JPH0649925B2 - Method for producing plated base steel sheet with excellent corrosion resistance for can manufacturing - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a plated base steel sheet having excellent corrosion resistance, which is used for a Sn-based plated steel sheet, a Cr-based plated steel sheet or the like which is a material for cans.

[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 can manufacturing. It is used. In recent years, in the field of can-making materials, the entry of competitive 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 corrosion resistance. To meet this demand, various thin Sn-based plated steel sheets have been developed as a method for making the plating layer thin and dense, and have already been put to practical use for some applications. However, since the plated layer is thin, the corrosion resistance of the processed part is inferior to that of ordinary tinplate, and it is necessary to improve the corrosion resistance of the plated base steel sheet itself for use in a wide range of applications. As an attempt to improve the corrosion resistance of the plated base steel sheet itself, a method of adding Cr or the like during steelmaking (Japanese Patent Laid-Open No. 61-6293, Japanese Patent Laid-Open No. 61-177378, Japanese Patent Laid-Open No. 61-253377, Japanese Patent Laid-Open No. 62-3089). , Etc., but also Ni plating on the steel plate surface and heat treatment in a non-oxidizing atmosphere to form a Ni diffusion layer on the steel plate surface (for example, JP-A-57-200592, JP-A-60-155685, etc.). )It has been known.

[Problems to be Solved by the Invention]

Certainly, the addition of Cr during steelmaking significantly improves the corrosion resistance of the steel sheet itself, but not only the cost of the steel sheet increases due to the addition of Cr, but also descaling after hot rolling, cold rolling workability, and Sn. It is difficult to say that it is a material suitable as an inexpensive plated base steel sheet for can manufacturing, because it causes various problems such as platability and processability of can manufacturing. In addition, the method of heat-treating plated Ni in a non-oxidizing atmosphere and diffusing it into the steel sheet surface layer is an inexpensive method, but it has little effect of improving corrosion resistance, and can be used for a wide range of applications. It is not a satisfactory base. In order to solve these problems at the same time, to develop a plating base steel sheet that is inexpensive, has a great effect on improving the corrosion resistance, and does not cause any special problems in the steps after cold rolling, various studies are conducted. As a result of repeating the above, the present invention has been achieved.

[Means for Solving the Problems]

The present invention is characterized by the cold rolling and the electrolytic cleaning
To provide a plated base steel sheet with excellent corrosion resistance by performing plating and then Ni plating and then heat treatment in a non-oxidizing atmosphere to form Cr and Ni diffusion layers on the surface layer of the steel sheet. is there.

