| 摘要 |
PURPOSE:To manufacture nontempered high tension steel plate superior in toughness, by controlling heating rolling condition and cooling condition to specified ranges, at working plate material by hot rolling slab of carbon steel or low alloy steel. CONSTITUTION:Carbon steel or low alloy steel contains by weight 0.01-0.20% C, 0.1-0.5% Si, 0.6-2.0% Mn or further 0.003-0.08% rare earth element, 0.003-0.06% Zr and regulated quantities of 0.005-0.05% Al, <0.005% N. Slab of the carbon steel or low alloy steel is heated to 930-1,060 deg.C range to finely precipitate AlN, and to refine and uniformize austenite structure, then rolled to thick plate at uncrystallized austenite range by >=70% draft, and rolling is discontinued at time point when temp. at center part in plate thickness reaches 750-850 deg.C range. When the temp. at center part in plate thickness reaches >=750 deg.C temp., the plate is cooled so that cooling rate at center part in plate thickness attains 1-8 deg.C, and cooling is stopped at 200-500 deg.C.
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