JPH01319661A - Alloying hot dip galvanized steel sheet excellent in press formability - Google Patents

Abstract

PURPOSE:To provide high powdering resistance and to carry out press working in accordance with material properties by providing a ferrous alloy plating layer having a specific hardness to an Fe-Zn alloying hot dip galvanizing layer formed on a steel sheet. CONSTITUTION:An alloying hot dip galvanizing layer consisting of Fe-Zn alloy is formed at least on one surface of a steel sheet by about 2-10g/m<2> coating weight. Then, an Fe or ferrous alloy plating layer of >=400 Vickers hardness is formed on the above layer. This plated steel sheet has superior press formability and shows deep drawability in accordance with the material properties of the steel sheet as a base material, and further, this plated steel sheet has sufficient powdering resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an alloyed hot-dip galvanized steel sheet used for press forming and painting for automobiles, building materials, etc.

(Prior art) Alloyed hot-dip galvanized steel sheet (hereinafter referred to as GA rust steel sheet)
Because it has a BE of 1 serving and 1 serving, it is used in applications that require high rust prevention properties such as automobile exterior panels.

Conventional G A i [sheets are made using the conditions in the alloying process by heating after hot-dip galvanizing to avoid powdering of the plating layer called powdering caused by compressive deformation during pressing of GA steel sheets. F in the alloyed hot-dip galvanized layer (hereinafter referred to as GA layer)
e 9Q degree is lowered.

On the other hand, another problem is based on the alloy composition and structure of the GA layer surface.
To reduce craters that occur when electrocoating GA rust steel sheets and improve secondary adhesion after painting, [1]
A method of alloying so that no pure Zn phase (η phase) remains on the surface of the GA layer after alloying, Fe-Zn alloy plating disclosed in Japanese Patent Publication No. 58-15554, Japanese Patent Application Laid-open No. 1983-15554, Fe--P alloy plating disclosed in Japanese Patent No. 253397 is known. However, nothing has disclosed the influence of such treatment on press formability or the conditions suitable for its improvement, and no attempt has yet been made to improve the press formability of GA rusted steel sheets.

(Invention or attempt to solve; I!I! Problem) GA rusted steel sheets used for press forming have a hard and brittle "phase" produced at the Fe/GA layer interface due to excessive alloying of the GA layer.
Suppresses the formation of Fe32n+o phase) and reduces powdering and
In order to provide sleeves, the Fe content in the GA layer is lowered. However, when such GA rusted steel sheets were actually pressed into automobile exterior panels, the press formability became a problem. That is, in order to improve the buttering resistance, F of the GA layer is
When the e concentration was lowered, the ζ phase (reZ
n+3 phase) or η phase (Zn phase) remained. Since these phases are soft, during press forming of GA rust steel sheet,
The deformation of the matte surface of the heated part becomes large, and as a result,
The sliding resistance becomes high, and it becomes difficult to know whether the steel plate will flow in, and the mother plate ∆
Although steel plates have a sufficient neck drop, they are prone to necking and cracking due to the extremely thin constrictions of the plate.

In view of the above facts, the present invention has been developed based on a study of the effect of Fe-based alloy plating, which is usually carried out as a measure against cratering in GA steel sheets, on press formability, and has been developed to provide buckling resistance that has not been achieved with conventional techniques. Despite its high durability, press molding (
G
A: GA that can be pressed according to the material properties of the rusted steel plate base material
The purpose of this article is to provide information on rusted steel plates.

(Means to Solve the Problem) The surface of the GA layer, especially when the surface is in the ζ phase or η phase, is soft and deforms when pressed against the mold during pressing, causing its sliding. The sliding resistance increases as the area increases and sometimes galling occurs. G.A.
In order to achieve sufficient press formability of a rusted steel sheet in accordance with the material properties of the base material, it is important to improve the sliding properties of the GA layer surface so as not to impede the flow of the steel sheet during pressing.

As a means of solving this problem, we thought it would be a good idea to form a thin, hard layer on the surface of the GA layer to suppress the increase in sliding area and the occurrence of galling due to the deformation of the ζ phase, and focused on the high hardness of electrolytic iron and its alloys. However, we came up with the idea of performing an appropriate amount of Fe-based electroplating on the ζ phase, leading to the present invention.

The present invention provides Fe-Zn on at least one surface of a steel plate.
It has an alloyed hot-dip galvanized layer made of an alloy, and on the alloyed hot-dip galvanized layer is an F having a Vickers hardness of 400 or more.
The present invention provides an alloyed hot-dip galvanized steel sheet having excellent press formability and having an e- or Fe-based alloy plating layer.

The amount of deposited Fe or Fe-based alloy plating layer is 2 g.
/m' or more and 10 g/m'' or less.

