JPS61119678A - Lead-tin alloy plated steel sheet of high corrosion resistance - Google Patents

Abstract

PURPOSE:To develop Pb-Sn alloy plated steel sheet superior in corrosion resistance and of small Fe dissolution from defective plated part, by forming substrate plated layer of Ni, Co or Ni-Co alloy on Cr bearing steel sheet, then plating Pb-Sn alloy thereon. CONSTITUTION:Cr bearing steel sheet contg. <0.10% C, 0.005-0.08% sol Al, 0.5-20% Cr or further 0.03-0.5% one or >=2 kinds among Ti, Nb, V, Zr respectively is pretreated, i.e. degreased or pickled, etc., then substrate plated layer of Ni, Co or Ni-Co alloy is formed. Next, said sheet is heated to 600-850 deg.C in nonoxidizing atmosphere, to change the plated surface to diffusion treated layer of Ni-Fe, Co-Fe, Ni-Co-Fe, etc. Pb-Sn plated layer contg. 7-15% Sn is formed by 2-10mu thickness on surface of the substrate diffusion treated layer. Dissolution of steel sheet from pinhole of plated layer is prevented, and Pb-Sn alloy plated steel sheet superior in corrosion resistance is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a lead-tin alloy plated steel sheet with a small amount of Fe elution and a T-grade corrosion resistance.

(Prior Art and its Problems) In general, lead-tin alloy hot-dip plated steel sheets have good corrosion resistance, solderability, workability, etc., and are therefore used for various purposes. However, lead does not easily react with iron, so it is difficult to form an alloy layer uniformly, or lead is relatively easily oxidized. Due to imperfections, pinholes often occur in lead-tin alloy plating.

Furthermore, since the lead-tin alloy is a very soft metal, during handling or processing, the plating layer may be scratched, pinholes may be enlarged, and red rust may occur in a corrosive environment.

In order to solve these problems, for example,
As introduced in Japanese Patent Application Laid-open No. 3345 and Japanese Patent Application Laid-Open No. 51-115240, zinc, tin, copper, nickel, and cobalt are applied before hot-dip lead-tin alloy plating.

The application method for nickel-cobalt alloys involves intermediate surface treatment. However, these intermediate base treatment methods, which involve plating with zinc and tin, do not provide sufficient pinhole prevention effects because these base plating layers dissolve in the hot-dip plating bath.

In addition, the method of performing copper plating as an intermediate base treatment method is because steel plating itself using an acid plating bath or a pyrophosphoric acid plating bath does not have sufficient plating adhesion to the steel material, so it is difficult to obtain sufficient pinhole prevention effects. I can't do it.

Nickel, cobalt, and nickel-cobalt alloy intermediate base treatment is applied to the lead-tin alloy plated steel sheet, which has fewer pinholes and is resistant to scratches on the plating layer due to handling or processing. Good corrosion resistance can be obtained because, due to the presence of the base plated metal, it is relatively rare for scratches to occur in the plated layer to reach the surface of the steel material. However, it is difficult to completely eliminate pinholes, and it is also difficult to completely prevent scratches during machining that reach the steel surface.

In recent years, there has been a trend toward higher-grade durable consumer goods, and a demand for lead-tin alloy plated steel sheets that can improve corrosion resistance from salt sprayed to prevent roads from freezing in the winter, and that can reduce corrosion due to harsh forming processes due to the shape of the tank. I'm here.

In general, a lead-tin alloy plating layer rN"x containing an alloy layer with Sn has corrosion resistance against moisture, Ct- ions, gasoline, etc. However, a lead-tin alloy plating layer etc. is not normally used. In a corrosive environment, it is significantly cathodic (potentially nobler) than the plated original plate, and the gap between the lead-tin plating layer and the plated original plate, and the Ni't-containing Sn alloy layer and the plated original plate The corrosion current is extremely large.

Therefore, if there is a defect in the plating layer that reaches the steel surface, a local battery is generated between the lead-tin plating layer and the plated original plate, or between the alloy layer of Sn containing a base metal such as Ni and the plated original plate. Since the plating original plate is anodic (potentially base), Fe is removed from the Fe exposed part of the plating layer defect.
There is a lot of bathing and dissolution, and in some cases, perforation corrosion occurs.

