阅读说明：本技术 热压成形体 (Hot press molded body ) 是由 中川浩行 阿久津宏树 于 2020-07-02 设计创作，主要内容包括：一种热压成形体,具有钢板和配置于所述钢板上的皮膜,所述钢板具有规定的化学组成。关于该皮膜,直到100μm深度的位置为止进行GDS测定时,作为Zn的累积量的Zn-(total)为10.0g/m～(2)以上且小于40.0g/m～(2),直到Al的峰位置为止进行GDS测定时,作为Zn的累积量的Zna与Mn的累积量之和为20.0g/m～(2)以下,Al的累积量、Si的累积量和Cr的累积量之和为60mg/m～(2)以上且240mg/m～(2)以下,所述Zn-(total)-所述Zna为3.0g/m～(2)以上且30.0g/m～(2)以下,算术平均粗糙度Ra小于1.50μm。(A hot press formed body has a steel sheet and a coating film disposed on the steel sheet, and the steel sheet has a predetermined chemical composition. In this coating, Zn is an accumulated amount of Zn when GDS measurement is performed up to a position of 100 μm depth total Is 10.0g/m 2 Above and below 40.0g/m 2 When GDS measurement was performed up to the peak position of Al, the sum of Zna, which is the cumulative amount of Zn, and the cumulative amount of Mn was 20.0g/m 2 Hereinafter, the sum of the cumulative amount of Al, the cumulative amount of Si and the cumulative amount of Cr is 60mg/m 2 Above 240mg/m 2 Hereinafter, the Zn total -said Zna is 3.0g/m 2 Above and 30.0g/m 2 Hereinafter, the arithmetic average roughness Ra is less than 1.50 μm.)

1. A hot press-formed article comprising a steel sheet and a coating film disposed on the steel sheet,

the steel sheet has a chemical composition containing, in mass%

C: 0.02% to 0.58%,

Mn: 0.10% to 3.00%,

Al: 0.001% to 1.000%,

Si: less than 2.00 percent,

P: less than 0.100 percent,

S: less than 0.005 percent,

N: less than 0.0100%,

Ti: 0% to 0.200%,

Nb: 0% to 0.200%,

V: 0% to 1.00%,

W: 0% or more and 1.00% or less

Cr: 0% to 1.00%,

Mo: 0% to 1.00%,

Cu: 0% to 1.00%,

Ni: 0% to 1.00%,

B: 0% to 0.0100%,

Ca: 0% or more and 0.05% or less, and

REM: 0% or more and 0.05% or less,

the balance of Fe and impurities,

the skin is formed by coating a surface of the skin,

zn as Zn accumulation amount when GDS measurement is performed from the surface of the coating to a position at a depth of 100 [ mu ] m from the surface_totalIs 10.0g/m²Above and below 40.0g/m²，

When GDS measurement is performed from the surface to the peak position of Al, the sum of Zna as the cumulative amount of Zn and the cumulative amount of Mn is 20.0g/m²Hereinafter, the sum of the cumulative amount of Al, the cumulative amount of Si and the cumulative amount of Cr is 60mg/m²Above 240mg/m²In the following, the following description is given,

said Zn_total-said Zna is 3.0g/m²Above and 30.0g/m²In the following, the following description is given,

the arithmetic average roughness Ra is less than 1.50 μm.

2. The thermocompression formed body according to claim 1,

the chemical composition of the steel sheet contains, in mass%, a chemical component selected from the group consisting of

Ti: 0.005% to 0.200%,

Nb: 0.005% to 0.200%,

V: 0.10% to 1.00%,

W: 0.10% to 1.00%,

Cr: 0.05% to 1.00%,

Mo: 0.05% to 1.00%,

Cu: 0.05% to 1.00%,

Ni: 0.05% to 1.00%,

B: 0.0010% to 0.0100%,

Ca: 0.0005% or more and 0.05% or less, and

REM: 0.0005% or more and 0.05% or less

1 or 2 of them.

Technical Field

The present invention relates to a hot press-formed body. More specifically, the present invention relates to a hot press molded body suitable for production of a member for non-rust prevention use such as an automobile member.

This application claims priority to patent application No. 2019-123334, which is filed on day 2, 7/2019, the contents of which are incorporated herein by reference.

Background

In recent years, methods for reducing the thickness of steel sheets by increasing the strength of steel sheets have been studied for the purpose of reducing the weight of automobiles. As a technique for press forming a material difficult to form such as a high-strength steel sheet, a hot forming method such as hot press (hot stamp) is used in which a steel sheet material to be formed is heated in advance and then formed.

Such a forming method is a forming method capable of achieving both high strength and excellent formability of a member because the forming is performed at a high temperature with a small deformation resistance and the quenching can be performed simultaneously with the forming. However, when this forming method is employed, the steel sheet material needs to be heated to a high temperature of 700 ℃ or higher before forming, and therefore, there is a problem that the steel sheet surface is oxidized during heating before hot pressing. There are the following problems: the scale made of iron oxide generated by oxidation of the steel sheet surface falls off during hot pressing and adheres to the die, which lowers productivity, and remains on the surface of the formed product after hot pressing, resulting in poor appearance. When such scale remains on the surface of the molded article, the adhesion between the molded article and the coating film is poor and the corrosion resistance is reduced when the coating is performed in a subsequent step. Therefore, after hot pressing, scale removal treatment such as shot blasting is required.

In order to solve such problems, there have been proposed: as a steel sheet material for hot forming, a plated steel sheet coated with zinc plating or aluminum plating is used for the purpose of suppressing oxidation of the surface of a base steel sheet and/or improving corrosion resistance of a press-formed product. Examples of hot forming using galvanized steel sheets include techniques described in patent documents 1 and 2.

Patent document 3 proposes a galvanized steel sheet for hot forming, in which the C concentration, Si concentration, P concentration and/or Ti concentration in the steel is controlled, and the Zn deposition amount on the surface of the steel sheet and the Al concentration in the coating film are controlled, thereby improving the adhesion between the oxide film formed during hot forming and the steel sheet, and simplifying or eliminating the step of removing the oxide on the surface of the press-formed product.

Prior art documents

Patent document

Patent document 1: japanese laid-open patent publication No. 2003-73774

Patent document 2: japanese unexamined patent publication No. 2001-353548

Patent document 3: japanese laid-open patent publication No. 2005-48254

Patent document 4: international publication No. 2014/024825

Disclosure of Invention

In patent documents 1 to 3, when the zinc oxide layer formed during hot pressing is excessively generated, fusion or sparks may occur during spot welding after hot pressing. As a technique for improving these, patent document 4 discloses a technique for suppressing fusion and sparking (spark) at the time of spot welding after hot forming.

