JPH03243755A - Organic composite alloying hot dip galvanized steel sheet excellent in press formability - Google Patents

Abstract

PURPOSE:To produce an organic composite alloying hot dip galvanized steel sheet excellent in press formability by successively coating a steel sheet with an alloying hot dip galvanizing layer in which Fe content, the thickness of gamma-phase in the interface between ferrite and plating, the main peak of X-ray diffraction, and coating weight are specified, respectively, and an organic layer of specific thickness. CONSTITUTION:An alloying hot dip galvanizing layer which has a composition consisting of 6-13% Fe and the balance Zn and in which gamma -phase in the interface between ferrite and plating layer is regulated to <=1.0mu and the main peak of the X-ray diffraction of plating layer is zeta-phase and, further, coating weight is regulated to 20-100 g/m<2> is formed on a steel sheet. Further, one side or both sides of this steel sheet having the above plating layer are coated with organic film (epoxy resin, etc.) to 0.2-3.0mu thickness. By this method, the organic composite alloying hot dip galvanized steel sheet having satisfactory powdering resistance and flaking resistance and excellent in press formability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an organic composite alloyed hot-dip galvanized steel sheet that has excellent press formability and satisfies both powdering resistance and flaking resistance.

Alloyed hot-dip galvanized steel sheet is produced by heating the hot-dip galvanized steel sheet after plating to diffuse the iron in the base steel sheet into the coating layer.
Although it is an iron-zinc alloy, it has superior corrosion resistance compared to galvanized steel sheets, so it is widely used as a material for automobiles, building materials, home appliances, etc.

(Conventional wave lf) In recent years, due to the demand for improved corrosion resistance, there has been a strong demand for thicker alloyed hot-dip galvanized steel sheets.

However, since alloyed hot-dip galvanized steel sheets are manufactured by thermal diffusion treatment, as the coating weight increases, the iron concentration gradient in the coating layer increases, and a brittle r-phase with a high Fe concentration forms at the interface with the base iron. In the vicinity of the surface of the -direction plating layer, a ζ phase with a low Fe concentration or, in extreme cases, an unalloyed η phase may remain.

If the r-phase is thick, powdering, which causes the plating layer to peel off during press processing, is likely to occur, resulting in scratches caused by plating peeling powder on the product, resulting in negative effects such as lower yields and lower efficiency due to frequent mold cleaning. Get out.

On the other hand, if the ζ phase is thick or the η phase remains on the surface of the plating layer, the sliding resistance of these phases is large, and mold galling is likely to occur during pressing, resulting in so-called flaking and damage to the mold bead. This also causes a decrease in yield and efficiency in the pressing process.

Such thick coating amount (adhesion amount of 45 g/rrr or more)
Alloyed hot-dip galvanized steel sheets are required to satisfy both powdering resistance and flaking resistance during the pressing process.

In addition, at low coating weights, alloyed hot-dip galvanized steel sheets with excellent press formability have been manufactured and put into practical use by forming a plating layer mainly composed of the δ1 phase, but improvement in formability continues to be difficult. desired.

(Problem to be Solved by the Invention) In the conventional method for producing an alloyed hot-dip galvanized steel sheet, the effective AQ amount (An%-Fc%) is set in a hot-dip zinc bath to, for example, 0.
The copper strip is plated by passing it through a bath containing 0.09 to 0.15%, and after adjusting the basis weight by gas wiping, etc., the strip is passed through an alloying furnace until the metallic luster on the plated surface disappears, that is, until the surface is alloyed. The manufacturing process was carried out by heat-treating until the alloying was completed and immediately cooling to control the degree of alloying (Japanese Patent Application Laid-open No. 1983
-223174), the composition of this plating layer is F
It consists of e: 8-13%, Afi: 0.25-0.35%, and the balance Zn.

However, when hot-dip galvanized steel sheets with a basis weight of 45 g/m or more are alloyed in this process, r
The thickness of the phase is, for example, about 1 to 3 μm, and the powdering resistance is not sufficient.

Therefore, the effective amount of AQ in the bath was reduced to about 0.10% or less, and the Fe-AQ alloy layer formed in the bath was made thinner.
- By making the formation of Zn alloy phase relatively easy,
Alloyed hot-dip galvanized steel sheets can be produced by heat treatment at lower temperatures. The composition of this plating layer is Fe:6
~11%, AQ: 0.05~0.25%, and the remainder Zn. However, when the basis weight is 45g/nf or more.

