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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
• • 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
  • B22D11/002—Stainless steels
• • 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
  • B22D11/0622—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels
• • 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
  • B22D11/0637—Accessories therefor
  • B22D11/0648—Casting surfaces
  • B22D11/0651—Casting wheels
• • 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
  • B22D11/0637—Accessories therefor
  • B22D11/0697—Accessories therefor for casting in a protected atmosphere
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/003—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting by using inert gases
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
• • 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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten

Definitions

• the invention relates to the continuous casting of metals, and more precisely the casting continuous, directly from liquid metal, of stainless steel strips of the type ferritic whose thickness is of the order of a few mm, by the process known as "casting between cylinders ".
• the process mainly used today is pouring said liquid metal between two internally cooled cylinders, rotating around their horizontal axes in opposite directions, and arranged opposite one another, the minimum distance between their surfaces being substantially equal to the thickness that is desired impart to the cast strip (for example a few mm).
• the casting space containing liquid steel is defined by the lateral surfaces of the cylinders, on which the solidification of the strip, and by side refractory closing plates applied against the ends of the cylinders.
• the liquid metal initiates its solidification on contact with external surfaces of the cylinders, on which it forms solidified "skins", of which ensures that they meet at the "neck", that is to say the area where the distance between cylinders is minimum.
• microcracks are cracks of small dimensions which are nevertheless sufficient to make them unfit for use cold processed products produced therefrom. They form during solidification steel and have a depth of about 40 ⁇ m and an opening of about 20 ⁇ m. Their appearance is linked to the conditions of contact, during solidification, between the steel and the surface of the cylinders along the length of their contact arc. These conditions can be described as comprising two successive stages. The first step concerns contact initial between the liquid steel and the surface of the cylinder, which leads to the formation of a skin solid steel on the surface of the cylinders.
• the second step concerns the growth of this skin up to the neck, where as we said, it joins the skin formed on the other cylinder to constitute the fully solidified strip.
• Contact between steel and cylinder surface is conditioned by the topography of the surface of the casting cylinders, combined with the nature of the inerting gas and the chemical composition of the steel. All these parameters involved in establishing heat transfers between the steel and the cylinder and govern the conditions of solidification of the skins.
• document EP-A-0 796 685 teaches to cast a steel whose Cr eq / Ni eq ratio is greater than 1.55 so as to minimize the phase changes at high temperature, and to carry out this casting by using cylinders the surface of which comprises contiguous dimples of diameter 100-1500 ⁇ m and depth 20-150 ⁇ m and by inerting the casting space with a gas soluble in steel, or a mixture of gases mainly composed of such a soluble gas.
• document JP-A-5337612 proposes cast a steel with low carbon contents (less than 0.05%) and nitrogen (less than 0.05%) and containing niobium (0.1 to 5%) and titanium. It is also necessary to cool the output strip cylinders at high speed, and then control the winding temperature of the bandaged. These preparation and pouring conditions are costly and restrictive, and the particular characteristics of the nuances required limit the fields of use of products thus obtained.
• the object of the invention is to propose a method for casting thin strips in ferritic stainless steel, the surface of which would be free of microcracks. This process does not would not require particularly restrictive casting conditions for its implementation work, and could be applied to a wide range of grades of such steels.
• the invention consists in combining conditions on the composition of the metal, governing the possibilities of high austenite formation temperature after metal solidification, a condition on roughness minimum pour surfaces and a condition on the composition of the inerting gas. In respecting this combination, we manage to avoid the formation of micro-cracks on the surface of the band without having to impose too restrictive limitations on the process without overly restricting the areas of use of the products which will be made from cast strips.
• This phase transformation causes local contractions of the metal, resulting from the density differences between these two phases which are sensitive to the level microscopic. These contractions can be significant enough to cause local loss of contact between the solidified skin and the surface of the cylinder. As we understands, these losses of contact radically modify the local conditions of transfers thermal. In conjunction with the surface condition of the cylinders and the nature of the inerting gas present in the depressions of said surface, the magnitude of this phase transformation, linked to the composition of the metal, therefore influences the intensity of heat transfers.
• ⁇ p The extent of the phase transformation ⁇ ⁇ ⁇ in ferritic stainless steels can be described by the index ⁇ p .
• ⁇ p constituted a good indicator of the level of the heat flux extracted by the casting rolls during solidification, all other things being equal.
• the heat flux extracted from the metal by the cylinders can be quantified experimentally by an average value, calculated from a measurement of the heating of the coolant of the cylinders.
• the average heat flux extracted from the metal by the cylinders is lower the higher the index ⁇ p .
• the inerting gas surrounding the surface of the liquid metal in the vicinity of the meniscus contains a gas soluble in l steel, or is entirely constituted by such a gas.
• Nitrogen is conventionally used for this purpose, but the use of hydrogen, ammonia or CO 2 would also be possible.
• insoluble gas ensuring the possible complement to 100% of the inerting atmosphere argon is conventionally used, but the use of another insoluble gas, such as helium, would also be possible.
• This last parameter is represented by the average roughness Ra, defined according to standard ISO 4287-1997 by the arithmetic mean of the deviations of the roughness profile on the average line within the measurement run 1 m .
• the mean line is defined as the line, produced by filtering, which cuts the palpated profile so that the surfaces which are greater than it are equal to those which are less than it.
• the microcracks are absent when the nitrogen content of the inerting gas (which is a nitrogen-argon mixture) is at least 60%. All these steels have a ⁇ p index of 45.7 to 53.4%, and were cast with cylinders having an Ra of 7 or 11 ⁇ m.
• the experiment carried out on steel C shows that, even with a Ra of 8.5 ⁇ m and an inert gas rich in nitrogen, microcracks are systematically obtained when a steel is cast with a low ⁇ p index. (29.5%).
• the flow must first thermal extract during the first contact between the metal and the cylinder is high. If the gas is not sufficiently soluble in steel, the average heat flux extracted is too weak, the steel does not solidify fairly uniformly and this favors the appearance of micro cracks. From this point of view, it would a priori also be desirable to have a low cylinder roughness. But if the roughness Ra is too low, the number and the area total of the solidification initiation sites becomes very high, which leads to a Too brutal cooling which causes the appearance of micro cracks. In addition, it is also necessary take into account the conditions required by the following stages of the solidification process and cooling the skins. Experience shows that by combining a gas content soluble at least 60% in the inerting gas and a roughness of the cylinders Ra greater at 5 ⁇ m, satisfactory results are obtained.
• the minimum roughness Ra of 5 ⁇ m is justified in that the roughness peaks serve as sites for initiation and development of solidification, and the parties hollow, in which the metal penetrates without necessarily going to the bottom of the hollow, act as contraction joints, absorbing changes in skin volume during its solidification and cooling. It is, however, not advisable to have a roughness Ra greater than 20 ⁇ m, because otherwise the roughness which is printed "in negative "on the tape surface is high, and will be difficult to reduce during the steps subsequent cold rolling and processing. We would therefore risk ending up with a final product whose surface appearance would not be satisfactory.
• the roughness of the cylinders sought can be obtained by any known means for this purpose, such as shot blasting, laser machining, photoengraving, EDM, etc.
• a high value of the index ⁇ p imposed by the composition of the metal amplifies the transformation ⁇ ⁇ ⁇ over the entire contact arc.
• the solidified skins are therefore subjected, on said contact arc, to detachments which moderate the extracted heat flux and maintain it at a suitable level, without however leading to microcracks which would be due to the fragility of the skin, when this- this is already sufficiently solidified.
• the lower limit to set for the index ⁇ p is 35%. Beyond a ⁇ p index of 60%, the detachments caused by the transformation ⁇ ⁇ ⁇ become too large, and lead to the appearance of microcracks by excessive embrittlement of the skins.
• the invention therefore achieves a compromise between requirements sometimes contradictory, dictated by the need to avoid the presence on the casting tape of surface micro-cracks, with multiple formation mechanisms. She permits to dispense with the compulsory presence of expensive alloying elements (elements stabilizers such as aluminum, titanium, zirconium, niobium may be present optionally). Similarly, it does not require cooling conditions and particular winding of the strip after it has left the cylinders.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Continuous Casting (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
• Moulds For Moulding Plastics Or The Like (AREA)
• Electroplating Methods And Accessories (AREA)
• Coating With Molten Metal (AREA)
• Heat Treatment Of Steel (AREA)

