JP2000064013A - Alloyed hot-dip galvanized steel sheet and method for producing the steel sheet - Google Patents

Abstract

(57) [Problem] To provide excellent sliding characteristics at low cost, as well as to suppress powdering, and to satisfactorily prevent the occurrence of slip flaws. SOLUTION: The coating weight is 45 g / m ² or less, the iron content in the plating layer is 11 wt% or more and 15 wt% or less, and the center line average roughness Ra of the plating layer is 0.5 μm or more and 0.8 μm or less. Alloyed hot-dip galvanized steel sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvannealed steel sheet used in, for example, press forming and a method for producing the same.

[0002]

2. Description of the Related Art Alloyed hot-dip galvanized steel sheets are widely used in automobile bodies and the like, but when processed into parts by press forming, sliding characteristics with a press die pose a problem. If the sliding properties are poor, the steel sheet is prevented from flowing into the press die, leading to material breakage. In particular, in order to suppress powdering (a phenomenon in which powdery stripped flakes cause flaws on the molded part due to plating flaking due to deformation of the steel plate during pressing), the iron content in the plating layer (degree of alloying) The alloyed hot-dip galvanized steel sheet with a relatively low temperature to obtain good plating adhesion has an increased ζ phase in the outermost layer and is inferior in sliding characteristics with the press die, causing material fracture in the pressing process. There are cases.

Therefore, in order to improve such sliding characteristics, as shown in Japanese Patent Application Laid-Open No. 6-15302, temper rolling is performed by using a work roll having a low roughness, so that the surface roughness of the plated steel sheet can be improved. Adjustment method, and JP-A-5-11783
As shown in Japanese Patent Publication No. 1, a method has been proposed in which the degree of distortion of the amplitude probability density distribution is controlled by adjusting alloying conditions and temper rolling conditions.

Further, recently, in order to improve the sliding characteristics, a technique for performing Fe-based electroplating on the upper layer of the galvannealed layer has become mainstream. In addition, JP-A-5
Under the alloying conditions disclosed in Japanese Laid-Open Patent Publication No. 117831, the upper limit of the iron content of the plating layer is set to 12 wt%,
It is said that if it exceeds the range, the adhesion of the plating deteriorates and powdering occurs.

[0005]

However, in Japanese Unexamined Patent Publication No. 6-15302, only the plate surface roughness is lowered, so that a slip flaw is generated between the roll and the steel plate during manufacturing, and the yield is increased. There is an inconvenience that the steel plates are deteriorated and slip flaws occur due to slippage between steel plates during use.

On the other hand, in Japanese Patent Laid-Open No. 5-117831, it is troublesome to set the condition of temper rolling for controlling the degree of distortion of the amplitude probability density distribution, and further, Fe is formed on the alloyed hot-dip galvanized layer. Since electroplating of the system leads to an increase in cost, it is required to abolish the upper layer plating and improve the sliding characteristics with the alloyed hot dip galvanized single layer.

The present invention has been made in order to eliminate such inconvenience, and of course, powdering can be suppressed, excellent sliding characteristics can be obtained at low cost, and further slipping can be achieved. It is an object of the present invention to provide an alloyed hot-dip galvanized steel sheet capable of satisfactorily preventing the occurrence of flaws and a method for producing the steel sheet.

[0008]

In order to achieve such an object, the alloyed hot-dip galvanized steel sheet according to claim 1 has a range of iron content in the plating layer at a coating weight of 45 g / m ² or less. Is 11 wt% or more and 15 wt% or less, and the range of the center line average roughness Ra of the plating layer is 0.5 μm or more and 0.8 μm or less.

The method for producing a galvannealed steel sheet according to claim 2 is a series of methods for producing a galvannealed steel sheet in which hot dip plating, alloying treatment and the like are performed on the steel sheet.
Determine the upper limit of good iron content of the powdering property based on the relationship between the iron content in the coating layer and the powdering property of the target plating deposition amount, and in the relationship between the iron content and the ζ phase strength. The lower limit of the iron content is determined based on the ζ-phase strength with good slidability, and the slidability is determined based on the relationship between the center line average roughness Ra of the plating layer and the slidability at the lower limit iron content. Is determined to determine the upper limit of the average centerline average roughness Ra.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a graph showing the relationship between the amount of hot-dip galvanizing, the powdering score, and the degree of alloying (iron content in the plating layer), and FIG.
Fig. 3 is a graph showing the relationship between ζ phase strength and alloying degree at 5 g / m ² or less. Fig. 3 shows plate surface roughness and sliding when the coating weight is 45 g / m ² or less and ζ phase strength is 200 cps or less. It is a graph which shows the relationship with a sex evaluation index.

Conventionally, when the alloying degree exceeds 12 wt%, there is a concern that the plating adhesion may deteriorate and the plating may peel during the press working, which results in powdering. As shown in FIG. 1, if the coating weight is 45 g / m ² (one side) or less, the alloying degree is 15
It has been found that up to wt%, deterioration of plating adhesion can be suppressed within an allowable range, and powdering can be suppressed. In the method of powdering evaluation in FIG. 1, a cellophane tape is attached to a test piece, bent at 90 °, and after bending back, the cellophane tape is peeled off and the number of zinc powder adhered to the tape is measured.
For the sake of simplicity, evaluation is made by comparison with a limit sample.

