| 摘要 |
A method of making welded steel pipe using dual-phase stainless steel comprises: (a) forming hot-rolled dual-phase stainless steel plate continuously into open pipe having opposed edges using multi-stage forming rolls, wherein the steel has composition: 0.03 wt.% or less C, 1 wt.% or less Si, 0.8 to 2.0 wt.% Mn, 0.03 wt.% or less P, 0.01 wt.% or less S, 20 to 30 wt.% Cr, 2.5 to 4 wt.% Mo, 4 to 7 wt.% Ni and 0.08 to 0.2 wt.% N and the balance essentially Fe; (b) welding said opposed edges of open pipe to form a welded pipe, while upsetting, by healing said edges to welding temperature by application of a laser beam thereto; (c) grinding the portion that increases in thickness during upsetting on the welding part, and (d) solid solution treating the welded part at a temperature ranging from 950 to 1100 {C for 30 to 300 seconds. Alternatively, the opposed edges of open pipe may be compression-joined by electric resistance heating and upsetting, and re-fusing the welded part with a laser beam after the grinding step. |
