Title of Invention: Hot-dip galvanized steel sheet with excellent bending workability and corrosion resistance and manufacturing method thereof
technical field
[One]
The present invention relates to a hot-dip galvanized steel sheet having excellent bending workability and corrosion resistance and a method for manufacturing the same.
background
[2]
When a zinc-coated hot-dip galvanized steel sheet is exposed to a corrosive environment, zinc, which has a lower oxidation-reduction potential than iron, corrodes first, thereby suppressing corrosion of the steel material. In addition, as the zinc of the plating layer is oxidized, a dense corrosion product is formed on the surface of the steel material to block the steel material from the oxidizing atmosphere, thereby improving the corrosion resistance of the steel material. Thanks to such advantageous properties, the range of application of hot-dip galvanized steel sheets to steel sheets for home appliances and automobiles has recently been expanded.
[3]
However, the corrosive environment is gradually worsening due to the increase in air pollution according to industrial advancement, and the need for the development of steel materials having better corrosion resistance than conventional galvanized steel materials is increasing due to strict regulations on resource and energy saving.
[4]
In order to improve this problem, various studies have been conducted on a zinc alloy-based plated steel manufacturing technology that improves the corrosion resistance of steel by adding elements such as aluminum (Al) and magnesium (Mg) to the zinc plating bath. As a typical example, as a zinc alloy-based plating material, research on a Zn-Mg-Al-based zinc alloy plated steel sheet manufacturing technology in which Mg is additionally added to the Zn-Al plating composition is being actively researched.
[5]
However, compared to the galvanized steel sheet, the Zn-Mg-Al-based zinc alloy plated steel sheet has excellent corrosion resistance, but has a disadvantage in that the bending workability is poor. That is, the zinc alloy plated steel sheet contains a large amount of Zn-Al-Mg-based intermetallic compounds formed by thermodynamic interaction of Zn, Al and Mg in the plating layer. It causes cracks, which has a disadvantage in that bending workability is deteriorated. Such cracks damage the appearance of the bent portion or cause deterioration of corrosion resistance.
[6]
There are various factors that affect crack formation during such processing, but it is known that the hardness of the plating layer and the interfacial alloy layer affect the physical properties of the material. To this end, various process changes have been attempted to suppress local coarsening of the MgZn 2 phase , which has the highest hardness among Zn-Al-Mg-based intermetallic compounds, and to uniformly distribute it in the plating layer.
[7]
However, even today, local coarsening of the MgZn 2 phase in the Mg-Al-Zn component system containing a large amount of Mg is fundamentally unavoidable. Attempts have been made to suppress the growth of the Fe-Al interface alloy phase formed between the plating layer and the base iron by adding a small amount of . Such an Fe-Al interfacial alloy phase generally grows as a Fe 2 Al 5 phase and is known to be vulnerable to interfacial fracture during processing when coarsely grown in a layer-like form due to high hardness. However, the technique of adding a small amount of Si is generally finely controlled to 0.1 to 0.2 wt%, but when it is excessively added, an additional alloy phase in the form of Mg 2 Si may be coarsely formed in the plating layer. Therefore, it can be seen that securing continuous bending workability is a very important characteristic related to stability of molding and corrosion resistance after processing.
[8]
[Prior art literature]
[9]
[Patent Literature]
[10]
(Patent Document 1) Japanese Patent Laid-Open No. JP2003-155549
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[11]
The present invention is to solve the problems of the prior art, and a hot-dip galvanized steel sheet having a Zn-Al-Mg-based plating layer capable of securing excellent bending workability and corrosion resistance by reducing cracks in the plating layer during bending forming, and its To provide a manufacturing method.
[12]
The object 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 general description of the present invention.
means of solving the problem
[13]
One aspect of the present invention is
[14]
Soji steel plate;
[15]
It is provided on at least one surface of the base steel sheet, and with respect to the remaining components except for iron (Fe) diffused from the base steel sheet, in weight%, Al: 5.1 to 25%, Mg: 4.0 to 10%, the remaining Zn and other inevitable a Zn-Mg-Al-based plating layer containing impurities; and
[16]
An interfacial alloy layer of Fe-Al-Zn composition formed between the base steel sheet and the plating layer,
[17]
The interfacial alloy layer has a thickness of 0.5 to 2 μm and has a dendritic form, and
[18]
The Zn-Mg-Al-based plating layer has a structure including at least one of Zn-Al-MgZn 2 ternary eutectic structure, Zn-MgZn 2 binary eutectic structure, Al single-phase structure in which Zn is dissolved, and Zn single-phase structure, , MgZn 2 It relates to a hot-dip galvanized steel sheet excellent in bending workability and corrosion resistance, characterized in that the aggregated Al is contained in the structure.
