JPS60215739A - High-carbon steel plate for vessel having excellent workability and corrosion resistance - Google Patents

Abstract

PURPOSE:To provide a high-carbon steel plate for a vessel having excellent workability and corrosion resistance by controlling respectively the contents of C, Si, Mn, Al, P, S, N and O and fining cementite. CONSTITUTION:The above-described steel plate consists of 0.10-0.30% C, <=0.03% Si, 0.05-0.60% Mn, <=0.01% Al, <=0.025% P, <=0.05% S, <=0.015% N, <=0.03% O and the balance Fe and unavoidable impurities and has <=0.5mu average particle size of cementite. Such steel plate is produced by subjecting a continuous casting slab, which is subjected to component adjustment in the abovementioned way, to hot finish rolling at the temp. in the austenite region then cooling the hot-rolled plate to an about 450-620 deg.C temp. range at a cooling rate of about 40-200 deg.C/sec and coiling the plate. Such steel plate is decreased in the content of Al by the increased rate of carbon and at the same time excellent workability and corrosion resistance are provided thereto by refining of cementite. The steel plate lends itself to various diversified applications as a blank material for vessels.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a high carbon steel sheet for cans that has excellent workability and corrosion resistance.

(Prior Art and its Problems) Metal containers, especially steel containers, have long been trusted by consumers as they do not lose their function as sealed containers even under harsh storage environments. Behind this is the constant efforts of related industries to improve quality and reduce costs. For example, steel manufacturers are switching from ingots to continuous cast materials with excellent quality uniformity, and by increasing the strength of materials. Examples include reducing the area weight by lowering the gauge or improving the plating function. In addition, in recent years, the workability of steel sheets has become even more demanding, as seen in 01 cans, which require excellent flange workability, and easy-open cans, which require excellent openability. Regarding this, the present inventors also reported in Japanese Unexamined Patent Publications No. 57-198244 and No. 58-52455 that a large amount of solid solute carbon, which is a cause of deterioration of ductility, is reduced by making cementite finer and having a higher carbon content. We have already proposed a technology to reduce this through dispersion and improve workability.

Through these efforts to improve quality, food cans have expanded the variety of contents and applications, and have come to be used on a daily basis in many parts of the world. When stored for a long period of time or depending on the type of contents, etc., the corrosion resistance of the inner surface of food cans is sometimes observed to be impaired.

There are two types of this phenomenon: one is a phenomenon in which the elution rate of the plating layer on the inner surface of can bodies mainly made of tinplate is abnormally accelerated (abnormal elution), and the other is a phenomenon in which the elution rate of the plating layer on the inner surface of cans mainly made of tinplate is accelerated (abnormal elution). This is a phenomenon in which corrosion cracks occur in the processed parts such as beads on the inner surface of the can lid of vacuum cans made of materials such as (tin-free steel). Under normal conditions, these do not impair the airtightness of food cans, and their occurrence frequency is small, but there is a risk that predicting the lifespan of food cans will be inaccurate.
Elucidation of the cause is urgently needed. Although the causes of occurrence are still unclear, the above-mentioned abnormal elution of the plating layer such as tin and corrosion cracking tend to occur more easily in continuously cast materials (aluminum guild steel) than in ingot materials. has been pointed out, and there is a view related to the cleanliness of the surface layer of the steel plate. Additionally, there are differences in the occurrence tendency depending on the annealing method, and it is said that abnormal elution of tin is more likely to occur in box-annealed materials, and corrosion cracking is more likely to occur in continuously fired materials.

Against this background, the inventors of the present invention have responded to the long-standing trust of consumers as described above, and sought to rationalize this problem in line with the trend towards high strength materials without compromising the direction of continuous casting and continuous firing. We have been conducting intensive studies to find a solution.

As a result, the main cause of these corrosion resistance deteriorations is that alumina-based nonmetallic inclusions on the surface of the steel sheet create defects (pinholes) in the plating layer and coating film, and corrosion starts from these pinholes. We obtained the knowledge that At this time, whether the form of corrosion progress is abnormal elution of the coating layer or not,
Or whether it will cause corrosion cracking depends on the type of plating as mentioned above.
Regarding the annealing method, it may be difficult to make a general rule because it depends on the contents, the annealing method of the material, etc. According to the research conducted by the present inventors, in the case of box annealed materials that promote enrichment of A1 on the steel plate surface, This A1-enriched layer inhibits the integrity of the alloy layer that forms at the interface between the plated metal and the base iron, causing abnormal elution of the entire surface of the plated layer. Since the uniformity tends to be large (stretcher strain is large), it was observed that corrosion cracking along the stretcher strain tends to occur as a starting point for the pitting corrosion generated at the pinholes described above.

