JP2001355052A - Hot dip zinc-aluminum alloy plated steel sheet excellent in spot weldability 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 spot weldability 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 composed of, by mass, 3 to 20% Al and 0.01 to 2% Si, and the balance Zn with inevitable impurities, and the plated layer is, if required, further incorporated with 0.1 to 10% Mg, and Si-based substances with an area of >=100 μm2 are contained by <=6×103 pieces per the unit cross- sectional area of the plated layer. Moreover, the plated layer of the steel sheet is, if required, incorporated with one or more kinds of elements selected from Ti, Cr, Ni and Sn by 0.01 to 2% as well. Further, the steel sheet is coated with an inorganic oxide film or an organic resin film as post treatment after plating. In the method for producing the same plated steel sheet, by controlling the plating bath temperature to >=400 deg.C, 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.

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 spot weldability 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. Particularly, Zn-5% Al hot-dip galvanized steel sheet is used mainly for building materials and the like because of its excellent corrosion resistance as compared with conventional hot-dip galvanized steel sheet. In recent years, Zn—Al—Mg plated steel sheets have been developed, and further improvement in corrosion resistance has been attempted.

[0003] However, such a Zn-high Al-based alloy-plated steel sheet has a drawback of poor weldability. This is because the melting point of hot-dip galvanizing is about 419 ° C,
The melting point of a high Al alloy plated steel sheet is generally low, and the plating layer is easily melted during spot welding to increase the contact area of the welded part, reduce the current density, decrease the nugget diameter, and generate a Cu-Zn alloy to form an electrode. Is worn out.
For this reason, there is a disadvantage that heating of the surface of the welding tip is excessive, a brittle alloy layer is deposited on the surface of the electrode tip, and chip wear becomes severe.

As a method of improving the weldability of an alloyed hot-dip galvanized steel sheet, Japanese Patent Application Laid-Open No. 2-4983 discloses Z
Although a technique for forming an oxide film containing nO as a main component is disclosed, it is difficult to easily form a ZnO film industrially, and it has not been put to practical use. Japanese Patent Application Laid-Open No. 5-263210 discloses the addition of Ti to promote the alloying of Fe to a Zn-5% Al-based alloy-plated steel sheet, and after plating, alloying the Fe using an alloying furnace and spot welding. A technique for improving the performance is described. However, this has a problem that an alloying furnace is indispensable and the cost is high. JP-A-6-336664 describes a technique for improving the spot weldability by immersing a steel sheet in a zinc-aluminum hot-dip bath and spraying a silicon-containing aqueous solution to form a silica coating on the plating surface. However, it is difficult to uniformly form a silica coating on a steel sheet with good adhesion, and there is a problem that it is not very effective at present.

[0005]

In view of such circumstances, it is an object of the present invention to provide a hot-dip zinc-aluminum-based alloy-coated steel sheet having improved spot weldability of a conventional zinc-aluminum-based alloy-coated steel sheet. is there.

[0006]

The deterioration of the spot weldability is caused by the lowering of the melting point of the plating alloy and the wear of the electrode due to the formation of a Cu-Zn alloy on the electrode. Based on the recognition that there is a large variation in welding performance in quality, the present inventors aimed to change the composition and structure of the plated alloy. As a result of intensive studies, they have found that it is effective to add Si into the plating bath. Although the reason is not clear, it is considered that Si suppresses the formation of the Cu—Zn alloy and that Si suppresses the formation of the Al-based oxide. Further, the present inventors have investigated the existence state of Si in the plating layer, and found that it is not necessarily due to the presence of silica in a wide variety of areas such as metal Si, SiO ₂ , and Mg ₂ Si. As a result of a more detailed investigation, it was found that when the size of the Si-based material in the plating layer was large, the spot weldability was deteriorated, and when the number was large, the spot weldability was significantly deteriorated. The present invention has been made based on these findings, and the gist thereof is as follows.

(1) Al: 3% by mass% on the surface of the steel sheet
20%, contains Si: 0.01 to 2%, has a plating layer composed of Zn and inevitable impurities, and has a thickness of 100 μm ^2.
A hot-dip zinc-aluminum alloy-plated steel sheet having excellent spot weldability, comprising not more than 6 × 10 ³ Si-based substances per unit cross-sectional area of a plating layer.

