JP2001355053A - HOT DIP Zn-Al-Mg-Si PLATED STEEL EXCELLENT IN SURFACE PROPERTY AND ITS PRODUCTION METHOD - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excellent hot dip Zn-Al-Mg-Si plated steel improved in surface properties and to provide its production method. SOLUTION: In this hot dip Zn-Al-Mg-Si plated steel excellent in surface properties, on the surface of plated steel having a plated layer having a composition containing, by mass, 5 to 18% Al, 1 to 10% Mg and 0.01 to 2% Si, if required, containing <=1% Fe, or further containing 0.1 to 2% Sn, and the balance Zn with unavoidable impurities, an Al phase is present by >=200 pieces per mm2. Then, in the production method, the cooling rate after plating is controlled to <10 deg.C/s.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip Zn-Al-Mg-Si plated steel material having excellent surface properties and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, the use of surface-treated steel materials 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 mass% Al hot-dip galvanized steel is used mainly for building materials and the like because of its superior corrosion resistance as compared with conventional hot-dip galvanizing. For hot-dip plating in which Al or Mg is added to Zn,
In U.S. Pat. No. 3,505,043, Al: 3 to 17
%, Mg: 1-5%, and various techniques have been proposed since the high corrosion-resistant hot-dip Zn-Al-Mg plated steel sheet using a hot-dip plating bath composed of Zn was proposed. For example,
In Japanese Patent Application Laid-Open No. H8-60324, the maximum Al content is 0.25
%, And Mg up to 3%. Also, Japanese Patent Application Laid-Open No. 9-1436
No. 59, Mg: 0.05-3%, Al: 0.1
-1%, Ni: 0.01-0.2%. Although these have the effect of improving the corrosion resistance, when the Mg content is close to 3%, thick oxide (dross) is deposited on the bath, which is not suitable for industrial production. Recently, Japanese Patent Application Laid-Open
0-226865, Al: 4-10%,
Mg: coated steel sheet with 1-4% addition, and Japanese Patent Application No. 11-1
JP-A-79913 discloses a hot-dip coated steel sheet in which Si is further added to a Zn-Al-Mg-based coated steel sheet.

However, in the case of Zn-Al-Mg-based plating, a dot-like appearance pattern of several mm to about 10 mm may be generated, which may cause a problem in a product. As a solution to this problem, for example, in the above-mentioned Japanese Patent Application Laid-Open No. 10-226865, it is assumed that the presence form of Mg is important, the plating bath temperature during production is set to 450 ° C. or less or less than 470 ° C. s or faster or set the bath temperature to 47
This can be avoided by controlling the cooling rate to 0.5 ° C./s or more by setting the cooling rate to 0 ° C. or more. Further, Japanese Patent Application Laid-Open No. 10-306357 states that by adding Ti and B to plating, restrictions on manufacturing conditions are relaxed. However, according to our research, these techniques cannot avoid the point-like surface defects of Zn-Al-Mg-Si plating, and the bath temperature is
There is a problem of corrosion of plating equipment, and it is difficult to raise the temperature to 470 ° C or more. Addition of Ti or B causes dross formation and deteriorates surface properties, and has many fatal drawbacks. Became clear.

[0004]

In view of such circumstances, it is an object of the present invention to provide a hot-dip Zn-Al-Mg-Si plated steel material having improved surface properties.

[0005]

SUMMARY OF THE INVENTION The inventors of the present invention, based on the above investigation, have found that Zn-Al-Mg plating and Zn-Al-Mg-S
Since it is presumed that the generation mechanism of the point defects of the i-plating is different, the surface properties of the Zn-Al-Mg-Si plating were studied diligently. And the spot defect is
Unlike the conventional knowledge, it was found that the occurrence of a remarkable increase when the cooling rate was increased. These spots are approximately 1.5
mm and a blackish smooth appearance compared to the surroundings. When the surface analysis of the spots was carried out with a light microscope, an electron beam probe micro-analysis device (CMA), etc., the dendritic structure of the Al phase did not protrude to the surface at the spots, while the spot-like defects were observed. If there is no normal part, A
The 1-phase dendritic structure protrudes from the surface in a protruding manner, and the point-like defect was found to be a difference in the precipitation form of the Al phase, and the present invention was completed. Here, the Al phase is defined as an Al-rich phase in which solidification precipitation starts first from the plating bath.