As described above, even if deterioration of corrosion resistance ultimately appears in any of the corrosion forms described above, it is essential to reduce the amount of Al as much as possible to improve the deterioration. In this case, since AI is added mainly for the purpose of deoxidation, it is effective to increase the carbon content of the steel component in order to reduce this. However, simply increasing the carbon content of the steel sheet deteriorates the workability of the steel sheet, making it unsuitable for use as a working steel sheet. However, as mentioned above, the present inventors have already shown in Japanese Patent Application Laid-Open No. 58-1987 that a high carbon material made of fine cementite and dispersed in a large amount exhibits excellent workability due to the effect of reducing the amount of solid solute C.
No. 52455, etc., and by layering this knowledge with the effect of improving corrosion resistance by reducing the amount of Al, it has become possible to provide a steel plate with excellent workability and corrosion resistance.

(Structure of the Invention) In other words, the present invention does not deteriorate the material properties even with high carbon content, but rather improves A by making cementite finer, having a large amount of dispersion effect, and having a high carbon content, which has a great effect of improving the material quality.
It was constructed with a focus on the effect of reducing I content, that is, reducing alumina-based nonmetallic inclusions that adversely affect corrosion resistance, and suppressing the enrichment of AI on the steel sheet surface. It has made it possible to provide a solution in line with the aim of reducing manufacturing costs through combustion and continuous firing, and its gist is that C: 0.1 at weight 2.
0~0.30X, Mn: 0.05~0.80%
3i: 0.03X or less, Al: 0.
Limited to 0.01X or less, P: 0.025X or less, S
: 0.05X or less, N: 0.015% or less, O:
0.03 or less, the balance consists of iron and unavoidable impurity elements, and the average particle diameter of cementite is 0.5 p
A high carbon steel sheet for containers having excellent workability and corrosion resistance, characterized in that the steel sheet has the following properties:

The details of the present invention will be explained below.

First of all, the lower limit of C3l was set at 0.10% (hereinafter referred to as weight 2) because if it is less than 0.10%, deoxidation is insufficient, so other deoxidizing elements (AI, etc.) must be increased, which improves corrosion resistance. This is because the improvement effect will be insufficient. Also, the upper limit of the amount of C is set to 0.
The reason why it is set at 30% is that if it exceeds 0.3z, the cold-rolled sheet becomes extremely hard, making cold-rolling work difficult.

However, if the Mn content is less than 0.05%, the strength of the steel sheet will be insufficient, and if the Mn content is increased to more than 0.8z, the strength of the steel plate will be insufficient during cold rolling. This is because the steel becomes extremely hard, making cold rolling difficult.

Next, since Si deteriorates plating adhesion and adversely affects corrosion resistance when plated with Sn, Cr, Ni, AI, etc. to form a surface-treated steel sheet, the upper limit was limited to 0.03.

Next, in the present invention, one of the important constituent requirements is to limit the amount of AI to 0.01 or less. That is, A1 forms alumina-based inclusions and has an adverse effect on corrosion resistance, so it is more effective to limit its amount to a lower level. In this case, the upper limit was set at 0.01% based on the knowledge obtained from the following experiment in relation to the cementite particle diameter described later.

That is, FIG. 1 shows the influence of the amount of A1 and the cementite particle size on corrosion resistance (abnormal elution of tin). Corrosion resistance was evaluated using unpainted solder cans (No. 5 cans) made using tinplate (plate thickness 0.20+am, box annealed material, skin bath pressure 1.0%, area weight #75). Packed mandarin oranges with acid syrup added and heated at 40℃ for 1 hour.
An accelerated test was conducted under storage conditions for two months, and the amount of tin eluted into the contents (ppm) was measured and evaluated. The composition of the steel plate used in the test was A1 of 0.001 (no additives).
〜0.048 and other elements are GO, IJχ9Mn
0.43N, S i 0.013X, P O,0
15LS O,014X, N O,0041L O
G, 004% Yes.

As is clear from FIG. 1, a steel plate with excellent corrosion resistance can be obtained by setting the AI amount to 0.011 or less and the cementite particle size to 0.5W or less. Furthermore, as is clear from the examples described later, the cementite particle size is 0.
．． A steel plate exceeding 51L has a large deterioration in workability, with an Erichsen value of less than 6.0, and the properties as a workable steel plate are insufficient.

