KR20110076650A - Choosing methods of corrosion proof factor with galva annealed coil for quality control - Google Patents

Abstract

PURPOSE: A corrosion resistance correlation factor selection method for quality control of alloying melting zinc galvanized steel is provided to manage correlation factors affecting the corrosion resistance through analysis of crater fraction, phase fraction, alloying degree, and the residue surface carbon of the alloying melting zinc galvanized steel. CONSTITUTION: A corrosion resistance correlation factor selection method for quality control of alloying melting zinc galvanized steel is as follows. The residual oil is removed from a specimen of the alloying melting zinc galvanized steel(S120). Phosphate seed is formed on the surface of the specimen. The specimen is dipped in a phosphate solution having a concentration of 3wt% at the temperature centigrade 45 for 120 seconds. A polymer resin is coated to a thickness of 20 micrometers through electron coating. A scratch of 10 cm in length is formed on one side of the specimen, which is electron-coated to expose a layer plated with zinc(S130). A maximum blister width and the average blister width are measured from the scratch of the specimen. The specimen is cut and crater fraction, zeta phase fraction, delta phase fraction, and alloying degree are measured from the cross section. A correlation coefficient of a factor according to the crater fraction, zeta phase fraction, delta phase fraction, and alloying degree and a factor according to the maximum blister width is analyzed and selected as a corrosion resistance correlation factor(S140,S150).

Description

Choosing methods of corrosion proof factor with galva annealed coil for quality control for quality control of alloyed hot dip galvanized steel sheet

The present invention is to control the quality of the galvanized galvanized steel (GA: GALVA ANNEALED) material by high-strength steel used in the interior and exterior of the automobile, in particular, to select the factor of high absolute value by analyzing the correlation coefficient of the corrosion resistance correlator The present invention relates to a method of selecting a corrosion resistance correlator for quality control of alloyed hot dip galvanized steel sheet which is produced with excellent corrosion resistance by intensive management with a quantified value.

Iron (Fe) is processed into steel sheets with a certain thickness through cold and hot rolling processes, and is used for building materials, automobiles, and home appliances, and is coated for corrosion protection and aesthetic appearance.

Painting is to prevent the coating by coating a paint film on the surface of the steel sheet, the labor cost generally accounts for 70 to 80% of the coating cost, the service life of the anti-rust effect is relatively short. As the technology for plating aluminum (Al), tin (Sn), zinc (Zn), etc. on the surface of the iron material is developed, the overall plating cost is reduced and the service life is increased.

In addition, by adding a coating on the plated surface of the metal, the service life can be further increased.

In the method of plating the surface of the iron material, there is a molten metal plating method or immersion plating method that melts zinc into the iron surface, and heat treatment in the zinc plated state to achieve an alloy state of iron and zinc This is an alloyed hot dip galvanizing method.

The present invention relates to a technique for further increasing the corrosion resistance of alloyed hot dip galvanized steel (GA) material.

In modern society, with the development of mechanical civilization, especially with the rapid growth of the automobile industry, human beings are able to move long distances safely, comfortably and quickly and move necessary objects and objects quickly.

As the demand for these vehicles increases and becomes a necessity of life, there is a tendency to demand improved quality in the direction of extending the corrosion resistance guarantee period for preventing corrosion of the steel sheet, which is an exterior material.

Corrosion resistance for rust protection of passenger cars should be 10 years free of hole rusting and 5 years of no scab on the outer shell.However, the warranty period for body hole rusting is 12 years. Increasingly, interest in corrosion protection in automobiles is increasing.

Therefore, research and development to improve corrosion resistance in various aspects including structural change of metal, shape change, improvement of coating quality, optimization design, etc. are continued, and one of the most fundamental solutions among them is the development of technology for improving the corrosion resistance of steel sheet materials. In particular, it is a technical development for improving the corrosion resistance of alloyed hot dip galvanized steel sheet (GA).

Since alloyed hot dip galvanized steel sheet undergoes annealing process by heat treatment, the alloying degree of iron (Fe) by alloying process, corrosion resistance by various properties such as gamma and delta and zeta phase fractions, craters, etc. The analysis should take into account.

However, despite many research and development, there is a problem that there is no clear quantification and management criteria for factors affecting the corrosion resistance of alloyed hot dip galvanized steel sheet.

