JP2018090879A - Steel plate for hot press molding, method for producing hot press molding, and hot press molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot press molding having excellent adhesion to a coating formed after hot press molding.SOLUTION: A steel plate for hot press molding is used for hot press molding. The steel plate has, on at least one side of a base steel plate, in order from the base steel plate side, a zinc plating layer and an Al layer. The amount of attachment of Al to the Al layer is 0.4 g/mor more.SELECTED DRAWING: None

Description

  The present invention relates to a steel plate for hot press forming, a method for producing a hot press formed product, and a hot press formed product. Specifically, the present invention relates to a hot press-molded product that requires high strength, such as the body and parts of various automobiles, and hot press-molding useful as a material for producing the hot press-formed product. It relates to a steel plate.

  In recent years, in order to reduce the weight of automobiles, high-strength steel sheets having a tensile strength exceeding, for example, 980 MPa have been applied to automobile bodies and parts. On the other hand, with the increase in strength of steel sheets, problems such as a decrease in mold life during part processing and part shape variations due to springback are increasing. In order to solve the above problems, a molding method called hot press molding or hot stamping has been developed. Hot press forming is a method in which a steel sheet is heated to a temperature equal to or higher than the Ac1 transformation point (for example, about 900 ° C.) to become austenite, which is easy to form and then press formed in a high temperature range and quenched. According to the hot press forming, the deformation resistance of the steel sheet can be reduced, so that the above-described problem of spring back hardly occurs. Furthermore, in the hot press molding, the desired high strength can be ensured because quenching is performed simultaneously with the press molding. Therefore, hot press forming is becoming widespread as a method for forming high strength steel sheets having a tensile strength of 1470 MPa or more.

  By the way, among automotive parts, parts such as side members, side sills, cross members, and pillar lower parts that require high corrosion resistance must exhibit a sacrificial anticorrosive effect. Therefore, until now, a galvanized steel sheet having excellent corrosion resistance has been used as a base steel sheet, and the galvanized steel sheet has been cold worked to produce automobile parts. In recent years, automobile parts having high strength and high corrosion resistance are manufactured by forming the galvanized steel sheet by hot press forming.

  However, when hot press forming is performed using a galvanized steel sheet, the zinc in the plating layer is oxidized by heating, and a zinc oxide film (zinc oxide) is formed on the surface of the steel sheet after hot press forming. Therefore, when a coating film is formed on the molded product obtained by hot press molding for the purpose of further rust prevention, and further by electrodeposition coating or the like, adhesion to the coating film ( (Coating film adhesion) decreases, and further, corrosion resistance (corrosion resistance after painting) decreases. As a result, there is a problem that the value as a product is reduced and it cannot be applied as an automobile part.

  Thus, for example, Patent Document 1 discloses a technique capable of stably obtaining both post-coating corrosion resistance after hot press molding and coating film adhesion. Specifically, Patent Document 1 describes that the coating film adhesion of a hot press-formed product is further stabilized by performing appropriate shot blasting after hot press forming using a zinc-based plated steel sheet. Has been. Moreover, when a zinc-based plated steel sheet is heated and formed, a coating structure having a zinc-based plated layer containing an iron-zinc intrinsic phase and a zinc oxide layer formed thereon is formed, and a part of the zinc oxide layer is removed. It is also described that a hot press-formed product having the intended performance can be obtained stably.

JP 2004-323897 A

  The above-mentioned Patent Document 1 is a technique for performing shot blasting after hot press forming, which leads to an increase in production process and production time, resulting in a decrease in productivity.

  The present invention has been made in view of the above circumstances, and the object thereof is a hot press-molded product and a hot press-molded product excellent in adhesion to a coating film formed by coating after hot press molding. And a hot press-formed steel sheet for producing the hot press-formed product.

The hot-press forming steel sheet of the present invention that has solved the above-mentioned problems is a steel sheet used for hot press forming, and on at least one surface of the base steel sheet, in order from the base steel sheet side, a zinc-based plating layer, and Al The gist of the present invention is that the adhesion amount of Al in the Al layer is 0.4 g / m ² or more.

In preferable embodiment of this invention, the adhesion amount of Zn in the said zinc-type plating layer is 40-100 g / m < ² > on one side per unit area of the steel plate for hot press molding.

