Patent ID: 9657365
Date: 2017-05-23
CPC Classifications: C21D,C22C,F16L

Claim:
1. A seamless quenched and tempered steel pipe comprising: a yield strength from 415 MPa to 635 MPa and a wall thickness WT higher than or equal to 6 mm and lower than 35 mm; wherein the steel pipe has a chemical composition consisting of: 0.050-0.090 wt % C; 0.80-1.65 wt % Mn; 0.10-0.45 wt % Si; 0.10-0.60 wt % Cr; 0.05-0.45 wt % Ni; 0.05-0.40 wt % Mo; 0.020-0.040 wt % Al; 0.0030-0.0090 wt % N; 0.0008-0.0050 wt % Ca; 0.000-0.040 wt % Nb; 0.000-0.020 wt % Ti; 0.000-0.070 wt % V; 0.000-0.030 wt % Zr; 0.000-0.030 wt % Ta; 0.00-0.25 wt % Cu; 0.000-0.003 wt % S; 0.000-0.018 wt % P; and 0.0000-0.0005 wt % B; the remainder being Fe; wherein at least one of Nb and V is present, (V+Nb) content being lower than 0.07 wt %; wherein, defining a first parameter: the chemical composition satisfies a first condition 10≦P1≦14.5; wherein the quenched and tempered steel pipe has, at mid thickness, a microstructure comprising, in volume percentage, tempered bainite greater than or equal to 40% and ferrite (V wherein the microstructure of the quenched and tempered steel pipe has an average prior austenite grain size, measured by ASTM Standard E112, smaller than 25 μm; and wherein the maximum hardness values, measured at 1.5-2.0 mm depth from the outer and inner surfaces, are not higher than 235 HV