The Dual Role of Nb Microalloying on the High-Cycle Fatigue of 1.0%C–1.5%Cr Bearing Steel

Abstract

The high-cycle tension–compression fatigue property of 1.0%C–1.5Cr% bearing steel with niobium (Nb) content of 180 and 800 ppm was investigated. The results indicated that the fatigue limit for both Nb-free and 0.018% Nb steel remained at 900 MPa, while 0.080% Nb steel increased to 950 MPa. Furthermore, Nb played a dual role in the high-cycle fatigue limit. First, it refined the undissolved carbides. In 0.080% Nb steel, the dissolution of rod-like carbides resulted in a 31% reduction in the size of undissolved carbides compared with Nb-free steel, and the roundness was increased with carbide aspect ratio decreasing from 1.37 to 1.16. Second, the stress field generated by the tip-shaped TiN crack source in 0.018% Nb steel exceeded that produced by the spherical oxide inclusions in Nb-free steel and the ellipsoidal NbC in 0.080% Nb steel, which negatively impacted the fatigue properties of the steel.