Coated steel sheet with thin aluminum alloy coating and coating method therefor

Abstract

To provide a coated steel sheet with a thin aluminum alloy coating and a coating method therefor.SOLUTION: The coated steel sheet of the present invention is used for hot stamping. A coating thickness of the coated steel sheet is 5 μm to 14 μm, an aluminum alloy coating includes a FeAlSi inhibitive layer adjacent to a substrate steel sheet and an Al alloy layer outside the FeAlSi inhibitive layer, and a thickness of the FeAlSi inhibitive layer is 60% or less of the coating thickness and is 1.5 μm to 6.0 μm. Diameters of Kirkendall voids within 2 μm from an interface between the FeAlSi inhibitive layer and the substrate steel to an interior of the substrate steel are 2.5 μm or less, and the number of the Kirkendall voids having a diameter of 0.5 μm or more and 2.5 μm or less does not exceed 15 per 35 μm. The present invention also discloses a coating method for applying a thin aluminum alloy coating to a substrate steel sheet for hot stamping. The method can eliminate skip-coating, and enable a hot-stamped part obtained by the coated steel sheet to have excellent resistance spot welding performance.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a plated steel sheet having a thin aluminum alloy plating and a plating method thereof.

Background Art

[0002] In recent years, as requirements in energy and environmental protection, collision prevention regulations, and passenger passive safety have become increasingly strict, the hot stamping process has been increasingly applied to the design and manufacture of automotive parts. In order to improve the strength and toughness of hot stamped parts formed by aluminum-silicon plated plates, Patent Document 1 (Chinese Patent Application Publication No. 108588612) proposes obtaining hot stamped parts using plates having a thin plating, and the initial plating thickness of the plated steel sheet before hot stamping is 3 μm to 19 μm. However, in the production of plates having a thin plating, it has been found that problems such as large variations in the plating thickness, unstable production, and local non-plating are likely to occur during production.

[0003] Also, during hot stamping, the blank of the plated steel sheet is first heated and held from 880°C to 960°C. As a result, Fe in the base steel and Al in the initial plating diffuse into each other to form an Fe-Al intermetallic compound on the plating side, and a mutual diffusion layer with a high Al content is formed between the base material and the Fe-Al intermetallic compound layer. Since the diffusion rate of Fe into the plating to form the Fe-Al intermetallic compound is much faster than the diffusion rate of Al into the base material, if the diffusion continues, a large amount of Fe will diffuse into the plating, and the vacancies in the mutual diffusion layer cannot be filled within the time, forming Kirkendall voids. The locations where these Kirkendall voids exist have high electrical resistance, so sparks are likely to scatter during the welding process, leading to a decrease in welding performance. Patent Document 1 found that the use of a thin initial plating can suppress the mutual diffusion during hot stamping to a certain extent. Therefore, compared with a thick initial plating, it can be expected that the thin initial plating can suppress the formation and growth of Kirkendall voids during hot stamping to a certain extent, resulting in an improvement in the resistance spot welding performance of hot-stamped parts.

[0004] However, the inventor of the present application found that even when using a thin initial plating, further improvement in the resistance spot welding performance is still required.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in consideration of the above problems existing in the prior art. One object of the present invention is to provide a plated steel sheet having a thin aluminum alloy plating for hot stamping, which can eliminate non-plating, and enables the hot stamped parts obtained from the plated steel sheet to have excellent resistance spot welding performance.

Means for Solving the Problems

[0007] To achieve the above object, the plating thickness of the aluminum alloy plating on at least one side of the plated steel sheet of the present invention is 5 μm to 14 μm. The aluminum alloy plating includes an FeAlSi suppression layer adjacent to the base steel and an Al alloy layer outside the FeAlSi suppression layer. The thickness of the FeAlSi suppression layer is 60% or less of the plating thickness and is 1.5 μm to 6.0 μm. Within 2 μm from the interface between the FeAlSi suppression layer and the base steel into the interior of the base steel, the diameter of the kirkendall voids is 2.5 μm or less, and the number of kirkendall voids with a diameter of 0.5 μm or more and 2.5 μm or less does not exceed 15 per 35 μm, preferably does not exceed 10 per 35 μm, and more preferably does not exceed 5 per 35 μm.

[0008] By reducing the thickness of the FeAlSi suppression layer, the non-plating situation is eliminated, the variation in the plating thickness is reduced, and the production stability is improved. Also, since the kirkendall voids in the base steel near the above interface become fewer and smaller, it becomes easier to further suppress the formation of large-sized voids during hot stamping, thereby improving the resistance spot welding performance of the hot stamped parts formed later.

[0009] Preferably, the plating thickness of the aluminum alloy plating on at least one side is from 6 μm to 13 μm, and the thickness of the FeAlSi suppression layer is 50% or less of the plating thickness and is from 1.5 μm to 5.0 μm. Within 2 μm from the interface into the interior of the base steel, the diameter of the kirkendahl void is 2.5 μm or less, and the number of kirkendahl voids having a diameter of 0.5 μm or more and 2.5 μm or less does not exceed 13 per 35 μm. More preferably, the diameter of the kirkendahl void is 2.0 μm or less, and the number of kirkendahl voids having a diameter of 0.5 μm or more and 2.0 μm or less does not exceed 15 per 35 μm, preferably does not exceed 10 per 35 μm, and more preferably does not exceed 5 per 35 μm.

[0010] Preferably, the plating thickness of the aluminum alloy plating on at least one side is from 7 μm to 12 μm, and the thickness of the FeAlSi suppression layer is 40% or less of the plating thickness and is from 2.45 μm to 3.95 μm. Within 2 μm from the interface into the interior of the base steel, the diameter of the kirkendahl void is 2.5 μm or less, and the number of kirkendahl voids having a diameter of 0.5 μm or more and 2.5 μm or less does not exceed 13 per 35 μm. More preferably, the diameter of the kirkendahl void is 2.0 μm or less, and the number of kirkendahl voids having a diameter of 0.5 μm or more and 2.0 μm or less does not exceed 15 per 35 μm, preferably does not exceed 10 per 35 μm, and more preferably does not exceed 5 per 35 μm.

[0011] The smaller and fewer the kirkendahl voids are, the more improved the resistance spot welding performance of the subsequently formed hot stamp parts will be.

[0012] Unless otherwise specified, the plating thickness, the thickness of the FeAlSi suppression layer, and the thickness of the Al alloy layer herein are each the average of at least three corresponding measured values.

