The present invention relates to an aluminum-iron-coated steel sheet for hot pressing excellent in corrosion resistance and weldability and a method for manufacturing the same.
background
[2]
Recently, due to the depletion of petroleum energy resources and high interest in the environment, regulations on improving fuel efficiency of automobiles are getting stronger day by day. In terms of material, reducing the thickness of the steel sheet used as a method for improving the fuel efficiency of a vehicle may be mentioned. should be
[3]
For this reason, the demand for high-strength steel sheets has been continuously generated, and various types of steel sheets have been developed. However, since these steel sheets have high strength by themselves, there is a problem in that the workability is poor. That is, since the product of the strength and the elongation for each grade of the steel sheet always tends to have a constant value, when the strength of the steel sheet increases, there is a problem that the elongation, which is an index of workability, decreases.
[4]
In order to solve this problem, a hot press forming method has been proposed. The hot press forming method is a method of increasing the strength of the final product by forming a low-temperature structure such as martensite in the steel sheet by processing the steel sheet at a high temperature suitable for processing and then rapidly cooling it to a low temperature. In this case, there is an advantage that the problem of workability can be minimized when manufacturing a member having high strength.
[5]
However, in the case of the hot press forming method, since the steel sheet must be heated to a high temperature, the surface of the steel sheet is oxidized. Patent Document 1 has been proposed as a method for solving this problem. In the present invention, the aluminum-plated steel sheet is used for hot press forming or room temperature forming, followed by heating and rapid cooling (simply 'post heat treatment'). Since the aluminum plating layer is present on the surface of the steel sheet, the steel sheet is not oxidized when heated.
[6]
In order to hot press-form the above-described aluminum plated steel sheet, a step of heating the steel sheet is performed. In this step, the temperature of the steel sheet rises, and as a result, the diffusion of Fe from the base iron of the steel sheet to the plating layer on the surface occurs, and alloying occurs in the plating layer.
[7]
When such an aluminum-plated steel sheet is hot press-formed, a problem occurs in that a crack is generated in the plating layer at a portion in close contact with the mold during pressing. In addition, a strong tensile stress is applied to the outermost surface of the plating layer in the portion where the bending occurs by the press. However, when the thickness of the aluminum plating layer is thin and the crack penetrates the plating layer and the surface of the base steel sheet is exposed, the corrosion resistance of the finally obtained hot press-formed member may be reduced.
[8]
(Patent Document 1) US Patent Publication No. 6,296,805
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[9]
According to one aspect of the present invention, it is possible to provide an aluminum-iron-based plated steel sheet for hot press forming excellent in corrosion resistance and weldability and a method for manufacturing the same.
[10]
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
[11]
An aluminum-iron-based plated steel sheet according to an aspect of the present invention includes a base steel sheet; and a plating layer formed on the surface of the steel sheet, wherein the plating layer is formed on the surface of the steel sheet and includes an alloying layer comprising at least one of Fe 3Al, FeAl(Si), Fe 2Al 5 and FeAl 3 ; and an aluminum layer formed on the alloying layer and having a thickness of less than 10% of the thickness of the plating layer; Including, the thickness of the plating layer is 20 ~ 35㎛, Mg measured by GDS at a depth of 0.1㎛ from the surface of the plating layer is 1 ~ 20% by weight, measured by GDS at a depth of 0.1㎛ from the surface of the plating layer Oxygen is 10% by weight or less.
[12]
According to one aspect of the present invention, the plating layer is, by weight, when the alloy composition excluding the Fe content diffused from the steel sheet is 100%, Si: 7 to 15%, Mg: 1.1 to 15%, the remainder Al and others It may contain unavoidable impurities.
[13]
According to an aspect of the present invention, the base steel sheet is C: 0.04 to 0.5%, Si: 0.01 to 2%, Mn: 0.01 to 10%, Al: 0.001 to 1.0%, P: 0.05% or less, S by weight% : 0.02% or less, N: 0.02% or less, the remainder may contain Fe and other unavoidable impurities.
[14]
According to one aspect of the present invention, the base steel sheet is the sum of one or more selected from the group consisting of Cr, Mo and W by weight: 0.01 to 4.0%, one or more from the group consisting of Ti, Nb, Zr and V Sum: 0.001 to 0.4%, Cu+Ni: 0.005 to 2.0%, Sb+Sn: 0.001 to 1.0%, and B: may further include one or more of 0.0001 to 0.01%.
[15]
According to another aspect of the present invention, the present invention provides a hot press-formed member obtained by hot press forming the above-described aluminum-iron-based plated steel sheet.
