JPS60211099A - Tin-free steel for welded can and production thereof - Google Patents

Abstract

PURPOSE:To obtain a tin-free steel for a welded can having excellent weldability, sulfide resistance, etc. by forming successively metallic chromium, zinc-nickel alloy layer and chromium oxide hydrate layer on the surface of a steel sheet. CONSTITUTION:Chromium is plated at 30-300mg/m<2> per side on the surface of a degreased and pickled steel sheet and thereafter the steel sheet is treated for 0.5-5sec at 30-70 deg.C and 2-50A/dm<2> cathode current density in an aq. soln. of sulfuric acid or hydrochloric acid or sulfuric acid and hydrochloric acid adjusted to 0.5-2pH to remove the chromium oxide hydrate remaining on the plated surface. A nickel-zinc alloy plating layer contg. 10-80wt% zinc is then formed thereon at 5-300mg/m<2> per side. A chromium oxide hydrate layer is further formed at 2-18mg/m<2> in terms of chromium thereon by the conventional method. The tin-free steel having such three-layered structure has excellent corrosion resistance, painting performance and surface color tone in addition to excellent sulfide resistance and weldability.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tin-free steel for welded cans having excellent weldability, sulfidation resistance, and coating performance, and a method for manufacturing the same. Chromium, a nickel-zinc alloy as a second layer thereon, and a chromium hydrated oxide (hereinafter, when expressing the amount in terms of chromium) as a third layer thereon. tin-free steel for welded cans and its manufacturing method.

Conventionally, as a surface-treated steel sheet for can manufacturing, electrolytic chromic acid treated steel sheet (hereinafter referred to as TFS-C) is made of two layers: an electrolytic tin-plated sheet (hereinafter referred to as tin plate), metallic chromium, and chromium hydrated oxide.
(referred to as T) is commonly used. Among these, tinplate has long been the mainstream material for cans due to its excellent corrosion resistance (1) surface gloss, solderability (9) surface lubricity, and low contact electrical resistance. Cans formed by processing 12) and materials for welded cans have also been widely used, but the price of tin used in plating 62 has risen year by year, making it an expensive material for cans.

On the other hand, TFS-CT is a cheaper material than tinplate.
Development of can manufacturing method developed 0 years ago and subsequently by Hibiki Hibiki 1
Second, its use as a material for cans instead of tinplate is increasing year by year. However, when trying to use TFS-CT, which has excellent corrosion resistance and paint adhesion and has a proven track record as a material for adhesive cans, as a material for welded cans, a surface film of metallic chromium, chromium hydrated oxide, etc. 2. It was necessary to remove it by means such as mechanical grinding. Removing the film before welding is not only disadvantageous in terms of can manufacturing cost, but also reduces the corrosion resistance of the welded area and causes hygienic problems due to scattering of the removed chromium powder. There was a strong desire for a material for welded cans that could be welded without any problems.

Therefore, as a material for TFS-CT welded cans, for example (1
) Metallic chromium layer of 3 to 40 mg on steel plate surface.

The upper part (= chromium-plated steel sheet with a porous C2 non-metallic chromium layer mainly composed of chromium oxide of 2 to 151 kg/We in terms of metallic chromium, (JP-A-55-31124
), (2) Anions such as sulfate radicals, nitrate radicals, chloride ions, etc. are intentionally added (2 is not added) 0.5 to 301 metallic chromium per side in an aqueous solution whose main component is chromic acid, dichromic acid, etc. , tin-free steel whose main component is 2 to 50 g/m of chromium hydrated oxide in terms of metallic chromium (Japanese Patent Application Laid-Open No. 55
-18542) (3) Chrome-plated steel plate Shizuji 209
A chromium-plated steel sheet (Japanese Patent Application Laid-Open No. 55-48406), which is characterized by being subjected to temper rolling of 6 or less, has been proposed.

In these T l' S -CTζ2, the technical idea for achieving improved weldability is as follows (=explained).

