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
  • C21D8/0421—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
• • 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
  • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B2201/00—Special rolling modes
  • B21B2201/04—Ferritic 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
  • C21D8/0421—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
  • C21D8/0421—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
  • C21D8/0431—Warm rolling

Definitions

• the invention relates to the steel industry. More specifically, it relates to manufacturing steel strips intended to be transformed into thin packaging, such as canned food and drink boxes.
• the thicknesses of the final strips after cold rolling and annealing are of the order of 0.09 to 0.40 mm. These strips are then cut into sheets and / or blanks, which are stamped to form the desired packaging.
• the strip thus cast then undergoes pickling, a first cold rolling, a recrystallization annealing and a second cold rolling.
• the total reduction rate undergone by the strip during cold rolling is between 85 and 95% if we want to obtain satisfactory results on the rate of the drawing horns, the anisotropy coefficient r and the planar anisotropy ⁇ r.
• the casting between rolls can be followed by a light hot rolling with a reduction rate of 20 to 50%, or even more.
• the manufacture of the hot strip which must then undergo cold rolling and the associated treatments is thus faster and more economical.
• the need for subsequent cold rolling in two stages separated by annealing tempers these advantages.
• Document JP 07118735 discloses the production of a steel strip by casting a thin strip no more than 10 mm thick followed by hot rolling in the austenitic region and forced cooling. The strip is then maintained at a temperature between Ar 1 at 600 ° C for at least 10 s and then wound.
• the object of the invention is to propose a more economical process than known processes for obtaining cold rolled steel strips usable for the manufacture of packaging, in particular for food packaging such as drink cans.
• the invention also relates to the use of a steel strip obtained according to this process for the manufacture of packaging.
• the invention is based on the use of a method of casting between rolls followed by at least one in-line hot rolling step and a particular cooling of the strip.
• a hot strip is thus obtained which tolerates not then undergo only one cold rolling step (apart from the conventional final passage to the skin-pass) to be given the properties that make it suitable for manufacturing steels for packaging.
• the process according to the invention begins with casting in the form of strips thin 0.7 to 10 mm thick (preferably 1 to 4 mm) of a semi-finished product low or ultra-low carbon content of a steel that can be used for the packaging of classic composition.
• This composition for the main elements present, meets the main criteria (the percentages are expressed in weight percentages): 0% ⁇ C ⁇ 0.15%; 0% ⁇ Mn ⁇ 0.6%; 0% ⁇ P ⁇ 0.025%; ⁇ 0% ⁇ S ⁇ 0.05%; 0% ⁇ Al ⁇ 0.12%; 0% ⁇ N ⁇ 0.04%.
• This steel also contains the usual impurities resulting from the development, and possibly of elements of alloy in small quantity which will not affect not adversely affect the properties of the products during their shaping or use as steels for packaging (it is thus known, in certain steels for packaging, introduce a few thousandths of% boron), the rest being iron.
• the alloying elements generally absent, may possibly be present in contents of up to 1%; These elements are notably Si, Cr, Ni, Mo, Cu.
• certain alloying elements must be excluded when the steel is intended for packaging; these elements are for example lead, cadmium and arsenic.
• the continuous casting of thin strips directly from liquid metal is a technique which has been tested for several years for the casting of carbon steels, stainless steels and other ferrous alloys.
• the most commonly used technique casting thin strips of ferrous alloys which is reaching the stage industrial, is the technique called "casting between cylinders", according to which we introduce liquid metal between two close cylinders with horizontal axes, rotated in direction reverse and internally cooled.
• the pouring space is closed laterally by refractory plates applied against the flat side faces of the cylinders.
• one of the advantages of casting between cylinders is the possibility of obtaining, if necessary, thickness profiles of the extremely flat crosswise band, thanks to the excellent control of the convex cylinders that allow the most advanced methods of practicing this process (see, for example, document EP 0 736 350).
• the strip preferably crosses an area such as an enclosure inerted by gas blowing, where it is subjected to a non-oxidizing environment (a neutral atmosphere of nitrogen or argon, or even a atmosphere containing a certain proportion of hydrogen to make it reductive), in order to avoid or limit the formation of scale on its surface.
• a non-oxidizing environment a neutral atmosphere of nitrogen or argon, or even a atmosphere containing a certain proportion of hydrogen to make it reductive
• a device for descaling the strip by spraying shot or solid CO 2 onto its surface or by brushing, in order to eliminate the scale which could have formed despite the precautions taken.
• This single stage of hot rolling can be carried out by means of the passage strip in a single rolling stand. It can also be done more progressive by passing the strip through two or more rolling stands.
• the first one cage can, for example, apply to the tape a reduction rate only sufficient to close the porosities, and the second cage then ensures most of the reduction thick to fulfill the other two functions of hot rolling.
• the bottom line is that the overall reduction rate caused by this or these passages in the or the successive cages and the temperature of the strip after it has passed through the last cage are within the prescribed ranges of values.
• hot rolling takes place in two stages, separated by reheating, and optionally by descaling.
• the first of these steps is carried out either in the austenitic domain, or in the ferritic domain of the cast strip, with a reduction rate of 20 to 70%. It has functions identical to those of the single hot rolling step of the first variant, and can also be carried out by passing the strip through one or more successive rolling mill stands.
