JP7047387B2 - Manufacturing methods for steel sheets, butt welded members, hot pressed molded products, steel pipes, hollow hardened products, and steel plates. - Google Patents

Description

The present disclosure relates to a steel plate, a butt weld member, a hot pressed molded product, a steel pipe, a hollow hardened molded product, and a method for manufacturing a steel plate.

In recent years, in order to reduce CO ₂ gas emissions from the viewpoint of protecting the global environment, weight reduction of automobile bodies has become an urgent issue in the automobile field. On the other hand, studies on applying high-strength steel sheets are being actively conducted, and the strength of the steel sheets is increasing more and more.

Hot pressing molding (hereinafter, may be referred to as "hot stamping") is attracting attention as one of the techniques for molding automobile members. The hot stamp heats the steel sheet to a high temperature, press-molds it in a temperature range of Ar ₃ transformation temperature or higher, cools it rapidly by removing heat from the die, and causes transformation at the same time as molding under the press pressure. As a result, it is a technique capable of producing a press-molded product having high strength and excellent shape freezing property (hereinafter, may be referred to as "hot stamp molded product").

Further, in order to improve the yield and functionality of the press-formed product of the automobile member, the end faces of at least two steel plates are butted and joined by laser welding, plasma welding, etc. (hereinafter, "tailored blank"). (Sometimes referred to as "material") is applied as a material for pressing. Since the tailored blank material joins a plurality of steel plates according to the purpose, the plate thickness and strength can be freely changed in one component. As a result, the tailored blank material can improve the functionality of the automobile member and reduce the number of automobile members. Further, by hot stamping using a tailored blank material, it is possible to manufacture a high-strength press-molded product in which the plate thickness, strength and the like are freely changed.

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

So far, various steel sheets having a plating layer have been studied as steel sheets for forming a tailored blank material (see, for example, Patent Documents 1 to 7).

Japanese Patent No. 5237263 Japanese Patent No. 6034490 Japanese Patent No. 6053918 Special Table 2015-536246 Japanese Patent No. 5316670 Chinese Patent Application Publication No. 106334875 Japanese Unexamined Patent Publication No. 03-09492

However, the conventional steel sheet does not fully satisfy both the static strength of the joint and the corrosion resistance after painting of the welded portion, and there is room for further improvement.

An object of the present disclosure is to provide a steel plate and a steel pipe which can obtain a butt welded member having excellent static strength of a joint and excellent post-painting corrosion resistance around a weld metal portion even after being coated on the welded portion. It is a thing.

The means for solving the above problems include the following aspects.

<1> Base steel plate and
The aluminum coating layers provided on both sides of the base steel plate and
Have,
The aluminum coating layer remains in the removed portion from which at least a part of the aluminum coating layer has been removed, and in the region on the center side of the steel sheet from the removed portion, on at least a part of both sides of the peripherally located end portion. Remaining part is formed,
When the boundary between the removed portion and the remaining portion is viewed from a cross section, the aluminum coating layer outer surface side of the boundary has a portion having the shortest removal width, and the base material is larger than the aluminum coating layer outer surface side of the boundary. A steel sheet having the longest removal width on the steel sheet side.
<2> Of the remaining portion, the remaining portion in the region on the end face side of the steel sheet from the virtual line extending in the direction along the plate thickness direction from the portion having the longest removal width of the boundary, and the area center of gravity is the above. The steel sheet according to <1>, which has a residual portion that is less than 50% of the thickness of the aluminum coating layer.
<3> The steel plate according to <1> or <2>, wherein the removed portion has an exposed portion where the base steel plate is exposed.
<4> The base steel sheet is, in terms of mass%, C: 0.02% to 0.58%, Mn: 0.20% to 3.00%, Al: 0.005% to 1.00%, Ti. : 0% to 0.20%, Nb: 0% to 0.20%, V: 0% to 1.0%, W: 0% to 1.0%, Cr: 0% to 1.0%, Mo : 0% to 1.0%, Cu: 0% to 1.0%, Ni: 0% to 1.0%, B: 0% to 0.0100%, Mg: 0% to 0.05%, Ca : 0% to 0.05%, REM: 0% to 0.05%,
Bi: 0% to 0.05%, Si: 0% to 2.00%, P: 0.03% or less, S: 0.010% or less, N: 0.010% or less, and the balance: Fe and The steel sheet according to any one of <1> to <3>, which has a chemical composition composed of impurities.
<5> The aluminum coating layer has an aluminum plating layer and an intermetallic compound layer, and the average thickness of the aluminum plating layer is 8 μm to 35 μm, and the average thickness of the intermetallic compound layer is 3 μm to 10 μm. The steel plate according to any one of 1> to <4>.
<6> A butt having at least one of the steel plates according to any one of <1> to <5>, and butt welding of at least two steel plates via an end having the removed portion of the steel plate. Welding member.
<7> A hot pressed product obtained by hot pressing the butt welded member according to <6>.
<8> A steel pipe welded through the end of an open pipe made of the steel plate according to any one of <1> to <5>.
<9> A hollow hardened molded product obtained by quenching the steel pipe according to <8>.
<10> The method for manufacturing a steel sheet according to any one of <1> to <5>, which comprises a step of forming the removed portion by machining.

According to the present disclosure, a steel plate and a steel pipe can obtain a butt welded member having excellent static strength of a joint and excellent post-painting corrosion resistance around the weld metal portion even after being coated around the weld metal portion. Is provided.

It is a schematic cross-sectional view which shows an example of the end part of the steel plate of this disclosure. It is the schematic sectional drawing which shows the other example of the end part of the steel plate of this disclosure. It is an enlarged schematic cross-sectional view which shows an example of the end part of the steel plate of this disclosure. It is an enlarged schematic cross-sectional view which shows an example of the end part of the steel plate of this disclosure. It is the schematic sectional drawing which shows the other example of the end part of the steel plate of this disclosure. It is the schematic sectional drawing which shows the other example of the end part of the steel plate of this disclosure. NO. 2 is an enlarged schematic cross-sectional view showing an end portion of a steel plate of 2. NO. 3 is an enlarged schematic cross-sectional view showing an end portion of the steel plate of 3. NO. 4 is an enlarged schematic cross-sectional view showing an end portion of the steel plate of No. 4. NO. 5 is an enlarged cross-sectional view showing an end portion of the steel plate of 5. NO. 6 is an enlarged cross-sectional view showing an end portion of the steel plate of 6. NO. 7 is an enlarged cross-sectional view showing an end portion of the steel plate of 7. NO. 8 is an enlarged cross-sectional view showing an end portion of the steel plate of No. 8.

Hereinafter, an example of a preferred embodiment of the present disclosure will be described in detail.
In the present specification, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.
In the present specification, the content of the component (element) may be referred to as "C amount" in the case of the content of C (carbon), for example. In addition, the content of other elements may be described in the same manner.
In the present specification, the term "process" is used not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes. included.

As used herein, the term "aluminum coating layer" refers to the entire aluminum plating applied to both sides of the base steel sheet. That is, the aluminum coating layer represents the whole of the aluminum plating layer and the intermetallic compound layer.
In the present specification, the term "intermetallic compound layer" refers to a layer of an intermetallic compound formed between a base steel plate and the aluminum plating when aluminum plating is applied to both surfaces of the base steel plate. ..
In the present specification, the term "aluminum plating layer" refers to a region of aluminum plating applied on a base steel sheet excluding an intermetallic compound layer.
In the present specification, the term "cross section" of a steel sheet refers to a cross section cut in the plate thickness direction.

<Steel plate>
The steel plate of the present disclosure has a base steel plate and aluminum coating layers provided on both sides of the base steel plate.
Further, the aluminum coating layer is provided in a removed portion from which at least a part of the aluminum coating layer has been removed from at least a part of both sides of the end portion located around the periphery, and a region on the center side of the steel sheet from the removed portion. The remaining remaining part is formed.
When the boundary between the removed portion and the remaining portion is viewed from a cross section, the boundary has a portion having the shortest removal width on the outer surface side of the aluminum coating layer of the boundary, and is larger than the outer surface side of the aluminum coating layer of the boundary. A part of the base steel plate side has a part having the longest removal width.
The shape of the steel plate is not particularly limited.

FIG. 1 is a schematic cross-sectional view showing an example of an end portion of a steel plate of the present disclosure. Further, FIG. 2 is a schematic cross-sectional view showing another example of the end portion of the steel plate of the present disclosure.
In FIGS. 1 and 2, 100 is a steel plate, 12 is a base steel plate, 14 is an aluminum plating layer, 16 is an intermetallic compound layer, 18 is an aluminum coating layer, 22 is a removal portion, and 26 is a residual portion.
Further, 100A is the end face of the steel sheet, 100B is the portion having the shortest removal width at the boundary between the removing portion 22 and the remaining portion 26, and 100D is the portion having the longest removing width at the boundary between the removing portion 22 and the remaining portion 26. show. In addition, in FIGS. 1 and 2, the portion 100B having the shortest removal width at the boundary between the removing portion 22 and the remaining portion 26 is located at the edge on the outer surface side of the aluminum coating layer at the boundary between the removing portion 22 and the remaining portion 26. positioned.

As shown in FIG. 1, in the steel plate 100 of the present disclosure, aluminum coating layers 18 are formed on both surfaces of the base steel plate 12. Further, the aluminum coating layer 18 has an aluminum plating layer 14 formed on both surfaces of the steel plate, and an intermetallic compound layer 16 formed between the base steel plate 12 and the aluminum plating layer 14.