[16]
According to another aspect of the present invention, a method for manufacturing an aluminum-iron-based plated steel sheet used for hot press forming includes preparing a base steel sheet; The base steel sheet is immersed in an aluminum plating bath containing Si: 7 to 15%, Mg: 1.1 to 15%, and the remainder Al and other unavoidable impurities in weight % and plated at a plating amount of 40 to 100 g/m2 based on one side of aluminum obtaining a plated steel sheet; performing initial cooling at a cooling rate of 0.1 to 5° C./sec to a temperature of 640° C. or higher immediately after aluminum plating; and obtaining an aluminum-iron-based plated steel sheet through on-line alloying in which heat treatment is performed by continuously maintaining for 1 to 20 seconds in a heating temperature range of 670 to 900° C. after the initial cooling; includes
[17]
According to an aspect of the present invention, after the initial cooling, the method may further include spraying aluminum powder on the surface of the aluminum-plated steel sheet.
[18]
According to one aspect of the present invention, the average particle diameter of the aluminum powder may be 5 to 40㎛.
Effects of the Invention
[19]
As described above, in the present invention, in the aluminum-iron-based plated steel sheet before hot press forming, by forming a plating layer on the base steel sheet in advance before heating for hot press forming and appropriately controlling the thickness and layer composition of the plating layer, hot press forming There is an effect that can improve the corrosion resistance and weldability of the member.
[20]
In addition, by appropriately adjusting the content of Si and Mg in the composition of the plating bath to enable on-line alloying heat treatment in which heat treatment is performed immediately after forming the plating layer, the manufacturing cost is reduced and the productivity is improved aluminum-iron plating There is an effect that can provide a method for manufacturing a steel sheet.
Brief description of the drawing
[21]
1 schematically shows a manufacturing apparatus in which a manufacturing method according to an aspect of the present invention is implemented.
[22]
2 is a photograph of a cross-section of the aluminum-iron-based plated steel sheet prepared in Inventive Example 1 observed with a scanning electron microscope (SEM).
[23]
3 is a photograph of a cross-section of the aluminum-iron-based plated steel sheet prepared in Comparative Example 1 observed with a scanning electron microscope (SEM).
[24]
4 is a photograph of a cross-section of the aluminum-iron-based plated steel sheet manufactured according to Invention Example 1 after hot press forming, observed with a scanning electron microscope (SEM).
[25]
FIG. 5 is a photograph of an aluminum-iron-based plated steel sheet prepared in Comparative Example 1 observed with a scanning electron microscope (SEM) of a plating cross-section after hot press forming.
Best mode for carrying out the invention
[26]
Hereinafter, an aluminum-iron-based plated steel sheet according to an aspect of the present invention will be described in detail.
[27]
In the present invention, when expressing the content of each element, it should be noted that, unless otherwise specified, it means weight %. In addition, the ratio of crystals or tissues is based on the area unless otherwise indicated.
[28]
[Aluminum-iron-coated steel sheet]
[29]
Aluminum-iron-based plated steel sheet according to an embodiment of the present invention includes a base steel sheet, and a plating layer formed on the surface of the base steel sheet, the plating layer is formed on the base steel sheet and Fe 3Al, FeAl(Si), Fe 2Al 5 and an alloying layer comprising at least one of FeAl 3 , and an aluminum layer formed on the alloying layer and having a thickness of less than 10% of the thickness of the plating layer, wherein the thickness of the plating layer is 20 to 35 μm, and in the thickness direction Mg measured by GDS at a depth of 0.1 μm from the surface of the plating layer is 1 to 20 wt%, and oxygen measured by GDS at a depth of 0.1 μm from the surface of the plating layer in the thickness direction is 10 wt% or less.
[30]
First, an aluminum-iron-based plated steel sheet according to an embodiment of the present invention includes a base steel sheet, and a plating layer formed on the surface of the base steel sheet. In addition, the plating layer is formed on the surface of the base steel sheet, and Fe 3Al, FeAl(Si), Fe 2Al 5 and FeAl 3 It includes an alloying layer made of at least one, and an aluminum layer formed on the alloying layer.
[31]
When the alloying heat treatment is performed after aluminum plating on the base steel sheet, Fe of the base steel sheet is diffused into the aluminum plating layer having a high Al content. As a result, an alloying layer made of an intermetallic compound of Al and Fe formed as a result of diffusion may be formed on the base steel sheet. Although not limited thereto, the alloy phase of the Al-Fe-based intermetallic compound constituting the alloying layer may include Fe 3Al, FeAl(Si), Fe 2Al 5, FeAl 3 and the like.
[32]
That is, the alloying layer may include at least one of Fe 3Al, FeAl(Si), Fe 2Al 5 and FeAl 3 . In addition, according to one aspect of the present invention, the alloying layer may preferably mainly include one or more of Fe 3Al, FeAl(Si), Fe 2Al 5 and FeAl 3 .
[33]
Specifically, the alloying layer is Fe At least one of 3Al, FeAl(Si), Fe 2Al 5 and FeAl 3 may be included in 50% or more, preferably in 80% or more, more preferably in 90% or more, most preferably It may contain 95% or more.
[34]
That is, according to one aspect of the present invention, the alloying layer mainly includes one or more alloy phases of Fe 3Al, FeAl(Si), Fe 2Al 5 and FeAl 3 , but there is room for inevitably included impurities and plating bath. Other elements present may also contain small amounts.
