EP3325678B1 - Formable lightweight steel with improved mechanical properties and method for producing semi-finished products from said steel - Google Patents

Formable lightweight steel with improved mechanical properties and method for producing semi-finished products from said steel Download PDF

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EP3325678B1
EP3325678B1 EP16750113.9A EP16750113A EP3325678B1 EP 3325678 B1 EP3325678 B1 EP 3325678B1 EP 16750113 A EP16750113 A EP 16750113A EP 3325678 B1 EP3325678 B1 EP 3325678B1
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steel
max
strip
annealing
cold
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German (de)
French (fr)
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EP3325678A1 (en
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Peter PALZER
Zacharias Georgeou
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Salzgitter Flachstahl GmbH
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Salzgitter Flachstahl GmbH
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    • 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • 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
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold 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
    • 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
    • C22C38/02—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
    • C22C38/06—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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/26—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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium 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
    • 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
    • C21D8/0231—Warm 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
    • C21D8/0273—Final recrystallisation annealing

Definitions

  • the invention relates to a formable lightweight structural steel with improved mechanical properties and a high resistance to delayed hydrogen-induced crack formation, according to claim 1. Furthermore, the invention relates to a method for producing semi-finished products from this steel.
  • semi-finished products are understood to mean hot or cold strip produced from this steel or an intermediate or end product produced therefrom, such as pipes, for example.
  • Known formable lightweight steel has, for example, the following alloy composition (in% by weight): C 0.04 to ⁇ 1.0, Al 0.05 to ⁇ 4.0, Si 0.05 to ⁇ 6.0, Mn 9, 0 to ⁇ 18.0, the remainder being iron including the usual accompanying steel elements
  • Cr, Cu, Ti, Zr, V and Nb can be added depending on the requirements.
  • This lightweight steel has a partially stabilized ⁇ mixed crystal structure with a defined stacking fault energy with a z. T. multiple TRIP effect, which enables the stress or strain-induced transformation of a face-centered ⁇ mixed crystal (austenite) into an ⁇ -martensite (hexagonal closest packing of spheres) and then with further deformation into a body-centered ⁇ -martensite and residual austenite.
  • TRIP Transformation Induced Plasticity
  • TWIP winning Induced Plasticity
  • an austenitic steel which is said to have excellent resistance to delayed crack formation.
  • the steel contains: 0.5 to 0.8 C, 10 to 17 Mn, at least 1.0 Al, at most 0.5 Si, at most 0.020 S, at most 0.050 P, 50 to 200 ppm N and 0.050 to 0.25 V.
  • a steel alloy for a high-strength cold-rolled steel sheet is known, which is also said to have an improved resistance to delayed cracking.
  • the steel contains: 0.05 to 0.3 C, 0.3 to 1.6 Si, 4.0 to 7.0 Mn, 0.5 to 2.0 Al, 0 .01 to 0.1 Cr, 0.02 to 0.1 Ni, 0.005 to 0.03 Ti, 5 to 30 ppm B, 0.01 to 0.03 Sb, and 0.008 or less S.
  • EP 2 128 293 A1 a lightweight steel with an improved elongation known, having in addition to iron and impurities in% by weight: 0.2 to 0.8 C, 2 to 10 Mn, 0.2 or less P, at most 0.015 S, 3.0 to 15 Al, at most 0.01 N and an Mn / Al ratio of 0.4 to 1.0.
  • EP 2 778 247 A1 discloses a steel sheet for hot forming with improved collision suitability, which in addition to iron and unavoidable impurities in wt .-% 0.01 to 0.5 C, 3 or less Si, 3 to 15 Mn, 0.0001 to 0.1 P, 0, 0001 to 0.03 S, 3 or less Al, and 0.03 or less N.
  • Cr, Mo, W, Ti, Nb, Zr, V, Cu, Ni, Sb, Sn or B can be added to the alloy.
  • the object of the invention is to provide a lightweight structural steel of the generic type which, while retaining very good mechanical properties (ductility, strength), does not have the effect of delayed crack formation or hydrogen embrittlement.
  • the product of tensile strength and elongation at break is advantageously used as a basis, which is a measure of the performance of the material.
  • the product or semi-finished product produced from the alloy according to the invention by forming which can be, for example, hot strip, cold strip, flexibly rolled hot or cold strip, a pipe or a body component, is therefore advantageously heat treated at 480 to 770 ° C for 1 minute to 48 hours, for example in a hood annealing with predominantly long annealing times or in a continuous annealing with predominantly short annealing times.
  • Such annealing can also take place before the final shaping into a finished product, for example on the cold strip, which is then further processed.
  • the time of annealing can therefore be flexibly adapted to the manufacturing process.
  • Annealing the end product in addition to annealing the semi-finished product can lead to a further improvement in the material properties.
  • the cast strip with a maximum thickness of 5 mm produced by means of a near-net-shape casting process it is particularly advantageous to cold-roll it to a uniform thickness or to flexibly cold-roll it to different thicknesses and then anneal the cold strip with the following parameters: Annealing temperature: 480 to 770 ° C Annealing time: 1 minute to 48 hours.
  • the annealing treatment is preferably carried out at temperatures of 670 to 770 ° C. for annealing times of 1 minute to 12 hours, since lower temperatures and longer annealing times lead to lower tensile strength and elongation at break.
  • continuous annealing is preferably used for short annealing times for hot strip, cold strip and flexibly rolled strip, and hood annealing is preferably used for long annealing times.
  • other annealing devices with the specified parameters such as a muffle furnace, can be used.
  • antimony also improves the behavior towards it Significantly improved hydrogen (delayed crack formation and hydrogen embrittlement).
  • the reason for the improvement in the material properties is that antimony hinders the diffusion of carbon and aluminum. Furthermore, antimony lowers the interfacial energy, which leads to a finer distribution of the carbides.
  • the reduced carbon diffusion thus delays the local accumulation of carbon at the grain boundaries and in the structure as well as, in connection with aluminum, the formation of kappa carbides or, in particular with V, Nb, Mo, Cr, W, Zr and Ti, the formation of larger local carbides. This improves the homogeneity of the material with the described positive effects on the mechanical properties and the resistance to delayed crack formation and hydrogen embrittlement.
  • the precipitation of finely divided carbides leads to a grain refinement in the structure, which is accompanied by an improvement in the behavior towards negative effects caused by hydrogen (delayed crack formation, hydrogen embrittlement) as well as an increase in strength and an improvement in toughness and elongation properties.
  • antimony according to the invention in low contents of up to a maximum of 0.3% by weight therefore significantly improves the behavior of the material with respect to influences caused by hydrogen.
  • antimony causes an undesirably strong precipitation of antimony at the grain boundaries and thereby reduces the toughness and elongation properties.
  • a content of at least 30 ppm is necessary for antimony to be effective.
  • antimony contents of more than 0.3% by weight make the material brittle and should therefore be avoided.
  • the optimum content of antimony is 0.1% by weight.
  • the small carbides (predominantly Cr, Mo, Ti, Nb, V, W, Zr and Kappa carbides), which are separated out much more finely than in the prior art, improve the degree of utilization of the corresponding alloying elements, which potentially allows a reduction in the amount added. Furthermore, due to the reduced carbon diffusion and the reduced grain growth due to the addition of antimony, the process window for the invention The resulting mechanical properties of the steel are less sensitive to process fluctuations (temperature, time).
  • An alloy according to claim 3, using optimized heat treatment parameters (see Tables 1 to 4), has a product of tensile strength and elongation at break of at least 20,000 MPa% and a tensile strength of at least 800 MPa.
  • the product of tensile strength and elongation at break is a measure of the performance of the material during forming.
  • An alloy according to one embodiment has a product of tensile strength and elongation at break of at least 30,000 MPa% and a tensile strength of at least 800 MPa.
  • An alloy according to a further embodiment has finely divided kappa carbide precipitates and a product of tensile strength and elongation at break of at least 30,000 MPa% and a yield strength of at least 700 MPa and a tensile strength of at least 800 MPa.
  • Table 1 shows the alloy compositions tested. The content of Sb and additions of Nb were varied while the chemical composition was otherwise approximately the same.

