EP3415646B1 - Tôle d'acier haute résistance à malléabilité améliorée - Google Patents

Tôle d'acier haute résistance à malléabilité améliorée Download PDF

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Publication number
EP3415646B1
EP3415646B1 EP18176405.1A EP18176405A EP3415646B1 EP 3415646 B1 EP3415646 B1 EP 3415646B1 EP 18176405 A EP18176405 A EP 18176405A EP 3415646 B1 EP3415646 B1 EP 3415646B1
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EP
European Patent Office
Prior art keywords
flat steel
steel product
hot
strip
temperature
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EP18176405.1A
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German (de)
English (en)
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EP3415646A1 (fr
Inventor
Fabian Nowara
Ekaterina Bocharova
Andreas Bongards
Roland Sebald
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ThyssenKrupp Steel Europe AG
ThyssenKrupp AG
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ThyssenKrupp Steel Europe AG
ThyssenKrupp AG
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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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • 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
    • 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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper

Definitions

  • the present invention relates to a method for producing a flat steel product, a corresponding flat steel product, components made from such flat steel product, and the use of the flat steel product.
  • Dual-phase steels are characterized by a good combination of properties of high strength and formability.
  • the structure of conventional DP steels consists of 70 to 90 vol .-% ferrite, the rest of martensite.
  • the hard martensite is embedded in the island in the soft ferritic matrix.
  • other carbon-rich transformation structures such as bainite and / or thermodynamically metastable residual austenite can be present in small quantities. Metastable residual austenite improves the forming properties during cold forming.
  • dual-phase steels combine different properties. Compared to conventional high-strength steel grades, they combine a low, continuous yield strength with high tensile strength while at the same time good elongation at break and elongation or high work hardening capacity. The high tensile strength combined with a low yield strength leads to a low yield strength ratio.
  • DP steels are preferred in vehicle construction. Due to the low yield strength ratio and the high work hardening potential, they are particularly suitable for complex-shaped, safety-relevant body components that require a high level of energy absorption. These components include Reinforcements, roof frames, B-pillars as well as longitudinal and cross members. With the high possible strengths, there is also great potential for lightweight construction by reducing the thickness of the sheets. DP steels therefore make a contribution to weight-optimized construction, especially from the point of view of energy saving and passive safety.
  • EP 0 796 928 A1 discloses a multi-phase steel and a method for its manufacture.
  • the multiphase steel is in the form of cold-rolled sheets containing 0.05 to 0.3% by weight of C, 0.8 to 3.0 wt% Mn, 0.4 to 2.5 wt% Al, 0.01 to 0.2 wt% Si, balance Fe and unavoidable impurities.
  • the cold-rolled sheet has high strength and good ductility.
  • the cold rolled sheet can also be surface coated.
  • EP 1 642 990 A1 discloses a high-strength steel sheet with a dual-phase structure, containing 0.03 to 0.2% by weight of C, 0.005 to 0.3% by weight of Si, 1.0 to 3.1% by weight of Mn, 0.001 to 0, 06 wt% P, 0.001 to 0.01 wt% S, 0.0005 to 0.01 wt% N, 0.2 to 1.2 wt% Al, less than 0.5 wt .-% Mo, rest Fe and unavoidable impurities.
  • This steel sheet has good ductility and can be surface coated.
  • High-strength steels are particularly suitable for use in vehicle construction, especially in automobile construction. Both uncoated and coated steel sheets are used for this, depending on the susceptibility to corrosion of the product and the location or environment in which they are used. In order to meet growing requirements with regard to lightweight construction (climate protection, resource efficiency, cost optimization) and crash safety in body and chassis construction due to more complex component structures, there is a need for high-strength flat steel products with improved forming properties.
  • the object of the present invention is to provide flat steel products and processes for their production which meet the above-mentioned requirements, in particular improved forming properties, which among other things. can be quantified in an increased elasticity compared to comparable products.
  • a flat steel product according to the invention obtainable by the method according to the invention, by a flat steel product made from a special steel, by a component made from the flat steel product according to the invention, and by the use of the flat steel product according to the invention in vehicle construction, in particular in body construction, for Safety-relevant components, which include, for example, longitudinal and cross members.
  • the alloying elements for adjusting the mechanical properties of the steel according to the invention are essentially C, Si, Mn, Al and Cr.
