PURPOSE: To produce a steel plate hardly causing fatigue crack propagation by specifying a composition consisting of C, Si, Mn, Al, Cr, Mo, Ni, Cu, Nb, Ti, V, and Fe and also specifying a hardness difference between the hard part and the soft part in a structure.
CONSTITUTION: This steel plate having a fatigue crack arresting effect can be obtained by providing a steel plate which has a composition consisting of, by weight, 0.01-0.3% C, 0.1-0.5% Si, 0.3-2.0% Mn, 0.005-0.1% sol.Al, 0-1.5% Cr, 0-0.6% Mo, 0-0.5% Ni, 0-1.0% Cu, 0-0.1% Nb, 0-0.1% Ti, 0-0.1% V, and the balance Fe with inevitable impurities and also has a structure consisting of a hard part and a soft part and having a hardness difference of ≥150 Vickers hardness between these two parts. Further, it is preferable that the above structure is composed of a soft part of 50μm average grain size dispersed in a matrix of hard part or the average spacing of the hard pant is regulated to ≤50μm.
FUJIWARA TOMOYA
ARIMOCHI KAZUSHIGE
YUKI HIDEAKI
OKAGUCHI HIDEJI
ICHINOSE TAKESHI
KUSHIDA TAKAHIRO
YODA NOBORU
