a long time to finish, the feedback to the heat treatment condition is delayed.

  In addition, according to the methods described in Patent Document 1 and Non-Patent Document 1, since the volume ratio of the ζ phase and the Γ phase in the plating layer is small, the reduction of these alloy phases with respect to the progress of alloying There was a problem that the rate of increase was small and the sensitivity was insufficient. Further, when the diffraction intensity of the Γ layer is used as an index for calculating the Fe concentration, since the Γ layer is formed in the lowermost layer of the plating, the diffraction intensity of the Γ layer is easily affected by attenuation, and the fluctuation due to the amount of plating adhered. There was a problem that the influence was great.

  Furthermore, in the methods described in Patent Documents 2 to 5, since the detection angle of each alloy phase is fixed, the steel plate temperature at the time of measurement and the concentration of Fe or Zn dissolved in each alloy phase change. Due to the accompanying shift of the diffraction peak position, there is a problem that an accurate strength cannot be measured and the degree of alloying cannot be evaluated correctly. Furthermore, the index of alloying degree in these methods is based on an empirical formula consisting of complicated calculation formulas, and there is a problem that calculation and analysis become very complicated. In addition, Patent Document 6 does not describe a specific relationship between the diffraction peak intensity of the Fe—Zn alloy phase and the degree of alloying. There was a problem that it could not be applied to quantitative measurement.

  The present invention has been made in view of the above, and provides a method for measuring the degree of alloying of an alloyed hot-dip galvanized steel sheet capable of measuring the degree of alloying of the alloyed hot-dip galvanized steel sheet in a nondestructive manner simply and accurately. The purpose is to do.

  In order to solve the above-described problems and achieve the object, a method for measuring the degree of alloying of an alloyed hot-dip galvanized steel sheet according to the present invention irradiates a sample having an alloyed hot-dip galvanized layer on the surface with X-rays. Measuring a diffraction peak angle of an alloy phase constituting the plating layer of the sample; calculating an average Fe concentration in the plating layer as a degree of alloying of the plating layer from a change in the diffraction peak angle; It is characterized by including.

Moreover, in the above invention, the method for measuring the degree of alloying of the galvannealed steel sheet according to the present invention is characterized in that the alloy phase is a δ ₁ phase.

  Further, in the method of measuring the degree of alloying of the galvannealed steel sheet according to the present invention, in the above invention, the step of calculating the average Fe concentration in the plating layer is a mathematical expression showing the change amount of the diffraction peak angle as follows: The method includes a step of calculating an average Fe concentration in the plating layer by substituting in (1).

Average Fe concentration = a × difference of diffraction peak angle + b (1)
Where a and b are constants

Moreover, in the above invention, the method of measuring the degree of alloying of the galvannealed steel sheet according to the present invention includes the step of measuring the diffraction peak angle using a one-dimensional X-ray detector or a two-dimensional X-ray detector. The method includes a step of measuring diffracted X-rays.

  According to the present invention, the degree of alloying of an alloyed hot-dip galvanized steel sheet can be easily and accurately measured nondestructively.

FIG. 1 is a schematic cross-sectional view showing a configuration of a plated layer of a GA steel plate to which the present invention is applied. FIG. 2 is a diagram showing the relationship between the average Fe concentration in the plating layer of the GA steel sheet and the volume ratio of each alloy phase constituting the plating layer. FIG. 3 is a diagram showing the Fe concentration in each alloy phase of the GA steel sheet. FIG. 4 is a diagram showing the relationship between the coating amount of the GA steel sheet and the average Fe concentration in the plating layer according to an embodiment of the present invention. FIG. 5 is a diagram showing theoretical diffraction angles of the respective alloy phases of the GA steel plate. FIG. 6 is a diagram showing the relationship between the diffraction peak intensity of each alloy phase and the average Fe concentration in the plating layer according to the present embodiment. FIG. 7 is a diagram showing the relationship between the deviation of the diffraction peak angle from the theoretical diffraction angle of each alloy phase and the average Fe concentration in the plating layer. FIG. 8 is a diagram showing the relationship between the shift of the diffraction peak angle of the δ ₁ phase and the amount of change in the sample tilt. FIG. 9 is a diagram showing the relationship between the shift in the diffraction peak angle of the δ ₁ phase and the amount of change in the distance in the direction perpendicular to the sample surface from the appropriate measurement position. FIG. 10 is a diagram showing the measurement results of the average Fe concentration in the plating layer in the examples and comparative examples of the present invention. FIG. 11 is a schematic diagram showing a configuration of a measurement head portion of an X-ray diffraction apparatus used when measuring the Fe concentration of an alloyed hot-dip galvanized steel sheet on-line according to the present invention. FIG. 12 is a diagram showing components in steel of a sample according to one embodiment of the present invention. FIG. 13 is a diagram showing the measurement results of the average Fe concentration in the plating layer of Example 3 according to the present invention. FIG. 14 is a diagram showing the measurement results of the average Fe concentration in the plating layer of Comparative Example 3 according to the conventional example.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment.

