JP5098864B2 - High strength automotive parts with excellent post-painting corrosion resistance and plated steel sheets for hot pressing - Google Patents

Description

  The present invention relates to a high-strength automobile member excellent in corrosion resistance after electrodeposition coating and a hot-press plated steel sheet used therefor.

  In recent years, in steel plate applications for automobiles (for example, automobile pillars, door impact beams, bumper beams, etc.) and the like, steel plates that have both high strength and high formability have been desired. There is TRIP (Transformation Induced Plasticity) steel using martensitic transformation of retained austenite. With this TRIP steel, it is possible to produce a high-strength steel sheet having excellent formability and a strength of about 1000 MPa, but it is possible to secure formability with ultra-high-strength steel having higher strength, for example, 1500 MPa or more. Have difficulty.

  Under such circumstances, hot press (also referred to as hot pressing, hot stamping, die quenching, press quenching, etc.) has recently been attracting attention as having both high strength and high formability. This hot press improves the formability of a high-strength steel sheet by heating it in an austenite region at 800 ° C. or higher and then forming it hot, and after it is formed, it is baked to obtain a desired material. It is.

  Hot press is promising as a method of forming ultra-high strength members, but usually has a step of heating the steel plate in the atmosphere, and at this time, oxide (scale) is generated on the steel plate surface. The process of removing the scale was necessary. However, such post-processes have problems such as the necessity of countermeasures from the viewpoints of scale removal ability and environmental load.

As a technique for improving this, a technique for suppressing the generation of scale during heating by using an Al-plated steel sheet as a steel sheet for hot pressing has been proposed (see, for example, Patent Documents 1 to 3).
JP-A-9-202953 JP 2004-2932 A JP 2004-244704 A

  Patent Document 2 discloses a technique for improving spot weldability, and Patent Document 3 discloses a technique for improving corrosion resistance after coating. Here, it is described that the corrosion resistance after coating is improved by using a surface composition containing 40% or more of Al. However, what is disclosed here is information about the composition only, and nothing is stated about the amount. Also, there is no description of the relationship between the heating conditions and the amount.

  Therefore, the present invention has been made in view of such problems, and aims to efficiently obtain a high-strength automobile part excellent in post-coating corrosion resistance using a hot press method and a hot-press plated steel sheet used therefor. To do.

  As a result of intensive research to solve the above problems, the present inventors have clarified the influencing factors to post-coating corrosion resistance and devised a manufacturing method that further improves post-coating corrosion resistance. Was completed.

That is, it is necessary to have this phase on the outermost surface because it is FeAl ₂ or Fe ₂ Al ₅ containing about 50% Al that ensures corrosion resistance after coating. An oxide film having a thickness of 0.5 μm or less is also formed on the surface of these phases. Here, however, an oxide film is not included and a phase that actually contributes to corrosion is considered. By containing 10 μm or more of these phases, it is possible to obtain post-coating corrosion resistance equivalent to or higher than that of GA (alloyed hot-dip galvanized steel sheet) that is usually used as a rust-proof steel sheet. Depending on the heating conditions, these phases may exist as single phases, or phases containing an Al concentration of 40% or less may be included therein.

The gist of the present invention is the following contents as described in the claims.
(1) Mass% as a steel component, C: 0.1-0.4%, Si: 0.01-0.6%, Mn: 0.5-3%, P: 0.005-0.05 %, S: 0.002-0.02%, Al: 0.005-0.1%, Ti: 0.01-0.1%, B: 0.0001-0.01%, Cr: 0.0. The outermost surface of the steel sheet containing 01 to 1%, the balance being Fe and inevitable impurities, has a phase mainly composed of Fe ₂ Al ₅ and FeAl ₂ of 10 μm or more, and the Al concentration at the bottom is 40% by mass . A high-strength automobile member excellent in corrosion resistance after painting, characterized by having the following phases.
(2) By mass% as a steel component, C: 0.1 to 0.4%, Si: 0.01 to 0.6%, Mn: 0.5 to 3%, P: 0.005 to 0.05 %, S: 0.002-0.02%, Al: 0.005-0.1%, Ti: 0.01-0.1%, B: 0.0001-0.01%, Cr: 0.0. On the outermost surface of the steel sheet containing 01 to 1%, the balance being Fe and inevitable impurities, a phase mainly composed of Fe ₂ Al ₅ and FeAl ₂ and having an Al concentration of 40% by mass or less dispersed therein A high-strength automobile member having excellent post-coating corrosion resistance, characterized in that Fe ₂ Al ₅ and FeAl ₂ have a thickness equivalent to 10 μm or more and have a phase having an Al concentration of 40% by mass or less at the bottom.
(3) Mass% as a steel component, C: 0.1-0.4%, Si: 0.01-0.6%, Mn: 0.5-3%, P: 0.005-0.05 %, S: 0.002-0.02%, Al: 0.005-0.1%, Ti: 0.01-0.1%, B: 0.0001-0.01%, Cr: 0.0. Containing 01 to 1%, the balance is made of Fe and inevitable impurities, and the surface roughness of the steel sheet adjusted to 0.3 to 1.2 μm with Ra contains Si: 3 to 15% by mass. and characterized by applying Al-plated, coated steel sheet for hot press used for the production of high strength automobile member according to (1) or (2).