Patent document 4 discloses: the amount of the coating is 40 to 110g/m²The zinc-based plated steel sheet for hot forming according to (1) is improved in seizure and sparking at the time of spot welding. Steel sheets for hot forming are roughly classified into rust prevention applications and non-rust prevention applications in terms of rust prevention as applications after hot forming. The former requires the same degree of corrosion resistance as that of a general galvanized steel sheet, and the greater the amount of Zn in a coating film contributing to corrosion resistance, the more excellent the corrosion resistance. However, since the latter steel sheet only requires corrosion resistance to the same extent as that of a normal cold-rolled steel sheet, the amount of Zn in the coating is not critical from the viewpoint of corrosion resistance, and it is sufficient that the amount of Zn is enough to suppress the scale after hot-pressing.

In patent document 4, in order to secure a Zn amount capable of suppressing oxidation of a steel sheet, 40g/m is required²The above plating adhesion amount. According to the research of the inventor, the method has the following advantages: in the technique described in patent document 4, if the amount of plating deposit is less than 40g/m²In a usual alloyed hot-dip galvanized layer, it is difficult to control the Al content in the coating film to 150mg/m²As described above, it is difficult to prevent sparking and seizure at spot welding.

Therefore, if the amount of deposit of the plating layer is set to less than 40g/m²Even in the case of (3), if the scale after hot pressing is suppressed and sparking and fusion at the time of spot welding are prevented, cost reduction by Zn amount reduction can be achieved, and it can contribute to suppression of Zn resource utilization.

Automotive body parts are assembled by joining parts that have been hot-pressed into various shapes to each other by resistance welding (particularly spot welding). Particularly in the case of spot welding, the nugget diameter is 4t^1/2The wider the current range (suitable welding current range) in which the above (t is the plate thickness of the component) and no spattering occurs, the higher the robustness (robust) against variations in manufacturing, and the higher the productivity can be contributed.

Generally, a plated steel sheet has a narrower suitable welding current range than a cold-rolled steel sheet. This is because the melting point is lowered by the plating layer, and therefore, the limit current at which sputtering occurs is lowered. If the amount of plating adhesion can be reduced, the appropriate welding current range is widened, but in the case of a general plated steel sheet, the lower limit of the amount of plating adhesion is limited in order to ensure corrosion resistance. In the case of a hot-press steel sheet for non-rust preventive use, it is considered that a large amount of Zn is not necessary from the viewpoint of ensuring corrosion resistance, and if the amount of Zn can be reduced, the appropriate welding current range is expanded, and productivity can be improved.

Automotive body parts are subjected to a coating treatment including a chemical conversion treatment and electrodeposition after the spot welding, and therefore are required to have coating film adhesion. When a zinc-based plated steel sheet is hot-pressed, the plated layer reacts with the steel substrate to form a new alloy, and the surface is oxidized to form a Zn-based oxide. The Zn-based oxide is known to have good adhesion to the chemical conversion coating. However, according to the study of the present inventors, it was found that: the surface oxide is not only Zn-based but also Mn-based, Al-based, Si-based, Cr-based, and the like in many cases, and when the amount of Zn is small, the coating adhesion is impaired depending on the conditions. Therefore, in order to apply a plating layer having a low Zn content to automotive applications, a new technique for controlling various oxides to ensure coating film adhesion is required.

Further, automotive body parts are required to absorb energy at the time of collision, while weight reduction by high-strength materials is required for good fuel economy. Although deformation at the time of collision is complicated, if the bendability is good, the possibility of suppressing early breaking increases, and therefore a member having high strength and good bendability is required. The strength of the hot-pressed member is approximately determined by the amount of carbon, but the bendability varies depending on the chemical composition and the production method even if the strength is the same. Therefore, if the bendability after hot pressing can be improved, applicable parts are expanded, and the industrial usefulness is greatly improved.

That is, a hot press molded body to be used for a vehicle body member of an automobile is required to have excellent coating film adhesion, and as a more preferable characteristic, excellent bendability is also required.

The present invention has been made in view of the above problems, and an object thereof is to provide a hot press-formed body having high strength, suppressed generation of scale, capable of preventing sparking and seizure at spot welding, having a wide appropriate welding current range, and having excellent coating film adhesion and bendability.

The present inventors have intensively studied conditions under which the formation of scale can be suppressed after hot pressing of a hot-press galvanized steel sheet. As a result, they found that: by controlling the chemical composition of the steel sheet to be provided with the zinc-plated coating, and the amount of plating, the Fe concentration, the Al amount, and the Al concentration of the zinc-plated coating within appropriate ranges, it is possible to form an Al oxide, if necessary, an Si oxide, and a Cr oxide on the coating surface during heating before hot pressing, suppress excessive oxidation and evaporation of metallic zinc in the coating, form an appropriate amount of zinc oxide on the coating surface, and suppress the formation of scale.

In addition, the inventor newly found that: when the Si content, Cr content, and Al content in the galvanized steel sheet for hot pressing and the Al content in the galvanized coating film become excessive, the adhesion between the zinc oxide in the coating film after hot pressing and the Fe — Zn solid solution formed thereunder decreases, and the coating film adhesion (the adhesion between the coating film and the coating film disposed thereon) decreases. Moreover, the inventors newly found that: if the surface roughness after hot pressing is reduced, the bendability after hot pressing can be improved.

The gist of the present invention completed based on the above findings is as follows.

[1] A hot press molded body according to one aspect of the present invention includes a steel sheet and a coating film disposed on the steel sheet,

the steel sheet has a chemical composition containing, in mass%

C: 0.02% to 0.58%,

Mn: 0.10% to 3.00%,

Al: 0.001% to 1.000%,

Si: less than 2.00 percent,

P: less than 0.100 percent,

S: less than 0.005 percent,

N: less than 0.0100%,

Ti: 0% to 0.200%,

Nb: 0% to 0.200%,

V: 0% to 1.00%,

W: 0% or more and 1.00% or less

Cr: 0% to 1.00%,

Mo: 0% to 1.00%,

Cu: 0% to 1.00%,

Ni: 0% to 1.00%,

B: 0% to 0.0100%,

Ca: 0% or more and 0.05% or less, and

REM: 0% or more and 0.05% or less,

the balance of Fe and impurities,

the skin is formed by coating a surface of the skin,

zn as Zn accumulation amount when GDS measurement is performed from the surface of the coating to a position at a depth of 100 [ mu ] m from the surface_totalIs 10.0g/m²Above and below 40.0g/m²，

When GDS measurement is performed from the surface to the peak position of Al, the sum of Zna as the cumulative amount of Zn and the cumulative amount of Mn is 20.0g/m²Hereinafter, the sum of the cumulative amount of Al, the cumulative amount of Si and the cumulative amount of Cr is 60mg/m²Above 240mg/m²In the following, the following description is given,

said Zn_total-said Zna is 3.0g/m²Above and 30.0g/m²In the following, the following description is given,

the arithmetic average roughness Ra is less than 1.50 μm.