  First, with reference to FIG. 1 and FIG. 2, the structure of the plating layer of the GA steel plate made into the object of this Embodiment is demonstrated. FIG. 1 is a schematic cross-sectional view showing the configuration of a plated layer of a GA steel sheet. FIG. 2 shows the relationship between the average Fe concentration (average Fe concentration) in the plated layer and the volume ratio of each alloy phase constituting the plated layer. FIG.

As shown in FIG. 1, in the plating layer 10 of the GA steel sheet 1, the Fe concentration increases from the surface toward the base steel sheet 20 due to thermal diffusion of Fe from the base steel sheet 20, and from the surface toward the base steel sheet 20 side. Thus, a ζ phase 11, a δ ₁ phase 12, and a Γ phase 13 are formed. As shown in FIG. 2, these alloy phases change their abundance with the progress of alloying of the plating layer 10. That is, the range of the average Fe concentration in the plating layer 10 that is actually used in the manufacturing process of the GA steel sheet 1 is 7 to 15% by weight. In this concentration range, the alloy in which the δ ₁ phase 12 constitutes the plating layer 10. Occupies most of the phase. In addition, in other concentration ranges, the heat treatment conditions such as the heating temperature and the heating time are different, and the appearance of the plating layer 10 is clearly different, so it is possible to easily determine whether the alloying is excessive or insufficient. is there. Therefore, in the average Fe concentration range of 7 to 15% by weight in the plating layer 10, if the change of the main component δ ₁ phase 12 can be captured, the degree of alloying of the GA steel sheet 1 is measured with high sensitivity and high accuracy. it can.

On the other hand, FIG. 3 is a diagram showing the Fe concentration (Fe solid solution amount) in each alloy phase. As shown in FIG. 3, the Fe solid solution amount of each alloy phase has a certain width. The Fe concentration in the alloy phase in the δ ₁ phase 12 which is the main component of the plating layer 10 is a relatively wide concentration range of 8.2 to 13.5 atomic%. In such a case, it is expected that Vegard's law holds that the lattice constant of the solid solution alloy changes linearly with the composition. Further, the relationship between the diffraction angle 2θ in the XRD method, the crystal plane interval d and the wavelength λ of the incident X-ray can be expressed by the Bragg law of the following equation (1).

  2 dsin θ = λ (1)

When the lattice constant of the alloy changes as the alloy composition changes, the crystal plane spacing d also changes, and the X-ray diffraction angle 2θ also shifts accordingly. At room temperature, the radius of Fe atom in α-Fe is 1.24Å, and the radius of Zn atom in Zn crystal is 1.33Å. If it is assumed that Vegard's law holds in the δ ₁ phase 12, since the Fe atomic radius is smaller, it can be expected that the lattice constant decreases as the Fe concentration increases, and the X-ray diffraction angle shifts to the higher angle side. That is, it is considered that the degree of alloying of the GA steel sheet 1 can be predicted from the change in the diffraction angle of the δ ₁ phase 12.

