Method of Making a High Strength, High Toughness, Fatigue Resistant, Precipitation Hardenable Stainless Steel and Product Made Therefrom

A method of making a precipitation hardenable, high strength, high toughness, stainless steel alloy to provide improved fatigue strength relative to a rare-earth-treated alloy, said method comprising the steps of:

• melting a martensitic steel alloy having the following composition in weight percent, about
• Carbon
• 0.02 max.
• Manganese
• 0.25 max.
• Silicon
• 0.25 max.
• Phosphorus
• 0.015 max.
• Sulfur
• 0.010 max.
• Chromium
• 10.5-12.5
• Nickel
• 10.75-11.25
• Titanium
• 1.5-1.7
• Molybdenum
• 0.75-1.25
• Copper
• 0.50 max.
• Aluminum
• 0.050 max.
• Niobium
• 0.050 max.
• Boron
• 0.001-0.005
• Nitrogen
• 0.015 max.
• and the balance being iron and usual impurities;
• adding calcium to the alloy while molten whereby the calcium combines with available sulfur and oxygen to form calcium-based inclusions selected from the group consisting of calcium sulfides, calcium oxides, calcium oxysulfides, and combinations thereof;
• processing said alloy to remove at least a portion of said calcium-based inclusions;
• and then
• solidifying said alloy;
• whereby after said processing and solidifying steps said alloy contains substantially no rare-earth based inclusions and has a matrix containing a sparse dispersion of said calcium-based inclusions and substantially no rare-earth base inclusions.

A method of making a precipitation hardenable, high strength, high toughness, stainless steel alloy to provide improved fatigue strength relative to a rare-earth-treated alloy, said method comprising the steps of:

• melting a martensitic steel alloy having the following composition in weight percent, about
• Carbon
• 0.015 max.
• Manganese
• 0.10 max.
• Silicon
• 0.10 max.
• Phosphorus
• 0.010 max.
• Sulfur
• 0.005 max.
• Chromium
• 11.0-12.0
• Nickel
• 10.85-11.25
• Titanium
• 1.5-1.7
• Molybdenum
• 0.9-1.1
• Copper
• 0.25 max.
• Aluminum
• 0.025 max.
• Niobium
• 0.025 max.
• Boron
• 0.0015-0.0035
• Nitrogen
• 0.010 max.
• and the balance being iron and usual impurities;
• adding calcium to the alloy while molten whereby the calcium combines with available sulfur and oxygen to form calcium-based inclusions selected from the group consisting of calcium sulfides, calcium oxides, calcium oxysulfides, and combinations thereof;
• processing said alloy to remove at least a portion of said calcium-based inclusions;
• and then
• solidifying said alloy;
• whereby after said processing and solidifying steps said alloy contains substantially no rare-earth based inclusions and has a matrix containing a sparse dispersion of said calcium-based inclusions and substantially no rare-earth base inclusions.