JPH0660387B2 - Manufacturing method of surface-treated steel sheet for can manufacturing with excellent processing corrosion resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a drawn and ironed can (DI can),
TECHNICAL FIELD The present invention relates to a method for producing a surface-treated steel sheet for can manufacturing, which has excellent processing corrosion resistance and is suitable as a material for cans that undergo severe processing such as drawn & redrawn cans (DRD cans), drawn cans and can lids.

[Conventional technology]

Sn-plated steel sheets, so-called tinplate, and steel sheets coated with a double-layered film of metal Cr and hydrated chromium oxide, so-called tin-free steel (hereinafter abbreviated as TFS) are widely used as materials for cans. ing. In recent years, in the field of can-making materials, the entry of competing materials such as aluminum has been remarkable, and it has been demanded to develop a surface-treated steel sheet for can-making which is inexpensive and has excellent work corrosion resistance. Although there is already TFS as an inexpensive surface-treated steel sheet for can manufacturing, TFS has excellent paint adhesion, but requires improvement in work corrosion resistance, and it was recently developed as an inexpensive surface-treated steel sheet for welding cans. There is a thin Sn-plated steel sheet, but since the plating layer is thin, the corrosion resistance of the machined part etc. is inferior to that of ordinary tinplate, and it is necessary to improve the corrosion resistance of the plated base steel sheet itself in order to use it in applications with severe processing. is there. As a method thereof, a method of adding Cr or the like at the time of steel making (Japanese Patent Laid-Open Nos. 61-6293 and 62-30
896), a method of forming a Ni diffusion layer on the steel sheet by subjecting the steel sheet surface to Ni plating and heat treatment (JP-A-57-200).
592, JP-A-60-155685), a method of forming Sn or a diffusion layer of Sn and Sn and Ni on the steel sheet by performing Sn plating or Sn-Ni alloy plating on the surface of the steel sheet (JP-A-60-5894, special feature). 60-89594),
In addition, a method of plating Cr first and then Sn and then heat treating it to diffuse Cr and Sn into the steel is being studied.

[Problems to be Solved by the Invention]

The method of adding Cr at the time of steel making, as disclosed in JP-A-62-30896, improves the corrosion resistance of the steel sheet itself, but not only increases the cost of the steel sheet by adding Cr, but also descales after hot rolling, Sn, etc. It is difficult to say that it is a material suitable for the tin plate and TFS base steel sheet, which causes problems in platability and can manufacturing. In addition, as described in JP-A-57-200592, a tin plate using a base steel plate in which Ni is diffused on the surface of the steel plate, TFS is likely to be cracked in the Ni diffusion layer when subjected to processing, and in this state, in a beverage such as fruit juice When exposed to Ni, the steel exposed in the cracks of the Ni diffusion layer is likely to cause anodic dissolution by the cathode of the Ni diffusion layer, which poses a risk of pitting corrosion. Further, the method of forming Sn or a diffusion layer of Sn and Ni disclosed in JP-A-60-5894 and JP-A-60-89594 does not show sufficient corrosion resistance with Sn alone,
In addition, when the Sn and Ni diffused, the corrosion resistance is improved when unprocessed, but when processed, the steel exposed in the cracks of the Sn and Ni diffusion layers in the beverage is the same as the Ni-diffused steel sheet. It is likely to cause anode melting and is not sufficient as a base steel sheet for surface-treated steel sheets for cans. Further, even if the purpose of diffusing Cr, Sn in the steel is the same, as a method of different methods, the method of applying Cr plating, then Sn plating, and thermally diffusing, the manufacturing method is also simple, The diffusion rate of Cr is also high. However, since it is a two-step method, in addition to the drawback of high equipment cost and maintenance cost, when it is installed in the current line, it may happen that space cannot be secured. It solves these problems, is cheap, and especially effective for processing corrosion resistance,
And the method for producing a surface-treated steel sheet for can manufacturing that does not cause any special problems in the steps after cold rolling, as a result of various studies from the aspect of the base steel sheet to be surface-treated, the present invention has been achieved. .

