JPS6029477A - Production of steel sheet for can vessel having excellent weldability and painting performance - Google Patents

Abstract

PURPOSE:To produce a steel sheet for a can vessel having excellent weldability and painting performance by electroplating Ni onto a steel sheet then heating the sheet to penetrate and diffuse Ni into the steel, subjecting the plated steel sheet to required rolling and further to electroplating of Sn and chromating. CONSTITUTION:A cold rolled steel sheet havng the component compsn. adequate as a can vessel is subjected to Ni plating with 30-500mg/m<2> coating weight per side by using a watts bath, etc. and is in succession subjected to a heat treatment at about 500-750 deg.C in a non-oxidizing atmosphere to penetrate and diffuse a part or the whole of the Ni plating layer into the steel, by which the steel sheet is made resistant to corrosion. The steel sheet is then subjected to temper rolling or cold rolling according to need followed by Sn electroplating at 100-15,000mg/m<2> coating weight per side by using a ferrostan bath, etc. to improve the corrosion resistance and appearance. The steel sheet is then electrochromated in a bath contg. 1 or 2 kinds of SO<2->4 and F<-> at a rate of 1/500-1/50 of the concn. of Cr<6+> in an aq. chromate soln., by which the steel sheet for a can vessel having excellent weldability and painting performance such as paintability, corrosion resistance before and after painting, appearance, etc. is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing steel sheets for cans and containers used as materials for food and beverage storage containers.

(Prior art) Nine-fist free steel (T, F, S), which has a tin plate and a two-layer coating of metallic chromium and hydrated chromium oxide on the surface, is used for steel plates for can containers, and these copper plates are used in various types. It is processed into a shaped can container, and the joint end is soldered to the tin plate.
T, F, and S use nylon adhesive to make food and beverage cans. In addition, can manufacturers have developed high-performance seam # can joining machines to solve the high can manufacturing costs and high leakage rate due to the soaring tin price for half-open cans, as well as the problem of poor adhesive strength in each adhesive. While striving to popularize shiso,
They are requesting the supply of steel plates for cans and containers with excellent weldability.

In addition, #25 tinplate, which has a particularly small amount of plating, has excellent weldability, but has the disadvantage that it turns black when heated during welding, deteriorating the appearance and paintability of the welded area. On the other hand, T, F, S
Because it has a relatively thick surface coating layer consisting of a metallic chromium layer and a water-containing chromium oxide layer, it has extremely poor weldability, and there was a problem in that it could not be used unless the coating layer was peeled off and welded during can manufacturing.

Therefore, future steel sheets for cans and containers are required to have excellent weldability in addition to paintability, corrosion resistance before and after painting, and appearance. Weldability has a wide allowable range for welding work conditions such as welding current and pressure, and stable and sufficient adhesive strength and uniform nuggets can be obtained, and the welding melt must be free from scattering and fine turbulence. It is desired that there be no dust phenomenon that causes deposits, and that there is little deterioration in the corrosion resistance of welded parts.

(Object of the Invention) In view of this situation, the present invention provides a steel sheet for cans and containers that has excellent coating performance such as weldability, coating properties, corrosion resistance before and after coating, and appearance.

(Structure and operation of the invention) The gist is that the amount of adhesion on a cold rolled steel plate is 30% per side.
After applying ~500 mg/rrf Ni electroplating, subsequently heating in a non-oxidizing atmosphere to infiltrate and diffuse part or all of the Ni plating layer into the steel, and performing temper rolling or cold rolling, Adhesion amount is 100-1500mg per side
/ m' of Sn electroplating, followed by chromate aqueous solution with a Cr6+ concentration of 11500-1150 5o
This is a method for manufacturing a steel sheet for cans and containers, which is subjected to electrolytic chromate treatment in a bath containing one or two types of 42-1F-.

The present invention will be explained in detail below.

