JPS6352045A - Quality assessment method for galvanized steel sheet - Google Patents

Abstract

PURPOSE:To enable prompt assessment of the quality of a zinc hot dip coated or zinc alloy hot dip coated surface by projecting a monochromatic X-ray to said surface and comparing the X-ray diffraction intensities of the arbitrary index plane of the Zn crystal in the plated surface and the index plane parallel therewith. CONSTITUTION:The monochromatic X-ray is projected to the zinc hot dip coated or zinc alloy hot dip coated surface and the X-ray diffraction intensities of the arbitrary index plane of the Zn crystal in the plated surface and the index plane parallel therewith are measured. The two intensities are then compared. The resistance of a galvanized steel sheet (more particularly zero spangle material) to exfoliation with lapse of time is evaluated by using preferably an online installed X-ray diffraction instrument (for example, deffractometer diffraction analyzer). The information obtd. in such a manner is not only helpful for the direct evaluation of the quality of said steel sheet but also feedable back to a production side by using an adequate control means.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for determining the plating quality of zinc-based plated steel sheets. More specifically, the present invention relates to a method for immediately determining the quality of hot-dip galvanized steel sheets by measuring X-ray diffraction intensity.

(Prior Art) Hot-dip galvanized steel sheets are used in a wide range of applications as inexpensive rust-proof steel sheets, and in recent years, so-called zero-spangle hot-dip galvanized steel sheets in which dendrites are made finer during solidification have been widely used. The steel plate is rapidly cooled while being sprayed with a nucleating agent during the solidification process during plating, and unlike conventional galvanized iron, the steel plate has a beautiful appearance and is suitable as a base for painting.

However, in recent years, as this steel plate has been used for various purposes, particularly in severe corrosive environments, the drawbacks of this type of zero spangle material have been exposed. That is, if this material is left in a highly humid environment, the plating layer may peel off. This is generally said to be caused by intergranular corrosion of the Zn-M alloy.

The cause of this intergranular corrosion is thought to be as follows.

The plating molten metal for hot-dip galvanizing should contain 0.1 to 0.
3% HeQ and less than 0.2% PB are added. AQ is added to suppress the formation of a brittle diffusion alloy layer.

PB is added for the purpose of forming spangles on the surface and improving the fluidity of the molten metal in response to the requests of specific customers. For this reason, in the non-equilibrium solidified Zn-A2 alloy, α-M is precipitated with aging from the η-Zn phase containing supersaturated AQ as a solid solution. It is generally believed that intergranular corrosion of Zn-AQ occurs due to the formation of corrosion cells with -Zn. During manufacturing, the zero-spangled material undergoes a rapid solidification operation during solidification, so a large amount of AQ is supersaturated in solid solution in the η-Zn solid phase, and in the subsequent process, α-AQ is precipitated by aging. Further, for the above-mentioned reasons, some PB coexists. For this reason, in the zero spangle material, intergranular corrosion of the plating layer occurs over time, which may lead to peeling of the plating layer (hereinafter, this phenomenon is referred to as peeling over time).

(Problem to be solved by the invention) Generally, hot-dip galvanizing equipment produces both zero-spangle material and spangled material, so whether or not the plated steel sheet obtained during production is likely to cause intergranular corrosion. It is necessary to quickly determine what is happening and feed that information back to the production line control section as quickly as possible. Conventionally, there is no established method for such instant quality judgment and quick feedback based on it. This is because analysis of bath components using fluorescent X-rays is not very successful. Therefore, in some cases, there is a possibility that products that are at risk of aging may be shipped to users who plan to use them in high-temperature environments.

The present invention solves the problems of the conventional technology, instantly determines the quality of a plated product, determines the risk of intergranular corrosion of that product, and quickly feeds it back, thereby improving the quality of the plated product. The purpose is to perform feedback management of operations such as adjusting bath composition, and to apply it to shipping product inspection.

(Means for Solving the Problems) The present inventors have conducted detailed studies on the relationship between the peeling phenomenon of the zero-spangle material film over time and the crystal structure of the plating film, and found that this type of The present invention was completed by determining that the film that causes peeling has unique crystal structure characteristics.

Therefore, the gist of the present invention is to irradiate a hot-dip galvanized or hot-dip zinc-based alloy plated surface with
This is a preliminary quality determination method for zinc-based plating RL, which measures linear diffraction intensity and compares the two intensities.

However, in the main text of this specification, hexagonal plane index (hk・it
) is abbreviated as (hk I ).

-C, the zero spangle galvanized steel sheet is characterized by a structure in which the hexagonal base planes of η-Zn, that is, the (002) index planes are arranged substantially parallel to the surface of the steel sheet. Therefore, if a zero-spangled galvanized steel sheet is diffracted >1 time, it will show a sharp peak at an angle corresponding to the l-Zn (002) index plane, whereas the η-Zn (004) index plane will be
2) Since the plane is parallel to the index plane, in principle η-Zn
An intensity proportional to the diffraction intensity of the (002) index plane is obtained. When crystallographically unbiased Zn powder is used, for example, when 5 is used for Co as X & 91, the η-Zn (004) index plane and the η-Zn (002
) The integrated intensity ratio of the index plane is 0.08. This is a result for random powder, but even when the crystal is perfect and the crystal has preferential orientation, the intensity ratio is 0.0.
The present inventors have determined that the η-Zn(004) index plane and the v-Zn(
002) As a result of a detailed study of the strength ratio of the index plane, it was found that there is a relationship between the strength ratio and the intergranular corrosion characteristics of the plating layer over time. They discovered that the intensity ratio was an abnormally large value and completed the present invention.