[0006] Then, with the aim of controlling the precipitation of the Al phase, the relationship between the plating bath temperature and cooling rate and the point-like defects was investigated. As a result, it was found that, unlike the conventional knowledge, the plating bath temperature did not affect the generation of point defects, and the cooling rate after plating was very important. In particular, for the latter, the cooling rate in the temperature range near the solidification end temperature is very important for the generation of spots, and by reducing the cooling rate in this range and controlling the precipitation of the Al phase, point-like defects can be generated. It was found that it could be avoided. Although this mechanism is not yet clear, if the cooling rate is high, a supercooled state occurs locally, the precipitation behavior of Al changes, the growth of the Al phase is delayed in the supercooled portion, and projections of the Al phase on the surface are formed. It is presumed that the number of spots decreases and spots occur. Here, the Al phase is defined as an Al-rich phase in which solidification precipitation starts first from the plating bath. The present invention has been completed based on such various new findings, and the gist is as follows.

(1) On the surface of a steel material, there is provided a plating layer composed of 5 to 18% by mass of Al, 1 to 10% by mass of Mg, 0.01 to 2% by mass of Si, the balance being Zn and unavoidable impurities. Al phase on the surface of plated steel material is 20 per mm ²
A hot-dip Zn-Al-Mg-Si plated steel material having excellent surface properties, characterized in that there are zero or more steels.

(2) Fused Zn—Al—Mg—S having excellent surface properties, characterized in that the plated layer of the plated steel material according to (1) further contains Fe: 1% by mass or less.
i-plated steel.

(3) Fused Zn excellent in surface properties, characterized in that the plated layer of the plated steel material according to (1) or (2) further contains Sn: 0.1 to 2% by mass.
-Al-Mg-Si plated steel material.

(4) A surface characterized by further comprising an inorganic oxide film on the plated layer of the plated steel material according to any one of (1) to (3) above, in an amount of 70 mg / m ^{2 to 2} g / m ^2. Hot-dip Zn-Al-Mg-Si plated steel with excellent properties.

(5) An organic resin film is further provided on the plated layer of the plated steel material according to any of (1) to (3) above, in an amount of from 100 mg / m ^{2 to} 2.0 g / m ^2. Hot-dip Zn-Al-Mg-Si plated steel with excellent surface properties.

(6) The cooling rate after plating is 10 ° C./s
The molten Zn-Al-Mg having excellent surface properties according to any one of the above (1) to (5), wherein
-A method for producing a Si-plated steel material.

(7) Solidification end temperature ± 10 ° C. after plating
Production of a hot-dip Zn-Al-Mg-Si plated steel material having excellent surface properties according to any one of the above (1) to (5), wherein the cooling rate in the temperature range described above is less than 10 ° C / s. Method.

(8) Solidification end temperature + 10 ° C. after plating
The cooling rate up to 10 ° C./s or more, and then the cooling rate in the temperature range of the solidification end temperature ± 10 ° C. to less than 10 ° C./s. Fused Zn-Al-Mg-
Manufacturing method of Si steel material.

[0015]

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 the purpose of improving corrosion resistance and forming a protruding Al phase dendritic structure on the plating surface. If it is less than 5% (mass%, the same applies hereinafter), the formation of a protruding Al phase on the surface is insufficient, and the corrosion resistance is poor. On the other hand, if it exceeds 18%, the sink-like unevenness becomes large, the surface appearance deteriorates, and the effect of improving the corrosion resistance is saturated. Therefore, the range is set to 5 to 18%.

Although Mg is generally said to have an effect of improving corrosion resistance, it affects the formation of the Al phase dendrites on the plating surface described above, and when it is less than 1%, this formation is substantially absent. On the other hand, if it exceeds 10%, the plating bath is oxidized by contact with the air, and a black oxide (dross) is generated.
Since plating production becomes difficult, the range was set to 1 to 10%.

Si is generally added for improving corrosion resistance and plating adhesion. If it is less than 0.01%, these effects are small, and if it is 2% or more, dross generation increases and the spot pattern of the Si oxide increases.
01 to 2%.

Fe is an Fe—Zn—Al alloy, Fe—Z
n, an Fe-Al intermetallic compound, etc. are formed to prevent the formation of primary Al dendrites and to induce the formation of spotted patterns.

Sn is an element added as needed for improving the corrosion resistance.
Addition of 1% or more is required. If it exceeds 2%, it becomes easy to form sink marks and irregularities, and the appearance is deteriorated.
２2%.

