JP7307307B2 - Aluminum-plated steel sheets for butt welding, butt-welding parts, and hot press-formed products - Google Patents

Description

TECHNICAL FIELD The present invention relates to an aluminum-plated steel sheet for butt welding, a butt-welded member, and a hot press-formed product.

In recent years, in order to protect the environment and prevent global warming, there has been an increasing demand for reducing the consumption of chemical fuels, and this demand is affecting various manufacturing industries. For example, automobiles, which are indispensable for daily life and activities as a means of transportation, are no exception, and there is a demand for improved fuel efficiency by reducing the weight of the vehicle body. However, in terms of product quality, simply reducing the weight of the vehicle body is not permitted for automobiles, and appropriate safety must be ensured.

Most automobile structures are made of iron (especially steel plates), and reducing the weight of these steel plates is important for reducing the weight of the vehicle body. However, as described above, simply reducing the weight of the steel sheet is not allowed, and it is also required to ensure the mechanical strength of the steel sheet. Demands for such steel sheets are made not only in the automobile manufacturing industry but also in various manufacturing industries. Therefore, by increasing the mechanical strength of the steel sheet, research and development is being carried out on a steel sheet that can maintain or increase the mechanical strength even if it is thinner than steel sheets that have been used before.

In general, a material having high mechanical strength tends to lose its shape fixability in forming such as bending, and when it is processed into a complicated shape, the processing itself becomes difficult. One of the means for solving this moldability problem is the so-called "hot press method (also called hot stamp method, hot press method, high temperature press method, or die quench method)". In the hot press method, the material to be formed is heated to a high temperature in the austenite region, and the steel plate softened by heating is pressed and formed, and then cooled while restrained in a mold. . According to the hot pressing method, the material is once heated to a high temperature in the austenite region and softened, so that the material can be easily pressed. can increase Therefore, the hot press method makes it possible to obtain a molded article having good shape fixability and high mechanical strength.

In addition, in order to improve the yield and productivity of press-formed products for automobile members, butt-welded members (hereinafter referred to as “tailored blank materials”) are joined by laser welding, plasma welding, etc. by matching the end faces of at least two steel plates. ) is applied as a material for pressing. Since a tailored blank joins a plurality of steel plates according to the purpose, it is possible to freely change the plate thickness and strength in one part. As a result, the tailored blank material makes it possible to improve the functionality of the automotive member and reduce the number of automotive members.

Further, by using a tailored blank material and forming the tailored blank material by hot pressing, it is possible to manufacture a high-strength pressed product in which the plate thickness, strength, etc. are freely changed.

When a tailored blank material is used as a press material to form an automobile member by hot pressing, the tailored blank material is heated to a temperature range of 800° C. to 1000° C., for example. For this reason, steel sheets plated with aluminum such as Al—Si, which has a high plating boiling point, are often used as tailored blanks for hot pressing.

Until now, as a steel sheet for forming a tailored blank material, for example, various aluminum-plated steel sheets containing mainly aluminum have been studied (see, for example, Patent Documents 1 to 3 below. ).

Patent Literature 1 below discloses a steel sheet having an aluminum plating layer in which an intermetallic alloy layer remains, in which the aluminum plating layer is partially removed from the periphery of the steel sheet.

In addition, the following Patent Documents 2 and 3 disclose conditions for maintaining the required strength of the welded portion in a tailored blank material for hot stamping formed by butt laser welding steel plates having an aluminum plating layer. ing.

Japanese Patent Publication No. 2009-534529 JP 2013-220445 A JP 2013-204090 A

However, when steel sheets having an aluminum plating layer are butt-welded to produce a tailored blank material, the weld metal at the butt-welded portion may break.

In particular, in Patent Document 1, a steel plate in which the aluminum plating layer of the portion to be welded is removed and the intermetallic compound layer is left is formed, and the end surfaces of the regions where the intermetallic compound layer is left are butt-welded in a state where they are butt-welded. Tailored blank material It is disclosed that it is possible to avoid breakage of the weld metal in the hot press-formed product.

Here, a welded member (tailored blank) obtained by butt-welding a steel plate plated with a metal mainly containing aluminum by a welding method such as laser welding or arc plasma welding has aluminum plating in the weld metal. A large amount of aluminum may be mixed in. In this case, when the obtained tailored blank material is hot-pressed, the weld metal may be fractured and the weld strength may be lowered. This is considered to be due to the fact that the weld metal with a high aluminum concentration has poor hardenability and sufficient joint strength cannot be obtained even after hot pressing.

In terms of avoiding breakage of the weld metal, Patent Document 1, in particular, removes the aluminum plating layer of the portion to be welded to be welded and leaves the intermetallic compound layer as described above. A tailored blank material is disclosed in which the portions to be welded are butt-welded. In a hot press-formed product using this tailored blank material, a decrease in weld strength can be suppressed.

However, in the steel sheet disclosed in Patent Document 1, the base steel sheet is provided with an aluminum plating (Al—Si metal plating) layer, and an intermetallic alloy layer is formed between the base steel sheet and the aluminum plating layer. It is Since the intermetallic compounds contained in the intermetallic alloy layer are relatively brittle, inhibitors are added to the molten metal bath to limit the growth of the intermetallic alloy layer. As a result, in the steel sheet disclosed in Patent Document 1, for example, the thickness of the aluminum plating layer is as thick as 20 μm, whereas the thickness of the intermetallic alloy layer is as thin as 5 μm.

In the steel plate disclosed in Patent Document 1, the aluminum plating layer is removed by brushing or laser ablation to the portion to be welded before manufacturing the tailored blank material, leaving a thin intermetallic alloy layer. As a result, due to the thin intermetallic alloy layer, the corrosion resistance of the weld zone after painting is inferior.

In addition, since the steel plate disclosed in Patent Document 1 has a thin intermetallic alloy layer, the amount of aluminum mixed in the weld metal is small. Therefore, in the steel plate disclosed in Patent Document 1, scales (compounds of iron) are likely to occur on the surface of the weld metal due to being heated to a high temperature during hot pressing. As a result, when the hot press-formed product is coated with the composition, the adhesion of the coating is lowered, and the corrosion resistance of the weld zone after coating is inferior.

Also, in the tailored blank materials for hot stamping disclosed in Patent Documents 2 and 3, there is still room for further improvement in terms of corrosion resistance after coating at welded portions after hot pressing.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide an aluminum plating for butt welding that can further improve the post-coating corrosion resistance of welds in tailored blank materials. An object of the present invention is to provide a steel plate, a butt-welded member, and a hot press-formed product.

The present inventors have made intensive studies in order to solve the above problems, and found that intermetallic compounds of aluminum, iron, and aluminum and iron generated in the hot press process, which may be present in the weld, On the other hand, it was conceived that the anodic dissolution reaction proceeds in a corrosive environment, and the adhesion of the paint is reduced.

As a result of further studies based on this idea, the present inventors have found that an intermetallic compound layer composed of aluminum and iron is added with a metal element having a noble potential or an element that becomes passive in a corrosive environment. The present inventors have completed the present invention based on the knowledge that corrosion resistance can be improved by containing Ni.
The gist of the present invention completed based on the above knowledge is as follows.

(1) A base steel plate, an aluminum plating layer provided on one or both sides of the base steel plate, and a first intermetallic compound containing aluminum formed between the base steel plate and the aluminum plating layer and a second intermetallic compound layer formed on one side or both sides of the base steel plate on at least a part of the edge positioned around the base steel plate, wherein the second intermetallic compound The layer contains 0.01 to 1% by mass in total of one or more A group elements selected from the group consisting of Ni, Cu, Cr, and Mn, and the second intermetallic compound layer (however, , excluding the state in which the second intermetallic compound layer is removed ), butt welding in which the aluminum plating layer does not exist or the aluminum plating layer with a reduced thickness exists on the Aluminized steel sheet for
(2) the aluminum plating layer contains one or more B group elements selected from the group consisting of Sr, Mg, and Ca in a total amount of 0.01 to 20 g/ ^m2 ; The aluminum-plated steel sheet for butt welding according to (1).
(3) On the upper layer of the aluminum plating layer, one or more C group elements selected from the group consisting of C group elements: Zn, Ti, V, Zr and Ce are added in a total amount of 0.00. The aluminum plated steel sheet for butt welding according to (1) or (2), wherein a surface coating layer containing 01 to 10 g/m ² is formed.
(4) The chemical composition of the base steel sheet is, in mass%, C: 0.10 to 0.60%, Si: 0.01 to 0.60%, Mn: 0.01 to 3.0%, P : 0.05% or less, S: 0.05% or less, Al: 0.01 to 1.0%, Ti: 0.001 to 0.10%, B: 0.0001 to 0.010%, N: The aluminum plated steel sheet for butt welding according to any one of (1) to (3), containing 0.01% or less and the balance being Fe and impurities.
(5) The chemical composition of the base steel plate is Ni: 0 to 2.0%, Cu: 0 to 1.0%, and Cr: 0 to 1.0% in place of part of the remaining Fe. The aluminum plated steel sheet for butt welding according to (4), containing one or more of
(6) A butt-welded member in which at least two aluminum-plated steel sheets for butt welding according to any one of (1) to (5) are butt-welded via the second intermetallic compound layer. .
(7) A hot press-molded product obtained by hot press-molding the butt-welded member according to (6).

