EP3405593A1

EP3405593A1 - Flat steel product and method for the production thereof

Info

Publication number: EP3405593A1
Application number: EP16701442.2A
Authority: EP
Inventors: Harald Hofmann; Hans Ferkel; Michael Gövert; Matthias Schirmer; Martin PALM; Dirk PONGE; Andreas Leitner
Original assignee: Max Planck Institut fuer Eisenforschung; ThyssenKrupp Steel Europe AG; ThyssenKrupp AG
Current assignee: Max Planck Institut fuer Eisenforschung; ThyssenKrupp Steel Europe AG; ThyssenKrupp AG
Priority date: 2016-01-20
Filing date: 2016-01-20
Publication date: 2018-11-28
Anticipated expiration: 2036-01-20
Also published as: EP3405593B1; CN108603257B; US20190032161A1; CN108603257A; WO2017125147A1

Abstract

The invention relates to a reliably producible flat steel product based on an Fe₃Al alloy and a method permitting the production of flat steel products of this type. The flat steel product is produced from a steel that consists of (in wt.%) Al: 12-20 %, Ti: 0.2-2 %, B: 0.1-0.6 %, and optionally at least one element from the group "Cr, C, Mn, Si, Nb, Ta, W, Zr, V, Mo, Ni, Cu, Ca, SEM, Co" in the following amounts: N: ≤ 0.1 %; Cr: ≤ 7 %; C: ≤ 0.15 %; Mn: ≤ 2 %; Si: 0.05-5 %; Nb, Ta, W: in total ≤ 0.2 %; Zr: ≤ 1 %; V: ≤ 1 %; Mo: ≤ 1 %; Ni: ≤ 2 %; Cu: ≤ 3 %; Ca: ≤ 0.015 %; SEM: ≤ 0.2 %; Co: ≤ 1 %, the remainder being Fe and unavoidable impurities, wherein the impurities include ≤ 0.03 % S and ≤ 0.1 % P. Here, for the Ti content % Ti and B content % B of the steel, it is the case that 0.33 ≤ %Ti/%B ≤ 3.75. At the same time, the structure of the flat steel products consists of 0.3-5 vol.% TiB₂ precipitations, which are embedded in a structure matrix comprising at least 80 vol.% Fe₃Al. The method according to the invention proposes casting a steel melt comprising the stated composition to form an intermediate product in the form of a slab, thin slab or a cast strip, hot-rolling said intermediate product at 1000-1300°C and a final hot-rolling temperature of at least 850°C to form a hot-rolled strip and finally winding the obtained hot strip at a winding temperature between room temperature and 750°C.

Description

Flat steel product and process for its production

The invention relates to a Fe-Al-Ti-B-based steel flat product and to a process for producing such a flat steel product.

If information is given in this text on contents of certain elements in an alloy, these contents always refer to the weight ("wt .-%") or the mass ("mass%") of the considered alloy, if nothing else is expressly stated. In contrast, information on parts of the structure always refers to the volume occupied by the respective structure ("% by volume"), unless otherwise stated.

When the term "flat steel products" is used, it refers to rolled products that are available as strip, sheet metal or blanks and blanks derived therefrom. In particular, the flat steel products according to the invention are heavy plate with typical sheet thicknesses of 6-200 mm or hot rolled strip or strip with typical sheet thicknesses of 1.5-6 mm.

Steels of the type in question are characterized by embedded in a FesAI matrix TiB ₂ precipitates. As a result of this peculiarity, such steels have a low density and, consequently, a low weight. This interesting for many applications

Properties in known materials of the type in question high brittleness up to high temperatures and a insufficient strength at temperatures above 500 ° C

across from.

The fundamental potential of materials on the basis of

intermetallic phases FesAI and FeAl were recognized about 100 years ago. Since then, there have always been attempts to develop especially materials based on the phase Fe ₃ AI. However, so far it has not been possible, strip and sheet products made of these materials

manufacture.

