KR20230169265A - Al-plated steel sheet, manufacturing method of Al-plated steel sheet, and manufacturing method of hot stamped molded body - Google Patents

Abstract

Provided is an Al-plated steel sheet that can suppress hydrogen embrittlement caused by hydrogen penetrating into the steel material as a result of oxidation of the Al plating during hot stamping. The Al-plated steel sheet 1 includes a steel base material having a predetermined chemical composition, an Al plating layer 20, which is a plating layer containing Al and Si, formed on the steel base material, and an oxide layer 30 formed on the Al plating layer 20. And, the thickness (d) of the oxide layer 30 is 10 to 400 nm, the oxide layer 30 includes the hydroxide layer 31, and the thickness (d) of the hydroxide layer 31 relative to the thickness (d) of the oxide layer 30 is 10 to 400 nm. The ratio of thickness d1 is 30% or less. Here, the thickness d of the oxide layer 30 is set as the depth from the surface when the integrated intensity of the oxide becomes 1/2 of the maximum value in depth direction analysis by X-ray photoelectron spectroscopy, and the hydroxide layer ( The thickness d1 in 31) is the depth from the surface when the integrated intensity of the hydroxide becomes 1/2 of the maximum value in depth direction analysis by X-ray photoelectron spectroscopy.

Description

Al-plated steel sheet, manufacturing method of Al-plated steel sheet, and manufacturing method of hot stamped molded body

The present invention relates to an Al-plated steel sheet, a method for manufacturing an Al-plated steel sheet, and a hot stamp molded body. More specifically, it relates to an Al-plated steel sheet for hot stamping, a method for manufacturing the same, and a method for manufacturing a hot stamp molded body using the same. will be.

The hot stamping method is known as a technology for forming high-strength steel (particularly, ultra-high-strength steel of 1500 MPa or more), for which it is difficult to secure formability, with high dimensional accuracy. The hot stamping method eliminates the problem of formability by forming a steel sheet while heated to a high temperature of 800°C or higher, and obtains the desired high strength by cooling after forming.

Since the hot stamping method involves heating in the air, scale is generated on the surface of the steel sheet, which needs to be removed in a later process. To improve this, a technique is known to suppress oxidation by applying Al plating containing Si to the steel sheet.

Japanese Patent Laid-Open No. 2003-193187 describes suppressing the occurrence of cracks during processing by setting the amount of Al in the Fe-Al-based coating to 35% or less. International Publication No. 2019/160106 describes a Fe-Al-based plating hot stamp member in which the Fe-Al-based plating layer has a predetermined structure in order to improve the corrosion resistance of the molded part and the corrosion resistance after painting.

In the hot stamping method, it is known that since hydrogen penetrates into the steel material during heating, the susceptibility of the steel material to hydrogen embrittlement increases. International Publication No. 2012/120692 describes generating an Fe-Mn-based composite oxide in a steel sheet and trapping hydrogen at the interface between the composite oxide and the matrix steel in order to improve delayed fracture resistance.

Japanese Patent Publication No. 2003-193187 International Publication No. 2019/160106 International Publication No. 2012/120692 Japanese Patent Publication No. 2016-65312 Japanese Patent Publication No. 2022-31677 Japanese Patent Publication No. 2022-513595 Japanese Patent Publication No. 6-272017

When a hot stamping process is performed on an Al-plated steel sheet, hydrogen may enter the steel material due to oxidation of the Al plating.

The object of the present invention is to provide a highly reliable Al-plated steel sheet that can suppress hydrogen embrittlement caused by hydrogen entering the steel material accompanying oxidation of the Al plating during hot stamping, and manufacturing the same. It provides a method. Another object of the present invention is to provide a hot stamp molded body in which hydrogen embrittlement is suppressed.