  The present invention also includes a method for producing a hot press-formed product in which the hot press-forming steel sheet is hot press formed.

  In addition, the hot press-formed product of the present invention that has solved the above problems is an aluminum oxide containing a zinc-based plating layer and 1.0% by mass or more of Al in order from the base steel plate side on at least one side of the base steel plate. An Al concentration in a region 2 μm deep from the surface of the zinc-based plating layer is 1.8% by mass or more, and Al at the interface between the base steel sheet and the zinc-based plating layer The concentration is summarized as being less than 1% by mass.

  According to the present invention, a hot press-formed product having excellent coating film adhesion can be obtained.

FIG. 14 is a photograph showing a cross-sectional view of FIG. FIG. 16 is a photograph showing a cross-sectional view of FIG. FIG. 3 is a schematic cross-sectional view of a steel plate used in the coating film peeling test.

  The present inventors have studied in order to achieve the above object. As a result, when a steel sheet having an Al layer containing a predetermined amount of Al on the zinc-based plating layer (hereinafter sometimes simply referred to as an Al layer) is used as the base steel sheet, The present invention has been completed by finding that a hot press-molded product having excellent coating film adhesion and further anti-corrosion resistance after coating can be obtained without extra rusting steps such as shot blasting after hot press molding.

  In the present specification, the coating film adhesion means adhesion with a coating film such as an electrodeposition coating film usually applied on the zinc-based plating layer. The coating film is usually formed on the zinc-based plating layer in order to improve corrosion resistance. If necessary, since a chemical conversion treatment film such as a zinc phosphate film is formed as an undercoat layer of the coating film, when the chemical conversion treatment film is included, the coating film on the chemical conversion treatment film is used. Means adhesion. The adhesion of the coating film is significantly deteriorated particularly in a corrosive environment containing chloride ions. The cause is considered to be that corrosion of the zinc-based plating layer existing under the zinc oxide proceeds due to dissolved oxygen and chloride ions contained in the water infiltrated into the coating film. According to the present invention, as demonstrated in the Examples section described later, the adhesion of a coating film in a severe corrosive environment containing chloride ions is enhanced.

  In addition, since the chemical conversion treatment film has good adhesion to the coating film due to the anchor effect of the crystals constituting the film, the adhesion between the chemical conversion treatment film and the coating film does not become a problem. .

  The reason why the coating film adhesion is improved by the present invention is unknown in detail, but is considered as follows.

  At the time of heating at the time of hot press forming, first, an alloying reaction proceeds between a part of the Al layer and a zinc-based plating layer thereunder to form an Al—Zn-based plating diffusion layer. Further, a part of the Al layer reacts with oxygen in the atmosphere following the start of the alloying reaction to form an Al oxide. In the oxidation reaction, in addition to zinc diffused from the lower zinc-based plating layer, Mn diffused from the lower base steel sheet also exists in the vicinity of the outermost surface, so the oxide is not only Al but also oxides of zinc and Mn Will also be included. As a result, an Al oxide layer containing 1.0% by mass or more of Al is formed on the zinc-based plated layer after heating, and the Al concentration in a region 2 μm deep from the surface of the zinc-based plated layer (Al concentration of the plating surface layer) and Al concentration at the interface between the base steel plate and the zinc-based plated steel plate (Al concentration at the interface with the base iron) are appropriately controlled. Thus, it is thought that by having a layer structure including an Al oxide layer in which the Al concentration is controlled within a predetermined range, the corrosion-inhibiting effect of the zinc-based plating layer by zinc oxide is exhibited, and the coating film adhesion is improved. .

  In addition, the zinc-based plating layer other than the above-described region (interface with the plating surface layer and the ground iron) has the same plating composition as when the zinc-based plating layer not having the Al layer is heated after heating. Therefore, by providing a zinc-based plating layer in which the amount of deposited Zn is appropriately controlled, not only the coating film adhesion but also the corrosion resistance after coating is improved.

  First, the hot press forming steel sheet of the present invention will be described. As described above, the hot press-formed steel sheet of the present invention is characterized in that it has a zinc-based plating layer and an Al layer containing a predetermined amount of Al in order from the base steel sheet side on at least one side of the base steel sheet.

