JPH01142097A - Flaking resistant galvanized steel sheet - Google Patents

Abstract

PURPOSE:To obtain a galvanized steel sheet having >=20g/m<2> coating amount, superior in corrosion and flaking resistances by controlling the crystal structure of a zinc layer formed by galvanizing by a proper means to regulate the orienta tion index of the (002) plane to <=1. CONSTITUTION:When a galvanized steel sheet having >=20g/m<2> coating amount is produced, the orientation index of the (002) face of the zinc layer is regulated to <=1. The flaking resistance of the galvanized steel sheet during press working can simply be improved without restriction by the base metal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is directed to the (002 This invention relates to an electrogalvanized steel sheet that has low surface orientation and excellent braking resistance during press working.

(Prior Art) In recent years, electroplated steel sheets for rust prevention have been used in a wide range of applications and in many fields. In particular, zinc-based electroplated steel sheets are not only inexpensive, but also have a significantly improved corrosion-resistant life, and are therefore increasingly being used in automobile bodies.

By the way, electroplated steel sheets for automobiles are used as press-formed panel products and are often used as outer panels that are visible to the public, so the paint finish must be clean and smooth. something is required. Surface roughness of 1.5 μr, m, s or less is generally used.

In addition, in many applications of electroplated steel sheets, such as those for automobiles, press forming is performed, so it is especially important to press the steel sheets without damaging the smooth surface condition obtained by rolling.

However, in reality, foreign particles adhering to the punch surface or material surface, deposits on the plating film, or scratches on the punch surface often cause minute impressions on the surface after pressing, resulting in so-called braking.

Such occurrence of braking is a problem for electroplated mesh plates, where beauty in appearance as well as corrosion resistance are particularly important. Various measures have been taken to counter this problem, such as polishing the press mold, cleaning the press mold and materials, preventing dust in the factory, and cleaning the press oil, but since there are a wide variety of factors related to the mechanism that causes braking, , it is extremely difficult to reduce this defect. If braking occurs frequently, the surface of the press mold must be cleaned frequently, which requires a lot of time and effort.

Furthermore, electrogalvanized coatings with a basis weight of 80 g/rrr or more are widely used as rust-preventing steel sheets for automobiles, mainly in the United States, due to their excellent large crack resistance. This phenomenon tends to occur more easily as the basis weight increases, so its valuable properties are not fully utilized.

There is a need for a plated steel sheet that satisfies both corrosion resistance and braking resistance.

Conventionally, such problems have been solved by regulating the surface roughness (see JP-A-57-85989 and JP-A-57-165000), adding Sn or Sr compounds to the plating bath (JP-A No. 61-69998, No. 55-1
31192" (see publication). However, there were problems such as restrictions on the base material and poor corrosion resistance.

(Problems to be Solved by the Invention) The purpose of the present invention is to provide sufficient corrosion resistance, and
It is an object of the present invention to provide an electrogalvanized steel sheet with excellent braking resistance during press working, particularly an electrogalvanized steel sheet with a coating weight of 20 g/% or more.

(Means for Solving the Problems) Therefore, in order to achieve the above object, the present inventors worked to clarify the braking phenomenon during press working, and based on the findings of preliminary experiments, the plating film and the I tried to improve myself. As a result, by controlling the crystal structure of the plating film by appropriate means and suppressing the orientation of the (002) plane to 1 or less, an electrogalvanized steel sheet with excellent braking resistance during press forming can be obtained. find out,
The invention has been completed.

Therefore, the gist of the present invention is that the plating deposition amount is preferably 2.
When obtaining an electrogalvanized steel sheet of 0g/rd or more,
For example, if the Fe ion concentration in a zinc sulfate-based plating bath is
Electrogalvanizing is performed by regulating the Ni ion concentration to 0 ppm or less and the Ni ion concentration to 130 ppm or less, or by limiting the Fe ion concentration to 2000 ppm or less and the Pb ion concentration to 10 ppm or less and adding dextrin. This is a braking-resistant electrogalvanized steel sheet with the orientation index of the (002) plane kept at 1 or less, which makes it difficult to cause braking during press working.

