Process for manufacturing hot-rolled plate, strip or coil made of 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.

What is claimed is: 
     
         1 . A process for manufacturing a hot-rolled plate, strip or coil made of steel comprising:
 providing an ingot or slab of a steel of composition comprising 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
 
 hot rolling the ingot or slab at a temperature between 1150 and 1280° C. in order to obtain plate, strip or coil. 
 
     
     
         2 . The process for manufacturing hot-rolled plate made of steel according to  claim 1 , in which:
 hot-rolling the ingot or slab at a temperature between 1150 and 1280° C. to obtain a quarto plate;   performing a heat treatment at a temperature between 900 and 1100° C.; and   cooling the plate by air quench.   
     
     
         3 . The process for manufacturing hot-rolled bar or rod made of steel comprising the steps of:
 providing a continuously cast ingot or bloom of steel of composition comprising 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%   a balance being iron and impurities resulting from the smelting;   hot-rolling the ingot or bloom from a temperature between 1150 and 1280° C. in order to obtain a bar, which is air-cooled, or a coil of wire stock which is water-cooled; and then, optionally:   performing a heat treatment at a temperature between 900 and 1100° C.; and   quench cooling the bar or coil of wire stock.   
     
     
         4 . The process for manufacturing according to  claim 3 , further comprising the step of:
 performing a cold-drawing operation carried out on the bar or a die-drawing operation on the rod, after being cooled.   
     
     
         5 . The process for manufacturing a steel section according to  claim 3 , further comprising the step of:
 performing a cold-forming operation on the hot-rolled bar.   
     
     
         6 . The process for manufacturing a steel forging comprising the steps of:
 providing a hot-rolled bar of  claim 3 ;   cutting the hot-rolled bar into slugs; and   performing a forging operation on the slugs between 1100° C. and 1280° C.   
     
     
         7 . The process for manufacturing according to  claim 1 , wherein 30.5≤I LCR ≤38.6. 
     
     
         8 . The process for manufacturing according to  claim 3 , wherein 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 
 where
     I   LCR =% Cr+3.3×% Mo+16×% N+2.6×% Ni−0.7−% Mn.
 
 
 
     
     
         9 . The process for manufacturing according to  claim 8 , wherein 30.5≤I LCR ≤38.6. 
     
     
         10 . A hot-rolled steel quarto plate, obtained by the process according to  claim 2  and having a thickness between 5 and 100 mm. 
     
     
         11 . Use of hot-rolled coil obtained by the process according to  claim 1 , for the manufacture of structural components for material production or energy production installations. 
     
     
         12 . Use according to  claim 11 , in which said material and energy production installations operate between −100 and 300° C., preferably between −50 and 300° C. 
     
     
         13 . A cold-rolled steel strip that can be obtained by cold-rolling a hot-rolled coil obtained by the process according to  claim 1 . 
     
     
         14 . A hot-rolled bar obtained by the process according to  claim 3  and having a diameter of 18 mm to 250 mm or a hot-rolled rod that can be obtained by the process according to  claim 3  and having a diameter of 4 to 30 mm. 
     
     
         15 . A cold-drawn bar that can be obtained by the process according to  claim 4 , having a diameter of 4 mm to 60 mm, or die-drawn rod or wire that can be obtained by the process according to  claim 3 , having a diameter of 0.010 mm to 20 mm. 
     
     
         16 . A mechanical part such as pumps, valve shafts, motor and engine shafts and couplings operating in corrosive media comprising:
 a bar according to  claim 14 .   
     
     
         17 . Use of a rod or wire according to  claim 14  for the manufacture 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. 
     
     
         18 . A steel section obtained by the process according to  claim 5 . 
     
     
         19 . A steel forging obtained by the process according to  claim 6 . 
     
     
         20 . Brackets or couplings comprising:
 a steel forging according to  claim 19 .