JP2712956B2 - Surface treated steel sheet with excellent corrosion resistance, lubricity and weldability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet excellent in corrosion resistance, lubricity and weldability, which is suitable as a steel sheet for automobiles.

[0002]

2. Description of the Related Art As a steel sheet for an automobile, for example, in a cold area, even in a severely corrosive environment such as rock salt or calcium chloride sprayed on a road in order to prevent freezing of ice and snow in winter, red rust or the like remains for a predetermined time. Excellent corrosion resistance that can withstand perforation is required. Also, in order to save energy, automobile body weight is being actively reduced.
Accordingly, there is a demand for reducing the thickness of a steel sheet for automobiles. When the thickness of the steel sheet is reduced, the rust allowance is reduced, so that it is necessary to further improve the corrosion resistance of the steel sheet. Therefore, if the plating amount is increased, the corrosion resistance is improved, but on the other hand, the weldability and the workability are deteriorated. From such a viewpoint, development of a surface-treated steel sheet having excellent corrosion resistance with a small amount of plating has been strongly desired.

[0003] Galvanized steel sheets have been widely used as automotive steel sheets because of their excellent corrosion resistance due to the sacrificial corrosion protection of zinc. However, the galvanized steel sheet has a relatively high corrosion rate because of the high activity of the galvanized layer formed on the surface of the steel sheet. Therefore,
In order to maintain the corrosion resistance of a galvanized steel sheet for a long time, the amount of galvanized steel sheet must be increased.

Therefore, in order to suppress the activity of the galvanized layer, a zinc-iron alloy-plated steel sheet or a zinc-iron alloy-plated steel sheet or a zinc-nickel alloy-plated layer is formed on the surface of the steel sheet. -Nickel alloy plated steel sheets have been put into practical use, and such alloy plated steel sheets are
Recently, it is widely used for automobile bodies, and its usage ratio is increasing.

[0005]

However, in recent years,
Even higher corrosion resistance is required for zinc-iron alloy plated steel sheets and zinc-nickel alloy plated steel sheets. In order to meet such requirements, it is necessary to increase the plating amount of the zinc-iron alloy plating layer or the zinc-nickel alloy plating layer. However, when the amount of plating is increased, there arises a problem that lubricity during press molding deteriorates and weldability deteriorates. Therefore, development of a surface-treated steel sheet having excellent corrosion resistance, lubricity and weldability is strongly desired.

As a surface-treated steel sheet which solves the above-mentioned problems, for example, Japanese Patent Publication No. 2-10236 discloses a high corrosion-resistant surface-treated steel sheet (hereinafter referred to as prior art) comprising: A zinc or zinc-based alloy plating layer as a lower layer formed on at least one surface of a steel sheet; and a cobalt-tungsten alloy plating as an upper layer formed on the zinc or zinc-based alloy plating layer as a lower layer Or a cobalt-chromium alloy plating layer, the content of tungsten or cobalt in the upper plating layer is 0.01 to 10 wt.%, And the plating amount of the upper plating layer is 0.003 to 3 g per side of the steel sheet. a / m ^2.

The above prior art has the following problems. That is, the effect of improving the corrosion resistance by the cobalt-tungsten alloy plating layer or the cobalt-chromium alloy plating layer as the upper layer is caused by depositing Zn (0H) ₂ , which is a corrosion product of Zn, in the upper porous plating layer. It is supposed to be. In this case, the corrosion resistance largely depends on the stability of Zn (0H) ₂ . However, in the corrosion process, in addition to Zn (0H) ₂ as a corrosion product of Zn, there is a possibility that ZnO having semiconductor properties may be generated, so that the above-described deposition of the corrosion product alone is not necessarily sufficient. Insulating properties cannot be provided.

[0008] Therefore, in such a coating, depending on the corrosive environment, the effect of improving corrosion resistance due to corrosion products may not be expected. In this case, in order to improve the corrosion resistance, it is necessary to rely on the plating amount of the zinc or zinc-based alloy plating layer as the lower layer, and when the plating amount is small, the corrosion resistance cannot be improved. .

