COBALT-CHROMIUM-IRON-NICKEL-ALLOYS AMENABLE TO NITRIDES STRENGTHENING

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PURPOSE : Noble wroughtable cobalt "superalloys" capable of through thickness nitridation and strengthening, using treatments of practical available duration(about 50 hours), for sheet stocks of practical available thickness(up to about 2 mm, or 0.08 inch) are provided, wherein the sheets can have stress rupture lives at least 150 hours at 980 deg.C(1, 800 deg.F) and 55 MPa(8 ksi), or at least 250 hours at 980 deg.C and 52 MPa(7.5 ksi), which are target stress rupture lives of the development of the alloys. CONSTITUTION : A wroughtable cobalt alloy capable of through thickness nitridation and strengthening comprises, by weight percent, 23 to 30%% of chromium, 15 to 25%% of iron, up to 27.3%% of nickel, 0.75 to 1.7%% of titanium, 0.85 to 1.9%% of niobium, zirconium, or a mixture thereof, up to 0.2%% of carbon, up to 0.015%% of boron, up to 0.015%% of rare earth elements, up to 0.5%% of aluminum, up to 1%% of manganese, up to 1%% of silicon, up to 1%% of tungsten, up to 1%% of molybdenum, and the balance of cobalt and impurities wherein the sum of titanium and niobium is from 1.6 to 3.6%%. The cobalt alloy comprises, by weight percent, 23.6 to 29.5%% of chromium, 16.7 to 24.8%% of iron, 0.56 to 27.3%% of nickel, 0.75 to 1.7%% of titanium, 0.85 to 1.92%% of niobium, up to 0.2%% of carbon, up to 0.012%% of boron, up to 0.015%% of rare earth elements, up to 0.5%% of aluminum, up to 0.92%% of manganese, up to 1%% of silicon, up to 1 %% of tungsten, up to 1%% of molybdenum, and the balance of cobalt and impurities, wherein the sum of titanium and niobium is from 1.6 to about 3.6 %%. The alloy is in a wrought form having a thickness of up to 2 mm. The alloy is subjected to a nitriding treatment. The nitriding treatment comprises the steps of : heating the alloy at a temperature of 1, 095 deg.C in a nitrogen atmosphere for 48 hours; heating the alloy at 1, 120 deg.C in an argon atmosphere for 1 hour; and heating the alloy at 1, 205 deg.C in an argon atmosphere for 2 hours. © KIPO 2008