Method for the Production of a Siderurgical Product Made of Carbon Steel with a High Copper Content, and Siderurgical Product Obtained According to Said Method

Abstract

The invention relates to a method for producing a siderurgical product made of carbon steel having a high copper content, according to which:—a liquid steel having the composition: 0.0005% 1%; 0.5 Cu 10%; 0 Mn 2%; 0 Si 5% 0 Ti 0.5%; 0 Nb 0.5%; 0 Ni 5%; 0 Al 2%, the remainder being iron and impurities, is produced;—said liquid steel is poured directly in the form of a thin strip having a thickness of no more than 10 mm;—the strip is subjected to forced cooling and/or is surrounded by a non-oxidizing atmosphere while having a temperature of more than 1000? C;—said thin strip is hot rolled at a reduction rate of at least 10%, the temperature at the end of the rolling process being such that all of the copper is still in a solid solution in the ferrite and/or austenite matrix;—and the strip is coiled. The invention also relates to a siderurgical product obtained according to said method.

1 - 18 . (canceled) 
     
     
         19 . Process for manufacturing a steel product made of copper-rich carbon steel, wherein:
 a liquid steel is produced, which has the following composition, expressed as percentages by weight:   0.0005%≦C≦1%   0.5≦Cu≦10%   0≦Mn≦2%   0≦Si≦5%   0≦Ti≦0.5%   0≦Nb≦0.5%   0≦Ni≦5%   0≦Al≦2%   
       the remainder being iron and impurities resulting from production;
 this liquid steel is cast directly into the form of a thin strip having a thickness less than or equal to 10 mm; 
 the strip is cooled rapidly to a temperature less than or equal to 1000° C. by spraying with water or a water/air mixture; 
 the thin strip is subjected to hot-rolling at a reduction rate of at least 10%, the end-of-rolling temperature being such that, at this temperature, all the copper is still in a solid solution in the ferrite and/or austenite matrix; 
 the strip is subjected to forced cooling so as to keep the copper in a supersaturated solid solution in the ferrite and/or austenite matrix; 
 and the strip thus cooled is coiled, 
 wherein the rate V of forced cooling after hot-rolling is such that V≧e 1.98(% Cu)−0.08 , wherein V is expressed in ° C./s and % Cu in % by weight. 
 
     
     
         20 . Process according to  claim 19 , characterised in that the Mn/Si ratio is greater than or equal to 3. 
     
     
         21 . Process according to  claim 19 , characterised in that the thin strip is cast on a casting installation between two internally cooled rolls rotating in opposite directions. 
     
     
         22 . Process according to  claim 19 , characterised in that hot-rolling of the strip is carried out in line with the casting of the strip. 
     
     
         24 . Process according to  claim 19 , characterised in that the carbon content of the steel is between 0.1 and 1% and in that the strip is coiled at a temperature higher than the temperature M s  at the beginning of martensitic transformation. 
     
     
         25 . Process according to  claim 19 , characterised in that the strip is coiled at less than 300° C. and in that the strip is then subjected to a copper precipitation heat treatment at between 400 and 700° C. 
     
     
         26 . Process according to  claim 25 , characterised in that the carbon content of the steel is between 0.1 and 1% and in that the strip is subjected to precipitation heat treatment without being uncoiled beforehand. 
     
     
         27 . Process according to  claim 19 , characterised in that coiling of the strip is carried out at a temperature which is both higher than the temperature M s  at which the martensitic transformation begins and lower than 300° C., and is followed by cold-rolling, recrystallisation annealing in a temperature range where the copper is in a supersaturated solid solution, forced cooling to keep the copper in a solid solution and precipitation tempering. 
     
     
         28 . Process according to  claim 27 , characterised in that said precipitation tempering is carried out at between 600 and 700° C. in a continuous annealing installation. 
     
     
         29 . Process according to  claim 27 , characterised in that said precipitation tempering is carried out at between 400 and 700° C. in a batch annealing installation. 
     
     
         30 . Process according to  claim 19 , characterised in that coiling of the strip is carried out at a temperature which is both higher than the temperature M s  at which the martensitic transformation begins and lower than 300° C. and is followed by cold-rolling and batch annealing at between 400 and 700° C. which acts as both recrystallisation annealing and precipitation tempering. 
     
     
         31 . Process according to  claim 27 , characterised in that the carbon content of the steel is between 0.1 and 1%. 
     
     
         32 . Process according to  claim 27 , characterised in that the carbon content of the steel is between 0.01 and 0.2%. 
     
     
         33 . Process according to  claim 27 , characterised in that the carbon content of the steel is between 0.0005% and 0.05% and in that its copper content is between 0.5 and 1.8%. 
     
     
         34 . Process according to  claim 33 , characterised in that, prior to precipitation hardening, the strip is cut to form a sheet which is shaped by drawing, and in that precipitation tempering is carried out on the drawn sheet. 
     
     
         35 . Process according to  claim 19 , characterised in that the strip is subjected to a final treatment in a skin-pass rolling mill. 
     
     
         36 . Steel product, characterised in that it is obtained by a process according to  claim 19 .