DE1254871B - Enamelled sheet steel and process for its manufacture - Google Patents

Description

BUNDESKEFUBLK GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

C22c

German class: 40 b -39/54

Number: 1254 871

File number: F 44708 VI a / 40 b

Filing date: December 14, 1964

Opening day: November 23, 1967

The invention relates to the composition of an enamelled steel sheet and a method its manufacture. There are already enamelled steel sheets known, for example the following composition to have:

0.06 to
0.01 to
0.003 to
0.006 to
0.02 to

0.09
0.02
0.02
0.01
0.01
0.01
and 0.01

0.106% C,
0.187% Mn,
0.58% Si,
0.09% P,
0.08% S,
0.70% Ti,
1.357 "Cu,
1.19% Al,
2.53% Ni,
1.63% Cr,
0.61% Mo,

until
until
until
until
until
until
up to 0.61% No.

The usual composition of the well-known related titanium steel is as follows: ao

0.04 to 0.08% C,

0.31 to 0.42% Mn,

0.01 to 0.08% Si,

0.008 to 0.01% P,

0.01 to 0.03% S,

0.26 to 0.44% Ti,

0.04 to 0.07% Cu,

and 0.01 to 0.09% Al.

Another well-known steel that is particularly good for enamelling and has a low strength and yield strength, has the following composition:

up to 0.12% carbon,
0.5 to 6% chromium,
0.2 to 1% molybdenum,
5 to 1.5% nickel,

The remainder is iron with the usual levels of manganese, silicon and impurities.

It is also known that steel sheet with a low carbon content tends to warp when enamelled, so that small protrusions or crater-shaped pores appear on the enamel surface and impair its appearance. These surface defects are commonly referred to as bubble defects. Immediately below these vesicles there are accumulations of carbides in the surface layer of the sheet. These bubbles are formed by released CO or CO ₂ from the reaction of oxygen in the basic materials of the enamel and the carbon in the steel.

Enamelled sheet steel and process
for its manufacture

Applicant:
Fuji Iron & Steel Company, Ltd., Tokyo
Representative:

Dipl.-Phys. F. Finally, patent attorney,
Unterpfaffenhofen, Blumenstr. 5

; 'Named as inventor:
Zensaku Yamamoto,
Susumu Sato,
Shujiro Ono,

Hiroshi Horiguchi, Muroran, Hokkaido;
Shozo Ariga,
Shogo Takaishi,
Hiroshi Sato, Tokyo (Japan)

Claimed priority:

Japan December 14, 1963 (38-67 288,
38-67 289, 38-67 290, 38-67 291),
of September 4, 1964 (39-50 761)

In the case of steel with a relatively high carbon content, so-called flaking also occurs as a surface defect, which is caused by hydrogen which escapes from the steel during or after the enamel is burned in.

As mentioned earlier, there will be certain surface imperfections caused by the carbon content of the steel. To the disadvantages involved too avoid, improved types of steel that can be enamelled are already known. For example, it has been suggested Use ultra-low carbon steel, which contains carbon With the help of a special steel manufacturing process below 0.03%, or by decarburization during tempering or by use a titanium-containing steel, in which the adverse effects of carbon through carbide formation of the added titanium can be reduced with the carbon.

The known, improved enamellable steels have good enamelling properties. When reducing the carbon content during the steel

709 689/379

3 4

production, however, increases the oxygen content of acid-soluble Al, and through an inner part, its does not return any smaller in proportion to the reduction in the carbon-C content before this heat treatment content, whereby a considerable amount is non-than that of the surface layer and between metallic inclusions generated in the steel and which is 0.04 and 0.15% C, as well as against the upper cold deformability of the steel is deteriorated. 5 surface layer an additional percentage of

