Increasing the fatigue limit of a bearing steel by dynamic strain ageing

Dynamic strain ageing processes may increase the fatigue limit of steels. To activate these processes, thermomechanical treatments with cyclic loadings at the temperature of the highest effectiveness of dynamic strain ageing can be applied. The treatments increase the dislocation density and change the dislocation structure to a more stable state by immobilisation of mobile dislocations due to locking processes by dissolved carbon atoms and small carbides. The generated dislocation structure requires higher stress amplitudes to induce dislocation movements, and consequently a longer crack initiation period, a lower crack propagation rate and a higher fatigue limit at room temperature occur.