[19]
[20]
In the present invention, the Al and Mg content may be determined to be located in the 2 eutectic line of MgZn 2 and Al in the Mg-Al-Zn ternary phase diagram .
[21]
[22]
The width of the bending crack generated during 90 degree bending and 0T bending of the plating layer including the base steel sheet may be 30 μm or less and 100 μm or less, respectively.
[23]
[24]
Also, the present invention
[25]
Preparing a base steel plate;
[26]
Hot-dip galvanizing the base steel sheet in a plating bath containing, by weight, Al: 5.1 to 25%, Mg: 4.0 to 10%, the remaining Zn and other unavoidable impurities; and
[27]
The interfacial alloy layer and Zn-Mg- on the base steel sheet by cooling the plated steel sheet using an inert gas at a cooling rate of 5 to 30° C./s from the start of cooling from the plating bath surface to the top roll section. Including; manufacturing a hot-dip galvanized steel sheet in which Al-based plating layers are sequentially formed;
[28]
Bending, characterized in that the steel sheet is immersed in a plating bath having a temperature (T) such that the thickness (H) of the interfacial alloy layer defined by the following relational formula 1 can satisfy the range of 0.5 to 2 μm for plating It relates to a method for manufacturing a hot-dip galvanized steel sheet having excellent workability and corrosion resistance.
[29]
[Relational Expression 1]
[30]
H(㎛) = 170.53+0.0008T 2 -0.7376T
[31]
[32]
The Zn-Mg-Al-based plating layer has a structure including at least one of Zn-Al-MgZn 2 ternary eutectic structure, Zn-MgZn 2 binary eutectic structure, Al single-phase structure in which Zn is dissolved, and Zn single-phase structure, , MgZn 2 Agglomerated Al may be included in the structure.
[33]
[34]
The temperature of the plating bath may be maintained in the range of 470 to 520 °C.
[35]
[36]
Al and Mg contents in the plating bath may be determined to be located in the MgZn 2 and Al 2 process line of the Mg-Al-Zn ternary phase diagram .
[37]
[38]
The bathing time in which the base steel sheet is immersed in the plating bath may be 1 to 5 seconds.
[39]
[40]
The inert gas may be one of N, Ar, and He.
[41]
Effects of the Invention
[42]
The hot-dip galvanized steel sheet according to the present invention has advantages of excellent bending workability and corrosion resistance. In addition, according to the present invention, the cracks measured by performing a 90 degree bending test on a hot-dip galvanized steel sheet having a plating layer containing no Si, Al: 5.1 to 25% by weight, and Mg: 4.0 to 10% by weight. It is possible to provide a hot-dip galvanized steel sheet having an excellent bending workability and excellent corrosion resistance even after processing as the width is as low as 30 μm or less.
Brief description of the drawing
[43]
1 is a cross-section of the hot-dip galvanized steel sheet of Inventive Example 1, which is a preferred embodiment of the present invention, observed with a Field Emission Scanning Electron Microscope (hereinafter referred to as 'FE-SEM') (magnification × 2,000 times) it's one picture
[44]
2 is a photograph of the surface of the interfacial alloy layer of the hot-dip galvanized steel sheet of Invention Example 1, which is a preferred embodiment of the present invention, observed by FE-SEM (magnification × 10,000 times).
[45]
3 is a mapping of Fe, Al, Zn components observed by TEM-EDS of a replica sample obtained from cross-sectional polishing of the interfacial alloy layer of the hot-dip galvanized steel sheet of Invention Example 1, which is a preferred embodiment of the present invention. ) is a picture.
[46]
4 is a weight percent (Wt%) detected along the yellow line shown in FIG. 3 for the interfacial alloy layer of the hot-dip galvanized steel sheet of Inventive Example 1, which is a preferred embodiment of the present invention.
[47]
5 is a 90 degree bending of the hot-dip galvanized steel sheet of Inventive Example 1, which is a preferred embodiment of the present invention, and observation of cracks generated at the top of the bending process by FE-SEM (magnification ×100, ×200, ×300 times) they are pictures
[48]
6 is a photograph obtained by observing (magnification ×100, ×200, ×300 times) cracks generated at the top of the bending process by FE-SEM after bending the hot-dip galvanized steel sheet of Comparative Example 1 by 90 degrees.
[49]
7 is a photograph obtained by observing the cross section of Comparative Example 4 by FE-SEM (magnification × 2,000 times).
[50]
8 is a photograph obtained by observing the cross section of Comparative Example 5 by FE-SEM (magnification × 2,000 times).
[51]
9 is a photograph obtained by observing the cross section of Comparative Example 6 by FE-SEM (magnification × 2,000 times).
Best mode for carrying out the invention
[52]
Hereinafter, the present invention will be described.