(2) Hot-dip zinc-aluminum alloy plating excellent in spot weldability, characterized in that the plated layer of the plated steel sheet according to (1) further contains Mg: 0.1 to 10%. steel sheet.

(3) The plating layer of the plated steel sheet according to (1) or (2) further contains Ti, Cr, Ni, S
A hot-dip zinc-aluminum alloy-plated steel sheet having excellent spot weldability, characterized by containing at least one kind of n in an amount of 0.01 to 2% by mass%.

(4) A spot characterized by having an inorganic oxide film of 70 mg / m ^{2 to 2} g / m ² on the plated layer of the plated steel sheet according to any one of (1) to (3). Hot-dip zinc-aluminum alloy plated steel sheet with excellent weldability.

(5) An organic resin film is formed on the plated layer of the plated steel sheet according to any of (1) to (3) above.
A hot-dip zinc-aluminum alloy-plated steel sheet having excellent spot weldability, having a content of from 00 mg / m ^{2 to 2} g / m ² .

(6) When manufacturing a hot-dip zinc-aluminum alloy-plated steel sheet, the plating bath temperature is set to 400 ° C. or more, so that the Si-based material having an area of 100 μm ² or more in the plated layer has a unit sectional area of the plated layer. 6 × 10 ³ per
The method for producing a hot-dip zinc-aluminum alloy-coated steel sheet excellent in spot weldability according to any one of the above (1) to (5), wherein the steel sheet contains not more than one steel sheet.

[0013]

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 20%, the effect of improving the corrosion resistance is saturated and the spot weldability is deteriorated, so that the content is set to 3 to 20%.

Si is an important element in the present invention, and is added for improving spot weldability. If it is less than 0.01%, spot weldability is not improved, and if it exceeds 2%, spot weldability deteriorates, so the content is made 0.01 to 2%.

Si-based materials (metallic Si, SiO ₂ , Mg ₂ S
i) etc. for the size in the plating layer is 100 μm ²
If some of them exceed the above, a difference in resistance microscopically occurs, explosion tends to occur during spot welding, and the spot weldability tends to deteriorate. If the Si-based substance having a size of not less than 6 × 10 ³ per unit sectional area of the plating layer, the spot weldability is remarkably deteriorated.
The number of Si-based materials having an area of 00 μm ² or more was set to 6 × 10 ³ or less per unit sectional area of the plating layer.

In general, Mg is often added because it has an effect of improving corrosion resistance. However, in the present invention, deterioration of weldability is suppressed by suppressing the generation of Al ₂ O ₃ that adversely affects weldability by adding Mg. I do. If it is less than 0.1%, there is no effect of addition, and if it exceeds 10%, bath dross often occurs and plating becomes difficult. Therefore, the content is set to 0.1 to 10%, preferably 0.5 to 10%.

[0018] Ti, Cr, Ni and Sn are added as necessary to stabilize the weldability. If it is less than 0.01%, there is no effect of addition, and if it exceeds 2%, the effect of improving the weldability is saturated.

There is no particular limitation on the plating base plate to be used.
It can be used regardless of the steelmaking method, the strength of the steel, hot rolled PO material, cold rolled material, and other products. 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.

The plating bath temperature affects the uniform dispersibility of Si in the bath. If the temperature is lower than 400 ° C., precipitation of Si occurs,
The system material becomes too coarse, which impairs weldability. In addition, the temperature is set to 400 ° C. or more because the plating bath tends to dross out, which leads to a decrease in the yield of the pot.

In order to improve the blackening resistance and the corrosion resistance, an aqueous or organic post-treatment may be performed after the plating without any problem, and the temper rolling may be performed.

On the plated layer after plating, further add Si, M
The effect of the present invention can be further improved by coating at least one or more inorganic oxides selected from g, Zr, Mo, Ce and Ca oxides. In this case, there is no problem in forming a composite oxide such as a phosphate. If the coating amount of the inorganic oxide film is less than 70 mg / m ² , the effect of improving the weldability is not sufficient, and 2 g / m 2
^If it exceeds ² , it becomes easy to de-energize and the weldability deteriorates.
The coating amount of the inorganic oxide film was 70 mg / m ^{2 to 2} g / m ² .

