Patent ID: 8636856

Claim:
A method of making a steel tube, comprising: providing a carbon steel composition comprising: about 0.20 wt. % to about 0.30 wt. % carbon; about 0.30 wt. % to about 0.70 wt. % manganese about 0.10 wt. % to about 0.30 wt. % silicon; about 0.90 wt. % to about 1.50 wt. % chromium; about 0.60 wt. % to about 1.00 wt. % molybdenum; about 0.020 wt. % to about 0.40 wt. % niobium; and about 0.01 wt. % to about 0.04 wt. % aluminum; forming the steel composition into a tube; heating the formed steel tube in a heating operation to a first temperature of about 880° C. to about 950° C. for about 10 to 30 minutes; quenching the formed steel tube in a quenching operation from the first temperature at a first rate such that the microstructure of the quenched steel is greater than or equal to about 95% martensite by volume; and tempering the formed steel tube after the quenching operation by heating the formed steel tube to a second temperature less than about 550° C.; wherein the steel tube after tempering has a yield strength greater than about 165 ksi and wherein the Charpy V-notch energy is greater or equal to about 80 J/cm 2 in the longitudinal direction and 60 J/cm 2 in the transverse direction at about room temperature.