JP6443599B1 - Galvanized steel sheet and heat treated steel - Google Patents

Abstract

A steel substrate having a zinc-based plating layer on the surface thereof, and a surface treatment layer formed on at least one surface of the substrate, the surface treatment layer having a content per one side and granular carbon black: 0. A zinc-based plated steel sheet containing 15 to 1.0 g / m ² , granular silica: 0.5 to 2.0 g / m ² , and granular zinc oxide: 0.20 to 2.0 g / m ² .

Description

  The present invention relates to a zinc-based plated steel sheet and a heat-treated steel material.

  In recent years, demands for reducing consumption of fossil fuels are increasing for environmental protection and prevention of global warming. This demand has affected various manufacturing industries. For example, an automobile that is indispensable for daily life and activities as a means of transportation is no exception, and there is a demand for improvement in fuel consumption by reducing the weight of the vehicle body.

  Many of the components of automobiles are made of ferrous materials, particularly steel plates. For this reason, reducing the weight of the steel plate is effective for reducing the weight of the vehicle body. However, in automobiles, it is not allowed to simply reduce the weight of the vehicle body, and appropriate safety must be ensured. For this reason, it is requested | required simultaneously to raise the mechanical strength of a steel plate.

  The demand for such steel sheets is equally strong not only in the automobile manufacturing industry but also in various manufacturing industries. Therefore, research and development of steel sheets that can maintain or improve the rigidity and strength of the component parts is promoted by increasing the mechanical strength of the steel sheets even when the steel sheets are thinner than those conventionally used.

  In general, a material having high mechanical strength tends to have a low shape freezing property in a molding process such as a bending process, and it is difficult to mold the material into a complicated shape. As one of means for solving this formability problem, a so-called hot press method (also called a hot stamp method, a hot press method, or a die quench method) is known. In the hot pressing method, a material to be formed is once heated to a high temperature, and the steel sheet softened by heating is pressed and formed and cooled.

  According to the hot pressing method, the material is once heated to a high temperature and softened, so that the target material can be easily press-formed into a desired shape. Furthermore, the mechanical strength of the material can be increased by quenching by cooling after press molding. Therefore, according to the hot press method, a molded product (heat treated steel) having high dimensional accuracy and mechanical strength can be manufactured.

  When the hot pressing method is applied to a steel plate, oxide scale (compound) is generated on the surface of the steel plate by being heated to a high temperature of 800 ° C. or higher. For this reason, a descaling process for removing the oxide scale after hot pressing is required, which increases the manufacturing cost. Moreover, in the member etc. which require corrosion resistance, it is necessary to perform a rust prevention process or a metal coating process to the surface of a member. For this reason, it is necessary to further perform surface cleaning treatment and surface treatment after hot pressing, which further increases the manufacturing cost.

  As a method for suppressing an increase in manufacturing cost, for example, there is a method in which a steel sheet that is subjected to hot pressing is previously coated. In general, various materials such as organic materials or inorganic materials are used for coating the steel plate. Among these, zinc (Zn) -based plated steel sheets that have a sacrificial anticorrosive action on steel sheets are widely used for automotive steel sheets.

  By applying the zinc-based metal coating, generation of oxide scale on the surface of the steel sheet can be prevented, and a descaling step after hot pressing is not necessary. Further, since the zinc-based metal coating also has a rust prevention effect, the corrosion resistance of the molded product is also improved. Patent Documents 1 to 4 disclose hot-press plated steel sheets in which a steel sheet having a predetermined chemical composition is coated with a zinc-based metal coating.

  In the invention disclosed in Patent Documents 1 to 3, a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet is used as a hot-press 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 hot press formed without forming oxide scale (iron oxide) on the surface.

  In Patent Document 4, when a zinc oxide layer is formed thick on the surface of a steel material hot-pressed on a galvanized steel sheet, shot blasting is applied to the steel material. An invention is disclosed in which the zinc oxide layer is removed to perform or the thickness of the zinc oxide layer is reduced before coating.

  Patent Documents 5 and 6 disclose inventions that improve coating film adhesion and post-coating corrosion resistance of a steel material obtained by hot pressing a zinc-based plated steel sheet. Patent Document 5 discloses an invention using a hot-dip galvanized steel sheet whose surface is coated with a silicone resin film, and Patent Document 6 discloses a barrier layer (P) containing phosphorus (P) and silicon (Si). An invention is disclosed in which a hot-dip galvanized steel sheet coated with a phosphate is exemplified as Si and colloidal silica is exemplified as Si as a steel sheet for hot pressing.

  Furthermore, in Patent Document 7, an element that is easier to oxidize than zinc (easily oxidizable element) is added to the galvanized layer, and the oxide layer of these easily oxidizable element is added to the zinc layer during temperature increase during hot pressing. An invention is disclosed in which volatilization of zinc is prevented by forming it on the surface layer of the plating layer.

  According to the invention disclosed in Patent Documents 5 to 7, since the zinc plating layer is covered with the above-described barrier layer, the evaporation of zinc is suppressed. Adhesion and corrosion resistance after painting are said to be good.

  Patent Document 8 discloses a heat-treated surface-treated steel sheet that has a surface treatment layer formed from a treatment liquid containing granular silica on a zinc-based plating layer and has good corrosion resistance. Furthermore, Patent Document 9 is provided with a surface treatment layer containing at least one selected from titanium oxide, nickel oxide and tin (IV) oxide on the surface of the base material, and for coating film adhesion after hot pressing. An excellent galvanized steel sheet is disclosed.

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 JP 2013-1981 International Publication No. 2016/159306

  When the hot pressing method is applied to a zinc-plated steel sheet, the zinc-plated steel sheet is heated to a high temperature of 800 ° C or higher, and the zinc in the plating film evaporates and oxidizes on the plating surface, forming a zinc oxide film. Is done. For this reason, since the effective zinc amount which contributes to corrosion resistance reduces, corrosion resistance falls, and since a zinc oxide film | membrane etc. peel easily with the growth of a zinc oxide layer, adhesiveness after coating falls. Furthermore, since the surface resistance of the film increases, spot weldability also decreases.

  In order to suppress the evaporation of zinc in the plating film, the present inventor performs hot pressing on a hot-dip galvanized steel sheet whose surface is covered with a silicone resin film, disclosed in Patent Document 5, and A supplementary test was conducted to manufacture. As a result, as will be described later, it was found that although the corrosion resistance after coating of the hot pressed steel material in the cyclic corrosion test in which the wet and dry environment is repeated is good, the coating adhesion of the hot pressed steel material is not necessarily good.

  For this reason, the hot-pressed steel material obtained by the invention disclosed in Patent Document 5 is, for example, a part or member where water tends to accumulate due to its structure (for example, a bag-like structure part under the door, a closed cross-section member in the engine compartment, etc. ) Is not suitable for use.

  On the other hand, the addition of an easily oxidizable element to the galvanized layer disclosed in Patent Document 7 requires measures for new operational issues such as temperature management of the plating bath and measures against dross in the plating tank. become.

  Moreover, the surface-treated steel sheet for heat treatment disclosed in Patent Document 8 is slightly inferior in terms of corrosion resistance in a more severe corrosive environment. Moreover, although the defect | deletion part is provided in Si containing film and the adhesiveness of an electrodeposition coating film is improved with the zinc oxide which appears on the surface through there, it cannot necessarily be said to be sufficient, but the room for improvement is left. Furthermore, although the zinc-based plated steel sheet disclosed in Patent Document 9 is excellent in coating film adhesion after hot pressing, there remains room for improvement in terms of chemical conversion treatment.

  The present invention has been made to solve the above problems, and provides a galvanized steel sheet and a heat-treated steel material that are excellent in spot weldability in addition to corrosion resistance after hot pressing, adhesion after coating, and chemical conversion treatment. The purpose is to do.

  The present invention is listed below.

(1) a base material having a zinc-based plating layer on the surface of the steel sheet;
A surface treatment layer formed on at least one side of the base material,
The surface treatment layer is a content per one side,
Granular carbon black: 0.15 to 1.0 g / m ²
Granular silica: 0.5-2.0 g / m ² , and
Containing granular zinc oxide: 0.20 to 2.0 g / m ² ;
Galvanized steel sheet.

(2) The content of the granular carbon black, the granular silica and the granular zinc oxide contained in the surface treatment layer satisfy the following formula (i):
The galvanized steel sheet according to (1) above.
C + Z <S <2 × (C + Z) (i)
However, the meaning of each symbol in the above formula is as follows.
C: Granular carbon black content (g / m ² )
S: Content of granular silica oxide (g / m ² )
Z: Content of granular zinc oxide (g / m ² )

(3) The surface treatment layer is a content per side,
Granular carbon black: 0.15 to 1.0 g / m ²
Granular silica: 0.5-1.5 g / m ² , and
Containing granular zinc oxide: 0.50 to 2.0 g / m ² ;
The galvanized steel sheet according to (1) or (2) above.

