EP1412548B1 - Mehrphasen-stahlblech mit verbesserter tiefziehfähigkeit und verfahren zu seiner herstellung - Google Patents

Mehrphasen-stahlblech mit verbesserter tiefziehfähigkeit und verfahren zu seiner herstellung Download PDF

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EP1412548B1
EP1412548B1 EP02751696A EP02751696A EP1412548B1 EP 1412548 B1 EP1412548 B1 EP 1412548B1 EP 02751696 A EP02751696 A EP 02751696A EP 02751696 A EP02751696 A EP 02751696A EP 1412548 B1 EP1412548 B1 EP 1412548B1
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steel sheet
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total amount
strength
microstructure
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French (fr)
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EP1412548A1 (de
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Osamu Nippon Steel Corp. Oita Works KAWANO
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Nippon Steel Corp
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Nippon Steel Corp
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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
    • C22C38/04—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
    • C22C38/02—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
    • 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
    • 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
    • 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

Definitions

  • the present invention relates to a multi-phase steel sheet excellent in hole expandability, aiming at the application for automobiles, such as passenger cars and trucks, etc., for industrial machines, or the like, and a method of producing the same.
  • a multi-phase steel sheet comprising retained austenite and/or martensite is widely known.
  • a steel sheet having an excellent balance between strength and elongation (a total elongation is 33.8 to 40.5% when a tensile strength is 60 to 69 kgf/mm 2 ) is obtained by containing retained austenite in an appropriate quantity therein.
  • Japanese Unexamined Patent Publication No. H3-180426 discloses a bainite sheet steel excellent in the balance between strength and hole expandability (a hole expansion ratio d/d0 is 1.72 to 2.02, namely 72 to 102% in terms of a net hole expansion rate, when a tensile strength is 60 to 67 kgf/mm 2 ).
  • a hole expansion ratio d/d0 is 1.72 to 2.02, namely 72 to 102% in terms of a net hole expansion rate, when a tensile strength is 60 to 67 kgf/mm 2 ).
  • this technology provides not a multi-phase structure but the equalization of a structure (a bainite single phase structure), as a means of improving the net hole expansion rate, the balance between strength and elongation is rather insufficient (a total elongation is 27 to 30% when a tensile strength is 60 to 67 kgf/mm 2 ) and the application is again limited.
  • punch stretch formability represented by the balance between strength and elongation and stretch flange formability represented by the balance between strength and hole expandability are two major components of forming, such a technology, satisfying both the components simultaneously, has not been available.and the excellence in both has been the key to the expansion of the application.
  • JP-A-11-323494 discloses a hot-rolled high strength steel sheet having a satisfactory strength-elongation balance and a stretch frangibility and with excellent formability.
  • the steel sheet contains C: 0.05 - 0.15%, Si: 0.5 - 2.0%, Mn: 0.5 - 2.0%, P: 0.05% or less, S: 0.010% or less, Al: 0.005 - less than 0.10%, wherein the metal structure mainly comprises three phases of ferrite, retained austenite and bainite, the amount of the ferrite [V(F)] is 60 - 95 area%, the amount of the retained austenite [V( ⁇ )] is 3 - 15 vol%, the amount of the bainite [V(B)] in the area ratio is 1.5 times or more of the amount of the retained austenite [V( ⁇ )], and the average hardness of the bainite is 240 - 400 Hv.
  • JP-A-07-252592 discloses C: 0.05 - 0.25%, Si + Al: 0.5 - 3.5%, Mn: 0.5 - 3.5%, P ⁇ 0.05%, S ⁇ 0.01%, wherein the metal structure mainly comprises three phases of ferrite, retained austenite and bainite, the amount of ferrite having the grain diameter less than 5 ⁇ m is 50 vol% and the Vickers hardness of the ferrite being more than 150, the amount of the retained austenite having a carbon concentration of more than 0.9% and a grain diameter of less than 2 ⁇ m is 5%, and tensile strength (TS) is 490 - 1180 MPa, and strength-elongation balance (tensile strength ⁇ total elongation) ⁇ 20000 MPa, strength-elongated flange balance (tensile strength ⁇ hole expansion rate) ⁇ 75000 MPa, sheared transition temperature ⁇ - 40°C, fatigue limit ratio ⁇ 0.45.
