KR20220074267A - Galva-annealed steel sheet having excellent surface quality, coating adhesion, and formability and method of manufacturing the same - Google Patents

Abstract

The present invention provides an alloyed hot-dip galvanized steel sheet excellent in surface quality, plating adhesion and formability, and a method for manufacturing the same. According to an embodiment of the present invention, the alloyed hot-dip galvanized steel sheet, a base material; and a plating layer formed on the base material and containing zinc, aluminum, and silicon, wherein the content of silicon and the aluminum in the plating layer is 35.5 x [Si content (weight %) of the plating layer] + 4.43 x [of the plating layer] Al content (wt%)] ≥ 212.

Description

Galva-annealed steel sheet having excellent surface quality, coating adhesion, and formability and method of manufacturing the same

The technical idea of the present invention relates to a steel material, and more particularly, to an alloyed hot-dip galvanized steel sheet having excellent surface quality, plating adhesion and formability, and a method for manufacturing the same.

Steel for automobile exterior is a part responsible for the exterior of the vehicle body, and strengthening has been promoted to improve the permanent preservation ability of the exterior of the vehicle. The strength of steel can be divided into yield strength and tensile strength, and in order to improve the permanent preservation of the exterior of the body, the yield strength, which is the critical stress of elastic and plastic deformation of the steel, must be high. Therefore, on the other hand, the final product must show high yield strength characteristics, but it has the duality of requiring low yield strength before molding in order to prevent surface defects such as bending during molding.

Therefore, although the initial yield strength is low, the amount of increase in yield strength during molding is large, and the baking hardenability after painting baking is excellent, so the application of abnormal-structured steel shell plates with high yield strength in final products is expanding. Irregular structure steel is a composite steel containing hard martensite on a ferrite matrix. It is mainly used as an exterior plate for automobiles by applying hot-dip galvanizing treatment with excellent corrosion resistance and weldability.

However, there is a problem in that problems such as surface problems and plating peeling during molding may occur due to elements such as silicon and aluminum added to improve ferrite cleanliness and strength of the abnormal structure steel.

Korean Patent Application No. 2005-7018419

The technical problem to be achieved by the technical idea of the present invention is to provide a hot-dip galvanized steel sheet having high strength, excellent surface quality, plating adhesion, and formability, and a method for manufacturing the same.

However, these tasks are exemplary, and the technical spirit of the present invention is not limited thereto.

According to one aspect of the present invention, there is provided a hot-dip galvanized steel sheet having excellent surface quality, plating adhesion and formability, and a method for manufacturing the same.

According to an embodiment of the present invention, the alloyed hot-dip galvanized steel sheet, a base material; and a plating layer formed on the base material and including zinc, aluminum, and silicon, wherein the content of silicon and the aluminum in the plating layer may satisfy Equation 1 below.

<Equation 1>

35.5 x [Si content (% by weight) of plating layer] + 4.43 x [Al content (% by weight) of plating layer] ≥ 212

According to an embodiment of the present invention, the content of aluminum in the plating layer and the content of aluminum in the base material may satisfy Equation 2 below.

<Equation 2>

[Al content of plating layer (wt%)]/[Al content of base material (wt.%)] ≤ 0.5

According to an embodiment of the present invention, the chromium and the molybdenum (Mo) may satisfy the relation of 0.3 ≤ [Cr content (weight %)] + 0.3 x [Mo content (weight %)] ≤ 2.0 .

According to an embodiment of the present invention, the base material, by weight, carbon (C): 0.01% to 0.06%, manganese (Mn): 1.0% to 2.5%, silicon (Si): 0.02% to 0.1%, Aluminum (Al): 0.01% to 1.0%, Chromium (Cr): >0% to 1.5%, Molybdenum (Mo): >0% to 1.0%, Phosphorus (P): >0% to 0.08%, Sulfur (S) ): more than 0% to 0.01%, and the balance may contain iron (Fe) and other unavoidable impurities.

According to an embodiment of the present invention, the alloyed hot-dip galvanized steel sheet may include a mixed structure of ferrite and martensite.

According to an embodiment of the present invention, the fraction of ferrite may be in the range of 90% to 98%, and the fraction of martensite may be in the range of 2% to 10%.

According to an embodiment of the present invention, the alloyed hot-dip galvanized steel sheet may satisfy tensile strength (TS): 340 MPa or more and elongation (El): 30% or more.

According to an embodiment of the present invention, the alloyed hot-dip galvanized steel sheet, a base material; and a plating layer formed on the base material and including zinc, aluminum, and silicon, wherein the content of aluminum in the plating layer and the content of aluminum in the base material may satisfy Equation 2 below.

