WO2021032858A1 - Procédé de production de tôles ou de bandes à haute résistance à partir d'un acier bainitique à haute résistance faiblement allié, et bande d'acier ou tôle d'acier fabriquée à partir de cet acier - Google Patents

Procédé de production de tôles ou de bandes à haute résistance à partir d'un acier bainitique à haute résistance faiblement allié, et bande d'acier ou tôle d'acier fabriquée à partir de cet acier Download PDF

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WO2021032858A1
WO2021032858A1 PCT/EP2020/073419 EP2020073419W WO2021032858A1 WO 2021032858 A1 WO2021032858 A1 WO 2021032858A1 EP 2020073419 W EP2020073419 W EP 2020073419W WO 2021032858 A1 WO2021032858 A1 WO 2021032858A1
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weight
steel
temperature
strip
alloy
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PCT/EP2020/073419
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German (de)
English (en)
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Philippe SCHAFFNIT
Nikolai Wieczorek
Thomas Brecht
Andreas Rost
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Ilsenburger Grobblech Gmbh
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Priority to EP20760453.9A priority Critical patent/EP4018007A1/fr
Publication of WO2021032858A1 publication Critical patent/WO2021032858A1/fr

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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
    • 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
    • C22C38/02—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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/24—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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/18—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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite

Definitions

  • the invention relates to a process for the production of high-strength sheets or strips from a low-alloy, high-strength bainitic and at the same time tough steel with excellent wear resistance.
  • the invention also relates to a steel strip or sheet steel made of this steel and an advantageous use for it.
  • the invention relates to strips or sheets with a proportion of bainite or bainitic ferrite of at least 50% by volume and a residual austenite content of at least 5% by volume, with a thickness of at least 3 mm and a minimum tensile strength Rm of 1000 MPa, preferably 1075 MPa, with a product of tensile strength Rm and elongation at break A5 of at least 2000 MPa% and a ratio of uniform elongation to elongation at break of at least 25%.
  • components for the automotive industry such as body panels, components of support structures or airbag tubes and cylinder tubes are made from these sheets or strips.
  • wear plates made of this alloy for excavator shovels or linings for blasting chambers are used.
  • Such steels are also used for applications where sudden impact energies have to be absorbed, e.g. B. as bulletproof armor or as an impact carrier or crash box.
  • Structural tubes or sheets made from this steel alloy can also be used for particularly highly stressed welded steel structures, for example in crane, bridge, ship, hoist and truck construction.
  • the demands for ever higher strengths and improved processing and component properties while reducing weight and / or costs have led, among other things, to the development of ultra-fine-grain duplex steels, which are also known as carbide-free bainitic steels under the term "super bainite".
  • the creation of such a structure, consisting of bainitic ferrite with retained austenite lamellae, is sketched schematically in FIG. 1, in contrast to the upper and lower bainite structure.
  • Characteristic for these steels is z.
  • B. a tensile strength Rm from 1000 to about 2000 and even up to 2500 MPa, depending on the strength, an elongation at break A5 of at least 5% and an extremely fine (nano) structured bainitic structure with proportions of retained austenite.
  • a corresponding bainitic steel is disclosed, for example, in the laid-open specification WO 2014/040585 A1.
  • a method for producing a sheet from a bainitic steel with at least 50% by volume of bainite is known from the laid-open specification WO 2009/075494 A1.
  • To set the required bainitic structure is an isothermal Conversion time from one minute to 48 hours required.