(Means 1 for solving all the problems) The present invention has been made in response to these problems, and its purpose is to provide a lead-tin alloy plated steel sheet that has better corrosion resistance than ever before. This is what I did.

The present inventors have developed a method using Ni, Co, Ni-Co alloys and their diffusion layers as base materials, which are less prone to elution and dissolution of Fe and less likely to cause pitting corrosion even if defects etc. exist or occur in the plating layer. As a result of various studies on the lead-tin alloy plated steel sheet that has the coating layer, we found that the plated original sheet (steel sheet) is
We discovered that this is possible by bringing the potential closer to the negative direction (cathodic) and increasing the corrosion resistance of the steel plate itself (reducing the self-corrosion rate).

The present invention was constructed based on this knowledge, and its gist is as follows:
C: 0.10% or less, 5olAt: 0.005 to 0.
08%, Cr: 0.5-20% or IIIi as necessary.

One or more types of Nb, V, and Zr are each added in an amount of 0.
Ni, Co, Ni-C
This is a highly corrosion-resistant lead-tin alloy plated steel sheet having a base coating layer of an o alloy or a diffusion base coating layer thereof, and a lead-tin alloy coating layer as an upper layer.

Details about the present invention below? I will explain this.

The molten steel in a converter, electric furnace, etc. is made into a slab through a continuous casting method, ingot making, or blooming method, and is then hot rolled, cold rolled, and annealed to produce a slab with C:O, 10% or less, sol At:
0.005-0.08%, Cr: 0.5-20%
A plated original plate is produced in which the remainder is substantially composed of Fe. C deteriorates the workability of the steel plate as the content increases;
A large amount of cementite precipitated dotted on the surface of the steel plate is
Many pinholes' (i-
cause it to occur. Therefore, the C component is a harmful element that deteriorates corrosion resistance and is preferably as small as possible, with the upper limit being 0.10% and preferably 0.01% or less.

At is a highly effective deoxidizing element, but if the amount of 5olAt remaining in the manufactured steel sheet is less than 0.005%, the occurrence rate of surface defects due to oxygen gas will be significantly increased, and it will cause damage to the surface treated surface or lead-tin alloy plating. A large number of pinholes occur on the surface, which deteriorates corrosion resistance. Also, excess 5olA exceeding 0.08%
t causes many At-based oxides to be scattered on the steel surface, causing unplated areas or pinholes to be formed, resulting in loss of healthy plating, and complete deterioration of corrosion resistance. Therefore, the s contained in steel
o l kl was limited to o, o o 5-Lo, and o sti as an amount that could stably ensure corrosion resistance.

The addition of Cr brings the potential of the steel sheet exposed to a corrosive environment closer to the positive direction, improving the corrosion resistance of the steel sheet itself, and also improves the corrosion resistance of the plated original sheet and Ni, Co, Ni-Co alloy base coating, or their diffusion base coating layer. , ■ An alloy layer that is a reaction product between the plating original plate and the Ni, Co, or Ni-Co alloy base coating layer or these diffusion base coating layers and Sn in the lead-tin alloy plating layer, ■ ■ The plating base plate and lead. - The potentials between the tin-based alloy coating layers are brought closer to each other, which has the effect of reducing the couple current between the plating original plate and each of the above layers.

In other words, the addition of Cr makes the steel sheet as described above, and although each layer has a base potential, it reduces the potential difference with each layer and reduces the couple current, thereby preferentially dissolving the Fe coating layer defects. It has the effect of significantly reducing

Therefore, the addition of Cr can cause plating defects in the lead-tin alloy plating layer, the base-Sn alloy layer, the base coating layer, etc., and scratches that reach the steel surface during handling, forming, etc.
Even if an exposed part of Fe is generated, elution of Fe in a corrosive environment, W! ! This reduces pitting corrosion from defective parts and extends the corrosion resistance life.

