JP2012207271A - HOT-DIP Sn-Zn-PLATED STEEL SHEET - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot-dip Sn-Zn-plated steel sheet which has excellent corrosion resistance and is particularly suitable as an automobile fuel tank material which can cope with a common rail type diesel engine.SOLUTION: In the hot-dip Sn-Zn-plated steel sheet, a steel sheet surface is overlaid with a hot-dip Sn-Zn plating layer comprising 91.2-99.0 mass% Sn, 1-8.8 mass% Zn, and the remainder being inevitable impurities. An Ni plating layer exists by 10-100 mg/mon an upper layer of the hot-dip Sn-Zn plating layer, preferably the Ni plating layer exists by 25-60 mg/mon the upper layer of the hot-dip Sn-Zn plating layer.

Description

  The present invention relates to a molten Sn—Zn-based plated steel sheet having excellent corrosion resistance and particularly suitable as an automobile fuel tank material.

  Conventionally, Pb—Sn alloy-plated steel sheets having excellent corrosion resistance, workability, solderability (weldability) and the like have been mainly used as fuel tank materials, and have been widely used as fuel tanks for automobiles. However, as Pb-free has been promoted, it has been found that Sn-Zn alloy-plated steel sheet mainly composed of Sn has excellent characteristics as a fuel tank material, and in the following Patent Documents 1 to 8, A molten Sn-Zn plated steel sheet is disclosed and widely used as a Pb-free fuel tank material.

Patent Document 9 listed below describes an invention for improving spot weldability by depositing Ni plating or Ni alloy plating on the surface layer of a Sn-containing plated steel sheet. In this Patent Document 9, the object to be coated is Sn, and the object is to suppress the Sn—Cu alloying reaction under high temperature during resistance welding by Ni present in the surface layer. During spot welding, a water tube is passed through the electrode to cool the electrode / steel plate, but the nugget formation site is still heated to nearly 2500 ° C, and the temperature between the electrode / steel plate also rises to about 700 ° C. Therefore, in Patent Document 9, in order to suppress the reaction between Sn, which is the main component of the plating, and Cu, which is the main component of the electrode, the Ni-based plating of the upper layer requires 0.1 to 1.0 g / m ² in the Ni content. It is more than the appropriate amount of Ni plating assumed by. In addition, the structure of the plating layer provides corrosion resistance as a barrier-type plating film, and there is a problem that the sacrificial anticorrosive ability due to Zn at the buttock and the end face is not sufficiently exhibited.

Japanese Unexamined Patent Publication No. 08-269734 Japanese Unexamined Patent Publication No. 09-071879 JP 2000-119867 A JP 2002-332556 A JP 2003-268521 JP JP 2003-268522 A JP 2005-320554 A JP 2011-006732 A JP 2010-100867

  The above-mentioned molten Sn-Zn plated steel sheet has excellent corrosion resistance, processability in the fuel tank manufacturing process, and joining characteristics, and is extremely balanced as a fuel tank for gasoline, ethanol-mixed gasoline, and light oil. It is a good material.

  However, in recent years, exhaust gas regulations and fuel economy regulations for diesel engines have been tempered year by year, so mechanical injection pumps that cause loss of engine driving power are gradually being abolished. Has appeared. The representative is a common rail type diesel engine, and if this system is used, very advanced combustion control becomes possible, and a high output and clean engine can be realized.

  However, there is a concern that the output of this common rail diesel engine will be low due to the small nozzle diameter and high temperature and high pressure of the fuel, especially when using Bio Diesel Fuel (hereinafter referred to as BDF) due to nozzle clogging of the nozzle. is there. Although there are various types of BDF, the raw material vegetable oil is produced by the methyl ester exchange reaction, and the double bond and triple bond contained in the raw material are included in the BDF as they are. I'll do it. For this reason, automakers and auto parts manufacturers stated, “In common rail diesel engines, metal ions that elute into the fuel mainly from the fuel circulation system when using BDF produce metal soap from the BDF degradation products and metal ions at the injection port. Or it is easy to deposit, and this is the cause of the nozzle clogging of the injection nozzle. ”I think that one of the elements that Zn adversely affects.

  With conventional technology, the composition and structure of the plating layer are controlled in order to suppress excessive elution of Zn in the hot-dip Sn-Zn plated steel sheet. However, since elution of trace amounts of Zn is inevitable, We decided to study the technology for further reduction.

