JPH068791B2 - Measuring method of alloying degree of galvannealed steel sheet - Google Patents

Description

The present invention relates to a method for continuously and accurately measuring the alloying degree of an alloyed galvanized steel sheet by an X-ray diffraction method.

For the purpose of improving the weldability of hot-dip galvanized steel sheets and electrogalvanized steel sheets, and the quality characteristics such as corrosion resistance after coating and coating adhesion, these galvanized steel sheets are subjected to heat treatment and Fe-Zn So-called galvannealed steel sheets are produced which have grown alloy phases. The plating layer is
Of the Fe-Zn alloy phases, the δ ₁ phase is the main component, but when there is an excess or deficiency of the heat treatment, a small amount of the Γ phase and ζ phase exist, and there is a case where metallic zinc, that is, the η phase remains. . The quality characteristics of the plated layer change significantly depending on the proportion of each phase in the plated layer. Therefore, in order to produce a high-quality alloyed galvanized steel sheet, the degree of alloying is accurately measured, and the heat treatment conditions, such as the heating temperature or the heating time, are controlled so that the alloying degree is always within a proper range. It is important to manage.

As a method capable of measuring the degree of alloying of an alloyed galvanized steel sheet with relatively high accuracy, for example, Japanese Patent Publication No. 58-4
The method described in 7659 is disclosed. This method measures the X-ray diffraction characteristics of the two Fe-Zn alloy phases in the plating layer and obtains the ratio of the two measured values to measure the degree of alloying. Since the alloying degree cannot be calculated, and the relationship between the alloying degree and the quality characteristics is not direct due to this, the measured value of the alloying degree is fed back to the heat treatment to improve the quality of the plating layer. It has problems such as difficulty in managing characteristics.

The problems of the prior art will be described in detail below.

Fig. 1 shows the Fe-Zn in the plating layer when the degree of alloying is changed by changing the degree of heat treatment, for example, the heating time.
Fig. 1a shows changes in alloy phase composition. Fig. 1a shows a case where a relatively low degree of alloying is obtained by relatively shortening a heating time, and Fig. 1b shows a heating time slightly longer than that of Fig. 1a.
When the degree of alloying is increased, FIG. 1c shows the case where the heating time is made longer than that of FIG. 1b and the degree of alloying is increased.
From FIG. 1, it can be seen that the thickness of the η phase becomes thinner as the alloying degree becomes higher, and conversely, the δ ₁ phase and the Γ phase become thicker as the alloying degree becomes higher. From these, it is possible to measure the alloying degree by measuring the X-ray diffraction characteristics of the Fe-Zn alloy phase and the η phase in light of the relationship between the previously obtained characteristics and the alloying degree. It is estimated that The above-mentioned conventional alloying degree measuring method was made based on this finding, and was invented, and its characteristic is that two units of the Fe-Zn alloy phase are assumed on the assumption that the basis weight varies. The point is to measure the X-ray diffraction characteristics, obtain the ratio of the measured values of the X-ray diffraction characteristics of the two phases, and measure the degree of alloying. However, studies by the present inventors have revealed that an accurate alloying degree cannot be obtained even if the ratio of the measured values of the X-ray diffraction characteristics of the two Fe-Zn alloy phases is obtained.