  The kind of the base steel plate (base material steel plate) used in the present invention is not particularly limited, and any of a hot rolled steel plate and a cold rolled steel plate can be used. Specifically, for example, a steel plate from which the oxide film on the surface of the hot-rolled steel plate has been removed, a steel plate obtained by subjecting a cold-rolled steel plate to heat treatment such as annealing, a steel plate whose surface has been cleaned after the heat treatment, and the like can be used.

  Although the chemical component composition of the said base steel plate is not specifically limited as long as a high intensity | strength hot press-molded product is obtained, For example, it is preferable to control as follows.

C: 0.15-0.4%
C is an important element for obtaining the strength of a press-molded product obtained by hot press molding. From the above viewpoint, the C content is preferably 0.15% or more, more preferably 0.18% or more, and further preferably 0.20% or more. On the other hand, if the amount of C is excessive, it is difficult to ensure the weldability of the press-formed product and the ductility during press forming. From the above viewpoint, the C content is preferably 0.4% or less, more preferably 0.38% or less, and still more preferably 0.35% or less.

Si: more than 0%, 3% or less Si has an action of forming retained austenite during quenching. Moreover, it has the effect | action which raises an intensity | strength, without reducing ductility so much by solid solution strengthening. In order to exhibit such an effect effectively, the Si amount is preferably 0.5% or more, more preferably 1.0% or more, and further preferably 1.2% or more. On the other hand, when the amount of Si becomes excessive, the toughness after hot pressing deteriorates. Accordingly, the Si amount is preferably 3% or less, more preferably 2.5% or less, still more preferably 2.0% or less, and even more preferably 1.8% or less.

Mn: 0 to 3%
Mn is an element added as necessary. Mn is an element that enhances hardenability, suppresses the formation of ferrite, pearlite, and bainite during cooling after heating, and contributes to securing high strength. In order to exhibit such an effect effectively, the amount of Mn is preferably 0.5% or more, more preferably 0.8% or more, and further preferably 1.0% or more. On the other hand, considering the hot rolling load, the Mn content is preferably 3% or less, more preferably 2.8% or less, still more preferably 2.5% or less, and even more preferably 2.1%. It is as follows.

Al: more than 0% and 0.10% or less Al is an element useful as a deoxidizing element. From the above viewpoint, the Al content is preferably more than 0%, more preferably 0.01% or more. However, if the amount of Al becomes excessive, ductility and the like deteriorate due to generation of Al ₂ O ₃ . Therefore, the Al content is preferably 0.10% or less, more preferably 0.08% or less, and still more preferably 0.05% or less.

B: 0 to 0.01%
B is an element added as necessary, and is an element effective for improving the hardenability of the steel sheet. In order to effectively exhibit such an effect, the B content is preferably 0.0002% or more, more preferably 0.0003% or more, and further preferably 0.0005% or more. On the other hand, when the amount of B becomes excessive, the above effect is saturated, so the amount of B is preferably 0.01% or less, more preferably 0.008% or less, and still more preferably 0.005% or less.

  The basic chemical composition of the base steel sheet used in the present invention is as described above, with the balance being iron and inevitable impurities. Examples of the inevitable impurities include impurities inevitably included in the production of P, S, N, O, H and the like. In addition, the present invention includes trace components that do not inhibit the above-described characteristics, for example, Mg, Ca, Sr, Ba, rare earth elements such as La, and carbide forming elements such as Zr, Hf, Ta, W, and Mo. May be.

  The base steel sheet is, as necessary, (a) Ti: more than 0%, 0.1% or less, (b) one or more selected from the group consisting of Cr, Ni, and Cu: total And more than 0%, 1% or less and the like.

Ti: more than 0% and 0.1% or less Ti is an element that contributes to improving hardenability by fixing N and maintaining B in a solid solution state. In order to effectively exhibit such an effect, the Ti content is preferably 0.04% or more, more preferably 0.05% or more, and further preferably 0.06% or more. However, when the amount of Ti becomes excessive and exceeds 0.1%, a large amount of TiC is formed, and the strength increases due to precipitation strengthening, but the ductility decreases. Therefore, the Ti content is preferably 0.1% or less, more preferably 0.09% or less, and still more preferably 0.08% or less.

