KR20120041542A - Galvannealed steel sheet having excellent frictional property and powdering resistance, and method for manufacturing the same - Google Patents

Abstract

PURPOSE: A galvannealed steel sheet and a method for manufacturing the same are provided to improve the quality of a galvannealed steel sheet by securing excellent frictional properties and powdering resistance at the same time. CONSTITUTION: A galvannealed steel sheet comprises a plated layer containing 5-20weight% of Fe and 0.2-2 weight% of a metal with higher Gibbs free energy than Fe. The content of the metal from the surface of a plated layer to half the depth of the plated layer is 0.35 weight% or more relative to the total content of the plated layer.

Description

Alloyed hot-dip galvanized steel sheet with excellent friction characteristics and powder resistance and manufacturing method thereof {GALVANNEALED STEEL SHEET HAVING EXCELLENT FRICTIONAL PROPERTY AND POWDERING RESISTANCE, AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to an alloyed hot-dip galvanized steel sheet having excellent friction characteristics and powder resistance, and to a method for manufacturing the same. More specifically, Ni includes a predetermined amount or more in the upper portion of the plating layer to improve the friction characteristics of the surface of the plating layer, and The present invention relates to an alloyed hot-dip galvanized steel sheet having a relatively low hardness near the plated layer interface and improving powdering resistance, and a method of manufacturing the same.

Hot-dip galvanized steel sheet has excellent corrosion resistance and is widely used in automobiles, building materials, structures, and home appliances. Hot-dip galvanized steel sheet includes general hot-dip galvanized steel sheet (GI steel sheet) and alloyed hot-dip galvanized steel sheet (GA steel sheet) that have not been subjected to alloying heat treatment. By diffusing the zinc with each other, the plated layer is made of an alloy of iron and zinc, and is used as an automobile material because it has better weldability and paintability than GI steel sheet.

In the case of the GA steel sheet, the amount of iron contained in the plating layer varies depending on the temperature and time of the alloying heat treatment, and the hardness of the plating layer varies according to the amount of iron contained in the plating layer, and the hardness of the plating layer is a frictional characteristic of the GA steel sheet. And an important factor in determining the powder resistance. In other words, when the amount of alloyed iron in the surface layer of the plating layer is large, the hardness of the steel plate surface is increased to reduce the friction with the die during forming the steel sheet, thereby improving the formability, but near the interface between the base steel plate and the plated layer, When the amount of iron is large, the plating layer powdering phenomenon that the hardness near the interface is increased is likely to occur.

Therefore, it is necessary to control the alloying temperature and time in consideration of the friction characteristics and the powdering resistance, rather than unconditionally increasing the amount of iron contained in the plating layer, but the iron contained in the steel sheet during the alloying of the steel sheet and the plating layer Since it diffuses to the surface layer portion of the plating layer through the interface, the iron in the plating layer increases, and if the hardness is high, the hardness is high in the vicinity of the interface. Only control has a limit in improving the friction characteristics and the powder resistance of the plated steel sheet.

Therefore, by increasing the hardness of the surface layer portion of the plating layer, and lowering the hardness near the interface between the base steel plate and the plated layer, it is a very urgent need for a technology that can simultaneously improve the friction characteristics and the powder resistance of the alloyed hot-dip galvanized steel sheet. .

The present invention provides an alloyed hot-dip galvanized steel sheet and a method of manufacturing the same that can solve the contradictions of friction characteristics and powder resistance and improve the two physical properties simultaneously.

The present invention has a plating layer containing 5 to 20% by weight of Fe and 0.2 to 2% by weight of a metal having a Gibbs free energy greater than Fe, wherein the Gibbs free energy is contained from the surface of the plating layer to a half point of the thickness of the plating layer. Provides an alloyed hot-dip galvanized steel sheet having excellent friction characteristics and powdering resistance, characterized in that the metal content of greater than Fe is not less than 0.35 by weight to the content of the metal of the Gibbs free energy contained in the entire plating layer. do.

