KR102177872B1 - Method of evaluating peelability of coated steel sheet - Google Patents

Abstract

A method of evaluating the peelability of a plated steel sheet is disclosed. The method for evaluating the peelability of a plated steel sheet according to an embodiment includes preparing a plated steel plate sample, processing the plated steel plate sample into a specimen for a high-speed tensile test, performing a high-speed tensile test on the specimen, and It comprises the step of collecting the fragments from and analyzing the collected fragments or specimens to rank the peelability of the plating layer.

Description

Method for evaluating peelability of plated steel sheet {METHOD OF EVALUATING PEELABILITY OF COATED STEEL SHEET}

The present invention relates to a method for evaluating the peelability of a plated steel sheet, and more particularly, to a method for evaluating the peeling phenomenon at the plated layer-base material interface regardless of strength, steel type, and type of plated layer using a high-speed tensile method.

Alloyed hot-dip plated steel sheet (Galvannealed: GA) has excellent corrosion resistance due to the physical protective film and chemical sacrificial method of zinc (Zn) compared to non-plated steel sheet, and the surface of weldability and paintability than general hot-dip galvanized (GI) steel sheet The quality is excellent. In addition, the alloyed hot-dip plated steel sheet can improve corrosion resistance by forming a zinc (Zn) coating layer on the surface of the steel sheet exposed to various environments, and ultimately extend the life of the structural material. However, the alloyed hot-dip galvanized steel sheet forms a Fe-Zn alloy phase in the plating layer through heat treatment after zinc hot dip plating.At this time, a hard alloy phase is formed, due to low toughness during molding, mold friction, and difference in elongation with the base material. There are problems in that powdering, which is peeling within the plating, and flaking, which is peeled off at the interface between the plating and the base material, occur. The problem of peeling of the plated steel sheet is that the steel sheet is exposed to the surface during press forming, thereby lowering the corrosion resistance and causing surface quality defects, which may lead to shortening of product life and sensitivity quality problems.

As a related prior art, there is Korean Laid-Open Patent Publication No. 10-2018-0102157 (name of the invention: high-strength hot-dip galvanized steel sheet having excellent impact peeling resistance and corrosion resistance of a processed portion).

An object to be solved by the present invention is to provide a method capable of evaluating the peeling phenomenon at the plating layer-base material interface regardless of strength, steel type, and plating layer type by using a high-speed tensile method.

A method for evaluating the peelability of a plated steel sheet according to an aspect of the present invention includes: preparing a plated steel plate sample; Processing the plated steel sheet sample into a specimen for a high-speed tensile test; Measuring the weight of the specimen; Performing a high-speed tensile test on the specimen; Measuring the weight of the specimen; And it characterized in that it comprises a step of grading the peelability of the plating layer.

In one embodiment of the present invention, in the step of grading the peelability of the plating layer, the difference may be graded by comparing the weight of the specimen before and after the high-speed tensile test.

A method for evaluating the peelability of a plated steel sheet according to another aspect of the present invention comprises: preparing a plated steel plate sample; Processing the plated steel sheet sample into a specimen for a high-speed tensile test; Performing a high-speed tensile test on the specimen; And grading the peelability of the plating layer by collecting fragments from the specimen and analyzing the collected fragments or specimens.

In the present invention, the step of grading the peelability of the plating layer may include removing debris from the specimen using a tape having good adhesive strength; Measuring the shade of the fragment; And grading the shade of the fragment.

In the present invention, the step of grading the peelability of the plating layer may include removing debris from the specimen using a tape having good adhesive strength; And measuring the length of the point where the fragments are generated from the end of the specimen from which the fragments have been removed, and rating.

In the present invention, the step of grading the peelability of the plating layer comprises: collecting debris from the specimen using a conductive tape; And measuring and rating the average size or distribution of the collected fragments.