  According to the present invention, the post-coating corrosion resistance of a high-strength member prepared by a hot press method can be equal to or higher than GA, and it can be used as a rust-proof component. .

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

The present inventors have studied various factors that affect the corrosion resistance after painting, and have improved the corrosion resistance after painting by having FeAl ₂ or Fe ₂ Al ₅ of 10 μm or more on the surface. Accordingly, the structure of the plated layer after heat-alloying the Al-plated steel sheet will be described with reference to FIG. In general, the Fe—Al alloy layer often has a five-layer structure. In FIG. 1A, these five layers are represented by 1 to 5 layers in order from the surface of the plated steel sheet. The Al concentration in the first and third layers is about 50% by mass, the Al concentration in the second layer is about 30% by mass, and the Al concentrations in the fourth and fifth layers are 15 to 30% by mass, respectively. The composition has a width of 1 to 15% by mass. The balance is Fe and Si. Void formation may be observed near the interface between the fourth layer and the fifth layer. The corrosion resistance of such an alloy layer substantially depends on the Al content, and the higher the Al content, the better the corrosion resistance. Therefore, the first layer and the third layer are most excellent in corrosion resistance. In addition, the structure below the fifth layer is a steel base, which is a hardened structure mainly composed of martensite.

FIG. 2 shows a binary phase diagram of Fe—Al. Referring to FIG. 2, it can be determined that the first layer and the third layer are mainly composed of Fe ₂ Al ₅ and FeAl ₂ , and the fourth layer and the fifth layer correspond to FeAl and αFe, respectively. In addition, the second layer is a layer containing Si that cannot be explained from the Fe—Al binary phase diagram, and its detailed composition is not clear, but the present inventors have found that the FeAl ₂ and Fe—Al—Si compounds are fine. It is presumed that it was mixed.

  On the other hand, unlike FIG. 1A, FIG. 1B does not have five distinct layers. It has been found that the structure after alloying changes depending on the temperature rise rate when the temperature of the Al-plated steel sheet is raised, and when the temperature rise rate is high, a structure as shown in (b) tends to be obtained. Also, depending on the amount of adhesion, the larger the amount of Al plating, the more easily the structure as shown in (b). At this time, it is known from the composition analysis by EPMA that the portion corresponding to the second layer of (a) is dispersed. In FIG. 2B, the first layer, the fourth layer, and the fifth layer are displayed for comparison with FIG.

  The present inventors obtained the following knowledge from the corrosion analysis of the samples having these structures. That is, the portions corresponding to the first layer and the third layer in FIG. 1A have a higher Al concentration and are more susceptible to corrosion in a salt damage environment. First, the first layer is corroded. However, when there are five layers, the corrosion stops at the second layer at the bottom of the first layer, and the corrosion proceeds horizontally through the first layer. When the first layer is corroded, the coating film adhering to the surface loses the adhesive force, and there is also a deposit expansion due to the corrosion product, which is visually observed as a coating film swelling.

  However, when the alloy layer has a structure as shown in FIG. 1 (b), the corrosion proceeds to a site of about 50% Al corresponding to the first layer. At this time, it becomes difficult to proceed in the horizontal direction as much as corrosion easily proceeds in the depth direction. That is, when the structure as shown in FIG. This can be said to be because the third layer hardly contributes to corrosion prevention in FIG. 1A, but in FIG. 1B it has contributed to corrosion prevention.