[Means for Solving the Problems]

The present invention is mainly cold rolling, Cr-Sn alloy plating on the surface of the steel sheet after electrolytic cleaning, or Cr-Sn-Ni
After alloy plating, heat treatment is applied in a non-oxidizing atmosphere of iron, and a surface-treated steel sheet and a heat treatment diffusion layer in which a heat treatment diffusion layer of Cr and Sn or Cr, Sn and Ni is formed on the surface layer of the steel sheet An object of the present invention is to provide a surface-treated steel sheet for can manufacturing which is excellent in corrosion resistance after processing, in which a so-called TFS-treated film, which is a film in which a lower layer is a metal Cr layer and an upper layer is a chromium hydrated oxide layer, is formed.

Hereinafter, the method of the present invention will be specifically described. Cr amount 3 to 150 mg on the surface of steel sheet after cold rolling and electrolytic cleaning
/ M ^2, Sn amount 25~800mg / m ² if subjected to a Cr-Sn alloy plating, or Cr amount 3~150mg / m ^2, Sn amount 25-80
After the weight ratio of 0 mg / m ^2, Ni amount 2 to 100 mg / m ^2, and Ni / Sn is subjected to Cr-Sn-Ni alloy plating is 0.50 or less, a heat treatment in a non-oxidizing atmosphere iron Included 95% or more of the Sn amount plated on the surface of the steel sheet and 1 mg / m ² or more of the plated Cr amount, or plated Sn amount, 95% or more of the Ni amount and 1 mg / m ² of the plated Cr amount A steel sheet including the above and having a heat treatment diffusion layer having a Cr / Sn + Cr weight ratio of 0.02 to 0.50 and a lower layer formed on the heat treatment diffusion layer by a known one-step method or two-step method. TF consisting of metal Cr and upper layer of hydrated chromium oxide
It forms an S-treated film.

First, a method for producing a surface-treated steel sheet which has been subjected to Cr-Sn alloy plating which can be used as a TFS-treated base steel sheet or as a surface-treated steel sheet for can making as it is, and then subjected to heat treatment in a non-oxidizing atmosphere of iron explain. If the amount of Cr in the Cr-Sn alloy plating applied after cold rolling or electrolytic cleaning is 3 mg / m ² or less, it does not hinder the TFS treatment that is applied thereafter, but the heat treatment does not affect 1 mg / m ² Since the above Cr cannot be diffused into the surface layer of the steel sheet, the surface-treated steel sheet excellent in work corrosion resistance, which is the object of the present invention, cannot be obtained. Metallic Cr is very susceptible to oxidation, and some of the plated Cr is oxidized by heat treatment of iron in a non-oxidizing atmosphere.
become. The plated Cr thus self-oxidizes to prevent the oxidation of iron and prevents the surface concentration of C contained in the steel sheet, but if it is left as it is, it has little effect of improving the corrosion resistance. It deteriorates the uniformity of the TFS-treated film and the deposition efficiency of the TFS-treated film during the TFS treatment. When the amount of Cr oxide is small, it can be removed by electrolytic cleaning performed before TFS treatment, and as a result, it contributes to the cleaning of the surface of the base steel sheet, but the amount of Cr in the Cr-Sn alloy plating is 1
If it is 50 mg / m ² or more, when it is used as it is, the rust resistance is improved, but the amount of Cr oxide formed during the heat treatment also increases, remains after electrolytic cleaning, and causes trouble during TFS treatment. Not preferable. Therefore, the amount of Cr in the Cr—Sn alloy plating is preferably in the range of 3 to 150 mg / m ² , and more preferably 10 to 70 mg / m ² . Next, the amount of Sn in the Cr-Sn alloy plating is 25 to 800 mg / m ²
Is preferred. When the Sn content is 25 mg / m ² or less, the surface-treated steel sheet excellent in work corrosion resistance intended by the present invention cannot be obtained, and when the Sn content is 800 mg / m ² or more, Cr formed on the surface layer of the steel sheet The heat treatment diffusion layer of Sn becomes thick and brittle, and the work corrosion resistance is not improved. Further, after the heat treatment, part of the plated Sn is likely to remain as oxidized Sn, and is not sufficiently removed by the electrolytic cleaning before the TFS treatment, which may reduce the uniformity of the TFS-treated film, which is not preferable. For this Cr-Sn alloy plating, sulfuric acid bath, chloride bath, sulfate-
A chloride mixed bath is suitable in terms of bath management and chemical costs. For _{example, SnSO 4 10~20g /, Cr 2} (SO 4) 3 5H 2
O40-120g /, sodium citrate 50-100g /
, NaF5~10g /, H ₃ BO ₃ and 20 to 40 g / a better adjusted to PH1.5～3.0, bath temperature 40 to 50 ° C. electrolysis time under the conditions of cathode current density 20~60A / dm ² in The Cr content limited in the present invention and
Cr-Sn alloy plating with Sn content is obtained. In the case of this Cr-Sn alloy plating, when the cathode current density is 15 A / dm ² or less, the precipitation of metal Cr hardly occurs, and the control of the current density is particularly important.