  • TS tensile strength
  • the object of the present invention is, by solving the problems of the conventional steel sheets, to provide a steel sheet having both the excellent balance between strength and hole expandability (not less than 35,000 MPa%, preferably not less than 46,000 MPa%, in terms of the value obtained by multiplying a tensile strength by a net hole expansion rate) and the excellent balance between strength and elongation (not less than 18,500 MPa%, preferably not less than 20,000 MPa%, in terms of the value obtained by multiplying a tensile strength by a total elongation), that is, a multi-phase steel sheet excellent in hole expandability, and a method of producing the same.
  • Both of the balance between strength and hole expandability (MPa ⁇ %), and the balance between strength and elongation (MPa ⁇ %) are indexes of press-formability. If these values are large, the resultant products exhibit excellent properties.
  • the balance between strength and hole expandability is represented by the product of the value of strength (MPa) obtained by tensile test and the value of hole expansion ratio (%) obtained by hole expansion test. Further, the balance between strength and elongation is represented by the product of the value strength (MPa) obtained by tensile test and the value of total elongation obtained by tensile test.
  • both of hole expansion ratio and elongation decrease and, as a result, both of the balance between strength and hole expandability (MPa ⁇ %), and the balance between strength and elongation (MPa ⁇ %) exhibit low values.
  • lowering the value both of hole expansion ratio and elongation can be restrained and it is possible to obtain the high values of the balance between strength and hole expandability (MPa ⁇ %), and the balance between strength and elongation (MPa ⁇ %).
  • the present inventors have earnestly studied, from the viewpoint of integrated manufacturing from steelmaking to hot rolling, and have finally invented a multi-phase steel sheet excellent in hole expandability and a method of producing the same.
  • C is an important element for stabilizing austenite and obtaining a multi-phase structure, and C is added at not less than 0.03 mass % in order to stabilize austenite and to obtain either one or both of retained austenite and martensite in the total amount of not less than 3% in area percentage.
  • the upper limit of C content is set at not more than 0.15 mass %, preferably not more than 0.11 mass %, in order to avoid the deterioration of weldability and an adverse influence on a net hole expansion rate.
  • FIG. 1 shows the result of the investigation on the relationship between the P content and the net hole expansion rate of a steel sheet, using the steel sheets having the chemical components of Steel No. 1 in Table 1.
  • Steel No. Chemical components (mass %) C Si Mn P S Al N Al+Si 1 0.11 1.88 1.40 0.006-0.034 0.001 0.03 0.003 1.41 2 0.10 1.40 1.40 0.008 0.001 0.04 0.002 1.44
  • a net hole expansion rate is calculated based on the Japan Iron and Steel Federation Standard JFS T 1001-1996. From Fig. 1, the net hole expansion rate improves remarkably and exponentially by controlling the P content to not more than 0.010 mass % and its effect on the net hole expansion rate, which has not yet been assumed within the range of conventional concepts, is recognized. By so doing, press cracking can be avoided.
  • the reduction of P content improves the properties of the edge of a punched hole (for instance: the minimization of facet size, the reduction of roughness and the reduction of microcracks on a fractured plane; the suppression of the deterioration of workability in a microstructure on a sheared plane; and the like), and leads to the improvement of a net hole expansion rate.
  • S content is set at not more than 0.003 mass %, preferably not more than 0.001 mass %, from the viewpoint of preventing the deterioration of a net hole expansion rate and weldability caused by sulfide-system inclusions.