  In the present embodiment, as shown in FIG. 4, four types of GA steel sheets 1 having different plating adhesion amounts and average Fe concentrations in the plating layer were prepared. Note that the plating adhesion amount and the average Fe concentration shown in FIG. 4 are values obtained by chemical analysis in the following procedure using a sample that has been measured by the XRD method (XRD measurement). That is, in accordance with JIS 0401, the non-target surface of XRD measurement was completely sealed, and the plating layer 10 was dissolved in a hydrochloric acid aqueous solution to which a small amount of hexamethylenetetramine was added. Calculated from the weight difference. The average Fe concentration was calculated from the result of ICP emission spectroscopic analysis of the solution after dissolution of the plating layer 10.

  FIG. 5 is a diagram showing a theoretical diffraction angle obtained by Bragg's law of the above formula (1) for each alloy phase. Based on the theoretical diffraction angle shown in FIG. 5, the GA steel sheet 1 shown in FIG. 4 was subjected to XRD measurement under the following conditions. As the XRD measurement apparatus, a concentrated beam optical X-ray diffractometer (Rigaku RU-300) is used. The incident X-ray is Cr-Kα ray, and the X-ray incident angle is 60 °. Further, the range of ± 0.5 ° from the theoretical diffraction angle of each Fe—Zn alloy phase was measured at a scan step of 0.05 ° and a scan speed of 0.4 ° / min. Furthermore, the maximum intensity in the measurement range of each alloy phase was defined as the diffraction peak intensity, and the angle at which the intensity was maximum was defined as the diffraction peak angle.

FIG. 6 is a diagram showing the relationship between the diffraction peak intensity of each alloy phase and the average Fe concentration in the plating layer. Focusing on the increase / decrease in the diffraction peak intensity of each alloy phase, as the average Fe concentration in the plating layer increases, the intensity of the ζ phase 11 decreases and becomes substantially constant at about 11% by weight, and the δ ₁ phase 12 and the Γ phase 13 It can be seen that the intensity of the diffraction peak increases slightly. This indicates that as the alloying progresses, the ζ layer having a low Fe concentration decreases / disappears, and the δ ₁ phase 12 and the Γ phase 13 having a high Fe concentration are generated and grown. Although the diffraction peak intensity of the ζ phase 11 is substantially reduced by about 700 counts, it becomes constant at about 11% by weight, so that the average Fe concentration actually used in the manufacturing process of the GA steel sheet 1 is 7 to 15% by weight. % Is not suitable as an index for high-accuracy measurement of the average Fe concentration in the plating layer 10 in the entire range. On the other hand, the diffraction peak intensities of the δ ₁ phase 12 and the Γ phase 13 monotonically increase over the entire range of the average Fe concentration of 7 to 15% by weight, but the increase is slight, about 200 counts. It is not suitable for measuring the average Fe concentration in the medium with high accuracy.

FIG. 7 is a diagram showing the relationship between the deviation of the diffraction peak angle from the theoretical diffraction angle obtained from the crystal plane spacing of each alloy phase shown in FIG. 5 and the average Fe concentration in the plating layer. Focusing on the change in the diffraction peak angle of each alloy phase, no clear correlation is found between the average Fe concentration and the ζ phase 11 and the Γ phase 13, but the diffraction peak angle of the δ ₁ phase 12 is the average Fe concentration. It can be seen that it is directly proportional to. This is because the Vegard law is established in the δ ₁ phase 12 in the GA plating layer 10 within this average Fe concentration range, and the amount of Fe solid solution in the δ ₁ phase 12 increases due to the diffusion of Fe accompanying the progress of alloying. It is shown that. Since the change amount (deviation) of the diffraction peak angle is as large as approximately 0.7 °, it is considered possible to measure the average Fe concentration with high accuracy.

From the above, the relationship between the average Fe concentration in the plated layer 10 of the GA steel sheet 1 and the amount of change in the diffraction peak angle of the δ ₁ phase can be expressed by a very simple relational expression represented by the following expression (2). It became clear that we could do it.

Average Fe concentration = a × difference in diffraction peak angle + b (2)
Where a and b are constants

As described above, according to the method for measuring the degree of alloying of the galvanized steel sheet according to the present embodiment, the relationship between the degree of alloying of the GA steel sheet 1 and the diffraction peak of each Fe—Zn alloy phase by the XRD method. In this case, in addition to the change in the diffraction peak intensity of each alloy phase as well as the change in the degree of alloying, this δ ₁ phase is based on the change in the diffraction peak angle of the δ ₁ phase 12 which is the main constituent of the plating layer 10. Since the average Fe concentration in the plating layer is calculated as the degree of alloying using the change in the diffraction angle of 12 as an index, non-destructive and quick and simple measurement can be performed.

