JP6759940B2 - Zn-based galvanized steel sheet for hot pressing - Google Patents

Description

The present invention relates to a Zn-based plated steel sheet.

In recent years, there has been an increasing demand to curb fossil fuel consumption in order to protect the environment and prevent global warming, and such demands are affecting various manufacturing industries. For example, automobiles, which are indispensable for daily life and activities as a means of transportation, are no exception, and improvement of fuel efficiency by reducing the weight of the vehicle body is required. However, in automobiles, simply reducing the weight of the vehicle body is not allowed in terms of product functions, and it is necessary to ensure appropriate safety.

Most automobile structures are made of iron-based materials, especially steel plates, and reducing the weight of such steel plates is important for reducing the weight of the vehicle body. However, as described above, it is not allowed to simply reduce the weight of the steel sheet, and it is required at the same time to secure the mechanical strength of the steel sheet. Requests for such steel sheets are made not only in the automobile manufacturing industry but also in various manufacturing industries. Therefore, research and development are being carried out on a steel sheet capable of maintaining or improving the mechanical strength even if the thickness is made thinner than the conventionally used steel sheet by increasing the mechanical strength of the steel sheet.

In general, a material having high mechanical strength tends to have a reduced shape freezing property in a molding process such as bending process, and it becomes difficult to form a complicated shape. As one of the means for solving the problem of moldability, there is a so-called "hot stamping method (also called a hot stamping method, a hot pressing method, or a diquenching method)". In the hot pressing method, the material to be molded is once heated to a high temperature, and the steel sheet softened by heating is pressed to form the steel sheet and then cooled. According to such a hot pressing method, since the material is once heated to a high temperature to be softened, the target material can be easily pressed. Furthermore, the mechanical strength of the material can be increased by the quenching effect of cooling after molding. Therefore, by the hot pressing method, it is possible to obtain a molded product having both good shape freezing property and high mechanical strength.

However, when such a hot pressing method is applied to a steel sheet, the surface of the steel sheet is oxidized by heating the steel sheet to a high temperature of 800 ° C. or higher, and scale (compound) is generated. Therefore, after the hot press working, a step of removing the scale (so-called descaling step) is required, and the productivity is lowered. Further, for a member or the like that requires corrosion resistance, it is necessary to apply a rust preventive treatment or a metal coating to the surface of the member after processing, which requires a surface cleaning step and a surface treatment step, further lowering the productivity.

As a method of suppressing such a decrease in productivity, for example, a method of pre-coating a steel sheet to be hot-pressed can be mentioned. As the coating on the steel sheet, various materials such as organic materials and inorganic materials are generally used. Among them, zinc (Zn) -based plated steel sheets, which have a sacrificial anticorrosion effect on steel sheets, are widely used for automobile steel sheets and the like from the viewpoint of their anticorrosion performance and steel sheet production technology.

By applying a Zn-based metal coating, it is possible to prevent scale from being generated on the surface of the steel sheet, and steps such as descaling are not required, so that the productivity of the molded product is improved. In addition, since the Zn-based metal coating also has a rust preventive effect, corrosion resistance is also improved. Patent Documents 1 to 4 below disclose a method of hot-pressing a plated steel sheet having a predetermined component composition coated with a Zn-based metal coating.

In the following Patent Documents 1 to 3, a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet is used as the hot-pressed steel sheet. By using the hot-dip galvanized steel sheet or the alloyed hot-dip galvanized steel sheet for hot pressing, the structural member can be formed without forming iron oxide (that is, scale) on the surface. Further, in Patent Document 4 below, if a thick Zn oxide layer is formed on the surface of a heat-treated steel material obtained by hot-pressing a Zn-based galvanized steel sheet, the adhesion of the heat-treated steel material to the coating film and the corrosion resistance after coating are adversely affected. An invention is disclosed in which a heat-treated steel material is shot-blasted to remove the Zn oxide layer, or the thickness of the Zn oxide layer is reduced before coating.

Further, Patent Documents 5 and 6 below disclose inventions for improving the coating film adhesion and post-coating corrosion resistance of a heat-treated steel material obtained by hot-pressing a Zn-based plated steel sheet. Patent Document 5 below discloses an invention in which a hot-pressed steel sheet whose surface is coated with a silicone resin film is used as a steel sheet for hot pressing, and Patent Document 6 below discloses phosphorus (P) and silicon (Si). ) Is coated with a barrier layer (phosphate is exemplified as P and colloidal silica is exemplified as Si), and an invention is disclosed in which a hot-pressed steel sheet is used as a hot-pressed steel sheet. ..

Further, in Patent Document 7 below, an element that is more easily oxidized than Zn (easily oxidizing element) is added to the Zn plating layer, and the oxide layer of these easily oxidizing elements is added to the Zn plating layer during temperature rise during hot pressing. A technique for preventing the volatilization of zinc by forming it on the surface layer of a Zn plating layer is disclosed.

According to the inventions disclosed in Patent Documents 5 to 7 below, the Zn plating layer is covered with the barrier layer described above, so that Zn evaporation is suppressed, whereby the intermediate coating film and the top coating film can be coated. It is said to have good adhesion and corrosion resistance after painting.

Japanese Unexamined Patent Publication No. 2003-73774 Japanese Unexamined Patent Publication No. 2003-129209 Japanese Unexamined Patent Publication No. 2003-126921 Japanese Unexamined Patent Publication No. 2004-323897 JP-A-2007-63578 JP-A-2007-291508 JP-A-2004-270029

However, when a Zn-based plated steel sheet is hot-pressed, a phosphate film formed by phosphate treatment, Zr ions and / or Ti ions and fluorine are contained, and 100 to 1000 ppm of free fluorine ions are contained. If the amount of adhesion of the treatment film (FF treatment film) using the aqueous solution (hereinafter referred to as FF chemical conversion treatment solution) is not sufficient, good post-coating adhesion may not be obtained.

Generally, when the chemical conversion processability is not sufficient (for example, when uneven adhesion, scoring, etc. occur), the adhesion between the steel sheet and the electrodeposition coating film is not sufficiently guaranteed, and as a result, the adhesion after coating is not sufficient. Inferior in sex. One of the causes of insufficient chemical conversion treatment is due to insufficient degreasing and surface adjustment before chemical conversion treatment, and insufficient concentration, temperature, time, etc. of the chemical conversion treatment liquid itself. Can be mentioned.

Another cause is that the chemicalability is lowered by Al contained in the molten Zn plating. Specifically, Al in the molten Zn plating layer is added when the plating film is formed, diffuses when the hot press is heated, and moves to the surface layer of the plating layer to form an Al oxide film. Since the Al oxide film is insoluble in phosphoric acid, the reaction between Zn and the phosphate (for example, zinc phosphate, etc.) is inhibited, and the phosphate film is less likely to be formed in the region where the Al oxide film is formed. .. As a result, the region where the Al oxide film is formed has low phosphate treatment property. In particular, in the hot pressing process, when the steel sheet is rapidly heated to ₃ or more Acc points by energization heating or induction heating and then quickly press-formed, the phosphate treatment property is significantly reduced, and as a result, coating adhesion is achieved. Sex also declines.

In addition, the present inventors retested a heat-treated steel material obtained by using a hot-pressed steel sheet whose surface is coated with a silicone resin film, which is disclosed in Patent Document 5, as a steel sheet for hot pressing. As will be described later, it was found that the corrosion resistance after coating was good in the cycle corrosion test in which the dry and wet environment was repeated, but the coating adhesion was not always good. Therefore, the heat-treated steel material obtained by the invention disclosed in Patent Document 5 is, for example, a portion or a member (for example, a bag-shaped structural portion under a door or a closed cross-section member in an engine compartment) in which water tends to collect structurally. It is not suitable for use as it is.

On the other hand, adding an easily oxidizable element to the galvanized layer disclosed in Patent Document 7 requires new operational measures such as temperature control of the plating bath and measures against dross.

Further, in the hot pressing process, when heating to Ac3 points or more by furnace heating or atmospheric atmosphere heating, a zinc oxide layer is more likely to be formed on the steel sheet surface as compared with rapid heating such as the above-mentioned energization heating or induction heating. Become. When the zinc oxide layer is formed on the surface of the steel sheet, the contact resistance value of the surface of the steel sheet increases and the spot weldability decreases.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to more easily provide a Zn-based plated steel sheet which is more excellent in coating film adhesion and weldability after hot pressing. To provide.

