JP2001355054A - Hot dip zinc-aluminum alloy plated steel sheet excellent in workability and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot dip zinc-aluminum alloy plated steel sheet improved in the workability of the conventional zinc-aluminum alloy plated steel sheet. SOLUTION: In this steel sheet, the surface of the steel sheet is provided with a plated layer having a composition containing, by mass, 3 to 18% Al, 2.1 to 10% Mg and Si by 1 to 50% of the Mg content, if required, containing <=1% Fe, and the balance Zn with unavoidable impurities, and further, the plated layer is incorporated with Si-based substances with an area of >=100 μm2 by 6×103 pieces per the unit cross-sectional area of the plated layer. If required, the surface of the plated layer is coated with an inorganic oxide film or an organic resin film as well. In the method for producing the hot dip zinc-aluminum alloy plated steel sheet, the plating bath temperature is controlled to <480 deg.C, and, after plating, cooling is continuously performed at a cooling rate of >=10 deg.C/s, by which the plated layer is incorporated with Si-based substances of >=100 μm2 by <=6×103 pieces per the unit cross-sectional area of the plated layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip zinc-aluminum alloy-coated steel sheet having excellent workability and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, the use of surface-treated steel sheets has been expanding in order to cope with prolonged service life of automobiles, household electric appliances, building materials and the like. In particular, Zn-5 wt% Al hot-dip coated steel sheets are used mainly for building materials and the like because of their excellent corrosion resistance as compared with conventional hot-dip galvanized steel sheets. In recent years, Zn—Al—Mg plated steel sheets have been developed, and further improvement in corrosion resistance has been attempted. However, the workability of the plating film of the Zn—Al-based alloy-plated steel sheet is not always sufficient, and there are cases where corrosion resistance is poor in portions subjected to severe processing. This is because an Fe-Al alloy layer is formed at the interface between the base material and the plating film,
Since this layer is hard and brittle, powdering or the like may occur at the time of press working or the like, and the processed part may be a starting point of corrosion.

[0003] As a technique for improving such a point, Fe
In order to suppress the alloying reaction of Al-Al, a technique of plating by adding Si to a plating bath of a Zn-Al alloy is disclosed in
-177446, Fe-Al
And formation of an intermetallic compound mainly composed of Fe-Al-Si cannot be suppressed, and the workability of the film is not sufficient. Also, Japanese Patent Application Laid-Open No. Hei 9-143657 discloses that
Ti, B, Zn-Al-Mg plating containing 1.5%
Although a technique for suppressing micro cracks by adding a small amount of Si or the like is disclosed, there are problems such as insufficient corrosion resistance and severe generation of bath dross. In addition, Japanese Patent Application Laid-Open
176238 discloses that Al in a plating bath is 20-80.
% And Fe-Al by limiting the steel components, especially the amounts of Si and P.
Although a technique for suppressing the Si reaction and obtaining good workability is described, there is a problem that the Al concentration is too high, so that it cannot be manufactured on a normal plating line, resulting in high cost. Have.

[0004]

In view of such circumstances, it is an object of the present invention to provide a hot-dip zinc-aluminum alloy coated steel sheet which has improved workability of a conventional zinc-aluminum alloy coated steel sheet. .

[0005]

It is important to suppress the formation of Fe-Al and Fe-Al-Si intermetallic compounds in the deterioration of workability of Zn-Al alloy plating. Thus, the present inventors have conducted intensive studies on the elements to be added to the plating bath, and found that the addition of Mg is effective in suppressing the deterioration of the workability. As a result, the formation of the intermetallic compound is suppressed, and the plating adhesion is improved. In addition, when the existence state of Si in the plating was investigated, it was found that the Si-based material in the plating layer was small and dispersed in a wide variety of areas such as metal Si, SiO ₂ , and Mg ₂ Si. Have better plating adhesion and better slidability. This is presumably because the concentration of the Si-based material decreases in the periphery of the large-sized one, and the difference in the sliding resistance in the surface layer in particular increases.

That is, the gist of the present technology is as follows.

