JPH0765219B2 - 2-layer plated steel sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a two-layer plated steel sheet having an Al alloy layer on the surface, which is industrially producible by an electroplating method and has excellent heat resistance and corrosion resistance.

More specifically, the present invention relates to a plated steel sheet that simultaneously satisfies all of workability, heat resistance (adhesion after heating), corrosion resistance after heating, and heat reflectivity. Since heat reflectivity affects heat resistance, it is expressed as heat resistance in the following unless otherwise specified.

(Prior Art) Al and Al alloy-plated steel sheets (hereinafter referred to as Al-based plated steel sheets) are more economical than ordinary Zn-plated steel sheets, and economically effective because they have a large effect of preventing oxidation of steel at high temperatures. Used as a heat resistant or corrosion resistant material.

However, most conventional Al-based plating is performed by the molten metal immersion plating method, and the coating amount is 20 ~
Only an Al-plated steel sheet with a relatively thick basis weight of 100 g / m ² was manufactured. In addition, since Al-based hot dipping is performed at a high temperature of 700 ° C. or higher, the base metal is adversely affected, and a brittle Fe-Al alloy layer develops between the plating film and the steel sheet substrate, resulting in workability of the steel sheet. There was a serious drawback that deterioration was inevitable.

On the other hand, it has been considered for some time to perform Al-based plating by an electroplating method that can be operated at a low temperature, but since aluminum cannot be electrodeposited from an aqueous solution, aluminum chloride (AlCl
Electroplating in a molten salt bath with a mixed chloride containing ₃ ) as the main component and alkali chloride added as a flux has been considered as a practical Al-based electroplating method from the past (eg, JP-B-45-29085). And 48-38064).

As pointed out in Japanese Patent Publication No. 48-38064, even in Al electroplated steel sheets, the Al plating film forms an alloy layer with Fe of the base material while being used at high temperature as a heat-resistant material, and adheres. Property deteriorates, and alloying spreads over the entire plating layer due to long-term use, and Fe-Al reaches the surface.
Become an alloy. This Fe-Al alloy film is effective for preventing high temperature oxidation of steel, but its corrosion resistance at room temperature is inferior to that of pure Al. Therefore, in the method described in the above publication,
By electroplating Ni with a sulfamine nickel bath as a base treatment and interposing a Ni plating layer as a lower layer, alloying of Al and Fe is prevented, and deterioration of heat resistance due to use at high temperature is prevented. However, the thickness of this underlayer Ni layer is 5 to 10 μm, which corresponds to about 40 to 80 g / m ² when converted to the amount of adhesion, and since it is quite thick, the cost is high, and it is more expensive than the upper plating layer. It was found that the adhesion with the lower plating layer was lowered, and the workability and the end face corrosion resistance were poor.

By the way, in the electroplating of Al using a molten salt bath, a beautiful plating film of good quality cannot be obtained unless it is operated at a low current density, and when it is operated in a practical current density range of 20 A / dm ² or more, the plating film becomes It has a dendritic structure or powdery form, and deterioration of the plating quality also deteriorates corrosion resistance. For the purpose of overcoming the drawbacks of such electric Al plating, a molten salt bath was used.
It has been proposed to add an Mn salt to form an Al-Mn alloy electroplating film. This Al-Mn alloy plating is said to have heat resistance comparable to that of Al plating, and its corrosion resistance is further superior to that of Al.

(Problems to be solved by the invention) The present inventors have examined the use of the Al-Mn alloy-plated steel sheet as a heat-resistant material, and even in the Al-Mn alloy plating, as in the case of pure Al plating, Al when exposed to high temperatures
Forms an alloy layer with the underlying Fe and deteriorates corrosion resistance.
It has been found that at a high temperature of 500 ° C or higher, the formation of an underlying Fe / Al alloy layer can be observed within a relatively short time of about 30 minutes, and the adhesion may deteriorate.

An object of the present invention is to provide an Al-Mn alloy-plated steel sheet which has excellent workability and is resistant to deterioration in corrosion resistance and adhesion even when used at high temperatures, and which is excellent in heat resistance and corrosion resistance.