At this time, it is more preferable that the content from the surface of the plating layer to the half point of the thickness of the plating layer to the content of the entire plating layer of the metal having the Gibbs free energy greater than Fe is 0.45 or more in weight ratio.

In addition, it is preferable to further include Al: 0.1 to 0.4% by weight in the plating layer.

In addition, the metal having a Gibbs free energy greater than Fe is preferably at least one selected from the group consisting of Ni, Co, Cu, Sn, and Sb.

On the other hand, the present invention is the first plating step of plating a metal having a Gibbs free energy greater than Fe to 50 ~ 3000mg / ㎡ on the steel sheet; Heating the first plated steel sheet in a reducing atmosphere; Cooling the heated steel sheet; A second plating step of immersing the cooled steel sheet in a hot dip galvanizing bath; And rapidly heating the second plated steel sheet at a temperature rising rate of 20 ° C./sec or more within 2 seconds after the second plating. 15. A method of manufacturing an alloyed hot dip galvanized steel sheet having excellent friction characteristics and powder resistance. To provide.

At this time, the heating step is preferably performed to 700 ~ 900 ℃.

In addition, the hot dip galvanizing bath temperature is 440 ~ 480 ℃, the hot dip galvanizing bath preferably contains 0.12 ~ 0.14% by weight of Al.

In addition, the cooling step is more preferably performed to a temperature 10 ~ 50 ℃ higher than the temperature of the hot dip galvanizing bath.

In addition, the metal having a Gibbs free energy greater than Fe is preferably at least one selected from the group consisting of Ni, Fe, Co, Cu, Sn, and Sb.

The present invention is to improve the quality of the alloyed hot-dip galvanized steel sheet by increasing the hardness of the surface layer of the plated layer in the alloyed hot-dip galvanized steel sheet while lowering the hardness of the interface between the base steel plate and the plated layer to ensure excellent friction characteristics and powder resistance at the same time. Can contribute.

1 is a graph showing the content of the composition with respect to the depth of the plated steel sheet according to the invention example.
Figure 2 is a graph showing the content of the composition of the depth of the plated steel sheet according to the comparative example.

EMBODIMENT OF THE INVENTION Hereinafter, the steel plate of this invention is demonstrated in detail.

One side of the present invention has a plating layer containing 5 to 20% by weight of Fe and 0.2 to 2% by weight of a metal having a Gibbs free energy greater than Fe, wherein the plating layer is included at a half point of the plating layer from the surface of the plating layer. Alloyed hot-dip galvanized zinc alloy excellent in friction properties and powder resistance, characterized in that the metal content of the Gibbs free energy is greater than Fe is 0.35 or more by weight relative to the metal content of the Gis free energy contained in the entire plating layer Provide the steel sheet.

First, Fe in the plating layer serves to increase the hardness of the plating layer by making an alloy with Zn, the Fe is preferably contained in 5 to 20% by weight in the plating layer, more preferably controlled to 7 to 12% by weight It is effective. If Fe is less than 5% by weight in the plated layer, the hardness of the plated layer is so low that there is a limit to securing the friction characteristics of the plated steel sheet even when controlling other compositions, if Fe exceeds 20% by weight in the plated layer Similarly, even if the other composition is controlled, the hardness of the interface between the base steel sheet and the plated layer is too high, which causes poor powdering resistance.

In addition, the metal having the Gibbs free energy greater than Fe refers to a component included in the plating layer such as Ni to increase the hardness of the plating layer, and preferably at least one selected from the group consisting of Ni, Co, Cu, Sn, and Sb. . The metal is preferably present at 0.2 to 2% by weight in the plating layer. If the content of the plating layer of the metal having a greater Gibs free energy than Fe is less than 0.2% by weight, the total content is too small to give the cast free oil to the upper part of the plating layer. Even if a large amount of metal having a larger energy than Fe is distributed, there is a limit in securing the hardness of the surface layer, so the friction property is not good, and the upper limit can be set to 2% by weight in consideration of economical efficiency.