A typical example of such experiments is described in EP 0 695 81 A1. The heat-resistant iron-base alloy presented there is to be composed of the general formula Fe _x Al _y C _z , where (in atomic% in each case) for the variable y, 1% <y, 28% and for the variable z, ^ 24 %, whereas the variable x is based on a

Diagram depending on the respective C and AI content of the steel to be determined. As an aside, it should be mentioned that the steel may contain more than forty further constituents, including TiB ₂ , with a content of 0.1 to 2 atomic% as the content for each of these constituents. How to obtain such steels

Processing flat steel products is left open.

Other research has focused on the fabrication of Fe ₃ Al casting alloys based on boride-reinforced alloys. The results of this work can be found in the articles "Microstructure and mechanical properties of FesAI-based alloys with strengthening boride precipitates" by Krein, R., et al. in Intermetallics, 2007. 15 (9): p. 1172-1182, and "The influence of Cr and B additions to the mechanical properties and oxidation behavior of L2i-ordered Fe-Al-Ti-based alloys at high temperatures" by Krein, R. and M. Palm in Acta mater., 2008.56 (10): p. 2400-2455, "L2 ordered Fe-Al-Ti alloys" by Krein, R., et al. in Intermetallics, 2010. 18: p. 1360-1364 been reported. Accordingly, on the basis of the system Fe-Al-Ti B produce fine-grained alloys whose microstructure consists of a FesAI matrix with very small borides (<1 pm) along the grain boundaries. The compositions of the alloys are chosen so that the Fe ₃ AI phase primarily precipitates, whereas the borides are excreted in the (residual) eutectic. The borides cause such an increase in the

Strength, an improvement in ductility and a fixation of the

Grain size of the Fe ₃ AI matrix.

For example, Li, X., P. Prokopcakova and M. Palm "Microstructure and mechanical properties of Fe-Al-Ti-B alloys with addition of Mo and W", Mat. Eng., 2014, A 611: p. 234 - 241, it is known that also Fe-Al-Ti-B casting alloys can be modified by adding further elements. In particular, elements are considered by which the DO3 / B2 transition temperature is increased. In addition, Mo promotes the Bildug of

Complex Boriden, so that no more TiB ₂ is formed.

Against the background of the above-described prior art, the object was to provide a steel flat product based on a Fe _ß AI alloy and to name a method that allow reliable production of such flat steel products.

With respect to the flat steel product, the invention has achieved this object by a steel flat product obtained according to claim 1.

For the reliable production of such flat steel products, the invention proposes the method specified in claim 11.

Advantageous embodiments of the invention are in the dependent

Claims and as the general inventive concept are explained in detail below. A flat steel product according to the invention is therefore distinguished by the fact that it is made of a steel which consists of (in% by weight)

AI: 12 - 20%,

Ti: 0.2-2%,

B: 0.1-0.6%,

and in each case optionally one or more of the elements of the group "Cr, C, Mn, Si, Nb, Ta, W, Zr, V, Mo, Ni, Cu, Ca, rare earth metals, Co" in the following contents:

N: up to 0.1%,

Cr: up to 7%,

C: up to 0.15%,

Mn: up to 2%

Si: 0.05 - 5%

Nb, Ta, W: in total up to 0.2%

Zr: up to 1%

V: up to 1%

Mo: up to 1%

Ni: up to 2%

Cu: up to 3%

Ca: up to 0.015%

Rare earth metals: up to 0.2%

Co: up to 1%

Remaining iron and unavoidable impurities, taking the

unavoidable impurities S contents of up to 0.03 wt .-% and P contents of up to 0.1 wt .-% can be attributed, there is.

It is crucial for the invention that applies to the Ti Ti content% and the B content% B of the steel formed ratio% Ti /% B applies 0.33 <% ΤΊ /% B <3.75 and that the structure of the steel or the resulting flat steel product consists of 0.3 to 5% by volume of TiB ₂ precipitates, which are at least 80 vol. % of Fe ₃ AI existing matrix are embedded.

The boride-reinforced Fe _ß Al alloy from which an inventive

Flat steel product, already indicates due to their special

Composition has a strength above 500 ° C and a ductility, which is significantly improved over conventional, known from the prior art alloys of this type. At the same time

According to the invention, the parameters of the generation of the invention

Flat steel product of such a composite steel so

adjusted that a microstructure optimization is achieved, through which the

Properties of a flat steel product according to the invention are further optimized.