In other words, in the above references +1) and (3), the metallic chromium layer itself obstructs the passage of welding current immediately after welding starts, so in order to increase the exposed area of the base steel on the steel plate surface, the amount of metallic chromium is increased. Even if the amount of metal chromium is small or the amount of metal chromium is large, temper rolling (slight elongation 4
This is to create a two-way rift. however,
In order to improve weldability, reducing the amount of bimetallic chromium in a steel plate or elongating the steel plate to cause cracks in the metallic chromium layer will prevent the corrosion resistance of TFS-CT from decreasing. Not only difficult:, TPS-
When CT is painted and used (=), there is a problem that iron oxides with high electrical resistance are likely to be generated during baking and heating, which has the opposite effect on weldability. It is stated that the qualitative improvement of the chromium hydrated oxide layer made it possible to reduce the metallic chromium weight, resulting in improved weldability.
It is the same as +31.

The present invention was discovered as a result of investigation from a completely different angle from the technical concept described above, and has excellent weldability even after being subjected to heat treatment by a paint baking sear, and is superior to the conventional TF'5- The present invention provides tin-free steel for welded cans that has sulfidation resistance and coating performance similar to CT, and a method for manufacturing the same.

As mentioned above, if you try to make cans by welding the conventional TFS-CT welded can material after coating and heating, you will not be able to weld it to a commercial level unless the surface film is removed by polishing. (1) Metallic chromium surface (2 chromium oxide with high electrical resistance is generated. (2) Chromium hydrated oxide is heated (2) Dehydrated and transformed into chromium oxide with higher electrical resistance. (3) Metal Iron oxides with high electrical resistance are formed on the surface of the base steel exposed through the plating pinholes in the chromium layer C2. Among these causes for reducing weldability, (1) and (3) are It turned out to be particularly large.

However, cause (1) originates from the essence of metallic chromium (C2), which is the formation of chromium oxide with high electrical resistance due to heating of metallic chromium (2).It took a great deal of effort to solve this problem, but in the end, The presence of divalent nickel on the metal chromium surface can greatly suppress the oxidation of the metal chromium surface; Nickel also adheres to the surface of the base steel exposed through the pinholes in the metal chromium layer, effectively solving cause (3).
It was discovered that the weldability was significantly improved compared to conventional TFS-CT (=metallic chromium as the first layer, nickel as the second layer, and 2) We have already proposed a tin-free steel for welded cans made of chromium hydrated oxide as a third layer on top of the 3-layered tin-free steel for welded cans. It has excellent corrosion resistance and paint adhesion C2, and is extremely practical, but in order to improve the sulfurization resistance against protein-containing contents such as fish and meat (C2), the first layer must contain 30 to 300 Lecture/
lri metallic chromium, 5-300 H/r as second layer
d nickel-zinc alloy with a zinc content of 10 to 90% by weight,
2 to 18 mg/d of chromium hydrated oxide as the third layer.
It has been found that this can be achieved by forming a layered structure when ≦2. The nickel-zinc alloy in the second layer of the present invention is in a trace amount,
In the case of a 2Pii structure without metallic chromium as the first layer, this nickel-zinc layer cannot sufficiently cover the base steel, and its practicality as a material for welded cans is insufficient. In other words, if the nickel-zinc alloy reaches such a small amount, it is not only impossible to prevent the inner surface of the can from turning black due to iron sulfide, which is a reaction product between the sulfur in the can contents and the base steel, without the underlying metal chromium. , weldability, and corrosion resistance after painting (both are not practical. Therefore, weldability, including sulfidation resistance.

The present invention, which is a material for welded cans with excellent corrosion resistance after painting, has a three-layer structure of metallic chromium as the first layer, nickel-zinc alloy as the second layer, and chromium hydrated oxide as the third layer. It is a feature.

The term "nickel-zinc alloy" as used in the present invention also includes a simple eutectoid of nickel and zinc obtained by cathodic electrolysis from a plating bath containing nickel ions and zinc ions. It does not necessarily refer only to nickel-zinc alloys with specific composition ratios based on chemical theory. Since it is common practice to refer to a simple eutectoid obtained by plating as an "alloy," the term "alloy" is used here.