INDUSTRIAL APPLICABILITY As described above, the present invention provides an aluminum-plated steel sheet for butt welding, which is capable of obtaining a butt-welded member having excellent post-coating corrosion resistance of the weld even after coating the hot-stamped product. be done.

FIG. 3 is a diagram schematically showing a cross-sectional structure of a normal portion (other than the end portions) of an aluminum plated steel sheet for butt welding when a surface coating layer is provided. FIG. 3 is a diagram schematically showing a cross-sectional structure of an end portion of an aluminum plated steel sheet for butt welding when a surface coating layer is provided. FIG. 2 is a diagram schematically showing a cross-sectional structure of a butt welded part in an aluminum plated steel sheet for butt welding when a surface coating layer is provided. FIG. 2 is a diagram schematically showing how group B elements and group C elements migrate to the weld metal at the butt welded portion of an aluminum plated steel sheet for butt welding when a surface coating layer is provided. It is the figure which showed typically the corrosion-resistant evaluation method after painting. FIG. 4 is a diagram schematically showing how corrosion products are formed at a butt welded portion of an aluminum-plated steel sheet for butt welding.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

(Concerning the ideas obtained by the present inventors)
In the process of manufacturing automobiles using plated steel sheets for hot stamping, the plated steel sheets for hot stamping are heated and shaped in a hot stamping process to form hot stamped members. A hot stamping member is made by laminating a chemical conversion treatment film represented by a zinc phosphate film on the surface of the member, then laminating an electrodeposition coating film on the upper layer, and depending on the case, further laminating a coating film on the upper layer. provided. Aluminum, iron, and intermetallic compounds of aluminum and iron generated in the hot stamping process, under a corrosive environment, when the paint film swells due to the anodic dissolution reaction shown in the following formulas (1) to (3) guessed.

Al→Al ³⁺ +3e ⁻ ··· Formula (1)
Fe→Fe ²⁺ +2e ⁻ ··· Equation (2)
Fe _x Al _y →xFe ²⁺ +yAl ³⁺ +(2x+3y)e ⁻ ··· Formula (3)

Therefore, the present inventors have found that in a corrosive environment, the intermetallic compound itself is treated as a metal with a noble potential to reduce the corrosion rate, or the corrosion products generated in the corrosive environment are passivated to If the progress of corrosion can be delayed by suppressing the penetration of corrosive factors such as oxygen, chloride ions, etc., it is possible to suppress swelling of the coating film and further improve the post-coating corrosion resistance of welds in tailored blank materials. Considering that it is possible, we conducted further investigations. As a result, for the intermetallic layer consisting of aluminum and iron, a noble metal of potential or an element (more particularly selected from the group consisting of Ni, Cu, Cr and Mn) that becomes passive in a corrosive environment One or two or more elements) was conceived, and an aluminum plated steel sheet for butt welding, a butt weld member, and a hot press-formed product according to the embodiments of the present invention described in detail below were realized. rice field.

(About aluminum-plated steel sheets for butt welding)
<Overall configuration of aluminum-plated steel sheet for butt welding>
Parts other than the ends of the aluminum plated steel sheet for butt welding according to the embodiment of the present invention are, as schematically shown in FIG. and an aluminum plating layer provided on one side or both sides of the material steel plate. An intermetallic compound layer (IMC) 1 as an example of a first intermetallic compound layer is formed between the base steel sheet and the aluminum plating layer, as schematically shown in FIG.

Here, in this specification, when one or both sides of the base steel sheet are plated with aluminum, the intermetallic compound layer formed between the base steel sheet and the aluminum plating is referred to as "metal called the intercompound layer (IMC). In addition, of the aluminum plating applied to the base steel sheet, a region excluding the intermetallic compound layer is called an “aluminum plating layer”.

In addition, in the aluminum plated steel sheet for butt welding according to the present embodiment, as schematically shown in FIG. 1, a surface coating layer may be formed further above the aluminum plating layer, if necessary.

Furthermore, the aluminum plated steel sheet for butt welding according to the present embodiment, as schematically shown in FIG. An intermetallic compound layer (IMC) 2 as an example of a second intermetallic compound layer is formed on the substrate.

The shape of the aluminum-plated steel sheet for butt welding is not particularly limited.

<About the base material steel plate>
The steel plate components of the base steel plate according to the present embodiment are not particularly limited. However, considering that the aluminum plated steel sheet for butt welding having such a base material steel sheet can be subjected to the hot pressing method, the base material steel sheet preferably has the following chemical components.

That is, the preferable base material steel plate according to the present embodiment is, in mass%, C: 0.10 to 0.60%, Si: 0.01 to 0.60%, Mn: 0.01 to 3.0%, P: 0.05% or less, S: 0.05% or less, Al: 1.0% or less, Ti: 0.001 to 0.10%, B: 0.0001 to 0.010%, N: 0. 01% or less, with the balance being Fe and impurities. Further, a more preferable base steel plate according to the present embodiment further includes Ni: 0 to 2.0%, Cu: 0 to 1.0%, Cr: 0 to 1, instead of part of the remaining Fe. .0% chemical composition containing one or more. These steel sheet components are briefly described below. In addition, in the following description of chemical components, the notation of % means % by mass unless otherwise specified.

[C: 0.10 to 0.60%]
C is an element contained to ensure desired mechanical strength. If the C content is less than 0.10%, sufficient improvement in mechanical strength cannot be obtained, and the effect of containing C becomes poor. Therefore, the C content is preferably 0.10% or more. The content of C is more preferably 0.20% or more. On the other hand, if the C content exceeds 0.60%, the strength of the steel sheet can be further improved, but the elongation properties and drawing properties tend to deteriorate. Therefore, the C content is preferably 0.60% or less. The C content is more preferably 0.45% or less.

[Si: 0.01 to 0.60%]
Si is one of the strength-enhancing elements that improve mechanical strength, and like C, it is an element contained to ensure desired mechanical strength. If the Si content is less than 0.01%, the effect of improving strength is difficult to obtain, and sufficient improvement in mechanical strength cannot be obtained. Therefore, the Si content is preferably 0.01% or more. The Si content is more preferably 0.10% or more. On the other hand, since Si is also an easily oxidizable element, when the Si content exceeds 0.60%, the wettability is reduced during hot dip plating due to the influence of Si oxides formed on the surface layer of the steel sheet. It may decrease and non-plating may occur. Therefore, the Si content is preferably 0.60% or less. The Si content is more preferably 0.40% or less.

[Mn: 0.01 to 3.0%]
Mn is one of the strengthening elements that strengthen steel and is also one of the elements that improve hardenability. Furthermore, Mn is an element effective in preventing hot embrittlement caused by S, which is one of unavoidable impurities. When the Mn content is less than 0.01%, these effects are difficult to obtain, and when the Mn content is 0.01% or more, the above effects are exhibited more reliably. Therefore, the content of Mn is preferably 0.01% or more. The content of Mn is more preferably 0.20% or more. On the other hand, since Mn is a γ-forming element, if the Mn content exceeds 3.0%, the residual γ phase may become too large and the strength may decrease. Therefore, the Mn content is preferably 3.0% or less. The content of Mn is more preferably 2.20% or less.

[P: 0.05% or less]
P is an element that deteriorates the toughness of the steel plate member after quenching. In particular, when the P content exceeds 0.05%, toughness deteriorates significantly. Therefore, the P content is preferably 0.05% or less. The P content is more preferably 0.005% or less. On the other hand, the lower the P content, the better, and the lower limit of the P content is not particularly specified. However, if the P content is reduced to less than 0.0080%, the P removal cost will increase significantly, which is economically disadvantageous. Therefore, the practical lower limit of the P content is 0.0080%.

[S: 0.05% or less]
S is an element that deteriorates the toughness of the steel plate member after quenching. In particular, when the S content exceeds 0.05%, toughness deteriorates significantly. Therefore, the S content is preferably 0.05% or less. The S content is more preferably 0.003% or less. On the other hand, the lower the content of S, the better, and the lower limit of the content of S is not particularly defined. However, if the S content is reduced to less than 0.0005%, the desulfurization cost will increase significantly, which is economically disadvantageous. Therefore, the practical lower limit of the S content is 0.0005%.

[Al: 0.01 to 1.0%]
Al is an element that enhances the hardenability of steel and makes it possible to stably secure the strength of steel plate members after hardening. Such an effect can be reliably exhibited by setting the Al content to 0.01% or more. Therefore, the Al content is preferably 0.01% or more. The Al content is more preferably 0.03% or more. On the other hand, when the content of Al exceeds 1.0%, the above effect is saturated and the economy is lowered. Therefore, the Al content is preferably 1.0% or less. The Al content is more preferably 0.7% or less.

