Nippon Steel Corporation

Kawasaki Steel Corporation

Japan As Represented by Director General, Technical Research and

Yoichiro Tobe

Seinosuke Yano

Syuzo Ueda

Ko Moriyama

Seimei Karino

Yasuho Imai

A high toughness, ultra high-strength steel having an excellent stress corrosion cracking resistance with a yield stress of not less than 110 kgf/mm.sup.2, which comprises 0.06-0.20 wt % of C, not more than 0.35 wt % of Si, 0.05-1.0 wt % of Mn, 8-11 wt % of Ni, 0.2-2.5 wt % of Cr, 0.7-2.5 wt % of Mo, 0.05-0.2 wt % of V, 0.01-0.08 wt % of Al, not more than 0.005 wt % of N, not more than 0.003 wt % of O, provided that the value of Al (%).times.N (%).times.10.sup.4 is not more than 1.5, and the balance being substantially Fe and inevitable impurities.

High toughness, ultra-high strength steel having an excellent stress

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Sagamihara, Japan

Yoichiro Tobe