[53]
As described above, it is a method of minimizing crack formation that occurs during bending of Mg-Al-Zn plated steel sheet containing a large amount of Mg in general. A method of suppressing the coarsening of the interfacial alloy phase has been proposed. However, this method has limitations in that an additional alloy phase in the form of Mg 2 Si may be coarsely formed in the plating layer.
[54]
Therefore, in order to maintain excellent corrosion resistance, which is the advantage of zinc-based alloy plated steel sheet containing a large amount of Mg, and at the same time minimize cracks occurring during bending, the present inventors have developed the composition, shape, and bending of the interfacial alloy phase depending on the presence or absence of Si addition. The cracks generated were reviewed in detail, and the present invention was completed based on the results.
[55]
[56]
The hot-dip galvanized steel sheet of the present invention, the base steel sheet; It is provided on at least one surface of the base steel sheet, and with respect to the remaining components except for iron (Fe) diffused from the base steel sheet, in weight %, Al: 5.1 to 25%, Mg: 4.0 to 10%, the remaining Zn and other inevitable a Zn-Mg-Al-based plating layer containing impurities; and an interfacial alloy layer of Fe-Al-Zn composition formed between the base steel sheet and the plating layer.
[57]
In addition, the interfacial alloy layer has a thickness of 0.5-2㎛ and has a dendritic form, and the Zn-Mg-Al-based plating layer is a Zn-Al-MgZn 2 ternary eutectic structure, Zn-MgZn 2 binary eutectic structure, It has a structure including at least one of Al single-phase structure in which Zn is dissolved and Zn single-phase structure, and aggregated Al is included in MgZn 2 structure.
[58]
[59]
First, a hot-dip galvanized steel sheet according to an aspect of the present invention, a base steel sheet; a Zn-Mg-Al-based plating layer provided on at least one surface of the base steel sheet; and an Fe-Al-Zn interface alloy layer formed between the base steel sheet and the plating layer.
[60]
At least one surface of the base steel sheet may be provided with a plating layer made of a Zn-Mg-Al-based alloy. The plating layer may be formed only on one side of the holding steel sheet, it may be formed on both sides of the holding steel sheet.
[61]
[62]
In the present invention, the Zn-Mg-Al-based plating layer is, with respect to the remaining components except for a small amount of iron (Fe) diffused from the base steel sheet, in wt%, Al: 5.1 to 25%, Mg: 4.0 to 10% , remaining Zn and other unavoidable impurities.
[63]
Al: 5.1~25%, Mg: 4.0~10%
[64]
Mg in the plating layer is an element that improves the corrosion resistance of the coated steel, and as a result, corrosion resistance is improved because corrosion products are uniformly generated and the corrosion products formed through this do not proceed further corrosion.
[65]
In general, when Mg is added in an amount of less than 1.0%, the effect of improving corrosion resistance is insignificant. When Mg exceeds 2.0%, floating dross in the plating bath due to Mg oxidation in the plating bath increases, and dross removal is frequently performed. A problem arises that the operability deteriorates because of the need to do so. For this reason, in the prior art, in the case of Zn-Mg-Al-based zinc alloy plating, Mg was added in an amount of 1.0% or more, but the upper limit of the Mg content was set around 3.0%.
[66]
However, in the present invention, the Mg content in the plating layer is added to 4.0% or more, and Al may be added to 5.1% or more to suppress Mg oxide dross in the zinc alloy plating bath. In addition, Al can also play a role in improving the corrosion resistance of the plated steel sheet in combination with Zn and Mg.
[67]
On the other hand, as described above, in the Zn-Mg-Al ternary alloy plating, Mg is known to play an auxiliary role in further stabilizing the formation of Zn corrosion products. Since the rate at which Mg is corroded by itself is faster than the rate, and the corrosion resistance of the plated steel sheet may be deteriorated, the upper limit of the Mg content in the plating layer may be limited to 10% or less.
[68]
In addition, when Al is added in excess of 25% at a Mg content of 4.0 to 10%, the melting point becomes 480°C or higher. When the plating bath temperature is too high, erosion of the plating bath structure and deformation of the steel may occur, so the Al content may be limited to 25% or less in consideration of this.
[69]
And the Al and Mg content may be determined to be located in the 2 eutectic line of MgZn 2 and Al in the Mg-Al-Zn ternary phase diagram . Here, the determination to be positioned in the second process line includes a case in which it is determined to be positioned exactly in the second process line, as well as a case in which it is slightly deviated from the second process line and determined to be positioned in the vicinity of the second process line.
[70]
In addition to the above-described composition of the plating layer, the remainder may be Zn and other unavoidable impurities. Inevitable impurities may be unintentionally mixed in the manufacturing process of a conventional hot-dip galvanized steel sheet, and it cannot be completely excluded, and those skilled in the art can easily understand the meaning.
