Title of Invention: Aluminum-based alloy plated steel sheet with excellent workability and corrosion resistance and manufacturing method thereof
technical field
[One]
The present invention relates to an aluminum-based alloy plated steel sheet having excellent workability and corrosion resistance, and a method for manufacturing the same.
[2]
background
[3]
Conventionally, an aluminum (Al) plated steel sheet or a zinc (Zn) plated steel sheet is used for hot forming, but there is a problem in that micro-cracks occur or corrosion resistance deteriorates due to an alloy phase formed during heat treatment. In addition, there is a problem in that liquefaction of the plating layer occurs during hot forming and fusion to the roll occurs, and the temperature cannot be rapidly raised to 900° C., so there is a problem that productivity is lowered. In addition, in the case of an aluminum-based plated steel sheet, since there is no sacrificial corrosion resistance of aluminum, corrosion resistance after processing may become a problem.
[4]
[5]
In order to improve such corrosion resistance and hot formability, conventionally, an aluminum alloy plated steel sheet is disclosed in which Si is 4% or less in the plating bath, the alloying temperature is 700° C., and the alloying time is 20 seconds, and the plating layer is alloyed.
[6]
[7]
However, under the above conditions, since the alloying time is 20 seconds, it is difficult to perform an alloying treatment in a seal line, and there is a problem that strong cooling is required after alloying. In addition, as the Si content decreases, the plating bath temperature is very high, about 700° C., so there is a problem in that durability of structures such as sink rolls immersed in the plating bath is remarkably deteriorated.
[8]
[9]
(Patent Document 1) Korean Patent Publication No. 1997-0043250
[10]
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[11]
According to one aspect of the present invention, it is an object of the present invention to provide an aluminum-based alloy plated steel sheet that suppresses the generation of microcracks generated during hot forming, and has excellent cauterization and corrosion resistance, and a method for manufacturing the same.
[12]
The subject of the present invention is not limited to the above. Those of ordinary skill in the art to which the present invention pertains will have no difficulty in understanding the additional problems of the present invention from the contents throughout the present specification.
[13]
means of solving the problem
[14]
One aspect of the present invention is
[15]
holding grater; and
[16]
Including an alloy plating layer formed on the base steel sheet,
[17]
The alloy plating layer contains, by weight, Fe: 30-50%, Zn: 1-20%, Si: 0.1-1.5%, the remainder Al and other unavoidable impurities,
[18]
It provides an aluminum-based alloy plated steel sheet having an interfacial roughness of 2.5 μm or less between the alloy plating layer and the base steel sheet.
[19]
[20]
In addition, another aspect of the present invention,
[21]
A method for manufacturing an aluminum-based alloy plated steel sheet used for hot press forming, comprising:
[22]
preparing a holding grater;
[23]
Obtaining an aluminum-plated steel sheet by immersing the base steel sheet in an aluminum plating bath containing, by weight, Zn: 3-30%, Si: 0.1-1.5%, the remainder Al and other unavoidable impurities;
[24]
After aluminum plating, a cooling step of supplying air heated to 200 ~ 300 ℃ to the aluminum plated steel sheet to form an oxide film on the surface of the aluminum plated steel sheet; and
[25]
After the cooling, the step of obtaining an aluminum-based alloy plated steel sheet through on-line alloying in which the heat treatment is continuously maintained for 1 to 20 seconds in a heating temperature range of 650 to 750 ° C.; A manufacturing method is provided.
[26]
[27]
In addition, another aspect of the present invention provides a hot-formed member obtained by hot press forming the above-described aluminum-based alloy plated steel sheet.
[28]
Effects of the Invention
[29]
Advantageous Effects of Invention According to the present invention, it is possible to provide an aluminum-based alloy plated steel sheet that suppresses microcracks generated during hot forming and has improved adhesion and corrosion resistance.
[30]
Brief description of the drawing
[31]
1 is a photograph observed with a scanning electron microscope (SEM) of a cross section of an aluminum-based alloy plated steel sheet prepared in Comparative Example 4. Referring to FIG.
[32]
2 is a photograph observed with a scanning electron microscope (SEM) of a cross-section of the aluminum-based alloy plated steel sheet prepared according to Inventive Example 1. Referring to FIG.
[33]
3 shows the results of phase analysis using XRD (X-Ray Diffraction) for the alloy plating layer formed in Inventive Example 1. FIG.
[34]
Best mode for carrying out the invention
[35]
Hereinafter, the present invention will be described in detail. First, an aluminum-based alloy plated steel sheet, which is an aspect of the present invention, will be described in detail.