Description

Die Erfindung betrifft einen umformbaren Leichtbaustahl mit verbesserten mechanischen Eigenschaften und einem hohen Widerstand gegen verzögerte wasserstoffinduzierte Rissbildung, gemäß Patentanspruch 1. Des Weiteren betrifft die Erfindung ein Verfahren zur Herstellung von Halbzeug aus diesem Stahl.The invention relates to a formable lightweight structural steel with improved mechanical properties and a high resistance to delayed hydrogen-induced crack formation, according to claim 1. Furthermore, the invention relates to a method for producing semi-finished products from this steel.

Unter Halbzeug wird im Folgenden aus diesem Stahl hergestelltes Warm- oder Kaltband oder ein daraus hergestelltes Zwischen- oder Endprodukt, wie zum Beispiel Rohre, verstanden.In the following, semi-finished products are understood to mean hot or cold strip produced from this steel or an intermediate or end product produced therefrom, such as pipes, for example.

In den letzten Jahren hat es große Entwicklungsfortschritte auf dem Gebiet der sogenannten Leichtbaustähle gegeben, die sich durch ein geringes spezifisches Gewicht bei gleichzeitig hohen Festigkeiten und Zähigkeiten auszeichnen sowie eine hohe Duktilität aufweisen und damit für den Fahrzeugbau von großem Interesse sind.In recent years there have been great advances in development in the field of so-called lightweight steels, which are characterized by a low specific weight combined with high strength and toughness and high ductility and are therefore of great interest for vehicle construction.

Bei diesen im Ausgangszustand austenitischen Stählen wird durch den hohen Anteil von Legierungsbestandteilen (Si, Al) mit einem spezifischen Gewicht weit unterhalb des spezifischen Gewichts von Eisen eine für die Automobilindustrie vorteilhafte Gewichtsreduzierung unter Beibehaltung der bisherigen Konstruktionsbauweise erreicht.With these steels, which are austenitic in their initial state, the high proportion of alloy components (Si, Al) with a specific weight far below the specific weight of iron achieves a weight reduction that is advantageous for the automotive industry while maintaining the previous design.

Der aus der Offenlegungsschrift DE 10 2004 061 284 A1 bekannte umformbare Leichtbaustahl weist zum Beispiel folgende Legierungszusammensetzung (in Gew.-%) auf: C 0,04 bis ≤ 1,0, Al 0,05 bis < 4,0, Si 0,05 bis ≤ 6,0, Mn 9,0 bis < 18,0, Rest Eisen einschließlich üblicher Stahlbegleitelemente. Optional können je nach Anforderung Cr, Cu, Ti, Zr, V und Nb zugegeben werden.The one from the publication DE 10 2004 061 284 A1 Known formable lightweight steel has, for example, the following alloy composition (in% by weight): C 0.04 to ≤ 1.0, Al 0.05 to <4.0, Si 0.05 to ≤ 6.0, Mn 9, 0 to <18.0, the remainder being iron including the usual accompanying steel elements Optionally, Cr, Cu, Ti, Zr, V and Nb can be added depending on the requirements.

Dieser Leichtbaustahl weist ein teilstabilisiertes γ-Mischkristall-Gefüge mit definierter Stapelfehlerenergie mit einem z. T. multiplen TRIP-Effekt auf, der die spannungs- oder dehnungsinduzierte Umwandlung eines flächenzentrierten γ-Mischkristalls (Austenit) in einen ε-Martensit (hexagonal dichteste Kugelpackung) und anschließend bei weiterer Verformung in einen raumzentrierten ε-Martensit und Restaustenit ermöglicht.This lightweight steel has a partially stabilized γ mixed crystal structure with a defined stacking fault energy with a z. T. multiple TRIP effect, which enables the stress or strain-induced transformation of a face-centered γ mixed crystal (austenite) into an ε-martensite (hexagonal closest packing of spheres) and then with further deformation into a body-centered ε-martensite and residual austenite.

Der hohe Umformgrad wird durch TRIP- (Transformation Induced Plasticity) und TWIP- (Twinning Induced Plasticity) Eigenschaften des Stahles erreicht.The high degree of deformation is achieved through TRIP (Transformation Induced Plasticity) and TWIP (Twinning Induced Plasticity) properties of the steel.

Bei diesem und vergleichbaren Stählen kann aber bei Vorliegen von Eigenspannungen im Material in Abhängigkeit vom Gefüge und der Festigkeit eine durch Wasserstoff ausgelöste verzögerte Versprödung und in Folge dessen eine Rissbildung auftreten.With this and comparable steels, however, if there are internal stresses in the material, depending on the structure and strength, delayed embrittlement caused by hydrogen and, as a result, cracking can occur.

Zur Überwindung dieses Problems ist in der Offenlegungsschrift DE 10 2004 061 284 A1 bereits vorgeschlagen worden, den Wasserstoffgehalt auf < 20 ppm vorzugsweise auf < 5 ppm zu begrenzen.To overcome this problem is in the laid-open specification DE 10 2004 061 284 A1 it has already been proposed to limit the hydrogen content to <20 ppm, preferably to <5 ppm.

Dieser Vorschlag ist zwar hilfreich aber noch nicht ausreichend, da selbst bei niedrig eingestellten Wasserstoffgehalten trotzdem noch der Effekt der verzögerten Rissbildung auftreten kann. Außerdem können bei der Stahlherstellung aus verschiedenen Gründen Überschreitungen des festgelegten Maximalwertes für Wasserstoff vorkommen, die legierungsmäßig zwar toleriert werden können, aber die Gefahr des Auftretens einer Wasserstoffversprödung vergrößern.Although this suggestion is helpful, it is not yet sufficient, since the effect of delayed crack formation can still occur even with low hydrogen contents. In addition, during steel production, the specified maximum value for hydrogen can be exceeded for various reasons, which can be tolerated in terms of alloying, but increase the risk of hydrogen embrittlement occurring.

Aus der Offenlegungsschrift WO 2011/154153 A1 ist ein austenitischer Stahl bekannt, der einen hervorragenden Widerstand gegen verzögerte Rissbildung aufweisen soll. Der Stahl enthält neben Eisen und Verunreinigungen in Gew.-%: 0,5 bis 0,8 C,10 bis 17 Mn, mindestens 1,0 Al, höchstens 0,5 Si, höchstens 0,020 S, höchstens 0,050 P, 50 bis 200 ppm N und 0,050 bis 0,25 V.From the disclosure document WO 2011/154153 A1 an austenitic steel is known which is said to have excellent resistance to delayed crack formation. In addition to iron and impurities in% by weight, the steel contains: 0.5 to 0.8 C, 10 to 17 Mn, at least 1.0 Al, at most 0.5 Si, at most 0.020 S, at most 0.050 P, 50 to 200 ppm N and 0.050 to 0.25 V.

