Formability and base metal and high-strength hot-rolled steel sheet having both the fatigue characteristics of the weld heat-affected zone .

摘要

PROBLEM TO BE SOLVED: To provide a high-strength hot-rolled steel sheet having excellent formability and improved fatigue characteristics not only in the base material but also in an HAZ (heat affected zone).;SOLUTION: The high-strength hot-rolled steel sheet includes a component composition comprising, in mass%, C: 0.05 to 0.20%, Si: not more than 2.0%, Mn: 1.0 to 2.5%, Al: 0.001 to 0.10%, and V: 0.0005 to 0.10%, and further comprising Ti: 0.02 to 0.20% and/or Nb: 0.02 to 0.20% in a manner of satisfying the equation: C-12×(V/51+Ti/48+Nb/93)0.03, with the balance being iron and inevitable impurities; and has a structure comprising, in an area ratio relative to the entire structure, ferrite: 50 to 90%, bainite: 10 to 50%, and the sum of martensite and retained austenite: less than 10%, wherein the mean particle diameter of a precipitated carbide present in the ferrite is smaller than 6 nm and the total content of V, Ti and Nb constituting the precipitated carbide is 0.02% or more.;COPYRIGHT: (C)2013,JPO&INPIT