EP3325677A1 - Acier à haute résistance doté d'une limite élastique minimale et procédé de fabrication d'un tel acier - Google Patents

Acier à haute résistance doté d'une limite élastique minimale et procédé de fabrication d'un tel acier

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Publication number
EP3325677A1
EP3325677A1 EP15744166.8A EP15744166A EP3325677A1 EP 3325677 A1 EP3325677 A1 EP 3325677A1 EP 15744166 A EP15744166 A EP 15744166A EP 3325677 A1 EP3325677 A1 EP 3325677A1
Authority
EP
European Patent Office
Prior art keywords
steel
temperature
weight
flat
product
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.)
Withdrawn
Application number
EP15744166.8A
Other languages
German (de)
English (en)
Inventor
Heinz-Werner BRUNS
Alexander Björn JUNGERMANN
Andreas Kern
Hans-Joachim Tschersich
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.)
ThyssenKrupp Steel Europe AG
ThyssenKrupp AG
Original Assignee
ThyssenKrupp Steel Europe AG
ThyssenKrupp AG
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 ThyssenKrupp Steel Europe AG, ThyssenKrupp AG filed Critical ThyssenKrupp Steel Europe AG
Publication of EP3325677A1 publication Critical patent/EP3325677A1/fr
Withdrawn legal-status Critical Current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
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • 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 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
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • 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 high-strength steel, which has a high minimum yield strength, a method for producing such a steel and its use.
  • hot rolled steel sheets which are characterized by good processability and high tensile strength. Even if the tensile strength exceeds a certain value, for example, 1 .200 MPa, a delayed breakage of the steel sheet may be caused. Such a fracture may be caused by hydrogen penetrating into the interior of the steel sheet under the influence of a corrosion reaction that occurs on the steel sheet over time. Consequently, despite its high tensile strength such a steel sheet has a defect. Steel sheets having a high yield strength of 1,300 MPa accordingly require a high resistance to a delayed breakage.
  • Steel sheets with a high tensile strength or a high minimum yield strength often have the disadvantage that they are difficult to process by cold forming due to their poor deformability. Moreover, steel sheets having a high tensile strength and a high minimum yield strength often have poor toughness properties. Especially at low temperatures of -40 ' ⁇ or below These steels have such low toughness values that they can not be used on construction machines that have to meet high toughness requirements at low temperatures.
  • EP 2 267 177 A1 discloses a high-strength steel sheet which is used as a structural element in industrial machines and which on the one hand has excellent resistance to delayed breakage and on the other hand good welding behavior.
  • the steel sheet according to the invention has a high minimum yield strength equal to or higher than 1 .300 MPa and a tensile strength equal to or higher than 1 .400 MPa.
  • the thickness of the steel sheet according to the invention is equal to or greater than 4.5 mm and equal to or less than 25 mm.
  • a first aspect of the invention relates to a high-strength steel, the steel comprising the following composition:
  • Pcm [C] + [Si] / 30 + [Mn] / 20 + [Cu] / 20 + [Ni] / 60 + [Cr] / 20 + [Mo] / 15 + [V] / 10 + 5 B]; wherein [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V], and [B] are the mass fractions of the respective elements in the high strength steel in wt%. are and where for Pcm applies:
  • Unavoidable impurities in the context of the invention include, for example, arsenic, cobalt and / or tin.
  • the steel according to the invention may additionally comprise one of the elements (I) to (t).
  • the content of nitrogen in the steel according to the invention is preferably in the range from 0.001 to 0.006% by weight.
  • the steel according to the invention comprises carbon in the range of 0.23 to 0.25 wt .-%, silicon in the range of 0.15 to 0.35 wt .-%, manganese in the range of 0.85 to 1.00 wt%, aluminum in the range of 0.07 to 0.10 wt%, chromium in the range of 0.65 to 0.75 wt%, niobium in the range of 0.02 to 0 , 03 wt .-%, molybdenum in the range of 0.55 to 0.65 wt .-%, vanadium in the range of 0.035 to 0.05 wt .-%, nickel in the range of 1, 10 to 1, 30 wt. % Boron in the range of 0.0020 to 0.0035% by weight, calcium in the range of 0.0007 to 0.0030% by weight and nitrogen in the range of 0.001 to 0.006% by weight.
  • the sum of the contents of carbon and manganese in the high strength steel is in the range of 1.10 to 1.24 wt%, more preferably in the range of 1.1 to 1.23 wt. -%, in the range of 1, 12 to 1, 22 wt .-%, in the range of 1, 13 to 1, 21 wt .-% or in the range of 1, 14 to 1, 20 wt .-%.
  • the high-strength steel according to the invention is preferably characterized by a high minimum yield strength R e H or R p0.2 .
  • the minimum yield strength refers to the tension up to which the steel according to the invention shows no plastic deformation in the case of uniaxial and torque-free tensile stress.
  • the minimum yield strength of the steel according to the invention is at least 1300 MPa, more preferably at least 1350 MPa, at least 1370 MPa, at least 1400 MPa, at least 1440 MPa, at least 1480 MPa or at least 1500 MPa.