  • the present invention preferably relates to the flat steel product according to the invention, containing (in% by weight) 0.070 to 0.15 C, max. 0.50 Si, 1.0 to 2.0 Mn, 0.6 to 1.5 Al and 0.2 to 1.0 Cr, balance Fe and unavoidable impurities.
  • carbon is alloyed in a range from 0.070% by weight to 0.15% by weight, preferably 0.095% by weight to 0.13% by weight.
  • the minimum content is necessary in order to be able to achieve the desired strength reliably by forming a sufficient amount of martensite.
  • the carbon is also required to stabilize the remaining austenite.
  • the formability is improved by using the TRIP effect. Levels above 0.15% by weight often lead to restrictions in welding and are therefore undesirable.
  • Silicon is inventively up to max. 0.50% by weight, preferably max. 0.40% by weight, alloyed. Silicon is required to stabilize the residual austenite by suppressing the precipitation of cementite during cooling after annealing and to increase the strength. Silicon contents above the specified amount make coating difficult due to the formation of silicon oxide on the strip surface during annealing.
  • manganese is alloyed in a range from 1.0% by weight to 2.0% by weight, preferably 1.2% by weight to 1.7% by weight.
  • the specified lower limit is determined by ensuring the strength of the steel sheet. Higher levels of Mn above the specified upper limit make production more difficult, since manganese tends to form segregations and higher process temperatures would be necessary for steel production.
  • Aluminum is required to stabilize the residual austenite and is used according to the invention in a range from 0.6% by weight to 1.5% by weight, preferably 0.7% by weight to 1.3% by weight. Levels above the specified upper limit, like silicon, make coating difficult.
  • Chromium also increases strength and is therefore alloyed according to the invention in a range from 0.2% by weight to 1.0% by weight, preferably 0.2% by weight to 0.7% by weight. With chrome contents above the specified upper limit, the elongation can be greatly reduced.
  • the elements C, Si, Mn, Al and Cr essentially have a strength-increasing effect. Therefore, according to the invention, the sum of the amounts of C, Si, Mn, Al and Cr is preferably 2.8 to 3.5% by weight.
  • the present invention therefore preferably relates to the method according to the invention, the sum of the amounts of C, Si, Mn, Al and Cr being 2.8 to 3.5% by weight.
  • the present invention therefore preferably also relates to the flat steel product according to the invention, the sum of the amounts of C, Si, Mn, Al and Cr being 2.8 to 3.5% by weight. According to this preferred embodiment, a preferred combination of tensile strength and minimum elongation at break is obtained.
  • the sum of the amounts of Si and Al is more preferably at most 1.5% by weight.
  • an advantageous surface finish is obtained, since there are no negative effects with regard to zinc adhesion due to detachment of the upper grain layers, deteriorated formability due to grain boundary oxidation at high reel and annealing temperatures.
  • alloying elements are preferably not added in a targeted manner. Therefore, the upper limit for the other explicitly specified elements is preferably: P 0,0 0.03% by weight, sulfur 0,00 0.005% by weight, Mo, Cu and Ni in each case 0,2 0.2% by weight, N and Ti in each case ⁇ 0.01%. All other possible elements are considered inevitable impurities.
  • the flat steel product according to the invention contains (in area%) 60 to 85, preferably 70 to 80, ferrite (F), 10 to 30, preferably 10 to 20, martensite (M), 5 to 12, preferably 7 to 11 , Residual austenite (RA) and at most 8, preferably at most 3, for example 0 to 8, others selected from pearlite, bainite, cementite and / or carbides.
  • the martensite content of 10 to 30% by area preferred according to the invention ensures the necessary strength, but at the same time it is so limited that there is no drop in elongation at break due to excessive strength.
  • Residual austenite contributes to the elongation at break. Too much residual austenite is at the expense of the martensite component, which would lead to a decrease in strength.
  • the sum of the other structural components is so small that there is no significant influence on the mechanical properties.
  • the present invention therefore preferably relates to the flat steel product according to the invention, it (in area%) 60 to 85, preferably 70 to 80, ferrite (F), 10 to 30, preferably 10 to 20, martensite (M), 5 to 12, preferably 7 to 11, residual austenite (RA) and at most 8, preferably at most 3, for example 0 to 8, others selected from pearlite, bainite, cementite and / or carbides, the sum of the components present being 100.
  • the present invention further preferably relates to the flat steel product according to the invention, the tensile strength Rm being 580 MPa to 710 MPa.
