Classifications

• • 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
  • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
  • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/26—Methods of annealing
• • 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
  • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
  • C21D8/0405—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing of ferrous alloys
• • 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
  • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
  • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
  • C21D8/0426—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
  • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
  • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
  • C21D8/0463—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing 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
  • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
  • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
  • C21D8/0473—Final recrystallisation annealing
• • 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
  • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
• • 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
  • 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
  • C21D2211/002—Bainite
• • 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
  • C21D2211/005—Ferrite
• • 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
  • C21D2211/008—Martensite

Definitions

• the invention relates to a cold-rolled flat steel product which has a low sensitivity to edge cracks and good formability, here characterized by a high Marciniak hole expansion (LAW), with a high tensile strength Rm, yield strength Rp and elongation at break A80.
• LAW Marciniak hole expansion
• Dual-phase steels (DP steels) with good hole expansion according to ISO 16630 are known from the prior art, for example in the application WO 2013/182622 .
• this hole expansion test does not adequately represent the real forming processes in automobile construction.
• the Marciniak hole expansion test offers the opportunity to test the DP steels in a practical manner, close to the actual later forming reality. This shows the need to change the known DP steels in order to create a special structure that is suitable for the demands in automobile construction. Such a steel with a special structure is the subject of this invention.
• the flat steel products described in the invention are typically rolled products, such as steel strips or sheets as well as blanks and blanks made from them.
• the structure is determined on cross sections that are etched with 3% Nital (alcoholic nitric acid).
• the structure is determined in a scanning electron microscope at 5000x magnification to determine the proportion of plate-like and other non-plate-like bainite and at 20,000 to 50,000x magnification to determine the plate length, width and distance between the plates.
• the proportion of retained austenite is determined using X-ray diffractometry.
• the grain boundaries of the structure are determined using electron backscatter diffraction (EBSD).
• EBSD electron backscatter diffraction
• samples are taken from the 1/3 layer of the strip thickness of the flat steel product. These samples are embedded and prepared as a longitudinal section. Immediately before the EBSD examination, the surface is treated again in a polishing step. The EBSD measurement is carried out in a 90*90 ⁇ m measuring field in 0.1 ⁇ m steps. Large-angle and small-angle grain boundaries are determined in the recorded data.
• a small angle grain boundary is a grain boundary that is a boundary between two grains with a small difference in orientation. The small angle grain boundary is defined up to a rotation angle ⁇ up to and including 15°. In the present invention, misorientations below five degrees ( ⁇ ⁇ 5) are not considered a grain boundary.
• the grain boundaries are referred to as high-angle grain boundaries.
• the grain boundary lengths are determined for all large-angle and small-angle grain boundaries by specifying the described definition of the small-angle and large-angle grain boundaries in the analysis software TSL OIM Analyzes 8.0 from Ametek and then automatically determining the grain boundary lengths for the measuring range.
• the hole diameters are measured using a camera from IDS type UI-1240ML-M-GL with a telecentric lens (TC13080 from Opto Engineering). To ensure sufficient lighting, an optional lighting ring is attached to the camera. The distance between the camera and the sample must be chosen so that sufficient image resolution is achieved in the evaluation area. The diameter of the expanded hole should fill >50% of the image axes.
• the test is carried out with a hold-down force of 400 kN and a pulling speed of 1 ⁇ 0.2 mm/s until a crack or constriction is present. During the experiment, images are recorded at a frequency of 10 Hz. In the evaluation, the last image is selected in which no constriction or crack can be seen.
• the object of the present invention is to adjust the structure in a DP steel in such a way that the steel is suitable for the stress in automobile construction, ie with a high Marciniak hole expansion (LAW) of at least 9.0% is suitable.
• LAW Marciniak hole expansion
• Carbon “C” is contained in the steel according to the invention in levels of 0.02% to 0.25%. Carbon ensures high strength in the steel according to the invention by playing a decisive role in the formation of martensite and expanding the area in which austenite is formed. An optimized setting was found at values of C ⁇ 0.140%, since from this value onwards sufficient martensite components or sufficiently hard martensite are formed to further increase the strength. However, if the carbon content is too high, excessively large carbides are formed, which are ineffective in increasing strength. In addition, the weldability is reduced. For this reason, the carbon content in the present invention is limited to 0.25%, preferably 0.17%.
• Silicon “Si” is an important solid solution hardener. In addition, it is needed to adjust the special structure in this invention, because it delays cementite precipitation and thus suppresses pearlite formation. It can also increase the residual austenite content, which can be converted to martensite later in the process. For this effect and increased corrosion resistance, a proportion of at least 0.05%, and especially a proportion of at least 0.11%, has proven to be particularly effective. On the other hand, too high a silicon content leads to grain boundary oxidation occurring and can deteriorate coatability and surface properties. In addition, if the silicon content is too high, recrystallization processes can be delayed, which affects the ratio of the large and small angle grain boundaries. Therefore, the silicon content is limited to 0.8%, preferably 0.6%, particularly preferably 0.45%.