For this purpose, the method according to the invention for producing a flat steel product designed according to the invention comprises the following steps: a) melting a steel which consists of (in% by weight)

AI: 12 - 20%,

Ti: 0.2-2%,

B: 0.1-0.6%,

N: up to 0.1%,

Cr: up to 7%,

C: up to 0.15%,

Mn: up to 2% Si: 0.05 - 5%

Nb, Ta, W: in total up to 0.2%

Zr: up to 1%

V: up to 1%

Mo: up to 1%

Ni: up to 2%

Cu: up to 3%

Ca: up to 0.015%

Rare earth metals: up to 0.2%

Co: up to 1%

Residual iron and unavoidable impurities, wherein the inevitable impurities S levels of up to 0.03 wt .-% and P contents of up to 0.1 wt .-% are attributable, and wherein for the Ti content % Ti and the B content% B of the steel formed ratio% Ti /% B applies

0.33 <% Ti /% B <3.75; b) casting the molten steel into a precursor in the form of a slab, thin slab or a cast strip; c) hot rolling the precursor to a hot rolled hot strip, wherein the precursor at the start of the hot rolling a

Hot rolling start temperature of 1000 - 1300 ° C and the

Hot rolling end temperature is at least 850 ° C; d) Coiling the hot strip at a reel temperature between room temperature and 750 ° C.

Aluminum is contained in a steel flat product according to the invention in contents of 12-20% by weight. At Al contents of at least 12 wt .-%, in particular more than 12 wt .-%, the intermetallic forms Iron aluminide phase Fe _β Al, which represents the main component of the structure of a flat steel product according to the invention. The high Al contents lead to a reduced density, a concomitant reduced weight, high corrosion and

Oxidation resistance, as well as a high tensile strength. However, too high Al contents would complicate the cold formability of steels of the invention. Also, too high Al contents will deteriorate

Weldability through the formation of a stable welding slag during the welding process, and increased electrical resistance during welding

Resistance welding. For these reasons, the Al content of a steel according to the invention is limited to at most 20% by weight, in particular up to 16% by weight.

Ti and B form titanium borides in the steel according to the invention, which produce a fine microstructure, an increased yield strength, a higher ductility, a higher modulus of elasticity and increased wear resistance. In order for these effects to be achieved, a Ti content of at least 0.2% by weight, in particular at least 0.4% by weight, and a B content of at least 0.10% by weight, in particular at least 0, 15% by weight, required.

It is essential for the invention that the Ti content% Ti is tuned to the B content% B of the steel, that the ratio% Ti /% B, ie the quotient of the Ti content% Ti as a dividend and the B content% B as a divisor, 0.33 to 3.75, in particular in particular 0.5-3.75 or 1, 0 to 3.75, is. The ratio of% Ti /% B being at least 0.33 reduces the risk of FeB formation. Otherwise, the low melting phase FeB could crack during hot rolling and too

Ductility loss (reduction of elongation at break) lead. This can be avoided particularly reliably if the ratio% Ti /% B is 0.5-3.75, in particular 1.0-0.375. In addition, the presence of Ti in the flat steel product of the present invention can improve the oxidation resistance and the heat resistance. Too high levels of Ti borides, however, would lead to strong solidifications when a flat steel product according to the invention is cold worked. Therefore, the upper limit of the Ti content is 2 wt%, more preferably at most 1.5 wt% or 1.1 wt%, and the upper limit of the B content is 0.60 wt%, especially not more than 0.4% by weight.

Chromium may optionally be present in the steel of the present invention at levels of up to 7% by weight, more preferably at least 0.3% or at least 0.5% or at least 1.0% by weight lower the brittle-ductile transition temperature and total ductility

improve. Also, the presence of Cr increases the resistance of the steel to low and high temperature corrosion, and the

Oxidation resistance improved. At contents of more than 7 wt .-%, there is no increase in these effects, which have been found weighing the cost / benefit Cr contents of up to 5 wt .-% to be particularly effective, which in practice also contents of up to 3% by weight have proven sufficient to effect the improvements of a steel according to the invention caused by the addition of Cr.