The present inventors have come up with the following Zn-based plated steel sheets based on the findings obtained as a result of diligent studies on the above-mentioned target plated steel sheets for hot pressing.
The gist of the present invention is as follows.

[1] A Zn-based plated steel sheet as a base material and a surface-treated layer formed on at least one surface of the Zn-based plated steel sheet are provided, and the surface-treated layer is titanium having an average particle size of 1 μm or more and 10 μm or less. The base steel sheet of the Zn-based galvanized steel sheet contains non-oxide ceramic particles containing the above in a range of 0.1 g / m ² or more and 2 g / m ² or less per side , and the base steel sheet is based on mass% of C :. 0.05 to 0.4%, Si: 0.5% or less, Mn: 0.5 to 2.5%, P: 0.03% or less, S: 0.01% or less, sol. Al: 0.1% or less, N: 0.01% or less, B: 0 to 0.005%, Ti: 0 to 0.1%, Cr: 0 to 0.5%, Nb: 0 to 0.1 %, Ni: 0 to 1.0%, Mo: 0 to 0.5%, Mn + Cr: 0.5 to 3.0%, and the balance has a chemical composition consisting of Fe and impurities. , Zn-based plated steel plate for hot pressing .
[2] The surface treatment layer contains at least one of a phosphorus-containing compound, a vanadium-containing compound, a copper-containing compound, an aluminum-containing compound, a silicon-containing compound, and a chromium-containing compound as the content per one side, as shown below. The Zn-based plated steel sheet for hot pressing according to [1], which is further contained in the range.
Phosphorus-containing compounds: P-terms, 0.00 g / ^{m 2} or more 0.01 g / ^{m 2} or less vanadium-containing compounds: in V terms, 0.00 g / ^{m 2} or more 0.01 g / ^{m 2} or less copper-containing compounds: Cu Conversion in, 0.00 g / ^{m 2} or more 0.02 g / ^{m 2} or less aluminum containing compounds: in terms of Al, 0.000g / ^{m 2} or more 0.005 g / ^{m 2} or less the silicon-containing compound: in terms of Si, 0.000g / m ² or more 0.005 g / ^{m 2} or less chromium-containing compound: with Cr terms, the content of the non-oxide ceramic particles containing 0.00 g / ^{m 2} or more 0.01 g / ^{m 2} or less [3] the titanium, The Zn-based plated steel sheet for hot pressing according to [1] or [2], which is 0.2 g / m ² or more and 1.5 g / m ² or less per side.
[4] The Zn-based galvanized steel sheet for hot pressing according to any one of [1] to [3], wherein the titanium-containing non-oxide ceramic particles are titanium nitride or titanium booxide.
[5] The surface treatment layer is further subjected to one or more oxides selected from the group consisting of zirconia, lanthanum oxide, cerium oxide and neodymium oxide having an average particle size of 5 nm or more and 500 nm or less per one side. The Zn-based galvanized steel sheet for hot pressing according to any one of [1] to [4], which contains 0.2 g / m ² or more and 2 g / m ² or less.
[6] The hot water according to [5], wherein the average particle size of one or more oxides selected from the group consisting of zirconia, lanthanum oxide, cerium oxide and neodymium oxide is 5 nm or more and 50 nm or less. Zn-based galvanized steel sheet for pressing .
[7] The content of one or more oxides selected from the group consisting of zirconia, lanthanum oxide, cerium oxide and neodymium oxide is 0.4 g / m ² or more and 1.5 g / m ² or less per side. The Zn-based galvanized steel sheet for hot pressing according to [5] or [6].
[8] The Zn-based galvanized steel sheet for hot pressing according to any one of [5] to [7], wherein the oxide is zirconia.

As described above, according to the present invention, it is possible to more easily improve the coating adhesion and weldability with the coating film applied after hot pressing.

Hereinafter, preferred embodiments of the present invention will be described in detail.

<1. Zn-based galvanized steel sheet>
The Zn-based plated steel sheet according to the embodiment of the present invention includes a Zn-based plated layer on a base steel sheet, and further, a surface-treated layer described in detail below is provided on at least one surface of the Zn-based plated layer. This surface treatment layer contains titanium-containing non-oxide ceramic particles having an average particle size of 1 μm or more and 10 μm or less in a range of 0.1 g / m ² or more and 2 g / m ² or less. Here, the surface treatment layer can contain one or more compounds of non-oxide ceramic particles containing titanium having the above average particle size. A Zn-based plated steel sheet having such a structure can be suitably used in the hot press method described above. Hereinafter, the configuration of the Zn-based plated steel sheet will be described in detail.

(1) Base Steel Sheet The base steel sheet used for the Zn-based plated steel sheet according to the present embodiment is not particularly limited, and various steel sheets having known characteristics and chemical compositions can be used. The chemical composition of the steel sheet is not particularly limited, but it is preferably a chemical composition capable of obtaining high strength by quenching. For example, in the case of obtaining a heat-treated steel material having a tensile strength of 980 MPa or more, the base steel plate is based on mass%, C: 0.05 to 0.4%, Si: 0.5% or less, Mn: 0. 5 to 2.5%, P: 0.03% or less, S: 0.01% or less, sol. Al: 0.1% or less, N: 0.01% or less, B: 0 to 0.005%, Ti: 0 to 0.1%, Cr: 0 to 0.5%, Nb: 0 to 0.1 It is exemplified that%, Ni: 0 to 1.0%, and Mo: 0 to 0.5% are contained, and the balance is made of hardened steel having a chemical composition consisting of Fe and impurities.

When a heat-treated steel material having a relatively low strength having a strength of less than 980 MPa at the time of quenching is to be obtained, the chemical composition of the base steel sheet does not have to be in the above range.

From the viewpoint of quenchability during quenching and the formation of Mn oxide and Cr oxide contained in the zinc oxide layer after heating, the Mn content and Cr content are Mn + Cr: 0.5. It is preferably ~ 3.0%. Further, the Mn content and Cr content are more preferably Mn + Cr: 0.7 to 2.5%.

When Mn and Cr are contained in the chemical composition of the steel sheet, a part of the zinc oxide layer formed on the surface layer after hot pressing becomes a composite oxide containing Mn and Cr. By forming the composite oxide containing Mn and Cr, the coating adhesion after the chemical conversion treatment of the phosphate system is further improved. Although the details are unknown, the formation of these composite oxides improves the alkali resistance of the phosphate-based chemical conversion-treated film to be formed as compared with zinc oxide, and exhibits good coating adhesion. It is considered to be.

When Mn and Cr are contained as the chemical composition of the steel sheet, the content thereof is preferably in the range of 0.5% or more and 3.0% or less in mass% as Mn + Cr as described above, more preferably. Is a mass% in the range of 0.7% or more and 2.5% or less. When the content of Mn + Cr is less than 0.5%, zinc oxide formed on the surface layer after hot pressing and the composite oxide containing Mn and Cr are insufficient, and better coating adhesion is obtained. May be difficult to express. On the other hand, when the content of Mn + Cr exceeds 3.0%, there is no problem in coating adhesion, but the cost increases, the toughness of the spot welded portion is significantly reduced, and the plating gets wet. Deterioration of sex may be significant.

(2) Zn-based plating layer The Zn-based plating layer according to the present embodiment is not particularly limited, and generally known Zn-based plating can be used. Specifically, as the Zn-based plating layer according to the present embodiment, molten Zn plating, alloyed fused Zn plating, fused Zn-55% Al-1.6% Si plating, fused Zn-11% Al plating, and fused Zn. -11% Al-3% Mg plating, molten Zn-6% Al-3% Mg plating, molten Zn-11% Al-3% Mg-0.2% Si plating, electric Zn plating, electric Zn-Ni plating, Examples thereof include electric Zn-Co plating. It is also effective to coat the plating of the above components by a method such as vapor deposition, and the plating method is not particularly limited.