[Ti: 0.001 to 0.10%]
Ti is one of the strength-enhancing elements. If the Ti content is less than 0.001%, it is difficult to obtain the effect of improving the strength and oxidation resistance, and if the Ti content is 0.001% or more, these effects are exhibited more reliably. Therefore, the Ti content is preferably 0.001% or more. The Ti content is more preferably 0.03% or more. On the other hand, if Ti is contained excessively, it may form carbides and nitrides, for example, and soften the steel. In particular, when the Ti content exceeds 0.10%, there is a high possibility that the desired mechanical strength cannot be obtained. Therefore, the Ti content is preferably 0.10% or less. The Ti content is more preferably 0.07% or less.

[B: 0.0001 to 0.010%]
B is an element that acts during quenching and has the effect of improving strength. If the B content is less than 0.0001%, such a strength improvement effect cannot be sufficiently obtained. Therefore, the content of B is preferably 0.0001% or more. The content of B is more preferably 0.0015% or more. On the other hand, when the content of B exceeds 0.010%, inclusions may be formed to cause embrittlement and reduce fatigue strength. Therefore, the content of B is preferably 0.010% or less. The content of B is more preferably 0.0070% or less.

[N: 0.01% or less]
N is an element that deteriorates the toughness of the steel plate member after quenching. In particular, when the N content exceeds 0.01%, coarse nitrides are formed in the steel, increasing the possibility of significantly deteriorating local deformability and toughness. Therefore, the N content is preferably 0.01% or less. The lower limit of the N content is not particularly limited, and the lower the better. However, since it is economically unfavorable to make the N content less than 0.0002%, the N content is preferably 0.0002% or more. The content of N is more preferably 0.0008% or more.

[Ni: 0 to 2.0%]
Ni is an element that enhances the hardenability of steel and makes it possible to stably ensure the strength of the steel plate member after hardening, so it may be contained. In order to reliably obtain such effects, the Ni content is preferably 0.01% or more. When Ni is included, the content of Ni is more preferably 0.05% or more. On the other hand, if the Ni content exceeds 2.0%, the above effects become saturated and the economy decreases. Therefore, when Ni is included, the content of Ni is preferably 2.0% or less. When Ni is included, the content of Ni is more preferably 1.0% or less.

[Cu: 0 to 1.0%]
Cu may be contained because it is an element that enhances the hardenability of steel and makes it possible to stably ensure the strength of steel plate members after hardening. Cu is also an element that improves pitting corrosion resistance in corrosive environments. In order to reliably obtain such effects, the Cu content is preferably 0.1% or more. When Cu is contained, the content of Cu is more preferably 0.15% or more. On the other hand, when the Cu content exceeds 1.0%, the above effects are saturated and the economy is lowered. Therefore, when Cu is included, the content of Cu is preferably 1.0% or less. When Cu is contained, the content of Cu is more preferably 0.50% or less.

[Cr: 0 to 1.0%]
Cr is an element that enhances the hardenability of steel and makes it possible to stably ensure the strength of the steel plate member after hardening, so it may be contained. In addition, Cr, like Si, is an element that plays a role in suppressing scale formation by forming FeCr ₂ O ₄ on the surface of the steel sheet during heat treatment and reducing FeO in the scale. Since this FeCr ₂ O ₄ serves as a barrier layer and blocks the supply of Fe into the scale, the thickness of the scale can be reduced. Furthermore, if the thickness of the scale is thin, there is the advantage that it is difficult to peel off during hot forming, and it is easy to peel off during descaling treatment after forming. In order to reliably obtain such effects, the Cr content is preferably 0.01% or more, more preferably 0.05% or more. On the other hand, if the Cr content exceeds 1.0%, the above effects become saturated and the economy decreases. Therefore, when Cr is contained, the content is preferably 1.0% or less, more preferably 0.80% or less.

[Remainder: Fe and impurities]
The remainder of the steel plate components of the base steel plate is Fe and impurities. Examples of impurities include elements that are inevitably mixed from steel raw materials or scraps and/or during the steelmaking process and that are allowed within a range that does not impair the properties of the aluminum plated steel sheet for butt welding according to the present embodiment.

In addition, in the base steel sheet according to the present embodiment, instead of part of the remaining Fe, one or more selected from the group consisting of V, Nb, Sn, Mo, W, Ca and REM shown below element may be contained.

[V: 0 to 1.0%]
V is an element that enhances the hardenability of steel and makes it possible to stably ensure the strength of the steel plate member after hardening, so it may be contained. In order to reliably obtain such effects, the V content is preferably 0.1% or more. The content of V when included is more preferably 0.15% or more. On the other hand, if the V content exceeds 1.0%, the above effects become saturated and the economy decreases. Therefore, when V is included, the content of V is preferably 1.0% or less. The content of V when contained is more preferably 0.8% or less.

[Nb: 0 to 1.0%]
Nb is an element that enhances the hardenability of steel and makes it possible to stably ensure the strength of the steel plate member after hardening, so it may be contained. In order to reliably obtain such effects, the Nb content is preferably 0.01% or more. When Nb is included, the content of Nb is more preferably 0.03% or more. On the other hand, when the content of Nb exceeds 1.0%, the above effect is saturated and the economy is lowered. Therefore, when Nb is included, the content of Nb is preferably 1.0% or less. The content of Nb when included is more preferably 0.5% or less.

[Sn: 0 to 1.0%]
Sn is an element that improves pitting corrosion resistance in a corrosive environment, so it may be contained. In order to reliably obtain such effects, the Sn content is preferably 0.01% or more. When Sn is included, the Sn content is more preferably 0.05% or more. On the other hand, when the Sn content exceeds 1.0%, the grain boundary strength may decrease and the toughness may deteriorate. Therefore, when Sn is included, the Sn content is preferably 1.0% or less. When Sn is included, the Sn content is more preferably 0.6% or less.

[Mo: 0 to 1.0%]
Mo is an element that enhances the hardenability of steel and makes it possible to stably ensure the strength of the steel plate member after hardening, so it may be contained. In order to reliably obtain such effects, the Mo content is preferably 0.1% or more. The content of Mo when contained is more preferably 0.2% or more. On the other hand, when the Mo content exceeds 1.0%, the above effects become saturated and the economy decreases. Therefore, when Mo is included, the content of Mo is preferably 1.0% or less. When Mo is included, the content of Mo is more preferably 0.5% or less.

[W: 0 to 1.0%]
W may be contained because it is an element that enhances the hardenability of steel and makes it possible to stably ensure the strength of the steel plate member after hardening. W is also an element that improves pitting corrosion resistance in corrosive environments. In order to reliably obtain such effects, the W content is preferably 0.01% or more. The content of W when it is included is more preferably 0.03% or more. On the other hand, when the content of W exceeds 1.0%, the above effect is saturated and the economy is lowered. Therefore, when W is included, the content of W is preferably 1.0% or less. The content of W when it is included is more preferably 0.8% or less.

[Ca: 0 to 0.01%]
Ca is an element that has the effect of refining inclusions in steel and improving the toughness and ductility after quenching, so it may be contained. In order to reliably obtain such effects, the Ca content is preferably 0.001% or more. When Ca is contained, the content of Ca is more preferably 0.002% or more. On the other hand, when the content of Ca exceeds 0.01%, the effect is saturated, resulting in an unnecessary increase in cost. Therefore, when Ca is contained, the content of Ca is preferably 0.01% or less. The content of Ca when it is included is more preferably 0.004% or less.

[REM: 0-0.3%]
REM (rare earth element), like Ca, is an element having the effect of refining inclusions in steel to improve toughness and ductility after quenching, and thus may be contained. In order to reliably obtain such effects, the content of REM is preferably 0.001% or more. The content of REM when included is more preferably 0.002% or more. On the other hand, if the REM content exceeds 0.3%, the effect is saturated, resulting in an unnecessary increase in cost. Therefore, the content of REM when it is included is preferably 0.3% or less. The content of REM when it is included is more preferably 0.2% or less.

Here, REM refers to a total of 17 elements of Sc, Y and lanthanoids, and the content of REM means the total content of these elements. REMs are added to molten steel using, for example, Fe--Si--REM alloys, which include, for example, Ce, La, Nd, Pr.

A steel sheet having the steel sheet composition as described above has a tensile strength of about 1000 MPa or more by heating and quenching by a hot press method. In the hot press method, since the material can be pressed in a state of being softened at a high temperature, it can be easily molded.

The base material steel sheet as described above is a steel sheet in a state before the aluminum plating layer is provided. The base material steel plate may be obtained by a normal method, and the manufacturing method is not particularly limited. Such a base material steel plate may be either a hot-rolled steel plate or a cold-rolled steel plate. Moreover, the thickness of the base material steel plate is not particularly limited as long as it is a thickness according to the purpose. For example, the thickness of the base steel sheet may be, for example, a thickness of 0.8 mm to 4 mm as the thickness of the entire steel sheet after the aluminum plating layer is provided. A plate thickness of 1 mm to 3 mm can be mentioned as the plate thickness of the entire steel plate after the provision.

