JPH04360A - Galvannealed steel sheet excellent in workability - Google Patents

Abstract

PURPOSE:To increase the range of use of a galvannealed steel sheet by coating a galvannealed layer contg. a specified percent of Fe and GAMMA and xsi phases in a specified METSUKE (unit) wt. with a specified amt. of a zinc phosphate film. CONSTITUTION:A galvannealed layer is applied on a steel sheet at 20-100g/m<2> METSUKE wt. The galvannealed layer contains 6-13% Fe and the balance Zn, the thickness of the GAMMA phase at the base iron-galvannealed layer interface is controlled to <=1.0mum, and the main peak of the galvanizing layer in X-ray diffraction is a phase. One or both surfaces of the steel sheet having the galvannealed layer are coated with a zinc phosphate film at 0.2-5.0g/m<2>. Consequently, the powdering and flaking properties of the galvannealed steel sheet are satisfied.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an alloyed hot-dip galvanized steel sheet with excellent workability, and in particular, powdering resistance and powdering resistance which are important for alloyed hot-dip galvanized steel sheets. Both flaking resistance is satisfactory.

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.

[Prior Art] In recent years, there has been a strong demand for thicker alloyed hot-dip galvanized steel sheets due to the demand for improved corrosion resistance. 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 η phase with a high Fe concentration forms at the interface with the base steel. On the other hand, near the surface of the plating layer, a ζ phase with a low Fe concentration or, in extreme cases, an unalloyed η phase may remain.

If the η 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 increased frequency of 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, so mold galling is likely to occur during press processing, resulting in so-called braking and damage to the mold bead. This also causes a decrease in yield and efficiency in the pressing process.

Such alloyed hot-dip galvanized steel sheets with a thick coating weight (coating weight of 45 g/m' or more) are required to satisfy both powdering resistance and flaking resistance during the pressing process.

In addition, at low area weights, alloyed hot-dip galvanized steel sheets with excellent workability have been manufactured and put into practical use by forming a plating layer consisting mainly of the δ1 phase, but improvements in formability have not been achieved. continues to be desired.

[Problems to be Solved by the Invention] Conventional methods for manufacturing alloyed hot-dip galvanized steel sheets effectively reduce the amount of Al (A4%-Fe%) during hot-dip galvanizing, for example, to 0.
The steel strip is plated by passing it through a steel strip with an addition adjustment of 0.09 to 0.15%, and after adjusting the basis weight by gas wiping etc., it is passed through an alloying furnace and alloyed until the metallic luster on the plated surface disappears, that is, until the surface is alloyed. It was manufactured by heat-treating until the completion of the alloying process, and immediately cooling it to control the degree of alloying.
-223174). The composition of this plating layer is F
e: 8 to 13%, A4: 0.25 to 0.35%, and the remainder Zn.

However, when hot-dip galvanized steel sheets with a basis weight of 45 g/m' or more are alloyed in this process, the thickness of the η phase formed at the interface between the base metals is, for example, about 1 to 3 μm, and the powdering resistance is insufficient. .

Therefore, the effective amount of Al in the Rakuchu was reduced to about 0.10% or less, and the Fe-Aj2 alloy layer formed in the Rakuchu was made thinner.
- By making the generation of the In alloy layer 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%, Afl: 0.05 to 0.25%, and the remainder Zn. However, when the basis weight is 45 g/m2 or more, although there is a condition that the thickness of the η phase is 1 μm or less, the η phase and the ζ phase tend to remain on the surface of the plating layer, and the flaking resistance is not sufficient.

In order to solve these drawbacks, for example, the formation of the η 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 problem] 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 for solving the above problems is based on Fe 6-1
3%, the balance being Zn, the η phase at the base steel-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/m2. A zinc phosphate film is applied on top of the alloyed hot-dip galvanized layer.
It is an alloyed hot-dip galvanized steel sheet with excellent workability and has a plating layer coated with 2 to 5.0 g/m" on one or both sides.

[Action: Although the ζ phase has high sliding resistance and is inferior in braking performance, it is stretchable and powdering is difficult to occur. In addition, in the case of only bending, it is effective to prevent the propagation of cracks that occur in the lower layer. By taking advantage of the advantages of this ζ phase and overcoming the disadvantage of sliding resistance with the lubricity of the hard zinc phosphate film on the upper layer, the present invention satisfies both powdering resistance and flaking resistance. It is a characteristic. In addition, by making the plating layer mainly consist of the ζ phase with low Fe%, the formation of the r layer, which is a major cause of powdering, is suppressed, and the presence of the zinc phosphate film provides excellent paintability even without pretreatment. Another important feature is that it is effective. Note that the present invention is applicable not only to thick coatings but also to coatings with a coating weight of 20 to 100 g/m.
2, which improves the workability of alloyed hot-dip galvanized steel sheets over a wide coating weight range.