An Al-plated steel sheet according to an embodiment of the present invention is an Al-plated steel sheet for hot stamping, comprising a steel base, an Al plating layer formed on the steel base, which is a plating layer containing Al and Si, and the Al plating layer. It has an oxide layer formed thereon, and the chemical composition of the steel base material, in mass%, is C: 0.1 to 0.6%, Si: 0.01 to 1.50%, Mn: 0.10 to 3.00%, P: 0.05% or less, S: 0.020%. Below, Al: 0.10% or less, Ti: 0.01~0.10%, B: 0.0001~0.0100%, N: 0.015% or less, Cr: 0~1.0%, Mo: 0~1.0%, Ni: 0~1.0%, Cu : 0 to 1.0%, Nb: 0 to 1.0%, balance: Fe and impurities, the thickness of the oxide layer is 10 to 400 nm, the oxide layer includes a hydroxide layer, and the hydroxide layer relative to the thickness of the oxide layer The thickness ratio is less than 30%. Here, the thickness of the oxide layer is the depth from the surface when the integrated intensity of the oxide becomes 1/2 of the maximum value in depth direction analysis by X-ray photoelectron spectroscopy, and the thickness of the hydroxide layer is In the depth direction analysis by line photoelectron spectroscopy, the depth from the surface when the integrated intensity of the hydroxide becomes 1/2 of the maximum value is taken as the depth from the surface.

A method of manufacturing an Al-plated steel sheet according to an embodiment of the present invention includes a preliminary oxidation process of heating the Al-plated steel sheet to a temperature of 120 to 600°C.

A hot stamped molded body according to an embodiment of the present invention includes the process of hot stamping the above Al-plated steel sheet.

According to the present invention, a highly reliable Al-plated steel sheet that can suppress hydrogen embrittlement caused by hydrogen penetrating into the steel material accompanying oxidation of the Al plating during hot stamping is obtained. According to the present invention, a hot stamp molded body with suppressed hydrogen embrittlement is obtained.

1 is a schematic cross-sectional view of an Al-plated steel sheet according to an embodiment of the present invention.
FIG. 2 is an enlarged schematic cross-sectional view showing the structure of the oxide layer in FIG. 1.
Figure 3 is an example of an O 1s spectrum measured by XPS.
Figure 4 is an example of a profile in the depth direction of the integrated intensity of oxides and hydroxides.

The present inventors studied the relationship between the oxide layer formed on the surface of an Al-plated steel sheet and the amount of hydrogen that penetrates into the steel material when the Al-plated steel sheet is subjected to a hot stamping process. In the process of examination, it was found that if a preliminary oxidation process of heating an Al-plated steel sheet was performed under predetermined conditions and then a hot stamping process was performed, the amount of hydrogen infiltrating the steel material was reduced.

Al-plated steel sheets have an oxidation layer (initial oxidation layer) with a thickness of several nm on the surface in the stage immediately after plating. This initial oxide layer includes, in order from the surface side, a hydroxide layer, which is a layer containing a large amount of hydroxide, and an oxide layer, which is a layer containing a small amount of hydroxide. The hydroxide herein is one that contains an OH group (hydroxyl group) in its structure, such as Al(OH) ₃ or AlOOH. On the other hand, oxide is expressed by a chemical formula of only metal and oxygen, such as Al ₂ O ₃ or AlFeO ₄ . In the initial oxidation layer, the ratio of the thickness of the hydroxide layer to the thickness of the oxide layer is relatively high. When a preliminary oxidation process is performed on an Al-plated steel sheet, the oxide layer becomes thicker and the ratio of the thickness of the hydroxide layer to the thickness of the oxide layer decreases.

Hydrogen entering the steel material during the hot stamping process is assumed to be hydrogen from hydroxide on the surface of the steel material and hydrogen from moisture in the atmosphere. It is believed that the above-mentioned preliminary oxidation process contributes to the reduction of both hydrogen. That is, the preliminary oxidation process promotes the release of hydrogen from the hydroxide on the surface of the steel material, and the oxidation layer with reduced hydroxide functions as a protective layer against further oxidation, suppressing the oxidation reaction in the hot stamping process, It is thought that the dissociation reaction of moisture in the atmosphere is suppressed.

The present invention was completed based on the above findings. BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. The same or significant parts in the drawings are given the same reference numerals and their descriptions are not repeated. The dimensional ratio between constituent members shown in each drawing does not necessarily represent the actual dimensional ratio.

