EP3872206A1 - Procédé de fabrication d'un produit plan en acier laminé à froid, traité ultérieurement et produit plan en acier laminé à froid, traité ultérieurement - Google Patents

Procédé de fabrication d'un produit plan en acier laminé à froid, traité ultérieurement et produit plan en acier laminé à froid, traité ultérieurement Download PDF

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EP3872206A1
EP3872206A1 EP21155199.9A EP21155199A EP3872206A1 EP 3872206 A1 EP3872206 A1 EP 3872206A1 EP 21155199 A EP21155199 A EP 21155199A EP 3872206 A1 EP3872206 A1 EP 3872206A1
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Prior art keywords
cold
flat steel
steel product
rolling
rolled flat
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German (de)
English (en)
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EP3872206B1 (fr
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Annette BÄUMER
Roland Sebald
Hans Ferkel
Karoline Schmidt
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ThyssenKrupp Steel Europe AG
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ThyssenKrupp Steel Europe AG
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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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C21D8/0268—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment between cold rolling steps
    • 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
    • C22C38/04—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
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—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
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • 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
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the invention relates to a cold-rolled flat steel product which has been aftertreated to increase strength and has an increased yield strength and an increased tensile strength, as well as a method for its production.
  • Flat steel products of the type in question are rolled products obtained by cold rolling, such as steel strips or sheets, as well as blanks and blanks made therefrom.
  • High-strength flat steel products are becoming increasingly important, especially in the field of vehicle construction, as they enable the vehicle's own weight to be reduced and the payload to be increased.
  • a low weight not only contributes to the optimal use of the technical performance of the respective drive unit, but also supports resource efficiency, cost optimization and climate protection.
  • a decisive reduction in the dead weight of sheet steel constructions can be achieved by increasing the mechanical properties, in particular the strength of the flat steel product being processed.
  • a flat steel product consisting of a two-phase steel is known.
  • the flat steel product is manufactured by hot and cold rolling. After cold rolling, it undergoes additional heat treatment to increase the yield strength.
  • the object of the invention was to provide a method for producing a flat steel product with a high yield strength and a high tensile strength R m , which can be carried out reliably and thereby leads to an optimal combination of properties in the flat steel product obtained.
  • the yield point of a flat steel product is understood to mean the lower yield point R el if the flat steel product has a pronounced yield point. Otherwise (that is, for flat steel products without a pronounced yield point), in the context of this application, the yield point of the flat steel product is understood to be the yield point R p02.
  • this object has been achieved by the invention in that, in the production of a cold-rolled flat steel product with a high yield strength and a high tensile strength R m , the work steps specified in claim 1 are carried out.
  • a flat steel product according to the invention that achieves the above-mentioned object has the features specified in claim 8.
  • the re-rolling takes place at room temperature, although there is usually a certain heating of the flat steel product due to the re-rolling.
  • the yield strength can be increased both by plastic deformation during re-rolling and by annealing.
  • plastic deformation new dislocations occur in the lattice structure, which contribute to increasing the strength.
  • Annealing leads to the formation and growth of precipitates which hinder dislocation sliding.
  • the subsequent annealing must be designed in such a way that sufficient thermal energy is introduced to enable the local recovery processes, but not too much thermal energy, as otherwise global microstructure formation occurs.
  • afterglow temperatures in the range from 100 ° to 400 ° C. have proven to be expedient.
  • the afterglow temperature is preferably greater than 130.degree. C. and / or less than 330.degree.
  • the annealing time is expediently 0.2-25 hours.
  • the tempering annealing provided according to the invention after the rerolling is carried out as a hood annealing.
  • the alloy of the steel from which the flat steel products to be processed according to the invention are made is selected such that optimal mechanical properties are achieved under the influence of the additional post-treatment step.
  • the C content is preferably at most 0.20% by weight, particularly preferably at most 0.18%. On the other hand, if the C content is below 0.05%, the desired strength is not obtained.
  • the C content is preferably at least 0.08% by weight, particularly preferably at least 0.12% by weight.
  • Si is present in the steel of a cold-rolled flat steel product processed according to the invention in contents of 0.05-0.6% in order to increase the strength by solid solution hardening without impairing the ductility.