(1) Al: 3% by mass% on the surface of the steel sheet
A steel sheet having a plating layer composed of 18%, Mg: 2.1 to 10%, the balance being Zn and inevitable impurities, wherein the plating layer further contains Si in an amount of 1 to 50% of the amount of Mg,
A hot-dip zinc-aluminum alloy plated steel sheet excellent in workability, characterized by containing not more than 6 × 10 ³ Si-based substances having an area of 100 μm ² or more per unit cross-sectional area of a plating layer.

(2) A hot-dip zinc-aluminum alloy coated steel sheet excellent in workability, characterized in that the steel sheet according to (1) further contains Fe: 1% or less.

(3) The plating layer of the steel sheet according to (1) or (2) further contains at least one of Pb and Sn in an amount of 0.01 to 2.0%. Hot-dip zinc-aluminum alloy plated steel sheet with excellent workability.

(4) 70 mg of an inorganic oxide film on the plating layer of the steel sheet according to any of (1) to (3) above.
A hot-dip zinc-aluminum alloy-plated steel sheet having excellent workability, characterized in that the thickness is in the range of ² g / m ^{2 to 2} g / m ² .

(5) 100 mg of an organic resin film on the plating layer of the steel sheet according to any of (1) to (3) above.
A hot-dip zinc-aluminum alloy-coated steel sheet having excellent workability, characterized in that the steel sheet has a ratio of / g ^{2 to} 2.0 g / m ² .

(6) When manufacturing a hot-dip zinc-aluminum alloy-plated steel sheet, by setting the plating bath temperature to be lower than 480 ° C., an Si-based material having an area of 100 μm ² or more in the plating layer has a unit sectional area of the plating layer. 6 × 10 ³ per
The method for producing a hot-dip zinc-aluminum alloy-coated steel sheet according to any one of the above (1) to (5), wherein the steel sheet contains not more than one piece.

(7) In producing a hot-dip zinc-aluminum alloy-coated steel sheet, the plating bath temperature is set to less than 480 ° C., and after plating, it is continuously cooled at a cooling rate of 10 ° C./s or more, so that the plating layer S with an area of 100 μm ² or more
6. A hot-dip zinc-aluminum alloy coated steel sheet having excellent workability according to any one of the above (1) to (5), characterized by containing not more than 6 × 10 ³ i-based substances per unit sectional area of the plating layer. Manufacturing method.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
First, the elements contained in the plating layer will be described.
Al in the plating layer is added for improving corrosion resistance.
If it is less than 3%, the corrosion resistance is inferior. If it exceeds 18%, the effect of improving the corrosion resistance is saturated and the workability is deteriorated.
8%.

In general, Mg is often added because it has an effect of improving corrosion resistance.
i Added to suppress the formation of intermetallic compounds.
If it is less than 2.1%, the formation of the Fe-Al-Si intermetallic compound cannot be suppressed, and the plating adhesion deteriorates. If it exceeds 10%, dross often occurs and plating becomes difficult.

Si is an important element in the present invention, and is added for improving workability. If the amount of added Mg is less than 1%, both the plating adhesion and the slidability deteriorate. on the other hand,
If the amount of Mg exceeds 50%, the bath dross becomes too large.

Regarding the size of the Si-based material in the plating layer, if there is one having a size exceeding 100 μm ² , the adhesion at the periphery tends to be deteriorated. If the number exceeds × 10 ^3, both the plating adhesion and the slidability deteriorate, so the number of Si-based substances having a thickness of 100 μm ² or more was set to 6 × 10 ³ / mm ² or less.

Fe is mixed into the plating bath as an impurity from a plating pot material or a steel plate to form an Fe—Al—Si intermetallic compound, which has an adverse effect on plating adhesion, and that Si in the plating layer is liable to dross out. Therefore, the effect of improving the slidability deteriorates, so the content is set to 1% or less.