[2] The hot press-formed body according to the above [1], wherein the chemical composition of the steel sheet may contain a chemical composition selected from the group consisting of

Ti: 0.005% to 0.200%,

Nb: 0.005% to 0.200%,

V: 0.10% to 1.00%,

W: 0.10% to 1.00%,

Cr: 0.05% to 1.00%,

Mo: 0.05% to 1.00%,

Cu: 0.05% to 1.00%,

Ni: 0.05% to 1.00%,

B: 0.0010% to 0.0100%,

Ca: 0.0005% or more and 0.05% or less, and

REM: 1 or 2 of 0.0005% to 0.05%.

According to the above aspect of the present invention, it is possible to provide a hot-pressed article having high strength, in which the formation of scale after hot pressing is suppressed, sparking and fusion at spot welding can be prevented, a wide appropriate welding current range is provided, and excellent coating film adhesion and bendability are provided.

The galvanized steel sheet for hot pressing according to the above aspect can be produced at low cost as an automobile part by hot pressing, spot welding, chemical conversion treatment, and electrodeposition because the amount of the galvanized coating is suppressed, and is suitable for use as an automobile part.

Drawings

Fig. 1 is a graph showing measurement results obtained by GDS measurement in the depth direction from the surface of the coating film of the hot-pressed article.

Fig. 2 is a graph showing measurement results obtained by GDS measurement in the depth direction from the surface of the coating film of the hot-pressed article.

Fig. 3 is a graph showing measurement results obtained by GDS measurement in the depth direction from the surface of the coating film of the hot-pressed article.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the configurations disclosed in the present embodiment, and various modifications can be made without departing from the scope of the present invention. In the numerical limitation ranges described below, the lower limit value and the upper limit value are included in the range. For values denoted as "more than" or "less than", the value is not included in the range of values. All of the "%" related to the chemical composition represent "% by mass".

A galvanized steel sheet for hot pressing (hereinafter, sometimes referred to as a "plated steel sheet") used for a hot press molded body according to the present embodiment includes a steel sheet and a galvanized coating film disposed on the steel sheet. First, a galvanized steel sheet for hot pressing to which the hot press formed body according to the present embodiment is applied will be described. Further, since the chemical composition of the steel sheet does not change before and after hot pressing, the chemical composition of the steel sheet constituting the hot-press galvanized steel sheet is the same as the chemical composition of the steel sheet constituting the hot-press formed body.

1. Chemical composition of steel sheet

[ C: 0.02% or more and 0.58% or less ]

C is an element that is important for improving the hardenability of the steel sheet and for obtaining the strength of the hot-press formed body after quenching (after hot-pressing). In addition, C is a lowering of Ac₃And (3) elements that lower the quenching temperature. If the C content is less than 0.02%, the above-mentioned effects cannot be sufficiently obtained. Therefore, the C content is set to 0.02% or more. Preferably 0.10% or more or 0.20% or more.

On the other hand, if the C content exceeds 0.58%, the toughness of the hot-pressed molded body after hot pressing is significantly deteriorated. Therefore, the C content is set to 0.58% or less. Preferably 0.55% or less or 0.50% or less.

[ Mn: 0.10% or more and 3.00% or less ]

Mn is an element important for improving the hardenability of a steel sheet and for stably obtaining the strength of a hot-press formed body after quenching. If the Mn content is less than 0.10%, the above-described effects cannot be sufficiently obtained. Therefore, the Mn content is set to 0.10% or more. Preferably 0.20% or more, 0.30% or more, or 0.40% or more.

On the other hand, if the Mn content is excessive, Mn diffuses into the zinc-plated film during heating before hot pressing, and Mn oxide is generated on the film surface in a large amount in the hot-pressed product, thereby deteriorating the spot weldability. Therefore, the Mn content is 3.00% or less. Preferably 2.80% or less, 2.60% or less, or 2.40% or less.

Al: 0.001% or more and 1.000% or less ]

Al has an effect of deoxidizing steel to thereby strengthen the steel material (suppress generation of defects such as pores in the steel material). If the sol.al content is less than 0.001%, the effects of the above-described actions cannot be obtained. Therefore, the sol.al content is set to 0.001% or more. Preferably 0.010% or more, 0.020% or more, or 0.030% or more.

On the other hand, if the sol.al content is excessive, sol.al diffuses into the zinc-plated film during heating before hot pressing, and Al oxide is formed on the surface of the film in a large amount in the hot-pressed product. This reduces the adhesion between the film and the chemical conversion coating. Thus. The al content is 1.000% or less. Preferably 0.800% or less, 0.100% or less, 0.075% or less, or 0.070% or less.

Al means acid-soluble Al, and means solid-solution Al present in the steel in a solid-solution state.

[ Si: 2.00% or less ]

Si is concentrated at the interface between the zinc oxide layer formed by heating and the steel sheet during heating before hot pressing, and adhesion between the zinc oxide layer and the steel sheet is reduced. Therefore, the Si content is 2.00% or less. The Si content is preferably 1.00% or less, 0.70% or less, or 0.50% or less. The Si content is preferably small, and the lower limit is not particularly limited, but the refining cost increases if the Si content is excessively reduced, so the Si content may be 0.01% or more.

[ P: 0.100% or less ]

P is contained as an impurity in steel, and has an effect of embrittling the steel, and therefore the P content is preferably low. Therefore, the P content is set to 0.100% or less. Preferably 0.050% or less, 0.020% or less, or 0.015% or less. The lower limit of the P content is not particularly limited, but the P content may be 0.001% or more because an excessive decrease in the P content causes an increase in refining cost.

[ S: 0.005% or less ]

S is an element contained as an impurity, and has an effect of forming MnS to embrittle the steel, and therefore the S content is preferably small. Therefore, the S content is set to 0.005% or less. Preferably 0.004% or less or 0.003% or less. The lower limit of the S content is not particularly limited, but the S content may be 0.0003% or more or 0.001% or more because an excessive reduction in the S content causes an increase in refining cost.

[ N: 0.0100% or less ]

N is an element that is contained as an impurity and forms an inclusion in steel to deteriorate the toughness of a hot press formed body, and therefore the content of N is preferably low. Therefore, the N content is 0.0100% or less. Preferably 0.0080% or less, 0.0070% or less, 0.0050% or less, or 0.0045% or less. The lower limit of the N content is not particularly limited, but the N content may be 0.0005% or more because an excessive reduction of the N content causes an increase in refining cost.

The balance of the chemical composition of the steel sheet according to the present embodiment is Fe and impurities. Examples of the impurities include elements that are inevitably mixed from steel raw materials or scraps and/or are inevitably mixed during steel production, and elements that are allowable within a range that does not impair the properties of the hot press formed body according to the present embodiment.

The steel sheet may contain any of the following elements in place of the balance of Fe. Any element described below may not be contained, and the content in the case of not containing any element is 0%.

