DE2115307A1 - Deep drawing steel - Google Patents

Description

Dipl.-Ing. H. Sauenland · Dr.-Ing. R. King

¹ ^ ^a Dipl.-Ing. K. Bergen ^a ^

Patent Attorneys · 4odo Düsseldorf · Cecilienallee 76 · Telephone 43Ξ7 3Ξ

Our file: 26 575 March 29, 1971

Ill / my

NIPPON STEEL CORPORATION No.6-3, 2-chome, Ohtemachi, Ghiyoda-ku, Tokyo / Japan

"Deep drawing steel"

The invention relates to a steel which is used as a material for can plates with excellent corrosion resistance particularly suitable for the contents of the can and can be deep-drawn extremely well.

Deep drawing is a tried and tested shaping process for producing tubular or hollow cylindrical ones Closed-bottom bodies that are cut flat using a punch and tool is deformed into a cup-shaped body. Of the The cup-shaped blank is again spaced apart using a drawing ring and a * in it The punch is deformed, the distance being less than the side wall thickness of the blank, which is normally about the Sheet thickness corresponds to or is slightly thicker * un on this Way to stretch the blank and reduce its wall thickness.

In order to determine the deformability of a sheet metal, the maximum reduction in cross-section is often used, as is the case with them takes place in conventional deep drawing. However, in order to express the deep-drawing ability more clearly, operated one looks at the ratio of the original thickness t

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of the starting material to the wall thickness t of the cup-shaped blank after deep drawing; In particular, the deformation ratio (t - t) / t and the ratio of the wall thickness of the cup-shaped blank t ^ at the time of deep drawing to the initial thickness t serve as indicators; in particular the critical deformation ratio (tt _f ) / t ₀ . '·

Conventional can sheet has seldom been subjected to severe deformation, which is why the main focus has been on corrosion resistance, while the material properties have not been fully investigated. k As a result, even can sheets with good deformability in themselves do not have sufficient deep-drawability. On the other hand, conventional metal sheets with sufficient deformability do not have sufficient corrosion resistance, as is required for can sheets, so that they are only suitable for low-corroding material.

Recently, due to newer methods of making cans as well as the cost of the can sheet and, in response to consumer demands, there has been a desire to use the conventional method of making cans to abandon three individual parts, - This procedure consists in the fact that the can jacket, the can bottom and the can- " lid can be manufactured individually and connected to one another. In contrast, a more recent method consists in the cans consist of two parts, i.e. a deep-drawn hollow cylinder made of sheet steel and closed on one side to produce a conventional lid.

For the reasons mentioned above, there is an increasing need for can sheets with good resistance to the different can contents on the one hand and high deformability. When making cans by deep

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will draw cylindrical bodies compared to making cans by the conventional method three individual parts subjected to severe cold deformation. When making cans from tin-plated sheet metal, surface cracks cannot be avoided, among them the steel surface is exposed. The corrosion resistance was made under practical considerations Less importance is attached, since the inner surface of such cans already has an organic lacquer coating requires. The different types of cans can be roughly divided into lacquered and non-lacquered cans. In the case of internally lacquered cans, the electrochemical corrosion protection of the tin coating is a consequence of the lacquering lost, so that the can sheet is often attacked via micropores of the paint coating and is independent of the Can contents result in pitting corrosion. In such cases, the durability of the contents of the can depends on the resistance to corrosion of the can plate itself, so that the can plate a must have high resistance to corrosion through the contents of the can. When manufacturing cans by deep drawing the bottom of the can is only subject to tensile stress, but not to any significant cold deformation, while the shell part is subject to cold deformation of more than 30% during deep drawing. These differences create education a galvanic element between the bottom of the can and the can jacket, the contents of the can containing the electrolyte forms, so that the life of the can is severely impaired as a result of galvanic corrosion. For this Basically, a can sheet suitable for deep drawing must have good corrosion resistance not only when immersed in corrosive solutions, i.e. against simple corrosion, but also good resistance to galvanic Have corrosion.

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The object on which the invention is based is to create a steel that can be used as a material for production of cans and with good resistance to galvanic corrosion a high deformability as well as good resistance to the various can contents, such as carbonated drinks in particular, Owns beverages containing phosphoric acid and citric acid.