[35]
For example, in the present invention, when Mg is added, Mg may be partially included in the Al-Fe-based alloy phase in the alloying layer, and the alloying layer also includes other alloy phases including the Al-Fe-Mg-based alloy phase. may include
[36]
On the above-mentioned alloying layer, the aluminum layer may be the same as the original plating layer component or containing Fe diffused in a small amount from the base steel sheet, and in some cases, the aluminum layer may not exist due to complete alloying.
[37]
The thickness of the plating layer may be 20 ~ 35㎛. When the thickness of the plating layer is less than 20 μm, corrosion resistance is too poor, whereas when the thickness of the plating layer exceeds 35 μm, there is a problem in that weldability is deteriorated. Therefore, in the present invention, it is preferable to limit the thickness of the plating layer to a thickness of 20 to 35 μm. More preferably, it may be 20-30 μm thick.
[38]
Meanwhile, Mg measured by a glow discharge spectrometer (GDS) at a depth of 0.1 μm from the surface of the plating layer may be 1 to 20 wt%. Mg is added in an amount of 1.1 to 15 wt % in the aluminum plating bath according to the manufacturing method of the present invention for the purpose of improving corrosion resistance and alloying speed, but Mg in the plating layer tends to diffuse toward the surface and concentrate, so the plating layer in the thickness direction The Mg content measured by GDS at a point 0.1 μm from the surface of may be 1 to 20 wt%. Preferably, it may be 2 to 15%, more preferably 3 to 10%.
[39]
In addition, oxygen measured by GDS (Glow Discharge Spectrometer) at a depth of 0.1 μm from the surface of the plating layer may be 10 wt% or less. In the present invention, when the aluminum plating layer is alloyed, it is possible to effectively suppress an increase in the oxygen content on the surface of the plating layer because the alloying heat treatment is performed in a short time by increasing the temperature without cooling after the hot-dip aluminum plating. When the oxygen content on the surface of the plated layer exceeds 10% by weight, the surface quality of the plated steel sheet may be inferior. On the other hand, since it is advantageous as the oxygen content on the surface of the plating layer is small, the lower limit thereof may not be separately limited.
[40]
An aluminum layer mainly made of aluminum may be formed on the surface side of the plating layer and on the alloying layer. In the present invention, the thickness of the aluminum layer may be controlled to be less than 10% of the thickness of the plating layer, and in some cases, sufficient alloying may be made so that the aluminum layer does not exist (that is, it includes 0% of the thickness of the plating layer) . Since the interface between the aluminum layer and the alloying layer in the plated steel sheet is unstable, if the thickness of the aluminum layer is 10% or more of the thickness of the plating layer, peeling of the aluminum layer may occur when winding after alloying heat treatment.
[41]
Since the thickness of the aluminum layer is preferably smaller, the lower limit of the thickness may not be specifically limited. Meanwhile, preferably, the thickness of the aluminum layer may be less than 5%, more preferably less than 1%, and most preferably 0%.
[42]
According to an embodiment of the present invention, the plating layer is in weight%, when the remaining alloy composition except for the Fe content diffused from the base steel sheet is 100%, Si: 7-15%, Mg: 1.1-15%, the balance Al and other unavoidable impurities.
[43]
The Si serves to uniformly alloy with Fe in the plating layer, and in order to obtain such an effect, it should be contained in at least 7% or more. On the other hand, since Si also serves to suppress the diffusion of Fe, when contained in an amount exceeding 15%, Fe diffusion is excessively suppressed, so that it may not be possible to obtain a desired plating structure in the present invention. The Si content may be preferably 7 to 14%, more preferably 7.5 to 13.1%.
[44]
The Mg serves to improve the corrosion resistance of the plated steel sheet, and also has the effect of increasing the alloying rate. In order to obtain the above effect, it should be contained at least 1.1% or more, on the other hand, if it is contained in excess of 15%, there may be a problem in that weldability and paintability are inferior. Preferably, it may be 1.1 to 11%, and more preferably, it may be 1.5 to 10.5%.
[45]
According to an embodiment of the present invention, the base steel sheet is a steel sheet for hot press forming, and may not be particularly limited as long as it is used for hot press forming. However, if one non-limiting example is given, the base steel sheet in weight %, C: 0.04 to 0.5%, Si: 0.01 to 2%, Mn: 0.01 to 10%, Al: 0.001 to 1.0%, P: 0.05% or less, It may have a composition including S: 0.02% or less and N: 0.02% or less.
[46]
C: 0.04 to 0.5%
[47]
The C may be added in an appropriate amount as an essential element in order to increase the strength of the heat treatment member. That is, in order to sufficiently secure the strength of the heat treatment member, 0.04% or more of C may be added. Preferably, the lower limit of the C content may be 0.1% or more. However, if the content is too high, in the case of producing a cold rolled material, the strength of the hot rolled material is too high when the hot rolled material is cold rolled, so not only the cold rolling property is greatly inferior but also the spot weldability is greatly reduced. In order to secure weldability, 0.5% or less may be added. In addition, the C content may be 0.45% or less, and more preferably, the C content may be limited to 0.4% or less.