Next, on the steel plate surface after cold rolling and electrolytic cleaning,
Instead of the previously described Cr-Sn alloy plating, the Cr content is 3 to 15
0mg / m ^2, Sn amount 25~800mg / m ^2, Ni amount 2~100mg
/ M ² and Cr-Sn having a Ni / Sn weight ratio of 0.50 or less
A method for manufacturing a surface-treated steel sheet that has been subjected to heat treatment in a non-oxidizing atmosphere of iron after plating with a Ni alloy will be described. When an appropriate amount of Ni is co-deposited on the Cr-Sn alloy plating, Ni
When aged with Sn at room temperature, Ni containing Sn
-Sn alloy is formed. This Ni-Sn alloy itself has excellent corrosion resistance, and even if it remains on the surface of the steel sheet without being diffused into the steel sheet surface layer by heat treatment, as compared with the case where metal Sn and oxide Sn remain, during the subsequent TFS treatment. There is little risk of causing trouble. That is, the Cr-Sn-Ni alloy plating is improved in rust resistance in the uncoated state as compared with the already described Cr-Sn alloy plating, and the amount of metal Sn and the amount of oxidized Sn that may remain after heat treatment. And has the effect of improving the uniformity of the coating formed by the subsequent TFS treatment. Therefore, the Cr amount and Sn amount in the Cr-Sn-Ni alloy plating are limited for the same reason as in the Cr-Sn alloy plating, but the Ni amount is limited for the following reason. When the amount of Ni is 2 mg / m ² or less, the bath composition is complicated, and even if eutectoid Ni is used, there is almost no effect of further improving the corrosion resistance of the steel sheet which is the base of the present invention. Also, if the amount of Ni is 100 mg / m ² , the plated Ni is N
In addition to Ni-Sn alloy mainly composed of i and Sn, metal N
There is a risk that i and Ni oxide will remain on the surface of the steel sheet, and the rust resistance in the unpainted state is improved, but when used as a beverage container material, it causes pitting corrosion, and in order to prevent this , Cr—Sn—Ni alloy plating requires an increase in the amount of Sn, and as a result, the thermal diffusion treatment layer formed by heat treatment becomes thicker, resulting in lower workability and increased risk of pitting corrosion. Therefore, the proper range of the amount of Ni in the Cr—Sn—Ni alloy plating to be plated is ² to 100 mg / m ² . Further, in the present invention, the amount of Ni is also limited by the weight ratio of Ni / Sn. If the weight ratio of Ni / Sn is 0.50 or more, that is, if there is a large amount of Ni in the alloy plating, it may remain on the surface of the steel sheet as metallic Ni and oxidized Ni as described above. Is limited to 0.50 or less, more preferably 0.37 or less. The Cr-Sn-Ni alloy plating _{SnSO 4 10~20g /, Cr 2 (} SO 4) 3 5H 2 O40~1
_{20g /, NiSO 4 · 6H 2} O40~80g /, sodium citrate _{50~90g /, H 3 BO 3 20~40g} /, NaF5~1
A bath mainly composed of 0 g / sulfate having a pH of 1.5 to 3.0 was used at a bath temperature of 40 to 50 ° C. and a cathode current density of 20 to 40.
By electrolyzing under the condition of A / dm ² , Cr-Sn-Ni alloy plating with the amounts of Cr, Sn and Ni limited in the present invention is possible. Particularly, when the cathode current density is set to 60 A / dm ² or more, the precipitation of Ni is suppressed, so that the control of the cathode current density is important. Since the plated Ni is also sufficiently diffused in the steel sheet surface layer under the heat treatment conditions already described, in the case of Cr-Sn-Ni alloy plating as well, under the same heat treatment conditions as in the case of Cr-Sn alloy plating, the plated Sn amount and Ni amount A thermal diffusion treatment layer containing 95% or more of 1% / m ² of plated Cr can be formed.