  • the minimum yield strength of the high-strength steel according to the invention is determined transversely to the rolling direction and determined according to DIN EN ISO 6892-1 / Method B.
  • the steel according to the invention is preferably characterized by a high tensile strength R m .
  • Tensile strength refers to the maximum mechanical tensile stress that the steel can withstand before it breaks.
  • the tensile strength R m of the steel according to the invention is at least 1400 MPa, more preferably at least 1480 MPa, at least 1500 MPa, at least 1550 MPa, at least 1580 MPa, at least 1600 MPa or at least 1650 MPa.
  • the tensile strength R m of the steel according to the invention is in the range of 1400 to 1700 MPa.
  • the tensile strength of the high-strength steel according to the invention is preferably determined transversely to the rolling direction and determined in accordance with DIN EN ISO 6892-1 / process B.
  • the steel according to the invention is preferably characterized by a high minimum breaking elongation A.
  • the minimum breaking elongation A is a material characteristic value which indicates the permanent extension of the steel after a break.
  • the minimum breaking elongation A is preferably determined in accordance with DIN EN ISO 6892-1 / Method B.
  • the minimum breaking elongation A of the steel according to the invention is preferably at least 8%, more preferably at least 9%, at least 10%, at least 11%, at least 12% or at least 13%.
  • the steel according to the invention is characterized by good toughness properties.
  • a characteristic for toughness properties of a material is, for example, the notch impact work Av.
  • the notched impact Av refers to the energy expended until complete breakage of a material.
  • the notched impact Av of the steel according to the invention is determined according to a Charpy-V test according to DIN EN ISO 148-1. If the specimen is oriented longitudinally to the rolling direction, the impact energy ⁇ V is at least 30 for a test temperature of -40 °. If the specimen is oriented transversely to the rolling direction, the impact energy Av at a test temperature of -40 ° C.
  • the notch impact Av is at a test temperature of -60 ' ⁇ , preferably at least 27 J. , more preferably at least 30 J, at least 40 J, at least 50 J, at least 60 J or at least 70 J. If the sample is oriented transversely to the rolling direction, the notch impact Av is at a test temperature of -60 ' ⁇ , preferably at least 27 J. , more preferably at least 30 J, at least 40 J, at least 50 J, at least 60 J or at least 70 J.
  • the steel according to the invention preferably has a martensitic structure which preferably consists of martensite needles with predominantly uniformly distributed nano-carbide precipitates (Nb, Mo) C or (Nb, Mo) C with traces of vanadium. If the steel according to the invention has such nano-carbide precipitates, they preferably have an average diameter in the range from 1 to 10 nm, more preferably in the range from 2 to 8 nm, in the range from 3 to 8 nm or in the range from 3.0 to 5 , 0 nm. Particularly preferably, the nano-carbide precipitates have a mean diameter of 4 nm.
  • the carbon content of 0.23 to 0.25 wt .-% is preferably required for curing the steel, in particular for setting a martensitic structure with appropriate strength properties.
  • the hardness of martensite increases with increasing carbon content.
  • a carbon content of at least 0.23 wt .-% is required.
  • the carbon content of the steel is limited to at most 0.25% by weight because higher carbon contents would adversely affect the processing behavior in terms of weldability and cold workability.
  • Silicon is preferably used on the one hand in the production of steel as a deoxidizer.
  • the element preferably contributes to increase the strength properties.
  • silicon is an element that preferably exerts a direct influence on the Ac3 transformation temperature.
  • a transformation temperature refers to a temperature at which a material undergoes a phase change or the temperature at which a transformation begins or ends when the transformation occurs in a temperature interval.
  • For steels is u.a. the Ac3 temperature of particular importance. It refers to the temperature at which the transformation of ferrite into austenite ends in a heat process.
  • Austenite is the name for the cubic face-centered modification of pure iron and its mixed crystals.
  • the steel according to the invention At least 0.15% by weight of silicon are required for the steel according to the invention. Adding too much silicon to the steel will have a negative impact on weldability, ductility and toughness properties.
  • the silicon content of the steel according to the invention is at most 0.35 wt .-%, since up to this silicon content preferably even more favorable toughness properties and welding properties can be adjusted.
  • Manganese is preferably used in fine-grain steels as a cost-effective alloying element for improving the mechanical-technological material properties.
  • a minimum content of 0.85% by weight of manganese is needed to achieve the required yield strength and strength levels.
  • Higher manganese contents> 1, 0 wt .-% can lead to a less favorable martensite structure, which may have a coarse Plattenmartensit which negatively the toughness properties and cold working behavior of the steel.
  • the addition of higher manganese contents increases the carbon equivalent CET, which in turn adversely affects the welding behavior and the forming behavior of the steel.
  • higher manganese contents lead to an unfavorable Seigerungs .
  • Segregation refers to demixing of a melt, which can lead directly to a local increase or decrease of certain elements within a mixed crystal.