[36]
In the prior art, by adding a large amount of Si to the aluminum plating bath, a dense Fe-Al-Si alloy phase was formed in the plating layer, thereby suppressing diffusion of the base iron into the plating layer. This required a high alloying temperature and a long alloying time.
[37]
To improve this, on-line alloying was attempted by limiting the Si content to 0.5 to 4%, but as the Si content decreased, an Al-Fe alloy phase was quickly generated and the melting point of the plating layer increased. there was For this reason, since diffusion of Fe of the base iron into the plating layer is suppressed, there is a problem in that it is difficult to perform alloying on-line.
[38]
Accordingly, the present inventors have intensively studied to solve the problems of the prior art described above, by controlling the composition of the alloy plating layer and the interfacial roughness of the alloy plating layer and the base steel sheet, it is found that the problems of the prior art can be solved, and The present invention has been completed.
[39]
Therefore, according to the present invention, alloying of the plated layer is possible in a relatively short time of 20 seconds or less, and at the same time, it is possible to effectively provide an aluminum-based alloy plated steel sheet excellent in causticity, corrosion resistance and adhesion of the plated layer.
[40]
[Aluminum alloy plated steel sheet]
[41]
That is, one aspect of the present invention is,
[42]
holding grater; and
[43]
Including an alloy plating layer formed on the base steel sheet,
[44]
The alloy plating layer contains, by weight, Fe: 30-50%, Zn: 1-20%, Si: 0.1-1.5%, the remainder Al and other unavoidable impurities,
[45]
It provides an aluminum-based alloy plated steel sheet having an interfacial roughness of 2.5 μm or less between the alloy plating layer and the base steel sheet.
[46]
[47]
The aluminum-based alloy-coated steel sheet according to an aspect of the present invention may include a base steel sheet and an alloy plating layer formed on the base steel sheet, and the alloy plating layer may be formed on one or both surfaces of the base steel sheet.
[48]
According to one aspect of the present invention, the alloy plating layer may have a composition including, by weight, Fe: 30-50%, Zn: 1-20%, Si: 0.1-1.5%, the remainder Al and other unavoidable impurities . In this case, the alloy plating layer may optionally further include Mn: 3% or less (including 0%), and more preferably Mn: 2% or less (including 0%) further.
[49]
According to one aspect of the present invention, in the alloy plating layer, Zn plays an important role in improving the adhesion and corrosion resistance of the plated steel sheet as well as improving the adhesion of the alloy plating layer after the alloying treatment. Therefore, it is preferable that the Zn content in the alloy plating layer is 1 to 20%. If the Zn content in the alloy plating layer is less than 1%, the effect of corrosion resistance cannot be expected, and when the Zn content in the alloy plating layer exceeds 20%, there is a problem in that the plating adhesion is deteriorated.
[50]
In addition, the Si content in the alloy plating layer is controlled to 0.1 ~ 1.5%. If the Si content in the alloying plating layer is less than 0.1%, the interfacial roughness between the alloying plating layer and the base steel sheet becomes too large, so that there is a problem in terms of ensuring adhesion of the plating layer, and when the Si content in the alloying plating layer exceeds 1.5%, Fe-Al By dissolving Si in the alloy phase of , it is possible to suppress the diffusion of Fe diffused in the base iron, which is not preferable because the alloying temperature may increase accordingly.
[51]
In addition, according to one aspect of the present invention, the alloy plating layer may optionally further include Mn, which is plated by immersing the base steel sheet in an aluminum plating bath, and then Mn, which is a component included in the base steel sheet through alloying heat treatment. This is because it flows into the plating layer side. As a result of this diffusion, Mn of 2% or less may be further included in the alloy plating layer of the aluminum-based alloy-coated steel sheet. The upper limit of the Mn content is preferably 2% or less in order to secure plating adhesion. Mn is an element that replaces Fe in the formation of the Al-Fe alloy phase, and plays a role in improving the adhesion with the base iron, but when it is 2% or more, the alloy phase of Al-Fe is formed into a dense Al-Fe(Mn) phase, resulting in alloying. may be delayed. In addition, since the Mn content in the alloy plating layer includes a case of 0%, the lower limit thereof is not specifically limited.
[52]
In addition, according to one aspect of the present invention, as components such as Fe included in the base steel sheet diffuse through the above-described alloying treatment, in the alloy plating layer, the content of Fe is 30 to 50% by weight. Preferably, it may be 36 to 48% more preferably. By satisfying the above-mentioned composition, it is possible to secure the desired seizure properties and corrosion resistance in the present invention, and furthermore, it is possible to secure the adhesion of the plating layer.