(4) The surface treatment layer is a content per one side,
Granular carbon black: 0.15 to 1.0 g / m ²
Particulate silica: 1.0 to 2.0 g / ^{m 2,} and,
Containing granular zinc oxide: 0.20 to 1.0 g / m ² ;
The galvanized steel sheet according to (1) or (2) above.

(5) The granular zinc oxide particles are granular doped zinc oxide particles.
The galvanized steel sheet according to any one of (1) to (4) above.

(6) The surface treatment layer is a content per one side, and
Titanium-containing compound: containing 0.2 to 2.0 g / m ²
The galvanized steel sheet according to any one of (1) to (5) above.

(7) The titanium-containing compound is titanium oxide having an average particle diameter of 1 to 200 nm and / or titanium-containing non-oxide ceramics having an average particle diameter of 0.2 to 5 μm.
The galvanized steel sheet according to (6) above.

(8) The surface treatment layer has a total content of at least one selected from zirconia, lanthanum oxide, cerium oxide, and neodymium oxide having a content per one side and an average particle size of 5 to 500 nm. Containing ² to 2.0 g / m ² ,
The galvanized steel sheet according to any one of (1) to (7) above.

(9) A base material and a surface forming layer formed on at least one surface of the base material,
The surface forming layer is a content per one side,
Silica: 0.5-2.0 g / m ² , and
Containing zinc oxide: 0.20 to 2.0 g / m ² , and
The area ratio occupied by zinc oxide having a particle diameter of 0.01 to 1 μm in the cross section perpendicular to the surface of the surface forming layer and from the surface to the center in the thickness direction is 10 to 50%.
Heat treated steel.

  ADVANTAGE OF THE INVENTION According to this invention, in addition to the corrosion resistance after hot pressing, adhesiveness after coating, and chemical conversion property, the zinc-plated steel plate and heat-treated steel material which are excellent also in spot weldability are obtained.

FIG. 1 is a diagram schematically showing a cross section of a heat-treated steel material according to an embodiment of the present invention. FIG. 2 is an SEM photograph of the surface of the heat-treated steel sheet according to the present invention after the phosphate treatment. FIG. 3 is a SEM photograph of the surface after the phosphate treatment of the heat-treated steel sheet according to the comparative example. FIG. 4 is a diagram schematically showing a cross section of the heat-treated steel material of the comparative example. FIG. 5 is a diagram schematically showing a cross section of a heat-treated steel material of a comparative example.

  The present invention will be described. In this specification, “%” related to chemical composition or concentration means “% by mass” unless otherwise specified.

1. Zinc-based plated steel sheet The zinc-based plated steel sheet according to the present invention includes a base material and a surface treatment layer formed on at least one side of the base material. The surface treatment layer contains the following amounts of granular carbon black, granular silica, and granular zinc oxide per side. The galvanized steel sheet according to the present invention is suitably used for the hot pressing method.
Granular carbon black: 0.15 to 1.0 g / m ²
Granular silica: 0.5-2.0 g / m ²
Granular zinc oxide: 0.20 to 2.0 g / m ²

(1) Base material The base material of the zinc-based plated steel sheet according to the present invention has a zinc-based plating layer on the surface of a steel sheet (base steel sheet).

(1-1) Base Steel Plate The base steel plate of the base material is not limited to a specific steel plate, and various steel plates having known characteristics and chemical compositions can be used. Although the chemical composition of a base steel plate is not specifically limited, It is preferable that it is a chemical composition which can obtain high intensity | strength by hardening.

  For example, when it is going to obtain the heat-treated steel materials whose tensile strength is 980 MPa or more, a base steel plate is C: 0.05-0.4%, Si: 0.5% or less, Mn: 0.5-2. 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%, with the balance being made of a hardened steel having a chemical composition consisting of Fe and impurities.

  When it is intended to obtain a relatively low strength heat treated steel material having a strength of less than 980 MPa during quenching, the chemical composition of the base steel sheet may not be the above chemical composition.

  From the hardenability at the time of quenching and the formability of the Mn oxide and Cr oxide contained in the heated zinc oxide layer, the total content of Mn and Cr is preferably 0.5 to 3.0%. Yes, more preferably 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 composite oxide containing Mn and Cr, the coating adhesion after the phosphate chemical conversion treatment is further improved. The reason for this is not clear, but the formation of these composite oxides improves the alkali resistance of the phosphate-based chemical conversion coating formed compared to zinc oxide, and provides good paint adhesion. Is estimated to be obtained.

  If the total content of Mn and Cr is less than 0.5%, the amount of composite oxide formed on the surface layer after hot pressing becomes insufficient, and better coating adhesion may not be obtained. On the other hand, if the total content of Mn and Cr exceeds 3.0%, the coating adhesion is not a problem, but the cost is increased, and the toughness of the spot welded portion is significantly reduced, or the wettability of plating. Deterioration may be significant.

  Examples of impurities contained in the base steel sheet include those contained in raw materials such as ore or scrap, or those mixed in the manufacturing process.

(1-2) Zinc-based plating layer The zinc-based plating layer of the base material is not particularly limited, and generally known zinc-based plating can be used. Examples of the zinc-based plating layer include hot-dip Zn plating, alloyed hot-dip Zn plating, hot-dip Zn-55% Al-1.6% Si plating, hot-melt Zn-11% Al plating, hot-melt 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, electric Zn-Co plating, etc. Illustrated.

  It is also effective to coat the above-described components by a method such as vapor deposition, and the plating method is not particularly limited.

  A specific hot dipping treatment is to immerse the steel plate in a plating bath in which Zn or a Zn alloy in a molten state is held, and to lift the steel plate from the plating bath. The amount of plating attached to the steel sheet is controlled by adjusting the pulling speed of the steel sheet or adjusting the flow rate or flow rate of the wiping gas ejected from the wiping nozzle provided above the plating bath. The alloying treatment after plating is performed by additionally heating the steel plate after plating in a gas furnace, an induction heating furnace, or a heating furnace using a combination thereof after the hot dipping treatment. The hot dipping may be performed by either a continuous coil plating method or a single plate cutting method.

  A specific electroplating process is performing an electrolysis process between a counter electrode with a steel plate as a negative electrode in the electrolyte solution containing Zn ion. Moreover, the amount of plating attached to the steel sheet is controlled by adjusting the composition of the electrolytic solution, the current density, or the electrolysis time.

The thickness of the zinc-based plating layer, that is, the adhesion amount of the zinc-based plating layer is preferably 10 to 100 g / m ² per side. If the thickness of the zinc-based plating layer is less than 10 g / m ² per side, the amount of effective zinc after hot pressing cannot be ensured, and the corrosion resistance of the heat-treated steel after hot pressing may be insufficient. On the other hand, if the thickness of the zinc-based plating layer exceeds 100 g / m ² per side, the workability and adhesion of the zinc-based plating layer may be reduced. The thickness of the zinc-based plating layer is more preferably 20 to 80 g / m ² per side.

  Furthermore, in order to suppress the evaporation of the plating, the zinc which plated Ni on the electric Zn-Ni plating, the alloyed hot-dip Zn plating, or the alloyed hot-dip Zn plating that improves the melting point of the zinc-based plating during hot pressing A plated steel sheet is preferred.

(2) Surface treatment layer A surface treatment layer containing granular carbon black, granular silica and granular zinc oxide is formed on the substrate. The effect and optimum form of each granular compound during hot pressing will be described.

(2-1) Granular Carbon Black “Granular carbon black” means carbon black that exists in the form of particles in the surface treatment layer. By using granular carbon black, it is possible to suppress the oxidation of zinc on the surface of the zinc-based plating by sacrificial oxidation of the granular carbon black during the heating of the hot press, and to improve the emissivity of the surface treatment layer, thereby improving the atmosphere. It is possible to increase the rate of temperature increase in heating in the atmosphere or furnace heating.

The granular carbon black contained in the surface treatment layer is 0.15 to 1.0 g / m ² as the content per one side. If the granular carbon black content is less than 0.15 g / m ² , the effect of suppressing the oxidation of zinc cannot be obtained because the absolute amount of carbon black is small. On the other hand, when the content of the granular carbon black exceeds 1.0 g / m ² , the effect of suppressing the oxidation of zinc is saturated and the corrosion resistance before hot pressing is lowered.

