EP2948572A1

EP2948572A1 - Methods for creating a flat steel product with an amorphous, partially amorphous or finely crystalline structure and flat steel product of such a type

Info

Publication number: EP2948572A1
Application number: EP14701377.5A
Authority: EP
Inventors: Dorothée DORNER; Christian Höckling; Harald Hofmann; Matthias Schirmer; Markus DAAMEN
Original assignee: ThyssenKrupp Steel Europe AG
Current assignee: ThyssenKrupp Steel Europe AG
Priority date: 2013-01-25
Filing date: 2014-01-24
Publication date: 2015-12-02
Also published as: EP2759614A1; EP2759614B1; BR112015017627B1; BR112015017627A2; WO2014114756A1; KR102203018B1; CN105143491A; KR20150110729A; JP6457951B2; US10730105B2; US20150360285A1; CN105143491B; JP2016507383A

Abstract

The invention provides methods for creating a 0.8 - 4.5 mm thick steel strip with an amorphous, partially amorphous or finely crystalline structure with grain sizes in the range from 10 - 10 000 nm and also a flat steel product of a corresponding type. According to the invention, for this purpose molten steel is cast in a casting device (2) to form a cast strip (B) and cooled at an accelerated rate. Apart from Fe and contaminants that are unavoidable for production reasons, the molten material contains at least two further elements from the group "Si, B, C, P". The following applies for the contents of these elements (in % by weight): Si: 1.2 - 7.0%, B: 0.4 - 4.0%, C: 0.5 - 4.0%, P: 1.5 - 8.0%. With a corresponding composition and a structure of a corresponding type, a flat steel product according to the invention has a hardness HV0.5 of 760 - 900.

Description

Process for producing a flat steel product with an amorphous, partially amorphous or fine-crystalline microstructure and steel fiber product obtained in this way

The invention relates to methods for producing a

Flat steel product having an amorphous, partially amorphous or finely crystalline structure, the fine-crystalline structure having particle sizes in the range from 10 to 10000 nm, and a flat steel product having an amorphous, partially amorphous or fine-crystalline structure of this type.

According to a first variant of the method, a molten steel in a casting device becomes a

poured cast tape and cooled accelerated.

According to another variant of the method, to produce a flat steel product having an amorphous, partially amorphous or fine-crystalline structure, a steel melt containing at least two further elements from the group "Si, B, C and P" in addition to iron and impurities which are unavoidable in terms of production

Casting device whose casting area on at least one of its longitudinal sides by a during the

Casting in the casting direction moving and cooled wall is formed, poured into a cast strip. In this case, the region of the casting device in which the cast strip is formed is referred to as the "casting region". From WO 2008/049069 A2 it is known that

Steel flat products of the type mentioned above can be produced by strip casting. In strip casting, the molten steel is cast with a casting device in which the casting region or solidification region in which the cast strip is formed is delimited on at least one of its longitudinal sides by a wall that is continuously moving during the casting process.

An example of such a close-to-the-ground,

continuous casting process or a casting device for producing a flat steel product is the like

called "two-roller caster", in the

Technical language also as "twin roller casting machine"

designated. In a two-roller casting machine

rotate in the casting operation two parallel to each other aligned casting rolls or casting rolls in opposite directions and limit in the region of their closest distance a casting gap defining pouring gap. The casting rolls are strongly cooled, so that the hitting them

Melt solidified to one shell. The

The direction of rotation of the casting rolls is chosen such that the melt and with it the shells formed from it on the casting rolls are transported into the casting gap. The trays entering the casting gap are compressed to the cast strip under the effect of sufficient banding force.

Another pouring device for strip casting is based on the principle of "belt casting" technology. In a casting casting casting machine, liquid steel is introduced via a feed system poured round casting tape. The direction of the tape is chosen so that the melt is conveyed away from the feed system. Above the lower first casting belt may be arranged a second casting belt, the

runs counter to the first casting belt.