  • Si and Al are elements useful for obtaining a multi-phase structure. They make either one or both of retained austenite and martensite account for not less than 3% in total in area percentage and have the function of improving a net hole expansion rate, by promoting the formation of ferrite and suppressing the formation of carbide, and further by strengthening ferrite, thus reducing the hardness difference between ferrite and hard phases (such as bainite and martensite) and contributing to the uniformity of a structure. Moreover, they act also as deoxidizing elements. From the above-mentioned viewpoint, the lower limit of the total addition amount of either one or both of Si and Al should be not less than 0.5 mass %. Considering the balance between the cost and the effect, the upper limit of the total addition amount is set at not more than 4 mass %.
  • either one of the means of avoiding Si scale by controlling the Si content to less than 0.1 mass %, preferably not more than 0.01 mass %, and the means of making Si scale harmless (making scale less conspicuous by forming the scale all over the surface) by controlling the Si content rather to more than 1.0 mass %, preferably more than 1.2 mass %, may be adopted.
  • Al may be limited to not more than 0.2 mass %, preferably not more than 0.1 mass %, considering the drawbacks in steelmaking, such as the erosion of refractory materials, nozzle clogging and the like, and the material properties.
  • Mn, Ni, Cr, Mo, and Cu are elements useful for obtaining a multi-phase structure, and also are elements which strengthen ferrite.
  • the lower limit of the total addition amount of one or more of them should be not less than 0.5 mass %.
  • the upper limit of the total addition amount is set at not more than 4 mass %.
  • Nb, V, Ti, B, Ca and REM may be added as selective elements.
  • Nb, V and Ti are elements effective for a higher strength. However, considering the balance between the cost and the effect, the total addition amount of one or more of those elements is set at not more than 0.3 mass %.
  • B has a function as a strengthening element, and may be added by not more than 0.01 mass %. In addition, B also has the effect of mitigating the adverse effect of P.
  • Ca may be added by not more than 0.01 mass % since Ca further improves a net hole expansion rate by controlling the shape of sulfide-system inclusions (spheroidizing).
  • REM may also be added by not more than 0.05 mass % for the same reason.
  • N may be added by not more than 0.02 mass %, if required, aiming at the stabilization of austenite and the strengthening of a steel sheet.
  • the crystal grain size of a microstructure affects the fractured surface size at the edge of a punched hole, it affects a net hole expansion rate remarkably. Even in the case where the average size of crystal grains in a microstructure is fine, if the maximum grain size is large, it adversely affects a net hole expansion rate. As a microstructure is composed of many crystal grains, a net hole expansion rate cannot be governed by the average grain size: when a big crystal grain exists among many crystal grains, it adversely affects the net hole expansion rate even if the average grain size is fine.
  • the size of a crystal grain not a circle-reduced diameter but the maximum length thereof affects a net hole expansion rate.
  • Fig. 2 shows the result of the investigation on the relationship between the maximum length of a microstructure in a steel sheet and the net hole expansion rate of the steel sheet, using the steel sheets having the chemical components of Steel No. 2 in Table 1.
  • the net hole expansion rate improves remarkably and exponentially when the maximum length of a microstructure is not larger than 10 microns, and its effect on the net hole expansion rate, which has not yet been assumed within the range of the conventional concept, is recognized. By so doing, press cracking can be avoided.
  • the maximum length of a microstructure was calculated from an optical micrograph under the magnification of 400 taken at a section perpendicular to the rolling direction of a steel sheet after the section was etched with Nitral and the reagent disclosed in Japanese Unexamined Patent Publication No. S59-219473, averaging all over the section along the thickness direction.
  • a net hole expansion rate can be improved by reducing the number of coarse inclusions.
  • the number of coarse inclusions was obtained by observing a polish-finished section along the rolling direction of a steel sheet with a microscope (400 magnifications) and integrating the number of coarse inclusions 20 microns or larger in maximum length.