Next, the heat treatment of iron in a non-oxidizing atmosphere after Cr-Sn alloy plating or Cr-Sn-Ni alloy plating will be described. The surface-treated steel sheet obtained by the method of the present invention is a material for can manufacturing, and it is an essential condition that it has not only excellent working corrosion resistance but also mechanical properties with good can manufacturing properties. Therefore, it is a premise in the present invention to form a heat-treated diffusion layer of Cr, Sn or Cr, Sn, Ni on the surface layer of the steel sheet by performing heat treatment under the same conditions as the base steel sheet of the steel sheet for cans such as tin plate and TFS. Is. That is, for example, by performing heat treatment for 15 to 30,000 seconds at a temperature of 520 to 750 ° C. in a non-oxidizing atmosphere of iron with 6% hydrogen and 94% nitrogen, 95% of the plated Sn amount is obtained.
Or more and 1 mg / m ² or more of plated Cr, or plated Sn amount, 95% or more of Ni amount and plated Cr amount of 1
It is essential in the method of the present invention to form a heat treatment diffusion layer containing mg / m ² or more on the surface of the steel sheet. For example, when forming a thermal diffusion treatment layer containing plated Cr and Sn using a continuous annealing facility that is a manufacturing process for a base steel sheet such as tinplate, the soaking time is as short as 15 to 60 seconds. Under this heat treatment condition, most of the plated Sn and Ni react with the base steel sheet, but it is difficult to diffuse 50% or more of the plated Cr into the surface layer of the steel sheet.
Only diffuses. Therefore, it is necessary to perform Cr-Sn alloy plating or Cr-Sn-Ni alloy plating having a Cr amount of at least about 3 times the amount of Cr to be diffused in the surface layer of the steel sheet before heat treatment. It is preferable to heat-treat at a high temperature to sufficiently diffuse the plated Cr, but if the heat treatment is performed at too high a temperature, the shape of the steel plate may become poor and a steel plate having the material required for the can material may be obtained. Therefore, the maximum temperature is limited to about 750 ° C. When a heat treatment is performed using a box-type annealing furnace, since the heating time is long, not only plated Sn and Ni but also plated Cr is considerably diffused even at a relatively low temperature. By this heat treatment,
If the weight ratio of Cr / Sn + Cr in the formed thermal diffusion treatment layer is 0.02 or less, the surface-treated steel sheet in which the Cr content is diffused by 1 mg / m ² or more in the steel sheet surface layer is further subjected to TFS treatment. , Processing corrosion resistance is not so much improved. This is due to the fact that even with a slight increase in the amount of Cr in the thermal diffusion treatment layer formed, the Si
It is considered that this is because the amount of the thermal diffusion treatment increases remarkably and the heat diffusion treatment layer becomes thick and brittle. Further, the weight ratio of Cr / Sn + Cr is set to 0.
In order to obtain 50 or more, it is necessary to increase the amount of Cr plated before the heat treatment, considering the diffusion degree of the plated Cr under the heat treatment conditions described above. As a result, the amount of Cr oxide remaining without being diffused after the heat treatment is increased, and the rust resistance in the uncoated state is improved, but when the TFS treatment is performed on the heat treated diffusion layer, it is spread before the TFS treatment. It is not sufficiently removed by the electrolytic cleaning performed, and there is a risk that the uniformity of the TFS coating and the deposition efficiency are reduced. Therefore, in the method of the present invention, in the thermal diffusion treatment layer formed by the heat treatment performed after Cr-Sn alloy plating
The weight ratio of Cr / Sn + Cr is an important factor.
The range of 0.50 is preferable, and the range of 0.05 to 0.20 is more preferable. Further, under the heat treatment conditions at the time of manufacturing the base steel sheet of the steel sheet for cans such as TFR, if the Sn content or the Ni content in the range limited in the present invention, it reacts with the base steel sheet as already described, and metal Sn, Sn oxide or metal N
i, Ni oxide hardly remains, but if it remains in the balance, it may interfere with the TFS treatment to be performed later, and 95% of the plated Sn amount or Ni amount is dared.
The above is limited to be included in the thermal diffusion treatment layer to be formed. Further, in the present invention, the lower limit of the amount of Cr diffused in the surface layer of the steel sheet is limited to 1 mg / m ² , but this lower limit is for obtaining the surface-treated steel sheet for can manufacturing excellent in work corrosion resistance which is the object of the present invention. Is an indispensable factor. If the amount of Cr diffused in the steel sheet surface layer is 1 mg / m ² or less, even if the amount of Cr is 3 mg
/ M ² or more of Cr-Sn alloy plating or Cr-Sn-Ni alloy plating, and then heat-treated surface-treated steel sheet with TF
Even if the S treatment is applied, the work corrosion resistance is not improved.