That is, according to the results of the studies conducted by the present inventors, in a hot-dip galvanized film that is prone to peeling over time, in an essentially perfect crystalline state, for example, when integral strengthening is used, a value of about 0.08 is obtained. It is expected that 77-Zl
The intensity ratio of the l(004) index plane and the η-Zn(002) index plane becomes an abnormally large value, and in some cases, 'f1
．． In some cases, it reaches a level of about o. Regarding this,
Please refer to the experimental results described below. As for the X-ray diffraction intensity used in the present invention, it is fully possible to use not only the integrated intensity but also the peak intensity.

(Example) Preferably an on-line installed xm diffraction device (for example, a defractometer diffraction analyzer using Co as a radiation source)
Hot dip galvanized steel sheet (especially zero spangle material)
Evaluate the quality (especially resistance to peeling over time).

The information obtained thereby is not only useful for directly evaluating the quality, but also fed back to the manufacturing side by using appropriate known control means.

For example, the η-Zn (004) index plane and the η-Zn(0
02) If the X-ray diffraction intensity ratio of the index plane exceeds a certain allowable upper limit, the plated steel strip is modified by heat treatment at a temperature below the melting point of Zn, either continuously or by batch treatment. Nao X
When Co 3 is used as a radiation source (wavelength: 1.790), the allowable upper limit is 0.35 in terms of integrated intensity ratio,
A peak intensity ratio of about 0.7 can be selected.

In another method, an IIJ control system may be provided to adjust the composition ratio of the drug solution and air in the zero spangle device (atomizer).

By specifically utilizing the technical idea of the present invention in this manner, the effects of the present invention are further enhanced.

Note that the >1 diffraction intensity of the (004) index plane and (002) index plane of the 1-Zn crystal does not necessarily have to be based on the integrated intensity obtained by integrating the diffraction angle as a parameter between the width of the diffraction angle, but rather the peak In addition, in this example, the diffraction intensity ratio of the η-Zn (004) index plane and the (002) index plane is used, but the diffraction intensity ratio of other parallel index plane pairs may be used. In principle, it is also possible to use η−Z
The relationship between the diffraction intensities of the n (004) index plane and the (002) index plane in materials that tend to peel off over time is crystallographically defined as η-Zn crystal (ah, mk
, mA) exponential plane and (h, k, 1) exponential plane (where k, 1 is an integer and Mouse is a positive integer).

The crystallographic background of the present invention is basically as follows:
This is thought to be due to the fact that the plating film of the plated plate, which tends to peel off over time, has a crystalline imperfection called a mosaic structure, but the details are still unclear.

(Effects of the Invention) Next, the results of experiments to confirm the effects of the method of the present invention will be explained with reference to the attached drawings.

In the Zenzima one-type hot-dip galvanizing pilot plan, a strip of width 30 mm was plated in various hot-dip galvanizing baths shown in the table below, and 6 g/n of ammonium phosphate-based aqueous solution was sprayed. At the same time, we prototyped a zero-spangle plated steel sheet.

X-ray diffraction intensity measurement was performed on the plated steel sheet obtained using a defractometer diffraction spectrometer using a Co target as an X-ray source. In addition, the sample was placed in a constant humidity chamber at 60°C and 90% relative humidity at 15.30.60.90.120.
After being stored for a test period of 1 day and removed, the adhesion of the plating layer was evaluated by the DuPont impact test. The attached drawings illustrate the experimental results, and the numbers attached to each O indicate the bath composition numbers in the table above, and 1 (004) on the horizontal axis.
) / + (002) in X-ray diffraction? -Zn
It is the integrated diffraction intensity ratio of the crystal (004) index plane and the (002) index plane.

As is clear from the figure, the (004) exponential plane and the (002
) It can be seen that there is a clear correlation between the diffraction intensity ratio of the index planes and the plating quality, and that highly reliable quality judgment is possible by comparing the diffraction intensities of a pair of parallel index planes in the crystal.

Furthermore, since the measurement of X-ray diffraction intensity in the present invention can be performed instantaneously, if quality is judged online, it becomes possible to directly feed the product to the production line within a short time. Therefore, the effect of the present invention in controlling plating quality is extremely large, and it is expected to play a major role in improving the quality of hot-dip galvanizing.

[Brief explanation of drawings]

The attached drawing is a graph showing the relationship between the measured X-ray diffraction intensity ratio of the galvanized surface and the galvanizing quality (constant temperature constant temperature test durability period).

Claims (2)

[Claims] (1) Irradiate the hot-dip galvanized or hot-dip zinc-based alloy plated surface with monochromatic X-rays, measure the X-ray diffraction intensity of an arbitrary index plane of the Zn crystal on the plated surface and an index plane parallel to it;
A method for determining the quality of galvanized steel sheets by comparing their strengths. (2) The selected index plane is (00・2) and parallel to this (
00.4) A method for determining the quality of a galvanized steel sheet according to claim 1.