As a specific plating operation in the present embodiment, when forming a molten Zn-based plating layer, a steel sheet is immersed in a plating bath in which a molten Zn or Zn alloy is held, and the steel sheet is immersed in the plating bath. Perform the operation of pulling up the steel plate. The amount of plating adhered to the steel sheet is controlled by adjusting the pulling speed of the steel sheet, the flow rate of the wiping gas ejected from the wiping nozzle provided above the plating bath, and the flow velocity. When the Zn-based plating layer is formed by electroplating, the steel sheet is negatively electrodeposited in an electrolytic solution containing ions of elements desired to be contained in the Zn-based plating layer such as Zn ions and other Ni ions and Co ions. Electrolytic treatment is carried out with the counter electrode. Further, the amount of plating adhered to the steel sheet is controlled by the electrolytic solution composition, the current density, and the electrolytic time. The alloying treatment is performed by additionally heating the plated steel sheet in a gas furnace, an induction heating furnace, a heating furnace using these, or the like after the plating treatment as described above. For such a plating operation, plating may be performed by either a continuous plating method of a coil or a plating method of a single cutting plate.

The thickness of such a Zn-based plating layer (i.e., the adhesion amount of Zn-based plating layer) is preferably in the range of per side ^{20g / m 2 ~100g / m 2} . When the thickness of the Zn-based plating layer is less than 20 g / m ² per side, the effective amount of Zn after hot pressing cannot be secured and the corrosion resistance becomes insufficient, which is not preferable. Further, when the thickness of the Zn-based plating layer exceeds 100 g / m ² per side, the processability and adhesion of the molten Zn-based plating layer are lowered, which is not preferable. The thickness of the more preferred Zn-based plating layer is in the range of per side ^{30g / m 2 ~90g / m 2} .

(3) Surface Treatment Layer On the Zn-based plating layer as described above, a surface treatment layer containing one or more compounds selected from non-oxide ceramic particles containing titanium is further formed. ing.

Here, "non-oxide ceramics" means ceramics composed of a compound containing no oxygen as an element. Moreover, such "non-oxide ceramics", the electrical resistivity of 25 ° C. (volume resistivity, specific resistance) is preferably in the range of ^{0.1 × 10 -6 Ωcm~185 × 10 -6} Ωcm ..

Examples of such non-oxide ceramics include boride ceramics, nitride ceramics, silicide ceramics and the like. Boride ceramics, nitride ceramics, and silicide ceramics are non-oxide ceramic particles containing titanium containing boron (B), nitrogen (N), and silicon (Si) as major non-metal constituent elements, respectively. That is.

Further, in the surface treatment layer according to the present embodiment, the particles of non-oxide ceramics as described above contain titanium. Non-oxide ceramic particles containing these titanium, electrical resistivity of either 25 ° C. is in the range of ^{0.1 × 10 -6 Ωcm~185 × 10 -6} Ωcm.

The non-oxide ceramic particles containing titanium are present in the state of particles in the surface treatment layer.

Specifically, the average particle size (primary average particle size) of the non-oxide ceramic particles containing granular titanium as described above is 1 μm or more and 10 μm or less. From the viewpoint of adhesion after coating, it is advantageous that the average particle size of the non-oxide ceramic particles containing titanium is smaller, but those having an average particle size of less than 1 μm are difficult to obtain and are disadvantageous in terms of cost. It is also inferior in weldability. When the average particle size of the titanium-containing non-oxide ceramic particles exceeds 10 μm, the contact area between the titanium-containing non-oxide ceramic particles and the plated steel sheet becomes small, and heating during hot pressing is performed. At this time, the influence of the titanium-containing non-oxide ceramic particles on the steel sheet is reduced, which is not preferable. The average particle size of the titanium-containing non-oxide ceramic particles is preferably 2 μm or more and 8 μm or less.

Further, in the Zn-based plated steel sheet according to the present embodiment, titanium-containing non-oxide ceramic particles having a particle size larger than the thickness of the surface treatment layer while having the above-mentioned average particle size are more present. It is preferable that there are many. When more such non-oxide ceramic particles are present in the surface treatment layer, a part of the non-oxide ceramic particles is exposed from the surface treatment layer, and the weldability can be further improved. ..

The average particle size (primary average particle size) of the titanium-containing non-oxide ceramic particles as described above can be measured by a known method. For example, a cross-section embedded sample is prepared after coating, and the sample obtained by using an optical microscope or an electron microscope is cross-sectionally observed in a plurality of fields of view, and the non-oxide ceramic particles containing titanium in the film are observed in each field of view. Measure the average particle size at several points. After that, the average particle size can be obtained by averaging the measurement results in all the obtained visual fields. The number of observation fields of view is not particularly limited, but may be, for example, about 5 to 20 fields of view.

Surface treatment layer Zn-base plated steel sheet according to the present embodiment comprises the non-oxide ceramic particles containing titanium having an average primary particle size as described above, per side 0.2 g / m ² or more 2 g / m ² It is contained in the following range. Here, when a plurality of types of non-oxide ceramic particles are contained in the surface treatment layer, the above-mentioned content means the total content of the plurality of types of non-oxide ceramic particles. The surface or part of some of the titanium non-oxide ceramic particles present in the surface treatment layer is oxidized during heating during hot pressing to generate various oxides such as titanium oxide. The content of titanium-containing non-oxide ceramic particles in the surface treatment layer (hereinafter, also simply referred to as “content of non-oxide ceramic particles”) is 0.2 g / m ² or more and 2 g / m ² or less per side. In the range of, the surface or part of the non-oxide ceramic particles containing titanium is oxidized after hot pressing and is present on the surface of the steel plate as an oxide of titanium oxide or the like, so that the electrodeposition during electrodeposition coating is performed. It has some effect on the coagulation and precipitation of the coating film, and the generated oxide and the electrodeposition coating film adhere firmly to each other. As a result, even when the chemical conversion treatment (phosphate treatment or FF chemical conversion treatment) is not sufficient, it is possible to develop strong adhesion.

In addition, the non-oxide ceramic particles containing titanium that remain unoxidized during heating during hot pressing reduce the contact resistance of the steel sheet surface because the particles themselves have excellent conductivity. As a result, the Zn-based plated steel sheet according to the present embodiment can exhibit excellent weldability.

When the content of the non-oxide ceramic particles in the surface treatment layer is less than 0.1 g / m ² per side, sufficient titanium oxide is not present during the hot pressing, and the coating adheres after the hot pressing. It is not possible to secure sufficient sex. In addition, since the amount of non-oxide ceramic particles containing titanium is not sufficient, the contact resistance on the surface of the steel sheet cannot be reduced, and excellent weldability cannot be exhibited. On the other hand, when the content of the non-oxide ceramic particles in the surface-treated layer exceeds 2 g / m ² per side, the cost of the Zn-based plated steel sheet according to the present embodiment increases and the cohesive force of the surface-treated layer increases. It is considered that the coating film formed on the surface treatment layer is easily peeled off after hot pressing.

The content of the non-oxide ceramic particles in such a surface treatment layer is preferably 0.2 g / m ² or more and 1.5 g / m ² or less per side.

When the surface-treated layer according to the present embodiment is formed with the content of the non-oxide ceramic particles in the above range, the thickness of the surface-treated layer is about 0.5 μm to 2 μm. As a result, at least a part of the non-oxide ceramic particles according to the present embodiment is exposed on the surface without being buried in the surface treatment layer.

Examples of the titanium-containing non-oxide ceramic particles include TiB (electrical resistivity at 25 ° C. 40 × ^10-6 Ωcm), TiB ₂ (28 × ^10-6 Ωcm), TiC (180 × 10 ^{−). 6} Ωcm), TiN (22 × ^10-6 Ωcm), TiSi (63 × ^10-6 Ωcm), TiSi ₂ (123 × ^10-6 Ωcm), at least one of the particles selected from the group. Seeds are mentioned.

The above-mentioned surface treatment layer can be formed by directly applying the above-mentioned titanium-containing non-oxide ceramic particles onto a Zn-based plated steel sheet. However, in order to improve the stability of the treatment liquid and the adhesion of the surface treatment layer, the non-oxide ceramic particles containing titanium are mixed with a resin or a cross-linking agent to prepare a treatment liquid, and the treatment liquid is Zn. It is preferable to form the surface-treated layer as described above by applying it on a system-plated steel sheet and then drying and baking it.

