EP3853385A1 - Procédé de fabrication de tôles en acier ultrarésistantes et tôle en acier correspondante - Google Patents

Procédé de fabrication de tôles en acier ultrarésistantes et tôle en acier correspondante

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Publication number
EP3853385A1
EP3853385A1 EP19772687.0A EP19772687A EP3853385A1 EP 3853385 A1 EP3853385 A1 EP 3853385A1 EP 19772687 A EP19772687 A EP 19772687A EP 3853385 A1 EP3853385 A1 EP 3853385A1
Authority
EP
European Patent Office
Prior art keywords
max
steel
steel sheet
strength
austenite
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP19772687.0A
Other languages
German (de)
English (en)
Inventor
Markus Sonnleitner
Martin Klein
Gerhard HUBMER
Helmut Spindler
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Voestalpine Stahl GmbH
Original Assignee
Voestalpine Stahl GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Voestalpine Stahl GmbH filed Critical Voestalpine Stahl GmbH
Publication of EP3853385A1 publication Critical patent/EP3853385A1/fr
Pending legal-status Critical Current

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    • 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
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • 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
    • 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
    • C21D1/22—Martempering
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys 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
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0242—Flattening; Dressing; Flexing
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys 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 of ferrous metals or ferrous alloys 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
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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
    • 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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of 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
    • C21D2211/001—Austenite
    • 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 method for producing ultra high-strength hot-rolled sheet steel and a hot-rolled sheet steel and the use thereof.
  • Hot-rolled structural steels or structural steels with minimum yield strengths above 960 MPa are not covered in relevant standards (EN 10025, EN 10049). At present there are structural steels and structural steels with such high yield strengths on the market under different brand names, but the manufacture is complex. High alloy contents of carbon and / or other elements are necessary to achieve the required strength. However, a high carbon content and in particular carbon contents above 0.22% noticeably impair the weldability of such steels. High levels of elements that delay conversion, such as molybdenum or nickel, are expensive or consume resources, increase the susceptibility to scaling or lead to high rolling forces.
  • Such steels are usually hot rolled and hardened in a subsequent hardening step.
  • Such an independent hardening process requires an energy-intensive reheating process.
  • the minimum austenite grain sizes that can be achieved are limited.
  • a high-strength steel material is known from WO2017 / 016582 A1, which has a minimum yield strength of 1300 MPa and a tensile strength of at least 1400 MPa.
  • the carbon content is between 0.23 and 0.25%.
  • a flat steel product is known from WO2017 / 041862 A1, which should have an optimized combination of toughness and fatigue strength for an application in the field of agriculture, forestry or comparable applications.
  • EP 22 67 177 B1 discloses a high-strength steel plate with 0.18 to 0.23% by mass of carbon, the welding and sensitivity index PCM of the plate being 0.36% by mass or less and the Ac3- The transformation point should be equal to or less than 830 ° C.
  • the microstructure should contain more than 90% martensite and the yield strength should be higher than 1300 MPa, whereby the tensile strength should be greater than 1400 MPa but less than 1650 MPa. These sheets are apparently quarto sheets that are subjected to a classic hardening process.
  • a wear-resistant steel with good toughness and hardness from 420 to 480 HB is known from WO2017 / 104995 A1.
  • the material has in particular 0.15 to 0.2% carbon, 2 to 4% manganese, 0.02 to 0.5% silicon and 0.2 to 0.7% chromium. Apparently this material is hardened classically.
  • a directly hardened hot strip with stretched PAG is known from EP 2576848 B1, which is annealed at 200 to 700 ° C.
  • the yield strength should be greater than 890 MPa, with the carbon content being relatively low at 0.075 to 0.12%.
  • the object of the invention is to provide a method for producing an ultra-high-strength, hot-rolled structural steel, with which it is possible to work in a cost- and resource-efficient manner, excellent weldability is ensured and sheet thicknesses of 2 mm and above can be achieved.
  • a steel material with adapted alloy element contents is used, which is hot-rolled and directly hardened after melting and heating for the purpose of hot rolling.
  • the hardened material thus obtained is then subjected to a straightening process and then tempered with a special tempering treatment according to the invention.
  • a plastic deformation that was carried out beforehand is necessary, so that a high dislocation density is produced in the martensite and a corresponding supply of positively dissolved carbon is stored in the structure
