The rotary shaft material having high strength and high toughness·

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An age hardenable, martensitic steel alloy that provides high strength, high toughness, and good low cycle fatigue life and a method of making same are disclosed. The alloy comprises a matrix having a weight percent composition consisting essentially of about Carbon 0.2-0.36 Manganese 0.20 max. Silicon 0.10 max. Phosphorus 0.01 max. Sulfur 0.004 max. Chromium 1.3-4 Nickel 10-15 Molybdenum 0.75-2.7 Cobalt 8-22 Aluminum 0.01 max. Titanium 0.02 max. Calcium 0.001 max. and the balance being iron and usual impurities. The alloy further contains a plurality of inclusions dispersed in the alloy matrix. The inclusions comprise calcium compounds that are about 0.4 mum to about 7.0 mum in major dimension, they have a median size of at least about 1.6 mum in major dimension, and the inclusions contain essentially no rare earth elements.