[53]
Further, according to one aspect of the present invention, in the alloy plating layer, the Al content is preferably 40 to 60% for the purpose of the present invention, and more preferably 40.5 to 53.9%. Al in the alloy plating layer By setting the content to 40% or more, the Fe-Al alloy phase having a high melting point is formed, and there is an effect of suppressing the occurrence of sintering properties and microcracks. There is a problem in that the melting point is lowered and the sintering property is inferior during heat treatment.
[54]
[55]
In addition, according to one aspect of the present invention, the thickness of the alloy plating layer may be 5 ~ 25㎛. Corrosion resistance can be ensured by the thickness of the said alloy plating layer being 5 micrometers or more, and weldability can be ensured by setting it as 25 micrometers or less. Therefore, in the present invention, the thickness of the alloy plating layer is preferably 5 to 25 μm, more preferably 5 to 20 μm.
[56]
On the other hand, according to an aspect of the present invention, the alloying degree As the gold layer is subjected to alloying after plating during the manufacturing process described above, Fe (or Mn) contained in the base steel sheet is diffused into the aluminum plating layer having a high Al and Zn content, and as a result, mainly as an intermetallic compound of Fe and Al. An alloy plating layer made of may be formed.
[57]
Although not particularly limited thereto, the alloy phase of the Fe-Al-based intermetallic compound mainly constituting the alloy plating layer may include Fe 3Al, Fe 2Al 5, FeAl 3, and the like, and elements such as Zn, Mn, and Si may be used in the alloy plating layer. may be employed within the
[58]
In particular, according to one aspect of the present invention, the single-layer alloy plating layer may include, as a phase fraction, 80% or more of the alloy phase of Fe 2Al 5 , more preferably 90% or more of the alloy phase of Fe 2Al 5 can do. In addition, according to one aspect of the present invention, the single-layer alloy plating layer may be formed of an alloy phase in which Zn, Mn and/or Si are dissolved based on Fe 2Al 5 (ie, 80% or more in phase fraction). .
[59]
In addition, according to an aspect of the present invention, the interfacial roughness of the alloy plating layer and the base steel sheet may be 2.5㎛ or less, more preferably in the range of 0.03 ~ 2.5㎛. Through this, good adhesion of the plating layer can be ensured. On the other hand, in the present specification, the interfacial roughness (Ra) is an average value calculated by arithmetic calculation of the degree of deviation from the profile center line up and down as shown in Equation 1 below with respect to the interface formed between the alloy plating layer and the base steel sheet. means Accordingly, mathematically, it corresponds to the height (amplitude) of the rectangular area having an area equal to the sum of the areas of all peaks and valleys of the roughness curve. At this time, the interfacial roughness (Ra) is taken with a scanning transfer microscope (SEM) of a cross section in the thickness direction (meaning a direction perpendicular to the rolling direction) with respect to the aluminum-based alloy plated steel sheet, the alloy plating layer and the base steel sheet It can be measured by observing the interface.
[60]
[Equation 1]
[61]

[62]
(In Equation 1, Ra represents the interfacial roughness of the above-mentioned alloy plating layer and the base steel sheet, l represents the total length of the interface line to be measured, Z(x) is the position change of the interface line along the x-axis longitudinal direction is a function representing
[63]
According to an aspect of the present invention, the base steel sheet included in the above-described plated steel sheet is a steel sheet for hot press forming, and is not particularly limited as long as it is used for hot press forming. However, if one non-limiting example is given, a steel sheet containing Mn in the range of 1 to 10% may be used as the base steel sheet. Or, more preferably, as a base steel sheet, in weight%, C: 0.05 to 0.3%, Si: 0.1 to 1.5%, Mn: 0.5 to 8%, B: 50 ppm or less, the balance Fe and other unavoidable impurities. Branches can use a steel plate.
[64]
That is, according to the present invention, it is possible to suppress the seizure of the plating layer attached to the press die or roll generated during hot forming, and at the same time, it is possible to provide an aluminum-based alloy plated steel sheet excellent in corrosion resistance and adhesion of the plating layer.
[65]
[Method for producing aluminum alloy plated steel sheet]
[66]
Hereinafter, an example of a method for manufacturing an aluminum-based alloy plated steel sheet used for hot press forming according to an aspect of the present invention will be described. However, the following manufacturing method of the aluminum-based alloy plated steel sheet for hot press forming is an example, and the aluminum-based alloy plated steel sheet for hot press forming of the present invention does not necessarily have to be manufactured by the present manufacturing method.
