JPH0695081B2 - Method for measuring iron concentration in galvannealed steel sheet during plating - Google Patents

Description

The present invention relates to a method for continuously and nondestructively measuring the Fe concentration during plating of an alloyed galvanized steel sheet.

<Prior art and its problems> In order to improve the weldability of hot-dip galvanized steel sheet and electrogalvanized steel sheet, the corrosion resistance after painting, and the coating quality, the galvanized steel sheet is heat treated. A so-called alloyed galvanized steel sheet in which an Fe-Zn alloy phase is grown in the plating layer is manufactured. In the plating layer
The Fe concentration is usually 10 to 13% by weight (hereinafter abbreviated as%), but the Fe concentration fluctuates when the heat treatment is excessive or insufficient. Fluctuations in the Fe concentration during plating significantly affect the quality characteristics of the plated layer.

FIG. 1 shows the relationship between the Fe concentration during plating and various quality characteristics of the plated layer according to the experiments by the inventors. For example, the workability of the plating layer deteriorates as the Fe concentration increases during plating, and the coating adhesion, post-coating corrosion resistance and spot weldability conversely improve as the Fe concentration increases.

Therefore, to obtain excellent plating layer quality characteristics,
It is essential to control the Fe concentration within an appropriate range, and it is important to properly control the heat treatment conditions in order to control the Fe concentration.

However, in the current production line for galvannealed steel sheets, the technology for continuously measuring the Fe concentration during plating in a non-destructive manner has been adopted, despite the fact that productivity is emphasized and continuous and faster speeds have been achieved. Has not been developed. For this reason, in the same production line, a method of empirically estimating the approximate Fe concentration by visual observation has been adopted, and the heating conditions have to be controlled based on this estimation.
In many cases, a large amount of defective products was generated due to excess and deficiency of the concentration.

In view of the above-mentioned actual situation, the present inventors keenly felt the necessity of a method capable of accurately measuring the Fe concentration during plating, and conducted various studies.

By the way, according to the research by the inventors, as conceptually shown in FIG. 2, the Fe concentration during plating and the Fe constituting the plating layer are
-Zn alloy phase and η phase thickness ratio in the plating layer of each phase, that is, there is a close relationship with the phase composition of the plating phase,
If the phase composition is known, the approximate Fe concentration can be known.

Further, FIG. 3 shows the relationship between the X-ray diffraction intensity obtained for each phase by X-ray diffraction of the plating layer studied by the inventors and the Fe concentration in the plating. There is a close relationship between the X-ray diffraction intensity of each phase such as ₁ phase and Γ phase and the Fe concentration during plating. By measuring the X-ray diffraction intensity of each phase,
It was found that the Fe concentration during plating can be obtained.

However, according to the research conducted by the inventors, in the alloyed galvanized steel sheets having different basis weights, the diffraction intensity of each phase and the Fe
It was found that the relationship with the concentration was remarkably different. That is, a measurement error occurs in the Fe concentration when the basis weight is different.

For this reason, in the current actual line for continuous high-speed production of galvannealed steel sheets, the basis weight changes for each coil according to the order, or a plate passing between two air dies for adjusting the basis weight is used. It is difficult to measure the true Fe concentration during plating because the amount of basis weight varies frequently due to the warpage in the width direction or the deviation of the plate in one die direction.

<Purpose of the invention> The present invention has been made in view of the above situation, and an object of the present invention is to provide a method for nondestructively and continuously measuring the Fe concentration during true plating.

<Structure of the Invention> The inventors of the present invention irradiate the alloyed galvanized steel sheet with characteristic X-rays to determine one or more phases selected from the Fe-Zn alloy phase and the η phase during plating, that is, metallic zinc. Of the X-ray diffraction intensity of one or more phases by measuring the X-ray diffraction intensity of It was found that the Fe concentration during plating can be accurately measured by substituting the measured value and the measured value of the basis weight into a regression equation having variables.

As described above, the feature of the present invention is that the alloyed galvanized steel sheet is irradiated with characteristic X-rays to be selected from the Fe-Zn alloy phase generated in the alloyed galvanized steel sheet and the η phase (metallic zinc). X-ray diffraction intensity was measured for one or more of the obtained phases, and at the same time, the basis weight was measured by some method, and the respective measured values were calculated from the previously determined Fe-Zn alloy phase and the η phase. Regression formula with X-ray diffraction intensity (X ₁ , X ₂ ... Xn) and measured value of basis weight (Xt) for one or more selected from as variables and Fe concentration in plating as function (Y) To measure the Fe concentration during plating of the galvannealed steel sheet.

Hereinafter, the present invention will be described in detail.