  The average particle size of the granular carbon black is preferably 10 to 100 nm. In order to suppress the oxidation of zinc, it is advantageous that the particle size of the granular carbon black is small, but carbon black having an average particle size of less than 10 nm is difficult to obtain, leading to an increase in cost. On the other hand, when the average particle diameter of the granular carbon black exceeds 100 nm, the contact area between the granular carbon black and the galvanized steel sheet is reduced, and the sacrificial oxidation of the granular carbon black during hot pressing is reduced. The average particle diameter of the granular carbon black is more preferably 20 to 50 nm.

  The average particle diameter (primary particle diameter) of the granular carbon black can be measured by a known method. For example, it can be measured by preparing a cross-section embedded sample after coating, measuring several particle sizes of granular carbon black in the film, and averaging the obtained measurement results to obtain an average particle size.

  Examples of the granular carbon black include carbon black used as a coloring pigment and the like, or a carbon black dispersion liquid in which carbon black is previously dispersed in a solvent. Specific commercial products include carbon black manufactured by Mitsubishi Chemical Corporation and high-concentration carbon black dispersion manufactured by Toyo Color Co., Ltd.

(2-2) Granular silica “Granular silica” does not exist in a state of being dissolved in the treatment liquid such as a silane coupling agent, but in a state of particles having a primary particle diameter of several nm or more. It means a substance mainly composed of Si oxide. By using granular silica, it is possible to suppress the evaporation of zinc from the zinc-based plating layer by forming a glassy film during the hot press heating.

The granular silica contained in the surface treatment layer is 0.5 to 2.0 g / m ² as the content per one side. When the content of the granular silica is less than 0.5 g / m ² , a glassy film is not uniformly formed on the surface of the zinc-based plating layer, and zinc evaporation cannot be sufficiently suppressed.

On the other hand, when the content of the granular silica is more than 2.0 g / m ² , the thickness of the glassy silica coating layer increases, so that the electrical resistance value of the coating surface increases and good spot weldability is obtained. I can't.

  The average particle diameter of the granular silica is preferably 2 to 100 nm. From the viewpoint of promptly forming a glassy film that suppresses the evaporation of zinc, it is advantageous that the particle size of the granular silica is smaller, but those having a particle size of less than 2 nm are difficult to obtain and cost increases. . On the other hand, when the particle size of the granular silica exceeds 100 nm, it is difficult to form a uniform film, and local evaporation of zinc is likely to occur. The particle size of the granular silica is preferably 7 to 40 nm.

  In addition, the average particle diameter (primary particle diameter) of granular silica can be measured by a known method. For example, it can be measured by preparing a cross-sectional embedded sample after coating, measuring several particle sizes of granular silica in the film, and averaging the obtained measurement results to obtain an average particle size.

  As the granular silica, colloidal silica previously dispersed in an aqueous solution is exemplified. Specific examples of commercially available products include the Snowtex (registered trademark) series manufactured by Nissan Chemical Co., Ltd.

(2-3) Granular Zinc Oxide “Granular zinc oxide” means zinc oxide present in the form of particles in the surface treatment layer. Due to the granular zinc oxide, the granular zinc oxide is present on the surface of the film after hot press heating, so that zinc phosphate crystals are easily formed during the phosphate treatment, which is a chemical conversion treatment for automobiles. The coating film adhesion after coating is improved.

  The mechanism of the formation of phosphate crystals due to the presence of zinc oxide is that when the chemical conversion treatment is performed with an acidic chemical conversion treatment solution, the zinc oxide exposed on the surface of the resin coating film is dissolved by the acidic chemical conversion treatment solution. Since the pH in the vicinity increases, components of the chemical conversion treatment liquid (for example, acid chlorides such as phosphates) precipitate and grow.

  Thereby, a chemical conversion treatment film is formed. At this time, the zinc oxide present in the surface layer of the resin coating film is also dissolved by the acidic chemical conversion treatment solution, and the components of the chemical conversion treatment solution are deposited inside the surface layer of the resin coating film. It is thought that it grows in a wedge shape so as to protrude from the surface.

The granular zinc oxide contained in the surface treatment layer is 0.20 to 2.0 g / m ² as the content per one side. If the content of granular zinc oxide is less than 0.20 g / m ² , the amount of zinc oxide present on the surface of the coating after heating in the hot press is not sufficient, resulting in a slaked chemical conversion crystal. The coating film adhesion after painting is poor.

On the other hand, if the content of granular zinc oxide is more than 2.0 g / m ² , the thickness of the coating layer containing zinc oxide increases, so that the cohesive strength of the coating is reduced. As a result, the adhesion of the coating film decreases and the electrical resistance value on the surface of the coating increases, and good spot weldability cannot be obtained.

  The average particle diameter of the granular zinc oxide is preferably 0.01 to 1 μm. In order to quickly form a glassy film that suppresses the evaporation of zinc, it is advantageous that the particle size of the granular zinc oxide is smaller, but those having a particle size of less than 0.01 μm are difficult to obtain, Cost increases.

  On the other hand, when the particle size of the granular zinc oxide exceeds 1 μm, zinc oxide is unevenly present on the surface of the coating, and a chemical conversion treatment coating with a scale is formed at the time of phosphate treatment. The film adhesion cannot be obtained. The average particle diameter of the granular zinc oxide is preferably 0.05 to 0.5 μm.

  The average particle diameter (primary particle diameter) of zinc oxide can be measured by a known method. For example, it can be measured by preparing a cross-sectional embedded sample after coating, measuring the particle size of granular zinc oxide in the film, and averaging the obtained measurement results to obtain the average particle size.

  Examples of the granular zinc oxide include zinc oxide powder, which is a commercially available chemical.

  By including the above-mentioned predetermined amounts of the above-described granular carbon black, granular silica, and granular zinc oxide, the above-described effects can be obtained. Specifically, (a) granular carbon black undergoes sacrificial oxidation during hot press heating to suppress zinc oxidation, and (b) granular silica forms a glassy film to suppress zinc evaporation. To obtain excellent corrosion resistance and spot weldability, and (c) the presence of zinc oxide on the coating surface after hot pressing to form a uniform zinc phosphate coating during phosphating, Good coating film adhesion after electrodeposition can be obtained.

(2-4) Resin, cross-linking agent For the formation of the surface treatment layer, granular carbon black, granular silica and granular zinc oxide may be applied as they are on the zinc-based plated steel sheet, but the stability of the treatment liquid In order to improve the adhesion of the surface treatment layer, it is preferable to apply it to a galvanized steel sheet as a treatment liquid in which a resin and a crosslinking agent are mixed.

  As the resin, when a carbon black dispersion is used as the granular carbon black and colloidal silica is used as the granular silica, it is preferable to use a water-soluble or water-dispersible resin. Examples of the resin include polyurethane resin, polyester resin, epoxy resin, (meth) acrylic resin, polyolefin resin, phenol resin, and modified products of these resins. When using granular carbon black, granular silica, and granular zinc oxide, in addition to the above-described aqueous resin, solvent-based resins using various solvents as solvents may be used.

  Examples of the crosslinking agent include silane coupling agents, 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.

(2-5) Content Ratio of Carbon Black, Silica and Zinc Oxide The content of granular carbon black, granular silica and granular zinc oxide preferably satisfies the following formula (i). When the following formula (i) is satisfied, the granular zinc oxide occupies the film formed during the heating of the hot press uniformly, and this does not hinder the effects of the above-described granular carbon black and granular silica. In addition, a uniform zinc phosphate coating can be formed during the phosphate treatment. As a result, coating film adhesion after electrodeposition coating is improved.
C + Z <S <2 × (C + Z) (i)
However, the meaning of each symbol in the above formula is as follows.
C: Granular carbon black content (g / m ² )
S: Content of granular silica oxide (g / m ² )
Z: Content of granular zinc oxide (g / m ² )

  When C + Z ≧ S, a glassy film formed of granular silica becomes non-uniform during heating in a hot press, and zinc may evaporate, resulting in poor corrosion resistance. On the other hand, if S ≧ 2 × (C + Z), the amount of zinc oxide formed during hot pressing decreases, so that it becomes difficult to form a uniform zinc phosphate coating during phosphating. There is a possibility that the adhesion of the coating film after the coating is inferior.

(2-6) Granular Doped Zinc Oxide The granular zinc oxide is preferably a granular doped zinc oxide because the spot weldability after hot pressing is more excellent. As the granular doped zinc oxide, for example, at least one element selected from the group consisting of Group 13 elements of Periodic Table and Group 15 elements of Periodic Table (hereinafter also referred to as “doping elements”) is used. And particles that are doped to develop conductivity.

