JP6733467B2 - Zn-based plated steel sheet for hot pressing - Google Patents

Description

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

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

Many of the structures of automobiles are made of iron-based materials, especially steel plates, and it is important to reduce the weight of the steel plates in order to reduce 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 also required 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 have been conducted on a steel sheet that can maintain or improve the mechanical strength even if it is made thinner than the conventionally used steel sheet by increasing the mechanical strength of the steel sheet.

In general, a material having a high mechanical strength tends to have a low shape fixability in a forming process such as a bending process, which makes it difficult to form a complex shape. As one of means for solving the problem about the moldability, there is a so-called "hot pressing method (also called hot stamping method, hot pressing method, or die quench 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 and molded, 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 by cooling after molding. Therefore, by the hot pressing method, it is possible to obtain a molded product having both good shape fixability 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 a scale (compound) is generated. Therefore, a step of removing the scale (so-called descaling step) is required after performing the hot pressing, and the productivity is reduced. Further, in the case of a member requiring corrosion resistance, it is necessary to perform rust prevention treatment or metal coating on the surface of the member after processing, which requires a surface cleaning step and a surface treatment step, further lowering productivity.

As a method of suppressing such a decrease in productivity, for example, a method of previously coating a steel sheet to be hot pressed can be mentioned. Various materials such as organic materials and inorganic materials are generally used as the coating on the steel sheet. Among them, zinc (Zn)-based plated steel sheets having a sacrificial anticorrosive action 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 the Zn-based metal coating, it is possible to prevent the generation of scale on the surface of the steel sheet and eliminate the need for steps such as descaling, thus improving the productivity of molded products. Moreover, since the Zn-based metal coating also has a rust preventive effect, the corrosion resistance is also improved. Patent Documents 1 to 4 below disclose methods for hot pressing a plated steel plate having a Zn-based metal coating on a steel plate having a predetermined component composition.

In the following Patent Documents 1 to 3, a hot-dip Zn-plated steel plate or an alloyed hot-dip Zn-plated steel plate is used as the hot-pressing steel plate. By utilizing 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, when a thick Zn oxide layer is formed on the surface of a heat-treated steel material obtained by hot-pressing a Zn-based plated steel sheet, it adversely affects the coating film adhesion of the heat-treated steel material and the corrosion resistance after coating, 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.

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

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

According to the inventions disclosed in the following Patent Documents 5 to 7, since the Zn plating layer is covered with the above-mentioned barrier layer, evaporation of Zn is suppressed, whereby the intermediate coating film and the top coating film can be formed. It is said that the adhesiveness and corrosion resistance after painting are good.

JP, 2003-73774, A JP, 2003-129209, A JP, 2003-126921, A JP, 2004-323897, A JP, 2007-63578, A JP, 2007-291508, A JP, 2004-270029, A

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

Generally, if the chemical conversion treatment is not sufficient (for example, if there is uneven adhesion or scaling), the adhesion between the steel sheet and the electrodeposition coating film is not sufficiently secured, and as a result, adhesion after coating Inferior in sex. One of the causes of insufficient chemical conversion treatment is due to insufficient degreasing and surface preparation before chemical conversion treatment, or insufficient concentration, temperature, time, etc. of the chemical conversion treatment liquid itself. Are listed.

Another cause is that Al contained in the hot-dip Zn plating lowers the chemical conversion property. Specifically, Al in the hot-dip Zn plating layer is added during the formation of the plating film and diffused during the heating of the hot press to move to the surface layer of the plating layer to form an Al oxide film. Since the Al oxide film is not dissolved in phosphoric acid, the reaction between Zn and phosphate (for example, zinc phosphate) is hindered, 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 step, when the steel sheet is rapidly heated to Ac ₃ point or more by electric heating or induction heating and then rapidly press-formed, the phosphate treatment property is remarkably reduced, resulting in coating adhesion. Sex is also reduced.

In addition, when the inventors of the present invention additionally tried a heat-treated steel material obtained by using the hot-dip Zn-plated steel sheet whose surface was coated with a silicone resin film as a steel sheet for hot pressing disclosed in Patent Document 5 above, As will be described later, it was found that although the post-coating corrosion resistance in a cycle corrosion test in which a dry and wet environment is repeated is good, the coating adhesion is not necessarily good. Therefore, the heat-treated steel material obtained by the invention disclosed in Patent Document 5 is, for example, a portion or member on which water is structurally likely to accumulate (for example, a bag-like structural portion under the door or a closed cross-section member in the engine compartment). Not suitable for use as is.

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

Further, in the hot pressing step, when heated to Ac3 point or higher 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 electric heating or induction heating. Become. When the zinc oxide layer is formed on the surface of the steel sheet, the contact resistance value on 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 that is further excellent in coating film adhesion and weldability after hot pressing. To provide.

The inventors of the present invention have come up with the following Zn-based plated steel sheet based on the knowledge obtained as a result of earnestly examining the plated steel sheet for hot pressing for the above purpose.
The gist of the present invention is as follows.