An example of such a base material steel plate is, for example, high mechanical strength (e.g., tensile strength, yield point, elongation, reduction of area, hardness, impact value, fatigue strength, creep strength, etc.) (meaning various properties related to deformation and fracture)).

<Regarding the intermetallic compound layer (IMC)>
[Regarding the intermetallic compound layer (IMC) 1]
The intermetallic compound layer (IMC) 1 as an example of the first intermetallic compound layer is formed by forming an aluminum plating layer on the base steel plate, as schematically shown in FIGS. and the aluminum plating layer. Specifically, the intermetallic compound layer (IMC) 1 is formed by reaction between iron (Fe) of the base steel sheet and a metal containing aluminum (Al) in a molten metal bath containing mainly aluminum. The intermetallic compound layer (IMC) 1 is mainly formed of one or more intermetallic compounds represented by Fe _x Al _y (x and y are each independently a real number of 1 or more). ing. When the aluminum _plating layer _contains Si (silicon), intermetallic compounds represented by _FexAly and _FexAlySiz ( _where x, y, and z are each independently a real number of 1 or more) It is formed of one or more kinds of.

[Regarding the intermetallic compound layer (IMC) 2]
Further, as schematically shown in FIG. 2, on one or both sides of the base steel sheet at least partly on one side or both sides of the edge portion located around the aluminum plated steel sheet for butt welding according to the present embodiment, , an intermetallic compound layer (IMC) 2 is formed. When a tailored blank material is manufactured by welding using at least two aluminum-plated steel sheets for butt welding according to the present embodiment, the intermetallic compound layers (IMC) 2 are butted against each other and subjected to welding. .

The intermetallic compound layer (IMC) 2 contains one or more A group elements selected from the group consisting of Ni, Cu, Cr and Mn. More specifically, the intermetallic compound layer (IMC) 2 contains elements contained in the base steel sheet by treating the edges using a method such as a laser gouging method, which will be described later. Among them, at least one element of Ni, Cu, Cr, and Mn constituting the A group elements is contained. That is, at least one of the group A elements derived from the base material steel plate diffuses into the intermetallic compound layer (IMC) 1 located at the end by the laser gouging method or the like performed on the end, An intermetallic compound layer (IMC) 2 is formed. At a temperature at which the intermetallic compound layer (IMC) 1 is formed, the group A element does not diffuse from the steel sheet, and the steel sheet From there, the group A elements begin to diffuse.

The intermetallic compound layer (IMC) 2 contains one or more A group elements selected from the group consisting of Ni, Cu, Cr, and Mn in a total amount of 0.01 to 1% by mass. be. If the total content of the A group elements is less than 0.01% by mass, the corrosion resistance after painting will be lowered. When the total content of the group A elements is 0.01% by mass or more, swelling of the coating film can be suppressed, and the post-coating corrosion resistance of the welded portion in the tailored blank material can be further improved. The total content of group A elements is preferably 0.05% by mass or more, more preferably 0.1% by mass or more. On the other hand, if the total content of the group A elements exceeds 1%, it causes an increase in cost, which is economically unfavorable. The total content of group A elements is preferably 0.7% by mass or less, more preferably 0.5% by mass or less.

In the aluminized steel sheet for butt welding according to the present embodiment, an intermetallic compound layer (IMC) 2 is formed on one or both sides of the base steel sheet on at least a part of one or both sides of the peripheral end portion. there is Here, the aluminum plating layer may be removed on the intermetallic compound layer (IMC) 2 formed at the end, and the aluminum plating layer having a thickness smaller than that of the region other than the end is formed. It may remain.

On the intermetallic compound layer (IMC) 2 formed on at least a portion of one or both sides of the edge portion located around the steel plate, the portion where the aluminum plating layer is removed or the thickness of the aluminum plating layer is reduced. It is preferable that the width (hereinafter referred to as "reduced thickness width") of the portion (hereinafter referred to as "reduced thickness portion") is within the range of 0.2 to 2.2 mm on average. The average width of these reduced-thickness portions is an average value obtained by measuring the width of the reduced-thickness portion at arbitrary 10 locations and averaging the obtained 10 measured values by the number of measurement locations.

In the aluminum-plated steel sheet for butt welding according to the present embodiment, there is no aluminum plating layer on the intermetallic compound layer (IMC) 2 formed in the weld-scheduled portion of the end portion located around the steel plate, or , there is an aluminum plating layer with a reduced thickness. The aluminum plated steel sheet for butt welding according to the present embodiment removes at least a part of the aluminum plating layer on one or both sides of the steel plate end of the part to be joined, and an intermetallic compound layer ( IMC) 2 is formed. Schematic cross-sectional views of such aluminum-plated steel sheets for butt welding are shown in FIGS.

As mentioned above, the intermetallic compound layer (IMC) 2 contains group A elements (one or more elements selected from the group consisting of Ni, Cu, Cr, and Mn). These group A elements are noble in potential or prone to passivation in corrosive environments. As a result, in a corrosive environment, the intermetallic compound layer (IMC) 2 itself becomes a noble metal and the corrosion rate decreases, or in some cases, these A group elements form dense corrosion products together with Al of the plating component. It forms and passivates, and slows down the progress of corrosion by suppressing the penetration of corrosion factors such as water, oxygen, and chloride ions. As a result, after manufacturing a tailored blank material using the aluminum plated steel sheet for butt welding according to the present embodiment, and coating the manufactured tailored blank material on a hot press-formed product, the welded portion (weld metal and its surroundings) The corrosion resistance of can be further improved.

Fig. 3 is a cross-sectional schematic diagram after butt welding the steel plates on which the aluminized layer on at least one side or both sides of the steel plate end of the portion to be joined is removed and the intermetallic compound layer 2 (IMC2) is formed. Indicated. In the aluminum plated steel sheet for butt welding according to the present embodiment, when the end faces of the ends having the intermetallic compound layer (IMC) 2 are butt welded, the weld metal contains a large amount of aluminum due to the aluminum plating layer. Mixing is suppressed, and deterioration of the hardenability of the weld metal is suppressed. As a result, the mechanical strength of the joint is ensured.

Here, the thickness of the intermetallic compound layer (IMC) 1 and the thickness of the intermetallic compound layer (IMC) 2 are preferably 0.1 to 10 μm and 0.3 to 15 μm, respectively. By setting the thicknesses of the intermetallic compound layer (IMC) 1 and the intermetallic compound layer (IMC) 2 within the ranges described above, the corrosion resistance after painting can be further improved. More preferably, the thickness of the intermetallic compound layer (IMC) 1 and the thickness of the intermetallic compound layer (IMC) 2 are 0.3 to 3 μm and 1 to 6 μm, respectively.

The intermetallic compound layer (IMC) 1 and the intermetallic compound layer (IMC) 2 according to this embodiment have been described in detail above.

<Regarding the aluminum plating layer>
The aluminum plating layer according to this embodiment is formed on one side or both sides of the steel sheet. Here, aluminum plating is plating containing aluminum as a main component, and means plating in which Al accounts for 50% or more in mass %. Elements other than Al may include, for example, at least one of about 0.1 to 20% by mass of Si and about 0.1 to 10% by mass of Fe. Si has the effect of improving workability by suppressing the formation of an alloy layer of Al and Fe. As for Fe, it is conceivable that Fe contained in equipment or the like is mixed into the plating layer. Moreover, the remainder of the aluminum plating layer consists of impurities.

The aluminum plating layer as described above may be formed on the surface of the steel sheet by, for example, a hot dip plating method, but the method for forming the aluminum plating layer is not limited to this method. , thermal spraying, and other known methods can be used. At the time of coating with a coating layer such as hot-dip metal coating, at least part of the aluminum coating layer is alloyed with Fe in the steel sheet to form an intermetallic compound layer (IMC) 1 . In addition, at least a part of the aluminum plating layer can be alloyed with Fe in the steel sheet even during a heating process such as a hot press method, so the aluminum plating layer is not necessarily formed of a single layer with a constant composition. is not limited to, and may include an appropriately alloyed layer.

The adhesion amount of the aluminum plating layer according to the present embodiment is preferably 10 g/m ² or more and 150 g/m ² or less per one side of the base steel sheet. By setting the adhesion amount per one side of the aluminum plating layer within the above range, it is possible to more reliably secure the heat resistance and corrosion resistance of the aluminum-plated steel sheet for butt welding. Incidentally, when the range of the adhesion amount as described above is converted into thickness, it becomes about 3.5 to 52 μm. The adhesion amount of the aluminum plating layer is more preferably 60 g/m ² or more and 100 g/m ² or less (approximately 21 to 36 μm).

