JPS61190077A - Manufacture of surface treated steel sheet for welded can - Google Patents

Abstract

PURPOSE:To manufacture inexpensively the titled steel sheet superior in thread rust resistance, by applying suitable quantities of metallic chromium plating and tin plating on steel sheet, then applying heat treating, further suitable chromate treatment or electrolytic chromic acid treatment to said sheet. CONSTITUTION:Metallic chromium plating is applied on steel sheet at 10-150mg/m<2> per one side surface. Next, tin is plated at 0.1-1.0g/m<2> while removing remaining hydrated chromium oxide. Thereafter, plated steel sheet is heated to 240-350 deg.C to melt tin. By this way, tin layer is made to island state and discontinuous cover having good adhesive property. Further the steel sheet is chromate treated to form hydrated chromium oxide of 2-20mg/m<2> calculated in chromium, or electrolytically chromic acid treated to form 3-30mg/m<2> metallic chromium and hydrated chromium oxide of 2-20mg/m<2> calculated in Cr.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The industrial field of application of the surface-treated steel sheet for welded cans according to the manufacturing method of the present invention is as a material for metal cans filled with food and beverages.

[Conventional technology]

As a conventional technique for manufacturing a surface-treated steel sheet in which aluminum is coated on a steel sheet and the upper layer is coated with tin, the Japanese Patent Publication No. 48-35
A chromium-tin two-layer plating method is known for No. 136. The method of this invention is to electrolessly immerse a steel plate in a chromium plating solution (=electroless immersion) after electroplating the steel plate with chromium.

After washing with water, it is electrolessly immersed in a pan plating bath, then strike plating is performed for 0.5 seconds or less at a current density higher than the gloss current density of pan plating, and then tin plating is performed at a gloss current density. This invention relates to a tin plating method for dissolving residual chromium hydrated oxide and improving the adhesion of tin on chromium after chromium plating, and targets C; tin as shown in Example C2. That is.

As a surface-treated steel sheet having chromium on the steel sheet and tin on the upper layer, some of the inventors of the present application have previously published a document titled "Surface-treated steel sheet for welded cans and its manufacturing method" (filed on March 9, 1980, application number 59- No. 43789) was filed. The surface-treated steel plate for welded cans of this patent application has a surface treatment of 30 to 300 cm per side on the steel plate.
/m2 chromium plating layer and 10~500cm on top layer
A tin plating layer or a tin-nickel alloy layer is formed as a layer, and a chromium hydrated oxide layer having a concentration of 2 to 18 mg/m 2 in terms of chromium is formed on top of the tin plating layer or tin-nickel alloy layer. The manufacturing method is that after chromium plating, 2
After treatment with a cathode current density of ~50 A/am2 for 0.5 to 5 seconds to remove the chromium hydrated oxide remaining on the chromium plating layer, 9wA or tin-nickel alloy plating was applied, and further chromium hydrated oxide was applied. It is a method of producing things. Furthermore, after chromium plating (= in order to perform tin or tin-nickel alloy plating while removing residual chromium hydrated oxide, a tin plating bath with a low tin ion concentration and low pH or tin and nickel ions is used (; It is also possible to use low alkaline earth gold plating baths or acidic alloy plating baths.

[Problem that the invention seeks to solve]

Traditionally, tinplate has been widely used as a surface-treated steel sheet for welded cans filled with food and beverages, but in order to reduce the cost of two cans, the amount of tin plating has been reduced to reduce the amount of tin plating. (below) and thin-film plated steel sheets pre-plated with nickel have been developed.

It is being used experimentally. The can performance of these surface-treated steel sheets is superior to that of tin plated with a tin plating amount of 2.8 g/i in all properties. Long-term storage (
: cannot withstand it and is used on a trial basis only for beverages with slightly less than 2 corrosive properties.

The problem to be solved by the present invention is that the wire seam weldability, paint adhesion, string rust resistance, and corrosion resistance that a surface-treated steel sheet for welded cans should have are insufficient in the above-mentioned thin film plated steel sheet, and the amount of anti-plating ZS is insufficient. ,.

/- It is not comparable to Noburiki. The present invention has a tin plating amount of 1. OV-52 below, the amount of tin plating that is often used is 2.8 g/fn! We not only provide a low-cost surface-treated steel sheet that rivals Noburiki can performance 52, but also provide a surface-treated steel sheet that has the can performance of chrome-type tin-free steel, which is often used in adhesive cans. This is the manufacturing method.