[1] A Zn-plated steel sheet that is a base material, and a surface-treated layer formed on at least one surface of the Zn-plated steel sheet. The surface-treated layer has an average particle diameter of 1 μm or more and 10 μm or less. Alternatively , a Zn-based plated steel sheet for hot pressing containing non-oxide ceramic particles containing lanthanum in a range of 0.1 g/m ² or more and 2 g/m ² or less per one surface.
[2] The surface-treated layer shows 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-plated steel sheet for hot pressing according to [1], further containing in a range.
Phosphorus-containing compound: 0.00g/m ² or more and 0.01 g/m ² or less in terms of P Vanadium-containing compound: 0.00g/m ² or more and 0.01 g/m ² or less in terms of V Copper-containing compound: 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 [3] content of the non-oxide ceramic particles containing the zirconium or lanthanum Is 0.2 g/m ² or more and 1.5 g/m ² or less per one side , the Zn-plated steel sheet for hot pressing according to [1] or [2].
[4] The Zn-based plating for hot pressing according to any one of [1] to [3], wherein the non-oxide ceramic particles containing zirconium or lanthanum are zirconium nitride or zirconium silicide. Steel plate.
[5] The surface-treated layer further has one or more oxides selected from the group consisting of titanium oxide, nickel oxide and tin (IV) oxide having an average particle diameter of 2 nm or more and 100 nm or less on one side. The Zn-based plated steel sheet for hot pressing according to any one of [1] to [4], which is contained in a range of 0.2 g/m ² or more and 2 g/m ² or less.
[6] The hot work according to [5], wherein the particle size of one or more oxides selected from the group consisting of titanium oxide, nickel oxide and tin (IV) oxide is 5 nm or more and 50 nm or less. Zn-based plated steel sheet for press .
[7] the titanium oxide, the content of one or more oxides selected from the group consisting of nickel oxide and tin oxide (IV) is, per side 0.4 g / ^{m 2} or more 1.5 g / ^{m 2} The following is a Zn-plated steel sheet for hot pressing according to [5] or [6].
[8] The Zn-plated steel sheet for hot pressing according to any one of [5] to [7], wherein the oxide is titanium oxide.

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

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

<1. Zn-based plated steel sheet>
A Zn-based plated steel sheet according to an embodiment of the present invention includes a Zn-based plating layer on a base steel sheet, and further includes a surface treatment layer described in detail below on at least one surface of the Zn-based plating layer. The surface-treated layer contains non-oxide ceramic particles containing zirconium or lanthanum having an average particle size of 1 μm or more and 10 μm or less in the 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 the non-oxide ceramic particles containing zirconium or lanthanum having the above-mentioned average particle diameter. The Zn-plated steel sheet having such a structure can be suitably used for the hot pressing method described previously. Below, the composition of such a Zn type plated steel plate is explained in detail.

(1) Base steel plate The base steel plate used for the Zn-plated steel plate according to the present embodiment is not particularly limited, and various steel plates having known characteristics and chemical compositions can be used. Although the chemical composition of the steel sheet is not particularly limited, it is preferably a chemical composition capable of obtaining high strength by quenching. For example, when trying to obtain a heat-treated steel material having a tensile strength of 980 MPa or more, the base steel sheet is, in 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. %, Ni:0 to 1.0%, and Mo:0 to 0.5%, and the balance is made of quenching steel having a chemical composition of Fe and impurities.

When it is desired to obtain a heat-treated steel material having a relatively low strength, which has a strength of less than 980 MPa during quenching, the chemical composition of the base steel sheet does not have to be in the above range.

From the viewpoint of hardenability at the time of quenching and the viewpoint of forming Mn oxide and Cr oxide contained in the zinc oxide layer after heating, Mn content and Cr content are Mn+Cr:0.5. It is preferably ˜3.0%. Further, the Mn content and the Cr content are more preferably Mn+Cr: 0.7 to 2.5%.

When Mn and Cr are contained as 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 complex oxide containing Mn and Cr, the coating adhesion after the phosphate chemical conversion treatment is further improved. Although the details are unknown, the formation of these complex oxides improves the alkali resistance of the phosphate-based chemical conversion coating film formed, as compared with zinc oxide, and develops good paint adhesion. Thought to be a thing.

When Mn and Cr are contained as the chemical composition of the steel sheet, the content thereof is preferably 0.5% or more and 3.0% or less by mass% as Mn+Cr as described above, and more preferably Is in the range of 0.7% to 2.5% in mass %. When the content of Mn+Cr is less than 0.5%, zinc oxide formed in the surface layer after hot pressing and the composite oxide containing Mn and Cr become insufficient, resulting in better coating adhesion. 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 becomes high, and the toughness of the spot welded part is significantly reduced, and the wetness of the plating There is a case where the deterioration of sex becomes remarkable.

(2) Zn-based plating layer The Zn-based plating layer according to the present embodiment is not particularly limited, and a generally known Zn-based plating can be used. Specifically, as the Zn-based plating layer according to the present embodiment, hot-dip Zn plating, alloying hot-dip Zn plating, hot-dip Zn-55% Al-1.6% Si plating, hot-dip Zn-11% Al plating, hot-dip Zn -11% Al-3% Mg plating, hot-dip Zn-6% Al-3% Mg plating, hot-dip Zn-11% Al-3% Mg-0.2% Si plating, electric Zn plating, electric Zn-Ni plating, Electric Zn-Co plating etc. can be mentioned. It is also effective to coat the above-mentioned components with a method such as vapor deposition, and the plating method is not particularly limited.

As a specific plating operation in the present embodiment, in the case of forming a molten Zn-based plating layer, the steel sheet is immersed in a plating bath holding Zn or Zn alloy in a molten state, Carry out the operation of pulling up the steel plate. The amount of coating adhered to the steel sheet is controlled by the pulling-up speed of the steel sheet, the flow rate of wiping gas ejected from a wiping nozzle provided above the plating bath, and the flow rate adjustment. When the Zn-based plating layer is formed by electroplating, the steel plate is negatively charged in an electrolytic solution containing Zn ions and ions of other elements such as Ni ions and Co ions to be contained in the Zn-based plating layer. As a result, electrolytic treatment is performed between the counter electrode and the counter electrode. In addition, the amount of plating adhered to the steel sheet is controlled by the electrolytic solution composition, the current density, and the electrolysis time. The alloying treatment is performed by additionally heating the plated steel sheet in a gas furnace, an induction heating furnace, a heating furnace that uses these in combination, or the like after the above-described plating treatment. With respect to such plating operation, plating may be performed by either a continuous coil plating method or a single plate plating method.