In addition, there is a problem in distinguishing which factors have a definite effect on the corrosion resistance.

Therefore, it is necessary to develop the technology to select the factors to be quantified by analyzing the characteristics of the alloyed hot-dip galvanized steel sheet and analyzing the correlation between the blister and each factor through the cyclic chromatography test (CCT). .

The present invention is to solve the problems and necessity of the prior art as described above by analyzing the alloyed hot-dip galvanized steel sheet (GA) through the cyclic chromatography test (CCT) has a correlation between the maximum value and the average value of the blister It is an object of the present invention to provide a method for selecting a corrosion resistance correlator for quality control of an alloyed hot dip galvanized steel sheet which efficiently selects a high corrosion resistance correlator for quality control.

In addition, the present invention quantitatively manages correlated factors that have a definite effect on corrosion resistance through crater fractionation, phase fraction, degree of alloying, residual surface carbon analysis, etc. of alloyed hot dip galvanized steel sheet, thereby ensuring uniform quality of corrosion resistance. It is an object of the present invention to provide a method of selecting a corrosion resistance correlator for quality control of an alloyed hot dip galvanized steel sheet.

In order to achieve the above object, the present invention provides a method for improving corrosion resistance by selecting a corrosion resistance correlator of an alloyed hot dip galvanized steel sheet, and degreasing to remove residual oil from a specimen of an alloyed hot dip galvanized steel sheet material. Surface treatment to produce seeds of phosphate, phosphate immersion in a phosphate solution at a temperature of 45 degrees Celsius and a concentration of 3 wt% for 120 seconds, and an electrodeposition coating that coats the polymer resin with a thickness of 20 micrometers. A first step of exposing the galvanized layer by forming a 10 cm long scratch on one side of the electrodeposited surface, and subjecting the specimen to 35 degrees Celsius, a 5% salt spray environment, and one cycle of 8 hours by drying and wetting. In the second step of the cyclic chromion test, which repeats 70 cycles, the maximum blister width and the average blister width from the The third step of measuring the crater fraction, the zeta phase fraction, the delta phase fraction, and the degree of alloying from the cross section by cutting the specimen, and the crater fraction, the zeta phase fraction, the delta phase fraction, the factor and maximum blister width by the degree of alloying. The fourth step of selecting the corrosion resistance correlator by analyzing the correlation coefficient with the factor and calculating the maximum allowable crater fraction as the value of the selected corrosion resistance correlator and the blister width factor, and calculating the management range of each correlation factor. A corrosion resistance correlator selection method for quality control of an alloyed hot dip galvanized steel sheet comprising a fifth step of setting is provided.

Preferably, three factors having a high absolute value of the correlation coefficient are selected as corrosion resistance correlation factors.

Then, as the three factors, the correlation factor between the crater fraction, the zeta phase fraction, and the alloying degree is selected, and the fitting line position on the table is calculated and drawn by applying the following equation.

[Equation]

On the other hand, the correlation calculates and draws the position of the engine line on the chart by applying the maximum blister width and the average blister width to the following equation.

[Equation]

In addition, the maximum allowable crater fraction is calculated by applying the maximum value of the X-axis coordinate value at the point where the fitting line and the engine line meet, the lower limit of the alloying degree, and the experimental value of the zeta phase fraction.

The phosphate solution here consists of ternary systems of phosphoric acid, manganese and zinc.

The electrodeposition coating was immersed for 120 seconds in a state where the polymer resin solution having a solid content of 20% was maintained at 30 degrees Celsius, and then, the electrodeposited coating was electrodeposited and coated at a voltage of 220 volts to be cured by annealing at 165 degrees Celsius. A micrometer thick polymer electrodeposition coating layer is formed.

On the other hand, one cycle of the cyclic chromion test exposed the specimen for 4 hours in an environment in which the specimen was sprayed at a rate of 35 degrees Celsius and 5% brine at a rate of 1 milliliter per hour, and 60 degrees Celsius, a relative humidity of 30%. The process of drying for 2 hours in an environment and 2 hours of wetting in an environment of 50 degrees Celsius and 95% relative humidity is sequentially processed.

