Abstract: There is provided a high-strength steel tube having excellent chemical conversion treatability and excellent formability and a method for manufacturing the high-strength steel tube. More specifically, in processing a mother steel sheet containing, on the basis of mass percent, 0.05% or more C, more than 0.7% Si, and 0.8% or more Mn into a pipe shape, the sum total of absolute circumferential surface strains each applied in individual process steps of the processing is 5% or more as nominal strain. A welded steel tube thus manufactured using a steel sheet even containing more than 0.7% Si can have excellent chemical conversion treatability without mechanical grinding or chemical pickling treatment.

Abstract: In a method for processing a high-strength member having a high Si content of more than 0.7% by mass, a high-strength steel material containing, on the basis of mass percent, 0.05% or more C, more than 0.7% Si, and 0.8% or more Mn is subjected to processing controlled such that the sum total of absolute surface strains in a predetermined direction each applied in individual process steps of the processing is 5% or more as nominal strain to form a member having a predetermined shape. The member, even containing more than 0.7% Si, can have markedly improved chemical conversion treatability without mechanical grinding or chemical pickling treatment.

Abstract: There is provided a high-strength steel tube having excellent chemical conversion treatability and excellent formability and a method for manufacturing the high-strength steel tube. More specifically, in processing a mother steel sheet containing, on the basis of mass percent, 0.05% or more C, more than 0.7% Si, and 0.8% or more Mn into a pipe shape, the sum total of absolute circumferential surface strains each applied in individual process steps of the processing is 5% or more as nominal strain. A welded steel tube thus manufactured using a steel sheet even containing more than 0.7% Si can have excellent chemical conversion treatability without mechanical grinding or chemical pickling treatment.