<Equation 2>

[Al content of plating layer (wt%)]/[Al content of base material (wt.%)] ≤ 0.5

According to an embodiment of the present invention, the base material, by weight, carbon (C): 0.01% to 0.06%, manganese (Mn): 1.0% to 2.5%, silicon (Si): 0.02% to 0.1%, Aluminum (Al): 0.01% to 1.0%, Chromium (Cr): >0% to 1.5%, Molybdenum (Mo): >0% to 1.0%, Phosphorus (P): >0% to 0.08%, Sulfur (S) ): more than 0% to 0.01%, and the balance may contain iron (Fe) and other unavoidable impurities.

According to an embodiment of the present invention, in the method for manufacturing the alloyed hot-dip galvanized steel sheet, in weight %, carbon (C): 0.01% to 0.06%, manganese (Mn): 1.0% to 2.5%, silicon (Si) : 0.02% to 0.1%, aluminum (Al): 0.01% to 1.0%, chromium (Cr): more than 0% to 1.5%, molybdenum (Mo): more than 0% to 1.0%, phosphorus (P): more than 0% ~ 0.08%, sulfur (S): more than 0% ~ 0.01%, and the remainder of manufacturing a hot-rolled steel sheet containing iron (Fe) and other unavoidable impurities; manufacturing a cold-rolled steel sheet by cold-rolling the hot-rolled steel sheet; annealing the cold-rolled steel sheet at a temperature in the range of 760°C to 840°C; manufacturing a hot-dip galvanized steel sheet by immersing the cold-rolled steel sheet in a hot-dip galvanizing bath and performing hot-dip galvanizing at a temperature of 450°C to 550°C; and performing alloying heat treatment on the hot-dip galvanized cold-rolled steel sheet at a temperature in the range of 450° C. to 550° C. to prepare an alloyed hot-dip galvanized steel sheet.

According to an embodiment of the present invention, the step of rapidly cooling the alloyed hot-dip galvanized steel sheet to a temperature of 250 °C or less at a cooling rate in the range of 20 °C / sec to 40 °C / sec; may further include.

According to an embodiment of the present invention, after performing the quenching step, the step of temper rolling the alloyed hot-dip galvanized steel sheet; may further include.

According to an embodiment of the present invention, the manufacturing of the hot-rolled steel sheet includes: preparing a steel material having the alloy composition; reheating the steel in the range of 1,150°C to 1,300°C; manufacturing a hot-rolled steel sheet by hot finish rolling the reheated steel at a finish rolling end temperature in the range of 820°C to 920°C; and winding the hot-rolled steel sheet in the range of 450°C to 700°C.

According to an embodiment of the present invention, the alloyed hot-dip galvanized steel sheet manufactured by the method for manufacturing the alloyed hot-dip galvanized steel sheet includes a mixed structure in which ferrite and martensite are mixed, and the fraction of ferrite is 90% ~ 98%, the fraction of martensite is in the range of 2% to 10%, tensile strength (TS): 340 MPa or more and elongation (El): 30% or more may be satisfied.

According to the technical idea of the present invention, by controlling in relation to the content of silicon and aluminum in the plating layer, or by controlling the content in relation to the aluminum content of the plating layer and the aluminum content of the base material, the alloying melt having excellent surface quality, plating adhesion and formability A galvanized steel sheet can be manufactured.

The above-described effects of the present invention have been described by way of example, and the scope of the present invention is not limited by these effects.

1 is a process flowchart schematically illustrating a method of manufacturing an alloyed hot-dip galvanized steel sheet according to an embodiment of the present invention.
2 is a process flowchart schematically illustrating a method of manufacturing an alloyed hot-dip galvanized steel sheet according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments of the present invention are provided to more completely explain the technical idea of the present invention to those of ordinary skill in the art, and the following examples may be modified in various other forms, The scope of the technical idea is not limited to the following examples. Rather, these embodiments are provided so as to more fully and complete the present disclosure, and to fully convey the technical spirit of the present invention to those skilled in the art. In this specification, the same reference numerals refer to the same elements throughout. Furthermore, various elements and regions in the drawings are schematically drawn. Accordingly, the technical spirit of the present invention is not limited by the relative size or spacing drawn in the accompanying drawings.

An object of the present invention is to provide an alloyed hot-dip galvanized steel sheet excellent in surface quality, plating adhesion and formability, and a method for manufacturing the same.

1 is a graph showing the distribution of elements according to the depth of an alloyed hot-dip galvanized steel sheet according to an embodiment of the present invention.