Carbon, in combination with high Al contents, tends to form embrittling phases (kappa carbides), through which the hot and cold

Cold formability is reduced. This would apply in particular if the C contents of a flat steel product according to the invention were more than 0.15% by weight. According to the invention therefore the lowest possible C-contents are sought. However, as an unavoidable impurity, C was able to be produced in the steel as a result of production, so that in practice levels of at least 0.005% by weight, in particular at least 0.01% by weight, must be expected. In practical experiments it has also been found that C contents of up to 0.05 wt .-%, in particular up to 0.03 wt .-%, only lead to comparable minor deterioration of the steel, so they are still acceptable.

The optional addition of manganese in amounts of up to 1% by weight can also lower the brittle-ductile transition temperature. In the course of steelmaking, Mn also enters the steel as unavoidable contamination due to production, when Mn is used for deoxidation. Mn contributes to increase the strength, but may deteriorate the corrosion resistance. This is prevented by the inventive maximum Mn content to 2 wt .-%, in particular max. 1% by weight or max. 0.3 wt .-%, is limited.

Silicon can reach the steel of a flat steel product according to the invention in steelmaking as a deoxidizer, but can also be added selectively to the steel in amounts of up to 5% by weight, in particular up to 2% by weight, in order to increase strength and corrosion resistance optimize, where too high Si contents can lead to brittle material behavior. The Si content of a flat steel product according to the invention is typically at least 0.05% by weight, in particular at least 0.1% by weight.

Phosphorus and sulfur are undesirable, but

production-related unavoidable contamination of a

attributable to steel according to the invention. The contents of P and S should therefore be kept so low that harmful effects are avoided. For this purpose, the P content is limited to at most 0.1 wt .-% and the S content to at most 0.03 wt .-%, wherein S contents of at most 0.01 wt .-% or P contents of Max. 0.05 wt .-% have been found to be particularly advantageous.

Although the optionally present elements niobium, tantalum, tungsten, zirconium and vanadium form with C in the steel according to the invention strength enhancing carbides and can improve the

Heat resistance, but at excessive levels will degrade cold formability and weldability. The latter applies in particular to Nb, Ta and W, which are therefore permitted in amounts of not more than 0.2% by weight, in particular not more than 0.1% by weight, in the steel according to the invention. The Zr and V contents in the steel according to the invention are limited to up to 1% by weight, with Zr contents of up to 0.1% by weight and V contents of up to 0.5% by weight as a particularly cheap

have exposed. At too high levels, Zr worsens that

Corrosion behavior, whereas by too high levels of V the

Oxidation behavior is impaired. The positive effects of Zr and V can be used in particular if in each case at least 0.02% by weight Zr or V are present in the steel.

Molybdenum may optionally be added to the steel of a flat steel product of the present invention to improve tensile strength and creep resistance and high temperature fatigue strength. Mo can additionally contribute to a fine microstructure by forming fine carbides and complex borides. These positive effects are achieved when the Mo content is at least 0.2 wt .-%. However, too high Mo content lead to a deterioration of the warm and

Cold formability. Therefore, the Mo content of a flat steel product according to the invention is limited to a maximum of 1% by weight, in particular at most 0.7% by weight.

Nickel may optionally be present in the flat steel product of the present invention in amounts of up to 2% by weight to improve its strength and toughness, as well as to improve its corrosion resistance. At Ni contents of more than 2% by weight, no significant increase in these effects occurs any more. The positive effects of Ni can be used in particular if at least 0.2% by weight, in particular at least 1% by weight, of Ni are present in the steel. Copper may also optionally be present in the steel of the present invention to improve corrosion resistance. For this purpose, up to 3% by weight of Cu, in particular up to 1% by weight of Cu, can be added to the steel. At higher Cu contents, on the other hand, the hot workability, the weldability and the recyclability of a flat steel product according to the invention deteriorate. The positive effects of Cu can be used especially when at least 0.2 wt .-% Cu are present in the steel.

Calcium may be added to the steel during steelmaking to bind S and prevent clogging during casting of the steel. Optimal effects are here in inventive

Steel compositions achieved when the Ca content is up to 0.015% by weight, in particular at most 0.01 wt .-%, wherein Ca is safe to use, if at least 0.001 wt .-% Ca are present in the steel.