A thin steel plate manufactured by adjusting the composition of normally used steel sheets for cans and containers, making molten steel into a slab using the ingot-blending method or continuous casting method, hot rolling it, and then roughly cold rolling it. After activating the surface by performing pre-treatments such as degreasing and pickling, use a known plating bath such as Watt bath or sulfamic acid bath to achieve a coating weight of 30 to 500 a+g/side.
Apply Ni electric spacing of rn'. The amount of Ni deposited is limited within the range in which the desired weldability and paintability of the present invention can be obtained; a small deposit of less than 30 mg/m' will not provide sufficient corrosion resistance, and an excessive amount of over 500+ mg/m' will not provide sufficient corrosion resistance. The amount of adhesion deteriorates weldability and appearance.

The steel plate plated with Ni in this manner is heated to improve corrosion resistance, and part or all of the old plating layer is infiltrated and diffused into the steel. Heating is performed in a continuous annealing furnace or a box annealing furnace in a non-oxidizing atmosphere such as inert gas or reducing gas in order to prevent deterioration of corrosion resistance due to oxidation of the steel base of the Ni-plated pinhole. Part or all of the plating layer is penetrated and diffused into the steel to coat the surface of the steel sheet with Fe-
Forms a dense square alloy layer of Ni, imparting remarkable corrosion resistance to Ni plating. The heating temperature in this case is 500-750℃
is preferable, and when it also serves as softening annealing of the steel plate, 600
It is preferable to carry out at a temperature of ~750°C.

Next, in order to correct the shape, skin pass rolling with a rolling reduction of 0.5 to 15%, or if high strength is required, cold rolling with a rolling reduction of 15 to 40% is repeated once or twice. After that, pre-treatments such as degreasing, cleaning and pickling are performed, and Sn electroplating is carried out at a deposition amount of 100 to 1500 mg7tn' per side. Sn coating has the effect of improving the corrosion resistance of the steel plate for cans and containers, which is the object of the present invention, and preventing deterioration of the appearance. For example, Ni-plated and chromate-treated steel sheets for cans and containers show excellent corrosion resistance against relatively weakly corrosive tomato juice, vegetable juice, coffee, etc., but they also exhibit excellent corrosion resistance against highly corrosive, acidic orange juice, mandarin orange, etc. It has no corrosion resistance. Furthermore, in the case of fish meat or livestock meat containing S, the Ni plating layer reacts with the S component, causing an appearance problem called sulfide blackening. On the other hand, Sn plating solves these problems and is economical, and has an area weight of 100"1 per side that improves weldability.
500+ag/m'. Further, the Sn electroplating bath is not particularly limited, and may include a ferrostane bath,
A halogen bath or an alkaline bath can be used.

Steel sheets that have been surface-treated in this manner are subjected to electrolytic chromate treatment to improve paint adhesion and corrosion resistance before and after painting. Electrolytic chromate treatment involves adding sulfuric acid,
By selecting and mixing 5042''' from chromium sulfate, etc., or F- ions from hydrogen fluoride, hydrofluoric acid, ammonium fluoride, sodium fluoride, sodium silicofluoride, borofluoric acid, etc., the current of electrolytic treatment can be reduced. It increases the efficiency and stably produces a uniform chromate coating.However, such an effect cannot be obtained when the concentration of hexavalent Cr ions is less than 11,500, and when it exceeds 1,150, the chromate coating is Anions increase and disappear.