Further, as shown in FIGS. 1 and 2, a removing portion 22 is formed on both sides of the end portion of the steel plate 100, and a remaining portion 26 is formed in a region on the center side of the steel plate with respect to the removing portion 22. ..
Further, as shown in FIGS. 1 and 2, when the boundary between the removed portion 22 and the remaining portion 26 is viewed from a cross section, the boundary between the removed portion 22 and the remaining portion 26 is the boundary between the removed portion 22 and the remaining portion 26. The portion 100B having the shortest removal width at the boundary protrudes toward the end face 100A of the steel sheet. Further, this boundary extends from the portion 100B having the shortest removal width of the boundary toward the portion 100D having the longest removal width of the boundary. The cross-sectional shape of this boundary is inclined toward the remaining portion 26 and has a concave shape. Specifically, the boundary (that is, the end face of the remaining portion 26) is provided on the outer surface side of the aluminum coating layer, and the protruding portion (for example, the protruding portion having 100B as the top) protruding toward the end face side of the steel sheet and the protruding portion. It has a recessed portion (for example, a recessed portion having 100D as a bottom) which is provided on the base steel plate side and is recessed on the center side of the steel plate. That is, the boundary between the removal portion 22 and the remaining portion 26 has a portion 100B having the shortest removal width on the outer surface side of the aluminum coating layer at the boundary, and is most on the base steel plate side than the outer surface side of the aluminum coating layer at the boundary. It is formed to have a portion 100D having a long removal width.

In the steel plate of the present disclosure, as shown in FIG. 1, at least a part of the base steel plate 12 may be removed together with the aluminum coating layer 18 at the removal portion 22 at the end of the steel plate. Further, as shown in FIG. 2, the aluminum coating layer 18 may be removed, but the base steel plate 12 may not be removed.

FIG. 3 is an enlarged schematic cross-sectional view showing an example of the end portion of the steel plate of the present disclosure. In FIG. 3, D represents the removal depth. Further, W1 represents the removal width at the edge on the outer surface side of the aluminum coating layer of the boundary, and W2 represents the removal width on the base steel plate side of the edge on the outer surface side of the aluminum coating layer at the boundary.

The removal depth represents the vertical depth from the virtual line extending the outer surface side surface of the aluminum plating layer (the surface of the aluminum coating layer) toward the end surface of the steel sheet to the surface of the base steel sheet.
Further, the removal width represents the length in the vertical direction from the virtual line in which the end face of the steel plate is extended in the plate thickness direction to the boundary between the removal portion and the remaining portion.

Here, referring to FIG. 3, the removal depth D is a base steel sheet from a virtual line in which the surface of the outer surface side (outer surface side of the aluminum plating layer 14) of the aluminum coating layer 18 is extended in the direction of the end surface 100A of the steel sheet. Represents the vertical depth to the surface of.
Further, as shown in FIG. 3, the removal width has a removal width W1 and a removal width W2.
The removal width W1 represents the vertical length from the virtual line obtained by extending the end surface 100A of the steel sheet in the plate thickness direction to the portion 100B having the shortest removal width on the outer surface side of the aluminum coating layer at the boundary. That is, from the virtual line extending the end face 100A of the steel sheet in the plate thickness direction, among the protruding portions provided on the outer surface side of the aluminum coating layer at the boundary and protruding toward the end face side of the steel sheet, the protrusion most protrudes to the end face side of the steel sheet. It shows the vertical length to the portion (in FIG. 3, the protruding portion having 100B as the top).
The removal width W2 is a vertical length from a virtual line obtained by extending the end face 100A of the steel plate in the plate thickness direction to a portion 100D having the longest removal width on the base steel plate side rather than the outer surface side of the aluminum coating layer at the boundary. Represents. That is, from the virtual line extending the end face 100A of the steel plate in the plate thickness direction, the portion provided on the base steel plate side from the protruding portion and recessed toward the center side of the steel plate, which is the most recessed portion on the center side of the steel plate. (In FIG. 3, the vertical length up to (the recessed portion having 100D as the bottom) is shown.
That is, as shown in FIG. 3, in the steel sheet of the present disclosure, the shortest removal width W1 is a part of the outer surface side of the aluminum coating layer of the boundary when the boundary between the removal portion 22 and the remaining portion 26 is viewed from a cross section. Existing. Further, the longest removal width W2 exists in a part on the base steel plate side of the portion having the shortest removal width W1.
In FIG. 3, the portion 100B having the shortest removal width at the boundary between the removing portion 22 and the remaining portion 26 is located at the edge on the outer surface side of the aluminum coating layer at the boundary between the removing portion 22 and the remaining portion 26. There is. Further, the portion 100D having the longest removal width is located at the edge on the base steel plate side at the boundary between the removal portion 22 and the remaining portion 26.

Although an example of the end portion of the steel sheet of the present disclosure has been described above with reference to FIGS. 1 to 3, the steel sheet of the present disclosure is not limited thereto. In FIGS. 1 to 3, the portion 100B having the shortest removal width at the boundary is shown at the position of the edge on the surface side of the aluminum coating layer at the boundary between the removed portion and the remaining portion, but is limited to this portion. It is not something that can be done. The portion 100B having the shortest removal width of the boundary may be formed around the surface-side edge of the aluminum coating layer. That is, in FIGS. 1 to 3, the portion 100B having the longest removal width at the boundary (in FIGS. 1 to 3, the position of the edge on the outer surface side of the aluminum coating layer at the boundary between the removal portion 22 and the remaining portion 26) is , The tip is formed in a pointed shape, but may be round or square.
Further, in FIGS. 1 to 3, the portion 100D having the longest removal width at the boundary is shown at the position of the base steel plate which is the edge on the base steel plate side at the boundary between the removal portion 22 and the remaining portion 26. However, it is not limited to this part. The portion 100D having the longest removal width of the boundary may be the central portion of the boundary (for example, any portion of the aluminum coating layer 18).

Conventionally, a tailored blank material is known in which a steel plate plated with a metal mainly containing aluminum is butt-welded by a welding method such as laser welding or plasma welding. In this tailored blank material, a large amount of aluminum due to aluminum plating may be mixed in the weld metal portion. When the tailored blank material thus obtained is hot-stamped, the weld metal portion of the butt weld may be softened and the static strength may decrease. For example, in the hot stamped product after this hot stamping, it has been reported that the result of the tensile strength test of the portion including the weld metal portion shows that the weld metal portion is broken.

In order to avoid breakage of the weld metal portion, for example, in Patent Document 1, the aluminum plating layer of the welded portion to be welded is removed to form a steel plate in which an intermetal compound layer remains, and the welded portion of this steel plate is designated as a steel plate. A tailored blank material that has been butt welded is disclosed.

However, when the hot stamped product using the tailored blank material disclosed in Patent Document 1 is coated, the corrosion resistance after coating around the weld metal portion is low.

In the steel sheet disclosed in Patent Document 1, the shape of the boundary between the portion where the intermetallic compound layer remains and the portion where the aluminum plating layer is not removed is formed in the direction along the plate thickness direction. Therefore, a tailored blank material is formed from the steel plate disclosed in Patent Document 1, and in the hot stamped product using this tailored blank material, the portion where the aluminum plating layer is not removed is the remaining intermetallic compound layer. Does not cover the surface. Further, the thickness of the remaining intermetallic compound layer is thin. Due to these, when the steel sheet disclosed in Patent Document 1 is used, it is considered that the corrosion resistance after painting around the weld metal portion is inferior.

Further, in Patent Documents 2 to 6, the entire aluminum coating layer is removed in the welded portion to be welded to obtain a steel plate in which the base steel plate is exposed. Then, a tailored blank material in which the end portions of the planned welding portions of the steel sheet are butt-welded is disclosed.

However, when the hot stamped product using the tailored blank material disclosed in Patent Documents 2 to 6 is coated, the corrosion resistance after coating around the weld metal portion is low.

In the steel sheets disclosed in Patent Documents 2 to 6, the shape of the boundary between the exposed portion of the base steel plate and the portion where the aluminum coating layer is not removed is 1) in the direction along the plate thickness direction, or 2). The base steel plate side of this boundary is formed so as to be inclined toward the end face side of the steel plate. Therefore, when the steel plates disclosed in Patent Documents 2 to 6 are used, the portion where the aluminum coating layer is not removed does not cover the surface of the portion where the base steel plate is exposed due to the shape of these boundaries. Therefore, in the portion where the base steel plate is exposed, the base steel plate remains exposed. As a result, it is considered that the hot stamped products using the steel plates disclosed in Patent Documents 2 to 6 have low corrosion resistance after painting around the weld metal portion.

On the other hand, Patent Document 7 discloses a tube making method for polishing and removing a plated metal by injecting a liquid containing abrasive grains.
However, in the technique disclosed in Patent Document 7, the plating metal formed on the plated steel sheet is removed by injecting a liquid containing abrasive grains. Therefore, it is difficult to control the shape of the boundary between the portion where the plated metal is removed and the portion where the plated metal is not removed. As a result, in the pipe after pipe formation, the surface of the portion from which the plated metal is removed is not covered by the portion from which the plated metal is not removed, and it is considered that the corrosion resistance after painting around the welded portion is inferior.

On the other hand, the steel sheet of the present disclosure has a portion having the shortest removal width on the outer surface side of the aluminum coating layer of the boundary when the boundary between the removed portion and the remaining portion is viewed from a cross section. Further, it has a portion having the longest removal width on the base steel plate side of the portion having the shortest removal width. Since the shape of the boundary between the removed portion and the remaining portion is formed in such a shape, in the hot stamp molded product obtained from the steel plate of the present disclosure, the remaining portion is a part of the surface of the removed portion (removed portion and remaining portion). It becomes possible to cover the peripheral part of the boundary with the part). It is considered that this is because, for example, the heat generated during hot stamping melts the aluminum component in the remaining portion and covers a part of the surface of the removed portion. Therefore, it is considered that the corrosion resistance after painting around the weld metal portion is excellent. Further, at the removing portion, at least a part of the aluminum coating layer is removed. As a result, the amount of aluminum mixed in the weld metal is reduced, and the decrease in static strength is suppressed. Therefore, by using the steel plate of the present disclosure, it is considered that a tailored blank material having excellent static strength of the joint and excellent corrosion resistance after painting around the weld metal portion can be obtained.