  • the present invention further preferably relates to the flat steel product according to the invention, the elongation at break A80 being at least 23%.
  • the method according to the invention comprises, as step (A), the production of a hot-rolled strip.
  • step (A) the production of a hot-rolled strip.
  • all methods or process steps known to the person skilled in the art can be used according to the invention in order to obtain a hot-rolled strip with the above-mentioned alloy elements according to the invention in the appropriate amounts.
  • Step (A) is preferably carried out by casting a corresponding preliminary product, a slab or a thin slab, from a steel melt from a steel which has the above-mentioned analysis.
  • the casting can be carried out by all methods known to the person skilled in the art.
  • the preliminary product obtained in this way is then kept at a temperature of 1100 to 1300 ° C. or reheated to this temperature and then optionally descaled and pre-rolled.
  • the heating of the preliminary product according to the invention can be carried out in all devices known to the person skilled in the art, for example in a walking beam or pusher furnace.
  • the temperature is preferably 1050 to 1150 ° C.
  • the actual hot rolling can be carried out by all methods known to the person skilled in the art.
  • the hot rolling according to the invention is preferably carried out in such a way that a final rolling temperature (ET) of 820 to 900 ° C., particularly preferably 840 to 880 ° C., is obtained at the end of the hot rolling.
  • a hot strip with a thickness of 1 to 10 mm, preferably 2 to 7 mm, is preferably obtained according to the invention.
  • step (A) of the process according to the invention is then transferred to step (B).
  • step (A) comprising the production of a preliminary product, in particular a slab or a thin slab, by casting a steel with appropriate analysis, and hot rolling the obtained preliminary product.
  • Step (B) of the method according to the invention comprises cooling the hot-rolled strip from the final rolling temperature to the coiling temperature and coiling this strip, the coiling taking place at a temperature of 540 to 620 ° C. Maintaining the reel temperature is crucial.
  • step (B) can be carried out by methods known to the person skilled in the art, it being necessary to ensure that the reeling temperature of 540 to 620 ° C. is maintained.
  • the cooling from the final rolling temperature (ET) from step (A) to the reel temperature (HT) preferably takes place in air and / or with water. It is particularly preferred if after leaving the hot rolling mill, i.e. after step (A), a holding time in air of at least 1 s is observed before water cooling begins. According to the invention, this leads to an advantageous, uniform recrystallization state in the hot strip and, associated therewith, uniform mechanical properties and a high strip flatness being obtained.
  • the method according to the invention can be carried out particularly advantageously and makes a particularly advantageous product accessible if the reel temperature according to the invention is maintained in step (B).
  • a reel temperature below the range according to the invention leads to a high tensile strength according to the invention and to low elongation at break in the annealed cold strip.
  • an undesirably high strength of the hot strip is obtained, which is disadvantageous for the subsequent cold rolling.
  • a reel temperature above the range according to the invention causes the tensile strength in the annealed cold strip to be too high according to the invention.
  • the risk of grain boundary oxidation and grain coarsening is promoted, which can lead to poor and / or uneven mechanical properties in the annealed cold strip.
  • Step (B) of the process according to the invention is particularly preferably carried out at a reel temperature of 560 to 600 ° C.
  • the present invention therefore preferably relates to the invention Process in which the reeling is carried out at a temperature of 560 to 600 ° C.
  • the hot strip is then cooled down to room temperature in the coiled state by methods known to those skilled in the art.
  • the hot strip obtained is fed to a pickling step after step (B) of the method according to the invention.
  • the present invention therefore preferably relates to the method according to the invention, the hot strip obtained in step (B) being fed to a pickling step.
  • the strip can be pickled both in a process step which is separate from the cold rolling subsequently carried out or in a system combined with a cold rolling unit.
  • the hot strip for pickling is preferably passed through a pickling tank known to the person skilled in the art.
  • the pickling agent used is preferably sulfuric acid H 2 SO 4 , preferably with a concentration of 15 to 40% by weight, for example 25% by weight, or hydrochloric acid HCl.
  • the temperature in the pickling step according to the invention is preferably 70 ° C to 100 ° C.
  • the person skilled in the art knows how to measure the pickling time, scale residues and / or grain boundary oxidation remaining on the strip surface if the pickling time is too short, and uneven removal of the surface may result if the pickling time is too long, which may result in a fluctuating strip thickness with possibly different mechanical properties can result.
  • the hot strip obtained after the pickling step according to the invention is then cold rolled in a preferred embodiment of the method according to the invention.
