JPS616294A - Production of sn-plated steel sheet having excellent corrosion and weldability for container - Google Patents

Abstract

PURPOSE:To obtain an Sn-plated steel sheet having excellent corrosion resistance and weldability for containers by sticking an adequate quantity of underlying plating of a Cr alloy contg. P and Mo on the surface of the steel sheet then subjecting the surface to plating of Sn followed by heating and melting as well as chromate film treatments. CONSTITUTION:The surface of the steel sheet for a container material, etc. is subjected to the underlying plating of P, MO or Cr-P, Cr-Mo, Cr-P-Mo alloy contg. 1-60% P and Mo in combination at a coating weight of 3-300mg/m<2> per side. The surface is then subjected to plating of Sn at >=300mg/m<2> per side. Or the surface is further subjected to the heating and melting treatment. The steel sheet is subjected to the chromate film treatment by the prescribed method in succession thereto. The Sn-plated steel plate having the excellent weldability by an electric resistance welding method, etc. and the excellent corrosion resistance required for beverage cans, etc. for containers is obtd. by the above-mentioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is a method for manufacturing Sn-metal and medium-sized steel alloys that have excellent weldability using electric resistance welding and also have excellent corrosion resistance required for beverage cans, general cans, etc. This invention relates to a method for producing steel sheets for containers.

(Prior Art) In recent years, can manufacturing methods and can designs for beverage cans and food cans have significantly advanced and diversified, and materials for containers that are compatible with these are required to be low-cost and high-performance.

In particular, electric resistance welding methods, such as Sudrony
The welding can making method has many advantages such as high material yield, high strength of welded parts, extremely low leakage rate due to poor joints, and can be applied to design cans of various shapes, and is beginning to be widely used.

Conventionally, this welded can making material has a Sn adhesion amount of ÷10 or more (8n adhesion amount 1.129/m"), preferably ÷2
5 or more (Sn adhesion amount 0.28.lil/m") 8nm.

Ki steel plates have been used.

However, the biggest drawback of this is that its price is extremely high due to the soaring price of 8N bullion. Therefore, various attempts have been made to reduce the cost by reducing the amount of Sn deposited, but in this case, problems arise such as reductions in corrosion resistance and weldability.

Recently, as an alternative material for containers, JP-A-57-
No. 23091, Japanese Unexamined Patent Publication No. 57-200592,
Steel plates having various plating layers or coating layers have been developed, as disclosed in Japanese Patent Application Laid-Open No. 57-110685. The manufacturing method is an arbitrary combination of N1 plating, thin Sn plating on the surface of the steel plate, alloying of these (heat melting treatment), and chromate coating treatment.

Steel sheets manufactured by this manufacturing method have reduced pinholes due to the superimposed effect of the two-layer coating, and the formation of a dense alloy layer of N1 and Sn in the plating layer, resulting in ATC (AttoyTin C).
Corrosion resistance can also be improved by lowering the outputs value.

In particular, an alloy layer consisting of Fe and Sn (FaSn2 alloy layer) that grows during the high-temperature heating process during N1 base plating, welding, can manufacturing, or high-temperature sterilization after filling.
This improves weldability and the appearance of the welded part.

(Problems to be Solved by the Invention) However, when these steel plates for containers are examined in detail, it is difficult to say that sufficient performance is necessarily ensured. When a double-layer plated steel sheet consisting of an N1 base plating layer and Sn plating is exposed to a corrosive environment, the dissolution rate of Sn decreases due to the above effect, as shown in Figure 1, and its initial corrosion resistance is excellent. . However, after being exposed to a corrosive environment for a long period of time, S
When n is dissolved and consumed and the alloy layer is exposed, no matter how dense the alloy layer is, there are still pinholes.
A local battery is formed in the N1 and Sn alloy layer, and corrosion is accelerated. In this case, the alloy layer of Nl and Sn becomes extremely noble (can-dic) in potential with respect to the steel base (base iron), so the base iron is preferentially eluted from the exposed portions of iron (pinholes). As a result, corrosion resistance deteriorates, and in some cases, drilling corrosion may occur.

In addition, such a phenomenon may expose the alloy layer or the base steel due to processing scratches during can manufacturing, and similarly to the above, it causes deterioration of corrosion resistance due to elution of the base steel, and eventually causes perforation corrosion.

