Classifications

• • 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
  • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
• • 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
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • 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
  • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0226—Hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0236—Cold rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
  • C21D8/0273—Final recrystallisation annealing

Definitions

• the invention relates to a cold strip from a ULC steel, which have good bake hardening properties and good ones Deformation properties with a high yield strength having.
• the invention relates to a Process for producing such a cold strip.
• the cold strip according to the invention is intended in particular Suitable for a zinc coating.
• a cold strip of the type mentioned above which especially for the production of panels with a excellent surface quality and are a process for its production known for example from EP 0 816 524 A1.
• the well-known steel sheet is made of an extremely little Carbon-containing steel manufactured, which (in % By weight) 0.0010 to 0.01% C, ⁇ 0.2% Si, 0.1 to 1.5% Mn, 0 to 0.05% P, ⁇ 0.02 S, 0.03 to 0.1% sol.
• Nb is in the range of 0.005 to 0.08% by weight and Ti in contents of 0.01 to 0.07% by weight available.
• EP 0 816 524 A1 known steel sheets for example from Automotive industry in terms of formability and general mechanical properties of such sheets not meet the requirements set out safely.
• the object of the invention was therefore a good malleable and at the same time for a zinc coating suitable steel sheet and a method for the same Creating manufacturing.
• a cold strip which (in% by weight) ⁇ 0.0030% C, ⁇ 0.005% Nb with the proviso that the content of Nb is ⁇ 93/12 *% C, with " % C "denotes the C content in% by weight, ⁇ 0.0050% Ti and optionally one or more of the following Alloying elements: Si: ⁇ , 10%, Mn: ⁇ 0.20%, P: ⁇ 0.015%, S: ⁇ 0.015%, Al g : 0.005 - 0.05%, N: ⁇ 0.0040%, Cr: ⁇ 0.05%, Cu: ⁇ 0.05%, Ni: ⁇ 0.05%, Mo: ⁇ 0.020%, Sn: ⁇ 0.020%, B: ⁇ 0.0004, and the balance contains iron and usual impurities.
• the steel sheet composed in this way according to the invention has good galvanizability and bake hardening properties of BH 0 > 15 N / mm 2 and BH 2 > 20 N / mm 2 , good deformation properties which are reflected in the n value ⁇ 0.18 and a Yield strength from 170 N / mm 2 to 230 N / mm.
• the tensile strength of cold strips according to the invention is regularly in the range from 280 to 340 N / mm 2 . Strains A 80 of ⁇ 35% and r m values> 1.3 are also achieved.
• Bake hardening values BH 0 of 25 N / mm 2 - 45 N / mm 2 and BH 2 of 25 N / mm 2 - 45 N / mm 2 can be achieved by using one or more of the options for optimizing the composition according to the invention explained below become.
• the peculiarity of the steel sheet according to the invention lies in addition to its improved over the prior art mechanical properties in that the titanium content is largely reduced and the Nb content in Relationship to the C content is chosen so that after a corresponding heat treatment more dissolved carbon is present than is the case with higher Ti contents. This is especially true when compared to such titanium and Steels containing niobium in which at least one is used for sufficient nitrogen stoichiometric binding Amount of titanium added to the steel. Therefore has a sheet according to the invention Taking into account his prescribed according to the invention Ratio of the Nb content of C added at least 0.005% by weight. They are particularly safe effects achieved by the invention reached when the Nb content remains unchanged The addition requirements are at least 0.008% by weight.
• Nb which is substoichiometric with respect to carbon
• the addition of Nb which is substoichiometric with respect to carbon is essential for reliably achieving such good values for the bake hardening property.
• Compliance with this Nb / C ratio is of particular importance if the heat treatment of the steel is to be carried out at temperatures below 850 ° C.
• annealing carried out at these temperatures leads to improved bake hardening properties compared to the prior art.
• BH 2 values can be guaranteed, which are safely in the range from 20 N / mm 2 to 40 N / mm 2 .
• the ratio of the contents of niobium and carbon above stoichiometric compositions such good bake hardening properties are only achieved at annealing temperatures well above 850 ° C.
• Ti-free steels Ti content ⁇ 0.0010% by weight
• Ti contents> 0.0050% by weight Mechanical properties that are only marginal increased Ti contents
• the yield strength and tensile strength according to the invention were largely Ti-free steels 10 to 20 N / mm 2 lower than in steels, the Ti contents of> 0.0050 to 0.0070% by weight at (Ti / N) atomic ratios from 0.67 to 0.90.
