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
  • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
  • C21D8/041—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing involving a particular fabrication or treatment of ingot or slab
  • C21D8/0415—Rapid solidification; Thin strip casting
• • 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
  • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
• • 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
  • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
  • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
  • C21D8/0426—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
  • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
  • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
  • C21D8/0473—Final recrystallisation annealing
• • 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
  • C22C38/12—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
  • 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
  • C21D2211/008—Martensite

Definitions

• the invention relates to a method for producing steel flat products, such as strips or sheet metal blanks, from high-strength, aluminum-alloyed steels.
• steels belong to the group of multiphase steels. These are usually steels whose properties are determined by the type, amount and arrangement of the phases of the structure.
• the structure therefore has at least two phases (eg ferrite, martensite, bainite). This gives them a strength / formability combination that is superior to conventional steels.
• This preparation route presents problems in particular when casting peritectically solidifying compositions.
• These steel grades there is the danger of the formation of longitudinal cracks during continuous casting.
• the formation of such longitudinal cracks can reduce the quality of the hot strips produced from the cast slabs or thin slabs so much that they become unusable.
• extensive measures such as increased insulation costs, are required, which can go so far that the processing of such steel grades becomes uneconomical.
• multiphase steels are of particular interest for the automotive industry because of their high strength, they allow the use of lower material thicknesses and concomitantly a reduction in vehicle weight and, secondly, the safety of the vehicle body in the event of a collision (crash behavior) .
• multiphase steels with at least constant strength of the overall body allow a reduction in the sheet thickness of a component produced from such multiphase steels compared to a body produced from conventional steels.
• multiphase steels are melted in the converter steelworks and cast on a continuous casting plant into slabs or thin slabs, which are then hot rolled into hot strip and coiled.
• the mechanical properties of the hot strip can be varied.
• the hot strips can be cold rolled to cold strip to provide thinner sheet thicknesses ( EP 0 910 675 B1 . EP 0 966 547 B1 . EP 1 169 486 B1 . EP 1 319 725 B1 . EP 1 398 390 A1 ).
• a problem in the production of flat products made of high-strength multiphase steels with tensile strengths of more than 800 MPa is that high rolling forces must be applied when rolling such steels. This requirement has the consequence that high-strength hot strips made of steels of the type in question can usually only be made available in width and thickness with the currently customarily available production facilities, which do not meet the demands made today in the field of automobile construction more fully. Above all, tapes of small thicknesses with sufficient widths can be poorly represented on conventional systems. It also turns out in conventional practice in practice difficult to produce multiphase steels cold strips with strengths of more than 800 MPa.
• the cast strip is then hot rolled in-line in one or more passes of between 25% and 70% strain to a hot strip.
• the final temperature of hot rolling is above the Ar 3 temperature.
• the hot strip obtained is then cooled in two stages. In the first stage of this cooling, a cooling rate of 5 - 100 ° C / s until a temperature between 400 - 550 ° C is reached. At this temperature, the hot-rolled strip is left to rest for a period of time required to allow bainitic transformation of the steel with a residual austenite content greater than 5%. The formation of perlite should be avoided.
• the conversion process is started by the beginning of the second stage of the Cooling stopped, in which the hot strip is brought to a temperature below 400 ° C, to then wrap it at a reel temperature lying below 350 ° C to form a coil.
• the object of the invention was therefore to provide a method by means of which high-strength steel flat products can be produced over a wide range of geometric dimensions with reduced manufacturing outlay.
• this object has been achieved by a method for producing steel flat products, in which a multiphase structure forming steel, the (in wt .-%) 0.10 - 0.14% C, 1 , 30 - 1.70% Mn, up to 0.030% P, up to 0.004% S, 0.10 - 0.30% Si, 0.90 - 1.2% Al, up to 0.0070% N, 0.070 0.130% Ti, 0.040-0.060% Nb, 0.140-0.260% Mo and the remainder contains iron and unavoidable impurities, is cast into a cast strip with a thickness of 1-4 mm, in which the cast strip in a continuous operation a degree of deformation of more than 20% in-line at a lying in the range of 850 - 1000 ° C hot rolling end temperature is hot rolled to a hot strip with a thickness of 0, 5 - 3.2 mm and the the hot strip is coiled at a coiler temperature of 350-480 ° C, so that a
• the invention uses the possibility of strip casting to process a particularly high-strength, peritectically solidifying multiphase steel into a hot strip. Since the cast strip itself already has a small thickness, in the course of hot rolling of this strip only relatively small degrees of deformation must be maintained in order to produce flat products with small thicknesses, as are required in particular in the automotive industry. Thus, by specifying a corresponding output thickness of the cast strip, it is easily possible to produce hot strips with the method according to the invention, which have a maximum property distribution of at most 1.5 mm and from which, for example, elements for the support structure of an automobile can be produced.