(Means for Solving the Problems) In order to achieve the above object, as a result of an examination focusing on the pre-plating method, one of Ni, Cr and Co was used as the base treatment.
The formation of an alloy layer of Al and Fe at high temperature is suppressed by forming a two-layer plated steel sheet in which Al-Mn alloy plating is performed in a molten salt bath after plating a metal of at least one kind with a relatively low deposition amount. That is, the present invention has been completed.

According to the present invention, the lower plating layer made of at least one metal selected from Ni, Cr and Co and having an adhesion amount of 0.5 to 20 g / m ² and an Mn content of 0.5 to 50% by weight are used. A two-layer plated steel sheet excellent in workability, heat resistance, and corrosion resistance, which has an upper coating layer consisting of an Mn alloy plating layer and an adhesion amount of 1 to 100 g / m ^{2 on} one side or both sides.

(Operation) Hereinafter, the present invention will be described in detail.

In the two-layer plated steel sheet of the present invention, the lower layer has an adhesion amount of 0.5 to 2
It is a plating layer made of 0 g / m ² of at least one metal selected from Ni, Cr and Co. Al by underplating
Regarding the effect of suppressing the formation of the Fe alloy, Ni exhibits the most excellent effect, but Cr and Co also have a practically sufficient substantial suppressing effect. When the lower layer is alloy-plated, it is preferable to use alloy plating of a metal selected from these three kinds of metals, but it may be alloy-plated in the presence of a small amount of other metal as the case may be.

When the adhesion amount of the lower plating layer is less than 0.5 g / m ² , formation of an alloy layer of Al in the upper layer and Fe as the base material cannot be effectively suppressed. Further, even if the lower plating layer is plated with an adhesion amount of more than 20 g / m ² , no further improvement is observed in the effect of suppressing the alloy formation, and it is also disadvantageous in terms of cost. If it becomes too thick, the adhesion of the plating generally tends to decrease. Furthermore, when the coating weight of the lower layer exceeds 20 g / m ² , when the lower metal is Ni, Ni is a noble metal, so the corrosion of the upper Al-Mn alloy layer easily proceeds, and the surface corrosion resistance is On the other hand, when the lower layer metal is Cr or Co, the workability deteriorates as will be shown in the examples later, and especially Co is expensive, so a high deposition amount is economically disadvantageous. For the above reasons, the adhesion amount of the lower plating layer is limited to 0.5 to 20 g / m ² .

The lower layer can be formed by a conventional method using a known Ni, Cr or Co electroplating bath.

The upper layer is an Al-Mn alloy plating layer having a deposition amount of 1 to 100 g / m ² . When the amount of adhesion is less than 1 g / m ² , good corrosion resistance and heat resistance as shown by Al-based plating cannot be obtained at all, while the amount of adhesion of the upper layer is 10
If it exceeds 0 g / m ² , the workability of the steel sheet is significantly deteriorated.

The Al-Mn alloy plating of the upper layer is carried out by using the conventional AlCl ₃ -XCl (X is an alkali metal) mixed molten salt bath in which an Mn is also added as a chloride to the known molten AlCl ₃ -XCl mixed electroplating bath. It can be implemented similarly. Mn in Al-Mn alloy
The content is 0.5 to 50% by weight. Outside this range, the plating appearance tends to deteriorate, and if the Mn content is too low, the corrosion resistance is significantly reduced, and conversely, if the Mn content exceeds 50% and is high, the workability is reduced. A particularly preferred Mn content is in the range of 10-40% by weight. Also, Al, other alloy elements other than Mn, as long as the performance of the plated steel sheet is not adversely affected,
A small amount (usually 1.0 wt% or less in total) can be added. Examples of such other alloying elements include Fe, Cr, Ni,
Although Ti and the like are included, the present invention is not limited to these, and two or more kinds of such other alloy elements may be added. These elements are also preferably added as chlorides to the molten salt bath.

Generally, the plating temperature of Al-Mn alloy plating by a mixed molten salt bath is about 150 to 200 ° C, and the current density is 20 to 100 A / dm ²
It is a degree.