The solution to the above-mentioned problem is based on the idea of the ratio of sulfur to phosphorus on the one hand and copper to phosphorus and sulfur on the other hand, and from copper to carbon in terms of the product to adjust the carbon and copper content in a steel in a certain way, which consists of less than 0.039% Carbon, 0.1 to 1.0% manganese, below 0.10% sulfur, below 0.5% copper and below 0.002% oxygen, the remainder inclusive there is impurities caused by the melting process.

The invention is explained in more detail below with reference to diagrams shown in the drawing. In the Drawing show the diagram of the

1 shows the dependence of the deformation capacity on the oxygen content,

2 shows the relationship between copper and carbon content at different degrees of deformation,

3 preferred ranges of the contents of copper and carbon,

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_ 5 -

4 shows the service life of a can as a function of the total content of phosphorus and sulfur with different copper contents and

5 shows the dependence of the service life on the carbon content at different ratios of Cu / (P + S).

In order to explain the invention in detail, the deep-drawability and the corrosion resistance are described below steels according to the invention treated separately from one another.

The deep drawability of sheet steel is strongest through non-metallic inclusions such as oxides, sulfides and Carbides impaired. The effect of oxide inclusions is particularly disadvantageous; so it follows from the diagram 1 that with oxygen kept above 0.0296 the critical value for the deep-drawability in unsuitable Way is lifted. For this reason, the oxygen content of the steel according to the invention must be below 0.02% and by suitable deoxidizing agents such as aluminum and silicon or by vacuum treatment carefully adjusted. In addition, the steel according to the invention may only be less than 0.10% deoxidizer such as Contains aluminum and silicon.

The sulphides are less harmful than the oxide inclusions because the sulphides are softer than the oxides and are therefore easier to deform. If the sulfur content is adjusted to 0.02 to 0.1% with regard to good corrosion resistance, the deep-drawability is somewhat impaired, but this can be limited to a minimum if the sulfides are very fine.

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In the steel according to the invention, the carbon and the copper content in terms of deep drawability or deformability of over 30% in a certain ratio that is over 50%. True, is in view of a high deep-drawability a certain carbon content is required, with regard to the corrosion resistance however, the carbon content should be as low as possible. Because of this, the carbon content exceeds 0.039% not. In conventional steels suitable as can material, the carbon content is 0.04 to 0.15%. A carbon content within these content limits | Although it guarantees good deep-drawability, it is impaired but the corrosion resistance is essential.

As can be seen from FIG. 2, the copper improves the deep-drawability at very low carbon contents. Included are the carbon contents lying outside the invention by the arrow A and the carbon contents according to the invention, in which, regardless of the respective copper content, good ductility results from the Marked with arrow B. Larger amounts of carbon and copper also have to be carefully matched to one another will; the upper and lower salary limits must meet the following condition:

3 χ 10 " ⁴ <C% χ (Cu% - 0.04) <1 χ 10" ² .

The maximum carbon content, which also prevents good deep drawability and corrosion resistance, is included 0.5%.

In Fig. 3, the curves C and E represent the boundary lines for the copper and carbon contents, which are high Allow deep drawability. With one in view of the

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Corrosion resistance and deep drawability to 0.02 up to 0.10% adjusted sulfur content are the upper limits for copper and carbon because of the harmful The influence of sulphides is somewhat low and must meet the following condition:

C% χ (Cu% - 0.04) <8 χ 10 " ³ · Curve C takes account of the above condition.

The corrosion resistance of steel depends on its composition and the corrosive medium away. With deep-drawn cans it happens because of the different Can contents essentially depend on choosing a steel composition that in all cases has good corrosion resistance results. In view of the extraordinary variety of foodstuffs and luxury foods that are considered to be Can contents come into question, it is extremely difficult to classify the corrosive properties of the can. Each can has its own corrosive properties. Has made numerous attempts it turns out that the corrosive properties of the canned material can be divided into two groups; in fact in canned goods that contain organic acids such as citric acid, tartaric acid and maleic acid as being essentially corrosive Contains media and is hereinafter referred to as citric acid-Gut and in phosphoric acid as Canned material containing essential corrosive medium, hereinafter referred to as phosphoric acid material. The steel according to the invention has proven to be resistant to both in numerous tests after deep drawing Types of canned goods proven.

