JP2005098922A - Quality control method for steel sheet having oxide film on surface, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a quality control method, capable of evaluating easily, quickly and accurately a thickness of an oxide film on a surface by an existing method, regarding a hot-dip galvanized plated steel sheet, an electro-zinc-plated steel sheet and a cold-rolled steel sheet having the oxide film on the surface, and to provide a manufacturing method for the steel sheets. <P>SOLUTION: This quality control method for the hot-dip galvanized steel sheet having the oxide film on the surface has a digitizing step for emitting an electron beam accelerated by an acceleration voltage selected out of a range of 0.1-5 kV toward the surface of the hot-dip galvanized steel sheet, and for measuring a signal intensity corresponding to a secondary electron amount generated in the surface to be digitized as a signal intensity value, and a determination step for determining the presence of the oxide film of a prescribed shape on the surface of the hot-dip galvanized steel sheet, based on whether the obtained signal intensity value is brought within a prescribed range. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a quality control method and a manufacturing method for a hot-dip galvanized steel sheet, an electrogalvanized steel sheet, and a cold-rolled steel sheet having an oxide film on the surface.

  In steel products, the coating applied to the surface may have a significant effect on performance. One specific example in which the surface film plays an important role in steel products is the slidability during press forming of steel sheets. The press formability of the galvannealed steel sheet will be described as an example.

  In recent years, steel plates used for home appliances and automobiles are often plated mainly with zinc from the viewpoint of high corrosion resistance. The plating mainly composed of zinc includes electroplating and hot dip plating. From the viewpoint of obtaining high corrosion resistance, a hot-dip galvanized steel sheet that is easily thickened is advantageous. However, the hot dip galvanized steel sheet has the disadvantage that the press formability is inferior to that of the cold rolled steel sheet. This is because the sliding resistance between the hot-dip galvanized steel sheet and the press die is larger than that of the cold-rolled steel sheet. That is, at a portion where the sliding resistance between the bead and the galvanized steel sheet is remarkably large, the hot dip galvanized steel sheet becomes difficult to flow into the press die, and the steel sheet is likely to break.

  As a method for improving the press formability of a galvanized steel sheet, a method of applying a high viscosity lubricating oil is widely used. However, this method has problems such as a coating defect due to poor degreasing in the coating process due to the high viscosity of the lubricating oil, and unstable press performance due to oil shortage during pressing. In order to solve the above problem, it is necessary to reduce the amount of the lubricating oil applied as much as possible. For this purpose, it is necessary to improve the press formability of the hot dip galvanized steel sheet itself.

In the hot dip galvanized steel sheet, a hot dip galvanized steel sheet obtained by galvanizing the steel sheet, and then heat treatment, and an alloying reaction in which Fe in the steel sheet and Zn in the plating layer are diffused occurs. There is an alloyed hot-dip galvanized steel sheet with a Zn alloy phase formed. The former plating is mainly a η phase of zinc, and the latter Fe—Zn alloy phase is usually a film consisting of a Γ phase, a δ ₁ phase, and a ζ phase, and as the Fe concentration decreases, that is, a Γ phase → δ Hardness and melting point tend to decrease in the order of ₁ phase → ζ phase → η phase. Therefore, from the viewpoint of slidability, an alloyed film having a high hardness, a high melting point, and a high Fe concentration is effective, and when emphasizing press formability, the average Fe concentration in the film is effective. An alloyed hot-dip galvanized steel sheet manufactured to a higher height is used.

  However, a film with a high Fe concentration has a problem that a hard and brittle Γ phase is likely to be formed at the plating-steel interface, and a phenomenon of peeling from the interface during processing, that is, so-called powdering is likely to occur. For this reason, in Patent Document 1, in order to achieve both slidability and powdering resistance, a method of applying a hard Fe-based alloy as a second layer to the upper layer by a technique such as electroplating is employed. However, having two plating films has a problem that the manufacturing cost is excessive.

  As a method for solving this problem, a method of forming an oxide film mainly composed of ZnO (see Patent Document 2 and Patent Document 3), a method of forming an oxide film mainly composed of P oxide (see Patent Document 4), Or the method (refer patent document 5) of producing | generating Ni oxide is disclosed.

  However, when Patent Documents 2 to 5 described above are applied to an alloyed hot-dip galvanized steel sheet, the effect of improving the press formability cannot be stably obtained. The inventors conducted a detailed study on this cause. As a result, it was found that the galvannealed steel sheet was caused by non-uniformity of surface reactivity due to non-uniform presence of Al oxide and large roughness of the plating surface. That is, when the above-described Patent Documents 2 to 5 are applied to an alloyed hot-dip steel sheet, the surface reactivity is non-uniform, so that even if electrolytic treatment, immersion treatment, coating oxidation treatment, heat treatment, etc. It is difficult to form a film uniformly on the surface. The plating surface has macro unevenness of several μm or more due to non-uniformity of the alloying reaction and the shape of the Fe—Zn alloy phase. The direct contact with the press mold during press molding is a convex part on the surface, but the sliding resistance at the contact part between the thin part of the convex part and the mold is increased, improving the press moldability. The effect cannot be obtained sufficiently. In addition, the electrolytic treatment described as a manufacturing method in Patent Documents 3, 4, and 5 has a problem that it is costly.

  As a result of intensive studies to achieve the above-described object, the present inventors have provided a flat portion on the plated surface of the alloyed hot-dip galvanized steel sheet, and an oxide and / or water containing Zn on the flat portion surface. It has been found that high press workability can be achieved at low cost by forming an oxide film (see Patent Document 6).

  The alloyed hot-dip galvanized steel sheet has macro roughness on the plating surface due to the difference in reactivity at the steel sheet-plating interface during the alloying treatment and the angular shape of the Fe-Zn alloy. A flat part is provided in such an alloyed hot-dip galvanized steel sheet. By providing a flat convex part, the unevenness | corrugation of the plating surface is relieve | moderated, the surface is smoothed, and the convex part of the plating surface is made flat. Further, by processing the flat portion, it is possible to make the adhesion of the treatment film as described later on the surface efficient and uniform. FIGS. 1A and 1B show a schematic cross-sectional view of such an alloyed hot-dip galvanized steel sheet and secondary electron images observed from the surface indicating the presence of a flat portion, respectively. In FIG. 1B, the dark part is a flat part and the bright part is a concave part.

Although the formation method of a flat part is not specifically limited, It is effective to serve as temper rolling. As a method for forming an oxide and / or hydroxide film mainly composed of Zn on a flat portion, it has been found that it is effective to contact an acidic solution and leave it for a certain period of time (see Patent Document 7). ).
Japanese Unexamined Patent Publication No. 1-319661 JP-A-53-60332 Japanese Patent Laid-Open No. 2-190483 JP-A-4-88196 Japanese Patent Laid-Open No. 3-191093 JP 2001-323358 A JP 2002-256448 A

  Forming the required oxide layer on a specific part of the surface of an alloyed hot-dip galvanized steel sheet has great benefits for press workability, but in order to fully satisfy customer satisfaction, stable and high-performance It is necessary to manufacture a steel plate. Even if the operating conditions that allow stable oxide formation are found, press workability may vary due to changes in the immersion treatment liquid and other manufacturing conditions. Therefore, product management is necessary. As described above, the press workability largely depends on the slidability. Therefore, it is effective to measure the friction coefficient as an index. However, the friction coefficient measurement needs to be performed using a friction coefficient measuring apparatus as shown in FIG. 11, and for that purpose, cutting of the test material, application of oil to the test material, pressing load, and measurement of sliding resistance force. -It is not suitable for performing measurements in a short time, including a data processing step for calculating the friction coefficient.