  • tempering is carried out in a temperature range of 120 to 200 ° for 1 to 30 minutes.
  • the proof stress R p 02 increases without the tensile strength R m decreasing.
  • an upper limit for the tempering treatment of 200 ° C is observed, there is no reduction in toughness.
  • Below a tempering temperature of 100 ° C there is no measurable effect for the yield point in technically relevant periods and above 200 ° C softening was found.
  • Fig. 8 the influence of the tempering temperature and time on the impact bending work
  • 11 a highly schematic straightening device
  • 12 the distribution of the stresses during straightening in a bending straightening system
  • Fig. 13 the extent of plasticization as a relative plasticized volume when directing the mechanical properties.
  • FIG. 1 shows the influence of the tempering temperature on the proof stress Rp02, the tensile strength Rm and the elongation at break A5 (holding time: 5 minutes).
  • the initial state is directly hardened and directed material.
  • FIG. 2 shows a schematic process sequence in the preparation of tempered sheet metal according to the prior art.
  • the rolling stock cools down comparatively slowly, so that a martensitic transformation of the austenite does not occur or only to a small extent.
  • the material is austenitized and quenched with a sufficiently high cooling rate to obtain a martensitic structure.
  • a tempering step can subsequently be carried out at 500-650 ° C to set the desired mechanical properties.
  • AI 0.015 to 0.055
  • a sufficient conversion delay i.e. Avoiding a diffusive transformation of the austenite is necessary to achieve a martensitic structure. In the present case, this is achieved by the elements manganese, chromium and boron.
  • FIG. 9 shows reference materials from the prior art, which has shown that the strength level which is desired in the present case (1300 MPa) necessitates carbon contents of greater than 0.2%.
  • the content of elements delaying conversion is high, which can naturally have an adverse effect on the manufacturing costs, the minimum thickness that can be achieved and the surface quality.
  • elements that make production costs more expensive can be dispensed with. These are also usually the elements which influence the minimum achievable thickness, the desired results being readily achieved with the alloy layer according to the invention.
  • Manganese is known to slow down conversion.
  • the influence of manganese on the tensile strength could be determined.
  • manganese contents greater than 2% make an additional contribution to strength in the directly hardened state (hardened in this example with a cooling rate of 40 K / s).
  • Chromium contributes to hardenability.
  • the susceptibility of the steel surface to pitted igniters increases with a higher chromium content. In the 0.2 to 0.5% range, balanced combinations of hardenability and acceptable surfaces were found on the outside.
  • higher chromium contents can be advantageous according to the invention, in particular up to 1% in the case of strip thicknesses and the resulting lower cooling rates.
  • niobium as a recrystallization-inhibiting element is not necessary.
  • An advantage of the alloy according to the invention is that the comparatively low content of elements that delay transformation reduces the resistance to deformation compared to conventional hardenable alloys according to the prior art. This can reduce the minimum product thickness.
  • the direct hardening process according to the invention (see FIG. 3) immediately follows the hot rolling process, the martensite structure being formed from the deformed austenite. Due to the absence of recrystallization-delaying alloy elements, the austenite structure is predominantly recrystallized, fine and only slightly stretched. This fine-grained former austenite structure provides an additional strength contribution to the martensite.
  • a high cooling rate is aimed for.
  • the cooling rate is at least 10 K / s, particularly preferably 30 to 100 K / s.
  • the cooling stop temperature usually room temperature
  • at least 95% of the austenite must be converted to martensite.
  • the material thus produced is then mechanically straightened and then tempered.
  • Mechanical straightening is necessary to provide sufficient movable dislocations that are fixed by carbon in the subsequent tempering process. Therefore, the volume fraction of the material that exceeds the yield point in the straightening process and is therefore plastically deformed should not be less than 70%.
  • the required straightening combines the aforementioned advantages with the need to remove the existing coil curvature in the manufacture of sheet metal.
  • high strength steel grades are not directly hardened after rolling. In the case of hot rolling mills, this is due to the fact that with conventional coiler systems these sheets cannot be reeled into coils and are therefore processed or released as sheet metal.
  • the strips are wound up, which has the advantage that the transport restriction does not apply to the high-strength material according to the invention due to the dimensions of sheet metal plates.
  • the disadvantage of the greater effort involved in coiling is offset by the advantage that the high-strength sheets are significantly improved in their mechanical properties due to the mechanical influence.