Aus der Offenlegungsschrift WO 2009/142362 A1 ist eine Stahllegierung für ein hochfestes kaltgewalztes Stahlblech bekannt, die ebenfalls einen verbesserten Widerstand gegen verzögerte Rissbildung aufweisen soll. Der Stahl enthält neben Eisen und Verunreinigungen in Gew.-%: 0,05 bis 0,3 C, 0,3 bis 1,6 Si, 4,0 bis 7,0 Mn, 0,5 bis 2,0 Al, 0,01 bis 0,1 Cr, 0,02 bis 0,1 Ni, 0,005 bis 0,03 Ti, 5 bis 30 ppm B, 0,01 bis 0,03 Sb und 0,008 oder weniger S.From the disclosure document WO 2009/142362 A1 a steel alloy for a high-strength cold-rolled steel sheet is known, which is also said to have an improved resistance to delayed cracking. In addition to iron and impurities in% by weight, the steel contains: 0.05 to 0.3 C, 0.3 to 1.6 Si, 4.0 to 7.0 Mn, 0.5 to 2.0 Al, 0 .01 to 0.1 Cr, 0.02 to 0.1 Ni, 0.005 to 0.03 Ti, 5 to 30 ppm B, 0.01 to 0.03 Sb, and 0.008 or less S.

Des Weiteren ist aus der Offenlegungsschrift EP 2 128 293 A1 ein Leichtbaustahl mit einer verbesserten Dehnung bekannt, aufweisend neben Eisen und Verunreinigungen in Gew.-%: 0,2 bis 0,8 C, 2 bis 10 Mn, 0,2 oder weniger P, höchstens 0,015 S, 3,0 bis 15 Al, höchstens 0,01 N und einem Verhältnis Mn/Al von 0,4 bis 1,0.Furthermore, is from the Offenlegungsschrift EP 2 128 293 A1 a lightweight steel with an improved elongation known, having in addition to iron and impurities in% by weight: 0.2 to 0.8 C, 2 to 10 Mn, 0.2 or less P, at most 0.015 S, 3.0 to 15 Al, at most 0.01 N and an Mn / Al ratio of 0.4 to 1.0.

Die Offenlegungsschrift EP 2 778 247 A1 offenbart ein Stahlblech zum Warmumformen mit verbesserter Kollisionstauglichkeit, das neben Eisen und unvermeidbaren Verunreinigungen in Gew.-% 0,01 bis 0,5 C, 3 oder weniger Si, 3 bis 15 Mn, 0,0001 bis 0,1 P, 0,0001 bis 0,03 S, 3 oder weniger Al und 0,03 oder weniger N beinhaltet. Wahlweise können auch beispielsweise Cr, Mo, W, Ti, Nb, Zr, V, Cu, Ni, Sb, Sn oder B der Legierung hinzugefügt werden.The disclosure document EP 2 778 247 A1 discloses a steel sheet for hot forming with improved collision suitability, which in addition to iron and unavoidable impurities in wt .-% 0.01 to 0.5 C, 3 or less Si, 3 to 15 Mn, 0.0001 to 0.1 P, 0, 0001 to 0.03 S, 3 or less Al, and 0.03 or less N. Optionally, for example, Cr, Mo, W, Ti, Nb, Zr, V, Cu, Ni, Sb, Sn or B can be added to the alloy.

Aus der Patentanmeldung EP 2 383 353 A2 ist ein Verfahren zur Herstellung eines umformbarkeitsverbesserten Stahls bekannt. Das Verfahren beinhaltet die Schritte des Vergießens des Stahls, des Warmwalzens, des Kaltwalzens und des Glühens.From the patent application EP 2 383 353 A2 a method for producing a formability-improved steel is known. The method includes the steps of casting the steel, hot rolling, cold rolling and annealing.

Ferner ist in der Offenlegungsschrift US 2009/0050622 A1 bereits ein Verfahren zur kontinuierlichen Wärmebehandlung von Bandstahl beschrieben, dessen Banddicke entlang seiner Länge variiert. Dieser Bandstahl mit variierender Dicke wird kontinuierlich durch sogenanntes flexibles Walzen hergestellt. Hierbei wird ein Walzspalt einer Walzanlage während der Produktion des Bandstahls gezielt variiert.Furthermore, in the laid-open specification US 2009/0050622 A1 a process for the continuous heat treatment of steel strip has already been described, the strip thickness of which varies along its length. This steel strip of varying thickness is continuously produced by so-called flexible rolling. Here, a roll gap of a rolling mill is varied in a targeted manner during the production of the steel strip.

Aufgabe der Erfindung ist es einen Leichtbaustahl der gattungsgemäßen Art anzugeben, der unter Beibehaltung sehr guter mechanischer Eigenschaften (Duktilität, Festigkeit) nicht den Effekt einer verzögerten Rissbildung bzw. Wasserstoffversprödung aufweist.The object of the invention is to provide a lightweight structural steel of the generic type which, while retaining very good mechanical properties (ductility, strength), does not have the effect of delayed crack formation or hydrogen embrittlement.

Diese Aufgabe wird ausgehend vom Oberbegriff in Verbindung mit den kennzeichnenden Merkmalen des Anspruches 1 und in Bezug auf ein Verfahren durch die Merkmale des Anspruchs 4 gelöst. Vorteilhafte Weiterbildungen sind Gegenstand von Unteransprüchen.Starting from the preamble in conjunction with the characterizing features of claim 1 and with regard to a method, this object is achieved by the features of claim 4. Advantageous further developments are the subject of subclaims.

Nach der Lehre der Erfindung weist der umformbare Leichtbaustahl mit TRIP- und TWIP-Eigenschaften folgende Elemente in Gew.-% auf:

  • C 0,03 bis ≤0,5, insbesondere vorteilhaft 0,1 bis 0,35
  • Mn 5 bis 9
  • Si 0,1 bis 3, insbesondere vorteilhaft 0,1 bis 1
  • Al 0,1 bis 4, insbesondere vorteilhaft 1 bis 3,5
  • Cr > 0,1 bis 5, insbesondere vorteilhaft 0,5 bis 4
  • V 0,005 bis 1, insbesondere vorteilhaft 0,02 bis 0,1
  • P max. 0,1
  • S max. 0,1
  • N max. 0,03
  • Sb 0,005 bis 0,3, vorteilhaft bis 0,01 bis 0,1
sowie optional mindestens eines oder mehrere der folgenden karbidbildenden Elemente in den angegebenen Gehalten (in Gew.-%):
  • Mo 0,05 bis 2
  • Ti 0,01 bis 2
  • Nb 0,005 bis 1
  • W 0,005 bis 1
  • Zr 0,001 bis 0,3
    Rest Eisen einschließlich üblicher stahlbegleitender Elemente, mit weiterer optionaler Zugabe folgender Elemente in Gew.-%: max. 5 Ni, max. 10 Co, max. 0,005 Ca, max. 0,01 B und 0,05 bis 2 Cu.
According to the teaching of the invention, the formable lightweight steel with TRIP and TWIP properties has the following elements in% by weight:
  • C 0.03 to 0.5, particularly advantageously 0.1 to 0.35
  • Mn 5 to 9
  • Si 0.1 to 3, particularly advantageously 0.1 to 1
  • Al 0.1 to 4, particularly advantageously 1 to 3.5
  • Cr> 0.1 to 5, particularly advantageously 0.5 to 4
  • V 0.005 to 1, particularly advantageously 0.02 to 0.1
  • P max. 0.1
  • S 0.1 or less
  • N 0.03 or less
  • Sb 0.005 to 0.3, advantageously to 0.01 to 0.1
and optionally at least one or more of the following carbide-forming elements in the specified contents (in% by weight):
  • Mo 0.05 to 2
  • Ti 0.01 to 2
  • Nb 0.005 to 1
  • W 0.005 to 1
  • Zr 0.001 to 0.3
    The remainder is iron including the usual steel-accompanying elements, with further optional addition of the following elements in% by weight: max. 5 Ni, max. 10 Co, max. 0.005 Ca, max. 0.01 B and 0.05 to 2 Cu.