• Manganese “Mn” is contained in the steel according to the invention. With a content of 1.0% or more, Mn enables martensite formation because pearlite formation is suppressed. A proportion of at least 1.2% and particularly advantageous a proportion of at least 1.5% have proven to be advantageous. However, too high a Mn content can lead to severe segregation, which is why the Mn content is limited to 3.0%. In addition, a high Mn content severely limits weldability and reduces corrosion resistance. Therefore, an Mn content of a maximum of 2.5% and in particular 2.3% has proven to be particularly advantageous.
• Sulfur "S” can lead to the formation of Mn sulfides, which severely impair the formable properties. Therefore, the content in the steel according to the invention is limited to 0.01%, although a limitation to 0.005% and in particular to 0.003% can be advantageous. Contamination with sulfur cannot be completely avoided during steel production.
• Nitrogen “N” can lead to the formation of coarse Ti and Al nitrides at levels above 0.010%. To avoid these nitrides, a maximum content of 0.007% has proven to be particularly advantageous. Nitrogen contamination cannot be completely avoided during steel production.
• impurities P, S, and N other elements can also be present as impurities in the steel. These other elements are grouped under the “unavoidable impurities”.
• the content of these “unavoidable impurities” is preferably a maximum of 0.2% in total, preferably a maximum of 0.1%.
• the optional alloying elements “Al, Cr, Cu, Nb, Mo, Ni, Ti, V, B, Co, W” described below, for which a lower limit is specified, can also occur in levels below the respective lower limit as unavoidable impurities in the steel substrate . In this case, they are also counted among the "unavoidable impurities", the total content of which is limited to a maximum of 0.2%, preferably a maximum of 0.1%.
• Aluminum “Al” can be added to the steel of the invention to increase corrosion resistance and increase the retained austenite content.
• a higher residual austenite content results from the addition of aluminum by delaying the formation of cementite precipitates.
• an aluminum content of greater than or equal to 0.05% in the flat steel product according to the invention has proven to be advantageous.
• too high an aluminum content can lead to the formation of coarse Al nitrides, which have an embrittling effect and thus poorer formability.
• higher Al contents can lead to poorer casting behavior, as aluminum compounds can lead to clogging.
• the present invention therefore limits the aluminum content to 1.0%, preferably 0.8%.
• chromium “Cr” By adding chromium “Cr”, the formation of bainite can be delayed, whereby a higher proportion of martensite is achieved in the flat steel product according to the invention.
• hardenability is increased by chromium.
• a chromium content of greater than or equal to 0.10% has proven to be particularly advantageous.
• chromium can lead to grain boundary oxidation through the formation of Cr oxides.
• the chromium content here is therefore limited to 1.0%, preferably 0.9%.
• the addition of copper "Cu” to the flat steel product according to the invention improves the corrosion resistance and can form very fine strength-increasing Cu precipitates. Therefore, an addition of at least equal to 0.01% may be advantageous in the present invention.
• the copper content should be limited to 0.5%, otherwise so-called red brittleness can occur in the hot rolling process, i.e. cracks can form in the slab.
• niobium “Nb” can be added to the flat steel product according to the invention.
• fine, strength-increasing carbon nitrides are formed.
• a content of at least 0.0005% has proven to be advantageous.
• the strength-increasing effect of carbon nitrides is exhausted as soon as the niobium content becomes too high.
• high levels of niobium can impair cold formability and welding properties.
• Molybdenum "Mo” also forms fine, strength-increasing carbon nitrides in small amounts. An addition of greater than or equal to 0.001% has therefore proven to be advantageous. However, the strength-increasing effect of carbon nitrides is exhausted as soon as the molybdenum content becomes too high. In addition, high levels of molybdenum can impair cold formability and welding properties. Here, a content of a maximum of 0.1%, preferably 0.050%, particularly preferably 0.007%, has proven to be advantageous.
• Nickel “Ni” increases the amount and stability of austenite and reduces red brittleness with Cu.
• nickel can improve Marciniak hole expansion (LAW). Therefore, at least 0.01%, particularly advantageously 0.015% Ni, is optionally added to the flat steel product according to the invention. For cost reasons, however, the addition should be limited as little as possible to a maximum of 0.2%, preferably 0.1% and particularly preferably to 0.06%.
• Titanium "Ti” binds nitrogen in the steel and thus prevents the formation of brittle boron nitrides.
• titanium can also form strength-increasing carbon nitrides.