[ Ti: 0% or more and 0.200% or less, Nb: 0% or more and 0.200% or less, V: 0% or more and 1.00% or less and W: 0% or more and 1.00% or less ]

Ti, Nb, V, and W are elements that promote interdiffusion of Fe and Zn in the zinc-plated film and the steel sheet and make the hot-dip Zn alloy-plated layer less likely to be generated during hot pressing. The formation of the hot dip Zn alloy-plated layer is not preferable because cracks may be generated during hot pressing. Therefore, the steel sheet may contain Ti, Nb, V, and W. In order to obtain the above effects reliably, the composition preferably contains Ti: 0.005% or more, Nb: 0.005% or more, V: 0.10% or more, W: more than 1 of 0.10% or more.

However, if the Ti content or Nb content exceeds 0.200%, or if the V content or W content exceeds 1.00%, the above effects are saturated, and the alloy cost increases. Therefore, the Ti content and Nb content are 0.200% or less, respectively, and the V content and W content are 1.00% or less, respectively. Preferably: the Ti content and Nb content are respectively below 0.150%, and the V content and W content are respectively below 0.50%.

[ Cr: 0% to 1.00% inclusive, Mo: 0% or more and 1.00% or less, Cu: 0% or more and 1.00% or less, Ni: 0% or more and 1.00% or less and B: 0% or more and 0.0100% or less ]

Cr, Mo, Cu, Ni, and B are elements that improve the hardenability of the steel sheet and improve the strength of the hot-press formed body. Therefore, 1 or 2 or more of these elements may be contained. In order to reliably obtain the above effects, the composition preferably contains Cr: 0.05% or more, Mo: 0.05% or more, Cu: 0.05% or more, Ni: 0.05% or more and B: 0.0010% or more of any 1 or more. However, if the Cr content, Mo content, Cu content, or Ni content exceeds 1.00%, or if the B content exceeds 0.0100%, the above effects are saturated, and the alloy cost increases. Therefore, the Cr content, Mo content, Cu content, and Ni content are each 1.00% or less, and the B content is 0.0100% or less. The B content is preferably 0.0080% or less.

[ Ca: more than 0% and less than 0.05% and REM: 0% or more and 0.05% or less ]

Ca and REM have the effect of refining inclusions in steel and preventing the occurrence of cracks during hot pressing due to the inclusions. Therefore, 1 or 2 or more of these elements may be contained. In order to obtain the above effects reliably, it is preferable to contain Ca: above 0.0005% and REM: more than 1 of 0.0005% or more. However, if the Ca content or the REM content exceeds 0.05%, the effect of refining inclusions in the steel is saturated, and the alloy cost increases. Therefore, the Ca content and the REM content are each 0.05% or less.

Here, REM means a total of 17 elements consisting of Sc, Y and lanthanoid, and the content of REM means the total content of these elements. REM is often contained in misch metal (misch metal), but elements of the lanthanoid series other than La and Ce may be contained in a composite manner. The hot press-formed body according to the present embodiment can exhibit its effects even when lanthanoid elements other than La and Ce are contained in a composite manner. Even if a metal REM such as La or Ce is contained, the hot-pressed molded body according to the present embodiment can exhibit its effect.

The chemical composition of the steel sheet may be measured by a general analytical method. For example, the measurement may be carried out by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Note that sol.al may be measured by ICP-AES using a filtrate obtained by thermal decomposition of a sample in an acid. C and S may be measured by a combustion-infrared absorption method, and N may be measured by an inert gas melting-thermal conductivity method. When the steel sheet has a zinc plating film or coating on the surface, the zinc plating film or coating may be removed by mechanical polishing and then analyzed for chemical composition.

2. Zinc-plated film of hot-pressing zinc-plated steel sheet

The hot-press galvanized steel sheet has a galvanized coating on the steel sheet. The zinc-plated coating film has a coating adhesion amount of 15.0g/m²Above and below 40.0g/m²The Fe concentration is 1.5-8.0 mass%, and the Al content is 100mg/m²Above and 400mg/m²Hereinafter, the Al concentration is 0.50 mass% or more and 3.00 mass% or less, and the remainder includes Zn and impurities. The zinc plating film will be described in detail below.

[ amount of deposit of plating ]

The hot-press galvanized steel sheet has a galvanized coating on the steel sheet. The amount of deposit of the zinc-plating film was set to 15.0g/m²Above and below 40.0g/m². In the present embodiment, the plating deposit amount refers to the amount of plating deposit on one surface of the steel sheet. If the coating adhesion is less than 15.0g/m²Scale is generated during heating before hot pressing. Thus, the amount of deposit was set to 15.0g/m²The above. Preferably 18.0g/m²Above or 20.0g/m²The above.

On the other hand, if the amount of deposit is 40.0g/m²As described above, in the hot press-formed body, the appropriate welding current range at the time of spot welding becomes narrow. Therefore, the amount of deposit of the plating layer is set to less than 40.0g/m². Preferably 35.0g/m²Below or 30.0g/m²The following.

The coating adhesion amount of the zinc coating was determined in accordance with JIS H0401: 2013, a test piece was prepared from an arbitrary position of the hot-press galvanized steel sheet, and the measurement was performed.

[ Fe concentration in Zinc-plated coating ]

When the Fe concentration in the zinc plating film is 8.0 mass% or less, the heating rate in heating before hot pressing is slow, and therefore the residence time at high temperature when holding in the heating furnace is reduced. As a result, the evaporation amount and oxidation amount of Zn are suppressed, and the generation of scale and the spark at the spot welding can be suppressed.

If the Fe concentration in the zinc plating film is too high, the heating rate at the time of heating before hot pressing becomes high, and the residence time at a high temperature at the time of holding in a heating furnace becomes long, so that the possibility of scale formation due to evaporation of Zn and the possibility of spark generation at the time of spot welding are increased. Therefore, the Fe concentration in the zinc plating film is set to 8.0 mass% or less. Preferably 7.5% by mass or less, 7.0% by mass or less, or 6.0% by mass or less.

[ amount and concentration of Al in the zinciferous plating coating ]

The amount of Al in the zinc-plated coating was set to 100mg/m²Above and 400mg/m²Hereinafter, the Al concentration is set to 0.50 mass% or more and 3.00 mass% or less. If the Al content in the zinc-plated coating is less than 100mg/m²Or if the Al concentration is less than 0.50 mass%, Al oxide formed on the surface layer of the zinc plating film during heating before hot pressing is reduced. As a result, Zn oxidation is not suppressed, Zn-based oxides are excessively generated, and sparks are generated and/or fusion occurs at the time of spot welding. Further, the evaporation amount of Zn also increases, the weight per unit area of Zn in the zinc plating film decreases, and scale is generated. Therefore, the amount of Al in the zinc-plated coating film was set to 100mg/m²The Al concentration is 0.50 mass% or more. Preferably, the amount of Al is 150mg/m²Above or 170mg/m²The above. Further, the Al concentration is preferably 0.65 mass% or more, 0.70 mass% or more, or 0.75 mass% or more.

