A process for the manufacture of a profiled wire of hydrogen-embrittlement-resistant, low-alloy carbon steel for flexible pipelines for the offshore oil and gas operations sector is provided. The process includes providing a low-alloy carbon steel wire rod having a composition including, expressed in percentages by weight of the total mass 0.75<C %<0.95; 0.30<Mn %<0.85; Cr0.4%; V0.16%; and Si1.40%, the rest being iron and the inevitable impurities from smelting of the metal in the liquid state. The process further includes hot-rolling the wire rod in an austenitic region above 900 C., cooling the wire rod to ambient temperature, subjecting the wire rod to isothermal quenching to obtain a homogeneous pearlitic microstructure, subjecting the wire rod to an operation of cold mechanical transformation, carried out with a global work-hardening ratio of from approximately 50 to 80%, to give the wire rod a diameter of from approximately 5 to 30 mm and subjecting the drawn wire to a short-duration recovery heat treatment carried out below an Ac1 temperature of the steel.

A process for the manufacture of a profiled wire of hydrogen-embrittlement-resistant, low-alloy carbon steel for flexible pipelines for the offshore oil and gas operations sector is provided. The process includes providing a low-alloy carbon steel wire rod having a composition including, expressed in percentages by weight of the total mass 0.75<C %<0.95; 0.30<Mn %<0.85; Cr0.4%; V0.16%; and Si1.40%, the rest being iron and the inevitable impurities from smelting of the metal in the liquid state. The process further includes hot-rolling the wire rod in an austenitic region above 900 C., cooling the wire rod to ambient temperature, subjecting the wire rod to isothermal quenching to obtain a homogeneous pearlitic microstructure, subjecting the wire rod to an operation of cold mechanical transformation, carried out with a global work-hardening ratio of from approximately 50 to 80%, to give the wire rod a diameter of from approximately 5 to 30 mm and subjecting the drawn wire to a short-duration recovery heat treatment carried out below an Ac1 temperature of the steel.

A filament according to an aspect of the present invention includes a predetermined chemical composition, in which a diameter r of the filament is 0.15 mm to 0.35 mm, a soft portion is formed along an outer circumference of the filament, the Vickers hardness of the soft portion is lower than that of a position of the filament at a depth of of the diameter r by Hv 50 or higher, the thickness of the soft portion is 1 m to 0.1r mm, the metallographic structure of a center portion of the filament contains 95% to 100% of pearlite by area %, the average lamellar spacing of pearlite in a portion from a surface of the filament to a depth of 1 m is less than that of pearlite at the center of the filament, the difference between the average lamellar spacing of pearlite in the portion from the surface of the filament to the depth of 1 m and the average lamellar spacing of pearlite at the center of the filament is 2.0 nm or less, and the tensile strength is 3200 MPa or higher.

A filament according to an aspect of the present invention includes a predetermined chemical composition, in which a diameter r of the filament is 0.15 mm to 0.35 mm, a soft portion is formed along an outer circumference of the filament, the Vickers hardness of the soft portion is lower than that of a position of the filament at a depth of of the diameter r by Hv 50 or higher, the thickness of the soft portion is 1 m to 0.1r mm, the metallographic structure of a center portion of the filament contains 95% to 100% of pearlite by area %, the average lamellar spacing of pearlite in a portion from a surface of the filament to a depth of 1 m is less than that of pearlite at the center of the filament, the difference between the average lamellar spacing of pearlite in the portion from the surface of the filament to the depth of 1 m and the average lamellar spacing of pearlite at the center of the filament is 2.0 nm or less, and the tensile strength is 3200 MPa or higher.