[71]
[72]
On the other hand, in general, a characteristic plated structure shape called spangle tends to appear in a hot-dip galvanized steel sheet. These spangles occur due to the nature of the coagulation reaction of zinc. That is, when zinc is solidified, dendrites in the form of branches grow from the solidification nucleus as a starting point to form the skeleton of the plating structure, and the unsolidified molten zinc pool remaining between the dendrites It is finally solidified to complete the solidification of the plating layer. If Al is separated from MgZn 2 to form a primary structure, the Al primary structure grows in the form of dendrites, and this Al dendrite form becomes more severe as the plating amount increases or the solidification rate is slow. When such a dendrite-type Al primary structure grows too large, the bending of the plating layer is deepened, which adversely affects the appearance of the surface. There may be problems with being inferior.
[73]
However, in the present invention, the Al and Mg contents can be solved by determining to be located in the 2 eutectic line of MgZn 2 and Al in the Mg-Al-Zn ternary phase diagram .
[74]
In addition, in the present invention, the Zn-Mg-Al-based plating layer includes at least one of Zn-Al-MgZn 2 ternary eutectic structure, Zn-MgZn 2 binary eutectic structure, Al single-phase structure in which Zn is dissolved, and Zn single-phase structure. has a microstructure that And since the MgZn 2 structure contains agglomerated Al, it is possible to solve the problem of sequin generation as described above.
[75]
[76]
In addition, in the hot-dip galvanized steel sheet of the present invention, a Fe-Al-Zn interface alloy layer made of an intermetallic compound of Fe-Al-Zn may be formed between the base steel sheet and the plating layer. The interfacial alloy layer may be formed by Al and Zn in the plating bath and Fe diffused from the base steel sheet at the initial stage of plating, and serves to improve the adhesion between the base steel sheet and the plating layer, and at the same time, Fe from the base steel sheet to the plating layer. It can act as a suppression layer to prevent further diffusion.
[77]
In the present invention, the interfacial alloy layer has a dendritic shape having a Fe-Al-Zn composition, and this dendritic interfacial alloy phase induces an anchoring effect (anchor effect), which is very advantageous in reducing cracks during bending.
[78]
In the present invention, the thickness of the Fe-Al-Zn interfacial alloy phase is limited to 0.5 µm or more and 2 µm or less. If the thickness is less than 0.5㎛, the shape of the interfacial alloy phase is not sufficiently grown in a dendritic form, it is not possible to induce an anchoring effect between the base steel sheet and the plating layer, and the bending workability is inferior. On the other hand, if it exceeds 2㎛, the lower portion of the interfacial alloy phase in the direction of the base steel sheet may be grown thickly in the form of a layer, making it vulnerable to interfacial fracture during processing.
[79]
[80]
The hot-dip galvanized steel sheet of the present invention having the configuration as described above, because the plating layer is composed of the alloy composition and microstructure described above, it can provide superior corrosion resistance than the conventional zinc-based alloy-coated steel sheet containing Mg within about 3.0%. In addition, the width of cracks during bending can be minimized.
[81]
[82]
Next, a method for manufacturing a hot-dip galvanized steel sheet according to another aspect of the present invention will be described in detail.
[83]
The method for manufacturing a hot-dip galvanized steel sheet of the present invention comprises the steps of preparing a base steel sheet; Hot-dip galvanizing the base steel sheet in a plating bath containing, by weight, Al: 5.1 to 25%, Mg: 4.0 to 10%, the remaining Zn and other unavoidable impurities; and cooling the plated steel sheet using an inert gas at a cooling rate of 5 to 30°C/s from the plating bath surface to the top roll section to cool the interfacial alloy layer and Zn-Mg on the base steel sheet. -Manufacturing a hot-dip galvanized steel sheet in which an Al-based plating layer is sequentially formed; And the base steel sheet is plated by immersion in a plating bath having a temperature (T) so that the thickness (H) of the interfacial alloy layer defined by the relational formula (1) can satisfy the range of 0.5 ~ 2㎛.
[84]
[85]
First, in the present invention to prepare a steel plate, the present invention is not limited to the specific type of the steel plate. For example, a cold-rolled steel sheet or a hot-rolled steel sheet, which is a general carbon steel, can be used without limitation.
[86]
[87]
Next, in the present invention, the base steel sheet is immersed in a plating bath containing, by weight, Al: 5.1 to 25%, Mg: 4.0 to 10%, the remaining Zn and other unavoidable impurities, and hot-dip galvanizing.
[88]
The plating bath of the present invention does not contain Si, by weight, Al: 5.1 to 25%, Mg: 4.0 to 10%, the remaining Zn and other unavoidable impurities are prepared by preparing a plating bath. In order to prepare a plating bath having the above composition, a composite ingot containing predetermined Zn, Al, or Mg or a Zn-Mg, Zn-Al ingot containing individual components may be used. In addition, Al and Mg contents in the plating bath may be determined to be located in the MgZn 2 and Al 2 process line of the Mg-Al-Zn ternary phase diagram .