• the invention makes it possible to manufacture high-strength hot strips consisting of a martensitic steel of the specified composition processed according to the invention, whose width is more than 1,200 mm, in particular more than 1,600 mm.
• the use according to the invention of the strip casting method in the processing of high-strength steels of the type assembled according to the invention offers the possibility, in addition to the above-mentioned advantages due to its process-specific properties and manipulated variables (eg hot rolling end temperature, cooling, coiling temperature), of also critical steel compositions according to the invention with regard to their solidification behavior to safely shed processed species.
• process-specific properties and manipulated variables eg hot rolling end temperature, cooling, coiling temperature
• critical steel compositions according to the invention with regard to their solidification behavior to safely shed processed species.
• the very rapid solidification of the cast strip which is characteristic of strip casting, leads to a significantly reduced risk of the formation of center segregations compared with conventional production, with the result that the hot strip produced according to the invention has a particularly uniform distribution of properties and microstructure over its cross section and its length.
• the hot strip produced according to the invention has high strengths of at least 800 MPa, without having to observe a special cooling cycle of the hot strip between the end of the hot rolling and the reeling, as described in US Pat EP 1 072 689 B1 is prescribed by the need for a cooling break.
• it merely has to be ensured that the hot rolling ends in a relatively narrow temperature window and that the reeling is also carried out in a precisely defined temperature range. In between there is a one-stage cooling down.
• Another advantage of the procedure according to the invention is that an extension of the range of mechanical properties of the strip produced according to the invention based on only one steel analysis by a Variation of the cooling and rolling conditions can be achieved.
• Hot strips produced according to the invention are particularly suitable for further processing into cold rolled strip. Accordingly, a practice-oriented embodiment of the invention provides that the hot strip is cold rolled to a cold strip having a thickness of 0.5-1.4 mm, in particular 0.7 mm to 1.3 mm, as is required for the construction of automobile bodies.
• the cold strip can be annealed at an annealing temperature of 750-850 ° C.
• tensile strengths of at least 800 MPa can be reliably ensured.
• the breaking elongation A 50 of the cold strip is just as safe at least 10%.
• the flat product produced according to the invention is characterized by a particularly good coatability.
• the cold strip is provided in a conventional manner with a metallic coating, which may be, for example, a galvanizing.
• the strength and elongation values according to the invention produced hot strips can be adjusted over a wide range by an appropriate vote of the Hotwalzend- and reel temperatures. If, for example, hot strips are to be produced which have a tensile strength R m of at least 800 MPa at an elongation at break A 80 of the resulting hot strip of at least 10%, this can be achieved by setting the hot rolling end temperature to 900-1000 ° C. and Coiler temperature 400 - 480 ° C amount.
• the hot rolling end temperature in the range of 850-1100 ° C and the coiler temperature in the range of 350-400 ° C selected.
• the tapes cast from steels A and B were hot rolled into a hot strip whose thickness was 1.25 mm in four different trials immediately after in-line strip casting at a hot rolling end temperature WET. Subsequently, each hot strip obtained has been cooled directly in a cooling step to a coiler temperature HT and coiled. After coiling, the hot strips produced from steels A and B each had a tensile strength R m and an elongation at break A 80 , which, like the hot rolling end temperature WET and reel temperature HT, respectively, maintained in their preparation, are given in Table 2.
• Table 2 attempt stolen WET [° C] HT [° C] R m [MPa] A 80 [%] 1 A 950 450 901 12.4 2 B 900 400 811 13.1 3 A 920 400 1184 5.6 4 B 900 390 1159 5.2
• the hot strip produced from steel A was cold rolled into a 0.74 mm thick cold strip and annealed at an annealing temperature of 800 ° C. in order to recrystallize the strip.
• the tensile strength R m of the cold strip thus obtained was 985 MPa.

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

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Publications (2)

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Citations (6)

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• 2006
  • 2006-10-30 EP EP06123140A patent/EP1918404B1/fr not_active Not-in-force
  • 2006-10-30 PL PL06123140T patent/PL1918404T3/pl unknown
  • 2006-10-30 DE DE502006003832T patent/DE502006003832D1/de active Active
  • 2006-10-30 AT AT06123140T patent/ATE432374T1/de active
  • 2006-10-30 ES ES06123140T patent/ES2325963T3/es active Active
• 2007
  • 2007-10-24 KR KR1020097007486A patent/KR101461584B1/ko not_active Expired - Fee Related
  • 2007-10-24 CN CN2007800393899A patent/CN101528966B/zh not_active Expired - Fee Related
  • 2007-10-24 US US12/447,627 patent/US20100065162A1/en not_active Abandoned
  • 2007-10-24 JP JP2009533823A patent/JP5350254B2/ja not_active Expired - Fee Related
  • 2007-10-24 WO PCT/EP2007/061391 patent/WO2008052920A1/fr not_active Ceased

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