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A new 9Cr-1Mo steel with significant improvement in elevated-temperature mechanical properties and toughness over 2 l/4Cr-1Mo and standard grade 9Cr-1Mo steel has been developed jointly by Oak Ridge National Laboratory and Combustion Engineering. The new alloy obtains its elevated-temperature strength from small additions of niobium, vanadium, and nitrogen. The alloy has been melted commercially in the United States and Japan. It also has been fabricated into tubes, pipes, plates, bars, and forgings.
National Forge saddle-forged a heavy-walled cylinder from a billet produced from an electroslag remelted ingot of this modified alloy. The 781-mm-outside diameter by 67-mm-thick wall by 762-mm-long cylinder was normalized at 1050°C and tempered at 760°C.
The production of the saddle forging and its mechanical properties and microstructure are described. A comparison between the mechanical properties of this forging with the results on plates, bars, and tubes fabricated from the same alloy is presented. Data show the forging to be highly isotropic in its properties and a strong promise for the use of modified 9Cr-1Mo alloy in hydrocrackers for operation at 500°C and higher temperatures.
9Cr-1Mo, heavy-walled forging, elevated temperature properties, creep strength, argon-oxygen deoxidation (AOD), electroslag remelted (ESR), impact transition temperature, fatigue crack propagation (da/dn), J, Ic
Senior Developmental metallurgist, National Forge Co., Irvine, PA
Metallurgist, Research Staff, Metals and Ceramics, Oak Ridge National Laboratory, Oak Ridge, TN