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 Zn amount after hot pressing cannot be secured and corrosion resistance becomes insufficient, which is not preferable. Further, if the thickness of the Zn-based plating layer exceeds 100 g/m ² per side, the workability and adhesion of the Zn-based plating layer will deteriorate, 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 further containing one or more compounds selected from non-oxide ceramic particles containing zirconium or lanthanum. Has been formed.

Here, “non-oxide ceramics” means ceramics composed of a compound that does not contain 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, and silicide ceramics. The boride ceramics, the nitride ceramics, and the silicide ceramics are non-oxide ceramic particles having boron (B), nitrogen (N), and silicon (Si) as main non-metal constituent elements, respectively. ..

Further, in the surface-treated layer according to the present embodiment, the non-oxide ceramic particles as described above contain zirconium or lanthanum. Non-oxide ceramic particles containing these zirconium or lanthanum, 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 zirconium or lanthanum (hereinafter sometimes simply referred to as "containing zirconium or the like") exist in the state of particles in the surface treatment layer.

Specifically, the average particle size (primary average particle size) of the above-mentioned non-oxide ceramic particles containing granular zirconium or the like is 1 μm or more and 10 μm or less. From the viewpoint of adhesion after coating, it is advantageous that the particle size of the non-oxide ceramic particles containing zirconium or the like is smaller, but particles having an average particle size of less than 1 μm are difficult to obtain and are disadvantageous in terms of cost. , Inferior in weldability. Further, when the average particle size of the non-oxide ceramic particles containing zirconium etc. exceeds 10 μm, the contact area between the non-oxide ceramic particles containing zirconium etc. and the plated steel sheet becomes small, and during hot pressing. The effect of non-oxide ceramic particles containing zirconium or the like on the steel sheet during heating is small, which is not preferable. The average particle size of the non-oxide ceramic particles containing zirconium or the like is preferably 2 μm or more and 8 μm or less.

Further, in the Zn-based plated steel sheet according to the present embodiment, while having the average particle diameter as described above, the non-oxide ceramic particles containing zirconium or the like having a particle diameter larger than the thickness of the surface treatment layer, It is preferable that more is present. Since more 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, which makes it possible to further improve the weldability. ..

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

The surface treatment layer included in the Zn-plated steel sheet according to the present embodiment contains non-oxide ceramic particles containing zirconium or the like having the above-mentioned primary average particle diameter of 0.2 g/m ² or more and 2 g/m ² per surface. It is contained in the range of ² or less. Here, when a plurality of types of non-oxide ceramic particles are contained in the surface treatment layer, the above content means the total content of the plurality of types of non-oxide ceramic particles. Some of the non-oxide ceramic particles such as zirconium present in the surface treatment layer are oxidized such as zirconium oxide (zirconia) or lanthanum oxide because the surface or a part thereof is oxidized during heating during hot pressing. Is generated. The content of non-oxide ceramic particles containing zirconium and the like of the surface treatment layer (hereinafter, simply "non-oxide ceramic content of the particles" as referred to.) Is per side 0.2 g / m ² or more 2 g / m ² When the content is within the following range, the Al oxide existing before the hot pressing and the Al oxide formed during the hot pressing are harmless to the oxide group such as the zirconium oxide and the lanthanum oxide generated during the heating. Turn into. This promotes the formation of zinc oxide during hot pressing, enhances the phosphate treatment after hot pressing, and improves the coating adhesion.

Regarding the detoxification of Al oxides during heating by oxides such as zirconia produced by oxidizing the surface or a part of non-oxide ceramic particles containing zirconium etc., details of the detoxification mechanism are unknown. Is. However, by dissolving the Al oxide formed on the steel sheet surface with an oxide such as zirconia, Zn, which is liable to be oxidized next to Al, is oxidized during hot pressing, and as a result, it has excellent chemical conversion properties. It is considered to promote the production of zinc oxide (ZnO).

Further, the non-oxide ceramic particles containing zirconium or the like that remain unoxidized during heating during hot pressing reduce the contact resistance on the surface of the steel sheet because the particles themselves have excellent conductivity. As a result, the Zn-plated steel sheet according to this 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 zirconia does not exist during hot pressing, and Al oxide on the plating surface is harmless. The effect of chemical conversion becomes small, and it is not possible to secure sufficient paint adhesion after hot pressing. In addition, since the amount of the non-oxide ceramic particles containing zirconium or the like 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 treatment layer is more than 2 g/m ² per one side, the cost of the Zn-based plated steel sheet according to this embodiment increases and the cohesive force of the surface treatment layer increases. It is considered that the coating film formed on the surface treatment layer after the hot pressing becomes easy to be peeled off.

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

When the surface treatment layer according to this embodiment is formed with the content of the non-oxide ceramic particles in the above range, the thickness of the surface treatment 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 in a state of being exposed on the surface without being buried in the surface treatment layer.

The non-oxide ceramic particles containing zirconium, for example, _ZrB 2 (electrical resistivity 60 × ^{10 -6} Ωcm at 25 ° C.), ZrC (the ^{70 × 10 -6 Ωcm), ZrN} ( the 14 × 10 ^{- 6} Ωcm), ZrSi (49×10 ⁻⁶ Ωcm) and ZrSi ₂ (76×10 ⁻⁶ Ωcm).

