Abstract: The cracking of large Francis turbine runner blades is mainly produced from fatigue process, which is related with great alternate stresses through forceful vibration and high value tensile residual stresses from the manufacturing processes. The research and application results show that the high values of residual stresses still remain after post-welded heat treatment with the process of 600 ℃8 h. The tensile residual stresses approaching to material’s yield strength deteriorate greatly the fatigue properties of components; promote the formation and growth of fatigue cracks. The compressive stress treatment on the runner blades easy to cracking may increase obviously the fatigue life. Comparing with the traditional industrial peening technique, the explosive shock waves treatment not only may produce compressive stresses, but also improve the fatigue properties of materials themselves, cure the defects, avoid the surface coursing and microcracks. For 16 Mn low-alloy steel, the fatigue strength can be increased by 60 MPa, the fatigue crack growth rate reduced 10 times. On the base of over 100 components treated acceptably with explosive shock weaves, it should be probable for increasing the fatigue life of runner blades with the compressive stress treatment.

Key words: Compressive stress treatment, Explosive shock waves, Fatigue cracks, Runner blades, Tensile residual stresses