The present invention devised to achieve the above object is degreasing to remove residual oil in the specimen of alloyed hot-dip galvanized steel sheet material, surface adjustment to generate the seed of the phosphate on the surface, phosphate dipping to immerse the seed in the phosphate solution The first step of the sequential treatment of electrodeposition coating for coating the polymer resin, and the second step of the cyclic chromatography test which repeats the cycle 70 cycles for 8 hours by sequential spraying of salt spray, drying and wetting the specimens. Step, cut a 10 centimeter scratch with a knife on the galvanized surface of the specimen, measure the maximum blister width and average blister width from the scratch, cut the specimen and cut the crater fraction, zeta phase fraction, delta phase fraction, The third step of measuring the degree of alloying, the crater fraction, the zeta phase fraction, the delta phase fraction, the factor by the degree of alloying and the maximum blister width The fourth step of selecting the corrosion resistance correlator by analyzing the correlation coefficient with the factor and calculating the maximum allowable crater fraction as the value of the selected corrosion resistance correlator and the blister width factor, and calculating the management range of each correlation factor. Including the fifth step of setting, and selecting the crater fraction, zeta phase fraction, alloying degree as a corrosion resistance correlator and proposes a corrosion resistance correlator selection method for quality control of alloyed hot-dip galvanized steel sheet quantified and managed in the production line do.

Preferably, the crater fraction is quantified to 7.7% or less to improve the corrosion resistance quality of the alloyed hot dip galvanized steel sheet is managed in the production line.

And the degree of alloying is quantified in the range of 9 to 12% to improve the corrosion resistance quality of the alloyed hot dip galvanized steel sheet is managed in the production line.

In addition, the zeta phase fraction is quantified to 4% or less in order to improve the corrosion resistance quality of the alloyed hot dip galvanized steel sheet is managed in the production line.

On the other hand, the maximum blister width, the average blister width, the crater fraction, the zeta phase fraction, the delta phase fraction, and the degree of alloying are precisely measured using a microscope.

The present invention having the above-described configuration efficiently analyzes the results of the cyclic cracking test of the alloyed hot-dip galvanized steel sheet to efficiently select correlation factors having a high correlation with the maximum value and the average value of the blister and having a great influence on the corrosion resistance. There is an industrial use effect.

In addition, the present invention of the above configuration is concentrated in the production line using the selected corrosion resistance correlation factors such as crater fraction, each phase fraction, alloying degree to produce alloyed hot-dip galvanized steel sheet with high corrosion resistance excellent quality There is a convenient effect to use.

In addition, the present invention as described above has the industrial use effect to uniformly maintain the production quality and specifications of the alloyed hot-dip galvanized steel sheet quantitative management by quantifying the selected corrosion resistance correlator.

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may properly define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Detailed descriptions of well-known functions and configurations that are determined to unnecessarily obscure the subject matter of the present invention and illustrations of the drawings will be omitted.

Blisters (blisters) occur when the metal surface is incompletely bonded to the base material in the plating or coating surface, and is a swelling of the coated surface of the base material.

Annealing process is annealing (annealing) or heat treatment of the metal to have a soft characteristic, for example, cold-rolled steel sheet has a problem of high hardness, poor workability, but annealing is maintained by heating in a range of 600 to 850 degrees Celsius It has a soft characteristic during the process.

Cyclic Corrosion Test (CCT) is a test to measure the corrosion resistance in a condensation atmosphere containing saline (NaCl). It is a test to measure the corrosion resistance of metal and protective film.

Alloy galvanized steel sheet (GA: Galva Annealed) is a zinc-plated steel sheet that undergoes a high temperature heat treatment process such as annealing, so that the Fe component of the steel sheet melts and diffuses into the plating layer. The hot dip galvanized steel sheet having the alloying plating layer formed thereon is excellent in corrosion resistance, paintability, weldability, and the like, and thus is widely used for home appliances or automotive steel sheets.

Degree of alloying (Degree of alloying) is the alloying hot-dip galvanized steel sheet indicates the alloying content by the iron (Fe) component diffused into the plating layer during the heat treatment process.

As the degree of alloying increases, the properties such as paintability are improved, but the powdering (powdering) phenomenon of the plating layer occurs. Therefore, in order to improve the quality of the alloyed hot-dip galvanized steel sheet, it is desirable to manage the alloying degree of the steel sheet with optimization.

In order to optimize the alloying degree, it is necessary to precisely control the alloying heat treatment process.

The correlation coefficient represents the relationship between two sets. The closer the coefficient value is to 1, the more the correlations exist between the two sets. The closer to the value of -1, the more the correlations are opposite. As suggested by Pearson.