  Examples of group 13 elements of the periodic table include B, Al, Ga, In and the like. Examples of group 15 elements of the periodic table include P and As. Among these elements, Al and Ga are preferable as doping elements for improving conductivity, and Al is more preferable from the viewpoint of cost. The content of the doping element is preferably 0.05 to 5 atm% and more preferably 0.1 to 5 atm% with respect to the undoped zinc oxide particles in order to improve conductivity.

  In the same manner as granular zinc oxide, granular dope-type zinc oxide is dissolved in a chemical conversion treatment solution, and then promotes the growth of crystals of the chemical conversion treatment film (for example, crystals of acid chlorides such as phosphates). The adhesion between the resin coating film and the coating film can be further improved by the crystal anchor effect of the chemical conversion film. The dope-type zinc oxide particles are dissolved in the chemical conversion treatment solution and then taken into the chemical conversion treatment film. In addition, the dope-type zinc oxide particles not only improve the adhesion of the coating film after electrodeposition coating, but also have conductivity, so that they also act as a conductive pigment to improve conductivity and provide excellent spot weldability. It is done.

The granular dope-type zinc oxide contained in the surface treatment layer has a content per side of 0.20 to 2.0 g / m ² in the same manner as the granular zinc oxide. If the content of granular dope-type zinc oxide is less than 0.20 g / m ² , the amount of zinc oxide present on the surface of the coating after heating in the hot press is not sufficient, resulting in a slaked chemical crystal. The film adhesion after electrodeposition coating may be inferior. On the other hand, if the content of the granular zinc oxide is more than 2.0 g / m ² , the thickness of the coating layer containing the dope-type zinc oxide is increased, so that the cohesive strength of the coating is reduced, and after electrodeposition coating There is a risk that the adhesion of the coating film will be reduced.

  The average particle diameter of the granular dope-type zinc oxide is preferably 0.1 to 1 μm. When the particle diameter is less than 0.1 μm, when dome-shaped zinc oxide is contained in the film, contact with the spot electrode cannot be made, and good spot weldability cannot be obtained. On the other hand, when the particle diameter exceeds 1 μm, zinc oxide is unevenly present on the surface of the film, and a chemical conversion treatment film with a scale is formed at the time of phosphating, resulting in good coating adhesion after electrodeposition coating. I can't. The average particle diameter of the granular zinc oxide is preferably 0.2 to 0.5 μm.

(2-7) Titanium-containing compound As another component that is preferably further contained in the surface treatment layer, a titanium-containing compound is exemplified.

  When a titanium-containing compound is contained in the surface treatment layer, the presence of titanium oxide, which is oxidized after hot pressing, on the surface of the steel sheet has some influence on the agglomeration and precipitation of the electrodeposition coating during electrodeposition coating. Further, by firmly adhering the oxide and the electrodeposition coating film, even if the chemical conversion treatment is not sufficient, strong coating film adhesion can be obtained.

Moreover, since the emissivity of a surface treatment layer improves like a carbon black mentioned above by containing a titanium containing compound, the temperature increase rate by the heating in an air atmosphere or a furnace heating can be raised. In order to obtain these effects more efficiently, the content of the titanium-containing compound is preferably 0.2 to 2.0 g / m ² .

  As the titanium-containing compound, it is preferable to use titanium-containing non-oxide ceramics having an average particle size of 0.2 to 5 μm.

  In addition to the above features, titanium-containing non-oxide ceramics having an average particle size of 0.2 to 5 μm have zinc oxide at the time of hot pressing because the surface or a part thereof becomes titanium oxide when heated by hot pressing. Inhibits oxidation and evaporation. Moreover, since the titanium-containing non-oxide ceramic remaining without being oxidized exhibits excellent conductivity, conductivity is improved and spot weldability is improved.

  Here, “non-oxide ceramics” means ceramics composed of a compound not containing oxygen as an element. Examples of 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 having boron (B), nitrogen (N) and silicon (Si) as the main non-metallic constituent elements, respectively. It is.

Examples of titanium-containing non-oxide ceramics include TiB (electric resistivity 40 × 10 ⁻⁶ Ωcm at 25 ° C.), TiB ₂ (electric resistivity 10 ⁻⁶ Ωcm at 28 ° C.), TiC (180 Electrical resistivity at 10 ° C. at 10 ⁻⁶ Ωcm), TiN (Electrical resistivity at 22 ° C. at 10 ⁻⁶ Ωcm), TiSi (Electrical resistivity at 63 ° C. at 10 ⁻⁶ Ωcm), TiSi ₂ (Electricity at 123 ° C.) Examples thereof include at least one kind of particles selected from the group consisting of particles having a resistivity of 10 ⁻⁶ Ωcm. Specific examples of commercially available products include titanium-containing non-oxide ceramics manufactured by Nippon Shin Metal Co., Ltd.

  Further, as the titanium-containing compound, titanium oxide having an average particle diameter of 1 to 200 nm may be used, or a mixture of the above titanium-containing non-oxide ceramics and titanium oxide may be used.

  In addition to the above features, titanium oxide having an average particle size of 1 to 200 nm suppresses zinc oxidation and evaporation during hot pressing, and in addition to coating adhesion after hot pressing, corrosion resistance after hot pressing. Can be increased.

  Titanium oxide usually exists stably in the form of a metal oxide, but it reacts with zinc oxide present in the film to form a complex oxide with zinc oxide, thereby further suppressing zinc oxidation and evaporation. It is estimated that. In order to obtain this effect more efficiently, the average particle diameter of titanium oxide is preferably 2 to 100 nm.

However, titanium oxide has a high emissivity, and unlike carbon black, which has the same emissivity, it exists as titanium oxide even in a heated state near 900 ° C., so that it is heated for a long time as described later during hot pressing. When performing, since the steel plate temperature rises to near the heating atmosphere temperature, Zn during plating is diffused by the base material steel plate, which may impair the corrosion resistance. Therefore, when performing prolonged heating during hot pressing, the titanium oxide content is preferably less than 0.2 g / m ^2, and more preferably 0.1 g / m ² or less.

  An example of titanium oxide is a titanium oxide dispersion previously dispersed in an aqueous solution. Specific examples of commercially available products include the Snowtex (registered trademark) series manufactured by Nissan Chemical Co., Ltd.

(2-8) Zirconia, lanthanum oxide, cerium oxide, and neodymium oxide Other components that are preferably contained in the surface treatment layer include zirconia (zirconium oxide), lanthanum oxide, cerium oxide, and neodymium oxide.

  When the surface treatment layer contains one or more selected from the above-mentioned zirconia, lanthanum oxide, cerium oxide and neodymium oxide, Al oxide which exists before hot pressing and is formed during hot pressing The zirconia, lanthanum oxide, cerium oxide, and neodymium oxide present in the surface treatment layer during heating are rendered harmless.

  Thereby, formation of zinc oxide at the time of hot pressing is promoted, phosphate treatment property after hot pressing is enhanced, and coating film adhesion is improved. In addition, the details of the detoxification mechanism are unclear regarding the detoxification of Al oxide during heating during hot pressing with zirconia, lanthanum oxide, cerium oxide, or neodymium oxide.

  However, by dissolving Al oxide formed on the steel sheet surface with zirconia, lanthanum oxide, cerium oxide, neodymium oxide, Zn, which is easily oxidized next to Al, is oxidized during hot pressing, and as a result It is considered that the production of zinc oxide (ZnO) excellent in chemical conversion is promoted.

In order to obtain these effects more efficiently, it is preferable to contain a total of 0.2 to 2.0 g / m ^{2 of} one or more selected from zirconia, lanthanum oxide, cerium oxide, and neodymium oxide. In addition, after the hot pressing, these oxides are present more uniformly on the surface of the steel sheet, and in order to realize adhesion with a stronger electrodeposition coating film, the average particle size of the above oxide is 5 It is preferably ˜500 nm.

(2-9) P-containing compound, V-containing compound In addition to the above compounds, the surface treatment layer contains at least one of a P-containing compound, a V-containing compound, and a Cu-containing compound at a predetermined content. Also good.

  The P-containing compound is a compound containing phosphorus as a constituent element. Examples of the P-containing compound include phosphoric acid, phosphorous acid, phosphonic acid, phosphonous acid, phosphinic acid, phosphinic acid, phosphine oxide, and phosphine, or ionic compounds having these compounds as anions. Illustrated.