  The inventors have found that in developing a high press workability alloyed hot-dip galvanized steel sheet, the properties of the flat portion, particularly the oxide thickness and the friction coefficient, are closely related. From this knowledge, the press workability can be evaluated by measuring the oxide thickness of the flat portion. However, existing methods are not sufficient to quickly measure oxide thickness to withstand product management. That is, as for the method of measuring the oxide thickness at a specific site, EPMA has a shorter measurement time than AES, but is not yet sufficient in time. In order to accurately evaluate the oxide thickness by AES or EPMA, it is desirable to evaluate the oxide thickness at least 10 flat portions instead of one flat portion. It will take.

  Furthermore, in AES and EPMA, the operator of the apparatus selects a measurement location (flat portion), but it is not known unless an oxide film is formed on the selected flat portion by actually measuring. Even in the flat portion, the oxide is not formed or there is a possibility that the oxide is lost by rubbing with something, but it is difficult to determine this by AES or EPMA. In EPMA, the measurement region tends to be wider than the beam irradiation region due to the effect that the incident electron beam spreads in the sample. If the area of the flat portion is small, the measurement accuracy is slightly disadvantageous. In particular, AES has the disadvantage that it requires skill in the operation of the apparatus because it requires an ultra-high vacuum, and the apparatus is expensive.

  The present invention has been made in view of the above circumstances, and the surface oxide thickness of the existing hot dip galvanized steel sheet, electrogalvanized steel sheet and cold rolled steel sheet having an oxide film on the surface is determined. It is an object of the present invention to provide a quality control method and a method for producing the steel sheet, which can be evaluated more simply, quickly and accurately than the method.

The features of the present invention that solve the above problems are as follows.
(1) The surface of the hot dip galvanized steel sheet is irradiated with an electron beam accelerated with an acceleration voltage selected from 0.1 to 5 kV, and the signal intensity corresponding to the amount of secondary electrons generated from the surface is measured. Whether or not the hot-dip galvanized steel sheet has an oxide film having a predetermined property on its surface, depending on a quantification step for quantifying as a signal intensity value and whether or not the obtained signal intensity value falls within a predetermined range. A quality control method for a hot-dip galvanized steel sheet having an oxide film on its surface.

  (2) The surface of the hot dip galvanized steel sheet is irradiated with an electron beam accelerated at an acceleration voltage selected from 0.1 to 5 kV, and an observation step for obtaining a secondary electron image thereof, and the amount of secondary electrons is 2 A quantification step for quantifying the brightness of the secondary electron image as a brightness value, and whether or not the obtained brightness value falls within a predetermined range, the hot dip galvanized steel sheet has an oxide film having a predetermined property on its surface. A quality control method for hot-dip galvanized steel sheet having an oxide film on its surface.

  (3) The relationship between the oxide film thickness on the surface of the hot dip galvanized steel sheet and the brightness numerical value is obtained in advance, and the brightness numerical value range in which the oxide film thickness is within a predetermined range is obtained from the result, or the hot dip zinc based A correspondence relationship between the oxide film thickness on the surface of the plated steel sheet and the signal intensity value is obtained, and from the result, a signal intensity value range in which the oxide film thickness is within a predetermined range is obtained, and the determination step includes the obtained brightness value. Whether or not the obtained galvanized steel sheet has a predetermined property on the surface depending on whether or not the obtained signal intensity value is within the predetermined signal intensity range. It is determined whether it has a film, The quality control method of the hot dip galvanized steel plate which has an oxide film on the surface as described in (1) or (2) characterized by the above-mentioned.

  (4) The brightness numerical value range in which the oxide film thickness is in a predetermined range is a brightness numerical value range in which the oxide film thickness is 20 nm or more, or the signal intensity value in which the oxide film is in a predetermined range is the oxide film thickness. The quality control method for a hot-dip galvanized steel sheet having an oxide film on the surface thereof according to any one of (1) to (3), wherein the signal intensity value range is 20 nm or more.

  (5) The brightness numerical value range in which the oxide film thickness is in a predetermined range is a brightness numerical value range in which the oxide film thickness is 30 nm or more, or the signal intensity value in which the oxide film is in a predetermined range is the oxide film thickness. The quality control method for a hot-dip galvanized steel sheet having an oxide film on the surface thereof according to any one of (1) to (3), wherein the signal intensity is in a numerical value range of 30 nm or more.

  (6) The relationship between the friction coefficient of the surface of the hot dip galvanized steel sheet and the brightness value is obtained in advance, and the brightness value range in which the friction coefficient falls within a predetermined range is obtained from the result, or the hot dip galvanized steel sheet. A correspondence relationship between the surface friction coefficient and the signal strength value is obtained, and from the result, a signal strength value range in which the friction coefficient falls within a predetermined range is obtained, and in the determination step, the obtained brightness value is the predetermined value. The hot-dip galvanized steel sheet has an oxide film with a predetermined property on its surface, depending on whether it is within the brightness numerical range or whether the obtained signal strength numerical value is within the predetermined signal intensity range. The quality control method of the hot dip galvanized steel sheet which has an oxide film on the surface as described in (1) or (2) characterized by determining whether or not.

  (7) The brightness value range in which the friction coefficient is in a predetermined range is a brightness value range in which the friction coefficient is 0.160 or less, or the signal strength value range in which the friction coefficient is in a predetermined range is 0. The quality of the hot-dip galvanized steel sheet having an oxide film on the surface according to any one of (1), (2), and (6) Management method.

  (8) The brightness numerical value range in which the friction coefficient is within a predetermined range is a brightness numerical range in which the friction coefficient is 0.140 or less, or the signal intensity numerical range in which the friction coefficient is within the predetermined range is 0 in the friction coefficient. The quality of the hot dip galvanized steel sheet having an oxide film on the surface thereof according to any one of (1), (2), and (6), characterized in that the signal intensity value range is 140 or less. Management method.

  (9) The numerical value step described in (1) is a numerical value of an intensity signal corresponding to the amount of secondary electrons generated from the flat portion of the plating surface, or the numerical value step described in (2) is a flat portion of the plating surface. The quality control method for a hot-dip galvanized steel sheet having an oxide film on the surface thereof according to any one of (1) to (8), wherein the brightness of the secondary electron image is numerically expressed.

  (10) The quantification step described in (1) quantifies an intensity signal corresponding to the amount of secondary electrons generated from a region including both a flat portion and a non-flat portion of the plating surface, or the above (2) In any one of (1) to (8), the digitizing step digitizes the brightness of the secondary electron image of the region including both the flat portion and the non-flat portion of the plating surface. Quality control method for hot-dip galvanized steel sheet having an oxide film on its surface.

  (11) The steel sheet is hot-dip galvanized and then temper-rolled, or hot-dip galvanized, then alloyed and temper-rolled, and further subjected to oxide formation to form an oxide film on the surface and melt. A manufacturing step for manufacturing a zinc-based plated steel sheet, and an evaluation step for performing quality control on the hot-dip galvanized steel sheet manufactured in the manufacturing step by the method according to any one of (1) to (10); The manufacturing method of the hot dip galvanized steel plate which has an oxide film on the surface characterized by having.

  (12) When it is determined in the evaluation step that the hot dip galvanized steel sheet has an oxide having a predetermined property, the hot dip galvanized steel sheet is used as a predetermined shipping object. The manufacturing method of the hot dip galvanized steel plate which has an oxide film on the surface of description.

