Previous work on Cr-Mo-Co stainless steels resulted in the development of a new hardenable high-strength steel, AFC-77, AFC-77, which contains nominally 0.15C-14,5Cr-5Mo-0.4V-13Co, exhibits an excellent combination of properties from subzero to about .1200 F and thus extends significantly the service tempera¬ture range attainable with hardenable stainless steels.nUnder the present contract, the complex precipitation reactions that are responsible for the strength of the Cr-Co-Mo steels were studied in detail. Strengthening after temperingnAt temperatures"" up to about 900 F is related to the precipitation of carbides. Above .1000 F, the Fe2Mo Laves phase and the chi phase have been identified as the primary strengthening agents.nAdditional mechanical and physical property determinations were made on the Cr-Mo-Co steels. AFC-77 exhibits high net fracture strengths after tempering in the 600 to 800 F temperature range. Stress corrosion tests in salt environment indicated that the susceptibility of AFC-77 to stress corrosion cracking depends considerably on heat treatment.
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