[0009] Accordingly, an object of the present invention is to solve the above-mentioned problems, exhibit excellent corrosion resistance in any corrosive environment, and have good lubricity during press molding and excellent weldability. It is to provide a treated steel sheet.

[0010]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems. As a result, a chromium in the range of 5 to 90 wt.% And a chromium in the range of 10 to 95 wt.% Are formed on the underlying zinc or zinc-based alloy plating layer formed on at least one surface of the steel sheet. It has been found that forming a manganese-chromium alloy plating layer as an upper layer composed of manganese can provide a surface-treated steel sheet having excellent corrosion resistance, lubricity, and weldability.

[0011] The present invention has been made based on the above findings, and a surface-treated steel sheet according to the present invention is a zinc-plated layer or a zinc-based alloy as a lower layer formed on at least one surface of a steel sheet. A plating layer and a manganese-chromium alloy plating layer as an upper layer formed on the zinc plating layer or the zinc-based alloy plating layer as a lower layer, and the zinc plating layer or the zinc-based alloy plating layer as a lower layer The plating amount is 5 to 10 per side of the steel sheet.
In the range of 0 g / m ^2, the manganese as an upper - chromium alloy plating layer is formed of a five and chromium in the range of 90 wt%, and in the range of 10 to 95 wt% manganese,.. And, the plating amount of the manganese-chromium alloy plating layer as the upper layer is 0.01 to 5 g / one side of the steel sheet.
those having features to be within the scope of m ^2.

[0012]

The invention is characterized in that it is formed on at least one surface of a steel plate.
The corrosion resistance of the zinc or zinc-based alloy plating layer as the lower layer is due to the sacrificial corrosion protection of the steel sheet by the zinc or zinc-based alloy plating layer. Therefore, in order to improve the corrosion resistance, it is necessary to maintain the sacrificial anticorrosion action of the zinc or zinc-based alloy plating layer on the steel sheet for a long time.

Under a corrosive environment having a relatively high pH and sufficient oxygen supply, manganese reacts with oxygen to form an oxide of Mn ₂ O ₃ which is extremely stable.

When a zinc plating layer or a zinc-based alloy plating layer is exposed to a corrosive environment, Zn0 or Zn (0H) ₂ , which is a corrosion product of Zn, is formed on the surface layer. Of these, Zn0
Has an n-type semiconductor characteristic, and thus is particularly conductive. Therefore, in a corrosive environment, electrons that contribute to the reduction reaction of dissolved oxygen easily conduct in the corrosion product, and as a result, the corrosion reaction of Zn proceeds.

Therefore, in order to reduce the n-type semiconductor characteristics of Zn0 described above, Cr ³⁺ is introduced into the corrosion product.
Cr ³⁺ prevents conduction of electrons in corrosion products, resulting in Zn0
Is given insulation. Therefore, the corrosion reaction of Zn can be suppressed. Further, since Cr forms a stable oxide, it is possible to fix the above-mentioned Zn corrosion product generated in the surface layer.

When a manganese-chromium alloy plating layer as an upper layer is formed on a zinc or zinc-based alloy plating layer as a lower layer, in a corrosive environment where oxides of manganese can be stably present, manganese and oxygen are removed. Reacts to form a stable protective film made of Mn ₂ O ₃ as described above. On the other hand, in a corrosive environment where manganese oxides cannot exist stably, active manganese elutes,
A chromium-enriched layer is formed on the upper layer. As a result, the upper layer is formed by a very dense passivation film of chromium or an oxide film of zinc and chromium.

Therefore, by forming a manganese-chromium alloy plating layer as an upper layer on a zinc or zinc-based alloy plating layer as a lower layer, extremely excellent corrosion resistance is imparted to the steel sheet in any corrosive environment. be able to.