  (13) In the evaluation step, when it is determined that the hot dip galvanized steel sheet does not have an oxide having a predetermined property, the brightness value falls within a predetermined range as a processing condition of the oxide forming process in the manufacturing step. Or the method for producing a hot-dip galvanized steel sheet having an oxide film on the surface thereof according to (11) or (12), wherein the signal intensity value is adjusted to fall within a predetermined range.

  (14) Instead of hot dip galvanized steel sheet having oxide on the surface, electrogalvanized zinc galvanized steel sheet having oxide on the surface by the method according to any one of (1) to (10) Quality control method for electrogalvanized steel sheet, characterized in that quality control is performed on the electroplated steel sheet.

  (15) In place of the hot dip galvanized steel sheet having oxide on the surface, the steel sheet having oxide on the surface is subjected to quality control by the method according to any one of (1) to (10). A quality control method for a steel sheet, characterized in that

  According to the present invention, it is possible to evaluate the oxide thickness of the surface that determines many of the characteristics of the steel sheet more easily, quickly and accurately than existing methods, and feedback to product management, shipping management, and manufacturing condition adjustment. It becomes possible. Product quality can be stabilized by providing quick feedback to adjustment of manufacturing conditions.

  Hereinafter, the present invention will be described in detail along with the background to the invention.

  The features of the present invention are as follows: (i) Focusing on the difference in secondary electron emission rate between the film material and the base material with respect to electron beam irradiation, and (ii) using an acceleration voltage adjusted by the film thickness, iii) Detecting a difference in film thickness as a difference in secondary electron emission rate.

  The inventors investigated the steel material sample by various physical analysis means using the ultra-low acceleration SEM technology, and when using the ultra-low acceleration SEM with an acceleration voltage of 1 kV or less, not only the contrast of the shape but also the difference in the materials. I noticed that the resulting material contrast image could be obtained. This material contrast has been found to occur even when an oxide layer is present on the metal. FIG. 2 schematically illustrates this.

  That is, as shown in FIG. 2A, at the normal acceleration voltage, secondary electron emission from the base material is dominant in both the portion with the film material and the portion without the film material. Therefore, the difference in the amount of secondary electron emission between the portion with the film material and the portion without the film material is small. On the other hand, when the acceleration voltage of the incident electrons is selected under such a condition that the diffusion of the electrons after the incidence is within the film material, as shown in FIG. The secondary electron emission is determined by the film material itself, and the amount of secondary electron emission in the portion without the film material is determined by the base material itself. At this time, a difference occurs in the amount of secondary electron emission between the film material and the base. For this reason, a material contrast is generated due to a difference in material between the portion with and without the film material.

  Selection of the accelerating voltage of incident electrons so that the diffusion of electrons after incidence can be accommodated in the film material can provide a guideline for the film material and film thickness using Monte Carlo simulation or the like. In the case of an oxide film having a thickness of several to several hundred nanometers, which is important as a steel sheet, from the viewpoint of press workability, the acceleration voltage should be 5 kV or less, preferably about 2 kV or less. An acceleration voltage of around 0.5 kV was effective for an oxide film having a thickness of several tens of nanometers. When a high accelerating voltage is used, charging at a film with low conductivity (including oxide) becomes remarkable, and a change in contrast due to charging is superimposed on the material contrast. In this sense, the acceleration voltage is 5 kV or less, preferably 2 kV or less.

  As a result of further investigation, when an appropriate acceleration voltage is selected, the secondary electron emission rate changes according to the thickness of the oxide film in a sample of the same system having a similar composition. It was found that it can be evaluated as a change in contrast. In the case of an oxide on zinc, it was found that the brightness of the secondary electron image on the oxide film surface was darker than that on the metal surface when irradiated with low acceleration electrons of about 0.5 kV.

  FIG. 3 is a secondary electron image illustrating the difference in brightness of the secondary electron image when electrons are irradiated to the alloyed hot-dip galvanized steel sheets having different oxide thicknesses at a low acceleration voltage (acceleration voltage: 0.5 kV). It is an example. In FIG. 3, (a) shows the case where the average film thickness of the oxide is 25 nm, (b) shows the case where the average film thickness of the oxide is 10 nm. It is what was observed in. As can be seen from the comparison between FIGS. 3A and 3B, the SEM image is dark when the film thickness is thick and bright when it is thin. Note that the lower part of FIG. 3 is an image obtained from a wide area including a flat part and a non-flat part, and the distribution of oxides can be clearly seen. That is, in the secondary electron image in the lower part of FIG. 3, a relatively dark area corresponds to a relatively large amount of oxide, and a bright area corresponds to a relatively small amount of oxide. ing. By examining the secondary electron image in detail, it is known that a relatively large amount of oxide is formed on the flat portion. By observing the secondary electron image in such a wide field of view, the oxide thickness in the region where the oxide is reliably formed can be evaluated.

  Therefore, the brightness of the SEM image was digitized (hereinafter referred to as the brightness value), and the oxide adhesion amount of various samples was examined using EPMA, and the relationship with the brightness value at that time was examined. As for the brightness, the brightness of the captured image was converted into a numerical value of 256 gradations using a commercially available software Photoshop, and an average value thereof was obtained. The oxide adhesion amount was evaluated by the secondary electron intensity of oxygen. The result is shown in FIG. From FIG. 4, it has been found that there is a corresponding relationship between the oxide deposition amount (oxygen intensity) and the brightness. The reason why the oxide brightness value is low in relation to the metal is that the oxide film portion has low conductivity and positive charges accumulate on the surface, so the amount of secondary electrons generated is suppressed and the secondary electron image becomes dark. Possible mechanism. In FIG. 4, [Max256] on the horizontal axis means that the brightness of the image is digitized in 256 gradations.

  This makes it possible to determine the oxide film properties (thickness or adhesion amount) by paying attention to the degree of brightness of the observed secondary electron image.

  Furthermore, when the brightness of the secondary electron image was investigated by sequentially changing the acceleration voltage of the electron beam, it was found that the brightness changed below a certain acceleration voltage. According to the explanation of FIG. 2, this can be considered because the amount of generation of secondary electrons changes near the acceleration voltage at which the acceleration voltage of the electron beam becomes such that the diffusion of incident electrons in the sample is contained in the film. . Thus, the thickness of the film can be evaluated by continuously changing the acceleration voltage and monitoring the change in the amount of secondary electrons generated or the change in the brightness of the secondary electron image.

  In the above method, the essence is the emission amount of secondary electrons, but the relative difference in the emission amount of secondary electrons, that is, the difference in the thickness of the film is obtained by using the SEM as the brightness value of the secondary electron image. The following advantages can be obtained. First, the shape and irregularities of the sample can be observed simultaneously. This can be used to evaluate the film thickness distribution. In addition, by observing the surface form, it is possible to appropriately evaluate the film thickness by performing evaluation while avoiding an unsuitable part such as a contaminated place. It is optimal when evaluating the film thickness of a specific part like the flat part of the above-mentioned alloyed hot-dip galvanized steel sheet. Second, the measurement time is short. Observation of a second electron image capturing time of 1 second or less is also possible. This is a measurement time of 1 to 1/100 compared with the measurement time by EPMA or AES.

  In order to evaluate the film thickness according to the present invention, a very low acceleration SEM is suitable, but for the purpose of obtaining average film thickness information, in a vacuum vessel drawn with a vacuum pump, A simple apparatus having a function of generating and irradiating an electron beam, a function of detecting and measuring the amount of secondary electrons, and a function of holding a sample can be used.