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In the case of phosphoric acid, a certain sulfur content is found to be very effective in increasing the resistance against simple corrosion of the can jacket after deep-drawing, severe pitting corrosion as a result is more severe Galvanic corrosion takes place between the can bottom and the can jacket when the carbon and the Sulfur content is above a certain limit. In particular, at a sulfur content of 0.02 to 0.10% and carbon contents above 0.02% compared to the synergistic ones The effects of carbon and sulfur cause violent galvanic corrosion. Is the carbon monkey On the other hand, if the content is below 0.019%, there is no galvanic effect Corrosion when the sulfur content is 0.02-0.10%. Although a sole addition of copper with regard to the corrosion of phosphoric acid material is not effective, the copper dampens the galvanic corrosion accelerating Effect of carbon and sulfur. For this reason, the corrosion resistance can be increased by adding can be enhanced by copper and sulfur. In this case, the carbon content can be up to 0.039%, without that the deep-drawability and corrosion resistance are impaired. With regard to deep-drawability . the copper content must satisfy the condition mentioned above in connection with Fig. (field A):

8 χ 10 ~ ³ ^ C χ (Cu - 0.04)> 3 x 10 ~ ⁴ .

The phosphorus content of the steel should be as low as possible, since higher phosphorus contents increase the susceptibility increase against simple and galvanic corrosion. Regarding the resistance to galvanic corrosion If only sulfur is added, the ratio of sulfur to phosphorus must be at least 2 and in the absence of it of copper indicates the ratio of copper to the total content Phosphorus and sulfur are at least 3.

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In the case of citric acid, the copper and carbon content are of decisive importance. The carbon content should be as low as it barely allows good thermoforming properties, in particular the following condition (Figure 3, C.) Should be fulfilled: C χ (Cu - 0.04)> 3 x 10 ^-4.

While a copper content of 0.1 to 0.5% is recommended with regard to corrosion resistance, it should Ratio of the copper content to the carbon content must be at least 5. In Fig. 3, curve B denotes the limit values for copper and carbon. Citric acid contains phosphorus and sulfur as low as possible, as these elements promote both simple and galvanic corrosion. In particular If the sulfur content is below 0.02%, because sulfur is the resistance to galvanic corrosion in severely impaired. To switch off and on the harmful effects of phosphorus and sulfur this way to increase the life of the d ese should the copper content is at least three times the total content of phosphorus and sulfur.

4 shows the effect of different total contents of phosphorus and sulfur with different copper contents on the corrosion resistance, while FIG. 5 shows the corrosion resistance as a function of the carbon content with certain ratios of the copper content to the total content of phosphorus and sulfur. In this case, the curves of Figs. 4 and 5 that increasing copper levels increase the corrosion resistance considerably, and that the life of the can material with increasing ratio of copper content to the total content of carbon and sulfur increases. The reason for this may be in this

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lie that the copper dampens galvanic corrosion between zones with and without cold deformation and at the same time the resistance to simple corrosion increases. The copper is therefore important both in terms of deep-drawability as well as with regard to the corrosion resistance.

The steel according to the invention can be processed into sheet metal and cans in the usual way. Accordingly, a steel melt according to the invention can, for example, melted in the converter, electric or open-hearth furnace, then gege- ψ appropriate, vacuumed and are cast including continuous casting. Thereafter, the blocks or strands can be ^{hot-rolled to over 850 °} C., cold-rolled and annealed ^{at 500 to 1000 ° C.} After a surface treatment, for example descaling and pickling, the rolled sheet is tinned, chrome-plated, phosphated or subjected to another chemical treatment and then deep-drawn.

The invention is explained in more detail below on the basis of exemplary embodiments:

example 1

Annealed steel sheet of the composition shown in Table 1 with a thickness of 0.3 nm was rolled with a decrease in cross section of 1.3% and then sintered. The critical deformation ratio and the deep-drawability when deep-drawing 211 × 413 cans in accordance with the US standard are listed in Table II, along with other technological properties. Since the wall Stärk © Do the β s after thermoforming. 0.15 Ms 0.16 mm, the deformation was 47 to

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Table I.