Next, the manufacturing method will be described. There is no particular limitation on the material of the plating raw material to be used.
Ultra low carbon steel, high C steel, various high tensile steels, Ni and Cr containing steels, etc. can be used. Further, the present invention can be applied to any of steel plates, steel wires, and the like, and there is no particular limitation on the pretreatment of a steel material such as a steelmaking method, steel strength, a hot rolling method, an acid pickling method, and a cold rolling method. The present technology is applicable to a plating manufacturing method regardless of a manufacturing method such as a two-bath method such as a Sendzimir type, a flux type, or a pre-plating type.

The bath temperature at the time of plating is not particularly limited. However, it is preferable that the bath temperature is less than 470 ° C. from the viewpoint of melting of the plating equipment. The wiping method after plating is not limited, and air and nitrogen wiping can be used. Although there is no particular limitation on the cooling method, it is desirable to perform gas cooling in order to avoid local overcooling. In order to control the precipitation of the Al phase, the relationship between the plating bath temperature and the cooling rate and the point-like defects was investigated. As a result, it was found that, unlike the conventional knowledge, the plating bath temperature did not affect the generation of point defects, and the cooling rate after plating was very important. In particular, for the latter, the cooling rate in the temperature range near the solidification end temperature is very important for the generation of spots, and by reducing the cooling rate in this range and controlling the precipitation of the Al phase, point-like defects can be generated. It was found that it could be avoided. Although this mechanism is not yet clear, if the cooling rate is high, a supercooled state occurs locally, the precipitation behavior of Al changes, the growth of the Al phase is delayed in the supercooled portion, and A
It is presumed that the number of l-phase protrusions decreases and spots occur. The cooling rate after plating is very important for the present invention, and the cooling rate from plating to the solidification end temperature must be less than 10 ° C./s in order to avoid the formation of spots. More specifically, near the freezing point, ie, the freezing end temperature ± 10 ° C
By setting the cooling rate in the range of less than 10 ° C./s, spot formation can be avoided. Excluding this temperature range, the cooling rate may be 10 ° C./s or more.

Co-flash, which is post-treatment after plating,
Even if an aqueous post-treatment such as Co-Ni flash is used, the effect of the present invention is not impaired.

On the plated layer after plating, further add Mg, Z
By coating at least one or more inorganic oxides selected from the oxides of r, Mo, Ce, and Ca, the corrosion resistance can be further improved. In this case, there is no problem in forming a composite oxide such as a sulfate, a nitrate, and a phosphate. When the sum of these is less than 70 mg / m ² , the effect of improving corrosion resistance is small. 2.0g of these
/ M ² , the effect of improving corrosion resistance is saturated.
mg / m ^{2 to} 2.0 g / m ² .

Alternatively, the corrosion resistance can be improved by coating an organic resin film instead. Adhesion amount of the coating in 100 mg / m ² or less, this effect is small, the corrosion resistance improving effect exceeds 2.0 g / m ² is in the range of 100mg / m ² ~2.0g / m ² so saturated. The organic resin may be in any form of a water-based resin, a solvent-based resin, a powder-based resin, or a solventless 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 a polyolefin resin, an acrylic olefin resin, a polyurethane resin,
Acrylic resins, polycarbonate resins, epoxy resins, polyester resins, alkyd resins, phenolic resins, and other heat-curable resins can be exemplified.
More preferably, it is crosslinkable. The organic resin may be used as a mixture of two or more or a copolymer. 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. Of course, there is no problem in performing various chromate treatments.

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. 80-160 ° 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.

Further, temper rolling may be performed.

The dendritic Al phase appearing on the plating surface is an Al phase having a diameter of several microns to several tens of microns,
These are linearly arranged to form a dendritic pattern.

By using the optical microscope and CMA together, it is easy to investigate, and if there are 200 or more in the range of 1 mm ² , the point defect is eliminated and the appearance is improved.