The base plated steel sheet of the present invention is, for example, A4: 0.003~
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 shoulder in the bath decreases. Therefore, it is possible to reliably manufacture the product mainly in the ζ phase. Electrolytic stripping and cross-sectional etching methods can be used to confirm that the ζ phase is the main component, but the results obtained vary depending on the conditions.
Undesirable. In the present invention, the term ζ-phase mainly 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. If Fe exceeds 13%, the r phase tends to exceed 1 μm, which is not preferable.

"Phase" It is preferable that the phase is 1 μm or less in order to improve powdering resistance. If it exceeds 1 μm, it is especially
If it exceeds 5 g/m2, powdering resistance deteriorates, and workability is adversely affected.

Zinc phosphate film The presence of the zinc phosphate film can suppress adhesion of plated metal to the mold and improve flaking resistance. The adhesion amount of the zinc phosphate film is preferably 0.2 to 5.037 m2. If it is less than 0.2 g/m2, it is difficult to completely cover the lower plating layer, and adhesion from the exposed portion of the lower layer to the mold may occur, which is not preferable. If it exceeds 5.037 m2, the zinc phosphate film is hard and the workability of the zinc phosphate film deteriorates, which is not preferable. The zinc phosphate film is made of phosphofluorite (Zn2Fe
(PO4)2'4H20) or hopite (In3
(PO4)2.4H70) alone or in a mixed composition, and the composition ratio is not particularly limited. In addition, N1. Even if elements such as Mn are contained, the same effect on workability can be achieved, so the addition of these elements also falls within the scope of the present invention. The method for forming the zinc phosphate film is not particularly limited, but the zinc phosphate film can be obtained, for example, by a commonly used immersion type film forming treatment.

The thickness of the alloyed hot-dip galvanized layer of the present invention is in the range of 20 to 100 g/m'' in terms of basis weight.2
If it is less than 0 g/m2, there is a problem in corrosion resistance.

If it exceeds 100 g/m2, 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 such as Al, Pb, and Cd may also be included.

Sn, In, Li, Sb, As, Bi, M
g, La, Ce, TiZr, Ni, Co,
Even if a small amount of Cr, Mn, P, S, 0, etc. is added or unavoidably mixed, the effects of the present invention essentially remain unchanged. In particular, regarding A2, in current processes, around 0.1% of A2 is added to the plating layer to control plating and alloying, and it is inevitably mixed into the plating layer. As long as the plating layer is mainly composed of ζ phase, the amount of Al has no effect on the present invention. Furthermore, the effect of the present invention can be exerted in terms of wood quality even in the case of thermal diffusion alloying material of electrogalvanized material without AN, which becomes an alloy phase mainly composed of ζ phase.

The plating layer of the present invention is preferably applied to both sides of a rust-preventing steel plate with a coating weight of 20 to 10,037 m2 on both sides, but it is preferable to apply the plating layer on both sides of a steel plate with a differential thickness of 20 to 10,037 m2 on one side and a small coating amount on the other side. In some cases, it may be applied only to thick surfaces. In the case of single-sided plated steel sheets, this is of course applied only to the plated side.

[Examples] Next, examples of the present invention will be described together with comparative examples. The material for plating is CC-AM- steel (0.8t x 1000
Immediately after plating, heat alloying treatment was performed continuously in an alloying treatment furnace in a non-oxidation furnace type continuous hot-dip galvanizing line.

The effective F9 in the plating bath is 0.10%, and the F in the plating layer is 0.10%.
The e concentration was manufactured by appropriately selecting the heating conditions of the alloying furnace.

Plating was carried out at a plate passing speed of 40 to 70 m/min and an immersion time of 2 to 5 seconds. Thereafter, a zinc phosphate coating was applied at a rate of 0.1 g/m2 to 7 g/m2.

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) Poor to ◎-O-81×) (◎, O means no problem in practical use) (2) Flaking resistance test Evaluated by tension molding with a square bead. 2.0kgf/cm2 between punchy soybeans (plug size 0.7 x 7
5 x 280 mm) and then pull the test piece to pass through the bead. 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-Δ-× (Poor) (◎, O means no problem in practical use) (3) Actual press test A fender part of an ordinary passenger car was formed 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 press mold was evaluated relative to each other. The evaluation was based on the degree of blackening of the metal powder transferred to the tape after attaching tape to each area and removing it.

(Good) ◎-〇-Δ-× (Poor) (◎ and ○ indicate no practical problem) The test results for each of the above are shown in Table 1 along with comparative examples.

(Effects of the Invention) As explained above, the plated steel sheet of the present invention satisfies both powdering properties and flaking properties, expands the uses of alloyed hot-dip galvanized steel sheets, and has great industrial effects.

4 others

Claims (1)

[Claims] 1. A composition consisting of 6 to 13% Fe, the balance being Zn,
The Γ phase at the base metal-plating interface is less than 1.0 μm, the main peak of the X-ray diffraction of the plating layer is the ζ phase, and the phosphorus is applied on the alloyed hot-dip galvanized layer with a basis weight of 20 to 100 g/m^2. An alloyed hot-dip galvanized steel sheet with excellent workability, having a plating layer coated with an acid zinc film of 0.2 to 5.0 g/m^2 on one or both sides.