Rare earth metals "SEM" may be added to the steel of the invention in amounts of up to 0.2% by weight, especially up to 0.05% by weight, to improve oxidation resistance. This effect is achieved in particular if at least 0.001 wt .-% SEM are present in the steel.

In the steel according to the invention, nitrogen is at most undesirable, but as a rule production-induced unavoidable impurity

available. To avoid harmful effects, however, the N content should be kept as low as possible. By the content of N to at most 0.1 wt .-%, in particular max. 0.03 wt%, the formation of disadvantageous Al nitrides can be reduced to a minimum, which is the

mechanical properties and deformability could worsen. Cobalt may optionally be present in the steel of the present invention at levels of up to 1% by weight to increase its hot strength. This effect is achieved in particular if at least 0.2% by weight of Co is present in the steel.

The proportion of TiB ₂ in the microstructure of a flat steel product according to the invention is 0.3 to 5% by volume. The presence of such amounts of TiB ₂ causes a ductilization of the Fe _β Al matrix as a result of a significantly increased dislocation density in the vicinity of the TiB ₂ particles and the

Promoted recrystallization of the microstructure. At the same time a

Grain coarsening prevented by grain boundary pinning. In order to achieve these effects, at least 0.3% by volume TiB ₂ in the microstructure is required, and they are particularly safe when the content of TiB ₂ in the microstructure of the steel according to the invention is at least 0.5% by volume, in particular

at least 0.8% by volume. Harmful effects of too high Ti boride contents can be reliably prevented by the TiB ₂ content in the structure of the flat steel product according to the invention to max. 3 vol .-%, is limited.

By the grain size of Fe ₃ AI the Gefügematrix to at most 500 μητι, in particular max. 100 pm, will have good strength and ductility at room temperature as well as good strength at high

Temperature achieved. Optimally, the average particle size of the Fe _ß Al of the matrix should be 20 - 100 pm in order to ensure sufficient ductility and good creep resistance of the steel at room temperature, wherein in practice average particle sizes of 50 pm have been found to be particularly advantageous.

The effect of TiB ₂ precipitates in the matrix of the

The flat steel product according to the invention can be further optimized by virtue of the fact that at least 70% of the TiB ₂ precipitates in the Microstructure matrix having a mean particle diameter of 0.5 to 10 μm, in particular 0.7 to 3 μm.

The matrix of a flat steel product according to the invention consists of at least 80 vol .-% of the intermetallic phase Fe _ß AI, wherein it is desirable that the matrix as completely as possible, optimally up to 100 vol .-%, consists of FesAI. However, besides Fe _ß AI the structural matrix can also contain optional amounts on the solid solution Fe (AI) or on the intermetallic phase FeAl. High contents of at least 80% by volume of Fe ₃ Al are required for adjusting the high corrosion resistance, heat resistance, hardness and wear resistance.

For the production of a flat steel product according to the invention is in

Step a) of the method according to the invention in the

previously explained manner melted molten steel according to the invention and cast in step b) to a precursor in the form of a slab, thin slab or a cast strip. Basically, the operational melting of a high-alloy steel of the type according to the invention via the electric furnace route due to their suitability for liquefaction of high amounts of alloy is better suited than the classic blast furnace converter route of an integrated steelworks. The use of a suitable casting powder

provided that the melt can be cast in conventional continuous casting. If this proves to be problematical at very high Al contents, it is possible to use a casting process close to the final dimensions, such as processes in which the melt is processed into thin slabs, which are processed without interruption after casting into hot strip (cast roll process), or to cast strip, the also immediately afterwards one

Hot rolling process, be avoided.