  The film measurement method as described above can be applied to the evaluation of press workability of hot dip galvanizing. The relationship between the brightness value and the friction coefficient at the flat part of the plated surface of the alloyed hot-dip galvanized steel sheet with different amounts of oxide applied to the surface was investigated. The coefficient of friction is the coefficient of friction when measured using the bead of FIG. 12 using the coefficient of friction measuring device of FIG. A specific method for measuring the friction coefficient is the same as the method described in Example 1 described later. The brightness values were obtained in the same manner as in FIG. The survey results are shown in FIG. From FIG. 5, it was found that this brightness value also corresponds to the friction coefficient, and as a result can be an index of press workability.

  As described in the problem to be solved by the invention, in a high press workability galvannealed steel sheet, the oxide film thickness of the flat part is closely related to the friction coefficient, so the oxide film thickness is the oxide film thickness in the flat part. Thought that it was necessary to measure. In this method, the relationship between the brightness value and the friction coefficient in a wide area (entire) including a flat portion and a portion other than the flat portion was investigated. The survey results are shown in FIG. From FIG. 6, it was found that the brightness value corresponding to the friction coefficient can be obtained even from a wide field of view. The reason for this is that (i) the flat portion exists at an area ratio of several tens of percent, and therefore there is a certain relationship as a whole. (Ii) The oxide thickness of the portion other than the flat portion (non-flat portion) is It seems that it is not as thick as the flat part but increases or decreases in the same tendency as the flat part. Therefore, even if the brightness value is measured over a wide area including a flat portion and a portion other than the flat portion, it is considered that a certain relationship is obtained between the brightness value and the friction coefficient.

  From this, the coefficient of friction can also be evaluated by obtaining an average brightness value of a wide field of view (for example, 1 mm × 1 mm) at a low magnification using SEM. Compared to the measurement of the brightness value in the flat part, information averaged with a small number of measurements (number of fields of view) is obtained, which is effective in shortening the measurement time.

The present invention has been made based on such findings. Hereinafter, an embodiment of the present invention will be further described with reference to FIGS. 7 to 10 by taking a high press workability galvannealed steel sheet as an example.
(1) Overall description of manufacturing method and quality (shipment) management of high press workability alloyed hot dip galvanized steel sheet An alloyed hot dip galvanized steel sheet imparting high press workability is usually manufactured by the following steps. That is, using a continuous hot dip galvanizing equipment (CGL) equipped with an alloying heating furnace, the steel sheet is immersed in a hot dip galvanizing bath by a conventional method, then hot dip galvanizing is performed, and then it is pulled up from the galvanizing bath to adjust the coating amount. (Melting plating process), alloying treatment is performed in an alloying heating furnace, and an Fe—Zn alloy layer is formed on the steel sheet surface (alloying treatment process). Next, after temper rolling (temper rolling process), an oxide formation treatment was performed to form an oxide film on the surface (oxide formation treatment process; S1 in FIGS. 7 to 10), and then wound The coil is wound up with an apparatus to produce an alloyed hot-dip galvanized steel sheet.

  In the present invention, quality inspection, determination, determination of a shipping method, or feedback to manufacturing condition control is performed on the alloyed hot-dip galvanized steel sheet manufactured in the above process.

  Specifically, first, a test sample is cut out from the coil of the galvannealed steel sheet produced as described above. The location and frequency can be appropriately determined according to variations in product performance and manufacturing stability. For example, it cuts out from the top and bottom of one coil. When the performance of the product is obtained stably, for example, sampling may be performed at a rate of one for every five coils. Next, after the cut sample is washed, its surface is observed with a very low acceleration SEM, and after taking an image, the brightness is digitized (S2 in FIGS. 7 to 10). Based on the obtained brightness value, the performance of the alloyed hot-dip galvanized steel sheet is judged (S3 in FIGS. 7 to 10), and based on the results, the shipping destinations are appropriately distributed (FIG. 7, FIG. 8) or change manufacturing conditions (FIGS. 9 and 10).

(2) Description of Evaluation Step (2-1) Description of Device Used (Ultra Low Acceleration SEM) An SEM that can constantly irradiate an electron beam with an acceleration voltage of 0.1 kV to 2 kV is used. In this acceleration voltage range, the acceleration voltage can be freely changed without losing the spatial resolution better than 5 nm, and it is desirable to have a Schottky field emission electron gun from the viewpoint of electron beam stability. As the secondary electron detector, one capable of selectively detecting many low energy secondary electrons, if possible, is desirable. In addition, it is desirable to have a sample preparation room because it can set up up to measurement quickly. As an example, the LEO 1500 series (LEO) is suitable for the above purpose.

(2-2) Description of measurement object An alloyed hot-dip galvanized steel sheet that has been plated, alloyed, temper-rolled and then subjected to oxidation treatment is an inspection object. In order to obtain high press formability, it is necessary to deposit the oxide deposit thicker than a certain thickness. The inventors have scrutinized the relationship between the oxide film thickness measured by Auger electron spectroscopy and the friction coefficient, and as a result, found that the thickness of the oxide film is preferably 15 nm or more, and more preferably 25 nm or more. If such an oxide film is obtained, alloyed hot-dip galvanized steel sheets having friction coefficients of 0.160 or less and 0.140 or less can be stably supplied. Of course, it is possible to set a standard depending on the purpose, but the oxide thickness on the galvannealed steel sheet is 20 nm or more, preferably 30 nm or more in view of safety in product management. One criterion is whether or not an object is given.

(2-3) Quantification of brightness value, concept, etc. It has already been described that there is a good relationship between the brightness of the secondary electron image observed at extremely low acceleration, the amount of oxide film, and the coefficient of friction. In order to quantitatively evaluate the oxide film thickness and performance from the obtained brightness, the brightness value obtained with the same observation / image capture and digitization conditions, and the oxide film thickness, oxide amount or It is necessary to determine the relationship with the friction coefficient and compare the results obtained by observing and digitizing the sample to be inspected under the same conditions. However, since it is not easy to keep all the conditions constant, observation and image digitization are performed on the reference sample at the same time as the inspection target sample under the same conditions, and the numerical value obtained from the inspection target sample and the reference material It is realistic to determine the performance of the sample to be inspected with reference to numerical values. As the reference sample, a stable substance whose surface does not easily change (for example, a Si wafer with a SiO ₂ film) or an actual material whose oxide film thickness and friction coefficient are known can be used. When an actual material having a known oxide film thickness and friction coefficient is used, the determination is facilitated by using a material at the boundary of the quality determination.

(2-4) Description of measurement procedure (i) Sampling Sample pieces cut out from the coil after production are to be observed and evaluated. For example, it is easy to use a punching machine having a diameter of 10 mm. The cutout location can be arbitrarily set. Since the manufactured coil is coated with anti-rust oil, it is cleaned. For example, it is possible to employ immersion in an organic solvent such as acetone for 5 to 10 minutes or ultrasonic cleaning. Although the method is not limited, it is unified between samples.

(Ii) Ultra-low acceleration SEM observation (observation step)
The sample is introduced into a very low acceleration SEM along with a reference sample. It is desirable that several hours have passed since the SEM was made movable for stabilization. For example, it is effective to hold the voltage with a Schottky electron gun applied. After checking the uniformity of oxide adhesion by SEM observation, an area for capturing an image is determined.