  • the steel comprises 0.2 to 1.0 wt% carbon (C), 0 to 3.0 wt% silicon (Si), 0 to 3.0 wt% manganese (Mn), 0 to 3 , 0% by weight.
  • a rolled hot strip made from a high-strength steel with excellent forming properties is also known from the European patent application EP 0997548 A1.
  • the steel has the following chemical composition: C: 0.05 to 0.15%; Si: 0.5 to 2.0%; Mn: 0.5 to 2.0%; AI: 0.005 to less than 0.10%; P: 0.05% or less; S: 0.010% or less; Remainder iron and unavoidable impurities.
  • an Al content of 0.035% is specified for this steel and a tensile strength in the range from 591 to 853 N / mm 2 .
  • the structure of the steel has 60 to 95% by volume ferrite, 3 to 15% by volume retained austenite and 4.5 to 22.5% by volume bainite.
  • high-strength steel strip with excellent processability is known from the European patent application EP 1 512 760 A2.
  • the structure of the steel has 0 to 60 volume percent ferrite, 5 to 40 volume percent retained austenite and 20 to 90 volume percent tempered martensite or tempered bainite.
  • the composition of the steel is as follows: C: 0.10 to 0.60%, Si: equal to or less than 1.0%, Mn: 1.0 to 3.0%; AI: 0.03 to 2.0%, P: 0.02% or less, S: 0.03% or less, the balance being iron and inevitable impurities.
  • the tensile strength of the steel is given as 750 to 1050 MPa.
  • the European laid-open specification EP 2 759614 A1 already relates to a method for producing a flat steel product with an amorphous, partially amorphous or finely crystalline structure by means of a two-roller casting device.
  • the fine crystalline structure should have grain sizes in the range from 10 to 10,000 nm.
  • the steel melt should also be cooled at a cooling rate of at least 200 K / s to below the glass transition temperature.
  • the object of the invention is to provide a method for the production of high-strength sheet metal or strips from a low-alloy, high-strength bainitic and at the same time tough steel with excellent wear resistance, which is easier and more cost-effective to carry out. Furthermore, a corresponding steel strip or steel sheet made of this steel and an advantageous use are to be specified.
  • P max. 0.05 S at least one of the elements Ti, V, Nb in contents of at least 0.005 to 0.5% by weight and a total of max. 0.75% by weight , optionally one or more elements of Mo, Ni, Co, W or Zr totaling up to 5.5% by weight and / or less common earths Ce, Hf, La, Re, Sc and / or Y totaling up to 1 weight -%, remainder iron with impurities from the melting process
  • Martensite finish temperature (Mf) with a cooling rate of 0.1 ° C / min to 50 ° C / min
  • low-alloy steels are understood to mean steels in which the sum of the alloying elements does not exceed a content of 10% by weight, preferably 7.5% by weight.
  • the structure according to the invention is also characterized by a volume fraction of Bainite or bainitic ferrite of greater than 50% by volume.
  • the present invention is based on the understanding that the claimed bainitic ferrite is distinguished from pure ferrite. The formation of ferrite and bainitic ferrite can be traced back to different processes in the structure.
  • the displacive conversion forces the conversion product (the bainitic ferrite) to have a high dislocation density, so that the crystal can retain the forced macroscopic shape.
  • the redistribution to austenite takes place over significantly shorter distances than in the case of ferrite.
  • This structural component (bainitic ferrite) is made use of in the present development through targeted processing.
  • the great advantage of the method according to the invention is that the required bainitic microstructure and the resulting mechanical Properties of the sheet or strip produced in this way no longer requires additional heat treatment by long isothermal holding at the transition temperature, for example in a salt bath.
  • the final rolling temperatures should be between 600 and 1100 ° C., advantageously between 600 and 1000 ° C., more advantageously between 700 and 1000 ° C. and particularly advantageously between 850 and 950 ° C.
  • the rolling forces are not too high during hot rolling, and, on the other hand, a fine-grain structure with good toughness is still achieved in this temperature range.
  • the final rolling temperature is set specifically for the alloy in order to set an optimum final rolling temperature for the specific alloy composition with regard to rolling forces and a structure that is as fine-grained as possible.