In the description of the present invention, one embodiment is interpreted as having the same meaning as one experimental example.

1 is a flowchart of a method for selecting a corrosion resistance correlator for quality control of an alloyed hot dip galvanized steel sheet according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings, degreasing, surface adjustment, phosphate immersion, electrodeposition coating to the specimen prepared to a predetermined size of the galvanized hot-dip galvanized steel sheet (GA) material is sequentially processed and a predetermined straight length on the electrodeposition coating surface First step (S110, S120) of forming a scratch to expose the galvanized layer, second step (S130) of performing a cyclic croton test, the maximum width and average width of the blister, the crater fraction, the zeta phase fraction, A delta phase fraction, a third step (S140) of measuring the degree of alloying, a fourth step (S150) of selecting a corrosion resistance correlation factor, and a fifth step (S160) of setting a management range of the correlation factor.

The first step is to prepare a specimen made of alloy galvanized galvanized steel sheet (GA) to a predetermined size (S110), the degreasing process for removing the oil remaining in the prepared specimen material, phosphate on the surface of the degreasing specimen material Surface adjustment process to produce seed that starts to grow, Phosphate dipping process to grow phosphate from seed, Electrodeposition coating process of electrodeposition coating (Coating) to about 20 micrometer thickness with polymer resin as main ingredient In order (sequential), the electrodeposited surface is scraped by a straight length of 10 centimeters (cm) using a knife, chisel, etc. to form a scratch so that the hot dip galvanized layer is exposed (S120). Here, the length and shape of the scratches are by way of example and may be lengthened or shortened by the user's requirements or specifications.

At this time, the size of the material to be used as the specimen is not limited and it is preferable to select a suitable size for the experiment by the laboratory environment. In addition, in the present invention, by selecting the alloyed hot-dip galvanized steel sheet of Model No. 440E, 590DP sold by POSCO company as the specimen material and the alloyed hot-dip galvanized steel sheet of Model No. 440E, 590DP, 780DP available in Japan market Used.

Here, the phosphate dipping process maintains a phosphate solution consisting of phosphate, manganese, and zinc ternary at a concentration of 3 wt% and 45 degrees Celsius, and immerses a specimen made of an alloyed hot dip galvanized steel sheet (GA) for 120 seconds. It is a process to immerse.

In the electrodeposition coating process, the positive electrode is connected to the material in the tank and the negative electrode is connected to the water-soluble paint in the tank, so that the current flows, so that the paint adheres to the surface of the material to form a coating film. It is a coating method, and it consists of undercoat, intermediate | middle, top coat, and clear coating, and electrodeposition coating in this invention shall only apply a undercoat.

At this time, in the present invention, the paint containing the polymer resin as a main component is maintained at a solid content (solid ratio of solution) at 20% and 30 degrees Celsius.

And after applying 220 volts (V) direct current (DC) between the material in the tank and flowing electrode for 120 seconds, the sample material taken out is subjected to electrodeposition coating by heat treatment by annealing process in an environment of 165 degrees Celsius. Is complete. Therefore, a polymer electrodeposition coating of about 20 micrometers (μm) in thickness is completed.

Here, the surface of one side of the electrodeposited coating is scraped off with a knife or chisel to form a scratch, and the electrodeposited coating is removed to expose the hot dip galvanized layer.

Scratches are preferably formed in a straight line of 10 centimeters (cm) in length, and the scratches can be formed by hand by a highly skilled worker or by using a precise mechanism.

The second step (S130) is to test the corrosion resistance of the specimen material of the alloyed hot-dip galvanized steel sheet after the electrodeposition coating is completed by the first step, also referred to as cyclic chromatography test (CCT).

The environment of the cyclic chromatography test is sprayed on the specimen material of the galvannealed steel sheet for 4 hours at a rate of 1 milliliter per hour while maintaining a concentration of 5% brine (salt) at 35 degrees Celsius. .

The material of the specimen is then dried for 2 hours in an environment with a relative humidity of 30% and an ambient temperature of 60 degrees Celsius.

The material of the specimens with this treatment is wetted for 2 hours in an environment of 95% relative humidity and 50 degrees Celsius.

Thus, the process which takes 4 hours for salt spray, 2 hours for drying, and 2 hours for wetting treatment is set to 1 cycle according to the cyclic chromatography test in the present invention.