On the surface of the steel sheet, the amount of zinc is relatively large,
In the zinc or zinc alloy plated steel sheet having the zinc or zinc alloy plated layer formed thereon, the zinc or zinc alloy plated layer is predominantly composed of an η layer having a low hardness. Therefore, when such a zinc or zinc alloy plated steel sheet is press-formed, the plated layer is easily deformed, and the area of the plated layer substantially in contact with the press fitting is increased. Furthermore, a part of the zinc or zinc alloy plating layer having a relatively low melting point is
It is welded to the press fitting by frictional heat. As a result of these,
The coefficient of friction of the plating layer during press molding increases,
Lubricity of the plated steel sheet decreases.

Therefore, if a manganese-chromium alloy plating layer having a relatively high melting point and hardness is formed as an upper layer on the zinc or zinc alloy plating layer, the plating layer is brought into contact with the press fitting during press forming. Deformation is small, and welding between the plating layer and the press fitting due to frictional heat does not occur. As a result, the coefficient of friction of the plated layer during press forming is reduced, and the lubricity of the plated steel sheet is improved.

In addition, when welding a zinc or zinc alloy-plated steel sheet, a copper electrode tip and a part of a zinc or zinc alloy plating layer are alloyed and adhere to the tip of the electrode tip. As a result, the weldability deteriorates. However, if the manganese-chromium alloy plating layer as the upper layer is formed on the zinc or zinc alloy plating layer, the electrode tip and the plating layer as described above are alloyed at the time of welding, and the tip of the electrode tip is formed. Does not occur. Therefore, the weldability, especially the continuous weldability, is significantly improved. Furthermore, the effect of improving corrosion resistance by the manganese-chromium alloy plating layer as the upper layer makes it possible to reduce the amount of plating as compared with the conventional case, and from this point, it is also effective in improving weldability.

The chromium content of the upper manganese-chromium alloy plating layer should be in the range of 5 to 90 wt.%, And its manganese content should be in the range of 10 to 95 wt.%. The chromium content of the manganese-chromium alloy plating layer is less than 5 wt.%, And the manganese content is 95%.
If it exceeds wt.%, the effect of improving corrosion resistance by chromium cannot be obtained. On the other hand, the chromium content of the manganese-chromium alloy plating layer is more than 90 wt.%, And the manganese content is 10 wt.%.
If it is less than the above range, the above-mentioned effect of forming a stable protective film made of Mn ₂ O ₃ by the reaction between manganese and oxygen cannot be obtained.

The amount of plating of the manganese-chromium alloy plating layer as the upper layer should be in the range of 0.01 to 5 g / m ² per one side of the steel sheet. Manganese - plating of chromium alloy plating layer is, in one surface per 0.01 g / m of less than ² of the steel sheet, corrosion resistance,
The effect of improving lubricity and weldability cannot be obtained. On the other hand, if the above-mentioned plating amount exceeds 5 g / m ² per one side of the steel sheet, further improvement effects of corrosion resistance, lubricity and weldability cannot be obtained, which is uneconomical.

The plating amount of the zinc or zinc alloy plating layer as the lower layer should be in the range of 5 to 100 g / m ² per one side of the steel sheet. If the plating amount of the zinc or zinc alloy plating layer is less than 5 g / m ² per one side of the steel sheet, the desired corrosion resistance cannot be obtained. On the other hand, when the plating amount of the zinc or zinc alloy plating layer exceeds 100 g / m ² per one side of the steel sheet, press formability deteriorates.

The surface-treated steel sheet of the present invention having excellent corrosion resistance, lubricity and weldability is produced as follows. A zinc or zinc-based alloy plating layer is formed as a lower layer on at least one surface of the steel sheet. The means for forming the zinc or zinc-based alloy plating layer is not particularly limited. Then 10-200 g / l manganese and 0.
Use an electroplating solution containing 1 to 50 g / l of chromium,
By electroplating, a manganese-chromium alloy plating layer as an upper layer is formed on a zinc or zinc-based alloy plating layer as a lower layer.

