Detailed description of the invention
Technical challenge
[13]
An aspect of the present invention is to provide a zinc alloy-plated steel material capable of securing excellent corrosion resistance after processing by reducing the occurrence of cracks in the plating layer during processing and preventing corrosion resistance by reducing the occurrence of cracks in the plating layer during processing.
[14]
The problems to be solved by the present invention are not limited to the problems mentioned above, and other problems that are not mentioned will be clearly understood by those skilled in the art from the following description.
[15]
Means of solving the task
[16]
One aspect of the present invention is Jicheol So;
[17]
A zinc alloy plating layer formed on the base iron; And
[18]
Including an inhibition layer (Inhibition layer) formed between the base iron and the zinc alloy plating layer,
[19]
The zinc alloy plating layer is a weight %, Mg: 0.5 to 3.5%, Al: 0.5 to 11.0%, Si: 10 to 350 ppm, the balance Zn and inevitable impurities,
[20]
It relates to a zinc alloy plated steel material having excellent corrosion resistance after processing including a Si enriched layer in the suppression layer.
[21]
[22]
Another aspect of the present invention is the step of preparing a hot-rolled steel having a grain size of 1 to 100 μm;
[23]
Cold rolling the hot-rolled steel to produce a cold-rolled steel having a surface roughness of 0.2 to 1.0 μm and a steepness of 0.2 to 1.2 μm;
[24]
Plating by immersing in a plating bath containing the cold-rolled steel base iron in wt%, Mg: 0.5 to 3.5%, Al: 0.5 to 11.0%, Si: 10 to 350 ppm, the balance Zn and unavoidable impurities;
[25]
It relates to a method of manufacturing a zinc alloy plated steel material having excellent corrosion resistance after processing, including the step of wiping and cooling the plated hot-dip galvanized steel material.
[26]
Effects of the Invention
[27]
According to the present invention, it is possible to provide a Zn-Al-Mg-based zinc alloy-plated steel material having excellent corrosion resistance after processing and a method of manufacturing the same. Through this, there is an advantage in that the use area can be widened to an area where conventional use is limited.
[28]
Brief description of the drawing
[29]
1 is a photograph of an analysis of the components of the inhibitory layer (inhibition layer) of a zinc-alloy plated steel manufactured according to an embodiment of the present invention.
[30]
2 is a photograph illustrating a cross section of the plating layer of Inventive Example 3 of the embodiments of the present invention.
[31]
3 is a photograph illustrating a cross section of a plating layer of Comparative Example 3 among Examples of the present invention.
[32]
Best mode for carrying out the invention
[33]
While conventional zinc plating solidifies into a single Zn phase, Zn-Al-Mg-based zinc alloy plating coexists with a Zn phase, an alloy phase of Mg and Zn, an Al phase, and the like. This plating structure forms a very complex plating structure according to the physical and chemical state of the surface of the base iron according to the trace elements in the plating bath and the manufacturing process.
[34]
[35]
Among the plating structures of the Zn-Al-Mg-based zinc alloy plating layer (hereinafter, the zinc alloy plating layer or the plating layer), the alloy phase of Zn and Mg may be made of various intermetallic compounds such as MgZn 2 , Mg 2 Zn 11 , and their hardness is Hv It reaches 250-300. In addition, an inhibition layer made of an intermetallic compound of Fe and Al may be formed at the interface between the plating layer and the base iron. The intermetallic compounds of Fe and Al include Fe 4 Al 13 and Fe 2 Al 5 . Since these intermetallic compounds also have high brittleness, cracks in the plating layer are likely to occur during physical deformation.
[36]
[37]
Accordingly, the present inventors devised a method of forming the suppression layer robustly and uniformly as a method of reducing the occurrence of cracks in the plating layer during processing of zinc alloy plated steel and securing excellent corrosion resistance after processing, and derived the present invention. Hereinafter, the present invention will be described in detail.
[38]
[39]
The zinc alloy-plated steel of the present invention includes a base iron, a zinc alloy plating layer formed on the base iron, and an inhibition layer formed between the base iron and the zinc alloy plating layer.