Further, even when an organic resin film is coated instead of the inorganic oxide film, the effect of the present invention can be further improved similarly to the case of the inorganic oxide film. 100m
If less than g / m ² , the effect of improving weldability is not sufficient,
If it exceeds g / m ² , it becomes easy to conduct electricity and the weldability deteriorates. Therefore, the coating amount of the organic resin film is 100 mg / m ^{2 to 2} g.
/ 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 a water-soluble resin but also a resin (a water-dispersible resin) which is inherently water-insoluble but can be finely dispersed in water, such as an emulsion or a suspension.

The resin that can be used as the organic resin is not particularly limited, but includes polyolefin resin, acrylic olefin resin, polyurethane resin, acrylic resin, polycarbonate resin, epoxy resin, polyester resin, alkyd resin, and phenol. Examples include a base resin and other heat-curable resins, and a crosslinkable resin is more preferable. The organic resin may be used as a mixture of two or more kinds, or may be used after being copolymerized. Further, a crosslinking agent such as various melamine resins and amino resins may be added as needed. Among these, it is particularly preferable to use an acrylic olefin resin or an acrylic resin when considering both the performance and the cost. Furthermore, the effect of the present invention is not impaired even if a small amount of fine silica or a lubricant is added in addition to the organic resin.

As a coating method for forming an inorganic oxide film or an organic resin film, any method such as spraying, curtain coating, flow coater, roll coater, bar coater, brush coating, dipping, and air knife drawing can be applied. . The baking temperature is 80-250 ° C
It is desirable that If the temperature is lower than 80 ° C., water in the paint is difficult to completely volatilize, which has an adverse effect such as a decrease in corrosion resistance. If the temperature is higher than 250 ° C., the alkyl portion of the organic resin is undesirably denatured by thermal decomposition or the like, or the curing of the film is excessively advanced and the corrosion resistance and workability are lowered. More preferably, it is 80 to 160 ° C. 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 also 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.

[0026]

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: 3.5 to 21%,
Mg: 0 to 10.5%, Si: 0 to 2.2%, Ti: 0
To 1.8%, Cr: 0 to 1.7%, Ni: 0 to 1.7
%, Sn: 0.4 to 1.8%, and a plating bath adjusted to Zn and inevitable impurities was used. Table 1 shows the composition of the obtained plated steel sheet. Plating bath temperature is 390-500 ° C
After plating, the amount of coating was adjusted to 90 g / m ² per one side by ordinary wiping. After plating, temper rolling was performed at 1%, and then, if necessary, chromate treatment was performed at an adhesion amount of ²⁰ to 30 mg / m ² . For Si-based material thus produced plated steel sheet, conducted EPMA observation of the plating section, was observed for each field of view of any of 100 [mu] m square, counts the number of 100 [mu] m ² or more of, unit cross-sectional of the plating layer cross-section Expressed as the number per area. Table 1 shows the results.

The evaluation of the weldability of the obtained plated steel sheet was carried out by an evaluation by a continuous hitting test and an evaluation by welding stability.

(Continuous spotting test) A continuous spotting test of spot welding was carried out by superposing two plated steel sheets.

The test conditions were as follows: electrode shape: tip dome diameter 12
φ, pressing force: 220 kgf, welding time: 12 cycles (50 cycles of AC), welding current: 12 kA,
The nugget diameter after shear tension was measured and the value was 4.5 m.
The time when the value reached m was regarded as the electrode life. When the electrode life is 2,000 points or more: ○, 1000 to 2000 points: Δ, 1000
Less than the point was marked as x, and △ and x were rejected.

(Welding stability) For those having an electrode life of 2,000 points or more, the variation in the nugget diameter size from 2000 points to 2010 points is indicated. The difference between the maximum and minimum nugget sizes is 0.3 mm or less. , 0.5 mm or less were evaluated as ○ and passed.