[0013] In order to meet the requirements of the hot stamping process regarding the hardenability of the steel sheet, that is, to form a fine structure with a martensite center in the hot stamped parts and reach a strength of 900 MPa to 2200 MPa, the base steel sheet contains the following components by weight, namely, 0.05% to 0.45% of C, 0.5% to 10% of Mn, 0% to 0.01% of B, 0% to 0.4% of Nb + Ti + V, 0.01% to 2% of Si, 0.01% to 2% of Al, 0.01% to 5% of Cr + Ni + Mo + Cu, where Cr is 0% to 2%, Ni is 0% to 2%, Mo is 0% to 2%, and Cu is 0% to 2%, and the balance consisting of Fe and inevitable impurity elements.

[0014] Preferably, the base steel sheet contains the following components by weight, namely, 0.09% to 0.39% of C, 0.6% to 3.5% of Mn, 0% to 0.004% of B, 0% to 0.4% of Nb + Ti + V, 0.01% to 2% of Si, 0.01% to 2% of Al, 0.01% to 5% of Cr + Mo + Ni + Cu, where Cr is 0% to 2%, Ni is 0% to 2%, Mo is 0% to 2%, and Cu is 0% to 2%, and the balance consisting of Fe and inevitable impurity elements.

[0015] More preferably, in order to obtain hot stamped parts having a fine structure with a martensite center and reaching a strength of 1400 MPa to 2100 MPa, the base steel sheet contains the following components by weight, namely, 0.18% to 0.39% of C, 0.6% to 3.5% of Mn, 0% to 0.004% of B, 0.05% to 0.3% of Nb + Ti + V, 0.01% to 2% of Si, 0.01% to 2% of Al, 0.01% to 5% of Cr + Mo + Ni + Cu, where Cr is 0% to 2%, Ni is 0% to 2%, Mo is 0% to 2%, and Cu is 0% to 2%, and the balance consisting of Fe and inevitable impurity elements.

[0016] Preferably, the thickness of the base steel sheet is 0.5 mm to 3.0 mm.

[0017] Another object of the present invention is a plating method for applying a thin aluminum alloy plating to a base steel plate for hot stamping, which can eliminate non-plating and enables the hot-stamped parts obtained from the plated steel plate to have excellent resistance spot welding performance.

[0018] To achieve the above object, in the plating method of the present invention, the composition of the plating solution contains 9% to 12% Si and 4% or less Fe by weight, and the balance consists of Al and unavoidable impurities.

[0019] Preferably, the Si content in the plating solution is 9.2% to 11.2% by weight.

[0020] The plating method according to the present invention a) a step of subjecting the base steel plate to a pretreatment before plating; b) after heating the base steel plate subjected to the pretreatment, cooling the base steel plate to a predetermined temperature within the range of 610°C to 650°C, preferably 620°C to 645°C, more preferably 625°C to 639°C, and still more preferably 625°C to 635°C; c) a step of immersing the base steel plate cooled to the predetermined temperature in step b) in a heated plating solution for 2 to 7 seconds for molten plating, wherein the temperature of the plating solution is higher than the predetermined temperature and is maintained at 630°C to 670°C, preferably 640°C to 660°C; d) after the base steel plate is taken out of the plating solution, removing the excess plating solution on at least one side by air knife purge before the plating solution on at least one side solidifies to control the plating thickness on at least one side; e) cooling the steel plate to room temperature to obtain a plated steel plate having a thin aluminum alloy plating.

[0021] The above plating method can be carried out in a continuous molten plating process. The step of pretreating the base steel plate includes, for example, degreasing, water washing, rust removal, warm water washing, auxiliary plating, drying, etc. In the process of molten aluminum plating on the above steel plate, the heating of the base steel plate can be carried out by induction heating, a heating furnace and other methods. Preferably, the temperature of the plating solution is 5°C to 20°C, more preferably 7°C to 15°C higher than the predetermined temperature of the steel plate before entering the plating solution (i.e., the temperature of the steel plate before entering the pot). In step e), the cooling rate of the steel plate is preferably 5°C / s or more. Also, those skilled in the art will understand that any range or any value within the above range can be applied to the present invention. For example, the above predetermined temperature can be taken from any range within the range of 610°C to 650°C, or any specific value within the range of 610°C to 650°C, any range such as 610°C to 620°C, 635°C to 650°C and 635°C to 645°C, or any value such as 612°C, 614°C, 616°C, 618°C, 620°C, 622°C, 624°C, 626°C, 628°C, 630°C, 632°C, 634°C, 636°C, 638°C, 640°C, 642°C, 644°C, 646°C, 648°C, etc.

[0022] The plated steel sheet obtained by the plating method of the present invention has a plating thickness of 5 μm to 14 μm, preferably 6 μm to 13 μm, more preferably 7 μm to 12 μm. The thickness of the FeAlSi suppression layer in the plating is 60% or less of the plating thickness and within the range of 1.5 μm to 6 μm, preferably 50% or less of the plating thickness and within the range of 1.5 μm to 5.0 μm, more preferably 40% or less of the plating thickness and within the range of 2.45 μm to 3.95 μm. Within 2 μm from the interface between the FeAlSi suppression layer and the base steel towards the inside of the base steel, the diameter of the Kirkendall voids is 2.5 μm or less, and the number of Kirkendall voids with a diameter of 0.5 μm or more and 2.5 μm or less does not exceed 15 per 35 μm, preferably does not exceed 13 per 35 μm, more preferably does not exceed 5 per 35 μm. Even more preferably, the diameter of the Kirkendall voids is 2.0 μm or less, and the number of Kirkendall voids with a diameter of 0.5 μm or more and 2.0 μm or less does not exceed 15 per 35 μm, preferably does not exceed 10 per 35 μm, more preferably does not exceed 5 per 35 μm.

[0023] In the method of the present invention, the temperature of the plating solution in the aluminum pot and the temperature of the steel sheet entering the aluminum pot are lowered, the Si content in the plating solution is increased, and the residence time of the steel sheet in the plating solution is shortened. Due to the synergistic effect of these factors, the mutual diffusion between Fe in the base material and Al in the plating is suppressed. On the one hand, the obtained plating has a stable plating thickness with no plating disappearance. On the other hand, the formation of Kirkendall voids in the base steel near the interface between the FeAlSi suppression layer and the base steel is suppressed, resulting in fewer voids and smaller diameters. Thereby, the resistance spot welding performance of the hot stamp parts formed by the plated steel sheet is improved.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be described in more detail below with reference to the exemplary embodiments. The following embodiments or experimental data are intended to illustrate the present invention by way of example. It will be apparent to those skilled in the art that the present invention is not limited to these embodiments or experimental data.

