Classifications

• • 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
• • 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
  • 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 method for producing a cold strip, cold-formed at low degrees of deformation and produced from a steel of known composition.
• a hot strip is first hot-rolled from a starting material such as slabs, thin slabs or cast strips.
• a cold strip is then cold rolled from the hot strip.
• this cold strip is then subjected to further cold-forming steps, such as straightening, skin-dressing, re-rolling and forming.
• This cold forming also includes the work steps which are summarized in the specialist world under the generic term "flexible rolling".
• Such a "flexible rolling” in which the roll gap is variably adjusted during the rolling process, enables the process-shortening production of sheets with a defined thickness profile in the rolling direction that is individually adapted to the load.
• the cold strips are usually annealed before they are cold-formed in order to achieve the deformability required for the cold-forming.
• a further recrystallizing annealing would be advantageous.
• such an annealing is generally dispensed with if only small degrees of deformation have been achieved in the course of cold working. Otherwise the formation of coarse grains in the structure of the cold deformed strips must be expected.
• the formation of coarse grain leads to a reduction in the deformability, which in particular makes deep-drawing deformation more difficult and creates a pitted surface structure (so-called "orange skin”) on the drawn part.
• Coarse grain formation can be avoided by avoiding recrystallizing annealing after cold working in practice.
• a restriction of the ductility and thus the usability, in particular the deformability when deep-drawing the cold strip or in comparable deforming steps, must be accepted.
• the object of the invention is to provide, starting from the prior art explained above, a method with which recrystallized, cold-formed cold-rolled strips can be produced from soft steels of known composition without the risk of coarse grain formation.
• B and the remainder iron and steel produced with unavoidable impurities, such as slabs, thin slabs or cast strips, are hot-rolled into a hot strip, in which the hot strip is cold-rolled into a cold strip, in which the cold strip is at a Annealing temperature is crystal-recovering, which is lower than the recrystallization temperature at which the cold-recovered cold-rolled strip is subjected to cold deformation at low degrees of deformation and at which the cold-formed cold-rolled strip is recrystallized in a second annealing.
• the temperature during the annealing carried out before the cold working is preferably set such that it is in the upper part of the crystal recovery. In this way, an optimized ductility can be achieved without the risk of coarse grain formation during the final recrystallization annealing.
• the annealing temperature during the crystal-restoring annealing should accordingly be at least 450 ° C and at most 550 ° C.
• the annealing temperature during crystal restoration annealing for the same purpose is at least 550 ° C and at most 650 ° C. Regardless of the type of steel, the annealing temperature should always be selected so that the cold strip is recrystallized to a maximum of 90% after the crystal-restoring annealing.
• the annealing temperature during the recrystallizing annealing carried out after the cold working is selected so that complete recrystallization is reliably achieved.
• the annealing temperatures required for steels of the type in question are between at least 650 ° C and at most 850 ° C
• the degrees of deformation achieved in the course of cold forming are usually at most 40%.
• the method according to the invention can be used particularly advantageously when the cold forming is carried out as flexible rolling. With this cold deformation, sheets can be produced for load-oriented components. Using the procedure according to the invention, cold-formed cold strips can be produced, the structure of which has a grain size of at most 6 ASTM.
• the table shows the alloy contents of a conventional mild steel A and an IF steel B.
• Slabs have been cast from steels A, B, which have been hot-rolled into hot strip.
• the hot strips produced from steel A were then cold-rolled into cold strips A1, A2 and the hot strips produced from steel B into cold strips B1, B2.
• the first cold strips AI and B1 were then subjected to crystal-restoring annealing.
• the annealing temperature for this crystal-restoring annealing was 500 ° C, while it was 600 ° C for the cold strip B1.
• the degree of recrystallization achieved was less than 90%.
• the second cold strip A2 or B2 was annealed completely recrystallizing.
• the annealing temperature was 720 ° C
• the cold strips A1, A2 or B1, B2 were cold-formed at various degrees of deformation between 0% and 50%.
• This cold forming comprised "flexible rolling", in which different degrees of rolling were set between approximately 5% and 50%.
• the cold-formed cold strips A1, A2 or B1, B2 have been recrystallized at an annealing temperature of 720 ° C.
• Diag. 1 are for the cold-formed cold strips A1, A2 produced from the steel A, which result after the final recrystallization annealing
• Grain sizes Gs in ASTM over the degree of deformation ⁇ have been applied in%. The individual measured values are symbolized by circles. It was found that the grain sizes of the cold strip A2, which had been annealed before the cold working until fully recrystallized, are significantly higher for all degrees of deformation than in the case of the cold strip AI, which according to the invention was only annealed before the cold working. The deviation is particularly significant with very low degrees of deformation in the range of less than 15%.
• Diag. 2 shows the diag for the cold strips B1, B2 produced from steel B. 1 corresponding representation of the grain size based on the cold rolling degree.
• the grain size of the cold strip B2 increases significantly with decreasing degree of deformation, while the grain size of the cold strip B1 produced according to the invention is at an even, significantly lower level.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Metal Rolling (AREA)

Applications Claiming Priority (3)

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• 2000
  • 2000-11-08 DE DE10055338A patent/DE10055338C1/de not_active Expired - Fee Related
• 2001
  • 2001-11-08 WO PCT/EP2001/012910 patent/WO2002038818A1/de not_active Application Discontinuation
  • 2001-11-08 US US10/416,108 patent/US20040050464A1/en not_active Abandoned
  • 2001-11-08 AU AU2002214043A patent/AU2002214043A1/en not_active Abandoned
  • 2001-11-08 JP JP2002541130A patent/JP2004513235A/ja active Pending
  • 2001-11-08 KR KR10-2003-7005410A patent/KR20030055286A/ko not_active Application Discontinuation
  • 2001-11-08 EP EP01982469A patent/EP1337673A1/de not_active Withdrawn

Non-Patent Citations (1)

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