Regardless of whether one or two casting tapes are provided, limited even in the above

Process at least one casting belt the mold through which the cast strip is formed. The respective casting belt is cooled intensively, so that with the

relevant casting tape in contact melt is solidified at the turning away from the feed system reversal point of the casting belt to form a band, which from the casting belt

can be removed.

The cast strip emerging from the respective casting device is drawn off, cooled and the

Forward processing forwarded. This further processing may include a heat treatment and a hot rolling. The particular advantage of strip casting here is that the steps following the tape casting can be completed in a continuous, uninterrupted sequence.

In the above-mentioned WO 2008/049069 A2 it is mentioned that steels used for the production of

Steel strips with an amorphous, partially amorphous or fine-crystalline structure are suitable, alloys based on iron and one or more elements from the group "B, C, Si, P, Ga" may be, in addition to these elements in addition contents of Cr, Mo, W, Ta, V, Nb, Mn, Cu, Al, Co and rare earths may be present. From alloys composed in this way, tapes cast by strip casting are to be produced, which are fine-grained, nanocrystalline or nearly

have nanocrystalline structure in which more than 90% of the grains are 5 .mu.m to 1 m in size, the melting point of the steel making up the cast strip being in the range of 800-1500.degree. C., the critical one

Cooling rate of the steel is less than 10 ⁵ K / s and the cast strip contains α-Fe and / or γ-Fe phases.

The considerations reproduced in WO 2008/049069 A2 are limited to a discussion of those for the

Production of cast strip with an amorphous, partially amorphous or fine-crystalline microstructure expedient steps.

In addition to the prior art explained above, US Pat. No. 6,416,879 B1 discloses an Fe-based amorphous material

Thin strip with a thickness of 10-100 μm, which is available in atomic% 78-90% Fe, 2-4.5% Si, 5-16% B, 0.02-4% C and 0.2-12%. P contains and should have optimized magnetic properties. For the production of

Thin bands will be a suitably compound

Melt under laboratory conditions on a fast

cast rotating cooling roller, solidifies there and is then removed from the roller. In this way, casting speeds are achieved, which are in the range of about 25 m / s. It is also mentioned that the production of such a thin strip should also succeed in a two-roll casting machine. However, more are missing Explanations. Also, it is not apparent from this prior art, as the known approach in the industrial practice, in the larger sheet thicknesses and other properties of the resulting tape are desired, could be implemented.

A prior art similar to the prior art described above is known from US 4,219,355. There is also the goal of producing a thin, film-like tape with a thickness of 30 - 100 μιη, which has optimized magnetic properties. For this purpose, also in this case, a suitably composed melt is poured onto a rotating roll, where it is cooled at a rate of 10 ⁵ - 10 ⁶ ° C / s to produce an amorphous structure. It remains just as open as this should be implemented on a large scale in practice, if

Flat products of greater thickness and with another

Requirement profile should be generated.

From DE 10 2009 048 165 AI is finally a

Method for strip casting a steel with a

Chromium content of more than 15 wt .-% is known in which a molten steel is poured in a horizontal strip caster, which comprises a melting furnace, a ladle and a conveyor belt for receiving and cooling of flowing out of the ladle liquid steel strip. The thickness of the steel strips produced in this way is 8 - 25 mm. What cooling rates can be achieved in such a system and if they would be suitable, for example one of the above explained steel flat products remains open.

Against the background of the prior art explained above, therefore, the object of the invention was to provide practical methods for the production of flat steel products which have an amorphous,

have teilamorphes or fine-grained structure.

In addition, a flat steel product should be specified, which can be produced inexpensively in a practical way. As a flat steel product is understood a cast or rolled steel strip or sheet and derived therefrom blanks, blanks or the like.

A according to the invention this object solving method is given in claim 1.

With regard to the flat steel product, the

inventive solution of the above-stated object is that such a flat steel product has the features mentioned in claim 15.

The various embodiments of the invention mentioned here are based on the common idea that by casting methods close to the final dimensions

Produce flat steel products, which consist of amorphous, teilamorph or nanocrystalline or fine crystalline solidifying steels. Here are the

According to the invention respectively processed steels so

composed, that the desired structure state safely set. If related here with

Steel alloys "%" statements are always to be understood as "% by weight", unless otherwise stated.