Furthermore, such steel ages because of its nitrogen content, at least one of the additives Cr, Mn, Ti, V or its material content, while its mechanical inherent acid-soluble aluminum contains the additive percentage not less than 0.05% for, in particular the cold deformability Cr, are deteriorated, so that flow figures occur after the deformation 0.05% for Mn, 0.02% for Ti or V and not less. , Is in a conventional emaillierfähigen io than 0.003% of acid-soluble Al during steel, carbon s bei_welchem du ff rch addition of a content of the other elements in the surface element, such as titanium layer by Karbidjrildmig_gebjjnden and in the inner part is about equal.
is, "can""only" killed steel with low pro - In an advantageous further development of the invention, duklion yield can be used to keep the surface layer no more than 0.004% N degassing additive in suitable proportions to the 15, while only the inner part one to allow additional carbon content and the oxygen content in the percentage of one or more of the additional steel, the steel because of the substances Ti, V and acid-soluble Al contains, which is harder for Ti alloy elements and the cold deformability not less than 0.02%, for V is deteriorated not less than 0.02%. Furthermore, these are known and for acid-soluble Al is not less than 0.005%. Enameable steels are relatively expensive, zo Furthermore, only the inner part can with a nitrogen-Therefore it has been customary up to now, ordinary incontinence of the surface layer of no more than calm steel with low carbon content in the 0.004% an additional percentage of acid-main thing for usual enamelled If it contains soluble Al together with Ti and / or V, turn. which is not less than 0.001% for Ti, not less than

Furthermore, if the decarburization after the open- 25 0.01% for V and not less than 0.003% for acidic

If the Bund process is carried out, only steel sheets with soluble Al can be used. Such a steel sheet can after

less than 2 mm thick can be decarburized because of the implementation of a suitable heat treatment

Carbon removal with thicker steel sheets too many known type with a surface layer

Would cause trouble. less than 0.02% C and an inner part with more

The invention is considering the 30 as having 0.04% C. A particularly useful one Behavior of the carbides immediately below the steel - Process for producing such a steel surface, which the surface defects during the sheet metal, which in the usual way before he-enamelling of steel with low carbon rigidity of an unkilled steel melt the additional content cause the underlying knowledge that the substances are added and the solidified raw slab The surface layer ("fat layer") of a slab made from 35 sheet steel is rolled out according to FIG unkilled steel with low carbon content invention characterized in that the additional and a sheet metal hot-rolled from it on the basis of materials after a surface layer has solidified, entdes The cooking process has a lower content of the upper carbon that is to be formed during rolling, Nitrogen, phosphorus and sulfur as a surface layer that are added to the molten steel, the core part has that but when tempering and when the 40 is expediently the additives in the form Burning in the enamel of the carbon in one of a rod or in the form of granules or powder Surprisingly added to the surface layer in a steel pipe.

comes out of the core as seen in Fig. 3b since chromium, manganese, etc. is the conversion. Furthermore, the invention is based on the knowledge at the temperature of the steel from austenite to ferrite. that this diffusion of carbon decreases at 45, the proportion tends to be greater higher temperatures is stronger, especially if it contains such elements, stronger to an environment Temperature above the Aj transformation point. Transformation to austenite during tempering or during lies. Burning than that part, which is less

As mentioned at the beginning, bad elements occur when it contains. The one converted into austenite

Quiet steel with a low carbon content can dissolve much more carbon. That's why

different surface defects occur when tempering migrates on a steel sheet that has a larger amount

takes place above the Aj transformation point, because such elements only contain in the inner part,

the carbon to a considerable extent in that of the carbon from the surface layer into the core.

Surface layer of the steel diffuses. If there- vanadium, titanium, aluminum etc. show a similar

against tempering below the A ^ conversion behavior to carbon such as chromium, manganese,

point takes place, is the diffusion of carbon in the although with these substances no lowering of the

Surface layer slightly less. However, transition temperature could be related.

So far the surface defects of enamelled sheet metal have not been found

can be satisfactorily prevented. Furthermore, the still normalized will be most of the

Deep drawability of the steel decreased. 60 carbon and nitrogen content in the inner part

An enamelling steel sheet is concentrated according to the Er- (core part) so that its content in the

Finding characterized by a surface layer surface layer is lower. Therefore it is possible

of at least 0.05 mm thickness, which must be treated in a satisfactory manner prior to a usual surface defect

Avoid heat treatment of more than 0.15% C and after, which occur during enamelling

this heat treatment no more than 0.04% C 65 could reduce the diffusion of carbon from the

contains, as well as not more than 0.6% Mn, 0.01% Si, core is prevented from outside.

0.03% P or S, 0.006% N, 0.03% Cr or Ni, for a steel sheet according to the invention

0.001% of Nb, V or Ti and not more than 0.003% of a desirable thickness of the surface layer

greater than about 0.05 mm. This means that an excess of chromium, manganese, vanadium, titanium and acid soluble aluminum only in the underlying Part is present. However, too thin a surface layer could result in the Surface layer by oxidation during a conventional heat treatment before enamelling or is lost during descaling by sandblasting or acid treatment.