Conventionally, plating various metals on chrome plating has been considered to be a very difficult technique, and was published in Japanese Patent Publication No. 33-1455 "
The method is proposed in ``Methods for plating various metals onto the surfaces of chromium and chromium alloys''. This method involves immersion in a caustic aqueous solution or anodization, but it takes too long to dissolve and remove the hydrated chromium oxide by immersion, making it impractical. This is disadvantageous because the first layer of chromium plating itself dissolves with high efficiency. In implementing the tin-free steel for welded cans of the present invention, it is important to uniformly coat the chromium plating layer (nickel/zinc alloy layer) and have good adhesion to the chrome surface, but this will be discussed later. The surface-treated steel sheet for welded cans of the present invention can be obtained for the first time by this method.

Next, the present invention will be explained in more detail.

The amount of metallic chromium in the first layer is 30~30゜u/per side.
It is defined as rye. This metallic chromium layer has the role of improving sulfidation resistance as a material for cans, corrosion resistance, two-surface color tone, and weldability by suppressing oxidation of the base steel, and if it is less than 30 w/Wi, it becomes difficult to ensure these properties. As the amount of metallic chromium increases, the above characteristics and the oxidation suppressing effect of the base steel tend to improve, but when it exceeds 300Q/d, the effect becomes saturated and the manufacturing cost increases, making it uneconomical, so the upper limit is 300Q/d. It is said to be a name. More preferably it is 70 to 150 my/rd.

As the second layer, a nickel-zinc alloy No. 5-300 is applied, with a zinc content of 10-90% by weight. As the zinc content increases, sulfidation resistance and weldability improve. The improvement in sulfidation resistance is thought to be due to the fact that the zinc present in the nickel-zinc alloy reacts preferentially with the sulfide decomposition components in the content, and this reaction product is white and therefore less noticeable. In addition, weldability is improved by
Zinc is softer than nickel and C, and is presumed to have the effect of lowering the electrical contact resistance, which is said to govern the quality of weldability. When the zinc content is less than 10% by weight, there is almost no difference in sulfidation resistance from that of nickel alone, which does not contain any zinc, and the content must be 10% by weight or more. In addition, the higher the zinc content, the better the sulfidation resistance and weldability, but when the zinc content exceeds 90% by weight, the properties of zinc alone (nearly 2), and during long-term storage without painting. (2) The upper limit is set at 90% by weight because so-called white rust, which reduces paint adhesion, is likely to occur.
More preferably, it is 30 to 70% by weight.

This second layer has nickel (dizinc) eutectoid, so
Single nickel 1: Comparatively softer, the contact electrical resistance of the copper electrode/material to be welded contact area through which welding current passes, and the joint of the material to be welded/material to be welded is small, and the amount of nickel-zinc alloy plating is Even if it is as small as 5 to 300 H/d, a sufficient improvement in weldability can be achieved. As the amount of nickel-zinc alloy plating increases, the surface color shifts from the metallic luster chrome plating color to a dull white C2, but weldability improves. Weldability improvement is saturated at 300 yny/lri, and the upper limit is 3
00 my/nl, but more preferably 30 to 150 u/d in view of ensuring weldability and surface color tone.

The chromium hydrated oxide in the third layer is defined as 2 to 181 (2).The purpose of this third layer is the same as the role of the chromium hydrated oxide in the conventional TF8-CTC2. Perfect sealing of plating pinholes (Securing sulfidation resistance, corrosion resistance, and coating performance) cannot be achieved even if 1 is perfect. Below 2■A, weldability is excellent, but corrosion resistance and coating performance are is not obtained.

If it exceeds 18+Hg/m, corrosion resistance and coating performance will be good, but weldability will deteriorate, so it should be 188/d or less.

More preferably, it is 4 to 12 my/nt.

In carrying out the present invention, the surface of the steel plate is first degreased and pickled by a known method, and then chromic anhydride is used as the main ingredient, with small amounts of sulfuric acid, sulfate, hydrofluoric acid, fluoride, silicofluoride, and borosilicate as plating aids. A metal chromium layer of 30 to 3001, which is the first layer, is obtained using a steel plate as a cathode in a known chromium plating bath (or also called an electrolytic chromic acid treatment bath) containing one or more fluorides. A hydrated chromium oxide, which is an intermediate reduction product of the chromium precipitation process, is necessarily formed on the first metal chromium layer. This chromium hydrated oxide inhibits the uniform coverage and adhesion of the second layer of nickel-zinc alloy plating to the metal chromium surface, so it is necessary to select chromium plating conditions to minimize the amount. However, the plating conditions for reducing the formation of hydrated chromium oxide using known chromium plating techniques (2) are well known from experience and are easy to implement.

