Nippon Kokan Kabushiki Kaisha

Kazuhide Takahashi

Makoto Yamada

Itaru Watanabe

Masataka Suga

Hisatoshi Tagawa

Toru Izawa

Kazuyuki Matsui

Nobuhiro Iwasaki

The steel plate having a high tensile strength is manufactured from a steel consisting essentially of 0.04-0.16% by weight of C, 0.02-0.50% by weight of Si, 0.4-1.2% by weight of Mn, 0.2-5.0% by weight of Ni, 0.2-1.5% by weight of Cr, 0.2-1.0% by weight of Mo, 0.01-0.10% by weight of acid soluble Al, 0.03-0.15% by weight of one or more of V, Ti and Nb, 0.015% or less by weight of P, 0.006% or less by weight of S and the balance of iron and inherent impurities. The steel is heated to a temperature above a temperature at which carbo-nitrides of V and Nb and carbides of Ti become complete solid solution state, rolled with total reduction of 40% or more below 950.degree. C., quenched by simultaneous cooling immediately after completion of the rolling from a temperature above (A.sub.3 -50).degree.C. and tempered at a temperature lower than Ac.sub.1 temperature. The density of cooling water (W) for the quenching is detemined by the following equation (I) or (II) in accordance with the plate thickness (t):

Method of manufacturing high tensile strength steel plates

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Kanagawa, Japan

Kazuhide Takahashi