For hot rolling (step c)), the respective precursor is brought to the preheating temperature of 1200 - 1300 ° C. This can be done in one separate heating process or by holding at the relevant temperature from the casting heat. If a separate heating is carried out, it should extend over a period of 15-1500 minutes to ensure homogeneous heating. Too low

Temperature or hold time this will be due to the low

Thermal conductivity of the steel is not achieved with the required safety, which can lead to cracks in the hot strip. A suitable hot rolling start temperature ensures the formability, especially in the last stitches and thus avoids high loads on the rolls. By selecting a hot rolling starting temperature in the range of 1000 ° to 1200 ° C., in particular 1100 ° to 1170 ° C., which is prescribed according to the invention, the risk of roller damage as a result of excessive rolling forces can therefore also be prevented. Too high

However, hot rolling start temperature would lead to a too low for hot rolling strength of the material. This can lead to unwanted deformations during processing and sticking of the rolling stock to the rollers. According to the invention, the hot rolling end temperature must be at least 850 ° C. in order to avoid excessive roll forces and to be able to achieve high degrees of deformation. Even with lower hot rolling temperatures, the required flatness of the hot strip could not be guaranteed with the necessary safety from an operational point of view.

After hot rolling, the hot strip is reeled in step d) at a reel temperature which is between room temperature and 750 ° C. As cooling media particularly suitable here are water or aqueous solutions with which a homogeneous cooling over the

Ensure band cross section.

Reel temperatures of at least 400 ° C, in particular at least 450 ° C, have proven particularly useful with regard to practical application, the upper limit of the reel temperature range being limited to at most 700 ° C, especially at most 550 ° C can cause excessive scale formation on the hot strip too

avoid.

The hot strip obtained after hot rolling has an elongation at break of 2-4% in the tensile test. In order to improve this property, an optional annealing of the hot strip at a annealing temperature of 200-1000 ° C. over an annealing time of 1 to 200 h may be carried out after the reeling. This serves to increase the ductility at room temperature. For the hot strip annealing, a bell annealing process with a tip temperature above 650 ° C is suitable. lower

Annealing temperatures or holding times show no effect, whereas higher annealing temperatures or holding times lead to ductility loss

Grain coarsening due to a coarsening of the Ti boride particles and the Fe3AI matrix can lead.

Optionally, the hot strip according to the invention can also be subjected to a pickling treatment with common media, wherein the pickling time is to be chosen so that even on the hot strip itself

adjusting stable AI oxides are eliminated.

In a steel flat product produced according to the invention, TiB ₂ particles are increasingly embedded in the intermetallic matrix of Fe ₃ Al due to the high Ti and B contents of the steel from which the flat steel product is made. A flat steel product alloyed according to the invention therefore has high yield strengths and tensile strengths. At the same time its density is greatly reduced compared to conventional steels of the same strength class. The typical density of steels of the invention is in the range of 6.2 to 6.7 g / cm ³ and is on average typically 6.4 g / cm ³ . This results in a high strength / density ratio compared to other heat-resistant materials. By selecting the rolling parameters according to the invention, the BDTT value (brittle-ductile transition) can be lowered to surprisingly low temperatures of about 75-100 ° C.

Above this temperature, the elongation at break increases with increasing temperature and reaches extremely high values at 650 ° C. Due to the increasing deformability with a rise in temperature is a component production with preheated sheets or a classic

Hot forming feasible.

Typical hot yield strengths of flat steel products according to the invention are at 650 ° C. with about 130-170 MPa in the range of conventional ferritic Cr steels, such as those under material number 1.4512

(Hot tensile strength about 70 MPa) standardized steel and the high

Heat resistance, under the material number 1.4509

(Hot yield strength approx. 150 MPa) standardized steel. At temperatures of at least 700 ° C, the tensile strength of inventive

Flat steel product still regularly at least 100 MPa.

Due to their property profiles, flat steel products produced and obtained in accordance with the invention are particularly suitable for the production of, in particular, heat-resistant components for plant engineering (e.g.

Heavy plate), for gas turbines, for offshore installations and in particular for heat-resistant components for the automotive industry, in particular here

Exhaust systems or turbocharger housing (hot strip). Other preferred uses are conceivable in the low temperature range (e.g.

Biogas plants, brake discs, vehicle underbody).

The invention will be explained in more detail by means of exemplary embodiments. In each case 60 kg of the alloys A - F indicated in Table 1 were melted in a vacuum induction furnace under argon and poured into molds measuring 250 × 150 × 500 mm. After solidification, the ingots obtained after a preheating to 1200 ° C on a duo Reversiergerüst are rolled down to 45 mm and divided into six blooms with a height of 40 mm. The resulting billets have been heated to a preheat temperature of 1200 ° C. over a preheat time of 80 minutes each.

