| 摘要 |
Seamless quenched and tempered steel pipe having a wall thickness (WT) higher than or equal to 35 mm and lower than or equal to 80 mm, wherein the steel pipe has a chemical composition consisting of 0.050-0.085 wt% C, 0.80-1.65 wt% Mn, 0.10-0.45 wt% Si, 0.10-0.70 wt% Cr, 0.08-0.45 wt% Ni, 0.08-0.40 wt% Mo, 0.015-0.040 wt% Al, 0.0008-0.0050 wt% Ca, 0.0030-0.0090 wt% N, 0.00-0.04 wt% Nb, 0.00-0.02 wt% Ti, 0.000-0.030 wt% Zr, 0.000-0.030 wt% Ta based on the composition weight, the remaining being iron and impurities; said impurities comprising 0.000-0.010 wt% V; wherein, defining a first parameter P1 = 50 x C + Cr + 10 x Mo + 70 x V, the chemical composition satisfies a first condition P1 = 8.0; wherein the quenched and tempered steel pipe has, at mid thickness, a microstructure comprising, in volume percentage, tempered bainite greater than or equal to 50% and ferrite (VF) lower than or equal to 50%; wherein the quenched and tempered steel pipe has, at a distance up to 2 mm starting from outer and inner surfaces of the steel pipe, a microstructure consisting of, in volume percentage, tempered martensite lower than 70% and tempered bainite higher than 30%; and wherein the maximum hardness values, measured at 1.5-2.0 mm depth from the outer and inner surfaces, are below 235HV10. |