  • the coiled material rolled up into coils must be straightened for further processing. According to the invention, this straightening is not only necessary to remove the existing coil curvature, but also leads to the sheet being formed in a homogeneous manner with the required movable dislocations.
  • Straightening is therefore necessary on the one hand to produce flat sheet metal from the curved strip material, but also to provide the offset.
  • Straightening is usually carried out by repeated bending back and forth in a roller straightening machine. The immersion depth of the straightening rollers decreases steadily from the inlet side to the outlet side, so that the strongest plasticization is achieved in the inlet of the straightening machine (Fig. 11).
  • this relative plasticized volume is at least 70%.
  • ultra-high-strength sheet metal sheets with at least Rp02 greater than 1100 MPa have not previously been produced on hot strip mills by means of direct hardening, but are first rolled on a four-high mill stand and sheet hardened in a subsequent process step. The reason for this is that the necessary vial forces are not available.
  • the weldability of the material is improved by the plastic deformation in connection with the tempering step, because it enables the alloy composition optimized according to the invention, in particular, to reduce the carbon content.
  • tempering process serves to set the desired yield or yield strength while at the same time maintaining the advantageous tensile strength, toughness and forming properties that exist after direct hardening. It was found that tempering temperatures below 100 ° C do not cause any significant effect, while tempering temperatures above 200 ° C lead to noticeable softening. Accordingly, tempering temperatures between 100 and 200 ° C. are aimed at according to the invention.
  • the quotient Rp02 / Rm the so-called yield point ratio
  • the quotient Rp02 / Rm increases significantly compared to the directly hardened and straightened state and lies in the interval 0.87 to 0.98 (longitudinal tensile tests).
  • Studies on a material according to the invention 0.18% carbon, 0.19% silicon, 2.26% manganese, 0.27% chromium, 0.021% titanium and 0.0024% boron rest iron and impurities after tempering with Variaton Holding time and tempering temperatures for the results according to FIGS. 4 to 8.
  • the corresponding material was rolled, directly hardened and, according to the invention, coiled on the hot wide strip mill.
  • the use of four-high scaffolding was not necessary here.
  • the material was then unwound, straightened and cross-divided, with the heat treatment being carried out on test panels in a laboratory furnace in air.
  • the time-temperature curve was measured using a thermocouple.
  • a composition is suitable as a steel composition as follows, all the data being in percent by mass.
  • AI 0.015 to 0.055 io
  • a steel with is particularly suitable
  • AI 0.015 to 0.055
  • a desired strength range from 1150 MPa to 1500 can be achieved MPa of tensile strength Rm must be covered. By avoiding contents> 0.2%, the susceptibility to cold cracking during welding can be prevented.
  • Silicon is an important element for deoxidizing the steel and leads to increases in strength. Silicon contents> 0.1% by mass make it easier to achieve low sulfur contents, but increase the susceptibility to scaling from 0.25% by mass.
  • Manganese is an important element in delaying conversion.
  • other conversion-delaying elements are not alloyed or only alloyed in lower contents, which is why a manganese content> 2% is preferably alloyed in order to achieve a martensitic structure in the direct hardening according to the invention.
  • the aluminum present in the mixture according to the invention is an important element for deoxidizing, but is not used in the present invention, unlike in the prior art, for setting the nitrogen, since titanium is used for this.
  • the salary is chosen accordingly.
  • chromium Another important element for delaying conversion is chromium, which is cheaper than molybdenum and nickel, whereby higher chromium contents increase susceptibility to scaling, but improve temper resistance.
  • vanadium is not absolutely necessary, but can be added in order to increase the temper resistance in areas exposed to local heat, contents> 0.12% impairing the toughness and should be avoided.
  • the specified niobium content is also not absolutely necessary, but it can be used for additional grain refinement.
  • the direct hardening according to the invention is not reliable with contents> 0.035 mass%, since the hardenability is reduced.
  • the titanium present in the steel according to the invention binds the nitrogen to titanium nitride and thus prevents the formation of boron nitride, which would greatly reduce the hardenability.
  • the boron present is an important element in delaying conversion.
  • the Ca content should not be less than 0.0010, since otherwise the sulfide shape cannot be adequately influenced. Furthermore, the Ca content should not exceed 0.0040 in order to avoid a reduction in toughness.
  • An advantage of the invention is that the special selection of the steel composition on the one hand and on the other hand through the direct hardening with a subsequent mechanical straightening process and a corresponding tempering treatment in the range between 100 and 200 ° C. very high strength structural steels are achieved which are good are weldable.