  • the upper limit of the manganese content is preferably limited to 1, 0 wt .-%.
  • An essential distinguishing feature with regard to the chemical composition of the steel according to the invention in comparison with the steel described in EP 2 267 177 A1 is that for setting a martensitic hardening structure with good toughness and strength properties preferably a higher carbon content in the range of 0.23 to 0.25% by weight and a low manganese content in the range of 0.85 to 1, 0 wt .-% must be set.
  • a carbon content in the range of 0.23 to 0.25% by weight, in conjunction with a coordinated manganese content is preferably required for setting a purely martensitic structure with corresponding strength properties.
  • carbon contents in the range from 0.23 to 0.25% by weight it is preferable for carbon contents in the range from 0.23 to 0.25% by weight to have matched manganese contents in the range from 0.85 to 1.0% by weight. to take into account.
  • the adapted combination of the elements manganese and carbon results in an optimally adjusted microstructure with very good toughness and strength properties. Therefore, according to the invention, the sum of the contents of carbon and manganese is at least 1.08% by weight and at most 1.25% by weight.
  • the condition that the sum of the contents of carbon and manganese is less than or equal to 1.17% by weight is particularly preferred.
  • the iron companion phosphor has a very strong toughness and counts in Baug. Fine grain steels to the unwanted accompanying elements.
  • phosphorus can lead to strong segregations during solidification of the melt.
  • the element phosphorus is therefore in the steel according to the invention to ⁇ 0.012 wt .-%, preferably on
  • Sulfur is an undesirable accompanying element which deteriorates the notched impact strength and the formability or the cold forming behavior.
  • the sulfur is present after solidification in the form of manganese sulfide inclusions, which are stretched during rolling to plates in parallel to or cell in the rolling direction and have a very unfavorable effect on the material properties, in particular on the isotropy of the material (toughness properties transverse to rolling direction).
  • the sulfur content of the steel according to the invention is therefore preferably limited to ⁇ 0.003 wt .-% and is preferably reduced by a targeted calcium treatment.
  • the calcium treatment is preferably used to specifically influence the sulfide form (spherical shape).
  • Aluminum is preferably used in the steel according to the invention in contents in the range of 0.07-0.10 wt .-%, both as a deoxidizer and as a micro-alloying element.
  • a deoxidizer it preferably contributes to binding off the nitrogen present in the steel, so that the boron, which is preferably present in amounts of 0.0020-0.0035% by weight, can exert its strength-increasing effect.
  • aluminum is preferably used as a micro-alloying element for grain refining. Of all the elements that are added to the steel to specifically influence the austenite grain size, aluminum is the most effective.
  • a fine dispersion of AIN particles preferably effectively inhibits austenite grain growth.
  • aluminum preferably increases the aging resistance of the steel and reduces voids and segregations.
  • the voids are a cavity formed during the solidification of cast parts.
  • the aluminum content is at least 0.07 wt.% To set the desired fine grain in the steel.
  • this aluminum content has a positive effect on the toughness properties and cold working behavior of the steel.
  • the aluminum content is at most 0.1% by weight, since aluminum contents above 0.1% by weight can lead to free aluminum, which increases the risk of the formation of undesired aluminum oxide.
  • Chromium in contents of 0.65-0.75 wt .-% preferably improves the hardenability of austenite. Due to the carbide-forming effect, chromium preferably supports the strength properties of the steel. For this reason, at least 0.65 wt.% Chromium is required. In addition, addition of the element chromium has a positive effect on the hardenability of steels and thus also increases the wear resistance. The addition of higher chromium contents reduces the toughness properties and adversely affects the sweat behavior by increasing the carbon equivalent CET. Therefore, according to the present invention, the upper limit of the range of chromium contents is limited to 0.75 wt%. Copper is one of the undesirable accompanying elements. The content of copper is preferably limited to ⁇ 0.1% by weight.
  • Niobium is used in amounts of 0.02-0.03 wt .-%, preferably for nitrogen setting. Moreover, niobium is preferably present in the steel of the present invention to aid austenite grain refinement; The finely divided niobium carbonitrides in austenite effectively hinder grain growth and thus have a positive effect on the strength and toughness properties of the steel.
  • the niobium content of the steel according to the invention is limited to at most 0.03 wt .-% in order to avoid the formation of toughness niobium carbide. Niobium is preferably effective from contents above 0.02 wt .-%.
  • niobium in water-hardened and tempered steels showed that the positive influence of niobium on the mechanical properties can be achieved in amounts of 0.02-0.03% by weight. It is known that niobium at levels of 0.02-0.03% by weight in water-hardened and tempered steels has a positive influence on the strength and toughness properties by its grain-refining effect. In addition, niobium in microalloyed boron steels contributes to the improvement of the degree of purity and has a positive effect on the toughness properties in the weld.
  • Molybdenum is added to the steel according to the invention in amounts of 0.55-0.65 wt .-% preferably for increasing the strength and improving the through-hardenability.