Hereinafter, the steel sheet of the present disclosure will be described.

[Base steel plate]
The base steel sheet is a steel sheet before the aluminum coating layer is provided. The base steel sheet may be obtained by an ordinary method and is not particularly limited. The base steel plate may be either a hot-rolled steel plate or a cold-rolled steel plate. Further, the thickness of the base steel sheet may be set according to the purpose, and is not particularly limited. For example, the thickness of the base steel sheet may be 0.8 mm to 4 mm as the total thickness of the steel sheet after the aluminum coating layer is provided, and further, the thickness may be 1 mm to 3 mm. The thickness is mentioned.

As an example of the base steel sheet, for example, various properties related to mechanical deformation and fracture such as high mechanical strength (for example, tensile strength, yield point, elongation, drawing, hardness, impact value, fatigue strength, etc.) It is preferable to use a steel plate formed so as to have (meaning).

As an example of the preferable chemical composition of the base steel sheet, the following chemical composition can be mentioned, for example.
By mass%, C: 0.02% to 0.58%, Mn: 0.20% to 3.00%, Al: 0.005% to 1.00%, Ti: 0% to 0.20%, Nb: 0% to 0.20%, V: 0% to 1.0%, W: 0% to 1.0%, Cr: 0% to 1.0%, Mo: 0% to 1.0%, Cu: 0% to 1.0%, Ni: 0% to 1.0%, B: 0% to 0.0100%, Mg: 0% to 0.05%, Ca: 0% to 0.05%, REM: 0% to 0.05%, Bi: 0% to 0.05%, Si: 0% to 2.00%, P: 0.03% or less, S: 0.010% or less, N: 0. It has a chemical composition of 010% or less, and the balance: Fe and impurities.
Hereinafter, "%" indicating the content of the component (element) means "mass%".

(C: 0.02% to 0.58%)
C is an important element that enhances the hardenability of the steel sheet and mainly determines the strength after quenching. Furthermore _, it is an element that lowers the A3 point and promotes the lowering of the quenching treatment temperature. If the amount of C is less than 0.02%, the effect may not be sufficient. Therefore, the amount of C is preferably 0.02% or more. On the other hand, when the amount of C exceeds 0.58%, the toughness of the hardened portion is significantly deteriorated. Therefore, the amount of C is preferably 0.58% or less. It is preferably 0.45% or less.

(Mn: 0.20% to 3.00%)
Mn is a very effective element for enhancing the hardenability of a steel sheet and stably ensuring the strength after quenching. If the amount of Mn is less than 0.20%, the effect may not be sufficient. Therefore, the amount of Mn is preferably 0.20% or more. It is preferably 0.80% or more. On the other hand, if the amount of Mn exceeds 3.00%, not only the effect is saturated, but also it may be difficult to secure stable strength after quenching. Therefore, the amount of Mn is preferably 3.00% or less. It is preferably 2.40% or less.

(Al: 0.005% to 1.00%)
Al functions as a deoxidizing element and has an action of improving the soundness of the steel sheet. If the amount of Al is less than 0.005%, it may be difficult to obtain the effect of the above action. Therefore, the amount of Al is preferably 0.005% or more. On the other hand, if the amount of Al exceeds 1.00%, the effect of the above action is saturated, which is disadvantageous in terms of cost. Therefore, the amount of Al is preferably 1.00% or less.

(Ti: 0% to 0.20%, Nb: 0% to 0.20%, V: 0% to 1.0%, W: 0% to 1.0%)
Ti, Nb, V, and W are elements that promote mutual diffusion of Fe and Al in the aluminum-plated layer and the base steel sheet. Therefore, at least one of Ti, Nb, V, and W may be contained in the base steel sheet. However, if 1) the amount of Ti and Nb exceeds 0.20%, or 2) the amount of V and W exceeds 1.0%, the effect of the above action is saturated, which is disadvantageous in terms of cost. Therefore, the Ti amount and the Nb amount are often 0.20% or less, and the V amount and the W amount are preferably 1.0% or less. The Ti amount and Nb amount are preferably 0.15% or less, and the V amount and W amount are preferably 0.5% or less. In order to obtain the effect of the above action more reliably, it is preferable that the lower limit of the Ti amount and the Nb amount is 0.01% or more, and the lower limit values of the V amount and the W amount are 0.1% or more.

(Cr: 0% to 1.0%, Mo: 0% to 1.0%, Cu: 0% to 1.0%, Ni: 0% to 1.0%, B: 0% to 0.0100% )
Cr, Mo, Cu, Ni, and B are elements that are effective in enhancing the hardenability of the steel sheet and stably ensuring the strength after quenching. Therefore, one or more of these elements may be contained. However, even if the content of Cr, Mo, Cu, and Ni is more than 1.0% and the amount of B is more than 0.0100%, the above effect is saturated and it is disadvantageous in terms of cost. Therefore, the content of Cr, Mo, Cu, and Ni is preferably 1.0% or less. The amount of B is often 0.0100% or less, preferably 0.0080% or less. In order to obtain the above effect more reliably, it is preferable that the content of Cr, Mo, Cu, and Ni is 0.1% or more, and the content of B is 0.0010% or more.

(Ca: 0% to 0.05%, Mg: 0% to 0.05%, REM: 0% to 0.05%)
Ca, Mg, and REM have the effect of refining the morphology of inclusions in steel and preventing the occurrence of cracks during hot stamping due to inclusions. Therefore, one or more of these elements may be contained. However, when added in excess, the effect of miniaturizing the morphology of inclusions in steel is saturated, which only increases the cost. Therefore, the Ca amount is 0.05% or less, the Mg amount is 0.05% or less, and the REM amount is 0.05% or less. In order to obtain the effect of the above action more reliably, it is preferable to satisfy any one of Ca amount of 0.0005% or more, Mg amount of 0.0005% or more, and REM amount of 0.0005% or more.

Here, REM refers to a total of 17 elements of Sc, Y and lanthanoid, and the content of REM refers to the total content of these elements. In the case of lanthanoids, they are industrially added in the form of misch metal.

(Bi: 0% to 0.05%)
Bi is an element that becomes a solidified nucleus in the solidification process of molten steel and has an effect of suppressing segregation of Mn and the like segregated within the dendrite secondary arm spacing by reducing the dendrite secondary arm spacing. Therefore, Bi may be contained. In particular, for steel sheets that often contain a large amount of Mn, such as steel sheets for hot stamping, Bi is effective in suppressing deterioration of toughness due to segregation of Mn. Therefore, it is preferable to include Bi in such a steel grade. However, even if Bi is contained in an amount of more than 0.05%, the effect of the above action is saturated, which leads to an increase in cost. Therefore, the Bi amount is set to 0.05% or less. It is preferably 0.02% or less. In order to obtain the effect of the above action more reliably, the Bi amount is preferably 0.0002% or more. More preferably, it is 0.0005% or more.

(Si: 0% to 2.00%)
Si is a solid solution strengthening element and can be effectively utilized up to 2.00%. However, if Si is contained in an amount of more than 2.00%, there is a concern that the plating property may be defective. Therefore, when Si is contained, the amount of Si is preferably 2.00% or less. The preferred upper limit is 1.40% or less, more preferably 1.00% or less. The lower limit is not particularly limited, but 0.01% or more is preferable in order to more reliably obtain the effect of the above action.

(P: 0.03% or less)
P is an element contained as an impurity. If P is contained in an excessive amount, the toughness of the steel sheet tends to decrease. Therefore, the amount of P is preferably 0.03% or less. It is preferably 0.01% or less. The lower limit of the amount of P does not need to be specified, but it is preferably 0.0002% or more from the viewpoint of cost.

(S: 0.010% or less)
S is an element contained as an impurity and has an action of forming MnS and embrittlement of the steel sheet. Therefore, the amount of S is preferably 0.010% or less. A more desirable amount of S is 0.004% or less. The lower limit of the amount of S does not need to be specified, but it is preferably 0.0002% or more from the viewpoint of cost.

(N: 0.010% or less)
N is an element contained as an impurity, forming inclusions in steel and deteriorating toughness after hot stamping. Therefore, the amount of N is preferably 0.010% or less. It is preferably 0.008% or less, more preferably 0.005% or less. The lower limit of the amount of N does not need to be specified, but it is preferably 0.0002% or more from the viewpoint of cost.

(Remaining)
Fe and impurities. Here, the impurities refer to components contained in raw materials such as ore and scrap, or components mixed in the manufacturing process, which are not intentionally contained in the steel sheet.

[Aluminum coating layer]
The aluminum coating layer is composed of an aluminum plating layer formed on the outer surface side of the steel sheet and an intermetallic compound layer formed between the base steel sheet and the aluminum plating layer.

The method for forming the aluminum coating layer is not particularly limited. For example, the aluminum coating layer may be formed on both sides of the base steel sheet by a hot-dip plating method in which the base steel sheet is immersed in a molten metal bath containing mainly aluminum to form an aluminum coating layer.

(Aluminum plating layer)
The aluminum plating layer is a plating layer containing aluminum as a main component, and may contain 50% by mass or more of aluminum. Depending on the purpose, it may contain an element other than aluminum (for example, Si), or may contain impurities that are mixed in during the manufacturing process. Specifically, the aluminum-plated layer may contain, for example, 5% to 12% of Si (silicon) in mass%, and the balance may have a chemical composition consisting of aluminum and impurities. Further, it may contain 5% to 12% of Si (silicon) and 2% to 4% of Fe (iron) in mass%, and the balance may have a chemical composition consisting of aluminum and impurities.
When Si is contained in the above range, deterioration of processability and corrosion resistance can be suppressed. In addition, the thickness of the intermetallic compound layer can be reduced.