  In this embodiment, the change in the diffraction peak angle of the Fe—Zn alloy phase is used as an index, and the influence of X-ray absorption is small, so that the degree of alloying can be measured without depending on the amount of plating adhesion. The present method can also be applied to online measurement of the Fe concentration of the GA steel sheet 1 generated on the surface of the traveling steel strip.

  However, when measuring the Fe concentration of the GA steel plate 1 generated on the surface of the running steel strip, the diffraction peak angle is affected by the plate thickness and the vibration of the steel plate, so the Fe concentration analysis accuracy decreases. . Therefore, the inventors of the present invention investigated the influence of the plate thickness and the vibration of the steel plate on the diffraction peak angle, and among the GA steel plates 1 shown in FIG. The XRD measurement was performed with As an apparatus for XRD measurement, AutoMATE manufactured by Rigaku Corporation equipped with a one-dimensional X-ray detector was used. The incident X-ray was measured as Cr-Kα ray, the collimator diameter as φ2 mm, and the integration time as 60 seconds.

Further, in the measurement for examining the influence of the change in the inclination of the steel sheet on the diffraction peak angle, the sample is placed at an appropriate measurement position, and the 2θ angle of the one-dimensional X-ray detector is set so that 127.0 ° is the center. With the arrangement of the radiation source and the one-dimensional X-ray detector maintained, measurement was performed by changing the X-ray incident angle to 60.5 °, 63.5 °, and 66.5 °. Further, in the measurement for examining the influence of the change in the distance in the surface vertical direction on the diffraction peak angle, the measurement was performed by changing the sample from the appropriate measurement position by ± 2 mm in 0.5 mm steps in the surface vertical direction. Furthermore, from these measurement results, the diffraction peak angle of the δ ₁ phase 12 was calculated by the centroid method.

FIG. 8 is a diagram showing the relationship between the deviation of the diffraction peak angle of the δ ₁ phase 12 and the amount of change in the sample tilt. FIG. 9 shows the deviation of the diffraction peak angle of the δ ₁ phase 12 and the sample surface from the appropriate measurement position. It is a figure which shows the relationship with the variation | change_quantity of the distance of a perpendicular direction. As shown in FIG. 8, the diffraction peak angle of the δ ₁ phase 12 hardly changes with changes in the tilt angle of the sample. On the other hand, as shown in FIG. 9, the diffraction peak angle of the δ ₁ phase 12 changed greatly with respect to the change of the distance in the surface vertical direction, and the change amount was about 0.25 ° / mm. . This is because the diffraction peak angle changes apparently by changing the angle of the diffracted X-rays emitted from the sample on the one-dimensional X-ray detector by changing the sample position in the direction perpendicular to the surface. The apparent deviation of the diffraction peak angle of the δ ₁ phase 12 is directly proportional to the distance in the surface vertical direction.

  Therefore, when measuring the Fe concentration of the GA steel sheet 1 generated on the surface of the running steel strip, it is only necessary to consider the change in the distance in the direction perpendicular to the surface. If measured, the apparent shift of the diffraction peak angle can be corrected and the Fe concentration can be measured with high accuracy. In order to reduce the apparent deviation of the diffraction peak angle, it is desirable to arrange a collimator, a solar slit, or the like in either or both of the X-ray source and the one-dimensional X-ray detector to form a parallel beam optical system. .

  Although the embodiment to which the invention made by the present inventor is applied has been described above, the present invention is not limited by the description and the drawings that form a part of the disclosure of the present invention according to this embodiment. That is, other embodiments, examples, operational techniques, and the like made by those skilled in the art based on this embodiment are all included in the scope of the present invention.