In particular, the present inventors not only control the content of the Fe or the metal in the plating layer, but also control the amount of metal in which the Gibbs free energy in the plating layer is larger than Fe to distribute a predetermined amount or more on top of the plating layer to ensure high hardness of the plating layer. On the contrary, it is recognized that the hardness of the base steel plate and the plating layer in the vicinity of the interface can be ensured to be low, and the present invention can achieve both excellent friction characteristics and powder resistance at the same time.

Therefore, when the content of the coating layer from the surface of the plating layer to half of the content of the entire plating layer of the metal having the Gibbs free energy greater than Fe is 0.35 or more in weight ratio, the hardness of the coating layer surface portion can be sufficiently secured to reduce friction during forming of the steel sheet. By reducing, excellent moldability can be obtained. In addition, at the same time, the hardness of the base steel plate and the plated layer can be relatively lowered, thereby significantly reducing the problems caused by powdering. More preferably, when the content from the surface of the plated layer to the 1/2 point to the content of the entire plated layer is 0.45 or more by weight ratio, the hardness increase effect and the hardness decrease effect of the surface of the plated layer may be maximized. Powdering property can be further improved.

In addition, it is preferable to further include Al: 0.1 to 0.4% by weight in the plating layer, if Al is contained less than 0.1% by weight in the plating layer to prevent the powdering phenomenon because the γ phase is formed thick at the interface between the base steel plate and the plating layer. If Al exceeds 0.4% by weight, the Fe-Al alloy layer becomes too thick at the interface, resulting in excessive suppression of alloying itself.

Hereinafter, the manufacturing method of the steel plate of this invention is demonstrated in detail.

Another aspect of the present invention is the first plating step of plating a metal having a Gibbs free energy greater than Fe to 50 ~ 3000mg / ㎡ in the steel sheet; Heating the first plated steel sheet in a reducing atmosphere; Cooling the heated steel sheet; A second plating step of immersing the cooled steel sheet in a hot dip galvanizing bath; And rapidly heating the second plated steel sheet at a temperature rising rate of 20 ° C./sec or more within 2 seconds after the second plating. 15. A method of manufacturing an alloyed hot dip galvanized steel sheet having excellent friction characteristics and powder resistance. To provide.

First, a metal having a larger Gibs free energy than Fe is first plated at 50 to 3000 mg / m 2 on the steel sheet. If the first plating amount is less than 50 mg / m 2, the plating amount is too small, regardless of the distribution position of the metal. It is difficult to secure the friction characteristics of the plated steel sheet, and the upper limit may be set to 3000 mg / m 2 in consideration of economic efficiency. In addition, after annealing after the first plating, it is preferable to heat in a reducing atmosphere, and after the heated steel sheet is cooled, it is immersed in a molten zinc plating bath to undergo a second plating.

In particular, the present inventors recognize that the metal can be sufficiently diffused to the surface layer of the plating layer only by rapidly heating at a high temperature rising rate within a very short time after the second plating, and controlling the time and temperature rising rate until heating after the second plating. The invention in which the Gibbs free energy is larger than Fe is sufficiently distributed in the plating layer surface layer rather than near the interface between the base steel plate and the plating layer.

Therefore, it is very important to include the step of rapidly heating the second plated steel sheet at a temperature rising rate of 20 ° C./sec or more within 2 seconds after the second plating. If, after the second plating has elapsed for 2 seconds or more, or the temperature increase rate is less than 20 ° C / sec, the diffusion of the metal is not active and it is difficult to sufficiently distribute the surface layer.

In addition, in the annealing step after the first plating, the heating temperature is preferably 700 to 900 ° C. If the heating temperature is less than 700 ° C., there is a problem that the material properties of the steel sheet are inferior due to insufficient recrystallization. In consideration of the saturation of, the upper limit may be set at 900 ° C.

