JPH0953189A - Hot rolled steel sheet excellent in chemical convertibility, lubricity and suitability to adhesive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely enable the sorting in production of hot rolled steel sheets having plural lubricity levels by forming an oxide film by specified mg/m<2> of Zn and P and the third elemental group by the specified total value expressed in terms of metal. SOLUTION: A hot rolled steel sheet, e.g. contg. 0.02 to 0.10% C, 0.2 to 0.4% Mn, <=0.005% Si, <=0.01% P, <=0.002% S, and the balance Fe with inevitable impurities and having 0.6 to 2.0mm sheet thickness is prepd. As for oxides formed on the surface of the above hot rolled steel sheet, a film, e.g. composed of the oxides of Zn and P and the oxides of one or >= two kinds among Mn, Ni, Mg, Fe, Co and Al in the third elemental group is prepd. As for the forming ranges of the oxide film, 1 to 200mg/m<2> is regulated as Zn, 1 to 200mg/m<2> is regulated as P, and the total value of the third elemental group expressed in terms of metal is regulated to 1 to 200mg/m<2> . Thus, its lubricity (press workability or the like), chemical convertibility and suitability to adhesives can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolled steel sheet excellent in chemical conversion treatment, lubricity and adhesive compatibility.

[0002]

_2. Description of the Related Art It is known to improve the lubricity of a zinc-based plated steel sheet during press forming and to form a chromate film (Cr ₂ O ₃ ) on the surface of the steel sheet in order to improve the formability.
It is disclosed in Japanese Patent No. 883. Also, on the surface of cold rolled steel sheet
JP-A-3-285024 discloses that an oxide film mainly composed of Fe ₂ O ₃ and Fe ₃ O ₄ is formed to improve press formability. Further, it is known that a chemical conversion treatment crystal film of manganese phosphate or the like is formed on the surface of the steel sheet to improve lubricity. In addition, JP-A-1-136952 discloses that an organic lubricating film or a lubricating oil is applied to the surface of a steel sheet to improve press formability.

[0003]

As described above, the chromate film, the oxide film mainly composed of Fe ₂ O ₃ and Fe ₃ O ₄ , and the chemical conversion treatment crystal film such as manganese phosphate are improved in lubricity such as press formability. However, when chemical conversion treatment is performed after press molding, these coatings may be insufficiently filled with the chemical conversion treatment liquid. Also, the coating may not dissolve. Further, the chemical conversion treatment film cannot be formed uniformly, and sometimes it cannot be formed at all. In particular, the chemical conversion treatment film, when adhered using an oil surface adhesive after press molding,
There is a problem such as a decrease in adhesive strength. Further, the improvement of press moldability by lubricating oil imposes a heavy load on the degreasing step after press molding, and there is also a problem that the adhesive strength is lowered when an oil-based adhesive is used after press molding. The present invention
In order to advantageously solve such a problem, an oxide film is formed on the surface of the steel sheet to improve lubricity and press formability, as well as chemical conversion treatment and adhesive compatibility, Moreover, it is an object of the present invention to provide a hot-rolled steel sheet capable of avoiding contamination of the degreasing liquid and the chemical conversion treatment liquid.

[0004]

The features of the method of the present invention are that the oxides of Zn and P and M of the third element group are present on the surface of the steel sheet.
A coating composed of one or more oxides of n, Ni, Mg, Fe, Co and Al is used as Zn at 1 to 200 mg / m ² and P as 1
~ 200 mg / m ² , the total metal equivalent of the third element group is 1 to 200
It is a hot-rolled steel sheet excellent in chemical conversion treatment, lubricity, and adhesive compatibility, characterized by producing mg / m ² .

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the hot rolled steel sheet which produces the above oxides include C: 0.02 to 0.10% and Mn: 0.2 to
0.4%, Si: 0.005% or less, P: O.O1% or less, S: 0.002% or less, the remaining unavoidable impurities and Fe. One type or two or more types are contained to improve moldability. Further, high strength hot rolled steel sheets and the like containing one or more kinds of P and Si added in a larger amount than the above P and Si, and a steel sheet having a plate thickness of 0.6 to 2.0 mm and oxides such as the following. To improve lubricity and the like.