(Effects of the Invention) As described above, the steel sheet for cans and containers of the present invention has a chromate coating with excellent paintability on the outermost layer, an Sn plating layer that improves corrosion resistance and weldability below it, and a corrosion-resistant layer below it. The coating layer consists of three Ni plating layers with good quality. Furthermore, to explain the effect between the coating layers, Sn
, Ni has a higher electrode potential than Fe of the base steel plate, has excellent corrosion resistance, and is a metal that has excellent performance as an anticorrosion coating. However, the plating layer does not completely cover the surface to be plated, and there are minute unplated portions called pinholes. In particular, when the amount of plating is small as in the present invention, an extremely large number of pinholes are present.
When a steel plate is exposed to a corrosive solution, the corrosion potential at the pinhole that reaches the base metal is in the order of Fe<Ni<Sn, so a local battery is formed between the base metal and the Ni and Sn plating layers. This accelerates corrosion of the base metal. Pinholes reaching this base metal are significantly reduced by the structure of N1-5n and the chromate coating thereon. In other words, the pinholes in the Ni plating layer are blocked by the Sn plating layer above it, and the pinholes in the Sn plating layer are blocked by the chromate film. There are very few. In the pinhole portion of the Sn plating layer up to the Ni plating surface, a local battery is formed between the Sn and Ni plating layers, and corrosion of the Ni plating layer progresses, but the potential difference therebetween is small and the corrosion rate is low. When there is no old plating layer, that is, when there is only a Sn plating layer, the local battery formed between the Sn plating layer and the base metal has a large potential difference, so corrosion of the base metal is significantly accelerated. In addition, when actually used in canned goods, Sn exhibits very characteristic corrosion behavior depending on the contents. In other words, as is generally well known, in foods containing organic acids, such as canned mandarin oranges, if chives are not present in the can, the potentials of Sn and Fe are reversed, and the Sn plating layer overwhelms the base metal. Sacrificial corrosion protection. Such a phenomenon does not occur between Nl and Fe; the potential of Ni is always nobler than that of Fe, and corrosion of the base metal is always promoted in the pinhole portion in the case of a single layer of Ni plating.

As described above, from the corrosion behavior in each plating layer, the steel sheet for containers of the present invention has excellent corrosion resistance compared to Sn plating or Ni plating with a chromate coating, and furthermore, the steel sheet for containers of the present invention has Sn plating on the upper layer. When used for foods containing highly corrosive organic acids, the sacrificial anti-corrosion effect of the Sn plating layer is exerted, preventing the occurrence of pitting corrosion that occurs in the Ni plating layer. I can do it.

The Sn plating layer also has a great effect on improving weldability.

Surface-treated steel sheets with Ni plating and chromate treatment are commercially available for use in welded cans. This product is a traditional TF
It has much better weldability than S, but is slightly inferior to #25 tin.

When a small amount of Sn plating layer as in the present invention is added to this, the weldability is greatly improved, and the performance is equal to or better than that of #25 tinplate. This is thought to be because the provision of the Sn plating layer lowers the electrical contact resistance between the plates and also because the melting point of Sn is low.

(Example) Examples of the present invention will be described below.

A cold-rolled steel plate with a thickness of 0.21 mm manufactured by the thin steel plate manufacturing method currently commonly used in the steel industry was made with 2% N
After brushing in an aqueous solution at 80°C consisting of aOH and 1% of a commercially available alkaline degreasing agent, it was washed with water, and then in a degreasing bath with the same composition, cathodic electrolytic degreasing was performed for 2 seconds at a current density of 10 A/dm2, followed by washing with water and 10% H2. 'Cathodic electrolytic pickling for 2 seconds at a current density of 10 A/di2 in an SO4 room temperature aqueous solution, followed by water washing, followed by 5 A/di using a Watt Folk at 50°C.
Plating amount per side 30mg/m' at a current density of d112
Ni plating was applied, followed by washing with water and drying. The above treatments were performed using a continuous electroplating line. The N1-plated steel plate was passed through a continuous annealing line and annealed at 850°C for 30 seconds to diffuse the N1 plating layer into the steel plate and form an Fe-Ni alloy layer on the steel plate surface. Next, the rolling reduction rate is 1
%, passed through a ferro staminate line, and was plated with Sn at 1300 mg/m' per side, followed by chromate treatment with 30 g/l Na2.
Cathode treatment was performed for 1 second at a current density of 4 A/dm2 in an aqueous solution of Cr207*2N20.45°C.

Example 2 Ni plating amount: 10On+g/m', Sn plating amount: 6
00mg/m', chromate treatment at 90°C 140A/
The process was carried out in the same manner as in Example 1, except that the dm2 time was 1 second.