In addition, the hot dip galvanizing bath temperature is 440 ~ 480 ℃, the hot dip galvanizing bath preferably contains 0.12 ~ 0.14% by weight of Al. If the temperature of the plating bath is less than 440 ° C., the viscosity of the plating bath decreases, making it difficult to drive the rolls in the plating bath, which may cause slippage, which may cause scratches on the steel sheet. The evaporation of contaminants may increase and contaminate the installation, and the evaporated zinc material may be buried in the steel sheet and cause defects. In addition, when Al is 0.12% by weight or more in the hot dip galvanizing bath, it is possible to form a Fe-Al alloy layer that is advantageous in improving the surface quality and affects the plating uniformity by securing the fluidity of the plating bath, but 0.14% by weight. If it exceeds the thickness of the alloy layer is too thick may cause a problem that the alloying is not good.

In addition, the cooling step is more preferably performed to a temperature 10 ~ 50 ℃ higher than the temperature of the hot dip galvanizing bath. If the cooling temperature is higher than the plating bath temperature to less than 10 ℃ or lower than the plating bath temperature, the Fe-Al alloy layer is not formed uniformly enough to cause a problem of poor plating adhesion, the cooling temperature is the plating bath temperature If it is higher than 50 ° C., the ferrous iron is excessively dissolved in the plating bath, thereby making a Fe—Zn compound called dross to degrade the quality of the plated steel sheet.

In addition, the metal having a Gibbs free energy greater than Fe is preferably at least one selected from the group consisting of Ni, Co, Cu, Sn, and Sb.

Hereinafter, the present invention will be described in detail by way of examples, which are intended for a more complete understanding of the present invention, and the scope of the present invention is not limited to the following individual examples.

( Example )

There is no restriction | limiting in the steel plate material of this invention, In this experiment, the low carbon cold-rolled steel sheet of thickness 1.2mm was made into the raw material. First, Ni plating was performed by varying the plating amount, and the Ni-plated steel sheet was heated at different heating temperatures in an atmosphere of 5% H ₂ -N ₂ , and maintained for 60 seconds and then cooled by varying the cooling temperature. Then, the steel sheet is introduced at the cooled temperature, immersed in a molten zinc plating bath having a different Al concentration at a plating bath temperature of 450 ° C. for 3 seconds, and the time until the alloy heat treatment is performed after leaving the molten zinc plating bath. And molten zinc-plated steel sheet was prepared by heating at different heating rate of the alloying heat treatment, the production conditions are shown in Table 1.

division
Ni plating amount
(g / ㎡) Heating temperature
(℃) Cooling temperature
(℃) Effective Al concentration in the plating bath (wt%) Time to heat after plating (seconds) Temperature rise rate
(℃ / sec) Inventory 1 0.08 760 460 0.13 One 30 Inventory 2 0.08 760 470 0.13 One 30 Inventory 3 0.1 780 470 0.12 One 30 Honorable 4 0.1 780 470 0.14 One 30 Inventory 5 0.5 780 470 0.13 One 20 Inventory 6 0.5 780 480 0.13 One 20 Honorable 7 0.5 780 480 0.13 1.5 30 Honors 8 0.5 850 480 0.13 1.5 40 Inventive Example 9 0.5 850 480 0.13 1.9 40 Inventive Example 10 0.5 850 480 0.13 One 40 Inventive Example 11 0.5 900 500 0.13 One 40 Inventive Example 12 One 780 500 0.13 One 30 Inventive Example 13 One 780 480 0.13 One 30 Inventive Example 14 One 780 480 0.13 1.5 30 Honorable Mention 15 3 780 480 0.13 1.5 30 Comparative Example 1 0 780 480 0.13 One 30 Comparative Example 2 0 800 480 0.12 1.5 30 Comparative Example 3 0.1 780 460 0.13 4 30 Comparative Example 4 0.1 780 480 0.13 1.5 10 Comparative Example 5 2 850 480 0.13 4 10

In order to evaluate the manufactured hot-dip galvanized steel sheet, after dissolving the plating layer using an aqueous hydrochloric acid solution, Fe content, Al content and Ni content in the plating layer were measured by ICP (Inductively Coupled Plasma), and also GDS (Glow Discharge Spectrometer) The distribution of the Ni component in the plating layer thickness direction was measured, and the Ni content ratio from the plating layer surface layer portion to the half point of the plating layer thickness with respect to the whole plating layer was measured. The boundary between the base steel plate and the plated layer, that is, the interface, set the point where the contents of iron and zinc intersect.

