Cyclic deformation behavior of steels with a nanolamellar microstructure and tensile strength of 1500 MPa

Abstract

An attempt is made to obtain a nanolamellar microstructure in common metallic engineering materials, including austenite, pearlite, bainite, and martensite steels, by alloying and tailoring process parameters. The tensile strength of all four steels is 1500 MPa. On the basis of the tensile and impact deformation behaviors, the cyclic deformation behaviors of the steels with nanolamellar microstructures are studied using the crystallographic phase as the critical factor. Results indicate that the cyclic stress amplitude of the steels with a nanolamellar microstructure depends on the yield and tensile strengths. The change in the dislocation mobility of the steels with a nanolamellar microstructure results in cyclic hardening during the initial cyclic deformation stage. The fatigue life, which is not indicated by the tensile properties, is mainly affected by the initiation and propagation of fatigue cracks. The hard, brittle cementite lamellae accelerate the initiation and propagation of fatigue cracks, thus deteriorating the fatigue properties of the steels with a nanolamellar microstructure. In contrast, film-like retained austenite effectively suppresses the initiation and propagation of fatigue cracks, extending the fatigue life.