The heated blooms are starting from a

Hot rolling start temperature WST were each hot rolled in a conventional manner at a hot rolling end temperature WET to hot strip with a thickness of 3 mm.

The resulting hot strips are based on the respective

Hot rolling end temperature WET was cooled to the respective reel temperature HT and wound at this temperature into a coil.

The parameters WST, WET and HT are given for the different samples A1 - F3 in Table 2.

Subsequently, for the samples A1 - F3, the mechanical properties yield strength Rp0.2, tensile strength Rm and elongation A50 are included

Room temperature (see Table 3) and for some samples selected from it also the mechanical properties yield strength Rp0.2, tensile strength Rm and elongation at break A at 650 ° C (see Table 4) and the

Structural characteristics "grain size of the matrix", "matrix" and "proportion of TiB _{2 in} the microstructure" (see Table 5) and the brittle transition temperature BDTT (see Table 6) have been determined.

The mechanical properties were determined in the tensile test according to DIN EN 10002, whereas the brittle-ductile transition temperature in the Point bending test has been determined. The four-point bending tests were performed on 3 x 6 x 18 mm ³ samples between room temperature and 500 ° C. The samples were wet ground longitudinally prior to the start of the test with 1000 grit sandpaper. The experiments were carried out with a deformation rate of phi = 1 x 10 ^"4 s ^" in air. For intermetallic phases this is the

Standard method for determining the brittle-ductile transition temperature (see D. Risanti et al., Dependence often he brittle-to-ductile transition

temperature BDTT on the AI content often he Fe-Al alloys "; Intermetallics, 13 (12), (2005) 1337-1342.) The grain size of the matrix is in the

Line cutting method according to DIN ISO 643 has been determined. The T1B2 particle size and volume fraction have been determined according to ASTM E 1245.

It was found that the alloys A - F were applied

industrial conditions on a laboratory scale could easily roll.

The experiments have thus confirmed that the tensile strengths Rm

at room temperature, typically 550-700 MPa and yield strengths Rp0.2 of 400-650 MPa at an elongation A50 of typically 2-5%. The tensile strength could be increased in particular, if pre-and finish rolling in

different rolling directions took place.

The Vickers HV5 hardness typically varies between 335 and 370 in flat steel products according to the invention.

The hot yield strength σ0.2 (measured transversely to the rolling direction according to DIN EN 10002) at 650 ° C. is typically 120 ± 170 MPa.

In the 4-point bending test, it was found that the sheets do not have a pronounced brittle-ductile transition temperature of 75 ° -00 ° C. you are already completely ductile at 100 ° C. This means an improvement of at least 150 ° C compared to the cast material and is due to the texture refinement by rolling. By a

Hot strip annealing of the type described above, the ductility can be increased still.

All data in% by weight, balance iron and other production-related unavoidable impurities

Table 1

Table 2

Table 3

Table 4 Average grain size of

Matrix share TiB ₂

Sample matrix

[μηι] [vol .-%] of longitudinal sample

A3 46 Fe ₃ AI (Type D0 ₃ ) 0.9

B3 53 FeaAl (Type D0 ₃ ) 1, 4

C3 55 FeaAl (Type D0 ₃ ) 1

D2 48 FesAI (Type D0 ₃ ) 1

E3 64 FesAI (Type D0 ₃ ) 1, 4

F3 46 FesAI (Type D0 ₃ ) 1

Table 5

Table 6

Claims

1. Flat steel product made from a steel made from (in% by weight)

AI: 12 - 20%,

Ti: 0.2-2%,

B: 0.1-0.6%, and in each case optionally one or more of the elements of the group "Cr, C, Mn, Si, Nb, Ta, W, Zr, V, Mo, Ni, Cu, Ca, rare-earth metals, Co "in the following contents:

N: up to 0.1%

Cr: up to 7%,

C: up to 0.15%,

Mn: up to 2%

Si: 0.05 - 5%

Nb, Ta, W: in total up to 0.2%

Zr: up to 1%

V: up to 1%

Mo: up to 1%

Ni: up to 2%

Cu: up to 3%

Ca: up to 0.015%

Rare earth metals: up to 0.2%

Co: up to 1% Remaining iron and unavoidable impurities, taking the

unavoidable impurities S contents of up to 0.03% by weight and P contents of up to 0.1% by weight are attributable to

exists, and

where the ratio is Ti /% B formed by the Ti content% Ti and the B content% B of the steel

0.33 <% Ti /% B <3.75 and the structure of the steel to 0.3 to 5 vol .-% of TiB ₂ precipitates consisting of at least 80 vol .-% of Fe _ß AI existing Microstructure matrix are embedded.

2. Flat steel product according to claim 1, characterized in that the ratio% Ti /% B

0.5 <% Ti /% B <3.75.

3. Flat steel product according to claim 2, characterized in that the ratio% Ti /% B

1.0 <% Ti /% B <3.75.

4. Flat steel product according to one of the preceding claims, characterized in that the grain size of the FesAI in the

Microstructure matrix is at most 500 pm.

5. Flat steel product according to claim 4, characterized in that the particle size of the FesAI in the microstructure matrix is preferably at most 100 μm.

6. Flat steel product according to one of the preceding claims, characterized in that at least 70% of the TiB ₂ precipitates in the microstructure matrix have a mean

Particle diameter of 0.5-10 [im.

7. Flat steel product according to one of the preceding claims, characterized in that the sum of its contents of Nb, Ta, W is up to 0.1% by weight.

8. flat steel product according to one of the preceding claims, dad u rch geken nze I net that its Cr content is at least 0.3 wt .-%.

9. Flat steel product according to one of the preceding claims, characterized in that the structure of the steel consists of at least 0.5% by volume of TiB ₂ precipitates.

10. Flat steel product according to one of the preceding claims, characterized in that the structure of the steel is at most

3 vol .-% consists of TiB ₂ precipitates.

11. A method of making one according to any one of the preceding

Claims trained flat steel product, comprising the following

Steps: a) melting a steel made of (in% by weight)

AI: 12 - 20%,

Ti: 0.2-2%,

B: 0.10-0.6%, and in each case optionally one or more of the elements of the group "Cr, C, Mn, Si, Nb, Ta, W, Zr, V, Mo, Ni, Cu, Ca, rare earth metals, Co "in the following contents:

N: up to 0, 1%,

Cr: up to 7%,

C: up to 0.15%,

Mn: up to 2%

Si: 0.05 - 5%

Nb, Ta, W: in total up to 0.2%

Zr: up to 1%

V: up to 1%

Mo: up to 1%

Ni: up to 2%

Cu: up to 3%

Ca: up to 0.015%

Rare earth metals: up to 0.2%

Co: up to 1%

Remaining iron and unavoidable impurities, taking the

unavoidable impurities S contents of up to 0.03 wt .-% and P contents of up to 0.1 wt .-% are attributable, and wherein for the consisting of the Ti content% Ti and the B content % B of steel formed ratio% Ti /% B is 0.33 <% T \ I% B <3.75; b) casting the molten steel into a precursor in the form of a

Slab, thin slab or a cast strip; c) hot rolling the precursor to a hot rolled hot strip, wherein the precursor at the start of the hot rolling a

Hot rolling start temperature of 1000 - 1300 ° C and the

12. The method according to claim 11, characterized

the hot strip obtained after the reeling (step d)) is annealed at an annealing temperature of 200-1000 ° C. over an annealing period of 1 to 200 hours.

13. The method according to any one of claims 11 or 12, characterized

characterized in that the intermediate product between the

Work steps b) and c) is heated to the hot rolling start temperature over a heating time of 15-1500 min.

14. The method according to any one of claims 11 to 13, characterized

characterized in that the reel temperature is at least 400 ° C.

15. Use of a trained according to one of claims 1-10

Flat steel product for the production of components for plant construction, for the production of components for gas turbines, for the production of in particular heat-resistant components for the automotive industry, for

Manufacture of components for installations used in the low-temperature range and for the manufacture of components by forming after a previous heating.