| 摘要 |
PROBLEM TO BE SOLVED: To provide a hot rolled steel sheet by which deformability or uniform deformability at secondary working can be improved. SOLUTION: The hot rolled steel sheet is composed mainly of ferrite phase and has a composition consisting of, by mass, 0.04 to 0.20% C, 0.01 to 2.0% Si, 0.5 to 3.0% Mn and the balance Fe with inevitable impurities and is characterized as follows: a ferrite grain size in a position at a depth one-fourth the sheet thickness from the surface of the steel sheet, D2, is <2.0μm; a relationship between a ferrite grain size in a position at a depth one-half the sheet thickness from the surface of the steel sheet, D3, and a ferrite grain size in a position at a depth of 50μm from the surface of the steel sheet, D1, satisfies (D3-D1)/D2≤0.4; and a grain size in a rolling direction, Dr, and a grain size in a sheet thickness direction, Dt, of the ferrite grain in a position at a depth of 50μm from the surface of the steel sheet satisfy inequality ¾(Dr-Dt)/((Dr+Dt)/2)¾≤0.25. COPYRIGHT: (C)2008,JPO&INPIT
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