[48]
Si: 0.01~2%
[49]
The Si not only has to be added as a deoxidizer in steelmaking, but also serves to suppress the formation of carbides, which have the greatest influence on the strength of the hot press-formed member. In the present invention, it may be added in an amount of 0.01% or more in order to secure retained austenite by concentrating carbon at the martensite lath grain boundary after martensite is formed in hot press forming. In addition, the upper limit of the Si content may be set to 2% in order to secure sufficient plating property when aluminum plating is performed on the steel sheet after rolling. Preferably, the Si content may be limited to 1.5% or less.
[50]
Mn: 0.01~10%
[51]
The Mn may be added in an amount of 0.01% or more in order to not only secure a solid solution strengthening effect, but also to lower a critical cooling rate for securing martensite in a hot press-formed member. In addition, the Mn content may be limited to 10% or less in terms of securing the workability of the hot press forming process by properly maintaining the strength of the steel sheet, reducing the manufacturing cost, and improving the spot weldability. Preferably, the Mn content may be 9% or less, and in some cases, 8% or less.
[52]
Al: 0.001~1.0%
[53]
The Al may increase the cleanliness of the steel by deoxidizing it together with Si, and may be added in an amount of 0.001% or more to obtain the above effect. In addition, the Al content may be limited to 1.0% or less in order to prevent the Ac3 temperature from becoming too high so that heating required for hot press molding can be performed in an appropriate temperature range.
[54]
P: 0.05% or less
[55]
The P is present as an impurity in the steel, and it is advantageous as the content thereof is as small as possible. Therefore, in the present invention, the P content may be limited to 0.05% or less, preferably limited to 0.03% or less. Since P is an impurity element which is advantageous as it is small, it is not necessary to specifically set an upper limit of its content. However, in order to excessively lower the P content, there is a concern that the manufacturing cost may increase, and in this case, the lower limit may be set to 0.001%.
[56]
S: 0.02% or less
[57]
S is an impurity in steel, and since it is an element that impairs ductility, impact properties, and weldability of members, the maximum content is limited to 0.02%, preferably 0.01% or less. In addition, if the minimum content is less than 0.0001%, the manufacturing cost may increase, so the lower limit of the content may be 0.0001%.
[58]
N: 0.02% or less
[59]
The N is an element included as an impurity in steel, and in order to reduce the sensitivity to cracking during continuous casting of the slab, and to secure impact properties, the lower the content, the more advantageous, and thus may be included in 0.02% or less. There is no need to set a lower limit in particular, but considering an increase in manufacturing cost, the N content may be set to 0.001% or more.
[60]
In the present invention, optionally, in addition to the above-described steel composition, the sum of at least one selected from the group consisting of Cr, Mo and W: 0.01 to 4.0%, the sum of at least one from the group consisting of Ti, Nb, Zr and V. One or more of: 0.001 to 0.4%, Cu + Ni: 0.005 to 2.0%, Sb + Sn: 0.001 to 1.0%, and B: 0.0001 to 0.01% may be additionally added.
[61]
The sum of at least one selected from the group consisting of Cr, Mo and W: 0.01 to 4.0%
[62]
The Cr, Mo, and W may be added by 0.01% or more based on the total content of Cr, Mo, and W because it is possible to improve hardenability and secure strength and grain refinement through the precipitation strengthening effect. In addition, in order to secure the weldability of the member, the content may be limited to 4.0% or less. In addition, if the content of these elements exceeds 4.0%, the effect may be saturated, so the content may be limited to 4.0% or less.
[63]
group consisting of Ti, Nb, Zr and V The sum of one or more selected from among: 0.001~0.4%
[64]
The Ti, Nb and V are effective in improving the steel sheet of the heat treatment member by forming fine precipitates and stabilizing the retained austenite and improving the impact toughness by crystal grain refinement. have. However, if the added amount exceeds 0.4%, the effect is not only saturated, but also may cause cost increase due to excessive addition of ferroalloy.
[65]
Cu + Ni: 0.005~2.0%
[66]
The Cu and Ni are elements that improve strength by forming fine precipitates. In order to obtain the above-described effect, the sum of one or more of these components may be 0.005% or more. However, if the value exceeds 2.0%, the upper limit may be set to 2.0% because excessive cost increases.
[67]
Sb + Sn: 0.001~1.0%
[68]
The Sb and Sn are concentrated on the surface during annealing heat treatment for Al-Si plating to suppress the formation of Si or Mn oxide on the surface, thereby improving plating properties. In order to obtain such an effect, 0.001% or more may be added. However, if the amount exceeds 1.0%, the upper limit is set to 1.0% because not only excessive cost of ferroalloy is required, but also it is dissolved in the slab grain boundary and may cause coil edge cracks during hot rolling.