As such a resin, a water-soluble or water-dispersible resin is preferably used, and the type of resin is a polyurethane resin, a polyester resin, an epoxy resin, a (meth) acrylic resin, a polyolefin resin, a phenol resin, or these resins. Examples of the denatured product of. When titanium powder is used, a solvent-based resin using various solvents as a solvent may be used in addition to the above-mentioned aqueous resin.

Examples of such a cross-linking agent include zirconium carbonate compounds, organic titanium compounds, oxazoline polymers, water-soluble epoxy compounds, water-soluble melamine resins, water-dispersed blocked isocyanates, and water-based aziridine compounds.

In addition, as other components that are preferably further contained in the surface treatment layer according to the present embodiment, one or more oxides selected from zirconium oxide (zirconia), lanthanum oxide, cerium oxide and neodymium oxide Can be mentioned.

If the surface treatment layer contains one or more oxides selected from the above-mentioned zirconia, lanthanum oxide, cerium oxide and neodymium oxide, it exists before the hot press and during the hot press. Zirconia, lanthanum oxide, cerium oxide, and neodymium oxide present in the surface treatment layer during heating detoxify the formed Al oxide. As a result, the formation of zinc oxide during hot pressing is promoted, the phosphate treatment property after hot pressing is enhanced, and the adhesion to the coating film is improved. Regarding the detoxification of Al oxide during heating during hot pressing with zirconia, lanthanum oxide, cerium oxide, and neodymium oxide, the details of the detoxification mechanism are unknown. However, when zirconia, lanthanum oxide, cerium oxide, and neodymium oxide dissolve the Al oxide formed on the surface of the steel plate, Zn, which is easily oxidized next to Al, is oxidized during hot pressing, and as a result, it is oxidized. , It is considered that it promotes the production of zinc oxide (ZnO) having excellent chemical properties. In order to obtain such an effect more efficiently, the average particle size of the above oxides is preferably 5 nm or more and 500 nm or less. Since the average particle size of one or more oxides selected from zirconia, lanthanum oxide, cerium oxide and neodymium oxide is 5 nm or more and 500 nm or less, these oxides are uniformly present on the surface of the steel sheet after hot pressing. This makes it possible to realize stronger adhesion to the electrodeposited coating film.

The average particle size of the above-mentioned zirconia, lanthanum oxide, cerium oxide and neodymium oxide is more preferably 10 nm or more and 30 nm or less. Further, the average particle size of the above-mentioned zirconia, lanthanum oxide, cerium oxide, and neodymium oxide can be measured in the same manner as the average particle size of the non-oxide ceramic particles.

The content of one or more oxides selected from zirconia, lanthanum oxide, cerium oxide and neodymium oxide in the surface treatment layer shall be in the range of 0.2 g / m ² or more and 2 g / m ² or less per side. Is preferable. When the content of one or more oxides selected from zirconia, lanthanum oxide, cerium oxide and neodium oxide in the surface treatment layer is less than 0.2 g / m ² per side, it is sufficient after hot pressing. Zirconia, lanthanum oxide, cerium oxide, and neodium oxide are absent, and the detoxification effect of Al oxide on the plating surface is reduced, making it difficult to ensure sufficient coating adhesion after hot pressing. Sometimes. On the other hand, when the content of zirconia or the like in the surface treatment layer exceeds 2 g / m ² per side, the cost of the Zn-based plated steel sheet according to the present embodiment increases and the cohesive force of the surface treatment layer becomes weak. Therefore, it is considered that the coating film formed on the surface treatment layer after hot pressing is easily peeled off.

Zirconia in such a surface treatment layer, the content of one or more oxides selected from lanthanum oxide, cerium oxide and neodymium, preferably, per side 0.4 g / m ² or more 1.5 g / m ² It is as follows.

Typical examples of the treatment liquid containing zirconia, lanthanum oxide, cerium oxide and neodymium oxide include zirconia sol, lanthanum oxide sol, cerium oxide sol, and neodymium oxide sol. Specific commercial products include Nissan Chemical Co., Ltd. Examples include the Nano Youth (registered trademark) series manufactured by Taki Chemical Co., Ltd. and the Ceramese series manufactured by Taki Chemical Co., Ltd.

In the surface treatment layer according to the present embodiment, in addition to the above oxides, the P-containing compound, the V-containing compound, the Cu-containing compound, the Al-containing compound, the Si-containing compound, or the Cr-containing compound described in detail below At least one of the above may be contained within a predetermined content range.

The P-containing compound is a compound containing phosphorus as a constituent element. Examples of the P-containing compound include compounds such as phosphoric acid, phosphite, phosphonic acid, phosphonic acid, phosphinic acid, phosphinic acid, phosphine oxide, and phosphine, and ionic compounds using these compounds as anions. Can be mentioned. All of these P-containing compounds are commercially available as reagents or products and can be easily obtained. These P-containing compounds exist in a state of being dissolved in the treatment liquid or in a state of being dispersed as a powder in the treatment liquid, and in a state of being dispersed as a solid in the surface treatment layer.

The V-containing compound is a compound containing vanadium as a constituent element. Examples of such V-containing compounds include vanadium oxide containing vanadium pentoxide, metavanadic acid-based compounds containing ammonium metavanadate, vanadium compounds containing sodium vanadate, and other V-containing compounds. it can. All of these V-containing compounds are commercially available as reagents or products and can be easily obtained. These V-containing compounds exist in a state of being dissolved in the treatment liquid or in a state of being dispersed as a powder in the treatment liquid, and in a state of being dispersed as a solid in the surface treatment layer.

The surface treatment layer according to the present embodiment contains one or more compounds selected from the above P-containing compounds and V-containing compounds in terms of P and V, each of which is 0.00 g / m ² or more per side. It is preferably contained in the range of 0.01 g / m ² or less.

One or more compounds selected from the above P-containing compounds and V-containing compounds are oxidized to oxides during hot pressing and are unevenly distributed at the interface between the Zn-based plating layer and the surface treatment layer. , P or V, and forms an oxide layer having a weak cohesive force. The content of one or more compounds selected from the P-containing compound and V-containing compounds, in P and V conversion is in the range 0.00 g / ^{m 2} or more 0.01 g / ^{m 2} or less per one surface, respectively As a result, the thickness of the oxide layer having a weak cohesive force as described above formed during hot pressing becomes thin, and the adhesion between the Zn-based plating layer and the surface treatment layer after hot pressing is further improved.

When the content of one or more selected from the P-containing compound and the V-containing compound in the surface treatment layer exceeds 0.01 g / m ² per side, the oxidation with weak cohesive force formed during hot pressing. The thickness of the material layer becomes thicker, and the adhesion between the Zn-based plating layer and the surface treatment layer decreases, and as a result, the adhesion after electrodeposition coating also decreases. From the viewpoint of adhesion between the Zn-based plating layer and the surface treatment layer after hot pressing, the content of one or more compounds selected from the P-containing compound and the V-containing compound in the surface treatment layer is P. and at V conversion, and more preferably each is per surface 0.000g / ^{m 2} or more 0.003 g / ^{m 2} or less.

The Cu-containing compound is a compound containing copper as a constituent element. Examples of such Cu-containing compounds include metallic Cu, copper oxide, various organic copper compounds, various inorganic copper compounds, and various copper complexes. All of these Cu-containing compounds are commercially available as reagents or products and can be easily obtained. These Cu-containing compounds exist in a state of being dissolved in the treatment liquid or in a state of being dispersed as a powder in the treatment liquid, and in a state of being dispersed as a solid in the surface treatment layer.

Surface treatment layer according to the present embodiment, one or more compounds selected from Cu-containing compound as described above, in Cu conversion, per side 0.00 g / ^{m 2} or more 0.02 g / ^{m 2} or less It is preferable that it is contained in the range of.