In the present invention, since one cycle, which takes 8 hours, is repeated 70 cycles, the cyclic chrominance test for a total of 560 hours is completed.

The third step S140 accurately measures the maximum and average widths of the blisters using a microscope or an electron microscope from the scratches of the respective materials for which the cyclic transcript test is completed.

In addition, the other side of the specimen that is not scratched is precisely cut and the fraction of crater generated by using a microscope or an electron microscope, the fraction of zeta (ζ) layer, the delta (delta) The fraction of) -layer) and the degree of alloying of iron (Fe) are measured accurately. The precision of each measured factor is based on the performance of the measuring equipment. If the cut surface is uneven and accurate measurement is impossible, the cut surface can be precisely polished.

The alloyed hot dip galvanized steel sheet undergoes alloying and melting of iron (Fe) and zinc (Zn) while undergoing heat treatment by zinc plating and annealing. In this case, alloying and melting of iron and zinc are performed by various oxides present on the iron surface. Where this is not done smoothly, blisters occur through outburst.

As described above, the portion where the blister is generated is a place where zinc (Zn) is not well plated, and thus, it is confirmed that the blister is extremely weak in corrosion resistance.

The fourth step S150 is plotted using the results measured in the third step, the Pearson correlation coefficient values are analyzed between factors, and the corrosion resistance correlation factor is selected.

In other words, the parameters of the precisely measured maximum blister width (mm) and the crater fraction (%) are plotted and the values of the correlation coefficients are analyzed.

The correlation coefficient R is 0.92, indicating a very high linear correlation. For example, Korean automaker GMDAT requires a maximum blister width of 6 mm and a crater fraction of 9.5% or less. Therefore, it can confirm that the conditions by this invention are enough.

The factors of the maximum blister width and the zeta phase fraction (%) are plotted and the values of the correlation coefficients are analyzed. Here again, the value of the correlation coefficient R is 0.81, which shows that the linear correlation is very high. It can be seen that the zeta phase (FeZn13) is very excellent in terms of powder resistance and weak in weldability and corrosion resistance. In addition, the ratio of zeta phase is 2 to 4%, which is not relatively large, but it can be confirmed that it has a significant relation with blister.

In addition, the maximum blister width factor and iron alloying degree (%) factor are plotted and the values of the correlation coefficients are analyzed.

The general degree of alloying in an alloyed hot dip galvanized steel sheet is known to be in the range of 8 to 12%, and the present invention also confirms similar levels of alloying. The higher the degree of alloying, the stronger the corrosion resistance, but the higher the correlation.

On the other hand, the maximum blister width factor and the delta phase fraction factor are plotted and the values of the correlation coefficient are analyzed. The delta phase fraction and the maximum blister width were difficult to identify.

This analysis shows that the maximum blister and crater fractions are of considerable relevance.

The crater fraction, the zeta phase fraction, and the alloying degree are identified as the factors highly correlated with the blisters of the alloyed hot dip galvanized steel sheet.

The fifth step S160 sets a management range of each of the selected correlation factors. At this time, the maximum allowable crater fraction is calculated by the formula of the maximum and average values of each selected correlation factor and the blister width.

In other words, since the selected corrosion resistance correlator acts on the corrosion resistance in a complex manner, considering the contribution of each factor, the correlation between the corrosion resistance evaluation index on the Y (Y) axis and the corrosion resistance influence factor on the X (X) axis is shown in the chart. The formula for calculating the position of the fitting line is as follows.

[Equation 1]

Here, the corrosion resistance evaluation index (Y) considers the maximum blister most, but it can be seen that the average blister is also very meaningful. The formula for calculating the position of the engine line to distinguish the engine (NG) section in the chart is as follows.

[Equation 2]

Since the lower limit value based on the general standard of iron (Fe) alloying degree is 9% and the maximum value of the zeta phase obtained by experiment is 4%, applying these values to Equation 1 and converting them as shown in the following equation.

[Equation 3]

5.13, which is the X value, reads the value of the X (X) axis at the point where the fitting line and the engine line overlap in the diagram, and will be described in detail later with reference to the drawings.

From these results, it is confirmed that managing the crater fraction (%) to 7.7% or less is very advantageous and desirable for securing the corrosion resistance quality of the alloyed hot dip galvanized steel sheet.