  Note that the peak of the diffraction curve used for the measurement needs to be a peak that does not overlap with the peak of the diffraction curve of another test component, and it is desirable to use a peak having a high intensity. In addition, since the amount of change in the diffraction angle associated with the change in crystal plane spacing becomes large and the change in crystal plane spacing can be measured with higher accuracy, it is more desirable to use a diffraction peak at a high angle. A plurality of peaks used for measurement may be used for each test component. The measurement range of each alloy phase peak is not limited to a range of ± 0.5 ° from the theoretical diffraction angle. Also, here, the angle at which the intensity is maximum or the angle obtained by the centroid method is used as the diffraction peak angle, but the value obtained by peak fitting the diffraction curve with the fitting function or the numerical value such as the centroid method or half-width method A more accurate peak angle can be obtained by using a value obtained by arithmetic processing or the like.

  Here, the detector is scanned to measure the change in the diffraction peak angle, but a one-dimensional detector or a two-dimensional detector may be used as the X-ray detector. If a one-dimensional detector or a two-dimensional detector is used, a change in the diffraction peak angle can be measured more quickly. The one-dimensional detector and the two-dimensional detector may be scanned or fixed at a certain angle. Further, the incident X-ray source and the X-ray incident angle are not limited to those described here.

(Example)
For the GA steel sheet 1, the average Fe concentration in the plating layer 10 was measured by the method of the present invention, the accuracy was calculated, and compared with the accuracy σd of the average Fe concentration obtained by the conventional method. The accuracy is represented by the following formula (3), and the “XRD analysis value” in the formula (3) is the average Fe concentration obtained by the example or the conventional example, and the “chemical analysis value” Is the average Fe concentration (reference value) obtained by chemical analysis.

σd = Σ {(XRD analysis value) − (chemical analysis value)} 2 / (n−1) (3)
Where n is the number of test materials

[Example 1]
As Example 1 of the present invention, 10 GA steel sheet test materials having a plating adhesion amount of 44.4 to 62.0 g / m ² and an average Fe concentration of 9.0 to 15.0 wt% in the plating layer 10 were prepared. In addition, the amount of plating adhesion and the average Fe concentration were determined by completely sealing the non-target surface of the XRD measurement of the sample after the XRD measurement, dissolving the plating layer in a hydrochloric acid aqueous solution to which a small amount of hexamethylenetetramine was added, and before and after the dissolution. This is a value calculated from the difference in the weight of the sample pieces (JISH0401) and the result of ICP emission spectroscopic analysis of the solution after dissolution. Using these concentrated beam optical system X-ray diffractometers, these samples were scanned in the range of 125.5 to 128.5 ° with the incident X-ray being Cr-Kα ray and the X-ray incident angle being 60 °. Was measured at 0.05 ° and the integration time was 40 seconds. Furthermore, the straight line in contact with both ends of the measurement range was divided as the background, and the diffraction peak angle of δ ₁ phase 12 was determined by the centroid method. Further, the equation (2) was subjected to multiple regression from the average Fe concentration by chemical analysis and the measured diffraction peak angle of the δ ₁ phase 12 to obtain the coefficients a and b.

[Example 2]
The usefulness of the one-dimensional detector or the two-dimensional detector in the method of the present invention was examined using the same test material as in Example 1. The XRD measurement apparatus uses a quasi-parallel beam X-ray diffractometer (AutoMATE manufactured by Rigaku Corporation) equipped with a collimator on the incident X-ray source and a one-dimensional detector for detecting the line X-ray. The measurement was performed with an integration time of 60 seconds in a state where the incident X-ray was Cr-Kα, the X-ray incident angle was 63.5 °, and the 2θ angle of the detector was fixed at 127.0 °. Further, data in the range of 125.5 to 128.5 ° is extracted from the measurement result, and the straight line in contact with both ends of this range is divided as the background in the same manner as in Example 1, and the diffraction peak angle of the δ ₁ phase 12 is calculated. Obtained by the center of gravity method. Further, the equation (2) was subjected to multiple regression from the average Fe concentration by chemical analysis and the measured diffraction peak angle of the δ ₁ phase 12 to obtain the coefficients a and b.