Referring to FIG. 1 , the content analysis of the element was calculated using a glow-discharge optical emission spectrometer (GD-OES) analysis. The alloyed hot-dip galvanized steel sheet has a galvanized layer formed on the base material. The 'plating layer' refers to the interface from the surface of the alloyed hot-dip galvanized steel sheet to the interface between the galvanized layer and the base material composed of the steel material, and the 'base material' is referred to from the interface to the inner direction of the base material. The thickness of the plating layer and the thickness of the base material are shown at the same level.

The content of iron (Fe) is high in the base material and decreases toward the inside of the plating layer. On the other hand, the content of zinc (Zn) is high in the plating layer and decreases toward the inside of the base material. In addition, aluminum (Al) and silicon (Si) show a relatively high content in the base material, and relatively low in the plating layer. In particular, silicon exhibits a rapidly degraded behavior at the interface.

The alloyed hot-dip galvanized steel sheet according to the technical idea of the present invention is required to have a tensile strength of 340 MPa or more, an elongation of 30% or more, and an aging resistance property of 12 months or more. The microstructure may have a two-phase structure of ferrite and martensite. In addition, the alloyed hot-dip galvanized steel sheet is required to have excellent surface quality and no plating peeling.

Hereinafter, an alloyed hot-dip galvanized steel sheet according to the technical spirit of the present invention will be described.

Exterior panels for automobiles should have resistance to wear in order to improve dimensional accuracy during molding. In order to implement this, it is necessary to secure a fraction of the martensite of 2.0% or more in the two-phase structure of ferrite and martensite in order to secure aging resistance for more than one year. Accordingly, the alloyed hot-dip galvanized steel sheet may contain a martensitic structure in a ferrite matrix, for example, in an amount of 2% to 10%.

An alloyed hot-dip galvanized steel sheet according to an embodiment of the present invention, a base material; and a plating layer formed on the base material and including zinc, aluminum, and silicon.

The base material, by weight, carbon (C): 0.01% to 0.06%, manganese (Mn): 1.0% to 2.5%, silicon (Si): 0.02% to 0.1%, aluminum (Al): 0.01% to 1.0 %, Chromium (Cr): >0% to 1.5%, Molybdenum (Mo): >0% to 1.0%, Phosphorus (P): >0% to 0.08%, Sulfur (S): >0% to 0.01%, and the balance includes iron (Fe) and other unavoidable impurities.

At this time, in the alloyed hot-dip galvanized steel sheet, chromium (Cr) and molybdenum (Mo) satisfy the relation of 0.3 ≤ [Cr content (weight %)] + 0.3 x [Mo content (weight %)] ≤ 2.0 .

Contents of silicon and aluminum in the plating layer may satisfy Equation 1 below.

<Equation 1>

35.5 x [Si content (% by weight) of plating layer] + 4.43 x [Al content (% by weight) of plating layer] ≥ 212

By Equation 1, the content of silicon and aluminum in the plating layer can be controlled, and thus the target properties of the hot-dip galvanized steel sheet can be satisfied. For the content control, control in the plating layer and control in the base material may be required together.

In addition, it is necessary to prevent the formation of oxides such as fayalite due to the addition of silicon. To this end, by reducing the silicon content, it is possible to provide an automobile exterior plate material having excellent surface properties and plating properties. At this time, the silicon content of the plating layer may be reduced, and thus Equation 1 may not be satisfied. In this case, by increasing the aluminum component in the base material to satisfy Equation 2 below, it is possible to provide an exterior plate material for automobiles having excellent surface properties and plating properties.

Accordingly, the content of aluminum in the plating layer and the content of aluminum in the base material may satisfy Equation 2 below.

<Equation 2>

[Al content of plating layer (wt%)]/[Al content of base material (wt.%)] ≤ 0.5

In addition, the case where the above Equation 1 and the above Equation 2 are simultaneously satisfied is also included in the technical concept of the present invention.

The role and content of each component included in the alloyed hot-dip galvanized steel sheet according to the present invention will be described as follows. At this time, the content of the component elements all mean weight % with respect to the entire steel sheet.

Carbon (C): 0.01% to 0.06%

The martensitic structure is a structure containing supersaturated carbon due to diffusionless transformation in the austenitic structure, and carbon contributes to the formation of the martensitic structure. If the carbon content is less than 0.01%, it may be difficult to form a martensitic structure. When the carbon content exceeds 0.06%, strength increases and ductility decreases, so it may be difficult to secure an elongation of 30% or more. Therefore, it is preferable to add the carbon content in an amount of 0.01% to 0.06% of the total weight of the steel sheet.