On the other hand, if the Al content in the zinc plating film exceeds 400mg/m²Or if the Al concentration exceeds 3.00 mass%, the coating adhesion in the hot-press formed body is lowered. Thus, the number of the first and second electrodes,the amount of Al in the zinc-plated coating was set to 400mg/m²The Al concentration is 3.0 mass% or less. The amount of Al is preferably 350mg/m²Hereinafter, more preferably 300mg/m²The following. Further, the Al concentration is preferably 2.00 mass% or less or 1.70 mass% or less.

The amount of Al in the zinc coating film of a hot-dip galvanized steel sheet produced on a continuous hot-dip galvanizing line is influenced by the atmosphere during heating before annealing, the bath temperature, the steel sheet temperature during dipping into the plating bath, the dipping time, the amount of plating deposit, the Al concentration in the bath, and the like. Therefore, by empirically obtaining and controlling the relationship between these production conditions and the amount of Al in the zinc-plated coating, the amount of Al in the zinc-plated coating can be made 100mg/m²The above.

[ allowance in Zinc-plated coating ]

The balance of the zinc plating film contains Zn and impurities, and the impurities are preferably 0.1% or less.

The Fe concentration, Al concentration, and Al amount in the zinc plating film were measured by the following methods.

Only the zinc coating film of the hot-press galvanized steel sheet was dissolved and removed by using a 5 vol% HCl aqueous solution to which an inhibitor (corrosion inhibitor) was added. The Zn concentration, Fe concentration and Al concentration in the obtained solution were measured by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) to obtain the Fe concentration, Al concentration and Al content in the zinc-plated coating film.

By heating and hot-pressing the hot-press galvanized steel sheet described above, a hot-pressed product excellent in coating film adhesion and bendability can be obtained. The hot press-formed body according to the present embodiment will be described below.

The hot press formed body according to the present embodiment includes a steel sheet having the above chemical composition and a coating film disposed on the steel sheet. The film of the hot press molded body according to the present embodiment will be described in detail below.

3. Film of hot press molded body

By heating before hot pressing, the zinc-plated coating film of the hot-press galvanized steel sheet reacts with the steel substrate, and various oxidation reactions occur on the surface. Fig. 1 shows the measurement results of Fe, O, and Zn in large amounts detected among the measurement results obtained by GDS measurement in the depth direction from the surface of the film, for a sample cut out from the hot-pressed molded body. As can be seen from the observation of FIG. 1: on the steel substrate, an Fe — Zn solid solution (iron-zinc solid solution) in which the steel substrate is dissolved in the zinc coating film is present, and zinc oxide is present thereon.

Fig. 2 shows the results of measurement of Fe, Zn, Mn, and Al in the same measurement results as in fig. 1. As can be seen from the observation of FIG. 2: although the amount is extremely small compared to Fe and Zn, Mn is detected at the same position as zinc oxide, and a Zn-based oxide (zinc oxide) and a Mn-based oxide are formed on the surface layer. As shown in the figure, it can be seen that: al was detected in the boundary region between zinc oxide and Fe-Zn solid solution although it was a small amount.

Fig. 3 shows the measurement results of Si, Cr, and Al in the same measurement results as in fig. 1 and 2. As shown in FIG. 3, peaks of Cr and Si were detected in the boundary region between the zinc oxide and the Fe-Zn solid solution, in which Al was detected, although in a small amount. The peaks of Cr and Si are considered to be detected because the sample contains Cr and Si.

From the measurement results shown in fig. 1 to 3, it is considered that: the upper layer of the oxide layer of the hot-pressed molded body mainly contains Zn-based oxide and Mn-based oxide, and the lower layer of the oxide layer mainly contains Al-based oxide, a trace amount of Cr-based oxide, and Si-based oxide.

The hot-pressed molded body according to the present embodiment has a Zn-based oxide, a Mn-based oxide, and an Al-based oxide on the surface of the coating film, and further has a Cr-based oxide and a Si-based oxide when the base steel sheet contains Cr and Si. The balance may include a P-based oxide, a Ti-based oxide, and a Nb-based oxide. The mechanism of formation of these oxide phases by heating before hot pressing is not necessarily clear, but is estimated from the results of measurement of GDS as follows.

In the initial stage of heating before hot pressing, an Al-based oxide is formed on the surface layer to suppress oxidation of Zn. By further heating, a Zn-based oxide is formed on the Al-based oxide. Therefore, if the amount of Al in the zinc plating film is large, the amount of Al-based oxide increases, and therefore the amount of Zn-based oxide decreases. Further, since these reactions occur concurrently with the integration of the steel substrate and the zinc plating film, oxides of the easily oxidizable elements Mn, Cr, and Si contained in the steel substrate are also formed in a small amount. Depending on the susceptibility to oxidation, Cr and Si form oxides at the same sites as Al, and Mn forms oxides at the same sites as Zn. Although it is difficult to accurately quantify these oxides, it is considered from the above structure that the total amount of the Zn amount and the Mn amount at the surface to the peak position of Al is an amount proportional to the total amount of the Zn-based oxide and the Mn-based oxide, and if the total amount is large, a spark is generated at the time of spot welding.

On the other hand, it is considered that the total amount of Al amount, Si amount, and Cr amount from the surface of the film to the peak position of Al can be approximated as an amount proportional to 1/2 which is the total amount of each Al-based oxide, Si-based oxide, and Cr-based oxide. If the amount is too large, the adhesion between zinc oxide and the Fe-Zn solid solution is deteriorated, and the coating film adhesion is deteriorated. Under the above-mentioned oxides, there is a solid solution phase of Fe and Zn in a metallic state (Fe — Zn solid solution), and if this solid solution phase is even locally deficient, scale is produced during heating.

[ film Structure ]

The coating film having the above-described various oxides has the following coating film structure.

In the hot press molded body according to the present embodiment, Zn as the Zn accumulation amount is measured from the surface of the coating to a position at a depth of 100 μm from the surface in GDS measurement_totalIs 10.0g/m²Above and below 40.0g/m²When GDS measurement was performed from the surface of the film to the peak position of Al, the sum of Zna as the cumulative amount of Zn and the cumulative amount of Mn was 20.0g/m²Hereinafter, the sum of the cumulative amount of Al, the cumulative amount of Si and the cumulative amount of Cr is 60mg/m²Above 240mg/m²Hereinafter, Zn_total-Zna was 3.0g/m²Above and 30.0g/m²The following.

The peak position of Al is set to be at the midpoint of 95% of the positions of the 2 highest Al intensities before and after the highest Al intensity, when GDS measurement is performed in the depth direction from the surface of the coating. The cumulative amount is a total amount of values obtained by GDS measuring the weight per unit area at intervals of 1 second in the depth direction to a predetermined depth.