(Iii) Image capture The sample to be measured and the reference sample are observed under the same observation conditions, and the image is captured as digital data under the same conditions. In this case, the same observation conditions are as follows.
Acceleration voltage: can be changed depending on the target film thickness. For example, an acceleration voltage of about 0.5 kV is effective for an oxide film of several to several tens of nm on the alloyed hot-dip galvanized steel sheet.
-Incident electron conditions: acceleration voltage, aperture, beam diameter (normally minimum), electron scanning range (magnification), scanning speed, scanning method-Detection conditions: detector conditions (applied voltage, etc.), brightness, contrast, Gain, offset / image capture conditions: number of capture points, capture time, brightness, contrast, gain, offset, capture field: When capturing only flat areas, the number of capture fields is, for example, in the range of 3-5 μm. 2 fields of view or more. In the case of uniform oxide deposition, two fields of view are sufficient. If the non-uniformity is high, increase the number of fields of view. For example, 5 fields of view are assumed. When observing in a wide area, two fields of view are sufficient if non-uniformity is not remarkable.

(Iv) Quantification of brightness (numericalization step)
The captured image is read by image processing software. This software can be self-made or commercially available. An example of the latter is Adobe Photoshop. On the software, the brightness of the image range excluding abnormal parts such as adhering matter is digitized. There is no limitation on the numerical conversion method. For example, it is possible to employ a method in which the brightness is divided into 256 gradations and averaged with the number of image data points within the above range. The image is digitized by the same method for both the inspection target sample and the reference sample.

(V) Judgment of performance (judgment step)
The correspondence relationship between the brightness of the secondary electron image and the oxide film thickness or oxide amount, or the brightness of the secondary electron image and the friction coefficient is obtained in advance. Specifically, an electron beam accelerated at an acceleration voltage selected from 0.1 to 5 kV on the surface of an alloyed hot-dip galvanized steel sheet having oxide films with different film thicknesses formed by the oxide formation process. The brightness of the secondary electron image generated from the surface is converted into a numerical value, and the correspondence between the oxide film thickness (which may be the amount of deposited oxide film; the same applies hereinafter) and the numerical value of brightness is obtained in advance. deep. Alternatively, the correspondence between the brightness value of the secondary electron image and the friction coefficient is obtained in advance.

  As described above, the above-described correspondence can be obtained for only a flat portion, a portion including a flat portion and a non-flat portion (a wide area portion). From the viewpoint of improving the evaluation accuracy, it is preferable to obtain the correspondence in the flat portion. From the surface to be simply evaluated, a correspondence relationship in a portion including the flat portion and the non-flat portion may be obtained and the result may be used.

  As shown in FIG. 13 of Example 1, the correspondence relationship may be obtained as a characteristic curve indicating the relationship between the oxide film thickness and the brightness value for the flat portion of the galvannealed steel sheet. From FIG. 13, for example, the threshold value of the brightness value at which the thickness of the oxide film is 20 nm or more can be seen. Similarly, the threshold value of the brightness value at which the film thickness is 30 nm or more is known.

  Moreover, as shown in FIG. 14 of Example 1, it may obtain | require as a characteristic curve which shows the relationship between an oxide film thickness and a numerical value of brightness about the area | region containing the flat part and non-flat part of an galvannealed steel plate. . From FIG. 14, for example, the threshold value of the brightness value at which the thickness of the oxide film is 20 nm or more can be seen. Similarly, the threshold value of the brightness value at which the film thickness is 30 nm or more is known.

  Moreover, as shown in FIG. 15 of Example 2, you may obtain as a characteristic curve which shows the relationship between the friction coefficient of an galvannealed steel plate, and the brightness value of a flat part. From FIG. 15, for example, the threshold value of the brightness value at which the friction coefficient is 0.160 or less is known. Similarly, the threshold value of the brightness value at which the friction coefficient is 0.140 or less is known.

  In addition, as shown in the respective drawings, the oxide film thickness and the brightness value, and the friction coefficient and the brightness value have a positive correlation or a negative correlation. Therefore, the film thickness determination is performed without obtaining the above-described characteristic curve. The value of the brightness value corresponding to the threshold value of the film thickness at the time may be obtained and used as the threshold value of the brightness value. Similarly, a brightness value corresponding to a friction coefficient threshold value in the friction coefficient determination may be obtained and used as the brightness value threshold value.

  Note that since the characteristic curves are different when the oxide species (oxide formation treatment) are different, it is preferable to obtain the relationship described above for each oxide species (oxide formation treatment).

  The brightness value obtained for the sample to be inspected is corrected with the brightness value of the reference sample, and the performance of the sample to be inspected is determined based on the corrected brightness value. An example of the correction is the ratio of the numerical value of the reference sample when the relationship between the brightness value of the secondary electron image and the oxide film thickness or the friction coefficient is calculated to the numerical value of the reference sample at the time of the inspection. Multiply the brightness value. Based on the relationship between the brightness value and the oxide film thickness / friction coefficient, the corrected brightness value of the sample to be inspected is a criterion for determining whether the performance is good (for example, an oxide film thickness of 20 nm or more, or a friction coefficient of 0.160 or less). It is determined whether it is within the range.

  If the apparatus is adjusted so that the numerical value of the reference sample matches the numerical value of the reference sample when the relationship between the brightness value of the secondary electron image and the oxide film thickness or the friction coefficient is obtained, Without performing this correction, it is possible to determine the performance directly from the numerical value of the sample to be inspected.

(3) Shipping judgment process (judgment step)
In the shipment judgment process, the sample to be inspected based on the brightness value (corrected brightness value) of the sample to be inspected and the threshold value of the brightness value determined in consideration of the performance of the galvannealed steel sheet. Judge the performance.

  As an example of the determination method in the determination step (S3), the grade of the product is previously classified based on the oxide film thickness or the friction coefficient, the brightness value corresponding to the grade is adopted as the determination criterion, and the brightness of the sample to be inspected. This is a method of classifying the coil from which the sample is collected based on the numerical value. For example, in the flow of FIG. 7, as a determination criterion in the determination step (S3), a material that satisfies the oxide film thickness of 20 nm or more or a friction coefficient of 0.16 or less is determined as a high grade product, and a material that does not satisfy the above is determined as a normal grade. Shipment destinations can be sorted based on the determination result. For example, it is possible to always carry out appropriate product shipment by delivering the former to a customer with severe press working conditions and the latter to a customer with loose press working conditions. By setting the judgment standard to an oxide film thickness of 30 nm or more (or friction coefficient 0.140 or less), products that pass the inspection standard can be stably supplied as products that are satisfied even by customers with severe processing conditions. Is possible. In this way, a plurality of determination criteria can be set. The above two references may be set, or more.

  The above is the case where the base material is soft steel, but the reference value can be changed by changing the base material even under the same processing conditions. For example, a difficult-to-process steel plate such as high-strength steel requires higher slidability, and therefore, the criteria can be tightened.

  Another example of the determination method in the determination step (S3) is an oxide film in advance based on performance targets determined from order conditions (press conditions, quality standards, base steel plate material designation, etc.) as shown in the flow of FIG. In this method, a reference value (threshold value) for thickness or friction coefficient is set, and a brightness value corresponding to the reference value is adopted as a determination criterion in the determination step (S3). In the determination step (S3), a coil that satisfies the reference value is determined as a material to be shipped to the order, and a coil that does not satisfy the reference value is determined not to be shipped to the order. In this way, appropriate shipment management can be performed. In addition, in cooperation with the customer, the customer's press molding conditions (pressing pressure, press speed, type and amount of press oil) are appropriately linked with the oxide thickness or friction coefficient of each coil evaluated in the present invention. By changing to, it becomes possible to realize press working with few defective products.