That is, as shown in FIG. 2, when X-ray diffraction is similarly performed on three galvannealed steel sheets having the same alloy phase composition but different basis weights, X-rays may pass therethrough and reach them. There is almost no difference in the distance between the three steel plates, but the basis weight (weight) is thin (small) (Fig. 2a), relatively thin (Fig. 2b), and thick (large) (2c). The difference in the physical phenomenon of X-rays is as follows. That is, while X-rays are incident on an object and reflected, they are absorbed, scattered, etc., and the amount of X-rays that enter and reach the steel sheet substrate varies depending on the thickness of the plating layer. Also, the amount of X-rays reflected from a certain diffractive surface to reach the detector, that is, the diffraction intensity also varies depending on the thickness of the plating layer closer to the surface layer than the target diffractive surface. The larger the thickness, the smaller the thickness, that is, the weaker the X-ray diffraction intensity. For example, in FIG. 2 in the case of FIG. 2a having a small basis weight and in the case of FIG. 2c having a large basis weight, the smaller the basis weight is, the stronger the diffraction intensity from the δ ₁ layer from the steel plate base is,
The higher the basis weight, the weaker it becomes. On the contrary, the diffraction intensity from the ζ phase is stronger when the basis weight is larger (the absolute amount of the ζ phase is larger),
The smaller the basis weight (the smaller the absolute amount of the ζ phase), the weaker it becomes. Therefore, when the ratio of the measured values of the X-ray diffraction characteristics of the ζ phase and the δ ₁ phase is taken, the difference in the degree of alloying depending on the basis weight is obvious.

On the other hand, recently, the quality characteristics required for the galvannealed steel sheet are severe. For example, when the basis weight becomes thicker, the workability and weldability of the plating layer deteriorate,
Since an alloyed galvanized steel sheet excellent in these properties is required even if it is thick, it is necessary to control the alloying degree within an extremely narrow range. In addition, while fine control of alloying degree according to the required quality characteristics is required, the line speed is increased for the purpose of improving productivity in the production line of alloyed plated steel sheet, and further As a result, the heating capacity for the heat treatment has significantly increased, and the measurement error of the instantaneous alloying degree has been forced to produce a large amount of defective products.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a technique capable of nondestructively continuously measuring the true alloying degree of an alloyed galvanized steel sheet by an X-ray diffraction method. To do.

The present invention relates to the degree of alloying of alloyed galvanized steel sheet Fe
When measuring the concentration, one or more phases selected from the η phase, the ζ phase, the δ ₁ phase, and the Γ phase in the plating layer of the galvannealed steel sheet, and α− of the galvanized steel substrate Fe
And X are respectively measured as X-ray diffraction characteristics by an X-ray diffraction method to measure peak height, area, or half-value, and in order to correct the phase and the coating weight, the measured X-ray diffraction characteristics of α-Fe are used as variables. , Coating weight is 18 ~ 120g
The present invention provides a method for measuring the degree of alloying of an alloyed zinc-plated steel sheet, which comprises measuring the degree of alloying of the alloyed zinc-plated steel sheet in a range of / m ² .

The true degree of alloying in the present invention is defined as the Fe concentration in the plating layer for the sake of simplicity.
The reason is as shown in FIG.
Phase, δ ₁ phase, Γ phase, etc. may be composed of three or more phases, and even one Fe-Zn phase has a relatively wide range of Fe concentration, and quality characteristics within that range. This is because it is complicated and it is not appropriate to express the plating layer only by the phase composition, because the influence on the plating layer is different.

In the present invention, the X-ray diffraction characteristic value of α-Fe of the steel sheet base material is closely related to the basis weight, but it is not affected by the degree of alloying, and the Fe-Zn alloy phase and the η phase in the plating layer. Of the X-ray diffraction characteristics of one or more phases selected from
It was made by discovering that the true alloying degree can be accurately measured by setting the alloying degree to a value obtained by using the measured value of the X-ray diffraction characteristic of Fe as a variable.

As described above, the alloying degree of the galvannealed steel sheet is determined by the X-ray diffraction characteristics of one phase selected from the Fe-Zn alloy phase such as ζ, δ ₁ and Γ and the η phase in the plated layer. The measured value of
Or, it is clear that it can be roughly obtained by the ratio of the measured values of the X-ray diffraction characteristics of the two phases, but the alloying degree by this conventional method is the true alloying degree when the basis weight varies. I don't get it. Therefore, the present invention provides one or more measurement values of X-ray diffraction characteristics selected from the Fe-Zn alloy phase and the η phase in the plating layer of the galvannealed steel sheet and the X-value of α-Fe of the steel sheet substrate. The true alloying degree is measured by taking the value obtained by using the measured value of the line diffraction characteristic as a variable as the alloying degree. Hereinafter, the present invention will be described in more detail.