One or more selected from the group consisting of Cr, Ni, and Cu: Total of more than 0% and 1% or less Cr, Ni, and Cu prevent the formation of ferrite, pearlite, and bainite during cooling after heating. It is an element that contributes effectively to securing retained austenite. These elements may be added alone or in combination of two or more. In order to effectively exhibit such an effect, the total amount of the above elements is preferably 0.01% or more, more preferably 0.05% or more, and further preferably 0.06% or more. The addition cost increases as the total amount of the elements increases, so the total amount of the elements is preferably 1% or less, more preferably 0.9% or less, and even more preferably 0.8% or less. It is.

  The hot press-forming steel sheet of the present invention has a zinc-based plating layer and an Al layer in order from the base steel sheet side on at least one side of the base steel sheet.

  Here, the layers of the “zinc-based plating layer and the Al layer” may be present on at least one surface of the base steel plate, and may be present on both surfaces of the base steel plate.

  Specifically, first, a zinc-based plating layer mainly composed of zinc is provided on (directly above) the base steel sheet. By using zinc-based galvanized steel sheets, the corrosion caused by chipping of coatings and plating layers caused by stepping stones during driving of automobiles is prevented, and the sacrificial corrosion resistance necessary to ensure the corrosion resistance of the chipped areas is ensured. can do.

  Here, “mainly” means a material containing approximately 75% by mass or more of zinc, and includes a pure galvanized steel sheet containing 100% by mass of zinc. In addition to zinc, alloy elements such as Fe, Ni, and Al may be included. Examples thereof include an Fe—Zn alloy-plated steel sheet (alloyed hot-dip galvanized steel sheet), an Ni—Zn alloy-plated steel sheet, and an Al—Zn alloy. It is done.

  Among these, as the Al—Zn alloy, for example, an Al—Zn plated steel sheet containing a small amount (about 0.05 to 0.2%) of Al as in typical hot dipping, or about 2% or less of Al. An Al—Zn plated steel sheet containing

From the viewpoint of improving the corrosion resistance after coating, the amount of Zn deposited on the zinc-based plating layer is preferably 40 g / m ² or more per one surface. More preferably, it is 45 g / m ² or more. However, even if there is too much adhesion amount of Zn, the above effect is saturated and it is economically wasteful, so it is generally preferable that the amount is 100 g / m ² or less. More preferably, it is 80 g / m ² or less.

  An Al layer is provided on (directly above) the zinc-based plating layer. The steel sheet of the present invention is particularly characterized in that an Al layer containing a predetermined amount of Al is provided, and this improves coating film adhesion.

  The Al layer used in the present invention is not particularly limited as long as it is a layer containing Al, and includes both pure Al and an alloy mainly composed of Al. Here, “mainly” means that Al is contained in an amount of about 80% by mass or more, and specific examples include Al—Mg alloys and Al—Si alloys.

In order to effectively exhibit the coating film adhesion improving effect by the Al layer, the Al amount in the Al layer is 0.4 g / m ² or more per side in terms of metal Al amount. Preferably it is 1 g / m ² or more, more preferably 1.5 g / m ² or more. The upper limit of the Al adhesion amount is not particularly limited from the viewpoint of coating film adhesion, but if it is excessive, sacrificial corrosion resistance after hot press molding may be reduced, and therefore preferably 5 g / m ² or less, more preferably. Is 3 g / m ² or less.

  Next, a preferred method for producing the hot press-formed steel sheet of the present invention will be described.

  First, a base steel plate is prepared. As described above, the type of the base steel sheet is not particularly limited, and both hot-rolled steel sheets and cold-rolled steel sheets are used. The method for producing the hot-rolled steel sheet is not particularly limited, and for example, it is produced at a heating temperature before hot rolling: about 1100 to 1300 ° C, a finish rolling temperature: about 800 to 950 ° C, and a winding temperature: about 500 to 700 ° C. be able to. The method for producing the cold-rolled steel sheet is not particularly limited. For example, the cold-rolled steel sheet can be produced by subjecting the hot-rolled steel sheet to cold rolling at a cold rolling rate of 3 to 70%, for example.

  If necessary, the cold-rolled steel sheet may be further subjected to heat treatment such as annealing. By annealing, the hardness of the base steel sheet can be adjusted, and the manufacturability, sheet feeding stability, etc. can be improved.