[0030]

EXAMPLES (Example 1) An SPCC plate having a thickness of 0.8 mm, which was produced by melting a steel slab and manufactured by a usual method, was used as a plating original plate. The plating was performed by heating, annealing and plating in a continuous hot-dip galvanizing line of a non-oxidizing furnace type. The annealing atmosphere is
10% hydrogen, 90% nitrogen gas atmosphere, dew point-
30 degrees. The annealing temperature is 730 ° C. and the annealing time is 3 minutes. Plating bath composition: Al: 3.9-19%, Mg:
0.3-11.3%, Si: 2.2% or less, Fe: 0.
The plating bath temperature is 430 ° C., which is composed of 01 to 1.2%, Sn: 0.05 to 2.5%, residual Zn and unavoidable impurities. The coating weight was 90 g / m ² per one side by a usual nitrogen gas wiping method. Cooling after plating was performed by air cooling at 8 ° C./s to 320 ° C., and then steam-water cooling was performed. In addition, the coagulation end temperature of the used bath is 340 ° C. Thereafter, temper rolling was performed at 1%.

Thereafter, post-processing was performed as required. The post-treatment was performed with an inorganic oxide coating or an organic resin coating and a chromate treatment. At the time of plating production, the amount of oxide (dross) generated on the plating bath surface was visually checked.
The corrosion resistance was evaluated by the weight loss after the salt spray test (SST) described in JIS-Z-2371 for 1000 hours. Less than 5 g / m ² ◎◎◎,
5 g / m ² or more and less than 10 g / m ² ◎◎ 10 g / m ² or more and less than 30 g / m ² ◎, 30 g / m ² or more and 40 g / m ²
Less than ○, 40 g / m ² or more and less than 60 g / m ² △, 60
g / m ² or more was evaluated as x, and ○ or more was evaluated as acceptable. Regarding the plating appearance, those with spotted patterns, generation of sink marks, dross adhesion, etc., were evaluated as x, and those with good appearance were evaluated as ○.
The number of protruding Al phases is counted by measuring the plating surface in the area of 1 mm x 1 mm with an optical microscope photograph and an electron probe micro-analysis device (Shimadzu Corporation) generally called CMA, which appears on the plating surface. Was. The plating adhesion was evaluated by peeling the bent portion with an adhesive tape after performing 180 ° bending.無 し indicates no peeling and × indicates peeling. The results are shown in Tables 1 and 2. Al is 5%
As described above, when the Mg content is 1% or more, the corrosion resistance is good.

No. No. 1 to No. 73 is an example of the present invention and is excellent in corrosion resistance and surface properties. No. 74 to N
o. No. 76 has poor corrosion resistance because Al is too small. N
o. 77 to No. If the amount of Al is too large as in 79,
Sinks occur during cooling, resulting in poor plating appearance.

No. No. 80 to No. No. 82 has poor corrosion resistance because the Mg content is too low. No. 83 to No. 85 is M
Since the g is too high, bath dross increases, and the plating appearance also deteriorates. No. No. 86 to No. 86. No. 88 has a small amount of Si and poor plating adhesion. No. No. 89 has too much Sn and poor plating appearance. No. 90 to No. The sample No. 92 has too much Si, has a lot of dross, and has a poor appearance. No. 93 to N
o. No. 95 has an excessively large amount of Fe, so that point-like defects are likely to appear, and all of bath dross, appearance, and plating adhesion are poor. N
o. No. 96 to No. 100 has a small amount of an inorganic oxide film or an organic film, and a small effect of improving corrosion resistance.

[0034]

[Table 1]

[0035]

[Table 2]

(Example 2) A steel slab is produced by melting
2.3mm-thick SPCC plate manufactured by the plating method
And Plating is non-oxidizing furnace type continuous hot-dip galvanizing
Heating, annealing and plating were performed in a line. Annealing atmosphere
Is an atmosphere of 10% hydrogen and 90% nitrogen gas with a dew point
Was set to −30 degrees. Annealing temperature is 730 ° C, annealing time is 3
Minutes. The plating bath temperature is 440 ° C. Plating weight
Reduces the coating weight by the normal nitrogen gas wiping method.
100g / m per surface^TwoAnd Air cooling after plating
At 5-22 ° C / s to 320 ° C continuously
Then, air-water cooling was performed. The coagulation end temperature of the bath used
The temperature is 340 ° C. Thereafter, temper rolling was performed at 1%. Spots
The presence / absence of a dot pattern and the presence of a protruding Al phase on the plating surface
The number was investigated. Table 3 shows the results. Cooling rate 10 ° C /
s, the number of Al phases is 200 / mm. ^Twothat's all
It turns out that a point defect does not occur.