According to the present invention, it is possible to evaluate the plating peelability of specimens that cannot be evaluated for peelability such as existing high-strength steel or ultra-high-strength steel using a high-speed tensile test, and various types of high-speed tensile test equipment are used. Peelability evaluation can be performed, and evaluation time is short since it is possible to easily evaluate without a separate special device after high-speed tensile test, and it is possible to further shorten the time and proceed with simple evaluation by converting various evaluation methods to a database after high-speed tensioning. In addition, in addition to the alloyed hot-dip plated steel sheet, there is an advantage in that it is possible to evaluate the peelability of various thin-film plating layers.

1 is a photomicrograph showing the results of a high-speed tensile test on a soft alloyed molten-plated steel sheet specimen.
2 is a photomicrograph showing the aspect of peeling fragments at the end of a specimen subjected to a high-speed tensile test.
3 is a micrograph showing the results of a high-speed tensile test on various soft hot-dip-plated steel sheets and alloyed hot-dip-plated steel sheets having different bonding strengths under a 500/s tensile speed condition.
FIG. 4 is a photograph of a fragment taped after performing a high-speed tensile test on specimens of three steel types having different bonding strengths.
5 is a flow chart illustrating a method for evaluating peelability of a plated steel sheet according to an embodiment of the present invention.
6 is a flow chart illustrating a method for evaluating peelability of a plated steel sheet according to another embodiment of the present invention.
7 is a flow chart illustrating a method for evaluating peelability of a plated steel sheet according to another embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention. The present invention may be implemented in a number of different forms, and is not limited to the embodiments described herein. The same reference numerals are assigned to the same or similar components throughout the present specification. In addition, detailed descriptions of known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

The method of evaluating the plating peelability of a plated steel sheet is generally evaluated differently according to the plating peeling phenomenon such as powdering or flaking. This is because it is understood that the two delamination phenomena mainly occur in different deformation modes. Accordingly, various tests such as V-bending, Cupping, Draw bead test, Hat channel drawing with bead test, etc. are applied to the evaluation of plating peelability. However, since most of the tests involve molding of the base material, there is a disadvantage that it cannot be used in high strength steel or ultra high strength steel. In other words, it is difficult to evaluate the degree of peeling of the plating layer because the base metal is destroyed by bending during the molding of the base material for evaluating the peelability. Therefore, it is necessary to develop an evaluation method that can be applied to various steel grades excluding fracture due to bending. On the other hand, in addition to the plated steel sheet, it is generally difficult to evaluate the bonding strength of the plated layer in the plating of a thin film (eg, 10 μm or less). In the case of thin films, it is common to measure the bonding strength by using the bending test method or the scratch method, but in the case of the bending test method, fracture of the specimen may occur in the case of (super) high-strength steel or brittle material, and in the case of the scratch method, metal Thin films are difficult to measure.

The present invention proposes a method of evaluating the peeling phenomenon at the plating layer-base material interface regardless of strength, steel type, and plating type using a high-speed tensile method. In addition to the plating layer bonding strength, the present invention can be said to have a wide range of applications because the bonding degree or peelability of thin-film plating layers of various materials can be evaluated.

The test conditions of the high-speed tensile test presented in the present invention can be applied differently according to the general or equipment specifications. Plating peelability evaluation is possible even at low tensile speeds, but the difference is more pronounced at high tensile speeds.

1 is a micrograph showing the result of a high-speed tensile test in the range of 0.1 / s to 500 / s for a soft alloyed molten-plated steel sheet specimen, Figure 2 is a micrograph showing the aspect of the peeling fragments at the end of the specimen .

Referring to FIG. 1, it can be seen that the range of peeling from the specimen differs depending on the tensile speed applied to the high-speed tensile test. As shown in FIG. 1, it can be seen that as the tensile speed increases from 0.1/s to 500/s, that is, the range of the white portion at the end of the specimen, that is, the area where peeling occurs, widens.

Referring to FIG. 2, as a result of dividing the tensile speed by 0.1/s, 50/s, and 500/s, it can be seen that the aspect of the peeled fragment differs according to the tensile speed. In other words, it can be seen that the higher the tensile speed, the larger the size of the fragment.