  The thickness of the base steel plate is preferably 2.0 to 3.5 mm in the case of a hot-rolled steel plate, for example, and preferably 0.8 to 1.8 mm in the case of a cold-rolled steel plate.

  Next, a zinc-based plating layer is formed on the base steel plate. The formation method of a plating layer is not specifically limited, Hot dip galvanization and electrogalvanization can be employ | adopted. The plating conditions are not particularly limited, and a generally performed method can be adopted. Moreover, you may further perform an alloying process after the said plating. Specifically, a suitable plating method may be employed as appropriate according to the type and film thickness of the zinc-based plating layer.

  For example, preferable plating conditions for forming the hot dip galvanized layer are a bath temperature of the plating tank: about 420 to 480 ° C. and an immersion time of about 1 to 10 seconds. Although the alloying treatment is not particularly limited, for example, it is preferably held at 470 to 580 ° C. for 20 seconds to 10 minutes in an atmosphere such as air or nitrogen. Although the cooling conditions from the said alloying temperature to room temperature are not specifically limited, For example, it is preferable to cool at the average cooling rate of about 10-50 degreeC / second. When employing electrogalvanizing, for example, using Ni—Zn plating is effective in suppressing whiskers.

In addition, from the viewpoint of improving the corrosion resistance after coating, in order to control the adhesion amount of the Zn amount in the zinc-based plating layer, preferably in the range of 40 to 100 g / m ² , for example, the plating time, the Zn amount in the plating layer, It is preferable to appropriately control the pulling rate from the plating bath, the gas flow rate of gas wiping, and the like.

  Next, an Al layer is formed on the zinc-based plating layer. Specifically, for example, after galvanized steel sheet is cut into a blank, it can be formed by a vapor deposition method such as sputter deposition.

  The hot press forming steel sheet of the present invention has been described above.

  The hot press-formed product of the present invention is manufactured by hot press-forming the steel sheet. The conditions for hot press molding are not particularly limited, and methods used in the technical field can be employed. Specifically, the blank of the base steel plate is heated to a temperature at which a desired part hardness is obtained by rapid cooling during subsequent hot press forming, generally about 900 ° C. in about 10 minutes, and conveyed to the press machine. After that, hot press molding is performed, and a hot press molded product is manufactured by quenching simultaneously with the molding.

  The hot press-formed product of the present invention has, on at least one surface of the base steel sheet, in order from the base steel sheet side, a zinc-based plating layer, and an Al oxide layer containing 1.0% by mass or more of Al, The Al concentration in the region 2 μm deep from the surface of the zinc-based plating layer is 1.8% by mass or more, and the Al concentration at the interface between the base steel sheet and the zinc-based plating layer is less than 1% by mass.

  As described above, a part of the Al layer constituting the hot press forming steel plate is changed to the Al oxide layer by heating. When the Al content of the Al oxide layer is less than 1.0% by mass, the oxidation reaction of the plating layer becomes unstable during hot pressing, and there may be a portion that is partially inferior in corrosion resistance. Preferably it is 2 mass% or more, More preferably, it is 3 mass% or more. However, if the Al amount in the Al oxide layer is excessive, the corrosion resistance after coating is lowered, and therefore it is preferably 50% by mass or less, more preferably 30% by mass or less.

  Furthermore, the Al concentration in the region 2 μm deep from the surface of the zinc-based plating layer (hereinafter sometimes abbreviated as plating surface layer) is 1.8% by mass or more, and the base steel sheet and the zinc-based plating layer The Al concentration in the vicinity of the interface (hereinafter sometimes abbreviated as the interface with the ground iron) is less than 1% by mass. Thereby, desired coating film adhesiveness is obtained.

  Here, the area | region of the said "plating surface layer" and the "interface with a ground iron" is demonstrated using FIG. 1 and FIG. FIG. 1 shows the No. in Table 2 described later. 14 is a cross-sectional view of FIG. 16 is a cross-sectional view of FIG.