  • a molybdenum content of at least 0.55 wt .-% is required.
  • molybdenum preferably improves the tempering resistance of the steel and has a positive effect on heat resistance and toughness properties.
  • molybdenum is preferably used as a carbide former for increasing the yield strength and toughness in contents of at most 0.7% by weight. Higher molybdenum contents increase the carbon equivalent CET and have a negative effect on the welding behavior. For optimum welding behavior, therefore, the molybdenum content of the steel according to the invention is limited to not more than 0.65% by weight.
  • the nitrogen content of the steel according to the invention for the melt analysis is preferably limited to ⁇ 0.006 wt .-%.
  • the content of nitrogen in the steel according to the invention is preferably in the range from 0.001 to 0.006% by weight.
  • the nitrogen present in the melt of the steel according to the invention is preferably hardened to form sparingly soluble nitrides (AIN).
  • the content of titanium in the steel according to the invention is preferably limited to ⁇ 0.008% by weight.
  • Vanadium is preferably added to the steel of the invention at levels of 0.035-0.05% by weight for grain refining and to increase yield strength and strength levels.
  • the fine-grained precipitates of vanadium carbonitrides also have a strong precipitation-hardening effect. Since higher vanadium contents reduce the toughness properties, the vanadium content of the steel according to the invention is at most 0.05% by weight.
  • nickel at levels of 1, 10-1, 30 wt .-% is preferably required to reach the strength and yield strength level.
  • nickel preferably increases the hardenability and through-hardening. Higher nickel contents have only a minor effect on the strength properties of the steel, whereas they lead to an improvement in the toughness properties.
  • the micro-alloying element boron atomically retards the microstructure transformation to ferrite and / or bainite and improves the hardenability and strength of fine-grained structural steels.
  • this mode of action of boron can only be used if the nitrogen is stably bound by strong nitride formers.
  • a boron content in the range of 0.0020-0.0035% by weight is added to the steel according to the invention.
  • the nitrogen bonding is preferably carried out via the elements aluminum and niobium.
  • the boron content of the steel according to the invention is limited to at most 0.0035 wt .-%, since the strength-increasing effect initially increases with increasing boron content and falls above a maximum again.
  • Tin is one of the undesirable accompanying elements.
  • the content of tin in the steel according to the invention is preferably ⁇ 0.03% by weight.
  • the element hydrogen is preferably reduced by vacuum treatment preferably to contents ⁇ 2.0 ppm.
  • Arsenic is one of the undesirable accompanying elements and its content in the steel according to the invention is therefore preferably ⁇ 0.01 wt .-%.
  • Calcium is preferably added to the melt as a desulfurizing agent and for controlled Sulphidformbeeinlung, which preferably leads to an altered plasticity of the sulfides in the hot working.
  • the cold-forming behavior of the steel according to the invention preferably also significantly improves by the addition of calcium.
  • the calcium content of the flat steel product according to the invention is therefore preferably 0.0007-0.0030% by weight.
  • Cobalt is one of the production-related unavoidable accompanying elements in the steel. Its content in the steel according to the invention is preferably ⁇ 0.01% by weight.
  • the welding behavior of a steel can be described by means of various carbon equivalents.
  • the carbon equivalent is a measure in material science for assessing the weldability of steels.
  • the carbon content and a variety of other alloying elements in the steel affect its behavior.
  • the carbon equivalent and the weighted proportion of the elements which influence the weldability of the steel in a similar way as would be expected from carbon are therefore summarized in a numerical value in the carbon equivalent.
  • a low value of the carbon equivalent implies a good weldability.
  • Higher values require preheating of the material, depending on the processing thickness.
  • the workpiece can be welded only with increased effort, since it can come to martensite by cold or hardening cracks. There is no generally valid procedure for the calculation of the carbon equivalent.
  • One possible carbon equivalent is the Pcm according to Ito & Bessyo.
  • the steel has an austenite grain size of> 1 1 according to DIN EN ISO 643.
  • the carbon equivalent Pcm of the steel according to the invention can be calculated with
  • Pcm [C] + [Si] / 30 + [Mn] / 20 + [Cu] / 20 + [Ni] / 60 + [Cr] / 20 + [Mo] / 15 + [V] / 10 + 5 B];
  • Ceq 0.38 wt% ⁇ Pcm ⁇ 0.44 wt%, more preferably 0.38% ⁇ Pcm ⁇ 0.41%.
  • Another carbon equivalent is Ceq according to Kihara.
  • the Ceq of the high-strength steel can be calculated with
  • the steel according to the invention can be welded well.
  • a prerequisite for welding high-strength fine-grained steels is that the welded joints are free from cracks. Whether a steel or weld metal is sensitive to cold cracks can be estimated by calculating the carbon equivalent CET.
  • the elements manganese, chromium, molybdenum, vanadium, copper and nickel favor the cold cracking behavior.
  • the CET can be calculated with
  • the preheating is used as an effective countermeasure to avoid cold cracking, wherein during welding, the cooling of the seam area is preferably delayed during and / or after welding.
