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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
• • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
  • C21D9/54—Furnaces for treating strips or wire
  • C21D9/56—Continuous furnaces for strip or wire
  • C21D9/561—Continuous furnaces for strip or wire with a controlled atmosphere or vacuum
• • 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
  • C23C2/0222—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating in a reactive atmosphere, e.g. oxidising or reducing atmosphere
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
  • C21D1/76—Adjusting the composition of the atmosphere

Definitions

• the present invention relates to dip galvanizing steel strips with improved mechanical properties in vertical ovens. It more specifically targets a process for performing chemical treatments of the strip, simultaneously or not with the heat treatment of the annealing, such as oxidation-reduction, etc., in atmospheres different from those of the usual sections from the oven.
• the tape circulates in an atmosphere reducing from the inlet to the outlet of the oven or, if there is an open preheating zone, from the outlet of it at the outlet of the oven.
• the reducing atmosphere is therefore kept in the oven at the latest from the exit from preheating is traditionally at a strip temperature from 650 to 700 ° C.
• the purpose of this process is purpose of limiting the formation of oxides, mainly of iron, to the surface of the strip and to reduce them if any exists or if it has formed in the preheater in order to allow good attachment of zinc to the surface of the strip to obtain a good quality galvanized product.
• the stay of the strip under this reducing atmosphere must be done in sufficient conditions (temperature, residence time, dew point of the furnace atmosphere) to allow cleaning of the tape compatible with good quality of subsequent coating, in particular zinc adhesion.
• the invention proposes to solve the technical problem exposed above by providing a process which makes it possible to hot-dip galvanizing of very different grades of steel loaded with hardening elements in furnaces traditional construction.
• this invention relates to a method of continuous metal strip thermochemical treatment, of the oxidation-reduction type according to which the strip moves at the through an oven, in a protective atmosphere, characterized in that the strip passes through at least a partial or total isolation device, positioned at within at least one section of the oven, or between two sections, the strip being heated in this device isolation, in dew point atmospheres suitable for each strip, depending on the specific composition of steel and applied thermal cycle.
• the process which is the subject of the invention mainly consists of allowing the strip to be heated in different dew point atmospheres depending on temperature ranges different from those known in the state of the art, and in particular at points of dew above the usual values, thanks to isolation devices.
• Oxygen goes then oxidize the atoms of Si, ... inside the metal. he then there will no longer be enough Si, ... available to migrate towards the surface and feed the surface oxidation, especially since the kinetics of oxygen diffusion through the joints is faster than the diffusion of atoms oxidizable in metal. Furthermore, this oxidation internal will block the diffusion of these atoms towards the surface, which further limits the amount of these oxides trained.
• the implementation of the method according to the invention consists in allow to precisely control the dew point of this atmosphere in the heating chamber so that this atmosphere is oxidizing for the targeted elements but remains reductive for iron, which should not be oxidize.
• the downstream section of the oven - the end of maintenance and the cooling - will remain reducing, to reduce iron oxides which may have been possibly formed in the high dew point section, which will not reverse the internal oxidation process of metallic additives steel, because the oxides formed from these additives are more stable than iron oxides.
• the dew point of the atmosphere can be modified according to the thermal cycle, i.e. the oven section temperature and the stay of the band in the latter, to integrate the variations in strip thickness.
• the process which is the subject of the invention therefore proposes to be able to confine a controlled atmosphere whose dew point is higher than that used in ovens according to the state art in order to be less reductive, this in a section of the high temperature oven of a line of conventional galvanization.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Coating With Molten Metal (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Furnace Details (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8866629

Family Applications (1)

Country Status (7)

Cited By (8)

Families Citing this family (11)

Citations (5)

Family Cites Families (1)

• 2001
  • 2001-08-21 FR FR0110957A patent/FR2828888B1/fr not_active Expired - Lifetime
• 2002
  • 2002-08-09 DE DE1285972T patent/DE1285972T1/de active Pending
  • 2002-08-09 ES ES02292018T patent/ES2188434T1/es active Pending
  • 2002-08-09 EP EP02292018A patent/EP1285972A1/de not_active Withdrawn
  • 2002-08-13 US US10/216,794 patent/US6913658B2/en not_active Expired - Lifetime
  • 2002-08-21 JP JP2002240292A patent/JP2003183799A/ja active Pending
  • 2002-08-21 BR BR0203383-6A patent/BR0203383A/pt not_active Application Discontinuation

Patent Citations (5)

Non-Patent Citations (1)

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