stole (δ) 0.33 0.010 0.009 (I) 0.28 (8th) A. 0.005 0.30 0o010 0.012 0.028 0.23 0.005 B. 0.006 0.37 0.011 0.011 0.027 0.08 0.010 C. 0.013 0 "31 0.009 0.010 0.010 0.04 0.015 D. 0.018 0.30 0.010 0.010 0.026 Q.02 0.018 •
E. 0.045 0.32 0.010 0.011 0.025 0.06 0.011 F. 0.005 Ο.Ο27 0.03

Table II

Steel stretch- tensile strength- elongation hardness critical low- deep drawing limit ability to draw

ο ο ratio

(kp / nrar) (kp / mnr) {%) (HR30-T) (%) 211x413

A. 25.8 30.9 41 49.3 77 Il B. 25.9 30.8 40 48.7 73 Il C. 26.2 32.1 38 50.7 62 Il D. 27.0 33.3 36 52.1 56 no E. 28.0 35.0 32 55.2 46 Il F. 26.0 30.7 34 49.1 40

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The corrosion resistance is shown in Table III below of deep-drawn 211 χ 413 cans against both phosphorus and carbonic acid goods and against Lemon and carbonated good. The service life is specified as the time up to the point in time at which 10% the cup-shaped deep-drawn cans filled with carbonated beverages and stored at 33 ° C are attacked by pitting corrosion was.

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Table III

phosphorus
acid-good Lifespan (Mon.) stole 15th and carbonic, citric and carbonic acid
Good A. 15th 17th B. 6th 15th C. 14th 9 D. 8th

As can be seen from Table II, steels A, B fall and D under the invention; they allow a critical deep-drawing or deformation ratio of over 50% and can therefore be thermoformed excellently. On the other hand, the compositions of steels E and F are in terms of their copper content or in terms of the ratio of carbon to copper content far outside of that Invention and therefore have only a low critical deformability; they could not be cup-shaped deform. Structural examinations revealed numerous carbide and oxide inclusions as well as cracks in their surroundings, which give rise to breakage. The data in Table III show that the steels of the invention are excellent Have resistance to phosphoric acid and citric acid. In terms of their carbon, Steels with a sulfur or copper content outside the scope of the invention, on the other hand, were completely inadequate

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Corrosion resistance. For example, Table III shows that steel C with low levels of copper and Sulfur has a particularly low corrosion resistance to phosphoric acid.

Example 2

Various steels with the composition listed in Table IV were blown in the converter. The steels

1 to 5 fall under the invention, the steels 1,

2 and 4 were decarburized and deoxidized in vacuo. After casting, the steels were "rolled" and then hot-rolled at a final temperature of 890 ° C., coiled at 62O ° C., pickled in acid and cold-rolled with a cross-section reduction of 85% to a final thickness of 0.34 mm 64o C ⁰ annealed in an atmosphere of 4% hydrogen and 96% nitrogen, re-rolled with a reduction of 1.5% and then tinned. in Table V, the mechanical properties and the critical deformation ratio during deep drawing of the sheet are shown.

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Table IV

stole

C.
(90

Mn (90

Si
(90

P (90

S (90

Cu
(90

0 (90

1 0.005 0.33 0.010 0.009 0.028 0.31 0.006 2 0.010 0.30 0.010 0.010 0.016 0.13 0.010 3 0.030 0.37 0.011 0.011 0.010 0.06 0.014 4th 0.005 0.31 0.009 0.010 0.026 0.06 0.010 5 0.035 0.32 0.010 0.010 0.022 0.22 0.010 6th 0.054 0.30 0.009 0.011 0.025 0.06 0.006 7th 0.025 0.32 0.010 0.010 0.010 0.04 0.032

Stretch
border
(kp / mm ² ) Table V strain
(90 hardness
(HR30-T) critical
Deep drawing
ratio
(90 23.8 39 47c 2 75 stole 23.8 Tensile strength
speed
(kp / mm) 40 47.5 70 1 25.0 29.6 41 49.2 71 2 22.1 30.6 40 46.1 <60 3 27.0 31.0 30th 53.2 90 4th 27.9 29.2 28 52.4 <60 5 24.0 35.0 34 49.1 <60 6th 32.6 7th 30.7

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As Tables IV and V show, the steels according to the invention, with the exception of steel 4, are excellent Deep drawability. The steel 4 has a fairly good resistance to phosphoric acid-good, although its deep-drawing ability is a little worse is. Although the steel 4 is covered by the invention because of its low carbon and copper contents its critical deformation ratio during deep drawing is low. The steel 6 lying outside the invention is' there is too high a carbon content and both poor deep-drawability and low corrosion resistance. The steel 7, which is also outside of the invention, has with regard to deep drawing not the right carbon content but was actually bad because of its very high oxygen content deformable.