  • the minimum preheating temperature required for welding the high-strength steel can be calculated using
  • T P ( ⁇ C) 700 CET + 160 tanh (d / 35) + 62 HD 0 35 + (53 CET - 32) Q - 330,
  • HD is the hydrogen content of the weld metal in cm 3 / 100g and Q is the heat input during welding in kJ / mm,
  • T p should be at most 220 ⁇ .
  • the steel according to the invention is preferably used in construction, in general mechanical engineering and / or in electrical engineering.
  • the steel according to the invention is particularly preferably used in crane and mobile crane construction.
  • a further aspect of the invention relates to a method for producing a flat steel product, the method comprising the following steps:
  • Chromium 0.65-0.75 wt%
  • Niobium 0.02-0.03 wt%
  • Molybdenum 0.55-0.65 wt%
  • Vanadium 0.035-0.05% by weight
  • Nickel 1, 10-1, 30% by weight
  • Phosphorus ⁇ 0.012 wt%
  • Copper ⁇ 0.10% by weight
  • Nitrogen ⁇ 0.006 wt%
  • Titanium ⁇ 0.008 wt%
  • Tin ⁇ 0.03 wt%
  • Arsenic ⁇ 0.01% by weight; and or
  • Cobalt ⁇ 0.01% by weight
  • the molten steel according to the invention may additionally comprise one of the elements phosphorus, sulfur, copper, nitrogen, titanium, tin, hydrogen, arsenic or cobalt.
  • the content of nitrogen in the steel according to the invention is preferably in the range from 0.001 to 0.006% by weight.
  • the molten steel according to the invention comprises carbon in the range of 0.23 to 0.25 wt .-%, silicon in the range of 0.15 to 0.35 wt .-%, manganese in the range of 0.85 to 1.00 wt%, aluminum in the range of 0.07 to 0.10 wt%, chromium in the range of 0.65 to 0.75 wt%, niobium in the range of 0.02 to 0 , 03 wt .-%, molybdenum in the range of 0.55 to 0.65 wt .-%, vanadium in the range of 0.035 to 0.05 wt .-%, nickel in the range of 1, 10 to 1, 30 wt. % Boron in the range of 0.0020 to 0.0035% by weight, calcium in the range of 0.0007 to 0.0030% by weight and nitrogen in the range of 0.001 to 0.006% by weight.
  • the molten steel is produced in a converter steelworks.
  • the molten steel is subjected to a vacuum treatment to reduce the hydrogen content, preferably ⁇ 2.00 ppm.
  • the desulfurization and the targeted calcium treatment for Sulfidformbeeinl ung to reduce the material anisotropy by a calcium treatment of the molten steel with calcium contents in the range of 0.0007 to 0.0030 wt .-%.
  • step (c) of the process according to the invention the molten steel is poured into a slab on a continuous casting plant.
  • the continuously cast strand solidifies over the formation of a solid strand shell, and then solidifies in the direction of the strand center. This can lead to accumulations of alloying elements on the solidification front. These can cause nuclear segregation in the solidified strand. Segregations are melts of a melt, which can lead directly to a local increase or decrease of certain elements within the mixed crystal. They arise at the transition of the melt in the solid state. The core segregations can lead to inhomogeneities and uneven properties over the strand cross-section.
  • the method of soft reduction is preferably used for the positive influence of the segregation zone in the slab. In this case, the still not completely solidified strand and thus the still liquid core is slightly rolled.
  • step (d) of the process of the invention the slab formed in step (c) is preferably heated to a temperature in the range of 1100 ° C to 1250 ° C, more preferably in the range of 1200 ° C to 1250 ° C.
  • the heating rate is preferably in the range of 1 to 4 K / min.
  • the slab is preferably descaled.
  • the slab is descaled with a high pressure slab scrubber.
  • the scale layer formed on the surface of steel at high temperatures preferably consisting of iron oxides.
  • the descaling can be carried out by customary methods known to the person skilled in the art, for example by pickling, brushing, blasting, bending descaling or flame blasting.
  • Descaling preferably takes place with water at a pressure in the range from 150 to 300 bar.
  • the hot rolling of the slab is preferably carried out to a flat steel product.
  • the rolling start temperature is in the range of 1050 ⁇ € to 1200 ⁇ €.
  • the final rolling temperature is preferably> 880 ° C and less than 1000 ° C.
  • a pass reduction e of> 10% is achieved in each rolling pass.
  • the stitch loss e for each rolling pass is in the range of 10 to 50%.
  • an overall ev is ev of 80 to 98% achieved.
  • the hot rolling of the slab to a flat steel product is reversing on a plate mill preferably with a duo or four-high rolling mill and an optionally subsequent finishing mill with multiple rolling mills or a hot strip mill, consisting of a roughing mill and a finishing train with up to seven stands.
  • the steel flat product according to the invention is subjected to at least one hardening treatment immediately after the hot rolling out of the rolling heat, the hardening treatment comprising a rapid quenching of the flat steel product to a temperature below 200 ° C., the cooling rate being at least 25 K / s is.