At the same time, the invention mentions operating conditions which are more adequate for practical use

Reproducibility from a steel containing, in addition to iron and unavoidable impurities, at least two further elements from the group "Si, B, Cu, P", cast cast strips of amorphous, partially amorphous or fine crystalline structure.

The inventive method for generating a

Steel bands with an amorphous, partially amorphous or

fine crystalline microstructure provides that the molten steel next to iron and production-related unavoidable

Contains at least two other elements from the group "Si, B, C, P". In this case, according to the invention, the contents of the respectively at least two elements from the group "Si, B, C, P" are in each case in the following ranges (in% by weight):

Si: 1.2 - 7.0 o,

o /

B: 0.4 - 4.0 o.

O

C: 0.5 - 4.0 o,

O

P: 1.5-8.0 0,

Ό

In principle, such alloys are preferred according to the invention, in which, in addition to the respective

production-related unavoidable, but with respect to the properties of the invention produced Steel flat products ineffective constituents in addition to iron only two other elements of the group "Si, B, C, P" are present in the inventively given levels. In such alloys are then in steel next to Fe and unavoidable impurities only the

Alloy element pairs Si and B, Si and C, Si and P, B and C, B and P or C and P are present. so

Composite steel alloys are particularly suitable for amorphous or teilamorphe solidification.

If necessary, you can do this within the

According to the invention specifications the said alloy pairs are supplemented by one or two other alloying elements of the group "Si, B, C, P". It is equally possible that the alloying elements of the group "Si, B, C, P", which are not within the specifications according to the invention, although present in measurable levels, where they may have an effect, but in which they at most subordinate contribute to the formation of the invention sought after structure. In other words, according to the invention, in each case two elements from the group "Si, B, C, P" must be present in the levels specified in accordance with the invention in a product for the production of flat steel product according to the invention, which is not

excludes that the other elements of the group "Si, B, C, P" are present in levels that are outside the specifications of the invention. A presence of an alloying element of the group "Si, B, C, P" which is in each case outside the specifications according to the invention is possible in particular if its content is below the lower limit prescribed according to the invention for the content of the relevant element. The widest composition of a steel according to the invention thus comprises as obligatory constituents at least two of the elements boron, silicon, carbon and phosphorus as well as the remainder iron and unavoidable impurities. These elements prove to be particularly advantageous because they can be procured at relatively low cost. With the contents of these elements mentioned in the claims, the inventive

Production method reproducible production of a steel product with an amorphous, partially amorphous or fine crystalline structure. A flat steel product produced according to the invention has a finely crystalline microstructure with particle sizes in the range from 10 to 10,000 nm, it being possible in practice to regularly produce flat steel products whose grain sizes are limited to a maximum of 1000 nm.

C in contents of up to 4.0 wt .-% promotes in

Steel flat products produced according to the invention

Ämorphisierung of the material. In order to surely achieve this effect, the C content can be set to at least 1.0% by weight, especially 1.5% by weight.

Practical adjustments of the contents of Si, B, C and P result for the practice if the Si content% Si is 2.0% by weight <% Si <6.0% by weight, in particular 3, 0 wt .-% <% Si <5.5 wt .-%, if for the B content% B is 1.0 wt .-% <% B ^ 3.0 wt .-%, in particular

1.5 Ge .-% <% B <3.0 wt .-%, if for the C content% C is 1.5 wt .-% ^% C ^ 3.0 wt .-% or if for the P content% P is 2.0% by weight P% 6.0% by weight. It may be convenient, each one or more of the elements Si, B, C and P are added in the specified narrow confined levels, while the other elements of the group "Si, B, C, P" are added within the maximum allowable according to the invention. Similarly, it may be appropriate to each of each in

contents present according to the invention admit existing elements in the narrower limits specified here.