Examples of the non-oxide ceramic particles containing lanthanum include particles having LaB ₆ (electrical resistivity at 25° C. of 1.5×10 ⁻⁵ Ωcm).

Further, in the surface treatment layer according to the present embodiment, it is more preferable to use non-oxide ceramic particles containing zirconium as the non-oxide ceramic particles.

The surface treatment layer as described above can be formed by directly applying the non-oxide ceramic particles containing zirconium or the like as described above onto the 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 zirconium or the like are treated with a resin or a cross-linking agent, and then the treatment liquid is added. It is preferable that the surface-treated layer as described above is formed by applying it on a Zn-based plated steel sheet and then drying and baking it.

As such a resin, it is preferable to use a water-soluble or water-dispersible resin. Examples of the type of resin include polyurethane resin, polyester resin, epoxy resin, (meth)acrylic resin, polyolefin resin, phenol resin, and modified products of these resins. When powder of zirconium or the like is used, solvent-based resins using various solvents as solvents may be used in addition to the above-mentioned water-based resin.

Examples of the crosslinking 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, other components that are preferably contained in the surface treatment layer according to the present embodiment include one or more oxides selected from titanium oxide, nickel oxide and tin (IV) oxide. ..

When the surface treatment layer contains one or more oxides selected from the above-mentioned titanium oxide, nickel oxide and tin (IV) oxide, these oxides are present on the surface of the steel sheet after hot pressing. This has some influence on the cohesive precipitation of the electrodeposition coating film during electrodeposition coating, and the oxide and the electrodeposition coating film firmly adhere to each other. As a result, even if the chemical conversion treatment (phosphate treatment or FF chemical conversion treatment) is not sufficient, it becomes possible to develop strong adhesion. In order to obtain such effects more efficiently, the average particle size of one or more oxides selected from the above-mentioned titanium oxide, nickel oxide and tin (IV) oxide is 2 nm or more and 100 nm or less. Is preferred. The average particle size of one or more oxides selected from titanium oxide, nickel oxide and tin (IV) oxide is 2 nm or more and 100 nm or less, so that these oxides become more uniform on the steel sheet surface after hot pressing. When it is present, it becomes possible to realize stronger adhesion with the electrodeposition coating film.

In addition to the above-mentioned characteristics, titanium oxide among one or more oxides selected from these titanium oxide, nickel oxide and tin (IV) oxide has an excessive Zn content during hot pressing. It becomes possible to suppress the oxidation and evaporation of the above, and in addition to the adhesion of the coating film after hot pressing, it becomes possible to enhance the corrosion resistance after hot pressing. Titanium oxide normally exists stably in the state of a metal oxide, but it reacts with zinc oxide formed during heating in hot pressing to form a complex oxide with zinc oxide, and It is presumed that it suppresses the oxidation and evaporation of Zn. In order to obtain such an effect more efficiently, the average particle size of the titanium oxide is preferably 2 nm or more and 100 nm or less.

The average particle size of one or more oxides selected from the above titanium oxide, nickel oxide and tin (IV) oxide is more preferably 5 nm or more and 50 nm or less.

Here, the average particle size of the titanium oxide, nickel oxide and tin (IV) oxide can be measured in the same manner as the average particle size of the non-oxide ceramic particles.

When the surface treatment layer contains an oxide of at least one of titanium oxide, nickel oxide and tin (IV) oxide, the content is within a range of 0.2 g/m ² or more and 2 g/m ² or less per one surface. It is preferable that the amount is 0.4 g/m ² or more and 1.5 g/m ² or less per one surface. When the content of at least one of titanium oxide, nickel oxide and tin (IV) oxide is less than 0.2 g/m ² per side, these oxides are not sufficiently present after hot pressing, In some cases, it may be difficult to exhibit even better adhesion with the electrodeposition coating film.

On the other hand, when the content of at least one of titanium oxide, nickel oxide, and tin (IV) oxide exceeds 2 g/m ² per side, the cost of the Zn-plated steel sheet according to the present embodiment increases, It is considered that the cohesive force of the surface treatment layer becomes weak and the coating film formed on the surface treatment layer after hot pressing is likely to peel off.

In addition, with respect to titanium oxide, when the content is less than 0.2 g/m ² per side, in addition to the above, it is not possible to form a sufficient complex oxide with zinc oxide, resulting in oxidation of Zn. In some cases, it may be difficult to efficiently suppress the evaporation.

The surface treatment layer according to the present embodiment includes, in addition to the above oxides, a P-containing compound, a V-containing compound, a Cu-containing compound, an Al-containing compound, a Si-containing compound, or a 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, phosphorous acid, phosphonic acid, phosphonous acid, phosphinic acid, phosphinic acid, phosphine oxide and phosphine, and ionic compounds having 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 a V-containing compound include vanadium oxide containing vanadium pentoxide, a metavanadate compound containing ammonium metavanadate, a vanadium compound containing sodium vanadate, and other compounds containing V. 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-described P-containing compound and V-containing compound in terms of P and V of 0.00 g/m ² or more per side, respectively. It is preferably contained in a range of 0.01 g/m ² or less.

One or more compounds selected from the P-containing compound and the V-containing compound as described above are oxidized during hot pressing into an oxide, which is unevenly distributed at the interface between the Zn-based plating layer and the surface treatment layer. , P or V is included to form 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, which is 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 compounds selected from P-containing compounds and V-containing compounds in the surface-treated layer is more than 0.01 g/m ² per side, the cohesive force formed during hot pressing is The thickness of the weak oxide layer is increased, the adhesion between the Zn-based plating layer and the surface treatment layer is reduced, and as a result, the adhesion after electrodeposition coating is also reduced. 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 the Cu-containing compound 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 to contain in the range of.

