HIGH TENSILE STRENGTH HOT ROLLED STEEL SHEET AND METHOD FOR PRODUCING SAME

摘要

Provided are: a high tensile strength hot rolled steel sheet provided with both high strength and favorable workability (stretch flangeability) and moreover has superior material uniformity; and a method for producing same. The hot rolled steel sheet has a tensile strength of at least 780 MPa and has: a composition containing by mass% at least 0.03% and less than 0.07% of C no greater than 0.3% of Si 0.5 2.0% inclusive of Mn no greater than 0.025% of P no greater than 0.005% of S no greater than 0.0060% of N no greater than 0.1% of Al 0.07 0.11% inclusive of Ti and at least 0.08% and less than 0.15% of V in a manner such that Ti and V satisfy 0.18 = Ti + V = 0.24 (Ti and V being the amount contained (mass%) of the respective elements) the remainder comprising Fe and unavoidable impurities; a matrix such that the area ratio of ferrite phase with respect to the total structure is at least 95%; and a structure such that minute carbides containing Ti and V and having an average grain size of less than 10 nm are dispersed/precipitated and the volume ratio of the minute carbides with respect to the total structure is at least 0.0020.