| 摘要 |
PROBLEM TO BE SOLVED: To stably guarantee the strength of a weld zone in the case of manufacturing a wide flange shape steel with welding by specifying the content of C, Mn, Al and the ratio of Mn and Si and controlling the hot rolling condition and cooling condition to reduce the occurrence of scale. SOLUTION: By wt., 0.02-0.15% C, 0.30-1.50% Mn, 0.005-0.10% Al are contained into this steel and moreover Si is contained within the range of satisfying Mn/Si=3 to 70. This composition of steel slab is hot rolled under the condition of <= the finish temperature 800 deg.C and next cooled at the speed of >=50 deg.C/sec to make the thickness of scale <=5μm. Or this steel slab is hot rolled under the condition of <= the finish temperature 850 deg.C and started cooling at the speed of >=50 deg.C/sec from the position within three meters in the outlet side of the hot rolling mill. Further, <=0.1% of at least one kind selected from Nb, V, Ti is contained into this steel, if necessary.
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