However, if the amount of Cr added is less than 0.5%, the above effects cannot be obtained, and if the amount of Cr added exceeds 20%, the yield point of the steel sheet will be high, causing problems in terms of formability and weldability. Undesirable. Therefore, the amount of Cr added is 0.5 to 2
It is regulated to 0%, preferably 5 to 10%. Particularly when the application is for fuel containers and the like, the Cr content is preferably 10% or less from the viewpoint of preventing sliding during molding.

In addition, in the present invention, for the above steel components, Ti,
Nb, V, Zr (7) Add 3 to 0.5% of O and Q on 18 or ii Z mK, respectively. This is because the present invention is suitable for applications where severe forming is required, for example, when the steel sheet itself is required to have excellent formability and corrosion resistance, such as fuel containers with complex deep drawing shapes, Ti, Nb, V
By adding one or more types of Zr, it is possible to combine with C in the steel, prevent the precipitation of chromium carbide, and make Cr more effective, resulting in good formability and improved corrosion resistance. Become. In this case, if the content of steel components such as Tl&I Nb is less than 0.03%, the effect of preventing precipitation of chromium carbide and improving formability and corrosion resistance will be small; If it exceeds this, the effect reaches saturation and becomes uneconomical, and the precipitation of these components tends to cause the material to become hard and deteriorate moldability. Particularly preferably, the content of these elements is in the range of 0.05 to 0.30%.

Unavoidable impurities such as P and S contained in steel precipitate at grain boundaries and embrittle the grain boundaries, so the smaller the amount, the better. In addition, in the present invention, depending on the application, Ti, Nb
For steel sheets added with etc., 0.0001 to 0.00
Bi may be added in an amount of 3% or less. In other words, since B precipitates at grain boundaries, bath welding or abrasion is an effective component for preventing the growth and coarsening of crystal grains in these heat-affected zones when subjected to high-temperature operations such as work. be.

The plated original plate having the above-mentioned composition is subjected to pre-plating treatment such as degreasing and pickling to coat Ni.

Base pretreatment for Co and Ni-Co alloy plating is performed.

In these base pretreatment methods, the plating bath composition, plating conditions, etc. are not particularly specified, but the current density is generally 3 to 3.
300A/d1r? , the plating temperature is preferably 80°C or less. An example of the plating bath composition and plating conditions are as follows.

(1) Ni plating bath Current density 15A/drr? <2) Co plating bath (Cobalt sulfate 300 g/l Current density 10A/d,,' (3) Ni-Co alloy plating bath Current density: 7.5A/dze Electroplating may be performed using, for example.

In addition, after pre-treatment of the base by electroplating, or after completely applying and drying an aqueous solution containing these metal ions, such as a nickel sulfate (100 g/l)-surfactant-based aqueous solution, a non-oxidizing acid or reducing solution is applied, respectively. 600~ for a sexual atmosphere
Heat diffusion treatment is performed at 850°C for 20 to 180 seconds, and N
i-Fe, Co-Fe, Ni-Co-Fe
Alternatively, a diffusion treatment layer consisting of the above-mentioned Ni, Co, Ni-C may be further provided on the upper layer of these diffusion coating layers.
o An alloy coating layer may be provided.

These base pretreatment layers are extremely effective in preventing scratches from reaching the steel surface during the subsequent pinhole reduction forming process of lead-tin alloy plating. When lead-tin alloy plating is performed using the hot-dip plating method, the increase in reactivity with Sn in the plating bath makes it difficult to form a uniform and dense alloy layer consisting of the base pretreatment layer and Sn. , pinholes are reduced.

In addition, in the case of electroplating, the superposition effect of the base coating layer and the electrolytic lead-tin alloy plating layer, and the room temperature diffusion between the base coating layer and the 8n in the plating layer after plating,
Perhaps due to the formation of a dense alloy layer on j7, the number of pinholes is significantly reduced.

Furthermore, due to the presence of these base coating layers,
During handling or molding, the lead-tin alloy coating layer is soft and is easily scratched, but there is a high probability that the scratches will be prevented from reaching the steel surface.