In the electroplating solution for forming the manganese-chromium alloy plating layer as the upper layer, cations such as Na ⁺ , K ⁺ , and NH ₄ ⁺ for imparting conductivity to the plating solution are added. Or a polymer as a Cr precipitation promoter may be added. PH value of plating solution is 1.0 to 3.0
Is preferably within the range. Since the plating current density can thereby change the composition of the coating,
Although not particularly specified, 10 to 200 A / dm ² is preferable. The flow rate of the plating solution is preferably 0.5 to 5 m / s as a relative speed to the steel sheet passing through the solution, and the temperature of the plating solution is preferably 30 to 70 ° C.

Next, the present invention will be described in more detail with reference to examples and comparative examples.

EXAMPLE A cold-rolled steel sheet (aluminum-killed steel) having a thickness of 0.7 mm is plated under one of the following seven types of plating conditions A to G, and on one surface of the cold-rolled steel sheet, A zinc or zinc alloy plating layer was formed as a lower layer. Next, such a cold-rolled steel sheet having a zinc or zinc alloy plating layer as a lower layer formed on the surface thereof is subjected to the following H method.
Electroplating was performed under the following plating conditions to form a manganese-chromium alloy plating layer as an upper layer on the zinc or zinc alloy plating layer. Thus, the specimens of the present invention (hereinafter referred to as the present invention specimens) Nos. 1 to 6 having two plating layers within the scope of the present invention and shown in Tables 1 to 4,
o.13-18, No.25-30, No.37-42, No.49-54, No.
Nos. 61-66 and Nos. 73-78 were prepared.

For comparison, a manganese-chromium alloy plating layer outside the scope of the present invention as an upper layer on a zinc plating layer or a zinc alloy plating layer, or a plating of the following I or J based on the prior art An alloy plating layer was formed according to the conditions. Thus, the comparative specimens Nos. 7 to 12, Nos. 19 to 24, Nos. 31 to 36, and Nos. Having two plating layers outside the scope of the present invention, which are also shown in Tables 1 to 4, are shown. 43 to 48, N
o.55-60, Nos.67-72 and Nos.79-84 were prepared.

A. Zn electroplating (lower layer) Composition of plating _{solution: ZnSO 4 · 7H 2 O:} 500g / l, Na 2 SO 4: 60g / l, the plating solution temperature: 50 ° C., the plating solution of pH values: 1.7, plating current density : 50~80A / dm ^2, plating amount: 40g / m ^2.

B. Zn-Ni alloy electroplating (lower layer) Composition of plating _{solution: ZnSO 4 · 7H 2 O:} 150g / l, Na 2 SO 4: 60g / l, NiSO 4 · 6H 2 O: 350g / l, the plating solution temperature: 50 ° C, pH value of plating solution: 1.3, plating current density: 50-100A / dm ² , plating amount: 30g / m ² .

C. Zn-Fe alloy electroplating (lower layer) Composition of plating _{solution: ZnSO 4 · 7H 2 O:} 200g / l, Na 2 SO 4: 30g / l, FeSO 4 · 7H 2 O: 300g / l, CH 3 CONa: 20g / l, the temperature of the plating solution: 50 ° C., the plating solution of pH values: 1.2, plating current density: 50 to 70A / dm ^2, plating amount: 40 g / m ^2.

D. Zn-Mn alloy electroplating (lower layer) Composition of plating _{solution: Zn (BF 4) 2:} 15g / l, Mn (BF 4) 2: 270g / l, H 3 BO 3: 20g / l, HO (CH 2 CH ₂ O) _n H: 2.5 g / l, temperature of plating solution: 60 ° C, pH value of plating solution: 2.5, plating current density: 50 to 80 A / dm ² , plating amount: 30 g / m ² .

E. Zn-Cr alloy electroplating (lower layer) Composition of plating _{solution: ZnSO 4: 200g / l,} Cr 2 (SO 4) 3: 120g / l, HO (CH 2 CH 2 O) n H: 2.5g / l, the plating liquid temperature: 50 ° C., the plating solution of pH values: 1.2, plating current density: 50~120A / dm ^2, plating amount: 20 g / m ^2.