  All of the P-containing compounds are commercially available as reagents or products and can be easily obtained. The P-containing compound exists in a state of being dissolved in the treatment liquid or dispersed as a powder in the treatment liquid, and is present 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 V-containing compounds include vanadium oxides containing vanadium pentoxide, metavanadate compounds containing ammonium metavanadate, vanadium compounds containing sodium vanadate, and other V-containing compounds.

  All of the V-containing compounds are commercially available as reagents or products and can be easily obtained. The V-containing compound exists in a state dissolved in the treatment liquid or dispersed as a powder in the treatment liquid, and exists in a state dispersed as a solid in the surface treatment layer.

The surface treatment layer preferably contains one or more compounds selected from P-containing compounds and V-containing compounds in an amount of 0.0 to 0.01 g / m ² per side in terms of P and V, respectively.

  One or more kinds of compounds selected from P-containing compounds and V-containing compounds are oxidized during hot pressing to become oxides, unevenly distributed at the interface between the zinc-based plating layer and the surface treatment layer, and at least either P or V An oxide layer having a weak cohesive force is formed.

It is formed during hot pressing because the content of one or more compounds selected from P-containing compounds and V-containing compounds is 0.0 to 0.01 g / m ² per side in terms of P and V, respectively. The thickness of the weakly cohesive oxide layer is reduced, and the adhesion between the hot-pressed zinc-based plating layer and the surface treatment layer 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 thickness of the oxide layer having a weak cohesive force formed during hot pressing The adhesion between the zinc-based plating layer and the surface treatment layer decreases, thereby decreasing the adhesion of the coating film after electrodeposition coating.

From the viewpoint of adhesion between the zinc-based plating layer after hot pressing and the surface treatment layer, 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 V converted. And it is more preferable that it is 0.0-0.003 g / m < ² > per one side, respectively.

(2-10) Cu-containing compound The Cu-containing compound is a compound containing copper as a constituent element. Examples of the Cu-containing compound include metal Cu, copper oxide, various organic copper compounds, various inorganic copper compounds, various copper complexes, and the like.

  All of the Cu-containing compounds are commercially available as reagents or products, and can be easily obtained. These Cu-containing compounds are present in a state dissolved in the treatment liquid or dispersed as a powder in the treatment liquid, and are present in a state dispersed as a solid in the surface treatment layer.

The surface treatment layer preferably contains at least one compound selected from Cu-containing compounds in an amount of 0.0 to 0.02 g / m ² per side in terms of Cu.

  One or more compounds selected from Cu-containing compounds are oxidized during hot pressing to become oxides, unevenly distributed at the interface between the zinc-based plating layer and the surface treatment layer, and containing Cu with weak cohesive force Form a layer.

Oxide with weak cohesive force formed during hot pressing when the content of one or more compounds selected from Cu-containing compounds is 0.0 to 0.02 g / m ² per side in terms of Cu The thickness of the layer is reduced, and the adhesion between the hot-pressed zinc-based plating layer and the surface treatment layer is further improved.

If 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 increases. Moreover, the adhesiveness of the interface of a zinc-type plating layer and a surface treatment layer falls, and the coating-film adhesiveness after electrodeposition coating also falls. In addition, since Cu is an element more noble than Fe, which is the main component of the base steel sheet, the corrosion resistance is also reduced.

From the viewpoint of adhesion between the zinc-based plating layer after hot pressing and the surface treatment layer, the content of one or more compounds selected from Cu-containing compounds in the surface treatment layer is 0. It is more preferably 0 to 0.005 g / m ² .

(2-11) Others Nickel oxide and tin oxide (IV) improve the durability of the film by being contained in the surface treatment layer. However, nickel oxide and tin (IV) oxide, like titanium oxide, have a relatively high emissivity, and unlike carbon black having the same emissivity, nickel oxide and tin oxide are also heated in the vicinity of 900 ° C. Since it exists as (IV), when performing heating for a long time as will be described later at the time of hot pressing, corrosion resistance may be impaired because Zn during plating diffuses through the base steel plate. Therefore, titanium oxide, the total content of nickel oxide and tin (IV) oxide is preferably less than 0.2 g / ^{m 2,} and more preferably 0.1 g / ^{m 2} or less.

2. Heat-treated steel material The heat-treated steel material according to the present invention includes a base material and a surface forming layer formed on at least one side of the base material. The surface forming layer contains the following amounts of silica and zinc oxide per side. Moreover, the area ratio which the zinc oxide which has a particle size of 0.01-1 micrometer in the cross section perpendicular | vertical to the surface of a surface formation layer and from the surface to the center of thickness direction occupies 10-50%.
Silica: 0.5-2.0 g / m ²
Zinc oxide: 0.20 to 2.0 g / m ²

  In the present invention, the heat-treated steel material refers to a steel material that can be hot-pressed on a predetermined steel plate. In the heat-treated steel material according to the present invention, the type of the base material is not particularly limited, but in the following description, a heat-treated steel material obtained by subjecting the above-described zinc-based plated steel sheet to hot pressing will be described as an example.

(1) Substrate FIG. 1 is a view schematically showing a cross section of a heat-treated steel material according to an embodiment of the present invention. In the configuration shown in FIG. 1, the base material 10 of the heat-treated steel material 100 has, for example, a zinc-based plating layer 12 on the surface of a steel plate (base steel plate) 11. About the kind of the base steel plate 11 and the zinc-type plating layer 12, since it is the same as the above-mentioned zinc-type plating steel plate, description is abbreviate | omitted.

  However, a boundary layer (not shown) is formed at the boundary portion between the base steel plate 11 and the zinc-based plating layer 12 by heating before hot pressing. As described later, there are two types of heating methods before hot pressing, short-time heating and long-time heating, and the configuration of the boundary layer varies depending on the heating method.

  Specifically, when heating is performed for a short time, a solid solution layer and an intermetallic compound layer are sequentially formed from the base steel material 11 side toward the zinc-based plating layer 12 side. The solid solution layer is formed by diffusing zinc in the plating layer into the base steel plate 11, and is a layer composed of an iron zinc solid solution phase containing 50 to 80% by mass of Fe. The intermetallic compound layer is a layer made of a zinc-based Γ phase containing 9 to 30% by mass of Fe. On the other hand, when heating is performed for a long time, a solid solution layer is formed between the base steel material 11 and the zinc-based plating layer 12.

  Since the iron zinc solid solution phase contains Zn, it exhibits excellent corrosion resistance by having a solid solution layer mainly composed of it. Moreover, since the Γ phase is a zinc-based intermetallic compound, it has a higher sacrificial anticorrosive ability than the iron zinc solid solution phase. Therefore, the sacrificial anticorrosive ability which was excellent by having an intermetallic compound layer is exhibited.

  The iron-zinc solid solution phase has the same crystal structure (body-centered cubic lattice) as that of the base steel plate, but since Zn is dissolved, the lattice constant is larger than that of the base steel plate and can be distinguished. .

(2) Surface Formation Layer As shown in FIG. 1, a surface formation layer 20 in which zinc oxide 22 is dispersed in a matrix 21 mainly composed of silica is provided on the substrate 10.

(2-1) Silica The silica contained in the matrix 21 in the surface forming layer 20 is obtained by changing the granular silica contained in the above-described surface treatment layer into a glassy state during hot press heating. By containing silica in the surface forming layer 20, evaporation of zinc from the zinc-based plating layer can be suppressed.

In addition, since silica is hardly lost at the time of hot press heating, the content of silica contained in the surface forming layer 20 depends on the content of granular silica contained in the surface treatment layer. Therefore, silica is 0.5-2.0 g / m < ² > as content per single side | surface.

(2-2) Zinc oxide The zinc oxide 22 in the surface forming layer 20 is obtained by dispersing granular zinc oxide contained in the surface treatment layer described above. As described above, the zinc oxide 22 dispersed in the surface forming layer 20 is included and is present on the surface of the surface forming layer 20, so that zinc phosphate crystals are formed during the phosphate treatment that is a chemical conversion treatment for automobiles. It becomes easy to produce | generate and the coating-film adhesiveness after electrodeposition coating improves.

Like zinc, zinc oxide is hardly lost during hot press heating, so the content of zinc oxide contained in the surface forming layer 20 is the content of granular zinc oxide contained in the surface treatment layer. Depends on. Therefore, silica is 0.20-2.0 g / m < ² > as content per single side | surface.

  Further, in order to sufficiently obtain the effect of improving the adhesion of the coating film, it is desirable that a sufficient amount of zinc oxide is dispersed in the vicinity of the surface in the surface forming layer 20. Specifically, the area ratio occupied by zinc oxide having a particle diameter of 0.01 to 1 μm in a cross section perpendicular to the surface 20a of the surface forming layer 20 and from the surface 20a to the center 20b in the thickness direction is 10 to 50. % Is desirable.