[69]
B: 0.0001~0.01%
[70]
B is an element that can improve hardenability even with a small amount of addition, and can suppress the brittleness of the hot press-formed member due to segregation at the grain boundary of P and/or S by segregation at the grain boundary of prior austenite. Therefore, B may be added in an amount of 0.0001% or more. However, if it exceeds 0.01%, the effect is not only saturated, but also causes brittleness in hot rolling, so the upper limit may be 0.01%, and in one embodiment, the B content may be 0.005% or less.
[71]
The remainder other than the above-mentioned components may include iron (Fe) and unavoidable impurities, and additional addition is not particularly limited as long as the components may be included in the steel sheet for hot press forming.
[72]
When an aluminum-iron-coated steel sheet having a plating layer having the above-described layer structure is heat-treated in a temperature range of 880 to 950° C. for 3 to 10 minutes and then hot press-formed to manufacture a hot press-formed member, the diffusion layer (FeAlSi and Fe 3Al) ), an alloying layer made of Fe 2Al 5 and FeAlSi is formed to improve corrosion resistance. In addition, the spot welding current range satisfies 1 kA or more, so that the spot weldability can be improved.
[73]
Next, a method of manufacturing an aluminum-iron-based plated steel sheet for hot press forming according to another aspect of the present invention will be described in detail. However, the following manufacturing method of the aluminum-iron-based plated steel sheet for hot press forming is only an example, and the aluminum-iron-based plated steel sheet for hot press forming of the present invention does not necessarily have to be manufactured by this manufacturing method, and any manufacturing method Even if it is a method that satisfies the claims of the present invention, it should be noted that there is no problem in using it to implement each embodiment of the present invention.
[74]
[Manufacturing method of aluminum-iron-coated steel sheet]
[75]
The aluminum-iron-based plated steel sheet according to another aspect of the present invention contains Si: 7 to 15%, Mg: 1.1 to 15%, the remainder Al and other unavoidable impurities in weight% on the surface of the hot-rolled or cold-rolled base steel sheet. It can be obtained by performing hot-dip aluminum plating at a plating amount of 40 to 100 g/m2 on a single-sided basis using an aluminum plating bath of
[76]
Steps to obtain aluminized steel sheet
[77]
In one embodiment of the present invention, a steel sheet is prepared, and the steel sheet is immersed in an aluminum plating bath containing Si: 7 to 15%, Mg: 1.1 to 15%, the remainder Al and other unavoidable impurities as weight%. An aluminum-coated steel sheet can be obtained by plating the surface of the steel sheet with aluminum at a coating amount of 40 to 100 g/m 2 per side. In addition, optionally, an annealing treatment may be performed on the steel sheet before plating.
[78]
The Si is an element that serves to uniformly alloy with Fe in the plating layer, and may be included in at least 7% or more in order to obtain the above effect. However, since Si serves to suppress the diffusion of Fe, when it is contained in excess of 15%, the alloying rate is lowered, so that it is difficult to obtain sufficient alloying. Therefore, in the present invention, the Si content included in the plating bath may be limited to 7 to 15%. Preferably, it may be 7 to 14%, and more preferably, it may be 7.5 to 13.1%.
[79]
On the other hand, the Mg serves to improve the corrosion resistance of the aluminum-iron-based plated steel sheet, and also serves to increase the alloying rate. In order to secure a sufficient alloying rate, it should be contained in at least 1.1% or more. On the other hand, when the Mg content exceeds 15%, there may be a problem in that weldability and paintability are inferior. Therefore, in the present invention, the Mg content included in the aluminum plating bath may be limited to 1.1 to 11%. Preferably it may be 1.5 to 10.5%, more preferably 2 to 7%.
[80]
In the case of the aluminum plating, the plating amount may be 40 to 100 g/m 2 based on one side. If the plating amount is less than 40g/m2, corrosion resistance is too poor, whereas if the plating amount exceeds 100g/m2, a problem occurs in that weldability is deteriorated. Therefore, in the present invention, it is preferable to limit the plating amount to 40 to 100 g/m 2 on a single side during aluminum plating. On the other hand, more preferably, the plating amount at the time of the aluminum plating may be 55 ~ 100 g / m 2 based on one side.
[81]
initial cooling stage
[82]
After the aluminum plating, the initial cooling may be performed at a cooling rate of 0.1 to 5° C./sec to 640° C. or higher. In addition, preferably, the initial cooling may be performed in a temperature range of 640° C. or higher and 680° C. or lower after aluminum plating, and the cooling rate may be 1 to 4° C./sec.
[83]
In the present invention, initial cooling after aluminum plating is important in that the desired corrosion resistance and spot weldability can be secured by optimizing the Mg content during alloying and/or hot press forming on the plating surface. If the initial cooling end temperature is less than 640 ℃, there is a problem that the equipment load may occur because more power must be applied for alloying in the subsequent on-line alloying heat treatment.