Table 1 shows the evaluation results. No. 1 to N
o. 36 is an example of the present invention, and has good weldability. In particular, no. 21-No. Reference numeral 36 denotes T in the plating layer.
This is an example in which i, Cr, Ni, or Sn is contained, and is excellent in welding stability in addition to continuous hitting property. On the other hand, No. 37 to No. 37 No. 45 is a comparative example.
No. 44 was inferior in weldability because Al was too high. 37,
No. 38, no. 40, no. 41, no. 42 is S
i amount is too low. No. 45 is No. 45 because Si is too high. No. 43 is No. 43 because Mg is too high.
Sample No. 39 was inferior in weldability because the bath temperature was too low.

[0032]

[Table 1]

(Example 2) A 0.8 mm-thick SPCC plate prepared by melting a steel slab to produce 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: 3.5 to 22%,
Mg: 0 to 10.5%, Si: 0 to 2.2%, Ti: 0
To 1.7%, Cr: 0 to 1.7%, Ni: 0 to 1.7
%, Sn: 0 to 1.9%, a plating bath adjusted to the balance of Zn and inevitable impurities was used. Table 2 shows the composition of the obtained plated steel sheet. The plating bath temperature was 390 to 510 ° C., and after plating, the amount of coating was adjusted to 90 g / m ² per side by ordinary wiping. After plating, temper rolling was performed at 1%. Thereafter, post-processing was performed. For post-treatment, the inorganic oxide coating treatment is performed at 70 mg / m ^{2 to} 2500 mg / m ^2.
It went in the range of.

The evaluation of the weldability of the obtained plated steel sheet was carried out by an evaluation by a continuous hitting test and an evaluation by welding stability.

(Continuous spotting test) A continuous spotting test of spot welding was carried out by superposing two coated steel sheets.

The test conditions were as follows: electrode shape: tip dome diameter 12
φ, pressing force: 220 kgf, welding time: 12 cycles (50 cycles of AC), welding current: 12 kA,
The nugget diameter after shear tension was measured and the value was 4.5 m.
The time when the value reached m was regarded as the electrode life. The electrode life was over 2,500 points for ◎, 2000 to 2500 points for ○, 1000 to 200
0 points were rated as △, less than 1000 points were rated as x, and × and x were rejected.

(Welding stability) For those having an electrode life of 2,000 points or more, the variation in the nugget diameter size from 2000 points to 2010 points is shown, and the difference between the maximum and minimum nugget sizes is 0.3 mm or less. , 0.5 mm or less were evaluated as ○ and passed.

The results are shown in Table 2. No. No. 46 to No.
77 is an example of the present invention, and all show good weldability. No. No. 78 to No. No. 86 is a comparative example.
78, no. 79, no. 85, no. No. 86 was inferior in weldability because the inorganic oxide film was too thick. 80-N
o. In the case of No. 85, the components in the plating layer are out of the range of the present invention, so that even if the inorganic coating treatment is performed, the weldability is insufficient.

[0039]

[Table 2]

Example 3 A 0.8 mm-thick SPCC plate produced by melting a steel slab to produce 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 composition of the plating bath is Al: 3.5-2.
2%, Mg: 0 to 10.5%, Si: 0 to 2.2%, T
i: 0 to 1.7%, Cr: 0 to 1.7%, Ni: 0 to 0%
A plating bath adjusted to 1.7%, Sn: 0 to 1.9%, the balance being Zn and unavoidable impurities was used. Table 3 shows the composition of the obtained plated steel sheet. Plating bath temperature is 390-510
C., and after plating, the coating weight was adjusted to 90 g / m ² per side by ordinary wiping. After plating,
Temper rolling was performed at 1%, and after the solvent was degreased, a resin-based organic resin film treatment shown in Table 3 was performed.

Evaluation of the weldability of the obtained plated steel sheet was performed by an evaluation by a continuous hitting test and an evaluation by welding stability.

(Continuous spotting test) A continuous spotting test of spot welding was performed by superposing two plated steel sheets.