The alloyed hot-dip galvanized layer is preferably a mixed phase of a δx phase, a ζ phase and a η phase, more preferably a mixed phase of a δx phase and a ζ phase.

The Fe-based alloy plating layer is made of B, P, S, Ti, ■, Cr.
, Mn, Co, Ni, Zn, Mo.

Preferably, the layer contains one or more elements selected from Sn, W, Re, and Pd.

Below, the alloyed hot-dip galvanized steel sheet that can be evaluated for press formability according to the present invention will be described in detail.

Alloyed hot-dip galvanized steel sheet (f) that improves the press formability of the present invention (Fe-Z
It has an alloyed hot-dip galvanized layer made of an n-alloy, and that layer has an Fe or Fe-based alloy plating layer, or
It is important that the hardness of the Fe or Fe-based alloy plating layer be equal to or higher than that of single phase Fe, and expressed in terms of Vickers hardness, be 400 or more for the ζ phase of 150 to 200.

The reason for this is that if the Fe or Fe-based alloy plating layer is soft, it will not be possible to prevent the occurrence of necking or cracking that occurs during press forming of GA rusted steel sheets.

In addition, the amount of deposit of GA rust steel plate with ``e'' or Fe-based alloy plating layer is 2 g on at least one GA layer surface.
/m' or more and 10 g/m' or less.

Since the surface of the GA layer is rich in fine irregularities, the amount of adhesion is approximately 2 g/
If it is less than m', the surface of the GA rusted steel sheet cannot be sufficiently covered with Fe or Fe-based alloy plating. Moreover, if it exceeds 10 g/m', a film of a high hardness Fe or f'e alloy patch layer is formed, and this film is
Since the rusted steel plate cannot follow the deformation during press forming, it flakes off, which is undesirable.

Formation of GA layer, i.e. Fe from the base steel sheet into the galvanized layer.
When alloying by diffusion, the GA layer is preferably a mixed phase of δx phase, ζ phase and η phase, more preferably δx phase.
Control is performed to create a mixed phase of phase and ζ phase.

The reason why the GA layer is defined in this manner is to prevent peeling of the plating layer (ie, powdering) during press molding. This is also to improve secondary adhesion after coating.

Furthermore, the Fe-based alloy plating layer contains B, P, S,
Ti, V, Cr, MnV
Co, Ni.

Preferably, it contains one or more elements selected from Zn, Mo, Sn, W, Re, and Pb.

This is because such elements have a favorable effect on crater resistance and also have the function of stably depositing a plating layer having a Vickers hardness of 400 or more.

Further, it is preferable to use dispersion plating in which silica, alumina, etc. are dispersed in addition to these elements for the Fe-based alloy plating layer, since this improves paint adhesion.

Below, a preferred method for manufacturing the alloyed hot-dip galvanized steel sheet of the present invention having excellent press formability will be described.

Cold-rolled steel sheets must be heated at a temperature required to sufficiently undergo recrystallization and obtain good press formability, specifically 700 to 880°C.
After being annealed at a temperature in the range of 430-50
After being immersed in a molten zinc bath maintained at a temperature of about 0°C, plated, and made into a predetermined zinc adhesion chamber by gas wiping, it is heated and maintained at a temperature of 450 to 600°C.
Through this operation, Fe is diffused from the base steel sheet into the galvanized layer and alloyed. Subsequently, the plated cold-rolled steel sheet is cooled and temper-rolled at a rolling reduction of 0.2 to 2%.

Through this temper rolling, the surface roughness is 5Ra-13 to 2.2
It becomes smaller from about μm (before rolling) to 07 to 14 μm (after rolling).

The GA laminate after temper rolling is finally plated with Fe or Fe-based alloy by electroplating.

(Example) Next, the present invention will be explained based on examples.

The GA rusted steel sheet of the present invention and the conventional GA rusted steel sheet were manufactured, the plating properties were evaluated, and the properties of the Δ material were tested and evaluated.

The base steel plates are all ultra-low carbon steel (C
: 0.002 to 0.004% by weight), and in order to increase or decrease the (Lankfort) value, the annealing conditions, the components added to the base steel sheet, and their content were slightly changed.
Table 2 shows the components added to the base steel sheet and the range of their content, and Table 3 shows the range of the first material characteristic values of each steel sheet.

Table 4 shows the test results for the polishing properties and coating properties of each steel plate tested and evaluated by the following methods. Further, FIG. 1 shows the relationship between the 〒 (Rank Four F) value obtained in the tensile test and the critical drawing ratio (L, D, R) obtained in the flat bottom cylindrical drawing test.

The plating properties include the GA layer basis weight, GA layer Fe concentration, GA layer phase composition, upper layer plating component composition, upper layer plating basis weight,
The surface roughness was described.

The evaluation conditions are as follows.