  In addition, the occupation area of said zinc oxide can be measured by a well-known method. For example, first, a cross-section embedded sample of a heat-treated steel material is prepared, and a cross section perpendicular to the surface of the surface forming layer and from the surface to the center in the thickness direction is observed with a scanning microscope. Subsequently, it is possible to specify zinc oxide having a particle diameter of 0.01 to 1 μm in the cross-sectional field of view and obtain the area ratio of zinc oxide by image processing.

(2-3) Others Since the state and content of each compound contained in the surface forming layer are the same as those of the surface treatment layer, detailed description thereof is omitted. For example, the zinc oxide in the surface forming layer may be a doped zinc oxide. Moreover, a titanium containing compound etc. may be contained. The preferred content is as described above.

3. Manufacturing method The manufacturing method of the zinc-based plated steel sheet and the heat-treated steel material according to the present invention is not particularly limited. For example, a galvanized steel sheet can be produced by forming a surface treatment layer on the surface of the substrate by the method described below. Moreover, a heat-treated steel material can be produced by subjecting the zinc-based plated steel sheet to hot pressing under the following conditions.

(1) Method for forming surface treatment layer The method for forming the surface treatment layer is as follows: a treatment liquid containing granular carbon black, granular silica and granular zinc oxide is applied to the surface of the substrate, followed by drying and baking. Good.

  The coating method is not limited to a specific method, and the substrate is immersed in the treatment liquid, or the treatment liquid is sprayed on the surface of the substrate, and then a roll or a gas spray is applied so that a predetermined adhesion amount is obtained. Examples of the method for controlling the adhesion amount by the coating method, or the method of applying with a roll coater, curtain coater or bar coater.

  The drying method and baking method may be any method that can volatilize the dispersion medium (mainly water), and are not limited to a specific method. When heated at an excessively high temperature, there is a concern that the uniformity of the surface treatment layer is lowered, and conversely, when heated at an excessively low temperature, there is a concern about a decrease in productivity. For this reason, in order to stably and efficiently produce a surface treatment layer having excellent characteristics, it is preferable to heat the surface treatment layer after coating at a temperature of about 80 to 150 ° C. for about 5 to 20 seconds. .

  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 a separate line or after blanking for forming. It may be.

  As a method for forming the surface treatment layer, a treatment liquid containing granular carbon black and granular silica is applied to the surface of a zinc-based plated steel sheet, and then a treatment liquid containing granular zinc oxide is applied to the upper layer to form a film. It is more preferable to form In this case, the resin layer may be applied and formed before applying zinc oxide.

  The coating may be dried and baked each time the coating is applied, or two or three layers may be applied simultaneously using a multilayer curtain coater and baked at once. By using the method for forming the surface treatment layer described above, the effects of the respective compounds can be obtained more easily, and in addition to the excellent corrosion resistance after hot pressing and adhesion after coating, spot weldability can be obtained. .

  The contents of granular carbon black, granular silica and granular zinc oxide in the surface treatment layer can be measured by a known method. For example, after confirming that the various compounds are silica or zinc oxide by means of cross-sectional energy dispersive X-ray (EDX) analysis, etc., the film is dissolved and ICP (Inductively Coupled Plasma, induction) It can be measured by using a coupled plasma emission spectroscopy. Further, the contents of the P-containing compound, the V-containing compound, and the Cu-containing compound in the surface treatment layer can be measured by the same method.

(2) Hot press working method In the hot working method shown below, after the zinc-based plated steel sheet is heated to a predetermined temperature, press forming and cooling are performed simultaneously. Each will be described in detail.

Since the galvanized steel sheet according to the present invention is subjected to hot press forming, it is usually heated to 700 to 1000 ° C., but after rapid cooling, it becomes a martensite single phase, or the martensite is 90% by volume. % Or higher, the heating temperature is Ac ₃ points or higher. In the present invention, the case of a two-phase region of martensite and ferrite after rapid cooling is also included, and thus the heating temperature is preferably 700 to 1000 ° C.

  The heating method before hot pressing can be roughly divided into two types, short-time heating and long-time heating, after reaching a predetermined temperature (around 900 ° C.) and depending on the standing time in the heating furnace (in-furnace time). . In short-time heating, after reaching a predetermined temperature, it is quickly removed from the furnace and pressed. On the other hand, in the long-time heating, after reaching a predetermined temperature, the zinc in the plating is kept in the heating furnace until the iron zinc solid solution phase formed by diffusing into the base steel sheet is sufficiently formed, Remove from the furnace and press.

  In any case, examples of the heating method used include an electric furnace, a gas furnace, flame heating, energization heating, high-frequency heating, induction heating, and the like. Also, the atmosphere during heating is not particularly limited.

  In the case of heating for a short time, after heating the galvanized steel sheet to a predetermined temperature, immediately remove it from the furnace or hold it for a very short time, remove it from the furnace, perform press molding, Quench quickly by contact. By performing such heating, a solid solution layer and an intermetallic compound layer are formed between the base steel material and the zinc-based plating layer.

  Note that the intermetallic compound layer composed of the Γ phase exists in a liquid phase state immediately after being taken out of the furnace. Therefore, in order to suppress grain boundary cracking of the base steel sheet during processing, it is necessary to perform press molding after cooling and solidifying the plating layer. Specifically, the press molding is preferably performed in a temperature range of 730 to 500 ° C.

  On the other hand, in the case of heating for a long time, after the zinc-based plated steel sheet is heated to a predetermined temperature, it is held for a certain time and then press-molded, and at that time, it is rapidly cooled by contact with a mold. At that time, the product characteristics after hot pressing may be controlled by heating the press die and changing the quenching temperature or the cooling rate. By holding for a certain period of time after reaching a predetermined temperature, the zinc being plated diffuses into the base steel sheet, and a solid solution layer consisting of iron zinc solid solution phase is formed between the base steel material and the zinc-based plating layer. The

(3) Other processing methods Unlike the above description, the zinc-based plated steel sheet according to the present invention is cold-formed to form a cold press-formed body, and this cold press-formed body is subjected to Ac ₃ points by gentle heating. It is good also as heating-processing steel materials by heating above and cooling using a metal mold | die.

  The heat-treated steel manufactured using the zinc-based plated steel sheet according to the present invention has excellent corrosion resistance, adhesion after electrodeposition coating, chemical conversion treatment, and spot weldability. In particular, the galvanized steel sheet according to the present invention has a long holding time so that the molten zinc in the galvanized layer is bonded to Fe and becomes a solid phase (iron zinc solid solution phase) by hot pressing by gentle heating. By making time, the effect is remarkably produced.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to these Examples.

<1> Base steel plate The molten steel which has the chemical composition shown in Table 1 was manufactured, and the slab was manufactured by the continuous casting method using each manufactured molten steel. The obtained slab was hot rolled to produce a hot rolled steel sheet. Subsequently, after pickling the hot-rolled steel sheet, cold rolling was performed to produce a cold-rolled steel sheet, and cold-rolled steel sheets # 1 to # 8 having chemical compositions shown in Table 1 were produced. Each of the cold-rolled steel plates # 1 to # 8 has a thickness of 1.6 mm.

<2> Zinc-based plating Cold-rolled steel plates # 1 to # 8 were subjected to hot dip galvanizing treatment and then subjected to alloying treatment. The maximum temperature in the alloying treatment was 530 ° C., and after heating for about 30 seconds, the alloyed hot-dip galvanized steel sheet GA (containing 0.2% Al) was manufactured.

  In addition, the hot dip galvanized steel sheet GI (containing 0.4% Al) was manufactured without subjecting the cold rolled steel sheet # 1 to a hot dip galvanizing process.

In addition, three types of plating baths 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 cold rolled steel plate # 1. Various hot dip galvanizations were carried out to produce hot dip 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

Further, various types of zinc plating such as electric Zn plating and electric Zn—Ni plating were performed on the cold-rolled steel plate # 1. As a specific plating operation in electroplating, electrolytic treatment was performed between a counter electrode and a steel plate as a negative electrode in an electrolytic solution containing Zn ions. The amount of plating attached to the steel sheet was controlled by the composition of the electrolytic solution, current density, and electrolysis time.
A4: Electrical Zn plating A5: Electrical Zn-12% Ni plating

In the above seven types of zinc-based plating processes, the adhesion amount of the zinc-based plating layer was 45 g / m ² per side.