As is well known, in Al-Mn alloy electroplating with a molten salt bath, it is important to avoid mixing of water for maintaining plating efficiency and plating quality. The plated steel sheet is thoroughly washed with water and then heated and dried to completely remove water. When a bare steel plate is heated and dried in the air, an oxide film is formed on the surface and the adhesion of the Al-based plating film is significantly impaired.
In the present invention, since the undercoating treatment is performed with a relatively noble metal as described above, no decrease in adhesion due to heat drying is observed.

The base material steel sheet of the two-layer plated steel sheet of the present invention is generally a cold rolled steel sheet, but a hot rolled steel sheet can also be used, and as the material, in addition to carbon steel, low alloy steel, low chromium content steel, stainless steel, etc. can be used. Can be mentioned. The two-layer plated steel sheet according to the present invention has the above-mentioned 2
It may be provided on one side or both sides of the layer-plated steel sheet.

In the case of double-sided coating, the amount of adhesion of the lower layer and the amount of adhesion of the upper layer are for one side.

Since the two-layer plated steel sheet of the present invention is excellent in workability, heat resistance and corrosion resistance, it can be used as it is as a corrosion resistance or heat resistant steel sheet, but it can be further coated depending on the purpose of use, and the adhesion of the coating film Since it is also good, a coated steel sheet having excellent coating corrosion resistance can be obtained. Incidentally, prior to coating, a chromate treatment can be applied by a conventional method.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example) A 0.8 mm thick, 100 mm wide, 200 mm long cold-rolled steel sheet was degreased,
After cleaning the surface by pickling, various amounts of Ni, Cr, Co, or Ni—Cr or Ni—Co alloy electroplated on one surface under the following plating conditions.

Electrical Ni plating conditions Plating bath _{composition: NiSO 4 · 7H 2 O 270g} / NiCl 2 · 6H 2 O 50g / H 3 BO 3 35g / pH: 5.5 Bath temperature: 50 ° C. Current density: 5A / dm ² electric Cr plating conditions Plating Bath composition: CrO ₃ 250g / H ₂ SO ₄ 2.5g / Bath temperature: 45 ° C Current density: 5A / dm ² Current Co plating conditions Plating bath composition: CoSO ₄・ 7H ₂ O 450g / H ₃ BO ₃ 40g / CoCl ₂・ 6H ₂ O 45g / KCl 20g / pH: 4.0 Bath temperature: 37 ° C Current density: 5A / dm ^{2 In the case of} Ni-Cr or Ni-Co alloy plating, the above Ni plating bath composition Using a plating bath containing CrO ₃ (in the case of Ni-Cr alloy) or CoSO ₄ · 7H ₂ O (in the case of Ni-Co alloy) so that the Cr or Co content becomes a predetermined weight%, Electroplating was performed under the conditions according to the Ni plating conditions.

Next, the steel sheet after the undercoating treatment is thoroughly washed with water, then dried for 1 minute in a hot air dryer at 70 ° C. to completely remove water, and immediately under the following conditions, Al-based mixed molten salt bath is used.
It was subjected to Mn alloy plating treatment.

Al-Mn alloy electroplating conditions Plating bath composition: AlCl ₃ 74.1% by weight NaCl 14.1% by weight KCl 11.8% by weight Bath temperature: 200 ° C Current density: 40 A / dm ^{2 For} Mn, the Mn content in the plating film is prescribed. weight%
MnCl ₂ was added to the molten salt bath so that The energization time is about 60 seconds when the upper layer deposition amount is 20 g / m ² . This molten salt electroplating was performed using a flow cell dedicated to molten salt [manufactured by Inconel 600 (registered trademark)].

The obtained two-layer plated steel sheet was tested for corrosion resistance and adhesion after heating and workability in the following manner. The test results are shown in the following Tables 1 to 5 together with the types of plating and the amounts of adhesion of the lower and upper layers.

Test method Corrosion resistance after heating: After heating in air at 500 ° C. for 24 hours, a salt spray test (JIS-Z2371) was performed, and the number of days until the occurrence of red rust was evaluated.

Adhesion after heating: After heating in air at 600 ℃ for 30 minutes, DuPont impact test (ball head diameter 1/2 inch, energy
0.8 kgf-m) was performed, and the adhesiveness was evaluated by the peeling condition in tape peeling.