[67]
Another aspect of the present invention is
[68]
A method for manufacturing an aluminum-based alloy plated steel sheet used for hot press forming, comprising:
[69]
Preparing a holding grater;
[70]
Obtaining an aluminum plated steel sheet by immersing the base steel sheet in an aluminum plating bath containing, by weight, Zn: 3 to 30%, Si: 0.1 to 1.5%, the remainder Al and other unavoidable impurities;
[71]
After aluminum plating, a cooling step of supplying air heated to 200 ~ 300 ℃ to the aluminum plated steel sheet to form an oxide film on the surface of the aluminum plated steel sheet; and
[72]
After the cooling, the step of obtaining an aluminum-based alloy plated steel sheet through on-line alloying in which the heat treatment is continuously maintained for 1 to 20 seconds in a heating temperature range of 650 to 750 ° C.; A manufacturing method is provided.
[73]
First, a base steel sheet is prepared in order to manufacture an aluminum alloy plated steel sheet. The above-described description may be equally applied to the base steel sheet.
[74]
Next, the aluminum-based alloy-coated steel sheet according to an aspect of the present invention is Zn: 3 to 30%, Si: 0.1 to 1.5%, and the remainder Al and other unavoidable impurities on the surface of the base steel sheet by weight%. It can be obtained by performing hot-dip aluminum plating using a bath, cooling continuously in the plating process, and then performing an on-line alloying treatment in which heat treatment is performed immediately.
[75]
Specifically, plating is performed by immersing the base steel sheet in a hot-dip aluminum plating bath, and the composition of the plating bath may include Zn: 3 to 30%, Si: 0.1 to 1.5%, the remainder Al and other unavoidable impurities, and more Preferably, Zn: 5 to 30%, Si: 0.1 to 1.5%, the remainder Al and other unavoidable impurities may be included. Alternatively, the hot-dip aluminum plating bath contains Zn: 5% or more and 30% or less, Si: 0.1% More than 0.5%, the balance may contain Al and other unavoidable impurities.
[76]
In addition, according to one aspect of the present invention, an additional element may be further added to the aluminum plating bath within a range that does not impair the object of the present invention.
[77]
According to one aspect of the present invention, Zn added to the aluminum plating bath is preferably added in an amount of 3 to 30% by weight. When the Zn content exceeds 30%, since a large amount of ash in the plating bath is generated, there is a problem in that workability is deteriorated due to generation of dust and the like. In addition, when the Zn content is less than 3%, the melting point of the plating bath is not significantly reduced, and Zn does not remain in the plating layer due to evaporation of Zn during alloying, so that improvement of corrosion resistance cannot be obtained. However, in order to further maximize the effect of the present invention, the lower limit of the Zn content is preferably 5%, and the upper limit of the Zn content is more preferably 20%.
[78]
In addition, according to an aspect of the present invention, the amount of Si added to the aluminum plating bath is preferably 0.1 to 1.5% by weight. When the Si content in the aluminum plating bath is less than 0.1%, the effect of improving plating adhesion cannot be obtained because the interfacial roughness between the alloy plating layer and the base steel sheet is too large, and when the Si content in the aluminum plating bath exceeds 1.5%, Fe-Al There is a problem in that the alloying temperature is increased because Si is dissolved in the alloy phase to suppress the diffusion of Fe diffused in the base iron.
[79]
On the other hand, according to one aspect of the present invention, the temperature of the plating bath is to be managed as high as 20 ~ 50 ℃ compared to the melting point (Tb) of the plating bath (that is, control in the range of Tb + 20 ℃ ~ Tb + 50 ℃) desirable. By controlling the temperature of the plating bath to Tb+20°C or higher, it is possible to control the plating adhesion amount due to the fluidity of the plating bath, and by controlling the temperature of the plating bath to Tb+50°C or lower, structural erosion in the plating bath is prevented. can be prevented
[80]
In addition, according to one aspect of the present invention, during the plating, the plating amount per side (the amount of adhesion per side of the plating layer) may be 20 to 100 g/m 2 , which after immersing the steel sheet in a hot-dip aluminum plating bath, air It can be controlled by applying an air wipping process. When the plating amount per side during the plating is 20 g/m 2 or more, the corrosion resistance effect is exhibited, and when the plating amount per single side during the plating is 100 g/m 2 or less, there is an effect that the plating layer can be alloyed as a whole.