As described above, the phase composition of the plating layer of the galvannealed steel sheet changes depending on the Fe concentration during plating (Fig. 2), and the X-ray diffraction intensity of each phase forming the plating layer is It changes following the middle Fe concentration (Fig. 3). Therefore, by measuring the X-ray diffraction intensity of each phase, the Fe concentration during plating can be measured. It has been found that the relationship can be accurately expressed by the relational expressions exemplified below.

Y ₁ = f (Xη), Y ₂ = f (XΓ), Y ₃ = f (Xη, Xδ ₁ ), Y ₄ = f (Xη, Xδ ₁ , XΓ), where the above relational expression Where: Y: Fe concentration in plating, Xη: Diffraction intensity of η phase, Xδ ₁ : Diffraction intensity of δ ₁ phase, XΓ: Diffraction intensity of Γ phase.

However, as shown in FIG. 4, for example, the above-mentioned relationship remarkably differs depending on the basis weight. That is, it was found that a significant error occurs in the measured value of the Fe concentration during plating due to the change in the basis weight.

On the other hand, according to the present invention, Y ₁ ′ = f (Xn, It) ... ′, Y ₂ ′ = f (X Γ, It) ′ ′, Y ₃ ′ = f (X η, Xδ ₁ , It) ′ ′, _{Y 4 '= f (Xη,} Xδ 1, XΓ, It) ...' equation such as, ie, eta-phase, [delta] _1-phase, X, such as Γ phase
A regression equation that uses the Fe concentration during plating as a function is obtained in advance using the line diffraction intensity and the measured value of the basis weight (It) as variables, and the X-ray diffraction of the η phase, δ ₁ phase, Γ phase, etc. By substituting the actual measurement value of strength and some actual measurement value relating to the basis weight, the Fe concentration during plating of the alloyed galvanized steel sheet is measured.

That is, the inventors obtained the deviation of the Fe concentration for each basis weight in each of the above equations, and arranged the relationship between the basis weight and the Fe concentration deviation. It has been found that it can be represented by a relational expression of ΔY = f (t) where is a variable.

By the way, the basis weight is obtained by the well-known fluorescent X-ray method, X-ray diffraction method, RI tracer method, etc., but in all of these, the basis weight is, for example, the X-ray dose per second (CPS).
Alternatively, it can be obtained by a relationship with a measured value such as a radiation dose (CPS), for example, a calibration curve of a relational expression of t = f (I) (where, t = basis weight, I = measured value). Therefore, the Fe concentration deviation is
It, that is, a measured value relating to the basis weight can be expressed.

<Examples> Hereinafter, the present invention will be specifically described with reference to Examples.

(Example 1) Fe concentration during plating of alloyed zinc-plated steel sheets having a basis weight of 30 g / m ² (one side), 60 g / m ² (one side), 90 g / m ² (one side) in a Zenzimer continuous hot dip galvanizing line 3-15% by weight
(However, the concentration analyzed by the atomic absorption spectrometry) was varied and manufactured. For these, the Fe concentration during plating was measured by the method of the present invention. The basis weight was measured by the fluorescent X-ray method, and the X-ray diffraction was performed under the following conditions. The measurement results are shown in Table 1.

X-ray diffractometer: Parallel beam optical system X-ray diffractometer Characteristic X-ray: Cr κ-α ray Diffraction angle (2θ): η phase 135.5 ° δ ₁ phase 126.8 ° Γ phase 139.0 ° As can be seen from Table 1 below. According to the method of the present invention, it can be seen that the Fe concentration during plating can be accurately measured, and that the measured value hardly changes depending on the basis weight.

The regression equation is as described above, that is, η phase, δ ₁ phase,
A regression equation in which the diffraction intensity of the Γ-phase three layers and the measured value of the basis weight by fluorescent X-ray were used as variables and the Fe concentration during plating was used as a function was used.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the Fe concentration during plating and various workability. FIG. 2 is a graph showing the relationship between the Fe concentration during plating and each alloy phase. FIG. 3 is a graph showing the relationship between the Fe concentration during plating and the X-ray diffraction intensity of each alloy phase. Figure 4 shows the measured Fe concentration in the plating and the actual Fe in the plating.
It is a graph which shows that a density changes according to a basis weight.

Claims (1)

[Claims] 1. A Fe-Zn alloy phase formed in a galvannealed steel sheet by irradiating the galvannealed steel sheet with characteristic X-rays and one or more phases selected from metallic zinc, that is, η phase, X X-ray diffraction of one or more phases selected from the Fe-Zn alloy phase and the η phase for which the measured values were obtained by measuring the line diffraction intensity and the basis weight at the same time. Measure the iron concentration in the galvanized steel sheet, which is characterized in that the strength and the measured value of the basis weight are used as variables and the Fe concentration in the plating is substituted into a regression equation to determine the Fe concentration in the plating. how to.