An enamelled steel sheet made from low carbon steel in its Core contain one or more of the special elements according to the invention in increased concentration has the following advantages:

1. Fewer surface defects on the enamel surface.

2. Higher tempering temperatures can easily be used for the cold-rolled rolling stock which results in better cold formability.

3. In the case of conventional enamelled steel sheet to which Ti, Nb, Zr or Sb is added, these are Elements evenly distributed in the steel. In contrast, the required amount is these elements are lower in the steel sheet according to the invention. Because according to the invention are contain these special elements only in the core of the steel sheet. This increases the cold deformability is improved and the manufacturing cost is reduced.

4. According to the invention, even for a relatively thick steel sheet of more than 2.0 mm thick a surface layer with a very low carbon content can be obtained, because the carbon from the surface layer easily through heat treatment in the core can be diffused and stabilized.

5. When Ti, Al, V, etc. are used as additives, the transformation point of α-iron increases to y-iron considerably, which is why it is possible to increase the baking temperature, as well as possible To reduce the stresses that can occur during baking.

The mentioned advantages can be achieved by the method according to the invention in that a Ingot or slab is produced in the following manner.

After molten steel has been poured into a mold, the steel is left for a few minutes cook then manganese, chromium, aluminum, titanium or vanadium or an alloy thereof is put in In the form of bars, powder or the like, together with or without a deoxidizer in the not yet solidified part of the slab given.

In the following, the production of a slab with a thickness of 700 to 800 mm will be explained in more detail will.

If the element or alloy to be added is added too early, none will be added sufficiently thick surface layer formed. Therefore, the surface quality cannot be satisfactory in the steel sheet are expected. If, on the other hand, the addition is made too late, the alloying Elements in the core part not evenly distributed. It is therefore appropriate to use the element or add the alloy about 3 to 10 minutes after casting, when the thickness of the solidified surface layer is about 30 to 70 mm.

For example, when steel sheet is made from a slab of 800 mm thickness, which is a Has an edge layer of 40 mm thickness, the steel sheet with a thickness of 2 mm has a 0.1 mm thick surface layer, while a steel sheet of 1 mm

ίο have a 0.05 mm thick surface layer would.

As the shape of the element or alloy to be added, a rod is preferred in view of the uniform distribution of the additive in the core part of the slab, although an additive of powder or granules, which substances may be filled in a steel pipe with a wall thickness of less than 1 mm , can also be beneficial.
If the additive is introduced into the molten core part in the form of a rod, a rod diameter of 20 to 30 mm is recommended. to ensure its dissolution and fine distribution.

Too short lengths of the rod result in a resolution of the addition only in the upper part of the block, thereby causing poor distribution in the core part. Therefore preferably a stick of about 40% of the height of the block using.

In Fig. 1 is an appropriate arrangement of the Rods shown in which the slab shape 1, the solidified surface layer 2 of the molten steel, which is not Solidified steel melt 3 and added rods 4 made of the elements or alloys mentioned are shown are.

Fig. 2a shows the distribution of acid-soluble aluminum in the raw slab for cold-rolled sheet according to the invention, using aluminum in the form of a rod 26 mm in diameter and 1400 mm in length. In Fig. 2 also shows the distribution of acid-soluble aluminum in unkilled steel with a low carbon content (Fig. 2b) and in Al-killed steel for deep drawing (Fig. 2c), which were produced by a method known for raw slabs. A comparison of the figures shows that the surface layer of a steel sheet according to the invention contains almost no acid-soluble aluminum and that the acid-soluble aluminum, on the other hand, is evenly distributed in the core part.
F i g. 4 a shows the distribution of manganese in a steel sheet according to the invention, a granulated Fe-Mn alloy being accommodated in a steel tube with a wall thickness of 0.6 mm, a diameter of 20 mm and a length of 1500 mm and introduced in the manner already mentioned. 4b shows the manganese distribution in unkilled steel with a low carbon content, which was produced for comparison by conventional production methods for raw slabs. A comparison shows that in the sheet according to the invention the manganese is concentrated in the core, while the content in the surface layer is considerably lower.

The steel for the production of steel sheets according to the invention can be in a converter, a Siemens-Martin furnace or in an electric furnace, etc.

getting produced.