  So far, a fuel tank material that has a Sn—Zn plating layer and finely dispersed Zn so that segregated Zn does not penetrate the plating layer has been used. Sn is a barrier-type anticorrosion to the environment inside and outside the fuel tank, and Zn is a sacrificial anti-corrosion function, such as anti-corrosion effects, and the design is to maximize each effect. It was an idea. This time, we focused on making surface Zn more precious metal. Specifically, Ni was used, and Zn in the outermost layer of plating was replaced with Ni, and then a chemical conversion treatment film was applied to try to suppress elution of Zn.

The gist of the present invention is the following contents as described in the claims.
(1) A molten Sn-Zn-based plated steel sheet in which a molten Sn-Zn plated layer consisting of Sn: 91.2-99.0% by mass, Zn: 1-8.8% by mass, and the balance of inevitable impurities is formed on the steel sheet surface, molten Sn-Zn-based plated steel sheet wherein the Ni-based plating layer of the molten Sn-Zn plating layer is characterized by the presence ^{2 10mg / m 2 ~100mg / m} .
(2) the molten Sn-Zn-based plated steel sheet according to the Ni-based plating layer of the molten Sn-Zn plating layer is characterized by the presence ^{2 25mg / m 2 ~60mg / m} (1).

  As described above, according to the present invention, a lead-free rust-proof steel sheet for fuel tanks excellent in corrosion resistance, workability, and weldability can be obtained, and even in a sensitive system with respect to the amount of eluted metal like a common rail type diesel engine, It has suitable characteristics.

The present invention is described in detail below. Steel strip that has been subjected to a series of processes such as hot rolling, pickling, cold rolling, annealing, temper rolling, etc., and using rolled material as a material to be plated, removing rolling oil or oxide film, etc. After the pretreatment, plating is performed. Regarding steel components, it must be a component system that can be processed into a complex shape of the fuel tank, the thickness of the alloy layer at the steel-plating layer interface is thin and plating peeling can be prevented, and the progress of corrosion inside and outside the fuel tank is suppressed. It must be a component system. For example, a component system in which C is 0.003, Si is 0.006, Mn is 0.06, P is 0.01, S is 0.01, Ti is 0.055, Nb is 0.003, and B is added in several ppm by mass%. In addition, high tension may be applied for thinning.

In the present invention, Sn—Zn alloy plating is basically performed by hot dipping. The biggest reason for adopting the hot dipping method is to secure the plating adhesion amount. Even if electroplating is performed for a long time, the amount of plating can be secured, but it is not economical. The plating adhesion range aimed at in the present invention is a relatively thick weight area of 20 to 100 g / m ² (single side), and the hot dipping method is optimal. Furthermore, when the potential difference between the plating elements is large, such as Sn and Zn, it is difficult to control the composition appropriately, so the Sn-Zn alloy is most suitable for the hot dipping method.

  Next, the reason for limiting the Zn of the plating composition is that it is limited by the balance of corrosion resistance between the inner surface and the outer surface of the fuel tank. The outer surface of the fuel tank is painted after the fuel tank is molded because perfect rust prevention capability is required. Therefore, although the coating thickness determines the rust prevention ability, the material prevents red rust by the anticorrosion effect of the plating layer. In particular, the anticorrosive effect of the plating layer is extremely important in the part where the coating is not good. Addition of Zn to Sn-based plating lowers the potential of the plating layer and provides sacrificial corrosion protection. For this purpose, it is necessary to add 1% by mass or more of Zn. Addition of excess Zn exceeding 8.8 mass%, which is the Sn-Zn binary eutectic point, promotes the growth of coarse Zn crystals, causing an increase in melting point and excessive intermetallic compound layer (so-called alloy layer) under plating. It must be 8.8% by mass or less for reasons such as leading to rapid growth. Coarse Zn crystals are not problematic in that they exhibit the sacrificial anticorrosive ability of Zn, but on the other hand, selective corrosion is likely to occur in the coarse Zn crystal part. Moreover, since the intermetallic compound itself is very brittle during the growth of the intermetallic compound layer under the plating layer, plating cracks are likely to occur during press molding, and the anticorrosion effect of the plating layer is reduced.

  On the other hand, corrosion on the inner surface of the fuel tank is not a problem with only normal gasoline, but there is a severe corrosive environment due to water contamination, chloride ion contamination, and the formation of organic carboxylic acids due to oxidative degradation of gasoline. May appear. If gasoline leaks outside the fuel tank due to piercing corrosion, it can lead to serious accidents, and these corrosions must be completely prevented. When the deteriorated gasoline containing the above corrosion-promoting components was prepared and the performance under various conditions was examined, it was confirmed that Sn-Zn alloy plating containing 8.8% by mass or less of Zn exhibits extremely excellent corrosion resistance. .