The test conditions were as follows: electrode shape: tip dome diameter 12
φ, pressing force: 220 kgf, welding time: 12 cycles (50 cycles of AC), welding current: 12 kA,
The nugget diameter after shear tension was measured and the value was 4.5 m.
The time when the value reached m was regarded as the electrode life. The electrode life was over 2,500 points for ◎, 2000 to 2500 points for ○, 1000 to 200
0 points were rated as △, less than 1000 points were rated as x, and × and x were rejected.

(Welding stability) For those having an electrode life of 2,000 points or more, the variation in the nugget diameter size from 2000 to 2010 points is represented by ◎, where the difference between the maximum and minimum nugget sizes is 0.3 mm or less. , 0.5 mm or less were evaluated as ○ and passed.

Table 3 shows the results. No. 87-No. 1
Reference numeral 32 is an example of the present invention, and all showed good weldability. N
o. 133 and no. In the case of No. 134, the amount of the film was small and no effect of improving the weldability was obtained. 135 and no. 136
On the contrary, the result is that the film is too thick and the weldability is poor.

[0046]

[Table 3]

[0047]

As described above, according to the present invention, it is possible to produce a hot-dip zinc-aluminum-based alloy-coated steel sheet having excellent weldability, which has an extremely great effect in industries such as automobiles and building materials. .

Continued on the front page (72) Inventor Akira Takahashi 1 Kimitsu, Kimitsu-shi Nippon Steel Corporation Kimitsu Works (72) Inventor Hisayoshi Komatsu 1 Kimitsu, Kimitsu-shi Nippon Steel Corporation Kimitsu Works (72) Inventor Go Miyake 1 Kimitsu City, Kimitsu City Nippon Steel Corporation Kimitsu Works (72) Inventor Yasuhide Morimoto 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division (72) Inventor Kazumi Nishimura 1 Fujimachi, Hirohata-ku, Himeji-shi Inside Hirohata Works, Nippon Steel Corporation (72) Inventor Kazuhiko Honda 1 Kimitsu, Kimitsu-shi Inside Kimitsu Works, Nippon Steel Corporation (72) Inventor Yasuo Takahashi 20-1 Shintomi, Futtsu-shi Nippon Steel Corporation Technology Development Division F-term (reference) 4K027 AA02 AA05 AA22 AB05 AB13 AB44 AC52 AC82 AC87 AE02 4K044 AA02 AB02 BA10 BA12 BA12 BA17 BA21 BB03 BC02 BC08 CA11 CA16 CA53

Claims (6)

[Claims] 1. Al: 3 to 20% by mass on the surface of a steel sheet.
%, Si: 0.01 to 2%, the balance having a plating layer composed of Zn and inevitable impurities, and a Si-based material having an area of 100 μm ² or more per unit cross-sectional area of the plating layer being 6 ×
Molten zinc excellent in spot weldability characterized by containing 10 ³ or less - aluminum alloy coated steel sheet. 2. A hot-dip zinc-aluminum alloy coated steel sheet excellent in spot weldability, characterized in that the coating layer of the coated steel sheet according to claim 1 further contains Mg: 0.1 to 10%. 3. The plating layer of the plated steel sheet according to claim 1, further comprising one of Ti, Cr, Ni, and Sn.
A hot-dip zinc-aluminum alloy-plated steel sheet having excellent spot weldability, characterized by containing 0.01% to 2% by mass of at least one kind. 4. An inorganic oxide film having a thickness of 70 m on a plating layer of the plated steel sheet according to any one of claims 1 to 3.
molten zinc excellent in spot weldability characterized by having ^{g / m 2 ~2g / m 2} - aluminum alloy coated steel sheet. 5. An organic resin film having a thickness of 100 m on a plating layer of the plated steel sheet according to any one of claims 1 to 3.
molten zinc excellent in spot weldability characterized by having ^{g / m 2 ~2g / m 2} - aluminum alloy coated steel sheet. 6. When producing a hot-dip zinc-aluminum alloy-plated steel sheet, by setting the plating bath temperature to 400 ° C. or higher, the area of 100 μm ² or more Si
The hot-dip zinc-aluminum alloy-coated steel sheet having excellent spot weldability according to any one of claims 1 to 5, wherein the coating material contains 6 x 10 ³ or less per unit sectional area of the plating layer. Production method.