The invention is to be explained in more detail using the exemplary embodiments shown in the drawing will. It shows

7 8

F i g. 1 is a schematic illustration which shows the weight of the raw slab 14 400 kg

Explanation of the addition of aluminum to the cross-section of the raw

Production of steel slabs according to the invention slab 1400 mm width and

serves, 800 mm thickness

ι? Λ ^{& 2a} ' ^2b .T ^{d 2c} the distribution of acidic 5 _{Height of the} raw slab ... 1800 mm
soluble aluminum in preliminary slabs for cold rolled sheet according to the invention as well as for common unused aluminum quenched steel sheet with a low carbon content
or Al-calmed deep-drawable sheet steel, number 4

3a and 3b show the structure of the cold-rolled io _ .. _n ", _. ,

enamelled steel sheet according to the invention and ^size , ² J ^mm diameter,

cold- ir -T ^ ο w <nn / Λ produced by a conventional process

rolled non-calmed steel sheet, both of which at uewiciit l, l kg puu g / t)

74O ⁰ C annealed for 3 hours, then 4 minutes time of onset

long to 830 ⁰ C, almost at the firing temperature 15 of ^the aluminum rods ... 3 minutes after the

held during enamelling and poured into salt water

were frightened

F i g. 4 a and 4 b the manganese distribution in cold F i g. 1 shows schematically the position of the used Rolled enamelled sheet steel according to the aluminum bars. After training an invention when using manganese as well as in such a rigid surface layer 2 with a thickness of 35 to 40 mm, the aluminum rods were in the. Steel calm Sheet steel, melt 3, introduced 1300 mm deep.

F i g. 4 c the structure of the cold-rolled steel sheet When analyzing cold-rolled steel sheet with

in Fig. 4a, which at 720 ⁰ C for 6 hours annealed 0.8 mm thick made of cast slab resulted

4 minutes at the stoving temperature 25 the following values:

kept almost the same temperature of 830 ° C and.

then quenched in salt water, C 0.06 0 / Mn 0.28%, Si 0.01%, P 0.009%,

5a shows the chromium distribution over the sheet thickness ^ 0.015 / ₀ ;

of a cold rolled steel sheet according to the invention, total N 0.0021%; acid soluble Al: 0.001%

to which chromium was added, 30 in the surface layer, 0.008% in the core part.

5b shows the structure of the same steel sheet

Annealing for 3 hours at 740 ^° C., holding for 4 minutes at the following mechanical properties were found

83O ⁰ C and quenching in salt water, after the three-hour annealing at 74O ⁰ C:

F i g. 6 the structure of enamellable cold yield strength 19 2 kg / mm ²

rolled steel sheet according to the invention, with aluminum 35 z _U af _es activity 33 ^ kg / mm ⁸

minium and chromium were used together, τννίηιτη »4fi '? ° /

which sheet was annealed at 720 ° C for 3 hours 11 1 mm

-, - _,. ₁ -. f ^ f-ndy-i t 1, 1 J-illUllaCU. ™ VV CIL Xl) I lili.ll

and held at 850 C for 3 minutes, resulting in hardness RB 46 2

corresponds almost to the stoving temperature, after which '

quenching in salt water was carried out, 40 for a comparison with the product in example 1

Fig. 7a is a photograph of the surface formation of unkilled steel from the same batch as

of ordinary unkilled steel sheet with low in Example 1 by ordinary methods of manufacture

Carbon content, on which two layers of enamel are processed on a raw slab. The raw slab was

were carried, so that 800 g (55 g / t) of aluminum granules

7b a receptacle 45 corresponding to FIG. 7a was added evenly during the casting, according to the surface finish of a steel sheet After the steel was allowed to boil for 21 minutes, of the invention, the central part of which is aluminum, the cover (700 kg) was placed on the block head is, and laid. -

7c and 7d recordings of the surface ■ ",", ■,

Characteristics of normal, unquenched sheet steel 50 ^ Da ₈ cold-rolled sheet steel of 0.8 mm

and a steel sheet according to the invention, the ^{thickness of which had the} following analysis:

central TeU chromium is added, both C 0.04%, Mn 0.27%, Si 0.01%, P 0.011%,

Sheets have two layers of enamel. S 0.017%;

“Total N 0.0023%;

OO

B ice ρ ie 1 1 SoIM : 0.001% in the surface layer and 0.001%

in the core layer.
The raw slab was made from molten steel

from an oxygen converter below the following yield point 23.1 kg / mm ²

produced under the conditions: 60 tensile strength. 33.0 kg / mm ²

Elongation 45.5%

Analysis of the steel melt (%) Erichsen value 10.9 mm

Hardness RB 48.5

C 0.07, Mn 0.28, Si 0.01, P 0.009, S 0.014.