(1) Chromic anhydride concentration 2 Normal chromium plating is 50~
It is carried out at 300 y/l, but 80 to 300 y/l
(The higher the concentration, the less chromium hydrated oxide is produced.

(2) Type and concentration of auxiliary agent: Sulfuric acid is a typical example. Hydrofluoric acid, silicofluoric acid, borofluoric acid, and alkali metal salts thereof may be added alone or in combination with sulfuric acid.

General (Difluorine-based auxiliary agents tend to reduce the formation of chromium hydrated oxides than sulfuric acid-based auxiliary agents.The amount of auxiliary agents is
The concentration of chromic acid is about 1 to 5% of the concentration of chromic acid, although it differs slightly from the two types.

(3) Bath temperature: Usually carried out at 30 to 60°C, but 5
The higher the temperature is from 0 to 60°C, the less chromium hydrated oxide tends to be produced.

(4) Cathode current density (2) Usually carried out at 10 to 100 A/dd, but higher 30 to 100 A/dll tends to produce less chromium hydrated oxide (there are two).

In the above-mentioned known chromium plating technology C2, it is necessary to select conditions that will reduce the generation of chromium hydrated oxide. From C2, chromium hydrated oxide will immediately dissolve (partially), so the amount of chromium hydrated oxide will be reduced by 3.
It is easy to reduce the amount to 10 mg/d or less, and in this way the first layer of chromium plating of the present invention is applied.

1st layer chrome plating (2nd layer 5~
Nickel-zinc alloy plating of 3001Rg/rye is applied. Applying this nickel-zinc alloy plating (per second, the chromium hydrated oxide remaining on the surface after chromium plating inhibits the uniform coverage of the nickel-zinc alloy plating and the adhesion to the chrome surface, and a small amount of nickel and zinc Although it was already mentioned that the alloy plating layer (second layer) must be reduced because the effect of improving weldability cannot be achieved, even if the amount of chromium hydrated oxide is 3 to 10 u/rye, the nickel-zinc alloy of the second layer Gold plating can be carried out by the method described below (2).

As a plating bath for applying this second layer of nickel/zinc plating, a known plating bath as described later can be used, but in this case, chromium hydrated oxidation, which is generated on the chromium plating, is sufficient. It is necessary to remove the object in advance,
It was found that cathodic electrolysis in a warm acidic solution is most effective.

Methods for removing chromium hydrate oxide include (1) pH
Immersion or cathode electrolysis (current density 2 to 100 A/41. time 0.5 to 5 seconds) in a hot alkaline aqueous solution (temperature 50 to 90°C) such as NaOH or KOH adjusted to 12 to 14%.

(21# Immersion or cathode electrolysis in a warm acid aqueous solution (temperature 30 to 70°C) such as sulfuric acid or hydrochloric acid adjusted to pH 0.5 to 2 (current density 2 to 50 A/dd, time 0.5 to 5 seconds) do.

(3) Mechanically scrape off the chromium hydrated oxide using a brush roll in the aqueous solution of (1) or (2) above.

However, using any of these removal methods, it is possible to apply the nickel-zinc alloy plating as the second layer, and the tin-free steel for welded cans of the present invention can be manufactured. However, among these three removal methods, method (2) of cathodic electrolysis in a warm acidic solution is the most effective in removing chromium hydrated oxides from the production outlet of the tin-free steel for welded cans of the present invention. Workability is also good.