Hereinafter, the method of the present invention will be specifically described. Metallic Cr2 to 150 on the surface of steel plate after cold rolling and electrolytic cleaning
Mg / m ² Cr plating is applied, then the upper layer is 20-5
Was subjected to Ni of 200 mg / m ^2, subjected to a heat treatment in a non-oxidizing atmosphere, plated Cr is 1 mg / m ² or more, 90% or more plated Ni, and the weight ratio of Cr / Ni 0. Cr and Ni are diffused in the surface layer of the steel sheet in the range of 05 to 0.2. First, chromic acid baths and chromium sulfate baths containing an appropriate amount of auxiliary agents can be considered as baths for Cr plating on the steel sheet surface after cold rolling and electrolytic cleaning. Chromic acid baths with added agents are suitable. This chromic acid bath includes a sergeant bath usually used for Cr plating, a chromic acid bath containing a proper amount of sulfuric acid and a fluorine compound used in the industrial production of TFS, or a chromic acid containing a fluorine compound. A bath is suitable. There is no particular limitation on the chromic acid concentration, but if there are many chromium hydrate oxides that are precipitated at the same time as the precipitation of metal Cr, it will interfere with the Ni plating in the next step,
It is preferable to use a Cr plating bath having a chromic acid concentration of 100 g / or more. When a low-concentration chromic acid bath with a chromic acid concentration of 100 g / or less is used, a large amount of chromium hydrate oxide is metallic.
Since it precipitates on Cr, it is necessary to immerse it in the chromic acid bath used before Ni plating in the next step to dissolve and remove the chromium hydrate oxide film on the surface. The amount of hydrated chromium oxide remaining after dissolution is ideally 0, but in practice, if the amount of chromium is 5 mg / m ² or less, it does not hinder the Ni plating in the next step. . Precipitated metal
The Cr amount is preferably in the range of ^{2 to} 150 mg / m ² , and more preferably 10 to 70 mg / m ² . When the amount of metallic Cr is 2 mg / m ² or less, the plated base steel sheet having excellent corrosion resistance, which is the object of the present invention, cannot be obtained. Further, metallic Cr is very easily oxidized, and a part of the plated amount becomes Cr oxide. Metal Cr
In this way, it self-oxidizes to prevent the oxidation of iron.
Prevents surface enrichment of C, but when metallic Cr exceeds 150 mg / m ² , Cr oxide also increases, and oxidation occurs even after electrolytic cleaning.
Part of Cr remains, which adversely affects the plating properties such as Sn plating,
Not preferable. Further, diffusion of Ni into the steel sheet is also suppressed, and the corrosion resistance of the plated base steel sheet is not improved, which is not preferable. Next, after the Cr plating, the known Ni plating is applied to the Ni plating.
A plating bath such as a Watt bath or a sulfamic acid bath is used. In the Watts bath _{NiSO 4 · 6H 2 O200~300g /,} Ni
Cl ₂ · 6H ₂ 020-50g /, H ₃ BO ₃ 20-40g /, sulfamate bath nickel flufamate 300-50
0 g /, H ₃ BO ₃ 20-40 g / bath composition with current density 2
By changing the electrolysis time under the conditions of 30 A / dm ² and a bath temperature of 30 to 70 ° C., the Ni amount necessary for the present invention can be obtained. The plated Ni is an element that easily diffuses into the steel sheet by heat treatment in a non-oxidizing atmosphere, and when the amount of Ni plated is 20 mg / m ² or less, the plated base steel sheet of the present invention has Corrosion resistance is not significantly improved. Also,
If the amount of Ni plated is 500 mg / m ² or more, there is a risk that it will remain as metallic Ni on the surface of the steel sheet even after heat treatment, promoting pitting corrosion of the steel sheet. Therefore, the amount of Ni plated on the metal Cr is in the range of ^{20 to} 500 mg / m ² , more preferably 5
A range of 0 to 200 mg / m ² is suitable in the present invention.
In the present invention, Cr plating is first applied and then Ni plating is applied, which is a necessary condition for obtaining the plated base steel sheet having excellent corrosion resistance of the present invention. That is, if the metal Cr is not in direct contact with the steel plate, it is very difficult to diffuse into the steel plate, so Cr plating is performed first, and then Ni to be plated suppresses the oxidation of the metal Cr and the metal Cr Has the effect of helping to diffuse into the steel sheet. Even if Ni is plated first, then Cr is plated, and then heat treated in a non-oxidizing atmosphere, Ni diffuses into the steel sheet, but the plated metal Cr is very easily oxidized. , Fe and Ni are not oxidized, and even a trace amount of oxygen is oxidized, and the diffusion is almost zero. Also, even when Cr plating is plated independently and similarly subjected to diffusion treatment, even if a small amount of metal Cr is in contact with oxygen unless the surface of metal Cr is covered with Ni, etc., metal Cr is oxidized and Almost no diffusion occurs, and a plated base steel sheet having excellent corrosion resistance and plating properties such as Sn plating cannot be obtained. For plated Ni, if a large amount of metal remains on the steel sheet after heat treatment in a non-oxidizing atmosphere, it causes pitting corrosion of the steel sheet as described above, and therefore at least 1% of the plated Cr is
It is essential in the present invention to diffuse mg / m ² or more and at least 90% or more of the plated Ni into the steel sheet. The ratio of Cr and Ni after the diffusion of Ni and Cr is also very important. Cr / Ni in the ternary diffusion layer of Cr-Ni-Fe
If the weight ratio of Cr is 0.05 or less, a plated base steel sheet with excellent corrosion resistance cannot be obtained. Conversely, if the ratio is 0.20 or more, the corrosion resistance of the steel sheet is somewhat improved, but the diffused Cr
The oxides of Cr are likely to appear on the surface of the steel sheet, which significantly deteriorates the plating properties such as Sn plating, and adversely reduces the overall corrosion resistance of the steel sheet for cans.Therefore, the Cr / Ni weight ratio is in the range of 0.05 to 0.20. preferable.

