| 摘要 |
PROBLEM TO BE SOLVED: To provide ultrahigh strength steel which has an excellent balance between tensile strength and ductility in spite of its having about 1,200 MPa class tensile strength and also has improved delayed fracture resistance. SOLUTION: The ultrahigh strength steel has a composition consisting of, by mass, 0.1 to 1.0% C,≤2% (not including 0%) Si, 0.5 to 3% Mn, 1.5 to 5% Cu and the balance Fe with inevitable impurities, and average old austenite grain size is≤7μm. Moreover, this steel has a structure which is composed mainly of tempered martensite and in which Cu particles of 1.5 to 50 nm average particle size are dispersed. Further, when the fluorescent X-ray spectrum of Cu is measured by an XAFS (X-ray Absorption Fine Structure) method, the peak height of 8.98 KeV near the K-absorption edge ranges from 0.340 to 0.38 by standardized fluorescence yield. COPYRIGHT: (C)2007,JPO&INPIT
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