Workability: A tape peeling test was performed after closely bending with a bending radius of 0.8 mm, and the adhesiveness was evaluated by the peeling condition.

For comparison, an Al-Mn-based single-layer plated steel sheet in which lower layer plating was omitted or a two-layer plated steel sheet in which various conditions were out of the scope of the present invention was similarly prepared, and the test results were also shown in Tables 1 to 5. It is also shown in the table.

As can be seen from the results in Table 5, when Ni-based plating is used as the lower layer of Al plating, the corrosion resistance after heating deteriorates. this is,
This is due to the combination of the precious Ni-based and Al plating. On the other hand, in the Al-Mn system, the plating film is more noble than Al, and especially when viewed after heating, the difference in corrosion resistance between Al and Al-Mn is remarkable. This is because in addition to the lower layer of Ni, Co, and Cr, the iron components of the base metal diffuse and penetrate into the plating film due to heating, and the corrosion resistance itself of the Al plating deteriorates.
While the noble plating Ni, Co, and Cr joints deteriorate the corrosion resistance more, Al-Mn does not almost deteriorate the corrosion resistance even when these metal components are mixed, and This is because the coating shifts to the noble side, the difference in corrosion potential from the lower layer plating is reduced, and the coating has a better balance.

Further, the presence of Mn in the film prevents the diffusion of components such as Ni, Co, Cr, and Fe, and consequently reduces the change in glossiness due to heating.

Table 6 shows the experimental results showing these relationships.

In Table 6, various Al and Al-Mn plated materials were heated in the atmosphere at 400 ° C for 10 days as in the case of Fig. 2 described later, and the change in gloss was measured. Since the initial glossiness is different, the change rate was compared. The Mn content of the Al-Mn alloy is 0.
When it is 5% or more, the change in glossiness decreases.

here, (Comparative Example) In this example, a galvanized steel sheet is plated with Al-Mn. Zinc plating was performed under the following conditions, and Al-Mn plating was performed according to that of the above-mentioned example.

Electrical Zn plating conditions Plating bath _{composition: ZnSO 4 · 7H 2 O:} 300g / Na 2 SO 4: 100g / pH: 4.5, bath temperature: 50 ° C. Current density: 10A / dm ² The results are summarized in Table 7, and as can be seen from this, the Fe-Zn alloy layer is generated by the heating in the Zn plating lower layer and peeling occurs, and a large amount of Zn is also present in the Al-Mn plating film.
Are diffused, the corrosion resistance after heating is significantly deteriorated. This is because Zn, which is a low melting point metal, is easily diffused into the Al-based metal.

(Effect of the invention) As can be seen from the results in the above tables, the two-layer plated steel sheet of the present invention is excellent in corrosion resistance and adhesion after heating,
It also has good workability.

Specifically, Table 1 shows changes in the amount of the lower layer deposited when the lower layer is Ni plating (No. 1 to 8) and changes in the amount of the upper Al-Mn alloy plating (No. 9 to 17). Shows the effect of. Excellent corrosion resistance and adhesion after heating are obtained when the amount of Ni plating of the lower layer is in the range of 0.5 to 20 g / m ² . If Ni plating is not performed, or if the amount deposited is less than 0.5 g / m ² , neither corrosion resistance nor adhesion after heating is sufficient. When the Ni plating coverage is 30.0 g / m ² (No. 8), the corrosion resistance and adhesion after heating are good, but Ni is noble, so
If the layer is thick like this, corrosion of the base Al, which is a base layer, easily progresses from the end face, and the end face corrosion resistance deteriorates, which is not preferable. It can be seen that when the amount of the Al-Mn alloy plating as the upper layer is less than 0.1 g / m ² , the corrosion resistance is extremely deteriorated, and conversely, when it exceeds 100 g / m ² , good workability cannot be obtained.

Tables 2 and 3 are examples when the lower layer is Cr and Co plating, respectively, and the amount of the lower layer deposited is 0.
If it is less than 5 g / m ² or if the lower layer is omitted, both the corrosion resistance and adhesion after heating are low, and the lower layer adhesion amount is low.
When it is as high as 30 g / m ² , the workability is significantly deteriorated.

