High-strength cold-rolled steel sheet excellent in workability and method for manufacturing the same

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A cold-rolled steel sheet contains (in mass %) carbon (0.10 - 0.3), silicon (1.0 - 3.0), manganese (1.5 - 3), aluminium (0.005 - 0.2), phosphorus (0.1 or below) and sulphur (0.05 or below), the balance comprising iron and inevitable impurities, and the metallurgical structure of the steel comprises bainite, residual austenite and tempered martensite, the bainite being constituted of a composite structure of high temperature range forming and low temperature range forming bainite, the area ratio of high temperature bainite with respect to the total metallurgical structure is 20 - 80%, the area ratio of low temperature bainite plus tempered martensite is 20 - 80%, the total area ratio of the three components is 70% or above, and the volumetric ratio of residual austenite is 3% or above. The steel may also contain chromium, molybdenum, titanium, niobium, vanadium, copper, nickel, boron, calcium, magnesium and rare earth metals. A method for manufacturing the steel sheet of the invention comprises the steps of soaking at a temperature of AC3or above for 50 seconds or more, cooling to between 400 and 540 degrees C and holding in this range for 5 - 100 seconds, and holding in the range 200 - 400 degrees C for 200 seconds or more.