| 摘要 |
PROBLEM TO BE SOLVED: To provide a martensitic stainless steel tube for line pipe excellent in reel barge construction property.SOLUTION: A steel tube having a composition containing, by mass%, C:less than 0.015%, N:less than 0.020%, Cr:10 to 14%, Ni:4.0 to 8.0%, Mo:1.0 to 4.0%, Ti:0.03 to 0.15% and V:0.02 to 0.10% and a structure containing a martensite phase as a main and a retained austenite phase of 5 to 20% by volume percentage is applied to a hot treatment to adjust so that its base material average hardness HVsatisfies, depending on a load distortion amount &egr;(%) assumed during reel barge construction, HV≤300-12&egr; when &egr;<1 and HV≤292-4&egr; when &egr;≥1, where &egr;(%)={r/(R+r)}×100, r:outer radius of the steel tube (mm), R:outer radium of the reel (mm), and HV:base material average hardness of the steel tube before reel barge construction (HV). |