Manganese (Mn): 1.0% to 2.5%

Manganese is an effective hardenable element and contributes to martensite formation upon cooling after annealing. When the manganese content is less than 1.0%, it may be difficult to implement a two-phase structure. When the manganese content exceeds 2.5%, ductility may decrease and surface quality may deteriorate due to surface oxidation. Therefore, it is preferable to add the manganese content in an amount of 1.0% to 2.5% of the total weight of the steel sheet.

Silicon (Si): 0.02% to 0.1%

Silicon is a ferrite stabilizing element and can be dissolved in ferrite to increase ferrite strength. When the content of silicon is less than 0.02%, the above effect may be insufficient. When the content of silicon exceeds 0.10%, red scale caused by fayolite, which is difficult to pickling during the hot rolling process, may occur and cause surface defects. Therefore, it is preferable to add the content of silicon to 0.02% to 0.1% of the total weight of the steel sheet.

Aluminum (Al): 0.01% to 1.0%

Aluminum is not only used as a deoxidizing agent, but also is an element that can increase the carbon concentration in austenite by delaying Ar3 transformation. to be. In addition, when aluminum is added, it is possible to improve plating quality by controlling alloying. When the content of aluminum is less than 0.01%, the austenite fraction rapidly increases in the abnormal temperature range during annealing, so material deviation increases, and the carbon concentration in austenite decreases, so that carbides such as bainite or pearlite during cooling Tissue is formed to increase yield strength and deteriorate aging resistance. When the content of aluminum exceeds 1.0%, the Ar3 temperature is increased to decrease the abnormal fraction during annealing, and finally, the formation of martensite structure is suppressed, as well as the risk of increasing inclusions and surface oxidation during the annealing process. may cause, and may deteriorate the plating quality. Therefore, it is preferable to add the content of aluminum in an amount of 0.01% to 1.0% of the total weight of the steel sheet.

Chromium (Cr) and Molybdenum (Mo)

A martensitic structure, which is a non-diffusion transformation structure, may be formed by rapid cooling of the austenite structure. However, since there is a limit to the cooling rate, a bainite structure having a high yield strength and a relatively low tensile strength may be formed by diffusion during cooling instead of the martensite. When such a bainite structure occurs, a resistive yield ratio cannot be obtained, so the formation of the bainite should be prevented as much as possible. Therefore, in order to suppress the formation of a diffusion structure in the cooling process, the content of chromium (Cr) and molybdenum (Mo) can be controlled as in Equation 3 below.

<Equation 3>

0.3 ≤ [Cr content (wt%)] + 0.3 x [Mo content (wt. %)] ≤ 2.0

When the [Cr content (weight %)] + 0.3 x [Mo content (weight %)] is less than 0.3, it is difficult to sufficiently exhibit the hardenability strengthening effect according to the addition of chromium and molybdenum. When the [Cr content (weight %)] + 0.3 x [Mo content (weight %)] exceeds 2.0, the hardenability effect is saturated, and price economics compared to efficiency may be lowered.

In addition, since the quenching effect of chromium (Cr) is saturated at 1.3% by weight or more, chromium can be managed at more than 0% to 1.5%.

Accordingly, molybdenum may react with an appropriate amount of chromium while satisfying Equation 3, and may be managed in an amount exceeding 0% to 1.0% in order to obtain a hardenability strengthening effect.

However, the content of chromium and molybdenum is exemplary, and the technical spirit of the present invention is not limited thereto, and a case containing chromium and molybdenum higher than the above-described upper limit is also included in the technical spirit of the present invention.

Phosphorus (P): >0% to 0.08%

Phosphorus is a solid solution strengthening element that simultaneously increases tensile strength and yield strength, and is added to supplement tensile strength and yield strength. can Therefore, it is preferable to limit the phosphorus content to more than 0% to 0.08% of the total weight of the steel sheet.

Sulfur (S): >0% to 0.01%

Sulfur is an element that is inevitably contained in the manufacture of steel, and combines with manganese to form MnS inclusions to reduce the effect of adding manganese, which is a quenching element, and increase inclusions and precipitates as the content increases, which may affect formability. Therefore, it is preferable to limit the sulfur content to more than 0% to 0.01% of the total weight of the steel sheet.

The remaining component of the alloyed hot-dip galvanized steel sheet is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in the normal steelmaking process, it cannot be excluded. Since these impurities are known to any person skilled in the art of manufacturing processes, all details thereof are not specifically mentioned in the present specification.