[40]
[41]
It is preferable that the zinc alloy plating layer contains, in weight%, magnesium (Mg): 0.5 to 3.5%, aluminum (Al): 0.5 to 11.0%, silicon (Si): 10 to 350 ppm, the balance Zn and unavoidable impurities. Hereinafter, each component will be described in detail.
[42]
The Mg plays a very important role in improving the corrosion resistance of the zinc-based plated steel, and by forming a dense zinc hydroxide-based corrosion product on the surface of the plated layer in a corrosive environment, corrosion of the zinc-based plated steel can be effectively prevented. For this purpose, the Mg content is preferably 0.5% by weight or more, and more preferably 0.8% by weight or more. However, if the content is excessive, Mg oxidizing dross on the plating bath surface rapidly increases on the bath surface of the plating bath, thereby canceling the oxidation prevention effect by the addition of trace elements. In order to prevent this, Mg is preferably included in an amount of 3.5% by weight or less, and more preferably 2.0% by weight or less.
[43]
The Al suppresses the formation of Mg oxide dross in the plating bath and reacts with Zn and Mg in the plating bath to form a Zn-Al-Mg-based intermetallic compound, thereby improving the corrosion resistance of the plated steel. In order to obtain the above effect in the present invention, it is preferable to include 0.5% by weight or more, and more preferably 0.8% by weight or more. However, if the content is excessive, the weldability and phosphate treatment properties of the plated steel may be deteriorated. In terms of preventing this, Al is preferably 11.0% by weight or less, and more preferably 6.0% by weight or less.
[44]
The Si is dissolved in the Fe-Al compound when the inhibition layer of the zinc alloy plating layer is formed to impart ductility. When the Si does not precipitate as Mg 2 Si and is concentrated in the suppression layer, it is advantageous to improve adhesion and fracture toughness of the plating layer. It is preferable to include 10 ppm by weight or more for the above effect. However, if the amount is increased, when the roughness or shape of the steel plate surface is uneven, a brittle Mg 2 Si precipitate is coarse formed at the interface between the plating layer and the base iron , causing cracks due to external stress. Therefore, it is preferable that the Si content does not exceed 350 ppm by weight.
[45]
The rest contains zinc (Zn) and unavoidable impurities.
[46]
[47]
Meanwhile, some Fe of the plating bath may be included in the plating layer, but the Fe mainly exists in the inhibition layer at the interface between the plating layer and the base iron.
[48]
[49]
The zinc alloy plating layer includes an alloy phase of Mg and Zn including an MgZn 2 phase and an Mg 2 Zn 11 phase, a Zn phase, an Al phase, and the like. The first solidification during solidification is the Zn phase, and a small amount of Al is dissolved in the inside. After solidification of the primary Zn, Zn and MgZn 2 are solidified in a lamella form, and the ternary phases of Zn and MgZn 2 and Al are finally solidified. When the cooling rate is relatively slow, in addition to MgZn 2 , Mg 2 Zn 11 may be formed. Since the hardness of MgZn 2 or Mg 2 Zn 11 is higher than that of the Zn phase, it may be the point of occurrence of cracks during external stress, whereas the corrosion resistance can be improved by including Mg.
[50]
[51]
The suppression layer includes a layer in which Si is enriched (Si enriched layer). In particular, it is preferable that the Si enriched layer is located under the suppression layer. The Si-enriched layer means that Si is dissolved in a suppression layer made of an Fe-Al-based compound, and is contained under the suppression layer. The suppression layer includes a Si-concentrated layer in a form in which Si is dissolved, so that even if mechanical toughness is imparted to the suppression layer such as external stress, mechanical damage from the suppression layer is reduced, and cracks are prevented from propagating to the plating layer. I can. Uniform formation of the suppression layer and uniform distribution of Si in the suppression layer requires control of the plating bath components, metallographic control of the surface of the base iron, and control of the surface structure and plate shape. If such control is insufficient, Si is formed between the base iron and the zinc alloy plating layer as a coarse Mg 2 Si alloy phase, and when external stress occurs, a stress concentration phenomenon occurs in the Mg 2 Si alloy phase, thereby promoting the occurrence and growth of cracks. I can. Therefore, it is preferable to form not more than 5 Mg 2 Si alloy phases having a size of more than 1000 nm in diameter per 100 μm of interface length between the base iron and the zinc alloy plating layer . More preferably, five or less Mg 2 Si alloy phases exceeding 500 nm are formed. As shown in Figure 3 below, the Mg 2The Si alloy phase can be observed directly on the suppression layer.