  • Fig. 3 shows the result of the investigation on the relationship between the number of coarse inclusions (20 microns or larger in maximum length) in a steel sheet and the net hole expansion rate, using the steel sheets having the chemical components of Steel No. 2 in Table 1. It is understood that, when the number of coarse inclusions (20 microns or larger in maximum length) is not more than a specified number (not more than 0.3 piece per square millimeter), the net hole expansion rate can be improved remarkably and press cracking can be avoided.
  • controlling the micro Vickers hardness of bainite to less than 240 acts preferably on the improvement of hole expandability.
  • the reduction of the hardness of bainite lowers the hardness difference between ferrite and bainite and thus contributes to the improvement of the uniformity of a structure.
  • the micro Vickers hardness of bainite exceeds 240, the hardness difference between ferrite and bainite deviates from the range desirable for hole expandability and further the deterioration of hole expandability is caused by the deterioration of workability of the bainite itself.
  • the reduction of P (not more than 0.01%) largely contributes to enhancing the effect, but details are not known.
  • the micro Vickers hardness of bainite is obtained by identifying bainite by etching a section perpendicular to the rolling direction of a steel sheet with the reagent disclosed in Japanese Unexamined Patent Publication No. S59-219473, and by averaging the values measured at five points (averaging the values excluding the maximum and minimum values from among the values measured at seven points) under a load of 1 to 10 g.
  • An excellent balance between strength and elongation (not less than 18,500 MPa% in terms of the value obtained by multiplying a tensile strength by a total elongation) and an excellent balance between strength and hole expandability (not less than 35,000 MPa% in terms of the value obtained by multiplying a tensile strength by a net hole expansion rate) are obtained by controlling the total area percentage of either one or both of retained austenite and martensite to 3 to 30%.
  • the upper limit of the total area percentage is set at 30%.
  • the area percentage of pearlite is determined to be not more than 3% at most, preferably not more than 1%.
  • the area percentage of retained austenite is set at not less than 3%.
  • the area percentage of martensite is set at not more than 3%.
  • the area percentage of martensite is set at not less than 3%.
  • the effect increases yet further.
  • the remainder structure of a microstructure consists of either one or both of ferrite and bainite, and by controlling the total area percentage of ferrite and bainite to not less than 80%, the deterioration of press formability, which is caused by hard structures other than ferrite and bainite combining with each other in the form of a network, can be suppressed.
  • both an excellent balance between strength and hole expandability (not less than 35,000 MPa%, preferably not less than 46,000 MPa%, in terms of the value obtained by multiplying a tensile strength by a net hole expansion rate) and an excellent balance between strength and elongation (not less than 18,500 MPa%, preferably not less than 20,000 MPa%, in terms of the value obtained by multiplying a tensile strength by a total elongation) can be obtained simultaneously, and press formability improves markedly.
  • the identification of the constitution of a microstructure, the measurement of an area percentage, and the measurement of the maximum length of retained austenite and/or martensite were carried out with an optical micrograph under the magnification of 1,000 taken at a section perpendicular to the rolling direction of a steel sheet after the section was etched with a nitral reagent and the reagent disclosed in Japanese Unexamined Patent Publication No. S59-219473, and by X-ray analysis.
  • the reflux of molten steel is represented by the amount of molten steel that circulates the inside of a secondary refining apparatus, such as an RH, per unit time, and there are various formulas for the computation.
  • Q Amount of refluxed molten steel (t/min.)
  • V Flow rate of refluxed gas (Nl/min.)
  • D Inner diameter of snorkel (m)
  • P0 Pressure in vacuum chamber (Pa)
  • P1 Pressure at injection port of refluxed gas (Pa)
  • k Constant (a constant determined based on secondary refinement apparatus, 4 in this case).
  • FIG. 4 The schematic drawing of the refining of molten steel using an RH is shown in Fig. 4.