  When the pure Sn or Zn content is less than 1% by mass, the plated metal has no sacrificial protection against the iron from the beginning when exposed to the corrosive environment. Pitting corrosion at the hole and early red rust on the outer surface of the tank are problematic. On the other hand, when Zn is contained in a large amount exceeding 8.8% by mass, Zn is preferentially dissolved, and a large amount of corrosion products are generated in a short period of time. There is a problem that tends to cause clogging. In terms of performance other than corrosion resistance, the Zn content increases, the workability of the plating layer also decreases, and good press formability, which is a feature of Sn-based plating, is impaired. Furthermore, the solderability is significantly reduced due to the melting point increase of the plating layer and the Zn oxide due to the increased Zn content. Therefore, in the present invention, the Zn content in the Sn—Zn alloy plating is preferably in the range of 1 to 8.8% by mass, and more preferably in the range of 4.0 to 8.8% by mass in order to obtain a more sufficient sacrificial anticorrosive action.

  Next, an alloy layer inevitably formed at the interface between the Sn—Zn plating layer and the ground iron, but can be controlled by utilizing pre-plating, adjusting the hot dipping bath temperature, and dipping time. Formation of an alloy layer is indispensable for ensuring plating wettability, but excessive growth of the alloy layer is not preferable because it adversely affects workability and the like. The recommended conditions are shown below.

<Pre-plating type and adhesion amount>
Ni simple plating ... The alloying of molten Sn-Zn and Fe (base metal) is suppressed in the place where Ni plating is covered. On the other hand, the alloying of the molten Sn—Zn metal and Fe (base metal) proceeds at a portion not covered with Ni plating. As a result, a fine uneven alloy phase is generated. If the amount of pre-plating is in the range of 0.01 to 0.5 g / m ² per side, a fine uneven alloy phase is generated, plating wettability can be ensured, and excessive alloy layer growth does not occur. For Ni plating, a commonly used watt bath is sufficient. For reference, the typical composition of Watt bath is 240 to 350 g / L of nickel sulfate, 30 to 60 g / L of nickel chloride, 30 to 45 g / L of boric acid, and plating conditions are pH = 2.5 to 4.5, bath temperature 40 to 60 ° C., Operation is possible within a current density range of ^{2 to} 10 A / dm ² .

Fe-Ni alloy plating ... Although it overlaps with the explanation of Ni alone, Fe and Ni have different alloying behavior with molten Sn-Zn metal, and Fe and molten Sn-Zn metal undergo alloying, and Ni and Sn -Zn metal suppresses alloying. As a result, a fine uneven alloy phase is generated. Therefore, the same effect can be obtained when the Fe—Ni alloy plating is pre-plated. There is no problem if the composition of the Fe—Ni alloy plating is not extremely biased with respect to either element, and there is no influence of the pre-plating composition in the range of Fe-10 mass% Ni to Fe-80 mass% Ni. Preferably, the region is stable in the range of Fe-25 mass% Ni to Fe-60 mass% Ni. The Fe—Ni alloy plating bath can be used with the addition of 30 to 200 g / L of iron sulfate to the above-described Ni plating watt bath. It is not necessary to set an upper limit because Ni is not necessarily non-uniform coated as single, the economic pre coating weight is suitably per side 0.5 to 1.5 g / m ^2.

<Hot plating bath temperature, immersion time>
Both the hot dip bath temperature and the immersion time affect the growth of the alloy phase. When the hot dip bath temperature is significantly low, the alloy phase does not grow, and when it is extremely high, the alloy phase is promoted to grow. However, from the viewpoint of operability, the hot dipping bath temperature is often set to the liquidus temperature of the molten metal +10 to 50 ° C., and the upper limit is set to the liquidus temperature + 100 ° C. at most. If the bath temperature is low, there is a risk of molten metal solidification due to variations in bath temperature in the hot dipping bath. On the other hand, if the bath temperature is high, excessive alloy phase growth, cooling capacity for solidification after hot dipping is necessary, uneconomical This is because of the disadvantages. In the Sn-Zn system of the present invention, when considering the Sn-Zn composition range, 240 to 300 ° C is an appropriate range of the hot dipping bath temperature, and in this temperature range, it is appropriate depending on the combination of the pre-plating and the immersion time described later. It is possible to generate a simple alloy phase.