[52]
When the suppression layer is uniformly formed, Si may be uniformly dissolved along the suppression layer. However, when the oxides present on the steel surface are not decomposed smoothly due to the shape non-uniformity of the steel surface and the shape non-uniformity, the thickness of the suppression layer may become non-uniform or not partially formed. In this case, coarse Mg 2 Si may be formed. Therefore, it is preferable that the suppression layer is uniformly formed between the base iron and the zinc alloy plating layer.
[53]
[54]
Figure 1 is a photograph of an analysis of the inhibition layer (inhibition layer) of the zinc-alloy plated steel manufactured as an embodiment of the present invention. As a method of analyzing the components of the suppression layer, a wet analysis method in which the plating layer is dissolved in a hydrochloric acid solution, analysis using a plasma generating source such as GDOES, GDMS, or a method of directly analyzing the components by TEM can be used. , Figure 1 is a component analysis by double TEM. As shown in FIG. 1, it can be seen that the suppression layer of the zinc alloy plated steel forms a layer in which Si is concentrated under the suppression layer. 1(a) is an observation of the suppression layer, and it can be seen that the suppression layer 12 is formed on the base iron 11. Meanwhile, reference numeral 13 denotes a protective film for TEM observation. (B) to (d) of Figure 1 shows the analysis of the Al, Fe, and Si components, respectively, in the suppression layer. In particular, it can be seen from FIG. 1(d) that Si is concentrated in the suppression layer.
[55]
[56]
Hereinafter, an embodiment of a method for manufacturing a zinc alloy plated steel of the present invention will be described in detail. The zinc alloy-plated steel of the present invention includes a process of preparing a base iron, and then immersing the prepared base iron in a plating bath to plate, and then wiping to adjust the thickness of the plating layer and cooling.
[57]
[58]
In preparing the base iron, first, it is preferable to make the metal structure of the hot-rolled steel uniform. It is preferable that the crystal grains of the hot-rolled steel be a surface layer (within 1/8 of the total thickness as a surface). When the structure of the hot-rolled steel, in particular, the non-uniformity of the surface structure occurs, the uniform formation of the suppression layer and the uniform concentration of Si occur due to the non-uniformity of the surface shape during cold rolling and the non-uniform diffusion of Fe from the base iron required for the formation of the suppression layer. And a coarse Mg 2 Si alloy phase is easily formed locally . For this purpose, it is preferable that the average grain size of the hot-rolled steel is 1 to 100 μm. More preferably, the size of the crystal grains is 1 ~ 50㎛, even more preferably 5 ~ 30㎛.
[59]
When the crystal grains of the hot-rolled steel are less than 1㎛, it is advantageous to secure strength, but surface roughness due to the crystal grains may increase during cold rolling. In addition, if it exceeds 100㎛, it is advantageous in terms of shape homogenization, but there is concern about scale defects due to excessive hot-rolling temperature rise, and product manufacturing cost increases. One example of a method for obtaining the crystal grain size of the hot-rolled steel is a method of performing a hot rolling temperature at a minimum of 800°C or a coiling temperature of 550°C or higher after hot rolling.
[60]
[61]
In manufacturing a cold-rolled steel by cold rolling the hot-rolled steel, it is preferable that the surface roughness (Ra) of the cold-rolled steel is 0.2 to 1.0 μm and the steepness is 0.2 to 1.2.
[62]
The surface roughness is determined according to the pressure of the roll and the surface shape of the roll when the roll rolls the material. When the surface roughness exceeds 1.0 µm, the roughness increases, so that a non-uniform suppression layer may be formed when the plating layer is formed, and there is a problem that the Si enriched layer is difficult to form homogeneously. On the other hand, if the thickness is less than 0.2 μm, the surface friction coefficient decreases, so that the steel material may slip on the roll.