Priority Applications (1)

Applications Claiming Priority (3)

Publications (2)

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• 1999
  • 1999-04-22 FR FR9905053A patent/FR2792561B1/fr not_active Expired - Fee Related
• 2000
  • 2000-03-20 US US09/959,118 patent/US6622779B1/en not_active Expired - Lifetime
  • 2000-03-29 BR BR0009881-7A patent/BR0009881A/pt not_active IP Right Cessation
  • 2000-03-29 SI SI200030034T patent/SI1187691T1/xx unknown
  • 2000-03-29 RU RU2001131422/02A patent/RU2242325C2/ru not_active IP Right Cessation
  • 2000-03-29 AT AT00915238T patent/ATE228905T1/de active
  • 2000-03-29 ES ES00915238T patent/ES2187456T3/es not_active Expired - Lifetime
  • 2000-03-29 WO PCT/FR2000/000781 patent/WO2000064613A1/fr not_active Application Discontinuation
  • 2000-03-29 TR TR2001/03013T patent/TR200103013T2/xx unknown
  • 2000-03-29 AU AU36619/00A patent/AU757307B2/en not_active Ceased
  • 2000-03-29 DE DE60000938T patent/DE60000938T2/de not_active Expired - Lifetime
  • 2000-03-29 EP EP00915238A patent/EP1187691B1/fr not_active Expired - Lifetime
  • 2000-03-29 CN CNB00806542XA patent/CN1210121C/zh not_active Expired - Lifetime
  • 2000-03-29 PT PT00915238T patent/PT1187691E/pt unknown
  • 2000-03-29 PL PL351310A patent/PL193187B1/pl not_active IP Right Cessation
  • 2000-03-29 DK DK00915238T patent/DK1187691T3/da active
  • 2000-03-29 KR KR1020017013391A patent/KR100647147B1/ko active IP Right Grant
  • 2000-03-29 SK SK1461-2001A patent/SK285817B6/sk not_active IP Right Cessation
  • 2000-03-29 JP JP2000613595A patent/JP4582916B2/ja not_active Expired - Fee Related
  • 2000-03-29 CZ CZ20013777A patent/CZ295816B6/cs not_active IP Right Cessation
  • 2000-04-13 TW TW089106845A patent/TW520306B/zh not_active IP Right Cessation
• 2001
  • 2001-10-22 ZA ZA200108667A patent/ZA200108667B/xx unknown

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