• the elongation at break of steels according to the invention was 2% to 3%, the rq value by 0.1 to 0.4 and the n value by 0.01 to 0.02 higher than in the compared low-Ti steels.
• the operational testing of the alloy concept according to the invention confirmed its advantages over the low-Ti steel compositions.
• the Ti content is therefore preferably limited to ⁇ 0.0015% by weight, in particular ⁇ 0.0010% by weight.
• the Mn content is up according to the invention at most 0.2% by weight, but preferably at most 0.15% by weight of Mn or lower values are limited. In order to safely set sulfur however, the Mn content should not be less than 0.11% by weight.
• the above mentioned object is achieved in that a steel melt having a composition of the invention, preferably in the strand is cast into a precursor material, that the starting material to hot band with a preferably above the A r3 temperature, in particular above 900 ° C, lying hot rolling end temperature is hot rolled, that the hot strip is coiled with a reel temperature that is preferably more than 650 ° C, in particular more than 700 ° C, that the hot strip is cold rolled into cold strip, and that the cold strip is subjected to a heat treatment in a continuous process , the temperature T HZ in the holding zone of the heat treatment device used for this is> 820 ° C.
• Annealing temperatures make the process according to the invention especially for combination with hot-dip galvanizing suitable. So the one that takes place in the run Heat treatment in the course of a hot-dip galvanizing treatment the cold strip.
• the cold strip obtained has good bake hardening properties without it annealing at high, 850 ° C considerably exceeding temperatures.
• the degree of forming achieved by dressing is 0.5% to 2.0%, preferably 1.0% to 1.5%.
• the hot strips were then cold-rolled into cold strips KB1, KB2, KB3, KB4, KB5 with a thickness of 0.8 mm suitable for processing into body components and subjected to annealing in a continuous furnace, in which the cold strips are placed in the holding zone of the furnace Temperature T HZ have been kept.
• the cold strips KB1 - KB5 were dressed at skin pass degrees G.
• the mechanical and technological properties of the yield strength R p , tensile strength R m , uniform elongation A g1, elongation A 80 , r value, n value, BH 0 value and BH 2 are for the sheets KB1 - KB5 that do not have yield strength in this state -Value of cold strips KB1, KB2 have been determined. Subsequently, samples of the cold strips KB1 - KB5 were subjected to an artificial aging treatment, in which they were kept at a temperature of 100 ° C. for one hour.
• Table 1.2 contains the mechanical-technological Properties of the cold strips KB1 to KB5 in the trained state.
• Table 1.4 shows the mechanical-technological properties of the samples of the Cold strips KB1 to KB5 indicated in the aged condition.
• the heat treatment of the cold strips KB1 to KB5 was part a coating process within which the Cold strips KB1 to KB5 in a known manner with a Galvannealed coating has been provided.
• Diag. 9 and in the diagram Diag. 10 are those after an annealing of 810 ° C and in the diagrams Diag. 11 and Diag. 12 the BH 0 - (Diag. 9,11) or BH 2 values (Diag. 10,12) that can be determined after annealing at 840 ° C for the samples C1 - C5, CH1 - CH5 and Cerf via the ratio Nb- Content / C content applied.
• the bake hardening properties the titanium-free sample Cerf according to the invention with the same Nb / C ratio at the level of the bake hardening values the low titanium variant ((Ti / N) at ⁇ 1).
• the inventive has Sample Cerf at the same time compared to the low Ti ones Samples improved mechanical properties.
• Diag. 9 to 12 are recognizable much worse bake hardening values with one too Nitrogen overstoichiometric addition of titanium.
• Table 3 shows the properties of the Cold strips produced according to the invention Properties from a conventional, a higher Ti content of ULC steel (C: 0.002%, Mn: 0.20%, P: 0.01%, S: 0.006%, Si: 0.046%, Al: 0.035%, N: 0.0022%, Cu: 0.011%, Cr: 0.026%, Ni: 0.019%, Nb: 0.002%, Ti: 0.012%, Mo: 0.002%, B: 0.0003%, Sn: 0.010 % (all figures in% by weight)) of cold rolled strip juxtaposed.
• the cold strips according to the invention were free from elongation limit. Even after artificial aging, it can be deduced from the mechanical properties that there is sufficient security to avoid flow figures when pressing components up to a period of at least 3 months (after the sheet has been produced).

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)

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Citations (6)

• 2002
  • 2002-07-03 EP EP02014692A patent/EP1380663A1/fr not_active Withdrawn

Patent Citations (6)

Non-Patent Citations (2)

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