Effect of surface rolling on fatigue strength as influenced by the strain hardening rate

Abstract

In this study, the authors examine the role of strain hardening during surface rolling and its effect on the direct stress fatigue strength. A thermomechanically mill treated (TMT) high strength low alloy (HSLA) steel with the weight percent alloy composition of: 0.10 C, 1.55 Mn, 0.014 P, 0.006 S, 0.27 Si, 0.040 Nb, 0.035 V, and 0.034 Al was selected and its strain hardening characteristics were manipulated by intercritically annealing in the dual phase (DP) region. This produced two steels with the same composition but different microstructures and strain hardening characteristics as follows: the TMT steel having a high yield strength and a low strain hardening rate, and the DP steel having a low yield strength and a high rate of strain hardening. After characterizing the mechanical properties of both steels, the authors quantified the surface rolling process using penetration depth of work hardening and magnitude of the compressive surface residual stress. Noting that yield strength can be a strong indicator of fatigue strength, the authors then investigated whether the low yield strength DP steel when compensated with a high strain hardening rate could achieve a greater increase in fatigue strength because of surface rolling in comparison to that ofmore » the high yield strength TMT steel.« less