[0026] The present invention provides a plated steel sheet for hot stamping and a plating method thereof.

[0027] In the molten aluminum plating process, an alloying reaction occurs between Fe in the surface of the base steel and Al and Si in the plating solution, and an FeSiAl intermetallic compound alloy layer, that is, an FeAlSi suppression layer, is formed on the surface of the base steel. Due to the formation of the FeAlSi suppression layer on the surface of the base steel, the mutual diffusion of Fe and Al is significantly reduced. There is an Al alloy layer outside the FeAlSi suppression layer, and its thickness can be adjusted by an air knife purge. When producing thin plates with thin plating, if the Al alloy layer in the plating is too thin for a determined plating thickness, it will lead to problems such as unstable plating thickness of the steel plate during continuous production and frequent occurrence of local non-plating phenomena. Therefore, the Al alloy layer should not be made too thin. Thus, in order to ensure a sufficient thickness of the Al alloy layer, it is necessary to obtain a thin FeAlSi suppression layer on the surface of the steel plate during plating.

[0028] Also, in the prior art, compared with the heating process of hot stamping, the temperature of the steel sheet before entering the plating solution is below 700°C, and the hot-dipping time is only a few seconds, so it is generally believed that the diffusion of alloying elements in the hot-dipping process is slow and the Kirkendall effect does not occur. However, after thorough investigation, the inventors of the present invention found that in the hot-dipping process, the outside of the steel substrate is liquid aluminum, so Fe atoms can still react quickly with Al and Si in the liquid aluminum to form intermetallic compounds (FeAlSi inhibition layer). The Kirkendall effect is essentially caused by the diffusion rate of Fe to the outside being much faster than the diffusion rate of Al into the iron substrate, and the existence of a few micrometers of FeAlSi inhibition layer in the plating formed by hot-dipping fully suggests that the phenomenon of Fe diffusion to the outside does indeed exist in the hot-dipping process, that is, Kirkendall voids can be formed. Through extensive microscopic observation, the inventors have found that a large number of Kirkendall voids do indeed exist within 2 μm into the substrate steel from the interface between the FeAlSi inhibition layer and the substrate steel, and are difficult to notice because their size is much smaller than the size of the voids after hot stamping. The present invention has found that the thicker the FeAlSi inhibition layer is, the more Fe diffuses to the outside, making it easier for Kirkendall voids to form. Therefore, by reducing the thickness of the FeAlSi inhibition layer, the diffusion of Fe elements in the substrate steel to the outside can be reduced, thereby reducing the formation of Kirkendall voids.

[0029] On the one hand, the present invention has found that in the subsequent hot stamping process, the Kirkendall voids formed in the molten plating process are quite likely to grow rapidly, significantly increasing the resistance of the plating during spot welding, causing sparks to scatter during welding, and being likely to have a serious impact on the resistance spot welding performance of the hot stamping parts. Therefore, in order to ensure the resistance spot welding performance of the final parts, the present invention aims to achieve the purpose of suppressing the formation of Kirkendall voids by controlling the conditions of the molten plating.

[0030] Therefore, the method of the present invention aims to obtain a thin FeAlSi suppression layer, suppress the formation of Kirkendall voids in the base steel near the interface between the FeAlSi suppression layer and the base steel, improve the stability of the plating thickness, eliminate the non-plated situation, and improve the resistance spot welding performance of the parts formed by subsequently hot stamping the plated steel sheet.

[0031] The plating solution used in the present invention contains, by weight, 9% to 12% Si, 4% or less Fe, Al or Al alloy, and the balance comprising inevitable impurities.

[0032] Preferably, the Si content in the plating solution is 9.2% to 11.2% by weight.

[0033] The plating method for the hot stamping plated steel sheet according to the present invention is a) a step of subjecting the base steel sheet to pretreatment before plating; b) after heating the base steel sheet subjected to the pretreatment, cooling the base steel sheet to a predetermined temperature within the range of 610°C to 650°C, preferably 620°C to 645°C, more preferably 625°C to 639°C, and even more preferably 625°C to 635°C; c) A step of dipping the base steel plate cooled to the predetermined temperature in step b) into a heated plating solution for 2 to 7 seconds for hot dip plating, wherein during the dipping, the temperature of the plating solution is higher than the predetermined temperature and is maintained at 630°C to 670°C, preferably 640°C to 660°C; d) After the base steel plate is taken out of the plating solution, before at least one side of the plating solution solidifies, removing the excess plating solution on at least one side by air knife purge to control the plating thickness on at least one side; e) A step of cooling the steel plate to room temperature to obtain a plated steel plate having a thin aluminum alloy plating.

[0034] In the above method, the step of pretreating the base steel plate includes, for example, degreasing, water washing, rust removal, warm water washing, auxiliary plating, drying, etc. In step c), preferably, the temperature of the plating solution is 5°C to 20°C, more preferably 7°C to 20°C higher than the predetermined temperature of the steel plate before entering the plating solution. In step e), the cooling rate of the steel plate is preferably 5°C / s or more.

[0035] In the method of the present invention, a plating solution with a high Si content is selected. The higher the Si content in the plating solution, the lower the melting point of the plating solution, and the easier it is to lower the temperature of the plating solution, thereby suppressing the mutual diffusion of Al atoms and Fe atoms, obtaining a FeAlSi suppression layer with a reduced thickness, and slowing down the formation and growth of kirkendall voids near the surface of the base steel plate during and after hot dip plating and when hot stamping the plated steel plate. Therefore, the Si content is 9% or more. However, if the Si content is too high, the resistivity of the alloying layer in the plating of the steel plate after hot stamping the plated steel plate will increase, and the welding performance of the hot stamping parts formed by the plated steel plate will deteriorate. Therefore, the Si content should not be too high. Therefore, the Si content cannot exceed 12%. Preferably, the Si content in the present invention is from 9.2% to 11.2%.