Here, the orientation index is determined by performing X-ray diffraction of a galvanized steel sheet and zinc powder as a standard sample, and using the peak height of each of the X-ray diffraction results using the following formula.

The present invention, by its nature, relates to electroplated steel sheets in general, and similar effects can be expected with any of them, but from a practical standpoint, it is limited to electrogalvanized steel sheets only.

(effect) Hereinafter, the present invention will be explained in detail based on experimental examples.

As mentioned above, the present inventors have developed a fabric weight ff120g/n (
As a result of examining the causes of braking during press working for the above electrogalvanized steel sheets, as shown in Figures 1 and 2, we found that the plating film In(
002) It was learned that braking is more likely to occur when the orientation index of the plane is high.

FIGS. 1 and 2 are graphs obtained by plotting the drawbead average load and plating film hardness against the (002) plane orientation index described above, respectively. The orientation index of the (002) plane was varied depending on the concentrations of Fe, Ni, and dextrin. Plating weight 100g/m, plating bath composition Z
n ion 61g/1, sodium sulfate 75g/e-2
The volume temperature was 50°C and the pH was 1.6.

The drawbead average load is calculated by sandwiching the specimen 5 between male and female molds 3.4 each having an uneven surface 1.2 at the center and pressing it from both directions, as shown in the cross section in Fig. 3. 5
The specimen 5 is pulled out in the direction of the black arrow in the figure without being brought into close contact with each other, and the tensile pressure at this time is expressed. This small average load means that deformation is easy and braking does not occur. For the dimensions of the mold and other details, refer to the examples described later.

Next, the steel plate to be plated was subjected to normal surface cleaning and pretreatment such as degreasing and pickling, and then electroplating was performed in an electrolytic bath composition as shown below.

Zinc ion 61g/7! Sothorium sulfate 75g/j! Or ammonium sulfate 55g/npH1.6,
In an electrolytic bath with a bath temperature of 50°, a current density of 80 A/dm2
When electroplating is carried out with a basis weight of 100 g/n,
The relationship between the Fe ion concentration and Ni ion concentration as impurity ions in the bath and the orientation index of the (002) plane of the plating film is shown in FIGS. 4 and 5.

Furthermore, as shown in Fig. 6, the Fe ion concentration is 1450 p.
In the same electrolytic bath as above with a Pb ion concentration of 10 ppm, the orientation index of the (002) plane decreases as the amount of dextrin added increases.

As already shown in relation to Figures 1 and 2, in order to obtain a galvanized steel sheet with excellent braking resistance during press working, the orientation index of the (002) plane of the plating film must be set to 1 or less. It is necessary. Then, the plating film (00
2) In order to make the orientation index of the plane 1 or less, from Figures 3 and 4, the Fe ion concentration in the bath should be 1000 ppm or less, and the N
It can be seen that it is necessary to reduce the i-ion concentration to 130 ppm or less.

Also, from Fig. 5, when Fe ions are allowed to some extent,
While limiting the Pb ion concentration, the dextrin
It can be seen that it is necessary to add ~20 ppm.

Note that dextrin is starch C (c', n, oos)
,) is a mixture of various degrees of decomposition products obtained during the intermediate steps of the reaction when hydrolyzed with acid or amylase.

Here, using a similar plating bath, the relationship between current density, plating amount, and orientation index of the (002) plane was investigated. The results are summarized in graphs in FIGS. 7 and 8, respectively.

Regarding the current density, as shown in Figure 7, the orientation index of the (002) plane tends to increase as the current density increases, so it is preferable to suppress the current density, for example, to 110 A/dm2 or less. .