Although it is considered advantageous according to the invention, the group of alloying elements of a

According to the invention, in addition to Fe and unavoidable impurities, it may be limited to Si, B, C and P for certain properties of the resulting steel

Flat steel products be useful to the steel optionally one or more of the elements from the group "Cu, Cr, Al, N, Nb, Mn, Ti, V" admit. The purpose

according to the invention in each case

Salary ranges are (in% by weight):

Cu: up to 5, 0%, in particular up to 2.0 Q,

Cr: up to 10, 0%, in particular up to 5.0 o

AI: up to 10.0%, especially up to 5.0 o

o /

N: up to 0.5%, in particular up to 0.2 o

Nb: up to 2.0%,

Mn: up to 3.0%,

Ti: up to 2.0%,

V: up to 2.0%.

The addition of Cu can increase the ductility of the

Material to be increased, whereas the effect of Cr mainly in an improvement of Corrosion resistance is. Also, the addition of Al increases the corrosion resistance, but also has a supporting effect on the formation of an amorphous structure. N can be considered as a possible substituent for C. Thus, the presence of N, as well as higher C contents, promotes the enhanced formation of an amorphous structure.

In order to be able to use the positive influences of the optionally added alloying elements Cu, Cr, Al and N, the molten steel can in each case optionally (in% by weight) at least 0.1% Cu, at least 0.5% Cr, at least 1.0% AI and at least 0.005% N included.

The steel alloy according to the invention can be used in the steel industry and comparatively

inexpensive alloying elements as

Compulsory components are produced.

Due to the high content of "light" elements, considerable lightweight advantages over conventional steels are conceivable due to their reduced density and high strength.

Typical cooling rates with which it succeeds

According to the invention to produce alloyed flat steel product with an amorphous, partially amorphous or fine crystalline structure, are in the range of 100 - 1100 K / s.

Surprisingly, it has been shown that it can be realized with such even on an industrial scale

Cooling rates is possible, bands with larger thicknesses, as in the above-mentioned state of Technique are provided to produce reliable with the desired structure.

In accordance with the above explanations, a variant of the method according to the invention for producing a steel strip with an amorphous, partially amorphous or finely crystalline structure is based on the fact that a

According to the invention composite molten steel is poured in a casting device into a cast strip whose casting region, in which the cast strip is formed, is formed on at least one of its longitudinal sides by a moving during the casting operation and cooled wall. The casting area

limiting, moving in the casting operation wall may be formed in particular by two counter-rotating casting rolls or a moving during the casting operation in the casting direction band. According to the invention, the molten steel is cooled by contact with the moving wall with at least 200 K / s.

The explanations given here apply to

Composition of the steel according to the invention for all the inventive methods presented here as well as for a flat steel product according to the invention.

The formation of the desired structure of the

Flat steel product can be ensured by the fact that the rapid cooling in practice to below the glass transition temperature T _{G of} the respective steel

is carried out. In this way, an amorphous or partially amorphous microstructure is first formed. On the basis of this structure can then by means of a subsequent heat treatment above the

Crystallization temperature T _x by the resulting nucleation and crystallization a fine crystalline structure are produced. These

The procedure has the advantage that the fine granularity can be set very precisely, with a very homogeneous particle size distribution with very little due to the large number of crystallization nuclei forming

Fluctuation range sets.

In order to ensure that the cast strip is cooled even after leaving the respective casting area in a sufficient for the formation of an amorphous or partially amorphous structure speed to the critical glass forming temperature of each processed steel, the rapid cooling of the cast strip starting in the casting area after Exit from the casting area will continue. The continued cooling is advantageously in the

Immediate connection to the exit from the

Casting area, so as far as possible

continuous accelerated temperature decrease in the

is guaranteed cast tape until the desired structure state is reached.

For this purpose, an additional cooling device can be provided which directly adjoins the casting area of the casting device used for casting the cast strip

connected. With such a cooling device, the molten steel can safely with the cooling rate according to the invention predetermined to below the glass transition temperature T _G. be cooled to an amorphous or partially amorphous

To produce microstructures in the cast steel flat product. In this case, the additional cooling device ensures that in cases where it is in the casting of the

Casting itself has come through the contact with the moving and cooled wall of the casting only to an insufficient heat dissipation, the

Cooling of the band is continued after the casting area so quickly that the microstructure state to be generated according to the invention is reliably achieved.