  • Two snorkels 3 of the degassing chamber 2 are dipped into the molten steel ladle 1, gas is blown from underneath one of these snorkels (in this case, Ar is blown from underneath one of the snorkels through the injection lance 4), then, the molten steel in the molten steel ladle 1 rises and enters the degassing chamber 2, and after the degassing process, the molten steel descends and returns from the other snorkel 3 to the molten-steel ladle.
  • a secondary refining apparatus employing an RH is used
  • it is needless to say that other apparatus for example, a DH may be used.
  • Fig. 5 shows the result of investigating the relationship between the frequency of the reflux of molten steel after flux for desulfurization is added when molten steel having the components of Steel No. 2 in Table 1 is refined and the number of inclusions 20 microns or larger in size per square mm at a section of a steel sheet obtained by hot-rolling a slab cast from the molten steel.
  • the surfacing of the desulfurization flux system inclusions is notably promoted, the number of coarse inclusions (20 microns or larger) can be reduced to not more than a prescribed number (not more than 0.3 per square mm), the net hole expansion rate is improved, and thus press cracking is avoided.
  • Fig. 6 shows the result of summarizing the relation among finish-rolling entry and exit temperatures when a slab having the components of Steel No. 2 in Table 1 is hot-rolled, and the maximum length of crystal grains in the microstructure at a section of the steel sheet obtained.
  • the maximum length of the microstructure is certainly controlled to not larger than 10 microns and, therefore, a net hole expansion rate can be improved and press cracking can be avoided.
  • a finish-rolling exit temperature exceeds 920°C, the whole microstructure coarsens, the drawbacks such as the deterioration of press formability and the generation of scale defects remarkably appear, and therefore the temperature is determined to be the upper limit.
  • the multi-step control of a cooling rate (the combination of quenching, slow cooling and isothermal retention) or immediate quenching at the finish-rolling exit, which are generally known, may be employed, aiming at the control of the area percentage of a microstructure and the promotion of the fining of a microstructure and the formation of a multi-phase structure.
  • the upper limit of a coiling temperature is set at 500°C in order for either one or both of retained austenite and martensite to account for 3% or more in total in area percentage. If a coiling temperature exceeds 500°C, the total area percentage of 3% or more cannot be secured and thus an excellent balance between strength and elongation (tensile strength multiplied by total elongation) is not obtained.
  • air cooling or forced cooling may be employed for the cooling of a steel sheet after it is coiled.
  • a slab may be subjected to rolling after once being cooled and then reheated, or rolling by HCR or HDR. Further, a slab may be produced by so-called thin slab continuous casting.
  • a steel sheet according to the present invention may be plated with Zn or the like for improving corrosion resistance, or may be coated with a lubricant or the like for further improving press formability.
  • a net hole expansion rate was calculated based on the Japan Iron and Steel Federation Standard JFS T1001-1996.
  • the maximum length of crystal grains in a microstructure was calculated from an optical micrograph under the magnification of 400 taken at a section perpendicular to the rolling direction of a steel sheet after the section was etched with a nitral reagent and the reagent disclosed in Japanese Unexamined Patent Publication No. S59-219473.
  • the number of coarse inclusions in a steel sheet was obtained by observing a polish-finished section perpendicular to the rolling direction of a steel sheet with a microscope (400 magnifications) and integrating the number of coarse inclusions 20 microns or larger in maximum length.
  • the identification of the constitution of a microstructure, the measurement of an area percentage, and the measurement of the maximum length of retained austenite and/or martensite were carried out with an optical micrograph under a magnification of 1,000 x taken at a section perpendicular to the rolling direction of a steel sheet after the section was etched with a nitral reagent, the reagent disclosed in Japanese Unexamined Patent Publication No. S59-219473 and the reagent disclosed in Japanese Unexamined Patent Publication No. H5-163590, and with X-ray analysis.
