Patent ID: 7559997

Claim:
A high strength cold rolled steel sheet comprising ferrite phases and second phases, said steel sheet consisting essentially of, by mass %, 0.005 to 0.05% C, 2.0% or less Si, 0.6 to 3.0% Mn, 0.08% or less P, 0.03% or less S, 0.01 to 0.1% Al, 0.004% or less N to avoid the presence of solid solution N and to promote an anti-ageing property, optionally at least one element selected from the group consisting of 1% or less Cr, 1% or less Mo, 1% or less V, 0.01% or less B, 0.1% or less Ti, 0.1% or less Nb, and a balance of Fe, wherein the ferrite phases have a mean grain size of 20 μm or less, the second phases have a volume fraction of not less than 0.1% to less than 10%, the absolute value of the in-plane anisotropy of the r value |Δr| is less than 0.15, and the thickness of the steel sheet is 0.4 mm or more, wherein the mean distance L in μm among adjacent second phases measured along the grain boundaries of the ferrite phase satisfies the following formula (1) when the mean grain size of the ferrite phases is d in μm: L < 3.5 ×d (1).