Therefore, we will explain the method for removing chromium hydrated oxide by cathodic electrolysis (2) in this warm acidic solution. In the water damage method C2, strong acids such as sulfuric acid and hydrochloric acid are used, and the pH is adjusted by 0.5 to 2. Even if the pH is less than 0.5, the removal of hydrated chromium oxides is more effective, but the action of acids (secondarily, dissolution of metallic chromium occurs). In addition, if the pH exceeds t2, it will take time to obtain the removal effect, which is not a good idea.If the temperature is below 30°C, it will take two hours to obtain the removal effect. However, if the temperature force exceeds 70°C, dissolution of metallic chromium tends to occur.The most effective cathodic electrolysis conditions in such a warm acidic solution are current densities of 2 to 50°C.
A/d, time is defined as 0.5 to 5 seconds. If the current density is below the lower limit condition for both hours, the removal effect of hydrated chromium oxide i will be insufficient. The higher the current density, the more significant the effect becomes, but it reaches saturation and there is no need for a circuit of 50A or more.) Furthermore, the longer the time, the greater the removal effect becomes, and if the time is longer than 5 seconds, the metal chromium tends to dissolve, which is not practical.

Methods other than cathodic electrolysis in a warm acidic aqueous solution, i.e. immersion in a warm acidic aqueous solution, immersion in a hot alkaline aqueous solution, cathodic electrolysis, brush roll method (these two methods can also remove chromium hydrated oxide; The tin-free steel for welded cans of the invention can be obtained.However, the hot alkaline aqueous solution method is inferior to the cathodic electrolysis method in a warm acidic solution in terms of the effect of improving weldability (=, an alkaline aqueous solution is easier to wash with water than an acidic aqueous solution). (
J! If rinsing is insufficient, the nickel/zinc alloy will be carried into the next acidic nickel/zinc alloy plating solution.
This method is disadvantageous in terms of work management, such as making the zinc alloy plating conditions unstable.The brush roll method is disadvantageous in that workability is reduced due to local wear of the brush roll.

After the chromium hydrate oxide removal treatment, a known nickel-zinc alloy plating bath is used. For example, in the Watt bath, which is the most common nickel plating bath (a method in which a small amount of zinc ions is added), in the Watt bath system, nickel sulfate... ...
・・15～80 Q/l←Tsuke 7Mty & Shiri Zinc Sulfate・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・0.5～16 g/Ic Zinc ion binding 0 Zinc/Nickel ion concentration ratio ・・・0.03～0.20 Boric acid ・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・30～40y/1bath temperature・・・・・・・・・
・・・・・・・・・・・・・・・・・・30～70℃Cathode current density・・・・・・・・・・・・・・・・・・・・・
・2 to 50 A/d In addition, when using a nickel sulfamate bath or a nickel chloride bath as the basic bath, the above concentration,
By selecting electrolytic conditions, the second layer of nickel-zinc alloy plating can be applied. In either type of bath, boric acid is added as a pH buffering agent, but its effect on plating uniformity and adhesion is not significant and is necessary (it can be added as needed.The anode is a soluble nickel plate, Or nickel beret etc. are used.

For the third layer of chromium hydrated oxide, a conventional chromate treatment method is used. For example, chromic acid dichromate (sodium dichromate, potassium dichromate.

It is formed from C2 by cathodic electrolysis in an aqueous solution such as ammonium dichromate. In addition, in order to improve the precipitation efficiency of chromium hydrated oxide in the above bath, it is possible to add a small amount of auxiliary agents such as sulfuric acid and fluoride, which are usually used in chromium plating. Chromium also tends to precipitate, which has the opposite effect on improving weldability, so it is necessary to select conditions such as reducing the amount added and current density to prevent the precipitation of metallic chromium.

When chromic acid dichromate is used and no auxiliary agent is added, the Cr +6 concentration is 5 to 30 y/l and the temperature is 3.
0-70°C, cathode current density 1-20A, 4. Electricity [1~
Processed in a 40 chlorine layer. When using chromic acid and adding an auxiliary agent, the Cram concentration is 10 to 50 y/l.The auxiliary agent is 0.2 to 196. Temperature 30-6
0°C, cathode current density 1~i0A/d, quantity of electricity 1~20°
Processed by C/d11.

Next (2) We will explain a manufacturing method that does not require any chromium hydrated oxide removal process when applying the second layer of nickel-zinc alloy plating after the first layer of chromium plating. 1st layer chrome plating → 2nd layer nickel plating
This manufacturing method involves three steps: zinc alloy plating → formation of the third layer of chromium hydrated oxide.