[81]
Subsequently, after aluminum plating, air heated to 200 to 300° C. may be supplied to the aluminum-plated steel sheet to be cooled to form an oxide film on the surface of the aluminum-plated steel sheet. This cooling step is important in the present invention in that it is a means of forming a uniform alloy layer. That is, an oxide film (aluminum oxide film; AlO x ) is formed on the surface of the aluminum plated steel sheet by supplying and exposing air heated to 200 to 300° C. to the aluminum plated steel sheet during cooling.
[82]
According to one aspect of the present invention, as described above, before the alloying treatment, an oxide film can be formed on the surface of the aluminum plated steel sheet by 10% or more (more preferably 10% or more and 20% or less) with respect to the total thickness of the hot-dip aluminum plating layer. have. As described above, by forming 10% or more of the oxide film, it is possible to prevent Zn contained in the plating layer from volatilizing during the alloying process, and thus it is possible to secure excellent cauterization, corrosion resistance and adhesion of the plating layer.
[83]
Next, an on-line alloying treatment in which heat treatment is performed continuously immediately after the aforementioned cooling may be performed. Through this alloying heat treatment, Fe and/or Mn of the base steel sheet is diffused into the aluminum plating layer, whereby alloying of the plating layer can be made.
[84]
Specifically, in the present invention, the alloying heat treatment temperature is in the range of 650 to 750 °C, and the holding time may be 1 to 20 seconds. do. In the online alloying heat treatment method according to the present invention, since the heat treatment for alloying starts before the plating layer is cooled and hardened after hot-dip aluminum plating, alloying is possible in a short time. In the conventionally known plating layer composition system of aluminum-plated steel sheet, since the alloying rate was slow and sufficient alloying could not be completed in a short time, it was difficult to apply an on-line alloying method in which heat treatment was performed immediately after plating. However, in the present invention, by controlling the composition and manufacturing conditions of the plating bath that affect the alloying rate, a relatively short heat treatment time of 1 to 20 seconds It is possible to achieve alloying of the aluminum plating layer in spite of the recovery time.
[85]
According to one aspect of the present invention, the alloying heat treatment temperature may be in the range of 650 ~ 750 ℃. The alloying heat treatment temperature is based on the surface temperature of the steel sheet to be heat treated, and if the heat treatment temperature is less than 650 ° C, there may be a problem that the alloying of the plating layer is insufficient, whereas when the heat treatment temperature exceeds 750 ° C, overalloying and adhesion In addition to this inferiority, cooling of the alloyed steel sheet is not easy, so that the plating layer falls off and adheres to the roll occurs.
[86]
In addition, according to one aspect of the present invention, the holding time during the alloying heat treatment may be performed in the range of 1 to 20 seconds. In the present invention, the holding time during the alloying heat treatment means the time during which the heating temperature (including deviation ±10° C.) is maintained in the steel sheet. By making the said holding time into 1 second or more, sufficient alloying becomes possible, and there exists an effect of ensuring productivity by making the said holding time into 20 seconds or less.
[87]
According to one aspect of the present invention, in order to further improve the effect of the present invention, the lower limit of the holding time during the alloying heat treatment may be 2 seconds, more preferably 5 seconds. Similarly, the upper limit of the holding time during the alloying heat treatment may be 15 seconds, more preferably 10 seconds.
[88]
As described above, in the prior art, since diffusion of Fe is suppressed by the inclusion of Si, it was impossible to alloy in a short time of 20 seconds or less, whereas, according to the present invention, the composition of the plating bath and conditions during the alloying heat treatment are controlled. By doing so, alloying can be made in a relatively short time of 20 seconds or less.
[89]
On the other hand, the method of manufacturing an aluminum alloy plated steel sheet according to an aspect of the present invention, may further include the step of cooling after the alloying treatment.
[90]
According to an aspect of the present invention, the cooling may cool the steel sheet at an average cooling rate of 5 to 50° C./s to 300° C. or less based on the surface temperature. Meanwhile, the cooling may be air cooling or mist cooling, and according to one aspect of the present invention, most preferably, the cooling may be mist cooling.
[91]
On the other hand, according to one aspect of the present invention, more preferably by setting the average cooling rate to 10 ~ 30 ℃ / s, there is an effect that can be cooled on-line using the existing hot-dip plating line without additional equipment. In addition, according to one aspect of the present invention, the cooling can be carried out for 5 to 20 seconds, and by setting the cooling time to 10 seconds or more, a sufficient cooling effect can be exhibited.
[92]
On the other hand, according to one aspect of the present invention, in the plated steel sheet manufactured through the present invention, the Fe content in the alloying plating layer can be expressed by the following relation 1, the heat treatment temperature during alloying and the Zn, Si content in the plating bath By controlling in an appropriate range, the effect of excellent cauterization, corrosion resistance and/or plating layer adhesiveness can be exhibited easily.