3 is a micrograph showing the results of a high-speed tensile test on various soft hot-dip-plated steel sheets and alloyed hot-dip-plated steel sheets having different bonding strengths under a 500/s tensile rate condition, of approximately 6.50 MPa, 23.80 MPa, and 22.40 MPa. These are pictures of high-speed tensile tests on soft alloyed hot-dip plated specimens with bonding strength.

Referring to FIG. 3, the peeling degree of the specimen having a bonding force of 6.5 MPa was greater than that of the specimen having a bonding force of 23.80 MPa and 22.40 MPa. In other words, it can be seen that as the bonding strength of the plated steel sheet increases, the degree of peeling decreases.

Referring to the results of FIGS. 1 to 3 above, since the peeling pattern appears differently depending on the variable of the high-speed tensile test, it is possible to quantify and grade the plating peelability in various forms by using the high-speed tensile test.

Specifically, first, when a high-speed tensile test is performed on a specimen, a portion of the plating layer is peeled off from the end of the specimen as shown in FIG. 2 due to high-speed tensile, and fragments are removed. Therefore, when the weight of the specimen is measured before and after the high-speed tensile test, a difference in weight occurs due to the peeled fragments, so the degree of peeling can be evaluated by grading according to the change in the weight of the specimen before and after the high-speed tensile test. Next, after the high-speed tensile test, tape the test site with a good adhesive tape to remove debris, and use a vision equipment to shoot light on the test site to measure the shade of the test site, or the length at which the debris exists from the end of the specimen. Can be measured and graded. Alternatively, debris may be collected from the specimen using a conductive tape such as carbon tape, and then the debris may be observed, and the average size and distribution of the debris may be measured and graded. This plating peelability evaluation method can be quantified and graded in various forms according to the user, and various methods other than the above-mentioned methods are possible. In addition, each plating peeling evaluation method presented above can be evaluated quickly and easily through individual automation.

5 is a flow chart illustrating a method for evaluating peelability of a plated steel sheet according to an embodiment of the present invention.

5, a specimen is prepared for a high-speed tensile test (S110). To this end, first, a sample of an alloyed hot-dip galvanized steel sheet is prepared, and then the sample is processed into a specimen for high-speed tensile test. The specimen for evaluating the peelability of the plated steel sheet presented in the present invention is manufactured and tested in accordance with the commonly used high-speed tensile specimen standard (ASTM D638), but it is based on the standard of the equipment used or at the convenience of the user. Accordingly, the shape of the specimen can be different. At this time, it is necessary to define different standards of plating peeling grade according to the shape of the specimen according to the user. After processing the specimen, cleaning is performed to remove foreign substances present on the surface of the specimen.

When the specimen is prepared, the weight of the specimen is measured (S120). In this example, the weight of the specimen before and after the high-speed tensile test is compared and the difference is graded to quantify and evaluate the plating peelability, and the weight of the specimen is measured before performing the high-speed tensile test.

After measuring the weight of the specimen, a high-speed tensile test is performed on the specimen (S130). The test conditions of the high-speed tensile test can be applied differently according to the general or equipment specifications. Although it is possible to evaluate the plating peelability even at a low tensile speed, the difference in weight of the specimen before and after the test is more pronounced at a high tensile speed.

A typical test method used as a technique for evaluating mechanical properties of metallic materials is the tensile test method, through which data such as yield strength, tensile strength, work hardening index, stress coefficient, and uniform elongation can be obtained. This tensile test method contributes to calculating the above-described mechanical properties by applying a tensile force to a test piece, and to apply steel suitable for mechanical properties to an appropriate field based on this. Among these tensile test methods, the dynamic tensile test method generally uses a high-speed tensile tester, which is a method of tensioning a specimen at a certain speed or higher, and is mainly used for evaluating the dynamic properties of a material. In recent years, due to the development of the automobile industry, the high-speed tensile test is preferred to the static tensile test because the mechanical properties of the steel material of the automobile due to external impact and collision that may occur in a high-speed vehicle are mainly required.

A high-speed tensile test is carried out by applying a tensile force to both ends of the specimen at a constant speed using a high-speed tensile tester on the weighed specimen. As the tensile force is applied, the specimen stretches to both sides, causing fracture at some point, and peeling of the plating layer occurs on the surface of the fractured portion.

