| 摘要 |
PROBLEM TO BE SOLVED: To provide an inexpensive galvannealed steel sheet excellent in workability by restraining the generation and the growth ofΓphase and the remaining ofζphase. SOLUTION: A steel sheet containing <=0.01% C, 0.005-0.10% Si, 0.05-0.5% Mn, 0.005-0.06% Al, <=0.025% P, 0.005-0.1% Ti and if necessary, 0.005-0.1% Nb and/or 0.0001-0.01% B, is used as the base material and plated layers containingδ1 phase,Γ1 phase and theΓphase having <=1 mm thickness, are formed at 30-90 g/m2 coating surface density per one side surface. After annealing the basis sheet for plating, the galvanization is applied by dipping into galvanizing bath containing 0.1-0.2% Al having bath temperature of 490-550 deg.C at 490-600 deg.C inlet temperature and the cooling is performed to 400 deg.C steel sheet temperature at 5-15 deg.C/sec cooling speed, and after adjusting the coating surface density, the alloying treatment is applied at 450-550 deg.C for 5-60 sec.
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