| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for inexpensively manufacturing a high-strength steel plate which does not contain a large amount of an alloy element but is superior in toughness at a welding heat-affected zone. SOLUTION: A slab for the high-strength steel plate superior in toughness at the welding heat-affected zone comprises, at least 0.02 but less than 0.07% C, 0.01-0.5% Si, 0.5-2.0% Mn, not more than 0.02% P, not more than 0.005% S, 0.005-0.07% Nb, 0.005-0.1% V, not more than 0.08% Al, 0.001-0.015% REM by mass%, while controlling Ceq expressed by the following equation (1): Ceq=C+Mn/6+(Cu+Ni)/15+(Cr+Mo+V)/5, to 0.38 or less, and the balance iron with unavoidable impurities. The manufacturing method comprises the steps of: heating the slab to 1,000 to 1,300°C; hot-rolling it at a finish temperature equal to or higher than the Ar3 temperature; acceleration-cooling the plate to 300 to 600°C at a cooling rate of 5°C/s or higher; and immediately reheating it to 550 to 700°C at a heating rate of 0.5°C/s or higher. Thus manufactured steel plate has a metallurgical structure which is a dual-phase structure substantially consisting of ferrite and bainite, and in which fine carbides containing Nb or V with particle sizes of less than 10 nm are dispersedly precipitated. COPYRIGHT: (C)2006,JPO&NCIPI
|