In the surface-treated steel sheet for welded cans obtained by implementing Patent Application No. 59-43789, tin or tin-nickel alloy plated on chromium remains plated and exists uniformly. It is known that yarn ends develop due to the formation of oxygen concentration batteries in areas where the paint film is scratched in a highly humid atmosphere containing chlorine or the like. As the layer becomes thinner, the amount of oxygen supplied to a part of the inert body at the end of the yarn increases, and tin, which promotes the oxygen reduction reaction, is uniformly present.1; As a result, the yarn rust resistance deteriorates. The first objective of the present invention is to improve thread rust resistance.

Heating such as baking after painting (=Therefore, iron diffuses through the bores present in the chromium layer, forming an iron pan alloy, but if the tin plated on the chromium remains plated, the tin will exist uniformly) However, since the surface area is large, the amount of alloy formed in the iron pot is large.The second object of the present invention is to further reduce the amount of formed alloy layer and to allow more metallic tin to remain.

In food and beverages, as-plated tin is susceptible to tin removal, or sub-film corrosion, which is the dissolution of tin from scratches in the paint. A third object of the present invention is to improve detining resistance and cold sub-film corrosion resistance.

[Means for solving problems]

The inventor conducted a detailed study on the can performance of a surface-treated steel sheet obtained by performing tin plating while removing the hydrated chromium oxide remaining on the chromium after chromium plating, and found that the presence of a tin layer on the chromium. It was discovered that the condition has a great influence on the performance of the can, leading to the present invention. That is, although the tin layer as electrically deposited is uniform, it lacks Pa density and is inferior to tinplate in thread rust resistance and under-coating corrosion resistance. This tin layer is 240 to 350'C above the melting point of tin.
By heating to melt the tin, it forms an island-like, discontinuous coating on the chromium. As is well known, Cnichrome and tin not only do not form solid solutions with each other, but also do not form intermetallic compounds. Therefore, when tin is melted on a chromium layer, a repelling phenomenon occurs, forming an island-like and discontinuous coating. The chromium layer ζ= varies somewhat depending on the amount of chromium plating.

It has many bores. For this reason, some iron and tin diffused from the bore during heating and melting form a very dense iron-tin alloy, so the tin layer forms an island-like and discontinuous coating, and the adhesion strength on the C nichrome increases, causing it to peel off. Does not cause In addition, compared to a case where the tin layer is uniform, the amount of iron pan alloy formed by heating such as baking of paint is smaller.An example is shown in which tin on the chromium layer is repelled and forms an island-like and discontinuous coating. 1st
Shown in the figure. In FIG. 1, the white island-like particles are the tin layer.

The matrix corresponds to the chromium surface.

The present invention solves the drawbacks of the above-mentioned thin tin-plated steel sheets and surface-treated steel sheets in which tin is uniformly plated on chromium.
Apply chromium plating of 0 to 150 ■ An2 and remove residual chromium hydrated oxide while 0.1 to 1.0 g/rn
2. Tin plating is applied, and the steel plate is heated to 240 to 350°C to melt the tin, forming an island-like and discontinuous tin layer coating,
Furthermore, this is a method for producing a surface-treated steel sheet for welded cans, which is subjected to chromate treatment or electrolytic chromic acid treatment.

The amount of chromium plating on the steel plate is 10 to 1 s o mg/
m" is preferable. If the amount of chromium plating is less than 10 ma/-, the amount of exposed iron will increase, and the repelling phenomenon of tin will be insufficient in the heat melting treatment after tin plating, and the amount of iron pot alloy formed will increase, causing metallic tin to deteriorate. In addition to reducing wire seam weldability, the relatively uniform presence of tin also reduces thread rust resistance.When the amount of chromium plating exceeds 150 layers, the bore of the chromium layer decreases. , because the exposed iron part is reduced 2
A strong repelling phenomenon occurs when gJ is heated and melted, and almost no iron pot alloy is formed, resulting in insufficient adhesion of chromium and tin.

Chrome plating is performed by electrolyzing a steel plate as a cathode in an aqueous solution containing chromic anhydride as the main ingredient and a small amount of sulfuric acid, sulfate, hydrofluoric acid, fluoride, silicofluoride, and borofluoride as auxiliary agents. Obtained by chromic acid treatment. It is necessary to use a bath and electrolytic conditions that produce a small amount of chromium hydrated oxide that remains unavoidable during chromium plating. In other words, it is preferable that the chromic anhydride concentration is as high as 100 to 100 g/l, and the amount of the auxiliary agent is 1 to 5 chromic anhydride.
Weight percent is preferred. Bath temperature and current density are each 50~
A higher value of 7o0c and 30 to 60 A/di is preferable.