The thickness of the aluminum plating layer is not particularly limited in the region other than the end portion of the steel sheet, but for example, the average thickness is often in the range of 8 μm to 35 μm, and may be in the range of 15 μm to 30 μm. preferable. The thickness of the aluminum-plated layer represents the average thickness in the region on the center side of the steel sheet.

The aluminum-plated layer prevents corrosion of the steel sheet. Further, the aluminum-plated layer prevents the generation of scale (iron compound) due to the oxidation of the surface even when the steel sheet is heated to a high temperature when the steel sheet is processed by hot stamping. Further, the aluminum plating layer has a higher boiling point and melting point than a plating coating made of an organic material or a plating coating made of another metal material (for example, a zinc material). Therefore, when molding by hot stamping, the coating does not evaporate, so that the surface protection effect is high.

The aluminum plating layer can be alloyed with iron (Fe) in the steel sheet by heating during hot-dip plating and hot stamping. Therefore, the aluminum-plated layer is not always formed of a single layer having a constant component composition, but includes a partially alloyed layer (alloy layer).

(Intermetallic compound layer)
The intermetallic compound layer is a layer formed at the boundary between the base steel plate and the aluminum-plated layer when the base steel plate is plated with aluminum. Specifically, the intermetallic compound layer is formed by a reaction between iron (Fe) of a base steel sheet and a metal containing aluminum (Al) in a molten metal bath containing aluminum as a main component. The intermetallic compound layer is mainly formed of a plurality of types of compounds represented by Fe _x Al _y (x and y represent 1 or more). When the aluminum-plated layer contains Si (silicon), it is formed of a plurality of compounds represented by Fe _x Al _y and Fe _x Al _y Si _z (x, y, z represent 1 or more).

The thickness of the intermetallic compound layer is not particularly limited in the region other than the end portion of the steel sheet, but for example, the average thickness is often in the range of 3 μm to 10 μm, and is in the range of 4 μm to 8 μm. Is preferable. The thickness of the intermetallic compound layer represents the average thickness in the region on the center side of the steel sheet. The thickness of the intermetallic compound layer can be controlled by the temperature and immersion time of the molten metal bath containing mainly aluminum.

Here, the confirmation of the base steel plate, the intermetallic compound layer, and the aluminum plating layer, and the measurement of the thickness of the intermetallic compound layer and the aluminum plating layer are performed by the following methods.

Cut so that the cross section of the steel sheet is exposed, and polish the cross section of the steel sheet. The cross section of the polished steel sheet is line-analyzed from the surface of the steel sheet to the base steel sheet by an electron probe microanalyzer (FE-EPMA), and the aluminum concentration and the iron concentration are measured. The measurement conditions are an acceleration voltage of 15 kV, a beam diameter of about 100 nm, an irradiation time of 1000 ms per point, a measurement pitch of 60 nm, and a measurement distance of 30 μm to 30 μm in the plate thickness direction. It should be about 80 μm. It is preferable to measure the thickness of the base steel plate with an optical microscope.

As a measured value of the aluminum concentration in the cross section of the steel sheet, the region where the aluminum (Al) concentration is less than 2% by mass is determined to be the base steel plate, and the region where the aluminum concentration is 2% by mass or more is determined to be the intermetallic compound layer or the aluminum plating layer. do. Further, among the intermetallic compound layer 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 determined to be an aluminum plating layer.
The distance between the boundary of the base steel plate and the boundary of the aluminum plating layer is defined as the thickness of the intermetallic compound layer. Further, the distance from the boundary of the intermetallic compound layer to the surface of the steel plate on which the aluminum plating layer is formed is defined as the thickness of the aluminum plating layer. The sum of the thickness of the intermetallic compound layer and the thickness of the aluminum plating layer is the thickness of the aluminum coating layer.

The thickness of the aluminum-plated layer and the thickness of the intermetallic compound layer are measured by line analysis from the surface of the steel sheet to the surface of the base steel sheet (the boundary between the base steel sheet and the intermetallic compound layer) as follows.
For the thickness of the aluminum-plated layer, the thickness from the surface of the steel plate having the aluminum-plated layer to the intermetallic compound layer is determined at arbitrary five positions according to the above-mentioned determination criteria. Then, the average value of the obtained values is taken as the thickness of the aluminum plating layer.
The thickness of the intermetallic compound layer is the thickness from the boundary between the intermetallic compound layer and the aluminum-plated layer to the boundary between the intermetallic compound layer and the base steel plate at any five positions according to the above-mentioned criteria. demand. Then, the average value of the obtained values is taken as the thickness of the intermetallic compound layer.

[End of steel plate]
The steel sheet of the present disclosure has a removal portion from which at least a part of the aluminum coating layer has been removed at least a part of both sides of the end portion located around the steel sheet. Further, the region on the center side of the steel sheet from the removed portion has a residual portion in which the aluminum coating layer remains.

(Removal part)
The removal portion is formed on both sides of the end portion where the steel plate is to be welded. Further, the removed portion is formed on the end face side of the steel sheet with respect to the remaining portion. That is, the removed portion is formed in the range from the edge of the end face of the steel sheet to the remaining portion at the end portion to be welded.

The removed portion has the shortest removal width (hereinafter, may be simply referred to as "removal width W1") on the outer surface side of the aluminum coating layer of the boundary when the boundary between the removed portion and the remaining portion is viewed from a cross section. Has a part. Further, the base steel plate side has a portion having the longest removal width (hereinafter, may be simply referred to as “removal width W2”) than the outer surface side of the aluminum coating layer at the boundary.

The removal width W1 is preferably 0.2 mm to 5.0 mm on average. When the butt welding is laser welding, it is preferably 0.6 mm to 1.5 mm. When the butt welding is plasma welding, it is preferably 1.0 mm to 4.0.
Further, the removal width W2 is preferably 0.3 mm to 5.1 mm on average. When the butt welding is laser welding, it is preferably 0.7 mm to 1.6 mm. When the butt welding is plasma welding, it is preferably 1.1 mm to 4.1.

Further, the removal depth D is preferably 15 μm to 200 μm in consideration of the static strength of the joint. The lower limit of the removal depth D may be 20 μm or more, or 25 μm or more. The upper limit of the removal depth D may be 150 μm or less, 120 μm or less, or 100 μm or less.

Here, as a method for measuring the removal depth D, the removal width W1 and the removal width W2 from the tailored blank material and the hot stamped product, the following methods can be mentioned.
In the tailored blank material and the hot stamped product, a steel plate having a removing portion adjacent to the weld metal portion is cut in the plate thickness direction, and the cut cross section is observed with a scanning electron microscope (SEM). With reference to FIG. 3, the distances corresponding to W1, W2, and D in FIG. 3 may be measured.

Further, the measurement of the removal width W1 and the removal width W2 is an average value measured by observing the removed portion by SEM and measuring at any five cross sections. The method for measuring the width of the exposed portion is as follows.
The steel sheet is cut so that the cross section is exposed, embedded in resin, polished, and the cross section is enlarged by SEM. Then, with reference to a virtual line extending from the end face of the steel sheet in the direction along the plate thickness direction, the distance from this virtual line to the edge of the surface of the aluminum plating layer is measured and used as the removal width W1. Further, the distance from this virtual line to the portion having the longest removal width at the boundary between the removal portion and the remaining portion is measured and used as the removal width W2.

(Remaining part)
The remaining portion is a portion where the aluminum coating layer is not removed at the end portion where the steel sheet is scheduled to be welded, and is formed in a region on the center side of the steel sheet with respect to the removed portion.

In the cross section of the steel sheet, the area on the end face side of the steel sheet (that is, surrounded by the boundary and the virtual line) than the virtual line extending in the direction along the plate thickness direction from the portion of the remaining portion having the longest removal width of the boundary. The area center of gravity of the remaining portion in the region) is preferably less than 50% of the thickness of the aluminum coating layer. When the area center of gravity of the remaining portion in this region is less than 50% with respect to the thickness of the aluminum coating layer, the corrosion resistance after painting around the weld metal portion becomes more excellent. The smaller the area center of gravity is, the better the corrosion resistance after painting around the weld metal portion is preferable. Therefore, the center of gravity of the area may be 45% or less, or 35% or less. The lower limit value is not particularly limited, but is preferably 25% or more, for example, in terms of facilitating the shape of the remaining portion in this region.

Here, with reference to FIG. 4, the area center of gravity of the remaining portion near the boundary between the removed portion and the remaining portion will be described. FIG. 4 is an enlarged schematic cross-sectional view showing an example of the end portion of the steel sheet, and shows the vicinity of the boundary between the removed portion and the remaining portion. In FIG. 4, the portion 100B having the shortest removal width at the boundary between the removing portion 22 and the remaining portion 26 is located at the edge on the outer surface side of the aluminum coating layer at the boundary between the removing portion 22 and the remaining portion 26. There is. Further, the portion 100D having the longest removal width is located at the edge on the base steel plate side at the boundary between the removal portion 22 and the remaining portion 26.

The area center of gravity y is obtained as follows. First, at the boundary between the removal portion 22 and the remaining portion 26, a virtual line extending in the direction along the plate thickness direction is drawn from the portion 100D having the removal width W2 (the longest removal width). Let a be the vertical distance from this virtual line to the portion 100B having the shortest removal width W1 (shortest removal width) at the boundary between the removal portion 22 and the remaining portion 26. Further, in this virtual line, the boundary between the removing portion 22 and the remaining portion 26 from the boundary portion between the base material steel plate 12 and the aluminum coating layer 18 (that is, the boundary portion between the base material steel plate 12 and the intermetallic compound layer 16). Let b be the vertical distance to. Further, let h be the total thickness of the aluminum coating layer 18. At this time, the end face of the steel plate is more than the virtual line extending in the direction along the plate thickness direction from the remaining portion (that is, the portion having the longest removal width) in the area surrounded by the boundary between the removing portion 22 and the remaining portion 26 and the virtual line. The area center of gravity y of the remaining portion) located in the side region is expressed by the following equation.
(Equation) y = (h (a + 2b)) / (3 (a + b))
The above equation is applied, for example, when obtaining the area center of gravity y in the case of a shape belonging to a trapezoid (including a triangle) as shown in FIG.