After the high-speed tensile test is performed, the fractured portion is taped to remove debris, the weight of the specimen is measured again, the difference in weight of the specimen before and after the test is calculated (S140), and the peelability of the plated layer is evaluated by quantifying this (S150). ).

Since a large number of fragments were generated from the specimen in the high-speed tensile test, a difference from the weight of the specimen before the test occurs as shown in Table 1 below.

Table 1 is a table showing the results of measuring the weight of the specimens before and after the high-speed tensile test for three steel types with different bonding strengths.The average weight difference of 0.0040g, 0.0017g and 0.0020g occurred before and after the tensile test, respectively. can confirm.

Sample type Before tensile test (g) After tensile test (g) Weight difference before/after (g) Average before/after weight difference (g) IF GA
(6.50MPa) One 26.6170 26.6152 0.0018
0.0040 2 26.7051 26.7007 0.0044 3 26.7552 26.7493 0.0059 IF GA
(23.80MPa) One 28.3298 28.3274 0.0024
0.0017 2 28.3446 28.343 0.0016 3 28.3423 28.3413 0.0010 IF GA
(22.40MPa) One 25.0667 25.0651 0.0016
0.0020 2 25.1094 25.1067 0.0027 3 25.3875 25.3859 0.0016

In this way, the peelability of the plated steel sheet can be evaluated by measuring and comparing the weight of the specimen before and after the test using a high-speed tensile test and quantifying it.

6 is a flow chart illustrating a method for evaluating peelability of a plated steel sheet according to another embodiment of the present invention.

6, a specimen is prepared for a high-speed tensile test (S210). To this end, first, a sample of an alloyed hot-dip galvanized steel sheet is prepared, and then the sample is processed into a specimen for high-speed tensile test. The specimen for evaluating the peelability of the plated steel sheet presented in the present invention is manufactured and tested in accordance with the commonly used high-speed tensile specimen standard (ASTM D638), but it is based on the standard of the equipment used or at the convenience of the user. Accordingly, the shape of the specimen can be different. At this time, it is necessary to define different standards of plating peeling grade according to the shape of the specimen according to the user. After processing the specimen, cleaning is performed to remove foreign substances present on the surface of the specimen.

When the specimen is prepared, a high-speed tensile test is performed on the specimen (S220). The test conditions of the high-speed tensile test can be applied differently according to the general or equipment specifications. Although it is possible to evaluate the plating peelability even at a low tensile speed, the difference in weight of the specimen before and after the test is more pronounced at a high tensile speed.

The prepared specimen is subjected to a high-speed tensile test by applying a tensile force to both ends of the specimen at a constant speed using a high-speed tensile tester. As the tensile force is applied, the specimen stretches to both sides, causing fracture at some point, and peeling of the plating layer occurs on the surface of the fractured portion.

After performing the high-speed tensile test, tape the specimen with a good adhesive tape to remove the fragments from the specimen (S230), and measure the shade of the fragments by shooting a light beam on the tape to which the fragments are adhered using a vision equipment ( S240), the peelability is evaluated by rating the shade and length ratio of the fragment (S250). The vision equipment is an equipment in which a null is used as an equipment indicating the degree of transmission by beaming light to the specimen, that is, the shade of the specimen in a numerical or graph form. The peelability of the plated layer can be evaluated by measuring the lightness of the debris adhered to the tape using a vision equipment or by measuring and rating the length of the debris at the end of the tensile test specimen.

Figure 4 is a photograph of the debris taped after performing a high-speed tensile test on the specimens of three steel types with different bonding strength, it can be seen that the length from the specimen end to the place where the debris exists is different depending on the bonding strength of the plating layer. Therefore, the peelability of the plated layer can be evaluated by measuring and rating the length from the end of the piece to the place where the piece is present.

7 is a flow chart illustrating a method for evaluating peelability of a plated steel sheet according to another embodiment of the present invention.