[0036] Next, the present invention proposes to lower the temperature of the plating solution and the predetermined temperature of the steel sheet entering the plating solution (i.e., the temperature of the steel sheet entering the pot) to suppress the formation of Kirkendall voids. As described above, when forming the FeSiAl suppression layer, Fe atoms in the base steel diffuse into the plating solution to form an FeSiAl intermetallic compound, while Al atoms diffuse into the Fe base material. The diffusion of Fe atoms and Al atoms in the base material occurs based on a vacancy mechanism, that is, the diffusion is achieved by exchanging the positions of metal atoms and vacancies. When the rate of Al atoms entering the base material is not sufficient to compensate for the number of Fe atoms diffusing out from the base material, voids will be formed in the base material due to the aggregation of vacancies. Therefore, by suppressing the thickness and growth rate of the FeAlSi suppression layer, the formation of Kirkendall effect voids can be substantially suppressed. Since it is well known that temperature has a great influence on the diffusion rate, by lowering the temperature of the plating solution and the predetermined temperature of the steel sheet entering the plating solution, the formation of Kirkendall voids can be suppressed. On the one hand, it is conceivable to lower the predetermined temperature of the steel sheet entering the plating solution. The difference in the diffusion rates of Fe atoms and Al atoms increases at high temperatures, resulting in the formation of a larger number of larger-sized Kirkendall voids. From experimental data, it can be seen that when the predetermined temperature of the steel sheet entering the plating solution was higher than 655 °C, a larger number of larger-sized Kirkendall voids were formed and could be observed in the base steel near the interface. However, during molten plating, in order to ensure the plating property of the steel sheet and prevent problems such as non-plating on the surface, the predetermined temperature of the steel sheet entering the plating solution should not be too low. From experimental data, it can be seen that serious non-plating occurred when the predetermined temperature of the steel sheet entering the plating solution was lower than 610 °C. Therefore, according to the present invention, the predetermined temperature of the steel sheet entering the plating solution is designed to be from 610 °C to 650 °C, preferably from 620 °C to 645 °C, more preferably from 620 °C to 639 °C, and even more preferably from 625 °C to 635 °C.On the other hand, by lowering the temperature of the plating solution, it is considered that the alloying reaction between Fe atoms, Al atoms, and Si atoms, which forms a thin suppression layer, is suppressed. However, correspondingly, in order to ensure the fluidity and uniformity of the plating solution, the temperature of the plating solution should not be too low. Therefore, the temperature of the plating solution is designed to be higher than the predetermined temperature and to be in the range of 630°C to 670°C, preferably 640°C to 660°C.

[0037] Furthermore, the present invention proposes to shorten the residence time of the steel sheet in the plating solution. First, if the residence time is too long, the continuous mutual diffusion of Fe and Al is promoted, the FeAlSi suppression layer becomes thick, and kirkendall voids are formed as a result. Next, the production line has a limit in length. If the residence time is too long, the operating speed of the production line must be reduced, the production efficiency is affected, and the cost increases. Therefore, the residence time of the steel sheet in the plating solution needs to be controlled within 2 seconds to 7 seconds.

[0038] Finally, the thickness of the Al alloy layer is controlled by maintaining a high-intensity purge of the air knife so as to obtain a steel sheet having a thin aluminum alloy plating. Therefore, after the base steel sheet is taken out of the plating solution, before at least one side of the plating solution solidifies, in order to control the plating thickness of at least one side, the excess plating solution on at least one side is removed by an air knife purge. Thereafter, the steel sheet is cooled to room temperature at a cooling rate of preferably 5°C / s or more to obtain a plated steel sheet having a thin aluminum alloy plating.

[0039] Also, preferably, a relatively high temperature of the plating solution for ensuring the plating property is made compatible with a low predetermined temperature of the steel sheet entering the plating solution for ensuring a low reaction rate at the interface and reducing the formation of kirkendall voids. The present invention particularly points out that plating is performed under the condition that the predetermined temperature is lower than the temperature of the plating solution. Preferably, by the predetermined temperature being 5°C or more lower than the temperature of the plating solution, while ensuring the plating property, the reaction rate at the interface is moderated, resulting in a reduction in kirkendall voids. On the other hand, if the difference between the temperature of the steel sheet and the temperature of the plating solution is too large, the temperature of the plating solution becomes unstable, so the temperature difference is designed not to exceed 20°C in the present invention. Preferably, the temperature difference is from 7°C to 15°C.

[0040] By the above method of the present invention, a plated steel sheet having a thin aluminum alloy plating for hot stamping is obtained. The thickness of the plated steel sheet is from 0.5 mm to 3.0 mm. On any surface of the steel sheet, the plating thickness of the aluminum alloy plating is from 5 μm to 14 μm, preferably from 6 μm to 13 μm, more preferably from 7 μm to 12 μm.

[0041] The above aluminum alloy plating is An FeAlSi suppression layer adjacent to the base steel, wherein the thickness of the FeAlSi suppression layer is 60% or less of the plating thickness and is from 1.5 μm to 6 μm, preferably 50% or less of the plating thickness and is from 1.5 μm to 5 μm, more preferably 40% or less of the plating thickness and is from 2.45 μm to 3.95 μm. Within 2 μm from the interface between the FeAlSi suppression layer and the base steel into the interior of the base steel, the diameter of the Kirkendall voids is 2.5 μm or less, and the number of Kirkendall voids having a diameter of 0.5 μm or more and 2.5 μm or less does not exceed 15 per 35 μm, preferably does not exceed 13 per 35 μm, more preferably does not exceed 5 per 35 μm, and even more preferably, the diameter of the Kirkendall voids is 2.0 μm or less, and the number of Kirkendall voids having a diameter of 0.5 μm or more and 2.0 μm or less does not exceed 13 per 35 μm, preferably does not exceed 10 per 35 μm, more preferably does not exceed 5 per 35 μm. An FeAlSi suppression layer, and an Al alloy layer outside the FeAlSi suppression layer, having a unique plating structure.

[0042] The FeAlSi suppression layer is a compound layer of FeSiAl alloy formed by the reaction between Al atoms and Si atoms in the plating solution and Fe atoms in the surface of the steel sheet when the steel sheet is immersed in the plating solution, and the main composition is Fe 2 SiAl 7 and is composed of, and the mass ratio of Si element to the total of Si element and Al element is higher than 0.12 and higher than the Si content in the plating solution. The thickness of the Al alloy layer is adjusted by an air knife to obtain aluminum-silicon plating with different thicknesses.