In order to improve the corrosion resistance of the weld metal portion after painting, a is often 150 μm or less, and 100 μm or less. In the same respect, b is often 80 μm or less, and 40 μm or less.

If the cross-sectional shape of the boundary between the removed portion and the remaining portion is a shape other than a shape belonging to a trapezoid such as a non-straight line or a zigzag, it becomes difficult to calculate the geometrical center of gravity of the cross section. Therefore, when the cross-sectional shape of the boundary between the removed portion and the remaining portion has such a shape, the area center of gravity y may be calculated by image processing from the cross-sectional observation photograph.

The thickness h of the aluminum coating layer may be measured by a cross-sectional observation photograph by SEM. Further, the above-mentioned method for measuring the distance a and the distance b may be measured by a cross-sectional observation photograph by SEM.

In the steel sheet of the present disclosure, at least the removed portion from which the aluminum coating layer has been removed is formed at the end of the planned welded portion. If there is a large amount of residual aluminum coating layer within the range of the removal width W1 (specifically, the range on the end face side of the steel sheet from the top of the protruding portion provided on the outer surface side of the aluminum coating layer in the removal portion), welding is performed. The amount of aluminum mixed in the metal increases and the static strength becomes inferior. In this respect, for example, as shown in FIGS. 1 and 2, the removed portion may be removed so as to have an exposed portion where the base steel plate is exposed.

In the removed portion within the range of the removed width W1, the outer surface of the removed portion facing the plate thickness direction may be inclined with respect to the surface direction of the base steel plate in the region on the center side of the steel plate. Further, the direction may be along a direction parallel to the surface of the base steel plate in the region on the center side of the steel plate. The outer surface of the removed portion within the range of the removed width W1 facing the plate thickness direction is a direction along the direction parallel to the surface of the base steel plate on the center side of the steel plate in that the corrosion resistance around the weld metal portion is excellent after painting. It should be. Further, the removal width W2 is preferably present at the edge of the boundary on the base steel plate side (for example, the position of 100D shown in FIGS. 1 and 2) in that the corrosion resistance around the weld metal portion after painting is excellent. ..

Here, from the viewpoint of corrosion resistance after painting around the weld metal portion, the angle formed by the following virtual line A and the following virtual line B, and the angle on the remaining portion side may be in the following range. This angle may exceed 90 °. Further, this angle may be specifically in the range of 100 ° to 150 °. The preferred lower limit is often 120 ° or higher, preferably 125 ° or higher. Further, the preferable upper limit is often 135 ° or less, and preferably 140 ° or less.
For example, referring to FIG. 2, this angle is an angle formed by the surface of the base steel plate 12 and the boundary between the removed portion 22 and the remaining portion 26, and represents the angle formed on the remaining portion 26 side.
Virtual line A: A virtual line in the direction along the surface of the base steel sheet in the remaining portion.
Virtual line B: The portion having the shortest removal width on the outer surface side of the aluminum coating layer at the boundary between the removed portion and the remaining portion (the protruding portion provided on the outer surface side of the aluminum coating layer at the boundary and protruding toward the end face side of the steel sheet). Of these, the part that protrudes most toward the end face side of the steel sheet) and the part that has the longest removal width on the base steel sheet side than the outer surface side of the aluminum coating layer at the boundary (virtual line with the end face of the steel sheet extended in the plate thickness direction). A virtual line connecting the dents provided on the base steel plate side of the protruding part and dented on the center side of the steel plate, which is the most dented on the center side of the steel plate).

When the portion having the shortest removal width at the boundary between the removed portion and the remaining portion is a continuous portion, the portion on the outermost surface side of the aluminum coating layer shall be adopted as the shortest removal width. Further, when the portion having the longest removal width of the above boundary has, for example, a plurality of portions or is a continuous portion, the portion on the outermost surface side in the plate thickness direction is adopted as the longest removal width. It shall be.

As long as the weld metal portion of the tailored blank material and the hot stamped product does not break, at least a part of the aluminum coating layer remains in the removed portion within the removal width W1. May be present. Specifically, the following relationship may be satisfied as long as at least a part of the aluminum coating layer is allowed to remain. Within the range of the removal width W1, when the cross-sectional area of half the thickness of the base steel sheet is Sb and the cross-sectional area of the remaining aluminum coating layer is Sp, the ratio of the cross-sectional area Sp to the cross-sectional area Sb (Sp). / Sb) may be in the range of 3.5% or less. The ratio of Sp / Sb is preferably small, and may be 2.0% or less, or 1.0% or less.

The method for measuring the cross-sectional area Sb of half the thickness of the base steel sheet and the cross-sectional area Sp of the aluminum coating layer remaining within the range of the removal width W1 may be measured by a cross-sectional observation photograph by SEM.

Here, referring to FIG. 5, at the end portion of the steel plate shown in FIG. 5, the intermetallic compound layer 16 remains in the removing portion 22. In the range on the end face 100A side of the steel sheet (that is, within the range of the removal width W1) than the portion 100B having the shortest removal width on the outer surface side of the aluminum coating layer at the boundary between the removal portion 22 and the remaining portion 26, (Sp / Sb). ) Is 3.5% or less, the intermetallic compound layer 16 may remain in the removing portion 22. For example, at the end of the steel plate shown in FIG. 5, when the plate thickness of the base steel plate 12 is 1.6 mm and the thickness of the remaining intermetallic compound layer 16 is 20 μm, the cut with respect to the cross-sectional area Sb described above. The ratio of the area Sp (Sp / Sb) is 2.5%.

Further, referring to FIG. 6, at the end portion of the steel plate shown in FIG. 6, the removing portion 22 has an exposed portion where the base steel plate is exposed and a residual portion where at least a part of the aluminum coating layer 18 remains. It has 24 and. The residual portion 24 is provided in a region in contact with the edge of the end face 100A of the steel sheet. The ratio of the cross-sectional area Sp to the above-mentioned cross-sectional area Sb (Sp) in the range on the end face 100A side of the steel sheet from the portion 100B having the shortest removal width on the outer surface side of the aluminum coating layer at the boundary between the removing portion 22 and the remaining portion 26. If / Sb) is 3.5% or less, it may have an exposed portion and a residual portion. In this case, for example, as in the end portion of the steel plate shown in FIG. 6, the residual portion 24 and the residual portion 26 may be provided so as to be separated from each other with the exposed portion interposed therebetween.

For example, when a steel plate is punched to obtain a punched member, sagging may occur due to a cutting means such as a shear in a region including an edge of the steel plate among the ends located around the steel plate. At the portion where sagging occurs, the thickness of the steel sheet gradually decreases toward the edge of the steel sheet. Therefore, when the intermetallic compound layer and the aluminum plating layer are removed from the steel sheet in which sagging has occurred, for example, at the end of the steel sheet by cutting, grinding, etc., at least the intermetallic compound layer remains in the portion where sagging has occurred. I have something to do. The portion where at least the intermetallic compound layer remains is the residual portion.

That is, in the present specification, if the ratio (Sp / Sb) of the cross-sectional area Sp to the above-mentioned cross-sectional area Sb is 3.5% or less in the "removed portion from which at least a part of the aluminum coating layer has been removed". , Is a concept that includes the following forms.
(1) A form in which the base steel plate has only an exposed portion where the base steel plate is exposed, and at least a part of the base steel plate is removed (see, for example, FIG. 1). Alternatively, a form having an exposed portion but not removing the base steel plate (see, for example, FIG. 2).
(2) A form having a residual portion in which at least a part of the aluminum coating layer remains and no exposed portion in which the base steel plate is exposed (see, for example, FIG. 5).
(3) A form having both the above-mentioned exposed portion and the residual portion (see, for example, FIG. 6).

Next, an example of a preferable manufacturing method for the steel sheet of the present disclosure will be described. An example of a preferred method for producing a steel sheet of the present disclosure includes a step of forming a removing portion. The formation of the removal portion is not particularly limited, and either laser processing or machining may be used. As an example of a more preferable manufacturing method, there is a step of forming a removing portion by machining. Hereinafter, an example of a preferable method for removing at least a part of both sides of the end portion located around the steel sheet will be described.
In the following description, as an example, a form in which the removing portion has only the exposed portion where the base steel plate is exposed will be described as an example.

There is a step of removing the aluminum coating layer formed on both sides of the base steel plate by cutting or grinding at least a part of the end portion located around the steel plate to form an exposed portion where the base steel plate is exposed. It may be done (formation method A).

The forming method A is a method of forming an exposed portion at an end portion of a steel sheet, for example, as follows. First, as a steel plate before forming a tailored blank material, a steel plate cut to a desired size is prepared. Next, the aluminum coating layer formed on both sides of the base steel sheet is removed by cutting or grinding at least a part of both sides of the end portion of the cut steel sheet. Then, an exposed portion is formed at the end of the steel sheet.

The method of removing by cutting or grinding is not particularly limited. For example, the cutting or grinding may be performed by machining a grindstone, a tool, a slicing machine, an end mill, a metal saw or the like. Further, these methods may be combined to remove the aluminum coating layer to form an exposed portion where the base steel sheet is exposed. The tools used in these machining may be selected so that the boundary between the removed portion and the remaining portion has a desired concave shape.