The aluminum plating layer according to the present embodiment preferably contains one or more B group elements selected from the group consisting of Sr, Mg and Ca. By including these B group elements in the aluminum plating layer, the corrosion resistance after painting after hot pressing can be further improved. Although the detailed mechanism is not clear, the corrosion products generated in the corrosion process by these B group elements act as barriers to the movement of corrosion factors such as water, oxygen, and salt, and the corrosion factors reach the plating layer. It is presumed that the anticorrosion effect by delaying the Here, the group B element as described above exists in at least one form of a simple substance, an intermetallic compound, or a solid solution in the aluminum plating layer according to the present embodiment.

The method for incorporating such a group B element into the aluminum plating layer is not particularly limited, but the group B element alone is melted in the aluminum plating bath used for forming the aluminum plating layer or melt the compound containing the group B element.

The post-coating corrosion resistance after hot pressing is evaluated by the bulging width of the electrodeposition coating film after the corrosion test from cuts perpendicular to the butt-welded portion, as described below. In the course of the corrosion test, corrosion resistance after painting is improved due to the effects of corrosion products produced by element migration from the intermetallic compound layer, aluminum plating layer, and surface film layer described later.

In the aluminum plated steel sheet for butt welding according to the present embodiment, the intermetallic compound layer (IMC) 1 contains an A group element (at least one of Ni, Cu, Cr, and Mn), so that steel (in more detail, , the potential of the intermetallic compound) is increased, and the potential difference with the aluminum plating layer is reduced, thereby suppressing the dissolution of the aluminum plating layer. Furthermore, Al-based corrosion products derived from group B elements that migrate and precipitate from the aluminum plating layer reduce the cathodic reaction on the weld metal, thereby further suppressing the progress of blistering due to anodic dissolution of the aluminum plating layer. be done.

If the content of these B group elements is too small, the effect will not be exhibited. On the other hand, if the content of the group B element is too large, it causes an increase in cost, and deteriorates corrosion resistance and appearance after plating. More specifically, when the content of the group B element is less than 0.01 g/m ² , there is a possibility that the effect derived from the inclusion of the group B element as described above may not be exhibited. Therefore, the content of the group B element is preferably 0.01 g/m ² or more. The content of the group B element is more preferably 0.03 g/m ² or more. On the other hand, when the content of the group B element exceeds 20 g/m ² , the amount of dissolution of the plating immediately after the start of corrosion becomes too large, which may rather deteriorate the corrosion resistance. Therefore, the content of the group B element is preferably 20 g/m ² or less. The content of group B elements is more preferably 10 g/m ² or less.

When the content of these B group elements in the aluminum plating layer is within the range of 0.01 to 20 g/m ² , these B group elements are eluted in a corrosive environment, and the cut parts and on the weld metal Combined with hydroxide ions generated by the oxygen reduction reaction, carbonate ions, chloride ions and, in some cases, aluminum ions, the B group elements form dense corrosion products. It is presumed that the generated corrosion products exhibit the effect of retarding the progress of corrosion by suppressing the penetration of corrosion factors such as water, oxygen, and chloride ions, thereby further improving corrosion resistance.

<How to confirm the position and how to measure the thickness>
Here, the following methods are used to confirm the positions of the base steel sheet, the intermetallic compound layer (IMC), and the aluminum plating layer, and to measure the thickness of the intermetallic compound layer and the aluminum plating layer. by

First, the aluminum plated steel sheet of interest is cut so as to expose the cross section thereof, and the cross section of the steel sheet is polished. A cross section of the polished steel sheet is analyzed by an electron probe microanalyser (EPMA) to measure the aluminum concentration and iron concentration. The measurement conditions are an acceleration voltage of 15 kV, a beam diameter of 20 μm, an irradiation time of 20 ms, and a measurement pitch of 20 μm.

In the aluminum plated steel sheet of interest, as the measured value of the aluminum concentration in the cross section, the region where the aluminum (Al) concentration is less than 2% by mass is determined as the base steel sheet, and the region where the aluminum concentration is 2% by mass or more is It is judged to be an intermetallic compound layer (IMC) or an aluminum plating layer. In addition, among the intermetallic compound layer (IMC) and the aluminum plating layer, a region having an iron (Fe) concentration of more than 4% by mass is determined to be an intermetallic compound layer, and a region having an iron concentration of 4% by mass or less. , is judged to be an aluminum plating layer.

The thickness of the intermetallic compound layer is defined as the distance from the boundary between the base steel sheet and the intermetallic compound layer to the boundary between the intermetallic compound layer and the aluminum plating layer. The thickness of the aluminum plating layer is defined as the distance from the boundary between the intermetallic compound layer and the aluminum plating layer to the surface of the aluminum plating layer.

More specifically, from the surface of the aluminum-plated steel sheet of interest to the surface of the base material steel sheet (the boundary between the base material steel sheet and the intermetallic compound layer), line analysis is performed on arbitrary 10 points by EPMA in the same manner as described above, The thickness of the aluminum plating layer and the thickness of the intermetallic compound layer are respectively measured, and the values obtained by averaging the obtained measured values at 10 locations are taken as the thickness of each layer.

<About the surface coating layer>
As schematically shown in FIGS. 1 and 2, the surface coating layer is formed as an upper layer on the surface of the aluminum-containing plating layer (aluminum plating layer) in the aluminum-plated steel sheet for butt welding. Typical examples of the form of the surface coating layer include a hot-dip plating layer, an electroplating layer, a thermal spraying layer, a coating film, and a powder-coated film (powder-baked layer). The form is not limited.

Such a surface coating layer may contain, as a C group element, one or two or more elements selected from the group consisting of Zn, Ti, V, Zr, and Ce, and/or compounds. preferable.

When the surface film layer is a coating film, the coating film may contain an organic binder. In addition, when the surface coating layer is a powder baking layer, the powder baking layer may contain an organic binder in addition to the simple substance and/or compound of the C group element.

When the surface coating layer contains a simple substance and/or compound of a C group element, an oxide of the C group element is formed on the surface due to reaction with moisture or oxygen at the interface between the surface coating layer and the atmosphere. When a simple substance or an oxide has solubility like a C group element, a sparingly soluble compound is formed after being dissolved in water or salt water under a corrosive environment. As a result, a protective effect against oxygen and chloride ions, which are corrosion-promoting factors, is exhibited, and an effect of further enhancing the corrosion resistance after painting is expected.

Regarding the content of the group C element in the surface coating layer, if the content of the group C element is too small, the effect of further improving the corrosion resistance after coating may not be sufficiently exhibited. From this point of view, the content of the group C elements in the surface coating layer is preferably 0.01 g/m ² or more per one side of the base steel sheet in terms of the total amount of the group C elements in terms of elements. The content of the C group elements in the surface coating layer is more preferably 0.1 g/m 2 or more, more preferably 0.2 g/m ² or ^more per one side of the base steel sheet, in terms of the total amount of the C group elements in terms of elements. is more preferable. On the other hand, if the content of the group C element is too high, the corrosion resistance after painting will be saturated, causing an increase in cost. From this point of view, the content of the group C elements in the surface coating layer is preferably 10 g/m ² or less per one side of the base steel sheet in terms of the total amount of the group C elements in terms of elements. The content of the C group elements in the surface coating layer is more preferably 5 g/m 2 or less, more preferably 3 g/m ^{2 or} less per one side of the base steel sheet, in terms of the total amount of the C group elements in terms of elements. More preferred.

Examples of compounds of C group elements include oxides, chlorides, sulfides, fluorides, hydroxides, carbides and nitrides containing C group elements. Specifically, as compounds of group C elements, zinc oxide, zinc bromide, zinc chloride, zinc fluoride, zinc hydroxide, titanium chloride, barium titanate, vanadyl acetylacetonate, vanadium acetylacetonate, vanadyl acetate, vanadyl sulfate, vanadium pentoxide, vanadium trioxide, vanadium dioxide, ammonium metavanadate, sodium metavanadate, zirconium oxide, ammonium zirconium carbonate, cerium oxide, cerium hydroxide, and hydrates of the above compounds; It is not limited.

Dissolved components in these surface coating layers (that is, simple substances and/or compounds of C group elements) precipitate on the weld metal when aluminum plated steel sheets for butt welding are butt welded together, and oxygen and water Intrusion of corrosive factors, such as , is suppressed, anodic dissolution of the plating layer is suppressed, and coating film swelling is reduced.

<Methods for Measuring Contents of Group A Elements, Group B Elements, and Group C Elements>
Here, the content of the group A element present in the intermetallic compound layer (IMC) 2, the content of the group B element that may be contained in the aluminum plating layer, and the content of the group C element that may be contained in the surface coating layer are It can be measured as follows.