The alloyed hot-dip galvanized steel sheet may include a mixed structure in which ferrite and martensite are mixed. The fraction of ferrite may be in the range of 90% to 98%, and the fraction of martensite may be in the range of 2% to 10%. The fraction means an area ratio derived from a microstructure photograph of a steel sheet through an image analyzer.

The alloyed hot-dip galvanized steel sheet may satisfy tensile strength (TS): 340 MPa or more and elongation (El): 30% or more. The alloyed hot-dip galvanized steel sheet may satisfy tensile strength (TS): 340 MPa to 590 MPa and elongation (El): 30% to 40%.

Hereinafter, a method for manufacturing an alloyed hot-dip galvanized steel sheet according to the present invention will be described with reference to the accompanying drawings.

Manufacturing method of alloyed hot-dip galvanized steel sheet

2 is a process flowchart schematically illustrating a method of manufacturing an alloyed hot-dip galvanized steel sheet according to an embodiment of the present invention.

Referring to FIG. 2 , in the method for manufacturing an alloyed hot-dip galvanized steel sheet according to an embodiment of the present invention, a hot-rolled steel sheet is manufactured using the steel of the composition (S110), and the hot-rolled steel sheet is cold-rolled to form a cold-rolled steel sheet. manufacturing step (S120); annealing the cold-rolled steel sheet (S130); hot-dip galvanizing the cold-rolled steel sheet (S140); and alloying and heat-treating the hot-dip galvanized cold-rolled steel sheet (S150).

In addition, the method of manufacturing the alloyed hot-dip galvanized steel sheet may further include the step of rapidly cooling the alloyed hot-dip galvanized steel sheet (S160).

In addition, the method of manufacturing the alloyed hot-dip galvanized steel sheet may further include the step of temper rolling the alloyed hot-dip galvanized steel sheet after performing the quenching step ( S160 ).

Hot-rolled steel sheet manufacturing step (S110)

A steel material such as a steel ingot or steel slab having the above alloy composition is prepared. The steel is, by weight, carbon (C): 0.01% to 0.06%, manganese (Mn): 1.0% to 2.5%, silicon (Si): 0.02% to 0.1%, aluminum (Al): 0.01% to 1.0 %, Chromium (Cr): >0% to 1.5%, Molybdenum (Mo): >0% to 1.0%, Phosphorus (P): >0% to 0.08%, Sulfur (S): >0% to 0.01%, and the remainder may include iron (Fe) and other unavoidable impurities.

At this time, in the steel, chromium (Cr) and molybdenum (Mo) satisfy the relation of 0.3 ≤ [Cr content (weight %)] + 0.3 x [Mo content (weight %)] ≤ 2.0.

The steel is reheated, for example, at a reheating temperature (Slab Reheating Temperature, SRT) in the range of 1,150° C. to 1,300° C. Through such reheating, the austenizing treatment is performed by destroying the cast structure, and at this time, re-dissolution of segregated components and re-dissolution of precipitates may occur during casting. When the reheating temperature is less than 1,150° C., there may be a problem in that the hot rolling load rapidly increases. When the reheating temperature exceeds 1,300° C., the amount of surface scale increases, which may lead to loss of material, and energy may be wasted.

After the reheating, hot rolling is performed by a conventional method, for example, hot finish rolling is performed at a finish delivery temperature (FDT) in the range of 820°C to 920°C to manufacture a hot-rolled steel sheet. When the finish rolling end temperature is less than 820°C, the rolling property may be reduced due to a phase change. When the finish rolling end temperature exceeds 920° C., the grains become coarse, and strength and yield ratio characteristics may be reduced.

Then, the hot-rolled steel sheet is cooled to a coiling temperature in the range of, for example, 450°C to 700°C. The cooling may be either air cooling or water cooling, for example, cooling at a cooling rate of 5° C./sec to 150° C./sec. The cooling may be performed by air cooling or water cooling. Preferably, the cooling is performed to a coiling temperature.

Then, the hot-rolled steel sheet is wound at a coiling temperature (CT) in the range of, for example, 440°C to 700°C. The range of the winding temperature may be selected from the viewpoint of cold rolling properties and surface properties. When the coiling temperature is less than 450° C., the structure becomes fine and strength and toughness may be increased, but the elongation may be reduced, and the rolling load during cold rolling may be significantly increased. When the coiling temperature exceeds 700° C., the yield ratio may increase due to the formation of coarse grains, and the strength may decrease.

