| 摘要 |
PROBLEM TO BE SOLVED: To obtain a high tensile strength hot rolled steel plate having excellent workability and small in the variation of the material. SOLUTION: A slab having chemical components contg., by weight, 0.04 to 0.15% C, 0.5 to 2.0% Mn, 0.5 to 2.0% Si, <=0.1% P, <=0.005% S, <=0.1% Al and <=0.1% N, in which B as impurities is present by <=0.0005%, and the balance Fe with inevitable impurities except B is used, hot rolling is finished in a ferritic-austenitic two phase region of <=Ar3 point, after the passage of 3 to 7 sec after the completion, cooling by the injection of water is started, and it is rapidly cooled to <=150 deg.C at the average cooling rate of >=30 deg.C/sec and is coiled. As its characteristics, a balance of strength-ductility (tensile strength×total elongation) is controlled to >=18000 (MPa.%), also, its variation in a coil is controlled to <3000 (MPa.%), and yield ratio YR is controlled to <=65%.
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