  • Si serves as a ferrite former. Excessively high Si contents can impair the surface quality, for example as a result of adhering scale or grain boundary oxidation.
  • the Si content can be limited to a maximum of 0.6% by weight.
  • the Si content is preferably at most 0.42%. If, on the other hand, the Si content is too low, the strength-increasing effect due to solid solution hardening in the ferrite phase is inadequate. If the desired effect of Si is to be available particularly reliably, the Si content can be set to at least 0.24% by weight.
  • Mn is present in the steel of a cold-rolled flat steel product processed according to the invention in contents of 1.0-3.0% by weight in order to support solid solution strengthening and martensite formation to increase strength. This is done by Mn stabilizing the austenite from which the martensite is formed. Targeted adjustment of the Mn content therefore adjusts the volume fraction of martensite.
  • the Mn content is preferably at least 1.5% by weight, in particular at least 1.7% by weight.
  • an excessive addition of Mn leads to an insufficient proportion of the martensite phase. Therefore, the Mn content is preferably at most 2.4% by weight.
  • Al is present in the steel of a cold-rolled flat steel product processed according to the invention in contents of 0.02-1.5% by weight, on the one hand to serve as a deoxidizer and nitrogen binding during melting and on the other hand to ensure the sufficient amount of ferrite and thus ductility increase.
  • the maximum content of 1.5% by weight should not be exceeded. Compliance with an upper limit of 0.9% by weight has proven to be particularly favorable.
  • N is an undesirable alloy component that is one of the unavoidable impurities. Therefore, its content in the steel of a cold-rolled flat steel product processed according to the invention must not exceed 0.02% by weight. Too high an N content impairs the processability and, if B and / or Al is also present, it can lead to the formation of harmful nitrides and thus prevent the effectiveness of these elements.
  • the N content is preferably at most 0.01% by weight. It is optimally limited to at most 0.008% by weight, in particular at most 0.006% by weight.
  • P is an undesirable alloy component that is one of the unavoidable impurities. Excessive addition of P can lead to embrittlement and thus to a reduction in the crash properties. In addition, the weldability is impaired by the P content. For these reasons, the P content should not exceed 0.2% by weight.
  • the P content is preferably at most 0.05%, in particular at most 0.03%.
  • S is an undesirable alloy component, which is to be assigned to the unavoidable impurities. Therefore, its content in the steel of a cold-rolled flat steel product processed according to the invention must not exceed 0.05% by weight. In order to ensure good ductility of the steel product, the formation of MnS or (Mn, Fe) S must be kept as low as possible.
  • the S content is preferably at most 0.01% by weight, particularly preferably at most 0.005% by weight.
  • the Cr and Mo contribute to increasing the strength in the steel of a flat steel product processed according to the invention. They promote the formation of martensite by shifting the ferrite-pearlite transformation areas during heat treatment.
  • the Mo content is at least 0.003% by weight, preferably at least 0.005% by weight.
  • the Cr content is at least 0.2% by weight, preferably at least 0.3% by weight.
  • the Mo content is therefore a maximum of 1.0% by weight, preferably a maximum of 0.3% by weight.
  • the Cr content is a maximum of 1.5% by weight, preferably a maximum of 0.8% by weight.
  • Ti, B and Nb contribute to the increase in strength in the steel of the cold-rolled flat steel product processed according to the invention and lead to a finer microstructure.
  • B By suppressing the formation of ferrite and bainite, B enables a higher proportion of martensite, but can only fully develop its effect through the additional addition of Ti, which prevents the formation of unwanted boron nitrides through the formation of fine Ti (C, N) precipitates.
  • C, N fine Ti
  • This increase in strength due to the formation of precipitates is promoted or reinforced by the additional addition of Nb. It has been shown that the sum of the contents of Ti, Nb and 15 times the content of B should be at least 0.02% by weight in order to achieve these properties (i.e. Ti + Nb + 15 ⁇ B ⁇ 0, 02% by weight).
  • the boron content is less than 0.005% by weight, preferably less than 0.003% by weight.
  • V in the steel of the cold-rolled flat steel product processed according to the invention leads to an improvement in the processability and an improved resistance to delayed crack formation due to a finer microstructure.