For deoxidation in the ⁶ S ^{the two} cold-rolled sheets mentioned above

Al added to pan .. 60 g / t were added for 3 hours at 740 ° C and for 4 minutes

heated to 830 ° C, which approximates the stoving

Tapping ^{temperature corresponds to 161O 0} C temperature, and then drained in salt water

9 10

frightens. Structural images are shown in Fig. 3a and 3b. Another advantage can be seen in the fact that the pickling, speed can be selected to be about twice as high which was produced from the comparison slab. Steel sheets.

From this it is readily apparent that the surface layer has a hardening structure of a steel with a decrease of 0.9% after annealing and cold re-rolling, the steel sheet according to the high carbon content, while the core invention has 1 hour at 100 ⁰ C aged and the tensile part has a ferrite structure. Most of the trials carried out. The results showed that the carbon content diffused from the core so that the yield point elongation is practically non-existent in the surface layer. 3a shows the structure io.

of a steel sheet according to the invention. A phase example 2
with high carbon content is in the surface

layer of sheet metal is practically non-existent. In contrast, steel of the following composition of a

If the carbon concentration is present in the core, the oxygen top-up converter was placed in a mold of the

where a relatively large amount of aluminum is dissolved, so that it is cast in the same size as in Example 1,

the surface layer has a ferrite phase with very low. . _,,

owns carbon content. ^Anal y ^{se of the melt:}

With the enamelling steel according to the Er- C 0.07%, Si 0.01%, Mn 0.26%, P 0.012%,

enamelling tests under the same S 0.015%, N 0.0016% were found.

Conditions as with the usual, unsettled ao tapping temperature 161O ⁰ C

Sheet steel from the same batch with the following results: deoxidation in the pan. "... Al additive 80 g / t carried out:

Cover enamel layers 2 ^{After a cooking time of 4} minutes and

Grundemaillierung. '.''.'.'.'.'.'.'.'.'.'.'.'.'.'. 3.7 g / dm * ^ vng ^d f ^r solidified peripheral layer, a granu -

Firing temperature 870 ° C * ⁵ lated alloy of Fe-Ti. With 45% titanium and Fe-V

Burning time 10 minutes. ⁵⁰ % vanadium each in a steel tube of

Top enamelling. Titanium white J3 mm in diameter, 1500 mm in length and 0 6 mm

Wall thickness in the non-solidified part of the melt

7 a and 7 b show photographs of the surfaces as introduced in Example 1.

of the two enamelled sheets. On the surface of the 30 An analysis of two hot rolled sheets of

known unkilled sheet metal are vesicles 3.2 mm thick, resulting from those described above

on the other hand, which were produced in the case of the sheet according to the raw slab, resulted in the following

finding are not available. Values:

Mn

Sheet containing Ti

Sheet containing V,

Sheet containing Ti

Sheet containing V

0.050 ~ 0.026

0.045 ~ 0.026

0.27

0.28

Ti

0.016
~ 0.010

0.018
~ 0.012

0.018
~ 0.010

0.019
~ 0.009

0.0026 ~ 0.0018

0.0027 ~ 0.009

Traces in the surface layer, 0.18 to
0.010 in the core

traces

V
traces

Traces in the surface layer, 0.03-0.025 in the core

These hot-rolled sheets were cold-rolled to 0.8 mm in thickness and tempered at 720 ° C. for 6 hours. Measured values of the mechanical properties of the tempered sheets belonging to the central part of the block are shown below.

invention

Containing Ti V containing sheet sheet 11.40 11.58 36.91 37.05 16.8 16.05 32.7 31.7 51.4 52.5 48.1 49.3 ■ 38.0 39.1

Non-calmed sheet steel for comparison

Erichsen value (mm) ...

C. C. V. (mm)

Yield point (kg / mm ² ). Tensile strength (kg / mm ² )

Stretching amount (%)

Elongation (%) ....; ... hardness (RB)

10.78

37.30

20.9

33.0

63.3

44.4

42.1

709 689/379

As can be seen from the table above, the Erichsen values, C.C.V. values and elongation values are better achieved with steel sheets containing Ti or V according to the invention than with unkilled ones Steel sheets made from the same melt and the same heat treatment although the tensile strength is practically the same. It can be seen from this that metal sheets have better mechanical properties according to the invention.

