| 摘要 |
PROBLEM TO BE SOLVED: To prevent the occurrence of grooving corrosion with certainty without performing particular heat treatment by incorporating specific amounts of one or more elements among S, Mg, Ca, Sr, and Ba into a steel composition. SOLUTION: One or >=2 elements selected from a group consisting of, by weight, <=0.003% S, 0.0015-0.0025% Mg, 0.0025-0.004% Ca, 0.0055-0.0085% Sr, and 0.009-0.013% Ba are incorporated into the steel composition of a resistance welded tube. Because MnS sulfides precipitating in the steel are allowed to enter into solid solution again owing to the heat at the time of welding and then cooled rapidly, solid-solution S remains in large amounts in the weld heat- affected zone of the resistance welded tube. In order to reduce the amount of the solid-solution S in the heat affected zone to <=0.0010 wt.%, Mg, Ca, Sr, and Ba are added as elements hard to allow to enter into solid solution again at the time of welding to prevent the occurrence of grooving corrosion. The upper limit of the amount of S is regulated to 0.003% which is possible without requiring particular desulfurizing treatment.
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