[89]
In the present invention, hot-dip plating is performed by immersing the base steel sheet in a plating bath having the above composition.
[90]
At this time, in the present invention, it is characterized in that the temperature of the plating bath is determined in consideration of the thickness of the interfacial alloy layer constituting the finally manufactured plated steel sheet. Specifically, it is characterized in that the plating is performed by immersion in a plating bath having a temperature (T) such that the thickness (H) of the interfacial alloy layer defined by the following relational formula 1 can satisfy the range of 0.5 to 2 μm. Accordingly, the morphology of the interfacial alloy layer of the Fe-Al-Zn composition constituting the hot-dip plated steel sheet to be manufactured can be prepared in a dendritic form. As described above, the interfacial alloy phase of such a dendritic form induces an anchoring effect (anchor effect), which is very advantageous in reducing cracks during bending.
[91]
[Relational Expression 1]
[92]
H(㎛) = 170.53+0.0008T 2 -0.7376T
[93]
[94]
If the plating bath temperature is too low, the dissolution of the ingot is very slow, and it may be difficult to secure an excellent plating layer surface quality because the plating bath has a high viscosity. On the other hand, if it is too high, there may be a problem that ash defects caused by Zn evaporation are induced on the plating surface. Above all, an excessively high plating bath temperature when Si is not added may induce excessive Fe elution from the base steel sheet to the plating layer, thereby causing outburst, which is the cause of peeling of the plating layer.
[95]
In order to prevent this phenomenon and at the same time form an interfacial alloy phase of a Fe-Al-Zn composition in a dendritic form, the temperature (T) of the plating bath should be set to a condition in the range of 470 to 520 °C, and the interfacial alloy phase The relation with the thickness (H) satisfies the above relation (1).
[96]
In addition, the temperature of the base steel sheet during immersion in the plating bath preferably has a range of 5°C or more and not more than 10°C than the temperature of the plating bath, and immersion in the plating bath with a bathing time of 1 to 5 seconds is desired.
[97]
[98]
Thereafter, in the present invention, the interfacial alloy layer on the base steel sheet by cooling the plated steel sheet using an inert gas at a cooling rate of 5 to 30° C./s from the plating bath surface to the top roll section. A hot-dip galvanized steel sheet in which a Zn-Mg-Al-based plating layer is sequentially formed is prepared.
[99]
That is, the plated steel sheet is pulled up and cooling is started from the hot water surface, and cooling is performed using an inert gas at a rate of 5 to 30°C/s until the top roll section. The inert gas may be one of N, Ar, and He, and it is more preferable to use N in terms of reducing manufacturing cost.
[100]
At this time, if the cooling rate from the hot water surface to the top roll section is 5° C./sec or less, the MgZn 2 structure develops too coarsely, and the surface curvature of the plating layer may be severe. In addition, since the Zn-MgZn 2 binary process structure is widely formed, it may be disadvantageous in securing uniform corrosion resistance and workability. On the other hand, when the cooling rate exceeds 30 ° C / s, solidification starts from the liquid phase to the solid phase during the hot dip plating process, and rapid solidification occurs in the solid-liquid section of 60 to 100 ° C, the temperature range during which all the liquid phases change to the solid phase, The alloy structure may not be uniformly formed, which may result in non-uniform local corrosion resistance. In addition, the diffusion of the Fe-Al-Zn phase is insufficient, so that the interfacial alloy phase cannot grow in a dendritic form and is excessively suppressed, which may result in poor workability. In addition, the amount of nitrogen used may increase for an excessive cooling rate, thereby increasing the manufacturing cost.
[101]
Modes for carrying out the invention
[102]
Hereinafter, the present invention will be described in more detail through examples. It should be noted that the following examples are only for the understanding of the present invention, and are not intended to specify the scope of the present invention.
[103]
(Example)
[104]
First, as a base steel sheet, a cold-rolled steel sheet containing C: 0.018%, Mn: 0.2%, Si: 0.001%, P: 0.009%, Al: 0.022%, and the balance consisting of Fe and unavoidable impurities was prepared. Thereafter , hot-dip galvanizing was performed so that the plating adhesion amount on one side of the cold-rolled steel sheet was 140 g/m 2 , and then cooled at a rate of 15° C./s from the molten metal surface to the top-roll to obtain a Zn-Mg-Al alloy plated steel sheet. .