The bone mass of the GA layer and the Fe concentration of the GA layer are determined by electrolyzing the Fe potential and plating before performing the upper layer plating.
The amounts of eluted Zn and Fe were measured by atomic absorption spectrometry.

The phase structure of the GA layer was determined from the potential change when the GA layer was dissolved with a constant current.

- The amount of F layer plating is determined from the difference in weight before and after the upper layer plating, and the component composition is determined using an energy dispersive X-ray analyzer (E
DX).

The surface roughness was expressed as an average roughness (SRa) measured with a three-dimensional roughness meter using a 5×5 mm test piece.

Material properties were determined by tensile test (〒 value), flat bottom cylindrical drawing test (L
, D, R,), Vickers hardness, powdering resistance,
Crater resistance was tested and evaluated. The test/evaluation conditions are as follows.

In the tensile test, the JISS No. test piece was pulled at a speed of 10 mm/m.
In tensile strength, yield point (ys), tensile strength (TS
) and elongation (Eu) were determined. Also, 15 of the applied strain
The plate thickness and plate width in % were measured and the 〒 value was determined.

The flat bottom cylindrical drawing test was performed using a punch diameter of 33 mm and a drawing speed of 0.
5 mm/see, wrinkle press pressure was set to 300 kgf, Toughuni Oil Coat Z5 (Idemitsu) was used as a lubricating oil, and the usual method was used. For Vickers hardness, use the micro Vickers hardness side, excluding the η phase.
and for upper layer plating (example of the present invention), 20 to 30
Using another sample plated on a cold-rolled steel plate to a rough size of g/m2, an indenter was pressed into the surface with a load of 0.5 to 5 g, and the indentation was measured using a microscope.

Powdering resistance is determined by using a steel plate (40mm width) with R = 90.
The plating that peels off during bending back is collected with cellophane tape that has been roughly measured, and the fluorescent X-rays of Zn (irradiated X-ray generation current 1.6 mA) are
(cps) and evaluated.

Crater resistance is determined by applying cationic electrodeposition coating to the steel plate after applying phosphate-based chemical conversion treatment using a dipping method.
The voltage generated was measured, and evaluation was made based on the voltage (V).

Electrodeposition conditions were: electrode ratio (counter electrode/sample) 2, electrode spacing 40.
mm, and the electrodeposited film thickness was 20±5 μm.

The evaluation criteria for powdering resistance and cratering resistance are as follows:
It is shown in Table 1.

Table 1 As is clear from FIG. 1, the GA rust steel sheet of the present invention has high strength, D, and R, and good press formability and deep drawability. Furthermore, L, D, and R show a good positive correlation with the 〒 value.

Engraved on this, conventional GA rust steel plate black circle) tfL, D,
R is low and press molding +4 is bad. Also, L, D, R
does not depend on the material (〒 value).

Furthermore, as is clear from Table 4, the GA rust steel sheets of the present invention all have high Vickers hardness, good bowering resistance and cratering resistance, and the conventional GA rust steel sheets,
Although the powdering resistance is good, the Vickers hardness is low and there are problems with crater resistance.

(Effects of the Invention) The present invention has good press formability, sufficient deep drawability according to the material properties of the base steel plate, and has sufficient powdering resistance when press working a GA wI plate. It has the effect of being able to provide GA rusted steel plates.

[Brief explanation of the drawing]

Figure 1 shows an uninvented GA rust steel plate, a conventional GA rust steel plate,
It is a graph showing the relationship between the T value in the tensile test and the critical drawing ratio (L, D, R,) in the flat bottom cylindrical drawing test.

Claims (4)

[Claims] (1) On at least one surface of the steel sheet, there is an alloyed hot-dip galvanized layer made of an Fe-Zn alloy, and on the alloyed hot-dip galvanized layer, there is a Fe or Fe-based alloy plated layer with a Vickers hardness of 400 or more. An alloyed hot-dip galvanized steel sheet having excellent press formability. (2) The amount of deposited Fe or Fe-based alloy plating layer is 2g/
The alloyed hot-dip galvanized steel sheet with excellent press formability according to claim 1, which has a tensile strength of not less than m^2 and not more than 10 g/m^2. (3) The alloyed hot-dip galvanized steel sheet with excellent press formability according to claim 1 or 2, wherein the alloyed hot-dip galvanized layer consists of a mixed phase of δx phase and ζ phase, or a mixed phase of δx phase, ζ phase, and η phase. . (4) Fe-based alloy plating layer includes B, P, S, Ti, V,
Cr, Mn, Co, Ni, Zn, Mo, Sn, W, Re
4. The alloyed hot-dip galvanized steel sheet having excellent press formability according to any one of claims 1 to 3, which contains one or more elements selected from Pb, Pb, and Pb.