  • the flat steel product when the flat steel product is subjected to a hardening treatment immediately after the hot rolling from the rolling heat, the flat steel product becomes the hardening treatment without further heating subjected.
  • the steel flat product after hot rolling has a final rolling temperature of at least 860 ° C.
  • the steel flat product after hot rolling is subjected to at least one hardening treatment, wherein the hardening treatment comprises the following steps:
  • the Ac3 temperature indicates the transformation temperature when heating the steel at which the transformation of the ferrite into the austenite ends.
  • the Ac3 temperature can be approximately calculated according to Hougardy with:
  • Heating the steel flat product to austenitizing temperature for hardening treatment is required in particular when the steel flat product cools after hot rolling.
  • the steel flat product for hardening treatment is first heated to an austenitizing temperature which is at least 40K above the Ac3 temperature of the steel according to the invention in order to achieve complete austenitization of the material.
  • the steel flat product for hardening treatment is brought to an austenitizing temperature in the range of 860 ° C to at most 920 ° C, more preferably in the range of 870 ° C to 920 ° C.
  • the flat steel product is quenched after heating in a suitable quenching medium so fast that at least 70% martensite, preferably 80% martensite, more preferably 90% martensite, most preferably 100% martensite forms.
  • Suitable quenching media are, for example, water or oil.
  • the flat steel product according to the invention is quenched rapidly, that is to say at a cooling rate of at least 25 K / s from the austenitizing temperature to a temperature of at most 200 ° C. Cooling rates of at least 25 K / s, more preferably at least 50 K / s, at least 100 K / s, at least 150 K / s or at least 200 K / s are preferably required between 800 ° C and 500 ° C.
  • the steel flat product is subjected to at least one further hardening treatment after the hardening treatment from the rolling heat, the hardening treatment comprising the following steps:
  • the minimum austenitizing temperature of the flat steel product according to the invention for uniform austenitization is preferably greater than or equal to 860 ' ⁇ .
  • Lower Austenitmaschinestemperaturen of less than 860 ' ⁇ lead in combination with the coordinated chemical composition of the flat steel product according to the invention preferably to an undesirable Generalaustenitmaschine which is to be prevented.
  • the austenitizing temperature should preferably be ⁇ 920 ⁇ , since higher temperatures promote austenite grain growth, which would lead to a reduction of the mechanical-technological properties. Investigations have shown that the optimum austenitizing temperature for the flat steel product according to the invention is preferably about 880 ' ⁇ .
  • the austenitic grain growth is preferably also influenced by the austenitizing time, but the temperature preferably has a greater influence on the austenite grain growth.
  • the holding time is at the austenitizing temperature of the inventive 60 minutes, more preferably at most 30 minutes or at most 15 minutes.
  • the hardening treatment of the flat steel product takes place several times, in particular twice or three times.
  • the fine granularity of the flat steel product according to the invention is preferably selectively influenced or preferably improved by a particle size class according to DIN EN ISO 643 by a specific repetition of the hardening process.
  • a second hardening treatment by the effect of austenite grain refinement preferably leads to a very fine martensitic structure with improved mechanical and technological properties.
  • the steel flat product may be subjected to a hardening treatment either immediately after hot rolling from the rolling heat, or the flat steel product may first be heated to an austenitizing temperature which is at least 40K above the Ac3 temperature of the steel of the invention and then be subjected to a hardening treatment.
  • the flat steel product is first heated to an austenitizing temperature which is at least 40 K above the Ac3 temperature of the steel according to the invention, and is then subjected to a hardening treatment.
  • the steel flat product is tempered after the hardening treatment, wherein the tempering time of the tempering treatment is less than 15 minutes and the temperature of the tempering treatment is below the Ac1 temperature, wherein the Ac1 temperature can be approximately calculated according to Hougardy
  • Ad [° C] 739-22 * [C] + 2 * [Si] - 7 * [Mn] + 14 * [Cr] + 13 * [Mo] - 13 * [Ni] + 20 * [V] wherein [C], [Si], [Mn], [Cr], [Mo], [Ni] and [V] are the mass fractions of the respective elements in the high-strength steel in% by weight.
  • the Ac1 temperature indicates the transformation temperature when heating the steel at which the formation of austenite begins.
  • the hold time is at most 10 minutes.
  • Tempering comprises a heat treatment in which the flat steel product according to the invention is specifically heated in order to influence its properties.
  • the tempering of the finely dispersed martensitic microstructure preferably takes place in the temperature range of 150 ° C to 300 ⁇ €, more preferably in the range of 225 ⁇ € to 275 ° C.
  • the short-term tempering of the finely-dispersed martensitic microstructure sets an optimum combination of strength and toughness, with some reduction in strength being necessary in favor of the toughness properties.
  • the flat steel product according to the invention is twice cured and tempered. More preferably, the steel compartment product according to the invention is triple-hardened and tempered.