  First, the above “plating surface layer” means a region having a depth of 2 μm from directly under the zinc oxide film formed on the surface of the zinc-based plating layer by heating. Actually, as shown in the figure, the outermost surface of the zinc-based plating layer has irregularities, so that the depth is 2 μm (longitudinal) from the outermost surface and the length in the range of 2 to 20 μm in parallel to the surface of the zinc-based plating layer ( A plurality of rectangular regions (□ in the figure) having a horizontal direction are selected, and the length (horizontal) constituting each rectangle (□) is measured. The measurement is performed until the total length (horizontal) constituting each rectangle reaches 100 μm or more, and an average value obtained by dividing the total length by the number of measured rectangles is defined as a “plating surface layer”. The Al concentration present in the “plating surface layer” is measured by a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX) as described in Examples below. To measure.

  In addition, the “interface with the base iron” is a thickness from the interface between the region where zinc is present and the region where zinc is not present toward the zinc-based plating layer side when the steel sheet cross section is observed with the SEM-EDX. This means an area of 2 μm. However, since the outermost surface of the zinc-based plating layer has irregularities, as in the case of the above-mentioned “plating surface layer”, the depth is 2 μm (longitudinal) from the outermost surface and the length in the range of 2 to 20 μm parallel to the interface. A plurality of rectangles (□ in the figure) having (horizontal) are selected, and the length (horizontal) constituting each rectangle (□) is measured. The measurement is performed until the total length (horizontal) constituting each rectangle reaches 100 μm or more, and an average value obtained by dividing the total length by the number of measurements of the rectangle is defined as “interface with the ground iron”. The Al concentration present in the “plating surface layer” is measured by the SEM-EDX.

  According to the results of experiments by the present inventors, it has been found that the Al concentration in the “plating surface layer” and “interface with the base metal” contributes closely to the improvement in coating film adhesion. In hot-pressed parts, the adhesion of the coating in a corrosive environment is thought to deteriorate due to the dissolution of the plating layer directly under the oxide film. By increasing the Al concentration of the above “plating surface layer” (the Al concentration directly under the plating layer), Adhesion can be improved. However, if the Al concentration increases to the lower layer of the plating layer, the sacrificial anticorrosion performance, which is the original characteristic of zinc-based plating, deteriorates. Therefore, the Al concentration at the above-mentioned interface with the base iron (Al concentration in the lower layer) The plating configuration was suppressed.

  Specifically, in order to effectively exhibit the desired coating film adhesion, the Al concentration in the plating surface layer is 1.8% by mass or more, preferably 2.0% by mass or more, more preferably 2. It is 5 mass% or more. However, since the sacrificial anticorrosion performance of the plating layer deteriorates when the concentration increases, the upper limit is preferably 15% by mass or less. Similarly, in order to effectively exhibit the desired coating film adhesion, the Al concentration at the interface with the base iron is less than 1% by mass, preferably 0.8% by mass or less, more preferably 0.7%. It is below mass%. The lower limit is about 0.1% by mass or more in consideration of the stability of the alloying reaction between the plating layer and the base steel sheet, the ease of control of the zinc adhesion amount, and the like.

  The hot press-molded product of the present invention sequentially has a chemical conversion treatment film and a coating film such as electrodeposition coating for the purpose of improving corrosion resistance, as in the case of a normal hot press-molded product. The coating film formed by electrodeposition coating is further excellent in the uniformity of the coating film. The method of electrodeposition coating is not particularly limited, and examples thereof include cationic electrodeposition coating. Moreover, the chemical conversion treatment film | membrane applied as needed is useful as a base layer of the said coating film, for example, a zinc phosphate film | membrane etc. are mentioned.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples, and can be implemented with modifications within a range that can meet the purpose described above and below. They are all included in the technical scope of the present invention.

  A steel material having the chemical composition of A to C shown in Table 1 below (the balance is inevitable impurities other than iron, P, and S) is melted and cast to obtain a slab, followed by a heating temperature of 1250 ° C. and finishing. Hot rolling was performed under conditions of a rolling temperature of 900 ° C. and a winding temperature of 600 ° C. to produce a hot-rolled steel plate having a plate thickness of 2.3 mm. This hot-rolled steel sheet was cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1.4 mm.

  The cold-rolled steel sheet thus obtained was subjected to hot dip galvanizing treatment to produce a hot dip galvanized steel sheet having a zinc-based plating layer on both surfaces of the steel sheet. Moreover, about some samples, the alloying process was performed immediately after the hot dip galvanization process, and the galvannealed steel plate was manufactured.