According to the present invention, after these alloy plating, heat treatment of iron in a non-oxidizing atmosphere, temper rolling is performed in the same manner as the base steel sheet such as tin plate, and then electrolytic chromic acid treatment (TFS) is performed by a known method.
Treatment), a film consisting of a metal Cr layer as the lower layer and a hydrated chromium oxide layer as the upper layer on the heat diffusion treated layer, so-called TFS
The corrosion resistance after coating by forming a film and further drawing is remarkably improved, but the amount of metallic Cr and the amount of hydrated chromium oxide are equivalent to those of commercially available TFS and are sufficient. That is, the amount of metallic Cr is 10 to 200 mg / m ² ,
The amount of chromium hydrate oxide is 5 to 30 mg / m ² of TF as Cr.
Thermal diffusion of S film by a one-step method of simultaneously forming a chromic acid solution to which an appropriate amount of sulfuric acid, a fluorinated compound, or other auxiliary agent is added, or a two-step method of forming a hydrated chromium oxide after depositing metal Cr. It may be formed on the treatment layer. Since the surface-treated steel sheet of the present invention having a heat diffusion treatment layer before TFS treatment has excellent corrosion resistance and paint adhesion as compared with the base steel sheet for cans such as tinplate, if the application does not require severe corrosion resistance, It is possible to use it as a material for cans without coating or after coating without TFS treatment.

〔Example〕

Hereinafter, examples of the present invention will be specifically described in comparison with comparative examples.

Example 1 A cold-rolled steel sheet having a thickness of 0.21 mm was degreased with rolling oil in a 4% aqueous solution of sodium orthosilicate at a temperature of 90 ° C., a current density of 20 A / dm ² , and an electrolysis time of 5 seconds, and washed with water. rear,
Cr-Sn alloy plating was performed under the conditions shown in (a), washed with water and dried. A non-oxidizing atmosphere of iron (hydrogen 6%, nitrogen 9
4%) and heat-treated at a temperature of 640 to 680 ° C. for 30 seconds.