[105]
At this time, the composition of the plating solution was changed to 2.8 to 13% Al and 2.2 to 5.1% Mg by weight%. Except for the components that are inevitably present in the plating bath, the rest is Zn. Component analysis of the plating layer was carried out by wet analysis of the solution after the plating layer was completely dissolved by immersion in 5% hydrochloric acid, and the results are shown in Table 1. For reference, in Table 1 below, Fe among the components of the plating layer is diffused from the base steel sheet during hot-dip galvanizing.
[106]
[107]
On the other hand, steel sheets having the plating layer composition of Table 1 were immersed in the plating bath temperature of Table 2 to prepare a plated steel sheet. In addition, for comparison, the target interfacial alloy layer thickness calculated according to the plating bath temperature by relation 1 is also shown in Table 2 below.
[108]
[Table 1]
No. Plating layer component (wt%)
Al Mg Fe Si
One 11.7 4.2 0.54 -
2 13.0 5.1 0.66 -
3 11.2 3.5 0.05 0.2
4 11.8 2.2 0.05 0.2
5 2.8 2.7 0.03 -
6 11.8 4.8 8.1 -
7 13.0 5.2 8.7 -
8 12.5 5.0 7.1 -
[109]
[110]
[Table 2]
No. division Relation 1 Average thickness of final interfacial alloy layer (㎛)
Plating bath temperature (℃) Calculated interfacial alloy layer thickness (㎛)
One Invention Example 1 490 1.186 1.1
2 Invention Example 2 500 1.73 1.4
3 Comparative Example 1 480 0.802 ∠0.1
4 Comparative Example 2 490 1.186 ∠0.1
5 Comparative Example 3 410 2.594 0.1
6 Comparative Example 4 530 4.322 (All plating layer alloying)
7 Comparative Example 5 540 5.506 (All plating layer alloying)
8 Comparative Example 6 570 10.018 (All plating layer alloying)
[111]
[112]
As can be seen from Table 1-2, Inventive Example 1-2 is a case in which plating is performed under conditions that satisfy both the plating component system and the plating bath temperature range proposed in the present invention. In Comparative Example 1-2, the Mg content was less than 4.0%, which is the range suggested by the present invention, and Si was added, and Comparative Example 3 was prepared using a plating bath containing both Mg and Al content. represents one case. In addition, Comparative Example 4-6 satisfies the plating Al and Mg component system proposed in the present invention, but unlike Inventive Example 1-2, the plating bath temperature range is high at 530° C. or higher, so that the alloying between the plating layer and the base steel sheet is excessive. Occurs, indicating a case in which the Fe component is contained at a level of 7.1 to 8.7% in the plating layer.
[113]
[114]
Table 2 shows the calculated thickness of the interfacial alloy layer calculated by Relation 1 and the average thickness of the final interfacial alloy layer according to the plating bath temperature. Inventive Example 1-2 satisfies the plating bath temperature range of 470 to 520° C. suggested in the present invention, and it can be confirmed that the thickness of the interfacial alloy layer calculated by Relation 1 and the thickness of the final interfacial alloy layer are similar. On the other hand, Comparative Example 1-3 is a case outside the plating component system limited by the present invention, and in Comparative Example 1-2, the component system containing Si, which is a component that inhibits alloying between the base steel sheet and the plating layer, is the thickness of the interfacial alloy layer. It can be seen that is less than 0.1 μm. Meanwhile, in Comparative Examples 4-6, the plating bath temperature is 530° C., 540° C., and 570° C., respectively, and is out of the plating bath temperature range applicable to Relational Equation 1.
[115]
[116]
Thereafter, each of the prepared plated steel sheets was cut in a direction perpendicular to the longitudinal direction, and then a 2,000-fold cross-section was taken with FE-SEM, and the results are shown in FIG. 1 below. In FIG. 1, the cross section of the hot-dip galvanized steel sheet of Inventive Example 1, which is a preferred embodiment of the present invention, is observed with a Field Emission Scanning Electron Microscope (hereinafter referred to as 'FE-SEM') (magnification × 2000 times) represents a picture. And FIG. 2 is a photograph of the surface of the interfacial alloy layer of the hot-dip galvanized steel sheet of Invention Example 1, which is a preferred embodiment of the present invention, observed by FE-SEM (magnification × 10,000 times).
[117]
As shown in FIG. 1, the plating layer of Inventive Example 1 includes a Zn-Al-MgZn 2 ternary eutectic structure and a Zn-MgZn 2 binary eutectic structure, and Al single-phase structure in which Zn is dissolved, Zn single-phase structure, and MgZn 2 It can be confirmed that the organization is included. In addition, it can be seen that the Al structure, which is darkly expressed, is located in the MgZn 2 structure. In addition, as shown in FIG. 2 , it can be confirmed that the interfacial alloy layer made of Fe-Al-Zn is formed in a dendritic form having a thickness of 0.5 μm or more and 2 μm or less.