The measured value of the X-ray diffraction characteristic of α-Fe is used as one variable, because the measured value of the X-ray diffraction characteristic of α-Fe is closely related to the basis weight, and the basis weight is X-ray of the α-Fe. It is based on the knowledge that the measured values of diffraction characteristics can be expressed as variables. That is, FIG. 3 shows the basis weight (Mg
/ M ² ) and the peak height of the X-ray (I _α-Fe ), M = −alog I _α-Fe + b That is, M = f (I _α-Fe ) ... (1) Is established. Such a relationship holds even if X-ray diffraction characteristics other than the peak height are used, that is, the peak area and the half width. Further, M = f (I _α-Fe ) ... (1) is applied to all the plated materials, though it is slightly different depending on the manufacturing history of the plated material, the plate thickness, the rolling reduction and the steel type. be able to.

Further, as described above, in order to measure the true alloying degree by the X-ray diffraction method, it is necessary to appropriately correct the error due to the variation of the basis weight, but fortunately, as described above, Since the measured value of the X-ray diffraction characteristic of α-Fe can be obtained as a variable, the relationship between the true alloying degree and the measured value of the X-ray diffraction characteristic can be obtained for a certain basis weight, and this can be predicted. If it is calculated for all the area weights, the amount of change in the measured value of the X-ray diffraction characteristic for each amount of weight from the certain amount of weight becomes clear. It comes as a variable. Therefore, the function (Y) of the true alloying degree in the entire basis weight range is defined by using a function {f (I _S )} representing the true degree of alloying in a certain basis weight and a basis weight (M) as variables. = F [{f (I _S )}, M] (2), and M is represented by I _α-Fe as a variable, Y = F [{f (I _S ), f (I _α-Fe )}] ... (3). (3) _{also, Y = f (I S,} I α-Fe) ... from expressed in (4), the true Fe content in the total basis weight range of η phase and Fe-Zn alloy phase X It can be seen that it can be obtained by using the measured value of the line diffraction characteristic and the measured value of the X-ray diffraction characteristic of α-Fe as variables.

As a method of continuously measuring the basis weight in a nondestructive manner, there is a method of measuring using fluorescent X-rays and RI, and a method of obtaining the true alloying degree by using the measured values as variables can be considered. According to the research conducted by the present inventors, these methods have a large measurement error of the basis weight and require a completely different measuring device in addition to the X-ray diffraction measuring device. It is known that the above disadvantages are involved.

Hereinafter, the present invention will be specifically described with reference to examples.

In a continuous hot-dip galvanizing line, a steel sheet with a plate thickness of 0.4 to 1.6 mm is passed through a plating bath with a line speed of 50 to 120 m / min and an Al concentration of 0.12 to 0.18 wt% in the plating bath, and a basis weight is adjusted by a gas jet basis weight adjusting device. 18-120g
Immediately after galvanizing in the range of / m ² (one side), in a line for producing an alloyed galvanized steel sheet by continuously performing heat treatment in a gas heating heat treatment furnace at a furnace temperature of 650 to 1000 ° C., The X-ray diffractometer according to the present invention was installed in the post-process of the heat treatment furnace, and the peak height (strength), peaks, and peaks were obtained as X-ray diffraction characteristics for α-Fe, η phase, ζ phase, δ ₁ phase, and Γ phase. Area and half width are measured continuously and η
Of the X-ray diffraction characteristics of one or more phases selected from the phase, ζ phase, δ ₁ phase and Γ phase, and α-Fe
Of the X-ray diffraction characteristics of (2) was added as a variable (the method of the present invention) and not added (the conventional method) to measure the alloying degree. Compared with the true alloying degree.