[Al plated steel sheet]

Figure 1 is a schematic cross-sectional view of an Al-plated steel sheet 1 according to an embodiment of the present invention. The Al-plated steel sheet 1 includes a steel base 10, an Al plating layer 20 formed on the steel base 10, and an oxide layer 30 formed on the Al plating layer 20. The Al plating layer 20 and the oxide layer 30 may be formed on one side of the steel substrate 10, or may be formed on both sides of the steel substrate 10.

[Oxidation layer]

The oxide layer 30 is a layer formed by oxidizing the surface of the Al plating layer 20, and contains Al oxide and Al hydroxide. The oxide of Al is, for example, Al ₂ O ₃ or AlFeO ₄ . Hydroxides of Al are, for example, Al(OH) ₃ or AlOOH. The oxide layer 30 may contain an oxide other than an oxide of Al or a hydroxide other than a hydroxide of Al.

FIG. 2 is an enlarged schematic cross-sectional view showing the structure of the oxide layer 30. The oxide layer 30 includes a hydroxide layer 31, which is a layer containing a large amount of hydroxide, and an oxide layer 32, a layer containing a small amount of hydroxide. Hydroxides contained in the oxide layer 30 are largely distributed on the surface side of the oxide layer 30. Therefore, a hydroxide layer 31 is formed on the surface side and an oxide layer 32 is formed on the substrate side.

In this embodiment, the thickness d of the oxide layer 30 is 10 to 400 nm, and the ratio of the thickness d1 of the hydroxide layer 31 to the thickness d of the oxide layer 30 is 30% or less.

The oxidation layer 30 functions as a protective layer against further oxidation of the Al-plated steel sheet 1. That is, by forming the oxidation layer 30 of a predetermined thickness on the Al-plated steel sheet 1 in advance, the oxidation reaction in the hot stamping process can be suppressed. As a result, the amount of hydrogen penetrating into the steel substrate 10 during the hot stamping process can be reduced. If the thickness d of the oxide layer 30 is less than 10 nm, this effect cannot be sufficiently obtained. On the other hand, when the thickness d of the oxide layer 30 exceeds 400 nm, the influence of hydrogen in the hydroxide contained in the oxide layer 30 increases. The lower limit of the thickness d of the oxide layer 30 is preferably 20 nm. The upper limit of the thickness d of the oxide layer 30 is preferably 300 nm, more preferably 200 nm, even more preferably 100 nm, and even more preferably 50 nm.

Hydroxide contained in the oxide layer 30 may become a source of hydrogen penetrating into the steel substrate 10. By setting the ratio of the thickness d1 of the hydroxide layer 31 to the thickness d of the oxide layer 30 to 30% or less, the amount of hydrogen penetrating into the steel material from the hydroxide can be reduced. The ratio of the thickness d1 of the hydroxide layer 31 to the thickness d of the oxide layer 30 is preferably 25% or less, more preferably 20% or less, and even more preferably 15% or less. .

The thickness d of the oxide layer 30 and the thickness d1 of the hydroxide layer 31 are measured as follows by depth direction analysis using X-ray photoelectron spectroscopy (XPS).

Figure 3 is an example of an O 1s spectrum measured by XPS. The O 1s spectrum includes oxide peaks and hydroxide peaks. The background is subtracted from this O 1s spectrum, the waveforms of the oxide peak and the hydroxide peak are separated, and the respective integrated intensities are determined. Background processing uses the typical Shirley method as XPS data processing. The ratio of integrated intensities obtained here coincides with the abundance ratio of oxides and hydroxides at the depth being measured.

While performing sputtering with Ar ⁺ ions, sputtering and XPS measurement are repeated to obtain a profile of the integrated intensity of the oxide and hydroxide in the depth direction. Figure 4 is an example of a profile in the depth direction of the integrated intensity of oxides and hydroxides.

Here, the position where the integrated intensity of the hydroxide is 1/2 of the maximum value is taken as the layer boundary between the hydroxide layer 31 and the oxide layer 32. Additionally, the position where the integrated intensity of the oxide is 1/2 of the maximum value is set as the layer boundary between the oxide layer 32 and the Al plating layer 20.