  • a V content in the range 0.0005-0.05% by weight should be selected, in particular it should be at least 0.003% by weight.
  • Cu and Ni contribute to the increase in strength in the steel of the cold-rolled flat steel product processed according to the invention and can be added individually or in combination.
  • the Cu content is at least 0.0001% by weight, preferably at least 0.001% by weight. However, the Cu content should not exceed 0.5% by weight, preferably 0.08% by weight.
  • the Ni content is at least 0.002% by weight, preferably at least 0.01% by weight. The maximum Ni content should be no greater than 0.2% by weight, preferably no greater than 0.1% by weight.
  • the addition of Ca in the steel of the cold-rolled flat steel product processed according to the invention leads to a finer distribution of the inclusions in the steel and forms spherical sulfides, which can reduce the disadvantages of other harmful sulfides in further processing.
  • the Ca content should be at least 0.0005% by weight. However, since too high a Ca content can have detrimental effects on castability and hot formability, it should be at most 0.007% by weight, preferably at most 0.003% by weight.
  • the steel has a carbon equivalent C eq that is between 0.3% and 1.3%.
  • the carbon equivalent is well suited to characterize the subsequent processability of the flat steel product. With values in the range 0.3% to 1.3%, the flat steel product can be welded well as well as coated without any problems compared to other steel alloys with a similar strength and a higher proportion of Alloy elements.
  • the carbon equivalent is preferably a maximum of 0.7% for this. Furthermore, the carbon equivalent is preferably at least 0.3%.
  • a cold-rolled flat steel product is preferably used as the starting material, the structure of which consists of at least two phases, of which martensite and ferrite are the dominant phases, with more than 10% by volume of martensite and more than 60% by volume of ferrite available.
  • the proportion of ferrite is preferably more than 70% by volume, in particular more than 80%.
  • the remaining portion can contain bainite or precipitates.
  • the structure of the flat steel product should contain at least 60% by volume ferrite in order to be able to set the necessary elongation.
  • At least 10% by volume of martensite should also be present in the structure of the flat steel product according to the invention in order, on the one hand, to achieve strength and, on the other hand, to enable a tempering effect.
  • the post-treated structure consists of at least two phases, of which ferrite and martensite are the dominant phases.
  • the martensite is now tempered martensite.
  • the ferrite phase has slightly elongated grains, any previously existing austenite has decayed.
  • the other phase components are unchanged compared to the starting product.
  • the post-treated flat steel product thus has a structure consisting of at least two phases, which (in % By volume) comprises more than 10% tempered martensite and more than 60% ferrite.
  • the proportion of ferrite is preferably more than 70% by volume, in particular more than 80%.
  • the cold-rolled flat steel product is coated between post-rolling and tempering. Coating has the advantage that corrosion protection is guaranteed.
  • the cold-rolled flat steel product is coated, in particular electrolytically coated, between post-rolling and annealing.
  • the advantage of a coating between post-rolling and tempering is that any hydrogen absorbed during the coating is removed again during tempering. Hydrogen can lead to hydrogen embrittlement and should therefore be avoided if possible.
  • An electrolytic coating has the advantage that the flat steel product is not heated to a high degree, for example in comparison to hot-dip coating. Excessive heating during coating could affect the set structure and thus the mechanical properties.
  • the cooling of the cold-rolled flat steel product to room temperature has two intermediate steps.
  • the cold-rolled flat steel product is cooled to a first cooling temperature T 1 in the first intermediate step and is kept at the first cooling temperature T 1 for a first holding time t 1.
  • the cold-rolled flat steel product is then cooled to a second cooling temperature T 2 in the second intermediate step and is held at the second cooling temperature T 2 for a second holding time t 2.
  • This two-stage cooling process has the advantage that ferrite is formed in the first intermediate step and the bainite and retained austenite components are set in the second intermediate step.
  • the cooling can also take place in a single cooling step to room temperature.
  • the cold-rolled flat steel product provided after-treated to increase strength can be provided with a metallic protective coating.
  • a metallic protective coating This is for example It is useful when the flat steel product is used to manufacture components that are exposed to a corrosive environment in practical use.