[93]
[Relational Expression 1]
[94]
160 - 0.41×[T]+3.35×10 -4×[T 2] - 0.3×[wt%Zn]- 3×[wt%Si] ≤ [wt%Fe] ≤ 180 - 0.41×[T]+3.35 ×10 -4×[T 2] - 0.3×[wt%Zn]- 3×[wt%Si]
[95]
[In relation 1, [T] represents the alloying heat treatment temperature (°C), [wt%Zn] represents the Zn wt% content in the plating bath, and [wt%Si] is the Si wt% content in the plating bath , and [wt%Fe] represents the content of Fe by weight in the alloy plating layer.]
[96]
On the other hand, another aspect of the present invention provides a hot-formed member obtained by hot press forming the above-described aluminum alloy plated steel sheet.
[97]
The hot press forming may use a method generally used in the art. For example, after the plated steel sheet is heated in a temperature range of 800 to 950° C. for 3 to 10 minutes, the heated steel sheet may be hot formed into a desired shape using a press, but is not limited thereto.
[98]
In addition, the composition of the holding steel sheet of the hot press-formed member may be the same as the composition of the holding steel sheet described above.
[99]
Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the following examples are only for exemplifying the present invention and not limiting the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and matters reasonably inferred therefrom.
[100]
Modes for carrying out the invention
[101]
(Example)
[102]
First, a cold-rolled steel sheet for hot press forming having a thickness of 1.2 mm having a composition shown in Table 1 below was prepared as a base steel sheet, and then the base steel sheet was immersed and ultrasonically cleaned to remove materials such as rolling oil present on the surface.
[103]
[Table 1]
Element C Si Mn Ti B Fe
Content (%) 0.22% 0.25% Mn:1.3% 0.03% 25ppm bal
[104]
Thereafter, after heat treatment at an annealing temperature of 800° C. and an annealing time of 50 seconds in a furnace maintained in a reducing atmosphere, the base steel sheet is immersed in a plating bath under the plating bath composition and plating bath temperature conditions shown in Table 2 below. Thus, aluminum plating was performed. When the plating bath was immersed, the immersion temperature was maintained at the same temperature as that of the plating bath, and the plating bath was maintained at a temperature that was raised by 40° C. for the melting point of each plating component system. The plating amount was kept constant at 60 g/m 2 on one side using air wiping to compare alloying.
[105]
Then, by supplying air heated to 200 ~ 300 ℃ the aluminum plated steel sheet to the aluminum plated steel sheet, cooling was performed by controlling to form an oxide film of 10% or more based on the total thickness of the hot-dip aluminum plating layer. Thereafter, alloying heat treatment was performed under the alloying heat treatment conditions shown in Table 2 below, and then, based on the surface temperature of the steel sheet, it was cooled by air cooling to 300° C. or less to prepare an aluminum alloy plated steel sheet.
[106]
[Table 2]
Remark Plating bath composition [wt%] alloying temperature
[℃] alloying holding time
[candle]
AlZnSi
Comparative Example 1 100 0 0 750 15
Comparative Example 2 bal. 0 1 770 20
Comparative Example 3 bal. 0 9 820 35
Comparative Example 4 bal. 3 0 740 15
Comparative Example 5 bal. 5 0 630 20
Invention Example 1 bal. 5 0.1 650 5
Invention Example 2 bal. 5 0.5 680 10
Invention Example 3 bal. 5 1.5 750 12
Comparative Example 6 bal. 5 0.5 780 35
Comparative Example 7 bal. 5 0.7 750 35
Comparative Example 8 bal. 20 0.5 630 35
Invention Example 4 bal. 20 0.1 650 5
Invention Example 5 bal. 20 0.5 680 3
Comparative Example 9 bal. 20 2 780 20
Comparative Example 10 bal. 20 3 750 25
Comparative Example 11 bal. 30 1.5 630 30
Invention example 6 bal. 30 0.1 650 5
Invention example 7 bal. 30 1.5 680 3
Comparative Example 12 bal. 32 1 650 30
[107]
On the other hand, in the aluminum alloy plated steel sheet manufactured by the above method, the content of each component in the alloy plating layer and the thickness of the alloy plating layer were measured and shown in Table 3 below. Components in the alloy plating layer were measured by a wet method using ICP (Inductive Coupled Plasma Spectroscopy), and the thickness was measured by observing the cross section with an electron microscope. In addition, the interfacial roughness (Ra) is taken with a scanning transfer microscope (SEM) of a cross section in the thickness direction (meaning a direction perpendicular to the rolling direction) of the aluminum alloy plated steel sheet, and the interface between the alloy plating layer and the base steel sheet It was measured by observation.