That is, the thickness d1 of the hydroxide layer 31 is the depth from the surface when the integrated intensity of the hydroxide becomes 1/2 of the maximum value. Additionally, the thickness d of the oxide layer 30 is the depth from the surface when the integrated intensity of the oxide becomes 1/2 of the maximum value. Additionally, the thickness d2 of the oxide layer 32 is obtained by subtracting the thickness d1 of the hydroxide layer 31 from the thickness d of the oxide layer 30.

[Al plating layer]

The Al plating layer 20 is a plating layer containing Al and Si. In the Al plating layer 20, intermetallic compounds of Al, Fe, and Si may be formed. The chemical composition of the Al plating layer 20 (average composition in the thickness direction, hereinafter the same in this paragraph) is not limited to this, but is, for example, Al: 20 to 100 mass%, Si: 1 to 20 mass%, Fe: 0 to 60 mass%. The lower limit of the Al content of the Al plating layer 20 is preferably 25% by mass. The upper limit of the Al content of the Al plating layer 20 is preferably 95 mass%, more preferably 90 mass%, further preferably 70 mass%, and even more preferably 55 mass%. The lower limit of the Si content of the Al plating layer 20 is preferably 2% by mass, and more preferably 5% by mass. The upper limit of the Si content of the Al plating layer 20 is preferably 15 mass%, and more preferably 12 mass%. The lower limit of the Fe content of the Al plating layer 20 is preferably 20% by mass. The upper limit of the Fe content of the Al plating layer 20 is preferably 50 mass%, more preferably 40 mass%.

The Al plating layer 20 may contain elements other than Al, Si, and Fe. Specifically, Be, Mg, Ca, Sr, Ba, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Zr, Y, Nb, Ce, and Ta may be added. The total content of elements other than Al, Si, and Fe is preferably 10 mass% or less, more preferably 5 mass% or less, further preferably 3 mass% or less, and even more preferably 1 mass%. It is as follows.

The thickness of the Al plating layer 20 is not particularly limited, but is, for example, 1 to 100 μm. The lower limit of the thickness of the Al plating layer 20 is preferably 5 μm, more preferably 10 μm, and still more preferably 15 μm. The upper limit of the thickness of the Al plating layer 20 is preferably 50 μm, more preferably 40 μm, and even more preferably 30 μm.

[Kang Ki-gi]

The steel base material 10 is, for example, a hot rolled steel sheet or a cold rolled steel sheet. Hereinafter, the chemical composition of the steel base material 10 will be described. In the following description, “%” of element content means mass%.

C: 0.1~0.6%

Carbon (C) is contained to secure the desired mechanical strength. When the C content is less than 0.1%, sufficient improvement in mechanical strength is not obtained. On the other hand, when the C content exceeds 0.6%, elongation and cross-sectional shrinkage tend to decrease. The upper limit of the C content is preferably 0.5%.

Si: 0.01~1.50%

Silicon (Si) is an element that improves mechanical strength, and, like C, is contained to ensure the desired mechanical strength. When the Si content is less than 0.01%, sufficient improvement in mechanical strength is not obtained. On the other hand, when the Si content exceeds 1.50%, there is a risk that wettability will decrease during plating and non-plating may occur due to the influence of Si oxide formed on the surface layer of the steel substrate. The upper limit of Si content is preferably 0.60%.

Mn: 0.10~3.00%

Manganese (Mn) is one of the reinforcing elements that strengthens steel, and is also one of the elements that improves hardenability. Mn is also effective in preventing hot embrittlement caused by S, which is one of the impurities. When the Mn content is less than 0.10%, these effects are not sufficiently obtained. On the other hand, if the Mn content exceeds 3.00%, there is a risk that the retained austenite increases too much and the strength decreases. The lower limit of the Mn content is preferably 0.50%. The upper limit of the Mn content is preferably 2.00%.

P: 0.05% or less

Phosphorus (P) is an impurity contained in the steel base material. P contained in the steel base material may segregate into the grain boundaries of the steel base material, thereby lowering the toughness of the steel base material. It is desirable to keep the P content as low as possible.

S: 0.020% or less

Sulfur (S) is an impurity contained in the steel base material. S contained in the steel base material may form sulfides and reduce the toughness of the steel base material. It is desirable to keep the S content as low as possible.