And it is confirmed that the alloying degree of iron (Fe) is managed in the range of 9% to 12%, and the zeta phase fraction is managed to be 4% or less.

In other words, in order to improve the corrosion resistance of the alloyed hot-dip galvanized steel sheet, the crater fraction is 7.7% or less, the alloying degree of iron is 9% to 12%, and the zeta phase fraction is quantified to 4% or less and managed in the production line. desirable.

FIG. 2 is a diagram illustrating a correlation between a blister width, a crater fraction, a zeta phase fraction, an alloying degree, and a delta phase fraction measured from a specimen in which a cyclic chromatography test is completed according to an embodiment of the present invention. to be.

Hereinafter, with reference to the accompanying drawings, the diagram in the upper left shows the correlation between the maximum blister width (mm) and the crater fraction (%), the width of the blister gradually increases as the crater fraction increases You can see the increase. Here, the R value of the correlation coefficient is 0.92, so it can be seen that it is a very linear correlation.

The alloyed hot-dip galvanized steel sheet is plated with zinc on iron (Fe), and then alloyed with iron (Fe) and zinc (Zn) during heat treatment by an annealing process, and alloying is performed by various oxides remaining on the surface. In the unsatisfactory part, blistering occurs due to outburst.

The diagram at the top right shows the correlation between the maximum blister width (mm) and the zeta (ζ) -layer fraction (%), with the blister width and the zeta phase having an R value of 0.81. As it is confirmed, it shows very high linear correlation.

That is, in this analysis, the zeta phase fraction is included in the range of 2% to 4%, which is not a large value, but the correlation coefficient R value is 0.81.

The lower left plot shows the correlation between the maximum blister width (mm) and the iron (Fe) alloying degree (%). Since the value of the correlation coefficient is negative (-), it is confirmed that the higher the alloying value, the stronger the corrosion resistance.

The alloying degree in the present invention is found to be 8% to 12%, and thus is similar to the general alloying degree known in theory.

The bottom right plot shows the correlation between the maximum blister width (mm) and the delta (Delta (δ) -layer) fraction (%), since the value of the correlation coefficient is nearly negative (-). Classify as having no relationship and meaning no management.

Therefore, the crater fraction, zeta-phase fraction, and alloying degree, which have large coefficient values, are confirmed to be quantitatively managed in a quantified state to improve the corrosion resistance of the galvanized steel sheet.

3 is a photographic view of a cross section taken by using an optical microscope according to an embodiment of the present invention, a state in which a cyclic chromescence test is completed on a specimen material.

Hereinafter, with reference to the accompanying drawings, 100 is an alloyed hot-dip galvanized steel sheet, 110 is a steel plate portion, 120 is a galvanized portion.

(a) is a state in which the cyclic croton test after galvanizing the selected specimen 1 of the alloyed hot dip galvanized steel sheet, and (b) is the state in which the cyclic croton test after galvanizing the selected specimen 2 is completed. to be.

It can be seen that the plating characteristics are different depending on the steel type (steel type) selected as the material of the specimen. to be.

In the drawing shown in (b), the part where the galvanization is corroded and the iron is exposed is blister.

FIG. 4 is a diagram illustrating a table of corrosion resistance correlation factors observed by an experiment as an evaluation index (Y) and an influence factor (X) according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings, the X (X) axis is a coordinate value by the operation of Equation 1, the Y (Y) axis represents a coordinate value by the operation of Equation 2.

The blue line is calculated by applying the crater fraction, zeta phase fraction, and ferroalloy degree to Equation 1, which are observed in the experiment of the present invention and selected as the corrosion resistance correlator, and are represented by diagonal lines, and the fitting line is do.

In addition, the red line is a value calculated by applying the value of the average blister width and the maximum blister width to Equation 2 and is represented by a horizontal line, and becomes an NG line.

Here, the value at the X coordinate of the point where the blue fitting line and the red engine line meet is confirmed as '5.13'.

Since the value of '5.13' identified as above is calculated by substituting Equation 3, the value of crater fraction to be quantified and managed can be determined.

FIG. 5 is a diagram illustrating an OK area and an engine area NG, which are classified by correlation between the alloying degree and the crater fraction due to the change in the zeta phase fraction.