“Although there is a condition that the phase thickness is 1 μm or less, the η phase and ζ phase tend to remain on the surface of the plating layer, and flaking resistance is not sufficient.

In order to solve these drawbacks, for example, the formation of the r phase generated in the lower layer of the plating layer (boundary with the base steel) is suppressed as much as possible, and the upper layer is made of a plating layer consisting of the η phase, δ1 phase, and ζ phase, and It is disclosed that iron plating is applied on the molten alloy layer (
However, the current situation is that satisfactory results have not yet been obtained.

(Means for Solving the Problems) Therefore, as a result of intensive study, the present inventors found that powdering,
We have found an alloyed hot-dip galvanized steel sheet that satisfies both flaking and flaking properties.

The present invention to solve the above problems includes Fe6 to 13%,
The composition consists of the remainder Zn, and the F at the base metal-plating interface
The organic film is coated on an alloyed hot-dip galvanized layer with a phase of 1.0 μm or less, the main peak of the X-ray diffraction of the plating layer being a ζ phase, and a basis weight of 20 to 100 g/g.
This is an organic composite alloyed hot-dip galvanized steel sheet with excellent press formability, characterized by having a QIL+m coated plating layer on one or both sides.

(Function) Although the ζ phase has high sliding resistance and is inferior in flaking properties, it is stretchable and does not easily cause re-powdering. Further, in the case of only one bending process, it is effective to prevent the propagation of cracks occurring in the lower layer. A feature of the present invention is that it satisfies both powdering resistance and flaking resistance by taking advantage of the advantages of this ζ phase and reducing the disadvantageous sliding resistance by the lubricity of the organic film coated on the upper layer. be. Also,
Another major feature is that by making the plating layer mainly composed of the ζ phase with a low Fe%, the formation of the r phase, which is a major cause of powdering, is suppressed, and the presence of the organic film improves corrosion resistance. Note that the present invention improves the press formability of alloyed hot-dip galvanized steel sheets not only in thick coatings but also in a wide coating weight range of 20 to 188 g/n (20 to 188 g/n).

The base plated steel sheet of the present invention has, for example, Aa: 0.003 to
When plating is applied in a 0.13% hot-dip galvanizing bath and then heat-treated, heat the plate at a temperature of 520 to 470°C within 15 seconds, and heat-treat at a lower temperature as the amount of AQ in the bath decreases. Therefore, it is possible to reliably manufacture the product mainly in the ζ phase. Confirmation that the ζ phase is the main component can be carried out by electrolytic peeling or cross-sectional etching, but these methods are not preferred because the results obtained vary depending on the conditions. In the present invention, the ζ-phase main component refers to the main peak of X-ray diffraction, which is relatively easy to understand and allows the structure of the plating layer to be determined.

Next, the limited range of each component will be explained.

Fe%: If Fe is less than 6%, the η phase tends to remain on the surface of the plating layer, and if Fe exceeds 13%, the F phase tends to exceed 1 μm, which is not preferable.

"Phase: It is preferable that the F phase is 1 μm or less in order to improve powdering resistance. If it exceeds 1 μm, the powdering resistance will deteriorate, especially if the basis weight is 45 g/rr? coming out.

Organic film: The presence of an organic film can suppress aggregation of plated metal on the mold and improve flaking resistance.

The thickness of the organic film is preferably 0.2 to 3.0 μm.

If it is less than 0.2μ1, it is difficult to completely cover the lower plating layer, and adhesion of the mold from the exposed portion of the lower layer may occur, which is not preferable. If it exceeds 3.0 μm, it is not preferable because it tends to deteriorate the electrodepositability, which is an important characteristic required for rust-proofing steel sheets for automobile bodies, which is the main application of alloyed hot-dip galvanized steel sheets. It should be noted that the resin for the organic film is preferably an epoxy resin that has excellent adhesion to the steel sheet, but since the surface condition of an alloyed hot-dip galvanized steel sheet is rich in irregularities, there is no problem in adhesion with any resin. Moreover, it does not particularly matter whether it is solvent-based or water-based. The presence of various pigments and additives in the organic film is effective as long as they do not impair lubricity. Further, addition of wax is preferable because it improves lubricity. Furthermore, chemical conversion treatments such as phosphate treatment and chromate treatment are effective as pre-painting treatments to improve the adhesion of the organic film, and these also fall within the scope of the present invention. The method of coating the organic film is not particularly limited, but commonly used methods such as a roll coater method are easy.