[63]
The measurement of the steepness is a method of measuring the degree of curvature of the steel after placing a steel material of 1 m or more in the width direction and 2 m or more in the length direction so that the surface can be closely adhered to the flat surface. It is expressed as a value multiplied by 100 after dividing the height (H) of the bend by the wavelength (P). That is, it is expressed by the expression of height (H)/wavelength (P) x 100. The smaller the steepness, the better the flatness of the steel. In the case where the steepness exceeds 1.2, the curvature of the steel material is large, causing deviation in surface flow when the steel material passes through the plating bath, which adversely affects the formation of the suppression layer and homogenization of the plating layer. The lower the steepness is, the more advantageous it is, but it is not preferable because an excessive process cost is required to manage it to less than 0.2.
[64]
The method for controlling the illuminance and steepness to an appropriate range is not limited to any one. In the final stage of cold rolling, the rolling reduction is preferably in the range of 2 to 5%. It is necessary to apply an appropriate tension to the steel sheet during rolling. In addition, as an example for imparting surface roughness, plasma treatment may be performed on the steel surface. That is, during the cold rolling, since the final shape is determined by the last rolling roll, the rolling rate is preferably 5% or less. However, in the case of a 0.5mm thick thin plate, it is preferable to set it to 2% or more in order to reduce the overload of shear rolling.
[65]
[66]
On the other hand, the cold-rolled material as described above may be annealed and heat treated at a temperature of 600 to 850°C as necessary. It is preferable to use a gas containing 1 to 10% by volume of hydrogen (H 2 ) in nitrogen (N 2 ) during the annealing . When the hydrogen concentration is less than 1% by volume, it is difficult to reduce the oxide on the steel surface, and when it exceeds 10% by volume, the manufacturing cost increases, and thus the hydrogen is preferably included in an amount of 1 to 10% by volume.
[67]
As the dew point temperature in the atmosphere during the annealing is different, not only the ratio of components constituting the oxide film formed on the surface of the base iron is different, but also the internal oxidation ratio is different, so the dew point temperature is -60 to -10 It is preferable to manage at ℃. If the dew point temperature is less than -60°C, it is not preferable because it may incur excessive cost in managing the purity of the raw material gas. On the other hand, when the dew point temperature exceeds -10°C, the reduction of contaminants on the surface of the base iron may not be performed well, and oxide films such as B and Mn, which are trace elements or impurities contained in steel, are formed to improve plating wettability. There is a risk of hindering.
[68]
[69]
The base iron prepared as described above is immersed in a plating bath to prepare a zinc alloy plated steel. The plating bath contains, in weight %, Mg: 0.5 to 3.5%, Al: 0.5 to 11.0%, Si: 10 to 350 ppm, the balance Zn and unavoidable impurities. Each of the above components is not different from the contents described in the above-described zinc alloy plating layer.
[70]
Meanwhile, the plating bath may additionally contain 10 to 80 ppm by weight of iron (Fe). The Fe is mainly dissolved from iron and is included in the plating bath. Fe exceeding the limit that can be dissolved in the plating bath is combined with Al to form an FeAl-based compound. In addition, part of Si in the plating bath is also absorbed by FeAl formed in the plating bath. As such, the FeAl-based compound generated in the plating bath exists in a solid form called dross, and may be mixed into the plating layer when manufacturing the plating layer, causing defects. In addition, the dross serves to reduce the concentration of soluble Si in the plating bath by absorbing Si in the plating bath. In this case, Si cannot be uniformly concentrated in the suppression layer. Therefore, it is preferable that the total Fe content in the plating bath does not exceed 80 ppm by weight. As an example of a method of managing the Fe content in the plating bath to 80 ppm or less, an inert gas is injected into the lower part of the plating bath so that the inert gas floats the compound consisting of Fe and Al in the plating bath to the upper portion of the plating bath. You can lower the concentration. The content of Fe at least does not have a problem, but since it takes an excessive process cost to manage it too low, 10 ppm or more is fine.