• an addition of greater than or equal to 0.001%, preferably 0.004%, has proven to be advantageous. If too much titanium is added, the advantage of the strength-increasing carbon nitrides is exhausted because they become too large.
• coarse, brittle Ti nitrides can form. Limiting the titanium content to a maximum of 0.1%, preferably 0.03% and particularly preferably 0.006%, has proven to be advantageous for the flat steel product according to the invention.
• vanadium "V” can be added to the steel according to the invention, which also forms fine carbon nitrides in small amounts.
• the carbon nitrides can pin the grain boundaries. Pinning reduces grain coarsening at high temperatures, which has a positive effect on the ratio of large-angle grain boundary lengths to small-angle grain boundary lengths.
• vanadium is added to the steel according to the invention. If too much vanadium is added, the carbon nitride precipitates become larger and therefore ineffective.
• the amount of vanadium added is limited for cost reasons. In the steel according to the invention, the amount is limited to 0.1%, preferably 0.030% and particularly preferably 0.0015%.
• boron "B” leads to an increase in strength.
• at least 0.0002%, particularly preferably at least 0.001%, can be added to the steel according to the invention become. If the amount of boron added is too high, iron borides are formed. These iron borides can melt at approx. 1200° C and cause material failure. For this reason, the boron content in the steel according to the invention is limited to 0.005%, preferably 0.0015%.
• Mg can have a desulfurizing and deoxidizing effect. Therefore, 0.0003% can be added to the steel according to the invention.
• the addition of Mg is limited to a maximum of 0.5% Mg, preferably 0.1%, particularly preferably 0.003%.
• Calcium "Ca” can be added to the flat steel product according to the invention in order to bind the free sulfur. Free sulfur segregates to the grain boundaries and thereby leads to failure of the material, i.e. the Marciniak hole expansion deteriorates. Therefore, an optional amount of at least equal to 0.0001% can be added to the flat steel product according to the invention. In large quantities, calcium is no longer soluble in the flat steel product, which is why the addition is limited to a maximum of 0.1%, preferably 0.010%, particularly preferably 0.003%.
• Cobalt “Co” increases the amount and stability of austenite.
• a cobalt addition of at least 0.001% has proven to be particularly advantageous.
• a maximum of 0.1%, preferably 0.010%, particularly preferably 0.0007%, of cobalt should be added to the steel according to the invention.
• Tungsten “W” has a desulphurizing and deoxidizing effect in the steel according to the invention.
• strength-increasing carbides can be formed with the help of tungsten.
• Tungsten can therefore optionally be added at a level of at least 0.01%. For cost reasons, a maximum of 0.3% tungsten is used in the present invention.
• the steel product according to the invention can optionally contain the rare earth metals (SEM) such as: cerium “Ce”, lathane "La” and yttrium “Y” in total with a maximum content of 0.5%. Larger SEM contents can lead to problems when casting the steel. A minimum sum of all SEM elements of at least 0.003% is advantageous, as this has a desulphurizing and deoxidizing effect.
• SEM rare earth metals
• the carbon equivalent should be a maximum of 1.30%, preferably 0.70%, otherwise there will be an excessive tendency for cracks in the weld metal or the heat-affected zone during welding. In addition, the heat-affected zone can become significantly brittle.
• resistance spot welding it is also desirable to set the carbon equivalent as low as possible to ensure welding under industrial conditions.
• the cold-rolled flat steel product according to the invention in particular according to the method according to the invention, is characterized in that the steel has a structure consisting of at least two phases, which comprises more than 5% martensite and more than 20% ferrite as well as up to 65% bainite and up to 10% retained austenite .
• the martensite content is limited to 90% and particularly preferably 80% in order to ensure sufficient ductility for component shaping.
• the martensite content preferably consists of fresh and tempered martensite.
• with martensite contents greater than 50% up to 10% of the martensite can be present as tempered martensite.
• the ferrite content in particular can be limited to 80% so that the desired strength can be adjusted.
• the ferrite content is at least 30%.
• the bainite content is limited to a maximum of 20%.
• the microstructure of the flat steel product according to the invention has a special ratio of the large angle grain boundary length to the small angle grain boundary length.
• High angle grain boundaries impede the movement of dislocations from one grain to the other. Due to their significantly higher dislocation density, small-angle grain boundaries cause hardening in the grain, which leads to different deformation resistances and is equivalent to a notch effect. This notch causes localized deformations and reduces hole expansion.
• the microstructure according to the invention is characterized by the ratio of the large-angle grain boundary lengths to the small-angle grain boundary lengths of more than 4.0, preferably more than 4.5, particularly preferably 6.0. It has been shown that under such conditions the mechanical properties are positively influenced, in particular the Marciniak hole expansion.
• the cold-rolled flat steel product is characterized by an elongation at break A80 of at least 8%, preferably at least 10%, particularly preferably at least 14%.