[108]
In addition, the result of phase analysis using XRD (X-Ray Diffraction) for the alloy plating layer formed in Inventive Example 1 is shown in FIG. 3, and the alloy plating layer is an alloy phase based on Fe 2Al 5 or FeAl 3 , and the phase fraction It was confirmed that 80% or more (that is, the alloy plating layer has a total phase fraction of Fe 2Al 5 and FeAl 3 of 80% by weight or more) as an alloy phase.
[109]
On the other hand, for the evaluation of the characteristics of the aluminum alloy plated steel sheet, the cauterization, corrosion resistance, plating adhesion and productivity were evaluated in the following manner, and the evaluation results are shown in Table 3 below.
[110]
[Adhesiveness]
[111]
The plated steel sheet thus prepared was heated at 900° C. for 5 minutes to evaluate the physical properties of the plating, and then visually observed whether the alloy plating layer was fused to the die and evaluated according to the following criteria.
[112]
○: No burning
[113]
×: Die adsorption due to melting of the plating layer occurs
[114]
[Corrosion resistance]
[115]
After the salt spray test was performed on the plated steel sheet, it was left for 720 hours, and then the corrosion product formed on the surface was removed to measure the maximum depth of the corrosion product formed on the surface.
[116]
Corrosion resistance: After the salt spray test for 720 hours, the corrosion product formed on the surface was removed, and the depth of corrosion formed by corrosion was measured.
[117]
○: 70㎛ or less
[118]
×: more than 70 μm
[119]
[Plating Adhesion]
[120]
Plating adhesion was tested for 60° banding of the plating layer after alloying, and after attaching and peeling the tape inside the banding, the area of ​​the plating layer attached to the tape was measured and evaluated according to the following criteria.
[121]
○: 4 mm or less
[122]
×: more than 4 mm
[123]
[productivity]
[124]
Productivity was evaluated based on the following criteria by measuring the time required for alloying.
[125]
◎: less than 15 seconds
[126]
○: 15 seconds or more and 20 seconds or less
[127]
×: more than 20 seconds
[128]
[Table 3]
Remarks alloy plating layer component (wt%) interfacial roughness
(Ra)
[㎛] alloying
plating layer
thickness
[μm] Corrosion-resistant plating
adhesion productivity
AlZnSiFeMn
Comparative Example 1 bal. 0 0 25 4 3.2 5 X X X ○
Comparative Example 2 bal. 0 1 41 3 2.4 5 ○ X X ○
Comparative Example 3 bal. 0 9 50 1 0.4 10 ○ X O X
Comparative Example 4 bal. 1 0 45 4 3.2 5 ○ X X ○
Comparative Example 5 bal. 2 0 15 2 3.2 20 X ○ ○ ○
Invention Example 1 bal. 2 0.1 43 1 2.5 5 ○ ○ ○ ◎
Invention Example 2 bal. 1.5 0.5 44 0.5 2.1 15 ○ ○ ○ ◎
Invention Example 3 bal. 1.5 1.5 48 2 1.2 15 ○ ○ ○ ◎
Comparative Example 6 bal. 1.5 0.5 48 2.2 2.1 30 ○ ○ X X
Comparative Example 7 bal. 1 0.7 46 2 1.4 30 ○ ○ X X
Comparative Example 8 bal. 17 0.5 25 1.5 2.1 30 X ○ ○ X
Invention Example 4 bal. 15 0.1 39 1 2.5 15 ○ ○ ○ ◎
Invention Example 5 bal. 12 0.5 39 3 2.1 20 ○ ○ ○ ◎
Comparative Example 9 bal. 12 2 40 3.5 1.0 20 ○ ○ X ○
Comparative Example 10 bal. 10 3 41 2 0.9 20 ○ ○ X X
Comparative Example 11 bal. 23 1.5 35 1 1.2 20 X ○ ○ X
Invention example 6 bal. 17 0.1 36 1.5 2.5 15 ○ ○ ○ ◎
Invention example 7 bal. 20 1.5 36 2 1.2 20 ○ ○ ○ ◎
Comparative Example 12 Bal. 23 1 35 1 2.4 20 ○ ○ X X
[129]
As shown in Table 3 above, in the case of Inventive Examples 1 to 7, which satisfy the composition and manufacturing conditions of the plating layer prescribed in the present invention, the burning properties, corrosion resistance, and plating adhesion were all good, and accordingly, press dies generated during hot forming It was possible to prevent the plating layer from burning on the roll or microcracks from occurring.