Regarding the basis weight, as shown in Figure 8, the orientation index of the (002) plane tends to increase as the basis weight increases.
By regulating the Fe and Ni ion concentrations according to the present invention, the rate of increase in the orientation index of the (002) plane as the basis weight increases is reduced, thereby obtaining an electroplated steel sheet with excellent braking resistance during press forming. be able to.

Note that no particular difference was observed between sodium sulfate and ammonium sulfate.

As described above, according to the present invention, Ni and Fe in the electrolytic bath can be
By regulating the amount of mixed in, and more preferably, the current density and area weight during electroplating, the electroplating film has a low orientation index of the (002) plane and has excellent braking resistance during press working. Galvanized steel sheets can be produced.

Examples of the present invention will be shown below.

(Example) Using a cold-rolled steel plate with a thickness of 0.8 mm, sodium orthosilicate? After degreasing with 8 liquid and pickling with sulfuric acid, zinc ion 6
1g#! Using an electrolytic bath composition consisting of 75 g of sodium sulfate or 55 g of ammonium sulfate/β, as shown in Table 1, Fe in the electrolytic bath, which is an important factor of the present invention,
The performance of manufactured galvanized steel sheets was evaluated by changing the impurity concentration of Ni ions. The evaluation method is as follows.

■Orientation index of plating film About plated steel sheet and zinc powder as standard sample ゛ζ
X-ray diffraction was performed using the following method, and the measurement angle was 2θ-10 to 6.
This was done by measuring the peak height corresponding to each crystal orientation at 0°. Further, the orientation of the (002) plane was defined by the above-mentioned formula (I).

Note that the X-ray diffraction conditions are shown in Table 2.

Reason table Mo target Filter: 21 filter Acceleration voltage: 40KV 5can speed = 2°
/min acceleration current: 20 mA ■ Draw bead test As shown in Figure 3, a sample was pulled out using a bead, and the braking performance during press working was evaluated based on the average load at that time. In other words, the higher the load, the more likely braking will occur.

・Sample shape 30mm depth x 300mm diameter ・Pull-out speed 500mm/min ・Press pressure 30kg/cJ ■Plating film hardness (microhysteresis) ・Load
Log - After measuring at 7 points, the lower the average plating film hardness at the 5 points excluding the maximum and minimum, the more likely braking will occur.

(Effects of the Invention) As described above, the electrogalvanized steel sheet according to the present invention has a low orientation index of the (002) plane of the plating film, is not subject to the restrictions of the base material, and can easily achieve braking resistance during press forming. It is possible to improve performance.

Moreover, even though the orientation index of the (002) plane of the plating film is limited to 1 or less, this is specifically achieved by cleaning the plating bath, and does not require any new equipment. Therefore, the practical effect is great.

[Brief explanation of the drawing]

Figures 1 and 2 are graphs showing the results of preliminary tests; Figure 3 is an explanatory diagram showing the outline of the drawbead test; Figures 4 to 6 are graphs showing the plating bath composition and plating skin H'J.
and FIGS. 7 and 8 are graphs showing the relationship between the current density and the amount of plating and the orientation index of the (002) plane, respectively. 1: Concave 2: Convex 3: Male - 4: Female
5: Test piece removed (PP book) Test piece sintered put (Ppyn) hae 1 [ garlic [

Claims (3)

[Claims] (1) A braking-resistant electrogalvanized steel sheet in which the orientation index of the (002) plane of the plating film is 1 or less in an electrogalvanized steel sheet with a coating weight of 20 g/m^2 or more. (2) Fe ion concentration in the electrolytic bath composition to 1000 ppm
The electrogalvanized steel sheet according to claim 1, obtained by electrogalvanizing with the Ni ion concentration limited to 130 ppm or less. (3) Fe concentration in the electrolytic bath composition is 2000 ppm or less,
The electrogalvanized steel sheet according to claim 1, which is obtained by electrogalvanizing with 5 to 20 ppm of dextrin added while limiting the Pb ion concentration to 10 ppm or less.