  As for immersion time, the growth of the alloy phase is generally insufficient on the short time side, and the growth of the alloy phase tends to be excessive on the long time side. However, in the present invention, the alloy phase has already grown by immersion for 1 second, and the growth of the alloy phase is gradually saturated even if immersed for a long time. In actual continuous hot dipping, the dipping time takes at least about 2 seconds, and it is usually not dipping for 15 seconds or longer due to the size of the hot dipping bath. A long immersion time means a reduction in productivity and is uneconomical. In the immersion time range of 2 to 15 seconds, an appropriate alloy phase can be generated by a combination of the pre-plating and the hot dipping bath temperature.

Next, it is recommended that the adhesion amount of the molten Sn—Zn plating layer be 10 to 150 g / m ² (single side), more preferably 30 to 50 g / m ² (single side). If it is less than 10 g / m ² , there is a concern that the molten Sn—Zn plating coverage becomes incomplete, and conversely if it exceeds 150 g / m ² , not only is it uneconomical, but also resistance weldability decreases. The reason why resistance weldability deteriorates is that the main component of Cu and molten Sn-Zn plating, which are mainly used for electrodes of resistance welders, easily generates Sn-Cu alloys (bronze), and electrode wear becomes severe. It is.

Is a Ni-plated in the upper layer of the Sn-Zn plating layer is then point of the present invention, it is preferable to 10mg / m ² ~100mg / m ² is deposited. This upper Ni-based plating plays a role of preventing Zn from eluting in the Sn—Zn plating layer. Since Sn in the Sn-Zn plating layer is a barrier type anticorrosion, the elution of Sn does not need to be considered. In the Sn—Zn plating composition of the present invention, the plating structures are “primary Sn” and “Sn—Zn binary eutectic”, and no intermetallic compound is formed between Sn and Zn. Therefore, Zn is Sn—Zn binary. It exists in the original eutectic as broken-lamellar or fiber. For this purpose, Ni does not need to be uniformly present in the upper layer of Sn-Zn plating, but is selectively present in the Zn phase of the Sn-Zn plating layer, covering the outermost Zn layer of Sn-Zn plating. It is enough. In order to selectively coat Zn on the outermost layer of Sn—Zn plating, an amount of Ni plating deposition of 10 mg / m ² is necessary, and coating over 100 mg / m ² saturates the effect and is uneconomical.

  Moreover, although it is a reason for limitation of Zn of the plating composition, it is limited by the balance of corrosion resistance between the inner surface and the outer surface of the fuel tank. The outer surface of the fuel tank is painted after the fuel tank is molded because perfect rust prevention capability is required. Therefore, although the coating thickness determines the rust prevention ability, the material prevents red rust by the anticorrosion effect of the plating layer. In particular, the anticorrosive effect of the plating layer is extremely important in the part where the coating is not good. Addition of Zn to Sn-based plating lowers the potential of the plating layer and provides sacrificial corrosion protection. For this purpose, it is necessary to add 1% by mass or more of Zn.

In the case where the upper layer Ni plating reacts with Zn of Sn—Zn plating due to displacement plating, if Zn is excessively replaced with Ni, the absolute amount of Zn in the plating layer decreases, and the sacrificial anticorrosive ability decreases. If a wrinkle that reaches the ground iron enters in such a state, the sacrificial anticorrosive ability that Zn should fulfill cannot be fully expressed. Automobile fuel tanks, which are often installed in the lower part of the car body, have a habit of reaching the railroad in the actual environment by jumping up pebble on the road surface or snow melting agent (rock salt may be used). It can happen. Therefore, the upper limit of Ni-based plating is set to 100 mg / m ² from the viewpoint of sacrificial anticorrosive ability as well as economic reasons. More preferably, since the Ni plating is Zn is less noble metal is replaced with a selectively Ni in if Sn and Zn any substitutable plating, Ni-based plating at 25mg / m ² ~60mg / m ² on the upper layer If there is, economically good Zn elution suppression is possible.

  Although the upper layer Ni plating method is used, the same watt bath-based electric Ni plating as the pre-plating method is also possible. However, electric Ni plating has a relatively good throwing power and coats uniformly, so that Ni is also applied unnecessarily on Sn, and the total amount of necessary Ni plating increases.