[130]
On the other hand, in the case of Comparative Examples 1 to 12, which did not meet the Zn content of the plating bath defined in the present invention or did not meet the manufacturing conditions, one or more properties of sintering property, corrosion resistance, and plating adhesion were not good. During linearization, problems such as sintering of the plating layer on the press die or roll or generation of microcracks occurred.
[131]
In particular, a photograph observed by a scanning electron microscope (SEM) of the cross section of the aluminum-based alloy plated steel sheet prepared in Comparative Example 4 is shown in FIG. 1 . In this case, the interfacial roughness of the alloy plating layer and the base steel sheet exceeded 2.5 μm, and corrosion resistance and plating adhesion were not good.
[132]
On the other hand, a photograph obtained by observing the cross section of the aluminum-based alloy plated steel sheet prepared in Inventive Example 1 with a scanning electron microscope is shown in FIG. 2 . In this case, the interfacial roughness between the alloy plating layer and the base steel sheet was 2.5 μm or less, and the sintering property, corrosion resistance, and plating adhesion were all excellent.
Claims
[Claim 1]
holding grater; and an alloy plating layer formed on the base steel sheet, wherein the alloy plating layer is, by weight, Fe: 30-50%, Zn: 1-20%, Si: 0.1-1.5%, the remainder Al and other unavoidable impurities And, the interfacial roughness of the alloy plating layer and the base steel sheet is 2.5㎛ or less, aluminum-based alloy plated steel sheet.
[Claim 2]
The aluminum-based alloy-coated steel sheet according to claim 1, wherein the alloy plating layer has a thickness of 5 to 25 µm.
[Claim 3]
The aluminum-based alloy-coated steel sheet according to claim 1, wherein the alloy plating layer contains an alloy phase of Fe 2Al 5 in a phase fraction of 80% or more.
[Claim 4]
The aluminum-based alloy-coated steel sheet according to claim 1, wherein the Al content in the alloying plated layer is 40.5-53.9% by weight.
[Claim 5]
According to claim 1, wherein the base steel sheet in weight%, by weight%, C: 0.05 to 0.3%, Si: 0.1 to 1.5%, Mn: 0.5 to 8%, B: 50ppm or less, the balance Fe and other unavoidable impurities Containing, aluminum-based alloy plated steel sheet.
[Claim 6]
The aluminum-based alloy-coated steel sheet according to claim 1, wherein the Si content in the alloy plating layer is 0.1 to 0.5% by weight.
[Claim 7]
A method of manufacturing an aluminum-based alloy plated steel sheet used for hot press forming, the method comprising: preparing a base steel sheet; Obtaining an aluminum-plated steel sheet by immersing the base steel sheet in an aluminum plating bath containing, by weight, Zn: 3-30%, Si: 0.1-1.5%, the remainder Al and other unavoidable impurities; After aluminum plating, a cooling step of supplying air heated to 200 ~ 300 ℃ to the aluminum plated steel sheet to form an oxide film on the surface of the aluminum plated steel sheet; and obtaining an aluminum-based alloy plated steel sheet through on-line alloying in which heat treatment is performed by continuously maintaining for 1 to 20 seconds in a heating temperature range of 650 to 750° C. after cooling. manufacturing method.
[Claim 8]
The method of claim 7, further comprising cooling after the alloying treatment.
[Claim 9]
The method of claim 7, wherein, during the plating, the plating amount per side is in the range of 20-100 g/m 2 .
[Claim 10]
The method of claim 8, wherein the cooling after the alloying treatment is air cooling.
[Claim 11]
The method of claim 7, wherein the oxide film is formed on the surface of the hot-dip aluminum plating layer by 10% or more of the total thickness.
[Claim 12]
The method according to claim 7, wherein the alloying temperature is controlled so as to satisfy the following relation (1). [Relational Expression 1] 160 - 0.41×[T]+3.35×10 -4×[T 2] - 0.3×[wt%Zn]- 3×[wt%Si] ≤ [wt%Fe] ≤ 180 - 0.41×[ T]+3.35×10 -4×[T 2] -0.3×[wt%Zn]- 3×[wt%Si] [In relation 1, [T] represents the alloying heat treatment temperature (°C), [wt %Zn] represents the Zn wt% content in the plating bath, [wt%Si] represents the Si wt% content in the plating bath, and [wt%Fe] represents the Fe wt% content in the alloy plating layer.]
[Claim 13]
A hot formed member obtained by hot press forming the aluminum-based alloy plated steel sheet according to claim 1 .