PURPOSE: To produce a steel for structures excellent in fatigue crack propagating resistance and used for vessels, marine structures, bridges, buildings, tanks, automobiles or the like under repeated loads. ;CONSTITUTION: This ferrite-bainite two-phase steel excellent in fatigue crack propagating resistance is the one in which the steel structure of the cross sections is composed of ferrite and bainite, the area ratio of the ferrite phase is regulated to 38 to 52%, its hardness is regulated to ≤0.02 by 150HV, the boundaries between the ferrite phase and bainite phase are present in a straight line drawn on the optional place in the cross section by 50 to 300places/mm density. As the compsn. of the steel, the following is preferable: the one cong., by weight, 0.08 to 0.2% C, 0.2 to 0.6% Si, 0.3 to 2.0% Mn, 0.01 to 0.1% Al, ≤0.1% Nb, ≤0.1% Ti, and the balance Fe with inevitable impurities.;COPYRIGHT: (C)1996,JPO
展开▼