Pb and Sn are elements that are added as needed to improve the slidability, and at least 0.01% must be added to improve the slidability. If it exceeds 2%, the adhesion of the plating deteriorates.
And

Next, the manufacturing method will be described. There is no particular limitation on the plating base plate to be used.
It can be used regardless of products such as hot rolled pickling material and cold rolled material. The present technology can be applied to plating without depending on a manufacturing method such as a Sendzimir type, a flux type, or a pre-plating type. If the plating bath temperature is too high, Fe is mixed into the plating bath from the steel plate, the plating pot or the plating equipment, and Fe-Al or Fe-Al-Si intermetallic compound is generated, and the plating adhesion is deteriorated. In addition, it leads to corrosion of the plating pot and plating equipment. To suppress this, the plating bath temperature is set to less than 480 ° C. The cooling rate after plating is set to 10 ° C./s or more in order to suppress local precipitation of the Si-based material and secure plating adhesion and slidability.
In addition, there is no particular problem even when an aqueous post-treatment of blackening resistance and corrosion resistance is performed, and, of course, temper rolling may be performed.

In particular, on the plated layer after plating,
Coating at least one or more inorganic oxides selected from the oxides of i, Mg, Zr, Mo, Ce, and Ca further improves the effects of the present invention. In this case, there is no problem in forming a composite oxide such as a phosphate. If the sum of these is less than 70 mg / m ² , there is no slidability improvement effect. If the sum of them exceeds ² g / m ² , the slidability is rather deteriorated, and therefore 70 mg / m ^{2 to 2} g / m ^2.
Range.

Alternatively, coating an organic resin film instead of this also improves the effect of the present invention. 100mg / m
^If it is less than ² , this effect is small, and if it exceeds ² g / m ² , the workability is rather deteriorated, so that 100 mg / m ^{2 to 2} g / m ²
m ² . The organic resin may be in any form of a water-based resin, a solvent-based resin, a powder-based resin, or a non-solvent-based resin. The term “aqueous resin” used herein includes not only water-soluble resins but also resins that are inherently water-insoluble but can be finely dispersed in water such as emulsions and suspensions (water-dispersible resins). . The resin that can be used as the organic resin is not particularly limited, but includes a polyolefin resin, an acrylic olefin resin, a polyurethane resin, an acrylic resin, a polycarbonate resin, an epoxy resin, a polyester resin, an alkyd resin, and a phenol resin. Resins and other heat-curable resins can be exemplified, and it is more preferable that the resin be crosslinkable. The organic resin may be used as a mixture of two or more kinds or copolymerized. If necessary, a crosslinking agent such as various melamine resins and amino resins may be added. There is no problem in adding fine silica or a lubricant in addition to the organic resin.

The coating methods for forming these inorganic oxide or organic films include spray, curtain,
Any method such as a flow coater, a roll coater, a bar coater, brush coating, dipping, and air knife drawing may be used. Further, the ultimate baking temperature is desirably 80 to 250 ° C. If the temperature is lower than 80 ° C., the corrosion resistance is reduced because the water in the paint is difficult to completely volatilize. If the temperature exceeds 250 ° C., the alkyl portion of the organic resin undergoes denaturation such as thermal decomposition or the film hardens too much. It is not preferable because corrosion resistance and workability are reduced. 70-160 ° C is more preferred. The drying equipment is not particularly limited, but a method using hot air blowing, an indirect heating method using a heater, a method using infrared rays, a method using induction heating, and a method using these in combination can be adopted. In addition, depending on the type of the organic resin used, the resin can be cured by energy rays such as ultraviolet rays and electron beams.

[0024]

EXAMPLES (Example 1) A 0.8 mm-thick SPCC plate produced by melting a steel slab and producing a thin steel plate by a usual method was used as a plating original plate. The plating was performed by heating, annealing and plating in a Sendzimir-type continuous hot-dip galvanizing line. The annealing atmosphere was a 10% hydrogen, 90% remaining nitrogen gas atmosphere, and the dew point was -30 degrees. The annealing temperature is 730 ° C. and the annealing time is 3 minutes. The plating bath is Al: 2.5 to 20%,
Mg: 1.5 to 10.5%, Si: 0.5 of the added amount of Mg
% To 60%, Fe: 0 to 1.5%, residual zinc and unavoidable impurities, using a plating bath adjusted to a plating bath temperature of 390.
Plating was performed at ５００500 ° C. After plating, the amount of plating was adjusted to 100 g / m ² per side by ordinary wiping. After plating, temper rolling was performed at 1%, and then chromate treatment was performed at an adhesion amount of ²⁰ to 30 mg / m2.
For the Si-based material of the plated steel sheet manufactured in this way, EPMA observation of the plating cross section was performed, and an arbitrary 100
Observation was carried out for each μm square visual field, and the number of those having a thickness of 100 μm ² or more was counted and expressed as the number per plating layer cross-sectional area of the plating cross section. Table 1 shows the obtained plated steel sheets.