Another advantage of the additional, subsequent to the casting device cooling is that with such a cooling a special

adjusted cooling curve controlled varies. This can be useful when deliberately cast strips with a teilamorphen or fine crystalline structure as

Result of the casting and cooling process to be obtained. Thus, the cooling can be carried out so that the glass transition temperature T _G accelerates, but is not cooled in a sufficient for the expression of a fully amorphous structure speed.

Alternatively, the cast strip may indeed be cooled accelerated according to the specifications of the invention, but this cooling before reaching the

Glass transition temperature T _G of each processed steel are terminated. This way represents a first possibility to produce a predetermined, fine-crystalline structure in the resulting flat steel product. The fine crystalline structure is here directly from the Melt formed by one over the additional melt

Cooling controlled crystallization is allowed.

Another way to produce a flat steel product according to the invention with a fine-crystalline structure is to first produce a ribbon with an amorphous or partially amorphous microstructure, which is then melted by an annealing process and crystallization caused thereby

fine crystalline state is transferred. The peculiarity of this procedure is that the

Crystallization takes place at a plurality of crystal nuclei and therefore the forming crystal grains are distributed very uniformly in the material.

The crystallization temperature T _{x, which} is important for the expression of the finely crystalline microstructure, is in the

Average about 30 - 50 K above the

Glass transition temperature T _G of each processed

Steel. For the preparation of an inventive

Flat steel product with amorphous or teilamorphem microstructure, it is therefore necessary when cooling the melt, the temperature T _G as fast as possible with a

Cooling v> v _crit to go below, where Vkrit s is inventively 200 K /. In this way, the amorphous state of the steel is "frozen", whereas when heated to a temperature above the temperature T _x heat treatment temperature uses the crystallization of the steel.

The inventively required if necessary additional cooling device can be designed so that a cooling medium is added directly to the cast strip becomes. This cooling medium may be water, liquid nitrogen or another equivalent

act effective coolant. Alternatively or

In addition, cooling gases, such as gaseous

Nitrogen, hydrogen, a gas mixture or water mist, are applied. Suitable cooling devices for this purpose are known from the prior art (KR2008 / 0057755A).

The critical to the achievement of an amorphous structure

Cooling speed depends, among other things, on the particular composition of the molten steel. Thus, it may be appropriate to provide the cooling rates of more than 250 K / s, more than 450 K / s or even more than 800 K / s.

By means of the method according to the invention, it is thus possible to selectively produce a band with an amorphous or partially amorphous microstructure alloyed in the manner according to the invention.

A particular aspect of finely crystalline steels of the type produced according to the invention is their ability to undergo structural superplasticity. Consequently, based on flat steel products according to the invention, the most complex component geometries can be achieved by grain boundary sliding operations at elevated temperatures (thermal activation).

being represented.

As mentioned above, one looks especially

reliable process of generating a

Steel flat product with fine crystalline structure before that emerging from the casting gap of the pouring device and optionally additionally cooled afterwards cast strip has an amorphous or teilamorphes structure and that the cast and thus created band then at least one of the

Crystallization temperature Tx of the respective steel corresponding annealing temperature T _G i _üh annealed until the desired structural state is reached. Within lying within the specifications of the invention

Steel compositions are suitable for this purpose annealing temperatures _G i _ü 500 - 1000 ° C. To get in

to achieve finely crystalline microstructure, are there,

depending on the particular concretely chosen

Composition typically annealing times of 2 s - 2 h sufficient.

The belt speeds with which the cast strip emerges from the casting gap are in practice

typically in the range of 0.3-1.7 m / s.

The strip thicknesses with which the cast and cooled strip according to the invention leaves the casting gap are typically in the range from 0.8 to 4.5 mm, in particular 0.8 to 3.0 mm.