  On the other hand, Ni plating can be performed by electroless plating. In this case, since Zn of Sn—Zn plating is a base metal, substitution reaction proceeds with noble Ni. Electroless plating has been proposed to generate various baths, but is not particularly limited. For example, using hypophosphorous acid as a reducing agent (nickel chloride: 50 g / L, sodium citrate: 10 g / L, sodium hypophosphite; 10 g / L, pH = 4-6, 80-90 ° C.), hydroxylation Using a boron compound as a reducing agent (nickel sulfate heptahydrate; 30 g / L, sodium malonate; 34 g / L, dimethylamine borane; 0.06 mol / L, pH = 5.1 to 6.0, temperature; 70 ° C.) Use it. Further, when the object to be plated is immersed in the electroless plating bath, nickel may be deposited simultaneously with the generation of hydrogen gas on the surface, and phosphorus (P) may be mixed therein. Therefore, the precipitate may become Ni-P plating, but this is not a problem, and it can be controlled by the amount of Ni deposited. The amount of adhesion in the case of electroless Ni plating can be controlled by immersion time and bath temperature.

  In the present invention, complete corrosion resistance is expected by performing chemical conversion treatment comprising an inorganic compound, an organic compound, or a composite thereof after Ni plating. Since the chemical conversion treatment can affect the adhesion to the paint, sliding resistance, and resistance weldability, an appropriate chemical conversion treatment may be selected as appropriate.

Next, the present invention will be described in more detail with reference to examples. An Fe-Ni plating bath (nickel sulfate: 125 g / L, nickel chloride: 100 g / L, boric acid: 30 g / L, iron sulfate: 110 g / L-Ph = 2.5) was applied with Fe-Ni plating 1.0g / m ² (bath temperature 50 ° C, current density 10A / dm ² per side). After applying a plating flux containing zinc chloride / ammonium chloride and hydrochloric acid to the steel sheet, it was introduced into a Sn—Zn hot dipping bath having various compositions at 260 ° C. After reacting the plating bath with the steel plate surface for 5 seconds, pull out the steel plate from the plating bath and adjust the adhesion amount by the gas wiping method, and the plating adhesion amount (total adhesion amount of Sn + Zn) is 40 g / m ² (per one side) Controlled. After gas wiping, the molten plating layer was solidified by cooling with an air jet cooler.

  The upper Ni plating is electroless plating and immersed in bath conditions (nickel chloride: 50 g / L, sodium citrate: 10 g / L, sodium hypophosphite: 10 g / L, pH = 4, bath temperature 90 ° C.) Then, after immersion, it was washed with water and dried. The amount of Ni plating deposited on the upper layer was controlled by changing the immersion time. The produced steel plate was formed into a cylindrical cup shape of 50 mmφ with a flange having a drawing ratio of 2.2 and a depth of 35 mm.

The metal dissolution test into fuel is shown below. A fuel containing 20 vol% of rapeseed oil-derived BDF (RME) and 80 vol% of light oil was oxidized for 24 hours (based on JIS-K2287) to produce a deteriorated BDF. Mixed with fuel a new deterioration BDF, total acid number; adjust TAN of (T otal A cid N umber) to of 0.13 mgKOH / g, water as a 0.1 vol% added tested fuel thereto. 50 mL of this fuel was sealed in the cylindrical cups of the various steel plates described above, and left in a 90 ° C. explosion-proof thermostat. The cylindrical cup containing the fuel is taken out after 168 hours, and all the fuel is incinerated with the suspended matter (fuel polymerization component) in the fuel, then leached in a mixed acid of nitric acid and hydrochloric acid, and diluted as appropriate to obtain ICP (Inductively Coupled). Plasma) The amount of Zn eluted in the fuel was calculated using an emission spectrometer.

  Evaluation is excellent when the Zn elution amount is less than 0.05 mg / L (◎), 0.05 to 0.1 mg / L is good (○), 0.1 to 0.5 mg / L is acceptable (△), 0.5 mg / L or more is not acceptable (× ). In addition, in order to evaluate sacrificial anticorrosive ability, the end face of a flat plate of 70 × 150 mm size was sealed, a cross cut was given so as to reach the base iron, and a salt spray test according to JIS-Z2371 was also conducted separately. Evaluated by red rust area ratio after 960 hours, red rust area ratio less than 5% is excellent (◎), 5-10% is good (○), 10-20% is acceptable (△), 20% or more is not possible (× ). If the sacrificial anticorrosive ability is insufficient, red rust will be generated early from the crosscut. Table 1 shows the results.