  • a former austenite grain size of particle size class 12 according to DIN EN ISO 643 is achieved.
  • the former austenitic grain is to be understood as the austenitic grain present before the hardening treatment. If the flat steel product according to the invention is subjected to a second hardening treatment or a double hardening, this preferably brings about a further halving of the grain size and a former austenite grain size of grain size class 13 according to DIN EN ISO 643 is preferably set.
  • the grain refining preferably contributes to an improvement in the mechanical-technological properties, in particular to an increase in the yield strength and toughness level.
  • the minimum yield strength of the flat steel product according to the invention after the hardening treatment is at least 1 .300 MPa, more preferably at least 1350 MPa, at least 1370 MPa, at least 1400 MPa, at least 1440 MPa, at least 1480 MPa or at least 1,500 MPa.
  • the tensile strength of the flat steel product according to the invention after the hardening treatment is at least 1 .400 MPa, more preferably at least 1480 MPa, at least 1500 MPa, at least 1550 MPa, at least 1580 MPa, at least 1600 MPa or at least 1650 MPa.
  • the flat steel product according to the invention before the hardening treatment has a former austenite grain size of> 1 1 according to DIN EN ISO 643 (05.2013) or according to G 0551 (2005), which in particular results in a finely dispersed martensitic microstructure with homogeneous strength. and toughness properties.
  • the flat steel product according to the invention has a substantially finer former austenite grain compared to the flat steel product known from EP 2 267 177 A1.
  • the flat steel product according to the invention is preferably hardened directly from the rolling heat after the last rolling pass by means of a suitable water quenching device.
  • the flat steel product according to the invention becomes fast, that is to say with a cooling rate of at least 25 K / s from a final rolling temperature> 880 ° C to a temperature of at most 200 ⁇ quenched.
  • the cooling rate between 800 ° C. and 500 ° C. is preferably at least 25 K / s, preferably at least 50 K / s, more preferably at least 100 K / s, at least 150 K / s or at least 200 K / s.
  • the flat steel product can be wound up into a coil.
  • the winding of rolled flat steel products is referred to and a coil is the name for a wound metal strip.
  • the flat steel product according to the invention is rewound, the reel temperature being at least 800 ° C.
  • the hot strip from the rolling heat is quenched by means of water to a temperature ⁇ 200 ⁇ .
  • a further distinguishing feature of the flat steel product according to the invention in comparison with the steel product known from EP 2 267 177 A1 is that the invention can be produced in sheet thicknesses of 3.0 mm to 40.0 mm and sheet widths of up to 3900 mm.
  • the sheet thickness of the flat steel product is in the range of 3.0 mm to 40.0 mm, more preferably in the range of 4.0 to 15.0 mm.
  • the sheet width of the flat steel product according to the invention is preferably ⁇ 3900 mm.
  • To produce the flat steel product according to the invention is preferably a higher carbon content in the range of 0.23 to 0.25 wt .-%, preferably in combination with a customized analysis grading of the elements chromium, nickel, manganese and molybdenum to adjust a preferably pure martensitic structure with appropriate strength properties up to a maximum sheet thickness of 40.0 mm needed.
  • a reduction in the carbon content would postpone the start of bainite formation to shorter cooling times, so that only lower sheet thicknesses would consist of a purely martensitic structure.
  • Higher sheet thicknesses would have an undesirable mixed structure of martensite and different bainite parts, which in turn would adversely affect the mechanical and technological properties of the flat steel product according to the invention.
  • the invention will be described below with reference to exemplary embodiments.
  • All steel melts were cast into slabs, which were then heated at a heating rate of 4 K / min to a slab temperature according to Table 2, descaled with water prior to rolling at a pressure of 200 bar and then with a drop of e 10-50% and a Total deformation ev between 81 and 98% were rolled out to flat steel products.
  • the flat steel products were quiescent in air or quiescent cooled in the stack.
  • the steel flat products were heated to an austenitizing temperature as shown in Table 3, held at that temperature for 15 minutes, then quenched from the austenitizing temperature with water to a cooling stop temperature.
  • Some flat steel products were then heated to a tempering temperature shown in Table 5, held at tempering temperature for 10 minutes and then cooled in air.
  • the mechanical properties of the tensile and the impact test as well as the surface hardness and the former austenite grain size can for the generated Steel flat products are taken from Table 6.
  • the austenite grain size shown in Table 6 is the former austenite grain size.
  • the determination of the former austenite grain size is carried out according to DIN EN ISO 643 on longitudinal sections, which were taken from the flat steel products in single- to triple-hardened state.
  • the etching was carried out by the method of Bechet-Beaujard with concentrated picric acid.
  • the tensile tests for determining the yield strength Rp0.2, the tensile strength R m and the elongation at break A were carried out according to DIN EN ISO 6892-1 on transverse samples.
  • the notched bar impact tests to determine the impact energy Av at test temperatures of -20 ° C, -40 ⁇ € and -60 ° C were carried out on transverse samples in accordance with DIN EN ISO 148-1. If hardness values are indicated, this is the Brinell hardness. The hardness is measured approx. 1 mm below the surface of the sheet and is determined in accordance with DIN EN ISO 6506-1.