[0043] In order to meet the requirements of the hot stamping process regarding the hardenability of the steel sheet, that is, to form a fine structure with a martensite center in the hot stamping parts and reach a strength of 900 MPa to 2200 MPa, the base steel sheet contains the following components by weight: namely, 0.05% to 0.45% of C, 0.5% to 10% of Mn, 0% to 0.01% of B, 0% to 0.4% of Nb + Ti + V, 0.01% to 2% of Si, 0.01% to 2% of Al, 0.01% to 5% of Cr + Ni + Mo + Cu, where Cr is 0% to 2%, Ni is 0% to 2%, Mo is 0% to 2%, and Cu is 0% to 2%, and inevitable impurity elements.

[0044] In the plated steel sheet of the present invention, a small amount of kirkendall voids exist in the base steel near the interface between the FeAlSi suppression layer and the base steel, and due to their small diameter, it helps to reduce the formation of large-sized voids in the plating of the hot stamping parts during hot stamping, thereby ensuring that the parts have good resistance spot welding performance. When the plating thickness is set, a thin FeAlSi suppression layer means that the Al alloy layer becomes thicker, which is beneficial for air knife control, improves the stability of the plating thickness, and prevents the occurrence of non-plating phenomenon.

[0045] As an example, the tested base steel sheet has the composition shown in Table 1, and its corresponding manufacturing process is as follows.

[0046] a) Steelmaking: Melt in a vacuum induction furnace, an electric furnace, or a converter according to the composition in Table 1, and produce a casting billet using continuous casting technology, or directly use the continuous casting and rolling process of thin slabs. b) Hot rolling: Heat the billet from 1120 °C to 1280 °C and perform hot rolling, with the total rolling ratio of the hot rolling being 50% or more, and perform the final rolling at a temperature of 800 °C or higher to obtain a hot-rolled steel sheet. Roll the steel sheet at a temperature of 700 °C or lower to form a hot-rolled steel strip, and pickle the hot-rolled strip to remove the oxide scale generated during the hot rolling process. c) Cold rolling: Cold roll the pickled hot-rolled strip, with the rolling reduction rate of the cold rolling being 30% to 70%, to obtain a cold-rolled steel strip of 1.4 mm.

[0047]

Table 1

[0048] Plate the obtained base steel plate according to the plating process presented in Table 2. The target plating thickness is 8 μm to 12 μm, and the plating solution contains, by weight, 9% to 12% of Si, 4% or less of Fe, and the balance consisting of Al or an Al alloy and inevitable impurities. In the plating process of Table 2, the influence of process parameters of the molten plating, such as the temperature of the plating solution, the predetermined temperature of the steel plate entering the plating solution (i.e., the temperature of the steel plate entering the pot), the temperature difference between the plating solution and the steel plate, the molten plating time, and the Si content in the plating solution, is comprehensively considered.

[0049]

Table 2

[0050] After the treatment by the above plating process, perform a macro inspection on the surface quality of the steel strip to detect the non-plated situation of the surface. Here, the non-plated situation of the surface refers to all situations of the exposure of the base steel plate and the exposure of the FeAlSi inhibition layer. On the other hand, the plating thickness and the thickness of the FeAlSi inhibition layer within the plating thickness are determined as follows. Select five positions of 1 / 6, 1 / 3, 1 / 2, 2 / 3, and 5 / 6 of the steel strip, measure the thickness of the FeAlSi inhibition layer and the plating thickness with a scanning electron microscope (SEM), and obtain the average value of the measurement results at the five positions together with the deviation.

[0051] Method for determining the number of Kirkendall voids: Within the field of view of the SEM, count the Kirkendall voids within a range of 35 μm in length along the surface of the base steel, and measure their diameters. Method for determining the diameter of a Kirkendall void: Within the same field of view, measure the longest diameter and the shortest diameter of the void, and use half of the sum of these two diameters as the diameter of the void.

[0052] Table 3 shows the statistical results regarding the plating structure, macroscopic surface, and the number of the Kirkendall voids.

[0053]

Table 3

[0054] Referring to Embodiments 1 to 8, when the target plating thickness is set to be from 8 μm to 12 μm, the thickness of the FeAlSi suppression layer obtained according to the method of the present invention is controlled to be from about 2.9 μm to about 4.1 μm, so that the thickness of the Al alloy layer is controlled to be from about 5.1 μm to about 8 μm, and the FeAlSi suppression layer occupies about 29% to about 45% of the plating thickness. In this case, although the plating thickness of the steel sheet is thin, since the FeAlSi suppression layer is relatively thin, the thickness of the Al alloy layer can still be adjusted by air knife purge, and the control of the target plating thickness in the production process can be easily achieved, there is no non-plating phenomenon, and the variation in the final plating thickness becomes small. Further, the maximum diameter of the Kirkendall voids near the interface between the base steel and the plating is 2 μm or less, and the number of the Kirkendall voids generally does not exceed 13 per 35 μm, and the resistance spot welding performance of the plated steel sheet after hot stamping can be easily improved. For example, from the comparison of the data of Embodiment 5 and Embodiment 8, it can be seen that the difference between the temperature of the plating solution and the temperature of the steel sheet put into the pot is 7 °C in Embodiment 5, and this difference is 5 °C in Embodiment 8. The number of Kirkendall voids in Embodiment 8 is about 8 per 35 μm, and the number of Kirkendall voids in Embodiment 5 is 5 per 35 μm. It can be seen that an appropriate temperature difference brings about a further reduction in the formation of Kirkendall voids.

[0055] FIG. 1 is a SEM photograph of a local plating form of the plated steel sheet according to Embodiment 5 of the present invention. The plating thickness is about 9.0 μm, the thickness of the FeAlSi suppression layer is about 3.2 μm, the diameter of the Kirkendall voids is 2.5 μm or less, and the number of Kirkendall voids in the range of 0.5 μm to 2.5 μm in diameter is about 5 per 35 μm.

[0056] Figure 2 is an SEM photograph of the local plating morphology of the plated steel sheet according to Comparative Example 4. The plating thickness was about 8.6 μm, the thickness of the FeAlSi suppression layer was about 6.7 μm, and the number of Kirkendall voids with diameters in the range of 0.5 μm to 2.5 μm was about 29 per 35 μm.

