Method and furnace for thermally treating a high-resistance steel strip comprising a temperature homogenisation chamber

Abstract

Method for thermally treating a scrolling steel strip ( 5 ), said method comprising the following steps: heating the strip ( 5 ) in a zone for heating with a direct flame ( 10 ); temperature homogenisation of the strip ( 5 ) in a homogenisation chamber ( 20 ) comprising at least one radiant heating tube (25), so as to homogenise the strip ( 5 ) in temperature after the passing thereof into the zone for heating with a direct flame ( 10 ) of the preceding step; oxidation of the strip ( 5 ) in an oxidation chamber ( 30 ) with an oxidising atmosphere having an oxygen volume concentration greater than 1 %; reduction of the strip ( 5 ) in a reduction zone ( 40 ).

1 . A method for thermally treating a scrolling high-resistance steel strip, said method comprising the following steps:
 a) heating the strip in a zone for heating with a direct flame;   b) temperature homogenisation of the strip in a homogenisation chamber comprising at least one radiant heating tube, so as to homogenise the strip in temperature after the passing thereof into the zone for heating with a direct flame of the preceding step;   c) oxidation of the strip in an oxidation chamber with an oxidising atmosphere having an oxygen volume concentration greater than 1%;   d) reduction of the strip in a reduction zone.   
     
     
         2 . The method according to  claim 1 , wherein the reduction zone has a reducing atmosphere having a hydrogen volume concentration greater than 3%. 
     
     
         3 . The method according to  claim 1 , wherein the oxidation step is carried out at a strip temperature of between 650° C. and 750° C. 
     
     
         4 . The method according to  claim 1 , wherein said oxygen volume concentration is between 1.5% and 5%, preferably between 2% and 5%. 
     
     
         5 . The method according to  claim 1 , wherein the temperature homogenisation step is carried out at a strip temperature of between 650° C. and 750° C. 
     
     
         6 . The method according to  claim 1 , wherein the heating step a) is carried out so as to obtain a strip temperature of between 650° C. and 750° C. 
     
     
         7 . The method according to  claim 1 , wherein the temperature homogenisation step is carried out with an atmosphere having an oxygen volume concentration less than 0.01% by volume, preferably with an atmosphere without oxygen. 
     
     
         8 . The method according to  claim 1 , wherein the heating step a) is carried out with an atmosphere having an oxygen volume concentration less than 0.01% by volume, preferably with an atmosphere without oxygen. 
     
     
         9 . The method according to  claim 1 , wherein the temperature homogenisation step is carried out by the scrolling of the strip in the proximity of said at least one radiant heating tube. 
     
     
         10 . The method according to  claim 1 , wherein said homogenisation section comprises two radiant heating tubes and in that the strip scrolls between said two radiant heating tubes. 
     
     
         11 . A furnace for the thermal treatment of a high-resistance steel strip by scrolling, comprising:
 a direct heating furnace section comprising:
 a zone for heating with a direct flame; 
   a radiant heating furnace section comprising:
 an oxidation chamber; 
 a reduction zone; 
   wherein the radiant heating furnace section further comprises a temperature homogenisation chamber positioned between said zone for heating with a direct flame and said oxidation chamber, said homogenisation chamber comprising at least one radiant heating tube.   
     
     
         12 . The furnace according to  claim 11 , wherein said homogenisation chamber comprises at least two radiant heating tubes and in a more preferred manner, at least three radiant heating tubes. 
     
     
         13 . The furnace according to  claim 12 , wherein that it is configured such that in the homogenisation chamber, the high-resistance steel strip is capable of being positioned scrolling between at least two radiant heating tubes. 
     
     
         14 . The furnace according to  claim 11 , wherein the oxidation chamber is isolated from the homogenisation chamber and from the reduction zone by two confinement means making it possible for the scrolling of the strip through said oxidation chamber. 
     
     
         15 . The furnace according to  claim 14 , wherein the two confinement means are two airlocks.