It is also possible to use a chromium plating bath containing trivalent chromium ions, which uses chromium sulfate or chromium chloride as the main ingredient, and also includes auxiliary agents, complexing agents, and activators. In this method, the amount of chromium hydrated oxide produced is extremely small, and tin plating can be performed in a ferrostane bath, a herogen bath, etc. without removing the chromium hydrated oxide.

Immersion in a chromium plating bath or a chromium plating bath whose temperature is higher than that of the chromium plating bath is effective in reducing as much as possible the amount of chromium hydrated oxide remaining on the chromium after chromium plating. To remove residual chromium hydrated oxide after chromium plating, cathodic electrolytic treatment in sulfuric acid or hydrochloric acid with a pH of 015 to 2 is also effective, but in this case, the adhesion of the tin plating layer to chromium is effective. is weak. Therefore, the most effective method is to perform tin plating while removing the remaining hydrated chromium oxide.

The amount of plating is preferably 0.1 to 1.0 g/nx''.

Below 0.1a/m", most of the tin becomes an iron pan alloy, which not only fails to provide sufficient wire seam weldability, but also makes the appearance equivalent to tin-free steel.
The tin luster is lost. At 1.0 g/m" or more, the wire seam weldability becomes equal to or better than that of tin plate and becomes saturated, and at the lower limit of the chromium plating amount, the non-uniformity of the tin island-like discontinuous coating decreases and the thread resistance increases. Rust resistance deteriorates.In addition, (increased continuity of double chains) corrosion on the paint film also increases, resulting in high costs, so it must be avoided.

For use in painted cans filled with foods and beverages (: when applying the method of the present invention, the tin amount is more preferably 0.4 to 0.79□.

Since the tin plating method performs tin plating while removing residual chromium hydrated oxide, known ferrostane baths and halogen baths are sufficient and it is difficult to obtain chromium and tin adhesion. Tin ion concentration is 2-15 g/l! An acidic calming bath with a pH of 0.5 to 3 or a tin ion concentration of 2 to 50 v/I! Dep
Preference is given to using an alkaline bath of H8-10. In either bath, it is necessary to reduce only the tin concentration to 1/3 or less of that of conventional baths.

The acid, alkali concentration, brightener concentration, etc. may be the same as conventional ones. As the tin concentration decreases, the current efficiency of tin deposition decreases and
~6096, hydrogen gas is generated and residual chromium hydrated oxide is removed, the chromium surface becomes active and at the same time (- tin is precipitated, so the adhesion and uniformity of tin are improved.

If tin plating is performed only with such a low-efficiency tin plating bath, the electricity cost will increase, so after the remaining chromium hydrated oxide is removed and the chromium surface is uniformly covered with tin, a ferrostane bath is used. It is necessary to use a known bath such as a halogen bath or a halogen bath.

The temperature of tin heating and melting treatment after tin plating is 240 to 350°.
C is preferred. At temperatures below 240° C., tin partially melts, but it is not possible to form all the tin into an island-like and discontinuous coating. In addition, islands can be formed sufficiently at temperatures above 350°C, but heating more than necessary will lead to oxidation of the tin and chromium surfaces.
It is also disadvantageous in terms of cost. The heating and melting treatment of tin can be carried out by a resistance heating method or an induction heating method, which are often used in tin manufacturing equipment.

Melting heat treatment of tin (2) As a result of tin forming an island-like and discontinuous coating, the surface of the treated steel sheet becomes a non-uniform structure consisting of tin and chromium. treatment or electrolytic chromic acid treatment.The amount of chromate film is 2 to 2 omta/ in terms of chromium.
Good rF. If it is less than 2 mg/In2, the paint adhesion after aging will deteriorate and the corrosion resistance will be insufficient, and if it is more than 20 mg/I-2, it will cause cohesive failure of the chromate film and the paint adhesion will deteriorate. However, the wire seam weldability is also reduced.The chromate treatment method can be carried out by cathodic electrolytic treatment in a dichromate aqueous solution of 20 to 40 v'l.The treatment temperature is 40 v'l.
~70℃.

A cathode current density of 2 to 10 A7 dm2 is suitable.