Examples of oxides formed on the surface of such a hot rolled steel sheet include oxides of Zn and P and M of the third element group.
It is a film made of one or more oxides of n, Ni, Mg, Fe, Co and Al. Mn, Ni, Mg, F of the 3rd element group
One or more oxides of e, Co and Al tend to be rich in the surface of the steel sheet in the coating, and prevent galling and adhesion between the metal of the steel sheet and the die during sliding such as pressing. With
By mixing with Zn and P 2 oxides in the film, the film becomes amorphous and the adhesiveness is improved when it is adhered using an oil surface adhesive after press molding. Further, the amorphous film dissolves the film in the chemical conversion treatment liquid during the chemical conversion treatment faster than the crystalline film, and facilitates the chemical conversion treatment. It is presumed that the amorphous film improves the adhesive strength because the film becomes homogeneous and it is difficult to generate a fracture starting point for peeling of the adhesive.

The oxides of Zn and P tend to be rich in the outer layer side of the coating and are finely broken during press working, strengthening the boundary lubrication layer of the oil coating layer (rust preventive oil, cleaning oil, etc.) on the steel plate surface. Improve lubricity. Although the structure of such an oxide film is not clear, it is presumed that it may be an amorphous film having a macromolecular structure composed of bonds such as Mn-O, Zn-O, PO, -OH, and -Co ₃ groups. There is. Further, since this film is an inorganic film and does not dissolve in the cleaning step before pressing, the lubricity does not decrease due to cleaning, and therefore the cleaning oil is not contaminated. Furthermore,
Since this film dissolves almost completely in the chemical conversion treatment liquid, the chemical conversion treatment film can be formed soundly, and the coating composition is the same as the chemical conversion treatment liquid component, so it does not contaminate the chemical conversion treatment liquid and loads it on other processes. There is no effect. The generation of such oxides on the surface of the steel sheet is performed by, for example, immersing the hot-rolled steel sheet in an acid such as sulfuric acid or hydrochloric acid or exposing it to a reducing atmosphere to remove or reduce the oxide on the surface and activate the surface. After the formation, the zinc layer is thinly formed, for example, 5 to 500 mg / m ² , and can be reliably produced by dipping in an aqueous solution or spraying. At this time, the alloy element components of the steel sheet and the impurities in the aqueous solution are slightly mixed in the oxide film, but this does not cause any trouble.

Next, the range of formation of the oxide film is Zn
1 to 200 mg / m ² as P, 1 to 200 mg / m ² as P, and the third
The total metal equivalent value of the element group is 1 to 200 mg / m ² . Unless the amount of Zn and P oxide in the film is 1 mg / m ² or more,
Lubricity is hardly improved, and either Zn or P is 200 mg / m
^When it exceeds ² , the film is not reliably dissolved in the chemical conversion treatment liquid and the chemical conversion treatment property deteriorates. Third element group (Mn, Ni, Mg, F
e, Co, Al) depends on the amount of Zn and P oxides in the coating, but unless the total metal equivalent is 1 mg / m ² or more, galling of the die and steel plate will occur due to high surface pressure during press working. In addition, the Zn and P oxide films are crystallized, the compatibility of the adhesive at the time of adhesion is lowered, the dissolution in the chemical conversion treatment liquid becomes non-uniform, and the chemical conversion treatability deteriorates. If the amount of these elements exceeds 200 mg / m ² , the coating becomes too thick and the chemical conversion treatability is rather adversely deteriorated.

As a method for forming the oxide film as described above, as the above-mentioned aqueous solution, for example, a phosphoric acid solution of potassium permanganate, nickel, magnesium, and aluminum is dissolved at a concentration of 1 g / l or more, and further reaction acceleration or solution is performed. For adjustment, a bath to which an acid such as sulfuric acid or nitric acid, sodium hydroxide, potassium hydroxide, zinc ion or the like is added can be used. By treating the above zinc layer with the aqueous solution as described above, most of the reacted layer becomes an oxide film consisting of Zn, P and the third element group, and the zinc layer remains less than traces. It does not become an obstacle.

In this way, for example, a simple rolled rust preventive oil can be applied to the hot-rolled steel sheet having the oxide produced before shipment.
In order to remove dust etc. as needed by the customer, the oxide film hardly peels off even after cleaning, so the lubricating oil is improved during press forming without contaminating the cleaning oil, and The drawability can be improved, and in the adhesion after pressing, the adhesion strength can be improved, and further the chemical conversion treatment film can be formed uniformly, and
The chemical conversion treatment liquid also does not become contaminated. You.

However, since the hot-rolled steel sheet on which such an oxide is formed is excellent in press formability (lubricity), for example, in order to improve the drawability of the steel sheet, Ti, Nb, B
It is customary to include etc., but depending on the application
Even if the inclusion of metal elements such as Ti, Nb, and B is omitted, necessary and sufficient formability can be secured. Further, by adjusting the metal element content of Ti, Nb, B, etc. based on the high lubrication function of the oxide of the steel sheet of the present invention, various hot rolled steel sheets having a plurality of lubrication levels can be precisely manufactured and classified. It is very meaningful because it can be adapted to the press moldability according to the application.