[0037]

[Table 3]

(Example 3) An SPCC plate having a thickness of 0.6 mm produced by melting a steel slab and producing it by a usual method was used as a plating original plate. The plating was performed by heating, annealing and plating in a continuous hot-dip galvanizing line of a non-oxidizing furnace type. The annealing atmosphere was a 10% hydrogen, 90% remaining nitrogen gas atmosphere, and the dew point was -30 degrees. Annealing temperature is 730 ° C, annealing time is 3
Minutes. The plating bath temperature is 420 ° C. The coating weight was 100 g / m ² per side by a usual nitrogen gas wiping method. The cooling after the plating was performed in the first to third stages. In addition, the coagulation end temperature of the used bath is 340 ° C. Table 4 shows the results. No. 133 to No. 147 will be described by way of example. First, the primary cooling rate is 14 ° C./s to 30 ° C.
/ S, and the cooling method is air cooling, air-water cooling, or water spray cooling. 133-No. 1
36, no. 138, no. 140-No. 143, N
o. 145, the primary cooling end temperature is set to the solidification temperature +
If the temperature is set to 10 ° C. or higher, point-like defects are eliminated, which is favorable.
On the other hand, No. When the primary cooling end temperature is lower than the solidification temperature + 10 ° C. as in 147, point defects occur.

In addition, No. 139, no. When the secondary cooling rate is 10 ° C./s or more as in 146, that is, when the cooling rate near the solidification temperature is high, point-like defects are generated. In addition, No. 137, no. 144, the secondary cooling end temperature becomes the solidification temperature -10 ° C or higher, and the solidification point ± 10 ° C.
When the cooling rate in the range is 10 ° C. or higher, point defects appear. Hereinafter, No. 148-No. A as shown at 175
Similar results were obtained when l and Mg were higher.

[0040]

[Table 4]

[0041]

As described above, according to the present invention, a highly corrosion-resistant Zn-Al-Mg-Si-plated steel having excellent surface properties can be manufactured, which has a great effect on 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 Takuho Ikeda 2-6-3 Otemachi, Chiyoda-ku, Tokyo Nippon Steel Corporation (72) Inventor Yasuhide Morimoto 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division ( 72) Inventor Kazuhiko Honda 1 Kimitsu, Kimitsu-shi F-term in Kimitsu Works, Nippon Steel Corporation 4K027 AA22 AB14 AB44 AC72 AE22 4K044 AA02 BA10 BA12 BA15 BA21 BB03 BC09 CA11 CA16 C A44 CA47 CA53

Claims (8)

[Claims] 1. A steel material having a surface of Al: 5 to 18% by mass,
Mg: 1 to 10% by mass, Si: 0.01 to 2% by mass, 200 or more Al phases per 1 mm ^{2 on the} surface of a plated steel material having a plating layer composed of Zn and unavoidable impurities. Zn with excellent surface properties
-Al-Mg-Si plated steel material. 2. A hot-dip Zn-Al-Mg-Si plated steel material having excellent surface properties, wherein the plated layer of the plated steel material according to claim 1 further contains Fe: 1% by mass or less. 3. A molten Zn—Al—Mg having excellent surface properties, wherein the plating layer of the plated steel material according to claim 1 or 2 further contains Sn: 0.1 to 2% by mass.
-Si plated steel material. 4. An inorganic oxide film is further formed on the plated layer of the plated steel material according to claim 1 by applying an inorganic oxide film.
0mg / m ² ~2g / m ² melt Zn-Al-Mg-Si plating steel having excellent surface properties, characterized in that it comprises. 5. An organic resin film is further formed on the plated layer of the plated steel material according to claim 1 by an organic resin film.
0mg / m ² ~2.0g / m ² melt Zn-Al-Mg-Si plating steel having excellent surface properties, characterized in that it comprises. 6. The molten Zn—Al—Mg—Si having excellent surface properties according to claim 1, wherein a cooling rate after plating is set to less than 10 ° C./s.
Manufacturing method of plated steel. 7. An excellent surface property according to claim 1, wherein a cooling rate in a temperature range of a solidification end temperature ± 10 ° C. after plating is set to less than 10 ° C./s. Of producing a hot-dip Zn-Al-Mg-Si plated steel material. 8. After the plating, the cooling rate to the solidification end temperature + 10 ° C. is set to 10 ° C./s or more, and further, the cooling rate in the temperature range of the solidification end temperature ± 10 ° C. is set to less than 10 ° C./s. The method for producing a molten Zn-Al-Mg-Si steel material having excellent surface properties according to any one of claims 1 to 5.