That is, in the case of the configuration as shown in FIG. 1A, the post-coating corrosion resistance is substantially determined by the thickness of the first layer. On the other hand, when it has a form like FIG.1 (b), corrosion resistance after coating is determined by the thickness of the 1st layer which has a dispersed phase equivalent to a 2nd layer. More precisely, it is determined by a net equivalent thickness of about 50% Al, which is obtained by multiplying the thickness of the first layer by the fraction of the portion corresponding to FeAl ₂ and Fe ₂ Al ₅ .

Hereinafter, the structure of the Al-plated steel sheet according to the present invention used for the production of the rapidly heated hot-press plated steel sheet having the coating layer as described above will be described in detail.
(About steel plate)
Since hot press performs press and quenching simultaneously with a mold, the plated steel sheet for rapid heating hot press according to the present invention needs to be a component that is easily quenched. Specifically, as steel components in the steel sheet, in mass%, C: 0.1 to 0.4%, Si: 0.01 to 0.6%, Mn: 0.5 to 3%, P: 0 0.005-0.05%, S: 0.002-0.02%, Al: 0.005-0.1%, Ti: 0.01-0.1%, B: 0.0001-0.01 %, Cr: 0.01 to 1% is preferable. The amount of C is preferably 0.1% or more from the viewpoint of improving hardenability, and if the amount of C is too much, the toughness of the steel sheet is remarkably lowered, so that it is 0.4% by mass or less. It is preferable. Further, if Si is added in excess of 0.6%, the Al plating property is lowered, and if it is less than 0.01%, fatigue characteristics are inferior, which is not preferable. Mn is an element that contributes to hardenability, and it is effective to add 0.5% or more, but it is not preferable to exceed 3% from the viewpoint of lowering toughness after quenching. Ti is an element that improves the heat resistance after aluminum plating, and it is effective to add 0.01% or more. However, if it is added excessively, it reacts with C and N to lower the steel sheet strength. It is not preferable to exceed 1%. B is an element that contributes to hardenability, and it is effective to add 0.0001% or more. However, since there is a concern of hot cracking, it is not preferable to exceed 0.01%. Cr is a strengthening element and is effective in improving hardenability. However, if it is less than 0.01%, it is difficult to obtain these effects. On the other hand, if the content exceeds 1%, the manufacturability during production and hot rolling is adversely affected. If P is added excessively, it causes brittleness of the steel sheet, so 0.05% or less is preferable. S becomes an inclusion in the steel as MnS, and if MnS is large, it becomes a starting point of fracture, and in order to inhibit ductility and toughness, 0.05% or less is preferable. Since Al is a plating-inhibiting element, 0.1% or less is preferable. In addition, other components such as Mo, Nb, Ni, Cu, V, Sn, and Sb can be contained as components in the steel sheet. Usually, in mass%, P: 0.05% or less, S: 0.02% or less, Al: 0.1% or less, N: 0.01% or less.
(About Al plating)
The hot-pressed plated steel sheet for manufacturing the high-strength automotive parts of the present invention is manufactured by applying Al plating to the steel sheet surface, but the method of Al plating on the steel sheet in the present invention is particularly limited. In addition, the electroplating method, the vacuum deposition method, the cladding method, and the like are possible including the hot dipping method. At present, the industrially most popular method is the hot dipping method. Usually, a plating bath containing 3% by mass to 15% by mass of Si can be used. Si has a function of suppressing alloy layer growth during Al plating. Although the necessity of suppressing the growth of the alloy layer is limited if it is limited to hot press applications, in the hot dip plating method, products for various uses are manufactured in one bath, so in applications that require the workability of Al plating, alloys are required. It is necessary to suppress layer growth. When the amount of Si is less than 3% by mass, the alloy layer grows, so the workability as an Al-plated steel sheet is lowered. On the other hand, if the amount of Si is too large, Fe ₂ Al ₅ and FeAl ₂ are difficult to remain. This is a compound that does not contain Si in both Fe ₂ Al ₅ and FeAl ₂ , Si is concentrated in the phase of about 30% Al, and as a result of the increase in the total amount of Si, about 30% of Si farmers This can be interpreted as a phenomenon in which the Al phase easily grows.

  Inevitable impurities such as Fe are mixed therein. Other additive elements may be Mn, Cr, Mg, Ti, Zn, Sb, Sn, Cu, Ni, Co, In, Bi, Misch metal, etc., but as long as the plating layer is mainly Al. Is possible. Addition of Zn and Mg is effective in terms of making red rust unlikely to occur, but excessive addition of these elements having a high vapor pressure causes generation of fumes of Zn and Mg, Zn on the surface, and powdery substances derived from Mg The addition of Zn: 60% by mass or more and Mg: 10% by mass or more is not preferable.