Al: 0.10% or less

Aluminum (Al) is generally used for deoxidation purposes in steel. However, when the Al content is high, the Ac ₃ point of the steel base increases, so it is necessary to increase the heating temperature necessary to ensure the hardenability of the steel during the hot stamping process. Therefore, the Al content is preferably 0.10% or less. The Al content is more preferably 0.05% or less, and even more preferably 0.01% or less.

Ti: 0.01~0.10%

Titanium (Ti) is one of the strength enhancing elements. When the Ti content is less than 0.01%, the strength improvement effect and the oxidation resistance improvement effect are not sufficiently obtained. On the other hand, when the Ti content exceeds 0.10%, there is a risk that carbides and nitrides may be formed, causing the steel to soften.

B: 0.0001~0.0100%

Boron (B) acts during quenching and has the effect of improving strength. When the B content is less than 0.0001%, the strength improvement effect is not sufficiently obtained. On the other hand, if the B content exceeds 0.0100%, there is a risk that inclusions are formed, the steel base material becomes embrittled, and the fatigue strength decreases.

N: 0.015% or less

Nitrogen (N) is an impurity contained in the steel base material. N contained in the steel base material may form nitrides and reduce the toughness of the steel base material. In addition, N contained in the steel base material may combine with B to reduce the amount of solid solution B, thereby lowering the hardenability improvement effect of B. It is desirable to keep the N content as low as possible. The upper limit of N content is preferably 0.010%.

The steel base material 10 may contain one or more of Cr, Mo, Ni, Cu, and Nb. Cr, Mo, Ni, Cu, and Nb are all arbitrary elements. That is, the steel base material 10 does not need to contain any or all of Cr, Mo, Ni, Cu, and Nb.

Cr: 0~1.0%

Chromium (Cr) improves hardenability and increases temper softening resistance by forming carbides. Additionally, it improves corrosion resistance and is effective in improving high-temperature strength. Therefore, it may be contained as needed. The lower limit of Cr content is preferably 0.01%. On the other hand, even if it is contained in excess of 1.0%, the effect is saturated, resulting in an increase in cost.

Mo: 0~1.0%

Molybdenum (Mo) is easy to form carbide and increases temper softening resistance. The effect is increased by complex addition with Cr. In addition, a small amount improves hardenability, increases the grain coarsening temperature, and has a high effect of preventing tempering embrittlement. Therefore, it may be contained as needed. The lower limit of Mo content is preferably 0.01%. On the other hand, even if it is contained in excess of 1.0%, the effect is saturated, resulting in an increase in cost.

Ni: 0~1.0%

Nickel (Ni) significantly lowers the A1 transformation point and improves strength, toughness, and hardenability. A synergistic effect is likely to occur through complex addition with Cr or Mo. It also improves corrosion resistance and prevents low-temperature embrittlement. Therefore, it may be contained as needed. The lower limit of Ni content is preferably 0.01%. On the other hand, even if it is contained in excess of 1.0%, the effect is saturated, resulting in an increase in cost.

Cu: 0~1.0%

Copper (Cu) improves hardenability and corrosion resistance. Therefore, it may be contained as needed. The lower limit of Cu content is preferably 0.01%. On the other hand, even if it is contained in excess of 1.0%, the effect is saturated, resulting in an increase in cost.

Nb: 0~1.0%

Niobium (Nb) improves hardenability. Nb has a larger metal radius and higher density than Fe, the main component of steel, so it is difficult to dissolve in the Fe matrix and plays a role in preventing coarsening of grains by precipitating at the grain boundaries of steel materials. Additionally, tempering embrittlement is suppressed. Therefore, it may be contained as needed. The lower limit of Nb content is preferably 0.01%. On the other hand, even if it is contained in excess of 1.0%, the effect is saturated, resulting in an increase in cost.

The remainder of the chemical composition of the steel base material 10 is Fe and impurities. The impurities referred to here refer to elements mixed from ore or scrap used as raw materials for steel, or elements mixed from the environment of the manufacturing process, etc. Impurities include, for example, Zn, Co, Sn, V, As, Zr, Ca, Mg, etc. in addition to the elements mentioned above.