In addition, the powder resistance of the plated layer was 60 ° V-Bending method, and the surface friction characteristics of the plated steel sheet was measured by applying a rust preventive oil on the surface of the steel sheet using a plane friction tester.

division Fe content in the coating layer (wt%) Ni content in the coating layer (wt%) Al content (wt%) in the plating layer Ni content ratio up to 1/2  Coefficient of friction Powder resistance Inventory 1 9.3 0.21 0.32 0.37 0.171 ◎ Inventory 2 9.3 0.22 0.33 0.50 0.168 ◎ Inventory 3 9.4 0.28 0.17 0.48 0.168 ◎ Honorable 4 9.2 0.28 0.39 0.54 0.167 ◎ Inventory 5 9.3 0.52 0.34 0.42 0.166 ◎ Inventory 6 10.1 0.52 0.32 0.47 0.161 ◎ Honorable 7 11.9 0.52 0.32 0.51 0.156 ○ Honors 8 9.8 0.49 0.33 0.49 0.162 ◎ Inventive Example 9 9.6 0.49 0.33 0.41 0.168 ◎ Inventive Example 10 9.7 0.49 0.33 0.61 0.159 ◎ Inventive Example 11 7.2 0.46 0.34 0.62 0.161 ◎ Inventive Example 12 9.4 0.84 0.33 0.51 0.159 ◎ Inventive Example 13 10.1 0.82 0.33 0.50 0.157 ◎ Inventive Example 14 10.3 0.82 0.32 0.48 0.159 ◎ Honorable Mention 15 9.8 1.83 0.31 0.47 0.152 ○ Comparative Example 1 9.7 0 0.33 - 0.183 ○ Comparative Example 2 10.5 0 0.17 - 0.182 △ Comparative Example 3 9.5 0.26 0.33 0.20 0.180 ◎ Comparative Example 4 8.3 0.27 0.33 0.24 0.185 ◎ Comparative Example 5 10.4 1.21 0.31 0.11 0.184 X

※ Ni content ratio up to 1/2 point = Ni content ratio up to 1/2 point of thickness of plating layer

※ Powder resistance: ◎ (Excellent), ○ (Excellent), △ (Poor), X (Extremely poor)

Inventive Examples 1 to 9 were carried out according to the conditions of the present invention, the friction coefficient was relatively low, and showed excellent friction characteristics, and it was found that the powdering resistance was also excellent.

However, Comparative Examples 1 and 2 did not contain additional components that increase the hardness of the coating layer because Ni plating was not performed, so the powder resistance was excellent, but the friction coefficient was very high as 0.18 or more, and thus the friction characteristics were not good. And it was found.

In addition, Comparative Example 3 was carried out in accordance with the conditions of the present invention, but Ni plating takes about 4 seconds to heat up after galvanizing, so the diffusion of Ni is not sufficient, so the Ni content ratio up to 1/2 is 0.20. As it was low, the powder resistance was very good, but the friction coefficient was very high, indicating that the friction characteristics were not good.

In addition, Ni plating was also performed according to the conditions of the present invention, Comparative Example 4, but the temperature increase rate during the alloying heat treatment is 10 ℃ / sec is also low enough to diffuse the surface layer portion of Ni to Ni content ratio up to 1/2 point to 0.25 Low, the powder resistance was very good, but the friction coefficient was found to be too high.