As another method other than machining, removal by laser machining such as laser gouging can be mentioned. However, when an exposed portion is formed by laser processing such as laser gouging, heat is applied depending on the heat input, and the base steel plate of the portion where the exposed portion is formed is caused by water vapor in the atmosphere. Hydrogen may be mixed. Further, when the base steel sheet of the portion where the exposed portion is formed is rapidly cooled after the laser processing, martensite is generated in the metal structure of the base steel plate of this portion. This may cause delayed fracture at the end face of the steel sheet before welding.
On the other hand, when the exposed portion is formed by machining, the temperature rise of the base steel sheet of the portion where the exposed portion is formed is suppressed and martensite is not generated. In addition, since hydrogen does not enter, the occurrence of delayed fracture is suppressed. In this respect, it is preferable to employ machining cutting or grinding as a method for forming the exposed portion.
Further, when the exposed portion is formed by machining, there is no need to take measures against light shielding against the laser beam when performing laser machining such as laser gouging, which is advantageous in terms of cost and the like.
Further, when the shape of the boundary between the removed portion and the remaining portion is inclined toward the remaining portion side by laser processing to form a concave shape, the aluminum coating layer is heated by the heat of laser processing. Therefore, the aluminum coating layer is likely to be melted by the heat of laser processing, and it may be difficult to control the shape of the boundary so as to be inclined toward the remaining portion and to have a concave shape.

As long as the exposed portion is formed on at least a part of both sides of the end portion located around the steel plate, the order of forming the exposed portion on the end portion is not limited to the above-mentioned forming method A.
As an example of another preferable method of forming an exposed portion on at least a part of both sides of an end portion located around a steel plate, for example, the following method can be mentioned.

The aluminum-plated layer and the intermetallic compound layer formed on both sides of the base steel sheet were removed by cutting or grinding in at least a part of both sides of the area other than the end of the steel sheet to expose the base steel sheet. The step of forming the exposed portion and the exposed portion where the base steel plate is exposed on at least a part of both sides of the end portion of the steel plate by cutting the steel plate so that the exposed portion of the base steel plate is held at the end portion of the steel plate. It may have a step of forming the above (formation method B).

Specifically, the forming method B is as follows. First, a steel sheet that has been punched and cut to a desired size is prepared. Next, the aluminum coating layer formed on the base steel plate is removed from the cut steel plate by cutting or grinding to form an exposed portion where the base steel plate is exposed. The exposed portion is formed in a region other than the end portion of the steel sheet so as to extend in one direction, for example. Then, in the cut steel plate, the exposed portion of the base steel plate is cut so that the exposed portion follows the edge of the end face of the steel plate. The steel sheet obtained by cutting is a steel sheet before forming the tailored blank material.

In the case of the forming method B, among the widths of the exposed portions formed by removing the aluminum coating layer, the removal width (removal width before cutting) when the boundary between the removed portion and the remaining portion is viewed from the cross section is as follows. It should be a range.
The removal width of the portion having the shortest removal width is often 0.4 mm to 10.0 mm, preferably 1.2 mm to 8.0 mm. Further, the removal width of the portion having the longest removal width is often 0.6 mm to 10.2 mm, preferably 1.4 mm to 8.2 mm. The position for cutting the exposed portion may be a position near the center line of the exposed portion so as to have a desired width.

Of the width of the exposed portion of the base steel sheet formed by the above forming method A, the removal width of the portion having the shortest removal width is the width of the molten region (welded metal portion) after the steel plates are butt-welded. It should be 10% to 50% larger than half.
Of the width of the exposed portion of the base steel sheet before cutting of the steel sheet formed as in the above forming method B, the removal width of the portion having the shortest removal width is the molten region (welding) after the steel sheets are butt-welded. It should be 10% to 50% larger than half the width of the metal part).
Within these ranges, aluminum is suppressed from being mixed into the weld metal portion after the steel sheets are butt-welded, so that a decrease in static strength is suppressed.

<But welding member>
Next, the butt weld member (tailored blank material) will be described.
The tailored blank material is a welded member having at least one steel plate of the present disclosure and butt-welding at least two steel plates through an end having a removing portion of the steel plate of the present disclosure. As long as it has at least one steel plate of the present disclosure, it may be welded in a state where the end faces of the two steel plates are butted against each other, or it may be welded with the end faces of the three steel plates butted against each other. For example, the tailored blank material may be a welded member welded in a state where the end face of the end portion of the steel plate of the present disclosure having a removing portion and the end face of the end portion of the planned welding portion of another steel plate are butted against each other. Further, the tailored blank material may be welded, for example, in a state where the end faces of the ends having the removal portions of the two steel plates of the present disclosure are butted against each other, and the ends of the three steel plates of the present disclosure having the removal portions. Welding may be performed with the end faces of the portions butted against each other.

That is, the tailored blank material is a weld metal portion that includes at least one steel plate of the present disclosure and joins the ends of at least two steel plates to the steel plate in which the ends of at least two steel plates are arranged so as to face each other. It has a welded metal portion provided adjacent to the removed portion of the steel plate of the present disclosure. For example, specifically, the removing portion is provided on both sides of the two steel plates joined by the weld metal portion, which are located on both sides around the weld metal portion.

Two or more steel plates for obtaining a tailored blank material may be used in combination according to the purpose. As the two or more steel plates for obtaining the tailored blank material, for example, steel plates of the same strength class may be used, or steel plates of different strength classes may be used. Further, as the two or more steel plates, steel plates having the same thickness may be used, or steel plates having different thicknesses may be used.
Further, the two or more steel plates for obtaining the tailored blank material may be steel plates having the same removal width W1 and removal width W2 of the removal portion formed at the end of the steel plate, or may be different steel plates. Further, the steel plate may have the same shape of the boundary between the removed portion and the remaining portion of the steel plate, or may have different steel plates. Further, the steel sheet may have the same mode of the removed portion of the steel sheet, or may be a steel sheet having a different aspect. For example, as a combination in which the mode of the removed portion of the steel sheet is different, there is a combination of a mode in which the removed portion has an exposed portion and a residual portion and a mode in which the removed portion has only an exposed portion.

The welding method for performing butt welding is not particularly limited, and examples thereof include welding methods such as laser welding (laser beam welding), arc welding, and electron beam welding. Further, examples of arc welding include plasma welding, TIG (Tungsten Inert Gas) welding, MIG (Metal Inert Gas) welding, MAG (Metal Active Gas) welding, and the like, and examples of suitable arc welding include plasma welding. .. Welding conditions may be selected according to the desired conditions such as the thickness of the steel sheet to be used.
Further, welding may be performed while supplying a filler wire, if necessary.

As described above, the tailored blank material is butt-welded in a state where the end faces of the ends having the removed portions are butted. Therefore, in the weld metal portion, the amount of aluminum mixed due to the intermetallic compound layer and the aluminum plating layer is small. Further, since the removed portion in which the intermetallic compound layer does not exist is adjacent to the weld metal portion, the decrease in the tensile strength (static strength) of the joint is suppressed.

<Hot pressed molded product>
Next, a hot pressed molded product (hot stamp molded product) will be described.
The hot stamped product is a molded product obtained by hot stamping a butt welded member (tailored blank material) having at least one steel plate of the present disclosure. That is, the hot stamped product obtained by hot stamping contains at least one steel plate of the present disclosure, and the steel plate in which the ends of the at least two steel plates are arranged so as to face each other and the end of at least two steel plates. It is a weld metal portion for joining the portions, and has a weld metal portion provided adjacent to the removal portion of the steel plate of the present disclosure. For example, specifically, the removing portion is provided on both sides of the two steel plates joined by the weld metal portion, which are located on both sides around the weld metal portion.
The hot stamped product is a welded member in which at least two steel plates of the present disclosure are butt welded through an end having a removed portion in terms of the static strength of the joint and the corrosion resistance after painting around the weld metal portion. It is preferably a molded product obtained by hot stamping.

The hot stamped product can be manufactured as follows.
First, the tailored blank material is heated to a high temperature to soften the tailored blank material. Then, using a mold, the softened tailored blank material is molded and cooled by hot stamping and quenched to obtain a hot stamped product having a desired shape. The hot stamped molded product is quenched by heating and cooling to obtain, for example, a molded product having a high tensile strength of about 1500 MPa or more.

As a heating method for hot stamping, in addition to a normal electric furnace and a radiant tube furnace, a heating method by infrared heating, energization heating, induction heating or the like can be adopted.

In hot stamped articles, the aluminum-plated layer of the steel sheet is transformed into an intermetallic compound that provides protection against oxidation of the steel sheet upon heating. For example, when the aluminum plating layer contains silicon (Si), when the aluminum plating layer is heated, the Al phase becomes an intermetal compound, that is, an Al—Fe alloy phase due to mutual diffusion with Fe. , Al—Fe—Si alloy phase. The melting points of the Al—Fe alloy phase and the Al—Fe—Si alloy phase are high, 1000 ° C. or higher. There are a plurality of types of Al—Fe alloy phase and Al—Fe—Si alloy phase, and when heated at high temperature or for a long time, the alloy phase changes to an alloy phase having a higher Fe concentration. These intermetallic compounds prevent the steel sheet from oxidizing.

The maximum temperature reached during hot stamping is not particularly limited, but is preferably 850 ° C to 1000 ° C, for example. In the hot stamp, the maximum temperature reached is usually about 900 ° C. to 950 ° C. because it is heated in the austenite region.

In hot stamping, a tailored blank material heated to a high temperature is press-molded in a die cooled by water cooling or the like, and at the same time, quenched by cooling in the die. Further, if necessary, water may be directly sprayed onto the blank material through the gap of the mold to cool the blank material. Then, a hot stamped product having a desired shape can be obtained. The hot stamped product may be used as it is as a part, or may be used after descaling the welded portion by shot blasting, brushing, laser cleaning, or the like, if necessary.

When the tailored blank material is heated to a high temperature, the metal structure of the base steel sheet becomes at least a part, preferably the whole, austenite single-phase structure. Then, when press-molded in a die, austenite is transformed into at least one of martensite and bainite by cooling under the desired cooling conditions. Then, in the obtained hot stamped product, the metal structure of the base steel sheet becomes either martensite, bainite, or martensite-bainite.