Next, as shown in FIG. 2, when the coating weight is 45 g / m ² or less, the alloying degree is 11 wt% or more and the ζ phase strength of the outermost layer of the plating is 200 cps or less,
It was found that the ζ phase, which hinders the sliding characteristics with the press die, can be reduced.

Therefore, the range of the degree of alloying is set to 11 wt% or more and 15 wt% or less in order to obtain both the effect of suppressing powdering and the effect of reducing the ζ phase that inhibits sliding characteristics. The ζ-phase strength in FIG. 2 is measured by RIN manufactured by Rigaku Denki Co., Ltd.
The measurement conditions are as follows:
Cu, tube voltage: 50 kV, tube current: 250 mA, sampling angle: 0.020 °, scan speed: 4.0
It was set to 0 ° / min.

Next, the relationship between the plate surface roughness and the slidability evaluation index when the coating weight is 45 g / m ² or less and the alloying degree is 11 wt% or more and 15 wt% or less is investigated. The range of the center line average roughness Ra is 0.5 μm or more.
Excellent sliding characteristics at 8 μm or less, and plate surface roughness Ra
If it exceeds 0.8 μm and becomes rough, the friction coefficient becomes large and the sliding characteristics deteriorate, while if it is less than 0.5 μm, slipping occurs during handling and slip defects occur.

As for the slidability evaluation index, when a 200 × 200 mm test piece was overhanged with a hemisphere of φ100 mm under the conditions of a wrinkle holding force of 20 tonf and a test speed of 0.5 mm / sec, the tension until breakage occurred. Height (m
m) (bulb head overhanging test), Ra was measured using a three-dimensional roughness meter based on JIS B0601, and measurement conditions were: measurement speed 0.3 mm / sec, feed pitch 5 μm, pressing force 0.4 gf, touch. Needle tip R = 5μm, cutoff 0.8
mm and an input gain of 50.

As is apparent from the above description, in this embodiment, powdering can be suppressed and excellent sliding characteristics can be achieved at low cost without performing Fe-based electroplating on the upper layer of the plating layer. It was possible to prevent the occurrence of slip flaws.

[0017]

EXAMPLES In Table 1, No. 1-No. No. 3 is an example of the present invention. 4 to No. 7 is a comparative example, both of the present invention example and the comparative example, using an ultra-low carbon steel plate having a plate thickness of 0.8 mm and a plate width of 1350 mm on which an alloyed galvanized layer is formed,
For the examples of the present invention, the coating weight range: 40 to 45 g /
m ² , the range of alloying degree: 11 to 15 wt%, Ra after temper rolling: 0.6 to 0.8 μm, and in the comparative example, the range of plating adhesion: 40 to 80 g / m ² , the alloying degree of Range: 10 to 16 wt%, Ra after temper rolling: 0.4 to
It was set to 0.8 μm, and the powdering property, the sliding property with the press die, and the presence or absence of slip flaws were examined. In addition, in the present invention example and the comparative example, Fe-based electroplating was not applied to the upper layer of the plating layer. The results are shown in Table 1.

[0018]

[Table 1] As is clear from Table 1, Comparative Example No. 1 having an alloying degree of less than 11 wt%. In Comparative Example No. 4, the desired sliding characteristics were not obtained and Ra was less than 0.5 μm. In Comparative Example No. 5, slip flaws occurred and the coating weight was more than 45 g / m ² .
In Comparative Example No. 6, the effect of suppressing powdering was not obtained, and the alloying degree exceeded 15 wt%. In No. 7, the effect of suppressing powdering was not obtained.

On the other hand, the coating weight is 45 g / m ²
Below, the alloying degree is 11 wt% or more and 15 wt% or less, Ra
Of the present invention N satisfying the following condition: 0.5 μm or more and 0.8 μm or less
o. 1-No. In No. 3, powdering was suppressed, sliding characteristics were excellent, and slip flaws did not occur.

[0020]

As is apparent from the above description, according to the present invention, not only powdering can be suppressed, but also excellent sliding characteristics can be obtained at low cost. The effect that the occurrence of slip defects can be effectively prevented is obtained.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a coating adhesion amount, a powdering score, and an alloying degree (iron content in a plating layer).

FIG. 2 is a graph showing the relationship between the ζ-phase strength and the degree of alloying when the coating weight is 45 g / m ² or less.

FIG. 3 is a graph showing the relationship between the plate surface roughness and the slidability evaluation index when the coating adhesion amount is 45 g / m ² or less and the ζ phase strength is 200 cps or less.

Claims (2)

[Claims] 1. The range of the iron content in the plated layer when the coating weight is 45 g / m ² or less is 11 wt% or more and 15 wt% or more.
The following is set and the range of center line average roughness Ra of the said plating layer was 0.5 micrometer or more and 0.8 micrometer or less, The galvannealed steel sheet characterized by the above-mentioned. 2. A method for producing a series of galvannealed steel sheets, which comprises subjecting a steel sheet to hot dip coating, alloying treatment, etc.,
Determine the upper limit of good iron content of the powdering property based on the relationship between the iron content in the coating layer and the powdering property of the target plating deposition amount, and in the relationship between the iron content and the ζ phase strength. The lower limit of the iron content is determined based on the ζ-phase strength with good slidability, and the slidability is determined based on the relationship between the center line average roughness Ra of the plating layer and the slidability at the lower limit iron content. A method for producing a galvannealed steel sheet, characterized in that the upper limit of the favorable centerline average roughness Ra is determined.