Since the plated base steel sheet of the present invention is used as a material for cans, its mechanical properties are also an important factor. The plated base steel sheet was subjected to heat treatment under the same conditions as those of the base material steel sheet for cans such as tin plate and TFS, and plated. Cr and Ni must be diffused on the steel plate surface. Therefore, heat treatment causes tint and TF.
It is a premise for obtaining the plated base steel sheet of the present invention that the same conditions as in the case of the S base steel sheet are obtained, and Cr and Ni plated under this heat treatment condition are diffused on the steel sheet surface, and the corrosion resistance of the plated base steel sheet is increased. As described above, the amounts of Cr and Ni to be plated and their ratios are limited in order to improve the above-mentioned properties and not to adversely affect the uniformity of plating such as Sn plating. A plated base steel sheet having mechanical properties required as a material for a can can be sufficiently obtained by subjecting it to a heat treatment for 15 to 30000 seconds at a temperature of 520 to 720 ° C. in a non-oxidizing atmosphere, and also in the present invention. Heat treatment may be performed under similar conditions. In addition, since the plated base steel sheet obtained by the method of the present invention has significantly improved corrosion resistance, it can be used as a material for a can without coating without coating with Sn or the like, or after being coated. Is.

(Example) Hereinafter, an example of the present invention will be specifically described in comparison with a comparative example.

Example 1 A cold-rolled steel sheet having a sheet thickness of 0.21 mm was degreased with rolling oil in a 4% sodium orthosilicate aqueous solution 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. Later, (a)
Cr plating was performed under the conditions shown in (1), and the plate was immersed in the same solution for 5 seconds and then washed with water. Then, Ni plating was applied under the conditions shown in (b), washed with water and dried. This sample was heat-treated at a temperature of 520 to 560 ° C. for 20 seconds in a non-oxidizing atmosphere (hydrogen 6%, nitrogen 94%).

(A) Cr plating conditions Bath composition CrO ₃ 150 g / NaF 5 g / H ₂ SO ₄ 0.8 g / bath temperature 55 ° C. Cathode current density 40 A / dm ² Metal Cr amount 15 mg / m ² Residual chromium hydrate oxide (as Cr ) 3 mg / m ² (b) Ni plating conditions Bath composition NiSO ₄・ 6H ₂ 0 250 g / NiCl ₂・ 6H ₂ 0 50 g / H ₃ BO ₃ 40 g / bath temperature 50 ° C Cathode current density 10 A / dm ² Ni plating amount 25 mg / M ² Example 2 After subjecting a cold-rolled steel sheet similar to that of Example 1 to the same pretreatment as that of Example 1, the electrolysis time was changed under the conditions shown in (a) and (b) of Example 1. It was plated with Cr and Ni, washed with water and dried. Then, heat treatment was performed in the same non-oxidizing atmosphere as in Example 1 at a temperature of 640 to 680 ° C. for 8 hours using a box-type annealing furnace.

Metal Cr amount 80 mg / m ² Residual chromium hydrate oxide (as Cr) 4 mg / m ² Ni plating amount 450 mg / m ² Comparative Example 1 A cold-rolled steel sheet similar to that of Example 1 was subjected to 4% orthosilicate as in Example 1. The rolling oil was degreased in an aqueous solution of acid soda, washed with water and dried.

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, 80 mg / m ² of Ni plating was applied under the conditions shown in (b) of Example 1, and then washed with water. Dried. Then, heat treatment was performed in the same non-oxidizing atmosphere as in Example 1.

Example 3 A cold-rolled steel sheet similar to that of Example 1 was subjected to the same pretreatment as that of Example 1, then subjected to Cr plating under the conditions shown in (a), washed with water,
Ni plating was applied under the conditions shown in (b), washed with water and dried. Then, in the same non-oxidizing atmosphere as in Example 1, temperatures of 640 to
After heat treatment at 680 ° C. for 30 seconds, temper rolling of 2% was performed, then Sn plating was performed under the conditions shown in (c), and further heat melting treatment was performed.

(B) Cr plating conditions Bath composition CrO ₃ 250 g / H ₂ SO ₄ 2.5 g / bath temperature 50 ° C Cathode current density 30 A / dm ² Metal Cr amount 20 mg / m ² Residual chromium hydrate oxide (as Cr) 3 mg / m ² (b) Ni plating conditions Bath composition Ni sulfamate 300 g / H ₃ BO ₃ 40 g / bath temperature 50 ° C Cathode current density 10 A / dm ² Ni plating amount 100 mg / m ² (c) Sn plating conditions Bath composition SnSO ₄ 60 g / Phenolsulfonic acid (as sulfuric acid) 15 g / Ethoxylated α-naphthol 7 g / Bath temperature 45 ° C. Cathode current density 20 A / dm ² Sn plating amount 2.7 g / m ² Comparative example 3 ² in the sample obtained in Comparative example 1 % After temper rolling,
2.7 g / m ² of Sn plating was applied under the conditions shown in (c) of Example 3 and further heat melting treatment was applied.