  # 1 and # 2 did not show sufficient sacrificial anticorrosive ability in the salt spray test because the Zn content of Sn—Zn plating was insufficient. On the other hand, for # 12 and # 13, the Zn content of the Sn—Zn plating exceeded the eutectic composition, so that coarse Zn crystals grew and Zn elution could not be suppressed. In # 14, # 15, and # 16, the amount of upper layer Ni deposited was not sufficient, and Zn elution could not be suppressed. In # 29, Zn was overplated with Ni, and the sacrificial anticorrosive ability decreased in the salt spray test. On the other hand, the examples of the present invention have sufficient corrosion resistance in both the metal elution test and the salt spray test.

An Fe-Ni plating bath (nickel sulfate: 125 g / L, nickel chloride: 100 g / L, boric acid: 30 g / L, iron sulfate: 110 g / L-Ph = 2.5) was applied with Fe-Ni plating 1.0g / m ² (bath temperature 50 ° C, current density 10A / dm ² per side). After applying a plating flux containing zinc chloride / ammonium chloride and hydrochloric acid to this steel sheet, it was introduced into a Sn-8% Zn hot dipping bath at 260 ° C. After reacting the plating bath with the steel plate surface for 5 seconds, pull out the steel plate from the plating bath and adjust the adhesion amount by the gas wiping method, and the plating adhesion amount (total adhesion amount of Sn + Zn) is 40 g / m ² (per one side) Controlled. After gas wiping, the molten plating layer was solidified by cooling with an air jet cooler.

  The upper Ni plating is performed in a watt bath (nickel sulfate 240 g / L, nickel chloride 45 g / L, boric acid 30 g / L, pH = 4.0 bath temperature; 50 ° C.) by electroplating. The time was changed and controlled. The subsequent evaluation method is the same as in Example 1. Table 2 shows the results.

  In # 30 to # 32, the amount of upper layer Ni deposited was not sufficient, and Zn elution could not be suppressed. # 45 has reduced sacrificial protection. On the other hand, the present invention example has sufficient corrosion resistance in both the metal elution test and the salt spray test, but when electroplating the upper layer Ni, Ni is coated on Sn, so to suppress Zn elution, substitution A slightly larger amount of Ni was required than the plating.

0.1mm / m2 Ni plating from watt bath (nickel sulfate 240g / L, nickel chloride 45g / L, boric acid 30g / L pH = 4.0) by electroplating method on steel plate of 0.8mm thickness annealed and pressure adjusted ² (bath temperature 50 ° C., current density 10 A / dm ² ) per side. After applying a plating flux containing zinc chloride / ammonium chloride and hydrochloric acid to this steel sheet, it was introduced into a Sn-8% Zn hot dipping bath at 260 ° C. After reacting the plating bath with the steel plate surface for 5 seconds, pull the steel plate out of the plating bath and adjust the amount of adhesion by gas wiping method, and the amount of plating adhesion (total amount of Sn + Zn adhesion) is 40 g / m ² (per side). Controlled. After gas wiping, the molten plating layer was solidified by cooling with an air jet cooler.

  The upper Ni plating is electroless plating, bath conditions (nickel sulfate heptahydrate; 30 g / L, sodium malonate; 34 g / L, dimethylamine borane; 0.06 mol / L, pH = 5.1 to 6.0, temperature ; 70 ° C), and after immersing, washed with water and dried. The amount of Ni plating deposited on the upper layer was controlled by changing the immersion time. The subsequent evaluation method is the same as in Example 1. Table 3 shows the results.

  In # 46 to # 48, the adhesion amount of the upper layer Ni was not sufficient, and Zn elution could not be suppressed. As for # 61, Zn was plated with Ni too much, and sacrificial anticorrosive ability decreased in the salt spray test. On the other hand, it has been clarified that the present invention example has sufficient corrosion resistance in both the metal elution test and the salt spray test, and even if the electroless Ni plating conditions for the upper layer Ni are changed, the upper layer Ni amount can be ensured.

Claims (2)

A molten Sn-Zn-based plated steel sheet in which a molten Sn-Zn plated layer consisting of Sn: 91.2-99.0% by mass, Zn: 1-8.8% by mass, and the balance of inevitable impurities is formed on the steel sheet surface, the molten Sn molten Sn-Zn-based plated steel sheet layer of Ni-based plating is characterized by the presence ² 10mg / m ^{2 ~100mg} / m of -Zn plating layer. Molten Sn-Zn-based plated steel sheet according to claim 1, wherein the Ni-based plating layer of the molten Sn-Zn plating layer is characterized by the presence ^{2 25mg / m 2 ~60mg / m} .