[Manufacturing method of Al-plated steel sheet]

Next, an example of a manufacturing method for the Al-plated steel sheet 1 will be described.

[Plating process]

An Al plating layer 20 is formed on the surface of the steel substrate 10 by a hot dip plating method. The temperature of the plating bath is preferably 600 to 700°C. If the temperature of the plating bath is lower than 600°C, the plating bath has a low viscosity, making uniform plating difficult. If the temperature of the plating bath is higher than 700°C, the components change in a short time due to volatilization, making process control difficult.

The plating bath contains Si in addition to Al. The Si content in the plating bath is, for example, 1 to 20 mass%, and is preferably 5 to 15 mass%. The plating bath may contain elements other than Al and Si. Specifically, in addition to Fe, Al, Si, O, and H, the plating bath contains Be, Mg, Ca, Sr, Ba, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Zr, Y, Nb, Ce, Ta, etc. may be added. The ratio of metal components in the Al plating layer 20 and the oxide layer 30 is modulated depending on the chemical composition of the plating bath, but is applicable as long as the plating layer formed in the plating process is a layer mainly composed of Al. The lower limit of the Al content in the plating bath is preferably 70 mass%, preferably 80 mass%, more preferably 85 mass%, and still more preferably 88 mass%.

The steel base material 10 is maintained at, for example, 700 to 800°C and then immersed in a plating bath. The entire plating process is preferably carried out in a non-oxidizing atmosphere (including a reducing atmosphere). In an oxidizing atmosphere, the surface of the steel base material 10 is oxidized, which may cause plating to become uneven, and in addition, loss may occur due to oxidation of the plating bath. The thickness of the Al plating layer 20 can be adjusted by the temperature of the plating bath, viscosity, immersion time, gas injection, etc.

Although the case where the plating layer is formed by the hot dip plating method has been described above, the plating layer may be formed by vapor deposition or thermal spraying instead of the hot dip plating method. In this case, an Al alloy may be used, or Al and additional elements may be separately deposited or sprayed.

[Preliminary oxidation process]

A preliminary oxidation process is performed in which the Al-plated steel sheet is heated under predetermined conditions. Specifically, the Al-plated steel sheet is heated to a temperature of 120 to 600°C (an arbitrary temperature within the range of 120°C to 600°C).

If the temperature of preliminary oxidation is lower than 120°C, the progress of dehydration from the initial oxidation layer is slow, and the ratio of the thickness (d1) of the hydroxide layer 31 to the thickness (d) of the oxide layer 30 cannot be sufficiently reduced. There is. On the other hand, if the temperature of preliminary oxidation exceeds 600°C, it may become difficult to appropriately control the thickness d of the oxidation layer 30. In addition, there are cases where the Al plating layer 20 forms an alloy with the steel base material 10 or the steel base material 10 deteriorates, thereby reducing workability and making it unsuitable as a steel sheet for hot stamping. The lower limit of the temperature for preliminary oxidation is preferably 150°C, and more preferably 180°C. The upper limit of the temperature for preliminary oxidation is preferably 400°C, more preferably 300°C, and even more preferably 250°C.

The holding time depends on temperature and other conditions, but is, for example, 1 minute to 48 hours. The lower limit of the holding time is preferably 20 minutes, and more preferably 40 minutes. The upper limit of the holding time is preferably 24 hours, more preferably 12 hours, still more preferably 4 hours, and still more preferably 2 hours.

The preliminary oxidation process is preferably performed in an oxidizing atmosphere, and is especially preferably performed in air from the viewpoint of cost. However, the preliminary oxidation process can be performed as long as it is not in an excessively non-oxidizing atmosphere. For example, the preliminary oxidation process can be performed under reduced pressure, in a reducing atmosphere, in an inert gas atmosphere, in a high dew point environment, etc., depending on the conditions. Accordingly, the desired oxidation layer 30 can be formed. The atmosphere of the preliminary oxidation process preferably has a dew point of -70°C or higher, more preferably -30°C or higher, and even more preferably 0°C or higher. The atmosphere of the preliminary oxidation process preferably has an oxygen partial pressure of 0.001 MPa or more, and more preferably 0.01 MPa or more.