[0057] The parameters of the plating process for Embodiment 5 and Comparative Example 4 differed only in the temperature of the steel sheet before it was placed in the pot. In Comparative Example 4, the temperature of the steel sheet before it was placed in the pot was significantly higher. Therefore, the reason why there were more Kirkendall voids and the FeAlSi suppression layer was thicker in Comparative Example 4 was that the high temperature of the steel sheet before it was placed in the pot was the inducing factor. It can be seen that it is not desirable for the temperature of the steel sheet before it is placed in the pot to be high.

[0058] Figure 3 is a photograph of typical non-plated defects of the plated steel sheet according to Comparative Example 4. It can be clearly seen that severe non-plating occurred in several places. This is because, compared with Embodiment 5, due to the high temperature of the steel sheet before it was placed in the pot in Comparative Example 4, the generated FeAlSi suppression layer became thicker, and accordingly the Al alloy layer became thinner, so that the diffusion was accelerated. As a result, the requirements for the air knife purge increased, the difficulty in control increased, and thus non-plating occurred.

[0059] Each comparative example shows a different degree of non-plating and has a large number of large-sized Kirkendall voids. This is because in Comparative Example 1, the Si content in the aluminum plating solution is too low; in Comparative Example 2, the residence time of the steel sheet in the aluminum plating solution is too long; in Comparative Example 4, the temperature of the steel sheet before entering the pot is too high; and in Comparative Example 6, the temperature of the plating solution is too high. All of the above four situations ultimately lead to an increase in the thickness of the finally obtained FeAlSi inhibition layer, reaching from 6.6 μm to 7.5 μm. As a result, the thickness of the Al alloy layer is thin, the measurement results of the thickness vary greatly depending on the position, the thickness uniformity is poor, the final plating thickness clearly varies, and there is locally non-plating, which affects the production stability of the steel sheet. Also, in the above four cases, the number of Kirkendall voids with a diameter of 0.5 μm to 2.5 μm in the base steel near the interface between the base steel and the FeAlSi inhibition layer is large, reaching from 17 to 29 per 35 μm. These large Kirkendall voids weaken the resistance spot welding performance of the later obtained hot stamp parts. Therefore, a low Si content, a long residence time, a high temperature of the steel sheet before entering the pot, and a high temperature of the plating solution all promote diffusion and result in the formation of more and larger Kirkendall voids. Therefore, it is necessary to control all of the above four factors simultaneously to suppress the formation of Kirkendall voids under these synergistic effects.

[0060] Also, in Comparative Example 3, due to the low temperature of the steel sheet before entering the pot, the surface temperature of the steel sheet is close to the freezing point of the Al-Si alloy. As a result, the steel sheet has poor plating properties, leading to non-plating problems in many places. A large deviation also suggests that there is significant unevenness in the thickness of the obtained FeAlSi inhibition layer and the plating thickness. In Comparative Example 5, since the temperature of the plating solution is too low, the fluidity and uniformity of the plating solution are poor. This also leads to poor plating quality, unevenness in the plating thickness (large deviation), and locally existing non-plating phenomena.

[0061] Considering the above and the data shown in Tables 2 and 3, it can be seen that the Si content in the plating solution, the temperature of the steel sheet before entering the pot, the temperature of the plating solution, and the hot-dip plating time all significantly affect the thickness uniformity of the plating, non-plating, and the formation of kirkendall voids. Any conditions exceeding the predetermined range will result in uneven plating thickness, non-plating, or the formation and growth of more kirkendall voids, weakening the performance of the product. Due to the synergistic effect of the range of the Si content in the plating solution selected in the present invention, the range of the temperature of the steel sheet before entering the pot, the range of the temperature of the plating solution, and the range of the hot-dip plating time, not only is the non-plating situation eliminated, but also the number of large-sized kirkendall voids decreases, improving the yield of the plated steel sheet.

[0062] Therefore, the resistance spot welding performance of the subsequently formed hot stamp parts is also affected by the synergistic effect of the Si content in the plating solution, the temperature of the steel sheet before entering the pot, the temperature of the plating solution, and the hot-dip plating time. The following is an explanation of the effect of the plating process on the resistance spot welding performance of hot stamp parts, using only Embodiment 5 and Comparative Example 4 as an example. In Embodiment 5 and Comparative Example 4, a pseudo hot stamp was performed on the thin plate with a thin plating. The heating process was carried out in a laboratory tube furnace. The heating temperature was 930 °C and it was held for 240 seconds as it was. Next, the heated sample plate was taken out and put into a hot stamp simulation device, and cooled to 100 °C or less within 8 to 10 seconds. The plating morphology of the obtained hot stamp sample plate was observed, and the results are shown in FIG. 4.

[0063] As can be seen from FIG. 4, under the same hot stamping conditions, the final plating thickness in Embodiment 5 was about 20 μm, and the thickness of the interdiffusion layer was about 8.55 μm. However, the final plating thickness in Comparative Example 4 was about 16.42 μm, and the thickness of the interdiffusion layer was about 9.83 μm. Also, the Kirkendall voids in Comparative Example 4 were substantially linearly distributed. This corresponds to the data in Table 3. In Embodiment 5 and Comparative Example 4, the number of initial Kirkendall voids with diameters ranging from 0.5 μm to 2.5 μm was 5 per 35 μm and 29 per 35 μm, respectively. The maximum diameter in Embodiment 5 was 0.65 μm, and the maximum diameter of the initial voids in Comparative Example 4 was 1.71 μm. Since Comparative Example 4 originally had more Kirkendall voids of a larger size, the voids in Comparative Example 4 became clearly more severe after undergoing the same hot stamping process.

[0064] A resistance spot welding experiment was conducted on the remembered hot stamp panel. The welding method and evaluation criteria refer to the AWS D8.9M:2012 standard. Single pulse welding was selected. The welding parameters are as follows. The diameter of the electrode cap end face is 7 mm, the electrode pressure is 5.5 kN, the electrode pre-pressure time is 400 ms, the energization time is 360 ms, and the holding time after energization is 200 ms. Figure 5 shows the spot welding evaluation results of two plated steel sheets after hot stamping. As can be seen from Figure 5, the weldable current range for spot welding the hot stamp sample plate in Embodiment 5 is 1.2 kA, and the minimum welding current at which spatter occurred was 7.8 kA. On the other hand, the weldable current range for spot welding the hot stamp sample plate in Comparative Example 4 is 0.8 kA, and the minimum welding current at which spatter occurred was 7.4 kA. Obviously, the weldable current range of the hot stamp sample plate in Comparative Example 4 is narrower, and the current at which spatter occurs is smaller. From the experimental results, it can be seen that the large amount of kirkendall voids in Comparative Example 4 increases the contact resistance of the plating, and even when the welding current is small during spot welding, spatter is likely to occur, resulting in a decrease in the weldable current range of the steel sheet. On the other hand, the plated steel sheet (Embodiment 5) with fewer and smaller kirkendall voids obtained according to the present invention improves the resistance spot welding performance of the hot stamp parts.