FIG. 4 shows the relationship between the true alloying degree (iron concentration% by chemical analysis) and the measured alloying degree obtained by measuring the peak height. From the same figure, the alloying degree measurement value (marked by ● in the figure) according to the present invention obtained by using the measured value and the basis weight of the X-ray diffraction characteristic of the Γ phase as variables, the X-ray diffraction characteristic of the η phase and the basis weight Values of the alloying degree according to the present invention (marked with ▲ in the figure), the X-ray diffraction characteristics of the ζ phase and the weight per unit area (marked with △ in the figure), and the η phase. X-ray diffraction characteristics / δ _1- phase X-ray diffraction characteristics ratio and basis weight were obtained as variables, and the measured alloying degree values (circle in the figure) according to the present invention are the true alloying degree and It is clear that there is a one-to-one correspondence, indicating that the method of the present invention exhibits a true degree of alloying. On the other hand, when the X-ray diffraction characteristic of α-Fe is not used as a variable and only the X-ray diffraction characteristic of the η phase / the X-ray diffraction characteristic of the δ ₁ phase is obtained as a variable, the basis weight is 90
g / m ² [□ on the curve (II) in the figure] and the basis weight is 30 g /
It can be seen that the measured alloying degree is markedly different from that of m ² [marked by ■ on the curve (III) in the figure], and the true alloying degree is not shown. The basis weight at each plot point on the curve (I) in FIG. 4 was randomly selected within the range of 18 to 120 g / m ² .

Further, even when the peak area and the half width are used as the X-ray diffraction characteristics, the basis weight is 18 to 120 g / m ² (one side) according to the present invention, as in the case of using the above-mentioned peak height. It was confirmed that the true degree of alloying can be obtained in the range of.

Furthermore, when the alloying degree measured by the method of the present invention is continuously fed back to the atmospheric temperature control of the heat treatment furnace to control the alloying degree, it is possible to always accurately control the desired alloying degree. I also confirmed that there is.

However, when measuring the X-ray diffraction characteristics described in the present invention, as shown in FIG. 5, the peak height (a) from the background G, the peak area (hatched portion, b) and the peak height 2 The width of the mountain in 1 / (a / 2) is the half width (c)
And

[Brief description of drawings]

Figure 1 shows Zn-Fe in the plating layer when the alloying degree is changed.
Fig. 2 is a diagrammatic sectional view showing changes in alloy composition, and Fig. 2 shows physical behavior of X-rays when X-ray diffraction is performed on three alloyed galvanized steel sheets having the same alloy phase composition but different basis weights. FIG. 3 is a diagram showing the relationship between the measured value of the X-ray diffraction characteristics and the basis weight, FIG. 4 is a diagram showing the relationship between the true alloying degree and the measured alloying degree, FIG. FIG. 4 is a diagram for explaining measurement of X-ray diffraction characteristics.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadao Fujinaga 1st Kawasaki-cho, Chiba-shi, Chiba Research Institute of Kawasaki Steel Co., Ltd. (72) Inventor Tadahiro Abe 1st Kawasaki-cho, Chiba-shi Kawasaki Steel Co., Ltd. In-house (56) References JP-A-60-58537 (JP, A) JP-B-58-47659 (JP, B1)

Claims (1)

[Claims] 1. A degree of alloying of a galvannealed steel sheet, F.
When measuring the e concentration, one or more phases selected from the η phase, the ζ phase, the δ ₁ phase, and the Γ phase in the plating layer of the alloyed galvanized steel sheet and the α of the plated steel sheet base material. -F
The peak height, the area, or the half-value are measured as X-ray diffraction characteristics by the X-ray diffraction method, respectively, and the measured X-ray diffraction characteristics of α-Fe are used as variables to correct the phase and the coating weight. The coating weight is 18 to 120
A method for measuring the degree of alloying of an alloyed galvanized steel sheet, which comprises measuring the degree of alloying of an alloyed galvanized steel sheet in the range of g / m ² .