The content of group A elements present in the intermetallic compound layer (IMC) 2 is determined by quantifying the intermetallic compound layer (IMC) 2 from the cross section by EPMA in the same manner as described above by embedding an aluminum-plated steel sheet in resin. It can be measured by analysis. Here, within the range of the thickness of the intermetallic compound layer (IMC) 2 × 10 mm field of view, quantitative analysis is performed at arbitrary 10 points, and the average value of the obtained 10 measurement values is taken as the content of each element. do.

The content of the group B element that can be contained in the aluminum plating layer is measured as follows.
In the same manner as above, the aluminum plating layer is measured from the cross section by EPMA. Regarding the aluminum plating layer, the positions are divided into range 1, range 2, range 3, . . . 1 point at any position in each range (if the range L is less than 1 μm, 1 point at any position in the range L, and if the thickness of the aluminum plating layer is less than 1 μm, at any position in the range 1 1 point) are measured, and the content (% by mass) of element X (X: element species detected by EPMA) is calculated by point analysis. Let p _xk be the content (% by mass) of element X in the k-th range, and a _x be the specific gravity of element X alone, then p _xk /Σ( _pxk /ax ₎ is the amount of element X attached in range k. Become. Here, Σ(p _xk /a _x ) is the sum of the values obtained by dividing the content of each element by the specific gravity of the element for all the elements detected in the range k. Assuming that the content of the B group element is q _k , q _k /Σ(p _xk / _ax ) is calculated for range 1, range 2, . and If multiple B group elements are detected, the calculated values for each are totaled.

The content of the C group element that can be contained in the surface coating layer is also measured by the same method as above. That is, the surface coating layer is measured by EPMA from a cross section. Let the content of the group C element be the sum of the contents of the group C elements detected in each range of 1 μm.

(Manufacturing method of aluminum-plated steel sheets for butt welding)
Next, a method for producing an aluminum-plated steel sheet for butt welding according to this embodiment will be described.

In the method for producing an aluminum plated steel sheet for butt welding according to the present embodiment, the chemical composition is adjusted in the steelmaking process so as to satisfy the chemical composition described above, and then continuous casting is performed to form a slab (base material). After that, the obtained slab (base material) is subjected to hot rolling, pickling, cold rolling, etc. to obtain a cold rolled steel sheet. Thereafter, the obtained cold-rolled steel sheet is used as a base steel sheet, and the surface of the base steel sheet is plated with aluminum by the method described above to obtain an aluminum-plated steel sheet. Part of the aluminum plating layer formed by such an aluminum plating treatment reacts with part of the base steel sheet to form an intermetallic compound layer (IMC) 1 .

<Method for Forming Intermetallic Compound Layer (IMC) 2>
As described above, the intermetallic compound layer (IMC) 2 is formed on at least one side or both sides of the steel plate end portion corresponding to the portion to be butt-welded (hereinafter also referred to as the “planned butt-welding portion”). formed in part. Preferred methods for forming the intermetallic compound layer (IMC) 2 on at least a portion of one or both surfaces of the steel plate ends in the portion to be butt welded include, for example, the following two forming methods.

[Method of Formation - Part 1]
A first method of forming the intermetallic compound layer (IMC) 2 is formed on at least a part of one or both sides of the end portion located around the aluminum plated steel sheet, on the surface of the aluminum plating layer of the portion to be butt welded. and removing the aluminum plating layer by a laser gouging method.

In the laser gouging method, the surface of the steel sheet to be processed is irradiated with a laser beam to melt the steel sheet. It is a processing method for gouging. Specifically, the assist gas is injected from behind while scanning the beam. In this forming method, such a laser gouging method is applied to the surface of the aluminum plating layer corresponding to the portion to be butt-welded of the aluminum-plated steel sheet, and the aluminum plating layer is heated with a laser to melt the steel sheet, assisting the molten product. Disperse with gas. At least a portion of the aluminum plating layer remaining without scattering becomes an intermetallic compound layer (IMC) 2 by the heat of the laser. As a result, an aluminum-plated steel sheet for butt welding on which an intermetallic compound layer (IMC) 2 is formed and which is used to form a butt weld member can be obtained.

In addition, the aluminum plating layer may remain on a part of the edge treated by the laser gouging method.

[Method of Forming - Part 2]
Another preferred method of forming the intermetallic compound layer (IMC) 2 on at least a portion of one or both sides of the steel plate end portion of the butt-welded portion is as follows.

A second method for forming the intermetallic compound layer (IMC) 2 is to extend at least a part of the area other than the edge of the steel sheet with respect to the surface of the aluminum plating layer formed on one or both sides of the base steel sheet. and a step of cutting the aluminum-plated steel sheet after laser gouging so that the portion subjected to the laser gouging process is positioned at the edge of the steel sheet. ing.

Specifically, the second forming method is the following method.
First, an aluminum-plated steel sheet is prepared by punching and cutting into a desired size. In the cut steel sheet, the surface of the aluminum plating layer formed on the base steel sheet is subjected to laser gouging treatment so that regions other than the ends of the steel sheet extend. As a result, an intermetallic compound layer (IMC) 2 is formed on the portion processed by the laser gouging method. Then, the aluminum-plated steel sheet after laser gouging is cut so that the portion where the intermetallic compound layer (IMC) 2 is formed is positioned at the edge of the steel sheet. As a result, an aluminum plated steel sheet for butt welding on which an intermetallic compound layer (IMC) 2 is formed and which is used to form a tailored blank can be obtained.

In the case of the second forming method, the width of the portion where the intermetallic compound layer (IMC) 2 is formed by laser gouging is preferably about 0.4 mm to 30 mm. The portion where the intermetallic compound layer (IMC) 2 is formed may be cut at a position near the center line of the portion where the intermetallic compound layer 2 (IMC2) is formed so as to have a desired width. It may be cut at a position other than the vicinity.

Also in the second forming method, the aluminum plating layer may remain on a part of the end portion which has been processed by the laser gouging method.

In addition, with respect to the method of forming the intermetallic compound layer (IMC) 2, the above description has dealt with the case of using the laser gouging method. A layer (IMC) 2 can be formed.

[Regarding the width of the intermetallic compound layer (IMC) 2]
In addition, the width of the portion where the intermetallic compound layer (IMC) 2 formed by the first formation method is formed (for example, from the position of the end of the aluminum plating layer in the right end portion of FIG. 2, the intermetallic The distance to the end position of the compound layer (IMC) 2) is preferably about 20% to 40% larger than half the width of the planned molten region (weld metal) after steel plate welding.

In addition, the width of the portion where the intermetallic compound layer (IMC) 2 is formed before cutting the steel plate formed by the second forming method is the width of the planned molten region (weld metal) after steel plate welding. It is preferably about 20 to 40% larger than the width.

When the width of the intermetallic compound layer (IMC) 2 is within the above range, mixing of a large amount of aluminum into the weld metal after butt welding the aluminum plated steel sheets for butt welding is further suppressed. As a result, the decrease in the tensile strength of the steel plate after hot stamping the manufactured butt-welded member is further suppressed.

Here, when the laser gouging method is used in the first formation method and the second formation method, the laser output from the laser oscillator is preferably 0.1 kW or more and 1.0 kW or less. If the laser output is less than 0.1 kW, the aluminum plating layer cannot be sufficiently removed, and there is a possibility that the welding strength will decrease when hot pressing the steel sheets that have been galvanized and welded. On the other hand, if the laser output exceeds 1.0 kW, the power consumption will be too large and the economic efficiency will decrease. Also, the laser scanning speed is preferably in the range of 6 m/min or more and 12 m/min or less. If the laser scanning speed is less than 6 m/min, productivity may be low. Moreover, when the laser scanning speed exceeds 12 m/min, the aluminum plating layer cannot be sufficiently removed, and the welding strength after hot pressing may decrease.

In addition, in the above-described first formation method and second formation method, when using the laser ablation method, it is preferable to use a Q-switched laser. The processing conditions are not particularly limited, but the laser scanning speed is preferably 5 m/min or more and 15 m/min or less. If the laser scanning speed is less than 5 m/min, the aluminum plating layer cannot be sufficiently removed, and the welding strength after hot pressing may decrease. On the other hand, if the laser scanning speed exceeds 15 m/min, the power consumption becomes too large and the economic efficiency is lowered.

The method for manufacturing the aluminum-plated steel sheet for butt welding according to the present embodiment has been briefly described above.

(About butt welding members)
The butt-welded member according to this embodiment is a welded member (tailored blank material). The butt-welded member according to the present embodiment may be one in which three or more aluminum-plated steel sheets for butt welding are welded with their ends having intermetallic compound layers (IMC) 2 butted against each other. .

The two or more aluminum-plated steel sheets for obtaining the butt-welded member may, for example, use steel sheets of the same strength class as the base material steel sheets, or use steel sheets of different strength classes as the base material steel sheets. can be anything. In addition, aluminum-plated steel sheets having the same thickness may be used for welding, or aluminum-plated steel sheets having different thicknesses may be used for welding.