  • the metallic coating can be applied in any suitable manner, an application by hot dip coating, for example in a continuous hot-dip coating system, being particularly suitable here.
  • an aftertreated, cold-rolled flat steel product has a yield strength of at least 1000 MPa if the yield strength is at least 1000 MPa in at least one direction (that is, for example, across or along the rolling direction).
  • the yield strength is at least 1000 MPa in at least one direction (that is, for example, across or along the rolling direction).
  • the post-treatment steps according to the invention, post-rolling and tempering, regularly result in a yield strength of at least 1000 MPa
  • preferred design variants have a yield strength of at least 1200 MPa, in particular of at least 1400 MPa.
  • a tensile strength of at least 1100 MPa is also achieved, preferred design variants having a tensile strength of at least 1200 MPa, in particular at least 1400 MPa.
  • the alloy-independent tensile strength R ⁇ m is at least 400 MPa, preferably at least 450 MPa.
  • the high tensile strength is not achieved by high alloying with elements that contribute to hardening (C, Si, Mn, Cr, Mo), but by the post-treatment steps according to the invention, post-rolling and tempering.
  • the cold-rolled flat steel product, which has been post-treated to increase strength, has the advantage that high strength is achieved without excessive additional alloying. It is therefore correspondingly cheaper to produce.
  • the negative effects of the high alloy content on subsequent processing steps such as welding or coating are eliminated. In this respect, low-alloy steels are easier to process.
  • the sum of the grain boundary lengths for small-angle grain boundaries of a square measuring field of 50 ⁇ m * 50 ⁇ m in a longitudinal section is greater than 10 mm, preferably greater than 15 mm, particularly preferably greater than 20 mm.
  • Orientation differences of the lattice of less than 15 ° are referred to as small-angle grain boundaries.
  • the sum of the grain boundary lengths is determined using the EBSD method.
  • the EBSD method electron backscattering diffraction
  • the information from the electrons backscattered from the sample is used.
  • the electron beam scans the surface of the sample during an analysis.
  • the impinging electrons are scattered in the sample. Some of these hit the grating surfaces of the examined grain under Bragg conditions and are diffracted.
  • the resulting diffraction patterns (Kikuchi patterns) are recorded with the help of a phosphor screen and processed and interpreted by software.
  • the Kikuchi patterns contain information about the existing crystal symmetries, which allow conclusions to be drawn about the examined crystallographic phases and the orientation of the examined grain, as well as lattice distortions, misorientations of grain boundaries, etc. If you now consider a square measuring field of 50 ⁇ m * 50m on the surface of a section taken along the direction of rolling (longitudinal section), it is possible to add up the total length of the small-angle grain boundaries which separate orientation differences of the grating of ⁇ 15 °.
  • Table 1 shows the carbon equivalent C eq determined from the composition.
  • the steel melts 1-17 were cast into slabs for the subsequent experiments 1-17.
  • the slabs cast from the steel melts have been reheated to a reheating temperature of 1260-1300 ° C and then hot-rolled in a conventional manner at a hot-rolling end temperature of 880-990 ° C to form a hot strip with a thickness of 2-3 mm.
  • the hot strips obtained were cooled to a coiling temperature of 525-585 ° C. and were wound into a coil at this coiling temperature.
  • the hot strips were cold-rolled to cold-rolled steel strips in an equally conventional manner with an overall cold-rolling degree of on average 20-60% achieved via cold-rolling.
  • the cold-rolled steel strips then underwent a continuous annealing treatment at an annealing temperature of 816-916 ° C.
  • the steel strips were cooled to room temperature in two intermediate steps.
  • the steel strips were cooled to a first cooling temperature T 1 with 650 ° C T 1 800 ° C and kept at the first cooling temperature for a first holding time t 1 with 0s t 1 20s.
  • the steel strips were then cooled to a second cooling temperature T 2 and held at the second cooling temperature T 2 for a second holding time t 2 .
  • the following applies to the second cooling temperature T 2 and the second holding time t 2 450 ° C ⁇ T 2 ⁇ 550 ° C and 60s ⁇ t 2 ⁇ 500s
  • All steel strips produced in this way had a structure with more than 10% martensite and more than 60% ferrite.