Here, both the hot dip galvanizing process and the alloying process have an experimental furnace capable of controlling the atmosphere, equipped with a heating / cooling mechanism and a crucible serving as a galvanizing bath, and capable of performing the plating process and the alloying process in an integrated process. Used. The hot dip galvanizing treatment was performed by immersing in a 0.13% Al—Zn bath at 460 ° C. for 3 seconds. Further, the alloying treatment was performed by holding at 550 ° C. for 20 seconds in an atmosphere of 5% H ₂ —N ₂ (dew point −45 ° C.). The alloying treatment was cooled by blowing Ar gas. The average cooling rate from the start of cooling to room temperature was 10 to 15 ° C./sec.

The Zn adhesion amount of the galvanized steel sheet and the alloyed galvanized steel sheet was adjusted by gas wiping, and the results were measured by ICP (Inductively Coupled Plasma) emission spectroscopic analysis. The amount of Zn deposited was 30 to 100 g / m ² per side.

After the hot dip galvanized steel sheet and the alloyed hot dip galvanized steel sheet manufactured by the above method were cut into a size of 50 mm × 150 mm, an Al layer was formed on the zinc-based plated layer by vacuum sputtering deposition. The adhesion amount of the Al layer was adjusted by the film formation time, and was 0 (no formation of the Al layer) to 10 g / m ² .

Next, the steel plate produced by the above method was heated by an electric heating method while simulating hot press forming. In the heating pattern, the range from room temperature to 900 ° C. was heated for 30 seconds, and then cooled by spraying N ₂ gas. Specifically, the cooling gas was set at a constant flow rate so that the average cooling rate in the range from 900 ° C. to 350 ° C. was 30 ° C./second. Then, the range from 350 degreeC to room temperature was stood to cool.

  As a result, it was confirmed that an Al oxide layer containing 1.0% by mass or more of Al was formed on the heated zinc-based plating layer (not shown in the table). The above confirmation was performed by measuring the average Al concentration of the surface layer having an oxygen concentration of 10% by mass or more using an element profile obtained by a glow discharge optical emission spectrometer (GD-OES).

(Measurement of each Al concentration)
After heating, the cross section of each steel plate was analyzed by the SEM-EDX described above, the Al concentration in the region (plating surface layer) 2 μm deep from the surface of the zinc-based plating layer, and the vicinity of the interface between the base steel plate and the zinc-based plating layer ( The Al concentration at the interface with the ground iron was measured. In this example, a field emission scanning electron microscope JSM-7001F (FE-SEM) manufactured by JEOL Ltd. was used as the SEM-EDX.

Each steel plate after the heating was subjected to alkaline degreasing, surface conditioning, and zinc phosphate treatment, and then electrodeposition coating was performed. Specifically, the zinc phosphate treatment was immersed in Palbond L3065 (PB-L3065) manufactured by Nippon Parkerizing Co., Ltd. for 2 minutes to adjust the adhesion amount of zinc phosphate to around 3 g / m ² . Moreover, the said surface adjustment used the thing corresponding to the said zinc phosphate process liquid. The electrodeposition coating is performed using a cationic electrodeposition paint (Powernicks Excel 1220) manufactured by Nippon Paint Co., Ltd. at a voltage of 170 V and baked at 180 ° C. for 15 minutes, and the film thickness of the coating film is 15 μm. Adjusted.

(Evaluation of coating film adhesion)
Each steel plate on which the coating film was formed as described above was immersed in a 5 wt% NaCl aqueous solution at 50 ° C. for 700 hours. When dipping, the end of each steel plate was sealed so that the corrosion from the end and the infiltration effect of the immersion water could be ignored. After completion of the immersion, the evaluation target shown in FIG. 3 was subjected to a coating film peeling test using a cellophane tape, and the peeled area ratio of the portion where the electrodeposition coating was peeled was evaluated. The area to be evaluated is about 100 mm in the longitudinal direction of the steel plate in which soaking is maintained during the heat treatment simulating hot press forming × about 40 mm in the width direction (evaluation area: 40 mm × 100 mm = 4000 mm ² ) did. The coating film peeling area ratio in the evaluation area (4000 mm ² ) was evaluated by image processing, and 3% or less was regarded as acceptable. At the time of immersion, the end of the sample was sealed so that the corrosion from the end and the infiltration effect of immersion water could be ignored.