  • This is set according to the invention using the following empirically determined formula (1) for the T-end temperature.
  • the T-end temperature corresponds to the final rolling temperature, which should be adhered to with a tolerance of ⁇ 100 ° C., advantageously ⁇ 50 ° C., in order to obtain the most homogeneous properties of the sheet or strip possible.
  • T-End [° C] 1100 ° C - 450 ° C / weight% x C (weight%) - 350 ° C / weight% x Si (weight%) + 350 ° C / weight% x AI (% by weight) + 6500 ° C /% by weight x Nb (% by weight) + 900 ° C /% by weight x Ti (% by weight) + 750 ° C /% by weight x V (% by weight)
  • This pancake structure is achieved through targeted precipitations of, for example, Nb (C, N) at the intersection of dislocations and grain boundaries, with the grain growth perpendicular to the rolling direction being severely hindered.
  • the cooling from the rolling heat takes place according to the invention to a temperature between 100 ° C. above the martensite start temperature (Ms) and 200 ° C. below the martensite finish temperature (Mf) at a cooling rate of 0.1 ° C./min to 50 ° C./min.
  • the strip or sheet that has already cooled down can also be austenitized again beforehand and then cooled accordingly.
  • the latent heat generated during the phase transition through the conversion of austenite into bainite is sufficient, a bainite content of at least 50% by volume, advantageously at least 75% by volume in To create a structure without the need for additional isothermal post-heat treatment. Time-consuming and costly post-heat treatments are therefore not absolutely necessary to achieve the properties according to the invention, but can of course be carried out to meet special requirements.
  • FIG. 3 shows the generation of latent heat during the phase transition using the test melts A and D according to Table 1.
  • the heat of conversion during the phase transition is therefore targeted exploited to adjust the desired microstructure.
  • the start of the martensitic transformation leads to the release of latent heat; this slows down the cooling process and favors the conversion of austenite into bainitic ferrite or the desired structure.
  • this controlled cooling is set in a targeted manner by adapting the composition in order to achieve the desired mechanical-technological properties
  • isothermal holding of the strip or sheet at a temperature between 100 ° C above the martensite start temperature (Ms) and 200 ° C below the martensite finish temperature (Mf) can be advantageous if, for example, a high uniform elongation Ag of over 6.5% of the product is required.
  • the martensite start temperature (Ms) according to formula (2) and the martensite finish temperature (Mf) according to formula (3) can be calculated as follows:
  • the resulting structure consists of carbide-free bainite and retained austenite with a proportion of at least 75 volume% bainitic ferrite, at least 10 volume% retained austenite and up to a maximum of 10 volume%, advantageously a maximum of 5 volume% martensite (or martensite phase and / or decomposed austenite).
  • the maximum carbon content C of the steel melt in% by weight is set at 0.70, preferably 0.50 and particularly preferably 0.40.
  • the other alloy components advantageously have the following contents in% by weight:
  • 0.25-3.00 Si preferably 0.50 to 2.50 and / or 0.05-2.00 Al, preferably 0.10 to 1.00 and / or 0.25-3.00 Mn, preferably 0.5 to 3.00 and / or 0.05-2.50 Cr, preferably 0.10 to 2.00 and / or 0.001-0.015 N, preferably 0.002 to 0.0125
  • the kinetics of ferrite formation can also be decisively controlled, so that the formation of coarse polygonal ferrite grains, which can negatively affect the material properties, is effectively avoided.
  • the interplay of aluminum and chrome is decisive here. While aluminum accelerates the ferritic and bainitic transformation, adding chromium delays the ferritic transformation (see also Figure 4). The kinetics of both ferrite and bainite formation can be controlled through a targeted combination of these two elements.
  • manganese (Mn) can also advantageously be replaced or exchanged by molybdenum (Mo) according to formula (4):
  • Mo-Gehalterforderiich (wt%): 5 x Mn (wt%) + Mo content vorha ligand (wt%)> 7.5