Electrolytic chromic acid treatment, which has better paint adhesion and corrosion resistance than chromate treatment, simultaneously produces metallic chromium and hydrated chromium oxide. In the present invention, metallic chromium 3 to 30@//m2. Chromium hydrate oxide is chromium equivalent 2
~2iV- is good.

If the metal chromium is less than 3rnQ/m2, the wire seam weldability is good, but the secondary adhesion of the coating film (paint adhesion in cans filled with food and beverages), corrosion resistance, and sulfidation resistance are insufficient. When it exceeds 30 ftIg/m2, contact resistance increases due to heating such as baking after processing and painting, and wire seam weldability tends to decrease. If the temperature of chromium hydrated oxide is below 240° C. in terms of chromium, not only the paint adhesion after aging deteriorates but also the corrosion resistance is insufficient. 20■
In a layer or more, the chromium hydrated oxide tends to undergo cohesive failure during processing, which not only reduces paint adhesion and corrosion resistance, but also increases contact resistance and reduces wire seam weldability, which is undesirable. To simultaneously generate metallic chromium and chromium hydrated oxide, cathode electrolysis treatment is performed using 20 to 80 g of chromic anhydride.
/'l bath: 20, 3 to 5% by weight of one or two of sulfuric acid, sulfate, fluorine, fluoride, silicofluoride, or borofluoride.
Add seeds and heat to 40-60°C.

It is necessary to conduct the process at a current density of 2 to 30 m/dm2.

[For production]

The surface-treated steel sheet for welded cans obtained by the manufacturing method of the present invention is completely different from conventional thin tin-plated steel sheets that are highly uniform because tin forms an island-like and discontinuous coating on the chromium. It has characteristics.

Since chromium does not form an alloy with tin, it acts as a barrier to the growth of the iron pot alloy, and growth of the iron pot alloy occurs only through the bore of the chromium layer. For this reason, compared to tin plating on a steel plate or tin plating pre-plated with nickel, which easily alloys with tin, the amount of iron pan alloy produced by heating such as baking after painting is extremely small. In addition, when C is plated after chromium plating and tin is not heated and melted, tin exists uniformly on the chromium and the tin layer lacks density.
=.

The total amount of iron-tin is increased compared to when tin is melted to form an island-like and discontinuous coating. By suppressing iron pan alloying as much as possible, leaving more metallic tin to remain, and making the tin island-like and discontinuous coating, reducing the resistance during wire seam welding and increasing the number of contact points, Provides wire seam weldability equivalent to that of

Thread rust resistance is due to the fact that tin, which promotes the oxygen reduction reaction, is not uniformly present and due to the repelling phenomenon, the tin thickness is thicker than before melting, so oxygen diffusion is insufficient and the growth rate of the steel is reduced. do. The parts where chrome is exposed have almost the same structure as tin-free steel, and like tin-free steel, it has excellent thread rust resistance.

Tinplate is usually inferior in paint adhesion to flat plates, and tin-free steel is superior, but in the present invention, the good adhesion of the chrome surface covers the entire surface, so it is superior to tinplate. Adhesion after processing is excellent for both tinplate and tin-free steel, but the tin-plated steel sheet is very poor.

In the present invention, even if the amount of tin is the same, it is very excellent due to the unrestricted structure C2. The secondary adhesion of paint deteriorates due to corrosion of exposed iron parts in food and beverages, but the present invention has a structure in which the chrome bores are filled with tin, so corrosion does not occur.

Secondary adhesion is excellent. Normally, the level of paint adhesion varies considerably depending on the post-treatment method, but in the present invention, it is based on the non-uniform structure of chromium and tin.

Another feature is that it is not easily affected by post-processing methods.

The food and beverage corrosion resistance of the surface-treated steel sheet of the present invention is considerably different from that of tin and tin-free steel. Iron in a test solution containing degassed citric acid and salt::
When a painted plate with scratches on it is immersed in tinplate, the tin around the scratches dissolves, causing corrosion under the paint film.
In tin-free steel, pitting occurs from scratches.

In the surface-treated steel sheet of the present invention, dissolution of tin occurs in the scratched area, but due to the coexistence of passivated chromium, the corrosion rate is extremely low, and it exhibits far superior corrosion resistance compared to tin and tin-free steel.

If the tin on the chrome is not melted, corrosion under the paint film will occur, similar to tinplate. As described above, by forming the tin layer on chromium into an island-like and discontinuous coating (2), an unprecedented surface-treated steel sheet can be obtained, and the effect of the non-uniform structure has a significant feature.

