| 摘要 |
Continuously thermal annealing steel sheet to improve its resistance to corrosion comprises heating the steel sheet in a reducing atmos., maintaining the sheet at a predetermined temp. (T1), then cooling it to a maturing temp. (T2) at which it is maintained for a predetermined period under an oxidising atmos., after which the sheet is cooled again. Pref. the oxidising atmos. is a mixt. of N2, H2 and steam which is in contact with the steel sheet. Pref. the maturing temp. (T2) is between 400-500 deg.C, the duration of the maturing stage is 1-3 mins., and the gas mixt. has a dew point of ca. 30 80 deg.C. USE/ADVANTAGE - Cuts process time to produce blued sheet steel with improved corrosion resistance to a few minutes compared to several hours for the conventional process. Blueing is performed on an expanded coil of the steel, and is also free from the long and complex handing operations involved in the traditional process. The treated steel produced is fully satisfactory w.r.t. corrosion resistance and adhesion of the protective surface layer produced.
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