In addition, welding operations have become faster in recent years, and better weldability than ever before is required. Weldability is determined by the amount of alloyed Sn plating ()IJ-Sn), which suppresses the alloying reaction during the paint baking process and suppresses the free Sn plating.
It is important to increase the amount remaining. however,
As mentioned above, today's steel plates for containers are coated with Nl undercoating, which has some effect, but the diffusion rate of Ni and Sn is quite fast, so it is difficult to improve weldability. Fu to do! It is difficult to secure J-8n,
In particular, good high-speed weldability has not always been obtained for steel plates with a low Sn deposition amount.

(Means for Solving the Problems) The object of the present invention is to solve these problems and provide a steel plate for containers having excellent corrosion resistance and weldability.

The present inventors (1) As mentioned above, in cases where there are corrosion conditions or defects where the alloy layer and base metal are exposed, N
without forming an alloy layer with Sn containing an extremely potentially sensitive metal such as I (for example, Ni-8n alloy, N1-8n-Fa gold alloy N1-P-8n alloy, etc.).
In addition to providing a base plating layer that can generate a dense alloy layer with Sn and reduce pinholes in the alloy layer (decreasing ATC value), the formed alloy layer with Sn also forms an alloy layer of Ni with Sn alloy plating. Potentially closer to the base railway than the layer,
A base plating layer that suppresses preferential iron elution from the base iron even in a corrosive environment. (2) During thermal diffusion processes such as heating, the reaction rate with 8N is extremely slow compared to the Nl base plating layer, and heat treatment is Various studies were conducted on the undercoat plating layer that allows more IJ-Sn to remain even after being exposed to oxidation.

As a result, a Cr alloy consisting mainly of Cr metal, which has no potential difference compared to the steel substrate, is used as the base plating layer, and it forms a dense alloy layer with Sn, and even when subjected to heat treatment, it remains the same as the base steel. Cr-P has the effect of preventing diffusion reaction with Sn.
, Cr-Mo, and Cr-P-Mo alloy plating layers were found to be effective.

That is, the gist of the present invention is that P is applied to the surface of the steel plate.
Or Cr containing 1 to 60% of Mo or its composite
-P or Cr-Mo or Cr-P-Mo alloy base plating on one side at 93~300η/m! Apply with a coating amount of
A Sn-plated steel sheet for containers with excellent corrosion resistance and weldability, characterized by applying Sn plating on one side of JlJ300~/m2 or more, or further heat-melting it, and then applying a chromate coating thereon. It is in the manufacturing method.

(for production) The present invention will be explained in detail below.

Cold-rolled steel sheets manufactured through normal steel manufacturing, rolling, and annealing processes are subjected to pretreatment performed in normal plating processes such as degreasing and pickling, and after cleaning and activating the surface,
Cr--P, Cr--Mo, or Cr--P--Mo based alloy base plating is performed.

The effect of this base plating layer is shown in Figures 1, 2, and 3.
As shown in the figure, (1) heating and melting treatment after Sn plating (
The alloy layer with Sn that is produced during the melting process or the heat treatment in the paint baking process that is carried out in the normal tinplate manufacturing process is dense and has few pinholes (AT
It is an alloy layer with a low C value (Figure 2), and the potential of the alloy layer is extremely close to the potential of the plated original plate with respect to the N1 and Sn alloy layer, so that a couple current (corrosion current) between the alloy layer and the base metal is generated. (Table 1). Furthermore, (2) Fern2
Suppresses the formation of an alloy layer and reduces the residual amount of Sn in the surface layer ()IJ
It has a barrier effect that increases the amount of Sn (Fig. 3).

(Note) Measurement method/test piece preparation method ■Calcination conditions 210°C x 20 minutes ■Free Sn electrolytic stripping conditions The test piece after firing was o, 5'16 Na2CO
Electrolytic degreasing is carried out cathodically in S, and then 54 Na
Electrolytic stripping is performed in OH to expose the alloy layer, washed with water, and dried.

・Couple current measurement method ■Test solution: 1.5 citric acid + 1.5% sodium chloride ■Measurement conditions: The test piece after Sn removal and the plated original plate are coupled in the test solution, and the couple is measured after 20 hours at 27°C in a nitrogen atmosphere. Current was measured with a resistanceless ammeter. Test area is 2x2c
rR.

That is, C of P or Mo or their composite P+Mo
The content in r-alloy is 1-60%, preferably 5-301
Also, the amount of adhesion of the base plating layer is 3 to 300 Da/-
(per side), preferably 10 to 20011197 m”
Within this range, the desired effects of the present invention can be obtained, and a steel plate for containers having excellent corrosion resistance and weldability can be obtained.

Here, if the content of P, Mo, or their composite P + Mo is less than 1, the underlying alloy plating layer produced by reacting with Sn will not be dense or have a low ATC value, and furthermore, it will not be possible to obtain a low ATC value during the heating process. It is not possible to prevent the diffusion of 8n from the base iron, and it is not possible to obtain a steel sheet for containers with excellent weldability and corrosion resistance.