  • the nitrogen content does not exceed the specified upper limit of 0.025% by weight, better 0.015% by weight, or optimally 0.0125% by weight, by the number and to minimize the size of harmful aluminum nitrides as primary precipitates in steel, whereby the condition AI c N ⁇ 5 c 10 3 (% by weight) must also be met.
  • a minimum nitrogen content of 0.001% by weight, optimally 0.002% by weight is required in order to enable the formation of niobium, vanadium or titanium carbonitride, which is necessary for increasing toughness through grain refinement.
  • a ratio of uniform elongation Ag to elongation at break A5 of at least 30% has proven to be advantageous in order to be able to meet the special requirements placed on a safety steel. It is also advantageous if a product of tensile strength Rm and elongation at break A5 of at least 12500 MPa x% is maintained.
  • wear parts such as excavator shovels or linings for blasting chambers or as parts for armor, is particularly advantageous.
  • Table 1 Chemical compositions of the alloys examined in% by weight
  • TRIP Transformation Induced Plasticity
  • steels that are usually referred to by the term TRIP are steels that have a very high strength and high ductility at the same time, which makes them particularly suitable for cold forming. These properties are obtained thanks to their special microscopic structure, whereby the deformation-induced martensite formation and the associated hardening are inhibited and the ductility is increased.
  • the effect of the TRIP effect is optimal with a residual austenite content of around 10 to 20% by volume in the structure.
  • the minimum content should not be less than 0.10% by weight. Such a minimum content of carbon is also advantageous because it leads to a sufficiently low martensite start temperature and thus the setting of a very fine microstructure. With a view to good weldability, the carbon content should not exceed 0.80% by weight. Maximum carbon contents of 0.70, preferably 0.50% by weight have proven to be favorable, with optimum properties being achieved when the carbon content is between 0.10 and 0.40% by weight. The minimum carbon content should be at least 0.10, better 0.15, preferably 0.20 and particularly preferably at least 0.25% by weight.
  • the essential element for achieving the required material properties after continuous cooling is aluminum, which dramatically accelerates the transformation kinetics.
  • the aluminum content should be at least 0.05% by weight, but not more than 3.00% by weight, since otherwise coarse polygonal ferrite grains can arise, which again worsen the mechanical properties.
  • the bainitic transformation becomes too slow and less relevant to the process Conditions are not sufficiently advanced, so that martensite is increasingly formed, which has an unfavorable effect on elongation at break and impact energy.
  • silicon can be added in contents of 0.25 to 4.00% by weight. Good material properties are achieved with aluminum contents between 0.05 and 2.00% by weight and optimally between 0.10 and 1.00% by weight. Corresponding silicon contents are 0.25 to 3.00% by weight or between 0.50 and 2.50% by weight.
  • chromium of at least 0.05 to 3.00% by weight
  • the ferritic transformation can be deliberately delayed and the kinetics of both ferrite and bainite formation can be adjusted through a combination with aluminum.
  • Advantageous chromium contents are 0.05 to 2.50% by weight or between 0.10 and 2.00% by weight.
  • Manganese The addition of manganese in the range from 0.25 to 4.00% by weight results from a compromise between strength, which can be achieved with higher additions, and sufficient toughness, which is achieved with lower contents, depending on the respective requirements on the steel alloy can be achieved. With regard to a very good or optimal combination of properties, the manganese content should be between 0.25 and 3.00% by weight or between 0.50 and 3.00% by weight.
  • a niobium content of 0.005 to 0.50% by weight should be set to ensure the formation of Nb (C, N).
  • the resulting grain refinement contributes to a significant improvement in the toughness properties.
  • a nitrogen content of 0.001 to 0.025% by weight is recommended for the formation of Nb (N), since NbN is more stable than NbC and thus leads to an increased contribution to grain refinement.
  • Advantageous niobium contents are 0.001 to 0.10 or 0.001 to 0.05% by weight, with advantageous nitrogen contents of 0.001 to 0.015 or 0.002 to 0.0125% by weight.