Coating amount: The thickness of the alloyed hot-dip galvanizing layer of the present invention is 20 to 100 g/rr in terms of basis weight! is the applicable range. 2
If it is less than 0 g/rd, there is a problem in corrosion resistance.

If it exceeds 100 g/rd, it is practically difficult to plate the r phase with a thickness of 1 μm or less.

Although only Fe is specified as the composition of the alloyed hot-dip galvanized layer, other components 1, such as AQ, Pb, and Cd.

Sn, In, Li, Sb, As, Bi, M
g, La, Ce.

Even if small amounts of at Cr, Mn, P, S, O, etc. are added to Ti, Zr, Ni, or unavoidably mixed, the effects of the present invention essentially remain the same. In particular, regarding AQ, in current processes, around 0.1% of AQ is added to the plating bath to control plating and alloying, and it is inevitably mixed into the plating layer. As long as the plated layer is mainly composed of the ζ phase, the amount of AQ has no effect on the present invention. Also.

Even in a thermal diffusion alloyed material of an electrogalvanized material in which Al1 is not present, the effects of the present invention can be essentially achieved if the alloy phase is mainly composed of the ζ phase.

The plating layer of the present invention is preferably applied to both sides in the case of a rust-preventing steel plate with a coating weight of 20 to 100 g/rrr on both sides. In the case of a steel plate with differential thickness plating, it can be applied only to the thickened surface.In the case of a single-sided plated steel plate, it can of course be applied only to the plated surface.

(Example) Next, examples of the present invention will be listed together with comparative examples.

The material for plating is CC-AQ-k steel (0.8t
Immediately after plating in a non-oxidation furnace type continuous hot-dip galvanizing line, heat alloying treatment was performed continuously in an alloying treatment furnace.

The effective AQ in the plating bath is 0.10%, and the F in the plating layer is
The e concentration was manufactured by appropriately selecting the heating conditions of the alloying furnace.

Plating was carried out under the conditions that the plate passing speed was 40 to 70 m/min and the immersion time was 2 to 5 seconds. In addition, coating type chromate (chromic anhydride 38 g/Q) is applied on the painting line.
An organic film (solvent type epoxy paint: bisphenol type) was applied at a thickness of 0.1 μm to 5 μm.

Next, the method for testing the workability of the plating layer will be described.

(1) Powdering resistance test Before processing, apply vinyl tape to the bent part, perform bending with the tape side on the inside (2T bending), remove the tape again, and check that the plating layer adheres to the tape. Judgment was made based on the degree of blackening.

(Good) 0-0-Δ-x (Poor) (0,0 means no problem in practical use) (2) Flaking resistance test Evaluation was performed by tension molding with a square bead. Bonchidai Iruma 2.0kgf/aJ (Plug size 0.7 x 75X
280 m), and then the test piece is passed through the bead without tension. 200 sheets were repeatedly molded, and the degree of deposition of the plating layer metal on the steel plate or bead portion was relatively evaluated.

(Good) 〇−〇−△−× (Poor) (0, 0 means no problem in practical use) (3) Actual press test A part of the fender of an ordinary passenger car was molded using an actual press. 300 sheets were repeatedly molded, and the degree of adhesion and accumulation of the plated metal on the steel plate or the breath mold was evaluated relative to it. For evaluation, tape was pasted on each part.

Judgment was made based on the degree of blackening of the metal powder transferred to the tape after peeling off.

(Good) O-0-Δ-x (Poor) (0,0 means no problem in practical use) The test results for each of the above are shown in Table 1 along with comparative examples.

(4) Electrodeposition coating test After standard chemical conversion treatment of Bt3020 (manufactured by Nippon Barker), PT-U2O5 (manufactured by Nippon Paint) was electrodeposited at 30 μι for 3 minutes at 2°OV, and the appearance after painting was evaluated.

(Good) 0-0-Δ-× (Poor) (0,0 means no practical problem) (Effect of the invention) As explained above, the plated steel sheet of the present invention satisfies both powdering property and flaking property. This will expand the uses of alloyed hot-dip galvanized steel sheets and will have great industrial effects.

Claims (1)

[Claims] The composition consists of 6 to 13% Fe and the balance Zn, the Γ phase at the base metal-plating interface is 1.0 μm or less, the main peak of the X-ray diffraction of the plating layer is the ζ phase, and the basis weight is 20 to 100.
g/m^2 alloyed hot-dip galvanized layer, which is coated with an organic film of 0.2 to 3.0 μm on one or both sides, and has excellent press formability. Organic composite alloyed hot-dip galvanized steel sheet.