US Patent 10538824 Steel sheet and method for producing same

Disclosed herein are a steel sheet having excellent aging resistance and low yield ratio properties, and a method for producing the same. The disclosed sheet comprises, by weight, 0.005-0.06% carbon (C), 0.2% or less silicon (Si), 1.0-2.0% manganese (Mn), 0.08% or less phosphorus (P), 0.01% or less sulfur (S), 0.2-2.0% aluminum (Al), one or more of chromium (Cr) and molybdenum (Mo) in an amount satisfying 0.3≤[Cr wt %]+0.3[Mo wt %]≤2.0, and 0.008% or less nitrogen (N), with the remainder being iron (Fe) and inevitable impurities, and has a single-phase structure of ferrite in a hot-rolled state, and a two-phase structure of ferrite and martensite in a cold-rolled state.