And the hot dip galvanized steel plates A6 and 7 which electroplated Ni on the GA mentioned above and performed Ni plating were also produced.
A6: GA + Ni plating (attachment amount per side 2 g / m ² )
A7: GA + Ni plating (adhesion amount per side 8 g / m ² )

<3> Surface Treatment Next, in order to prepare chemical solutions having the compositions shown in Tables 2 and 3 in a solid content ratio, the following compounds and chemicals were blended using water. The obtained treatment liquid was applied with a bar coater, and dried using an oven under conditions such that it was held at a maximum temperature of 100 ° C. for 8 seconds to produce a zinc-based plated steel sheet.

  Moreover, after apply | coating and drying the chemical | medical solution which becomes a composition of Table 2 on the above-mentioned conditions, the zinc type which has two or more surface treatment layers by apply | coating and drying the chemical | medical solution which becomes the composition of Table 2 on the above-mentioned conditions further A plated steel sheet was produced.

  The adhesion amount of the treatment liquid was adjusted by dilution of the liquid and the number of the bar coater so that the total adhesion amount of the non-volatile content in the treatment liquid became the values shown in Tables 4-8. In Tables 2 and 3, the solid content concentration of each component is described as the ratio (unit: mass%) of the nonvolatile content of each component such as “granular carbon black” to the nonvolatile content of the entire treatment liquid.

  The brands of granular carbon black, granular silica and granular zinc oxide used are shown below.

(I) Powdered carbon black C1: Carbon black powder (Mitsubishi Chemical Corporation # 2650), particle size 13 nm (catalog value)
C2: carbon black powder (Mitsubishi Chemical Corporation MA100), particle size 24 nm (catalog value)
C3: Carbon black powder (Mitsubishi Chemical Corporation MA220), particle size 55 nm (catalog value)
C4: carbon black powder (carbon powder of high purity chemical), particle size 5 μm (catalog value)

(Ii) Powdered silica S1: Colloidal silica (Nissan Chemical Co., Ltd. Snowtex (registered trademark) OXS), particle size of about 4 nm to 6 nm (catalog value)
S2: Colloidal silica (Nissan Chemical Co., Ltd. Snowtex (registered trademark) O), particle size of about 10 nm to 15 nm (catalog value)
S3: Colloidal silica (Nissan Chemical Co., Ltd. Snowtex (registered trademark) OYL), particle size of about 50 nm to 80 nm (catalog value)
S4: Porous silica (Fuji Silysia Chemical Co., Ltd. silo mask 02), particle size 2 μm
S5: Silicone resin (Shin-Etsu Chemical Co., Ltd. KR-300)

(Iii) Powdered zinc oxide Z1: Zinc oxide powder (Huxitec Co., Ltd. fine particle zinc oxide F-1), particle size 0.1 μm (catalog value)
Z2: Zinc oxide powder (Zinc oxide, high purity chemical), particle size 1μm (catalog value)
Z3: Conductive zinc oxide powder (Huxitec Co., Ltd. conductive zinc oxide 23-k), particle size 0.12 μm to 0.25 μm (catalog value)
Z4: Conductive zinc oxide powder (Huxitec Co., Ltd. conductive zinc oxide Pazet CK), particle size 0.02 μm to 0.04 μm (catalog value)

(Iv) 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. Vylonal (registered trademark) MD1480)

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

(Vi) Titanium-containing compound T1: Titania sol (Taika Co., Ltd. Titania sol TKS-203), particle size 6 nm (catalog value)
T2: Titania powder (Ioritech Co., Ltd.), particle size 10-30 nm (catalog value)
T3: Titanium oxide (Ishihara Sangyo Co., Ltd. titanium oxide R-930), particle size 250 nm (catalog value)
T4: Titanium nitride (NiShin Metals Co., Ltd. TiN), particle size 700-1190nm (catalog value)

(Vii) Other compounds Zr: Zirconia (Nissan Chemical Co., Ltd. Nanouse ZR40BL)
P: Calcium phosphite (general reagent) (P-containing compound)
V: Potassium vanadate (general reagent) (V-containing compound)
Cu: Copper (II) oxide (general reagent) (Cu-containing compound)

  The chemical solution No. The chemical solution No. 45 had a small amount of silica and an excessive amount of titanium oxide, so that it could not be uniformly applied to the surface of the substrate without being dispersed. Therefore, it is not used for subsequent tests.

<4> Hot press After forming the surface treatment layer, the hot-pressed steel sheet of each number was hot-pressed by one of the following two methods to produce a heat-treated steel material.

Method 1: Heating for a short time Hot pressing was performed by a furnace heating method, and hot pressing was performed. In the furnace heating, the atmosphere in the furnace was 910 ° C., the air-fuel ratio was 1.1, and the steel sheet was quickly taken out of the furnace after reaching 890 ° C. and air-cooled until it reached 700 ° C.

  After air-cooling to 700 ° C., a plate-shaped heat-treated steel material was produced by sandwiching the steel plate using a flat plate mold equipped with a water-cooling jacket. Even in a portion where the cooling rate during hot pressing was slow, the steel was cooled and quenched to a cooling rate of 50 ° C./second or more to about 360 ° C., which was the martensite transformation start point.

Method 2: Long-time heating The hot press was heated by the furnace heating method, and the hot press was performed. In the furnace heating, the furnace atmosphere: 910 ° C., the air-fuel ratio: 1.1, the steel sheet temperature reached 890 ° C. and left in the furnace for 5 minutes, and then quickly removed from the furnace.

  After the hot press heating, a plate-shaped heat-treated steel material was produced by sandwiching the steel plate using a flat plate mold equipped with a water-cooled jacket. Even in a portion where the cooling rate during hot pressing was slow, the steel was cooled and quenched to a cooling rate of 50 ° C./second or more to about 360 ° C., which was the martensite transformation start point.

  About the obtained heat-treated steel material, a cross-section embedded sample was prepared, and an area occupied by zinc oxide having a particle diameter of 0.01 to 1 μm was obtained with respect to a cross section perpendicular to the surface of the surface forming layer and from the surface to the center in the thickness direction. It was measured. Specifically, a cross-section embedded sample of each heat-treated steel material is prepared, and included in a cross-section from the surface to the center in the thickness direction perpendicular to the surface of the surface forming layer at a field of view of 5000 times with a scanning microscope. Zinc oxide having a particle diameter of ˜1 μm was specified, and the area ratio of zinc oxide was determined by image processing. This measurement was performed in 10 fields of view, and the average value was defined as the occupation area ratio of each sample.

  “D” in the “occupied area” column in the table means an area ratio of less than 5%, “C” means an area ratio of 5% or more and less than 10%, and “B” means an area ratio of 10%. More than 25%, “A” means an area ratio of 25% or more and 50% or less, and “E” means an area ratio of more than 50%. In the area ratio evaluation, “B” or “A” was used as a surface forming layer of a good heat-treated steel material.

  Tables 9 to 12 show the composition of the surface forming layer of the heat-treated steel material of each test number and the area occupied by zinc oxide.

<5> Evaluation method By using the heat-treated steel materials of the obtained test numbers, the following tests are conducted to improve phosphate treatment (chemical conversion treatment), post-coating adhesion, corrosion resistance, and spot weldability. Evaluation was performed.

[5-1] Phosphate treatability evaluation test Surface treatment was performed at room temperature for 20 seconds using the surface conditioning treatment preparation Preparen X (trade name) manufactured by Nihon Parkerizing Co., Ltd., for each heat-treated steel material of each test number. It was.

  Furthermore, the phosphate treatment was performed using the zinc phosphate processing liquid Palbond 3020 (trade name) manufactured by Nippon Parkerizing Co., Ltd. The temperature of the treatment liquid was 43 ° C., and the heat-treated steel was immersed in the treatment liquid for 120 seconds, and then washed and dried.

  Any five visual fields (125 μm × 90 μm) on the surface of the heat-treated steel material after the phosphate treatment were observed with a 1000 × 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 coating that is the chemical conversion coating is formed and the portion where the phosphate coating is not formed. Therefore, the numerical value 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 visual field, the area A1 of the region showing the contrast within the numerical value range X1 was obtained by image processing. And based on the following (1) Formula, transparent area ratio TR (%) of each visual field was calculated | required.

TR = (A1 / A0) × 100 (1)
In the 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 visual fields was defined as the see-through area ratio (%) of the heat-treated steel material having the test number.

  In Tables 9 to 12, “F” in the “phosphate treatment property” column means a transparent area ratio: 30% or more, “E” means a transparent area ratio: 20% or more and less than 30%, and “D "" Means transparent area ratio: 15% to less than 20, "C" means transparent area ratio: 10% to less than 15%, and "B" means transparent area ratio: 5% to less than 10%. Furthermore, “A” means a transparent area ratio: less than 5%. In the sheer evaluation, “C”, “B”, or “A” was considered to be excellent in phosphate treatment.

