Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
  • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0226—Hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/004—Dispersions; Precipitations

Definitions

• the invention relates to a Fe-Al-Ti-B-based steel flat product and to a process for producing such a flat steel product.
• flat steel products refers to rolled products that are available as strip, sheet metal or blanks and blanks derived therefrom.
• 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.
• 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
• 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
• 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
• 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.
• the invention has achieved this object by a steel flat product obtained according to claim 1.
• the invention proposes the method specified in claim 11.
• 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)
• Ti Ti content% and the B content% B of the steel formed ratio% Ti /% B applies 0.33 ⁇ % ⁇ /% 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.
• 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
• 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)
• Hot rolling start temperature 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 ⁇ 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
• too high Al contents would complicate the cold formability of steels of the invention.
• too high Al contents will deteriorate
• 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.
• 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.
• 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.
• 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
• 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.
• Mn manganese in amounts of up to 1% by weight can also lower the brittle-ductile transition temperature.
• 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.
• the contents of P and S should therefore be kept so low that harmful effects are avoided.
• 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.
• niobium, tantalum, tungsten, zirconium and vanadium form with C in the steel according to the invention strength enhancing carbides and can improve 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
• 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
• 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.
• the N content should be kept as low as possible.
• 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
• 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 ⁇ Al matrix as a result of a significantly increased dislocation density in the vicinity of the TiB 2 particles and the
• 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
• 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.
• the Geyoggematrix to at most 500 ⁇ , in particular max. 100 pm, will have good strength and ductility at room temperature as well as good strength at high
• 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 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 ⁇ m, in particular 0.7 to 3 ⁇ m.
• 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.
• 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.
• step b) 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.
• 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.
• 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
• 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
• a suitable hot rolling start temperature ensures the formability, especially in the last stitches and thus avoids high loads on the rolls.
• 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
• 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.
• 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.
• the hot strip is reeled in step d) at a reel temperature which is between room temperature and 750 ° C.
• cooling media particularly suitable here are water or aqueous solutions with which a homogeneous cooling over the
• 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
• the hot strip obtained after hot rolling has an elongation at break of 2-4% in the tensile test.
• 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.
• 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.
• 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
• 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.
• 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
• 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
• 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 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 Vickers HV5 hardness typically varies between 335 and 370 in flat steel products according to the invention.
• the hot yield strength ⁇ 0.2 (measured transversely to the rolling direction according to DIN EN 10002) at 650 ° C. is typically 120 ⁇ 170 MPa.

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• 2016
  • 2016-01-20 WO PCT/EP2016/051109 patent/WO2017125147A1/de active Application Filing
  • 2016-01-20 US US16/071,566 patent/US20190032161A1/en not_active Abandoned
  • 2016-01-20 CN CN201680079664.9A patent/CN108603257B/zh active Active
  • 2016-01-20 EP EP16701442.2A patent/EP3405593B1/de active Active

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