JP2848250B2 - Hot-dip galvanized steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a minimum spangle or zero spangle and a regular spangle hot-dip galvanized steel sheet having excellent peel resistance with time and corrosion resistance after processing.

[0002]

2. Description of the Related Art Today, hot-dip galvanized steel sheets are used in large quantities in automobiles, home appliances, building materials, and the like, and their application sites are widely spread. For this reason, the shapes have also been complicated and diversified, and higher quality is required.

[0003] Conventionally, a hot dip galvanizing bath composition of a steel material generally uses a mixture of about 0.2 wt% of Al and 0.1 to 0.2 wt% of Pb as a spangle sublimation element. However, such a plating bath composition causes a problem of peeling of a plating layer, and the frequency of occurrence thereof becomes remarkable particularly when the plating bath is stored in a high-temperature and high-humidity environment or indoors for a long time.

[0004] Such peeling of the plating layer over time is apt to occur in a zero spangle material and becomes remarkable when the Al and Pb concentrations in the bath exceed a predetermined amount. Alternatively, the problem can be solved by reducing the Pb concentration to a very small amount. However, it cannot produce spangled wood, and as long as there is demand for spangled wood,
A spangle-forming element such as Pb is required and does not solve the fundamental problem. This delamination over time is mainly caused by intergranular corrosion, and Pb
When low-melting metals with low solid solubility coexist, for example, Pb
Is finally solidified, and it is said that the formation of voids due to solidification shrinkage at that time facilitates the penetration of corrosive solutes, and that the noble properties of Pb promote the corrosion of the surrounding α phase or η phase.

In the case of zero spangle material, if Pb coexists, a considerable amount of Pb may solidify in the final solidification process near the base material, leaving a void in the vicinity thereof. It is considered that, when this is aged under high temperature and high humidity, α-Al is separated to cause cracks or the like due to its volume fluctuation, thereby facilitating permeation of moisture and oxygen and leading to corrosion delamination.

As one of the countermeasures, see, for example,
In Japanese Patent No. 128539, the composition of the plating coating layer is set to Al: 0.2 to 17
wt%, Sb: 0.02-0.15 wt%, and Pb: ≦ 0.02 wt%. Sb is well known as an additive element that does not cause exfoliation over time (Materials and Process vol.3 (1990) -65
5) By replacing with Pb, peeling over time can be suppressed. However, when spangle-subliming elements such as Pb and Sb are added to the Zn bath, the workability of the film is reduced. Satisfactory performance has not been obtained in the current situation where formability is being strictly required for hot-dip galvanized steel sheets.

[0007]

SUMMARY OF THE INVENTION It is a first object of the present invention to provide a galvanized steel sheet containing a minimized material, a zero spangle material, and a recurring spangle material, which is excellent in aging resistance and corrosion resistance after processing. It is.

[0008] A second object of the present invention is to reduce the corrosion resistance after processing because the deterioration of the corrosion resistance is caused by the cracks in the plating film formed without following the deformation of the base steel sheet. It is an object of the present invention to provide a hot-dip galvanized steel sheet including a minimized material, a zero spangle material, and a regular spangle material, which is difficult to form.

[0009]

SUMMARY OF THE INVENTION Temporal peeling of a minimized or zero spangle material can be prevented by adding Sb as a spangle sublimation element. However, since Sb has a greater spangle forming effect than Pb, it is necessary to limit the maximum addition amount in order to achieve zero spangle formation.

Furthermore, cracks formed in the coating during processing are caused by an increase in hardness of the coating and an increase in the (111) plane of Zn relative to the base surface when elements such as Pb and Sb are added to the Zn bath. Although it tends to be formed and tends to be improved by reducing the spangle diameter, it cannot be applied to severely processed parts.

Therefore, as a result of intensive studies, it was recognized that the formation of cracks was suppressed and the corrosion resistance of the processed portion was significantly improved by adding a predetermined amount of Ni and / or Cr to the Zn bath.

