| 摘要 |
A cold rolled steel sheet excellent in strain aging hardening property, characterized in that it has a chemical composition, in mass %; C: less than 0.01 %, Si: 0.005 to 1.0 %, Mn: 0.01 to 1.0 %, Nb: 0.005 to 0.050 %, Al: 0.0 05 to 0.030 %, N: 0.005 to 0.040 %, B: 0.0005 to 0.0015 %, P: 0.05 % or less, S ; 0.01 % or less and balance: substantially Fe, with the proviso that the composition satisfies the following formulae (1) and (2): N % >= 0.0015 + 14/93 .bullet. Nb% + 14/27 .bullet. Al% + 14/11 .bullet. B% ---(1) C % <= 12/93 .bullet. Nb% ---(2); and an alloyed hot dip galvanized steel sheet produced from the cold rolled sheet. The steel sheet exhibits a significantl y enhanced tensile strength when it is subjected to press forming heat treatment, while maintaining excellent deep drawing properties in press forming.
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