JPH05156463A - Phosphate treatment for high manganese high tensile steel material - Google Patents

Abstract

PURPOSE:To easily form a phosphate coating film excellent in adhesive strength, crystallinity, corrosion resistance and chemical conversion by phosphate-treating a high manganese high tensile steel with a treating solution containing PO4 ion, NO3 ion, Zn ion as essential components and a specific amount of free F ion. CONSTITUTION:The phosphate treating solution containing e.g. about 1-50g/l PO4 ion, about 1-50g/l NO3 ion and about 0.3-3.0g/l Zn ion as the essential components and, if necessary, a prescribed amount of ions such as NO2, ClO3, Ni, Co, Mn is made to contain 50-700ppm preferably 100-500ppm free F ion. The high manganese high tensile steel containing 1.0-3.5% Mn is phosphate- treated with the treating solution. As a result, a chemical coating film, which is bonded with the steel base and is composed of fine crystal, is formed and a excellent protective coating film is obtained as a undercoating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a Mn content of 1.0 to
The present invention relates to a high-Mn-based high-strength steel material of 3.5% and a phosphate treatment method in a coating pretreatment line for a composite member composed of the high-tensile steel material and another metal material.

[0002]

2. Description of the Related Art High-strength steel is a name based on the property of high tensile strength, but from the viewpoint of composition, it belongs to the category of low-alloy steel and medium-alloy steel, and in general, including Mn,
It contains a considerable amount of alloying elements such as Si, Cr, Ni, Mo, W, Nb, Ta, Ti and B. Therefore, even if the surface properties and conditions are not as good as those of heat-resistant steel,
Since it is quite different from ordinary steel, it becomes very difficult to form a zinc phosphate film.

In forming a phosphate coating on the surface of a normal low alloy steel such as ordinary steel or weathering steel, phosphoric acid containing a fluorine ion is included in order to facilitate the formation of the coating. It is known to treat with a salt treatment liquid. (For example, Japanese Patent Application Laid-Open No. 1-142088, Japanese Patent Publication No. 58-39.
915, JP-A-64-68481, and JP-A-2-277781) However, on the surface of a high-tensile steel sheet having a higher content of alloying elements, for example, a high Mn-based high-tensile steel sheet (fluorine ion) It is not known to promote the formation of a good phosphate coating).

[0004]

In view of the situation of the prior art as described above, the present invention is suitable for the surface of a high Mn-based high strength steel plate and a composite member made of the high strength steel plate and another metal material. It is intended to provide a treatment method capable of forming a phosphate film. More specifically, the present invention provides a method for forming a good phosphate coating on the surface of a bumper member manufactured from an automobile part, for example, a high-strength steel sheet used under severe operating conditions.

[0005]

The method of the present invention is disclosed in JP-A-64-68481 and JP-A-2-277781.
It is not intended for ordinary steel as described in Japanese Patent Publication No. JP-A-2003-242, and the phosphate coating formed by the method of the present invention is
The above-mentioned Japanese Patent Laid-Open No. 1-142088 or Japanese Patent Publication No. 58-58
Since it is not a temporary coating as described in Japanese Patent Publication No. 39915, but a permanent protective coating as a base of coating,
It must have excellent adhesion and crystallinity to the surface of the high-strength steel sheet, and sufficient corrosion resistance and chemical conversion.

The high Mn-based high-strength steel sheet with a high Mn content is
Since the Mn concentration on the surface of the steel sheet is strong and the steel sheet itself has properties different from those of ordinary steel sheets, the chemical conversion properties of ordinary phosphating solutions show behavior that is different from that of ordinary steel sheets and significantly deteriorate. .. Therefore, it is necessary to devise a method for improving the chemical conversion property of the phosphate coating so that the phosphate coating formed on the surface of the high-Mn high-strength steel sheet is firmly bonded to the steel sheet matrix to form a dense crystal.