[84]
On the other hand, if the cooling rate is less than 0.1 °C / sec, the solidification layer is not sufficiently formed on the plating surface, and Mg is excessively diffused to the surface during online alloying, which may deteriorate the spot weldability of the hot-formed member. On the other hand, if the cooling rate exceeds 5 °C / sec, the plating layer is excessively cooled, and the equipment load and time are lengthened to secure a predetermined temperature for alloying, thereby impairing productivity.
[85]
step of spraying aluminum powder
[86]
After the initial cooling, if necessary, aluminum powder may be sprayed on the surface of the aluminum-plated steel sheet. Aluminum powder not only locally cools the surface, but can also refine surface spangles. At this time, if only the surface is locally cooled by the aluminum powder, the diffusion of Mg in the plating layer to the surface during the subsequent online alloying process is further suppressed, thereby reducing Mg oxide generated by Mg diffusion to the surface after hot press forming. can improve In addition, there is an advantage in that the surface can be uniformly generated after hot press molding by refining the surface spangles.
[87]
The average particle diameter of the aluminum powder may be 5 to 40 μm, more preferably 10 to 30 μm, and most preferably 10 to 25 μm. When the average particle diameter of the aluminum powder is less than 5 μm, the effect of surface cooling and sequin refinement is insufficient. On the other hand, when the average particle diameter exceeds 40 μm, it is not sufficiently dissolved in the plating layer and remains on the surface, causing surface quality problems.
[88]
In the present invention, the injection amount of the aluminum powder may be determined within the limit that satisfies the condition that the surface temperature does not fall below 640°C after the powder injection. If the surface temperature of the steel sheet falls below 640°C after powder spraying, equipment load may occur because more output must be applied for alloying in the subsequent online alloying heat treatment. The injection amount of aluminum powder is related to the surface temperature of the steel sheet, but the surface temperature of the steel sheet cannot be uniformly determined because it can vary greatly depending on the process conditions, equipment, environmental conditions, etc. at the time of implementation. Therefore, the aluminum powder injection amount is sufficient to satisfy the above conditions, and the specific injection amount range may not be particularly limited. However, as a non-limiting embodiment, the aluminum powder may be sprayed within the range of 0.01 to 10 g per 1 m 2 of the aluminum plated steel sheet.
[89]
Obtaining an aluminum-iron-based plated steel sheet by alloying heat treatment
[90]
After the initial cooling and/or after spraying the aluminum powder, an on-line alloying treatment in which heat treatment is continuously performed may be performed. In addition, the heating temperature range during the alloying heat treatment may be 670 ~ 900 ℃, the holding time may be 1 ~ 20 seconds. On the other hand, more preferably, the heating temperature range may be 680 ~ 880 ℃, the holding time may be 1 ~ 10 seconds.
[91]
In the present invention, the on-line alloying process refers to a process of heat-treating by increasing the temperature after hot-dip aluminum plating, as can be seen in the schematic diagram shown in FIG. 1 . In the online alloying heat treatment method according to the present invention, since the heat treatment for alloying starts before the plating layer is cooled and hardened after hot-dip aluminum plating, there is no need for a separate temperature rise process, so alloying is possible in a short time. However, in the conventionally known plating layer composition of aluminum-plated steel sheet, since the alloying rate was slow and sufficient alloying could not be completed in a short time, it was difficult to apply the on-line alloying method of heat treatment immediately after plating. However, in the present invention, the plating bath affecting the alloying rate Since the alloying rate of the plating layer is increased by controlling the content of components, particularly Si and Mg, the alloying of the aluminum plating layer can be effectively completed despite the short heat treatment time of 1 to 20 seconds.
[92]
The heating temperature is based on the surface temperature of the steel sheet to be heat treated. If the heating temperature is less than 670 ℃, the problem of insufficient alloying may occur. On the other hand, if the heating temperature exceeds 900 ℃, it is difficult to cool after alloying. can Therefore, the heating temperature during the alloying heat treatment is preferably limited to 670 ~ 900 ℃, more preferably 700 ~ 800 ℃ may be.
[93]
Meanwhile, during the alloying heat treatment, the holding time may be limited to 1 to 20 seconds. In the present invention, the holding time means the time during which the heating temperature (including deviation ±10°C) is maintained in the steel sheet. If the holding time is less than 1 second, the heating time is too short, so that sufficient alloying is not achieved. On the other hand, if the holding time exceeds 20 seconds, there may be a problem in that productivity is too reduced. Therefore, the holding time during the alloying heat treatment is preferably limited to 1 to 20 seconds, more preferably 1 to 10 seconds.
