Abstract: Provided are a cold-rolled steel sheet which undergoes a small load at the time of cold-rolling, has excellent press formability and high strength, and a method of manufacturing the cold-rolled steel sheet. A hot-rolled steel sheet having the composition comprising by mass %, 0.10 to 0.30 C, 0.2 or more Mn, 0.01 or more Ni, 0.5 to 2.5 Mn+Ni, 1.2 to 9.0 Cr, and Fe and unavoidable impurities as a balance, and has a tensile strength of 1000 MPa or less is subjected to pickling and, is subjected to cold rolling at a total rolling reduction of 60% or more thus forming a cold-rolled steel sheet. A final continuous annealing treatment is performed at a soaking temperature of 750° C. or above and at a cooling rate of 3° C./s to 100° C./s so that the cold-rolled steel sheet which has a tensile strength of 1280 MPa or more, breaking elongation of 3% or more, and a thickness of 0.05 to 0.60 mm is manufactured.

Abstract: The present invention provides a new high-strength and Si—Cr containing hot rolled steel plate provided with higher strength as well as excellent workability and a method for manufacturing the steel plate. The high-strength steel plate can be obtained by controlling the particle size of prior austenite to be 10 ?m or less, and properly selecting the coiling temperature. The steel plate obtained includes a retained austenite phase in a volume fraction of 5% to 20%; a martensite phase in a volume fraction equal to or less than 10%; and a bainite phase in the remaining volume fraction. The particle size of the retained austenite particle is 1 ?m or less and the retained austenite particles are dispersed uniformly.