  • F ⁇ (%) (2/3) ⁇ 100/(0.7 x ⁇ (211) / ⁇ (220)+1) ⁇ + (1/3) ⁇ 100/(0.78 x ⁇ (211) / ⁇ (311)+1) ⁇ , where, ⁇ (211), ⁇ (220), ⁇ (211), and ⁇ (311) represent the intensity on the respective planes.
  • the present invention has made it possible to provide, stably and at a low cost, a multi-phase steel sheet excellent in press formability, having both an excellent balance between strength and hole expandability and an excellent balance between strength and elongation, and a method of producing the steel sheet, and, consequently, the ranges of the application and the service conditions have markedly been expanded and the industrial and economical effects of the present invention are remarkable.

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
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Claims (4)

  1. Mehrphasiges Stahlblech mit ausgezeichneter Lochaufweitbarkeit, dadurch gekennzeichnet, dass
       das Stahlblech enthält, als chemische Bestandteile in Massenprozent:
    C: 0,03 bis 0,15 %,
    P: nicht mehr als 0,010 %,
    S: nicht mehr als 0,003 % und
    Si und/oder Al in einer Gesamtmenge von 0,5 bis 4 %, und
    eines oder mehrere von Mn, Ni, Cr, Mo und Cu in einer Gesamtmenge von 0,5 bis 4 %, optional eines oder mehrere von Nb, V und Ti mit einer Gesamtmenge von 0,3 % oder weniger, und ferner optional eines oder mehrere Elemente ausgewählt aus Ca mit 0,01 % oder weniger, Seltene-Erdelemente mit 0,05 % oder weniger, B mit 0,01 % oder weniger und N mit nicht mehr als 0,02 %, mit dem Rest bestehend aus Fe und unvermeidbaren Verunreinigungen;
       die Mikrostruktur eines Stahlblechabschnitts aus Restaustenit und/oder Martensit zusammengesetzt ist, welche mit 3 bis 30 % zum Gesamtflächenprozentanteil beitragen und der Rest aus Ferrit und/oder Bainit besteht;
       die Maximallänge der Kristallkörner der Mikrostruktur nicht mehr als 10 µm beträgt und
       die Anzahl der Einschlüsse mit einer Größe von 20 µ oder mehr an dem Stahlblechabschnitt nicht mehr als 0,3 Stück pro Quadratmillimeter beträgt.
  2. Mehrphasiges Stahlblech mit ausgezeichneter Lochaufweitbarkeit, dadurch gekennzeichnet, dass
       das Stahlblech enthält, als chemische Bestandteile in Massenprozent:
    C: 0,03 bis 0,15 %,
    P: nicht mehr als 0,010 %,
    S: nicht mehr als 0,003 % und
    Si und/oder Al in einer Gesamtmenge von 0,5 bis 4 %, und
    eines oder mehrere von Mn, Ni, Cr, Mo und Cu in einer Gesamtmenge von 0,5 bis 4 %, optional eines oder mehrere von Nb, V und Ti mit einer Gesamtmenge von 0,3 % oder weniger, und ferner optional eines oder mehrere Elemente ausgewählt aus Ca mit 0,01 % oder weniger, Seltene-Erdelemente mit 0,05 % oder weniger, B mit 0,01 % oder weniger und N mit nicht mehr als 0,02 %, mit dem Rest bestehend aus Fe und unvermeidbaren Verunreinigungen;
    die Mikrostruktur eines Stahlblechabschnitts aus Restaustenit und/oder Martensit zusammengesetzt ist, welche mit 3 bis 30 % zum Gesamtflächenprozentanteil beitragen, aus Perlit, der mehr als 0 % und nicht mehr als 3 % Flächenprozentanteil ausmacht, und der Rest aus Ferrit und/oder Bainit besteht;
    die Maximallänge der Kristallkörner der Mikrostruktur nicht mehr als 10 µm beträgt und
    die Anzahl der Einschlüsse mit einer Größe von 20 µ oder mehr an dem Stahlblechabschnitt nicht mehr als 0,3 Stück pro Quadratmillimeter beträgt.