• this first rolling step takes place in the ferritic area when it is desired to obtain a final thickness of the strip that is small, because less effort is required to deform the strip evenly over its entire width than when the strip is in the austenitic domain.
• this first hot rolling step is carried out by distributing it over several cages, it is however possible to begin this first step in the austenitic field, for example by a relatively light rolling which would mainly aim at closing the porosities, and finish in the ferritic area where the rest of the thickness reduction would be carried out.
• the strip is allowed to cool down to the ferritic region if it is not already there (if necessary using a slight forced cooling), then a treatment is applied to it. thermal reheating which brings it back into the austenitic domain, therefore above the temperature Ar 3 . This causes an additional phase change in the strip, which results in an even further refinement of the grains of the metallurgical structure.
• the second stage of hot rolling in the austenitic field, is carried out with a reduction rate of 10 to 30%.
• This second hot rolling has the essential function of correcting the geometric defects (poor flatness, saber ...) that the first hot rolling could have caused.
• Intermediate heating can be achieved by means of an inductor through which the strip passes. For a strip 0.75 mm thick and 850 mm wide running at a speed of 200 m / min, a power of 1.04 MW is necessary if a temperature rise of 100 ° C is sought.
• the two variants which have just been described therefore have the common point of ending with a rolling carried out on the strip in the austenitic phase, which therefore ends above the temperature Ar 3 .
• the method according to the invention continues with cooling of the strip which includes a forced cooling step at a speed of 80 to 400 ° C / s, preferably 100 to 300 ° C / s.
• This cooling ends in the ferritic field of cast steel, and in general brings the strip to a temperature close to its winding temperature. Its purpose is to avoid excessive growth in the size of the grains before winding and during the stay of the strip in the form of a reel.
• This winding temperature is typically less than 750 ° C.
• the winding temperature can be chosen around 550 ° C or 600 ° C or 700 ° C in order to more or less favor the precipitation of aluminum nitrides.
• This forced cooling can start immediately after the austenitic rolling of the strip, but it is advisable to start it only after having allowed the strip to cool at low speed (about 10 ° C / s, which is accessible by a simple exposure in the open air) and pass into the ferritic domain, therefore below Ar 3 .
• low speed about 10 ° C / s, which is accessible by a simple exposure in the open air
• rapid cooling which would begin in the austenitic domain would substantially interfere with the homogeneity of the microstructure.
• the accelerated cooling should preferably not start at a temperature below Ar 3 - 10 ° C.
• the strip wound and then unwound then undergoes cold rolling at a rate of reduction of at least 85%, preferably more than 90%.
• This cold rolling can perfectly be executed by simple reduction, i.e. in a single step, and not imperatively in two stages with intermediate annealing as was the case in the document JP 09-001207 already cited (double reduction cold rolling).
• double reduction cold rolling We get stamping skills comparable to those obtained by known methods, and access to strip thicknesses smaller than 0.09 mm of known methods without however, it is necessary to resort to cold rolling with double reduction. If we don't want get thinner strips than usual, we can get the classic thicknesses with lower reduction rates during cold rolling, which is more economical. he is, of course, possible to carry out a cold rolling of the strip in double reduction if one wishes to obtain an even smaller thickness or mechanical characteristics higher.
• table 1 can be presented which gives examples of final thicknesses of the strip as a function of its initial thickness after casting and of the rolling rates applied during the hot rolling steps (in one or two steps depending on the chosen variant) and cold rolling. Thickness of the strips obtained as a function of the various casting parameters and rolling Thickness of the casting strip (mm) Rolling rate at hot (%) Strip thickness hot (mm) Rolling rate Cold (%) Final thickness of the strip (mm) 3 65 1.05 85 to 92 0.158 to 0.084 3 70 0.9 85 to 92 0.135 to 0.072 2 60 0.8 85 to 92 0.12 to 0.064 1.5 50 0.75 85 to 92 0.113 to 0.060
• the strip After cold rolling, the strip undergoes the usual annealing (basic or continuous) intended to give it its mechanical properties. This annealing can be followed, as usually by stripping, coating and / or passing the skin-pass.
• the exit speeds of the strip from the hot rolling mill being of the order of 250 m / min or less, these speeds are compatible with placing on a single line of this rolling mill (therefore the entire casting line) and one or more of the cold rolling, annealing and cold treatment of steels for packaging, whose metal flow is compatible with that of the hot rolling mill.
• the invention finds a preferred field of application in the manufacture of steel strips intended to be stamped to form packaging for beverages or canned food, it goes without saying that it can be applied to the manufacture of steel strips intended for other uses for which similar qualities would be required for tapes produced.

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

Applications Claiming Priority (3)

Publications (2)

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• 1999
  • 1999-09-24 FR FR9911925A patent/FR2798871B1/fr not_active Expired - Lifetime
• 2000
  • 2000-09-20 US US10/088,176 patent/US6852180B1/en not_active Expired - Lifetime
  • 2000-09-20 CN CN00813199.6A patent/CN1128889C/zh not_active Expired - Lifetime
  • 2000-09-20 JP JP2001525400A patent/JP4620310B2/ja not_active Expired - Lifetime
  • 2000-09-20 ES ES00964323T patent/ES2225221T3/es not_active Expired - Lifetime
  • 2000-09-20 EP EP00964323A patent/EP1228254B1/fr not_active Revoked
  • 2000-09-20 CA CA2385685A patent/CA2385685C/fr not_active Expired - Lifetime
  • 2000-09-20 DE DE60014145T patent/DE60014145T2/de not_active Expired - Lifetime
  • 2000-09-20 AT AT00964323T patent/ATE277202T1/de not_active IP Right Cessation
  • 2000-09-20 BR BR0014195-0A patent/BR0014195A/pt not_active IP Right Cessation
  • 2000-09-20 WO PCT/FR2000/002597 patent/WO2001021844A1/fr active IP Right Grant

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