INCREASED RELIABILITY OF A HIGH STRENGTH STEEL THROUGH THERMAL-MECHANICAL TREATMENTS.
Final rept. Jul 63-May 66,
AIR FORCE MATERIALS LAB WRIGHT-PATTERSON AFB OH
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The relationships between strength, toughness, and environmental delayed failure resistance of low alloy, high strength martensitic D6-AC steel were investigated as a function of thermal and thermal-mechanical treatments. Three processing treatments were investigated 1 ausforming, 2 conventional austenitizing and quenching, and 3 aus-bay quenching. Tensile strength levels of 200,000 to 360,000 psi were obtained. Aus-bay quenching was found to produce essentially equivalent strength and toughness properties when compared to conventionally processed D6-AC steel at the same tempering temperature. Plane strain fracture toughness measurements demonstrated that the ausformed material had a significantly greater level of fracture toughness than conventional or aus-bay processed material at equal strength levels. Environmental delayed failure test results, obtained on unnotched samples in a distilled water environment, established, at equivalent strength levels, that the ausformed steel had an order-of-magnitude greater resistance to environmental-induced delayed failure than the conventionally processed steel. The superior fracture toughness of the ausformed steel is attributed to the reduced martensite plate size and the smaller, and more uniform distribution of carbide precipitates. Author
- Metallurgy and Metallography