Überraschend wurde im Rahmen von umfangreichen Untersuchungen erkannt, dass durch Zulegieren von Antimon (Sb) in den angegebenen Grenzen die Diffusion von Elementen, insbesondere C, N und O, behindert wird und dadurch in Verbindung mit einer gezielten Wärmebehandlung das Werkstoffverhalten vorteilhaft beeinflusst werden kann.Surprisingly, extensive investigations revealed that adding antimony (Sb) to the alloy within the specified limits hampers the diffusion of elements, in particular C, N and O, and can thereby advantageously influence the behavior of the material in conjunction with targeted heat treatment.

Die Zugabe von Antimon führt dazu, dass die Karbide langsamer wachsen und somit feiner verteilt und kleiner ausgeschieden werden. Dadurch werden Legierungselemente effektiver genutzt, was zu kostengünstigeren Legierungskonzepten führt bei verbesserten mechanischen Eigenschaften und einer deutlichen Verbesserung im Hinblick auf die Vermeidung von verzögerter wasserstoffinduzierter Rissbildung (delayed fracture) und Wasserstoffversprödung (hydrogen embrittlement).The addition of antimony leads to the fact that the carbides grow more slowly and are therefore more finely distributed and less excreted. As a result, alloying elements are used more effectively, which leads to more cost-effective alloy concepts with improved mechanical properties and a significant improvement in terms of avoiding delayed hydrogen-induced crack formation (delayed fracture) and hydrogen embrittlement.

Als günstig hat es sich herausgestellt, wenn das Verhältnis von Sb/C einen Wert von 1,5 nicht überschreitet. Werte über 1,5 bringen keinen weiteren Vorteil im Sinne der Erfindung und bewirken vor allem negative Effekte wie beispielsweise einen Verlust an Duktilität und Zähigkeit durch Ausscheidung von Antimon an den Korngrenzen.It has been found to be favorable if the ratio of Sb / C does not exceed a value of 1.5. Values above 1.5 bring no further advantage within the meaning of the invention and primarily cause negative effects such as a loss in ductility and toughness due to the precipitation of antimony at the grain boundaries.

Vorteilhaft wird bei der Beurteilung der mechanischen Eigenschaften das Produkt aus Zugfestigkeit und Bruchdehnung zugrunde gelegt, das ein Maß für die Leistungsfähigkeit des Werkstoffes ist.When assessing the mechanical properties, the product of tensile strength and elongation at break is advantageously used as a basis, which is a measure of the performance of the material.

Bei Versuchen wurde festgestellt, dass bei den erfindungsgemäßen Legierungen die Zugfestigkeit und Bruchdehnung durch die Zugabe von Antimon im Vergleich zu Stahllegierungen, bei denen kein Antimon zugegeben wird, deutlich höher ist, wodurch kostengünstigere und höherwertigere Stähle erzeugt werden können.Tests have shown that the tensile strength and elongation at break in the alloys according to the invention are significantly higher due to the addition of antimony compared to steel alloys in which no antimony is added, which means that cheaper and higher quality steels can be produced.

Es wurde außerdem erkannt, dass die oben beschriebene Wirkung von Antimon durch eine Wärmebehandlung des Stahls deutlich gesteigert werden kann.It was also recognized that the above-described effect of antimony can be significantly increased by heat treatment of the steel.

Um eine weitere Verbesserung der geforderten Eigenschaften zu erzielen, wird das aus der erfindungsgemäßen Legierung durch Umformung erzeugte Produkt bzw. Halbzeug, das zum Beispiel Warmband, Kaltband, flexibel gewalztes Warm- oder Kaltband, ein Rohr oder ein Karosseriebauteil sein kann, daher vorteilhaft einer Wärmebehandlung bei 480 bis 770 °C für 1 Minute bis 48 h Stunden, beispielsweise in einer Haubenglühe mit vorwiegend langen Glühzeiten oder in einer Durchlaufglühe mit vorwiegend kurzen Glühzeiten unterzogen.In order to achieve a further improvement in the required properties, the product or semi-finished product produced from the alloy according to the invention by forming, which can be, for example, hot strip, cold strip, flexibly rolled hot or cold strip, a pipe or a body component, is therefore advantageously heat treated at 480 to 770 ° C for 1 minute to 48 hours, for example in a hood annealing with predominantly long annealing times or in a continuous annealing with predominantly short annealing times.

Eine solche Glühung kann aber auch bereits schon vor der endgültigen Formgebung zu einem Fertigprodukt stattfinden, beispielsweise am Kaltband, welches anschließend weiterverarbeitet wird. Der Zeitpunkt der Glühung kann daher flexibel dem Fertigungsprozess angepasst werden. Eine Glühung des Endproduktes zusätzlich zu einer bereits erfolgten Glühung des Halbzeuges kann zu einer weiteren Verbesserung der Werkstoffeigenschaften führen.Such annealing can also take place before the final shaping into a finished product, for example on the cold strip, which is then further processed. The time of annealing can therefore be flexibly adapted to the manufacturing process. Annealing the end product in addition to annealing the semi-finished product can lead to a further improvement in the material properties.

Weiterhin wird die Erfindung durch ein Verfahren zur Herstellung des erfindungsgemäßen Stahls mit folgenden Schritten realisiert:

  • Vergießen des Stahls nach dem Stranggussverfahren oder Dünnbrammengießverfahren oder einem endabmessungsnahen horizontalen oder vertikalen Bandgießverfahren,
  • Warmwalzen der gegossenen Bramme beziehungsweise des gegossenen Bandes mit einer Dicke von mehr als 5 mm auf eine einheitliche Dicke oder flexibles Warmwalzen der gegossenen Bramme beziehungsweise des gegossenen Bandes mit einer Dicke von mehr als 5 mm auf unterschiedliche Dicken,
  • Optionales Kaltwalzen des auf eine einheitliche Dicke gewalzten Warmbandes oder mittels endabmessungsnahem Gießverfahren hergestellten maximal 5 mm dicken gegossen Bandes auf eine einheitliche Dicke oder optionales flexibles Kaltwalzen des auf eine einheitliche Dicke gewalzten Warmbandes oder mittels endabmessungsnahem Gießverfahren hergestellten maximal 5 mm dicken gegossen Bandes auf unterschiedliche Dicken,
  • Optionales Glühen des Warm- oder Kaltbandes mit folgenden Parametern: Glühtemperatur: 480 bis 770 °C, Glühdauer: 1 Minute bis 48 Stunden.
Furthermore, the invention is implemented by a method for producing the steel according to the invention with the following steps:
  • Casting of the steel by the continuous casting process or thin slab casting process or a near-net-shape horizontal or vertical strip casting process,
  • Hot rolling of the cast slab or the cast strip with a thickness of more than 5 mm to a uniform thickness or flexible hot rolling of the cast slab or the cast strip with a thickness of more than 5 mm to different thicknesses,
  • Optional cold rolling of the hot strip rolled to a uniform thickness or a maximum of 5 mm thick cast strip produced by means of a near-net-shape casting process to a uniform thickness or optional flexible cold rolling of the hot strip rolled to a uniform thickness or maximum 5 mm thick cast strip produced by means of a near-net-shape casting process to different thickness
  • Optional annealing of the hot or cold strip with the following parameters: annealing temperature: 480 to 770 ° C, annealing time: 1 minute to 48 hours.