When GDS measurement is performed from the surface of the film to a position of 100 μm depth, Zn is accumulated as Zn_totalLess than 10.0g/m²Then, the formation of scale after hot pressing cannot be suppressed. Thus, Zn_totalSet to 10.0g/m²The above. Preferably 15.0g/m²Above or 20.0g/m²The above.

In addition, if Zn_totalIs 40.0g/m²As described above, the amount of deposit of the plating layer increases, and the appropriate welding current range at the time of spot welding becomes narrow. Thus, Zn_totalSet to less than 40.0g/m². Preferably 35.0g/m²The following.

When GDS measurement is performed from the surface of the film to the peak position of Al, the sum of the Zn accumulation Zna from the surface of the film to the peak position of Al and the Mn accumulation from the surface of the film to the peak position of Al exceeds 20.0g/m²In the case of (3), the amount of Zn-based oxide and Mn-based oxide is large, and therefore, a spark occurs at the time of spot welding. Therefore, the sum of Zna and the cumulative Mn from the surface to the peak position of Al is set to 20.0g/m²The following. Preferably 18.0g/m²Below, 15.0g/m²Below or 13.0g/m²The following.

Zna and the lower limit of the sum of the Mn accumulation from the surface to the Al peak position is not particularly limited, but may be 0.1g/m²Above, 2.0g/m²Above or 5.0g/m²The above.

When GDS measurement is performed from the surface of the film to the peak position of Al, if the sum of the Al accumulation amount, the Si accumulation amount and the Cr accumulation amount is less than 60mg/m²The amounts of Zn-based oxide and Mn-based oxide increase, and sparks are generated at the spot welding. Therefore, in the region from the surface of the film to the peak position of Al, the sum of the Al accumulation amount, the Si accumulation amount and the Cr accumulation amount is 60mg/m²The above. Preferably 100mg/m²Above or 130mg/m²The above.

In addition, if the elements are accumulatedThe sum of the amounts exceeds 240mg/m²The coating film adhesion is deteriorated. Therefore, in the region from the surface of the film to the peak position of Al, the sum of the Al accumulation amount, the Si accumulation amount and the Cr accumulation amount is 240mg/m²The following. Preferably 220mg/m²Below or 200mg/m²The following.

When the steel sheet does not contain Cr or Si, Cr or Si cannot be detected even if GDS measurement is performed on the coating, but it is important to control the sum of the Al accumulation amount, the Si accumulation amount, and the Cr accumulation amount, and therefore there is no problem even if Cr or Si is not detected. That is, when the steel sheet does not contain Cr and Si, the cumulative amount of Al is 60mg/m in the region from the surface of the film to the peak position of Al²Above 240mg/m²The following may be used.

Zn accumulation amount of Zn at a depth of 100 μm from the surface of the film_totalA value obtained by subtracting the Zn accumulation Zna at the peak position from the surface of the coating to Al (Zn)_total-Zna) less than 3.0g/m²Oxide scale is generated. Thus, Zn_total-Zna was set to 3.0g/m²The above. Preferably 4.0g/m²Above, 8.0g/m²Above or 10.0g/m²The above.

In addition, if Zn_total-Zna exceeding 30.0g/m²The proper welding current range is narrowed. Thus, Zn_total-Zna was set to 30.0g/m²The following. Preferably 25.0g/m²Below or 20.0g/m²The following.

GDS measurement was performed by the following method.

In any 3 points of the hot-pressed article, the weight of Fe, Al, Si, Mn, Cr and Zn was measured from the surface of the coating up to 100 μm in the depth direction (thickness direction). The Zn accumulation amount at the surface of the film to a depth of 100 μm was obtained by calculating the Zn accumulation amount from the measurement results obtained at 3 points and calculating the average value_total. Further, after the peak position of Al defined above was obtained from the obtained measurement results, the cumulative amount of each element (Zn, Mn, Al, Si, and Cr) from the surface to the Al peak position was obtained. By finding the relationThe average of the obtained cumulative amounts of the respective elements is measured at 3, thereby obtaining the cumulative amount of the respective elements. For the measurement, a high-frequency glow discharge emission spectrum surface analyzer (GD-Profiler) model マーカス manufactured by horiba, Ltd.

[ arithmetic average roughness Ra ]

The arithmetic average roughness Ra of the coating is less than 1.50 μm. When the arithmetic mean roughness Ra is less than 1.50 μm, since the irregularities that become the starting points of bending are small, the bendability of the hot-press molded article can be improved while ensuring the coating film adhesion. Thus, the arithmetic average roughness Ra is set to less than 1.50 μm. Preferably 1.30 μm or less, 1.10 μm or less, 1.00 μm or less, or 0.90 μm or less.

The lower limit of the arithmetic average roughness Ra is not particularly limited, but may be 0.01 μm or more, 0.10 μm or more, or 0.50 μm or more.

The arithmetic average roughness Ra of the coating of the hot-pressed article was measured by the following method. A test piece 50 mm. times.50 mm was cut from a position 10mm or more from the end face of the hot press molded body, and 3-line analysis was performed in an arbitrary direction and in a direction perpendicular to the direction using a confocal microscope (manufactured by レーザーテック Co., Ltd.). According to the obtained results, the following were measured in accordance with JIS B0601: 2001, the arithmetic average roughness Ra was calculated, and the arithmetic average roughness Ra of the film was obtained by calculating the average of 6 lines in total.

The hot press-formed article according to the present embodiment preferably has a tensile strength of 900MPa or more. The tensile strength is set to 900MPa or more, and thus the composition can be suitably applied to automobile parts. The tensile strength is preferably 1000MPa or more, 1500MPa or more, or 1800MPa or more. The upper limit of the tensile strength is not particularly limited, but may be 3000MPa or less or 2800MPa or less.

The tensile strength of the hot press-molded article was determined by preparing a test piece of JIS5 from a position of the hot press-molded article excluding a region within 10mm from the edge, and adjusting the tensile strength in accordance with JIS Z2241: 2011 is obtained by performing a tensile test.

4. Method for producing galvanized steel sheet for hot pressing

The hot-press galvanized steel sheet is heated to a temperature region in the austenite region or its vicinity, and hot-pressed in this temperature region. Therefore, the mechanical properties of the hot-press galvanized steel sheet at room temperature before heating are not important. Therefore, the metal structure of the hot-press galvanized steel sheet before heating is not particularly specified. That is, the steel sheet before being provided with the zinc coating film may be either a hot-rolled steel sheet or a cold-rolled steel sheet, and the method for producing the steel sheet is not limited. From the viewpoint of productivity, a suitable method for producing a steel sheet will be described below.