With the mentioned sheets according to the invention, enamelling tests were carried out under the same conditions as carried out according to Example 1 with the above-mentioned unkilled steel sheets. In the Blisters appeared on unskilled steel sheets, which was not the case with sheets according to the invention. The tests carried out to test the usefulness of enamel goods on the basis of 200 steam pots Comparative tests with metal sheets according to the invention showed that no bubbles occurred on any of the parts.

Example3

Steel from a converter with the following composition was used:

Analysis of the melt:

CO, O6%, Si 0.01%, Mn 0.22%, P 0.008%, S 0.011%, N 0.0018%.

Tapping temperature 1600 ⁰ C

Deoxidation in the pan .. Al addition: 80 g / t

This melt was made under the following conditions potted:

Weight of the raw slab .... 14 400 kg

Cross-section of the slab .... 1400 mm width and

800 mm thick

Height of the slab 1800 mm.

After the formation of a solidified surface layer approximately 60 mm thick after boiling for 7 minutes was a granulated alloy of Fe-Mn with 78% Mn in a steel tube of 20 mm diameter, 1500 mm length and 0.6 mm wall thickness in the residual melt like the aluminum rod in FIG. 1 introduced.

An analysis of a cold-rolled sheet 0.8 mm thick made from the above raw slab gave the following results Values:

was then quenched in salt water. In this picture, the black parts indicate the hardened structure that previously corresponded to austenite ^{at 830 ° C.} The Fe-C phase diagram shows that this hardened structure contains about 0.2% carbon. The picture shows that the surface ^{layer remained as ferrite even at 840 °} C. and that the carbon content of this layer is below about 0.02%, which is the solubility limit of

ίο there is carbon in the ferrite.

It was also found that even carried out in the structure of the above annealed sheet after heating to 83O ⁰ C and air cooling no precipitation of carbides in the surface layer and that a precipitation of carbides occurred only in the core.

Example 4

The melt of the same ladle as in Example 1 was in a mold of the same size as in Example 1 was poured and after the formation of a solidified edge layer of about 60 mm thickness a granulated alloy of Fe-Cr with 65% chromium in a steel tube of 20 mm diameter, 1500 mm Length and 0.6 mm wall thickness introduced into the residual melt according to Example 1.

The analysis of a hot-rolled sheet with a thickness of 2.3 mm gave the following values:

C 0.06%, Si 0.01%, Mn 0.021%, P 0.010%, S 0.013 _^0/0, Cr 0.011% in the surface layer, 0.072% in the core.

The distribution of chromium over the sheet thickness of the cold-rolled sheet is shown in FIG. 5a.
There were the following mechanical properties of the cold-rolled sheet of 1.0 mm thickness that was produced from the above hot rolled sheet and annealed for 3 hours at a temperature of 74o C ^0:

Yield strength 21.3 kg / mm ³

Tensile strength 33.0 kg / mm ²

Elongation 43.7%

Erichsen value 10.2 mm

Hardness RB 45.1.>

The microstructure of the above annealed sheet when heated to 830 ° C. for 4 minutes and then Quenching in salt water according to the example in Fig. 1 is shown in Fig. 5b.

C 0.06%, Si 0.01%> Mn 0.21% in the surface layer, 0.32% in the core part, P 0.009%, S 0.013%, acid-soluble Al 0.001%.

The distribution of manganese over the sheet thickness of the sheet according to the invention and the ordinary Unkilled steel sheet is shown in FIG. 4 a and 4 b shown.

After tempering for ⁶ hours at 720 ° C., the following mechanical properties were found for the rolled sheet according to the invention:

Yield strength 19.3 kg / mm ² . ^6o

Tensile strength 32.9 kg / mm ²

Elongation at 500 mm measuring length 45.2%

Erichsen value 10.7 mm

Hardness RB 44.2.

Fig. 4c shows a micrograph of the sheet that has been annealed at 83O ⁰ C for 4 minutes, which temperature is approximately equal to the baking temperature, and

Example 5

A melt with 0.08% carbon, 0.01% silicon, 0.25% manganese, 0.012% phosphorus, 0.012% Sulfur (melt analysis) was poured into a mold for 14.4 t. After cooking for 3 minutes 20 kg of Fe-Cr and 1 minute later aluminum were added as in Example 1. Two aluminum bars were used in the center of the residual melt.