In Bezug auf das mittels eines endabmessungsnahen Gießverfahrens hergestellte maximal 5 mm dicke gegossene Band ist besonders vorteilhaft, dies auf eine einheitliche Dicke kaltzuwalzen wird oder auf unterschiedliche Dicken flexibel kaltzuwalzen und dann das Kaltband mit folgenden Parametern zu glühen: Glühtemperatur: 480 bis 770 °C, Glühdauer: 1 Minute bis 48 Stunden.With regard to the cast strip with a maximum thickness of 5 mm produced by means of a near-net-shape casting process, it is particularly advantageous to cold-roll it to a uniform thickness or to flexibly cold-roll it to different thicknesses and then anneal the cold strip with the following parameters: Annealing temperature: 480 to 770 ° C Annealing time: 1 minute to 48 hours.

Bei Legierungen mit Al-Gehalten von > 1 Gew.-% wird die Glühbehandlung bevorzugt bei Temperaturen von 670 bis 770 °C bei Glühzeiten von 1 Minute bis 12 Stunden durchgeführt, da niedrigere Temperaturen und längere Glühzeiten zu geringerer Zugfestigkeit und Bruchdehnung führen.In the case of alloys with an Al content of> 1% by weight, the annealing treatment is preferably carried out at temperatures of 670 to 770 ° C. for annealing times of 1 minute to 12 hours, since lower temperatures and longer annealing times lead to lower tensile strength and elongation at break.

Für die Glühung selbst wird bei Warmband, Kaltband und flexibel gewalzten Bändern für kurze Glühzeiten bevorzugt eine Durchlaufglühe und für lange Glühzeiten bevorzugt eine Haubenglühe genutzt. Für andere Halbzeuge und Produkte können andere Glühvorrichtungen, mit den vorgegebenen Parametern, wie zum Beispiel ein Muffelofen, eingesetzt werden.For the annealing itself, continuous annealing is preferably used for short annealing times for hot strip, cold strip and flexibly rolled strip, and hood annealing is preferably used for long annealing times. For other semi-finished products and products, other annealing devices with the specified parameters, such as a muffle furnace, can be used.

Mit der Erfindung ist die Herstellung kostengünstiger Sb-legierter höher manganhaltiger Stähle möglich, die eine bessere Zugfestigkeit und Bruchdehnung aufweisen als nicht Sb-legierte höher manganhaltige Stähle mit gleicher chemischer Zusammensetzung.With the invention, it is possible to produce inexpensive Sb-alloyed steels with a higher manganese content, which have better tensile strength and elongation at break than non-Sb-alloyed steels with a higher manganese content and with the same chemical composition.

Außerdem wird durch die Zugabe von Antimon auch das Verhalten gegenüber Wasserstoff (verzögerte Rissbildung und Wasserstoffversprödung) deutlich verbessert.In addition, the addition of antimony also improves the behavior towards it Significantly improved hydrogen (delayed crack formation and hydrogen embrittlement).

Ursächlich für die Verbesserung der Werkstoffeigenschaften ist, dass durch Antimon die Diffusion von Kohlenstoff und Aluminium behindert wird. Des Weiteren senkt Antimon die Grenzflächenenergie, was zu einer feineren Verteilung der Karbide führt. Die verminderte Kohlenstoffdiffusion verzögert somit die lokale Anreicherung von Kohlenstoff an den Korngrenzen und im Gefüge sowie in Verbindung mit Aluminium die Bildung von Kappa-Karbiden beziehungsweise insbesondere mit V, Nb, Mo, Cr, W, Zr und Ti die Bildung lokaler größerer Karbide. Die Homogenität des Werkstoffs wird dadurch verbessert mit den beschriebenen positiven Auswirkungen auf die mechanischen Eigenschaften und den Widerstand gegen verzögerte Rissbildung und Wasserstoffversprödung. Die Ausscheidung fein verteilter Karbide führt zu einer Kornfeinung im Gefüge, welche mit einer Verbesserung des Verhaltens gegenüber wasserstoffbedingter negativer Effekte (verzögerte Rissbildung, Wasserstoffversprödung) sowie einer Erhöhung der Festigkeit und Verbesserung der Zähigkeits- und Dehnungseigenschaften einher geht.The reason for the improvement in the material properties is that antimony hinders the diffusion of carbon and aluminum. Furthermore, antimony lowers the interfacial energy, which leads to a finer distribution of the carbides. The reduced carbon diffusion thus delays the local accumulation of carbon at the grain boundaries and in the structure as well as, in connection with aluminum, the formation of kappa carbides or, in particular with V, Nb, Mo, Cr, W, Zr and Ti, the formation of larger local carbides. This improves the homogeneity of the material with the described positive effects on the mechanical properties and the resistance to delayed crack formation and hydrogen embrittlement. The precipitation of finely divided carbides leads to a grain refinement in the structure, which is accompanied by an improvement in the behavior towards negative effects caused by hydrogen (delayed crack formation, hydrogen embrittlement) as well as an increase in strength and an improvement in toughness and elongation properties.

Durch die erfindungsgemäße Zugabe von Antimon in geringen Gehalten bis max. 0,3 Gew. % wird das Verhalten des Werkstoffs gegenüber wasserstoffbedingten Einflüssen daher deutlich verbessert.The addition of antimony according to the invention in low contents of up to a maximum of 0.3% by weight therefore significantly improves the behavior of the material with respect to influences caused by hydrogen.

Die Zugabe zu großer Mengen Antimon bewirkt dagegen eine unerwünscht starke Ausscheidung von Antimon an den Korngrenzen und vermindert dadurch die Zähigkeit- und Dehnungseigenschaften. Damit Antimon wirksam werden kann, sind mindestens Gehalte von 30 ppm notwendig. Antimon-Gehalte von über 0,3 Gew.-% verspröden allerdings den Werkstoff und sind deshalb zu vermeiden. Optimal liegt der maximale Gehalt an Antimon bei 0,1 Gew.-%.Adding too large amounts of antimony, on the other hand, causes an undesirably strong precipitation of antimony at the grain boundaries and thereby reduces the toughness and elongation properties. For antimony to be effective, a content of at least 30 ppm is necessary. However, antimony contents of more than 0.3% by weight make the material brittle and should therefore be avoided. The optimum content of antimony is 0.1% by weight.