• the tensile strength Rm is at least 570 MPa, preferably at least 590 MPa.
• This product of elongation at break A80 and tensile strength Rm can be achieved by effectively preventing dislocation movements. These dislocation movements are reduced by the special ratio of large-angle grain boundary lengths to small-angle grain boundary lengths.
• the yield strength Rp0.2 of the steel is 350 MPa to 850 MPa.
• the Marciniak hole expansion in a special embodiment of the flat steel product is at least 9.0%, preferably at least 10.0%, particularly preferably 12.0%.
• the Marciniak hole expansion test offers the opportunity to test the DP steels in a practical manner, close to the actual later forming reality.
• composition according to the invention of the slab according to the invention applies to the composition according to the invention of the slab according to the invention and the optional possible variations.
• the slab according to the invention is reheated to a temperature of 1200-1300 ° C.
• This causes austenite to form in the product.
• the lower limit of the reheating temperature T HOM should be at least 1200 ° C so that homogeneity in the structure in the slab is achieved. If an upper limit of 1300° C is exceeded at the heating temperature, melting can occur on the slab or the slab can break because the high-temperature strength is exceeded.
• the slabs have a thickness of 200-300 mm.
• the product according to the invention is hot-rolled in a conventional manner using units known from the prior art to a final thickness of 1.5 to 7 mm, preferably 1.7 to 4 mm.
• the hot rolling final temperature (T WE for short) is at least 800° C., preferably 920° C.
• the hot rolling final temperature is particularly preferably above the Ac3 temperature.
• the hot strip After hot rolling, the hot strip is coiled at a temperature of 400 °C - 700 °C, preferably at 500 °C - 600 °C.
• T HA reel temperatures
• martensite forms too quickly, which leads to high strength and makes later deformation problematic. Above 600°C the risk of grain boundary oxidation increases.
• the coil After reeling, the coil is cooled to room temperature.
• the hot strip is pickled in order to remove the scale.
• Pickling can preferably be carried out chemically using hydrochloric and/or sulfuric acid. Pickling is particularly preferably carried out in a temperature range of 80 to 95 °C.
• the flat steel product is cooled to room temperature.
• the cold-rolled flat steel product is then brought to an annealing temperature T annealing of more than 800 ° C in a continuous furnace.
• the heating intensity is preferably: 3000 kJ s ⁇ mm and particularly preferred 3150 kJ s ⁇ mm .
• the average heating intensity according to the invention leads to recrystallization processes taking place preferably before recovery processes. This will make more large-angle grain boundaries are formed, so that the inventive ratio of large-angle grain boundaries to small-angle grain boundaries can be established.
• a typical annealing time during which the flat steel product is kept at the annealing temperature is preferably at least 10 s.
• the maximum annealing time is preferably 1000 s.
• the cooling to room temperature can take place in two intermediate steps, with the cold-rolled flat steel product in the first intermediate step from annealing temperature to a first cooling temperature T 1 with an average cooling rate ⁇ 1 of less than 100 K/s, preferably less than 10 K/s, particularly preferably less than 5 K /s, and wherein cold-rolled flat steel product is cooled in the second intermediate step to a second maximum cooling temperature T 2 with a cooling rate ⁇ 2 less than 100 K/s, the following applies to the cooling temperatures T 1 , T 2 : T 1 > T 2 , 450°C ⁇ T 1 ⁇ 800 °C (preferably 650°C ⁇ T 1 ⁇ 750 °C) and 400 °C ⁇ T 2 ⁇ 600 °C
• the flat steel product according to the invention can be provided with a metallic protective layer.
• a metallic protective layer In particular, zinc-based hot-dip coatings can be used. This coating occurs between steps f) and g) in the process described above.
• the flat steel product can be tempered to level out pronounced yield points, strip waviness and to achieve ideal roughness.
• a cold deformation of 0.2-3% is particularly preferred.
• the flat steel product can optionally be oiled between or after the last processing step.
• the oiling serves as temporary corrosion protection until the next processing step or for transport.
• melts AF were produced.
• the composition of the melts is given in Table 1.
• the melts were cast into slabs in a conventional continuous casting plant and the slabs were then reheated.
• the slabs were then rolled into hot strips with a specific hot rolling final temperature T WE .
• the hot strip was then coiled and pickled at a coiling temperature T HA .
• the corresponding process temperatures can be found in Table 2.
• the hot strip thus obtained was then rolled in a conventional manner into a cold strip with a strip thickness d.
• This cold strip was then heated with a heating intensity I to an annealing temperature T and cooled to room temperature.
• the rates during cooling are given in Table 2.

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Citations (4)

• 2022
  • 2022-04-13 EP EP22168199.2A patent/EP4261309A1/fr active Pending

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