[0065] In summary, the plating thickness of the aluminum alloy plating on the plated steel sheet of the present invention is from 5 μm to 14 μm, the thickness of the FeAlSi suppression layer is from 1.5 μm to 6 μm, which is 60% or less of the plating thickness. Within 2 μm from the interface between the FeAlSi suppression layer and the base steel into the interior of the base steel, the diameter of the kirkendahl voids is 2.5 μm or less, and the number of kirkendahl voids with a diameter of 0.5 μm or more and 2.5 μm or less does not exceed 15 per 35 μm. The aluminum alloy plated steel sheet having the above plating characteristics can be a hot stamping part having excellent resistance spot welding performance. By the plating method for producing the plated steel sheet described in the present invention, the uniformity of the plating thickness is ensured, the occurrence of non-plating on the surface is avoided, and at the same time, the formation of large-sized kirkendahl voids is suppressed, ensuring good resistance spot welding performance of the hot stamping part.

[0066] The above embodiments and experimental data are intended to illustrate the present invention by way of example. It will be apparent to those skilled in the art that the present invention is not limited to these embodiments, and various modifications can be made without departing from the scope of protection of the present invention.

[0067] 〔Other Embodiments〕 (A1) Another embodiment of the present invention is a plated steel sheet having an aluminum alloy plating for hot stamping, comprising a base steel sheet and the aluminum alloy plating applied to at least one side of the base steel sheet, wherein the base steel sheet contains, by weight, the following components: 0.05% to 0.45% of C, 0.5% to 10% of Mn, 0% to 0.01% of B, 0% to 0.4% of Nb + Ti + V, 0.01% to 2% of Si, 0.01% to 2% of Al, 0.01% to 5% of Cr + Ni + Mo + Cu, where 0% to 2% of Cr, 0% to 2% of Ni, 0% to 2% of Mo, and 0% to 2% of Cu, and the balance consisting of Fe and inevitable impurity elements, the plating thickness of the aluminum alloy plating is from 5 μm to 14 μm, The aluminum alloy plating includes an FeAlSi suppression layer adjacent to the base steel and an Al alloy layer outside the FeAlSi suppression layer. The thickness of the FeAlSi suppression layer is 60% or less of the plating thickness, and the thickness of the FeAlSi suppression layer is from 1.5 μm to 6 μm. Within 2 μm from the interface between the FeAlSi suppression layer and the base steel into the base steel, the diameter of the Kirkendall voids is 2.5 μm or less, and the number of Kirkendall voids having a diameter of 0.5 μm or more and 2.5 μm or less does not exceed 15 per 35 μm. It can be a plated steel sheet.

[0068] (A2) In the embodiment of the present invention according to (A1), the base steel sheet contains, by weight, the following components, namely, 0.09% to 0.39% of C, 0.6% to 3.5% of Mn, 0% to 0.004% of B, 0% to 0.4% of Nb + Ti + V, 0.01% to 2% of Si, 0.01% to 2% of Al, 0.01% to 5% of Cr + Mo + Ni + Cu, where 0% to 2% of Cr, 0% to 2% of Ni, 0% to 2% of Mo, and 0% to 2% of Cu, and the balance consisting of Fe and inevitable impurity elements.

[0069] (A3) In the embodiment of the present invention according to (A1), the base steel sheet contains, by weight, the following components, namely, 0.18% to 0.39% of C, 0.6% to 3.5% of Mn, 0% to 0.004% of B, 0.05% to 0.25% of Nb + Ti + V, 0.01% to 2% of Si, 0.01% to 2% of Al, 0.01% to 5% of Cr + Mo + Ni + Cu, where 0% to 2% of Cr, 0% to 2% of Ni, 0% to 2% of Mo, and 0% to 2% of Cu, and the balance consisting of Fe and inevitable impurity elements.

[0070] (A4) In the embodiment of the present invention described in (A1), the plating thickness of the aluminum alloy plating is from 6 μm to 13 μm, the thickness of the FeAlSi suppression layer is 50% or less of the plating thickness, and the thickness of the FeAlSi suppression layer can be from 1.5 μm to 5 μm.

[0071] (A5) In the embodiment of the present invention described in (A1), the plating thickness of the aluminum alloy plating is from 7 μm to 12 μm, the thickness of the FeAlSi suppression layer is 40% or less of the plating thickness, and the thickness of the FeAlSi suppression layer can be from 2.45 μm to 3.95 μm.

[0072] (A6) In the embodiment of the present invention described in any one of (A1) to (A5), within 2 μm from the interface between the FeAlSi suppression layer and the base steel into the base steel, the number of kirkendall voids having a diameter of 0.5 μm or more and 2.5 μm or less does not exceed 13 per 35 μm.

[0073] (A7) In the embodiment of the present invention described in any one of (A1) to (A5), within 2 μm from the interface between the FeAlSi suppression layer and the base steel into the base steel, the number of kirkendall voids having a diameter of 0.5 μm or more and 2.5 μm or less does not exceed 10 per 35 μm.

[0074] (A8) In the embodiment of the present invention described in any one of (A1) to (A5), within 2 μm from the interface between the FeAlSi suppression layer and the base steel into the base steel, the diameter of the kirkendall voids is 2.0 μm or less, and the number of kirkendall voids having a diameter of 0.5 μm or more and 2.0 μm or less does not exceed 10 per 35 μm.

[0075] (A9) In the embodiment of the present invention described in any one of (A1) to (A5), the thickness of the base steel plate can be from 0.5 mm to 3.0 mm.