One or more compounds selected from the above Cu-containing compounds are oxidized during hot pressing to form oxides, which are unevenly distributed at the interface between the Zn-based plating layer and the surface treatment layer and contain Cu. Form an oxide layer with weak cohesive force. The content of one or more compounds selected from the Cu-containing compounds, in Cu conversion, by the range 0.00 g / ^{m 2} or more 0.02 g / ^{m 2} or less per one surface, during hot pressing The thickness of the oxide layer having a weak cohesive force as described above becomes thin, and the adhesion between the Zn-based plating layer and the surface treatment layer after hot pressing is further improved.

When the content of one or more selected from Cu-containing compounds in the surface treatment layer exceeds 0.02 g / m ² per side, the thickness of the oxide layer with weak cohesive force formed during hot pressing. As a result, the adhesion at the interface between the Zn-based plating layer and the surface treatment layer decreases, and as a result, the adhesion after electrodeposition coating also decreases. In addition, since Cu is a more noble element than Fe, which is the main component of the base steel sheet, the corrosion resistance also tends to decrease. From the viewpoint of adhesion between the Zn-based plating layer and the surface treatment layer after hot pressing, the content of one or more compounds selected from the Cu-containing compounds in the surface treatment layer is one side in terms of Cu. More preferably, it is 0.000 g / m ² or more and 0.005 g / m ² or less per unit.

The Al-containing compound is a compound containing aluminum as a constituent element. Examples of such Al-containing compounds include metal Al, aluminum oxide, aluminum hydroxide, and ionic compounds having aluminum ions as cations. All of these Al-containing compounds are commercially available as reagents or products and can be easily obtained. These Al-containing compounds exist in a state of being dissolved in the treatment liquid or in a state of being dispersed as a powder in the treatment liquid, and in a state of being dispersed as a solid in the surface treatment layer.

The Si-containing compound is a compound containing silicon as a constituent element. Examples of such Si-containing compounds include Si alone, silica (silicon oxide), organic silane, a silicone resin that is also used as a binder resin, and other Si-containing compounds. All of these Si-containing compounds are commercially available as reagents or products and can be easily obtained. These Si-containing compounds exist in a state of being dissolved in the treatment liquid or in a state of being dispersed as a powder in the treatment liquid, and in a state of being dispersed as a solid in the surface treatment layer.

The surface treatment layer according to the present embodiment contains one or more compounds selected from the above Al-containing compound and Si-containing compound in terms of Al and Si, each of which is 0.000 g / m ² or more per side. It is preferably contained in the range of 0.005 g / m ² or less.

One or more compounds selected from the above Al-containing compounds and Si-containing compounds are oxidized to oxides during hot pressing and concentrated on the surface of the surface treatment layer. The content of one or more compounds selected from the Al-containing compound and the Si-containing compound is in the range of 0.000 g / m ² or more and 0.005 g / m ² or less per side in terms of Al and Si, respectively. As a result, the abundance ratio of the oxide containing Al or Si formed on the surface of the surface treatment layer during hot pressing becomes small, and the adhesion between the surface treatment layer after hot pressing and the electrodeposition coating film is further improved. improves.

When the content of one or more selected from the Al-containing compound and the Si-containing compound in the surface treatment layer exceeds 0.005 g / m ² per side, it contains Al or Si formed during hot pressing. The abundance ratio of oxides is increased. These Al or Si-containing oxides are formed during hot pressing because they inhibit the formation of the chemical conversion treatment film and also reduce the adhesion between the surface treatment layer and the electrodeposition coating film after hot pressing. As the abundance ratio of the oxide containing Al or Si increases, the adhesion between the surface treatment layer and the electrodeposition coating film decreases. One or more selected from Al-containing compounds and Si-containing compounds in the surface-treated layer from the viewpoint of adhesion between the surface-treated layer after hot pressing and the electrodeposition coating film (that is, adhesion after coating). the content of the compound of Al and Si in terms, and more preferably each is per surface 0.000g / ^{m 2} or more 0.002 g / ^{m 2} or less.

The Cr-containing compound is a compound containing chromium as a constituent element. Examples of such Cr-containing compounds include metal Cr, chromium compounds having various valences, and ionic compounds having chromium ions having various valences as cations. These Cr-containing compounds exist in a state of being dissolved in the treatment liquid or in a state of being dispersed as a powder in the treatment liquid, and in a state of being dispersed as a solid in the surface treatment layer.

The performance and properties of Cr-containing compounds differ depending on the valence, and there are many harmful compounds for hexavalent chromium compounds. In view of the recent tendency that consideration for environmental protection is strongly required, the surface treatment layer according to the present embodiment preferably does not contain the above Cr-containing compound as much as possible, and more preferably chromium-free.

From the above viewpoint, the surface treatment layer according to the present embodiment contains one or more compounds selected from the above Cr-containing compounds in terms of Cr, 0.00 g / m ² or more per side. It is preferably contained in the range of 0.01 g / m ² or less, and more preferably not contained in a Cr-containing compound.

Further, as long as the effect of the present invention based on containing one or more compounds selected from non-oxide ceramic particles containing titanium is not impaired, the surface treatment layer may be a pigment such as carbon black or titania. , Various rust preventive pigments and the like used in coated steel sheets may be contained. In this case as well, the surface treatment layer contains titanium-containing non-oxide ceramic particles in the range of 0.1 g / m ² or more and 2 g / m ² or less per side.

The addition of these pigments does not directly improve the adhesion and corrosion resistance of the coating film after hot pressing, but for pigments such as carbon black and titania, the surface of the steel sheet is heated by hot pressing in a furnace. By increasing the emissivity of, it is possible to shorten the heating time. As for the rust preventive pigment, it is possible to suppress the corrosion of the steel sheet before the hot press heating.

As a method for forming such a surface treatment layer, as mentioned above, for example, a treatment liquid containing one or more compounds selected from non-oxide ceramic particles containing titanium is applied to the surface of a galvanized steel sheet. It may be applied, dried and baked.

The coating method is not limited to a specific method, and the base steel sheet is immersed in the treatment liquid or the treatment liquid is sprayed on the surface of the base steel sheet, and then a roll or gas is used so as to have a predetermined adhesion amount. Examples include a method of controlling the amount of adhesion by spraying and a method of applying with a roll coater or a bar coater.

Further, the drying / baking method is not limited to a specific method as long as it can volatilize the dispersion medium (mainly water or the like). Here, if the surface treatment layer is heated at an excessively high temperature, the uniformity of the surface treatment layer may be lowered, and conversely, if the surface treatment layer is heated at an excessively low temperature, the productivity may be lowered. Therefore, in order to stably and efficiently produce a surface-treated layer having excellent properties, it is necessary to heat the coated surface-treated layer at a temperature of about 80 ° C. to 150 ° C. for about 5 seconds to 20 seconds. preferable.

Further, it is economical and preferable that the surface treatment layer is formed in-line in the production line of the plated steel sheet, but it may be formed in another line or after blanking for forming. It may be formed.

Here, the contents of titanium-containing non-oxide ceramic particles and zirconia, lanthanum oxide, cerium oxide and neodium oxide in the surface treatment layer can be measured by a known method. For example, various compounds are previously subjected to cross-sectional energy. It is possible to measure by dissolving the film after confirming by distributed X-ray (Energy Dispersive X-ray: EDX) analysis, etc., and using ICP (Inductive Coupled Plasma, inductively coupled plasma) emission spectroscopy, etc. is there. Further, the contents of the P-containing compound, V-containing compound, Cu-containing compound, Al-containing compound, Si-containing compound, and Cr-containing compound in the surface treatment layer can also be measured by the same method.

<2. About hot pressing process>
When the hot press method is applied to a Zn-based plated steel sheet as described above, the Zn-based plated steel sheet is heated to a predetermined temperature and then press-formed. In the case of the hot-dip Zn-based plated steel sheet according to the present embodiment, since hot press forming is performed, it is usually heated to 700 to 1000 ° C., but after rapid cooling, martensite becomes a single phase or martensite is 90 in volume fraction. In the case of% or more, it is important that the lower limit of the heating temperature is Ac ₃ points or more. In the case of the present invention, since the case of the two-phase region of martensite / ferrite after rapid cooling is also included, the heating temperature is preferably 700 to 1000 ° C. as described above.