It has been found that by specifying the second layer of nickel-zinc alloy plating under the following conditions, it is not necessary to remove chromium hydrated oxide after chromium plating.

■Nickel ion concentration: 15~Boy/1 ■Zinc ion concentration = 0.5~16 Q/1 ■Zinc-to-secondary nickel ion concentration ratio: 0.03~0.2 ■pH: 0.5~2 ■ Bath temperature: 30-70℃ ■Cathode current density = 2-50 A/dd As is well known (2. is 2
If the pH is lower than 5.5, hydrogen gas generation due to hydrogen discharge will increase, and the nickel deposition efficiency will decrease.
When the temperature is around 1 or more, N1(OH) becomes easier to generate.
Since precipitation of nickel becomes difficult, the pH is set at 2 to 5.5, and a more preferable pH range is 3 to 5.5.

However, by limiting the pH to <0.5 to 2 as described above, the first layer of metallic chromium can be removed without removing in advance the chromium hydrated oxide that is unavoidably released after chromium plating. As a result, nickel-zinc alloy plating can be applied on top.
The tin-free steel for welded cans of the present invention can be manufactured.

The reason for this is that when the pH is lowered to <0.5 to 2 compared to the present invention, hydrogen generation becomes even more intense, and chromium hydrated oxide is peeled off from the chromium surface due to intense agitation by hydrogen gas. : Combined with dissolution by the action of strong acid C, the metal chromium surface becomes extremely active over the entire surface, and at the same time nickel-zinc alloy precipitates, resulting in uniform coverage and good adhesion of the nickel-zinc alloy. It is presumed that the effect of improving weldability and sulfidation resistance was obtained.

In addition, by lowering the pH to 0.5 to 2, the deposition current efficiency of the nickel-zinc alloy decreases, but the amount of nickel-zinc alloy plating in the present invention is 5 to 300,/d.
This is so small that it does not pose a problem in terms of manufacturing costs. The nickel ion concentration in nickel-zinc alloy plating condition 42 was specified as 15 to 80 y/1.
If g/ is less than 42, it will be susceptible to other mixed impurities (iron ions from the base steel sheet, chromium ions brought in from the chrome plating process), and the concentration of added zinc ions will be too low, causing The zinc alloy deposition current efficiency becomes unstable and is not practical. In addition, even if the nickel ion concentration exceeds 80 y/l, the deposition current efficiency of the nickel-zinc alloy (there is no significant change, and there is an effect of improving weldability,
Although there are no disadvantages in terms of properties, the amount of nickel contained in the scooping liquid during the plating process increases, which is economically disadvantageous. To replenish nickel ions, use nickel sulfate,
This can be done by adding nickel salts such as nickel sulfonate or nickel chloride, or by partially using a soluble anode (it is also possible to do it twice or more consecutively.) Replenishment of zinc ions can be done with zinc sulfate, zinc chloride, etc. When a nickel soluble anode is partially used, 5 to 40 y/1 of nickel chloride, ammonium chloride, etc. is added as an anode dissolution promoter.

The zinc ion/nickel ion concentration ratio in the nickel/zinc alloy plating bath must be controlled to 0.03 to 0.20 (secondarily, nickel/nickel with a zinc content of 10 to 90% by weight).
Zinc alloy plating is obtained.

pH is defined as 0.5-2. The pH can be adjusted by adding sulfuric acid, hydrochloric acid, or sulfamino acid alone or in combination (this can be done more easily by using acids such as nitric acid or phosphoric acid) in any of the nickel sulfate-based baths, nickel chloride-based baths, and nickel sulfamate-based baths. Although it is possible to adjust the pH within the specified range C2, it is not practical to add nitric acid directly because it is highly corrosive to the electrolytic cell.
When H is adjusted, phosphorus may eutectoid in the nickel/zinc alloy layer, albeit in a small amount, and this film has a high electrical resistance, which is disadvantageous in terms of improving weldability. bath p
Weldability tends to improve as n decreases, but at pH 0
If it is less than 15, the activated metallic chromium surface becomes susceptible to dissolution by acid 1, making it difficult to ensure a stable amount of metallic chromium in the first layer after nickel-zinc alloy plating (=).