A suitable method for producing a galvanized steel sheet for hot pressing is a method in which the following steps are sequentially performed: a heating step of heating the slab having the chemical composition at 1200 ℃ or higher for 5 minutes or longer; a hot rolling step of performing hot rolling on the slab so that the finish rolling temperature is 800 ℃ to 980 ℃ inclusive, and coiling the slab at a coiling temperature of 450 ℃ to 800 ℃ inclusive to obtain a hot-rolled steel sheet; a cold rolling step of subjecting the hot-rolled steel sheet to acid washing and then cold rolling so that a cumulative reduction ratio becomes 30% to 80% to obtain a cold-rolled steel sheet; and a galvanizing step of annealing the cold-rolled steel sheet at a temperature range of 700 ℃ to 900 ℃ inclusive to obtain a steel sheet, and immersing the steel sheet in a molten zinc bath (hot dip galvanizing bath) having an Al concentration of 0.155 mass% to 0.175 mass% for a period of 1.0 second to 15.0 seconds to form a galvanized coating on the steel sheet.

[ heating Process ]

The slab having the above chemical composition is heated at 1200 ℃ or higher for 5 minutes or longer. If the slab heating temperature is less than 1200 ℃ or the heating time is less than 5 minutes, hot rolling described later cannot be performed.

[ Hot Rolling Process ]

The hot rolling is performed so that the finish rolling temperature is 800 ℃ to 980 ℃. If the finish rolling temperature is too low, the deformation resistance becomes high, and rolling becomes difficult. If the finish rolling temperature is too high, a large amount of scale is formed, and surface flaws increase. After the finish rolling, the steel sheet is coiled so that the coiling temperature is 450 ℃ to 800 ℃ inclusive, thereby obtaining a hot-rolled steel sheet. If the winding temperature is too low, wrinkles are generated to deteriorate flatness, and it becomes difficult to perform cold rolling. If the coiling temperature is too high, the thickness of the scale becomes thick, and a long time is required for pickling, which lowers productivity.

[ Cold Rolling Process ]

The hot-rolled steel sheet is subjected to acid washing and then cold rolling to obtain a cold-rolled steel sheet. The cold rolling is performed so that the cumulative reduction ratio is 30% to 80%. Since the steel sheet according to the present embodiment contains a large amount of carbon, the rolling mill is burdened with an excessive cumulative reduction ratio when cold rolling is performed. If the cumulative reduction ratio is excessively decreased, the productivity is decreased. Therefore, the cumulative reduction in cold rolling is 30% to 80%.

The cumulative reduction is obtained by setting the thickness of the hot-rolled steel sheet before cold rolling to t₀And the thickness of the cold-rolled steel sheet after cold rolling is defined as t₁When it is used { (t)₀-t₁)/t₀And (c) } × 100 (%).

[ Zinc plating Process ]

The formation of the zinc plating film is preferably performed by using a continuous hot dip galvanizing line having excellent production efficiency. Hereinafter, a method for forming a zinc-plated coating film using a continuous hot-dip galvanizing line will be described.

In the continuous hot dip galvanizing, first, a cold-rolled steel sheet is heated in a heating furnace and annealed. In the case of hot pressing applications, the annealing temperature is not particularly limited, and may be 700 ℃ or higher, since there is no particular limitation on the mechanical properties before hot pressing. If the annealing temperature is set to exceed 900 ℃, the manufacturing cost increases, and therefore the annealing temperature is set to 900 ℃ or lower. The annealing time is not particularly limited, and may be 1 to 5 minutes from the viewpoint of productivity. The annealing atmosphere of the continuous hot-dip galvanizing production line can be the annealing atmosphere of the conventional method, and the dew point can be below-20 ℃. Preferably below-35 ℃.

The steel sheet was obtained by the above-described method.

The hot-press formed body according to the present embodiment is obtained by dipping the steel sheet obtained by the above-described method in a molten zinc bath and then pulling up the steel sheet to form a zinc-plated coating film on the steel sheetThe hot-press galvanized steel sheet is used. In the method for producing a galvanized steel sheet for hot pressing, unlike the conventional technique, the amount of the galvanized coating deposited is 15.0g/m²Above and below 40.0g/m²The Al content in the zinc-plating film is 100-400 mg/m²The conditions for applying the zinc plating film are strictly controlled. Specifically, the Al concentration in the molten zinc bath is set to 0.155 mass% or more and 0.175 mass% or less, and the steel sheet is immersed in the molten zinc bath for a period of 1.0 second or more and 15.0 seconds or less. The Al concentration in the molten zinc bath is preferably 0.157 mass% or more or 0.160 mass% or more. The Al concentration in the molten zinc bath is preferably 0.172 mass% or less or 0.170 mass% or less.

The amount of the zinc-plated coating deposited may be controlled by adjusting the lifting speed or the flow rate of the wiping gas blown out from the nozzle. The Al concentration in the zinc plating film can be adjusted by controlling the plating bath composition, the plating bath temperature, and the immersion time in the plating bath. The amount of Al in the zinc-plated coating can be adjusted by controlling the amount of plating deposited on the zinc-plated coating.

If temper rolling is performed after the galvanizing process, the surface shape of the hot-press galvanized steel sheet can be flattened and the surface roughness can be adjusted. Therefore, temper rolling can be performed as necessary after the galvanization step according to the application.

5. Method for producing hot-press molded body

In the method for producing a hot-pressed body according to the present embodiment, a steel sheet for hot pressing is heated to a temperature range of 600 to 700 ℃ inclusive and held for 30 minutes to 2 hours inclusive, then heated to a temperature range of 700 to 1000 ℃ inclusive and held for 1 minute to 20 minutes inclusive in this temperature range, and then hot pressed. In this heating condition, the zinc-plated film before hot pressing can be made into a solid solution of iron and zinc (Fe-Zn solid solution phase), and thus Liquid Metal Embrittlement does not occur (LME: Liquid Metal Embrittlement). Further, by performing the above-described preheating, the zinc-plated film can be made into a solid solution without passing through the solid-liquid coexisting region, and therefore the surface roughness of the zinc-plated film can be reduced. As a result, the bending property of the hot press-formed body can be improved.

Examples of the heating method before hot pressing include heating by an electric furnace, a gas furnace, or the like, flame heating, energization heating, high-frequency heating, induction heating, and the like. When the material is to be quenched by heating before hot pressing, the material is heated under the above-described heating conditions, and hot pressing is performed in a high temperature state using, for example, a die through which a water-cooled tube is passed, and at this time, rapid cooling is performed by contact with the die. The mold may be heated in advance to change the quenching temperature or cooling rate, thereby controlling the properties of the hot-pressed product.

Examples

Next, examples of the present invention will be described, but the conditions in the examples are only one conditional example adopted for confirming the feasibility and the effects of the present invention, and the present invention is not limited to this conditional example. The present invention can employ various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

Hot-press galvanized steel sheets shown in table 2B were obtained by heating, hot-rolling, cold-rolling, and galvanizing slabs having the chemical compositions shown in table 1 under the conditions shown in table 2A. Further, pickling was performed after hot rolling.