Cold-rolled steel sheet manufacturing step (S120)

A pickling treatment of washing the hot-rolled steel sheet with acid is performed. Next, the pickling-treated hot-rolled steel sheet is subjected to cold rolling at an average reduction ratio of 40% to 70%, for example, to form a cold-rolled steel sheet. As the average reduction ratio is higher, there is an effect of increasing the formability due to the effect of refining the tissue. When the average reduction ratio is less than 40%, it is difficult to obtain a uniform microstructure. When the average reduction ratio exceeds 70%, the roll force is increased to increase the process load.

Annealing heat treatment step (S130)

The cold-rolled steel sheet is annealed and heat treated in a continuous annealing furnace having a normal slow cooling section. The annealing heat treatment, for example, is performed at a temperature in the range of 760 ℃ ~ 840 ℃. This annealing heat treatment is a process of securing the strength and yield resistance characteristics and aging resistance of the steel material, and heat treatment can be performed for 30 seconds or more at a temperature in the range of 760 ° C. to 840 ° C. in order to secure a tensile strength of 340 MPa or more. The annealing heat treatment is performed to secure an initial austenite fraction of 50% or more. When the annealing heat treatment temperature is less than 760° C., the initial austenite fraction may not be secured, and thus strength may not be secured. When the annealing heat treatment temperature exceeds 840 °C, the initial austenite fraction is too high, it may be difficult to control the transformation of the third phase such as pearlite and bainite during cooling.

After performing the annealing heat treatment, the cold-rolled steel sheet may be cooled to room temperature, for example, to a temperature in the range of 0° C. to 40° C., or immersed in a hot-dip galvanizing bath to perform the following hot-dip galvanizing step. . In this case, the cold-rolled steel sheet may be cooled to a temperature similar to that of the plating bath.

Hot-dip galvanizing step (S140)

In the hot-dip galvanizing step (S140), the cold-rolled steel sheet is immersed in a hot-dip galvanizing bath to form a hot-dip galvanized layer on the surface of the cold-rolled steel sheet to form a hot-dip galvanized steel sheet. Hot-dip galvanizing is performed by holding the cold-rolled steel sheet, for example, at a temperature in the range of 450° C. to 550° C. for a time in the range of 30 seconds to 100 seconds. Then, the hot-dip galvanized steel sheet may be manufactured by cooling it to room temperature at a cooling rate of 1° C./sec to 100° C./sec.

alloying heat treatment step (S150)

In the alloying heat treatment step (S150), the hot-dip galvanized cold-rolled steel sheet, for example, at a temperature in the range of 450 ℃ ~ 550 ℃ alloying heat treatment for a time of 10 seconds ~ 100 seconds may be performed. The alloying heat treatment step (S150) may be performed continuously without cooling after performing the previous hot-dip galvanizing step. Under the above conditions, while the hot-dip galvanized layer is stably grown during the alloying heat treatment, the adhesion of the plating layer may be excellent. When the alloying heat treatment temperature is less than 450° C., the soundness of the hot-dip galvanizing layer may be deteriorated because alloying may not proceed sufficiently. When the alloying heat treatment temperature exceeds 550 °C, the material may change as the temperature goes to an abnormal temperature range. Then, by cooling to room temperature, an alloyed hot-dip galvanized steel sheet may be manufactured.

Quenching step (S160)

In the quenching step, the alloyed hot-dip galvanized steel sheet is quenched to a temperature of 250 °C or less at a cooling rate in the range of 20 °C/sec to 40 °C/sec, for example, to a temperature in the range of 0 °C to 250 °C. By suppressing the diffusion of the element by the rapid cooling, the austenite structure is formed into a martensitic structure.

temper rolling step (S170)

In the temper rolling step (S170), it is carried out for shape control and surface quality improvement of the alloyed hot-dip galvanized steel sheet. If the temper rolling is excessive, it can be limited to 1.0% or less because the yield strength and yield ratio increase.

Experimental example

Hereinafter, preferred experimental examples are presented to help the understanding of the present invention. However, the following experimental examples are only for helping understanding of the present invention, and the present invention is not limited by the following experimental examples.

Steel having the composition (unit: weight %) shown in Table 1 below was prepared, and a steel sheet was prepared through predetermined hot rolling, cold rolling process, hot-dip galvanizing and alloying heat treatment as described above. The element content of Examples and Comparative Examples was the same. The remainder in Table 1 is iron (Fe) and other unavoidable impurities.