Here, an example of the process from the production of the steel sheet to the production of the hot stamped product is as follows. The case where the removed portion has only the exposed portion where the base steel plate is exposed will be described as an example.
First, an aluminum coating layer is formed on both sides of the base steel sheet to obtain a steel sheet. At this time, an aluminum plating layer is formed on the base steel plate, and an intermetallic compound layer is formed between the base steel plate and the aluminum plating layer.

Next, the steel sheet having aluminum plating on both sides of the base steel sheet is wound into a coil. Next, the steel plate wound in a coil shape is pulled out and punched to obtain a punched member.

Next, the aluminum coating layer is removed from at least a part of both sides of the end portion located around the steel sheet to form an exposed portion of the base steel sheet to obtain the steel sheet of the present disclosure.
Here, the exposed portion formed at the end of the steel sheet may be formed in a state where the steel sheet is wound into a coil and then the steel sheet wound into the coil is pulled out. In this case, after the exposed portion is formed, a punching process is performed so that the exposed portion is held at the end of the steel sheet to obtain a punched member.
Further, the exposed portion formed at the end of the steel plate may be formed after the steel plate wound in a coil shape is pulled out and the pulled out steel plate is punched to form a punched member. In this case, an exposed portion may be formed at the end of the punched member. Further, after forming an exposed region in a portion other than the end portion of the punched member so as to extend in one direction, for example, the exposed region of the punched member is cut so that the exposed portion is formed at the end portion of the steel plate. You may.

Next, at least one punched member having an exposed portion formed at the end of the steel plate is prepared. For example, one punched member or two punched members having an exposed portion may be prepared.
Next, in a state where the ends of the punched members are butted, butt welding is performed to obtain a tailored blank material. Specifically, when two punched members having exposed portions are prepared, butt welding is performed with the ends having the exposed portions abutted to obtain a tailored blank material.

Next, the tailored blank material is heated in a heating furnace.
Next, the heated tailored blank material is pressed, molded and quenched by a pair of upper and lower dies.
Then, by removing it from the mold, the desired hot stamped product can be obtained.

The hot stamp molded product is useful, for example, for application to various automobile members such as automobile bodies as well as various members of industrial machines.

<Steel pipe>
Next, the steel pipe will be described.
The steel pipe is welded through the end of the open pipe made of the steel plate of the present disclosure. That is, the steel pipe is a steel pipe obtained by welding the steel plate of the present disclosure as an open pipe in a state where the end faces of the ends having the removed portions are butted against each other. That is, the steel pipe has at least one weld metal portion (that is, a weld metal portion that joins the end portions of the open pipes of the steel plate), and is removed from both sides of the tubular body made of the steel plate of the present disclosure adjacent to the weld metal portion. Has a part.

Examples of the steel pipe include those obtained as follows.
1) A steel plate having a first removing portion provided at the first end portion and a second removing portion provided at the second end portion is prepared. This single steel plate is formed into a tubular shape to form an open tube. Then, in the obtained open pipe, a steel pipe obtained by welding in a state where the end face of the end portion provided with the first removing portion and the end face of the end portion provided with the second removing portion are butted may be used.
2) Prepare two or more steel plates having a first removing portion at the first end and a second removing portion at the second end. When there are two steel plates, the end face of the end portion of the first steel plate provided with the first removing portion and the end face of the second steel plate having the second removing portion are butted against each other. Weld with to make a tailored blank material. Then, this tailored blank material is formed into a tubular shape to form an open tube. After that, in the obtained open pipe, the end face of the end portion of the first steel plate portion provided with the second unwelded removing portion and the second steel plate provided with the first unwelded removing portion. It may be a steel pipe obtained by welding in a state where the end face of the end portion of the portion is butted against each other.

When forming a steel pipe from a tailored blank material, the two or more steel plates forming the tailored blank material for forming the steel pipe are not limited to the above, and may be used in combination according to the purpose. Examples of the combination of two or more steel plates include the same combination as the steel plate described in the above-mentioned steel plate for forming a tailored blank material.

The method of forming into a tubular shape is not particularly limited, but any method such as a UOE method or a bending roll method may be used.
Further, the welding after forming into a tubular shape is not particularly limited, and examples thereof include laser welding; plasma welding; electric resistance welding, and electric sewing welding in which welding is performed by high frequency induction heating welding.

<Hollow hardened molded product>
Next, a hollow hardened molded product will be described.
The hollow hardened molded product (hereinafter, may be referred to as “hollow hot stamp molded product”) is a steel pipe formed from the steel plate of the present disclosure or a tailored blank material obtained by butt welding the steel plate of the present disclosure. Is a hollow molded product obtained by quenching.
That is, the hollow hardened molded product obtained by hot stamping the steel pipe has at least one weld metal portion (that is, a weld metal portion that joins the ends of the steel plates) and is adjacent to the weld metal portion. The hollow molded body made of the steel plate of the present disclosure has removal portions on both sides.

The hollow hardened molded product is obtained, for example, as follows.
A steel pipe obtained by using the steel plate of the present disclosure is formed by a bender. Next, it is heated by a heating furnace, energization heating, or high frequency induction heating. Since the temperature for heating the steel pipe needs to be in the austenite region, it is often set to, for example, 850 ° C to 1000 ° C, and preferably 900 ° C to 950 ° C. Next, the heated steel pipe is cooled by water cooling or the like and quenched.
In addition, molding and quenching may be performed at the same time. This is called three-dimensional hot bending quenching (3DQ). For example, the steel pipe is heated and deformed by applying a load, and immediately after that, it is cooled by water cooling or the like. By going through these processes, the desired hollow hardened molded product can be obtained. The hollow hardened molded product may be used as it is as a part. Further, if necessary, the welded portion may be descaled (for example, shot blasting, brushing, laser cleaning, etc.) before use.

The use of the hollow hardened molded product of the present disclosure is not particularly limited, and examples thereof include various automobile members such as automobile bodies and various members of industrial machines. Specific examples of automobile members include various pillars; reinforcements such as stabilizers, door beams, roof rails and bumpers; frames; and various parts such as arms.

Hereinafter, examples of the present disclosure will be illustrated, but the present disclosure is not limited to the following examples.
It is clear that a person skilled in the art can come up with various modifications or amendments within the scope of the ideas described in the claims, and of course, these are also the technical scope of the present disclosure. It is understood that it belongs to.

<Example>
As the test material below, a steel plate having a strength class of 1470 MPa class after hot stamping, a quadrangle having a side of 15 cm, and a plate thickness of 1.6 mm was used.
Test material 1: A test material 1 having a plating basis weight of 80 g / m ² per side was prepared. The thickness of the aluminum-plated layer of the test material 1 is 28 μm, and the thickness of the intermetallic compound layer is 4 μm. The chemical composition of the base steel sheet of the test material 1 is as shown in Table 1.
Test material 2: A test material 2 having a plating basis weight of 60 g / m ² per side was prepared. The thickness of the aluminum-plated layer of the test material 2 is 22 μm, and the thickness of the intermetallic compound layer is 4 μm. The chemical composition of the base steel plate of the test material 2 is the same as that of the test material 1.

Next, on both sides of the end portion of the steel sheet, the aluminum coating layer was cut off by an end mill over a total length of 15 cm on only one of the four sides. A carbide cutter with a reverse taper shape was used as the tool for the end mill. The blade diameter is φ5 mm and the blade length is 1 mm. The removal depth was adjusted in the range of 26 μm to 60 μm. The removal width is the removal width of the outer surface side of the aluminum coating layer of the boundary (removal width W1 in Table 2) and the outer surface side of the aluminum coating layer of the boundary when the boundary between the removed portion and the remaining portion is viewed from the cross section. The removal width (removal width W2 in Table 2) on the base steel plate side was adjusted to be the value shown in Table 2. Further, the shape of the one-sided portion when the boundary between the removed portion and the remaining portion is viewed from the cross section is the shape shown in FIGS. 7 to 13. Table 2 shows the prepared steel sheets. In addition, No. In No. 5, the test material 2 was used as No. Test materials 1 were used except for 5.

Next, two steel sheets that had been subjected to each removal treatment were prepared, the end faces of the ends of the steel sheets that had undergone the removal treatment were abutted against each other, and butt welding was performed by laser welding to prepare a tailored blank material. The conditions for laser welding were a spot diameter of Φ0.9 mm, a laser output of 3.2 kW, and a laser scanning speed of 3 m / min, using a fiber laser as the oscillator without using a filler wire.
Next, the prepared tailored blank material was held in a furnace heated to 920 ° C. for 4 minutes, then molded with a water-cooled mold and quenched to prepare a flat plate hot stamped product. As a result, the hot stamp molded product has a tensile strength of 1470 MPa class.
Here, the rotation speed of the end mill used for cutting removal was set to 10000 rpm.

The remaining portions a (distance a), b (distance b), and h (thickness h of the aluminum coating layer) in Table 2 were measured by SEM observation to determine the area center of gravity y.

[evaluation]
(Corrosion resistance test after painting)
After the hot stamp molded product obtained above was subjected to chemical conversion treatment, electrodeposition coating was performed, and a corrosion resistance test was performed after coating. The chemical conversion treatment was carried out with a chemical conversion treatment liquid PB-SX35T manufactured by Nihon Parkerizing Co., Ltd. Then, as the electrodeposition paint, a cationic electrodeposition paint Powernics 110 manufactured by Nippon Paint Co., Ltd. was used, and the electrodeposition coating was performed with a target of an electrodeposition film thickness of about 15 μm. After washing with water, it was heated at 170 ° C. for 20 minutes and baked to prepare a test plate. The size of the test plate was 65 mm in length and 100 mm in width (the welded portion is in the center of the width).
Using this test plate, the automobile parts appearance corrosion test JASO M610-92 was used to evaluate the corrosion resistance after painting under the corrosion condition after 360 cycles (120 days).