One or more compounds selected from the above-mentioned Cu-containing compounds are oxidized during hot pressing into oxides, and are unevenly distributed at the interface between the Zn-based plating layer and the surface treatment layer to contain Cu. An oxide layer having a weak cohesive force is formed. 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 formed oxide layer having a weak cohesive force is reduced, 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-treated layer is more than 0.02 g/m ² per side, the thickness of the oxide layer having a weak cohesive force formed during hot pressing. Becomes thicker, the adhesiveness at the interface between the Zn-based plating layer and the surface treatment layer is reduced, and as a result, the adhesiveness after electrodeposition coating is also reduced. In addition, since Cu is an element that is more precious than Fe, which is the main component of the base steel sheet, the corrosion resistance 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, in terms of Cu, one side. More preferably, it is 0.000 g/m ² or more and 0.005 g/m ² or less.

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 simple substance, silica (silicon oxide), organic silane, a silicone resin 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 compounds and Si-containing compounds in an amount of 0.000 g/m ² or more per one surface in terms of Al and Si. It is preferable that the content is 0.005 g/m ² or less.

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

When the content of one or more selected from Al-containing compounds and Si-containing compounds in the surface treatment layer is more than 0.005 g/m ² per side, it contains Al or Si formed during hot pressing. The ratio of existing oxides increases. These Al- or Si-containing oxides inhibit the formation of the chemical conversion coating and reduce the adhesion between the surface-treated layer after hot pressing and the electrodeposition coating film, so they are formed during hot pressing. When the abundance ratio of the Al- or Si-containing oxide is large, the adhesion between the surface treatment layer and the electrodeposition coating film is reduced. From the viewpoint of adhesion between the surface treatment layer after hot pressing and the electrodeposition coating film (that is, adhesion after coating), one or more selected from Al-containing compounds and Si-containing compounds in the surface treatment layer. 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 metallic Cr, chromium compounds having various valences, and ionic compounds having cations of chromium ions having various valences. 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 Cr-containing compound has different performance and properties depending on the valence, and many hexavalent chromium compounds are harmful. In view of the recent tendency in which consideration for environmental protection is strongly demanded, it is preferable that the surface treatment layer according to the present embodiment does not contain the above Cr-containing compound as much as possible, and it is more preferable that the surface treatment layer is 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 an amount of 0.00 g/m ² or more per surface in terms of Cr. The content is preferably 0.01 g/m ² or less, and more preferably no Cr-containing compound.

The surface treatment layer is a pigment such as carbon black or titania unless the effect of the present invention based on containing one or more compounds selected from non-oxide ceramic particles containing zirconium or the like is impaired. Alternatively, various rust preventive pigments used in coated steel sheets may be contained. Also in this case, the surface treatment layer contains non-oxide ceramic particles containing zirconium or the like in the range of 0.1 g/m ² or more and 2 g/m ² or less per one surface.

Addition of these pigments does not directly improve the coating adhesion and corrosion resistance after hot pressing, but for pigments such as carbon black and titania, the steel plate surface during hot pressing in a furnace is heated. The heating time can be shortened by increasing the emissivity of. With respect to the rust preventive pigment, it is possible to prevent the steel sheet from corroding before the hot press heating.

As a method of 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 zirconium etc. is treated with a zinc-plated steel sheet surface. It can be applied to, 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 applied so that a predetermined adhesion amount is obtained. Examples thereof include a method of controlling the amount of adhesion by spraying and a method of coating with a roll coater or a bar coater.

The drying and baking methods are not limited to specific methods as long as they can vaporize the dispersion medium (mainly water etc.). Here, heating at an excessively high temperature may reduce the uniformity of the surface treatment layer, and conversely, heating at an excessively low temperature may reduce productivity. Therefore, in order to stably and efficiently produce a surface-treated layer having excellent properties, the surface-treated layer after coating may be heated at a temperature of about 80° C. to 150° C. for about 5 seconds to 20 seconds. preferable.

In addition, 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 is performed. It may be formed.

Here, the content of non-oxide ceramic particles containing zirconium or the like, titanium oxide, nickel oxide, tin (IV) oxide in the surface treatment layer can be measured by a known method, for example, various compounds in advance. After confirming by cross-sectional energy dispersive X-ray (Energy Dispersive X-ray: EDX) analysis, etc., the film is dissolved, and measurement can be performed by using ICP (Inductively Coupled Plasma) emission spectroscopy etc. It is possible. 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. Hot pressing process>
When the hot pressing method is applied to the 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-plated steel sheet according to the present embodiment, it is usually heated to 700 to 1000° C. because hot press forming is performed, but after rapid cooling, it is made into a martensite single phase, or martensite has a volume ratio of 90. When it is set to be not less than %, it is important that the lower limit temperature of the heating temperature is not less than Ac ₃ point. 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.

The hot pressing method includes two methods, that is, hot pressing by gentle heating and hot pressing by rapid heating. Examples of the heating method used include electric furnaces, gas furnaces, flame heating, electric current heating, high-frequency heating, and induction heating, and the atmosphere during heating is not particularly limited, but the effect of the present invention is remarkably obtained. As a heating method, it is preferable to use rapid heating such as electric heating or induction heating.