An analysis of the cold rolled sheet 0.8 mm thick made from this raw slab gave the following values for the sheet metal that was at 720 ° C Glowing for 3 hours "was:"

Analysis:

C 0.08%, Si 0.01%, Mn 0.25%, P 0.013%, S 0.014%, total N 0.0023%, Cr 0.010% in of the surface layer and 0.051% in the core part, acid-soluble Al 0.001% in the surface layer and 0.005% in the core part.

Claims (1)

13 14 Mechanical properties: and after this heat treatment no more than Yield strength 21.1 kg / mm ² °> ⁰⁴ ° / o C and not more than 0.6% Mn, Tensile strength 34 0 kg / mm * °> ⁰¹ ° / o Si, 0.03% P or S, 0.006% N, 0.03% Cr Elongation 45 8 ° / ₅ or Ni, 0.001% Nb, V or Ti and not more than Erichsen value .................... 10 ^ 9 mm ° ' ⁰⁰³ ° / <> acid-soluble Al, and by an internal clarification j ^ g 4-7 3 part, its C-content before this heat treatment not smaller than that of the surface layer For comparison purposes, unkilled steel of is and is between 0.04 and 0.15% C, as well as the same batch, were produced using customary processes. In this case an additional 25 minutes was boiled and a 10 percent of at least one of the additives small lids were placed on the block in order to interrupt the decooking of the Cr, Mn, Ti, V or acid-soluble aluminum. . holds, the additional percentage of not small investigations of a cold rolled sheet of than 0.05% for Cr, 0.05% for Mn, 0.02% for Ti 0.8 mm thickness from this comparative material, which or V and not less than 0.003% for acid annealing at 720 ° C for 3 hours resulted in: 15 is soluble Al, while the content of the analysis · remaining elements in the surface layer and / -. ÄrMiw o · ΛΑ-tn / λ κ ηΛίη / η c \ maim ^m ^ ^em inner part is about the same.
C 0.04%, Si 0.01%, Mn 0.23%, P 0.014%, ₂ sheet steel according to claim 1, characterized in that S 0.015%, Cr 0.010% in both the surface layer indicates that the surface layer is not as well as in the core zone, 20 contains more than 0.004% N and that the inner part acid-soluble Al 0.001% both in the edge- only an additional percentage of one or layer as well as in the core zone. Tf ¹ "^ I ^Z _f ^usa H ^{stofi [e} J] ^{'Y un?} Acid soluble Contains Al, which is not less than 0.02% for Ti and not less than 0.02% for V Mechanical properties: not less than 0.02% and for acid-soluble Al Yield point 25.0 kg / mm ^{2 25 ni <} ; ^{hi is} finer than 0.00f »%. Tensile strength 34.4 kg / mm ² , ³ steel sheet according to claim 1, characterized Elongation 43 9 ° / indicates that the surface layer is not Erichsen value ΐο'ό mm ^{more than} °> ⁰⁰⁴ ° / o N and that the inner part Hardness RB 49 0 ^{only an} additional percentage of acidic '30 soluble Al together with Ti and / or V From Fig. 6, the structure 3 is holding a cold-rolled, of not less than 0.001% of Ti, not sheet, the 3 hours, according to the invention can be seen less than 0.01% for V and not annealed smaller than at 72o ⁰ C, Is at 0.003% for acid soluble Al for minutes.
85O ⁰ C was held, which temperature is almost equal to 4. Steel sheet according to one of the preceding the baking temperature, and then in salt 35 claims, characterized in that the upper water was quenched. surface layer less than 0.02% C and the The test experiments to determine the practical inner part contains more than 0.04% C.
Utilization of the sheet metal for steam pots, which 5. Process for the production of an enamelling according to the invention was produced, showed no bubbles in capable steel sheet with a composition of all 130 parts. 40 according to one of the preceding claims, at before the solidification of an unsettled steel claims: melt the additives added, thereby characterized in that the additives according to 1. Enamelled sheet steel, g e k e η η - are added to the solidification of a surface layer. is characterized by a surface layer 45 of at least 0.05 mm thick, the documents considered before any: usual heat treatment no more than 0.15% C German Auslegeschrift No. 1036 297, For this purpose 2 sheets of drawings 709 689/579 11.67 © Bundesdruckerei Berlin