| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel sheet which stably has the strength of 650 MPa or greater, and is used for a member for an automobile or the like.SOLUTION: The high strength hot rolled steel sheet contains, by mass%, 0.03-0.08% C, 0.01-1.50% Si, 0.1-1.5% Mn, 0.03-0.20% Ti, 0.0002-0.0030% B, 0.1% or less P, 0.005% or less S, 0.5% or less Al, and 0.009% or less N, and the balance comprising Fe and inevitable impurities. In the steel sheet, (a) Pcm defined by the following equation is 0.130 or more, (b) a dislocation density is 1×10to 1×10m, (c) an average diameter of a TiC precipitate within a crystal grain is 8 nm or smaller, and an average number density is 3×10to 2×10(pieces/cm) or lower, and (d) the Ti amount of the TiC precipitate present on dislocation is 40% or more of the Ti amount contained in the steel sheet. P=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B. In this case, C, Si, Mn, Cu, Ni, Cr, Mo, V and B are contents (mass%) of respective elements. |