[5-2] Paint adhesion evaluation test After the above-described phosphate treatment, a cation-type electrodeposition paint manufactured by Nippon Paint Co., Ltd. was applied to the heat-treated steel material of each test number by slope energization with a voltage of 160V. Electrodeposition coating was performed, and baking was further 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 any test number.

After electrodeposition coating, the heat-treated steel was immersed in a 5% NaCl aqueous solution at 50 ° C. for 500 hours. After immersion, a polyester tape was applied to the entire surface of the test surface 60 mm × 120 mm (area A10 = 60 mm × 120 mm = 7200 mm ² ). Thereafter, 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) × 100 (2)

  “F” in the “Coating adhesion” column in Tables 9 to 12 means a coating film peeling rate: 30.0% or more, “E” means a coating film peeling rate: 20% or more and less than 30%, "D" means coating film peeling rate: 10% or more and less than 20%, "C" means coating film peeling rate: 5% or more and less than 10%, and "B" means coating film peeling rate: 2.5. % Means less than 5%, and “A” means coating film peeling rate: less than 2.5%. In the paint adhesion evaluation, “C”, “B” or “A” was considered excellent in paint adhesion.

[5-3] Cyclic corrosion test For the coating of the evaluation surface, a cut was made with a cutter knife (load 500 gf, 1 gf≈9.8 × 10 ⁻³ N), and “salt water spray (SST, 5% NaCl, 35 ° C. atmosphere) ) 2 hours → dry (60 ° C.) 2 hours → wet (50 ° C., 98% RH) 4 hours ”A cycle corrosion test under a cycle condition of 1 cycle was performed 360 cycles.

  Then, the presence or absence of the swelling of the coating film which generate | occur | produces in a 1 cm width area | region from a cut part was observed. "F" in the "Corrosion resistance" column of Tables 9 to 12 means the occurrence of film swelling of 4.0 mm or more, "E" means the occurrence of film swelling of 3.0 mm or more and less than 4.0 mm, “D” means the occurrence of a film swelling of 2.0 mm or more and less than 3.0 mm, “C” means the occurrence of a film swelling of 1.5 mm or more and less than 2.0 mm, and “B” is 1. It means a minute film swelling of 0 or more and less than 1.5 mm, and “A” means that there was an extremely minute film swelling of less than 1.0 mm. In this cyclic corrosion test, “C”, “B” or “A” was considered to be excellent in corrosion resistance.

[5-4] Spot weldability test The surface-treated metal plate before the chemical conversion treatment (phosphate treatment) was applied with a DC power supply using a CF type Cr—Cu electrode having a tip diameter of 5 mm and R40, and a pressure of 350 kgf. Spot welding was performed. Tests are performed with various welding currents, and the value where the nugget diameter of the weld exceeds 4√t (t is the thickness of the test piece) is set as the lower limit, and the value of the welding current is increased appropriately. The value obtained was taken as the upper limit. A value between the upper limit value and the lower limit value was set as an appropriate current range.

  “F” in the “Weldability” column in Tables 9 to 12 means that this value is not present, “E” means that this value is 0.00 kA or more and less than 0.5 kA, and “D”. Means that this value is 0.25 kA or more and less than 0.5 kA, “C” means that this value is 0.5 kA or more and less than 0.75 kA, and “B” means that this value is 0. 75 kA or more 1.0. It means that it is less than A, and “A” means that this value is 1.0 kA or more. In this spot weldability test, “C”, “B” or “A” was considered to be excellent in spot weldability.

  Underlines in Tables 9-12 indicate that they are outside the scope of the present invention or that the test results are not good. As is apparent from Tables 9 to 12, the heat-treated steel material produced using the zinc-based plated steel sheet according to the present invention has not only excellent corrosion resistance but also excellent chemical conversion property, coating film adhesion, and spot weldability. You can see that

  FIG. 2 is an SEM photograph of the surface of the heat-treated steel sheet according to the present invention after the phosphate treatment. As can be seen from FIG. 2, in the heat-treated steel sheet manufactured from the zinc-based plated steel sheet that satisfies the provisions of the present invention, the zinc oxide is uniformly dispersed in the surface forming layer. A zinc film is formed.

  On the other hand, FIG. 3 is a SEM photograph on the surface after the phosphate treatment of the heat-treated steel sheet according to the comparative example. As shown in FIG. In L7, the amount of carbon black in the surface treatment layer of the used zinc-based plated steel sheet is small, and granular zinc oxide is not included. Therefore, as shown in a schematic cross section in FIG. 4, the coating 41 was cracked and the zinc oxide 42 derived from the plating layer 32 appeared on the surface. As a result, as shown to Fig.3 (a), the phosphate membrane | film | coat was formed only slightly and became a result in which a phosphate processability is inferior.

  In addition, as shown in FIG. In L32, a silicone resin was contained in the surface treatment layer of the used galvanized steel sheet instead of granular silica. As a result, zinc oxide was not dispersed in the vicinity of the surface layer of the surface forming layer, and a phosphate film was hardly formed, resulting in extremely poor phosphate treatment properties.

  Furthermore, the heat-treated steel plate No. L121 is a plated steel plate No. in which no surface treatment layer is formed. It is a comparative example using 130. In this example, since the zinc-based plated steel sheet does not have a surface treatment layer, the zinc in the plating layer 32 becomes zinc oxide 50 by hot pressing, as schematically shown in cross section in FIG. As schematically shown in FIG. 5, the adhesion of the zinc oxide 50 was poor, causing peeling, resulting in poor adhesion after coating and poor corrosion resistance.

10. Base material 11. Steel plate (base steel plate)
12 Zinc-based plating layer 20. Surface forming layer 20a. Surface 20b. Center in thickness direction 21. Matrix 22. Zinc oxide

Claims (9)

A substrate having a zinc-based plating layer on the surface of the steel plate;
A surface treatment layer formed on at least one side of the base material,
The surface treatment layer is a content per one side,
Granular carbon black: 0.15 to 1.0 g / m ²
Granular silica: 0.5-2.0 g / m ² , and
Containing granular zinc oxide: 0.20 to 2.0 g / m ² ;
Galvanized steel sheet. Content of the granular carbon black, the granular silica oxide and the granular zinc oxide contained in the surface treatment layer satisfies the following formula (i):
The galvanized steel sheet according to claim 1.
C + Z <S <2 × (C + Z) (i)
However, the meaning of each symbol in the above formula is as follows.
C: Granular carbon black content (g / m ² )
S: Content of granular silica oxide (g / m ² )
Z: Content of granular zinc oxide (g / m ² ) The surface treatment layer is a content per one side,
Granular carbon black: 0.15 to 1.0 g / m ²
Granular silica: 0.5-1.5 g / m ² , and
Containing granular zinc oxide: 0.50 to 2.0 g / m ² ;
The galvanized steel sheet according to claim 1 or 2. The surface treatment layer is a content per one side,
Granular carbon black: 0.15 to 1.0 g / m ²
Particulate silica: 1.0 to 2.0 g / ^{m 2,} and,
Containing granular zinc oxide: 0.20 to 1.0 g / m ² ;
The galvanized steel sheet according to claim 1 or 2. The granular zinc oxide particles are granular doped zinc oxide particles,
The galvanized steel sheet according to any one of claims 1 to 4. The surface treatment layer is a content per one side,
Titanium-containing compound: containing 0.2 to 2.0 g / m ²
The galvanized steel sheet according to any one of claims 1 to 5. The titanium-containing compound is titanium oxide having an average particle diameter of 1 to 200 nm and / or titanium-containing non-oxide ceramics having an average particle diameter of 0.2 to 5 μm.
The galvanized steel sheet according to claim 6. The surface treatment layer has a total content of one or more selected from zirconia, lanthanum oxide, cerium oxide and neodymium oxide having a content per one side and an average particle size of 5 to 500 nm in a total amount of 0.2 to 2. Containing 0.0 g / m ² ,
The galvanized steel sheet according to any one of claims 1 to 7. A base material, and a surface forming layer formed on at least one side of the base material,
The surface forming layer is a content per one side,
Silica: 0.5-2.0 g / m ² , and
Containing zinc oxide: 0.20 to 2.0 g / m ² , and
The area ratio occupied by zinc oxide having a particle size of 0.01 to 1 μm in the cross section perpendicular to the surface of the surface forming layer and from the surface to the center in the thickness direction is 10 to 50%.
Heat treated steel.

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