[0012]

Next, examples of the present invention will be described together with comparative examples.

[Table 1] Note 1) Treated steel plate A normal hot-rolled steel plate with a plate pressure of 1.6 mm was pickled to remove scale, and then electrozinc flash plating was performed at 10 to 1000 mg / m ² to produce an inorganic oxide. Note 2) Inorganic oxide generation method ・ P oxide is phosphoric acid or sodium phosphate, potassium phosphate, ammonium phosphate ・ Mn oxide is potassium permanganate or manganese carbonate ・ Ni oxidation The substances are nickel nitrate and nickel carbonate.-Mg oxides are magnesium carbonate and magnesium nitrate.-Fe oxides are soluble iron phosphate, iron nitrate and iron carbonate.-Co oxides are cobalt nitrate. Cobalt carbonate, ・ Al oxide, aluminum carbonate and aluminum nitrate are mixed in the element concentration range of 0.1 to 50 g / l, immersed or coated, and the coating amount is adjusted by air knife or roll squeezing. The oxide was produced and dried. Further, dipping or washing with coating water and further electrolysis were carried out as required. In order to secure the solubility of the above elements, pH adjustment was optionally performed with sulfuric acid, nitric acid, zinc carbonate, sodium hydroxide, or potassium hydroxide. The produced amount is the amount of the measured element that is chemically analyzed. Note 3) Film structure X-ray diffraction was used to determine the presence or absence of crystal peaks. Note 4) Zn residual amount The steel sheet on which the inorganic oxide film was formed was immersed in a 5% CrO ₃ solution (70 ° C) for 10 minutes to dissolve the inorganic oxide film, and then the metal Zn remaining on the steel sheet was converted to hydrochloric acid. The residual amount of metal Zn was measured by dissolution and chemical analysis. Note 5) Press moldability Sample size: 17 mm x 300 mm, tensile speed: 5
00 mm / min, square bead R: 3.0 / 5.0 mm, sliding length: 200 mm, oiling: Knox Thrust 530F40
(Manufactured by Parker Kosan Co., Ltd.) Under the condition of 1 g / m ² , the surface pressure is 10
The pull-out load was measured by a several-point test between 0 and 600 Kgf, and the friction coefficient was obtained from the surface pressure and the slope of the pull-out load. Note 5) Chemical conversion treatment As the chemical conversion treatment solution, SD5000 (manufactured by Nippon Paint Co., Ltd.) was used for degreasing according to the prescription and surface post-treatment for chemical conversion treatment. SEM (secondary electron beam image) is used to judge the chemical conversion coating.
As a result, the case where the film was uniformly formed was judged to be ◯, the case where the film was partially formed was judged to be Δ, and the case where the film was not formed was judged to be ×. Note 6) Adhesive compatibility A steel plate is made into a strip with a width of 25 mm, and 1 g / m ^{2 of} rust preventive oil (Knoxlast 30F40 (manufactured by Parker Kosan Co., Ltd.) is applied, and then an epoxy adhesive (EP190, Cemedine Co.) Adhesive for hemming) with a lapping margin of 8 mm and an adhesive thickness of 0.15 mm, and two layers are adhered and baked and cured at 170 ° C. for 20 minutes, then the shear peeling force is obtained using a tensile tester, and one side is 1 Cm ² Shear force was calculated.

[0013]

According to the present invention, lubricity (pressability, etc.), chemical conversion treatment property, and adhesive compatibility are improved, and
It is possible to prevent the cleaning oil, the degreasing liquid, and the chemical conversion treatment liquid from being contaminated, and to prevent the functional deterioration thereof, and it is possible to reduce the cost without shortening the life of the treatment liquid. In addition, since hot rolled steel sheets with multiple lubrication levels can be precisely manufactured based on the high lubrication function of the oxide film, it is possible to adapt the press formability according to various applications industrially. It can bring about an extremely large effect.

Front Page Continuation (72) Inventor Akihiro Miyasaka 5-3 Tokai-cho, Tokai-shi, Aichi Nippon Steel Co., Ltd. Nagoya Steel Works

Claims (1)

[Claims] 1. A Zn film containing 1 to 2 kinds of oxides of Zn and P and one or more oxides of Mn, Ni, Mg, Fe, Co and Al of the third element group on the surface of a steel plate as Zn. 200 mg / m ^2, P as 1~200 mg / m ^2, in terms of metal sum of the third element group 20
A hot-rolled steel sheet excellent in chemical conversion treatment, lubricity, and adhesive compatibility, characterized by producing 0 mg / m ² .