The heating method for the preliminary oxidation process is arbitrary, and for example, a high-temperature furnace or electric heating can be used. The temperature increase rate and temperature decrease rate are arbitrary, and can be, for example, 10 to 1000°C/s.

The preliminary oxidation process can be performed at any timing after the plating process but before the plated steel sheet is subjected to the hot stamping process. The preliminary oxidation process may be performed at any of the following timings: for example, during the winding process after the plating process, during roll storage after winding, or during roll unfolding before the hot stamping process.

Through the above process, the Al-plated steel sheet 1 is manufactured. In the Al-plated steel sheet (1), the thickness (d) of the oxide layer (30) is 10 to 400 nm, and the ratio of the thickness (d1) of the hydroxide layer (31) to the thickness (d) of the oxide layer (30) is 30% or less. am. As a result, a highly reliable Al-plated steel sheet that can suppress hydrogen embrittlement caused by hydrogen penetrating into the steel material accompanying oxidation of the Al plating during hot stamping is obtained.

The Al-plated steel sheet 1 can be suitably used as a steel sheet for hot stamping. The hot stamping process performed on the Al-plated steel sheet 1 is not particularly limited, but examples are as follows. The Al-plated steel sheet (1) is shaped to a predetermined size and then heated. The heating method may be either a high-temperature furnace or electric heating. The holding temperature is preferably 850 to 950°C, and the holding time is preferably 2 minutes or more. After heating, it is molded into a mold and simultaneously cooled by the mold.

[Method for manufacturing hot stamp molded body]

A method for manufacturing a hot stamp molded body according to an embodiment of the present invention includes a process of hot stamping an Al-plated steel sheet (1). The Al-plated steel sheet 1 can suppress hydrogen embrittlement caused by hydrogen penetrating into the steel material accompanying oxidation of the Al plating during hot stamping. Therefore, according to the method for manufacturing a hot stamp molded body according to the present embodiment, a hot stamp molded body with suppressed hydrogen embrittlement is obtained.

Example

Hereinafter, the present invention will be described in more detail through examples. The present invention is not limited to these examples.

For a steel sheet having the chemical composition shown in Table 1, an Al plating layer was formed on both sides of the steel sheet by a hot dip plating method.

The chemical composition of the plating bath was Al-10 mass% Si-2 mass% Fe. Fe in the plating bath is inevitably supplied from plating equipment or steel sheets. The temperature of the plating bath during hot dip plating was 700°C. After the steel sheet was immersed in the plating bath, the adhesion amount was adjusted to 70 g/m ² per side using a gas wiping method.

After that, a preliminary oxidation process was performed under the conditions shown in Table 2 below to produce an Al-plated steel sheet. A plurality of Al-plated steel sheets that had undergone a preliminary oxidation process under the same conditions were produced, and surface analysis by XPS was performed on some of them.

[Surface analysis by XPS]

For the XPS measurement, PHI Quantera SXM manufactured by Ulvac-Pi Co., Ltd. was used. As an

Short-term sputtering and XPS measurements were repeated to obtain a profile of the integrated intensity of oxides and hydroxides in the depth direction. Sputtering with Ar ⁺ ions was performed at an acceleration voltage of 4 kV and a sputtering area of 1 mm x 1 mm. The sputtering rate was 75.1 nm/min in SiO ₂ conversion.

From the profile in the depth direction of the integrated intensities of the oxide and hydroxide, the thickness d of the oxide layer 30 and the thickness d1 of the hydroxide layer 31 were determined by the method described above.

[Hot stamp process and hydrogen analysis]

The Al-plated steel sheet after the preliminary oxidation process was heated in an electric resistance furnace at a furnace temperature of 900°C so that the soaking time was 5 minutes. After that, it was molded using a mold and simultaneously cooled with a mold to obtain a hot stamp molded body.

The hot stamp molded body was stored in liquid nitrogen, and a temperature-elevated desorption analysis was performed as it was to quantify the amount of hydrogen. The integrated value of hydrogen up to 250°C was obtained. Additionally, if the hydrogen amount exceeds 0.7 mass ppm, it is unsuitable for 1.5 GPa grade steel materials, and if it exceeds 0.5 mass ppm, it is unsuitable for 1.8 GPa grade steel materials.