Moreover, in this invention, it does not specifically limit about the plating pre-processing and post-processing of Al plating. Ni, Cu, Cr, Fe pre-plating and the like may be used as the plating pretreatment, but this is also applicable. Further, as a post-plating treatment, chromate treatment, resin coating treatment, or the like may be performed for the purpose of primary rust prevention and lubricity. However, with regard to the chromate treatment, a trivalent treatment film such as electrolytic chromate is preferable in consideration of recent hexavalent chromium regulations. In addition, post-treatment other than inorganic chromate is also applicable. In order to impart lubricity, it is also possible to perform surface treatment in advance using alumina, silica, MoS ₂ or the like.

The high-strength automobile member according to the present invention has an Al—Fe alloy layer on the surface. At this time, the thickness of the entire Al—Fe alloy layer is preferably 10 to 45 μm. Since the surface has FeAl ₂ and Fe ₂ Al ₅ of 10 μm or more, the total thickness is naturally 10 μm or more. As the thickness increases, the corrosion resistance tends to work preferentially. However, even if the thickness of phases other than FeAl ₂ and Fe ₂ Al ₅ that contribute to the corrosion resistance increases, there is no effect on the corrosion resistance. On the other hand, the larger the sum of the thickness of the Al plating layer and the thickness of the Fe—Al alloy layer, the easier it is for the coating layer generated by the heating process to be lost during processing, so the thickness of the coating layer is preferably 45 μm or less. .
[Method for Producing High-Strength Automotive Member According to the Present Invention]
Note that the Al-plated steel sheet obtained as described above is heated in a subsequent hot press process. The heating method is not particularly limited, and it is possible to use a normal infrared heating method using a furnace or radiant heat, but rapid heating at a heating rate of 50 ° C./second or more is possible. It is also possible to use a heating method using electricity such as energization heating or high frequency induction heating. The upper limit of the rate of temperature rise is not specified, but when using the heating method such as the current heating or high frequency induction heating, the upper limit is economically about 200 ° C./second depending on the power source capacity of the apparatus. It becomes.

  Moreover, in this heating process, it is preferable that the maximum reached plate temperature is 850 ° C. or higher. The reason why the maximum attainable plate temperature is set to this temperature is that the steel plate is heated to the austenite region and the alloying is sufficiently advanced to the surface.

When the holding time is long, or when the ultimate plate temperature is high, the diffusion of the plating and the steel plate proceeds accordingly. A schematic diagram of the structure change at this time is shown in FIG. Depending on the heating rate, there are 5 layers (corresponding to (a) in FIG. 1) and dispersion (corresponding to (b) in FIG. 1). In any case, as the diffusion proceeds, the fraction of sites having a composition of about 30% Al increases. In other words, this means that a phase with a high Fe concentration grows, and the Fe concentration during plating increases accordingly. At that time, since 50% Al (FeAl ₂ , Fe ₂ Al ₅ ) that ensures corrosion resistance decreases, the corrosion resistance tends to decrease.

In other words, a predetermined amount of FeAl ₂ and Fe ₂ Al ₅ thicknesses are necessary to ensure post-coating corrosion resistance. In order to ensure the thickness of these phases as much as possible, it is desirable that these phases do not change to about 30% Al when heated. In other words, it means that a smaller diffusion rate of Fe and Al is desirable. The diffusion rate of Fe and Al depends on the steel plate, the component of plating, the structure of the steel plate, etc., but since the steel plate and plating component are determined from other constraints, this is controlled by the surface shape of the steel plate in the present invention. Shall. That is, when the surface roughness is large, the reaction surface area is large, and thus the apparent diffusion rate is increased. Therefore, in the present invention, by reducing the surface area of the steel sheet as much as possible, an attempt is made to leave as much as possible a phase that contributes to corrosion resistance. Specifically, by setting Ra to 0.3 to 1.2 μm, even if the same thermal history is given, a predetermined amount of FeAl ₂ and Fe ₂ Al ₅ thickness easily remains. If it is less than 0.3 μm, seizure during rolling tends to occur, which is not preferable, and if it exceeds 1.2 μm, it is difficult to obtain the effect of reducing the diffusion rate, which is not preferable.

  The steel sheet after hot pressing becomes a final product through welding, chemical conversion treatment, electrodeposition coating, and the like. Usually, cationic electrodeposition coating is often used, and the film thickness is about 1 to 30 μm. After electrodeposition coating, coating such as intermediate coating and top coating may be applied.

Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
Using a cold-rolled steel sheet (thickness: 1.2 mm) having a steel component as shown in Table 1 that has undergone a normal hot-rolling process and cold-rolling process, hot-dip Al plating was performed. At this time, the surface roughness of the steel sheet was adjusted by adjusting the roll roughness of the cold rolling. For the hot-dip Al plating, a non-oxidation furnace-reduction furnace type line was used. After plating, the amount of plating was adjusted to ²⁰ to 100 g / m ² on one side by a gas wiping method, and then cooled. The plating bath composition at this time was Al-9% Si-2% Fe. Fe in the bath is inevitable supplied from plating equipment or strips in the bath. The plating appearance was good with no unplating.

  The characteristics of the sample thus prepared were evaluated. As heating under conditions equivalent to hot pressing, a 200 × 200 mm-sized test piece is heated to 900 ° C. or higher in the air, cooled to a temperature of about 700 ° C. in the air, and then crimped between dies having a thickness of 50 mm. It quickly cooled down. The cooling rate between the molds at this time was about 150 ° C./second. In order to observe the influence of the heating rate, three types of heating methods, namely, electric heating, near infrared heating, and electric furnace radiation heating were used. The heating rate at this time was about 60 ° C./second for electric heating, about 25 ° C./second for near infrared heating, and about 5 ° C./second for electric furnace radiation heating.

これらの試料の塗装後耐食性を評価した。また、加熱した後の鋼板について、垂れによるめっきの厚みの不均一性を評価するため、加熱前後の板厚変化を測定した。

The corrosion resistance after painting of these samples was evaluated. Moreover, in order to evaluate the nonuniformity of the plating thickness by dripping about the steel plate after a heating, the plate | board thickness change before and behind a heating was measured.

  In the evaluation of the corrosion resistance after coating, chemical conversion treatment was performed with a conversion treatment solution PB-SX35T manufactured by Nippon Parkerizing Co., Ltd., and then a cationic electrodeposition paint Powernics 110 manufactured by Nippon Paint Co., Ltd. was applied with a thickness of about 20 μm. After that, a cross cut was put into the coating film with a cutter, a composite corrosion test (JASO-M609) determined by the automobile engineering association was performed for 180 cycles (60 days), and the swollen width from the cross cut (maximum swollen width on one side) was measured. .

  Table 2 summarizes the heating conditions, structure, and property evaluation results. When the rate of temperature increase is increased by near-infrared heating or current heating, a dispersed structure is obtained. Even with furnace heating, a large amount of adhesion resulted in a distributed structure. When the dispersion structure was obtained, the thickness and fraction of about 50% Al corresponding to the first layer were read from the cross-sectional photograph, and the power of the thickness and the fraction was defined as the equivalent thickness. In the case of a 5-layer structure, the thickness of the first layer was read from the cross-sectional photograph. The results of evaluating the corrosion resistance after coating by varying the plating adhesion amount and the ultimate plate temperature are shown together with the GA result of the comparative material. In order to show post-coating corrosion resistance surpassing GA, about 10 μm was required as a thickness of about 50% Al regardless of whether it was a five-layer type or a dispersion type. When the amount of adhesion was small, when the ultimate plate temperature was high, the amount of about 50% Al could not be secured, and the corrosion resistance was lowered. Further, when the roughness of the cold-rolled steel sheet is increased, an influence is recognized particularly in the vicinity of the upper limit temperature for ensuring the corrosion resistance, and the manufacturable range of the hot press has been expanded by reducing the roughness.

（実施例２）
第３表に示した様々な鋼成分を持つ冷延鋼板（板厚１．２ｍｍ）に実施例１と同じ要領で溶融Ａｌめっきを施した。めっき付着量は片面６０ｇ／ｍ^２とした。

(Example 2)
Cold-rolled steel sheets (plate thickness 1.2 mm) having various steel components shown in Table 3 were subjected to hot Al plating in the same manner as in Example 1. The amount of plating was 60 g / m ^{2 on} one side.

  Next, heating was performed at a temperature rising rate of 60 ° C./second and an ultimate temperature of 900 ° C. between 600 to 890 ° C. by electric heating, and then the mold was quenched. The results of measuring the hardness after quenching (Vickers hardness, load 10 kg) are also shown in Table 3. However, if the C content in the steel is low, the hardness after quenching decreases, so the C content is 0.05 mass. % Is preferable. At this time, no sag occurred in all the test pieces.