The evaluation of corrosion resistance after painting was performed by visually determining the ratio of red rust to the red rust occurrence rate (rounded off) around the weld metal part and the weld metal part according to the following criteria. Evaluation B (○) is allowed.
-criterion-
A (◎): Red rust occurrence rate 25% or less B (○): Red rust occurrence rate 26% to 50%
C (△): Red rust occurrence rate 51% to 75%
D (×): Red rust occurrence rate 76% to 100%

(Joint static strength)
From the obtained hot stamped product, a dumbbell-shaped test piece having a welded portion was collected as a test piece for a tensile strength test. The test piece had a parallel portion distance of 50 mm and a width of the parallel portion of 25 mm, and was cut out so as to have a welded portion in the central portion of the parallel portion over the entire width so as to be orthogonal to the longitudinal direction. A static tensile strength test was carried out using this test piece. Judgment was made according to the following criteria. Evaluation B (○) is allowed.
-criterion-
A (◎): 1500 MPa or more B (○): 1400 MPa or more and less than 1500 MPa C (Δ): 1300 MPa or more and less than 1400 MPa D (×): less than 1300 MPa

In Table 2, the notations "A" to "G" in the removed portion type column indicate the following shapes of the boundary between the removed portion and the remaining portion in the cross section of the end portion of the steel sheet.

"A": No removal part (Aluminum coating layer is not removed; Test material 1 remains).
"B": See FIG. The removed portion has an exposed portion in which a part of the base steel plate is removed and the base steel plate is exposed. The boundary between the removed portion and the remaining portion extends in the direction along the plate thickness direction. The removal width (W1) on the surface side of the aluminum coating layer and the removal width (W2) on the base steel plate side are the same (W1 = W2).
"C": See FIG. The removed portion has an exposed portion in which a part of the base steel plate is removed and the base steel plate is exposed. The boundary between the removed part and the remaining part is inclined, the edge on the aluminum coating layer side of the boundary is located on the center side of the steel plate, and the edge on the base steel plate side of the boundary is located on the end face side of the steel plate. There is. The removal width (W1) on the surface side of the aluminum coating layer is larger than the removal width (W2) on the base steel plate side (W1> W2).

"D": See FIG. The removed portion has an exposed portion in which a part of the base steel plate is removed and the base steel plate is exposed. The boundary between the removed portion and the remaining portion has a protruding portion where the edge on the outer surface side of the aluminum coating layer protrudes most toward the end surface side of the steel sheet. The apex of the protruding portion is the portion having the shortest removal width (W1). Further, the edge on the base steel plate side has the most recessed recessed portion on the center side of the steel plate. The bottom of the recess is the portion with the longest removal width (W2). W1 is smaller than W2 (W1 <W2).
"E": See FIG. The removed portion has an exposed portion in which the intermetallic compound layer is removed and the base steel plate is exposed. The boundary between the removed portion and the remaining portion has a protruding portion where the edge on the outer surface side of the aluminum coating layer protrudes most toward the end surface side of the steel sheet. The apex of the protruding portion is the portion having the shortest removal width (W1). Further, the central portion of the boundary between the removed portion and the remaining portion is an aluminum-plated layer portion, and has the most recessed recessed portion on the central side of the steel sheet. The bottom of the recess is the portion with the longest removal width (W2). Further, the boundary between the removed portion and the remaining portion has a step formed on the base steel plate side with respect to the portion having the removed width W2. W1 is smaller than W2 (W1 <W2).
"F": See FIG. The removed portion has an exposed portion in which a part of the base steel plate is removed and the base steel plate is exposed. The boundary between the removed portion and the remaining portion has a protruding portion in which the edge on the surface side of the aluminum coating layer protrudes most toward the end face side of the steel sheet. The apex of the protruding portion is the portion having the shortest removal width (W1). Further, the edge on the base steel plate side has the most recessed recessed portion on the center side of the steel plate. The bottom of the recess is the portion with the longest removal width (W2). However, W2 is shorter than W2 of the removal unit type "D". W1 is smaller than W2 (W1 <W2).
"G": See FIG. The removed portion has an exposed portion in which a part of the base steel plate is removed and the base steel plate is exposed. The boundary between the removed portion and the remaining portion has a protruding portion in which the edge on the surface side of the aluminum coating layer protrudes most toward the end face side of the steel sheet. The apex of the protruding portion is the portion having the shortest removal width (W1). Further, the central portion of the boundary between the removed portion and the remaining portion is an aluminum-plated layer portion, and has the most recessed recessed portion on the central side of the steel sheet. The bottom of the recess is the portion with the longest removal width (W2). Further, the boundary between the removed portion and the remaining portion is inclined toward the end face side of the steel plate on the base steel plate side of the portion having the longest removal width. W1 is smaller than W2 (W1 <W2).

"H": See FIG. The removed portion has an exposed portion in which a part of the base steel plate is removed and the base steel plate is exposed. The boundary between the removed portion and the remaining portion has a protruding portion in which the periphery of the edge on the surface side of the aluminum coating layer protrudes toward the end face side of the steel sheet. The protruding portion is continuously formed in the plate thickness direction. The protruding portion has a portion having the shortest removal width (W1). Further, it has a recessed portion on the center side of the steel plate in the range extending from the protruding portion to the base steel plate side to the aluminum plating layer, the intermetallic compound layer, and the base steel plate. The recessed portion is continuously formed in the plate thickness direction. The recessed portion has a portion having the longest removal width (W2). W1 is smaller than W2 (W1 <W2).

As shown in Tables 2 and 3, No. With the test material 1 as it is, the corrosion resistance after painting around the weld metal portion is excellent. However, the static tensile strength was inferior due to the large amount of aluminum mixed in the weld metal.
As shown in Tables 2 and 3, No. 2 and No. In No. 3, the aluminum plating layer is removed at the end of the steel sheet. Therefore, the amount of aluminum mixed in the weld metal is reduced, and the static tensile strength is excellent. However, when the boundary between the removed portion and the remaining portion is viewed from the cross section, the cross-sectional shape of the boundary is formed as shown in FIGS. 7 and 8, respectively. Therefore, the corrosion resistance after painting around the weld metal part was inferior.

On the other hand, as shown in Tables 2 and 3, No. 4-No. In No. 8, when the boundary between the removed portion and the remaining portion is viewed from the cross section, the cross-sectional shape of the boundary is such that the outer surface side of the aluminum coating layer of the remaining portion protrudes to the end face side of the steel plate and the base steel plate side is to the center side of the steel plate. It is dented. Therefore, it is considered that a part of the remaining part covers a part of the surface of the removed part, and the corrosion resistance after painting around the weld metal part is excellent. Further, since the aluminum plating layer is removed, the amount of aluminum mixed in the weld metal is small, and the static tensile strength is excellent.

12 Base steel plate 14 Aluminum plating layer 16 Intermetallic compound layer 18 Aluminum coating layer 22 Removal part 26 Remaining part 100 Steel plate

Claims (10)

Base steel plate and
The aluminum coating layers provided on both sides of the base steel plate and
Have,
The aluminum coating layer remains in the removed portion from which at least a part of the aluminum coating layer has been removed, and in the region on the center side of the steel sheet from the removed portion, on at least a part of both sides of the peripherally located end portion. Remaining part is formed,
When the boundary between the removed portion and the remaining portion is viewed from a cross section, the aluminum coating layer outer surface side of the boundary has a portion having the shortest removal width, and the base material is larger than the aluminum coating layer outer surface side of the boundary. It has a part with the longest removal width on the steel plate side,
At the shortest removal width, the outer surface of the removal portion facing the plate thickness direction is along the direction parallel to the surface of the base steel sheet in the region on the central side of the steel plate.
Of the remaining portion, the remaining portion in the region on the end face side of the steel sheet from the virtual line extending in the direction along the plate thickness direction from the portion having the longest removal width of the boundary, and the area center of gravity is the aluminum coating layer. A steel sheet having a residual portion that is less than 50% of the thickness of the steel sheet. The steel sheet according to claim 1, wherein the difference between the longest removal width and the shortest removal width is 0.06 mm or more. The steel plate according to claim 1 or 2 , wherein the removal portion has an exposed portion where the base steel plate is exposed. The base steel sheet is by mass%
C: 0.02% to 0.58%,
Mn: 0.20% to 3.00%,
Al: 0.005% to 1.00%,
Ti: 0% to 0.20%,
Nb: 0% to 0.20%,
V: 0% to 1.0%,
W: 0% to 1.0%,
Cr: 0% to 1.0%,
Mo: 0% to 1.0%,
Cu: 0% to 1.0%,
Ni: 0% to 1.0%,
B: 0% to 0.0100%,
Mg: 0% -0.05%,
Ca: 0% to 0.05%,
REM: 0% to 0.05%,
Bi: 0% to 0.05%,
Si: 0% to 2.00%,
P: 0.03% or less,
S: 0.010% or less,
The steel sheet according to any one of claims 1 to 3 , which has a chemical composition of N: 0.010% or less and the balance: Fe and impurities. The aluminum coating layer has an aluminum plating layer and an intermetallic compound layer, and the average thickness of the aluminum plating layer is 8 μm to 35 μm, and the average thickness of the intermetallic compound layer is 3 μm to 10 μm. The steel plate according to any one of claims 4 . A butt-welded member having at least one steel plate according to any one of claims 1 to 5 , and butt-welding at least two steel plates via an end portion of the steel plate having the removed portion. A hot pressed molded product obtained by hot pressing the butt welded member according to claim 6 . A steel pipe welded through an end portion of an open pipe made of the steel plate according to any one of claims 1 to 5 . A hollow hardened molded product obtained by quenching the steel pipe according to claim 8 . The method for manufacturing a steel sheet according to any one of claims 1 to 5 .
A method for manufacturing a steel sheet, which comprises a step of forming the removed portion by machining.

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