In the experiment of the present invention, since the alloying degree is measured from 9% to 12%, there is a transition section indicated by the '3' region in the figure. There is a change in the baseline determined by the OK area 1 and the engine area 2 by this transition section '3' area.

The ok area 1 is an area in which the value of the blister width satisfies the criterion of 2 mm or less on average and up to 6 mm, and is capable of satisfying corrosion resistance.

The engine area | region 2 is an area | region which does not satisfy corrosion resistance by the blister width reference value by 2 mm or less on average and 6 mm at maximum.

And the safe area near the origin is the area of satisfaction of the corrosion resistance criteria analyzed through the independent calculation of the crater fraction and the zeta phase fraction.

Therefore, the position of the safety zone can be changed by determining the final values of the crater fraction, the zeta phase fraction and the alloying degree, but using these charts, it is possible to efficiently determine the management criteria of the galvanized steel sheet.

The present invention having the above-described configuration selects the crater fraction factor, the zeta phase fraction factor, and the alloying factor factor that are highly correlated with corrosion resistance of the alloyed hot dip galvanized steel sheet, and calculates and quantifies the quantification value to provide excellent corrosion resistance. There is an advantage to manage.

Although the present invention has been described in detail only with respect to the described embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made within the technical spirit of the present invention, and such modifications and modifications belong to the appended claims.

1 is a flowchart of a method for selecting a corrosion resistance correlator for quality control of an alloyed hot dip galvanized steel sheet according to an embodiment of the present invention;

FIG. 2 is a diagram illustrating a correlation between a blister width, a crater fraction, a zeta phase fraction, an alloying degree, and a delta phase fraction measured from a specimen in which a cyclic chromatography test is completed according to an embodiment of the present invention. ,

3 is a photograph showing a cross-sectional view taken by using an optical microscope in accordance with an embodiment of the present invention in a state in which a cyclic chromescence test is completed on a specimen material;

FIG. 4 is a diagram illustrating a table of corrosion resistance correlation factors observed by an experiment as an evaluation index (Y) and an influence factor (X) according to an embodiment of the present invention.

And

FIG. 5 is a diagram illustrating an OK area and an engine area NG, which are classified by correlation between the alloying degree and the crater fraction due to the change in the zeta phase fraction.

          ** Explanation of symbols on the main parts of the drawing **

100: alloyed hot dip galvanized steel sheet 110: steel sheet portion

120: zinc plated

Claims (13)

In the method of improving the corrosion resistance quality by selecting the corrosion resistance correlator of alloyed hot dip galvanized steel sheet, Degreasing to remove residual oil in the specimen of the alloyed hot-dip galvanized steel sheet, surface adjustment to generate a seed of phosphate on the surface, phosphate immersion for 120 seconds in a phosphate solution of 45 degrees Celsius temperature 3 wt% concentration, polymer resin A first step of sequentially treating electrodeposition coating coated with a thickness of 20 micrometers and forming a 10 cm long scratch on the electrodeposited side of the specimen to expose the galvanized layer; The second cyclic chromatography test, in which the specimen of the alloyed hot-dip galvanized steel sheet material according to the first step was repeated 70 cycles of 35 degrees Celsius, 5% salt spray environment, and one cycle unit of 8 hours by drying and wetting. step; A third step of measuring a maximum blister width and an average blister width from the scratched portion of the specimen according to the second step, and cutting the specimen to measure a crater fraction, a zeta phase fraction, a delta phase fraction, and an alloying degree from a cross section; ; A fourth step of analyzing the correlation coefficient values between the crater fraction, the zeta phase fraction, the delta phase fraction, the alloying factor and the factor of the maximum blister width to select the corrosion resistance correlation factor; And A fifth step of calculating an allowable maximum crater fraction with values of the selected corrosion resistance correlator and the factor of the blister width, and setting a management range of each correlator; Corrosion resistance correlator selection method for quality control of alloyed hot dip galvanized steel sheet comprising a. The method of claim 1, Corrosion resistance correlator selection method for quality control of an alloyed hot-dip galvanized steel sheet, characterized in that the three factors having a high absolute value of the correlation coefficient is selected as a corrosion resistance correlator. The method of claim 2, The three factors are A method of selecting a corrosion resistance correlator for quality control of an alloyed hot dip galvanized steel sheet comprising selecting a crater fraction, a zeta phase fraction, and an alloying degree as correlation factors, and calculating fitting lines on a chart by applying the following equation. [Equation]