The hot pressing method by gentle heating utilizes the radiant heating of a heating furnace. First, the Zn-plated steel sheet according to the present embodiment is used as a steel sheet for hot pressing and placed in a heating furnace (gas furnace, electric furnace, etc.). In the heating furnace, the hot-pressing steel sheet is heated to 700 to 1000° C. and, depending on the conditions, held at this heating temperature (soaking). As a result, Zn in the Zn-based plating layer bonds with Fe to form a solid phase (Fe-Zn solid solution phase). After the molten Zn in the Zn-based plating layer is combined with Fe and solidified, the steel sheet is extracted from the heating furnace. The molten Zn in the Zn-based plating layer may be combined with Fe by soaking 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 with a short holding time. In such a case, after the steel sheet is heated to 700 to 1000° C., press forming or the like is performed until the molten Zn in the Zn-based plating layer is combined with Fe to form a solid phase (Fe—Zn solid solution phase or ZnFe alloy phase). Thereby cools the steel sheet without applying stress. Specifically, cooling is performed until at least the temperature of the steel plate becomes 782° C. or lower. After cooling, as described below, cooling is performed while pressing the steel sheet using a mold.

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

The extracted steel plate is pressed using a mold. When pressing the steel sheet, 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 plate to cool it. Through the above steps, the hot pressed steel product is manufactured by normal heating.

The hot-pressed steel material manufactured using the Zn-based plated steel sheet having the surface treatment layer according to the present embodiment has excellent phosphate treatment property, coating adhesion property, and weldability. In the former performance, in particular, the Zn-plated steel sheet according to the present embodiment is heated to 700 to 1000° C. by hot pressing by rapid heating or hot pressing by gentle heating, with no holding time or holding time. In the latter performance, the Zn-based plated steel sheet according to the present embodiment is heated to 700 to 1000° C. by hot pressing by furnace heating or air atmosphere heating, and the holding time is extended when the heating time is set to a short time. The effect is remarkably exhibited when the time is set.

When performing hot pressing by ordinary heating using a conventional plated steel sheet, the steel sheet is soaked in a heating furnace. In this case, an Al oxide film is formed on the surface layer of the plating layer of the hot-press steel sheet, but the Al oxide film is cracked and divided to some extent by soaking for a long time, so the adverse effect on the chemical conversion treatability is small. On the other hand, when performing hot pressing by rapid heating, the soaking time is extremely short. Therefore, the Al oxide film formed on the outermost surface is not easily destroyed. Therefore, in the hot press by rapid heating when using the conventional plated steel sheet, the phosphate treatment property and coating adhesion of the hot pressed steel material are low as compared with the hot press by normal heating.

On the other hand, the Zn-plated steel sheet for hot pressing according to the present embodiment contains one or more compounds selected from non-oxide ceramic particles containing zirconium or the like in the surface treatment layer, Since Al oxidation is made harmless during hot pressing to promote the formation of zinc oxide, good phosphating property and coating adhesion can be exhibited.

Hereinafter, the working effects of the Zn-plated steel sheet according to the embodiment of the present invention will be described more specifically with reference to examples. The following examples 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 sheet>
In the following, first, molten steel having the chemical composition shown in Table 1 below was manufactured. Then, the slab was manufactured by the continuous casting method using each of the manufactured molten steels. The obtained slab was hot rolled to produce a hot rolled steel sheet. Then, after pickling the hot rolled steel sheet, cold rolling was carried out to manufacture 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 plate thickness of each steel plate was 1.6 mm.

<Zn-based plating layer>
The steel plates of Steels #1 to #8 were subjected to hot dip Zn plating treatment, and then subjected to alloying treatment. The maximum temperature in the alloying treatment was 530° C. in all cases, and after heating for about 30 seconds, it was cooled to room temperature to produce a galvannealed steel sheet (GA). Further, a hot-dip Zn-plated steel sheet (GI) was manufactured by performing hot-dip Zn-plating treatment using Steel #1 and not performing alloying treatment.

In addition, three types of plating of 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 plate of Steel #1. Various hot-dip Zn plating was performed using a bath, and hot-dip Zn-based plated steel sheets A1 to A3 were manufactured.

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 plating such as electric Zn plating, electric Zn-Ni plating, and electric Zn-Co plating was performed on Steel #1.

As a specific plating operation in the case of utilizing electroplating, electrolytic treatment was carried out between a counter electrode and a steel plate as a negative electrode in an electrolytic solution containing Zn ions. In addition, the amount of plating adhered to the steel sheet was controlled by the composition of the electrolytic solution, the current density, and the electrolysis time.

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

In addition, in the eight types of Zn-based plating steps, the amount of the Zn-based plated layer deposited was set to 60 g/m ² per side.

<Surface treatment layer>
Next, the following compounds and agents were blended using water in order to prepare a drug solution having the composition shown in Table 2 in terms of solid content ratio. The obtained treatment liquid was applied with a bar coater and dried using an oven under the condition that the highest temperature reached 100° C. was maintained for 8 seconds to produce a plated steel sheet for hot pressing. The amount of the treatment liquid deposited was adjusted by the dilution of the liquid and the bar coater count so that the total amount of the nonvolatile components in the treatment liquid would be the 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 nonvolatile content of each component such as “Compound A” to the nonvolatile 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 as a particulate substance other than non-oxide ceramic particles containing zirconium and the like were also examined, but in this case, non-oxide ceramic particles containing vanadium were referred to as “ Compound A". Similarly, titanium oxide, nickel oxide and tin (IV) oxide were designated as “oxide B”.