[Conventional example]
As a conventional example, a method of obtaining an average Fe concentration from the relationship between the diffraction intensity of the Γ phase 13 and the background intensity (see Patent Document 1 and Non-Patent Document 1) was also examined using the same test material. The measurement conditions were the same concentrated beam optical system X-ray diffractometer as in Example 1, the incident X-ray was Cr-Kα ray, the X-ray incident angle was 60 °, the integration time was 40 seconds, and the diffraction angle was 139.0 °. The X-ray intensity IΓ was measured. The background intensity IBG at a diffraction angle of 139.0 ° was calculated by interpolation or extrapolation using the X-ray intensity at a diffraction angle of 90 ° and the X-ray intensity at a diffraction angle of 150 °.

  From the average Fe concentration by chemical analysis and these values, the following equation (4) (see Comparative Example 1, Patent Document 1) and the following equation (5) (Comparative Example 2, see Non-Patent Document 1) are subjected to multiple regression to obtain coefficients. c to f were obtained.

Average Fe concentration = c × (IΓ−IBG) / IΓ + d (4)
Average Fe concentration = e × ln (IΓ / IBG) + f (5)
Where c, d, e, and f are constants.

  FIG. 10 is a diagram showing the measurement results of the average Fe concentration in the plating layer in the above examples and Comparative Examples 1 and 2, and for each example, the average Fe concentration obtained by XRD measurement and the chemical analysis. The relationship with the degree of alloying is shown. As shown in FIG. 10, according to the example, it can be seen that the deviation from the degree of alloying obtained by chemical analysis is smaller than in the conventional examples (Comparative Examples 1 and 2). When the accuracy σd of the average Fe concentration analysis was obtained, it was 0.9% by weight in both Comparative Example 1 and Comparative Example 2, whereas it was 0.3% by weight in both of Example 1 and Example 2, which was conventional. It was considerably better than the example. Moreover, the measurement time of Example 1 and Example 2 was about 41 minutes and 60 seconds, respectively. Therefore, by using a one-dimensional detector as a diffracted X-ray detector, it is possible to greatly shorten the measurement time while maintaining the same analysis accuracy.

Example 3
FIG. 11 is a schematic diagram showing the configuration of the measurement head portion of the X-ray diffraction apparatus according to the present invention used when measuring the Fe concentration of the galvannealed steel sheet on-line. The measurement head unit 30 is provided with a Cr target X-ray tube 31 that emits X-rays to the alloyed hot-dip galvanized steel sheet 34 so as to have a predetermined incident angle α. The one-dimensional detector 32 measures the X-rays radiated from the Cr target X-ray tube 31 and diffracted by the galvannealed steel plate 34. The one-dimensional detector 32 is installed at an angle corresponding to the δ ₁ phase, and is configured to measure a diffracted X-ray profile. A laser displacement meter 33 is installed immediately above or near the position where the diffraction X-ray profile is measured. The laser displacement meter 33 is configured to measure the distance between the measuring head and the galvannealed steel plate 34 simultaneously with the diffraction X-ray profile. Reference numeral 35 in the figure denotes a collimator, and reference numeral 36 denotes a Kβ filter.

The measurement head is connected to an X-ray generator (not shown) and a cooling water feeding device for cooling the X-ray tube and a thermostatic device for keeping the temperature in the measurement head constant. Furthermore, an arithmetic processing unit is connected to the measurement head. The arithmetic processing unit performs angle correction and peak position calculation from the diffracted X-ray profile of δ ₁ phase measured by the one-dimensional detector 32 and the distance measured by the laser displacement meter 33, and calculates the degree of alloying. To do.

In the continuous alloying hot dip galvanized steel strip production line, the steel strips of steel grade A and steel grade B having the components shown in FIG. Is controlled to perform hot dip galvanizing alloying treatment (plating adhesion amount 44.4 to 62.0 g / m ² , Fe concentration 9.0 to 15.0 wt%), and then the steel plate temperature becomes 100 ° C. or lower. The on-line alloying degree measurement system shown in FIG. 11 (Example 3) and Non-Patent Document 1 (Comparative Example 3) is installed on the line, and the alloying degree of the galvannealed steel strip is measured online for 30 seconds. It was measured.