  • the present invention therefore preferably relates to the method according to the invention, the hot strip obtained after the pickling step being fed to a cold rolling step.
  • the method according to the invention therefore preferably comprises a step (C), comprising cold rolling and subsequent annealing, preferably in a continuous continuous furnace, with an optionally following coating.
  • the thickness of the strip after cold rolling is preferably between 0.6 mm and 3.0 mm.
  • the cold strip is preferably further treated after the cold rolling in a continuous annealing process, optionally with a subsequent coating of the strip (metallic coatings such as Zn, Mg or alumina coatings).
  • the present invention therefore preferably relates to the method according to the invention, the cold strip obtained in the cold rolling step being fed to an annealing step.
  • the strip is brought to a temperature GT of 780 to 880 ° C. in one or more steps.
  • the heating rate to these temperatures is preferably up to 20K / s.
  • the throughput speed is preferably between 40 and 125 m / min.
  • the holding time in the annealing furnace which is preferably between 20 and 340 s, depends on the throughput speed.
  • the holding time and holding temperature according to the invention should preferably not be fallen short of according to the invention, so that sufficient austenite is formed and the recrystallization can be ensured.
  • this is preferably relevant for the strength due to the formation of martensite
  • stable residual austenite is preferably required at room temperature in order to be able to achieve the required elongation at break.
  • an incomplete recrystallization or incomplete heating in the annealing step in particular in the case of thicker dimensions, could lead to different microstructures across the strip width and strip thickness, which is reflected in undesirable, scattering mechanical properties.
  • the cold strip is preferably cooled according to the invention to an intermediate temperature of 400 to 530 ° C., for example at a cooling rate greater than 5K / s.
  • the cooling can take place in one or more steps.
  • a hot-dip coating can optionally be carried out according to the invention.
  • Processes for hot-dip coating are known per se to the person skilled in the art. Coating baths with a proportion of at least 75% by weight of zinc or aluminum are preferably used here. After coating, there is a cooling to a temperature ⁇ 100 ° C. with an average cooling rate> 5K / s, whereby this cooling can be designed in one or more steps.
  • a cooling rate of at least 5K / s and at most 100K / s is maintained in a temperature range from 680 to 530 ° C. This prevents the formation of pearlite, which leads to a lowering of the strength. If the cooling rate is too high, for example more than 100K / s, too much martensite can be formed and the elongation at break can be reduced.
  • a galvannealing process can be carried out after coating, whereby a reheating to max. 650 ° C takes place.
  • the sheet can be cooled according to the invention below the above-mentioned intermediate temperature without a coating treatment continuously at a cooling rate of, for example, 0.1 to 50 K / s in one or more step (s) to room temperature.
  • An electrolytic coating is optionally available after cooling to room temperature.
  • the steel sheet can be optionally dressed, the degree of skin-pass should preferably be a maximum of 1.5%. If a higher degree of skin-pass is used, the yield strength can increase according to the invention with an undesirable loss of elongation at break and loss of n value. If the optional skin pass step is carried out, a skin pass degree of at least 0.3% is necessary to ensure a defined surface structure.
  • step (C) comprising a pickling step, a cold rolling step, an annealing step, optionally a hot-dip coating, optionally an electrolytic coating and / or a skin pass step.
  • the present invention also relates to a component containing the flat steel product according to the invention or the flat steel product obtained by the method according to the invention.
  • the component according to the invention particularly preferably consists of the flat steel product according to the invention or of the flat steel product obtained by the method according to the invention.
  • Components of this type are preferably safety-relevant components, for example longitudinal and cross members, A-pillars or B-pillars.
  • the present invention also relates to the use of a flat steel product according to the invention or a flat steel product obtained by the method according to the invention, for use in vehicle construction, preferably in body construction, for example as longitudinal or transverse beams, A-pillars or B-pillars.
  • a steel from the analyzes given in Table 1 is cast into a preliminary product (slab) and reheated to a temperature VT of 1100 to 1300 ° C. and then pre-rolled. To heat slabs, they are heated in a walking beam furnace. The entrance to the finishing train takes place at a temperature of 1050 to 1150 ° C.
  • the slabs are rolled to the final hot strip thickness in at least five passes.
  • the final rolling temperature ET is between 820 and 900 ° C, see Table 2.