  3. Mehrphasiges Stahlblech mit ausgezeichneter Lochaufweitbarkeit gemäß Anspruch 1 oder 2, dadurch gekennzeichnet , dass die Vickers-Mikrohärte des Bainits weniger als 240 beträgt.
  4. Verfahren zum Herstellen eines mehrphasigen Stahlblechs mit ausgezeichneter Lochaufweitbarkeit gemäß einem der Ansprüche 1 bis 3, wobei das Stahlblech die folgenden chemischen Bestandteile in Massenprozent enthält:
    C: 0,03 bis 0,15 %,
    P: nicht mehr als 0,010 %,
    S: nicht mehr als 0,003 % und
    Si und/oder Al in einer Gesamtmenge von 0,5 bis 4 %, und
    eines oder mehrere von Mn, Ni, Cr, Mo und Cu in einer Gesamtmenge von 0,5 bis 4 %, optional eines oder mehrere von Nb, V und Ti mit einer Gesamtmenge von 0,3 % oder weniger, und ferner optional eines oder mehrere Elemente ausgewählt aus Ca mit 0,01 % oder weniger, Seltene-Erdelementen mit 0,05 % oder weniger, B mit 0,01 % oder weniger und N mit nicht mehr als 0,02 %, mit dem Rest bestehend aus Fe und unvermeidbaren Verunreinigungen, dadurch gekennzeichnet, dass
    die Stahlschmelze nicht weniger als 1,5 mal zirkuliert wird, nachdem Flußmittel zur Entschwefelung am Zeitpunkt der Entschwefelung der Stahlschmelze zugegeben wurde, wenn die Stahlschmelze mit den Bestandteilen gefeint wird,
    ferner, wenn ein Stahlblech durch Warmwalzen einer durch Gießen der Stahlschmelze erhaltenen Platte hergestellt wird, wobei das Endwalzen durchgeführt wird, indem die Eintrittstemperatur beim Endwalzen auf 950° C oder höher und die Austrittstemperatur beim Endwalzen im Bereich von 780 bis 920° C geregelt wird, und
    das so erhaltene Stahlblech bei einer Temperatur von 500° C oder niedriger aufgewickelt wird.
EP02751696A 2001-07-25 2002-07-25 Mehrphasen-stahlblech mit verbesserter tiefziehfähigkeit und verfahren zu seiner herstellung Expired - Fee Related EP1412548B1 (de)

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WO2016164788A1 (en) * 2015-04-10 2016-10-13 The Nanosteel Company, Inc. Improved edge formability in metallic alloys

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JP4235030B2 (ja) * 2003-05-21 2009-03-04 新日本製鐵株式会社 局部成形性に優れ溶接部の硬さ上昇を抑制した引張強さが７８０ＭＰａ以上の高強度冷延鋼板および高強度表面処理鋼板
DE102004025717B9 (de) * 2004-05-26 2011-05-26 Voestalpine Stahl Gmbh Höherfester Multiphasenstahl mit verbesserten Eigenschaften
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US10465260B2 (en) 2015-04-10 2019-11-05 The Nanosteel Company, Inc. Edge formability in metallic alloys
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WO2016164788A1 (en) * 2015-04-10 2016-10-13 The Nanosteel Company, Inc. Improved edge formability in metallic alloys
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DE60206771D1 (de) 2006-03-02
CN1535323A (zh) 2004-10-06
KR20040013156A (ko) 2004-02-11
EP1412548A1 (de) 2004-04-28
CN1243844C (zh) 2006-03-01
DE60206771T2 (de) 2006-07-20
JP2004536965A (ja) 2004-12-09
KR100548117B1 (ko) 2006-02-02
TW567231B (en) 2003-12-21
JP4181036B2 (ja) 2008-11-12

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