| 摘要 |
PROBLEM TO BE SOLVED: To produce a high tensile strength hot rolled steel plate small in the variation in mechanical properties and excellent in ductility and hole expansibility. SOLUTION: This high tensile strength hot rolled steel plate is the one having a compsn. contg. 0.01 to 0.10% C, 0.01 to 1.5% Si, 0.1 to 2.5% Mn, 0.01 to 0.10% Al, <=0.010% S, <=0.01% N and <=0.04% Ti, and in which the content of Ti is controlled according to the relation between the S content and the N content so as to satisfy (48/32)×S<=Ti<=(48/32)×S+(48/14)×N. Moreover, the steel plate may contain one or >= two kinds among 0.03 to 0.15% P, 0.1 to 1.0% Cu, 0.05 to 1.0% Ni and 0.01 to 0.05% Nb. The steel whose components have been controlled is subjected to continuous casting into a slab, which is subjected to hot rolling in such a manner that the finishing temp. is controlled to >=Ar3 transformation point, the average cooling rate from finishing temp. to coiling temp. to >=20 deg.C/sec, and the coiling temp. to 400 to 600 deg.C.
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