  • micro-alloy elements based on vanadium can be used up to 0.20% by weight and / or titanium up to 0.10% by weight. A total content for Nb, Ti, V of max. 0.75% by weight should be observed.
  • z. B. molybdenum (up to 2.00% by weight), nickel (up to 5.00% by weight), cobalt (up to 2.00% by weight) or tungsten (up to 1.50% by weight) can be added as mixed crystal hardeners.
  • a minimum content of 0.005% by weight and a total content of a maximum of 5.50% by weight should be observed. In order to be able to utilize the effect of these alloying elements, a minimum content of 0.01% by weight should be observed.
  • Rare earths and reactive elements The optional addition of rare earths and reactive elements such as Ce, Hf, La, Re, Sc and / or Y can be used to set a specific lamella spacing and thus to further increase strength and toughness in total contents of 0, 0020 up to 1% by weight.
  • the microstructure of the steel according to the invention consists of bainitic ferrite and retained austenite lamellae. It can have proportions of up to 10% by volume of martensite, advantageously up to 5% by volume (or martensite / austenite phase and / or disintegrated austenite).
  • the two most important parameters of the structure which significantly influence the mechanical properties of the steel, are the distance between the retained austenite lamellae in the bainitic ferrite and the proportion of retained austenite. It has been shown that the strength becomes higher, the smaller the lamella spacing and the greater the elongation at break of the material, the higher the proportion of retained austenite.
  • the average lamella spacing should be less than 750 nm, advantageously less than 500 nm.
  • a residual austenite content of at least 10% and a Martensite content of at most 10% by volume, preferably of at most 5% by volume, are present.
  • the average former austenite grain size should not exceed a value of 100 ⁇ m.
  • the microstructure is very fine, the structural components can hardly be distinguished by light microscopy, so that a combination of electron microscopy and X-ray diffraction can then be used on a case-by-case basis.
  • the structural components can be differentiated using scanning electron microscopy. In this way, an average lamella spacing of about 300 nm was determined.
  • Figures 7 to 12 show the results for calculating the mechanical parameters for tensile strength (Rm), elongation at break (A5), uniform elongation (Ag) and the retained austenite content (% by weight), as well as the ratio of uniform elongation (Ag) to elongation at break ( A5) and the product of tensile strength (Rm) x elongation at break (A5) according to the Hollomon-Jaffe parameter.
  • the Hollomon-Jaffe parameter log (i)) describes the effect of tempering or heat treatment of steel. It is a function of the tempering duration t and the tempering temperature T. The temperature T in Kelvin and the time t in hours are included in this non-unitary formula. C is a material-dependent constant. Different combinations of duration and temperature of the heat treatment can result in identical Hollomon-Jaffe parameters; the initial effect is then also comparable.
  • FIG. 7 shows the tensile strength as a function of the Hollomon-Jaffe parameter
  • FIG. 8 shows the elongation at break as a function of the Hollomon-Jaffe parameter
  • FIG. 9 the uniform elongation as a function of the Hollomon-Jaffe parameter.
  • FIG. 10 the residual austenite content as a function of the Hollomon-Jaffe parameter.
  • FIG. 11 the ratio of uniform elongation to elongation at break depending on the Hollomon-Jaffe parameter Dependence of the Hollomon-Jaffe parameter
  • FIGS. 7 to 10 an approximation function curve with a wider line width and, in relation to this, upper and lower deviations with further approximation function curves with a narrower line width are shown in relation to measured values for the melts A to F according to the invention.
  • FIGS. 11 and 12 also each show an approximation function curve with a dashed curve in relation to measured values for the melts A to F according to the invention. Dashed lines are also shown for the ratio of uniform elongation Ag to elongation at break A5 of 25% and 30% and for the product of tensile strength Rm and elongation at break A5 of 2,000 MPa% and 12,500 MPa%.