Although the mechanism of this improvement is not clear, it is not possible to use Zn if at least one of Ni and Cr coexists in the film.
It is presumed that the decrease in the (111) plane reduces the number of cracks in the coating, and that stable corrosion products are formed at the cracks.

Here, the present invention relates to Al: 0.10 to 0.30 wt%,
Sb: 0.003 to 0.10 wt%, one or two of Ni and Cr are contained in a total of 0.001 to 2.0 wt%, and the total of inevitable impurities including Pb, Cd, or Sn excluding Fe is less than 0.03 wt%. If the minimized material or zero spangle material is characterized in that the remainder has a plating coating layer of Zn
It is a hot-dip galvanized steel sheet that can produce regular spangle materials .

[0014]

The operation of the present invention will be described in detail below, together with the reasons for limiting the composition of the plating layer as described above.

Al: 0.10 to 0.30 wt% Al addition in a Zn bath is generally added to suppress a brittle Fe-Zn alloy layer formed at a steel-plating interface when a steel material is immersed and plated. If the Al concentration is less than 0.10 wt%, the formation of this Fe-Zn alloy layer cannot be suppressed, and the temporary adhesion of the plating film cannot be sufficiently ensured. Further, even if the Al concentration is increased beyond 0.30 wt%, the effect of improving the temporary adhesion is saturated, so the Al concentration in the Zn bath is limited to 0.10 to 0.30 wt%.
Of course, the Al content of the plating layer of the plated steel sheet according to the present invention obtained using this plating bath is also 0.10 to 0.10.
0.30 wt%.

Sb: 0.003 to 0.10 wt% Sb is added as a spangle sublimation element.
If it is less than wt%, spangles will not be formed sufficiently. 0.10wt
%, It is difficult to simultaneously produce zero spangle material in this bath, so the amount of Sb added is 0.003 to 0.10 wt%.
Limited to.

At this time, the reason that the inevitable impurity elements such as Pb, Cd and Sn are limited to less than 0.03 wt% in total is that any of these elements has an adverse effect on the separability with time.
This is because when the content exceeds 01 wt%, the peeling resistance with time decreases.

One or two of Ni and Cr: 0.001 to 2.0
wt% Deterioration of corrosion resistance after processing can be improved by adding Ni or Cr alone or both in the plating layer.
If the content is less than 001 wt%, the improvement effect is insufficient, and if the content exceeds 2.0 wt%, the improvement effect is saturated and the cost increases, so the plating layer concentration is limited to 0.001 to 2.0 wt%. Preferably, it is 0.01 to 1.0 wt%.

The hot-dip galvanized steel sheet having the composition of the plating layer adjusted as described above is used as a regular spangle material, a zero spangle material or a minimized spangle material according to the purpose. The process is performed through the following steps.

In the production of a plated steel sheet according to the present invention, first, a steel sheet to be plated is prepared, and
l: 0.1-0.3 wt%, Sb: 0.003-0.1 wt%, Ni and C
one or two kinds of r in total of 0.001 to 2.0 wt%, and the total of unavoidable impurities including Pb, Cd, or Sn excluding Fe is less than 0.03 wt%, and the balance is Zn.
Immerse in the bath.

In the production of a hot-dip galvanized steel sheet using the above-mentioned plating composition bath, after immersion in a Zn bath at 450 to 480 ° C., gas wiping is performed to obtain a predetermined plating film thickness to produce a regular spangle material. In this case, a predetermined spangle particle size is formed while keeping the cooling rate of the steel sheet at 15 ° C./s or less, or keeping and heating.

When a zero spangle material or a minimized spangle material is formed, it is manufactured by applying mist cooling, a phosphate aqueous solution, and zinc powder spraying, which are already known in the art. Therefore, in the present invention, the hot-dip galvanized steel sheet includes the coated steel sheet manufactured as described above, and the treatment after the hot-dip galvanizing is not particularly limited.