The method of claim 3, wherein The correlation is A method of selecting a corrosion resistance correlator for quality control of an alloyed hot-dip galvanized steel sheet, by applying the maximum blister width and the average blister width to the equation below. [Equation]

The method according to any one of claims 3 and 4, Hot-dip galvanized alloy characterized in that the maximum allowable crater fraction is calculated by applying the maximum value of the X-axis coordinate value, the lower limit of the alloying degree and the experimental value of the zeta-phase fraction at the point where the fitting line and the engine line meet on the table. Corrosion resistance correlator selection method for quality control of coated steel sheet. The method of claim 1, The phosphate solution, A method of selecting a corrosion resistance correlator for quality control of an alloyed hot dip galvanized steel sheet, comprising a ternary system of phosphoric acid, manganese, and zinc. The method of claim 1, The electrodeposition coating, A 20 micrometer-thick polymer was cured by immersing the specimen for 120 seconds while maintaining a 20% solid polymer resin solution at 30 degrees Celsius, followed by electrodeposition coating at a voltage of 220 volts, followed by heat treatment by annealing process at 165 degrees Celsius. A method of selecting a corrosion resistance correlator for quality control of an alloyed hot dip galvanized steel sheet, comprising forming an electrodeposition coating layer. The method of claim 1, One cycle of the cyclic croton test, Exposing the specimen for 4 hours in an environment in which the specimen was sprayed at a rate of 1 milliliter per hour with a brine at a concentration of 35 degrees Celsius, 5%, Dried for 2 hours in an environment of 60 degrees Celsius, 30% relative humidity, A method of selecting a corrosion resistance correlator for quality control of an alloyed hot-dip galvanized steel sheet, characterized in that the step of wetting for 2 hours in an environment of 50 degrees Celsius and 95% relative humidity is performed sequentially. Degreasing to remove residual oil on the specimen of alloyed hot-dip galvanized steel sheet, surface adjustment to generate seeds of phosphate on the surface, phosphate dipping to soak seeds in phosphate solution, and electrodeposition coating to coat polymer resin Forming a scratch on one side of the electrodeposited coating of the specimen to expose the galvanized layer; A second step of the cyclic chromatography test, wherein the specimen of the alloyed hot-dip galvanized steel sheet material according to the first step is repeated 70 cycles for 8 hours by the sequential treatment of salt spray, drying and wetting; A third blister width and an average blister width are measured from the scratched portion of the specimen according to the second step, and the specimen is cut to measure a crater fraction, a zeta phase fraction, a delta phase fraction, and an alloying degree from a cross section; step; A fourth step of analyzing the correlation coefficient values between the crater fraction, the zeta phase fraction, the delta phase fraction, the alloying factor and the factor of the maximum blister width to select the corrosion resistance correlation factor; And A fifth step of calculating an allowable maximum crater fraction with values of the selected corrosion resistance correlator and the factor of the blister width, and setting a management range of each correlation factor; Including, Selecting the crater fraction, the zeta phase fraction, and the degree of alloying as a corrosion resistance correlator, and quantifying and managing the alloyed hot-dip galvanized steel sheet for quantitative management in a production line. The method of claim 9, The crater fraction, A method of selecting a corrosion resistance correlator for quality control of an alloyed hot dip galvanized steel sheet, which is quantified to 7.7% or less and managed in a production line to improve the corrosion resistance quality of an alloyed hot dip galvanized steel sheet. The method of claim 9, The alloying degree is, Corrosion resistance correlator selection method for quality control of alloyed hot-dip galvanized steel sheet characterized in that it is quantified in the range of 9 to 12% in order to improve the corrosion resistance quality of the alloyed hot-dip galvanized steel sheet. The method of claim 9, The zeta phase fraction is, A method of selecting a corrosion resistance correlator for quality control of an alloyed hot dip galvanized steel sheet, which is quantified to 4% or less and managed in a production line to improve the corrosion resistance quality of the alloyed hot dip galvanized steel sheet. The method of claim 9, The maximum blister width, the average blister width, the crater fraction, the zeta phase fraction, the delta phase fraction, and the degree of alloying are precisely measured using a microscope, and the corrosion resistance correlator for quality control of the alloyed hot-dip galvanized steel sheet. How to choose.

Images