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
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • 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
  • 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
  • C21D8/0463—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 following hot rolling
• • 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
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
  • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
  • C23C2/0224—Two or more thermal pretreatments
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
  • C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
• • 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
  • C21D8/0436—Cold rolling

Definitions

• the invention relates to the field of the manufacture of steel sheets of low thickness intended to be stamped. More specifically, it concerns steel sheets ordinary low and very low carbon.
• composition of these sheets can be summarized as follows (the percentages are weight percentages).
• low carbon sheets there must be a carbon content less than 0.1%, preferably less than 0.03%, with even more preferably a sum of the carbon and nitrogen contents of less than 0.03%, a manganese content between 0.03 and 0.3%, a silicon content between 0.05 and 0.3%, a phosphorus content of between 0.01 and 0.1%.
• a carbon content is imposed less than 0.03% and a manganese content of between 0.3 and 2%. Additions of boron (up to 0.008%) and titanium (from 0.005 to 0.06%) in low carbon sheets are also possible.
• ultra-low carbon sheets there must be a carbon content less than 0.007%, and preferably a nitrogen content also very low, does not not exceeding a few tens of ppm.
• the contents of the other elements are the same than for low carbon sheets, with optionally titanium microadditions (from 0.005 to 0.06%) and / or niobium (0.001 to 0.2%).
• a process which can replace the previous one consists in casting the steel in slabs thin at their exit from the mold for continuous casting (for example 40 to 100 mm) and then carry out their hot rolling on rolling mill stands in line with the casting installation, this rolling may include various stages during which the steel is in the ferritic or austenitic state (see document WO 97/46332).
• this process at least one reheating of the slab, preceding the first hot rolling, is necessary, as well as subsequent cooling and reheating to allow carry out the desired metallurgical transformations of the product.
• the speed of running of the strip at the outlet of the hot rolling installation is of the order of 600 at 950 m / min depending, in particular, on the thickness of the product.
• These speeds are relatively high, in particular in relation to the usual running speeds of the products in the installations ensuring the “cold” treatments of the strips obtained in the rest of the manufacturing process, for example in compact annealing lines, hardened or plating.
• This induces productivity differences between these various installations, which oblige to store the products in their intermediate states in the form of coils, pending “cold” treatments.
• US-A-5,901,177 discloses the manufacture of sheets of steel having a composition according to the invention and a thickness of 0.9-2.7 mm from of a directly cast strip of thickness, for example, 3 mm from metal liquid between two casting cylinders.
• the cast strip is lime-rolled in the austenitic phase in line with casting essentially without being reheated and then wound at 500-700 ° C.
• the object of the invention is to provide a method of manufacturing sheet metal with high stampability with better productivity than traditional methods, by a shortening of manufacturing chains.
• the strip can then undergo cold treatments, or be cut to form sheets which will be shaped directly.
• the subject of the invention is also a sheet which can be obtained from tapes produced by the above process.
• the invention is first based on the use of a process for the direct casting of thin strips from liquid metal, known per se.
• the process of casting the strip between two internally cooled horizontal cylinders and rotated in opposite directions is well suited for this purpose.
• the strip coming out of the cylinders is then subjected to thermal and thermomechanical treatments which make it suitable for undergo the usual cold treatment operations that are applied to the laminated strips hot obtained by traditional methods.
• the respective productivities usual installations for direct casting of thin strips and installations for cold treatment of said strips being very comparable, the management of the production of sheet metal suitable for stamping is very simplified. It is even sometimes possible to completely pass from the cold rolling step, necessary in conventional dies, this which makes the manufacture of sheets and the resulting products faster and more economic.
• the method according to the invention is particularly suitable for the manufacture of sheets with high drawability, low steel (less than 0.1%, preferably less than 0.05%) and ultra-low (less than 0.007%) carbon content.
• Their manganese content can vary from 0.03 to 2%, the highest grades (from 0.3%) corresponding to steels for which a particularly high resistance is required.
• Their silicon content can range from 0 to 0.5%.
• their phosphorus content ranges from 0 to 0.1%.
• Additions of boron (up to 0.002%) and titanium (up to 0.15%) are possible.
• these steels have a low nitrogen content. For low carbon steels, the sum of the carbon and nitrogen contents does not optimally exceed 0.03%.
• ultra-low carbon steels the sum of the carbon and nitrogen contents must not optimally not exceed 0.007%.
• These ultra-low carbon steels can also contain small amounts of elements such as titanium and niobium (with Ti + Nb not exceeding 0.04%) whose function is to trap carbon and nitrogen under form of carbonitrides.
• Other chemical elements resulting from the production of metal may be present as impurities which do not radically modify the properties of sheets obtained thanks to the compositions which have just been described.
• Ultra-low contents in carbon and nitrogen are preferred because these elements will be in solid solution during the deformation, taking into account the method of manufacturing sheets according to the invention; their presence can create dynamic aging problems during deformation, and therefore increase the rolling forces to be applied in the ferritic field.
• the casting is carried out directly at from liquid metal with a thin strip of 1.5 to 10 mm thick, usually 1.5 to 4 mm thick.
• the casting of this strip between two cylinders, as we said, is well suited to this process and to the thicknesses most commonly cast, and it is this nonlimiting example which will be considered in the following description.