As described above, the butt-welded member performs butt-welding with the end faces of the ends on which the intermetallic compound layer 2 (IMC2) is formed, butt-welding, so that the weld metal, especially the aluminum plating layer less aluminum contamination. Therefore, it is possible to suppress a decrease in the tensile strength of the steel sheet after hot stamping.

<Welding method for butt welding>
Here, the welding method for performing butt welding is not particularly limited, and various known welding methods can be used. Examples of such welding methods include welding methods such as laser welding (laser beam welding), arc welding, and electron beam welding. Arc welding includes plasma welding, TIG (Tungsten Insert Gas) welding, MIG (Metal Inert Gas) welding, MAG (Metal Active Gas) welding, etc. Plasma arc welding is preferred as arc welding. be done. Welding conditions may be appropriately selected according to target conditions such as the thickness of the steel plate to be used. Welding may also be performed while feeding a filler wire, if desired.

Moreover, the method of adding Ni, Cu, and Cr to the intermetallic compound layer (IMC) 2 is not limited to the inclusion of these elements in the base steel sheet. For example, these elements can be contained in the intermetallic compound layer (IMC) 2 after butt welding by including these elements in filler components used during butt welding.

The butt weld member according to the present embodiment has been briefly described above.

(About hot press-molded products)
The hot press-formed product (hot stamped product) according to the present embodiment is a butt-welded member (tailored blank material) obtained by butt-welding the aluminum-plated steel sheets for butt-welding according to the present embodiment. It is a molded product obtained by

Here, the aluminum plating layer of the butt-welded member prevents corrosion of the steel plate. In addition, even if the aluminum plating layer of the butt-welded member is heated to a high temperature when the steel plate that constitutes the butt-welded member is processed by hot press forming, the surface is oxidized to produce scale (iron scale). compounds). In addition, the aluminum plating layer of the butt-welded member has a higher boiling point and melting point than those of the plating coating made of organic materials and the plating coating made of other metallic materials (for example, zinc-based materials). Therefore, since the coating does not evaporate during hot press molding, molding at a high temperature is possible, and the moldability in hot press molding is further improved, making molding easier.

Such a hot press-formed product can be produced as follows.
First, a butt-welded member (tailored blank material) obtained by butt-welding the aluminum-plated steel sheets for butt-welding according to the present embodiment is heated to a temperature in the γ region to soften the butt-welded member. Then, using a mold, the softened butt-welded member is molded by a hot press method, cooled and quenched in the mold to obtain a hot press-formed product of the desired shape. . A hot press-formed product is quenched by heating and cooling, so that it has a high tensile strength of, for example, about 1500 MPa or more.

A heating method in the hot press method is not particularly limited, and various known heating methods can be applied. As such a heating method, for example, in addition to heating by a normal electric furnace and heating by a radiant tube furnace, it is possible to apply a heating method by infrared heating, electrical heating, induction heating, and the like.

A hot press-formed product is obtained by heating the aluminum plating layer of the steel sheet to a temperature higher than the melting point, thereby converting the aluminum plating layer into an intermetallic compound and providing protection against corrosion and oxidation of the steel sheet throughout the aluminum plating layer. For example, when silicon (Si) is contained in the aluminum plating layer, the aluminum plating layer melts when heated to the melting point or higher, and at the same time, due to interdiffusion with Fe, the Al phase becomes an intermetallic compound, That is, it changes into an Al--Fe alloy phase and an Al--Fe--Si alloy phase. The Al--Fe alloy phase and the Al--Fe--Si alloy phase have a high melting point of about 1150.degree. There are multiple types of Al--Fe phase and Al--Fe--Si phase, and when heated at a high temperature or for a long period of time, it changes to an alloy phase with a higher Fe concentration. These intermetallic compounds prevent corrosion and oxidation of the steel sheet.

In addition, as schematically shown in FIG. 4, the weld metal is moderately mixed with aluminum resulting from the intermetallic compound layer (IMC) 2 formed on at least part of both sides of the end of the steel plate. contain the same intermetallic compounds as above. In particular, by having the above alloy layer on the surface of the weld metal, the potential of the steel becomes noble, and the corrosion products containing Al that have migrated to the joint become dense, causing corrosion such as oxygen, water, and chloride ions. By suppressing permeation of factors, the post-coating corrosion resistance of the weld is excellent. In addition, when B group elements are present in the aluminum plating layer, or when C group elements are present in the surface coating layer, as shown in FIG. 4, these B group elements and Group C elements also come to be mixed in the weld metal. As a result, the post-coating corrosion resistance of the welded portion is further improved.

The state of the aluminum plating layer that is preferable as a hot press-formed product is a state in which the surface is alloyed and the Fe concentration in the alloy phase is not high. If unalloyed Al remains, only this portion will rapidly corrode, degrading the corrosion resistance after coating and making the coating film blister very easily, which is not preferable. On the other hand, if the Fe concentration in the alloy phase becomes too high, the corrosion resistance of the alloy phase itself is lowered, the corrosion resistance after coating is deteriorated, and the coating film is likely to blister. That is, the corrosion resistance of the alloy phase depends on the Al concentration in the alloy phase. Therefore, in order to improve the corrosion resistance after painting, it is preferable to control the state of alloying by the Al adhesion amount and the heating conditions.

The maximum temperature reached during hot pressing is not particularly limited, but is preferably within the range of 850°C to 1000°C, for example. In hot press forming, the highest temperature must be heated in the austenite region, so a temperature of about 900° C. to 950° C. is often adopted.

When the butt-welded member is heated to a temperature in the γ region, the metal structure of the base steel plate is at least partially, preferably entirely, an austenitic single-phase structure. After that, when press working is performed with a mold cooled by water cooling or the like, austenite is transformed into at least one of martensite and bainite by cooling under target cooling conditions. Then, in the obtained hot press-formed product, the metal structure of the base steel plate becomes any one of martensite, bainite, or martensite-bainite.

The hot press-formed product according to the present embodiment has been briefly described above.

Examples of the present invention are illustrated below, but the present invention is not limited to the following examples.

(Example 1)
An aluminum-plated steel sheet for butt welding was prepared using a 1470 MPa class steel sheet having a thickness of 1.6 mm as a base material steel sheet. More specifically, a test material having an aluminum plating weight per side of 80 g/m ² was prepared. The thickness of the aluminum plating layer of the test material was 28 μm, and the thickness of the intermetallic compound layer (IMC) 1 was 4 μm. The chemical composition of the base material steel plate of the test material is as shown in Table 1 below.

Aluminum plating layers were formed on both sides of the steel sheets shown in Table 1 by hot-dip plating. The temperature of the plating bath during hot-dip plating was 550 to 700° C. After the steel sheet was immersed in the plating bath, the coating weight was adjusted by a gas wiping method so that the coating weight was 80 g/m ² per side. The plating bath contained 9% by mass of Si and 2% by mass of Fe as elements other than Al.

Next, at least a part of both sides of the obtained aluminum-plated steel sheet was surface-treated by a laser gouging method with a width of 1.5 mm to prepare an aluminum-plated steel sheet for butt welding. Some of the steel sheets were either treated by laser ablation instead of laser gouging or left untreated. As a result, an intermetallic compound layer (IMC) 2 containing at least one of group A elements: Mn, Ni, Cu, and Cr was formed as shown in Table 2 below. Reference numerals A1 to A20 and a2 to a5 in Table 2 are those subjected to laser gouging treatment, and reference numerals A21 to A38 are those subjected to laser ablation treatment.

In Table 2 below, symbols A1 to A38 correspond to examples of the present invention in which an intermetallic compound layer (IMC) 2 containing a group A element is formed, and symbols a1 to a5 are intermetallic compound layers (IMC). 2 was not formed, and a comparative example in which the total content of group A elements in the intermetallic compound layer (IMC) 2 was below the lower limit of the present invention. The mass % and the like of each group A element are shown in the table. The content of the group A element in the intermetallic compound layer (IMC) 2 was measured by EPMA observation of the cross section according to the method described above.

Here, the conditions of the laser gouging method are as follows.
A semiconductor laser was used as a laser oscillator in the laser gouging process. A flat nozzle was followed from behind the laser irradiation part, and nitrogen gas was injected at a pressure of 0.54 MPa. A line beam with a width of 1.5 mm and a length of 1 mm was used. The laser output was appropriately adjusted within the range of 0.1 kW to 1.0 kW, and the laser scanning speed was appropriately adjusted within the range of 6 m/min to 12 m/min. A laser output of 0.3 kW and a laser scanning speed of 8 m/min were used. Under these conditions, the front and back surfaces of the ends to be butt-welded were treated. Due to the treatment, the Al—Si alloy did not exist in the plating layer, and the intermetallic compound layer remained.

Moreover, the conditions of the laser ablation method are as follows.
A Q-switched laser was used as the laser oscillator in the laser ablation process. The processing conditions are a pulse width of 70 ns, a nominal output of 450 W, a pulse energy of 51 mJ, and a laser scanning speed of 10 m/min.