Example 3 Ni plating amount is 200 mg/m', Sn plating amount is 500
mg/m', chromate treatment 80g/l CrO3
0.8 g/l NH4F and 0.32 g/l Na
60A/dI1 in an aqueous solution at 60°C with addition of BF4
The treatment was carried out in the same manner as in Example 1, except that the cathode treatment was carried out for 1 second in No. 12.

Example 4 In Example 1, the plate thickness was 0.22 mm, the Ni coating was 300 mg/m', the thermal reduction rate was 1O%, and the Sn coating amount was 4.
00mg/m', chromate treatment is 80g/II Cr
The treatment was carried out in the same manner as in Example 1, except that the cathodic treatment was carried out at 5 A/dm2 for 1 second in an aqueous solution at 40° C. in which 0.05 g/4 H2SO0 and 0.11 g/b HF were added to O3.

Example 5 In Example 1, the plate thickness was 9.22 mm, Ni metal, and the amount of metal was 5.
00mg/rrf, thermal reduction rate 5%, Sn plating amount 2
00mg/m', chromate treatment 80g/l C
0.11g/i HF and 0.32g/i Na in rO3
20A/dm2 in an aqueous solution at 40°C with addition of BF4
The treatment was carried out in the same manner as in Example 1, except that the cathode treatment was performed for 1 second.

Example 6 In Example 1, the Ni plating amount was 400 mg/m', S
n coating amount 100mg/m', chromate treatment 80g
/-QC: r03 with 0.8 gin NH4F and 0.
Except for cathodic treatment at 60 A/dm2 for 1 second in a 50°C aqueous solution containing 57 g/b Na75IF6.
It was treated in the same manner as in Example 1.

Example 7 In Example 1, the chromate treatment was carried out using Bog/lCrO.
3 to 0.1 g/uH2sOa, 0.2XNa2
The treatment was carried out in the same manner as in Example 1, except that the cathodic treatment was performed at 5 A/dm2 for 2 seconds in an aqueous solution at 35° C. to which SiF6 and 0.22 g/uHF were added.

Example 8 In Example 1, N1 plating F4 100mg/m'
, Sn plating! 600 mg/rn', chromate treatment 100 g/liter CrO3, 3 g/l N2
IOA/d in an aqueous solution at 50 °C with addition of SO4
The treatment was carried out in the same manner as in Example 1, except that the cathode treatment was performed at m2 for 1 second.

Example 9 In Example 1, the plate thickness was 0.243 mm, Ni metal
Clearance amount 3oomg/m', cold rolling with a reduction rate of 30% instead of temper rolling, Sn-metal open space 500mg/m',
Chromate treatment is Q, 1 to 50g/fLCrO13
331 sentences in an aqueous solution at 50 °C with addition of H2SO4
The treatment was carried out in the same manner as in Example 1, except that the cathode treatment was performed at 0 A/dII+2 for 1 second.

Example 1O In Example 9, Ni plating 500mg/rr
f, Sn plating amount 500mg/m', chromate treatment 0.52g/m' for 50g 1 CrO3) (, so4g
50A/dm2 in an aqueous solution at 50°C with addition of /i
The treatment was carried out in the same manner as in Example 9, except that the cathode treatment was carried out for 1 second.

Comparative Example 1 A commercially available #25 tin plate (Sn) with a plate thickness of 0.21 mm and a fillet amount of 2800 mg/m was used in a comparative example. This tin plate was manufactured by the Ferrostan electric tin plate line.

Chromate treatment is 25g/l Na7 Cr707
*2 4A/dII in an aqueous solution of N20 at 45°C
+2 and cathodic treatment for 1 second.

Comparative Example 2 In Comparative Example 1, the chrome-I treatment was carried out at a temperature of 90°C.
It is the same as Comparative Example 1 except that the cathode treatment was performed at 140 A/c 1 m2 for 1 second.

Comparative Example 3 In Comparative Example 1, the plating amount was changed to #15 (1700 m
The procedure was the same as in Comparative Example 1, except that the temperature was set at 100 g/m').

Comparative Example 4 In Comparative Example 3, the same procedure as Comparative Example 3 was carried out except that the chromate treatment was changed to the treatment in Comparative Example 2.