(B) Cr-Sn alloy plating condition bath composition _{Cr 2 (SO 4) 3 ·} 5H 2 O 80g / SnSO 4 12g / sodium citrate _{50g / H 3 BO 3 30g /} NaF 5g / pH 2.0 bath temperature 45 ° C. Cathode current density 20 A / dm ² Cr amount in Cr—Sn alloy plating 22 mg / m ² Sn amount in Cr—Sn alloy plating 65 mg / m ² Example 2 A cold rolled steel sheet similar to Example 1 was used as Example 1. After performing the same pretreatment, Cr-Sn-Ni alloy plating was performed under the conditions shown in (a), washed with water and dried. Then, heat treatment was performed under the same conditions as in Example 1.

(B) Cr-Sn-Ni alloy plating condition bath composition _{Cr 2 (SO 4) 3 ·} 5H 2 O 60g / SnSO 4 15g / NiSO 4 · 6H 2 Contact 50 g / sodium citrate _{60g / H 3 BO 3 30g /} NaF 6g / pH 2.0 Bath temperature 50 ° C Cathode current density 33A / dm ² Cr amount in Cr-Sn-Ni alloy plating 25mg / m ² Sn amount in Cr-Sn-Ni alloy plating 150mg / m ² Cr-Sn -Ni content in Ni alloy plating 28 mg / m ² Comparative Example 1 A cold-rolled steel sheet similar to that of Example 1 was subjected to the same pretreatment as that of Example 1, washed with water and dried, and then heat-treated under the same conditions of Example 1. did.

Comparative Example 2 After cold-rolled steel sheet similar to that of Example 1 was subjected to the same pretreatment as that of Example 1, CrO ₃ 250 g /, H ₂ SO ₄ having a bath temperature of 55 ° C. 2.
1 in a 5g / bath with a cathode current density of 40A / dm ^2.
It was plated with 5 mg / m ² of Cr, washed with water and dried. Then, heat treatment was performed under the same conditions as in Example 1.

Comparative Example 3 A cold rolled steel sheet similar to that of Example 1 was subjected to the same pretreatment as that of Example 1, and then NiSO ₄ .6H ₂ O 250 g /, NiC having a bath temperature of 50 ° C.
40 mg / m ² of Ni was plated in a bath of 50 g of l ₂ · 6H ₂ O / 40 g of H ₃ BO ₃ at a cathode current density of 10 A / dm ² and washed with water and dried. Then, heat treatment was performed under the same conditions as in Example 1.

Comparative Example 4 After cold-rolled steel sheet similar to that of Example 1 was subjected to the same pretreatment as that of Example 1, SnSO ₄ 60 g / at a bath temperature of 45 ° C., phenolsulfonic acid 15 g / (as sulfuric acid), ethoxylated α ·
In a ferrostan bath containing 7 g of naphthol, 200 mg / m ² of Sn was plated under the condition of a cathode current density of 20 A / dm ² , washed with water and dried. Then, heat treatment was performed under the same conditions as in Example 1.

Example 3 Example 1 After subjecting the obtained sample to 2% temper rolling,
TFS treatment was performed under the conditions shown in (a), washed with water and dried.

(B) TFS treatment conditions after heat treatment and temper rolling Bath composition Cro ₃ 80 g / NaF 4 g / H ₂ SO ₄ 0.5 g / bath temperature 50 ° C. Cathode current density 40 A / dm ² Metal Cr amount 89 mg / m ² Chromium water Amount of hydrated oxide (as Cr) 14 mg / m ² Example 4 A cold-rolled steel sheet similar to that of Example 1 was subjected to the same pretreatment as that of Example 1, and then the time was changed under the conditions shown in (a) of Example 1. Instead Cr
-Sn alloy plating was applied, washed with water and dried. Then, in the same non-oxidizing atmosphere as in Example 1, at a temperature of 560 to 600 ° C., 8
Heat treatment was performed using a time box type annealing furnace, and further 2% temper rolling was performed. Then, a TFS film was formed by the two-step method shown in the following (a), washed with water and dried.