Die kleinen im Vergleich zum Stand der Technik sehr viel feiner verteilt ausgeschiedenen Karbide (vorwiegend Cr-, Mo-, Ti-, Nb-, V-, W-, Zr- und Kappa-Karbide) verbessern den Nutzungsgrad der entsprechenden Legierungselemente, was potentiell eine Verringerung der Zugabemenge ermöglicht. Des Weiteren wird durch die verringerte Kohlenstoffdiffusion und das verringerte Kornwachstum aufgrund der Zulegierung von Antimon das Prozessfenster für die erfindungsgemäß notwendigen Wärmebehandlungen vergrößert, das heißt, der Stahl reagiert bezüglich der resultierenden mechanischen Eigenschaften unempfindlicher auf Prozessschwankungen (Temperatur, Zeit).The small carbides (predominantly Cr, Mo, Ti, Nb, V, W, Zr and Kappa carbides), which are separated out much more finely than in the prior art, improve the degree of utilization of the corresponding alloying elements, which potentially allows a reduction in the amount added. Furthermore, due to the reduced carbon diffusion and the reduced grain growth due to the addition of antimony, the process window for the invention The resulting mechanical properties of the steel are less sensitive to process fluctuations (temperature, time).

Nachfolgend werden die positiven Effekte der erfindungsgemäß verwendeten Legierungs-elemente beschrieben:

  • Al: Verbessert die Festigkeits- und Dehnungseigenschaften, senkt die spezifische Dichte, und beeinflusst das Umwandlungsverhalten der erfindungsgemäßen Legierungen. Gehalte an Al von mehr als 15 Gew.-% verschlechtern die Dehnungseigenschaften, weshalb ein Maximalgehalt von 4 Gew.-% festgelegt wird. Hohe Al-Gehalte von größer gleich 4 Gew.-% wirken in Verbindung mit hohen C-Gehalten von größer gleich 0,6 Gew.-% als Karbidbildner für Kappa-Karbide. Unter 4 Gew.-% verzögert Al die Ausscheidung von Karbiden.
  • B: Verbessert die Festigkeit und stabilisiert den Austenit. Gehalte von mehr als 0,01 Gew.-% führen zu einer Versprödung des Werkstoffs, weshalb ein Maximalgehalt von 0,01 Gew.-% festgelegt wird. Die Zugabe von B ist optional.
  • C: Wird benötigt zur Bildung von Karbiden, stabilisiert den Austenit und erhöht die Festigkeit. Gehalte von mehr als 1 Gew.-% C verschlechtern die Schweißeigenschaften und führen zur Ausscheidung unerwünscht großer Karbide und damit zur Verschlechterung der Dehnungs- und Zähigkeitseigenschaften, weshalb ein maximaler Gehalt von 0,5 Gew.-% festgelegt wird. Um eine ausreichende Festigkeit des Werkstoffs zu erreichen, ist eine Mindestzugabe von 0,01 Gew.-% erforderlich.
  • Ca: Dient zur Modifikation nichtmetallischer oxidischer Einschlüsse, welche zu Inhomogenitäten und einem unerwünschten Werkstoffversagen führen können. Aufgrund seines hohen Dampfdrucks in flüssigem Stahl wird der Gehalte auf maximal 0,005 Gew.-% begrenzt. Die Zugabe von Ca ist optional.
  • Co: Erhöht Festigkeit des Stahls, stabilisiert den Austenit und verbessert die Warmfestigkeit. Gehalte von über 10 Gew.-% verschlechtern die Dehnungseigenschaften, weshalb ein Maximalgehalt von 10 Gew.-% festgelegt wird. Die Zugabe von Co ist optional.
  • Cr: Verbessert die Festigkeit und verringert die Korrosionsrate, verzögert die Ferrit- und Perlitbildung und bildet Karbide. Der maximale Gehalt wird mit. 5 Gew.-% festgelegt, da höhere Gehalte eine Verschlechterung der Dehnungseigenschaften zur Folge haben. Der Minimalwert beträgt > 0,1 Gew.-%.
  • Cu: Verringert die Korrosionsrate und steigert die Festigkeit. Gehalte oberhalb 2 Gew.-% verschlechtern die Herstellbarkeit durch Bildung niedrig schmelzender Phasen beim Vergießen und Warmwalzen weshalb ein Maximalgehalt von 2 Gew.-% festgelegt wird. Die Zugabe von Cu ist optional.
  • Mn: Stabilisiert den Austenit, erhöht die Festigkeit und die Zähigkeit und ermöglicht eine verformungsinduzierte Martensit- und/oder Zwillingsbildung in den erfindungsgemäßen Legierungen. Gehalte kleiner 3 Gew.-% sind nicht ausreichend zur Stabilisierung des Austenits und verschlechtern somit die Dehnungseigenschaften, während bei Gehalten größer 30 Gew.-% keine weiteren Vorteile erwartet werden und die Herstellung aufgrund des niedrigen Mn-Dampfdrucks erschwert wird. Ein optimaler Gehalt an Mn liegt bei 5 bis 9 Gew.-%.
  • Mo: Wirkt als starker Karbidbildner und erhöht die Festigkeit. Gehalte an Mo von über 2 Gew.-% verschlechtern die Dehnungseigenschaften, weshalb ein Maximalgehalt von 2 Gew.-% festgelegt wird. Die Zugabe von Mo ist optional.
  • Nb + V: Wirken insbesondere durch die Bildung von Karbiden kornfeinend, wodurch gleichzeitig die Festigkeit, Zähigkeit und Dehnungseigenschaften verbessert werden. Gehalte von über 1 Gew.-% bringen keine weiteren Vorteile. Die Zugabe von Nb + V ist optional.
  • Ni: Stabilisiert den Austenit und verbessert Dehnungseigenschaften insbesondere bei niedrigen Anwendungstemperaturen. Mehr als die Zugabe von 5 Gew.-% Ni bringt keinen weiteren Vorteil. Die Zugabe von Ni ist optional.
  • Si: Behindert die Kohlstoffdiffusion, verringert die spezifische Dichte und erhöht die Festigkeit und Dehnungs- sowie Zähigkeitseigenschaften. Des Weiteren konnte eine Verbesserung der Kaltwalzbarkeit durch Zulegieren von Si beobachtet werden. Gehalte von mehr als 4 Gew.-% führen zu einer Versprödung des Werkstoffs und beeinflussen die Warm- und Kaltwalzbarkeit negativ, weshalb ein maximaler Gehalt von 3 Gew.-% festgelegt wird. Der Minimalwert beträgt 0,1 Gew.-%.
  • Ti: Wirkt als Karbidbildner kornfeinend, wodurch gleichzeitig die Festigkeit, Zähigkeit und Dehnungseigenschaften verbessert werden und vermindert die interkristalline Korrosion. Gehalte an Ti von über 2 Gew.-% verschlechtern die Dehnungseigenschaften, weshalb ein Maximalgehalt von 2 Gew.-% festgelegt wird. Die Zugabe von Ti ist optional.
  • W: Wirkt als Karbidbildner und erhöht die Festigkeit und Warmfestigkeit. Gehalte an W von über 1 Gew.-% verschlechtern die Dehnungseigenschaften, weshalb ein Maximalgehalt von 1 Gew.-% festgelegt wird. Die Zugabe von W ist optional.
  • Zr: Wirkt als Karbidbildner und verbessert die Festigkeit. Gehalte an Zr von über 0,3 Gew-% verschlechtern die Dehnungseigenschaften, weshalb ein Maximalgehalt von 0,3 Gew.-% festgelegt wird. Die Zugabe von Zr ist optional.
The positive effects of the alloy elements used according to the invention are described below:
  • Al: Improves the strength and elongation properties, lowers the specific density and influences the transformation behavior of the alloys according to the invention. Al contents of more than 15% by weight deteriorate the elongation properties, which is why a maximum content of 4% by weight is specified. High Al contents of greater than or equal to 4% by weight act in conjunction with high C contents of greater than or equal to 0.6% by weight as carbide formers for kappa carbides. Below 4% by weight, Al retards the precipitation of carbides.
  • B: Improves strength and stabilizes austenite. Contents of more than 0.01% by weight lead to embrittlement of the material, which is why a maximum content of 0.01% by weight is specified. The addition of B is optional.
  • C: It is required for the formation of carbides, stabilizes the austenite and increases the strength. Contents of more than 1% by weight of C impair the welding properties and lead to the precipitation of undesirably large carbides and thus to a deterioration in the elongation and toughness properties, which is why a maximum content of 0.5% by weight is specified. In order to achieve sufficient strength of the material, a minimum addition of 0.01% by weight is required.
  • Ca: Used to modify non-metallic oxidic inclusions, which can lead to inhomogeneities and undesired material failure. Due to its high vapor pressure in liquid steel, the content is limited to a maximum of 0.005% by weight. The addition of Ca is optional.
  • Co: Increases the strength of the steel, stabilizes the austenite and improves the high temperature strength. Contents of more than 10% by weight impair the elongation properties, which is why a maximum content of 10% by weight is specified. The addition of Co is optional.
  • Cr: Improves the strength and reduces the corrosion rate, delays the formation of ferrite and pearlite and forms carbides. The maximum salary is with. 5% by weight, since higher contents result in a deterioration in the elongation properties. The minimum value is> 0.1% by weight.
  • Cu: Decreases the rate of corrosion and increases strength. Contents above 2 wt.% Worsen the producibility due to the formation of low-melting phases during casting and hot rolling, which is why a maximum content of 2 wt.% Is specified. The addition of Cu is optional.
  • Mn: Stabilizes austenite, increases strength and toughness and enables deformation-induced martensite and / or twin formation in the alloys according to the invention. Contents less than 3% by weight are not sufficient to stabilize the austenite and thus worsen the elongation properties, while with contents greater than 30% by weight no further advantages are expected and production is made more difficult due to the low Mn vapor pressure. An optimal Mn content is 5 to 9% by weight.
  • Mo: Acts as a strong carbide former and increases strength. Mo contents of more than 2% by weight deteriorate the elongation properties, which is why a maximum content of 2% by weight is specified. The addition of Mo is optional.
  • Nb + V: In particular, they have a grain-refining effect through the formation of carbides, which at the same time improves strength, toughness and elongation properties. Contents of more than 1% by weight bring no further advantages. The addition of Nb + V is optional.
  • Ni: Stabilizes the austenite and improves elongation properties, especially at low application temperatures. More than the addition of 5% by weight Ni brings no further advantage. The addition of Ni is optional.
  • Si: hinders the carbon diffusion, reduces the specific density and increases the strength and elongation and toughness properties. Furthermore, a Improvement in cold rollability can be observed by adding Si by alloying. Contents of more than 4% by weight lead to embrittlement of the material and have a negative effect on hot and cold rollability, which is why a maximum content of 3% by weight is specified. The minimum value is 0.1% by weight.
  • Ti: Has a grain-refining effect as a carbide former, which at the same time improves strength, toughness and elongation properties and reduces intergranular corrosion. Contents of Ti of more than 2% by weight deteriorate the elongation properties, which is why a maximum content of 2% by weight is specified. The addition of Ti is optional.
  • W: Acts as a carbide former and increases strength and heat resistance. W contents of more than 1% by weight deteriorate the elongation properties, which is why a maximum content of 1% by weight is specified. The addition of W is optional.
  • Zr: Acts as a carbide former and improves strength. Contents of Zr of more than 0.3% by weight deteriorate the elongation properties, which is why a maximum content of 0.3% by weight is specified. The addition of Zr is optional.