  • Each of the cold-rolled steel strips obtained in the tests as described above was then first subjected to re-rolling with a re-rolling degree W G2 and then an additional tempering anneal carried out as a hood annealing, in which it was held for more than 20 minutes at a temperature T G2 .
  • cold-rolled steel strips according to the invention are ideally suited for the production of components which have high strength but do not have the high-alloy chemical analysis typical for this strength. This reduces the associated welding problems and the cost of the alloy components.
  • the Figures 1 and 2 show by way of example for the steel from the above-described example no.13 (see Table 1) the increase in the yield strength by re-rolling without annealing ( Figure 1 ) and by annealing without prior rolling ( Figure 2 ).
  • the difference in the yield strength between the condition after re-rolling or annealing and the initial condition is shown in each case.
  • the yield strength was determined in all cases across the rolling direction.
  • Figure 1 shows this difference as a function of the degree of rolling.
  • Figure 2 shows the difference as a function of the annealing temperature during tempering.
  • the annealing time was 20 minutes in each case. Both figures show a significant increase in the yield strength as a result of the respective aftertreatment.
  • Figure 3 shows for steel no. 13 the synergetic effect of re-rolling and annealing on the strength.
  • the difference in the yield strength between the condition after re-rolling and tempering and the condition after re-rolling without tempering is plotted.
  • a degree of rolling of 0% means the case without re-rolling. If the two effects (re-rolling and tempering) on the strength were independent of one another, there should be no dependence on the degree of rolling, since the rolling effect has just been subtracted.
  • For all three afterglow temperatures 200 ° C, 300 ° C and 400 ° C) there should be a curve parallel to the x-axis. Instead, however, at all three afterglow temperatures an increase with increasing rolling degree can be seen.
  • Figures 4 and 5 show light microscopic longitudinal sections of steel No. 13 after nital etching.
  • the high ferrite content of more than 60% by volume can be clearly seen in both figures.
  • Figure 4 shows the steel in its initial state without any aftertreatment.
  • steel no. 13 is shown after an after-treatment to increase strength according to Table 2, in which the steel was initially re-rolled with a rolling degree of 30% and then annealed at 300 ° C. for more than 20 minutes.
  • the rolling direction is included Figure 5 in the plane of the drawing and runs horizontally.
  • Figure 5 the slightly elongated grains of the ferrite phase can be clearly seen.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
EP21155199.9A 2020-02-28 2021-02-04 Procédé de fabrication d'un produit plan en acier laminé à froid, traité ultérieurement et produit plan en acier laminé à froid, traité ultérieurement Active EP3872206B1 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115948692A (zh) * 2022-09-22 2023-04-11 马鞍山钢铁股份有限公司 一种抗拉强度450MPa级汽车用冷轧罩式退火高强钢及其制造方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2684975A1 (fr) * 2012-07-10 2014-01-15 ThyssenKrupp Steel Europe AG Produit plat en acier laminé à froid et son procédé de fabrication
WO2015158731A1 (fr) 2014-04-15 2015-10-22 Thyssenkrupp Steel Europe Ag Procédé de production d'un produit plat en acier laminé à froid à limite d'élasticité élevée et produit plat en acier laminé à froid
WO2016177420A1 (fr) * 2015-05-06 2016-11-10 Thyssenkrupp Steel Europe Ag Produit laminé plat en acier et son procédé de fabrication

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2684975A1 (fr) * 2012-07-10 2014-01-15 ThyssenKrupp Steel Europe AG Produit plat en acier laminé à froid et son procédé de fabrication
WO2015158731A1 (fr) 2014-04-15 2015-10-22 Thyssenkrupp Steel Europe Ag Procédé de production d'un produit plat en acier laminé à froid à limite d'élasticité élevée et produit plat en acier laminé à froid
WO2016177420A1 (fr) * 2015-05-06 2016-11-10 Thyssenkrupp Steel Europe Ag Produit laminé plat en acier et son procédé de fabrication

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115948692A (zh) * 2022-09-22 2023-04-11 马鞍山钢铁股份有限公司 一种抗拉强度450MPa级汽车用冷轧罩式退火高强钢及其制造方法

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