| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength steel sheet superior in workability and fatigue characteristics, and a method for efficiently manufacturing such a steel sheet. SOLUTION: The high-strength steel sheet includes, by mass%, 0.06-0.25% C, 0.5-3% Si+Al, 0.5-3% Mn, 0.15% or less P, 0.02% or less S; has a mother phase structure, which consists of martensite or tempered bainite having a space factor of 50% or higher to the whole structure, or which consists of martensite or bainite having the space factor of 15% or higher, along with containing ferrite; and has the second phase structure, which consists of retained austenite having the space factor of 3-30%, may contain martensite, and satisfies the expression (1): (S1/S)×100<=20, where S means a total area of the second phase structure, S1 means the total occupation area of the coarse second phase crystal grains (Sb) in the second phase structure (Sb), and Sb satisfies three times as wide as the area (Sm) of the average crystal grains in the second phase structure, or wider.
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