Furtherance C Mn Si Al Cr Mo P S content 0.03 1.5 0.05 0.5 0.8 0.5 0.01 0.005

Table 2 shows the contents of silicon and aluminum in the plating layers of Examples and Comparative Examples of the alloyed hot-dip galvanized steel sheet according to an embodiment of the present invention, and the contents of aluminum in the base material. The above contents are each in % by weight. In Table 2, a case in which the condition of Equation 1 or 2 is not satisfied is indicated by "X", and a case in which the condition of Equation 1 or 2 is satisfied is indicated by "O".

division plating layer base material Equation 1 Equation 2 Si Al Al calculated value ≥212 calculated value ≤0.5 Comparative Example 1 3.56 16.54 18.52 199.52 X 0.89 X Comparative Example 2 3.41 17.76 12.03 179.67 X 1.48 X Comparative Example 3 3.54 16.43 15.10 198.32 X 1.09 X Comparative Example 4 2.83 16.30 11.38 172.72 X 1.43 X Example 1 4.64 24.29 184.80 272.48 O 0.13 O Example 2 5.10 23.88 183.27 286.95 O 0.13 O Example 3 5.09 17.50 18.50 258.15 O 0.95 X Example 4 4.95 16.59 17.90 249.09 O 0.92 X Example 5 2.97 16.54 185.30 178.53 X 0.09 O Example 6 3.04 17.29 179.00 184.51 X 0.10 O

Referring to Table 2, Comparative Examples are cases in which the conditions of Equations 1 and 2 are not satisfied. Examples 1 and 2 are cases where both the conditions of Equations 1 and 2 are satisfied, Examples 3 and 4 are cases where the conditions of Equation 1 are satisfied but the conditions of Equation 2 are not satisfied, Example In Examples 5 and 6, the condition of Equation 1 is not satisfied and the condition of Equation 2 is satisfied.

In order to examine the surface quality, the visual surface quality and the degree of plating peeling prevention were evaluated. The plating peeling prevention was evaluated using HCI (Hat-bead contrast index). In the plating peel test, the clamp force was 30 kN, the punch speed was 300 mm/s, and the drawing height was 65 mm. High HCI means that a large amount of plating layer is peeled off, and shows low plating properties. On the other hand, a low HCI means that a small amount of the plating layer is peeled off, and shows a high plating property. Hereinafter, the result of high HCI will be described as poor prevention of plating peeling, and the result of low HCI will be described as good prevention of plating peeling.

Table 3 shows the mechanical properties and surface quality of Examples and Comparative Examples of the alloyed hot-dip galvanized steel sheet according to an embodiment of the present invention. In Table 3, "O" means good as a product, and "X" means bad as a product.

division The tensile strength
(MPa) elongation
(%) surface quality Prevention of plating peeling Comparative Example 1 473 35 O X Comparative Example 2 525 33 O X Comparative Example 3 434 38 O X Comparative Example 4 517 32 O X Example 1 431 36 O O Example 2 464 37 O O Example 3 506 33 O O Example 4 542 31 O O Example 5 506 32 O O Example 6 515 33 O O

Referring to Table 3, the tensile strength, elongation, and surface quality achieved the targets in both Comparative Examples and Examples. On the other hand, different results were shown for the prevention of plating peeling. In Comparative Examples that did not satisfy both the conditions of Equation 1 and Equation 2, the plating peeling phenomenon was prominent. On the other hand, it can be seen that, in the embodiments satisfying at least one of the conditions of Equations 1 and 2, plating peeling hardly occurs in all cases, thereby providing excellent plating peeling prevention.

Therefore, Equations 1 and 2 derived from the composition of aluminum and silicon can be effective standards for quality control of the alloyed hot-dip galvanized steel sheet.

The technical spirit of the present invention described above is not limited to the above-described embodiments and the accompanying drawings, and it is the technical spirit of the present invention that various substitutions, modifications and changes are possible within the scope without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in the art to which this belongs.

Claims (14)