F. Hot-dip Zn plating (lower layer) Composition of plating solution: Zn containing Al: 0.12 wt.%, Temperature of plating solution: 465 ° C, entry temperature of steel sheet: 470 ° C, plating amount: 60 g / m ² .

G. Hot-dip Zn-Fe alloy plating (lower layer) Composition of plating solution: Zn containing 0.12wt.% Al, Temperature of plating solution: 465 ° C, Entry temperature of steel sheet: 470 ° C, Alloying temperature: 495 ° C, Plating amount : 40g / m ^2.

H. Mn-Cr alloy plating (upper layer) Composition of plating _{bath: Mn (BF 4) 2:} 50~450g / l, Cr (BF 4) 3: 10~200g / l, PEG ( polyethylene glycol): 2.5 g / l , Plating bath temperature: 50 ° C., Plating bath pH value: 2.0, Plating current density: 10 to 200 A / dm ² , Plating amount: Depends on the plating current density and the composition of the plating solution.

I. Co-W alloy plating (upper layer) Composition of plating solution: Tank Bu Sodium Sten _{acid: 10g / l, NH 4 Cl} : 60g / l, CoSO 4: 200g / l, H 3 BO 3: 30g / l, the plating solution temperature: 40 ° C, pH value of plating solution: 6.0, plating current density: 1 to 10 A / dm ² , plating amount: 2 g / m ² .

J. Co-Cr alloy plating (upper layer) Plating solution _{composition: CoSO 4: 200g / l,} H 3 BO 3: 30g / l, NH 4 Cl: 60g / l, CrCl 3: 20g / l, the plating solution temperature: 40 ° C, pH value of plating solution: 3.0, plating current density: 1 to 10 A / dm ² , plating amount: 2 g / m ² .

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

[Table 4]

With respect to each of the thus-prepared specimens of the present invention and the comparative specimens, corrosion resistance, lubricity and weldability were examined by performance tests described below.

(1) Corrosion resistance test: a. Bare corrosion resistance test: Each specimen was subjected to a salt spray test specified in JIS Z 2371, and evaluated by the time until red rust was generated.

B. Corrosion resistance test after painting: Each specimen was subjected to immersion type phosphate treatment in a phosphating solution to form a phosphate film on the surface of each specimen,
Subsequently, a cationic type electrodeposition coating treatment was performed to form a coating film having a thickness of 20 μm on the phosphate coating film. Then, after intermediate coating and top coating were performed on the coating film, a cross cut was performed.

The specimens thus cross-cut were subjected to two types of corrosion promotion tests A and B having different wetting times and drying times, with one cycle of salt spray, drying and wetting being performed once a day. For 120 cycles. A. Drying time: 1 hour, Wetting time: 5 hours, B. Drying time: 5 hours, Wetting time: 1 hour.

The swelling width at the cross-cut portion of the specimen subjected to the corrosion promotion test as described above was measured and evaluated as follows. ◎: swollen width 0 to less than 1 mm,: swollen width 1 mm to less than 3 mm, Δ: swollen width 3 mm to less than 5 mm, ×: swollen width 5 mm or more.

(2) Lubricity test: The lubricity of each specimen was examined by using a friction coefficient measuring device shown in a schematic front view in FIG. As shown in FIG. 1, the friction coefficient measuring device includes a horizontally movable slide table 2 on which a test piece 1 is placed, and a holding tool 3 for pressing the test piece 1 on the slide table 2 from above. A vertically movable slide table support 5 having a roller 4 for contacting the lower surface of the slide table 2, provided at a position below the slide table 2 and symmetrically with the presser 3, and attached to the slide table support 5. The slide table support 5
Load cell 6 for measuring vertical pressure N by
And a second load cell 7 for measuring a pulling force F by the slide table 2 attached to an end of the slide table 2 in the horizontal movement direction.