[71]
[72]
On the other hand, in the plating bath, the amount of Al, Mg, and Zn is determined according to the composition of the plating layer. During the plating, the temperature of the plating bath is preferably 10°C or more and 90°C or less at the melting point of the plating bath composition. If the plating bath temperature is not more than 10°C compared to the melting point of the plating bath, the fluidity of the plating bath is deteriorated and the amount of uniform plating adhered is hindered. On the other hand, when the plating bath temperature exceeds 90°C compared to the melting point of the plating bath, an increase in oxides on the surface of the plating bath due to oxidation of Mg in the plating bath, and infiltration of refractory materials in the plating bath by Al and Mg may be problematic.
[73]
The temperature of the base iron immersed in the plating bath should be higher than the temperature of the plating bath to be advantageous in terms of decomposition of surface oxides and concentration of Al. In order to maximize this effect, the temperature of the base iron introduced into the plating bath is preferably 5°C or higher, and more preferably 10°C or higher compared to the temperature of the plating bath. However, if the temperature of the base iron entering the plating bath is too high, it may be difficult to manage the temperature of the plating port, and since the base iron component may be excessively eluted into the plating bath, the temperature of the plating bath does not exceed 30℃. It is preferable, and it is more preferable that the plating bath temperature is not higher than 20°C.
[74]
[75]
The zinc alloy-plated steel material plated in the plating bath is gas-wiped to control the amount of plating deposited and cool.
[76]
Mode for carrying out the invention
[77]
Hereinafter, embodiments of the present invention will be described in detail. The following examples are only for understanding the present invention, and do not limit the scope of the present invention.
[78]
[79]
(Example)
[80]
A hot-rolled steel sheet having an average grain size shown in Table 1 was prepared, and then cold-rolled to prepare a holding steel sheet of Table 1 below. During the cold rolling, a steel sheet having a surface roughness (Ra) and a steepness as shown in Table 1 was prepared by adjusting the tension and reduction rate of the steel sheet. The base steel sheet has a composition of weight %, C: 0.03%, Si: 0.02%, Mn: 0.15%, P: 0.01%, S: 0.01%, and the rest contains Fe and inevitable impurities.
[81]
[82]
The prepared base steel sheet was immersed in a zinc alloy plating bath, adjusted to an adhesion amount of 50 g/m 2 on one side, and then cooled to prepare a Zn-Al-Mg-based zinc alloy plated steel sheet. At this time, the Al, Mg, and Si components of the prepared zinc alloy plated steel were measured and shown in Table 1, and the Fe content in the plating bath was measured and shown in Table 1. The Fe content was analyzed by collecting a half point between the bath noodles at the bottom of the plating bath.
[83]
[84]
By examining the cross section of the plating layer of the zinc alloy plated steel sheet, the formation of a Si enriched layer in the inhibition layer formed between the zinc alloy plating layer and the base iron, and the size and number of Mg 2 Si alloy phases were measured, and the results are shown in Table 1 Shown together. The formation of the Si-enriched layer and the size and number of Mg 2 Si alloy phases were measured after observing the cross section of the plating layer through SEM.
[85]
In addition, in order to evaluate the corrosion resistance after processing of the zinc alloy plated steel plate, the zinc alloy plated steel plate was cut into a circle having a diameter of 100 mm, and then processed into a cup shape using a punch having a diameter of 50 mm. At this time, the curvature of the corner of the punch is 5mm, and the drawing ratio is 2.0.
[86]
The processed cup-shaped specimen was subjected to a cyclic corrosion test specified in ISO TC 156. While putting the specimen in the corrosion tester with the bottom of the cup-shaped specimen facing upward, it was checked whether red rust occurred in the specimen at every corrosion cycle, and the results are shown in Table 1.