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  • Heat Treatment Of Sheet Steel (AREA)

Abstract

L'invention concerne un procédé de fabrication de tôles ou de bandes à haute résistance, ayant une épaisseur d'au moins 3 mm, une résistance à la traction (Rm) minimale de 1000 MPa, de préférence de 1075 MPa, un produit de la résistance à la traction (Rm) et de l'allongement à la rupture (A5) d'au moins 2000 MPa %, et un rapport d'allongement uniforme (Ag) à l'allongement à la rupture (A5) d'au moins 25 %, à partir d'un acier faiblement allié ayant une portion de bainite ou de ferrite bainitique égale à au moins 50 pour cent en volume et une teneur en austénite résiduelle d'au moins 5 pour cent en volume, le procédé comprenant les étapes suivantes : production d'une masse fondue d'acier ayant la composition chimique suivante (en pourcentage massique) : 0,10-0,80 de C, 0,25-4,00 de Si, 0,05-3,00 d'Al, 0,25-4,00 de Mn, 0,05-3,00 de Cr, 0,001-0,025 de N, max. 0,15 de P, max. 0,05 de S, au moins l'un des éléments Ti, V, Nb dans une teneur d'au moins 0,005 à 0,5 pour cent en poids et d'au plus 0,75 pour cent en poids au total, facultativement un ou plusieurs des éléments Mo, Ni, Co, W ou Zr jusqu'à 5,5 pour cent en poids au total et/ou des terres rares Ce, Hf, La, Re, Sc et/ou Y à jusqu'à 1 pour cent en poids au total, le reste étant du fer avec des impuretés liées à la fusion ; coulée de la masse fondue de métal pour former une ébauche, un bloc ou une bande mince en tant que pré-produit ; laminage à chaud du pré-produit pour former une tôle ou une bande, avec une température de laminage finale (extrémité T) entre 1150 et 600 °C ; refroidissement de la bande ou de la tôle de la chaleur de laminage à une température comprise entre 100 °C au-dessus de la température de départ de la martensite (Ms) et 200 °C au-dessous de la température de fin de la martensite (Mf) à une vitesse de refroidissement de 0,1 °C/min à 50 °C/min, ou réchauffement de la bande ou de la tôle jusqu'à la température d'austénitisation et ensuite refroidissement à une température comprise entre 100 °C au-dessus de la température de début de martensite (Ms) et 200 °C au-dessous de la température de fin de martensite (Mf) à une vitesse de refroidissement de 0,1 °C/min à 50 °C/min, puis maintien éventuel de la bande ou de la tôle à une température comprise entre 100 °C au-dessus de la température de début de martensite (Ms) et 200 °C au-dessous de la température de fin de martensite (MF) pendant un maximum 24 h ; refroidissement à partir de cette plage de température jusqu'à la température ambiante. L'invention concerne en outre une bande d'acier ou une tôle d'acier fabriquée à partir de cet acier et une utilisation avantageuse de celle-ci.
PCT/EP2020/073419 2019-08-21 2020-08-20 Procédé de production de tôles ou de bandes à haute résistance à partir d'un acier bainitique à haute résistance faiblement allié, et bande d'acier ou tôle d'acier fabriquée à partir de cet acier WO2021032858A1 (fr)

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EP20760453.9A EP4018007A1 (fr) 2019-08-21 2020-08-20 Procédé de production de tôles ou de bandes à haute résistance à partir d'un acier bainitique à haute résistance faiblement allié, et bande d'acier ou tôle d'acier fabriquée à partir de cet acier

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DE102019122515.9 2019-08-21
DE102019122515.9A DE102019122515A1 (de) 2019-08-21 2019-08-21 Verfahren zur Herstellung von hochfesten Blechen oder Bändern aus einem niedrig legierten, hochfesten bainitischen Stahl sowie ein Stahlband oder Stahlblech hieraus

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CN114717389A (zh) * 2022-04-18 2022-07-08 燕山大学 一种耐磨低温贝氏体热作模具钢及其制备方法
CN115110004A (zh) * 2022-07-20 2022-09-27 武汉科技大学 一种超高冲击韧性中碳贝氏体钢及其热处理方法
CN115927959A (zh) * 2022-11-15 2023-04-07 北京科技大学 一种2.2GPa级低成本低碳非均质片层超高强双相钢及制备方法

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CN113699463A (zh) * 2021-08-25 2021-11-26 哈尔滨工程大学 一种多相强化超高强马氏体时效不锈钢及其制备方法

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Publication number Priority date Publication date Assignee Title
CN114717389A (zh) * 2022-04-18 2022-07-08 燕山大学 一种耐磨低温贝氏体热作模具钢及其制备方法
CN114717389B (zh) * 2022-04-18 2023-09-22 燕山大学 一种耐磨低温贝氏体热作模具钢及其制备方法
CN115110004A (zh) * 2022-07-20 2022-09-27 武汉科技大学 一种超高冲击韧性中碳贝氏体钢及其热处理方法
CN115110004B (zh) * 2022-07-20 2023-10-24 武汉科技大学 一种超高冲击韧性中碳贝氏体钢及其热处理方法
CN115927959A (zh) * 2022-11-15 2023-04-07 北京科技大学 一种2.2GPa级低成本低碳非均质片层超高强双相钢及制备方法
CN115927959B (zh) * 2022-11-15 2023-07-18 北京科技大学 一种2.2GPa级低成本低碳非均质片层超高强双相钢及制备方法

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