[118]
[119]
3 is a mapping of Fe, Al, and Zn components observed by TEM-EDS of a replica sample obtained from cross-sectional polishing of the interfacial alloy layer of the hot-dip galvanized steel sheet of Invention Example 1, which is a preferred embodiment of the present invention. ) is a picture. 4 is a weight percentage (wt%) detected along the yellow line shown in FIG. 3 for the interfacial alloy layer of the hot-dip galvanized steel sheet of Invention Example 1, which is a preferred embodiment of the present invention.
[120]
As shown in Figure 3-4, Si is not contained in the components of the interfacial alloy layer, Fe: 20 to 35% by weight, Al: 15 to 30% by weight, Zn: alloy in a composition range of 30 to 36% by weight It can be seen that the phase is formed.
[121]
[122]
Meanwhile, for Inventive Examples 1-2 and Comparative Examples 1-3, physical properties were evaluated according to the following criteria to evaluate bending workability and corrosion resistance of the steel sheet according to the components of the plating layer. At this time, for Comparative Examples 4-6, the entire plating layer was alloyed, and physical property evaluation was performed except for corrosion resistance evaluation.
[123]
(1) Corrosion resistance evaluation
[124]
Each plated steel sheet was loaded into a salt spray tester, and the appropriate generation time was measured according to the international standard (ASTM B117-11). At this time, 5% brine (temperature 35 ℃, pH 6.8) was used, and 2ml/80cm 2 brine was sprayed per hour. And in order to exclude the effect of the difference in the amount of plating, the time elapsed (hr) until the occurrence of red rust was divided by the amount of plating (g/m 2 ) and expressed as a corrosion resistance index for evaluation.
[125]
○: over 50
[126]
△: in the case of 10 to 50
[127]
×: less than 10
[128]
[129]
(2) Bending workability
[130]
After bending 90 degrees (bending diameter: 3R), 3T bending, 1T bending, 0T bending with the same material thickness (1.2 t) and the same coating amount (275~285 g/m 2 ), SEM the length of the top of the bending 1mm After observation, the width of the bending crack was observed and evaluated by averaging.
[131]
(double-circle): width of a bending crack 30 micrometers or less
[132]
○: Bending crack width greater than 30 µm and less than or equal to 60 µm
[133]
△: Bending crack width greater than 60 µm and less than or equal to 100 µm
[134]
X: The width of the bending crack exceeds 100 μm
[135]
[136]
[Table 3]
division corrosion resistance Interfacial
alloy layer
components Interfacial
alloy layer
shape bending workability
90 degrees 3T 1T 0T
Invention Example 1 ○ Fe-Al-Zn dendritic form ◎ ◎ ○ △
Invention Example 2 ○ Fe-Al-Zn dendritic form ◎ ◎ ○ △
Comparative Example 1 △ Fe-Al-Zn-Si - ○ △ X X
Comparative Example 2 △ Fe-Al-Zn-Si - ○ △ △ X
Comparative Example 3 △ Fe-Al-Zn - ◎ ◎ ○ △
Comparative Example 4 - Fe-Al-Zn - X X X X
Comparative Example 5 - Fe-Al-Zn - X X X X
Comparative Example 6 - Fe-Al-Zn - X X X X
[137]
As can be seen in Table 3, in the case of Comparative Example 1-3, in which the composition of Mg and Al among the plating layer components did not satisfy the conditions of the present invention, the corrosion resistance was inferior to that of Inventive Example 1-2. In particular, in the case of Comparative Example 1-2, the bending workability was inferior, and the width of the bending crack generated during 90 degree bending and 0T bending processing did not satisfy the conditions of 30 μm or less and 100 μm or less, respectively, It can be seen that the width of the bending crack is significantly reduced compared to Inventive Example 1-2 from the 3T bending processing, which is a more severe condition than the 90 degree bending processing. It is considered that the excellent bending properties of Inventive Example 1-2 are attributed to the fact that the interfacial alloy phase in the dendritic form induces an anchoring effect (anchor effect) and advantageously acts on the reduction of cracks during bending. In addition, although the composition of the plating bath is within the range of the present invention, in the case of Comparative Examples 4-6 in which the plating bath temperature is outside the range of the present invention, the interfacial alloy layer is not in the dendritic form proposed in the present invention, and alloying proceeds throughout the plating layer. As a result, it can be confirmed that the width of the bending crack exceeds 100 μm, and the bending workability is very poor.
[138]
[139]
5 is an observation of cracks generated at the top of the bending process by FE-SEM after bending the hot-dip galvanized steel sheet of Inventive Example 1, which is a preferred embodiment of the present invention, by 90 degrees (magnification ×100, ×200, ×300 times) they are pictures
[140]
6 is a photograph obtained by observing (magnification ×100, ×200, ×300 times) cracks generated at the top of the bending process by FE-SEM after bending the hot-dip galvanized steel sheet of Comparative Example 1 by 90 degrees.