〔Example〕

A mild steel plate with a thickness of 0 or 20 mm that has been cold rolled, continuously annealed, and temper rolled by the usual method is electrolytically degreased (N
aOH70a/l, temperature 85℃, current density 5νdi2
time 5 seconds) and pickling (H2SO470ta/l).

(temperature: 20° C., 2 hours, 5 seconds), and chromium plating was performed using the following bath and conditions.

Chrome plating bath composition CrO3100g/INaF
5 g/l Chromium plating conditions Temperature: 50'C Current density: 30 A/dm2 Time: 0.3 to 1.8 seconds After washing the obtained chromium-plated steel sheet with water, the chromium hydrate remaining on the chromium was removed using the following bath and conditions. The first tin plating was performed while removing the oxide.

First tin plating bath composition Sn” 5 Jl phenol sulfonic acid 30 g/l ethoxylated α-naphthol
5 ta/11th tin plating conditions Temperature 40°C Current density 20 A7dm 2 hours
After washing the obtained tin-plated steel plate with water for 0.1 to 0.4 seconds, the second tin plating was performed in the following bath and conditions.

Second tin plating bath composition Sn4+ 40 v/I! Phenolsulfonic acid 30 g/l Etquinated α-naphthol 5 g/12th tin plating conditions Temperature 40'C Current density 10 A/dm 2 hours
The obtained steel plate plated with chromium and tin was heated for 0.7 to 1.0 seconds by a resistance heating method to about 300'C above the melting point of tin to melt the tin and cause a repellent phenomenon.

The coating was made into an island-like, discontinuous coating and cooled with water. After drying, post-treatment was carried out to produce metallic chromium and hydrated chromium oxide under the following bath and conditions.

Post-treatment bath composition Cr0a 60 v'1H2
SO40,3v/l! Post-treatment conditions Temperature: 45°C Current density: 10 A/'dm2 Time: 0.4 seconds Amount of coating on the surface-treated steel sheet thus obtained.

After heating at 210°C for 20 minutes, we carried out tests on the amount of alloy in an iron pan, wire seam weldability (contact resistance), thread rust resistance, secondary adhesion of paint, and corrosion on the paint film after flat plate and Eclysene processing, and the test results. are shown in FIG. 2 and Table 1 C:.

[Comparative example]

Bath and plating conditions similar to those in Examples (Secondly, surface-treated steel sheets with a coating amount outside the claimed range and surface-treated steel sheets with a coating amount within the claimed range and manufactured without heat-melting treatment of tin) The steel plate was subjected to the same post-treatment as in the example.

The obtained surface-treated steel sheet was subjected to the same test as in the example, and the test results are shown in FIG. 2 and Table 's1.

Furthermore, the amount of tin plating is 2.4867m2. The amount of chromate is chromium equivalent s, 9 v@/rr? Noburiki and metal chromium 118■An2. Chromium hydrate oxide is equivalent to chromium 1
Tests similar to those in the Examples were conducted using 7■/4i tin-free steel, and the test results are shown in Table 1.

Test methods for various tests in Examples and Comparative Examples (2) will be explained.

1) Wire seam weldability test Wire seam weldability is expressed as the difference l between the lower limit of current necessary for the mechanical strength of the weld to exceed the strength of the base metal and the upper limit of current that generates dust from the weld.

The larger the difference, the better the wire seam weldability.

This difference was layered with two sheets of surface-treated steel plate for welded cans.

The contact electrical resistance value was determined by inserting two disc electrodes (two discs, applying a load of sokg, rotating at a circumferential speed of 5 m/min, and measuring the voltage between the electrodes by passing a direct current through five people) There is a good inverse correlation with
It was expressed as contact resistance after heating at 210°C for 20 minutes.

2) Thread rust resistance test The obtained surface-treated steel plate was coated with vinyl organosol for 75 minutes and baked for 200°C.

After making two series of iron C scratches, Erichsen processing was performed on 5 cylinders, and after soaking in 396 saline solution for 1 hour, the salt water was wiped off and left in a constant temperature bath at 45℃ and relative humidity 8596 for 10 days. Evaluation was made using a 5-point method.

5 is good and 1 is bad.

3) Secondary adhesion test Apply 65% phenol epoxy paint to the surface-treated steel sheet obtained.
mg/dm2 paint, baked at 210°C for 10 minutes, height 1.0 mm, pitch 4. After bead processing of OTM, a part is immersed in a stainless steel tank filled with milk coffee at 95℃, the tank is sealed and heated to 1300C.
Retort treatment was performed for 1 hour. After retort treatment, two Samples C were used and the paint film near the air-liquid interface was subjected to a sellotape peel test to examine paint adhesion.

