| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength cold-rolled steel sheet having an improved balance between elongation and stretch-flangeability and better formability, and to provide a method for producing the same. SOLUTION: The cold-rolled steel sheet has a composition containing, by mass, 0.05-0.30% C,≤3.0% Si, 0.1-5.0% Mn,≤0.1% P,≤0.010% S, 0.001-0.10% Al, and 0.02-0.40% Nb, wherein ([%Nb]/96+[%Ti]/51+[%V]/48)×48=0.01-0.20% is satisfied in at least one of 0.01-0.20% Ti and 0.01-0.20% V, and the remainder being mainly iron, and has a structure comprising, by an area rate,α=10-80%, retentionγ+M<5%, and a hard second phase as the remainder, wherein for a KAM value frequency distribution curve, anαparticle diameter is 5μm or below, while the relationship between the proportion X<SB>KAM≤0.4°</SB>of sites having a KAM value≤0.4°and the arealαproportion V<SB>α</SB>satisfies X<SB>KAM≤0.4°</SB>/V<SB>α</SB>≥0.8 and the proportion X<SB>KAM=0.6-0.8°</SB>of sites having a KAM value in the range of 0.6-0.8 is 10-20%. In the hard second phase adjoining theα, three or lessθparticles having a diameter of 0.1μm or larger and five or less deposition materials containing Nb, Ti and V and having a diameter of 20 nm or larger are dispersed perμm<SP>2</SP>of the hard second phase. COPYRIGHT: (C)2011,JPO&INPIT
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