Patent ID: 8414715

Claim:
A method of making a steel tube, comprising: providing a carbon steel composition; forming the steel composition into a tube; heating the formed steel tube in a first heating operation to a first temperature of about 900° C. to about 950° C. for about 10 to 30 minutes; quenching the formed steel tube in a first 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; heating the formed steel tube after the first quenching operation in a second heating operation to a second temperature, less than the first temperature, of about 880° C. to about 930° C. for about 10 to 30 minutes; quenching the formed steel tube in a second quenching operation from the second temperature at a second rate such that the microstructure of the quenched steel is greater than or equal to about 95% martensite by volume, wherein the formed steel tube has a smaller grain size as compared to the grain size after the first quenching operation; and tempering the formed steel tube after the second quenching operation by heating the formed steel tube to a third temperature less than about 550° C.; wherein the steel tube after tempering has a yield strength greater than about 175 ksi and wherein the Charpy V-notch energy is greater or equal to about 50 J/cm 2 in the traverse direction and 65 J/cm 2 in the longitudinal direction at about room temperature.