(4) Description of the feedback process to the operating conditions The performance judgment result of the present invention is effective not only for the shipping destination allocation judgment but also for adjusting the manufacturing conditions of the high press workability galvannealed steel sheet. . For example, as shown in the flow of FIG. 9, when the brightness value of the sample to be inspected is within the threshold value of the brightness value set in advance in the determination step (S3), the processing condition of the oxidation process is changed. First, when the brightness value of the sample to be inspected deviates from a preset brightness value threshold value, the processing condition of the oxidation treatment step (S1) is adjusted to a condition that the brightness value falls within the threshold value. This greatly contributes to stable production of products. Since the inspection time required for the present invention can be determined in about 10 minutes after sampling, it can be sufficiently reflected in adjusting the conditions of the oxidation treatment process. Manufacturing conditions to be changed by feedback include the composition of the oxidation treatment liquid, pH, temperature, the amount of treatment liquid deposited, or the treatment time. By obtaining the relationship between these conditions and the film thickness in advance, the processing conditions can be easily adjusted. For example, when the oxide film thickness is thinner than a specified value, the oxide film thickness can be increased by slowing the line speed and lengthening the oxidation treatment time. If the oxide film is too thick, it can be dealt with by increasing the line speed.

  Also, as shown in the flow of FIG. 10, when implementing the present invention, based on performance targets determined from order conditions (press conditions, quality standards, base steel plate material designation, etc.), the oxide film thickness or the friction coefficient in advance. In the determination step (S3), the brightness value corresponding to the reference value (threshold value) is adopted as the determination reference. In the determination step (S3), if the brightness value clears the reference value, the manufacturing is performed. When it is determined that the ordered product can be assigned to the order and the brightness value does not satisfy the reference value, the manufactured product is determined not to be assigned to the order, and the manufacturing conditions of the oxidation treatment step (S1) Is controlled so as to change the numerical value of brightness so as to fall within a predetermined range. Two types of reference values may be set. That is, the first reference value for determining whether to assign to an order and the first reference value are provided separately from the first reference value, and the second reference value that is stricter than the first reference value is provided. You may make it perform feedback control which changes conditions. By doing so, it is possible to perform appropriate shipment management as well as manufacturing without waste.

  In the above-described embodiment, the method of once taking the secondary electron image of the ultra-low acceleration SEM and digitizing it as the numerical value of brightness has been described, but the essence is the amount of secondary electrons generated from the surface of the target material. . Therefore, a signal that depends on the amount of secondary electron emission (for example, the output of the secondary electron detector) is directly measured and digitized, and the signal (signal intensity signal) is used instead of the above-described brightness value, and the oxide film It can also be used for property determination.

(5) Application to other varieties In the above-described embodiments, from the viewpoint of improving press workability, an alloyed hot-dip galvanized steel sheet that imparts an oxide to the surface has been described as an example. The present invention may be applied to a case where the target oxide may contain a hydroxide, and the oxide is provided for purposes other than press workability.

  The target steel sheet is not limited to the alloyed hot-dip galvanized steel sheet, but can also be applied to hot-dip galvanized steel sheets with oxides (including hydroxides) added to the surface for the purpose of improving press formability. is there.

  The hot dip galvanized steel sheet is manufactured without performing the alloying process in the manufacturing process of the galvannealed steel sheet. In the present specification, the alloyed hot dip galvanized steel sheet and the hot dip galvanized steel sheet are collectively referred to as a hot dip galvanized steel sheet.

  In addition, the present invention provides feedback to quality inspection, management, and production conditions (oxide addition treatment conditions) of steel sheets such as electrogalvanized steel sheets having oxides on the surface and cold rolled steel sheets having oxides on the surfaces. Application to the manufacturing method to be performed is possible.

  Electro-galvanized steel sheet with oxide on the surface is manufactured by performing electro-galvanizing on an annealed and temper-rolled steel sheet, forming a zinc-based plating layer on the surface, and then performing oxide formation treatment To do.

  A cold-rolled steel sheet having oxide on the surface is manufactured by annealing and temper-rolling a cold-rolled steel sheet and then performing an oxide formation treatment. In combination with performing an oxide formation treatment after temper rolling, or instead of performing an oxide formation treatment after temper rolling, an oxide may be applied in the annealing step. The present invention can be applied to the surface of a hot-rolled steel sheet as well as the cold-rolled steel sheet.

  In the above description, the press formability has been described. However, the present invention can be applied to other than the press formability as long as the oxide thickness is involved. Specific application destinations include, for example, feedback to quality control / manufacturing methods of corrosion resistance, conductivity, weldability, adhesion, and chemical conversion treatment.

Next, an example explains the present invention.
On a cold-rolled steel sheet having a thickness of 0.8 mm, a plating film having an Fe concentration of 9.5 wt% to 10.5 wt% by a conventional alloying hot dip galvanizing method with a target of 50 to 60 g / m ² per side. Formed. This alloyed hot-dip galvanized steel sheet was subjected to temper rolling to form a flat portion of the surface with an area ratio of the flat portion of 40% to 60%, and then ferrous sulfate (about 40 g / liter) and sodium acetate ( It is immersed in an acidic solution (about 40 g / liter) (pH: 2, temperature: 20 ° C. ± 5 ° C.), allowed to run in the air for 4 to 8 seconds, and then subjected to an oxidation treatment by washing with water and drying. An oxide mainly composed of Zn was applied to the surface. Seven coils were arbitrarily extracted from a total of 40 coils manufactured by this method, and the following evaluation was performed on the front side.

(1) Thickness of treatment layer: The thickness of the treatment film in the flat part of the plating surface was evaluated by scanning Auger electron microscopy (SAM) combined with Ar ⁺ ion sputtering. The apparatus used is a SAM660 manufactured by PHI. The flat part of the plating surface was confirmed by the secondary electron image, the electron beam was scanned, and a region of about 3 μm × 3 μm was measured on the flat part surface. Sputtering and measurement were repeated to a depth at which the oxygen concentration was almost constant by Ar ⁺ ion sputtering with an acceleration voltage of 3 kV, and the composition at each depth was determined by correcting the relative sensitivity factor from the detected peak intensity of the element. . The thickness of the treated layer, the content of O is at the position deeper than the maximum value, 1/2 become sputtering time of the sum of a constant and is a value of the maximum value and the internal thickness known SiO ₂ It calculated | required by converting into the depth based on the sputtering rate calculated | required with the film | membrane. The measurement was performed on at least three flat portions per sample, and the average value was used.

(2) Press formability evaluation test "Friction coefficient measurement test"
In order to evaluate press formability, the friction coefficient of each specimen was measured as follows.

  FIG. 11 is a schematic front view showing a friction coefficient measuring apparatus. As shown in FIG. 11, a friction coefficient measurement sample 1 collected from a specimen is fixed to a sample table 2, and the sample table 2 is fixed to the upper surface of a horizontally movable slide table 3. A slide table support 5 having a roller 4 in contact with the slide table 3 is provided on the lower surface of the slide table 3, and when this is pushed up, a pressing load N applied to the friction coefficient measurement sample 1 by the bead 6. A first load cell 7 is attached to the slide table support 5. A second load cell 8 for measuring a sliding resistance force F for moving the slide table 3 in the horizontal direction in a state where the pressing force is applied is attached to one end of the slide table 3. In addition, the test was performed by applying NOXLAST 550HN manufactured by Nippon Parkerizing Co., Ltd. to the surface of Sample 1 as a lubricating oil.