• the solidified strip leaving the casting space delimited by the cylinders then optimally crosses an area in which measures are taken to avoid or at least strongly limit the formation of scale on its surface, such as an enclosure inerted by a non-oxidizing atmosphere, ie a neutral (nitrogen, argon) or reducing atmosphere (atmosphere containing hydrogen), in which the oxygen content is lowered as much as possible.
• a non-oxidizing atmosphere ie a neutral (nitrogen, argon) or reducing atmosphere (atmosphere containing hydrogen
• Such a device can also be installed at the outlet of an inerting zone to remove the small amount of scale which may have formed there.
• the strip undergoes a first in-line hot rolling. It is in particular because of this rolling that the presence of scale on the surface of the strip must optimally be avoided, since the presence of scale imposes greater rolling forces than in its absence. In addition, the scale can become embedded in the surface of the strip during rolling, and a poor surface finish of the final product is thus obtained, which can make this final product unsuitable for the most demanding uses from this point of view. .
• This first rolling takes place in the temperature range between 950 ° C and the temperature Ar 3 of the cast grade, that is to say in the lower region of the austenitic range. Its role is multiple.
• the strip After this first hot rolling in the austenitic phase, the strip to cool and pass into the ferritic area, where it will undergo a second rolling hot.
• This cooling can take place naturally, by simple radiation tape in the open air, or can be obtained by forced projection of air or water on the surface of the strip, which shortens the path traveled by the strip between the two rolling stages. Forced cooling can take place, at the option of the operator, before, during, or after the ferritic transformation of the strip, or with several of these stages. The exact methods of forced cooling depend on the parameters casting operations, such as the thickness of the strip, its running speed, the distance between the two rolling mills, etc.
• the bottom line is that by the time the tape undergoes its second hot rolling, it is in the ferritic area at a temperature below 850 ° C, preferably below 750 ° C to have a work hardened structure and avoid recrystallization.
• This second hot rolling takes place with a reduction rate of at least 50%, from preferably at least 70%, obtained by passing the strip through a single cage or in several successive cages. Its objective is to develop the textures of the product which will then be favorable to the drawing properties. Deformation rates high will favor the development of ⁇ 111 ⁇ crystal orientation in the future recrystallization. This lamination must be carried out in the presence of a lubricant, in order to to homogenize the textures in the thickness of the sheet avoiding the development of shear textures at a quarter of the strip thickness. It also reduces the forces to be exerted on the strip during the ferritic deformation.
• first and the second rolling hot inerting and / or descaling means of the strip similar to those previously described, in order to prevent the second rolling from taking place on a strip slightly burned. Because of the high reduction rates applied during the second hot rolling, avoid scale encrustation at this stage if you want to obtain excellent surface condition of the strip.
• the strip in the ferritic state After the second rolling, the strip in the ferritic state must be recrystallized. For this purpose, it can be wound at high temperature, between 700 and 800 ° C (typically 750 ° C), so that its recrystallization is complete over its entire thickness and that one is assured of obtaining an optimal texture. If after the second rolling the strip temperature is lower than 700 ° C, the strip must be reheated to bring it back to the desired temperature range. This reheating will, in most cases, of the order of a hundred degrees and can be obtained by passing the strip through an induction furnace.
• the advantage of an induction oven compared to an oven equipped, for example, with gas burners, is that it makes it possible to obtain rapid heating of the product, and above all uniform over the entire thickness of the band.
• recrystallization can then take place at least in large part during this reheating.
• the reheating rates of the strip which can usually be obtained by induction furnaces with the usual configuration and power (from 0.5 to 1.5 MW / mm 2 of strip) make it possible to reheat approximately 100 ° C of a 0.75 mm thick strip in an oven with a length of about 2 m.
• the installation of such an oven between the second rolling installation and the winding installation is therefore entirely possible on a conventional thin strip casting installation without excessively lengthening it.
• the hot sheets obtained by the process according to the invention have a thickness less than or equal to 2 mm, preferably less than or equal to 1 mm, depending on the thickness of the initial strip and the rolling rates applied to it. According to intended uses, it is possible to use them directly, especially if their thickness is particularly weak, for example less than 0.7 mm (while hot sheets obtained by traditional processes are too thick for direct use), or then subject them to the usual "cold" treatment operations: cold, annealed (continuous or base annealed), skin-pass, especially if you want to obtain end of very thin sheets. To these operations can be added surface treatments usual (descaling, pickling ...) which accompany them in the classic processes of manufacture of sheet metal for stamping.
• the speed of travel of the strips leaving the second rolling mill at hot is generally less than 250 m / min, it is compatible with an execution in line of at least the first of said “cold” transformation operations.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Thermal Sciences (AREA)
• Physics & Mathematics (AREA)
• Crystallography & Structural Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Metal Rolling (AREA)
• Heat Treatment Of Steel (AREA)
• Compositions Of Oxide Ceramics (AREA)
• Continuous Casting (AREA)
• Coating With Molten Metal (AREA)

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• 1999
  • 1999-06-17 FR FR9907660A patent/FR2795005B1/fr not_active Expired - Fee Related
• 2000
  • 2000-05-19 AT AT00401369T patent/ATE281535T1/de not_active IP Right Cessation
  • 2000-05-19 EP EP00401369A patent/EP1061139B1/fr not_active Expired - Lifetime
  • 2000-05-19 DE DE60015434T patent/DE60015434T2/de not_active Expired - Lifetime
  • 2000-05-19 ES ES00401369T patent/ES2231136T3/es not_active Expired - Lifetime
  • 2000-05-24 AU AU36388/00A patent/AU760095B2/en not_active Ceased
  • 2000-06-06 CA CA002311172A patent/CA2311172C/fr not_active Expired - Fee Related
  • 2000-06-19 US US09/597,407 patent/US6290787B1/en not_active Expired - Lifetime
  • 2000-06-19 BR BR0002687-5A patent/BR0002687A/pt not_active IP Right Cessation
  • 2000-06-19 JP JP2000183320A patent/JP4763880B2/ja not_active Expired - Fee Related

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