If the pH exceeds 2, less hydrogen gas will be generated and the effect of improving weldability will be reduced, perhaps because an active metal chromium surface cannot be obtained, so the pH is set at 2 or less, but a pH of 1.5 or less is more preferable. At pH 2 or higher, slight changes in the nickel ion or zinc ion concentration, sulfate ion concentration, etc. in the bath (on the other hand, the pH also tends to fluctuate), whereas at pH 2 or lower, the fluctuation is gradual, making it very advantageous to control the bath pH. be.

The temperature of the nickel-zinc alloy plating bath is specified as 30 to 70°C. The higher the temperature, the higher the activity of the metal chromium surface, which is more effective in achieving the objective of the present invention. However, when the temperature exceeds 70°C, the metal chromium surface becomes It becomes easy to dissolve and is not practical.This may be because the activity of the chromium surface decreases when the bath temperature is less than 30℃.
In this case, the effects of the present invention cannot be obtained sufficiently.

The cathode current density is defined as 2 to 50 A/d. 2A/d
If it is less than d, nickel-zinc alloy precipitation (2) The required current application time becomes longer, which is inconvenient for industrial production.

Conversely (2) The higher the cathode current density, the shorter the plating current application time will be, but if it exceeds 50 A, nickel hydroxide will be excessively produced and precipitation of nickel-zinc alloy will be difficult to occur.

Of course, the nickel-zinc alloy plating conditions described above may be applied to the nickel-zinc alloy plating after removing the chromium hydrated oxide after plating the first layer of chromium.

As explained above, the tin-free steel for welded cans of the present invention has much better weldability than the conventional TF8-CT, and has better weldability than the three-layer tin-free steel proposed in Japanese Patent Application No. 59-15260. Although it has excellent sulfidation resistance, it also has properties other than weldability and sulfidation resistance, namely corrosion resistance, coating performance, and surface color tone, which are almost the same as T F 8- C"I" and are superior in weldability. It can also be used for purposes other than cans, such as can lids, DRIJ cans (double drawing method (double-drawing cans), cement side seam cans, etc.).

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

〔Example〕

Degrease in the usual way (NaOH 70y/l, temperature 80'
C.

Current density 5A/7. time 5 seconds), pickling (H-80470
The test was carried out using a steel plate (thickness: 0.22 m) which had been immersed for 5 seconds at a temperature of 25°C. Formation of the first layer (metallic chromium), removal of hydrated chromium oxide, formation of the second layer (nickel alloy), and third layer (chromium Eiwa oxide) were carried out under the treatment conditions shown in Table 1. Table 2 shows the results of those characteristic evaluations.

In Examples 1 and 2, after the first layer of chromium plating was applied, chromium φ hydrated oxide was removed by cathodic electrolysis in a warm acidic aqueous solution, and nickel-zinc alloy plating was applied using a known bath. It is something. In Example 3.4, the first layer was plated with chromium, and then nickel-zinc alloy plating was directly applied using a low-pH nickel-zinc alloy plating bath. Both examples were TFS-C shown as Comparative Example 1.
The weldability is much improved compared to T.

Comparative Example 2 is a case in which there is no metallic chromium as the first layer, but it has much better weldability and durability than Example 2.3, which has the same amount of nickel-zinc alloy plating layer and has a metallic chromium amount in the base layer. The sulfidation property is poor, and the importance of metallic chromium as the first layer is well understood.Comparative Example 3 in which zinc was not eutectoid Combined with this effect, sulfidation resistance is improved.

The test method for evaluating the characteristics shown in Table 2 C2 is explained below (
1) Weldability test Weldability is determined by the difference between the lower current limit required to form uniform nuggets and sufficient welding strength and the upper limit current that causes part of the base steel plate to melt and scatter (splash generation). It is expressed by the magnitude of the welding current range, and it is said that the larger the range, the better the weldability. This appropriate welding current range has a good correlation with the contact electrical resistance value when two sheets of steel sheet material for welding cans are stacked (for example, the Iron and Steel Institute of Japan's 106th Conference Lecture No. 507, 1983, No. 13).

