| 摘要 |
PROBLEM TO BE SOLVED: To produce deformed bar steel for a reinforcing bar stably satisfying mechanical properties on an SD 490 standard and excellent in gas pressure weldability. SOLUTION: This bar steel contains, by weight, 0.22 to 0.32% C and >0.95 to 1.20% Mn, for forming the structure of the surface layer part into the martensitic one, hot rolling in which the finishing temp. in finish rolling is controlled to the temp. range of (the Ar3 transformation point + 50 deg.C) to (the Ar3 transformation point + 250 deg.C) is executed, and, thereafter, it is rapidly cooled under the conditions in which the surface temp. is controlled to the one equal to or below the Ms point, and also, the surface temp. is controlled to the range of 620 to 780 deg.C by recuperation after the stop of the rapid cooling.
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