There are two hot press methods, a hot press by slow heating and a hot press by rapid heating. Examples of the heating method used include electric furnace, gas furnace, flame heating, energization heating, high frequency heating, induction heating, etc., and the atmosphere at the time of heating is not particularly limited, but the effect of the present invention can be remarkably obtained. As the heating method, it is preferable to use electric heating, induction heating, etc., which are rapid heating.

In the hot pressing method by slow heating, radiant heating of a heating furnace is used. First, the Zn-based plated steel sheet according to the present embodiment is used as a steel sheet for hot pressing and charged into a heating furnace (gas furnace, electric furnace, etc.). In the heating furnace, the steel sheet for hot pressing is heated to 700 to 1000 ° C., and depending on the conditions, it is maintained (equalized heat) at this heating temperature. As a result, Zn in the Zn-based plating layer is bonded to Fe to form a solid phase (Fe—Zn solid solution phase). The molten Zn in the Zn-based plating layer is bonded to Fe to solid-phase it, and then the steel sheet is extracted from the heating furnace. The molten Zn in the Zn-based plating layer may be bonded to Fe by soaking heat to solidify the Fe—Zn solid solution phase and the ZnFe alloy phase, and then the steel sheet may be extracted from the heating furnace.

On the other hand, the Zn-based plated steel sheet may be heated to 700 to 1000 ° C., and the steel sheet may be extracted from the heating furnace with no holding time or a short holding time. In such a case, after heating the steel sheet to 700 to 1000 ° C., press molding or the like is performed until the molten Zn in the Zn-based plating layer is bonded to Fe to form a solid phase (Fe—Zn solid solution phase or ZnFe alloy phase). Cools the steel sheet without applying stress. Specifically, the steel sheet is cooled at least until the temperature of the steel sheet becomes 782 ° C. or lower. After cooling, as described below, cooling is performed while pressing the steel sheet using a die.

Similarly, in the hot press by rapid heating, the Zn-based plated steel sheet according to the present embodiment is used as the hot press steel sheet and rapidly heated to 700 to 1000 ° C. Rapid heating is carried out, for example, by energization heating or induction heating. The average heating rate in such a case is 20 ° C./sec or more. In the case of rapid heating, after heating the Zn-based plated steel sheet to 700 to 1000 ° C., until the molten Zn in the Zn-based plated layer combines with Fe to form a solid phase (Fe—Zn solid solution phase or ZnFe alloy phase). Cool the steel sheet without applying stress by press forming or the like. Specifically, the steel sheet is cooled at least until the temperature of the steel sheet becomes 782 ° C. or lower. After cooling, as described below, cooling is performed while pressing the steel sheet using a die.

The extracted steel sheet is pressed using a die. When the steel sheet is pressed, the steel sheet is cooled by the mold. A cooling medium (for example, water) circulates in the mold, and the mold removes heat from the steel sheet to cool it. Through the above steps, hot pressed steel is usually produced by heating.

In the hot-pressed steel material produced by using the Zn-based plated steel sheet having the surface-treated layer according to the present embodiment, even if the chemical conversion treatment after the hot-pressing is insufficient due to the influence of the treatment time, concentration, temperature, etc. , Titanium oxide formed on the surface of the steel plate exhibits excellent adhesion to the electrodeposition coating film, so that good adhesion after coating can be exhibited.

Hereinafter, the action and effect of the Zn-based plated steel sheet according to the embodiment of the present invention will be described more specifically while showing examples. The examples shown below are merely examples of the Zn-based plated steel sheet according to the present invention, and the Zn-based plated steel sheet according to the present invention is not limited to the following examples.

<Base steel plate>
In the following, first, molten steel having the chemical composition shown in Table 1 below was produced. Then, a slab was manufactured by a continuous casting method using each of the manufactured molten steels. The obtained slab was hot-rolled to produce a hot-rolled steel sheet. Subsequently, the hot-rolled steel sheet was pickled and then cold-rolled to produce a cold-rolled steel sheet, and steel sheets # 1 to # 8 having the chemical compositions shown in Table 1 were produced. As shown in Table 1, the thickness of the steel plate of each steel type was 1.6 mm.

<Zn-based plating layer>
Steel plates # 1 to # 8 were subjected to a hot-dip Zn plating treatment and then an alloying treatment. The maximum temperature in the alloying treatment was 530 ° C., and the mixture was heated for about 30 seconds and then cooled to room temperature to produce an alloyed hot-dip Zn-plated steel sheet (GA). Further, a hot-dip Zn-plated steel sheet (GI) was produced by performing a hot-dip Zn plating treatment using steel # 1 and performing a hot-dip Zn-plated steel sheet (GI) without performing an alloying treatment.

Further, three types of plating, molten Zn-55% Al, molten Zn-6% Al-3% Mg, and molten Zn-11% Al-3% Mg-0.2% Si, are applied to the steel sheet of steel # 1. Various hot-dip Zn platings were performed using a bath to produce hot-dip Zn-based galvanized steel sheets A1 to A3.

A1: Molten Zn-55% Al
A2: Molten Zn-6% Al-3% Mg
A3: Molten Zn-11% Al-3% Mg-0.2% Si

In addition, various Zn-based platings such as electric Zn plating, electric Zn-Ni plating, and electric Zn-Co plating were performed on steel # 1.

As a specific plating operation in the case of using electroplating, an electrolytic treatment was performed in an electrolytic solution containing Zn ions with the steel plate as the negative electrode and the counter electrode. The amount of plating adhered to the steel sheet was controlled by the composition of the electrolytic solution, the current density, and the electrolytic time.

A4: Electric Zn plating A5: Electric Zn-Ni plating A6: Electric Zn-Co plating

In the above eight types of Zn-based plating steps, the amount of the Zn-based plating layer adhered was adjusted to 60 g / m ² per side.

<Surface treatment layer>
Next, in order to prepare a chemical solution having the composition shown in Table 2 in terms of solid content ratio, the following compounds and chemicals were blended with water. A plated steel sheet for hot pressing was produced by applying the obtained treatment liquid with a bar coater and drying it in an oven under conditions such that the maximum temperature reached was 100 ° C. for 8 seconds. The adhering amount of the treatment liquid was adjusted by diluting the liquid and counting the bar coater so that the total adhering amount of the non-volatile components in the treatment liquid became the numerical values shown in Table 3. In Table 2 below, the solid content concentration of each component is described as the ratio (unit: mass%) of the non-volatile content of each component such as "Compound A" to the non-volatile content of the entire treatment liquid.

Each component (symbol) in Table 2 is as follows.
As will be described later, non-oxide ceramic particles containing vanadium were also examined as granular substances other than titanium-containing non-oxide ceramic particles. In this case, vanadium-containing non-oxide ceramic particles were referred to as “compounds”. It was regarded as "A". Similarly, titanium oxide, nickel oxide and tin (IV) oxide were designated as "oxide B".

(I) Compound A: TiB ₂ , TiN, TiSi ₂ , VB ₂ , VN
TB1: TiB ₂ particles (Nippon Shinkinzoku Co., Ltd., average particle size 2.5-4.5 μm (catalog value))
TB2: TiB ₂ particles (Nippon Shinkinzoku Co., Ltd., average particle size 1.0 to 2.0 μm (catalog value)
TN1: TiN particles (Nippon Shinkinzoku Co., Ltd., average particle size 1.5-2.5 μm (catalog value)
TN2: TiN particles (Nippon Shinkinzoku Co., Ltd., average particle size 0.7 μm (produced by dispersing TN1 with a disperser)
TN3: TiN particles (Nippon Shinkinzoku Co., Ltd., average particle size 0.3 μm (produced by dispersing TN1 with a disperser)
TS1: TiSi ₂ particles (Nippon Shinkinzoku Co., Ltd., average particle size 2-5 μm (catalog value)
TS2: TiSi ₂ particles (Nippon Shinkinzoku Co., Ltd., average particle size 5-10 μm (catalog value)
VB: VB ₂ particles (Nippon Shinkinzoku Co., Ltd., average particle size 2-5 μm (catalog value)
VN: VN particles (Nippon Shinkinzoku Co., Ltd., average particle size 4-7 μm (catalog value))