  • the hot strip with a thickness according to Table 2 is cooled at a cooling rate of 30 - 300 K / s to a coiling temperature HT of 540 to 620 ° C and then coiled.
  • the cooling from ET to HT takes place with water.
  • the hot strip is cooled in the coiled state in air to room temperature.
  • the hot strip is pickled to remove the scale layer and rolled with a KWG cold rolling degree between 50 and 73%.
  • the cold strip thickness is between 0.8 and 2.8 mm, see Table 2.
  • the strip is passed through a pickling tank containing 25% sulfuric acid H 2 SO 4 at a temperature of approx. 95 ° C.
  • the cold strip is processed further with a continuous annealing process.
  • the strip is brought to a temperature GT in accordance with Table 2 in one or more steps and kept at this temperature for a time t_glow.
  • the mixture is cooled to an intermediate temperature ZT in accordance with Table 2.
  • An optional coating is carried out here.
  • the strip is cooled to a temperature ⁇ 100 ° C and then subjected to skin pass rolling (skin pass degree D °).
  • Tables 1 and 2 show the alloys of the respective processed preliminary products as well as the respective manufacturing parameters for tests 1 to 32. Experiments 1 to 24 were carried out in the manner according to the invention both with regard to the alloy of the respectively processed slabs and with regard to the production parameters, while in experiments 25 to 32 either the alloy or the production parameters were not in accordance with the invention.
  • the mechanical properties are determined in tests on longitudinal samples (DIN EN ISO 6892-1, sample form 2 according to DIN EN ISO 6892-1, measuring length 80 mm, sample width 20 mm).
  • the longitudinal samples are taken from the strip axis, ie from a position in the middle of the strip width.
  • the n values were also determined in accordance with DIN ISO 10275 in conjunction with DIN EN ISO 6892-1 as n 10-20 / Ag values.
  • the details of the structural components relate to area percent.
  • the cut is etched with alcoholic nitric acid, which contains 3% by volume of nitric acid (so-called nital).
  • the sample position is considered in 1/3 or 2/3 of the thickness of the steel sheet at 1000x magnification in a reflected light microscope.
  • the residual austenite content is determined using a microdiffractometer on the same longitudinal section. During the measurement, the acceleration voltage is 35kV and the current is 30 mA. The lower detection limit is 1% residual austenite.
  • Table 1 Analyzes of the steel compositions used ⁇ /u> ⁇ /b> analysis C.
  • Rp0.2 Rm A80 n 10-20 / Ag value structure MPa MPa % - F M RA Other M + RA A 1 369 637 28 0.21 70 20 8.0 2.0 28.0 A 2nd 355 609 32 0.22 75 15 8.0 2.0 23.0 A 3rd 357 632 29 0.22 70 20 7.5 2.5 27.5 A 4th 354 624 30th 0.20 70 20 7.5 2.5 27.5 B 5 343 626 27 0.21 70 20 8.5 1.5 28.5 B 6 361 625 30th 0.22 70 20 9.0 1.0 29.0 B 7 367 615 31 0.22 75 15 10.0 0.0 25.0 B 8th 360 612 30th 0.22 75 15 8.5 1.5 23.5 C. 9 347 607 29 0.25 75 15 8.0 2.0 23.0 C.
  • the flat steel product according to the invention can advantageously be used in vehicle construction.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
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  • Metallurgy (AREA)
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  • Physics & Mathematics (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Claims (12)

  1. Procédé, destine à fabriquer un produit plat en acier à partir d'un acier, constitué (en % en poids) :
    de 0,070 à 0,15 de C,
    d'un maximum de 0,50 de Si,
    de 1,0 à 2,0 de Mn,
    de 0,6 à 1,5 d'Al et
    de 0,2 à 1,0 de Cr
    d'un reste de Fe et d'impuretés inévitables,
    comprenant au moins les étapes consistant dans :
    (A) la fabrication d'une bande laminée à chaud,
    (B) le dévidage de la bande laminée à chaud, le dévidage s'effectuant à une température de 540 à 620 °C, et
    (C) le cas échéant, un laminage à froid et une recuisson par la suite, avec une enduction optionnelle consécutive.
  2. Procédé selon la revendication 1, caractérisé en ce que l'étape (A) comprend la fabrication d'un produit semi-fini, notamment d'une brame ou d'une brame mince, par coulage d'un acier avec une analyse correspondante et par laminage à chaud du produit semi-fini obtenu.