Example 3

Further examples of the corrosion resistance are obtained for the steels of the composition according to Table VI Table VII. The bars 8 9, 11, 13 and 14 fall under the invention and have an excellent corrosion resistance W. Steels 8 and 9 have a particularly preferred composition; their differences in corrosion behavior result from the different carbon content. Steels 11, 13 and 14 also correspond to preferred compositions according to the invention.

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Table VI

Steel C Mn Si P S Cu O

OO OO OO OO OO OO OO

8 0.005 0.27 0.02 0.008 0.010 0.21 0.009

9 0 .024 0. 38 0. 04 Ί Phosphoric acid good 0 .011 0 .014 0. 24 0. 012 10 0 .005 0. 31 0. 01 0 .018 0 .015 0. 03 0. 010 11 0 .036 4.0. 28 0. 01 0 .010 0 .024 0. 18th 0. 009 12th 0 .013 0. 41 0. 02 0 .026 0 .009 0. 04 0. 014 13th 0 .015 0. 36 0. 03 0 .011 0 .029 0. 05 0. 011 14th 0.009 O ₀ 45 O ₀ 01 0 .017 0 .045 0. 07 0. 013 table VII Lifespan (Mon.) 13th stole 12th Citric acid good 8th 12th 9 17th 10 8th 11 14th 12th 15th 13th 14th 18th 16 11 17th 10 9 10 I.

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Claims (5)

NIPPON STEEL CORPORATION, No. 6-3, 2-chome, Ohtemachi, Chiyoda-ku, Tokyo / Japan claims; 1. Deep drawing steel with high corrosion resistance, best Consisting of less than 0.039% carbon, 0.10 to 1.00% manganese, less than 0.10% sulfur, less than 0.50% copper and less than 0.02% oxygen, the remainder including iron-related impurities, at least one of the following Conditions are sufficient:
) (a) less than 0.019% carbon, 0.02 to 0.10% sulfur, below 0.08% copper with a sulfur to phosphorus ratio of at least 2; (b) below 0.039% carbon, 0.02 to 0.10% sulfur for: Cu / (P + S) ^, 3 and 8 χ 10 " ³ ^ C χ (Cu - 0.04) £ 3x10 ~ S (c) below 0.039% carbon, below 0.02% sulfur, 0.10 to 0.50% copper with a ratio of the copper and carbon contents of at least 5 and a ratio of the copper content to the total phosphorus and sulfur content of at least 3 and 1 χ 10 ~ ² > _ C χ (Cu - 0.04) 2: 3 χ 10 ~ ^. 2. Steel according to claim 1, but which is below 0.019% carbon, 0.1 to 1.00% manganese, 0.02 to 0.10% sulfur, less than 0.08% copper, less than 0.02% oxygen, the remainder including iron-related impurities and whose ratio of sulfur and phosphorus is greater than 2. 3. Steel according to claim 1, but which is below 0.039% carbon, 0.10 to 1.00% manganese, 0.02 to 0.010% sulfur 109844/1054 and contains less than 0.02% oxygen, the remainder including impurities caused by the smelting process, iron and its ratio of the copper content to the total content of phosphorus and sulfur is at least 3 and that of the! .. Condition: 8 χ 10 ~ ³ >"C χ (Cu - 0, 04) Z ~ 5 x 10 "^ is sufficient. 4. Steel according to claim 1, but which is below 0.039% carbon, 0.10 to 1.00% manganese, 0.10 to 0.50% copper, less than 0.02% sulfur, less than 0.02% oxygen, the remainder including impurities caused by the melting process Contains iron and its ratio of the copper content to the carbon content at least 5 and the copper content to the total content of phosphorus and sulfur is at least 3 and that of the condition: 1 χ 10 2Γ C χ (Cu - 0.04 Z 3 x 10 ~ ⁴ is sufficient. 5. Use of a steel according to one of claims 1 to 4 as a material for objects such as can sheet good deep-drawability must have high resistance to simple and galvanic corrosion. 109844/1054