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  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

L'invention concerne un procédé de fabrication d'un acier de construction ultrarésistant laminé à chaud, permettant de produire un acier dont la teneur en carbone est d'au plus 0,2 %. Pour éviter une transformation austénitique diffuse, un retardement suffisant de la transformation étant atteint au moyen de l'addition de manganèse, de chrome et de bore, le matériau d'acier étant coulé d'une manière connue, et le matériau coulé étant soumis à une augmentation de température aux fins du laminage à chaud, la bande étant trempée directement immédiatement après le processus de laminage, la structure martensitique étant formée à partir de l'austénite préformé et le matériau ainsi produit étant ensuite redressé mécaniquement afin de fournir des dislocations mobiles, le matériau étant ensuite revenu pour régler la limite d'élasticité ou d'allongement souhaitée tout en conservant les propriétés de résistance à la traction, de ténacité et de formage présentes après la trempe directe, la température de revenu étant comprise entre 100 et 200°C.
EP19772687.0A 2018-09-18 2019-09-17 Procédé de fabrication de tôles en acier ultrarésistantes et tôle en acier correspondante Pending EP3853385A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102018122901.1A DE102018122901A1 (de) 2018-09-18 2018-09-18 Verfahren zur Herstellung ultrahochfester Stahlbleche und Stahlblech hierfür
PCT/EP2019/074815 WO2020058244A1 (fr) 2018-09-18 2019-09-17 Procédé de fabrication de tôles en acier ultrarésistantes et tôle en acier correspondante

Publications (1)

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EP3853385A1 true EP3853385A1 (fr) 2021-07-28

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EP19772687.0A Pending EP3853385A1 (fr) 2018-09-18 2019-09-17 Procédé de fabrication de tôles en acier ultrarésistantes et tôle en acier correspondante

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US (1) US11970753B2 (fr)
EP (1) EP3853385A1 (fr)
KR (1) KR20210062003A (fr)
CN (1) CN112714798B (fr)
DE (1) DE102018122901A1 (fr)
WO (1) WO2020058244A1 (fr)

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EP3964592A1 (fr) * 2020-09-07 2022-03-09 ThyssenKrupp Steel Europe AG Produit en acier plat laminé à chaud et procédé de fabrication d'un produit en acier plat laminé à chaud
EP4047105A1 (fr) * 2021-02-17 2022-08-24 ThyssenKrupp Steel Europe AG Produit en acier plat laminé à chaud et procédé de fabrication d'un produit en acier plat laminé à chaud
WO2025219741A1 (fr) * 2024-04-15 2025-10-23 Arcelormittal Pièce en acier présentant une grande résistance et une grande flexibilité

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WO2020058244A1 (fr) 2020-03-26
KR20210062003A (ko) 2021-05-28
US20210317544A1 (en) 2021-10-14
CN112714798B (zh) 2023-10-20
DE102018122901A1 (de) 2020-03-19
CN112714798A (zh) 2021-04-27
US11970753B2 (en) 2024-04-30

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