After casting the strip and optionally additionally cooling thereafter, the cast strip may be subjected to hot rolling in which the hot rolling start temperature should be 500-1000 ° C. By inline on the casting and Äbkühlvorgang

Following hot rolling steps can on the one hand the desired final thickness of the tape and on the other hand

Surface texture set as well as the

Microstructure can be optimized by, for example, in poured state still existing cavities are closed. In addition, in order to maintain an amorphous or partially amorphous state of the cast strip, the hot rolling may take place at a temperature in the range between the glass transition temperature T _G and the crystallization temperature T _x

hot rolling start temperature are hot rolled to the hot strip.

As pouring device for the implementation of

The method according to the invention is suitable, for example, for a two-roller casting device whose revolving axes rotate relative to one another about axes parallel to one another and which form a continuously moving cooled longitudinal wall of the casting area in the casting direction in which the strip is formed.

The methods of the invention require only minor changes to existing methods and devices for the continuous production of close-to-scale flat steel products.

Hereinafter, the invention with reference to a

Embodiment illustrative drawing explained in more detail. The single figure shows schematically a device for producing cast strip in FIG

lateral view.

The plant 1 for producing a cast strip B comprises a casting device 2, which is constructed as a conventional two-roller casting device and

Accordingly, two against each other about axially parallel to each other and aligned at the same height axes XI, X2 comprises rotating rollers 3,4. The rollers 3, 4 are arranged with a thickness defining the thickness D of the cast strip B to be produced, and thus delimit on their longitudinal sides a casting area 5 in the form of a casting gap, in which the cast strip B is formed. On its narrow sides, the casting area 5 is sealed in a likewise known manner by side plates (not visible here), which are pressed against the end faces of the rollers 3, 4.

During the casting operation, the intensively cooled rollers 3, 4 rotate and in this way form longitudinal walls of a casting mold formed by the rollers 3, 4 and the side plates, which move continuously in the casting operation. The direction of rotation of the rollers 3,4 is in the direction of gravity R in the casting area 5 inside

directed, so that as a result of the rotation melt S is conveyed from a in the space above the casting area 5 between the rollers 3,4 pending melt pool in the casting area 5. In this case, the melt S solidifies when it touches the peripheral surface of the rollers 3,4, due to the there taking place intense heat dissipation to one shell. The adhering to the rollers 3.4 shells are by the rotation of the rollers 3,4 in the

Gießbereich 5 promoted and there under the action of a band-forming force K to the cast strip B

compressed. The effective in the casting area 5

Cooling power and the band forming force K are coordinated so that the continuously emerging from the casting area 5 cast strip B is largely completely solidified. In order to suppress crystallization effects, the cast strip B, following the casting area 5, enters a cooling device 7, which applies a cooling medium to the cast strip B, so that it cools further. The cooling by the cooling device 7 sets in the immediate connection to the casting area 5 and takes place so strong that the temperature T of the cast strip B decreases steadily until they are below the glass transition temperature T _G of each potted

Melt S is located. Any crystallization of the structure of the cast strip B is thus suppressed, so that it is still in an amorphous state on reaching the conveying path 6.

The emerging from the casting area ^' 5 band B is

initially discharged vertically in the direction of gravity R and then in a known manner in a

continuously curved arc deflected in a horizontally oriented conveying path 6.

On the conveyor line 6, the cast strip B

then pass through a heating device 8, in which the band B at one above the

Crystallization temperature Tx of each potted molten steel S lying annealing temperature T _G i _üh over a glow time t _G iu _{h is} heated. Goal of this

Heat treatment is the controlled formation of a fine crystalline microstructure with grain sizes ranging from 10 to 10,000 nm in the cast strip B. The cast strip B thus heat treated is then hot rolled in a hot rolling mill 9 to hot strip WB. In plant 1, a cast strip B has been produced in each case from three steel melts S with the compositions Z1, Z2, Z3 given in Table 1. For every

Composition Z1, Z2, Z3 is the thickness D of the strips B cast from the respective molten steel S, the cooling rate AR achieved in each case during the cooling of the melt S in the casting region 5, which in each case occurs during the cooling of the cast strip B in FIG the additional cooling device 7 scored cooling rate ARZ and the target temperature T _{z of} the additional cooling specified. Furthermore, in Table 2 of

Structure state and the possibly existing structural components of the resulting band listed.

