| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a high-strength hot-rolled steel sheet having both high strength and excellent workability (especially, stretch flange formability), and a method for producing the same. <P>SOLUTION: The high-strength hot-rolled steel sheet has a composition which contains, in terms of mass%, excluding 0.035%-0.07% C, up to 0.3% Si, excluding 0.35%-0.7% Mn, up to 0.03% P, up to 0.03% S, up to 0.1% Al, up to 0.01% N, and 0.135%-0.235% Ti, while the contents of C, S, N, and Ti satisfy the relationship ((Ti-(48/14)N-(48/32)S)/48)/(C/12)<1.0 (C, S, N, and Ti are the contents of the respective elements (mass%)), with the remainder comprising Fe and incidental impurities; and has a structure which includes a matrix comprising a ferrite phase in an areal proportion of higher than 95%, and titanium carbide having an average grain diameter of less than 10 nm finely precipitated in the crystal grains of the ferrite phase. This steel sheet hence has a tensile strength of 780 MPa or higher. <P>COPYRIGHT: (C)2013,JPO&INPIT |