Comparative Example 4 After subjecting the sample obtained in Comparative Example 2 to 2% temper rolling,
2.7 g / m ² of Sn plating was applied under the conditions shown in (c) of Example 3 and further heat melting treatment was applied.

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, under the conditions shown in (a) and (b) of Example 1, the electrolysis time was changed and Cr plating and It was plated with Ni, washed with water and dried. Then, in the same non-oxidizing atmosphere as in Example 1, heat treatment was performed at a temperature of 640 to 680 ° C. for 30 seconds. further,
After temper rolling of 2%, electrolytic chromic acid treatment (TFS treatment) was applied under the conditions shown in (a), and the product was washed with water and dried.

Metal Cr amount 20 mg / m ² Residual chromium hydrate oxide (as Cr) 3 mg / m ² Ni plating amount 90 mg / m ² (b) Electrolytic chromic acid treatment conditions (TFS treatment conditions) Bath composition CrO ₃ 30 g / NaF 1. 2 g / bath temperature 40 ° C. cathode current density 40 A / dm ² metal Cr amount 105 mg / m ² chromium hydrate oxide amount (as Cr) 18 mg / m ² Comparative Example 5 2% tempering of the sample obtained in Comparative Example 1 After rolling
TFS treatment was performed under the conditions shown in (a) of Example 4, 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 (a) of Example 4, washed with water and dried.

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

(1) Diffusion amount of Cr and diffusivity of Ni by heat treatment The diffusion amount of Cr was 1 A / cm ^{2 in} a 1N-NaOH solution,
After positive and cathodic electrolysis under the condition of 20 seconds, the amount of residual Cr was determined. The Ni diffusivity was measured using a photoelectron spectrometer, and when Ar was sputtered from the surface layer of the sample, the intensity ratio of Ni and Fe was Ni / Fe> 1.
The amount of Ni sputter was defined as the amount of non-diffused Ni, and the ratio of the remaining amount of Ni to the total amount of Ni was obtained.

(2) Rust resistance by salt spray test In accordance with JISZ2371, an unpainted sample is leaned against a vertical line at an angle of 30 degrees from a vertical line and sprayed with a 5% NaCl aqueous solution at 35 ° C for 3 hours to generate rust. Was evaluated in 10 steps. 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 Unpainted samples were left indoors for one month in the factory near the coast.
The degree of rust generation was evaluated in 10 grades. No occurrence of rust was set to 10, and a rusted area of 25 to 50% 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 coating 60 mg / dm ² (dry weight) of phenol / epoxy paint was applied to the surface of the sample, and after curing at 210 ° C for 10 minutes, a sample with a test area of 20 cm was 0.4% at 25 ° C. The sample was immersed in 100 ml of CH ₃ COOH aqueous solution for 2 weeks, the amount of eluted Fe was measured by an atomic absorption method, and converted into mg / dm ² · day.

(6) Corrosion resistance after coating processing A sample baked as in (5) was subjected to 5 mm overhanging processing using an Erichsen tester, and then tested under the same conditions as (5).

(Effect of the invention) Since the plated base steel sheet obtained by the method of the present invention has excellent corrosion resistance and plating properties such as Sn, it is not only used as a plated base steel sheet for can-making, but also as a steel sheet for cans as it is. It is very useful industrially.

Claims (1)

[Claims] 1. The amount of metallic Cr per surface is 2 to 15
0 mg / m ² and chromium hydrate oxide amount is Cr plating of 5 mg / m ² or less as Cr amount, and the Ni amount in the upper layer is 20 to 500
Mg / m ² Ni plating is applied, followed by heat treatment in a non-oxidizing atmosphere to diffuse 1 mg / m ² or more of the plated Cr and 90% or more of the plated Ni into the steel sheet, and Cr-Ni- Fe
A method for producing a plated base steel sheet for can manufacturing having excellent corrosion resistance, characterized in that the weight ratio of Cr / Ni in the ternary diffusion layer is 0.05 to 0.20.