| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength cold rolled steel sheet which has a tensile strength of 340 MPa or more, and has excellent resistance to planar strain and bulging characteristics, and to provide a method for production thereof. SOLUTION: The high strength cold rolled steel sheet has a structure comprising ferrite grains having an average grain diameter of 10μm or less, wherein, in the ferrite grain, Nb(C, N)'s having a diameter of 50 nm or more are present in an average number per unit area (average area density) of 7.0×10<SP>-2</SP>pieces/μm<SP>2</SP>, and along the grain boundary of the ferrite grain, a region is formed which has a width of 0.2 to 2.4μm and has an average area density of NbC being 60% or less of an average area density of NbC deposited in the central portion of the ferrite grain. In the method for production thereof, slab heating temperature SRT (°C) is controlled to≤1,350°C, and 1,050°C≤SRT≤ä770+([sol.Al]-0.085)<SP>0.24</SP>×820}°C is satisfied. COPYRIGHT: (C)2005,JPO&NCIPI
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