  • the structural analysis was carried out by means of light and scanning electron microscopy on longitudinal sections, which were removed from the flat steel products and etched with Nital.
  • the field emission transmission electron microscope (FE-TEM) was used to determine both the state of the microstructure and the state of precipitation.
  • FE-TEM field emission transmission electron microscope
  • STEM bright field STEM
  • dark field STEM mode were used.
  • the cold forming behavior was tested by bending tests according to DIN EN ISO 7438 with the bending line perpendicular and parallel to the rolling direction, with a bending angle> 90 °.
  • melts A to D were produced in the laboratory and included as comparative examples.
  • these melts In comparison with the analysis of the flat steel product according to the invention (molten steels E and F), these melts have a lower carbon content, which leads to a lower yield strength and tensile strength level.
  • the required for the flat steel product according to the invention strength properties are not met by the steel melts of the comparative examples.
  • the tested in the laboratory molten steel E has in comparison to the comparative examples, a higher carbon content, so that the required yield strength and tensile strength level is achieved at the same time sufficient toughness for the flat steel product according to the invention.
  • an operating melt F was produced for the flat steel product according to the invention.
  • the mechanical-technological characteristics of the operating melt F were 880 ° C after " hardening and tempering" (samples F1 to F1 1), after 2x hardening and tempering (samples F12 to F37) and after 3x hardening and tempering (samples 38 to F50) for the austenitizing temperatures or 920 ⁇ and can be found in Tables 6 and 7.
  • variants I x curing at austenitizing temperatures of 880 ⁇ € (samples F7 to F1 1) or 920 ⁇ € (samples F1 to F6) and for the variant 2 x curing at an austenitizing temperature A satisfactory yield strength and tensile strength level with good toughness was achieved after tempering at 920 ° C. (sample F12)
  • the cold working behavior of these variants can be described as satisfactory
  • the variants mentioned have an austenite grain size of particle size class KG-12 according to DIN EN ISO 643
  • coarser martensite plates with coarser precipitates of (Nb, Mo) C or (Nb, Mo) C are detected with traces of vanadium.
  • the precipitates have a majority average diameter of about 8 nm. Residual austenite was not detected but partially acicular cementite (Fe 3 C) was present. Cementite and coarse precipitates extract carbon from the microstructure and soften their martensite. Therefore, these variants have a lower level of strength compared to the 2-time hardening process at an austenitizing temperature of 880 ° C and tempering (samples F13 to F37).
  • a comparison of the sample F4 with the sample F12 and a comparison of the samples F7 to F1 1 with the samples F13 to F37 shows that in samples with otherwise identical conditions, the yield strength, tensile strength and impact energy for the variants with dual hardening and Tempering is improved compared to simple hardening and tempering.
  • a comparison of samples F13 to F37 with samples F38 to F50 shows that the yield strength and tensile strength for the triple hardening and tempering samples (F38 to F50), by further reducing the former austenite grain size, are again increased over the double-sample samples Hardening and tempering (F13 to F37).
  • a comparison of the samples F1 to F6 with the samples F7 to F1 1 and a comparison of the sample F12 with sample F35 shows that under otherwise identical conditions mechanical properties, yield strength, tensile strength and toughness are improved for the variants having lower austenitizing temperatures of 880 ° C compared to an elevated austenitizing temperature of 920 ° C. Particularly good results and an improvement in the cold forming behavior could be obtained for samples which were both double or triple hardened and austenitized at lower temperatures of 880 ' ⁇ for the hardening process (samples F13 to F37).
  • the flat steel product according to the invention has very uniformly distributed nano-carbide precipitations (Nb, Mo) C or (Nb, Mo) C with traces according to the process of hardening at an austenitizing temperature of 880 ° C. and tempering Vanadium contains.
  • the majority of nano-carbide precipitates have a mean diameter of 4 nm. Retained austenite was not detected. There was also no acicular cementite (Fe 3 C) present.
  • the special matrix of the martensitic microstructure consisting of very fine martensite needle packs, in combination with the very fine and uniformly distributed nano-carbide precipitates in the flat steel product according to the invention to a significant increase in the yield strength and strength level at the same time good cold workability ,
  • the yield strength and strength level of the flat steel product according to the invention lies in the choice of the process 2x hardening (austenitizing temperature of 880 ° C) and tempering, compared to the variant I x hardness (austenitizing temperature of 880 ° C) and tempering, with a stable good toughness level round 60 MPa higher.

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Abstract

L'invention concerne un acier à haute résistance offrant une limite élastique minimale de 1.300 MPa, un procédé de fabrication d'un tel acier et son utilisation.
EP15744166.8A 2015-07-24 2015-07-24 Acier à haute résistance doté d'une limite élastique minimale et procédé de fabrication d'un tel acier Withdrawn EP3325677A1 (fr)

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