The slide table support 5 is pushed upward by a drive mechanism (not shown) to
The test piece 1 placed on top is brought into contact with the presser 3 with a vertical pressing force N as shown by an arrow, and the slide table 2 is shown together with the test piece 1 by an arrow by another drive mechanism (not shown). As described above, it is horizontally moved at a speed of 1 m / min with a pulling force F. The friction coefficient was measured by the ratio of the vertical pressing force N and the tensile force F during this horizontal movement, that is, F / N, and the lubricity was evaluated.

(3) Weldability test: Two specimens superposed with their plated surfaces outside were subjected to spot welding, and the number of spots at which continuous welding was possible was evaluated. ◎: Number of continuous dots 6000 or more, ○: Number of continuous dots 4000 or more, less than 6000, Δ: Number of continuous dots 2,000 or more, less than 4000, ×: Number of continuous dots 2,000 or less.

Tables 5 to 8 show the test results of each specimen described above.
Shown in

[0051]

[Table 5]

[0052]

[Table 6]

[0053]

[Table 7]

[0054]

[Table 8]

As apparent from Tables 1 to 4 and Tables 5 to 8, all of the test samples of the present invention were excellent in bare corrosion resistance, corrosion resistance after coating, lubricity and weldability.
On the other hand, a comparative specimen No. 7, 19, 31, 43, in which only a zinc or zinc alloy plating layer was formed on the surface of the steel sheet.
Nos. 55, 67 and 79 were inferior in all of the bare corrosion resistance, the corrosion resistance after painting, the lubricity, and the weldability as compared with the test specimen of the present invention.

Even if a Mn-Cr alloy plating layer as an upper layer was formed on the lower layer, the comparative specimens No. 8, 20, 32, 44 having a large Cr content beyond the scope of the present invention. , 56, 68, 80, and the comparative sample No. 9, 21, 33, 45, 57, 69, 81, in which the content of Cr is out of the range of the present invention, is smaller than the test sample of the present invention. The corrosion resistance after painting was poor. In addition, Mn-
The comparative specimens No. 10, 22, 34, 46, 58, 70, and 82, in which the plating amount of the Cr alloy plating layer is larger than the scope of the present invention, have corrosion resistance,
Improvements in lubricity and weldability were saturated and uneconomical.

As the upper layer, a comparative specimen No. 11, 23, 35, 47, 59, 71, 83 having a prior art Co-Cr alloy plating layer formed thereon
, And the comparative specimen No. 12, 24, 36, 48, 60, 72, and 84 on which the Co-W alloy plating layer of the prior art was formed, compared with the specimen of the present invention, in terms of bare corrosion resistance and after coating. Was inferior in corrosion resistance.

[0058]

As described above, according to the present invention,
An industrially useful effect that exhibits excellent corrosion resistance in any corrosive environment, has good lubricity during press forming, and has excellent weldability, and provides a surface-treated steel sheet suitable for automotive steel sheets. Is brought.

[Brief description of the drawings]

FIG. 1 is a schematic front view of a friction coefficient measuring device for testing the lubricity of a surface-treated steel sheet.

[Explanation of symbols]

 1 Test piece, 2 Slide table, 3 Holder, 4 Roller, 5 Slide table support, 6 First load cell, 7 Second load cell.

Claims (1)

(57) [Claims] 1. A zinc-plated layer or a zinc-based alloy plating layer as a lower layer, formed on at least one surface of a steel sheet, and formed on the zinc-plated layer or the zinc-based alloy plating layer as a lower layer. , Manganese as upper layer
A chromium alloy plating layer, the plating amount of the zinc plating layer or the zinc-based alloy plating layer as a lower layer is in a range of 5 to 100 g / m ² per one surface of the steel sheet, and the manganese-chromium as an upper layer is Alloy plating layer is 5 to 90
wt.% chromium and manganese within a range of 10 to 95 wt.%, and the plating amount of the manganese-chromium alloy plating layer as the upper layer is from 0.01 to 0.01 per one side of the steel sheet. A surface-treated steel sheet having excellent corrosion resistance, lubricity and weldability, characterized by being within the range of 5 g / m ² .