(Ii) Oxide B: zirconia, lanthanum oxide, cerium oxide, neodymium oxide ZA: zirconia sol (Nissan Chemical Industry Co., Ltd. Nanouse (registered trademark) ZR-30AL), average particle size 70 to 110 nm (catalog value)
La: Lanthanum oxide sol (Taki Chemical Co., Ltd. Bailal La-C10), average particle size 40 nm (catalog value)
Ce: Celium oxide sol (Taki Chemical Co., Ltd. Needral P-10), average particle size 20 nm (catalog value)
Nd: Neodymium oxide sol (Taki Chemical Co., Ltd. Bailal Nd-C10), average particle size 40 nm (catalog value)

(Iii) Resin A: Urethane resin emulsion (Daiichi Kogyo Seiyaku Co., Ltd. Superflex (registered trademark) 150)
B: Urethane resin emulsion (Daiichi Kogyo Seiyaku Co., Ltd. Superflex (registered trademark) E-2000)
C: Polyester resin emulsion (Toyobo Co., Ltd. Byronal (registered trademark) MD1480)

(Iv) Crosslinking agent M: Melamine resin (Mitsui Cytec Co., Ltd. Cymel (registered trademark) 325)
Z: Zirconium ammonium carbonate (Kishida Chemical Co., Ltd. Zirconium ammonium carbonate solution)
S: Silane coupling agent (Himi Shoji Co., Ltd. Sila Ace S510) (Si-containing compound)

(V) Pigment PA: Condensed Al Phosphate (Taika Co., Ltd. Condensed Aluminum K-WHITE ZF150W) (P, Al-containing compound)
PZ: Zinc phosphate (Toho Pigment Co., Ltd. NP-530) (P-containing compound)
Si1: Silica particles (Fuji Silysia Chemical Ltd. silo mask 02) (Si-containing compound)
Si2: Colloidal silica (Nissan Chemical Industries, Ltd. Snowtex O) (Si-containing compound)
Al: Alumina sol (Nissan Chemical Industries, Ltd. AS-200) (Al-containing compound)
V: Potassium vanadate (general reagent) (V-containing compound)
Cr: Oxidized Cr (VI) (general reagent) (Cr-containing compound)
Cu: Copper oxide (II) (general reagent) (Cu-containing compound)

<Hot press process>
After the step of forming the surface treatment layer, the steel sheet of each test number was hot-pressed by two types of heating methods, energization heating and atmospheric heating, and hot-pressed.

In the energization heating method, hot press heating was performed by the energization method, and hot pressing was performed. At this time, the heating rate was set to 85 ° C./sec and 42.5 ° C./sec, and the mixture was heated to 870 ° C.

After hot press heating, the steel sheet was cooled to 650 ° C. After cooling, a hot-pressed steel material (steel plate) was manufactured by sandwiching a steel plate using a flat plate mold equipped with a water-cooled jacket. Even the portion where the cooling rate during hot pressing was slow was cooled to a cooling rate of 50 ° C./sec or higher up to about 360 ° C., which is the starting point of martensitic transformation, and then quenched.

In the air heating method, a muffle furnace was used, the temperature was set to 910 ° C. in the air atmosphere, and the steel sheet was heated for 5 minutes after reaching 900 ° C.

After heating by hot press, a flat plate mold equipped with a water-cooled jacket was used to sandwich a steel plate to produce a hot press steel material (steel plate). Even the portion where the cooling rate during hot pressing was slow was cooled to a cooling rate of 50 ° C./sec or higher up to about 360 ° C., which is the starting point of martensitic transformation, and then quenched. In the following, Table 3 shows the results of performing the following evaluations by hot-pressing the steel sheets of each test number by the above-mentioned energization heating method and atmospheric heating method.

<Evaluation method>
[Phosphate treatment evaluation test]
Surface adjustment was performed at room temperature for 20 seconds using the surface adjustment treatment agent Preparen X (trade name) manufactured by Nihon Parkerizing Co., Ltd. on the plate-shaped hot pressed steel materials of each test number shown in Table 3 below. did. Further, a phosphate treatment was carried out using a zinc phosphate treatment liquid Palbond 3020 (trade name) manufactured by Nihon Parkerizing Co., Ltd. The temperature of the treatment liquid was 43 ° C., and the plate-shaped hot pressed steel material was immersed in the treatment liquid for 10 seconds or 30 seconds with respect to 120 seconds, and then washed and dried. The reason why the immersion time in the treatment liquid is shorter than the normal immersion time is to simulate a situation in which the amount of the phosphate treatment subsequently performed on the molten Zn-based galvanized steel sheet is not sufficient.

The surface of the hot-pressed steel material after the phosphate treatment was observed with an arbitrary five fields (125 μm × 90 μm) with a 1000-fold scanning electron microscope (SEM) to obtain a reflected electron image (BSE image). In the reflected electron image, the observation area was displayed in gray scale. In the backscattered electron image, the contrast is different between the portion where the phosphate film, which is a chemical conversion film, is formed and the portion where the phosphate film is not formed. Therefore, the numerical range X1 of the brightness (multiple gradations) of the portion where the phosphate film is not formed was determined in advance by SEM and EDS (Energy Dispersive X-ray Spectrometer).

In the reflected electron image of each field of view, the area A1 of the region showing contrast within the numerical range X1 was obtained by image processing. Then, based on the following equation (1), the see-through area ratio TR (%) of each visual field was obtained.

TR = (A1 / A0) x 100 ... (1)

Here, in the above formula (1), A0 is the total area of the visual field (11250 μm ² ). The average of the see-through area ratio TR (%) of the five fields of view was defined as the see-through area ratio (%) of the hot-pressed steel material of the test number.

“J” in the “phosphate treatment property” column in Table 3 means that the see-through area ratio was 30% or more. “I” means that the see-through area ratio was 25% or more and less than 30%. “H” means that the see-through area ratio was 20% or more and less than 25%. “G” means that the see-through area ratio was 15% or more and less than 20%. “F” means that the see-through area ratio was 13% or more and less than 15%. “E” means that the see-through area ratio was 11% or more and less than 13%. “D” means that the see-through area ratio was 10% or more and less than 11%. “C” means that the see-through area ratio was 8% or more and less than 10%. “B” means that the see-through area ratio was 6% or more and less than 8%. "A" means that the see-through area ratio was less than 6%. In the see-through evaluation, when it was "F", "E", "D", "C", "B" or "A", it was judged that the phosphate treatment property was excellent.

[Paint adhesion evaluation test]
After performing the above-mentioned phosphate treatment, a cationic electrodeposition paint manufactured by Nippon Paint Co., Ltd. was electrodeposited on the plate-shaped hot-pressed steel material of each test number by energizing a slope with a voltage of 160 V. Further, baking was performed at a baking temperature of 170 ° C. for 20 minutes. The average film thickness of the paint after electrodeposition coating was 10 μm in all test numbers.

After electrodeposition coating, the hot pressed steel material was immersed in a 5% NaCl aqueous solution having a temperature of 50 ° C. for 500 hours. After the immersion, a polyester tape was attached to the entire surface of the test surface 60 mm × 120 mm (area A10 = 60 mm × 120 mm = 7200 mm ² ). After that, the tape was peeled off. The area A2 (mm ² ) of the coating film peeled off by peeling off the tape was determined, and the coating film peeling rate (%) was determined based on the formula (2).

Coating film peeling rate = (A2 / A10) x 100 ... (2)

"M" in the "paint adhesion" column in Table 3 means that the coating film peeling rate was 50.0% or more. “L” means that the coating film peeling rate was 35% or more and less than 50%. “K” means that the coating film peeling rate was 20% or more and less than 35%. “J” means that the coating film peeling rate was 10% or more and less than 20%. “I” means that the coating film peeling rate was 8% or more and less than 10%. “H” means that the coating film peeling rate was 6% or more and less than 8%. “G” means that the coating film peeling rate was 5% or more and less than 6%. “F” means that the coating film peeling rate was 4% or more and less than 5%. “E” means that the coating film peeling rate was 3% or more and less than 4%. “D” means that the coating film peeling rate was 2.5% or more and less than 3%. “C” means that the coating film peeling rate was 1.3% or more and less than 2.5%. “B” means that the coating film peeling rate was 0.5% or more and less than 1.3%. “A” means that the coating film peeling rate was less than 0.5%. In the coating adhesion evaluation, when it is "I", "H", "G", "F", "E", "D", "C", "B" or "A", the coating adhesion is excellent. I decided.