In addition, when the content of P, Mo, or their composite exceeds 60%, the densification effect of the alloy plating layer and the diffusion prevention effect of the base metal and Sn become saturated, and the alloy layer with Sn containing the base coating layer becomes saturated. The electric potential of the base metal becomes more cathodic,
In order to increase the amount of F eluted from defective parts of the alloy layer and to cause drilling corrosion, the upper limit of the content of P, Mo and their composites was limited to 60 parts.

In addition, if the coating amount of this base metal coating layer is less than 3~/m2 (one side applied), it will not be effective as a base plating layer, and if it exceeds 300~/m2, the effect will reach saturation. , Sn, and the alloy layer including the base coating layer is thick, which deteriorates the processability.

Next, how to obtain such a base plating layer.

Although the conditions are not particularly limited, electroplating is preferred in terms of controlling the coating amount and adjusting the content of alloying elements.

An example of how to provide these base coating layers is as follows.

(1) Cr-P alloy base plate by electroplating method, raw treatment Crys 1001/L(NH4)2
So45.31/l Plating bath composition (NH4)2HC6H50, 3009/1
HPH20□ 251/1 HsPO4509/ Current density 10 A/dm” Plating bath temperature 50°C (2) Cr-Mo alloy base plating treatment by electroplating method
a) 2SO45,311/l Plating bath composition (NH4)2HC6H50,3001/
/1M00s 251/INa
2 Co s 25 y/1 current density
10A/dm" Plating bath temperature: 50°C Next, a base plating layer made of Cr-P, Cr-Mo, or Cr-P-Mo alloy is applied to the steel sheet thus obtained, and then Sn plating or further SfI plating is applied. After plating, heat melting treatment (melt treatment) is performed.In this case, the Sn plating conditions and the heat melting treatment conditions after 8N plating may be the same as the usual plating conditions and heat melting treatment conditions, and the plating bath composition , plating conditions or heat-melting treatment conditions are not particularly restricted.For example, phenolsulfonic acid 10-30.9/based on base sulfuric acid) 5nS0440-80g/1 ENSA (additive, manufactured by DuPont) 5-i 5 p7t
(2) Plating bath composition: (halokene bath) stannous chloride 50-1001/l, sodium chloride
15~3511/ potassium sulfur hydride 40~
60 E/l of sodium chloride 30-601/l naphtholsulfonic acid 1-511/l at a current density of 5-100 A/dm" and a bath temperature of 30-60°C.

Further, the heat melting treatment is carried out to improve the appearance by increasing the metallic luster of the Sn plating layer, and to further improve the corrosion resistance by making the base alloy plating layer and the 8N alloy layer more uniform and dense.

The heat melting treatment is performed by washing with water after Sn plating, and forming an 8N plating layer as it is or by applying an aqueous flux at 240 to 350°C, preferably 250 to 300°C, in air or a non-oxidizing atmosphere (for example, N2 atmosphere). is melted.

The flux is applied by dipping or spraying, for example, if the plating bath is a ferrostane bath, phenolsulfonic acid 2 to 1011/l (in terms of sulfuric acid) S n8
042-1011/1 is applied and melted.

In addition, the steel sheet of the present invention having a Cr-F or Cr-Mo alloy base plating layer and a Sn plating layer or a heat-melted Sn plating layer on the surface thereof can prevent the formation of an oxide film on the surface of the Sn plating layer during storage. Chromate treatment is also performed to improve coating performance. The chromate treatment is carried out after Sn plating or further heating and melting treatment, removing residues on the surface by washing with water, or preliminarily removing the oxide film etc. on the surface of the methane layer with ammonium carbonate, soda carbonate, etc.

For this reason, after Sn plating or further heat melting treatment,
After removing the residue on the surface, one or two of chromic anhydride, chromate (ammonium chromate, sodium chromate) or dichromate (ammonium dichromate, sodium dichromate, etc.) The above mixed aqueous solution and an aqueous solution to which 5o4-2 ions, F- ions, etc. are added are used.

In this case, the chromate treatment aqueous solution bath or treatment conditions are not particularly specified, but for example, the following chromate bath is used and the treatment is carried out under chromate conditions.

