An Evaluation of High Strength Steel Forgings
Technical Report,01 Jan 1962,31 Jan 1963
GENERAL DYNAMICS CORP FORT WORTH United States
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This report presents the results of an investigation of the mechanical properties of high strength steel aircraft forgings. Republic Steel Corporations 9Ni-4Co and 18 NiCoMo300 were examined in detail for smooth and notched tensile and fatigue strength, stress corrosion resistance and fracture toughness properties. To a lesser extent forged SAE 4340 and H-11 steels were evaluated for comparison. The forgings evaluated were two configurations, a 235-lb. M.L.G. shock strut cylinder and a 275-lb. M.L.G. axle beam forging. The effects of grain flow, forging temperature, and heat treatment were examined. Variations from heat to heat and forging lot to forging lot were analyzed. In general, the 18 NiCoMo300 steel was capable of attaining the highest tensile strength, particularly yield strength. However, this higher strength did not manifest itself under fatigue loading conditions. As a result, the 9Ni-4Co steel had higher notched and smooth axial fatigue strength. From a stress corrosion standpoint the 9Ni-4Co steel was superior to 18 NiCoMo where no stress raiser was present. The reverse was true for the partial cracked test specimens. In both cases 4340 had extremely low stress corrosion strength.