Patent ID: 9644248
Date: 2017-05-09
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 35 mm and lower than or equal to 80 mm; wherein the steel pipe has a chemical composition consisting of: wherein CE wherein, defining a first parameter P 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 (V 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 comprising, in volume percentage, tempered martensite lower than 70% and tempered bainite higher than 30%; 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