Cr amount in Cr-Sn alloy plating 85 mg / m ² Sn amount in Cr-Sn alloy plating 260 mg / m ² (a) TFS treatment condition after heat treatment and temper rolling * Cr plating condition Bath composition CrO ₃ 180 g / Na ₂ SiF ₆ 5g / H ₂ SO ₄ 0.5g / Bath temperature 50 ° C Cathode current density 40A / dm ² * Chromium hydrate oxide film forming conditions Bath composition CrO ₃ 30g / NaF 1.5g / Bath temperature 40 ° C Cathode current Density 24 A / dm ² Metal Cr amount 105 mg / m ² Chromium hydrated oxide amount (as Cr) 16 mg / m ² Example 5 After subjecting the sample obtained in Example 2 to 2% temper rolling,
TFS treatment was performed under the conditions shown in (3) of Example 3, washed with water and dried.

Comparative Example 5 After subjecting the sample obtained in Comparative Example 1 to 2% temper rolling,
TFS treatment was performed under the conditions shown in (3) of Example 3, washed with water and dried.

Comparative Example 6 After subjecting the sample obtained in Comparative Example 2 to 2% temper rolling,
TFS treatment was performed under the conditions shown in (3) of Example 3, washed with water and dried.

Comparative Example 7 After subjecting the sample obtained in Comparative Example 3 to 2% temper rolling,
TFS treatment was performed under the conditions shown in (a) of Example 4, washed with water and dried.

Comparative Example 8 After subjecting the sample obtained in Comparative Example 4 to 2% temper rolling,
TFS treatment was performed under the conditions shown in (a) of Example 4, washed with water and dried.

The surface coating composition of the steel sheet obtained by the above method was measured by the fluorescent X-ray method, and then the rust resistance without coating, the corrosion resistance and the processing corrosion resistance after coating were investigated by the following methods. The results are collectively shown in Table 1.

(1) Diffusion amount and rate of Cr, Sn and Ni in steel sheet by heat treatment After measuring the total Cr content, total Sn content and total Ni content of the sample before TFS treatment by fluorescent X-ray method, cathodic electrolysis and anodic electrolysis under the condition of current density 5A / dm ^{2 in} 1N NaOH aqueous solution at room temperature. For 30 seconds respectively, metal Cr, Cr oxide, metal Sn and Sn oxide on the surface layer of the steel sheet were dissolved, and then the residual Cr amount and the residual Sn amount were measured again by the fluorescent X-ray method. The amount of residual Cr and the amount of residual Sn were taken as the amount of Cr and Sn in the heat-treated diffusion layer formed by the heat treatment. Further, the diffusion rate of Sn was calculated from the Sn amount before and after this treatment. The diffusivity of Ni was determined by using a photoelectron spectrometer, and when the sample was sputtered from the surface layer, the amount of sputtered until the area intensity ratio of Ni and Fe became Ni / Fe <1 Was calculated.

(2) Uncoated rust resistance by salt spray test JIS Z
In accordance with 2371, an unpainted sample was stood up to a salt spray tester at an angle of 30 degrees from a vertical line, a 5% NaCl aqueous solution at 35 ° C was sprayed for 3 hours, and the degree of rust generation was evaluated in 10 stages. Rust generation area is 25 to 50% with no occurrence of rust as 10
Was set to 1.

(3) Rust resistance by indoor exposure test An unpainted sample was set up at an angle of 45 degrees inside the factory near the coast and left for 1 month, and the degree of rust was divided into 10 levels. No rust generation is 10 and rust area is 25-5
0% was set to 1.