The dross of the plating bath was visually determined, and was evaluated as good when the dross was good, x when the dross was slightly observed, and o. For workability evaluation, an impact test and a slidability test were performed. The adhesion test is performed by an impact test, using a die with a diameter of 12 mm and a punch with a diameter of 12 mm, dropping a weight of 1.6 kg from a height of 1 m, peeling off the overhang-formed part with adhesive tape, and plating. The degree of peeling of the film was visually determined. When no peeling of the film was observed, the result was evaluated as ○ (pass), when the powdery peeling was partially observed, and when the peeling was observed, ×.
Δ and × were rejected.

The sliding test was a cylinder cup drawing test. Punch diameter 50φ, punch shoulder 5R, die shoulder 5
R, draw ratio 2.1, oilless oil, molding speed 5mm / mi
n was set, and 100 squeezing operations were continuously performed, and the cup and the mold after the test were visually observed to determine the slidability. When plating peeling or adhesion of the cup to the mold did not occur, ○ (pass); for powdery peeling, △; for adhesion of the cup to the mold, the cup was broken. X, and × and x were rejected.

Table 1 shows the results. No. No. 1 to No. Numeral 30 is an example of the present invention and has good workability. N
o. 31 to No. 31 No. 44 is a comparative example. No. 31 has too much Al. Sample No. 32 has poor workability due to too little Mg. No. No. 33 has too much Mg and therefore has a lot of dross and is rejected. No. 34 to No. 34. 36
Has poor workability because Si is too small. No. 37 is S
Since i is too large, dross is large and workability is poor. No. No. 38 to No. 38. In No. 40, the workability is poor because of too much Fe. No. 41, no. Sample No. 42 has poor workability because the cooling speed is too small and the amount of Si-based material is too large. N
o. 43, no. 44 has poor workability because the bath temperature is too high.

[0028]

[Table 1]

(Example 2) A 0.8 mm-thick SPCC plate obtained by melting a steel slab to produce a thin steel plate by a usual method was used as a plating original plate. As for the plating, those having a plating composition as shown in Table 2 were heated, annealed, and plated in a continuous hot-dip galvanizing line of Sendzimir type. Annealing atmosphere is 10%
The atmosphere was a gas atmosphere of hydrogen and 90% nitrogen gas with a dew point of -30 degrees. The annealing temperature is 730 ° C. and the annealing time is 3 minutes.
After plating, reduce the coating weight by 90% by ordinary wiping.
g / m ² . After plating, temper rolling was performed at 1%. Thereafter, post-processing was performed. Postprocessing covers the inorganic oxide was performed in the range of 70 mg / ^{m 2} of 2400 mg / ^{m 2} in total. In the test, the limit drawing ratio was determined by cylindrical deep drawing.
The punch diameter was 50φ, the punch shoulder 3R, the die shoulder 3R, and the drawing ratio was 2.1 to 2.3. Molding speed 5mm /
min. Table 2 shows the results. No. No. 45 to No. Up to 86, examples of the present invention are shown. No. 87 to N
o. No. 90 is a comparative example. 87, no. In No. 88, the thickness of the oxide film treatment on the plating is too small. No. 8
9, No. No. 90 has a large thickness and poor slidability.

[0030]

[Table 2]

Example 3 An SPCC plate having a thickness of 0.8 mm, in which a steel slab was melted to produce a thin steel plate by a normal method, was used as a plating original plate. As for the plating, those having a plating composition as shown in Table 3 were heated, annealed, and plated by a Sendzimir-type continuous hot-dip galvanizing line. Annealing atmosphere is 10%
The atmosphere was a gas atmosphere of hydrogen and 90% nitrogen gas with a dew point of -30 degrees. The annealing temperature is 730 ° C. and the annealing time is 3 minutes.
After plating, reduce the coating weight by 90% by ordinary wiping.
g / m ² . After plating, temper rolling was performed at 1%, and an organic resin film shown in Table 3 was applied after solvent degreasing. In the test, the limit drawing ratio was determined by cylindrical deep drawing. Punch diameter 50φ,
Punch shoulder 3R, die shoulder 3R, drawing ratio is 2.1 to 2.
It was set to 3. The molding speed was 5 mm / min with no oil coating. Table 3 shows the results. No. Nos. 126 to 129 are comparative examples. 126, no. No. 127, since the film thickness of the organic resin film was smaller than the range of the present invention, 128,
No. 129, on the other hand, has a poor sliding property because the organic resin film is too thick.