Therefore, by providing these base coating layers, it is important to reduce the exposed portion of Fe as described above, and no matter how much the steel base is improved, pinholes in the lead-tin alloy layer and unplated If there are many scratches that reach the steel base, the effect of reducing iron leakage, reducing the amount of dissolution, and reducing pitting corrosion will be reduced. Therefore, a base coating layer is provided to reduce the exposed portion of Fe. Furthermore, since the alloy layer with Sn that contains the base coating layer has a higher potential than the alloy layer consisting of Fe and Sn, the corrosion current between the steel base and the alloy layer will decrease. This has the effect of reducing Fe elution rate,
This is advantageous in terms of reducing pitting corrosion.

Therefore, the thickness of the base coating layer is preferably 0.01 to 1 μm, whether it is an alloy plating layer or a diffusion coating layer. If the thickness of the base coating layer is less than 0.01μ,
It is less effective in reducing pinholes and less effective in preventing scratches from the surface reaching the base metal. Therefore, the thickness of the base coating layer is preferably 0.01 μm or more, preferably 0.05 μm or more.

On the other hand, when the thickness of the base coating layer exceeds 1μ, the effect of reducing the exposed portion of Fe is saturated and
10 It is not preferable because the workability deteriorates.

Therefore, the thickness of these base coating layers is desirably 1 μm or less, preferably 0.5 μm or less.

Furthermore, the form of these base coating layers after lead-tin alloy plating on the steel surface varies depending on the thickness of the base coating layer, the plating conditions of lead-tin alloy plating, etc., but the form is not specifically specified. do not have.

That is, when only an alloy layer of the base metal and Sn constituting the base coating layer is formed on the steel surface, a coating layer of the metal constituting the base coating layer and an upper layer of these metals and S are formed on the steel surface.
When an alloy layer consisting of n is formed, or when a diffusion base coating layer is provided, the diffusion layer and the base metal constituting the diffusion layer, Fe, and an alloy layer consisting of Sn are formed. Either a metal layer or an alloy layer consisting of a base metal and Sn may be formed.

Next, the conditions for lead-tin alloy plating are not particularly stipulated, but those with an Sn content of 3 to 50%, preferably 7 to 15%, are used, and the plating thickness is 2.
A thickness of ~10μ, preferably 3~7.5μ may be used. Regarding the component composition of the plating layer, if the Sn content is less than 3%, a large amount of pinholes will be generated and it will be disadvantageous in terms of solderability.
Good n content.

Further, if the Sn content is high, there is no particular problem, but since it becomes uneconomical, a coating layer with a Sn content of less than 50%, preferably 15% or less is preferable.

The thickness of the lead-tin alloy plating layer is 2 to 10 μm.
Good thickness. If the thickness is less than 2μ, a large number of pinholes will be formed, and the steel base will be easily scratched, which is not desirable in terms of corrosion resistance. administered. In addition, if the thickness exceeds 10μ, moldability and weldability tend to deteriorate.
It is preferable to apply a lead-tin alloy plating layer with a thickness of 10 μm or less, preferably 7.5 μm or less.

The method for providing this lead-tin alloy plating layer as an upper layer of the base coating layer is a hot-dip plating method.

Any method such as electroplating or vapor phase plating may be used.

The lead-tin alloy plating layer has not only a binary alloy composition of Pb and Sn, but also sb and Zns as impurities.
There is no problem even if it is contained in the tin-based alloy plating layer.

Furthermore, in the present invention, the surface of the lead-tin alloy coating layer is chemically treated (immersed) with a water bath solution such as phosphoric acid, phytic acid, or chromic acid for the purpose of improving paint adhesion or further reducing pinholes. or electrolytic treatment, etc.).

(Example) Examples of the present invention will be described below.

Using Cr-added steels with varying amounts of Cr as shown in Table 1, the samples were subjected to surface cleaning and activation treatments, such as degreasing and pickling, which are commonly applied to surface-treated steel sheets.