Further, as to steel sheet No.29 of Table 2B, after the galvanization, the alloying treatment was performed by holding at 520 ℃ for 20 seconds.

The thickness of the hot-rolled steel sheet obtained by hot rolling was 2.8mm, and the thickness of the cold-rolled steel sheet obtained by cold rolling was 1.4 mm.

The galvanization is implemented by adopting a continuous hot-dip galvanizing production line. The annealing conditions were set to a temperature range of-40 ℃ in dew point, maintained at the temperature shown in Table 2A for 200 seconds, and then cooled to 540 ℃ or less at an average cooling rate of 6 ℃/sec. The temperature of the plating bath is set to 450 to 460 ℃. The amount of the zinc plating film deposited was adjusted by adjusting the speed of lifting from the molten zinc bath or the flow rate of the wiping gas blown out from the nozzle.

The obtained hot-press galvanized steel sheet was measured for the amount of deposit, Fe concentration, Al amount, and Al concentration by the methods described above. The measurement results obtained are shown in table 2B.

TABLE 2A

Underlining indicates unsatisfactory manufacturing conditions.

TABLE 2B

Underlining indicates unsatisfactory manufacturing conditions.

A hot-press test piece (test piece size: 250mm in the plate width direction X200 mm in the rolling direction) was prepared from the obtained hot-press galvanized steel sheet. The test piece was placed in a heating furnace to make the steel sheet temperature reach the temperatures shown in tables 3A and 4A, and after the steel sheet was held at the temperatures for the holding times shown in tables 3A and 4A, the steel sheet was taken out of the heating furnace, and thereafter, hot-pressed using a steel mold for a flat plate and quenched, thereby obtaining a hot-pressed molded body. Further, a part of the hot press molded article was produced by preheating at 650 ℃ for 1 hour.

The film structure and arithmetic average roughness Ra of the obtained film of the hot press molded article were measured by the methods described above. The obtained measurement results are shown in table 3B and table 4B.

(Spot weldability evaluation)

In the hot press formed bodies of tables 3B and 4B, 2 test pieces of 230mm in the sheet width direction × 180mm in the rolling direction were prepared from positions excluding the region within 10mm from the edge, and these test pieces were stacked and subjected to spot welding by changing the current under the following conditions. The nugget diameter was set to 4t^1/2(t is the thickness of the test piece) as the lower limit, the current at which spattering occurs as the upper limit, and the interval between the upper limit and the lower limitAs a suitable welding current range. Further, welding was performed at a current value 0.5kA lower than the upper limit value at which spattering occurred, and a 1000-point continuous dotting test was performed to evaluate the presence or absence of occurrence of seizure.

In tables 3B and 4B, the example in which the suitable welding current range is 1.2kA or more was judged as "OK", and the example in which the suitable welding current range is less than 1.2kA or the nugget diameter is 4t^1/2The case where the spatter was generated at the current of (1) was judged as a failure, and is described as an appropriate welding current range "NG" in the table. In addition, the example in which no fusion occurred was judged as pass, and the example in which fusion occurred was judged as fail, and the example in which fusion occurred was judged as pass. In addition, the number of sparks generated in 1000 points was counted. The example in which the spark is generated at 50 points or more is judged to be not good, and is referred to as "NG" in the table, and the example in which the spark is not generated at 50 points or more is judged to be not good, and is referred to as "OK" in the table.

Pressurizing pressure: 400kgf

Energization time: 15 cycles (cycle)

Retention time: 9 period (c)

Electrode tip shape: DR type, apex diameter 6 mm-radius of curvature R40mm

(evaluation of film adhesion)

With respect to the hot press molded bodies in tables 3B and 4B, test pieces (70 mm. times.150 mm) cut out from positions excluding the region within 10mm from the edge were subjected to a usual chemical conversion treatment under PBL-3080 manufactured by Japan パーカライジング (Ltd.) so that the adhering amount was 3g/m²The zinc phosphate treatment was performed. Then, the electrodeposition paint GT-10 manufactured by Kansai ペイント was applied by electrodeposition by applying electricity through a slope (slope) of 200V, and the paint was baked at a baking temperature of 150 ℃ for 20 minutes. The thickness of the coating film was set to 20 μm. The test piece was immersed in ion-exchanged water at 50 ℃ and taken out after 240 hours, and a peel test was performed using a polyester tape manufactured by ニチバン (strain) with scratches cut out in a checkered pattern having a width of 1mm by a cutter knife. The number of remaining blocks of the coating film was compared to evaluate the adhesion of the coating filmAnd (4) sex. The total number of blocks is 100. Regarding the evaluation criteria, the number of remaining blocks is considered to be good, OK, and 0 to 89 are considered to be bad, NG.

(evaluation of tensile Strength)

With respect to the hot press-molded articles in tables 3B and 4B, JIS5 test pieces were prepared from positions excluding the region within 10mm from the edge, and the hot press-molded articles were prepared in accordance with JIS Z2241: 2011 tensile test was conducted to obtain tensile strength TS. When the tensile strength TS is 900MPa or more, it is determined as high strength and is acceptable, and when the tensile strength TS is less than 900MPa, it is determined as not having strength desired as a hot press-formed body and is determined as defective.

(evaluation of bendability)

With respect to the hot press molded bodies in tables 3B and 4B, test pieces of 60mm × 60mm were prepared from positions excluding the region within 10mm from the edge, and a bending test was performed in accordance with VDA238-100, whereby a bending angle α (°) was obtained. The apparatus used a 20KN load cell group (loadcell) manufactured by ツヴィック.

The product (TS x α (MPa °)) of the tensile strength TS and the bending angle α obtained by the above method was used as an index of the bendability. The test piece was judged to be satisfactory if the bending property was excellent in the case where TS.alpha. (MPa.DEG) was 95000 MPa.DEG or more, and judged to be defective if the bending property was poor in the case where TS.alpha. (MPa.DEG) was less than 95000 MPa.DEG.

TABLE 3A

Underlining indicates that the manufacturing conditions are not satisfactory or that the present invention is out of the scope.

TABLE 3B

Underlining indicates that the manufacturing conditions are not satisfactory or that the present invention is out of the scope.

TABLE 4A

Underlining indicates that the manufacturing conditions are not satisfactory or that the present invention is out of the scope.

TABLE 4B

Underlining indicates that the manufacturing conditions are not satisfactory or that the present invention is out of the scope.

As can be seen from the observation of tables 3B and 4B: the present invention has high strength, prevents sparking and seizure during spot welding, has a wide appropriate welding current range, and is excellent in coating film adhesion and bendability. In the invention examples in tables 3B and 4B, no scale was formed after hot pressing.

Industrial applicability

According to the above aspect of the present invention, it is possible to provide a hot-pressed article having high strength, in which the formation of scale after hot pressing is suppressed, sparking and fusion at spot welding can be prevented, a wide appropriate welding current range is provided, and excellent coating film adhesion and bendability are provided.