Volume 69) The lower the contact electrical resistance, the larger the appropriate welding current range. Therefore, as a weldability test of the tin-free steel for welded cans of the present invention, this contact electrical resistance value measurement was carried out.

This contact electrical resistance value was measured by the method described below (2).The contact area (12 plates) of two copper disc electrodes (diameter 65 m, thickness 2 cm) was set so that each circumference was in contact at one point. A stacked sample plate (20 pieces x 100 mm) is sandwiched between the electrodes and pressure is applied with a load of 50 kg.A direct current of 5A is applied between the two disc electrodes, and the sample plate is moved by rotating at a circumferential speed of 5/-. While doing so, the voltage between the electrodes was measured, and the contact electrical resistance value (unit: milliohms) was calculated.All sample plates were subjected to a heat treatment at 210° C. for 20 minutes before being subjected to measurement.

(2) Apply 60 mg of epoxy/phenol-based internal paint to the sulfur resistance test sample plate.
/drIt was applied, baked at 210°C for 12 minutes, and then molded into a can lid. Commercially available canned tuna pickled in oil is ground in a mixer, mixed with the same volume of water, and then boiled to degas it to obtain a sulfur resistance test solution. A molded sample was placed in this test liquid (double lid), and after retort treatment at 130°C for 3 hours, the degree of blackening on the can lid surface was evaluated on the following five scales.

5: Extremely good 4: Good 3: Slightly poor 2: Poor l
: Significantly inferior.

(3) Corrosion resistance test sample after painting (Nieboxy phenolic internal paint i60, /
After applying the DD coating and baking at 210℃ for 12 minutes, use a sharp knife to make a cross-shaped flaw from the coating surface to the base steel plate, and make a 1.59! After dipping in a corrosive solution consisting of citric acid and 1,596 chloride salt and aging at 50°C for 7 days (the coating near the bottom was peeled off with a chlorine phantom table, the corrosion state including the corrosion condition was determined as shown below. Evaluation was made using the three-step method (2).

52: Very good, 4: Good, 3: Slightly poor, 2: Poor.
1: Significantly inferior (4) Paint adhesion test A painted sample baked in the same manner as the post-painting corrosion resistance test was punched out into a disk with a diameter of 801 m, cup C was drawn twice at a drawing ratio of 2, and the coating film on the outer side wall of the cup was coated with cellophane. Tape (peeled from 2 and evaluated using the following three-step method: 5: no peeling, 4: slight peeling, 3: slight peeling, 2: mostly peeling, l2: entire peeling)

Claims (3)

[Claims] (1) 30 to 300 H/lri per side on the copper plate surface
5 chrome plating layer per side on the chrome plating layer.
It is characterized by a nickel-zinc alloy plating layer with a zinc content of ~3001 #/ni and a zinc content of 10 to 90% by weight, and a chromium hydrated oxide layer of 2 to 181 d per side in terms of chromium formed thereon. Tin-free steel for welded cans. (2) After applying chromium plating of 30 to 300 mm per side on the steel sheet surface, in sulfuric acid, hydrochloric acid, or an aqueous solution of sulfuric acid and hydrochloric acid with a pH of 0.5 to 2, at a temperature of 30 to 70 °C and a cathode current density of 2 to 50 - for 0.5 to 5 seconds to remove the chromium hydrated oxide remaining on the chromium plated surface, and then nickel-zinc with a zinc content of 10 to 90% by weight with 5 to 3001 d per side. Alloy plating layer applied, -j! A method for producing tin-free steel for welded cans, which comprises forming a chromium hydrated oxide having a ratio of 2 to 18 in terms of ζ nichrome. (3) Steel plate surface (after applying chromium plating of 30 to 300%/ld per two sides, nickel ion concentration of 15 to 80%)
y/l, zinc ion concentration 0.5-16 y/l, zinc ion/nickel ion concentration 0.03-0
．． 1) Ho, using an acidic nickel-zinc alloy plating bath of 5-2, with a zinc content of 10-300%
A method for producing tin-free steel for welded cans, which comprises plating with a 90% nickel-zinc alloy and further forming a chromium hydrated oxide having a concentration of 2 to 18 chromium in terms of chromium.