[0007] That is, the inventors of the present invention, as a result of earnest research,
It has been discovered that this object is achieved by constantly presenting a fixed amount of free F ions in a zinc phosphate chemical conversion treatment solution having a known composition. Regarding the content of free F ions in the phosphate treatment solution, as a result of repeated theoretical studies and experiments, it is necessary to set it in the range of 50 to 700 ppm, and the range of 100 to 500 ppm is more preferable. confirmed. That is, the present invention is "PO ₄ ion, NO ₃ ion and Zn 50-700Ppm free F ions in phosphating solution mainly composed of ions, it is preferably used processing solution which contains 100-500ppm High Mn containing 1.0 to 3.5% of Mn characterized by
Method for phosphating high-strength steel.

The technical basis for limiting the Mn content to the range of 1.0 to 3.5% in the high Mn high strength steel targeted by the method of the present invention is as follows. That is, as described above, the high-Mn high-strength steel of the present invention is used under extremely harsh conditions and environments, and has a pressure of 1000 MPa (1
Since a tensile strength of at least 00 kg / mm ² ) and high toughness are required, it depends on the contents of other alloy elements, but 1.
A minimum Mn content of 0% or more is required. On the other hand, if the Mn content exceeds 3.5%, it becomes extremely difficult to process a steel sheet, and further strength and toughness are not required. Was set to 3.5%.

[0009]

The basic component of the phosphating solution used in the method of the present invention may be one having a known general composition as described above, and it is not particularly specified in the present invention. , Specifically, as the main component; PO ₄ ion 1
-50 g / l, NO ₃ ion 1-50 g / l, Zn ion 0.3-3.0 g / l, and as a promoter; NO ₂ ion 0.01-0.2 g / l and / or ClO ₃ ion 0.5-5.0 g / l, as a heavy metal ion for improving the adhesion and corrosion resistance of the coating film; Ni ion,
It contains any one or more of Co ions and Mn ions. With respect to this basic component, free F ions were further measured by a free fluorine ion meter, and were 50 to 700 ppm, preferably 10
0-500 ppm, more preferably 200-400 p
What was made to contain pm is the phosphate processing liquid of this invention.
The preferred range for this free fluoride ion concentration was determined experimentally as described in the Examples.

A large amount of the fluorine component needs to be present in the phosphating bath, and its source is HF or Na.
F, KF, NH ₄ F, NaBF ₄ , HBF ₄ and H ₂ Zr
One or more kinds of fluorides selected from the group forming F ₆ isofluoride ions and complex fluoride ions are used. H ₂ SiF ₆ , which has a relatively weak dissociated state in the treatment liquid and has a mild reactivity with the object to be treated, was suitable as a conventional source of free F ions, but in the method of the present invention, free F The ion supply rate is slow and cannot be used alone. Rather, it is more effective to use a compound such as HF, which easily dissociates free fluorine ions, for controlling the concentration of free F ions, and by increasing the etching action on the surface of the high-strength steel sheet, phosphate The chemical conversion property of the treatment and the crystallinity of the film can be improved.

By mixing such a fluoride with a phosphating solution and applying it to the surface of a high-Mn-based high-tensile steel plate, the adhesion and crystallinity of the phosphate coating on the surface of the high-tensile steel plate, The chemical conversion property is remarkably improved to the same level as that on the surface of ordinary steel, and sufficient corrosion resistance and coating adhesion after coating can be obtained. Specific examples of the present invention will be described below.

【Example】

First, C0.09%, Si0.21%,
Specimen cut out from a high-Mn high-strength steel sheet containing 3.1% Mn, 0.034% P, and 0.005% S (vertical 1
50 mm, width 100 mm, thickness 2 mm) was immersed for 2 minutes in a degreasing solution at 43 ° C. containing 20 g / l of a degreasing agent (trade name; Fine Cleaner L4410, manufactured by Nippon Parkerizing Co., Ltd.). Then, the test material was used as a surface conditioner (trade name; PL-Z
N, manufactured by Nippon Parkerizing Co., Ltd.) was immersed in a treatment liquid containing 1 g / l at room temperature for 30 seconds. Next, Zn ion 1.0
g / l, Mn ion 0.4 g / l, Ni ion 1.0
g / l, PO ₄ ion 11-14g / l, NO ₃ ion
5-10 g / l, total fluorine 1 g / l, pH
With respect to the basic composition of the phosphating solution of 2.8 to 3.3,
Phosphoric acid-treated liquid groups were prepared by adding 0 to 700 ppm of free F ions, and the test material was kept at 43 ° C. in these liquids.
It was immersed for 2 minutes. The relationship between the free fluorine ion concentration and the coating weight in this treatment is shown in FIG. 1, and the data is shown in Table 1.
Shown in.