[0023]

EXAMPLES Next, the present invention will be further described by way of examples. In this example, an unannealed cold-rolled steel sheet after cold rolling of 0.8 mm was used as a test material for a plating base material.

After this cooled steel sheet was cut into 100 × 250 mm, solvent degreasing, water washing and drying were performed as pretreatments. The pre-treated steel sheet was subjected to 50
After performing heat treatment at 600 ° C x 10 seconds in an atmosphere of 0 ppm O ₂ + N ₂ , reduction annealing at 750 ° C x 60 seconds in a 25% H ₂ + N ₂ atmosphere, holding at 460 ° C, The basic plating bath composition with different amounts is Al: 0.1 to 0.3 wt%, Sb: 0.003 to
0.1 wt%, one or two of Ni and Cr in total 0.00
1 to 2.0 wt%, the total of unavoidable impurities including Pb, Cd, or Sn excluding Fe is less than 0.03 wt%, and the balance is
It was immersed in a Zn bath made of Zn and plated.

The adhesion amount is 100 g / m ² by the wiping process.
Was adjusted. The cooling means after the plating was slow cooling in the furnace and mist cooling. The mist cooling was adjusted by changing the amount of mist, and regular spangled material and minimized spangled material (zero spangled material) were prepared.

The regular spangle material and the minimized spangle material thus obtained were evaluated as follows. Tables 1 and 2 show the results together with the composition of the plating layer.

1) Primary Adhesion The hot-dip Zn-coated steel sheet prepared as described above was evaluated by a tape peeling area of a plating film after a ball impact test. Punch diameter / Die diameter: 0.5 / 1 inch Load: 1 kg weight Height: 50 cm Visual evaluation after tape peeling ◎: No film peeling ○: Slight film peeling is observed △: Film peeling is thin and visible over the entire surface ×: Peeling of the film is observed on the entire surface.

2) Corrosion resistance after processing A sample cut to 25 mm x 100 mm is subjected to 10R bending,
After the following cycle test, the occurrence of red rust at the bent portion was visually evaluated. 1 cycle salt spray (5% NaCl, 35 ℃ × 4hrs) ↓ Drying (60 ℃ × 2hrs) ↓ Moisture (relative humidity: 95%, 50 ℃ × 2hrs) Visual evaluation after 50 cycles ◎: No red rust observed Not possible ○: Slight red rust is observed at the edge portion △: Red rust is observed linearly in the width direction of the bent portion ×: Red rust is observed over the entire bent portion.

3) Peeling property over time A sample cut into a size of 25 mm × 100 mm was subjected to a temperature of 80 ° C. and a relative temperature of 95.
%, And a corrosion test of 240 hr was performed, and the tape was peeled off from the 2t bent portion to evaluate visually. ：: No peeling was observed at all. ：: Slight peeling was observed at the edge portion. △: Separation was observed in a linear shape in the width direction of the bent portion.

4) Evaluation of spangles In the case of slow cooling in the furnace ○: Spangles with a particle size of 10 mm or more are formed ×: No spangles with a particle size of 10 mm or more are formed In case of mist rapid cooling ○: Minimum or zero with a particle size of less than 2 mm Spangles are formed. ×: Minimum or zero spangles having a particle size of less than 2 mm are not formed.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

According to the present invention, even when a minimized and zero spangled material is used in combination with a regular spangled material, the minimized spangled material and the zero spangled material exhibiting both excellent anti-peeling property and corrosion resistance after processing. Material and regular spangle material can be manufactured.

Claims (1)

(57) [Claims] 1. Al: 0.10 to 0.30 wt%, Sb: 0.003 to 0.10
wt%, one or two of Ni and Cr in total 0.001 to
2. A minimized material or zero spangle, characterized in that the total amount of unavoidable impurities including Pb, Cd, or Sn excluding Fe is less than 0.03% by weight, and the balance has a plating coating layer composed of Zn. Hot-dip galvanized steel sheet capable of producing materials and regular spangle materials.