(1) Chromate bath composition 601/LCrO, -0,3
11/1804-2 Current density 7,5A/d
m” bath temperature 60℃ Chromate coating amount (Cr conversion) 14.5 my/
m" (2) Chromate bath composition 3QI/sodium dichromate current density 10 A/dm" bath
Temperature: 50°C Chromate coating amount: 6.5 da/mm Particularly, coating performance (
In order to improve paint adhesion and post-painting corrosion resistance, Cry
, -804-2 system, or CrOs -F- system, etc., to simultaneously deposit a metallic chromium layer and a chromate coating layer consisting of chromium hydroxide.

Chromate coatings are ideal for applications in which the shape of cans is required to have good flexibility and are subjected to harsh processing, as well as applications that require excellent coating performance.

In addition, the container steel sheet manufactured by the method of the present invention has a very large diffusion prevention effect between the base plating layer, the base metal, and the 8N plating layer, so the residual amount of F-IJ-Sn is large, and the Sn adhesion amount is, for example, 1. Excellent weldability is achieved even at a low deposition amount of 0.121//m'' (deposition amount per side) or less, preferably 0.7017 m'' (deposition amount per side).

In other words, even if a steel plate with a low Sn adhesion is subjected to heat treatment for paint baking, the amount of metal Or is less than 1011 m9/m'' and is generated on the surface because there is a large amount of IJ-8n remaining. 30 in total with chromium hydroxide coating
Excellent weldability can be obtained even at mg/m2 or less.

Furthermore, excellent corrosion resistance can be obtained due to the effect of preventing pinholes caused by metal Cr even though some pinholes are generated due to the low amount of Sn attached. In particular, due to the effect of improving paint adhesion, when the can is subjected to impact during transportation, it is extremely preferable from the viewpoint of corrosion resistance that the paint is hard to peel off due to the low Sn adhesion amount.

As described above, the steel sheet for containers obtained by the method of the present invention has improved corrosion resistance due to the formation of a dense metal alloy due to the appropriate base plating layer for the Sn plating layer, and the use of other metals or other alloys as the base plating layer. Compared to the case where the potential of the alloy layer is less noble (cathodic) than that of the base steel, there is less concern about preferential dissolution of F from defective parts of the plating layer and, ultimately, drilling corrosion. In addition, when subjected to heat treatment, the diffusion prevention effect between the base steel and the Sn plating layer increases, resulting in improved weldability due to the residual effect of F-Q-an, and improved corrosion resistance, etc., resulting in excellent performance. It will be done.

Incidentally, the base plating layer of the present invention is made of Cr-P, Cr-Mo
Although the alloy has been described, similar effects can be obtained with a ternary alloy of Cr-P-Mo. In the plating process on an actual industrial line, there are many difficulties with ternary alloys, such as component adjustment and bath management, so explanations are omitted in this invention.
Since almost the same technique and the same effect as the present invention can be obtained, it is included in the scope of the present invention.

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

After degreasing and pickling the steel plate using the usual electrolytic method, (
a) Chromic acid - ammonium citrate - hypophosphorous acid -
10 A/d each using a phosphoric acid aqueous solution and (b) a chromic acid-niammonium citrate-molybdenum oxide aqueous solution.
Electroplating was performed at a current density of m''.The content of each P or Mo was adjusted by the content of hypophosphorous acid or molybdenum oxide in the solution, and the amount of deposition was adjusted by the number of coulombs. A predetermined base plating layer was obtained.Also, in (dip coating → thermal diffusion treatment method), after dipping in (C) iron chloride-sodium hypophosphite aqueous solution and (d) ammonium molybdate aqueous solution, roll drawing method was used. Each base plating layer was obtained by annealing diffusion while adjusting the amount of adhesion.

After washing with water, 13n plating was applied to each coating amount at a current density of 30 A/dm in a ferrostane bath, and heat melting treatment was performed in some cases. Next, a 3011/l gychromate bath (no metal chromium precipitation) or 601/l gychromate bath (no metal chromium precipitation) /1cro,
A predetermined amount of chromate coating was obtained using a -0,3y7t 5o4-2 bath (metallic chromium precipitation) at a temperature of 60°C and varying the current density and electrolysis time.

The welding performance and corrosion resistance of the container steel sheets obtained in this manner were compared with known steel sheets with a base plating layer and with Sn-plated steel sheets ('f Riki) without a base plating layer. Examined. The results are shown in Table 2.

1. Welding performance After dry-baking the plated plate at 210°C for 20 minutes and then at 190°C for 10 minutes in a cycle equivalent to the paint baking process, we used a Suudronic welder at a frequency of 400 Hz.
, lap width 0.5+w+, welding speed 50m/ml
Seam welding was carried out using the welding method, and the occurrence of dust in the welded part and the occurrence of nuggets in the cross section of the welded part were investigated, and the welding performance was comprehensively judged.