[0076] (B1) Another embodiment of the present invention is a plating method for applying a thin aluminum alloy plating to at least one side of a base steel plate for hot stamping, comprising a) a step of pretreating the base steel plate before plating; b) after heating the pretreated base steel plate, cooling the base steel plate to a predetermined temperature within the range of 610°C to 650°C; c) a step of dip-melting plating by immersing the base steel plate cooled to the predetermined temperature in step b) in a heated plating solution for 2 to 7 seconds, wherein the composition of the plating solution comprises, by weight, 9% to 12% Si and the balance consisting of Al or an Al alloy and inevitable impurities, and in the process of this step, the temperature of the plating solution is higher than the predetermined temperature and is maintained at 630°C to 670°C; d) after the base steel plate is taken out of the plating solution, removing excess plating solution on at least one side of the base steel plate by air knife purge before the plating solution on at least one side of the base steel plate solidifies, to control the plating thickness on at least one side; e) a step of cooling the base steel plate to room temperature to obtain a plated steel plate having a thin aluminum alloy plating, wherein the base steel plate may comprise, by weight, the following components: 0.05% to 0.45% C, 0.5% to 10% Mn, 0% to 0.01% B, 0% to 0.4% Nb+Ti+V, 0.01% to 2% Si, 0.01% to 2% Al, 0.01% to 5% Cr+Ni+Mo+Cu, wherein Cr is 0% to 2%, Ni is 0% to 2%, Mo is 0% to 2%, and Cu is 0% to 2%, and the balance consisting of Fe and inevitable impurity elements.

[0077] (B2) In the embodiment of the present invention described in (B1), it is possible that the predetermined temperature is in the range of 620°C to 639°C, and the temperature of the plating solution is 5°C to 20°C higher than the predetermined temperature.

[0078] (B3) In the embodiment of the present invention described in (B2), it is possible that the predetermined temperature is in the range of 625°C to 635°C, and the temperature of the plating solution is 7°C to 15°C higher than the predetermined temperature.

[0079] (B4) In the embodiment of the present invention described in any one of (B1) to (B3), the Si content in the aluminum solution for melt plating can be 9.2% to 11.2% by weight.

Claims

1. A plated steel sheet having an aluminum alloy plating for hot stamping, comprising a base steel sheet and the aluminum alloy plating applied to at least one surface of the base steel sheet, the aluminum alloy plating includes an FeAlSi inhibition layer adjacent to the base steel sheet, and an Al alloy layer outside the FeAlSi inhibition layer, the thickness of the FeAlSi inhibition layer is 60% or less of the total plating thickness of the aluminum alloy plating, and the thickness of the FeAlSi inhibition layer is 1.5 μm to 6 μm; A plated steel sheet, wherein within 2 μm from an interface between the FeAlSi inhibiting layer and the base steel sheet into the base steel sheet, Kirkendall voids have a diameter of 2.5 μm or less, and the number of Kirkendall voids having a diameter of 0.5 μm or more and 2.5 μm or less does not exceed 15 per 35 μm.

2. 2. The plated steel sheet according to claim 1, wherein the base steel sheet comprises the following components by weight: 0.09 to 0.39% C, 0.6 to 3.5% Mn, 0 to 0.004% B, 0 to 0.4% Nb+Ti+V, 0.01 to 2% Si, 0.01 to 2% Al, and 0.01 to 5% Cr+Mo+Ni+Cu, where 0 to 2% Cr, 0 to 2% Ni, 0 to 2% Mo, and 0 to 2% Cu, with the balance consisting of Fe and unavoidable impurity elements.

3. 2. The plated steel sheet according to claim 1, wherein the base steel sheet comprises the following components by weight: 0.18 to 0.39% C, 0.6 to 3.5% Mn, 0 to 0.004% B, 0.05 to 0.25% Nb+Ti+V, 0.01 to 2% Si, 0.01 to 2% Al, and 0.01 to 5% Cr+Mo+Ni+Cu, where 0 to 2% Cr, 0 to 2% Ni, 0 to 2% Mo, and 0 to 2% Cu, with the balance consisting of Fe and unavoidable impurity elements.

4. 2. The plated steel sheet according to claim 1, wherein the base steel sheet comprises the following components by weight: 0.05 to 0.45% C, 0.5 to 10% Mn, 0 to 0.01% B, 0 to 0.4% Nb+Ti+V, 0.01 to 2% Si, 0.01 to 2% Al, and 0.01 to 5% Cr+Ni+Mo+Cu, where 0 to 2% Cr, 0 to 2% Ni, 0 to 2% Mo, and 0 to 2% Cu, with the balance consisting of Fe and unavoidable impurity elements.

5. 2. The plated steel sheet according to claim 1, wherein a total plating thickness of the aluminum alloy plating is from 6 μm to 13 μm, and a thickness of the FeAlSi inhibiting layer is 50% or less of the total plating thickness.

6. 2. The plated steel sheet according to claim 1, wherein a total plating thickness of the aluminum alloy plating is from 7 μm to 12 μm, and a thickness of the FeAlSi inhibiting layer is 40% or less of the total plating thickness.

7. The plated steel sheet according to any one of claims 1 to 6, wherein within 2 µm from the interface between the FeAlSi inhibit layer and the base steel sheet to the inside of the base steel sheet, the number of Kirkendall voids having a diameter of 0.5 µm or more and 2.5 µm or less does not exceed 13 per 35 µm.

8. The plated steel sheet according to any one of claims 1 to 6, wherein within 2 µm from the interface between the FeAlSi inhibit layer and the base steel sheet into the interior of the base steel sheet, the number of Kirkendall voids having a diameter of 0.5 µm or more and 2.5 µm or less does not exceed 10 per 35 µm.

9. 7. The plated steel sheet according to claim 1, wherein within 2 μm from the interface between the FeAlSi inhibit layer and the base steel sheet into the interior of the base steel sheet, the Kirkendall voids have a diameter of 2.0 μm or less, and the number of Kirkendall voids having a diameter of 0.5 μm or more and 2.0 μm or less does not exceed 10 per 35 μm.

10. The plated steel sheet according to any one of claims 1 to 6, wherein the base steel sheet has a thickness of 0.5 mm to 3.0 mm.

11. The plated steel sheet according to any one of claims 1 to 4, wherein the aluminum alloy plating has a total plating thickness of 5 µm to 14 µm.

12. The plated steel sheet according to any one of claims 1 to 5, wherein the FeAlSi inhibiting layer has a thickness of 1.5 µm to 5 µm.

13. The plated steel sheet according to any one of claims 1 to 6, wherein the FeAlSi inhibiting layer has a thickness of 2.45 µm to 3.95 µm.

Images