The degree of peeling was evaluated using a 5-point scale. 5 indicates no peeling or whitening, and 1 indicates peeling at the gas-liquid interface.

4) Corrosion resistance test 65% phenol epoxy paint was applied to the surface-treated steel sheet obtained.
! Painted at 11g/dm2 and baked at 210℃ for 10 minutes.
A cross-shaped scratch was made with a load of 200g.

The corrosion resistance of the flat plate remains the same, and the corrosion resistance after processing is as follows: 1.5% citric acid and 1.5% Erichsen processing.
% common salt mixed aqueous solution ζ and degassed using nitrogen gas, the two flat samples C were stored at 37° C. for 15 days, and the sample C after processing was stored for 10 days. After the test, the flat plate sample was evaluated for corrosion from scratches, and for the sample after processing, the degree of corrosion at the processed part was evaluated using a 5-point method. 5 is good and 1 is bad.

〔Effect of the invention〕

The surface-treated steel sheet manufactured by the manufacturing method of the present invention is obtained by forming an island-like and discontinuous coating of tin on chromium.

Figure 2 (=As shown, the iron pot alloy growth rate is low.

Since more metallic tin remains after the paint is baked, wire seam weldability is equivalent to tinplate. Because the tin is discontinuously coated in island-like shapes, the thread rust resistance is equivalent to tinplate and superior to tin-free steel. The secondary adhesion of the paint is equivalent to that of tin-tinted steel, which has very little exposed iron, and is superior to tin-free steel. Its corrosion resistance is good due to its non-uniform structure, its under-coating corrosion resistance is better than that of tinplate, and its pitting resistance is better than that of tin-free steel. Although the cost is higher than tin-free steel due to the use of expensive tin, it is cheaper than tin-free steel (compared to tin-free steel).From the above, the surface-treated steel sheet for welded cans manufactured by the manufacturing method of the present invention can be used to fill foods and beverages. It is very suitable as a material for metal cans.

[Brief explanation of the drawing]

FIG. 1 is a secondary electron beam image of the surface of a surface-treated steel sheet obtained by the manufacturing method of the present invention. The white particles are island-like (= tin layer) and the matrix is the chromium layer. Figure 2 shows tin plating amount of 0.64 to 0.68 B/-. Treated steel sheets with varying chromium plating amount. This shows the relationship between the amount of tin in the iron-tin alloy and the amount of chromium plating formed after heating at 210°C for 20 minutes, assuming paint baking.When tin is heated and melted, it becomes an iron pot alloy. The amount of production will be extremely small. $ 1 Figure (I @ 41 aso a view) Figure 2 Procedural amendment (method) % formula % 1, Indication of case Patent application No. 27564 of 1985 2,
Title of the invention Method for manufacturing surface-treated steel sheets for welded cans 3, Relationship to the case of the person making the amendment Patent applicant 4, Agent address (residence) 4-3-6 Kasumigaseki-chome, Chiyoda-ku, Tokyo
, Subject of amendment Contents of amendment to attached specification and drawings (1) Specification Page 17 Line 12 r Sn "J"
Sn”J. Specification page 18 2nd line rsn”, J is r Sn”J
shall be. (2) On page 24 of the specification, line 6 (brief description of the drawings), it says, ``This is a secondary electron beam image of the surface of a treated steel sheet.'' It says, ``This is an electron micrograph of the surface structure of a treated steel sheet. ”. (3) Figure 1 of the drawings shall be amended as shown in the attached sheet. 8. List of attached documents (1) Figure 1 of drawings Figure 1 of 1 copy (magnification: 850x) ~1 10μrr+

Claims (1)

[Claims] Metal chromium plating of 10 to 150 mg/m^2 per side is applied to a steel plate, and while removing residual chromium hydrated oxide, tin plating is applied to 0.1 to 1.0 g/m^2, and the steel plate is is heated to 240 to 350°C to melt the tin, form a tin layer into an island-like and discontinuous coating, and further add 2 to 20 m in terms of chromium.
g/m^2 of chromium hydrated oxide or 3 to 30 mg/m^2 of metallic chromium, chromium equivalent 2 to 2
A method for producing a surface-treated steel sheet for welded cans, characterized by producing 0 mg/m^2 of chromium hydrated oxide.