Eine Legierung nach Anspruch 3 weist unter Nutzung optimierter Wärmebehandlungsparameter (siehe Tabelle 1 bis 4) ein Produkt aus Zugfestigkeit und Bruchdehnung von mindestens 20.000 MPa% und eine Zugfestigkeit von mindestens 800 MPa auf. Das Produkt aus Zugfestigkeit und Bruchdehnung ist ein Maß für die Leistungsfähigkeit des Werkstoffs bei der Umformung.An alloy according to claim 3, using optimized heat treatment parameters (see Tables 1 to 4), has a product of tensile strength and elongation at break of at least 20,000 MPa% and a tensile strength of at least 800 MPa. The product of tensile strength and elongation at break is a measure of the performance of the material during forming.

Obwohl die Wärmebehandlung 680°C 10 min aus Tabelle 2 noch nicht optimale Werte für das Produkt aus Zugfestigkeit und Bruchdehnung von mindestens 20.000 MPa% liefert, erkennt man aber auch hier bereits die positive Wirkung der Zulegierung von Antimon.Although the heat treatment at 680 ° C. for 10 minutes from Table 2 does not yet provide optimal values for the product of tensile strength and elongation at break of at least 20,000 MPa%, the positive effect of the addition of antimony can also be seen here.

Eine Legierung nach einer Ausführungsform weist ein Produkt aus Zugfestigkeit und Bruchdehnung von mindestens 30.000 MPa% und eine Zugfestigkeit von mindestens 800 MPa auf.An alloy according to one embodiment has a product of tensile strength and elongation at break of at least 30,000 MPa% and a tensile strength of at least 800 MPa.

Eine Legierung nach einer weiteren Ausführungsform weist fein verteilte Kappa-Karbidausscheidungen und ein Produkt aus Zugfestigkeit und Bruchdehnung von mindestens 30.000 MPa% sowie eine Streckgrenze von mindestens 700 MPa und eine Zugfestigkeit von mindestens 800 MPa auf.An alloy according to a further embodiment has finely divided kappa carbide precipitates and a product of tensile strength and elongation at break of at least 30,000 MPa% and a yield strength of at least 700 MPa and a tensile strength of at least 800 MPa.

In Tabelle 1 sind die untersuchten Legierungszusammensetzungen angegeben. Variiert wurde bei sonst annähernd gleicher chemischer Zusammensetzung der Gehalt an Sb sowie Zugaben von Nb.Table 1 shows the alloy compositions tested. The content of Sb and additions of Nb were varied while the chemical composition was otherwise approximately the same.

Aus diesen Stählen wurden 2 mm dicke Warmbänder hergestellt und diese nach dem Warmwalzen an Luft abgekühlt. Aus diesen Warmbändern wurden Proben entnommen und daran die Zugfestigkeit und Bruchdehnung ermittelt.From these steels, 2 mm thick hot strips were produced and these were cooled in air after hot rolling. Samples were taken from these hot strips and the tensile strength and elongation at break were determined on them.

