High-characteristic steel for large-size parts

Abstract

High-strength steel of which the chemical composition comprises, by weight: 0.03%≦C<0.2% Si≦0.49% 3%<Mn≦4% Ni≦0.9% 1%≦Cr≦5% Mo+W/2≦1% Cu≦0.9% S+Se/2+Te/3<0.020% Al≦0.1%, the remainder being iron and impurities resulting from production. Block and plates obtained.

1 . Method for manufacturing a steel block or plate, comprising the steps of:
 providing a semi-finished product having a chemical composition comprising, by weight:
   0.03%≦C<0.2%
 
   Si≦0.49%
 
   3%<Mn≦4%
 
   Ni≦0.9%
 
   1%≦Cr≦5%
 
   Mo+W/2≦1%
 
   Cu≦0.9%
 
   S+Se/2+Te/3<0.020% 
   Al≦0.1%,
 
   
       the remainder being iron and impurities resulting from production,
 shaping said semi-product by hot plastic deformation, by forging or by rolling, to obtain a blank having a thickness greater than or equal to 20 mm and lower or equal to 1 m, 
 quenching said blank by air cooling to obtain said steel block or plate. 
 
     
     
         2 . Method for manufacturing a steel block or plate according to  claim 1 , wherein between the shaping of the semi-product and the quenching by air cooling, the blank is austenized. 
     
     
         3 . Method for manufacturing a steel block or plate according to  claim 2 , wherein providing said semi-finished product comprises the steps of casting a steel having said chemical composition. 
     
     
         4 . Method for manufacturing a steel block or plate according to  claim 3 , wherein the semi-product is shaped by hot plastic deformation immediately after the casting. 
     
     
         5 . Method for manufacturing a steel block or plate according to  claim 1 , wherein the steel has a structure consisting of bainite and/or martensite, and the difference in hardness between the harder regions and the less hard regions of the block or plate, resulting from the segregated veins, is less than 20% of the average hardness of the block or plate.