Table 4 shows the results when the lower layer plating changed the amount of the lower layer deposited in the Ni-Cr alloy plating, and shows the same tendency as in Tables 2 and 3 above.

Table 5 shows that when the lower layer is a Ni-Co alloy, the upper layer of Al-
It is an example in which the Mn content of the Mn alloy plating layer was changed. It can be seen that when the upper layer is pure Al, the corrosion resistance after heating is extremely reduced. Further, if the Mn content exceeds 50%, it is difficult to obtain good workability.

Further, the attached FIG. 1 (a) shows a plated steel plate outside the scope of the present invention of No. 1 in Table 1 above, that is, an Al-20% Mn alloy plating layer with a coating amount of 20 g / m ² Is a photomicrograph showing the cross-sectional structure of a 1-layer plated steel sheet directly provided on the Al-Mn layer and the base metal after being heated at 600 ° C for 30 minutes in the atmosphere. It can be seen that the Fe-Al alloy layer is formed, and as a result, the plating layer is lifted and easily peeled off.

On the other hand, in FIG. 1 (b), the same Al-20% Mn alloy plating layer as the upper layer is used as an upper layer, and a Ni plating layer having an adhesion amount of 4 g / m ² is provided as a lower layer in the same condition as in the above embodiment. 3 is a photomicrograph showing the cross-sectional structure of the two-layer plated steel sheet of the present invention, which was likewise subjected to atmospheric heating at 600 ° C. for 30 minutes. It can be seen that the formation of the Fe-Al alloy layer is completely suppressed by providing the very thin Ni layer in contact with the base material.

Further, FIG. 2 shows that No. 1 and No. 6 in Table 1 above, that is, the upper layer is an Al-20% Mn alloy plating layer, and there is no lower Ni layer (No. 1) and the adhesion amount is 10 g. / m ² with a lower Ni layer (No. 6)
It is a graph which shows the change of the plating appearance by the number of heating days when it is heated at 0 ° C for a long time with the glossiness as a scale. The decrease in glossiness is considered to occur as a result of generation of surface oxides and diffusion of the base material Fe to the surface, resulting in poor appearance and corrosion resistance after heating. Even when heating for a long period of time, as in the case above, the gloss level will decrease immediately if the lower Ni layer is not provided, whereas if a Ni layer is provided, the rate of decrease will be greatly suppressed. It can be seen that the plated steel sheet of the invention has good heat resistance.

As described above, the double-layer plated steel sheet of the present invention can be efficiently manufactured at a relatively low cost by the electroplating method, and further, the deterioration of the corrosion resistance and the adhesion is suppressed even when used under heating conditions in the atmosphere. Since it has good workability, it is useful as a relatively inexpensive heat-resistant or corrosion-resistant material.

[Brief description of drawings]

FIG. 1 (a) is a cross-sectional micrograph showing the steel structure of a single-layer plated steel sheet having an Al-20% Mn alloy plated layer of 20 g / m ^{2 on} the surface of the steel sheet after atmospheric heating at 600 ° C. for 30 minutes, FIG. 1 (b) is a cross-sectional micrograph showing a similar steel structure after heating of the same two-layer plated steel sheet as the above except that the above-mentioned plated layer is the upper layer and a lower Ni layer of 4 g / m ² is provided, and Figure shows the same Al-Mn alloy layer as the upper layer, with and without the Ni plating layer of 10g / m ² as the lower layer, and the case of not provided It is a graph which shows change.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Uchida 1-3, Nishi-Nagasumotodori, Amagasaki-shi, Hyogo Sumitomo Metal Industries, Ltd. Research Institute (56) Reference Japanese Patent Laid-Open No. 61-213393 A)

Claims (1)

[Claims] 1. At least one selected from Ni, Cr and Co
A lower plating layer of the deposited amount 0.5 to 20 g / m ² consisting of species of the metal, the upper layer plating deposition amount 1 to 100 g / m ² of Mn content is from Al-Mn alloy electroplating layer is 0.5 to 50 wt% Two layers and a steel sheet having a layer and one or both sides of the steel sheet and having excellent workability, heat resistance and corrosion resistance.