On two samples of the cast strip B produced as described above from the molten steel S having the composition ZI are different

Heat treatments in the heating device 8

Have been carried out. The respectively set

Annealing temperature T _G i _üh and the annealing time t _G i _üh the

Heat treatment are compared in Table 3.

It turned out that the cast band B before the

Heat treatment already had a fine crystalline structure of α-Fe, Fe ₂ B, Fe ₃ B and Fe ₃ Si at a hardness HV0.5 of 840-900 had. Even after the heat treatment, the microstructure consisted of α-Fe, Fe ₂ B, Fe ₃ B and Fe ₃ Si, but the hardness was now HV0.5 760-810.

It is understood that the described heat treatment by means of the heating device 8 and the hot rolling with the hot rolling stand 9 are only optional process steps.

The invention thus provides methods for producing a steel strip B having an amorphous, partially amorphous or fine-crystalline structure with grain sizes in the range from 10 to 10000 nm and a correspondingly procured

Flat steel product available. According to the invention, a molten steel in a casting device (2) is cast into a cast strip (B) and cooled down at an accelerated rate. The melt contains besides Fe and

At least two further elements which belong to the group "Si, B, C, P" due to production-related unavoidable impurities. According to a first process variant, the contents of these elements (in% by weight) Si: 1.2 to 7.0%, B: 0.4 to 4.0%, C: 0.5 to 4.0% , P: 1.5-8.0%. According to a second process variant, the molten steel containing Si, B, C and P in a

Casting device (2) whose casting region (5) is formed on at least one of its longitudinal sides by a wall which moves and cools in the casting direction (G) during the casting operation, to form a cast strip (B)

wherein the molten steel (S) is cooled by contact with the moving cooled wall at a cooling rate of at least 200 K / s.

REFERENCE NUMBERS

1 system for producing a cast strip B

2 casting device

3.4 rolls of the casting device 2

5 casting area

6 horizontally aligned conveyor line

7 cooling device

8 heating device

9 hot rolling stand

B cast tape

D Thickness of the cast strip B

R gravity direction

S melt

K banding force

Xl _r X2 axes of rotation of the rollers 3,4

Data in wt .-%, balance iron and unavoidable impurities

Table 1

Table 2

Table 3

Claims

P A T E N T A N S P R E C H E

1. A method for producing a flat steel product having an amorphous, teilamorphen or finely crystalline microstructure, wherein the finely crystalline structure has particle sizes in the range of 10 - 10000 nm, in which a molten steel in a casting device (2) cast into a cast strip (B) and thereby accelerated is cooled, thereby

The thickness of the cast strip (B) is 0.8-4.5 mm and the molten steel is adjacent to iron and steel

at least two further elements belonging to the group "Si, B, C, P", with the proviso (in% by weight)

Si: 1.2 - 7.0%,

B: 0.4 - 4.0%,

C: 0.5-4.0%,

P: 1.5 - 8.0%

and optionally one or more of the elements from the group "Cu, Cr, Al, Nb, Mn, Ti, V" contains, with the proviso (in Ge .-%):

Cu: up to 5.0 o.

Cr: up to 10, 0 o

AI: up to 10, 0 g.

0

N: up to 0, 5 o.

o,

Nb: up to 2.0 g,

° /

Mn: up to 3.0 g.

Ti: up to 2.0 g,

O

V: up to 2.0 0,

0. Method according to claim 1, characterized

e n c ia n, the s

Molten steel is cooled at a cooling rate of 100 - 1100 K / s.

Method according to one of the preceding claims, characterized in that the molten steel at a cooling rate of

at least 200 K / s below the

Glass transition temperature T _{G is} cooled.