[141]
As can be seen from FIGS. 5-6 , it can be seen that the bending properties of Inventive Example 1 are superior to those of Comparative Example 1, and there is no coarse Al, MgZn 2 structure in the plating layer, so it is equivalent to Comparative Example 3 excellent in bending workability level can be seen.
[142]
[143]
Meanwhile, FIG. 7 is a photograph obtained by observing the cross section of Comparative Example 4 by FE-SEM (magnification × 2,000 times). And Figure 8 is a photograph of the cross section of Comparative Example 5 observed by FE-SEM (magnification × 2,000 times), Figure 9 is a photograph of the cross section of Comparative Example 6 observed by FE-SEM (magnification × 2,000 times).
[144]
As shown in Figs. 7-9, in Comparative Examples 4-6, alloying with the base steel sheet was performed on the entire plating layer, and it was confirmed that the interfacial alloy layer made of Fe-Al-Zn was generated to a thickness of more than 2㎛. can
[145]
[146]
The present invention is not limited to the above embodiments and examples, but can be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains can use other methods without changing the technical spirit or essential features of the present invention. It will be understood that it may be embodied in specific forms. Therefore, it should be understood that the embodiments and embodiments described above are illustrative in all respects and not restrictive.
Claims
[Claim 1]
Soji steel plate; It is provided on at least one surface of the base steel sheet, and with respect to the remaining components except for iron (Fe) diffused from the base steel sheet, in weight %, Al: 5.1 to 25%, Mg: 4.0 to 10%, the remaining Zn and other inevitable a Zn-Mg-Al-based plating layer containing impurities; and an interfacial alloy layer of Fe-Al-Zn composition formed between the base steel sheet and the plating layer, wherein the interfacial alloy layer has a thickness of 0.5 to 2 μm and has a dendritic form, and the Zn-Mg-Al-based The plating layer of Zn-Al-MgZn 2 ternary eutectic structure, Zn-MgZn 2 binary eutectic structure, Al single-phase structure in which Zn is dissolved, and Zn single-phase structure have a structure including at least one, and are aggregated in the MgZn 2 structure. A hot-dip galvanized steel sheet with excellent bending workability and corrosion resistance, characterized in that it contains Al.
[Claim 2]
[2] The hot-dip galvanized steel sheet having excellent bending workability and corrosion resistance according to claim 1, wherein the Al and Mg contents are determined to be located in the 2 process line of MgZn 2 and Al in the Mg-Al-Zn ternary phase diagram.
[Claim 3]
The hot-dip galvanized steel sheet having excellent bending workability and corrosion resistance according to claim 1, characterized in that the width of the bending cracks generated during 90 degree bending and 0T bending of the plating layer including the base steel sheet is 30 μm or less and 100 μm or less, respectively. .
[Claim 4]
Preparing a base steel plate; Hot-dip galvanizing the base steel sheet in a plating bath containing, by weight, Al: 5.1 to 25%, Mg: 4.0 to 10%, the remaining Zn and other unavoidable impurities; And the interfacial alloy layer and Zn-Mg on the base steel sheet by cooling the plated steel sheet using an inert gas at a cooling rate of 5 ~ 30 °C/s from the plating bath surface to the top roll section from the start of cooling. -Manufacturing a hot-dip galvanized steel sheet in which an Al-based plating layer is sequentially formed; and, in the base steel sheet, the thickness (H) of the interfacial alloy layer defined by the following Relational Equation 1 is in the range of 0.5 to 2 μm A method for manufacturing a hot-dip galvanized steel sheet having excellent bending workability and corrosion resistance, characterized in that plating is performed by immersion in a plating bath having a satisfactory temperature (T). [Relational Expression 1] H(㎛)= 170.53+0.0008T 2 -0.7376T
[Claim 5]
5. The method of claim 4, wherein the Zn-Mg-Al-based plating layer is at least one of Zn-Al-MgZn 2 ternary eutectic structure, Zn-MgZn 2 binary eutectic structure, Al single-phase structure in which Zn is dissolved, and Zn single-phase structure. A method for manufacturing a hot-dip galvanized steel sheet having excellent bending workability and corrosion resistance, characterized in that it has a structure containing
[Claim 6]
[Claim 5] The method according to claim 4, wherein the temperature of the plating bath is maintained in a range of 470 to 520 °C.
[Claim 7]
[Claim 5] The hot-dip galvanized steel sheet having excellent bending workability and corrosion resistance according to claim 4, wherein the Al and Mg contents in the plating bath are determined to be located in the MgZn 2 and Al 2 process line of the Mg-Al-Zn ternary phase diagram. manufacturing method.