Referring to FIG. 7, a specimen is prepared for a high-speed tensile test (S310). To this end, first, a sample of an alloyed hot-dip galvanized steel sheet is prepared, and then the sample is processed into a specimen for high-speed tensile test. The specimen for evaluating the peelability of the plated steel sheet presented in the present invention is manufactured and tested in accordance with the commonly used high-speed tensile specimen standard (ASTM D638), but it is based on the standard of the equipment used or at the convenience of the user. Accordingly, the shape of the specimen can be different. At this time, it is necessary to define different standards of plating peeling grade according to the shape of the specimen according to the user. After processing the specimen, cleaning is performed to remove foreign substances present on the surface of the specimen.

When the specimen is prepared, a high-speed tensile test is performed on the specimen (S320). The test conditions of the high-speed tensile test can be applied differently according to the general or equipment specifications. Although it is possible to evaluate the plating peelability even at a low tensile speed, the difference in weight of the specimen before and after the test is more pronounced at a high tensile speed.

The prepared specimen is subjected to a high-speed tensile test by applying a tensile force to both ends of the specimen at a constant speed using a high-speed tensile tester. As the tensile force is applied, the specimen stretches to both sides, causing fracture at some point, and peeling of the plating layer occurs on the surface of the fractured portion.

After performing the high-speed tensile test, debris is collected from the specimen using a conductive tape such as carbon tape (S330). By observing the collected fragments and measuring the average size or distribution of fragments (S340), the peelability of the plated steel sheet can be evaluated by rating the average size and distribution of fragments (S350).

As mentioned with reference to FIGS. 2 and 3, when a high-speed tensile test is performed on a specimen of a plated steel sheet, peeling occurs at the fractured portion and fragments are formed.The size and distribution of fragments differ depending on the bonding strength of the plating layer. Therefore, if the size of the fragments is measured after the high-speed tensile test and the average size of the fragments and the distribution of fragments are graded, the peelability of the plated steel sheet can be evaluated.

As described above, according to the present invention, it is possible to evaluate the plating peelability of a specimen in which peelability evaluation is impossible, such as a conventional high-strength steel or ultra-high strength steel, using a high-speed tensile test. In addition, by using the high-speed tensile test equipment commonly used to evaluate the properties of steel, the change in weight before and after the high-speed tensile test, taping after the high-speed tensile test, and grading through vision equipment, and debris after high-speed tensile test. Various types of peelability evaluation can be performed according to users such as rating through size distribution. In addition, according to the present invention, the evaluation time is short since it is possible to easily evaluate without a separate special device after the high-speed tensile test, and it is possible to further shorten the time and easily proceed with the evaluation by making a database of various evaluation methods that proceed after the high-speed tensile test. , In addition to the alloyed hot-dip-plated steel sheet, there is an advantage that it is possible to evaluate the peelability of various thin-film plating layers.

In the above, the embodiments of the present invention have been mainly described, but various changes or modifications may be made at the level of those skilled in the art. These changes and modifications can be said to belong to the present invention as long as they do not depart from the scope of the present invention. Therefore, the scope of the present invention should be determined by the claims set forth below.

Claims (6)

delete delete delete Preparing a plated steel sample;
Processing the plated steel sheet sample into a specimen for a high-speed tensile test;
Performing a high-speed tensile test on the specimen;
Removing debris from the specimen using a tape having good adhesion;
Measuring the shade of the fragment; And
It characterized in that it comprises the step of grading the shade of the fragment,
Method for evaluating peelability of plated steel sheet. Preparing a plated steel sample;
Processing the plated steel sheet sample into a specimen for a high-speed tensile test;
Performing a high-speed tensile test on the specimen;
Removing debris from the specimen using a tape having good adhesion; And
It characterized in that it comprises the step of measuring and rating the length of the point where the fragments have occurred from the end of the specimen from which the fragments are removed,
Method for evaluating peelability of plated steel sheet. Preparing a plated steel sample;
Processing the plated steel sheet sample into a specimen for a high-speed tensile test;
Performing a high-speed tensile test on the specimen;
Collecting debris from the specimen using a conductive tape; And
It characterized in that it comprises the step of measuring and rating the average size or distribution of the collected fragments,
Method for evaluating peelability of plated steel sheet.

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