In addition, in Comparative Example 5, the time required for heating after galvanizing was 4 seconds, and the temperature increase rate was 10 ° C./sec, so that the Ni content ratio up to 1/2 was 0.11. It can be seen that it is located near the interface. As a result, the hardness near the interface is extremely poor, and the powdering resistance is extremely poor. On the contrary, the hardness of the surface layer of the plating layer is very low, and the friction coefficient is very high.

1 is a graph showing the results of experiments in accordance with the conditions of the comparative example in which the time until heating after galvanization exceeds 2 seconds or the temperature increase rate during the alloying heat treatment is less than 20 ° C./sec. It is a graph showing the results of experiments in accordance with the conditions of the invention example that the time until the within 2 seconds and the temperature increase rate during the alloying heat treatment is 20 ℃ / sec or more.

1, it is confirmed that Ni does not easily diffuse into the plating layer surface layer portion, so that most of Ni is located near the interface between the base steel sheet and the plating layer. On the contrary, as shown in FIG. 2, as Ni is rapidly heated within a rapid time after galvanizing, Ni is sufficiently diffused into the surface layer, and thus, most of Ni is located closer to the surface layer rather than the interface.

Claims (9)

5-20% by weight of Fe and 0.2-2% by weight of a metal having a Gibbs free energy greater than Fe, and having a plating layer, wherein the Gibbs free energy contained in a half of the thickness of the plating layer is greater than Fe. The alloyed hot-dip galvanized steel sheet having excellent friction characteristics and powdering resistance, characterized in that a large metal content of the Gibbs free energy contained in the entire plating layer is 0.35 or more by weight relative to the metal content of Fe.
The method according to claim 1,
The Gibbs free energy contained in the coating layer from the surface of the plating layer up to 1/2 of the thickness of the plating layer is greater than Fe, and the Gibbs free energy contained in the entire plating layer is 0.45 in weight ratio. Alloyed hot-dip galvanized steel sheet excellent in friction characteristics and powder resistance, characterized in that the above.
The method according to claim 1,
Al: 0.1 to 0.4% by weight in the plating layer, the alloying hot-dip galvanized steel sheet excellent in friction characteristics and powder resistance.
The method according to any one of claims 1 to 3,
The metal having a higher Gibbs free energy than Fe is at least one selected from the group consisting of Ni, Co, Cu, Sn and Sb. The alloyed hot-dip galvanized steel sheet having excellent friction and powdering resistance.
A first plating step of plating a metal having a Gibbs free energy greater than Fe to 50 to 3000 mg / m 2 on the steel sheet; Heating the first plated steel sheet in a reducing atmosphere; Cooling the heated steel sheet; A second plating step of immersing the cooled steel sheet in a hot dip galvanizing bath; And rapidly heating the second plated steel sheet at a temperature rising rate of 20 ° C./sec or more within 2 seconds after the second plating.
Method for producing an alloyed hot-dip galvanized steel sheet excellent friction characteristics and powdering resistance comprising a.
The method according to claim 5,
The heating step is a method of producing an alloyed hot-dip galvanized steel sheet excellent in friction characteristics and powder resistance, characterized in that performed to 700 ~ 900 ℃.
The method according to claim 5,
The hot dip galvanizing bath is a temperature of 440 ~ 480 ℃, the hot dip galvanizing bath is characterized in that it comprises 0.12 ~ 0.14% by weight of Al characterized in that the hot dip galvanized steel sheet having excellent friction characteristics and powdering resistance.
The method according to claim 5,
The cooling step is a method of producing an alloyed hot-dip galvanized steel sheet excellent in friction characteristics and powdering resistance, characterized in that performed to a temperature 10 ~ 50 ℃ higher than the temperature of the hot dip galvanizing bath.
The method according to any one of claims 5 to 8,
The metal having a Gibbs free energy greater than Fe is at least one selected from the group consisting of Ni, Co, Cu, Sn and Sb, characterized in that the alloying hot-dip galvanized steel sheet excellent friction properties and powdering resistance.

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