| 摘要 |
According to an embodiment of the present invention, a high strength galvannealed steel sheet with excellent stretch flangeability comprises, in wt%, 0.065-0.075% of C, 0.1-0.3% of Si, 1.7-2.0% of Mn, 0.01-0.03% of Al, 0.01-0.02% of P, 0.006% or less of S, 0.15-0.35% of Cr, 0.03-0.07% of Mo, and residual Fe and unavoidable impurities. A refined structure of a manufactured steel sheet comprises, in an area fraction, 61-70% of ferrite, 11-20% of martensite, and 15-25% of bainite, and an average crystal grain size of the martensite structure is 3μm or less in diameter. An alloying degree of a plating layer of the manufactured steel sheet is 9-13%, and a delta (δ) phase of the plating layer is 85-95% in an area fraction. |
