| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel sheet excellent in toughness and having a tensile strength of 980 MPa or more and a method of producing the same.SOLUTION: The high strength hot rolled steel sheet has a composition containing, by mass%, C:0.05% to 0.18%, Si:1.0% or less, Mn:1.0% to 3.5%, P:0.04% or less, S:0.006% or less, Al:0.10% or less, N:0.008% or less, Ti:0.05% to 0.20% and V: over 0.1% and 0.3% or less and the balance Fe with inevitable impurities and has structure in which: a main phase is a bainite phase with an area ratio of over 85%; a second phase is one or more kind of a ferrite phase, a martensite phase and a retained austenite phase; the second phase has an area ratio of 0% or more and less than 15% in total; an average lath interval between laths of the bainite phase is 400 nm or less; and an average major axis length of the lath is 5.0μm or less. As a result, the high strength hot rolled steel sheet has a tensile strength TS of 980 MPa or more and excellent toughness.</p> |
