Duplex stainless steel

Abstract

The invention relates to a duplex stainless steel composition, the composition of which consists of, in % by weight: C≦0.05% 21%≦Cr≦25% 1%≦Ni≦2.95% 0.16%≦N≦0.28% Mn≦2.0% Mo+W/2≦0.50% Mo≦0.45% W≦0.15% Si≦1.4% Al≦0.05% 0.11%≦Cu≦0.50% S≦0.010% P≦0.040% Co≦0.5% REM≦0.1% V≦0.5% Ti≦0.1% Nb≦ 0.3% Mg≦0.1% the balance being iron and impurities resulting from the smelting, and the microstructure consisting of austenite and 35 to 65% ferrite by volume, the composition furthermore satisfying the following relationships: 40≦I F ≦70 where I F =6×(% Cr+1.32×% Mo+1.27×% Si)−10×(% Ni+24×% C+16.15×% N+0.5×% Cu+0.4×% Mn)−6.17 and I LCR ≧30.5 where I LCR =% Cr+3.3×% Mo+16×% N+2.6×% Ni−0.7×% Mn, and also to a process for manufacturing plate, strip, coil, bar, rod, wire, sections, forgings and castings made of this steel.

1 . Duplex stainless steel, the composition of which consists of, in % by weight:
 C≦0.05%   21%≦Cr≦25%   1%≦Ni≦2.95%   0.16%≦N≦0.28%   Mn≦2.0%   Mo+W/2≦0.50%   Mo≦0.45%   W≦0.15%   Si≦1.4%   Al≦0.05%   0.11%≦Cu≦0.50%   S≦0.010%   P≦0.040%   Co≦0.5%   REM≦0.1%   V≦0.5%   Ti≦0.1%   Nb≦0.3%   Mg≦0.1%   the balance being iron and impurities resulting from the smelting, and the microstructure consisting of austenite and 35 to 65% ferrite by volume, said composition furthermore satisfying the following relationships:
   40≦I F ≦70 
   where   I F =6×(% Cr+1.32×% Mo+1.27×% Si)−10×(% Ni+24×% C+16.15×% N+0.5×% Cu+0.4×% Mn)−6.17   and
   I LCR ≧30.5 
   where   I LCR =% Cr+3.3×% Mo+16×% N+2.6×% Ni−0.7×% Mn.   
   
   
       2 . Steel according to  claim 1 , furthermore characterized in that:
   I LCR ≧32.   
   
   
       3 . Steel according to  claim 1  or  2 , furthermore characterized in that the proportion of ferrite is between 35 and 55% by volume. 
   
   
       4 . Steel according to any one of  claims 1  to  3 , furthermore character-ized in that:
   40≦I F ≦60.   
   
   
       5 . Steel according to any one of  claims 1  to  4 , furthermore character-ized in that the chromium content is between 22 and 24% by weight. 
   
   
       6 . Steel according to any one of  claims 1  to  5 , furthermore character-ized in that the manganese content is less than 1.5% by weight. 
   
   
       7 . Steel according to any one of  claims 1  to  6 , furthermore character-ized in that the calcium content is less than 0.03% by weight. 
   
   
       8 . Steel according to any one of  claims 1  to  7 , furthermore character-ized in that the molybdenum content is greater than 0.1% by weight. 
   
   
       9 . Process for manufacturing hot-rolled plate, strip or coil made of steel according to any one of  claims 1  to  8 , in which:
 an ingot or slab of a steel of composition according to any one of  claims 1  to  8  is provided; and   said ingot or slab is hot-rolled at a temperature between 1150 and 1280° C. in order to obtain plate, strip or coil.   
   
   
       10 . Process for manufacturing hot-rolled plate made of steel according to  claim 9 , in which:
 said ingot or slab is hot-rolled at a temperature between 1150 and 1280° C. in order to obtain what is called quarto plate,   a heat treatment is carried out at a temperature between 900 and 1100° C.; and   said plate is cooled by an air quench.   
   
   
       11 . Hot-rolled steel quarto plate, which can be obtained by the process as claimed in  claim 10  and having a thickness between 5 and 100 mm. 
   
   
       12 . Use of quarto plate according to  claim 11  or of hot-rolled coil obtained by the process according to  claim 9 , for the manufacture of structural components for material production or energy production installations. 
   
   
       13 . Use according to  claim 12 , in which said material and energy production installations operate between −100 and 300° C., prefer-ably between −50 and 300° C. 
   
   
       14 . Cold-rolled steel strip that can be obtained by cold-rolling a hot-rolled coil obtained by the process according to  claim 9 . 
   
   
       15 . Process for manufacturing hot-rolled bar or rod made of steel according to any one of  claims 1  to  8 , in which;
 a continuously cast ingot or bloom of steel of composition according to any one of  claims 1  to  8  is provided;   said ingot or bloom is hot-rolled from a temperature between 1150 and 1280° C. in order to obtain bar, which is air-cooled, or a coil of wire stock which is water-cooled;   
     and then, optionally:
 a heat treatment is carried out at a temperature between 900 and 1100° C.; and 
 said bar or coil of wire stock is quench-cooled. 
 
   
   
       16 . Hot-rolled bar that can be obtained by the process according to  claim 15  and having a diameter of 18 mm to 250 mm and hot-rolled rod that can be obtained by the process according to  claim 15  and having a diameter of 4 to 30 mm. 
   
   
       17 . Manufacturing process according to  claim 15 , in which a cold-drawing operation is carried out on said bar or a die-drawing opera-tion is carried out on said rod, after being cooled. 
   
   
       18 . Cold-drawn bar that can be obtained by the process according to  claim 17 , having a diameter of 4 mm to 60 mm, and die-drawn rod or wire that can be obtained by the process according to  claim 17 , having a diameter of 0.010 mm to 20 mm. 
   
   
       19 . Use of a bar according to  claim 16  or  18  for the manufacture of mechanical parts such as pumps, valve shafts, motor and engine shafts and couplings operating in corrosive media. 
   
   
       20 . Use of a rod or wire according to  claim 16  or  18  for the manufac-ture of cold-formed assemblies, for the agri-foodstuff industry, for oil and ore extraction, or for the manufacture of woven or knitted metal fabrics for the filtration of chemicals, ores or foodstuffs. 
   
   
       21 . Process for manufacturing a steel section, in which a cold-forming operation is carried out on a hot-rolled bar obtained by the process according to  claim 15 . 
   
   
       22 . Steel section that can be obtained by the process according to  claim 21 . 
   
   
       23 . Process for manufacturing a steel forging, in which a hot-rolled bar obtained by the process according to  claim 15  is cut up into slugs and then a forging operation is carried out on said slugs between 1100° C. and 1280° C. 
   
   
       24 . Steel forging that can be obtained by the process according to  claim 23 . 
   
   
       25 . Use of a forging according to  claim 24  for the manufacture of brackets or couplings. 
   
   
       26 . Casting that can be obtained by casting a steel according to any one of  claims 1  to  8 .