[94]
The alloying of the plating layer through the alloying heat treatment depends on the heat treatment temperature and the holding time, but at the same time is also affected by the Si and Mg contents contained in the aluminum plating layer. As the amount of Si included in the aluminum plating layer increases and the amount of Mg increases, the alloying rate increases, and thus the thickness of the alloyed region may be increased. When the on-line heat treatment is performed continuously after the plating step as in the present invention, since the heat treatment time is relatively short compared to the normal annealing (BAF) method, a sufficiently alloyed plating layer cannot be obtained unless the process conditions are precisely controlled. Therefore, the present inventors can effectively obtain a sufficiently alloyed plating layer despite a short heat treatment time of 1 to 20 seconds by appropriately controlling the Si and Mg content and heat treatment conditions.
[95]
After the alloying is completed as described above, it can be manufactured as a molded member by performing hot press forming. At this time, the hot press forming may use a method generally used in the art, for example, after heating the aluminum-iron-based plated steel sheet according to the present invention in a temperature range of 880 to 950° C. for 3 to 10 minutes, press The heated steel sheet may be hot-formed into a desired shape by using, but is not limited thereto. In addition, the composition of the base steel sheet of the hot press-formed member may be the same as the composition of the base steel sheet of the above-aluminum-iron-based alloy little steel sheet.
Modes for carrying out the invention
[96]
Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the following examples are only intended to illustrate the present invention in more detail and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and matters reasonably inferred therefrom.
[97]
(Example)
[98]
First, a cold-rolled steel sheet for hot press forming having the composition shown in Table 1 below was prepared as a base steel sheet, and aluminum plating was performed on the surface of the base steel sheet at a plating bath composition shown in Table 2 below at a plating bath temperature of 660°C. Thereafter, initial cooling and alloying heat treatment were performed under the conditions of initial cooling and alloying heat treatment shown in Table 2 below. Whether or not the plating layer peels off is indicated by X when peeling of the plating layer occurs at a bending angle of 30 degrees when a 60 mm × 60 mm specimen is subjected to a three-point bending test using a punch having a diameter of 5 mm, and O when peeling does not occur. In addition, the surface spangle determination was expressed as X when the diameter was 5 mm or more, and O when it was less than 5 mm.
[99]
[Table 1]
[100]

[101]
[Table 2]
[102]

[103]
Thereafter, each aluminum-iron-based plated steel sheet was heated at 930° C. for 6 minutes in an atmospheric atmosphere, and then hot press forming was performed to obtain a hot press-formed member. Thereafter, the plating layer structure and GDS of the member were observed (using GDS 850A from LECO, USA), and corrosion resistance and spot weldability were measured and shown in Table 3 below. For corrosion resistance, a crosscut was made on the member after phosphate treatment and painting, and the blister width was measured after 52 CCT cycles. Spot weldability was evaluated according to ISO 18278 and the current range was analyzed. In the case of corrosion resistance, if the blister width is 2.5mm or more, and in the case of spot welding, if the spot welding current range is less than 1 kA, it was judged to be inferior.
[104]
[Table 3]
[105]

[106]
As can be seen in Tables 1 to 3, Inventive Examples 1 to 9 satisfy all of the plating bath components, plating layer thickness, surface Mg and O content, and aluminum layer ratio and alloying heat treatment conditions presented in the present invention, It can be seen that the blister width is less than 2.0mm and the spot welding current range is 1.0kA or more, so it can be confirmed that the corrosion resistance and spot weldability are excellent.
[107]
However, in Comparative Examples 1, 2 and 6, when the alloying heat treatment temperature was less than 670 ° C., alloying did not occur sufficiently, so that the alloying layer thickness ratio was less than 90%, that is, the ratio of the aluminum layer was 10% or more, and peeling of the plating layer was observed. .
[108]
In Comparative Examples 3 and 8, a thick plating layer was formed and alloying heat treatment was performed at a temperature exceeding 900°C, and the surface spangle diameter was 5 mm or more, and the surface quality was inferior.
[109]
In Comparative Example 4, since alloying heat treatment was not performed, the alloying layer thickness ratio was 13%, and the formation of the alloying layer was insignificant, so that the plating layer peeling occurred.
[110]
On the other hand, in Comparative Examples 5 and 7, the holding time during the alloying heat treatment was outside the scope of the present invention, and in Comparative Example 5, the heat treatment time was very short, so that the plating layer was not sufficiently alloyed. This was lowered. In addition, in the case of Comparative Example 7, it was confirmed that the corrosion resistance was deteriorated as a result of applying a long heat treatment time of 25 seconds by forming a thick plating layer to a thickness of 40.8 μm.
[111]
Comparative Examples 9 to 11 are examples in which the content of Si and/or Mg in the aluminum plating bath component does not satisfy the conditions of the present invention. First, Comparative Example 9 was a case where both Si and Mg contents were not satisfied, and the alloying layer ratio was small because a sufficient alloying rate was not secured. it was done Moreover, peeling of a plating layer and generation|occurrence|production of surface spangle were also confirmed. On the other hand, in Comparative Example 10, when the Mg content was excessive, Mg was concentrated on the surface of the plated steel sheet more than necessary, and the occupancy viscosity was lowered. Also, in Comparative Example 11, when the Si content was excessively added, the alloying rate was lowered and the alloying layer ratio was decreased, and as a result, peeling of the plating layer was observed.