[0032]

[Table 3]

[0033]

According to the present invention, it is possible to produce a hot-dip zinc-aluminum alloy-plated steel sheet having excellent workability, which has an extremely great effect in industries such as automobiles and building materials.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Akira Takahashi, 1st Kimitsu, Kimitsu City, Nippon Steel Corporation Kimitsu Works (72) Inventor, Hisayoshi Komatsu 1st, Kimitsu, Kimitsu City Nippon Steel Corporation, Kimitsu Inside the steelworks (72) Inventor Go Miyake 1 Kimitsu, Kimitsu City Inside Nippon Steel Corporation Kimitsu Works (72) Inventor Gen Moto Onozawa 1 Kimitsu, Kimitsu City Inside Nippon Steel Corporation Kimitsu Works ( 72) Inventor Yasuhide Morimoto 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Headquarters (72) Inventor Kazumi Nishimura 1 Fujimachi, Hirohata-ku, Himeji-shi Hirohata Works, Nippon Steel Corporation (72) Inventor Kazuhiko Honda 1 Kimitsu, Kimitsu City F-term in the Nippon Steel Corporation Kimitsu Works (reference) 4K027 AA05 AA22 AB02 AB44 AC51 AC64 AC87 AE02

Claims (7)

[Claims] 1. A steel sheet having a mass percentage of Al: 3 to 18 on the surface thereof
%, Mg: 2.1 to 10%, a steel sheet having a plating layer composed of a balance of Zn and unavoidable impurities, further containing 1 to 50% of the amount of Mg in the plating layer.
It is characterized by containing not more than 6 × 10 ³ Si-based materials having an area of 0 μm ² or more per unit sectional area of the plating layer,
Hot-dip zinc-aluminum alloy plated steel sheet with excellent workability. 2. The steel sheet according to claim 1, wherein:
A hot-dip zinc-aluminum alloy-plated steel sheet excellent in workability, characterized by further containing Fe: 1% or less. 3. A process characterized in that the plating layer of the steel sheet according to claim 1 or 2 further contains at least one of Pb and Sn in an amount of 0.01 to 2.0%. Hot-dip zinc-aluminum alloy plated steel sheet. 4. An inorganic oxide film having a thickness of 70 mg / m ² on the plating layer of the steel sheet according to claim 1.
A hot-dip zinc-aluminum alloy-plated steel sheet having excellent workability, characterized by having a content in the range of from ^{2 to 2} g / m ² . 5. An organic resin film having a thickness of 100 mg / m ² on the plating layer of the steel sheet according to claim 1.
A hot-dip zinc-aluminum alloy-plated steel sheet having excellent workability, characterized in that the steel sheet has a thickness of from 2.0 to 2.0 g / m ² . 6. When producing a hot-dip zinc-aluminum alloy-plated steel sheet, the plating bath temperature is set to less than 480 ° C., so that the area of 100 μm ² or more Si
6. A hot-dip zinc-aluminum alloy-coated steel sheet having excellent workability according to any one of claims 1 to 5, wherein the composition contains not more than 6 x 10 < ³ > per unit cross-sectional area of the plating layer. Method. 7. When producing a hot-dip zinc-aluminum alloy-plated steel sheet, the plating bath temperature is set to less than 480 ° C., and the plating layer is continuously cooled at a cooling rate of 10 ° C./s or more, so that 100 μm ^The hot-dip zinc-aluminum alloy coated steel sheet having excellent workability according to claim 1, wherein 6 × 10 ³ or less Si-based materials having an area of ² or more are contained per unit cross-sectional area of the plating layer. Manufacturing method.