High performance tubulars for critical oil country applications and improved process for their preparation

Claim 1

A process for manufacturing high performance tubulars having minimum yield strengths ranging from 80,000 to 140,000 psi characterized by improved sulfide stress cracking resistance and improved dimensional control comprising the steps of providing a killed steel bloom comprising in amounts by weight 0.20 to 0.35 percent carbon, 0.35 to 0.90 percent manganese, 0.75 to 1.50 percent chromium, 0.15 to 0.75 percent molybdenum, 0.25 percent maximum nickel, 0.35 percent maximum copper, 0.040 percent maximum phosphorus, 0.04 percent maximum sulfur, 0.35 percent maximum silicon, and the balance iron, except normal steelmaking impurities, upset forging the killed steel bloom in a closed end cylindrical die to form an extrusion billet, hot piercing the extrusion billet while still in the upset forging die, cold machining the outside diameter and the inside diameter to be concentric and cold machining the nose of the extrusion billet, reheating and extruding the extrusion billet to form an extruded shell wherein the cross-sectional area of the extruded shell is in the range of 10 to 40 percent larger than the cross-sectional area of the finished tubular, subjecting the extruded shell to a first intercritical heat treatment to recrystallize and refine the grain structure, removing surface defects by grinding, sizing the ground, heat treated extruded shell by cold working to the finished tubular dimensions, subjecting the sized tubular to a second intercritical heat treatment to recrystallize and refine the grain structure, and subjecting the finished tubular to a quench and temper process wherein the tubular is austenitized, quenched, and tempered to produce a substantially tempered martensitic structure having a minimum yield strength in the range of 80,000 to 140,000 psi.