Corrosion pitting resistant martensitic stainless steel and method for making same

A method of making a forged, martensitic, stainless steel alloy, comprising:

• providing a forged preform of martensitic, pitting corrosion resistant stainless steel alloy comprising, by weight:
• about 12.0 to about 16.0 percent chromium;
• greater than 16.0 to about 20.0 percent cobalt, about 6.0 to about 8.0 percent molybdenum, about 1.0 to about 3.0 percent nickel, about 0.020 to about 0.040 percent carbon;
• and the balance iron and incidental impurities, wherein the alloy has a microstructure that comprises a retained austenite phase less than or equal to 2 percent by volume of the microstructure;
• heating the forged preform to a solutionizing temperature for a time sufficient to form a solutionized microstructure, wherein the solutionizing temperature is in a range between about 1100° C. to about 1150° C. (about 2000° F. to about 2100° F.) for a time in a range between about 1 hour to about 3 hours;
• cooling the forged preform and solutionized microstructure with a liquid to room temperature at a rate of 0.25° C./sec, wherein the liquid is an oil and the forged preform is immersed in the oil, and subsequently;
• immersing the forged preform in a cryo-liquid to transform the retained austenite phase in the microstructure to martensite, wherein the cryo-liquid is liquid nitrogen or liquid helium, and is at a temperature of less than −185° C. (−300° F.);
• heating the forged preform to a tempering temperature of less than 315° C. (600° F.) for a tempering time in a range between about 3 hours and about 6 hours sufficient to form a tempered forged preform comprising a tempered martensitic microstructure;
• and
• cooling the tempered forged preform to room temperature, whereby the forged, martensitic, stainless steel alloy has a Charpy V-notch impact toughness of about 20 Joules (16 ft-lbs.).