| 摘要 |
The invention deals with a process for manufacturing a hot-dip galvanized or galvannealed steel sheet having a TRIP microstructure, said process comp rising 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 = 0.4 0%, Ni = 1.0%, Nb = 0.20%, the balance of the composition being iron and una voidable impurities resulting from the smelting, - oxidizing said steel shee t 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 h aving a thickness from 0.05 to 0.2 µm 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 µm/s, in order to achieve a reduction of the layer of iron oxide, - hot-dip galvanis ing said reduced steel sheet to form a zinc-coated steel sheet, and - option ally, subjecting said hot-dip coated steel sheet to an alloying treatment to form a galvannealed steel sheet. |