  Furthermore, the alloyed hot-dip galvanized steel pieces are collected from almost the same position as the XRD measurement position calculated from the line speed and the length of the steel strip, and the non-target surface of the XRD measurement is completely sealed to obtain hexamethylenetetramine. The plating layer was dissolved in an aqueous hydrochloric acid solution with a small amount of added, and the plating adhesion amount and the average Fe concentration were calculated from the results of ICP emission spectroscopic analysis of the weight difference (JISH4011) between the sample pieces before and after dissolution and the solution after dissolution.

  Furthermore, for steel type A and steel type B, the coefficients a, b, e, f in Example 3 and Comparative Example 3 were subjected to multiple regression of Equation (2) and Equation (5) from the average Fe concentration by chemical analysis and the measurement results. Was calculated respectively.

  FIGS. 13 and 14 are diagrams showing the measurement results of the average Fe concentration in the plating layers in Example 3 and Comparative Example 3, respectively. For each example, the average Fe concentration obtained by XRD measurement and the chemical analysis were obtained. The relationship with the obtained alloying degree is shown. Moreover, about each example, the result of having calculated | required the Fe density | concentration of the steel type B with the formula for steel type A is also shown. As shown in FIG. 13 and FIG. 14, according to Example 3, the deviation from the degree of alloying obtained by chemical analysis is small compared to the conventional example (Comparative Example 3), and the average of steel types A and B The accuracy σd of the Fe concentration analysis was 0.9 and 0.8% by weight in Comparative Example 3, respectively, whereas 0.3 and 0.4% by weight in Example 3, respectively. It was considerably better than that.

Also, when the average Fe concentration was determined using calibration curves of different steel types, the analysis accuracy was 3.1 wt% in Comparative Example 3, whereas 0.9 wt% in Example 3. there were. Thereby, according to Example 3, it turns out that the shift | offset | difference with the alloying degree calculated | required by the chemical analysis is far smaller compared with a prior art example (comparative example 3). This is because the conventional example (Comparative Example 3) calculates the Fe concentration using the change in the X-ray diffraction intensity of the Γ phase 13 generated in a small amount near the interface between the plating layer 10 and the base steel plate 20, This is because the amount of phase 13 produced varies depending on the components of the base steel plate 20 and the alloying conditions. On the other hand, in Example 3 according to the present invention, since the Fe concentration is calculated using the change in the diffraction peak angle of the δ ₁ phase 12 which is the main component of the GA plating layer 10, the components and alloys of the base steel plate 20 Less affected by differences in conversion conditions. Therefore, according to this method, even when the components and alloying conditions of the base steel plate are different, the Fe concentration of the GA steel plate 1 can be accurately measured online.

  From the above, if the degree of alloying is measured by the method of the present invention using the X-ray diffractometer shown in FIG. 11, the result can be quickly fed back to the control of the production conditions. A plated steel sheet can be manufactured with a higher yield.

DESCRIPTION OF SYMBOLS 1 GA steel plate 10 Plating layer 11 ζ phase 12 δ ₁ phase 13 Γ phase 20 Base steel plate

Claims (4)

Irradiating a sample having an alloyed hot-dip galvanized layer on the surface with X-rays;
Measuring the diffraction peak angle of the alloy phase constituting the plating layer of the sample;
Calculating the average Fe concentration in the plating layer from the change in the diffraction peak angle as the degree of alloying of the plating layer;
A method for measuring the degree of alloying of an alloyed hot-dip galvanized steel sheet using an X-ray diffraction method. The method for measuring the degree of alloying of an galvannealed steel sheet according to claim 1, wherein the alloy phase is a δ ₁ phase. The step of calculating the average Fe concentration in the plating layer includes the step of calculating the average Fe concentration in the plating layer by substituting the change amount of the diffraction peak angle into the following mathematical formula (1). The method for measuring the degree of alloying of the galvannealed steel sheet according to claim 1 or 2.
Average Fe concentration = a × difference of diffraction peak angle + b (1)
Where a and b are constants The step of measuring the diffraction peak angle includes a step of measuring diffracted X-rays using a one-dimensional X-ray detector or a two-dimensional X-ray detector. The method for measuring the degree of alloying of the galvannealed steel sheet according to item 1.

Images