  FIG. 12 is a schematic perspective view showing the shape and dimensions of the used beads. The bead 6 slides with the lower surface pressed against the surface of the sample 1. The bead 6 has a width of 10 mm, a length of 12 mm in the sliding direction of the sample, and a lower portion at both ends of the sliding direction is formed by a curved surface with a curvature of 4.5 mmR. It has a 3 mm plane. The friction coefficient measurement test was performed under the following conditions. The bead shown in FIG. 12 was used, the pressing load N was 400 kgf, and the sample drawing speed (horizontal moving speed of the slide table 3) was 100 cm / min. The coefficient of friction μ between the specimen and the bead was calculated by the formula: μ = F / N.

(3) Brightness Evaluation of Secondary Electron Image A sample punched to 12 mmφ from the vicinity of the center of the length of each coil and from the vicinity of the center of the plate thickness was used as an evaluation object. Ultrasonic cleaning was carried out in acetone for 5 minutes for degreasing. As the SEM, LEO1530 (manufactured by LEO) is used, the sample to be measured and the reference sample are observed under the same observation conditions, and an image is captured as digital data under the same conditions. In this case, the same observation conditions are as follows.

  Acceleration voltage: 0.5 kV, aperture: 30 μm, beam diameter (minimum), magnification: 500 times, scanning speed: 25.7 μs / point, number of data points: 1024 × 768, detector brightness and contrast The image data of 2 fields per sample was taken in constant.

  The brightness of the captured image was digitized with 256 gradations using a commercially available software Photoshop, and an average value was obtained. The average value of the brightness of the image was obtained in two types: (a) only the flat part of the visual field, and (b) the entire visual field.

  FIG. 13 shows the relationship between the brightness of the secondary electron image of only the flat portion and the oxide film thickness evaluated by Auger electron spectroscopy. FIG. 14 shows the relationship between the brightness of the secondary electron image evaluated over the entire field of view and the oxide film thickness evaluated by Auger electron spectroscopy.

  It can be seen from FIG. 13 that there is a good inverse correlation between the brightness of the secondary electron image of the flat portion and the oxide film thickness. That is, the oxide film thickness becomes thicker as the sample with lower brightness of the secondary electron image. In FIG. 14 evaluated over the entire observation field, the correlation is slightly worse, but there is a similar tendency. The friction coefficient of three samples having an oxide film thickness of 20 nm or less showed a value exceeding 0.160, and other than that was 0.160 or less. From this result, for example, in FIG. 13, when the brightness value 147 of the secondary electron image is used as a reference, the sliding performance can be determined based on the friction coefficient 0.160.

On a cold rolled steel sheet having a thickness of 0.8 mm, a plating film having an Fe concentration of 9.5 wt% to 10.5 wt% was formed at a target of 45 g / m ² per side by a conventional alloying hot dip galvanizing method. . The alloyed hot-dip galvanized steel sheet was subjected to temper rolling on the CGL line to form a flat surface portion, and then prepared in advance with Zn sulfate (20 g / liter) and ferrous sulfate (30 g / liter). ) And sodium acetate (40 g / liter), soaked in an acidic solution (pH: 1.5, temperature: 20 ° C.-35 ° C.), allowed to run in the air for 5-7 seconds, and then sodium hydroxide solution (50 g / Liquid) for 3 seconds, followed by an oxidation treatment by washing with water and drying. Here, 16 coils were extracted every 5 coils from the manufactured 80 coils, and were used as evaluation targets.

Evaluation similar to Example 1 was performed about the obtained sample. At that time, the press workability was judged from the following two types based on the friction coefficient.
Judgment (1) Pass: Less than 0.160, Fail: 0.160 or more Judgment (2) Grade 1: Less than 0.140, Grade 2: 0.140 or more and less than 0.160, Grade 3: 0.160 or more The observation and image capture of the secondary electron image are performed at a different chance from those in Example 1, the brightness / contrast value at the time of image capture is also different, and correction with a standard sample is not performed. A direct comparison with Example 1 is not possible. The obtained results are shown in Table 1 and FIG. The sample number is not related to the production order.

  In the determination (1), the brightness coefficient 165 of the secondary electron image is used as a reference, and a value less than that is determined to be good and a value higher than that is determined to be poor, thereby determining whether the friction coefficient is good or not. Further, in the determination (2), it can be seen that the grade of the friction coefficient can be identified by setting the threshold values of the grades 1 and 2 to 140 and the brightness numerical value threshold values of the grades 2 and 3 to 165. From the above results, it is possible to perform appropriate quality control related to press workability based on the brightness value, and to select an appropriate shipping coil in accordance with customer needs.

  In the manufacture of Example 2, the manufacturing conditions for changing the composition of the treatment liquid were optimized based on the brightness value of the secondary electron image. Even if the manufacturing conditions are made constant, the performance of the product may change due to a change in the composition of the treatment solution over time, and thus the manufacturing conditions must be controlled.

  FIG. 16 shows the brightness of the secondary electron image in the order of coil manufacture. In FIG. 16, the part where the manufacturing conditions (composition of the treatment liquid) were changed is indicated by “↑”. By using the brightness of the secondary electron image as an index and feeding back to the production conditions, it became possible to stably produce an alloyed hot-dip galvanized steel sheet having high press workability.

  The present invention is particularly effective for the surface properties of steel materials, especially thin steel plates. The alloyed hot-dip galvanized steel sheet greatly contributes to manufacturing that provides product management, proper shipping management, and stable performance based on judgment of press workability.

It is a figure explaining the galvannealed steel plate which has high press workability, (a) is a cross-sectional schematic diagram of an galvannealed steel plate, (b) is the secondary electron image observed from the surface which shows the presence of a flat part It is. In this invention, it is a schematic diagram which shows the mechanism which can visualize the existence part of a thin oxide film layer, (a) explains the secondary electron emission in normal acceleration voltage, (b) shows the acceleration voltage of incident electrons after incidence. Secondary electron emission when a low accelerating voltage is selected so that the diffusion of electrons in the film material is contained. In the example of the secondary electron image explaining the difference in the brightness of the secondary electron image when electrons are irradiated to the alloyed hot-dip galvanized steel sheets having different oxide thicknesses with a low acceleration voltage (acceleration voltage: 0.5 kV), (A) The average film thickness of the oxide is 25 nm, (b) the average film thickness of the oxide is 10 nm, each of the upper stage is observed at a high magnification, and the lower stage is at a low magnification. . It is a figure which shows the relationship between the brightness numerical value of the secondary electron image by an ultra-low acceleration voltage, and the surface oxygen amount measured by EPMA. It is a figure which shows the relationship between the brightness numerical value of the secondary electron image by the ultra-low acceleration voltage of a flat part, and a friction coefficient. It is a figure which shows the relationship between the brightness numerical value of the secondary electron image by the ultra-low acceleration voltage obtained from the wide area including a flat part and a non-flat part, and a friction coefficient. In this invention, based on the determination result of a determination step, it is a figure explaining the flow which determines the destination of a galvannealed steel plate. In this invention, based on the determination criteria set based on the order, it is a figure explaining the flow which determines the destination of a galvannealed steel plate. In this invention, based on the determination result of a determination step, it is a figure explaining the flow which feedback-controls the process conditions of the oxidation treatment process of an galvannealed steel plate manufacturing process. In the present invention, the flow for feedback control of the determination destination of the alloyed hot-dip galvanized steel sheet and the oxidation treatment process of the alloyed hot-dip galvanized steel sheet manufacturing process will be described based on the criteria set based on the order. FIG. It is a schematic front view which shows a friction coefficient measuring apparatus. It is a schematic perspective view which shows the bead shape and dimension in FIG. In Example 1, it is a figure which shows the relationship between the secondary electron image brightness numerical value of a flat part, and an oxide film thickness. In Example 1, it is a figure which shows the relationship between the secondary electron image brightness numerical value obtained from the wide area including a flat part and a non-flat part, and an oxide film thickness. In Example 2, it is a figure which shows the relationship between the secondary electron image brightness numerical value of a flat part, and a friction coefficient. In Example 3, it is a figure which shows the change of the friction coefficient of the coil evaluated in order of manufacture.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sample for friction coefficient measurement 2 Sample stand 3 Slide table 4 Roller 5 Slide table support stand 6 Bead 7 1st load cell 8 2nd load cell 9 Rail N Push load F Sliding resistance force P Tensile load

