Welded steel pipe and method for manufacturing welded steel pipe

Abstract

The purpose of the present invention is to provide: a welded steel pipe excellent in fatigue crack development resistance in a hydrogen environment; and a method for manufacturing the same.　The present invention pertains to a welded steel pipe having a specific component composition in terms of mass%, wherein: the steel structure contains bainite in an area ratio of 90% or more in a range up to a position that is 1 / 4 of the pipe thickness from the surface; the percentage of the area ratio of bainite in which crystal grains have an equivalent circle diameter of less than 18 μm to the area ratio of total bainite is 50% or more; the total bainite has an interface having a crystal orientation difference of at least 0.5° and less than 2.0°; and there are an average of at least 10 interfaces in the total bainite that are the at least 0.5° but less than 2.0° on any 100 μm straight line drawn for measurement in the bainite. Total bainite refers to all the bainite in the steel structure.

Images