2. Under-coating corrosion (UCC) Epoxyphenol paint after plating 559/dm
After coating and baking at 210°C for 10 minutes, crosscuts were made on the surface of the sample plate to reach the base metal, and immersed in a 1.5% citric acid-1,5'4 NaCA aqueous solution at 55°C for 4 days. Judgment was made based on the degree of rust spread from the cut portion and the peeling status of the coating after peeling off the cellophane tape (loss-cut portion and flat portion).

3. Pitting corrosion resistance (pitting corrosion status of defective areas after painting) Painted under the same conditions as in 2 above, made a cross cut that reached the base metal, and immersed it in the corrosion test solution shown in Table 2 at 50°C for 12 days. Afterwards, the corrosion resistance of the cross-cut portion was evaluated by observing the corrosion state in the depth direction using a cross-sectional microscope.

4. Apply 55~/d of epoxy phenol paint to a salt water retort-resistant plated plate, bake at 210°C for 10 minutes, bend the sample closely, and heat it in a 5% NaC2 aqueous solution at 12°C.
Retort treatment was performed at 0°C for 60 minutes. Immediately after the salt water retort treatment, cellophane tape was peeled off, and the state of paint film peeling on the bent portion and the flat plate portion was evaluated.

After conducting the above performance test, the performance of the Example and Comparative materials was judged, and the judgment criteria were as shown below.

◎...Very good ○...Relatively goodΔ...Slightly poor ×...Very poor, P..., Mo
... indicates the amount of P or Mo attached.

(Effects of the Invention) As described above, the steel plate manufactured by the method of the present invention has extremely superior corrosion resistance, welding performance, and performance as a material for containers, compared to nine-plated products.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a comparison of Sn elution rates in model corrosive liquids (1.5 citric acid + 1.5 chloride NaCA, measurement conditions: 27°C, N2 atmosphere) of various steel plates for containers. The coating composition of the test piece is as follows: O... Base (F/-20%Nl) Alloy plating (200% Nl)
da/R) → Sn metal, plating 0019/m') → heating melting treatment → chromate treatment (9■/ff/) Δ...base Nl metal (25m9/n?) → 8n plating (soomp/m") →Chromate treatment (8111
9/1el) O... Base (F・-10Nl) Diffusion coating amount (Nl plating amount 50■/rr? → Diffusion treatment) → An plating (800 ml) → Heating melting treatment → Chromate treatment (
8■/-)×...Sn plating (ssomp/m')→
Heat melting treatment → chromate treatment (9 da/-) Mu... base (Nl-161F) alloy plating (60yn
y/m”)→Sn plating (850mg/m”)
4 Chromate treatment Figure 2 shows Sn medium steel plate with Cr-P or Cr-Mo underlayer alloy (coating amount per side 780~/-)
It is a figure showing the relationship between P or Mo content and ATC value. The test solution used for measurement was 1 part tomato juice mixed with distilled water.
Dilute to 1:1, add 0.1 S nCL2/2H20 after boiling
Added 9g/ (Sn aged 10100pp was used.The measurement conditions were to hydroxylate the free Sn on the test piece) Electrolytic stripping was performed in IJium to expose the alloy layer,
It was coupled with Sn in the above test solution, and the force and sol current were measured after 20 hours at 27° C. in a N2 gas atmosphere. (S
Figure 3 shows the elution rate of Cr-P or Cr-M.
FIG. 3 is a diagram showing the relationship between the P or Mo content of a Sn-plated steel sheet having an underlying alloy plating layer and the residual amount of Sn after heat-melting treatment. The steel plate used for the measurement was coated with Cr-P and Cr-Mo alloy base coating on one side F) 751Q
After washing with water and applying an Sn plating amount of 550~/FPI* per side, heat treatment (
Heating conditions: 210°C x 20 minutes (9 tKlng) to measure the amount of free Sn. The amount of Sn was calculated from the electrolytic peeling curve of Sn elution shown in FIG. (S
The amount of Sn before and after elution was measured using fluorescent X-rays, and the difference was confirmed as the amount of free Sn)

Claims (1)

[Claims] The content of P or Mo or their composite on the steel plate surface is 1 to 1.
60% Cr-P or Cr-Mo or Cr-P-M
o Apply an alloy base plating with a coating weight of 3 to 300 mg/m^2 per side, then apply Sn plating of 300 mg/m^2 or more per side on top of this, or further heat-melt it, and then apply a chromate coating on top of it. A method for manufacturing a Sn-plated steel sheet for containers, which has excellent corrosion resistance and weldability.