| 摘要 |
<p>This improved high-strength cold-rolled steel sheet comprises C (0.010% or less), Mn (0.05-0.5%), Si (1.0% or less), S (0.001-0.30%), P (0.03% or less), N (0.0050% or less), Sol Al (0.005-0.10%), Cu (0.8-2.2%), Fe and unavoidable impurities (the residual). Ni (0.15-0.2%) and/or B (0.001-0.0030%) can be added as components. Ti (0.01-0.2%) and/or Nb (0.005-0.20%) can also be added to the above compsn. The cold-rolled steel sheet is composed mainly of recrystallised ferritic single phase and is specified to have a high gamma-value. The cold-rolled steel is produced by the following process: (i) steel having the above-mentioned compsn. is hot-rolled at the Ar3 temp. or higher, (ii) the obtd. hot-rolled steel is wound at a temp. of 450 deg.C or less into a coil, (iii) the wound coil is cold-rolled, (iv) the obtd. cold-rolled steel sheet is recrystallising-annealed at a temp. of 750 deg.C or higher, and (v) the obtd. annealed steel sheet is heat-treated at a temp. between 450 and 700 deg.C for 1 min. or longer. Step (v) can be replaced by a step (vi) in which the obtd. annealed steel sheet is cooled to a temp. lower than 450 deg.C within 1 min., and is then moulded and heat-treated (at 450 deg.C or higher).</p> |
