Novel additive comprising lead and/or a lead alloy intended to treat baths of liquid steel

Abstract

The present invention relates to an additive in the form of flux-cored wire for treating baths of liquid steel with a view to obtaining steels having a high lead content. The additive comprising metallic lead and/or one or more lead alloys according to the invention for treating baths of liquid steel, and is in the form of flex-cored wire composed of a metal sheath and a finely divided filling material, the latter being composed of a powder of metallic lead and/or of lead alloy and of a powder containing a material capable of releasing a gas, which is inert with respect to the liquid steel, at the temperature of the liquid steel bath. Characteristically, the powder of metallic lead and/or of lead alloy includes a particle size fraction G R between 200 μm and 500 μm and the particle size fraction G R has the following characteristics: —through a 200 μm sieve: G R <5%; —through a 300 & μm sieve: 90% 3 G R 3 10%; —through a 400 μm sieve: 40% £ G R <100%; —through a 500 μm sieve: 100% 3 G R 3 90%.

1 . Additive comprising metallic lead and/or one or more lead alloys, for treating baths of liquid steel, said additive being in the form of flux-cored wire composed of a metal sheath and a finely-divided filling material, the latter being formed of a metallic lead powder and/or lead alloy powder and of a powder containing a material able to release a gas, which is inert with respect to the liquid steel, at the temperature of the bath of liquid steel, said additive being characterised in that said metallic lead powder and/or lead alloy powder consists of a particle size fraction G R  between 200 μm and 500 μm, and in that said particle size fraction G R  has the following characteristics:
 through a 200 μm sieve: G R ≦5%;   through a 300 μm sieve: 90%≧G R ≧10%;   through a 400 μm sieve: 40%≦G R ≦100%;   through a 500 μm sieve: 100%≧G R ≧90%.   
   
   
       2 . Additive according to  claim 1 , wherein the metal sheath is made of unalloyed mild steel. 
   
   
       3 . Additive according to  claim 1 , wherein the metal sheath is from 0.1 to 1 mm thick, preferably from 0.2 to 0.5 mm thick. 
   
   
       4 . Additive according to  claim 1 , wherein the flux-cored wire has a diameter from 5 to 20 mm, preferably from 9 to 15 mm. 
   
   
       5 . Additive according to  claim 1 , wherein the filling material has a particle size which does not exceed 1 mm. 
   
   
       6 . Additive according to  claim 1 , wherein the flux-cored wire contains from 100 to 1000 g of lead per metre. 
   
   
       7 . Additive according to  claim 1 , wherein the material able to release a gas, which is inert with respect to the liquid steel, is a mineral compound formed of limestone (calcium carbonate) or non-calcined dolomite, the gas released thus being carbon dioxide. 
   
   
       8 . Additive according to  claim 7 , wherein the mineral material is present in an amount of 3 to 30% by weight based on the weight of lead or lead alloy (or alloys) used. 
   
   
       9 . Method for treating baths of liquid steel using an additive comprising metallic lead and/or one or more lead alloys, the method comprising a step of adding to said bath an additive in the form of a flux-cored wire composed of a metal sheath and a finely-divided filling material, the latter being formed of a metallic lead powder and/or lead alloy powder and of a powder of a material able to release a gas, which is inert with respect to the liquid steel, at the temperature of the bath of liquid steel, said metallic lead powder and/or lead alloy powder consisting of a particle size fraction G R  between 200 μm and 500 μm and having the following characteristics:
 through a 200 μm sieve: G R ≦5%;   through a 300 μm sieve: 90%≧G R ≧10%;   through a 400 μm sieve: 40%≦G R ≦100%;   through a 500 μm sieve: 100%≧G R ≧90%.   
   
   
       10 . Method according to  claim 9 , wherein 0.1 to 10 kg of flux-cored wire is added per tonne of liquid steel to be treated. 
   
   
       11 . Method according to  claim 10 , wherein the flux-cored wire is added to the bath of liquid steel at a speed of 50 to 200 m/min, preferably of 100 to 150 m/min. 
   
   
       12 . (canceled) 
   
   
       13 . Rolled steel product having a high lead content and containing lead nodules smaller than 100 μm, obtained by the method according to  claim 1 , characterised in that, when the distribution of the nodules is defined corresponding to the following formula: 
     
       
         
           
             
               I 
               R 
             
             = 
             
               
                 ( 
                 
                   100 
                   / 
                   D 
                 
                 ) 
               
               ⋆ 
               
                 ( 
                 
                   
                     ∑ 
                     
                       i 
                       = 
                       1 
                     
                     NI 
                   
                    
                   
                     
                       ( 
                       
                         d 
                         i 
                       
                       ) 
                     
                     / 
                     NI 
                   
                 
                 ) 
               
             
           
         
       
     
     where:
 I R : distribution index 
 D: diagonal of the analysis zone 
 D i : minimum distance between the closest lead nodules 
 NI: number of lead nodules with an associated minimum distance, 
 
     I R  is greater than 1.4%. 
   
   
       14 . Additive according to  claim 2 , wherein the metal sheath is from 0.1 to 1 mm thick, preferably from 0.2 to 0.5 mm thick.