| 摘要 |
PURPOSE:To form the finer crystal grains in the weld zone of an electric welded steel pipe having a specific compsn. contg. Nb and to obtain the high-toughness electric welded steel pipe by subjecting the weld zone after welding of said pipe to a special heat treatment. CONSTITUTION:The electric welded steel pipe is produced by using a steel contg. <=0.30wt.% C, <=2.0% Mn, <=0.80% Si, 0.01-0.10% Al, and 0.01-0.15% Nb, contg. >=1 kinds of 0.01-0.20% V and 0.005-0.100% Ti and consisting of the balance Fe and unavoidable impurities as a stock. The weld zone after electric welding is held for 1-100sec in a 600-850 deg.C range to finely deposit the Nb introduced therein by the temp. history at the time of the solution electric welding. The weld zone is then heated up to the austenite temp. to form the finer crystal grains. The toughness in the weld zone of the electric welded steel pipe is thereby improved.
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