[112]
As described above, in the detailed description of the present invention, a preferred embodiment of the present invention has been described, but those of ordinary skill in the art to which the present invention pertains may make various modifications without departing from the scope of the present invention. Of course, this is possible. Therefore, the scope of the present invention should not be limited to the described embodiments and should be defined by the claims to be described later, as well as equivalents thereof.
[113]
[114]
[Explanation of code]
[115]
1: Heat treatment furnace
[116]
2: Aluminum plating bath
[117]
3: Initial cooling device
[118]
4: Aluminum powder spraying device
[119]
5: alloying heat treatment device
Claims
[Claim 1]
An aluminum-iron-based plated steel sheet used for hot press forming, comprising: a base steel sheet; and a plating layer formed on the surface of the steel sheet, wherein the plating layer is formed on the surface of the steel sheet and includes an alloying layer comprising at least one of Fe 3Al, FeAl(Si), Fe 2Al 5 and FeAl 3 ; and an aluminum layer formed on the alloying layer and having a thickness of less than 10% of the thickness of the plating layer; Including, the thickness of the plating layer is 20 ~ 35㎛, Mg measured by GDS at a depth of 0.1㎛ from the surface of the plating layer is 1 ~ 20% by weight, measured by GDS at a depth of 0.1㎛ from the surface of the plating layer An aluminum-iron plated steel sheet containing 10 wt% or less of oxygen.
[Claim 2]
The method according to claim 1, wherein the plating layer is 100% by weight except for the Fe content diffused from the steel sheet, Si: 7-15%, Mg: 1.1-15%, the remainder Al and other unavoidable impurities An aluminum-iron-based plated steel sheet comprising a.
[Claim 3]
According to claim 1, wherein the base steel sheet is C: 0.04 to 0.5%, Si: 0.01 to 2%, Mn: 0.01 to 10%, Al: 0.001 to 1.0%, P: 0.05% or less, S: 0.02 by weight% % or less, N: 0.02% or less, and the remainder Fe and other unavoidable impurities.
[Claim 4]
According to claim 3, wherein the base steel sheet is, by weight %, Cr, Mo, and at least one sum selected from the group consisting of W: 0.01 to 4.0%, Ti, Nb, Zr, and one or more sums from the group consisting of: 0.001 to 0.4%, Cu+Ni: 0.005 to 2.0%, Sb+Sn: 0.001 to 1.0%, and B: 0.0001 to 0.01% of an aluminum-iron-based plated steel sheet.
[Claim 5]
A hot press formed member obtained by hot press forming the aluminum-iron-based plated steel sheet according to any one of claims 1 to 4.
[Claim 6]
The hot press-formed member according to claim 5, wherein the hot press-formed member has a spot welding current range of 1 kA or more.
[Claim 7]
A method of manufacturing an aluminum-iron-based plated steel sheet used for hot press forming, the method comprising: preparing a base steel sheet; The base steel sheet, Si: 7 to 15%, Mg: 1.1 by weight Obtaining an aluminum-coated steel sheet by immersing in an aluminum plating bath containing ~15%, the remainder Al and other unavoidable impurities and plating at a plating amount of 40-100 g/m2 based on one side; performing initial cooling at a cooling rate of 0.1 to 5° C./sec to a temperature of 640° C. or higher immediately after aluminum plating; and obtaining an aluminum-iron-based plated steel sheet through on-line alloying in which heat treatment is performed by continuously maintaining for 1 to 20 seconds in a heating temperature range of 670 to 900° C. after the initial cooling; A method of manufacturing an aluminum-iron-based plated steel sheet comprising a.
[Claim 8]
8. The method of claim 7, further comprising spraying aluminum powder on the surface of the aluminum-coated steel sheet after the initial cooling.
[Claim 9]
The method of claim 8, wherein the aluminum powder has an average particle diameter of 5 to 40 μm.
[Claim 10]
The method according to claim 7, wherein the base steel sheet is C: 0.04 to 0.5%, Si: 0.01 to 2%, Mn: 0.01 to 10%, Al: 0.001 to 1.0%, P: 0.05% or less, S: 0.02 by weight% % or less, N: 0.02% or less, the balance Fe and other unavoidable impurities, characterized in that it contains an aluminum-iron-based plated steel sheet manufacturing method.
[Claim 11]
11. The method of claim 10, wherein the base steel sheet by weight, Cr, Mo, and at least one sum selected from the group consisting of W: 0.01 to 4.0%, Ti, Nb, Zr, and one or more sums from the group consisting of: 0.001 to 0.4%, Cu + Ni: 0.005 to 2.0%, Sb + Sn: 0.001 to 1.0%, and B: 0.0001 to 0.01% of an aluminum-iron-based plated steel sheet manufacturing method, characterized in that it further comprises at least one.