Method according to one of the preceding claims, characterized in that the molten steel in a casting device (2) whose casting region (5) is formed on at least one of its longitudinal sides by a moving and cooled wall in the casting direction (G) during the casting operation, to the cast Band (B) is poured, and that the molten steel (S) is cooled by contact with the moving cooled wall at a cooling rate of at least 200 K / s.

Method according to one of the preceding claims 4, characterized in that the cast strip (B) after leaving the

Casting area (5) continues to be cooled at a cooling rate of at least 200 K / s. Method according to one of claims 4 or 5, characterized in that the cast strip (B) emerging from the casting area (5) is cooled continuously until the glass transition temperature T _{G of} the respective steel has been reached.

Method according to one of claims 4 to 6,

The cast strip (B) is hot rolled to a hot strip at a hot rolling start temperature of 500-1000 ° C, using a hot strip tempering mill.

Method according to one of the preceding claims, characterized in that the band (B) cast in amorphous or partially amorphous form at a position in the region between the

Glass transition temperature T _G and the

Crystallization temperature T _x lying

Hot rolling start temperature to the hot strip

is hot rolled

Method according to one of Claims 3 to 7, characterized in that the cast strip (B) emerging from the casting area (5) of the casting device (2) and optionally additionally cooled has an amorphous or partially amorphous structure and in that the cast strip (B) thus obtained at least one of Crystallization temperature T _{x of} the respective steel corresponding annealing temperature T _G iu _h annealed.

10. The method of claim 8, d a d u r c h

e n c ia n, the s

Annealing temperature T _G i _üh in the range of 500 - 1000 ° C.

11. The method according to any one of claims 3 to 9,

The steel melt (S) next to the at least two elements from the group of Si, B, C and P is d a d u r c h e c e n e s

contains at least one element from the group of Cu, Cr, Al, N, Nb, Mn, Ti and V.

12. The method of claim 10, d a d u r c h

e n c ia n, the s

Molten steel (S) next to iron and

unavoidable impurities due to production (in% by weight)

Si: 1.2 - 7, 0%,

B: 0.4 - 4, 0%,

C: 0.5 - - 4.0 o.

O,

P: 1.5 - - 8.0 g_

0

and optionally one or more of the group of Cu, Cr, Al, N, Nb, Mn, Ti, and V, with the proviso

Cu: up to 5.0%,

Cr: up to 10.0%, AI: up to 10.0%,

N: up to 0.5%,

Nb: up to 2.0%,

Mn: up to 3.0%,

Ti: up to 2.0%,

V: up to 2.0%.

13. Method according to one of the preceding claims, wherein in each case one of the following provisos applies (in% by weight) to at least one of the elements from the group "Si, B, C, P":

Si: 2.0-6.0%,

B: 0.4 - 3.0%,

C: 0.5 - 3.0%

or

P: 2.0 - 6.0%.

Method according to one of the preceding claims, wherein the molten steel each optionally (in wt .-%) at least 0.1% Cu, at least 0.5% Cr, at least 1.0% AI and at least 0.005% N contains.

Steel flat product with a thickness of 0.8-4.5 mm and consisting of a steel which, in addition to iron and unavoidable impurities, contains at least two further elements from the group of Si, B, C and P with the proviso (in% by weight ): Si: 1.2 - 7.0%,

B: 0.4 - 4.0%,

C: 0.5-4.0%,

P: 1.5-8.0%,

and optionally one or more of the elements from the group "Cu, Cr, Al,, b, Mn, Ti, V" with the proviso contains (in wt .-%):

Cu: up to 5.0%,

Cr: up to 10.0%

AI: up to 10.0%

N: up to 0.5%,

Nb: up to 2.0%,

Mn: up to 3.0%,

Ti: up to 2.0%,

V: up to 2.0%.

and an amorphous, partially-amorphous or fine-crystalline microstructure having particle sizes ranging from 10 to 10,000 nm, the hardness HVO, 5 of the flat steel product being 760 to 900.