Based on the above results, the upper limit of All was determined to be 0.011. As mentioned above, the lower the content, the more effective it is.
Although it is desirable that the impurities be substantially zero, the presence of some impurities that are inevitably mixed in from raw materials in normal manufacturing processes is unavoidable.

Since P, S, and N can deteriorate the ductility and corrosion resistance of steel sheets, the L limits for each are set at 0.025 $ and 0.0
5$, and 0.015g.

0 is MnO, SiOx, A1. Oi and other inclusions exist in steel, and coarse ones have a negative effect on workability and can easily become a source of pitting corrosion, so the upper limit is set at 0.03%.
And so.

Next, in the present invention, the average particle diameter of cementite is 0.
The reason for this is that, as is clear from the results shown in Figure 1 above, if it exceeds 0.5, the effect of improving workability and corrosion resistance disappears. Furthermore, processing cracks and pitting corrosion due to coarse cementite particles occur, resulting in deterioration of workability and corrosion resistance.

Next, a method for manufacturing the steel plate of the present invention will be explained.

Hot rolling of the continuously cast slab, which has been subjected to the compositional adjustment as described above, is carried out under conditions such that the main structure of the hot rolled sheet is a bainite structure, from the viewpoint of refining the cementite in the annealed sheet. That is, the hot rolling conditions are such that after hot finish rolling the steel having the above components at the temperature of the austenitic castle, the obtained hot rolled sheet is rolled at approximately 40°C.
It may be cooled to a temperature range of approximately 450°C to 620°C at a cooling rate of 0°C/sec to 200'O/sec and then wound.

After hot rolling, pickling, cold rolling, and recrystallization annealing are performed. The annealing method may be continuous annealing or box annealing. A ferrite castle with an annealing temperature of 700°C or less is desirable.
If the temperature exceeds 700°C, cementite may become coarse. When annealing is carried out by continuous annealing, an overaging treatment is performed at a temperature of about 300 to 450° C. according to a conventional method, if necessary. In addition, after recrystallization annealing, there is usually a pressure of about 1~3z.
Temper rolling is performed at a high pressure reduction rate, but a high pressure reduction rate is desirable from the viewpoint of suppressing corrosion cracking. Furthermore, for the purpose of imparting strength to the steel sheet, it can be cold rolled a second time at a cold rolling reduction of about 3 to 40% and used as a so-called ZCR material.

The steel sheet that achieves the highest reduction in A1 through high carbonization and has fine cementite has excellent workability and corrosion resistance, and can be used as a material for cans using Sn, N, etc.
i, Single-layer, multi-layer or composite plating of Cr etc. is applied according to conventional methods for various uses such as can lids such as easy-open cans, 3-piece cans such as welded cans, drawn cans, draw and iron cans, etc. It is offered to

Next, the effects of the present invention will be illustrated in more detail with reference to Examples.

(Example) Twelve types of steel plates were prepared according to the processing conditions shown in Table 1 (thickness: 0.20 mm, skin pass reduction rate: 1.0%,
A tin elution test and a corrosion cracking test using a real mother sample were conducted using a sample with a tin weight of #25/75.

In the tin elution test, mandarin oranges with citric acid syrup added as contents were packed in an unpainted solder can (No. 5 can) with the inner surface of the steel plate having a tin weight of #75 and stored at 40°C for 12 months. An accelerated test was conducted to determine the amount of tin eluted (ppm).

The corrosion cracking test was carried out using a fully coated solder can with a tin coating of #25 on the steel plate surface as the inner surface of the can lid, the contents of which were packed with mackerel and tomato stew by vacuum sealing, and stored at 23°C for 12 months. The cans were opened and opened to investigate the occurrence of cracks in processed parts such as beads on the can lids, and the number of cracked can lids per 100 cans was expressed as a percentage. Further, the workability of the steel plate was evaluated by the Erichtsen test, and the results are shown in Table 1.

From these results, it is clear that the steel sheet of the present invention has much better corrosion resistance and workability than the comparative steel sheet.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the results of organizing the effects of AI content and cementite particle size on abnormal tin elution. Patent Applicant Representative Patent Attorney Tomoyuki Yafuki (and 1 other person)

Claims (1)

[Claims] C: 0.10 to 0.30% by weight Si: 0.03X or less M n: 0.05 to 0.80 g Al: 0.01% or less p: o, o 25% or less S: 0.05% or less N: 0.015% or less 0: 0.03% or less The remainder consists of iron and unavoidable impurity elements, and the processing is characterized in that the average particle size of cementite is 0.5p or less High carbon steel sheet for containers with excellent durability and corrosion resistance.