STEEL EXCELLENT IN DUCTILE FRACTURE RESISTANCE IN HIGH STRAIN-LOADED STATE AND ITS PRODUCTION METHOD

摘要

PROBLEM TO BE SOLVED: To provide steel excellent in ductile fracture resistance in a high strain-loaded state caused by, e.g. big earthquake and to provide its production method.;SOLUTION: Steel having a steel composition containing, by mass, 0.03 to 0.25% C, 0.01 to 1.0% Si, 0.5 to 2.0% Mn and one or more kinds selected from Cu, Ni, Cr, Mo, V, Nb and Ti, and the balance Fe with inevitable impurities is hot-rolled, is thereafter subjected to accelerated cooling from a two phase region to make its metallic structure into the one containing ferrite of 20 to 90% by area fractional ratio and to control the yield shelf after yielding in a nominal stress-nominal strain curve to ≥1% and also the work hardening exponent (n) found from the nominal strain (εu) in which the nominal stress reaches the maximum to ≥0.15.;COPYRIGHT: (C)2002,JPO