Various groundwork pretreatments were applied. Next, the following performance evaluations were performed on the steel plates each coated with a lead-tin alloy plating layer having a predetermined thickness. In addition, as a comparison material, 5crf,
A similar evaluation test was conducted on a steel plate without additives and a steel plate with a base coating treatment and a lead-tin alloy plating layer. Table 2 shows the performance evaluation results. The evaluation tests and evaluation criteria were conducted in accordance with the following methods.

■ Corrosion resistance by salt spray test The corrosion resistance was evaluated by measuring the amount of reduction in plate thickness at the area where red rust occurred after conducting the salt spray test for 4000 hours.

◎・・・Plate thickness reduction amount 0.15 tm p lower 0...0
．． 25 mm or less Δ... 0.35 m or less ×... 0.35 m or less ■ Corrosion resistance by cyclic commission test Figure 1 (
The cycle shown here is one cycle, 150 cycles.
The corrosion resistance was evaluated by measuring the amount of plate thickness reduction in the area where red rust occurred after the test.

◎...Plate thickness reduction: 0.10 m or less O・" 0.20 m or less Δ - 0.30 m or less A fine stone with a diameter of about 7.5μ is applied to the surface coated with 5μ of alkyd paint for 10 seconds at a pressure of 3.5 kg//cd so that about 2g of the stone collides with the surface, and then A Seki cycle test was conducted under cycle test conditions.Then, the amount of plate thickness reduction in the area where red rust occurred was measured to evaluate corrosion resistance.

◎・・・Plate thickness reduction 0.3 tm or less ○・-・IO, 4- or less Δ・” I O, 5van or less X ・・・I
O, over 5m ■Accelerated corrosion resistance test results for gasoline-based fuel Blank size 0.8 x 500 x 5005m*
, after applying lubricating oil, under the condition of wrinkle presser pressure 30T.
X Use a 150mm square punch to squeeze out the square tube, depth 1
The following solution was filled into the inside of a 20 tm rectangular tube drawing material, and its corrosion resistance was evaluated.

Evaluation method (■): Filled with a solution consisting of gasoline (7 parts) and distilled water (3 parts), and after standing for 180 days, the occurrence of red rust and the amount of decrease in plate thickness in the area where red rust occurred were measured.

Evaluation method ■: Gasoline (7 parts) + 2% NaCL aqueous solution (3 parts)
After filling with a solution consisting of [part] and leaving it to stand for 180 days, the state of red rust occurrence and the amount of decrease in plate thickness at the part where red rust occurred were measured.

The corrosion resistance of each was evaluated.

◎・・・Number of red rust occurrences is 10 or less, pitting depth is 0.1w
The following ○... I ke and below, z Q.

1m or less Δ... Addition s'
0.20m+ or less
10.20 Cod Super ■Moldability Blank size 0.8 x 500 x 500 Cod, after applying lubricating oil, 150
Surface condition of the outer surface of the rectangular tube drawing material (particularly the degree of damage to the lead-tin alloy coating layer on the outer surface of the drawn material) and forming '101 when drawing the rectangular tube to a depth of 140m using a 150m square punch
The degree of occurrence of 00 cracking was evaluated using the following evaluation criteria.

◎...There is almost no damage to the coating layer, and no processing cracks occur.○...Almost no damage to the coating layer is observed, but processing cracks of the test material are less than 10%, but occur Δ...・Some damage to the coating layer is observed, and processing cracks occur in 20% or less of the test material.
20% more occurrences

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing one cycle when evaluating corrosion resistance in an example of the present invention.

Claims (2)

[Claims] (1) Ni, Co, Ni- A highly corrosion-resistant lead-tin alloy plated steel sheet comprising a Co alloy base coating layer or a lead-tin alloy coating layer on the diffusion base coating layer. (2) C: 0.10% or less solAl: 0.005-0.08% Cr: 0.5-20% One or more of Ti, Nb, V, and Zr, each 0
．． A base coating layer of Ni, Co, Ni-Co alloy, or a lead-tin alloy coating as a layer above the diffusion base coating layer of Ni, Co, Ni-Co alloy, etc. A highly corrosion-resistant lead-tin alloy plated steel sheet that is coated with a layer.