The following performance tests were conducted on the welded can materials of the present invention and comparative old materials manufactured as described above.

(1) Surface Contact Electrical Resistance Measurement Place a specimen heated in the air at 210°C for 10 minutes and cooled between the polar axes of a seam welding machine for food cans, apply a pressure of 35 kg and apply a DC voltage between the polar axes. The electrical resistance when was applied was measured and taken as the contact resistance of the specimen surface. The lower the contact resistance, the better the weld.

(2) Weldability test Using a seam welder for food cans, welded area overlap l] 0.4
mm, pressing force 45kg, welding speed IE1m/ll1in
Welding was carried out by varying the welding current. Measure the tensile strength of the weld, measure the number of dust particles, observe the state of discoloration, and observe the state of nugget formation using a cross-sectional microscope. I set the range. The evaluation was performed using commercially available #25 tinplate as a standard, and was performed as follows.

■: Equivalent to or better than #25 tin.

0: Slightly inferior to #25 tinplate, but no problem in practical use.

Δ: Inferior to #25 tin; strict control of welding conditions is required in practical use.

X: Inferior to #25 tin and not practical. (However, discoloration is #
25, #17 Puriki was marked as x and used as a standard. ) (3) Under-paint corrosion test: An epoxy paint for cans was applied to the surface of the test specimen using a roll coater so that the amount of film adhesion after firing was [f5mg/di2], and the specimen was fired at 205°C for 10 minutes. . Make an X-marked scratch on the coating surface with a sharp knife that reaches the base metal, 1.5
%NaC9j +1. D Place in citric acid solution, 55°
C and held for 86 hours. After 96 hours had elapsed, the sample was taken out, washed with water and dried, and then observed under a 50x microscope for the spread of corrosion in the spruce part, the extent of pitting corrosion, and the occurrence of corrosion under the paint film outside the spruce part. In addition, sellotape was applied to the entire surface of the sample (5 cm x 5 cm) and rapidly peeled off, and the peeling status of the coating film was observed. The evaluation was performed as follows.

(4) Salt water resistance test A 5cm x 5cm test piece painted in the same manner as in the previous section (3)
Cut it out, bend it 90' from the center with the painted side outside, immerse it in 5% saline solution, put it in a high-pressure steam oven, 1
It was heated to 25°C and held for 1 hour. A mock test piece was taken out for 1 hour, washed with water, dried, bent back to a flattened part, affixed cellophane tape to the entire surface, and rapidly peeled it off to observe the state of peeling of the coating film. The evaluation was performed as follows.

0: No peeling of paint film at all.

O: Coating and peeling #5% or less.

Δ: Paint film peeling 195.1% to 50%.

×: Paint film peeling of 51% or more.

(5) Resistance to sulfurization and blackening After painting, bend the specimen at 80° in the same manner as in the previous section (4).
．． The sample was immersed in an aqueous solution of 4z ammonia sulfide, placed in a high-pressure steam oven, heated to 125°C, and maintained for 1 hour.

The 1-hour mock specimen was taken out, washed with water and dried, and then the degree of discoloration (blackening) at the bent portion was evaluated by visual observation. The evaluation was performed as follows.

■2 No discoloration at all.

0: Almost no discoloration.

△: Slight discoloration.

X: Obvious discoloration.

Table 1 shows the results of various tests conducted as described above.

All of the products of the present invention exhibit performance equivalent to or better than those of the comparative examples.

Claims (1)

[Claims] The adhesion amount on cold rolled steel plate is 30-500m per side.
g/m' Ni electroplating, followed by heating in a non-oxidizing atmosphere to penetrate and diffuse part or all of the Ni plating layer into the steel, followed by temper rolling or cold rolling.
S with adhesion amount of 100 to 15000mg/rn' per side
n electroplating followed by Cr6 in chromate aqueous solution.
+ 5O42-1F- in an amount of 11500 to 1150 at a concentration
A method for manufacturing a steel sheet for cans and containers with excellent weldability and coating performance, characterized by electrolytic chromate treatment in a bath containing one or two of the above.