The conditions of the pre-oxidation process, the results of surface analysis by XPS, and the results of hydrogen analysis are shown in Table 2.

As shown in Table 2, the Al-plated steel sheets labeled A01 to A11 have an oxide layer thickness (d) in the range of 10 to 400 nm, and the ratio of the hydroxide layer thickness (d1) to the oxide layer thickness (d) is It was less than 30%. The hydrogen content of the hot stamped bodies manufactured from these Al-plated steel sheets was all 0.2 mass ppm or less.

In contrast, the hydrogen content of the hot stamped molded bodies manufactured from the Al-plated steel sheets of labels a1 to a8 was all 0.5 mass ppm or more.

The Al-plated steel sheet labeled a1 is an example in which the preliminary oxidation process was not performed. In the Al-plated steel sheet labeled a1, the oxide layer thickness (d) was less than 10 nm, and the ratio of the hydroxide layer thickness (d1) to the oxide layer thickness (d) was higher than 30%.

For the Al-plated steel sheets labeled a2, a4, and a6, the thickness (d) of the oxide layer was in the range of 10 to 400 nm, but the ratio of the thickness (d1) of the hydroxide layer to the thickness (d) of the oxide layer was higher than 30%. .

In the Al-plated steel sheet of label a3, the ratio of the thickness (d1) of the hydroxide layer to the thickness (d) of the oxide layer was 30% or less, but the thickness (d) of the oxide layer was greater than 400 nm. In the Al-plated steel sheets of labels a5 and a7, the ratio of the thickness (d1) of the hydroxide layer to the thickness (d) of the oxide layer was 30% or less, but the thickness (d) of the oxide layer was less than 10 nm. In the Al-plated steel sheet of label a8, the ratio of the thickness (d1) of the hydroxide layer to the thickness (d) of the oxide layer was higher than 30%, and the thickness (d) of the oxide layer was also smaller than 10 nm.

Although embodiments of the present invention have been described above, the above-described embodiments are only examples for carrying out the present invention. Accordingly, the present invention is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments without departing from the spirit thereof.

1 Al plated steel sheet
10 lectures
20 Al plating layer
30 Oxide layer
31 Hydroxide layer
32 Oxide layer

Claims (3)

As an Al-plated steel sheet for hot stamping,
Steel substrate,
An Al plating layer, which is a plating layer containing Al and Si, formed on the steel substrate,
Provided with an oxide layer formed on the Al plating layer,
The chemical composition of the steel base material is expressed in mass%,
C: 0.1~0.6%;
Si: 0.01~1.50%;
Mn: 0.10~3.00%,
P: 0.05% or less,
S: 0.020% or less,
Al: 0.10% or less,
Ti: 0.01~0.10%,
B: 0.0001~0.0100%,
N: 0.015% or less,
Cr: 0~1.0%,
Mo: 0~1.0%,
Ni: 0~1.0%,
Cu: 0~1.0%,
Nb: 0~1.0%,
Rest: Fe and impurities,
The thickness of the oxide layer is 10 to 400 nm,
The oxide layer includes a hydroxide layer, and the ratio of the thickness of the hydroxide layer to the thickness of the oxide layer is 30% or less.
Here, the thickness of the oxide layer is the depth from the surface when the integrated intensity of the oxide becomes 1/2 of the maximum value in depth direction analysis by X-ray photoelectron spectroscopy, and the thickness of the hydroxide layer is In the depth direction analysis by line photoelectron spectroscopy, the depth from the surface when the integrated intensity of the hydroxide becomes 1/2 of the maximum value is taken as the depth from the surface. A method for manufacturing an Al-plated steel sheet according to claim 1, comprising:
A method of manufacturing an Al-plated steel sheet, comprising a preliminary oxidation process of heating the Al-plated steel sheet to a temperature of 120 to 600°C. A method for producing a hot stamped molded body, comprising the step of hot stamping the Al-plated steel sheet according to claim 1.

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