(I) Compound A: ZrB ₂ , ZrC, ZrN, ZrSi ₂ , VB ₂ , VN
ZrB: ZrB ₂ particles (Nihon Shinkin Co., Ltd., average particle size 1.5 to 2.5 μm (catalog value)
ZrC: ZrC particles (Nippon Shin Metal Co., Ltd., average particle size 1.5 to 2.5 μm (catalog value)
ZrN1: ZrN particles (Nihon Shinkin Co., Ltd., average particle size 1-2 μm (catalog value)
ZrN2: ZrN particles (Nippon Shin Metal Co., Ltd., average particle size 0.7 μm (prepared by dispersing ZrN1 with a disperser))
ZrN3: ZrN particles (Nihon Shinkin Co., Ltd., average particle size 0.3 μm (prepared by dispersing ZrN1 with a disperser)
ZrS1:ZrSi ₂ particles (Nihon Shinkin Co., Ltd., average particle size 2-5 μm (catalog value)
ZrS2: ZrSi ₂ particles (Nippon Shin Metal Co., Ltd., average particle size 5 to 10 μm (catalog value)
LaB: LaB ₆ particles (Nihon Shinkin Co., Ltd., average particle size 1 to 2 μm (catalog value)
VB: VB ₂ particles (Nihon Shinkin Co., Ltd., average particle size 2 to 5 μm (catalog value)
VN: VN particles (Nihon Shinkin Co., Ltd., average particle size 4 to 7 μm (catalog value)

(Ii) Oxide B: titanium oxide, nickel oxide, tin oxide (IV)
Ti1: titanium oxide sol (Taika Co., Ltd. TKS-203), average particle size of about 6 nm
Ti2: Titanium oxide (Titanium oxide R-930, Ishihara Sangyo Co., Ltd.), average particle size 250 nm (catalog value)
Ni: Nickel oxide (Iolitec nickel oxide), average particle size 20 nm
Sn: Tin (IV) oxide sol (Ceramece C-10, Taki Chemical Co., Ltd.), average particle size 10 nm

(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. Bayronal (registered trademark) MD1480)

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

(V) Pigment PA: Condensed phosphate Al (Taika Co., Ltd. condensed aluminum phosphate K-WHITE ZF150W) (P, Al-containing compound)
PZ: Zinc phosphite (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 (Snowtex O, Nissan Chemical Co., Ltd.) (Si-containing compound)
Al: Alumina sol (Nissan Chemical Co., Ltd. AS-200) (Al-containing compound)
V: Potassium vanadate (general reagent) (V-containing compound)
Cr: Cr(VI) oxide (general reagent) (Cr-containing compound)
Cu: Copper (II) oxide (general reagent) (Cu-containing compound)

<Hot pressing process>
After the step of forming the surface treatment layer, the steel plate of each test number was subjected to hot press heating by two types of heating methods of electric heating and atmospheric heating, and hot pressing was performed.

In the electric heating method, hot press heating was performed by the electric method, and hot pressing was performed. At this time, the heating rate was set to 85° C./second and 42.5° C./second, and heating was performed at 870° C.

After hot press heating, it was cooled until the steel plate temperature reached 650°C. After cooling, a steel plate was sandwiched by using a flat plate mold equipped with a water cooling jacket to manufacture a hot-press steel product (steel plate). Even in the portion where the cooling rate during hot pressing was slow, the material was cooled to a martensitic transformation start point of about 360° C. at a cooling rate of 50° C./sec or more and quenched.

In the atmospheric heating method, a muffle furnace was used, and the temperature was set to 910° C. in the atmospheric atmosphere, and heating was performed for 5 minutes after the steel plate temperature reached 900° C.

After hot press heating, a steel plate was sandwiched by using a flat plate mold equipped with a water cooling jacket to produce a hot press steel product (steel plate). Even in the portion where the cooling rate during hot pressing was slow, the material was cooled to a martensitic transformation start point of about 360° C. at a cooling rate of 50° C./sec or more and quenched. In the following, Table 3 shows the results of performing the following evaluations by hot pressing the steel plate of each test number by the above-mentioned electric heating method and atmospheric heating method.

<Evaluation method>
[Phosphate processability evaluation test]
Surface conditioning was carried out for 20 seconds at room temperature on the plate-shaped hot-pressed steel materials with the respective test numbers shown in Table 3 below using the surface conditioning agent PREPAREN X (trade name) manufactured by Nippon Parkerizing Co., Ltd. did. Furthermore, a phosphate treatment was performed using a zinc phosphate treatment liquid PALBOND 3020 (trade name) manufactured by Nippon 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 120 seconds, washed with water and dried.

The surface of the hot-pressed steel material after the phosphate treatment was observed with a scanning electron microscope (SEM) of 1000 times in arbitrary 5 fields of view (125 μm×90 μm) to obtain a backscattered electron image (BSE image). In the backscattered electron image, the observation area was displayed in gray scale. In the backscattered electron image, the contrast is different between the part where the phosphate film which is the chemical conversion film is formed and the part where the phosphate film is not formed. Therefore, the numerical value range X1 of the lightness (a plurality of gradations) of the portion where the phosphate film is not formed was previously determined by SEM and EDS (energy dispersive X-ray spectroscope).

In the backscattered electron image of each visual field, the area A1 of the region showing the contrast within the numerical range X1 was obtained by image processing. Then, the transparent area ratio TR (%) of each visual field was obtained based on the following formula (1).

TR=(A1/A0)×100 (1)

Here, in the above formula (1), A0 is the total area of the visual field (11250 μm ² ). The average of the transparent area ratio TR (%) of the 5 fields of view was defined as the transparent area ratio (%) of the hot-pressed steel material of the test number.

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

[Paint adhesion evaluation test]
After carrying out the above-mentioned phosphate treatment, a cation-type electrodeposition coating made by Nippon Paint Co., Ltd. is electrodeposited by a slope current of 160 V on the plate-shaped hot-pressed steel material of each test number, Furthermore, 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 the 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 of 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 by peeling off the tape was obtained, and the coating film peeling rate (%) was obtained based on the equation (2).

