High strength steel sheet having excellent workability and method for manufacturing same

A steel sheet comprising:

• by wt %, C:
• 0.25 to 0.75%, Si:
• 4.0% or less, Mn:
• 0.9 to 5.0%, Al:
• 5.0% or less, P:
• 0.15% or less, S:
• 0.03% or less, N:
• 0.03% or less, and a balance of Fe and unavoidable impurities;
• and
• as microstructures, 30 to 70 vol % of tempered martensite, 10 to 45 vol % of bainite, 10 to 40 vol % of retained austenite, 3 to 20 vol % of ferrite, and unavoidable structures,
• wherein the steel sheet satisfies the following [Relational Expression 1] and [Relational Expression 2];
• 1.1≤[Si+Al]F/[Si+Al]γ≤3.0 [Relational Expression 1]
• in the above Relational Expression 1, [Si+Al]F is an average total content (wt %) of Si and Al included in the ferrite, and [Si+Al]γ is an average total content (wt %) of Si and Al included in the retained austenite;
• and
• V(1.2 μm,γ)/V(γ)≥0.1 [Relational Expression 2]
• in the above Relational Expression 2, V(1.2 μm, γ) is a fraction (vol %) of the retained austenite having an average grain size of 1.2 μm or more, and V(γ) is the fraction (vol %) of the retained austenite.