| 摘要 |
PROBLEM TO BE SOLVED: To prevent oxidation of a zinc-plated layer caused by heating of a material to be processed even when the heating is performed at a temperature higher than before when a zinc-plated steel material is used as the material to be processed in a bending method etc., disclosed in an international publication 2006/093006 pamphlet.SOLUTION: A steel pipe including a Zn-Fe alloy plated film on at least one surface with a deposition amount of 30-90 g/mper one surface and an Fe content of 8-35 mass% is maintained under atmospheric conditions or under atmosphere including 20 vol.% or less of oxygen, with the balance comprising nitrogen, carbon dioxide, and water vapor, in a temperature range of 500-800°C for 1-60 minutes, then brought into contact with a solution capable of dissolving a plated layer, thereby dissolving at least 0.2 g/mof the plated layer, dried, then heated to a temperature range capable of hardening with a rate of temperature rise of at least 30°C/sec, and then cooled with a cooling rate of at least 30°C/sec. |