Die Ergebnisse aus dem Produkt aus Zugfestigkeit und Bruchdehnung sind in den Tabellen 2 bis 4 dargestellt, wobei jene Wärmebehandlung mit dem höchstens Produkt aus Zugfestigkeit und Bruchdehnung als am günstigsten für die jeweilige Legierung angesehen wird. Es wird deutlich, dass die erfindungsgemäß mit Sb legierten Stähle stets ein höheres Produkt aus Zugfestigkeit und Bruchdehnung aufweisen als die Vergleichslegierungen. Tabelle 1: Legierungszusammensetzung Legierung C Mn Al Si Cr V Sb sonstiges L1 0,19 7,1 2 0,55 1 0,05 0 nicht erfindungsgemäß L2 0,19 7,1 2 0,55 1 0,05 0,012 erfindungsgemäß L3 0,19 7,1 2 0,55 1 0,05 0,027 erfindungsgemäß L4 0,19 7,1 2 0,55 1 0,05 0,041 erfindungsgemäß L5 0,21 6,3 2 0,2 1 0,06 0 Nb 0,05 nicht erfindungsgemäß L6 0,21 6,3 2 0,2 1 0,05 0,039 Nb 0,05 erfindungsgemäß L7 0,25 7,9 1 0,5 0,9 0,08 0 nicht erfindungsgemäß L8 0,25 7,9 1 0,5 0,9 0,08 0,04 erfindungsgemäß Tabelle 2: ermittelte Produkte aus Zugfestigkeit und Bruchdehnung L1 bis L4 Wärmebehandlung TS*El L1 L2 L3 L4 650 °C, 24 h 22453 23195 23772 22633 680 °C, 10 min 15263 16695 16830 16111 680 °C, 5 h 27162 27997 28258 29000 680 °C, 24 h 26660 28985 30546 29720 Tabelle 3: ermittelte Produkte aus Zugfestigkeit und Bruchdehnung L5 und L6 Wärmebehandlung TS*El L5 L6 690 °C, 3 h 19368 21449 750 °C, 10 min 22751 25502 500 °C, 10 min 23525 26737 Tabelle 4: ermitteltes Produkt aus Zugfestigkeit und Bruchdehnung L7 und L8 Wärmebehandlung TS*El L7 L8 650 °C, 24 h 18378 20457 The results from the product of tensile strength and elongation at break are shown in Tables 2 to 4, the heat treatment with the maximum product of tensile strength and elongation at break being regarded as the most favorable for the respective alloy. It is clear that the steels alloyed with Sb according to the invention always have a higher product of tensile strength and elongation at break than the comparison alloys. Table 1: Alloy Composition alloy C. Mn Al Si Cr V Sb miscellaneous L1 0.19 7.1 2 0.55 1 0.05 0 not according to the invention L2 0.19 7.1 2 0.55 1 0.05 0.012 according to the invention L3 0.19 7.1 2 0.55 1 0.05 0.027 according to the invention L4 0.19 7.1 2 0.55 1 0.05 0.041 according to the invention L5 0.21 6.3 2 0.2 1 0.06 0 Nb 0.05 not according to the invention L6 0.21 6.3 2 0.2 1 0.05 0.039 Nb 0.05 according to the invention L7 0.25 7.9 1 0.5 0.9 0.08 0 not according to the invention L8 0.25 7.9 1 0.5 0.9 0.08 0.04 according to the invention Heat treatment TS * El L1 L2 L3 L4 650 ° C, 24 h 22453 23195 23772 22633 680 ° C, 10 min 15263 16695 16830 16111 680 ° C, 5 h 27162 27997 28258 29000 680 ° C, 24 h 26660 28985 30546 29720 Heat treatment TS * El L5 L6 690 ° C, 3 h 19368 21449 750 ° C, 10 min 22751 25502 500 ° C, 10 min 23525 26737 Heat treatment TS * El L7 L8 650 ° C, 24 h 18378 20457

Claims (6)

  1. Formable lightweight structural steel having improved mechanical properties and a high resistance to delayed hydrogen-induced crack formation and hydrogen embrittlement, consisting of the following elements (in wt.%):
    C 0.03 to ≤ 0.5, in a particularly advantageous manner 0.1 to 0.35 Mn 5 to 9
    Si 0.1 to 3, in a particularly advantageous manner 0.1 to 1
    Al 0.1 to 4, in a particularly advantageous manner 1 to 3.5
    Cr > 0.1 to 5, in particularly advantageous manner 0.5 to 4
    V 0.005 to 1, in a particularly advantageous manner 0.02 to 0.1 P max. 0.1
    S max. 0.1
    N max. 0.03
    Sb 0.005 to 0.3, in a particularly advantageous manner 0.01 to 0.1
    and optionally one or more of the following carbide-forming elements in the contents indicated (in wt.%):
    Mo 0.05 to 2
    Ti 0.01 to 2
    Nb 0.005 to 1
    W 0.005 to 1
    Zr 0.001 to 0.3,
    with the remainder being iron, including typical steel-associated elements, with a further optional addition of the following elements in wt.%: Ni max. 5, Co max. 10, Ca. max. 0.005, B max. 0.01 and Cu 0.05 to 2.
  2. Lightweight structural steel as claimed in claim 1, characterised in that the ratio Sb/C is less than or equal to 1.5.
  3. Lightweight structural steel as claimed in claim 1 or 2, characterised in that the steel has a product of tensile strength and elongation at fracture of at least 20000 MPa% and has a tensile strength of at least 800 MPa.
  4. Method for producing a steel as claimed in claims 1 to 3, comprising the steps of:
    - casting the steel according to the continuous casting method, thin slab casting method or a horizontal or vertical strip casting method approximating the final dimensions,
    - hot rolling the cast slab or the cast strip with a thickness of more than 5 mm to a uniform thickness or flexibly hot rolling to different thicknesses,
    - optionally cold rolling the strip which is hot-rolled to a uniform thickness, or the maximum 5 mm thick cast strip, which is produced by means of casting methods approximating the final dimensions, to a uniform thickness, or flexibly cold rolling to different thicknesses,
    - optionally annealing the hot strip or cold strip with the following parameters:
    annealing temperature: 480 to 770°C, annealing duration: 1 minute to 48 hours.
  5. Method as claimed in claim 4, characterised in that the maximum 5 mm thick cast strip produced by means of a casting method approximating the final dimensions is cold-rolled to a uniform thickness or is flexibly cold-rolled to different thicknesses and then the cold strip is annealed with the following parameters:
    annealing temperature: 480 to 770°C, annealing duration: 1 minute to 48 hours.
  6. Method as claimed in claim 4 or 5, characterised in that for alloys comprising Al > 1 wt.%, annealing procedures are preferably performed at temperatures of 670 to 770°C with annealing times of 1 minute to 12 hours.
EP16750113.9A 2015-07-22 2016-07-20 Formable lightweight steel with improved mechanical properties and method for producing semi-finished products from said steel Active EP3325678B1 (en)

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CN107841691B (en) * 2017-10-25 2019-05-21 河北工业大学 A kind of 750MPa grade super strength Fe-Mn-Al-C system lightweight cast steel and preparation method thereof
DE102017223633A1 (en) * 2017-12-21 2019-06-27 Voestalpine Stahl Gmbh Cold-rolled flat steel product with metallic anticorrosion layer and method for producing the same
RU2721681C1 (en) * 2019-12-23 2020-05-22 Федеральное Государственное Унитарное Предприятие "Центральный научно-исследовательский институт черной металлургии им. И.П. Бардина" (ФГУП "ЦНИИчермет им. И.П. Бардина") Method of producing cold-rolled continuously annealed flat products from if-steel
CN111593263A (en) * 2020-06-24 2020-08-28 安徽工业大学 Preparation method of high-strength low-density steel and high-strength low-density steel
CN111607740A (en) * 2020-06-24 2020-09-01 安徽工业大学 Preparation method of high-strength low-density steel and high-strength low-density steel
CN114752867B (en) * 2022-04-25 2022-10-11 燕山大学 High-strength and high-toughness lightweight steel and preparation method and application thereof

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