base material; and
It is formed on the base material and includes a plating layer comprising zinc, aluminum, and silicon,
The content of silicon and the aluminum in the plating layer satisfies Equation 1 below,
<Equation 1>
35.5 x [Si content (% by weight) of plating layer] + 4.43 x [Al content (% by weight) of plating layer] ≥ 212
Alloyed hot-dip galvanized steel sheet. The method of claim 1,
The content of aluminum in the plating layer and the content of aluminum of the base material satisfy Equation 2 below,
<Equation 2>
[Al content of plating layer (wt%)]/[Al content of base material (wt.%)] ≤ 0.5
Alloyed hot-dip galvanized steel sheet. The method of claim 1,
The chromium and the molybdenum (Mo) satisfy the relation of 0.3 ≤ [content (% by weight) of Cr] + 0.3 x [content (% by weight) of Mo] ≤ 2.0,
Alloyed hot-dip galvanized steel sheet. The method of claim 1,
The base material, by weight, carbon (C): 0.01% to 0.06%, manganese (Mn): 1.0% to 2.5%, silicon (Si): 0.02% to 0.1%, aluminum (Al): 0.01% to 1.0 %, Chromium (Cr): >0% to 1.5%, Molybdenum (Mo): >0% to 1.0%, Phosphorus (P): >0% to 0.08%, Sulfur (S): >0% to 0.01%, And the balance includes iron (Fe) and other unavoidable impurities,
Alloyed hot-dip galvanized steel sheet. The method of claim 1,
The alloyed hot-dip galvanized steel sheet,
Containing a mixed structure of ferrite and martensite,
Alloyed hot-dip galvanized steel sheet. 6. The method of claim 5,
The fraction of ferrite is in the range of 90% to 98%,
The fraction of martensite is in the range of 2% to 10%,
Alloyed hot-dip galvanized steel sheet. The method of claim 1,
The alloyed hot-dip galvanized steel sheet,
Tensile strength (TS): 340 MPa or more and elongation (El): 30% or more,
Alloyed hot-dip galvanized steel sheet. base material; and
It is formed on the base material and includes a plating layer comprising zinc, aluminum, and silicon,
The content of aluminum in the plating layer and the content of aluminum in the base material satisfy Equation 2 below,
<Equation 2>
[Al content of plating layer (wt%)]/[Al content of base material (wt.%)] ≤ 0.5
Alloyed hot-dip galvanized steel sheet. 9. The method of claim 8,
The base material, by weight, carbon (C): 0.01% to 0.06%, manganese (Mn): 1.0% to 2.5%, silicon (Si): 0.02% to 0.1%, aluminum (Al): 0.01% to 1.0 %, Chromium (Cr): >0% to 1.5%, Molybdenum (Mo): >0% to 1.0%, Phosphorus (P): >0% to 0.08%, Sulfur (S): >0% to 0.01%, And the balance includes iron (Fe) and other unavoidable impurities,
Alloyed hot-dip galvanized steel sheet. By weight%, carbon (C): 0.01% to 0.06%, manganese (Mn): 1.0% to 2.5%, silicon (Si): 0.02% to 0.1%, aluminum (Al): 0.01% to 1.0%, chromium ( Cr): >0% to 1.5%, Molybdenum (Mo): >0% to 1.0%, Phosphorus (P): >0% to 0.08%, Sulfur (S): >0% to 0.01%, and balance iron Preparing a hot-rolled steel sheet containing (Fe) and other unavoidable impurities;
manufacturing a cold-rolled steel sheet by cold-rolling the hot-rolled steel sheet;
annealing the cold-rolled steel sheet at a temperature in the range of 760°C to 840°C;
manufacturing a hot-dip galvanized steel sheet by immersing the cold-rolled steel sheet in a hot-dip galvanizing bath and performing hot-dip galvanizing at a temperature of 450°C to 550°C; and
Including; performing an alloying heat treatment on the hot-dip galvanized cold-rolled steel sheet at a temperature in the range of 450 ° C. to 550 ° C. to prepare an alloyed hot-dip galvanized steel sheet.
A method for manufacturing an alloyed hot-dip galvanized steel sheet. 11. The method of claim 10,
The step of rapidly cooling the alloyed hot-dip galvanized steel sheet to a temperature of 250 °C or less at a cooling rate in the range of 20 °C/sec to 40 °C/sec; further comprising,
A method for manufacturing an alloyed hot-dip galvanized steel sheet. 12. The method of claim 11,
After performing the quenching step,
Further comprising; temper rolling the alloyed hot-dip galvanized steel sheet;
A method of manufacturing an alloyed hot-dip galvanized steel sheet. 11. The method of claim 10,
The step of manufacturing the hot-rolled steel sheet,
preparing a steel material having the alloy composition;
reheating the steel in the range of 1,150°C to 1,300°C;
manufacturing a hot-rolled steel sheet by hot finish rolling the reheated steel at a finish rolling end temperature in the range of 820° C. to 920° C.; and
Including; winding the hot-rolled steel sheet in the range of 450 ° C to 700 ° C.
A method for manufacturing an alloyed hot-dip galvanized steel sheet. 11. The method of claim 10,
The alloyed hot-dip galvanized steel sheet manufactured by the manufacturing method of the alloyed hot-dip galvanized steel sheet,
It contains a mixed structure in which ferrite and martensite are mixed,
The fraction of ferrite is in the range of 90% to 98%, and the fraction of martensite is in the range of 2% to 10%,
Tensile strength (TS): 340 MPa or more and elongation (El): 30% or more,
A method for manufacturing an alloyed hot-dip galvanized steel sheet.

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