[0013]

[Table 1]

The weight of the formed film per unit area hardly changes in the free fluorine ion concentration range of 0 to 600 ppm. However, significant differences occur in the crystal size and density of the coating. When a normal NO ₂ -based accelerator is used, the free fluorine ion concentration is 0
If it is as small as ~ 100ppm, the size of the crystals generated is large and voids are seen in the film, but the free fluorine ion concentration is 10
The coating formed when it is large, such as 0 to 600 ppm, is dense and fine. Free fluorine ions, the crystal gradually becomes smaller at 600 ppm or more, and becomes very small at 700 ppm, which can hardly be confirmed even in an electron micrograph.

Here, the free fluorine ion concentration is 80 pp
Scanning backscattered electron micrographs (SEM) of the formed coating film at two points of m and 250 ppm are shown in FIGS. According to this, the structure of the phosphate coating obtained using the treatment solution of free fluorine ion 250ppm (invention) is very dense and fine, whereas the treatment of free fluorine ion 80ppm (comparative example) The structure of the phosphate coating obtained by the solution was rough and coarse.

Further, as a result of evaluating the corrosion resistance after coating for a free fluorine ion concentration of 0 to 700 ppm by a salt hot water immersion test, there was no problem at 100 to 500 ppm of free fluorine ion, but it was inferior at 0 to 80 ppm and 600 ppm or more. It was Next, in order to investigate the relationship between the free fluorine ion concentration and the robustness of the above-mentioned phosphate coating applied on the produced phosphate coating, after the above-mentioned phosphate treatment, electrodeposition coating (trade name: Succe- Do # 700, manufactured by Shinto Paint Co., Ltd., film thickness;
20 μ) was applied to the surface of the test material with a cutter knife to cut diagonally to reach the substrate, and the cut was heated to 55 ° C. 5
% Aqueous NaCl solution for 240 hours, an adhesive tape was applied along the cut, and the tape was immediately peeled off, and the peeling width of the coating film from the surface of the test material was measured. The measurement result is shown in FIG. The smaller the peeling width, the higher the robustness of the coating film.

From this experiment, the free fluorine ion concentration was
It has been found that it affects the weight of the coating produced per unit area and the fastness of the coating, but the influence on the latter is particularly important. Then, the optimum content of free fluorine ions in the phosphating solution was determined based on the experiment of FIG. 6 and was found to be 50-700 ppm, preferably 100-500.
It was determined to be ppm.

[0018]

As described above in detail, according to the present invention,
By adding a predetermined amount of free fluorine ions to the phosphating solution, it is possible to use high Mn-based high-strength steel sheets and ordinary steel sheets with black skin adhered, which had been difficult to form phosphating chemical conversion coatings. It became possible to easily form a chemical conversion coating.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the concentration of free fluorine ions in a phosphate treatment solution and the weight of a produced coating film per unit area.

[Fig. 2] High Mn high tensile strength steel plate with a fluorine ion concentration of 80
It is an electron micrograph which shows the crystal structure of the produced | generated film | membrane when a phosphate treatment liquid of ppm is processed.

FIG. 3 is an electron micrograph of a different coating formed when treated under the same conditions as in FIG.

[Fig. 4] High Mn high strength steel plate with a fluorine ion concentration of 25
It is an electron micrograph which shows the crystal structure of the formed film when a 0 ppm phosphate treatment liquid is processed.

FIG. 5 is an electron micrograph of a different coating formed when treated under the same conditions as in FIG.

FIG. 6 is a diagram showing the relationship between the concentration of free fluorine ions in a phosphate treatment solution and the robustness (peeling resistance) of a coating film after electrodeposition coating.

Claims (2)

[Claims] 1. Free F ions are added to a phosphating solution containing PO ₄ ions, NO ₃ ions and Zn ions as main components.
Using the treatment liquid containing 0-700 ppm, Mn
A method of phosphating a high-Mn high-strength steel containing 1.0 to 3.5%. 2. The phosphate treatment method according to claim 1, wherein free F ions are contained in an amount of 100 to 500 ppm.