(Evaluation of corrosion resistance after painting)
Artificial coating film scratches were formed on the coating film formed as described above by 60 ° cross cut. Next, it exposed for 90 days in the environment of JASO-CCT mode using the combined cycle tester by Suga Test Instruments Co., Ltd. Next, after peeling off and removing the coating film using Neos CS500, rust removal treatment by liquid honing was performed, and then the erosion depth of the crosscut portion was measured. Specifically, in the cross-cut portion, the erosion depths at 10 locations selected at equal intervals along the cut line were measured with a contact-type needle, and the average value was taken as the erosion depth. The case where the erosion depth thus obtained was 0.10 mm or less was evaluated as excellent (good) after coating, and the case where the erosion depth exceeded 0.10 mm was evaluated as poor (bad) after coating.

  These results are shown in Table 2.

No. 1 in Table 2 using steel type symbol A in Table 1. 12, 13, 16, 17, 20, 21; No. 2 in Table 2 using steel type symbol B in Table 1. 23, 24; No. 2 in Table 2 using steel type symbol C in Table 1. Both 26 and 27 are examples of the present invention in which the Al adhesion amount in the Al layer is appropriately controlled, and the Al concentration of the plating surface layer after heating is 1.8% by mass or more, and Al at the interface with the base iron The concentration was less than 1% by mass. As a result, regardless of the steel type and regardless of the presence or absence of alloying, all the steel plates are excellent in coating film adhesion. In the steel sheet, the zinc adhesion amount of the zinc-based plating layer was No. Since it is all controlled to be 40 g / m ² or more instead of 35 g / m ² as in 3-5, 8 and 9, it is excellent in corrosion resistance after painting.

  On the other hand, the following examples are comparative examples that do not satisfy the requirements of the present invention, and have the following problems.

First, No. 2 in Table 2 was used. 1, 6, 10, 14, 18, 22, 25 are all examples in which an Al layer was not formed on the zinc-based plating layer (Al layer column 0). As a result, since the Al concentration at the interface with the plating surface layer and the ground iron after heating was reduced, the oxidation of zinc in the zinc-based plating layer was not suppressed, and the coating film adhesion was lowered. Of these, No. In Nos. 1 and 6, since the zinc adhesion amount of the zinc-based plating layer was less than 40 g / m ² , the corrosion resistance after coating was also lowered.

In Table 2, No. 2, 7, 11, 15 and 19 are all examples in which an Al layer was formed on the zinc-based plating layer, but the amount of Al adhesion was small, and the Al concentration in the plating surface layer after heating was low, and the coating film adhered. Decreased. Of these, No. In Nos. 2 and 7, since the zinc adhesion amount of the zinc-based plating layer was less than 40 g / m ² , the corrosion resistance after coating was also lowered.

For reference, similar to the commercial Al-plated steel sheet (SA1C of JIS G 3314, Al coating weight per one side 45 g / m ² or 72 g / m ^2, thickness 1.2 mm) of Al deposition amount differs prepared above The coating film adhesion and the corrosion resistance after coating were measured. As a result, the coating film adhesion was good, but since it did not have a galvanized layer, the corrosion resistance after coating decreased (not shown in the table).

Claims (4)

A steel plate used for hot press forming,
It has a zinc-based plating layer and an Al layer in order from the base steel plate side on at least one surface of the base steel plate, and the amount of Al deposited in the Al layer is 0.4 g / m ² or more. Steel sheet for hot press forming. The hot press-forming steel sheet according to claim 1, wherein the zinc adhesion amount in the zinc-based plating layer is 40 to 100 g / m ^{2 on} one side per unit area of the hot-press forming steel sheet.   A method for producing a hot press-formed product, wherein the hot press-formed steel plate according to claim 1 or 2 is hot press formed. In order from at least one side of the base steel plate, from the base steel plate side, a zinc-based plating layer, and an Al oxide layer containing 1.0 mass% or more of Al,
The Al concentration in the region having a depth of 2 μm from the surface of the zinc-based plating layer is 1.8% by mass or more,
A hot press-formed product, wherein an Al concentration at an interface between the base steel plate and the zinc-based plating layer is less than 1% by mass.