[Spot weldability evaluation test]
A sample of 30 × 50 mm was cut out from the above-mentioned plate-shaped hot-pressed steel test piece, and the appropriate current range in spot welding was investigated. Welding conditions are pressurized 300 kgf (1 kgf is about 9.8 N), DC power supply, energization time 15 cycles (60 Hz), chrome copper, DR (tip 6φ: 40R) electrode, and the lower limit is 4 (t). ^The appropriate range was investigated, assuming that ^0.5 and the upper limit was Chile.

"E" in the "spot weldability" column in Table 3 means that the appropriate current range was less than 0.5 kA. “D” means that the appropriate current range was 0.5 kA or more and less than 1.0 kA. “C” means that the appropriate current range was 1.0 kA or more and less than 1.5 kA. “B” means that the appropriate current range was 1.5 kA or more and less than 2.0 kA. “A” means that the appropriate current range was 2.0 kA or more. In the spot weldability evaluation, when it was "C", "B", and "A", it was judged that the spot weldability was excellent.

Further, for the plate-shaped hot-pressed steel material in which each test number shown in Table 4 below was hot-pressed by the energization heating method, Zr ions and / or Ti ions were replaced with the above zinc phosphate treatment. And fluorine, and a treatment using an aqueous solution containing 100 to 1000 ppm of free fluorine ions (hereinafter referred to as FF chemical conversion treatment liquid) was carried out, and the coating adhesion and coating adhesion of the obtained test piece and Corrosion resistance was verified.

The FF chemical conversion treatment solution dissolves free fluorine (hereinafter abbreviated as FF), an Al oxide film, and a Zn oxide film. Therefore, FF etches the Zn-containing layer formed in the hot stamping step while dissolving a part or all of the Al oxide film and the Zn oxide film. As a result, a chemical conversion treatment layer (hereinafter, referred to as a specific chemical conversion treatment layer) composed of an oxide of Zr and / or Ti or a mixture of an oxide of Zr and / or Ti and fluoride is formed. If the FF concentration is controlled so that the Al oxide film and the Zn oxide film can be etched, the Al oxide film and the Zn oxide film are etched to form a specific chemical conversion treatment layer.

In order to obtain such an FF chemical conversion treatment solution, H ₂ ZrF ₆ (hexafluorozirconate) and H ₂ TiF ₆ (hexafluorotitanic acid) were placed in a container so as to have a predetermined metal concentration, and diluted with ion-exchanged water. Then, hydrofluoric acid and an aqueous solution of sodium hydroxide were placed in a container, and the fluorine concentration and the free fluorine concentration in the solution were adjusted to be predetermined values. The free fluorine concentration was measured using a commercially available concentration measuring device. After the adjustment, the container was filled with ion-exchanged water to prepare an FF chemical conversion treatment liquid.

The FF chemical conversion treatment was carried out as follows. First, as a preliminary treatment, an alkaline degreasing agent (EC90 manufactured by Nippon Paint Co., Ltd.) was used to perform immersion degreasing at 45 ° C. for 2 minutes. Then, the chemical conversion treatment was carried out by immersing in the FF chemical conversion treatment solution shown in Table 5 below at 40 ° C. for 10 seconds or 30 seconds, which is usually 120 seconds. After the chemical conversion treatment, the test piece was washed with water and dried. The reason why the immersion time in the treatment liquid is shorter than the normal immersion time is to simulate a situation in which the amount of adhesion of the FF chemical conversion treatment subsequently performed on the molten Zn-based plated steel sheet is not sufficient.

Regarding the obtained test material, the chemical conversion treatment property of the specific chemical conversion treatment layer was obtained by measuring the adhesion amount of Zr or Ti by fluorescent X-ray analysis, and the measured value of the adhesion amount was 10 to 100 mg / m ^2. "A" was used, and the measured value of the adhered amount was less than 10 mg / m ² or more than 100 mg / m ² as "B", and the obtained results are shown in Table 5. For systems containing zirconia, the amount of adhesion before the Zr system FF treatment was measured in advance by fluorescent X-ray analysis, and the amount of Zr adhesion before the treatment was subtracted from the amount of Zr adhesion after the chemical conversion treatment. , The amount of adhesion of Zr-based FF chemical conversion treatment. The method and evaluation criteria for the coating adhesion evaluation test on the obtained test material are the same as those on the coating adhesion evaluation test conducted on the test material on which the phosphate film is formed.

As is clear from Tables 3 and 4, the Zn-based plated steel sheet according to the present invention has not only excellent coating film adhesion after hot pressing, but also excellent chemical conversion treatment property and spot weldability. You can see that there is.

Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such examples. It is clear that anyone with ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

Claims (8)

Zn-based plated steel sheet, which is the base material, and
A surface treatment layer formed on at least one side of the Zn-based plated steel sheet and
With
The surface treatment layer contains titanium-containing non-oxide ceramic particles having an average particle size of 1 μm or more and 10 μm or less in a range of 0.1 g / m ² or more and 2 g / m ² or less per side .
The base steel sheet of the Zn-based plated steel sheet is a base steel sheet having a mass% of C: 0.05 to 0.4%, Si: 0.5% or less, Mn: 0.5 to 2.5%, P: 0.03% or less, S: 0.01% or less, sol. Al: 0.1% or less, N: 0.01% or less, B: 0 to 0.005%, Ti: 0 to 0.1%, Cr: 0 to 0.5%, Nb: 0 to 0.1 %, Ni: 0 to 1.0%, Mo: 0 to 0.5%, Mn + Cr: 0.5 to 3.0%, and the balance has a chemical composition consisting of Fe and impurities. , Zn-based plated steel plate for hot pressing . The surface treatment layer further contains at least one of a phosphorus-containing compound, a vanadium-containing compound, a copper-containing compound, an aluminum-containing compound, a silicon-containing compound, and a chromium-containing compound as the content per side within the range shown below. The Zn-based plated steel sheet for hot pressing according to claim 1, which is contained.
Phosphorus-containing compounds: P-terms, 0.00 g / ^{m 2} or more 0.01 g / ^{m 2} or less vanadium-containing compounds: in V terms, 0.00 g / ^{m 2} or more 0.01 g / ^{m 2} or less copper-containing compounds: Cu Conversion in, 0.00 g / ^{m 2} or more 0.02 g / ^{m 2} or less aluminum containing compounds: in terms of Al, 0.000g / ^{m 2} or more 0.005 g / ^{m 2} or less the silicon-containing compound: in terms of Si, 0.000g / m ² or more 0.005 g / ^{m 2} or less chromium-containing compound: with Cr terms, 0.00 g / ^{m 2} or more 0.01 g / ^{m 2} or less The Zn-based galvanized steel sheet for hot pressing according to claim 1 or 2, wherein the content of the non-oxide ceramic particles containing titanium is 0.2 g / m ² or more and 1.5 g / m ² or less per side. .. The Zn-based galvanized steel sheet for hot pressing according to any one of claims 1 to 3, wherein the titanium-containing non-oxide ceramic particles are titanium nitride or titanium booxide. The surface treatment layer further contains 0.2 g of one or more oxides selected from the group consisting of zirconia, lanthanum oxide, cerium oxide and neodymium oxide having an average particle size of 5 nm or more and 500 nm or less per side. The Zn-based galvanized steel sheet for hot pressing according to any one of claims 1 to 4, which contains / m ² or more and 2 g / m ² or less. The Zn for hot pressing according to claim 5, wherein the average particle size of one or more oxides selected from the group consisting of zirconia, lanthanum oxide, cerium oxide and neodymium oxide is 5 nm or more and 50 nm or less. System-plated steel sheet. The content of one or more oxides selected from the group consisting of zirconia, lanthanum oxide, cerium oxide and neodymium oxide is 0.4 g / m ² or more and 1.5 g / m ² or less per side. The Zn-based galvanized steel sheet for hot pressing according to claim 5 or 6. The Zn-based galvanized steel sheet for hot pressing according to any one of claims 5 to 7, wherein the oxide is zirconia.