（実施例３）
第１表に示した鋼成分を有する冷延鋼板（板厚１．４ｍ、Ｒａ０．６７μｍ）に溶融Ａｌめっきを施した。このときの浴組成は１８質量％Ａｌ−２質量％Ｆｅで、Ｆｅは不可避的不純物であった。付着量を８０g/m²とし、この素材をホットプレス相当条件で再度加熱し、大気炉中で９００℃まで到達させた後、１分保定し、金型内で急冷し、実施例１と同じ条件で評価した。その結果、５層組織で、約５０％Ａｌの厚みは８μｍであった。塗膜膨れ幅は８ｍｍとなり塗装後耐食性不良であった。実施例１の番号４との対比より、Ｓｉが悪影響を及ぼしていると判断される。
以上、添付図面を参照しながら本発明の好適な実施形態について説明したが、本発明はかかる例に限定されないことは言うまでもない。当業者であれば、特許請求の範囲に記載された範疇内において、各種の変更例または修正例に想到し得ることは明らかであり、それらについても当然に本発明の技術的範囲に属するものと了解される。

(Example 3)
A cold-rolled steel plate (steel thickness 1.4 m, Ra 0.67 μm) having the steel components shown in Table 1 was subjected to hot Al plating. The bath composition at this time was 18 mass% Al-2 mass% Fe , and Fe was an inevitable impurity. The amount of adhesion was set to 80 g / m ² , this material was heated again under conditions equivalent to hot pressing, reached 900 ° C. in an atmospheric furnace, held for 1 minute, and rapidly cooled in the mold. The condition was evaluated. As a result, in a five-layer structure, the thickness of about 50% Al was 8 μm. The swollen width of the coating film was 8 mm, indicating poor corrosion resistance after painting. From the comparison with No. 4 in Example 1, it is determined that Si has an adverse effect.
As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

It is an optical microscope photograph which shows the structure of the cross-sectional structure | tissue after heat-alloying an Al plating steel plate. It is explanatory drawing which shows the binary system phase diagram of Fe-Al. It is a schematic diagram of the structure of the cross-sectional structure | tissue of the coating layer which concerns on this invention.

Claims (3)

As a steel component in mass%,
C: 0.1-0.4%
Si: 0.01 to 0.6%,
Mn: 0.5-3%,
P: 0.005 to 0.05%,
S: 0.002 to 0.02%,
Al: 0.005 to 0.1%,
Ti: 0.01 to 0.1%,
B: 0.0001 to 0.01%
Cr: 0.01% to 1%, the balance being Fe and unavoidable impurities on the outermost surface of the steel sheet has a phase mainly composed of Fe ₂ Al ₅ and FeAl ₂ of 10 μm or more, and Al concentration at the bottom Has a phase of 40% by mass or less, a high-strength automobile member excellent in corrosion resistance after painting. As a steel component in mass%,
C: 0.1-0.4%
Si: 0.01 to 0.6%,
Mn: 0.5-3%,
P: 0.005 to 0.05%,
S: 0.002 to 0.02%,
Al: 0.005 to 0.1%,
Ti: 0.01 to 0.1%,
B: 0.0001 to 0.01%
On the outermost surface of the steel sheet containing Cr: 0.01 to 1%, the balance being Fe and inevitable impurities, a phase mainly composed of Fe ₂ Al ₅ and FeAl ₂ and having an Al concentration of 40% by mass or less inside. A high-strength automobile member having excellent post-painting corrosion resistance, characterized in that the dispersed phase has a thickness equivalent to 10 μm or more as Fe ₂ Al ₅ and FeAl ₂ thickness, and has an Al concentration of 40% by mass or less at the bottom. . As a steel component in mass%,
C: 0.1-0.4%
Si: 0.01 to 0.6%,
Mn: 0.5-3%,
P: 0.005 to 0.05%,
S: 0.002 to 0.02%,
Al: 0.005 to 0.1%,
Ti: 0.01 to 0.1%,
B: 0.0001 to 0.01%
On the outermost surface of the steel sheet containing Cr: 0.01 to 1%, the balance consisting of Fe and inevitable impurities, and adjusting the surface roughness to 0.3 to 1.2 μm with Ra, Si: 3 to 15 mass plated steel sheet for hot press used for the production of percent and wherein the applying Al plating containing, high strength automobile member according to claim 1 or 2.

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