  3. Procédé selon la revendication 1 ou 2, caractérisé en ce que le dévidage s'effectue à une température de 560 à 600 °C.
  4. Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce que l'étape (C) comprend une étape de décapage, une étape de laminage à froid, une étape de recuisson, le cas échéant une étape d'enduction par immersion à chaud, le cas échéant une enduction électrolytique, et/ou une étape de dressage.
  5. Procédé selon l'une quelconque des revendications 1 à 4, caractérisé en ce que la somme des quantités de C, de Si, de Mn, d'Al et de Cr s'élève à de 2,8 à 3,5 % en poids.
  6. Produit en acier plat, contenant en tant qu'élément d'alliage du C, du Si, du Mn, de l'Al et du Cr, un reste de Fe et des impuretés inévitables, caractérisé en ce que l'équation suivante (I) est satisfaite : 3,5 ≤ A ≤ 8,8
    Figure imgb0005
     dans laquelle A = (74,96 + 8039,1 ∗ C - 1498,18 ∗ Si - 121,63 ∗ Mn - 408,97 ∗Al + 1093,38 ∗ Cr) / 100
    et
    C : est la teneur en C % en poids,
    Si : est la teneur en Si en % en poids,
    Mn : est la teneur en Mn en % en poids,
    Al : est la teneur en Al en % en poids et
    Cr : est la teneur en Cr en % en poids,
    l'acier du produit en acier plat étant constitué (en % en poids) :
    de 0,070 à 0,15 de C,
    d'un maximum de 0,50 de Si,
    de 1,0 à 2,0 de Mn,
    de 0,6 à 1,5 d'Al et
    de 0,2 à 1,0 de Cr
    d'un reste de Fe et d'impuretés inévitables.
  7. Produit en acier plat selon la revendication 6, caractérisé en ce que la somme des quantités de C, de Si, de Mn, d'Al et de Cr s'élève à de 2,8 à 3,5 % en poids.
  8. Produit en acier plat selon l'une quelconque des revendications 6 et 7, caractérisé en ce qu'il contient de 60 à 85 % en % en surface de ferrite (F), de 10 à 30 % de martensite (M), de 5 à 12 % d'austénite résiduelle (RA) et au maximum 8 % d'autres, sélectionnés parmi la perlite, la bainite, la cémentite et/ou des carbures, la somme des composants présents étant de 100 %.
  9. Produit en acier plat selon l'une quelconque des revendications 6 à 8, caractérisé en ce que la résistance à la traction Rm s'élève à de 580 MPa à 710 MPa.
  10. Produit en acier plat selon l'une quelconque des revendications 6 à 9, caractérisé en ce que l'allongement à la rupture A80 s'élève à un minimum de 23 %.
  11. Élément structurel contenant un produit en acier plat selon l'une quelconque des revendications 6 à 10.
  12. Utilisation du produit en acier plat selon l'une quelconque des revendications 6 à 10 dans la construction de véhicules.
EP18176405.1A 2017-06-13 2018-06-07 Tôle d'acier haute résistance à malléabilité améliorée Active EP3415646B1 (fr)

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US20230151468A1 (en) * 2020-04-22 2023-05-18 Thyssenkrupp Steel Europe Ag Hot-Rolled Flat Steel Product and Method for the Production Thereof

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DE19610675C1 (de) * 1996-03-19 1997-02-13 Thyssen Stahl Ag Mehrphasenstahl und Verfahren zu seiner Herstellung
DE10161465C1 (de) * 2001-12-13 2003-02-13 Thyssenkrupp Stahl Ag Verfahren zum Herstellen von Warmband
EP1396550A1 (fr) * 2002-08-28 2004-03-10 ThyssenKrupp Stahl AG Procédé pour la fabrication d' une bande à chaud
JP4214006B2 (ja) 2003-06-19 2009-01-28 新日本製鐵株式会社 成形性に優れた高強度鋼板およびその製造方法
EP1918406B1 (fr) * 2006-10-30 2009-05-27 ThyssenKrupp Steel AG Procédé pour la fabrication de produits plats à partir d'un acier à plusieurs phases micro-allié en bore
EP2690184B1 (fr) * 2012-07-27 2020-09-02 ThyssenKrupp Steel Europe AG Cold rolled steel flat product and method for its production
EP2924141B1 (fr) * 2014-03-25 2017-11-15 ThyssenKrupp Steel Europe AG Produit plat en acier laminé à froid et son procédé de fabrication

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