Reference a1 of the comparative example was not subjected to the laser gouging method and the laser ablation method (untreated), and references a2 to a5 were performed at a laser scanning speed of 20 m/min in the laser gouging method.

Next, prepare two aluminum-plated steel sheets for butt welding corresponding to the same reference numerals in Table 2, which have been subjected to each treatment, and the end faces of the ends of the steel sheets subjected to the above treatment are butt welded by laser welding. was performed to produce a butt-welded member (tailored blank material). The laser welding conditions were as follows: no welding material was used, a fiber laser was used as the laser oscillator, the spot diameter was φ0.9 mm, the laser output was 3.2 kW, and the laser scanning speed was 3 m/min.

Next, the prepared butt-welded member (tailored blank material) is held in a furnace heated to 920 ° C. for 4 minutes, molded with a water-cooled mold under a load of 1500 MPa, quenched, and hot pressed into a flat plate. A molded article was produced. As a result, the hot press-formed product has a tensile strength of 1470 MPa class.

In the hot press method, the obtained butt-welded member (tailored blank material) is blanked (punched) as necessary, then heated to a temperature in the austenite region to be softened, and pressed in the softened state. Molded and then cooled.

Corrosion resistance after coating was examined and evaluated for each of the obtained hot pressed members as follows.

[evaluation]
(Corrosion resistance test after painting)
The resulting hot pressed member was cut into a length of 150 mm x width of 70 mm (a welded portion exists in the center in the length direction), and a test piece was treated with a chemical conversion treatment liquid (PB-SX35) manufactured by Nihon Parkerizing Co., Ltd. After chemical conversion treatment, an electrodeposition paint (Powernics 110) manufactured by Nippon Paint Co., Ltd. was applied to a coating thickness of 20 μm, and baked by heating at 170° C. for 20 minutes. The post-paint corrosion resistance of the obtained test piece was examined according to the method specified in JASO M609 established by the Society of Automotive Engineers of Japan.

That is, as schematically shown in FIGS. 5 and 6, the coating film was scratched with a cutter parallel to the longitudinal direction, and the coating film blister from the cut scratches after 480 cycles of the corrosion test at the butt weld. The width (maximum value on one side) was measured. Based on the measurement results, the post-painting corrosion resistance was evaluated according to the following grades Y1 to Y4. It should be noted that those with grades Y1 to Y3 were regarded as acceptable. The obtained results are also shown in Table 2.

[Corrosion resistance rating after painting]
Y1: swelling width 0 mm or more and less than 1 mm Y2: swelling width 1 mm or more and less than 2 mm Y3: swelling width 2 mm or more and less than 3 mm Y4: swelling width 3 mm or more

As is clear from Table 2 above, in A1 to A38, which correspond to the examples of the present invention, the evaluation results of corrosion resistance after painting reach the acceptable level, whereas in a1 to a5, which correspond to the comparative examples, the acceptable level is reached. Corrosion resistance after painting could not be obtained.

(Example 2)
An aluminum-plated steel sheet for butt welding was used, in which a 1470 MPa class steel sheet having a thickness of 1.6 mm was used as a base material steel sheet. More specifically, a test material having an aluminum plating weight per side of 80 g/m ² was prepared. The thickness of the aluminum plating layer of the test material was 28 μm, and the thickness of the intermetallic compound layer (IMC) 1 was 4 μm. The chemical compositions of the base material steel sheets of the test materials are as indicated by symbols S1 to S7 in Table 1 above.

Aluminum plating layers were formed on both sides of the steel sheets indicated by symbols S1 to S7 in Table 1 by hot-dip plating in the same manner as in Example 1. Here, a plurality of plating baths for use in the hot-dip plating method were prepared, and at least one B group element of Sr, Mg, and Ca was added. As a result, an aluminum plating layer containing a group B element was formed as shown in Table 3 below. The content of the B group element in the aluminum plating layer was controlled by the amount of the B group element added to the plating bath. Also, the content of the B group element in the aluminum plating layer was measured by EPMA observation of the cross section according to the method described above. In addition, for examples in which two or more compounds of the B group elements were added, the adhesion amount of each was described in the table.

An intermetallic compound layer (IMC) 2 is formed by a laser gouging method or a laser ablation method in the same manner as in Example 1 on at least a part of both sides of the end portion of the obtained aluminum-plated steel sheet, and is used for butt welding. An aluminum plated steel sheet was obtained. The content of the group A element in the intermetallic compound layer (IMC) 2 was measured by EPMA observation of the cross section according to the method described above. The contents of group A elements are summarized in Table 3 below. In Table 3, symbols B1 to B20 used the laser gouging method, and symbols B21 to B32 used the laser ablation method.

Using the obtained aluminum-plated steel sheets for butt welding, a butt-welded member was produced in the same manner as in Example 1, and the obtained butt-welded member was hot-pressed in the same manner as in Example 1. Corrosion resistance after painting was evaluated in the same manner as in Example 1 for the obtained hot press-molded product. The evaluation method and evaluation criteria are as shown in Example 1. The obtained evaluation results are summarized in Table 3 below.

As is clear from Table 3 above, the inclusion of the group B element in the aluminum plating layer resulted in a score of Y2 for the corrosion resistance after painting, indicating that the corrosion resistance after painting was further improved.

(Example 3)
Aluminum-plated steel sheets having a layer structure as shown in Table 4 below were produced in the same manner as in Example 2 using base material steel sheets indicated by symbols S7 to S34 in Table 1. In Table 4 below, the laser gouging method was used for C1 to C20, and the laser ablation method was used for C21 to C32. After that, a surface film layer containing a C group element as shown in Table 4 below was formed on the aluminum plating layer of the obtained aluminum plated steel sheet. In forming the surface coating layer, an aqueous dispersion of a compound such as an oxide of a group C element was applied to the surface of the aluminum plating layer with a roll coater, and then dried at a final plate temperature of 80°C. The content of the group C element in the surface treatment layer was controlled by the content of the compound of the group C element in the aqueous dispersion. In addition, the content of the group C element in the surface treatment layer was measured by EPMA observation of the cross section according to the method described above. For examples in which two or more types of compounds of the C group elements were added, the respective adhesion amounts were described in the table.

Using the obtained aluminum-plated steel sheets for butt welding, a butt-welded member was produced in the same manner as in Example 1, and the obtained butt-welded member was hot-pressed in the same manner as in Example 1. Corrosion resistance after painting was evaluated in the same manner as in Example 1 for the obtained hot press-molded product. The evaluation method and evaluation criteria are as shown in Example 1. The obtained evaluation results are summarized in Table 4 below.

As is clear from Table 4 above, the surface treatment layer contains a group C element, or the aluminum plating layer contains a group B element and the surface treatment layer contains a group C element. , the grade of corrosion resistance after painting was Y1, and it can be seen that the corrosion resistance after painting was further improved.

Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

Claims (7)

a base material steel plate;
an aluminum plating layer provided on one or both sides of the base steel sheet;
a first intermetallic compound layer containing aluminum formed between the base steel plate and the aluminum plating layer;
a second intermetallic compound layer formed on one side or both sides of the base steel plate on at least part of the edge portion located around the base steel plate;
with
The second intermetallic compound layer contains 0.01 to 1 mass% in total of one or more A group elements selected from the group consisting of Ni, Cu, Cr, and Mn,
On the second intermetallic compound layer (excluding the state in which the second intermetallic compound layer is removed ), the aluminum plating layer does not exist or has a reduced thickness. An aluminized steel sheet for butt welding in which an aluminum plating layer is present. Claim 1, wherein the aluminum plating layer contains one or more B group elements selected from the group consisting of Sr, Mg, and Ca in a total amount of 0.01 to 20 g/ ^m2 . The aluminum plated steel sheet for butt welding according to . One or more C group elements selected from the group consisting of Zn, Ti, V, Zr, and Ce are contained in the upper layer of the aluminum plating layer in a total amount of 0.01 to 10 g / m ² 3. The aluminum plated steel sheet for butt welding according to claim 1 or 2, wherein a surface coating layer is formed. The chemical composition of the base steel plate is expressed in mass %,
C: 0.10-0.60%
Si: 0.01-0.60%
Mn: 0.01-3.0%
P: 0.05% or less S: 0.05% or less Al: 0.01 to 1.0%
Ti: 0.001-0.10%
B: 0.0001 to 0.010%
The aluminum plated steel sheet for butt welding according to any one of claims 1 to 3, which contains N: 0.01% or less and the balance is Fe and impurities. The chemical composition of the base material steel plate is replaced with part of the remaining Fe, and further Ni: 0 to 2.0%, Cu: 0 to 1.0%, Cr: 0 to 1.0%. Or the aluminum plated steel sheet for butt welding according to claim 4, containing two or more kinds. A butt-welded member in which at least two aluminum-plated steel sheets for butt welding according to any one of claims 1 to 5 are butt-welded via the second intermetallic compound layer. A hot press-formed product obtained by hot press-forming the butt-welded member according to claim 6 .

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