Claims (15)

The surface of the hot dip galvanized steel sheet is irradiated with an electron beam accelerated with an acceleration voltage selected from 0.1 to 5 kV, and the signal intensity corresponding to the amount of secondary electrons generated from the surface is measured to obtain a numerical value of signal intensity. It is determined whether or not the hot-dip galvanized steel sheet has an oxide film having a predetermined property on its surface, depending on whether the obtained signal strength numerical value falls within a predetermined range. A quality control method for a hot-dip galvanized steel sheet having an oxide film on its surface. The surface of the hot dip galvanized steel sheet is irradiated with an electron beam accelerated at an accelerating voltage selected from 0.1 to 5 kV, and an observation step for obtaining a secondary electron image thereof is obtained. The galvanized steel sheet has an oxide film having a predetermined property on its surface depending on whether the brightness value is a numerical value, and whether the obtained brightness value is within a predetermined range. A quality control method for a hot-dip galvanized steel sheet having an oxide film on its surface. Obtain the relationship between the oxide film thickness on the surface of the hot dip galvanized steel sheet and the brightness value in advance, and from that result, obtain the brightness numerical range where the oxide film thickness is within the predetermined range, or the hot dip galvanized steel sheet A correspondence relationship between the surface oxide film thickness and the signal intensity value is obtained, and from the result, a signal intensity value range in which the oxide film thickness falls within a predetermined range is obtained, and in the determination step, the obtained brightness value is the predetermined value. The galvanized steel sheet has an oxide film with a predetermined property on its surface, depending on whether it is within the brightness numerical value range or whether the obtained signal strength numerical value is within the predetermined signal strength range. The quality control method of the hot dip galvanized steel sheet having an oxide film on the surface according to claim 1 or 2, characterized in that it is determined whether or not. The brightness numerical value range in which the oxide film thickness is in a predetermined range is a brightness numerical value range in which the oxide film thickness is 20 nm or more, or the signal intensity value in which the oxide film is in a predetermined range is oxide film thickness is 20 nm or more. The quality control method for a hot-dip galvanized steel sheet having an oxide film on the surface according to any one of claims 1 to 3, wherein the signal intensity is in a numerical value range. The brightness numerical value range in which the oxide film thickness is in a predetermined range is a brightness numerical value range in which the oxide film thickness is 30 nm or more, or the signal intensity value in which the oxide film is in a predetermined range is oxide film thickness is 30 nm or more. The quality control method for a hot-dip galvanized steel sheet having an oxide film on the surface according to any one of claims 1 to 3, wherein the signal intensity is in a numerical value range. Obtain the relationship between the friction coefficient of the surface of the hot dip galvanized steel sheet and the brightness value in advance, and from that result, obtain the brightness value range where the friction coefficient is within the predetermined range, or the surface of the hot dip galvanized steel sheet A correspondence relationship between the friction coefficient and the signal strength value is obtained, and from the result, a signal strength value range in which the friction coefficient falls within a predetermined range is obtained. In the determination step, the obtained brightness value is the predetermined brightness value. Whether or not the hot-dip galvanized steel sheet has an oxide film having a predetermined property on its surface, depending on whether or not the obtained signal intensity value is within the predetermined signal intensity range. The quality control method for a hot-dip galvanized steel sheet having an oxide film on the surface according to claim 1 or 2, wherein the quality is determined. The brightness numerical range where the friction coefficient is within a predetermined range is the brightness numerical range where the friction coefficient is 0.160 or less, or the signal strength numerical range where the friction coefficient is within the predetermined range is a friction coefficient of 0.160 or less. The quality control method of the hot dip galvanized steel sheet having an oxide film on the surface according to any one of claims 1, 2, and 6, characterized in that the signal intensity numerical value range is as follows. The brightness numerical range where the friction coefficient is within a predetermined range is the brightness numerical range where the friction coefficient is 0.140 or less, or the signal intensity numerical range where the friction coefficient is within the predetermined range is a friction coefficient of 0.140 or less. The quality control method of the hot dip galvanized steel sheet having an oxide film on the surface according to any one of claims 1, 2, and 6, characterized in that the signal intensity numerical value range is as follows. The digitizing step according to claim 1 digitizes an intensity signal corresponding to the amount of secondary electrons generated from the flat portion of the plating surface, or the numerical step according to claim 2 includes a secondary electron image of the flat portion of the plating surface. The quality control method of the hot dip galvanized steel sheet which has an oxide film on the surface in any one of the Claims 1 thru | or 8 characterized by quantifying the brightness of this. The quantification step according to claim 1 quantifies an intensity signal corresponding to the amount of secondary electrons generated from a region including both a flat portion and a non-flat portion of the plating surface, or the quantification step according to claim 2 includes plating. The surface of any one of claims 1 to 8, characterized in that the brightness of a secondary electron image in a region including both a flat portion and a non-flat portion of the surface is quantified. Quality control method for hot dip galvanized steel sheet. Hot-dip galvanized steel sheet is hot-dip galvanized and then temper-rolled, or hot-dip galvanized, then alloyed and temper-rolled, and further subjected to oxide formation treatment to form an oxide film on the surface, thereby hot-dip galvanizing It has the manufacturing step which manufactures a steel plate, and the evaluation step which performs quality control by the method in any one of Claims 1 thru | or 10 with respect to the hot dip galvanized steel plate manufactured at the said manufacturing step. The manufacturing method of the hot dip galvanized steel plate which has an oxide film on the surface. The surface according to claim 11, wherein, in the evaluation step, when it is determined that the hot dip galvanized steel sheet has an oxide having a predetermined property, the hot dip galvanized steel sheet is a predetermined shipping object. Of a hot-dip galvanized steel sheet having an oxide film on the surface. When it is determined in the evaluation step that the hot dip galvanized steel sheet does not have an oxide having a predetermined property, the processing conditions of the oxide formation process in the manufacturing step are set so that the brightness value falls within a predetermined range or a signal. The method for producing a hot dip galvanized steel sheet having an oxide film on the surface according to claim 11 or 12, wherein the strength value is adjusted to fall within a predetermined range. It replaces with the hot dip galvanized steel plate which has an oxide on the surface, About the electro galvanized steel plate which has an oxide on the surface, it is an electro galvanized steel plate by the method in any one of Claims 1 thru | or 10. Quality control method for electrogalvanized steel sheet, characterized by performing quality control of It replaces with the hot dip galvanized steel plate which has an oxide on the surface, and performs the quality control of the cold-rolled steel plate by the method of any one of Claims 1 thru | or 10 about the steel plate which has an oxide on the surface. A quality control method for steel sheets.

Images