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

"M" in the "Coating 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 evaluation of coating adhesion, 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 30×50 mm sample was cut out from the plate-shaped hot-pressed steel material test piece described above, and an appropriate current range in spot welding was investigated. Welding conditions were a pressure of 300 kgf (1 kgf is about 9.8 N.), DC power supply, energization time 15 cycles (60 Hz), chrome copper, DR (tip 6φ: 40 R) electrode, lower limit is 4 (t). ^0.5 , the upper limit is dust occurrence, and an appropriate range was investigated.

“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 proper current range was 1.0 kA or more and less than 1.5 kA. "B" means that the proper current range was 1.5 kA or more and less than 2.0 kA. "A" means that the proper current range was 2.0 kA or more. In the spot weldability evaluation, when “C”, “B”, and “A”, it was judged that the spot weldability was excellent.

In addition, instead of the zinc phosphate treatment, Zr ions and/or Ti ions were applied to the plate-shaped hot-pressed steel materials obtained by hot pressing the test numbers shown in Table 4 below by the electric heating method. 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 of the obtained test piece and The corrosion resistance was verified.

The FF chemical conversion treatment solution dissolves free fluorine (hereinafter abbreviated as FF), Al oxide film and Zn oxide film. Therefore, the FF etches the Zn-containing layer formed in the hot stamping step while melting 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) made of a Zr and/or Ti oxide or a mixture of a Zr and/or Ti oxide and a 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 and the specific chemical conversion treatment layer is formed.

In order to obtain such an FF chemical conversion treatment liquid, H ₂ ZrF ₆ (hexafluorozirconic acid) 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 concentration of fluorine and the concentration of free fluorine in the solution were adjusted to predetermined values. The free fluorine concentration was measured using a commercially available concentration measuring instrument. After the adjustment, the container was made to have a constant volume with ion-exchanged water to obtain an FF chemical conversion treatment liquid.

The FF chemical conversion treatment was performed as follows. First, as a pretreatment, immersion degreasing was performed at 45° C. for 2 minutes using an alkaline degreasing agent (EC90 manufactured by Nippon Paint Co., Ltd.). Then, the FF chemical conversion treatment liquid shown in Table 5 below was immersed for 120 seconds at 40° C. to perform the chemical conversion treatment. After the chemical conversion treatment, the test piece was washed with water and dried.

Regarding the obtained test material, the chemical conversion treatability of the specific chemical conversion treatment layer was measured by measuring the amount of Zr or Ti adhesion by fluorescent X-ray analysis, and the measured adhesion amount was 10 to 100 mg/m ^2. "A", the measured adhesion amount was less than 10 mg/m ² or more than 100 mg/m ^{2 was} designated as "B", and the obtained results are also shown in Table 5. In addition, regarding the system containing zirconia, the amount of the deposit before the Zr-based FF treatment was measured by fluorescent X-ray analysis in advance, and the amount obtained by subtracting the amount of the Zr deposit before the treatment from the amount of the Zr deposit after the chemical conversion treatment was used. , Zr-based FF chemical conversion treatment adhesion amount. Moreover, the method and the evaluation standard of the coating adhesion evaluation test for the obtained test material are the same as the coating adhesion evaluation test performed for the above-described test material having the phosphate film formed thereon.

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

The preferred embodiment of the present invention has been described above in detail, but the present invention is not limited to this example. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

Claims (8)

Zn-based plated steel sheet as a base material,
A surface treatment layer formed on at least one side of the Zn-plated steel sheet;
Equipped with
The surface treatment layer is a non-oxide ceramic particles having an average particle diameter containing zirconium or lanthanum is 1μm or more 10μm or less, containing on one side per 0.1 g / m ² or more 2 g / m ² or less of the range, heat Zn-based plated steel sheet for hot pressing . The surface treatment layer is a phosphorus-containing compound, a vanadium-containing compound, a copper-containing compound, an aluminum-containing compound, a silicon-containing compound, or at least one of the chromium-containing compound, as a content per one side, in the range shown below The Zn-based plated steel sheet for hot pressing according to claim 1, which contains.
Phosphorus-containing compound: 0.00g/m ² or more and 0.01 g/m ² or less in terms of P Vanadium-containing compound: 0.00g/m ² or more and 0.01 g/m ² or less in terms of V Copper-containing compound: 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 system for hot pressing according to claim 1 or 2, wherein the content of the non-oxide ceramic particles containing zirconium or lanthanum is 0.2 g/m ² or more and 1.5 g/m ² or less per one surface. Plated steel sheet. The Zn-based plated steel sheet for hot pressing according to any one of claims 1 to 3, wherein the non-oxide ceramic particles containing zirconium or lanthanum are zirconium nitride or zirconium silicide. The surface-treated layer further contains one or more oxides selected from the group consisting of titanium oxide, nickel oxide, and tin (IV) oxide having an average particle diameter of 2 nm or more and 100 nm or less per one surface of 0. containing at 2 g / ^{m 2} or more 2 g / ^{m 2} or less of the range, the hot-press Zn-based plated steel sheet according to any one of claims 1-4. Zn for hot pressing according to claim 5, wherein the particle size of one or more oxides selected from the group consisting of titanium oxide, nickel oxide and tin (IV) oxide is 5 nm or more and 50 nm or less. Series plated steel sheet. The content of one or more oxides selected from the group consisting of titanium oxide, nickel oxide and tin (IV) oxide is 0.4 g/m ² or more and 1.5 g/m ² or less per one surface. The Zn-based plated steel sheet for hot pressing according to claim 5 or 6. The Zn-plated steel sheet for hot pressing according to any one of claims 5 to 7, wherein the oxide is titanium oxide.