(4) Corrosion resistance without coating A sample having a test area of 20 cm ² was immersed in 100 ml of 100% grapefruit solution at 25 ° C. for 1 month, and the amount of eluted Fe was measured by an atomic absorption method and converted into mg / dm ² · day.

(5) Corrosion resistance after painting The surface of the sample was coated with 60 mg / dm ² (dry weight) of phenol / epoxy paint, cured at 210 ° C for 10 minutes, and then overhanged by 5 mm using an Erichsen tester. A sample having a test area of 20 cm ² was immersed in 100 ml of a CH ₃ COOH aqueous solution at 25 ° C. for 2 weeks, and the amount of eluted Fe was measured by an atomic absorption method and converted into mg / dm ² · day.

[Effects of the Invention] The surface-treated steel sheet obtained by the method of the present invention has excellent corrosion resistance after painting, and can be continuously produced industrially at high speed, and is industrially used as an inexpensive surface-treated steel sheet for can manufacturing. Above all very useful.

Claims (4)

[Claims] 1. The amount of Cr per surface of the steel sheet is 3 to 150 mg of Cr.
/ M ² , the amount of Sn is 25-800 mg / m ² Cr-Sn alloy plating is applied, and subsequently heat-treated in a non-oxidizing atmosphere of iron,
It contains 95% or more of the amount of plated Sn and 1 mg / m ² or more of the amount of plated Cr, and the weight ratio of Cr / Sn + Cr is 0.
A method for producing a surface-treated steel sheet for can making, which is excellent in working corrosion resistance, characterized in that a heat diffusion treated layer of 02 to 0.50 is formed. 2. The amount of Cr per surface of the steel sheet is 3 to 150 mg.
/ M ² , Sn content 25-800mg / m ² , Ni content 2-100mg
/ M ² , and the weight ratio of Ni / Sn is 0.50 or less Cr-
Sn-Ni alloy plating, followed by heat treatment in a non-oxidizing atmosphere of iron, containing plated Sn amount, Ni content 95% or more, and plated Cr amount 1 mg / m ² or more, and A method for producing a surface-treated steel sheet for can making, which is excellent in work corrosion resistance, characterized in that a heat diffusion treated layer having a Cr / Sn + Cr weight ratio of 0.02 to 0.50 is formed. 3. The amount of Cr per surface of the steel plate is 3 to 150 mg.
/ M ² , the amount of Sn is 25-800 mg / m ² Cr-Sn alloy plating is applied, and subsequently heat-treated in a non-oxidizing atmosphere of iron,
It contains 95% or more of the amount of plated Sn and 1 mg / m ² or more of the amount of plated Cr, and the weight ratio of Cr / Sn + Cr is 0.
A heat diffusion treated layer having a thickness of 02 to 0.50 is formed on the heat diffusion treated layer, the lower layer is 10 to 200 mg / m ² of metallic Cr, and the upper layer is 5 to 30 mg / m ² of chromium hydrate oxide. A process for producing a surface-treated steel sheet for can manufacturing, which is excellent in processing corrosion resistance, characterized in that a film made of is formed. 4. The amount of Cr per surface of the steel sheet is 3 to 150 mg of Cr.
/ M ² , Sn content 25-800mg / m ² , Ni content 2-100mg
/ M ² , and the weight ratio of Ni / Sn is 0.50 or less Cr-
Sn-Ni alloy plating is applied, followed by heat treatment in a non-oxidizing atmosphere of iron, containing Sn content of plating, 95% or more of Ni content, and 1 mg / m ² or more of Cr content of plating, and , Cr / Sn + Cr weight ratio is 0.02 to 0.50, and a lower layer is formed on the heat diffusion treated layer.
~ 200 mg / m ² of metallic Cr, the upper layer is Cr as 5 to 30 mg /
A method for producing a surface-treated steel sheet for can manufacturing, which is excellent in work corrosion resistance, characterized in that a film made of hydrated chromium oxide of m ² is formed.