To provide a method for producing a steel pipe in which local buckling is hardly caused by compression and bending stress acted in the axial direction in case of a big earthquake and in the laying of a submarine pipe, and which is suitable for gas pipelines, water piping, the columns of civil engineering and construction or the like.
A steel sheet obtained by hot rolling steel having a composition containing, by mass%, 0.03 to 0.15% C, 0.05 to 0.5% Si and 1 to 2% Mn, and the balance substantially Fe, and in which PCM shown by the following formula (1) satisfies 0.10 to 0.20 is made into a steel pipe by cold or hot forming. After that, the steel pipe is reheated at 800°C to 1,100°C. Successively, the steel pipe is cooled at a cooling rate of ≥5°C/sec. In this way, the steel pipe in which the stress ratio (σr) as a ratio between the yield strength in the axial direction of the pipe and the stress in the case the nominal strain is 1.5% (σ1.5) is ≥1.05, or the stress ratio (σr) as a ratio between the yield strength in the circumferential direction of the steel pipe and in the axial direction of the pipe and stress in the case the nominal strain is 1.5% (σ1.5) is ≥1.05, and having excellent buckling resistance is produced: PCM=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5xB (1).
ISHIKAWA NOBUYUKI
SUZUKI NOBUHISA
KONDO JO