[87]
[88]
[Table 1]
division Average particle diameter of hot rolled sheet (㎛) Cold rolled sheet average roughness (Ra) Cold rolled sheet steepness Plating bath Fe (ppm by weight) Plating layer component Mg 2 Si with a diameter of more than 1000 nm per 100 μm (number) Whether to form a Si enriched layer in the suppression layer Processed part red rust generation time (CCT cycle)
Mg (% by weight) Al (% by weight) Si (ppm by weight)
Invention Example 1 36 0.7 0.4 80 1.2 1.0 15 0 ○ 32
Invention Example 2 43 0.8 0.4 60 1.4 1.6 130 0 ○ 37
Invention Example 3 15 0.6 0.6 50 1.5 1.5 80 0 ○ 40
Invention Example 4 56 0.9 0.8 50 3.0 2.5 30 0 ○ 43
Invention Example 5 56 1.0 0.5 60 3.0 3.0 25 0 ○ 47
Inventive Example 6 80 0.8 1.0 40 3.0 11.0 350 One ○ 50
Comparative Example 1 40 0.6 1.0 100 1.5 1.6 Not detected 0 × 19
Comparative Example 2 70 0.8 1.3 120 1.3 1.6 60 5 × 21
Comparative Example 3 21 0.7 0.5 40 1.5 1.4 600 7 ○ 22
Comparative Example 4 50 1.4 1.2 30 1.6 1.7 5 0 × 24
Comparative Example 5 49 0.8 0.5 110 1.6 1.6 9 0 × 25
Comparative Example 6 12 1.3 1.5 140 1.4 1.6 50 4 × 25
[89]
[90]
Meanwhile, FIG. 2 is a cross-sectional view of the plating layer of Inventive Example 3, and FIG. 3 is a cross-sectional view of the plating layer of Comparative Example 3. In FIG. 2, the suppression layer formed between the plating layer 22 and the base iron 21 was uniformly formed, but in FIG. 3, a plurality of Mg 2 Si 33 was formed in the suppression layer between the plating layer 32 and the base iron 31. Can be confirmed.
[91]
[92]
As can be seen from the results of Table 1 and FIGS. 2 and 3, it was confirmed that the inventive examples meeting the conditions of the present invention had excellent corrosion resistance even after processing. In contrast, in the comparative example that did not meet the conditions of the present invention, it was confirmed that the processed portion has corrosion resistance for heat.
Claims
[Claim 1]
So Ji-cheol; A zinc alloy plating layer formed on the base iron; And an inhibition layer formed between the base iron and the zinc alloy plating layer, wherein the zinc alloy plating layer is in weight%, Mg: 0.5 to 3.5%, Al: 0.5 to 11.0%, Si: 10 to 350 ppm, Zinc alloy plated steel having excellent corrosion resistance after processing, including the balance Zn and unavoidable impurities, and including a Si enriched layer in the suppression layer.
[Claim 2]
The zinc alloy plated steel according to claim 1, wherein the number of Mg 2 Si alloy phases having a diameter of more than 1000 nm per 100 μm is 5 or less between the zinc alloy plating layer and the base iron .
[Claim 3]
The zinc alloy plated steel according to claim 1, wherein the number of Mg 2 Si alloy phases having a diameter of more than 500 nm per 100 μm is 5 or less between the zinc alloy plating layer and the base iron .
[Claim 4]
Preparing a hot-rolled steel having a grain size of 1 to 100 μm; Cold rolling the hot-rolled steel to produce a cold-rolled steel having a surface roughness of 0.2 to 1.0 μm and a steepness of 0.2 to 1.2 μm; Plating by immersing in a plating bath containing the cold-rolled steel base iron in wt%, Mg: 0.5 to 3.5%, Al: 0.5 to 11.0%, Si: 10 to 350 ppm, the balance Zn and unavoidable impurities; Wiping and cooling the plated hot-dip galvanized steel.
[Claim 5]
The method of claim 4, wherein the plating bath additionally contains 10 to 80 ppm of Fe and has excellent corrosion resistance after processing.
[Claim 6]
The method according to claim 4, wherein the plating bath temperature is a melting point of +10 to +90°C in the plating bath, after processing, having excellent corrosion resistance.
[Claim 7]
The method of claim 4, wherein the temperature of the base iron during plating is a plating bath temperature of +5 to +30°C.
[Claim 8]
The method of claim 4, further comprising: annealing and heat treating the cold-rolled steel at a temperature of 600 to 850°C.
[Claim 9]
The method of claim 8, wherein the furnace atmosphere of the annealing heat treatment is hydrogen (H 2 ) 1 to 10% by volume, and the remainder is nitrogen (N 2 ).
[Claim 10]
The method according to claim 8, wherein the annealing heat treatment has a dew point temperature of -60 to -10°C and has excellent corrosion resistance after processing.