This paper describes the dependence of fatigue properties of high-strength steels on a number of factors. The fatigue tests were performed on specimens machined from 3 to 4½ in. round or square steel sections subsequently heat treated to strength values between 210,000 and 290,000 psi. The steels investigated were aircraft quality 4340, 98B40, V-Mod. 4330, Hy-Tuf and Super Hy-Tuf.

The variables studied in this program of testing were: (a) specimen position in the steel section, (b) as-processed section size, (c) strength level or tempering temperature, (d) stress concentration, and (e) fibering or directionality. Properties modifications are discussed, correlated and evaluated.

Furthermore, a section is devoted to the discussion of bend-fatigue properties of both smooth and notched specimens at low cycles. The trends established from experiment for ductile and brittle materials are evaluated, and good agreement with the results of other investigators is observed.