| 摘要 |
<p>The invention deals with a process for manufacturing a hot-dip galvanized or galvannealed steel sheet having a TRIP microstructure, said process comprising the steps consisting in: - providing a steel sheet whose composition comprises, by weight: 0.01 ⤠C ⤠0.22%, 0.50 ⤠Mn ⤠2.0%, 0.2 ⤠Si ⤠2.0%, 0.005 ⤠Al ⤠2.0%, Mo < 1.0%, Cr ⤠1.0%, P < 0.02%, Ti ⤠0.20%, V ⤠0.40%, Ni ⤠1.0%, Nb ⤠0.20%, the balance of the composition being iron and unavoidable impurities resulting from the smelting, - oxidizing said steel sheet in a direct flame furnace where the atmosphere comprises air and fuel with an air-to-fuel ratio between 0.80 and 0.95, so that a layer of iron oxide having a thickness from 0.05 to 0.2 Î1/4m is formed on the surface of the steel sheet, and an internal oxide of Si and/or Mn and/or Al is formed, - reducing said oxidized steel sheet, at a reduction rate from 0.001 to 0.010 Î1/4m/s, in order to achieve a reduction of the layer of iron oxide, - hot-dip galvanising said reduced steel sheet to form a zinc-coated steel sheet, and - optionally, subjecting said hot-dip coated steel sheet to an alloying treatment to form a galvannealed steel sheet.</p> |
